A waterproof printing process for paper printed matter

Abstract

The present application relates to paper printing technical field, specifically to a waterproof printing process of paper printing product, the present application overcomes the problem of poor waterproof effect and poor adhesion of printing product caused by the imperfect traditional printing process, the present application obtains the printing product by pretreatment, bottom coating, surface coating and mirror roller calendering to the base material, by changing the parameters of corona treatment and micron level embossing treatment in pretreatment, the bottom coating liquid is prepared by mixing the modified acrylic resin with nanometer silicon dioxide, the transition layer is arranged between the bottom coating and surface coating, the special treated hydrophobic nanometer aluminum oxide is introduced into the surface coating liquid, and the modified polyurethane is synergistically used to improve the waterproof effect and adhesion of the printing product.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of paper printing, in particular to a waterproof printing process for paper printed matter. BACKGROUND

[0002] As a high-value-added packaging printed matter, cigarette boxes need to have both exquisite visual effects and good functionality. Paper cigarette boxes dominate the market due to their low cost and good printing adaptability, with more than 80% of cigarette boxes using paper materials. However, paper cigarette boxes face serious waterproofing problems. In a humid environment, the paper of traditional paper cigarette boxes easily absorbs water, causing the cigarette box to become soft and deformed, which not only affects the appearance but also can cause the internal tobacco products to become damp and deteriorate, reducing product quality. At the same time, the printed patterns and text on the surface of the cigarette box are easily blurred and faded when exposed to water, affecting brand image display and product information identification. Therefore, waterproofing technology is often used in the printing process of cigarette boxes. Traditional cigarette box waterproofing processes mainly rely on the following methods:

[0003] 1. Film coating process: covering a polyethylene (PE) or polypropylene (PP) plastic film on the printed surface, which can improve waterproofing, but the film coating material is not degradable, resulting in poor environmental friendliness, and the surface of the printed matter after film coating is prone to glare, hard touch, and covering some details of the printed patterns, affecting the texture of the cigarette box;

[0004] 2. Local UV varnish coating: spraying UV varnish locally after printing to form a waterproof layer, but traditional UV varnish curing requires high-energy ultraviolet light sources, and the coating is prone to cracking due to mechanical friction or temperature changes, with poor long-term waterproofing effect;

[0005] 3. Water-based coating process: using water-based resin to form a waterproof layer, which has a lower cost, but the adhesion and density of a single coating are insufficient, which can easily delaminate and become white in a humid environment, and the coating thickness can easily affect the clarity of the printed patterns.

[0006] In summary, it is of great practical significance to develop a waterproof printing process for paper printed matter with good waterproofing effect and strong adhesion. SUMMARY

[0007] The present application aims to provide a waterproof printing process for paper printed matter, which obtains the printed matter by pretreating the substrate, coating the bottom layer, coating the surface layer, and mirror roller calendering. By changing the parameters of corona treatment and micron-level embossing treatment in the pretreatment, modifying the acrylic resin, and mixing it with nano-silicon dioxide to obtain the bottom coating liquid, setting a transition layer between the bottom coating and the surface coating, and introducing specially treated hydrophobic nano-aluminum oxide into the surface coating liquid and cooperating with modified polyurethane to improve the waterproofing effect and adhesion of the printed matter.

[0008] To achieve the above object, the present application provides the following technical solutions.

[0009] It should be noted that the parts in the present application are mass parts.

[0010] The present application provides a waterproof printing process for paper printed matter, and the printing process is as follows:

[0011] S1 pretreatment: the substrate is placed in an environment with humidity of 50% and temperature of 25℃ for 24h, and then subjected to corona treatment and micron-level embossing treatment to obtain a pretreated substrate;

[0012] S2 bottom coating: the bottom coating liquid is coated on the surface of the pretreated substrate using an anilox roller, and then subjected to infrared drying to obtain a bottom coated substrate; the bottom coating liquid is prepared from modified acrylic resin, nano-silicon dioxide and silane coupling agent; the modified acrylic resin is prepared from acrylic acid, methyl methacrylate, butyl acrylate, hydroxyethyl acrylate and dodecyl acrylate;

[0013] S3 surface coating: the transition layer is sprayed on the surface of the bottom coated substrate and subjected to UV pre-curing with a wavelength of 395nm and an energy of 150mJ / cm 2 , and then the surface coating liquid is coated on the transition layer using a micro-gravure coating device, followed by UV curing and hot air curing to obtain a surface coated substrate; the transition layer is obtained by reaction of epoxy-acrylic hybrid resin and photoinitiator; the surface coating liquid is obtained by reaction of hydrophobic nano-alumina and modified polyurethane; the modified polyurethane is prepared from polytetrahydrofuran diol, isophorone diisocyanate, dimethylol propionic acid, perfluorohexyl ethyl acrylate and fluorine-containing benzoxazine monomer;

[0014] S4 post-processing: the surface coated substrate is calendered using a mirror roll to obtain a printed matter with a linear pressure of 50N / mm, a temperature of 90℃ and a speed of 10m / min.

[0015] Preferably, in S1, the power of the corona treatment is 50-80W, the speed is 5-10m / min, and the electrode spacing is 1.5mm; the micron-level embossing treatment has an embossing depth of 10-25μm, a pressure of 25N / cm 2 , and an embossing speed of 5m / min.

[0016] Preferably, in S2, the preparation steps of the bottom coating liquid are as follows: 80 parts of modified acrylic resin and 20 parts of nano-silicon dioxide are mixed in a stirring container, 1.5 parts of silane coupling agent KH550 is added, stirring is carried out at a speed of 800rpm for 2h, and then deionized water is added to adjust the viscosity to 50-80mPa·s to obtain the bottom coating liquid.

[0017] Preferably, the modified acrylic resin is prepared as follows: 3 parts of sodium dodecyl sulfate, 2 parts of alkylphenol polyoxyethylene ether and 80 parts of deionized water are added to a reaction kettle and stirred until dissolved, acrylic acid, methyl methacrylate, butyl acrylate, hydroxyethyl acrylate and dodecyl acrylate are added in a mass ratio of 8-15:12-20:2-6:5-8:1, stirred at 500 rpm for 40 min, heated to 76℃, add ammonium persulfate, the dropwise addition rate is 3 mL / min, after the dropwise addition is completed, keep the reaction for 1.5 h, cool to 40℃, add ammonia water to adjust the pH value to 7.5, and filter to obtain the modified acrylic resin.

[0018] Preferably, the infrared drying temperature in S2 is 60-80℃, and the time is 3 min.

[0019] Preferably, the surface layer coating liquid in S3 is prepared as follows: the nano-aluminum oxide is subjected to plasma treatment under the conditions of a pressure of 50 Pa and a power of 300 W, the working gas is obtained by mixing argon and oxygen in a volume ratio of 4:1, the treatment time is 5 min, and pretreated aluminum oxide is obtained; the heptadecafluorodecyltrimethoxysilane is added to an ethanol solution, ultrasonically dispersed at room temperature for 10 min at a power of 40 kHz, and then acetic acid is added, hydrolyzed by stirring at 50℃ for 30 min to obtain a pre-hydrolysis liquid; the pretreated aluminum oxide is added to the pre-hydrolysis liquid, and the zwitterionic surfactant tetradecyl dimethyl betaine is added, transferred to a microwave reaction kettle for reaction for 20 min, centrifuged and washed with ethanol and dried to obtain hydrophobic nano-aluminum oxide; 95 parts of modified polyurethane and 5 parts of hydrophobic nano-aluminum oxide are premixed and ultrasonically dispersed at 30℃ for 1 h, 0.5 parts of wetting agent TEGO Wet 270 is added, and stirred until the viscosity is 100-150 mPa·s to obtain the surface layer coating liquid.

[0020] Preferably, the modified polyurethane is prepared as follows: 100 parts of polytetrahydrofuran diol and 75 parts of isophorone diisocyanate are uniformly mixed and reacted at 70℃ for 2 h, nitrogen is introduced during the reaction, then 26-36 parts of dimethylol propionic acid and 15-35 parts of perfluorohexyl ethyl acrylate are added, the temperature is lowered to 60℃ and reacted for 1 h, 15 parts of fluorine-containing benzoxazine monomer is added dropwise, and the isophorone diisocyanate continues to react until the NCO content meets the standard, then 10 parts of double-end mercapto polyethylene glycol is added for ultraviolet light irradiation to obtain the modified polyurethane.

[0021] Preferably, the UV curing wavelength in S3 is 365 nm, and the energy is 500-800 mJ / cm 2 ; the hot air curing temperature is 100-120℃, and the time is 50 s.

[0022] Preferably, the transition layer preparation step in S3 is as follows: 60 parts of bisphenol A epoxy resin and 40 parts of propylene glycol methyl ether acetate are added to a three-necked flask, and stirred at 50-65 DEG C until the bisphenol A epoxy resin is completely dissolved, 30 parts of acrylic monomer is added thereto, and stirring is continued for 30 min to obtain a mixed solution; the mixed solution is transferred into a photo-reacting device, nitrogen is introduced for protection, the nitrogen flow rate is 8 L / min, 0.3-1.5 parts of a photo initiator 2-hydroxy-2-methyl-1-phenyl-1-propanone is added at a rotating speed of 120 rpm, and irradiation is carried out with ultraviolet light of a wavelength of 365 nm, the light intensity is 50-100 mW / cm 2 , and reaction is carried out for 45 min to obtain an oligomer; the oligomer is removed from the photo-reacting device, warmed to 75-90 DEG C, 0.8 parts of a catalyst tetrabutylammonium bromide is added, and reaction is continued for 3.5 h, and after cooling to room temperature, distillation is carried out under reduced pressure to obtain an epoxy-acrylic hybrid resin; the epoxy-acrylic hybrid resin, 1.5 parts of a photo initiator TPO and 0.4 parts of a leveling agent BYK-333 are stirred and mixed at a rotating speed of 600 rpm at room temperature for 1 h to obtain the transition layer; the acrylic monomer is obtained by mixing acrylic acid and hydroxyethyl acrylate in a mass ratio of 1:2.

[0023] Compared with the prior art, the present application has the following beneficial effects:

[0024] 1、The present application improves the adhesion of the coating layer to the paper surface from micro and macro levels by the corona treatment and micron-level embossing treatment in the pretreatment stage. The corona treatment oxidizes the surface of the paper fibers to form a large number of oxygen-containing polar groups, changes the molecular structure, increases the surface energy, and significantly improves the reactivity with the coating material. The micron-level embossing treatment forms small grooves on the surface of the paper by mechanical means, increases the specific surface area, and produces a mechanical anchoring effect between the coating and the paper. The synergistic effect of the two provides excellent adhesion conditions for the subsequent primer coating liquid and the entire coating system, ensuring that the coating can be firmly attached to the paper.

[0025] 2、The present application prepares a primer coating liquid, mixes long-chain alkyl-modified acrylic resin and nano-silica, and then adds a silane coupling agent to lay a solid foundation for improving adhesion. The modified acrylic resin itself has good affinity for the paper substrate, and the nano-silica fills the pores of the paper, increasing the contact area. The silane coupling agent reacts with the nano-silica on one end and combines with the modified acrylic resin on the other end, forming a stable chemical bond connection that greatly enhances the adhesion of the primer to the paper. Moreover, the primer coating liquid is dried by infrared, which can promote the nano-silica to penetrate more fully into the interior of the paper fibers, together with the modified acrylic resin, to form a more intimate combination with the paper, improving the adhesion of the primer to the paper and making the coating less likely to fall off.

[0026] 3、The present application is provided with a transition layer between the bottom coating and the surface coating, the rigid network of the epoxy component in the transition layer provides a support skeleton, and the acrylic segment penetrates into the micro pores of the bottom coating to form molecular level entanglement, effectively eliminating the internal stress of the interface; the active groups such as epoxy group and hydroxyl group in the transition layer react with the carboxyl group of the bottom coating to form covalent crosslinking, and the surface of the transition layer is rich in acrylate double bond, which is photo-induced grafted with the polyurethane prepolymer of the surface coating to form a gradient chemical bonding structure; and the UV pre-curing can form an open crosslinking network, facilitating the penetration and interlocking of the surface coating liquid, enhancing the bonding force between the coatings, and preventing the coatings from delaminating.

[0027] 4、The present application introduces hydrophobic nano-aluminum oxide into the surface coating liquid, which cooperates with the modified polyurethane to build a highly hydrophobic protective layer on the surface of the printed matter. The surface of the plasma-modified nano-aluminum oxide is rich in active sites, which form chemical grafting with the long-chain fluoroalkyl group in the silane hydrolysis liquid, ensuring the stable anchoring of the nano-particles in the coating; the low surface energy characteristics of the perfluoro segment in the fluorinated polyurethane make the fluorinated molecular layer densely arranged on the surface of the coating, which together with the nano-aluminum oxide forms a composite structure, mimicking the lotus leaf effect, improving the water resistance of the printed matter, and realizing the long-acting self-maintenance function; in addition, during the curing process, the thiol-ene reaction induced by UV fixes the distribution of nano-particles, and the orientation and arrangement of fluoroalkyl group are optimized through molecular chain thermal motion in the hot air curing stage, further improving the water resistance of the printed matter. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 The process flow chart of the waterproof printing process for paper printed matter according to the present application is shown in the figure. DETAILED DESCRIPTION

[0029] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0030] Please refer to Figure 1 The present application provides a waterproof printing process for paper printed matter, which obtains the printed matter through corona treatment, micron embossing treatment, bottom coating, transition layer spraying, surface coating and polishing treatment of the substrate; the technical solutions are as follows:

[0031] The substances involved in the present application are as follows:

[0032] Silane coupling agent KH550 CAS:919-30-2; sodium dodecyl sulfate CAS:151-21-3; acrylic acid CAS:79-10-7; methyl methacrylate CAS:80-62-6; butyl acrylate CAS:141-32-2; hydroxyethyl acrylate CAS:818-61-1; dodecyl acrylate CAS:2156-97-0; ammonium persulfate CAS:7727-54-0; nano-alumina CAS:11092-32-3; heptadecafluorodecyltrimethoxysilane CAS:83048-65-1; acetic acid CAS:64-19-7; polytetrahydrofuran glycol CAS:25190-06-1; isophorone diisocyanate CAS:4098-71-9; dimethylol propionic acid CAS:4767-03-7; perfluorohexylethyl acrylate CAS:17527-29-6; bisphenol A epoxy resin CAS:25085-99-8; propylene glycol methyl ether acetate CAS:108-65-6; 2-hydroxy-2-methyl-1-phenyl-1-propanone CAS:7473-98-5; tetrabutylammonium bromide CAS:1643-19-2; photoinitiator TPO CAS:75980-60-8; nano-silica purchased from Xuancheng Jingrui New Material Co., Ltd.; alkylphenol polyoxyethylene ether purchased from Jiangsu Bosite Chemical Technology Co., Ltd.; tetradecyl dimethyl betaine purchased from Guangdong Wengjiang Chemical Reagent Co., Ltd.; wetting agent TEGO Wet 270 purchased from Hubei Zhonglongkangsheng Fine Chemical Co., Ltd.; double-end mercapto polyethylene glycol purchased from double-end mercapto polyethylene glycol; leveling agent BYK-333 purchased from Guangzhou Qiangang Trading Co., Ltd.; fluorine-containing benzoxazine was prepared according to the method in “Synthesis of Fluorine-Containing Benzoxazine and Its Application in Coating Field”.

[0033] Example 1

[0034] The preparation steps of the primer coating solution are as follows: 3 parts of sodium dodecyl sulfate, 2 parts of alkylphenol polyoxyethylene ether and 80 parts of deionized water are added into a reaction kettle and stirred until dissolved, acrylic acid, methyl methacrylate, butyl acrylate, hydroxyethyl acrylate and 4 parts of dodecyl acrylate are added therein according to a mass ratio of 8:12:2:5:1, stirring at a speed of 500 rpm for 40 min, heating to 76℃, adding ammonium persulfate, the dropping speed is 3 mL / min, after the completion of dropping, keeping the reaction for 1.5 h, cooling to 40℃, adding ammonia water to adjust the pH value to 7.5, and filtering to obtain a modified acrylic resin; 80 parts of the modified acrylic resin and 20 parts of nano-silica are mixed in a stirring container, 1.5 parts of silane coupling agent KH550 is added, stirring at a speed of 800 rpm for 2 h, then deionized water is added to adjust the viscosity to 50 mPa·s, and the primer coating solution is obtained;

[0035] The surface layer coating liquid preparation steps are as follows: 12 parts of nano-alumina is subjected to plasma treatment under the condition of a pressure of 50 Pa and a power of 300 W, the working gas is obtained by mixing argon and oxygen according to a volume ratio of 4:1, the treatment time is 5 min, and a pretreated alumina is obtained; 2 parts of heptadecafluorodecyltrimethoxysilane is added into 30 parts of an ethanol solution, ultrasonic dispersion is carried out at room temperature for 10 min under a power of 40 kHz, then 0.4 parts of acetic acid is added, hydrolysis is carried out for 30 min by stirring at a temperature of 50℃, and a pre-hydrolysis liquid is obtained; the pretreated alumina is added into the pre-hydrolysis liquid, and 0.8 parts of a zwitterionic surfactant tetradecyldimethylbetaine is added, then the mixture is transferred into a microwave reaction kettle for reaction for 20 min, centrifugation and ethanol washing are carried out, and drying is carried out to obtain hydrophobic nano-alumina; 100 parts of polytetrahydrofuran glycol and 75 parts of isophorone diisocyanate are uniformly mixed, and then reacted for 2 h at 70℃, and nitrogen protection is carried out during the reaction, then 26 parts of dimethylol propionic acid and 15 parts of perfluorohexyl ethyl acrylate are added, the temperature is lowered to 60℃, and reaction is carried out for 1 h, 15 parts of a fluorine-containing benzoxazine monomer is added dropwise, and the isophorone diisocyanate continues to react until the content of -NCO reaches the standard (the content is 1.2%), then 10 parts of a double-terminated mercapto polyethylene glycol is added, and ultraviolet light irradiation is carried out to obtain a modified polyurethane; 95 parts of the modified polyurethane and 5 parts of the hydrophobic nano-alumina are premixed, ultrasonic dispersion is carried out for 1 h at 30℃, 0.5 parts of a wetting agent TEGOWet 270 is added, stirring is carried out until the viscosity is 100 mPa·s, and a surface layer coating liquid is obtained.

[0036] The transition layer preparation steps are as follows: 60 parts of bisphenol A epoxy resin and 40 parts of propylene glycol methyl ether acetate are added into a three-necked flask, stirring is carried out at 50℃ until the bisphenol A epoxy resin is completely dissolved, 30 parts of an acrylic monomer is added into the mixture, and stirring is continuously carried out for 30 min to obtain a mixed liquid; the mixed liquid is transferred into a photo reaction device, nitrogen protection is carried out, the nitrogen flow rate is 8 L / min, 0.3 parts of a photoinitiator 2-hydroxy-2-methyl-1-phenyl-1-propanone is added at a rotation speed of 120 rpm, ultraviolet light irradiation is carried out at a wavelength of 365 nm, the light intensity is 50 mW / cm 2 , and reaction is carried out for 45 min to obtain an oligomer; the oligomer is removed from the photo reaction device, the temperature is raised to 75℃, 0.8 parts of a catalyst tetrabutylammonium bromide is added, and reaction is continuously carried out for 3.5 h, the temperature is cooled to room temperature, and pressure reduction distillation is carried out to obtain an epoxy-acrylic hybrid resin; the epoxy-acrylic hybrid resin, 1.5 parts of a photoinitiator TPO and 0.4 parts of a leveling agent BYK-333 are stirred and mixed at a rotation speed of 600 rpm at room temperature for 1 h to obtain a transition layer; the acrylic monomer is obtained by mixing acrylic acid and hydroxyethyl acrylate according to a mass ratio of 1:2.

[0037] The printing process is as follows:

[0038] S1 pretreatment: the substrate (white card) was placed in an environment with humidity of 50% and temperature of 25℃ for 24h, followed by corona treatment and micron embossing treatment to obtain a pretreated substrate; the corona treatment power was 50W, the speed was 5m / min, and the electrode distance was 1.5mm; the micron embossing treatment had an embossing depth of 10μm, a pressure of 25N / cm, and an embossing speed of 5m / min. 2

[0039] S2 primer coating: the primer coating liquid was coated on the surface of the pretreated substrate using an anilox roller, followed by infrared drying at 60℃ for 3min to obtain a primer coated substrate, and the infrared wavelength was 10μm; the primer coating wet film thickness was 8μm.

[0040] S3 top coating: the transition layer was sprayed (spraying amount 2g / m 2 ) on the surface of the primer coated substrate and UV pre-cured for 40s, the wavelength was 395nm, and the energy was 150mJ / cm 2 ; then the top coating liquid was coated on the transition layer using a micro gravure coating device, followed by UV curing and hot air curing to obtain a top coated substrate; the UV curing wavelength was 365nm, and the energy was 500mJ / cm 2 ; the hot air curing temperature was 100℃, and the time was 50s; the top coating wet film thickness was 12μm.

[0041] S4 post-processing: the top coated substrate was calendered using a mirror roll to obtain a printed product, the linear pressure was 50N / mm, the temperature was 90℃, and the speed was 10m / min.

[0042] Examples 2-4

[0043] The preparation method and parameter conditions of Reference Example 1 were referred to, and the specific differences are shown in Table 1.

[0044] Comparative Example 1

[0045] The preparation method and parameter conditions of Reference Example 1 were referred to, except that no corona treatment was performed in the S1 pretreatment.

[0046] Comparative Example 2

[0047] The preparation method and parameter conditions of Reference Example 1 were referred to, except that no micron embossing treatment was performed in the S1 pretreatment.

[0048] Comparative Example 3

[0049] The preparation method and parameter conditions of Reference Example 1 were referred to, except that no pretreatment was performed on the substrate.

[0050] Experimental Example 1 Adhesion Test

[0051] ​The adhesion was detected according to GB / T13217.7-2009, and the tape method was used in the test. The tape was pasted on the surface of the substrate, and the pressure roller was rolled back and forth for 3 times. After 5 minutes, the tape was peeled off at a speed of 0.8 m / s according to the method disclosed in GB / T7707-2008, and the adhesion was observed and calculated. The results are shown in Table 1.

[0052] Table 1 Adhesion test of Examples 1-4 and Comparative Examples 1-3

[0053]

[0054]

[0055] As can be seen from Table 1, in Examples 1-4, the adhesion of the coating to the paper surface is improved from the micro and macro levels by corona treatment and micron-level embossing treatment of the substrate. Corona treatment oxidizes the surface of the paper fibers, forming a large number of oxygen-containing polar groups, changing the molecular structure, increasing the surface energy, and significantly improving the reactivity with the coating material. Micron-level embossing treatment forms micro grooves on the surface of the paper by mechanical means, increasing the specific surface area, and producing a mechanical anchoring effect between the coating and the paper. The synergistic effect of the two provides excellent adhesion conditions for the subsequent primer coating liquid and the entire coating system, ensuring that the coating can be firmly attached to the paper and significantly improving the durability of the printed matter. In Example 2, when the corona power is 60 W, the corona speed is 7 mm / min, and the embossing depth is 15 μm, the adhesion of the coating is best, with an adhesion of 96.3%. In Comparative Example 1, no corona treatment was performed in S1 pretreatment, and the surface fibers of the paper substrate were in a low-energy inert state, reducing the reactivity with the coating material, and increasing the porosity of the substrate, resulting in reduced adhesion of the coating. In Comparative Example 2, no micron-level embossing treatment was performed in S1 pretreatment, which destroyed the mechanical anchoring effect of the coating and the substrate, resulting in a significant reduction in the resistance of the adhesion to dynamic stress. In Comparative Example 3, no pretreatment was performed on the substrate, and the combination of the coating and the paper substrate relied on simple physical adsorption, resulting in a serious deterioration of the adhesion. The absence of both the polar activation of corona treatment and the mechanical reinforcement of embossing made it difficult for the primer coating liquid to penetrate the fiber pores, and the active groups in the resin were also unable to form stable bonds with the substrate.

[0056] Examples 5-7

[0057] The preparation method and parameters of Comparative Example 2 were used as reference, with the specific differences shown in Table 2. The mass ratio in Table 2 is the mass ratio of acrylic acid, methyl methacrylate, butyl acrylate, hydroxyethyl acrylate, and dodecyl acrylate.

[0058] Comparative Example 4

[0059] The preparation method and parameters of Example 2 were referred to, except that the acrylic resin was not modified when preparing the primer coating solution, but the water-based acrylic resin emulsion (Shandong Zouping Dazhan New Material Co., Ltd.) was directly used.

[0060] Comparative Example 5

[0061] The preparation method and parameters of Example 2 were referred to, except that acrylic acid was not added when preparing the modified acrylic resin.

[0062] Comparative Example 6

[0063] The preparation method and parameters of Example 2 were referred to, except that methyl methacrylate was not added when preparing the modified acrylic resin.

[0064] Comparative Example 7

[0065] The preparation method and parameters of Example 2 were referred to, except that butyl acrylate was not added when preparing the modified acrylic resin.

[0066] Comparative Example 8

[0067] The preparation method and parameters of Example 2 were referred to, except that hydroxyethyl acrylate was not added when preparing the modified acrylic resin.

[0068] Comparative Example 9

[0069] The preparation method and parameters of Example 2 were referred to, except that infrared drying was replaced by hot air drying in the primer coating of step S2.

[0070] Adhesion test of experimental example 2

[0071] The adhesion was tested according to the method of Experimental Example 1; the results are shown in Table 2.

[0072] Table 2 Adhesion test of Example 2, Examples 5-7 and Comparative Examples 4-9

[0073]

[0074] As can be seen from Table 2, in Examples 2, 5-7, by preparing the primer coating liquid, the modified acrylic resin is mixed with nano-silica, and then the silane coupling agent is added, to lay a solid foundation for improving the adhesion. The modified water-based acrylic resin itself has good affinity for the paper substrate, and the nano-silica fills the pores of the paper, increasing the contact area; the silane coupling agent reacts with the nano-silica on one end, and combines with the modified acrylic resin on the other end, forming a stable chemical bond connection, greatly enhancing the adhesion of the primer to the paper; and the primer coating liquid is dried by infrared, which can promote the nano-silica to penetrate more fully into the interior of the paper fibers, together with the modified acrylic resin, to form a more close combination with the paper, improving the adhesion of the primer to the paper, and making the coating less likely to fall off. In Example 6, when the mass ratio of the four is 12:16:6:8:1, the viscosity of the primer coating liquid is 70 mPa·s, and the infrared drying temperature is 70°C, the adhesion of the coating is best, and the adhesion strength reaches 97.5%. In Comparative Example 4, when preparing the primer coating liquid, the acrylic resin is not modified, but a water-based acrylic resin emulsion is directly used, the directional bonding ability of the functional monomer is missing in the coating, the base resin cannot effectively combine with the corona-treated paper substrate oxide layer through hydrogen bonds or covalent bonds, and the interface bridging effect of the nano-silica is lost due to the lack of sufficient carboxyl or hydroxyl groups to react with the silane coupling agent, resulting in a significant decrease in adhesion. In Comparative Example 5, when preparing the modified acrylic resin, acrylic acid is not added, the carboxyl content in the resin chain segment is sharply reduced, and the silane coupling agent of the nano-silica cannot form stable ionic bonds or amide bonds, resulting in weakened interface bonding between the nano-particles and the resin; in addition, the lack of carboxyl groups reduces the ability of the primer coating liquid to wet the polar surface of the substrate, and the resin cannot tightly engage the anchor points formed by the micron embossing during drying. In Comparative Example 6, when preparing the modified acrylic resin, methyl methacrylate is not added, the primer coating film cannot effectively fill the recessed areas of the micron embossing during the hot air drying stage due to severe softening, and the loose resin structure weakens the mechanical interlocking effect, resulting in a decrease in adhesion. In Comparative Example 7, when preparing the modified acrylic resin, butyl acrylate is not added, the primer coating film is too rigid to buffer the deformation stress of the substrate fibers when the calendering or humidity changes, resulting in the expansion of interface micro-cracks. In Comparative Example 8, when preparing the modified acrylic resin, hydroxyethyl acrylate is not added, the primer resin cannot form stable siloxane bonds with the silane coupling agent of the nano-silica, and the nano-particles migrate to the surface during the drying process to form a weak interface layer. In Comparative Example 9, in the primer coating in step S2, the infrared drying is replaced by hot air drying, compared with infrared radiation drying, the heat transfer rate is low and the temperature distribution is uneven, the slow evaporation of the solvent causes the surface of the primer coating film to form a film quickly but the internal solvent to remain, causing the volume shrinkage stress to concentrate, forming micron-sized pores, and the adhesion decreases.

[0075] Examples 8-10

[0076] The preparation method and parameters of Example 6 were referred to, and the specific differences are shown in Table 3; temperature one in Table 3 is the temperature for stirring the bisphenol A epoxy resin to complete dissolution during preparation of the epoxy-acrylic hybrid resin; light intensity is the UV light irradiation intensity after adding the photoinitiator during preparation of the epoxy-acrylic hybrid resin; temperature two is the temperature for heating after moving the oligomer out of the light reaction device during preparation of the epoxy-acrylic hybrid resin.

[0077] Comparative Example 10

[0078] The preparation method and parameters of Example 6 were referred to, except that no transition layer was added between the bottom coating and the surface coating.

[0079] Comparative Example 11

[0080] The preparation method and parameters of Example 6 were referred to, except that the acrylic monomer was obtained by mixing acrylic acid and hydroxyethyl acrylate in a mass ratio of 1:1 during preparation of the epoxy-acrylic hybrid resin.

[0081] Comparative Example 12

[0082] The preparation method and parameters of Example 6 were referred to, except that the amount of the photoinitiator was 3 parts during preparation of the epoxy-acrylic hybrid resin.

[0083] Adhesion test of Experimental Example 3

[0084] The adhesion was tested according to the method of Experimental Example 1; the results are shown in Table 3.

[0085] Table 3 Adhesion test of Example 6, Examples 8-10, and Comparative Examples 10-12

[0086]

[0087]

[0088] As can be seen from Table 3, in Example 6, Examples 8-10, by providing a transition layer between the bottom coating and the surface coating, the rigid network of the epoxy component in the transition layer provides a support skeleton, and the acrylic segment penetrates into the small pores of the bottom coating to form molecular entanglement, effectively eliminating the internal stress at the interface; the active groups such as epoxy groups and hydroxyl groups in the transition layer react with the carboxyl groups of the bottom coating to form covalent crosslinking, and the acrylic ester double bonds enriched on the surface of the transition layer are photoinitiated to graft with the polyurethane prepolymer of the surface coating to form a gradient chemical bonding structure; and the UV pre-curing can form an open crosslinking network, which facilitates the penetration and interlocking of the surface coating liquid, enhances the bonding force between the coatings, makes it difficult for the coatings to delaminate, and avoids the entry of moisture into the interlayer to erode the bottom coating and cause the adhesion to decrease. In Example 9, when temperature one is 60°C, the amount of the photoinitiator is 1 part, and the light intensity is 75 mW / cm2 In Comparative Example 10, no transition layer was added, and the polar difference between the acrylic resin of the bottom layer and the fluorinated polyurethane of the surface layer made it difficult for the surface coating solution to spread uniformly on the bottom layer. The lack of a transition layer made the interlayer rely only on weak van der Waals forces for bonding, and the penetration of interfacial water molecules accelerated delamination, reducing adhesion. In Comparative Example 11, the acrylic monomer used to prepare the epoxy-acrylic hybrid resin was a mixture of acrylic acid and hydroxyethyl acrylate in a mass ratio of 1:1. The imbalance in the mass ratio significantly weakened the cross-layer reactivity of the epoxy hybrid resin, and delamination between the layers easily occurred, leading to a decrease in adhesion. In Comparative Example 12, the amount of photoinitiator used to prepare the epoxy-acrylic hybrid resin was 3 parts. The excess photoinitiator caused uncontrolled reactions during UV curing, destroying the structural uniformity of the transition layer. The decomposition of unspent photoinitiator during the hot air curing stage produced gas that increased interfacial porosity, reducing adhesion.

[0089] Examples 11-13

[0090] The preparation method and parameter conditions of Example 9 were used as reference, with specific differences shown in Table 4.

[0091] Table 4 Specific preparation parameters of Examples 11-13

[0092]

[0093]

[0094] Comparative Example 13

[0095] The preparation method and parameter conditions of Example 9 were used as reference, except that in the preparation of the surface coating solution, hydrophobic nano-aluminum oxide was replaced with nano-aluminum oxide.

[0096] Comparative Example 14

[0097] The preparation method and parameter conditions of Example 9 were used as reference, except that in the preparation of the hydrophobic nano-aluminum oxide, the nano-aluminum oxide was not subjected to plasma treatment.

[0098] Comparative Example 15

[0099] The preparation method and parameter conditions of Example 9 were used as reference, except that in the preparation of the surface coating solution, no hydrophobic nano-aluminum oxide was added.

[0100] Comparative Example 16

[0101] The preparation method and parameter conditions of Example 9 were used as reference, except that in the preparation of the surface coating solution, the modified polyurethane was replaced with ordinary polyurethane (purchased from Guangdong Wengjiang Chemical Reagent Co., Ltd., model RM-12W).

[0102] Comparative Example 17

[0103] The preparation method and parameters of Example 9 were referred to, except that no fluorine-containing benzoxazine monomer was added during the preparation of the modified polyurethane.

[0104] Comparative Example 18

[0105] The preparation method and parameters of Example 9 were referred to, except that the surface layer coating liquid was coated on the transition layer in step S3, followed by UV curing only.

[0106] Comparative Example 19

[0107] The preparation method and parameters of Example 9 were referred to, except that the surface layer coating liquid was coated on the transition layer in step S3, followed by hot air curing only.

[0108] Experimental Example 4: Waterproof performance test

[0109] Water contact angle test was performed by using an automatic contact angle tester. 5 μl water droplets were injected onto the surface of the printed products prepared in Example 9, Examples 11-13 and Comparative Examples 13-19, and the contact angle was tested when the shape of the water droplets no longer changed.

[0110] The printed substrate was cut into a sample of 5 cm x 10 cm, immersed in deionized water for 24 h, and then taken out to wipe off the surface moisture. The mass of the sample before and after immersion was measured, and the water absorption rate of the sample was calculated. The results are shown in Table 5.

[0111] Table 5: Waterproof performance test of Example 9, Examples 11-13 and Comparative Examples 13-19

[0112]

[0113]

[0114] It can be seen from Table 4 and Table 5 that in Example 9, Example 11-13, by introducing hydrophobic nano-alumina in the surface coating liquid, synergistic effect with modified polyurethane, a highly hydrophobic protective layer is constructed on the surface of the printed matter. The surface of the plasma modified nano-alumina is rich in active sites, which forms chemical grafting with long-chain fluoroalkyl in the silane hydrolysis solution, ensuring the stable anchoring of nano-particles in the coating; while the low surface energy characteristics of perfluoro segment in fluorinated polyurethane make the coating surface form a dense layer of fluorinated molecules, which together with nano-alumina forms a composite structure, mimics the lotus leaf effect, improves the water resistance of the printed matter, and realizes the long-acting self-maintenance function; in addition, during the curing process, the thiol-ene reaction induced by UV fixes the distribution of nano-particles, and the thermal wind curing stage optimizes the orientation arrangement of fluoroalkyl through molecular chain thermal motion, further improving the water resistance of the printed matter. In Example 12, when the amount of dimethylol propionic acid is 33 parts, the amount of perfluoro hexyl ethyl acrylate is 25 parts, the viscosity of the surface coating liquid is 130 mPa·s, the UV curing energy is 700 mJ / cm 2 , and the hot air curing temperature is 110℃, the water resistance of the printed matter is best, the water contact angle is 168.5°, and the water absorption rate is 2.18%. In Comparative Example 13, when preparing the surface coating liquid, replace the hydrophobic nano-alumina with nano-alumina, which is not modified by fluorosilane, and the surface energy is high. When water contacts the surface of the printed matter, nano-alumina cannot repel water like hydrophobic nano-alumina, which makes it easier for water to adhere to the surface of the coating and penetrate into the interior of the coating, thereby reducing the water resistance of the printed matter. In Comparative Example 14, when preparing hydrophobic nano-alumina, the nano-alumina is not subjected to plasma treatment, and the surface thereof has a hydroxyl passivation layer and organic contaminants, which reduces the reactivity of the nano-alumina with heptadecafluorodecylsilane and decreases the water resistance. In Comparative Example 15, when preparing the surface coating liquid, no hydrophobic nano-alumina is added, and only the hydrophobicity of the modified polyurethane is relied on to form an effective hydrophobic network, making it easier for water to break through the coating barrier and penetrate into the interior of the printed matter. In Comparative Example 16, when preparing the surface coating liquid, replace the modified polyurethane with ordinary polyurethane, which has relatively high surface energy and cannot form an efficient water-resistant coating with hydrophobic nano-alumina. In Comparative Example 17, when preparing the modified polyurethane, no fluorine-containing benzoxazine monomer is added, which results in insufficient stability and durability of the water-resistant barrier of the printed matter. In Comparative Example 18, the surface coating liquid is coated on the transition layer in step S3, followed by only UV curing, which results in incomplete surface curing. The coating has large intermolecular gaps, which makes it easier for water to penetrate into the coating and reduces the water resistance of the printed matter. In Comparative Example 19, the surface coating liquid is coated on the transition layer in step S3, followed by only hot air curing, which results in a loose overall structure of the coating and affects the water resistance.

[0115] While embodiments of the application have been shown and described, it is to be understood that the embodiments described are merely exemplary of the principles and application of the present application. Numerous modifications and adaptions can be effected without departing from the spirit and scope of the present application, which is not limited to the exact construction and arrangement described. It is intended, therefore, to cover all modifications and adaptions that fall within the scope of the claims and their equivalents.

Claims

1. A waterproof printing process for paper printed matter, characterized by: The printing process is as follows: S1 pretreatment: the substrate is subjected to corona treatment and micron-level embossing treatment to obtain a pretreated substrate; S2 primer coating: a primer coating liquid is applied to the surface of the pretreated substrate, followed by infrared drying to obtain a primer coated substrate; the primer coating liquid is prepared from modified acrylic resin, nano-silicon dioxide and silane coupling agent; the modified acrylic resin is prepared from acrylic acid, methyl methacrylate, butyl acrylate, hydroxyethyl acrylate and dodecyl acrylate; S3 topcoat coating: a transition layer is sprayed on the surface of the primer coated substrate and cured, then a topcoat coating liquid is applied on the transition layer, followed by UV curing and then hot air curing to obtain a topcoat coated substrate; the transition layer is obtained by reaction of epoxy-acrylic hybrid resin and photoinitiator; the topcoat coating liquid is obtained by reaction of hydrophobic nano-alumina oxide and modified polyurethane; the modified polyurethane is prepared from polytetrahydrofuran diol, isophorone diisocyanate, dimethylol propionic acid, perfluorohexyl ethyl acrylate and fluorine-containing benzoxazine monomer; S4 post-processing: the topcoat coated substrate is subjected to calendering treatment to obtain a printed product.

2. A waterproof printing process for paper printed matter as claimed in claim 1, wherein: The corona treatment power in S1 is 50-80 W, the speed is 5-10 m / min, and the electrode distance is 1.5 mm; the micron-level embossing treatment embossing depth is 10-25 μm, the pressure is 25 N / cm 2 , and the embossing speed is 5 m / min.

3. A waterproof printing process for paper printed matter as claimed in claim 1, wherein: The preparation steps of the primer coating liquid in S2 are as follows: the modified acrylic resin and the nano-silicon dioxide are mixed in a stirring container, the silane coupling agent is added and stirred, then deionized water is added to adjust the viscosity to 50-80 mPa·s to obtain the primer coating liquid.

4. A waterproof printing process for paper printed matter as claimed in claim 1, wherein: The preparation steps of the modified acrylic resin are as follows: sodium dodecyl sulfate, alkylphenol polyoxyethylene ether and deionized water are added to a reaction kettle and stirred until dissolved, the acrylic acid, the methyl methacrylate, the butyl acrylate, the hydroxyethyl acrylate and the dodecyl acrylate are added to the reaction kettle in a mass ratio of 8-15:12-20:2-6:5-8:1, the temperature is raised to 76℃, ammonium persulfate is added, the dropwise addition is completed, the reaction is maintained for 1.5 h, the temperature is lowered to 40℃, ammonia water is added to adjust the pH value, and the modified acrylic resin is obtained by filtration.

5. A waterproof printing process for paper printed matter as claimed in claim 1 wherein: The infrared drying temperature in S2 is 60-80℃.

6. A waterproof printing process for paper printed matter as claimed in claim 1, wherein: The preparation steps of the topcoat coating liquid in S3 are as follows: the nano-alumina oxide is subjected to plasma treatment to obtain pretreated alumina oxide; heptadecafluorodecyltrimethoxysilane is added to an ethanol solution, ultrasonically dispersed, then acetic acid is added, the temperature is raised to 50℃ and stirred to obtain a pre-hydrolysis liquid; the pretreated alumina oxide is added to the pre-hydrolysis liquid, and a zwitterionic surfactant is added, transferred to a microwave reaction kettle and reacted for 20 min, centrifuged and washed with ethanol and dried to obtain the hydrophobic nano-alumina oxide; The modified polyurethane and the hydrophobic nano-alumina oxide are pre-mixed and ultrasonically dispersed, a wetting agent is added, and stirred until the viscosity is 100-150 mPa·s to obtain the topcoat coating liquid.

7. A waterproof printing process for paper printed matter as claimed in claim 1 wherein: The modified polyurethane is prepared by the following steps: mixing the polytetrahydrofuran diol and the isophorone diisocyanate uniformly, then reacting at 70 DEG C for 2h, then adding 26-36 parts of the dimethylol propionic acid and 15-35 parts of the perfluorohexyl ethyl acrylate, cooling to 60 DEG C and reacting for 1h, then adding the fluorine-containing benzoxazine monomer dropwise, and then adding the double-end mercapto polyethylene glycol and performing ultraviolet irradiation to obtain the modified polyurethane.

8. A waterproof printing process for paper printed matter as claimed in claim 1 wherein: The UV curing wavelength in S3 is 365 nm, and the energy is 500-800 mJ / cm 2 ; the hot air curing temperature is 100-120℃, and the curing time is 50 s.

9. A waterproof printing process for paper printed matter as claimed in claim 1 wherein: The preparation steps of the transition layer in S3 are as follows: Bisphenol A epoxy resin and propylene glycol methyl ether acetate are added into a three-neck flask, stirred at 50-65°C, and then acrylic monomer is added and stirred to obtain a mixed solution; the mixed solution is transferred into a photo reaction device, protected by nitrogen, 0.3-1.5 parts of the photoinitiator is added, and irradiated by ultraviolet light with an intensity of 50-100 mW / cm 2 ; the reaction obtains an oligomer; the oligomer is removed from the photo reaction device, heated to 75-90°C, and a catalyst is added for continuous reaction for 3.5 h; after cooling to room temperature, the epoxy-acrylic hybrid resin is obtained by reduced pressure distillation; the epoxy-acrylic hybrid resin, the photoinitiator, and the leveling agent are mixed and stirred to obtain the transition layer; the acrylic monomer is obtained by mixing the acrylic acid and the hydroxyethyl acrylate at a mass ratio of 1:2.

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