Patent Description:
To be able to have a functional printing process with printing cylinders fulfilling a desired printing result, these printing cylinders must more or less often be cleaned. Many different cleaning methods have been used in the past, for example spraying a cleaning liquid on the cylinders or cleaning the cylinders one by one by means of a type of cleaning cloth.

One type of cleaning fabric and cleaning method is known from <CIT> which discloses a cleaning system using a pre-soaked cleaning fabric for cleaning a printing press. The pre-soaked cleaning fabric is kept wrapped up around a core and is sealed by means of a sleeve such that the cleaning fabric may be transported and stored away without compromising its cleaning abilities until the seal is broken and the cleaning fabric shall clean the printing press. The cleaning fabric is soaked with an organic compound solvent.

Different types of solvents have been tried in order to get the desired cleaning effect, but there are problems with the compounds used today. For example, so called toning is caused when the printing cylinders, after being cleaned, start rolling and printing again. Toning is when the colour distribution on the printed surface is uneven, creating an undesired printing result. The toning will eventually even out after the printers have been in operation for a while, but the already printed material goes to waste.

<CIT> discloses a certain type of cleaning fabric. It describes the use of a non-woven material as a cleaning fabric in combination with organic solvents as the cleaning liquid. This WO publication illustrates the need for a low-volatility cleaning liquid and the importance of the strength and abrasion resistance of the cleaning fabric. Hence, the known cleaning fabric presented therein gives no solution to the problems of toning, which can be very costly, for instance when the printers need to be cleaned more often and large amount of material has to be thrown away.

Further background art is reflected for instance in the documents <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT> and <CIT>.

However, none of these publications presents a reliable solution to the issues with toning. Thus, there is room for improvement.

An object of the present invention is to provide improvements over prior art. This object, and other objects that will appear from the following description, have now been achieved by the technique defined in the appended independent claims; certain embodiments being set forth in the related dependent claims.

In a first aspect of the present invention, there is provided an assembly according to claim <NUM> comprising a roll of cleaning fabric for cleaning printing cylinders of a printing system and a removable sealing bag. The cleaning fabric comprises a liquid absorbable material soaked with a cleaning liquid which comprises a polar additive containing either a glycol ether or a long-chain alcohol or both. The polar additive is configured to make the cleaning liquid polar. The cleaning fabric is wrapped or wound around a core to form the roll, wherein said roll is inserted in said removable sealing bag which is configured to seal around said roll of cleaning fabric in order to prevent said cleaning liquid from evaporating before use, wherein said roll of cleaning fabric is vacuum packed in said removable sealing bag, the latter being tubular and built up by a multi-layer plastic film. An advantage with a cleaning fabric soaked with a polar cleaning liquid is that the liquid is easily dissolved in water which is beneficial during a printing process. Thus, remaining cleaning liquid from the cleaning process integrated with the water mitigate the problems with toning leading to reduced waste of prints. When the long-chain alcohol option is employed, a <NUM>-<NUM> carbon atom compound is used. Cleaning fabrics soaked with cleaning liquid of this structure has proven to be particularly efficient. According to the invention, the cleaning liquid comprises the polar additive in a range of <NUM>-<NUM> wt%.

Depending on the circumstances under which cleaning is to take place, the cleaning fabric may be soaked with the cleaning liquid either before or after being wrapped or wound around the core for forming the roll.

In a second aspect of the present invention, there is provided a cleaning cassette according to claim <NUM> which comprises supporting means configured to support a roll of cleaning fabric of the type described above, and a collecting roller around which used cleaning fabric is configured to be wrapped or wound. This cassette is beneficial since it constitutes a compact and robust unit which is easy to incorporate in the printing system. According to the invention, the supporting means is a rotatable shaft which is spaced from and parallel to the rotatable collecting roller.

In an embodiment, the cleaning cassette is arranged in the printing system in such a way that it is movable between an idle position in which the cleaning fabric is out of contact with any printing cylinder, and an active position in which the cleaning fabric is in contact with a printing cylinder to be cleaned. By this design, an efficient cleaning operation is achieved since the cleaning fabric is in cleaning contact only when required.

The cleaning cassette may comprise a pad configured to press the cleaning fabric against a printing cylinder to be cleaned. Hereby, a favourable press action of the cleaning fabric against the cylinder to be cleaned is achieved. The pad may be provided with an elastic element on the pad surface which is adapted to be press the cleaning fabric against the cylinder to be cleaned.

According to a preferred embodiment, there is provided a printing system comprising a cleaning cassette which is of the type described above and which preferably is movable between an idle position and a cleaning position. The printing system may comprise printing cylinders, inking rollers, damping rollers, an ink source and a damping source. Hence, this improved printing system incorporates an efficient cleaning function.

In a third aspect of the present invention, there is provided a method for cleaning printing cylinders of a printing system by means of a cleaning cassette of the design described above and including a roll of cleaning fabric as described above. The method comprises the steps defined in claim <NUM>. This method makes it possible to clean printing cylinders in a more efficient manner than what has been possible in the art hitherto.

Used cleaning fabric is wound around the collecting roller included in the cleaning cassette which makes the cleaning procedure smooth and functional.

It is also preferred that the cleaning cassette - when cleaning is to be performed in accordance with the present cleaning method - is moved from an idle position in which the cleaning fabric is out of contact with any printing cylinder, to an active position in which the cleaning fabric is in contact with a printing cylinder to be cleaned.

In a fourth aspect of the present invention, it is proposed to use a cleaning fabric for cleaning printing cylinders of a printing system, in which the cleaning fabric is soaked with a cleaning liquid of the type described above. Its use ensures cleaning which is improved over prior art.

Embodiments of the invention will be described in the following, reference being made to the appended diagrammatic drawings which illustrate non-limiting examples of how the inventive concept can be reduced into practice and in which:.

With reference to <FIG> there is shown a printing unit or system <NUM> with a number of printing cylinders and rollers <NUM>, <NUM>, <NUM>, <NUM>, <NUM>. The printing system <NUM> described herein has an impression cylinder <NUM> (the largest printing cylinder, down to the left in <FIG>), a blanket cylinder <NUM> (the medium sized cylinder next to the impression cylinder) which has a rubber sheet (not shown) and a plate cylinder <NUM> (the medium sized cylinder next to the blanket cylinder). The printing system <NUM> further has a number of inking rollers <NUM> (small rollers not being damping rollers) and a number of damping rollers <NUM> (the five small sized rollers down to the right). The set of inking rollers <NUM> is associated with an ink source <NUM> which provides the inking rollers <NUM> with ink. The set of damping rollers <NUM> is associated with a damping source, in this case a water bath <NUM> which provide the damping rollers <NUM> with water.

When the printing system <NUM> is performing printing work, water is firstly transported via the damping rollers <NUM> from the damping source <NUM> towards the cylinders. The water is then present at the non-pressured surfaces occurring between the cylinders <NUM>, <NUM>, <NUM>. Secondly, ink is then transported by means of the ink rollers <NUM> from the ink source <NUM> towards the cylinders <NUM>, <NUM>, <NUM>. The print is then transferred to the blanket cylinder <NUM> and the material, e.g. paper, receiving the print is arranged between the blanket cylinder <NUM> and the impression cylinder <NUM> where the printing work is conducted and the print is transferred from the rubber sheet to the material. The set up of the cylinders and rollers shown and described herein is only an example of a set up.

More or less often the printing cylinders have to be cleaned. This is made by means of a cleaning machine or cassette <NUM> which houses a cleaning device or roll <NUM> with a cleaning fabric <NUM>, also referred to as a cleaning cloth. Before the cleaning process begins, the cleaning roll <NUM> is taken out of its package or bag <NUM> (see <FIG>) and placed in the cleaning cassette <NUM>.

The cleaning roll <NUM> shown in <FIG> is pre-packed and stored until it is to be used in the cleaning process. As shown in <FIG>, the cleaning roll <NUM> includes a bobbin or core <NUM> around which the cleaning fabric <NUM> is wrapped or wound. The core <NUM> can be solid or hollow and made of any suitable material, for example plastic, paper or metal. It can also have different cross sections, and the design described herein has a circular cross section.

The cleaning fabric <NUM> consists of a liquid or solvent absorbable material, such as a non-woven material, which is adapted to be soaked with a cleaning liquid before starting a cleaning process. Preferably, the cleaning fabric <NUM> is soaked with the cleaning liquid before being packed and stored or transported, i.e. it can be soaked long before it is to be used in a cleaning process. Further, the cleaning fabric <NUM> can be soaked either before or after being wrapped around the core <NUM>.

The cleaning liquid includes a polar additive or polar compound which is configured to make the cleaning liquid polar. Since liquids with similar polarity dissolve in each other, the polar additive is water soluble. By adding the polar additive to the cleaning liquid, this liquid is thus provided with a desired polar ability. This desired feature will be further explained below.

The polar additive includes glycol ether, for example butyl ether, and/or a long chain alcohol. The long chain alcohol is an alcohol with a carbon chain between ten and sixteen carbon atoms.

Further, the cleaning liquid includes the polar additive in a range of <NUM>-<NUM> wt%, can also be expressed as <NUM>-<NUM>/m%. To clarify, the amount of polar additive in respect of the total amount of liquid is between <NUM>-<NUM>%.

Other possible compounds of the cleaning liquid with different abilities can be aliphatic hydrocarbon for cleaning power, vegetable ester for cleaning power and reduction of evaporation, corrosion inhibitor for preventing corrosion and emulsifier for emulsification with water.

An advantage with a polar liquid is that it is water soluble, since water is also a polar liquid. A non-polar liquid is not water soluble and would instead - if brought into contact with water - gather on its surface, and form a layer on top of the water surface.

During a cleaning process of a printing system as shown in <FIG>, the cylinders are rotated in an opposite direction with respect to the direction during a printing process. So, if a non-polar cleaning liquid is applied to the blanket cylinder <NUM> of <FIG> during a cleaning process, which is the case in known cleaning processes today, the non-polar cleaning liquid will travel from the blanket cylinder <NUM> to the plate cylinder <NUM> further onto the damping rollers <NUM> and down into the water bath <NUM>. When in the water bath <NUM>, the non-polar cleaning liquid will create a type of skin or a layer on the surface of the water. Once the printing process is restarted after the cleaning process, the cylinders and rollers will start to roll in the opposite direction compared to the direction during the cleaning process. This means that the roller/s <NUM>' in contact with the water will not at first only transport water to the other rollers and cylinders but also the non-polar cleaning liquid.

The residue of the non-polar cleaning liquid on the printing surfaces is the reason why toning occurs on the printed paper. In order to reduce the amount of waste due to toning after a cleaning process, different types of cleaning liquids have been tried in the past with poor results. However, tests conducted by the inventors of the present patent application have surprisingly shown that if the cleaning liquid is made polar it will dissolve in the water of the water bath <NUM> and thus create a situation where a reduced amount of cleaning liquid is transferred back to the cylinders. In turn, this surprisingly results in reduced waste of printed paper due to toning. In order to create a polar cleaning liquid either glycol ether or long chain alcohol is used in the described embodiment. However, according to the invention other suitable compositions with the same desired abilities include both glycol ether and long-chain alcohol.

As shown in <FIG>, the cleaning roll <NUM> is inserted in a removable, sealable bag <NUM> configured to seal around the core <NUM> and cleaning fabric <NUM> before use. Since the cleaning fabric <NUM> is soaked with the cleaning liquid before being stored away or transported, it is desired that the cleaning fabric <NUM> contains the right amount of cleaning liquid when it is about to be used in a cleaning process. The bag <NUM> is designed to prevent the cleaning liquid soaked in the cleaning fabric <NUM> from evaporating during storage or transportation of the cleaning device <NUM>.

The cleaning roll <NUM> is vacuum packed until the bag <NUM> is broken before a cleaning process starts. According to the invention, the bag <NUM> is tubular and built up by a multi-layer plastic film. A suitable plastic film for this purpose is a three-layer film based on a first layer of polyethylene (PE) providing a fluid barrier, a second mid layer of polyamide (PA) providing strength and a third layer of polyethylene (PE) providing a fluid barrier and a sealing layer. This three-layer plastics film has proven to be favourable in practical tests. The thickness of the sealing film is designed in such a way that it is easy to remove from the roll <NUM>, as is shown in <FIG>.

In <FIG>, the cleaning cassette <NUM> included in the printing system of <FIG> is shown separately and in more detail. The cassette <NUM> includes two spaced side members 10a and 10b interconnected by a transverse member 10c. These members 10a-c form the frame of the cleaning cassette <NUM>.

Furthermore, the cassette <NUM> includes mounting means in the shape of a transverse shaft <NUM> configured to support the core <NUM> of the roll <NUM> of cleaning fabric <NUM> (shown in bold in <FIG>). The hollow core <NUM> has internal engagement means (not shown) configured to engage with matching engagement means (not shown) provided on the outside of the shaft <NUM>. Hence, the shaft <NUM> and the roll <NUM> supported thereon are rotatable together. For simplifying reasons, the roll/core assembly <NUM>/<NUM> is not shown in <FIG>.

At the free transverse end portion of the cassette <NUM>, there is a front pad <NUM> configured to press the cleaning fabric <NUM> against a cylinder to be cleaned. At its front surface, the pad <NUM> has a transverse element <NUM> of elastic material, preferably rubber, which serves to press the cleaning fabric <NUM> against the cylinder to be cleaned with a suitable pressure. The elongate elastic element <NUM> protrudes from the surface of the pad <NUM> where it is fastened.

The cassette <NUM> also includes a transverse return roller or collecting roller <NUM> around which used cleaning fabric <NUM> is wrapped after been in cleaning contact with a cylinder. In this way, used cleaning fabric <NUM> can easily be collected and handled after a cleaning process. The shaft <NUM> and the collecting roller <NUM> are spaced apart and parallel. The collecting roller <NUM> is also referred to as a take-up roller since the free end of the cleaning fabric <NUM> is fastened to this roller before the cleaning process is initiated.

In operation, collecting roller <NUM> and the shaft <NUM> are rotated - stepwise - so that fresh portions of the cleaning fabric <NUM> are applied to the rotating cylinder to be cleaned. This rotational movement of the cleaning fabric <NUM> is illustrated diagrammatically by arrows in <FIG>. In the embodiment described herein, the collecting roller <NUM> is rotationally driven so that the cleaning cloth <NUM> is rolled off from the roll <NUM> supported by the rotatable shaft <NUM> which may have means for preventing rotation in the opposite direction (not shown).

As shown by a double arrow in <FIG>, the cleaning cassette <NUM> is movable between two positions. In an idle position, the cleaning cassette <NUM> is kept at a distance from the cylinders and out of contact with the same. In an active position (see <FIG>), the cleaning cassette <NUM> is in contact with a printing cylinder <NUM> to be cleaned. The printing system <NUM> includes means (not shown) for performing this reciprocating movement of the cleaning cassette <NUM> between the idle and active positions. In certain embodiments (not shown), the cleaning cassette <NUM> can be moved in different directions and between different positions in order to clean various cylinders included in the printing system.

Hence, the cleaning equipment is operated in accordance with a method for cleaning printing cylinders of a printing system <NUM> with a cleaning roll <NUM> including the steps of:.

Claim 1:
An assembly comprising:
a roll (<NUM>) of cleaning fabric (<NUM>) for cleaning printing cylinders of a printing system (<NUM>); and
a removable sealing bag (<NUM>),
said cleaning fabric (<NUM>) comprising a liquid absorbable material soaked with a cleaning liquid, wherein said cleaning liquid comprises a polar additive containing either a glycol ether or a long-chain alcohol or both, said long-chain alcohol comprising <NUM>-<NUM> carbon atoms; wherein said polar additive is configured to make the cleaning liquid polar; and wherein said cleaning fabric (<NUM>) is wrapped around a core (<NUM>) to form said roll (<NUM>);
wherein the roll (<NUM>) is inserted in said removable sealing bag (<NUM>) which is configured to seal around said roll (<NUM>) of cleaning fabric (<NUM>) in order to prevent said cleaning liquid from evaporating before use;
wherein said roll (<NUM>) of cleaning fabric (<NUM>) is vacuum packed in said removable sealing bag (<NUM>);
wherein said removable sealing bag (<NUM>) is tubular and built up by a multi-layer plastic film, and
wherein said cleaning liquid comprises the polar additive in a range of <NUM>-<NUM> wt%.