Photo-crosslinkable waterborne polyolefin emulsion as well as preparation method and application thereof

Abstract

The invention relates to a photo-crosslinkable water-based polyolefin emulsion as well as a preparation method and application thereof. The emulsion comprises modified polyolefin and water, the modified polyolefin is prepared from raw materials including polyolefin resin, maleic anhydride, a grafted photo-initiation monomer and a free radical initiator through graft polymerization; the grafted photo-initiation monomer contains vinyl and a photo-initiation group. The emulsion is prepared by melting the modified polyolefin to form an oil phase; dissolving an emulsifier in part of water to obtain a water phase; and adding the water phase into the oil phase while stirring, and then adding the rest of water to prepare the oil-in-water composite oil-in-water composite oil-in-water composite oil-in-water composite. The emulsion can be subjected to photo-crosslinking, and after photo-crosslinking, a coating film has excellent water resistance, solvent resistance, hardness and adhesive force.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of high polymer material synthesis, and particularly relates to a water-based polyolefin emulsion capable of photo-crosslinking, and a preparation method and application thereof. BACKGROUND

[0002] The water-based polyolefin emulsion has the advantages of low VOC content, non-toxicity, good wettability for difficultly adhering substrates such as polyolefin, etc., and is widely used in the industries of coatings, inks and adhesives. However, the linear polyolefin molecules lack active functional groups, and the emulsion has the problems of poor water resistance, solvent resistance, heat resistance and mechanical strength after film formation, which seriously restricts its application in high-performance fields. In order to improve the performance, the conventional technology usually adopts the method of adding small molecule crosslinking agents or thermal crosslinking, but these methods have the problems of complex operation process, high toxicity of crosslinking agents, poor storage stability or high energy consumption, etc., and are not suitable for heat-sensitive substrates. The photo-crosslinking technology is an efficient, energy-saving and environmentally friendly curing method, but its application in the water-based polyolefin system faces the following core challenges: firstly, the small molecule photoinitiator has poor compatibility with the polyolefin, and simple physical blending easily leads to problems such as migration and precipitation, low efficiency and influence on film performance; secondly, the polyolefin chain lacks functional groups capable of photo-crosslinking, and cannot form an effective three-dimensional network structure after film formation, resulting in low photo-crosslinking density. SUMMARY

[0003] The present application aims at overcoming the deficiencies of the prior art, and provides an improved water-based polyolefin emulsion which can be photo-crosslinked, and after photo-crosslinking, the coating film has excellent water resistance, solvent resistance, hardness and adhesion.

[0004] To achieve the above-mentioned purposes, the present application adopts the following technical solutions:

[0005] A water-based polyolefin emulsion capable of photo-crosslinking, the emulsion comprising a modified polyolefin and water; the modified polyolefin is prepared by graft polymerization of raw materials comprising a polyolefin resin, maleic anhydride, a grafting photoinitiating monomer and a free radical initiator; the grafting photoinitiating monomer contains a vinyl group and a photoinitiating group.

[0006] By introducing the grafting photoinitiating monomer, the polyolefin molecular chain is simultaneously introduced with a photosensitive group and a double bond, and the free radicals generated by the photosensitive group under UV irradiation can directly initiate the crosslinking reaction of the double bond on the adjacent molecular chain, without adding any additional crosslinking agent or small molecule photoinitiator, so as to realize the photo-crosslinking effect of the emulsion and the coating film. The maleic anhydride is a hydrophilic monomer, and after being grafted onto the polyolefin resin, it can improve the hydrophilicity of the polyolefin resin, so that the polyolefin resin can be emulsified to prepare a stable emulsion.

[0007] In some embodiments, the grafting photoinitiating monomer is selected from 4-acryloyloxybenzophenone

[0008] 4-methacryloyloxybenzophenone

[0009] 2-hydroxy-4-methacryloyloxybenzophenone 4-hydroxyethylenoxylbenzophenone methacrylate 1,4-bis(4-(2-methacryloyloxyethyl)phenylamino)anthraquinone 2-vinylanthraquinone a combination of one or more of the foregoing.

[0010] In some embodiments, the polyolefin resin is selected from a combination of one or more of polyethylene, polypropylene, ethylene-propylene copolymer. The polyethylene can be low density polyethylene, linear low density polyethylene, etc.

[0011] In some embodiments, the polyolefin resin has a melt index of 5-50 g / 10 min at 190 °C, 2.16 kg. The polyolefin resin with this melt index ensures good fluidity of the resin in the melt grafting stage and is conducive to subsequent emulsification.

[0012] In some embodiments, the polyolefin resin has a melt index of 15-25 g / 10 min at 190 °C, 2.16 kg.

[0013] In some embodiments, the raw materials include 100 parts of polyolefin resin, 1-5 parts of maleic anhydride, 1-10 parts of grafting photoinitiating monomer, and 0.2-1 part of free radical initiator, by mass fraction. When the amount of maleic anhydride is too small, the hydrophilicity of the modified polyolefin is not enough, which is not conducive to the formation of stable emulsion; when the amount of maleic anhydride is too large, maleic anhydride is prone to homopolymerization, and the degradation of the polyolefin main chain is intensified. When the amount of grafting photoinitiating monomer is too small, the effective grafting rate of the photoinitiating group decreases; when the amount of grafting photoinitiating monomer is too large, the hydrophobicity of the modified polyolefin increases, which is not conducive to emulsification.

[0014] In some embodiments, the grafting polymerization is melt grafting polymerization. Melt grafting polymerization refers to grafting reaction of raw materials under melting. Grafting polymerization under melting can realize the intrinsic modification of material performance, which can significantly improve the hydrophilicity to facilitate water-based (subsequent emulsification) and directly impart the light crosslinking property, thereby overcoming the problems of component migration and uneven performance that may be caused by physical blending.

[0015] Further, the melt grafting polymerization reaction may, for example, be carried out in an extruder. The product of the melt grafting polymerization, the modified polyolefin, is directly prepared in the form of a masterbatch.

[0016] In some embodiments, the raw materials further include an antioxidant.

[0017] In some embodiments, the antioxidant is selected from the group consisting of one or more of tetrakis [beta-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate] pentaerythritol ester, octadecyl beta-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate, tris(2,4-di-tert-butylphenyl) phosphite, 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl) benzene, 2,6-di-tert-butyl-p-cresol.

[0018] In some embodiments, the raw material comprises 100 parts of polyolefin resin, 1-5 parts of maleic anhydride, 1-10 parts of grafted photoinitiating monomer, 0.2-1 part of free radical initiator, 0.1-0.5 part of antioxidant, by mass fraction.

[0019] In some embodiments, the emulsion further comprises an emulsifier.

[0020] Further, the emulsifier is a composite emulsifier.

[0021] Preferably, the composite emulsifier comprises an anionic emulsifier and a non-ionic emulsifier.

[0022] Further, the anionic emulsifier is selected from the group consisting of sodium dodecyl sulfate SDS, sodium dodecyl benzene sulfonate; the non-ionic emulsifier is selected from the group consisting of alkyl phenol polyoxyethylene ether, fatty alcohol polyoxyethylene ether, polyoxyethylene sorbitan fatty acid ester (Tween).

[0023] Further, the alkyl phenol polyoxyethylene ether can be OP-10, NP-10, etc.; the fatty alcohol polyoxyethylene ether can be AEO-3, AEO-7, AEO-9, etc.; the Tween can be Tween-20, Tween-60, Tween-80, etc.

[0024] Further, the mass ratio of the anionic emulsifier and the non-ionic emulsifier is 2:1-1:2.

[0025] Further, the emulsifier is 5-15 parts by mass relative to 100 parts by mass of the polyolefin.

[0026] In some embodiments, the emulsion is prepared by melting the modified polyolefin to form an oil phase; dissolving the emulsifier in part of the water to obtain an aqueous phase; adding the aqueous phase to the oil phase under stirring, and then adding the remaining water.

[0027] In some embodiments, the solid content of the emulsion is 35%-55%. In the present application, the solid content is the mass percentage concentration.

[0028] In some embodiments, the initiator is one or both of dicumyl peroxide and benzoyl peroxide.

[0029] The present application also provides a preparation method of the aforementioned photo-crosslinkable waterborne polyolefin emulsion, comprising the following steps:

[0030] 1) melt grafting polymerization of the polyolefin resin, maleic anhydride, grafting photo-initiating monomer, free radical initiator and optional antioxidant to obtain a modified polyolefin;

[0031] 2) melting the modified polyolefin to form an oil phase; dissolving the emulsifier in part of water to obtain an aqueous phase;

[0032] 3) adding the aqueous phase to the oil phase under stirring, and then adding the remaining water to obtain the photo-crosslinkable waterborne polyolefin emulsion.

[0033] In some embodiments, in step 1), the melt grafting polymerization is performed in an extruder.

[0034] In some embodiments, the extruder is a twin-screw extruder.

[0035] In some embodiments, the screw rotation speed of the extruder is 200-400 rpm.

[0036] In some embodiments, the temperature of the melt grafting polymerization is 150-190°C.

[0037] In some embodiments, the time of the melt grafting polymerization is 10-15 minutes.

[0038] In some embodiments, the preparation method further comprises a step of pre-mixing the polyolefin resin, maleic anhydride, grafting photo-initiating monomer, free radical initiator and optional antioxidant before the melt grafting polymerization.

[0039] In some embodiments, the pre-mixing time is 5-15 minutes.

[0040] In some embodiments, in step 2), the melting temperature is 160-190°C.

[0041] In some embodiments, in step 2), the temperature of the part of water is 80-90°C.

[0042] In some embodiments, in step 2), the mass of the part of water accounts for 80%-90% of the mass of water.

[0043] In some embodiments, in step 3), the stirring rotation speed is 400-800 rpm.

[0044] In some embodiments, in step 3), when the remaining water is added, the stirring rotation speed is 1000-1500 rpm.

[0045] In some embodiments, the preparation method further comprises a step of adjusting the pH of the emulsion to 7.5-9.0 using a pH adjuster.

[0046] In some embodiments, the pH adjuster is ammonia water or the like.

[0047] In some embodiments, the preparation method comprises the following steps:

[0048] The polyolefin resin, maleic anhydride, grafted photoinitiating monomer, free radical initiator and antioxidant are pre-mixed in a high-speed mixer at room temperature for 5-15 minutes to obtain a pre-mixture; the pre-mixture is subjected to melt reaction extrusion through a twin-screw extruder, the extrusion temperature is controlled at 150-190℃, the screw rotation speed is 200-400 rpm, the reaction residence time is 10-15 minutes, and the product is cooled by water and granulated to obtain the photo-crosslinkable polyolefin functional masterbatch;

[0049] The polyolefin functional masterbatch is put into a reaction kettle with a heating jacket and a stirrer, heated to 160-190℃ to make it fully melt to form an oil phase; in another container, the composite emulsifier is dissolved in hot water (80-90℃) to prepare an aqueous phase. The preheated aqueous phase is slowly added to the oil phase under a stirring speed of 400-800 rpm. The mixing system will undergo a phase inversion process: at the beginning, it is water-in-oil (W / O), and with the increase of water, the viscosity first rises sharply and then suddenly drops, and it is changed into an oil-in-water (O / W) emulsion. After phase inversion, the stirring speed is increased to 1000-1500 rpm, the remaining water is added, and the solid content of the final emulsion is controlled at 30%-45%. After continuous high-speed stirring for a period of time, it is cooled to room temperature, the pH is adjusted to weak alkaline (7.5-9.0) with ammonia water, filtered, discharged, and the photo-crosslinkable water-based polyolefin emulsion is obtained.

[0050] The application also provides the use of the aforementioned photo-crosslinkable water-based polyolefin emulsion as a photocuring coating.

[0051] The photo-crosslinkable water-based polyolefin emulsion prepared by the application is applied to the surface of a substrate (such as metal, plastic, wood) by means of scraping, rolling or spraying, etc., and dried at 60-80℃ for 3-5 minutes to form a coating film. Subsequently, the coating film is irradiated for 5-120 seconds using a UV curing device (medium-pressure mercury lamp, wavelength main peak is 365 nm, light intensity is 300-1000 mJ / cm 2 ) to achieve rapid crosslinking and curing.

[0052] Thanks to the above technical solutions, the application has the following advantages compared with the prior art:

[0053] The present application solves the problems of migration and exudation of small molecule photoinitiators by chemically grafting photosensitive groups to the polyolefin molecular chain, and the coating film has safety and crosslinking stability. By introducing the grafted photoinitiating monomer, the polyolefin molecular chain is simultaneously introduced with photosensitive groups and double bonds. When UV irradiation, the free radicals generated by the photosensitive groups can directly initiate the crosslinking reaction of the double bonds on the adjacent molecular chain, without adding any additional crosslinking agent or small molecule photoinitiator, the effect of photo-crosslinking can be achieved, and the formula and process are simplified. The coating film after UV curing can form a three-dimensional network structure, compared with the coating film without crosslinking or physically adding photoinitiator, the coating film density is improved, and various properties of the coating film such as water resistance, solvent resistance, hardness and adhesion are improved.

[0054] The photo-crosslinking efficiency of the water-based polyolefin emulsion of the present application is high, and it belongs to the intrinsic photo-crosslinkable water-based polyolefin emulsion, which has excellent water resistance, solvent resistance, that is, good stability, and high hardness and adhesion, that is, high mechanical strength.

[0055] In addition, based on the mature melt grafting and water-based process, the process is simple and easy to industrialize, the whole system uses water as the dispersion medium, the VOC content is extremely low, and it is green and environmentally friendly. DETAILED DESCRIPTION

[0056] The application of photo-crosslinking technology to water-based polyolefin systems faces core challenges: first, the poor compatibility of small molecule photoinitiators with polyolefin, which can easily lead to migration, precipitation and other problems, low efficiency and affect film performance; second, the lack of functional groups in the polyolefin chain that can be photo-crosslinked, which cannot form an effective three-dimensional network structure after film formation, and the photo-crosslinking density is low.

[0057] The present application introduces the grafting photoinitiating monomer containing polymerizable vinyl and photoinitiating groups into the polyolefin main chain through melt grafting reaction, together with maleic anhydride, so as to introduce hydrophilic carboxyl and photosensitive groups into the polyolefin molecular chain at the same time. Subsequently, a stable emulsion is obtained by emulsification, and after UV irradiation after film formation, the free radicals generated by the photosensitive groups bonded on the molecular chain initiate the polymerization reaction of the double bonds between the molecular chains, forming a three-dimensional network structure, that is, photo-crosslinking. Grafting maleic anhydride can improve the hydrophilicity of polyolefin, so that the modified polyolefin can be prepared into a stable emulsion; introducing photosensitive groups and double bonds on the polyolefin side chain can enable the modified polyolefin to be subsequently photo-crosslinked, obtaining a photo-crosslinkable water-based polyolefin emulsion.

[0058] The technical solutions of the present application will be described in detail below with specific examples, so that those skilled in the art can better understand and implement the technical solutions of the present application. However, the present application is not limited in the scope of the examples described.

[0059] The following parts are all mass parts.

[0060] Example 1

[0061] (1) Pre-mixing 100 parts of low density polyethylene (melt index MI at 190°C, 2.16 kg is 20 g / 10 min), 2.5 parts of maleic anhydride, 5 parts of 4-acryloyloxybenzophenone, 0.5 parts of dicumyl peroxide and 0.3 parts of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] in a high-speed mixer at room temperature for 15 minutes to obtain a pre-mix; melt reaction extruding the pre-mix through a twin-screw extruder, the extruding temperature is controlled at 180°C, the screw rotating speed is 300 rpm, the reaction residence time is 10 minutes, water-cooling and pelletizing to obtain a photo-crosslinkable polyolefin functional masterbatch.

[0062] (2) Putting the obtained functional masterbatch into a reaction kettle with a heating jacket and a stirrer, heating to 170°C to make it melt sufficiently to form an oil phase; in another container, dissolving 5 parts of sodium dodecyl sulfate and 5 parts of alkylphenol polyoxyethylene ether NP-10 in 160 parts of hot water (90°C, accounting for 80% of all water) to prepare an aqueous phase. Slowly adding the preheated aqueous phase into the oil phase under the stirring speed of 400-800 rpm. The viscosity of the system first rises sharply and then suddenly drops to complete the phase transition. Increasing the stirring speed to 1000-1500 rpm, adding the remaining 40 parts of water to control the final emulsion solid content at about 37.2% (solid matter is 108.3 parts of polyolefin functional masterbatch, and 10 parts of emulsifier, a total of 118.3 parts, and the total emulsion is 318.3 parts). After continuous high-speed stirring for a period of time, cooling to room temperature, adjusting the pH to weak alkaline (7.5) with ammonia water, filtering, discharging to obtain a photo-crosslinkable water-based polyolefin emulsion.

[0063] (3) Coating the photo-crosslinkable water-based polyolefin emulsion on the surface of the substrate tinplate by spraying, drying at 60°C for 5 minutes to form a coating film. Then using a UV curing equipment (medium pressure mercury lamp, wavelength main peak is 365 nm, light intensity is 300-1000 mJ / cm 2 ) to irradiate the coating film for 60 seconds to form a final coating film.

[0064] Example 2

[0065] The photo-crosslinkable water-based polyolefin emulsion provided in this example is basically the same as that in Example 1, the only difference is that the low density polyethylene is replaced by polypropylene (melt index MI at 190°C, 2.16 kg is 20 g / 10 min).

[0066] Example 3:

[0067] The photo-crosslinkable water-based polyolefin emulsion provided in this example is basically the same as that in Example 1, except that the amount of 4-acryloyloxybenzophenone is replaced by 10 parts.

[0068] Example 4:

[0069] The photo-crosslinkable water-based polyolefin emulsion provided in this example is basically the same as that in Example 1, except that the amount of maleic anhydride is replaced by 5 parts.

[0070] Example 5:

[0071] The photo-crosslinkable water-based polyolefin emulsion provided in this example is basically the same as that in Example 1, except that the amount of 4-acryloyloxybenzophenone is replaced by 10 parts.

[0072] Example 6:

[0073] The photo-crosslinkable water-based polyolefin emulsion provided in this example is basically the same as that in Example 1, except that the amount of water added finally is controlled to make the solid content of the emulsion 45%.

[0074] Comparative Example 1

[0075] The photo-crosslinkable water-based polyolefin emulsion provided in this example is basically the same as that in Example 1, except that maleic anhydride is not added. It is found that the oil and water layers separate and a stable emulsion cannot be formed.

[0076] Comparative Example 2

[0077] The photo-crosslinkable water-based polyolefin emulsion provided in this example is basically the same as that in Example 1, except that 4-acryloyloxybenzophenone is not added.

[0078] Comparative Example 3

[0079] The photo-crosslinkable water-based polyolefin emulsion provided in this example is basically the same as that in Example 1, except that 4-acryloyloxybenzophenone is not added in step (1), but a small molecule benzophenone photoinitiator with the same molar amount as 4-acryloyloxybenzophenone is physically incorporated into the emulsion after emulsification in step (2).

[0080] Comparative Example 4

[0081] The photo-crosslinkable water-based polyolefin emulsion provided in this example is basically the same as that in Example 1, except that no ultraviolet light is used in step (3) and the emulsion is directly dried into a film.

[0082] The coating films of Examples 1-6 and Comparative Examples 1-4 were tested, wherein the water absorption was tested according to GB / T 9755-2014; the acetone wiping was tested according to GB / T 23989-2009; the pencil hardness was tested according to GB / T 6739-2022; the adhesion was tested according to GB / T 9286-2021; and the results are shown in Tables 1-2 below:

[0083] Table 1 Performance test results of the coating films of Examples 1-6

[0084]

[0085]

[0086] Table 2 Performance test results of the coating films of Comparative Examples 1-4

[0087] Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Water absorption (24h, wt%) 33.7 26.1 15.8 21.9 Acetone rub (100 times) Breakage Whiteness Slight whiteness Whiteness Pencil hardness B H H H Adhesion (crosshatch method) 3 2 1 2

[0088] As can be seen from Tables 1-2, the emulsion prepared in the examples of the present application has a coating film with significantly improved water resistance, solvent resistance, hardness and adhesion after UV curing, and the performance is much better than that of Comparative Example 2 which does not have a double bond type of grafted photoinitiator, Comparative Example 3 which physically blends a small molecule photoinitiator, and Comparative Example 4 which is not subjected to light curing.

[0089] The above examples are only for illustrating the technical concept and characteristics of the present application, and the purpose is to enable those skilled in the art to understand the content of the present application and implement it, and it cannot limit the protection scope of the present application. Any equivalent changes or modifications made according to the spirit and essence of the present application should be covered within the protection scope of the present application.

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Claims

1. A photo-crosslinkable waterborne polyolefin emulsion, characterized by: The emulsion comprises modified polyolefin and water; the modified polyolefin is prepared by graft polymerization of raw materials comprising polyolefin resin, maleic anhydride, grafting photoinitiating monomer, free radical initiator; the grafting photoinitiating monomer contains vinyl and photoinitiating group.

2. The photocrosslinkable waterborne polyolefin emulsion according to claim 1, characterized by: The grafting photoinitiating monomer is selected from the group consisting of one or more of 4-acryloyloxybenzophenone, 4-methacryloyloxybenzophenone, 2-hydroxy-4-acryloyloxybenzophenone, 4-hydroxyvinylbenzophenone methyl methacrylate, 1,4-bis(4-(2-methacryloyloxyethyl)phenylamino)anthraquinone, 2-vinylanthraquinone; and / or, the polyolefin resin is selected from the group consisting of one or more of polyethylene, polypropylene, ethylene-propylene copolymer; and / or, the melt index of the polyolefin resin at 190℃, 2.16kg is 5-50g / 10min.

3. The photocrosslinkable waterborne polyolefin emulsion according to claim 1, characterized by: The raw materials comprise 100 parts of polyolefin resin, 1-5 parts of maleic anhydride, 1-10 parts of grafting photoinitiating monomer, 0.2-1 part of free radical initiator, by mass fraction.

4. The photocrosslinkable waterborne polyolefin emulsion according to claim 1, characterized by: The graft polymerization is melt graft polymerization; and / or, the raw materials further comprise antioxidant; preferably, the raw materials comprise 100 parts of polyolefin resin, 1-5 parts of maleic anhydride, 1-10 parts of grafting photoinitiating monomer, 0.2-1 part of free radical initiator, 0.1-0.5 part of antioxidant, by mass fraction.

5. The photocrosslinkable waterborne polyolefin emulsion according to claim 1, characterized by: The emulsion further comprises emulsifier; preferably, the emulsifier is a composite emulsifier of anionic emulsifier and nonionic emulsifier; and / or, the emulsifier is 5-15 parts by mass, relative to 100 parts by mass of the polyolefin.

6. The photocrosslinkable waterborne polyolefin emulsion according to claim 5, characterized in that: The emulsion is prepared by melting the modified polyolefin to form oil phase; dissolving emulsifier in part of water to obtain water phase; adding the water phase to the oil phase under stirring, and then adding the remaining water.

7. The photocrosslinkable waterborne polyolefin emulsion according to claim 1, characterized by: The solid content of the emulsion is 35%-55%.

8. Process for the preparation of a photocrosslinkable aqueous polyolefin emulsion according to any one of claims 1 to 7, characterized in that: The preparation method comprises the following steps: 1) melt graft polymerization of the polyolefin resin, maleic anhydride, grafting photoinitiating monomer, free radical initiator and optional antioxidant to obtain modified polyolefin; 2) melting the modified polyolefin to form oil phase; dissolving emulsifier in part of water to obtain water phase; 3) adding the water phase to the oil phase under stirring, and then adding the remaining water to obtain the photo-crosslinkable water-based polyolefin emulsion.

9. The method for preparing a photocrosslinkable waterborne polyolefin emulsion according to claim 8, characterized by: In step 1), the melt graft polymerization is carried out in an extruder; and / or, the temperature of the melt graft polymerization is 150-190℃; and / or, the time of the melt graft polymerization is 10-15 minutes; and / or, the preparation method further comprises a step of premixing the polyolefin resin, maleic anhydride, grafting photoinitiating monomer, free radical initiator and optional antioxidant before the melt graft polymerization.

10. The method for preparing the photocrosslinkable aqueous polyolefin emulsion according to claim 8, characterized in that: In step 2), the melting temperature is 160-190℃; and / or, in step 2), the temperature of the part of water is 80-90℃; and / or, in step 2), the mass of the part of water accounts for 80%-90% of the mass of water.

11. The method of preparing a photocrosslinkable aqueous polyolefin emulsion according to claim 8, characterized by: In step 3), the stirring speed is 400-800 rpm; and / or, in step 3), when the remaining water is added, the stirring speed is 1000-1500 rpm; and / or, the preparation method further comprises a step of adjusting the pH of the emulsion to 7.5-9.0 using a pH adjuster.

12. Use of the photocrosslinkable aqueous polyolefin emulsion according to any one of claims 1 to 8 as a photocured coating.

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