WO2019236107A1

WO2019236107A1 - Multilayer coatings

Info

Publication number: WO2019236107A1
Application number: PCT/US2018/036738
Authority: WO
Inventors: Chalam Kashyap; Kuan-Ting Wu; Chi-Hao Chang
Original assignee: Hewlett-Packard Development Company, L.P
Priority date: 2018-06-08
Filing date: 2018-06-08
Publication date: 2019-12-12

Abstract

A multilayer coating is provided. The multilayer coating includes a coating layer having about 2-15% calcium silicate with hexagonal boron nitride (hBN) and/or graphene. The multilayer coating also includes an intermediate layer between the coating layer and a substrate.

Description

MULTILAYER COATINGS

BACKGROUND

[0001] Many substrate surfaces have low hardness and low resistance to wear, abrasion, and corrosion. Protective surface coatings are one means by which the negative aspects of substrates are mitigated. Therefore, surface coatings in the form of primer/paints and/or powder coats are applied to substrates in order to increase hardness, thereby increasing the corrosion or wear resistance of the substrate surface.

BRIEF DESCRIPTION OF THE DRAWINGS

[0002] FIG. 1 illustrates an example of a multilayer coating.

[0003] FIG. 2 illustrates another example of a multilayer coating.

[0004] FIG. 3 illustrates yet another example of a multilayer coating.

[0005] FIG. 4 illustrates still yet another example of a multilayer coating.

[0006] FIG. 5 illustrates an example of another multilayer coating.

[0007] FIG. 6 illustrates an example of yet another multilayer coating.

[0008] FIG. 7 illustrates an example of a process flow for producing a coating composition for a multilayer coating.

[0009] FIG. 8 illustrates an example of another process flow for producing a coating composition for a multilayer coating.

[00010] FIG. 9 illustrates an example of yet another process flow for producing a coating composition for a multilayer coating.

DETAILED DESCRIPTION

[00011] Many portable electronic devices and computers (e.g., notebooks, tablet computers, desktop computers) are painted to provide color and to protect the underlying surfaces. Many of these paints include minerals such as calcium silicate. However, these materials tend to lack adequate hardness and therefore suffer wear and in some cases corrosion. Consequently, these materials may be unsatisfactory for use on many portable electronic devices.

[00012] This disclosure relates to a coating composition and a multilayer coating. The coating and coating composition includes calcium silicate with inserted layers of two- dimensional hexagonal boron nitride (hBN) and/or graphene. The coating may be formed as a corresponding solution by blending calcium silicate with graphene, hBN or both. A corresponding solution can be applied to a substrate to produce a painting layer having high strength and toughness with a pencil hardness that is greater than about 6H. In one example, the presence of hBN and/or graphene results in a composition capable of forming a coating that is about 3 times stronger and approximately 25% stiffer than a coating that includes only a calcium silicate (tobermorite) filler.

[00013] The composition disclosed herein may be three times stronger and

approximately 25% stiffer than the plain material calcium silicate (e.g., tobermorite). Additionally, it provides better surface coverage and favorable coating uniformity. On metal substrates, the coating also affords desirable corrosion resistance. The pencil hardness of the coatings described herein provide for adequate substrate surface corrosion and/or wear resistance allowing for use of the coatings in health care, portable electronic, construction, nuclear refractory and aerospace coating applications.

[00014] In some examples, the coating composition can include a liquid medium allowing the coating to be applied over an intermediate layer disposed over a substrate. The intermediate layer between the coating layer and the substrate can include one or more of an oxide layer, a primer layer, a base coat layer, a clear top coat layer, and a powder coat layer. The individual layers of the intermediate layer are not limited to any particular order when layered over the substrate.

[00015] As an example, the coating composition described herein can comprise a coating layer that includes about 2-15% (w/w) calcium silicate with two dimensional hexagonal boron nitride (hBN) and/or graphene. [00016] Fig. 1 illustrates an example of a multilayer coating 100. The multilayer coating 100 includes a coating layer 1 10 and one or more intermediate layers 120 between the coating layer 1 10 and a substrate 130. For example, the coating layer 1 10 includes about 2-15 wt% calcium silicate with two dimensional hexagonal boron nitride (hBN) and/or graphene. The high aspect ratio of graphene and hBN enhances the hardness of the coating layer 1 10 and can provide better surface coverage and coating uniformity as well as offer a corrosion resistant barrier coating on the substrate 130. In some examples, the coating layer has an average thickness of about 10pm to about 25pm. In one example, the coating layer includes about 4-10 wt% (w/w) calcium silicate.

[00017] As an example, the amount of hBN in a coating composition used to provide the coating layer 1 10 can range from 3-15 wt% based on the total weight of calcium silicate. The hBN can have an aspect ratio of about 5-50. hBN has a higher aspect ratio and increased viscosity compared to standard boron nitride (BN) due to the platy shape of hBN.

[00018] As another example, the amount of graphene in a coating composition used to provide the coating layer 1 10 can range from 0.3-5.0 wt% based on total weight of calcium silicate. The graphene can have an aspect ratio of about 100-5000. In one example, the term "graphene" is defined as a one-atom-thick sheet of sp2 bonded carbon atoms that are densely packed in a honeycomb crystal lattice. The graphene may be graphite free or essentially graphite free (e.g., less than 0.5% graphite). In another example, these coating compositions may also contain varying amounts of graphite. Several production techniques are available for the fabrication of "graphene". For example, graphene material is selected from the group consisting of single layer graphene, multi-layer graphene, graphene nanosheets, graphene microsheet, graphene nanoribbon, reduced graphene, and any combination thereof.

[00019] In one example, the substrate 130 is a metal substrate. Examples of metals that may be used as the substrate 130 include aluminum, an aluminum alloy, magnesium, a magnesium alloy, lithium, a lithium alloy, titanium, a titanium alloy, and combinations thereof.

[00020] By way of further example, the intermediate layer 120 may be an oxide layer. The oxide layer 120 can be disposed over the substrate 130 using an electrochemical surface treatment process for generating oxide coatings on metals. In one example, the oxide coating 120 is disposed on the substrate 130 using microarc oxidation (MAO). In another example, an electrolytic passivation process, such as anodization, is applied to the metal substrate to increase the thickness of the natural oxide layer on the surface of the metal substrate. The process used to apply the oxide layer 120 may vary depending on the metal used as the substrate. In one example, average thickness of the oxide layer 120 can range from about 3-5pm.

[00021] Fig. 2 illustrates an example of a multilayer coating 200. The multilayer coating 200 includes a coating layer 210 and an oxide layer 220 disposed over a substrate 230 (e.g., a metal substrate). The coating layer 210, oxide layer 220 may be provided as described in reference to Fig. 1 above.

[00022] In the example of FIG. 2, the multilayer coating 200 also includes a primer layer 240 disposed between the coating layer 210 and the oxide layer 220. Thus, the oxide layer 220 and the primer layer 240 can define an intermediate layer between the coating layer 210 and the substrate 230. In some examples, the average thickness of the primer layer 240 can range from about 10-15pm. The primer layer 240 functions as a leveler and protector, and to facilitate application of the coating. The primer layer 240 can be included in the multilayer coating 200, for example, to mitigate the coating from bubbling or peeling off the substrate 230. The primer layer 240 may also protect the substrate 230 from corrosion, heat differences, and/or UV-light. Examples of primer compositions for the primer layer 240 include polyacrylic primers, polyurethane primers and epoxy primers.

[00023] Examples of primer fillers can include carbon black, titanium dioxide, clay mica, talc, barium sulfate, calcium carbonate, synthetic pigment, metallic powder, aluminum oxide, graphene, graphite, organic or inorganic powders. In addition, primers can include one or more fillers depending on the desired application and/or substrate layer 230 of the multilayer coating 200.

[00024] Fig. 3 illustrates another example of a multilayer coating 300. The multilayer coating 300 includes a coating layer 310 disposed over a base coat layer 350, the base coat layer disposed over a primer layer 340. The primer layer 340 is disposed over a substrate 330. In this example, the base coat layer 350 is applied over a primer layer 340 that has been applied to the substrate 330. Examples of the material composition and thicknesses of the coating layer 310, the primer layer 340 and the substrate 330 are as described in Figs. 1 and 2 above. The average thickness of the base coat layer 350 can range from about 10-25pm.

[00025] By way of example, the base coat layer 350 can include barium sulfate, talc dyes or color pigments. The base coat layer 350 can include the desired visual properties of color and effects. Three general categories of base coats that may be used as the base coat layer include solid, metallic, and pearlescent pigments. For example, a metallic base coat can include aluminum flakes to create a metallic finish. In one example, the primer layer 240 is applied to a porous substrate layer (e.g., metal in the absence of an oxide layer) and the base coat layer 350 is applied over the primer layer.

[00026] Fig. 4 illustrates another example of a multilayer coating 400. The multilayer coating 400 includes a clear top coat layer 460 disposed over a coating layer 410, the coating layer 410 disposed over a primer layer 440, and the primer layer 440 disposed over a substrate 430. The material composition and thicknesses of the coating layer 410, the primer layer 440 and the substrate 430 are as described in Figs. 1 and 2 above, and reference may be made back to such description for additional information. The clear top coat layer 460 may provide a glossy and transparent coating that forms the final interface with the environment. For this reason, an example clear top coat layer 460 is formulated to resist abrasion and chemically stable enough to withstand UV light.

[00027] In one example, the clear top coat layer 460 can be applied to the multilayer coating in the form of either a solvent or water-borne clear coat. For example, the formulation of the clear coat is chosen so that it will not "re-dissolve" the layer it is disposed over. In one example, a clear top coat layer is a UV resistant and/or an anti fingerprint oleophobic coating layer. In another example, the clear top coat layer 460 includes a polyurethane resin to give the top coat layer 460 a soft feel. In some examples, the average thickness of the clear top coat layer 460 can range from about 10-25pm.

[00028] Fig. 5 illustrates another example of a multilayer coating 500. The multilayer coating 500 includes a coating layer 510 disposed over a base coat layer 550. The base coat layer 550 is disposed over a primer layer 540, and the primer layer 540 disposed over a powder coat 570. The powder coat 570 is disposed over a substrate 530. The material composition and thicknesses of the coating layer 510, the base coat layer 550, the primer layer 540 and the substrate 530 are as described in Figs. 1 -3 above, and reference may be made back to such description for additional information.

[00029] As an example, the average thickness of the powder coat layer 570 can range from about 30-50pm. The powder coat layer 570 (e.g., pigment encapsulated in a powdered resin) can include a resin, such as an acrylic, urethane, polyurethane, polyester, silicon polyester, polyester TGIC, PVDF, epoxy resin, or silicon epoxy resin. Some resins, such as PVDF, have outstanding weatherability, while epoxy coatings are typically intended for interior use. Powder coatings and liquid coatings made from the same resin and pigment will have practically the same performance characteristics. For a given resin, the decision to use a powder or liquid coating mainly depends on the application technique.

[00030] In addition, powder coats used to form the powder coat layer 570 can include one or more fillers depending on the desired application and/or the particular substrate 530 of the multilayer coating 500. Examples of powder coat fillers can include carbon black, titanium dioxide, clay mica, talc, barium sulfate, calcium carbonate, synthetic pigment, metallic powder, aluminum oxide, graphene, organic or inorganic powders.

[00031] Fig. 6 illustrates another example of a multilayer coating 600. The multilayer coating 600 includes a clear top coat layer 660, which is disposed over a coating layer 610. The coating layer 610 is disposed over a primer layer 640, and the primer layer 640 disposed over a powder coat layer 670. The powder coat layer 670 is disposed over a substrate 630. The material composition and thicknesses of the clear top coat layer 660, the coating layer 610, the primer layer 640, the powder coat 670 and the substrate 630 are as described in Figs. 1 -5 above, and reference may be made back to such descriptions for additional information.

[00032] FIG. 7 illustrates an example of a process flow 700 for producing a coating composition for a multilayer coating described herein. At 705, an amount of calcium oxide is provided, and at 710, an amount of silicon dioxide is provided. At 720, the calcium oxide 705 and silicon dioxide 710 are mixed, such as at about pH 2-4 to produce calcium silicate. As an example, at 705, the amount of calcium oxide that is provided to the mixture can range from about 60-70 wt% based on the total

composition. As another example, at 710, the amount of silicon dioxide provided can range from about 30-40 wt%.

[00033] At 730, a corresponding amount of graphene is provided based on the total weight of calcium silicate. For example, the amount of graphene for the mixture can range from about 0.3-5.0 wt% based on the total weight of calcium silicate. At 740, the calcium silicate and graphene are blended. In one example, the calcium silicate and graphene are blended using a churner or drum mixing apparatus. At 750, the pH of the calcium silicate-graphene mixture is adjusted to a range of between about 6.5-7.5. At 760, the calcium silicate-graphene mixture is spray dried to produce a corresponding coating composition (e.g., in powder form). The coating composition may be reconstituted in a liquid (e.g., with pigments and fillers) to provide a paint solution that can be applied onto a substrate through to provide a multilayer coating, such as disclosed herein (see, e.g., Figs. 1 -6).

[00034] FIG. 8 illustrates another example of a process flow 800 for producing a coating composition for a multilayer coating described herein. At 805, an amount of calcium oxide is provided, and at 810, an amount of silicon dioxide is provided for mixing. For example, at 805, the amount of calcium oxide in the mixture to produce calcium silicate can range from about 60-70 wt% based on the total composition. As a further example, at 810 the amount of silicon dioxide provided can range from about 30- 40 wt%. At 820, the calcium oxide and silicon dioxide are mixed, such as at about pH 2-4 to produce calcium silicate. At 830, an amount of hBN is provided. For example, the amount of hBN provided at 830 can range from about 3-15 wt% based on the total weight of calcium silicate. At 840, the calcium silicate and hBN are blended. In one example, the calcium silicate and hBN are blended using a churner or drum mixing apparatus. At 850, the pH of the calcium silicate-hBN mixture is adjusted to a range of between about 6.5-7.5. At 860, the calcium silicate-hBN mixture is spray dried to produce a corresponding coating composition (e.g., in powder form). The coating composition may be reconstituted in a liquid (e.g., with pigments and fillers) to provide a paint solution that can be applied onto a substrate through to provide a multilayer coating, such as disclosed herein (see, e.g., Figs. 1 -6).

[00035] FIG. 9 illustrates another example of a process flow for producing a coating composition for a multilayer coating described herein. At 920, calcium oxide and silicon dioxide are mixed at about pH 2-4 to produce calcium silicate. At 905, the amount of calcium oxide provided in the mixture to produce calcium silicate can range from about 60-70 wt% based on the total composition and at 910 the amount of silicon dioxide provided can range from about 30-40 wt%. At 930, the amount of graphene provided can range from about 0.3-5.0 wt% based on the total weight of calcium silicate. At 935, the amount of hBN provided to the mixture can range from about 3-15 wt% based on the total weight of calcium silicate. At 940, the calcium silicate, hBN and graphene are blended. In one example, the calcium silicate, graphene and hBN are blended using a churner or drum mixing apparatus. At 950, the pH of the calcium silicate with hBN and graphene mixture is adjusted to a range of between about 6.5-7.5. At 960, the calcium silicate with hBN and graphene mixture is spray dried to produce a corresponding coating composition (e.g., in powder form). The coating composition may be

reconstituted in a liquid (e.g., with pigments and fillers) to provide a paint solution that can be applied onto a substrate through to provide a multilayer coating, such as disclosed herein (see, e.g., Figs. 1 -6).

[00036] As a further example, to supply the liquid medium of the coating composition (e.g., produced according to Figs. 7, 8 or 9), water will usually be used in combination with organic liquid, which organic liquid may also be referred to herein as the“solvent”.

In one example, the solvent is selected from solvents capable of dispersing the calcium silicate, hBN and/or graphene in the liquid medium. In some examples,

the coating compositions will be solvent based. Example coating compositions that contain water tend to be infinitely dilutable with water. Water is present in a coating composition in an amount from at least about 20, and generally not above about 70 wt%, based on total composition weight. The organic liquid can be a low-boiling organic liquid, although it also can be a high-boiling organic liquid, and may include mixtures of the foregoing. High-boiling organic liquids boil above about 100° C. The low-boiling organic liquids have a boiling point at atmospheric pressure below about 100° C, and may be water-soluble. Examples of such liquids include acetone, or low molecular weight alcohols such as methanol, ethanol, n-propylalcohol and isopropylalcohol, and further include ketones that boil below 100° C., such as water-soluble ketones, e.g., methyl ethyl ketone. In one example, the coating composition includes sufficient vehicle solvents to produce the viscosity desired for the particular method of applying the liquid coating composition to a substrate.

[00037] In some examples, the coating layer and/or intermediate layers of a multilayer coating are applied as a liquid by brush application, curtain coating, dipping, rolling or spraying techniques. For example, the coating compositions may be applied by any of these various techniques, such as immersion techniques, including dip drain and dip spin procedures. In another example, a spray technique may be used as well as combinations, e.g., spray and spin and spray and brush techniques. Coated articles that are at an elevated temperature may be coated, often without extensive cooling, by a procedure such as dip spin, dip drain or spray coat. As a further example, spraying is accomplished with an air sprayer. In another example, rollers are used to smooth the wet spray applied layer of a multilayer coating composition.

[00038] By way of further example, a coating layer and/or intermediate layer composition is applied to a substrate at a level of about 50-1000 square feet/gallon, and more preferably from about 250-500 square feet/gallon. In one example, the coating layer and/or intermediate layer compositions are applied at 50-80°C.

[00039] An applied coating composition is either allowed to dry on the substrate (or an intermediate layer) surface disposed on the substrate, usually under ambient or greater heat conditions, or rinsed from the surface after a sufficient reaction time. In one example, the coating composition is allowed to dry for 10-30 minutes. Once the layer has dried it can be cured. In one example, the multilayer coating is cured at 150-180°C for about 20-40 minutes.

[00040] What has been described above are examples. One of ordinary skill in the art will recognize that many further combinations and permutations are possible.

Accordingly, this disclosure is intended to embrace all such alterations, modifications, and variations that fall within the scope of this application, including the appended claims. Additionally, where the disclosure or claims recite "a," "an," "a first," or "another" element, or the equivalent thereof, it should be interpreted to include one or more than one such element, neither requiring nor excluding two or more such elements. As used herein, the term“includes” means includes but not limited to, and the term“including” means including but not limited to. The term“based on” means based at least in part on.

Claims

CLAIMS What is claimed is:

1. A multilayer coating comprising:

a coating layer that includes about 2% -15% calcium silicate with hexagonal boron nitride (hBN) and/or graphene; and

an intermediate layer disposed between the coating layer and a substrate.

2. The multilayer coating of claim 1 , wherein the intermediate layer comprises an oxide layer disposed over the substrate.

3. The multilayer coating of claim 2, wherein the intermediate layer further comprises a primer layer disposed over the oxide layer.

4. The multilayer coating of claim 1 , wherein the intermediate layer comprises a primer layer and a base coat layer disposed over the substrate.

5. The multilayer coating of claim 1 , wherein:

the intermediate layer comprises a primer layer disposed over the substrate, and the multilayer coating further comprises a clear top coat layer disposed over the coating layer.

6. The multilayer coating of claim 1 , wherein the intermediate layer comprises a powder coat layer, a primer layer, and a base coat layer disposed over the substrate.

7. The multilayer coating of claim 1 , wherein:

the intermediate layer comprises a powder coat layer, and a primer layer disposed over the substrate, and the multilayer coating further comprises a clear top coat layer disposed over the coating layer.

8. The multilayer coating of claim 1 , wherein the substrate comprises a metal selected from the group consisting of aluminum, aluminum alloys, magnesium, magnesium alloys, lithium, lithium alloys, titanium, titanium alloys, and combinations thereof.

9. The multilayer coating of claim 1 , wherein the coating layer has pencil hardness greater than or equal to 6H.

10. The multilayer coating of claim 1 , wherein the coating layer comprises about 4%- 10% (w/w) calcium silicate.

1 1. The multilayer coating of claim 1 , wherein the coating layer has an average thickness of about 10 pm to about 25 pm.

12. A method comprising:

applying an intermediate layer over a substrate; and

applying a coating layer that includes about 2%-15% (w/w) calcium silicate with hexagonal boron nitride (hBN) and/or graphene over the intermediate layer.

13. The method of claim 12, wherein applying the intermediate layer further comprises applying one or more of an oxide layer, a primer layer, a powder coat layer, and a base coat layer.

14. The method of claim 12, further comprising applying a clear top coat over the coating layer.

15. A coating composition comprising:

2%-15 % calcium silicate;

hexagonal boron nitride (hBN) and/or graphene; and

a liquid medium, wherein the coating composition provides a pencil hardness of greater than or equal to 6H as a cured coating on a substrate.