Acrylic resin varnish for paperboard and its preparation method and paperboard

Abstract

The present application relates to the technical field of paint, and discloses an acrylic resin varnish for card paper, a preparation method thereof and card paper.The raw materials of the acrylic resin varnish include 100 parts by weight of alkenyl monomer, 2.6-3.3 parts by weight of emulsifier, 0.5-0.7 parts by weight of initiator, 3-10 parts by weight of amino-modified lignin, etc.The alkenyl monomer includes acetoacetoxy ethyl methacrylate.Lignin is grafted into the acrylic resin matrix, so that the paint film has higher pencil hardness, and the mass loss before and after friction is lower, and the mechanical properties and wear resistance are better.After esterification of lignin, the hydrophilic phenolic hydroxyl group is reduced, the hydrophobic ester group is generated, and the hydrophobic alkyl long chain is introduced, which is bonded to the acrylic resin, so that the water contact angle and waterproof performance of the paint film are improved, and the practical application in card paper and the like is better.

Description

Technical Field

[0001] This invention relates to the field of coating technology, specifically to an acrylic resin varnish for cardboard, its preparation method, and the cardboard itself. Background Technology

[0002] Acrylic resins possess excellent color and gloss retention, chemical resistance, and weather resistance, making them widely used in gold and silver cardboard, electronics, leather fabrics, and other applications. However, ordinary water-based acrylic resins suffer from poor hydrophilicity and waterproofing, and their abrasion resistance is also poor, hindering their practical application in cardboard and other similar applications.

[0003] Lignin is a byproduct of the pulping and papermaking process. It is a natural, green, and environmentally friendly renewable resource with important applications in dispersants, emulsifiers, and superabsorbent resins. Patent CN116444802B discloses a lignin-acrylate aqueous dispersion and its preparation method and applications. Using monomers containing vinyl and epoxy groups, alkenyl monomers, initiators, and lignin as raw materials, the prepared lignin-acrylate aqueous dispersion exhibits good film-forming properties. However, this patent does not address the issue of poor waterproofing properties of acrylic resins. Summary of the Invention

[0004] This invention solves the problem of poor wear resistance and waterproof performance of acrylic resin varnish coatings.

[0005] The technical solution of the present invention is: an acrylic resin varnish and its preparation method, wherein the raw materials of the acrylic resin varnish include 100 parts by weight of alkenyl monomer, 2.6-3.3 parts by weight of emulsifier, 0.5-0.7 parts by weight of initiator, 0.2-0.6 parts by weight of defoamer, 0.15-0.5 parts by weight of wetting agent, 6-10 parts by weight of film-forming aid, and 3-10 parts by weight of amino-modified lignin.

[0006] Alkenyl monomers include ethyl acetoacetate methacrylate, acrylic acid, butyl acrylate, methyl methacrylate, and isooctyl methacrylate.

[0007] The preparation methods of acrylic resin varnish include:

[0008] (1) Add lignin to N,N-dimethylformamide, stir, add boc-amino acid, dicyclohexylcarbodiimide and 4-dimethylaminopyridine, stir the reaction, pour the solution into ethanol, stir and filter, wash the product with ethanol, dry and obtain lignin precursor.

[0009] (2) The lignin precursor was added to a trifluoroacetic acid-dichloromethane solution, and after stirring, the solution was distilled under reduced pressure. The product was washed with saturated sodium bicarbonate solution and dried to obtain amino-modified lignin. The preparation reaction formula is as follows:

[0010] .

[0011] (3) Add alkenyl monomer and emulsifier to water and stir to obtain monomer solution; add 25-30% volume of monomer solution dropwise into reaction vessel, add initiator aqueous solution dropwise in nitrogen atmosphere to carry out prepolymerization reaction, then add the remaining monomer solution and add initiator aqueous solution dropwise to carry out polymerization reaction, add neutralizer after cooling, add film-forming aid, defoamer and wetting agent, stir and add amino modified lignin, shear dispersion to obtain acrylic resin varnish.

[0012] Preferably, the emulsifier includes OP-10 and sodium dodecyl sulfate.

[0013] Preferably, the initiator includes ammonium persulfate.

[0014] Preferably, the film-forming aid includes waterborne polyurethane.

[0015] Preferably, in (1), the mass ratio of lignin, boc-amino acid, dicyclohexylcarbodiimide, and 4-dimethylaminopyridine is 100:(10-35):(8-24):(0.6-2).

[0016] Preferably, boc-amino acids include BOC-8-aminooctanoic acid, BOC-10-aminodecanoic acid, and 12-(Boc-amino)dodecanoic acid.

[0017] Preferably, the reaction temperature in (1) is 20-35℃ and the reaction time is 12-18h.

[0018] Preferably, in (2), the reaction temperature is 20-30℃ and the reaction time is 4-6h.

[0019] Preferably, the temperature of the prepolymerization reaction in (3) is 70-85℃ and the reaction time is 30-50min.

[0020] Preferably, the polymerization temperature in (3) is 70-85℃ and the reaction time is 3-5h.

[0021] Preferably, a neutralizing agent is added to (3) to adjust the pH of the solution to 7-8.

[0022] Preferably, in (3), the neutralizing agent includes ammonia or triethylamine.

[0023] Preferably, acrylic resin varnish can be applied to cardboard. By spraying acrylic resin varnish onto the surface of cardboard, waterproof and wear-resistant cardboard is obtained.

[0024] The beneficial technical effects of this invention are as follows: This invention involves esterifying the hydroxyl groups of lignin with the carboxyl groups of boc-amino acids and removing the boc protecting groups to obtain amino-modified lignin. This modified lignin is then added to acrylic resin varnish. During the curing process, the amino groups of lignin react with the ketone carbonyl groups in the acrylic resin molecular chain, thereby grafting lignin into the acrylic resin matrix and improving the interfacial bonding force between the two. The lignin contains a large number of rigid benzene rings, which gives the paint film higher pencil hardness and reduces the mass loss before and after friction, resulting in better mechanical properties and wear resistance.

[0025] After the lignin of the present invention undergoes an esterification reaction, the hydrophilic phenolic hydroxyl groups are reduced, generating hydrophobic ester groups. At the same time, hydrophobic alkyl long chains are introduced and bonded to the acrylic resin, which improves the water contact angle and waterproof performance of the coating film, and has better practical applications in areas such as cardboard. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments.

[0027] Example 1

[0028] (1) Add 50g of lignin to 0.8L N,N-dimethylformamide, stir, add 5g BOC-8-aminooctanoic acid, 4g dicyclohexylcarbodiimide and 0.3g 4-dimethylaminopyridine, stir and react at 25℃ for 12h, pour the solution into ethanol, stir and filter, wash the product with ethanol, dry and obtain lignin precursor.

[0029] (2) Add 80g of lignin precursor to 1L of 30% trifluoroacetic acid-dichloromethane solution, stir and react at 25℃ for 4h, distill the solution under reduced pressure, wash the product with saturated sodium bicarbonate solution, and dry to obtain amino-modified lignin.

[0030] (3) Add 30g of ethyl acetoacetate, 45g of acrylic acid, 370g of butyl acrylate, 302g of methyl methacrylate, 253g of isooctyl methacrylate, 1g of OP-10, and 2.1g of sodium dodecyl sulfate to 1.6L of water and stir to obtain a monomer solution; add 25% of the monomer solution dropwise into the reaction vessel, add 20mL of ammonium persulfate (1.2g) aqueous solution dropwise under a nitrogen atmosphere, heat to 75℃, stir and react for 50min, then add the remaining monomer solution and add 100mL of ammonium persulfate (4.8g) aqueous solution dropwise, react for 5h, cool, add 20% ammonia water as a neutralizing agent to adjust the pH of the solution to 7.5, add 70g of waterborne polyurethane (model Tangyi 6516, the same below) and 3g of defoamer (TEGO). 825 (hereinafter the same), 4g wetting agent (TEGOWet270, hereinafter the same), after stirring, add 30g amino-modified lignin, shear and disperse to obtain acrylic resin varnish.

[0031] Example 2

[0032] (1) Add 50g of lignin to 0.8L N,N-dimethylformamide, stir, add 9g of 12-(Boc-amino)dodecanoic acid, 5.2g of dicyclohexylcarbodiimide and 0.5g of 4-dimethylaminopyridine, stir and react at 20℃ for 18h, pour the solution into ethanol, stir and filter, wash the product with ethanol, dry and obtain lignin precursor.

[0033] (2) Add 80g of lignin precursor to 1L of 30% trifluoroacetic acid-dichloromethane solution, stir and react at 20℃ for 6h, distill the solution under reduced pressure, wash the product with saturated sodium bicarbonate solution, and dry to obtain amino-modified lignin.

[0034] (3) Add 40g of ethyl acetoacetate, 57g of acrylic acid, 336g of butyl acrylate, 350g of methyl methacrylate, 217g of isooctyl methacrylate, 1g of OP-10, and 2g of sodium dodecyl sulfate to 1.6L of water and stir to obtain a monomer solution; add 30% of the monomer solution dropwise into the reaction vessel, add 20mL of ammonium persulfate (1g) aqueous solution dropwise under a nitrogen atmosphere, heat to 70℃, stir and react for 50min, then add the remaining monomer solution and add 100mL of ammonium persulfate (4g) aqueous solution dropwise, react for 5h, cool and add triethylamine to adjust the pH of the solution to 7, add 60g of waterborne polyurethane, 2g of defoamer, and 5g of wetting agent, stir and add 50g of amino-modified lignin, shear and disperse to obtain acrylic resin varnish.

[0035] Example 3

[0036] (1) Add 50g of lignin to 1L of N,N-dimethylformamide, stir, add 14g of 12-(Boc-amino)dodecanoic acid, 6.5g of dicyclohexylcarbodiimide and 0.7g of 4-dimethylaminopyridine, stir and react at 35℃ for 12h, pour the solution into ethanol, stir and filter, wash the product with ethanol, dry and obtain lignin precursor.

[0037] (2) Add 80g of lignin precursor to 1L of 40% trifluoroacetic acid-dichloromethane solution, stir and react at 25℃ for 6h, distill the solution under reduced pressure, wash the product with saturated sodium bicarbonate solution, and dry to obtain amino-modified lignin.

[0038] (3) Add 55g of ethyl acetoacetate, 38g of acrylic acid, 394g of butyl acrylate, 276g of methyl methacrylate, 246g of isooctyl methacrylate, 0.8g of OP-10, and 1.8g of sodium dodecyl sulfate to 1.8L of water and stir to obtain a monomer solution; add 30% of the monomer solution dropwise into the reaction vessel, add 20mL of ammonium persulfate (1.6g) aqueous solution dropwise under a nitrogen atmosphere, heat to 85℃, stir and react for 30min, then add the remaining monomer solution and add 100mL of ammonium persulfate (5.4g) aqueous solution dropwise, react for 3h, cool and add 20% ammonia water to adjust the pH of the solution to 7, add 100g of waterborne polyurethane, 6g of defoamer, and 1.5g of wetting agent, stir and add 75g of amino-modified lignin, shear and disperse to obtain acrylic resin varnish.

[0039] Example 4

[0040] (1) Add 50g of lignin to 1L of N,N-dimethylformamide, stir, and then add 17.5g of 12-(Boc-amino)dodecanoic acid, 8g of dicyclohexylcarbodiimide and 1g of 4-dimethylaminopyridine. Stir the reaction at 25℃ for 18h, pour the solution into ethanol, stir and filter, wash the product with ethanol, and dry to obtain the lignin precursor.

[0041] (2) Add 80g of lignin precursor to 1L of 40% trifluoroacetic acid-dichloromethane solution, stir and react at 30℃ for 5h, distill the solution under reduced pressure, wash the product with saturated sodium bicarbonate solution, and dry to obtain amino-modified lignin.

[0042] (3) Add 65g of ethyl acetoacetate, 47g of acrylic acid, 342g of butyl acrylate, 336g of methyl methacrylate, 210g of isooctyl methacrylate, 1.2g of OP-10, and 2.1g of sodium dodecyl sulfate to 2L of water and stir to obtain a monomer solution; add 25% of the monomer solution dropwise into the reaction vessel, add 20mL of ammonium persulfate (1.3g) aqueous solution dropwise in a nitrogen atmosphere, heat to 80℃, stir and react for 50min, then add the remaining monomer solution and add 100mL of ammonium persulfate (5g) aqueous solution dropwise, react for 4h, cool and add 20% ammonia water to adjust the pH of the solution to 8, add 70g of waterborne polyurethane, 5g of defoamer, and 2g of wetting agent, stir and add 100g of amino-modified lignin, shear and disperse to obtain acrylic resin varnish.

[0043] Comparative Example 1

[0044] (1) Add 30g of ethyl acetoacetate, 45g of acrylic acid, 370g of butyl acrylate, 302g of methyl methacrylate, 253g of isooctyl methacrylate, 1g of OP-10, and 2.1g of sodium dodecyl sulfate to 1.6L of water and stir to obtain a monomer solution; add 25% of the monomer solution dropwise into the reaction vessel, add 20mL of ammonium persulfate (1.2g) aqueous solution dropwise in a nitrogen atmosphere, heat to 75℃, stir and react for 50min, then add the remaining monomer solution and add 100mL of ammonium persulfate (4.8g) aqueous solution dropwise, react for 5h, cool and add 20% ammonia water as a neutralizing agent to adjust the pH of the solution to 7.5, add 70g of waterborne polyurethane, 3g of defoamer, and 4g of wetting agent, shear and disperse to obtain acrylic resin varnish.

[0045] Comparative Example 2

[0046] (1) Add 30g of ethyl acetoacetate, 45g of acrylic acid, 370g of butyl acrylate, 302g of methyl methacrylate, 253g of isooctyl methacrylate, 1g of OP-10, and 2.1g of sodium dodecyl sulfate to 1.6L of water and stir to obtain a monomer solution; add 25% of the monomer solution dropwise into the reaction vessel, add 20mL of ammonium persulfate (1.2g) aqueous solution dropwise in a nitrogen atmosphere, heat to 75℃, stir and react for 50min, then add the remaining monomer solution and add 100mL of ammonium persulfate (4.8g) aqueous solution dropwise, react for 5h, cool and add 20% ammonia water as a neutralizing agent to adjust the pH of the solution to 7.5, add 70g of waterborne polyurethane, 3g of defoamer, and 4g of wetting agent, stir and add 30g of lignin, shear and disperse to obtain acrylic resin varnish.

[0047] Comparative Example 3

[0048] (1) Add 50g of lignin to 0.8L N,N-dimethylformamide, stir, and then add 5g of BOC-β-alanine (CAS No. 3303-84-2), 4g of dicyclohexylcarbodiimide, and 0.3g of 4-dimethylaminopyridine. Stir the reaction at 25℃ for 12h, pour the solution into ethanol, stir, filter, wash the product with ethanol, and dry to obtain the lignin precursor.

[0049] (2) Add 80g of lignin precursor to 1L of 30% trifluoroacetic acid-dichloromethane solution, stir and react at 25℃ for 4h, distill the solution under reduced pressure, wash the product with saturated sodium bicarbonate solution, and dry to obtain amino-modified lignin.

[0050] (3) Add 30g of ethyl acetoacetate, 45g of acrylic acid, 370g of butyl acrylate, 302g of methyl methacrylate, 253g of isooctyl methacrylate, 1g of OP-10, and 2.1g of sodium dodecyl sulfate to 1.6L of water and stir to obtain a monomer solution; add 25% of the monomer solution dropwise into the reaction vessel, add 20mL of ammonium persulfate (1.2g) aqueous solution dropwise under a nitrogen atmosphere, heat to 75℃, stir and react for 50min, then add the remaining monomer solution and add 100mL of ammonium persulfate (4.8g) aqueous solution dropwise, react for 5h, cool and add 20% ammonia water as a neutralizing agent to adjust the pH of the solution to 7.5, add 70g of waterborne polyurethane, 3g of defoamer, and 4g of wetting agent, stir and add 30g of amino-modified lignin, shear and disperse to obtain acrylic resin varnish.

[0051] Comparative Example 4

[0052] (1) Add 50g of lignin to 0.8L of water, stir, add sodium hydroxide, adjust the pH to 9, add 5g of diethylenetriamine and 7mL of 36% formaldehyde aqueous solution, heat to 80℃, stir, reflux and condense for 4h, add hydrochloric acid solution to adjust the pH to 6, precipitate, filter, wash with water, dry, and obtain amino-modified lignin.

[0053] (2) Add 30g of ethyl acetoacetate, 45g of acrylic acid, 370g of butyl acrylate, 302g of methyl methacrylate, 253g of isooctyl methacrylate, 1g of OP-10, and 2.1g of sodium dodecyl sulfate to 1.6L of water and stir to obtain a monomer solution; add 25% of the monomer solution dropwise into the reaction vessel, add 20mL of ammonium persulfate (1.2g) aqueous solution dropwise under a nitrogen atmosphere, heat to 75℃, stir and react for 50min, then add the remaining monomer solution and add 100mL of ammonium persulfate (4.8g) aqueous solution dropwise, react for 5h, cool and add 20% ammonia water as a neutralizing agent to adjust the pH of the solution to 7.5, add 70g of waterborne polyurethane, 3g of defoamer, and 4g of wetting agent, stir and add 30g of amino-modified lignin, shear and disperse to obtain acrylic resin varnish.

[0054] Acrylic resin varnish was sprayed onto the substrate surface, left at room temperature for 24 hours, and then dried at 70℃ for 6 hours to form a paint film. The hardness of the paint film was tested according to standard GB / T 6739-2022. The mass loss and abrasion resistance before and after friction were tested according to standard GB / T 1768-2006. The water contact angle was tested according to standard GB / T 30693-2014.

[0055] Table 1 Performance Tests

[0056] Pencil hardness Mass loss (mg) Water contact angle (°) Example 1 3H 38.3 97.4 Example 2 3H 31.8 101.7 Example 3 4H 25.4 107.5 Example 4 4H 27.1 114.9 Comparative Example 1 2H 45.2 89.6 Comparative Example 2 2H 43.8 86.0 Comparative Example 3 3H 37.9 93.4 Comparative Example 4 3H 39.5 85.7

[0057] The acrylic resin varnish coating of Comparative Example 1 has a low pencil hardness, a large mass loss before and after friction, poor mechanical properties and abrasion resistance, and a low water contact angle, resulting in poor waterproof performance.

[0058] Examples 1-4 incorporated amino-modified lignin, which contains chemical amino groups that can react with the ketone carbonyl groups in the acrylic resin molecular chain. This grafts lignin into the acrylic resin matrix, improving the interfacial bonding between the two. The lignin contains numerous rigid benzene rings, which enhances the mechanical properties of the coating film, resulting in higher pencil hardness, significantly improved abrasion resistance, and reduced mass loss. Simultaneously, after esterification, the hydrophilic phenolic hydroxyl groups of the lignin decrease, generating hydrophobic ester groups. Furthermore, hydrophobic alkyl long chains are introduced and bonded to the acrylic resin, improving the water contact angle and waterproofing performance of the coating film.

[0059] Compared with Comparative Example 1, the lignin added in Comparative Example 2 does not contain amino groups and cannot react with the ketone carbonyl groups in the acrylic resin molecular chain. The lignin has poor compatibility and poor dispersibility in the acrylic resin matrix, which is not conducive to improving the hardness and wear resistance of the paint film. In addition, the lignin contains a large number of hydrophilic hydroxyl groups, resulting in a low water contact angle of the paint film and poor waterproof performance.

[0060] Comparative Example 3: BOC-β-alanine and the prepared amino-modified lignin do not contain hydrophobic alkyl long chains, resulting in a low water contact angle of the coating film and poor waterproof performance.

[0061] Comparative Example 4 uses diethylenetriamine, formaldehyde and the ortho carbon atom of the phenolic hydroxyl group of lignin to carry out the Mannich reaction to obtain amino-modified lignin. Its hydrophilic hydroxyl groups are not reduced and it does not contain hydrophobic alkyl long chains. The water contact angle of the paint film is low and the waterproof performance is poor.

[0062] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details of the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

Claims

1. An acrylic resin varnish, characterized in that, The raw materials of the acrylic resin varnish include 100 parts by weight of alkenyl monomer, emulsifier, 0.5-0.7 parts by weight of initiator, 0.2-0.6 parts by weight of defoamer, 0.15-0.5 parts by weight of wetting agent, 6-10 parts by weight of film-forming aid, and 3-10 parts by weight of amino-modified lignin. The amount of the emulsifier used is 0.3 parts by weight, 0.31 parts by weight, or 0.33 parts by weight; The alkenyl monomer includes ethyl acetoacetate methacrylate; The amino-modified lignin is prepared by the following method: (1) Add lignin to N,N-dimethylformamide, stir, then add boc-amino acid, dicyclohexylcarbodiimide, and 4-dimethylaminopyridine. Stir and react at 20-35℃ for 12-18h. Pour the solution into ethanol, stir, filter, wash the product, and dry to obtain the lignin precursor. The mass ratio of lignin, boc-amino acid, dicyclohexylcarbodiimide, and 4-dimethylaminopyridine is 100:(10-35):(8-24):(0.6-2). (2) Add the lignin precursor to a trifluoroacetic acid-dichloromethane solution and stir at 20-30℃ for 4-6 h. Distill the solution under reduced pressure, wash the product, and dry to obtain amino-modified lignin. The boc-amino acids include BOC-8-aminooctanoic acid, BOC-10-aminodecanoic acid, and 12-(Boc-amino)dodecanoic acid.

2. The acrylic resin varnish according to claim 1, characterized in that, The alkenyl monomers also include acrylic acid, butyl acrylate, methyl methacrylate, and isooctyl methacrylate.

3. The acrylic resin varnish according to claim 1, characterized in that, The emulsifier includes OP-10 and sodium dodecyl sulfate, the initiator includes ammonium persulfate, and the film-forming aid includes waterborne polyurethane.

4. A method for preparing an acrylic resin varnish as described in any one of claims 1-3, characterized in that, The preparation method includes: adding an alkenyl monomer and an emulsifier to water and stirring to obtain a monomer solution; adding 25-30% by volume of the monomer solution dropwise into a reaction vessel; adding an aqueous solution of an initiator dropwise under a nitrogen atmosphere to carry out a prepolymerization reaction; then adding the remaining monomer solution and adding an aqueous solution of an initiator dropwise to carry out a polymerization reaction; after cooling, adding a neutralizing agent, a film-forming aid, an antifoaming agent, and a wetting agent; stirring and then adding amino-modified lignin; shearing and dispersing to obtain an acrylic resin varnish.

5. The method for preparing acrylic resin varnish according to claim 4, characterized in that, The prepolymerization reaction is carried out at a temperature of 70-85℃ for 30-50 minutes.

6. The method for preparing acrylic resin varnish according to claim 4, characterized in that, The polymerization reaction is carried out at a temperature of 70-85℃ for 3-5 hours.

7. The method for preparing acrylic resin varnish according to claim 4, characterized in that, The addition of a neutralizing agent adjusts the pH of the solution to 7-8. The neutralizing agent includes ammonia or triethylamine.

8. The application of an acrylic resin varnish as described in any one of claims 1-3 in cardboard, characterized in that, Cardboard coated with the aforementioned acrylic resin varnish.