Thursday, 30 May 2013

Tile Inkjet Printing
How it works

Part 2 of 2

Technology specifics
In digital printing there is no contact with the tile surface. The most popular technology adopted by most producers of machines is called Drop-On-Demand (DOD). It is based on a piezoelectric device that deforms under voltage enabling droplet expulsion. The most popular color system is the CMYK standard. This is an acronym for the colors Cyan, Magenta, Yellow and Black (for black K is used instead of B to avoid confusion with Blue). In the CMYK system the black separation or Key Plate contains the fine details. Cyan, magenta and yellow overlap in different percentages to produce the colors in the circles below. All three overlap in the middle to produce a very dark brown, for this reason the additional black ink is used.

The image is electronically separated in a graphics program like Photoshop and a set of signals is sent to each of the different colour print heads, usually the CMYK four but on some machines six or more. The final image is reproduced by overlaying these ink colours.

Drop on Demand
The ink is made from a suspension of very fine pigment particles, at a specific temperature and viscosity. It is held in a main reservoir and fed under pressure to the print reservoir which has a tiny 0,04mm nozzle. The ink is shot from a distance of a few millimeters to the tile. Piezoelectric crystals change shape when an electric current is passed through them so a computer can minutely control the size, speed and frequency of the drops.

Variable Drop Size
A further variation on this is a technology that produces drops of different sizes from the same nozzle. This produces different colour intensities depending on the size of the drops. Larger drops will literally make bigger heavier ‘puddles’ of colour on the tile and cover better whereas a finer spray of smaller drops will give a lighter cover. Changes in drop size can be made by changing the frequency and length of pulses in the piezoelectric element. So a standard nozzle could fire one big drop or fire a burst of 6 drops in the same time but producing two very different effects. Overlapping different sized drops with different colors can create an wider range of tones and colors.

Spray on Demand
This technology uses a spray instead of drops. The ink reservoir is connected to a thin vibrating tube that shoots the spray of ink. By controlling the frequency of the vibrations the nozzle tube describes a cone so the intensity of the color can be controlled. The drops are dispersed at around 1000Hz. The spray tubes are around 10 times the diameter of DoD sytems so they use more ink but the advantage is that pigments are more stable when fired precisely because they are bigger and rougher.

Masters and variations
In ink jet printing a large Master design of the tile pattern is produced. Like this marble-look tile below. Since this is a digital file on a computer it is easy to select different parts of the master to print onto individual tiles.

Inks solvents & glazes

The slightest change in any parameter can affect color, intensity and definition of the deposited ink. If the density, viscosity or surface tension of the ink changes, the quality will change. Thus it is critical to keep both the inks and solvents used at a constant temperature. Inks are constantly stirred and recycled and the tubes and nozzles are cleaned as part of the printing process without any pause in production because solvents are essential to drop formation. The first inks used for inkjet printing on tiles were organometallic which offered low viscosity, moderate surface tension and high coverage using non-toxic solvents.
Inkjet printers use a very limited number of colours in careful combinations to produce all other colours but there are limits. Because tiles are fired in a kiln between 900-1200°C, chemical and solid state reactions occur between the body, the ink, the solvent and the glaze that cannot easily be predicted but the industry continues experimenting and advances are made all the time. For example true magenta and true black are very difficult to produce so conventional tile printing processes are used for tiles requiring these colours. Nonetheless the versatility of ink jet printing and being able to create multiple variations of tile designs means that ink jet tiles will soon be an intrinsic component of tile production lines everywhere.

We are presently in China assessing and appointing factories for our seven new ranges of ink jet tiles. Watch this blog for our new ink-jet gres porcelain catalogues coming soon soon.

Thursday, 23 May 2013

Tile Inkjet Printing - How it works.
Part 1 of 2

Amazingly the concept of inkjet printing has actually been around two hundred years but the technology was first extensively developed in the early 1950s. By the late 1970s inkjet printers that could reproduce digital images generated by computers were developed.
Using the technology to print onto tiles began in 2000 where it was showcased at that year’s Cevisama exhibition in Spain. Since then there has been a steady evolution of mechanical, electronic, ink, pigment and chemical technology in a highly competitive market. Today there are a wide variety of machines being made and used across the world.
Typically print heads use piezoelectric crystals to control ink-flow out of microscopic nozzles directly onto the tile body. The technology is essentially the same as your desktop inkjet printer at home however there are significant differences in scale, resolution and speed of operation.
Instead of using four heads which scan across the page tile inkjet printers use four or more rows that span the entire width of the tiles so the inks can be laid down in succession. The array may have up to 1000 heads per row.

Inkjet printers can easily be integrated into glazing production lines and the race is now on to develop machines able to decorate tiles 24/7 at 1000 to 1500m2 per hour. The problem is that there’s a trade-off between speed and resolution or coverage, just like the printer on your desk at home, photo quality takes a lot longer than a page of black text.
Some tile printers can produce very high definition images at up to 1000 dpi which is beyond the ability of the human eye to resolve. For most tiles around 200-300 dpi is adequate, roughly the resolution a colour magazine or book. However, the most important feature is the amazing versatility of inkjet printing.

Different machines for digital inkjet printing are available with a variety of characteristics but these are the main advantages.
·         The image printed is chemically stable
·         Inkjet printing is efficient and there’s far less wastage than with contact printing systems like rollers.
·         Removing rollers from the process reduces moving parts and thus costs of installation and maintenance.
·         Excellent potential to reproduce natural stones and pictures.
·         Much faster change-over times to new colours or designs.
·         Greatly improved consistency of colour because storage and control of all printing parameters is more finely controlled and easier.
·         Because the inkjet process occurs at a distance it is possible decorate relief surfaces and up to the edges.
·         Inkjet decoration shortens the path from idea to product.
There are more advantages but we must also admit that digital printing cannot always substitute for traditional methods of printing, especially when we need higher thicknesses of paste or when we need strongly colored surface areas. Work is in progress so we can expect improvements and further cost reductions because inkjet technology is still in evolution (after overcoming initial problems). Inkjet technology is currently expanding its reach to different kinds of tile and, of course, the technology aspect itself is arousing the interest of more developers.
Part 2 next week.