It is known to fabricate booklets with a starting point from preprepared covers of the kind in question. Such covers and methods of booklet fabrication with a starting point from said covers are described in WO 94/265 35, among other publications.

These known covers and methods enable high quality booklets to be produced in a simple and rational manner in environments which do not primarily relate to the production of booklets, folders or books. Even though the known covers and methods can be used and applied in such primary production, they are primarily intended for the fabrication of booklets which are sub-handling products, e.g. products in office environments in which different types of printing matter is to be presented in a functional manner, and which afford the greatest advantages in such production. The area of use extends from booklets that contain only a few sheets of paper to compendiums that include several hundreds of sheets or pages. The method of production enables the fabrication of booklets ranging from just a few booklets to relatively large series comprising several tens of thousands of booklets to be achieved in an economic manner with method implementations that are adapted to the size of the series intended.

However, the known covers and the methods applied in the fabrica- tion of booklets on the basis of these covers are encumbered with a binding-agent related problem. The binding agent is comprised of a strip of adhesive material or adhesive substance applied

firmly to one side of the spine of the cover, this adhesive material or adhesive layer being brought into abutment with the bundle of paper sheets inserted between the cover sheets and the adhesive thereafter activated, e.g., by applying heat thereto.

The binding agent is therewith changed from a solid state to a molten or semi-molten state, so as to enable the sheets to penetrate into the binding agent. The binding agent is then caused to harden, so that the sheets will be firmly anchored in the cover and therewith provide a complete booklet.

In the fabrication of such booklets, the strength with which the sheets, or pages, are bonded to the cover is an important part of manufacture. The stronger the bonding, the rougher the booklet can be handled and the greater number of times that the booklet can be opened and closed without the pages or sheets loosening.

Although known booklets satisfy reasonable requirements in this respect, there is still space for improvement in maximizing the strength of the bond.

GB-2 218 043 teaches a booklet of the kind intended, in which a metal wire net is embedded in the binder. The purpose of the net is to strengthen the spine. Although the net will, of course, strengthen the folder, the fact that it is made partially of metal presents other drawbacks and complicates the method of manufacture.

Accordingly, an object of the present invention is to fasten the sheets, or pages, more strongly than has hitherto been achieved, in a simple fashion.

This object has been achieved in accordance with a first aspect of the invention with a cover of the kind defined in the preamble of Claim 1 and having the special characteristic features set forth in the characterizing clause of said Claim.

By providing the binding agent with an abutment support in this way, such that the edge-surface of each sheet, or at least parts of said edge-surface, will not be in contact with the spine, the total surface area of the sheet exposed to the binding agent is increased. In the fabrication of a booklet in accordance with conventional techniques, the sheets are inserted towards the spine of the cover until they come into contact with the spine.

The end-edge surface of a sheet is not therefore utilized as a gluing surface, meaning that all of the adhesive strength will be taken-up by that part of the side surfaces of a sheet which is immersed in the binder. The enlarged gluing surface obtained by means of the invention, by virtue of utilizing the surface of the end-edge of each sheet, contributes to enhancing the bonding strength. A copntributory feature in this regard is that the glue joint on the end edge-surface is in more favourable alignment than the glue joint abtained against the side surfaces of a sheet with respect to the direction of the forces that the glue bond is subjected when leafing through the booklet.

The primary function of the abutment support is to fasten the sheets or pages more strongly, by increasing the glue surface area. It has been found that precisely this aspect is decisive in achieving the desired effect. Mechanical stiffening of the spine is less important in this context. Consequently, it is possible for the support to be comprised of a strip of woven textile material in accordance with the invention, i.e. a material that has no stiffening function, but which solely serves to prevent contact between the edge surfaces of a sheet and the spine. When using woven textile material, the support can be applied very easily with only slight changes to the properties of the folder.

The abutment support may be embedded in the binding agent or affixed to that side of the binding agent which faces away from or which faces towards the spine of the cover, each alternative affording different advantages.

When the abutment support is mounted on the surface of the binding agent that lies remote from the spine, the covers can be nested one inside the other without risk of adhesion between the binding agent and an adjacent cover, since the abutment support will prevent direct contact therebetween.

In a further preferred embodiment of the invention, the abutment support has the form of a perforated element which extends along the spine, parallel therewith. The element may conveniently comprise a strip of woven material. The use of an abutment support in the form of such a perforated element enhances the quality of the binding, also from another aspect. When binding in accordance with conventional techniques, a problem arises in the inability to fully control the binding agent when it is brought to a molten state. In this state, the binding agent tends to flow or migrate to other, undesirable locations, primarily between the lowermost parts of the inner surface of each cover and a corre- sponding part of each adjacent sheet or page, said glue flowing unevenly and too far out from the spine. The perforated abutment support used in accordance with this embodiment of the invention inhibits the freedom of the binding agent to flow in this way, since the surface tension of the binding agent in combination with the flow resistance offered by the perforated element has an inhibiting effect on the molten binding agent.

Such an abutment support will also reduce the amount of binding agent required by about 20%, which also reduces costs. The fact that less binding agent is used will also further counteract the tendency of the binding agent to flow.

These and other advantageous embodiments of the inventive cover will be apparent from the Claims dependent on Claim 1.

From a second aspect of the invention, the object has been achieved with a method of the kind defined in the preamble of

Claim 1 that comprises the steps set forth in the characterizing clause of said Claim.

Just how the method results in a cover that has improved proper- ties with regard to the strength with which the sheets or pages are attached to the cover will be evident from the above descrip- tion of the advantages afforded by the inventive booklet.

The Claims depending on Claim 8 disclose advantageous embodiments of the inventive method, these embodiments finding correspondence in the preferred embodiments of the inventive booklet.

The invention will now be described in more detail with reference to preferred embodiments thereof and with reference to the accompanying drawings, in which Fig. 1 is a view of an inventive booklet in one perspective; Fig. 2 is a perspective view of a booklet fabricated in accor- dance with a known technique; Fig. 3 is a cross-sectional view of part of the spine of a booklet fabricated in accordance with a known technique; Fig. 4 is a cross-sectional view corresponding to Fig. 3 and illustrating a cover according to the present invention; and Fig. 5 is a cross-sectional view similar to the view of Fig. 3 and showing a finished booklet according to the present inven- tion.

The booklet illustrated in Fig. 1 is comprised of a cover that includes respective front and back cover sheets 1, 2 and an interconnecting spine 3. The booklet is fabricated by applying a binding agent (not seen in Fig. 1) onto the inner surface of the

cover spine. The binding agent is comprised of a glue string which is solid at room temperature. In the fabrication of a booklet, a bundle of paper sheets 4 is inserted between the cover sheets, with one edge of respective sheets in abutment with the glue string. The glue is then brought to a molten state by heating and the bundle of sheets penetrates into and through the binding agent until the end-edge surfaces of the sheets are in contact with the actual spine. The binding agent is then allowed to harden, so as to glue the sheets firmly to the spine and therewith obtain a booklet.

Fig. 3 shows how the inside edge-surfaces 6 of respective sheets 4 rest against the inner surface of the spine 3 and are held firmly by the binding agent 5. Because the inner end-edge surfaces 6 lie against the spine, these surfaces are not used in achieving a glue joint between the sheet 4 and the spine. Only the inner part 7 of each side-surface 8 of a sheet will be exposed to the glue. The drawbacks associated herewith have been discussed in the aforegoing.

Fig. 4 shows a binding device that includes partly a binding agent 5, in a known manner, and an abutment support 10 which is embedded in the string of binding agent. In the illustrated embodiment, the abutment support is comprised of a strip of relatively coarse-mesh woven material, for instance an adhesive gauze comprised of 100% cotton and of a kind typically used in the graphic industry. Only those cotton threads that extend perpendicular to the plane of the paper are visible in the Figure, while those threads that extend parallel with the plane of the paper are not visible in the Figure and have been shown in broken lines. The cover is pre-prepared for the fabrication of a booklet and includes the binding agent 5 and the abutment support embedded in the binding agent and fastened to the spine 3 of the cover. The binding agent may be any known EVA-based (Ethylene Vinyl Acetate) melt glue used conventionally in the graphic industry.

Fig. 5 shows the cover of Fig. 4 with a bundle of sheets 4 fastened therein so as to form a complete booklet. This has been achieved by inserting the bundle of sheets towards the spine until the inner end-edge surface 6 of each sheet has reached the upper surface 9 of the string of binding agent. The glue string is heated at the same time, as described above, so that the end- edge of the sheets are able to penetrate in towards the woven material 10 (see Fig. 4) and lie in abutment therewith. The sheets continue to penetrate the glue while pressing the woven material 10 towards the spine 3 until said material reaches the position shown in Fig. 5, in which the woven material reaches abutment with the spine 3, while preventing contact of the end- edge surfaces 6 of respective sheets 4 with the spine 3. A space corresponding to the thickness of the woven material (0.1-0.2 mm) is thus formed between the spine and the inner end-edge surface of the sheet bundle, these end-edge surfaces of the sheets forming part of the glue joint.

The stabilizing effect of the woven material 10 on the molten glue 3 means that spreading of the glue in the manner illustrated in Fig. 2 is avoided. Fig. 2 shows how glue has spread slightly out on the inner surface of each cover sheet 1, 2 to some extent, and also unevenly.

In Fig. 4, the abutment support is shown initially embedded in the glue string. It will be understood, however, that the abutment support may be fastened to the upper side or to the lower side of the glue string. Naturally, the abutment support need not consist of woven material. The abutment support may be affixed to the spine itself and may possibly consist of irregu- larities in the inner surface of the spine, for instance trans- verse stampings in the spine of the cover such as to form transverse ridges that will function as an abutment support.