FR2811255A1 - Manufacturing procedure for flexography sleeve with integral stabilising ribs uses spiral-wound layers impregnated with resin - Google Patents

Abstract

The procedure, especially for making a flexography sleeve of composition material from a number of spiral-wound resin-impregnated layers, consists of forming a first layer (16) e.g. of strips with a preferable width of 6 - 8 cm, impregnating it simultaneously with resin (20), winding a second resin-impregnated layer (24 + 26) over the first to give the desired outside diameter, and coating with a thin finishing layer (32) of resin. The gaps (28) between the windings, which can be continuous or discontinuous, form stabilising ribs (30) of accumulated resin. The resins are polymerised together or independently, as required.

Description

METHOD FOR MANUFACTURING A SLEEVE WITH INTEGRATED NETWORK

  OF STABILIZING CORDS, ESPECIALLY FOR FLEXOGRAPHY AND

SLEEVE OBTAINED

  The present invention relates to a method of manufacturing a sleeve with an integrated network of stabilizing cords, in particular for flexography

as well as the sleeve obtained.

  The manufacture of sleeves for flexography is well known and many types of sleeves made of composite materials have been developed, in particular described in European patent N 683,040 having the same inventor. These composite sleeves comprise, in known manner, superimposed windings of strips of fiber-based materials, woven or non-woven, of varying thicknesses and types depending on requirements and

  especially depending on the desired applications.

  Indeed, the principle of having sets of sleeves made of composite materials makes it possible to reduce the number of support cylinders necessarily made of metallic material for mechanical drive reasons. The composite sleeves can be produced in different external diameters for identical internal diameters so that one can have a large range of developments from sleeves in

  composite materials for the same set of support cylinders.

  These composite material sleeves are placed on the support cylinders by radial expansion. In fact, the support cylinders are hollow and include a supply of pressurized air from inside the cylinder which forms a chamber and nozzles which allow the pressurized air to escape. These nozzles are suitably distributed along the generators

of each cylinder.

  Thus, for assembly, air is supplied under pressure to the chamber, the sleeve is presented at the end of the cylinder and the sleeve is pushed to ensure pre-introduction. As soon as the end of the sleeve is superimposed on the first series of nozzles, the pressure ensures a radial expansion of the sleeve, at least of its inner layers, close to the center, which causes the formation of a layer of air or air cushion that allows a

  slip of the sleeve on the outside surface of the support cylinder.

  When the sleeve is positioned, it suffices to eliminate the supply of pressurized air and the sleeve, by its memorization and its capacities of elastic radial return, due to the nature and the composition of its

  layers, squeeze the support cylinder and come to rest on it.

  We know that one of the main problems of a sleeve is its retention on the support cylinder in order to avoid any relative rotation because the sleeve being intended to support a plate, there would be a shift, in particular in the positioning of the printed colors. , incompatible with

  the application of the flexographic process.

  In the sleeves, there are essentially three types of families.

  The first family consists in making a first thin sleeve from a winding of fiber fabric, impregnated with resins such as a fabric

  of glass impregnated with an epoxy resin with hardener.

  On this sleeve thus produced and after polymerization, there is a compressible material such as an elastomer over a greater thickness, of several millimeters. In the case of an elastomer, this is wound, calendered and vulcanized on the first sleeve. We can replace this

  elastomer by foam with positioning adhesive.

  The additional thickness is achieved by a layer of filling material, consisting of coils of layers, in suitable numbers, which are incompressible and of great hardness. This layer is obtained for example from polyester felt impregnated with an epoxy resin / hardener composition. A finishing resin ensures the perfect final surface condition, at the

  desired geometry, after going through mechanical grinding.

  The second family of sleeves is substantially identical to the previous one, but with the filling material, polyurethane foam added by gluing or by injection, in place of the felt.

impregnated polyester.

  The exterior finish remains the same.

  The third family consists in making the entire sleeve with the same product, for example a polyester felt impregnated with a composition of

epoxy resin / hardener.

  The presence of a finishing layer with a finishing resin is

  maintained with a passage in mechanical rectification.

  i15 The sleeves of the first and second families have assembly facilities due to the fact that the intermediate compressible material facilitates

radial expansion.

  On the other hand, what is an advantage turns into a disadvantage because the compressible material leads, after positioning the plate and during printing, to irregular deformation points when there is application

  against the printing machine back pressure cylinder.

  In order not to cause print quality defects, you must

  often decrease the printing speed.

  In addition, for purely economic reasons, the establishment of

  foam with fixing adhesive are very expensive.

  When using polyurethane foam, the life of the sleeves is relatively limited by the lower resistance in particular

mechanical, of this material.

  The third family, due to its radial stiffness, provides excellent print quality. On the other hand, the air pressure necessary to obtain the expansion

  radial during assembly is more important.

  In addition, such a sleeve presents risks of delamination of the inner layers in the case of frequent assembly / disassembly. Therefore, it is often expected to have a nonwoven of polyester material with additives and impregnated with a resin in an inner layer without this completely compensating for this problem. It should also be noted that there is a problem with the manufacture of the sleeves which use materials of the polyester felt type since there may be variations in geometry due to the rise in temperature and the occasions

  humidity, detrimental to quality.

  In addition, it is also known that this type of felt used, although easy to impregnate with resin, ultimately has qualities of mechanical resistance to crushing as well as to deformation under the effects of centripetal forces which can be improved. This is a problem and this stiffness

  follows the degree of quality of the subsequent printing after mounting the plate.

  The object of the present invention is to alleviate these problems and to make it possible to obtain, through the implementation of the method, a sleeve which allows very good resistance on the support cylinder by suitable radial tightening, excellent print quality. by a good homogeneity of the resumption of the efforts of application of the back-pressure roller, a very good dimensional stability allowing a greater speed of rotation, an ease of assembly / disassembly while remaining insensitive to

  numerous assemblies / disassemblies thus conferring a greater lifespan.

  The process is now described in detail according to a particular, non-limiting embodiment, with the accompanying drawings by way of illustration of the various stages and of the configuration of the product obtained. The figures of the drawings represent: - Figure 1, a schematic perspective view of the product obtained with cutouts allowing the different layers to appear, - Figure 2, a view in enlarged cross-section of the first layer called compensation bridges , - Figure 3, a perspective view of the second layer of filling material, - Figure 4, a detailed view in cross section of the sleeve according to the present invention, and - Figures 5A and 5B, schematic views developed layers of

  sleeve according to the present invention, during assembly and once fitted.

  In FIG. 1, the manufacturing cylinder 10 which is at the exact dimension of the support cylinder on which the sleeve 12 is to be mounted, is coated with

  preferably a gel-coat 14 for frosting the inner face.

  A first layer 1 6 of a woven or nonwoven 1 7 of fibers of synthetic material, in this case, is then wound in a spiral, crossed fashion.

  it is a nonwoven of aramid fibers.

  Aramid fibers are mechanically and heat resistant and

  are marketed under the names "Kevlar", "Nomex" for example.

  The grammage is very light since it is preferably between 10 and 80 g / m2 and more particularly between 40 and 60 g / m2. Such products are

  therefore quite accessible from the cost point of view, especially in nonwoven.

  In order to facilitate the application around the rotating tool, it is useful to have rolls of strips of small width, 5 to 10 cm to fix

  an order of magnitude, preferably between 6 and 8 cm.

  This nonwoven also has an important feature compared to the product currently sold: it includes holes 18, made

prior to winding.

  Indeed, it is necessary to provide a perforation, for example of the whole of the mother reel or of the bands, when scrolling. Preferably, these holes are obtained by drilling with heated needles to ensure drilling with good geometry and good

finishing the hole edge.

  We thus obtain a strip with regularly distributed holes and this

  with a perforation density depending on the desired effects.

  These nonwoven webs are wound with a simultaneous impregnation of a resin composition. This is preferably a

  combination of polyamide resin / polyurethane resin.

  This impregnation must be carried out very meticulously so as to fill all the perforations 18 and not to simply distribute the

  composition on the surface of the nonwoven leaving the holes empty.

  The resin composition is subject to at least one important rule for the present invention, that of having a high modulus of elasticity

after polymerization.

  An exemplary embodiment is shown in FIG. 2.

  In this manufacturing method, it is noted that the aramid fiber layers are two in number, which leads to a thickness substantially from 3 / 10th to 10 / 10th mm, more particularly 6 / 10th. Aramid fibers have many advantages such as their excellent mechanical resistance, their low heat expansion but also their low wettability which requires a small amount of impregnation resin and they

are insensitive to moisture.

  We note in this figure 2, the holes 18 perfectly calibrated and the

  presence of resin 20 in each of them.

  The density of the holes is variable and the geometry as the section

  can be changed as required.

  Then, the sleeve is brought to its outside diameter by producing at least one filling layer 22 comprising a superposition of windings of a filling material 24 such as those known from the prior art and in particular windings are carried out. strips of polyester felt combined with additives. There is provided a resin 26 for impregnating this felt and in this embodiment, the resin is an epoxy resin with

hardener.

  These felts can have thicknesses of 2,3,4 or 5 mm to show the difference with the nonwoven of the first layer. They are of a cost price perfectly suited to filling material, such as epoxy resin. In the case of large diameters requiring a large number of superimposed layers, it is useful to regularly have a layer of material such as that used previously, namely a nonwoven of aramid fibers, which

strengthens rigidity.

  Indeed, the solution which consists in adding intermediate fabrics made up of very technical fibers like carbon fibers or aramides poses the problem of the cost in the necessary quantities, especially for these

types of application.

  According to another of the characteristics of the invention, filiform depressions 28 are produced on the surface of the filling material 24. These depressions may have a given orientation relative to the edge of the strip of material to be wound or be parallel to the edge as in the

  illustrated embodiment. This is shown in Figure 3.

  Preferably, these filiform depressions 28 are produced by hot stamping, during unwinding, by heating rollers which partially melt the material like polyester felt and mark in hollow, according to the profile of the roller. This gives a depression in U or V section. Thus, during winding as shown in Figure 3, the depressions are oriented along the winding angle so as to obtain a helicoid. The superposition of the windings with change of

  direction provides a network.

  After winding, the impregnation resin 28, accumulated in the depressions, makes it possible to obtain beads 30 of resin, stabilizers, which gives the representation of FIG. 4 when the sleeve is cut transversely. The resin being an epoxy resin, one obtains a significant mechanical resistance and this network of stabilizing cords makes it possible to lock the layers with respect to each other, without requiring high-tech materials and therefore expensive or even a material different from the materials used. artwork. In addition, radial deformation is prohibited by this network of

  stabilizing cords integrated into the thickness of the material.

  A finishing resin 32 is again necessary to allow rectification and to give the assembly a finished surface finish ready for

  receive the photographs in satisfactory conditions.

  The embodiment described provides for producing filiform depressions, but these depressions could also take the form of successive, adjacent and distinct filiform basins or else the form of continuous or discontinuous sinusoids depending on the possibilities of

  manufacturing and corresponding costs.

  The sleeve thus produced allows easy mounting on a support cylinder because the resin which filled the holes forms so-called compensation bridges in the first layer. Each bridge thus constitutes a

  elastic return module, like an elastic pad.

  During the introduction of the sleeve, under the effect of the air pressure, an air cushion A is formed, the 18/20 compensation bridges compress, this i15 which allows a controlled controlled radial expansion sufficient for the translational movement along the cylinder, as shown in Figure 5A. In particular by varying the diameters of the holes, one can control the value

radial expansion.

  The thickness e of the first layer 1 6 is reduced by a value _, the height H of the second layer remains unchanged and the thickness E of the sleeve, including the thickness of the finishing layer 32 is also reduced d 'a

  value c. The outside diameter also remains unchanged.

  After complete assembly, the interruption of the pressurized air supply causes the expansion of the 18/20 compensation bridges which press on the surface of the support cylinder either directly or through the superimposed layers of the aramid fiber fabric. This is indicated in Figure B. These compensation bridges are oriented perpendicular to the surface of the support cylinder, that is to say substantially radially, so that the pressure force is maximum. These radial forces are represented by

arrows in Figure 5B.

  The different layers resume their nominal thickness obtained by

exit from manufacturing.

  In addition, when, in combination, provision is made to produce resin cords 30 which immobilize / stabilize and lead to high external rigidity, the elastic restoring forces are not only oriented radially but also directed towards the support cylinder, the intermediate layer ensuring a total reaction of the restoring effort of the

compensation bridges.

  Within the framework of the process, it is advisable during the production, to envisage the phases of polymerization of the different resins of the different layers either at room temperature or by passage in the oven. The complete sleeve can be passed through an oven to allow total crosslinking of the different layers if the temperatures are compatible, but it can also

  be necessary to polymerize the different layers independently.

Claims (10)

  1. Method for manufacturing a sleeve, in particular for flexography, of composite materials, of the type comprising several coiled layers, generally helically with resin impregnation, characterized by the succession of the following steps - production of a first layer, - impregnation of this winding - making at least a second layer by winding at least one filling material impregnated with a resin to achieve the desired outside diameter, said material having depressions formed in the thickness so as to form cords of resin by accumulation during winding, and   - depositing a thin layer of finishing resin.   2. A method of manufacturing a sleeve according to claim 1, characterized in that a network of cords is formed during the winding in the filling material from continuous depressions. 3. Method of manufacturing a sleeve according to claim 1 or 2,   characterized in that the depressions are discontinuous.   4. Method for manufacturing a sleeve according to any one of   previous claims, characterized in that depressions are produced   on the surface of the material by hot stamping.   5. Method for manufacturing a sleeve according to any one of   previous claims, characterized in that bridges of   compensation in the first layer.   6. Sleeve made of composite materials, in particular for flexography,   obtained by the implementation of any one of the claims   previous, of the type comprising several coiled layers, generally helically with resin impregnation, characterized in that it comprises - a first layer (16), - a composition (20) of impregnation resins of the first layer (16 ), - at least one layer (22) of filling material (24) impregnated with a resin (26) to achieve the desired external diameter, said material comprising a set of depressions (28) forming an integrated network, and   - a thin layer (32) of finishing resin.   7. Sleeve according to claim 6, characterized in that the depressions (28) of the network are filled with the accumulated resin and form   resin stabilizer cords (30).   8. Sleeve according to claim 6 or 7, characterized in that the depressions (28) are continuous.   9. Sleeve according to claim 6 or 7, characterized in that the   depressions (28) are discontinuous.   10. Sleeve according to any one of claims 6 to 9,   characterized in that it comprises a first layer (16) with bridges (18/20) of compensation, said layer comprising windings of a nonwoven or a woven fabric (17) provided with holes (18) filled with '' a composition (20) resin.