Laser processing of the hottest polyether block am

2022-07-30
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Laser processing of polyether block amide pipe fittings

polyether block amide (PEBA), also known as PEBAX, is a thermoplastic elastomer that can be used in medical catheters. It has the advantages of both thermoplastic materials and rubber elastic materials. The thermoplastic property of PEBA means that it is easier to process, extrude and form at high temperature, and the elasticity makes it recover its original length or shape after cooling after stretching, compression or deformation

peba has outstanding performance among similar thermoplastic elastomers due to its light weight, flexibility and hardness, higher energy return rate, better fatigue resistance and better dimensional stability under physical and thermal stress (see Table 1). The material has strong resistance to various chemicals and is not easy to be corroded by salt or sulfuric acid. It meets the requirements of USP class VI certification and can be sterilized by various methods, including gamma radiation, high-pressure steam and ethylene oxide

tube extruders and catheter manufacturers in the medical device industry report that PEBA is a model material in many ways. It has a wide thermal working range, and its melting point ranges from 134 ° C to 174 ° C depending on the hardness. PEBA can be coextruded with thermoplastic polyurethane, enabling designers to manufacture composite pipe fittings. PEBA is easily combined with other materials by heating or epoxide. This characteristic makes PEBA an ideal axial material for composite balloon catheter

peba's stiffness range, stable density under various hardness, and the characteristics of the CPC Central Committee and the State Council that adhere to the "two never wavers" and are easy to melt processing also make it the first material for manufacturing multi hardness conduit shafts composed of molten PEBA components. The catheter with this design provides excellent propulsion and torque through the high hardness proximal part, and flexible handling in the low hardness distal part. In order to better transfer the torque on the shaft to the end, stainless steel webbing is usually used for reinforcement

advantages of laser processing

many conduit designs require machining features such as holes and grooves, sometimes grooves and cones. Mechanical methods such as drilling, grinding, and scraping can be used to achieve these properties, but may leave burrs on the edges of the features and may impose unwanted heat and stress on the conduit material. In addition, the stainless steel webbing on the conduit wall may hinder the contact machining method using a drill or blade. It is widely used in many industries to use laser energy for non-contact catheter processing, which can remove the polymer material from the embedded webbing without applying stress or heat, so it becomes an attractive alternative method (Figures 1 and 2). In addition, if necessary, specific forms of laser energy can also cut off the polymer and braid at the same time

FIGURE 2: Laser marking PEBA catheters embeds product data and creates permanent traceability.

process

the laser energy is highly coherent, that is, the laser only emits energy at a specific wavelength. The laser energy is also highly oriented, which means that the photons of the laser beam are closely clustered and transmitted in parallel. This characteristic enables the energy of the laser beam to be controlled (shadowing, focusing and changing direction) through the optical fiber or lens and mirror beam transmission system

in the laser processing process, laser ablation is to match the absorption characteristics of the material with the appropriate laser wavelength, and then apply the selected wavelength to the specific material with the correct energy density and time, so as to vaporize the material. When the process variables such as power, pulse, focal length and duration are properly set, the laser energy can destroy the molecular bonds of the material and cause the evaporation of the material. Real laser ablation does not rely on heat to melt or burn materials, so laser ablation has the characteristics of cleaning and finishing, and will not produce thermal effect on the surrounding area

peba is a kind of UV sensitive material, which is easy to degrade after UV radiation. When designing the laser ablation process for PEBA, the above material characteristics should be considered first. The wavelength range of UV spectrum is from near ultraviolet light (400 nm) close to purple to extreme ultraviolet light (10 nm) close to X-ray. The UV wavelength emitted by commercial laser ranges from 355 nm of the third generation nd:yag solid-state laser to 157 nm of fluorine gas excimer laser. Due to the poor ablation effect of PEBA under long wavelength UV radiation, the shorter the actual UV wavelength is, the better

the pursuit of short UV wavelengths usually leads laser processors to use the 193 nm wavelength of argon fluorine excimer lasers. But this choice is not without challenges. The wavelength of 193nm belongs to the vacuum ultraviolet band of the energy spectrum and can be rapidly absorbed by oxygen in the air. Therefore, laser ablation with 193 nm wavelength UV must be carried out in vacuum or inert oxygen free environment

despite the above infrastructure challenges, the argon fluorine excimer laser wavelength and the laser beam size generated by all excimer laser wavelengths are attractive. The original excimer laser Chinese enterprises have the talent to produce by themselves and found that their own plastic extrusion mechanical beam is up to 12 mm high × 24 mm wide. After shadowing and focusing, the original beam can still form a large working beam, enabling the laser processor to apply higher-order energy with a width of more than 2.5 mm in the workplace, and remove a large number of PEBA materials in a relatively short time. For example, 0.084 mm3 of PEBA material can be removed every minute, which is equivalent to removing 100 mm long and 0.051 mm deep materials every minute. Increasing the laser pulse rate can further accelerate the batch cutting process

Table 1: characteristics of PEBA (source: Arkema)

this may be the biggest advantage that laser processing brings to PEBA catheter manufacturers. Laser processing can cut off a large section of PEBA on the catheter shaft to form a small diameter area, which is the best bonding position for low hardness PEBA. It is conceivable that compared with the manufacturing method of fusing PEBA discrete parts with inner shaft and heat shrinkable shell, this method is easier to convert single hardness extrudate into multi hardness shaft, thus simplifying the tube manufacturing process

precision and efficiency

peba is an ideal conduit material due to its quality. Its compatibility with laser processing further makes it a material suitable for medical device applications. This method can avoid the common superfluous defects in machining, and can efficiently and accurately cut a large number of materials to obtain specific conduit parts

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