Improved paper chemistry provides multiple benefits

Published: January 01, 1996, By Smith, Karen

Don't assume that the chemistry of paper is of interest only to your paper supplier. If you convert paper, what you don't know can hurt you.

If you effortlessly convert packages, cartons, or labels with high recycled fiber and high ash content and flawlessly print in four or more colors, then don't read on. But, if you sometimes have trouble with dusting, changing printing blankets too often, or fretting over bottle labels that can't stand up to a bath, then you should know about a breakthrough in paper chemistry called "microparticle technology."

First a few words about the composition of paper today. The more you know about what's in your sheet, the better able you will be to achieve the properties you need during converting. And that's not easy, considering the way the composition of most grades has changed over the past few years. Just because the paper you use has the same brand name doesn't necessarily mean it contains the same ingredients.

As you know, waste furnish and ash content are usually higher these days. In addition, many other, sometimes incompatible, additives and contaminants are in the sheet. The combination of ingredients can have significant impact on end performance.

Seeking Harmony

For this reason new chemistry has been needed to bring "harmony" to the sheet and to program in the properties to meet specifications that you or your customers seek.

In fact, silica-based microparticle technology is already revolutionizing paper and actually helping converters, who may not even be aware of it. The discovery has been used in fine paper grades, liquid packaging, and linerboard for about 15 years. In papermaking the simultaneous control of retention, dewatering, and strength of the sheet while it's being made is key to a high quality base sheet. If you can control those functions, you can actually take control of the way molecules lock together in the sheet.

From this foundation your paper supplier can enhance this "interactive" sheet with complementary chemicals that improve sizing, formation, and other qualities. The result is better printability and moldability, better adhesion to glass or plastic, and other desired properties. For converters wanting to reduce basis weight of recycled linerboard, microparticle technology can address that also.

Since the paper you buy isn't labeled "Microparticle" or "Containing Molecular Harmony," how do you know if all the desired properties you want are built into the sheet you buy?

Trial and error is one way. Another approach is to ask your paper supplier for a breakdown of precisely what your sheet contains. Just as the phrase "Intel Inside" has become important to users of advanced personal computers, you may want to know if microparticle technology is in your sheet. You may also want the provider of microparticle technology to be included in a problem-solving or product-development effort with your paper supplier.

Over the long term many problems will be minimized, including dusting due to higher ash content in the sheet, sheets that have improper register because they slip, or labels that are poorly printed or fall off.

It is expected by many that the application of microparticle technology will become status quo for most grades within a decade. In the meantime it may be helpful to understand how silica microparticle technology works for various applications and pursue it for your own specific needs.

Poor Esthetics Can Result

Printing is nothing more than a process of "painting" dots on the surface of your sheet. If the dots spread out or sink into the sheet, the lack of micro-uniformity of the sheet will become evident to the naked eye. Sometimes what initially appears to be a problem on the surface is actually a problem in the base paper.

Caliper is critical as the sheet goes through different presses. If paper is weaker or less dense, it compresses differently. The ink that's picked up differs from spot to spot. Uniformity of the surface relies upon its foundation of uniformity in the base sheet, comprised of fillers, fibers, starchy sizing, and, sometimes, microparticle chemistry.

Just as enhancements in converting equipment can improve quality, modifying or replacing a paper machine can also have an impact on sheet quality. But, machinery can never reach into the sheet the way interactive chemistry can, to actually program molecules to meet desired end-product requirements.

Rebuilding a machine gives some results over time, but you may have to wait several years to see something close to what you are looking for.

Simply stated, if your paper supplier's paper machine is not doing its job, interactive papermaking can often smooth out the papermaking process itself. This will, in turn, improve converting and the end product you are expected to produce.

When coating isn't uniform, it can come apart and pick on your printing presses. Once again, if you have a good base sheet to accept the coating, you shouldn't have spotty printing. Your papermaking supplier needs a sheet that can be compressed evenly and polished through the super calenders to give you the gloss you need.

Advantages for Labels

Hard sizing in a well-formed base sheet is especially important with labels. The dual job of accepting color printing on one side and bonding well on the other is critical. If formation is not uniform, the label won't print or attach well.

Wet processes for liquor and other glass bottles place even tougher demands on labels. The color printing process requires a strong label in itself; the bath stages demand even more in the way of strength. If your base sheet wasn't formed well, this will become evident through picks in the printing, or, even worse, it will fall apart as it goes through the various baths. Silica microparticle application at the mill can add strength, allow sizing to be more uniform, and, thus, give better printing and label integrity during the hostile wet processes.

Slitter dust can be a growing problem as filler content increases. If fillers are better distributed in the sheet, they will be held tighter in fine paper or board. When filler distribution is poor, it's like hitting a chalk motherload in the sheet, generating a lot of dust. Once again, better formation of the sheet distributes chalk evenly through the sheet. Silica microparticle technology accomplishes this by locking molecules in place to meet a desired outcome.

Since the Rule 41 change allowed the use of lower basis weight linerboard, provided that it has equal strength, some converters are helping their customers to lower shipping costs with thinner board. This savings is achieved by adding a proprietary combination of silica and cationic starch while the board is being made. Beyond the straightforward savings through lowered weight, issues such as improved scoring and flexibility of board are also being tested.

Converting by design adds to the end performance of the product. The paper you use should contribute to that objective. If your paper supplier is using microparticle technology, additives, and advanced sizing in an interactive way to meet your needs, paper won't be a bottleneck to your success in the marketplace. The hidden advantage of paper chemistry could help you open the way to exciting new possibilities.