HP Photosmart 7960 printer

Page 13.

The end of the story, which may take 73 years

Having a great printer with great inks is only two thirds of the story, the media itself is an equally important part of the picture. Thinking about the media, perhaps this is the most important component, after of a long line of digital activity - taking the picture, editing the image, preparing the image and finally printing. This is the end product – the photograph itself.

Made up with HP paper

Papers are made up from two main components, the substrate and the image coating. The substrate is basically the thickness of the paper, the thicker the paper the less prone it’s likely to be to physical damage, i.e. folds, tears. Thickness gives the media a quality feel, people still want a “traditional photographic” feel to their pictures rather than a flimsy paper feel. The image coating is what receives the ink, the coating gives the image quality and image permanence.

The three types of substrates that HP uses are;

· Paper substrate

The paper base is made up from cellulose fibres, these are random fibres which together do not make a smooth surface. In order to make the paper smoother, fillers are added. These are small white particles approximately 200 nanometres in size that fill up the spaces on the surface in order to make a smooth white glossy paper substrate. A relatively thin image coating is applied on top of this. The ink penetrates through the fillers to the paper substrate.

· Plastic photo base – similar to Resin Coated photographic paper

At the core of this media is a very high quality paper. The fibres are not as random as on the paper substrate media, the fibres lay neatly together and the paper used is a premium high quality refined paper. The paper is encapsulated in a plastic barrier which gives its durable, waterproof quality and it also prevents the ink from reaching the paper. Therefore, the image coating has to be quite thick as it has to absorb all the ink.

· White film base.

A pure plastic base made from Mylar, which makes it extremely durable and 100% waterproof. It has a high gloss finish, but can feel synthetic for most use.

HP papers are swell

HP uses two types of image coatings, Swellable and Porous.

· Swellable coating

	1. Ink is fired at the paper
	2. Coating swells with ink
	3. Coating dries and encapsulates the dye

In terms of material, it’s a polymer that swells and absorbs liquid, or inks in this case. The ink is fired at the coating and it swells to absorb it. The coating swells to two or three times its original thickness. Starting directly after printing, for two or three minutes, or even for several hours, the coating returns to its original thickness. Now the coating has absorbed all the ink dye and has encapsulated it within the coating.

· Porous coating

	1. Ink is fired at the paper
	2. Ink seeps into pores
	3. Ink dries, leaving dye on the particles

Porous technology is used by manufacturers that claim instant dry prints. This technology differs from swellable in as much that the inks are absorbed into the coating through microscopic pores. This technology relies on very small particles, approximately 100 nanometres in size, which are glued together in such a way that there are air spaces between the pores, hence the name porous. These air spaces let, or suck the inks in, using a capillary action. The water in the inks dries out leaving a layer of dye embedded in the coating. This is not the same as encapsulating the ink, here the ink is spread out evenly over the surface within the coating.

All photographic papers on the market today have either a swellable or porous coating - it’s the coating that determines the quality of print rather than the substrate. It is therefore very important to correctly match the ink to the paper. A high ink output printer may work well on swellable coating, but use the same ink on media with a porous coating and that ink may be overloading the coating. The side effect of placing too much ink on a swellable media is that the ink takes too long to dry - hours or even days. Porous papers should be dry to touch almost instantly. If not, then this could most probably be put down to the pores being over saturated with ink. Again, there has been a mismatch between inks and paper. Generally, swellable coatings respond better to excessive amounts of ink than porous coatings.

HP inks and swellable coatings take in the region of 60 seconds before they are dry to touch, but ideally any print should be left for five or ten minutes before handling or stacking.

Faded memories

Fading prints is perhaps the biggest issue the customer has with inkjet photographs. Pictures that looked vibrant last year or even a few months ago are now beginning to pale, pictures are degrading and fading away in front of their eyes. The average customer doesn’t know or understand what the mechanism is that causes their prints to fade, they just know their pictures are fading.

There are two process that cause fading - light fade and air fade. Light fade is the one that the user generally regards as responsible for the deterioration of image colours. Light, over time gently breaks up the molecules that display the colours. Place the print in a dark draw and this process is halted. Light fading affects both types of prints, swellable and porous.

Air fade resistance on swellable coating	Cause of air fade on porous media

The other type of fading – air fade, only affects porous prints. Air fading occurs when pollutants in the air are absorbed into the pores of a print. (ozone is the key pollutant responsible for air fade). These pollutants get in between the small particles in the porous coating and attack the dyes. On the swellable coating the air pollutants are bounced off by the encapsulation.

It is this encapsulation on the swellable media that gives the HP prints their 73 year life (I will report my findings in 2076). If you use other manufacturers or porous media then the life span of a print will be the same as on any other dye based inkjet printer.

Life expectancy of prints

Kodak silver halide print 22yrs
HP Premium Plus 73yrs
Epson Colourlife 27yrs
Canon Photo Paper Pro 27yrs
Epson Premium glossy (on 2100) 56yrs (pigment ink)

The first three papers above are swellable, the Canon and Epson 2100 are porous. The figures above are for light fade only, add air fade to the porous papers and there could be significant fading within months. Porous photographs that are laminated or sealed behind glass will be better protected against air fade.

HP media in our test.

The papers performed as expected delivering vibrant colours on a heavyweight paper base, (Premium Plus Photo paper 280 g/m). As the paper travels through a U turn I wouldn't expect a much heavier paper to be available. However, 280 g/m should be more than adequate for most home and exhibition work. On completion of printing the print is tacky to touch, prints need to be handled with the great care at this stage otherwise the delicate coating can be marked. I have a wonderful impression of my fingerprint at the edge of one print.

The back of the paper has a special coating to prevent prints from sticking to each other, this has a strange furry feel to it. I would not recommend stacking prints for at least 15 minutes after printing. Prints on plain paper looked good especially when using the No 56 cartridge, but on several occasions during the test I had multiple sheets go through at one time. I suspect this is more to do with the actual paper rather than the printer feed mechanism. (Kodak Bright White Inkjet paper 90 g/m). You can fit a two sided printer accessory on the back of the printer by removing the back cover, this removable cover also makes it easy to clear any paper jams should they occur.

HP paper range;

HP premium high-gloss film - 230 g/m - (porous)
HP premium plus photo paper - 280 g/m, glossy and matte - (swellable)
HP premium photo paper - 240 g/m, glossy and matte - (swellable)
HP photo paper - 175 g/m, glossy - (porous)
HP everyday photo paper - 175 g/m, semi-gloss - (swellable)
HP photo quality paper, two sided - 160 g/m - (porous),

© Vincent Oliver 2003 www.photo-i.co.uk
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