A manufacturing process of F4 star grade all-junk wood floor base material

Abstract

The present application belongs to the technical field of artificial board, and relates to a manufacturing process of F4-star full-mixed wood floor base material, which comprises the following steps: feeding, peeling, slicing, screening, washing, pre-cooking, cooking, hot grinding, glue adjusting, drying, sorting, paving, pre-pressing, hot pressing, turning plate cooling, curing, sanding, sawing, inspection grading and packaging and warehousing. In the feeding step, the wood raw material is mixed wood. In the glue adjusting step, the super-low free formaldehyde content melamine modified urea-formaldehyde resin is applied, and the glue application amount is 12-18% of the weight proportion of the absolute dry resin to the absolute dry fiber. In the paving step, the unique leveling roller design is adopted to eliminate the board blank fluctuation caused by the property difference of the mixed wood fiber. The preparation method of the applied glue is also disclosed. The resin itself has a low molar ratio, the process of adding urea and melamine for multiple times is adopted, and the acetone is added during the resin reaction. The water resistance is improved, the cost is considered, and the formaldehyde release amount of the base material reaches the F4-star standard.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of artificial board, and relates to the preparation of artificial fiber board, in particular to a manufacturing process of F4-star full mixed wood floor substrate. BACKGROUND

[0002] The reinforced wood floor has been the first choice for people to decorate indoor floor due to its natural wood texture, natural warmth, beautiful pattern and good surface wear resistance. Generally, high-density fiber board is used as the floor substrate, which is made of wood as raw material, fiber preparation, synthetic resin application, and pressed under heating and pressure. Nowadays, the fiber board industry is generally faced with two problems. One is that the urea-formaldehyde resin adhesive used in the production of fiber board has poor water resistance, the glue layer is easy to age, and there is formaldehyde pollution in the production and use process, which is difficult to meet the requirements of people for green and environmentally friendly home concept. The second is that the wood resources are increasingly scarce, and high-quality pine wood is in short supply. In the future, only mixed wood can be used for production. Mixed wood is the trade name of broad-leaved wood, which refers to a variety of tree species, and the single tree species resource is not concentrated.

[0003] GB / T 39600-2021 "Formaldehyde Emission from Wood-based Panels and Their Products" divides the formaldehyde emission standard into E1, E0 and E NF NF The "F4 star" is the highest health level of Japanese standard environmental protection, which is better than the national standard E0 level, but does not reach the E NF If the floor reaches the F4 star standard, the formaldehyde emission is required to be less than 0.3mg / L. Corresponding to the fiber board substrate, the formaldehyde emission is required to be ≤3mg / 100g (the formaldehyde emission corresponding to the national standard E0 level is ≤5mg / 100g). However, the improvement of environmental protection level will inevitably lead to the problems of mechanical property and water resistance. The characteristics of mixed wood, such as multiple species and large differences between fibers, are more difficult to control the product quality.

[0004] The present application aims to develop a kind of ultra-low free formaldehyde content melamine modified urea-formaldehyde resin, and apply it to F4-star full mixed wood floor substrate. The produced F4-star full mixed wood floor substrate has fine fiber morphology and reasonable surface core layer density, uniform internal quality, good mechanical properties and water resistance, and higher environmental protection level, with formaldehyde emission below 3mg / 100g. SUMMARY

[0005] In view of the problems existing in the prior art, the present application aims to disclose a manufacturing process of F4-star full mixed wood floor substrate.

[0006] A kind of F4 star grade full mixed wood floor substrate manufacturing process, comprising the following steps: feeding→ peeling→ chip→ screening→ washing→ pre-cooking→ cooking→ hot grinding→ glue→ drying→ sorting→ paving→ pre-pressing→ hot pressing→ board cooling→ curing→ sanding→ sawing→ inspection grading→ packaging storage, wherein:

[0007] In the feeding step, the wood raw material is selected from mixed wood;

[0008] In the glue adjusting step, ultra-low free formaldehyde content melamine modified urea-formaldehyde resin is applied in the fiber spraying pipeline, and the glue application amount is 12-18% of the absolute dry resin weight proportion of the absolute dry fiber; At the same time, composite curing agent is applied, and the addition amount is 2-4% of the absolute dry resin weight;

[0009] In the drying step, the fiber moisture content is 8-10%;

[0010] In the paving step, the board density is 820-860 kg / m 3 ;

[0011] In the hot pressing step, continuous hot pressing process is adopted, and the board is hot pressed at a temperature of 150-250 DEG C, and the pressure factor is 7-10 s / mm.

[0012] In the preferred disclosure of the application, the composite curing agent in the glue adjusting step is mixed by ammonium sulfate and oxalic acid in a mass ratio of 3:1, and the remaining 75% is water.

[0013] In the preferred disclosure of the application, four flat rollers are installed at the outlet of the paving chamber in the paving step, wherein the front two flat rollers are selected from needle type teeth; The rear two flat rollers are selected from spiral teeth.

[0014] In the preferred disclosure of the application, for the thickness ≤8mm thin plate, the hot pressing temperature and hot pressing pressure are set as follows: five temperature zones are adopted: 225±5 DEG C, 215±5 DEG C, 200±5 DEG C, 175±5 DEG C, 165±5 DEG C; Hot pressing pressure distribution: the pressure of the inlet section rises to 3.2-3.6 MPa, the pressure of the rebound section gradually decreases to 2.0-3.0 MPa, the pressure of the core layer gradually decreases to 0.2-0.8 MPa, and the pressure of the thickness setting section is 1.2-1.8 MPa.

[0015] In the preferred disclosure of the application, for the thickness >8mm thick plate, the hot pressing temperature and hot pressing pressure are set as follows: five temperature zones are adopted: 235±5 DEG C, 230±5 DEG C, 210±5 DEG C, 195±5 DEG C, 180±5 DEG C; Hot pressing pressure distribution: the pressure of the inlet section rises to 3.0-3.5 MPa, the pressure of the rebound section gradually decreases to 1.6-2.8 MPa, the pressure of the core layer gradually decreases to 0.05-0.15 MPa, and the pressure of the thickness setting section is 1.0-1.5 MPa.

[0016] The super low free formaldehyde content melamine modified urea-formaldehyde resin described in the present application does not use the traditional "alkali-acid-alkali" synthesis process, but "alkali-acid-acid-alkali" synthesis process. Among them, formaldehyde is added once, urea is added four times, and melamine is added twice. The whole synthesis process is divided into four stages of alkaline addition reaction, acid one-step condensation, acid two-step condensation and alkaline post-treatment.

[0017] In order to achieve the above purpose, the present application is implemented according to the following technical scheme.

[0018] The preparation method of the super low free formaldehyde content melamine modified urea-formaldehyde resin described above comprises the following steps:

[0019] A. First, the reaction kettle is charged with formaldehyde, and the pH value is adjusted to 8.3-8.5 with sodium hydroxide solution;

[0020] B. Add the first urea and the first melamine, open the steam to warm up, and slowly warm up to 88-90℃ (including the self-heating time after closing the steam) for 55-60 minutes. The pH value during heating should not be lower than 7.2;

[0021] C. Keep the temperature at 88-90℃ for 30 minutes, and measure the pH value and viscosity;

[0022] D. Adjust the pH value to 5.0-5.3 by adding formic acid three times, add acetone, and react at 89-90℃. Observe the changes of pH value and viscosity constantly to ensure that the pH value is not lower than 5.0, and the reaction end point viscosity is controlled at 16-18 seconds (30℃, cup-4);

[0023] E. After reaching the viscosity, immediately add liquid alkali to adjust the pH value to 6.4-6.8;

[0024] F. After the pH value reaches, add the second urea and the second melamine, and react at 80-85℃ for 30 minutes. The reaction end point viscosity is controlled at 17-19 seconds (30℃, cup-4), and the pH value should be 6.3-6.5;

[0025] G. After reaching the viscosity, add alkali to adjust the pH value to 8-9, and cool to 75℃. Add the third urea and keep the temperature for 20 minutes;

[0026] H. Cool to 70℃, add the fourth urea;

[0027] I. Cool to below 43℃, add alkali to adjust the pH value to 8.5-9.5, detect the pH value and viscosity, and discharge the glue.

[0028] The various materials participating in the reaction are as follows: the concentration of formaldehyde is 37%, the concentration of formic acid is 30%, the concentration of liquid alkali is 20% sodium hydroxide solution, the weight of melamine accounts for 4-10% of the total weight of the resin, the weight of urea accounts for 40-46% of the total weight of the resin, the molar ratio of formaldehyde to urea and melamine F / (U+M) is 0.82-0.86, and the addition amount of acetone accounts for 1-1.5% of the total weight of urea.

[0029] In the preferred disclosure of the application, the distribution ratio of the four times of urea is as follows: the first time of urea accounts for 32-36% of the total weight of urea; the second time of urea accounts for 16-20% of the total weight of urea; the third time of urea accounts for 29-33% of the total weight of urea; and the fourth time of urea accounts for 15-19% of the total weight of urea.

[0030] In the preferred disclosure of the application, the distribution ratio of the two times of melamine is as follows: the first time of melamine accounts for 65-70% of the total weight of melamine; and the second time of melamine accounts for 30-35% of the total weight of melamine.

[0031] The super-low free formaldehyde content melamine modified urea-formaldehyde resin prepared by the application has a pH value of 8.5-9.5, a viscosity of 15-17 seconds (25 DEG C, coating-4 cup), a solid content of 55±2%, a curing time of 250-350 seconds, and a free formaldehyde content of 0.02-0.05%.

[0032] Advantages

[0033] The preparation method of the super-low free formaldehyde content melamine modified urea-formaldehyde resin disclosed by the application and applied to F4 star grade full mixed wood floor base material has the following advantages:

[0034] 1. The resin itself has a low molar ratio; the process of adding urea and melamine multiple times can better capture the excess formaldehyde in the resin and reduce the free formaldehyde content in the resin; the use of a composite curing agent promotes the complete curing of the resin, and in particular, the oxalic acid in the composite curing agent can react with more formaldehyde during curing, thereby reducing the formaldehyde release amount. Through the above three methods, the formaldehyde release amount of the full mixed wood floor base material produced can reach the F4 star grade standard.

[0035] 2. The resin is synthesized by adding a low proportion of melamine, which improves water resistance and also takes cost into account. Most of the melamine is added in the addition reaction stage, which facilitates the formation of more methylol melamine and the synthesis of linear resin with longer molecular chains in the polycondensation reaction. The addition of acetone during the first polycondensation increases the flexibility of the molecular chain and improves the brittleness of the resin. The hydroxy aldehyde condensation reaction occurs under acid catalysis, increasing the carbon chain, solidifying and cross-linking the molecular chain into a body-type insoluble and infusible structure, and improving moisture absorption, thereby solving the problem of poor water resistance of F4 star-grade floor base materials due to the use of all mixed wood as raw material.

[0036] 3. The mixed wood board blank is first scattered and recombined using a needle-type tooth equalization roller, and then the board blank fibers are transported horizontally using a spiral tooth equalization roller, which improves the horizontal uniformity of the board blank and eliminates fluctuations in the board blank caused by differences in the properties of the mixed wood fibers. Through the matching of appropriate hot pressing processes, the F4 star-grade mixed wood floor base material produced has reasonable surface-core layer density and good mechanical properties. DETAILED DESCRIPTION

[0037] The application will be described in detail below with reference to examples, so that those skilled in the art can better understand the application, but the application is not limited to the following examples.

[0038] Example 1

[0039] 1. Preparation method of melamine-modified urea-formaldehyde resin with ultra-low free formaldehyde content

[0040] The weight of melamine accounts for 8% of the weight of the modified urea-formaldehyde resin, the weight of urea accounts for 40% of the weight of the modified urea-formaldehyde resin, and the molar ratio of formaldehyde to urea and melamine F / (U+M) is 0.83. Formaldehyde is all added at once, urea is added in four batches, and melamine is added in two batches.

[0041] The preparation process is as follows:

[0042] A. First, add formaldehyde to the reaction kettle, and adjust the pH value to 8.3-8.5 with sodium hydroxide solution;

[0043] B. Add the first batch of urea and the first batch of melamine (the first batch of urea accounts for 35% of the total weight of urea; the first batch of melamine accounts for 70% of the total weight of melamine), heat with steam, and slowly heat to 88-90°C (including the self-heating time after the steam is turned off) for 55-60 minutes. The pH value during heating should not be lower than 7.2;

[0044] C. Keep the temperature at 88-90°C for 30 minutes, and measure the pH value and viscosity;

[0045] D. Add formic acid to adjust pH value to 5.0-5.3, add acetone (acetone addition amount accounts for 1.5% of total weight of urea), and react at 89-90℃, constantly observe the change of pH value and viscosity, and ensure that the pH value is not lower than 5.0; the viscosity at the end of reaction is controlled to be 16-18 seconds (30℃, cup-4);

[0046] E. After the viscosity is reached, immediately add liquid alkali to adjust the pH value to 6.4-6.8;

[0047] F. After the pH value is reached, add second urea and second melamine (the second urea accounts for 18% of the total weight of urea; the second melamine accounts for 30% of the total weight of melamine), and react at 80-85℃ for 30 minutes; the viscosity at the end of reaction is controlled to be 17-19 seconds (30℃, cup-4), and the pH value should be 6.3-6.5;

[0048]

[0049] G. After the viscosity is reached, add alkali to adjust the pH value to 8-9, cool to 75℃, add third urea (the third urea accounts for 30% of the total weight of urea), and keep warm for 20 minutes;

[0050] H. Cool to 70℃, and add fourth urea (the fourth urea accounts for 17% of the total weight of urea);

[0051] I. Cool to below 43℃, add alkali to adjust the pH value to 8.5-9.5, detect the pH value and viscosity, and glue out.

[0052] 2. Manufacturing process of 7.7mm F4 star grade full mixed wood floor base material

[0053] The manufacturing process of a 7.7mm F4 star grade full mixed wood floor base material comprises the following steps: feeding→ peeling→ slicing→ screening→ washing→ pre-cooking→ cooking→ hot grinding→ glue adjusting→ drying→ sorting→ paving→ pre-pressing→ hot pressing→ turning plate cooling→ curing→ sanding→ sawing→ inspection and grading→ packaging and warehousing, wherein:

[0054] In the feeding step, only mixed wood is selected as the wood raw material.

[0055] In the screening step, qualified wood pieces with a length and width of 4-55mm and a thickness of 3-5mm are screened out.

[0056] In the washing step, the wood pieces are washed by water to remove impurities such as mud, stones and metals, so as to ensure the cleanliness of the wood pieces.

[0057] In the pre-cooking step, the pre-cooking temperature is controlled to be 95±5℃.

[0058] ​In the cooking step, the wood chips are softened by cooking, the cooking pressure is 8-9 bar, and the cooking time is 4 min.

[0059] In the hot grinding step, the wood chips are fed into the hot grinder by a belt screw, molten paraffin or emulsified paraffin is added to the grinder, the paraffin application amount is 7-8 kg / m 3 , the gap between the grinding discs is controlled at 0.15 mm, and the fiber separation yield is 20-25 tons / hour.

[0060] In the glue adjusting step, an ultra-low free formaldehyde content melamine modified urea-formaldehyde resin is applied in the fiber spraying pipeline, the glue application amount is 14% of the absolute dry fiber weight; at the same time, a composite curing agent is applied, the addition amount is 2.5% of the absolute dry resin weight.

[0061] The composite curing agent is mixed by ammonium sulfate and oxalic acid in a ratio of 3:1, and the rest is 75% water.

[0062] In the drying step, the fiber moisture content is controlled at 9-10%.

[0063] In the laying step, the mat density is controlled at 840-860 kg / m 3 . At the outlet of the laying room, four leveling rollers are installed, among which the front two are needle-tooth leveling rollers, and the back two are spiral-tooth leveling rollers.

[0064] In the hot pressing step, a continuous hot pressing process is adopted, the mat is hot pressed at a temperature of 160-230°C, and the pressure factor is 8-8.5 s / mm. The hot pressing temperature and pressure are set as follows: five temperature zones are adopted: 225±5°C, 215±5°C, 200±5°C, 175±5°C, and 165±5°C; the hot pressing pressure distribution: the inlet segment pressure rises to 3.2-3.6 MPa, the rebound segment pressure gradually decreases to 2.0-3.0 MPa, the core layer insulation segment gradually decreases to 0.2-0.8 MPa, and the thickness setting segment pressure is 1.2-1.8 MPa.

[0065] In the curing step, the cooled board is stacked and cured for 48 hours to balance the board performance.

[0066] In the sanding step, the "two coarse sand + two fine sand" method is adopted, and the four sanding sanding amounts are distributed as follows: the first sanding amount is 55-60% (50 mesh sand belt), the second sanding amount is 20-25% (80 mesh sand belt), the third sanding amount is 10-15% (100 mesh sand belt), and the fourth sanding amount is 5-10% (150 mesh sand belt).

[0067] The 7.7 mm F4 star grade full-junk wood floor base material prepared by the above steps is detected according to the standard requirements of LY / T 1611-2011 "Fiberboard for floor base material", and the results are as follows:

[0068]

[0069] Example 2

[0070] 1. Preparation method of melamine modified urea-formaldehyde resin with ultra-low free formaldehyde content

[0071] The weight of melamine accounts for 6% of the weight of the modified urea-formaldehyde resin, the weight of urea accounts for 44% of the weight of the modified urea-formaldehyde resin, and the molar ratio of formaldehyde to urea and melamine F / (U+M) is 0.85. Formaldehyde is all added at one time, urea is added in four batches, and melamine is added in two batches.

[0072] The preparation process is as follows:

[0073] A. First, add formaldehyde into the reaction kettle, and adjust the pH value to 8.3-8.5 with sodium hydroxide solution;

[0074] B. Add the first urea and the first melamine (the first urea accounts for 34% of the total weight of urea; the first melamine accounts for 70% of the total weight of melamine), heat with steam, and slowly heat to 88-90°C (including the self-heating time after stopping steam) for 55-60 minutes. The pH value during heating should not be lower than 7.2;

[0075] C. Keep the temperature at 88-90°C for 30 minutes, and measure the pH value and viscosity;

[0076] D. Adjust the pH value to 5.0-5.3 by adding formic acid three times, add acetone (the amount of acetone added accounts for 1.2% of the total weight of urea), and react at 89-90°C. Continuously observe the changes of pH value and viscosity to ensure that the pH value is not lower than 5.0. The reaction end-point viscosity is controlled at 16-18 seconds (30°C, cup-4);

[0077] E. After reaching the viscosity, immediately add liquid alkali to adjust the pH value to 6.4-6.8;

[0078] F. After the pH value reaches, add the second urea and the second melamine (the second urea accounts for 18% of the total weight of urea; the second melamine accounts for 30% of the total weight of melamine), and react at 80-85°C for 30 minutes. The reaction end-point viscosity is controlled at 17-19 seconds (30°C, cup-4), and the pH value should be 6.3-6.5;

[0079]

[0080] ​G. After reaching the desired viscosity, add alkali to adjust the pH to 8-9, cool to 75°C, add the third urea (the third urea accounts for 30% of the total weight of urea), and keep warm for 20 minutes.

[0081] H. Cool down to 70°C and add the fourth batch of urea (the fourth batch of urea accounts for 18% of the total weight of urea);

[0082] I. Cool down to below 43℃, add alkali to adjust the pH value to 8.5-9.5, test the pH value and viscosity, and then discharge the adhesive.

[0083] 2. Manufacturing process of 11.7mm F4 star-rated mixed wood flooring substrate

[0084] A manufacturing process for an 11.7mm F4 star-rated mixed wood flooring substrate includes the following steps: feeding → peeling → chipping → screening → washing → pre-cooking → cooking → hot grinding → glue preparation → drying → sorting → laying → pre-pressing → hot pressing → cooling → curing → sanding → sawing → inspection and grading → packaging and warehousing, wherein:

[0085] In the feeding step, only mixed hardwoods are selected as the raw material.

[0086] In the screening step, qualified wood chips with a length and width of 4 to 55 mm and a thickness of 3 to 5 mm are selected.

[0087] In the water washing step, the wood chips are washed with water to remove impurities such as mud, sand, stones, and metal, ensuring that the wood chips are clean.

[0088] In the pre-cooking step, the pre-cooking temperature is controlled at 95±5℃.

[0089] In the steaming step, the wood chips are softened by steaming at a pressure of 8-9 bar for 4 minutes.

[0090] In the hot grinding step, wood chips are fed into the hot mill via a belt screw conveyor, and molten paraffin or emulsified paraffin is added to the mill at a rate of 6.5–7 kg / m³. 3 The grinding disc gap is controlled at 0.15mm, and the fiber separation output is 20-25 tons / hour.

[0091] In the adhesive preparation step, melamine-modified urea-formaldehyde resin with ultra-low free formaldehyde content is applied into the fiber spraying pipe, and the amount of adhesive applied is 12% of the weight of the oven-dry resin to the weight of the oven-dry fiber; at the same time, a composite curing agent is applied, and the amount added is 3% of the weight of the oven-dry resin.

[0092] The composite curing agent is composed of ammonium sulfate and oxalic acid in a 3:1 ratio, with the remaining 75% being water.

[0093] During the drying step, the fiber moisture content is controlled at 8-9%.

[0094] In the paving step, the slab density is controlled at 830-850 kg / m 3 At the exit of the paving chamber, four flattening rollers are installed, of which the front two are needle-tooth flattening rollers and the rear two are spiral-tooth flattening rollers.

[0095] In the hot pressing step, the slab is hot pressed at a temperature of 180-240℃ using a continuous hot pressing process, and the pressure factor is 7.5-8.5 s / mm. The hot pressing temperature and pressure are set as follows: five temperature zones are used: 235±5℃, 230±5℃, 210±5℃, 195±5℃, and 185±5℃; the hot pressing pressure distribution is: the pressure at the inlet section is raised to 3.0-3.5 MPa, the pressure at the rebound section is gradually reduced to 1.6-2.8 MPa, the pressure at the core layer insulation section is gradually reduced to 0.05-0.15 MPa, and the pressure at the thickness setting section is 1.0-1.5 MPa.

[0096] In the curing step, the cooled slab is stacked and cured for 48 hours to balance the slab performance.

[0097] In the sanding step, a "two coarse sanding + two fine sanding" method is used, and the sanding amount distribution of the four sanding steps is as follows: the first sanding amount accounts for 55-60% (50 mesh sand belt), the second sanding amount accounts for 20-25% (80 mesh sand belt), the third sanding amount accounts for 10-15% (100 mesh sand belt), and the fourth sanding amount accounts for 5-10% (150 mesh sand belt).

[0098] The 11.7 mm F4 star-rated full-junk wood floor base material prepared through the above steps is detected according to the LY / T 1611-2011 "Fiberboard for Floor Base Material" standard requirements, and the results are as follows:

[0099]

[0100]

[0101] The above only describes the embodiments of the present application, and does not limit the patent scope of the present application, and any equivalent structure or equivalent process transformation made by the present application specification, or direct or indirect application in other related technical fields, are also included in the patent protection scope of the present application.

Claims

1. A manufacturing process of F4 star-rated all-hybrid wood flooring substrate, comprising the following steps: The process comprises the following steps: feeding, peeling, slicing, screening, washing, pre-cooking, cooking, hot grinding, glue mixing, drying, sorting, laying, pre-pressing, hot pressing, turning, curing, sanding, sawing, testing, grading and packing. In the feeding step, the wood raw material is selected from mixed wood; In the glue mixing step, the melamine modified urea-formaldehyde resin with ultra-low free formaldehyde content is applied in the fiber spraying pipeline, the glue application amount is 12-18% of the absolute dry resin weight based on the absolute dry fiber weight, and a composite curing agent is simultaneously applied, the addition amount being 2-4% of the absolute dry resin weight; the composite curing agent is prepared by mixing ammonium sulfate and oxalic acid in a mass ratio of 3:1, and the remaining 75% being water; the preparation method of the melamine modified urea-formaldehyde resin with ultra-low free formaldehyde content comprises the following steps: A. First, formaldehyde is put into the reaction kettle, and the pH value is adjusted to 8.3-8.5 by using sodium hydroxide solution; B. First-time urea and first-time melamine are added, steam heating is started, and the temperature is slowly raised to 88-90℃ for 55-60 minutes, and the pH value should not be lower than 7.2 during the temperature rising period; C. The temperature is kept at 88-90℃ for 30 minutes, and the pH value and viscosity are measured; D. The pH value is adjusted to 5.0-5.3 by adding formic acid three times, and acetone is added, and the reaction is carried out at 89-90℃, and the changes of pH value and viscosity are observed constantly to ensure that the pH value is not lower than 5.0, and the reaction end-point viscosity is controlled to be 16-18 seconds, 30℃, and co-4 cups; E. After the viscosity is reached, liquid alkali is immediately added to adjust the pH value to 6.4-6.8; F. After the pH value is reached, second-time urea and second-time melamine are added, and the reaction is carried out at 80-85℃ for 30 minutes, and the reaction end-point viscosity is controlled to be 17-19 seconds, 30℃, and co-4 cups, and the pH value should be 6.3-6.5; G. After the viscosity is reached, the pH value is adjusted to 8-9 by adding alkali, the temperature is lowered to 75℃, and third-time urea is added, and the temperature is kept for 20 minutes; H. The temperature is lowered to 70℃, and fourth-time urea is added; I. The temperature is lowered to below 43℃, the pH value is adjusted to 8.5-9.5 by adding alkali, and the pH value and viscosity are detected, and the glue is discharged; The concentrations of the various materials participating in the reaction are as follows: the concentration of formaldehyde is 37%, the concentration of formic acid is 30%, the concentration of liquid alkali is 20% sodium hydroxide solution, the weight of melamine accounts for 4-10% of the total weight of the resin, the weight of urea accounts for 40-46% of the total weight of the resin, the molar ratio of formaldehyde to urea and melamine F / (U+M) is 0.82-0.86, and the addition amount of acetone accounts for 1-1.5% of the total weight of urea; In the drying step, the water content of the fiber is 8-10%; In the paving step, at the exit of the paving chamber, 4 flattening rollers are installed, wherein the front 2 flattening rollers are selected as needle tooth flattening rollers, and the rear 2 flattening rollers are selected as spiral tooth flattening rollers, and the density of the slab after paving is 820-860 kg / m 3 ; In the hot pressing step, the continuous hot pressing process is adopted, and the board blank is hot pressed at a temperature of 150-250℃, and the pressure factor is 7-10 s / mm.

2. The manufacturing process of F4 star-rated all-junk wood floor base material according to claim 1, characterized in that: For the thin plate with thickness ≤8mm, the hot pressing temperature and pressure are set as follows: five temperature zones are adopted: 225±5℃, 215±5℃, 200±5℃, 175±5℃, 165±5℃; the hot pressing pressure distribution is: the pressure of the inlet section is raised to 3.2-3.6MPa, the pressure of the rebound section is gradually reduced to 2.0-3.0MPa, the pressure of the core layer holding section is gradually reduced to 0.2-0.8MPa, and the pressure of the thickness setting section is 1.2-1.8MPa.

3. The manufacturing process of F4 star-rated all-junk wood floor base material according to claim 1, characterized in that: For the thick plate with thickness >8mm, the hot pressing temperature and pressure are set as follows: five temperature zones are adopted: 235±5℃, 230±5℃, 210±5℃, 195±5℃, 180±5℃; the hot pressing pressure distribution is: the pressure of the inlet section is raised to 3.0-3.5MPa, the pressure of the rebound section is gradually reduced to 1.6-2.8MPa, the pressure of the core layer holding section is gradually reduced to 0.05-0.15MPa, and the pressure of the thickness setting section is 1.0-1.5MPa.

4. The manufacturing process of F4 star-rated all-junk wood floor base material according to claim 1, characterized in that, The distribution ratio of the four urea is: the first urea accounts for 32-36% of the total weight of urea; the second urea accounts for 16-20% of the total weight of urea; the third urea accounts for 29-33% of the total weight of urea; and the fourth urea accounts for 15-19% of the total weight of urea.

5. The manufacturing process of F4 star-rated all-junk wood floor base material according to claim 1, characterized in that, The distribution ratio of the two melamine is: the first melamine accounts for 65-70% of the total weight of melamine; and the second melamine accounts for 30-35% of the total weight of melamine.

6. The manufacturing process of F4 star-rated all-junk wood floor base material according to claim 1, characterized in that: The temperature rising time in step B includes the self-heating time after the steam is turned off.

7. The manufacturing process of F4 star-rated all-junk wood floor base material according to claim 1, characterized in that: The melamine modified urea-formaldehyde resin with ultra-low free formaldehyde content has a pH value of 8.5-9.5, a viscosity of 15-17 seconds at 25℃, a coating-4 cup, a solid content of 55±2%, a curing time of 250-350 seconds, and a free formaldehyde content of 0.02-0.05%.

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