Masked coating blade

Abstract

In a general aspect, a coating blade for application of coating color to a fibrous web can include an elongate substrate having a longitudinal edge. Within an operating zone of the coating blade intended for contact with a coating color, the elongate substrate can include a longitudinal wear-resistant deposit adjacent to the longitudinal edge. The coating blade, within the operating zone, can also include a longitudinal masking deposit adjoining the longitudinal wear-resistant deposit.

Claims

1. A coating blade for application of a coating color to a fibrous web, the coating blade comprising: an elongate substrate having a width in a width direction between a first end and a second end of the elongate substrate, and a longitudinal edge at the first end, the elongate substrate, within an operating zone of the coating blade intended for contact with the coating color, includes: a longitudinal wear-resistant deposit disposed on and in contact with the elongate substrate, the longitudinal wear-resistant deposit being adjacent to the longitudinal edge of the elongate substrate, the longitudinal wear-resistant deposit including a ceramic material and having a width in the width direction in a range of 1-9 millimeters; a longitudinal masking deposit disposed on and in contact with the elongate substrate, the longitudinal masking deposit being next to, and adjoining the longitudinal wear-resistant deposit, the longitudinal masking deposit including a polymer material; and a transition, in the width direction, between a surface of the longitudinal wear-resistant deposit intended for contact with the coating color and a surface of the longitudinal masking deposit intended for contact with the coating color, the transition being substantially flush.

2. The coating blade of claim 1, wherein the longitudinal masking deposit has a lower elastic modulus than the elongate substrate.

3. The coating blade of claim 1, wherein the longitudinal masking deposit has an elastic modulus of less than 50 Gpa.

4. The coating blade of claim 1, wherein the polymer material is polyurethane.

5. The coating blade of claim 1, wherein the longitudinal masking deposit tapers towards a surface of the elongate substrate.

6. The coating blade of claim 1, wherein the longitudinal masking deposit adjoins the longitudinal wear-resistant deposit to define a substantially seamless surface intended for contact with the coating color.

7. The coating blade of claim 1, wherein a portion of the longitudinal masking deposit overlaps the longitudinal wear-resistant deposit.

8. The coating blade of claim 1, wherein a thickness of the longitudinal masking deposit is less than or equal to 200 μm.

9. The coating blade of claim 1, wherein a width of the longitudinal masking deposit is in a range of 5-30 mm.

10. The coating blade of claim 1, wherein a width of the longitudinal wear-resistant deposit is in a range of 1-2.5 mm.

11. The coating blade of claim 1, wherein a thickness of the longitudinal wear-resistant deposit is less than or equal to 200 μm.

12. The coating blade of claim 1, wherein the longitudinal wear-resistant deposit includes at least one bevel.

13. The coating blade of claim 1, wherein the longitudinal wear-resistant deposit adjoins the longitudinal edge.

14. The coating blade of claim 1, wherein the elongate substrate is a steel substrate.

15. The coating blade of claim 1, wherein the longitudinal masking deposit is arranged a distance from the longitudinal edge in the width direction.

16. The coating blade of claim 1, wherein the elongated substrate has a top surface extending between the first end and the second end, and wherein the longitudinal wear-resistant deposit and the longitudinal masking deposit are in contact with the top surface.

17. A coating blade for application of a coating color to a fibrous web, the coating blade comprising: an elongate substrate having a width in a width direction between a first end and a second end of the elongate substrate, and a longitudinal edge at the first end, the elongate substrate, within an operating zone of the coating blade intended for contact with the coating color, includes: a longitudinal wear-resistant deposit disposed on and in contact with the elongate substrate, the longitudinal wear-resistant deposit being adjacent to the longitudinal edge of the elongate substrate, the longitudinal wear-resistant deposit including a ceramic material and having a width in the width direction in a range of 1-9 millimeters; and a longitudinal masking deposit disposed on and in contact with the elongate substrate, the longitudinal masking deposit being arranged next to, and adjoining the longitudinal wear-resistant deposit at a distance of 1-9 millimeters from the longitudinal edge in the width direction, the longitudinal masking deposit including a polymer material and wherein the longitudinal masking deposit is arranged rearward of the longitudinal wear-resistant deposit in the width direction and with regard to the longitudinal edge.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will be described in the following with reference to the appended drawings.

(2) FIG. 1 shows diagrammatically in a side view a paper coating arrangement.

(3) FIGS. 2-6 show diagrammatical side views of five different embodiments of masked coating blades.

DETAILED DESCRIPTION

(4) FIG. 1 shows a paper coating arrangement provided with a coating blade 1 having a substrate 2 with a wear-resistant deposit 3 and a masking deposit 4, to be further described in connection with FIGS. 2-6. Furthermore, the paper coating arrangement has a backing roll 5, rotating in the direction of the arrow, supporting and feeding a fibrous web 6, onto which coating color liquid 7 is provided. The coating color liquid 7 is provided in excess amounts. The coating blade 1 applies a pressure onto the coating color liquid 7, which causes excess amounts of coating color liquid 7 to be wiped, or doctored, off. The pressure applied by the coating blade 1 determines the amount of coating color fluid 7 that is applied to the fibrous web.

(5) FIG. 2 shows in a side view a masked coating blade 21 having a substrate 22 being provided with a longitudinal wear-resistant deposit 23 and a longitudinal masking deposit 24 adjoining the wear-resistant deposit 23. FIG. 2 furthermore illustrates schematically the thickness t and the width w of the substrate 22, as referred to herein. FIG. 2 also illustrates schematically the thickness wrt and width wrw of the wear-resistant deposit 23 and the thickness mt and width mw of the masking deposit 24, as referred to herein.

(6) FIG. 3 shows an alternative arrangement wherein a part of the masking deposit 34 partially overlaps the wear-resistant deposit 33 in order to cover the steep transition from the surface of the wear-resistant deposit 33 to the surface of the substrate 32.

(7) FIG. 4 shows an embodiment wherein the width of the wear-resistant deposit 43 has been reduced and the width of the masking deposit 44 has been extended. The masking deposit 44 tapers at a constant rate towards the surface of the substrate 42. The thickness of the masking deposit thus decreases following a straight path. The wear-resistant deposit 43 and the masking deposit 44 are shown without the masking deposit 44 overlapping the wear-resistant deposit 43, but the masking deposit may alternatively overlap the wear-resistant deposit.

(8) FIG. 5 shows an embodiment wherein the masking deposit 54 tapers along a curved path towards the surface of the substrate 52. The thickness of the masking deposit decreases strongly near the wear-resistant deposit 53 and weakly more remote from the wear-resistant deposit.

(9) FIG. 6 shows an embodiment wherein the substrate 62 has a pre-ground bevel 68. The substrate 62 is provided with a wear-resistant deposit 63, extending over the pre-ground bevel 68, and an adjoining masking deposit 64. The wear-resistant deposit 63 has a sliding bevel 69. FIG. 6 also illustrates schematically the width bw of the sliding bevel 69 and the angle α between the sliding bevel 69 and the surface of the wear-resistant deposit 63, as referred to herein.

EXAMPLE

(10) A reference coating blade was manufactured by providing a stainless steel substrate of 100 mm width and 0.457 mm thickness with a Cr.sub.2O.sub.3 based wear-resistant deposit of 5 mm width. A test coating blade according to the invention was manufactured by providing a stainless steel substrate of 100 mm width and 0.457 mm thickness with a Cr.sub.2O.sub.3 based wear-resistant deposit of 5 mm width and an adjoining polyurethane masking deposit of 15 mm width. The masking material was applied as a solvent based dispersion of methyl diphenyl diisocyanate (MDI) based polyurethane. The wear-resistant deposits had a sliding bevel of 10°.

(11) The test and reference coating blades, respectively, were used to top-coat a paper web in a Jagenberg Combiblade coater at the following machine conditions and settings.

(12) Coating Station Configuration:

(13) Pre-coat (both paper sides—film press; 5-7 g/m.sup.2)

(14) Middle-coat (top paper side—coating rod; 7-8 g/m.sup.2)

(15) Top-coat (top paper side—bent blade; 9-10 g/m.sup.2)

(16) Machine speed: 800 m/min

(17) Base paper: 150-180 g/m.sup.2, 100% recycled fibers

(18) Coating color: CaCO.sub.3 85%+clay 15%+latex binder (solids content 66-67%), viscosity 950 cPs

(19) The quality of the “mirror” (i.e. the appearance of the wet coated paper surface just after the blade) was noticed by the machine operators to be better for the test blade than for the reference blade. After 8 hours of operation, the blades were taken out of operation and washed. There was more build-up of coating color residues at the rear of the wear-resistant deposit on the reference blade than on the test blade. As concerns the test blade, the masking deposit was perfectly clean.

(20) Visual inspection of the used test blade confirms that the polymeric masking deposit at the back of the ceramic wear-resistant deposit resisted to the friction of the coating color back flow during coating of the paper: no dissolution or change (chemical process), no wear (abrasion/erosion process) or delamination of the masking deposit has been noticed. The behaviour of the test blade has been similar to the reference blade regarding coating quality criteria.

ITEMIZED LIST

(21) The coating blade according to the present invention can be defined according to the following itemized list.

(22) 1. A coating blade for application of coating color to a fibrous web, the coating blade comprising an elongate substrate having a longitudinal edge, wherein, within an operating zone, intended for contact with a coating color, of the coating blade, the substrate is provided with:

(23) a longitudinal wear-resistant deposit adjacent to the longitudinal edge; and

(24) a longitudinal masking deposit adjoining the longitudinal wear-resistant deposit.

(25) 2. A coating blade according to item 1, wherein the masking deposit has a lower elastic modulus than the substrate.

(26) 3. A coating blade according to item 1 or 2, wherein the masking deposit has an elastic modulus of less than about 50 GPa, preferably less than about 20 GPa.

(27) 4. A coating blade according to anyone of the previous items, wherein the masking deposit comprises a polymer material.

(28) 5. A coating blade according to item 4, wherein the polymer material is polyurethane.

(29) 6. A coating blade according to any of the previous items, wherein the masking deposit tapers towards the surface of the substrate.

(30) 7. A coating blade according to any one of the previous items, wherein the transition between the surface intended for contact with the coating color of the wear-resistant deposit and the surface intended for contact with the coating color of the masking deposit is substantially flush.

(31) 8. A coating blade according to any one of the previous items, wherein the masking deposit adjoins the wear-resistant deposit forming a substantially seamless surface intended for contact with the coating color.

(32) 9. A coating blade according to any one of the previous items, wherein a part of the masking deposit overlaps the wear-resistant deposit.

(33) 10. A coating blade according to any one of the preceding items, wherein the thickness of the masking deposit is up to about 200 μm, preferably up to about 100 μm.

(34) 11. A coating blade according to any one of the previous items, wherein the width of the masking deposit is in the range of about 5-30 mm, preferably about 6-16 mm.

(35) 12. A coating blade according to any one of the previous items, wherein the wear-resistant deposit comprises a ceramic material, such as a metal oxide, metal carbide, metal nitride or metal boride.

(36) 13. A coating blade according to any one of the previous items, wherein the width of the wear-resistant deposit is in the range of about 1-9 mm, preferably about 3-7 mm, more preferably about 4-6 mm.

(37) 14. A coating blade according to any one of items 1-12, wherein the width of the wear-resistant deposit is in the range of about 1-2.5 mm, preferably about 1.5 to 2.5 mm.

(38) 15. A coating blade according to any one of the preceding items, wherein the thickness of the wear-resistant deposit is up to about 200 μm, preferably up to about 100 μm.

(39) 16. A coating blade according to any one of the previous items, wherein the wear-resistant deposit is provided with at least one bevel.

(40) 17. A coating blade according to any one of the previous items, wherein the longitudinal wear-resistant deposit adjoins the longitudinal edge.

(41) 18. A coating blade according to any one of the previous items, wherein the substrate is a steel substrate.

(42) 19. A coating blade according to any one of the previous items, wherein the fibrous web is a paper web.