EP1755791A1

EP1755791A1 - Apparatus for applying varnish onto a film

Info

Publication number: EP1755791A1
Application number: EP04778962A
Authority: EP
Inventors: Maximilian Zaher
Original assignee: Demaxz LLC
Current assignee: DeMaxZ AG
Priority date: 2004-02-23
Filing date: 2004-07-23
Publication date: 2007-02-28
Also published as: EP1755791A4; WO2005084823A1; CN1942253A; EP1618967A1

Abstract

The present invention provides an apparatus and process for applying varnish onto a film. The apparatus comprises a coating roller (10) for transferring varnish from the coating roller onto the film (16) and a pressure roller (12) arranged adjacent the coating roller. A means is provided for advancing the film at a first velocity through a gap (44) between the coating roller and the pressure roller in addition to means for rotating the coating roller such that the circumference of the coating roller adjacent the film moves at a second velocity different to the first velocity.

Description

Apparatus for Applying Varnish onto a Film This application claims priority to U.S. Patent Application Serial No. 60/546,736 filed on February 23, 2004 which is incorporated by reference herein in its entirety. BACKGROUND OF INVENTION Technical Field The invention is concerned with an apparatus and process for applying varnish or lacquer onto a film. Background Art It is well known in the prior art to use a so-called coating roller and a so- called pressure roller (also sometimes called a counter roller) for applying varnish onto a flexible film. The flexible film may preferably have so-called release properties such that the layer of varnish can be transferred from the film onto an object, e.g. after curing (cross-linking) or partial curing of the varnish, by peeling off the varnish layer. Films formed of materials such as polypropylene, polyethylene, polyvinyl alcohol, polyvinyl chloride, polymethylmeth-acrylate, or polyethylene terephthalate typically have favorable release properties. The release properties of films may also be enhanced with physical processes such as manipulating the surface tension of the firm (for example through a conventional corona treatment) or chemical processes such as the application of various conventional release agents. Films having so-called release properties are well known in the prior art; see for example, EP 1 053 793 Al and EP 0 573 676 Bl. The prior art includes both paper-based films and films made of a resin, the surfaces of which are prepared such that the film comprises release properties. When layers of colour or varnish are applied to such a film having release properties, the layers can be transferred onto an object to be decorated in such a way that the layers of varnish and colour are peeled off from the film. The prior art according to. EP 0 573 676 Bl discloses a process of decorating an object wherein a layer of varnish is applied on a film having release properties. That layer of varnish is partially cured. A layer of colour is applied onto the partially cured varnish layer and a second layer of varnish is applied onto the colour layer.

The second layer of varnish is also partially cured. Thereafter, the layers of varnish and colour, respectively, are transferred onto the object to be decorated (the

"substrate"). After the transfer by release, the first and second varnish layers are completely cured. The "curing" referred to herein is also called "cross-linking". EP 1 053 793 Al teaches the application of varnish and colour onto an object by means of a release film, wherein a glue is applied on top of the varnish and colour layers of the release film. When transferring the layers onto the object to be decorated, the glue is in direct contact with the object. The present invention is, in particular, directed to applying a varnish layer onto such a film which, preferably, has release properties. The film may be printed, before or after applying the varnish layer, with a colour layer. In the prior art it was very difficult, if not impossible, to apply relatively thick layers of varnish onto a film. The films in question here typically have a width of more than 100 cm, e.g. a width in the range of 160 to 180 cm. The machines according to the prior art were only capable of applying varnish layers having a thickness typically less than 60 μm. The present invention aims at providing an apparatus that is capable to be adapted to apply a variety of varnish layers of different thickness, in particular relatively thick varnish layers. The present invention provides an apparatus and process for applying varnish onto a film. The apparatus comprises a coating roller for transferring varnish from the coating roller onto the film and a pressure roller arranged adjacent the coating roller. A means is provided for advancing the film at a first velocity through a gap between the coating roller and the pressure roller in addition to means for rotating the coating roller such that the circumference of the coating roller adjacent the film moves at a second velocity different to the first velocity. According to one preferred embodiment of the invention, the means for advancing the film advances the film in a first direction through the gap between the coating roller and the pressure roller, and the means for rotating the coating roller rotates the coating roller such that the circumference of the coating roller adjacent the film moves in a second direction opposite to the first direction. In one alternate embodiment, the film enters the gap at an angle (α) different from zero with a plane that is tangential to both the coating roller and the pressure roller. According to another preferred embodiment of the invention, the coating roller comprises a rubber surface. According to a still further embodiment of the invention, a means is provided for moving at least one the pressure roller or coating roller in a direction parallel to the plane that is tangential to both the coating roller and the pressure roller. Brief Description of the Drawings Figure 1 illustrates schematically one embodiment of the present invention for applying varnish onto a film. Detailed Description of Invention The apparatus comprises a coating roller 10 and a pressure roller 12. Pressure rollers are also sometimes called "counter rollers". The pressure roller 12 is non-steered; i.e. it is not powered and may rotate freely. A dosing roller 14 is arranged adjacent the coating roller 10 for transferring varnish from a supply (not shown) onto the coating roller 10. A plane 16 is tangential to both the coating roller 10 and the pressure roller 12, i.e. the plane 16 passes in-between the rollers, which are adjacent to each other. A film 18 having release properties is advanced in the figures from the right hand side to the left hand side. In one embodiment, the release properties may be defined as the film having a surface tension (or surface energy) of between approximately 30 and 42 dynes. This surface tension may be obtained by selection of a material naturally having this surface tension or by modification of the surface tension, such as by a corona treatment process. The coating roller 10 is rotated around its axis 20 in a counter-clockwise direction as indicated by arrow 46 in the figure. Pressure roller 12 rotates about its axis 22 and is driven at the speed at which the film 18 is advanced. Both coating roller 10 and pressure roller 12 are driven by a conventional drive mechanism such as seen in co-pending application PCT Application Serial No. , filed on 23 July 2004, to inventor

Maximilian Zaher which is incorporated by reference herein in its entirety. The film 18 is guided via rollers 24 and 26 such that, before being advanced between the coating roller and the pressure roller, it is not positioned in the tangential plane 16, but rather defines an angle α between the film 18 and the tangential plane 16, as indicated in the figure. That angle α is acute, and is preferably in the range between about 10° and 30°. As described above, film 18 is advanced in the figure from right to left. Pulling means for pulling the film in the direction 42 are not shown, but they are typically arranged in the figure to the left of the coating roller 10 and the pressure roller 12.

For example, a conventional driven collecting roller would be suitable for pulling the film in the direction 42. Varnish is transferred by the coating roller 10 onto the film 18, and in particular onto the upper surface of film 18, as shown in the figure. The varnish is, preferably, curable by so-called cross-linking, which as such is well known in the art.

For example, curing means (not shown) may be arranged to the left of the coating roller 10 and the pressure roller 12. A varnish container 28 is arranged underneath the pressure roller 12 to collect excess varnish not used for coating the film 18, e.g. varnish applied at the edges of the film 18. A support 30, which supports both the pressure roller 12 and the coating roller 10, allows rotation of the coating roller 10 and the pressure roller 12 in the direction of arrows 32, i.e. both the coating roller 10 and the pressure roller 12 can be rotated about an axis A that is passing through the axes 20 and 22 in the middle of both rollers. Since the figure shows a centre cross section through the rollers, the axis A is also in the plane of the drawings. By the rotation about axis A in direction of arrows 32, the relative arrangement and positioning between the rollers and the film 18 can be adjusted so that crinkles are avoided. Pressure roller 12 always rotates anti-clockwise as indicated by the arrow. Coating knifes 36, 38, which may be "soft" knives formed of a polyolefin material, are arranged to control the transfer of varnish from the dosing roller onto the coating roller, as is known in the art as such. The coating roller 10 and the dosing roller 14 rotate typically in opposite directions, as indicated by the arrows 46, 48. As is known in the art, the amount of varnish transferred to the film may be regulated by the distance between the coating knives and rollers and the pressure exerted on the film by coating roller 10 and pressure roller 12. Typical dimensions of the rollers are as follows: The coating roller 10 may have a typical diameter in the range between 180 and 300 mm, preferably about 240 mm. The pressure roller 12 may have the same dimensions. The dosing roller 14 has a diameter in the range of 100 to 200 mm, preferably about 160 mm. The dosing roller 14 is smaller than the coating roller. The width of the film is typically 160 to 180 cm. A soft knife 40 is arranged near the varnish collecting container 28 in order to clean the pressure roller 12 from excess or non-used varnish. As described above, the film 18 is advanced in the direction of arrow 42. The film 18 passes through a gap 44 between the coating roller 10 and the pressure roller 12. In one embodiment, the direction of rotation 46 of coating roller 10 and the speed of rotation are controlled such that the circumference of the coating roller 10 adjacent the film 18, i.e. the circumference of the coating roller actually transferring the varnish onto the film, is moving in the opposite direction with reference to the movement of the film. Therefore, the circumferential surface of the coating roller 10 has a velocity relative to the velocity of the film 18 in the opposite direction. That is, in a (moving) coordinate system in which the film 18 is at rest, the circumferential surface of the coating roller 10, which transfers the varnish onto the film, moves relative to the film with a definite velocity different from zero. Most preferably, in a stationary (non-moving) coordinate system (i.e. the coordinate system of the figure), the coating roller 10 has a circumferential surface that rotates counter-clockwise as indicated by arrow 46 in the figure. The dosing roller 14 rotates in a direction opposite to the direction of rotation of the coating roller 10, i.e. dosing roller 14 rotates clockwise. Typical examples of the velocities are as follows: The speed of advancement (velocity) of the film 18 in direction 42 may be in a range of 1-50 m/min, and more

5 preferably 10 to 20 m/min. If the speed of advancement (velocity) of the film 18 is 20 m/min, the preferred rotational speed of the coating roller 10 is such that its surface velocity is 10 m/min. Generally speaking, if the speed X of the film 18 is relatively fast, e.g. over about 15 m/min, the rotational speed of the coating roller is such that its surface velocity is in a range of 30-70% of X. When the film speed iso relatively fast, the drum and film velocities are in the same direction, i.e. the film is advanced in direction 42 and the coating roller rotates clockwise. If, on the other hand, the speed of advancement (velocity) of the film 18 is relatively slow, e.g. in the range of 1-5 m/min, the coating roller may rotate anti-clockwise in direction of arrow 46 with surface velocities in the range of 5-10 m/min. The velocities ares adjusted in accordance with the specific requirements of the varnish coating to be applied onto the film, in particular the thickness of the varnish and the properties of the varnish. Depending on the thickness of the layer of varnish to be applied onto the film 18, the coating roller 10 may also rotate clockwise (i.e. opposite to arrow 46) with a0 circumferential speed smaller than the speed of advancement of the film 18 in the direction of arrow 42. For example, if the speed of advancement of film 18 in direction of arrow 42 is 1O m/min, a thicker layer may be applied by adjusting the circumferential speed of coating roller 10 in clockwise direction (opposite to arrow 46) to be between 3 m/min and 7 m/min, resulting in a corresponding lower relative5 speed between be circumference of the coating roller and the film. The amount of varnish applied onto the film 18 can also be controlled by how varnish 50 is fed in between the coating roller 10 and the dosing roller 14 as shown in the drawing. By adjusting the pressure between the dosing roller 14 and the coating roller 10 and/or the relative velocity between coating roller 10 and dosingo roller 14, the amount of varnish applied by the coating roller 10 onto the film 18 is variably controllable. If only a very small amount of varnish shall be applied onto the film, i.e. a relatively thin varnish layer is to be applied onto the film 18, the dosing roller 14 may rotate in opposite direction as compared to the coating roller 10. This is indicated by the double-arrow 48. With the apparatus described above, layers of varnish can be applied onto the film 18 which are much thicker than possible with prior art machines, e.g. it is possible to apply a varnish layer having a thickness in the range of 120 μm to 130 μm with a constant thickness along the width and length of the film 18. A film 18 having release properties and coated with a varnish layer having a thickness in the afore-mentioned range is very suitable for applying varnish onto an object with a high degree of homogeneity of the varnish layer, especially in the area of the edges. Cracks and similar imperfections in the varnish layer are eliminated to a substantially greater degree than in the prior art. While the present invention is described in terms of applying a varnish layer, the invention's scope could include applying coating materials other than varnish. Also, as used herein, the term "velocity" is a vector quantity having both magnitude and direction. Thus, if film 18 is moving at 5 m/min in a first direction and the circumferential speed of coating roller 10 is 5 m/min in a second direction, the velocity of film 18 and coating roller 10 should be considered different.

Claims

1. An apparatus for applying varnish onto a film, said apparatus comprising: a. a coating roller for transferring varnish from the coating roller onto the film; b. a pressure roller arranged adjacent said coating roller; c. a means for advancing said film at a first velocity through a gap between said coating roller and said pressure roller; and d. a means for rotating said coating roller such that the circumference of the coating roller adjacent said film moves at a second velocity different to said first velocity.

2. Apparatus according to claim 1, wherein said means for advancing said film advances said film through the gap in a first direction, and said means for rotating said coating roller rotates said coating roller such that the circumference of the coating roller adjacent said film moves in a second direction opposite to said first direction.

3. Apparatus according to claim 1 or claim 2, wherein said film, before entering said gap, defines an angle ( ) different from zero with a plane that is tangential to both the coating roller and the pressure roller.

4. Apparatus according to any one of claims 1 to 3, wherein said coating roller comprises a rubber surface.

5. Apparatus according to any one of claims 1 to 4, wherein means are provided for moving at least one of said pressure roller or coating roller in a direction parallel to a plane that is tangential to both the coating roller and the pressure roller.

6. An apparatus for applying a coating material onto a film, said apparatus comprising: a. a coating roller positioned in contact with a source of coating material; b. a pressure roller arranged adjacent said coating roller; c. a film advancing at a first velocity through a gap between said coating roller and said pressure roller; and d. wherein a circumference of said coating roller adjacent said film moves at a second velocity different to said first velocity.

7. Apparatus according to claim 6, wherein said first velocity and said second velocity produce a relative velocity between about 10 and 20 m/min.

8. A process for applying varnish onto a film, said process comprising the steps of: a. providing a coating roller arranged adjacent to a pressure roller; b. applying an amount of varnish to said coating roller; c. advancing a film between said coating roller and said pressure roller at a first velocity; d. rotating a circumference of said coating roller at a second velocity different from said first velocity; and e. a means for rotating said coating roller such that the circumference of the coating roller adjacent said film moves at a second velocity different to said first velocity.