Edited by Jeff Peterson, editor-in-chief, PostPress

As with most bindery and finishing equipment, there is a great deal of planning involved in executing perfect-bound printed materials. It is vitally important that there is ample communication from the design, print and finishing portions of the job to help decrease waste and run at efficient speeds. PostPress talked with Mike Wing, solutions manager of Book Technology and Digital Solutions at Muller Martini, on some of the important aspects of a perfect-bound job and how to avoid challenges before they happen.      

When designing and printing perfect-bound material, what paper stocks work best for perfect binding? What stocks are to be avoided?

Wing: Unfortunately, there is no “one size fits all” paper stock for all perfect binding jobs. It typically is the end-use application (e.g., trade book, magazine, photobook/yearbook, etc.) that dictates the type of paper that needs to be considered. For perfect binding, uncoated or lightly coated offset stocks in the 50-70 lb range for text and 80-100 lb cover stocks generally are optimal. These stocks allow the adhesive to penetrate and form a strong bond with the fibers. Papers that are heavily coated, glossy or very dense (like cast-coated or laminated stocks) pose challenges in the binding process and make it difficult to form a good bond between the glue and paper fibers. Additionally, extremely lightweight papers may not hold up well during the milling and binding process, leading to page pullout or poor durability. However, in many cases, lightweight papers cannot be avoided on books with high page counts (e.g., Bibles, reference catalogs, etc.) to maintain a usable format size and thickness.

Another key element that needs to be clearly understood when selecting the proper stock of a printed perfect-bound product is the grain direction of the paper. Because moisture content varies in the paper at the time of binding, the binding edge always should be designed to be parallel with the grain direction of the paper. This allows the paper to expand or contract without causing undesirable waves or cockling when the spine of the book is bound by the adhesive.

What determines the best type of glue to use on a perfect-bound job? What are the choices available?

Wing: The selection of glue primarily depends on the paper stock, ink coverage, book thickness and, very importantly, the intended use of the finished product. The most common book binding adhesives are Ethylene Vinyl Acetate (EVA) hotmelts and Polyurethane Reactive (PUR) glues. EVA is versatile and cost-effective for most standard jobs on uncoated stocks. PUR offers superior flexibility and adhesion, especially for coated or thicker stocks, but requires longer curing times before trimming or opening the pages.

A relatively new trend in book binding adhesives is what I call “hybrid” hotmelts (e.g., metallocene or polyolefin compounds) that offer an alternative to the traditional glues mentioned above. This type of glue has similar application characteristics (e.g., thermal stability, fast cure time, lower process costs, isocyanate-free, etc.) to that of EVA hotmelt while providing some of the benefits of PUR from the standpoint of better bind strength, heat/cold resiliency and spine flexibility. No matter which type of glue finally is decided upon, testing in a production environment with the actual perfect-bound materials always is recommended to ensure optimal performance.

What suggestions do you have for equipment maintenance on a perfect binder? Why is this important to help decrease waste and maintain optimum running speeds?

Wing: As with any advanced production system, routine preventative maintenance (PM) is essential for consistent/reliable machine performance and minimizing downtime on the perfect binding line. Basic requirements to ensure a binding line is properly operating include performing daily housekeeping activities, ensuring both spine preparation tooling and trimmer knives are sharp, frequently lubricating moving parts and confirming all sensors and safety systems are functioning as designed. A well-maintained book production solution reduces the risk of unplanned delays and/or quality issues, which contribute to higher costs due to waste or customer complaints in the field. A good PM regimen especially is critical in the digital manufacturing world where penalties can be assessed if time-sensitive service level agreements (SLAs) are not met.

What common challenges have you seen recently with printed materials and perfect binding? What suggestions do you have for solving these challenges?

Wing: Many of the current challenges faced by the perfect binding department are in the areas of cover finishing and paper properties.

Covers either can be laminated (gloss or matte) or coated to provide a level of protection or durability to the end user. To streamline or optimize the manufacturing process, several companies are moving towards inline coating, which provides a significant reduction in production steps and subsequent costs. However, this creates other downstream issues related to marking or cracking in the binding of the books or catalogs. While lamination might be a more complex production method, it does provide the benefit of less marking or cracking on the covers in the bindery, which must be considered in the overall cost analysis.

As mentioned previously, paper also plays a major role in the overall perfect binding of books. The typical challenges bindery operators face when it comes to paper stocks can be attributed to the production environment. Temperature and relative humidity play a big role in how paper will react in the manufacturing process. Maintaining ambient conditions in a range of 65-80 degrees and 40-60% relative humidity will help reduce the various factors (e.g., static, curl, waviness, etc.) that operators deal with when handling paper in the bindery.

Do digitally printed materials cause any specific challenges with the perfect binding process? How do operators solve these challenges?

Wing: In the area of digital book block production, rolls of printed paper coming from the digital press either can be slit and stacked into loose sheets or cut and folded into uniform glued book blocks. With loose, cut-sheet book blocks, feeding into the binder clamp either is manual or via a cobot. Both processes can be slow and inefficient in comparison to having a glued book block which lends itself well to automated de-stackers or de-palletizers. This can significantly reduce labor and provide a level of consistent feeding to the infeed of the binder. Loose, cut-sheet book blocks also have more opportunity to jam or lose a top/bottom sheet, resulting in a defective book.

Also, digitally inkjet-printed books can have special coatings for ink bonding and durability, as well as inconsistent levels of moisture content in the paper that can result in waves in the final book. Unfortunately, there is not a lot that can be done to overcome some of these attributes. Utilizing PUR adhesives can address many of the material-related variables that are encountered in the production of digitally printed books. Additionally, having a good communication channel back to the publisher can go a long way to heading off design issues (e.g., placement of heavy ink coverage, thin borders near the edge of the book, type on the spine of thin books, etc.) that inevitably will result in delays or quality issues in the binding of the book.

How has automation played a role in perfect binding efficiencies and decreasing overall waste?

Wing: Automation is more than just adding servo motors to the different axes of a machine and calling it automated. The goal in today’s manufacturing plant is to have a true smart factory where there is minimal labor and manual intervention involved in the production process. However, for this to become reality, companies need more than automation. The factory also needs connected machines capable of receiving data (e.g., job parameters, packaging requirements, etc.) to automate the set-up process, as well as delivering accurate data (e.g., KPI, production results, job status, etc.) back for the purpose of making informed business decisions.

One key contributor to a highly efficient perfect binding process is exception handling. What I mean by this is how the automated system handles poor quality or unexpected inputs. In the past, a person would have to identify that a problem existed and then correct it, or maybe the binder would continually jam or stop. However, modern binding equipment now offers new solutions like barcode-driven set-up, product buffering and resequencing systems, book/cover rejection, glue application monitoring and cover registration correction – just to name a few. These recent developments are proving to be game changers when it comes to book production optimization and a true touchless workflow. 

Mike Wing is the solutions manager, Book Technology and Digital Solutions, for Muller Martini Corp. For more information on Muller Martini’s full line of print finishing systems, visit www.mullermartini.com.