EP1551631B1 - null - Google Patents

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

The present invention relates to a doctor blade, in particular for screen printing, with at least one elongated profiled strip of a flexible material, wherein the doctor has an attachable to a printing screen, longitudinally extending doctor blade edge and a transverse extending side edge, wherein, a large area with the soft elastic profile strip is provided connected to the rigidity of the doctor blade increasing reinforcement, said reinforcement containing fibers which are at least partially carbon fibers and / or plastic fibers and / or fibers having a modulus of elasticity ≥ 100 GPa and / or an elongation at break ≤ 3%.

Such doctor blade are screen-printed on a printing screen, which may consist of a textile or metallic material, applied, wherein the printing screen to a print carrier (eg, a paper to be printed) by applying pressure above the printing screen arranged doctor can be applied. Under displacement of the squeegee, a printing medium can be applied through the mesh of the printing screen on the print carrier, whereby a flat print image is generated. On the other hand, in screen printing, the doctor blade can also be arranged in a stationary manner and the printing screen, which is designed, for example, as a cylindrical rotary screen, can be moved relative to the doctor blade.

To the squeegee are to produce a high quality printed image high demands on the exact time and place shape of the doctor edges, adjustability of the angle of attack of the squeegee against the printing screen under pressure of the squeegee, solvent resistance to the solvent of Verdruckmediums, homogeneity of the material properties and the local and the life of the doctor blade to provide temporal consistency of physical properties of the doctor blade such as elasticity or stiffness, hardness, swelling properties, etc. Among other things, these properties determine the print medium consumption.

The squeegee must also be able to withstand changing loads such as, for example, contact with the printing screen under deflection of the squeegee or during the movement of the squeegee, as well as under constant loading, e.g. during the printing process under constant force against the printing screen, have an excellent long-term behavior to avoid unwanted temporal or spatial changes of the printed image or frequent Rakelaaustausch. Furthermore, it is often necessary to rework the doctor blade in the area of the doctor edge in order to obtain a defined and as smooth as possible doctor blade edge. Since the squeegee is mostly worked out of larger plate-shaped pieces, the cut surfaces must, if possible, meet the requirements for the squeegee.

The US 4,549,933 describes a multilayer blade with spacers made of uniaxially oriented carbon fibers.

The invention has for its object to provide a squeegee that meets the above requirements in particular.

This object is achieved by a doctor blade according to claim 1. Advantageous developments emerge from the subclaims.

The reinforcement of the doctor blade contains fibers which are at least partially carbon fibers and / or plastic fibers and / or fibers having a modulus of elasticity (modulus of elasticity) ≥ 100 GPa and / or an elongation at break ≦ 3%. The at least one reinforcing layer may comprise such fibers in addition to other fibers or only such fibers. Other fibers may be ≦ 75% by weight, preferably ≦ 50% by weight, more preferably ≦ 25 to 10% by weight of the fiber weight of the reinforcing layer or ≤ 10-20% by weight, preferably ≤ 2-5% by weight or ≤ 1% by weight of the total weight of the reinforcing layer, or be absent, without being limited thereto.

In this way, in each case a reinforcement with excellent long-term behavior with respect to a dynamic and static load is provided, which due to the fiber materials mentioned provides very smooth and easily reworked working surfaces compared with the use of reinforcements consisting of glass fibers. In the case of reinforcing layers with glass fibers, the reinforcing 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 adjoins directly to the soft-elastic doctoring strip provided with the doctor edge in order to support it. The layer immediately adjacent to the soft-elastic squeegee can, based on the total weight of the reinforcing layer or based on the fiber weight of the same, ≤ 10 wt .-% or ≤ 5 wt .-% glass fibers, preferably this layer is at least substantially or completely free of glass fibers ,

By applying the fibers in the reinforcing layer, the doctor blade can be given a well-defined restoring force when pressed against a transfer medium for the printing medium (printing ink), which can be a printing screen but also, for example, a printing cylinder used in gravure printing, so that the printing medium over the life the squeegee can be applied evenly. On the other hand, can be given by the soft elastic doctor blade a particularly well-defined and sealing system of the doctor on the transmission means. Since the fibers are present only in the reinforcing layer, For example, the soft elastic doctor blade edge can be particularly easily adapted to the respective requirements with regard to its geometry, hardness or the like. Since the squeegee edges are often to be processed in the production of the doctor blade or in a post-processing, for example, to be ground with material removal, is made possible by the inventively introduced fibers that are different from glass fibers, a simple post-processing to be applied to a printing screen blade edge.

Preferably, the soft-elastic doctor blade layer and / or the reinforcing layer has no particulate additives, in particular no abrasive particles such as aluminum trioxide, SiC or the like. Preferably, the squeegee is free of particulate additives, in particular abrasive particles, but also particles such as carbon black, fillers such as silica, or the like.

The reinforcement may have two or more adjacently arranged, ie provided on one side of the soft-elastic doctor blade part, different reinforcement layers. Due to the different design of the reinforcing layers, the doctor blade can be particularly easily adapted to the particular requirements, in particular 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 plurality of different reinforcing layers, since, for example, the outer reinforcing layer or the fibers embedded therein are more easily severable and / or have a higher impact strength and the further inner sleeve layer can have, for example, higher strengths. The reinforcing layers of these squeegees, which are not directly adjacent to the soft-elastic squeegee strip, may contain, in addition to or as an alternative to the above-mentioned types of fibers, also glass fibers, both or one of the reinforcing layers also consisting exclusively of one of the abovementioned fiber types, For example, glass fibers, may exist. The glass fiber content of this reinforcing layer may be 5% by weight, ≥ 10% by weight or ≥ 25% by weight, based on the total fiber weight of the layer or based on the total weight of the layer. The layers which delimit the squeegee on the outside, ie the squeegee layer on the front and / or back side, preferably have a lower carbon fiber content than an inner layer, for example a content of ≦ 25% by weight, ≦ 10% by weight or 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 reinforcing layers are preferably carbon fibers and / or plastic fibers such as polyamides, polyesters, polyamide-imides, polybenzimidazoles, polyterephthalates such as aramid fibers (m and / or P-aramid fibers), acrylic fibers, PVC fibers or other suitable fibers.

Carbon fibers have been found to be particularly preferred because of their mechanical and electrical properties. It has been found that by introducing carbon fibers into the reinforcing layer with a sufficient content, the printed image produced by means of the doctor blade on a support can be qualitatively substantially improved. Here, the carbon fibers are introduced in particular in a manner in the doctor blade, that a continuous electrical conduction path, for example, the fact that the individual fibers are only slightly spaced in the reinforcing layer, fiber contacts between separate fibers arise, for example by the fibers as fleece or Fabric present, or fibers or threads are present, which extend continuously over the height of the doctor blade and thus allow an electrical discharge of at the doctor blade edge facing the end of the doctor blade to the opposite, fixed to a doctor blade holder end .. It is understood that the individual fibers may optionally consist of a plurality of individual filaments. Without being bound by theory, it is believed in the case of the pressurized guiding of the doctor blade by means of the transfer means used in the respective printing process, for example a printing screen, electrostatic charges can be generated by the doctor blade. These can be significantly influenced as a function of boundary conditions of the respective printing process, for example by the feed rate 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 of the printed image, such as increase the tendency of the Verdruckmediums to splash or cause unevenness of the pressure medium application to the transfer agent or the passage of the Verdruckmediums by a printing screen or the like. Surprisingly, it was found that the arrangement of the carbon fibers in the reinforcing layer, a significantly smoother printed image on the respective support, such as a paper web to be printed, can be generated. Surprisingly, the printed image can also be significantly improved if only the armor layer spaced apart from the soft elastic doctor edge is electrically conductive, for example by the use of carbon fibers, or if the electrically conductive armor layer is enclosed on both sides by layers of significantly lower conductivity in the area of the doctor edge , It is believed that the electrostatic charges may be dissipated from the squeegee edge to the carbon fiber-containing reinforcing layer through the squeeze medium and through to the squeegee holder.

The reinforcing layer provided with carbon fibers thus preferably extends from the narrow side of the doctor blade facing the doctor edge over its height to the holding region of the doctor blade to be defined in a doctor blade holder.

It has also been found that when using inventive Squeegee with carbon fiber reinforcing layers of the printing process as a whole is more uniform and trouble-free, which also includes the process steps following the printing of the carrier, such as the ejection of the print carrier such as a paper sheet, a plastic film or the like from the printing press.

One, several or all or all of the reinforcing layers with the above-mentioned features can each be provided only in the region of the squeegee edge which 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. Preferably, the reinforcement also extends over the entire doctor blade length.

A multiple or all reinforcing layers preferably form a continuous layer on the soft-elastic doctor blade part, which is preferably congruent with the dimensions of the soft-elastic doctor blade part. Alternatively, one, several or all reinforcing layers can also extend in height over the soft-elastic doctor blade part and serve, for example, as a fastening region for clamping the doctor blade in a doctor blade holder, so that the doctor blade holder does not act on the soft-elastic part of the doctor blade. This is especially true for the reinforcing layer highest strength and / or bending stiffness.

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

The reinforcement may in particular partially or completely fibers, in particular carbon fibers, having in the form of a Tissue, mesh, fleece, mat, rovings and / or present as individual threads. A net is in this case understood as meaning a fabric with threads crossing one another, wherein the threads can be connected to one another directly, ie independently of a matrix, or by a matrix material surrounding the threads, the threads, in particular in the crossover points, touching or being spaced apart from one another could be. The fibers can also be present as cut fibers or be used as short fiber prepreg.

The fibers may have diameters of 1 micrometer to 1 mm, preferably 5 to 100 micrometers, more preferably 10 to 20 micrometers, and it is also possible to use fibers of smaller or larger diameters for certain applications.

In particular, in the case of carbon fibers, the monofilaments of the fibers may have a diameter of 1 micron to 25 microns, preferably 4 to 10 microns. The individual filaments can be joined together into threads, for example, a thread can have a number of 500 to 6000, for example 2500 to 3500 individual filaments, which can be plied. Independently of this, the threads (fibers) can have a thread weight of 50 to 500 Tex (1 Tex = 1 g / 1000 linear meters of the thread), preferably about 100 to 300 Tex, for example about 200 Tex. It is understood that the thread weight also has an influence on the electrical properties of the doctor blade.

The basis weight of the carbon fiber material, for. B. carbon fiber fabric may be about 50 to 500 g / m ² , preferably 100 to 300 g / m ² , more preferably about 120 to 240 g / m ² .

Preferably, a carbon fiber fabric is present in which in warp and / or weft 1 to 10 or to 20 threads / cm, preferably 2 to 6 threads / cm, for example 3 to 5 threads / cm are used.

It is understood that, where appropriate, other carbon fiber fabrics, for example in the form of fabrics or nonwovens, can be produced which, for example, have the same electrical properties as the abovementioned carbon fiber fabrics.

If the threads are in the form of mesh or 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 can. 0.5 to 2 mm, in particular about 1 mm. The corresponding dimensions can also exist for the distance of individual fibers or fiber bundles which do not cross one another, the distances in the fiber bundles referring to the bundle longitudinal axes.

The reinforcement according to the invention can be arranged on at least one flat outer side of the doctor blade, in particular on exactly one outer side, and / or within the doctor blade, wherein the reinforcement partially or completely on both sides of moldings of soft elastic elastomer, preferably each with a can be applied to a printing screen doctor edge are provided, can be surrounded. The reinforcement is arranged on the blade side in the direction of advance of the doctor blade. The squeegee edge which can be applied to the printing screen is arranged on the profiled strip of soft elastic material.

The reinforcement advantageously has at least partially fibers which extend parallel to the squeegee edge which can be applied to the printing screen, as a result of which the doctor edge can be uniformly stiffened over the squeegee length. In contrast to a nonwoven, the fibers can extend practically over their entire length parallel to the squeegee longitudinal direction. Alternatively or additionally, the reinforcement may comprise fibers which extend transversely to the squeegee longitudinal direction, for example at an angle of ≥ 10 or 30 °, ≥ 60 ° or perpendicular thereto. The reinforcing fibers extending parallel and / or transversely to the squeegee longitudinal direction can in each case extend by more than a single, two, five or ten times the doctor blade thickness or, with respect to a selected cross section, parallel to the doctor edge in the respective above-mentioned direction, or via the entire extent of the doctor in the respective direction, ie for example over the entire doctor blade length or doctor height.

The average length or minimum length of the reinforcing fibers may be one to two, five times or ten times the doctor blade thickness based on the average doctor blade thickness or the doctor blade thickness at a predetermined location, or the extension of the doctor blade in the fiber longitudinal direction.

It has proved to be particularly advantageous if the doctor has different bending stiffnesses in different directions of the doctor main plane. In particular, the bending stiffness of the doctor blade in the longitudinal direction of the transverse stiffness, ie the stiffness transverse to the longitudinal direction, in particular perpendicular to this differ. The different stiffnesses may be due to different basis weights of the reinforcing material in the different doctor directions (ie weight of the fibers with a particular direction of extent to the total weight of the reinforcing fibers of this layer or to the total weight of the reinforcing layer), use of reinforcing material of different stiffnesses eg due to different fiber types or different fiber diameter and / or or different fiber lengths and different structure of the reinforcing material such as a different mesh size caused. Due to the different stiffnesses in different squeegee directions, in particular in the longitudinal direction of the pressure screen can be applied and in the direction perpendicular thereto, the squeegee can be particularly easily adapted to different requirements, for example, the restoring force of the squeegee when force against the pressure support supporting the printable support on the one hand, which is determined essentially by the stiffness 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 stiffness in the longitudinal direction thereof. Due to the different stiffnesses of the doctor blade and the sectional image of the doctor blade edge can be influenced, if the stiffness is adjusted for example by different fiber weights or different fiber types in different directions.

Particularly advantageously, the bending stiffness of the doctor blade in the longitudinal direction is smaller than bending stiffness over the height of the doctor blade.

The ratio of the blade stiffnesses and / or the longitudinal reinforcement to the bending stiffness in a perpendicular direction located in the squeegee main plane may be in the ratio of 20: 1 to 1.1: 1 or 1: 1.1 to 1: 20, preferably in the range of 5: 1 to 1.5: 1 or 1: 1.5 to 1: 5, more preferably in the range of 3: 1 to 2: 1 or 1: 2 to 1: 3. The flexural rigidity of the doctor blade is determined essentially by the bending stiffness of the reinforcement, but the bending stiffnesses are not directly proportional to each other due to the composite structure of the doctor blade.

If the reinforcing fibers are carbon fibers then the fiber types HM1 (High Modulus 1), HM2 (High Modulus 2), HST (High Strain) and / or IM (Intermediate Type) can be used. In the case of aramid fibers, the types HM (High Modulus) and / or LM (Low Modulus) can be used.

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

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

Preferably, the fibers have anisotropic properties, such as may be produced, for example, by production of the fibers under stretching.

Preferably, fibers are present in at least one reinforcing layer which have a higher tensile strength and / or a higher modulus of elasticity and / or a smaller elongation at break than glass fibers (E or R glass fibers), preferably with a simultaneous reduction in density.

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

Preferably, in addition to a first reinforcing layer having a first type of fiber preferably adjacent the squeegee soft-elastic squeegee layer, the reinforcement has a second layer on the same side of the soft-squeegee part which is preferably immediately adjacent the first layer, the reinforcing fibers of the second layer Contain or are glass fibers. The layer can have a Have glass fiber content of ≥ 2 wt .-%, preferably ≥ 5 to 10 wt .-% or ≥ 25 or 50 wt .-% based on the coating weight or the fiber weight of the layer. Preferably, the fibers are exclusively glass fibers.

The glass fibers may be a continuous sheet, e.g. in the form of a net, grid and / or non-woven fabric or in any other form mentioned above, including as single fibers or fiber bundles. Preferably, the first layer does not contain glass fibers.

The sheet is preferably preformed embedded in the Armierungsmatrix. This ensures a defined arrangement of the fibers relative to each other, for example, the alignment of the fibers in one or more preferred directions in preferably defined proportions or basis weights of the fibers of the plurality of preferred directions relative to each other, and created the possibility of standardization of the structure. The preferred directions may in particular be the doctor longitudinal direction and / or a direction perpendicular or transverse to this, preferably in the doctor blade plane.

Particularly preferably, the reinforcing layer containing glass fibers is arranged facing the outside of the doctor blade with respect to the first or all other reinforcing layers. As a result, there is an outer reinforced layer with high impact strength, wherein inner reinforcing layers can be optimized in terms of other properties such as the bending stiffness with respect to the requirements of a doctor blade. Optionally, the outermost reinforcing layer may partially or completely also contain other fibers, so that this layer has a higher impact strength and / or better absorbency for resin than at least one or all of the inner reinforcing layers.

This outermost reinforcing layer can with a or several other non-armored cover layers.

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

The basis weight of the carbon fiber sheet or fibers further defined in the surface weight of the glass fiber sheet (g / m ² ) may be in the ratio of 1: 1 to 10: 1 or 20: 1 or more, preferably 3: 1 to 7: 1. The two mentioned reinforcing layers are preferably arranged directly adjacent to each other, but if appropriate, an intermediate layer may also be provided which may contain fibers or be fiber-free.

Preferably, the outermost reinforcing layer has a fibrous structure, for example in the form of a non-woven or short fibers, which, after penetration with a resin, forms a smoother structure than at least one further inside reinforcing layer or inwardly adjacent reinforcing layer. The latter preferably has a higher flexural rigidity and / or strength than the further outward reinforcing layer. The ratios of the bending stiffness and strength of the layers can be determined, for example, by incremental layer removal, if appropriate also including layer removal of the soft-elastic profile strip. In this way, a doctor blade of high rigidity can be created with a relatively smooth outer surface in the region of the reinforcement, which can be easily cleaned of the printing medium and defined in the doctor blade clamped.

The reinforcing layers arranged on one or both sides of the soft-elastic doctor strip can each have a total thickness or individual thickness of 2.5-50%, preferably 5-30% or 5-50%, particularly preferably 10-20% of the doctor blade thickness.

The doctor blade may have a thickness of 1 to 10 mm or to 15 mm, preferably about 4 mm - 10 mm, without being limited thereto.

In particular, the doctor blade may be in the form of a patch having plane-parallel front and back sides, e.g. in the form of a flat strip of uniform thickness.

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

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

The reinforcing layer, which may be fibrous and which abuts the soft-elastic doctor blade-provided doctor blade layer, may have a hardness of 80 to 150 Shore A, for example, 90 to 120 Shore A, without being limited thereto.

The doctor according to the invention also results, in particular in the case of the use of carbon fibers as reinforcing fibers, in a material that is easier to process, in particular in occupational safety aspects and in manufacturing technology, which material is easier to dispose of and which also has higher strength and / or elasticity.

Each provided on one side, namely the front and / or back of the doctor blade, each armament, exactly two or exactly three but depending on the requirements also more or less reinforcing layers, which may be preferably carried out differently based on the reinforcement of one side , The number of reinforcing layers on the front and back of the doctor blade can be different. Preferably, the reinforcement of the doctor back consists of exactly two or exactly three reinforcing layers.

The front and / or back side doctor layer preferably has a carbon fiber content of ≦ 25% by weight, preferably ≦ 5-10% by weight, more 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 squeegee layer, more preferably the front and back squeegee layers are carbon fiber free.

It is understood that the reinforcing layer, which directly supports the squeegee layer having a squeegee edge which can be applied to a printing screen, can likewise be adjacent to a soft-elastic squeegee layer on the opposite side, which can have substantially or exactly the same properties as described here for FIGS the squeegee edge soft elastic doctor blade layer are described. Optionally, the soft-elastic doctor blade layer adjoining the reinforcing layer on the back can also have a further doctor blade edge which can be applied to a printing screen or another printing medium transfer means. The doctor blade layer having the doctor edge and / or a further soft elastic doctor blade layer provided on the opposite side of the reinforcing layer may have a minimum thickness of 0.5-1 mm, preferably a thickness of ≥ 2 or ≥ 4 mm, so that the deformation properties of the doctor edge substantially or completely determined by the soft-elastic doctor blade layer. Optionally, further layers may be added to the soft elastic doctor blade layer covering the reinforcement layer on the back side, for example a further fiber-containing reinforcement layer, 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 squeegee edge, an adjacent fiber-containing, in particular carbon fiber-containing reinforcing layer, an adjoining substantially carbon fiber-free reinforcing layer and optionally a cover layer applied thereto.

Preferably, the doctor has a printed layer, for example of paper, a non-woven or other suitable printable material, which is preferably connected via the Armierungsmatrix with the doctor. The nonwoven may be, for example, the abovementioned glass fleece or another suitable fleece. The printed layer is thus preferably at least under pressure resin permeable or impregnated with resin. The printing may include technical data, advertising or the like. Possibly For example, the printed layer, in particular as a paper layer, can be laminated with a nonwoven.

The printed layer may be visibly interposed between the top surface of the squeegee elastomer and the top armor layer or above the top armor layer and is preferably covered on top by another layer. The uppermost layer of the doctor blade is preferably a synthetic resin layer which can directly cover the printed layer or even be provided in the absence of the printed layer.

Preferably, the attachment region of the doctor blade, by means of which the doctor blade can be fixed in a doctor blade holder, is designed as an electrical contacting region in such a way that a discharge of electrical charges from at least one armor coating to the doctor front side and / or doctor back side is facilitated compared to a doctor blade region closer to the doctor blade edge ,

Such a fastening region can be provided, for example, by partially or completely removing at least the holding region of the doctor blade layers which are frontally and / or rearwardly adjacent to a doctor blade layer having high electrical conductivity, for example a carbon fiber-containing doctor blade layer, thus making possible an electrical charge drainage can be contacted with the doctor blade holder, for which it may be sufficient to determine the doctor as intended in the doctor blade holder. For example, a cover layer containing backside glass fibers may be removed to expose an adjacent carbon fiber-containing reinforcing layer. Any additional metallic discharges can be dispensed with. The cover layer may also be unevenly removed, for example, tapering in thickness to the doctor edge of the clamping end of the doctor blade. Conveniently, all layers are up to a layer with the highest electrical Conductivity of the doctor in the holding area of the doctor at least partially removed. It is understood that on the other hand, the cover layer in the region received by the doctor blade holder can likewise have an increased electrical conductivity than the cover layer region arranged outside the holding region of the doctor blade or adjacent to the doctor blade edge. For this purpose, for example, the cover layer can be made sufficiently electrically conductive only at the level of the holding region of the doctor, 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 adjoin one another directly or else 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 the doctor blade holder may consist of a metallic material such as aluminum or may have a sufficiently high content of carbon in the form of carbon black, carbon fibers or the like , Preferably, the squeegee holder as a whole consists of said material, but where appropriate, there may also be localized contacting regions.

Optionally, electrical contacting of the doctor blade layer with high electrical conductivity can also take place in that this layer or a portion thereof such as fibers with high electrical conductivity protrude from the squeegee narrow side, for example projecting from the squeegee narrow side of the holding portion, so that these areas by the doctor blade holder electrically are contactable. Preferably, a discharge of the electrical charges through the contacting region to the doctor front side and / or doctor back side is facilitated.

The doctor blade preferably has a flexible electrical discharge on the rear side opposite the doctor blade edge, which can be applied to a printing screen at least over a part or the entire doctor blade length. The electrical discharge can be fixed permanently or detachably on the doctor blade. The electrical discharge can also have carbon fibers to increase the conductivity. The length of the electrical discharge can be chosen such that, at the usual intended angle of attack of the doctor relative to the printing screen or other Verdruckmediumübertragungsmittel there is a linear contact with the printing screen based on a given cross-section of the doctor. Preferably, the electrical discharge is so flexible that it exerts no or no significant pressure force on the printing screen even with different angles of attack of the doctor relative to a printing screen. Preferably, the electrical discharge is in direct electrical contact with a doctor blade layer of high electrical conductivity, in particular a layer containing carbon fibers. The electrical discharge can only extend over a comparatively small part of the doctor blade length or over the entire doctor blade length.

Preferably, the electrical discharge and / or the doctor blade layer with high electrical conductivity or the doctor blade is 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 onto which the preferably prefabricated layer of the reinforcing material is applied, whereupon the mold is then closed. Subsequently, a resin forming the reinforcing matrix can be pressed into the mold under pressure, for example under compressed air, so that the fiber-containing reinforcing material is impregnated by the synthetic resin. At the same time thereby the reinforcing 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 prior to the pressing in of the reinforcing matrix-forming synthetic resin, so that when the synthetic resin is pressed in in a one-step process step, the printed layer is simultaneously joined to the reinforcing material. If appropriate, applied after pressing the resin, a printed layer and then provided with a cover layer. By producing in a mold, the doctor blade can be produced in a particularly well-defined thickness.

Furthermore, the invention relates to a doctor blade holder according to the invention with doctor. Preferably, the holder and the squeegee are designed in such a way that an electrical conductivity path is present with a sufficient electrical conductivity in order to allow electrostatic charges in the area of the squeegee edge to flow off via the squeegee holder into an electric potential well.

Furthermore, the invention relates to a printing method according to claim 18,

Fig.1

eine perspektivische Darstellung einer in einem Ra- kelhalter angeordneten Rakel,

Fig.2

eine perspektivische Darstellung einer in einem Ra- kelhalter angeordneten erfindungsgemäßen Rakel nach einer zweiten Ausführungsform,

Fig.3

eine schematische Ansicht einer erfindungsgemäßen Rakel in einer Druckanordnung, und

Fig.4

schematische Querschnittsdarstellungen unterschied- licher Ausführungen erfindungsgemäßer Rakeln.

The invention is described below by way of example and explained by way of example with reference to the figures. Show it:

Fig.1

3 is a perspective view of a doctor blade arranged in a socket holder;

Fig.2

3 a perspective view of a doctor blade according to the invention arranged in a doctor holder according to a second embodiment,

Figure 3

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

Figure 4

schematic cross-sectional views of different versions of inventive doctor blades.

Fig. 1 shows a arranged in a doctor blade 1 doctor blade 2, which is by means of a rail 3 over its entire length pressurization in the holder 1 by clamping elements 4 can be fixed. The doctor blade 2 has an elongated profiled strip 5 made of a flexible material, in particular a thermoplastic material such as a polyurethane with a hardness of 70 Shore A, wherein the doctor blade edge 6a arranged on the front side 6 viewed in the feed direction can be applied to a printing screen for distributing a printing medium is. On the back of the profile strip 5, a first reinforcing layer 7 is provided, which supports the soft elastic profile strip 5 back, which in turn is the back of a second reinforcing layer 8 and covered over the entire surface. The individual layers of the composite system, namely the soft-elastic part 5, the first, and the second reinforcing layer 7, 8, are each made congruent here, all over each other connected and are each detected at its upper end by the doctor blade holder. The doctor has a fixable in the doctor holder mounting portion 14.

The reinforcing layer 7 consists of carbon fibers having a tensile strength of about 3000 MPa, a modulus of elasticity of about 300 GPa and an elongation at break of about 1%, but other carbon fibers can be advantageously used. The fiber diameter is about 5 to 7 microns, the fibers each extend over the entire blade extension in the respective fiber direction.

In the fabrics produced by the carbon fibers, the fibers 12 extend parallel to the doctor edge 6a and the fibers 13 extend parallel to the side edge 9 which is perpendicular to the doctor edge 6a. The fibers form a mesh with a width of about 1 x 1 mm. The fibers are embedded in a matrix 10 forming thermosetting resin, according to the embodiment of a thermoset polyurethane. The individual intersecting fibers of the sheet produced by these are interconnected only by the matrix material, which may abut each other in the crossover points or in areas of their longitudinal extent.

The reinforcing layer 8 consists of a glass fleece 11, which is impregnated pore-free with a resin according to the embodiment of the same resin as the material of the matrix 10. The glass fleece is sewn to the carbon fibers of the reinforcing layer 7. The fleece may be printed or covered with a printed layer.

The reinforcing layer 7 has longitudinally and transversely doctor blades of different basis weights of the carbon fibers, which are here 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 length in its longitudinal direction, and in its transverse direction or height to a comparatively high flexural rigidity, wherein the bending stiffness is approximately in the ratio of 1/3 to 2/3. As a result, the doctor blade is relatively rigid with respect to a force applied to the printing screen, but comparatively flexible with respect to a contour adaptation to the surface of the printing screen, whereby on the squeegee length a special consistent print image regardless of the pressing force of the squeegee to the printing screen can be achieved.

By the reinforcing layer 7 of the soft elastic doctor blade part is supported, wherein both the tensile strength and the modulus of elasticity of the fibers exceeds the properties of the glass fibers. As a result, a long-term behavior of the doctor which is particularly outstanding under dynamic and static loading and thus a very consistent printed image can be obtained over very long periods of time. Through the glass fleece 11, a relative to the reinforcing layer 7 comparatively smooth rear side 16 of the doctor blade is further formed, whereby the holder thereof is improved in the doctor blade holder and the cleaning of the doctor blade is facilitated. Furthermore, due to the composite structure, the squeegee has a particularly smooth cut surface when the squeegee is cut out of a larger plate material. Further, by the arrangement of the glass mat, the resin of the reinforcing layer 7, 8 can be more rapidly distributed over the surface, thereby speeding up the manufacturing process.

To produce the doctor blade, the fabric of the Armierunsfasern according to the embodiment, the sewn to the carbon fiber mesh glass fleece are spread flat in a form in which a thermosetting resin filled, distributed and then pressed by high compressive forces in the fiber structure until it passes this pore-free. Subsequently, the resin is cured by suitable measures. On this Armierungsstruktur the soft elastic, preferably thermoplastic, part of the doctor blade layer is applied, for example as a prefabricated layer or through Application as a melt, for example by extrusion, and connected by suitable measures over a large area, optionally with the aid of a primer.

Fig. 2 shows a doctor according to the invention, wherein like features are given the same reference numerals. With the sole difference to the squeegee Fig. 1 The soft elastic part 5 and the second reinforcing layer 8 do not extend beyond the height of the reinforcing layer 7, whose upper free end can be fixed in a doctor blade holder. According to a further alternative, the layer 8 may also have the height of the layer 7. According to a further alternative, the layer 8 may also have the height of the layer 7. The doctor blade is fastened to the doctor blade holder by means of the fastening region 14.

Optionally, in the two squeegees of FIGS. 1 and 2 the reinforcing layer 8 also missing.

FIG. 3 shows a doctor blade according to the invention 20 in a printing arrangement with a doctor blade holder 21, a printing screen 22 and arranged below the printing screen to be printed carrier in the form of an article 23, wherein by moving the doctor in the feed direction (arrow) used as a printing medium printing ink 24 through the printing screen 22 on a support, that is, the object to be printed 23, is applied. By pressing the doctor blade edge 25 while moving the doctor blade in the direction of the arrow, electrostatic charges can be generated which influence the properties of the printing medium and disturb the printing process as a whole, such as, for example, particles of the printing medium that bounce off. The doctor 20 can according to the embodiments of the FIGS. 1 . 2 or 4 be executed, without being limited thereto. The squeegee 20 also has, in addition to the soft elastic Räkelschicht 26 having the doctor edge 25 and the reinforcing layer 27 supporting this back, a glass fiber cover layer 28. The fiberglass topcoat is here at the upper doctor blade end, ie the blade edge 25 opposite, removed, so that the carbon fiber-containing reinforcing layer 27 is exposed and is electrically contacted by the doctor blade holder 21. The doctor blade has this also a high carbon content, for example in the form of carbon fibers or carbon black or other suitable materials. The doctor is further provided on the blade edge 25 facing end face with an electrical outlet 29 in the manner of a sliding contact, which also consists essentially of carbon fibers, which are electrically conductively connected to the reinforcing layer. For this purpose, pins are provided, if necessary, the cover layer 28 may also be removed in some areas. The printing medium 24 in this case surrounds the doctor blade not only in the area of the doctor blade edge but also partially adjacent to the doctor blade edge narrow side 30 at least with a film, so that electrostatic charges can be transmitted through the reinforcing layer 27 to the doctor blade holder in the usual implementation of the printing process.

The carbon fibers of the reinforcing layer 27 are in the form of a carbon fiber fabric with a basis weight of about 200 g / m ² , wherein the fabric fibers are arranged in warp and weft in a density of 5 threads (fibers) per cm. It is understood that such fibers are made up of a large variety of filaments, for example about 3000 filaments per thread. The thread weight in warp and weft is approx. 200 Tex. By such a carbon fiber fabric, sufficient electrical conductivity of the reinforcing layer can be provided to avoid electrostatic charges.

In FIG. 4 further doctor blades according to the invention are shown by way of example. FIG. 4a shows a doctor blade 40 with a soft-elastic blade layer 41 with doctor blade edge 42, a fibrous, in particular carbon fiber-containing reinforcing layer 43, which supports the doctor blade layer 41 back and turn in turn is surrounded by another soft-elastic blade layer 44. The doctor blade layer 44 may have substantially the same chemical and / or mechanical properties as the doctor blade layer 41. For example, the doctor blade layer 44 have a differently shaped doctor edge 45.

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

LIST OF REFERENCE NUMBERS

1

squeegee holder

2

doctor

3

rail

4

clamping element

5

Soft elastic part

6

front

6a

squeegee edge

7

First reinforcement layer

8th

Second reinforcing layer

9

side edge

10

matrix

11

glass mat

12

Carbon fiber in the longitudinal direction

13

Carbon fiber in the transverse direction

20

doctor

21

squeegee holder

22

printing screen

23

object

24

Verdruckmedium

25

squeegee edge

26

reinforcing layer

27

electrical discharge

28

topcoat

29

narrow side

40

doctor

41

squeegee layer

42

squeegee edge

43

reinforcing layer

44

squeegee layer

45

squeegee edge

46, 47

squeegee layer

46a

doctor

48

reinforcing layer

49

topcoat

50

narrow side

Claims (18)

1. Squeegee, particularly for silk-screen printing, comprising at least one elongate profile strip (5) from a soft-elastic material, the squeegee having a longitudinally extending squeegee edge (6) in the region of the soft-elastic profile strip adapted to be applied against a printing screen, and a lateral edge (9) extending transversely thereto, wherein a reinforcing layer (7, 8) is provided that increases the stiffness of the squeegee and that is connected to the soft-elastic profile strip over a large area, wherein the reinforcement (7) contains fibers and wherein the fibers are at least partially carbon fibers and/or plastic fibers and/or fibers having an elastic modulus of ≥ 100 GPa and/or a stretch at break of ≤ 3%, characterized in that the electric properties of the squeegee are such
   that the fiber-containing reinforcing layer has an electric conductivity sufficient for preventing electrostatic charging of the squeegee and/or of a printing medium which directly contacts the squeegee and which is printed by means of the squeegee through the cooperating screen, which electrostatic charging results in irregularities of the printed image during a printing operation,
   and/or
   that the reinforcement (7) contains fibers continuously extending or forming a continuous electric conductivity path from a part of the squeegee edge (6a) that can be applied against a screen, up to a fixing portion (14) of the squeegee opposite the squeegee edge,
   and/or
   that the fixing portion (14) of the squeegee, by means of which the squeegee can be fixed to the squeegee holder, is constructed as an electric contacting portion in such a way that it is possible, compared to a part of the squeegee situated more closely to the squeegee edge (25), for electric charges to flow off from at least one reinforcement layer (26) towards the front side
   and/or
   rear side of the squeegee, and/or that one squeegee layer having a high electric conductivity or a portion thereof protrudes from the narrow side of the squeegee, so that this squeegee layer or the portion thereof can be electrically contacted by such a squeegee holder.
2. Squeegee according to claim 1, characterized in that the reinforcement includes two different reinforcing layers (7, 8) and that at least one or two of the reinforcing layers contain fibers.
3. Squeegee according to one of the claims 1 or 2, characterized in that the fibers of the reinforcement are at least partially present in the form of a lattice, tissue, fibrous web and/or as single filaments.
4. Squeegee according to one of the claims 1 to 3, characterized in that the fibers of the reinforcement form a two-dimensional structure having a mesh size of 0.1 to 5 mm.
5. Squeegee according to one of the claims 1 to 4, characterized in that at least one or all of the reinforcing layers (7, 8) are congruent with the profile strip (5) from soft-elastic material.
6. Squeegee according to one of the claims 1 to 5, characterized in that on the squeegee rear side opposite the squeegee edge a flexible electric discharge line (15) is fixed that can be applied against a print screen at least over a part or the entire length of the squeegee.
7. Squeegee according to one of the claims 1 to 6, characterized in that a different bending stiffness of the squeegee exists in two different directions of the plane formed by the squeegee edge (6a) and the lateral edge (9).
8. Squeegee according to claim 7, characterized in that the different bending stiffness in different directions is produced at least partially by different masses per unit area of the fibers of the reinforcing layers extending in the different directions.
9. Squeegee according to one of the claims 1 to 8, characterized in that the bending stiffness is smaller in the longitudinal direction of the squeegee than the stiffness perpendicular to the same.
10. Squeegee according to claim 7, characterized in that the ratio of the bending stiffness of the squeegee in the longitudinal direction and perpendicular thereto is in the range of 20 : 1 to 1.1 : 1 or in the range of 1 : 1.1 to 1 : 20.
11. Squeegee according to one of the claims 1 to 10, characterized in that the reinforcing layer includes fibers having a tensile strength of ≥ 3500 MPa and/or having an elastic modulus of ≥ 100 GPa and/or a stretch at break of ≤ 3%.
12. Squeegee according to one of the claims 1 to 11, characterized in that the reinforcement includes in one and/or in different layers reinforcing fibers at a different percentage (percent by weight in relation to the weight of the reinforcement layer) and/or of a different kind or composition.
13. Squeegee according to claim 12, characterized in that a first reinforcing layer facing the soft-elastic profile strip and a second, more distant reinforcing layer are provided and that the fibers of the second reinforcing layer are partly or completely glass fibers.
14. Squeegee according to one of the claims 1 to 13, characterized in that the fibers of the reinforcing layer that is the one situated farthest to the outside from the soft-elastic profile strip are present in the form of a fibrous web and/or that in the outermost reinforcing layer fibers are present which have a shorter fiber length and/or a smaller fiber diameter than a reinforcing layer situated farther to the inside.
15. Squeegee according to one of the claims 1 to 14, characterized in that two or more fiber-containing reinforcing layers are provided, each of which including a matrix material surrounding the reinforcing fibers which has the same basic component, and that the soft-elastic part of the squeegee consists of a material which is different from this material.
16. Squeegee holder having a squeegee according to one of the claims 1 to 15.
17. Squeegee holder having a squeegee according to one of the claims 1 to 16, characterized in that the squeegee holder (1) comprises a holding portion for fixing the squeegee, that the holding portion at least partly consists of an electrically conducting material, and that the reinforcing layer having an electric conductivity superior to that of the soft-elastic profile strip provided with the squeegee edge is electrically conductively connected to the holding portion.
18. Printing process, in particular silk-screen printing process, in which a printing medium is applied to or forced through a transfer means by using a squeegee, whereupon the printing medium is printed onto a carrier, said squeegee including at least one elongate profile strip (5) that is made of a soft-elastic material and that is provided with a squeegee edge (6a) extending in the longitudinal direction of the squeegee and adapted to be applied against the transfer means, and with a lateral edge (9) extending transversely thereto, wherein a reinforcement (7, 8) is provided increasing the stiffness of the squeegee and connected to the soft-elastic profile strip over a large area, wherein the squeegee (2) is passed over the transfer means with the squeegee edge applied against the transfer means and the printing medium is thus printed onto the carrier over or through the transfer medium while producing a printed image, 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 squeegee layer including the fibers is electrically conductively connected to the squeegee holder, and that the electric conductivity of the squeegee is so adjusted that any disturbing electrostatic charging is avoided under the conditions of the printing operation for the printed image.

Images