Aqueous polyurethane brightener and method for its preparation

Abstract

The present application belongs to the field of leather finishing agent, and particularly relates to a water-based polyurethane brightener and a preparation method thereof. The water-based polyurethane brightener comprises the following raw materials: an anionic aliphatic water-based polyurethane dispersion, a silicone-modified water-based polyurethane resin, a leveling agent, a wetting agent, a bactericide, a light stabilizer, a thickening agent, a defoaming agent and deionized water. The present application is prepared by compounding the silicone-modified water-based polyurethane resin and the aliphatic polycarbonate polyurethane dispersion, and the covalently bonded silicone segments are stably enriched on the surface of the coating, so that the coating is endowed with persistent anti-sticking performance; and the light stabilizer is used to significantly improve the ultraviolet resistance and moisture resistance and aging resistance. The obtained brightener has the advantages of high gloss, yellowing resistance, non-sticking in stacking, balanced physical properties and natural comfortable hand feeling, and is suitable for leather top coating.

Description

Technical Field

[0001] This invention belongs to the field of leather finishing agents, specifically relating to a water-based polyurethane brightener and its preparation method. Background Technology

[0002] As the top-layer material for leather finishing, leather polish plays a decisive role in the appearance, physical properties, and feel of leather products. With consumers' increasing demands for the quality of leather products, the industry is placing higher requirements on the performance of polish. While existing water-based polyurethane polishes have made progress in environmental friendliness, they still have many shortcomings: for example, some products have poor resistance to yellowing, especially under ultraviolet light and humid conditions; the coating is prone to sticking together during stacking, leading to damage to the film; resistance to wet friction and abrasion is poor, easily causing coating damage and peeling; and the feel is stiff, with a heavy plastic texture, resulting in poor adhesion to natural leather.

[0003] The patent with application number CN110724461A discloses a leather brightener, which has good gloss and water resistance, but the film is relatively hard, which will affect the softness of the leather, and there is still room for improvement in terms of anti-sticking properties.

[0004] The patent application number CN110305287A discloses a glossy waterborne polyurethane and its preparation method. It has the characteristics of high gloss, soft feel and good water fastness after the finished polyurethane film is formed. However, it does not mention the problems of yellowing and stacking. When the relatively soft polyurethane film is stacked together under high temperature and humidity, it is easy to cause adhesion, which will destroy the gloss of the coating and even damage the coating when it is peeled off.

[0005] Patent application number CN108485504A discloses a water-based surface coating agent for glossy polyurethane synthetic leather. This gloss agent has high gloss, natural shine, and good anti-stick properties. However, the addition of organosilicon feel agents often reduces the stability of the system and leads to poor durability of the feel. In addition, free silicone oil is prone to migration, resulting in uneven film atomization and decreased gloss.

[0006] Therefore, developing a polyurethane gloss agent that combines excellent resistance to damp heat aging and UV aging, non-stick stacking, excellent physical properties, and a natural and comfortable feel has significant market value. Summary of the Invention

[0007] To solve the above-mentioned technical problems, the present invention provides a waterborne polyurethane brightener, which comprises the following raw materials in parts by weight: 60-70 parts of anionic aliphatic waterborne polyurethane dispersion, 1-4 parts of organosilicon-modified waterborne polyurethane resin, 0.1-1 parts of leveling agent, 0.1-0.5 parts of wetting agent, 0.1-0.5 parts of bactericide, 0.1-0.5 parts of light stabilizer, 0.5-1.0 parts of thickener, 0.02-0.05 parts of defoamer, and 22-38 parts of deionized water.

[0008] Preferably, the waterborne polyurethane brightener comprises the following raw materials in parts by weight: 65 parts of anionic aliphatic waterborne polyurethane dispersion, 2 parts of silicone-modified waterborne polyurethane resin, 0.5 parts of leveling agent, 0.3 parts of wetting agent, 0.2 parts of bactericide, 0.2 parts of light stabilizer, 0.5 parts of thickener, 0.03 parts of defoamer, and 31.3 parts of deionized water.

[0009] To facilitate understanding of this invention, some of the raw materials used in this invention are described below: The anionic aliphatic aqueous polyurethane dispersion is of polyether, polyester, or polycarbonate type. Its film-forming material has moderately soft physical properties (100% tensile strength around 5 MPa, tensile strength 20-30 MPa, and elongation at break 500-700%). The solid content of the anionic aliphatic aqueous polyurethane dispersion is 30-35%, and its appearance is bluish and semi-transparent. Preferably, it is DOWELLIU RU2312 or DOWELLIU RU2630 produced by Sichuan Dawei Technology Co., Ltd.

[0010] The silicone-modified waterborne polyurethane resin is Dolphin 1859R or Dolphin 1099R manufactured by Sloco. The introduction of this component aims to adjust the stackability of the final coating, preventing the coating from being too soft, resulting in thermal stickiness and poor stackability. By adding this silicone-modified polyurethane, surface stickiness, uneven film atomization, and decreased gloss caused by free silicone oil migration can be avoided.

[0011] The leveling agent is a modified polyether siloxane copolymer (TEGO Glide 410), which provides excellent substrate wetting and leveling and a smooth feel, reduces the surface energy of the coating, and imparts certain anti-stick and high-gloss properties.

[0012] The wetting agent is a polyether-modified polysiloxane wetting agent (TEGO Wet KL 245), which has excellent wetting effect, spreads quickly, effectively avoids pinholes, has good compatibility with waterborne polyurethane resin, and can improve the adhesion and uniform gloss of the resin film to the coating.

[0013] The bactericide is one or a combination of two or more of IPBC, OIT, MIT or BIT.

[0014] The light stabilizer is one or a combination of two or more of the following: ultraviolet light absorber and hindered amine radical scavenger (BASF Tinuvin 5333-DW or Chiguard 101 WB).

[0015] The thickener is a nonionic polyurethane associative thickener (Wanhua Vesmody U605 / U905).

[0016] The defoamer is a polyether siloxane copolymer containing fumed silica (TEGO Foamex 810 or TEGO Foamex 825).

[0017] Based on the same technical concept, the present invention further provides a method for preparing a waterborne polyurethane brightener, the preparation method comprising the following steps: (1) Mix deionized water, bactericide, wetting agent and leveling agent in sequence until uniform to obtain mixture A; (2) Add anionic aliphatic waterborne polyurethane dispersion, organosilicon modified waterborne polyurethane resin and light stabilizer to the mixture A in sequence. After the addition is completed, increase the speed and continue stirring to obtain mixture B. (3) Reduce the stirring speed, add thickener to the mixture B, and stir until it is completely dispersed and uniform to obtain mixture C; (4) Reduce the stirring speed and add defoamer to the mixture C to defoam. After defoaming, filter and discharge the material to obtain the water-based polyurethane brightener.

[0018] Preferably, in step (1), deionized water, bactericide, wetting agent and leveling agent are added to the dispersion vessel in sequence at a rotation speed of 200-400 r / min and stirred until uniform to obtain mixture A.

[0019] Preferably, in step (2), anionic aliphatic waterborne polyurethane dispersion, organosilicon-modified waterborne polyurethane resin and light stabilizer are slowly added to the mixture A in sequence under continuous stirring. After the addition is completed, the rotation speed is increased to 400-600 r / min and stirring is continued for 50-70 min to obtain mixture B.

[0020] Preferably, in step (3), the stirring speed is reduced to 300-500 r / min, the thickener is slowly added to the mixture B, and the mixture is stirred for 30-50 min until it is completely dispersed and uniform. The viscosity of the system is adjusted so that the outflow time of the No. 4 Ford cup is 15-20 s (25℃) to obtain the mixture C.

[0021] Preferably, in step (4), the stirring speed is reduced to 200-300 r / min, and a defoamer is added to the mixture C to defoam. After defoaming, the mixture is filtered through a 300-mesh filter to obtain the water-based polyurethane brightener.

[0022] The beneficial effects of this invention are as follows: 1. Excellent resistance to yellowing: The coating uses polycarbonate-type anionic aliphatic waterborne polyurethane dispersion as the main resin and is compounded with light stabilizers, which gives the coating outstanding resistance to UV aging and damp heat aging. The UV yellowing resistance ΔE can be as low as 0.3 and the damp heat yellowing resistance ΔE can be as low as 0.9, which effectively solves the problem of traditional waterborne polyurethane brighteners easily yellowing and discoloring under light and damp heat environments.

[0023] 2. Durable and stable anti-sticking properties: The introduction of silicone-modified waterborne polyurethane resin allows silicone segments to be embedded in the polyurethane molecular chain through chemical bonds. Unlike physically mixed free silicone additives, the covalent bond anchoring prevents the silicone segments from migrating freely. This allows them to be stably enriched on the coating surface and form a protective layer with extremely low surface energy, giving the coating a long-lasting anti-sticking effect. It does not stick even after being stacked at 60℃ for 48 hours, completely preventing coating adhesion and damage when leather products are stacked and stored.

[0024] 3. Balanced and excellent physical properties: The coating uses polycarbonate-based waterborne polyurethane dispersion as the main film-forming component, combined with the synergistic reinforcing effect of silicone-modified polyurethane resin, so that the wet friction resistance and wear resistance of the coating can reach level 4-5; at the same time, it maintains the original softness and hardness of the leather blank, avoiding the defects of traditional brighteners that form an overly hard film and affect the feel of the leather blank.

[0025] 4. Natural and comfortable feel: The leveling agent and silicone-modified waterborne polyurethane resin work synergistically to give the coating a dry and smooth feel with no obvious plasticity, which is close to the feel of natural leather and significantly improves the tactile quality of leather products.

[0026] 5. High and long-lasting uniform gloss: The combination of wetting agent and leveling agent effectively enhances the wetting and spreading ability of the gloss agent on the substrate, avoids pinholes, and makes the coating smooth with uniform and natural gloss. The gloss level can reach 85 or above at 60°. Moreover, the silicone component does not migrate, and there are no problems of uneven film formation and gloss reduction caused by free silicone oil, resulting in good gloss durability.

[0027] 6. Good system stability: The components have excellent compatibility. The organosilicon component is chemically bonded to the polyurethane chain, and there is no problem of free silicone oil migration. The system has excellent storage stability and construction stability. The preparation process is simple and controllable, and it is easy to industrialize. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be described in detail below. Obviously, the described embodiments are merely some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other implementation methods obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0029] Example 1 This embodiment provides a waterborne polyurethane brightener, prepared from the following raw materials by weight: 31.3g deionized water, 0.2g bactericide (IPBC, the same below), 0.3g wetting agent (TEGO Wet KL 245, the same below), 0.5g leveling agent (TEGOGlide 410, the same below), 65g anionic aliphatic polycarbonate type waterborne polyurethane dispersion (30% solid content, 100% tensile strength approximately 5MPa, DOWELLIU RU2312, the same below), 2g silicone-modified waterborne polyurethane resin (Dolphin 1859R, the same below), 0.2g light stabilizer (BASF Tinuvin 5333-DW, the same below), 0.5g thickener (Wanhua Vesmody U605, the same below), and 0.03g defoamer (TEGO Foamex 810, the same below).

[0030] The preparation method of the waterborne polyurethane brightener includes the following steps: (1) Preparation of Mixture A: Add the prescribed amount of deionized water to the dispersion vessel, turn on the stirrer and control the speed at 300 r / min, and add the bactericide, wetting agent and leveling agent in sequence. After each component is added, stir for 2-3 min until completely dissolved and dispersed. After all components are added, continue stirring for 5 min to obtain a uniform and transparent mixture A. In this step, the small molecule additives are pre-dispersed in the aqueous phase to avoid agglomeration or uneven dispersion of the additives when the resin is added later, ensuring that each functional component is evenly distributed in the system, providing a uniform aqueous phase basis for subsequent resin mixing.

[0031] (2) Preparation of Mixture B: While maintaining a stirring speed of 300 r / min, slowly add the anionic aliphatic polycarbonate-type waterborne polyurethane dispersion and the silicone-modified waterborne polyurethane resin to mixture A in sequence. The addition time is controlled at 10-15 min. After the addition is completed, add the light stabilizer, and then increase the stirring speed to 500 r / min and continue stirring for 60 min to obtain a uniform mixture B. In this step, the resin is added at a low speed first to prevent splashing and bubble generation, and then the speed is increased to ensure that the two polyurethane resins are fully mixed and form a uniform blend system; at the same time, the light stabilizer is uniformly dispersed in the resin phase, laying the foundation for the ultraviolet absorption and free radical scavenging functions after subsequent film formation.

[0032] (3) Preparation of Mixture C: Reduce the stirring speed to 400 r / min, slowly add the thickener to Mixture B over a period of about 5 min, and continue stirring for 40 min after addition until the thickener is completely and evenly dispersed. Use a No. 4 Ford cup to test the viscosity of the system (25℃), and adjust the outflow time to 15-20 s to obtain Mixture C. In this step, adding the thickener after reducing the stirring speed can avoid high-speed shearing from damaging the polyurethane associative structure of the thickener, ensuring a stable and controllable thickening effect; adjusting the viscosity allows the gloss agent to reach a suitable application viscosity range, facilitating subsequent spraying or roller coating operations.

[0033] (4) Defoaming and filtration: Further reduce the stirring speed to 250 r / min, add defoamer to the mixture C, stir for 10 min for defoaming treatment, and after defoaming, filter through a 300-mesh filter to obtain the waterborne polyurethane brightener. In this step, low-speed defoaming can reduce the generation of new bubbles, and the defoamer can quickly eliminate the bubbles entrained during stirring; 300-mesh filtration can remove condensates and mechanical impurities in the system, ensuring that the final coating has a delicate and particle-free appearance.

[0034] Example 2 This embodiment provides a waterborne polyurethane brightener, prepared from the following raw materials by weight: 32.3g deionized water, 0.2g bactericide, 0.2g wetting agent, 0.6g leveling agent, 62g anionic aliphatic polycarbonate type waterborne polyurethane dispersion (30% solid content, 100% tensile strength approximately 5MPa), 4g silicone-modified waterborne polyurethane resin, 0.2g light stabilizer, 0.5g thickener, and 0.03g defoamer.

[0035] The preparation method of the waterborne polyurethane brightener includes the following steps: (1) Preparation of Mixture A: Add the prescribed amount of deionized water to the dispersion vessel, start stirring and control the speed at 300 r / min, and add the bactericide, wetting agent and leveling agent in sequence. After each component is added, stir for 2-3 minutes until completely dissolved and dispersed. After all components are added, continue stirring for 5 minutes to obtain a uniform and transparent mixture A. In this step, the small molecule additives are pre-dispersed in the aqueous phase to ensure that each functional component is evenly distributed. In this embodiment, the amount of leveling agent is relatively high, so the pre-dispersion step is particularly important to avoid pinholes or fisheyes caused by excessively high local concentrations when the leveling agent is directly added to the resin phase.

[0036] (2) Preparation of Mixture B: Maintaining a stirring speed of 300 r / min, slowly add the anionic aliphatic polycarbonate-type waterborne polyurethane dispersion and the silicone-modified waterborne polyurethane resin to mixture A in sequence. The addition time is controlled at 10-15 min. After the addition is completed, add the light stabilizer, and then increase the stirring speed to 500 r / min and continue stirring for 60 min to obtain a uniform mixture B. In this step, the amount of silicone-modified waterborne polyurethane resin used in this embodiment is relatively high. The slow addition at low speed can ensure that it is fully compatible with the main resin and avoid phase separation due to excessive local concentration. After increasing the speed, the two resins are stirred thoroughly to form a uniform blend system. The silicone segments are evenly distributed in the polyurethane matrix, providing conditions for migration and enrichment to the surface during subsequent film formation.

[0037] (3) Preparation of Mixture C: Reduce the stirring speed to 400 r / min, slowly add the thickener to Mixture B over a period of about 5 min, and continue stirring for 40 min after addition until the thickener is completely and evenly dispersed. Use a No. 4 Ford cup to test the viscosity of the system and adjust the outflow time to 15-20 s to obtain Mixture C. In this step, the thickener is added at a lower speed to protect its associative structure from high-speed shear damage, ensuring thickening efficiency and stable rheological properties of the system, so that the brightener has a suitable application viscosity and sag resistance.

[0038] (4) Defoaming and filtration: Further reduce the stirring speed to 250 r / min, add defoamer to the mixture C, stir for 10 min for defoaming treatment, and after defoaming, filter through a 300-mesh filter to obtain the water-based polyurethane brightener. In this step, the low-speed defoaming combined with the defoamer can effectively eliminate the microbubbles generated during stirring; the 300-mesh filtration ensures that the fineness of the product meets the appearance requirements of high-grade leather finishing.

[0039] Comparative Example 1 This comparative example provides an aqueous polyurethane brightener and its preparation method. The difference from Example 1 is that no organosilicon-modified aqueous polyurethane resin is added, and deionized water is used in place of it in equal weight. The amounts of other raw materials and the preparation method are the same as in Example 1.

[0040] Objective: To verify the effect of silicone-modified waterborne polyurethane resin on the anti-sticking properties, feel, and gloss durability of gloss coatings.

[0041] Comparative Example 2 This comparative example provides a waterborne polyurethane brightener and its preparation method. The difference from Example 1 is that the anionic aliphatic polycarbonate type waterborne polyurethane dispersion is replaced with an equal weight of anionic aliphatic polyester type waterborne polyurethane dispersion (solid content 30%). The remaining raw material amounts and preparation methods are the same as in Example 1.

[0042] Purpose of comparison: To compare the differences in aging resistance, abrasion resistance, feel, and stackability of coatings when polycarbonate-based and polyester-based waterborne polyurethane dispersions are used as the main resin.

[0043] Comparative Example 3 This comparative example provides an aqueous polyurethane brightener and its preparation method. The difference from Example 1 is that no light stabilizer is added, and deionized water is used in place of it. The amounts of other raw materials and the preparation method are the same as in Example 1.

[0044] Objective: To verify the effect of light stabilizers on improving the UV resistance and humid heat resistance of gloss coatings.

[0045] Comparative Example 4 This comparative example provides an aqueous polyurethane brightener and its preparation method. The difference from Example 1 is that no wetting agent is added, and deionized water is used in place of it in equal weight. The amounts of other raw materials and the preparation method are the same as in Example 1.

[0046] Objective of the comparison: To investigate the effect of wetting agents on the wetting and spreading ability of gloss agents on substrate surfaces, coating gloss, and adhesion to the substrate.

[0047] Comparative Example 5 This comparative example provides an aqueous polyurethane brightener and its preparation method. The difference from Example 1 is that no leveling agent is added, and deionized water is used in place of the same weight. The amounts of other raw materials and the preparation method are the same as in Example 1.

[0048] Objective of the comparison: To investigate the effect of leveling agents on the leveling properties, gloss, feel and adhesion of the coating.

[0049] Verification Example The gloss agents prepared in Examples 1-2 and Comparative Examples 1-5 were applied to the same batch and style of cowhide sofa leather and split-edge bead leather blanks using the same spraying process, and dried according to conventional processes. Various properties were tested according to relevant standards, and the results are shown in Table 1.

[0050] Note: Leather blanks: cowhide sofa leather (for testing physical properties, feel, and fit), split bead leather blanks (for testing gloss, yellowing, fit, and stackability).

[0051] Table 1

[0052] As shown in Table 1: The polyurethane brighteners prepared in Examples 1 and 2 of this invention exhibit excellent and balanced performance in terms of gloss, UV yellowing resistance, damp heat yellowing resistance, anti-stick properties, physical properties, and feel. In particular, their stacking properties are significantly better than those of Comparative Example 1, which does not contain silicone-modified waterborne polyurethane. This is because the silicone segments achieve excellent anti-sticking effects by accumulating on the coating surface and having extremely low surface energy. Since the silicone-modified waterborne polyurethane embeds silicone segments into the polyurethane molecular chain through chemical bonds, unlike the free segments of physically mixed additives, this covalent bond anchoring prevents the silicone segments from migrating freely, thus ensuring long-lasting and stable anti-sticking properties. Comparative Example 2, due to the use of a polyester-type main resin, shows a significant decrease in yellowing resistance, stacking properties, wet rubbing resistance, and abrasion resistance. This is because the ester bonds in the polyester soft segments are less chemically stable than the carbonate bonds, indicating that the selection of a polycarbonate-type resin is crucial to achieving the intended effects of this invention. Furthermore, Comparative Example 3 shows that the addition of a light stabilizer significantly improves resistance to damp heat and UV aging. Comparative Example 4, lacking a wetting agent, experienced a slight decrease in gloss and adhesion, resulting in poor coating transparency. The wetting agent primarily wets the substrate, facilitating the penetration and wetting of the gloss agent, allowing it to adhere tightly and quickly to the substrate, improving coating smoothness, and achieving stronger gloss and gloss durability. Comparative Example 5, with its reduced leveling agent dosage, experienced a slight decrease in gloss, feel, and adhesion, particularly affecting the feel significantly, indicating that this leveling agent can significantly improve the coating's feel. The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A water-based polyurethane brightener, characterized in that, The raw materials contain the following parts by weight: 60-70 parts of anionic aliphatic waterborne polyurethane dispersion, 1-4 parts of silicone-modified waterborne polyurethane resin, 0.1-1 part of leveling agent, 0.1-0.5 parts of wetting agent, 0.1-0.5 parts of bactericide, 0.1-0.5 parts of light stabilizer, 0.5-1.0 parts of thickener, 0.02-0.05 parts of defoamer, and 22-38 parts of deionized water.

2. The waterborne polyurethane brightener according to claim 1, characterized in that, The raw materials contain the following parts by weight: 65 parts of anionic aliphatic waterborne polyurethane dispersion, 2 parts of silicone-modified waterborne polyurethane resin, 0.5 parts of leveling agent, 0.3 parts of wetting agent, 0.2 parts of bactericide, 0.2 parts of light stabilizer, 0.5 parts of thickener, 0.03 parts of defoamer, and 31.3 parts of deionized water.

3. The method for preparing the waterborne polyurethane brightener according to claim 1 or 2, characterized in that, The preparation method includes the following steps: (1) Mix deionized water, bactericide, wetting agent and leveling agent in sequence until uniform to obtain mixture A; (2) Add anionic aliphatic waterborne polyurethane dispersion, organosilicon modified waterborne polyurethane resin and light stabilizer to the mixture A in sequence. After the addition is completed, increase the speed and continue stirring to obtain mixture B. (3) Reduce the stirring speed, add thickener to the mixture B, and stir until it is completely dispersed and uniform to obtain mixture C; (4) Reduce the stirring speed and add defoamer to the mixture C to defoam. After defoaming, filter and discharge the material to obtain the water-based polyurethane brightener.

4. The preparation method of the waterborne polyurethane brightener according to claim 3, characterized in that, In step (1), at a speed of 200-400 r / min, deionized water, bactericide, wetting agent and leveling agent are added to the dispersion vessel in sequence and stirred until uniform to obtain mixture A.

5. The method for preparing the waterborne polyurethane brightener according to claim 3, characterized in that, In step (2), under continuous stirring, anionic aliphatic waterborne polyurethane dispersion, organosilicon-modified waterborne polyurethane resin and light stabilizer are slowly added to the mixture A in sequence. After the addition is completed, the rotation speed is increased to 400-600 r / min and stirring is continued for 50-70 min to obtain mixture B.

6. The method for preparing the waterborne polyurethane brightener according to claim 3, characterized in that, In step (3), the stirring speed is reduced to 300-500 r / min, and the thickener is slowly added to the mixture B. The mixture is stirred for 30-50 min until it is completely dispersed and uniform. The viscosity of the system is adjusted so that the outflow time of the No. 4 Ford cup is 15-20 s, and the mixture C is obtained.

7. The method for preparing the waterborne polyurethane brightener according to claim 3, characterized in that, In step (4), the stirring speed is reduced to 200-300 r / min, and defoamer is added to the mixture C to defoam. After defoaming is completed, the mixture is filtered through a 300-mesh filter to obtain the water-based polyurethane brightener.

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