WO2004037536A2

WO2004037536A2 - Squeegee, particularly for screen printing

Info

Publication number: WO2004037536A2
Application number: PCT/DE2003/003486
Authority: WO
Inventors: Rudolf August KÜRTEN
Original assignee: Rk Siebdrucktechnik Gmbh
Priority date: 2002-10-18
Filing date: 2003-10-17
Publication date: 2004-05-06
Also published as: AU2003287847A1; ATE433863T1; EP1551631A2; DE10394002D2; EP1551631B1; DE50311615D1; WO2004037536A3; DE20216016U1; AU2003287847A8

Abstract

The invention relates to a squeegee, particularly for screen printing, comprising at least one longitudinally extended profiled strip (5) made of a flexible material. The squeegee comprises, in the area of the flexible profiled strip, a squeegee edge (6), which can be placed against a printing screen and which extends in a longitudinal direction, and comprises a lateral edge (9) that extends transversal to said squeegee edge. A reinforcing layer (7, 8) is provided, which is joined to the flexible profiled strip over a large area and which increases the rigidity of the squeegee. The aim of the invention is to create a squeegee which can be advantageously used and which is to be subsequently worked. To this end, the reinforcement (7) is provided with fibers, whereby the fibers consist, at least in part, of carbon fibers and/or synthetic fibers and/or of fibers that have a modulus of elasticity of = 100 GPa and/or a breaking elongation of = 3 %. The squeegee can have an electrical conductivity that is high enough to prevent the occurrence of unwanted spatters during the printing process. A number of reinforcing layers can be provided, and the rear side of the squeegee can be reinforced by a glass-fiber fleece.

Description

Squeegees, especially for screen printing

The present invention relates to a squeegee, in particular for screen printing, with at least one elongated profile strip made of a soft elastic material, the squeegee having a squeegee edge which can be placed on a printing screen and extends in the longitudinal direction and a lateral edge which extends transversely thereto, with a large area with the soft elastic profile strip connected reinforcement is provided to increase the rigidity of the squeegee.

Squeegees of this type are applied in a screen printing process to a printing screen, which may consist of a textile or metallic material, the printing screen being able to be placed on a printing medium (e.g. a paper to be printed) by pressurizing the doctor blade arranged above the printing screen. Under

When the doctor blade is displaced, a printing medium can be applied to the print carrier through the mesh of the printing screen, as a result of which a flat print image is generated. On the other hand, in the case of screen printing, the squeegee can also be arranged stationary and the printing screen, which e.g. is designed as a cylindrical rotary screen, to be movable relative to the squeegee.

The squeegees are used to produce a high quality

Print image high requirements with regard to the exact shape of the doctor blade edges in terms of time and location, adjustability of the Angle of attack of the squeegee against the printing screen when the squeegee is pressurized, solvent resistance to the solvent of the printing medium, homogeneity of the material properties and the local and temporal constancy of the physical properties of the squeegee such as elasticity or rigidity, hardness, swelling properties etc. over the life of the squeegee put. These properties also determine the printing medium consumption.

The squeegee must also with changing loads such as when contacting the printing screen while bending the squeegee or when moving the same as well as with constant load, e.g. exhibit an excellent long-term behavior during the printing process with constant application of force against the printing screen, in order to avoid undesired changes in the time or place of the printed image or a frequent doctor blade exchange. Furthermore, it is often necessary to rework the squeegee in the area of the squeegee edge in order to obtain a defined and as smooth as possible squeegee edge. Since the squeegee is usually made out of larger, plate-shaped pieces, the cut surfaces must, if possible, meet the requirements desired for the squeegee.

The object of the invention is to create a doctor blade which particularly meets the above-mentioned requirements.

The object is achieved by a doctor blade, in which the reinforcement contains fibers and the fibers are at least partially carbon fibers and / or plastic fibers and / or fibers with a

Modulus of elasticity (modulus of elasticity)> 100 GPa and an elongation at break <3%. The at least one reinforcement layer can have such fibers in addition to other fibers or exclusively such fibers. Other fibers can contain <75% by weight, preferably <50% by weight, particularly preferably <25 to 10% by weight of the fiber make up weight of the reinforcement layer or <10-20% by weight, preferably 5 2-5% by weight or <1% by weight of the total weight of the reinforcement layer, or be absent, without being restricted to this.

This provides reinforcement with excellent long-term behavior with regard to dynamic and static loads, which, because of the fiber materials mentioned, provides very smooth and easy to rework processing surfaces compared to the use of reinforcements made of glass fibers. In the case of reinforcement layers with glass fibers, the reinforcement layer according to the invention is preferably arranged between the glass fiber layer and the soft-elastic doctor blade layer.

The reinforcing layer containing the fibers according to claim 1 preferably borders directly on the soft-elastic squeegee strip provided with the squeegee edge in order to support it. The layer immediately adjacent to the soft elastic squeegee strip can be based on the total weight of the reinforcing layer or based on the fiber weight thereof, 10 10% by weight or 5 5% by weight of glass fibers, preferably this layer is at least substantially or completely free of glass fibers ,

By using the fibers in the reinforcement layer, the doctor blade can have a well-defined restoring force when pressed against a transfer medium for the printing medium (printing ink), which can be a printing screen or, for example, a printing cylinder used in gravure printing, so that

Printing medium can be applied particularly evenly over the life of the squeegee. On the other hand, the soft elastic squeegee layer can give the squeegee a particularly well-defined and sealing contact with the transfer medium. Since the fibers are only present in the reinforcement layer conditions, the soft elastic squeegee edge, for example with regard to its geometry, hardness or the like, can be particularly easily adapted to the respective requirements. Since the squeegee edges are often to be processed during the manufacture of the squeegee or during post-processing, for example to be reground with material removal, the fibers introduced according to the invention, which are different from glass fibers, enable simple post-processing of the squeegee edge to be applied to a printing screen.

The soft-elastic doctor blade layer and / or the reinforcement layer preferably has no particulate additives, in particular no abrasive particles such as aluminum trioxide, SiC or the like. The doctor blade as a whole is preferably free of particulate additives, in particular abrasive particles, but also particles such as soot, fillers such as silica, or the like.

The reinforcement can be two or more, e.g. have different reinforcement layers provided on one side of the soft-elastic squeegee part. Due to the different design of the reinforcement layers, the doctor blade as a whole can be particularly easily adapted to the respective requirements and in particular also to the long-term behavior of the dynamic and static load capacity. Furthermore, the sectional image of the doctor blade edges can be influenced by the several different reinforcement layers, since, for example, the outer reinforcement layer or the fibers embedded in it can be cut more easily and / or have a higher impact resistance and the inner one

Reinforcing layer can have higher strengths, for example. The reinforcing layers of this doctor blade, which do not directly adjoin the soft-elastic doctor blade strip, can also contain glass fibers in addition to or as an alternative to the above-mentioned types of fiber, both or one of the reinforcing layers also consisting exclusively of one of the above-mentioned types of fibers, for example glass fibers. The glass fiber content of this reinforcement layer can be 5 5% by weight, 10 10% by weight or 25 25% by weight, based on the total fiber weight of the layer or on the total weight of the layer. The layers delimiting the doctor blade on the outside, ie the front and / or rear doctor blade layer, preferably have a lower carbon fiber content than a layer lying further inside, for example a content of 25 25% by weight, 10 10% by weight or 2 2% by weight .-% based on the layer weight or the total fiber weight of the layer, or is free of carbon fibers.

The fibers of the reinforcement layers are preferably carbon fibers and / or plastic fibers such as, for example, made of polyamides, polyesters, polyamideimides, polybenzimidazoles, polytetraphthalates such as aramid fibers (m and / or P-aramid fibers), acrylic fibers, PVC fibers or other suitable fibers.

Carbon fibers have proven to be particularly preferred due to their mechanical and electrical properties. It was found that by introducing carbon fibers into the reinforcement layer with a sufficient content, the printed image produced by means of the doctor blade on a carrier can be significantly improved in quality. Here, the carbon fibers are introduced into the doctor blade in particular in such a way that a continuous electrical conduction path is created, for example in that the individual fibers are only slightly spaced in the reinforcement layer, fiber contacts between separate fibers are created, for example by the fibers being Fleece or fabric are present, or fibers or threads are present, which consistently extend over the height of the

Extend doctor blade and thus enable electrical derivation from the end of the doctor blade facing the doctor blade edge to the opposite doctor blade end fixed on a doctor blade holder. It goes without saying that the individual fibers can optionally consist of a large number of individual filaments. Without being bound by theory, it is assumed against the fact that when the doctor blade is guided under pressure via the transmission means used in the respective printing process, for example a printing screen, the doctor blade can generate electrostatic charges. These can be significantly determined depending on the boundary conditions of the respective printing process, for example by the feed speed and contact pressure of the doctor blade, the printing medium used, the properties of the printing screen, etc. It is assumed here that such electrostatic charges lead to irregularities in the printed image, such as, for example, increasing the tendency of the printing medium to spatter or causing irregularities in the application of pressure medium to the transfer medium or the passage of the printing medium through a printing screen or the like. Surprisingly, it was found that the arrangement of the carbon fibers. a significantly more uniform print image on the respective carrier, such as, for example, a paper web to be printed, can be produced in the reinforcement layer. Surprisingly, the printed image can also be significantly improved if only the reinforcement layer spaced from the soft elastic doctor edge is made electrically conductive, for example by using carbon fibers, or if in the area of the doctor edge the electrically conductive reinforcement layer on both sides of layers with significantly lower conductivity is included. It is assumed that the electrostatic charges can be dissipated from the knife edge over the printing medium to the reinforcing layer containing carbon fibers and through this to the doctor holder.

The reinforcement layer provided with carbon fibers thus preferably extends from the narrow side of the doctor facing the doctor edge over its height to the holding area of the doctor to be fixed in a doctor holder.

It was also found that when using invented squeegees according to the invention with carbon fiber-containing reinforcing layers, the printing process as a whole is more uniform and trouble-free, which also includes the process steps which take place after the printing of the carrier, such as the ejection of the printing carrier such as, for example, a sheet of paper, a plastic film or the like from the printing press.

One, several or all of the reinforcement layers with the above-mentioned features can only be provided in the area of the doctor edge that can be applied to the printing screen, the one, several or all layers can also extend over a larger area, e.g. extend more than 25% or more than 50% of the height or over the entire height of the squeegee. The reinforcement preferably also extends over the entire length of the squeegee.

One or more or all of the reinforcement layers preferably form a continuous layer on the soft-elastic doctor part, which is preferably congruent with the dimensions of the soft-elastic doctor part. Alternatively, one, several or all of the reinforcement layers can also extend in height above the soft-elastic squeegee part and serve, for example, as a fastening area for clamping the squeegee in a squeegee holder, so that the squeegee holder does not attack the soft-elastic part of the squeegee. This applies in particular to the reinforcement layer of the highest strength and / or bending stiffness.

The soft-elastic doctor blade layer having the doctor blade edge can likewise extend over the entire height of the doctor blade, it can optionally also end below the holding area of the doctor blade and, for example, extend over less than 75% or less than 25% of the doctor blade height.

The reinforcement can in particular partially or completely have fibers, in particular carbon fibers, which are in the form of a Fabric, net, fleece, mat, rovings and / or as individual ^threads are present. In this case, a network is understood to mean a flat structure with threads crossing one another, the threads being able to be connected to one another directly, ie independently of a matrix, or by means of a matrix material surrounding the threads, the threads touching one another, in particular in the crossover points can be spaced apart. The fibers can also be cut fibers or used as short fiber prepregs.

The fibers can have diameters of 1 micrometer to 1 mm, preferably 5 - 100 microns, more preferably 10 - 20 microns comprise ^', wherein lesser or greater for certain applications and fiber diameters can be used.

In the case of carbon fibers in particular, the individual filaments of the fibers can have a diameter of 1 micrometer to 25 micrometers, preferably 4 to 10 micrometers. The individual filaments can be combined to form threads, for example a thread can have a number of 500 to 6000, for example 2500 to 3500 individual filaments, which can be folded. Independently of this, the threads (fibers) can have a thread weight of 50 to 500 tex (1 tex = 1 g / 1000 running meters of the thread), preferably approx. 100 to 300 tex, for example approx. 200 tex. It goes without saying that the thread weight also has an influence on the electrical properties of the doctor blade. The basis weight of the carbon fiber material, e.g. B. carbon fiber fabric, can be approximately 50 to 500 g / m ² , preferably 100 to 300 g / m ² , particularly preferably approximately 120 to 240 g / m ² .

Preferably, there is a carbon fiber fabric, wherein in the warp and / or weft 1 to 10 or to 20 threads / cm, preferential example 2 to 6 threads / cm, for example 3 to 5 strands / cm turned ^¬ sets. It goes without saying that other carbon fiber sheet-like structures, for example in the form of woven or non-woven fabrics, may also be produced, for example, which have, for example, the same electrical properties as the above-mentioned carbon fiber fabrics.

If the threads are in the form of a net or woven fabric, this fabric can have a mesh size of 0.1 to 5 or 10 mm, but depending on the application, it can also be larger or smaller, preferably approximately 0.5 to 2 mm, in particular approximately 1 mm exhibit. The corresponding dimensions can also exist for the distance from individual fibers or fiber bundles which do not cross one another, the distances relating to the bundle longitudinal axes relating to the fiber bundles.

The reinforcement according to the invention can be arranged on at least one flat outside of the squeegee, in particular on exactly one outside, and / or inside the squeegee, with the reinforcement partially or completely on both sides of profiled strips made of flexible elastomer, each preferably with a squeegee edge that can be placed on a printing screen are provided, can be surrounded. The reinforcement is arranged on the back of the doctor blade in the feed direction of the doctor blade. The squeegee edge that can be placed on the printing screen is arranged on the profiled strip made of flexible material.

The reinforcement advantageously has at least partially fibers that extend parallel to the squeegee edge that can be placed on the printing screen, as a result of which the squeegee edge can be stiffened uniformly over the squeegee length. In contrast to a nonwoven, the fibers can extend practically over their entire length parallel to the longitudinal direction of the doctor blade. Alternatively or additionally, the reinforcement can have fibers which extend transversely to the longitudinal direction of the squeegee, for example at an angle of> 10 or 30 °,> 60 ° or perpendicular to this ser. The reinforcing fibers extending parallel and / or transversely to the longitudinal direction of the doctor blade can each extend by more than one, two, five or ten times the doctor blade thickness, the mean doctor blade thickness or, based on a selected cross section, parallel to the doctor blade edge in the direction mentioned above, or over the entire extent of the doctor blade in the respective direction, ie for example over the entire doctor blade length or doctor blade height.

The average length or minimum length of the reinforcing fibers can correspond to the single, double, five or ten times the doctor blade thickness based on the average doctor blade thickness or based on the doctor blade thickness at a predetermined point, or the extension of the doctor blade in the fiber longitudinal direction.

It has proven to be particularly advantageous if the doctor blade has different bending stiffnesses in different directions of the main doctor blade plane. In particular, the bending stiffness of the doctor blade in the longitudinal direction can differ from the transverse stiffness, ie the stiffness transverse to the longitudinal direction, in particular perpendicular to it. The different stiffnesses can be caused by different basis weights of the reinforcement material in the different doctor blade directions (ie the proportion by weight of the fibers with a certain extension direction to the total weight of the reinforcement fibers of this layer or to the total weight of the reinforcement layer), use of reinforcement material of different stiffnesses, for example due to different fiber types or different fiber diameter and / or different fiber lengths and different structure of the reinforcement material, such as a different mesh size. Due to the different stiffnesses in different doctor blade directions, in particular in the longitudinal direction of the direction that can be applied to the printing screen and in the direction perpendicular thereto, the doctor blade can be adapted particularly easily to different requirements, for example to the restoring force of the doctor blade when force is applied. impact against the print support supporting the printable print carrier on the one hand, which is essentially determined by the rigidity in the transverse direction, and adaptation to the contour of the printing screen over the length of the doctor blade on the other hand, which is determined in particular by the doctor blade rigidity in the longitudinal direction thereof. The sectional stiffness of the doctor blade edge can also be influenced by the different stiffnesses of the doctor blade if the stiffness is set in different directions, for example by different fiber weights or different fiber types.

The bending stiffness of the doctor blade in the longitudinal direction is particularly advantageously less than the bending stiffness over the height of the doctor blade.

The ratio of the bending stiffness of the doctor blade and / or the reinforcement in the longitudinal direction to the bending stiffness in a direction perpendicular thereto, which lies in the main doctor blade plane, can be in the ratio of 20: 1 to 1.1: 1 or 1: 1.1 vary up to 1:20, preferably in the range from 5: 1 to 1.5: 1 or 1: 1.5 to 1: 5, particularly preferably in the range from 3: 1 to 2: 1 or 1: 2 to 1: 3 The bending stiffness of the doctor blade is essentially determined by the bending stiffness of the reinforcement, but the bending stiffness is not directly proportional to one another due to the composite structure of the doctor blade.

If the reinforcing fibers are carbon fibers, the fiber types HM1 (high modulus 1), HM2 (high modulus 2), HST (high strain) - and / or IM (intermediate type) can be used. in the

In the case of aramid fibers, the types HM (high modulus) and / or LM (low modulus) can be used.

Regardless of the type of fiber, but especially in the case of carbon and / or plastic fibers such as aramid fibers, the fibers have one, several or all reinforcing preferably have a tensile strength of> 3500 MPa, preferably> 3700 MPa, particularly preferably> 4000 MPa. The modulus of elasticity of the reinforcing fibers is preferably> 100 GPa, preferably> 200 GPa, in particular> 300 GPa.

The elongation at break of the reinforcement fibers of one, several or all of the reinforcement layers is preferably <3%, particularly preferably <2.5 or 2%, in particular <1.5% or <0.5%. The fibers of one, several or all of the reinforcement layers preferably have a modulus of elasticity which is greater than that of E-glass fibers or that of R-glass fibers.

The fibers preferably have anisotropic properties such as can arise, for example, by producing the fibers with stretching.

Fibers are preferably contained in at least one reinforcement layer, which have a higher tensile strength and / or a higher modulus of elasticity and / or a lower elongation at break compared to glass fibers (E or R glass fibers), preferably with a simultaneous reduction in density.

The fiber content in one, several or all of the reinforcement layers, which is different from glass fibers, can be> 5%,> 20%,> 50 or 75%, preferably> 95% or 100%. This content can refer to a single reinforcement layer or overall reinforcement.

Preferably, the reinforcement adjacent to a first armouring layer having a first fiber adjacent preferably to the soft elastic blade layer having blade edge, a second layer on the same side of the soft elastic blade ^¬ part on which the first layer directly be ^¬ is preferably nachbart, wherein the reinforcing fibers of the second layer contain or are glass fibers. The shift can do one Glass fiber content of ≥ 2 wt .-%, preferably ≥ 5 to 10 wt .-% or ≥ 25 or 50 wt .-% based on the layer weight or the fiber weight of the layer. The fibers are preferably exclusively glass fibers.

The glass fibers may form or be present as individual fibers including ^'or fiber bundle in another above-mentioned form a coherent sheet, eg in the form of a net, grating and / or fleece. The first layer preferably contains no glass fibers.

The fabric is preferably assembled in the reinforcement matrix. This ensures a defined arrangement of the fibers relative to one another, for example the orientation of the fibers in one or more preferred directions in preferably defined proportions or basis weights of the fibers of the multiple preferred directions relative to one another, and creates the possibility of a standardization of the structure. The preferred directions can in particular be the longitudinal direction of the doctor blade and / or a direction that is perpendicular or transverse to it, preferably running in the doctor blade plane.

The reinforcement layer containing glass fibers is particularly preferably arranged so that it faces the outside of the doctor blade with respect to the first or all other reinforcement layers. As a result, there is an outer reinforced layer with high impact strength, whereby inner reinforcement layers can be optimized with regard to other properties such as the bending stiffness with regard to the requirements of a doctor blade. If necessary, the outermost reinforcement layer can also partially or completely contain other fibers, so that this layer has a higher impact resistance and / or better absorbency for resin than at least one or all reinforcement layers located further inside.

This most external reinforcement layer can be ner or several other non-reinforced cover layers.

The two or more adjacent reinforcement layers of the squeegee can be permanently connected to one another regardless of the matrix material surrounding the reinforcement fibers, preferably by a connection by means of fibers, for example by sewing. In particular, a fabric of a first reinforcement layer lying further inside can be sewn with a glass fleece of a reinforcement layer lying further outside.

The weight per unit area of the carbon fiber fabric or the plasticases or fibers further defined according to claim 1 to the weight per unit area of the glass fiber fabric (g / m ² ) can be in the ratio of 1: 1 to 10: 1 or 20: 1 or more, preferably 3: 1 up to 7: 1. The two reinforcement layers mentioned are preferably arranged immediately adjacent to one another, but an intermediate layer can optionally also be provided, which can contain or be free of fibers.

The outermost reinforcement layer preferably has a fiber structure, for example in the form of a fleece or short fibers, which, after penetration with a resin, forms a smoother structure than at least one reinforcement layer located further inwards or the reinforcement layer adjacent to the inside. The latter preferably has a higher bending stiffness and / or strength than the reinforcement layer located further out. The ratios of the bending stiffness and strength of the layers can be determined, for example, by incremental layer removal, possibly including layer removal of the flexible profile strip. In this way, a squeegee with high rigidity can be created with a relatively smooth outer surface in the area of the reinforcement, which can be easily cleaned of the printing medium and can be clamped in a defined manner in the squeegee holder. Arranged on one or both sides of the soft elastic blade strip reinforcing layers may each have a total thickness or ^'single strength from 2.5 to 50%, preferably 5- 30% or 5-50%, particularly preferably 10-20% of the blade thickness exhibit ..

The doctor blade can have a thickness of 1 to 10 mm or up to 15 mm, preferably approximately 4 mm to 10 mm, without being limited to each.

The doctor blade can in particular represent the shape of a surface piece with plane-parallel front and back sides, e.g. in the form of a flat strip of uniform thickness.

The fibers of the reinforcement layer are preferably embedded in a resin which is different from the material of the soft-elastic squeegee part, which provides the squeegee edge which can be applied to a pressure medium transmission means such as a printing screen. In particular, the soft-elastic doctor part can consist of a thermoplastic material. The resin surrounding the reinforcing fibers can be a non-thermoplastic, for example thermosetting, material. Independently of this, the matrix material of the reinforcement layer can be a polyurethane, for example Adipren (trade name of the Du Pont company) or Vulkollan (trade name of the Bayer company). The carbon fibers are preferably embedded in a polyurethane matrix. The material of the soft, elastic doctor blade layer which has the doctor edge can optionally also be a polyurethane. The base material of the soft-elastic doctor blade layer and one or all of the reinforcement layers, in particular the reinforcement layer immediately adjacent to the soft-elastic doctor blade layer, can also be the same.

The soft elastic material can have a hardness of 50 to 95 Shore A, in particular 65 to 80 Shore A. For connection of the soft-elastic squeegee part with the reinforcement, one or both parts can be pretreated to improve the adhesion before the connection, in particular roughened and / or provided with an adhesion promoter.

The reinforcing layer, which can contain fibers and which adjoins the soft, elastic doctor blade layer provided with the doctor edge, can have a hardness of 80 to 150 Shore A, for example 90 to 120 Shore A, without being limited to this.

The squeegee according to the invention results in a material which is easier to work with, particularly in terms of occupational safety and manufacturing technology, which is easier to dispose of and also has a higher strength and / or elasticity when carbon fibers are used as reinforcing fibers.

The reinforcement provided on each side, namely the front and / or back of the doctor blade, can each have exactly two or exactly three but, depending on the requirements, also more or fewer reinforcement layers, which can preferably be designed differently with respect to the reinforcement on one side , The number of reinforcement layers on the front and back of the doctor blade can be different. The reinforcement of the back of the doctor blade preferably consists of exactly two or exactly three reinforcement layers.

The front and / or back doctor blade layer preferably have a carbon fiber content of <25% by weight, preferably <5-10% by weight, particularly preferably <1-2% by weight, based on the total weight of the respective doctor blade layer or based on the total fiber weight of this doctor blade layer, particularly preferably the front and back doctor blade layers are free of carbon fibers. It goes without saying that the reinforcing layer, which directly supports the doctor layer having a doctor edge that can be applied to a printing screen, can also adjoin on the opposite side to a soft-elastic doctor layer, which can have essentially or exactly the same properties as here for those with the soft edge of the doctor blade provided soft doctor blade layer are described. If necessary, the soft-elastic doctor blade layer adjoining the reinforcement layer on the back can also have a further doctor blade edge that can be placed on a printing screen or another printing medium transfer medium. The doctor blade layer comprising the doctor blade edge and / or a further soft-elastic doctor blade layer provided on the opposite side of the reinforcement layer can have a minimum thickness of 0.5-1 mm, preferably a thickness of 2 2 or 4 4 mm, so that the deformation properties of the doctor blade edge essentially or completely determined by the soft elastic doctor layer. Optionally, further layers can follow the soft-elastic doctor blade layer covering the reinforcement layer on the back, for example a further fiber-containing, in particular carbon fiber or glass fiber-containing reinforcement layer or other layers. However, the squeegee preferably consists of a soft, elastic squeegee layer with a squeegee edge, an adjoining fiber-containing, in particular carbon-fiber-containing reinforcement layer, an essentially carbon-fiber-free reinforcement layer adjoining the rear side and, if appropriate, a cover layer applied thereon.

Preferably, the doctor blade a printed layer beispiels- .weise of paper, a nonwoven fabric or any other suitable printable material, which is preferably connected to the armouring ^• matrix with the squeegee. The fleece can be, for example, the glass fleece mentioned above or another suitable fleece. The printed layer is thus preferably resin-permeable or impregnable with resin, at least under pressure. The printing may include technical data, advertising or the like. overall if necessary, the printed layer, in particular as a paper layer, can be laminated with a fleece.

The printed layer can be arranged visibly between the top of the doctor blade elastomer and the uppermost reinforcement layer or above the uppermost reinforcement layer and is preferably covered on the upper side by a further layer. The top layer of the doctor blade is preferably a synthetic resin layer, which can cover the printed layer directly or can also be provided in the absence of the printed layer.

The attachment area of the squeegee, by means of which the squeegee can be fixed in a squeegee holder, is preferably designed as an electrical contact area in such a way that, compared to a squeegee area closer to the squeegee edge, it is easier for electrical charges to flow away from at least one reinforcement layer to the squeegee front and / or squeegee back ,

Such a fastening area can be provided, for example, in that layers which adjoin the front and / or rear side of a doctor blade layer with high electrical conductivity, for example a doctor blade layer containing carbon fibers, are at least partially or completely removed at least on the holding region of the doctor blade, so that these enable an electrical charge discharge can be contacted with the squeegee holder, for which it may be sufficient to fix the squeegee as intended in the squeegee holder. For example, a cover layer containing glass fibers on the back can be removed in order to expose an adjacent reinforcement layer containing carbon fiber. Any additional metallic leads may not be necessary. The cover layer can also be removed unevenly, for example tapering in thickness towards the doctor edge of the clamping end of the doctor. All layers are expediently up to. to a layer with the highest e- The electrical conductivity of the doctor blade is at least partially removed in the holding area of the doctor blade. It goes without saying that, on the other hand, the cover layer in the area accommodated by the doctor blade holder can likewise have increased electrical conductivity than the cover layer area arranged outside the holding area of the doctor blade or adjacent to the doctor blade edge. For this purpose, for example, the cover layer can only be made sufficiently electrically conductive at the level of the holding area of the doctor blade, for example by an increased content of electrically conductive fibers such as carbon fibers or the like. The cover layer should then be electrically conductively connected to the doctor blade layer of high electrical conductivity, for which purpose the layers mentioned can directly adjoin one another or insulating intermediate layers can be bridged in an electrically conductive manner.

The doctor blade holder thus preferably also consists of an electrically conductive material in order to be able to discharge electrical charges from the doctor blade, for which purpose the doctor blade holder can consist of a metallic material such as aluminum or a sufficiently high content of carbon in the form of carbon black, carbon fibers or the like can have. The squeegee holder preferably consists entirely of the material mentioned, but if necessary, locally limited contacting areas can also be present.

If necessary, electrical contacting of the doctor blade layer with high electrical conductivity can also take place in that this layer or a partial region thereof, such as fibers with high electrical conductivity, protrude from the doctor blade narrow side, for example from the doctor blade narrow side of the holding region, so that these regions are electrical by the doctor blade holder are contactable. Preferably, a flow of the electric charges by the Kontaktie- approximate range of blade front and / or rear squeegee side ^■ relieved. The doctor blade preferably has a flexible electrical lead on the rear side opposite the doctor blade edge, which can be applied to a printing screen at least over part or the entire doctor blade length. The electrical lead can be attached to the doctor blade in a non-detachable or detachable manner. The electrical discharge can also have carbon fibers to increase the conductivity. The length of the electrical discharge line can be selected in such a way that, given the customary intended setting angle of the doctor blade relative to the printing screen or another printing medium transmission means, there is a linear contact with the printing screen in relation to a given cross section of the doctor blade. The electrical discharge line is preferably so flexible that it exerts no or no appreciable compressive force on the printing screen, even when the squeegee is different in relation to a printing screen. The electrical lead is preferably in direct electrical contact with a doctor blade layer of high electrical conductivity, in particular a layer containing carbon fibers. The electrical derivation can only extend over a comparatively small part of the doctor blade length or over the entire doctor blade length.

The electrical discharge line and / or the doctor blade layer with high electrical conductivity or the doctor blade as a whole is preferably free of metal fibers or metallic particles.

To produce the doctor blade, an elastomer forming the soft, elastic doctor blade strip can be pressed into a mold to which the preferably pre-assembled layer of the reinforcing material is applied, after which the mold is closed. A synthetic resin forming the reinforcing matrix can then be pressed into the mold under pressure, for example under compressed air, so that the synthetic resin contains the reinforcing material containing fibers. At the same time, the reinforcement material is connected to the soft elastic layer. The resin should have a particularly high breaking strength. The printed layer can be placed on the fiber-containing reinforcing material before the synthetic resin forming the reinforcing matrix is pressed in, so that when the synthetic resin is pressed in, the printed layer is simultaneously connected to the reinforcing material in a one-step process step. If necessary, apply a printed layer after pressing in the synthetic resin and then provide it with a cover layer. The squeegee can be produced in a particularly well-defined thickness by the production in a mold.

Furthermore, the invention relates to a squeegee holder with a squeegee according to the invention and also to a print head with a squeegee holder and a squeegee arranged in the squeegee, wherein preferably at least one reinforcement is provided in the feed direction of the squeegee at the rear. The holder and doctor blade are preferably designed such that there is an electrical conductivity path with sufficient electrical conductivity to allow electrostatic charges in the area of the doctor blade edge to flow off via the doctor blade holder into an electrical potential sink.

Furthermore, the invention relates to a printing method by means of a doctor blade according to the invention, in which a printing medium such as a printing ink is applied to a transfer medium by means of a doctor blade or is printed through it. The transmission means can be a printing screen, a printing plate which can be used in a gravure printing process or the like. The printing medium is then printed onto a carrier, such as a paper web, plastic film or the like to be printed _, by transferring it from the transfer medium to the carrier. In particular, in order to avoid electrostatic charging of the doctor blade in the area of the doctor blade edge that can be applied to the transfer medium, at least one doctor blade layer is provided with fibers such as carbon fibers that increase the electrical conductivity of the doctor blade. The fiber content and the arrangement of the fibers in the reinforcement layer are selected such that under electrostatic charges that interfere with the conditions of the printing process can be avoided, as a result of which the quality of the printed image can be significantly improved.

The invention is described below by way of example and explained using the figures as an example. Show it:

1 is a perspective view of a doctor blade arranged in a doctor blade holder,

2 shows a perspective illustration of a doctor blade according to the invention arranged in a doctor blade holder according to a second embodiment,

3 shows a schematic view of a doctor blade according to the invention in a printing arrangement, and

4 shows schematic cross-sectional representations of different designs of doctor blades according to the invention.

1 shows a squeegee 2 which is arranged in a squeegee holder 1 and which can be pressurized by means of a rail 3 over its entire length in the holder 1 by means of clamping elements 4. The doctor blade 2 has an elongated profile strip 5 - a soft elastic material, in particular a thermoplastic material such as, for example, a polyurethane with a hardness of 70 Shore A, the doctor blade edge 7 arranged on the front side 6 viewed in the feed direction being connected to a printing screen for distributing a printing medium can be created. On the back of the profile strip 5, a first reinforcement layer 7 is provided, which supports the soft elastic profile strip 5 on the back, which in turn is covered over the entire area by a second reinforcement layer 8. The individual layers of the composite system, namely the flexible part 5, the first and the second reinforcement layers 7, 8, are each congruent here, connected to each other and are grasped at their upper end by the doctor holder.

The reinforcement layer 7 consists of carbon fibers with a tensile strength of approx. 3000 MPa, a modulus of elasticity of approx. 300 GPa and an elongation at break of approx. 1%, but other carbon fibers can also be used advantageously. The fiber diameter is approximately 5 to 7 μm, the fibers each extend over the entire doctor extension in the respective fiber direction.

In the fabric produced by the carbon fibers, the fibers 12 extend parallel to the doctor edge 7 and the fibers 13 parallel to the side edge 9, which is perpendicular to the doctor edge 7. The fibers form a mesh network with a width of approx. 1 x 1 mm. The fibers are embedded in a thermosetting resin forming a matrix 10, in the exemplary embodiment made of a thermosetting polyurethane. The individual crossing fibers of the fabric produced by them are only connected to one another by the matrix material, it being possible for these to rest against one another at the crossing points or in areas of their longitudinal extent.

The reinforcement layer 8 consists of a glass fleece 11 which is impregnated with a resin without pores, according to the exemplary embodiment the same resin as the material of the matrix 10

Glass fleece is sewn to the carbon fibers of the reinforcement layer 7. The fleece can be printed or covered with a printed layer.

The reinforcement layer 7 has doctor blades of different basis weights of the carbon fibers in the longitudinal and transverse directions, which here are in a ratio of 1/3 to 2/3. The different basis weight is generated by an increased number of fibers with the same fiber diameter. Due to the different basis weights, the doctor blade has a comparatively small lengthwise direction and its transverse direction or height has a comparatively high bending stiffness, the bending stiffness being approximately in the ratio of 1/3 to 2/3. As a result, the doctor blade is comparatively rigid with respect to the application of force to the printing screen, but is comparatively flexible with regard to a contour adaptation to the surface of the printing screen, so that the length of the doctor blade ei. it constant print image regardless of the pressure of the doctor blade on the printing screen can be achieved.

The soft-elastic doctor blade part is supported by the reinforcement layer 7, with both the tensile strength and the elastic modulus of the fibers exceeding the properties of the glass fibers. In this way, a particularly long-term behavior of the doctor blade, which is particularly excellent under dynamic and static loading, and thus a very constant print image can be obtained over very long periods of time. The glass fleece 11 also forms a relatively smooth rear side 16 of the doctor blade in relation to the reinforcement layer 7, as a result of which the mounting thereof in the doctor blade holder is improved and cleaning of the doctor blade is facilitated. Furthermore, due to the composite structure, the doctor blade has a particularly smooth cut surface when the doctor blade is cut out of a larger plate material. The arrangement of the glass fleece also allows the resin of the reinforcement layer 7, 8 to be distributed more quickly over the surface, as a result of which the production process is accelerated.

To manufacture the doctor blade, the sheet of reinforcement fibers according to the exemplary embodiment, the glass fleece sewn onto the carbon fiber grid, can be spread out flat in a form into which a hardening thermosetting resin is poured, distributed and then pressed into the fiber structure by high compressive forces until it penetrates it without pores. The resin is then cured by suitable measures. The soft-elastic, preferably thermoplastic, part of the doctor blade is applied in layers to this reinforcing structure, for example as a prefabricated layer or through Application as a melt, for example by extrusion, and connected over a large area by suitable measures, optionally with the aid of an adhesion promoter.

Fig. 2 shows a doctor blade according to the invention, wherein the same features are given the same reference numerals. With the only difference from the doctor blade according to FIG. 1, the soft elastic part 5 and the second reinforcement layer 8 do not extend over the height of the reinforcement layer 7, the upper free end of which can be fixed in a doctor blade holder. According to a further alternative, layer 8 can also have the height of layer 7.

If necessary, the reinforcement layer 8 may also be missing in the two doctor blades of FIGS. 1 and 2.

FIG. 3 shows a squeegee 20 according to the invention in a printing arrangement with a squeegee holder 21, a printing screen 22 and a support to be printed in the form of an object 23 arranged underneath the printing screen

Printing ink 24 is applied through the printing screen 22 to a support, ie the object 23 to be printed. By pressing the squeegee edge 25 while moving the squeegee in the direction of the arrow, electrostatic charges can be generated which influence the properties of the printing medium and interfere with the printing process as a whole, such as particles of the printing medium that jump away. The doctor blade 20 can be designed in accordance with the exemplary embodiments in FIGS. 1, 2 or 4, without being limited to this. The doctor blade 20 also has the doctor blade edge next to it _. e 25 having soft-elastic doctor blade layer 26 and - the reinforcing layer 27 supporting this on the back a glass fiber cover layer 28. The glass fiber cover layer is removed on the upper doctor end, ie opposite the doctor edge 25, so that the reinforcing layer 27 containing carbon fiber is exposed and can be electrically contacted by the doctor holder 21. The squeegee points here also have a high carbon content, for example in the form of carbon fibers or carbon black or other suitable substances. The doctor blade is also provided on the end face facing the doctor blade edge 25 with an electrical lead 29 in the manner of a sliding contact, which likewise essentially consists of carbon fibers which are connected to the reinforcing layer in an electrically conductive manner. Pins are provided for this purpose, if necessary the cover layer 28 can also be removed in partial areas. The printing medium 24 surrounds the doctor blade not only in the area of the doctor blade edge but also partially on the narrow side 30 adjacent to the doctor blade edge, at least with a film, so that electrostatic charges are transferred to the doctor blade holder via the reinforcement layer 27 can.

The carbon fibers of the reinforcement layer 27 are in the form of a carbon fiber fabric with a weight per unit area of approximately 200 g / m ² , the fabric fibers being arranged in warp and weft with a density of 5 threads (fibers) per cm. It goes without saying that the fibers of this type are made up of a large number of filaments, for example approximately 3000 filaments per thread. The thread weight in warp and weft is approx. 200 Tex. A sufficient electrical conductivity of the reinforcing layer can be provided by such a carbon fiber fabric in order to avoid electrostatic charges.

In Figure 4 further doctor blades according to the invention are shown as an example. FIG. 4 a shows a doctor blade 40 with a soft-elastic doctor blade layer 41 with a doctor blade edge 42, a fiber-containing, in particular carbon fiber-containing reinforcing layer 43, which supports the doctor blade layer 41 on the rear side and in turn is surrounded on the back side by another soft-elastic doctor blade layer 44. Doctor blade layer 44 can have essentially the same chemical and / or mechanical properties as doctor blade layer 41. For example, doctor blade layer 44 have a differently designed doctor blade edge 45.

FIG. 4b shows a doctor blade corresponding to the doctor blade according to FIG. 4a, with the difference that the two soft-elastic doctor blade layers 46, 47, one or both of which can have doctor edges that can be applied to a printing screen, the reinforcing layer 48 only over part of the height thereof surround so that only the reinforcement layer provides the holding area for fixing the doctor blade in a doctor blade holder. Optionally, in a modification of the doctor blade according to FIG. 4b, the reinforcement layer 48a can be provided on the front and / or rear side with a cover layer 49, which can have glass fibers, in particular in the form of a glass fleece, the cover layer extending up to the upper narrow doctor side 50 or can end below the same (Fig. 4c).

l o squeegee, especially for screen printing

LIST OF REFERENCE NUMBERS

1 squeegee holder

15 2 squeegees

3 rails

4 clamping element

5 Soft elastic part

6 front

2 0 6a squeegee edge

7 First reinforcement layer

8 Second Ar ieruήgsschicht

9 side edge

10 matrix

2 5 11 glass fleece

12 carbon fiber lengthways

13 carbon fiber in the transverse direction

20 squeegees

21 squeegee holder

3 0 22 pressure screen

23 object

24 printing medium

25 squeegee edge

26 reinforcement layer

35 27 electrical discharge topcoat

narrow side

doctor

squeegee layer

squeegee edge

reinforcing layer

squeegee layer

Squeegee edge, 47 squeegee layer a squeegee

reinforcing layer

topcoat

narrow side

Claims

Squeegees, especially for screen printing

1. Doctor blade, in particular for screen printing, with at least one elongated profile strip (5) made of a soft-elastic material, the doctor blade in the area of the soft-elastic profile strip having a doctor blade edge (6) that can be placed on a printing screen and runs in the longitudinal direction and one that extends transversely to it extending side edge (9), wherein a reinforcing layer (7, 8) is provided, which is connected to the soft elastic profile strip and increases the rigidity of the squeegee, characterized in that the reinforcement (7) contains fibers and that the fibers are at least partially carbon fibers and / or plastic fibers and / or fibers that have an elastic modulus> 100 GPa and / or an elongation at break <3%.

2. Squeegee according to claim 1, characterized in that the reinforcing layer containing the fibers has an electrical conductivity which is sufficient during a printing process to electrostatically charge the squeegee and / or one which comes into direct contact with the squeegee and by means of the Squeegee due to the interacting printing screen least to prevent as far as possible.

3. Doctor blade according to claim 1 or 2, characterized in that the reinforcement has at least two different reinforcement layers (7, 8) and that at least one or two of the reinforcement layers contain fibers.

4. Doctor blade according to one of claims 1 to 3, characterized in that the fibers of the reinforcement are at least partially in the form of a mesh, fabric, fleece and / or individual threads.

5. Squeegee according to one of claims 1 to 4, characterized in that the fibers of the reinforcement form a flat structure with a mesh size of 0.1 to 5 mm.

6. Squeegee according to one of claims 1 to 5, so that at least one or all reinforcing layers (7, 8) are congruent with the profile strip (5) made of flexible material.

7. Squeegee according to one of claims 1 to 6, characterized in that the reinforcement (7) contains fibers that extend from the area of the squeegee edge (2a) that can be placed on the printing screen to a fastening area (14 ) extend the doctor blade continuously or form a continuous electrical conductivity path while making contact with other fibers.

8. Squeegee according to one of claims 1 to 7, characterized in that the fastening area (14) of the squeegee, by means of which the squeegee can be fixed in a squeegee holder, is used as an electrical contacting device. is richly designed such that, compared to a doctor area adjacent to the doctor edge, it is easier for electrical charges to flow away from at least one reinforcement layer to the doctor front and / or doctor back.

9. Squeegee according to one of claims 1 to 8, characterized in that a flexible electrical lead (15) is fastened on the opposite side of the squeegee to the squeegee edge and can be applied to a printing screen over at least part or the entire length of the squeegee.

10. Squeegee according to one of claims 1 to 9, characterized in that at least two different directions of the plane spanned by the squeegee edge (6) and the side edge (9) have different bending stiffnesses of the squeegee.

11. Doctor blade according to claim 10, characterized in that the different bending stiffnesses in different directions are generated at least in part by different basis weights of the fibers of the reinforcing layers extending in different directions.

12. Doctor blade according to one of claims 1 to 11, so that the bending stiffness with respect to the longitudinal direction of the doctor blade is smaller than the stiffness perpendicular to it.

13. Doctor blade according to claim 12, characterized in that the ratio of the bending stiffness of the doctor blade in the longitudinal direction and perpendicular to it in the range from 20: 1 to 1.1: 1 or in the range from 1: 1.1 to 1: 20 lies.

14. Doctor blade according to one of claims 1 to 13, characterized in that the reinforcing layer has fibers with a tensile strength> 3500 MPa and / or with an elastic modulus of> 100 GPa and / or an elongation at break <3%.

15. Squeegee according to one of claims 1 to 12, characterized in that the reinforcement in one and / or in different layers has reinforcement fibers with different contents (in percent by weight based on the weight of the reinforcement layer) and / or different types or compositions.

16. Squeegee according to claim 15, characterized in that a first reinforcing layer facing the soft-elastic profile strip and a second further spaced reinforcing layer is provided and that the fibers of the second reinforcing layer are partially or completely glass fibers.

17. Doctor blade according to one of claims 1 to 16, characterized by the fact that the fibers of the reinforcement layer lying outermost of the soft elastic profile strip are present as a fleece and / or that fibers with shorter fiber length and / or are present in the outermost reinforcement layer. or smaller fiber diameter than a further inner reinforcement layer.

18. Doctor blade according to one of claims 1 to 17, characterized in that two or more fiber-containing reinforcement layers are provided, each having a matrix material surrounding the reinforcement fibers with the same basic component, and that the soft-elastic part of the doctor blade consists of one of these different material.

19. Doctor blade holder with a doctor blade according to one of claims 1 to 18.

20. Doctor blade holder with a doctor blade according to one of claims 1 to 18, characterized in that the doctor blade holder (1) has a holding area for fixing the doctor blade, that the holding area consists at least partially of an electrically conductive material and that a reinforcing layer with a higher electrical Conductivity than that of the soft-elastic profile strip provided with the doctor edge is electrically conductively connected to the holding area.

21. Printing process, in particular screen printing process, in which a printing medium is applied to or pressed through a transfer medium by means of a doctor blade (2), the printing medium being subsequently printed onto a carrier, the doctor blade at least one elongated profile strip (5) made of a soft elastic Material which is provided with a squeegee edge (6) which can be applied to the transmission means and runs in the longitudinal direction of the squeegee, and has a side edge (9) extending transversely thereto, one of which is connected to the soft-elastic profile strip over a large area

Reinforcement (7, 8) increasing the rigidity of the squeegee is provided, the squeegee (2) being guided over the transfer means while the edge of the squeegee abuts against the transfer means, thereby printing the printing medium over or through the transfer means to produce a print image on the carrier , characterized in that the reinforcement (7) contains fibers and that the fibers are at least partially carbon fibers and / or other electrically conductive fibers, that the doctor layer comprising the fibers is electrically conductively bonded to the doctor holder and that the electrical conductivity of the kel is set such that, under the conditions of the printing process for the printed image disruptive electrostatic charges are at least largely avoided.