Epoxy resin modified cationic waterborne polyurethane emulsion and preparation method thereof

Abstract

The present application relates to a kind of epoxy resin modified cationic waterborne polyurethane emulsion and its preparation method, the emulsion is introduced epoxy group in polyurethane side chain, when preparing emulsion, first synthesis the cationic hydrophilic chain extender of specific structure containing epoxy group, then cooperate other hydrophilic chain extender and introduce hydrophilic group, wherein, the dosage of hydrophilic chain extender containing epoxy group and other hydrophilic chain extender accounts for 1-5% and 6-12% respectively;The cationic hydrophilic chain extender of specific structure containing epoxy group is prepared by using molar ratio 1:1 diethanolamine and bifunctionality alkyl alcohol diglycidyl ether compound reaction at low temperature.The epoxy group is introduced into polyurethane side chain in the present application, overcome the inherent shortcomings of traditional cationic waterborne polyurethane, significantly improve the corrosion resistance of film-forming material, adhesion and mechanical strength and other properties, can satisfy the performance requirement of cationic waterborne polyurethane emulsion in high-end application fields such as metal surface passivation treatment.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of high polymer material synthesis, and particularly relates to an epoxy resin modified cationic waterborne polyurethane emulsion and a preparation method thereof. The emulsion is particularly suitable for use in the field of chromium-free passivation pretreatment of metal surfaces. BACKGROUND

[0002] About 1 / 4 of the metal materials in the world are corroded by rust every year. In order to avoid the corrosion of metal materials, a relatively common method is to perform passivation treatment on the metal surface. Metal surface passivation treatment is a key process for improving the corrosion resistance and prolonging the service life of materials. Traditional passivation technology mainly uses chromium-containing passivation agents (such as hexavalent chromium or trivalent chromium compounds), which can form a dense passivation film on the metal surface and has excellent corrosion resistance. However, chromium ions are extremely harmful to the environment and human health, and especially hexavalent chromium products have been strictly limited by international environmental protection regulations (such as RoHS, REACH, etc.). Therefore, the development of environmentally friendly chromium-free passivation technology for metal surfaces has become a research hotspot in recent years.

[0003] At present, chromium-free passivation technology for metal surfaces mainly includes zirconium-based, titanium-based, molybdenum-based, silane coupling agent and organic polymer systems. Organic polymer systems, especially high molecular weight cationic waterborne polyurethane emulsion, have excellent adsorption and penetration on negatively charged surfaces (such as leather, fibers, paper, metals, etc.) due to the positive charges on the molecular chain, and are widely used as coatings, adhesives, treating agents, etc. However, the traditional cationic waterborne polyurethane emulsion is a linear polymer, which lacks reactive chemical groups that can be cross-linked and cured. After film formation, there are some inherent defects, such as relatively poor water resistance, solvent resistance, heat resistance and mechanical strength, which limit its application in high-end fields. Epoxy resin is a thermosetting resin containing epoxy groups, which is known for its excellent thermal stability, chemical stability, high modulus and strong adhesion. Therefore, by introducing epoxy groups into the polyurethane molecular chain, the flexibility, high elasticity of polyurethane and the rigidity, high strength of epoxy resin can be combined to achieve performance complementation and obtain a composite material with more excellent comprehensive performance.

[0004] At present, although there are some related researches on epoxy-modified polyurethane, most of them are focused on anionic or solvent-based systems. For cationic emulsion systems, especially how to efficiently and stably introduce epoxy resin while maintaining good storage stability and application performance of the emulsion, is still a technical difficulty. The introduction of epoxy resin may lead to emulsion demulsification and stability decline, or cause the emulsion particle size to be too large due to its hydrophobicity.

[0005] Therefore, it is of great significance to develop an epoxy resin modified cationic waterborne polyurethane emulsion which can be used for metal surface passivation, has simple synthesis process, good emulsion stability and excellent comprehensive performance. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of existing technologies and provide an epoxy resin-modified cationic polyurethane emulsion and its preparation method. This method, through molecular design, introduces reactive epoxy groups into the side chains of cationic polyurethane via chemical bonding, successfully preparing a modified emulsion with high stability, good corrosion resistance, strong adhesion, and excellent mechanical properties, while also meeting environmental protection requirements, thus providing a new solution for the development of metal surface passivation technology.

[0007] The objective of this invention is achieved through the following technical solution: an epoxy resin-modified cationic waterborne polyurethane emulsion, which introduces epoxy groups into the side chains of a cationic waterborne polyurethane polymer. In preparing the waterborne polyurethane prepolymer, a cationic hydrophilic chain extender containing epoxy groups with a specific structure is first synthesized. The specific steps include:

[0008] Step 1: First, synthesize a cationic hydrophilic chain extender containing an epoxy group with a specific structure. The cationic hydrophilic chain extender containing an epoxy group with a specific structure is prepared by reacting diethanolamine and a difunctional alkyl alcohol diglycidyl ether compound at low temperature.

[0009] Step 2: The oligomeric polyol, small molecule chain extender and crosslinking agent are dehydrated under stirring and vacuum, and then diisocyanate is added dropwise at 80℃~90℃. The reaction is carried out for 2~3 hours. Then, the cationic hydrophilic chain extender with specific structure containing epoxy groups obtained in Step 1, other cationic hydrophilic monomers and solvents are added, and the reaction is continued for 2~3 hours to obtain the prepolymer.

[0010] Step 3: Cool the prepolymer obtained in Step 2 to below 40°C, and then perform acid neutralization, water dispersion, and vacuum desolventizing treatment to obtain a cationic aqueous polyurethane emulsion with epoxy groups in the side chain.

[0011] In the above-mentioned epoxy resin modified cationic waterborne polyurethane emulsion, in step one, the molar ratio is diethanolamine: difunctional alkyl alcohol diglycidyl ether compound = 1:1.

[0012] In the first step of the above-mentioned epoxy resin modified cationic waterborne polyurethane emulsion, diethanolamine is added dropwise to a difunctional alkyl alcohol diglycidyl ether compound at room temperature. During the dropwise addition, the reaction temperature is controlled below 35°C and the addition is completed in 1 hour. After the dropwise addition is completed, the temperature is raised to 35-40°C and the reaction is continued for 1 hour to obtain a cationic hydrophilic chain extender with a specific structure containing epoxy groups.

[0013] The epoxy resin modified cationic water-based polyurethane emulsion, in step one, the bifunctional alkyl alcohol diglycidyl ether compound is one or more of 1,4-butanediol diglycidyl ether, neopentyl glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether.

[0014] The epoxy resin modified cationic water-based polyurethane emulsion, in step two, according to weight fraction, 30-50 parts of oligomer polyol, 0.5-2 parts of small molecule chain extender, 0.5-1 part of crosslinking agent, 30-50 of diisocyanate, 1-5 parts of cationic hydrophilic chain extender with specific structure containing epoxy group, and 6-12 parts of other cationic hydrophilic monomer.

[0015] The epoxy resin modified cationic water-based polyurethane emulsion, in step two, the oligomer polyol is one or more of polypropylene glycol polyol with a molecular weight of 1000-2000, polytetrahydrofuran polyol with a molecular weight of 1000-2000, polycaprolactone polyol with a molecular weight of 1000-2000, and polycarbonate polyol with a molecular weight of 1000-2000.

[0016] The epoxy resin modified cationic water-based polyurethane emulsion, in step two, the small molecule chain extender is one or more of 1,4-butanediol and dimethylolcyclohexane; the crosslinking agent is trimethylolpropane or pentaerythritol; and the diisocyanate is one or more of hexamethylene diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, and isophorone diisocyanate.

[0017] The epoxy resin modified cationic water-based polyurethane emulsion, in step two, the other cationic hydrophilic monomer is one or more of N-methyldiethanolamine, N-ethyldiethanolamine, and 3-dimethylamino-1,2-propanediol; and the solvent is acetone or butanone.

[0018] The epoxy resin modified cationic water-based polyurethane emulsion, in step three, the neutralizing agent used for acid neutralization is glacial acetic acid or formic acid.

[0019] Compared with the prior art, the present application has the following advantages:

[0020] 1. Chain extender innovation: the cationic hydrophilic chain extender synthesized in the present application retains an active epoxy group in the molecule, and the molecular structure design is flexible, and a series of cationic hydrophilic chain extenders containing epoxy groups with similar structures can be easily derived by changing the bifunctional alkyl alcohol diglycidyl ether raw material.

[0021] 2. Chemical bonding, excellent performance: By chemical reaction, the epoxy group is connected to the polyurethane side chain in a chemical bond, rather than physical blending, avoiding phase separation, and achieving a rigid and flexible molecular structure. When the obtained emulsion is formed, the epoxy group can further react with other groups with active hydrogen, increasing the crosslinking degree, and after film formation, it has the excellent elasticity of polyurethane and the high strength, high adhesion, and corrosion resistance of epoxy resin. It can meet the performance requirements of water-based polyurethane emulsion for metal chromium-free passivation pretreatment agents.

[0022] 3. Excellent emulsion stability: Since the introduced epoxy group is located on the hydrophilic monomer, the problems of emulsion demulsification and particle size coarsening caused by the introduction of hydrophobic epoxy resin are effectively avoided, and the obtained emulsion has uniform particle size and storage stability of more than 6 months.

[0023] 4. Environmentally friendly and controllable process: The acetone method is mature and controllable, and the solvent is finally removed to obtain a water-based emulsion with low VOC content and environmental friendliness. The whole reaction process is mild and easy to industrialize, and has broad application prospects. DETAILED DESCRIPTION

[0024] The application will be further described below in conjunction with examples, but is not limited thereto.

[0025] The raw materials used in the examples are commercially available industrial products unless otherwise specified.

[0026] Example 1 Preparation of epoxy resin modified cationic water-based polyurethane emulsion

[0027] Step one: synthesis of cationic hydrophilic chain extender containing epoxy group. First, add 20.2 g (0.1 mol) of 1,4-butanediol diglycidyl ether to a four-necked flask equipped with a stirrer, thermometer, dry nitrogen inlet tube and reflux condenser, and drop 10.5 g (0.1 mol) of diethanolamine at room temperature. The reaction temperature is controlled below 35°C during the dropping process, and after the dropping process is completed, the temperature is raised to 35-40°C and the reaction is continued for 1 hour to obtain a cationic hydrophilic chain extender containing epoxy group with a specific structure, which is ready for use.

[0028] Step two: preparation of prepolymer. First, add 18 g of polycarbonate diol (M = 1000), 0.3 g of dimethylolcyclohexane, and 0.3 g of trimethylolpropane to a four-necked flask equipped with a stirrer, thermometer, condenser, and vacuum outlet tube, and heat to 110°C for 60 minutes. Then, cool to 85°C, and drop 16.7 g of isophorone diisocyanate, followed by 4.2 g of N-methyldiethanolamine, 2 g of the specific structure cationic hydrophilic chain extender containing epoxy group obtained in step one, and 20 g of acetone. Continue to react for 3 hours to obtain the prepolymer.

[0029] Step three: the prepolymer obtained in step two is cooled to below 40°C, neutralized with 2 g of glacial acetic acid, then 95 g of ice water is added to form an emulsion by high-speed emulsification and dispersion, vacuum desolvation, and the product is filtered to obtain a cationic waterborne polyurethane emulsion with epoxy groups in the side chain.

[0030] Example 2 Preparation of an epoxy resin modified cationic waterborne polyurethane emulsion

[0031] Step one: synthesis of a cationic hydrophilic chain extender containing epoxy groups. First, 23 g (0.1 mol) of 1,6-hexanediol diglycidyl ether is added to a four-necked flask equipped with a stirrer, thermometer, dry nitrogen inlet tube, and reflux condenser. 10.5 g (0.1 mol) of diethanolamine is added dropwise at room temperature, and the dropwise addition is completed within 1 hour. The reaction temperature is controlled below 35°C during the dropwise addition. After the dropwise addition is completed, the temperature is raised to 35-40°C and the reaction is continued for 1 hour to obtain a cationic hydrophilic chain extender containing epoxy groups with a specific structure, which is ready for use.

[0032] Step two: preparation of a prepolymer. First, 30 g of polytetrahydrofuran diol (M = 2000), 0.5 g of dimethylolcyclohexane, and 0.6 g of trimethylolpropane are added to a four-necked flask equipped with a stirrer, thermometer, condenser, and vacuum outlet. The temperature is raised to 110°C and vacuum dehydration is maintained for 60 minutes. Then the temperature is lowered to 85°C, 22.2 g of isophorone diisocyanate is added dropwise, and the reaction is continued for 3 hours. Then 6.2 g of 3-dimethylamino-1,2-propanediol and 2 g of the cationic hydrophilic chain extender containing epoxy groups with a specific structure obtained in step one are added dropwise, and 30 g of solvent acetone is added. The reaction is continued for another 3 hours to obtain a prepolymer.

[0033] Step three: the prepolymer obtained in step two is cooled to below 40°C, neutralized with 2 g of glacial acetic acid, then 95 g of ice water is added to form an emulsion by high-speed emulsification and dispersion, vacuum desolvation, and the product is filtered to obtain a cationic waterborne polyurethane emulsion with epoxy groups in the side chain.

[0034] Comparative Example 1 Preparation of a general cationic waterborne polyurethane emulsion

[0035] Step one: preparation of a prepolymer. First, 18 g of polycarbonate diol (M = 1000), 0.3 g of dimethylolcyclohexane, and 0.3 g of trimethylolpropane are added to a four-necked flask equipped with a stirrer, thermometer, condenser, and vacuum outlet. The temperature is raised to 110°C and vacuum dehydration is maintained for 60 minutes. Then the temperature is lowered to 85°C, 16.7 g of isophorone diisocyanate is added dropwise, and the reaction is continued for 3 hours. Then 5 g of N-methyldiethanolamine and 20 g of acetone are added, and the reaction is continued for another 3 hours to obtain a prepolymer.

[0036] Step two: the prepolymer obtained in step one was cooled to below 40°C, neutralized by adding 2 g of glacial acetic acid, then emulsified and dispersed by adding 95 g of ice water at high speed to form an emulsion, vacuum desolvation, and the filtrate was obtained to obtain a common cationic waterborne polyurethane emulsion.

[0037] Comparative example 2 preparation of common cationic waterborne polyurethane emulsion

[0038] Step one: preparation of prepolymer. First, a four-necked flask equipped with a stirrer, thermometer, condenser and vacuum outlet was charged with 30 g of polytetrahydrofuran diol (M = 2000), 0.5 g of dimethylol cyclohexane, 0.6 g of trimethylolpropane, heated to 110°C, vacuum dehydrated for 60 minutes, then cooled to 85°C, and then 22.2 g of isophorone diisocyanate was added dropwise and reacted for 3 hours, then 7 g of 3-dimethylamino-1,2-propanediol cationic hydrophilic chain extender and 30 g of solvent acetone were added dropwise and reacted for another 3 hours to obtain the prepolymer.

[0039] Step two: the prepolymer obtained in step one was cooled to below 40°C, neutralized by adding 3 g of glacial acetic acid, then emulsified and dispersed by adding 140 g of ice water at high speed to form an emulsion, vacuum desolvation, and the filtrate was obtained to obtain a common cationic waterborne polyurethane emulsion.

[0040] Comparative example 3 preparation of epoxy resin modified cationic waterborne polyurethane emulsion

[0041] Step one: synthesis of cationic hydrophilic chain extender containing epoxy group. The same as example 1

[0042] Step two: preparation of prepolymer. First, a four-necked flask equipped with a stirrer, thermometer, condenser and vacuum outlet was charged with 18 g of polycarbonate diol (M = 1000), 0.3 g of dimethylol cyclohexane, 0.3 g of trimethylolpropane, heated to 110°C, vacuum dehydrated for 60 minutes, then cooled to 85°C, and then 16.7 g of isophorone diisocyanate was added dropwise and reacted for 3 hours, then 3.6 g of N-methyldiethanolamine and 3.5 g of the specific structure of the cationic hydrophilic chain extender containing epoxy group obtained in step one above and 20 g of acetone were added dropwise and reacted for another 3 hours to obtain the prepolymer.

[0043] Step three: the prepolymer obtained in step two was cooled to below 40°C, neutralized by adding 2 g of glacial acetic acid, then emulsified and dispersed by adding 95 g of ice water at high speed to form an emulsion, vacuum desolvation, and the filtrate was obtained to obtain a common cationic waterborne polyurethane emulsion.

[0044] Example 3 performance test

[0045] (I) emulsion performance

[0046] The appearance, viscosity and emulsion storage stability of the epoxy resin modified cationic waterborne polyurethane emulsion of the application are mainly investigated, and the test method is as follows:

[0047] 1. Appearance: visual inspection

[0048] 2. Emulsion viscosity: a rotary viscometer with model NDJ-1 is used to measure the viscosity of the emulsion with a solid content of 30wt% at 25℃.

[0049] 3. Storage stability: observe the changes of the emulsion in a 40℃ incubator for six months.

[0050] (II) Coating film performance

[0051] 1. Sample preparation

[0052] The emulsions of each example and the comparative example are sprayed on the degreased galvanized steel plate, the film thickness is controlled between 15-20μm, and after surface drying at room temperature, the sample to be tested is obtained by drying in an 80℃ oven for 30 minutes;

[0053] 2. Test method

[0054] The adhesion is tested according to the method of GB / T 9286-1998;

[0055] The tensile strength is tested according to the method of GB / T 1040-2006;

[0056] The corrosion resistance is tested according to the method of GB / T 10125-1997;

[0057] The solvent resistance is tested by wiping the surface of the prepared sample to be tested with a cotton ball soaked with solvent ethanol back and forth for 50 times, and the change of the appearance of the coating film surface is determined by visual inspection. The solvent resistance is divided into four levels: 1st level, no trace on the wiped part; 2nd level, only slight trace on the wiped part; 3rd level, slight trace on the wiped part; 4th level, obvious trace or coating film dissolution on the wiped part. The 1st level is the best, and the 4th level is the worst.

[0058] The test results are shown in the following table:

[0059] Table 1 Comparison of emulsion performance of examples and comparative examples

[0060]

[0061] From the detection results of the above table, it can be seen that the epoxy resin modified cationic waterborne polyurethane emulsion prepared by the method has moderate viscosity, good storage stability when the weight fraction of epoxy groups is 1-5, excellent adhesion to the substrate after film formation, and great improvement in solvent resistance, tensile strength and corrosion resistance of the coating film with the increase of the content of epoxy groups, so that the performance requirements of the waterborne polyurethane emulsion in high-end application fields such as metal chromium-free passivation treatment agents can be met, and the method has wide application prospect.

[0062] The above examples are the preferred embodiments of the present application, but the embodiments of the present application are not limited to the above examples, and any modification, replacement or improvement based on the present application is within the protection scope of the present application.

Claims

1. The application of an epoxy resin-modified cationic waterborne polyurethane emulsion in metal surface passivation, characterized in that, This involves introducing epoxy groups into the side chains of a cationic waterborne polyurethane polymer. In preparing the waterborne polyurethane prepolymer, a cationic hydrophilic chain extender with a specific structure containing epoxy groups is first synthesized. The specific steps include: Step 1: First, synthesize a cationic hydrophilic chain extender with a specific structure containing epoxy groups. Specifically, diethanolamine is added dropwise to a difunctional alkyl alcohol diglycidyl ether compound at room temperature. During the dropwise addition, the reaction temperature is controlled below 35°C, and the addition is completed in 1 hour. After the dropwise addition is completed, the temperature is raised to 35-40°C and the reaction is continued for 1 hour to obtain a cationic hydrophilic chain extender with a specific structure containing epoxy groups. The molar ratio is diethanolamine: difunctional alkyl alcohol diglycidyl ether compound = 1:

1. Step 2: 30-50 parts of oligomeric polyol, 0.5-2 parts of small molecule chain extender, and 0.5-1 part of crosslinking agent are stirred and dehydrated under vacuum. Then, 30-50 parts of diisocyanate are added dropwise at 80℃-90℃, and the reaction is carried out for 2-3 hours. Next, 1-5 parts of the cationic hydrophilic chain extender containing epoxy groups with a specific structure obtained in Step 1, 6-12 parts of other cationic hydrophilic monomers, and solvent are added, and the reaction is continued for 2-3 hours to obtain the prepolymer. The small molecule chain extender is one or more of 1,4-butanediol and dimethylolcyclohexane. The other cationic hydrophilic monomers are one or more of N-methyldiethanolamine, N-ethyldiethanolamine, and 3-dimethylamino-1,2-propanediol. Step 3: Cool the prepolymer obtained in Step 2 to below 40°C, and then perform acid neutralization, water dispersion, and vacuum desolventizing treatment to obtain a cationic aqueous polyurethane emulsion with epoxy groups in the side chain.

2. The application of the epoxy resin-modified cationic waterborne polyurethane emulsion according to claim 1 in metal surface passivation, characterized in that, In step one, the difunctional alkyl alcohol diglycidyl ether compound is one or more of 1,4-butanediol diglycidyl ether, neopentyl glycol diglycidyl ether, and 1,6-hexanediol diglycidyl ether.

3. The application of the epoxy resin-modified cationic waterborne polyurethane emulsion according to claim 1 in metal surface passivation, characterized in that, In step two, the oligomeric polyol is one or more of the following: polypropylene oxide polyol with a molecular weight of 1000-2000, polytetrahydrofuran polyol with a molecular weight of 1000-2000, polycaprolactone polyol with a molecular weight of 1000-2000, and polycarbonate polyol with a molecular weight of 1000-2000.

4. The application of the epoxy resin-modified cationic waterborne polyurethane emulsion according to claim 1 in metal surface passivation, characterized in that, In step two, the crosslinking agent is trimethylolpropane or pentaerythritol.

5. The application of the epoxy resin-modified cationic waterborne polyurethane emulsion according to claim 1 in metal surface passivation, characterized in that, In step two, the diisocyanate is hexamethylene diisocyanate. 4,4'-two One or more of cyclohexylmethane diisocyanate and isophorone diisocyanate.

6. The application of the epoxy resin-modified cationic aqueous polyurethane emulsion according to claim 1 in metal surface passivation, characterized in that, In step two, the solvent is acetone or butanone.

7. The application of the epoxy resin-modified cationic waterborne polyurethane emulsion according to claim 1 in metal surface passivation, characterized in that, In step three, the neutralizing agent used for acid neutralization is glacial acetic acid or formic acid.

Images