METHOD FOR COATING STAINLESS STEEL PRESS PLATES AND COATED PRESS PLATES PRODUCED THEREBY

Abstract

A method for coating stainless steel press plates includes preparing the stainless steel press plate for coating and coating the stainless steel press plate with a diboride doped with 1%-5% by weight aluminum to produce a diboride-aluminum coating. The step of coating includes applying the diboride-aluminum coating to a stainless steel press plate using a magnetron sputter coating system.

Claims

1. A method for coating stainless steel press plates, comprising: preparing the stainless steel press plate for coating; coating the stainless steel press plate with a diboride doped with 1%-5% by weight aluminum to produce a diboride-aluminum coating, wherein the step of coating includes applying the diboride-aluminum coating to a stainless steel press plate using a magnetron sputter coating system.

2. The method according to claim 1, wherein the diboride is titanium diboride.

3. The method according to claim 1, wherein the stainless steel press plate is a 410 stainless steel high gloss press plates.

4. The method according to claim 1, wherein the stainless steel press plate is a 300 stainless steel press plate, a 410 stainless steel press plate, a 420 stainless steel press plate, a 630 stainless steel press plate, or a 633 stainless steel press plate.

5. The method according to claim 1, wherein the diboride-aluminum coating has a Vickers hardness of at least 35 GPa.

6. The method according to claim 5, wherein the diboride-aluminum coating has a Vickers hardness of 46 GPa.

7. The method according to claim 1, wherein the diboride-aluminum coating has a thickness of about 3 microns.

8. The method according to claim 1, wherein the step of coating includes doping the diboride with 2% by weight aluminum.

9. The method according to claim 8, wherein the step of coating includes applying the diboride-aluminum coating at a substrate bias of 60-90 V and at temperature of 200° C.

10. The method according to claim 1, wherein the diboride-aluminum coating has a minimum bond strength of 1.6 kilogram force.

11. The method according to claim 10, wherein the diboride-aluminum coating has a minimum bond strength of 1.8 kilogram force.

12. The method according to claim 1, wherein the step of preparing the stainless steel press plate includes cleaning a pressing side of the stainless steel press plate.

13. The method according to claim 12, wherein the step of preparing the stainless steel press plate includes etching the pressing side of the stainless steel press plate.

14. The method according to claim 12, wherein the step of preparing the stainless steel press plate includes applying a layer of titanium directly onto the pressing side of the stainless steel press plate.

15. The method according to claim 1, wherein the step of coating includes applying multiple layers of the diboride-aluminum coating.

16. The method according to claim 1, wherein the diboride-aluminum coating is applied in a two-stage process composed of a gradient based diboride-aluminum coating layer and a top titanium diboride-aluminum coating layer.

17. The method according to claim 16, wherein the gradient based diboride-Al coating layer is 600 nm in thickness.

18. The method according to claim 17, wherein the top diboride-aluminum coating layer is 1,240 nm in thickness.

19. A coated stainless steel press plate manufactured in according with the method comprising: preparing the stainless steel press plate for coating; coating the stainless steel press plate with a diboride doped with 1%-5% by weight aluminum to produce a diboride-aluminum coating, wherein the step of coating includes applying the diboride-aluminum coating to a stainless steel press plate using a magnetron sputter coating system.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0035] FIG. 1 is a schematic of the present coated press plates used in the manufacture of high pressure decorative laminate.

[0036] FIG. 2 is a schematic of an embodiment of a coated press plate in accordance with the present invention.

[0037] FIG. 3 is a schematic of a magnetron sputter coating system for use in accordance with the present invention.

[0038] FIGS. 4 to 25 represent test results generated in accordance with Example 1 as discussed below.

[0039] FIG. 26 is a schematic of layered coatings in accordance with Example 2.

[0040] FIG. 27 is a schematic of alternative layered coatings in accordance with Example 2.

[0041] FIGS. 28 to 31 represent test results generated in accordance with Example 2 as discussed below.

[0042] FIGS. 32 to 40 represent test results generated in accordance with Example 3 as discussed below.

[0043] FIGS. 41 to 47 represent test results generated in accordance with Example 4 as discussed below.

[0044] FIG. 48 is a schematic of an embodiment of a coated press plate in accordance with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0045] The detailed embodiments of the present invention are disclosed herein. It should be understood, however, that the disclosed embodiments are merely exemplary of the invention, which may be embodied in various forms. Therefore, the details disclosed herein are not to be interpreted as limiting, but merely as a basis for teaching one skilled in the art how to make and/or use the invention.

[0046] In accordance with a preferred embodiment, and with reference to FIG. 1, stainless steel press plates 10 are coated with a diboride doped with 1%-5% by weight aluminum (Al) 12 to produce a coated press plate 14 with an aluminum doped diboride-aluminum (diboride-aluminum (Al)) coating 12 used in the manufacture of high pressure decorative laminates. In accordance with the present invention, the hardness of diboride coatings used in the manufacture of stainless steel press plates for the production of high pressure decorative laminates is enhanced by applying the diboride coating to a stainless steel press plate using a magnetron sputter coating system and simultaneously doping the diboride with 1%-5% aluminum (Al).

[0047] As those skilled in the art will appreciate, the stainless steel press plates 10 used in accordance with the present invention are sized for the manufacture of decorative laminate sheets and include parallel first and second planar surfaces 10a, 10b. For example, press plates are commonly made in a variety of sizes depending upon the specific application for which the plate is destined. For example, press plates currently used come in 38 inch (96.52 cm), 50 inch (127 cm) and 62 inch (157.48 cm) widths, 7 foot (2.1336 m), 8 foot (2.4384 m), 10 foot (3.048 m), and 12 foot (3.6576 m) lengths and 0.085 inch (0.2159 cm) to 0.250 inch (0.635 cm) thicknesses. While specific dimensions are disclosed herein, the stainless steel press plates may take a variety of forms without departing from the spirit of the present invention.

[0048] In accordance with the present invention, the diboride is titanium diboride (TiB.sub.2), although it is appreciated it may be possible to achieve results similar to the claimed invention through the use of other diborides known to those skilled in the art to achieve high hardness characteristics when applied to a stainless steel substrate. Titanium diboride is more commonly used commercially for coating surfaces than other diborides, because it can be sputter coated in a magnetron sputtering system at a higher deposition rate.

[0049] As for the press plates 10 used in accordance with the present invention, they are preferably 410 stainless steel high gloss press plates, although those skilled in the art will appreciate that 300, 410, 420, 630, and 633 stainless steel press plates have been coated (exhibiting the same enhancement in surface hardness regardless of the substrate) and used in the manufacture of decorative laminates. As such, it is appreciated a variety of stainless steel high gloss press plates may be used within the spirit of the present invention. As for the 410 stainless steel high gloss press plates, and as those skilled in the art will appreciate, 410 stainless steel press plates are 12% chromium martensitic stainless steel plates that can be heat treated to obtain a wide range of mechanical properties. The alloy has good corrosion resistance along with high strength and hardness. By way of example, a 410 stainless steel press plate in accordance with the present invention has the following composition: chromium 11.5%-13.5% by weight; nickel 0.75% by weight; carbon 0.08%-0.15% by weight; manganese 1.0% by weight; phosphorus 0.04% by weight; sulfur 0.03% by weight; silicon 1.0% weight; and iron 83.53%-85.6% by weight.

[0050] The aluminum doped titanium diboride coating (TiB.sub.2—Al coating) 12 of the present invention is applied on stainless steel press plates 10 used in the production of high pressure laminates. The resulting coated press plates 14 are fabricated with a hardness sufficient for pressing high pressure decorative laminate with 25-60 micron or larger alumina particles at the pressing surface 16 of the high pressure decorative laminate 18 without being scratched. In accordance with the present invention, the TiB.sub.2—Al coating 12 (which is also referenced as “TBA” in the figures) when applied to a stainless steel press plate 10 in the manner described below has a Vickers hardness of at least 35 GPa, and preferably 46 GPa. It has been found that a TiB.sub.2—Al coating 12 of about 3 microns in thickness has sufficient hardness to resist scratching by alumina particles on the pressing surface 16 of a high pressure decorative laminate 18 during the manufacture of thereof. As will be explained below in greater detail, such a TiB.sub.2—Al coating 12 is achieved by doping the TiB.sub.2 with Al at approximately 1%-5% by weight Al, and preferably 2% by weight Al, with a substrate bias of 60-90 Volts (V) (as it has been found that use of a substrate bias level of 60-90 V increases film hardness) and at temperature of 200° C. In order to produce such a thickness, a target power of 200 Watts (W)×2 for the TiB.sub.2 and 3-15 (preferably 5) W×1 for Al is preferred. It is also preferred that a Ti base layer 22 be applied between the TiB.sub.2—Al coating 12 and the stainless steel press plate 10. Further, the TiB.sub.2—Al coating 12 has a minimum bond strength of 1.6 kilogram force (kgf) and preferably 1.8 kgf as determined by a diamond stylus scratch tester.

[0051] In accordance with each of the examples presented below, bonding of the TiB.sub.2—Al coating 12 to the stainless steel press plate 10 is enhanced by thoroughly cleaning the pressing side 20 (that is, the side of the stainless steel press plate 10 that is intended to face the high pressure decorative laminate 18 during the manufacture process and that corresponds to the first planar surface 10a of the present stainless steel press plate 10) of the stainless steel press plate 10 before introducing the pressing side 20 of the stainless steel press plate 10 into a magnetron sputter coating system 100. Bonding is further enhanced by etching the pressing side 20 of the stainless steel press plate 10 prior to applying the TiB.sub.2—Al coating 12. Cleaning, anodic etching, cathodic etching and etching with radio frequency (RF) is accomplished by methods known to those skilled in the use of a magnetron sputter coating system. In accordance with one embodiment as shown with reference to FIG. 2, it has been found that a base layer of titanium 22 applied directly onto the pressing side 20 of the stainless steel press plate 10 before applying the TiB.sub.2—Al coating 12 of this invention further enhances the bonding of the TiB.sub.2—Al coating 12. Improving bonding by cleaning, etching and the use of an intermediate layer between the TiB.sub.2—Al coating 12 and the stainless steel press plate 10 are known to those skilled in the art of using magnetron sputter coating systems.

[0052] It will be appreciated by those skilled in the art that magnetron sputter coating systems are well known and the present invention employs a magnetron sputter coating system well known to those skilled in the art. With that in mind, and with reference to FIG. 3 and considering the operating parameters discussed below, it should be appreciated, the magnetron sputter coating system 100 of the present invention employs 3 applicators 102, 104, 106, wherein two applicators 102, 104 are used in applying TiB.sub.2 and the other applicator 106 is used in applying the Al. This arrangement is designated below where the Targets are identified as “TiB.sub.2×2, Al×1.”

Example 1

[0053] A TiB.sub.2—Al coating was applied via the magnetron sputtering system in accordance with the following conditions (Table 1) with Target Power (DC) for the Al varied to 3 W, 5 W, 7 W, 10 W, 15 W, 20 W, 25 W, 50 W, 100 W, 150 W and 200 W:

TABLE-US-00001 TABLE 1 Substrate (Sub.) Silicon (Si)(100), Stainless Steel (SS) Targets TiB.sub.2 × 2, Al × 1 Target power (DC) TiB.sub.2: 200 W × 2 Al: 3 W, 5 W, 7 W, 10 W, 15 W, 20 W, 25 W, 50 W, 100 W, 150 W, 200 W Substrate bias (RF) −60 V dc Working Pressure (8 × 10.sup.−3 torr) Reactive gas Ar (40 sccm (standard cubic centimeter per minute)) Deposition Time 2 hrs Substrate Temperature 200° C.

[0054] As the results of FIGS. 4 and 5 show, the variation of Target power results in an Al percentage ranging from 1% to 40%. As discussed herein, preferred Al content is 1%-5% by weight, preferably 2%. Complete results gathered from this example are shown in FIGS. 4 to 25.

Example 2

[0055] A TiB.sub.2—Al coating was applied via the magnetron sputtering system in accordance with the following conditions (Table 2) with the gradient layers varied. In particular, a Ti base layer was applied (for example, a base layer having a thickness of 300 nm) and a TiB.sub.2—Al coating was applied at a target power of 5 W (to a thickness of 1240 nm) (see FIG. 26). In addition, a TiB.sub.2—Al coating was applied to the Ti base layer with varying Al contents (see FIG. 27 where a TiB.sub.2—Al coating with layers of various compositions from its lowermost portion to its uppermost portion). In particular, different Al contents were applied using applied target powers ranging from 5 W to 100 W (referenced as TBA5-TBA100, respectively, which stands for TiB.sub.2—Al applied with target power of #W (which designation is used throughout the figures) to produce layered coatings of different Al contents which were then tested as shown below.

TABLE-US-00002 TABLE 2 Substrate (Sub.) Silicon (Si)(100), Stainless Steel (SS) Target TiB.sub.2 × 2, Al × 1 Target power (DC) TiB.sub.2: 200 W × 2 Al: 5 W (resulting in a TiB.sub.2—Al coating with 2% Al) TiB.sub.2: 200 W × 2 Al: 5 W-100 W Substrate Bias (RF) −60 V dc Working Pressure (8 × 10.sup.−3 torr) Reactive gas Ar (40 sccm) Deposition time 2 hrs Substrate temperature 200° C.

[0056] The results of this example are shown in FIGS. 28 to 30. Based upon these results it is apparent a Ti base layer between the TiB.sub.2—Al coating and the stainless steel press plate is desirable. While the inclusion of the Ti base layer may result in slightly reduced hardness, the enhanced adhesion characteristics when using a Ti base layer dictate the desirability of the use of a Ti base layer in the manufacture of a coated press plate in accordance with the present invention.

Example 3

[0057] A TiB.sub.2—Al coating was applied via the magnetron sputtering system in accordance with the following conditions (Table 3) with the substrate bias varied:

TABLE-US-00003 TABLE 3 Substrate (Sub.) Silicon (Si)(100), Stainless Steel (SS) Target TiB.sub.2 × 2, Al × 1 Target power (DC) TiB.sub.2: 200 W × 2 Al: 5 W (resulting in a TiB.sub.2—Al coating with 2% Al) Substrate bias (RF) Floating, −30 V, −60 V, −90 V, −120 V Working pressure (8 × 10.sup.−3 torr) Reactive gas Ar (40 sccm) Deposition time 2 hr Substrate Temperature 200° C. Substrate rotation 5 rpm

[0058] The results of this example are shown in FIGS. 31 to 40, and support the conclusion to use a substrate bias of 60-90 V and at a temperature of 200° C. in accordance with the fabrication of coated press plates in accordance with the present invention.

Example 4

[0059] A TiB.sub.2—Al coating was applied via the magnetron sputtering system in accordance with the following conditions (Table 4) with the nitrogen doping at various levels:

TABLE-US-00004 TABLE 4 Substrate (Sub.) Silicon (Si)(100), Stainless Steel (SS) Target TiB.sub.2 × 2, Al × 1 Target power (DC) TiB.sub.2: 200 W × 2 Al: 5 W (resulting in a TiB.sub.2—Al coating with 2% Al) Substrate bias (RF) −60 V Working pressure (8 × 10.sup.−3 torr) Reactive gas Ar (40 sccm) N.sub.2 (1, 2, 3, 4 sccm) Deposition time 2 hr Substrate temperature 200° C. Substrate rotation 5 rpm

[0060] The results of this example are shown in FIGS. 41 to 47, and dictate the conclusion that nitrogen doping is not desirable when fabricating coated press plates in accordance with the present invention.

[0061] Based upon the results of Examples 1-4, the following preferred criteria, as shown with reference to FIG. 48, for the application of the TiB.sub.2—Al coating 12 have been established. First, the stainless steel press plate 10 (preferably, composed high gloss 410 stainless steel) is prepared for the application of the TiB.sub.2—Al coating 12. The pressing side 20 of the stainless steel press plate 10, that is, the side of the press plate 10 to which the TiB.sub.2—Al coating 12 is to be applied, is thoroughly cleaned and etched. Thereafter, a base layer of titanium 22, preferably with a thickness of 300 nm is applied directly onto the pressing side 20 of the stainless steel press plate 10 via the magnetron sputtering system 100.

[0062] The TiB.sub.2—Al coating 12 is then applied. The TiB.sub.2—Al coating 12 is applied in a two-stage process composed of a gradient based TiB.sub.2—Al coating layer 12a and top TiB.sub.2—Al coating layer 12b. The gradient based TiB.sub.2—Al coating layer 12a is preferably 600 nm in thickness. The target power of 200 W×2 for the TiB.sub.2 is used in conjunction with a sequentially increased target power of 5 W×1, 7 W×1& 10 W×1 for the Al. As such, the gradient based TiB.sub.2—Al coating layer 12a will have a 200 nm thickness layer of TiB.sub.2—Al 12a′ applied at a target power of 200 W×2 for the TiB.sub.7 and a target power of 5 W×1 for the Al, a 200 nm thickness layer of TiB.sub.2—Al 12a″ applied at a target power of 200 W×2 for the TiB.sub.2 and a target power of 7 W×1 for the Al, a 200 nm thickness layer of TiB.sub.2—Al 12a′″ applied at a target power of 200 W×2 for the TiB.sub.2 and a target power of 10 W×1 for the Al, The TiB.sub.2—Al coating layer 12a is preferably applied with a substrate bias of 60-90 V and at a temperature of 200° C.

[0063] The top TiB.sub.2—Al coating layer 12b is preferably 1,240 nm in thickness. The top TiB.sub.2—Al coating layer 12b is applied at a target power of 200 W×2 for the TiB.sub.2 and a target power of 5 W×1 for the Al to product a top TiB.sub.2—Al coating layer 12b with 2%-3% by weight Al. The top TiB.sub.2—Al coating layer 12b is preferably applied with a substrate bias of 60-90 V and at a temperature of 200° C.

[0064] While high hardness is achieved it is found that poor adhesion for the TiB.sub.2—Al coating may be encountered. In deciding upon a desired hardness, and ultimately ranges for the operating parameters discussed above, it should be appreciated that hardness must be balanced with the desire to protect the press plate from protection against grit, which has a Vickers hardness of at least 1,200 HV (11.77 GPa), and is preferably 1800 HV (17.65 GPa) to 2000 HV (19.61 GPa), contained in high pressure laminates being pressed as well as adhesion of the coating to the substrate wherein adhesion is known to increase when the coating is softer and thinner.

[0065] Enhanced adhesion is achieved by optimizing film crystallinity and preferred orientation, reducing grain sizes, and providing solid solution induced film compressive stress. As the examples above demonstrate, doping a few percent of Al in TiB.sub.2—Al reduces grain size (FESEM (Field Emission Scanning Electron Microscope) and XRD (FWHM (Full width at half maximum)), enhance TiB.sub.2 (001) texture, Al atoms substitute Ti or B to form solid solution, and increases film compressive stress. It was found that approximately 2% Al in TiB.sub.2 makes the hardest films of 46 GPa, but with the highest stress and poor adhesion, while at 9% to 12% Al in TiB.sub.2 the coating was found to have only moderate hardness of 15 GPa to 30 GPa and better adhesion level. This is believed to result from amorphous structure and low film stress (transition from compressive to tensile). It has further been found that a gradient TiB.sub.2—Al film or intermediate metal Ti layer is effective to improve film adhesion.

[0066] In addition, to those operating criteria disclosed above, it is preferred that the magnetron sputtering system 100 be operated under the following conditions: a working pressure of 8×10.sup.−3 torr and reactive gas of Ar (40 sccm). With regard to the scan rate, it is appreciated the scan rate when will be determined so as to curtail temperature gradient within the substrate.

[0067] While the preferred embodiments have been shown and described, it will be understood that there is no intent to limit the invention by such disclosure, but rather, is intended to cover all modifications and alternate constructions falling within the spirit and scope of the invention.