阅读说明：本技术 香豆素封端的水性聚氨酯及制备方法、水性聚氨酯丙烯酸酯的固化膜的制备方法 (Coumarin-terminated waterborne polyurethane, preparation method thereof and preparation method of waterborne polyurethane acrylate curing film ) 是由 董秋静 齐晓慧 孙长瑞 胡彦 罗春华 于 2021-01-14 设计创作，主要内容包括：本发明公开了一种香豆素封端的水性聚氨酯,其中制备水性聚氨酯的原料包括以下重量份的组分：多异氰酸酯20～40份；低聚物多元醇40～65份；香豆素封端剂10～25份。本发明还公开了一种香豆素封端的水性聚氨酯的制备方法、水性聚氨酯丙烯酸酯的固化膜的制备方法。本发明所提供的香豆素封端的水性聚氨酯具有长期贮存的稳定性的优点,而且在制备过程中避免了有机溶剂的使用,也无需添加丙酮降低体系黏度,减少了VOC的排放。(The invention discloses coumarin terminated waterborne polyurethane, wherein the raw materials for preparing the waterborne polyurethane comprise the following components in parts by weight: 20-40 parts of polyisocyanate; 40-65 parts of oligomer polyol; 10-25 parts of a coumarin end-capping agent. The invention also discloses a preparation method of the coumarin terminated waterborne polyurethane and a preparation method of a curing film of the waterborne polyurethane acrylate. The coumarin-terminated waterborne polyurethane provided by the invention has the advantage of long-term storage stability, avoids the use of an organic solvent in the preparation process, does not need to add acetone to reduce the viscosity of a system, and reduces the discharge of VOC.)

1. The coumarin terminated waterborne polyurethane is characterized in that raw materials for preparing the waterborne polyurethane comprise the following components in parts by weight:

20-40 parts of polyisocyanate;

40-65 parts of oligomer polyol;

10-25 parts of a coumarin end-capping agent.

2. The waterborne polyurethane of claim 1, wherein the raw materials further comprise the following components in parts by weight:

3. the aqueous polyurethane according to claim 1,

the waterborne polyurethane is decomposed at 250-290 ℃,

the maximum fluorescence excitation wavelength of the waterborne polyurethane is 330 nm-340 nm, and the maximum fluorescence emission wavelength is 370 nm-390 nm.

4. A preparation method of coumarin terminated waterborne polyurethane is characterized by comprising the following steps:

step 1, feeding, including adding a polyisocyanate and oligomer polyol mixture;

and 2, adding a coumarin end-capping reagent.

5. The method of claim 4, wherein the coumarin capping agent comprises 7-hydroxyethyloxy-4-methylcoumarin, 7-amino-4-trifluoromethylcoumarin, or 7-hydroxy-4-methylcoumarin, preferably 7-hydroxyethyloxy-4-methylcoumarin.

6. The method of claim 4 or 5, wherein in step 1, the adding further comprises adding an aqueous chain extender and a cross-linking agent.

7. The production method according to one of claims 4 to 6,

the reaction temperature of the step 1 is 75-85 ℃, and the reaction time is 3-4 h; and/or

The reaction temperature of the step 2 is 75-90 ℃, and the reaction time is 2.5-3.5 h.

8. The method of manufacturing according to claim 4, further comprising:

and 3, emulsifying, namely adding a neutralizing agent and water.

9. The production method according to claim 8, wherein, in step 3,

the reaction temperature after the neutralizer is added is 30-60 ℃ and the reaction time is 20-45 min; and/or

The reaction temperature after adding water is 20-30 ℃ and the reaction time is 1-2 h.

10. A method for producing a cured film of an aqueous urethane acrylate, preferably using the coumarin-terminated aqueous polyurethane according to any one of claims 1 to 3, which comprises:

step 1, mixing coumarin-terminated waterborne polyurethane, epoxy acrylate and water to obtain a waterborne polyurethane acrylate emulsion, optionally, preparing the waterborne polyurethane according to the method of any one of claims 4 to 9;

step 2, adding a photoinitiator into the waterborne polyurethane acrylate emulsion to obtain an intermediate product;

and 3, coating the intermediate product on the surface of a substrate, and performing ultraviolet radiation curing to obtain the cured film.

Technical Field

The invention relates to the technical field of photocuring materials, in particular to coumarin-terminated waterborne polyurethane and a preparation method thereof, and a preparation method of a curing film of waterborne polyurethane acrylate.

Background

With the continuous development of the polyurethane industry, more and more industries and enterprises apply polyurethane, and the polyurethane material has wide application, can replace rubber, plastic, nylon and the like, and is used in various building fields. The solvent type polyurethane in the polyurethane adhesive has flammable, explosive, volatile and strong odor, causes air pollution when in use, and has toxicity. The curing speed is slow, the production efficiency is low, and the method is not suitable for rapid automatic production. The waterborne polyurethane is a novel polyurethane system which takes water as a dispersion medium instead of an organic solvent, and has the advantages of no pollution, safety, reliability, excellent mechanical property, good compatibility, easy modification and the like. With the increasing call and pressure for ecological environment protection, the environmental awareness of people is continuously enhanced, and some developed countries successively establish related fire-fighting regulations and solvent regulations to limit the use of solvent-based polyurethane, so that the development of waterborne polyurethane materials becomes a research hotspot.

Studies have shown that coumarin compounds have physiological and biological activities in many aspects, and thus are widely used in pharmaceutical and engineering fields. Through a large number of experiments, the coumarin compound has an intramolecular conjugated structure, can generate electron transfer, and therefore has a fluorescent property. In addition, the coumarin derivative has a benzopyran ring rigid structure, so that the thermal stability of the polyurethane can be improved. The UV-cured polyurethane coating has better effects on reducing atmospheric pollution and saving energy due to the adoption of UV curing, meets the development requirements of the current environment-friendly, energy-saving and safe materials, and thus becomes the development direction of the current polyurethane coating.

However, the structure of the existing waterborne polyurethane contains more hydrophilic groups, so that the waterproof and waterproof performances of the existing waterborne polyurethane are poor. In addition, as the fluorescent chromophore generally consists of a large number of conjugated double bond benzene rings or heterocycles, the fluorescent polyurethane material containing the structure has poor weather resistance, and the problems of yellowing, reduced gloss and the like easily occur under the condition of ultraviolet illumination. Currently, there are few solutions in the literature that can simultaneously improve the stability of fluorescent polyurethane materials.

Disclosure of Invention

Based on the problems, the fluorescent high-solid-content waterborne polyurethane is prepared by performing end-capping treatment on polyurethane molecules by using fluorescent coumarin and introducing a fluorescent substance into a polyurethane chain through a covalent bond, and has long-term storage stability. In addition, the cured film made of polyurethane has good thermal stability and strong adhesive force, thereby completing the invention.

In order to achieve the above object, in one aspect, the present invention provides a coumarin terminated aqueous polyurethane, wherein the raw materials for preparing the aqueous polyurethane comprise the following components in parts by weight:

20-40 parts of polyisocyanate;

40-65 parts of oligomer polyol;

10-25 parts of a coumarin end-capping agent.

In another aspect, the present invention provides a method for preparing coumarin terminated waterborne polyurethane, comprising:

step 1, feeding, including adding a polyisocyanate and oligomer polyol mixture;

and 2, adding a coumarin end-capping reagent.

In another aspect, the present invention provides a method for preparing a cured film of a waterborne urethane acrylate, comprising:

step 1, mixing coumarin-terminated waterborne polyurethane, epoxy acrylate and a water cross-linking agent to obtain a waterborne polyurethane acrylate emulsion;

step 2, adding a photoinitiator into the aqueous polyurethane acrylate emulsion to obtain an intermediate product;

and 3, coating the intermediate product on the surface of the substrate, and performing ultraviolet radiation curing to obtain a cured film.

The coumarin-terminated waterborne polyurethane, the preparation method thereof and the method for preparing the waterborne polyurethane acrylate curing film have the beneficial effects that:

(1) according to the invention, the polyurethane molecules are subjected to end-capping treatment by using the fluorescent coumarin, and the fluorescent substance is introduced into a polyurethane chain through a covalent bond, so that the fluorescent high-solid-content waterborne polyurethane is prepared, and the fluorescent high-solid-content waterborne polyurethane has the advantage of long-term storage stability;

(2) in the process of preparing the coumarin terminated waterborne polyurethane, water is used for replacing an organic solvent, the excellent performance of the traditional solvent type is reserved, and the coumarin terminated waterborne polyurethane has the advantages of safety, no combustion, small smell, excellent mechanical performance, good compatibility, no pollution, low VOC (volatile organic compound) emission, easiness in operation and processing and the like;

(3) the cured film prepared from the waterborne polyurethane acrylate has good thermal stability and stronger adhesive force;

(4) in the invention, the light curing process preferably adopts a UV curing mode, and compared with the traditional heat curing technical scheme, the UV curing has the characteristics of energy conservation, environmental protection, greenness and high efficiency;

(5) the preparation method provided by the invention is simple, mild in condition, high in preparation efficiency and great in application potential.

Drawings

FIG. 1 is a schematic diagram of differential scanning calorimetry analysis of purified CWPU prepared according to different formulations in examples 1 to 3;

FIG. 2 is a schematic view of differential scanning calorimetry analysis of cured films prepared according to different formulations in examples 1 to 3;

FIG. 3 is a schematic representation of thermogravimetric analysis of purified CWPU prepared according to different formulations of examples 1-3;

FIG. 4 is a schematic view of thermo-gravimetric analysis of cured films prepared according to different formulations in examples 1-3;

FIG. 5 is a schematic diagram of the fluorescence spectrum analysis of purified CWPU prepared according to different formulations in examples 1 to 3;

FIG. 6 is a schematic view of fluorescence spectrum analysis of cured films prepared according to different formulations in examples 1 to 3;

FIG. 7 is a schematic representation of gel permeation chromatography analysis of purified CWPU prepared according to different formulations of examples 1-3;

FIG. 8 is a graph showing the results of performance tests on cured films prepared according to different formulations in examples 1 to 3.

Detailed Description

The present invention will be described in further detail below with reference to preferred embodiments and examples. The features and advantages of the present invention will become more apparent from the description. The word "exemplary" is used exclusively herein to mean "serving as an example, embodiment, or illustration. Any embodiment described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments.

The main chain of polyurethane contains repeated-HNCOO-structural unit, which is generally prepared by the addition polymerization of polyisocyanate and cross-linking agent polymer, and has the characteristics of high strength, high wear resistance, solvent resistance and the like. By varying the ratio of NCO to OH in the polymer, both thermoset and thermoplastic polyurethanes can be obtained.

Due to the particularity of the isocyanate reaction, the preparation of the aqueous polyurethane cannot adopt the free radical emulsion polymerization method of the common aqueous vinyl synthetic resin. The principle in the preparation of aqueous polyurethanes is that the crosslinker raw materials must be incorporated into the polyurethane molecular structure prior to aqueous processing. The preparation of most waterborne polyurethanes involves two main steps: (1) synthesizing a polyurethane solution or a polyurethane prepolymer with the participation of oligomer diol; (2) dispersed in water under shear.

Based on the steps, the invention provides coumarin terminated waterborne polyurethane in a first aspect. In the first aspect, the raw materials for preparing the waterborne polyurethane comprise the following components in parts by weight:

20-40 parts of polyisocyanate;

40-65 parts of oligomer polyol;

10-25 parts of a coumarin end-capping agent.

In particular, coumarin, also known as 1, 2-benzopyrone, is an important fragrance. It is characterized in that double bonds on a coumarin lactone ring undergo dimerization reaction under the irradiation of 350nm ultraviolet light or sunlight to form a quaternary ring structure; then, the reverse dimerization reaction is carried out under the irradiation of 254nm, and the four-membered ring is opened and reduced into the original coumarin monomer.

The coumarin has a special molecular structure, so that the coumarin derivatives with different absorption and fluorescence generation wavelengths can be obtained by modifying substituents at different positions on a coumarin ring. Coumarin derivatives have strong fluorescence in different light area ranges, so that the coumarin derivatives are used in the research fields of fluorescent sensors, fluorescent probes, biological food, plant research, chemistry, pesticides, environment and the like.

The fluorescence property of the coumarin compound depends on the function of substituent groups at each position of a coumarin ring to a great extent, and the functions of the substituent groups at the 3-position and the 7-position are particularly obvious. The change of the property of the 7-position electron supply group and the 3-position and 4-position electron absorption groups can cause the color of the coumarin compound to generate different fluorescence properties.

In the prior art, isocyanate can react with some weak reactive hydrides, and the obtained product is stable at normal temperature and reversely reacts under certain conditions, namely, a 'blocking' reaction and a 'deblocking reaction'. Common blocking agents include phenols, caprolactam, ethyl acetoacetate, acetylacetone, diethyl malonate, sodium bisulfite, imidazoles, 3, 5-dimethylpyrazole, and the like.

In the present invention, preferably, the coumarin capping agent comprises 7-hydroxyethyloxy-4-methylcoumarin, 7-amino-4-trifluoromethylcoumarin or 7-hydroxy-4-methylcoumarin. More preferably, the coumarin capping agent is 7-hydroxyethyloxy-4-methylcoumarin.

In the invention, the addition of the 7-ethoxyl-4-methylcoumarin not only can increase the water resistance of the aqueous polyurethane, but also is beneficial to increasing the stability of the fluorescent polyurethane material.

Specifically, polyisocyanates are a special class of chemicals having-N ═ C ═ O functional groups, which are used primarily as raw materials for the manufacture of polyurethane materials. In the present invention, the polyisocyanate is preferably at least one of isophorone diisocyanate, tolylene isophorone diisocyanate, hexamethylene diisocyanate, diphenylmethane diisocyanate, tolylene diisocyanate, xylylene diisocyanate, naphthalene-1, 5-diisocyanate, methylcyclohexyl diisocyanate, dicyclohexylmethane diisocyanate, and tetramethylxylylene diisocyanate.

Since the polyurethane adhesive prepared from isophorone diisocyanate (IPDI) has excellent optical stability and chemical resistance, the polyurethane adhesive is generally used for preparing high-grade polyurethane adhesives and is a curing agent of hydroxyl prepolymer (namely polypropylene glycol) required by polyurethane adhesives of composite propellants. More preferably, therefore, in the present invention, the diisocyanate is isophorone diisocyanate. Preferably, the weight part of the isophorone diisocyanate is 25-35 parts.

Polyisocyanates form polyurethanes with hydroxyl-containing compounds. The hydroxyl-containing compounds commonly used in the preparation of polyurethane are polyether crosslinking agents, polyester crosslinking agents and the like. The ether group in the polyether cross-linking agent structure is easy to rotate, so that the polyether cross-linking agent has good flexibility and excellent low-temperature performance, and the ether group is not easy to hydrolyze and also has good hydrolysis resistance. However, the α carbon of the ether bond is easily oxidized, and a series of oxidative degradation reactions are likely to occur. The polyester polyurethane has high strength, good adhesive force, poor water resistance and short storage stability period.

Preferably, the oligomer polyol comprises at least one of polyether diol and polyester diol with molecular weight of 400-2000, wherein

The polyether glycol comprises at least one of polyethylene oxide glycol, polypropylene oxide glycol, polytetramethylene ether glycol and polytetrahydrofuran ether glycol;

the polyester diol comprises at least one of polycaprolactone diol, polyethylene adipate diol, polypropylene adipate diol, polybutylene adipate diol, polycarbonate diol, and polyhexamethylene adipate diol.

Specifically, polytetrahydrofuran ether glycol is a linear polyether glycol having hydroxyl groups at both molecular terminals, and the molecule is in a linear formula HO [ CH₂CH₂CH₂CH₂O]_nThe structure of H, ether bond is connected on the skeleton, two ends are primary hydroxyl groups, and the structure has orderly arranged molecular structure. It is readily soluble in alcohols, esters, ketones, aromatic hydrocarbons and chlorinated hydrocarbons, and insoluble in aliphatic hydrocarbons and water.

Since the polytetrahydrofuran ether glycol has good low temperature resistance, hydrolysis resistance, salt water resistance and mold resistance, in the present invention, it is preferable that the oligomer polyol is polytetrahydrofuran ether glycol. Preferably, the weight part of the polytetrahydrofuran ether glycol is 45-60 parts.

Meanwhile, the polyester polyol used in the invention has high molecular weight, so that the waterborne polyurethane has good thermal stability. The solid content of the waterborne polyurethane emulsion is improved by optimizing the raw material composition and the proportion.

In fact, the aqueous chain extender is a substance which contains an ionic group or a group capable of being ionized and introduces a polyurethane chain segment while the prepolymer is subjected to chain extension. Wherein, the length of the chain extension reaction time and the dosage of the aqueous chain extender have influence on the solid content of the aqueous polyurethane.

The length of chain extension time is a key for influencing the solid content of the emulsion, and with the increase of chain extension reaction time, the central H atom of a urea bond structure can generate overhigh crosslinking degree among system molecules, so that the relative molecular mass of the system is rapidly increased in a short time, and the system finally generates a gel phenomenon due to the association of a hydrophobic chain segment, so that the system cannot be dispersed in water.

The amount of aqueous chain extender used also has an effect on the emulsion solids content. The content of the aqueous chain extender is closely related to the volume of the water swelling layer, the content of the hydrophilic group is reduced, the volume of the water swelling layer can be reduced, and the high-solid-content aqueous polyurethane emulsion is obtained, but the emulsion is in a lime water state and has poor storage stability. The aqueous chain extender is an important component for well dispersing the polyurethane in water, and has influence on the solid content of the emulsion, so that the aqueous polyurethane with high solid content can be obtained by balancing the relationship between the aqueous chain extender and the aqueous chain extender.

In the present invention, preferably, the aqueous chain extender is at least one of a sulfonate-type chain extender and a carboxylate-type chain extender; wherein

The sulfonate chain extender comprises at least one of ethylenediamine ethanesulfonic acid sodium salt and 1, 4-butanediol-2-sodium sulfonate,

the carboxylate type chain extender comprises at least one of dimethylolpropionic acid, dimethylolbutyric acid, dimethylolvaleric acid, dimethylolhexanoic acid, dimethylolheptanoic acid, dimethylolnonanoic acid and dimethyloldecanoic acid.

As dimethylolpropionic acid is not only a chain extender in the preparation process of the waterborne polyurethane, but also can enable the polyurethane to obtain self-emulsifying property, and can prepare the self-emulsifying waterborne polyurethane with excellent stability, the invention preferably selects dimethylolpropionic acid as the waterborne chain extender.

In the present invention, the weight part of the aqueous chain extender is preferably 4.0 to 6.5 parts. More preferably, 4.5 to 6.0 parts.

In the present invention, the crosslinking agent mainly functions as a crosslinking agent. The cross-linking agent is also called curing agent, which can convert linear or slightly branched chain type macromolecules into three-dimensional network structure so as to improve the strength, heat resistance, wear resistance, solvent resistance and other properties of the macromolecules. In the present invention, preferably, the crosslinking agent is trimethylolpropane.

In the present invention, the crosslinking agent is preferably 0.40 to 3.3 parts by weight. More preferably, 0.45 to 3 parts.

In the invention, in order to stabilize the waterborne polyurethane, a certain amount of neutralizing agent needs to be added, wherein the neutralizing agent is an organic base which can be at least one of diethanolamine, triethanolamine, triethylamine, N-dimethyl isopropanolamine, triethylene diamine and dimethyl cyclohexylamine.

In the present invention, it is preferable that the neutralizing agent is 2 to 10 parts by weight. More preferably, 5 to 7 parts.

In the invention, a proper amount of water can be added to obtain the waterborne polyurethane emulsion. Preferably, the amount of water is such that the solids content of the emulsion is from 40 wt.% to 45 wt.%.

In the invention, in order to make the reaction rapidly proceed, a certain amount of catalyst needs to be added, wherein the catalyst is at least one of dibutyltin dilaurate, stannous octoate, tetramethylbutanediamine and triethylenediamine.

In the present invention, the weight part of the catalyst is preferably 0.05 to 0.21 part. More preferably, 0.08 to 0.18 parts.

In one embodiment of the invention, the raw materials for preparing the waterborne polyurethane mainly comprise:

30 parts by weight of isophorone diisocyanate;

53 parts by weight of polytetrahydrofuran ether glycol;

0.17 part by weight of dibutyltin dilaurate;

5.3 parts by weight of dimethylolpropionic acid;

0.54-2.7 parts by weight of trimethylolpropane;

6 parts of triethylamine;

17.46 parts by weight of 7-ethoxyl-4-methylcoumarin;

water was used in an amount to give an emulsion having a solids content of 40 wt.%.

In a first aspect of the present invention,

according to the invention, the polyurethane molecules are subjected to end-capping treatment by using the fluorescent coumarin, and the fluorescent substance is introduced into a polyurethane chain through a covalent bond, so that the fluorescent high-solid-content waterborne polyurethane is prepared, and the fluorescent high-solid-content waterborne polyurethane has the advantage of long-term storage stability. In addition, the coumarin has a benzopyran ring rigid structure, so that the thermal stability of the coumarin is enhanced. The glass transition temperature of the waterborne polyurethane is about-40 ℃, and the waterborne polyurethane tends to be stable at 450 ℃.

Compared with the traditional solvent type polyurethane, the coumarin terminated waterborne polyurethane prepared by the invention replaces organic solvent with water, retains the excellent performance of the traditional solvent type polyurethane, and has the advantages of safety, no combustion, small smell, excellent mechanical performance, good compatibility, no public hazard, low VOC (volatile organic compound) emission, easy operation and processing and the like.

In a second aspect, the present invention provides a method for preparing a coumarin terminated waterborne polyurethane, comprising:

step 1, feeding, including adding a polyisocyanate and oligomer polyol mixture;

and 2, adding a coumarin end-capping reagent.

In this embodiment, the adding in step 1 further comprises adding an aqueous chain extender and a cross-linker.

In a specific embodiment of the invention, the reaction temperature of the step 1 is 75-85 ℃ and the time is 3-4 h; and/or

The reaction temperature of the step 2 is 75-90 ℃, and the reaction time is 2.5-3.5 h.

In this embodiment, the reaction conditions of step 1 enable the reaction of the polyisocyanate and the oligomeric polyol to be controlled and sufficient, and the reaction conditions of step 2 enable the coumarin capping agent to be reacted with maximum efficiency.

In one embodiment of the present invention, a method of preparing a coumarin terminated waterborne polyurethane further comprises: and 3, emulsifying, namely adding a neutralizing agent and water.

In the present embodiment of the method of the present invention,

the reaction temperature after the neutralizing agent is added in the step 3 is 30-60 ℃, and the reaction time is 20-45 min; and/or

The reaction temperature after adding water in the step 3 is 20-30 ℃ and the reaction time is 1-2 h.

In the specific embodiment, the mixture prepared in step 2 is further emulsified and cooled, which is beneficial to obtaining the room-temperature multi-curing aqueous polyurethane emulsion.

In one embodiment of the invention, the method for preparing coumarin terminated waterborne polyurethane mainly comprises the following steps:

step 1, mixing 20-40 parts of diisocyanate, 40-65 parts of oligomer diol, 0.40-3.3 parts of cross-linking agent and 4.0-6.5 parts of aqueous chain extender, heating to 75-85 ℃, adding 0.08-0.18 part of catalyst, and reacting for 3-4 hours, preferably 2.5-3 hours to obtain isocyanate-terminated polyurethane;

preferably, the reaction is carried out under nitrogen exchange.

In order to mix the crosslinking agent with other raw materials, the crosslinking agent may be first dissolved in a ketone solvent, such as acetone, butanone, N-methylpyrrolidone, etc.

In step 1, the preferred crosslinking agent is Trimethylolpropane (TMP).

In the present invention, the ratio of TMP to oligomeric diol has a significant impact on the isocyanate-terminated polyurethane synthesis and subsequent photocured crosslinking. In the synthesis of isocyanate-terminated polyurethane, when TMP exceeds 5%, such as 7%, of oligomer diol, the reaction is uncontrollable, and the isocyanate-terminated polyurethane is gelled after reacting for half an hour, so that the reaction is incomplete, and the subsequent coumarin termination and emulsification cannot be carried out. When TMP is 5% of oligomer diol, the reaction system is very viscous after 2.5h of reaction, and coumarin end capping and emulsification can be carried out. If TMP is not added, the molecular weight of emulsifier molecules is increased only through the coumarin group light addition reaction in the light curing process, and the light crosslinking can not be realized, so that the stability of the light curing film is improved.

Step 2, adding 10-25 parts of coumarin end-capping agent into the obtained isocyanate end-capped polyurethane, reacting at 75-90 ℃ for 2.5-3.5 h to obtain coumarin end-capped waterborne polyurethane;

step 3, respectively adding 2-10 parts of neutralizing agent into the coumarin terminated waterborne polyurethane, cooling to 30-60 ℃, and reacting for 20-45 min; then adding a certain amount of water, cooling to 20-35 ℃, reacting for 1-2 h at the rotating speed of 700-1000 r/min to obtain the coumarin terminated aqueous polyurethane emulsion with the solid content of 40%.

Specifically, the aqueous polyurethane emulsion is obtained by stirring uniformly in a stirring manner such as magnetic stirring or glass rod stirring, and the reaction speed can be increased and the reaction can be more sufficient by stirring. In order to disperse the emulsion uniformly, the rotation speed is preferably 800r/min to 900 r/min.

In one embodiment of the present invention, a method of preparing a coumarin terminated waterborne polyurethane further comprises: purifying the coumarin terminated aqueous polyurethane emulsion with the solid content of 40%, wherein the purification steps mainly comprise:

(1) taking 3ml of coumarin terminated aqueous polyurethane emulsion with the solid content of 40 percent to form a film on a substrate. Preferably, the emulsion is applied to the glass slide by means of a coating tool or spin coating.

(2) The film on the substrate is dried. Preferably, the mixture is firstly dried in a constant temperature oven at 60 ℃ for 24 hours and then dried in a vacuum oven at 60 ℃ for 6 hours.

(3) Extraction was performed with tetrahydrofuran and diethyl ether. Preferably, it is dissolved in 15ml of tetrahydrofuran, precipitated in 150ml of diethyl ether to give a viscous solid, and the supernatant diethyl ether is decanted.

(4) The viscous solid was dried. Preferably, the preservative film is dried in a vacuum oven at 60 ℃ for 24 hours, and the preservative film is taken out and the number of the preservative film is sealed for standby.

In a second aspect of the present invention,

according to the invention, the polyurethane molecules are subjected to end-capping treatment by using the fluorescent coumarin, and the fluorescent substance is introduced into a polyurethane chain through a covalent bond, so that the fluorescent high-solid-content waterborne polyurethane is prepared, and the fluorescent high-solid-content waterborne polyurethane has the advantage of long-term storage stability. In addition, the coumarin has a benzopyran ring rigid structure, so that the thermal stability of the coumarin is enhanced.

In the process of preparing the coumarin terminated waterborne polyurethane, water is used for replacing an organic solvent, the excellent performance of the traditional solvent type is reserved, and the coumarin terminated waterborne polyurethane has the advantages of safety, no combustion, small smell, excellent mechanical performance, good compatibility, no pollution, low VOC (volatile organic compound) emission, easiness in operation and processing and the like.

The preparation method provided by the invention is simple, mild in condition, high in preparation efficiency and great in application potential.

In a third aspect, the present invention provides a method for preparing a cured film of an aqueous urethane acrylate, comprising:

step 1, mixing coumarin-terminated waterborne polyurethane, epoxy acrylate and water to obtain waterborne polyurethane acrylate emulsion;

step 2, adding a photoinitiator into the aqueous polyurethane acrylate emulsion to obtain an intermediate product;

and 3, coating the intermediate product on the surface of the substrate, and performing ultraviolet radiation curing to obtain a cured film.

Preferably, the photoinitiator is a uv photoinitiator. The photoinitiator is at least one selected from 2-hydroxymethyl phenyl propane-1-ketone, diethoxy acetophenone, 1-hydroxycyclohexyl benzophenone, 2-hydroxy-2-methyl-1-p-ethyl ether phenyl acetone and isopropyl thioxanthone. More preferably, the photoinitiator is 2-hydroxymethylphenylpropan-1-one. The photoinitiator has the advantages of high activity, high initiation efficiency, good solubility, low odor, low pollution, yellowing resistance and good intermiscibility with the crosslinking agent in the application, so that the curing time can be effectively reduced by adding the photoinitiator into the curing film in the application, and the photoinitiator is more environment-friendly and energy-saving.

In one embodiment of the invention, the aqueous polyurethane acrylate comprises the following raw materials in parts by weight:

11-30 parts of coumarin terminated waterborne polyurethane;

5-15 parts of epoxy acrylate;

35-50 parts of water.

In the embodiment, the method further comprises adding 0.7-2.5 parts of a cross-linking agent.

In particular, the above-mentioned crosslinking agents also function as diluents, acting as solvents and/or for reducing the viscosity of the reactant blend.

The cross-linking agent is selected from one or more of trimethylolpropane trimethacrylate, ethylene glycol dimethacrylate, trimethylolpropane triacrylate and pentaerythritol tetraacrylate.

Preferably, the crosslinking agent is selected from one or more of trimethylolpropane trimethacrylate and trimethylolpropane triacrylate.

More preferably, the crosslinker is trimethylolpropane trimethacrylate. In the experimental process, the trimethylolpropane trimethacrylate has moderate crosslinking density and high activity, particularly, the product obtained after photocuring has better toughness, the shock resistance of the product is improved, the price of the product is low, and the cost can be reduced.

In one embodiment of the invention, the preparation method of the cured film of the waterborne polyurethane acrylate mainly comprises the following steps:

step 1, stirring and mixing 11-30 parts of coumarin terminated aqueous polyurethane emulsion with the solid content of 40%, 5-15 parts of epoxy acrylate, 35-50 parts of water and 0.7-2.5 parts of trimethylolpropane triacrylate in a beaker at a high speed until the emulsion is completely dispersed to obtain aqueous polyurethane acrylate white emulsion with the solid content of 40%.

Step 2, taking 1-3 parts of the white emulsion of the waterborne polyurethane acrylate with the solid content of 40% in the step 1, and adding 0.036-0.198 part of a photoinitiator into the white emulsion of the waterborne polyurethane acrylate to obtain the white emulsion of the waterborne polyurethane acrylate;

and 3, coating the white emulsion of the waterborne polyurethane acrylate on a substrate, drying at a constant temperature, drying in vacuum, finally illuminating by using an ultraviolet lamp in a nitrogen environment to obtain a cured film, and cooling to room temperature.

In a third aspect of the present invention,

the cured film prepared from the waterborne polyurethane acrylate has good thermal stability and strong adhesive force. The glass transition temperature of the cured film was about 70 ℃. The cured film starts to decompose at about 240 to 270 ℃ and finishes decomposing at about 430 ℃, so that the heat resistance of the cured film is improved. The hardness of the cured film is smaller and is between 1B and 2B; the glossiness is 123-117; the adhesive force is strong and is between 2-3 grades; the water absorption is easy, and the contact angle is 50-70.

The light curing process of the invention preferably adopts a UV curing mode, and compared with the traditional heat curing technical scheme, the UV curing has the characteristics of energy conservation, environmental protection, greenness and high efficiency.

Examples

To further illustrate the present invention, the following examples (1%, 3%, 5% by mass of Trimethylolpropane (TMP) to the oligomer diol) will be described in detail. The starting materials used in the following examples of the present invention are all commercially available products.

The present invention is further described below by way of specific examples, which are, however, merely exemplary and do not limit the scope of the present invention in any way.

Example 1

(1) The preparation method of the coumarin terminated aqueous polyurethane emulsion comprises the following steps:

step 1, under the protection of nitrogen, adding 30g of isophorone diisocyanate (IPDI), 53g of polytetrahydrofuran ether glycol (PTMG-1000), 5.3g of dimethylolpropionic acid (DMPA) and 0.54g of Trimethylolpropane (TMP) into a container, heating to 75-85 ℃, adding 0.17g of dibutyltin dilaurate (DBTDL), and reacting for 2.5-3 hours to obtain isocyanate-terminated polyurethane;

step 2, adding 17.46g of coumarin (HEOMC), reacting at 75-90 ℃ for 2.5-3.5 h to obtain coumarin terminated waterborne polyurethane;

step 3, cooling to 40-50 ℃, adding 6g of TEA, and reacting for 20-30 min; and cooling to 25-30 ℃, adding a certain amount of deionized water to control the solid content to be 40 wt.%, and stirring at a high speed for 1-2 h to obtain the coumarin terminated waterborne polyurethane emulsion CWPU, which is marked as 1.

(2) Purification of No. 1:

taking 3ml of the emulsion to form a film on a substrate, drying in a constant temperature oven at 60 ℃ for 24h, drying in a vacuum oven at 60 ℃ for 6h, dissolving in 15ml of tetrahydrofuran, precipitating in 150ml of diethyl ether to obtain a viscous solid, pouring out the supernatant diethyl ether clear solution, drying in the vacuum oven at 60 ℃ for 24h, taking out the preservative film, and sealing for later use.

(3) Preparation of curing film prepared from compound emulsion

11g of coumarin-terminated aqueous polyurethane emulsion, 5g of epoxy acrylate and 38g of deionized water are added into a container, 0.75g of trimethylolpropane Triacrylate (TPGMA) is added into the mixture, and the mixture is stirred and dispersed until the emulsion is completely dispersed, so that the aqueous polyurethane acrylate emulsion with the solid content of 40% is obtained.

132mg 1173 photoinitiator was added to the emulsion to give a mixture of intermediate products.

Coating the mixture of the intermediate products on a substrate, drying for 24h in a constant-temperature oven at 50 ℃, taking out, drying for 24h in a vacuum oven at 60 ℃, then illuminating for 10 min-30 min in a nitrogen atmosphere by using an ultraviolet lamp to obtain a cured film, and cooling to room temperature for later use. The cured film is labeled M1.

Example 2

The preparation method of the coumarin-terminated aqueous polyurethane emulsion in this example is similar to the preparation method in example 1, and the only difference is that the mass of Trimethylolpropane (TMP) in the preparation method of the coumarin-terminated aqueous polyurethane emulsion is 1.62g, and the obtained coumarin-terminated aqueous polyurethane emulsion CWPU is recorded as 2. The cured film is labeled M2.

Example 3

The preparation method of the coumarin-terminated aqueous polyurethane emulsion in this example is similar to the preparation method in example 1, and the only difference is that the mass of Trimethylolpropane (TMP) in the preparation method of the coumarin-terminated aqueous polyurethane emulsion is 2.7g, and the obtained coumarin-terminated aqueous polyurethane emulsion CWPU is recorded as 3. The cured film is labeled M3.

Examples of the experiments

Experimental example 1

Differential scanning analysis of cured films of the coumarin terminated waterborne polyurethane and waterborne polyurethane acrylate purified in the embodiments 1-3 comprises the following specific steps:

a DSC-2000 differential scanning calorimeter is adopted, an air-aluminum tray is taken as a reference, the nitrogen flow rate is 50mL/min, the temperature rise rate is 10 ℃/min, and the temperature range is-100-200 ℃ in a pure nitrogen atmosphere.

FIG. 1 shows differential scanning calorimetry analysis of purified CWPU prepared according to different formulations in examples 1 to 3 of the present invention; FIG. 2 shows the differential scanning calorimetry analysis of cured films of different formulations of aqueous urethane acrylates in examples 1 to 3 of the present invention;

from the differential scanning calorimetry curves in fig. 1-2, it can be seen that the glass transition temperatures of different polymers are different, and from fig. 1, it can be seen that the glass transition of the coumarin terminated waterborne polyurethane synthesized with the TMP content of 1%, 3% and 5% is near-40 ℃, but is not obvious, and as the TMP content increases, the branching degree increases and the glass transition disappears. As shown in FIG. 2, the glass transition temperature of the waterborne polyurethane emulsion after being compounded with epoxy acrylate is increased to about 70 ℃ after photocuring.

Experimental example 2

Thermogravimetric analysis of the cured films of the coumarin terminated waterborne polyurethane and waterborne polyurethane acrylate purified in the embodiments 1-3 specifically comprises the following steps:

a Q600 thermogravimetric analyzer is adopted, an empty porcelain crucible is used as a reference, a heating speed of 10 ℃/min is set under the atmosphere of pure nitrogen, and the temperature of a test sample is 0-600 ℃.

FIG. 3 shows thermogravimetric analysis of purified CWPU prepared according to different formulations in examples 1 to 3 of the present invention; FIG. 4 shows the cured film thermogravimetric analysis of the aqueous urethane acrylates of different formulations in examples 1 to 3 of the present invention.

It can be seen from fig. 3 that the purified CWPU starts to decompose at 250-290 c, and after decomposition is complete at 450 c, it tends to stabilize. The CWPU is water-based polyurethane, so that the water is easily absorbed to increase the self gravity, the water in the polymer is separated from the polymer in the form of water vapor when the temperature begins to rise and reaches the boiling point of water, the weight of the polymer is rapidly reduced, and the weight cannot be greatly reduced when the water in the polymer is basically evaporated at the temperature of more than or equal to 400 ℃. From FIG. 4, it is found that the decomposition of the cured film of the aqueous urethane acrylate starts from about 240 ℃ to 270 ℃ and almost ends when the temperature reaches about 430 ℃, and as compared with FIG. 3, the molecular weight of the cured film increases, the water absorption decreases, the water content in the polymer decreases, and the heat resistance increases accordingly.

Experimental example 3

The fluorescence spectrum analysis of the cured films of the coumarin terminated waterborne polyurethane and waterborne polyurethane acrylate purified in the embodiments 1-3 comprises the following specific steps:

the fluorescence emission spectrum is measured by adopting an F97pro fluorescence spectrophotometer, absolute ethyl alcohol is used as a solvent, the excitation bandwidth is set to be 5nm, the emission bandwidth is set to be 5nm, and the scanning speed is set to be 300 nm/min.

FIG. 5 shows the fluorescence spectrum analysis of purified CWPU prepared according to different formulations in examples 1 to 3 of the present invention; FIG. 6 shows fluorescence spectrum analysis of cured films of aqueous urethane acrylates of different formulations in examples 1 to 3 of the present invention.

As the coumarin molecule contains fluorescent components, the product obtained by the reaction of the coumarin molecule also has fluorescence, and as can be seen from figure 5, the maximum excitation spectrum of the polymer is between 330nm and 340nm, the emission spectrum is between 370nm and 390nm, and the maximum fluorescence value is 3500. It can be seen from fig. 5 that the excitation and emission spectra exhibit mirror symmetry. The three different ratios of TMP polymers do not differ much. As can be seen from FIG. 6, the maximum absorption of the cured film of the aqueous urethane acrylate has an excitation wavelength of 350nm to 360nm, and the maximum fluorescence value of 8300 has a wavelength of 380nm to 400 nm. Wherein the fluorescence spectrum in FIG. 5 is measured in solution and the fluorescence spectrum in FIG. 6 is measured in a solid film.

Experimental example 4

And (3) analyzing the performances of the cured films of the coumarin terminated waterborne polyurethane and waterborne polyurethane acrylate purified in the embodiments 1-3.

(1) Gel permeation chromatography: an N2000 type gel permeation chromatograph is adopted, the column temperature is 40 ℃, tetrahydrofuran is used as a mobile phase, the flow rate is set to be 1.0ml/min, the temperature of a differential detector is 35 ℃, a sample solution is prepared according to the concentration of about 2g/ml, and narrow-distribution polystyrene is used as a standard sample for calibration.

(2) Measurement of hardness of cured film: this experiment was performed according to GB/T1730-1993.

(3) Measurement of gloss of cured film: ETB-0686 type gloss meter.

(4) Hardness of the cured film: GB/T1730-1993 standard.

(5) And (3) adhesive force of a cured film: GB/T9286-1998 standard.

(6) Contact angle of cured film: JC2000D1 model contact angle measuring instrument.

FIG. 7 shows gel permeation chromatography analysis of purified CWPU prepared according to different formulations in examples 1 to 3 of the present invention; FIG. 8 shows the results of the performance test of the cured films of the aqueous urethane acrylates of different formulations in examples 1 to 3 of the present invention.

It can be seen from fig. 7 that the relative molecular weight of the resulting aqueous polyurethane is greater as the TMP content is greater. As can be seen from FIG. 8, the cured film of the waterborne polyurethane acrylate has the characteristics of small hardness, small adhesive force, high viscosity, easy water absorption and the like.

The present invention has been described in detail with reference to the specific embodiments and the exemplary embodiments, but the description should not be construed as limiting the present invention. Those skilled in the art will appreciate that various equivalent substitutions, modifications or improvements may be made to the technical solution of the present invention and its embodiments without departing from the spirit and scope of the present invention, which fall within the scope of the present invention.