UTILIZING THE CLEARWELD TM PROCESS FOR MEDICAL APPLICATIONS

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1 UTILIZING THE CLEARWELD TM PROCESS FOR MEDICAL APPLICATIONS Michelle Burrell, Nicole Woosman GENTEX Corporation, Carbondale, PA , USA Abstract The Clearweld TM process is a through-transmission laser welding technique which allows for a wide range of colored or water-white plastics to be joined. In order to obtain a water-white joint, a laser absorbing agent is applied only at the interface of the faying surfaces. Colored plastics can be joined in this manner or by compounding the absorbing agent into the resin used to form the lower substrate. The Clearweld process has the same advantages as other through-transmission laser welding process, such as the process does not generate particulates, and the parts are not vibrated, therefore sensitive features are not damaged. The Clearweld process has the added benefits of welding multiple layers simultaneously, welding entire tube circumferences simultaneously, and avoiding the need for carbon black. Due to the appealing aspects, the Clearweld process can be used in a wide variety of medical applications including IV bags, IV ports, filters, connectors, microfluidics, etc. The Clearweld coating passed cytotoxicity and USP Class VI tests. The additives for Clearweld resins have been shown to be non-toxic through cytotoxicity testing. Introduction Through-Transmission Laser Welding Substrate Material Similar to other welding processes, TTLW melts two substrates together to form a weld. Therefore, the substrate materials must be able to melt. Thermoplastics polymers melt and solidify with minimal polymer degradation, as a result, thermoplastics can be welded. Thermoset plastics decompose upon heating, therefore are not weldable. The second material requirement is the top substrate must transmit the laser energy. Plastics that are transmissive to the laser are not restricted to water-white plastics. Many opaque and colored plastics transmit sufficient laser energy needed for welding. For example, nylon, polyethylene, and polypropylene have been successfully welded. Inorganic pigments and fillers, such as glass fibers and talc, reduce the transmission and should be minimized. Semi-crystalline plastics or substrate containing fillers or pigments scatter the laser energy; therefore, the thickness of the top substrate is limited. Laser Absorbing Additive The Clearweld TM process [1] was developed to enable through-transmission laser welding of water-white or a wide variety of colored plastics. Through-transmission laser welding (TTLW) is based on the principal that polymers, in their natural state, transmit electromagnetic energy in the near-infrared region. (Although some polymers enable laser welding in the visible region [2], this paper focuses on near-infrared wavelengths.) The laser energy must pass through the top substrate. A laser absorbing additive is placed between the faying surfaces or is dispersed/dissolved throughout the resin used to form the lower substrate. The laser energy transmits through the top substrate and is absorbed at the weld interface. The absorbing additive converts the laser energy into heat and melts the two substrates together. There are four components that enable TTLW: 1. Substrate material 2. Laser absorbing additive 3. Laser source 4. Clamping pressure In traditional through-transmission laser welding, carbon black is used as the absorbing additive. Carbon is typically dispersed throughout the lower substrate. Utilizing carbon black limits the variety of colors, and the substrate is generally opaque. Opaque and especially black plastics are unacceptable for many medical applications. The Clearweld process uses organic laser absorbing additives to generate heat for welding. The organic additives allow for a water-white weld to be generated and also expand the number of colors from which to select. The Clearweld additives are available in two product forms. The first form is a coating that is applied to the surface of one of the substrates. The second form is a resin containing the additive used as the lower substrate. The coatings and resins are be discussed below in more detail. Clearweld TM Coating

2 Clearweld coatings are a solution of laser absorbing additives and solvents. The additives are targeted for laser wavelengths from 940nm to 1064nm. The additive is dissolved in solvents because the additive is insoluble in water. The coatings have a low viscosity similar to water. The coatings are available in three solvent systems: ethanol-based, acetone-based, and MEK-based. The coating is selected according to the customer s, for example substrate material, drying rate, welding speed, and color. A number of methods including spray, dip, and liquid dispensing can be used to apply the coating. Spraying allows the coating to be applied over large surface areas. Dipping the part into the coating is another possibility, but is not highly recommended due to the fast evaporation of the solvents used in the coatings. Liquid dispensing is used to precisely apply the coating to specific areas that are to be welded. The needle tip valve EFD 740v-ss, has been thoroughly evaluated for applying the coating. Microsolenoid valves, such as BioDot LD2500 BioJet Dispenser and PDI NanoDispense System are also recommended. The dispensing techniques apply the coating on to one of the faying surfaces. The solvent evaporates prior to assembling the part. The evaporation rate is fast, but may be aided by heating with an external heat source, such as a heat lamp. The amount of solvent used in the process is very low, therefore does not create a significant safety issue. The only recommendation is to use localized air exhaust to dissipate the odor. After the solvent evaporates, the part may be welded immediately or stored for future use up to 6 months under proper storage conditions. The welding process entails exposing the coating to the laser energy for a short period of time. Weld cycles less than 1 second are possible. The laser energy is absorbed only at the weld interface since the coating is at the surface. Upon absorbing the laser energy, the additive becomes colorless and is no longer absorptive. This enables water-white plastics to be joined. The coating may also be used to weld colored plastics. The limitation of using the coating is the additional step to apply the coating. Clearweld TM Resins The Clearweld laser absorbing additives are also available compounded into resins. The additives are dissolved or dispersed into the resin used to manufacture the lower substrate. The resins are available for absorbing laser wavelengths between 808nm and 1064nm. The resins are custom manufactured based on substrate material, laser wavelength, and color. Because the additives add color to the resin, the lower substrate can not be water-white; however colored dyes or pigments may be added to produce the desired color. Absorption of the laser energy does not affect the color of the substrate, in contrast to coatings where color is eliminated upon exposure. The advantage of compounding the laser absorbing additive into the resin is there is not need to for a secondary step to apply the additive. In addition to using the resin in the lower substrate, the resin may be extruded into a film. The film can be placed between the two substrates to be joined, or can be insert molded to the surface of one substrate. The film reduces the amount of additive used since the film is located only at the weld interface. There are several factors that considered when choosing between the coatings, resins or films. Table 2 shows a comparison between the carbon black, Clearweld coating, and Clearweld resins. Table 2 contains general guidelines for selecting a coating or a resin. Biocompatibility/Toxicity The by-products of the coating additives after welding were identified to ensure the products were not harmful. The by-products of the welding process includes two species. The first species is excess additive that was not used up in the welding process. The second species is a pre-cursor to the additive. The manufacturing of the additive begins with a material called the pre-cursor. The pre-cursor undergoes an oxidation reaction to form the absorbing additive. The additives used in the Clearweld resins, LWA195, LWA208, LWA290, and Clearweld coatings, LWA194 were submitted for cytotoxicity tests. The additives were submitted for testing as a powder. Because the additive was a powder, the concentration was significantly higher than required for welding. All of the laser additives were found to be non-toxic. The laser absorbing additive used in the Clearweld coatings, LWA194 was submitted USP Class VI tests. The samples included the additive prior to exposure to the laser and after exposure to the laser. The additive met all of the for USP Class VI. Table 3 summarizes the biocompatibility and cytotoxicity tests. The results and information about the Clearweld coatings have been submitted to the FDA as a Master File for Medical Devices. Laser Source The third requirement for TTLW is the laser energy. The wavelength of the laser must match that of the absorbing properties of the additive. For example, the Clearweld additives absorb in the nm range, therefore diode lasers (808nm, 940nm, 980nm, 1051nm) or Nd:YAG lasers (1064nm) are suitable for the Clearweld process. The laser power is based on the production

3 , specifically the weld speed. Higher laser power allows for faster welding. The laser beam can be directed on to the part by a number of techniques: 1. Single beam contour 2. Quasi-simultaneous - scanning beam 3. Curtain 4. Simultaneous When welding using a single beam, the laser hits the weld interface as a beam, or point. Moving the part under the beam or moving the beam across the part produces the weld. The part can be moved by a number of means, including a conveyor belt, x-y table, or rotary table. The laser can be moved by attaching it to a CNC router or a robotic arm. Quasi-simultaneous[3], or scanning beam also uses a single beam, however a series of mirrors attached to galvanometer motors deflects the beam to the appropriate shape. The beam is deflected very rapidly, which in effect welds the entire weld area almost simultaneously. The advantage of this system is the laser and welded part remain stationary. A curtain laser system uses a series of laser beams combined side by side, or one or more laser beams spread out by optics, to form a line (or curtain). The laser curtain or part is moved to expose the weld interface. When a curtain beam is used in traditional through transmission laser welding, a mask is required to weld only in specific areas. A mask is not needed when using Clearweld coatings since welding occurs only where the absorber is applied. Simultaneous systems [4] consist of a series of laser beams arranged in the shape of the part to be welded. There are no moving parts, and the entire weld interface is heated at one time. The advantage of simultaneous welding is collapse is uniform since the entire weld area melts at the same time. A comparison of the different configurations is shown in Table 4. Clamping Pressure The fourth requirement for TTLW is clamping pressure. Clamping pressure is required for many reasons: Provide intimate contact between the two surfaces to be welded, Transfer heat from one substrate to the other, Prevent separation of the substrates during the cooling phase. Contraction is not as much of an issue with the Clearweld coating since the amount of material melted is very small due to localized heating. clamping pressure must take into consideration the tolerance of the parts and the amount of collapse required. Medical Applications The Clearweld process has been proven to weld a large variety of polymers, for example, polycarbonate, polymethyl-methacrylate (PMMA), multi-polymer acrylics, MABS, PVC, Nylon, polypropylene, etc. The applications that would benefit from the Clearweld process are (but not limited to): Microfluidics Blood filters IV bags Connectors Syringes IV ports Medical packaging Ostomy products Test equipment housings/casings. The main reasons for using the Clearweld process over other technologies are: 1. No generation of particulates 2. Replace environmentally unsafe methods such as solvent bonding 3. Allow for alternative polymers to be used, for example, replace PVC with polypropylene 4. Fast cycle time, less than one second cycle time can be achieved 5. Water-white parts can be welded together 6. No vibration, sensitive features are not damaged 7. Wide variety of color options 8. Allow for unique designs that cannot be joined by other techniques. Conclusions The Clearweld process has the same benefits are traditional through-transmission laser welding, including no generation of particulates, no vibration, and fast cycle time. The range of Clearweld products offers welding of water-white to a variety of colored parts. Biocompatibility and cytotoxicity testing show the Clearweld coatings are appropriate for use in medical devices. The additives used in the Clearweld resins were shown to be non-toxic from cytotoxicity tests; therefore the resins have a high probability of passing biocompatibility tests. Clamping pressure was not covered in detail in this paper, however, clamping pressure is one of the most challenging aspects of TTLW. The fixture for applying the

4 References 1. Jones, I.A., Wise, R.J.: Welding Method, Patent WO 00/20157, 1 Oct Sallavanti, R.A., Frieder, III, L.P.: Visibly transparent dyes for through-transmission laser welding, US Patent 6,656,315, 2 Dec Potente, H., Fiegler, G., Becker, F., Korte, J., Comparative Investigations on Quasi-Simultaneous Welding on the Basis of the Materials PEEK and PC, ANTEC Society of Plastics Engineers Conference, Rooney, P., Plastic Laser Welding, ANTEC Society of Plastics Engineers Conference, Key Words Clearweld, laser welding, coatings, compounded resin, cytotoxicity, biocompatibility Table 1 Comparison of the use of Clearweld coatings, resin, and film. Requirement Carbon Clearweld Coating Clearweld Resin Additive Colorless x + x weld Highly x + + transparent part Biocompatible Processable in + N/A o most polymers Color o + + Flexibility Multiple layer x + x welding No secondary processing step allowed + x can achieve requirement o - limited success in achieving requirement x - cannot achieve requirement Table 2 Guidelines for selecting Clearweld coating versus Clearweld resin. Coating Large parts Clear or colored parts Production can tolerate a secondary dispensing step Small weld area Resin Small parts Parts that are colored (dye in bottom substrate) Production cannot tolerate a secondary dispensing step Large weld area

5 Table 3 Cytotoxicity and biocompatibility results. Test Clearweld Additive Results Cytotoxicty LWA194, LWA195, Non-toxic LWA208, LWA290 Systemic Toxicity LWA194* Intracutaneous LWA194* Muscle Implantation LWA194 * Only additive LWA194 was tested per USP ClassVI. The other additives will be tested in the future. Table 4 Comparison of the various laser beam delivery methods. Factor Single Beam Quasi-Simultaneous Curtain Simultaneous Weld Speed 2* 1 2* 1 1-fast, 3-slow Flexibility of welding various geometries 1-high, 3-none Welding of 3-D shapes 1-possible, 2- limited, 3-not possible Efficiency high, 3-low Maximum part size Depends on size of equipment 500mm x 500mm with a 10mm beam Large parts possible but may be cost prohibited. *speed limited by motion equipment Multiple laser heads, mirrors, or robotics can be used to weld large areas and 3-dimensional parts. large portion a beam is not used at any given time Large parts possible but may be cost prohibited.