Quality Policy >> Application problems & solutions
Common problems faced by users of Coated Duplex Boards and their possible solutions
Hickeys are specks in print that look like doughnuts or white spots. Hickeys occur when a contaminate sticks to the plate or blanket and interferes with the print quality.
Causes : Doughnut hickeys are caused by solid particles sticking to the plate or blanket. These particles accept ink and reject water. Because of its thickness, the particle is inked but the surrounding area is not. The ring around the particle makes it look like doughnut.
Solutions : Blanking the Board or running a thicker ink film may wash the contaminate away. Blanking the board is running the board through the press with no ink or fountain solution because blankets can remove the debris from the board. Sometimes, damping media may be used in the first unit and other units can function as usual.
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Mottle is non-uniform ink lay, or when the printed reproduction has a pattern, which is not present in the original art work.
Causes : Mottle can occur due to several ink, board, press or systems problems.
Solutions : If the printer is experiencing ink lay problem, the following items should be checked.
 Tack-graded inks to be used. To print with the highest tack ink first. |
| Quick release blankets may minimise the problem. |
| Turn over 50 sheets and print on the opposite side to determine if the ink lay changes. |
| Run another lot of board for comparison. |
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Setting : Ink-setting time is the amount of time required for the ink to gel or set-up to the point where the sheet can be re-worked through the press.
Drying : The process of ink drying is a chemical reaction that may require more tan 24 hours so that the print film not subject to deformation when handled roughly.
Causes :
| The setting speed or formulation of the ink. |
| Inadequate amount of offset spray. |
| Formulation of ink. |
| The substrate is too acidic |
Possible solutions :
| Check the mixture of the fountain solution and adjust the pH to be in the range of 4.5 to 5.5. |
| Add some driers in the inks. |
| Avoid putting excess quantity of ink. |
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Causes : Blistering takes place on printed surface due to either escape of entrapped moisture or due to blow-up of coating film or ink film or due to rupture/breaking of coating / fibre surface under heat / plasticity. Sometimes, highly tacky ink coupled with high cylinder pressure or printing machine speed can lead to such problem especially when the printing is of solid colour.
Possible remedies : The machine operator can optimise the machine speed, ink tackiness, the cylinder pressure and by controlling the surrounding factors like humidity and temperature to overcome this problem. The printer can also keep the material in AC and Humidity Control Room to condition the paper before use.
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Causes : The structure of Board is made of several layers of fibre agglomerates formed during drainage of water. These are pressed together during drying and subsequent operations. The outermost layer of fibres are rather loosely held because it consists of more fibres. This could be because fibres are made to bind themselves to the board surface by process of sizing in the size press or by application of chemicals like PVA.
Such loose fibres stick to the blanket / plate during printing process or accumulate as dust in the system or various parts. During the process of printing, these fibres may pick up the coating from the board.
Possible solutions :
| Make sure that enough board has been run through the press for the system before attempting to address the problem. |
| Decrease impression squeeze to minimum. |
| Reduce the tackiness of the ink. |
| Use a quick release blanket. |
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We can define 'Crease" as a carefully controlled Deformation of the Paper Board that makes an accurate folding along the predetermined line(s) possible.
The creasing operation requires the following :
| A good condition creasing rule. |
| A good condition female groove / the channel. |
| A punching machine to mount these. |
The following are the most important variables in the creasing operation :
| Thickness of the board to be creased |
| Thickness of the creasing rule : Between 150 - 700 microns, a 2 point creasing rule is to be used. Below 150 microns, 1 or 1.5 point rule is to be used. |
| Width of the female groove / channel : It is the thickness of creasing rule plus twice the thickness of the board to be creased. |
| Depth of the groove / channel : Generally, it is 1.5 times the thickness of the material to be creased in boards upto 450 microns and approx. equal to the thickness of the material over 450 microns. |
| Closure Distance - The distance between the base of the channel and tip of the creasing rule. This can vary from machine to machine and in most creasing machines, it is 23.80 mm or 0.937 inches. |
If the board cracks during creasing operations, there could only be two possible reasons
| Insufficient moisture in the board |
| Use of improper creasing rule |
Possible Solutions :
| Water damping of the board |
| Correct the depth and width of grooving |
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