Manufacturing process of fiberboard for running board of running machine

Abstract

The invention belongs to the technical field of artificial boards, and relates to a manufacturing process of a fiberboard for a running board of a treadmill, which comprises a complete process from raw wood feeding to packaging and warehousing, and is characterized in that mountain miscellaneous wood stacked for not more than one month is selected as a raw material, and water-resistant high-strength melamine modified urea resin and a latent composite curing agent are applied; and drying, paving and hot pressing parameters are optimized. The water-resistant high-strength melamine modified urea-formaldehyde resin is synthesized by adopting an alkali-acid-acid-alkali process, and has the advantages of fast curing, strong bonding and good water resistance; the composite curing agent can avoid pre-curing and promote curing of the core layer; and hot pressing adopts a five-section warm-pressing zoning design. The surface layer density of the product is high, the static bending intensity reaches 49-55 MPa, the internal bonding strength, the water resistance and the environmental protection property are excellent, and the use requirements of the running board of the running machine are completely met.

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 fiber board for treadmill running board. BACKGROUND

[0002] With the improvement of national health consciousness, the fitness equipment market continues to expand, and the market demand for treadmills as the mainstream indoor fitness equipment is increasing year by year. The treadmill running board, as the core bearing component of the treadmill, directly affects the safety, comfort and service life of the equipment, so strict requirements are put forward for its performance, and the treadmill running board has become a new application direction of high-density fiber board. The fiber board for treadmill running board is a high-density fiber board prepared by using wood fiber or other plant fiber as raw material, preparing fiber, applying synthetic resin, and pressing under the condition of heating and pressing. The board has high density, high static bending strength, high surface density, high internal bonding strength, good flatness, uniform thickness, and can be used as a treadmill running board after veneering. Among the key indicators of the fiber board for treadmill running board, the static bending strength is about 40-50% higher than that of ordinary high-density fiber board, which is the core technical difficulty in the current industry.

[0003] In the prior art, the production of the fiber board for treadmill running board mainly has the following problems: 1. Insufficient resin performance: the traditional urea-formaldehyde resin has defects such as slow curing speed, low bonding strength, poor water resistance, etc., which makes it difficult to meet the key indicators of the fiber board such as static bending strength, internal bonding strength and water absorption thickness expansion rate, and the fiber board cannot withstand the repeated impact load during long-term use of the treadmill; 2. Contradiction of hot pressing process: in order to improve the surface density and static bending strength, the hot pressing pressure and pressure rising speed need to be increased, but the rapid densification of the surface layer will hinder the heat transfer to the core layer, resulting in incomplete curing of the resin in the core layer, and quality problems such as internal bonding strength reduction and board delamination; 3. Poor compatibility of curing agent: the conventional curing agent is prone to pre-curing during the fiber drying stage, which not only wastes resin and increases production cost, but also affects the bonding effect in the subsequent hot pressing process; 4. Unreasonable use of raw materials: some manufacturers choose soft and miscellaneous wood or wood that has been stored for too long as raw materials, which has low fiber strength and is prone to rot and deterioration when stored for too long, resulting in a decrease in fiber quality and ultimately affecting the mechanical properties of the board.

[0004] In view of the above technical problems, the present application aims to develop a water-resistant high-strength melamine-modified urea-formaldehyde resin and optimize the supporting fiber board manufacturing process. Through multi-dimensional improvement such as raw material optimization, resin modification, curing agent compounding and hot pressing parameter optimization, the defects in the prior art are solved, and a fiber board for treadmill running board with excellent performance is produced to meet the market demand for high-performance treadmill running boards. SUMMARY

[0005] In view of the problems in the prior art, the purpose of the present application is to disclose a manufacturing process of a fiberboard for a treadmill running board, which realizes the performance advantages of high surface layer density, high static bending strength, excellent internal bonding strength, good water resistance, and good flatness, and fully meets the use requirements of the treadmill running board.

[0006] Technical scheme

[0007] A manufacturing process of a fiberboard for a treadmill running board, comprising the following steps: log feeding, debarking, slicing, screening, water washing, pre-cooking, cooking, hot grinding, glue mixing, drying, sorting, paving, pre-pressing, hot pressing, board turning cooling, curing, sanding, sawing, inspection and grading, and packaging and warehousing, and the key technical parameters and control requirements of each step are as follows:

[0008] Log feeding: select mountain miscellaneous wood with a stacking time of not more than one month as the wood raw material. The reason for selecting mountain miscellaneous wood is that it is hard and has high density, and its fiber strength is significantly better than that of conventional soft miscellaneous wood; limiting the stacking time to not more than one month can effectively prevent the destruction of the fiber structure due to mold and rot of the wood, and ensure the stability of the fiber quality, laying a foundation for improving the mechanical strength of the board.

[0009] Debarking: mechanical debarking equipment is used to remove the bark on the surface of the log. The bark has low fiber content and many impurities, and removing it can improve the purity of the wood chips and avoid affecting the subsequent fiber preparation and board performance.

[0010] Slicing: a slicing machine is used to process the debarked logs into wood chips, and the size of the wood chips needs to be controlled to be 4-55mm in length, 4-55mm in width, and 3-5mm in thickness. The wood chips in this size range are easy to operate in the subsequent screening and water washing processes, and can ensure uniform penetration of heat and moisture during cooking and hot grinding, improving the fiber separation effect.

[0011] Screening: a vibrating screen is used to classify and screen the sliced wood chips, remove the broken wood chips with a length of less than 4mm, a width of less than 4mm, and a thickness of less than 3mm, and the oversized wood chips with a length of more than 55mm, a width of more than 55mm, and a thickness of more than 5mm, and only the qualified wood chips are retained for the next process to ensure the consistency of the raw materials.

[0012] Water washing: the screened wood chips are sent to a water washing equipment and washed with flowing water for 5-10min at a water temperature of 50-60℃. The purpose is to remove impurities such as sand, stones, and metals from the wood chips to prevent damage to the subsequent processing equipment, and to ensure the cleanliness of the wood chips to prevent impurities from affecting the internal bonding quality of the board.

[0013] Pre-cooking: the cleaned wood chips are sent to the pre-cooking tank, the pre-cooking temperature is controlled at 95±5℃, and the holding time is 10-15 min. Through low-temperature pre-cooking, the wood chips are preliminarily softened, which creates conditions for subsequent high-temperature and high-pressure cooking and fiber separation, and reduces the energy consumption in the hot grinding process.

[0014] Cooking: the wood chips after pre-cooking enter the cooking tank, and a high-temperature and high-pressure cooking process is adopted. The cooking pressure is controlled at 8.2-8.5 bar, and the cooking time is 2.5-3 min. Through the action of high temperature and high pressure, the lignin in the wood chips is softened, the hemicellulose is partially degraded, and the binding force between the wood fibers is destroyed, which facilitates the full separation of fibers in the subsequent hot grinding process.

[0015] Hot grinding: the wood chips after cooking are sent to the hot grinder through the belt screw conveyor. During the hot grinding process, molten paraffin or emulsified paraffin is added to the grinder as a water-proof agent. The paraffin application amount is 5.5-7 kg / m 3 ; the gap between the grinding discs of the hot grinder is controlled at 0.10-0.12 mm, and the fiber separation yield is 18-24 tons / hour. By controlling the gap between the grinding discs and the paraffin application amount, fibers with uniform length and good dispersion can be obtained, and a waterproof film is formed on the surface of the fibers, which improves the water resistance of the board.

[0016] Glue adjustment: in the pipeline where the fibers are sprayed from the hot grinder, a water-resistant high-strength melamine modified urea-formaldehyde resin is uniformly applied through an atomizing glue application device. The glue application amount (the proportion of absolute dry resin to the weight of absolute dry fibers) is 16-22%; at the same time, a latent composite curing agent is applied, and the addition amount is 2-4% of the weight of the absolute dry resin.

[0017] The water-resistant high-strength melamine modified urea-formaldehyde resin is synthesized by a "alkali-acid-acid-alkali" four-stage process. Formaldehyde is added once, urea is added four times, and melamine is added twice. The specific preparation steps are as follows:

[0018] A. Add formaldehyde with a concentration of 37% to the reaction kettle, add 7-8% water based on the total weight of the resin, and stir uniformly. Then adjust the pH value to 8.0-8.5 with a 20% sodium hydroxide solution. Subsequently, add the first urea (36-42% of the total weight of urea), the first melamine (60-70% of the total weight of melamine), and 2-3% phenol based on the total weight of the resin, and stir to mix uniformly.

[0019] B. Start the heating device of the reaction kettle, and heat to 90℃. Control the steam node to avoid sudden temperature rise. Keep the temperature at 90-92℃ for 30 minutes. After the holding period is over, detect the pH value of the reaction system. Ensure that the pH value is ≥6.5.

[0020] C. Stop heating, naturally cool to 86℃, start slowly drop 30% concentration of formic acid solution, adjust the pH value of the reaction system to 5.4-5.6 in 10-1 minutes, control the system temperature to maintain at 90-92℃ during the drop process, if the temperature exceeds 94℃ or the temperature rises too fast, the cooling device needs to be started to cool down;

[0021] D. After the pH value is adjusted, the resin viscosity is detected every 5-10 minutes (changed to continuous detection when approaching the reaction endpoint), the viscosity is controlled at 16.5-17.5 seconds (30℃, coating-4 cup) in this stage; the reaction time is controlled at 60-70 minutes from the start of droping the formic acid solution;

[0022] E. After reaching the preset viscosity, adjust the pH value to 6.4-6.8 with 20% concentration of sodium hydroxide solution, add 0.3-0.5% of p-toluenesulfonamide based on the total weight of the resin, then add the second urea (24-26% of the total weight of urea) and the second melamine (30-40% of the total weight of melamine), control the reaction temperature at 81-83℃, detect the viscosity every 5 minutes (changed to continuous detection in the later stage), and the reaction is stopped when the viscosity reaches 18.0-19.0 seconds (30℃, coating-4 cup), the control time in this stage is 20-25 minutes;

[0023] F. Immediately adjust the pH value to 8.0-8.5 with 20% concentration of sodium hydroxide solution, add the third urea (16-18% of the total weight of urea), and incubate at 72-74℃ for 20 minutes;

[0024] G. Adjust the pH value to 8.5-9.0 with 20% concentration of sodium hydroxide solution, add the fourth urea (18-20% of the total weight of urea), and incubate at 62-64℃ for 20 minutes, then cool the resin to below 45℃, adjust the pH value to 8.3-8.8, and then take a sample for detection.

[0025] In the above water-resistant high-strength melamine-modified urea-formaldehyde resin, the weight ratio of each raw material to the total weight of the resin is: formaldehyde 46-53%, water 7-8%, urea 35-38%, melamine 3-5%, phenol 2-3%, and p-toluenesulfonamide 0.3-0.5%; the key performance indicators of the resin are: the molar ratio of formaldehyde to urea and melamine F / (U+M) is 0.96-1.02, the pH value is 8.3-8.8, the viscosity is 14-16 seconds (25℃, coating-4 cup), the solid content is 50-53%, the curing time is 90-120 seconds, and the free formaldehyde content is 0.05-0.15%.

[0026] The latent complex curing agent consists of the following components by mass percentage: 12-15% ammonium sulfate, 7-9% triethanolamine, 4-6% phosphoric acid, and the rest is water.

[0027] Drying: After sizing, the fibers are dried using an air flow dryer to control the moisture content of the dried fibers to 7-9%. If the moisture content is too high, the water will not evaporate sufficiently during hot pressing, causing the board to bubble and delaminate. If the moisture content is too low, the fibers will become brittle, reducing heat transfer efficiency, fiber bonding, and affecting the internal bonding strength of the board.

[0028] Sorting: After drying, the fibers are sorted by a sorting device to remove incomplete fiber bundles, impurities, and glue blocks, ensuring uniform dispersion of the fibers and avoiding uneven internal structure of the board caused by fiber agglomeration, affecting flatness and mechanical properties.

[0029] Paving: After sorting, the fibers are evenly paved into a board blank using air flow paving or mechanical paving, with a board blank density of 820-840 kg / m 3 . The board blank paving must ensure uniform thickness and consistent density to avoid excessive local density deviation causing board deformation or uneven performance after hot pressing.

[0030] Pre-pressing: The paved board blank is sent to a pre-pressing machine under a pressure of 13-17 MPa for 20-50 seconds to initially form the board blank, improve its overall strength and facilitate subsequent hot pressing process transportation and positioning, avoiding board blank scattering during transportation.

[0031] Hot pressing: A continuous hot pressing process is used to hot press the pre-pressed board blank at a temperature of 185-250°C, with a pressure factor of 10-14 s / mm (i.e., hot pressing time per millimeter of board thickness).

[0032] The hot pressing temperature is controlled by five temperature zones, from the inlet to the outlet: 245±5°C, 238±5°C, 220±5°C, 200±5°C, and 190±5°C, achieving rapid curing of the board surface and sufficient curing of the core through gradient cooling.

[0033] The hot pressing pressure is controlled by segmenting the pressure distribution: the inlet segment pressure rises to 3.2-3.6 MPa to promote rapid densification of the upper and lower surfaces of the board blank, increasing the surface density; the rebound segment pressure gradually decreases to 1.8-3.0 MPa to release the internal stress of the board blank; the core layer temperature maintaining segment gradually decreases to 0.02-0.15 MPa to ensure sufficient curing of the core layer resin and remove the water generated during the hot pressing process; the thickness maintaining segment pressure is maintained at 1.0-1.5 MPa to ensure the thickness accuracy of the board.

[0034] Turnover cooling: after hot pressing, the plate is turned over by a turnover device and cooled to room temperature under natural ventilation conditions, and the cooling time is not less than half an hour, so that the internal temperature and moisture of the plate are uniformly diffused, the internal stress is reduced, and deformation in the subsequent curing or use process is avoided.

[0035] Curing: the cooled plate is stacked and cured, and a batten is placed between the plates during stacking to ensure good ventilation, and the curing time is not less than 48 hours. Through curing, the moisture content and stress in the plate can be balanced, the performance of the plate can be stabilized, and the consistency of the dimensional stability and mechanical properties can be improved.

[0036] Sanding: the cured plate is subjected to surface treatment by adopting a sanding process of "two coarse sands + two fine sands", and the sanding amount is distributed as follows: the first coarse sand (80 mesh sand belt) accounts for 55-60% of the total sanding amount, mainly to remove burrs and uneven parts on the surface of the plate; the second coarse sand (100 mesh sand belt) accounts for 20-25% of the total sanding amount, to further smooth the surface; the third fine sand (120-150 mesh sand belt) accounts for 10-15% of the total sanding amount, to improve the surface finish; and the fourth fine sand (180 mesh sand belt) accounts for 5-15% of the total sanding amount, to finally ensure that the surface flatness deviation of the plate is ≤0.1 mm / m, meeting the requirements of veneer processing.

[0037] Sawing: according to customer requirements, the sanded plate is sawn into a specified size by a precision sawing equipment, and the size deviation is controlled to be ≤±0.5 mm during sawing, to ensure the accuracy of the plate specifications.

[0038] Inspection and grading: according to the performance requirements of ordinary high-density fiberboard (HDF-GP REG) in GB / T 31765-2015 "High-density fiberboard", the density, static bending strength, elastic modulus, internal bonding strength, surface bonding strength, moisture content, water absorption thickness swelling rate, formaldehyde release amount and appearance quality of the sawn plate are detected, and according to the detection results, the plate is divided into superior products, first-class products and qualified products, and unqualified products are prohibited from entering the warehouse.

[0039] Packaging and storage: the qualified plate is packaged with moisture-proof packaging materials, and the surface of the plate is prevented from being scratched during packaging; after packaging, the plate is stored in the warehouse according to the grade and specification, and the warehouse needs to be kept dry and ventilated to prevent the plate from being damp and deteriorated.

[0040] Advantages

[0041] The water-resistant high-strength melamine modified urea-formaldehyde resin disclosed in the application and the fiber plate applied to the running board of a treadmill have the following advantages:

[0042] 1、The mountain miscellaneous wood is preferably stacked for not more than one month as raw material, on the one hand, the mountain miscellaneous wood is hard in material quality, high in density, and higher in fiber strength than conventional soft miscellaneous wood, and on the other hand, the stacking time is short, so that the wood is prevented from rotting and deteriorating to cause fiber quality to decrease, and the mechanical strength of the fiberboard is improved.

[0043] 2、The water-resistant high-strength melamine modified urea-formaldehyde resin developed by the application has the characteristics of fast curing speed, high bonding strength and good water resistance. By adding most of the melamine and a certain proportion of phenol in the alkaline addition reaction stage, the melamine can promote the crosslinking of the urea-formaldehyde resin, form a three-dimensional network structure, increase the curing speed of the resin, close the water absorption group, and improve the water resistance of the urea-formaldehyde resin; the phenol is added together with urea for hydroxymethylation, and then co-condensation, the addition of benzene ring increases the rigidity of the side chain, improves the mechanical strength and water resistance of the resin. In addition, a small amount of modifier p-toluenesulfonamide is added in the acidic secondary polycondensation reaction stage, a benzyl side chain is introduced into the molecular chain of the resin, the intermolecular attraction is reduced, the viscosity of the resin is reduced, the penetration and diffusion of the adhesive are improved, and the bonding strength of the resin is improved.

[0044] 3、By greatly increasing the hot pressing pressure and pressure increasing speed of the press inlet section, the upper and lower surfaces of the board blank are quickly cured and formed, which is beneficial to improve the surface layer density and static bending strength, and meet the use requirements of the treadmill running board. However, since the heat of the fiberboard hot pressing is gradually transferred from the surface to the core layer, the heat transfer efficiency is slow due to the densification of the surface layer, which affects the curing effect of the core layer of the board blank, and the internal bonding strength is easily reduced, and in severe cases, the fiberboard may be layered. In view of this situation, the application provides a special latent composite curing agent, which is prepared by compounding triethanolamine and phosphoric acid with conventional curing agent ammonium sulfate, so that the initial temperature of hydrogen ion release of the composite curing agent can be effectively increased, the pre-curing of the sizing fiber during drying is reduced, and the production cost is reduced. Since the board blank hot pressing is in a high temperature environment, the ionization process of phosphoric acid is easier, the acidity of the composite curing agent is enhanced, the curing of the adhesive in the board blank is promoted, and the production efficiency and product quality are improved. DETAILED DESCRIPTION

[0045] The application will be described in detail below with reference to the embodiments, so that those skilled in the art can better understand the application, but the application is not limited to the following embodiments.

[0046] Example 1

[0047] 1、Preparation method of water-resistant high-strength melamine modified urea-formaldehyde resin

[0048] A kind of water-resistant high-strength melamine modified urea-formaldehyde resin, the molar ratio F / (U+M) of formaldehyde and urea and melamine is 0.97.The weight of formaldehyde accounts for 49.3% of the total weight of the resin, the weight of water accounts for 7.6% of the total weight of the resin, the weight of urea accounts for 36.0% of the total weight of the resin, the weight of melamine accounts for 4.5% of the total weight of the resin, the weight of phenol accounts for 2.2% of the total weight of the resin, and the weight of p-toluenesulfonamide accounts for 0.4% of the total weight of the resin.Among them, formaldehyde is all put in at one time, urea is put in in four batches, and melamine is put in in two batches.

[0049] The preparation process is as follows:

[0050] A.Formaldehyde is added to the reaction kettle, water is added, and after stirring, alkali solution is added to adjust the pH value to 8.0-8.5, the first urea is added, the first melamine is added (the first urea accounts for 41% of the total weight of urea; the first melamine accounts for 65% of the total weight of melamine), and phenol is added;

[0051] B.Heat to 90℃, control the steam node well, keep at 90-92℃ for 30 minutes, and detect the pH value greater than or equal to 6.5;

[0052] C.Cool to 86℃, start to slowly add acid solution, adjust the pH value to 5.4-5.6 within 10-15 minutes, keep the temperature at 90-92℃, and cool down when the temperature exceeds 94℃ or the temperature rises too fast;

[0053] D.After adjusting the pH value, measure the viscosity every 5-10 minutes (measure continuously when approaching the end), and control the viscosity at 16.5-17.5 seconds (4-cup, 30℃ temperature measurement). Start timing after adding acid solution, and control the reaction time at 60-70 minutes;

[0054] E.Adjust the pH value to 6.4-6.8 with alkali solution, add p-toluenesulfonamide, add the second urea, and add the second melamine (the second urea accounts for 24% of the total weight of urea; the second melamine accounts for 35% of the total weight of melamine), and control the reaction temperature at 81-83℃. Measure the viscosity every 5 minutes (measure continuously in the later stage), and the reaction time is 18.0-19.0 seconds. Control the time at 20-25 minutes in this stage;

[0055] F.Immediately adjust the pH value to 8.0-8.5 with alkali solution, add the third urea (the third urea accounts for 16% of the total weight of urea), and keep at 72-74℃ for 20 minutes;

[0056] G.Adjust the pH value to 8.5-9.0 with alkali solution, add the fourth urea (the fourth urea accounts for 19% of the total weight of urea), keep at 62-64℃ for 20 minutes, cool to below 45℃, detect the pH value again, adjust to 8.3-8.8, take sample, and glue.

[0057] 2. A manufacturing process of a fiberboard for a 12mm treadmill running board

[0058] A manufacturing process of a fiberboard for a 12mm treadmill running board, comprising the following steps: raw wood feeding→ peeling→ slicing→ screening→ water washing→ pre-cooking→ cooking→ hot grinding→ glue adjusting→ drying→ sorting→ laying→ pre-pressing→ hot pressing→ turning board cooling→ curing→ sanding→ sawing→ inspection grading→ packaging storage, wherein:

[0059] In the raw wood feeding step, the wood raw material is selected from mountain miscellaneous wood with a stacking time of not more than one month.

[0060] In the screening step, the qualified wood chips with a length and width of 4-55mm and a thickness of 3-5mm are screened out.

[0061] In the water washing step, the wood chips are washed by water to remove impurities such as mud, stones and metals, so as to ensure the cleanliness of the wood chips.

[0062] In the pre-cooking step, the pre-cooking temperature is controlled at 95±5℃.

[0063] In the cooking step, the wood chips are softened by cooking, the cooking pressure is 8.5bar, and the cooking time is 3min.

[0064] In the hot grinding step, the wood chips enter the hot grinder through a belt screw, and molten paraffin or emulsified paraffin is added to the grinder, the paraffin application amount is 6.5-7kg / m 3 , the gap between the grinding discs is controlled at 0.12mm, and the fiber separation yield is 20-24 tons / hour.

[0065] In the glue adjusting step, water-resistant high-strength melamine modified urea-formaldehyde resin is applied in the pipeline for fiber spraying, the glue application amount (the proportion of absolute dry resin to the weight of absolute dry fiber) is 20%, and a latent composite curing agent is also applied, the addition amount is 2% of the weight of the absolute dry resin.

[0066] The latent composite curing agent is composed of the following components in mass percentage: 15% ammonium sulfate, 7% triethanolamine, 4% phosphoric acid, and the rest is water.

[0067] In the drying step, the moisture content of the fiber is 8-9%.

[0068] In the laying step, the board blank density is 830-840kg / m 3 .

[0069] In the hot pressing step, the continuous hot pressing process is adopted to hot press the plate blank under the temperature condition of 185-240℃, and the pressure factor is 10-11 s / mm. The hot pressing temperature and pressure are set as follows: five temperature zones are adopted: 240℃, 235℃, 218℃, 198℃, and 185℃; the hot pressing pressure distribution is: the pressure of the inlet section is increased to 3.4-3.6 MPa, the pressure of the rebound section is gradually reduced to 2.2-3.0 MPa, the pressure of the core layer holding section is gradually reduced to 0.08-0.1 MPa, and the pressure of the thickness setting section is 1.3-1.5 MPa.

[0070] In the health maintenance step, the cooled plate is stacked and maintained for 48 hours to balance the performance of the plate.

[0071] In the sanding step, the "two coarse sands + two fine sands" mode is adopted, and the sanding amount of the four sanding steps is distributed as follows: the first sanding amount accounts for 55-60% (80 mesh sand belt), the second sanding amount accounts for 20-25% (100 mesh sand belt), the third sanding amount accounts for 10-15% (120 mesh sand belt), and the fourth sanding amount accounts for 5-15% (180 mesh sand belt).

[0072] The fiber plate for a 12mm treadmill running board prepared through the above steps is detected according to the performance requirements of ordinary high-density fiber plate (HDF-GP REG) in GB / T 31765-2015 "High-density fiber plate", and the results are as follows:

[0073]

[0074] Example 2

[0075] 1. Preparation method of water-resistant high-strength melamine modified urea-formaldehyde resin

[0076] A water-resistant high-strength melamine modified urea-formaldehyde resin, the molar ratio of formaldehyde to urea and melamine F / (U+M) is 0.99. The weight of formaldehyde accounts for 49.9% of the total weight of the resin, the weight of water accounts for 7.6% of the total weight of the resin, the weight of urea accounts for 36.3% of the total weight of the resin, the weight of melamine accounts for 3.6% of the total weight of the resin, the weight of phenol accounts for 2.2% of the total weight of the resin, and the weight of p-toluenesulfonamide accounts for 0.4% of the total weight of the resin. Among them, all the formaldehyde is added at one time, the urea is added in four batches, and the melamine is added in two batches.

[0077] The preparation process is as follows:

[0078] A. Add formaldehyde to the reaction kettle, add water, stir, add alkali solution to adjust the pH value to 8.0-8.5, add the first batch of urea, add the first batch of melamine (the first batch of urea accounts for 41% of the total weight of urea; the first batch of melamine accounts for 69% of the total weight of melamine), and add phenol.

[0079] B. Heating to 90℃, control the steam node, keep 30 minutes at 90-92℃, check pH value greater than or equal to 6.5.

[0080] C. Cooling to 86℃, start to add acid liquid, adjust pH value to 5.4-5.6 in 10-15 minutes, keep temperature at 90-92℃, cool down when temperature is higher than 94℃ or temperature rises too fast.

[0081] D. Check viscosity every 5-10 minutes after adjusting pH value, check continuously when close to the end, control viscosity at 16.5-17.5 seconds (4 cups, 30℃), start to add acid liquid, control reaction time at 60-70 minutes.

[0082] E. Adjust pH value to 6.4-6.8 with alkali liquid, add p-toluenesulfonamide, add second urea, add second melamine (second urea accounts for 25% of total urea weight; second melamine accounts for 31% of total melamine weight), control reaction temperature at 81-83℃, check viscosity every 5 minutes (check continuously in later stage), control reaction time at 18.0-19.0 seconds, control time at 20-25 minutes.

[0083] F. Immediately adjust pH value to 8.0-8.5 with alkali liquid, add third urea (third urea accounts for 16% of total urea weight), keep 20 minutes at 72-74℃.

[0084] G. Adjust pH value to 8.5-9.0 with alkali liquid, add fourth urea (fourth urea accounts for 18% of total urea weight), keep 20 minutes at 62-64℃, cool down to below 45℃, check pH value again, adjust to 8.3-8.8, take sample, and glue.

[0085] 2. Manufacturing process of fiberboard for 18mm treadmill running board

[0086] The manufacturing process of fiberboard for 18mm treadmill running board comprises the following steps: raw wood feeding, peeling, slicing, screening, water washing, pre-steaming, steaming, hot grinding, glue mixing, drying, sorting, paving, pre-pressing, hot pressing, turning plate cooling, curing, sanding, sawing, inspection and grading, and packaging and warehousing, wherein:

[0087] In the raw wood feeding step, the wood raw material is selected from mountain miscellaneous wood with a stacking time of not more than one month.

[0088] In the screening step, qualified wood chips with a length and width of 4-55mm and a thickness of 3-5mm are screened out.

[0089] In the water washing step, the wood chips are washed by water to remove impurities such as mud, stones, and metals, so as to ensure the cleanliness of the wood chips.

[0090] The pre-cooking temperature is controlled at 95±5℃.

[0091] The cooking step is to soften the wood chips by cooking, the cooking pressure is 8.2 bar, and the cooking time is 2.5 min.

[0092] The hot grinding step is to feed the wood chips into the hot grinder by a belt screw, melt paraffin or emulsified paraffin is added into the grinder, the paraffin application amount is 5.5-6 kg / m 3 , the gap between the grinding discs is controlled at 0.10 mm, and the fiber separation yield is 18-20 tons / hour.

[0093] The glue adjusting step is to apply water-resistant high-strength melamine modified urea-formaldehyde resin to the fiber spraying pipeline, the glue application amount (absolute dry resin accounts for the weight proportion of absolute dry fiber) is 19%, and a latent composite curing agent is also applied, the addition amount is 3% of the weight of the absolute dry resin.

[0094] The latent composite curing agent is composed of the following components in mass percentage: 15% ammonium sulfate, 8% triethanolamine, 6% phosphoric acid, and the rest is water.

[0095] The drying step is to control the moisture content of the fiber at 7-8%.

[0096] The laying step is to control the board blank density at 820-830 kg / m 3 .

[0097] The hot pressing step is to use a continuous hot pressing process to hot press the board blank at a temperature of 195-245℃, and the pressure factor is 13-14 s / mm. The hot pressing temperature and pressure are set as follows: five temperature zones are used: 245℃, 238℃, 220℃, 202℃, and 195℃; the hot pressing pressure distribution: the inlet segment pressure rises to 3.2-3.4 MPa, the rebound segment pressure gradually decreases to 1.8-2.6 MPa, the core layer insulation segment gradually decreases to 0.05-0.07 MPa, and the thickness setting segment pressure is 1.0-1.3 MPa.

[0098] The curing step is to stack the cooled board for 48 hours for performance balancing.

[0099] The sanding step is to use the method of "two coarse sand + two fine sand", and the four sanding sanding amounts are distributed as follows: the first sanding amount accounts for 55-60% (80 mesh sand belt), the second sanding amount accounts for 20-25% (100 mesh sand belt), the third sanding amount accounts for 10-15% (150 mesh sand belt), and the fourth sanding amount accounts for 5-15% (180 mesh sand belt).

[0100] The fiberboard prepared by the above steps was detected according to the performance requirements of ordinary high-density fiberboard (HDF-GP REG) in GB / T 31765-2015 "High-density fiberboard", and the results were as follows:

[0101]

[0102] Comparative example

[0103] A 12mm fiberboard was prepared by using traditional urea-formaldehyde resin ("alkali-acid-alkali" process synthesis), soft mixed wood raw material, ammonium sulfate single curing agent, constant temperature (200℃) and constant pressure (2.0MPa) control in the hot pressing process, and other steps were consistent with example 1. The performance detection results were as follows:

[0104]

[0105] As can be seen from the comparative example, the fiberboard prepared by the traditional process cannot meet the national standard or the use requirements of the treadmill running board in terms of density, static bending strength, elastic modulus, internal bonding strength, surface bonding strength, water resistance, environmental protection and the like. However, the present application significantly improves the comprehensive performance of the product through multi-dimensional technical improvement, and has obvious technical advantages and market competitiveness.

[0106] The above is only an embodiment of the present application, and does not limit the patent scope of the present application. Any equivalent structure or equivalent process transformation in the specification, or direct or indirect application in other related technical fields, is also included in the patent protection scope of the present application.

Claims

1. A manufacturing process for fiberboard used in treadmill running boards, comprising the following steps: The log feeding process involves: bark removal, chipping, screening, washing, pre-steaming, steaming, hot grinding, glue preparation, drying, sorting, laying, pre-pressing, hot pressing, cooling, curing, sanding, sawing, inspection and grading, and packaging. The key feature is that the glue preparation step involves applying water-resistant, high-strength melamine-modified urea-formaldehyde resin and a latent composite curing agent. The glue application rate is 16-22% of the oven-dry resin weight to the oven-dry fiber weight, and the curing agent addition rate is 2-4% of the oven-dry resin weight. After drying, the fiber moisture content is 7-9%, and the density of the board after laying is 820-840 kg / m³. 3 Hot pressing adopts a continuous hot pressing process with a temperature of 185-250℃ and a pressure factor of 10-14s / mm.

2. The manufacturing process of the fiberboard for treadmill running boards according to claim 1, characterized in that: In the log loading step, the raw material is mixed mountain timber that has been stored for no more than one month.

3. The manufacturing process of the fiberboard for treadmill running boards according to claim 1, characterized in that: In the hot grinding step, molten paraffin or emulsified paraffin is added to the mill as a waterproofing agent during the hot grinding process. The amount of paraffin applied is 5.5–7 kg / m³. 3 .

4. The manufacturing process of the fiberboard for treadmill running boards according to claim 1, characterized in that: The water-resistant, high-strength melamine-modified urea-formaldehyde resin is synthesized via the following steps: A. Add 37% formaldehyde to the reactor, add water accounting for 7-8% of the total weight of the resin, stir evenly, adjust the pH value to 8.0-8.5 with 20% sodium hydroxide solution, then add the first urea accounting for 36-42% of the total weight of urea, the first melamine accounting for 60-70% of the total weight of melamine, and phenol accounting for 2-3% of the total weight of the resin, and stir to mix evenly; B. Start the heating device of the reactor and heat it to 90℃. Control the steam shut-off point to avoid a sudden temperature rise. Maintain the temperature at 90-92℃ for 30 minutes. After the holding period, check the pH value of the reaction system and ensure that the pH value is ≥6.

5. C. Stop heating and allow the temperature to cool naturally to 86℃. Begin slowly adding a 30% formic acid solution. Adjust the pH of the reaction system to 5.4-5.6 within 10-15 minutes. During the addition process, maintain the system temperature at 90-92℃. If the temperature exceeds 94℃ or the temperature rises too quickly, start the cooling device to lower the temperature. D. After pH adjustment, check the resin viscosity every 5-10 minutes. When the reaction is nearing its end, switch to continuous monitoring. During this stage, the viscosity should be controlled at 16.5-17.5 seconds. Use a Forte 4 cup at 30°C. Start timing from the addition of formic acid solution. The reaction time during this stage should be controlled at 60-70 minutes. E. After reaching the preset viscosity, adjust the pH value to 6.4-6.8 with a 20% sodium hydroxide solution. Add 0.3-0.5% p-toluenesulfonamide by weight of the resin, followed by the second addition of urea (24-26% of the total urea weight) and the second addition of melamine (30-40% of the total melamine weight). Control the reaction temperature at 81-83℃ and check the viscosity every 5 minutes, later switching to continuous monitoring. React until the viscosity reaches 18.0-19.0 seconds. Use a Forecast cup (Cup 4) at 30℃. Control the reaction time for this stage to 20-25 minutes. F. Immediately adjust the pH value to 8.0-8.5 with a 20% sodium hydroxide solution, add the third batch of urea, accounting for 16-18% of the total weight of urea, and keep warm at 72-74℃ for 20 minutes; G. Adjust the pH value to 8.5-9.0 with a 20% sodium hydroxide solution, add the fourth urea, accounting for 18-20% of the total weight of urea, keep it at 62-64℃ for 20 minutes, then cool the resin to below 45℃, test the pH value again, and adjust it to 8.3-8.

8. After the sample test is qualified, the resin can be released.

5. The manufacturing process of the fiberboard for treadmill running boards according to claim 4, characterized in that: The raw materials of the resin have the following weight percentages: formaldehyde 46-53%, water 7-8%, urea 35-38%, melamine 3-5%, phenol 2-3%, and p-toluenesulfonamide 0.3-0.5%.

6. The manufacturing process of the fiberboard for treadmill running boards according to claim 4, characterized in that: The resin has a formaldehyde to urea and melamine molar ratio F / (U+M) of 0.96 to 1.02, a pH value of 8.3 to 8.8, a viscosity of 14 to 16 seconds, a Fork-4 cup temperature of 25°C, a solid content of 50 to 53%, a curing time of 90 to 120 seconds, and a free formaldehyde content of 0.05 to 0.15%.

7. The manufacturing process of the fiberboard for treadmill running boards according to claim 1, characterized in that: The latent composite curing agent is composed of 12-15% ammonium sulfate, 7-9% triethanolamine, 4-6% phosphoric acid, and the balance water by mass percentage.

8. The manufacturing process of the fiberboard for treadmill running boards according to claim 1, characterized in that, The hot pressing step employs a five-stage temperature zone: 245±5℃, 238±5℃, 220±5℃, 200±5℃, and 190±5℃; the pressure distribution is as follows: inlet section 3.2~3.6MPa, rebound section 1.8~3.0MPa, core layer insulation section 0.02~0.15MPa, and fixed thickness section 1.0~1.5MPa.

9. Fiberboard for treadmill running boards manufactured using any one of the processes described in claims 1-8.

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