imagepac superclear & xtra Support

Summary

Ensure you have a dark black negative. Hold the sachet by its seam, never its middle- this avoids creasing it. Make sure the sachet is at least 7mm (3/8”) larger than the text in the negative to avoid the curvature at the sachet edge ruining your plate. Use correct depth of bearers; plates must always be flat- uneven plates produce uneven relief. When compressed, ensure sachet is free from creases. Place imagepac down so that the printed ‘imagepac’ is readable. The flexible side will always be next to the negative. Always mask off around the negative with light-stopping material. Use a back exposure time to achieve about 40% floor. Use a main exposure time that holds fine relief while not closing fine reverse. If you are trying to hold very fine relief then you can increase the floor to about 60% of the total plate thickness as this makes it easier to hold fine relief.

More in depth details can be found below

The Negative

Create your design in a software program and directly print it on an inkjet or laser printer on imageblack film. If your negative is smaller than the lower exposure glass then light will come up around it and bounce off the machine and the upper glass to fill in the floor, in particular at the edges, leading to an uneven or filled in floor. Avoid this happening by blacking-off around the negative. Lay a masking template around your negative to make it the same size as the lower glass. Otherwise, A8 will produce a much larger floor than A4 with the same exposure times. Using the masking template means that now all the sizes will expose the same.

 

To check the quality of your negative, hold it up to the light and see if you can see light through the black parts, or use a densitometer to accurately measure it- a figure of 1.8 is the absolute minimum to work with, but a figure of above 3.0 is desirable. If you can see through the negative, then it is almost certain that the plate will be of poor quality as well (although UV-transmitting and daylight-transmitting are not always the same). If your negative lets light through then you may be able to use it, but you will have to reduce the amount of time on the 2nd exposure to a minimum, poor negatives can make good plates with the minimum main exposure time through the negative, after that the plate will fill in. The plate quality will ultimately only be as good as the quality of the negative.

Exposing imagepac

The 1st exposure time will make the floor or support, the 2nd will make the detail by shining light through the negative. If you are using your exposure machine for the first time that day, warm the bulbs up for three minutes before exposing. The critical time in plate making is the 1st or back exposure. Bulbs give out much more light when hot; the back exposure is done first and is the shortest, so cold bulbs have the largest effect on the depth of floor. A small variance in the 1st exposure time has a much greater effect than a similar change in the 2nd exposure. Cold bulbs often give low plate floors which lead to wobbly lines or text falling off. Use spacers (bearers) to ensure even compression. These should be the imagepac thickness that you are using plus the negative thickness (usually 0.15mm) and the front film (0.06mm). For a 2.3mm (90”) thick imagepac use 2.4 – 2.5mm spacers. For a 2.55mm imagepac (100”) use 2.7 – 2.8mm spacers. Ensure that the glass bed is clean and dry. The negative should be dry and with the dark enough to stop UV. Lay your imagepac sachet on the negative, making sure that you can read the printed “imagepac” on the edge of the sachet. Close your exposure unit. The upper glass should exert enough pressure to remove all wrinkles and flatten the sachet. If you are using your existing exposure unit then you should use the same exposure times as you were using with liquid resin. Different exposure units have different light configurations producing different light intensities, also, as bulbs age they produce less light, often less evenly distributed down the tube. For these reasons, it is not possible to state exact times to expose a perfect imagepac on every machine.

 

This method will help you set the exposure times accurately when you use imagepac.  It will also help you perfect plate quality if you are finding it difficult to hold fine relief or you are filling in fine reverses. Set your current back exposure time, to save cost you can use A7, A8 or A9 sized sachets, lay the sachet on the negative on your exposure unit with ‘imagepac’ readable. Black-off completely around the negative. Expose the sachet for 30 seconds on the back only- do not use the main exposure.  Remove the sachet, cut the front plastic with a scalpel not scissors, and wash it gently as it will be delicate without relief. Measure the floor, aim for a floor depth that is just under half the total plate thickness (35-45% is ideal). Adjust this time accordingly to achieve the desired floor thickness, this is your correct back exposure time. Now calculate the main exposure time, if you only have one set of bulbs or the upper and lower lights are the same, then the main exposure will be, as a rule of thumb, about 8 x the back exposure time you have just set. Use a negative that has fine relief and reverse on it. Ideally, use a specially made test negative. Place the negative on the unit and the sachet on top of it, imagepac readable. Expose for the back exposure time that you have just set, then expose for the main exposure time through the negative for 8 x that time. In some cases, you should adjust your main and back exposure according to your artwork.  Calculating the correct main exposure time depends upon how deep the floor is, how much of the negative is black and the fineness of the artwork. Remove the sachet and without cutting it open, press it between your finger and thumb. The relief should be firm to the touch surrounded by liquid resin.  If the plate is under-exposed the relief will not be attached to the floor.  In this case if you squeeze the sachet, the text will move freely in the resin. To rectify this, increase the main exposure time by 30 seconds and repeat the process until the text holds.  If the plate is over-exposed, the pools of liquid resin will be shallow or non-existent and the fine reverses will have filled in.  The plate will feel rigid with very little liquid resin present. To rectify this, decrease the main exposure time by 30 seconds and repeat the process until the text is surrounded by liquid resin.  When you have perfected the main exposure time, wash this plate out, post-expose it and check that you are happy with the fine reverses and reliefs in detail using an eye glass.

Processing imagepac

You need to cut the imagepac open to reveal the liquid resin. You can either cut the border off with scissors or the preferred method which provides greater support, is to cut the plastic front out with a scalpel.  Place the imagepac on a flat surface, with the side with the text in reverse, facing up.  Cut through the outer film only, around all four sides, just in from the seal.  Open the wash out unit lid and ensure the sticky green base plate is dry. You can use a squeegee to dry it quickly. Stick the sachet to the base plate with the cut side facing you, press the edges down firmly and peel off the cut piece of plastic. Ensure that you have added the correct concentration of wash out developer (typically 2% of volume) to the water bath.  An ideal water temperature is 40C. Wash out for 3-4 minutes, remove the plate and rinse it, check it is clean before going any further. Normal brushing will not damage the image on a well-made plate.

 

To make your stamp sheets really shiny, dry the sheet before post exposing. You now need to post expose the stamps to finish the hardening. If you wish to ensure a completely dry tack-free printing surface then dissolve a teaspoon of imagepac de-tac salts in the post exposure water, this will give the stamp a slightly chalky appearance so it is not advisable for craft stamps. Leave the rear side of the plastic on to get a naturally sticky back, remove this if you want a dry back to your stamps. Germicidal post exposure light will give a very dry surface finish, alternatively you can use a tray of water in sunlight. Rinse and dry before applying to a self-inker or sticking to a printed acetate. imagepac can be stretched, so take care when applying. You can apply tape to the back of the imagepac plate, lay the plate face down on a clean smooth surface, then apply the tape to the back of it in a sweeping motion to avoid air bubbles.  Alternatively, attach one edge of the plate to the adhesive stamp base and let the rest fall into place or lay the plate face down and lower the adhesive stamp mount down onto it.

Plate Making Problems

Start with the negative:

The most common problem of all is that the negative is not made dark enough. You will see this as a stamp that has a grainy high floor with no depth of relief. Check this by looking at your negative against the light and seeing if you can see through the black, it should be solid and dark not speckled and full of holes.

Then measure the stamp:

Measure the total thickness (relief) this should be as accurate as possible, certainly across a stamp you would want less than 10 microns of variation in relief. Error in this is adjusted by the bearer thickness, remember the bearers should be about 0.25mm higher than the final stamp height to take account of the front imagepac plastic (0.05mm), the negative (0.12mm) and any shrinkage (3%). If the relief is level now check the base or floor, this can only be out if the upper bulbs that generate the floor are not giving an even light distribution.

Stamp exposing problems:

Always fix the first exposure that makes the floor first, set this to between 35 and 45% of the total plate thickness, then get the relief right to be neither over nor under exposed on that floor thickness. base orThe main exposure timeOver-exposure means too much light and you will see this as a solid stamp or your text being blurred. Take care that the negative that you have used is not too small and light is coming around the side of it and over-exposing the stamp. It is safer to entirely black-off the area around a negative.

Under-exposure means too little light and you will see this as a liquid stamp or that part of your stamp falls away in the washing process.

Washing problems:

If you failed to wash a stamp out properly it will give an unattractive plate with specs or lines on it where the liquid that should have been removed has hardened in the post exposure or final hardening. The floor will look rough and not smooth and areas between two close parts of relief will be clogged up losing print detail, the print effect is similar to over-exposure.

Post exposing problems:

If the part is not rinsed off properly or if the post exposure water is full of particles, those loose particles may stick back onto the non-post exposed stamp and again it will loose detail. If you fail to harden the stamp under water for long enough it will be soft, susceptible to damage later on and will be sticky on the surface.

There are a few things that change every time you make a stamp, and the more you understand how to control them, the more repeatable your process will be.

Factors listed in order of importance:

  1. The length of time bulbs have been on: bulbs level out output after a few minutes, the difference from cold to hot will be around 50%.
    2. The external temperature governs the reactivity of the resin (this will be affected by around 30% from cold to hot) and also the light output of the tubes changes significantly as tubes give out more light, the hotter they are.
    3. The amount of open area (not covered by a negative) on the bed: in typical exposure units with lower and upper lights, the light reflects around the negative, bouncing back and filling in the floor, this affects exposure times from small to large negatives by about 25%.
    4. Variations in cure speed of the resin is about 15% maximum.

Helpful hints: Check that your negative is solid black as this could let light through and give you a shorter time window to make a good plate. First warm up your bulbs to ensure that they are not too warm or cold.  Keep your resin at room temperature. Black out the area around the negative when using smaller sizes to ensure that the light does not get bounce off around the negative.