WO2015114433A1

WO2015114433A1 - A continuous press belt for ceramic slabs having a structured surface, and a method for manufacture of the belt and use thereof

Info

Publication number: WO2015114433A1
Application number: PCT/IB2015/000045
Authority: WO
Inventors: Claudio Ricci; Vanes TERZIARI
Original assignee: Sacmi Cooperativa Meccanici Imola Societa' Cooperativa
Priority date: 2014-01-30
Filing date: 2015-01-16
Publication date: 2015-08-06
Also published as: ES2792990T3; CN105939843B; CN105939843A; PT3099478T; EP3099478B1; RU2690382C2; PL3099478T3; EP3099478A1; BR112016010171A2; RU2016114560A; MX2016006037A; BR112016010171B1; RU2016114560A3

Abstract

A method for manufacturing a continuous press belt or a vulcanizing matrix (100) of a punch of a ceramic die for creating ceramic slabs having a structured surface, comprising following steps: advancing the belt or the matrix by steps of a submultiple of a length of the belt or the matrix; at each advancement step, subjecting a strip of belt or matrix having a width equal to the step to action of at least a piezo-electrically-controlled ink-jet printing head (104), piloted by an image, in order to obtain on the belt or on the matrix a deposit of ejected material reproducing the image, the head being movable transversally to the belt or the matrix and suitable for ejecting an ink jet which belongs to a class of inks that are controlledly hardenable by ultraviolet radiation; subjecting the strip of material emitted by the head to action of an ultraviolet lamp (107) for hardening the ink.

Description

A CONTINUOUS PRESS BELT FOR CERAMIC SLABS HAVING A STRUCTURED SURFACE, AND A METHOD FOR MANUFACTURE OF THE BELT AND USE THEREOF TECHNICAL FIELD

The present invention relates to manufacture of ceramic slabs, preferably having a small thickness, such as tiles for flooring and wall-cladding, having a side destined to be in view that comprises random reliefs, commonly defined as a structured surface, or having a structured effect.

BACKGROUND

The "structured" effect gives the ceramic product a particular pleasant aesthetic value, especially in the case of imitation of natural materials such as woods and stones.

The slabs or tiles with the structured in-view side are at present constructed by means of pressing of powders in a usual die for ceramic tiles, in which the punch destined to form the structured side includes a negative of the design that is to appear on the surface of the tile or slab.

In particular the punch is clad by a layer of elastomer which bears, in negative, the design of the structured side.

The elastomer layer is constructed as follows.

A rigid die matrix, bearing the design in positive (i.e. entirely similar to the one to be reproduced on the ceramic slab or tile) is realized by means of a numerically- controlled precision mechanical working starting from three-dimensional data. The matrix is usually made of aluminium or another suitable material for rapid machining by removal of shavings or laser ablation.

When the matrix is finished, it is used for vulcanisation of the layer of elastomer (typically polyurethane with hardness 90 Shore A) applied on the active side of the punch. It is commonly defined "vulcanising matrix").

The vulcanising process requires heating to an appropriate temperature (about 150°) and a contemporary pressing action. On completion of the vulcanisation, an elastomer layer is present on the punch, generally a few millimetres thick and bearing the negative profile of the structure. The punch is therefore ready to be mounted as an "in-view side" punch on a conventional die for pressing of ceramic powders, enabling production of tiles having a surface entirely alike to the surface of the initial metal matrix.

Apart from being complicated and expensive, this method is not suitable for realising continuous structured-surface press conveyors suitable for continuous belt compacting lines.

In particular, the difficulty lies in realising the upper pressing belt, destined to form the structured side of the slab, on which a relief structure is to be created, always various and continuous, i.e. without interruptions.

Further, rapid substitution of the relief structure must be possible.

The only prior art able to realise high-resistance continuous structured steel belts is chemical etching, in which the belt is clad with an emulsion bearing the negative pattern and is then immersed in aggressive baths which etch the metal where it is not protected.

This method is very complex, laborious and has a negative environmental impact.

Further, the chemical attack does not enable precise differentiation of the incisions, with obvious aesthetic limits.

Laser ablation also exhibits limits and drawbacks, as the belt has to be mounted on a horizontal-axis rotating drum, which due to present proportions would be excessively large (more than 2 metres in diameter); and implies a working time (tens of hours) that is incompatible with an economical and industrially- exploitable production.

Also known is a method for creating three-dimensional structures on a substrate, by means of jet printers using inks that harden on the action of UV rays.

However this method, described in document WO 02/053338, is not usable for realizing structured press belts having the requisites for continuously creating ceramic slabs, as the substrate of the prior art is a belt of an undefined length, not loop-wound, and the zone subjected to the ink jet is curved.

Further, the known method is not suitable for creating a three-dimensional surface suitable for pressing ceramic tiles in the usual dies, as the nature of the structures created with the known method does not possess the mechanical and wear-resistance characteristics necessary for enduring the large number of pressing cycles and the high pressures reached in usual ceramic dies.

SUMMARY OF THE INVENTION

The object of the patent is primarily a method for manufacturing punches of ceramic dies destined to press ceramic slabs or tiles having a structured surface.

A further object of the invention is a method destined for manufacture of a loop- closed press belt for continuous pressing of ceramic slabs having a structured surface.

A further object of the invention is a punch for ceramic dies, and a loop-closed continuous press belt for continuous pressing of ceramic slabs, having the surface destined to come into contact with the ceramic powder conformed according to a suitably-predisposed three-dimensional geometry.

The closed belt must exhibit the characteristics and requisites suitable for the action of compacting for a continuous high-pressure compacting plant, according to what is illustrated for example in application PCT/IB2012/001977 belonging to the present Applicant.

In particular the belt must exhibit a high resistance to traction, in order to be able to sustain the cumulative stresses of pre-tensioning and the crushing action of the powders; a high elastic limit, in order to resist the alternating flexion stresses due to the continuous winding and unwinding about the tensioning rollers; a high degree of dimensional stability and absence of joints, which would give rise to visually-perceptible surface defects, or defects identifiable by touch, to the ceramic slabs produced. The belt further must exhibit a structured surface, i.e. comprising the design in relief without interruptions - seamless - and resistant to high compacting pressure and abrasion due to the powders.

The structured surface must intimately adhere to the base belt, and be realizable with limited costs and very rapidly.

All the aims of the invention are attained by a method having the characteristics recited in the independent claim; the dependent claims relate to further advantageous characteristics of the invention.

In particular, in the invention the structure in relief is realised on the matrix destined to form the structured surface of the punch of a die or directly on the continuous press belt, using in particular additive synthesis methods, in particular using the ink-jet printing method with photo-hardening plastic materials, i.e. plastic materials comprising a heat-hardening fraction.

In a case in which the ink to be sprayed is 100% of the photo-hardening type, i.e. made up of acrylate or epoxy monomers or oligomers, with the addition of photo-initiator substances, reticulation occurs only by effect of the UV radiation coming from a suitable lamp.

Alternatively in order to give the layer exhibited on the belt special characteristics of resistance, the above-cited ink can be of the bi-stage type, with mixed UV and heat reticulation.

Inks of this type contain a fraction, variable from 10% to 90%, of monomers and oligomers selected from among the following families: pure acrylics, polyester acrylates, polyurethane acrylates, epoxy acrylates, vinyls, epoxies.

These monomers and oligomers do not reticulate by UV effect, but require for the radical polymerisation thereof a heat treatment at a temperature comprised between 150°C and 200°C for a time of at least 15 minutes.

UV light therefore functions as a temporary block which by acting on the fraction that is sensitive to ultraviolet light prevents the design from deteriorating; the final heat treatment definitively fixes the whole mass. In general the structure final heat treatment definitively fixes the whole mass. In general the structure can be realized with a succession of applied layers of different materials (photo- hardening and bi-stage).

In the case of a punch, a steel matrix is located on special drawing means that step-advance below a beam on which a mobile head can slide in a transversal direction to an axis of the matrix, in both directions.

The mobile head bears a series of inkjet heads of the piezoelectrically-controlled type, which can at each step print a portion of punch over a whole width corresponding to the step.

At each passage of the head the matrix advances by a step equal to a whole printing width of the head p, i.e. a sub-multiple p_s thereof.

Each head is piloted in a known way by means of a suitable image, so as to obtain a deposit of ejected material reproducing the image on the matrix.

The matrix is used to vulcanise, on the in-view side of the punch of the die, a layer of rubber that is able to resist wear caused by the powder during printing operations.

Alternatively, the depositing of material ejected to create the structured surface can be done directly on the in-view side of the punch.

In the case of a continuous press belt, a smooth press belt made of a non- absorbent material, generally metal or made of composite materials comprising glass, carbon or Kevlar fibres, is keyed on a pair of rollers and tensioned.

A beam is positioned above the upper horizontal portion of the belt, on which beam a mobile head can slide in a transversal direction to the axis of the belt, in both directions.

The belt is step-rotated using motorised drawing means; the mobile head bears a series of piezoelectrically-controlled inkjet heads, and can at each step print on a portion of belt over a whole width, which portion is equal to a step.

At each passage of the head, the belt advances by a step equal to a whole printing width of the head p, or a sub-multiple p_s thereof. As in the preceding case, each head is piloted in a known way by means of an appropriate image, in order to obtain, on the belt, a deposit of ejected material that reproduces the image.

The information to be sent to the heads is obtained by processing graphic images entirely alike to normal digital images, with the difference that data relating to colour is superfluous.

For this reason grey-scale images are used, with a colour depth of at least 8 bits (corresponding to 256 shades of grey); the electronic control system will correctly interpret the data, assigning more drop-volume where the image has a darker shade.

Appropriate "ripping" algorithms, of known type, will be used to optimise the variability of the shades by spatially distributing the drops of ink in such a way as to obtain the desired effect, thickening them where the required tone is darker and thinning them out where it is lighter.

The ink projected from the head can be a UV reticulation ink that enables a perfect adhesion to the belt and, once radiated with ultraviolet light, reticulates and hardens instantly, or a mixture of UV reticulating ink and heat reticulating ink.

To perform reticulation UV lamps are generally used which are mounted directly on the head, flanked to the printing heads, so as to instantly solidify the drops as soon as they are deposited at each passage.

To carry out the heat reticulation, heating means are used that act on the completely-formed three-dimensional structure.

The materials projected by the heads in the class of UV controlled-hardening inks are generally mixtures of acrylate or epoxy monomers and oligomers, with the addition of photo-initiator substances. In normal conditions these are easily- ejectable liquids (viscosity of about 10 mPa s); when they are struck by UV light of appropriate wavelength the electronic bonding configuration is modified, thus activating the reticulation process and starting-up a rapid hardening, up to solidification. The liquid completely solidifies and there is no presence of volatile (and therefore pollutant) solvents.

The UV light is normally applied immediately following the projection of the drops, which land on the belt as liquid and are solidified by the passage of the UV lamp, which is solidly constrained in transversal motion to the inkjet heads. Once solidified, the drops of material are covered in the following passages, up to when the desired thickness is obtained.

The UV light of the single passage can be modulated to an lower energy level so as to realize only the start of the solidification (pinning) and thus enable a better adhesion of the following layers. At the end of the application a higher-intensity UV treatment is applied.

Alternatively to the use of UV inks, bicomponent plastic materials can be used (for example polyurethanes) projecting in sequence (with different heads) superposed drops of the two components (for example polyol and isocyanate, in the case of polyurethane) which solidify during mixing, directly on the surface of the belt 1 . These materials harden by heat action.

Alternatively, in order to give the layer on the belt special resistance characteristics, the above-mentioned ink can be of the bi-stage type, with mixed UV and heat reticulation.

In this case, apart from the UV lamp, obviously a heating module is present, which completes the hardening of the heat-hardening resins.

While the UV lamp acts together with the ink jet heads, the heating module acts on termination of the printing.

Though the belt is constituted by material having a high modulus of elasticity, once mounted on the printing machine and appropriately tensioned, there will be however a lengthening, in general difficult to evaluate.

This might generate problems when the printing of the relief on completion of one passage has to be joined-up with great precision (about 0.05-0.1 mm). To obviate this problem/ the method of the invention comprises precise detecting of the position of the belt using an encoder. Once the virgin belt has been loaded and the tensioning done, the belt is set in rotation. The head prints a few reference markers on the external band of the belt that will not be involved in the crushing of the powder, and an optical detection system determines the position of the markers, at the same time acquiring the exact lengthwise extension of the tensions belt.

At this point the electronic control system of the printing heads, according to the invention, automatically adapts the graphic image to be printed, lengthening it or restricting it proportionally by a small corrective entity (the stretching function), not perceptible to the naked eye. In this way, the printing of the belt will be perfectly adapted to the real dimension, with no superposing effect nor any non- printed stripes.

In a possible operating configuration, the head houses four inkjet heads of piezoelectric type mod. 1001 GS6 (constructor Xaar GB), having a printing width of d = 70 mm, and arranged in such a way as to exactly involve the same printing band.

In these conditions, the printing is done at a resolution of 360 dpi, i.e. the drops are arranged according to a squared grid with a 70 pm step; the drops have a maximum volume of 42 pi (1 picolitre = 10^"12 litres) and a print footstep having a diameter of about 80 μιη. The thickness of each footstep is estimable at about 8 - 10 pm, depending on physical and rheological parameters of the liquid (density, viscosity, surface tension, temperature etc.) and the surface of the belt. In general, it can therefore be stated that at each printing passage the design grows by about 10 pm in the direction Z perpendicular to the belt surface.

By increasing the number of heads which work on the same printing strip, i.e. reducing the step p_s (thus increasing the number n of sub-steps, so that p = n times ps), many superposed drops can easily be deposited on each pixel of the image.

For example, by piloting four heads with the same image, and applying a reduction of the step by a factor of n=4, there will be 16 drops for each physical pixel on the belt; consequently, on termination of the passage about the printing system, the belt will exhibit reliefs (according to the design graphic introduced in the control system) which at the highest points will be of a thickness of up to 160 μιτι.

If this value of maximum "depth" of the design graphic is not sufficient, the print can be repeated (obviously synchronized with the previous print) a certain number of times, up to reaching the desired height.

In the case of a print repeated 4 times (theoretical maximum height 4 x 4 x 4 x 10 pm = 640 pm) zones have been experimentally obtained where heights of over 500 pm have been reached.

If the structure of the surface of the belt is to be changed, in the invention this can be done on the same machine that creates the structure, in which upstream of the distributor head of the ink there is a removal system present which can remove the structure created thereon.

In a further variant of the method, the station creating the structure on the belt is not a separate machine with respect to the belt compacter, but is instead an integrated accessory of the compactor, positioned in a convenient non-active zone of the belt (for example the upper part). Obviously during this pressing step the station is not functioning, while when a new structure is being created, the pressing is not active.

BRIEF DESCRIPTION OF THE DRAWINGS

The advantages and constructional and functional characteristics of the invention will emerge from the detailed description that follows, in reference to the figures of the appended tables of drawings, in which:

figure 1 is a plan view of the machine for creating the structured surface of a matrix.

Figure 2 is the machine of figure 1 seen in a side view.

Figure 3 is section Ill-Ill of figure 1.

Figure 4 is a plan view of the machine for creating the structured surface of a press belt.

Figure 5 illustrates the machine of figure 4 in a lateral view. Figure 6 shows section VI-VI of figure 4.

Figure 7 illustrates the machine for creating the structured surface integrated with the slab-forming machine, in a lateral view.

Figure 8 shows section VIII-VIII of figure 7.

DETAILED DESCRIPTION

Figures from 1 to 3 illustrate a matrix 100 positioned on a conveyor belt 101 which advances in equal steps p or a fraction p_s of p.

The belt is destined to accommodate at least two matrices 100, which are positioned perfectly aligned and equidistant from a side of the belt.

A description of the positioning means of the matrices is omitted, as it is obvious to an expert in the sector.

The beam 103 on which the printing head 104 runs is positioned in a transversal direction to the movement direction of the belt 101.

The mechanical means for moving the head 104 are not illustrated as they are known to the expert in the field.

The printing head 104 bears the inkjet heads 141 which will decorate a strip of the matrix equal to the step p or p_s.

An ultraviolet lamp 142 is located downstream of the heads 141 , in the movement direction, which causes the hardening of the material just deposited on the belt.

A sensor 144, located on-board the printing head 104, is able to follow the edge of the matrices during the advancement in order to command appropriate corrections of the printing means with the aim of recuperating any transversal errors of the matrix.

Full-width heating means 107, for example infrared heating means, are positioned downstream of the beam and transversally of the advancement of the belt.

Detection sensors of the position, for example photocell devices 105, signal the position of the slab 100 in order to initiate the printing cycle. Figures from 4 to 8 detect the belt 1 placed under tension between two rollers 2 of which one is motorised to step-advance by entities of p or p_s.

The belt 1 is made of a material selected from among the following: steel, stainless steel, composite material with carbon and/or Kevlar and/or glass fibres, and exhibits a thickness of from 0.5 mm to 2 mm.

The beam 3 on which the printing head runs is transversal to the movement direction of the belt and overlies the belt.

The mechanical means for moving the head 4 are not illustrated, as they are known to an expert in the sector.

The printing head 4 bears the inkjet heads 41 able to decorate a strip of the belt 1 of a step p or p_s.

A UV lamp is located downstream of the heads 41 , in the motion direction, which

UV lamp causes a hardening of the material just deposited on the belt.

In the particular embodiment illustrated in figure 7, the upper belt 1 can be mounted, in unused or virgin form, directly on the slab-forming machine, and overlies the lower belt 10 which bears the layer 5 of powder.

In both the embodiments of figure 5 and figure 7, an abrasive device 6 is located in a position upstream of the beam 3, for removing the relief structure from the upper surface of the belt 1.

The abrasive device 6 comprises a horizontal-axis rotating brush 61 , drawn at high speed by a motor group (not illustrated) which is pressed against the belt 1 by press means (not illustrated). The dragging effect of the brush 61 causes the detaching of portions of the relief structure, which are distanced from the work zone by aspirating devices 62 (see figure 5).

Lastly, in proximity of an end of the beam 3, a sensor 31 is positioned, which reads off a series of equidistant references 310, which are previously printed by the head 4 on an edge of the belt not interested by the printing with the aim of controlling the precise development thereof after the tensioning so as to adapt the dimension of the image printed. Further, on-board the printing head 4 a sensor 4 is positioned, which detects even minimal transversal deviations of the belt in order to adapt the position of the image in real-time.

Application example 1

Λ virgin press belt, with a width of 2000 mm and a total extension of 7500 mm, loop-wound, is mounted stretched on two rollers having horizontal axis, parallel to one another, about 2500 mm distant from one another, having a diameter of 750 mm. The printing system automatically tensions the belt, applying a force of about 100 kN, equal to about 25 N/mm.

The printing system is provided with 4 heads 1001 GS6 (constructor Xaar GB), arranged in a battery, able to dispense 42 picolitres per drop, at the optimal resolution of 360 dpi (step between pixels = 70 pm). The printing width is 70 mm.

The belt is advanced with a longitudinal step of ¼ having a head width of (p_s = 17.5 mm); in this way four different nozzles pass on a same point of the belt, increasing the density of the printed dots by a factor of 4.

By piloting the 4 heads with the same graphic image, a further multiplication is obtained of the quantity dispensed by a factor of 4.

The printing process was repeated 3 times, obtaining a maximum growth factor of 4 x 4 x 3 = 48 drops per pixel on the belt, equal to a theoretical height of about 480 μιη. The real maximum height measured at the end of the printing (by a three-dimensional profilometer) is 400 pm.

The ink used is the UV hardening type, belonging to the series Unijet Thunder 1000 produced by Unico Digital (BE).

Before printing the true length of the tensioned belt was assessed, by printing at the external edge thereof a series of markers, read off by an optical sensor. The image to be printed (initial length 7500 mm) was linearly deformed up to adapting to the detected length, so as to perfectly cover the external surface of the belt. The result of the application of the method of the invention is a press conveyor suitable for continuous compacting lines, having on an external surface thereof a relief that is variable between 0 and 2 mm, preferably between 0 and 1 mm, realised by inkjet application of liquid materials polymerised by UV light, i.e. polymerisable by mixing two or more liquid components.

The "structuring" treatment of the belt actuated by the present method enables reaching the following objectives: excellent spatial definition of the reliefs (up to 360 dpi and above, according to the inkjet heads used); possibility of having an endless relief over all the extension of the belt; precise control of the height of the relief (resolution of better than 10 m); possibility of realizing high transport of thicknesses (theoretically without limit, practically about 1 mm); short realization times (about 30 min/sq.mt); an economical solution and great flexibility of use.

The invention is not limited to the embodiments described, and any variants and improvements can be brought thereto without forsaking the scope of the following claims, for example the press belt, once provided with the structured surface, can be sectioned into portions, each of which suitable for application to the active side of the punch of a normal die for ceramic powders.

Claims

1 . A method for manufacturing a continuous press belt or a vulcanizing matrix of a punch of a ceramic die for creating ceramic slabs having a structured surface, comprising following steps:

advancing the belt or the matrix by steps of a sub-multiple of a length of the belt or the matrix;

at each advancement step, subjecting a strip of belt or matrix having a width equal to the step to action of at least a piezo-electrically-controlled ink-jet printing head, piloted by an image, in order to obtain on the belt or on the matrix a deposit of ejected material reproducing the image, the head being movable transversally to the belt or the matrix and suitable for ejecting an ink jet which belongs to a class of inks being controlledly hardenable by ultraviolet radiation; - subjecting the strip of material emitted by the head to action of an ultraviolet lamp for hardening the ink;

repeating the printing and hardening operations on the same strip at least once.

2. The method of claim 1 , characterised in that the belt or matrix are constructed with a material selected from among the following: metal or a composite material with glass, carbon or kevlar fibres.

3. The method of claim 1 , characterised in that the ink is a mixture of acrylate or epoxy monomers and oligomers, with an addition of photoinitiator substances.

4. The method of claim 1 , characterised in that the UV energy of a single passage, apart from a last passage, is modulated at an energy level able to realise only a start of the hardening so as to enable a better adhesion of the layers of ink applied in following passages.

5. The method of claim 1 , characterised in that the ink ejected contains a fraction comprised between 10% and 90% of monomers and oligomers selected from among following families: pure acrylics, polyester acrylates, polyurethane acrylates, epoxy acrylates, vinyls, epoxies, which initiates solidification by action of UV rays and heat.

6. The method of claim 5, characterised in that it comprises a further activity of subjecting the belt, or the matrix, following application of all layers, to a heat treatment at a temperature comprised between 150°C and 200°C for a time of at least 15 minutes.

7. The method of claim 1 , characterised in that the information to be sent to the heads is obtained by processing images in grey scale, with a colour depth of at least 8 bits corresponding to 256 shades of grey.

8. The method of claim 1 , characterised in that a virgin belt is arranged stretched between two rollers, and following tensioning thereof a length of the belt is detected so as to acquire an exact extension of the tensioned belt, and in order to enable the electronic control system of the heads to automatically detect the dimensions of the graphic image to be printed to the effective length of the belt.

9. The method of claim 8, characterised in that the lengthening of the tensioned belt and the exact development thereof are detected by means of optical control of a series of reference markers fixed on the belt.

10. The method of claim 1 , characterised in that upstream of the action of the printing head the belt is subjected to action of abrasive means which clean the surface of a previously-printed image.

1 1 . A continuous press belt for creating ceramic slabs exhibiting a structured surface having, on an external surface thereof, a three-dimensional structure, characterised in that the three-dimensional structure comprises at least a layer realized by means of a resin comprising a mixture of acrylate or epoxy monomers and oligomers, with addition of photoinitiator substances, which hardens on action of ultraviolet rays.

12. The belt of claim 1 1 , characterised in that the resin contains a fraction comprised between 10% and 90% of monomers and oligomers selected from among following families: pure acrylics, polyester acrylates, polyurethane acrylates, epoxy acrylates, vinyls, epoxies, which begins to solidify by action of the UV rays and the heat.

13. A matrix for vulcanisation of the surface of a punch of a ceramic die having, on an external surface, a three-dimensional structure, characterised in that the three-dimensional structure comprises at least a layer realized by means of a resin comprising a mixture of acrylate or epoxy monomers and oligomers, with an addition of photoinitiator substances.

14. The matrix of claim 13, characterised in that the resin contains a fraction comprised between 10% and 90% of monomers and oligomers selected from among following families: pure acrylics, polyester acrylates, polyurethane acrylates, epoxy acrylates, vinyls, epoxies, which begins to solidify by action of the UV rays and the heat.

15. The matrix of claims 13 and 14, characterised in that the matrix is the portion of a continuous belt for creating ceramic slabs exhibiting a structured surface having, on an external surface thereof, a three-dimensional structure.