A scratch-resistant water-based gravure varnish, its preparation method and application

Abstract

The present invention discloses a scratch-resistant water-based gravure varnish and its preparation method and application. By mass percentage, the varnish comprises the following components: 10% - 80% of a mixed resin, 1 - 3% of a non-ionic surfactant, 0.01 - 0.2% of an antifoaming agent, 1 - 5% of ethanol, and the balance of deionized water; the mixed resin comprises a styrene-acrylate copolymer A, a styrene-acrylate copolymer B, and an aqueous polyurethane dispersion; in the mixed resin, by mass percentage of the non-volatile components, the mixed resin comprises 15 - 45% of the styrene-acrylate copolymer A, 45 - 75% of the styrene-acrylate copolymer B, and 10 - 40% of the aqueous polyurethane dispersion; the Tg of the styrene-acrylate copolymer A is 80 - 120 °C; the Tg of the styrene-acrylate copolymer B is < -20 °C. The water-based varnish obtained by the present invention can achieve excellent scratch resistance and abrasion resistance without adding scratch-resistant and abrasion-resistant aids, and has good storage stability.

Description

Technical Field

[0001] The present invention relates to the technical field of water-based inks, and particularly to a water-based gravure varnish and a preparation method thereof. Background Art

[0002] Varnish is a decorative and protective coating applied to printed paper products, films or leather substrates. Coating a varnish layer can not only enhance brightness and protect printed graphics and texts, but also does not affect the recycling of paper, saving resources and protecting the environment. Therefore, varnish is widely used in the surface treatment of packaging printed products.

[0003] Most traditional varnishes are solvent-based varnishes, which do not meet the current environmental protection requirements. Water-based varnishes mainly use water as a solvent and have been widely used due to many advantages such as non-toxic, odorless, safe and environmentally friendly. At present, the main resin of most water-based varnishes is water-based acrylic resin. However, water-based acrylic resin has problems such as hot stickiness and cold brittleness, poor water resistance and poor adhesion to some substrates. Moreover, the film formed by water-based varnish is easily scratched or damaged, and subsequent processes such as hot stamping, die cutting, and bonding will be carried out in the subsequent processing of high-quality packaging printing. Scratches or damages on the surface of the varnish will affect the subsequent processes. Currently, the problem of poor scratch resistance of water-based varnishes greatly troubles the printing industry and seriously affects the application of water-based varnishes in packaging printing.

[0004] The invention patent with application number CN202010343483.0 discloses a water-based film gravure composite ink, which includes water-based resin, pigment, wetting agent, defoaming agent, and dispersion medium components. The water-based resin is water-based polyurethane resin and water-based acrylic resin, and the dispersion medium is water and ethanol. It combines water-based polyurethane and water-based acrylic resin to reduce costs and improve the surface adhesion ability, peel strength and other properties of the ink. However, the proportion of water-based polyurethane in the ink formula of this invention is relatively high, resulting in a relatively high cost of the ink, and this invention does not pay attention to the scratch resistance of the ink.

[0005] The invention patent with application number CN202010653620.0 discloses a water-based varnish, which improves the anti-blocking performance and wear resistance of the varnish by adding fluorinated olefin monomers and triallyl isocyanurate monomers during the preparation of the film-forming resin styrene-acrylate emulsion. However, the fluorinated olefin monomers in this invention are all toxic gases, there are great safety hazards during the preparation process of the film-forming emulsion, and the preparation process is complex. And introducing fluorinated monomers into the film-forming resin will reduce the surface energy of the varnish and deteriorate the wettability to the substrate, restricting the application of the varnish.

[0006] A high scratch-resistant waterborne transparent ink is disclosed in the invention patent with the publication number of CN106519796A. Its film-forming resin package consists of a multi-functional styrene-acrylic copolymer emulsion and a high molecular weight solid acrylic resin. The multi-functional styrene-acrylic copolymer emulsion is a styrene-acrylic copolymer soft emulsion and a styrene-acrylic copolymer hard emulsion. This invention forms a high crosslinking density through the multi-functional styrene-acrylic copolymer emulsion to improve the hardness of the ink and thus enhance the scratch resistance. At the same time, nano-silica is added to assist in improving the scratch resistance. It can be seen that this invention essentially improves the scratch resistance by enhancing the hardness of the varnish coating. However, the hardness of the varnish coating is relatively large, and the scratches are difficult to repair after being scratched. Moreover, adding inorganic nano-silica to the coating will cause the gloss of the varnish to decrease and also make the touch of the coating worse, making it difficult to obtain a coating with a good feel.

[0007] The invention patent with the application number of CN201810271473.3 discloses a waterborne varnish for label paper, which is composed of 50-68 parts of silicone-acrylic emulsion, 5-8 parts of wax additive, 0.5-2 parts of feel agent, 0.05-0.15 parts of wetting agent, 10-17 parts of low molecular alcohol, and 15.9-22.95 parts of deionized water. Among them, the silicone-acrylic emulsion is a self-made silicone-acrylic emulsion with a unique structure of "inner crosslinked core - silicon-containing shell layer" as the film-forming resin of the waterborne varnish. The obtained varnish coating has good anti-adhesion, tape peeling resistance, and oil resistance. However, the versatility of this varnish is poor and the cost is relatively high.

[0008] The invention patent with the application number of CN202111273507.0 discloses a waterborne gravure preprint varnish, which includes components such as a film-forming high-temperature resistant styrene-acrylic emulsion, a soft film-forming high-temperature resistant styrene-acrylic emulsion, a hard non-film-forming high-temperature resistant styrene-acrylic emulsion, and a quick-drying modified maleic anhydride resin liquid A. A large amount of non-film-forming resin components are included in this varnish, and the obtained varnish has a relatively low gloss and poor film-forming compactness.

[0009] On the other hand, in the art, the scratch resistance and anti-scratch effect of the varnish are usually improved by adding anti-scratch additives such as high molecular weight polysiloxane DC-51. However, adding anti-scratch additives to the varnish often causes the surface dyne value of the varnish to decrease, affecting the recoating performance of the varnish film. Moreover, anti-scratch additives are often difficult to disperse, easily causing the formation of shrinkage holes in the varnish film and poor leveling property. Summary of the Invention

[0010] In order to overcome the above-mentioned disadvantages and deficiencies of the prior art, the present invention discloses a scratch-resistant waterborne varnish and its preparation method. The scratch-resistant waterborne varnish obtained by the present invention does not need to add anti-scratch or anti-scratch additives. The obtained varnish film has characteristics such as high gloss, good abrasion resistance, anti-adhesion, and scratch resistance, and good freeze-thaw stability and high-temperature storage stability.

[0011] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0012] A scratch-resistant water-based gravure varnish, characterized in that, by mass percentage, it comprises the following components:

[0013] Mixed resin 10% - 80%, non-ionic surfactant 1 - 3%, defoaming agent 0.01 - 0.2%, ethanol 1 - 5%, deionized water as the balance.

[0014] The sum of the mass percentages of the components of the above varnish is 100%.

[0015] Further, the mass percentage of the mixed resin is 30 - 80%.

[0016] The solid content of the mixed resin is 25 - 50%.

[0017] The mixed resin comprises styrene-acrylate copolymer A, styrene-acrylate copolymer B and aqueous polyurethane dispersion.

[0018] In the mixed resin, by mass percentage of the non-volatile components, styrene-acrylate copolymer A is 15 - 45%, styrene-acrylate copolymer B is 45 - 75%, and aqueous polyurethane dispersion is 10 - 40%.

[0019] The Tg of the styrene-acrylate copolymer A is 80 - 120°C. The Tg of the styrene-acrylate copolymer B < -20°C.

[0020] The Tg of the styrene-acrylate copolymer A and the styrene-acrylate copolymer B can be obtained by testing their dry films with a differential scanning calorimeter DSC.

[0021] Both the styrene-acrylate copolymer A and the styrene-acrylate copolymer B can be obtained by market purchase and self-preparation, and the present invention does not limit their sources.

[0022] For commercially available products, the styrene-acrylate copolymer A can be selected from JONCRYL 61, JONCRYL HPD96, JONCRYL 354, JONCRYL DFC3025. The styrene-acrylate copolymer B can be selected from JONCRYL624, JONCRYL 1695, JONCRYL 8052.

[0023] For self - preparation, the glass transition temperature and the minimum film - forming temperature of the styrene - acrylate copolymer can be adjusted by adjusting the ratio of the polymerizable soft monomer to the hard monomer, which is well - known to those skilled in the art. The styrene - acrylate copolymer is obtained by an emulsion polymerization process, and the solid content of the styrene - acrylate copolymer emulsion is 30 - 50 wt%.

[0024] The non - ionic surfactant is a fatty alcohol polyoxyethylene ether - type non - ionic surfactant.

[0025] The aqueous polyurethane dispersion is from self - preparation, and its raw materials for preparation include polymer diol, diisocyanate, mono - terminal dihydroxy polysiloxane, carboxylate - type hydrophilic chain extender, sulfonate - type hydrophilic chain extender, amine chain extender, surfactant, organic amine neutralizer and deionized water.

[0026] The average particle size of the aqueous polyurethane dispersion is 50 - 120 nm, and the solid content is 30 - 50%.

[0027] The polymer diol has a number - average molecular weight of 1500 - 2000 g / mol (for example, it can be 2000 g / mol or about 2000 g / mol); the type of the polymer diol is one or more of polycarbonate diol, polycaprolactone diol, and aromatic polyester diol.

[0028] The diisocyanate is one or more of isophorone diisocyanate, hexamethylene diisocyanate, and 4,4 - dicyclohexylmethane diisocyanate.

[0029] Further, the diisocyanate is preferably 4,4 - dicyclohexylmethane diisocyanate.

[0030] There is no restriction on the selection of the mono - terminal dihydroxy polysiloxane. Common selections can be Shin - Etsu X - 22 - 176DX and X - 22 - 176GX - A.

[0031] The mass ratio of the mono - terminal dihydroxy polysiloxane in the solid content of the polyurethane dispersion is 2 - 5%.

[0032] The carboxylate - type hydrophilic chain extender is dimethylolpropionic acid, the sulfonate - type hydrophilic chain extender is sodium 2 - aminoethanesulfonate, and the organic amine neutralizer is triethylamine or N,N - dimethylethanolamine.

[0033] The mass ratio of the carboxylate - type hydrophilic chain extender in the solid content of the polyurethane dispersion is 3.5 - 5.5%.

[0034] The mass ratio of the sulfonate - type hydrophilic chain extender in the solid content of the polyurethane dispersion is 0.2 - 0.6%.

[0035] The surfactant is at least one of an anionic surfactant and a non-ionic surfactant. The HLB range of the surfactant is 14 to 24.

[0036] Preferably, the surfactant is a non-ionic surfactant. Common grades of the surfactant are Clariant LCN287, LCN070, and LCN407.

[0037] The mass proportion of the surfactant in the solid content of the polyurethane dispersion is 0.2 to 0.8%.

[0038] Furthermore, the mass proportions of the mono-terminal dihydroxy polysiloxane, carboxylate-type hydrophilic chain extender, sulfonate-type hydrophilic chain extender, and surfactant in the solid content of the polyurethane dispersion are all the mass proportions of the active ingredients or non-volatile components of the above raw materials in the solid content of the polyurethane dispersion.

[0039] The amine chain extender is one or more of 1,4-cyclohexanediamine, diethylenetriamine, and triethylenetetramine.

[0040] Furthermore, the amine chain extender is preferably diethylenetriamine or a combination of diethylenetriamine and 1,4-cyclohexanediamine.

[0041] A preparation method of a scratch-resistant water-based gravure varnish, characterized by comprising the following steps:

[0042] Step 1: Prepare styrene-acrylate copolymer A, styrene-acrylate copolymer B, and a water-based polyurethane dispersion;

[0043] Step 2: Add styrene-acrylate copolymer A, styrene-acrylate copolymer B, and the water-based polyurethane dispersion into a draw tank and disperse (for example, it can be dispersed at a low speed) to obtain a mixed resin;

[0044] Step 3: Under the condition of dispersion, add a non-ionic surfactant to the mixed resin, disperse for 5 - 10 min, add an antifoaming agent and ethanol within 5 - 15 min, and then adjust the solid content to a set value with deionized water;

[0045] Step 4: Stop dispersion, let it stand, and sieve through a filter cloth (for example, it can be sieved through a 400-mesh filter cloth) to obtain the finished product of the water-based gravure varnish.

[0046] The solid content of the finished product of the water-based gravure varnish is 10 - 35%, and the pH is 6 - 9, and both can be adjusted by those of ordinary skill in the art according to application requirements.

[0047] Even further, the preparation of the water-based polyurethane dispersion comprises the following steps:

[0048] Step (1): Prepare each raw material component. Add polymer diol, mono - terminal dihydroxy polydimethylsiloxane, and carboxylate - type hydrophilic chain extender into a reaction kettle, start stirring, heat up to 115 - 125 °C (for example, it can be 120 °C), evacuate to vacuum, dehydrate, and then cool down to 45 - 55 °C (for example, it can be 50 °C).

[0049] Step (2): Add diisocyanate into the reaction kettle, heat up to 75 - 85 °C (for example, it can be 80 °C) and react for 2 - 5 h.

[0050] Step (3): Cool down to 45 - 55 °C (for example, it can be 50 °C), add organic amine neutralizer, and react for 20 - 40 min to obtain a neutralized prepolymer.

[0051] Step (4): Add deionized water containing surfactant and sulfonate - type hydrophilic chain extender into the neutralized prepolymer, disperse (for example, it can be high - speed dispersion) for 5 - 10 min to obtain a dispersion.

[0052] Step (5): Add amine chain extender into the dispersion, continue to disperse for 5 - 10 min to obtain an aqueous polyurethane dispersion.

[0053] The beneficial effects of the present invention are as follows:

[0054] In the present invention, by selecting styrene - acrylate copolymer A with high Tg, styrene - acrylate copolymer B with low Tg, and an aqueous polyurethane dispersion with wear resistance, both hardness and adhesion, and containing branched polysiloxane as the film - forming resin component of the aqueous gravure varnish, without adding anti - scratch or anti - scuffing additives, the obtained aqueous gravure varnish has good storage stability, and the coating has high gloss, good hand feeling, and excellent properties such as resistance to friction, anti - adhesion, and scratch resistance. Specific embodiments

[0055] The present invention will be further described below in conjunction with specific embodiments:

[0056] It should be understood that the specific embodiments described herein are part of the embodiments of the present invention, rather than all of the embodiments. They are only used to explain the embodiments of the present invention and are not used to limit the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the protection scope of the present invention.

[0057] The selection of raw materials in the following examples and comparative examples is as follows:

[0058] (1) Styrene - acrylate copolymer

[0059] Styrene-acrylate copolymer A: JONCRYL 61 has a solids content of approximately 36% and a Tg of approximately 85°C; JONCRYL HPD96 has a solids content of approximately 34% and a Tg of approximately 88°C; JONCRYL 354 has a solids content of approximately 32% and a Tg of approximately 101°C.

[0060] JONCRYL LMV7085 has a solids content of approximately 35% and a Tg of approximately 77°C (for comparison). All of the above raw materials are obtained from BASF.

[0061] The styrene-acrylate copolymer B: JONCRYL 624 has a solids content of approximately 48% and a Tg of approximately -30°C; JONCRYL 1695 has a solids content of approximately 40% and a Tg of approximately -50°C; JONCRYL 8052 has a solids content of approximately 47% and a Tg of approximately -35°C.

[0062] JONCRYL 2640 has a solids content of approximately 49% and a Tg of approximately -18°C (for comparison). All of the above raw materials are obtained from BASF.

[0063] The non-ionic surfactant: Clariant LCN287 and ethanol are both commercially available.

[0064] (2) Aqueous polyurethane dispersion

[0065] PCD-2000, manufactured by Ube Industries, Japan; 4,4'-dicyclohexylmethane diisocyanate (HMDI), manufactured by Evonik; mono-terminal dihydroxy polysiloxane, Shin-Etsu X-22-176DX; dimethylolpropionic acid (DMPA), manufactured by Perstorp; surfactant Clariant LCN287; triethylamine, sodium 2-(2-aminoethylamino)ethanesulfonate, 1,4-cyclohexanediamine, and diethylenetriamine are all commercially available.

[0066] Synthesis Example 1

[0067] Aqueous polyurethane dispersion A, and its preparation method is as follows:

[0068] Step (1): By mass, add 100 parts of PCD-2000, 5 parts of mono-terminal dihydroxy polysiloxane X-22-176DX, and 7 parts of DMPA to the reaction kettle, start stirring at 120 rpm, heat up to 120°C, evacuate to remove water, and cool down to 50°C;

[0069] Step (2): Add 48.3 parts of diisocyanate HMDI to the reaction kettle, and heat up to 80°C for reaction for 4 hours;

[0070] Step (3): Cool down to 50°C, add 5.2 parts of neutralizer triethylamine, and react for 20 minutes to obtain the neutralized prepolymer;

[0071] Step (4): Add 1 part of surfactant LCN287, 1.2 parts of sodium 2-(2-aminoethylamino)ethanesulfonate, and 250 parts of deionized water to the neutralized prepolymer, and disperse at a high speed of 1200 rpm for 5 min to obtain a dispersion.

[0072] Step (5): Add 2 parts of diethylenetriamine and 5.2 parts of 1,4-cyclohexanediamine to the dispersion, continue to disperse at 300 rpm for 5 min, add an appropriate amount of deionized water, and adjust the solid content to 32% to obtain an aqueous polyurethane dispersion.

[0073] Among them, surfactant LCN287 accounts for about 0.4% of the solid content weight of the aqueous polyurethane dispersion, sodium 2-(2-aminoethylamino)ethanesulfonate as a sulfonic acid-type hydrophilic chain extender accounts for about 0.34% of the solid content weight, dimethylolpropionic acid (DMPA) as a carboxylic acid-type hydrophilic chain extender accounts for about 4.0% of the solid content weight, and mono-terminal dihydroxy polydimethylsiloxane accounts for about 2.9% of the solid content weight.

[0074] Synthesis Example 2

[0075] Aqueous polyurethane dispersion B, based on Preparation Example 1, without adding surfactant LCN287 during the synthesis and dispersion process.

[0076] Synthesis Example 3

[0077] Aqueous polyurethane dispersion C, based on Preparation Example 1, without adding sodium 2-(2-aminoethylamino)ethanesulfonate as a sulfonic acid-type hydrophilic chain extender during the synthesis and dispersion process, and replacing the effective component of sodium 2-(2-aminoethylamino)ethanesulfonate with an equimolar amount of DMPA.

[0078] Synthesis Example 4

[0079] Aqueous polyurethane dispersion D, based on Preparation Example 1, during the synthesis process, replacing part of 1,4-cyclohexanediamine with sodium 2-(2-aminoethylamino)ethanesulfonate, and increasing the content of sodium 2-(2-aminoethylamino)ethanesulfonate in the solid content weight to about 0.8%.

[0080] Synthesis Example 5

[0081] Aqueous polyurethane dispersion E, based on Preparation Example 1, during the synthesis process, increasing the content of mono-terminal dihydroxy polydimethylsiloxane in the solid content weight to about 6%. Among them, surfactant LCN287 accounts for about 0.39% of the solid content weight, sodium 2-(2-aminoethylamino)ethanesulfonate as a sulfonic acid-type hydrophilic chain extender accounts for about 0.3% of the solid content weight, and dimethylolpropionic acid (DMPA) as a carboxylic acid-type hydrophilic chain extender accounts for about 3.9% of the solid content weight.

[0082] Synthesis Example 6

[0083] Waterborne polyurethane dispersion F. Based on Preparation Example 1, during the synthesis process, the content of the mono-terminal dihydroxy polysiloxane in the solid content was reduced to about 1%. Among them, the surfactant LCN287 accounted for about 0.4% of the solid content, the sulfonic acid type hydrophilic chain extender sodium 2-aminoethanesulfonate accounted for about 0.35% of the solid content, and the carboxylic acid type hydrophilic chain extender DMPA accounted for about 4.1% of the solid content.

[0084] Synthesis Example 7

[0085] Waterborne polyurethane dispersion G. Based on Preparation Example 1, during the synthesis process, the mono-terminal dihydroxy polysiloxane X-22-176DX was replaced with an equal mass of the linear terminal hydroxy siloxane Dow Corning PMX-0156.

[0086] Synthesis Example 8

[0087] Waterborne polyurethane dispersion G. Based on Preparation Example 1, during the synthesis process, the PCD2000 was replaced with an equal mass of polytetrahydrofuran ether glycol PTMEG2000 as the polymer diol.

[0088] Preparation of waterborne gravure ink

[0089] The preparation method is as follows:

[0090] Step 1: According to the raw materials and dosages of the mixed resin in Table 1, add the styrene-acrylate copolymer A, styrene-acrylate copolymer B, and waterborne polyurethane dispersion into the draw tank, and disperse at a low speed of 120 rpm to obtain the mixed resin; add deionized water to adjust the solid content of the mixed resin to 30%.

[0091] Step 3: Under the condition of low-speed dispersion at 120 rpm, add 1 part of the non-ionic surfactant LCN287 to 70 parts of the mixed resin with a solid content of 30%, disperse at a low speed for 10 min, add 0.2 part of the defoamer tego904W and 5 parts of ethanol within 5 min, and then adjust the solid content to 25% with an appropriate amount of deionized water;

[0092] Step 4: Stop dispersion, let it stand, and filter through a 400-mesh filter cloth to obtain the finished product of waterborne gravure varnish.

[0093] Table 1 records the composition and ratio of the mixed resin in the varnish of different examples. The dosages of the styrene-acrylate copolymer and the waterborne polyurethane dispersion are calculated based on the content of the non-volatile components.

[0094] Table 1: Composition and ratio of the mixed resin

[0095]

[0096]

[0097] Performance Test

[0098] High-temperature storage stability: Place the finished varnish in an oven at 60°C, record the stability status of the varnish every other day, and the test duration is one month.

[0099] Freeze-thaw stability: Place the finished varnish in a freezer at -20°C, record the stability status of the varnish every other day, and the test duration is one month.

[0100] Gloss: Coat the varnish on the test cardboard, dry at 50°C, the dry film thickness is about 2.5μm, and use a gloss meter to measure the 60° gloss value of the dry film of the varnish.

[0101] Scratch resistance: Test according to GB / T9279.1-2015, and the weight of the weight is 500g.

[0102] Abrasion resistance: With a load of 9.8N, wipe back and forth 10 times on the surface of the colored varnish coating with dry and wet gauze, observe the coloring situation on the surface of the gauze for scoring, 5 points is the best, and 1 point is the worst.

[0103] Anti-blocking performance: Place the varnish coatings coated on the test cardboard "face to face", and place them under the conditions of 5Kg pressure and 80°C temperature for 24h.

[0104] Film appearance: Visually inspect and evaluate the leveling and pinhole conditions on the surface of the film, 5 points is the best, and 1 point is the worst.

[0105] The test results are shown in Table 2.

[0106] Table 2: Performance Test Results

[0107]

[0108]

[0109] As can be seen from the results in Table 2 above, when a styrene-acrylate copolymer and an aqueous polyurethane dispersion with a specific dosage range and a specific Tg range are used in combination as the mixed film-forming resin of the aqueous varnish, the obtained aqueous varnish has good application properties such as gloss, storage stability, scratch resistance, abrasion resistance, and anti-blocking performance.

[0110] The film-forming resin of Comparative Example 1 is a high-Tg non-film-forming resin, and no coating can be obtained. The coating obtained from the film-forming resin of Comparative Example 2 is too soft and has poor application properties. In Comparative Example 3, all polyurethane dispersions are used as the film-forming resin, but the freeze-thaw stability of the varnish is poor, and the abrasion resistance and anti-blocking performance are also poor. Comparative Example 4 does not contain polyurethane dispersion, and the scratch resistance, abrasion resistance, and anti-blocking performance are poor. In Comparative Example 5, the Tg of the styrene-acrylate copolymer is not within the range, and the freeze-thaw stability, scratch resistance, abrasion resistance, and anti-blocking performance of the obtained varnish also do not meet the requirements.

[0111] On the basis of Example 1, the aqueous polyurethane dispersions B to H obtained in Synthesis Examples 2-8 were used to replace the aqueous polyurethane dispersion A obtained in Synthesis Example 1 in the varnish mixed resin, and the corresponding aqueous varnishes were marked as Comparative Examples 6-12. The corresponding application test results are shown in Table 3.

[0112] Table 3: Performance test results

[0113]

[0114]

[0115] From the above test results, it can be seen that the selection of the synthesis raw materials and their dosages of the aqueous polyurethane dispersion also have a significant impact on the application performance of the aqueous varnish.

[0116] In Comparative Example 6, no surfactant was added during the synthesis and dispersion of the aqueous polyurethane dispersion B used. In Comparative Example 7, no sodium N-(2-aminoethyl)-2-aminoethanesulfonate was added during the synthesis and dispersion of the aqueous polyurethane dispersion C used. The particles of the obtained polyurethane dispersion were not stable enough, resulting in poor high-temperature and low-temperature storage stability of the varnish, and the viscosity of the varnish increased during storage.

[0117] In Comparative Example 8, too much sodium N-(2-aminoethyl)-2-aminoethanesulfonate was added during the synthesis and dispersion of the aqueous polyurethane dispersion D used. During the dispersion of the obtained aqueous polyurethane dispersion, the reaction between the isocyanate group and the amino group was too violent, resulting in the generation of more microgel particles, and the storage stability and leveling performance of the varnish became poor.

[0118] In Comparative Example 9, the content of the mono-terminal dihydroxy polysiloxane added during the synthesis and dispersion of the aqueous polyurethane dispersion E used was excessive, resulting in the formation of a large number of bubbles during the dispersion process. The obtained dispersion had many particles and was difficult to filter, and the leveling property of the corresponding varnish was poor during coating.

[0119] In Comparative Example 10, the content of the mono-terminal dihydroxy polysiloxane added during the synthesis and dispersion of the aqueous polyurethane dispersion F used was too low, and its function was limited, resulting in poor scratch resistance, abrasion resistance, and anti-blocking properties of the varnish coating.

[0120] In Comparative Example 11, the siloxane added during the synthesis and dispersion of the aqueous polyurethane dispersion G used was a linear siloxane, and the siloxane chain segments were embedded in the carbon chain, unable to effectively achieve the anti-scratch and anti-blocking effects, and unable to improve the wear resistance and anti-blocking effects of the varnish coating.

[0121] In Comparative Example 12, the aqueous polyurethane dispersion H used common PTMEG as the polymer diol, and the corresponding varnish of the obtained dispersion had poor anti-blocking and scratch resistance properties and did not meet the application requirements.

[0122] It can be seen that by selecting specific styrene-acrylate copolymer A, styrene-acrylate copolymer B and aqueous polyurethane dispersion as the film-forming resins of the aqueous gravure varnish, the varnish can obtain excellent application properties such as scratch resistance and abrasion resistance without adding wear-resistant additives. Moreover, the varnish has high gloss and good storage stability.

[0123] The above are only the preferred embodiments of the present invention, and do not impose any form of limitation on the present invention. Any brief modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A scratch-resistant water-based gravure varnish, characterized in that: In terms of mass percentage, it includes the following components: Mixed resin 10%~80%, non-ionic surfactant 1~3%, defoamer 0.01~0.2%, ethanol 1~5%, deionized water balance; The mixed resin includes styrene-acrylate copolymer A, styrene-acrylate copolymer B and waterborne polyurethane dispersion; The mixed resin comprises, by mass percentage of non-volatile components, 15-45% of styrene-acrylate copolymer A, 45-75% of styrene-acrylate copolymer B, and 10-40% of aqueous polyurethane dispersion. The Tg of the styrene-acrylate copolymer A is 80-120°C; the Tg of the styrene-acrylate copolymer B is less than -20°C; The raw materials for preparing the aqueous polyurethane dispersion include polymer diol, diisocyanate, single-terminal dihydroxy polysiloxane, carboxylate type hydrophilic chain extender, sulfonate type hydrophilic chain extender, amine chain extender, surfactant, organic amine neutralizer and deionized water; The type of the polymer diol is one or more of polycarbonate diol, polycaprolactone diol, and aromatic polyester diol; the polymer diol has a number average molecular weight of 1500-2000 g / mol; The mass proportion of the single-terminal dihydroxy polysiloxane in the waterborne polyurethane dispersion solids is 2-5%, the mass proportion of the carboxylate type hydrophilic chain extender in the polyurethane dispersion solids is 3.5-5.5%, the mass proportion of the sulfonate type hydrophilic chain extender in the polyurethane dispersion solids is 0.2-0.6%, and the mass proportion of the surfactant in the polyurethane dispersion solids is 0.2-0.8%; The mass proportions of the single-terminal dihydroxy polysiloxane, carboxylate type hydrophilic chain extender, sulfonate type hydrophilic chain extender and surfactant in the solid content of the polyurethane dispersion are all the mass proportions of the effective ingredients or non-volatile components in the solid content of the polyurethane dispersion.

2. The scratch-resistant water-based gravure varnish according to claim 1, characterized in that: The diisocyanate is one or more of isophorone diisocyanate, hexamethylene diisocyanate, and 4,4-dicyclohexylmethane diisocyanate.

3. The scratch-resistant water-based gravure varnish according to claim 1, characterized in that: The nonionic surfactant is fatty alcohol polyoxyethylene ether.

4. The scratch-resistant water-based gravure varnish according to claim 1, characterized in that: The carboxylate type hydrophilic chain extender is dimethylol propionic acid, the sulfonate type hydrophilic chain extender is sodium ethylenediamine ethanesulfonate, and the organic amine neutralizer is triethylamine or N,N-dimethylethanolamine.

5. The scratch-resistant water-based gravure varnish according to claim 1, characterized in that: The amine chain extender is one or more of 1,4-cyclohexanediamine, diethyltriamine and triethyltetramine.

6. The method for preparing a scratch-resistant water-based gravure varnish according to claim 1, characterized in that: The steps include: Step 1: preparing an aqueous polyurethane dispersion; Step 2: adding styrene-acrylate copolymer A, styrene-acrylate copolymer B, and aqueous polyurethane dispersion into a pull cylinder, dispersing, and obtaining a mixed resin; Step 3: Under dispersed conditions, add nonionic surfactant to the mixed resin, disperse for 5-10 minutes, add defoamer and ethanol within 5-15 minutes, and then adjust the solid content to the set value with deionized water; Step 4: Stop dispersing, let stand, and sieve through filter cloth to obtain the finished water-based gravure varnish.

7. The method for preparing a scratch-resistant water-based gravure varnish according to claim 6, characterized in that: The preparation of the aqueous polyurethane dispersion comprises the following steps: Step (1): adding polymer polyol, single-end dihydroxy polysiloxane, and carboxylate type hydrophilic chain extender into a reaction kettle, stirring, heating to 115-125° C., evacuating, dehydrating, and cooling to 45-55° C.; Step (2): Add diisocyanate to the reaction kettle, raise the temperature to 75-85°C and react for 2-5 hours; Step (3): Cooling to 45-55°C, adding an organic amine neutralizer, and reacting for 20-40 minutes to obtain a neutralized prepolymer; Step (4): adding deionized water containing a sulfonate-type hydrophilic chain extender and a surfactant to the neutralized prepolymer and dispersing for 5-10 minutes to obtain a dispersion; Step (5): Add the amine chain extender to the dispersion and continue dispersing for 5-10 minutes to obtain an aqueous polyurethane dispersion.

8. The use of a scratch-resistant water-based gravure varnish according to any one of claims 1 to 5, characterized in that: Used for surface coating of paper, film and leather.

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