SE2251595A1

SE2251595A1 - Composite doctor blade

Info

Publication number: SE2251595A1
Application number: SE2251595A
Authority: SE
Inventors: Bartek Kaplan
Original assignee: Primeblade Sweden Ab
Priority date: 2022-12-29
Filing date: 2022-12-29
Publication date: 2024-06-30
Also published as: WO2024141386A1

Abstract

A doctor blade (101) comprises an active first blade substrate (103) which first blade substrate comprises a first major surface (105) and a second major surface (107), wherein said first blade substrate has a maximum width W1 , a maximum length L1 and a maximum thickness T1 , and a second blade substrate (109) which second blade substrate comprises a first major surface (111) and a second major surface (113), wherein said second blade substrate has a maximum width W2, a maximum length L2 and a maximum thickness T2 which is equal to or greater than T1, and wherein said first blade substrate has a Young’s modulus Y1 and said second blade substrate has a Youngs’ modulus Y2, and Y2 is or equal to or greater than 80% of Y1 and equal to and less than 120% of Y1, preferably Y2 is or equal to or greater than 90% of Y1 and equal to and less than 110% of Y1, more preferably Y2 is or equal to or greater than 95% of Y1 and equal to and less than 105% of Y1 and yet more preferably Y2 is or equal to or greater than 99% of Y1 and equal to and less than 101% of Y1 and the second major surface (107) of the first blade substrate (103) is adhered to said first major surface (111) of the second blade substrate (109).

Description

TECHNICAL FIELD The present disclosure relates to composite doctor blades.

BACKGROUND Doctor blades are blades for removing excess material from rollers or cylinders. The excess material may be coatings provided on, for example, paperrnaking machines rollers or ink applied to printing rollers. The surfaces of some printing or inking rollers comprise depressions separated by lands. Ink is applied to the Whole surface of the roller and excess ink on the lands is removed by the doctor blade, leaving ink only in the depressions. Thus, the purpose of the doctor blade is to remove ink for the raised lands on the surface of the roller While leaving the ink in the depressions. The doctor blade may subject to Wear on the edge Which is in contact With the surface of the cylinder and often is made from a Wear resistant metal alloy. Such alloys are expensive Which leads to high costs for metal doctor blades. Attempts to reduce the cost of doctor blades have been made by, for example, providing composite doctor blades in Which the tip of the blade intended to contact the surface of a roller is coated With a layer of a Wear-resistant material and the remainder of the blade is made from less Wear-resistant material. Such a blade is taught in WO20l 1088583 in Which the ﬂat and elongated body of a doctor blade is coated With a coating layer based on a nickel- phosphorus allow Which improves the Wear behavior of the blade.

PROBLEMS WITH THE PRIOR ART Solid metal doctor blades are expensive. Composite doctor blades made of polymers and rubbers are cheaper than metal doctor blades but are less rigid and Wear more quickly than metal blades. Composite doctor blades made of metal With a layer of Wear-resistant material on the tip have a limited life deterrnined by the thickness of the layer and cannot be reground if the tip Wears unevenly. Another problem Which they may suffer from is a buildup of the ink or coating material in the contact region. Such a buildup may leave the blade at irregular intervals and splatter onto the roller, causing stains, streaks and other irregularities on the product being coated from the roller.

There is thus a need for an improved doctor blade.

SUMMARY Some or all of the above described problems are addressed by the claimed doctor blade.

The scope of the inVention is defined by the claims, which are incorporated into this section by reference. A more complete understanding of embodiments of the invention will be afforded to those skilled in the art, as well as a realization of additional advantages thereof, by a consideration of the following detailed description of one or more embodiments. Reference will be made to the appended sheets of drawings that will first be described brieﬂy.

BRIEF DESCRIPTION OF THE DRAWINGS Figure la) schematically illustrates a plan View of a first embodiment of a doctor blade according to the present inVention. Figure lb) shows an end View of the doctor blade of figure la). Figure l c) shows a lateral View of the doctor blade of figure la).

Figure 2a) schematically illustrates a plan View of a second embodiment of a doctor blade according to the present inVention. Figure 2b) shows an end View of the doctor blade of figure 2a). Figure 2c) shows a lateral View of the doctor blade of figure 2a).

Figure 3 schematically illustrates an end View of a third embodiment of a doctor blade according to the present inVention.

Figure 4 schematically illustrates an end View of a fourth embodiment of a doctor blade according to the present invention.

Figure 5 schematically illustrates an end View of a fifth embodiment of a doctor blade according to the present inVention.

Figure 6 schematically illustrates an end View of a sixth embodiment of a doctor blade according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION Embodiments of the present disclo sure and their advantages are best understood by referring to the detailed description that follows. It should be appreciated that like reference numerals are used to identify like elements illustrated in one or more of the figures. The figures are schematic and are not drawn to scale, with some dimensions being exaggerated for clarity of illustration.

In the following references to Young°s modulus refer to Young°s modulus measured using ASTM E111-July 2017 "Standard Test Method for Young°s Modulus, Tangent Modulus, and Chord Modulus" for metals and ASTM D412 - May 2021 (Standard Test Methods for Vulcanized Rubber and Therrnoplastic Elastomers-Tension) for rubbers and therrnoplastic elastomers.

References to hardness for metals refer to hardness measured by ASTM E 92-17 of May 25, 2017 Standard Test Methods for Vickers Hardness and Knoop Hardness of Metallic Materials", references to hardness for plastic materials refer to hardness measured by ASTM D785 March 2008 "Standard Test Method for Rockwell Hardness of Plastics and Electrical Insulating Materials", references to hardness for vulcanized or therrnoplastic rubber materials refer to hardness measured by ASTM D1415 June 2018 "Standard Test for Rubber Property - Intemational Hardness", references to wear resistance refer to wear resistance measured using ASTM G195 June 2022 "Standard Guide for Conducting Wear Tests Using a Rotary Platform Abraser" or ASTM G77 Adhesive Wear Test.

Figures la) to lc) show schematically a first embodiment of a rectangular composite doctor blade 101 according to the present invention. The doctor blade is dimensioned to withstand the forces acting on it during use by being made of materials with the dimensions and the stiffnesses necessary to withstand these forces. The doctor blade comprises an active first blade substrate 103, which is intended to be in contact with such as the surface of a rotating roller or cylinder or the like or a coating applied to the surface of such a rotating component, upon which it acts with a relative motion. The doctor blade further comprises a passive second blade substrate 109 which is not intended to be in contact with the surface of the cylinder or roller or the like. The first blade substrate is subject to wear due to the relative motion and thus is made of a ﬁrst blade substrate material M1 with a high resistance to wear. A first material with a high resistance to wear, for example a steel alloy, is usually more expensive than a similar second material, for example another steel alloy with a similar Young°s modulus, With a lower resistance to wear as such a second material can be made of an alloy with less expensive alloying elements and/or which has been subject to less expensive heat treatments. The first blade substrate has two parallel short sides 104, 104" of width Wl, two parallel long sides 106, 106" of length Ll, and a depth D1. It comprises a first major surface 105 and a second major surface 107.

The second blade substrate 109 comprises a first major surface 111 and a second major surface 113, wherein said second blade substrate has two parallel short sides 114, 114" of width W2, two parallel long sides 116, 116" of length L2, and a depth D2 which is equal to or greater than the depth D1 of the first blade substrate. As the second blade substrate is not subject to relative motion against a roller it is not subject to wear and is made of a second blade substrate material M2 which has a lower resistance to wear compared to the first blade substrate material M1. Thus, the material costs of the composite doctor blade will be less than that of a comparable doctor blade made of only the first blade substrate material M1 while retaining the same wear properties of such a blade.

The second major surface 107 of the first blade substrate is adhered to said first major surface 111 of the second blade substrate. This is achieved by placing an adhering layer 115 between said first and second major surfaces and pressing said first and second major surfaces together. This may be performed in a laminating machine in which the two substrates are laminated together by a laminating film (which forms the adhering layer) while being subjected to heat and/or pressure.

The adhering layer may be made of an adhesive such as a transfer adhesive which is a film of adhesive which is not supported by a substrate, or a double-sided adhesive film with a film substrate coated on two, opposite major sides with adhesive, or a laminating film made of a polymer which adheres to the first and second blade substrate materials when subject to heat and/or pressure.

The composite doctor blade is subject to bending forces while in use and should be dimensionally stable during use and therefore needs to have a predeterrnined stiffiiess. In order to achieve the desired stiffiiess of the doctor blade without having to use more material- which might increase the material cost of the blade as well as increasing its weight and size - it is preferable that the Young°s modulus Y2 of the second blade substrate material is similar to the 4 Young°s modulus Y1 of the first blade substrate material. Preferably Y2 is or equal to or greater than 80% of Y1 and equal to and less than 120% of Yl. More preferably Y2 is or equal to or greater than 90% of Y1 and equal to and less than 110% of Yl. Even more preferably Y2 is or equal to or greater than 95% of Y1 and equal to and less than 105% ofY1. Yet more preferably Y2 is or equal to or greater than 99% of Y1 and equal to and less than 101% ofY1. The use of two materials with similar Young°s moduli has the advantage that the composite doctor blade has substantially the same stiffness as a comparable blade made of only the first blade substrate material M1 while reducing the material costs. Furthermore, the composite doctor blade can have substantially the same dimensions as a doctor blade made of only the first blade substrate material M1 which means that it can replace similar prior art doctor blades without requiring new mountings.

Using an adhesive is an inexpensive method of joining materials and using substrates made of materials of similar Young"s modulus means that forces acting on the doctor blade are distributed evenly thought the blade which is expected to minimize shear forces acting on the adhering layer.

However, it is also conceivable that the passive material could be a material which is much cheaper than the active material but which has a significantly lower Young°s modulus, for example, a polymer, a rubber, a f1bre-reinforced composite material, a honeycomb material or the like. In such cases when the passive substrate material has a lower Young°s modulus than in order to achieve the equivalent stiffness of a doctor blade made entirely out of the active material, the thickness of the passive material would have to be increased in order to compensate for its reduced Young°s modulus. For example, if the passive material had a Young°s modulus of only 50% of the active material which it is intended to replace, then it should be approximately twice as thick as the layer of active material which it is replacing. The advantages of lower cost of this passive material compensate for the increased thickness of the resulting composite doctor blade.

As the substrates of the composite doctor blade are of similar Young°s modulus it is expected that in some cases this will reduce the forces exerted on the adhering layer 115 when the composite doctor blade is subject to bending forces during use.

In the example of an embodiment of the present invention shown schematically in figure la) to lc), L1 = L2, W1 is greater than W2, D2 is greater than D1 and the first and second blade substrates are aligned with each other so that the first major surface 111 of the second blade substrate 109 is fully covered by the first major surface 107 of the ﬁrst blade substrate 103. This leaves a portion 121 of the second major surface of the first blade substrate exposed. The adhering layer 115 may be placed only between the two mating surfaces of the two substrates, but optionally it may cover the exposed portion 121 of the second major surface of the first blade substrate as shown by dotted lines. It has been found that having some types of exposed excess adhering material 115" covering the exposed portion 121 of the second major surface of the first blade substrate provides the advantage that the buildup of coatings which have been scraped off the roller or cylinder to which the doctor blade is applied is reduced. Such buildups are undesirable as they are unstable and can slip off the doctor blade during use and splatter on to surrounding surfaces, which may cause iiregularities upon the surface of a roller or a web being processed by the roller.

Figures 2a) to 2c) show schematically a second embodiment of a doctor blade according to the present invention, in which L1 the same as L2 and W1 is greater than W2. The shorts side of the substrates are aligned and the second blade substrate is arranged symmetrically on the first blade substrate. This leaves two portions 121, 121" of the second major surface of the first blade substrate exposed. The adhering layer 115 may be placed only between the two mating surfaces of the two substrates, but optionally it may cover one or both of the exposed portions 121, 121" of the second major surface of the first blade substrate.

Figure 3 shows a schematic end view of a reversable third embodiment of the present invention in which the first blade substrate 303 and the second blade substrate 309 are both active blade substrates. Preferably L1 is equal to L2. They are adhered together by adhering layer 115. The two substrates only partly overlap and form a doctor blade with two active edges 331, 331" - one on each of the substrates. Only one such edge is in contact with a roller or the like at any time and when it becomes wom the doctor blade can be ﬂipped 180 degrees in order to present the unused edge in the active position. In this example of the third embodiment of the invention the first blade substrate and the second blade substrate are substantially identical, i.e. they are made of the same material and L1 = L2, W1 = W2 and D1 = D2. However, it is conceivable that they are made of different materials. This allows a user to choose between different doctor blade properties by simply reversing the doctor blade in its holder.

Figure 4 shows a schematic end view of a fourth embodiment of the invention, similar to that shown in figure 3 in which the first blade substrate 403 and the second blade substrate 409 may be both active blade substrates but the depth of the second blade substrate D2 is greater than the depth of the first blade substrate Dl. In such examples the doctor blade will have two active edges which are of different thicknesses and therefore different stiffnesses. This allows a user to choose between different doctor blade properties by simply reversing the doctor blade in its holder.

Figure 5 shows a schematic end view of a ﬁfth embodiment of the present invention in which the second blade substrate 509 is a passive blade substrate and the first blade substrate 503 is an active substrate. The width W2 of the second blade substrate is less than the width Wl of the first blade substrate which is symmetrically arranged on the first major surface of the second blade substrate. Thus, the second blade substrate in adhered centrally on the first blade substrate, thereby leaving exposed two portions 521, 52l° of the first major surface of the second blade substrate, resulting in a blade where inexpensive passive material is combined with more expensive active material with two active edges 53 l , 53 l ", thus maximizing the potential degree of utilization of the blade.

Figure 6 shows a schematic end view of a sixth embodiment of the present invention, similar to Figure 5, differing only in the thickness of the passive material.

In one embodiment of the invention, the composite doctor blade is made of two strips of steel of the same or differing grades, with the same or differing thicknesses, joined by the adhering layer ll5, in accordance with Figures l-6.

In another embodiment of the invention, at least one of the component strips of the composite doctor blade are made out of a polymeric material, with the same or differing thicknesses, joined by the adhering layer ll5, in accordance with Figures l-6.

For metal doctor blades, preferably the Young°s modulus is equal to or greater than 180 GPa and less than or equal to 250 GPa, more preferably the Young°s modulus is equal to or greater than 200 GPa and less than or equal to 240 GPa.

Preferably the depth Dl of the active first blade substrate is: equal to or greater than 50 uni and equal to or less than 500 uni and the depth D2 of the second blade substrate is: equal to or greater than 50 uni to and equal to or less than 500 uni.

Preferably the Width Wl of the active first blade substrate is equal to or greater than 8 mm and equal to or less than 80 n1n1.

Preferably the Width W2 of the second blade substrate is equal to W1 or up to 5 n1n1 less than Wl.

Preferably, the stiffness of the passive substrate in the Width direction and/or the length direction is equal to or greater than 30 % of the corresponding stiffness of the active substrate. More preferably, the stiffness of the passive substrate in the Width direction and/or the length direction is equal to or greater than 50 % of the corresponding stiffness of the active substrate. Even n1ore preferably, the stiffness of the passive substrate in the Width direction and/or the length direction is equal to or greater than l00 % of the corresponding stiffness of the active substrate. Yet n1ore preferably, the stiffness of the passive substrate in the Width direction and/or the length direction is equal to or greater than l50 % of the corresponding stiffness of the active substrate. Yet even n1ore preferably, the stiffness of the passive substrate in the Width direction and/or the length direction is equal to or greater than 200 % of the corresponding stiffness of the active substrate.

Preferably the stiffness of the passive substrate in the Width direction and/or the length direction is equal to or less than 500 % of the corresponding stiffness of the active substrate. More preferably the stiffness of the passive substrate in the Width direction and/or the length direction is equal to or less than 400 % of the corresponding stiffness of the active substrate. Even n1ore preferably the stiffness of the passive substrate in the Width direction and/or the length direction is equal to or less than 300 % of the corresponding stiffness of the active substrate.

In order to provide the composite doctor blade With a useful Working life With respect to the Wear Which occurs on the active substrate, the active substrate should not be too thin and preferably the thickness of the second blade substrate is equal to or less than 400 %of the thickness of the active first blade substrate, n1ore preferably equal to or less than 300% of the thickness of the active first blade substrate and n1ost preferably equal to or less than 200% of the thickness of the active first blade substrate.

In order to achieve savings in the cost of materials the cheaper second blade substrate should not be too thin, and preferably the thickness of the second blade substrate is equal to or greater than 50 %of the thickness of the active first blade substrate, preferably equal to or greater than 100% of the thickness of the active first blade substrate and more preferably equal to or greater than 200% of the thickness of the active first blade substrate.

In all embodiments of the invention, the contacting surfaces of the first and second blade substrates are preferably adhered to each other by an adhesive. Suitable adhesives are epoxy adhesives, acrylic metal glues, cyanoacrylate adhesives, polyurethane adhesives and anaerobic metal adhesives.

The passive or active substrates do not have to be made of metal but can be any material Which is suitable for the operating conditions Which the doctor blade is to be used under. This includes, but is not limited to, rubbers, polymers, fibre-reinforced composite materials and honeycomb composite materials.

The first and second blade substrates can be bonded together by an interrnediate therrnoplastic polymer to form a metal-polymer-metal sandWich construction. The therrnoplastic may be draWn from a Wide range of polymeric materials such as polyethylene terephthalate, cellulose acetate, polyethylene, polypropylene, therrnoplastic polyurethane, nylon or the like. The therrnoplastic may also contain f1ller materials such as talc, glass, carbon, and metallic particles, etc.

Claims

1. Doctor blade (101) comprising: a first blade substrate (103) which first blade substrate comprises a first major surface (105) and a second major surface (107), wherein said first blade substrate has a maximum width W1, a maximum length L1, and a maximum thickness D1, and a second blade substrate (109) which second blade substrate comprises a first major surface (111) and a second major surface (113), wherein said second blade substrate has a maximum width W2, a maximum length L2,and a maximum thickness D2 wherein D2 is equal to or greater than D 1 , characterized in that: the second major surface (1 07) of the first blade substrate (103) is adhered to said first major surface (111) of the second blade substrate (109) and. i) said first blade substrate has a Young°s modulus Y1 and said second blade substrate has a Youngs” modulus Y2, and Y2 is or equal to or greater than 80% of Y1 and equal to and less than 120% of Yl, preferably Y2 is or equal to or greater than 90% of Y1 and equal to and less than 110% of Y1 , more preferably Y2 is or equal to or greater than 95% of Y1 and equal to and less than 105% of Y1 and yet more preferably Y2 is or equal to or greater than 99% of Y1 and equal to and less than 101% of Y1 when measured using ASTM E111-17; and/or ii) the stiffness of the second blade substrate in the width direction and/or the length direction is equal to or greater than 30 % and equal to or less than 500% of the corresponding stiffness of the first blade substrate.

2. Doctor blade according to claim 1 characterized in that said second major surface (107) of the first blade substrate is adhered to said first major surface (111) of the second blade substrate by an adhering layer (115) wherein said adhering layer is a solidified laminating polymer or a transfer adhesiVe or an epoxy adhesiVe or an acrylic metal glue or a cyanoacrylate adhesive or a polyurethane adhesiVe or an anaerobic metal adhesiVe or the like.

3. Doctor blade according to claim 1 or 2 characterized in that each said first and second blade substrates is made of metal or of plastic or of rubber and the hardness of said first blade substrate is greater than the hardness of said second blade substrate when measured using ASTM E 92- 17 of May 25, 2017 Standard Test Methods for Vickers Hardness and Knoop Hardness of Metallic Materials” for metal substrates, ASTM D785 March 2008 “Standard Test Method for Rockwell Hardness of Plastics and Electrical Insulating Materials” for plastic substrates, and ASTM D1415 June 2018 “Standard Test for Rubber Property - Intemational Hardness” for rubber substrates..

4. Doctor blade according to any of the previous characterized in that the Wear resistance of said first blade substrate is greater than the Wear resistance of said second blade substrate When measured by ASTM G195 June 2022 “Standard Guide for Conducting Wear Tests Using a Rotary Platform Abraser”.

5. Doctor blade according to any of the previous claims characterized in the length L2 of the second blade substrate is equal to or greater than the length Ll of the first blade substrate and/or the Width W2 of the second major surface is equal to or greater than the Width Wl of the ﬁrst blade substrate, and the first major surface of the second blade substrate comprises at least one portion (223) of the surface Which is exposed.

6. Doctor blade according to any of claims 1 to 4 characterized in the length L2 of the second blade substrate is less than the length Ll of the first blade substrate and/or the Width W2 of the second blade substrate is less than the Width Wl of the first blade substrate and the second major surface of the first blade substrate comprises at least a portion (l2l) of the surface (107) Which is exposed.

7. Doctor blade according to any of the previous claims characterized in that the first and second blade substrates are mutually offset, such that the first major surface of the second blade substrate comprises at least one exposed surface and/or the second major surface of the first blade substrate comprises at least one exposed surface.

8. Doctor blade according to any of claims 5 to 7 characterized in that said at least one exposed surface is covered by said adhering layer.

9.. Doctor blade according to any of the previous claims characterized in that the thickness of the second blade substrate is equal to or less than 400 %of the thickness of the active first blade substrate, preferably equal to or less than 300% of the thickness of the active first blade substrate and more preferably equal to or less than 200% of the thickness of the active first blade substrate.

10. Doctor blade according to any of the previous c1ain1s characterized in that the thickness of the second blade substrate is equal to or greater than 50 %of the thickness of the first blade substrate, preferably equal to or greater than 100% of the thickness of the first blade substrate and n1ore preferably equal to or greater than 200% of the thickness of the first blade substrate.