Curing adhesive as well as preparation method and application thereof

Abstract

The invention provides a curing adhesive as well as a preparation method and application thereof. The preparation method of the curing adhesive comprises the following steps: carrying out polymerization reaction on polyol and 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 hours; and adding second diisocyanate into the polymerization product, and carrying out a reaction at 120-130 DEG C for 0.5-1 h to obtain the curing adhesive, wherein the first diisocyanate comprises polymethylene polyphenyl isocyanate, and the second diisocyanate comprises polymethylene polyphenyl isocyanate. According to the invention, the curing adhesive with excellent initial viscosity can be prepared.

Description

Technical Field

[0001] The present invention relates to the technical field of new materials, and in particular to a curing adhesive and a preparation method and application thereof. Background Art

[0002] Particleboard is a board material obtained by applying curing glue to wood particles and then pre-cold pressing and hot pressing. The pre-cold pressed board (pre-pressed board) needs to be transferred to the hot pressing section through a series of discontinuous devices for hot pressing. During the above-mentioned transfer process, the integrity of the pre-pressed board has a key impact on the effect of the hot pressing section. For example, if the surface of the pre-pressed board is loose or broken, it will result in the inability to produce a complete particleboard.

[0003] The integrity of the pre-pressed board depends on the initial viscosity of the curing glue, but the initial viscosity of the existing curing glue is low, which is not enough to keep the pre-pressed board intact during the transportation process. Therefore, when using the curing glue, an additional tackifier needs to be added to improve the adhesion between the wood chips, thereby ensuring the integrity of the pre-pressed board, which increases the inconvenience of using the curing glue. Summary of the invention

[0004] The invention provides a curing adhesive and a preparation method and application thereof, which can prepare a curing adhesive with excellent initial viscosity.

[0005] The present invention provides a method for preparing a curing adhesive, comprising: subjecting a polyol and a first isocyanate to a polymerization reaction to obtain a polymerization product; wherein the molecular weight of the polyol is greater than or equal to 2000, the polymerization reaction temperature is 120-130° C., and the polymerization reaction time is 2-4 hours; adding a second isocyanate to the polymerization product, reacting at 120-130° C. for 0.5-1 hour to obtain the curing adhesive; wherein the second isocyanate comprises 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 groups in the first isocyanate to the hydroxyl groups in the polyol is (1.1-1.3):1.

[0008] Optionally, based on the sum of the masses 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 includes one or more of poly(methyl propylene adipate) diol, poly(butylene adipate) neopentyl glycol diol, poly(methyl propylene adipate) isophthalate diol, poly(ethylene adipate) glycol butylene adipate diol, poly(butylene adipate) glycol butylene adipate diol, poly(hexylene adipate) glycol ether diol, and polycaprolactone, preferably poly(methyl propylene adipate) diol and / or poly(propylene glycol ether diol); and / or, 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.

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

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

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

[0013] The invention provides a method for preparing a particleboard, comprising: mixing curing glue, wood chips and water to obtain a mixed material; the curing glue comprises the curing glue as described above; and sequentially subjecting the mixed material to cold pressing and hot pressing to obtain the particleboard; wherein the pressure of the cold pressing is 3-6MPa, the pressure of the hot pressing is 3-6MPa, preferably 4-5MPa, and the temperature of the hot pressing is 200-280°C, preferably 220-240°C.

[0014] The present invention provides a particle board, and the particle board is obtained according to the preparation method as described above.

[0015] The present invention provides a curing adhesive and a preparation method and application thereof. A polyol having a molecular weight greater than or equal to 2000 is polymerized with a first isocyanate to obtain a polymer product having a high molecular weight. The polymer product is reacted with a second isocyanate including polymethylene polyphenyl isocyanate. Meanwhile, the reaction temperature and other conditions are limited, which is conducive to obtaining a curing adhesive with a high molecular weight and improving its initial viscosity. DETAILED DESCRIPTION

[0016] In order to enable those skilled in the art to better understand the scheme of the present invention, the present invention is further described in detail below. The specific implementation methods listed below are only for describing the principles and features of the present invention. The examples are only used to explain 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 implementation methods obtained by ordinary technicians in the field without creative work are within the scope of protection of the present invention.

[0017] Limited by the existing curing glue preparation process, the initial viscosity of the curing glue is generally poor. Therefore, in order to make up for the shortcomings of the curing glue with low initial viscosity, it is necessary to add an additional tackifier to be used in combination with the curing glue. For example, in the production process of particleboard, the curing glue with low initial viscosity will cause the pre-pressed board to have problems such as loose edges and cracks during the processing. Therefore, in order to ensure the integrity of the pre-pressed board, the curing glue and the tackifier are generally used in combination to make up for the shortcomings of the curing glue with low initial viscosity and enhance the integrity of the pre-pressed board.

[0018] However, the use of thickeners will bring other problems. For example, after applying curing glue and thickener to the wood chips, airflow laying or diamond roller laying is required to shape the wood chips after the glue application, so as to facilitate pre-cooling pressing to form a pre-pressed board. However, since the viscosity of the thickener is difficult to control, the effect of pre-cooling pressing is unstable. Specifically, if the viscosity of the thickener is too strong, the wood chip particles will be bonded into a mass and then block the screen used for airflow laying, or it will be difficult for the diamond roller to separate the wood chip mass, which will deteriorate the effect of pre-cooling pressing, reduce the quality of the pre-pressed board, and further affect the quality of the particleboard and reduce production efficiency. In addition, most of the thickeners sold on the market are emulsion-type thickeners, which need to be used separately from isocyanate (PMDI adhesive) curing glues, and the emulsion-type thickeners are used in large amounts and need to be fully stirred and mixed with water before use, which is complicated to operate, increasing production costs and reducing production efficiency.

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

[0020] According to the research and analysis of the inventors: the molecular weight of the obtained polymer product is high by polymerizing a polyol having a molecular weight greater than or equal to 2000 with the first isocyanate, which is conducive to obtaining a high molecular weight cured adhesive and improving its initial viscosity. Further, by controlling the temperature of the above-mentioned polymerization reaction to 120-130°C and the polymerization reaction time to 2-4h, the hydroxyl group (such as residual polyol) in the polymer product is kept at an appropriate amount, which is conducive to improving the reaction effect of the polymer product and the second isocyanate including polymethylene polyphenyl isocyanate. Further, the second isocyanate is added to the polymer product and reacted at 120-130°C for 0.5-1h, ensuring that the reaction of the second isocyanate and the polymer product has a good effect, which is conducive to improving the initial viscosity of the cured adhesive, and then a cured adhesive with excellent initial viscosity is obtained. The cured adhesive has good initial viscosity, can be used directly alone, is easy to use, and can effectively avoid the above-mentioned problems caused by the additional addition of a tackifier.

[0021] The above preparation method can obtain a curing adhesive with excellent initial viscosity, which can be used to prepare particleboard, which is beneficial to improve the processing stability of particleboard, improve the strength of particleboard, and improve production efficiency. Specifically, in the process of preparing particleboard, the curing adhesive and particleboard need to be mixed first, and then the mixture is paved and formed, and then cold pressed and hot pressed in sequence to obtain particleboard. In the above process of preparing particleboard, curing adhesive with too high initial viscosity will cause the mixture of curing adhesive and particleboard to stick together into a mass, and the massed mixture will block the airflow paving screen and will be difficult to be separated by the diamond roller paving equipment. At the same time, curing adhesive with too high initial viscosity will also cause the board to adhere to the conveyor belt and affect the structural integrity of the board, which will cause the quality of particleboard to deteriorate, reduce the processing stability of particleboard, and reduce production efficiency. In addition The curing glue with too low initial viscosity may cause the pre-pressed plate to have loose edges or breakage during the cold pressing process, affecting the quality, processing stability and production efficiency of the particle board. The curing glue prepared in the embodiment of the present invention has excellent initial viscosity. On the basis of not affecting the mechanical properties of the board (maintaining good bonding strength within the board), it not only makes the mixture of the curing glue and the particles have moderate looseness and no agglomeration, but also can improve the bonding and forming ability between the particles after cold pressing, which is beneficial to maintaining the integrity of the slab in the hot pressing process, and further helps to improve the processing stability of the particle board, improve the strength of the particle board, and improve the production efficiency.

[0022] In addition, the curing agent can be directly applied without adding any tackifiers, which solves the problems of some curing adhesives having poor initial viscosity, needing to be used in combination with tackifiers, and needing to be fully stirred and mixed with water before use. It saves production costs such as procurement, transportation, and equipment, and significantly improves the efficiency of the use of the curing adhesive.

[0023] The preparation method of the curing adhesive is simple in process, the raw materials are easily available, and industrial production can be easily realized.

[0024] Illustratively, the polymerization reaction temperature may be 120°C, 121°C, 122°C, 123°C, 124°C, 125°C, 126°C, 127°C, 128°C, 129°C, 130°C or a range consisting of any two thereof, preferably 130°C, and the polymerization reaction time may be 2h, 3h, 4h or a range consisting of any two thereof, preferably 2-3h.

[0025] It is understandable that in order to enhance the effect of the polymerization reaction and improve the initial viscosity of the cured adhesive, the raw materials such as the polyol and the first isocyanate should be mixed under a constant temperature condition to perform the polymerization reaction.

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

[0027] Specifically, the above-mentioned polyol can include one or more of poly(methyl propylene adipate) glycol ester diol, poly(butylene adipate) glycol neopentyl glycol ester diol, poly(methyl propylene adipate) glycol isophthalate diol, poly(ethylene adipate) glycol ester diol, poly(butylene adipate) glycol ester diol, poly(hexylene adipate) glycol ester diol, polypropylene glycol ether diol, and polycaprolactone, preferably poly(methyl propylene adipate) glycol ester diol and / or polypropylene glycol ether diol, further preferably poly(methyl propylene adipate) glycol ester diol having a molecular weight of 3900 to 4200 and / or polypropylene glycol ether diol having a molecular weight of 2000 to 2020.

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

[0029] The first isocyanate may include isocyanate containing phenyl. In the preparation system of the embodiment of the present invention, the use of the first isocyanate containing phenyl is conducive to obtaining a curing adhesive with higher initial viscosity, and the strength of the board made using the curing adhesive is higher.

[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] Under the preparation system of the embodiment of the present invention, the dosage of the polyol, the first isocyanate and the second isocyanate can meet the following requirements: based on the mass sum 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%; it is conducive to obtaining a cured adhesive with excellent initial viscosity.

[0032] The inventors have found in their research that a higher molecular weight cured adhesive with higher initial viscosity can be obtained when the molar ratio of isocyanate groups in isocyanate to hydroxyl groups in polyol is 1.1 to 1.3.

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

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

[0035] In addition, based on the sum of the masses of the polyol and the first isocyanate, the mass fraction of the catalyst may be 0 to 200 ppm, and the mass fraction of phosphoric acid may 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 a specific implementation, the polyol is heated to 120-130° C. under a nitrogen atmosphere, and then the polyol is stirred at a rotation speed of 150-200 r / min, and the first isocyanate is added at the same time.

[0038] In order to improve the reactivity of the second isocyanate, the second isocyanate may be preheated before adding the second isocyanate to the polymer product. That is, the second isocyanate is added to the polymer product, reacted at 120-130°C for 0.5-1h to obtain a cured adhesive, including: preheating the second isocyanate to 80-100°C, then adding it to the polymer product, reacting at 120-130°C for 0.5-1h to obtain a cured adhesive. Exemplarily, the preheating temperature may be 80°C, 90°C, 100°C, or a range consisting of any two thereof, preferably 80°C, and the reaction time may be 0.5h, 0.6h, 0.7h, 0.8h, 0.9h, 1h, or a range consisting of any two thereof, preferably 1h.

[0039] It is understandable that in order to improve the effect of the reaction between the second isocyanate and the polymer product, the second isocyanate may be added to the polymer product under stirring.

[0040] Nowadays, the adhesives commonly used in the wood-based panel industry are mostly aldehyde adhesives, such as urea-formaldehyde adhesives, melamine-modified formaldehyde resin adhesives, phenolic adhesives, etc. These adhesives all use formaldehyde as a production raw material and contain a large amount of free formaldehyde. Formaldehyde release problems are inevitable during use, polluting the indoor environment and endangering health. Formaldehyde-free adhesives, such as polymerized diphenylmethane diisocyanate adhesives (PMDI adhesives), are widely used because they do not release formaldehyde, do not cause pollution and health problems, and have the advantages of 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, and do not have good initial adhesion effects.

[0041] The embodiment of the present invention adopts raw materials without aldehydes to prepare a formaldehyde-free curing adhesive (high initial viscosity formaldehyde-free curing adhesive). The formaldehyde-free curing adhesive has excellent initial viscosity and can be used to prepare artificial boards, especially formaldehyde-free particleboards.

[0042] The embodiment of the present invention further provides a curing adhesive, which can be obtained according to the above-mentioned preparation method of the curing adhesive. The curing adhesive has excellent initial adhesion.

[0043] The curing adhesive can be used for preparing boards, such as artificial boards, and is particularly suitable for preparing particle boards.

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

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

[0046] Exemplarily, the cold pressing pressure may be 3MPa, 4MPa, 5MPa, 6MPa or a range consisting of any two thereof, the hot pressing pressure may be 3MPa, 4MPa, 5MPa, 6MPa or a range consisting of any two thereof, preferably 4-5MPa, and the hot pressing temperature may be 200°C, 220°C, 240°C, 260°C, 280°C or a range consisting of any two thereof, preferably 220-240°C.

[0047] The cold pressing time may be 10 to 50 s, for example 10 s, 20 s, 30 s, 40 s, 50 s or a range consisting of any two thereof, and the hot pressing time may be 50 to 100 s, for example 50 s, 60 s, 70 s, 80 s, 95 s, 100 s or a range consisting of any two thereof.

[0048] Generally, before cold pressing, the mixed material needs to be laid out and formed. The mixed material can be evenly spread in the mold frame by air flow laying or diamond roller laying. After moderate extrusion and forming, it is cold pressed (pre-cold pressing) to form a slab, and then the slab is hot pressed (high temperature hot pressing) to obtain particleboard.

[0049] In some embodiments, the process of mixing curing glue, wood shavings, and water to obtain a mixed material includes: spraying curing glue and water sequentially onto the wood shavings in a stirring state to mix the curing glue, wood shavings, and water to obtain a mixed material. For example, the wood shavings are placed in a blender for stirring, and then a spray gun is used to spray the curing glue and water onto the wood shavings in a stirring state to fully stir and mix to obtain a mixed material.

[0050] The wood chips mentioned above may include wood chips.

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

[0052] Based on the sum of the masses of the curing glue, water and wood shavings, the mass percentage of the curing glue can be 2% to 3%, for example, 2%, 2.2%, 2.4%, 2.6%, 2.8%, 3% or a range consisting of any two of them, 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 a range consisting of any two of them, preferably 10% to 10.1%, and the mass percentage of wood shavings can be 87% to 88%, for example, 87%, 87.2%, 87.5%, 87.8%, 88% or a range consisting of any two of them, preferably 87% to 87.5%.

[0053] The embodiment of the present invention further provides a particle board, which can be obtained according to the above-mentioned preparation method.

[0054] Since the curing adhesive includes formaldehyde-free curing adhesive, the formaldehyde-free particleboard can be prepared by using the formaldehyde-free curing adhesive (high initial viscosity formaldehyde-free curing adhesive) in the above-mentioned particleboard preparation method system. The formaldehyde-free particleboard does not release formaldehyde during use, is healthy and environmentally friendly, and also has good mechanical properties and bonding strength and other properties, and has good application prospects.

[0055] The present invention is further described below by specific examples and comparative examples. Unless otherwise specified, the reagents, materials and instruments used below are all conventional reagents, conventional materials and conventional instruments, which can be commercially available, and the reagents and materials involved can also be synthesized by conventional synthesis 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] Dehydrating poly(methyl propane adipate) diol (polyol) having a molecular weight of 4000 at 110° C. and a vacuum state of 0.1 MPa for 1 h to remove moisture, then heating it to 130° C. under a nitrogen atmosphere, adding 4,4'-diphenylmethane diisocyanate (MDI) (first isocyanate) under stirring at 180 r / min, and performing a polymerization reaction at 130° C. for 2 h to obtain a polymerization product;

[0062] After preheating polymethylene polyphenyl isocyanate (PM) (second isocyanate) to 80°C, add it to the above-mentioned polymer product under stirring at 200 r / min, and mix thoroughly for 1 hour to obtain a formaldehyde-free curing adhesive;

[0063] Among them, based on the sum of the masses of the polyol, the first isocyanate and the second isocyanate, the mass percentage of polymethyl propylene 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] The wood shavings are placed in a glue mixer for stirring, and then the formaldehyde-free curing glue and water are sprayed onto the wood shavings in sequence by using a spray gun to fully mix the formaldehyde-free curing glue, water and wood shavings to obtain a mixed material; the mixed material is evenly spread and formed, and then cold-pressed at a pressure of 4 MPa for 20 seconds, and then hot-pressed at a pressure of 4 MPa at 220° C. for 95 seconds to obtain a formaldehyde-free particleboard;

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

[0067] Comparative Example 1

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

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

[0070] Among them, based on the sum of the masses of polyvinyl acetate emulsion (PVAC emulsion C), water, PM and wood shavings, the mass percentage of polyvinyl acetate emulsion (PVAC emulsion C) is 0.4%, the mass percentage of water is 9.6%, the mass percentage of PM is 3%, and the mass percentage of wood shavings is 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 by a commercially available ethylene-vinyl acetate copolymer emulsion (EVA emulsion D), and the mass percentage of the 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 the formaldehyde-free particleboard in this comparative example comprises:

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

[0077] Wherein, based on the sum of the masses of polymethylene polyphenyl isocyanate (PM), water and wood chips, the mass percentage of polymethylene polyphenyl isocyanate (PM) is 3%, the mass percentage of water is 10%, and the mass percentage of wood chips is 87%.

[0078] Referring to Example 1, the curing adhesive (formaldehyde-free curing adhesive) and particle board (formaldehyde-free particle board) in Examples 1 to 12 and Comparative Examples 4 to 6 were prepared, wherein in the examples using a catalyst and phosphoric acid, the catalyst and phosphoric acid were added to the reaction system simultaneously with the first isocyanate.

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

[0080] Table 1

[0081]

[0082]

[0083] Table 2

[0084]

[0085]

[0086] Test example

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

[0088] 1) Initial viscosity of the curing adhesive: The initial viscosity of the curing adhesive was measured according to the "inclined push plate measurement method". Specifically, the wood chips after the glue application (the mixture obtained by fully mixing the formaldehyde-free curing adhesive, water and wood chips in each embodiment) were placed in a 30*30 cm mold frame, evenly spread and then appropriately squeezed and molded with a mold cover. After the molding, it was placed in a press for cold pressing (cold pressing at a pressure of 4 MPa for 20 seconds). The thickness of the slab after the cold pressing was 18 mm, and then multiple pieces of the slab after the cold pressing were placed in a press. The slab is placed on a 45° slope and pushed down the slope at a speed of 2 cm / s. The number of broken slabs and the width of the slab when it first breaks are recorded. The slab is picked up by hand to feel the looseness and the looseness is scored on a scale of 1-5. The higher the score, the harder the slab is. For example, 5 points means the slab is harder and 1 point means the slab is looser. The fewer the broken pieces and the wider the width of the slab when it first breaks, the higher the score of the slab looseness is, and the better the initial adhesion of the curing adhesive.

[0089] 2) Screen blocking of wood chips after sizing: The wood chips after sizing (the mixture obtained by fully mixing the formaldehyde-free curing glue, water and wood chips in each embodiment) were evenly sprinkled into the feed port of the blower, and the screen blocking of the discharge port was observed; wherein the wind speed of the blower was 3m / s, and the larger the screen blocking area, the more serious the agglomeration of wood chips after sizing and the more serious the screen blocking;

[0090] 3) Internal bonding strength of formaldehyde-free particleboard: The shavings after gluing (the mixture obtained by fully mixing the formaldehyde-free curing glue, water and shavings in each embodiment) are placed in a 30*30 cm mold frame, evenly spread and properly extruded with a mold cover, and after molding, placed in a press and hot-pressed at 220°C and a pressure of 4MPa for 95s to obtain a board, the thickness of which is controlled at 12mm with a thickness gauge, and tested with reference to the internal bonding strength test method in the national standard GBT 17657-2022;

[0091] 4) Formaldehyde emission of formaldehyde-free particleboard: Tested in accordance with the national standard GBT 17657-2022, Formaldehyde Emission Determination-Dryer Method.

[0092] Test results

[0093] Table 3 Initial viscosity, mesh blocking, mechanical properties and formaldehyde release

[0094]

[0095] Data Analysis:

[0096] It can be seen from the data in the above table that the formaldehyde-free curing adhesive (high initial adhesion formaldehyde-free curing adhesive) for formaldehyde-free particleboard (artificial board) prepared in the embodiment of the present invention has excellent initial adhesion performance, and its cold pressing adhesion is stronger than that of the commercially available PVAC emulsion of Comparative Example 1 and Comparative Example 3, and there is no mesh blocking compared with the commercially available EVA emulsion of Comparative Example 2, and the looseness of the wood particles can be maintained before cold pressing, and the good adhesion after cold pressing prevents the pre-pressed board from frayed edges or broken;

[0097] Compared with the comparative example, the internal bonding strength of the particleboard after hot pressing is basically not affected at all, and the preparation process of the high initial viscosity formaldehyde-free curing glue does not contain organic solvents, and does not use formaldehyde as a synthetic raw material, which reduces the release of formaldehyde from the board, reduces the harm of formaldehyde to health, and improves the environmental protection performance of the artificial board. In addition, the high initial viscosity formaldehyde-free curing glue for artificial boards prepared in the embodiment of the present invention can be directly applied when used without adding a tackifier, saving production costs such as transportation and equipment, greatly improving factory production efficiency, and can be widely used in the fields of particleboard, oriented strand board, straw board, etc.

[0098] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements 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: Allowing a polyol and a first isocyanate to undergo a polymerization reaction to obtain a polymerization product; wherein the molecular weight of the polyol is greater than or equal to 2000, the polymerization reaction temperature is 120 to 130° C., and the polymerization reaction time is 2 to 4 hours; The second isocyanate is added to the polymer product, and reacted at 120-130° C. for 0.5-1 hour to obtain the cured adhesive; wherein the second isocyanate includes polymethylene polyphenyl isocyanate.

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

3. The method for preparing a curing adhesive according to claim 1, characterized in that: The molar ratio of the isocyanate group in the first isocyanate to the hydroxyl group in the polyol is (1.1-1.3):

1.

4. The method for preparing a curing adhesive according to claim 1, characterized in that: Based on the sum of the masses 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%.

5. The method for preparing a curing adhesive according to claim 1, characterized in that: The polyol comprises one or more of poly(methyl propylene adipate glycol), poly(butylene adipate glycol), poly(methyl propylene adipate isophthalate glycol), poly(ethylene adipate glycol), poly(butylene adipate glycol), poly(hexylene adipate glycol), polypropylene glycol ether glycol, and polycaprolactone, preferably poly(methyl propylene adipate glycol) and / or polypropylene glycol ether glycol; And / or, 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.

6. The method for preparing a curing adhesive according to claim 1, characterized in that: The process of polymerizing the polyol and the first isocyanate to obtain a polymer product comprises: 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 sum of the polyol and the first isocyanate, the mass fraction of the catalyst is 0 to 200 ppm, and the mass fraction of the phosphoric acid is 0 to 200 ppm, 0 to 30 ppm, preferably 0 to 20 ppm; the catalyst comprises one or more of zinc octoate, stannous octoate, and dibutyltin dilaurate, preferably dibutyltin dilaurate; And / or, adding the second isocyanate to the polymerization product and reacting at 120-130°C for 0.5-1h to obtain the cured adhesive comprises: preheating the second isocyanate to 80-100°C, then adding it to the polymerization product and reacting at 120-130°C for 0.5-1h to obtain the cured adhesive.

7. A curing adhesive, characterized in that: The curing adhesive is obtained according to the preparation method of the curing adhesive according to any one of claims 1 to 6.

8. The curing adhesive according to claim 7, characterized in that: The curing glue is formaldehyde-free curing glue.

9. A method for preparing a particleboard, characterized in that: include: Mixing curing glue, wood shavings and water to obtain a mixed material; the curing glue includes the curing glue according to claim 7; The mixed material is subjected to cold pressing and hot pressing in sequence to obtain the particle board; wherein the pressure of the cold pressing is 3-6MPa, the pressure of the hot pressing is 3-6MPa, preferably 4-5MPa, and the temperature of the hot pressing is 200-280°C, preferably 220-240°C.

10. A particle board, characterized in that: The particle board is obtained according to the preparation method described in claim 9.

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