RU2690382C2 - Continuous press belt for ceramic plates having a structural surface, a method of making the tape and use thereof - Google Patents

Abstract

FIELD: machine building.

SUBSTANCE: invention relates to machine building and can be used in production of continuous press belt for production of ceramic plates. Belt is advanced to steps equal to lengthwise unit of belt length. At each step of movement on belt strip, width of which is equal to pitch, impact, at least, head for jet printing. Layer of ejected material reproducing the image is obtained on the tape. Head moves in transverse direction relative to belt and ejects jets of ink curable under action of ultraviolet radiation. To harden ink on strip material is exposed to ultraviolet lamp. Printing and hardening operations on the same strip are repeated at least once. Three-dimensional structure on the outer surface of the continuous tape contains at least a layer obtained using rubber containing a mixture of acrylate or epoxide monomers and oligomers, with addition of particles of photoinitiators which are curable under the action of ultraviolet rays.

EFFECT: as a result, improved mechanical characteristics and wear resistance of the obtained tape.

9 cl, 9 dwg

Description

The technical field to which the invention relates.

The present invention relates to the manufacture of ceramic plates, preferably having a small thickness, such as plates for flooring and wall cladding, and having a side designed to be visible, which contains an arbitrary relief, usually called a structural surface, or having a structural effect.

The level of technology

The “structural” effect gives a ceramic product a special aesthetic value, especially when imitating natural materials such as wood and stone.

Currently, slabs or tiles with a structurally visible side are made by pressing powders in the usual form for ceramic tiles, in which the punch intended to form the structural side contains a negative pattern that must be made on the surface of the slab or tile.

In particular, the punch is covered with a layer of elastomer, on which is located the negative of the structural side pattern.

The elastomeric layer is made as follows.

A hard form matrix is performed, and a positive pattern is placed on the matrix (i.e., a pattern completely identical to that which will be reproduced on a ceramic plate or tile) by performing an exact mechanical process with digital program control based on three-dimensional data.

The matrix is usually made of aluminum or other material suitable for high-throughput processing by chip removal or laser ablation.

After processing the matrix, it is used to cure an elastomer layer (usually polyurethane with a Shore A hardness of 90) applied to the active side of the punch. It is often called the "vulcanization matrix."

To carry out the vulcanization process, it is necessary to perform heating to a suitable temperature (about 150 °) with simultaneous pressing.

After the end of vulcanization, an elastomeric layer remains on the punch, usually several millimeters thick, with a negative structure profile located on it. Thus, the punch is ready to be installed as a “visible side” punch on the appropriate form for pressing ceramic powders to ensure the production of plates having a surface that completely coincides with the surface of the original metal matrix.

In addition to its complexity and high cost, this method is not suitable for making continuous press conveyors with a structural surface suitable for use in pressing lines with a continuous belt.

In particular, the difficulty lies in the implementation of the upper pressing belt, designed to form the structural side of the plate on which the relief structure is to be created, constantly changing and continuous, that is, without interruptions.

In addition, it is necessary to provide the ability to quickly replace the relief structure.

The only method that provides the ability to perform continuous structural steel tapes with high resistance is chemical etching, in which the tape is covered with an emulsion on which a negative image is placed, and then immersed in baths with an aggressive solution that provides etching of the metal on unprotected areas.

This method is very difficult, labor costs and has a negative impact on the environment.

In addition, chemical exposure does not allow for precise separation of the slits, which entails obvious limitations in terms of aesthetics.

Laser ablation also has limitations and disadvantages, since the tape must be mounted on a drum rotating around a horizontal axis, which due to the existing proportions must be performed very large (more than 2 meters in diameter). In addition, the amount of working time spent (tens of hours) is unacceptable from the point of view of economics and industrial production.

Also known is a method of creating three-dimensional structures on a substrate by means of inkjet printers using inks that are cured by ultraviolet rays.

However, this method, described in WO 02/053338, is not applicable to making structural press tapes designed for the continuous creation of ceramic plates, since the substrate known from the prior art is a tape of indeterminate length, not wound by a loop, and designed for the implementation of inkjet printing, is curved.

In addition, the known method is not suitable for creating a three-dimensional surface suitable for pressing ceramic tiles in conventional forms, since the structures created in a known manner do not have the mechanical and wear resistance characteristics necessary to withstand a large number of pressing cycles and high pressures ceramic forms.

DISCLOSURE OF INVENTION

The object of the patent application in the first place is a method of manufacturing punches of ceramic molds, intended for pressing ceramic plates or tiles having a structural surface.

Another object of the invention is a method for the manufacture of a tape press with a closed loop for continuous pressing of ceramic plates having a structural surface.

Another object of the invention is a punch for ceramic molds, and a continuous press loop with a closed loop for continuous pressing of ceramic plates, having a surface designed to come into contact with a ceramic powder arranged according to a corresponding predetermined three-dimensional arrangement.

A closed tape must have characteristics suitable for performing the compaction action in continuous high-pressure presses for pressing powders, as, for example, disclosed in PCT / IB2012 / 001977 belonging to the present applicant.

In particular, the tape must have a high tensile strength in order to withstand the total prestressing forces and the crushing action of the powders; high elastic limit to resist changing flexural stresses due to constant winding and unwinding of the tension rollers; a high degree of dimensional stability and the absence of compounds that would lead to the appearance of visible surface defects, or defects that are felt by touch, on fabricated ceramic plates.

The tape should also have a structural surface, i.e., it should contain an embossed pattern without interruptions, that is, not have seams, and should have resistance to high sealing pressure and abrasion due to the action of powders.

The structural surface should fit snugly to the main belt, while it should be possible to produce it cheaply and quickly.

All the tasks of the invention are performed in a method having distinctive features disclosed in the independent clause, and the dependent claims disclose additional preferred features of the invention.

In particular, in the invention, the relief structure is made on a matrix designed to form a structural surface on a mold punch or directly on a continuous press belt, using additive synthesis methods, in particular, using an inkjet method using photo-curable plastic materials, that is, plastic materials containing fractions, cured by heat.

If the sprayed ink is 100% made of photo-curable ink, that is, made of acrylate or epoxy monomers or oligomers, with the addition of photoinitiator particles, reticulation occurs only when exposed to ultraviolet radiation from a suitable lamp.

Alternatively, in order to impart to the layer located on the tape special resistance characteristics, the above-mentioned inks can be of a “two-stage” type, having reticulation properties under the influence of both ultraviolet and heat.

Inks of this type contain fractions in the amount of from 10% to 90% of monomers and oligomers selected from the following types: pure acrylic polymers, polyester acrylates, polyurethane acrylates, epoxy acrylates, polyvinyl chloride, epoxy resins.

Reticulation of these monomers and oligomers does not occur under the influence of ultraviolet, for their radical polymerization it is necessary to perform their heat treatment at a temperature from 150 ° C to 200 ° C for at least 15 minutes.

Thus, ultraviolet radiation acts as a temporary unit, protecting the design from damage by acting on fractions sensitive to ultraviolet radiation, and the final heat treatment finally fixes the whole mass. In general, the final heat treatment of the structure finally fixes the entire mass. In general, the structure can be made as a sequence of superimposed layers of different materials (photo-cured and “two-stage”).

In the case of using a punch, there is provided a steel matrix on a special sliding tool, made with the possibility of protruding under the beam, on which a movable head is located, made sliding on both sides in the transverse direction relative to the axis of the matrix.

On the movable head there is a row of inkjet heads of the type controlled in a piezoelectric manner, and the heads provide the possibility, at each step, to print on the part of the punch along the entire length corresponding to the step.

With each pass of the head, the matrix advances by a step equivalent to the entire width p of the print of the head, that is, equal to its fractional unit p _s .

Each head is controlled in a known manner through an appropriate image, so as to ensure the application of the sprayed material, reproducing the image on the matrix.

The matrix is used for vulcanization, on the visible side of the punch form, of a rubber layer made to resist wear due to the impact of the powder during printing operations.

Alternatively, the application of the material sprayed to create a structural surface can be performed directly on the visible side of the punch.

In the case of using a continuous press belt, a pair of rollers are fastened and the tension of a smooth press belt made of a non-absorbent material, usually metal, or made of composite materials containing glass, carbon or kevlar fibers is performed.

Above the upper horizontal part of the belt there is a beam on which a movable head is located, which is slidable in both directions in the transverse direction relative to the belt axis.

The tape is made with the possibility of step-by-step rotation using equipped with a sliding withdrawable means, while on the movable head there is a series of piezoelectric controlled inkjet heads, and the movable head provides the possibility, at each step, to print on a part of the tape along the entire length, and step.

With each head pass, the ribbon advances by a step equivalent to the entire width p of the head print, or its longitudinal unit ps.

As in the previous case, each head is controlled in a known manner by means of a corresponding image, so as to ensure that the sprayed material is applied to the tape, with reproduction of the image on the matrix.

Information intended to be sent to the heads is obtained by processing graphic images completely analogous to ordinary digital images, with the difference that the data relating to color is redundant.

For this reason, images in grayscale are used, with a color depth of at least 8 bits (corresponding to 256 shades of gray); the electronic control system correctly interprets the data, ensuring the presence of a larger volume of droplets in areas where the image has a darker shade.

To optimize the variability of shades by spatially distributing ink droplets in such a way as to obtain the desired effect, increasing them where a darker tone is required and reducing where a lighter tone is required, use appropriate RIP processing algorithms.

The ink sprayed from the head can be ink, the reticulation of which occurs under the influence of ultraviolet, and which provide perfect adhesion to the tape and, after irradiation with ultraviolet radiation, they are instantly reticulated and cured, or a mixture of ink, reticulated by ultraviolet radiation, and ink, reticulation of which occurs under the influence of heat.

For the implementation of reticulation usually use ultraviolet lamps mounted directly on the head so that they are located on the side of the head, to ensure the immediate solidification of the drops immediately after their application during each pass.

To perform reticulation under the influence of heat, a heating means acting on a fully formed three-dimensional structure is used.

Head sprayed materials in the UV-curable ink class are usually a mixture of acrylate or epoxy monomers and oligomers, with the addition of photoinitiator particles. Under normal conditions, they are readily sprayable liquids (with a viscosity of about 10 mPas); when ultraviolet radiation with a suitable wavelength falls on them, the electronic spatial configuration of the bonds changes, thus triggering the reticulation process and starting immediate solidification, up to complete solidification. The liquid hardens completely and there are no volatile (and therefore contaminating) solvents.

The exposure to ultraviolet radiation is usually carried out immediately after spraying droplets that fall on the tape as a liquid and harden when passing an ultraviolet lamp fixedly mounted in the transverse direction relative to the inkjet heads.

After curing, further coating is performed with drops of material on subsequent passes until the desired thickness is reached.

The intensity of the ultraviolet radiation can be changed to a lower level of energy in order to carry out only the beginning of solidification (fixation) and thus ensure better adhesion of subsequent layers. After the end of the application, ultraviolet radiation of higher intensity is performed.

As an alternative to using UV-curable inks, you can use two-component plastic materials (for example, polyurethanes) sprayed sequentially (with different heads) in the form of superimposed droplets of two components (for example, polyol and isocyanate, in the case of using polyurethane), the final solidification of which occurs during mixing directly on the surface of the tape 1. These materials harden under thermal influence.

Alternatively, to impart special resistance characteristics to a layer on a tape, the aforementioned ink can be a “two-stage” type of ink, the reticulation of which occurs under the influence of ultraviolet and heat.

In this case, obviously, in addition to the ultraviolet lamp, a heating module is provided to ensure the completion of the hardening of heat-cured rubber.

If the UV lamp operates simultaneously with inkjet heads, then the heating module operates at the end of printing.

Although the tape is made of a material having a high modulus of elasticity, nevertheless, after installation on the printing machine and the implementation of the necessary tension, an increase in length will arise, which is generally difficult to estimate.

This can cause problems when printing a relief after the completion of a single pass is necessary to attach with high precision (about 0.05-0.1 mm). In order to avoid this problem, the method according to the invention comprises the step of accurately determining the position of the tape using a position sensor.

After installing the raw tape and the implementation of its tension provide rotation of the tape. Then, by means of a head, several control markers are printed on the outer side of the tape, which will not be used for squeezing the powder, and the position of the markers is determined by means of an optical detection system, while at the same time providing accurate longitudinal stretching of the tape.

At this stage, they automatically align the graphic image that needs to be printed by means of the electronic control system of the printheads according to the invention, proportionally increasing the length or compressing the image by a small correction value (stretch function) that is not visible to the naked eye. Thus, the print on the tape will be perfectly aligned to the actual size without the effect of overlapping or unprinted strips.

In a possible working configuration, four 1001 GS6 piezoelectric-type inkjet heads (manufactured by Xaar, United Kingdom) are located in the head, having a print width of d = 70 mm and positioned to provide printing of exactly that print width.

Under these conditions, printing is performed with a resolution of 360 dpi, that is, the drops are arranged in accordance with the grid with a step of 70 μm; The drops have a maximum volume of 42 mp (1 picoliter = 10 ^-12 l) and a printed imprint having a diameter of about 80 microns. The estimated size of each print is about 8-10 microns, depending on the physical and rheological parameters of the fluid (density, viscosity, surface tension, temperature, etc.) and the surface of the tape. Thus, in the general case, it can be said that with each printed pass, the length of the image increases by about 10 microns in the Z direction, perpendicular to the surface of the tape.

With an increase in the number of heads working on the same printed strip, that is, with decreasing pitch p _s (and thus increasing the number of substeps, so that p = n times p _s ) a number of overlapping drops can easily be applied to each pixel. Images.

For example, when controlling four heads with the same image, and reducing the step by a factor of n = 4, 16 drops will fall on each physical pixel on the tape; consequently, after the completion of the passage of the passes by the printing system, the relief will be applied to the tape (in accordance with the graphic image entered into the control system), which at its highest points will have a thickness of up to 160 μm.

If this maximum “depth” of the graphic image is not enough, the printing can be repeated (obviously, with ensuring alignment with the previously performed printing) a certain number of times, until the required height is reached.

If the print is repeated 4 times (the theoretical maximum height is 4 × 4 × 4 × 10 μm = 640 μm), the experimentally obtained zones in which the height of more than 500 μm was reached.

If it is necessary to change the structure of the tape surface, this can be done according to the invention on the same machine on which the structure was created, since on the machine, upstream relative to the ink distributor head, there is a removal system configured to remove the structure created on this machine.

In yet another embodiment of the method, the station for creating a structure on a belt is not a separate machine for a belt press, but an integrated press device located in a convenient inactive area of the belt (for example, in the upper part). Obviously, the station does not work when pressing is performed, and no pressing is performed during the creation of a new structure.

Brief Description of the Drawings

The advantages and structural and functional characteristics of the invention are evident from the following detailed description given with reference to the accompanying drawings, in which:

- in fig. 1 shows a top view of a machine for creating a structural matrix surface;

- in fig. 2 shows the machine shown in FIG. 1, in side view;

- in fig. 3 is a sectional view taken along line III-III shown in FIG. one;

- in fig. 4 shows a top view of a machine for creating a structural surface of a press belt;

- in fig. 5 shows the machine shown in FIG. 4, in the side view;

- in fig. 6 shows a sectional view along line VI-VI shown in FIG. four;

- in fig. 7 shows a machine for creating a structural surface, integrated into a machine for forming plates, in a side view;

- in fig. 8 is a sectional view taken along line VIII-VIII shown in FIG. 7;

- in fig. 9 is a sectional view taken along line IX-IX shown in FIG. 7

The implementation of the invention

FIG. 1-3, the matrix 100 is shown located on a conveyor belt 101 propelled by equal steps p or parts p _{s of} step p.

The tape is designed to accommodate at least two matrices 100 located with perfect alignment and at the same distance from the side of the tape.

The description of the matrix positioning tool is omitted, as it is obvious to a person skilled in the art.

Beam 103, which moves the print head 104, is located in the transverse direction relative to the direction of movement of the tape 101.

The mechanical means for moving the head 104 is not shown, as it is known to a person skilled in the art.

The inkjet heads 141 are located on the print head 104, ensuring that a strip of ink is applied to the matrix corresponding to step p or p _s .

Downstream relative to the heads 141 there is an ultraviolet lamp 142 providing curing of the material that has just been applied to the tape.

The sensor 144, located on the print head 104, is configured to monitor the position of the edge of the dies during advancement to issue instructions to the appropriate adjustments for the printing means in order to correct the matrix offset errors in the transverse direction.

Downstream along the beam and in the transverse direction relative to the progress of the tape across the entire width, the heating means 107 is located.

Position sensors, such as devices 105 with a photocell, provide a signal about the position of the plate 100 to start the print cycle.

FIG. 4-9 shows a belt 1 located with tension between two rollers 2, one of which is equipped with a drive for step-by-step advancement by the value of p or p _s .

Tape 1 is made of a material selected from the group comprising: steel, stainless steel, composite material with carbon and / or kevlar and / or glass fibers, and has a thickness of from 0.5 mm to 2 mm.

Beam 3, which moves the print head, is located in the transverse direction relative to the direction of movement of the tape and above the tape.

The mechanical means for moving the head 4 is not shown, since it is known to a person skilled in the art.

The inkjet heads 41 are arranged on the print head 4 and are configured to paint a strip of tape 1 with a pitch p or p _s .

Downstream relative to the heads 41 there is an ultraviolet lamp, which cures the material that has just been applied to the tape.

In a separate embodiment of the invention shown in FIG. 7, the upper tape 1, unused or unprocessed, may be located directly on the machine for forming slabs, and said tape may be located above the lower tape 10 on which the powder layer 5 is located.

In both embodiments of the invention shown in FIG. 5 and FIG. 7, in the position above in the direction of travel relative to the beam 3, there is an abrasive device 6 for removing the relief structure from the upper surface of the belt 1.

Abrasive device 6 contains a brush 61, made with the possibility of rotation around a horizontal axis, moreover, this brush is made with the possibility of its driving at high speed through a group of engines (not shown) and pressing to the tape 1 by means of a clamping means (not shown). The friction effect of the brush 61 provides for the separation of particles of a relief structure, which are removed from the working area by means of suction devices 62 (shown in FIG. 5).

Finally, near the end of the beam 3 is a sensor 31, configured to read sequences of equally spaced control marks 310, pre-printed by means of the head 4 on the edge of the tape that is not printed, in order to control the precise application of the print after the tension has been completed, to fit the size of the printed image.

Additionally, a sensor 4 is located on the print head 4, detecting even minimal deviations of the tape in the transverse direction in order to perform an image position adjustment in real time.

Example 1 application.

Untreated press belt, having a width of 2000 mm and a total length of 7500 mm, with a closed loop, is installed with tension on two rollers having horizontal axes parallel to each other, spaced about 2500 mm from each other, and having a diameter of 750 mm. The printing system performs automatic belt tension, applying a force of about 100 kN, equal to about 25 N / mm.

The printing system is equipped with 4 heads of 1001 GS6 (manufactured by Xaar, UK), arranged in a group and made with the ability to emit 42 picoliter per drop, with an optimal resolution of 360 dpi (pixel pitch = 70 μm). Print width - 70 mm.

The tape advances with a pitch in the longitudinal direction equal to% of the width of the head (p _s = 17.5 mm); Thus, four different nozzles pass through the same point of the ribbon, providing an increase in the density of printed points 4 times.

When managing 4 heads with one graphic image, an additional 4 times increase in the quantity ejected is obtained.

The printing process is repeated 3 times, obtaining a maximum magnification factor of 4 × 4 × 3 = 48 drops per pixel of the ribbon, which is equal to a theoretical height of about 480 microns. The actual maximum height, measured at the end of printing (using a three-dimensional profilometer), is 400 µm.

The inks used are UV-curable inks of the Unijet Thunder 1000 series, manufactured by Unico Digital (Belgium).

Before printing, the actual length of the tensioned tape was determined by printing a sequence of markers read by an optical sensor on its outer edge. The image to be printed (having an initial length of 7500 mm) was linearly deformed to coincide with a previously determined length in order to perfectly cover the outer surface of the tape.

As a result of applying the method according to the invention, a press conveyor is obtained, suitable for use in continuous sealing lines, having on its outer surface a relief varying from 0 to 2 mm, preferably from 0 to 1 mm, made by spraying a liquid material polymerized by ultraviolet light, that is, polymerized by mixing two or more liquid components.

"Structural" tape processing performed by this method provides the solution to the following tasks: obtaining an excellent volumetric resolution of reliefs (up to 360 dpi and higher, depending on the inkjet heads used); ensuring the possibility of an infinite relief along the entire length of the tape; providing accurate control of the height of the relief (resolution better than 10 microns); providing the ability to perform high transfer thickness (theoretically unlimited, almost - about 1 mm); ensuring short implementation time (about 30 min / sq.m); obtaining an economical solution and great flexibility of use.

The invention is not limited to the variants of its implementation described above, and any variants and improvements are possible that are not beyond the legal protection defined by the following formula, for example, a press belt, after applying a structural surface to it, can be divided into parts, each of which is suitable for use on the active side of the punch conventional forms for ceramic powders.

Claims (14)

1. A method of manufacturing a continuous tape press to create ceramic plates having a structural surface, comprising the following steps: - advancement of the tape on steps equal to a submultiple unit of length of the tape; - impact at each step of advancing a strip on a strip, having a width equal to the step, by means of at least an inkjet head controlled in a piezoelectric manner by means of an image, in order to obtain on the tape a layer of ejected material reproducing an image, the head being able to moving in the transverse direction relative to the ribbon and ejecting a jet of ink belonging to an ink of a type that is cured in a controlled manner by means of ultraviolet radiation; - the impact on the strip of material emitted through the head, UV lamp for curing ink; - repeating the printing and curing operations on one strip at least once; characterized in that the untreated tape is placed with stretching between two rollers, and then tensioned, the length of the tape is determined so as to obtain an exact expansion of the tensioned tape and to enable the electronic control system to automatically align the dimensions of the graphic image with the control system on the estimated length of the tape. 2. The method according to p. 1, characterized in that the tape is made of a material selected from the following materials, including metal or composite material with glass, carbon or kevlar fibers. 3. The method according to p. 1, characterized in that the ink is a mixture of acrylate or epoxy monomers and oligomers with the addition of particles of photoinitiators. 4. The method according to p. 1, characterized in that the energy of ultraviolet radiation in one pass, with the exception of the last pass, change to the level of energy that allows the start of curing to ensure better adhesion of ink layers applied during the next passes. 5. The method according to p. 1, characterized in that the ejected ink contains fractions containing from 10 to 90% of monomers and oligomers selected from the following types, including pure acrylic polymers, polyester acrylates, polyurethane acrylates, epoxyacrylates, polyvinyl chlorides, epoxy resins, causing curing by exposure to ultraviolet rays and heat. 6. The method according to p. 5, characterized in that it contains an additional step in which the tape after applying all the layers is subjected to heat treatment at a temperature of from 150 to 200 ° C for at least 15 minutes 7. A method according to claim 1, characterized in that the information intended for sending it to the heads is obtained by processing images in grayscale with a color depth of at least 8 bits corresponding to 256 shades of gray. 8. The method according to p. 1, characterized in that the elongation of the tensioned tape and the exact value of its increase is determined by tracking optically a number of control markers located on the tape. 9. The method according to p. 1, characterized in that the upstream relative to the place of action of the print head on the tape is affected by abrasive means to clean the surface from the previously printed image.

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