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PUR in every glue pot?

Apr 1, 2005 12:00 AM

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What’s in your perfect binder’s glue pot? Many trade binderies and commercial printers are adding polyurethane reactive (PUR) alongside the more familiar ethylene vinyl acetate (EVA) hot melt and polyvinyl acetate (PVA) cold emulsion adhesives.

PUR’s advantages include:

  • Excellent flexibility and layflat qualities, because the adhesive’s thickness is about one-third that of a standard hot melt.
  • Ability to withstand temperature extremes without glue failure.
  • Bondability to lacquer and UV-cured coatings as well as Mylar and other films.
  • Binding quality that is virtually unaffected by ink migration into a book’s gutter.
  • Page pulls that reportedly average up to 40 to 60 percent better than a traditional adhesive.

The other side of the PUR coin
On the equipment side—provided you already own a perfect binder that can be retrofitted with a PUR system—you can anticipate a capital investment of about $100,000. Although PUR-bound books use much less glue, PUR adhesive at about $5 per lb. is more expensive than $1.50-per-lb. traditional hot melts.

Unlike other adhesive options, you can’t leave PUR in a glue pot overnight and reheat it for future use. It has a pot life of about three hours—whatever hasn’t been used must be thrown out.

PUR isn’t the fastest binding optiona PUR- equipped binder has a top output of 7,000 to 8,000 books per hour vs. a conventionally equipped binder that can churn out 16,000 to 18,000 books per hour. Also, most PUR adhesives currently require a 24-hour curing period.

Nonetheless, PUR offers one thing some users call priceless: peace of mind. "Previously, stitching was the only way to guarantee signatures wouldn’t fall apart," explains Mike Roswell of Roswell’s Bindery (Phoenix). "With PUR, you can safely say that the paper will fail before the glue does." (See "Minding the binding," Oct. 2004.)

Peter Ferrier, manager bookbinding/graphic arts for Henkel Corp. (Elgin, IL), says PUR is a natural fit for trade binderies that see a little bit of everything. "Unlike a publication printer that prints the same job on the same stock, the binderies might get three or four different jobs a day on a variety of paper stocks and with different grain directions," explains Ferrier. "So PUR is a very valuable tool."

Over the past year and half, about one of every three Muller Martini perfect binders sold in the U.S. had PUR as well as standard hot-melt capabilities. According to Kerry Burroughs, bookbinding division manager, Muller Martini (Hauppauge, NY), hotbeds of PUR activity include Boston, Houston, parts of New Jersey and Rochester, NY. "As one printer or binder puts it in and starts winning customers, others get interested," says Burroughs.

Kolbus (Cleveland) and Wohlenberg (distributed in the U.S. by Paramus, NJ-based Colter & Peterson) report that more than half of the perfect binders going to trade binderies are equipped with both PUR and traditional hot melt.

Most of the major perfect binder vendors offer a PUR option with new equipment and can retrofit some older equipment.

"It’s easy for us to retrofit an existing machine, either with a Kolbus glue applicator or one of the aftermarket systems, such as Nordson’s," says Kolbus president Bob Shafer. "But the most important aspect of the equipment isn’t so much the nozzle or roller application system as proper spine preparation. Many of the older machines might not have enough spine prep stations to properly prepare the backbone. So, you need a binder with enough spine prep stations (at least three, ideally four), a glue application system and a delivery system that minimizes the impact on the book."

Kolbus offers a patented "gripper carriage delivery system" on its Ratiobinder line. "This system captures the book while it is still in the clamp and gently brings it to the laydown position," explains Shafer. "Other machine manufacturers simply open the clamp and the book drops from the clamp onto a belt, potentially distorting the backbone and adversely affecting the integrity, if not the appearance, of the binding."

Muller Martini’s Burroughs explains that because PUR is applied in 10- to 12-mil thicknesses (vs. hot melt’s 28 to 30 mils), the clamp above the glue pot must remain steady. "If the book moves up or down, you’re not going to get an even adhesive coverage," he explains. "Therefore, PUR usually works better with binders that have parallel closing clamps rather than hinged clamps."

Muller’s Corona, Bolero and Accoro binders are offered with PUR glue pots. Although the company no longer manufacturers the Normbinder, Monostar, Starplus or Trendbinder models, it offers PUR retrofits for them. Beyond the glue pot, a PUR system includes a heated hose and premelter. Muller offers three premelter options: a 55-gallon drum, a five-gallon pail and PUR "candles."

Burroughs explains that the candles are about eight inches in diameter and 16 inches long. "You slide them into a premelter and close the lid," he says. "When the glue pot calls for adhesive, it heats the bottom of a candle to melt a small puddle of adhesive and pumps it through a heated hose into a pot. When the pot is no longer calling for adhesive, a refrigeration unit inside the premelter solidifies the adhesive again. It’s always in a solid state unless it’s being pumped into the pot. It really cuts down on waste."

Tom Welby, regional sales manager for Colter & Peterson, reports that Wohlenberg has offered plug-in glue pots for several years. The modular pots enable users to quickly switch from hot melt to PUR or to cold glue and can be used with Wohlenberg binders ranging from 2,000 to 8,000 books per hour.

"Wohlenberg binders that aren’t equipped with the plug-in modules can be easily retrofitted with PUR systems from several suppliers," adds Welby.

UV speeds PUR cure
Most PUR systems are offered with a wheel applicator, a style similar to that used for conventional hot melts. Nordson’s recently introduced EP48V "slot" system is unique in that it doesn’t have wheels. The closed system reportedly is easy to control and reduces waste.

When handled properly with adequate ventilation and at the correct temperatures, PUR doesn’t pose health or safety issues. But all PURs contain methylene diphenyl disocyanate (MDI)—it’s required to facilitate the curing process. Prolonged exposure to MDI can cause respiratory and other health problems. Most PUR hot melts contain less than 0.1 percent MDI. Henkel claims its MicroEmission PUR further reduces this low level of exposure by 90 percent.

Originally designed for edition-bound books, Henkel’s Dual Cure could enable higher speed perfect binding. Its special PUR formulation reacts with UV light for speedier curing. While current PUR adhesives generally require 24 hours to cure, Henkel’s Dual Cure reportedly can effect an 80 percent cure in about three minutes.

Prior to Dual Cure, operators using PUR for edition binding typically had to set aside the bound book blocks to let them cure before lining up and casing in. "It became a hit or miss process," says Ferrier. "Dual Cure enables you to glue off a book block, expose it to UV light, cap it and take it straight into the lining up and casing in processes. The PUR is sufficiently cured so that when it goes into the rounder backer and the round is put in the spine, the book is cured enough to hold it." Dual Cure is being used in Germany, Spain and Italy and will appear in the U.S. soon. See

Outstanding in the field: How five binderies are using PUR
By Chris Wagenseller

Early adopter
Seaboard Bindery (Woburn, MA)—a 17,000 sq.-ft. company with 25 employees specializing in catalog, art book, layflat and reference materials—has been using PUR adhesives since 1994. Frank Shear, Seaboard Bindery’s president, says his company added PUR capabilities to its Kolbus Ratiobinder in part to offer improved strength for books printed on coated paper. He soon found that the adhesive was the answer for almost every tough project.

"Thick books, enamel and gloss stocks, heavily-coated stocks—You name it, PUR has been able to bind every project we’ve thrown at it," says Shear. "Customers love that the old limitations of perfect binding—such as watching coating and ink coverage—can be tossed out the window."

After Seaboard began using PUR glue, it was contracted to bind a multicolor college view book printed on uncoated paper and covered completely with solvent-based inks. "You could smell the solvents out in the parking lot," says Shear.

Seaboard began the project using hot-melt adhesive as instructed, but stopped after a few hundred pieces when the customer decided to change the cover. In the three days it took to print and deliver the new covers, the books Seaboard had produced had begun to fall apart. "We did everything right, but the hot melt was being attacked by the solvents in the ink," says Shear. "We discussed it with the customer and finished the job with PUR—and no problems."

The project taught Shear to trust his nose. "Thanks to those inks and solvents, we can literally smell a PUR job coming."

Customer comfort
Perfect- and mechanical-binding specialist Spiral of Ohio (Cleveland) is a 100-employee operation that occupies 55,000 sq.ft. Spiral added PUR adhesive binding capabilities to its perfect binding lines in 1998.

According to part owner Jeff Klein, PUR is an excellent tool for ensuring customer satisfaction. "We consult with customers about their project needs and weigh the advantages of both EVA and PUR. Once a customer has that first project that truly needs PUR, they almost begin to rely on it," said Klein. "We’ll get PUR requests for jobs that wouldn’t really need it, but many customers insist on it because the bond is so strong it creates a feeling of comfort."

Klein cites PUR’s ability to bind coated material effectively and withstand temperature extremes as reasons for its success, at both Spiral of Ohio and Action Bindery (Atlanta), a 30,000-sq-ft., 40-employee bindery Spiral of Ohio acquired in 2001. "PUR is not only great in every environment, it is particularly good for coated stocks," says Klein. "It is perfect for high-end promotional or business publications, which often are done on heavily coated substrates."

Less waiting, faster turnaround
Most perfect binding providers that use PUR have found bound books require at least 24 hours to fully cure. New glue formulas and binding techniques, however, have narrowed that window by allowing books to be handled much sooner.

Allied Bindery (Detroit) has been using PUR adhesives extensively since early 2003. To help reduce turnaround times, the 45-employee, 40,000-sq.-ft. company asked its PUR adhesive supplier, Henkel Technologies (Lewisville, TX), to help determine how much page-pull strength Allied Bindery’s books were able to achieve at various points during curing. "While our customers love all of the benefits of PUR, a lot of them have inquired about exactly when in the curing process PUR-bound books can be handled," said Kris Koch, president of Allied Bindery. "We were equally curious, so we turned to Henkel."

Using a "typical" PUR project—a 190-page, 1⁄2-inch-thick catalog printed on 50-lb. coated offset paper—Henkel pulled 50 books from a production run and began testing the books’ page pull strength at hourly intervals. Henkel found that PUR-bound books cured in less than four hours achieved average page-pull strength of greater than 2.5, which is the GPO industry standard page pull strength for fully-cured EVA adhesive-bound books. According to Henkel, the results from Allied Bindery are consistent with those from other binderies using the latest PUR adhesive formulas.

"Though books bound with PUR have proven to be strong within a few hours of binding, it’s wise to schedule those projects with the understanding that the books shouldn’t be heavily used or handled within the first 12 to 14 hours," says Koch.

100% PUR
Seidl’s Bindery (Houston) has been using PUR adhesives for several years with a Muller Martini Corona perfect binder. Customers of the 67,000-sq.-ft. bindery have been so happy with the results that the company made the decision a couple years ago to use PUR exclusively on all its adhesive binding projects.

"Switching to 100 percent PUR was the best decision for us and our customers," says Bill Seidl, president of Seidl’s Bindery. "Customers can be confident that their books will have outstanding strength, flexibility and durability. On our end, eliminating the setup time required for switching adhesives allows for faster turnaround and reduced prices."

Nothing is impossible
In 1993, The Riverside Group (Rochester, NY), a 138,000-sq.-ft. bindery, became one of the first binderies to use PUR when it added a Nordson (Westlake, OH) applicator to its Muller Martini StarPlus perfect binder. The company now uses PUR for perfect binding as well as gluing off case-bound books. According to Fred Daubert, president of the Riverside Group, the greatest value of PUR adhesive is its ability to "save" projects that would otherwise need to be reprinted.

"Last year, we were contracted to do a high-end toy catalog that included a hefty amount of dense color," says Daubert. "In addition, most pages included flood UV coating that ran into the spine. We ran the project with PUR adhesives, and the customer was thrilled with the results. The project would have been nearly impossible to produce properly with standard binding adhesives. In this case, PUR definitely helped our customer avoid a reprint."

Chris Wagenseller is affiliated with Grow Sales, Inc., a marketing, Web development, public relations and sales support organization serving the graphic arts. See

A little dab’ll do ya
PUR application runs counter to what the average (conventional hot-melt) operator intuitively thinks," says Bob Shafer, president, Kolbus (Cleveland). "But more is not better."

"It’s a hard lesson for many operators to learn," concurs Peter Ferrier, manager of bookbinding/ graphic arts for Henkel Corp. (Elgin, IL). "The general PUR target is 10 to 12 mil of adhesive, which is about half of what’s used for a regular EVA. So [new PUR] operators typically put down twice as much as they need because they’re so used to EVA. Using more results in longer cure times, less flexible books and wasted money. As much as we want to sell adhesive, we say, ‘Please use less.’"

Safety first
The main constitutents of PURs are isocyanate propolymers which are formed by the reaction of polyester and/or polyester diols with methylene diphenyl disocyanate (MDI). Prolonged exposure to high levels of MDI can lead to respiratory problems and other health issues. As with any adhesive, users should ensure ventilation is adequate.


  • Read the Material Safety Data Sheet (MSDS).
  • Conduct an air analysis to ensure you are in compliance with OSHA regulations.
  • Don’t exceed the manufacturer’s suggested application temperature.
  • Avoid repeated skin contact.
Source: "Working with polyurethane-based hot-melt adhesives," Henkel Adhesives (Elgin, IL).

PUR & related products
NORDSON | Nordson (Duluth, GA) offers the EP48V PUR application system. This closed adhesive system uses an applicator head and bulk melter to replace open wheel pots. Advantages include increased production speed, the elimination of pot cleanup and faster startup/shutdown.
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H.B. FULLER | (Minneapolis) OptiPUR HL9650 is applied at a temperature 25°F lower than conventional PUR. Because it is applied cooler, it reportedly sets faster, is more stable and generates fewer vapors. Excellent flow allows for uniform coating with slot or conventional applicators.
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VALCO | Valco Cincinnati’s (Cincinnati) line of ThermojetII hot-melt systems produces tighter joints, stronger spines and lasting durability. ThermojetII can be used for casing-in, pot-filling/premelters, side-seam binding, tipping and inserting. Units can be equipped with nitrogen blankets for use with PUR adhesives. Valco also offers hot melt drum unloaders.
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NATIONAL ADHESIVES | Pur-Fect Bind polyurethane reactive hot melt adhesives from National Adhesives (Bridgewater, NJ) perform well on all substrates, including heavily coated stocks. It reportedly provides unparalleled strength and durability. The adhesives are unaffected by printing ink solvents, have outstanding spine flexibility and high heat and cold resistance.
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HEIDELBERG | The recently announced JDF-enabled Eurobind 4000 perfect binder is rated at 4,000 books per hour. Glue options include hot melt or polyurethane. The tanks are on wheels and can be interchanged easily. The binder targets industrial bookbinders and full-service shops with an annual volume of approximately two million perfect-bound brochures and average 5000-piece run lengths.
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To learn more about PUR and its history, see PUR: A brief history of a popular perfect binding hot-melt adhesive.