A seamless preparation method of a gradient hot melt-based laminated tube and a laminated tube

Abstract

The application discloses a kind of based on gradient hot melt's laminated tube seamless preparation method and laminated tube.The method is by decomposing heating process into two temperature accurate control steps: first, at first temperature T1 to the edge of interface laminated sheet and overall fusion, form high-strength initial weld;Subsequently, outside weld is heated on one side, wherein T2 is higher than the melting point of outer layer but lower than the melting point of barrier layer and inner layer, so that selectively make outer layer material secondary melt flow, form the final joint that visual is invisible. Optionally, the final joint can be laser textured to match the optical properties of the tube body. The present application breaks through the limitations of traditional lap joint process on structural protrusions and printing prohibited areas, achieving 360° full-width printing effect without visual interruption for laminated tubes, with excellent sealing strength and single material recyclability, especially suitable for high-end packaging field.

Description

Technical Field

[0001] This invention relates to the field of packaging container technology, and in particular to a seamless manufacturing method for laminated tubes based on gradient thermal melting and the laminated tube itself. Background Technology

[0002] Laminated tubes, composed of multiple functional films, are widely used in the packaging of daily chemical products such as toothpaste, cosmetics, and pharmaceuticals due to their excellent barrier properties, flexibility, and good printability. Currently, the industry's common production process involves winding pre-made laminated sheets into tubes, overlapping their longitudinal edges, and then performing high-frequency welding to form what is known as an "overlap seam."

[0003] However, this process based on the overlapping and fusion of materials has fundamental and interconnected aesthetic and design flaws.

[0004] First, there is the degradation in appearance caused by the physical structure. Because the sheet material itself is quite thick (typically 200-400 micrometers), structural thickening inevitably occurs in the seam area due to material stacking. This thickened area not only alters the circumferential curvature of the tube but also creates visible linear bulges or "humps" on the outer surface. The gloss and texture at the seam differ significantly from the main body of the tube, causing the printed pattern to break or deform in this area.

[0005] To ensure reliable weld seals, the joint area must be fused under clean, uncontaminated conditions. However, chemical components in printing inks (such as varnish solvents) can easily contaminate the weld interface during this process, leading to decreased seal strength or even failure. Therefore, in actual production, the joint area is forced to remain as an unprinted blank strip.

[0006] These two factors combined constitute the dual technical limitations faced by laminated tubes in the pursuit of aesthetically pleasing packaging: 1. Physical protrusions at the joints disrupt the smoothness and continuity of the outer surface of the pipe. 2. The non-printing area (also known as the "unprinted strip") that must be reserved to ensure the reliability of the welded seal not only visually forms a fixed blank strip that is disconnected from the overall design, but also physically limits the surface area available for printing from the product design stage, making it technically impossible to achieve 360° continuous full-width printing, thus restricting the overall visual appeal of the packaging.

[0007] Especially in high-value-added sectors like cosmetics and personal care, where packaging appearance is paramount, the market demands a high degree of visual integrity and continuity. Traditional lap joint processes, due to their inherent dual technical flaws of "structural thickness abrupt changes" and "functional printing no-go zones," have become major obstacles to achieving this goal. Although attempts have been made to mitigate the visual abruptness of the seams by optimizing welding parameters and pre-treating the lap edges with bevel cuts, these improvements have not broken through the fundamental process paradigm of "material overlap and fusion." Therefore, they cannot fundamentally eliminate the changes in cross-sectional thickness caused by material stacking, nor can they resolve the fundamental contradiction between the risk of welding interface contamination and the incompatibility of surface printing processes.

[0008] It should be noted that the above description of the background technology is only for the purpose of providing a clear and complete explanation of the technical solutions of the present invention and facilitating understanding by those skilled in the art. It should not be assumed that the above technical solutions are known to those skilled in the art simply because they have been described in the background section of the present invention. Summary of the Invention

[0009] This invention aims to solve the industry problem of poor aesthetics of seams in existing laminated pipes due to limitations in manufacturing processes. Specifically, it provides a manufacturing method that addresses the obvious raised seam lines formed on the outer surface of the pipe body by traditional lap joint processes, making the outer surface of the seam area smooth, continuous, and visually invisible.

[0010] After in-depth research, the inventors discovered that even if the edges of the sheet were changed to a butt joint method, the inherent differences in material, melting point, and melt viscosity among the layers constituting the laminated sheet (such as the outer layer, barrier layer, and inner layer) made it difficult for the melting and flow behaviors of each layer to coordinate during a single high-temperature fusion process. This resulted in uneven interweaving, penetration, and cooling contraction of the different material melts at the butt joint interface, ultimately leaving a visible "seam mark" on the outer surface of the tube caused by microscopic inhomogeneities. This mark differs from the main body of the tube in terms of gloss and texture, and is essentially an inherent contradiction that cannot be reconciled when multiple dissimilar materials are fused synchronously. Therefore, it still cannot meet the ultimate requirements of the high-end market for a "seamless" appearance.

[0011] Based on this understanding, this invention creatively proposes a two-step "gradient thermal fusion" process. Its core concept lies in strategically "decoupling" the two conflicting goals of "structural sealing" and "smooth appearance" that are intertwined in traditional processes, through precise step-by-step and temperature-controlled processes. First, a first temperature ensures the overall fusion of multiple layers of material, achieving a structural seal; then, a second temperature selectively allows only the outer layer to melt and flow a second time, specifically eliminating microscopic traces on the surface, thus fundamentally overcoming the appearance defects of the butt joint fusion.

[0012] To address the aforementioned technical problems, this invention provides a method for preparing seamless joints in laminated pipes based on gradient thermal fusion, comprising the following steps: S1. Provide raw materials: Provide laminated sheets, which include at least an outer layer, a barrier layer and an inner layer; S2, First heating and fusion: The longitudinal edges of the above-mentioned laminated sheets are joined together, and the joined area is heated at the first temperature T1 so that the materials of each layer, including the outer layer, barrier layer and inner layer, are fused together at the joint to form an initial weld with structural strength. S3. Second heating and smoothing: The outer side of the initial weld is locally heated on one side at a second temperature T2, wherein the second temperature T2 is higher than the melting point of the outer layer and lower than the melting points of the barrier layer and the inner layer, so that the outer layer material at the initial weld is selectively melted and flowed a second time, thereby forming a final joint with a smooth outer surface and invisible to the eye.

[0013] As a further improvement of the present invention, in step S2, the docking area is heated by a double-sided heating method; the temperature of the double-sided heating is independently controlled, and the heating temperature on the side closer to the inner layer is not lower than the heating temperature on the side closer to the outer layer.

[0014] As a further improvement of the present invention, steps S2 and S3 are completed at the same forming station; wherein, by controlling the working state of the heating devices located inside and outside the docking area, the above-mentioned double-sided heating and the above-mentioned single-sided heating are respectively achieved.

[0015] As a further improvement of the present invention, in step S2, before the longitudinal edges of the laminated sheet are joined, the edges are beveled, and the bevel angle is 30°-90°; preferably, the bevel angle is 45°-60°.

[0016] As a further improvement of the present invention, the first temperature T1 is 170°C-230°C and the second temperature T2 is 115°C-145°C; preferably, the first temperature T1 is 180°C-210°C and the second temperature T2 is 120°C-135°C.

[0017] As a further improvement of the present invention, the outer layer comprises at least one of low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), or ultra-low-density polyethylene (VLDPE), with a melting point of 105°C-125°C and a melt flow index of 0.5-50 g / 10min; the inner layer comprises high-density polyethylene (HDPE), with a melt flow index of 0.1-50 g / 10min.

[0018] As a further improvement of the present invention, the barrier layer is a blend of polyethylene and ethylene-vinyl alcohol copolymer, and the mass percentage of ethylene-vinyl alcohol copolymer in the barrier layer is not greater than 5% of the total mass of the laminated tube.

[0019] As a further improvement of the present invention, the barrier layer is made by co-extruding and stretching a polyethylene-ethylene-vinyl alcohol copolymer.

[0020] As a further improvement of the present invention, after step S3, the method further includes: S4. Laser texturing: The outer surface of the final joint is subjected to laser texturing to form a micron-level texture in the area, thereby reducing the specular reflectivity of the area.

[0021] The present invention also provides a laminated tube, the tube body of which is made by the above-mentioned seamless preparation method of laminated tube based on gradient thermal fusion.

[0022] Compared with the prior art, the seamless joint preparation method for laminated pipes based on gradient thermal fusion provided by the present invention has the following beneficial effects: By decomposing the heating process into two steps—a first fusion at a higher temperature (T1) and a second smoothing at a lower temperature (T2)—this invention creatively decouples the two mutually restrictive core objectives of "structural sealing" and "smooth appearance" in traditional processes. The key lies in precisely controlling the second temperature T2 (T2 > outer layer melting point, and T2 < barrier layer / inner layer melting point) to selectively allow only the outer layer material to melt and flow a second time. This eliminates any microscopic interface traces, unevenness, or gloss differences formed on the outer surface after the first fusion, ultimately resulting in a smooth, continuous, and visually invisible seam.

[0023] Based on this, the laminated tube body prepared by this method can achieve full-width printing with no visual interruption at 360°. Since the seams are physically and visually integrated with the tube body, the unprinted bands that were forced to be reserved due to "structural thickness abrupt changes" and "functional printing forbidden zones" in traditional processes are fundamentally eliminated. This allows the printed pattern to continuously and completely cover the entire tube body, greatly improving the overall aesthetic level and design freedom of the packaging, thus meeting the stringent requirements for packaging appearance in high-end cosmetics, personal care products and other fields.

[0024] Meanwhile, the core process of this invention exhibits excellent compatibility and scalability with respect to material systems. When a specific combination of polyethylene (PE)-based materials is preferably used, the seamless appearance described above can be achieved while simultaneously ensuring a highly uniform overall material composition of the hose (PE content exceeding 95%). This makes the prepared laminated pipe readily compliant with the current global trend towards "single-material" recyclable design, possessing the potential to be directly recycled into existing polyethylene recycling systems, combining excellent visual appeal with environmental value. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the structure of the laminated pipe body of the present invention. The longitudinal region (a) indicated by the dashed frame on the outer surface of the pipe body is the location of the joint prepared by the method of the present invention. The joint is smooth and continuous in appearance and is not visible to the naked eye.

[0026] Figure 2 This is a cross-sectional view of the layered structure of the laminated sheet material of the present invention.

[0027] Figure 3 This is a process flow diagram of the gradient thermal melting preparation method of the present invention.

[0028] Figure 4 This is a schematic diagram of the molding and heating device used for the first heating and melting process.

[0029] Figure 5 The image shows a photograph of the laminated tube body produced by the first heating and fusion process in step S2, where arrow b points to the visible seam.

[0030] Figure 6 A photograph of the laminated tube body produced by the second heating and smoothing process in step S3.

[0031] Explanation of reference numerals in the attached figures: 100-tube body, 10-Laminated sheet, 11-Outer layer, 12-First adhesive layer, 13-Barrier layer, 14-Second adhesive layer, 15-Inner layer, 101, 102-Longitudinal edges; 20-Forming device, 21-Mandrel, 221, 222, 223-Forming rollers, 23-Heating device, 231-First heating element, 232-Second heating element; a - Joint area, b - Initial weld marks. Detailed Implementation

[0032] The present invention will now be described in detail with reference to the embodiments shown in the accompanying drawings. However, it should be noted that these embodiments are not intended to limit the present invention. Equivalent changes or substitutions in function, method, or structure made by those skilled in the art based on these embodiments are all within the scope of protection of the present invention. Example 1

[0033] Please see Figures 1 to 6 This embodiment provides a seamless fabrication method for laminated tubes based on gradient thermal melting. For example... Figure 3 As shown, this preparation method mainly includes three core steps: providing a laminated sheet (S1), first heating and fusion (S2), and second heating and smoothing (S3). The basic process flow and specific process parameters are illustrated below: Step S1: Provide laminated sheets.

[0034] Preparation Figure 2 The laminated sheet 10 shown is a multi-layer composite structure, comprising at least an outer layer 11, a barrier layer 13, and an inner layer 15 arranged sequentially from the outside to the inside. The melting point of the outer layer 11 must be lower than that of the inner layer 15. This "melting point gradient" is the key physical basis for achieving "selective secondary melting" in the subsequent process.

[0035] In a preferred and complete embodiment of the present invention, the laminated sheet 10 adopts a five-layer co-extrusion structure, consisting of, from the outside to the inside: an outer layer 11, a first adhesive layer 12, a barrier layer 13, a second adhesive layer 14, and an inner layer 15. Specific material selection and structural features are as follows: Outer layer 11: As a "functional layer" that determines the final appearance, it is made of polyethylene material with a low melting point, such as at least one of low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), or ultra-low-density polyethylene (VLDPE). Its melting point ranges from 105°C to 125°C, and its melt flow index (MFI, 2.16 kg, 190°C) is 0.5-50 g / 10 min. In practical applications, outer layer 11 can be a single-layer or multi-layer composite structure that meets printing and appearance requirements.

[0036] First adhesive layer 12 and second adhesive layer 14: These are used to ensure a strong bond between layers. They can be made of coated polyethylene layers, and adjacent layers are bonded by extrusion lamination. Specifically, polyethylene resin is heated and melted in an extruder, and the molten polyethylene coating is extruded from the die, which acts as an adhesive to bond the outer layer 11 to the barrier layer 13, and the barrier layer 13 to the inner layer 15, respectively.

[0037] Barrier layer 13: is a blend of polyethylene (PE) and ethylene-vinyl alcohol copolymer (EVOH), preferably formed by co-extrusion blown film followed by unidirectional or bidirectional stretching. This process allows for efficient dispersion and thinning of the EVOH component, thereby ensuring excellent oxygen and water vapor barrier performance while controlling the EVOH mass percentage to no more than 5% of the total mass of the laminated pipe, a significant reduction compared to traditional structures.

[0038] Inner layer 15: As a "functional layer" providing heat-sealing performance, it is made of polyethylene material with a high melting point, such as high-density polyethylene (HDPE). Its melting point range is 130°C to 137°C, and its melt flow index is 0.1-50 g / 10 min.

[0039] Through the above material and structural design, the total mass of polyethylene (PE) in the pipe body can exceed 95%, thus meeting the design requirement of single material recyclability.

[0040] Step S2: First heating and fusion.

[0041] To improve the docking accuracy and fusion area, it is preferable to bevel the longitudinal edges 101 and 102 of the laminated sheet 10, with a bevel angle of 30°-90°, more preferably 45°-60°. For example, in one specific embodiment, a 45° angle can be used for the bevel pretreatment.

[0042] To achieve the "first heating and fusion" described in step S2, the following can be used: Figure 4 The tube forming device 20 shown is mainly composed of a mandrel 21, multiple forming rollers (221, 222, 223) mounted on a base 22, and a heating device 23.

[0043] Multiple freely rotatable forming rollers 221, 222, and 223 are arranged on the outer periphery of the mandrel 21. The axial position of each forming roller (221, 222, and 223) is adjustable to precisely guide and wrap the laminated sheet 10 around the circumferential surface of the mandrel 21, and to make the two longitudinal edges 101 and 102 of the laminated sheet 10 abut against each other at a predetermined mating position.

[0044] A heating device 23 is arranged around the docking position and includes a first heating element 231 and a second heating element 232. The first heating element 231 is located outside the docking position, and the second heating element 232 corresponds to the inner side of the docking position, together forming a double-sided heating layout. The temperatures of the first heating element 231 and the second heating element 232 can be independently controlled and maintained at a first temperature T1, where the first temperature T1 represents a temperature range that meets process requirements. In some specific embodiments, the first temperature T1 is 170°C-230°C; preferably, the first temperature T1 is 180°C-210°C.

[0045] Depending on the different requirements of material properties and process optimization, the temperature control of dual-sided heating can adopt the following two modes: Mode 1: Dual-sided isothermal heating As a basic implementation, the first heating element 231 and the second heating element 232 can be set to the same first temperature T1. During operation, the laminated sheet 10 is conveyed and wraps around the mandrel 21, and its edges are precisely joined under the pressure of the forming rollers. Subsequently, the heating device 23 is activated, applying uniform heat of temperature T1 to the joining area from both the inner and outer sides, causing the materials of each layer, including the outer layer 11, the first adhesive layer 12, the barrier layer 13, the second adhesive layer 14, and the inner layer 15, to fuse and diffuse together at the joining interface, thereby forming an initial weld with high structural strength.

[0046] It should be noted that while the initial weld formed through this step ensures structural sealing, the complex interplay of the melting behavior of each layer of material at high temperature T1 may still leave a visible trace on its outer surface (i.e., the initial weld mark), such as... Figure 5 The middle arrow b points to this. This process is simple to control and can effectively ensure the overall fusion of multi-layer materials, but its appearance is not yet perfect. Therefore, it needs to be specially treated for appearance through the subsequent step S3 (second heating and smoothing).

[0047] Mode 2: Dual-sided differential heating As a further optimized implementation, the temperatures on both sides can be differentially controlled based on the melting point differences of the outer layer, barrier layer, and inner layer materials. Specifically, the temperature of the second heating element 232 on the side closer to the inner layer 15 is set to be slightly higher than the temperature of the first heating element 231 on the side closer to the outer layer 11. For example, in a specific example, such as Figure 4 As shown, the temperature of the first heating element 231 is set to 200°C, and the temperature of the second heating element 232 is set to 205°C. The heating time is approximately 2 seconds.

[0048] This "high inside, low outside" temperature gradient design has dual advantages. First, the slightly higher inner temperature ensures that the inner layer 15 and the barrier layer 13, which have higher melting points, receive sufficient heat to achieve complete melting, thus guaranteeing the core structural strength and sealing of the weld. Second, the relatively lower outer temperature prevents the outer layer 11 from being overheated or flowing during the first fusion, preserving a more regular and smoother initial morphology. This creates more ideal conditions for the subsequent "selective secondary melting" finishing of the outer layer material in step S3, making it easier to achieve a perfect smooth appearance.

[0049] The advantage of this step is that, through the dual-sided (especially independently temperature-controlled) heating design, the thermal field distribution can be flexibly optimized according to the material properties, ensuring the uniformity and reliability of the fusion of multi-layer heterogeneous materials and the connection with subsequent processes, thus laying a solid structural foundation for the entire gradient thermal fusion process.

[0050] Step S3: Second heating and smoothing.

[0051] After the initial weld is formed, a second heating process is performed to refine its appearance. This step can also be done at [other locations]. Figure 4 The same tube forming device 20 shown is used to complete the process, which is achieved by switching the working mode of the heating device 23.

[0052] Specifically, the second heating element 232 located inside the docking area is turned off, and only the first heating element 231 located on the outside is activated. The temperature of the first heating element 231 is precisely adjusted and maintained at a second temperature T2. The setting of the second temperature T2 must meet the core condition: higher than the melting point of the outer layer 11, but lower than the melting points of the barrier layer 13 and the inner layer 15. In some specific embodiments, the second temperature T2 is 115°C to 145°C; preferably, the second temperature T2 is 120°C to 135°C.

[0053] During operation, the outer side of the initial weld is locally heated using the first heating element 231. Since the second temperature T2 is precisely controlled within the aforementioned "process window", the heat mainly acts on the outer layer 11, causing it to be selectively melted a second time and begin to flow; while the inner layer 15 and the barrier layer 13 remain solid due to their higher melting points, and the internal structural strength and barrier function are not affected.

[0054] In other words, the core of this step is to induce "controlled selective melting and flow of the outer layer material." The molten outer layer 11 material flows and spreads under surface tension, completely covering and filling any microscopic interface traces, unevenness, or gloss differences left from step S2 (first heating and fusion). After cooling and solidification, a smooth, continuous, and visually invisible final seam (such as...) is formed on the outer surface of the tube body 100. Figure 1 The area shown in the dashed box is region a).

[0055] In one specific embodiment, the outer layer 11 is LLDPE (melting point approximately 120°C), and the inner layer 15 is HDPE (melting point approximately 135°C). The temperature of the first heating element 231 is adjusted to T2 = 128°C, and the outer side of the initial weld is momentarily heated for approximately 0.5 seconds. This temperature is higher than the melting point of LLDPE, ensuring its full melting and flow; at the same time, it is lower than the melting point of HDPE, effectively protecting the inner layer structure. This process yields a pipe body 100 with a perfect appearance. Figure 6 As shown, after step S3, the seam marks on the outer surface of the tube body 100 have completely disappeared, and the appearance is smooth and continuous.

[0056] This step, through precise unilateral temperature control, achieves "selective remelting" of the outer layer material, completely resolving the surface aesthetics issue without damaging the existing weld structure, thus ultimately achieving a completely seamless laminated pipe joint. (Comparison) Figure 5 (After step S2, the initial weld mark b) and Figure 6 (After step S3, the seam is not visible), which can intuitively demonstrate the significant effect of the "gradient heat fusion" two-step method of the present invention in solving the problem of seam appearance.

[0057] The above Example 1 illustrates the specific operation process and effects of the gradient thermal melting process under typical material combinations. To further illustrate the broad adaptability and operational flexibility of the process of the present invention within the parameter range defined in the claims, two sets of implementation examples for different material properties and performance requirements will be provided below. Example 2

[0058] This embodiment demonstrates that when an outer layer material with a low melting point and good fluidity is used, the process can operate efficiently in the lower limit of the recommended temperature range, making it suitable for products with requirements for production efficiency or heat sensitivity.

[0059] Step S1: Provide laminated sheets: the outer layer 11 is made of ultra-low density polyethylene (VLDPE) film with a melting point of about 110°C and an MFI of 8 g / 10 min; the barrier layer 13 is a PE / EVOH blend (EVOH content 4.5%); the inner layer 15 is made of high melt flow rate HDPE film with a melting point of about 132°C and an MFI of 25 g / 10 min.

[0060] Step S2, First Heating and Fusion: The mating area is heated to a first temperature T1 = 175℃. At this temperature, all layers of material can fully melt. Double-sided heating is used, with a heating time of approximately 1.5 seconds, to form the initial weld.

[0061] Step S3, Second Heating and Smoothing: Adjust the outer heating temperature to the second temperature T2 = 118℃. This temperature is higher than the melting point of the outer VLDPE layer (110℃), but significantly lower than the melting point of the inner HDPE layer (132℃). Heating the outer side of the initial weld for about 0.8 seconds causes selective melting and flow of the VLDPE surface layer, completing the smoothing process.

[0062] The feature of this embodiment is that, by utilizing the low melting point and good fluidity of VLDPE, the gradient hot melting process can be efficiently completed near the lower limit of the recommended temperature range (T1=175℃, T2=118℃), which has the advantages of low energy consumption, small heat input and short production cycle. Example 3

[0063] This embodiment demonstrates that when a product requires higher structural strength and the inner layer uses a high melting point material, the gradient hot melt process can be precisely operated in the upper limit of the recommended temperature range.

[0064] Step S1: Provide laminated sheets: the outer layer 11 is made of LDPE film with a melting point of about 118°C and an MFI of 2.0 g / 10 min; the barrier layer 13 is a PE / EVOH blend (EVOH accounts for 4%); the inner layer 15 is made of high-rigidity HDPE film with a melting point of about 136°C and an MFI of 0.5 g / 10 min.

[0065] Step S2, First Heating and Fusion: To ensure sufficient fusion of the high-melting-point inner layer (136℃) and optimize the heat field distribution, this step adopts a dual-sided differential heating mode. Specifically, the first temperature T1 is controlled as a temperature gradient: the temperature of the inner second heating element 232 is set to 225℃, and the temperature of the outer first heating element 231 is set to 220℃, with a heating time of approximately 2.5 seconds, to obtain a deep fusion and an initial weld with extremely high strength.

[0066] Step S3, Second Heating Smoothing: Precisely adjust the outer heating temperature to T2 = 132℃. This temperature is higher than the melting point of the outer LDPE layer (118℃), but strictly lower than the melting point of the inner high-melting-point HDPE layer (136℃). Perform a brief (approximately 0.3 seconds) precise heating on the outer side of the weld, allowing the LDPE surface to just melt and flow, while ensuring that the inner structure remains completely unaffected.

[0067] The feature of this embodiment is that by setting a high first temperature gradient T1 (225°C / 220°C), the ultimate strength of the overall weld is guaranteed, while the second temperature T2 (132°C) achieves precise "selective melting" within an extremely narrow process window (only 14°C above the outer melting point), which reflects the precision of process control.

[0068] Examples 2 and 3 demonstrate that the gradient hot-melt process provided by the present invention has a wide operating window and good material adaptability within the temperature and material parameter range defined in the claims. It can flexibly adjust the temperature parameters according to the strength, appearance and production efficiency requirements of different products, and can achieve a seamless effect for the seams. Example 4

[0069] Based on the basic gradient hot-melt process provided in Example 1 (or Example 2 or 3), in order to further eliminate the reflective "light seam" phenomenon caused by the slight differences in micromorphology or crystal state between the joint area a and the tube body under a specific illumination angle, and to obtain the ultimate visual uniformity, this example provides an optional optimization step: laser texturing processing (S4).

[0070] Step S4 involves precision laser processing of the final, macroscopically smooth outer surface of the joint, which has been processed in step S3, in order to actively control its optical properties by changing the surface microstructure.

[0071] In practice, a nanosecond pulsed fiber laser can be used in conjunction with a galvanometer scanning system. The processing parameters of the laser equipment are as follows: laser power of 10W-100W, pulse frequency of 20kHz-500kHz, and scanning speed of 100mm / s-2000mm / s.

[0072] A preferred combination of processing parameters is as follows: laser power 30W, pulse frequency 100kHz, scanning speed 1000mm / s, and spot diameter approximately 50μm. Under these parameters, micron-level textures with a depth of approximately 5-20μm can be formed on the joint surface.

[0073] The core mechanism of this treatment is to introduce controllable microscopic optical structures into the seam area 'a' through laser processing. These microstructures effectively scatter incident light, thereby significantly reducing the specular reflectivity (gloss) of this area. Actual measurements show that the 60° gloss (GU) of the laser-treated area can be reduced by more than 30% compared to the adjacent untreated tube body area.

[0074] As a result, the optical characteristics (including gloss and reflectivity) of the seam area a can be adjusted to achieve a high degree of matching with the main body printing area of ​​the tube that has been matte-finished or has a specific texture. This completely eliminates the visual presence of the seam from an optical perception perspective, ensuring a 360° uninterrupted full-width printing effect even under demanding lighting conditions, meeting the aesthetic requirements of the highest-end products.

[0075] The tube body 100 prepared by any one of the methods in Examples 1 to 4 above has seamless seams and excellent overall strength and visual effect. The tube body 100 can be further assembled with components such as tube shoulders, tube caps, and tube nozzles through conventional secondary processing processes such as injection molding and capping to finally produce a finished laminated tube.

[0076] The detailed descriptions listed above are merely specific descriptions of feasible embodiments of the present invention, and are not intended to limit the scope of protection of the present invention. All equivalent embodiments or modifications made without departing from the spirit of the present invention should be included within the scope of protection of the present invention.

[0077] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0078] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for seamless fabrication of laminated tubes based on gradient thermal melting, characterized in that, Includes the following steps: S1. Providing raw materials: Providing laminated sheets, which include at least an outer layer, a barrier layer, and an inner layer. The melting point of the outer layer is lower than that of the inner layer. The outer layer includes at least one of low-density polyethylene, linear low-density polyethylene, or ultra-low-density polyethylene, with a melting point of 105°C-125°C and a melt flow index of 0.5-50 g / 10 min. The inner layer is high-density polyethylene, with a melt flow index of 0.1-50 g / 10 min. The barrier layer is a blend of polyethylene and ethylene-vinyl alcohol copolymer, and the mass percentage of the ethylene-vinyl alcohol copolymer in the barrier layer is not greater than 5% of the total mass of the laminated tube. S2, First heating and fusion: The longitudinal edges of the laminated sheets are butted together, and the butt joint area is heated at a first temperature T1, so that the materials of each layer, including the outer layer, barrier layer and inner layer, are fused together at the butt joint to form an initial weld with structural strength; before butting the longitudinal edges of the laminated sheets, the longitudinal edges are beveled at an angle of 30°-90°; the butt joint area is heated by a double-sided heating method; the temperature of the double-sided heating is independently controlled, and the heating temperature on the side closer to the inner layer is not lower than the heating temperature on the side closer to the outer layer; S3. Second heating and smoothing: The outer side of the initial weld is locally heated on one side at a second temperature T2, wherein the second temperature T2 is higher than the melting point of the outer layer and lower than the melting points of the barrier layer and the inner layer, so that the outer layer material at the initial weld is selectively melted and flowed a second time, thereby forming a final joint with a smooth outer surface and invisible to the eye. The first temperature T1 is 170°C-230°C, and the second temperature T2 is 115°C-145°C.

2. The seamless fabrication method for laminated tubes based on gradient thermal melting according to claim 1, characterized in that, Steps S2 and S3 are completed at the same forming station; wherein, by controlling the working state of the heating devices located inside and outside the docking area, the double-sided heating and the single-sided local heating are respectively achieved.

3. The seamless fabrication method for laminated tubes based on gradient thermal melting according to claim 1, characterized in that, In step S2, the angle of the beveling is 45°-60°.

4. The seamless fabrication method for laminated tubes based on gradient thermal melting according to claim 1, characterized in that, The first temperature T1 is 180°C-210°C, and the second temperature T2 is 120°C-135°C.

5. The seamless fabrication method for laminated tubes based on gradient thermal melting according to claim 1, characterized in that, The barrier layer is made by co-extruding and stretching a polyethylene-ethylene-vinyl alcohol copolymer.

6. The seamless fabrication method for laminated tubes based on gradient thermal melting according to claim 1, characterized in that, Following step S3, the following is also included: S4. Laser texturing: The outer surface of the final seam is subjected to laser texturing to form a micron-level texture in the area, thereby reducing the specular reflectivity of the area.

7. A laminated pipe, characterized in that, Its tube body is made by any one of the gradient thermal fusion-based seamless lamination tube preparation methods according to any one of claims 1 to 6.

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