A method for molding a chopped fiber prepreg containing a photonic crystal interference sheet and a molded product thereof

Abstract

The present application relates to the technical field of composite material molding, and particularly relates to a chopped fiber prepreg molding method containing photonic crystal interference sheets and a molded product thereof. The present application locks the gel time at the molding temperature by curing the prepreg, and completes multiple exhausts within the gelation window after the mold is closed and before the mold is opened, and cooperates with segmented pressurization, so that the gas is fully released before the channel is closed. The method significantly reduces the porosity and hole size of the product, improves the density and appearance uniformity, and takes into account the structural strength and optical effect.

Description

Technical Field

[0001] This invention relates to the field of composite material compression molding technology, specifically to a method for compression molding short fiber prepreg containing a photonic crystal interferometer and the resulting molded product. Background Technology

[0002] Composite material compression molding is widely used in the manufacture of automotive parts, electronic and electrical housings, sporting goods, and high-end decorative parts due to its advantages such as high production efficiency, stable product dimensions, and the ability to mold complex structures in one step. Among the many composite material systems, chopped fiber reinforced resin matrix composites (such as common bulk molding compounds (BMC), sheet molding compounds (SMC), or chopped fiber prepreg systems) have become an important material choice for structural and aesthetic components due to their combination of good mechanical properties and molding flowability.

[0003] In actual production, in order to give products unique appearance effects (such as angle-dependent shimmering colors, interference colors, or a sense of depth and layering), the industry has begun to explore the introduction of photonic crystal interference sheets or similar optical functional sheets with sheet-like geometric shapes into molding systems. These sheet-like functional materials differ from traditional granular inorganic fillers (such as calcium carbonate and talc); their two-dimensional sheet-like structure can produce rich optical effects, significantly increasing the added value of products.

[0004] However, conventional compression molding processes face a series of technical challenges when dealing with composite systems of such chopped fibers and sheet-like functional materials:

[0005] First, chopped fibers readily form a spatial network structure within the continuous resin phase. While this network imparts strength to the product, it also significantly increases the flow resistance within the system. When sheet-like photonic crystal interferometers are further introduced into the system, the sheet material is prone to orientation deflection, local stacking, or even breakage during molding flow. The combined effect of the fiber network and the sheet structure creates numerous tortuous and closed microcavities within the mold cavity, making it difficult for gases originally present within the material or trapped by the packing to escape smoothly.

[0006] Secondly, venting control in conventional molding processes often relies on experience, such as performing several opening and closing actions during mold closing (i.e., micro-opening venting). This experience-based venting logic typically involves multiple venting operations or extended venting time, assuming that sufficient venting or holding time will eventually expel internal gases. However, in the specific system described above, as the mold temperature rises, the resin viscosity changes rapidly and approaches its gel point. Once the resin enters the irreversible gel stage, the network structure formed by fibers and sheets is solidified and locked, closing the gas migration channels. At this point, even with continued additional venting or increased molding pressure, the trapped gas cannot escape, ultimately forming pinholes and voids inside the product, or white spots and hazy whitening on the surface, resulting in surface defects.

[0007] Furthermore, in order to improve flowability or reduce costs, traditional solutions often tend to add a large amount of micron-sized inorganic fillers (such as calcium carbonate). While this approach can reduce volume and resin shrinkage to some extent, the high filler content dilutes the proportion of the effective reinforcing phase (chopped fibers), weakens the mechanical properties of the product, and fails to solve the rheological obstacles and gas release problems caused by the introduction of sheet-like functional materials.

[0008] Therefore, it is of great significance to develop a short fiber prepreg molding method for photonic crystal interference sheets that can balance the internal density and appearance of the product and improve mass production stability. Summary of the Invention

[0009] The purpose of this invention is to address the problem of gas venting difficulties during the molding of chopped fiber prepreg containing photonic crystal interferometers in existing processes, which easily leads to defects such as voids and white spots in the product. This application addresses this issue by curing the prepreg to lock in the gelation time window, and by performing multiple venting operations within the pregelation window after mold closing, combined with segmented pressurization, to ensure that the gas is fully released before the channel is closed. This significantly reduces porosity and pore size, and improves the density and uniformity of the product.

[0010] The first aspect of the present invention provides a method for molding short-cut fiber prepreg containing a photonic crystal interferometer, comprising the following steps:

[0011] Step 1: The chopped fiber prepreg system containing chopped fibers, a continuous resin phase, and a photonic crystal interferometer is subjected to a curing treatment. By controlling the degree of curing, the gel time of the chopped fiber prepreg system at a preset molding temperature falls within the target window range.

[0012] Step 2: Put the chopped fiber prepreg system after curing into the mold that has been preheated to the preset molding temperature. After the mold is closed, before the resin enters the irreversible gelation state, perform segmented pressurization in the pre-gelation venting window, and complete multiple venting actions before the end of the pre-gelation venting window.

[0013] Step 3: After all the venting actions are completed, continue to increase the pressure to a high-pressure state for pressure holding and curing until the product is set.

[0014] Furthermore, the preset molding temperature is 120°C-150°C; the target window range refers to the gelation time of the chopped fiber prepreg system after curing treatment being 2min-5min at the preset molding temperature.

[0015] Furthermore, the number of venting actions is no less than 5 times, and all venting actions are completed within the first 3 minutes after mold closing; and / or, the venting action is achieved by micro-mold opening, with a micro-mold opening gap of 0.1 mm-2 mm, and / or the duration of a single venting action is 5s-20s.

[0016] Furthermore, the segmented pressurization specifically includes:

[0017] First stage: Apply initial pressure to bring the material into initial contact with the mold surface and expel a large volume of gas;

[0018] Second stage: Apply a second pressure higher than the first pressure to make the material flow and spread within the mold cavity;

[0019] Third stage: After the venting action is completed, a third pressure higher than the second pressure is applied for pressure holding and curing; and all the multiple venting actions are completed within the first stage and / or the second stage.

[0020] Furthermore, at least one of the following conditions must be met:

[0021] (1) The content of the photonic crystal interferometer is 3 wt%-10 wt% of the total mass of the chopped fiber prepreg system, and / or the diameter of the photonic crystal interferometer is 0.2 mm-2 mm;

[0022] (2) The chopped fiber is a chopped glass fiber or a chopped carbon fiber with a length of 3 mm to 6 mm, and / or the content of the chopped fiber accounts for 40 wt% to 60 wt% of the total mass of the chopped fiber prepreg system.

[0023] Furthermore, in the pressure holding and curing step, the total pressure holding and curing time t and the product thickness h satisfy the following: t = 10 + k·h, where t is in min, h is in mm, and k is a coefficient related to the material system.

[0024] Furthermore, the preparation of the chopped fiber prepreg system includes: first dispersing a photonic crystal interferometer sheet in a resin matrix to form a premix, and then adding chopped fibers for impregnation and coating to form a chopped fiber prepreg system with a continuous resin phase coating structure.

[0025] A second aspect of the present invention provides a chopped fiber prepreg molded article containing a photonic crystal interferometer, the molded article being prepared by the method described above.

[0026] Furthermore, the porosity of the molded article is less than 5%, and / or the maximum internal pore size is less than 0.2 mm.

[0027] Furthermore, the molded article satisfies at least one of the following conditions:

[0028] (1) The content of the photonic crystal interferometer is 3 wt%-10 wt%, and / or the diameter is 0.2 mm-2 mm;

[0029] (2) The length of the chopped fibers is 3 mm-6 mm, and / or the content is 40 wt%-60 wt%;

[0030] (3) The product thickness h and the total pressure holding and curing time t during preparation satisfy: t = 10 + k·h, where t is in minutes, h is in millimeters, and k is a coefficient related to the material system.

[0031] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0032] This invention provides a method for molding short-cut fiber prepreg containing photonic crystal interferometers and the molded product thereof. By curing the short-cut fiber prepreg system, the gel time of the material at the molding temperature falls within the target window range, ensuring stable and predictable gel behavior when different batches of material enter the mold. Multiple venting actions are completed within the limited window before gelation after mold closing, combined with segmented pressurization, allowing the gas to fully migrate and release before the resin viscosity jumps and the venting channels close. This effectively prevents gas from being trapped between the fiber network and the sheet-like interferometer, significantly reducing defects such as internal pores and surface white spots in the product, and improving the product's density and appearance consistency. Attached Figure Description

[0033] Figure 1 This is a viscosity-time curve of the resin system under different isothermal conditions in an embodiment of the present invention.

[0034] Figure 2 This is a comparison chart of the average porosity and the average number of white spots per unit area between Embodiment 1 and various comparative examples of the present invention.

[0035] Figure 3 This is a comparison chart of the average maximum hole size between Embodiment 1 of the present invention and various comparative examples.

[0036] Figure 4 The appearance of the molded article prepared in Example 1 is shown in the figure.

[0037] Figure 5 The appearance of the molded article prepared for Comparative Example 1.

[0038] Figure 6 The appearance of the molded product prepared for Comparative Example 6. Detailed Implementation

[0039] The present invention will now be described in further detail with reference to specific embodiments. However, this should not be construed as limiting the scope of the present invention to the following embodiments; all technologies implemented based on the content of the present invention fall within the scope of the present invention.

[0040] It should be noted that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. Furthermore, in the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0041] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0042] To facilitate understanding of the invention, certain technical and scientific terms are specifically defined below. Unless otherwise expressly defined elsewhere in this document, all other technical and scientific terms used herein have the meanings commonly understood by one of ordinary skill in the art to which this invention pertains.

[0043] In this document, the terms “comprising” or “including” are open-ended expressions, meaning that they include the contents specified in this invention, but do not exclude other aspects.

[0044] In this document, the terms “optionally,” “optionally,” or “optionally” generally refer to an event or condition that may, but may not, occur, and the description includes both cases in which the event or condition occurs and cases in which the event or condition does not occur.

[0045] The first aspect of this embodiment provides a method for molding short-cut fiber prepreg containing a photonic crystal interferometer, including the following steps:

[0046] Step 1: The chopped fiber prepreg system containing chopped fibers, a continuous resin phase, and a photonic crystal interferometer is subjected to a curing treatment. By controlling the degree of curing, the gel time of the chopped fiber prepreg system at a preset molding temperature falls within the target window range.

[0047] Step 2: Put the chopped fiber prepreg system after curing into the mold that has been preheated to the preset molding temperature. After the mold is closed, before the resin enters the irreversible gelation state, perform segmented pressurization in the pre-gelation venting window, and complete multiple venting actions before the end of the pre-gelation venting window.

[0048] Step 3: After all the venting actions are completed, continue to increase the pressure to a high-pressure state for pressure holding and curing until the product is set.

[0049] By curing the chopped fiber prepreg system, the gel time of the material at the molding temperature falls within the target window range, ensuring stable and predictable gel behavior when different batches of material enter the mold. Multiple venting actions are completed within the limited window before gelation after mold closing, combined with segmented pressurization, so that the gas can fully migrate and be released before the resin viscosity jumps and the venting channel is closed. This effectively avoids the gas being trapped between the fiber network and the sheet interference plates, significantly reducing defects such as internal pores and surface white spots in the product, and improving the density and appearance consistency of the product.

[0050] There is an inseparable synergistic relationship between curing treatment, staged pressurization, and centralized venting. The gel time window locked by curing treatment provides a temporal deterministic guarantee for centralized venting—without curing treatment, the gel time of different batches of materials can vary by several times, and the start and length of the venting window cannot be predicted, making subsequent staged pressurization and venting arrangements unworkable. In staged pressurization, low-pressure bonding and venting of large volumes of gas, and medium-pressure spreading and further venting ensure that the venting channel remains unobstructed within the window period of optimal material fluidity; and concentrating all venting actions within this window maximizes venting efficiency.

[0051] In some embodiments, the curing process is to maintain the temperature at 30°C-60°C for 8-48 hours.

[0052] In some embodiments, the preset molding temperature is 120°C-150°C; the target window range refers to the gelation time of the chopped fiber prepreg system after curing treatment being 2 min-5 min at the preset molding temperature.

[0053] By limiting the molding temperature to 120°C to 150°C and locking the gel time after curing to 2 to 5 minutes, the resin has both good fluidity and a sufficiently long venting window in the early stage of molding. This ensures both venting effect and curing efficiency, which is conducive to obtaining low-defect products stably within the mass production cycle.

[0054] In some embodiments, the number of venting actions is not less than 5 times, and all venting actions are completed within the first 3 minutes after mold closing; and / or, the venting action is achieved by micro-mold opening, the micro-mold opening gap is 0.1 mm-2 mm, and / or the duration of a single venting action is 5 s-20 s.

[0055] The number of venting operations is limited to no less than 5 times and all of them are concentrated within the first 3 minutes after mold closing to ensure that all venting actions fall within the effective window before gelation, and to avoid ineffective venting after the channel is closed due to delayed venting. At the same time, micro-mold opening venting is adopted and the gap and duration are limited, which can efficiently remove gas without disturbing the material distribution or damaging the orientation of the photonic crystal interferometer, and further reduce porosity and the number of white spots.

[0056] In some embodiments, the micro-mold opening action is performed by a servo press with position control functionality.

[0057] In some embodiments, the segmented pressurization specifically includes:

[0058] First stage: Apply initial pressure to bring the material into initial contact with the mold surface and expel a large volume of gas;

[0059] Second stage: Apply a second pressure higher than the first pressure to make the material flow and spread within the mold cavity;

[0060] Third stage: After the venting action is completed, a third pressure higher than the second pressure is applied for pressure holding and curing; and all the multiple venting actions are completed within the first stage and / or the second stage.

[0061] A three-stage segmented pressurization path of low-pressure bonding, medium-pressure spreading, and high-pressure curing is adopted, which allows the material to complete initial contact, flow spreading and gas release sequentially within the window period, avoiding premature closure of the exhaust channel by one-time high pressure; the exhaust action is limited to the low-pressure and medium-pressure stages to ensure that the gas is fully discharged before the material is completely compacted, thereby further improving the internal density of the product.

[0062] In some embodiments, at least one of the following conditions is met:

[0063] (1) The content of the photonic crystal interferometer is 3 wt%-10 wt% of the total mass of the chopped fiber prepreg system, and / or the diameter of the photonic crystal interferometer is 0.2 mm-2 mm;

[0064] (2) The chopped fiber is a chopped glass fiber or a chopped carbon fiber with a length of 3 mm to 6 mm, and / or the content of the chopped fiber accounts for 40 wt% to 60 wt% of the total mass of the chopped fiber prepreg system.

[0065] Limiting the content of photonic crystal interferometer sheets to 3 wt% to 10 wt% and the sheet diameter to 0.2 mm to 2 mm can ensure that the product produces optical effects such as angle-dependent interference colors and scintillation levels, while avoiding excessive obstruction of the exhaust channel by excessive sheet material or excessive size. Limiting the length of chopped fibers to 3 mm to 6 mm and the content to 40 wt% to 60 wt% can form an effective reinforcing network while maintaining good molding flowability of the system, taking into account both mechanical properties and processability.

[0066] In some embodiments, during the pressure holding and curing step, the total pressure holding and curing time t and the product thickness h satisfy: t = 10 + k·h, where t is in min, h is in mm, and k is a coefficient related to the material system.

[0067] By establishing a correlation formula between the total pressure holding and curing time and the product thickness, the curing time can be reasonably determined for products of different thicknesses, avoiding performance defects caused by insufficient curing or production efficiency losses caused by over-curing, thus improving the process applicability of this method in thin and thick parts scenarios.

[0068] In some embodiments, the preparation of the chopped fiber prepreg system includes: first dispersing a photonic crystal interferometer sheet in a resin matrix to form a premix, and then adding chopped fibers for impregnation and coating to form a chopped fiber prepreg system with a resin continuous phase coating structure.

[0069] By adopting a preparation sequence of first dispersing the photonic crystal interferometer sheet and then adding short-cut fibers, the interferometer sheet can be uniformly dispersed in the resin matrix under low shear conditions. This reduces the breakage and agglomeration of sheet materials during the mixing process, thereby reducing the risk of air entrapment from the source. At the same time, it helps to maintain the structural integrity of the photonic crystal interferometer sheet and ensures the appearance of the final product.

[0070] The second aspect of this embodiment provides a chopped fiber prepreg molded article containing a photonic crystal interferometer, the molded article being prepared by the method described above.

[0071] The short-fiber prepreg molded products containing photonic crystal interferometers prepared by the above method have the characteristics of high internal density and few appearance defects, which can simultaneously meet the dual requirements of mechanical properties for structural components and visual effects for appearance components.

[0072] In some embodiments, the porosity of the molded article is less than 5%, and / or the maximum internal pore size is less than 0.2 mm.

[0073] Products with a porosity of less than 5% and a maximum internal pore size of less than 0.2 mm indicate that the internal structure of the product is dense, gas is fully discharged, and pore defects are effectively controlled, which is conducive to improving the mechanical reliability and appearance uniformity of the product.

[0074] In some embodiments, the molded article satisfies at least one of the following conditions:

[0075] (1) The content of the photonic crystal interferometer is 3 wt%-10 wt%, and / or the diameter is 0.2 mm-2 mm;

[0076] (2) The length of the chopped fibers is 3 mm-6 mm, and / or the content is 40 wt%-60 wt%;

[0077] (3) The product thickness h and the total pressure holding and curing time t during preparation satisfy: t = 10 + k·h, where t is in minutes, h is in millimeters, and k is a coefficient related to the material system.

[0078] The content and diameter of the photonic crystal interferometer, as well as the length and content of the chopped fibers, are all within the optimized range in the product. This results in a product that exhibits rich optical interference effects while maintaining a reasonable internal fiber network structure, balancing aesthetic appeal with structural load-bearing capacity. The correlation between product thickness and curing time further ensures the consistency of curing quality for products of different thicknesses.

[0079] To better understand the technical solutions of the above embodiments, the following more detailed experimental examples are provided for further explanation. Those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of this disclosure. Where specific techniques or conditions are not specified in the examples, they are performed according to the techniques or conditions described in the literature in the art or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all commercially available conventional products.

[0080] I. Raw Materials and Testing Methods

[0081] 1. Raw materials

[0082] Resin system: Bisphenol A type epoxy resin (epoxy equivalent 180-190 g / eq), with matching amine curing agent;

[0083] Chopped fiber: Chopped glass fiber, 3-6 mm in length, 10-13 μm in diameter;

[0084] Photonic crystal interferometers: These sheet-like structures are produced by peeling and breaking up alternating layers of dielectric materials with different refractive indices (such as TiO2 / SiO2 multilayer films). They possess a photonic bandgap structure along their thickness direction, enabling them to produce angle-dependent interference colors within the visible light range. The planar diameter of the interferometers used is 0.2-2 mm, and the thickness is approximately 2-5 μm. After being dispersed in a resin matrix, they impart a shimmering gloss effect to the product that changes with the viewing angle.

[0085] Other additives: Defoamer and wetting / dispersing agent in appropriate amounts.

[0086] 2. Testing Methods

[0087] (1) Gel time determination: Take about 0.5g of prepreg sample and place it on a heating plate that has been kept at the test temperature. Use a probe to continuously pick up the fibers and record the time from when the sample touches the hot plate until the resin stops picking up fibers. This is the gel time. Perform 5 parallel measurements for each condition and take the average value. For prepreg systems containing short-cut fibers, large fibers need to be removed before testing to ensure the representativeness of the continuous resin phase.

[0088] (2) Viscosity-time curve determination: The viscosity of the resin system was measured over time using a rotational rheometer under constant temperature conditions (125°C, 130°C, 135°C, 140°C), in parallel plate mode, with an oscillation frequency of 1 Hz and a strain of 1%.

[0089] (3) Porosity test: The cross-section of the product was observed and photographed using a scanning electron microscope. The proportion of pore area to the total field of view was calculated using image analysis software. Five fields of view were randomly selected for each sample and the average value was taken.

[0090] (4) Hole size test: Based on the above microscopic images, measure the maximum diameter of each hole in the field of view, record the maximum hole size and the average hole size, and randomly select 5 fields of view for each sample to take the average value.

[0091] (5) Count of white spots: Under fixed lighting conditions, observe the surface of the product and count the number of white spots visible to the naked eye within a unit area (10 cm × 10 cm).

[0092] (6) Appearance effect evaluation: Visually observe the interference color change, shimmering layers and uniformity of the product surface at different angles, and divide it into three levels: excellent (rich and uniform color), good (color is visible but slightly uneven in some areas) and poor (dull or severely uneven color).

[0093] (7) Evaluation of the integrity of photonic crystal interferometers: The cross-section of the molded product is observed using an optical microscope or a scanning electron microscope. Five fields of view are randomly selected, and the proportion of broken interferometers (defined as those with an area less than 50% of the original average area or with obvious cracks) in the field of view is counted to evaluate the degree to which the process maintains the structure of the interferometer.

[0094] II. Determination of viscosity-time curve and pre-gel exhaust window

[0095] Test Example 1: Determination of viscosity-time curves of resin systems at different temperatures

[0096] The viscosity of the epoxy resin system used in the examples was measured over time using a rotational rheometer under isothermal conditions of 125°C, 130°C, 135°C, and 140°C. The results are as follows: Figure 1 As shown.

[0097] like Figure 1 As shown, each temperature point exhibits a typical "first decrease in viscosity, then increase in viscosity" characteristic, indicating that the resin system has a clear low-viscosity flow stage and a subsequent rapid viscosity-increasing stage under isothermal conditions. The lowest viscosity in all four sets of data occurred at approximately 30 s, indicating that the system can quickly enter a low-viscosity state in the initial stage of heating, possessing the basic conditions for degassing, spreading, and interfacial wetting.

[0098] It should be noted that, Figure 1 The rheological test was conducted using a small sample (approximately 0.5 g) placed directly on a preheated parallel plate. The sample heating rate was extremely high, resulting in an early occurrence of the lowest viscosity. In actual molding, after the prepreg system is placed in the preheated mold, the actual time to reach the mold temperature is slightly longer than in the rheological test due to the influence of material thickness and thermal conductivity. However, by preheating the prepreg in an oven (e.g., at 60-80°C for 5-10 min before placing it in the mold), the viscosity change curve during actual molding can be made more consistent with the rheological test. Figure 1 This allows for closer proximity, ensuring precise control of the exhaust window.

[0099] In terms of the length of the effective venting window before gelation: at 125°C, no significant viscosity surge occurred within 450 s, with the longest window; at 130°C and 135°C, significant viscosity jumps occurred at approximately 300 s; at 140°C, the rapid viscosity increase zone was entered at approximately 120 s, with the shortest window.

[0100] From a process perspective, higher temperatures lead to faster improvement in the initial flowability of the resin, but significantly shorten the effective flow window before gelation. Considering both the window length and curing efficiency, 135°C shows a good balance, with a significant viscosity jump occurring around 300 s (i.e., 5 min). The first 3 mins represent a low-viscosity stability period, which is the optimal time for concentrated venting.

[0101] Based on the above test results, the present invention preferably sets the molding temperature to 120°C to 150°C, more preferably 135°C; and sets the gelation time target window range of the cured material at 135°C to 2 min to 5 min, preferably 3 min; and the venting action is all concentrated within the first 3 min after mold closing.

[0102] Specifically, such as Figure 1-6 As shown.

[0103] Example 1

[0104] Step 1: Take about 45% of the epoxy resin system by mass percentage, add about 5% of the photonic crystal interferometer (about 1 mm in diameter), and disperse it evenly by low-speed stirring to form a premix; then add about 50% of the short glass fibers (3-6 mm in length), mix and impregnate under low shear conditions to ensure that the short fibers are fully coated by the continuous resin phase to form the SFP system.

[0105] Step 2: Place the above SFP system in a 40°C oven for 24 h to mature. By controlling the degree of maturation, the gelation time of the material at 135°C is locked at about 3 min.

[0106] It should be noted that the specific conditions of the above-mentioned curing treatment (such as temperature and time) can be adjusted according to the reaction characteristics of the resin system and the target gel time. Generally, the curing temperature can be selected from room temperature to 80°C, and the curing time can be determined by establishing a relationship curve between "curing temperature-time" and "gel time at molding temperature" through preliminary experiments. For example, for the bisphenol A type epoxy resin / amine curing agent system used in this embodiment, curing at 40°C for 24 hours can shorten the gel time at 135°C from about 8 minutes before curing to about 3 minutes; similar gel times can also be achieved by curing at 60°C for 8 hours. Those skilled in the art can determine suitable curing conditions for specific resin formulations based on conventional experiments to ensure that the gel time of the material at the preset molding temperature falls within the target window of 2-5 minutes.

[0107] Step 3: Preheat the mold to 135°C, pour the cured SFP system into the mold, and close the mold. After mold closing, perform segmented pressurization (taking a mold projection area of ​​approximately 100 cm² as an example): Apply the first pressure of approximately 1.0 MPa (closing force of approximately 10 kN) within 0-60 s for low-pressure bonding and complete the first- and second venting (micro-opening of approximately 0.5 mm, each time for approximately 10 s); apply the second pressure of approximately 5.0 MPa (closing force of approximately 50 kN) within 60-120 s for medium-pressure spreading and complete the third- and fourth venting; maintain approximately 5.0-6.0 MPa within 120-180 s to complete the fifth venting. All five venting operations are completed within the first 3 minutes after mold closing.

[0108] Step 4: After venting, increase the pressure to approximately 20 MPa (clamping force approximately 200 kN) to enter the high-pressure holding and curing stage. The total holding and curing time is approximately 12 minutes. After curing, demold and perform post-curing treatment if necessary to obtain a thin decorative product (approximately 3 mm thick).

[0109] The pressure values ​​mentioned above refer to the pressure applied to the unit projected area of ​​the mold. In actual production, the clamping force can be adjusted proportionally according to the mold size.

[0110] Example 2

[0111] Example 2-1: The content of the photonic crystal interferometer was adjusted to 3%, and the diameter was adjusted to 0.2 mm;

[0112] Example 2-2: The content of the photonic crystal interferometer was adjusted to 10%, and the diameter was adjusted to 2 mm;

[0113] Examples 2-3: The content of chopped fibers was adjusted to 40%, and the length was adjusted to 3 mm;

[0114] Examples 2-4: The content of short-cut fibers was adjusted to 60%, and the length was adjusted to 6 mm;

[0115] Examples 2-5: The molding temperature was adjusted to 120°C, and the gelation time was locked at 5 min;

[0116] Examples 2-6: The molding temperature was adjusted to 150°C, and the gelation time was locked at 2 min.

[0117] The remaining steps and process conditions are the same as in Example 1.

[0118] Example 3

[0119] Based on Example 1, the thickness of the product was increased to approximately 20 mm. The total pressure holding and curing time t was determined according to t = 10 + k·h, where h = 20 mm and k is approximately 1.0, so t is approximately 30 min. The remaining steps and process conditions are the same as in Example 1.

[0120] The coefficient k is related to the thermal conductivity and reaction kinetics of the material system. For the epoxy resin / chopped glass fiber system used in this application, by monitoring the minimum holding time required to achieve a degree of cure of over 95% on products of different thicknesses, k was obtained as approximately 0.9-1.1 min / mm through linear fitting. In actual production, the value of k can be determined by preliminary experiments for specific formulations and mold conditions. Generally, for carbon fiber systems with good thermal conductivity, the value of k can be reduced to 0.6-0.8 min / mm; for thick-walled or poorly thermally conductive systems, the value of k can be increased to 1.2-1.5 min / mm.

[0121] In the formula t = 10 + k·h, the constant 10 (unit: min) represents the minimum base time required to ensure the resin matrix completes the initial curing network construction, and is independent of the product thickness. The coefficient k (unit: min / mm) reflects the time increment required for heat conduction along the thickness direction and for the central layer to reach the curing temperature. When the product thickness is extremely small (e.g., h < 1 mm), the k·h term in the formula approaches 0, and the total pressure holding and curing time is mainly determined by the reaction kinetics of the resin system itself, i.e., approximately 10 min. Those skilled in the art can determine the precise value of k by measuring the degree of curing of the central layer of products with different thicknesses and using linear regression, based on the specific resin system and mold heat conduction conditions.

[0122] Example 4

[0123] Based on Example 1, the feeding order was changed: first, chopped fibers were added and mixed with resin, then the photonic crystal interferometer sheet was added for dispersion. The remaining steps and process conditions were the same as in Example 1.

[0124] Example 5

[0125] Based on Example 1, the product thickness was controlled to approximately 1.5 mm. The total pressure holding and curing time t was determined according to t = 10 + k·h, where h = 1.5 mm and k is approximately 1.0, so t is approximately 11.5 min. The remaining steps and process conditions are the same as in Example 1.

[0126] Example 6

[0127] Based on Example 1, the product thickness was controlled to approximately 10 mm. The total pressure holding and curing time t was determined according to t = 10 + k·h, where h = 10 mm and k is approximately 1.0, so t is approximately 20 min. The remaining steps and process conditions are the same as in Example 1.

[0128] Comparative Example 1

[0129] The difference from Example 1 is that the curing time in step 2 is less than 6 hours, which is insufficient, resulting in unstable gelation time (exceeding 5 minutes) of the material at 135°C and uncontrollable window behavior. The remaining steps and process conditions are the same as in Example 1.

[0130] Comparative Example 2

[0131] The difference from Example 1 is that the venting action in step 3 is mainly arranged to be completed within 7 minutes after mold closing, and does not fall within the effective window before gelation. The remaining steps and process conditions are the same as in Example 1.

[0132] Comparative Example 3

[0133] The difference from Example 1 is that in step 3, venting is only performed once or not at all within the first 3 minutes after mold closing. The remaining steps and process conditions are the same as in Example 1.

[0134] Comparative Example 4

[0135] The difference from Example 1 is that the molding temperature in step 3 is adjusted to 100°C. The remaining steps and process conditions are the same as in Example 1.

[0136] Comparative Example 5

[0137] The difference from Example 1 is that in step 3, after mold closing, the pressure is directly increased to approximately 20 MPa, without the segmented process of low-pressure bonding and medium-pressure spreading. The remaining steps and process conditions are the same as in Example 1.

[0138] Comparative Example 6

[0139] The difference from Example 1 is that: in step 2, no curing treatment is performed, and the uncured SFP system is directly put into the mold; in step 3, after the mold is closed, no segmented pressurization is performed, and the pressure is directly increased to about 200 kg load (about 20 MPa) for high-pressure holding, and no venting is performed during the entire molding process. The remaining steps and process conditions are the same as in Example 1.

[0140] Comparative Example 7

[0141] The difference from Example 1 is as follows: in step 2, no curing treatment is performed, and the material gelation time is not locked (measured at approximately 10 minutes at 135°C); in step 3, after mold closing, no segmented pressurization is performed, and the pressure is directly increased to approximately 200 kg load for high-pressure holding, but micro-mold opening and venting are performed 5 times within the first 3 minutes after mold closing (micro-mold opening gap 0.5 mm, 10 s each time). The remaining steps and process conditions are the same as in Example 1.

[0142] Comparative Example 8

[0143] The difference from Example 1 is that: no curing treatment is performed in step 2; in step 3, segmented pressurization (low pressure 1.0 MPa, medium pressure 5.0 MPa, high pressure 20 MPa) is performed after mold closing, but no venting is performed during the entire molding process. The remaining steps and process conditions are the same as in Example 1.

[0144] Comparative Example 9

[0145] The difference from Example 1 is that in step 3, the first two of the five venting actions are completed within the first 3 minutes after mold closing, and the last three are completed within the 4th-5th minute after mold closing. The remaining steps and process conditions are the same as in Example 1.

[0146] Comparative Example 10

[0147] The difference from Example 1 is that after the material is put into the mold and before the mold is closed, three micro-opening venting actions are performed first, and then the mold is closed. Within the first 3 minutes after the mold is closed, only two venting actions are performed. The remaining steps and process conditions are the same as in Example 1.

[0148] The cross-sections of the samples from Example 1 and the comparative examples were observed and photographed using an optical microscope. Porosity, maximum pore size, average pore size, pore number density, and number of white spots per unit area were statistically analyzed. The results are shown in Table 1. Figure 2 , Figure 3 As shown.

[0149] Table 1 Comparison of performance test results between Example 1 and each comparative example

[0150] Group Mean porosity (%) Average maximum hole size (mm) Number of white spots per unit area Example 1 3.390 0.173 1.000 Comparative Example 1 24.367 2.500 6.000 Comparative Example 2 15.867 2.324 6.333 Comparative Example 3 17.267 1.380 6.000 Comparative Example 4 12.548 1.826 5.667 Comparative Example 5 11.235 1.652 5.333 Comparative Example 6 31.256 3.124 8.333 Comparative Example 7 19.847 2.156 6.667 Comparative Example 8 22.431 2.678 7.000 Comparative Example 9 9.876 1.245 4.667 Comparative Example 10 12.543 1.568 5.333

[0151] Figure 2 The comparison shows the average porosity and white spot count for different groups. From Figure 2 It can be seen that the average porosity of Example 1 is significantly lower than that of the other pairs, and the number of white spots per unit area is also significantly lower than that of the other pairs.

[0152] Figure 3 The comparison of the average hole size for different groups is shown. From Figure 3 It can be seen that the average maximum hole size in Example 1 is significantly smaller than that in each of the pairs.

[0153] The integrity of the interferometer in the product of Example 1 was evaluated. The results showed that the proportion of broken interferometers in the field of view was less than 8%, indicating that the method of the present invention can maintain the sheet structure of the photonic crystal interferometer well under the low shear flow conditions of effective exhaust, thereby ensuring the optical effect of the final product.

[0154] The performance test results of each sub-scheme in Embodiment 2 are shown in Table 2.

[0155] Table 2 Performance test results of each sub-scheme in Example 2

[0156] plan Porosity (%) Maximum hole size (mm) Example 1 3.390 0.173 Example 2-1 3.125 0.158 Example 2-2 4.021 0.215 Example 2-3 3.856 0.198 Examples 2-4 4.523 0.241 Examples 2-5 3.672 0.185 Examples 2-6 3.945 0.203

[0157] As shown in Table 2, the porosity of each sub-scheme in Example 2 is within the range of 3.1%-4.6%, and the maximum pore size is within the range of 0.15-0.25 mm, all significantly better than the comparative examples. It is noteworthy that in Examples 2-4, increasing the chopped fiber content to 60% only slightly increased the porosity to approximately 4.523%. This indicates that the segmented pressurization and centralized venting process described in this invention can effectively alleviate the blockage effect of the network structure on the venting channels under high fiber content, thereby maintaining a low defect level while ensuring improved mechanical properties. The maximum pore size in Examples 2-2 and 2-4 is slightly higher than 0.2 mm, but still much smaller than the comparative examples, and the corresponding porosity is still below 5%, indicating that the internal density of the product remains high even under the upper limits of sheet diameter or fiber content. In actual product specifications, the allowable maximum pore size threshold can be adjusted according to the specific application scenario. For example, for non-load-bearing exterior parts, pores below 0.25 mm have no significant impact on performance.

[0158] Among them, Example 1 achieved the best balance among porosity, pore size and appearance.

[0159] The 20 mm thick product prepared in Example 3, after being cured under pressure for 30 min as determined by t = 10 + k·h, had a porosity of approximately 3.852% and a maximum pore size of approximately 0.195 mm. The appearance was rated as excellent.

[0160] Example 4 uses a sample prepared by first fiber and then interference sheet. The porosity was tested to be approximately 4.215%, the maximum pore size was approximately 0.232 mm, and the appearance was rated as good (the interference sheet was unevenly distributed and slightly broken in some areas).

[0161] The porosity of the product in Example 5 was approximately 3.125%, the maximum pore size was approximately 0.152 mm, and the number of white spots per unit area was 0.667 (no obvious white spots were observed within 10 cm × 10 cm).

[0162] The porosity of the product in Example 6 is approximately 3.478%, the maximum pore size is approximately 0.188 mm, and the number of white spots per unit area is 1.333.

[0163] The molded product prepared in Example 1 was tested and found to have a porosity of approximately 3.390%, which is less than 5%; a maximum pore size of approximately 0.173 mm, which is less than 0.2 mm; a photonic crystal interferometer content of approximately 5% and a diameter of approximately 1 mm; and short-cut fibers with a length of 3-6 mm and a content of approximately 50%. The product surface exhibits rich angle-correlated interference colors, and its appearance is rated as excellent.

[0164] As can be seen from the test results of the above embodiments and comparative examples, the present invention can significantly reduce the porosity and pore size of the product, reduce surface white spot defects, and improve the internal density and appearance uniformity of the product by locking the gelation time window through aging treatment, completing multiple venting actions within the pre-gelation window, and cooperating with segmented pressurization path.

[0165] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," "some implementations," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0166] The above description is merely a preferred embodiment of the present invention and is 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 method for molding short-cut fiber prepreg containing a photonic crystal interferometer sheet, characterized in that, Includes the following steps: Step 1: The chopped fiber prepreg system containing chopped fibers, a continuous resin phase, and a photonic crystal interferometer is subjected to a curing treatment. By controlling the degree of curing, the gel time of the chopped fiber prepreg system at a preset molding temperature falls within the target window range. Step 2: Put the chopped fiber prepreg system after curing into the mold that has been preheated to the preset molding temperature. After the mold is closed, before the resin enters the irreversible gelation state, perform segmented pressurization in the pre-gelation venting window, and complete multiple venting actions before the end of the pre-gelation venting window. Step 3: After all the venting actions are completed, continue to increase the pressure to a high-pressure state for pressure holding and curing until the product is set.

2. The method according to claim 1, characterized in that, The preset molding temperature is 120°C-150°C; the target window range refers to the gelation time of the chopped fiber prepreg system after curing treatment being 2 min-5 min at the preset molding temperature.

3. The method according to claim 1, characterized in that, The number of venting actions is no less than 5 times, and all venting actions are completed within the first 3 minutes after mold closing; and / or, the venting action is achieved by micro-mold opening, with a micro-mold opening gap of 0.1 mm-2 mm, and / or the duration of a single venting action is 5s-20s.

4. The method according to claim 1, characterized in that, The segmented pressurization specifically includes: a first stage: applying a first pressure to allow the material to initially contact the mold surface and expel a large volume of gas; a second stage: applying a second pressure higher than the first pressure to allow the material to flow and spread within the mold cavity; a third stage: after the venting action is completed, applying a third pressure higher than the second pressure for pressure holding and curing; and all of the multiple venting actions are completed within the first stage and / or the second stage.

5. The method according to claim 1, characterized in that, The following conditions must be met: (1) the content of the photonic crystal interferometer is 3 wt%-10 wt% of the total mass of the chopped fiber prepreg system, and / or the diameter of the photonic crystal interferometer is 0.2 mm-2 mm; (2) the chopped fiber is chopped glass fiber or chopped carbon fiber with a length of 3 mm-6 mm, and / or the content of the chopped fiber is 40 wt%-60 wt% of the total mass of the chopped fiber prepreg system.

6. The method according to claim 1, characterized in that, In the pressure holding and curing step, the total pressure holding and curing time t and the product thickness h satisfy: t = 10 + k·h, where the unit of t is min, the unit of h is mm, and k is a coefficient related to the material system.

7. The method according to any one of claims 1-6, characterized in that, The preparation of the chopped fiber prepreg system includes: first, dispersing a photonic crystal interferometer in a resin matrix to form a premix, and then adding chopped fibers for impregnation and coating to form a chopped fiber prepreg system with a continuous resin phase coating structure.

8. A molded product made of chopped fiber prepreg containing a photonic crystal interferometer, characterized in that, The molded article is prepared by the method according to any one of claims 1-7.

9. The molded article according to claim 8, characterized in that, The porosity of the molded article is less than 5%, and / or the maximum internal pore size is less than 0.2 mm.

10. The molded article according to claim 8, characterized in that, The molded product satisfies at least one of the following conditions: (1) the content of the photonic crystal interferometer is 3 wt%-10 wt%, and / or the diameter is 0.2 mm-2 mm; (2) the length of the chopped fiber is 3 mm-6 mm, and / or the content is 40 wt%-60 wt%; (3) the product thickness h and the total pressure holding and curing time t during preparation satisfy: t = 10 + k·h, where t is in minutes, h is in millimeters, and k is a coefficient related to the material system.

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