Preparation method of polyurethane microcapsule curing agent

Abstract

The invention discloses a method for preparing a polyurethane microcapsule curing agent. The polyurethane microcapsule curing agent comprises a microcapsule structure, wherein the microcapsule structure comprises a wall material and a core material enclosed in the wall material. The preparation method comprises the following steps: mixing and emulsifying an oil phase solution containing an isocyanate monomer and a catalyst and an aqueous phase solution containing an emulsifier to form an emulsion; adding an amine solution to the emulsion and mixing the mixture, so that the amine reacts with the isocyanate monomer at the interface to form the wall material of the microcapsule; heating the emulsion after adding the amine solution to a set temperature within 1 to 10 seconds, wherein the isocyanate monomer in the oil phase droplets reacts to be converted into an isocyanate dimer and / or an isocyanate trimer, and the isocyanate dimer and / or the isocyanate trimer constitute the core material of the microcapsule; and cooling the system after heat preservation to a set temperature within 1 to 10 seconds.

Description

[0001] This application is a divisional application of the invention patent application with application date of April 25, 2022, application number 2022104413173, and invention name "Polyurethane microcapsule curing agent, adhesive, film and respective preparation methods". Technical Field

[0002] The invention belongs to the technical field of polyurethane curing agent and polyurethane material, and particularly relates to a preparation method of a polyurethane microcapsule curing agent. Background Art

[0003] Curing agent, also known as hardener, curing agent or curing agent, is a kind of substance or mixture that promotes or controls the curing reaction. Curing agent is an indispensable additive for resin curing. Whether it is used as adhesive, coating or casting material, curing agent must be added, otherwise the resin cannot be cured.

[0004] In order to facilitate the use of coatings, adhesives, etc., a one-component polyurethane material system is used in many applications. The isocyanate is released by heating, so that it reacts with the component containing active hydrogen to increase the crosslinking density and then achieves curing. The above-mentioned one-component polyurethane material system contains a latent curing agent component that can only act as a curing agent under certain conditions. The latent curing agent will be unblocked at a certain temperature to undergo a crosslinking reaction, but will not react at room temperature.

[0005] In the prior art, a microcapsule structure is formed by deactivating the surface of TDI (toluene diisocyanate) dimer, MDI (diphenylmethane diisocyanate) dimer, IPDI (isophorone diisocyanate) dimer or IPDI trimer, and a stable suspension is prepared by protecting a colloid. The suspension is added to an emulsion to prepare a single-component polyurethane material system that can be quickly unblocked. This method of forming a microcapsule structure using solid dimers and trimers as raw materials is usually called a solid interstitial encapsulation scheme.

[0006] There are two main solid-state intermittent encapsulation schemes in the prior art: spray drying granulation and mechanical grinding. The above two methods have the following problems: pyridine is used as a solvent in the process of spray drying granulation, and the smell of pyridine is very strong. The particle size of the particles in the suspension prepared is generally 15-60um. After a period of storage, the particles with larger particle size will sink to the bottom irreversibly, so that the product is completely ineffective; the particles prepared by mechanical grinding will release a certain amount of unreacted monomers due to the crushing of large particles during the grinding process. This monomer is wrapped in it during the crystallization process and is difficult to separate after granulation. After release, it will generate a certain amount of invalid solid content components with the co-grinded amine and water, thereby affecting the overall performance. In addition, this process produces a large number of bubbles that affect processing and reduce the pH value of the polyurethane dispersion. The pH value of the product drops rapidly within a period of time after production is completed. Some pH-sensitive emulsions will immediately gel and precipitate when used.

[0007] The microcapsule curing agent is mixed with polyurethane dispersion (PUD) to form glue. After the glue forms a film, the PUD is activated at high temperature and penetrates into the microcapsule through the wall material to crosslink. However, the TDI dimer particles made by the above two schemes have irregular appearances, such as Figure 1 (TDI dimer particles prepared by spray drying granulation method) and Figure 2 (TDI dimer particles prepared by mechanical grinding method) As shown, the microcapsules formed after they react with deactivated amine in water are still irregular, and the thickness of the microcapsule wall material is also inconsistent. The microcapsules made by the above two schemes are greatly affected by the process batch. The shape and thickness of the wall material affect the penetration speed and quantity, thereby affecting the cross-linking process and the performance of the final material.

[0008] The disclosure of the above background technology content is only used to assist in understanding the inventive concept and technical solution of the present invention. It does not necessarily belong to the prior art of this patent application. In the absence of clear evidence that the above content has been disclosed on the filing date of this patent application, the above background technology should not be used to evaluate the novelty and creativity of the present application. Summary of the invention

[0009] In view of this, in order to overcome the defects of the prior art, the object of the present invention is to provide a method for preparing an improved polyurethane microcapsule curing agent.

[0010] The present invention also provides a polyurethane microcapsule curing agent prepared by the preparation method and an application thereof. The polyurethane microcapsule curing agent avoids excessive reaction of highly active isocyanate with water during the production process, thereby reducing the generation of carbon dioxide, facilitating continuous production, and avoiding a rapid decrease in pH, so that it has good compatibility with a variety of emulsions. The microcapsule particles prepared by the interfacial reaction have a uniform and smooth surface and a uniform wall material thickness, and have a more stable and controllable penetration rate and curing and cross-linking rate for polymerization under a heated state.

[0011] In order to achieve the above object, the present invention adopts the following technical solutions:

[0012] A method for preparing a polyurethane microcapsule curing agent, the polyurethane microcapsule curing agent comprises a microcapsule structure, the microcapsule structure comprises a wall material and a core material enclosed in the wall material, the preparation method comprises the following steps:

[0013] An oil phase solution containing an isocyanate monomer and a catalyst and an aqueous phase solution containing an emulsifier are mixed and emulsified to form an emulsion, wherein the aqueous phase solution constitutes an aqueous phase (continuous phase) and the oil phase solution forms droplets (dispersed phase);

[0014] adding an amine solution to the emulsion and mixing the mixture, so that the amine reacts with the isocyanate monomer at the interface to form the wall material of the microcapsule;

[0015] The emulsion after adding the amine solution is heated to 50-80° C. and kept warm for 1-8 minutes, wherein the isocyanate monomers in the droplets react and are converted into isocyanate dimers and / or isocyanate trimers, and the isocyanate dimers and / or isocyanate trimers constitute the core material of the microcapsules, and the heating rate during the heating is greater than or equal to 20° C. / s;

[0016] The system after heat preservation is cooled to 20-30° C., and the cooling rate during the cooling is greater than or equal to 20° C. / s.

[0017] In some embodiments, the entire system is heated to 50-80° C. within 1-10 seconds by controlling the heating rate to avoid water penetration during a long heating process.

[0018] Preferably, the preparation method comprises the step of adding a thickener to the cooled system for thickening, and the viscosity of the thickened system at 25° C. is 1000-2000 cps.

[0019] Preferably, the preparation method includes the step of allowing the thickened system to stand for aging, wherein the aging is to keep the thickened polyurethane microcapsule curing agent at 20-30°C for 12-36 hours. During the aging process, the remaining isocyanate monomers in the core material will be fully converted into dimers under the action of the catalyst, forming microcapsules with isocyanate dimers inside and wall materials with certain strength on the outer wall.

[0020] According to some preferred implementation aspects of the present invention, before the oil phase solution and the water phase solution are mixed, the temperature of the oil phase solution is controlled to be 20-22° C. The isocyanate monomer and the catalyst are put into the premix bin at about 20-22° C. and mixed evenly. Too low a temperature will cause the isocyanate monomer to crystallize, which is not conducive to forming uniform droplets in the water phase, while too high a temperature will cause the isocyanate monomer to be converted into a large amount of dimer crystals early, which is also not conducive to forming uniform droplets.

[0021] According to some preferred implementation aspects of the present invention, during emulsification and addition of amine solution for reaction, the temperature of the system is controlled to be 0-5°C. The low temperature of 0-5°C can significantly reduce the reaction rate of isocyanate monomer and water, reduce the generation of bubbles, make the emulsified particle size controllable, and obtain a smooth micelle interface. In some embodiments of the present invention, the aqueous phase solution is formed by adding an emulsifier to ice water, and then the temperature of the aqueous phase solution is controlled to be 0-5°C.

[0022] According to some preferred embodiments of the present invention, during emulsification, the mass ratio of the emulsifier in the aqueous solution to the isocyanate monomer in the oil solution is 0.01% to 5%, and in some embodiments, preferably 0.1% to 2%.

[0023] According to some preferred implementation aspects of the present invention, the particle size of the microcapsules in the polyurethane microcapsule curing agent is 1 to 10 μm, preferably 5 μm, and the corresponding equipment speed during emulsification is 1000 to 9000 rpm. The particle size is controlled by the amount of emulsifier and the speed of the emulsification equipment, that is, the particle size can be regulated during the reaction process, while in the traditional method, since the isocyanate dimer is prepared first, the particle size cannot be regulated in the subsequent process.

[0024] According to some preferred embodiments of the present invention, the isocyanate monomer is an isocyanate having at least two isocyanate groups -NCO, preferably toluene diisocyanate TDI, such as T80, T100, etc., and diphenylmethane diisocyanate MDI can also be used as the core material to form microcapsules.

[0025] According to some preferred embodiments of the present invention, a tubular reactor is used to heat and cool the emulsion to achieve rapid heating and cooling, the front section of the tubular reactor is used to heat the emulsion to a set temperature within 1 to 10 seconds, and the rear section of the tubular reactor is used to cool the emulsion to a set temperature within 1 to 10 seconds. The continuous production process formed by the tubular reactor does not have stability problems between batches, and the heating and cooling are rapid.

[0026] According to some preferred embodiments of the present invention, the catalyst is selected from 4-dimethylaminopyridine, pyridine, tri-tert-butylphosphine, tributylphosphine, triethylenediamine, 2,4,6-tris(dimethylaminomethyl)phenol, bis(dimethylaminoethyl)ether, 1,8-diazabicyclo[5.4.0]undecane-7-N-methylmorpholine, pentamethyldipropylenediamine, 1-methyl-4-(2-dimethylaminoethyl)piperazine, dimethylaminopyridine, 2,2'-dimorpholine diethyl ether, N,N-dimethylbenzylamine, N,N'-dimethylethanolamine, pentamethyldiethylenetriamine, one or more combinations thereof. The molar ratio between the catalyst and the isocyanate monomer is 0.001-0.5%. Too little catalyst is insufficient to produce crystallization in a short time through the tubular reactor to improve the structural strength of the microcapsule, and too much catalyst will lead to premature crystallization and inability to emulsify.

[0027] According to some preferred implementation aspects of the present invention, the amine in the amine solution is a combination of one or more selected from ammonia water, urea, ethylenediamine, pentamethylenediamine, hexamethylenediamine, hydrazine hydrate, guanidine, adipic acid dihydrazide, polyetheramine, isophoronediamine, 4,4'-diaminodicyclohexylmethane, and diethanolamine. The molar ratio between the amine in the amine solution and the isocyanate monomer is 6-12%. The mass percentage concentration of the amine solution is 5-35%, preferably about 10%-30%.

[0028] The amine solution is the encapsulation component used to transform micelles into particles, causing the surface of the micelles to undergo an interfacial reaction to form a uniform wall material. At the same time, the temperature of the ice water inhibits the reaction between water and NCO, causing NCO to react mainly with amines, and the amines and NCO undergo an interfacial reaction to form a thin layer of polyurea, i.e., the wall material, which prevents moisture from entering the core material.

[0029] According to some preferred embodiments of the present invention, the emulsifier in the aqueous phase solution is a Span emulsifier of the polyoxyethylene ether type and / or a Tween emulsifier of the polyoxyethylene ether type.

[0030] According to some preferred embodiments of the present invention, a defoamer is added to the aqueous phase solution during the emulsification, and the defoamer is a silicone defoamer and / or a mineral oil defoamer.

[0031] According to some preferred embodiments of the present invention, the thickener is a combination of one or more selected from xanthan gum, guar gum, cellulose, polyurethane thickener, polyacrylic thickener, and polyvinyl pyrrolidone. The amount of the thickener is 0.01-1%, and the viscosity of the thickened system at 25° C. is 1000-2000 cps.

[0032] According to some preferred implementation aspects of the present invention, the preparation method further comprises the step of adding a preservative to the system after thickening, wherein the preservative is an isothiazolinone fungicide, such as kasone.

[0033] In a preferred embodiment of the present invention, by controlling the heating rate and the cooling rate, the emulsion system containing the particles is rapidly heated to 50-80°C within a few seconds and maintained for about 2 minutes. At this time, due to the rapid reaction rate of the aromatic monomer, the wall material has a certain strength, and at this temperature, the isocyanate monomer has been partially converted into a dimer solid, and the entire microcapsule has a certain strength. Then, the temperature is rapidly cooled to a safe temperature (room temperature of about 20-30°C), avoiding water penetration during the process and not affecting the isocyanate monomer and dimer in the core material.

[0034] In existing application scenarios, such as pesticide and flavor microcapsules, the core material is liquid. In order to make the microcapsules reach a certain strength, the suspension is usually stirred at 40-50°C for 1-8 hours to form a solid wall material to prevent adhesion. However, in the application scenario of the present invention, such a long period of high temperature will cause a large amount of water to penetrate and react with the internal isocyanate monomers and dimers, while generating a large number of bubbles, which reduces the pH of the system. Therefore, in the present invention, by raising the temperature to about 50-80°C in a very short time, part of the wall material is rapidly matured to reach a certain strength, and the core material is also converted into a large amount of solid dimer. At this time, the microcapsules already have a certain strength, and then the temperature is rapidly reduced to 20-30°C within a few seconds, and the core material is matured to fully convert into a dimer, which prevents water from entering the core material and avoids adhesion between microcapsules.

[0035] In some embodiments of the present invention, a tubular reactor can be used to continuously heat and cool the emulsion. The tubular reactor can be divided into two sections, the front section realizes rapid heating, and the rear section realizes cooling, and the heating, cooling and insulation time can be controlled by the length and distance of the tubular reactor. After cooling to room temperature, the material is discharged, and a thickener is added to the system to thicken and prevent sedimentation, and then it is left to stand for aging.

[0036] In the preparation process of the microcapsule curing agent, all raw materials used in the present invention are in liquid state. In some embodiments of the present invention, the preparation method specifically includes the following steps:

[0037] 1) At about 20-22°C, TDI and catalyst are added into a premix bin and mixed evenly to form a solution containing isocyanate monomer and catalyst, i.e., an oil phase solution.

[0038] 2) adding an emulsifier into ice water to form an aqueous solution, which is a continuous phase; dropping the oil solution into the aqueous solution and emulsifying at high speed to form droplets with controllable particle size and smooth interface, which is a dispersed phase.

[0039] 3) Then, the capsule forming component amine solution is added dropwise and stirred to mix evenly, so that the amine reacts with the isocyanate monomer on the surface of the droplet to form a uniform wall material.

[0040] 4) The emulsion system obtained in step 3) is rapidly heated to 50-80° C. in a tubular reactor within a few seconds for about 2 minutes to rapidly mature the wall material and simultaneously convert the isocyanate monomers inside into isocyanate dimers, and then rapidly cooled.

[0041] 5) Finally, the temperature is lowered to room temperature for discharging, the system is thickened to prevent sedimentation, and then the system is aged so that the remaining TDI inside is fully converted into dimers under the action of the catalyst, thereby obtaining microcapsules and polyurethane microcapsule curing agent. The whole process is called the encapsulation scheme of the liquid continuous method.

[0042] Another object of the present invention is to provide a polyurethane microcapsule curing agent prepared by the preparation method as described above, wherein the polyurethane microcapsule curing agent includes an emulsion and microcapsules dispersed in the emulsion, wherein the microcapsules include a core material of isocyanate dimer inside and a polyurea layer wall material formed by the reaction of amine and isocyanate outside; the mass proportion of the microcapsules in the polyurethane microcapsule curing agent is 35-45%. In some embodiments, the emulsion includes components such as an emulsifier, a thickener, a preservative, and water. More specifically, in some embodiments of the present invention, by mass percentage, the polyurethane microcapsule curing agent includes 35-45% microcapsules; 0.1-2% emulsifier; 0.1-0.5% thickener; 0.1-0.5% preservative; 54-65% water. Preferably, the polyurethane microcapsule curing agent includes 39.5% microcapsules; 0.1% emulsifier; 0.3% thickener; 0.1% preservative; 60% water.

[0043] Another object of the present invention is to provide an application of the microcapsule curing agent as described above in the preparation of polyurethane materials, such as being configured into polyurethane glue (adhesive) or coating, film and other products.

[0044] The present invention provides a method for preparing a polyurethane adhesive, comprising the following steps:

[0045] 1) preparing a polyurethane microcapsule curing agent according to the preparation method described above;

[0046] 2) Adding vinyl acetate-ethylene emulsion to the polyurethane dispersion, adjusting the pH value to 6-8, adding the polyurethane microcapsule curing agent, auxiliary agent and water, stirring to obtain the polyurethane adhesive; the addition amount of the microcapsule curing agent in the polyurethane adhesive is 3-20%. The mass ratio of the polyurethane dispersion to the vinyl acetate-ethylene emulsion is preferably 6:4.

[0047] According to some preferred embodiments of the present invention, the polyurethane dispersion is prepared by the following method: heating and dehydrating a polyether polyol and / or a polyester polyol, and adding a chain extender to extend the chain;

[0048] adding diisocyanate and a catalyst to react until a set isocyanate group content is reached to obtain an isocyanate-terminated prepolymer;

[0049] After adding solvent for dilution and cooling, sodium ethylenediamine sulfonate is added for chain extension again;

[0050] After adding tris(hydroxymethyl)aminomethane for end-capping, adding water for dispersion, and removing the solvent to obtain the polyurethane dispersion. The solvent may be preferably acetone.

[0051] In some embodiments of the present invention, the method for preparing the polyurethane dispersion specifically comprises the following steps:

[0052] 1) Two polyester polyols with different molecular weights are put into a reactor, heated and dehydrated, and then a chain extender 1,4-butanediol (BDO) is added for chain extension, while the temperature is lowered to 60° C. while stirring.

[0053] 2) adding diisocyanate and catalyst, maintaining stirring at 80° C.-90° C. until the set isocyanate group NCO content is reached, to obtain an isocyanate-terminated prepolymer; the set isocyanate group content is about 1.3%.

[0054] 3) Add a solvent such as acetone to the system to dilute it and cool it to 50°C.

[0055] 4) Add an aqueous solution of sodium ethylenediaminesulfonate (AAS) and stir vigorously for 30 minutes to perform hydrophilic chain extension.

[0056] 5) adding an aqueous solution of tris(hydroxymethyl)aminomethane (TRIS) to completely react the remaining isocyanate, and then distilling off the solvent acetone to obtain an aqueous polyurethane dispersion.

[0057] Compared with the polyurethane dispersion prepared by the traditional process, the preparation method of the polyurethane dispersion of the present invention uses trishydroxymethylaminomethane for end-capping, so that the two ends of the prepared PUD molecular chain have three more hydroxyl groups, which is conducive to reaction with the curing agent.

[0058] According to some preferred embodiments of the present invention, a multifunctional amine auxiliary such as Dow's AMP95 is used to adjust the pH value.

[0059] According to some preferred embodiments of the present invention, the added auxiliary agent includes one or more of a wetting agent, a defoaming agent, and a thickening agent.

[0060] According to some preferred implementation aspects of the present invention, the viscosity of the polyurethane adhesive at 25° C. is 1500 to 3000 mPa·s; and the solid content is 35 to 60%.

[0061] The present invention provides a polyurethane adhesive prepared by the above preparation method, comprising a polyurethane dispersion and a microcapsule curing agent; the mass ratio of the polyurethane dispersion to the microcapsule curing agent is 100:5-20. In some embodiments, the polyurethane dispersion accounts for 70-85%, the microcapsule curing agent accounts for 7-12%, and the additive and water account for 10-18% in the polyurethane adhesive.

[0062] The present invention provides a method for preparing a polyurethane film, comprising the following steps: preparing a polyurethane adhesive according to the above-mentioned preparation method; coating the polyurethane adhesive on a release paper, and drying to obtain the polyurethane film. The drying temperature is lower than 60°C, preferably lower than 55°C, to avoid premature activation of a microcapsule curing agent and reaction.

[0063] The present invention provides a polyurethane film prepared by the above-mentioned preparation method.

[0064] Due to the implementation of the above technical scheme, the present invention has the following advantages compared with the prior art: the preparation method of the polyurethane microcapsule curing agent in the present invention, the wall material formed by the interfacial reaction after the liquid raw material is emulsified is continuous and uniform, and the wall material is quickly matured by rapidly heating up and then rapidly cooling down, thereby avoiding water penetration and not affecting the isocyanate monomers and dimers in the core material; the effective content of isocyanate dimers inside the microcapsule is greatly increased, thereby improving the efficiency of the cross-linking reaction. BRIEF DESCRIPTION OF THE DRAWINGS

[0065] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0066] Figure 1 This is a scanning electron microscope (SEM) photograph of TDI dimer (ADDOLINK TT) used in the preparation process of the existing commercially available microcapsule curing agent;

[0067] Figure 2 is a scanning electron microscope (SEM) image of dimer particles prepared by mechanical grinding method;

[0068] Figure 3 This is a scanning electron microscope (SEM) photograph of microcapsule particles in the polyurethane microcapsule curing agent prepared in Example 1-1 of the present invention;

[0069] Figure 4 This is a schematic diagram of the process of preparing a polyurethane microcapsule curing agent in Example 1 of the present invention;

[0070] Figure 5 It is a schematic diagram of the experimental method principle in Experiment 1 and Experiment 4 of the present invention;

[0071] Figure 6 The DSC test curve of the dry film obtained in Experiment 2 of the present invention corresponding to Example 1;

[0072] Figure 7 It is a DSC test curve diagram of the dry film obtained in Experiment 2 of the present invention corresponding to Example 2;

[0073] Figure 8 It is a DSC test curve diagram of the dry film obtained in Experiment 2 of the present invention corresponding to Example 2;

[0074] Fig. 9 This is the infrared test spectrum obtained in Experiment 3 of the present invention;

[0075] Fig.10 This is a schematic diagram of the experimental method principle in Experiment 5 of the present invention;

[0076] In the attached drawings, MDF board-1, adhesive film-2, PVC film-3, weight-4, substrate-5, push-out hole-6, and adhered object-7. DETAILED DESCRIPTION

[0077] In order to enable those skilled in the art to better understand the technical solution of the present invention, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0078] Table 1 below shows the Chinese ingredients or functions of some reagent abbreviations used in the examples and the manufacturer's abbreviations:

[0079] Table 1 Description of some reagents

[0080] Serial number abbreviation Ingredients or effects Manufacturer Abbreviation 1 TDI Toluene diisocyanate Covestro 2 IPDI Isophorone diisocyanate Covestro 3 HDI Hexamethylene diisocyanate Covestro 4 BL2514 Latent curing agent (TDI dimer) Covestro 5 AAS Sodium EDTA Evonik 6 TBUP Tributylphosphine Sigma 7 TRIS Tris(hydroxymethyl)aminomethane Sigma 8 BDO 1,4-Butanediol China-Thailand 9 T403 Polyoxypropylene triamine Huntsman 10 ALA Thickener OMG 11 L75N Thickener OMG 12 MB20 Organic bismuth catalyst Air Chemicals 13 DS2130 Dispersants Osgaard 14 UL5120 Silicone wetting agent Osgaard 15 F908 Silicone defoamer Osgaard 16 F8916 Silicone defoamer Osgaard 17 Polyester polyol I 2000 molecular weight Osgaard 18 Polyester polyol II 1800 molecular weight Osgaard 19 NE580 Water-based HDI curing agent with NCO=20.5% Osgaard 20 Span 60 Emulsifier Haishihua 21 VAE706 Vinyl acetate-ethylene emulsion WACKER 22 AMP95 Multifunctional amine additives Dow

[0081] Example 1 Preparation of microcapsule curing agent

[0082] The traditional method for preparing polyurethane microcapsule curing agent is to first make TDI into dimer solid and then disperse it in water for deactivation. Figure 1 This is the appearance of the commonly used dimer particles on the market. Figure 2 The dimer is made by grinding. It can be seen that the solid is of different sizes and the surface is extremely uneven. The shell shape of the product generated by deactivation is uncontrollable, which is manifested in the uncontrollable permeability of water to the microcapsules and the permeability of heated polymers such as polyurethane dispersions to the microcapsules during actual use. The present invention adopts a liquid continuous method to prepare a polyurethane microcapsule curing agent, and the particle size of the obtained microcapsules is relatively controllable and the surface is smooth. Figure 3 As shown, the rate at which water penetrates the wall material and the permeability of the heated polymer during use can be controlled.

[0083] Interfacial polymerization refers to emulsifying or dispersing the core material in a continuous phase containing the wall material, and then forming microcapsules on the surface of the core material through monomer polymerization reaction. The interfacial polymerization method can well prepare microcapsules with smooth and continuous particle surfaces, thereby solving the problem of irregular particles. Although this encapsulation scheme exists in the pesticide, flavor and other industries, the difference is that when the interfacial polymerization method is applied in the prior art, it is not necessary to consider the residual isocyanate during the encapsulation maturation process, so the wall material will be heated for a long time (basically more than 1h) to reach a certain strength as soon as possible to prevent adhesion between microcapsules. However, a large amount of isocyanate (isocyanate-NCO) needs to be retained in the polyurethane microcapsule curing agent for subsequent cross-linking reactions. If the temperature exceeds 40°C for a long time, a large amount of water will penetrate into the microcapsule through the wall material, resulting in a significant reduction in the internal effective ingredients. Therefore, heating and maturing microcapsules to prevent adhesion and low-temperature storage to retain a large amount of isocyanate (dimer) form a contradiction, and the existing implementation scheme of the interfacial polymerization method cannot solve this problem.

[0084] In order to solve the above problems and achieve the above objectives, the preparation method of the polyurethane microcapsule curing agent of the present invention adopts the following steps:

[0085] 1) At about 20-22°C, TDI and catalyst are added into a premix bin and mixed evenly to form a solution containing isocyanate monomer and catalyst, i.e., an oil phase solution.

[0086] 2) Add the emulsifier into ice water to form an aqueous solution (control the temperature at 0-5°C), and drop the oil phase solution into the aqueous solution to emulsify at high speed into droplets with controllable particle size and smooth interface.

[0087] 3) Then, the capsule forming component amine solution is added dropwise and stirred to mix, so that the amine reacts with the isocyanate monomer on the surface of the droplet to form a uniform wall material.

[0088] 4) The emulsion is rapidly heated to 50-80°C in a tubular reactor within a few seconds and maintained at this temperature for about 2 minutes to allow the wall material to mature rapidly and the isocyanate monomers inside to be converted into isocyanate dimers, and then the temperature is rapidly lowered.

[0089] 5) Finally, the temperature is lowered to room temperature for discharging, the system is thickened to prevent sedimentation, and then the system is aged so that the remaining TDI inside is fully converted into dimers under the action of the catalyst, thereby obtaining microcapsules and polyurethane microcapsule curing agents.

[0090] Example 1-1

[0091] like Figure 4 As shown, the preparation method of the polyurethane microcapsule curing agent in this embodiment adopts the following steps:

[0092] 1) Preparation of oil phase solution

[0093] At 20°C, 500 kg of TDI and 0.25 kg of tributylphosphine were added into a premixing bin and mixed evenly to form a solution containing isocyanate monomer and catalyst, namely, an oil phase solution.

[0094] 2) Preparation of aqueous solution

[0095] 5 kg of emulsifier and 0.5 kg of defoamer were added into 500 L of ice water and mixed evenly to form an aqueous solution containing the emulsifier, i.e., the aqueous phase solution, and the temperature thereof was controlled to be 1°C.

[0096] 3) Emulsification

[0097] The oil phase solution obtained in step 1) is introduced into an emulsifying device (continuous high-speed emulsifier) ​​at a flow rate of 27.5 kg / h and the water phase solution obtained in step 2) is introduced into an emulsifying device at a flow rate of 30 kg / h for high-speed emulsification, so that the oil phase solution forms an emulsion with a controllable particle size and a solid content of 47.8%. The particle size of the droplets can be achieved by the amount of emulsifier added and the speed of the control equipment. The temperature of the system is controlled to be 1°C during the emulsification process.

[0098] 4) Preparation of amine solution

[0099] 1.64 kg of polyetheramine was added to 17.5 kg of deionized water and stirred to form a uniform amine solution with a concentration of 9.4%, i.e., the capsule component.

[0100] 5) Interface reaction

[0101] The emulsion emulsified in step 3) is fed into a continuous mixer at a flow rate of 57.5 kg / h and the amine solution obtained in step 4) is fed into a continuous mixer at a flow rate of 17.5 kg / h, so that the diluted amine solution and isocyanate react at the surface of the droplets to form a polyurea layer, i.e., the wall material. The temperature of the system is controlled to be 1°C during the interfacial reaction.

[0102] 6) Curing of wall materials

[0103] The emulsion system was rapidly heated to 80°C within 4 seconds at a heating rate of 20°C / s through a tubular reactor and continued for 2 minutes to allow the wall material to mature rapidly. At the same time, the TDI monomer in the core material was rapidly converted into a dimer under the action of the catalyst and temperature, and then rapidly cooled to 20°C within 2 seconds at a cooling rate of 30°C / s and continued for 30 seconds.

[0104] 7) Anti-settling and anti-corrosion

[0105] The temperature is lowered to 20° C. and the material is discharged at room temperature. 0.3% by weight of a thickener xanthan gum is added to the system to thicken and prevent sedimentation. 0.1% (by weight) of an isothiazolinone fungicide, such as kasone, is added to the system.

[0106] 8) Core material maturation

[0107] The system was placed at room temperature for static aging and maintained at 25°C for 24 hours, so that the TDI in the core material that had not yet dimerized was fully converted into dimers under the action of the catalyst, and microcapsules and polyurethane microcapsule curing agents were obtained with a solid content of 39.2% and a viscosity of 1580cps.

[0108] Example 1-2

[0109] The process was carried out with reference to Example 1-1. The difference from Example 1-1 was that in step 3) of this example, 3.28 kg of amine was added to 17.5 kg of deionized water, and the other steps and parameters remained unchanged.

[0110] Examples 1-3

[0111] The process was carried out with reference to Example 1-1. The difference from Example 1-1 was that in step 1) of this example, 2.2 kg of catalyst 4-dimethylaminopyridine was added to 500 kg of TDI, and other parameters remained unchanged.

[0112] Comparative Example 1-1

[0113] The difference between this comparative example and Example 1-1 is that 100% concentration of amine is directly used in the interfacial reaction (encapsulation) instead of a diluted amine solution, which results in a large amount of agglomerate precipitation during the reaction and fails to form a stable microcapsule dispersion.

[0114] Comparative Example 1-2

[0115] The difference between this comparative example and Example 1-1 is that the wall material is matured by stirring at 50°C for 6 hours. The other steps and parameters are basically the same as those of Example 1-1. A large number of bubbles are generated during the wall material maturation process, and a small amount of agglomerate precipitation is generated. After filtering the precipitate, the dispersion has a viscosity of 4530 cps and a solid content of 35.8%.

[0116] Comparative Examples 1-3

[0117] The difference between this comparative example and Example 1-1 is that no thickener is added to the system for anti-settling treatment. The other steps and parameters are basically the same as those of Example 1-1. A dispersion with a dispersant viscosity of 320 cps and a solid content of 39.4% is obtained. After two days, a large amount of precipitation occurs in the system, which can be restored to the initial state after stirring, but will soon settle again. After a week, it will form a hard lump, and stirring cannot restore the initial state.

[0118] Example 2-1 Preparation of thermosetting one-component polyurethane adhesive

[0119] The preparation method of the thermosetting one-component polyurethane adhesive in this embodiment specifically includes the following steps:

[0120] 1) Preparation of microcapsule curing agent

[0121] Add 500g TDI monomer and 0.05g tributyl phosphine into a container, keep the temperature between 20 and 25°C, stir evenly to form an oil phase solution; add 8g Span 60 into 828g ice water, stir evenly to form an aqueous phase solution; slowly drip the above oil phase solution into the aqueous phase solution, and disperse at high speed for half an hour to form a stable emulsion.

[0122] 100 g of 30% polyetheramine aqueous solution was slowly added dropwise to the emulsion, and stirred for half an hour. The emulsion was fed into a tubular reactor, and the temperature was rapidly raised to 80°C within 3 seconds, maintained for 2 minutes, and then rapidly lowered to 25°C within 2 seconds. The temperature was maintained for 30 seconds, and the emulsion was discharged into a stirring container. 20 g of DS2130 dispersant, 2 g of F908 defoamer, and 2 g of ALA thickener were added while stirring. After aging for 36 hours, microcapsule curing agent A was obtained. The viscosity at 25°C was 1540 mPa·s, the solid content was 39%, and the microcapsule particle size was D 50 =5um.

[0123] 2) Preparation of waterborne polyurethane dispersion

[0124] 500g of polyester polyol I and 50g of polyester polyol II were put into a reactor, heated to 115°C for dehydration for 1h, and then 2.5g of BDO was added, and the temperature was lowered to 60°C while stirring. Then 42g of HDI, 28g of IPDI, and 3g of MB20 were added, and the temperature was kept at 80°C-90°C and stirred until the isocyanate content reached 1.28%. 850g of acetone was added, and the system temperature was cooled to 50°C.

[0125] 7.0 g of AAS was diluted in 55 g of water, then added to the system and stirred for 30 min; then 8 g of TRIS was dissolved in 555 g of aqueous solution and added to the system for dispersion, and finally acetone was distilled off to obtain an aqueous polyurethane dispersion B. The melting point of the solid content of the obtained polyurethane dispersion was 44.12° C., the solid content was 49.2% by weight, and the viscosity at 25° C. was 1290 mPa·s.

[0126] 3) Preparation of polyurethane adhesive

[0127] 300 g of aqueous polyurethane dispersion B and 200 g of VAE706 were added to a container, and the pH value was adjusted to about 7 using AMP95. Then, 35 g of microcapsule curing agent A, 0.5 g of wetting agent UL5120, 0.5 g of defoaming agent F8916, and 50 g of water were added. After stirring for half an hour, 0.5 g of thickener L75N was added to obtain a finished polyurethane adhesive with a viscosity of 2130 mPa·s at 25°C and a solid content of 45%.

[0128] Example 2-2:

[0129] On the basis of Example 2-1, the dosage of microcapsule curing agent A was increased from 35 g to 50 g, and the others remained unchanged.

[0130] Example 2-3

[0131] On the basis of Example 2-1, the dosage of microcapsule curing agent A was increased from 35 g to 100 g, and the others remained unchanged.

[0132] Comparative Example 2-1

[0133] On the basis of Example 2-1, 35 g of microcapsule curing agent A was replaced with 35 g of Covestro Dispercoll XP BL2514, and the rest remained unchanged.

[0134] Comparative Example 2-2

[0135] Based on Example 2-1, 35 g of microcapsule curing agent A was replaced with 50 g of Covestro Dispercoll XP BL2514, and the rest remained unchanged.

[0136] Comparative Examples 2-3

[0137] On the basis of Example 2-1, 35 g of microcapsule curing agent A was replaced with 100 g of Covestro Dispercoll XPBL 2514, and the rest remained unchanged.

[0138] Comparative Examples 2-4

[0139] On the basis of Example 2-1, the amount of Span 60 added was increased to 18 g, and other conditions remained unchanged, and a microcapsule curing agent B was obtained, which had a solid content of 39%, a viscosity of 4130 mPa·s, and a particle size of D 50 <1um.

[0140] Comparative Examples 2-5

[0141] On the basis of Example 2-1, 35 g of microcapsule curing agent A was replaced with 35 g of microcapsule curing agent B, and the rest remained unchanged.

[0142] Comparative Examples 2-6

[0143] On the basis of Example 2-1, 35 g of microcapsule curing agent A was replaced with 50 g of microcapsule curing agent B, and the rest remained unchanged.

[0144] Comparative Examples 2-7

[0145] On the basis of Example 2-1, 35 g of microcapsule curing agent A was replaced with 100 g of microcapsule curing agent B, and the rest remained unchanged.

[0146] Comparative Examples 2-8

[0147] On the basis of Example 2-1, 35 g of microcapsule curing agent A was replaced with 35 g of NE580 curing agent, and the rest remained unchanged.

[0148] Comparative Examples 2-9

[0149] On the basis of Example 2-1, no microcapsule curing agent A or microcapsule curing agent B was added, and the others remained unchanged.

[0150] Example 3 and Comparative Example 3 Polyurethane Film

[0151] The glue prepared in Example 2 and Comparative Example 2 was coated on release paper (film) by roller coating or slit coating, and dried into film by variable temperature drying tunnel to form Example 3 and Comparative Example 3. The drying temperature was lower than 55° C. to prevent activation of the microcapsule curing agent.

[0152] Tests and Results

[0153] 1) Scanning electron microscopy (SEM)

[0154] The raw materials of the commercially available microcapsule curing agent products (TDI dimer, ADDOLINK TT), the dimer particles obtained by the grinding scheme, and the microcapsule curing agent prepared in Example 1-1 were tested by scanning electron microscopy (SEM), and the scanned images obtained were as follows: Figure 1 , Figure 2 and Figure 3 shown.

[0155] from Figure 1 , Figure 2 It can be seen that the solid TDI dimer is of different sizes and has an extremely uneven surface. The shell shape of the product generated after deactivation is uncontrollable, which is reflected in the uncontrollable permeability to water and the permeability of the subsequent PUD. Figure 3 The microcapsules shown have relatively controllable particle sizes, smooth surfaces, and controllable rates of water penetration through the wall material and polymer permeability during use. Figure 3 The microcapsules prepared in Example 1-1 have a diameter of about 5 um.

[0156] 2) Related tests

[0157] Experiment 1

[0158] The microcapsule curing agent prepared in Example 1-1, Example 1-2, Example 1-3 and Comparative Example 1-2 was made into glue according to the same formula, and was scraped on the MDF board 1 using a 50um preparation device, with a glue application area of ​​50*200mm. After drying, a glue film 2 was obtained, and a PVC film 3 (45 threads) was attached to the glue film 2, and a 180° peeling test was performed. After hot pressing at a temperature of 100°C for 2 minutes, a 10N weight 4 was immediately hung, and the weight was immediately placed in an oven to observe the peeling distance (within 5 minutes) of the weight at different temperatures (70-90°C). Figure 5 As shown, 70℃, 80℃ and 90℃ are independent experiments. The test results (unit: cm) are shown in Table 2:

[0159] Table 2 Test results

[0160] Example 1-1 Example 1-2 Examples 1-3 Comparative Example 1-2 70℃ <1 <1 <1 12 80℃ 2 5 5 20 90℃ 3 7 8 20

[0161] From the experimental results in Table 2, it can be seen that after hot pressing at 100°C for 2 minutes, Examples 1-1, 1-2, and 1-3 showed high initial temperature resistance at 70°C, indicating that PUD and isocyanate have reacted to a certain extent to increase the molecular weight and have high reaction efficiency, while the crosslinking degree of Comparative Example 1-2 is lower than that of the Examples, which means that the polyurethane microcapsule curing agent prepared in the Examples can achieve traditional unblocking and crosslinking at a lower temperature and in a shorter time, while the traditional curing agent may need to react at 120°C for 1 hour. And the peeling effect of the Examples at 80°C and 90°C is much better than that of the Comparative Examples.

[0162] Experiment 2

[0163] The polyurethane microcapsule curing agents prepared in Example 1-1, Example 1-2 and Comparative Example 1-2 were used to prepare glue according to the same glue formula, and were coated on release paper to prepare dry films with a thickness of 50 μm. The dry film samples were tested using DSC, and the obtained spectra were as follows: Figure 6-8 shown.

[0164] pass Figure 6-8 It can be seen that the enthalpies of the DSC test curves of the dry films corresponding to Example 1-1, Example 1-2 and Comparative Example 1-2 are 22.616 J, 23.723 J and 12.093 J, respectively, that is, the enthalpy of the DSC test curve of Comparative Example 1-2 is much smaller than that of Example 1-1 and Example 1-2, indicating that the reaction efficiency of the polyurethane microcapsule curing agent prepared in the Example with PUD is greater than that of Comparative Example 1-2.

[0165] Experiment 3

[0166] The three dry films prepared in Experiment 2 were subjected to infrared tests respectively. The results are as follows: Fig. 9 shown.

[0167] pass Fig. 9 The infrared spectrum shows that the -1 In the region, the peak values ​​of Examples 1-1 and 1-2 are much larger than those of Comparative Example 1-2. 2240-2280cm -1 The region corresponds to the stretching vibration peak of -N=C=O, indicating that the curing agents prepared in Example 1-1 and Example 1-2 contain more effective isocyanate components. The PUD polymer activated at a temperature of 70-100°C will penetrate into the microcapsule through the wall material of the microcapsule and react with the encapsulated isocyanate. The more effective isocyanate the curing agent contains, the higher the efficiency of the reaction.

[0168] Experiment 4

[0169] like Figure 5As shown, some polyurethane adhesives in the above Example 2 (2-1 to 2-3) and Comparative Example 2 (2-1 to 2-9) were subjected to initial temperature resistance test:

[0170] Use a preparation device to scrape the polyurethane adhesive onto the MDF board 1 to form a 50um wet film thickness adhesive layer (width 5cm, length 20cm), then place it in an oven at room temperature or below 40°C to dry until it is not sticky, forming an adhesive film 2, and then cover the 35-thread-thick PVC film 3 on top of the adhesive film 2 for a 180° peel test. Use a hot press machine to heat press at 60°C for 2min or 80°C for 2min, then immediately put the workpiece into an oven at 80°C, hang a 1kg weight 4, and observe the displacement distance of the PVC film (within 5min). The following is the initial heat resistance test displacement result (cm):

[0171] Table 3 Test results

[0172]

[0173] Through the experiment and the results in Table 3 above, it can be seen that the effect of the embodiment is significantly better than that of the comparative example. And the microcapsule curing agent with a particle size of about 1 to 5 um is more suitable, although the microcapsules in comparative examples 2-5 to 2-7 have a smaller particle size (D 50 <1um), larger specific surface area, but because the wall material occupies too much isocyanate, the invalid solid content is high, and the effective isocyanate content is low, resulting in poor actual crosslinking effect. Moreover, the result of comparative example 2-9 without any curing agent under the initial temperature resistance test conditions is that all the materials are peeled off, while in comparative example 2-8 with a two-component curing agent (NE580), the initial temperature resistance is not improved because the crosslinking reaction fails to occur in a short time.

[0174] Experiment 5

[0175] like Fig.10 As shown, the polyurethane adhesive film prepared in Example 3 and Comparative Example 3 was subjected to a push-out test: the adhesive film 2 was sandwiched between a substrate 5 (size 4*4cm) and an adhered material 7 (diameter 2.1cm), hot pressed at 80°C for 120-240s, and a stick-like object was moved to a push-out hole 6 (diameter 0.9cm) at a speed of V=10mm / min to push out the adhered object. The maximum pressure on the adhered object when it falls was converted into pressure (MPa), which is the push-out value. The test substrate 5 was 304 stainless steel treated with a primer (such as silane, primer, UPUV, etc.), and the adhered object was PC, PET, PI, fabric, etc. The following are the results of the push-out test (MPa):

[0176] Table 4 Test results

[0177]

[0178] Through the experiment and the data in Table 4 above, the effect of the embodiment is obviously better than that of the comparative example. And corresponding to the result of Experiment 4, the microcapsule curing agent with a particle size of about 1 to 5 um is more suitable, and the smaller particle size (D 50 <1um) has a larger specific surface area, but the wall material occupies too much isocyanate, the invalid solid content is high, resulting in poor actual cross-linking effect and poor test results.

[0179] Since the cross-linking efficiency is proportional to the specific surface area of ​​the latent curing agent within a certain range, and the emulsion particles (15-60 μm) of the prior art are relatively large, the amount of latent curing agent added is relatively large, and the excess latent curing agent is equivalent to a solid filler that affects the final performance of the film. In the preparation method of the polyurethane microcapsule curing agent of the present invention, the particle size of the microcapsule is controllable (1-5 μm), which prevents the emulsion from settling too quickly. Even if there is partial sedimentation after long-term storage, it can be restored to a normal state by simple stirring; the wall material formed by the interface reaction after the liquid raw material is emulsified is continuous and uniform, so that the penetration ability of PUD to the latent curing agent after activation is stable, and there is no problem of large-scale release of carbon dioxide in the later stage; and there is no batch stability problem in continuous production. On the other hand, the existing PUD has a large molecular weight, a small number of terminal hydroxyl groups or amine groups, and a small number of latent curing agents that can react; when preparing the polyurethane dispersion, the present invention introduces TRIS to increase the hydroxyl content without reducing the molecular weight, which is more conducive to reacting with the microcapsule curing agent and improving the cross-linking density and efficiency.

[0180] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with this technology to understand the contents of the present invention and implement them accordingly. They cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a polyurethane microcapsule curing agent, wherein the polyurethane microcapsule curing agent comprises a microcapsule structure, characterized in that: The microcapsule structure includes a wall material and a core material enclosed in the wall material, and the preparation method includes the following steps: An oil phase solution containing an isocyanate monomer and a catalyst and an aqueous phase solution containing an emulsifier are mixed and emulsified to form an emulsion; adding an amine solution to the emulsion and mixing the mixture, so that the amine reacts with the isocyanate monomer at the interface to form the wall material of the microcapsule; The emulsion after adding the amine solution is heated to 50-80° C. within 1-10 seconds, wherein the isocyanate monomers in the oil phase droplets react and are converted into isocyanate dimers and / or isocyanate trimers, and the isocyanate dimers and / or isocyanate trimers constitute the core material of the microcapsules; The system after heat preservation is cooled down to 20-30℃ within 1-10s.

2. The preparation method according to claim 1, characterized in that: A tubular reactor is used to heat and cool the emulsion. The front section of the tubular reactor is used to heat the emulsion to 50-80°C within 1-10 seconds, and the rear section of the tubular reactor is used to cool the emulsion to 20-30°C within 1-10 seconds.

3. The preparation method according to claim 1 or 2, characterized in that: When heating, raise the temperature to 50~80℃ and keep it warm for 1~8min.

4. The preparation method according to claim 1 or 2, characterized in that: The heating rate during the heating is greater than or equal to 20°C / s, and the cooling rate during the cooling is greater than or equal to 20°C / s.

5. The preparation method according to claim 1, characterized in that: The mass ratio of the emulsifier to the isocyanate monomer in the aqueous solution is 0.01% to 5%.

6. The preparation method according to claim 5, characterized in that: The mass ratio of the emulsifier to the isocyanate monomer in the aqueous solution is 0.1% to 2%.

7. The preparation method according to claim 5, characterized in that: The corresponding equipment speed during emulsification is 1000~9000rpm.

8. The preparation method according to claim 1, 5 or 7, characterized in that: The particle size of the microcapsules in the polyurethane microcapsule curing agent is 1-10 μm.

9. The preparation method according to claim 1, characterized in that: The preparation method comprises the steps of adding a thickener to the cooled system for thickening, wherein the viscosity of the thickened system at 25° C. is 1000-2000 cps; and / or the step of keeping the cooled system at 20-30° C. for 12-36 hours.

10. The preparation method according to claim 9, characterized in that: The preparation method comprises firstly adding a thickener to a cooled system for thickening, and then keeping the cooled system at 20-30° C. for 12-36 hours.

11. The preparation method according to claim 1, characterized in that: Before mixing the oil phase solution and the water phase solution, the temperature of the oil phase solution is controlled to be 20-22°C.

12. The preparation method according to claim 1, characterized in that: The emulsification and the addition of the amine solution are controlled to react at 0-5°C.

13. The preparation method according to claim 12, characterized in that: The aqueous phase solution is formed by adding an emulsifier into ice water.

14. The preparation method according to claim 1, characterized in that: The mass percentage concentration of the amine solution is 5-35%.

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