A water-based paint fiber flat plate directly molded door plate and a preparation method thereof

Abstract

The application provides a water-based paint fiber flat plate directly molded door plate, characterized in that an integrated process of coating and molding is adopted for preparation, the process comprises the following steps: fiber flat plate pretreatment, water-based paint coating, leveling and drying, storage and high-temperature and high-pressure molding; the pretreatment is chemical softening treatment with a pH value of 8-13, the high-temperature and high-pressure molding is controlled by a PLC controller to regulate key process parameters, and the molding adopts a mold with a positioning structure; through the integrated process of coating and molding, the cumbersome step of secondary coating after molding in the traditional process is omitted, the production efficiency is improved by more than 40%, the delivery cycle is shortened by 30%, the number of handling times is reduced, the door plate damage rate is reduced to below 1%, and the production cost is significantly reduced.

Description

Technical Field

[0001] This invention relates to the field of door panel manufacturing technology, specifically to a door panel directly molded from a water-based paint fiber flat sheet and its preparation method. Background Technology

[0002] With increasing environmental awareness and growing international demand for green home furnishing products, water-based paint-coated fiber-molded composite doors are experiencing a sustained rise in demand in the international market due to their advantages such as being environmentally friendly, having clear textures, and natural shapes. However, existing door panel manufacturing processes generally employ a separate "forming first, then coating" process, where the fiber substrate is first pressed into a textured door panel substrate, and then water-based paint is applied to its surface. This process has several insurmountable drawbacks: First, the cumbersome process leads to low production efficiency. Molding and coating require separate equipment, facilities, and operations, which not only increases the production process and costs but also raises the breakage rate of the door panel substrate due to repeated handling. Second, the adhesion between the paint film and the substrate is insufficient. When water-based paint is applied to the surface of the molded door panel, it is difficult to penetrate into the fiber gaps of the substrate, especially at stress concentration areas such as the edges and corners of the door panel, where paint film peeling is prone to occur, affecting the product's lifespan. Third, the decorative appearance is limited. Traditional coating methods cannot achieve uniform paint film coverage, and defects such as particles and runs are prone to appear on the door panel surface, resulting in a hazy three-dimensional effect and unclear simulated wood grain. In addition, some processes still rely on oil-based paints, resulting in excessive VOC emissions, which does not meet environmental protection regulations. Even when using water-based paints, the separate process has high energy consumption, which is not in line with the trend of low-carbon and energy-saving development.

[0003] To address the aforementioned technical problems, this invention proposes an integrated molding process that combines coating and forming. By optimizing material selection, pretreatment methods, and molding parameters, it achieves efficient, high-quality, and environmentally friendly door panel manufacturing, thereby enhancing the product's competitiveness in the international market. Summary of the Invention

[0004] This invention provides a door panel directly molded from a water-based paint fiber flat sheet and its preparation method, aiming to solve the problems mentioned in the background art.

[0005] This invention is achieved by directly molding a door panel from a water-based paint fiber sheet using an integrated coating and molding process. The process includes fiber sheet pretreatment, water-based paint coating, leveling and drying, aging, and high-temperature and high-pressure molding steps. The pretreatment is a chemical softening treatment with a pH value of 8-13. The high-temperature and high-pressure molding uses a PLC controller to regulate key process parameters, and the molding process employs a mold with a positioning structure.

[0006] Preferably, the fiber plate has a uniform density, no glue spots, water stains, oil stains and bark impurities on the surface, is flat and smooth, and has good and uniform moisture absorption properties.

[0007] Preferably, the chemical softening treatment involves soaking in an alkaline aqueous solution to improve the toughness of the fiber sheet to adapt to subsequent molding.

[0008] Preferably, the water-based paint is an environmentally friendly, high-adhesion water-based paint, and the coating method is spraying or coating.

[0009] Preferably, the leveling and drying temperature is 140-150℃, so that the water-based paint film can be evenly spread and cured.

[0010] Preferably, the temperature of the high-temperature and high-pressure molding is 180-200℃, and the temperature, pressure and holding time are precisely controlled by a PLC controller.

[0011] Preferably, the mold with positioning structure includes a horizontal height positioning block, a horizontal position positioning block, and a restraint component to ensure accurate positioning of the sheet material during the molding process.

[0012] Preferably, the aging process includes two stages: the first aging occurs after chemical softening treatment, and the second aging occurs after leveling and drying. Each aging stage is used to stabilize the state of the board and eliminate internal stress.

[0013] A preferred method for preparing a door panel by direct molding of water-based paint fiber flat sheets includes the following steps: (1) Take the fiber plate, subject it to chemical softening treatment at pH 8-13, and then let it stand for the first time; (2) The softened fiber sheet is coated with the water-based paint described above; (3) Place the coated fiber sheet in an environment of 140-150℃ for leveling and drying; (4) After drying, allow for a second aging process; (5) The aged fiber plate is placed into the mold and molded under high temperature and high pressure by the control of the PLC controller; (6) After molding, the door panel is cooled and demolded to obtain the finished door panel.

[0014] Preferably, the two aging periods are both 1-3 hours to ensure that the moisture content and internal stress of the board are in a stable state.

[0015] Due to the adoption of the above solution, the beneficial effects of the present invention are: The production process is greatly simplified: by integrating coating and molding, the cumbersome secondary coating process after molding in the traditional process is eliminated, the production efficiency is increased by more than 40%, the delivery cycle is shortened by 30%, the number of handling is reduced, the door panel breakage rate is reduced to less than 1%, and the production cost is significantly reduced.

[0016] Significantly improved paint film adhesion: After water-based paint is applied and initially cured by leveling and drying, it is then deeply bonded to the fiber plate under high temperature and high pressure molding. The paint film penetrates into the gaps between the substrate fibers, resulting in an adhesion that is more than 50% higher than that of traditional processes. There is no paint film peeling off at edges or corners, and the product's service life is extended.

[0017] Optimized appearance and decoration: The precise positioning of the mold and the synergistic effect of high temperature and high pressure molding create a thick and full concave shape on the door panel surface, with a distinct three-dimensional effect; the leveling and drying process and the molding process together ensure that the paint film is smooth and flat, free of particles and drip defects, and the simulated wood grain is clearly displayed, meeting consumers' high requirements for decoration.

[0018] The environmental protection and energy-saving advantages are outstanding: the use of environmentally friendly water-based paint results in VOC emissions that are significantly lower than those of traditional processes, meeting the GB18581-2020 environmental protection standard; the integrated process reduces the number of equipment start-ups and shutdowns and energy consumption, reducing electricity and heat consumption by more than 25%, achieving low-carbon and green production.

[0019] Improved product cost-effectiveness: While simplifying processes and reducing energy consumption and breakage rates, product quality stability has been improved, and the advantages in appearance and performance are significant, greatly enhancing the competitiveness of molded doors in the international market. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the process flow of the present invention. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0022] like Figure 1 As shown, this invention utilizes an integrated process of "chemical softening pretreatment → water-based paint coating → leveling and drying → secondary aging → high-temperature and high-pressure molding → cooling and forming" to achieve deep bonding between the water-based paint and the fiber plate during the molding process. This process not only shapes the door panel but also ensures the firm adhesion of the paint film. At the same time, precise control of process parameters guarantees the stability of product quality.

[0023] Specifically, material selection Fiberboard: The base material is made of fiberboard with uniform density, fine and long fibers that are tightly interwoven and have a certain degree of water resistance. Its surface is free of defects such as glue spots, water stains, oil stains, dust spots, bark impurities, etc. The surface is flat and smooth, with good and uniform moisture absorption performance. The initial moisture content meets the requirements of subsequent processing, ensuring that it is not easy to crack or deform during the molding process.

[0024] Water-based paint: We select water-based paints with excellent environmental performance, strong adhesion, high temperature resistance and fast drying speed. Different colors and gloss levels can be selected according to actual needs. This process prefers white water-based white primer, whose VOC emissions meet environmental protection standards and can maintain stable performance in high temperature molding environment without deterioration or yellowing.

[0025] Pretreatment process Chemical softening treatment: Add alkaline substances (such as sodium hydroxide, sodium carbonate, etc.) to the clean water in the softening tank, and adjust the pH value of the mixed water to 8-13 according to seasonal weather changes. Immerse the fiber plate in the mixed water to allow the water to fully penetrate into the fiber gaps, break some of the hydrogen bonds between the wood fibers, soften the wood fibers, improve the flexibility of the substrate, and lay the foundation for subsequent molding of complex concave shapes.

[0026] First aging: After the softened fiber sheet is taken out, it is aged at room temperature for 12-24 hours to stabilize the moisture content of the substrate at 8-12% and eliminate the internal stress generated during the softening process to avoid deformation during subsequent coating and molding.

[0027] Water-based paint coating: Water-based white primer is applied to the surface of the fiberboard after it has been left to stand using a reciprocating spraying method. During the spraying process, the spraying pressure and speed are controlled to ensure that the water-based paint evenly covers the surface of the fiberboard without defects such as sagging, bubbling, or missed coating, and the paint film thickness is uniform.

[0028] Leveling and drying: The coated fiber sheet is fed into a 13-meter-long leveling dryer, and the drying temperature is controlled at 140-150℃ to allow the water-based paint to flow fully, form a smooth and flat paint film and initially cure it, so as to avoid paint film damage during subsequent molding.

[0029] Second aging: The leveled and dried fiber sheet is aged at room temperature for 4 hours to further stabilize the paint film state and substrate moisture content, eliminate thermal stress generated during the drying process, and ensure the coordinated deformation ability of the substrate and paint film during molding.

[0030] High temperature and high pressure molding Mold preparation: A molding mold with a precise positioning structure is adopted. The mold includes an upper mold and a lower mold. The upper mold is equipped with positioning guide pillars, and the lower mold is equipped with corresponding positioning guide pillar countersunk holes. Through the cooperation of the positioning guide pillars and countersunk holes, the precise positioning is achieved when the mold is closed, ensuring the dimensional accuracy of the door panel. The shape and size of the mold are customized according to the door panel order requirements and can be adapted to concave shapes of different complexity.

[0031] Molding parameter control: After the second curing, the fiberboard is placed into the mold, the molding machine is started, and the process parameters are set and controlled through the PLC control system, including the upper and lower limits of the high pressure, the baking time of the 6 stages, the holding time, and the two-stage venting time. The molding heating temperature is controlled at 180-200℃ to ensure that the water-based paint is fully dried and firmly bonded to the substrate. The pressure is adjusted according to the thickness and complexity of the door panel to ensure that the door panel structure is tight and the surface is flat after molding. The venting stage is used to remove water vapor and residual air in the mold to avoid defects such as bubbles and hollows in the door panel.

[0032] Cooling and molding: After molding, the door panel is removed and left to cool. During the cooling process, the door panel is protected from external impact or pressure. It is allowed to cool naturally to room temperature to stabilize the door panel structure and paint film and prevent subsequent deformation.

[0033] Post-processing Quality inspection: After cooling, the door panels are inspected for indicators such as dimensional accuracy, shape consistency, paint film adhesion, and surface smoothness to ensure that the door panel size and model meet customer requirements and are free from defects such as paint film peeling, cracking, and deformation.

[0034] Packaging and storage: Qualified door panels are stored after being packaged in a moisture-proof and scratch-proof manner, in preparation for the subsequent door pressing process or direct shipment. Example

[0035] Material preparation: Select fiber sheets with uniform density and no glue spots, water stains or bark impurities on the surface. The fibers are fine, long and tightly interwoven, with good moisture absorption performance. Select environmentally friendly white water-based primer with strong adhesion, high temperature resistance, fast drying speed, and VOC emissions that meet environmental protection standards.

[0036] Chemical softening treatment: Add clean water to the softening tank, add sodium hydroxide to adjust the pH of the mixed water to 10 (normal temperature environment in summer), immerse the fiber plate in the water for 30 minutes to ensure that the water fully penetrates the fiber gaps.

[0037] First aging: The softened fiber plate was taken out and aged at room temperature for 18 hours. The moisture content was found to be 10%, and the state was stable without deformation.

[0038] Spraying water-based white primer: Use reciprocating spraying equipment and adjust the spraying pressure to 0.3MPa to evenly spray water-based white primer onto the surface of the fiberboard, ensuring that the paint film is free of sagging and bubbling, and that it is completely covered.

[0039] Leveling and drying: The sprayed fiberboard is sent into a 13-meter-long leveling dryer, the drying temperature is set to 145℃, and the drying time is controlled to 20 minutes according to the thickness of the board. After being taken out, the paint film is smooth and flat, and has been initially cured.

[0040] Second aging: Let the dried fiber sheet age at room temperature for 4 hours to eliminate internal thermal stress.

[0041] High-temperature and high-pressure molding: The fiber plate is placed in the positioning mold, and the process parameters are set through the PLC control system: the upper limit of high pressure is 16MPa, the lower limit is 12MPa, the baking time of the 6 stages is 5min, 8min, 10min, 12min, 8min and 5min respectively, the holding time is 30min, and the venting time of the two stages is 3min each; the molding temperature is set to 190℃, and the molding machine is started to complete the mold closing, heating, pressurization and venting process.

[0042] Cooling: After molding, remove the door panel and allow it to cool naturally to room temperature, avoiding external impact.

[0043] Quality Inspection: The door panel dimensions meet the order requirements, the surface recessed design is three-dimensional and full, the paint film is smooth and flat, the simulated wood grain is clear, the paint film adhesion reaches GB / T 9286-1998 standard level 1, there is no peeling, and VOC emissions meet the standards. Example

[0044] Material preparation: Select fiberboard and water-based white primer of the same specifications as in Example 1.

[0045] Chemical softening treatment: In the low temperature environment of winter, add sodium carbonate to the water in the softening tank to adjust the pH value to 12, and soak the fiber plate for 40 minutes to ensure that the fiber is fully softened.

[0046] First aging: After aging at room temperature for 24 hours, the moisture content was measured at 12%, indicating a stable condition.

[0047] Spraying water-based white primer: Adjust the spraying pressure to 0.35MPa to ensure uniform paint film coverage in low-temperature environments.

[0048] Leveling and drying: Set the temperature of the leveling dryer to 150℃ and the drying time to 25 minutes to allow the paint film to fully level and cure.

[0049] Second aging: Aging at room temperature for 4 hours.

[0050] High temperature and high pressure molding: PLC control system settings: upper limit of high pressure 18MPa, lower limit of high pressure 14MPa, baking time of 6 stages is 6min, 10min, 12min, 15min, 10min, 6min respectively, holding time 40min, venting time of each stage 4min; molding temperature 200℃, start molding machine to form.

[0051] Cooling: Allow to cool naturally to room temperature.

[0052] Quality inspection: The door panel has a precise shape, strong paint adhesion, smooth and defect-free surface, and energy consumption is reduced by 30% compared with traditional processes. Example

[0053] Material preparation: Select fiberboard and water-based white primer of the same specifications as in Example 1.

[0054] Chemical softening treatment: In spring, at normal temperature, adjust the pH of the mixed water to 8 and soak the fiber plate for 25 minutes.

[0055] First aging: Aging at room temperature for 12 hours, moisture content 8%.

[0056] Spray water-based white primer: spray pressure 0.28MPa, apply evenly.

[0057] Leveling and drying: drying temperature 140℃, drying time 18 minutes.

[0058] Second aging: Aging at room temperature for 4 hours.

[0059] High temperature and high pressure molding: The PLC sets the upper limit of high pressure to 15MPa and the lower limit to 11MPa. The baking time for the 6 stages is 4min, 7min, 9min, 11min, 7min and 4min respectively. The holding time is 25min and the degassing time is 2min each. The molding temperature is 180℃.

[0060] Cooling: Allow to cool naturally to room temperature.

[0061] Quality inspection: All indicators of the door panel meet the requirements, the appearance and decoration are excellent, and the environmental protection and energy consumption meet the standards.

[0062] The key to this invention lies in the integrated coating and molding process design. Chemical softening pretreatment enhances the substrate's flexibility, and precise coating, drying, and aging steps lay the foundation for compression molding. During high-temperature, high-pressure molding, the synergistic effect of the PLC control system and the positioning mold ensures precise door panel shaping and firm paint adhesion, ultimately achieving comprehensive advantages in production efficiency, quality, and environmental protection. Those skilled in the art can adjust process parameters such as pH value, temperature, and time according to actual production needs within the scope of the claims of this invention, and all such adjustments fall within the protection scope of this invention.

[0063] The above description of the embodiments is intended to enable those skilled in the art to understand and use the present invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments. Improvements and modifications made by those skilled in the art based on the principles of the present invention without departing from the scope of the invention should be within the protection scope of the present invention. The above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A door panel directly molded from a water-based paint fiber sheet, characterized in that, The product is prepared using an integrated coating and molding process, which includes fiber sheet pretreatment, water-based paint coating, leveling and drying, aging, and high-temperature and high-pressure molding steps. The pretreatment is a chemical softening treatment with a pH value of 8-13. The high-temperature and high-pressure molding uses a PLC controller to control key process parameters, and the molding process uses a mold with a positioning structure.

2. The door panel according to claim 1, characterized in that, The fiber flat sheet has a uniform density, and its surface is free of glue spots, water stains, oil stains, and bark impurities. It is flat, smooth, and has good and uniform moisture absorption properties.

3. The door panel according to claim 1, characterized in that, The chemical softening treatment involves soaking the fiber sheet in an alkaline aqueous solution to improve its toughness and adapt it to subsequent molding.

4. The door panel according to claim 1, characterized in that, The water-based paint is an environmentally friendly, high-adhesion water-based paint, and the coating method is either spraying or coating with a wet coat.

5. The door panel according to claim 1, characterized in that, The leveling and drying temperature is 140-150℃, which allows the water-based paint film to spread evenly and cure.

6. The door panel according to claim 1, characterized in that, The high-temperature and high-pressure molding temperature is 180-200℃, and the temperature, pressure and holding time are precisely controlled by a PLC controller.

7. The door panel according to claim 1, characterized in that, The mold with positioning structure includes a horizontal height positioning block, a horizontal position positioning block, and a restraint component to ensure accurate positioning of the sheet material during the molding process.

8. The door panel according to claim 1, characterized in that, The aging process includes two stages: the first aging occurs after chemical softening treatment, and the second aging occurs after leveling and drying. Each aging stage is used to stabilize the state of the board and eliminate internal stress.

9. The method for preparing a door panel by direct molding of water-based paint fiber flat sheet according to any one of claims 1-8, characterized in that, Includes the following steps: (1) Take the fiber plate, subject it to chemical softening treatment at pH 8-13, and then let it stand for the first time; (2) The softened fiber sheet is coated with the water-based paint described above; (3) Place the coated fiber sheet in an environment of 140-150℃ for leveling and drying; (4) After drying, allow for a second aging process; (5) The aged fiber plate is placed into the mold and molded under high temperature and high pressure by the control of the PLC controller; (6) After molding, the door panel is cooled and demolded to obtain the finished door panel.

10. The preparation method according to claim 9, characterized in that, The two aging periods are each 1-3 hours to ensure that the moisture content and internal stress of the board are stable.

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