A method of coating a plant fiber board

Abstract

The present application belongs to the technical field of artificial board surface coating, and particularly relates to a coating method for plant fiber board, comprising the following steps: preheating treatment: preheating the plant fiber board; light sanding and dust removal treatment on the surface after preheating; adhesion primer coating: coating primer on the surface of the board after preheating treatment; penetration type sealing primer coating: roll coating penetration type sealing primer on the surface of the board after coating primer; solidification and leveling: solidifying the board after roll coating, and sanding after cooling to obtain a smooth sealing base; topcoat construction: sequentially coating primer and topcoat on the sealing base to complete the overall coating, the present application completely seals the micropores of the plant fiber board through the synergistic effect of preheating exhaust, medium viscosity penetration primer and pressurized roller, eliminates the risk of pinholes and shrinkage holes in the subsequent coating layer, and significantly improves the overall coating quality and production efficiency.

Description

Technical Field

[0001] This invention belongs to the field of surface coating technology for engineered wood panels, and specifically relates to a coating method for plant fiberboard. Background Technology

[0002] Plant fiberboard is made by non-woven fabric composed of plant fibers (such as hemp, bamboo, and straw fibers) and synthetic fibers (such as polyester fibers), which are then hot-pressed. This type of board makes full use of plant fiber resources and has advantages such as being lightweight, environmentally friendly, and sound-absorbing, leading to its increasing application in furniture, decoration, and interior building materials. However, precisely because it is made by pressing layers of fiber fabric, the surface and shallow layers contain numerous micropores and tiny gaps between fibers, with pore sizes ranging from a few micrometers to hundreds of micrometers.

[0003] When directly coating this type of board, conventional primers or topcoats, due to their low viscosity and low surface tension, easily penetrate directly into the pores, making it difficult to completely fill and seal these micropores during conventional coating processes. During subsequent drying or curing, the air, moisture, or volatile substances trapped within the micropores expand and escape upon heating, easily forming pinholes, bubbles, and shrinkage cavities on the coating surface, severely affecting the coating's appearance integrity and protective performance. Even the traditional method of multiple putty roller coatings and sanding is not only cumbersome and inefficient, but the difference in elastic modulus between the putty layer and the substrate can easily cause cracking or interface peeling during temperature and humidity changes, failing to fundamentally solve the problem. Summary of the Invention

[0004] To address the problem of coating defects caused by micropores in plant fiber boards in existing technologies, this invention provides a coating method for plant fiber boards. This method is designed for plant fiber boards made by interlacing composite fibers into a cloth and pressing it together. It aims to eliminate coating defects caused by a large number of micropores in the substrate and obtain an overall coating with a smooth surface and excellent adhesion.

[0005] The technical problem solved by this invention is achieved by the following technical solution:

[0006] The present invention aims to provide a coating method for plant fiber boards, comprising the following steps:

[0007] S1 Preheating Treatment: Preheating the plant fiberboard; after preheating, the surface is lightly sanded and dusted.

[0008] S2 Adhesion Primer Coating: Apply primer to the surface of the board after S1 preheating treatment;

[0009] S3 Penetrating Sealing Primer Coating: A penetrating sealing primer is rolled onto the surface of the board after the S2 primer has been applied;

[0010] S4 Curing and Leveling: Curing the S3 roller-coated board, cooling it, and then sanding it to obtain a smooth, closed base surface;

[0011] S5 Topcoat Construction: Apply primer and topcoat sequentially on a sealed substrate to complete the overall coating.

[0012] Furthermore, in S1, the plant fiberboard is preheated at 60-80℃ for 8-15 minutes, so that the surface temperature of the board is 50±2℃ and the moisture content is reduced to below 2.5%.

[0013] Furthermore, in S3, the viscosity of the penetrating sealing primer is 1600–4300 mPa·s.

[0014] Furthermore, in S3, the coating amount of the penetrating sealing primer is 150–200 g / m², and the roller pressing depth is 0.6–1 mm.

[0015] Furthermore, in S3, the penetrating sealing primer includes component A and component B. Component A includes polyisocyanate prepolymer, hydroxy acrylate, diluent, defoamer and nanofiller; component B is a modified amine curing agent.

[0016] Furthermore, component A comprises, by weight, 40-60 parts of polyisocyanate prepolymer, 20-35 parts of hydroxy acrylate, 15-20 parts of diluent, 0.2-0.5 parts of defoamer, and 1.5-2.0 parts of nanofiller; the weight ratio of component A to component B is 80:20-25.

[0017] Furthermore, the polyisocyanate prepolymer is hexamethylene diisocyanate (HDI) trimer, isophorone diisocyanate (IPDI) prepolymer, or diphenylmethane diisocyanate (MDI) prepolymer; the diluent is hydroxyethyl acrylate (HEMA) or tripropylene glycol diacrylate (TPGDA); and the nanofiller is nano-calcium carbonate or nano-silica with an average particle size of 20-50 nm.

[0018] Furthermore, in S4, curing is performed under UV light irradiation with a curing energy of 150–250 mJ / cm. 2 The curing time is 20–40 seconds.

[0019] Furthermore, the coating amount of the adhesion primer in S2 is 20–40 g / m², and the coating amount of the primer in the S5 topcoat is 30–50 g / m².

[0020] A method for integral coating of plant fiberboard, wherein the plant fiberboard is formed by hot pressing after being woven from plant fibers and synthetic fibers, and has a large number of micropores on its surface, includes the following steps:

[0021] (1) Composite fiberboard production: Plant fibers are cut and screened to obtain fiber scraps with a length of 8-10 mm. The moisture content is controlled at about 12%. 20 kg of synthetic fibers are fed into an opening machine. The scraps are thoroughly mixed by the opening machine, opening machine, and blending machine to form a blended cotton. Then, a double cylinder double channel double random carding machine is used to card the cotton into a thin fiber web composed of two layers of single fibers. After double-layer stacking, a three-dimensional randomized fiber web is formed. The fiber web is stacked to 53 layers to form a cotton web. After preliminary compression, it is sent to a high-speed needle punching machine to reinforce the front and back sides of the cotton web by downward unidirectional needle punching. Finally, a non-woven fabric blank with a thickness of 7-8.5 mm is formed. The non-woven fabric semi-finished product is put into a hot press. The hot press plate temperature is preset to 220℃, the pressure is 4 MPa, and the holding time is calculated at 40 seconds per millimeter of board thickness, for a total of 160 seconds (4 mm). After the hot press is started, the pressure is released and the air is vented 40 seconds later. (2) Preheating treatment: The plant fiberboard is preheated in an environment of 60-80℃ to make the board temperature reach a surface temperature of 45-55℃ and the moisture content of the board drop to below 3%; after preheating, the surface is lightly sanded and dusted. Preheating is not only used to remove moisture and some air from the micropores, but also to increase the temperature of the substrate to reduce the viscosity of the subsequent primer and enhance its permeability. Preferably, the preheating temperature is 60-80℃ and the preheating time is 8-15 min, so that the surface temperature of the board is stabilized at 50±2℃ and the moisture content drops to below 2.5%. (3) Adhesion primer coating: Adhesion primer is uniformly coated on the surface of the board after preheating and sanding to enhance the adhesion between the subsequent paint and the board and prevent the subsequent paint from falling off. (4) Penetrating sealing primer coating: Penetrating sealing primer is uniformly rolled on the surface of the board after the adhesion primer is coated. The penetrating sealing primer is made by mixing component A and component B in a weight ratio of 80:20-25 and is prepared and used immediately. The viscosity of the mixture at 25°C is 1600–4300 mPa·s. Component A mainly includes polyisocyanate prepolymer, hydroxy acrylate, diluent, defoamer, and nanofiller. Component B is a modified amine curing agent. The coating weight of the penetrating sealing primer is 150–200 g / m². Preferably, the polyisocyanate prepolymer is hexamethylene diisocyanate (HDI) trimer, isophorone diisocyanate (IPDI) prepolymer, or diphenylmethane diisocyanate (MDI) prepolymer. The diluent is hydroxyethyl acrylate (HEMA) or tripropylene glycol diacrylate (TPGDA), which not only adjusts the viscosity of the system but also participates in the curing reaction, improving the toughness of the sealing layer. The nanofiller is nano-calcium carbonate or nano-silica with an average particle size of 20–50 nm, and its dosage is 1–3% of the total weight of component A, used to provide excellent anti-sagging and penetrating filling properties.Polyisocyanate prepolymers, when combined with modified amine curing agents, can form an interpenetrating network structure (IPN) under UV curing conditions, combining the flexibility of polyurethane with the hardness of acrylate. This is particularly suitable for fiberboard substrates with slight deformation. Modified amine curing agents are products of chemical or physical modification of traditional organic amine curing agents. The core purpose is to reduce toxicity, improve low-temperature curing performance, and extend operating time. In this invention, the modified amine curing agent can be a conventional modified amine curing agent in the field, such as phenolic amine modified amine curing agent, alicyclic amine modified amine curing agent, and polyamide modified amine curing agent, etc., which can be prepared by conventional modification methods in the field. Preferably, the roller pressing depth during the roller coating process is 0.6 to 1 mm. This pressure is coordinated with the coating amount of 150 to 200 g / m² to ensure that the primer fully fills the micropores while avoiding surface material accumulation. (5) Curing and leveling: The roller-coated board is cured at 150 to 250 mj / cm. 2 Curing under the given conditions for 20–40 seconds allows the sealing primer to fully cure, filling and sealing the micropores. After cooling, sand the surface with a 320-grit or higher sanding belt to remove excess cured layer and obtain a smooth sealed substrate. (6) Topcoat construction: Apply the primer and topcoat sequentially on the sealed substrate to complete the overall coating. The primer and topcoat can be UV-cured or a two-component polyurethane system, without affecting the core effect of the sealing layer in eliminating pore defects.

[0022] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0023] 1. The purpose of the preheating treatment in this invention is to expel moisture and some air from the micropores, while simultaneously increasing the substrate temperature, reducing the viscosity of the subsequent primer coating, and enhancing its permeability. The penetrating sealing primer uses a medium-viscosity polyurethane system combined with an active diluent, which can quickly penetrate into fine pores under external force. The rolling step allows the primer to deeply fill the micropores under the combined action of pressure and capillary action, and squeezes out residual air along the fiber gaps. The curing agent and polyurethane resin undergo an irreversible cross-linking reaction, solidifying the liquid resin that has penetrated into the pores in situ, forming a high-strength, high-density three-dimensional network polymer structure, thereby completely sealing the substrate. After curing, sanding and smoothing are performed to obtain a solid sealing layer, providing an excellent non-porous substrate for the subsequent topcoat, and ultimately completely eliminating pore defects.

[0024] 2. This invention completely seals the micropores of plant fiberboard through the synergistic effect of preheating and venting, medium-viscosity penetrating primer, and pressure roller pressing. Compared with conventional putty coatings, the sealing layer of this invention has a better match with the elastic modulus of the fiber substrate, achieving high adhesion (national standard level VI) while maintaining excellent flexibility. Tests have shown that substrates prepared using this method, after being coated with the same amount of topcoat, exhibit no cracking or blistering during thermal cycling tests from -20℃ to 100℃, significantly improving overall coating quality and production efficiency.

[0025] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention, it can be implemented according to the contents of the specification. Furthermore, in order to make the above contents, objectives, features and advantages of the present invention more obvious and understandable, specific embodiments of the present invention are described below. Detailed Implementation

[0026] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are merely illustrative and explanatory of the present invention and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0027] In addition, unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be obtained by purchasing them from the market or prepared by existing methods.

[0028] Example 1

[0029] A coating method for plant fiberboard:

[0030] The plant fiberboard used is a composite needle-punched nonwoven fabric made of jute fiber and polypropylene fiber in a weight ratio of 70:30. Five layers are stacked and hot-pressed at 220℃ and 4 MPa for 10 min to make a thickness of 4 mm. The surface of the board shows obvious fabric texture and micropores. (1) Preheating treatment: The board is placed in a 70℃ forced-air oven for 10 min for preheating. The temperature of the board surface is measured to reach 50℃ and the moisture content is reduced from 7% to 2.5%. Then, it is lightly sanded with 320 and 400 mesh sandpaper and dusted with compressed air. (2) Adhesion primer coating: A layer of adhesion primer is evenly coated on the surface of the fiberboard with a coating amount of 30 g / m² and UV cured. (3) Preparation of penetrating sealing primer: Component A: 50 kg HDI trimer, 30 kg hydroxy acrylate monomer, 18 kg reactive diluent TPGDA, 0.3 kg defoamer BYK-066N, 1.7 kg nano calcium carbonate, dispersed and mixed evenly at high speed; Component B: alicyclic amine modified amine curing agent. Mix A and B evenly at a weight ratio of 80:20, and the viscosity at 25℃ is measured to be 1800 mPa·s. (4) Coating and forced penetration: Apply the mixed primer evenly to the preheated board surface using a roller coater, with the roller pressed down 0.8 mm and the coating amount 170 g / m². During the rolling process, the primer can be seen to quickly penetrate the fabric texture and micropores, and there is no obvious floating material on the surface. (5) Curing and leveling: Send the board into a UV curing machine, with an energy of 200 mJ / cm 2 Under the conditions of complete curing of epoxy primer. After leaving the curing machine, it is allowed to cool naturally and sanded with 320-grit sandpaper to remove the very thin resin-rich layer on the surface, so as to obtain a dense, smooth, and closed substrate with no micropores visible to the naked eye. (6) Construction of topcoat: A layer of UV transparent primer (coating amount 40 g / m²) is rolled onto the closed substrate, lightly sanded after UV curing, and then UV high gloss topcoat is rolled onto. After curing, the finished board is obtained.

[0031] Example 2

[0032] A coating method for plant fiberboard:

[0033] The formulation of the penetrating sealing primer was changed, and the rest of the process was the same as in Example 1.

[0034] Component A: 45 kg MDI prepolymer, 35 kg hydroxy acrylate oligomer, 18 kg HEMA reactive diluent, 0.4 kg defoamer, and 1.6 kg nano-silica. Component B: Polyamide-modified amine curing agent. The viscosity after mixing is approximately 2200 mPa·s. The resulting sealed substrate is also free of micropores, and the final coating is flawless. Comparative Example 1

[0035] Using the same plant fiberboard, after preheating, the surface was directly sanded and roller-coated with conventional UV transparent putty (viscosity > 2000 mPa·s), without any penetrating sealing treatment. After drying, the same UV primer and topcoat were applied. Performance comparison: The coating obtained in Example 1 had a uniform gloss surface. Inspection with a 20x magnifying glass revealed no pinholes or shrinkage cavities. The adhesion (cross-cut adhesion test) met the GB / T17657-2022 standard, reaching level 6. No cracking occurred after three thermal cycles (-20℃ to 60℃). Comparative Example 1 showed numerous pinholes on its surface, with a density of approximately 11 pinholes / cm², and some pinholes were surrounded by star-shaped microcracks. Furthermore, in the bending resistance test, the coating prepared in Example 1 remained intact when the board's bending radius was 50 mm, while the coating in Comparative Example 1 showed significant cracking, demonstrating that the sealing layer of this invention has a better match with the elastic modulus of the fiber substrate and exhibits excellent flexibility.

[0036] Table 1

[0037]

[0038] This invention discloses a method for overall coating of plant fiberboard. Plant fiberboard is formed by hot pressing composite fibers woven into a fabric, resulting in numerous micropores on its surface, which are prone to defects in conventional coatings. This method first preheats the board to 45–55°C and dehumidifies it. Then, a polyurethane-based penetrating sealing primer with a viscosity of 1600–4300 mPa·s is applied. This primer consists of component A (containing polyisocyanate prepolymer and hydroxyl acrylate) and component B (a modified amine curing agent). After UV curing, a tightly sealed substrate is formed. Finally, the primer and topcoat are applied. This invention, through the synergistic effect of preheating and degassing, a medium-viscosity penetrating primer, and pressure roller pressing, thoroughly seals the micropores of the plant fiberboard, eliminating the risk of pinholes and shrinkage cavities in subsequent coatings. Furthermore, the sealing layer exhibits strong adhesion and crack resistance, significantly improving overall coating quality and production efficiency.

[0039] The sequence numbers of the above embodiments of the present invention are for descriptive purposes only and do not represent the superiority or inferiority of the embodiments.

[0040] The embodiments of the present invention have been described above, but the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of the present invention without departing from the spirit and scope of the claims, and all of these are within the protection scope of the present invention.

Claims

1. A coating method for plant fiberboard, characterized in that, Includes the following steps: S1 Preheating Treatment: Preheating the plant fiberboard; after preheating, the surface is lightly sanded and dusted. S2 Adhesion Primer Coating: Apply primer to the surface of the board after S1 preheating treatment; S3 Penetrating Sealing Primer Coating: A penetrating sealing primer is rolled onto the surface of the board after the S2 primer has been applied; S4 Curing and Leveling: Curing the S3 roller-coated board, cooling it, and then sanding it to obtain a smooth, closed base surface; S5 Topcoat Construction: Apply primer and topcoat sequentially on a sealed substrate to complete the overall coating.

2. The coating method for a plant fiber board as described in claim 1, characterized in that: In S1, the plant fiberboard is preheated at 60-80℃ for 8-15 minutes to bring the surface temperature of the board to 50±2℃ and reduce the moisture content to below 2.5%.

3. The coating method for a plant fiber board as described in claim 1, characterized in that: In S3, the viscosity of the penetrating sealing primer is 1600–4300 mPa·s.

4. The coating method for a plant fiber board as described in claim 1, characterized in that: In S3, the coating amount of the penetrating sealing primer is 150–200 g / m², and the roller pressing depth is 0.6–1 mm.

5. The coating method for a plant fiber board as described in claim 1, characterized in that: In S3, the penetrating sealing primer includes component A and component B. Component A includes polyisocyanate prepolymer, hydroxy acrylate, diluent, defoamer and nanofiller; component B is a modified amine curing agent.

6. The coating method for a plant fiber board as described in claim 5, characterized in that: Component A, by weight, comprises 40-60 parts of polyisocyanate prepolymer, 20-35 parts of hydroxy acrylate, 15-20 parts of diluent, 0.2-0.5 parts of defoamer, and 1.5-2.0 parts of nanofiller; the weight ratio of component A to component B is 80:20-25.

7. The coating method for a plant fiber board as described in claim 6, characterized in that: The polyisocyanate prepolymer is hexamethylene diisocyanate trimer, isophorone diisocyanate prepolymer, or diphenylmethane diisocyanate prepolymer; the diluent is hydroxyethyl acrylate or tripropylene glycol diacrylate; and the nanofiller is nano-calcium carbonate or nano-silica.

8. The coating method for a plant fiber board as described in claim 1, characterized in that: In S4, curing is performed under UV light irradiation with a curing energy of 150–250 mJ / cm². 2 The curing time is 20–40 seconds.

9. The coating method for a plant fiber board as described in claim 1, characterized in that: The application rate of the adhesion primer in S2 is 20–40 g / m², and the application rate of the primer in the topcoat construction of S5 is 30–50 g / m².

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