Method for preparing flexographic matrixes for printing cylinders, typically for decorating ceramic tiles, disposable flexographic matrixes obtained thereby and modular printing cylinders equipped therewith

Abstract

 A method for preparing flexographic printing matrixes, characterised by the following operative stages: providing a form comprising a thin-walled rigid cylindrical sleeve provided with two outer circumferential end shoulders, and locking it in an upright position at an injection station; creating about said sleeve a first annular forming chamber extending between said shoulders; filling said first chamber with a first fluid elastomeric material which on termination of curing is soft and elastically deformable; creating about said first material, when cured, a second annular forming chamber narrower than the preceding; filing said second chamber with a second fluid elastomeric material which on termination of curing is flexible and non-deformable; and removing the piece formed in this manner from said station when said second material is

Description

[0001] This invention relates generally to the decoration of substantially flat plate-like articles and products, typically ceramic tiles, and more particularly to a method for preparing disposable matrixes for flexographic printing cylinders.

[0002] The invention also relates to the disposable matrixes obtained by said method, and to the modular printing cylinders which comprise them.

[0003] For flexographic printing, cylinders are known consisting substantially of a composite tubular monolithic body comprising: an inner metal roll, usually of aluminium, provided with two end flanges for its mounting on the support and drive heads of a flexographic machine; a relatively thick intermediate cladding of elastically deformable elastomer which clings to that part of said roll between said two flanges; and a relatively thin outer layer of flexible elastomer which covers said cladding.

[0004] The outer layer is subsequently engraved to carry the pattern which is to be applied to the tiles.

[0005] It is considered unnecessary to describe the method of engraving this layer, or to list the possible constituent materials of said layer and cladding as these are not involved in the characterising part of the invention.

[0006] A description will however be given of the method used to construct such known flexographic cylinders.

[0007] This comprises essentially the following operations: forming in the wall of the metal roll a series of through apertures, and mounting over the roll a jacket which defines therewith an annular chamber closed at its ends; mounting the combined roll and jacket onto a fixture able to rotate it about itself; feeding into the roll of said combination, while it rotates at high speed, a quantity of substantially liquid synthetic material sufficient to fill said chamber by the effect of the centrifugal forces in play; removing said jacket once the synthetic material is cured, to form said elastically deformable cladding; and applying said layer of flexible material onto said cladding.

[0008] The aforesaid known method has proved unsatisfactory at least for the following reasons.

[0009] The first is the need to drill the metal roll and provide the fixture for rotating the combined roll and jacket, the costs thereof obviously increasing the cylinder cost.

[0010] Moreover, if the outer layer of such known flexographic cylinders becomes worn during operation, the total flexographic cylinder has necessarily to be replaced, seeing that to regenerate it would involve greater cost.

[0011] Again, if diversified printing is involved, as is generally the case in the ceramics sector, purchase of the relative flexographic cylinders involves considerable investment, with evident increase of the finished product cost.

[0012] The main object of the present invention is to provide means for overcoming the aforesaid complex problem.

[0013] Said object is attained by a method for forming a flexographic matrix, the actual disposable flexographic matrix obtained thereby, and a modular printing cylinder comprising said matrix, having the characteristics indicated in the claims.

[0014] According to said method, which is described in detail hereinafter, a disposable form is provided, consisting essentially of a rigid cylindrical sleeve provided with two outer terminal circumferential ribs and locked in an upright position at a fixed injection station; about said sleeve a first annular forming chamber is created between said ribs, and a first fluid elastomeric material with known properties is injected thereinto; creating, about said first material after its curing, a second annular forming chamber narrower than the preceding and injecting therein a second fluid elastomeric material with known properties; and after the curing of said second material, removing the form covered in this manner from said station.

[0015] Preferably said cylindrical sleeve consists of a piece of relatively thin synthetic tube.

[0016] In particular, said annular chambers are created by two rigid jackets, to be temporarily sealed onto the terminal ribs of said form as stated hereinafter.

[0017] The piece obtained in this manner constitutes a disposable flexographic matrix comprising a relatively thin inner layer of rigid synthetic material, a relatively thick intermediate layer of elastically deformable soft synthetic material, and a relatively thin outer layer of non-deformable flexible synthetic material.

[0018] According to the invention, said matrix is intended to be removably associated with a rigid modular support core, typically of metal such as aluminium, to be mounted on a printing machine to provide a modular flexographic cylinder, and more precisely a cylinder with an interchangeable matrix.

[0019] Specifically, said core comprises a cylindrical tube on which said matrix is mounted as a precise fit, and which presents two end retention flanges torsionally engaged with the opposing ends of the matrix, at least one of said flanges being removable associated with the respective end of said tube.

[0020] For certain known configurations of the printing machine, one of the end retention flanges can be omitted.

[0021] All the objects of the invention are attained by virtue of the aforegoing.

[0022] In this respect, the preparation of a flexographic printing cylinder in accordance with the invention is less complex and less costly than with the known method described in the introduction as drilling operations are not required, and in practice the usual equipment used in this sector is utilized.

[0023] Moreover, the modularity of a cylinder of the invention enables the same core to be used when the matrix has to be replaced either because it is worn or because the decoration is to be changed.

[0024] This makes the packaging, despatch and storage of the matrixes much simpler. The characteristics and merits of the invention will be apparent from the ensuing detailed description given hereinafter with reference to the figures of the accompanying drawings, which illustrate a particular preferred embodiment thereof by way of non-limiting example.

[0025] Figure 1 is an exploded perspective view with interruptions, showing the constituent elements of a rigid form for preparing a disposable flexographic matrix according to the invention.

[0026] Figure 2 is an axial section showing the elements of Figure 1 in their assembled configuration.

[0027] Figure 3 shows the circled detail III of Figure 2 on an enlarged scale.

[0028] Figure 4 is a view similar to Figure 2 showing said form mounted on a support template.

[0029] Figure 5 is a view similar to Figure 4 showing said form on termination of the injection of a first elastomeric material.

[0030] Figure 6 shows the same form on termination of the injection of a second elastomeric material.

[0031] Figure 7 is a partial longitudinal section through a disposable flexographic matrix obtained by the method of the invention.

[0032] Figure 8 is an exploded perspective view with parts cut away showing a modular flanged tube for forming the support core for the flexographic matrix of Figure 7.

[0033] Figure 9 is a longitudinal section through a modular printing cylinder obtained by assembling the matrix of Figure 7 and the core of Figure 8.

[0034] Said figures, and in particular Figures 1 to 3, show two identical circular rings 1 to be fixed to the opposite ends of a thin cylindrical sleeve 2.

[0035] Said two rings 1 and said sleeve 2 are formed of a convenient rigid synthetic material. The sleeve 2 consists of a piece of commercial tube of small thickness, which in the illustrated example is about 2.5 mm.

[0036] The inner hole of each ring 1 presents two portions of different diameter, the greater of which receives the respective end of the sleeve 2 as a forced fit.

[0037] To facilitate said forced fit, the rings 1 and the sleeve 2 are provided with suitable bevels as shown in Figure 3 and, if appropriate, the connection between said elements can be made more firm by interposing a suitable glue.

[0038] It should be noted that the inner diameter of the sleeve 2 is less than the lesser inner diameter of the rings 1 (see Figure 3), the significance of which will be evident hereinafter.

[0039] As can be seen from Figure 2, in the aforedescribed manner a rigid tubular body 12 is obtained provided with two outer end circumferential shoulders, and intended to act as a form for the preparation of a disposable flexographic matrix.

[0040] The outer surface of each ring 1 comprises (see Figure 3) two cylindrical portions of different diameter separated by a narrow circumferential groove 4. The portion of lesser diameter also presents a channel 3 for receiving a suitable seal gasket 30 of 0-ring type, that of greater diameter being provided with a channel 5 for a respective gasket 50.

[0041] The cross-section of the inner channel 3 is less than that of the outer channel 5, the base of the channel 3 being sunken relative to that of the channel 5, and the outer generators of the gasket 50 extend beyond those of the gasket 30.

[0042] In Figure 3 said gaskets 30 and 50 are shown with dashed and dotted lines because of the fact that they are not permanently and simultaneously associated with the respective channels 3 and 5, but are temporarily utilized in the ensuing manner.

[0043] From Figure 1 it will be noted that along the circumferential extension of one of said rings 1 there are a longitudinal injection hole 6 and a diametrically opposite longitudinal phasing hole 8.

[0044] Along the circumferential extension of the other ring 1 there are a longitudinal phasing hole coaxial with the preceding, and four angularly equidistant longitudinal bleed holes 7.

[0045] The provision of the aforedescribed tubular body 12 constitutes the first operative stage of the proposed method, the next stage consisting of mounting the body 12 on a support template 9 (see Figure 4).

[0046] Said template 9 comprises a cylindrical block of vertical axis extending upwards from a bed 91, and having a diameter such as to receive the sleeve 2 of the body 12 as a precise free sliding fit.

[0047] In the illustrated example said block 90 is solid, but there is nothing to prevent it being hollow.

[0048] In the upper face of the bed 91 there is a circular groove 10 coaxial with the block 90 and having an outer diameter greater than the rings 1 (see Figure 4).

[0049] The bed 91 presents an injection port 11 situated radially inwards of said groove 10, and aligned with the injection hole 6 of the body 12 when this latter is mounted on the template 9.

[0050] If appropriate, at least the phasing hole 8 of the lower ring 1 is closed with an adequate plug.

[0051] After (or even before) said mounting, the gaskets 30 are inserted into the inner channels 3 of the rings 1 (see Figures 4 and 5).

[0052] Over these latter there is then placed a thin-walled rigid cylindrical jacket 13, the opposing ends of which are disposed overlooking the channels 4 in the rings 1.

[0053] Said jacket 13 comprises two identical half-shells which can be either separate or hinged together along a generator.

[0054] In the first case, suitable clips are provided to clamp the two half-shells onto the gaskets 30, whereas in the second case along the free longitudinal edges of the half-shells there are provided suitable devices for their engagement and locking together.

[0055] Via the injection port 11 and the injection hole 6 provided in the bed 91 and lower ring 1 respectively,, a first fluid elastomeric material is injected into the annular forming chamber defined between the body or form 12 and the jacket 13, the air present in the chamber discharging to atmosphere through the bleed holes 7 in the upper ring 1.

[0056] Said elastomeric material is a silicone-based material usually used in this specific sector, which during polymerization expands so that on termination of curing it provides an elastically deformable soft layer 120 (Figure 5).

[0057] The jacket 13 is either constructed of a material to which said elastomeric material cannot adhere or is surface-coated or treated with a product for this purpose.

[0058] After said curing, the jacket 13 is removed and the gaskets 30 are extracted from their seats 3 for reuse.

[0059] After this, the respective gaskets 50 are inserted in the channels 5 of the rings 1, see Figure 6, and over these a second thin-walled rigid cylindrical jacket 14 in the form of a one-piece tube is sealedly mounted.

[0060] The lower end of the jacket 14 is rested on the base of the groove 10 in the bed 91, where it is engaged as a lightly forced fit with the outer side of the groove 10.

[0061] This ensures that the jacket 14 and block 90 are perfectly coaxial.

[0062] After this mounting, a second fluid elastomeric material is injected into the annular forming chamber between the jacket 14 and the layer 120.

[0063] This is done via a radial hole 15 provided at the base of the jacket 14 (see Figure 6), above the lower gasket 50, the air present in the chamber discharging through at least one radial hole 16 provided at the top of the said jacket 14, below the upper gasket 50.

[0064] In the same manner as the jacket 13, the jacket 14 is also formed in a manner preventing any inconvenient adhesion of said second elastomeric material.

[0065] This latter is a silicone-based material usually used in this specific sector for flexographic printing operations. It is preferably water-repellent.

[0066] When cured or polymerized, the material forms a non-deformable relatively thin flexible layer of thickness of the order of 2 mm, its opposing ends gripping the channels 3 and grooves 4 in the rings 1, as shown in Figures 6 and 7.

[0067] Said layer 121 is available for engraving in known manner, as required by the user.

[0068] When said layer 121 is completely cured, the jacket 14 is withdrawn, the gaskets 50 are extracted and the resultant formed piece is removed from the block 90 to provide a disposable flexographic matrix 17 (see Figure 7) comprising three mutually adhering concentric synthetic layers, as previously explained.

[0069] Further matrixes 17 are formed by an identical procedure.

[0070] For its installation on a flexographic printing machine, not shown as it is well known to the expert of the art, according to the invention the matrix, after suitable finishing, is associated with a rigid modular support core, shown in Figure 8.

[0071] It comprises a metal tube 18, typically of aluminium, which at one end presents a fixed flange 19, whereas with its other end there is associated a removable flange or ring 20.

[0072] Said two flanges 19 and 20 have an outer diameter of the same order of magnitude as that of the matrix 17, each of them presenting on their inner face (i.e. that facing the tube 18) a retention peg 21, and in their outer face a diametrically opposite drive recess 22.

[0073] The ring 20 differs from the flange 19 by the presence of a coaxial skirt 23 to be inserted, as an exact or lightly forced fit, into the respective end of the tube 18. Preferably between said skirt 23 and said tube 18 there are provided means for torsionally locking them together, such as a keying device.

[0074] The free or useful length of said tube 18 is practically equal to that of the matrix 17.

[0075] Again, the tube 18 has an outer diameter such that it can receive the matrix 17 as a precise freely slidable fit.

[0076] A printing cylinder according to the ii, shown in Figure 9, is assembled as follows.

[0077] The matrix 17 is mounted over the tube such that the peg 21 of the flange 19 engages the respective facing phasing hole 8 of the matrix 17, after which the ring 20 is mounted, while simultaneously engaging the respective peg 21 in the other hole 8 of the matrix 17.

[0078] The aforesaid recesses 22 act as seats for engaging the cylinder 33 by respective matching drive keys provided on the drive heads of the printing machine.

[0079] The merits and advantages of the invention are apparent from the aforegoing and from an examination of the accompanying figures.

[0080] The invention is not limited to that illustrated and described, but also comprises those variants and improvements falling within the meaning of the ensuing claims.

Claims

1. A method for preparing flexographic printing matrixes, characterised by comprising the following operative stages:

- providing a form comprising a thin-walled rigid cylindrical sleeve provided with two outer circumferential end shoulders, and locking it in an upright position at a fixed injection station;

- creating about said sleeve a first annular forming chamber extending between said shoulders;

- filling said first chamber with a first fluid elastomeric material which on termination of curing is soft and elastically deformable;

- creating about said first material, when cured, a second annular forming chamber narrower than the preceding;

- filing said second chamber with a second fluid elastomeric material which on termination of curing is flexible and non-deformable; and

- removing the piece formed in this manner from said station when said second material is cured.

2. A method as claimed in claim 1, characterised in that said first chamber is created by a first rigid enclosing jacket which is sealedly coupled to said shoulders after previously inserting two first gaskets into respective grooves provided along a lesser-diameter inner portion of the outer surface of said shoulders.

3. A method as claimed in claim 1, characterised in that said first annular chamber is filled by injecting said first material from below, through at least one longitudinal passage provided in the lower shoulder of the form, the air present in the chamber discharging through at least one longitudinal bleed port provided in the upper shoulder of the form.

4. A method as claimed in claim 2, characterised by removing said first chamber and said first gaskets after said first material is cured.

5. A method as claimed in claim 1, characterised in that said second forming chamber is created by a second rigid enclosing jacket which is coupled to said shoulders after previously inserting two second gaskets into respective grooves provided along a greater-diameter outer portion of the outer surface of said shoulders.

6. A method as claimed in claim 1, characterised in that said second annular chamber is filled by injecting said second material from below, through at least one lateral passage provided at the base of said second chamber, the air present in the chamber discharging through at least one lateral bleed port provided at the top of the jacket.

7. A method as claimed in claim 5, characterised by removing said second chamber and said second gaskets after said second material is cured.

8. A disposable flexographic matrix obtained by the method claimed in claims 1 to 7, characterised by consisting of an overall rigid cylindrical tubular body comprising a relatively thin inner layer consisting of a rigid material and having two opposing end shoulders, a relatively thick intermediate layer consisting of an elastically deformable soft synthetic material extending between said shoulders, and a relatively thin outer covering layer of a non-deformable flexible synthetic material.

9. A matrix as claimed in claim 8, characterised in that said inner layer consists of a piece of synthetic tube to which two end rings of synthetic material are fixed.

10. A matrix as claimed in claim 8, characterised in that the end portions of said covering layer grip at least two outer circumferential grooves provided in said shoulders.

11. A flexographic printing cylinder, characterised by comprising a rigid cylindrical tube provided with at least one end flange and about which a matrix claimed in claims 8 to 10 is mounted as an exact fit, said matrix being in contact with said at least one end flange.

12. A flexographic printing cylinder as claimed in claim 11, characterised by comprising a rigid cylindrical tube provided with two opposing end flanges, between which said matrix lies and is torsionally engaged, at least one of said flanges being removably associated with said tube.

13. A cylinder as claimed in claim 11, characterised in that said tube and said flanges are constructed of metal, such as aluminium.

14. A cylinder as claimed in claim 12, characterised in that the torsional engagement between said matrix and each flange is achieved by a projection, such as a peg, and a matching cavity, such as a hole, these being provided on the facing transverse faces of the matrix and the facing flange.

15. A cylinder as claimed in claim 12, characterised in that said at least one removable flange comprises a ring provided with a skirt to be contained as an exact fit in the respective end of the tube.

16. A cylinder as claimed in claim 11, characterised in that said at least one flange is provided with means for its torsional coupling with said tube, such as a keying device.

17. A cylinder as claimed in claim 11, characterised in that said at least one flange is provided with means to be coupled to matching support and drive means of a printing machine.

Drawing