EP3480013A1

EP3480013A1 - Offset printing machine and corresponding printing method

Info

Publication number: EP3480013A1
Application number: EP17382738.7A
Authority: EP
Inventors: Joan Trenchs Agulló; Albert Carbó Bech
Original assignee: Rotatek Printing Machinery SLU
Current assignee: Rotatek Printing Machinery SLU
Priority date: 2017-11-03
Filing date: 2017-11-03
Publication date: 2019-05-08

Abstract

Offset printing machine and corresponding printing method. For printing ink on a laminar substrate, comprising a horizontal roller (1) comprising a hollow cylindrical body (2) the outer surface (3) of which is configured to receive said substrate and is arranged facing a light source for drying said ink on said substrate, said roller (1) having a first end (101), a second end (102) and an axis (100), and where said roller (1) is secured at said second end (102) to rotation means configured for causing said roller (1) to rotate about said axis (100) in both directions of rotation, wherein that said cylindrical body (2) has cooling conduits (4) provided under said outer surface (3), extending along said cylindrical body (2), and with a coolant fluid circulating through them when said machine is in use.

Description

Field of the Invention

The invention is comprised in the field of offset printing.
More specifically, the invention relates to an offset printing machine for printing ink on a laminar substrate, comprising a horizontal roller comprising a hollow cylindrical body the outer surface of which is configured to receive said substrate and is arranged facing a light source for drying said ink on said substrate, said roller having a first end, a second end and an axis, and where said roller is secured at said second end to rotation means configured for causing said roller to rotate about said axis in both directions of rotation.
The invention also relates to an offset printing method for printing by means of an offset printing machine comprising a horizontal roller that has a first end and a second end and is provided with a hollow cylindrical body, the outer surface of which receives a laminar substrate on which ink has been printed, such that said substrate is arranged facing a light source for drying said ink, and in which said roller can rotate in its two directions of rotation.

State of the Art

Rotary machines that print layers of ink on a laminar substrate, typically paper or the like, are known in the offset printing sector. After being deposited, said layers of ink are dried and set by means of exposure to a light source, typically UV light. A side effect of this exposure to drying light is the heating of the substrate, which can reach high temperatures.
Most conventional printing substrates have considerable heat tolerance, however some applications require substrates the physical properties of which may be affected by exposure to a heat source. This is, for example, the case of film-type paper or thin polymer layers. In particular, given that the substrate is driven by means of rollers inside the printing machine, if the temperature is too high, deformations in said substrate may occur.
In order to reduce these effects, applications have been developed in which the roller located under the drying lamp is a hollow cylinder, and in which a liquid coolant, generally water, is circulated through the center thereof. This allows reducing the temperature on the surface of the cylinder and preventing deformations in the substrate.
This is a feasible solution if the substrate moves forward in a single direction like in the so-called rotary machines. However, solutions of this type are not applicable in the case of the so-called semi-rotary machines, in which the substrate is driven forward and backward. Indeed, the presence of a volume of moving liquid inside the cylinder affects the correct alignment of the substrate when the roller changes the direction of rotation. This results in poor printing, causing different ink colors to become misaligned, for example.
There is therefore a need for a solution to offset printing which allows printing on a heat-sensitive substrate, preventing deformations and irregularities in printing quality, particularly for semi-rotary machines.

Description of the Invention

The object of the invention is to provide an offset printing machine of the type indicated above which allows solving the aforementioned problems. Another object of the invention is a corresponding printing method.
This object is achieved by means of an offset printing machine of the type indicated above, characterized in that said cylindrical body has cooling conduits provided under said outer surface, extending along said cylindrical body, and with a coolant fluid circulating through them when said machine is in use.
Therefore, instead of a central conduit through which liquid circulates, in the present invention the roller has a plurality of conduits close to the surface, each having a smaller individual volume compared to the solution having a single central conduit. This way is possible to maintain a substantially uniform temperature on the surface. Given that the volume of fluid is distributed among conduits having a smaller volume, turbulences and inertias of the coolant fluid circulating inside the cylinder are significantly reduced, which results in a more predictable kinetic behavior. This in turn allows regulating the movement of the roller with greater precision even when the roller changes its direction of rotation, which results in an improved substrate alignment, preventing the problems described above. At the same time, the thermal efficiency of cooling increases and power consumption decreases.
Preferred embodiments the features of which are described in the dependent claims have been provided based on the invention defined in the main claim.
Said fluid is preferably liquid water, a low-cost solution that is readily accessible in the installations.
Said cylindrical body is preferably manufactured in a lightweight metal, preferably aluminum. These metals have a good thermal conductivity and at the same time are lightweight, reducing the inertias and total weight of the roller. On the other hand, aluminum can also be readily machined. Furthermore, if the coolant fluid is water, it is resistant to the oxidizing action of aluminum.
In a preferred embodiment, said conduits are arranged parallel to said axis. This means that the coolant fluid circulates in a direction which is orthogonal to the rotation of the cylinder, resulting in a more constant center of masses and an improved inertial behavior. The conduits are preferably arranged radially equidistant with respect to said axis, which contributes to a more constant center of masses and a lower inertia.
Said conduits preferably run through said cylindrical body in its entirety. This makes it easier to manufacture the cylindrical body, particularly if the conduits are straight conduits.
In a preferred embodiment, said conduits are grouped into a plurality of cooling circuits, in which each of said cooling circuits of said plurality of cooling circuits has a fluid inlet and a fluid outlet, said fluid inlet and said fluid outlet of each cooling circuit being provided at said first end of said roller. The coolant fluid therefore enters and exits the roller through the same side of the roller, this makes it easier to secure said roller at the other end to cause it to rotate using the rotation means. This minimizes the risk of said rotation means, for example, an electric servomotor, coming into contact with the coolant fluid. At the end opposite the end where the rotation means are, the roller is preferably seated in bearing means, for example roller bearings, configured for allowing the rotation of the roller caused by said rotation means. On the other hand, the existence of circuits with an inlet and an outlet on the same side implies the existence of a longitudinal back-and-forth component in the movement of the coolant fluid inside the circuit. This also collaborates in obtaining a uniform temperature on the surface of the roller.
Each of said cooling circuits preferably comprises an even number of said conduits, arranged parallel to one another, and parallel and radially equidistant with respect to said axis, running through said cylindrical body in its entirety, such that said cooling circuit at least partially surrounds said axis and has a zigzag shape, in which the fluid connection between said conduits is established by means of elbows provided at said second end, and if said cooling circuit comprises more than two conduits, elbows are also provided at said first end. Therefore, the coolant fluid travels inside the cooling circuit from the fluid inlet of said circuit at the first end to the second end, going through the elbow and returning from the second end to the first end. If the cooling circuit only comprises two conduits, the fluid enters through said fluid inlet, goes through the first conduit of the circuit, through an elbow at the second end, returns through the second conduit and exits through the fluid outlet of the cooling circuit. If the circuit comprises more conduits, the fluid also goes through an elbow provided at the first end to the next conduit, establishing a zigzag circuit under the outer surface of the cylinder. Therefore, for each pair of conduits of a circuit, the coolant fluid travels in one direction in one of the conduits and in the opposite direction in the other. Each cooling circuit surrounds a section of the axis. By way of example, if there are only two circuits, each one can surround a 180º section. This arrangement has the advantages described above for the arrangement of conduits and circuits, furthermore providing an easy-to-build solution, which minimizes the manufacturing cost and results in a robust design that is less inclined to mechanical failures.
It preferably comprises four of said cooling circuits, each with six of said conduits. Using numerical computation models, this has been found to result in suitable thermal uniformity, maintaining a behavior of the center of masses and inertia that allows working with known substrates. Preferably, the distance between adjacent conduits is the same for all of them, that is, the gap distance between two adjacent conduits is the same for each pair of adjacent conduits. Preferably, even for those corresponding to different cooling circuits. Thus, thermal uniformity is thereby improved. The roller preferably comprises 3 or 4 of said circuits, depending on the dimensions of the roller, to assure that the difference between the temperature of the fluid at the inlet and at the outlet of each circuit is not excessively high, which would lead to thermal gradients on the surface of the roller that would be too high for the desired thermal uniformity.
In an advantageous embodiment, it further comprises:

a rotary joint arranged in said axis, comprising a fluid inlet channel and a fluid outlet channel;
a fluid distributor provided at said first end and configured to establish a fluid connection between said inlet channel and each of said fluid inlets of said cooling circuits; and
a fluid collector provided at said first end and configured to establish a fluid connection between each of said fluid outlets of said cooling circuits and said outlet channel.

This therefore provides a solution for the introduction of coolant fluid into a rotating roller and the removal therefrom, which allows the fluid to come from an external source and makes it unnecessary to provide cooling means inside the roller itself.
Said distributor and said collector are preferably formed in a cylindrical metal part arranged between said cylindrical body and said rotary joint. This configuration simplify mounting and dismounting operations, also facilitating the maintenance and increasing the durability. Preferably, said cylindrical metal part is manufactured in stainless steel. Unlike the lightweight metal in which the cylindrical body is preferably manufactured, this part can have a smaller size, so manufacturing costs and the weight added to the roller are not significantly affected. In turn, the material has low oxidation and high mechanical strength. Though not described in detail for the sake of clarity and simplicity, the skilled person will understand that the roller can further comprise other support parts such as sealing gaskets, etc.
The invention also relates to an offset printing method of the type indicated above, characterized in that said method comprises causing a coolant fluid, preferably liquid water, to circulate through the cooling conduits provided under the outer surface of said roller, extending along said cylindrical body. This entails technical effects equivalent to those described above, so they will not be repeated here for the sake of brevity.
Said conduits are preferably grouped into a plurality of cooling circuits, in which each of said cooling circuits has a fluid inlet and a fluid outlet, said fluid inlet and said fluid outlet of each cooling circuit being provided at said first end of said roller.
Each of said cooling circuits preferably comprises an even number of said conduits, arranged parallel to one another, and parallel and radially equidistant with respect to said axis, running through said cylindrical body in its entirety, such that said cooling circuit at least partially surrounds said axis and has a zigzag shape, in which the fluid connection between said conduits is established by means of elbows provided at said second end, and if said cooling circuit comprises more than two conduits, elbows are also provided at said first end.
It preferably comprises four of said cooling circuits, each with six of said conduits, in which the distance between adjacent conduits is preferably the same for all of them.
It preferably further comprises:

a rotary joint arranged in said axis, comprising a fluid inlet channel and a fluid outlet channel;
a fluid distributor which is provided at said first end and establishes a fluid connection between said inlet channel and each of said fluid inlets of said cooling circuits; and
a fluid collector which is provided at said first end and establishes a fluid connection between each of said fluid outlets of said cooling circuits and said outlet channel.

Said coolant fluid preferably has a temperature less than 60ºC when it exits said roller, preferably equal to or less than 50ºC, more preferably equal to or less than 40ºC. This means that the coolant fluid absorbs a large enough amount of heat to maintain the characteristics of the substrate within tolerance ranges. Preferably, said coolant fluid has a temperature equal to or less than 20º when it enters said roller, more preferably 15º, which allows cooling the surface so that the substrate is kept at about room temperature.
The invention also covers other detail features illustrated in the detailed description of an embodiment of the invention and in the attached drawings.

Brief Description of the Drawings

The advantages and features of the invention can be seen from the following description in which preferred embodiments of the invention are described in reference to the drawings without limiting the scope of the main claim.

Figure 1 is a perspective view of the horizontal roller for the machine of the invention in which the axis has been indicated with a discontinuous line.
Figure 2 is a front view of the same roller of Figure 1.
Figure 3 is an exploded view of the roller of the machine according to the invention.
Figure 4 is a perspective view of the roller with a partial section.
Figure 5 shows the hollow cylindrical body of the roller from the first end.
Figure 6 is a sectioned perspective view of the roller in which the coolant fluid entry path has been indicated with a discontinuous line.
Figure 7 is another sectioned perspective view of the roller in which the coolant fluid exit path has been indicated with a discontinuous line. The section plane is different from the one of Figure 6.
Figures 8A and 8B are perspective views of the cylindrical metal part in which the distributor and collector are formed. The faint lines indicate inner or non-visible portions. Figure 8A is shown from the face closest to the cylinder, whereas Figure 8B is shown from the face farthest away from the cylinder.

Detailed Description of Several Embodiments of the Invention

The drawings show part of the offset printing machine of the invention for printing ink on a laminar substrate. Particularly, the drawings show a horizontal roller 1 comprised in said machine. Said roller 1 comprises a hollow cylindrical body 2 the outer surface 3 of which is configured to receive said substrate and is arranged facing a light source for drying said ink on said substrate.
For the sake of clarity, only the roller 1 is shown as it the component that is the most extensively described herein. Similarly, neither the substrate nor the light source is shown, given that they are standard components in the art, so the skilled person should have no difficulty in understanding the general operation of the machine of the invention based on this document and the attached drawings.
The roller 1 has a first end 101, a second end 102 and an axis 100, where said roller 1 is secured at said second end 102 to rotation means configured for causing said roller 1 to rotate about said axis 100 in both directions of rotation. Figure 1 and Figure 2 depict said axis 100 by means of a discontinuous line. In the example, said rotation means comprise a servomotor, not shown in the drawings.
Said cylindrical body 2 is manufactured in aluminum and has cooling conduits 4 provided under said outer surface 3, extending along said cylindrical body 2, and with a coolant fluid circulating through them when said machine is in use. For the example, the coolant fluid is liquid water. Figure 4 and Figure 5 show how said conduits 4 are arranged parallel and radially equidistant with respect to said axis 100, running through said cylindrical body 2 in its entirety.
Furthermore, said conduits 4 are grouped into a plurality of cooling circuits 5, in which each of said cooling circuits 5 has a fluid inlet 51 and a fluid outlet 52, both provided at said first end 101. The components and conduits 4 of one of said cooling circuits 5 have been indicated in Figure 5. Figure 6 shows the entry of fluid through two of said fluid inlets 51, whereas Figure 7 shows the exit of fluid through two of said fluid outlets 52. The skilled person will understand that the section planes of Figure 6 and Figure 7 are different.
Therefore, as seen in Figure 5, each of said cooling circuits 5 comprises an even number of said conduits 4. As can be observed in the example, four of said cooling circuits 5 run through the cylindrical body 2, each formed by a cluster of six of said conduits 4. In turn, said conduits 4 are arranged parallel to one another, and parallel and radially equidistant with respect to said axis 100, running through said cylindrical body 2 in its entirety. Each of the four cooling circuits 5 of the example is provided in a 90º segment. Said cooling circuit 5 therefore at least partially surrounds said axis 100 in an arc which in the example is somewhat less than 90º. In the example, the distance between adjacent conduits is the same for all of them. Likewise, each cooling circuit 5 has a zigzag shape, in which the fluid connection between said conduits 4 is established by means of elbows 6 provided at said second end 102 and also at said first end 101.
The exemplary machine further comprises a rotary joint arranged in said axis 100, comprising a fluid inlet channel and a fluid outlet channel. The joint per se is not shown in the drawings, although it is envisaged to be arranged at the first end 101. Figure 6 and Figure 7 show how the fluid connection of the entry and exit, as well as their path, is established.
Figure 8A shows a fluid distributor 11 provided at said first end 101 and configured to establish a fluid connection between said inlet channel and each of said fluid inlets 51 of said cooling circuits 5. Particularly, the inner channels of said distributor 11 have been depicted with a faint line in the shape of a cross, each of which for being connected to a fluid inlet 51 of a cooling circuit 5.
Additionally, Figure 8B shows a fluid collector 12 provided at said first end 101 and configured to establish a fluid connection between each of said fluid outlets 52 of said cooling circuits 5 and said outlet channel. In the example, said distributor 11 and said collector 12 are formed in a cylindrical metal part 10 arranged between said cylindrical body 2 and said rotary joint, and manufactured in stainless steel.
In the example, the coolant fluid is liquid water and it is in a closed circuit, such that there is a cooling device at the outlet of the roller 1 which cools the water and introduces it back into the circuit again. Said coolant fluid has a temperature less than 40ºC when it exits said roller 1.
In other embodiments, the number of conduits 4 per cooling circuit 5 and the number of cooling circuits 5 is different, depending on the size of the cylinder. However, said coolant fluid has a temperature less than 60ºC when it exits said roller 1.
The embodiments described so far represent non-limiting examples, such that the person skilled in the art will understand that beyond the examples that have been shown, multiple combinations of the claimed features are possible within the scope of the invention.

Claims

An offset printing machine for printing ink on a laminar substrate, comprising a horizontal roller (1) comprising a hollow cylindrical body (2) the outer surface (3) of which is configured to receive said substrate and is arranged facing a light source for drying said ink on said substrate, said roller (1) having a first end (101), a second end (102) and an axis (100), and where said roller (1) is secured at said second end (102) to rotation means configured for causing said roller (1) to rotate about said axis (100) in both directions of rotation, characterized in that said cylindrical body (2) has cooling conduits (4) provided under said outer surface (3), extending along said cylindrical body (2), and with a coolant fluid circulating through them when said machine is in use.
The machine according to claim 1, characterized in that said fluid is liquid water.
The machine according to any one of claims 1 or 2, characterized in that said cylindrical body (2) is manufactured in a lightweight metal, preferably aluminum.
The machine according to any one of claims 1 to 3, characterized in that said conduits (4) are arranged parallel and preferably radially equidistant with respect to said axis (100), and preferably running through said cylindrical body (2) in its entirety.
The machine according to any one of claims 1 to 4, characterized in that said conduits (4) are grouped into a plurality of cooling circuits (5), in which each of said cooling circuits (5) has a fluid inlet (51) and a fluid outlet (52), said fluid inlet (51) and said fluid outlet (52) of each cooling circuit (5) being provided at said first end (101) of said roller (1).
The machine according to claim 5, characterized in that each of said cooling circuits (5) comprises an even number of said conduits (4), arranged parallel to one another, and parallel and radially equidistant with respect to said axis (100), running through said cylindrical body (2) in its entirety, such that said cooling circuit (5) at least partially surrounds said axis (100) and has a zigzag shape, in which the fluid connection between said conduits (4) is established by means of elbows (6) provided at said second end (102), and if said cooling circuit (5) comprises more than two conduits (4), elbows are also provided at said first end (101).
The machine according to claim 6, characterized in that it comprises four of said cooling circuits (5), each with six of said conduits (4), in which the distance between adjacent conduits (4) is the same for all of them.
The machine according to any one of claims 5 to 7, characterized in that it further comprises:
- a rotary joint arranged in said axis (100), comprising a fluid inlet channel and a fluid outlet channel;

- a fluid distributor (11) provided at said first end (101) and configured to establish a fluid connection between said inlet channel and each of said fluid inlets (51) of said cooling circuits (5); and

- a fluid collector (12) provided at said first end (101) and configured to establish a fluid connection between each of said fluid outlets (52) of said cooling circuits (5) and said outlet channel.
The machine according to claim 8, characterized in that said distributor (11) and said collector (12) are formed in a cylindrical metal part (10) arranged between said cylindrical body (2) and said rotary joint, said cylindrical metal part (10) being preferably manufactured in stainless steel.
An offset printing method for printing by means of an offset printing machine comprising a horizontal roller (1) that has a first end (101) and a second end (102) and is provided with a hollow cylindrical body (2), the outer surface (3) of which receives a laminar substrate on which ink has been printed, such that said substrate is arranged facing a light source for drying said ink, and in which said roller (1) can rotate in its two directions of rotation, characterized in that said method comprises causing a coolant fluid, preferably liquid water, to circulate through cooling conduits (4) provided under the outer surface (3) of said roller (1), extending along said cylindrical body (2).
The method according to claim 10, characterized in that said conduits (4) are grouped into a plurality of cooling circuits (5), in which each of said cooling circuits (5) has a fluid inlet (51) and a fluid outlet (52), said fluid inlet (51) and said fluid outlet (52) of each cooling circuit (5) being provided at said first end (101) of said roller (1).
The method according to claim 11, characterized in that each of said cooling circuits (5) comprises an even number of said conduits (4), arranged parallel to one another, and parallel and radially equidistant with respect to said axis (100), running through said cylindrical body (2) in its entirety, such that said cooling circuit (5) at least partially surrounds said axis (100) and has a zigzag shape, in which the fluid connection between said conduits (4) is established by means of elbows (6) provided at said second end (102), and if said cooling circuit (5) comprises more than two conduits (4), elbows are also provided at said first end (101).
The method according to claim 12, characterized in that it comprises four of said cooling circuits (5), each with six of said conduits (4), in which the distance between adjacent conduits (4) is the same for all of them.
The method according to any one of claims 11 to 13, characterized in that it further comprises:
- a rotary joint arranged in said axis (100), comprising a fluid inlet channel and a fluid outlet channel;

- a fluid distributor (11) which is provided at said first end (101) and establishes a fluid connection between said inlet channel and each of said fluid inlets (51) of said cooling circuits (5); and

- a fluid collector (12) which is provided at said first end (101) and establishes a fluid connection between each of said fluid outlets (52) of said cooling circuits (5) and said outlet channel.
The method according to any one of claims 10 to 14, characterized in that said coolant fluid has a temperature less than 60ºC when it exits said roller (1), preferably equal to or less than 50ºC, more preferably equal to or less than 40ºC.