A holder of this kind, such as an envelope, is generally known and comprises a planar holder body which, on at least one side, has an opening which can be closed. A substantially quadrilateral shape is in this context understood to mean any more or less quadrilateral shape, such as rectangles, squares, rhombi; however, it may also be the case that one or more of the sides have been altered by incisions, with the substantially quadrilateral shape nevertheless being maintained. The known holders, such as envelopes, are generally composed of a so-called blank which is formed by folding and joining to form a holder.

Known holders of this kind have the drawback that they have a relatively large number of joins or a con- siderable length thereof, so that the risk of them becoming detached is relatively great, and also there is a high possibility that the envelope may be opened without permission.

The risk of the joins becoming prematurely detached increases as the stiffness of the material from which the holder, such as an envelope, is produced increases. For envelopes which have to hold relatively large quantities of paper, or expensive documents, the material selected will be relatively thick and strong, with the risk of the joins becoming detached increasing as the stiffness of the material increases.

The object of the present invention is to provide a holder, in particular an envelope, of the type mentioned in the preamble which may be composed of a relatively stiff

material but in which the number of joins which may become detached or are easy to open is reduced by comparison with the holder which is generally known.

To this end, the holder according to the invention is characterized in that the holder body is composed of a plurality of layers which are joined to one another, each of the layers comprising a plurality of strips placed parallel to one another, the directions of which strips differ from one another in different layers, while the two body surfaces form a single piece and are connected to one another via two sides, which take the form of fold seams, and at least one of the other sides comprises a closure.

By producing the holder body from a material which comprises a plurality of layers which are joined to one another and also making the holder body form a single piece in which the body surfaces are joined to one another via two sides which take the form of fold seams, the result is a holder which comprises a considerably shorter length of joins.

In particular, in the above-described holder according to the invention, a strip is cut away at the location of the closure of one of the body surfaces, including parts of the fold seams, and the exposed part of the other body surface can be folded over against the said one body surface and attached thereto.

Expediently, on the side situated opposite the above-described closure the body surfaces are joined to one another in a sealed manner with the aid of, for example, an adhesive bond.

Obviously, based on a holder of quadrilateral shape, a closure may also be formed on both open sides, for which purpose in that case a strip is cut away from both sides of one of the body surfaces in order to form a closure on both sides.

The body surfaces can be joined together to form a closure by means of an adhesive bond, in which case, however, the term adhesive bond should be interpreted very broadly. The bonding may be carried out using a conventional adhesive composition, but consideration may

also be given to a hot-melt adhesive. Obviously, closure may also be effected using means other than adhesive bonds, such as stitching with wire, riveting, etc.

The material for the holder body, which comprises a plurality of layers and in which the layers are joined to one another, is known per se and will be explained in more detail in the discussion of the method according to the invention which follows below. Material of this nature is often based on paper which, in connection with certain applications, may, if desired, comprise a plastic constituent in order to provide the material of the holder with certain desired properties.

The invention also relates to a method for producing a holder, in particular an envelope, based on paper and having a substantially planar holder body which comprises two body surfaces, is of substantially quadri- lateral shape and is provided on at least one side with an opening which can be sealed, in which method a holder is formed from a basic shape of the holder by folding and forming joins.

This method is generally used for producing holders, such as envelopes, in which a blank is produced and then formed into an envelope by folding and forming joins.

A known method of this kind is used on a very large scale and is relatively labour-intensive. First of all, it is necessary to form a basic shape for the holder, a so- called blank, by cutting or stamping, after which the holder is made ready for use by folding and forming joins.

A method of this kind is relatively difficult to automate, so that it is first necessary to produce a stock of blanks, which are then formed into ready-to-use holders in a device.

The object of the present invention is to provide a method which is better suited to automation and is characterized in that, starting from a cylindrical tube or sleeve of paper-based material which is produced in a manner known per se by winding strips of suitable material and comprises a plurality of layers of this material which

are joined to one another, this tube is compressed along its entire length to form a substantially planar holder body with two fold seams, after which at least one of the open sides is provided with a closure. Following the compression or following the forming of the closure, the holder formed is dried, which causes the adhesive employed to reveal its full adhesive nature. Drying may be carried out at room temperature or at elevated temperature.

In order to produce a holder according to the invention using this method, a cylindrical tube can be formed continuously, after which a tube formed is com- pressed, outside the production machine, over its entire length in order to form a holder body, after which at least one of the open sides is provided with a closure.

A device for forming a cylindrical tube by winding strips of suitable material is known per se and is used for the production of a wide variety of tubes with a diameter which can be set as desired. Devices of this kind can operate continuously, and the tubular material coming out of these devices can be continuously processed to form holders.

As an alternative, it is also possible to start from a long, separately produced tube which is divided into pieces of the desired length, after which these pieces are compressed separately over their entire length and are then processed so as to form a ready-to-use holder.

If, during the continuous forming of the tube, it is labelled or a pattern is applied which has to adopt a predetermined location on the surface of the substantially planar holder eventually produced, the following method is advantageously employed. Part of a tube of the desired length is positioned, in a state in which it is still sufficiently moist, over two bars of appropriate diameter, for example 20-40 mm, preferably 20 mm, with the surface of the bars bearing substantially against the inner surface of the tubular part. The positions where the bars are in contact and of the labelling or pattern are accurately matched to one another. The bars are moved apart over a short distance and for a short period of time (distance 10-

20 mm; time 2-8 sec.), so that slight pre-folds are formed in the tubular part.

When the tubular part is subsequently pressed completely flat, the fold seams will be formed at the location of the pre-folds, with the result that the labelling or pattern will adopt a predetermined location on the surface of the finished holder.

Preferably, the abovementioned bars are disposed vertically during the forming of the pre-folds.

After the tubular part has been pressed flat, it is dried at ambient temperature or elevated temperature in order to dry the adhesive used and the paper of the layers.

A closure may be formed before or after drying. To form a closure on one open side, a strip of one of the body surfaces, including parts of the fold seams, is expediently removed on the said open side, and that a strip of the other body surface which protrudes beyond the said body surface is made suitable for joining, by being folded over, to the said one body surface. Obviously, a closure feature of this kind may also be present on both open sides.

The other open side may be sealed by joining the body surfaces to one another with the aid of an adhesive composition, a hot-melt composition or a mechanical join, such as by stitching, riveting, etc.

The cylindrical sleeve is formed in a manner known per se by winding strips onto a cylindrical core, the strips being provided, prior to winding, with an adhesive composition in a suitable manner, so that when they are wound onto one another, optionally with an overlap, a layered material is formed which, owing to the presence of the adhesive composition, is cohesive. Currently, adhesives of this nature are frequently water-based, so that a wound tube is of a relatively flexible nature immediately after the winding. The compression which is then carried out over the length of the tube can then take place with little force and has the advantage that, owing to the moist nature of the paper material forming the tube, there is relatively little damage to the paper at the location of the fold seams, so that the integral nature of the holder body is

maintained to an optimum extent. Following the usual drying, the substantially planar tube or the substantially planar tubular part exhibits its usual level of cohesion and strength. Drying is carried out at ambient temperature or elevated temperature, for example 30-600C.

As an alternative, if the tubes are completely "dry", they can be remoistened in order to make the tubes flexible, after which they can be compressed without damage at the location of the fold seams. The moisture is less important for tubes which have been produced from a small number of layers of paper-type material; in this case, they can be compressed at any time without damage in the fold- seam area.

The adhesive material used to produce the tubes is formed, for example, by a solution of polyvinyl acetate in water; obviously, other water-based adhesive materials may also be used, as may solvent-based adhesive systems.

The paper-based material in the form of strips may, if desired, contain a certain quantity of synthetic material, in order to provide the paper material with desired properties, such as tear strength, water-resis- tance, resistance to cutting, etc. Naturally, it is also possible for part of the strip material which is used to assemble the tube to be replaced by plastic strip material, in order for part of the structure of the layers to consist of plastic.

Finally, the invention relates to a device for producing a holder, such as an envelope, in which a basic shape of the holder is formed, by folding, into a holder body, which is formed into a holder by forming joins.

A device of this kind is characterized in that it comprises pressure-exerting means, with which an inserted cylindrical tube based on paper, which has been formed in a manner known per se by winding and comprises a plurality of layers, which are joined to one another, can be compressed over its entire length to form a substantially planar holder body. The pressure-exerting means may be formed by pressure plates, between which the tube, which may still be moist, can be placed in order to be compressed over its

entire length. The pressure-exerting means may also be roller means within which a tube can be compressed over its length.

Advantageously, the device comprising the pressure- exerting means described above forms part of a device for producing cylindrical tubes of paper-based material by winding. The cylindrical tubes, which are formed continuously or intermittently, can be fed to the device comprising the said pressure-exerting means in order in this way to be compressed into holder bodies, after which the requisite operations are then carried out to form a sealed closure on one side and a closure which is to be sealed subsequently on the other, open side.

The invention will now be described with reference to the drawing, in which: - Figure la shows a basic form of a holder accord- ing to the invention, - Figure lb shows a holder body formed by com- pressing the starting form shown in Figure la, and - Figure 2 shows a holder body from Figure lb which is provided with a closure.

In Figure la, reference numeral 1 indicates a tube which has been formed in a known manner by winding strips of paper material; the strips optionally overlap each other partially.

Figure lb diagrammatically shows the tube from Figure la which, by being compressed over its entire length, has been formed into a holder body with body surfaces 2 and 3; open sides 4 and 5 and fold seams 6 and 7. For the sake of clarity, the fold seams 6 and 7 are drawn here with a certain dimension; naturally, this dimension depends on the thickness of the material of the tube 1 and may vary from substantially zero to a few millimetres.

Figure 2 shows a holder body of the type shown in Figure lb, but with a closure feature having been provided.

The holder body comprising body surfaces 10 and 11; fold seams 12 and 13 is processed by cutting in such a manner that part of the body surface 10 is cut away, so that part

of body surface 11 remains protruding. Obviously, when the body surface 10 is cut away, the associated part of the fold seams 12 and 13 is also cut away. If the fold seams have a thickness which is substantially zero, obviously the part cut away will therefore also be substantially zero.

The projecting part of the body surface 11 may, for example, be provided with a strip of double-sided adhesive tape which, as is known, can be covered with a detachable protective film. By removing the protective film and folding the exposed part of the body surface 11 over, a join can be produced between the inside of the body surface 11 and the outside of the body surface 10, under the action of the adhesive film applied to the body surface 11.

Obviously, the adhesive film with covering layer may also be applied to the appropriate location on the body surface 10. On the open side 14, closure may be effected by applying an adhesive composition between the inner sides of the body surfaces 10 and 11; the adhesive composition may be a conventional water-based or solvent-based adhesive composition, but may also be formed by a hot-melt material.

As stated earlier, the closure may also be effected by mechanical means, such as by stitching with a wire, riveting, etc.

The holder according to the invention has been found to be extremely strong and, depending on the production method, may have all kinds of additional properties, such as tear resistance, water resistance and the like.

By comparison with conventional holders, such as envelopes, the length of join present in the holder is considerably less, with the result that the risk of the joins becoming detached is reduced.