Pultrusion and coating integrated forming process for composite material

Abstract

The invention provides a composite material pultrusion and coating integrated molding process, relates to the field of composite material molding, and aims to solve the problem that the pultrusion and coating of the composite material are difficult to realize integration at present, and the rapid cooling after pultrusion is realized in manners of preliminary air cooling, rapid cooling to form microcracks, profile spraying and irradiation curing. A profile surface structure state and a temperature state facilitating spraying are established, pultrusion and spraying integration is achieved, controlled thermal stress generated by quick cooling is utilized, micro cracks are generated on a resin-rich layer on the surface of the profile through induction, the coating permeates into the cracks under the effect of temperature difference, dense-distribution solid micro rivets are formed after curing, and therefore the micro rivets are formed. The problems of high surface inertia and poor adhesive force of the composite material are solved; the internal-hot and external-cold temperature gradient formed after rapid cooling is utilized, while the surface layer is blocked by external irradiation, internal waste heat is heated upwards from the bottom layer, internal and external bidirectional curing is achieved, the defect that the coating curing time is short in online production is effectively overcome, and energy consumption is reduced.

Description

Technical Field

[0001] This invention relates to the field of composite molding, and more specifically to an integrated pultrusion coating molding process for composite materials. Background Technology

[0002] Fiber-reinforced polymer (FRP) pultrusion molding is widely used in aerospace, wind turbine blades, rail transportation, and building profiles due to its continuous, highly automated process and stable mechanical properties. To improve the weather resistance, UV resistance, and aesthetics of the composite material, coating is typically applied to the surface of the pultruded profile. However, current pultrusion coating processes for composite materials generally suffer from production discontinuities. Traditionally, after pultrusion molding, the composite material is first cut to a fixed length and "offline." Then, the semi-finished profile is transferred to a separate coating workshop for a series of processes including mounting, cleaning, grinding, spraying, and drying. This segmented production model of "offline first, coating later" results in cumbersome process flows, inventory buildup, significantly extended production time, and overall low production efficiency.

[0003] The inability to perform online coating is primarily due to the fact that pultruded profiles typically leave the mold at temperatures of 150°C-200°C, along with significant internal residual heat. Direct contact with high-temperature surfaces using traditional solvent-based coatings can lead to solvent boiling, coating blistering (orange peel effect), and poor leveling. Therefore, existing production lines typically require extremely long natural cooling sections or air-cooling equipment to thoroughly cool the profiles to room temperature, consuming considerable factory space. Cooling through a medium with a large temperature difference can cause internal stress-induced cracks and other defects, affecting profile quality and making it difficult to effectively reduce the time and space required for the cooling process. Furthermore, the pultrusion process requires internal release agents to ensure smooth demolding, leaving a difficult-to-remove hydrophobic oil or wax film on the profile surface, severely impacting coating adhesion. Removing the release agent at high temperatures is also inconvenient; mechanical grinding after cooling to lower temperatures is inefficient and can damage the reinforcing fibers on the profile surface, reducing structural strength. Summary of the Invention

[0004] In view of this, the purpose of this invention is to provide an integrated molding process for composite material pultrusion coating, which removes the release agent by rapid cooling and shortens the cooling time. During the cooling process, microcracks are formed in the interlocking coating layer through thermal shock, thereby improving the coating adhesion stability.

[0005] The first objective of this invention is to provide an integrated pultrusion coating molding process for composite materials, employing the following solution: include: Composite materials are continuously output as profiles through pultrusion molding, forming a resin-rich layer on the surface of the profiles, and a release agent layer is applied to the outer surface of the profiles. After the profile undergoes initial air cooling, it is then rapidly cooled. During rapid cooling, the release agent layer is peeled off, and microcracks are formed in the resin-rich layer on the profile surface, causing the profile surface temperature to be lower than the core temperature. The sprayed profiles are coated, and the coating contacts the profile surface and penetrates into the microcracks to form an anchor. The coating on the exterior of the profile is irradiated, and the residual heat from the core of the profile is used to heat and cure the coating from the inside out.

[0006] Furthermore, the composite material uses carbon fiber or glass fiber as reinforcing fiber and resin as matrix, with the reinforcing fiber distributed outside the resin-rich layer distribution area.

[0007] Furthermore, after the profile is initially cooled by air cooling, it changes from a rubber state to a glass state, and then undergoes thermal shock during rapid cooling in the glass state to induce brittle microcracks.

[0008] Furthermore, temperature and microcrack monitoring are performed on the profile surface, with dry ice used as a cooling medium for heat exchange with the profile.

[0009] Furthermore, the dry ice has two forms: granular and powdered. If it is determined that the adhesion of the profile surface is insufficient, granular dry ice is used to impact the profile surface to actively create cracks. If it is determined that the adhesion of the profile surface meets the requirements, powdered dry ice is used to exchange heat with the profile, soften the thermal shock, and perform cleaning and cooling.

[0010] Furthermore, after cleaning the microcracks, spraying is performed. The paint comes into contact with the warm profile surface, and after the viscosity decreases, it flows into the depths of the microcracks.

[0011] Furthermore, after the profile is sprayed, the coating is given time to level and penetrate before irradiation.

[0012] Furthermore, the coating is cured by UV / EB irradiation.

[0013] Furthermore, during irradiation, the outer layer of the coating first cures and seals the surface, and the residual heat in the core of the profile is used to cure the coating inside the microcracks. The cured coating forms solid fulcrums in the microcracks, achieving chemical bonding and physical micro-rivet locking.

[0014] Furthermore, after the coating on the profile surface has cured, the profile is then cut.

[0015] Compared with the prior art, the advantages and positive effects of this invention are: To address the challenge of achieving integrated coating in composite material pultrusion processes, this method utilizes a series of steps, including initial air cooling, rapid cooling to create microcracks, profile spraying, and irradiation curing, to achieve rapid cooling after pultrusion molding. This process establishes a suitable surface structure and temperature profile for easy spraying, enabling integrated pultrusion spraying. Controlled thermal stress generated by rapid cooling induces microcracks in the resin-rich layer on the profile surface. These microcracks do not damage the structure but instead act as microscopic anchor points. The coating penetrates these cracks under temperature differences, forming densely distributed micro-rivets after curing. This avoids damage to structural strength without the need for traditional mechanical grinding, solving the problems of high surface inertia and poor adhesion in composite materials. Furthermore, the internal and external temperature gradient created by rapid cooling converts the residual heat that would otherwise be dissipated into curing energy. While external irradiation seals the surface, internal residual heat heats the material from the bottom up, achieving bidirectional curing. This effectively solves the defects of short curing time, surface-dry-in-the-middle or incomplete deep curing in online production, thus reducing energy consumption.

[0016] By utilizing the rapid cooling thermal stress, which is considered risky in traditional processes, dense microcracks are induced in the resin-rich layer on the surface of the profile through rapid cooling starting from the glassy state. The microcracks exist only in the resin-rich layer and do not damage the internal reinforcing fiber structure, but provide mechanical anchoring points for subsequent coatings. Combined with the micro-rivet effect after the coating penetrates and cures, its adhesion is far superior to traditional mechanical sanding, and it avoids dust pollution and fiber damage caused by sanding.

[0017] By replacing lengthy natural or air cooling with rapid cooling, the length of the cooling section is significantly shortened, saving factory space. At the same time, it enables continuous production across the entire process of pultrusion, surface treatment, coating, curing, and cutting, eliminating cumbersome processes such as semi-finished product removal, transfer, inventory, and secondary processing, thus improving production efficiency.

[0018] By dynamically adjusting the form of dry ice through a monitoring system, using either granular or powdered dry ice, the kinetic energy of granular dry ice is used to actively create textures when the surface of the profile is too smooth and the adhesion is insufficient. When the surface condition is good or the wall thickness is thin, powdered dry ice is used for gentle cleaning. While ensuring cleanliness and adhesion, this effectively avoids damage to the substrate that may be caused by excessive impact, thus achieving refined process control.

[0019] The coating process is set to be carried out when the profile surface is warm. At this time, the surface temperature of the profile is lower than the core temperature but higher than the room temperature. After the paint comes into contact with the warm surface, the viscosity decreases rapidly. It can efficiently penetrate into the depth of microcracks by using capillary action, while improving the leveling properties. This results in a final paint surface that is both smooth and beautiful, and has a strong bond. Attached Figure Description

[0020] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0021] Figure 1 This is a schematic diagram of the integrated molding process for composite material pultrusion coating in an embodiment of the present invention. Detailed Implementation

[0022] In a typical embodiment of the present invention, such as Figure 1 As shown, a composite material pultrusion coating integrated molding process is presented.

[0023] The internal release agent used in pultrusion processes affects the adhesion of the coating during spraying and is difficult to remove effectively. Furthermore, pultruded profiles typically leave the mold at temperatures of 150°C-200°C with significant internal residual heat. Direct contact between the coating and the high-temperature surface can lead to solvent boiling, coating blistering, and poor leveling. The cooling process for achieving a suitable spraying state requires substantial factory space. Pultrusion production is continuous and high-speed (typically 0.5-1.5 m / min), while traditional thermosetting coatings have long drying times, resulting in a severe mismatch in production cycles. In addition, composite materials have smooth surfaces, strong chemical inertness, and lack effective mechanical anchoring points. Therefore, this embodiment provides an integrated pultrusion coating molding process for composite materials. Utilizing controlled thermal shock-induced microcrack anchoring and bidirectional curing with internal heat and external cooling, this process achieves efficient and environmentally friendly release agent removal, efficient utilization of residual heat, and high-strength coating adhesion without interrupting continuous pultrusion production, thus overcoming the aforementioned shortcomings.

[0024] like Figure 1 As shown, the integrated pultrusion coating molding process for composite materials includes: Composite materials are continuously output as profiles through pultrusion molding, forming a resin-rich layer on the surface of the profiles, and a release agent layer is applied to the outer surface of the profiles. After the profile undergoes initial air cooling, it is then rapidly cooled. During rapid cooling, the release agent layer is peeled off, and microcracks are formed in the resin-rich layer on the profile surface, causing the profile surface temperature to be lower than the core temperature. The sprayed profiles are coated, and the coating contacts the profile surface and penetrates into the microcracks to form an anchor. The coating on the exterior of the profile is irradiated, and the residual heat from the core of the profile is used to heat and cure the coating from the inside out.

[0025] In this composite material, carbon fiber or glass fiber is used as the reinforcing fiber, and resin is used as the matrix. The reinforcing fiber is distributed outside the resin-rich layer distribution area.

[0026] The composite material is pultruded at 150-250℃. Through process control, a resin-rich layer with a thickness of approximately 30-50 micrometers is formed on the surface of the profile. The resin-rich layer is made of pure resin and serves as a safe carrier for subsequent "micro-cracks," ensuring that cracks remain on the surface and do not damage the internal load-bearing fibers.

[0027] The profiles are cooled in a natural air-cooling zone, reducing the surface temperature from 200℃ to 120-140℃. This transforms the resin-rich layer on the profile surface from a "rubber state" to a hard and brittle "glass state." Only in the glass state can instantaneous thermal shock induce brittle microcracks; if impacted in the high-temperature, soft state, only elastic deformation will occur, and no anchoring points can be formed.

[0028] Dry ice thermal shock cleaning and microcrack induction are employed. The material enters the dry ice treatment unit, where sublimation endothermics create an instantaneous temperature difference, achieving a dual function: firstly, it removes the release agent for cleaning; secondly, it utilizes the difference in thermal expansion and contraction to induce dense, irregular micron-sized cracks on the surface of the resin-rich layer.

[0029] To control the cooling process, infrared thermal imagers can be used to monitor the surface temperature of the profile and the formation of surface cracks, or the temperature drop rate can be used to indirectly estimate the temperature.

[0030] Dry ice comes in two forms: granular and powdered. If it is determined that the adhesion of the profile surface is insufficient, granular dry ice is used to impact the profile surface to actively create cracks. If it is determined that the adhesion of the profile surface meets the requirements, powdered dry ice is used to exchange heat with the profile, softening the thermal shock, and cleaning and cooling.

[0031] If the surface is found to be too smooth or the adhesion is insufficient, increase the particle diameter of the dry ice pellets or the spray pressure to enhance thermal shock and actively create cracks. If the resin-rich layer of the profile is found to be too thin or the cooling is too rapid, switch to powdered dry ice to soften the thermal shock and perform only cleaning and gentle cooling in order to avoid damaging the core.

[0032] After being rapidly cooled by dry ice, the profile temperature drops to 60-80℃, forming densely distributed microcracks on the surface. Micro-nano pores are formed within the microcracks, and the profile remains clean after the dry ice sublimates.

[0033] Online spraying / dipping is performed at 60-80℃. Upon contact with the warm composite surface, the viscosity of the coating decreases significantly. The low-viscosity coating penetrates deep into the "micro-cracks" created in step S3, achieving capillary penetration. After the profile is sprayed, a leveling and penetration time is allowed before irradiation. In this embodiment, a leveling and penetration time of 0.5-1 second is allowed.

[0034] For the curing process, the coating uses either UV-curable or electron beam-curable coatings. Externally, UV / EB radiation is used to instantly seal the surface and prevent the coating from flowing out. Internally, the residual heat from the pultrusion core is used to heat the coating from within, allowing it to penetrate deep into the microcracks and cure.

[0035] The cured coating forms densely distributed, hard solid support points in the microcracks, which not only form chemical bonds but also establish physical micro-rivet interlocking.

[0036] The profiles are cut and packaged after the coating has cured.

[0037] In this embodiment, carbon fiber is used as the reinforcing fiber and epoxy resin is used as the matrix for illustration.

[0038] After impregnating an epoxy resin matrix, carbon fiber bundles are introduced into a heated mold for pultrusion curing. The mold temperature is set at 160-220℃, and the pultrusion speed is 0.8-1.2 m / min. By controlling the mold outlet design and resin content, a resin-rich layer with a thickness of approximately 30-60 micrometers is formed on the surface of the output continuous profile, within which no reinforcing fibers are distributed. At this point, the profile surface is covered with an oil film formed by the migration of the internal release agent, and the overall profile temperature is approximately 180℃.

[0039] After leaving the mold, the profile enters a natural air-cooling zone or is equipped with gentle air cooling, allowing the surface temperature of the profile to naturally drop to 130℃-150℃. This temperature range is slightly lower than the glass transition temperature of the resin, ensuring that the resin matrix transforms from a highly elastic / viscous flow state to a hard glassy state. This step prepares the physical state for the subsequent fabrication of brittle microcracks.

[0040] An online dry ice cleaning system is used to treat the surface of profiles in a glassy state. Dry ice is sprayed from nozzles, and the instantaneous temperature difference generated by the sublimation and heat absorption of the dry ice creates a thermal shock.

[0041] In this process, on the one hand, it plays a cleaning role, as the stubborn release agent layer on the surface is completely peeled off due to cold embrittlement and the impact of dry ice waves; on the other hand, it plays a texturing role, as the resin-rich layer generates thermal stress due to rapid shrinkage, inducing the formation of dense, irregular micron-level cracks; and on the third hand, it plays a cooling role, as the surface temperature of the profile drops rapidly to 60-80℃, while the core of the profile remains at a high temperature above 100℃ due to the lag in heat conduction, forming a temperature gradient of "hot inside and cold outside".

[0042] After the profile surface is cleaned and heated to 60-80℃, it enters the spray booth for UV coating. Upon contact with the warm surface, the viscosity of the coating droplets decreases instantly. Under surface tension and capillary action, they flow along the microcracks and penetrate deep into their roots. Allow the coating approximately 1-3 seconds for leveling and penetration.

[0043] The profile enters the curing zone, where it is subjected to high-intensity irradiation using UV lamps (ultraviolet light). The outermost layer of the coating reacts and cross-links rapidly within 0.5 seconds, sealing the surface and shaping the coating surface. Meanwhile, the residual heat conducted from the core of the profile is transferred from the inside out to heat and cure the coating that has penetrated into the microcracks and the bottom of the coating.

[0044] After curing, the coating forms root-like solid support points in the microcracks, achieving a dual combination of chemical bonding and physical micro-rivet interlocking.

[0045] After the coating has fully cured and the overall temperature of the profile has cooled to a suitable range, it is cut to a fixed length using a flying saw to complete the finished product.

[0046] Before rapid cooling, an online monitoring device is installed, including an infrared thermometer and a surface roughness / gloss sensor.

[0047] Corresponding to the active texture creation mode: When the monitoring device determines that the profile surface is too smooth and difficult to adhere to, or that the wall thickness is too thick and can withstand greater thermal stress, the dry ice equipment is controlled to output granular dry ice, with the dry ice particle diameter controlled to be approximately 2-3 mm. Granular dry ice has greater kinetic energy and concentrated cooling capacity, generating strong thermal stress when it impacts the profile surface. It actively impacts and ignites sufficient microcracks in the resin-rich layer, enhancing the physical adhesion of subsequent coatings.

[0048] Corresponding gentle cleaning mode: When the monitoring device determines that the profile wall thickness is too thin, thermal stress may cause structural damage, or the surface already has a certain degree of roughness, it controls the dry ice equipment to output powdered dry ice through the ice crushing mechanism. Powdered dry ice has a large contact area and low impact kinetic energy, and mainly utilizes sublimation heat absorption for gentle cooling and cleaning, avoiding the formation of excessively deep cracks that could damage the substrate.

[0049] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A composite material pultrusion-coating integrated forming process, characterized in that, include: Composite materials are continuously output as profiles through pultrusion molding, forming a resin-rich layer on the surface of the profiles, and a release agent layer is applied to the outer surface of the profiles. After the profile undergoes initial air cooling, it is then rapidly cooled. During rapid cooling, the release agent layer is peeled off, and microcracks are formed in the resin-rich layer on the profile surface, causing the profile surface temperature to be lower than the core temperature. The sprayed profiles are coated, and the coating contacts the profile surface and penetrates into the microcracks to form an anchor. The coating on the exterior of the profile is irradiated, and the residual heat from the core of the profile is used to heat and cure the coating from the inside out.

2. The composite material pultrusion-coating integrated forming process according to claim 1, wherein, The composite material uses carbon fiber or glass fiber as reinforcing fiber and resin as matrix, with the reinforcing fiber distributed outside the resin-rich layer distribution area.

3. The composite material pultrusion-coating integrated forming process according to claim 1, wherein, After initial air cooling, the profile changes from a rubbery state to a glassy state, and then undergoes thermal shock during rapid cooling in the glassy state to induce brittle microcracks.

4. The composite material pultrusion-coating integrated forming process according to claim 3, wherein, Temperature and microcrack monitoring are performed on the profile surface, and dry ice is used as a cooling medium to exchange heat with the profile.

5. The composite material pultrusion-coating integrated forming process according to claim 4, wherein, The dry ice comes in two forms: granular and powdered. If the adhesion of the profile surface is deemed insufficient, granular dry ice is used to impact the profile surface to actively create cracks. If the adhesion of the profile surface is deemed sufficient, powdered dry ice is used to exchange heat with the profile, softening the thermal shock and performing cleaning and cooling.

6. The composite material pultrusion-coating integrated forming process according to claim 1 or 3 or 4 or 5, characterized in that, After cleaning the microcracks, spraying is performed. When the paint comes into contact with the warm profile surface, its viscosity decreases and it flows into the depths of the microcracks.

7. The composite material pultrusion-coating integrated forming process according to claim 6, wherein, After the profile is sprayed, allow the coating time to level and penetrate before irradiating.

8. The composite material pultrusion-coating integrated forming process according to claim 1, wherein, The coating is cured by UV / EB irradiation.

9. The composite material pultrusion-coating integrated forming process according to claim 1 or 8, wherein, During irradiation, the outer layer of the coating first cures and seals the surface. The residual heat in the core of the profile is used to cure the coating inside the microcracks. The cured coating forms solid fulcrums in the microcracks, achieving chemical bonding and physical micro-rivet locking.

10. The composite material pultrusion-coating integrated forming process according to claim 1, wherein, After the coating on the profile surface has cured, the profile is then cut.

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