Inkjet printers work great for making transparencies used in photoresist methods for PCB's. Unfortunately, I made transparencies less frequently than needed to keep my inkjet cartridges from drying out and decided to develop a method that would work as well with my laser printer. My printer is an HPLaserJet 4101mfp. It cannot be adjusted to make dense transparencies.

The method I developed uses a black dry erase marker to make the image on the transparency more opaque. It does not smudge any of the lines or other details. It simply fills in the grain on the transparency. Dry erase markers are most commonly used on white boards when making an oral presentations. That is, they substitute for chalk used on black boards. I use Expo brand. I have not tried other brands. Expo was the cheapest at my office supply store. Permanent markers will not work. The procedure is simple. Just paint over the entire laser transparency on the toner side, let it dry, and wipe off with a soft tissue like Kleenex.

Procedural Details:

1) Black markers work best. It is harder to get all of the color removed from color markers. I have not tried colored markers, but I do not think they will work.

2) Do not scrub with the marker. Just lay on a nice wet layer like when painting with water colors. The transparency image is slightly softened by the solvent in the ink and can be scratched by the felt tip if scrubbed. If completely dry, you can put on a second layer, which I have not found to be necessary, unless I miss a few spots.

3) Let the marker dry thoroughly (at least 5 min.)

4) The dried marker comes off in tiny flakes. These can scratch the surface, if they get caught beneath the tissue and you scrub back and forth. Just wipe in one direction, then another, etc.

5) Fold the tissue as needed to get a clean surface. If you need to go back over an area, you can do that, but be careful. Once the majority of the marker is off of the clear areas, you can be much more aggressive to get the last traces of ink out of crevices, such as around thermals. You can then wipe back and forth or in circles as needed. I rarely have to do that.

Attached are some photos of the process. The first image shows a transparency that has been coated with the marker, but not wiped off. The second compares a treated transparency with one that has not been treated.

John

Figure 1_dry_erase_gross.jpg
Figure 2_untreated vs treated.jpg