| WO2015148772A1 | 2015-10-01 |
| EP3543012A2 | 2019-09-25 | |||
| US20100199869A1 | 2010-08-12 | |||
| US20110168043A1 | 2011-07-14 |
| CLAIMS A painting plate made of extruded thermoplastic material for plate-holding cylinder of a flexographic painting unit for painting a printed support, comprising at least one painting layer (10), at least one coupling adhesive layer (20) and at least one support layer (30), characterised in that said at least one painting layer (10) is formed by a material with a thermoplastic polyurethane (TPU) base mixed with at least one silicone polymer, said painting layer (10) having a hardness comprised between 50 and 60 Shore A. The painting plate according to claim 1, characterised in that said coupling adhesive layer (20) is a solid layer of paint or lacquer (20) with UV surface drying/cross-linking with an excimer lamp or a mercury vapor lamp. The painting plate according to the preceding claim, characterised in that said solid paint or lacquer layer (20) has a surface that forms a film having a uniform distribution of corrugations to which said painting layer (10) grips mechanically. The painting plate according to the preceding claim, characterised in that said corrugations have a height, i.e. a distance between the peak and trough comprised between 10 nm and 1000 nm, more particularly between 100 nm and 500 nm. The painting plate according to any preceding claim, characterised in that said painting layer (10) has a hardness of 55 Shore A. The painting plate according to one or more of the preceding claims, characterised in that said silicone polymer is present in said painting layer (10) in percentages from 2% to 25% in weight. The painting plate according to one or more of the preceding claims, characterised in that it comprises an auxiliary support layer (40) made of recycled thermoplastic polyurethane additivated with expanding cells and having density comprised between 0.80 g/cm3 and 0.90 g/cm3 The painting plate according to one or more of the preceding claims, characterised in that it has a thickness of 1,150 mm ± 0,050 mm or 1.350 mm ± 0.050 mm or 1.950 mm ± 0.050 mm. The painting plate according to claim 7, characterised in that with said auxiliary support layer (40) the thickness of the layer can be modulated between 1.150 mm ± 0.050 mm and 3.450 mm ± 0.050 mm. The painting plate according to any preceding claim, characterised in that said painting layer (10) does not contain plasticisers. The painting plate according to one or more of the preceding claims, characterised in that said material with a thermoplastic polyurethane (TPU) base is further mixed at least with at least one detaching additive present in said painting layer (10) in percentages from 0.0001% to 3% by weight. The painting plate according to one or more of the preceding claims, characterised in that said painting layer (10) has a thickness comprised between 0.740 mm and 0.980 mm. The painting plate according to one or more of the preceding claims, characterised in that said support layer (30) is made of polyethylene terephthalate (PET). A flexographic painting unit for painting a printed support, comprising an ink cylinder, an anilox cylinder, a painting plate-holding cylinder adapted to transfer the paint from the anilox cylinder to the printed support, and a pressure cylinder cooperating with the painting plate-holding cylinder, characterised in that said painting plate-holding cylinder has a painting plate according to any preceding claim. A method for making a painting plate according to one or more of claims 1 to 13, characterised in that said painting layer (10) is made by extrusion of the thermoplastic polymer mixed with the colours and the suitably selected additives with a single-screw extruder and flat head matrix and lamination above softening temperature with an expendable support. |
DESCRIPTION
The present invention refers to a painting plate made of thermoplastic material for a plate-holding cylinder of a flexographic painting unit of a printed support.
In the field of offset printing technology, specific processes exist that enable the printed product to be given particular finishes or protections.
One of these processes is the application of overprint painting.
These paints are typically acrylic water-based or UV cross-linked paints; they are normally applied by using one or more special units known as “painting units” positioned as final elements of the machine and followed, if necessary, by kilns or lamps for drying or cross-linking the paints.
The paint is transferred to the printed support by using a rubberised fabric (blanket) or a painting plate that has the function of collecting the paint from the anilox cylinder and transferring the paint to the support to be printed.
These painting plates can be used both with UV paints and for water-based (acrylic) paints.
The mechanical and chemical characteristics of the painting plate greatly affect printing quality and the printing process itself.
The factors affected by the mechanical and chemical characteristics of a plate are: print quality (homogeneity of the coat and shine) ink accumulation (only with water-based paints) peeling (insertion into machine) Painting plates have been present on the market for some time that are divided into the following categories according to the materials with which they are made:
• photopolymer plates, specially designed for painting printed matter that require reserves (notch zones) with a high degree of detail;
• plates made of thermoplastic material (thermoplastic elastomers, like TPU), and rubber plates (thermosetting elastomers like vulcanised rubber) that are used for more common applications.
It is known that the manufacturers of painting plates seek continuously to optimise products, trying to improve both painting and peeling performance.
It is also known that the market requires painting plates , also made of thermoplastic material, which are always more able to dissipate effectively vibrations and mechanical energy, maintaining and improving performance in terms of painting quality and peeling.
The difficulty of painting printed matter with matt paints using thermoplastic painting plates is known; for matt painting finishes, rubber painting plates are used. Hardness (Shore A) that is less than the rubber plates enables a more homogeneous transfer of the matt paint onto the printed product to be obtained. Lastly, matt paints contain inorganic particles that are difficult to transfer to the printed support unless painting plates of appropriate hardness and roughness are used.
There is therefore a need to improve the structure of known painting plates that are made of thermoplastic material.
The technical task of the present invention is, therefore, to provide a painting plate made of thermoplastic material which eliminates the decried technical drawbacks of the prior art. Within the scope of this technical task, an object of the invention is that of making a painting plate made of thermoplastic material that obtains a reduction of mechanical noise and increases the dissipation of mechanical energy generated in the printing process.
Another object of the invention is that of making a painting plate made of thermoplastic material that has optimum printing results, both in terms of shine of the painted zones and the low degree of accumulation of ink.
Another object of the invention is that of making a painting plate made of thermoplastic material that is usable both with gloss and matt paints.
The technical task, as well as these and other objects according to the present invention, are attained by creating a painting plate made of extruded thermoplastic material for plate-holding cylinder of a flexographic painting unit for painting a printed support, comprising at least one painting layer, at least one coupling adhesive layer and at least one support layer, characterised in that said at least one painting layer is formed by a material with a thermoplastic polyurethane base mixed with at least one silicone polymer, said painting layer having a hardness comprised between 50 and 60 Shore A.
Advantageously, with the painting plate of the present invention, it is possible to reduce up to 10% the mechanical noise generated by the flexographic painting unit that typically reaches values comprised between 75 and 80 decibels.
With the painting plate of the present invention, it is possible to reduce the vibrations induced by the passage of the printing support between the painting plate-holding cylinder and the pressure cylinder. In this manner, it is possible to reduce or eliminate the mechanical abutments, thus improving the transfer of the paint and the quality of the painting. It is common practice to use subcoatings, positioned between the painting plate made of thermoplastic material and the plateholding cylinder, also to reduce or eliminate mechanical abutments. Owing to the plate of the present invention, it is possible to use only traditional non functional coatings to reduce mechanical abutments or eliminate the subcoating.
Further, the painting plate of the present invention is more resistant to abrasion and thus less susceptible to marking due to changes in the size of the printing support.
In addition, owing to the use of a painting layer that has less hardness than known thermoplastic painting plates, it is possible to obtain a correct transfer of matt paints.
In order to ensure a correct transfer of the paint, it has been found to be particularly appropriate to provide a painting layer having surface roughness Ra comprised between 0.2 and 0.6 micron.
Other characteristics of the present invention are further defined in the following claims.
Further characteristics and advantages of the invention will become more apparent from the description of a preferred, but not exclusive, embodiment of the painting plate according to the invention, which is illustrated by way of approximate and non-limiting example in the attached drawings, in which: figure 1 shows a partial section raised side view of a painting plate according to the invention; figure 2 shows a partial section raised side view of a painting plate according to the invention provided with an auxiliary support layer.
With reference to the figures mentioned, a partial section is shown of a painting plate that is indicated in its entirety with the reference number 1.
The painting plate 1 is applied to a painting plate-holding cylinder of a flexographic painting unit of a printed support, further comprising an ink cylinder, an anilox cylinder, and a pressure cylinder cooperating with the painting plateholding cylinder.
The painting plate-holding cylinder, as known, is adapted to transfer the paint from the anilox cylinder to the printed support.
The painting plate 1 comprising at least one painting layer 10, at least one coupling adhesive layer 20, and at least one support layer 30.
The painting layer 10 is formed by a material with a thermoplastic polyurethane (TPU) base, for example an aromatic TPU, mixed with at least one silicone polymer.
Advantageously, the painting layer 10 has a hardness comprised between 50 and 60 Shore A, preferably equal to 55 Shore A.
This particular characteristic was suitably selected for optimum propensity to absorption of vibrations and dissipation of mechanical energy.
The silicone polymer is present in the painting layer 10 in percentages from 2% to 25% by weight, preferably between 5% and 15%.
The silicone polymer improves printing quality and decreases accumulation, improves resistance to abrasion, and contributes to the vibration dissipating property.
Preferably, the painting layer 10 has a specific weight comprised between 1.15 g/cm 3 and 1.20 g/cm 3 .
Advantageously, the painting layer 10 does not contain plasticisers, the use of which can entail surface migration phenomena with resulting deterioration of print properties.
Preferably, the material with a thermoplastic polyurethane (TPU) base is further mixed with at least one detaching additive present in the painting layer 10 in percentages from 0.0001% to 3% by weight.
One characteristic of the present invention is that the painting layer 10 is made by extrusion of the mixed thermoplastic polymer with the appropriately selected colours and additives.
To sum up, the composition (percentage by weight) of the painting layer 10 is as follows: thermoplastic polyurethane (TPU): 80%-95.99% silicone polymer: 2%-25% detaching additive: 0.0001% to 3% other (e.g. antistatic additive): 0% - 2%
The extrusion is performed by a single-screw extruder with flat head matrix.
The painting layer 10 made of thermoplastic polyurethane (TPU) for the painting plate 1 according to the present invention has a thickness comprised between 0.740 mm and 0.980 mm.
The painting plate 1 according to the present invention can have various thicknesses, for example 1.150 mm ± 0.050 mm or 1.350 mm ± 0.050 mm or 1.950 mm ± 0.050 mm, according to the various types of commercial product.
The coupling layer 20 of the painting plate 1 can comprise water-based polyurethane adhesive, applied by spreading on the lower face 111 of the painting layer 10 and on the upper face 31 of the support layer 30, before coupling; the finished coupling layer 20 has a thickness comprised between 0.020 mm and 0.050 mm.
According to another embodiment of the invention, the coupling layer 20 can be a solid layer of paint or lacquer 20 with UV surface drying/cross-linking with excimer lamp or mercury vapor lamp.
In this case, the coupling layer 20 is characterised in that the interface surface thereof with the painting layer 10 forms a film having an even distribution of corrugations to which the painting layer 10 grips mechanically.
Typically, these surface corrugations have a height, i.e. a distance between peak and trough, comprised between 10 nm and 1000 nm, more particularly between 100 nm and 500 nm.
The lacquers or paints used are of the type that can be cross-linked/dried with UV rays produced by an excimer lamp or a mercury vapor lamp having 100% solid residue.
Preferably, the solid layer of paint or lacquer 20 that is dried/cross-linked with UV is applied liquidly to the surface of the support layer 30, the surface drying/cross- linking with UV rays is then performed to create the surface film having the aforesaid corrugations, then massive drying/cross-linking of the paint layer or lacquer is performed with traditional UV lamps.
Once drying/cross-linking of the paint or lacquer layer 20 has been completed, the painting layer 10 is applied thereto by hot calendering or hot extrusion.
In order to perform surface drying/cross-linking with excimer UV rays, a laser source is used with a typical wavelength of 172 nm.
In order to avoid absorption of the photons generated by the excimer UV laser source by the oxygen and formation of ozone, the process takes place in an atmosphere that is made inert by nitrogen.
This solution has numerous advantages.
The surface film of the paint or lacquer layer 20 creates, owing to the uniformly distributed corrugations, a uniform force of adhesion at a precise and repeatable value that can be comprised between 3 and 12 N/cm 2 , preferably between 4 and 8 N/cm 2 .
This enables specific zones of the painting layer 10 to be peeled accurately to create so-called “reserves” that are predetermined material recess zones in the painting layer 10.
Compared with a traditional adhesive, the use as a coupling layer 20 of a solid layer of paint or lacquer 20 that is UV dried/cross-linked with an excimer lamp or a mercury vapor lamp enables not only a more precise, uniform and repeatable adhesion force to be created between the coupling layer 20 and the painting layer 10, but also a more precise, uniform and repeatable thickness of the coupling layer 20.
The support layer 30 of the painting plate 1 according to the present invention is made of polyethylene terephthalate (PET).
As shown in figure 2, an auxiliary support layer 40 to reach a given overall thickness of the painting plate 1 can be applied to the lower face 32 of the support layer 30.
For example, in order to achieve the thickness 1.950 mm, an auxiliary support layer 40 made of low density extruded polyurethane material can be applied below the support layer 30 of the painting plate 1. This auxiliary support layer is based on material coming from the circular economy. The appropriately processed auxiliary support layer undergoes a decrease in density by the addition of expanding cells in percentages comprised between 2% and 15%. In practice, the auxiliary support layer 40 can have density comprised between 0.80 g/cm 3 and 0.90 g/cm 3 .
Using the auxiliary support layer 40, the thickness of the plate can be modulated at will, for example can be taken from a value of 1.150 mm ± 0.050 mm to a value of 1.350 mm ± 0.050 mm, or from a value of 1.350 mm ± 0.050 mm to a value of 1.950 mm ± 0.050 mm, or from a value of 1.950 mm ± 0.050 mm to a value of 3.450 mm ± 0.050 mm, or to other values comprised between the minimum value and the maximum value indicated above.
In this manner, the user can be provided with a single package ready for use consisting of the plate and the support layer to reach the overall desired thickness.
The auxiliary support 40 can be applied by extrusion that is for example achieved by a single-screw extruder with flat head matrix.
The painting plate of the invention has characteristics that contribute to the dissipation of the mechanical energy and the reduction of noise and the elimination of the mechanical abutments.
It has been found in practice that a painting plate according to the invention is particularly advantageous for a reduction in mechanical noise and increasing dissipation of the mechanical energy generated in the printing process.
Further, a painting plate according to the invention has optimum printing results, both in terms of shine of the painted zones and the low degree of accumulation of ink arising from the printing process of the offset units.
A painting plate as conceived herein is susceptible to many modifications and variants, all falling within the scope of the inventive concept as defined by the claims; furthermore, all the details are replaceable by technically equivalent elements.
For example, its use is possible in another sector, in particular as a top of a rubberised fabric of a cylinder of a digital printing machine.
In practice, the materials used, as well as the dimensions, can be any according to the needs and the state of the art.