Lightweight and high-strength honeycomb composite advertising board panel and preparation method thereof

Abstract

The invention relates to the technical field of advertisement display equipment manufacturing, and discloses a light high-strength honeycomb composite material advertisement vertical board panel and a preparation method thereof, and the panel is formed by compounding an upper layer PVC panel, a lower layer PVC panel, a resin reinforced paper honeycomb core located in the middle layer and a two-component polyurethane structural adhesive. Wherein the resin reinforced paper honeycomb core is prepared by impregnating and curing raw paper with modified phenolic resin containing polyvinyl alcohol and a silane coupling agent; the two-component polyurethane structural adhesive contains castor oil polyhydric alcohol and fumed silica. The preparation method comprises the steps of core material dipping and curing pretreatment, double gluing of panel gluing and core material gluing, high-temperature hot pressing and pressure maintaining cooling shaping. By utilizing the toughening effect of the modified resin and the thixotropic property of the structural adhesive, the problems of high brittleness and low interface bonding strength of the paper honeycomb are effectively solved, and the flatness, the peel strength and the weather resistance of the plate are effectively improved.

Description

Technical Field

[0001] This invention relates to the field of advertising display equipment manufacturing technology, and in particular to a lightweight and high-strength honeycomb composite advertising sign panel and its preparation method. Background Technology

[0002] Large outdoor advertising billboards, as important carriers of information display, have strict requirements for the strength, flatness, and weather resistance of their materials. Traditional large outdoor advertising billboards typically use metal materials such as galvanized steel or aluminum sheets. While these materials offer high strength, their heavy weight leads to cumbersome transportation and installation, high support structure costs, and the risk of corrosion with long-term outdoor use. Solid plastic sheets such as PVC foam boards or PP boards, although less dense than metals, require increased thickness to meet wind load and rigidity requirements as the billboard size increases, which also increases the weight of the sheets. Furthermore, these sheets have poor thermal stability and are prone to warping and deformation under the influence of sunlight and temperature differences, making it difficult to balance weight, strength, and cost. Wooden boards, on the other hand, are limited by their weather resistance, are prone to moisture damage, warping and cracking, and have insufficient fire resistance, making them unsuitable for long-term outdoor use.

[0003] Honeycomb sandwich structures, by distributing panel material away from the bending neutral axis, achieve high bending stiffness with less material and have been successfully applied in the aerospace and rail transportation fields. To promote this efficient structure and control costs in the advertising industry, replacing expensive metal honeycomb cores with paper honeycomb cores has become a viable technological approach.

[0004] However, directly applying paper honeycomb composite materials to outdoor advertising stands still faces technical bottlenecks. Firstly, ordinary paper honeycomb core materials have limited strength, high moisture absorption, and are quite brittle after traditional resin impregnation curing, making them prone to breakage or collapse under wind loads. Secondly, the PVC panels commonly used in advertising stands have smooth, flat surfaces, while the honeycomb core and panel only contact each other through narrow pore wall end faces, resulting in a small effective bonding area. Existing adhesive processes struggle to create sufficient anchoring force at the interface, leading to low peel strength and easy delamination under prolonged outdoor loads. Furthermore, due to the significant difference in thermal expansion coefficients between the PVC panel and the paper honeycomb core, internal stress easily accumulates within the board during composite molding and subsequent temperature changes, causing severe warping or surface waviness in the finished product, failing to meet the requirements of high-quality advertising displays for panel flatness and durability. Summary of the Invention

[0005] The purpose of this invention is to provide a lightweight and high-strength honeycomb composite advertising stand panel and its preparation method, which solves the technical problems of existing honeycomb composite advertising stand panels, such as high core material brittleness, poor impact resistance, low bonding strength between the panel and the core material, and easy warping and deformation of the panel.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] In a first aspect, the present invention provides a lightweight and high-strength honeycomb composite advertising sign panel, which is made of raw materials comprising the following components: an upper and lower PVC panel, a resin-reinforced paper honeycomb core located in the middle layer, and a two-component polyurethane structural adhesive for bonding the PVC panel to the resin-reinforced paper honeycomb core.

[0008] The resin-reinforced paper honeycomb core is formed by impregnating and curing base paper with a modified phenolic resin impregnation solution. The modified phenolic resin impregnation solution is made from the following raw materials in parts by weight: 95-105 parts phenol, 120-140 parts formaldehyde solution with a concentration of 36%-38%, 5-15 parts polyvinyl alcohol, 3-5 parts sodium hydroxide solution with a concentration of 28%-32%, 0.5-1.0 parts silane coupling agent, and 90-110 parts deionized water.

[0009] The two-component polyurethane structural adhesive is composed of a mixture of component A and component B. Component A contains 60-70 parts of castor oil polyol, 25-35 parts of polyether polyol, 3-5 parts of fumed silica, and 0.1-0.3 parts of catalyst. Component B is polymeric MDI, and the weight ratio of component A to component B is 3.5-4.5:1.

[0010] By adopting the above technical solution, and using polyvinyl alcohol-modified phenolic resin as the core material reinforcing agent, combined with a two-component polyurethane structural adhesive containing fumed silica, a composite board with both high strength and high toughness was obtained. The specific mechanism of action is analyzed as follows:

[0011] First, regarding the toughening modification of the core material resin. Ordinary phenolic resin, after curing, has a high crosslinking density and exhibits significant brittleness. In this solution, under alkaline conditions, one end group of the silane coupling agent reacts with the phenolic hydroxyl or hydroxymethyl groups in the phenolic oligomer, while the other end group undergoes condensation or addition reactions with the hydroxyl groups on the polyvinyl alcohol molecular chain, acting as a chemical bridge. The long-chain polyvinyl alcohol molecules interweave within the rigid three-dimensional crosslinked network of the phenolic resin, increasing the intermolecular distance of the cured resin and reducing the internal stress of the crosslinked network, thereby improving the resin's impact strength and toughness. Furthermore, the silane coupling agent can also chemically bond with the hydroxyl groups on the surface of the original paper fibers, incorporating chemical bonding forces into the bond between the modified resin and the paper fibers, thus enhancing the overall compressive strength of the honeycomb core.

[0012] Secondly, regarding the thixotropy and adhesion of the structural adhesive. The narrow end faces of the honeycomb core result in a small effective contact area when bonded to a flat PVC panel. The fumed silica added to the two-component polyurethane structural adhesive has a high specific surface area. The silanol groups on its surface form a physical network structure through hydrogen bonding within the system, imparting thixotropy to the adhesive. Under the application shear force, the adhesive viscosity decreases, facilitating application. After standing, the viscosity recovers, preventing adhesive loss along the honeycomb cell walls. When the panel and core material are laminated, the thixotropic adhesive accumulates at the root of the honeycomb cell wall where it contacts the panel, forming a rounded adhesive corner, increasing the actual bonding area, avoiding insufficient adhesive application, and improving peel strength. Simultaneously, the long-chain fatty acid ester structure of castor oil polyol imparts hydrophobic properties to the adhesive layer, enhancing its hydrolysis resistance.

[0013] Preferably, the modified phenolic resin impregnation solution is prepared by the following method: first, phenol, formaldehyde solution and part of sodium hydroxide solution are mixed and reacted at 60-70℃ for 40-60 minutes, then the temperature is raised to 80-90℃ and the remaining sodium hydroxide solution is added to react until the water solubility of the resin reaches 1:2-1:4; after cooling to 55-65℃, a polyvinyl alcohol aqueous solution and silane coupling agent prepared in advance at 85-95℃ for 2-3 hours are added, and the mixture is kept at a constant temperature and stirred for 20-40 minutes for graft modification, and finally vacuum dehydrated to a solid content of 45-50%.

[0014] By employing the above technical solution, the segmented reaction process controls the resin structure. In the low-temperature stage, addition reactions primarily occur to generate polyhydroxymethylphenol; the heating stage promotes condensation reactions, and controlling specific water solubility parameters ensures a suitable resin molecular weight, allowing the resin to penetrate the paper fibers while minimizing curing volatilization. Cooling to 55-65℃ and adding polyvinyl alcohol and a silane coupling agent prevents rapid resin gelation due to excessive temperature, ensuring sufficient time for the graft copolymerization reaction and guaranteeing the homogeneity of the modified system. The vacuum dehydration step adjusts the solid content and viscosity of the impregnation solution to meet the needs of industrial production.

[0015] Preferably, the silane coupling agent is one of γ-aminopropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane; the catalyst is one of organobismuth and organotin. The thickness of the resin-reinforced paper honeycomb core is 9-20 mm, and the side length of the honeycomb pores is 5-8 mm; the dry adhesion amount of the modified phenolic resin in the resin-reinforced paper honeycomb core is 15%-25% of the weight of the original paper.

[0016] By adopting the above technical solution, fully hydrolyzed polyvinyl alcohol provides sufficient hydroxyl reaction sites and exhibits good water resistance. Fumed silica with a specific surface area provides a suitable thickening and thixotropic effect, ensuring the colloid's anti-sagging properties on vertical surfaces. The resin adhesion amount is controlled within the range of 15%-25%, balancing strength and weight; too low an adhesion amount results in insufficient reinforcement, while too high an amount increases brittleness and makes drying difficult.

[0017] Secondly, the present invention provides a method for preparing a lightweight and high-strength honeycomb composite advertising sign panel, comprising the following steps:

[0018] S1. Core material pretreatment: The stretched and shaped paper honeycomb core is immersed in modified phenolic resin impregnation liquid. After removing the excess adhesive, it is heated and cured to obtain resin-reinforced paper honeycomb core.

[0019] S2. Apply adhesive: Apply two-component polyurethane structural adhesive to the inner surface of the upper and lower PVC panels, and at the same time apply adhesive to the end face of the resin-reinforced paper honeycomb core.

[0020] S3. Composite hot pressing: The lower PVC panel after gluing, the resin-reinforced paper honeycomb core, and the upper PVC panel are stacked in sequence and sent into a hot press. The press is held at a temperature of 60-80℃ and a pressure of 0.2-0.5MPa for 60-120 minutes.

[0021] S4. Post-processing: Maintain the pressure, cool the board to 35-45℃, release the pressure, and then cure at room temperature, cut and seal the edges to obtain the finished product.

[0022] By adopting the above technical solution, the problem of poor flatness of composite boards caused by the large coefficient of thermal expansion of PVC panels has been solved. The specific process control principle is as follows:

[0023] Core material pretreatment transforms the paper honeycomb from a hygroscopic, porous paper material into a hydrophobic, high-strength composite skeleton, preventing excessive adhesive absorption by the paper during subsequent gluing and resulting in insufficient adhesive at the interface. The gluing process combines panel gluing with core material adhesive application, ensuring sufficient adhesive at the composite interface and facilitating the formation of a full adhesive layer anchoring structure. In the post-processing stage, because PVC material is in a softened and expanded state during hot pressing at 60-80℃, direct high-temperature depressurization can cause internal stress in the PVC panel during cooling and shrinkage due to the inconsistent shrinkage rate with the core material, leading to board warping. This method employs a pressure-holding cooling process, using the hot press cooling system to forcibly cool the board to 35-45℃. At this point, the adhesive layer has initially solidified and set, balancing the internal stress of the PVC. After depressurization, the board maintains flatness and dimensional stability.

[0024] Preferably, in step S1, the impregnation time is 2-5 minutes; the heat curing treatment adopts a segmented curing process, specifically including: first drying at 85-95℃ for 15-25 minutes, and then heating to 145-155℃ for curing for 10-15 minutes.

[0025] By employing the above technical solution, the segmented curing process ensures the density of the resin layer. The drying stage at 85-95℃ is below the boiling point of water, allowing the deionized water solvent to evaporate slowly before the resin undergoes vigorous cross-linking, preventing the rapid vaporization of moisture at high temperatures that could form micropores or bubbles within the resin layer. After the solvent evaporates, the temperature is raised to 145-155℃ to promote a full cross-linking reaction between the phenolic resin, polyvinyl alcohol, silane coupling agent, and fibers, forming the final reinforced structure.

[0026] Preferably, in step S2, the amount of adhesive applied to the inner surface of the PVC panel is 180-250 g / m². 2 The amount of adhesive applied to the end face of the resin-reinforced paper honeycomb core is 50-70 g / m². 2 In step S3, the application of the two-component polyurethane structural adhesive, after mixing components A and B, is completed within 30-50 minutes. In step S4, the room temperature curing time is 20-30 hours; the edge sealing uses a single-component polyurethane sealant.

[0027] By adopting the above technical solution, the weight of the board is controlled while ensuring bonding strength by adjusting the adhesive application ratio. The pot life is controlled at 30-50 minutes, utilizing the low viscosity of polyurethane in the early stage of the reaction for penetration, followed by the gelation period to build strength. The room temperature curing process allows the residual isocyanate groups in the polyurethane adhesive layer to react completely, eliminating residual stress introduced by the processing and ensuring the dimensional stability of the product during long-term use.

[0028] In summary, the present invention has at least one of the following beneficial technical effects:

[0029] 1. This invention improves the brittleness of traditional phenolic resin after curing by treating paper honeycomb cores with a phenolic resin impregnation solution modified with polyvinyl alcohol and a silane coupling agent. The introduction of flexible polyvinyl alcohol molecular chains improves the toughness of the resin cross-linking network, and the chemical bonding effect of the silane coupling agent on the resin-paper fiber interface enhances the impact resistance of the paper honeycomb core while maintaining its high compressive strength, thus solving the problem of easy breakage of the core material under stress in advertising standees.

[0030] 2. This invention utilizes a two-component polyurethane structural adhesive containing fumed silica and castor oil polyol to solve the problem of low peel strength caused by the small bonding area between the narrow end face of the honeycomb core and the PVC panel. Fumed silica imparts thixotropic properties to the adhesive, causing it to form an arc-shaped accumulation at the contact point between the honeycomb cell wall and the panel, increasing the effective bonding area; at the same time, the hydrophobic structure introduced by the castor oil polyol improves the hydrolysis resistance and aging resistance of the adhesive layer, thus meeting the long-term use requirements of outdoor advertising stands.

[0031] 3. The manufacturing process of this invention, which combines hot-pressing composite with pressure-holding cooling, effectively controls the warping and deformation of the PVC panel caused by its large coefficient of thermal expansion. Cooling under pressure balances the internal stress of the PVC panel during the cooling and shrinkage process. Combined with the simultaneous curing and shaping of the structural adhesive, this ensures that the finished panel has good flatness and dimensional stability, avoiding surface defects caused by material springback after high-temperature depressurization. Detailed Implementation

[0032] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the preparation examples, comparative examples, and test examples. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] Preparation Examples 1-4:

[0034] Preparation Example 1:

[0035] This preparation example provides a modified phenolic resin impregnation solution A, comprising the following steps:

[0036] S1. Add 8 parts of polyvinyl alcohol to 92 parts of deionized water and stir at 90°C for 2 hours to obtain an 8% PVA aqueous solution for later use.

[0037] S2. Add 100 parts of molten phenol and 130 parts of 37% formaldehyde solution to a reaction vessel equipped with a stirrer, reflux condenser and thermometer, and start stirring to mix them evenly; then add 2 parts of 30% sodium hydroxide solution, slowly raise the temperature to 65°C and keep the reaction at this temperature for 50 minutes.

[0038] S3. Continue heating the reaction system to 85°C, add 2 parts of 30% sodium hydroxide solution, and carry out the polycondensation reaction at a constant temperature for 40 minutes. Take a sample to test the water solubility of the resin until it reaches 1:3.

[0039] S4. Cool the reactor to 60°C, slowly add all the PVA aqueous solution prepared in step S1 and 0.8 parts of γ-aminopropyltriethoxysilane, and stir at a constant temperature for 30 minutes to carry out grafting modification.

[0040] S5. Vacuum dehydration is carried out under reduced pressure to adjust the resin solid content to 48%, and the material is cooled to room temperature to obtain modified phenolic resin impregnation solution A.

[0041] Preparation Example 2:

[0042] This preparation example provides a high-toughness modified phenolic resin impregnation solution B, which includes the following steps:

[0043] S1. Add 12 parts of polyvinyl alcohol to 108 parts of deionized water and stir to dissolve for 2 hours at 90°C to obtain a polyvinyl alcohol aqueous solution for later use.

[0044] S2. Add 100 parts of molten phenol and 130 parts of 37% formaldehyde solution to the reaction vessel and start stirring; add 2 parts of 30% sodium hydroxide solution and heat to 65℃ to react for 50 minutes.

[0045] S3. Continue heating to 85℃, add 2 parts of 30% sodium hydroxide solution, keep the reaction at this temperature for 40 minutes, until the water solubility of the resin reaches 1:3.

[0046] S4. Cool to 60℃, add all the polyvinyl alcohol aqueous solution prepared in step S1 and 0.8 parts of γ-aminopropyltriethoxysilane, and stir at a constant temperature for 30 minutes to carry out modification.

[0047] S5. Vacuum dehydration is performed to adjust the solid content to 48%, followed by cooling and discharge to obtain modified phenolic resin impregnation solution B.

[0048] Preparation Example 3:

[0049] This preparation example provides a common phenolic resin impregnation solution C, including the following steps:

[0050] S1. Add 100 parts of phenol and 130 parts of 37% formaldehyde solution to the reaction vessel, and start stirring to mix evenly.

[0051] S2. Add 4 parts of 30% sodium hydroxide solution at once, heat to 85℃, and react at a constant temperature for 80 minutes.

[0052] S3. After the reaction is completed, the polyvinyl alcohol modification step is not carried out. Instead, vacuum dehydration is performed directly under reduced pressure to adjust the solid content to 48%. The product is then cooled to room temperature and discharged to obtain ordinary phenolic resin impregnation solution C.

[0053] Preparation Example 4:

[0054] This preparation example provides a two-component polyurethane structural adhesive D, comprising the following steps:

[0055] Preparation of S1 and component a: 65 parts castor oil polyol, 30 parts polyether polyol, 4 parts fumed silica and 0.2 parts organic bismuth catalyst were added sequentially to a high-speed disperser. The mixture was dispersed and degassed under vacuum for 30 minutes by high-speed stirring to obtain component A.

[0056] S2, component b preparation: Take 100 parts of polymeric MDI directly as component b.

[0057] S3. Preparation and Application: When using, mix component a and component b evenly at a weight ratio of 4:1 to obtain two-component polyurethane structural adhesive D.

[0058] Examples 1-3:

[0059] Example 1:

[0060] This embodiment provides a lightweight and high-strength honeycomb composite advertising sign panel and its preparation method, including the following steps:

[0061] S1. Core material preparation: The kraft paper honeycomb core is stretched and shaped into a regular hexagonal structure, with the side length of the pore diameter controlled at 5 mm and the cutting height at 14 mm. It is then completely immersed in the modified phenolic resin impregnation solution A prepared in Preparation Example 1 for 3 minutes. After removal, excess adhesive is blown off with an air knife, and the amount of resin dry adhesion is controlled at 18% of the weight of the original paper. Subsequently, a segmented curing treatment is carried out: first, it is dried at 90°C for 20 minutes, and then the temperature is raised to 150°C for 12 minutes to obtain the resin-reinforced kraft paper honeycomb core.

[0062] S2. Adhesive Application Process: Two 0.5mm thick PVC calendered films are used as the upper and lower surface plates, respectively. The two-component polyurethane structural adhesive D prepared in Example 4 is rolled onto their inner surfaces, controlling the single-sided coating amount to be 200g / m². 2 Simultaneously, the upper and lower end faces of the honeycomb core obtained in step S1 are coated with adhesive, and the amount of adhesive is controlled at 60g / m².

[0063] S3. Hot pressing composite: Lay the lower PVC film, the glued honeycomb core, and the upper PVC film in sequence on the positioning fixture, and send the stacked blank into the flat hot press; set the hot pressing temperature to 70℃, the unit pressure to 0.3MPa, and the holding time to 90 minutes.

[0064] S4. Post-treatment and edge sealing: After cooling with water to 40°C under pressure, the pressure is released and the board is removed. It is then stacked and cured at room temperature (23±2°C) for 24 hours to eliminate internal stress. The board is cut into standard specifications of 1200mm×2400mm using a CNC cutting machine. Finally, a single-component polyurethane sealant is applied to the edges of the board, and a U-shaped PVC profile is inserted to complete the edge sealing.

[0065] Example 2:

[0066] This embodiment provides a lightweight and high-strength honeycomb composite advertising sign panel and its preparation method, including the following steps:

[0067] S1. Core material preparation: The kraft paper honeycomb core is stretched and shaped into a regular hexagonal structure, with the side length of the pore diameter controlled to be 6 mm and the cutting height to be 19 mm; it is completely immersed in the modified phenolic resin impregnation solution B prepared in Preparation Example 2, and the amount of resin dry adhesion is controlled to be 22% of the weight of the original paper; then it is subjected to segmented curing treatment (drying at 90°C for 20 minutes and curing at 150°C for 12 minutes) to obtain a high-toughness resin-reinforced honeycomb core.

[0068] S2. Adhesive application process: Take two 0.5mm thick PVC calendered films and roll-coat the inner surface with the two-component polyurethane structural adhesive D prepared in Example 4, controlling the single-sided coating amount to be 180g / m². 2 At the same time, adhesive is applied to the upper and lower surfaces of the honeycomb core.

[0069] S3. Hot pressing composite: Lay the lower PVC film, the glued honeycomb core, and the upper PVC film in sequence on the positioning fixture, and send the stacked blank into the flat hot press; set the hot pressing temperature to 60℃, the unit pressure to 0.2MPa, and the holding time to 120 minutes.

[0070] S4. Post-treatment and edge sealing: Maintain pressure and cool to below 40°C to release pressure. After curing at room temperature for 24 hours, cut to the required size and use a single-component polyurethane sealant in conjunction with the U-shaped PVC profile for edge sealing.

[0071] Example 3:

[0072] This embodiment provides a lightweight and high-strength honeycomb composite advertising sign panel and its preparation method, including the following steps:

[0073] S1. Core material preparation: The kraft paper honeycomb core is stretched and shaped into a regular hexagonal structure, with the side length of the pore diameter controlled to be 8 mm and the cutting height to be 9 mm; it is completely immersed in the modified phenolic resin impregnation liquid A prepared in Preparation Example 1, and the amount of resin dry adhesion is controlled to be 15% of the weight of the original paper; then it is subjected to segmented curing treatment (drying at 90°C for 20 minutes and curing at 150°C for 12 minutes) to obtain the resin-reinforced honeycomb core.

[0074] S2. Adhesive application process: Take two PVC calendered films with a thickness of 0.5 mm, and roll-coat the inner surface of them with the two-component polyurethane structural adhesive D prepared in Example 4, controlling the amount of adhesive applied on one side to be 250 g / m²; at the same time, apply adhesive to the upper and lower end faces of the honeycomb core.

[0075] S3. Hot pressing composite: Lay the lower PVC film, the glued honeycomb core, and the upper PVC film in sequence on the positioning fixture, and send the stacked blank into the flat hot press; set the hot pressing temperature to 80℃, the unit pressure to 0.5MPa, and the holding time to 60 minutes.

[0076] S4. Post-treatment and edge sealing: Maintain pressure and cool to below 40°C to release pressure. After curing at room temperature for 24 hours, cut to the required size and use a single-component polyurethane sealant in conjunction with the U-shaped PVC profile for edge sealing.

[0077] Comparative Examples 1-4:

[0078] Comparative Example 1:

[0079] This comparative example is a 15mm thick white skinned PVC foam board; the difference from Example 1 is that it is integrally extruded and foamed without a honeycomb sandwich structure.

[0080] Comparative Example 2:

[0081] Compared with Example 1, the difference is that the kraft paper honeycomb core is not subjected to any resin impregnation treatment, and the original paper core is directly bonded to the PVC surface layer, while the rest are the same.

[0082] Comparative Example 3:

[0083] Compared with Example 1, the difference is that the core material is impregnated with the ordinary phenolic resin impregnation solution C prepared in Preparation Example 3, and the rest are the same.

[0084] Comparative Example 4:

[0085] Compared with Example 1, the difference is that the U-shaped PVC edge banding was not installed after the board was cut, and the honeycomb holes were directly exposed on the side. All other aspects are the same.

[0086] Test Example 1-2:

[0087] Test Example 1: Surface Processing Suitability and Interfacial Bonding Performance Test

[0088] Experimental steps:

[0089] Comparative Examples 1 and 2 were selected as references. An industrial-grade UV flatbed printer equipped with a Ricoh G5 printhead was used at an 18m... 2Test patterns containing fine lines and color blocks were printed using standard UV ink at a speed of / h. After printing and curing, cross-cutting and 3M 600 tape peel tests were performed according to GB / T9286-1998 standard to check ink layer adhesion; simultaneously, a 50x magnifying glass was used to observe the sharpness of line edges and the flatness of solid color blocks. A surface roughness meter was used to perform multi-point scanning of the board surface (sampling length 50mm), recording the arithmetic mean deviation Ra value of the profile, and visually assessing the presence of periodic patterns on the surface. According to GB / T2790-1995 standard, the board was cut into 25mm wide samples, and a universal testing machine was used to perform a 180° peel test at a speed of 100mm / min, recording the failure mode and average peel force.

[0090] Test data:

[0091] Table 1: Summary Table of Surface Compatibility and Physical Properties Test Data

[0092] Test Project Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 UV ink layer adhesion Level 0 Level 0 Level 0 Level 0 Level 0 Print line clarity Clear and sharp Clear and sharp Slightly blurred edges Clear and sharp Clear Surface roughness 0.84 0.92 1.63 0.65 1.12 Visual flatness No visible traces No visible traces Faintly visible smooth Visible dents Average peel strength of adhesive layer 42.6 38.9 45.1 - 12.4 Destruction Mode Core material cohesive failure Core material cohesive failure Mixed destruction - Interface debonding

[0093] Conclusion Analysis:

[0094] Peel strength data shows that the bonding strength between unimpregnated kraft paper fibers and polyurethane structural adhesive is weak, and the interlayer strength of the base paper is low, making it prone to interfacial debonding. This solution uses PVA-modified phenolic resin impregnation. The resin penetrates the fibers and cures, effectively improving the cohesive strength of the core material. Furthermore, the surface polarity of the cured phenolic resin matches the isocyanate groups in the polyurethane adhesive, further enhancing the bonding strength.

[0095] Regarding surface quality, Examples 1 and 2 exhibited surface roughness close to that of solid boards with no visible defects. This is attributed to the addition of fumed silica to the two-component polyurethane adhesive, which imparts thixotropic properties to the adhesive, allowing it to establish a yield value on porous surfaces, filling unevenness at the top of the honeycomb and forming a buffer layer, thus suppressing the orange peel effect caused by curing shrinkage. Example 3 showed increased surface roughness and slightly blurred printing edges, indicating that in the preparation of thin panels, excessive adhesive application under heat and pressure leveling can lead to slight deformation of the panel, requiring precise control of the adhesive amount and pressure balance. All samples showed UV ink adhesion of grade 0, confirming the good suitability of this PVC calendered film formulation for UV inks.

[0096] Test Example 2: Comparison Test of Physicochemical Properties and Environmental Weather Resistance

[0097] Experimental steps:

[0098] Cut 100mm × 100mm specimens, weigh them, and measure their volume. Calculate the relative weight loss rate using a solid PVC board as a reference. Following ASTM C365, place 50mm × 50mm specimens in the center of the testing machine's pressure plate and load them at a speed of 0.5mm / min until failure or deformation reaches 10%. Determine the flat compressive strength. Separately, take specimens from the same batch and completely immerse them in deionized water at 25℃ for 48 hours. After drying, determine the flat compressive strength and calculate the wet strength retention rate. Horizontally support the specimens (span 200mm) and use a 500g steel ball to freely drop from a height of 1.0m to impact the center, recording the indentation depth and failure mode. Perform a three-point bending test according to ASTM C393, with a span of 300mm and a loading speed of 5mm / min, and determine the bending stiffness.

[0099] Test data:

[0100] Table 2: Summary of Measured Data on Comprehensive Physical and Chemical Properties and Weather Resistance

[0101] Testing items Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Measured thickness (mm) 15.02 20.15 10.05 15.00 15.06 15.03 15.02 Surface density (kg / m²) 3.63 3.42 2.85 12.48 3.19 3.71 3.55 Relative weight loss rate (%) 70.9 72.6 77.2 - 74.4 70.3 71.6 Initial compressive strength (MPa) 2.84 2.15 2.93 - 0.42 3.12 2.79 <![CDATA[Flexural rigidity (×10 5 N·mm 2 )]]> 6.27 8.65 2.78 5.82 3.05 6.58 6.15 Water absorption rate (24h, %) 0.85 0.76 0.92 0.12 68.5 0.88 15.6 Wet strength retention rate (%) 98.4 98.6 97.5 99.8 14.2 98.9 62.3 Impact dent depth (mm) 1.2 0.8 2.1 0.5 6.5 1.1 1.3 Destruction Mode Plastic depression slight marks Surface material slightly cracked Surface marks Core material collapse Brittle crushing Plastic depression

[0102] Conclusion Analysis:

[0103] Example 1 shows that, with weight reduction, the bending stiffness exceeds that of a solid PVC board, verifying that the sandwich structure, by placing a high-modulus panel on the outer layer and utilizing the core material to bear shear stress, can effectively improve the cross-sectional moment of inertia of the material.

[0104] Impact tests showed that the comparative example using ordinary phenolic resin exhibited brittle fragmentation, while the example using PVA-modified phenolic resin only produced plastic indentation without structural collapse. This indicates that the introduction of long-chain PVA molecules reduces the crosslinking density of the phenolic resin and imparts flexibility, improving the resin's inherent brittleness and ensuring that the material maintains its structural integrity under impact.

[0105] In the water resistance test, the untreated paper core absorbed water and swelled, resulting in a loss of strength. However, the modified phenolic resin impregnation treatment effectively penetrated and sealed the hydrophilic groups of the fibers. Combined with the side sealing process, it blocked the water intrusion path, allowing the board to maintain a high strength retention rate after long-term immersion in water, thus solving the application problem of paper-based materials in outdoor high-humidity environments.

Claims

1. A lightweight and high-strength honeycomb composite advertising sign panel, characterized in that, Made from raw materials containing the following components: The upper and lower PVC panels, the resin-reinforced paper honeycomb core in the middle layer, and the two-component polyurethane structural adhesive for bonding the lower PVC panels to the resin-reinforced paper honeycomb core. The resin-reinforced paper honeycomb core is formed by impregnating and curing base paper with a modified phenolic resin impregnation solution. The modified phenolic resin impregnation solution is made from the following raw materials in parts by weight: 95-105 parts phenol, 120-140 parts formaldehyde solution with a concentration of 36%-38%, 5-15 parts polyvinyl alcohol, 3-5 parts sodium hydroxide solution with a concentration of 28%-32%, 0.5-1.0 parts silane coupling agent, and 90-110 parts deionized water. The two-component polyurethane structural adhesive is composed of component A and component B. Component A contains 60-70 parts castor oil polyol, 25-35 parts polyether polyol, 3-5 parts fumed silica, and 0.1-0.3 parts catalyst by weight. Component B is polymeric MDI, and the weight ratio of component A to component B is 3.5-4.5:

1.

2. The lightweight and high-strength honeycomb composite advertising sign panel according to claim 1, characterized in that, The modified phenolic resin impregnation solution was prepared using the following method: First, mix 95-105 parts of phenol, 120-140 parts of formaldehyde solution and 1.5-2.5 parts of sodium hydroxide solution, react at 60-70℃ for 40-60 minutes, then raise the temperature to 80-90℃ and add the remaining sodium hydroxide solution to react until the water solubility of the resin reaches 1:2-1:

4. After cooling to 55-65℃, add 95-125 parts of polyvinyl alcohol aqueous solution prepared by dissolving at 85-95℃ for 2-3 hours and 0.5-1.0 parts of silane coupling agent, stir at constant temperature for 20-40 minutes for graft modification, and finally dehydrate under vacuum to a solid content of 45-50%.

3. The lightweight and high-strength honeycomb composite advertising sign panel according to claim 1, characterized in that, The silane coupling agent is one of γ-aminopropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane; the catalyst is one of organobismuth and organotin.

4. The lightweight and high-strength honeycomb composite advertising sign panel according to claim 1, characterized in that, The thickness of the resin-reinforced paper honeycomb core is 9-20 mm, and the side length of the honeycomb pores is 5-8 mm.

5. The lightweight and high-strength honeycomb composite advertising sign panel according to claim 1, characterized in that, The amount of the modified phenolic resin dry-adhered in the resin-reinforced paper honeycomb core is 15%-25% of the weight of the original paper.

6. A method for preparing a lightweight, high-strength honeycomb composite advertising sign panel according to any one of claims 1-5, characterized in that, Includes the following steps: S1. Core material pretreatment: The stretched and shaped paper honeycomb core is immersed in modified phenolic resin impregnation liquid. After removing the excess adhesive, it is heated and cured to obtain resin-reinforced paper honeycomb core. S2. Apply adhesive: Apply two-component polyurethane structural adhesive to the inner surface of the upper and lower PVC panels, and at the same time apply adhesive to the end face of the resin-reinforced paper honeycomb core. S3. Composite hot pressing: The lower PVC panel after gluing, the resin-reinforced paper honeycomb core, and the upper PVC panel are stacked in sequence and sent into a hot press. The press is held at a temperature of 60-80℃ and a pressure of 0.2-0.5MPa for 60-120 minutes. S4. Post-processing: Maintain the pressure, cool the board to 35-45℃, release the pressure, and then cure at room temperature, cut and seal the edges to obtain the finished product.

7. The method for preparing a lightweight and high-strength honeycomb composite advertising sign panel according to claim 6, characterized in that, In step S1, the soaking time is 2-5 minutes; The heat curing process adopts a segmented curing process, which specifically includes: first drying at 85-95℃ for 15-25 minutes, and then heating to 145-155℃ for 10-15 minutes.

8. The method for preparing a lightweight and high-strength honeycomb composite advertising sign panel according to claim 6, characterized in that, In step S2, the amount of adhesive applied to the inner surface of the PVC panel is 180-250 g / m². 2 The amount of adhesive applied to the end face of the resin-reinforced paper honeycomb core is 50-70 g / m². 2 .

9. The method for preparing a lightweight and high-strength honeycomb composite advertising sign panel according to claim 6, characterized in that, In step S3, the application of component A and component B of the two-component polyurethane structural adhesive is completed within 30-50 minutes after mixing.

10. The method for preparing a lightweight and high-strength honeycomb composite advertising sign panel according to claim 6, characterized in that, In step S4, the room temperature curing time is 20-30 hours; The edge sealing uses a single-component polyurethane sealant.