Dip-coating equipment and dip-coating method for PI (Polyimide) conduit

Abstract

The invention discloses dip-coating equipment and a dip-coating method for a PI guide pipe, and relates to the field of forming equipment of plastic pipes, the dip-coating equipment and the dip-coating method for the PI guide pipe are characterized in that the dip-coating equipment comprises a plurality of dip-coating diameter control molds, a drying device and a rolling device which are horizontally arranged in sequence, a base material sequentially penetrates through all units along a vertical path, and high-precision construction of a multi-layer PI coating is achieved. The rolling device is arranged between the adjacent dip-coating diameter control dies, a flexible heat-resisting roller is matched with a heat auxiliary device, physical compaction and heat activation treatment are conducted on the preliminarily dried PAA layer after each layer is coated, residual gas and solvent are effectively extruded out, the interface bonding area and the molecular nesting depth are increased, the interlayer adhesive force is enhanced, and the layering problem is restrained; and the PI guide pipe with the wall thickness of 0.01 mm or below can be efficiently prepared at low cost.

Description

Technical Field

[0001] The invention relates to the field of plastic pipe molding equipment, and in particular to a PI catheter dip coating equipment and a dip coating method. Background Art

[0002] Medical polyimide (PI) catheters are widely used in high-precision medical scenarios such as in vivo delivery, sampling, and minimally invasive operations due to their excellent thermal stability, chemical inertness, mechanical strength, and dimensional stability.

[0003] There are various methods for forming PI tubes, and common technologies include: A. Extrusion method: The PI raw material used is thermoplastic PI, which has poor temperature resistance, generally only below 300°C, and cannot meet the use requirements under higher temperature resistance; B. The winding method is prone to gaps in the production of PI tubes, which cannot meet the air tightness requirements; C. Dipping method, using a multi-layer coating-curing process; D. Compression molding is suitable for large pipes with a wall thickness of more than 1mm, but cannot meet the needs of thinner wall thickness.

[0004] The production of existing PI catheters mainly adopts a multi-layer coating-curing process, that is, by coating the PI emulsion on the substrate multiple times and performing high-temperature curing treatment after each coating, a tubular structure with target thickness and strength is formed layer by layer.

[0005] In the process of repeated coating and curing, since the interface between the coatings is mostly physically attached, microscopic defects such as delamination, shedding, interface bubbles, and weak bonding are prone to occur, which have an adverse effect on the mechanical integrity, radial strength, and air tightness of the catheter. In addition, the traditional method of repeated coating and curing is not sufficient to produce PI tubes with a wall thickness of less than 0.01 mm due to the difficulty of delamination control. Summary of the invention

[0006] The purpose of the present invention is to provide a dip-coating device for PI catheters, a rolling device with flexible pressing and heating functions, which for the first time uses micro-pressure shaping, heat activation and interface compaction to improve the adhesion and density between coating layers, which not only effectively suppresses traditional process problems such as delamination and interface detachment, but also significantly improves the dimensional consistency and mechanical stability of catheter products.

[0007] The above technical objectives of the present invention are achieved through the following technical solutions: A PI catheter dip coating device comprises a plurality of dip coating diameter control dies arranged in sequence in a horizontal direction, the dip coating diameter control dies are suitable for a substrate used for the PI catheter to pass through, the substrate passes through the dip coating diameter control dies so that a PI solution is attached to the surface, and further comprises a drying device and a rolling device, wherein the dip coating diameter control dies, the drying device and the rolling device are arranged in sequence; the rolling device comprises: A mounting structure, which is mounted between two adjacent dip-coating diameter-controlling dies and aligned with a vertical movement path of the substrate; At least one pair of pressing rollers arranged opposite to each other, used to clamp the surface of the substrate and apply radial rolling force, wherein the pressing rollers are made of a flexible heat-resistant material; A radial movement mechanism, used to act on the pressing rollers, suitable for adjusting the pressing force between the pressing rollers; The heating device is arranged inside the pressing roller and is suitable for heating the pressing roller to a set temperature.

[0008] Further configuration: the rolling device also includes a quick release structure, including: The movable roller bracket is used to support the pressing roller on one side and allow it to swing outward in a non-pressing state; The driver is used to quickly release the pressed state between the rollers and restore the movable roller bracket to the original pressed position after the unlocking operation is completed.

[0009] Further configuration: also includes an intermediate layer pretreatment module, the intermediate layer pretreatment module is arranged downstream of the rolling device and between two adjacent dip coating diameter control molds; the intermediate layer pretreatment module includes a plasma activation device arranged around the substrate movement path and a microwave preheating device arranged downstream of the plasma activation device, the microwave preheating device includes a microwave radiation source and an annular heating cavity, and the substrate passes through the annular heating cavity during movement.

[0010] Further configuration: the die hole of each dip coating diameter control die is composed of a plurality of gradient sections, and the inside of the die hole along the moving direction of the substrate includes: The guide section is a rounded cone structure, which is used to guide the PI emulsion to enter the die hole stably; The shear section is a straight pipe section used to apply stable shear to the PI emulsion to form a uniform liquid film; The sizing section expands toward the outlet side and is used to control the outer diameter of the coating and alleviate the disturbance of the flow field outlet.

[0011] It is further provided that the inner wall surface of the die hole of each dip-coating diameter-controlling die is provided with a fluoride anti-stick coating.

[0012] Further configuration: it also includes a solution tank for coating, and the substrate is moved in a vertical direction by a driving device and vertically passes through the solution tank so that the PI solution infiltrates the surface of the substrate.

[0013] It is further arranged that the PI solution is a PAA precursor solution, and the PAA precursor solution is obtained by polycondensation reaction of aromatic dibasic anhydride and aromatic diamine in a polar solvent.

[0014] It is further configured that the dibasic anhydride includes pyrophthalic anhydride (PMDA), the diamine includes oxydiphenylamine (ODA), and the polar solvent includes NMP or DMF.

[0015] Further configuration: also includes a thermal imidization curing device, located at the end of the dipping device; the thermal imidization curing device includes: an enclosed heated chamber for containing the multi-layer coated substrate; An inert gas input system is used to introduce inert gas into the closed heating chamber; The multi-stage temperature-controlled heating unit has multiple independently temperature-controlled heating zones to achieve staged temperature rise and curing.

[0016] Another object of the present invention is to provide a dip coating method for a PI catheter, comprising the following steps: S1: Substrate pretreatment Choose stainless steel wire as the base material; Remove impurities from the substrate surface by ultrasonic cleaning, plasma treatment or chemical cleaning.

[0017] S2: Preparation of PAA precursor solution Adding dibasic anhydride (PMDA) and diamine (ODA) in a proportion into a polar solvent (NMP or DMF) for polycondensation reaction to obtain a PAA precursor solution; S3: Dipping and initial drying The substrate was vertically immersed in the PAA precursor solution for a certain time to ensure sufficient surface wetting; The substrate is pulled up at a speed of 1–10 mm / s to form a continuous liquid film on the surface; Low-temperature drying is performed at 60-100° C. to evaporate the solvent and obtain a preliminarily cured PAA layer; S4: Rolling treatment The dried substrate is passed through a pair of soft heat-resistant rollers arranged opposite to each other for radial pressing; S5: Intermediate layer preprocessing The substrate is treated with plasma activation; Then it enters the microwave preheating device for non-contact heating, so that the surface temperature reaches 60-120°C, which helps the next layer of coating to bond; S6: Repeat coating Repeating steps S3 to S5 to increase the coating thickness by multiple coatings until the target thickness is reached; S7: Thermal imidization curing placing the coated substrate into a hot imidization furnace; Under the protection of inert atmosphere, heat to 80℃, 150℃, 250℃, and 300℃ in a step-by-step procedure; Promoting the PAA precursor solution to undergo a dehydration ring-closing reaction and ultimately converting it into polyimide (PI); S8: Post-processing After cooling, the substrate was removed to obtain an independent PI conduit.

[0018] In summary, the present invention has the following beneficial effects: First, in the present invention, radial pressure is applied to the surface of the PI catheter by a flexible pressing roller after each layer is coated, so that the PAA solid layer formed just after drying is physically compacted and micro-deformed while still in a "low cross-linking" state, which squeezes out the residual gas and solvent on the interface, increases the real contact area between the new and old interfaces, improves the nesting depth of the molecular chain, and provides a smooth, gap-free attachment surface for the infiltration of the next layer of PI emulsion, enhances the interlayer bonding force, and inhibits stratification. In the process of multi-layer PI catheter coating, flexible micro-pressure and heat-assisted rolling are introduced. Heat-assisted rolling can activate the reactive groups (carboxyl groups, anhydride groups) on the surface of PAA and soften the surface structure. On this basis, the next layer of PAA solution is prone to interface penetration and chemical intercalation reaction, which improves the control accuracy of "micron-level stratification" and produces PI tubes with a wall thickness of less than 0.01 mm at a lower cost.

[0019] Second, in the present invention, after the PI emulsion coating is initially dried, the PAA layer is prone to surface "wrinkles" or "thick edges" due to shrinkage or gravity; roller pressing can flatten the coating film as a whole on a micrometer scale; the starting base surface of each coating can be calibrated, which is helpful for thickness control and concentricity correction during the multi-layer construction process. In addition, the coating after initial drying has a certain degree of brittleness and is prone to internal stress. The roller pressing releases the coating structure through slight stress release, and the heat-assisted roller increases the temperature on the contact surface, which is helpful for the slippage and stress rearrangement of the PAA molecular chain, reducing the risk of microcracks in the subsequent thermal imidization process.

[0020] Third, in the present invention, a quick release structure is introduced into the rolling device, which realizes the quick loosening and self-recovery of the pressing unit before operation, during abnormality, and during maintenance, which not only greatly improves production efficiency and reduces downtime, but also improves the safety and flexibility of equipment operation.

[0021] Fourth, in the present invention, the intermediate layer pretreatment module is provided downstream of the rolling device; first, the surface polarity and functional group density of the PI layer are improved by plasma activation, and the plasma will introduce -OH, -COOH, -NH 2Isopolar groups significantly improve the wettability and chemical affinity of PAA emulsion when attached to the upper layer. Secondly, microwave preheating realizes non-contact surface molecular activation and heat flow rearrangement. Microwaves have heating and activation effects on the vibration of residual solvents and chain segments in the PAA layer, which can improve the flexibility and fluidity of the surface chain segments, making it easier to cross-link and intercalate with the next layer. The combination of plasma and microwaves: it not only provides surface "attachment points", but also improves the "dynamic activity" of the surface chain segments; on this basis, the next layer of PAA coating will have stronger interface extensibility and intercalation reactivity, thereby achieving "quasi-chemical fusion" rather than simple "physical attachment". The micron-level multi-layer structure has extremely high requirements for the uniformity and interface integrity of each layer of coating; the introduction of plasma + microwave joint pretreatment module helps to solve the blind spots of traditional methods in "interface quality control", which is suitable for high-end manufacturing scenarios of small-diameter, thin-walled, and multi-layer fine catheters.

[0022] Fifth, in the present invention, the die hole of each dip coating diameter control die is composed of multiple gradient sections, and the guide section is a rounded cone structure. The rounded cone structure provides a smooth transition surface, and the PI emulsion can flow along the wall in a more stable manner when flowing into the die hole, reducing the "retention zone" and "shear mutation". The straight pipe section provides a channel with a constant cross-sectional area + fixed flow rate; the PI emulsion forms a symmetrical and stable shear band around the core shaft to prevent local thickening or vacancies. The sizing section that expands toward the outlet side can slowly release the internal pressure; reduce the "tensile stress" mutation at the outlet of the coating, and effectively alleviate the peeling tendency between the coating and the core shaft. The three-section sequential transition forms a complete "flow-shear-control" module.

[0023] Sixth, in the present invention, the PI solution is a PAA precursor solution. The PAA precursor can remain liquid at room temperature or medium temperature, and is suitable for dip coating. The polyamic acid generated by the polycondensation reaction has a linear structure and has good film-forming and adhesion properties; PMDA and ODA have strong rigidity and thermal stability, providing good film-forming support; NMP and DMF, as high-polarity solvents, can fully dissolve the reactants and stably disperse the nano-scale fillers. The PAA structure formed by PMDA and ODA is highly symmetrical and unbranched, and has a dense and regular molecular arrangement after conversion to PI; after each overlay coating, the PAA layer that is not fully imidized continues to react under subsequent high-temperature curing, and "synchronous imidization" between layers can be achieved; structural continuity and mechanical uniformity between interfaces are ensured.

[0024] Seventh, in the present invention, the thermal imidization curing device at the end of the equipment can significantly reduce thermal oxidation reactions by closing the cavity and protecting it with inert gas; avoid exposure to air, which may cause oxidation and chain breakage of PAA or PI, resulting in yellowing of the film layer and performance degradation; the segmented temperature control heating path prevents microscopic stress cracking and improves the density between layers. The multi-layer PAA coating will produce structural stress during the heating process due to glass transition, solvent volatilization, and thermal expansion differences; avoid one-step high-temperature heating causing: film warping, local delamination, surface cracking, or bubble implosion. Multi-stage temperature control, such as the low temperature (80~120℃) section for slow drying and early volatilization; the medium temperature section (150~200℃) for imidization pre-reaction; the high temperature section (250~300℃) completes the cyclization reaction; control the heating rate, relieve gradient stress concentration, and ensure the consistency of the finished product. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic diagram of the structure of the dip coating equipment of the PI catheter; Figure 2 It is a schematic diagram of the structure of the dip coating diameter control die and the solution tank; Figure 3 It is a structural schematic diagram of a rolling device; Figure 4 It is a schematic diagram of the structure of the middle layer preprocessing module; Figure 5 It is a structural schematic diagram of the die hole of the dip coating diameter control die; Figure 6 It is a schematic diagram of the structure of a thermal imidization curing device.

[0026] In the figure, 100 is a dip coating diameter control die; 101 is a solution tank; 102 is a flow guide section; 103 is a shearing section; 104 is a sizing section; 200. Drying device; 300, rolling device; 301, mounting structure; 302, pressing roller; 303, radial moving mechanism; 304, movable roller bracket; 305, pivot; 306, quick release structure; 307, heating device; 308, driver; 400, intermediate layer pretreatment module; 401, plasma activation device; 402, annular heating cavity; 403, microwave preheating device; 500. thermal imidization curing device; 501. inert gas input system; 502. closed heating chamber; 600. Pretreatment device; 700. Rewinding and unwinding device. DETAILED DESCRIPTION

[0027] The present invention is further described in detail below in conjunction with the accompanying drawings.

[0028] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0029] A PI catheter dip coating device, such as Figure 1 and Figure 2 As shown, it includes a plurality of dip coating diameter controlling dies 100 arranged in sequence in the horizontal direction, and a drying device 200 and a rolling device 300 arranged downstream of the plurality of dip coating diameter controlling dies 100. The dip coating diameter controlling dies 100 are used for allowing the substrate used for the PI catheter to pass through in the vertical direction and for the surface of the substrate to adhere to the PI solution; the drying device 200 is arranged on the discharge path after each coating, and is used for drying the substrate adhered with the PI solution; the rolling device 300 is arranged downstream of the drying device 200, and is used for pressing and shaping the dried coating in the multi-layer coating process.

[0030] In this embodiment, the substrate is a stainless steel wire, and a reeling and unreeling mechanism is provided at the head and tail of the dip coating device to unreel or reel the substrate. Before entering the dip coating diameter control die 100, a pretreatment device 600 is provided to perform ultrasonic cleaning, plasma treatment or chemical cleaning on the surface of the stainless steel wire to effectively remove oil, particles and oxide layer on the surface of the substrate and improve the surface cleanliness.

[0031] like Figure 1 and Figure 3 As shown, the rolling device 300 includes a mounting structure 301, which is arranged between two adjacent dip coating diameter control molds 100 and is coaxially aligned with the vertical movement path of the substrate to support the entire rolling device 300; it further includes at least one pair of pressing rollers 302 arranged radially opposite to each other along the substrate, and the outer surface of the pressing roller 302 is made of a flexible heat-resistant material so that a clamp is formed on its surface when the substrate passes through and a uniform radial rolling force is applied; the pressing roller 302 can be relatively displaced in the radial direction through a radial moving mechanism 303 to accurately adjust the pressing force between the rollers; in addition, the rolling device 300 is also provided with a heating device 307, which is integrated in the internal structure of the pressing roller 302 and is connected to the heat conduction member of the pressing roller 302 to heat the pressing roller 302 to a preset temperature, thereby performing heat-assisted treatment on the coating during the pressing process.

[0032] In this embodiment, the radial moving mechanism 303 is a micro cylinder, and the pressure applied by the micro cylinder ranges from 5kPa to 30kPa. In this embodiment, the material of the pressing roller 302 is silicone, polyimide, fluororubber or other polymer materials with an elastic modulus between 0.5 and 5MPa and a temperature resistance of not less than 150°C. In this embodiment, the heating device 307 includes a thermally conductive ceramic insert or an embedded electric heating film, which is embedded in the pressing roller 302, and its temperature can be adjusted in the range of 40°C to 100°C.

[0033] On the basis of the above implementation manner, as a further limited implementation manner, Figure 3 As shown, a quick release structure 306 is further provided on the rolling device 300, and the quick release structure 306 is arranged adjacent to the radial moving mechanism 303 and located at the other side of the pressing roller 302. The quick release structure 306 includes: a movable roller bracket 304, which is connected to the mounting structure 301 through a pivot 305 and swings outward in the radial direction in a non-pressing state.

[0034] The quick release structure 306 also includes a driver 308, which is arranged on one side of the movable roller bracket 304 and is linked to the movable roller bracket 304 through a connecting piece, so as to quickly release the pressed state between the two rollers when needed; in this embodiment, the driver 308 can be a cylinder, which acts on the movable roller bracket 304 to push the movable roller bracket 304 to swing, thereby quickly pushing out or retracting the movable roller bracket 304. As an alternative embodiment, the driver 308 can also be a motor, which drives the movable roller bracket 304 to swing by rotating the pivot 305. As an alternative embodiment, the driver 308 can also be a manual release structure with a rotating pull rod.

[0035] On the basis of the above implementation manner, as a further limited implementation manner, Figure 1 and Figure 4 As shown, an intermediate layer pretreatment module 400 is also provided at the downstream position of the rolling device 300 and between two adjacent dip-coating diameter-controlling molds 100, which is used to perform interface activation and preheating treatment on the surface of the substrate after the previous layer is coated and dried and pressed, so as to improve the adhesion effect of the next layer of PI coating. The intermediate layer pretreatment module 400 is arranged along the vertical movement path of the substrate, and specifically includes: a plasma activation device 401 arranged around the movement path of the substrate, and the plasma activation device 401 forms an activation area covering the substrate through an annular or jet structure, which is used to improve its surface energy and enhance the interface bonding ability.

[0036] The intermediate layer pretreatment module 400 further includes a microwave preheating device 403 disposed downstream of the plasma activation device 401. The microwave preheating device 403 includes a microwave radiation source and an annular heating cavity 402 connected thereto. The annular heating cavity 402 is disposed around the substrate and is suitable for uniformly preheating the substrate in a non-contact manner so that its surface temperature reaches a set temperature zone. The substrate passes through the plasma activation area and the annular heating cavity 402 in sequence during the vertical movement, thereby completing the intermediate layer pretreatment process.

[0037] On the basis of the above implementation manner, as a further limited implementation manner, Figure 2 and Figure 5 As shown, the die hole of each dip coating diameter control die 100 is composed of a plurality of gradient sections arranged in sequence along the vertical movement direction of the substrate. Specifically, the inside of the die hole includes: a guide section 102, a shear section 103 and a sizing section 104 in sequence. Among them, the guide section 102 is located in the inlet area of ​​the die hole, and is a rounded cone structure, which is used to guide the PI emulsion to smoothly transition and stably enter the inside of the die hole; the shear section 103 is arranged immediately after the guide section 102, and is a straight pipe section structure of equal diameter, which is used to apply a stable shear force to the emulsion flow, thereby forming a uniform and continuous liquid film on the surface of the substrate; the sizing section 104 is arranged downstream of the shear section 103, and gradually expands toward the die hole outlet direction, presenting a micro-conical structure, which is used to accurately control the outer diameter of the coating, and plays a role in buffering disturbances and reducing fluid demolding stress during the derivation of the flow field. In addition, in order to further prevent the PI emulsion from remaining on the wall surface of the mold hole and avoid scaling or wall hanging, a layer of fluoride anti-stick coating is provided on the surface of the mold hole wall of each dip coating diameter control mold 100. The coating has a low surface energy and effectively improves the mold's pollution resistance and cleaning stability.

[0038] On the basis of the above implementation manner, as a further limited implementation manner, Figure 1 and Figure 2As shown, the dip coating equipment also includes a solution tank 101 for coating treatment, which is arranged in the upstream area of ​​the plurality of dip coating diameter control dies 100 and is suitable for containing PI solution for substrate dipping. The substrate is driven by the driving device to reciprocate in the vertical direction, and passes through the solution tank 101 vertically during the coating process, so that its surface is fully infiltrated with the PI solution, thereby forming a pre-coating liquid film on the surface, creating conditions for subsequent molding through the dip coating diameter control die 100. The PI solution is a precursor solution of polyimide (PI), that is, a polyamic acid (PAA) solution, and the PAA precursor solution is formed by polycondensation reaction of aromatic dianhydrides and aromatic diamines in a polar solvent. Preferably, the aromatic dianhydride includes pyrophthalic anhydride (PMDA), the aromatic diamine includes oxydiphenylamine (ODA), and the polar solvent is selected from N-methylpyrrolidone (NMP) or dimethylformamide (DMF). The PAA solution has good solubility, film-forming property and reactivity, and is suitable for being gradually converted into a polyimide coating as an intermediate in a multi-layer coating process.

[0039] On the basis of the above implementation manner, as a further limited implementation manner, Figure 1 and Figure 6 As shown, a thermal imidization curing device 500 is provided at the end of the dipping equipment for performing high-temperature heat treatment on the substrate after multi-layer coating, so as to promote the dehydration and cyclization of the polyamic acid (PAA) coating coated on the surface of the substrate into a polyimide (PI) structure, thereby obtaining the desired thermal stability and mechanical properties. The thermal imidization curing device 500 includes a closed heating chamber 502, which is arranged along the movement path of the substrate, for accommodating the coated substrate and providing a relatively closed heat treatment environment; the closed heating chamber 502 is connected to the inert gas source through an inert gas input system 501, which is used to continuously introduce inert gases such as nitrogen or argon into the closed heating chamber 502 to prevent oxidative degradation of the PAA material during the high-temperature reaction; the thermal imidization curing device 500 also includes a multi-stage temperature-controlled heating unit, which is arranged along the length direction of the heating chamber to form a plurality of independently temperature-controlled heating zones, each of which is set to a different temperature range, so as to achieve staged gradual temperature increase treatment, and control the entire process from low-temperature drying, medium-temperature pre-imidization to high-temperature complete imidization, effectively avoiding the occurrence of stress accumulation, blistering or cracking inside the coating.

[0040] The specific manufacturing method of the PI conduit dip coating device of the above embodiment is not limited. This embodiment also provides a PI conduit dip coating method, including the following steps: Step S1: substrate pretreatment.

[0041] Stainless steel wire is selected as the forming substrate of the catheter, preferably 304 stainless steel material with good flexibility and thermal stability. In order to ensure the adhesion and uniformity of the subsequent coating layer, the substrate surface is pretreated, and the pretreatment includes ultrasonic cleaning, plasma treatment or chemical cleaning in sequence or optionally to effectively remove oil, particles and oxide layer on the substrate surface and improve surface cleanliness.

[0042] Step S2: Preparation of PAA precursor solution.

[0043] Aromatic dianhydride (preferably PMDA) and aromatic diamine (preferably oxydiphenylamine (ODA)) are added in a molar ratio to a polar organic solvent for polycondensation reaction, wherein the polar solvent includes but is not limited to N-methylpyrrolidone (NMP) or dimethylformamide (DMF). The reaction conditions are controlled within the range of room temperature to 60°C, and the reaction time is several hours, to finally form a PAA (polyamic acid) precursor solution with a certain viscosity and fluidity, which is used for subsequent coating and film-forming operations.

[0044] Step S3: Dip coating and preliminary drying.

[0045] The pre-treated substrate is vertically immersed in the prepared PAA solution tank 101, and maintained for several seconds to tens of seconds to ensure that the surface is fully wetted, and then the substrate is slowly pulled up at a constant speed of 1-10 mm / s to form a continuous and uniform liquid film on its surface. The pulled substrate enters the preliminary drying area and is subjected to low-temperature drying treatment at a temperature of 60-100°C to evaporate most of the solvent and convert the PAA solution into a preliminary cured coating layer.

[0046] Step S4: rolling process.

[0047] The dried substrate is clamped and rolled in the radial direction by a pair of pressing rollers 302 arranged between the two upstream and downstream dip coating diameter control molds 100. The pressing rollers 302 are made of flexible heat-resistant materials, and can further compact the coating, release internal stress, and improve the surface flatness of the film layer during the rolling process, providing a stable foundation for subsequent multi-layer coating.

[0048] Step S5: Intermediate layer preprocessing.

[0049] The rolled substrate passes through the intermediate layer pretreatment module 400 in sequence, including plasma activation and microwave preheating processes. First, the substrate passes through the annular plasma area to activate the coating surface and introduce polar functional groups; then, the substrate enters the microwave preheating device 403, which includes a microwave radiation source and an annular heating cavity 402, and uniformly heats the coating film under non-contact conditions to increase its surface temperature to 60-120°C, thereby enhancing the wettability and bonding strength of the next coating layer.

[0050] Step S6: Repeat coating.

[0051] Repeat the above steps S3 to S5, i.e., perform multiple cycles of dipping, drying, rolling and intermediate treatment to build a PAA coating structure of target thickness in a multi-layer step-by-step manner. The thickness of each coating can be controlled within a few microns, and a dense multi-layer structure is formed by stacking.

[0052] Step S7: thermal imidization curing.

[0053] The substrate after multiple coatings is introduced into the thermal imidization curing device 500 for final curing. The device is protected by an inert atmosphere (such as nitrogen or argon) and is heated in stages according to a set temperature increase program. The temperature is raised to about 80°C, 150°C, 250°C and 300°C in sequence. Each stage is kept warm for a set time to achieve gradual dehydration and ring-closing reaction of the PAA coating, and finally complete the structural transformation from PAA to polyimide (PI).

[0054] Step S8: post-processing.

[0055] After thermal imidization, the catheter is naturally cooled or forcefully cooled to room temperature, and then the substrate is separated from the PI catheter by mechanical or chemical means to obtain a PI catheter with complete structure, uniform wall thickness and stable size, which is suitable for application requirements of high-precision medical delivery or interventional scenarios.

[0056] The above-mentioned embodiments are merely explanations of the present invention, and they are not limitations of the present invention. After reading this specification, those skilled in the art may make modifications to the embodiments without any creative contribution as needed. However, as long as they are within the scope of the claims of the present invention, they are protected by the patent law.

Claims

1. A PI catheter dip coating device, comprising a plurality of dip coating diameter control dies (100) arranged in sequence in a horizontal direction, the dip coating diameter control dies (100) being suitable for allowing a substrate used for the PI catheter to pass through, the substrate passing through the dip coating diameter control dies (100) so that a PI solution is attached to the surface, characterized in that: It also includes a drying device (200) and a rolling device (300), wherein the dip coating diameter-controlling mold (100), the drying device (200), and the rolling device (300) are arranged in sequence; the rolling device (300) includes: A mounting structure (301) is mounted between two adjacent dip-coating diameter-controlling dies (100) and aligned with a vertical movement path of the substrate; At least one pair of pressing rollers (302) arranged opposite to each other, used to clamp the surface of the substrate and apply radial rolling pressure, wherein the pressing rollers (302) are made of a flexible heat-resistant material; A radial movement mechanism (303) is used to act on the pressing roller (302) and is suitable for adjusting the pressing force between the rollers; The heating device (307) is arranged inside the pressing roller (302) and is suitable for heating the pressing roller (302) to a set temperature.

2. The PI catheter dip coating equipment according to claim 1, characterized in that: The rolling device (300) further comprises a quick release structure (306), comprising: A movable roller bracket (304) is used to support the pressing roller (302) on one side and allow it to swing outward in a non-pressing state; The driver (308) is used to quickly release the pressed state between the pressing rollers (302) and restore the movable roller bracket (304) to the original pressed position after the unlocking operation is completed.

3. The PI catheter dip coating device according to any one of claims 1-2, characterized in that: The invention also comprises an intermediate layer pretreatment module (400), wherein the intermediate layer pretreatment module (400) is arranged downstream of the rolling device (300) and between two adjacent dip coating diameter-controlling dies (100); the intermediate layer pretreatment module (400) comprises a plasma activation device (401) arranged around the movement path of the substrate and a microwave preheating device (403) arranged downstream of the plasma activation device (401); the microwave preheating device (403) comprises a microwave radiation source and an annular heating cavity (402), and the substrate passes through the annular heating cavity (402) during the movement process.

4. The PI catheter dip coating device according to any one of claims 1-2, characterized in that: The die hole of each dip coating diameter control die (100) is composed of a plurality of gradient sections, and the interior of the die hole includes the following in sequence along the moving direction of the substrate: The flow guide section (102) is a rounded cone structure and is used to guide the PI emulsion to stably enter the die hole; A shearing section (103), which is a straight pipe section and is used to apply stable shear to the PI emulsion to form a uniform liquid film; The sizing section (104) expands toward the outlet side and is used to control the outer diameter of the coating and alleviate the disturbance of the flow field outlet.

5. The PI catheter dip coating device according to claim 4, characterized in that: The inner wall surface of the die hole of each dip-coating diameter-controlling die (100) is provided with a fluoride anti-sticking coating.

6. The PI catheter dip coating device according to any one of claims 1-2 and 5, characterized in that: The invention also comprises a solution tank (101) for coating, and the substrate moves in a vertical direction and vertically passes through the solution tank (101) so that the PI solution infiltrates the surface of the substrate.

7. The PI catheter dip coating device according to claim 6, characterized in that: The PI solution is a PAA precursor solution, and the PAA precursor solution is obtained by polycondensation reaction of aromatic dibasic anhydride and aromatic diamine in a polar solvent.

8. The PI catheter dip coating device according to claim 7, characterized in that: The dibasic anhydride includes pyrophthalic anhydride (PMDA), the diamine includes oxydiphenylamine (ODA), and the polar solvent includes NMP or DMF.

9. The PI catheter dip coating device according to any one of claims 1-2 and 5, characterized in that: Also included is a thermal imidization curing device (500) located at the end of the dipping device; The thermal imidization curing device (500) comprises: A closed heating chamber (502) for accommodating a multi-layer coated substrate; An inert gas input system (501) for introducing an inert gas into the closed heating chamber (502); The multi-stage temperature-controlled heating unit has multiple independently temperature-controlled heating zones to achieve staged temperature rise and curing.

10. A dip coating method for a PI catheter, characterized in that: The steps include: S1: Substrate pretreatment Choose stainless steel wire as the base material; Remove impurities from the substrate surface by ultrasonic cleaning, plasma treatment or chemical cleaning; S2: Preparation of PAA precursor solution Adding dibasic anhydride (PMDA) and diamine (ODA) in a proportion into a polar solvent (NMP or DMF) for polycondensation reaction to obtain a PAA precursor solution; S3: Dipping and initial drying The substrate was vertically immersed in the PAA precursor solution for a certain time to ensure sufficient surface wetting; The substrate is pulled up at a speed of 1–10 mm / s to form a continuous liquid film on the surface; Low-temperature drying is performed at 60-100° C. to evaporate the solvent and obtain a preliminarily cured PAA layer; S4: Rolling treatment The dried substrate is passed through a pair of soft heat-resistant rollers arranged opposite to each other for radial pressing; S5: Intermediate layer preprocessing The substrate is treated with plasma activation; Then it enters the microwave preheating device (403) for non-contact heating, so that the surface temperature reaches 60-120°C, which helps the next layer of coating to bond; S6: Repeat coating Repeating steps S3 to S5 to increase the coating thickness by multiple coatings until the target thickness is reached; S7: Thermal imidization curing placing the coated substrate into a hot imidization furnace; Under the protection of inert atmosphere, heat to 80℃, 150℃, 250℃, and 300℃ in a step-by-step procedure; Promoting the PAA precursor solution to undergo a dehydration ring-closing reaction and ultimately converting it into polyimide (PI); S8: Post-processing After cooling, the substrate was removed to obtain an independent PI conduit.

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