Printing
Jack Knight is director international technical service for INX International Ink Co. In his latest article, he talks about the role of the pressman
What is a pressman? Twenty years ago I came across an article written by J.C. Kernan about offset pressmen. I have adapted it so that it fits the guys who work in the metal packaging industry and wanted to pay tribute to pressmen around the world. I have honoured them in the words below and added a bit of humour.
Somewhere between the can salesman and the shipping department you will find an extraordinary character known as the pressman. Pressmen are all different, but each has the same creed, which is to do the best job they can and to protest loudly and strongly about anything that gets in their way while they are perfecting the craft of applying ink to metal.
A pressman can be found almost everywhere:
• In the water
• Between the ink rollers
• Beside the gripper bars
• Over the feeder
• Under the delivery
• On a coffee break
• Arguing in the plate room.
Management needs them, the salesmen kid them, their helpers cuss them and plate makers hate them!
Pressmen are a strange breed of contradictions. They like single colour jobs, line work, greasy compounds they can mix into their inks, the occasional beer, and inventing new names for the foreman.
But they can’t very well tolerate the foreman, the pre-press department, off colour inks, replacing blankets, short runs, tough registration jobs, and above all the guy that talked them into being a pressman!
If you look in a pressman’s pocket you will usually find the following:
• A few open end wrenches
• An ink knife
• Allen wrenches – a complete set except for the one he
needs
• A depth gauge
• An HFI sheet – he hates these but wants to make sure the
sorting department has steady work.
A pressman is a conscientious tradesman with grease on his face, a genius with oil on his shirt and an artist with ink under his fingernails. Yes a pressman is a complex creature. He says he hates his job, but he would never be happy without the smell of ink. He says he cannot stand the site of a press, but he knows in his heart that he would not give it up for all the tea in China.
And when he goes home at night, after all the headaches and frustrations of a difficult day, he can make himself feel like new by merely taking a can off the shelf at home and setting it on the kitchen table and saying to his kids, ‘Your old man printed that. I’m an artist. But most of all, I’m a damned good pressman.’ Please make sure you let them know how much you appreciate them and what they do for our process in providing decorated cans for the industry.
The role of a pressman
Here is what a pressman needs to know about his presses inking roller system:
A worn out roller, a roller with damaged bearings, rollers set with too much pressure or a roller that has not been properly cleaned can cause the following problems:
• Colour inconsistency
• Poor solids
• Streaks
• Dot gain.
Also if the rollers look shiny and have a glassy feel to them, they are glazed. When rollers are glazed, the texture in the ink rollers surface does not transfer ink effectively, which means you will need to run more ink and water on the press to achieve the required ink densities. Yes ink rolls have a texture to them when they are brand new. You want to maintain that texture for proper control.
Fountain solutions, wash-up solvent and ink are bound together and trapped in the ink rollers texture on the surface of the roll causing a glazed surface. Cleaning with solvent will not remove the trapped materials in the ink rollers surface texture.
Böttcher Rollers recommends the following steps to properly clean ink rolls:
Step one: Use a water miscible wash (solvent that mixes with water) to remove both the solvent-soluble and water-soluble particles that are near the top of the rolls texture. This leaves the insoluble particles.
Step two: Use a non-grit roller paste to remove the insoluble particles. Be sure to use a paste that is designed and tested for the type of rollers you have.
Step three: With the layer of insoluble particles removed, most of the remaining soluble particles will be exposed and can be washed out with a second water-miscible rinse. You can use warm water during the final rinse which will help dissolve any fountain solution and synthetic gum. Never use pure gum Arabic, the pH of the gum will increase with age and if you use it on a printing plate it will absorb moisture in the atmosphere which will oxidize the plate’s surface.
Setting the pressure
Now we have clean ink rolls that will be receptive to ink and water. So the next step is ink roller pressure. Setting rollers with too much pressure is a common mistake and an expensive one. Pressmen sometimes think that the pressure is what moves the ink and water. It’s not. It’s the shearing forces generated by the different speeds of rollers with different diameters.
More pressure does not help, and it can actually affect the quality of the print and lead to extra downtime and operating costs. Too much pressure will also affect dot gain on halftones and print quality on small reverse type being printed in solid ink areas of a design. Too much ink roll pressure will also cause the rolls to wear out prematurely. Minimal settings roll to roll or roll to the printing plate are best. Press manufacturers will specify the amount of pressure that they consider ideal. I recommend that you contact them for these recommendations or look them up in your operator manual. Pressure is a critical setting, big increases should be avoided, small changes are best. An increase in a roller stripe can result in a big increase of pressure to the rolls.
Finally monitor the ink roll durometer. If you notice a 10 point increase in ink durometer you have glazed ink rolls. If you are using alcohol free fountain solution then you should be using a lower durometer on your ink and water form rolls. You should use a higher durometer if you run alcohol. When alcohol is removed from the fountain solution, the viscosity of the solution becomes thinner. You need softer durometer rolls with lighter pressure stripes to help move the water down through the ink roller train and through the dampening system. Ultimately you should run less water using an alcohol free fountain solution versus using alcohol.
The bottom line to achieving a quality impression is to control your process. When a quality defect occurs it is necessary to stop printing and check the basics I have listed. Check and change, if necessary, one basic at a time to determine if it corrects the problem. If too many basics are checked and changed at the same time you will never know what corrected the problem. Remember, “A metal decorated container has a quality image that sells product on the store shelves.”
If you have a problem or process that you would like to discuss please feel free to contact Jack anytime via email at [email protected].
Alternatively you can contact Alec at [email protected]
More than 200 years and the can is still king!
Let’s work together to keep it that way.
