TOO MOIST PAPER MOTTLINNG - TOO DRY PAPER MOTTLINNG - BAD PAPER FORMATION
MOTTLINNG - UNSUITABLE TRANSFER CURRENT(WHEN ADJUSTABLE) LINES,STREAKS AND BANDS -CRACKING LINES, STREAKS AND BANDS - LOW SCRATCH RESISTANCE
BACKGROUND NOISE SPOTS,BLISTERING - BLISTERING OF THE PRINTED SURFACE PAPER PROPERTIES AND PRINTING - CURLING
PAPER MANUFACTURING AND CONVERTING - WAVINESS AND SLACK EDGES PAPER MANUFACTURING AND CONVERTING - PAPER DUSTING  
     

Problem

Cause

Solution

TOO MOIST PAPER
This defect can be seen as a motting structure, with the defect diameter on the area of 1.5min, It can be observed most clearly on areas covered with multiple toner layers, like the solid green. If the paper is very moist the toner transfer efficiency and the print density can be reduced to a very low level (lower image). When printing two sided prints, the second side print quality is better than on the side printed first.
The paper is too moist and because of this too conductive in the toner transfer phase.

Keep the paper ream closed until the paper is used. Try another, unopened ream. The moisture level of the paper can be adjusted by the paper manufacturer to fit the other paper properties that effect the toner transfer efficiency.

Acclimatize the paper shipments in the printing room conditions with out opening the moisture barrier packaging, until the paper has reached room temperature.
With paper that is too moist it may be possible to enhance the print quality of a duplex job by printing the more critical side during the second pass, because paper loses moisture in the fuser.


Problem

Cause

Solution

MOTTLING - TOO DRY PAPER
seen mores clearly on the areas covered with multiple toner layers.
The paper is too dry and resistive in the toner transfer phase.

Keep the paper reams closed until the paper is used. In dry condition the paper can loose too much moisture. Try another unopened ream.

With paper that is too dry it may be possible to enhance the print quality of duplecx job by printing the more critical side during the first pass.


Problem

Cause

Solution

MOTTLINNG - BAD PAPER FORMATION
Fomation relates to the degrees of uniformity of the distribution of the fiber in the sheet. Bad formation can be seen as a mottling pattern in the printed sheet. with some machine this mottling pattern may look similar to that created with paper that is too moist. The defect can be seen more clearly on areas covered with multiple solid color layers, like the solid green.
Because a sheet of paper that has a bad formation is clearly un - uniform, the resistively characteristics vary from spot to spot over the sheet. These local variation cause local difference in transfer efficiency over the sheet seen as mottling of specially solid tone areas.

To examine the formation of the sheet, hold it against a light and see if the sheet is uniform and well formed. Incase the sheet is irregular, the mottling can be related to bad formation. In this case another paper type should be tested.

If the moisture layer of the paper is too high, the defects related to bad formation become more severe. Because of this it is necessary to keep the paper reams closed until the paper is used.


Problem

Cause

Solution


MOTTLINNG - UNSUITABLE TRANSFER CURRENT( WHEN ADJUSTABLE)
In some electrophotography machine it is possible adjust the transfer current to suit the substrate used. Unsuitable level of transfer current may cause low transfer efficiency, or in some case toner already placed on the substrate to be moved from the sheet before the fusing phase. This type of problems can then be seen as mottling in specially those area that have multiple toner layers on top of each other, like for example on solid green.

The level of transfer current effect the print quality, as it is the parameter used in controlling the electric field applied to move the toner to the substrate.

Try to optimize the transfer current by altering the transfer current in small steps and making test prints. Select the starting point based on a similar type and grammage paper printed earlier. When the paper is moist ( conductivity) it requires lower transfer current than when the same paper is dry (resistive). Keep the paper reams close until the paper is used.


Incase the paper is unsuitable for the process, for example because of vary bad formation, the solid color area print quality cannot be optimized to can excellent level.


Problem

Cause

Solution

LINES, STREAKS AND BANDS - CRACKING

The defect is visible as tiny ruptures at a fold. It is most common on coated grade and on high grammage papers. The defect is most visible when the folded area is printed.
The tensile strength of the fold decrease with decreasing moisture content of the paper, as shown in chart 5.1. Therefore cracking problem are more severe when the paper is folede when two dry, or against the fiber direction.

Acclimatize printed sheets when possible and crease heavy grammage paper before folding. High grammage paper will be in most cases give problems in critical print jobs, if folded without creasing, specially if folded dry directly after printint.

If possible, the design of page layout should be done so that the folds are in line with the grain direction. Grain direction of paper can be determined by bending and sequare piece of paper. The paper is about twice as stiff against the grain than in the grain direction, so sheets will resist the bending more strongly when folded against the grain.


Problem

Cause

Solution

LINES, STREAKS AND BANDS - LOW SCRATCH RESISTANCE
The toner layers have not fixed properly. The printed image can have a very low scratch resistance.

There has not been a sufficient amount of fusing energy to melt the toner onto the paper. This may happen specially when high grammage papers are run with high process speeds.

Some paper grades may contain compounds negatively affectig toner adhesion. In case these compounds migrate to the surface of the paper, only a weak bond is formed between the toner layer and paper sheet, creating low scratch resistance. The surface energy of the paper surface should match the toner used, to enhance the adhesion.

In the liquid toner processes good adhesion is achieved when the chemical properties of the paper surface matches those of the liquid toner.

Check the machine manufacturer specifications on grammages that should be run from by pass tray and or with lower process speeds. In case where the defect is related to poor or unsuitable surface characteristics of the paper, another paper type should be used.

Problem

Cause

Solution

BACKGROUND NOISE
Single toner particles appear on unprinted areas, in quantities high enough to cause an overall brightness decrease of unprinted areas. Single particles can easily be seen with a loup
  Check the developer age and the service interval for the color units. For example, if the developers are overaged there can be unacceptably high level of backround toner.

Problem

Cause

Solution

SPOTS, BLISTERING - BLISTERING OF THE PRINTED SURFACE
Small blisters can appear on coated grades on heavy toner coverage areas. On a multicolor plane, the underlying process colors may be seen. The blistered toner surface has a reduced gloss level and a rough surface.
This defect is caused by the heat applied to the paper in the fuser. The water inside the paper evaporates too quickly through the coating and toner layers, causing the small blisters. Therefore this phenomenon is more likely to appear on heavy grammage multi coated papers that have very closed surface.

The paper must be run with a lower process speed, so that the water doesnot evaporate too rapidly in the fusing phase. To avoid paper gaining moisture before printing, donot open the reams until the paper will be used. Incase the printing machine has options to either dry the paper before the toner transfer or to reduce the fusing temperature, these adjustments reduce blistering.

Try to avoid unnecessarily high toner coverages, for example by using under color removal and raplacing three and four color blacks with one color black when possible.


Problem

Cause

Solution

PAPER PROPERTIES AND PRINTING - CURLING
Severe curling of unprinted paper can deteriorate the runnability, especially in duplex printing. In some machines curling can also cause registration and other image quality problems. Curling of the printed sheets affects the visual appearance and hinders the finishing.

The change in humidity releases internal stresses in the paper and the result can be curling. This type of curling appears especially when the internal stress distribution of the paper is not even.

Curl of printed sheets can occur when on one side of the paper a large, high coverage toner layer is printed, and printed paper is left in an a moist environment. Paper sheet dimensions expand after printing as the sheets regains moisture from the air, this may cause curl when one side of the sheet is bound with the toner layer.

When paper related curling tendency is a continuous problem,another paper type should be tried. The paper should not be left unwrapped, to avoid the moisture change before printing. If possible, try to avoid high toner coverages on one side of the sheet with low grammage papers. The one - sided toner coverage related curl reduces in low humidity environment.

Problem

Cause

Solution

PAPER MANUFACTURING AND CONVERTING - WAVINESS AND SLACK EDGES

The edges of the pile of paper are wavy.
Wavy edges are generally caused by moisture pick up of paper exposed to ambient air containig high relative moisture. The edges gain moisture and expand more rapidly than the center of the pile. This problem can occur with unprinted paper, it is more likely to happen with a pile of printed paper. After the paper has dried in the electrophotographic printing process, the moisture difference between the air and the paper pile has increased.

Unwrap the paper just before printing, and follow the storage and handling guidelines of your paper supplier.

The waviness of the printed sheets relaxes if it is possible to keep the printed paper in the room conditions until the moisture level has reached the equilibrium with the surrounding air. Unfortunately this may take a long time, in some cases even days. This process can be speeded up by dividing the printed batches in to smaller piles.


Problem

Cause

Solution


PAPER MANUFACTURING AND CONVERTING - PAPER DUSTING
As an offset printing also in electrophotographic processes the dusting (linting) of paper is an important quality criteria. In dry toner electrophotoghaphy, even if there is no tacky inks stressing paper, the static electricity and electrical charges applied are dominat for generaing dusting from paper.

The dusting will accumulate on the transfer and photoconductive belts causing print quality defects. Dusting may then shorten the problem free lifetime of these senstive components and increase the service costs.
To reduce these effects it is important to use papers with lower dusting influence. Since it is almost impossible to know before usage of paper which products are good in terms of dust and which are not, the printers should require from the supplier from dust quality evidence about the products to be used. The paper producer should have in the quality management procedure calibrated method to evaluate potential dust (in ream dust) and generated dust (process dust).

Grater roller. Install grater roller with sharper points. Increase pigment strength of ink so as to decrease in ink film thickness carried on web.
Web bustle wheels. Move wheels so as to contact non image areas only. If moving wheels is not possible, apply teflon tape to lessen abrasiveness of wheel surface.
Improper air flow through oven causing web to flutter and make contact with oven apparatus. Consult oven manufacturer for proper adjustment or adjust web tension.
Chill role no cool enough. Reduce chill role temperature so that post chill role web temperature is 900 F or less. Recommended chill role water temperature is 72 - 750 F. Caution : If chill roll are too cold, condensation can occur. Reduce oven temperature to minimum necessary to get the web through chilling and press folding delivery operation.
Web temperature reached in the oven is not high enough to drive off sufficient ink solvents. If flame impingement drier used adjust flame tips to impinge properly. If high velocity forced air drier used, raise circulating air temperature in oven until making is eliminated. Caution : Remember paper will burn it 4510 F and can scorch at lesser temperatures. Decrease press speed. Increase air velocity through oven as to remove air and vapor layer clinging to moving web. Consult ink manufacturer to obtain faster drying ink.
Dryer does not have capacity to properly handle press speeds reached or type of work printed. Consult dryer manufacturer.
Paper is very absorbent, very little ink penetration occurs to provide basic for binding to paper. Consult paper manufacturer, change paper.
Ink film thickness is too great. Raise air temperature circulating in dryer. Increase air velocity circulating to help remove solvent vapor layer. Consult ink manufacturer, change to faster drying inks.

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