Trouble shooting in flocking

Flocking is a sensitive process. There are many factors that can influence the final result and therefore should not be neglected. Be it materials that react differently in the electrostatic field, the compatibility of some flock preparations and adhesives or the shape of the substrate. In addition, parameters such as field strength, relative humidity, flock and adhesive conductivity and earth discharge must be taken into account in the electrostatic process.

If one of these influencing factors is not optimal, the end result cannot fulfil all defined functions.

Damage patterns & their causes

Adhesive

If the adhesive runs off the substrate, shows flow problems, cannot be processed, does not react sufficiently or does not hold, this can have various causes. 

When the adhesive runs off the substrate, it is possible that it is already outdated, that there is an incorrect mixing ratio, that it was stored incorrectly or that too much adhesive was applied. If the adhesive does not process or only processes poorly, this may be due to material aging, incorrect storage conditions, frost damage, nozzles that are too fine during application, exceeding the pot life, an incorrect mixing ratio or an incorrect ambient temperature. 

In the case of flow disturbances during adhesive application, the causes are contamination of the substrate, insufficient pretreatment of the substrate, insufficient surface tension or an unsuitable adhesive.

If the adhesive is too liquid or does not react sufficiently, this may be due to an incorrect mixing ratio, missing or incorrect hardener, inhomogeneity, insufficient fixing time or temperature, or incorrect drying. 

If the adhesive does not adhere to the substrate, it may be unsuitable, the substrate may be dirty or insufficiently pretreated, or the surface tension may be too low.

Flock

With the flock fibres it can be that these can be dosed badly or show a bad jumping behaviour.

Poor dosing can be attributed to too low a dosing speed, too fine a screen, poor preparation or excessive moisture in the fibres.

If the flock jumps badly, it is possible that the humidity is not in the recommended range between 55 % and 65 %, the high voltage is too low, the flock is too dry or there are too many old, excess flock fibres. If the preparation of the flock is defective, the manufacturer must improve or renew it.

If excess flock fibres are used, the poor springing behaviour can be attributed to an unbalanced mixing ratio.

Flocking

Further damage patterns can occur in the flocking process. These are a rough and hard end result, different lengths of the fibres in the pile, bare edges and tips, a so-called cloudy or a sparse flocking and an irregular flight behaviour of the flock.

Causes for the irregular flight behaviour of the flock can be a too low high voltage, a defective preparation of the flock fibres, a too low air humidity, too high air speed during electropneumatic flocking or a too high dosage.

A sparse flocking result occurs when the open time is exceeded, the high tension is too low, the preparation of the fibres is defective, the air humidity is too low, too little adhesive has been applied or the dosage of the flock is too high. It is also possible that too few flock fibres are used or that the flocking time is too short.

Also a so-called double stock formation can lead to a thinning result. In this case, the charged flock fibres do not anchor normally in the adhesive but on the already anchored fibres and detach during cleaning.

Causes for a rough and hard surface of the final result are too much tension during flocking or too much adhesive on the substrate.In case of bare edges and tips it is possible that the substrate has too sharp edges or too thin tips which are difficult to flock.

The longer fibres in the flock pile are due to irregularly cut fibres.

The cause of cloudy flocking is a so-called electrostatic shadow, which occurs when the voltage is too high or the distance between the applicator and the substrate is too small.

Damage patterns & their causes

For all these damage patterns of adhesive, flock fibres or the flocking result, general rules and parameters must be observed:

  • Observe the best-before date of the adhesive and hardener & store accordingly
  • Observe mixing ratio & mix components together thoroughly
  • Observe rule of thumb for layer thickness when applying adhesive
  • Use suitable nozzle for adhesive application
  • Keep ambient temperature constant
  • Note pot & drying time
  • Cleaning of the substrate if necessary
  • If the surface tension is too low (min. 38 dyn), pretreat with plasma or fluorine, flame, plasma or primer
  • In the case of flock fibres, care must be taken to ensure that the preparation is of high quality
  • Appropriate storage of the fibres
  • Quality check of the flock fibres before flocking
  • Adjust the sieve & the dosing speed to the size of the flock fibre and the air speed.
  • Adjust high voltage
  • Regular thorough cleaning of the machines
  • Carrying out adhesive application and flocking at separate workstations
  • Observe the manufacturer's safety instructions
  • Use protective equipment

To protect health and the environment, extraction systems, collection containers and booths should be used. This way, the excess flock can be collected and recycled or further processed.

Experience plays an important role in flocking. Over time, you get to know the limits of electrostatics and different challenges, materials and conditions and can use this knowledge purposefully in flocking.

In general, the storage and processing conditions should be observed and controlled in order to achieve an optimum flocculation result.

In order to counteract all these challenges, holistic quality assurance is indispensable. A checklist as a starting point for quality assurance in flocking can be found here:

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