March 15, 2010
What this means is that you have got to great a space between successive gear teeth.
This is usually the result of wear that occurs to the teeth of the gears and although they must have a small gap to allow them to be correctly engaged when adequately lubricated, to great a gap is generally what excessive back lash alludes to.
This wear will mean that your gears will not mesh correctly, which in turn changes the position of the driven cylinder in relation to the drive cylinder.
This generally leads to mis-registration and no amount of adjustment will correct it until you replace the gears that are worn.
If you have multiple gears in a chain then this problem will simply be multiplied and will make the registration issue even worse.
Backlash can and will cause vibration on the machine as well; this normally shows in the amount of plate bounce you may experience and will certainly add to even more print issues.
Bottom line excessive spacing between the teeth of your gears as they wear will make the achievement of good quality print impossible. As a result some gear trains are built with anti-backlash gears that allow on press adjustment without the need to immediately replace the worn gears immediately.
March 8, 2010
This is a common issue that many printers have to struggle with on a daily basis.
While flexo is proving to be more than a match for offset it still uses a compressible plate and therefore allowances have to be made for sublimation and compression when creating the necessary color separations whether in hard copy or digital format.
Such areas that need particular attention are font sizes, intaglio and relief line dimensions, range of colors and screening technique and dot size and shape used.
March 3, 2010
It would be to easy to say good old fashioned “elbow grease” was the solution ie : manual scrubbing of the anilox, but to some extend there is some truth in this statement. Manual scrubbing with the right type of brush, in combination with the appropriate cleaning solution, can and will help to get an anilox roll clean. If you note, I did say “will help” but the truth is that while manual cleaning does just that it is not efficient, is hugely labor intensive, and absolutely cannot get into the bottom of the individual cells where the real hardening of the ink and coating is taking place.
The solution has to be and is mechanical cleaning, but before you say eureka there are several options to consider.
These include Ultrasonics- this method can only be done off press and uses sound waves to implode microscopic air bubbles in a tank of heated liquid which very quickly and efficiently can clean all sizes of rolls. This method is very effective and generally only needs short cleaning times for most rolls.
Media Blasting- this process uses an abrasive medium that is blasted at the roll surface, and again is done off press. Rotational speed, dwell time, air pressure, traverse speeds need to be carefully monitored at all times.
Baking soda cleaning- Similar to the media blasting but utilizes baking soda as the cleaning media but can be done off and on press. Same consideration needs to be made to speeds, rotational, traverse and blast pressure as media blasting.
Cyrogenic cleaning- A very environmentally friendly process that uses dry ice pellets to remove the contamination from the roll surface and cell structure, but cannot reach into the smaller cell engravings. Air velocity is a serious consideration. Can be done off and on press.
Laser cleaning – A very high tech cleaning method that can be done off and on press, thermally ablates material from engraving but can be slow.
March 1, 2010
This is perhaps one of the most debated questions in every flexographic market today. It is a question that is asked in every area of flexographic printing, but there are some basic questions you need to ask yourself when setting off down this path, and are as follows:
- What surface will the blade have to wipe against? – for example chrome or ceramic.
- What ink/coating system will you be using, such as solvent,water based or UV.
- What viscosity will you generally be running at?
- What line count will you have on your anilox?
- What volume of ink will your anilox be carrying?
- What print length do you intend to run?
- Is employee safety an issue when handling the blade?
- Is it a single blade or chamber blade set up?
- How clean of a wipe must you have?
- Will it be running in a corrosive environment?
- How Corrosive is the ink or coating that you will be running?
- What speed will you be running at?
- How skilled are your operators?
- What quality of graphics do you intend to run?
Quite a list I am sure you are thinking, and truthfully not everything that could be asked for every application but if you have made the right choice of vendor they will be only to willing to provide the best advice, you just need to ask for their help.
March 1, 2010
Well, the simple answer is No, but I am sure you all ready knew that when you penned the question. Yes, there are plates available that are able to handle a wider range of demands, but with so many variables to be taken into account it is unlikely there will ever be one plate to suit all your needs, unless of course you are printing the same job, on the same machine, with the same ink on the same substrates.
In today’s competitive market place and buyer demands the reality is most printers have to take on what ever work the salesman brings through the door, be it 4 color process, solid & line work or screens in excess of 175lpi.
The good and the bad news is that there is a wide range of solid and liquid plates available for the printer to choose from and most reputable suppliers will be only to willing to help you to make the right choice for your unique application.