GB2188856A - Bookbinding tape - Google Patents

Abstract

A heat-actuable tape for the on-line binding together of stacks of sheets output from a reprographic machine has a flexible substrate coated on one face with a central stripe of a quick-setting polyamide resin bounded by two outer stripes of a heat-actuated high-tack adhesive.

Description

SPECIFICATION Bookbinding tape This invention relates to a bookbinding tape for binding together a plurality of sheets to form a book-like assembly, particularly to a tape which is suitable for use in an automated processforthe binding of sets of sheets, such as those compiled in the finishing station of a reprographic machine.

It is often desirable to secure together a plurality of sheets forming a document such as a report ore book. Numerous arrangements for binding sheets together are known. One common method of binding sheets is by stapling, using either preformed staples or staples which are cut and formed in the stapling machine from a supply of wire. This method is particularly suited for application in a finishing station of a photocopier, but has the disadvantage that, particularly after sustained use of the bound document, sheets may tear out or otherwise work loose. In addition, staples can be used forsecuring only a limited number of sheets, because ofthe difficulties of driving the staple limbs through more than, say, 50 sheets.

Othertechniques employed commercially in bookbinding include the application of adhesive directly to the sheets, as by means of a brush or other suitable applicator, and the use of a thread to stitch sections (signatures) together. However, neither of these techniques is particularly suitable for use in the office environment, where productivity is important.

As one solution to the problems associated with the above-described techniques, it has been proposed to use bookbinding tape by which the sheets are bound together by the use of heat and pressure applied to the tape. Such tapes are described generally in US 3 930 082, and comprise a substrate or backing strip, which may be of paper or plastics material, coated with a layer of adhesive. An improved tape is described in US 3 788 921,in in which the substrate is provided along one face with a relatively-thick central portion of heat-activated adhesive, and thinner marginal portions of heat-activated adhesive along each side of the central portion. lnthespecifictapedescribed in US 3 788 the central adhesive is of a low-tack material, whilethe marginal portions are of a high-tack material.

The requirements of such tapes is that the central adhesive can flow sufficiently during the bookbinding operation to penetrate between the compressed sheets forming the eventual 'spine' of the book, to ensure thatsufficientsurfacearea of each sheet is 'wetted' by the adhesive so that, when cured, the adhesive grips the sheets sufficiently tightly to resist their accidental separation from the backing tape.

The marginal strips of the tape are intended to form flaps which are adhered to the respective edge portions of the two outermost sheets of the document. the significantly-greater area of contact of each flap with its respective sheet means that the flap adhesive has a significantly-different function from that of the central stripe, so that the two adhesives are not necessarily the same.

In additional to needing to be tough, the adhesive of the central strip must also be flexible and, to permit its use in the on-line binding of stacked sheets outputfrom a reprographic machines, quick-setting.

Up to now, an adhesive of adequate bonding strength and flexibility has had a base of ethylene vinyl acetate (EVA). However, such an adhesive is impractical for on-line binding because it takes too long (up to five minutes) for the adhesive to set, if reasonable productivity is to be achieved.

Thus the present invention aims at providing a bookbinding tape with a quick-setting central adhesive stripe, and accordingly is as claimed in the appended claims.

The present invention will now be described by way of example with reference to the accompanying drawing, in which: Figure 1 is a diagrammatic iso metric view of one form of bookbinding tape ofthe present invention; Figure2 is a view, similarto Figure 1, of a second form of bookbinding tape, and Figure 3 is a diagrammaticview of a stack of sheets having the tape of either Figure 1 or Figure 2 applied to it during a bookbinding operation.

The tape 1 shown in Figure 1 has as a substrate 2 a tape oftough and flexible material. The tape substrate may be made of a textile, such as of a close-mesh cloth, so that the adhesive on one surface does not migrate through the tape to its outer surface during the bookbinding operation.

Alternatively, the tape can be of a latex-saturated cellulosicfibre matrix, which is absorbent enough for the adhesive to form a good bond with it, but too dense to permit any adhesive to migrate through it during the bookbinding operation.

The 'spine' adhesive 4, applied in a central stripe extending along the axis of the tape 2, is a thermoplastic, hot-melt, polyamide resin. One suitable adhesive has been found to be that sold under the trade name 'Versalon 1138'. This is a poiymeric adhesive, having a steep viscosity/temperature curve, that sets by cooling only, unlike a conventional EVA adhesive which sets by crystallisation, which isatime-dependent reaction rendering it unsuitable for online bookbinding.

It would of course be possible to use other polyamide resins forthe central stripe, and to incorporate therein rosin or other derivatives to increase its tackiness, and/or a plasticizer to improve its flexibility. However, the incorporate of these modifiers is well known, and so will not be described herein in anyfurtherdetail.

The adhesive 6forthetwo longitudinally-extending 'flaps' does not need to be as strong or flexible, requiring only an aggressive tack in order to ensurevirtually-permanentadhesion of the flaps to the outer sheets orcoverofthe bound document. Thus it is possible to usefortheflap adhesive a thin layer of an EVA-base adhesive. One such which has been found to be effective is that which is sold underthetrade name 'Thermaflo 7509', although there are many commercial formulations which would be adequate. The flap adhesive would generally consist of an EVA copolymer hot-melt adhesive incorporating an EVA resin to give strength; a tackifier resin, and wax to control viscosity.

In the other Figures, those components which are the same as in Figure 1 have been given the same references.

In that form ofthetape shown in Figure 2, the substate 2 has an overall layer 6 offlap adhesive coated on it, while the central strip 4 of spine adhesive is deposited on top ofthe layer 6. This arrangement has the same reaction during the bookbinding operation, but is perhaps easierto manufacture than the tape shown in Figure 1.

In both forms of tape, the layer of flap adhesive is significantly thinner than that of spine adhesive. For example, the flap adhesive may be up to 75 um thick, whereas the thickness of the spine adhesive is in the range of 500 - 625 yam thick As shown in Figure 3, during the bookbinding oepration, the stack8 of sheets which are to be bound are gripped between a pair of jaws 10 at a location slightly inwards from that edge of the stack which isto be bound. Sufficient pressure is exerted on the jaws 10, in the direction shown bythe opposed arrows, both to hold the stack of sheets firmly in placeandto resisttheirmoving underthe force applied to the intended 'spine' ofthe book during the binding operation.The tape 1 is applied by having its central portion pressed firmly against the respective side face of the stack 8 by means of a pressure plate 12 which, as shown diagrammatically, is heated by a resistor 14.

Afterthe central portion of the tape 1 has been urged against the spine, the protruding flaps of the tape are folded aboutthe edges of the stack into a broad-area contact with the outer sheets of the stack 8, being held there by a pair of pressure plates 16 similarly able to be heated electrically by like resistors 14. As indicated in Figure 3, the clamping jaws and pressure plates extend along the length of the stack so that the spine of the book produced by the binding process has applied to it an integral tape.

The time during which the heated pressure plates are applied against the tape, and the pressure exerted on the tape bythe plates, are chosen so asto give the heat-activated spine and flap adhesives sufficienttimeto achieve their desired tackiness and mobility.

The advantage of using a polyamide spine adhesive is that it sets within a few seconds of being allowed to cool, so that the book produced by the binding operation may be opened and used normally within a very short period after having been removed from the outputtray of the reprographic machine incorporating the bookbinding means (not otherwise shown) in its finisher.

The means by which the sheets are assembled to form the stackwhich is to constitute the desired 'book'; the way in which the stack is gripped bythe jaws 10, and contacted by the respective pressure plates, and the manner in which the pressure plates are heated to a desired operating temperature, do notform part of the subject-matter of this invention, and so will not be described herein in anyfurther detail.

In an ideal world, the width of the central strip of spine adhesive would be related to the thickness of the stack 8. However, when the tape 1 is being manufactured, or rather coated with the respective flap and spine adhesives, it is often not known what the thickness of the book is going to be. Thus the width of the spine adhesive, and therefore of the flaps, is chosen to be an effective compromise whatever the thickness of the book. For books which are thinnerthan the width ofthe spine adhesive, the lines offold of the flaps would lie within that portion covered with spine adhesive.This results in spine adhesive being applied to the outermost parts of the sheets forming the front and back pages of the book, but this is of no consequence, because it is the flaps which adhere to the sheets. However, it would not be desirable to have the thickness of the book much greater than the width ofthe strip of spine adhesive, because that would mean thatthe outermost sheets of the stack would not have spine adhesive applied to them, and itwould also result in the effective length of the flaps being reduced. Thus it would be desirable to make the width of the strip of spine adhesive correspond to the maximum thickness of the bookto be bound by use of the tape 1.

It will thus be seen that the present invention provides a bookbinding tape which is effective for being used in an on-line copying and binding operation, to result in the production of successive books, each bound by use of the tape in such a way that it is available for use immediately after leaving the reprographic machine.

Claims (4)

1. Abookbindingtapeincludingatapeofflexible material having on one of its faces a longitudinally-extending central stripe of a heat-activated, quick-setting, adhesive, and two outer stripes of heat-actuated adhesive, the quick-setting adhesive comprising a polyamide resin.

2. Atape as claimed in Claim 1, in which the quick-setting adhesive incorporates additives to increase its tackiness, and/or a plasticizer to control its flexibility.

3. Atape as claimed in Claim 1 or 2, in which the layer of the quick-setting adhesive is significantly thickerthanthe layer of adhesive applied to the integral 'flaps' ofthetape.

4. Atape as claimed in any preceding claim, in which the central stripe of adhesive is applied on top of an overall layer of a different adhesive, the stripe being significantly narrowerthan the width ofthe tape, so as to expose the said outer stripes of the different adhesive.