Book block making is a complex operation. And it does not get the credit it deserves. The "hard case" hogs the limelight for a well bound hard cover book.

Let us examine a few of operations involved in book block making:

Gluing-off or first gluing

The object of this operation is to seal the sewn sections together. This forms a firm - and "roundable" book block. The adhesive chosen should have properties discussed below:

  1. It should have low-viscosity with high solids content. The low viscosity will allow the adhesive to 'flow in' between the signatures. The high solids content will prevent the flow up the sewing holes.

  2. If the spine is to be rounded, then the adhesive should have the property to retain the shape. 

  3. Compatibility with the lining adhesive (check the type of adhesive to be used). It is not possible to use an emulsion for gluing-off and then apply a hotmelt for lining. In such a case one should have a paper membrane between the two or very specially adapted machinery.

  4. The adhesive should come off easily from the brushes while they are cleaned after the application.

  5. It should be such that the book blocks do not stick to each other when stacked one on top of the other.

Problem area

coat layer
A too-heavy coating can cause the adhesive to split

The main cause of problems is the application of excess adhesive. This means that the film thickness and tenacity are stronger than the coating on some papers. This also means they cannot be rounded. A too heavy coating can cause adhesive to split.

The emulsion should form a thin skin over the folds or bolts of the signatures and not a solid wedge of adhesive from one signature to the next. The gluing-off emulsion chosen should be tested taking into consideration the next operation. For flat-back work, a firmer spine is desirable. If rounding and backing is to follow, then the adhesive should have more flexibility and have better "forming" characteristics.

Caution

Gluing-off emulsion can flow through the holes made for thread sewing. This happens mostly in cases where the paper is hard. One can do a smashing in order to close the punch and holes

The next process in the book block making is lining. You can have single, double or triple lining using a wide range of adhesives.

Single lining with emulsion

The lining of book blocks generally uses emulsion adhesives. The following parameters decide the choice of adhesive:
  • Type of application
  • Drying process
  • Subsequent bindery operation

In some machines, the adhesive has to be first pumped up to a feeder tank before it flows down an application tube. In such applications, the adhesive must be "pump-stable" and have an acceptable flow. If a product is not pump-stable and breaks down then the flow could be too great and the adhesive would flow too far between the signatures and certainly into any sew holes. Conversely, if it thickens then this will cause adhesive starvation. Lining machines with roller applicators applying the emulsion to the spine of the book and to the liner require a high tack adhesive. Otherwise, the lining material can come off during the cutting operation. Some times the spine swells, as the lining moves with the applied pressure.

When RF (Radio Frequency) / HF assisted drying is used, the choice of emulsion is critical. Here the vibration of the molecules creates so much heat that there could be a drop in "tack" in case of an ordinary emulsion. Therefore, the emulsion used should resist such a drop. It should not have the tendency to swell, as this will result in an unsatisfactory spine. A temperature of 60-70 degree centigrade is often registered as a book emerges from the RF- HF tunnel. This will have to be reduced to 23 to 25 degree centigrade before the book enters the three-knife trimmers.

Book blocks that have to be rounded subsequently should have a flexible but firm emulsion and a stretchable lining material.

Hotmelt Single Lining

Hotmelt single lining is proving to be very successful, especially if large punch and needle holes cannot be sealed before the lining operation. It also offers a greater amount of insurance if coated or heavily inked areas are observed on the signature folds. The lining material should have a good stretchability. In fact it is seen that a hotmelt that is preheated before rounding holds shape better as it chills in the moulded form. The over-application of hotmelt is not recommended as this makes the rounding difficult. 

Roundablehotmelts with a good stretch and very low shrink-back are now being used in this operation.

Care must be taken when setting the liner nip station. This is because insufficient spine pressure will result in bubbles appearing after trimming operation. 

A J (Tony) Clark has an enormous reputation in the bookbinding industry. Most of his working life was spent at National Starch & Chemical, from which he retired in 1996. He works now as an independent consultant.

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