A high-adhesion, hydrolysis-resistant polylactic acid-based waterborne polyurethane ink binder for flexographic printing and its preparation method.

Abstract

This invention discloses a high-adhesion, hydrolysis-resistant polylactic acid-based waterborne polyurethane ink binder for flexographic printing and its preparation method. The binder comprises: a polyether polyol, a bio-based long-fatty acid diol, an aliphatic diisocyanate, a hydrophilic chain extender, a small molecule chain extender, a neutralizing agent, a catalyst, a post-chain extender, and deionized water. The bio-based long-fatty acid diol is obtained by ring-opening polymerization of bio-based D- and L-lactide and a long-fatty acid diol. The bio-based long-fatty acid diol proposed in this invention enhances the intermolecular forces between the waterborne ink binder and PLA and its composites, reduces the surface tension of the coating film, enhances the wettability between the ink binder and the printing substrate, and improves the adhesion and hydrolysis resistance between the ink and PLA and its composites. The ink binder prepared by this method meets the performance requirements of waterborne polyurethane inks for flexographic printing of PLA and its composites.

Description

Technical Field

[0001] This invention belongs to the field of polymer material synthesis technology, specifically relating to a high-adhesion, hydrolysis-resistant polylactic acid-based waterborne polyurethane ink binder for flexographic printing and its preparation method. Background Technology

[0002] Plastic films are widely used in food, medical, and chemical packaging due to their excellent transparency, water resistance, and ductility. However, the production of traditional plastic films still heavily relies on petroleum resources. With the global shortage of petrochemical resources and the increasingly serious environmental pollution caused by the petrochemical industry, traditional plastic films are gradually being replaced by bio-based plastic films. Among them, polylactic acid (PLA) and its composites have seen their market share in green plastic packaging materials increase year by year due to their good biodegradability and wide availability of biological sources. In the packaging field, processes such as color printing are often required on the surface of PLA and its composites. With the rapid development of industrial technology, traditional textile printing and inkjet painting industries have placed higher demands on the stability of the printing process and the clarity of the patterns. Simultaneously, with the development of digital inkjet printing technology, there is a need for inks with better performance and higher safety. my country's water-based ink industry has gradually developed various types, including water-based acrylic and water-based polyurethane inks. Due to its unique soft and hard segment structure, polyurethane possesses excellent transparency, gloss, flexibility, and adhesion. These properties enable inks to have good printability, and water-based polyurethane resins are safe and pollution-free, making them a key focus for the printing industry.

[0003] Waterborne polyurethane, using water as the dispersion medium, features low volatile organic compound emissions, low toxicity, and environmental friendliness, meeting the requirements of green production and is widely used in the preparation of coatings, leather, inks, and adhesives. However, to achieve waterborne polyurethane, hydrophilic chain extenders need to be added during the production process, leading to drawbacks such as decreased hydrolysis resistance, reduced adhesion, and poor wettability on non-polar plastic films. Furthermore, the current preparation of waterborne polyurethane still relies on fossil resources; therefore, using green and renewable polymers to replace petroleum-based raw materials is a key research focus. Polylactic acid (PLA), due to its green and environmentally friendly nature and wide availability of biological sources, can be used as a substitute for petroleum-based raw materials in the preparation of waterborne polyurethane. However, because of the high density of ester groups in the PLA molecular chain, it is prone to hydrolysis and has poor aging resistance. Therefore, waterborne polyurethane containing PLA structures is difficult to meet the application requirements of underwater or humid environments. Preparing PLA-based waterborne polyurethane with good hydrophobicity and strong adhesion remains a research challenge.

[0004] Improving the hydrolysis resistance of waterborne polyurethanes typically involves chemical crosslinking, introducing hydrophobic groups and hydrophobic aliphatic chains, etc.

[0005] Chemical crosslinking modification is not conducive to maintaining good flexibility of waterborne polyurethane. The infiltration of hydrophobic organic fluorine groups is limited by the stiffness of the polymer chain, resulting in poor surface migration and reduced mechanical properties. Publication No. CN115058183A discloses a preparation method for improving the hydrophobicity of waterborne polyurethane by introducing organic fluorine. In this method, due to the short molecular chain of the organic fluorine chain alkyl compound, the organic fluorine cannot be effectively oriented on the surface, and the organic fluorine compound is fixed on the polyurethane backbone, which restricts the migration behavior of organic fluorine to the surface. In addition, the introduction of hydrophobic organosilicon groups will reduce the emulsion stability of waterborne polyurethane.

[0006] Introducing hydrophobic aliphatic chains can give waterborne polyurethanes good hydrophobicity and hydrolysis resistance. Publication number CN201910713272.9 discloses an aromatic polyester diol containing two hydrophilic groups and a hydrophobic long carbon chain structure with surface activity. Using this as the soft segment, high solid content waterborne polyurethanes are synthesized. A one-step esterification method is used to simultaneously introduce the diol containing the long carbon chain hydrophobic structure and two hydrophilic monomers into the polyurethane backbone, making it surface active. The long carbon chain structure is conducive to adsorption and spreading on non-polar plastic films, reducing surface tension and enhancing adhesion to non-polar plastic substrates. However, the crystallinity will improve with the increase of molecular weight, and the mechanical properties will decrease with the increase of solid content, thus affecting the practical application of waterborne polyurethanes. Summary of the Invention

[0007] This invention proposes a high-adhesion, hydrolysis-resistant polylactic acid-based waterborne polyurethane ink binder for flexographic printing and its preparation method, which can enhance the flexibility of waterborne polyurethane while improving its hydrophobicity and hydrolysis resistance.

[0008] To solve the above-mentioned technical problems, the present invention is achieved through the following technical solution.

[0009] This invention proposes a high-adhesion, hydrolysis-resistant polylactic acid-based waterborne polyurethane ink binder for flexographic printing, wherein the ink binder comprises at least the following components:

[0010]

[0011] The general structural formula of the bio-based long fatty acid side-chain polylactic acid diol is as follows:

[0012] Where m is an integer between 5 and 25, and x is an integer between 4 and 18.

[0013] In one embodiment of the present invention, the polyether polyol includes one or a mixture of polytetrahydrofuran diol, polypropylene glycol, polyethylene glycol, or tetrahydrofuran-propylene oxide copolydiol.

[0014] In one embodiment of the present invention, the aliphatic diisocyanate includes one or more of isophorone diisocyanate, hexamethylene diisocyanate, or 4,4'-dicyclohexylmethane diisocyanate.

[0015] In one embodiment of the present invention, the small molecule chain extender includes one or more of 1,4-butanediol, glyceryl monostearate, glyceryl monolaurate, glyceryl palmitate, or glyceryl monooleate.

[0016] This invention also proposes a method for preparing a high-adhesion, hydrolysis-resistant polylactic acid-based waterborne polyurethane ink binder for flexographic printing, comprising at least the following steps:

[0017] Preparation of bio-based polylactic acid diol with long fatty side chain: The reactor was preheated under vacuum at 100-110°C for 2-3 hours, and then nitrogen gas was introduced into the reactor. Under the nitrogen atmosphere, 200-400 parts of D- and L-lactide, 80-110 parts of diol containing long fatty side chain and 1-2 parts of 4-dimethylaminopyridine were added. The reaction was carried out at 140-160°C for 12-16 hours and then cooled to room temperature to obtain bio-based polylactic acid diol with long fatty side chain.

[0018] Preparation of prepolymer: Polyether polyol and the bio-based long aliphatic side chain polylactic acid diol were subjected to vacuum dehydration at 100-110°C for 1-2 hours, then cooled to 80-90°C, aliphatic diisocyanate was added, and the reaction was carried out for 1.5-2 hours. Then the temperature was lowered to 70-80°C, hydrophilic chain extender and small molecule chain extender were added, and the reaction was carried out for 2-3 hours. Then the temperature was lowered to 60-70°C, catalyst was added, and the reaction was carried out for 2-3 hours to obtain the prepolymer.

[0019] Waterborne polyurethane ink binder: The reaction system temperature is lowered to 30-40℃, a neutralizing agent is added to the prepolymer, and the reaction is carried out for 30-45 minutes. The mixture is mechanically stirred at a speed of 1500-2000 r / min, and the reaction system temperature is lowered to 0-10℃. A chain extender and deionized water are added to the reaction system, and the mixture is dispersed and emulsified for 25-45 minutes to obtain a waterborne polyurethane dispersion. Acetone is removed from the waterborne polyurethane dispersion to obtain the waterborne polyurethane ink binder.

[0020] In one embodiment of the present invention, the diol containing a long fatty side chain includes one or more of glyceryl monostearate, glyceryl monolaurate, glyceryl palmitate, or glyceryl monooleate.

[0021] In one embodiment of the present invention, the step of preparing the prepolymer further includes adding acetone to the prepolymer to reduce the viscosity of the prepolymer.

[0022] This invention proposes a high-adhesion, hydrolysis-resistant polylactic acid-based waterborne polyurethane ink binder for flexographic printing and its preparation method. The raw materials have the advantages of being green, environmentally friendly, renewable, and widely available from biological sources, meeting the requirements of green production. The polylactic acid diol containing bio-based flexible long aliphatic chains has a low ester group density, which can improve the rigid structure of the polylactic acid diol and enhance its hydrolysis resistance. This strengthens the intermolecular forces between the waterborne ink binder and PLA and its composite materials. Simultaneously, the long aliphatic side chains aggregate on the surface of the waterborne polyurethane, reducing the surface tension of the coating film, thereby improving the adhesion between the ink binder and the printing substrate, and enhancing the hydrophobicity and hydrolysis resistance of the waterborne polyurethane. Attached Figure Description

[0023] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is a flowchart illustrating a method for preparing a high-adhesion, hydrolysis-resistant polylactic acid-based waterborne polyurethane ink binder for flexographic printing, as described in this invention. Detailed Implementation

[0025] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0026] It should be understood that the present invention can be implemented in various forms and should not be construed as being limited to the embodiments set forth herein. Rather, providing these embodiments will make the disclosure thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Unless otherwise specified, “%” and “parts” as shown in the following embodiments refer to “% by mass” and “parts by mass”, respectively.

[0027] The technical solution of the present invention will be further described in detail below with reference to several embodiments and accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] This invention proposes a high-adhesion, hydrolysis-resistant polylactic acid-based waterborne polyurethane ink binder for flexographic printing, comprising at least a polyether polyol, a bio-based long-aliphatic side-chain polylactic acid diol, an aliphatic diisocyanate, a hydrophilic chain extender, a small molecule chain extender, a neutralizing agent, a catalyst, a post-chain extender, and deionized water. The bio-based long-aliphatic side-chain polylactic acid diol has the following general structural formula: in, m is an integer between 5 and 25, and x is an integer between 4 and 18. Polylactic acid diols containing bio-based flexible long aliphatic side chains have low ester group density, improving the rigid structure of the polylactic acid diol while enhancing its hydrolysis resistance. Furthermore, the introduction of bio-based long aliphatic side chains into the polylactic acid diol strengthens the intermolecular forces between waterborne polyurethane and PLA and its composites. The long aliphatic side chains aggregate on the surface of the waterborne polyurethane, reducing the surface tension of the coating film, thereby enhancing the adhesion between the ink binder and PLA and its composites. Introducing long aliphatic side chains into the waterborne polyurethane structure improves the hydrophobicity and hydrolysis resistance of the waterborne polyurethane. Moreover, the introduction of bio-based long aliphatic side chain polylactic acid diol results in a polylactic acid-based waterborne polyurethane ink binder with advantages such as strong adhesion, good hydrolysis resistance, and high color development, meeting the performance requirements of waterborne polyurethane inks for flexographic printing of PLA and its composites.

[0029] In one embodiment of the present invention, the ink binder, by weight, includes, for example, 50.0 to 70.0 parts of polyether polyol, 30.0 to 50.0 parts of bio-based long aliphatic side-chain polylactic acid diol, 30.0 to 50.0 parts of aliphatic diisocyanate, 5.0 to 10.0 parts of hydrophilic chain extender, 1.0 to 5.0 parts of small molecule chain extender, 1.0 to 5.0 parts of neutralizer, 0.1 to 2.0 parts of catalyst, 0.5 to 3.0 parts of post-chain extender, and 150.0 to 200.0 parts of deionized water.

[0030] In one embodiment of the present invention, the polyether polyol includes, for example, one or a mixture of polytetrahydrofuran diol, polypropylene glycol, polyethylene glycol, or tetrahydrofuran-propylene oxide copolyol. The aliphatic diisocyanate includes, for example, one or a mixture of isophorone diisocyanate, hexamethylene diisocyanate, or 4,4'-dicyclohexylmethane diisocyanate. The small molecule chain extender includes, for example, one or a mixture of 1,4-butanediol, glyceryl monostearate, glyceryl monolaurate, glyceryl palmitate, or glyceryl monooleate. The hydrophilic chain extender includes, for example, 2,2-dimethylolpropionic acid; the neutralizing agent is selected from triethylamine; the post-chain extender includes, for example, ethylenediamine; and the catalyst includes, for example, dibutyltin dilaurate.

[0031] Please see Figure 1As shown, the present invention also proposes a method for preparing a high-adhesion, hydrolysis-resistant polylactic acid-based waterborne polyurethane ink binder for flexographic printing, including but not limited to steps S10-S30.

[0032] Step S10: Preparation of bio-based long fatty side chain polylactic acid diol: The reactor is preheated under vacuum at 100-110°C for 2-3 hours, and then nitrogen gas is introduced into the reactor. Under the nitrogen atmosphere, 200-400 parts of D, L-lactide, 80-110 parts of diol containing long fatty side chains and 1-2 parts of 4-dimethylaminopyridine are added. The reaction is carried out at 140-160°C for 12-16 hours, and then cooled to room temperature to obtain bio-based long fatty side chain polylactic acid diol.

[0033] Step S20: Preparation of prepolymer: Polyether polyol and bio-based long aliphatic side-chain polylactic acid diol are subjected to vacuum dehydration at 100-110℃ for 1-2 hours, then cooled to 80-90℃, aliphatic diisocyanate is added, and the reaction is carried out for 1.5-2 hours. Then, the temperature is lowered to 70-80℃, hydrophilic chain extender and small molecule chain extender are added, and the reaction is carried out for 2-3 hours. Then, the temperature is lowered to 60-70℃, catalyst is added, and the reaction is carried out for 2-3 hours to obtain the prepolymer.

[0034] Step S30, Waterborne polyurethane ink binder: Lower the temperature of the reaction system to 30-40°C, add a neutralizing agent to the prepolymer, react for 30-45 minutes, mechanically stir at a speed of 1500-2000 r / min, lower the temperature of the reaction system to 0-10°C, add a chain extender and deionized water to the reaction system, disperse and emulsify for 25-45 minutes to obtain a waterborne polyurethane dispersion, remove acetone from the waterborne polyurethane dispersion to obtain a waterborne polyurethane ink binder.

[0035] Please see Figure 1 As shown, in step S10, in one embodiment of the present invention, the diol containing long fatty side chains includes, for example, one or more mixtures of glyceryl monostearate, glyceryl monolaurate, glyceryl palmitate, or glyceryl monooleate. Using 4-dimethylaminopyridine as a catalyst, the diol containing long fatty side chains undergoes ring-opening copolymerization with D,L-lactide to form a bio-based long fatty side chain polylactic acid diol. The general structural formula of the bio-based long fatty side chain polylactic acid diol is, for example, [insert structural formula here]. in, m is an integer between 5 and 25, and x is an integer between 4 and 18. Polylactic acid diols containing bio-based flexible long aliphatic side chains have low ester group density, which improves the rigid structure of polylactic acid diols while enhancing their hydrolysis resistance.

[0036] Please see Figure 1As shown, in step S20, in one embodiment of the present invention, the polyether polyol includes, for example, one or more mixtures of polytetrahydrofuran diol, polypropylene glycol, polyethylene glycol, or tetrahydrofuran-propylene oxide copolyol. For example, 50.0 to 70.0 parts of the polyether polyol and 30.0 to 50.0 parts of bio-based long-chain aliphatic polylactic acid diol are subjected to vacuum dehydration. In one embodiment of the present invention, the aliphatic diisocyanate includes, for example, one or more mixtures of isophorone diisocyanate, hexamethylene diisocyanate, or 4,4'-dicyclohexylmethane diisocyanate. The amount of aliphatic diisocyanate added is, for example, 30.0 to 50.0 parts.

[0037] Please see Figure 1 As shown, in step S20, in one embodiment of the present invention, the small molecule chain extender includes, for example, one or more mixtures of 1,4-butanediol, glyceryl monostearate, glyceryl monolaurate, glyceryl palmitate, or glyceryl monooleate. The amount of the small molecule chain extender added is, for example, 1.0 to 5.0 parts. In one embodiment of the present invention, the hydrophilic chain extender includes, for example, 2,2-dimethylolpropionic acid, and the amount of the hydrophilic chain extender added is, for example, 5.0 to 10.0 parts. The catalyst includes, for example, dibutyltin dilaurate, and the amount of the catalyst added is, for example, 0.1 to 2.0 parts. A small amount of acetone may be added to the prepolymer to reduce the viscosity of the prepolymer.

[0038] Please see Figure 1 As shown, in step S30, in one embodiment of the present invention, the neutralizing agent includes, for example, triethylamine, and the amount of neutralizing agent added is, for example, 1.0 to 5.0 parts; the chain extender includes, for example, ethylenediamine, and the amount of chain extender added is, for example, 0.5 to 3.0 parts; and the amount of deionized water added is, for example, 150.0 to 200.0 parts.

[0039] The present invention will be explained in more detail below by referring to embodiments, which should not be construed as limiting. Appropriate modifications can be made within the scope of the present invention, and all such modifications fall within the technical scope of the present invention.

[0040] Example 1

[0041] Step S10: Preparation of bio-based polylactic acid diol with long fatty side chains: The reactor was preheated under vacuum at 110°C for 3 hours, followed by nitrogen gas purging. Under nitrogen atmosphere, 400 parts of D,L-lactide, 110 parts of glyceryl monostearate, and 2 parts of 4-dimethylaminopyridine were added, and the reaction was carried out at 140°C for 12 hours. After cooling to room temperature, bio-based polylactic acid diol with long fatty side chains was obtained.

[0042] Step S20: Preparation of the prepolymer: 70 parts of polytetrahydrofuran diol and 30 parts of bio-based long aliphatic side-chain polylactic acid diol were subjected to vacuum dehydration at 110°C for 1 hour. The temperature was then lowered to 90°C and 40 parts of isophorone diisocyanate were added. The reaction was carried out for 1.5 hours. The temperature was then lowered to 80°C and 5 parts of hydrophilic chain extender 2,2-dimethylolpropionic acid and 2 parts of small molecule chain extender 1,4-butanediol were added. The reaction was carried out for 2 hours. The temperature was then lowered to 70°C and 1 part of catalyst dibutyltin dilaurate was added. The reaction was carried out for 3 hours to obtain the prepolymer.

[0043] Step S30: Preparation of waterborne polyurethane ink binder: The reaction system temperature was lowered to 40℃, and 5 parts of triethylamine, a neutralizing agent, were added to the prepolymer. The reaction was allowed to proceed for 30 minutes. The mechanical stirring speed was controlled at 1800 r / min, and the reaction system temperature was lowered to 0℃. Under high shear rate, 2 parts of ethylenediamine, a chain extender, and 150 parts of deionized water were added to the reaction system for dispersion and emulsification for 30 minutes to obtain a waterborne polyurethane dispersion. Acetone was removed from the waterborne polyurethane dispersion to obtain the waterborne polyurethane ink binder.

[0044] Example 2

[0045] Step S10: Preparation of bio-based polylactic acid diol with long fatty side chains: The reactor was preheated under vacuum at 100°C for 2 hours, followed by nitrogen gas purging. Under nitrogen atmosphere, 300 parts of D,L-lactide, 100 parts of glyceryl monolaurate, and 2 parts of 4-dimethylaminopyridine were added, and the reaction was carried out at 160°C for 16 hours. After cooling to room temperature, bio-based polylactic acid diol with long fatty side chains was obtained.

[0046] Step S20: Preparation of the prepolymer: 60 parts of polypropylene glycol and 40 parts of bio-based polylactic acid diol with long fatty side chains were vacuum dehydrated at 100°C for 1 hour. The temperature was then lowered to 80°C and 40 parts of isophorone diisocyanate were added. The reaction was carried out for 2 hours. The temperature was then lowered to 70°C and 5 parts of hydrophilic chain extender 2,2-dimethylolpropionic acid and 5 parts of small molecule chain extender 1,4-butanediol were added. The reaction was carried out for 2 hours. The temperature was then lowered to 60°C and 2 parts of catalyst dibutyltin dilaurate were added. The reaction was carried out for 3 hours to obtain the prepolymer.

[0047] Step S30: Preparation of waterborne polyurethane ink binder: The reaction system temperature is lowered to 30°C, and 5 parts of triethylamine, a neutralizing agent, are added to the prepolymer. The reaction is allowed to proceed for 45 minutes. The mechanical stirring speed is controlled at 2000 r / min, and the reaction system temperature is lowered to 10°C. Under high shear rate, 3 parts of ethylenediamine, a chain extender, and 200 parts of deionized water are added to the reaction system for dispersion and emulsification for 25 minutes to obtain a waterborne polyurethane dispersion. Acetone is removed from the waterborne polyurethane dispersion to obtain the waterborne polyurethane ink binder.

[0048] Comparative Example 1

[0049] Step S10, Preparation of prepolymer: 100 parts of polytetrahydrofuran diol were vacuum dehydrated at 110℃ for 1 hour, then cooled to 90℃ and 40 parts of isophorone diisocyanate were added. The reaction was carried out for 2 hours, then cooled to 80℃ and 5 parts of hydrophilic chain extender 2,2-dimethylolpropionic acid and 2 parts of small molecule chain extender 1,4-butanediol were added. The reaction was carried out for 2 hours, then cooled to 70℃ and 1 part of catalyst dibutyltin dilaurate was added. The reaction was carried out for 3 hours to obtain the prepolymer.

[0050] Step S20: Preparation of waterborne polyurethane ink binder: The reaction system temperature was lowered to 40℃, and 5 parts of triethylamine, a neutralizing agent, were added to the prepolymer. The reaction was allowed to proceed for 30 minutes. The mechanical stirring speed was controlled at 1800 r / min, and the reaction system was placed at 0℃. Under high shear rate, 2 parts of ethylenediamine, a chain extender, and 200 parts of deionized water were added to the reaction system for dispersion and emulsification for 30 minutes to obtain a waterborne polyurethane dispersion. Acetone was removed from the waterborne polyurethane dispersion to obtain the waterborne polyurethane ink binder.

[0051] The waterborne polyurethane ink binders prepared in Examples 1-2 and Comparative Example 1 were made into films, and the films were tested according to relevant standards for solid content, coloring power, adhesion, and wet rubbing 10 times.

[0052] The water contact angle test was conducted according to the method described in GB / T 30693-2014.

[0053] The solid content test is calculated according to the following formula: W=(m2-m0) / (m1-m0)×100%, where W is the solid content / %; m2, m1 and m0 are the total mass of the sample and vessel after drying / g, the total mass of the sample and vessel before drying / g and the mass of the vessel / g, respectively.

[0054] The tinting strength test was conducted according to the method described in GB / T 14624.2 2008.

[0055] The adhesion test was conducted according to the method described in GB / T 13217.7 2009.

[0056] Table 1. Performance test results of waterborne polyurethane films in Examples 1-2 and Comparative Example 1

[0057]

[0058] As shown in Table 1, the water contact angle of the waterborne polyurethane ink binder prepared by the present invention can reach up to 106.6°, and there is no whitening phenomenon after soaking in water for 1 hour after film formation. This indicates that the prepared polylactic acid-based waterborne polyurethane has high hydrophobicity and hydrolysis resistance, which can meet the practical application of ink in humid environments.

[0059] Table 2. Performance test results of water-based inks in Examples 1-2 and Comparative Example 1

[0060]

[0061]

[0062] As shown in Table 2, when the waterborne polyurethane ink binder prepared according to this invention is combined with PLA and its composite materials to produce waterborne ink, the resulting ink exhibits 100% tinting strength and shows no color fading after 10 wet rubs, indicating that the waterborne polyurethane ink binder prepared according to this invention can improve the tinting strength of the ink. Furthermore, the waterborne polyurethane ink binder prepared according to this invention has excellent adhesion to PLA and its composite materials, achieving an adhesion strength of grade 1. Moreover, the raw material cost is low, it is easy to industrialize, and it can be applied to the field of waterborne polyurethane inks for flexographic printing.

[0063] In summary, this invention proposes a high-adhesion, hydrolysis-resistant polylactic acid-based waterborne polyurethane ink binder for flexographic printing and its preparation method. The method involves copolymerizing a diol containing long aliphatic side chains with D and L-lactide to form a bio-based polylactic acid diol with long aliphatic side chains. This diol is then introduced as a chain extender into the hard segments of the waterborne polyurethane. Introducing long aliphatic side chains into the waterborne polyurethane enhances its flexibility and facilitates the migration of these flexible side chains to the surface. The aggregation of these long aliphatic side chains on the surface of the waterborne polyurethane reduces the surface tension of the coating film, thereby enhancing the adhesion between the ink binder and PLA and its composite materials. The introduction of hydrophobic long aliphatic chains improves the hydrophobicity and hydrolysis resistance of the waterborne polyurethane. The polylactic acid-based waterborne polyurethane ink binder prepared by this method exhibits a water contact angle between 100° and 110° after film formation, shows no whitening after immersion in water for 1 hour, and demonstrates Grade 1 adhesion to PLA and its composite materials, meeting the performance requirements of waterborne polyurethane inks for flexographic printing of PLA and its composite materials. Furthermore, the raw materials selected have the advantages of being green, environmentally friendly, renewable, and widely available from biological sources, which meets the requirements of green production.

[0064] The above description is merely a preferred embodiment of this application and an explanation of the technical principles used. Those skilled in the art should understand that the scope of the invention involved in this application is not limited to the technical solutions formed by a specific combination of the above-mentioned technical features, but should also cover other technical solutions formed by any combination of the above-mentioned technical features or their equivalent features without departing from the inventive concept. For example, technical solutions formed by replacing the above-mentioned features with technical features with similar functions disclosed in this application (but not limited to) each other.

[0065] Apart from the technical features described in the specification, the other technical features are known to those skilled in the art. To highlight the innovative features of this invention, the other technical features will not be described in detail here.

Claims

1. A high adhesion hydrolysis resistant polylactic acid based waterborne polyurethane ink vehicle for flexographic printing, characterized by, The ink vehicle comprises at least the following components: The general structure of the bio-based long fatty side chain polylactic acid diol is: wherein m is an integer between 5 and 25, and x is an integer between 4 and 18; The bio-based long fatty side chain polylactic acid diol is obtained by ring-opening polymerization of D, L-lactide and a diol containing long fatty side chains.

2. The high adhesion hydrolysis resistant polylactic acid based waterborne polyurethane ink vehicle for flexographic printing according to claim 1, characterized in that, The polyether polyol comprises a mixture of one or more of polytetrahydrofuran diol, polypropylene glycol, polyethylene glycol or tetrahydrofuran- propylene oxide copolymer diol.

3. The high adhesion hydrolysis resistant polylactic acid based waterborne polyurethane ink vehicle for flexographic printing according to claim 1, characterized in that, The aliphatic diisocyanate comprises a mixture of one or more of isophorone diisocyanate, hexamethylene diisocyanate or 4,4'-dicyclohexyl methane diisocyanate.

4. The high adhesion hydrolysis resistant polylactic acid based waterborne polyurethane ink vehicle for flexographic printing according to claim 1, characterized in that, The small molecule chain extender comprises a mixture of one or more of 1,4-butanediol, glycerol monostearate, glycerol monolaurate, glycerol monopalmitate or glycerol monooleate.

5. A method of preparing a high adhesion hydrolysis resistant polylactic acid based waterborne polyurethane ink vehicle for flexographic printing according to any one of claims 1 to 4, characterized in that, The method comprises at least the following steps: Preparation of the bio-based long fatty side chain polylactic acid diol: the reactor is preheated at 100-110 DEG C for 2-3 hours under vacuum, then nitrogen is introduced into the reactor, 200-400 parts of D, L-lactide, 80-110 parts of a diol containing long fatty side chains and 1-2 parts of 4-dimethylaminopyridine are added under nitrogen atmosphere, and the mixture is reacted at 140-160 DEG C for 12-16 hours, and then cooled to room temperature to obtain the bio-based long fatty side chain polylactic acid diol; Preparation of the prepolymer: the polyether polyol and the bio-based long fatty side chain polylactic acid diol are subjected to vacuum water removal operation at 100-110 DEG C for 1-2 hours, then cooled to 80-90 DEG C, and the aliphatic diisocyanate is added, and the mixture is reacted for 1.5-2 hours, then cooled to 70-80 DEG C, and the hydrophilic chain extender and the small molecule chain extender are added, and the mixture is reacted for 2-3 hours, then cooled to 60-70 DEG C, and the catalyst is added, and the mixture is reacted for 2-3 hours to obtain the prepolymer; The aqueous polyurethane ink vehicle is obtained by removing acetone from the aqueous polyurethane dispersion.

6. The process for preparing a high adhesion hydrolysis resistant polylactic acid based waterborne polyurethane ink vehicle for flexographic printing according to claim 5, characterized in that, The diol containing long fatty side chains comprises a mixture of one or more of glycerol monostearate, glycerol monolaurate, glycerol monopalmitate or glycerol monooleate.

7. The process for preparing a high adhesion hydrolysis resistant polylactic acid based waterborne polyurethane ink vehicle for flexographic printing according to claim 5, characterized in that, The step of preparing the prepolymer further comprises adding acetone to the prepolymer to reduce the viscosity of the prepolymer.

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