Patent Application
20220145128
The present application relates to nanostructured hybrid sol-gel coatings for surface protection.
The present invention is particularly useful for providing coatings on metal surfaces, however it is to be understood that the coatings of the invention can also be used on plastic surfaces, including metal coated plastics surfaces and 3D printed/additive manufactured products.
Metals are used as structural materials in many industries including construction, mechanical and electrical engineering, transport and medical. The most commonly used metals are iron, aluminium, copper, titanium and zinc.
After aluminium, iron is the second most abundant metal in the Earth's crust, and it's production exceeds the production of all other metals put together. 98% of iron is used for the fabrication of steel in all its forms (stainless, mild steel and others), which is primarily used in the construction, engineering and transport industries. The world production of steel has been constantly increasing from 1996 (750 millions of tonnes) to exceed 1,600 millions of tonnes in 2016.
Aluminium is the most abundant metal in the Earth's crust and the second most produced metal. Its good electrical and heat conductivity along with its favourable high strength-to-weight ratio made it an excellent material for the electronics and transport industries. For example, modern aircrafts are composed of 75-80% of aluminium for the fabrication of fuselage components, skin material and for frame and wing construction. The global automotive industry (excluding China) consumed 2.87 million tonnes of aluminium in 2014, with this figure expected to reach 4.49 million tonnes by 2020. Key factors of this growth include both rising automotive production and wider use of aluminium in modern cars. The main reason for this trend is to reduce the weight of vehicles, by replacing heavy steel parts, and consequently reducing the overall fuel consumption. For this reason, more and more car parts are being made from aluminium: engine radiators, wheels, bumpers, suspension parts, engine cylinder blocks, transmission bodies and body parts: the hoods, the doors and the frame. As a result, since the 1970s the share of aluminium in the overall weight of an average car increased from 35 kg to 152 kg. Experts project that by 2025 average aluminium content in a car will reach 250 kg.
Because of its high conductivity and low production cost, copper is the most utilised metal for electrical applications. Copper forms alloys more freely than any other metal and, as such, is widely employed as alloying element of a large number of metals, including aluminium, tin, nickel, steel and zinc. Copper is however, highly sensitive to environmental corrosion.
Titanium and its alloys have a very favourable strength to mass ratio. They are also resistant to corrosion because their surface develops a thin and resilient oxide layer. They are mainly employed in the aerospace and medical industries where strength, lightness and resistance to corrosion are needed. The major issue of titanium is however, its high cost in comparison with aluminium, copper or steel.
Zinc is mainly used as a sacrificial coating to protect ferrous materials (iron and steel) from corroding in ambient atmosphere. Zinc is also used as alloy and/or alloying element for semi-manufactured products, such as coins, small electrical fuses, anode ribbon for buried pipelines, and to make both decorative and functional products like door handles, marine fittings, plumbing components and screw fixings. Zinc is water resistant but is quite sensitive to acidic and basic environments.
The most widely used metals described above are vulnerable to corrosion and associated environmental effects, and often require a surface treatment to be applied to provide additional corrosion resistance. Surface treatments commonly applied include anodization, conversion coatings, phosphatation and highly cross-linked organic polymeric coatings (water borne or solvent based). These treatments are particular to a specific metal and are therefore not versatile for any metal surface. In addition to this, these treatments are either not fulfilling the current environmental regulations, or more demanding corrosion resistances, processing simplicity or cost.
The inclusion of crosslinking chemistries in pre-determined proportions can decrease the porosity of the coatings and improve the structural strength and anticorrosion properties. Examples of crosslinking chemistries include bis-silanes, diaminoalkanes, diisocyanates, divinylbenzenes, acrylics, amides & polyam ides, aziridines, benzoguanamines, carbodiimide resins, glyourils, isocyanates, melamines, polyols, silicon based compounds, urea-formaldehydes, urethanes & polyurethanes.
One of the most important aspects of the design of coatings for corrosion protection is the use of environmentally friendly compounds in the formulation. While many attempts have been reported in the literature focusing on waterborne systems, hybrid sol-gel coatings have received particular attention over the last few decades, as they can be adapted for use as a pre-treatment layer or as a primer on different metallic alloys. Offering a promising alternative to the chromate based systems outlined above, transparent, zirconium based hybrid sol-gel coatings have excellent potential to provide a complete anticorrosive, durable and aesthetically desirable system for the above-mentioned metals.
The critical requirements in the design of protective coatings for the protection of metals are high corrosion resistance, including barrier properties and/or corrosion inhibition, high adhesion properties to the substrate to be protected, along with thermal and UV resistance in both neutral and acid humidity. Known metal coatings do not achieve all of these critical requirements. This problem is addressed by the present invention.
In another aspect, the problem of adhesion between two surface layers, and the introduction of multifunctionality to the sol-gel coating, is addressed by the present invention. One of the core challenges, in the use of standard hybrid sol-gels as a direct replacement for chromium based coatings on bare metals, is the poor adhesion between the two surfaces. As a result of this poor adhesion, anticorrosion performances are strongly affected, with delamination observed after short exposure times to corrosive environments.
The present invention seeks to alleviate the disadvantages of known surface coatings, in particular metal surface coatings, including metal coated plastics.
Accordingly, one aspect of the present invention provides compositions as claimed in claim 1, for forming nanostructured hybrid sol-gel coatings for surface protection. The present invention also provides nanostructured hybrid sol-gel coatings and methods of producing said nanostructured hybrid sol-gel coatings as set forth in other independent claims of the appended claims.
The present invention provides compositions for forming multifunctional hybrid sol-gel coatings, the compositions of the present invention comprising combinations of methacrylate silanes and a zirconium alkoxide-based complexes for the protection of metal surfaces against environmental degradation including corrosion, UV exposure, thermal resistance, acid weathering and humidity.
The present invention has the advantage that it provides formulations that are particularly suitable for coating metal surfaces, including metal coated plastics materials. The present invention is particularly useful for forming coatings on metal surfaces, however it is to be understood that the coatings of the present invention can also be used for coating plastics surfaces, including metal coated plastics surfaces and 3D printed/additive manufactured products.
The compositions and coatings of the present invention have the advantage that they provide transparent, zirconium-based hybrid sol-gel coatings which provide a complete anticorrosive, durable and aesthetically desirable system for the above-mentioned metals.
The coatings of the present invention for protection of metals provide the advantages of high corrosion resistance, including barrier properties and/or corrosion Inhibition, high adhesion properties to the substrate to be protected along with thermal and UV resistance in both neutral and acid humidity. The coatings formed by the composition of the present invention have the significant advantage of simultaneously achieving and providing all these properties by providing highly densified hybrid sol-gel coatings with surfaces functionalised with highly adherent inorganic chemistries.
The invention provides for the use of a sol-gel coating composition as described herein as an anti-corrosion coating suitable for a metal surface.
The invention also provides for the use of a chelate as described herein as an anti-corrosion coating suitable for a metal surface.
The present invention provides highly densified hybrid sol-gel coatings with surfaces functionalised with highly adherent inorganic chemistries.
The invention also provides a method for preparing the hybrid sol-gel coatings of the present invention. Advantageous embodiments of the hybrid sol-gel coating and of the method of preparation, respectively, are provided in the dependent claims.
An advantage of the present invention is that it simultaneously demonstrates properties of high corrosion resistance, including barrier properties and/or corrosion inhibition as well as high adhesion properties to the substrate to be protected, together with thermal and UV resistance in both neutral and acid humidity.
Zr Chemistry
The organometallic precursor of the present invention, is preferably, a transition metal precursor which most preferably, comprises zirconium. The zirconium precursor may be zirconium (VI) propoxide (Zr(OPr)4).
In one embodiment the organometallic precursor is a transition metal precursor for example, a precursor of zirconium. The inclusion of a zirconium precursor is understood to improve the adhesion of the coating, and/or the pH stability of the coating, and/or the film hardness. The zirconium precursor of choice is zirconium (VI) n-propoxide (Zr(OPr)4) (70% weight in 2-propanol). The zirconium precursor has a greater reactivity to water when compared to the reactivity of the organosilane precursor. Therefore, to avoid formation of undesired zirconium oxide precipitate, the Zr(OPr)4 must be chelated, reducing its potential for binding from 4 to 2 (or 1) sites. This is achieved by using a bidentate (or monodentate) ligand in an equimolar ratio. Typical chelates include carboxylic acids such as methacrylic acid and acetic acid (and also (3-aminopropyl)triethoxysilane). When MAPTMS is used at the host matrix former, methacrylic acid is the preferred ligand as it contains methacrylic functionalities which can further polymerize with the organic counterpart of the silane and minimise porosity of the coatings.
Tridentate Silanes
In another aspect of the present invention, the problem of poor adhesion in the use of sol-gel coatings is addressed. The most popular known strategy to increase adhesion of organic and sol-gel coatings on metal is by mechanical interlocking through an anodic layer deposited on the metal. The present invention also provides tridentate silanes that will simultaneously enable the irreversible immobilisation of sol-gel nanomaterials on a metal surface while also contributing to the densification process of the coating on the metal substrate. In this aspect, the present invention accordingly also provides a method, outlined at
APTES is included to form a coordination bond with the zirconium propoxide via sharing its pair of free electrons located on the nitrogen atom with the d free orbitals of the zirconium atom (
BTSPA is included as a tridentate silane sol-gel reactive precursor and is used within the transition metal interlocked silane nanomaterial system. The tridentate silane is first activated by the catalyst prior to being incorporated at the end of the sol-gel synthesis, thus reacting as a surface modifier of the interlocked nanomaterial material, as shown in
In the first aspect, the present invention provides a formulation for forming a novel highly densified hybrid sol-gel coating based on the interconnectivity of two hybrid networks formed from a methacrylate silane, preferably, 3-(trimethoxysilyl)propyl methacrylate (MAPTMS) and a transition metal complex, preferably a complex of zirconium, as shown in
In a second aspect, the present invention provides the development and use of a novel highly densified hybrid sol-gel coating based on the interconnectivity of two hybrid networks formed from combinations of the silane precursors (PhTEOS (phenyltriethoxysilane)/TEOS (tetraethyl orthosilicate)/MAPTMS) in varying combinations and ratios, and a transition metal complex, preferably a complex of zirconium (and optionally TIOP (titanium isopropoxide)), chelated with either MAAH or APTES, and optionally an additive selected from colloidal silica, BTSPA and/or BTA (benzotriazole). The varying combination and ratios of the sol-gel formulation ingredients is outlined in Table 1, and the method for forming the sol-gel coatings according to the second aspect of the invention is outlined at
Preferably, the present invention provides a highly densified hybrid sol-gel coating based on the interconnectivity of two hybrid networks formed from a methacrylate silane and a transition metal complex.
In a first aspect of the invention, in the final stages of a process for forming coatings of the present invention, tetraethyl orthosilicate (TEOS) may be added to improve the ability of the Si/Zr sol to form a dense coating. The TEOS essentially coats the colloidal Si/Zr and improves their ability to bond together. The addition of TEOS has been found to achieve improved coating formation.
In a second aspect of the invention, in the final stages of a process for forming coatings of the present invention, additives (BTA, BTSPA, colloidal silica etc.) may be added to improve the performance of the resulting sol-gel coatings.
The present invention provides a highly densified hybrid sol-gel coating based on the interconnectivity of two hybrid networks formed from a methacrylate silane and a transition metal complex.
Accordingly, the present invention provides a hybrid sol-gel coating formulation comprising the following:
Preferably the formulation comprises a catalyst, and more preferably the catalyst comprises HNO3.
Preferably, the additive comprises any one or more selected from the following: BTSPA (bis[3-(trimethoxysilyl)propyl]amine), BTA (benzotriazole), TEOS (tetraethyl orthosilicate), colloidal silica, or a combination thereof.
In one preferred embodiment, the additive comprises a corrosion inhibitor, which is preferably BTA;
Optionally, BTSPA is included as an additive to promote adhesion to the surface, when in use, by forming a tridentate based interlocked hybrid silane sol.
When used as an additive, TEOS improves the bonding between the silane precursors and the metal complex, and has been found to achieve improved coating formation.
Preferably, the solvent comprises any one or more selected from C1-C4 alcohols.
In a preferred embodiment, the alcohol comprises ethanol.
Preferably, the ethanol is in the range of 0-25% w/w.
When colloidal silica is used as an additive, it is used preferably in the range of 0.25-1.25% w/w.
Preferably, BTSPA is used in the range of 0.5-10% w/w.
Preferably, BTA is in the range of 0.2-1.5% w/w.
Preferably, BTSPA is catalysed by using 0.1M HNO3 (nitric acid) prior to the addition in step (d) of the method for preparing the hybrid sol-gel formulation.
Preferably, the organosilane comprises one or a combination of organosilane precursors selected from PhTEOS (phenyltriethoxysilane), TEOS or MAPTMS, or a combination thereof, more preferably wherein the methacrylate silane comprises MAPTMS.
Preferably, the metal complex comprises Zirconium and/or Titanium, and more preferably wherein the metal complex comprises Zirconium (IV) propoxide and/or titanium isopropoxide.
In one embodiment, Titanium isopropoxide is used in conjunction with Zirconium (IV) propoxide for improved cross-linking and surface energy.
Preferably the metal complex comprises a monodentate or a bidentate ligand.
In one preferred embodiment, the ligand comprises MAAH (methacrylic acid).
In another embodiment the ligand comprises APTES ((3-aminopropyl)triethoxysilane).
In one preferred embodiment, the molar ratio of the ingredients of the formulation comprise a molar ratio of 80:20, silane precursor:metal complex, more preferably wherein the ingredients of the formulation are included in the molar ratio of 75:5:10:10, MAPTMS:TEOS:Zr:MAAH.
Preferably, the molar ratio of ingredients comprise a molar ratio of organosilane precursors:metal complex of 50:50 to 99:1, and preferably in the ratio of 80:20.
In another aspect, the present invention also provides a method for preparing a hybrid sol-gel formulation, the method comprising the following steps:
It is to be understood that in one embodiment, the “pre-final” sol can be used as a formulation for coating on the substrate.
In a preferred embodiment, in step (a), the silane precursors are hydrolysed with an aqueous solution of HNO3, and wherein the HNO3 solution is added dropwise to the mixture.
In a preferred embodiment, in step (d), the intermediate sol is hydrolysed with deionised water.
The present invention also provides a coating formed according to the formulation of the present invention.
The present invention also provides a coated substrate prepared by coating the formulation of the present invention onto a surface.
In a first aspect, the present invention provides a sol-gel coating composition comprising a hydrolysed organosilane, an organometallic precursor and a ligand, wherein the ligand is a chelator for the organometallic precursor and wherein the ratio of the organosilanes to Zirconium complex is 8:2. The organosilane comprises methacryloxypropyltrimethoxysilane (MAPTMS) and/or tetra-ethyl-ortho-silicate (TEOS).
Preferably, the ingredients are included in the molar ratio of 75:5:20:20, MAPTMS: TEOS:Zr:MAAH. This can also be expressed as a preferred molar ratio of 80:20, Silanes:Zirconium.
Preferred Ratios in the Formulation:
The ratios used are
Or this can also be expressed as:
Silanes:Zirconium 80:20
In a second aspect, the present invention also provides sol-gel formulations prepared according to the flow diagram of
Hybrid sol-gel coatings based on the combination of a silane network former and a transition metal network interlocker, stabilised by a kinetic silane and a tridendate silane, using BTSPA, may be prepared according to the method of the second aspect of the invention.
The present invention will now be described more particularly with reference to the accompanying drawings and in the following Examples.
In the drawings:
Referring to the flow diagram of
(a) Organosilane Hydrolysis to Form the Silane Sol
A first organosilane hydrolysis was effected by hydrolysing the organosilane, MAPTMS with an aqueous HNO3 0.01M solution in a 1:0.75 volume ratio (below this ratio, precipitation of zirconium species occurred during the second hydrolysis). As MAPTMS and water are not miscible, the hydrolysis was performed heterogeneously. After 20 minutes of stirring, the production of methanol became sufficient to allow the miscibility of all species present in solution;
(b) Zirconium Chelation to Form the Zirconium Complex
MAAH was added dropwise to ZPO with a molar ratio of 1:1 MAAH reacted on ZPO agent to form a modified zirconium alkoxide Zr(OPr)4-2 x(MAA)x where MAA is the deprotonated form of MAAH;
(c) Organosilane Zirconium Combination to Form the Si/Zr Sol
After a pre-determined time has elapsed, preferably about 45 minutes, the partially hydrolysed MAPTMS was slowly added to the zirconate complex. This mixture is characterized by a temperature increase, demonstrating the formation of irreversible chemical bonds;
(d) Hydrolysis to Form the Pre-Final Sol
Following another pre-determined time has elapsed, preferably, about 2 minutes, water was then added to this mixture. This second hydrolysis leads to a stable and homogeneous sol after a pre-determined hydrolysis time, preferably, about 45 minutes; and
(e) Formation of the Final Sol
TEOS (0.33 g) was added to the Pre-final Sol to form the Final Sol.
In all Examples, methacrylic acid (MAAH) was used as the chelating agent.
The following process was carried out:
(a) Organosilane Hydrolysis to Form the Silane Sol
Organosilane hydrolysis was effected by hydrolysing MAPTMS (61.22 g) with an aqueous HNO3 0.01M solution in a 1:0.75 volume ratio (below this ratio, precipitation of zirconium species occurred during the second hydrolysis). As MAPTMS and water were not miscible, the hydrolysis was performed in a heterogeneous way. After 20 minutes of stirring, the production of methanol became sufficient to allow the miscibility of all species present in solution.
(b) Zirconium Chelation to Form the Zirconium Complex
MAAH (5.30 g) was added dropwise to ZPO (28.25 g) with a molar ratio of 1:1 MAAH reacted on ZPO agent to form a modified zirconium alkoxide Zr(OPr)4-2x(MAA)x where MAA is the deprotonated form of MAAH.
(c) Organosilane Zirconium Combination to Form the Si/Zr Sol
After 45 minutes, the partially hydrolysed MAPTMS was slowly added to the zirconate complex. This mixture is characterized by a temperature increase, demonstrating the formation of irreversible chemical bonds.
(d) Hydrolysis to Form the Pre-Final Sol
Following another predetermined time, about 2 minutes, water was then added to this mixture. This second hydrolysis leads to a stable and homogeneous sol after a hydrolysis time of about 45 minutes.
(e) Formation of the Final Sol
TEOS (0.33 g) was added to the Pre-final Sol to form the final Sol with a final molar ratio of 75:5:20:20, MAPTMS:TEOS:Zr:MAAH or 80:20, Silanes:Zirconium.
The process steps were carried out as for Example 1 with the following amounts being used:
The process steps were carried out as for Example 1 with the following amounts being used:
The coatings of the present invention provide surprisingly effective metals coating protection and provide all of the above referenced requirements of a coating.
6 Sol-gel formulations (F001-F006) were prepared according to a second aspect of the present invention as follows, and according to the flow diagram of
Regarding the synthesis of formulation F005:
The activated BTSPA should only be added to the sol-gel just before a part is to be coated. This is especially important for high concentrations of BTSPA (e.g. 5.0% weight) as the sol-gel will gel rapidly (<2 hours) with constantly increasing viscosity.
Prior to dip coating, the sol-gel is filtered using a 1.0 micron PTFE syringe filter to remove any large agglomerates or contaminates. If needed, the sol-gel can be diluted down with a solvent (e.g. ethanol or isopropanol) to decrease viscosity and increase shelf-life.
Each formulation is briefly described in Table 1 with each formulation broken down into three main components; 1) the mixture of Silane Precursors, 2) the Metal Complex & 3) the Additives. The full chemical names of the abbreviated description used in Table 1 are shown in in the “Summary of Invention” Section.
Formulations F001-to-F003 were developed as hard, hydrophobic & scratch resistant coatings, and aesthetic surface finishes. F004 was developed as a corrosion resistance sealer for anodized aluminium alloys. Formulation F005 is intended as having adhesion promoting properties. Formulation 6 is intended to be both a corrosion resistance sealer and an adhesion promoter.
Sol-Gel Formulations F001-F006
A more detailed breakdown of each of the sol-gel formulations, F001-to-F006, are shown in Table 2 to Table 41. Each formulation contains of a mixture of Silane Precursors, a Metal Complex and, where applicable, an additive to impart additional functionality, and also where applicable, a solvent. The percentage of the additives are expressed in % w/w of the wet sol-gel to which they are added. The tables corresponding to the formulations used in testing the performance of the sol-gel formulations are labelled with an asterix (*):
Testing of Formulations F001-F005 on Metal Substrates
Several metal substrates (mostly aluminium “A” and mild steel “R” and R-ICF” substrates) were used for the purposes of testing the sol-gel formulations F001-F005. They were procured from Q-Lab & Amari. Table 41 outlines the metal substrates type and surface finish from Q-Lab. The Q-panels prepared with an iron phosphate pre-treatment were used and dip-coated as-is. However, the bare aluminium, ‘A’, and mild steel, ‘R’, were degreased with a 0.5M solution of sodium hydroxide (NaOH) in deionised water and then rinsed with deionised water followed by isopropyl alcohol (IPA). The panels were then dried with hot air prior to dip coating.
Grade 2024T3 aluminium alloy panels (cut to size 6″×3″×1.5 mm thick) were procured from Amari. This substrate was used for anodising with sol-gel as a sealer. Prior to sol-gel coating, the panels were anodised in sulphuric acid. As part of the anodising process, the aluminium alloy was cleaned in an alkaline degreaser (Socomore A3432) as well as de-oxidized (Socomore A1859/A1806) before anodising. After anodising, the panels were soaked in IPA for a few minutes to drive off any water entrapped in the anodic layer. A final hot air blow dry then removed the IPA solvent. At this stage, the panels were dip-coated in the sol-gel. The anodised panels were allowed to dwell in the sol-gel for 2.5 min to allow the sol-gel to permeate into the anodic layer.
The following experimental methods were used in the testing of formulations [F001]-[F005] and prepared samples. Where applicable, the test standard is referenced.
Viscosity
Viscosity of the sol-gel was measured using an AND SV-10 Viscometer. The system can be seen in
Thermogravimetric Analysis (TGA)
TGA was used to give an insight into the cure behaviour of the different sol-gel formulations. Tests were performed on a Shimadzu DTG 60M TGA. Two different TGA heating profiles were used. The first was a dynamic scan from 25° C. to 250° C. at a rate of 5° C./min. This was performed on the liquid sol-gel as well as pre-cured samples. The second was a simulated cure cycle that replicated the cure profile of dip coated parts cured in a conventional oven. In this case, the sol-gel was heated at a rate of 10° C./min up to the cure temperature (typically between 100° C. and 160° C., depending on the formulation) and then held for 60 mins. In all cases, the liquid sol-gel sample was approximately 20-30 mg in weight.
Pendulum Damping Testing
The pendulum damping test was carried out in accordance with ISO 1522-2006. A König pendulum test was used to give an indication of the hardness of each of the sol-gel coatings. The softer the coating, the quicker the pendulums oscillation will dampen (i.e. lower number of swings).
Pencil Hardness Testing
Pencil hardness testing was conducted in accordance with ISO 15184-2012 (Determination of film hardness by pencil test). This particular test is a common industry method to rank the relative hardness of different coatings.
Water Contact Angle
The water contact angle (WCA) was determined using a First Ten Angstrom (FTA) system. Five drops of deionised water were used per coated sample. The WCA values presented in this report are the average of the five measurements. A lower contact angle (<90°) would be an indication of a hydrophilic coating that may be suitable for subsequent painting or adhesive bonding. A higher contact angle (>90°) would indicate a hydrophobic coating that may be suitable for self-cleaning solutions.
Dip-Coating
Samples were dip coated using a Bungard RDC 21-K system. Q-panel samples were held in place using alligator clamps and immersed into a bath containing the sol-gel at a constant speed. The panels were held in the sol-gel for up to 20 seconds (longer for anodised panels) and then withdrawn at a constant speed. The withdrawal speed was varied to control the final coating thickness and was typically in the range of 50 mm/min for thin coatings (<5 μm) to 500 mm/min for thicker coatings (10-to-20 μm).
Curing
After dip coating, the samples were cured in an air-circulated oven at the required temperature. The temperature varied depending on the sol-gel formulation. F001-to-F003 & F005 were typically cured at 140° C. for 1 hr while F004 was cured at 120° C. for 2 hrs.
Neutral Salt Spray
Accelerated corrosion tests were performed in a neutral salt spray (NSS). The NSS chamber was maintained in accordance with ISO 9227:2017. Dip-coated and cured samples were sealed on one face with packing tape. The back and edges were further sealed with electrical insulation tape. This was to ensure that only the front face of the samples were exposed to the corrosion environment. For this report, samples were monitored over time up to a maximum of 672 hrs (4 weeks).
Viscosity Results
The viscosity of the sol-gel can have a significant effect on the resulting coating thickness after dip coating. The study was split between formulations F001-to-F004 and then F005 separately. This was because the effect of BTSPA concentration was also considered as part of the dilution study.
Formulations F001-to-F004 were prepared at three different dilutions of ethanol (EtOH). These were 0%, 10% & 25% wt. EtOH. The addition of a solvent can help to decrease the viscosity as well as extend the shelve life of the sol-gel. The viscosity was monitored up to 84 days (12 weeks) after synthesis. Formulations F001-to-F004 exhibited a general increase in viscosity over time at each dilution. The formulations with the highest molar concentration of the metal complex (i.e. F001 & F004) appear to start with highest viscosity and also increase the fastest over time. When diluted with 25% wt. EtOH, all sol-gels remain relatively stable over time, maintaining a viscosity of approximately between 20 & 40 mPa·s.
Formulation F005 was diluted with four different levels of ethanol. These were 0, 10, 25 & 50% wt. EtOH. The level of BTSPA was also considered at five different concentrations. These were 0.0, 0.5, 1.0, 2.5 & 5.0% wt. BTSPA. The viscosity was monitored up to a period of 84 days (12 weeks) or until the viscosity reached approximately 100 mPa·s. At this viscosity level, the sol-gel was deemed to have expired.
Thermogravimetric Analysis (TGA)
TGA experiments were performed on liquid sol-gel samples to determine the cure behaviour at different cure temperatures ranging from 100° C. to 160° C. A simulated cure cycle (SCC) was programmed into the TGA that included a ramp of 10° C./min up to the cure temperature (i.e. 100, 120, 140 or 160° C.) followed by a hold (or dwell) at the cure temperature for 60 mins. For this series of tests, the sol-gels were un-diluted.
The results presented in
TGA experiments have not been performed on formulation F005. However, given the relatively similar silane chemistry of F004 (i.e. MAPTMS & ZPO), a cure cycle of 120° C. for 120 mins was used for F005 as well.
Pendulum Damping Test
The pendulum damping tests were performed on cured samples. The results presented used an R-ICF substrate from Q-Lab (mild steel with iron phosphate pre-treatment). The dip speed was set to 100 mm/min for all samples. The results are presented in
Pencil Hardness Testing
The results from the pencil hardness test for each of the four sol-gel formulations can be seen in Table 43. The sol-gel coatings were applied to aluminium ‘A’ spec Q-panels. The ‘Pencil Hardness’ is the specific pencil that does not mark the coating. The ‘Plastic Deformation’ is the pencil hardness that results in a mark on the coating. The ‘Cohesive Failure’ is the hardness that results in removal of the coating. Note that ‘Plastic Deformation’ and ‘Cohesive Failure’ can occur at the same pencil hardness value. The results show that the pencil hardness test has difficulty in distinguishing between the different coatings compared to the pendulum damping test. The only noticeable difference was that F004 results in ‘Cohesive Failure’ at a slight higher hardness (3H instead of 2H).
Water Contact Angle (WCA)
The water contact angle results are presented in
Neutral Salt Spray (NSS) Testing
Various studies were conducted on the performance of the sol-gel coatings in a neutral salt spray (NSS) environment. The individual studies are separated by substrate type and sol-gel formulation.
R-ICF Q-panels (Mild Steel with Iron Phosphate Pre-Treatment) & F001-to-F004
Examination of the corrosion protection performance was carried out as follows:
Sol-gel formulations (F001-F004) on substrates were evaluated, at different dip speeds (100, 250 & 500 mm/min) and different numbers of coatings (×1, ×2 & ×3). The goal was to determine if a thicker sol-gel coating or a multi-coat system would improve the level of corrosion protection in an NSS. For this study, R-ICF mild-steel pre-treated with iron phosphate Q-panels were used as-received with no additional surface treatment.
Mild Steel, Galvanised Steel and a 6000 Series Aluminium Alloy
The three substrates under investigation with the sol-gel formulations are mild steel, galvanised steel and a 6000 series aluminium alloy. Some of these substrates were also supplied pre-treated with a 3rd party silane (referred to as 3PS) to be used as a benchmark comparison.
A number of different sol-gel systems were investigated as part of this work. A total of 10 sol-gel systems were considered and are outlined in Table. Each system was given a unique identifying code ‘A’-to-‘J’. As can be seen, several combinations of F001, F003, F004 & F005 were considered. F002 was excluded from this study due to its similarity to F001. Several single coat and dual coat systems were investigated.
The coated panels were evaluated in a neutral salt spray for 336 hrs (2 weeks).
Anodised Aluminium 2024T3 & F004
The effect of using a sol-gel as a sealer after an anodising process was investigated using aluminium alloy grade AA2024T3. Panels of aluminium were anodised in sulphuric acid for 10 or 30 mins and then coated as described above.
Sol-Gel Coatings on Additive Manufactured Parts
Additive manufacturing has opened up new opportunities for the production of extremely complex shapes that would otherwise be impossible via traditional manufacturing methods. However, this also presents new coating challenges. The printed parts, particularly metal ones, can have a very thick oxide layer. Line of sight coating methods may also have difficulty coating the entire part.
The 3D printing material being used is titanium grade 23 (G23/Ti-6Al-4V ELI). However, the coating systems will be applicable to any 3 D printed metal or selected plastics parts. The sol-gel was based on formulation F005.
It will of course be understood that various modifications can be made and that the scope of the invention is defined by the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1902390.2 | Feb 2019 | GB | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2020/054555 | 2/20/2020 | WO | 00 |
