This type of binding is great for consistent page size, large page counts, mixing different paper types and a strong attractive finished product. It’s been the dominant binding method for annual reports and used for years on magazines like National Geographic and Vogue.
Specifying the right type of glue for your project is one key to meeting the clients expectations. There are two primary types of glues used for perfect binding: EVA (ethylene vinyl acetate) and PUR (polyurethane reactive); both are holt melt types. Which should you specify?
EVAs or hot glues were the original glues used for perfect binding. They have been around for many years, are inexpensive, cure almost instantly, and form a strong bond under most conditions. They do not hold up well in extreme temperatures and tend to crack as a result when too cold, fall apart when too hot or crack when overstressed. Hot-melts should be avoided when working with heavy coated stocks, stocks over 70# in weight, or finished products that will be exposed to excessive heat or cold weather. Expect the book to fail if you keep it in your car during a Palm Springs summer. Most monthly national publications use hot melt glue for economy…..of course they are using lightweight coated paper.
EVA hot melt glues are a good choice for binding uncoated paper (60# and lighter), economical short runs and very thin spines (provided the binding is supported with side stitching). The cost to bind a short run catalog with EVA hot melt is MUCH less expensive than the setup costs for the bigger PUR glue binding lines. BUT be aware the client needs to understand the tradeoffs of an economical EVA hot melt product as opposed to the superior features of PUR glue. EVA hot melt glues are very popular on the short run small foot print binding machines (Duplo or Horizon) found in smaller binderies and in-house operations. (inexpensive Duplo machine below)
PUR glues came along in the early 1990's; they seemed to answer many of the challenges inherent to perfect bound books: primarily flexibility, layflat qualities, and durability. Technically speaking, the polymers in PUR adhesives cross-link onto the stock via a chemical reaction with MOISTURE, thus facilitating adherence, increasing pull strength, providing greater resistance to hot and cold temperatures, and reducing waviness in wrong-grain projects. They have made an incredible impact on the perfect binding industry.
The market for PUR glue was originally driven by products such as software manuals, reference books, and high-end catalogs and now includes hard-cover books, catalogs, and annual reports. Check out the following advantages of PUR glue, as described by one chemical supplier:
1. Heat Resistance - Perfect bound materials hold up in temperature ranges all the way up to 200F. Conventional hot melts generally fail at 120F or less.
2. Cold Resistance - PUR does not fracture at temperatures as low as minus (-) 45F. EVAs are generally flexible to plus (+) 25F.
3. Adhesion - Because of their chemistry and molecular weight, PURs are formulated to adhere difficult stocks. This is particularly important in jobs with heavily coated stocks against the grain, traits common to annual reports, for example.
4. Flexibility - Books bound with PUR glue have excellent layflat qualities. The adhesive is very pliable, and less of it is required on the backbone. This is perhaps the most appealing aspect of PUR glue. Not only does it answer the problem of books that snap shut, or the "mousetrap" effect as it is called, there is far less unsightly glue seepage into the spine of the book.
5. Ink Solvent Resistance - PURs are virtually unaffected by the migration of printing ink vehicles. (PUR adhesives will not dissolve with exposure to things such as alcohol, toluene, and gasoline.)
6. Durability - All of the aforementioned benefits provide the printing industry with a ten-fold improvement in durability. Books destined for a long life or heavy use will retain their integrity. Durability is one of the premier reasons PUR glue has been such a success. In the past, perfect bound books were notorious for their lack of strength and durability over time. Now, even high-end catalogs that were previously sewn hold up well using PUR adhesives. Both page pull tests and flex tests measure substantially higher in books produced using PUR glue, with page pulls that average up to 40 to 60 percent better than with traditional adhesives.
There are many considerations when choosing an adhesive. As with any product, PUR glue has its limitations. It’s more expensive than traditional glues making it cost prohibitive for certain jobs (monthly publications). [PUR glues require special equipment as the adhesive cannot come into contact with air during application. It’s not simply a matter of changing the glue.]
Other downsides to PUR glue include the extra curing time necessary for acceptable handling because of the high moisture content necessary to activate the adhesive. PUR bound products should be lightly handled for the first 24 hours. PUR achieves 95% strength within 24 hours and therefore needs to remain exposed to natural air; it further cures over 72 hours. Post binding services, such as drilling, will need to wait 24 hours until the glue has a chance to set up. This adds time to your schedule.
Large Perfect binding line
Whether PUR adhesives are right for a given job is contingent on several factors: the life expectancy of the book, the end-use, and the budget. My best advice is to be diligent about discussing these details before producing the job.
PS: One of my vendors is installing a new 20 pocket PUR machine this week. The HOT new feature on this machine is “optical image recognition” which insures sequential signature positioning and results in error free production! It's the only one of its kind on the West Coast. If your books or catalogs require rigorous QC inspection upon arrival, you need to be using this equipment. Ask me for details.
