Think of it as the modern form of alchemy that can be applied to plastic printing and bonding plastic to different materials.
Plasma treatment converts plastic parts into high-value products, such as pipes.
Improving durability, printability, flow control in microfluidics, and coating adhesion are critical to the safety, quality, and efficiency of plastic products. Injection and blow molders quickly realized that using plasma treatment can create a competitive advantage and transform specific parts into professionally engineered parts worth 100 to 1000 times.
Plasma is a state of matter—such as a solid, liquid, or gas—that is produced by the combination of energy and gas, which causes the gas to ionize. For example, injection molding machines and blow molding machines can control collective plasma elements (ions, electrons, and reactive species) to clean, activate, chemically graft, and deposit various chemicals on the material.
Plasma is now used to process everything from syringes to trucks and car bumpers. Plastic parts manufacturers are always looking for unique ways to gain technological advantages to become market leaders. In plastics, the most common plasma application is to improve the adhesion of chemical adhesives; this may involve combining metals and plastics, silica gel and glass, polymers and other polymers, biological components and polymer microtiter plates, or even Bonding with fluoropolymers (such as PTFE).
Plasma processing is used to solve difficult challenges when manufacturing parts for consumer products, automobiles, military, and medical equipment. Usually, this is related to the application of plastic materials with incompatibility issues. Plasma can change the surface properties of plastics to achieve goals that are not normally achieved without treatment. This may include cleaning surfaces, solving the difficulties of applying printing inks to plastics, improving the adhesion of plastics to different materials, and applying protective coatings that repel or attract fluids. When you treat plastic with plasma, it can turn a $2 item into a $50 product.
Let us look at some of the basic areas of plasma processing, including printing on plastics, microfluidic equipment, bonding plastics to dissimilar materials, processing plastic laboratory equipment, coating plastics to prevent leaching, and promoting research and development.
Plasma is now used to process everything from syringes to trucks and car bumpers.
When printing on plastics, it can sometimes be difficult to bond the ink to the surface. This happens when the printing beads are on the surface or do not adhere sufficiently to the surface. Higher printing durability may be required, including fade resistance under high temperature or repeated washing.
For many applications, plasma treatment is used to increase the surface energy of the material. Surface energy is defined as the sum of all intermolecular forces on a material, that is, the degree of attraction or repulsion exerted by the surface of the material on another material. When the substrate has high surface energy, it tends to attract. For this reason, adhesives and other liquids are usually easier to spread across the surface. This "wettability" promotes excellent adhesion using chemical adhesives.
For example, to solve the problem of beading, plasma treatment can make the surface hydrophilic (attracted by water). This treatment helps spread the ink on the surface, so it will not bead.
On the other hand, without first changing the surface to increase free energy, substrates with low surface energy (such as silicone or polytetrafluoroethylene) are difficult to adhere to other materials. If needed, silicones can also be used to create intermediate bonding surfaces with polar or dispersed surface energy to help printing inks adhere to plastic surfaces. This method can permanently print the logo on the surface of the bottle without fading after the first wash. Another application includes printing on plastics used in syringes, which are not easily bonded to human-friendly biodegradable inks.
Plasma can change the surface properties of plastics to achieve goals that are not usually achieved, such as promoting the permanent printing of logos on the surface of bottles.
Generally, microfluidic systems for medical or industrial applications use plastic channels to transport, mix, separate, or otherwise process small amounts of fluid, ranging in size from tens to hundreds of microns. Microfluidic devices usually have various pores containing different chemicals, mixed or kept separate. After the chemical passes through the channel, the flow in the channel must be maintained or any residual liquid in the channel must be prevented from flowing.
For microfluidics, plasma treatment is used to disperse the liquid on the surface to make it easy to flow through. Or, it can make the surface more hydrophobic (waterproof) to prevent fluids from gathering together in unintended areas. This minimizes the chance of sticking or staying when the fluid is "pushed away".
In this case, the plasma treatment of the plastic surface can promote the smooth and precise flow of the liquid in the narrow channel. This is not only essential for the safety of medical procedures, but also for the quality of industrial processes.
Like printing, adhesion promotion is achieved by increasing surface free energy. The net effect is a significant improvement in adhesion.
In the automotive industry, the use of plastics is being promoted to reduce the weight of vehicles and make them safer. However, getting plastic to adhere to metal, rubber, or even other types of plastic can sometimes be very difficult. When traditional chemical adhesives cannot adequately bond different types of materials, or if the company wants to reduce the amount of chemical waste generated, engineers usually turn to plasma treatment to solve complex bonding problems.
Although treating the plastic alone can improve adhesion, treating both materials at the same time can enhance adhesion by improving the wicking of the adhesive on the surface. Like printing, adhesion promotion is achieved by increasing surface free energy through a variety of mechanisms. This includes precision cleaning, chemical or physical modification of surfaces, roughening to increase surface area, and the use of primers. The net effect is a significant improvement in adhesion. In some cases, the bond strength can be increased by 50 times.
When traditional chemical adhesives cannot adequately bond different materials, or if the company wants to reduce the amount of chemical waste generated, engineers usually turn to plasma treatment to solve complex bonding problems.
Every year, billions of multiwell plates, pipettes, bottles, flasks, vials, Eppendorf tubes, culture plates and other polymer laboratory equipment are produced for research, drug discovery, and diagnostic testing. Although many are simple and cheap consumables, more and more people are now using gas plasma for surface treatment or with specially designed functional coatings to improve the quality of research and increase the complexity of diagnosis. One of the goals of surface modification is to improve the adhesion and proliferation of antibodies, proteins, cells and tissues.
Most laboratory ware plasma applications can be classified as "simple" treatments, such as oxygen or argon plasma used to clean substrates at the molecular level. The use of plasma is also well used for surface conditioning, making the polymer more hydrophobic or hydrophilic. Potential plasma treatment applications include coating PP or PS panels with alcohol or promoting protein binding to the surface. Before adsorbing biomolecules (proteins/antibodies, cells, carbohydrates, etc.) or biomimetic polymers, gas plasma can provide surface conditioning for in vitro diagnostic platforms.
Multiwell plates or microtiter plates are standard tools in analytical research and clinical diagnostic testing laboratories. The most common material used to make microtiter plates is PS because it is biologically inert, has excellent optical transparency, and is strong enough to withstand daily use. Most disposable cell culture dishes and plates are made of PS.
Other polymers such as PP and PC are also used in applications that must withstand a wide temperature range, such as polymerase chain reaction (PCR) for DNA amplification. However, untreated synthetic polymers are highly hydrophobic and provide insufficient binding sites for cells to effectively anchor to their surface. In order to improve the adhesion, viability and proliferation ability of biomolecules, the surface of the material must be modified with plasma to make it more hydrophilic.
If the PS is treated with oxygen plasma, it will become very hydrophilic, so water will diffuse everywhere. This allows aqueous solutions containing biological components to diffuse and deliver biomolecules to the surface, while providing a hydrogen bonding platform to adhere to them. Treating the surface in this way has many benefits, including improved wetting of the wells by the analyte; larger cell proliferation without clumping; reducing the amount of serum, urine or reagents required for testing; and reducing spillage and cross-well Risk of contamination.
Plasma treatment is used to solve the difficult challenges of producing plastic parts for medical devices.
The use of plastic laboratory equipment can cause concerns about the leaching of materials from the plastic. Since plastic labware is easy to leach out plasticizers, stabilizers and polymer residues, plasma is used to coat the inside of the container with a layer of barrier material similar to quartz. These quartz-like flexible coatings are polymerized onto plastics by plasma-enhanced chemical vapor deposition. The resulting coating can be a very thin (100-500 nm), amorphous, highly conformal and highly flexible (180º ASTM D522) coating.
Similarly, people may be concerned that plastics that come in contact with food and beverages may ooze. To prevent plastic leaching, industrial manufacturers can use plasma treatment to coat the plastic. Two options are PTFE-type coatings, or on the other side of the spectrum, a silicon-quartz coating to create a nearly glass-like surface. An example is a sports water bottle whose inner surface has been modified, usually due to the application of plasma treatment or coating.
Since laboratory equipment is easily leached from plasticizers, stabilizers, and polymer residues, plasma is used to coat the inside of the container with a barrier material similar to quartz.
When injection molding and blow molding companies are developing new products or processes that may require plasma treatment, the two options are to purchase in-house plasma equipment and develop the necessary expertise to use them, or to use paid processing services.
If R&D assistance is needed, plasma treatment is sufficiently standard, and leading equipment suppliers can modify existing and mature equipment and technologies to complete fixtures to provide essentially plug-in solutions. As in the case of PVA TePla, some vendors provide access to on-site R&D equipment and engineering expertise.
For custom molders who may work for manufacturers in all walks of life, purchasing a plasma treatment system is a flexible option, not specific to an application. You can perform plasma treatment on multiple parts and have multiple recipes in one system. You can use it on multiple product lines.
However, for molders who need plasma treatment of parts or components without investing in in-house equipment and training, the solution is to use contract processors. In this way, parts are shipped, processed and returned within the agreed time frame. For small or infrequent batches, this can significantly reduce the price of each part. Cooperating with contract processors has advantages in utilizing years of technical expertise in applying various plasma treatments, which can often speed up research and development efforts.
Plasma treatment can be used to solve problems in the packaging of medical test kits.
With the continuous development of applications and production volumes, working with partners with important plasma treatment expertise can provide customers with faster time to market for their products.
Most conduits on the market today are made of PVC or silicone. These two materials often do not have much lubricity, so it is difficult for surgeons to insert them into the body. In the past few years, lubricating coatings with unique properties have been developed and applied to materials to overcome this problem and reduce physical damage to patients undergoing surgery. Both PVC and silicone have high contact angles and cannot well wet or disperse the liquid on the surface, which makes the deposition and adhesion of liquid coatings a major challenge for the industry.
Traditionally, primers have been used with certain success. The application of plasma activation and primer surface has been optimized and adopted by the entire medical industry. Gas plasma shows an advantage because the coating will adhere to the conduit and has the strong pulling force required to shear or break the coating. Gas plasma also helps medical device manufacturers provide a safe and effective method to achieve similar or improved results while minimizing waste in the process. As the company's goal is to become more environmentally friendly, they are looking for alternatives to the old wet chemistry-a shift that has occurred in the semiconductor market for some time.
A recent trend is for companies to modify their dedicated non-stick coatings to promote better bonding with connecting chemicals—a proprietary method that allows chemical groups in the coating molecules to be added to the coating through plasma-enhanced chemicals. The functional groups on the surface of the catheter interact with vapor deposition (PECVD). This method improves the chemical bond with the surface through non-covalent chemical linkage.
An additional mechanism that can further enhance bonding uses these additional non-covalent bonds that have been integrated into the now modified surface of the catheter outer diameter. These new functional groups are not natural groups on the surface of PVC or silicone. This proprietary technology enables the adhesion of the lubricating coating to reach the highest achievable level.
▪ A leading medical device manufacturer switched from using various chemicals and abrasives to clean the surface of the catheter to plasma treatment. In order to eliminate the additional chemical waste, the customer studied the benefits of PVA TePla's plasma system after understanding it. Plasma treatment reduces costs, eliminates additional processing, reduces production time, and reduces chemical waste. Plasma not only replaces wet chemical processes, but also improves the adhesion of lubricating coatings applied later.
▪ Another leading medical device manufacturer uses PVA TePla plasma to treat plastic catheters to improve its products. This uses a proprietary gas-mixed plasma to clean the plastic, significantly improve its wettability and promote the adhesion of the post-treatment process.
About the author: Ryan Blaik is the sales manager of PVA TePla America, a system engineering company specializing in plasma systems. Blaik has a background in physics, chemistry, and biology, and has extensive work experience in the medical device industry. He worked in the surface modification R&D laboratory of PVA TePla in Corona, California, and started his current position in 2020. Contact: 951-371-2500; sales@pvateplaamerica.com; pvateplaameria.com.
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