Method for reducing shrinkage stress of near infrared light-cured resin using shape memory microcapsules

Abstract

This application relates to a method for reducing shrinkage stress in photocurable coatings using shape memory microcapsules, belonging to the field of photocurable coatings. Shape memory polyurethane / graphene oxide microcapsules are prepared through interfacial polymerization, and these microcapsules are applied to near-infrared photocurable resins to reduce shrinkage stress during the curing process. Utilizing the photothermal conversion effect of graphene oxide, the microcapsules rapidly recover their shape, transforming from an ellipsoidal shape to a spherical shape while maintaining wall thickness. This significantly increases the microcapsule volume, alleviating shrinkage stress generated during curing. Reduction of shrinkage stress in photocurable coatings can be achieved with relatively low addition amounts; at an addition amount of 5 wt%, shrinkage stress can be reduced by approximately 30.4%. Simultaneously, the addition of microcapsules improves coating adhesion. The microcapsules of this application are suitable for photocurable coatings, adhesives, electron beam-cured coatings, adhesives, etc.

Description

Technical Field

[0001] This application relates to a method for reducing shrinkage stress in near-infrared photocurable resins using shape-memory microcapsules, and belongs to the field of photocurable coatings. Background Technology

[0002] Shape memory polymers are a class of smart materials that can be designed into a temporary shape under certain conditions and recover their shape under the influence of external light, heat, magnetism, etc. The shell material of shape memory microcapsules is a shape memory polymer. After being made into microcapsules, they can be deformed (e.g., into an ellipsoid) using certain techniques and maintained in that state. Subsequently, under certain stimuli, the deformed ellipsoidal shape can return to its initial spherical state. For example, common thermally responsive shape memory refers to the shape memory microcapsules recovering their shape after reaching a specific temperature (generally the melting point or glass transition temperature of the shell).

[0003] Near-infrared light-curing resins can be rapidly cured by irradiation with near-infrared light. Since the wavelength range of near-infrared light is 700-1500 nanometers, which is longer than that of ultraviolet light, it can penetrate the resin better and has less thermal impact on the material during the curing process.

[0004] Solid particles such as graphene oxide have a strong absorption effect on near-infrared light, undergoing photothermal conversion under near-infrared irradiation and releasing a large amount of heat. UV-curable coatings all suffer from shrinkage during the curing process. The fundamental reason is that the intermolecular forces involved in the curing reaction change from van der Waals forces to covalent bonds, reducing the intermolecular distance. This manifests macroscopically as dimensional shrinkage, flexing, deformation, and even stress cracking, affecting their service life and potentially endangering life and property. Compared to traditional UV-curable resin systems, near-infrared curing systems have the advantage of greater penetration depth, thus attracting widespread attention; however, shrinkage stress during the curing process remains unavoidable. In recent years, researchers have addressed this issue by adding inorganic fillers and intumescent monomers to coating formulations, and by improving curing processes. However, these methods all have significant drawbacks. Inorganic fillers require large amounts and do not participate in the coating's curing reaction, reducing its performance. The preparation methods for intumescent monomers are expensive and economically unviable, hindering widespread industrial application. While improving curing processes is widely used in industry, it does not fundamentally reduce the shrinkage rate.

[0005] Patent application number 202310035211.8 discloses a method for reducing the volume shrinkage of photocurable coatings by using shape memory microcapsules. The method utilizes the volume change of the microcapsules during the transformation of their morphology from ellipsoidal to spherical to alleviate the shrinkage stress generated during the curing process.

[0006] However, the shape recovery is only achieved through shrinkage stress generated during the curing process of the resin system, and the speed and effectiveness of this shape recovery need to be improved. Therefore, a new technology needs to be developed to address this issue. Summary of the Invention

[0007] To address this issue, this application designs a shape memory microcapsule that can significantly reduce shrinkage stress generated during curing. This application prepares a shape memory microcapsule with a shell doped with solid particles that strongly absorb near-infrared light. After being stretched and deformed, this microcapsule can recover its shape under the thermal effect of near-infrared light irradiation. The shape memory microcapsule recovers its shape by utilizing the combined effect of the thermal effect generated by solid particles such as graphene oxide during near-infrared light curing and the shrinkage stress generated during resin curing. The volume change of the microcapsule during the transformation from ellipsoidal to spherical shape alleviates the shrinkage stress generated during curing. The volume / surface area ratio decreases when the shape memory microcapsule becomes ellipsoidal; it increases during shape recovery. That is, the volume increases significantly while the surface area of ​​the microcapsule remains constant or changes very little. By adding deformed shape memory microcapsules to a near-infrared curable coating, the ellipsoidal microcapsules recover their spherical shape during resin curing, increasing in volume and reducing shrinkage stress within the curing system, thus solving this problem.

[0008] To achieve the above objectives, the present invention provides the use of shape memory microcapsules in near-infrared light-curing resins. The shape memory microcapsules, after being stretched and deformed, are added to the light-curing resin to reduce shrinkage stress during resin curing. The shell of the shape memory microcapsules is doped with solid particles that strongly absorb near-infrared light. The thermal effect generated by the solid particles under infrared light irradiation is used as a stimulus to promote the shape memory microcapsules to recover their shape.

[0009] In some preferred embodiments, the amount of shape memory microcapsules added to the photocurable resin is 0.01wt%-5wt%;

[0010] Furthermore, the shrinkage stress during the curing of the UV-curable resin is reduced by 10%-40%.

[0011] Furthermore, the near-infrared light-curing resin includes, but is not limited to, acrylic near-infrared light-curing resin, vinyl near-infrared light-curing resin, siloxane near-infrared light-curing resin, polyimide near-infrared light-curing resin, and polyurethane near-infrared light-curing resin.

[0012] Furthermore, the preparation method of shape memory microcapsules includes the following steps:

[0013] S1. Preparation of aqueous phase: The aqueous phase is an aqueous solution containing stabilizer, solid particles and oligomeric polyol;

[0014] S2. Preparation of the oil phase: The oil phase is a liquid phase containing isocyanate and oil-soluble solvent;

[0015] S3. Emulsion preparation: Mix the oil phase and the aqueous phase, disperse them evenly, and prepare an emulsion;

[0016] S4. The droplets in the emulsion are thermally solidified through a reaction device, and then polyols or polyamines are added for chain extension to form the shape memory microcapsules.

[0017] S5. Disperse the shape memory microcapsules in a PVA film and perform thermal stretching to obtain the stretched and deformed shape memory microcapsules.

[0018] The solid particles mentioned in step S1 are particles with a particle size of 10nm-5μm that have strong absorption of near-infrared light.

[0019] Furthermore, the stabilizers include, but are not limited to, one or a combination of alkylphenol polyoxyethylene ethers, fatty alcohol polyoxyethylene ethers, fatty amine polyoxyethylene ethers, and polymeric additives;

[0020] In some preferred embodiments, the stabilizer is an alkylphenol polyoxyethylene ether compound, selected from one or a combination of nonylphenol polyoxyethylene ether, octylphenol polyoxyethylene ether, bis / tributylphenol polyoxyethylene ether, alkylphenol polyoxyethylene ether, phenethylphenol polyoxypropylene polyoxyethylene ether, benzylphenol polyoxyethylene ether, di / tribenzylphenol polyoxyethylene ether, benzyl dimethylphenol polyoxyethylene ether, dibenzyl isopropylphenylphenol (also known as dibenzyl compound phenol) polyoxyethylene ether, benzyl biphenol polyoxypropylene polyoxyethylene ether, phenethylphenol polyoxyethylene ether, phenethylphenol polyoxyethylene ether, phenethyl isopropylphenylphenol polyoxyethylene ether, diphenylethyl compound phenol polyoxyethylene ether, phenethyl biphenol polyoxyethylene ether, and phenethyl naphthol polyoxyethylene ether.

[0021] In some preferred embodiments, the co-stabilizer is a fatty alcohol polyoxyethylene ether or a similar product, selected from one or a combination of lauryl alcohol polyoxyethylene ether, isooctyl polyoxyethylene ether, octadecyl alcohol polyoxyethylene ether, isothietrol polyoxyethylene ether, fatty alcohol polyoxyethylene ether, phenethylphenol polyoxyethylene ether, phenethylphenylpropylphenol polyoxyethylene ether, and phenethyl biphenol polyoxyethylene ether.

[0022] In some preferred embodiments, the stabilizer is a fatty amine polyoxyethylene ether compound, selected from fatty amine (also known as alkylamine) polyoxyethylene ether, fatty amide polyoxyethylene ether, alkylamine oxide, quaternary ammonium alkoxide and similar products.

[0023] In some preferred embodiments, the stabilizer is a polymeric additive selected from alkylphenol polyoxyethylene ether formaldehyde condensate, arylalkylphenol polyoxyethylene ether formaldehyde condensate, phenethylphenol polyoxyethylene ether formaldehyde condensate, isopropylphenylphenol polyoxyethylene ether formaldehyde condensate, benzylphenol polyoxyethylene ether formaldehyde condensate, biphenol polyoxyethylene ether formaldehyde condensate, 98-99% of fully hydrolyzed polyvinyl alcohol, and partially hydrolyzed polyvinyl alcohol with a degree of hydrolysis of 88-89%, and ethylene oxide polyoxypropylene. Block copolymers, ethylene oxide-butane copolymers, ethylene oxide-propylene oxide-butane copolymers, polycarboxylate salts: polyacrylic acid, sodium polyacrylate, polyacrylamide, alkylphenol polyoxyethylene ether formaldehyde condensate sulfate, alkyl naphthalene sulfonic acid formaldehyde condensate and similar varieties, phenol sulfonate naphthalene sulfonic acid formaldehyde condensate sodium salt, phenol formaldehyde condensate sodium salt, phenol-urea-formaldehyde condensate sulfonate, methyl cellulose and its derivatives, xanthate gum, desaccharified lignin sulfonate, etc.

[0024] Furthermore, the oligomeric polyols include, but are not limited to, any one or a combination of polyether polyols and polyester polyols;

[0025] Furthermore, the polyether polyols mentioned include, but are not limited to, polyols such as trimethylolethane, xylitol, sorbitol, pentaerythritol, ethylene glycol, 1,2-propanediol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, diethylene glycol, dipropylene glycol, trimethylolpropane, and glycerol, or polyamines such as ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, dimethylaminopropylamine, diethylaminopropylamine, trimethylhexamethylenediamine, and diethyltriamine, which are used as initiators and are ring-opened polymerized with ethylene oxide, propylene oxide, etc., under the action of a catalyst.

[0026] Furthermore, the polyester polyols include, but are not limited to, those obtained by polycondensation of polyols such as trimethylolethane, xylitol, sorbitol, pentaerythritol, ethylene glycol, 1,2-propanediol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, diethylene glycol, dipropylene glycol, trimethylolpropane, and glycerol with dicarboxylic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, octanoic acid, azelaic acid, sebacic acid, undecanoic acid, dodecadic acid, tridecanoic acid, tetradecanoic acid, pentadecanoic acid, hexadecanoic acid, heptadecadic acid, octadecanoic acid, phthalic acid, isophthalic acid, and glutamic acid.

[0027] Furthermore, the isocyanate includes, but is not limited to, one or a combination of polyisocyanates and isocyanate polymers;

[0028] In one embodiment, the isocyanate is a polyisocyanate compound, including but not limited to one or a combination of toluene diisocyanate, isophorone diisocyanate, diphenylmethane diisocyanate, dicyclohexylmethane diisocyanate, hexamethylene diisocyanate, lysine diisocyanate, trimethylhexane diisocyanate, tetramethylbenzene xylene diisocyanate, etc.

[0029] In one embodiment, the isocyanate is an isocyanate polymer compound, including but not limited to toluene diisocyanate dimer, isophorone diisocyanate dimer, diphenylmethane diisocyanate dimer, dicyclohexylmethane diisocyanate dimer, hexamethylene diisocyanate dimer, lysine diisocyanate dimer, trimethylhexane diisocyanate dimer, tetramethylbenzene xylene diisocyanate dimer, toluene diisocyanate trimer, isophorone diisocyanate trimer, diphenylmethane diisocyanate trimer, dicyclohexylmethane diisocyanate trimer, hexamethylene diisocyanate trimer, lysine diisocyanate trimer, trimethylhexane diisocyanate trimer, and tetramethylbenzene xylene diisocyanate trimer.

[0030] Furthermore, the oil-soluble solvent includes any one or a combination of alkanes, ketones, and esters.

[0031] In one embodiment, the oily solvent includes one or a combination of alkanes, ketones, and esters; alkane solvents such as n-heptane and isoheptane, ketone solvents such as acetone and n-butanone, and ester solvents such as γ-butyrolactone, ethyl acetate, and butyl acetate.

[0032] In some preferred embodiments, the aqueous phase further includes a surfactant, including anionic surfactants, cationic surfactants, and nonionic surfactants.

[0033] Furthermore, in step S3, the volume ratio of the oil phase to the water phase is 1:4-1:20;

[0034] Furthermore, the emulsification methods in step S3 include, but are not limited to, cell disruptor dispersion, homogenizer dispersion, and mechanical stirring.

[0035] In one implementation, emulsification is performed using a high-speed dispersion method.

[0036] In one embodiment, the high-speed disperser operates at a speed of 5000 rpm to 10000 rpm for 3 to 10 minutes.

[0037] In one embodiment, the temperature of the thermosetting reaction apparatus can be from 20 to 150°C.

[0038] Furthermore, the solid particles are solid particles with photothermal conversion capabilities, including one or a combination of metal particles, metal oxide particles, and carbon-based material particles.

[0039] Furthermore, the metal particles include, but are not limited to, gold nanoparticles, silver nanoparticles, platinum nanoparticles, and copper nanoparticles.

[0040] Furthermore, the metal oxide particles include, but are not limited to, iron oxide particles, iron oxide particles, titanium dioxide particles, and titanium trioxide particles;

[0041] Furthermore, the carbon-based materials include, but are not limited to, graphene particles, graphene oxide particles, carbon nanotube particles, graphite particles, and carbon black particles.

[0042] In some preferred embodiments, the solid particles have a particle size of 10 nm to 5 μm;

[0043] In a preferred embodiment, the solid particles are graphene oxide, and the resulting microcapsules are shape memory polyurethane / graphene oxide microcapsules.

[0044] Furthermore, the average particle size of the shape memory polyurethane / graphene oxide microcapsules is 10μm-30μm;

[0045] Furthermore, the strain of the shape memory polyurethane / graphene oxide microcapsules is 0-50%, 50%-100%, or 100%-150%.

[0046] Furthermore, the near-infrared light-curing resin is an acrylic near-infrared light-curing resin;

[0047] Furthermore, the main components of the acrylic near-infrared light-curing resin include oligomers, light-curing reactive diluents, photoinitiators, upconversion particles, and shape memory microcapsules after stretching and deformation.

[0048] Furthermore, the oligomer is selected from acrylates, acrylate derivatives, methacrylates, and methacrylate derivatives.

[0049] Furthermore, the oligomer is a (meth)acrylate. The (meth)acrylate refers to the corresponding acrylate, i.e., a derivative of acrylic acid, and a methacrylate, i.e., a derivative of methacrylate.

[0050] Furthermore, the oligomer includes any one or a combination of epoxy (meth)acrylate, polyester (meth)acrylate, polyether (meth)acrylate, amino acrylate, polyurethane (meth)acrylate, and photosensitive acrylate resin.

[0051] In some embodiments, the epoxy acrylate is specifically a bisphenol A type epoxy acrylate, a bisphenol F type epoxy acrylate, a fatty acid modified epoxy acrylate, etc.

[0052] In some embodiments, the polyester (meth)acrylate includes, but is not limited to, polyester acrylates containing different polybasic acids and different polyols, as well as polyester (meth)acrylates obtained by modifying these resins. The modified polyester acrylates include polyurethane-modified polyester acrylates, polyether-modified polyester acrylates, silicone-modified polyester acrylates, and fluorine-containing monomer-modified polyester acrylates, etc.

[0053] In some preferred embodiments, the epoxy acrylate is specifically a bisphenol A type epoxy acrylate, a bisphenol F type epoxy acrylate, a fatty acid modified epoxy acrylate, etc.

[0054] In some embodiments, the polyether acrylate includes, but is not limited to, polyether acrylates of different chain lengths obtained from ethylene glycol, propylene glycol, and tetrahydrofuran, as well as polyether acrylates obtained by modifying these resins. The modified polyether acrylate includes polyurethane-modified polyether acrylate, silicone-modified polyether acrylate, and fluorinated monomer-modified polyether acrylate, etc. Specifically, it can be silicone-modified polyether acrylate, polyurethane-modified polyether acrylate, etc.

[0055] In some embodiments, the amino acrylate includes, but is not limited to, urea-formaldehyde acrylate, melamine-formaldehyde acrylate, benzo-melamine-formaldehyde acrylate, and amino acrylates obtained by modifying these resins.

[0056] In some embodiments, the polyurethane acrylate includes, but is not limited to, aliphatic polyurethane acrylates, alicyclic polyurethane acrylates, aromatic polyurethane acrylates, and polyurethane acrylates obtained by modifying these resins. The modified polyurethane acrylates include silicone-modified polyurethane acrylates, polyether-modified polyurethane acrylates, and fluorinated monomer-modified polyurethane acrylates.

[0057] In some embodiments, the photosensitive acrylate resin includes, but is not limited to, glycidyl acrylate modified acrylate resin (meth)acrylate, maleic anhydride modified acrylate resin, etc.

[0058] In some embodiments, the oligomer is bisphenol A type epoxy acrylate, epoxy soybean oil acrylate, photocurable reactive diluent trimethylolpropane triacrylate, tetrahydrofuran acrylate, and photoinitiator 2-hydroxy-2-methyl-1-phenyl-1-propanone.

[0059] Furthermore, the photocurable reactive diluent includes, but is not limited to, a class of acrylate compounds that contain one or more acrylate groups in their structure, have an average molecular weight of less than 3000, and a viscosity of less than 9000 cp.

[0060] Further, the reactive diluent includes β-hydroxyethyl (meth)acrylate, isobornyl (meth)acrylate, tetrahydrofuran acrylate, 2-phenoxyethyl acrylate, 1,6-hexanediol di(meth)acrylate, dipropylene glycol diacrylate, dipropylene glycol diacrylate, tripropylene glycol diacrylate, glycidyl methacrylate, polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, ethoxylated tri... hydroxymethylpropane tri(meth)acrylate, propoxylated trimethylolpropane tri(meth)acrylate, caprolactone-modified trimethylolpropane tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, ethoxylated pentaerythritol tetra(meth)acrylate, propoxylated pentaerythritol tetra(meth)acrylate, caprolactone-modified pentaerythritol tetra(meth)acrylate, dimethylolpropane tetra(meth)acrylate, caprolactone-modified dimethylolpropane tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, ethoxylated dipentaerythritol penta(meth)acrylate Pentaerythritol penta(meth)acrylate, propoxylated dipentaerythritol penta(meth)acrylate, caprolactone-modified dipentaerythritol penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, ethoxylated dipentaerythritol hexa(meth)acrylate, propoxylated dipentaerythritol hexa(meth)acrylate, caprolactone-modified dipentaerythritol hexa(meth)acrylate, bisphenol A di(meth)acrylate, bisphenol F di(meth)acrylate, ethoxylated bisphenol A di(meth)acrylate, ethoxylated bisphenol F di(meth)acrylate, Propoxylated bisphenol A di(meth)acrylate, propoxylated bisphenol F di(meth)acrylate, caprolactone-modified bisphenol A di(meth)acrylate, caprolactone-modified bisphenol F di(meth)acrylate, ethoxylated hydrogenated bisphenol A di(meth)acrylate, ethoxylated hydrogenated bisphenol F di(meth)acrylate, propoxylated hydrogenated bisphenol A di(meth)acrylate, propoxylated hydrogenated bisphenol F di(meth)acrylate, caprolactone-modified hydrogenated bisphenol A di(meth)acrylate, caprolactone-modified hydrogenated bisphenol F di(meth)acrylate, etc.

[0061] Furthermore, the photoinitiator includes, but is not limited to, a class of substances that can initiate the polymerization of acrylates under ultraviolet or visible light irradiation.

[0062] In some embodiments, the photoinitiator includes, but is not limited to, 2-hydroxy-methylphenylpropane-1-one, 1-hydroxycyclohexylphenyl ketone, benzoin ethyl ether, benzoin propyl ether, 2-methyl-1-(4-methylthiophenyl)-2-morpholino-1-propanone, benzoin dimethyl ether, camphorquinone, 1-phenyl-1,2-propanedione, 2,4,6-trimethylbenzoyldiphenoxyphosphine, bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylphenylphosphine oxide, isopropylthioxanthone, bis(1-(2,4-difluorophenyl)-3-pyrrolithyl)dicentectan and 2-benzyl-2-methylamino-1-(4-morpholinophenyl)-1-butanone, etc.

[0063] In a preferred embodiment, the oligomer in the photocurable coating is polyurethane acrylate, the photocurable reactive diluent is trimethylolpropane triacrylate, and the photoinitiator is phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide.

[0064] In one embodiment, the photocurable resin further includes a thermoplastic resin. The shape memory microcapsules described above can also be applied to thermoplastic resins.

[0065] In one embodiment, the thermoplastic resin includes, but is not limited to, one or a combination of acrylic resin, polyester, and epoxy resin.

[0066] In one embodiment, the acrylic resin comprises a polymer obtained by copolymerization of any one or more of (meth)acrylic acid, styrene, hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, ethylhexyl acrylate, isobornyl (meth)acrylate, glycidyl (meth)acrylate, fluorinated acrylate monomers, and silicone acrylate monomers.

[0067] In one embodiment, the polyester includes, but is not limited to, polyesters containing different polyacids and different polyols, as well as polyester resins obtained by modifying these resins. The modified polyester resins include polyurethane-modified epoxy resins, polyether-modified polyester resins, silicone-modified polyester resins, and fluorine-containing monomer-modified polyester resins.

[0068] In one embodiment, the epoxy resin includes, but is not limited to, bisphenol A type epoxy resin, phenolic epoxy resin, and epoxy resins obtained by modifying these resins. The modified epoxy resin includes, but is not limited to, alcohol-modified epoxy resin, acid or anhydride-modified epoxy resin, polyurethane-modified epoxy resin, silicone-modified epoxy resin, and fluorine-containing monomer-modified epoxy resin.

[0069] In some preferred embodiments, the polyols include, but are not limited to, trimethylolethane, xylitol, sorbitol, pentaerythritol, ethylene glycol, 1,2-propanediol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, diethylene glycol, dipropylene glycol, trimethylolpropane, and glycerol.

[0070] In some preferred embodiments, the polyamines include, but are not limited to, ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, dimethylaminopropylamine, diethylaminopropylamine, trimethylhexamethylenediamine, diethyltriamine, etc.

[0071] Furthermore, the upconversion particles include, but are not limited to, materials that emit light with short wavelengths and high frequencies when excited by light with long wavelengths and low frequencies.

[0072] Furthermore, the upconversion particles include materials that, when excited by near-infrared light, emit visible or ultraviolet light.

[0073] Upconversion particles are typically composed of an inorganic matrix and rare earth doped ions embedded within it. Inorganic compounds of rare earth metals, alkaline earth metals, and some transition metal ions can serve as ideal rare earth ion doping matrices, such as yttrium oxysulfide, yttrium oxide, lanthanum fluoride, sodium yttrium fluoride, and sodium gadolinium fluoride.

[0074] A second aspect of the present invention is to provide the application of the shape memory microcapsules described above and the near-infrared photocurable resin prepared based on the microcapsules in the fields of coatings, inks and adhesives.

[0075] A third aspect of the present invention is to provide a method for using the shape memory microcapsules described above in a near-infrared photocurable resin: first, the oligomer, photocurable reactive diluent, photoinitiator and upconversion particles are mixed, then the shape memory microcapsules are added, and the sample is mixed evenly under light-protected conditions.

[0076] Beneficial effects:

[0077] Compared with existing technologies, this application utilizes graphene oxide loaded on the surface of microcapsules, leveraging its strong absorption of near-infrared light, to enable shape memory polyurethane / graphene oxide microcapsules to recover their shape under thermal stimulation during photocuring. This allows for their application in near-infrared photocurable coatings to reduce shrinkage stress during curing. The method of this application has the following advantages:

[0078] 1. Utilizing the properties of shape memory polyurethane / graphene oxide microcapsules, the microcapsules are first made into ellipsoids to reduce their volume / surface area ratio. During the curing process, due to the photothermal effect of graphene oxide, the heat in the system increases. Under the combined action of the shrinkage stress of the resin system and thermal stimulation, the shape memory polyurethane / graphene oxide microcapsules recover their shape, and the volume / surface area value increases. This allows the microcapsules to increase in volume significantly while maintaining the wall thickness, thus alleviating the shrinkage stress generated during the curing process.

[0079] 2. At a low addition amount, the shrinkage stress of the UV-cured coating can be reduced. At an addition amount of 5wt%, the shrinkage stress can be reduced by about 30.4%. Moreover, the microcapsule shape recovery speed is fast and the recovery effect is good. The shape recovers to a spherical shape in 90s.

[0080] 3. The addition of microcapsules not only reduces the shrinkage stress of the resin system but also effectively improves coating adhesion. At an addition amount of 5 wt%, adhesion can be increased by 31.9%. Attached Figure Description

[0081] Figure 1 Photothermal conversion efficiency of microcapsules prepared with graphene oxide of different masses;

[0082] Figure 2 Microcapsule melting point test chart;

[0083] Figure 3 Temperature changes during the curing process of photocurable resins with different amounts of microcapsules;

[0084] Figure 4 The microcapsule shape recovery process during solidification;

[0085] Figure 5 Comparative examples and Examples 2-6: Shrinkage stress versus time curves;

[0086] Figure 6 Example 7: Curve showing the change of shrinkage stress over time. Specific implementation methods

[0087] The present invention will be further described and illustrated below with reference to embodiments. The present invention can be better understood from the following embodiments. However, those skilled in the art will readily understand that the specific material ratios, process conditions, and results described in the embodiments are for illustrative purposes only and should not, and will not, limit the present invention as described in detail in the claims.

[0088] Shrinkage stress testing method: A Mars 60 rotational rheometer coupled with a near-infrared light source was used to monitor the changes in axial shrinkage stress during polymerization in real time. The test was conducted in the rheometer's controlled strain mode, with a strain value of 1%, a sample thickness of 0.3 mm, a sample diameter of 20 mm, and a test duration of 400 s. The near-infrared light source was activated at 50 s, with a data acquisition interval of 4 s. The same sample was tested three times, and the average value was taken.

[0089] Double bond conversion rate testing method: The exposed sample was continuously scanned using a total internal reflection infrared platform, and the double bond of acrylic acid was measured at 1396 cm⁻¹. -1 ~1422cm -1 The double bond conversion rate was calculated from the change in peak area. The same sample was tested three times, and the average value was taken.

[0090] Adhesion testing method: Using a BYK frame-type coating applicator, the prepared sample was uniformly coated onto an iron plate. The wet coating was placed on the moving platform of the dispensing machine, which reciprocated under near-infrared light irradiation to obtain a near-infrared cured coating. The coating curing process was carried out inside a nitrogen glove box. The pull-out adhesion of the UV-cured resin coating was determined using a BEVS-2201 automatic pull-out adhesion tester from Guangzhou Shenghua Industrial Co., Ltd., according to GB / T 5210-2006 standard. The result was the average of five tests.

[0091] Monitoring of microcapsule deformation process: Stretched and deformed ellipsoidal microcapsules were added to a photocurable resin system and thoroughly mixed. A sample was placed onto a glass slide using a dropper and compacted with a coverslip. The slide was placed on the microscope stage, and the sample was simultaneously cured using a light source to observe the microcapsule shape recovery process.

[0092] The graphene oxide used in the examples was purchased from Suzhou CarbonFeng Technology.

[0093] Upconversion particles were purchased from Shanghai Ziqi Trading Co., Ltd.

[0094] The preparation method of this invention includes: emulsifying an oil-in-water (O / W) droplet from an aqueous solution and an oil solution using a high-speed disperser; heating the emulsified droplet in a reaction apparatus, and then adding a chain extender to carry out a chain extension reaction. The product is dispersed in a PVA film and thermally stretched to obtain shape memory microcapsules. Specifically, it includes:

[0095] (1) Configuration of the aqueous phase system: The aqueous phase is an aqueous solution containing a stabilizer, solid particles and oligomeric polyols; in some embodiments, a surfactant may also be added to the aqueous phase.

[0096] (2) Preparation of the oil phase system: The oil phase is a solution containing an oil-soluble solvent and a polyisocyanate.

[0097] (3) The emulsified O / W droplets are heated and solidified, and then a polyol or polyamine chain extender is added to carry out the chain extension reaction.

[0098] (4) The product was dispersed in a PVA film and then thermally stretched to prepare shape memory microcapsules.

[0099] (5) The prepared shape memory microcapsules were added to a photocurable material and the shrinkage stress and adhesion were measured.

[0100] Example 1: Effect of different graphene oxide contents on the photothermal conversion efficiency of microcapsules

[0101] This embodiment investigated the effect of different graphene oxide contents on the photothermal conversion performance of shape memory polyurethane / graphene oxide microcapsules.

[0102] The raw materials are as follows: In the aqueous phase, the stabilizer is polyvinyl alcohol (PVA), the solid particles are graphene oxide (GO), and the oligomeric polyol is polyethylene glycol (PEG4000) with a molecular weight of 4000; In the oil phase, the solvent is butyl acetate, the core material is dioctyl terephthalate (DOT), the isocyanate is hexamethylene diisocyanate trimer (DN3300), and the catalyst is dibutyltin dilaurate (DBTDL); the chain extender is 1,4-butanediol (BDO).

[0103] The specific preparation process is as follows:

[0104] 1. Preparation of aqueous system: 40 ml of 0.2 wt% polyvinyl alcohol aqueous solution and different masses of graphene oxide were mixed with polyethylene glycol with a molecular weight of 4000.

[0105] 2. Preparation of the oil phase system: Use 3 ml of butyl acetate as a solvent, add hexamethylene diisocyanate trimer and mix well.

[0106] 3. After mixing the aqueous and oil phases, emulsify the mixture in a high-speed disperser at 7,000 rpm for 5 minutes to form O / W emulsion droplets. After heating and reaction, add 1,4-butanediol for chain extension. The specific formulation is shown in Table 1.

[0107] 4. Shape memory microcapsules were obtained after centrifugation and washing. Temperature changes under near-infrared light were measured using an infrared thermal imager. Microcapsules prepared with different amounts of GO were named PU MCs-0.4wt%GO, PU MCs-0.6wt%GO, and PU MCs-0.8wt%GO, respectively. Microcapsules prepared without GO were named PU MCs.

[0108] Table 1. Microcapsules prepared from graphene oxide of different masses

[0109]

[0110] like Figure 1 As shown, the temperature change of the microcapsules under different near-infrared light powers was tested. With the increase of graphene oxide mass, the photothermal conversion efficiency of the microcapsules improved. Figure 2 As shown, the melting point of microcapsules prepared with different GO addition amounts was tested using differential scanning calorimetry. The melting point changes were not significant, all remaining around 55 degrees Celsius. The temperature change during the curing process was tested when PU MCs-0.8wt% GO was added to the resin system. Figure 3 As shown, increasing the amount of microcapsules increases the temperature during the curing process, eventually reaching a temperature above the melting point of the shell shape memory material.

[0111] Comparative example: No shape memory microcapsules added

[0112] 1. Weigh 10g PUA and 10g TPGDA at a mass ratio of 1:1, mix them evenly, then add 0.1g photoinitiator 819 and 0.4g upconversion particles, and mix evenly.

[0113] 2. Place the sample in a vacuum oven to remove air bubbles, take a small amount of the sample and coat it on an aluminum plate, then cure it to obtain a light-cured coating.

[0114] 3. The coating properties and infrared-rheology combined tests were performed on the materials respectively.

[0115] Example 2: Adding 0.2g of shape memory microcapsules

[0116] 1. Preparation of shape memory microcapsules

[0117] (1) Preparation of aqueous system: Add 2.5g polyethylene glycol 4000 and 0.32g graphene oxide to 40ml of 0.2wt% PVA aqueous solution and mix thoroughly.

[0118] (2) Preparation of the oil phase system: Add 0.42g of toluene diisocyanate trimer and 0.01g of dibutyltin dilaurate to 3ml of butyl acetate.

[0119] (3) After emulsifying at 7000rpm for 5 minutes, the O / W droplets were heated and solidified. After reacting for 2 hours, 0.057g of 1,4-butanediol was added and the reaction continued for 1 hour. After washing and drying, microcapsules were obtained.

[0120] (4) The microcapsules were dispersed in a PVA film and subjected to hot stretching at 80°C with a tensile strain of 150%.

[0121] 2. Weigh 10g PUA and 10g TPGDA at a mass ratio of 1:1, mix them evenly, add 0.1g photoinitiator 819, 0.4g upconversion particles, and 0.2g of the microcapsules prepared in step 1, and mix evenly.

[0122] 3. Place the sample in a vacuum oven to remove air bubbles, then take a small amount of sample and pour it into a mold. Take a small amount of sample and coat it on an aluminum plate, then cure it to obtain a light-cured coating.

[0123] 4. The coating properties and infrared-rheology combined tests were performed on the materials respectively.

[0124] Example 3: Adding 0.4g of shape memory microcapsules

[0125] 1. Preparation of shape memory microcapsules

[0126] The preparation method is the same as in Example 2.

[0127] 2. Weigh 10g of PUA and 10g of TPGDA at a mass ratio of 1:1, mix thoroughly, then add 0.1g of photoinitiator 819, 0.4g of upconversion particles, and 0.4g of the microcapsules prepared in step 1. Mix thoroughly.

[0128] 3. Place the sample in a vacuum oven to remove air bubbles, take a small amount of the sample and coat it on an aluminum plate, then cure it to obtain a light-cured coating.

[0129] 4. The coating properties and infrared-rheology combined tests were performed on the materials respectively.

[0130] Example 4: Adding 0.6g of shape memory microcapsules

[0131] 1. Preparation of shape memory microcapsules

[0132] The preparation method is the same as in Example 2.

[0133] 2. Weigh 10g of PUA and 10g of TPGDA at a mass ratio of 1:1, mix thoroughly, then add 0.1g of photoinitiator 819, 0.4g of upconversion particles, and 0.6g of the microcapsules prepared in step 1. Mix thoroughly.

[0134] 3. Place the sample in a vacuum oven to remove air bubbles, take a small amount of the sample and coat it on an aluminum plate, then cure it to obtain a light-cured coating.

[0135] 4. The coating properties and infrared-rheology combined tests were performed on the materials respectively.

[0136] Example 5: Adding 0.8g of shape memory microcapsules

[0137] 1. Preparation of shape memory microcapsules

[0138] The preparation method is the same as in Example 2.

[0139] 2. Weigh 10g PUA and 10g TPGDA at a mass ratio of 1:1, mix thoroughly, then add 0.1g photoinitiator 819, 0.4g upconversion particles, and 0.8g of the microcapsules prepared in step 1. Mix thoroughly.

[0140] 3. Place the sample in a vacuum oven to remove air bubbles, take a small amount of the sample and coat it on an aluminum plate, then cure it to obtain a light-cured coating.

[0141] 4. The coating properties and infrared-rheology combined tests were performed on the materials respectively.

[0142] Example 6: Adding 1.0g of shape memory microcapsules

[0143] 1. Preparation of shape memory microcapsules

[0144] The preparation method is the same as in Example 2.

[0145] 2. Weigh 10g PUA and 10g TPGDA at a mass ratio of 1:1, mix thoroughly, then add 0.1g photoinitiator 819, 0.4g upconversion particles, and 1.0g of the microcapsules prepared in step 1. Mix thoroughly.

[0146] 3. Place the sample in a vacuum oven to remove air bubbles, take a small amount of the sample and coat it on an aluminum plate, then cure it to obtain a light-cured coating.

[0147] 4. The coating properties and infrared-rheology combined tests were performed on the materials respectively.

[0148] The comparison of the components and their contents in the photocuring systems of the above comparative examples and Examples 2-6 is summarized in Table 2 below:

[0149] Table 2. Components and their mass for near-infrared photocuring (unit: g)

[0150]

[0151]

[0152] Comparative analysis of results:

[0153] 1. Results of infrared-rheology combined testing

[0154] The infrared-rheology combined test results for the comparative examples and embodiments are shown in Table 2.

[0155] Table 3 Infrared-rheology combined test results

[0156] Components tgel / s Microcapsule addition amount Shrinkage stress Reduction rate (%) Comparative Example 162.0 - 5.6 0 Example 2 173.8 1wt% 5.1 8.9％ Example 3 174.9 2wt% 4.9 12.5％ Example 4 176.4 3wt% 4.9 12.5％ Example 5 177.2 4wt% 4.6 17.9％ Example 6 187.4 5wt% 3.9 30.4％

[0157] Note: t gel The gel point time represents the time at which the material begins to form a cross-linked structure, reflecting the speed of curing.

[0158] Figure 5 Table 3 shows the shrinkage stress of the resin systems in the comparative examples and Examples 2-6 as a function of time. As shown in Table 3, with the increase of microcapsule addition, the gel point time is delayed, which is beneficial to the release of shrinkage stress. Compared with the comparative examples, Examples 2-6 show a significant reduction in shrinkage stress. When the addition amount is 1 wt%, the shrinkage stress is reduced by 8.9%; when the addition amount is 5 wt%, the shrinkage stress is reduced by 30.4%.

[0159] 2. Pull-out adhesion test results

[0160] Table 4. Pull-out adhesion test results

[0161] Components Adhesion (MPa) Comparative Example 3.13±0.86 Example 2 3.51±1.01 Example 3 3.72±0.49 Example 4 4.11±1.62 Example 5 4.05±0.91 Example 6 4.12±0.38

[0162] As shown in Table 4, after adding the shape memory microcapsules after stretching deformation, the shrinkage stress of the photocurable resin system is greatly reduced, and the coating adhesion is also significantly affected. Compared with the comparative examples, the pull-out adhesion of Examples 2-6 is greatly increased, up to a maximum of 4.12 MPa.

[0163] Example 7: Effect of shape memory microcapsules prepared with different thermal tensile strains on resin shrinkage stress

[0164] This embodiment investigates the effect of shape memory microcapsules prepared with different thermal tensile strains on resin shrinkage stress.

[0165] The raw materials are as follows: in the aqueous phase, the stabilizer is polyvinyl alcohol, the solid particles are graphene oxide, and the oligomeric polyol is polyethylene glycol with a molecular weight of 4000; in the oil phase, the solvent is butyl acetate, the isocyanate is hexamethylene diisocyanate trimer, and the chain extender is 1,4-butanediol; the prepared microcapsules are dispersed in a 10wt% polyvinyl alcohol aqueous solution to form a film.

[0166] The specific preparation process is as follows:

[0167] 1. Preparation of aqueous system: Add 2.5g of polyethylene glycol with a molecular weight of 4000 and 0.32g of graphene oxide to 40ml of 0.2wt% polyvinyl alcohol aqueous solution and mix well.

[0168] 2. Preparation of the oil phase system: Take 3 ml of butyl acetate as solvent, add 0.42 g of hexamethylene diisocyanate trimer and 0.01 g of dibutyltin dilaurate and mix well.

[0169] 3. After mixing the aqueous and oil phases, emulsify the mixture for 5 minutes using a high-speed disperser at 7,000 rpm to form O / W emulsion droplets. After heating and reacting for 2 hours, add 0.057 g of 1,4-butanediol for chain extension reaction for 1 hour. The molar ratio of isocyanate groups to hydroxyl groups in the system is 1:1.

[0170] 4. Shape memory microcapsules were obtained after centrifugation and washing.

[0171] 5. The obtained microcapsules were dispersed in a 10 wt% PVA aqueous solution to form a film, and then hot-stretched at 80°C with tensile strains of 50%, 100%, and 150%.

[0172] 6. Weigh 10g PUA and 10g TPGDA at a mass ratio of 1:1, mix them evenly, add 0.1g photoinitiator 819, 0.4g upconversion particles, and 1.0g microcapsules and mix evenly.

[0173] Table 5. Effect of different tensile strains on reducing shrinkage stress

[0174] Tensile strain (%) Shrinkage stress (N) Reduction rate (%) 50 4.4 21.4 100 4.0 28.6 150 3.9 30.4

[0175] Figure 6 Table 5 shows the curve of shrinkage stress of the resin system in Example 7 changing over time. As can be seen from Table 5, under the same conditions, as the aspect ratio of the microcapsules increases, the shrinkage stress reduction rate increases, with a maximum of 30.4%. The increase in the aspect ratio of the microcapsules results in a greater degree of deformation, and they can play a more effective role in volume compensation during the shape recovery process.

[0176] The microcapsules with a tensile strain of 150% prepared in Example 7 were added to a photocurable resin and observed using a super depth-of-field microscope. Figure 4 As shown in (a), before resin curing, the microcapsules are ellipsoidal; after resin curing in the same test area, the microcapsules return to a spherical shape. Figure 4 As shown in (d). Figure 4 (b) and Figure 4 (c) These are the microcapsule morphologies at different times during the resin curing process. Figure 4 (a)- Figure 4 (d) This indicates that the microcapsules can recover their shape under the action of shrinkage stress and thermal effect during the resin curing process; and due to the action of dual driving forces, the shape recovery speed is fast and the recovery effect is good. Figure 4 (d) After 60 seconds, all microcapsules in the field of view returned to their spherical shape.

[0177] The above description is only a preferred embodiment of this application. It should be noted that although this application has been disclosed above with preferred embodiments by those skilled in the art, it is not intended to limit this application. Anyone skilled in the art can make several improvements and modifications without departing from the principle of this application, and these improvements and modifications should also be considered within the scope of protection of this application.

Claims

1. Use of shape memory microcapsules in near infrared light-cured resins, characterized in that, The shape memory microcapsule after tensile deformation is added in the light curing resin to reduce the shrinkage stress during the curing of the resin; The solid particles with strong absorption to near infrared light are doped in the shell of the shape memory microcapsule; the heat effect generated by the solid particles under the irradiation of near infrared light is used as a stimulation source to promote the shape memory microcapsule to restore the shape, thereby reducing the shrinkage stress; The shape memory microcapsule is added in the light curing resin in an amount of 0.01wt%-5wt%; The shrinkage stress during the curing of the light curing resin is reduced by 10%-40%; The preparation method of the shape memory microcapsule comprises the following steps: S1, preparing an aqueous phase: the aqueous phase is an aqueous solution containing a co-stabilizer, solid particles and an oligomeric polyol; S2, preparing an oil phase: the oil phase is a liquid phase containing isocyanate and an oil-soluble solvent; S3, preparing an emulsion: the oil phase and the aqueous phase are mixed and uniformly dispersed to prepare an emulsion; S4, the droplets in the emulsion are subjected to thermal curing through a reaction device, and then polyol or polyamine is added for chain extension to form the shape memory microcapsule; S5, the shape memory microcapsule is dispersed in a PVA film and subjected to thermal tensile deformation to obtain the shape memory microcapsule after tensile deformation; The solid particles in step S1 are particles with strong absorption to near infrared light, with a particle size of 10nm-5μm; The near infrared light curing resin comprises an oligomer, a light curing active diluent, a photoinitiator and upconversion particles.

2. Use of shape memory microcapsules according to claim 1 in near infrared light-cured resins, characterized in that, The near infrared light curing resin comprises an acrylic near infrared light curing resin, a vinyl near infrared light curing resin, a siloxane near infrared light curing resin, a polyimide near infrared light curing resin and a polyurethane near infrared light curing resin.

3. Use of the shape memory microcapsules according to claim 1 in near infrared light-cured resins, characterized in that, The co-stabilizer is selected from one or a combination of alkylphenol polyoxyethylene ethers, fatty alcohol polyoxyethylene ethers, fatty amine polyoxyethylene ethers and high molecular co-stabilizers; The oligomeric polyol is selected from any one or a combination of polyether polyols and polyester polyols; The isocyanate is selected from any one or a combination of polyisocyanates and isocyanate multimers; The oil-soluble solvent is selected from any one or a combination of alkanes, ketones and esters; In step S3, the volume ratio of the oil phase to the aqueous phase is 1:4-1:

20.

4. The shape memory microcapsule for use in the near infrared light curing resin according to claim 1, wherein In step S3, high-speed dispersion is used for emulsification, and the high-speed dispersion time is 3-10min; In step S4, the temperature of the reaction device is 20-150℃.

5. The shape memory microcapsule for use in the near infrared light curing resin according to claim 1, wherein The solid particles are one or a combination of metal particles, metal oxide particles and carbon-based material particles with light-heat conversion capability; The metal particles are selected from gold nanoparticles, silver nanoparticles, platinum nanoparticles and copper nanoparticles; The metal oxide particles are selected from magnetite particles, iron oxide particles, titanium dioxide particles and titanium oxide particles; The carbon-based material is selected from graphene particles, graphene oxide particles, carbon nanotube particles, graphite particles and carbon black particles.

6. The use of the shape memory microcapsule according to claim 1 in a near-infrared light-cured resin, characterized in that, the solid particles are graphene oxide, and the prepared microcapsule is a shape memory polyurethane / graphene oxide microcapsule; the average particle size of the shape memory polyurethane / graphene oxide microcapsule is 1-30 μm; the strain of the shape memory polyurethane / graphene oxide microcapsule is 50%-150%.

7. Use of the shape memory microcapsules according to claim 1 in near infrared light-cured resins, characterized in that, the near-infrared light-cured resin is an acrylic near-infrared light-cured resin.

8. The use of the shape memory microcapsule according to claim 1 in a near-infrared light-cured resin, characterized in that, the oligomer is selected from acrylate, a derivative of acrylate, methacrylate, and a derivative of methacrylate; and the photo-curing active diluent is an acrylate compound having more than one acrylate group in the structure, an average molecular weight less than 3000, and a viscosity less than 9000 cp; the up-conversion particles are materials that emit visible light or ultraviolet light when excited by near-infrared light.

9. Use of the shape memory microcapsules according to any one of claims 1 to 8 in near infrared light-cured resins, characterized in that, application in the fields of coatings, inks, and adhesives.

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