Advice Centre

Welcome to the Advice Centre! Here you will find useful information and oodles of advice related to all things print.  From the basics such as indepth information about the printing services we provide, to reports on important topics in the industry like the environment, this is the place to come to if you have a question about print and you need an answer.  Regularly updated, we’ll endeavour to provide you with the goodies that you won’t find elsewhere.

Everything you’ve ever wanted to know about our printing services

Our Printing Services section covers the principle services that we provide here at Purely Digital and answers every question you could have.  From the basics of digital printing, through to our finishing services, this section will give you a clear overview of what we can do for you.  We also run through useful information for newbies to the print world with our dictionary of print terms and we look at the pros and cons of picking a particular type of printed item, like scratch cards or business cards.

A Guide to Hot-Melt & PUR Glue Binding

What is Perfect Binding?

Perfect binding just means using glue to bind your pages. It's the technique that is used to bind paperback books and you'll frequently come across brochures, magazines, manuals, telephone directories and the like that have been bound using this method. It doesn't necessarily require any specialist equipment; technically you could do some DIY perfect binding using ordinary glue to stick your pages and cover together, but since this is often unreliable we definitely recommend using a professional binding service, especially when binding digitally printed signatures.

There are basically two different types of perfect binding, hot-melt glue and PUR glue. Both methods offer high-quality, high-strength binding.

Hot-Melt Glue

Hot-melt glue is suitable for books with a starting spine width of 3mm and paper up to a maximum weight of 170gsm. This technique uses EVA (Ethylene Vinyl Acetate) to glue the pages. Customers who want business card booklets bound often choose this option. Hot-melt glue works best with uncoated and matt papers and ink free spines. It can struggle to offer the same strength as PUR glue if the spine is flood coated with ink. Hot-melt is a great option if you're on a budget.

PUR Glue

PUR stands for polyurethane resin which is extremely strong glue, so strong and reliable, in fact, that it is used to construct fire doors. This is also because once the glue has been activated by heat to make it liquid (and to adhere something) it won't re-melt after cooling. If you want the scientific explanation, the PUR chemically reacts to the moisture in the paper or surrounding air and the glue's higher molecular weight is what delivers such a strong bond. That's why it's understood as a permanent adhesive. PUR glue is three to four times stronger than hot-melt glue and it can easily cope with inks and coatings without being compromised.

PUR has become increasingly popular with printers and customers alike not only because of its increased strength when compared to hot-melt, but also because it is easier to recycle. PURs are easily separated and removed from paper fibres during recycling whereas hot melt doesn't always allow for paper recycling. PUR also initially melts at lower temperatures, which means less electricity use and a better carbon footprint. The lower temperature also makes it safer to handle in the print room.

How does Perfect Binding Work?

Both hot-melt and PUR binding use the same basic principles to bind.

Step 1: Grind down the binding edge (the spine) so that the surface is even and flat and then coat the spine with a layer or layers of hot glue to hold the pages together.

Step 2: Use a flexible adhesive to adhere the cover to the spine.
Hot-Melt: The Morgana KB2000s

For hot-melt binding we use the Morgana KB2000s which is considered one of the best binders in the industry. It is a single-clamp binder that only uses hot-melt adhesive. The clamp does the whole spine prep, bind, cover nip and delivery in one pass which makes it much faster than alternative binders. It can do up to 320 books per hour.

Specifications:

320 books per hour
Max Book Size: 310mm x unlimited width
Min Book Size: 85x55mm
Max Spine Thickness: 60mm

The biggest challenge of binding digitally printed items is that toner-based digital presses cover the sheet in a very thin but resilient layer of fuser oil which is designed to preserve the toner by keeping everything else out, including glue. The Morgana KB-2000 has a really clever function that can overcome this. It uses an optional slitter that cuts into the spine of the book so that the glue can soak in deeper and provide a stronger bind. These are simply rows of single cuts at 2-3mm intervals made by a knife-blade.

Process

The book is clamped and rolled over a spine prep head to cut into the spine.
The spine is fanned out by about 10% of its original width to allow the glue to get in.
The book passes over three rollers: the first applies the glue, the second a thinner coating and the third uses a blade to scrape off excess. The book travels into the cover area where the cover is fixed onto the book. The KB2000s doesn't have trimmer so you'll have to take it away and trim it using a guillotine if necessary. You'll also want to pre-score the cover so that nothing cracks when the book is folded.

Further Reading:

Print Week Product of the Week:KB2000

The Morgana KB2000s

Examples of Hot-Melt Binding:

   

PUR Glue Binding

PUR glue used a very fine layer of glue to bind. The process is very similar to that of the hot-melt binder. Our PUR binding machine is semi-automatic. The item is clamped in, pushed across rollers, and the glue is applied. The glue will cool very quickly but the item must be left in the clamp to bind properly. In the early days of PUR printers would run in to trouble by administering a ‘pull test' straight after binding – this is a bad idea! The item needs to be left for at least a few hours and the glue will only reach full strength after 24 hours. It's without doubt worth the wait though, as the eventual strength of PUR binding is hard to compare to that of hot-melt.

On average we get through about 60 PUR bindings per hour. It is a slightly slower process than conventional EVA binding, but in our opinion it's worth it for the results. PUR binding generally works better with digital printing than alternatives.

Examples of PUR glue binding:

  


 

 

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