Hot melt composite antiskid pallet and its mold forming process

Abstract

The application discloses a hot-melt composite anti-skid tray and a molding process thereof, and belongs to the technical field of plastic processing. The tray comprises a polypropylene body with a thickness of 5-8 mm and an anti-skid film with a thickness of 0.4-0.6 mm made of a mixture of polyethylene and ethylene-vinyl acetate copolymer and hot-melt combined with the upper surface of the body, an integrally-formed hot-melt transition layer is arranged between the body and the anti-skid film, the transition layer is formed by high-temperature penetration and cross-linking of macromolecular chains, and the bottom surface of the anti-skid film is provided with pre-set exhaust micro-ridges. The molding process is as follows: the anti-skid film is fixed by gradient electrostatic adsorption without air bubbles; injection is carried out at 180-250 DEG C, and pressure is maintained at 10 MPa, during which the temperature of the front mold is controlled at 40-60 DEG C to prevent the anti-skid surface from melting and collapsing; an asymmetric differential temperature mechanism of rear mold rapid cooling and front mold slow cooling is adopted to offset warping stress; and finally, constant temperature annealing is carried out. The application solves the problems of blistering, peeling of the anti-skid layer and warping of the double-material composite molding, and realizes high strength and long-term durability of the tray.

Description

[Technical Field] This invention relates to the field of plastic molding and processing technology, specifically to a hot melt composite anti-slip tray and its compression molding process. [Background Technology] Anti-slip pallets are commonly used load-bearing tools in hotels, restaurants, and logistics facilities. The durability of their surface anti-slip performance directly determines the product's lifespan. Traditional anti-slip pallets often employ a process of secondary glue injection and pasting of rubber anti-slip mats after the pallet is formed, or using mechanical clips to fix the anti-slip layer. However, these methods are prone to aging and failure after long-term washing and alternating high and low temperatures, leading to the anti-slip layer curling and peeling off. Furthermore, the gaps in mechanically assembled anti-slip layers easily trap dirt and grime. Although there are attempts in the industry to use molding to combine the anti-slip layer with the pallet bottom, this often requires the introduction of additional... The intermediate transition layer, such as the complex composite of fiber mesh and thermosetting resin, not only involves a complex material system and high manufacturing cost, but also a cumbersome production process. In conventional in-mold bonding molding processes, if thermoplastic film is directly composited with rigid plastic body, bubbles are easily generated at the high temperature and high pressure interface, leading to poor welding or bulging. Furthermore, due to the significant difference in the thermal shrinkage rate of the two materials, the overall warping and deformation of the pallet is easily caused during the cooling stage after molding and demolding, making it difficult to meet the requirements of high strength and high flatness for pallets in industrial and commercial scenarios. [Summary of the Invention] The purpose of this invention is to provide a hot-melt composite anti-slip tray and its molding process, which aims to solve the technical problems of easy peeling of the anti-slip layer, cumbersome process, and easy generation of air bubbles and warping deformation in conventional composite processes.

[0004] This application is achieved through the following technical solution: A hot-melt composite anti-slip tray includes a tray body and an anti-slip film hot-melt bonded to the upper surface of the tray body. The tray body is made of polypropylene with a thickness of 5-8 mm. The anti-slip film is made of polyethylene and ethylene-vinyl acetate copolymer with a thickness of 0.4-0.6 mm. An integrally formed hot-melt transition layer is provided between the anti-slip film and the tray body. The hot-melt transition layer is formed by the cross-linking of polyethylene and ethylene-vinyl acetate copolymer molecular chains on the bottom surface of the anti-slip film and polypropylene molecular chains on the surface of the tray body at high temperature.

[0005] As described above, a hot-melt composite anti-slip tray includes an anti-slip working surface on the upper surface and a hot-melt bonding surface on the bottom. The hot-melt bonding surface is corona treated before molding, and its surface tension reaches 38-42 dyn / cm to increase the interfacial compatibility with the tray body made of polypropylene.

[0006] As described above, a hot-melt composite anti-slip tray has a micron-level anti-slip rough surface on the anti-slip working surface and exhaust micro-textures on the hot-melt bonding surface for accommodating hot-melt gas.

[0007] As described above, in a hot-melt composite anti-slip tray, the edge of the anti-slip film extends to the side wall of the tray body to form an edge-binding mechanism. The extension length of the edge-binding mechanism is 1-2 mm, and the thickness of the anti-slip film at the edge-binding mechanism gradually decreases.

[0008] As described above, a hot-melt composite anti-slip tray also includes a reinforcing rib mesh area embedded in the tray body, which is correspondingly located in the stress concentration area on the bottom surface of the tray body.

[0009] A molding process for a hot melt composite anti-slip tray as described in any of the preceding claims includes the following steps: Step S1: Place an anti-slip film made of polyethylene and ethylene-vinyl acetate copolymer with a thickness of 0.4-0.6mm into the mold cavity, and fix the anti-slip film in the mold by electrostatic adsorption to prevent displacement or wrinkling; Step S2: Within a heating temperature range of 180-250℃, inject polypropylene material into the mold and combine it with the anti-slip film to fully form the tray body. At the same time, the surface of the anti-slip film in contact with the tray body reaches a melt-penetrating state, and the upper surface of the anti-slip film does not collapse. Step S3: Apply a pressure of 10MPa to the mold and set the holding time to 25 seconds to ensure the bonding strength after hot melting; Step S4: Cool and shape the mold by introducing 20°C cold water into the rear mold, then open the mold and remove the finished product tray.

[0010] In the molding process described above, in step S1, electrostatic adsorption adopts a zoned and stepped electrostatic application control method. Specifically, electrostatics are first applied to the central area of ​​the anti-slip film to make it adhere to the mold, and then electrostatics are radiated to the edge area of ​​the anti-slip film to expel the air between the anti-slip film and the mold surface.

[0011] In the compression molding process described above, in steps S2 and S3, the temperature of the front mold is 40-60°C to prevent the upper surface of the anti-slip film from collapsing, and the temperature of the rear mold is consistent with the heating temperature in the initial stage of injection to ensure the fluidity of the polypropylene material.

[0012] In the compression molding process described above, in step S4, an asymmetric differential temperature cooling mechanism is adopted. Specifically, while the rear mold is forced to cool with 20°C cold water, the front mold is naturally cooled or slowly cooled with 35-45°C warm water to counteract the warping stress caused by the difference in thermal shrinkage rates between the anti-slip film made of polyethylene and ethylene-vinyl acetate copolymer and the tray body made of polypropylene.

[0013] The molding process described above also includes step S5: placing the finished product tray in a constant temperature environment of 60-80℃ for annealing for 30-60 minutes to further solidify the heat-melt bonding force of the interface.

[0014] Compared with the prior art, this application has the following advantages: 1. This invention uses a specific thickness ratio, with a 5-8mm polypropylene tray body and a 0.4-0.6mm polyethylene and ethylene-vinyl acetate copolymer anti-slip film, to directly promote the interpenetration and cross-linking of macromolecular segments under high temperature and pressure without any intermediate adhesive layer, forming a physically inseparable hot-melt transition layer. Experiments have proven that the finished product still shows no separation after 1000 cycles of dishwasher testing, significantly improving the service life of the tray.

[0015] 2. The hot-melt bonding surface of the anti-slip film is pre-treated with corona to increase the surface tension to 38-42 dyn / cm, which activates the polar groups on the surface of polyethylene and ethylene-vinyl acetate copolymer, and improves its affinity with polypropylene material; at the same time, the venting micro-texture at the bottom can effectively contain and expel the trace amount of gas generated during high-temperature molding, avoiding poor welding or bulging caused by interface bubbles.

[0016] 3. It overcomes the defect of easy wrinkling of thin films in conventional IML molding. By applying static electricity in stages from the center to the edge, it is equivalent to ironing and venting the film in the mold, ensuring a high yield of 0.4-0.6mm ultra-thin anti-slip film.

[0017] 4. To address the issue of deformation caused by differences in the thermal shrinkage rates of different polymer materials, this invention innovatively adopts an asymmetrical temperature control mechanism of slow cooling at 40-60℃ for the front mold and rapid cooling at 20℃ for the rear mold. This mechanism utilizes the shrinkage tension at the bottom of the tray to offset the shrinkage stress of the anti-slip film, ensuring that the tray maintains a high degree of flatness after demolding. Furthermore, the subsequent constant-temperature annealing step releases internal stress. [Attached Image Description] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a three-dimensional perspective view of the anti-slip tray according to an embodiment of this application; Figure 2 yes Figure 1 An exploded view of the tray body and the anti-slip film. Figure 3 yes Figure 1 A bottom view; Figure 4 yes Figure 3 Cross-sectional view at point AA; Figure 5 This is a schematic diagram of the microstructure of the anti-slip film in the embodiments of this application; Figure 6 This is a schematic diagram of the microstructure of the tray body and the anti-slip film thermally fused together in this application; Figure 7 This is a schematic flowchart of the molding process in an embodiment of this application.

Detailed Implementation Methods

[0021] Please see Figures 1 to 7 A hot-melt composite anti-slip tray includes a tray body 1 and an anti-slip film 2 hot-melt bonded to the upper surface of the tray body 1. The tray body 1 is made of polypropylene with a thickness of 5-8 mm. The anti-slip film 2 is made of polyethylene and ethylene-vinyl acetate copolymer with a thickness of 0.4-0.6 mm. An integrally formed hot-melt transition layer 3 is provided between the anti-slip film 2 and the tray body 1. The hot-melt transition layer 3 is formed by the cross-penetration and cross-linking of the polyethylene and ethylene-vinyl acetate copolymer molecular chains on the bottom surface of the anti-slip film 2 and the polypropylene molecular chains on the surface of the tray body 1 at high temperature.

[0022] In this embodiment, the tray body 1 is preferably made of polypropylene (PP), and its thickness is controlled within the range of 5-8mm. This is because a thickness less than 5mm can easily cause the tray to flex and deform when fully loaded or lifted, while a thickness greater than 8mm would unnecessarily increase the injection molding cycle, manufacturing costs, and the user's carrying load. Meanwhile, as a functional layer that directly provides surface friction, the anti-slip film 2 is made of a mixture of polyethylene (PE) and ethylene-vinyl acetate copolymer (EVA), and its thickness is precisely limited to between 0.4-0.6mm. Within this specific thickness range, a thickness of 0.5mm is preferred. The anti-slip film 2 not only provides sufficient flexibility due to the EVA component, but also... The softness and high static friction coefficient prevent the tableware from slipping, and also enable optimal heat conduction during subsequent molding. This avoids insufficient heat melting at the bottom due to an excessively thick film layer, and also prevents the film layer from being broken or collapsing under high injection pressure due to an excessively thin film layer. More importantly, in the core connection mechanism of this invention, the anti-slip film 2 and the tray body 1 completely abandon the traditional chemical adhesive bonding or mechanical snap-fit ​​splicing. Instead, an innovative one-piece hot-melt transition layer 3 is provided. Its microscopic working principle is that under the high temperature and high pressure physical field provided by molding, the polyethylene and ethylene-vinyl acetate copolymer macromolecular segments on the bottom surface of the anti-slip film 2 and the polypropylene macromolecular segments on the surface of the tray body 1 are both... The material possesses extremely high thermal kinetic energy. Because all three belong to a highly compatible polyolefin material system, they rapidly overcome surface tension limitations at the contact surface. The molecular chains, in a molten, highly elastic state, undergo deep interpenetration, diffusion, and three-dimensional entanglement, and are firmly locked in the subsequent cooling and solidification process, thus forming the indivisible hot-melt transition layer 3 at the physical interface. This structural design, which directly utilizes the hot-melt cross-linking characteristics of the material's macromolecular chains, brings significant beneficial effects. It not only greatly simplifies the cumbersome production process of multi-layer composites or secondary adhesive coatings, improving production yield, but also eliminates the problems of adhesive aging and failure, edge curling and detachment, and seam defects that easily occur in traditional anti-slip mats after long-term washing and alternating high and low temperatures. Addressing critical industry pain points such as long-term accumulation of dirt and grime in gaps, the anti-slip working surface and pallet frame have a consistent lifespan, achieving long-term product durability. The material of the pallet body 1 can also be flexibly modified polypropylene with similar heat-melt affinity properties. For example, adding appropriate amounts of inorganic fillers such as talc or glass fiber to the PP matrix can further enhance the impact resistance and heat resistance rigidity in special industrial scenarios. Alternatively, based on the different needs of end customers for the surface feel of the pallet, the blending ratio of PE and EVA in the anti-slip film 2 can be flexibly adjusted during the film-making stage. For example, the mass fraction of EVA can be appropriately increased to obtain a softer feel and higher anti-slip resistance, or the proportion of PE can be increased to enhance the surface's scratch and wear resistance.

[0023] Furthermore, as a preferred embodiment of this solution and not a limitation thereof, the anti-slip film 2 includes an anti-slip working surface 21 on the upper surface and a hot-melt bonding surface 22 on the bottom. The hot-melt bonding surface 22 is corona treated before molding, and its surface tension reaches 38-42 dyn / cm to increase the interfacial compatibility with the tray body 1 made of polypropylene.

[0024] In this embodiment, polyethylene and ethylene-vinyl acetate copolymer are non-polar or weakly polar materials with low initial surface energy. While direct hot-melt bonding with polypropylene can achieve cross-linking, there may be a few microscopic fusion dead zones. By applying a high-frequency, high-voltage electric field to ionize air and generate localized plasma that continuously bombards the hot-melt bonding surface 22, oxygen-containing polar groups such as hydroxyl and carboxyl groups can be forcibly introduced into its polymer chains. Simultaneously, a slight etching and roughening effect is produced at the microscale, thereby precisely increasing and stabilizing its surface tension within the optimal process range of 38-42 dyn / cm. This parameter setting is a key technology. The significance lies in the fact that if the surface tension is below 38 dyn / cm, the number of activated polar groups is insufficient, making it impossible to achieve instantaneous high-strength wetting and deep compatibility with the polypropylene melt. Conversely, if the surface tension is above 42 dyn / cm, it indicates excessive corona bombardment, which can lead to severe degradation and breakage of the polymer backbone on the bottom surface of the anti-slip film 2. This results in a fragile boundary layer and weakens the final peel strength, potentially causing severe self-adhesion and scrapping of the film during the roll-up and storage stages before molding. By controlling the surface tension between 38-42 dyn / cm, the compatibility between the anti-slip film 2 and the polypropylene material is significantly increased. The interfacial compatibility and thermodynamic affinity of the tray body 1 have a direct beneficial effect: at the moment of molding contact, the high-temperature polypropylene melt can spread and penetrate into the activated hot-melt bonding surface 22 instantly, like a capillary action, eliminating the tiny gaps between the interfaces. This avoids the phenomenon of incomplete welding or edge micro-peeling of the tray during subsequent high-frequency water washing or stress deformation, and improves the shear strength of the finished product. In addition to using a conventional atmospheric pressure air corona treatment machine, the surface modification of the hot-melt bonding surface 22 can also be equivalent to using low-temperature plasma surface treatment technology under nitrogen protection, high-energy flame treatment technology, or... The same dense and firm thermal bonding effect can be achieved by pre-coating an extremely thin layer of environmentally friendly polymer adhesion-promoting primer and other physical and chemical methods. As long as these equivalent alternative methods can stimulate the surface activity of the anti-slip film bottom surface to the same tension level that can completely miscible and wet polypropylene, or for some modified anti-slip film raw materials with higher EVA content and slightly higher initial surface energy, by proportionally reducing the discharge power of corona treatment or accelerating the belt speed, so that the surface tension after the final treatment still falls precisely within the optimal compatibility range of 38-42 dyn / cm, the same dense and firm thermal bonding effect can be achieved without difference.

[0025] Furthermore, as a preferred embodiment of this solution and not a limitation thereof, the anti-slip working surface 21 is provided with a micron-level anti-slip rough surface area 211, and the hot-melt bonding surface 22 is provided with exhaust micro-textures 221 for accommodating hot-melt gas.

[0026] In this embodiment, the anti-slip working surface 21 is specially imprinted or etched with micron-level anti-slip rough areas 211. Its anti-slip working principle lies in breaking the smooth mirror effect that the film might otherwise possess at the microscopic physical scale. Through a densely distributed micron-level peak-valley interlaced rough structure, the effective contact area and microscopic mechanical interlocking force between the bottom of the tableware and the tray surface are increased. Especially when the tray surface is accidentally contaminated with oil, water stains, or other media that easily cause slippage, these micron-level concave-valley structures can act like a miniature drainage network, quickly accommodating droplets and piercing the lubricating film on the bottom of the tableware. This instantly transforms unstable sliding friction into reliable static friction and microscopic shear resistance, significantly and continuously ensuring the safety of service personnel on inclined surfaces. The invention enhances safety and stability during periods of rapid movement or swaying. Furthermore, its ingenious concealed structural design is evident in the venting micro-textures 221 on the bottom hot-melt bonding surface 22, specifically designed to contain hot-melt gases. During the high-pressure filling of the mold cavity in injection molding or compression molding, a small amount of free air inevitably gets trapped inside. Additionally, the high-temperature polypropylene melt may also release a very small amount of low-molecular-weight gas. If the interface is perfectly smooth, these gases will be instantly sealed between the anti-slip film 2 and the tray body 1, leaving no escape. This inevitably leads to the formation of visible micro-bulges, white spots, or weld defects within the hot-melt transition layer 3. The densely packed venting micro-textures 221, however, prevent these defects from escaping during the extremely short time of mold closure. Inside the window, like an interwoven network of miniature air ducts, the gases that expand due to heat are actively guided and briefly contained, rapidly escaping towards the film edge and the mold venting channels. As the subsequent pressure-holding process continues, the high-pressure polypropylene melt, like a wedge, gradually fills and completely occupies the original space of these venting micro-textures 221. Ultimately, this not only eliminates bubble defects but also further expands the actual physical contact area of ​​the hot-melt cross-linking by utilizing the concave-convex mosaic structure formed by these micro-textures. This results in a flawless, dense, and uniform interface after molding, eliminating the risk of blistering or localized peeling of the anti-slip film at the source of physical mechanics. The specific three-dimensional morphology of the anti-slip rough surface area 211 is not limited to irregular frosted textures but can be... The anti-slip material can be flexibly designed into regular micron-level pyramidal arrays, dome-shaped hemispherical arrays, or interlaced rhomboid and honeycomb grid textures to achieve directional reinforcement of anti-slip effects in specific stress directions. Similarly, the venting micro-textures 221 on the hot-melt bonding surface 22 can also be designed, according to the overall shape of the anti-slip film and the location and layout of the venting system inside the mold, into unidirectionally guided parallel slender lines, radial lines radiating from the center to the surroundings, or micro-grid grooves connected end to end. In specific industrial manufacturing processes, these micro-surface morphologies can be directly calendered in one step using cooling and shaping rollers with corresponding reverse micro-textures during the extrusion and casting production stage of the anti-slip film roll, thereby achieving extremely low manufacturing costs.Alternatively, for special high-end customized trays, subsequent processing methods such as laser micro-engraving, plasma surface etching, or chemical micro-corrosion can be used to precisely construct the tray. As long as the microscopic physical morphology constructed on the upper and lower surfaces of the film can respectively achieve the technical objectives of piercing the water film on the top surface to enhance interlocking friction and achieving air venting and flow guidance on the bottom surface to promote dense filling of the high-temperature melt, then they undoubtedly constitute a reasonable implementation and equivalent extension of the core inventive concept of this invention.

[0027] Furthermore, as a preferred embodiment of this solution and not a limitation, the edge of the anti-slip film 2 extends to the side wall of the tray body 1 to form an edge-binding mechanism 4. The extension length of the edge-binding mechanism 4 is 1-2 mm, and the thickness of the anti-slip film at the edge-binding mechanism 4 gradually decreases.

[0028] In this embodiment, in the traditional flat-applied anti-slip layer structure, the cross-section of the film is often directly exposed at the corner where the bottom of the tray meets the side wall. Under the long-term exposure to the extremely high water pressure of commercial dishwashers, frequent physical impacts, and unintentional scratches by users, this exposed vertical edge easily becomes a weak point of stress concentration, thus becoming a breakthrough point for high-temperature water stains, oil stains, and detergents to penetrate and cause the film to curl and peel off. This invention, however, by having the anti-slip film 2 spread out on the bottom plane and then continue to climb slightly upwards along the side wall by 1-2mm to form the edge-sealing mechanism 4, hides and transfers the most vulnerable bonding edge to a side force blind area less susceptible to direct scratches, achieving 360-degree all-around sealing protection for the bottom anti-slip area. At the same time, strictly limiting the extension length to a small range of 1-2mm comprehensively considers the physical extensibility of the film material and the mold adhesion. The optimal parameter selection for the process is crucial because if the extension length is too long, the film, originally a two-dimensional plane, will inevitably produce excess material accumulation and cause severe surface wrinkles and scrap when climbing towards the three-dimensional sidewall. If the extension is too short, it cannot form an effective physical wrapping loop. The anti-slip film thickness at the four points of the edge-wrapping mechanism gradually thins, which means that the outermost edge of the film, due to its smaller cross-sectional area and lower heat capacity, can reach a completely melted state faster than the central body when heated during molding. Thus, it completely sinks into and dissolves into the shallow layer of the sidewall of the polypropylene tray body 1 like a water droplet. This not only completely eliminates the abrupt step feeling and edge sharpness caused by splicing different materials in terms of tactile sensation, achieving a warm and smooth feel like a single material injection molding, but also eliminates the structural stress concentration at the edge in terms of mechanics, further consolidating the shear and peel resistance of the finished product.

[0029] Furthermore, as a preferred embodiment of this solution and not a limitation, the pallet body 1 is also provided with a reinforcing rib mesh area 5, which is correspondingly located in the stress concentration area on the bottom surface of the pallet body 1.

[0030] In this embodiment, in practical applications in commercial catering environments, when a tray carries multiple stacked heavy ceramic tableware pieces or large-capacity soup bowls, the geometric center area of ​​the tray's bottom and the edge corners transitioning from the bottom to the sidewalls often bear extremely high bending moment stress and shear tensile force. If only increasing the absolute thickness of the base plate is used to resist deformation, it not only leads to a significant increase in the injection molding cooling cycle and easily produces unsightly shrinkage marks on the surface, but also makes the product excessively heavy, greatly increasing muscle fatigue for service personnel carrying it for extended periods. This invention, by embedding reinforcing rib mesh areas 5 in these specific stress-concentrated areas, utilizes the geometric mechanical principle of the moment of inertia of the cross section, achieving a reduction in overall material consumption and weight with almost no increase in material usage or weight. In this case, the bending section modulus of the bottom of the tray is increased. This not only effectively prevents the tray from sagging, bending or even breaking under heavy load, but also prevents permanent warping deformation caused by the release of thermal expansion stress when using a high-temperature commercial dishwasher. This ensures the absolute stability and safety of the tableware and liquids placed on the tray. At the same time, during the product manufacturing stage, these raised reinforcing ribs 5 can also serve as excellent high-speed flow channels during the high-temperature and high-pressure melt injection molding process. This greatly improves the flowability of polypropylene melt in the wide bottom area of ​​the tray, avoiding molding defects such as incomplete filling, insufficient glue or cold flow marks caused by excessive material flow. This further ensures the density and yield of the tray body 1.

[0031] A molding process for a hot melt composite anti-slip tray as described in any of the preceding claims includes the following steps: Step S1: Place the anti-slip film 2, which is made of polyethylene and ethylene-vinyl acetate copolymer with a thickness of 0.4-0.6mm, into the mold cavity, and fix the anti-slip film 2 in the mold by electrostatic adsorption to prevent displacement or wrinkling; Step S2: Within a heating temperature range of 180-250℃, inject polypropylene material into the mold and combine it with the anti-slip film 2 to fully form the tray body 1. At the same time, the surface of the anti-slip film 2 in contact with the tray body 1 reaches a melt-penetrating state, and the upper surface of the anti-slip film 2 does not collapse. Step S3: Apply a pressure of 10MPa to the mold and set the holding time to 25 seconds to ensure the bonding strength after hot melting; Step S4: Cool and shape the mold by introducing 20°C cold water into the rear mold, then open the mold and remove the finished product tray.

[0032] In this embodiment, in traditional injection molding or compression molding processes, extremely thin polymer films are prone to displacement, overturning, or severe wrinkling when subjected to high-speed, high-pressure melt flow, leading to mass product scrap. However, by using non-contact electrostatic force to pre-press and adhere the film, not only are defects caused by film displacement or wrinkling avoided and the contour accuracy of the anti-slip area maintained, but the cumbersome physical fixture positioning is also eliminated, significantly shortening the preparation time for each mold opening. Then, in step S2, within the set heating temperature range of 180-250℃, where polypropylene has an excellent melt flow index, the flowing polypropylene material is injected through the injection molding machine. The high-speed injection into the closed mold causes intense physical contact with the electrostatically fixed anti-slip film 2. At this point, relying on the enormous enthalpy of the polypropylene melt, not only is the entire tray body 1 instantly filled and fully formed within the cavity, but more importantly, this specific temperature range achieves a perfect balance with the thickness of the anti-slip film. The high temperature allows the bottom surface of the anti-slip film 2 in contact with the tray body 1 to quickly cross the melting baseline and reach a melt-penetration state, promoting deep cross-linking of the molecular chains. Simultaneously, the heat absorption and conduction effect of the metal on the inner wall of the mold cavity ensures that the temperature of the upper surface of the anti-slip film 2, which is in closest contact with the mold wall, remains below its melting point. If any melt collapse or texture damage occurs, the pre-set anti-slip micro-rough structure is preserved. Subsequently, in step S3, to further solidify the physical bonding limit of the hot-melt interface, the mold applies a holding pressure of up to 10 MPa to the fully filled cavity, and the high-pressure holding time is precisely set to 25 seconds. The mechanical and thermodynamic principle is that the hydrostatic pressure of up to 10 MPa can act like an invisible forging hammer, forcibly squeezing the polypropylene melt into any tiny gaps or even the gaps between macromolecular chains at the bottom of the anti-slip film, fundamentally squeezing out all micro air bubbles. At the same time, the continuous holding pressure for up to 25 seconds effectively compensates for the cooling process of the polypropylene from liquid to solid phase change. The volume shrinkage of up to 1.5% to 2% generated during the process prevents unsightly shrinkage cavities or depressions from forming on the tray surface due to shrinkage and stretching. This ensures an indestructible overall bond strength after cooling and hot melting from both microscopic and macroscopic dimensions. Finally, in step S4, 20°C circulating cold water is introduced into the internal cooling water channel of the rear mold (usually the moving mold side) for forced cooling and shaping. Low-temperature quenching causes the polymer chains to freeze rapidly and lose their mobility, thoroughly shaping the cross-linked and permeated physical structure. Subsequently, the mold is opened and the finished product tray is safely removed through the ejector mechanism, which greatly reduces the molding cycle of a single product and significantly improves mass production efficiency.

[0033] Furthermore, as a preferred embodiment of this solution and not a limitation, in step S1, the electrostatic adsorption adopts a zoned and stepped electrostatic control method, specifically: first, electrostatics are applied to the central area of ​​the anti-slip film 2 to make it adhere to the mold, and then electrostatics are radiated to the edge area of ​​the anti-slip film 2 to expel the air between the anti-slip film 2 and the mold surface.

[0034] In this embodiment, a local high-voltage electrostatic charge is first applied to the geometric center region of the anti-slip film 2 to make it firmly adhere to the mold surface. Then, using this central anchor point as a reference, electrostatic charge is applied radially towards the edge region of the anti-slip film 2 according to a preset time difference. Its core working principle and extremely significant beneficial effect are that when a robotic arm transports an extremely thin and highly flexible polymer film material with a thickness of only 0.4-0.6 mm into the mold cavity, if the traditional method of applying global electrostatic charge instantaneously to the entire surface is used, various parts of the film will simultaneously be subjected to strong electric field attraction and instantly slap against the mold. This... This inevitably traps a large amount of free air between the film's belly and the mold's inner wall, leaving it nowhere to escape. This results in persistent micro-bulges, dark spots, or fine, interlaced wrinkles on the film surface. These tiny adhesion defects are then amplified instantly by the relentless impact of the high-pressure, high-temperature polypropylene melt (up to 10 MPa), leading to localized film tearing, boundary distortion and shrinkage, or unsightly creases on the finished product surface, directly resulting in product scrap. This invention, however, employs a tiered electrostatic application method radiating from the center outwards. The sequence of electric field forces acts as an invisible "scraper," with the electrostatic radiation... As the injection ring gradually expands outward, the film is as if it is being smoothly pushed and rolled out from the center outward by a pair of invisible hands, which extremely smoothly and thoroughly expels all residual air between the anti-slip film 2 and the mold surface, achieving true vacuum-level seamless zero-distance bonding. This not only completely eliminates the risk of wrinkling and displacement during molding from a physical source, but also gives the product extremely high appearance flatness and yield. For standard rectangular catering trays, the end effector of the robot arm can be designed with the longitudinal central axis of the tray as the first-level electrostatic generation area, and then extend to the left and right side wing areas by 0.2 to 0. The second and third stage electrostatic generators are activated in 5 seconds to achieve bidirectional flat-push exhaust. For round pastry trays, multiple sets of concentric ring-shaped electrostatic emission electrodes can be used. The programmable logic controller (PLC) controls the discharge from the inner ring to the outer ring in sequence to achieve perfect 360-degree radial wave-like exhaust. Even in some semi-automatic production lines with a slightly lower degree of automation, flexible brush rollers or Teflon rollers with static charge can be used, driven by the operator or a simple cylinder, to perform unidirectional linear rolling discharge adsorption from one end of the anti-slip film 2 to the other.

[0035] Furthermore, as a preferred embodiment of this solution and not a limitation, in steps S2 and S3, the temperature of the front mold is 40-60°C to prevent the upper surface of the anti-slip film 2 from collapsing, and the temperature of the rear mold is consistent with the heating temperature in the initial stage of injection to ensure the fluidity of the polypropylene material.

[0036] In this embodiment, during the molding stage, the temperature of the front mold (usually the fixed mold side), which is responsible for directly contacting and molding the upper surface of the anti-slip film 2, is independently and precisely controlled at 40-60°C. Its physical working principle and decisive beneficial effect are that when the polyethylene and ethylene-vinyl acetate copolymer blend film, with a thickness of only 0.4-0.6mm, is subjected to the relentless impact and heat conduction of the polypropylene melt at a high temperature of 180-250°C on the back side, its internal temperature will instantly soar above the melting point. If the front mold temperature is too high, the entire film will completely liquefy, causing the carefully designed micron-level anti-slip rough surface area 211 on its anti-slip working surface 21 to be completely flattened or even experience severe melting and molding phenomena. The front mold... The temperature is forcibly maintained in a low-temperature range of 40-60℃, making it act like a giant heat-absorbing cold plate. This allows it to instantly remove heat from the outermost layer of the film through heat conduction, forcibly establishing a steep temperature gradient along the extremely thin anti-slip film thickness. This ensures that the bottom surface of the film is fully melted and cross-linked while perfectly freezing and maintaining the upper surface of the anti-slip film 2 and its microscopic anti-slip texture without any melting or morphological distortion. Simultaneously, to ensure the macroscopic molding quality of the tray frame, the temperature of the rear mold (usually the moving mold side) responsible for molding the back of the tray body 1 is specifically set at the initial injection stage to be highly consistent with the heating temperature of 180-250℃. The significance of this setting is that the polypropylene melt, in terms of area... When flowing at high speed within a wide cavity with a thickness of only 5-8mm, a surface condensation and solidification layer will quickly form if it encounters a relatively cold mold wall, greatly increasing flow resistance and leading to incomplete filling, stress marks, or weld line defects. By maintaining the rear mold at the same high temperature as the melt in the initial stage, the flow viscosity of the melt front is reduced, ensuring the ultimate fluidity of the polypropylene material throughout the entire long-flow cavity. This allows complex and micro-structures such as the bottom reinforcing rib area 5 and the outermost edge-binding mechanism 4 to be fully filled. The temperature control of the front and rear molds is not limited to the traditional static temperature control method of continuously flowing constant-temperature cooling water or hot oil, but can be equivalently introduced with high-temperature quenching and cooling (RHCM) technology. Light-based seamless temperature-controlled injection molding technology, for example, involves instantly introducing high-temperature, high-pressure steam into the rear mold water channel during the initial injection stage to achieve an extremely high heating temperature to ensure absolute fluidity. Subsequently, when the holding pressure ends and the cooling step begins, cold water is instantly introduced for quenching. Alternatively, for modified polypropylene materials with different melt indices and PE / EVA film formulations of different thicknesses, the temperature control range of the front mold can be adjusted between 35-65℃ using a high-precision mold temperature controller for closed-loop PID fine-tuning control, depending on the seasonal environment of different workshops. At the same time, the rear mold heating can also be equivalent to using electric heating tubes inside the inserts for auxiliary heating, infrared surface radiation preheating, or electromagnetic induction heating technology to achieve faster temperature response and more uniform heat field distribution.

[0037] Furthermore, as a preferred embodiment of this solution and not a limitation, in step S4, an asymmetric differential cooling mechanism is adopted, specifically: while the rear mold is forced to cool with 20°C cold water, the front mold is naturally cooled or slowly cooled with 35-45°C warm water, in order to counteract the warping stress caused by the difference in thermal shrinkage rates between the anti-slip film 2 made of polyethylene and ethylene-vinyl acetate copolymer and the tray body 1 made of polypropylene.

[0038] In this embodiment, 20°C cold water is continuously supplied to the cooling water channel of the rear mold (corresponding to the back of the tray body) for high-intensity forced rapid cooling. Simultaneously, the front mold (corresponding to the front of the anti-slip film) completely cuts off the forced cooling water source and uses natural cooling, or 35-45°C warm water is supplied to its internal water channel for controlled slow cooling. The core working principle and significant beneficial effect of this asymmetric thermodynamic control mechanism lies in the fact that polymer materials inevitably undergo volume shrinkage during the cooling process from a high-temperature molten state to a room-temperature solid phase. The polypropylene material used in this invention (constituting the tray body 1) and polyethylene and ethylene-vinyl acetate copolymer (constituting the anti-slip film 2) have drastically different molecular crystallinity and thermal shrinkage coefficients. If traditional symmetrical isothermal cooling is used on both sides of the mold before demolding, this difference in thermal expansion coefficients, similar to a bimetallic strip, will inevitably cause the tray to severely indent or bulge outwards towards the side with the larger shrinkage rate after demolding, resulting in severe warping when the finished tray is placed on a flat table. Unacceptable chassis wobbling or seesaw-like behavior severely compromises the fundamental stability requirements of catering load-bearing equipment. This invention addresses this issue with asymmetric differential cooling, using 20°C cold water from the rear mold to rapidly and forcibly freeze the thick polypropylene body with significant shrinkage stress. This allows it to cross the glass transition temperature in the shortest possible time, losing the fluidity of the polymer chains and its ability to shrink and deform significantly, thus forcibly locking its physical dimensions. Simultaneously, the front mold uses 35-45°C warm water for slow cooling or natural cooling, providing the extremely thin anti-slip film 2 with a relatively long stress relaxation and dimensional adaptation time window. This allows the anti-slip film to fully release its own shrinkage tensile stress during the slow cooling process and spontaneously conform to the flat contour of the polypropylene skeleton that has been forcibly frozen and shaped by the rear mold. This macroscopically and mechanically perfectly offsets the huge warping stress caused by the different thermal shrinkage rates of the two dissimilar materials, ensuring absolutely perfect geometric flatness after demolding and avoiding the potential for delayed deformation due to the slow release of residual internal stress.

[0039] Furthermore, as a preferred embodiment of this solution and not a limitation, step S5 is also included: placing the finished product tray in a constant temperature environment of 60-80℃ for annealing for 30-60 minutes to further solidify the heat-fusion bonding force of the interface.

[0040] In this embodiment, although the aforementioned asymmetric differential temperature cooling mechanism has macroscopically offset the warpage deformation at the moment of product demolding, after high-pressure injection and drastic cooling phase change, a large amount of residual thermal stress and frozen orientation stress of polymer segments still remain at the microscopic level inside the polypropylene body and in the hot-melt transition layer formed by the cross-linking of two heterogeneous macromolecular chains. If it is directly placed in a commercial catering environment, these internal stresses will be slowly released when subjected to long-term high-temperature hot water washing or accidental physical impact, which may eventually lead to irreversible delayed warpage of the tray or microscopic cleavage and peeling of the anti-slip film edge. However, by placing it in a constant temperature environment of 60-80℃, which is exactly between the material softening point and the safe working limit, it is possible to provide appropriate thermal kinetic energy to the polymer segments that are in a forced frozen state, causing them to undergo micro Brownian motion, thereby preventing changes in the macroscopic physical properties of the tray. Under the premise of size, the chain segments are relaxed and rearranged spontaneously, eliminating all residual internal stress caused by uneven shrinkage and forced cooling. More importantly, this continuous constant temperature time gives the PE / EVA molecules on the bottom of the anti-slip film and the PP molecules on the surface of the tray a second opportunity for deep mutual dissolution. This promotes deeper secondary thermal diffusion and three-dimensional network entanglement of the polymer chains in the hot melt transition layer, pushing the hot melt bonding force of the interface to the physical limit of material mechanics. This allows the finished product to maintain its durability without bubbling or peeling even when subjected to thousands of cycles of extreme high temperature and strong water jets in commercial dishwashers. The specific physical implementation of this constant temperature annealing environment is not limited to traditional electric heating blast constant temperature ovens, but can be highly compatible with the needs of automated production lines. It is equivalent to using an infrared radiation heating tunnel oven, a low-speed automatic conveyor belt with an insulated shell and hot air circulation.

[0041] The working principle of this embodiment is as follows: During the molding preparation stage, the ultra-thin anti-slip film activated by corona discharge is precisely and bubble-freely fixed to the inner wall of the front mold through tiered electrostatic adsorption. At the moment of high temperature and high pressure filling, the polypropylene melt at 180-250℃ rapidly fills the tray body and the bottom reinforcing rib cavity, and comes into intense contact with the venting micro-textures on the bottom surface of the anti-slip film. Under the high pressure of 10MPa, the polypropylene macromolecular chains and the PE / EVA macromolecular chains of the film undergo deep mutual dissolution and cross-linking across the physical interface, forming an unbreakable hot melt transition layer. During this period, the front mold is controlled at a low temperature of 40-60℃ to perfectly protect the anti-slip rough surface area from melting and collapse. After molding, the asymmetric differential cooling mechanism of rapid cooling of the rear mold and slow cooling of the front mold is used to macroscopically offset the warping tension caused by the difference in thermal shrinkage rates of the two materials. Finally, the residual internal stress is completely released microscopically and secondary cross-linking is promoted through constant temperature annealing, thereby producing an anti-slip tray with good bonding effect and no warping in one go.

[0042] The above are implementation methods provided in conjunction with specific content, and it is not intended that the specific implementation of this application is limited to these descriptions. Any methods or structures that are similar to those of this application, or any technical deductions or substitutions made based on the concept of this application, should be considered within the scope of protection of this application.

Claims

1. A hot-melt composite anti-slip tray, characterized in that, The tray includes a tray body (1) and an anti-slip film (2) hot-melt bonded to the upper surface of the tray body (1). The tray body (1) is made of polypropylene with a thickness of 5-8 mm. The anti-slip film (2) is made of polyethylene and ethylene-vinyl acetate copolymer with a thickness of 0.4-0.6 mm. An integrally formed hot-melt transition layer (3) is provided between the anti-slip film (2) and the tray body (1). The hot-melt transition layer (3) is formed by the cross-linking of the polyethylene and ethylene-vinyl acetate copolymer molecular chains on the bottom surface of the anti-slip film (2) and the polypropylene molecular chains on the surface of the tray body (1) at high temperature.

2. The hot-melt composite anti-slip tray according to claim 1, characterized in that, The anti-slip film (2) includes an anti-slip working surface (21) on the upper surface and a hot-melt bonding surface (22) on the bottom. The hot-melt bonding surface (22) is corona treated before molding, and its surface tension reaches 38-42 dyn / cm to increase the interfacial compatibility with the tray body (1) made of polypropylene.

3. The hot-melt composite anti-slip tray according to claim 2, characterized in that, The anti-slip working surface (21) is provided with a micron-level anti-slip rough surface area (211), and the hot melt bonding surface (22) is provided with exhaust micro-textures (221) for accommodating hot melt gas.

4. The hot-melt composite anti-slip tray according to claim 1, characterized in that, The edge of the anti-slip film (2) extends to the side wall of the tray body (1) and forms an edge-binding mechanism (4). The extension length of the edge-binding mechanism (4) is 1-2 mm, and the thickness of the anti-slip film at the edge-binding mechanism (4) gradually decreases.

5. The hot-melt composite anti-slip tray according to claim 1, characterized in that, The pallet body (1) is also embedded with a reinforcing rib mesh area (5), which is located in the stress concentration area on the bottom surface of the pallet body (1).

6. A molding process for a hot-melt composite anti-slip tray as described in any one of claims 1-5, characterized in that, Includes the following steps: Step S1: Place the anti-slip film (2) made of polyethylene and ethylene-vinyl acetate copolymer with a thickness of 0.4-0.6mm into the mold cavity, and fix the anti-slip film (2) in the mold by electrostatic adsorption to prevent displacement or wrinkling; Step S2: Within a heating temperature range of 180-250℃, inject polypropylene material into the mold and combine it with the anti-slip film (2) to fully form the tray body (1). At the same time, the surface of the anti-slip film (2) in contact with the tray body (1) reaches a melt-penetration state, and the upper surface of the anti-slip film (2) does not collapse. Step S3: Apply a pressure of 10MPa to the mold and set the holding time to 25 seconds to ensure the bonding strength after hot melting; Step S4: Cool and shape the mold by introducing 20°C cold water into the rear mold, then open the mold and remove the finished product tray.

7. The compression molding process according to claim 6, characterized in that, In step S1, electrostatic adsorption adopts a zoned and stepped electrostatic control method, specifically: first, electrostatics are applied to the central area of ​​the anti-slip film (2) to make it adhere to the mold, and then electrostatics are applied radially to the edge area of ​​the anti-slip film (2) to expel the air between the anti-slip film (2) and the mold surface.

8. The compression molding process according to claim 6, characterized in that, In steps S2 and S3, the temperature of the front mold is 40-60°C to prevent the upper surface of the anti-slip film (2) from collapsing, and the temperature of the rear mold is consistent with the heating temperature in the initial stage of injection to ensure the fluidity of the polypropylene material.

9. The molding process according to claim 6, characterized in that, In step S4, an asymmetric differential cooling mechanism is adopted, specifically: while the rear mold is forced to cool with 20°C cold water, the front mold is cooled naturally or slowly with 35-45°C warm water to counteract the warping stress caused by the difference in thermal shrinkage rates between the anti-slip film (2) made of polyethylene and ethylene-vinyl acetate copolymer and the tray body (1) made of polypropylene.

10. The molding process according to claim 6, characterized in that, It also includes step S5: placing the finished product tray in a constant temperature environment of 60-80℃ for annealing for 30-60 minutes to further solidify the heat-fusion bonding force of the interface.

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