Here’s a quick look at the difference between EVA and PUR glues for perfect binding
Whether to use PUR is a constant question asked in today’s marketplace when it comes to perfect binding. Many businesses who want to step into the world of book binding are left standing at a crossroad; do I go left with (EVA glue) OR do I go right with (PUR glue). So how do we determine the right course for your business? To help with that decision it’s best to understand what qualities each glue brings to the table.
Ethylene Vinyl Acetate (EVA) has been the preferred method of perfect binding for many years. During the binding process the spine is first run over a notching or milling blade to further expose the fibres of the paper for the adhesive to bind to. The glue itself is applied with applicator rollers that are in a heated glue pot. The glue is capable of being reheated many times which ensures minimal waste of the main consumable. The glue sets within seconds of being applied to the spine of the book which allows for immediate handling without fear of compromising the book itself.
Typically, EVA is strictly recommended for most offset papers. When coated papers are introduced to the binding process, the EVAs once beneficial quick cure times becomes more of an issue. The glue does not have time or the right chemistry to penetrate and bind to the fibres of the coated papers, especially with full colour print on it, a common example being a photo book. There are some EVA glues designed for running with coated stocks such as the Sterling iglue® or the glue by Dural - Dural M-837 Hot Melt Glue and these glues both perform well in most cases but certainly not a guarantee for every application. Shops doing heavy colour coverage all the time will find a higher failure rate.
When considering single clamp EVA perfect binders there are two levels available. A popular example of an entry level perfect binder is the Duplo DB 290 which is user-friendly and an automatic Perfect Binder that can be placed on a desktop. Producing up to 200 books per hour, the DB-290 is ideal for short-run, on-demand applications. The operator is responsible for placing the book block into the clamp, then while the notching/milling is occurring the cover can be placed in the clamping station for completion of the binding process.
For business with a higher volume needs, The DB-500 Perfect Binder is fully automatic with a cover feeder, this single clamp design will process up to 525 cycles per hour. This machine is controlled through an easy to use touch screen which allows operators to make quick adjustments. The side glue wheels, scoring wheels, and cover positioning guide will automatically move into the desired position according to the thickness of the loaded book. Once the size change is completed, covers can be loaded into the cover feed section and production can commence.
Polyurethane Reactive (PUR) glue, in recent years, has become the leading option in the print industry. It has been met with some resistance though as the initial investment for the machinery can be up to 2-3 times the amount of an EVA perfect binder. It is the science behind it all that makes PUR the leader in today’s marketplace as the true “belt and suspender” solution for perfect binding.
The operations of a PUR perfect binder are much the same as a traditional EVA machine, utilizing notching and milling blades to expose the fibers of the paper for the glue to bond to. Once PUR glue has been heated and exposed to the moisture in the air the curing process cannot be stopped or reversed. This characteristic is what gives PUR a long-lasting bind that is not as sensitive to heat or cold after it has fully cured. PUR has a heat resistance of 350°F (177°C) compared with 165°F (74°C) to 200°F (93°C) for most EVA glues. Extreme cold also poses a challenge with EVA as its prone to cracking due to its brittle nature while PUR has been tested to -20°F (-28°C). A few factors play in the relationship between PUR cure time and the bind strength: low moisture levels, poor spine preparation, low book storage temperatures, or to much glue being applied to the spine of the book can lead to a longer cure time.
PUR binds well with coated stocks because the glue forms a molecular bond with the fibers of the paper. This process leads to a longer cure time for PUR to reach 100% of its strength. The wait is 24 hours but with the advancement in technology the more recent glues have a “quick cure time” where you will see over 50% of its strength within just a few hours. This cure time means you need to do a bit more planning for production as rushing the process only increases the risk of book failures.
This bonding process gives the PUR up to 50% more strength in pull test vs EVA glues. With this increased strength it also is extremely flexible. This flexibility gives you a lay flat capability for your perfectly bound books which cannot be found with EVA glues due to its brittle characteristics.
When considering machine options, there are two ways to apply PUR glues to the spine of the book which are; an open glue pot system or a nozzle system.
The more traditional open glue pot system can be found on the Horizon BQ 160PUR Perfect Binder. This is a great entry level machine for shops looking to get into the short run photo book business. What you need to consider with the open glue pot system is that it requires a longer cleanup process with a higher amount of glue waste. Open tank systems should be professionally vented to remove odors and ensure safety. Each time you run your job, you must fill the glue pot to at least its minimum required level to then run the 1, 10 or 500 books that you must complete. Once you are done production, the machine must be cooled to complete the cleaning process. You must wait for the remaining glue to cure for it to then be removed in its solid state from the glue pot. For a better understanding of his process please click here . The glue pot and its components are Teflon treated, so this allows you to easily clean out the cured PUR, but you may require recoating every few years.
The more recent technology for applying PUR is a nozzle system. Morgana offers a patented nozzle system, which is available on their full range starting with the entry level Morgana 150 PUR - Digital PUR perfect Binder, Morgana 200 PUR - another Morgana Perfect Binder, Morgana 300XL PUR - an advanced model with added features, up to the fully automated Morgana 450 PUR with in-line cover scoring and cover feeder. The application is direct and hermetically sealed, without odour or toxic fume emissions, and does not require extraction fans. It is possible to set different temperatures for the glue melting tank and the applicator giving greater flexibility and glue life. Another feature of this applicator is it can be cleaned and sealed automatically from the touch screen allowing for minimum glue wastage (can be seen here) . The PUR glue is applied on the book spine and on the sides by independent glue slots, each of which can be adjusted to give the best possible spine and side glue results. PUR glue activates with moisture in the air thus the hermetically sealed tank system gives you the ability to re-heat the PUR glue up to 10 times before the performance of the glue becomes compromised and you may need to purge the tank of any remaining PUR.
The investment into perfect binding is certainly worth while for any business. It is crucial take a step back and understand the qualities that both EVA and PUR will bring to your business. Both are relevant in today’s market and understanding how each glue works will hopefully help you take the right steps for your business and to get the most out your perfect binding investment.