ADVANTAGES AND DISADVANTAGES OF USING HOT-MELT POLYURETHANE (PUR) VERSUS STANDARD HOT-MELT IN BOOKBINDING.
Disadvantages of PUR:
- More rigid, the book can have a clamping effect (it closes by itself and is difficult to keep open).
- There are few varieties of PUR and for thick books they are not very suitable. They cannot be used for rounding the spine of the book.
- Deteriorates in about one hour with ambient humidity
- Depending on the glue application system, machine downtime causes a certain amount of adhesive to deteriorate and become unusable.
- It does not always react in the same way, as it depends on the ambient humidity and the humidity of the paper. In summer it reacts faster than in winter. If the paper is very dry, it reacts very little. This means that there are differences in the setting time (crosslinking) of the adhesive to make it fully workable.
- The book cannot be fully handled for 24 hours. Dropping the book when picking it up or other manipulations deform the book.
- It contains isocyanate, even the so-called ecological ones contain a small amount and this product is toxic and can cause skin and eye irritations. Prolonged inhalation can cause asthma.
- Normal hotmelt allows higher application speeds and therefore higher efficiency and productivity than PUR.
- Much higher price compared to hotmelt (about 3 to 4 times more).
- It generates waste cans from the packaging, which have to be destroyed in an authorised landfill, which represents a cost, while the bags are household waste or can be sold.
Advantages of PUR:
- Stronger chemical bonding in PUR. The bonding of hotmelt is physical. PUR reacts with ambient humidity and with the humidity of the paper, so it chemically bonds to the paper fibre.
- It is more resistant to extreme temperatures, especially below freezing.
- It is best used on paper with low absorption or with a lot of ink or highly glossy or heavily varnished paper and on paper with cross-fibre (counter-fibre) where normal hotmelt adhesive has difficulty penetrating the paper.
Conclusion:
PUR adhesives are excellent for problematic papers such as heavily varnished, heavily inked, highly glossy and/or low absorption papers such as catalogues and the like, but for all other books or magazines with more normal papers it is not justified by price, performance or toxicity.
In addition, there are many more standard hot-melt varieties for all types of books, machine or rounded, while PUR is much more limited and produces books with low flexibility.
