Here are a few thoughts on the nature of paper to help you make prudent design and print buying decisions:
Custom Printing on Colored Paper Changes Ink Colors
When you print on white paper, the white substrate reflects the light back to the viewer without changing it. It does not add or subtract anything from the ambient light, except where the actual commercial printing inks provide color. In contrast, when you print on colored paper stock, the substrate changes the hues of the inks. A yellow or beige paper, for instance, will add a yellowish tint to the inks printed on it.
Therefore, you may not get what you expect when your job comes back from the custom printing supplier, and you definitely won’t see an on-screen image that will look exactly like the final printed product. If your brochure or booklet includes images of people, their skin tone may be less than attractive.
That said, this doesn’t mean you shouldn’t print on a colored stock. To get a more accurate view of how the final printed product will look, you may want to produce an inkjet proof on a sample of the paper substrate.
If you don’t like what you see, you have an option. Asking your commercial printing vendor to add a base of opaque white ink on the colored substrate under the photos will ensure that the paper reflects all wavelengths of light equally and therefore does not add a color cast to the process inks used in the images.
Paper Is Affected by Its Surroundings
Paper is organic. Therefore, it is affected by the surrounding temperature and humidity. Knowing this and accounting for the ambient conditions in the transport and storage of paper is important if you don’t want unexpected results during the custom printing process.
More specifically, the fibers that constitute a sheet of paper can change in thickness as much as 300 percent depending on the humidity. In addition, the same expansion of paper fibers in humid conditions can cause uneven growth or expansion of the paper in its length and width. Since paper expands more along the dimension perpendicular to the grain (known as cross grain), it can “grow” three times as much in this direction as in the direction parallel to the grain. This can wreak havoc with your printing plans.
In addition, exposure to light can change the color of paper and also affect its aging process.
To avoid problems, it’s important to transport and store paper in the proper temperature and humidity conditions and to make sure the paper is adequately wrapped to avoid exposure to light. Your paper manufacturer or printer can explain the specific requirements for your chosen paper stock. They will differ between paper stocks used for different purposes.
(For instance, the paper used for xerox printing is ideally stored at 30 percent humidity at a temperature of 20 degrees centigrade (68 degrees fahrenheit), whereas offset printing paper is ideally stored at 50 percent humidity at a temperature of 20 degrees centigrade. Due to the high heat used in laser printing, xerox or digital printing paper prefers a lower relative humidity.)
Finally, plan to have the paper delivered to your printer with adequate time for it to become acclimated to the pressroom temperature and humidity. (This may take 24 or more hours depending on the difference between the indoor and outdoor temperatures.)
Uncoated Paper Works Better Than Coated Stock for Glue Binding
When you perfect bind a print book, the bindery usually grinds off the spine of the collated press signatures to allow the glue to seep into the paper. This improves glue adhesion, so the pages don’t fall out of the book.
When you use an uncoated sheet for your print book, the paper is both rougher and more absorbent than a coated press sheet. Therefore, the glue has more surface area to grip and hold. This strengthens the binding. In contrast, a coated press sheet (gloss or dull) has a smooth surface and therefore does not provide as much surface area as an uncoated press sheet for the glue to grip.
Here are two ways to counteract this limitation and strengthen the glue bond if you do choose a coated stock for a perfect bound publication like a print book or magazine:
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- Use a heavier rather than lighter weight printing paper.
- Use a cold adhesive glue rather than a hot-melt glue to bind the printed product.
Discuss these options with your book printer. He may have other ideas as well.
This entry was posted
on Sunday, November 10th, 2013 at 3:36 pm and is filed under Paper and finishing.
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