Using the Right Glue for the Right Application

Technology Feature
Using the Right Glue for the Right Application

by: B&R Moll, Inc.

Spring, 2008

Today, trade finishers face the challenge of having to select the most effective gluing product for a myriad of specific applications. This results in a constant balancing of pricing and the wide range of product effectiveness. Binderies must select the right glue after considering such factors as the intended end use of the product, the specified coatings or finishes, different types of paper stock, and storage conditions. Given these factors, binders also must weigh the cost savings of using a lower-priced glue against the possibility of performance failure in a specific application.

Adherence
Glues must be carefully selected to adhere to whatever coatings or finishes have been required by the bindery’s customers. To complicate that selection, the coatings and paper stock that have been used successfully with certain glues frequently change in composition, causing the glues to lose their effectiveness. A plethora of coatings – such as UV, aqueous, and standard varnishes – are constantly changing in composition due to the varying availability of certain chemicals. Some chemicals can no longer be used because of raw material availability, a situation that is out of the binder’s control. The use of different paper stocks, too, changes regularly. Paper stocks range from recyclable paper that is widely used in the printing and carton industries, to standard offset, cover weight stocks, and fluted carton material that are finding wide acceptance in direct mailers, brochures, and information packets. As a result, binderies must deal with a wide range of adhesion issues. For example, flood coating of paper is commonly used in applying certain coatings. This sometimes creates a problem for gluing because these coatings have high resistance to adhesion.

There are several effective ways to combat loss of adhesion. One is to block out the glueable area on the paper. This will create an opportunity for the glue to bypass the coating and adhere directly to the substrates below the coating. If using a block out is not an option, binders can add a glue assist to their existing dies or new dies at the time of die-making.

Multipurpose Adhesives
Binders clearly need to use glues that are highly versatile, can be counted on to perform effectively under a wide range of conditions, and work well with other technologies and diverse materials. Are there glues that can be considered to be multipurpose, reliable adhesives?

The major trend toward the use of multipurpose glues has been the increasing acceptance of hot melt adhesives. In this connection, hot melt glues have been replacing liquid “cold” glues, when a ready-to-use glue and quick set-up times are required. Hot melts are considered the glues of choice in a broad range of end products, such as void fillers in some heavy carton applications, short-run applications such as packaging, and fulfillment items. Here, a glue must not only provide adherence to the product, but also to fulfillment information in cartons, pocket folders, and shelf talkers. Hot melts work well with diverse paper stocks, but are the best glues for any stocks that are flood coated or laminated.

For use with UV, aqueous, and varnish coatings, hot melts are the most effective glues on the market. Hot melt adhesives break through these coatings and secure a good bond for the coating and the paper substrate. Also, hot melts provide excellent adhesion in box applications, brochures, pharmaceutical inserts, direct mailers, and pocket folders. Typically, hot melts are used in the preparation of presentation folders, which requires a high concentration of ink coverage, because they provide excellent adhesion to folder pockets and coatings. In addition, hot melts provide high performance in short-run carton and sleeve applications because they have an instant adhesion to both substrates.

Hot Melt Glue Versatility and Cold Glue Advantages
Hot melt glues demonstrate their versatility by performing well in applications that have a wide range of temperatures. They provide excellent adhesion in situations where temperatures reach well over 100 degrees in shipping trailers, and where temperatures are below freezing in food packaging.

Hot melts work well on coated and uncoated paper stocks, but liquid glues also have performed satisfactorily on uncoated stocks. However, cold glues have not performed satisfactorily on some coated stocks because of their inability to adequately penetrate these stocks. However, there are some cold glues that work on these stocks. Testing is important to determine what works best.

Hot melts not only offer excellent adhesion to numerous substrates, but also meet ‘machinability’ requirements. They can be applied with little or no stringing and with a clean cut off. Hot melts are recognized as having superior ‘machinability’, reflecting their wide acceptance in high-speed carton and box gluing applications. Where dealing with difficult coatings is an issue, hot melt glues are preferred.

Despite the predominance of hot melts in the market today, there are a number of important applications where cold glues are as effective in breaking through coatings and creating an excellent bond with the two substrates. These are applications in which longer drying times are required, such as cartons and pocket folders. What’s more, in these applications cold glues are more forgiving in the bonding process due to their ability to allow both boxes and sleeves to find their natural configurations. Because liquid glues are thinner in viscosity than hot melts, they are able to be applied more quickly. For this reason, cold glues get the nod over hot melts for use in long-run carton and box applications found in the printing and binding industries.

The ‘storageability’ of cold glues is on par with that of hot melts. Depending on the application, the coating, and the paper, cold glues are generally as effective as hot melts in temperature extremes that range from below freezing to 100 degrees plus.

There are several specialty hot melt adhesives that are finding important niches in the marketplace. One is a repositionable hot melt that is used in self-mailing applications where the end user can receive information and re-secure the product for other mailings.

Hot melt and liquid cold glues can form another effective type of gluing product for binder managers to have at their disposal. These are known as ‘fugitive’ glues. Fugitive glues can be applied to a substrate – such as a folder, pockets, and standard bond paper – to which a binder can secure products such as credit cards, pharmaceutical inserts, and information cards. At the same time, these glues allow removal of these products relatively smoothly, with no tearing, and without defacing the information found underneath the fugitive glue.

Cold glues used to be the recommended glue for fugitive applications. Now hot melts are regarded as the better choice because they are more durable during the handling and mailing processes.

Another form of specialty glue has been designed for remoistable applications: remoistable hot melts. These hot melts are used for straight-line envelopes that function as self-mailers. Frequently used in fulfillment programs, remoistables start out as hot melt glues, then change in composition after application to the paper. After the paper is dry, these glues become remoistable to secure the information inside the envelope.

Cost savings should not be the major consideration when deciding on glues for specific applications. Lower-priced glues may not perform well for a broad range of applications. At this time, trade finishers should ask their glue suppliers for recommendations on the use of a type of glue that will provide the required adherence.

Today, trade binders must meet the demanding, constantly changing, and time-sensitive requirements of their customers. To successfully and economically meet these customer needs, binders must rely on the expertise of their glue suppliers to provide the right glue for a host of applications. Binders must pick their glue suppliers carefully, seeking the guidance of only performance-proven glue experts, if they are to grow their businesses by maintaining current customers and adding new accounts. For astute trade binders, choosing a qualified glue expert is simply a matter of dollars and sense.

Headquartered in Ivyland, Penn., B&R Moll, Inc. is an international manufacturing company with over 60 years of experience providing innovatively-designed folding and gluing equipment, accessories, replacement parts, other technical expertise, and service for the printing, diecutting, and finishing industries. For more information, contact Lorenzo Boscaino and Rick Moll at B&R Moll, Inc. at (866) 438-4583 or visit www.mollbrothers.com.