27 Dec 8 STEPS TO RESOLVING REGISTRATION PROBLEMS
Registration can be one of the most nerve wreaking tasks in the screenprinting technologies for anyone who has to print multiple colors or produce a print that must register on the substrate perfectly with each print. You may be surprised that the downtime you experience trying to line up that job that did not want to cooperate is really not necessary. With a little knowledge and taking the right steps, you can all but eliminate registration problems from your life.
Granted there are dozens of reasons why images do not register on press. For example, if you are a textile printer and using a flash gel unit to slightly set the ink when printing multiple colors you may expect the material can shrink under too much heat as the moisture level of the material is reduced or in the instance of synthetic materials where the material shrinks from the heat that slightly melts the material.
Or, oftentimes, the screens are poorly made and are not flat, which could pose a huge problem in setups and printing problems. When you are printing multicolor work, it is a good idea to stack the set of screens on top of one another and tap the four colors to see if there is any play between them. If there is a difference, you can expect registration problems.
But, wait, there’s more! While you were attempting to register that job, there was a lot more going on that was causing you even more financial loss. The very things that caused the registration problem are decreasing not only your productivity but also a loss of quality. You may have an increase of dot gain or dot loss that will rampant from one substrate to another. The ink deposit will be uneven across the image plane and will result in loss of color consistency.
The most likely problem causing misregistration is that it could be that your press is out of parallel. You are not alone my friend, many printers, if not most, suffer from this same problem. All this can go away. You don’t have to work that hard to achieve excellent quality and increased productivity. All you need is to gain knowledge and put that knowledge to work for you.
The most important solution is to bring your press into a parallel and geometric plane. While many of the variables we are faced with are unavoidable or simply beyond what we can fix given the constraints of time and money, bringing your press into a parallel and geometric plane is certainly within anyone’s reach.
For anyone having registration problems, you need to first look at several variables, and decide which are causing the issue. Once you know where the problem lies, then fix that problem so you will not be continuously plagued with problems.
Here are 8 Steps to Resolving Registration Problems
- You must begin with films that are in register. If you are printing with roll film, registration could be an issue caused by drag from the weight of the roll. Heat and humidity could be creating a shift in the film positive during storage or exposure. There will be accumulation of heat as your exposure one screen after another without time for the unit and glass to cool down. The same heat and humidity can create a slight shift in the image area on the stencil after processing as compared to the image on the film positive. This is why you can expect to see a slight shift if you place the film on the stencil as a check.
You should have sufficient tension on the mesh that it won’t move during printing. Mesh tension should be maintained at the manufacturers suggested minimum tension level. If one screen is under tensioned and another is the correct tension level, they may not register well with one another.
The exposure unit glass must be flat. Heat from the exposure will cause the glass to sag in the middle and if so, it should be replaced. Check it with thread stretched from one corner to the opposite corner. Be sure to always align the screens in the exposure unit in the same directions, i.e. with the top of the screen always to either the left or right.
The press must be capable of holding the screens tightly in place. Side clamps on a manual press are always a necessity for properly securing frames in place.
The print head must be held tightly at the registration gate. It can usually be adjusted or the Teflon rollers may need to be replaced.
If you are working on a multiple head machine, all printing surfaces should be on a plane with one another. This can be easily checked by placing a screen in one head of the press and bringing it parallel with the first print surface. Assure that the printing surface is correctly aligned with this screen with the same off-contact at each corner of the printing surface. Next, bring the second printing surface under the same screen and adjust that printing surface to the screen so that the off-contact is the same on all four corners. Repeat until all printing surfaces are aligned on plane with one another and are in parallel with the screen in Head One. Any printing surface that is bowled or bowed should be replaced immediately. On some printing surface (especially those that have a single arm to which they are attached) if someone touches the printing surface with only a slight force it could be tilted to one side. This causes the image on that screen to travel further to reach the printing surface on that corner and thus creates a problem. Do not touch the printing surface to rotate them. Use the printing surface arm to move them.
Next, make sure that all Print Heads are in parallel with the printing surfaces. Since you placed all of the printing surfaces in a plane with one another and in parallel with Head Number One, simply place the same screen in Head Number Two and bring the screen into parallel and geometric plane with the first printing surface. Do not adjust the printing surface, only adjust the Print Head. Repeat this process on all Print Heads, so that they are all on a plane with one another and in parallel with all printing surface.
Since screenprinting is an off-contact method of printing, the mesh must be moved down to touch the substrate. If the screen is not on geometric plane with the printing surface, then the mesh will be moved more in the direction in which it is further from the printing surface. This will throw the registration in that cover off.
If all else fails, you can always use a band-aid such as trapping or choking the image to allow for some play in your system, while you continue to improve the other variables. Know that high-end printers are capable of butt-register and even sometimes leave a slight gap between colors when printing on absorbent materials where the ink will spread.
There is more to registration than explained in an article, and that is why I wrote the book, Parallelism and Geometric Plane. I hope this helps those with registration problems come with a quicker solution.
What do you think?
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