Anti-cracking composite wood board and preparation method thereof

Abstract

The present application relates to the technical field of composite wood board, in particular to a crack-proof composite wood board and a preparation method thereof.The present application reacts 1,4-butanediol and phenylphosphonic dichloride to obtain phosphorus-containing dihydric alcohol; reacts 1,1,3,3-tetramethyldisiloxane and allyl isocyanate to obtain silicon-containing diisocyanate; mixes and reacts the phosphorus-containing dihydric alcohol and the silicon-containing diisocyanate according to a molar ratio of hydroxyl group to isocyanate group of 1:2, and then adds diethanolamine to obtain a polyol modifier; adds the polyol modifier to a melamine formaldehyde resin reaction system to obtain modified melamine formaldehyde resin glue liquid; mixes the modified melamine formaldehyde resin glue liquid, ammonium chloride and flour to obtain a modified melamine formaldehyde adhesive.The modified melamine formaldehyde adhesive is coated on the surface of a wood board, and hot pressing is combined to obtain a crack-proof composite wood board.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of composite wood board, in particular to a crack-proof composite wood board and a preparation method thereof. BACKGROUND

[0002] The composite wood board is a wooden material formed by gluing two or more different types of wood layers. The multi-layer composite structure provides many advantages for the composite wood board, such as customizing wood grain, patterns, and colors according to consumer preferences, and various surface aesthetic options. Through multi-layer compounding, the composite wood board also has stronger wear resistance and heat resistance, and a longer service life.

[0003] However, after compounding the multi-layer wood board, the problem of easy cracking often exists. Patent CN111015856 discloses a process of setting glass fiber mesh and carbon fiber mesh in the wood board, which improves the dimensional stability of the composite wood board and makes it less likely to crack and deform. Patent CN106393374 modifies the glass fiber by adding wood chips and bamboo fiber strips to strengthen and consolidate the internal structure, thereby improving the toughness of the composite wood board and preventing cracking. The above-mentioned technologies mainly modify the structure of the composite wood board, but in the actual production process, since the composite wood needs to be bonded by adhesive, the commonly used adhesive such as melamine formaldehyde resin has the advantages of good hardness, high thermal stability, etc., but also has the disadvantages of high brittleness and poor toughness. In a humid environment, the wood swells due to moisture, generating uneven internal stress, and the melamine formaldehyde resin is prone to cracking under stress, resulting in cracking of the composite wood board, which seriously affects normal use and indoor aesthetics. Therefore, it is necessary to invent a crack-proof composite wood board. SUMMARY

[0004] The present application aims to provide a crack-proof composite wood board and a preparation method thereof to solve the problems in the background art.

[0005] To solve the above technical problems, the present application provides the following technical solutions: a crack-proof composite wood board and a preparation method thereof, comprising the following steps:

[0006] Step 1:

[0007] S11: 1,4-butanediol is added to anhydrous tetrahydrofuran to obtain mixture A; phenylphosphonic dichloride is added to anhydrous tetrahydrofuran to obtain mixture B; under nitrogen environment, 0℃, triethylamine is added to the mixed solution A, after stirring, mixture B is added dropwise, the temperature of the reaction system is kept at 0℃, and the stirring reaction is carried out for 7-8h, then the temperature is increased to 25-35℃, and the stirring reaction is continued for 10-12h; after the reaction is completed, filtration is carried out, and the filtrate is subjected to rotary distillation, after removing the excess anhydrous tetrahydrofuran, the remaining is washed, filtered and distilled to obtain a phosphorus-containing diol;

[0008] S12: 1,1,3,3-tetramethyldisiloxane and Karstedt catalyst are dispersed in anhydrous toluene, under nitrogen environment, the temperature is increased to 80-90℃, and allyl isocyanate is added, the reaction is carried out for 12-15h to obtain a silicon-containing diisocyanate;

[0009] S13: the phosphorus-containing diol and the silicon-containing diisocyanate are mixed, dibutyltin dilaurate is used as a catalyst, and the reaction is carried out at 50-60℃ for 3-4h to obtain an intermediate;

[0010] S14: at 0-5℃, the intermediate is mixed with diethanolamine, the temperature is kept for 30-60min, then the temperature is increased to 60-70℃, and the reaction is continued for 1-2h to obtain a polyol modifier; wherein the diethanolamine reacts with the isocyanate group in the intermediate at a molar ratio of 1:1;

[0011] Step 2:

[0012] S21: according to the weight fraction, 200-220 parts of deionized water is added to a 25% sodium methoxide solution, the pH of the system is adjusted to 9.0-10.0, 50-60 parts of melamine and 36-40 parts of polyformaldehyde are added under stirring, and the stirring reaction is carried out at 75-85℃ for 30-40min to obtain a hydroxymethyl melamine solution; the pH of the hydroxymethyl melamine solution is adjusted to 5-5.5 by adding a catalyst toluenesulfonic acid, and the polyol modifier is added, the amount of the polyol modifier is 6-13% of the amount of melamine according to the mole fraction; the temperature is increased to 80-90℃, the stirring reaction is carried out for 30-45min, then triethylamine is added to adjust the pH of the system to 8.5-9.5, and the reaction is continued until the water dissolving multiple of the reaction solution is 2-2.5 at 25℃, and the modified melamine formaldehyde resin glue solution is obtained;

[0013] S22: ammonium chloride, flour and modified melamine formaldehyde resin glue solution are mixed and stirred to obtain a modified melamine formaldehyde adhesive;

[0014] Step 3:

[0015] S31: the pine is rotary cut to obtain pine veneer with a thickness of 2-5 mm, and hot air drying is performed until the veneer has a moisture content of 6-8 %;

[0016] S32: wood chips on the surface of the pine veneer are removed, and the modified melamine formaldehyde adhesive is coated on both sides to obtain a coated wood board; a plurality of coated wood boards are taken, stacked in turn with the textures perpendicular to each other, pre-pressed for 15-20 min, and then hot-pressed and combined to obtain a crack-resistant composite wood board.

[0017] Further, in S11, the 1,4-butanediol and phenyl phosphoric dichloride are reacted at a molar ratio of 2:1.

[0018] Further, in S12, the 1,1,3,3-tetramethyldisiloxane and allyl isocyanate are reacted at a molar ratio of 1:2.

[0019] Further, in S13, the phosphorus-containing diol and the silicon-containing diisocyanate are mixed at a molar ratio of hydroxyl groups to isocyanate groups of 1:2.

[0020] Further, in S22, the amount of ammonium chloride is 1-2 % of the total mass of the melamine formaldehyde resin, and the amount of flour is 12-18 % of the total mass of the melamine formaldehyde resin.

[0021] Further, in S32, the amount of adhesive coated on one side of the coated wood board is 300-350 g / m 2 .

[0022] Further, in S32, the hot-pressing and combining method is hot-pressing and combining at 0.9-1.2 MPa and 140-150 DEG C for 60-90 min.

[0023] Compared with the prior art, the present application has the beneficial effects that a polyol modifier is prepared for modifying the adhesive melamine formaldehyde resin, and the modified melamine formaldehyde resin is mixed with flour to obtain an adhesive for composite wood boards.

[0024] The present application reacts 1,4-butanediol and phenyl phosphorodichloridate in a molar ratio of 2:1 to obtain a phosphorus-containing diol; reacts 1,1,3,3-tetramethyldisiloxane and allyl isocyanate in a molar ratio of 1:2 to obtain a silicon-containing diisocyanate; and reacts the phosphorus-containing diol and the silicon-containing diisocyanate, which reaction process is similar to the synthesis process of polyurethane prepolymer, to obtain a product which may be terminated by a hydroxyl group or an isocyanate group, depending on the amount of reactants. When the phosphorus-containing diol and the silicon-containing diisocyanate are mixed in a molar ratio of hydroxyl group to isocyanate group of 2:1, the end group of the product is a hydroxyl group, and at this time the product has only two sites that can participate in polycondensation reaction, so the inventors try to change the reaction ratio of the two, mix the phosphorus-containing diol and the silicon-containing diisocyanate in a molar ratio of hydroxyl group to isocyanate group of 1:2 to obtain a product terminated by an isocyanate group, and then add an isocyanate group equivalent of diethanolamine to terminate, to obtain a polyol modifier containing four hydroxyl groups. More crosslinking sites make the crosslinking density of the resin greater, and the flexible siloxyl group in the polyol modifier provides good toughness and hydrophobicity for the melamine formaldehyde resin; the phenyl phosphorodichloridate contains a rigid benzene ring, so it also improves the hardness and wear resistance of the resin. In addition, the phenyl phosphorodichloridate can act as a carbon source and a phosphorus source, and the melamine formaldehyde resin contains a rich nitrogen source, and the combination of the two further improves the fire resistance of the resin. The modified melamine formaldehyde resin is used to prepare composite wood boards, effectively improving the bonding effect between the wood boards, and at the same time imparting good water resistance and fire resistance to the wood boards. The modified melamine formaldehyde resin overcomes the problem of poor toughness of conventional melamine formaldehyde resins after curing, effectively preventing the problem of wood board cracking caused by cracking of the adhesive.

[0025] When the polyol modifier is used to modify the melamine formaldehyde resin, the researchers found that too much polyol modifier will cause the modification effect to become poor, and the possible reason is that the polyol modifier contains a large amount of silicon element, and the content is too high to cause phase separation with the melamine formaldehyde resin, resulting in poor stability of the adhesive, so when the polyol modifier is added, the amount of the polyol modifier is 6-13% of the amount of melamine based on the molar fraction, and the modification effect is best. DETAILED DESCRIPTION

[0026] The materials used in the present application and their sources: paraformaldehyde from Chengdu Kelong Chemical Reagent Factory (analytical pure); flour from Huatai Biotechnology (Shaanxi) Co., Ltd., product code HTSW-0151.

[0027] Example 1: A crack-resistant composite wood board and a preparation method thereof, comprising the following steps:

[0028] Step 1:

[0029] S11: 1,4-butanediol is added to anhydrous tetrahydrofuran to obtain mixture A; phenylphosphonic dichloride is added to anhydrous tetrahydrofuran to obtain mixture B; under the environment of nitrogen, 3-aminopropyltrimethoxysilane is added to mixture A at 0°C, and after stirring uniformly, mixture B is added dropwise, the temperature of the reaction system is kept at 0°C, and after stirring for 7h, the temperature is raised to 25°C, and the stirring reaction is continued for 10h; after the reaction is completed, filtration is carried out, and the filtrate is subjected to rotary distillation, after removing the excess anhydrous tetrahydrofuran, the remaining is washed, filtered and distilled to obtain a phosphorus-containing diol; wherein 1,4-butanediol and phenylphosphonic dichloride are reacted in a molar ratio of 2:1;

[0030] S12: 1,1,3,3-tetramethyldisiloxane and Karstedt catalyst are dispersed in anhydrous toluene, stirred and heated to 80°C under the environment of nitrogen, and then allyl isocyanate is added, and the reaction is carried out for 12h to obtain a silicon-containing diisocyanate; wherein 1,1,3,3-tetramethyldisiloxane and allyl isocyanate are reacted in a molar ratio of 1:2;

[0031] S13: the phosphorus-containing diol and the silicon-containing diisocyanate are mixed in a molar ratio of hydroxyl group to isocyanate group of 1:2, and a dibutyltin dilaurate catalyst is used to react at 50°C for 3h to obtain an intermediate;

[0032] S14: the intermediate is mixed with diethanolamine at 0°C, and after incubation for 30min, the temperature is raised to 60°C and the reaction is continued for 1h to obtain a polyol modifier; wherein diethanolamine and the isocyanate group in the intermediate are reacted in a molar ratio of 1:1;

[0033] Step 2:

[0034] S21: 25% sodium methoxide solution is added to 200g of deionized water, the pH of the system is adjusted to 9.0, 50g of melamine and 36g of polyformaldehyde are added under stirring, and the stirring reaction is carried out at 75°C for 30min to obtain a hydroxymethyl melamine solution; an acid catalyst toluenesulfonic acid is added to adjust the pH of the hydroxymethyl melamine solution to 5, and a polyol modifier is added, and the amount of the polyol modifier is 6% of the amount of melamine in terms of molar fraction; after the temperature is raised to 80°C and the stirring reaction is carried out for 30min, triethylamine is added to adjust the pH of the system to 8.5, and the reaction is continued until the water solubility of the reaction solution is 2 at 25°C, and the modified melamine formaldehyde resin glue solution is obtained after discharging;

[0035] S22: ammonium chloride, flour and modified melamine formaldehyde resin glue solution are mixed and stirred to obtain a modified melamine formaldehyde adhesive; wherein the amount of ammonium chloride is 1.5% of the total mass of melamine formaldehyde resin, and the amount of flour is 16% of the total mass of melamine formaldehyde resin;

[0036] Step 3:

[0037] S31: The pine wood is rotary cut to obtain pine wood veneer with a thickness of 3 mm, and hot air drying is performed until the veneer has a moisture content of 8%;

[0038] S32: The wood chips on the surface of the pine wood veneer are removed, and the pine wood veneer is coated with modified melamine formaldehyde adhesive on both sides to obtain a coated wood board, the coated wood board having a single-side coating amount of 350 g / m 2 ; A plurality of coated wood boards are taken, stacked in turn with the textures perpendicular to each other, pre-pressed for 15 min, and then hot-pressed at 0.9 MPa and 140°C for 60 min to obtain a crack-resistant composite wood board.

[0039] Embodiment 2: A crack-resistant composite wood board and a preparation method thereof, comprising the following steps:

[0040] Step 1:

[0041] S11: 1,4-Butanediol is added to anhydrous tetrahydrofuran to obtain a mixture A; phenylphosphonic dichloride is added to anhydrous tetrahydrofuran to obtain a mixture B; under a nitrogen environment, 0°C, triethylamine is added to the mixed solution A, after stirring uniformly, the mixture B is added dropwise, the reaction system temperature is kept at 0°C, after stirring for 7.5 h, the temperature is increased to 30°C, and the stirring reaction is continued for 11 h; after the reaction is completed, filtration is performed, and the filtrate is subjected to rotary distillation, after removing the excess anhydrous tetrahydrofuran, the remaining is washed, filtered, and distilled to obtain a phosphorus-containing diol; wherein, 1,4-butanediol and phenylphosphonic dichloride are reacted in a molar ratio of 2:1;

[0042] S12: 1,1,3,3-tetramethyldisiloxane and Karstedt catalyst are dispersed in anhydrous toluene, under a nitrogen environment, stirring is performed to increase the temperature to 85°C, and then allyl isocyanate is added, and the reaction is performed for 13 h to obtain a silicon-containing diisocyanate; wherein, 1,1,3,3-tetramethyldisiloxane and allyl isocyanate are reacted in a molar ratio of 1:2;

[0043] S13: The phosphorus-containing diol and the silicon-containing diisocyanate are mixed in a molar ratio of hydroxyl group to isocyanate group of 1:2, and a dibutyltin dilaurate catalyst is used to react at 55°C for 3.5 h to obtain an intermediate;

[0044] S14: The intermediate is mixed with diethanolamine at 0°C, and after incubation for 45 min, the temperature is increased to 65°C and the reaction is continued for 1.5 h to obtain a polyol modifier; wherein, diethanolamine and the isocyanate group in the intermediate are reacted in a molar ratio of 1:1;

[0045] Step 2:

[0046] S21: A mass concentration of 25% sodium methoxide solution was added to 200 g of deionized water, the pH of the system was adjusted to 9.5, 50 g of melamine and 36 g of paraformaldehyde were added under stirring, and the mixture was stirred at 80℃ for 35 min to obtain a hydroxymethyl melamine solution; an acid catalyst toluenesulfonic acid was added to adjust the pH of the hydroxymethyl melamine solution to 5.3, a polyol modifier was added, and the amount of the polyol modifier was 9% of the amount of melamine based on the mole fraction; the temperature was raised to 85℃, and the mixture was stirred for 40 min, then triethylamine was added to adjust the pH of the system to 9, and the reaction was continued until the water dissolving multiple of the reaction solution was 2 at 25℃, and the modified melamine formaldehyde resin glue solution was obtained after discharging;

[0047] S22: Ammonium chloride, flour and modified melamine formaldehyde resin glue solution were mixed and stirred to obtain a modified melamine formaldehyde adhesive; wherein the amount of ammonium chloride was 1.5% of the total mass of melamine formaldehyde resin, and the amount of flour was 16% of the total mass of melamine formaldehyde resin;

[0048] Step 3:

[0049] S31: Pine wood was rotary cut to obtain pine veneer with a thickness of 3 mm, and hot air drying was performed until the moisture content of the veneer was 8%;

[0050] S32: The wood dust on the surface of the pine veneer was removed, and the modified melamine formaldehyde adhesive was applied on both sides of the pine veneer to obtain a glued wood board, and the single-sided glue application amount of the glued wood board was 350 g / m 2 ; A plurality of glued wood boards were taken, stacked in turn with the textures perpendicular to each other, pre-pressed for 18 min, and then hot-pressed at 1.1 MPa and 145℃ for 75 min to obtain a crack-resistant composite wood board.

[0051] Example 3: A crack-resistant composite wood board and a preparation method thereof, comprising the following steps:

[0052] Step 1:

[0053] S11: 1,4-Butanediol was added to anhydrous tetrahydrofuran to obtain a mixture A; phenylphosphoryl dichloride was added to anhydrous tetrahydrofuran to obtain a mixture B; under nitrogen environment and at 0℃, triethylamine was added to the mixed solution A, and after stirring uniformly, the mixture B was added dropwise, the reaction system was kept at 0℃, and stirring was continued for 8 h, then the temperature was raised to 35℃, and stirring was continued for 12 h; after the reaction was completed, the filtrate was filtered and rotary distilled, and after the excess anhydrous tetrahydrofuran was removed, the remaining was washed, filtered and distilled to obtain a phosphorus-containing diol; wherein the molar ratio of 1,4-butanediol to phenylphosphoryl dichloride was 2:1.

[0054] S12: 1,1,3,3-tetramethyldisiloxane and Karstedt catalyst were dispersed in anhydrous toluene, stirred and heated to 90 DEG C under nitrogen, and then allyl isocyanate was added, and the reaction was carried out for 15 h to obtain a silicon-containing diisocyanate; wherein the molar ratio of 1,1,3,3-tetramethyldisiloxane to allyl isocyanate was 1:2;

[0055] S13: the phosphorus-containing diol and the silicon-containing diisocyanate were mixed in a molar ratio of 1:2, and then reacted at 60 DEG C for 4 h to obtain an intermediate, with dibutyltin dilaurate as a catalyst;

[0056] S14: the intermediate was mixed with diethanolamine at 0 DEG C, and the reaction was carried out for 60 min, and then the temperature was increased to 70 DEG C and the reaction was continued for 2 h to obtain a polyol modifier; wherein the molar ratio of diethanolamine to isocyanate groups in the intermediate was 1:1;

[0057] Step 2:

[0058] S21: 25% sodium methoxide solution was added to 200 g of deionized water, the pH of the system was adjusted to 10.0, 50 g of melamine and 36 g of polyformaldehyde were added under stirring, and the reaction was carried out at 85 DEG C for 40 min to obtain a hydroxymethyl melamine solution; the pH of the hydroxymethyl melamine solution was adjusted to 5.5 by adding an acid catalyst toluenesulfonic acid, and then the polyol modifier was added, and the amount of the polyol modifier was 13% of the amount of melamine based on the molar fraction; the temperature was increased to 90 DEG C, and the reaction was carried out for 45 min under stirring, then triethylamine was added to adjust the pH of the system to 9.5, and the reaction was continued until the water dissolving multiple of the reaction solution was 2 at 25 DEG C, and then the modified melamine formaldehyde resin glue solution was obtained by discharging;

[0059] S22: ammonium chloride, flour and the modified melamine formaldehyde resin glue solution were mixed and stirred to obtain a modified melamine formaldehyde adhesive; wherein the amount of ammonium chloride was 1.5% of the total mass of the melamine formaldehyde resin, and the amount of flour was 16% of the total mass of the melamine formaldehyde resin;

[0060] Step 3:

[0061] S31: pine wood veneer with a thickness of 3 mm was obtained by rotary cutting, and hot air drying was carried out until the moisture content of the veneer was 8%;

[0062] S32: the wood dust on the surface of the pine wood veneer was removed, and the modified melamine formaldehyde adhesive was applied on both sides of the veneer to obtain a glued wood board, and the single-sided glue application amount of the glued wood board was 350 g / m 2 ; a plurality of glued wood boards were stacked in turn with the textures perpendicular to each other, pre-pressed for 20 min, and then hot-pressed at 1.2 MPa and 150 DEG C for 90 min to obtain a crack-resistant composite wood board.

[0063] Comparative Example 1: The melamine formaldehyde resin is not modified, and the remaining parameters are the same as in Example 1.

[0064] Step 1:

[0065] S11: A mass concentration of 25% sodium methoxide solution is added to 200 g of deionized water, the pH of the system is adjusted to 9.0, 50 g of melamine and 36 g of polyformaldehyde are added under stirring, and the mixture is stirred at 75°C for 30 min to obtain a methylol melamine solution; an acid catalyst, toluenesulfonic acid, is added to adjust the pH of the methylol melamine solution to 5, and the temperature is raised to 80°C; after stirring for 30 min, triethylamine is added to adjust the pH of the system to 8.5, and the reaction is continued until the water dissolving multiple of the reaction solution is 2 at 25°C; the product is discharged to obtain a melamine formaldehyde resin glue solution;

[0066] S12: Ammonium chloride, flour and melamine formaldehyde resin glue solution are mixed and stirred to obtain a modified melamine formaldehyde adhesive; wherein the amount of ammonium chloride is 1.5% of the total mass of the melamine formaldehyde resin, and the amount of flour is 16% of the total mass of the melamine formaldehyde resin;

[0067] Step 2:

[0068] S21: Pine wood is rotary cut to obtain pine veneer with a thickness of 3 mm, which is hot air dried to a moisture content of 8%;

[0069] S22: The wood dust on the surface of the pine veneer is removed, and the modified melamine formaldehyde adhesive is applied to both sides of the pine veneer to obtain a glued wood board, wherein the single-side glue application amount of the glued wood board is 350 g / m 2 ; A plurality of glued wood boards are taken, stacked in turn with the textures perpendicular to each other, pre-pressed for 15 min, and then hot-pressed at 0.9 MPa and 140°C for 60 min to obtain a crack-resistant composite wood board.

[0070] Comparative Example 2: A polyol modifier is prepared by mixing a phosphorus-containing diol and a silicon-containing diisocyanate at a molar ratio of hydroxyl groups to isocyanate groups of 2:1, and the remaining parameters are the same as in Example 2.

[0071] Step 1:

[0072] S11: 1,4-Butanediol is added to anhydrous tetrahydrofuran to obtain a mixture A; phenylphosphoryl dichloride is added to anhydrous tetrahydrofuran to obtain a mixture B; under a nitrogen environment at 0°C, triethylamine is added to the mixed solution A as an acid binding agent, the mixture is stirred uniformly, then the mixture B is added dropwise, the temperature of the reaction system is maintained at 0°C, and the stirring is continued for 7.5 h; the temperature is then raised to 30°C, and the stirring is continued for 11 h; after the reaction is completed, the filtrate is filtered and rotary distilled to remove excess anhydrous tetrahydrofuran; the remaining filtrate is washed, filtered and distilled to obtain a phosphorus-containing diol; wherein the molar ratio of 1,4-butanediol to phenylphosphoryl dichloride is 2:1.

[0073] S12: 1,1,3,3-tetramethyldisiloxane and Karstedt catalyst were dispersed in anhydrous toluene, stirred and heated to 85°C under nitrogen, and then allyl isocyanate was added and reacted for 13h to obtain a silicon-containing diisocyanate; wherein the molar ratio of 1,1,3,3-tetramethyldisiloxane to allyl isocyanate was 1:2;

[0074] S13: The phosphorus-containing diol and the silicon-containing diisocyanate were mixed in a molar ratio of hydroxyl group to isocyanate group of 2:1, and a dibutyltin dilaurate catalyst was used to react at 55°C for 3.5h to obtain a polyol modifier;

[0075] Step 2:

[0076] S21: A 25% mass concentration sodium methoxide solution was added to 200g of deionized water, the pH of the system was adjusted to 9.5, 50g of melamine and 36g of paraformaldehyde were added under stirring, and the mixture was stirred and reacted at 80°C for 35min to obtain a hydroxymethyl melamine solution; an acid catalyst toluenesulfonic acid was added to adjust the pH of the hydroxymethyl melamine solution to 5.3, and a polyol modifier was added; the amount of polyol modifier was 9% of the amount of melamine based on the molar fraction; after the temperature was raised to 85°C and stirred for 40min, triethylamine was added to adjust the pH of the system to 9, and the reaction was continued until the water dissolving multiple of the reaction solution was 2 at 25°C, and the modified melamine formaldehyde resin glue solution was obtained;

[0077] S22: Ammonium chloride, flour and modified melamine formaldehyde resin glue solution were mixed and stirred to obtain a modified melamine formaldehyde adhesive; wherein the amount of ammonium chloride was 1.5% of the total mass of melamine formaldehyde resin, and the amount of flour was 16% of the total mass of melamine formaldehyde resin;

[0078] Step 3:

[0079] S31: Pine wood veneer with a thickness of 3mm was obtained by rotary cutting, and hot air drying was performed until the moisture content of the veneer was 8%;

[0080] S32: The wood dust on the surface of the pine wood veneer was removed, and the modified melamine formaldehyde adhesive was applied to both sides of the veneer to obtain a glued wood board; the single-sided glue application amount of the glued wood board was 350g / m 2 ; A plurality of glued wood boards were stacked in turn with the textures perpendicular to each other, pre-pressed for 18min, and then hot-pressed at 1.1MPa and 145°C for 75min to obtain a crack-resistant composite wood board.

[0081] Comparative Example 3: The amount of polyol modifier was increased, and the other parameters were the same as those of Example 3.

[0082] Step 1:

[0083] S11: 1,4-butanediol is added to anhydrous tetrahydrofuran to obtain mixture A; phenylphosphonic dichloride is added to anhydrous tetrahydrofuran to obtain mixture B; under the environment of nitrogen, 3-ethylamine is added to the mixed solution A at 0°C, after stirring, mixture B is added dropwise, the temperature of the reaction system is kept at 0°C, and the stirring reaction is carried out for 8h, then the temperature is raised to 35°C, and the stirring reaction is continued for 12h; after the reaction is completed, filtration is carried out, and the filtrate is subjected to rotary distillation, after removing the excess anhydrous tetrahydrofuran, the remaining is washed, filtered and distilled to obtain a phosphorus-containing diol; wherein 1,4-butanediol and phenylphosphonic dichloride are reacted in a molar ratio of 2:1;

[0084] S12: 1,1,3,3-tetramethyldisiloxane and Karstedt catalyst are dispersed in anhydrous toluene, stirred and heated to 90°C under the environment of nitrogen, and then allyl isocyanate is added, and the reaction is carried out for 15h to obtain a silicon-containing diisocyanate; wherein 1,1,3,3-tetramethyldisiloxane and allyl isocyanate are reacted in a molar ratio of 1:2;

[0085] S13: the phosphorus-containing diol and the silicon-containing diisocyanate are mixed in a molar ratio of hydroxyl group to isocyanate group of 1:2, and a dibutyltin dilaurate catalyst is used to react at 60°C for 4h to obtain an intermediate;

[0086] S14: the intermediate is mixed with diethanolamine at 0°C, and after incubation for 60min, the temperature is raised to 70°C for continuous reaction for 2h to obtain a polyol modifier; wherein diethanolamine and the isocyanate group in the intermediate are reacted in a molar ratio of 1:1;

[0087] Step 2:

[0088] S21: 25% sodium methoxide solution is added to 200g of deionized water, the pH of the system is adjusted to 10.0, 50g of melamine and 36g of polyformaldehyde are added under stirring, and the stirring reaction is carried out at 85°C for 40min to obtain a hydroxymethyl melamine solution; the pH of the hydroxymethyl melamine solution is adjusted to 5.5 by adding toluenesulfonic acid as an acid catalyst, and the polyol modifier is added, and the amount of the polyol modifier is 20% of the amount of melamine in terms of molar fraction; after the temperature is raised to 90°C and the stirring reaction is carried out for 45min, triethylamine is added to adjust the pH of the system to 9.5, and the reaction is continued until the water solubility of the reaction solution is 2 at 25°C, and the modified melamine formaldehyde resin glue solution is obtained after discharging;

[0089] S22: ammonium chloride, flour and modified melamine formaldehyde resin glue solution are mixed and stirred to obtain a modified melamine formaldehyde adhesive; wherein the amount of ammonium chloride is 1.5% of the total mass of melamine formaldehyde resin, and the amount of flour is 16% of the total mass of melamine formaldehyde resin;

[0090] Step 3:

[0091] S31: The pine wood is rotary cut to obtain pine veneer with a thickness of 3 mm, and hot air drying is performed until the veneer has a moisture content of 8%;

[0092] S32: The wood chips on the surface of the pine veneer are removed, and the modified melamine formaldehyde adhesive is applied on both surfaces to obtain a glued wood board, wherein the amount of the adhesive applied on one surface of the glued wood board is 350 g / m 2 ; a plurality of glued wood boards are taken, stacked in turn with the textures perpendicular to each other, pre-pressed for 20 min, and then hot-pressed at 1.2 MPa and 150°C for 90 min to obtain a crack-resistant composite wood board.

[0093] Experiment:

[0094] The composite wood boards in Examples 1-3 and Comparative Examples 1-3 are subjected to performance testing. Among them, the bonding strength between two pine veneers is tested according to the standard GB / T 15036.2-2018; the static water contact angle is tested by a contact angle tester to represent the hydrophilic and hydrophobic properties; and the ignition time of the wood surface is tested according to the standard IS0 5660-1:2002.

[0095] In order to more intuitively test the wear resistance and toughness of the adhesive, the base paper (white base paper with a specification of 80 g / m 2 , Changzhou Oubai Decorative Material Co., Ltd.) is cut into a standard size paper sample with a size of 30 cm x 30 cm, and then placed flat in the adhesive for 2 min. After taking it out, a round iron rod is continuously rolled back and forth on its surface to squeeze out the excess resin on the surface, so as to ensure that the impregnation amount of the paper is constant at 200 g / m 2 . The paper is naturally air-dried; the wear resistance is tested according to the method 4.44 in GB / T 17657-2013; the sample is cut into a long strip with a size of 250 mm x 10 mm, and then placed in a constant temperature and humidity box with a temperature of 25°C and a humidity of 35% for 24 h of equilibrium treatment; a tensile testing machine is used for testing, the tensile rate of the instrument is 1 mm / min, the maximum tensile breaking force is measured, and the formula R=F / b is used, wherein F is the maximum tensile breaking force (N), b is the sample width (cm), and R is the tensile strength (kN / m).

[0096]

[0097] Conclusion: The data of Examples 1-3 show that the composite wood board prepared by the present application has good performance. The data of Example 1 and Comparative Example 1 show that after adding the polyol modifier, the performance of the melamine formaldehyde resin is obviously improved. The data of Example 2 and Comparative Example 2 show that because the polyol modifier in Comparative Example 2 has fewer reaction sites, the effect after modification is poorer than that of Example 2. The data of Example 3 and Comparative Example 3 show that because the polyol modifier contains more silicon elements, too much use will cause poor compatibility of the melamine formaldehyde resin, phase separation occurs, and thus adverse effects are produced.

[0098] All other examples obtained by those of ordinary skill in the art based on the examples in the present application without making creative efforts are within the scope of protection of the present application.

[0099] Finally, it should be noted that: the above only describes the preferred embodiments of the present application and is not intended to limit the present application. Although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions recorded in the foregoing embodiments or make equivalent replacements to some technical features. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the scope of protection of the present application.

Claims

1. A method for preparing a crack-resistant composite wood board, characterized in that: Includes the following steps: Step 1: Rotary cut the pine wood to obtain pine veneer, and dry it with hot air for later use; Step 2: Remove the sawdust from the surface of the pine veneer, and apply modified melamine-formaldehyde adhesive to both sides to obtain glued wood boards; take several glued wood boards, stack them in order with the grain perpendicular to each other, pre-press for 15-20 minutes, then hot-press to bond them together, and cool to obtain crack-resistant composite wood boards. The modified melamine-formaldehyde adhesive is prepared by mixing ammonium chloride, flour, and modified melamine-formaldehyde resin solution, and stirring to obtain the adhesive; wherein the amount of ammonium chloride is 1-2% of the total mass of melamine-formaldehyde resin, and the amount of flour is 12-18% of the total mass of melamine-formaldehyde resin; The preparation method of the modified melamine-formaldehyde resin adhesive is as follows: Add 25% sodium methoxide solution to 200-220 parts by weight of deionized water to adjust the pH of the system to 9.0-10.

0. Add 50-60 parts by weight of melamine and 36-40 parts by weight of paraformaldehyde while stirring. Stir and react at 75-85°C for 30-40 minutes to obtain hydroxymethyl melamine solution. Add toluenesulfonic acid as an acid catalyst to adjust the pH of the hydroxymethyl melamine solution to 5-5.

5. Add polyol modifier, the amount of which is 6-13% of the amount of melamine by molar. Heat to 80-90°C and stir for 30-45 minutes. Add triethylamine to adjust the pH of the system to 8.5-9.

5. Continue the reaction until the water solubility ratio of the reaction solution at 25°C is 2-2.

5. Discharge the product to obtain modified melamine-formaldehyde resin solution. The preparation method of the polyol modifier includes the following steps: S1: 1,4-Butanediol was added to anhydrous tetrahydrofuran to obtain mixture A; phenylphosphodichloro was added to anhydrous tetrahydrofuran and mixed to obtain mixture B; under nitrogen atmosphere and at 0°C, triethylamine, an acid-binding agent, was added to mixture A and stirred until homogeneous. Then, mixture B was added dropwise, and the reaction system temperature was maintained at 0°C. After stirring for 7-8 hours, the temperature was raised to 25-35°C and the reaction was continued for 10-12 hours; after the reaction was completed, the mixture was filtered, and the filtrate was subjected to rotary distillation to remove excess anhydrous tetrahydrofuran. The remaining filtrate was washed, filtered, and distilled to obtain a phosphorus-containing diol; 1,1,3,3-tetramethyldisiloxane and Karstedt catalyst were dispersed in anhydrous toluene, and under nitrogen atmosphere, the temperature was raised to 80-90°C. Allyl isocyanate was added while maintaining the temperature, and the reaction was carried out for 12-15 hours to obtain a silicon-containing diisocyanate; S2: A phosphorus-containing diol and a silicon-containing diisocyanate are mixed and reacted at 50–60 °C for 3–4 h with dibutyltin dilaurate as a catalyst to obtain an intermediate; S3: The intermediate is mixed with diethanolamine at 0–5 °C, and the mixture is kept at this temperature for 30–60 min, then heated to 60–70 °C and reacted for another 1–2 h to obtain a polyol modifier.

2. The method for preparing a crack-resistant composite wood board according to claim 1, characterized in that: In step 1, the pine veneer thickness is 2-5 mm; it is dried with hot air until the veneer moisture content is 6-8%.

3. The method for preparing a crack-resistant composite wood board according to claim 1, characterized in that: In step 2, the amount of glue applied to one side of the glued wood board is 300-350 g / m². 2 .

4. The method for preparing a crack-resistant composite wood board according to claim 1, characterized in that: In step 2, the hot-pressing pressure is 0.9–1.2 MPa, the temperature is 140–150 °C, and the time is 60–90 min.

5. The method for preparing a crack-resistant composite wood board according to claim 1, characterized in that: In S1, 1,4-butanediol and phenylphosphodichloro react in a molar ratio of 2:1; 1,1,3,3-tetramethyldisiloxane and allyl isocyanate react in a molar ratio of 1:

2.

6. The method for preparing a crack-resistant composite wood board according to claim 1, characterized in that: In S2, phosphorus-containing diol and silicon-containing diisocyanate are mixed at a molar ratio of hydroxyl to isocyanate group of 1:

2.

7. The method for preparing a crack-resistant composite wood board according to claim 1, characterized in that: In S3, diethanolamine reacts with the isocyanate group in the intermediate at a molar ratio of 1:

1.

8. The crack-resistant composite wood board prepared by any one of claims 1 to 7.

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