The Centexbel coating & finishing platform is composed of several semi-industrial and labscale surface modification, coating and lamination lines for prototyping purposes and to carry out experiments in the framework of collective and private research projects.
The scale of the different pilot lines is appropriate for the rapid production of prototypes and samples with a limited material use.
Because the platform is integrated in the entire centexbel organisation, all samples can subsequently be submitted to relevant testing and be discussed with our researchers and technological experts for further improvements and fine-tuning.
Centexbel invests in new energy-efficient machinery and equipment to be ahead of new evolutions in sustainable processing.
Coating is a technique by which a formulation paste is applied onto a substrate by means of a knife; it is used to functionalise textiles and to create sophisticated and innovative textiles. The formulation paste usually consists of a binder and functional additives.
- simple and widely used process
- introduction of barrier properties and/or novel functionalities to textiles
- evaluation of novel binder systems
Coating application techniques
- knife over roll, knife in air, transfer coating
- thermal or IR drying, UV curing
- A4-size (Mathis labcoater): aqueous, solvent-based, 100% or high solid systems
- roll-to-roll system (0.5 m width, Matex): aqueous or 100% systems
Slot-Die Hotmelt Coating
Hotmelt coating is the application of a layer to a substrate by pre-melting the desired material and then allowing the material to cool, solidifying the layer.
Hotmelts are melted and applied onto textiles or other substrates. The melting of polymers is carried out in a conventional or a drum melter according to the type of polymer.
There are two types of hotmelt polymers - thermoplastic polymers and reactive polymers - requiring different curing methods: thermoplastic polymers are cured by cooling, whereas reactive polymers need a reaction with e.g. moisture in order to be cured.
- Thermoplastic polymers become liquid (=melt) in contact with heat (varying temperatures according to the chemical composition of the polymer) and become hard (=solid form) when cooled. This is a reversible process that can be repeated.
- Examples: PE (polyethylene) and PP (polypropylene), EVA (ethylene vinylacetate), TPU (thermoplastic polyurethane)…
- Reactive polymers cannot be melted again, once they have been cured, because the reaction with e.g. moisture results into a permanent solidification.
- Examples: moisture curing PU, moisture curing APAO (amorphous poly-alpha-olefines), UV-curing acrylates...
The melted polymer can be applied by means of various "applicators". Centexbel disposes of a "slot-die" hotmelt coater. The melted polymer is pushed through a slot and thus applied onto the substrate. The appliance with an operational width of 45 cm is appropriate for both coating and lamination trial runs.
Thermoplastic (biobased) hotmelts
- PO, PES, PA, EVA, PLA, PHBV, PHA are polymers types that can be melted again (reversible process) and recycled
Hotmelt coating application techniques
- roll-to-roll slot-die coater (width 0.5 m)
- a first screening of the hotmelt glue can be easily performed by using a glue gun
- Twin screw compounder to functionalise hotmelts: flame retardancy, antimicriobial properties, etc.
- the system requires no water or solvents: less emission and no evaporation
- recycling: thermoplastic hotmelts can be melted and reused
- absence of residual baths reduces waste
- no need of additional drying oven (space and energy saving)
A laminated textile is composed of two or more layers, at least one of which is a textile fabric, bonded closely together by means of an added adhesive, or by the adhesive properties of one or more of the component layers.
- easy and widespread process
- applicable to multiple types of substrates: textiles, films, membranes, foils…
Textile laminating application techniques
- focus on wet lamination
- production of A4-samples on Mathis labcoater
- roll-to-roll applications on Matex semi-industrial line (0.5 m)
A coloured textile is the result of a highly specific and accurate dyeing process. Textile dyeing consists of multiple - often energy and water consuming - steps. Due to the impact of certain dyes on the environment, textile dyeing requires a dedicated waste water management.
Inhouse Dyeing processes
- laboratory infrared type dyeing machine with 16 dye pots to test several different formulations in one run
- reel type dyeing machine (for textiles of 3m x 0.3m)
- accredited in-house testing of colour fastness to rubbing, washing, UV, perspiration, etc.
The Centexbel platform is equipped with different modules for yarn and multifilament coating that can be dynamically combined:
- yarn winder
- corona treatment unit
- UV curing
- IR oven
- conventional ovens
- dipping appliance
- dynamic nozzle systems
To obtain the optimal yarn coating, the Centexbel researchers have access to an extensive range of in-house test methods to determine the morphological, physical and chemical characteristics and parameters of yarns and coating formulations.
By coating a PU wire with conductive layers, Centexbel was able to create an energy storing wire (serves as a battery), that can subsequently be knitted or woven to create energy storage textiles for applications in remote areas without access to a power grid.
Although screen printing is a commonly used technique to print decorative and functional patterns on textiles, Centexbel deploys the flatbed auto-magnetic screen printing technique to create smart textiles and other high-end products based on conductive inks or specialty formulations.
Characteristics of the flatbed auto-magnetic screenprinter
- maximum dimensions: 50 cm x 80 cm
- creating decorative prints and conductive printed tracks for smart textiles
- direct/indirect printing
- ink development for the creation of conductive, functional textiles
- encapsulation and integration of prints on textiles
UV and UV-LED curing
UV curing is a rapid and eco-friendly curing process in which high intensity ultraviolet light is used to create a photochemical reaction that instantly cures inks, adhesives and coatings.
- on both hard and flexible substrates
- appropriate technique in the preparation of prepregs and glass fibre reinforced polymers
- waterbased or completely solvent-free (100% systems) formulations
- eco-friendly technology to cure functional coatings & finishes on textiles: low VOC emission and less waste
- suitable for heat sensitive substrates
- fast, low energy consumption
- can be installed on existing coating lines
- small dimensions
UV-LED curing is a similar technology using monochromatic instead of broad spectrum UV-light to cure a coating layer.
Additional advantages to conventional UV curing
- no preheating of lamp (easy on an off)
- no harmful UV-C and UV-B radiation
- mercury-free lamp
- no ozone generation
- no infrared radiation (important for highly heat-sensitive textiles)
Multifunctional materials require a stronger multidisciplinary approach as well as the merging of the traditional scientific disciplines (chemistry, physics, biology,…) into new cross-boundary technologies. Moreover, these novel technologies have to be able to bridge the gap between polymers, ceramics or metals, between organic and inorganic materials, or between the mineral and biological world. Sol-gel technology might offer a solution.
The first experiments on sol-gel already took place in the fifties of the previous century. By their inorganic nature, sol-gel layers are extremely strong and wear resistant. Therefore, very thin 'nanometric' layers suffice to obtain the desired effects. Since several years, there is an increasing interest in the application of the sol-gel technology for textile treatment. However, the formulas and methods used in other industrial branches have to be adapted to the raw materials and specific textile properties.
The solgel principle
The preparatory material (or precursor) used to produce the "sol" usually consists of inorganic metal salts or metal organic components, such as metal alkoxides. These precursors are submitted to a series of hydrolyse and polymerisation reactions to create a colloidal suspension (or "sol").
By further processing this suspension, this sol is transformed into a ceramic material in different forms for different applications:
- thin layers (films) are applied by spin-coating or dip-coating
- by moulding the "sol" we obtain a wet gel that
- will form a dense ceramic structure after evaporation and heat treatment
- under super critical conditions, it will form a very porous material with an extremely low density (aerogel)
- by adjusting the sol's viscosity it is possible to manufacture ceramic fibres
- by precipitation, spray pyrolysis or emulsion techniques we will obtain ultra-fine and uniform ceramic powders
Plasma treatment is a surface treatment that modifies the textile surface without altering the bulk properties (tear resistance, flexibility, density...) of the textile material.
The use of atmospheric plasma is a both economically as ecologically interesting textile treatment.
The drawing below illustrates the working principle: by means of a plasma source, a plasma zone is generated with energetic and active particles (photons, electrons, ions). The textile material is guided through this zone and treated accordingly.
By varying the type of gas and - possibly - precursor, we may alter the surface properties in order to:
- increase the affinity to dyeing and printing
- improve adhesion
- apply antibacterial products
- influence the electrical conductivity
- apply a fire retardant finish
- confer anti-crimp properties to wool
- desize cotton...