A method for preparing a crack-proof impregnated film paper veneer plywood

Abstract

The present application relates to the technical field of impregnated film paper veneer plywood, in particular to a preparation method of a crack-proof impregnated film paper veneer plywood, which comprises the following steps: S1. preparation of modified melamine; S2. preparation of modified melamine-formaldehyde resin solution; S3. preparation of modified melamine-formaldehyde resin adhesive; S4. impregnation-glue impregnation of impregnated film paper; S5. generation of veneer plywood. The adhesive modifier realizes uniform dispersion of nano-filler and synergistic enhancement of external toughening, and synergistically acts with the polyester modifier to improve the mechanical properties of the overall coating. In the system synergistically acting with the polyester modifier, the adhesive modifier and the modified acrylic ester adhesive, the veneer layer can be deformed in coordination with the wood substrate, significantly overcoming the technical bottleneck of easy cracking of traditional products in dry or cold areas, and the product adaptability is wide, and the durability is significantly better than that of the veneer plywood produced by the traditional process.

Description

Technical Field

[0001] This invention relates to the field of impregnated paper-faced plywood technology, specifically to a method for preparing crack-resistant impregnated paper-faced plywood. Background Technology

[0002] Impregnated paper is an important veneer material for engineered wood products, playing a protective and aesthetic role in papermaking and its products. Impregnated paper-faced plywood (commonly known as eco-board) has seen rapid development in recent years. However, because the surface layer of plywood is usually made of tangentially cut wood veneer, it is prone to significant shrinkage and swelling due to temperature and humidity changes. Impregnated paper typically uses thermosetting melamine-formaldehyde resin as the impregnating adhesive, which has low deformation capacity and high brittleness, making it difficult to match the deformation of the surface veneer, thus causing cracking. Especially in plywood products produced in southern regions, cracking is highly likely to occur when used in cold northern regions or dry western regions. To solve the problem of cracking in veneer panels, it is necessary to toughen and modify the impregnated melamine-formaldehyde resin. Furthermore, plywood veneer processes include direct veneer and composite veneer. Compared to direct veneer, which requires a flat substrate but does not require composite engineered wood veneer, saving on veneer costs and reducing processes, the substrate still needs to be primed with adhesives that have adhesive and leveling properties, thus significantly reducing the basic requirements. Therefore, for impregnated paper direct-veneered plywood, this technology combines internal and external toughening methods with modified melamine-formaldehyde resin through a combination of various modifiers to construct a high-strength and tough flexible impregnated decorative paper resin process system. This allows for the development of highly crack-resistant impregnated paper, and the use of low-cost acrylic adhesives for roller-coating the substrate provides a leveling effect, increasing the adhesion between the substrate and the melamine paper, which is conducive to its industrial application in the manufacture of high-performance decorative plywood. Summary of the Invention

[0003] To address the shortcomings of existing technologies, the present invention aims to provide a method for preparing crack-resistant impregnated paper-faced plywood. This invention involves, during the reaction polymerization stage, increasing the double bonds of the melamine amino group and the alcohol diacrylate in the polyester modifier to undergo an incomplete Michael addition reaction under the action of a weakly polar, aprotic solvent. Furthermore, by adjusting the melamine-formaldehyde molar ratio, acrylate functional groups are introduced to modify the internal toughening of the melamine-formaldehyde resin. Then, the long-chain polyol in the adhesive modifier participates in the melamine-formaldehyde resin co-condensation reaction, achieving external toughening modification through flexible chain connections between the two triazine rings. The reaction formula is attached. Figure 2The addition of nanofillers allows for strong adsorption onto the molecular chains of melamine-formaldehyde resin, forming an effective physical network. This improves the compatibility and interfacial adhesion between long-chain polyols and alcohol-modified melamine-formaldehyde resin. The resin system formed by the synergistic effect of adhesive modifiers and polyester modifiers is stable and firmly bonded. The modified acrylate adhesive and the acrylate-modified melamine-formaldehyde resin in the impregnated paper exhibit good compatibility and contain functional groups such as hydroxyl and amino groups that can react with melamine-formaldehyde resin, enhancing the interfacial forces between the substrate and the impregnated paper. Ultimately, a balance is achieved between the flexibility and rigidity of the impregnated paper.

[0004] To achieve the above objectives, the present invention provides the following technical solution: A method for preparing a crack-resistant impregnated paper-faced plywood includes the following steps: S1. Preparation of modified melamine: S11. By weight, mix 35-45 parts of melamine, 20-25 parts of polyester modifier and 0.005-0.01 parts of acrylate polymerization inhibitor in a four-necked flask, and continuously introduce nitrogen gas while stirring at 300-400 r / min for 5-10 min to obtain preliminarily modified melamine. S12. Add 0.01-0.03 parts of 10% sodium hydroxide solution to the preliminarily modified melamine, control the temperature at 80-90℃ and react for 10-12 hours, then use a rotary evaporator to evaporate and remove the non-protic polar solvent to obtain modified melamine. S2. Preparation of modified melamine-formaldehyde resin solution: Add 30-40 parts formaldehyde and 15-25 parts water to modified melamine, then adjust the pH value to 8.8-9.0 with sodium hydroxide, raise the reaction temperature to 70-80℃ within 20-30 minutes, then slowly raise the temperature to 90-95℃ and hold for 35-40 minutes, then cool to 40-45℃, and adjust the pH value to 8.8-9.0 with sodium hydroxide to obtain modified melamine-formaldehyde resin solution; S3. Preparation of modified melamine-formaldehyde resin adhesive: The modified melamine-formaldehyde resin solution obtained in step S2, 2-5 parts of adhesive modifier and 0.05-0.1 parts of emulsifier are added to a disperser and dispersed to obtain modified melamine-formaldehyde resin adhesive; S4. Impregnation-Glue Impregnation of Impregnated Film Paper: On the production line, two decorative base papers are impregnated-glue impregnated with urea-formaldehyde resin and dried in an oven at 120-125℃ for 10-12 seconds. The impregnated-glue impregnated decorative base paper as the surface layer is impregnated with the above-mentioned modified melamine-formaldehyde resin adhesive, and the impregnated-glue impregnated decorative base paper as the back layer is impregnated with a modified melamine-formaldehyde resin solution. The glue amount is 23-25% of the mass of the decorative base paper. It is then dried in a drying oven at 140-145℃ for 30-40 seconds to obtain the treated impregnated film paper, which is then sealed in a plastic bag for later use. S5. Formulation of Decorative Plywood: The treated impregnated paper prepared in step S4 is applied to the plywood using a hot-pressing process. First, a layer of modified acrylic adhesive (60-80 g / m²) is roller-coated onto the plywood. 2 Then, the two treated impregnated paper sheets are bonded to the plywood substrate with modified acrylic adhesive on the surface by roller coating. The hot pressing temperature is 90-95℃, the time is 5-6min, and the pressure is 0.8-1.0MPa to obtain crack-resistant impregnated paper-faced plywood. The preparation of modified acrylic adhesives includes the following steps: S51. By weight, add 1-1.5 parts of sodium perdodecylbenzenesulfonate and 32-35 parts of deionized water to an emulsifier, then add 20-21 parts of methyl methacrylate, 2.2-2.5 parts of methacrylic acid and 18-20 parts of styrene and mix well. Emulsify for 35-40 minutes to obtain a preliminary mixture. S52. Add 1.5-1.8 parts of 10% ammonium sulfate aqueous solution and 18-20 parts of deionized water to the reactor. After heating to 80-85℃, slowly add the preliminary mixture obtained in step S51. The addition is completed within 90-100 minutes to obtain the secondary mixture. S53. Control the temperature in the reactor at 38-42℃, add ammonia water to adjust the pH value to 7.5, then add 4-5 parts of kaolin, mix evenly to obtain modified acrylic adhesive.

[0005] Preferably, the preparation of the polyester modifier includes the following steps: S111. By weight, mix 10-20 parts of cyclopentyl methyl ether, 0.5-1 parts of KH-550 and 3-5 parts of hydroxyl-terminated polybutadiene under light-protected conditions, and stir at 300-400 r / min for 20-30 min at 40-50℃. S112. Add 10-15 parts of alcohol diacrylate, 2-4 parts of hydroxyethyl acrylate and 0.1-0.3 parts of antioxidant 1010 to the mixture obtained in step S111, and stir at 400-500 r / min for 50-60 min at 40-50℃ to obtain the polyester modifier.

[0006] Preferably, the preparation of the adhesive modifier includes the following steps: S31. By mass, mix 0.56-1 parts of nanofiller, 0.1-0.2 parts of sodium hexametaphosphate and 2-4 parts of deionized water, and disperse in a high-speed disperser at a speed of 1500-2000 rpm for 15-20 min to obtain a dispersion. S32. Add 1.8-3.6 parts of long-chain polyol and 0.5-1 parts of dibutyl phthalate to the dispersion obtained in step S31, and continue to disperse at a speed of 1500-2000 rpm for 10-15 min to obtain the adhesive modifier.

[0007] Preferably, the acrylate polymerization inhibitor is one or more of hydroquinone monomethyl ether polymerization inhibitor, hydroquinone, and copper dibutyldithiocarbamate.

[0008] Preferably, the emulsifier is one or more of sodium dodecyl sulfate, sodium octyl sulfonate, and sodium dodecylbenzene sulfonate, which prevents filler agglomeration and ensures the stability of the adhesive system.

[0009] Preferably, the alcohol diacrylate is one of diethylene glycol diacrylate, triethylene glycol diacrylate, 1,6-hexanediol diacrylate, polyethylene glycol 200, diacrylate, polyethylene glycol 400, and diacrylate. The double bond of the alcohol diacrylate undergoes a Michael addition reaction with the amino group of melamine. The initial addition produces a β-amino ester, but due to the weak conjugation effect between the lone pair electrons of the nitrogen atom and the ester group, the nucleophilicity of the subsequent amino group is reduced, hindering continuous addition. Therefore, the amino group in melamine is mono- or di-substituted, thereby introducing a weather-resistant and flexible alcohol diacrylate group to toughen the melamine-formaldehyde resin without affecting subsequent hydroxymethylation and polycondensation reactions with formaldehyde.

[0010] Preferably, the nanofiller is silica solid particles with a particle size of 50-200 nm. It strongly adsorbs onto the melamine-formaldehyde resin molecular chain, forming an effective physical network that evenly distributes the load under external force, reducing the possibility of breakage.

[0011] Preferably, the long-chain polyol is one or more of polypropylene glycol, polypropylene-ethylene glycol, polyethylene adipate glycol, and diethylene glycol phthalate. The long-chain polyol has a relative molecular weight of 200-1000 and a viscosity of 60-200 mPa·s. It exhibits good compatibility with melamine-formaldehyde resin and can bond with the hydroxymethyl groups of the melamine-formaldehyde resin. Starting from the two triazine rings, it is linked by a long-chain flexible structure, giving the molecular chain greater intramolecular deformability and a lower resin crosslinking density than the methyl-linked chain, thus improving the toughness of the adhesive.

[0012] Preferably, the dispersion speed in step S3 is 1500-2000 rpm and the time is 10-15 min.

[0013] Preferably, in step S4, the impregnation speed of the impregnation-glue impregnation is 23-25 ​​m / min, and the amount of glue applied is 50-60% of the mass of the base paper.

[0014] Preferably, the concentrations of melamine and formaldehyde are 100% and 99.7%, respectively, and the product is of industrial grade. Melamine and formaldehyde undergo hydroxymethylation and condensation reactions to form a strong and stable three-dimensional network resin.

[0015] Cyclopentyl methyl ether, as a chemically stable carbanion intermediate, can enhance the nucleophilicity of amino groups and inhibit the proton transfer step of Michael addition, thus facilitating the accumulation of mono / disubstituted intermediates.

[0016] Compared with the prior art, the beneficial effects of the present invention are: 1. The polyester modifier of this invention achieves efficient and stable internal toughening modification of melamine resin, which not only significantly reduces the crosslinking density of the subsequently formed melamine-formaldehyde resin, but also endows the resin body with higher flexibility and deformation ability, thereby effectively resisting stress concentration caused by the drying shrinkage and wetting expansion of the substrate from the source.

[0017] 2. The adhesive modifier of this invention achieves synergistic enhancement of uniform dispersion of nanofillers and external toughening, and works synergistically with the polyester modifier to improve the overall mechanical properties of the coating. The synergistic system of polyester modifier, adhesive modifier, and modified acrylic adhesive allows the veneer layer to deform in coordination with the wood substrate, significantly overcoming the technical bottleneck of traditional products being prone to cracking in dry or cold regions. The product has wide adaptability and significantly better durability than veneer plywood produced by traditional processes. Attached Figure Description

[0018] Figure 1 This is a process flow diagram for preparing the anti-cracking impregnated paper-faced plywood of the present invention; Figure 2 This is a schematic diagram of the copolymerization reaction product of melamine-formaldehyde resin modified with 1,6-hexanediol diacrylate and polyethylene adipate diol in Example 3 of the present invention. Figure 3 This is a flow chart of the preparation process of the polyester modifier of the present invention; Figure 4 This is a flow chart of the preparation process of the adhesive modifier of the present invention; Figure 5 This is a process flow diagram for preparing the modified acrylic adhesive of the present invention; Figure 6These are field photos of the surface crack resistance test of the anti-cracking impregnated paper-faced plywood obtained in Example 1 of the present invention. Figure 7 This is a field photo of the surface crack resistance test of the anti-cracking impregnated paper-faced plywood obtained in Comparative Example 1 of the present invention. Detailed Implementation

[0019] The present invention will now be clearly and completely described in conjunction with embodiments thereof. Obviously, the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0020] Please see Figure 1-7 The present invention provides a technical solution: Example 1 A method for preparing crack-resistant impregnated paper-faced plywood: Before preparing crack-resistant impregnated paper-faced plywood, the following steps are taken: preparation of ester modifier, adhesive modifier, and modified acrylic adhesive. The preparation of the polyester modifier includes the following steps: S111. Mix 10g cyclopentyl methyl ether, 0.5g KH-550 and 3g hydroxyl-terminated polybutadiene under light-protected conditions and stir at 300r / min for 20min at 40℃. S112. Add 10g of diethylene glycol diacrylate, 2g of hydroxyethyl acrylate and 0.1g of antioxidant 1010 to the mixture obtained in step S111, and stir at 400r / min for 50min at 40℃ to obtain the polyester modifier. The preparation of adhesive modifiers includes the following steps: S31. Mix 0.56g of nanofiller (silica solid particles with a particle size of 50nm), 0.1g of sodium hexametaphosphate and 2g of deionized water, and disperse in a high-speed disperser at a speed of 1500rpm for 15min to obtain a dispersion. S32. Add 1.8g of polyoxypropylene glycol and 0.5g of dibutyl phthalate to the dispersion obtained in step S31, and continue to disperse at 1500rpm for 10min to obtain the adhesive modifier. The preparation of modified acrylic adhesives includes the following steps: S51. Add 1g of sodium perdodecylbenzenesulfonate and 32g of deionized water to an emulsifier, then add 20g of methyl methacrylate, 2.2g of methacrylic acid and 18g of styrene and mix well. Emulsify for 35 minutes to obtain a preliminary mixture. S52. Add 1.5g of 10% ammonium sulfate aqueous solution and 18g of deionized water to the reactor, heat to 80℃ and slowly add the preliminary mixture obtained in step S51, and add it all within 90min to obtain the secondary mixture. S53. Control the temperature in the reactor at 38℃, add ammonia water to adjust the pH value to 7.5, then add 4g of kaolin, mix evenly to obtain modified acrylate adhesive; S1. Preparation of modified melamine: S11. Mix 35g of melamine, 20g of polyester modifier and 0.005g of hydroquinone monomethyl ether polymerization inhibitor in a four-necked flask, and continuously introduce nitrogen gas. Stir at 300r / min for 5min to obtain preliminarily modified melamine. S12. Add 0.01g of 10% sodium hydroxide solution to the preliminarily modified melamine, control the temperature at 80℃ and react for 10h, then use a rotary evaporator to evaporate and remove the non-protic polar solvent to obtain modified melamine; S2. Preparation of modified melamine-formaldehyde resin solution: Add 30g formaldehyde and 15g water to modified melamine, then adjust the pH value to 8.8 with sodium hydroxide, raise the reaction temperature to 70℃ within 20min, then slowly raise the temperature to 90℃ and hold for 35min, then cool to 40℃, and adjust the pH value to 8.8 with sodium hydroxide to obtain modified melamine-formaldehyde resin solution; S3. Preparation of modified melamine-formaldehyde resin adhesive: The modified melamine-formaldehyde resin solution obtained in step S2, 2g of adhesive modifier and 0.05g of sodium dodecyl sulfate are added to a disperser and dispersed (dispersed at 1500rpm for 10min) to obtain modified melamine-formaldehyde resin adhesive. S4. Impregnation-Glue Impregnation of Impregnated Film Paper: On the production line, two decorative base papers are impregnated-glue impregnated with urea-formaldehyde resin at an impregnation speed of 23 m / min and a glue amount of 50% of the base paper mass. They are then dried in an oven at 120°C for 10 seconds. The impregnated-glue impregnated decorative base paper, which serves as the surface layer, is impregnated with the above-mentioned modified melamine-formaldehyde resin adhesive. The impregnated-glue impregnated decorative base paper, which serves as the back layer, is impregnated with a modified melamine-formaldehyde resin solution and a glue amount of 23% of the decorative base paper mass. It is then dried in a drying oven at 140°C for 30 seconds to obtain impregnated film paper with a pre-curing degree of 50%. It is then sealed in a plastic bag for later use. S5. Formulation of Decorative Plywood: The treated impregnated paper prepared in step S4 is applied to the plywood using a hot-pressing process. First, a layer of modified acrylic adhesive (60 g / m²) is roller-coated onto the plywood. 2Then, the two treated impregnated paper sheets are bonded to the plywood substrate with modified acrylic adhesive on the surface by roller coating. The hot pressing temperature is 90℃, the time is 5min, and the pressure is 0.8MPa to obtain crack-resistant impregnated paper-faced plywood.

[0021] Example 2 A method for preparing crack-resistant impregnated paper-faced plywood: Before preparing crack-resistant impregnated paper-faced plywood, the following steps are taken: preparation of ester modifier, adhesive modifier, and modified acrylic adhesive. The preparation of the polyester modifier includes the following steps: S111. Mix 20g of cyclopentyl methyl ether, 1g of KH-550 and 5g of hydroxyl-terminated polybutadiene under light-protected conditions, and stir at 400r / min for 30min at 50℃. S112. Add 15g of triethylene glycol diacrylate, 4g of hydroxyethyl acrylate and 0.3g of antioxidant 1010 to the mixture obtained in step S111, and stir at 500r / min for 60min at 50℃ to obtain the polyester modifier. The preparation of adhesive modifiers includes the following steps: S31. Mix 1g of nanofiller (silica solid particles with a particle size of 200nm), 0.2g of sodium hexametaphosphate and 4g of deionized water, and disperse in a high-speed disperser at a speed of 2000rpm for 20min to obtain a dispersion. S32. Add 3.6g of polyoxypropylene-ethylene glycol and 1g of dibutyl phthalate to the dispersion obtained in step S31, and continue to disperse at 2000rpm for 15min to obtain the adhesive modifier. The preparation of modified acrylic adhesives includes the following steps: S51. Add 1.5g sodium perdodecylbenzenesulfonate and 35g deionized water to an emulsifier, then add 21g methyl methacrylate, 2.5g methacrylic acid and 20g styrene and mix well. Emulsify for 40 minutes to obtain a preliminary mixture. S52. Add 1.8g of 10% ammonium sulfate aqueous solution and 20g of deionized water to the reactor, heat to 85℃ and slowly add the preliminary mixture obtained in step S51, and add it all within 100min to obtain the secondary mixture. S53. Control the temperature in the reactor at 42℃, add ammonia water to adjust the pH value to 7.5, then add 5g of kaolin, mix evenly to obtain modified acrylic adhesive; S1. Preparation of modified melamine: S11. Mix 45g of melamine, 25g of polyester modifier and 0.01g of hydroquinone in a four-necked flask, and continuously purge with nitrogen gas. Stir at 400r / min for 10min to obtain preliminarily modified melamine. S12. Add 0.03g of 10% sodium hydroxide solution to the preliminarily modified melamine, control the temperature at 90℃ and react for 12h, then use a rotary evaporator to evaporate and remove the non-protic polar solvent to obtain modified melamine; S2. Preparation of modified melamine-formaldehyde resin solution: Add 40g formaldehyde and 25g water to modified melamine, then adjust the pH value to 9.0 with sodium hydroxide, raise the reaction temperature to 80℃ within 30min, then slowly raise the temperature to 95℃ and hold for 40min, then cool to 45℃, and adjust the pH value to 9.0 with sodium hydroxide to obtain modified melamine-formaldehyde resin solution; S3. Preparation of modified melamine-formaldehyde resin adhesive: The modified melamine-formaldehyde resin solution obtained in step S2, 5g of adhesive modifier and 0.1g of sodium octyl sulfonate were added to a disperser and dispersed (dispersed at 2000 rpm for 15 min) to obtain the modified melamine-formaldehyde resin adhesive. S4. Impregnation-Glue Impregnation of Impregnated Film Paper: On the production line, two decorative base papers are impregnated-glue impregnated with urea-formaldehyde resin at an impregnation speed of 25 m / min and a glue application amount of 60% of the base paper mass. They are then dried in an oven at 125°C for 12 s. The impregnated-glue impregnated decorative base paper, which serves as the surface layer, is impregnated with the above-mentioned modified melamine-formaldehyde resin adhesive. The impregnated-glue impregnated decorative base paper, which serves as the back layer, is impregnated with a modified melamine-formaldehyde resin solution and a glue application amount of 25% of the decorative base paper mass. It is then dried in a drying oven at 145°C for 40 s to obtain impregnated film paper with a pre-curing degree of 60%. It is then sealed in a plastic bag for later use. S5. Formulation of Decorative Plywood: The treated impregnated paper prepared in step S4 is hot-pressed onto the plywood to apply a decorative finish. A direct-lamination process is used, first roller-coating the plywood with a layer of modified acrylic adhesive 80g / m². 2 Then, the two treated impregnated paper sheets are bonded to the plywood substrate with modified acrylic adhesive on the surface by roller coating. The hot pressing temperature is 95℃, the time is 6min, and the pressure is 1.0MPa to obtain crack-resistant impregnated paper-faced plywood.

[0022] Example 3 A method for preparing crack-resistant impregnated paper-faced plywood: Before preparing crack-resistant impregnated paper-faced plywood, the following steps are taken: preparation of ester modifier, adhesive modifier, and modified acrylic adhesive. The preparation of the polyester modifier includes the following steps: S111. Mix 12g of cyclopentyl methyl ether, 0.6g of KH-550 and 3.5g of hydroxyl-terminated polybutadiene under light-protected conditions and stir at 320r / min for 22min at 42℃. S112. Add 11g of 1,6-hexanediol diacrylate, 2.5g of hydroxyethyl acrylate and 0.15g of antioxidant 1010 to the mixture obtained in step S111, and stir at 420r / min for 52min at 42℃ to obtain the polyester modifier. The preparation of adhesive modifiers includes the following steps: S31. Mix 0.6g of nanofiller (silica solid particles with a particle size of 100nm), 0.15g of sodium hexametaphosphate and 2.5g of deionized water, and disperse in a high-speed disperser at a speed of 1600rpm for 16min to obtain a dispersion. S32. Add 2g of polyethylene adipate diol and 0.6g of dibutyl phthalate to the dispersion obtained in step S31, and continue to disperse at 1600 rpm for 11 min to obtain the adhesive modifier. The preparation of modified acrylic adhesives includes the following steps: S51. Add 1.1g of sodium perdodecylbenzenesulfonate and 33g of deionized water to an emulsifier, then add 20.2g of methyl methacrylate, 2.3g of methacrylic acid and 18.5g of styrene and mix well. Emulsify for 36 minutes to obtain a preliminary mixture. S52. Add 1.6g of 10% ammonium sulfate aqueous solution and 18.5g of deionized water to the reactor, heat to 81℃ and slowly add the preliminary mixture obtained in step S51, and add it all within 92min to obtain the secondary mixture. S53. Control the temperature in the reactor at 39℃, add ammonia water to adjust the pH value to 7.5, then add 4.2g of kaolin, mix evenly to obtain modified acrylate adhesive; S1. Preparation of modified melamine: S11. Mix 38g of melamine, 21g of polyester modifier and 0.006g of copper dibutyldithiocarbamate in a four-necked flask, and continuously introduce nitrogen gas. Stir at 320r / min for 6min to obtain preliminarily modified melamine. S12. Add 0.015g of 10% sodium hydroxide solution to the preliminarily modified melamine, control the temperature at 82℃ and react for 10.5h, then use a rotary evaporator to evaporate and remove the non-protic polar solvent to obtain modified melamine; S2. Preparation of modified melamine-formaldehyde resin solution: Add 32g formaldehyde and 18g water to modified melamine, then adjust the pH value to 8.9 with sodium hydroxide, raise the reaction temperature to 72℃ within 22min, then slowly raise the temperature to 91℃ and hold for 36min, then cool to 41℃, and adjust the pH value to 8.9 with sodium hydroxide to obtain modified melamine-formaldehyde resin solution; S3. Preparation of modified melamine-formaldehyde resin adhesive: The modified melamine-formaldehyde resin solution obtained in step S2, 3g of adhesive modifier and 0.06g of sodium dodecylbenzenesulfonate were added to a disperser and dispersed (dispersed at 1600rpm for 11min) to obtain modified melamine-formaldehyde resin adhesive. S4. Impregnation-Glue Impregnation of Impregnated Film Paper: On the production line, two decorative base papers are impregnated-glue impregnated with urea-formaldehyde resin at an impregnation speed of 24 m / min and a glue application amount of 52% of the base paper mass. They are then dried in an oven at 121°C for 11 s. The impregnated-glue impregnated decorative base paper, which serves as the surface layer, is impregnated with the above-mentioned modified melamine-formaldehyde resin adhesive. The impregnated-glue impregnated decorative base paper, which serves as the back layer, is impregnated with a modified melamine-formaldehyde resin solution and a glue application amount of 24% of the base paper mass. It is then dried in a drying oven at 141°C for 32 s to obtain impregnated film paper with a pre-curing degree of 52%. It is then sealed in a plastic bag for later use. S5. Formulation of Decorative Plywood: The treated impregnated paper prepared in step S4 is applied to the plywood using a hot-pressing process. First, a layer of modified acrylic adhesive (65 g / m²) is roller-coated onto the plywood. 2 Then, the two treated impregnated paper sheets are bonded to the plywood substrate with modified acrylic adhesive on the surface by roller coating. The hot pressing temperature is 91℃, the time is 5.5min, and the pressure is 0.9MPa to obtain crack-resistant impregnated paper-faced plywood.

[0023] Example 4 A method for preparing crack-resistant impregnated paper-faced plywood: Before preparing crack-resistant impregnated paper-faced plywood, the following steps are taken: preparation of ester modifier, adhesive modifier, and modified acrylic adhesive. The preparation of the polyester modifier includes the following steps: S111. Mix 18g of cyclopentyl methyl ether, 0.8g of KH-550 and 4.5g of hydroxyl-terminated polybutadiene under light-protected conditions and stir at 370r / min for 27min at 45℃. S112. Add 14g of polyethylene glycol 200, 3g of hydroxyethyl acrylate and 0.25g of antioxidant 1010 to the mixture obtained in step S111, and stir at 480r / min for 56min at 48℃ to obtain the polyester modifier. The preparation of adhesive modifiers includes the following steps: S31. Mix 0.7g of nanofiller (silica solid particles with a particle size of 140nm), 0.18g of sodium hexametaphosphate and 3g of deionized water, and disperse in a high-speed disperser at a speed of 1800rpm for 18min to obtain a dispersion. S32. Add 3.1g of poly(ethylene glycol) phthalate and 0.8g of dibutyl phthalate to the dispersion obtained in step S31, and continue to disperse at 1800 rpm for 14 min to obtain the adhesive modifier. The preparation of modified acrylic adhesives includes the following steps: S51. Add 1.4g of sodium perdodecylbenzenesulfonate and 34g of deionized water to an emulsifier, then add 20.6g of methyl methacrylate, 2.4g of methacrylic acid and 19g of styrene and mix well. Emulsify for 38 minutes to obtain a preliminary mixture. S52. Add 1.7g of 10% ammonium sulfate aqueous solution and 19g of deionized water to the reactor, heat to 84℃ and slowly add the preliminary mixture obtained in step S51, and add it all within 98min to obtain the secondary mixture. S53. Control the temperature in the reactor at 41℃, add ammonia water to adjust the pH value to 7.5, then add 4.8g of kaolin, mix evenly to obtain modified acrylate adhesive; S1. Preparation of modified melamine: S11. Mix 41g of melamine, 24g of polyester modifier and 0.009g of hydroquinone in a four-necked flask, and continuously purge with nitrogen gas. Stir at 380r / min for 8min to obtain preliminarily modified melamine. S12. Add 0.025g of 10% sodium hydroxide solution to the preliminarily modified melamine, control the temperature at 88℃ and react for 11.5h, then use a rotary evaporator to evaporate and remove the non-protic polar solvent to obtain modified melamine; S2. Preparation of modified melamine-formaldehyde resin solution: Add 38g formaldehyde and 24g water to modified melamine, then adjust the pH value to 8.9 with sodium hydroxide, raise the reaction temperature to 78℃ within 28min, then slowly raise the temperature to 94℃ and hold for 38min, then cool to 44℃, and adjust the pH value to 8.9 with sodium hydroxide to obtain modified melamine-formaldehyde resin solution; S3. Preparation of modified melamine-formaldehyde resin adhesive: The modified melamine-formaldehyde resin solution obtained in step S2, 4g of adhesive modifier and 0.08g of sodium octyl sulfonate were added to a disperser and dispersed (dispersed at 1800 rpm for 14 min) to obtain modified melamine-formaldehyde resin adhesive. S4. Impregnation-Glue Impregnation of Impregnated Film Paper: On the production line, two decorative base papers are impregnated-glue impregnated with urea-formaldehyde resin at an impregnation speed of 24 m / min and a glue application amount of 57% of the base paper mass. They are then dried in an oven at 124°C for 11 s. The impregnated-glue impregnated decorative base paper, which serves as the surface layer, is impregnated with the above-mentioned modified melamine-formaldehyde resin adhesive. The impregnated-glue impregnated decorative base paper, which serves as the back layer, is impregnated with a modified melamine-formaldehyde resin solution and a glue application amount of 24% of the base paper mass. It is then dried in a drying oven at 144°C for 37 s to obtain impregnated film paper with a pre-curing degree of 57%. It is then sealed in a plastic bag for later use. S5. Formulation of Decorative Plywood: The treated impregnated paper prepared in step S4 is applied to the plywood using a hot-pressing process. First, a layer of modified acrylic adhesive (75 g / m²) is roller-coated onto the plywood. 2 Then, the two treated impregnated paper sheets are bonded to the plywood substrate with modified acrylic adhesive on the surface by roller coating. The hot pressing temperature is 94℃, the time is 5.5min, and the pressure is 0.9MPa to obtain crack-resistant impregnated paper-faced plywood.

[0024] Comparative Example 1 The only difference between Comparative Example 1 and Example 1 is that the modified melamine-formaldehyde resin solution used for back layer impregnation in step S4 is replaced with a modified melamine-formaldehyde resin adhesive. The remaining steps are exactly the same in Comparative Example 1 and Example 1.

[0025] Comparative Example 2 The only difference between Comparative Example 2 and Example 1 is that no polyester modifier and adhesive modifier were added in this comparative example; the other steps are exactly the same in Comparative Example 2 and Example 1.

[0026] Performance testing: Referring to standard GB / T 34722—2017 "Impregnated Paper-Faced Plywood and Blockboard", the surface abrasion resistance, surface scratch resistance, surface crack resistance, surface resistance to thermal cycling, surface resistance to pollution and corrosion, surface resistance to water vapor, and surface bonding strength of the veneered plywood were tested. The data obtained are shown in Tables 1, 2, and 3 below: Table 1 Comparison of appearance, solid content, and viscosity properties Table 2 Comparison of surface abrasion resistance, surface scratch resistance, and surface crack resistance. Table 3 Comparison of surface resistance to thermal cycling, surface resistance to contamination and corrosion, surface resistance to water vapor, and surface bonding strength. Table 1 shows that the addition of polyester modifiers and adhesive modifiers affects the viscosity of melamine-formaldehyde resin, but does not affect the surface impregnation treatment of the base paper in practical applications. (See Table 2 and Appendix...) Figure 6 , 7 (Appendix) Figure 6 , 7 (Photos of the surface crack resistance test of the crack-resistant impregnated paper-faced plywood obtained in Example 1 and Comparative Example 1 are shown respectively.) As can be seen, compared to Comparative Example 2, the crack-resistant impregnated paper-faced plywood prepared in Example 1 under the synergistic effect of the polyester modifier, adhesive modifier, and modified acrylate adhesive showed no cracking, blistering, discoloration, or wrinkling in the surface crack resistance and thermal cycling tests, and also exhibited good abrasion resistance and scratch resistance. Comparative Example 2 and its data show that the data of the crack-resistant impregnated paper-faced plywood obtained in Comparative Example 2 and Example 1 are basically the same. Therefore, using only modified melamine-formaldehyde resin for the surface layer is sufficient to prepare solid-color impregnated paper-faced plywood that meets the crack resistance and thermal cycling test requirements of currently available plywoods with high basis weight and high ash content.

[0027] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a crack-resistant impregnated paper-faced plywood, characterized in that, Includes the following steps: S1. Preparation of modified melamine: S11. By weight, mix 35-45 parts of melamine, 20-25 parts of polyester modifier and 0.005-0.01 parts of acrylate polymerization inhibitor in a four-necked flask, and continuously introduce nitrogen gas while stirring at 300-400 r / min for 5-10 min to obtain preliminarily modified melamine. S12. Add 0.01-0.03 parts of 10% sodium hydroxide solution to the preliminarily modified melamine, control the temperature at 80-90℃ and react for 10-12 hours, then use a rotary evaporator to evaporate and remove the non-protic polar solvent to obtain modified melamine. S2. Preparation of modified melamine-formaldehyde resin solution: Add 30-40 parts formaldehyde and 15-25 parts water to modified melamine, then adjust the pH value to 8.8-9.0 with sodium hydroxide, raise the reaction temperature to 70-80℃ within 20-30 minutes, then slowly raise the temperature to 90-95℃ and hold for 35-40 minutes, then cool to 40-45℃, and adjust the pH value to 8.8-9.0 with sodium hydroxide to obtain modified melamine-formaldehyde resin solution; S3. Preparation of modified melamine-formaldehyde resin adhesive: The modified melamine-formaldehyde resin solution obtained in step S2, 2-5 parts of adhesive modifier and 0.05-0.1 parts of emulsifier are added to a disperser and dispersed to obtain modified melamine-formaldehyde resin adhesive; S4. Impregnation-Glue Impregnation of Impregnated Film Paper: On the production line, two decorative base papers are impregnated-glue impregnated with urea-formaldehyde resin and dried in an oven at 120-125℃ for 10-12 seconds. The impregnated-glue impregnated decorative base paper as the surface layer is impregnated with the above-mentioned modified melamine-formaldehyde resin adhesive, and the impregnated-glue impregnated decorative base paper as the back layer is impregnated with a modified melamine-formaldehyde resin solution. The glue amount is 23-25% of the mass of the decorative base paper. It is then dried in a drying oven at 140-145℃ for 30-40 seconds to obtain the treated impregnated film paper, which is then sealed in a plastic bag for later use. S5. Formulation of Decorative Plywood: The treated impregnated paper prepared in step S4 is applied to the plywood using a hot-pressing process. First, a layer of modified acrylic adhesive (60-80 g / m²) is roller-coated onto the plywood. 2 Then, the two treated impregnated paper sheets are bonded to the plywood substrate with modified acrylic adhesive on the surface by roller coating. The hot pressing temperature is 90-95℃, the time is 5-6min, and the pressure is 0.8-1.0MPa to obtain crack-resistant impregnated paper-faced plywood. The preparation of the modified acrylic adhesive includes the following steps: S51. By weight, add 1-1.5 parts of sodium perdodecylbenzenesulfonate and 32-35 parts of deionized water to an emulsifier, then add 20-21 parts of methyl methacrylate, 2.2-2.5 parts of methacrylic acid and 18-20 parts of styrene and mix well. Emulsify for 35-40 minutes to obtain a preliminary mixture. S52. Add 1.5-1.8 parts of 10% ammonium sulfate aqueous solution and 18-20 parts of deionized water to the reactor. After heating to 80-85℃, slowly add the preliminary mixture obtained in step S51. The addition is completed within 90-100 minutes to obtain the secondary mixture. S53. Control the temperature in the reactor at 38-42℃, add ammonia water to adjust the pH value to 7.5, then add 4-5 parts of kaolin, mix evenly to obtain modified acrylic adhesive.

2. The method for preparing a crack-resistant impregnated paper-faced plywood according to claim 1, characterized in that, The preparation of the polyester modifier includes the following steps: S111. By weight, mix 10-20 parts of cyclopentyl methyl ether, 0.5-1 parts of KH-550 and 3-5 parts of hydroxyl-terminated polybutadiene under light-protected conditions, and stir at 300-400 r / min for 20-30 min at 40-50℃. S112. Add 10-15 parts of alcohol diacrylate, 2-4 parts of hydroxyethyl acrylate and 0.1-0.3 parts of antioxidant 1010 to the mixture obtained in step S111, and stir at 400-500 r / min for 50-60 min at 40-50℃ to obtain the polyester modifier.

3. The method for preparing a crack-resistant impregnated paper-faced plywood according to claim 1, characterized in that, The preparation of the adhesive modifier includes the following steps: S31. By mass, mix 0.56-1 parts of nanofiller, 0.1-0.2 parts of sodium hexametaphosphate and 2-4 parts of deionized water, and disperse in a high-speed disperser at a speed of 1500-2000 rpm for 15-20 min to obtain a dispersion. S32. Add 1.8-3.6 parts of long-chain polyol and 0.5-1 parts of dibutyl phthalate to the dispersion obtained in step S31, and continue to disperse at a speed of 1500-2000 rpm for 10-15 min to obtain the adhesive modifier.

4. The method for preparing a crack-resistant impregnated paper-faced plywood according to claim 1, characterized in that, The acrylate polymerization inhibitor is one or more of hydroquinone monomethyl ether polymerization inhibitor, hydroquinone, and copper dibutyldithiocarbamate.

5. The method for preparing a crack-resistant impregnated paper-faced plywood according to claim 1, characterized in that, The emulsifier is one or more of sodium dodecyl sulfate, sodium octyl sulfonate, and sodium dodecylbenzene sulfonate.

6. The method for preparing a crack-resistant impregnated paper-faced plywood according to claim 2, characterized in that, The alcohol diacrylate is one of diethylene glycol diacrylate, triethylene glycol diacrylate, 1,6-hexanediol diacrylate, polyethylene glycol 200, diacrylate, polyethylene glycol 400, and diacrylate.

7. The method for preparing a crack-resistant impregnated paper-faced plywood according to claim 3, characterized in that, The nanofiller is a silica solid particle with a particle size of 50-200 nm.

8. The method for preparing a crack-resistant impregnated paper-faced plywood according to claim 3, characterized in that, The long-chain polyol is one or more of polypropylene glycol, polypropylene-ethylene glycol, polyethylene adipate glycol, and diethylene glycol phthalate.

9. The method for preparing a crack-resistant impregnated paper-faced plywood according to claim 1, characterized in that, The dispersion speed in step S3 is 1500-2000 rpm, and the time is 10-15 min.

10. The method for preparing a crack-resistant impregnated paper-faced plywood according to claim 1, characterized in that, In step S4, the impregnation speed is 23-25 ​​m / min, and the amount of glue applied is 50-60% of the mass of the base paper.

Images