A halogen-free flame retardant suitable for urea-formaldehyde resin, flame-retardant urea-formaldehyde resin using the same, and flame-retardant plywood.

Abstract

This invention discloses a halogen-free flame retardant suitable for urea-formaldehyde resin, flame-retardant urea-formaldehyde resin using the same, and flame-retardant plywood. The halogen-free flame retardant of this invention comprises the following components: lightly calcined magnesium oxide, magnesium sulfate heptahydrate, retarder, water, boron-based flame retardant, water-reducing agent, blending agent, and magnesium calcium carbonate. The flame-retardant urea-formaldehyde resin is obtained by uniformly mixing the above-mentioned halogen-free flame retardant, urea-formaldehyde resin, and ordinary flour. Then, the flame-retardant urea-formaldehyde resin and veneer are cold-pressed and hot-pressed to obtain flame-retardant plywood. The halogen-free flame retardant of this invention, through a magnesium gel system, improves the bonding strength and flame-retardant properties of urea-formaldehyde resin. Combined with the boron-based flame retardant, it exhibits good stability in urea-formaldehyde resin, exerting a synergistic flame-retardant effect. This invention adds magnesium cement to urea-formaldehyde resin, which, along with other flame-retardant components, can be fully dispersed in the urea-formaldehyde resin. Plywood treated with this invention can achieve a B1 flame-retardant rating, and the addition of the halogen-free flame retardant significantly reduces the corrosivity of the flame-retardant plywood.

Description

Technical Field

[0001] This invention relates to the field of flame retardants, and more particularly to a halogen-free flame retardant suitable for urea-formaldehyde resin, flame-retardant urea-formaldehyde resin using the same, and flame-retardant plywood. Background Technology

[0002] In recent years, with the continuous improvement of people's living standards, plywood has been widely used in the construction, furniture, and decoration industries. However, its flammability is a fatal weakness, which inevitably limits its application. Therefore, flame-retardant treatment of plywood is necessary. Most domestic and international flame-retardant treatments for plywood involve impregnating the veneer with inorganic or organic flame-retardant agents. This process is complex, and the veneer has poor resistance to leaching, easily absorbs moisture, and generally reduces the bonding strength of the boards. Using flame-retardant urea-formaldehyde resin adhesive can achieve both bonding and flame-retardant functions. Flame-retardant plywood produced without altering the plywood production process meets the requirements of the Japanese JISD1201-77 standard for Class 1 flame-retardant organic materials used in automobile interiors.

[0003] Traditional impregnation processes for producing fire-retardant plywood are complex, time-consuming, costly, and inefficient. Conventional wood flame retardants are acidic and highly corrosive to the impregnation equipment, affecting its lifespan and product stability. Furthermore, the veneers need to be air-dried outdoors after impregnation, making them highly susceptible to weather and site limitations. In contrast, new adhesive-grade flame retardants can be directly added to urea-formaldehyde resin, simplifying the process and increasing production efficiency. Urea-formaldehyde resin is produced by the condensation of urea and formaldehyde under alkaline or acidic catalysts to form initial urea-formaldehyde resin, which is then further processed into an insoluble final resin adhesive under the action of curing agents or additives. To enhance the fire-retardant properties of urea-formaldehyde resin, a specialized flame retardant needs to be added. However, phosphorus-nitrogen-based flame retardants, when directly added to urea-formaldehyde resin, can disrupt its stability and pH balance, affecting plywood quality, resulting in poor flame retardant performance and high costs. Summary of the Invention

[0004] To address the problems of unstable flame retardant effect, cumbersome process, long board production cycle, and corrosion during application of existing flame-retardant plywood prepared with veneer impregnation flame retardants using urea-formaldehyde resin, this invention provides a halogen-free flame retardant suitable for urea-formaldehyde resin, flame-retardant plywood using it, and its preparation method. By adding magnesium gel material to urea-formaldehyde resin, the resin acquires some of the characteristics of magnesium cement. During cold-press pre-curing and hot-press curing, the inorganic gel system can absorb water from the urea-formaldehyde resin while absorbing water and releasing heat, resulting in faster curing, reduced pressing time, and improved production efficiency. In this invention, active magnesium oxide and magnesium sulfate heptahydrate undergo a hydration reaction in water to produce basic magnesium sulfate and magnesium hydroxide, both excellent refractory materials. This is a key technical point in the halogen-free flame retardant composition of this invention.

[0005] To solve the above-mentioned technical problems, the specific technical solution of the present invention is as follows:

[0006] A halogen-free flame retardant suitable for urea-formaldehyde resins, comprising the following components by weight:

[0007]

[0008] The lightly calcined magnesia is produced by calcining magnesite at a temperature of 400℃-600℃. The magnesia content in the lightly calcined magnesia is not less than 85%, of which the active magnesia powder content is not less than 70%. The fineness of the lightly calcined magnesia powder is 50 mesh-500 mesh. The content of active magnesia directly affects the physical and chemical properties of the formed plate.

[0009] Furthermore, the retarder of the present invention is selected from any one or more of anhydrous citric acid, sodium citrate, oxalic acid, and phosphoric acid.

[0010] Furthermore, the boron-based flame retardant described in this invention is sodium tetraborate.

[0011] Furthermore, the water-reducing agent described in this invention is sodium lignosulfonate; the main function of sodium lignosulfonate as a water-reducing agent is to increase hydration efficiency, reduce the unit water consumption, and prevent the moisture in the flame-retardant adhesive from being lost too quickly, thus preventing the adhesive from being heat-cured under hot-pressing conditions.

[0012] Furthermore, the blending agent described in this invention is selected from any one or a mixture of two of ammonium sulfate and potassium citrate; the main function of the blending agent is to adjust the curing time of the flame retardant adhesive.

[0013] In this invention, the lightly calcined magnesium oxide, magnesium sulfate heptahydrate, retarder, and water are all magnesium gel system materials, which mainly play a role in flame retardancy and cementitious bonding. Boron-based flame retardant and calcium magnesium carbonate are respectively soluble flame retardant and insoluble inorganic substances. Inorganic substances themselves are non-flammable, while boron-based flame retardant has the effect of flame retardancy and smoke suppression, thereby improving the overall flame retardant performance of the flame retardant adhesive.

[0014] This invention also provides a flame-retardant urea-formaldehyde adhesive using the above-mentioned halogen-free flame retardant, which is obtained by thoroughly mixing the above-mentioned halogen-free flame retardant with urea-formaldehyde adhesive and ordinary flour. The mass fraction of urea-formaldehyde adhesive is 300-500 parts, and the mass fraction of ordinary flour is 80-150 parts. The mass fraction basis of both is consistent with the mass fraction basis of each component in the above-mentioned halogen-free flame retardant. By using ordinary flour to increase the initial tack of the adhesive and adjust the consistency of the flame-retardant adhesive, the veneers can be initially bonded to each other during the subsequent cold pressing process, and the veneer will not fall apart.

[0015] The preparation method of the flame-retardant urea-formaldehyde resin of the present invention includes:

[0016] (1) Mix magnesium sulfate heptahydrate, retarder, blender and water and heat to 50-70℃ to accelerate the dissolution of crystals in water until they are completely dissolved to obtain solution I;

[0017] (2) Pour solution I into urea-formaldehyde resin, then add lightly calcined magnesium oxide, sodium tetraborate, sodium lignosulfonate, calcium magnesium carbonate and ordinary flour and stir thoroughly to obtain the flame-retardant urea-formaldehyde resin of the present invention.

[0018] This invention also provides a flame-retardant plywood using the above-mentioned flame-retardant urea-formaldehyde adhesive. The preparation method is as follows: the core board is coated with the above-mentioned urea-formaldehyde adhesive on both sides using a double-sided adhesive applicator, while the veneers are not coated with adhesive. This adhesive application method can improve the installation efficiency and adhesive application efficiency of the plywood. The veneers serve as the two outer surfaces of the plywood. Several veneers and the coated core board are sequentially spliced ​​together, with the same type of board not in contact. The splicing direction is perpendicular. Then, the boards are pressed sequentially by a cold press and a hot press to completely cure the adhesive, thus producing the flame-retardant plywood of this invention.

[0019] The solid content of the flame-retardant urea-formaldehyde resin described in this invention is 45%-55%.

[0020] The adhesive application rate on one side of the core board described in this invention is 500-580 g / m². 2 The amount of adhesive applied to both sides of the core board is the same.

[0021] The cold press described in this invention has a pressing time of 1-4 hours and a unit pressure of 0.8-1.5 MPa; the hot press has a pressing condition of 1.5-2 MPa, a hot pressing temperature of 120°C, and a hot pressing time of 12-20 minutes.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] By utilizing the hydration reaction of lightly calcined magnesium oxide and magnesium sulfate heptahydrate in water with other additives, moisture in the urea-formaldehyde resin is absorbed, allowing the heated urea-formaldehyde resin to quickly form a film and act as an adhesive. The basic magnesium sulfate and magnesium hydroxide generated during hydration are excellent refractory materials. Combined with the soluble boron-based flame retardant sodium tetraborate, the modified urea-formaldehyde resin exhibits strong flame retardant properties. Furthermore, the magnesium sulfate-oxygenate gel solidifies rapidly upon heating, and both urea-formaldehyde resin and magnesium sulfate-oxygenate gel have the same curing time at 120°C. Both can act as adhesives between veneers, thus maintaining the bonding strength of the plywood. In addition, the halogen-free flame retardant of this invention does not precipitate after absorbing moisture, while commercially available impregnated flame retardants easily precipitate after absorbing moisture, leading to flame retardant loss and corrosion of the metal in direct contact.

[0024] The halogen-free flame retardant of this invention utilizes a magnesium gel system to improve the bonding strength and flame retardant properties of urea-formaldehyde resin. Combined with a boron-based flame retardant, it exhibits good stability within the urea-formaldehyde resin, resulting in a synergistic flame retardant effect. This invention incorporates magnesium cement into the urea-formaldehyde resin, allowing it to disperse fully with other flame retardant components. Plywood treated with this invention achieves a B1 flame retardant rating, and the addition of the halogen-free flame retardant significantly reduces the corrosiveness of the flame-retardant plywood. Detailed Implementation

[0025] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0026] Example 1

[0027] A method for preparing flame-retardant plywood using flame-retardant urea-formaldehyde resin containing halogen-free flame retardants includes the following steps:

[0028] (1) Take 4 kg of magnesium sulfate heptahydrate, 0.04 kg of anhydrous citric acid and 0.5 kg of ammonium sulfate and add them to 3 kg of water. Heat to 60°C and stir until completely dissolved to obtain solution I;

[0029] (2) Pour solution I into 37 kg of urea-formaldehyde resin, then add 6.5 kg of lightly calcined magnesium oxide (the magnesium oxide content in the lightly calcined magnesium oxide is 90%, the active magnesium oxide content is 85%, and the fineness of the lightly calcined magnesium oxide powder is 325 mesh), 1.25 kg of sodium tetraborate, 0.06 kg of sodium lignosulfonate, 1.5 kg of calcium magnesium carbonate, and 11 kg of ordinary flour. Stir thoroughly to obtain flame-retardant urea-formaldehyde resin.

[0030] (3) Apply the flame-retardant urea-formaldehyde resin obtained in step (2) to a 2.8mm thick poplar veneer that has been dried using a double-sided gluing machine at room temperature, with a glue application rate of 540g / m². 2 A poplar veneer with glue applied (i.e., the core board) is spliced ​​with two un-glued veneers. The veneer is then pressed in a cold press for 4 hours at room temperature, maintaining a unit pressure of 0.8 MPa. After that, it is sent to a hot press for 20 minutes at a unit pressure of 2 MPa and a temperature of 120°C to obtain a flame-retardant plywood.

[0031] Example 2

[0032] A method for preparing flame-retardant plywood using flame-retardant urea-formaldehyde resin containing halogen-free flame retardants includes the following steps:

[0033] (1) Take 3 kg of magnesium sulfate heptahydrate, 0.02 kg of phosphoric acid and 0.1 kg of ammonium sulfate, add 2 kg of water, heat to 50 °C and stir until completely dissolved to obtain solution I;

[0034] (2) Pour solution I into 31 kg of urea-formaldehyde resin, then add 5 kg of lightly calcined magnesium oxide (the magnesium oxide content in the lightly calcined magnesium oxide is 85%, the active magnesium oxide content is 70%, and the fineness of the lightly calcined magnesium oxide powder is 500 mesh), 0.02 kg of sodium lignosulfonate, 1 kg of sodium tetraborate, 1 kg of calcium magnesium carbonate, and 9.3 kg of ordinary flour. Stir thoroughly to obtain flame-retardant urea-formaldehyde resin.

[0035] (3) Apply the flame-retardant urea-formaldehyde resin obtained in step (2) to a 2.8mm thick poplar veneer that has been dried using a double-sided gluing machine at room temperature, with a glue application rate of 500g / m². 2 A poplar veneer with glue applied (i.e., the core board) is spliced ​​with two un-glued veneers. The veneer is then pressed in a cold press for 1 hour at room temperature, maintaining a unit pressure of 1.5 MPa. After that, it is sent to a hot press for 12 minutes at a unit pressure of 1.5 MPa and a temperature of 120°C to obtain a flame-retardant plywood.

[0036] Example 3

[0037] A method for preparing flame-retardant plywood using flame-retardant urea-formaldehyde resin containing halogen-free flame retardants includes the following steps:

[0038] (1) Take 5 kg of magnesium sulfate heptahydrate, 0.08 kg of oxalic acid and 1 kg of ammonium sulfate and add them to 4 kg of water. Heat to 70°C and stir until completely dissolved to obtain solution I;

[0039] (2) Pour solution I into 50 kg of urea-formaldehyde glue, then add 8 kg of lightly calcined magnesium oxide (the magnesium oxide content in the lightly calcined magnesium oxide is 85%, the active magnesium oxide content is 80%, and the fineness of the lightly calcined magnesium oxide powder is 50 mesh), 1.5 kg of sodium tetraborate, 0.1 kg of sodium lignosulfonate, 2 kg of calcium magnesium carbonate and 11 kg of ordinary flour and stir thoroughly to obtain flame-retardant urea-formaldehyde glue.

[0040] (3) Apply the flame-retardant urea-formaldehyde resin obtained in step (2) to a 2.8mm thick poplar veneer that has been dried using a double-sided gluing machine at room temperature, with a glue application rate of 580g / m². 2 A poplar veneer with glue applied (i.e., the core board) is spliced ​​with two un-glued veneers. The veneer is then pressed in a cold press for 2.5 hours at room temperature, maintaining a unit pressure of 1 MPa. After that, it is sent to a hot press for 15 minutes at a unit pressure of 1.8 MPa and a temperature of 120°C to obtain a flame-retardant plywood.

[0041] Comparative Example 1

[0042] A method for preparing flame-retardant plywood, comprising the following steps:

[0043] (1) Take 35kg of ammonium polyphosphate, 30kg of ordinary flour and 100kg of urea-formaldehyde glue, mix them and stir evenly to obtain flame retardant glue;

[0044] (2) Apply the flame-retardant urea-formaldehyde resin obtained in step (1) to a 2.8mm thick poplar veneer that has been dried using a double-sided gluing machine at room temperature, with a glue application rate of 540g / m². 2 A poplar veneer with glue (i.e., core board) is spliced ​​with two unglued veneers. The veneer is then pressed in a cold press for 3 hours at room temperature, maintaining a unit pressure of 1.5 MPa. After that, it is sent to a hot press for 20 minutes at a unit pressure of 2 MPa and a temperature of 120°C to obtain flame-retardant plywood.

[0045] Comparative Example 2

[0046] A method for preparing flame-retardant plywood, comprising the following steps:

[0047] (1) Take 4 kg of magnesium sulfate heptahydrate, 0.04 kg of anhydrous citric acid and 0.5 kg of ammonium sulfate and add them to 3 kg of water. Heat to 60°C and stir until completely dissolved to obtain solution I;

[0048] (2) Pour solution I into 37 kg of urea-formaldehyde glue, then add 6.5 kg of lightly calcined magnesium oxide (the magnesium oxide content in the lightly calcined magnesium oxide is 85%, the active magnesium oxide content is 70%, and the fineness of the lightly calcined magnesium oxide powder is 500 mesh), 0.06 kg of sodium lignosulfonate, 1.5 kg of calcium magnesium carbonate and 11 kg of ordinary flour and stir thoroughly to obtain flame-retardant urea-formaldehyde glue;

[0049] (3) Apply the flame-retardant urea-formaldehyde resin obtained in step (2) to a 2.8mm thick poplar veneer that has been dried using a double-sided gluing machine at room temperature, with a glue application rate of 540g / m². 2 A poplar veneer with glue (i.e., the core board) is spliced ​​with two unglued veneers. The veneer is then pressed in a cold press for 2 hours at room temperature, maintaining a unit pressure of 1 MPa. After that, it is sent to a hot press for 20 minutes at a unit pressure of 2 MPa and a temperature of 120°C to obtain a flame-retardant plywood.

[0050] Comparative Example 3

[0051] A method for preparing flame-retardant plywood includes the following steps:

[0052] (1) Take 4 kg of magnesium sulfate heptahydrate, 0.04 kg of anhydrous citric acid and 0.5 kg of ammonium sulfate and add them to 3 kg of water. Heat to 60°C and stir until completely dissolved to obtain solution I;

[0053] (2) Pour solution I into 37 kg of urea-formaldehyde glue, then add 6.5 kg of lightly calcined magnesium oxide (the magnesium oxide content in the lightly calcined magnesium oxide is 85%, the active magnesium oxide content is 50%, and the fineness of the lightly calcined magnesium oxide powder is 200 mesh), 1.25 kg of sodium tetraborate, 0.06 kg of sodium lignosulfonate, 1.5 kg of calcium magnesium carbonate and 11 kg of ordinary flour and stir thoroughly to obtain flame-retardant urea-formaldehyde glue;

[0054] (3) Apply the flame-retardant urea-formaldehyde resin obtained in step (2) to a 2.8mm thick poplar veneer that has been dried using a double-sided gluing machine at room temperature, with a glue application rate of 540g / m². 2 A poplar veneer with glue applied (i.e., the core board) is spliced ​​with two un-glued veneers. The veneer is then pressed in a cold press for 4 hours at room temperature, maintaining a unit pressure of 1.5 MPa. After that, it is sent to a hot press for 20 minutes at a unit pressure of 2 MPa and a temperature of 120°C to obtain a flame-retardant plywood.

[0055] Comparative Example 4

[0056] A method for preparing flame-retardant plywood includes the following steps:

[0057] (1) Take 4 kg of magnesium sulfate heptahydrate, 0.04 kg of anhydrous citric acid and 0.5 kg of ammonium sulfate and add them to 3 kg of water. Heat to 60°C and stir until completely dissolved to obtain solution I;

[0058] (2) Pour solution I into 37 kg of urea-formaldehyde glue, then add 6.5 kg of lightly calcined magnesium oxide (the magnesium oxide content in the lightly calcined magnesium oxide is 85%, the active magnesium oxide content is 70%, and the powder fineness is 500 mesh), 1.25 kg of sodium tetraborate, 0.06 kg of sodium lignosulfonate and 11 kg of ordinary flour and stir thoroughly to obtain flame-retardant urea-formaldehyde glue;

[0059] (3) Apply the flame-retardant urea-formaldehyde resin obtained in step (2) to a 2.8mm thick poplar veneer that has been dried using a double-sided gluing machine at room temperature, with a glue application rate of 540g / m². 2 A poplar veneer with glue (i.e., core board) is spliced ​​with two unglued veneers. At room temperature, it is pressed in a cold press for 1 hour, maintaining a unit pressure of 1.5 MPa. Then, it is sent to a hot press for 20 minutes, with a unit pressure of 2 MPa and a temperature of 120°C, to obtain flame-retardant plywood.

[0060] Comparative Example 5

[0061] A method for preparing flame-retardant plywood includes the following steps:

[0062] (1) Take 4 kg of magnesium sulfate heptahydrate, 0.04 kg of anhydrous citric acid and 0.5 kg of ammonium sulfate and add them to 3 kg of water. Heat to 60°C and stir until completely dissolved to obtain solution I;

[0063] (2) Pour solution I into 37 kg of urea-formaldehyde glue, then add 6.5 kg of lightly calcined magnesium oxide (the magnesium oxide content in the lightly calcined magnesium oxide is 85%, the active magnesium oxide content is 70%, and the powder fineness is 500 mesh), 1.25 kg of sodium tetraborate, 0.06 kg of sodium lignosulfonate, 1.5 kg of calcium magnesium carbonate and 11 kg of ordinary flour and stir thoroughly to obtain flame-retardant urea-formaldehyde glue;

[0064] (3) Apply the flame-retardant urea-formaldehyde resin obtained in step (2) to a 2.8mm thick poplar veneer that has been dried using a double-sided gluing machine at room temperature, with a glue application rate of 540g / m². 2 A poplar veneer with glue (i.e., core board) is spliced ​​with two unglued veneers. At room temperature, it is pressed in a cold press for 30 minutes, maintaining a unit pressure of 0.5 MPa, and then sent to a hot press for 10 minutes, maintaining a unit pressure of 1.5 MPa and a temperature of 90°C, to obtain flame-retardant plywood.

[0065] The results of the single-unit combustion test (GB / T20284-2006) and limiting oxygen index test (GB / T 2406-2009) of the flame-retardant plywood obtained in Examples 1-3 and Comparative Examples 1-5 are shown in Table 1.

[0066] Table 1. Test results of plywood obtained in Examples 1-3 and Comparative Examples 1-5

[0067]

[0068] The test results in Table 1 show that the flame retardant properties of the plywood obtained in Examples 1-3 all meet the national standard requirements of B1-B. Comparing the combustion performance test results of Example 1 and Comparative Examples 1-5, it can be concluded that the addition of sodium tetraborate can improve the overall flame retardant performance of the adhesive; insufficient activity of magnesium oxide will affect the formation of magnesium hydroxide, thus having a certain impact on the flame retardant effect; and calcium magnesium carbonate can improve the fire resistance of the adhesive to a certain extent. In Comparative Example 2, the combustion performance of the individual components decreased significantly without sodium tetraborate. Compared with Comparative Example 4, the addition of calcium magnesium carbonate in the examples of this application helps to improve the flame retardant performance.

[0069] The bonding strength of the flame-retardant plywood obtained in Examples 1-3 and Comparative Examples 1-5 was tested (GB / T17657-2013), and the results are shown in Table 2.

[0070] Table 2. Test results of the bonding strength of fire-retardant plywood obtained in Examples 1-3 and Comparative Examples 1-5.

[0071]

[0072] As can be seen from the bonding strength test results in Table 2, the bonding strength of Comparative Example 1 failed to meet the standard. This is because after the soluble flame retardant and urea glue are mixed and pressed into flame-retardant plywood using cold and hot presses, the soluble flame retardant inside the urea glue will recrystallize after the moisture evaporates, causing the urea glue to lose its original adhesiveness on the veneer. Moreover, this type of flame retardant will be lost in the air, especially in humid environments, which will have a significant adverse effect on the bonding performance and flame retardant performance of the plywood. Some cheap flame retardants, after being lost, will also have a strong corrosive effect on metal parts, seriously endangering building safety. The main problem causing the bonding strength to fail in Comparative Examples 3 and 5 is that the active magnesium oxide content in Comparative Example 3 is insufficient. The magnesium gel system formed by it has low strength and does not play a strong adhesive role between the veneers. The use of conventional active magnesium oxide content in Comparative Example 3 not only affects the flame retardant performance but also the bonding performance. In Comparative Example 5, due to the substandard cold and hot pressing conditions, the glue could not fully cure and react, so the bonding strength failed to meet the standard.

Claims

1. A halogen-free flame retardant suitable for use in urea-formaldehyde glue, characterized in that, By mass fraction, including the following components: Light-burned magnesium oxide 50-80 parts, Magnesium sulfate heptahydrate 30-50 parts, Retarder 0.2-0.8 parts, Water 20-40 parts, Boron-based flame retardant 10-15 parts, Water reducing agent 0.2-1 parts, Harmonizing agent 1-10 parts, Calcium magnesium carbonate 10-20 parts; The light-burned magnesium oxide is calcined from magnesite at a temperature of 400-600 ℃, the content of magnesium oxide in the light-burned magnesium oxide is not less than 85%, and the content of active magnesium oxide powder is not less than 70%, the fineness of the light-burned magnesium oxide powder is 50-500 mesh; The harmonizing agent is selected from any one or mixture of two of ammonium sulfate and potassium citrate; The boron-based flame retardant is sodium tetraborate.

2. A halogen-free flame retardant suitable for use in urea-formaldehyde glue according to claim 1, characterized in that, The retarder is selected from one or more of anhydrous citric acid, sodium citrate, oxalic acid, and phosphoric acid.

3. A halogen-free flame retardant suitable for urea-formaldehyde glue according to claim 1, characterized in that, The water reducing agent is sodium lignosulfonate.

4. A flame-retardant urea-formaldehyde adhesive comprising the halogen-free flame retardant of any one of claims 1 to 3, characterized in that, The halogen-free flame retardant is uniformly mixed with urea-formaldehyde glue and ordinary flour, wherein the mass fraction of urea-formaldehyde glue is 300-500 parts, the mass fraction of ordinary flour is 80-150 parts, and the mass fraction of the two is consistent with the mass fraction of each component in the halogen-free flame retardant.

5. A process for the preparation of the fire-retardant urea-formaldehyde adhesive of claim 4, characterized in that, It includes: (1) Mix magnesium sulfate heptahydrate, retarder, harmonizing agent, and water, heat to 50-70 ℃, accelerate the dissolution of crystals in water until completely dissolved, to obtain solution I; (2) Pour solution I into urea-formaldehyde glue, then add light-burned magnesium oxide, sodium tetraborate, sodium lignosulfonate, calcium magnesium carbonate, and ordinary flour, mix well to obtain the flame-retardant urea-formaldehyde glue.

6. A method for preparing fire-retardant plywood using the fire-retardant urea-formaldehyde adhesive according to claim 4, characterized in that, It includes: Use a double-sided glue spreader to coat the core board with the urea-formaldehyde glue on both sides, do not coat the single board, use the single board as the outer surface of the plywood, sequentially splice the single boards and the coated core board, the same board does not contact, the splicing direction is vertical, then sequentially pass through the cold press and the hot press to completely cure the glue, to produce the flame-retardant plywood; The cold press pressing time is 1-4 h, and the unit pressure is 0.8-1.5 MPa; the hot press pressing condition is a unit pressure of 1.5-2 MPa, a hot pressing temperature of 120 ℃, and a hot pressing time of 12-20 min; The solid content of the flame-retardant urea-formaldehyde glue is 45%-55%. The single-side sizing amount of the core board is 500-580 g / m 2 The two-side sizing amounts of the core board are the same.

Images