Surface treatment of plastics
The surface energy of a solid is a measure for the surface wettability with liquids such as ink, adhesive or varnish. Adhesion between solid and liquid bonding partners also depends on whether the surface energy of the solid matches the surface tension of the liquid.
Surface energies of untreated plastics are typically relatively low at less than 50 mN/m. The polar fraction of the surface energy is particularly low for this group of materials. Depending on the manufacturing process, contamination by organic release agents and lubricants can further reduce the surface energy. Therefore, the surface treatment of plastics is particularly important. Here, pretreatment with atmospheric pressure plasma is an effective option, and can be carried out either manually or inline.
In a combined process of fine cleaning and activation, plastic parts produced by injection molding can thus be freed from release agents, for example, and optimally prepared for subsequent adhesion processes by functionalizing the plastic surface. Especially for adhesives and sealants with polar properties, increasing the corresponding polar fraction of the surface energy of the respective bonding partner is crucial.
The accompanying figure shows the surface energies of selected plastics in an untreated state and after surface treatment with the inline-capable PAA Plasmajet plasmabrush® PB3 and also after treatment with the PDD plasma handheld piezobrush® PZ3. The process speeds of the two plasma treatments are 200 mm/s and 20 mm/s, respectively. The surface energies are represented here as the sum of their disperse and polar fractions. Through this graph, it becomes apparent that most plastics without surface treatment have a low surface energy, especially due to the low polar fraction. As a result of plasma treatment, polar end groups are attached to the surface of many of these materials. This can effectively increase the polar fraction of the surface energy in particular.
The result is that, when a suitable adhesive system is used, the adhesion between the two bonding partners is significantly improved by the plasma activation of the plastic surface.
- Polyamide / PA
- Polyoxymethylene / POM
- Polyethylene terephthalate / PET
- Polybutylene terephthalate / PBT
- Polypropylene / PP
- Polytetrafluoroethylene / PTFE
- Polyvinylidene fluoride / PVDF
- Polyvinyl chloride / PVC
- Polyether ether ketone / PEEK
- Polyurethane / PUR
- Polystyrene / PS
- Polycarbonate / PC
- Polysulfone / PSU
- Polyetherimide / PEI
- Polyethersulfone / PES
- Polymethyl methacrylate / PMMA
- Ethylene Propylene Diene Monomer / EPDM
- Acrylonitrile Butadiene Rubber/ NBR
- Perfluoroelastomer / FFKM (FFPM)
- Fluoroelastomers / FKM (FPM)
- Ethylene, Vinylacetate / EVA
- Silicones, Silicone Rubber / VMQ
- Acrylonitrile-butadiene-styrene copolymer / ABS
Polyamide is commonly used as a term for synthetic thermoplastic materials suitable for technological applications. Polyamides are often used as construction materials due to their excellent firmness and ductility. They have good chemical resistance against organic solvents, but they are very susceptible to acids and oxidizing chemicals. Most non-fiber polyamides reach the market in form of plastic granulate and are processed via injection molding.
The biggest part of the polyamides produced are used as synthetic fibers for textiles.
Furthermore, the material is used to produce unbreakable household articles and technical parts which have to be abrasion-proof such as wall plugs, screws, casings, bearings, insulation components in electronic engineering, cable straps, adhesive sockets, joints for ambulance tents, kitchen utensils (e. g. dippers, spoons), machinery parts (covers, gears, bearings, rollers) and bristles for toothbrushes. Due to its resistance against lubricants and fuels at temperatures up to more than 150 °C (300 °F), it is also used in vehicle construction for motor components such as intake systems, fuel lines, motor shrouds, oil slumps and for compressed air systems like chassis and brakes.
- Altech, brand name for PA6 and PA66 / Company Albis Plastic
- Akulon, brand name for PA6 / Company DSM
- Grilon, brand name of the swiss poyamid producer Ems-Chemie
- Nylon, Zytel DuPont de Nemours
- Timbrelle, brand name for PA6.6 filaments / Company TWD Fibres
- Miramid, Ultramid, Capron, brand name of polyamids / Company BASF
- Cordura fabric (Invista; www.invista.com)
- Vestamid (Evonik Industries)
Their uniformly smooth surface makes polyamides very suitable suture material in surgery. Polyamide suture material can be knotted easily and is especially tension-proof.
Polyoxymethylene (POM, also called polyacetal, polyformaldehyde) is a highly molecular thermoplastic material. It is often used as an engineering grade plastic, especially for precision parts, due to its high degree of stiffness, low friction coefficient, as well as dimensional and thermal stability.
POM is extremely solid, hard and stiff in a wide temperature range. It maintains its high ductility up to -40 °C (-40 °F) and has excellent abrasion and heat resistance, a low friction coefficient, good electrical, dielectrical and lubricant properties, and permits only minimal water absorption. In many cases, it can replace metal.
POM is processed via injection molding, extrusion, extrusion blow molding or machining.
- Gear wheels, sliding elements, guide elements, housing components, spring elements, chains, screws, nuts, fan wheels, pump parts, valve bodies
- Electrical engineering: insulators, coil bodies, plug connectors
- Vehicle manufacturing: steering column (e. g. levers for lights, indicators), window regulators, door lock systems, sockets
- Furniture making: locks, handles, hinges or curtain rails
- Clothing: zip fasteners
POM belongs to the group of plastics with low surface energy and is very difficult to bond without special surface treatment. Atmospheric plasma treatment improves the adhesion of glues on the surface.
Manufacturer & further informations:
- Ticona/Celanese Hostaform, Kematal, Celcon
- DuPont Delrin
- Polyplastics Duracon
- Korea Engineering Plastics Kepital
- Mitsubishi Lupital
- BASF Ultraform
Polyethylene terephthalate (PET)
PET is an engineering thermoplastic from the polyester family. It is found in a wide range of applications and is used to produce plastic bottles (PET bottles), plastic films and textile fibers, among other things. Its mechanical properties are excellent.
PET is used as a textile fiber because it is crease-resistant, tearproof and weather-resistant. The fiber absorbs only very little water and is suitable as a fabric for sportswear which needs to dry fast. Ultrathin, highly transparent foils and sheets are also made of PET.
Polybutylene terephthalate (PBT)
PBT is an engineering thermoplastic. It belongs to the group of polyesters and shows excellent process behavior in injection molding.
PBT is appreciated for its firmness and stiffness, its very high dimensional stability (much better than that of POM or PA) and its good friction and wear resistant properties. Typical application temperatures range from -50 to 150 °C (-60 to 300 °F).
Applications are found in the construction of casings in electrical engineering, for plug connections, in vehicle manufacturing and for components of household appliances that are subject to thermal stress.
Manufacturer & further informations:
- Arnite (DSM)
- Celanex (Ticona)
- Crastin (DuPont)
- DYLOX (Hoffmann + Voss GmbH)
- RIALOX (RIA-Polymers GmbH)
- Ultradur (BASF)
- Valox (Sabic Innovative Plastics)
- VESTODUR (Evonik Industries AG)
Polypropylene (PP) is a semi-crystalline thermoplastic and belongs to the group of polyolefins. PP is odorless and skin compatible, it is suitable for applications in the food industry as well as pharmaceutics, and is physiologically entirely harmless. It can be processed via injection molding, extradition, blow molding, hot shaping, welding, deep drawing and machining. Additionally, it is used to produce foam.
PP can be filled with mineral fillers such as talcum, chalk or glass fibers. This significantly widens the spectrum of mechanical properties (stiffness, operating temperatures etc.).
Polypropylene at room temperature is resistant to greases and almost all organic solvents, apart from powerful oxidizers. Due to its low surface energy, polypropylene is hard to glue or print.
PP is used in machine and vehicle manufacturing for the interior of cars, instrument panels, battery cases and crash-absorber elements, as well as for child seats and bicycle helmets.
In electronic engineering, it is used for transformer housings, insulating foils, wire sheathings and cable sheathings. BBOP-oriented polypropylene foil is especially important as a dielectric of plastic film capacitors and power capacitors.
In the building industry, it is used for armatures, fittings and piping; in ventilation and air-conditioning technology, it is used in conditions favorable for corrosion, and for the extraction of corrosive gases, mostly in the form of PP-s (s=low flammability).
In medical technology, the food industry, in households and in packaging technology, many products containing PP are used: tubs for dairy products, bottle caps, inner parts of dishwashers, reusable containers and so on.
PTFE (Polytetrafluoroethylene) belongs to the class of thermoplastic polyhalogenolefins.
PTFE is highly inert and thermally stable up to 260°C (500°F). Even aggressive acids such as aqua regia cannot corrode PTFE; it is also extremely resistant against all bases, alcohols, ketones, fuels, oils etc.
PTFE has a very low friction coefficient. There is virtually no material that can adhere to PTFE, as its surface energy is extremely low. PTFE is very hard to wet and almost impossible to glue. Its angle of contact with water is 126°.
Due to its chemical inertness, PTFE is used as a coating for applications which include aggressive chemicals. The great variety of possible compounds and the relatively simple solutions provided by this allow for the preparation of highly specific mixtures for a wide spectrum of applications such as shaft seals, groove seals, bellows, or screw joints.
Due to its low friction properties, PTFE is relevant as a dry lubricant (solid lubricant) and as a coating for bearings and seals.
In medical applications, PTFE is used for implants, among other things. On the one hand, its remarkable chemical resistance makes for high durability and good compatibility, on the other hand its smooth surface reduces the risk of blood clotting.
Because it is extremely heat resistant, PTFE can be autoclaved at 130 °C (270 °F). There are also PTFE face implants, which are used in plastic surgery.
In high frequency technology, PTFE is a popular material e.g. for cable insulation, due to its low permittivity and its minimal losses.
In high voltage technology, PTFE is suitable as an electrical insulator due to its high partial discharge resistance and its low adhesive properties regarding surface contamination.
Expanded or elongated PTFE (ePTFE) is a specially processed form of polytetrafluoroethylene with a membrane so fine-pored that it is permeable to steam, but not to water in its liquid state. It thus lends itself to the manufacturing of waterproof, breathable foils for the clothing industry and medical technology.
Manufacturer & further informations:
Polyvinylidene fluoride (PVDF)
Polyvinylidene fluoride (PVDF) is an opaque, semi-crystalline thermoplastic fluoroplastic.
Due to its high thermal and chemical resistance, PVDF is used to coat pipes, tubes or exterior components, as well as seals, membranes and packaging foil. Yet another field of application is medical technology, where PVDF is a suitable material for prostheses. Membrane technology uses PDVF widely, e.g. for high-quality bacteria filters, water filtration and reverse osmosis.
Manufacturer & further informations:
Polyvinyl chloride (PVC)
Polyvinyl chloride (PVC) is an amorphous engineering thermoplastic. Hard and brittle, it only becomes soft, ductile and suitable for technical applications by the addition of softening agents and stabilizers.
- In the building industry, it is used mainly as a basic material for window profiles, pipes, flooring and roof panels
- PVC is also made into flame-proof cable sheathing, insulation material for electric cables, electric switch boxes and cable conduits
- PVC foil has different applications, e.g. synthetic leather or credit cards, telephone cards and other smart cards
Polyether ether ketone (PEEK)
Polyether ether ketone is an engineering thermoplastic resistant to high temperatures, with its melting point at 335 °C (635 °F). Up until 280°C (540°F), PEEK is resistant against hydrolysis and almost every organic or inorganic chemical. PEEK can be formed by injection molding in its liquid state or via extrusion.
- Automotive and aerospace industry
- High voltage industry (as an insulating material)
- Medical technology (as it can be sterilized repeatedly and is biocompatible as well as x-ray transparent)
- In dental compound materials as a matrix
- In pharmaceutics and food technology (in production facilities for components with product contact)
- Flexible film circuit carriers in electronics
- Vacuum technology, for very low outgassing rates
Brand names for PEEK:
Polyurethanes are plastics which can be elastomers, thermoplastics or duroplastic materials (thermosets), depending on their chain structures and cross-linking degree.
In terms of quantity, polyurethane foams, whether hard or soft, are the most prevalent. However, they are also used as molding compounds for compression molding, as casting resins (isocyanate resins), elastic fibrous fabrics, polyurethane varnishes and as polyurethane glues.
Soft PUR foams are used for an extremely wide range of applications, but above all as upholstery material for mattresses, seat cushions for furniture or car seats, carpet backings, for lining textiles, for cleaning sponges, shoe soles or as filter material. Soft PUR foams are mostly multicellular (open-celled) and are available in many varying degrees of hardness and density.
Hard PUR foams are mainly applied for thermal insulation, e.g. in buildings, cooling devices, heat and cold storage as well as in a number of pipe systems (composite pipe sheaths made of plastic, flexible composite pipes).
Amorphous Polystyrene is a semi-crystalline engineering thermoplastic that is prevalent in many areas of our daily life. An expanded material, PS is used as an ultra-light foam material. Its weather and UV resistance is limited, its melting point is low and it is very sensitive against many organic solvents.
Polystyrene lends itself extremely well to injection molding for mass-produced articles. Its low tendency to evanesce or shrink during processing allows for components in near net shape.
In electrical engineering, polystyrene is used for its good insulating properties to make switches, coil bodies and casings.
In food packaging, PS is common in thermoformed cups or foam trays.
Foamed polystyrene is used as a shock-absorbing packaging material, insulation material and as a buoyancy device.
Polycarbonates (PCs) are highly transparent engineering thermoplastics. They are exceedingly firm, stiff, hard and impact resistant, plus they are very suitable for electrical insulators.
Polycarbonates are resistant against water, many mineral acids as well as watery solutions of neutral salts and oxidizing agents. They can be processed with any methods commonly applied to thermoplastics.
Their low scratch resistance can be compensated with coatings based on e. g. polysiloxane, polyepoxy or polyurethane acrylate. Even a polysiloxane varnish only 5-8 micrometers thick is sufficient to provide the semi-finished polycarbonate product or workpiece with a surface as hard as glass, without diminishing its hot forming properties.
The material’s chemical and UV resistance can be significantly enhanced through suitable varnishes. Moreover, specialized coatings provide polycarbonates with self-cleaning or waterproof surfaces. As a compound with transparent thermoplastic polyutheranes (TPUs), polycarbonate can easily be made into lightweight, UV-resistant laminated safety glass panes.
Among other things, polycarbonates are used for:
- CDs, DVDs and blu-ray discs
- Spectacle lenses and optical lenses
- Headlight diffusers
- Aircraft windows
- Anti-theft glazing
- Underwater housing for cameras
- Back covers over mobile phones (mostly smart phones) and tablets
- Conservatory and greenhouse glazing
- Solar panels
- Helmets and visors
- Camping crockery
Polysulfone (PSU) is an amorphous high-performance thermoplastic that belongs to the group of high-temperature resistant plastics.
It is applied in electrical engineering, electronics, vehicle and mechanical engineering, for household appliances and in medical technology in cases where high heat-resistance coupled with transparency are necessary.
- Udel (BP-Amoco / Solvay)
- Ultrason S (BASF)
Polyetherimide (PEI) is a high-performance thermoplastic that belongs to the group of heat-resistant plastics. It is processed primarily via injection molding. PEI components can be bonded using epoxy, polyurethane or silicone glue.
It is mostly made into plastic parts for electronics or the aircraft industry, as it offers high flame retardancy and impact resistance for fiber composite structures.
Membranes made of polyetherimide are successfully used in many industries because of their excellent mechanical and thermal resistance, good film-forming capacities and relatively cost-efficient production. The material’s surface properties can be specifically modified to range from hydrophilic to hydrophobic
Polyethersulfone (PESU or PES) is a high-performance thermoplastic that belongs to the group of polysulfones. It is mainly used for components under high thermal stress (medical devices, automobile and aircraft construction, electrical and electronic components).
Additionally, it is a high-quality material for the production of baby articles (especially drinking bottles)
Polymethyl methacrylate (PMMA)
Polymethyl methacrylate is a highly transparent thermoplastic. Starting at 100 °C (210 °F), PMMA possesses plastic ductility which is thermally reversible. It is well suitable for machining, can easily be cut or engraved using CO2 lasers, and is more scratch resistant than other thermoplastic. Adhesive or welded connections are possible. It transmits light better than mineral glass, is easy to dye and resistant to weathering and ageing.
- Automotive industry: Indicator and rear light glass, reflectors, light conductors, casing elements
- Building industry: glazing, sanitary and furnishing components
- Light technology and optics
- Aircraft construction: panes, hoods, headlight covers
- Machinery protection: protective covers and safety door
- Optometry: hard intraocular lenses, spectacle glasses
- Dental medicine: Partial dentures, temporaries, occlusal splints
Ethylene Propylene Diene Monomer (EPDM)
Ethylene propylene diene monomer (M-class) rubber is a synthetic elastomer (rubber) with high resistance to weather and ozone as well as high thermal stability. Due to its high elasticity and chemical resistance, it is used for various types of seals, such as for example O-rings for shaft seals or also for flat seals.
EPDM is commonly used for steam and hot water hoses, weatherproof foils and close-pored foam mats.
Acrylonitrile Butadiene Rubber (NBR)
Nitrile rubber is a synthetic rubber used to produce vulcanized materials with high resistance against oils, greases and carbohydrates, good aging and abrasion properties and high remaining elasticity at temperatures down to -40°C (-40°F).
They are processed into seals, tubes, rubber gloves and rubber strings.
Perfluorelastomer (FFKM or FFPM) is a fully fluorinated elastomer. Chemically it is very similar to polytetrafluorethylene (PTFE). It is used primarily in applications where high thermal and/or chemical resistance is crucial. FFKM can be used at temperatures ranging from -20 °C to +325 °C (-5 °F to +620 °F).
The term fluoroelastomers (FKM according to DIN ISO 1629 [previously: FPM] and FKM according to ASTM D 1418) stands for an entire group of fluorinated rubbers that, as a common characteristic, have vinylidene (di)fluoride (VDF) as one of their monomers. Fluorinated rubbers were developed by DuPont (VITON) in the 1950s, but are also supplied today by
- Lanxess (Levatherm F)
- Solvay-Solexis (Tecnoflon)
- Dyneon (Dyneon™ Fluoroelastomers) und
- Daikin Chemical (Dai-El)
Ethylen / Vinylacetat (EVA)
The acronym EVA is used to describe a group of co-polymers.
Examples include cold-resistant extractable spouts of canisters, plastic sheets used in agriculture and horticulture, shrink-wraps (office supplies, solar modules), shower curtains, and flooring.
A subclass of EVAs extending up to 28%VA is mainly used as melt adhesive.
In photovoltaics, solar cells are embedded in EVA. In this process, the EVA contained in plastic sheets is melted at a temperature of about 150 °C (300 °F), becomes crystal clear and cross-links three-dimensionally. When cooled off, the resulting bond is highly durable and serves to protect the cells against environmental stress.
If VA content is higher than 30% (it may reach up to 90%), the resulting elastomer is similar to natural rubber. It is often called EVM (DIN I ISO 1629:1995), and is primarily used for shoe soles or as a polyblend together with other elastomers.
Leading supplies are – in order of market share:
Registered brand names include
- Ultrathene (US)
Silikone, Silikon-Kautschuk (VMQ)
Silicones are a group of synthetic elastomers, which hold a special position due to their silicon-oxygen structure. This leads to a number of specific characteristics:
- Chemically stable
- Thermally resistant (mainly stable properties from -100 to 250 °C / -150 to 480 °F).
- Waterproof and water-repellent
- Separation effect towards many other materials
- Inert against the build-up of micro organisms
- Resistant against UV light, oxygen and ozone
- Efficient electronic insulator with high dielectric strength
- High gas permeability
- Good wetting properties when bonded with glass
Electric insulators, high-quality seals, elastic suspension systems, medical implants, wound dressings, mold making
The good separating effect of silicone is utilized in mold making to produce precision molds made of synthetic resin, with demolding being facilitated by the high elasticity of silicone.
Manufacturer & further informations
Silicone has a very low surface energy and very little wettability. Atmospheric plasma treatment allows for the surface energy to be enhanced substantially. It is to be noted that surface energy is recovered within the short timespan of minutes, especially by silicones with low shore hardness
Acrylonitrile-butadiene-styrene copolymer (ABS)
Acrylonitrile-butadiene-styrene copolymer, also abbreviated as ABS, is a thermoplastic terpolymer consisting of the monomers acrylonitrile, 1,3-butadiene and styrene. The quantity ratio is approximately the same:
- 15-35 % Acrylonitrile
- 5-30 % Butadien
- 40-60 % Styrene
ABS is a colourless to grey solid that is frequently used in the manufacture of household and consumer products. In Europe, ABS is also widely used in the automotive and electrical industries.