How it works – Hydrochromic

LCR Hallcrest supply a range of Hydrochromic materials that change either reversibly or permanently in response to exposure to water and liquid.

WET & REVEAL SCREEN INK

This is a water based screen ink which dries to give a white opaque print. When wet the ink film takes up water and becomes transparent allowing any print beneath to become visible. If the water dries out the opacity is regained and the original white print colour is restored.

A fairly heavy print is required, which essentially means the ink is supplied as a screen ink. More than one print may be required to obscure an underlying print. As the coating weight of wet & reveal ink is increased the transparency when wet can be reduced so careful tests should be carried out to determine optimum printing parameters. Careful choice of underlying text / patterns can help by selecting something that will be easier to hide, such as images without large bold text or areas of substantial contrast.

Wet and Reveal Screen ink can be printed on various substrates such as paper, cards, print receptive plastics and even textiles. Tests should be carried out to determine suitability for the substrate and application chosen.

When a highly permanent print on textiles is required the dried wet and reveal print can be crosslinked by baking for 3 – 5 minutes at 130ºC.

Good results have been achieved with prints on absorbent substrates without additional curing but if a crosslinked film is desired, but temperature treatment is not an option because of the choice of substrate, then chemical crosslinking agents such as aziridine may be employed.

Ink when dry (1, 2, 3 ink layers)

Ink when wet (1, 2, 3 ink layers)

Available in:

  • Water based Screen Ink
  • Sprayable Ink
  • Labels – custom made labels can be produced

Ink when dry                                      Ink wetted with damp cloth

IRREVERSIBLE HYDROCHROMIC INKS & LABELS 

These water sensitive inks can be used to create a wide range of effects changing from a solid colour to colourless when wet.

The irreversible hydrochromic inks are available in various colours.  Stock colours are:

  • Black
  • Blue

Special colours are:

  • Magenta
  • Green
  • Brown
  • Orange
  • Vermillion

They have good colour strength. Exposure to water denatures the dye and the colour change becomes permanent if the water either washes the dye away or absorbs it into a paper substrate, or it does not dry out on top of the print.

Substrates used can affect the speed of response with ink printed on non-absorbent material generally changing more rapidly than on substrates such as paper. Colour reversion after drying out is more likely with prints on non-absorbent material than on paper though.

These Irreversible hydrochromics can also be affected by high levels of humidity and are not suitable for exposure to such conditions.

Irreversible Ink (screen printed)

– becomes invisible when water applied

Available in

  • Solvent Based Flexographic
  • Water Based Flexographic
  • Water Based Screen Inks
  • We also produce custom made Labels with hydrochromic inks.

WASH OFF AND REVEAL SCREEN INK

This is a water based screen ink which dries to give an opaque print. When washed or placed under running water the ink film dissolves and washes away allowing any print beneath to become visible.

Suitable for non absorbent substrates such as plastic or laminated board.

A fairly heavy print is required, which means the ink is supplied as a screen ink.

Colours available are black, navy blue, and white.

Careful choice of underlying text / patterns can help by selecting something that will be easier to hide, so tests should be carried out to determine optimum printing parameters.

Before and After

Before

Under running water

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