Hard sheet material and preparation method thereof, ultra-thin fiberboard

Abstract

The present application is applicable to the field of material technology and provides a hard sheet material and a preparation method thereof, as well as an ultra-thin fiberboard. The present application uses a special melamine formaldehyde resin and a water-based hot melt adhesive as the main adhesive, and uses glass fiber non-woven fabric and glass cloth as the base material. The glass fiber non-woven fabric and glass cloth are impregnated with the adhesive and then dried to form a semi-cured sheet, which is then pressed into a board according to a specific combination method. The resulting hard sheet material is closer to transparent in color, has better aesthetics, and has a low water absorption thickness expansion rate. At the same time, using glass cloth as a balance can avoid the inconsistency of thermal expansion coefficients between different layers that may cause the board to crack. The glass fiber non-woven fabric and glass cloth mixed solution used has a small specific surface area, can reduce the amount of glue used, and has low formaldehyde emission. The ultra-thin fiberboard prepared by the present application has an internal bonding strength of more than 1.2MPa, and can meet the Class II plywood standard after impregnation and peeling. The 24h water absorption thickness expansion rate is less than 5%.

Description

Technical Field

[0001] The present application belongs to the field of material technology, and in particular relates to a hard sheet material and a preparation method thereof, and an ultra-thin fiberboard. Background Art

[0002] Currently, there are three main types of flooring substrates on the market: fiberboard (wood fibers bonded together with glue), plywood (wood veneer bonded together with glue), and solid wood. Plywood is popular among consumers due to its high cost-effectiveness. After the plywood substrate is prepared, a layer of impregnated paper impregnated with melamine glue is applied to the surface. This impregnated paper is in a semi-cured state and then cured by hot pressing at high temperature and high pressure. Because the surface of the plywood substrate is not smooth enough and direct pressing can produce ribs, which affects the overall aesthetics, it is necessary to first press the impregnated paper and ultra-thin fiberboard (approximately 1mm thick) together, and then glue the ultra-thin fiberboard and plywood substrate together.

[0003] However, the use of existing ultra-thin fiberboard has the following disadvantages: ① Since the main formaldehyde-containing urea-formaldehyde glue or phenol-formaldehyde glue used is easy to cause the overall formaldehyde content of the board to exceed the standard; ② Because ultra-thin fiberboard is a fiberboard after all, it is easy to cause the water absorption thickness expansion rate to be too high after contact with water, affecting the overall performance indicators; ③ When observed from the side, the addition of a layer of brown fiberboard in the middle of the plywood affects the overall aesthetics; ④ It requires multiple pressings through a continuous press, which is costly and complicated.

[0004] It can be seen that the existing ultra-thin fiberboard has problems such as excessive formaldehyde, high water absorption thickness expansion rate, complex production process and poor aesthetics. Summary of the Invention

[0005] The purpose of the embodiments of the present application is to provide a method for preparing a hard sheet, aiming to solve the problems of existing ultra-thin fiberboards such as excessive formaldehyde, high water absorption thickness expansion rate, complex procedures and poor aesthetics.

[0006] The embodiment of the present application is implemented as follows: a method for preparing a hard sheet material, comprising:

[0007] Add a polyol, a crosslinking agent, and isophorone diisocyanate in a mass ratio of (35-40):(2-10):(16-40) to a reaction vessel, heat the mixture to 60-70° C., stir and mix thoroughly, then add a catalyst, heat the mixture to 75-90° C., continue the reaction for 1-2 hours, add 2,2-dimethylolpropionic acid and 1,4-butanediol, continue the reaction for 2-3 hours, cool the mixture to 40-45° C., then sequentially add triethylamine, deionized water, and ethylene-acrylic acid copolymer and mix to obtain a water-based hot melt adhesive;

[0008] Add formaldehyde, water, and a modifier to a reaction vessel, adjust the pH to 9.0-9.5, add melamine, and when the temperature reaches 70-90° C., add caprolactam. Keep the mixture warm at 90-94° C. for reaction until the water solubility ratio of the mixture reaches 1:(1.8-2.0). When cooling, adjust the pH to 9.0-9.5, cool to 30-40° C., add a coupling agent, and mix to obtain a melamine formaldehyde resin.

[0009] impregnating glass cloth with the aqueous hot melt adhesive and impregnating glass fiber non-woven fabric with the melamine formaldehyde resin, and drying to obtain glass cloth prepregs and glass fiber non-woven fabric prepregs, respectively;

[0010] The glass fiber non-woven fabric prepreg is arranged in the order of an upper layer and a glass cloth prepreg is arranged in the lower layer, and a one-step hot pressing process is performed to obtain a hard sheet.

[0011] Another object of an embodiment of the present application is to provide a hard sheet, which is prepared by the above-mentioned hard sheet preparation method.

[0012] Another purpose of an embodiment of the present application is an ultra-thin fiberboard, which is obtained by hot pressing a plywood substrate, the above-mentioned hard sheet, a printing layer impregnated paper, and a wear-resistant layer impregnated paper in order from bottom to top, and then cooling them by cold pressing.

[0013] The preparation method of the hard sheet provided in the embodiment of the present application uses modified low-formaldehyde melamine formaldehyde resin and water-based hot melt adhesive as the main adhesive, glass fiber non-woven fabric and glass cloth as the base material, impregnates the glass fiber non-woven fabric and glass cloth with the adhesive and then dries to form a semi-cured sheet, which is then pressed into a board according to a specific combination method. The obtained hard sheet has the following characteristics: ① Since glass fiber is used as the main material, the color is closer to transparent and it will be more beautiful; ② Since glass fiber lacks a large number of hydroxyl groups on wood cellulose, it will not easily absorb water, resulting in an excessively high water absorption thickness expansion rate; ③ The glass fiber non-woven fabric and glass cloth mixed scheme has a small specific surface area, which can reduce the amount of glue used and avoid excessive formaldehyde release affecting the overall formaldehyde release of the board.

[0014] In addition, the embodiments of the present application only require the plywood, hard sheet, printed layer impregnated paper, and wear-resistant layer impregnated paper to be arranged smoothly and then pressed together using a conventional hot press, saving a gluing and pressing process. The glass fiber non-woven fabric uses a modified melamine formaldehyde resin, which can produce a semi-cured sheet with a relatively uniform expansion rate. The surface of the hard sheet formed after curing is smoother and flatter, and it is not easy to form an uneven bond with the printed layer impregnated paper. The glass cloth is impregnated with a water-based hot melt adhesive, which can be heated, melted, and then solidified after cooling. At the same time, the glass cloth can be used as a balance to avoid cracking caused by different thermal expansion coefficients between different layers. The ultra-thin fiberboard prepared by this application can achieve an internal bonding strength of more than 1.2MPa, and the impregnation peeling can meet the Class II plywood standard. The 24-hour water absorption thickness expansion rate is less than 5%. DETAILED DESCRIPTION

[0015] In order to make the purpose, technical solutions and advantages of this application more clear, the following further describes this application in detail with reference to the embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0016] The current technology is to stick a layer of printing paper and wear-resistant paper on the surface of the board. Both types of paper are impregnated with melamine formaldehyde resin and then dried into semi-cured sheets, and then further cured into fully cured sheets through the high temperature of a hydraulic press. Because plywood cannot be pressed directly, otherwise moiré patterns are easily produced, the industry has added a layer of ultra-thin fiberboard. Therefore, ultra-thin fiberboard is a very special existence in this industry. At present, continuous presses are mainly used for paving production. When ultra-thin fiberboard with a thickness of less than 1mm needs to be produced, it will be very difficult, because the fiberboard production line can only use urea-formaldehyde resin and other glues with high formaldehyde content to mix with wood fibers for paving and hot pressing, which has high investment costs. At the same time, ultra-thin fiberboard is too thin to be prepared into formaldehyde-free products using MDI glue. The thinner it is, the more difficult it is to control the paving, brushing and pre-curing layer. However, the embodiment of the present application uses a special water-based hot melt adhesive and melamine formaldehyde resin, which can be dried normally to form a semi-cured sheet, and can be pressed and pasted once to prepare an ultra-thin fiberboard with controllable thickness and formaldehyde release. The equipment only needs to use the current conventional multi-layer hot press. The process is simple and flexible. The product is light-colored and will not be combined with plywood to be unsightly. There is no need to apply another layer of glue on the plywood to increase the formaldehyde industry and add a hot pressing process.

[0017] Specifically, the present invention provides a method for preparing a hard sheet, comprising the following steps:

[0018] Step S1: Add a polyol, a crosslinker, and isophorone diisocyanate in a mass ratio of (35-40): (2-10): (16-40) to a reaction vessel, heat to 60-70°C, stir and mix evenly, then add a catalyst, heat to 75-90°C and continue to react for 1-2 hours, then add 2,2-dihydroxymethylpropionic acid and 1,4-butanediol and continue to react for 2-3 hours. After cooling to 40-45°C, triethylamine, deionized water, and ethylene-acrylic acid copolymer are added in sequence and mixed to obtain a water-based hot melt adhesive.

[0019] Optionally, the polyol, cross-linker and isophorone diisocyanate IPDI dehydrated at 110-120° C. are added to a three-necked flask equipped with a stirrer and a reflux condenser in a ratio of 35-40:2-10:16-40 by mass, the mixture is heated to 60-70° C. and stirred to mix evenly, and then an appropriate amount of dibutyltin dilaurate catalyst (the addition amount is conventionally 0.2%-0.4%) is added dropwise and the temperature is raised to 75-90° C. for reaction. After 1-2 hours of reaction, 4-7 general parts of 2,2-dihydroxymethylpropionic acid and 5-7 parts of 1,4-butanediol are added respectively, and the reaction is continued for 2-3 hours. A small amount of acetone is added as a viscosity adjustment (the viscosity is generally adjusted to within the range of 2000-3000 MPa.s). The reaction solution is then cooled to 40-45°C, 3-5 parts of triethylamine are added to react for 10-30 minutes, 110-130 parts of deionized water are added under high-speed stirring and dispersed for 30-60 minutes, and ethylene-acrylic acid copolymer (EAA emulsion) is added according to the mass ratio of polyurethane prepolymer (water-based polyurethane synthesized by the reaction of the aforementioned polyol and isocyanate), deionized water, and EAA emulsion of 3: (1-4): 1 and mixed to obtain a water-based hot melt adhesive emulsion.

[0020] Wherein, the polyol is one of poly(1,4-butylene adipate), polyethylene adipate, and polytetramethylene glycol monoethylene glycol ether.

[0021] Wherein, the cross-linking agent is one or more of polypropylene oxide ether triol, trimethylolpropane, trimethylolpropane triglycidyl ether, and trimethylolpropane trimethacrylate; more preferably, it is trimethylolpropane glycidyl ether.

[0022] The cross-linking agent has an average molecular weight of 2000, 500 or a mixture of several of them.

[0023] It is worth noting that the selection of polyol and cross-linking agent has a great influence on the performance of the prepared ultra-thin fiberboard. It is difficult to achieve the strength and melting temperature required by this application by using other conventional polyester polyols or polyether polyols, and they may even fail to pass the immersion peeling test.

[0024] In addition, the present application introduces polyoxypropylene ether triol in the water-based hot melt adhesive, and controls the overall hardness and degree of cross-linking by introducing epoxy groups. Traditional water-based hot melt adhesives are relatively soft and cannot meet the requirements for preparing ultra-thin fiberboards; secondly, the EAA resin emulsion is mixed to enable it to participate in the overall cross-linking reaction. The EAA resin has good bonding to the glass fiber and can be heat-sealed and melted at a lower temperature. Therefore, it can achieve 120°C hot pressing molding in the artificial board industry, while other industries use 150°C high-temperature hot pressing. That is, after modification by this application, it can better adapt to the process requirements of this industry.

[0025] Step S2: adding formaldehyde, water, and a modifier to a reaction container, adjusting the pH to 9.0-9.5, adding melamine, and adding caprolactam when the temperature reaches 70-90° C., and carrying out a heat-insulating reaction at 90-94° C. until the water-soluble ratio of the mixture reaches 1:(1.8-2.0). When cooling, adjusting the pH to 9.0-9.5, cooling to 30-40° C., and adding a coupling agent for mixing to obtain a melamine formaldehyde resin.

[0026] Optionally, 110-130 parts of 30-40% concentration formaldehyde, 50-80 parts of water, and 8-15 parts of a modifier are added to a reactor, the pH value is adjusted to 9.0-9.5 with caustic soda, and then 110-130 parts of melamine are added. When the temperature reaches 70-90°C, 2-5 parts of caprolactam are added, and then the temperature is kept at 90-94°C. The reaction is kept for about 110-150 minutes, and the water solubility is measured. The water solubility of the glue is required to be 1:(1.8-2.0). Caustic soda is added during cooling to adjust the pH to 9.0-9.5. The temperature is cooled to 30-40°C. After the glue preparation is completed, 1-10 parts of a coupling agent are added and mixed.

[0027] The modifiers include a brightener, a toughening agent, and a release agent, which are added in 3-10 parts by weight, 2-10 parts by weight, and 2-10 parts by weight, respectively, to improve toughness and achieve rapid continuous curing and demolding. Optionally, the brightener, toughening agent, and release agent used in the examples of this application were purchased from WIZ Magic Chemicals of Italy, with the models ALTON PLAST58, ALTON 856, and ALTON HM 1010, respectively.

[0028] Wherein, the coupling agent is 560 silane coupling agent or 570 coupling agent or a mixture of several thereof.

[0029] It is noteworthy that the examples of this application, by introducing caprolactam into the synthesis of melamine-formaldehyde resin, can improve the toughness and impact resistance of the melamine-formaldehyde resin, resulting in better mechanical strength in the molded product, while also reducing formaldehyde release during the resin curing process. Furthermore, corresponding modifiers, modification aids, and coupling agents are used to enhance the desired properties. Conventional melamine-formaldehyde resin is typically modified with dioctyl phthalate or white sugar, but caprolactam offers relatively better performance and avoids the whitening problem associated with pressing.

[0030] Step S3: impregnating the glass cloth with the water-based hot melt adhesive and impregnating the glass fiber non-woven fabric with the melamine formaldehyde resin, and drying them to obtain a glass cloth prepreg and a glass fiber non-woven fabric prepreg, respectively.

[0031] In this embodiment, glass cloth is impregnated with water-based hot melt adhesive and dried to obtain a glass cloth prepreg; glass fiber non-woven fabric is impregnated with melamine formaldehyde resin and dried to obtain a glass fiber non-woven fabric prepreg.

[0032] The glass cloth has a weight of 100 g / m 2 , woven in a horizontal and vertical interlaced manner; the quantitative weight of the glass fiber non-woven fabric is 80g / m 2 .

[0033] Among them, a drying tunnel is used for drying, the drying tunnel temperature is 110-140°C, and the operating speed is 40-60m / min.

[0034] Among them, the glass fiber non-woven fabric impregnated with melamine formaldehyde resin is controlled to have a pre-curing degree of 5%-15% after drying in the drying oven to avoid over-curing affecting subsequent processes.

[0035] Step S4: Arranging the glass fiber non-woven fabric prepreg in the upper layer and the glass cloth prepreg in the lower layer in this order and performing a one-step hot pressing treatment to obtain a hard sheet.

[0036] Among them, in the one-step hot pressing treatment, a hot pressing machine is used for hot pressing, the hot pressing temperature is 110-130°C, the hot pressing time is 1-5min, and the hot pressing pressure is 1-5mpa.

[0037] The embodiment of the present application also provides an ultra-thin fiberboard, which is obtained by hot pressing a plywood substrate, the above-mentioned hard sheet, a printing layer impregnated paper, and a wear-resistant layer impregnated paper in order from bottom to top, and then cooling them by cold pressing.

[0038] Among them, a hot press is used for one-time hot pressing and then quickly transferred to the cold pressing zone for cooling. The hot press temperature is 180℃-210℃, the time is 15-30s, the pressure is 1-5MPa, the cold pressing zone pressure is 1-5MPa, the temperature is room temperature, and the time is 10-40s.

[0039] The present application is described in detail below with reference to specific examples, as shown below. Unless otherwise specified, the experimental methods used in the following examples are conventional methods; the materials and reagents used are all commercially available unless otherwise specified.

[0040] Example 1: Preparation of hard sheet and ultra-thin fiberboard

[0041] ①First, the synthesis of water-based hot melt adhesive

[0042] After dehydration at 110°C, poly(1,4-butylene adipate), poly(propylene oxide ether triol) and isophorone diisocyanate (IPDI) were added to a three-necked flask equipped with a stirrer and a reflux condenser in a ratio of 40:5:16 by mass. The mixture was heated to 70°C and stirred for uniform mixing. An appropriate amount of dibutyltin dilaurate catalyst was added dropwise and the temperature was raised to 90°C for reaction. After 2 hours of reaction, 5 parts of 2,2-dihydroxymethylpropionic acid and 5 parts of 1,4-butanediol were added respectively. The reaction was continued for 2 hours, and a small amount of acetone was added for viscosity adjustment. The reaction solution was then cooled to 45°C, 3 parts of triethylamine were added and reacted for 30 minutes. 110 parts of deionized water were added and dispersed for 30 minutes under high-speed stirring. EAA emulsion was added and mixed in a mass ratio of 3:1 of polyurethane prepolymer to EAA emulsion to obtain a water-based hot melt adhesive emulsion.

[0043] ②Synthesis of melamine formaldehyde resin

[0044] First, add 110 parts of 37% concentration formaldehyde, 80 parts of water, 3 parts of brightener, 2 parts of toughening agent and 3 parts of release agent into the reactor, adjust the pH value to 9.5 with caustic soda, then add 120 parts of melamine, add 2 parts of caprolactam when the temperature reaches 90℃, then keep it at 90℃, and keep it warm for about 110 minutes. Measure the water solubility ratio, which is required to be 1:2.0. Add caustic soda when cooling, adjust the pH to 9.0, cool to 40℃, and the glue making is completed. Then add 2 parts of coupling agent 570 and mix.

[0045] ③ Use water-based hot melt adhesive as the water-based impregnation liquid to impregnate only the glass cloth, and use melamine formaldehyde resin as the water-based impregnation liquid to impregnate only the glass fiber non-woven fabric. After impregnation, use a drying tunnel for drying at a drying tunnel temperature of 110°C and a running speed of 60m / min.

[0046] ④ Place the impregnated prepreg in the order of glass cloth prepreg on the bottom layer and glass fiber non-woven fabric on the top layer, and use a hot press to hot press to form a hard sheet. The hot pressing temperature is 110℃, the hot pressing time is 5min, and the hot pressing pressure is 3Mpa.

[0047] ⑤ Arrange the plywood substrate, hard sheet, printed layer impregnated paper and wear-resistant layer impregnated paper in order from bottom to top, use a hot press to hot press them once, then quickly transfer them to the cold pressing area to cool down, and then take them out. The hot press temperature is 180℃, the time is 30s, the pressure is 3Mpa, the cold pressing area pressure is 3Mpa, the temperature is room temperature, and the time is 20s.

[0048] Example 2: Preparation of hard sheet and ultra-thin fiberboard

[0049] ①First, the synthesis of water-based hot melt adhesive

[0050] After dehydration at 120°C, polytetramethylene glycol ether, trimethylolpropane trimethacrylate, and isophorone diisocyanate (IPDI) were added to a three-necked flask equipped with a stirrer and a reflux condenser in a ratio of 35:4:16 by mass. The mixture was heated to 70°C and stirred for uniform mixing. An appropriate amount of dibutyltin dilaurate catalyst was added dropwise and the temperature was raised to 75°C for reaction. After 2 hours of reaction, 4 parts of 2,2-dimethylolpropionic acid and 5 parts of 1,4-butanediol were added respectively. The reaction was continued for 3 hours, and a small amount of acetone was added for viscosity adjustment. The reaction solution was then cooled to 40°C, 3 parts of triethylamine were added, and the mixture was reacted for 30 minutes. 110 parts of deionized water were added and dispersed under high-speed stirring for 30 minutes. EAA emulsion was added and mixed in a mass ratio of 3:1 of polyurethane prepolymer to EAA emulsion to obtain a water-based hot melt adhesive emulsion.

[0051] ②Synthesis of melamine formaldehyde resin

[0052] First, add 130 parts of 40% concentration formaldehyde, 80 parts of water, 3 parts of brightener, 2 parts of toughening agent and 3 parts of release agent into the reactor, adjust the pH value to 9.0 with caustic soda, then add 110 parts of melamine, add 2 parts of caprolactam when the temperature reaches 70℃, then keep warm at 90℃, and keep warm for about 150 minutes. Measure the water solubility ratio, which is required to be 1:2.0. Add caustic soda when cooling, adjust the pH to 9.0, cool to 40℃, and complete the glue making. Then add 3 parts of coupling agent 570 and mix.

[0053] ③ Use water-based hot melt adhesive as the water-based impregnation liquid to impregnate only the glass cloth, and use melamine formaldehyde resin as the water-based impregnation liquid to impregnate only the glass fiber non-woven fabric. After impregnation, use a drying tunnel for drying at a drying tunnel temperature of 140°C and a running speed of 60m / min.

[0054] ④ Place the impregnated prepreg in the order of glass cloth prepreg on the bottom layer and glass fiber non-woven fabric on the top layer, and use a hot press to hot press to form a hard sheet. The hot pressing temperature is 130℃, the hot pressing time is 1min, and the hot pressing pressure is 1Mpa.

[0055] ⑤ Arrange the plywood substrate, hard sheet, printed layer impregnated paper and wear-resistant layer impregnated paper in order from bottom to top, use a hot press to hot press them once, then quickly transfer them to the cold pressing area to cool down, and then take them out. The hot press temperature is 210℃, the time is 30s, the pressure is 5Mpa, the cold pressing area pressure is 3Mpa, the temperature is room temperature, and the time is 10s.

[0056] The hard sheet and ultra-thin fiberboard prepared in Examples 1-2 were subjected to performance tests using GB / T 17657-2013 and GB / T 11718-2021 standards. The test results showed that the internal bonding strength reached 1.42 MPa, the immersion peeling reached the Class II plywood standard without debonding, the 24-hour water absorption thickness expansion rate reached 3.7%, and the formaldehyde value was 0.022 mg / m 3 .

[0057] In addition, under the same conditions, a conventional ultra-thin fiberboard with a thickness of 1 mm on the market was pressed with impregnated paper on a 9 mm substrate at the same time as the hard sheet prepared in the embodiment of the present application. After one week, the formaldehyde emission values ​​of the two were 0.35 mg / L and 0.23 mg / L, respectively. That is, the formaldehyde emission of the hard sheet prepared in the present application was significantly lower than that of the conventional ultra-thin fiberboard on the market.

[0058] The following are some modification experiments on water-based hot melt adhesives during the early development of the hard sheet material of this application, as follows:

[0059] Comparative Example 1: Preparation of water-based hot melt adhesive

[0060] Dehydrated polyethylene adipate and toluene diisocyanate (TDI) at 120°C were added in a ratio of 35:16 by mass to a three-necked flask equipped with a stirrer and reflux condenser. The mixture was heated to 60°C and stirred until uniformly mixed. An appropriate amount of dibutyltin dilaurate catalyst was then added dropwise, and the temperature was raised to 75°C for reaction. After one hour of reaction, 4.5 parts of 2,2-dihydroxymethylpropionic acid and 5.5 parts of 1,4-butanediol were added, respectively. The reaction continued for another two hours, with a small amount of acetone added to adjust the viscosity. The reaction solution was then cooled to 40°C, and 4.5 parts of triethylamine were added for 10 minutes. Finally, 110 parts of deionized water were added and dispersed for 30 minutes under high-speed stirring.

[0061] Experimental results: The product is prone to yellowing (TDI is not resistant to yellowing), and the TDI experimental synthesis process is difficult to control. The immersion peel strength does not meet the standard, and cracking occurs when boiled in water at 63°C.

[0062] Comparative Example 2: Preparation of water-based hot melt adhesive

[0063] Polyethylene adipate and isophorone diisocyanate (IPDI), dehydrated at 120°C, were added in a ratio of 35:16 by mass to a three-necked flask equipped with a stirrer and reflux condenser. The mixture was heated to 60°C and stirred until uniformly mixed. An appropriate amount of dibutyltin dilaurate catalyst was then added dropwise, and the temperature was raised to 75°C for reaction. After one hour of reaction, 4.5 parts of 2,2-dihydroxymethylpropionic acid and 5.5 parts of 1,4-butanediol were added, respectively. The reaction continued for another two hours, with a small amount of acetone added to adjust the viscosity. The reaction solution was then cooled to 40°C, and 4.5 parts of triethylamine were added for 10 minutes. Finally, 110 parts of deionized water were added and dispersed for 30 minutes under high-speed stirring.

[0064] Experimental results: The experiment was better controlled and yellowing was no longer likely to occur, but the immersion peel strength still did not meet the standard, and cracking occurred when boiled in water at 63°C. Subsequent research will be conducted to adjust the type of polyol.

[0065] Comparative Example 3: Preparation of water-based hot melt adhesive

[0066] After dehydration at 120°C, poly(1,4-butylene adipate) and isophorone diisocyanate (IPDI) were added in a 35:16 mass ratio to a three-necked flask equipped with a stirrer and reflux condenser. The mixture was heated to 60°C and stirred until uniform. An appropriate amount of dibutyltin dilaurate catalyst was then added dropwise, and the temperature was raised to 75°C for reaction. After 1 hour of reaction, 4.5 parts of 2,2-dihydroxymethylpropionic acid and 5.5 parts of 1,4-butanediol were added, and the reaction continued for 2 hours. A small amount of acetone was added to adjust the viscosity. The reaction solution was then cooled to 40°C, and 4.5 parts of triethylamine were added for 10 minutes. Then, 110 parts of deionized water were added and dispersed for 30 minutes under high-speed stirring.

[0067] Experimental results: The experiment is better controlled and less prone to yellowing. The impregnation peeling meets the standard and the internal bonding strength meets the standard. However, after impregnation with the glass fiber non-woven fabric, it was found that the water absorption thickness expansion rate was greater than 6%. The type and dosage of the chain extender will be adjusted in the future.

[0068] Comparative Example 4: Preparation of water-based hot melt adhesive

[0069] Based on Comparative Example 3, only the type or amount of the chain extender was adjusted, specifically: the chain extender was replaced from DMPA (2,2-dihydroxymethylpropionic acid) to sodium ethylenediamineethanesulfonate (AAS-Na), or the amount of DMPA was halved.

[0070] Experimental results: After replacing DMPA with sodium ethylenediaminesulfonate (AAS-Na), the water absorption thickness expansion rate was greater than 7%, which actually increased; while the amount of DMPA was halved, the experiment could not be emulsified due to the reduction of hydrophilic groups.

[0071] Comparative Example 5: Preparation of water-based hot melt adhesive

[0072] Based on Comparative Example 3, a crosslinking agent was added. Specifically, poly(1,4-butylene adipate), poly(propylene oxide ether triol), and isophorone diisocyanate (IPDI), dehydrated at 120°C, were added in a ratio of 35:2:16 by mass to a three-necked flask equipped with a stirrer and a reflux condenser. The mixture was heated to 60°C and stirred for uniform mixing. An appropriate amount of dibutyltin dilaurate catalyst was then added dropwise, and the temperature was raised to 75°C for reaction. After one hour of reaction, 4.5 parts of 2,2-dimethylolpropionic acid and 5.5 parts of 1,4-butanediol were added, respectively. The reaction continued for another two hours, and a small amount of acetone was added to adjust the viscosity. The reaction solution was then cooled to 40°C, and 4.5 parts of triethylamine were added for 10 minutes. Finally, 110 parts of deionized water were added and dispersed for 30 minutes under high-speed stirring.

[0073] Experimental results: All performances meet the standards, but it is not easy to melt at 120°C, which is not conducive to one-step direct hot pressing processing. The subsequent addition of EAA emulsion can adjust the overall hot pressing temperature.

[0074] The above-described embodiments merely represent several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person of ordinary skill in the art may make various modifications and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

[0075] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present application should be included in the scope of protection of the present application.

Claims

1. A method for preparing a hard sheet, characterized in that: include: Add a polyol, a crosslinking agent, and isophorone diisocyanate in a mass ratio of (35-40):(2-10):(16-40) to a reaction vessel, heat the mixture to 60-70° C., stir and mix thoroughly, then add a catalyst, heat the mixture to 75-90° C., continue the reaction for 1-2 hours, add 2,2-dimethylolpropionic acid and 1,4-butanediol, continue the reaction for 2-3 hours, cool the mixture to 40-45° C., then sequentially add triethylamine, deionized water, and ethylene-acrylic acid copolymer and mix to obtain a water-based hot melt adhesive; Add formaldehyde, water, and a modifier to a reaction vessel, adjust the pH to 9.0-9.5, add melamine, and when the temperature reaches 70-90° C., add caprolactam, and keep the mixture at 90-94° C. for reaction until the water solubility ratio of the mixture reaches 1:(1.8-2.0). When cooling, adjust the pH to 9.0-9.5, cool to 30-40° C., add a coupling agent, and mix to obtain a melamine formaldehyde resin. impregnating glass cloth with the aqueous hot melt adhesive and impregnating glass fiber non-woven fabric with the melamine formaldehyde resin, and drying to obtain glass cloth prepregs and glass fiber non-woven fabric prepregs, respectively; The glass fiber non-woven fabric prepreg is arranged in the order of an upper layer and a glass cloth prepreg is arranged in the lower layer, and a one-step hot pressing process is performed to obtain a hard sheet.

2. The method for preparing a hard sheet according to claim 1, wherein: The polyol is one of poly(1,4-butylene adipate), polyethylene adipate, and polytetramethylene glycol monoethylene ether.

3. The method for preparing a hard sheet according to claim 1, wherein: The cross-linking agent is one or more of polypropylene oxide ether triol, trimethylolpropane, trimethylolpropane triglycidyl ether, and trimethylolpropane trimethacrylate.

4. The method for preparing a hard sheet according to claim 3, wherein: The molecular weight of the cross-linking agent is 2000, 500 or a mixture of several kinds.

5. The method for preparing a hard sheet according to claim 1, wherein: The modifiers include brighteners, tougheners and release agents.

6. The method for preparing a hard sheet according to claim 1, wherein: The glass cloth has a basis weight of 100 g / m 2 , woven in a horizontal and vertical interlaced manner; the quantitative weight of the glass fiber non-woven fabric is 80g / m 2 .

7. The method for preparing a hard sheet according to claim 1, wherein: The drying process is carried out in a drying tunnel with a temperature of 110-140°C and a running speed of 40-60m / min.

8. The method for preparing a hard sheet according to claim 1, wherein: In the one-step hot pressing treatment, the hot pressing temperature is 110-130° C., the hot pressing time is 1-5 min, and the hot pressing pressure is 1-5 MPa.

9. A hard sheet, characterized in that: The hard sheet is prepared by the method for preparing a hard sheet according to any one of claims 1 to 8.

10. An ultra-thin fiberboard, characterized in that: The ultra-thin fiberboard is obtained by hot pressing a plywood substrate, the hard sheet material according to claim 9, a printing layer impregnated paper and a wear-resistant layer impregnated paper in order from bottom to top, and then cooling the same by cold pressing.