A curing adhesive and its preparation method and application

Abstract

The application provides a curing adhesive and a preparation method and application thereof. The preparation method of the curing adhesive comprises the following steps: carrying out a polymerization reaction on polyol and a first isocyanate to obtain a polymerization product; wherein the molecular weight of the polyol is greater than or equal to 2000, the temperature of the polymerization reaction is 120-130 DEG C, and the time of the polymerization reaction is 2-4 h; a second isocyanate is added into the polymerization product, and a reaction is carried out at 120-130 DEG C for 0.5-1 h to obtain the curing adhesive; wherein the second isocyanate comprises polymethylene polyphenyl isocyanate. The application can prepare a curing adhesive with excellent initial adhesion.

Description

Technical Field

[0001] This invention relates to the field of new materials technology, specifically to a curing adhesive, its preparation method, and its application. Background Technology

[0002] Particleboard is a type of board material made by applying curing adhesive to wood chips and then pre-cooling and hot-pressing them. After pre-cooling and pressing, the pre-pressed board blank (pre-pressed board) needs to be conveyed to the hot-pressing section through a series of discontinuous devices for hot pressing. During the above conveying process, the integrity of the pre-pressed board has a critical impact on the effect of the hot-pressing section. For example, if the surface of the pre-pressed board is frayed or broken, it will be impossible to produce complete particleboard.

[0003] The integrity of the pre-press plate depends on the initial tack of the cured adhesive. However, the initial tack of the existing cured adhesive is low and insufficient to maintain the integrity of the pre-press plate during the transfer process. Therefore, when using the cured adhesive, additional tackifiers are required to improve the adhesion between the wood chips and thus ensure the integrity of the pre-press plate. This increases the inconvenience of using the cured adhesive. Summary of the Invention

[0004] This invention provides a curing adhesive, its preparation method, and its application, which can produce a curing adhesive with excellent initial tack.

[0005] This invention provides a method for preparing a cured adhesive, comprising: polymerizing a polyol and a first isocyanate to obtain a polymer product; wherein the molecular weight of the polyol is greater than or equal to 2000, the polymerization temperature is 120-130°C, and the polymerization time is 2-4 hours; adding a second isocyanate to the polymer product and reacting at 120-130°C for 0.5-1 hours to obtain the cured adhesive; wherein the second isocyanate includes polymethylene polyphenyl isocyanate.

[0006] Optionally, the molecular weight of the polyol is 2000-4200, preferably 2000-2020 or 3900-4200.

[0007] Optionally, the molar ratio of the isocyanate group in the first isocyanate to the hydroxyl group in the polyol is (1.1 to 1.3):1.

[0008] Optionally, based on the total mass of the polyol, the first isocyanate, and the second isocyanate, the mass percentage of the polyol is 3% to 12%, preferably 4.5% to 9.5%, the mass percentage of the first isocyanate is 0.2% to 0.8%, preferably 0.4% to 0.8%, and the mass percentage of the second isocyanate is 88% to 96%, preferably 90% to 95%.

[0009] Optionally, the polyol comprises one or more of polymethyl propylene adipate diol, polybutylene adipate neopentyl adipate diol, polymethyl propylene adipate isophthalate diol, polyethylene glycol butylene adipate diol, polybutylene adipate diol, polyhexyl adipate diol, polypropylene glycol ether diol, and polycaprolactone, preferably polymethyl propylene adipate diol and / or polypropylene glycol ether diol; and / or, the first isocyanate comprises one or more of 4,4'-diphenylmethane diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, and dicyclohexylmethane diisocyanate, preferably 4,4'-diphenylmethane diisocyanate and / or hexamethylene diisocyanate.

[0010] Optionally, the process of polymerizing the polyol and the first isocyanate to obtain the polymer product includes: polymerizing the polyol and the first isocyanate under the action of a catalyst and phosphoric acid to obtain the polymer product; wherein, based on the mass of the polyol and the first isocyanate, the mass fraction of the catalyst is 0-200 ppm, and the mass fraction of the phosphoric acid is 0-30 ppm, preferably 0-20 ppm; the catalyst includes one or more of zinc octanoate, stannous octanoate, and dibutyltin dilaurate, preferably dibutyltin dilaurate; and / or, the step of adding the second isocyanate to the polymer product and reacting it at 120-130°C for 0.5-1 h to obtain the cured adhesive includes: preheating the second isocyanate to 80-100°C and then adding it to the polymer product, reacting it at 120-130°C for 0.5-1 h to obtain the cured adhesive.

[0011] The present invention provides a curing adhesive, which is obtained by the curing adhesive preparation method described above.

[0012] Optionally, the curing adhesive is a formaldehyde-free curing adhesive.

[0013] This invention provides a method for preparing particleboard, comprising: mixing a curing adhesive, wood shavings, and water to obtain a mixture; the curing adhesive includes the curing adhesive described above; and subjecting the mixture to cold pressing and hot pressing sequentially to obtain the particleboard; wherein the cold pressing pressure is 3-6 MPa, the hot pressing pressure is 3-6 MPa, preferably 4-5 MPa, and the hot pressing temperature is 200-280°C, preferably 220-240°C.

[0014] The present invention provides a particleboard, which is obtained by the preparation method described above.

[0015] This invention provides a curing adhesive, its preparation method, and its application. A polyol with a molecular weight greater than or equal to 2000 is polymerized with a first isocyanate to obtain a polymer product with a high molecular weight. This polymer product is then reacted with a second isocyanate, which includes polymethylene polyphenyl isocyanate. By limiting the reaction temperature and other conditions, it is beneficial to obtain a curing adhesive with a high molecular weight, thereby improving its initial tack. Detailed Implementation

[0016] To enable those skilled in the art to better understand the present invention, the present invention will be further described in detail below. The specific embodiments listed below are merely descriptions of the principles and features of the present invention, and the examples are only for explaining the present invention and are not intended to limit the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0017] Due to limitations in existing curing adhesive preparation processes, the initial tack of cured adhesives is generally poor. Therefore, to compensate for the shortcomings of low initial tack cured adhesives, tackifiers need to be added in combination with the cured adhesive. For example, in the production process of particleboard, low initial tack cured adhesives can cause problems such as frayed edges and cracks in the pre-pressed board during processing. Therefore, to ensure the integrity of the pre-pressed board, the cured adhesive and tackifier are generally used together to compensate for the shortcomings of low initial tack cured adhesives and enhance the integrity of the pre-pressed board.

[0018] However, the use of tackifiers can bring other problems. For example, after applying curing adhesive and tackifier to the wood shavings, air-laid or diamond roller laid methods are needed to shape the shavings and facilitate pre-cooling pressing to form a pre-press. However, because the viscosity of the tackifier is difficult to control, the pre-cooling pressing effect is unstable. Specifically, if the tackifier is too viscous, it will cause the wood shavings to clump together and clog the screen used in air-laid, or make it difficult for the diamond roller to separate the clumps of wood shavings, thus deteriorating the pre-cooling pressing effect, reducing the quality of the pre-press, and consequently affecting the quality of the particleboard and reducing production efficiency. In addition, most tackifiers sold on the market are emulsion-type tackifiers, which need to be used separately from isocyanate (PMDI adhesive) curing adhesives. Moreover, the amount of emulsion-type tackifier used is large, and it needs to be thoroughly mixed with water before use, which is complicated and increases production costs and reduces production efficiency.

[0019] Based on this, embodiments of the present invention provide a method for preparing a curable adhesive, comprising: performing a polymerization reaction of a polyol and a first isocyanate to obtain a polymer product; wherein the molecular weight of the polyol is greater than or equal to 2000, the polymerization temperature is 120-130°C, and the polymerization time is 2-4 h; adding a second isocyanate to the polymer product and reacting at 120-130°C for 0.5-1 h to obtain a curable adhesive; wherein the second isocyanate includes polymethylene polyphenyl isocyanate.

[0020] According to the inventors' research and analysis, polymerizing a polyol with a molecular weight greater than or equal to 2000 with a first isocyanate yields a polymer product with a higher molecular weight, which is beneficial for obtaining a high-molecular-weight cured adhesive and improving its initial tack. Furthermore, by controlling the polymerization reaction temperature to 120–130°C and the reaction time to 2–4 hours, the amount of hydroxyl groups (e.g., residual polyol) in the polymer product is kept appropriate, which is beneficial for improving the reaction effect between the polymer product and the second isocyanate, including polymethylene polyphenyl isocyanate. Further, adding the second isocyanate to the polymer product and reacting it at 120–130°C for 0.5–1 hour ensures a good reaction effect between the second isocyanate and the polymer product, which is beneficial for improving the initial tack of the cured adhesive, thus obtaining a cured adhesive with excellent initial tack. This cured adhesive has good initial tack and can be used directly alone, offering high ease of use and effectively avoiding the problems caused by adding additional tackifiers.

[0021] The above preparation method yields a cured adhesive with excellent initial tack, which can be used to prepare particleboard, improving its processing stability, strength, and production efficiency. Specifically, in the particleboard preparation process, the cured adhesive and wood shavings are first mixed, then the mixture is laid out and subsequently subjected to cold pressing and hot pressing to obtain the particleboard. However, in this process, excessively high initial tack of the cured adhesive can cause the mixture to clump together. These clumps can clog the airflow laying screen and are difficult to separate by the diamond roller laying equipment. Furthermore, excessively high initial tack can cause the board to adhere to the conveyor belt, affecting the structural integrity of the board. All of these factors contribute to the deterioration of the particleboard quality, reduced processing stability, and decreased production efficiency. Low initial tack of the cured adhesive can lead to problems such as frayed edges or breakage of the pre-pressing plate during the cold pressing process, affecting the quality, processing stability, and production efficiency of the particleboard. However, the cured adhesive prepared in this embodiment of the invention has excellent initial tack. Without affecting the mechanical properties of the board (maintaining good internal bond strength), it not only makes the mixture of cured adhesive and particleboard moderately loose and non-clumping, but also improves the bonding and forming ability between the particleboard particles after cold pressing. This is beneficial to maintaining the integrity of the board blank during the hot pressing process, thereby improving the processing stability, strength, and production efficiency of the particleboard.

[0022] In addition, this curing agent can be applied directly without adding any tackifier, which solves the problems of poor initial tack of some cured adhesives, the need to use them with tackifiers, and the need to be thoroughly mixed with water before use. It saves production costs such as procurement, transportation, and equipment, and significantly improves the efficiency of cured adhesive use.

[0023] The above-mentioned method for preparing the curing adhesive is simple, the raw materials are readily available, and it is easy to achieve industrial production.

[0024] For example, the temperature of the above polymerization reaction can be a range of 120°C, 121°C, 122°C, 123°C, 124°C, 125°C, 126°C, 127°C, 128°C, 129°C, 130°C or any combination thereof, preferably 130°C, and the time of the polymerization reaction can be a range of 2h, 3h, 4h or any combination thereof, preferably 2 to 3h.

[0025] Understandably, in order to improve the polymerization effect and enhance the initial tack of the cured adhesive, the polyol, isocyanate, and other raw materials should be mixed and polymerized under constant temperature conditions.

[0026] In some embodiments, the molecular weight of the polyol (macromolecule polyol or macromolecule polyester polyol) is 2000 to 4200, preferably 2000 to 2020 or 3900 to 4200, which is beneficial to improving the initial tack of the cured adhesive.

[0027] Specifically, the aforementioned polyols may include one or more of the following: polymethyl propylene adipate diol, polybutylene adipate neopentyl glycol adipate diol, polymethyl propylene adipate isophthalate diol, polyethylene glycol butylene adipate diol, polybutylene adipate diol, polyhexyl adipate diol, polypropylene glycol ether diol, and polycaprolactone, preferably polymethyl propylene adipate diol and / or polypropylene glycol ether diol, and more preferably polymethyl propylene adipate diol with a molecular weight of 3900 to 4200 and / or polypropylene glycol ether diol with a molecular weight of 2000 to 2020.

[0028] In specific implementation, the above-mentioned polyols can be dehydrated under vacuum to remove water, for example, at a vacuum of 105-125°C, such as 105°C, 110°C, 115°C, 120°C, 125°C or any combination thereof, and at a vacuum of 0.05-0.15 MPa, such as 0.05 MPa, 0.1 MPa, 0.15 MPa or any combination thereof, for 0.5-2 hours, such as 0.5 hours, 1 hour, 2 hours or any combination thereof.

[0029] The first isocyanate may include isocyanates containing phenyl groups. In the preparation system of this invention, using a first isocyanate containing phenyl groups is advantageous for obtaining a cured adhesive with higher initial tack, and the resulting board material has higher strength.

[0030] In some embodiments, the first isocyanate includes one or more of 4,4'-diphenylmethane diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, and dicyclohexylmethane diisocyanate, preferably 4,4'-diphenylmethane diisocyanate and / or hexamethylene diisocyanate.

[0031] In the preparation system of this invention, the amounts of polyol, first isocyanate, and second isocyanate can meet the following requirements: based on the mass of polyol, first isocyanate, and second isocyanate, the mass percentage of polyol is 3% to 12%, preferably 4.5% to 9.5%, the mass percentage of first isocyanate is 0.2% to 0.8%, preferably 0.4% to 0.8%, and the mass percentage of second isocyanate is 88% to 96%, preferably 90% to 95%; this is beneficial for obtaining a cured adhesive with excellent initial tack.

[0032] The inventors discovered in their research that a molar ratio of isocyanate groups in isocyanate to hydroxyl groups in polyol of 1.1 to 1.3 can yield a cured adhesive with a higher molecular weight and higher initial tack.

[0033] In some embodiments, the process of polymerizing a polyol and a first isocyanate to obtain a polymerized product includes: polymerizing the polyol and the first isocyanate under the action of a catalyst and phosphoric acid to obtain a polymerized product. The catalyst helps to lower the activation energy of the polymerization reaction and improve the polymerization efficiency; phosphoric acid can control the polymerization rate, avoiding uneven polymerization in the polymerization system at temperatures of 120–130°C, preventing localized gelation of the polymerization system due to excessively fast polymerization rates, and also preventing isocyanate self-polymerization side reactions, such as the self-polymerization side reaction of diphenylmethane diisocyanate (MDI-100), thereby preventing a decrease in the reaction rate.

[0034] The catalyst may include one or more of zinc octanoate, stannous octanoate, and dibutyltin dilaurate, preferably dibutyltin dilaurate.

[0035] Furthermore, based on the mass of the polyol and the first isocyanate, the mass fraction of the above catalyst can be 0 to 200 ppm, and the mass fraction of phosphoric acid can be 0 to 30 ppm, preferably 0 to 20 ppm.

[0036] The above polymerization reaction can be carried out under a nitrogen atmosphere.

[0037] In practice, under a nitrogen atmosphere, the polyol is heated to 120-130°C and stirred at a speed of 150-200 r / min while the first isocyanate is added.

[0038] To improve the reactivity of the second isocyanate, it can be preheated before being added to the polymerization product. Specifically, adding the second isocyanate to the polymerization product and reacting it at 120–130°C for 0.5–1 hour to obtain a cured adhesive includes: preheating the second isocyanate to 80–100°C, then adding it to the polymerization product and reacting it at 120–130°C for 0.5–1 hour to obtain a cured adhesive. Exemplarily, the preheating temperature can be 80°C, 90°C, 100°C, or any combination thereof, preferably 80°C, and the reaction time can be 0.5 hours, 0.6 hours, 0.7 hours, 0.8 hours, 0.9 hours, 1 hour, or any combination thereof, preferably 1 hour.

[0039] Understandably, in order to improve the reaction between the second isocyanate and the polymerization product, the second isocyanate can be added to the polymerization product under stirring.

[0040] Currently, most adhesives used in the engineered wood products industry are aldehyde-based adhesives, such as urea-formaldehyde resin, melamine-modified formaldehyde resin, and phenolic resin. These adhesives all use formaldehyde as a raw material and contain a large amount of free formaldehyde. During use, formaldehyde release is inevitable, polluting the indoor environment and harming health. Formaldehyde-free adhesives, such as polymeric diphenylmethane diisocyanate adhesives (PMDI adhesives), are widely used because they do not release formaldehyde, do not cause pollution or health problems, and have advantages such as high bonding strength, good water resistance, and low dosage. However, these formaldehyde-free curing adhesives are limited by existing preparation processes, inherent properties, and low usage, resulting in less than ideal initial tack.

[0041] This invention provides an example of a formaldehyde-free curing adhesive (high initial tack formaldehyde-free curing adhesive) prepared using aldehyde-free raw materials. This formaldehyde-free curing adhesive exhibits excellent initial tack and can be used to prepare engineered wood products, particularly formaldehyde-free particleboard.

[0042] This invention also provides a curing adhesive, which can be obtained according to the above-described method for preparing the curing adhesive. This curing adhesive exhibits excellent initial tack.

[0043] This cured adhesive can be used to prepare boards, such as engineered wood products, and is especially suitable for preparing particleboard.

[0044] In some embodiments, the curing adhesive includes a formaldehyde-free curing adhesive.

[0045] This invention also provides a method for preparing particleboard, comprising: mixing a curing adhesive, wood chips, and water to obtain a mixture; subjecting the mixture to cold pressing and hot pressing in sequence to obtain formaldehyde-free particleboard; wherein the cold pressing pressure is 3-6 MPa, the hot pressing pressure is 3-6 MPa, preferably 4-5 MPa, and the hot pressing temperature is 200-280°C, preferably 220-240°C.

[0046] For example, the pressure of the cold pressing can be a range of 3MPa, 4MPa, 5MPa, 6MPa or any two of them, the pressure of the hot pressing can be a range of 3MPa, 4MPa, 5MPa, 6MPa or any two of them, preferably 4 to 5MPa, and the temperature of the hot pressing can be a range of 200°C, 220°C, 240°C, 260°C, 280°C or any two of them, preferably 220 to 240°C.

[0047] The cold pressing time can be 10 to 50 seconds, for example, 10 seconds, 20 seconds, 30 seconds, 40 seconds, 50 seconds or any combination thereof, and the hot pressing time can be 50 to 100 seconds, for example, 50 seconds, 60 seconds, 70 seconds, 80 seconds, 95 seconds, 100 seconds or any combination thereof.

[0048] Generally, before cold pressing, the mixture needs to be laid out and shaped. Airflow paving or diamond roller paving can be used to evenly spread the mixture in the mold frame, and after appropriate extrusion and shaping, it is then cold-pressed (pre-cold pressing) to form a slab. Then the slab is hot-pressed (high-temperature hot pressing) to obtain particleboard.

[0049] In some embodiments, the process of mixing the curing adhesive, wood shavings, and water to obtain a mixture includes: sequentially spraying the curing adhesive and water onto the wood shavings while they are being stirred, thereby mixing the curing adhesive, wood shavings, and water to obtain a mixture. For example, the wood shavings are placed in a mixer and stirred, and then the curing adhesive and water are sprayed onto the stirred wood shavings using a spray gun to thoroughly mix them and obtain a mixture.

[0050] The aforementioned wood shavings may include wood shavings.

[0051] The above-mentioned method for preparing particleboard is applicable to the preparation of particleboard from most forms of wood shavings raw materials, and in actual production, for example, to maintain the stable operation of the production equipment.

[0052] Based on the sum of the masses of the curing adhesive, water, and wood shavings, the mass percentage of the curing adhesive can be 2% to 3%, for example, 2%, 2.2%, 2.4%, 2.6%, 2.8%, 3%, or any combination thereof, preferably 2.4% to 3%. The mass percentage of water can be 10% to 11%, for example, 10%, 10.1%, 10.2%, 10.3%, 10.4%, 10.5%, 11%, or any combination thereof, preferably 10% to 10.1%. The mass percentage of wood shavings can be 87% to 88%, for example, 87%, 87.2%, 87.5%, 87.8%, 88%, or any combination thereof, preferably 87% to 87.5%.

[0053] This invention also provides a particleboard, which can be obtained by the above-described preparation method.

[0054] Since the aforementioned curing adhesive includes a formaldehyde-free curing adhesive, formaldehyde-free particleboard can be produced using the aforementioned formaldehyde-free curing adhesive (high initial tack formaldehyde-free curing adhesive) within the above-mentioned particleboard preparation method system. This formaldehyde-free particleboard does not release formaldehyde during use, is healthy and environmentally friendly, and also possesses good mechanical properties and bonding strength, showing promising application prospects.

[0055] The present invention will be further described below through specific embodiments and comparative examples. Unless otherwise specified, the reagents, materials and instruments used below are all conventional reagents, materials and instruments, all of which are commercially available, and the reagents and materials involved can also be synthesized by conventional synthetic methods.

[0056] The polyvinyl acetate emulsion (PVAC emulsion C) in Comparative Example 1 was purchased from Jiangsu Sunrise Chemical Co., Ltd.

[0057] The ethylene-vinyl acetate copolymer emulsion (EVA emulsion D) in Comparative Example 2 was purchased from Shanghai Tongyi Chemical Co., Ltd.

[0058] Polymethylene polyphenyl isocyanate (PM) was purchased from Wanhua Chemical Group Co., Ltd.

[0059] Example 1

[0060] 1) Preparation of formaldehyde-free curing adhesive

[0061] Polymethyl propylene glycol adipate (polyol) with a molecular weight of 4000 was dehydrated at 110 °C and under vacuum of 0.1 MPa for 1 h to remove water. Then, under a nitrogen atmosphere, it was heated to 130 °C and 4,4'-diphenylmethane diisocyanate (MDI) (primary isocyanate) was added with stirring at 180 r / min. The polymerization reaction was carried out at 130 °C for 2 h to obtain the polymer product.

[0062] Polymethylene polyphenyl isocyanate (PM) (second isocyanate) was preheated to 80°C and then added to the above polymerization product under stirring at 200 r / min. After mixing thoroughly for 1 h, formaldehyde-free curing adhesive was obtained.

[0063] Of which, based on the mass of polyol, first isocyanate and second isocyanate, the mass percentage of polymethyl propylene glycol adipate diol (polyol) is 9.3%, the mass percentage of 4,4'-diphenylmethane diisocyanate (first isocyanate) is 0.7%, and the mass percentage of polymethylene polyphenyl isocyanate (second isocyanate) is 90%.

[0064] 2) Preparation of formaldehyde-free particleboard

[0065] Wood shavings are placed in a mixing machine and stirred. Then, the formaldehyde-free curing adhesive and water are sprayed onto the wood shavings in sequence using a spray gun to fully mix the formaldehyde-free curing adhesive, water and wood shavings to obtain a mixture. The mixture is then evenly spread and shaped, and then cold-pressed at 4MPa for 20s, and then hot-pressed at 220℃ at 4MPa for 95s to obtain formaldehyde-free particleboard.

[0066] The total mass percentage of the formaldehyde-free curing adhesive, water, and wood shavings is 3%, based on the sum of their masses. The water content is 10%, and the wood shavings content is 87%.

[0067] Comparative Example 1

[0068] The process of preparing formaldehyde-free particleboard in this comparative example includes:

[0069] Wood shavings are placed in a glue mixer and stirred. Then, polymethylene polyphenyl isocyanate (PM) and tackifier (prepared by mixing commercially available polyvinyl acetate emulsion (PVAC emulsion C) and water) are sprayed onto the wood shavings in sequence using a spray gun to ensure that PM, tackifier and wood shavings are fully mixed to obtain a mixture. The mixture is then evenly spread and shaped, and then cold-pressed at 4 MPa for 20 seconds, and then hot-pressed at 220°C at 4 MPa for 95 seconds to obtain formaldehyde-free particleboard.

[0070] Based on the sum of the masses of polyvinyl acetate emulsion (PVAC emulsion C), water, PM, and wood shavings, the polyvinyl acetate emulsion (PVAC emulsion C) has a mass percentage of 0.4%, water has a mass percentage of 9.6%, PM has a mass percentage of 3%, and wood shavings has a mass percentage of 87%.

[0071] Comparative Example 2

[0072] This comparative example is basically the same as Comparative Example 1, except that:

[0073] The polyvinyl acetate emulsion (PVAC emulsion C) was replaced with a commercially available ethylene-vinyl acetate copolymer emulsion (EVA emulsion D), and the mass percentage of ethylene-vinyl acetate copolymer emulsion (EVA emulsion D) was adjusted to 0.3%, and the mass percentage of water was adjusted to 9.7%; other conditions remained unchanged.

[0074] Comparative Example 3

[0075] The process of preparing formaldehyde-free particleboard in this comparative example includes:

[0076] Wood shavings are placed in a glue mixer and stirred. Then, polymethylene polyphenyl isocyanate (PM) and water are sprayed onto the wood shavings in sequence using a spray gun to fully mix the polymethylene polyphenyl isocyanate (PM), water and wood shavings to obtain a mixture. The mixture is then evenly spread and shaped, and then cold-pressed at 4 MPa for 20 seconds, and then hot-pressed at 220°C at 4 MPa for 95 seconds to obtain formaldehyde-free particleboard.

[0077] The product comprises, based on the sum of the masses of polymethylene polyphenyl isocyanate (PM), water, and wood shavings, 3% by mass of polymethylene polyphenyl isocyanate (PM), 10% by mass of water, and 87% by mass of wood shavings.

[0078] The curing adhesive (formaldehyde-free curing adhesive) and particleboard (formaldehyde-free particleboard) in Examples 1-12 and Comparative Examples 4-6 were prepared with reference to Example 1. In the examples using catalyst and phosphoric acid, both the catalyst and phosphoric acid were added to the reaction system simultaneously with the first isocyanate.

[0079] Table 1 summarizes the following information regarding the polyols, first isocyanate, molar ratio of isocyanate groups in the first isocyanate to hydroxyl groups in the polyol, molecular weight of the polyol, mass percentage of the polyol, mass percentage of the first isocyanate, mass percentage of the second isocyanate, polymerization temperature and time, type and mass fraction of catalyst, and mass fraction of phosphoric acid in Examples 1-12 and Comparative Examples 4-6. Table 2 summarizes the following information regarding the reaction temperature and time of the second isocyanate and polymerization product in Examples 1-12 and Comparative Examples 4-6, preheating temperature of the second isocyanate, mass percentage of wood shavings, mass percentage of formaldehyde-free curing adhesive, mass percentage of water, cold pressing pressure, hot pressing pressure, and hot pressing temperature.

[0080] Table 1

[0081]

[0082]

[0083] Table 2

[0084]

[0085]

[0086] Test case

[0087] The following parameters of the above embodiments and comparative examples were tested:

[0088] 1) Initial tack of the cured adhesive: The initial tack of the cured adhesive was measured using the "sloping plane push plate measurement method." Specifically, the shavings (a mixture of formaldehyde-free cured adhesive, water, and shavings thoroughly mixed in each embodiment) after applying the adhesive were placed in a 30*30cm mold frame, spread evenly, and then moderately pressed into shape using the mold cover. After shaping, the mold was placed in a press for cold pressing (4MPa pressure for 20s). The thickness of the blank after cold pressing was 18mm. Then, multiple blanks after cold pressing were... The slab is placed on a 45° slope and pushed down the slope at a speed of 2 cm / s. The number of broken pieces and the width of the first break are recorded. The slab is picked up by hand to feel its looseness and scored from 1 to 5. The higher the score, the harder the slab is. For example, 5 points means the slab is hard and 1 point means the slab is loose. The fewer the broken pieces, the wider the width of the first break, and the higher the looseness score, the better the initial tack of the cured adhesive.

[0089] 2) Screen clogging of wood shavings after sizing: The shavings after sizing (the mixture obtained by thoroughly mixing formaldehyde-free curing adhesive, water and wood shavings in each embodiment) were evenly sprinkled into the feed inlet of the blower, and the screen clogging at the discharge outlet was observed; the wind speed of the blower was 3m / s, and the larger the clogging area, the more serious the agglomeration of wood shavings after sizing and the more serious the screen clogging.

[0090] 3) Internal bond strength of formaldehyde-free particleboard: The shavings after gluing (the mixture obtained by thoroughly mixing formaldehyde-free curing adhesive, water and shavings in each embodiment) are placed in a 30*30cm mold frame, spread evenly and then moderately squeezed into shape with the mold cover. After shaping, it is placed in a press and hot-pressed at 220℃ with a pressure of 4MPa for 95s to obtain the board. The thickness is controlled at 12mm with a thickness gauge. The internal bond strength test method in the national standard GBT 17657-2022 is used for testing.

[0091] 4) Formaldehyde emission of formaldehyde-free particleboard: The formaldehyde emission determination - desiccator method in the national standard GB / T 17657-2022 was used for testing.

[0092] Test results

[0093] Table 3 Initial tack, clogging, mechanical properties and formaldehyde release

[0094]

[0095] Data Analysis:

[0096] As can be seen from the data in the table above, the formaldehyde-free curing adhesive (high initial tack formaldehyde-free curing adhesive) for formaldehyde-free particleboard (artificial board) prepared in the embodiments of the present invention has excellent initial tack performance. Its cold-pressed adhesion is stronger than that of the commercially available PVAC emulsion of Comparative Example 1 and Comparative Example 3. Compared with the commercially available EVA emulsion of Comparative Example 2, it does not cause screen clogging. It can maintain the looseness of the particleboard before cold pressing. The good adhesion after cold pressing prevents the pre-pressed board from fraying or breaking.

[0097] Compared to the comparative example, the internal bond strength of the particleboard after hot pressing is essentially unaffected. Furthermore, the high initial tack formaldehyde-free curing adhesive is prepared without organic solvents and does not use formaldehyde as a synthetic raw material, reducing formaldehyde release from the board, mitigating the health hazards of formaldehyde, and improving the environmental performance of the engineered wood products. In addition, the high initial tack formaldehyde-free curing adhesive for engineered wood products prepared in this embodiment can be applied directly without the need for additional tackifiers, saving on transportation and equipment costs, significantly improving factory production efficiency, and can be widely used in particleboard, oriented strand board, and strawboard industries.

[0098] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a curing adhesive, characterized in that, include: A polyol and a first isocyanate are subjected to a polymerization reaction to obtain a polymer product; wherein the molecular weight of the polyol is 2000~4200, the polymerization reaction temperature is 120~130℃, and the polymerization reaction time is 2~4h; The second isocyanate is added to the polymerization product and reacted at 120~130°C for 0.5~1h to obtain the cured adhesive; wherein the second isocyanate includes polymethylene polyphenyl isocyanate; The molar ratio of the isocyanate group in the first isocyanate to the hydroxyl group in the polyol is (1.1~1.3):1; Based on the total mass of the polyol, the first isocyanate, and the second isocyanate, the mass percentage of the polyol is 3% to 12%, the mass percentage of the first isocyanate is 0.2% to 0.8%, and the mass percentage of the second isocyanate is 88% to 96%.

2. The method for preparing the curing adhesive according to claim 1, characterized in that, The molecular weight of the polyol is 2000~2020 or 3900~4200.

3. The method for preparing the curing adhesive according to claim 1, characterized in that, Based on the total mass of the polyol, the first isocyanate, and the second isocyanate, the mass percentage of the polyol is 4.5% to 9.5%, the mass percentage of the first isocyanate is 0.4% to 0.8%, and the mass percentage of the second isocyanate is 90% to 95%.

4. The method for preparing the curing adhesive according to claim 1, characterized in that, The polyols include one or more of the following: polymethyl propylene adipate diol, polybutylene adipate neopentyl glycol adipate diol, polymethyl propylene adipate isophthalate diol, polyethylene glycol butylene adipate diol, polybutylene adipate diol, polyhexyl adipate diol, polypropylene glycol ether diol, and polycaprolactone. And / or, the first isocyanate comprises one or more of 4,4'-diphenylmethane diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, and dicyclohexylmethane diisocyanate.

5. The method for preparing the curing adhesive according to claim 4, characterized in that, The polyol is polymethyl propylene glycol adipate diol and / or polypropylene glycol ether diol; the first isocyanate is 4,4'-diphenylmethane diisocyanate and / or hexamethylene diisocyanate.

6. The method for preparing the curing adhesive according to claim 1, characterized in that, The process of polymerizing a polyol and a first isocyanate to obtain a polymer product includes: based on the mass of the polyol and the first isocyanate, polymerizing the polyol and the first isocyanate under the action of a catalyst with a mass fraction of 0-200 ppm and phosphoric acid with a mass fraction of 0-30 ppm to obtain the polymer product; the catalyst includes one or more of zinc octanoate, stannous octanoate, and dibutyltin dilaurate; And / or, the step of adding the second isocyanate to the polymerization product and reacting it at 120~130°C for 0.5~1h to obtain the cured adhesive includes: preheating the second isocyanate to 80~100°C and then adding it to the polymerization product, reacting it at 120~130°C for 0.5~1h to obtain the cured adhesive.

7. The method for preparing the curing adhesive according to claim 6, characterized in that, The phosphoric acid has a mass fraction of 0-20 ppm; the catalyst is dibutyltin dilaurate.

8. A curing adhesive, characterized in that, The cured adhesive is obtained according to the method for preparing the cured adhesive according to any one of claims 1-7.

9. The curing adhesive according to claim 8, characterized in that, The curing adhesive is a formaldehyde-free curing adhesive.

10. A method for preparing particleboard, characterized in that, include: The curing adhesive, wood shavings, and water are mixed to obtain a mixture; the curing adhesive includes the curing adhesive according to claim 8. The mixture is subjected to cold pressing and hot pressing in sequence to obtain the particleboard; wherein the pressure of cold pressing is 3~6MPa, the pressure of hot pressing is 3~6MPa, and the temperature of hot pressing is 200~280℃.

11. The method for preparing particleboard according to claim 10, characterized in that, The pressure of the hot pressing is 4~5MPa, and the temperature of the hot pressing is 220~240℃.

12. A type of particleboard, characterized in that, The particleboard is obtained according to the preparation method of claim 10.

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