COMPONENTS

Field of the invention

The present invention relates to a coating applied onto hard disk drive (HDD) enclosures or components with one or more surfaces exposed within the (HDD) clean enclosure resulting in increased reliability by lowering the number and size of free, third body particles as described in PCT Application No. PCT/SG2009/000065. In particular, the present invention relates to a coating system using either non-hybrid or a hybrid coating material and an associated coating process as described in PCT Application No. PCT/SG2010/000100 with additional processing for the explicit purpose to eliminate cracks at the high stress areas within the coating, the highest stresses found at the edges with small radius of curvature, for example small holes in thin substrate sections.

Background of the invention

Industry Requirements for coating enclosures or components exposed within the HDD clean enclosure

Coatings with film properties including precise uniformity and zero particle contamination are crucial for the reliable operation and for the required life span of hard disk drives. Typically these film coatings are of 0.1 μηι to 5μηι thickness, with one film coating application as thin as 0.001 ym. These film properties are particularly critical for device reliability due to the current and new recording technologies associated with HDD high Arial Density Designs. Any free, including loosely attached, particle from any surface within the HDD clean enclosure; any particle left on the surface after any pre-treatment but before coating; any particle left on the surface during the coating; or any particle generating from the substrate surface or from the coating; will adversely impact the HDD reliability and life. Hard particles, for example metallic particles, have always been considered high risk defects in the hard disk drive industry; as such defects may potentially lead to the loss of customer data. Soft particles, for example small organic polymer particles, previously have been considered high risk defects due to potential polymerization at the head disk interface, resulting in device failure. The introduction new recording technologies have increased the HDD susceptibility to these soft, organic particles to the same level as hard particles.

An effective coating applied onto HDD enclosures or components with one or more surfaces of the component exposed within the HDD clean enclosure should hence satisfy all of the following requirements: coated surface is easily cleaned, smooth, and with very small surface porosity; coated surface is uniform; there is no shedding of any particles either from the coating or the underlying substrate material; the coating has the properties of corrosion resistance, solvent resistance, and no gaseous or condensable material out-gassing; and finally, the coating material and the coating process is "green" having no environmentally or humanly hazardous waste. The coating material and the coating processing costs must be inexpensive and compatible with high volume manufacturing.

Current Industrial Processes Used for Coating Application

One typical and currently applied coating for HDD enclosures and components is nickel plating. Nickel plated surfaces are known sources of loose hard particles. Recent advancements in nickel plating technology have reduced the number of hard particle on, or generated from, the nickel plated surface. Few further reductions in the number of particles generated from the nickel surface can be expected due to the physical nature of the Ni or any other metal plated surface. No known post processing of the Nickel surface itself can eliminate the number of loosely attached nickel metal particles. After exposure to humidity, the number of nickel metal particles generated at the nickel surface increases due to the loosely attached grains on the surface. Nickel also has the disadvantages of its variable metal costs and of its environmentally unfriendly coating processes.

Another typical coating technique for HDD enclosures and components is spray coating. Spray coating involves the application of a coating, such as a gel coat or plastic coating, to a component by means of a spray gun. Unfortunately, all currently available spray coating materials and spray coating processes do not offer precise film uniformity because areas such as the edges, corners, and uneven surfaces on the housing do not receive an equivalent amount of coating material as compared to the centre and flat surfaces of the housing. Hence, precise thickness control is difficult to achieve with currently available spraying technologies including all available spray coating techniques.

Another typical coating technique using the dip coating process involves the immersing of a component into a tank containing coating material, removing the component from the tank, and allowing it to drain. The coated component can then be burnished, washed, rinsed and dried by force-drying or baking. Currently, such a dip coating process is used specifically for the lubrication applied to magnetic media installed into the HDD clean enclosure. The surface of the magnetic media if first plated, sputtered, coated using vapour deposition process, and then highly polished and cleaned to remove the majority of loosely attached particles before coating with a thin film of lubricant. The lubrication does not change the cleanliness of the magnetic surface as the lubrication is applied in a controlled and clean environment. An additional process step for the magnetic media uses a burnishing head on the rapidly rotating media surface to remove all loosely attached particles. This burnishing process cannot be applied to any of the other surfaces within the HDD, only the magnetic media surface, due to the mechanical shape of the magnetic media being a thin disk which is very flat and easily rotated at high speed. Thus, the dip coating processes with it's the associated pre-treatment processes used on magnetic media are not appropriate for coatings of other component surfaces exposed within the HDD clean enclosure.

In a conventional industrial dip coating process, the excess coating is allowed to drip from any point or edge or corner. This not only creates a non-uniform coating, but accumulation and coagulation of the coating may occur, resulting in lumps on the coating. Furthermore, conventional dip coating processes are limited by improper control of the withdrawal speed and dip coating apparatus. The drag force on the coated hard disk component is not uniform across the surface of the component, which inadvertently affects the uniformity of the film. Due to the uneven drag force, the film thicknesses at the edge and corners of the components are normally larger than that the center of the components. Thus, even though conventional dip coating processes are more efficient than spray coating, these dip coating processes are not acceptable, due to the excess and uneven coating of the components. Furthermore, these areas with uneven coating are also the same areas with high stresses within the coating. Furthermore, typical dipping materials used for coatings are known to have poor adhesion to the substrate and poor resistance to corrosion. Dip coating of HDD enclosures and components is possible by loading onto a dip coating apparatus which is defined in PCT Application No. PCT/SG2010/000146, which is then immersed in a curable, coating bath. After the hard disk component is coated, the dip coating apparatus loaded with the component is removed from the coating bath. Coating uniformity is improved with better uniformity at the substrate's edges, corners, and uneven surfaces. However, coating cracking and delamination can still be observed under Highly Accelerated Stress (HAS) testing.

Existing Sol-Gel Coating Chemistry The current invention involves previously existing Sol coating (also called a sol-gel film) on substrates which achieves resin-to-substrate bonding via chemical linkages (covalent bonds, hydrogen bonds, or van der Waals forces) while minimizing environmental impacts otherwise caused by the traditional use of highly diluted hazardous metals used in metal plating.

Sol-gel chemistry has been generally used in coatings outside of the hard disk drive industry. Typically, sol-gel systems are characterized in that a mixture of the starting components is reacted by a hydrolysis and condensation process to form a viscous liquid phase.

Representative sol-gel hydrolysis and condensation reactions, using alkoxysilanes as an example, are shown in equations (1 )-(3).

≡Si-OR + H ₂ 0→≡Si-OH + ROH

≡Si-OH +≡Si-OH→≡Si-0-Si≡ + H ₂ 0

≡Si-OR +≡Si-OH→≡Si-0-Si≡ + ROH

The alkoxy group containing a hydrolysable alkoxy group (-OR), e.g. Methoxy (- OCH ₃ ) or ethoxy (-OC ₂ CH ₃ ) will hydrolyze in presence of water to form silanols (Si- OH). The silanol group can then condense to form siloxane groups with the elimination of water or alcohol.

Organically modified silicates (organoalkoxysilanes) are hybrid organic-inorganic materials formed through the hydrolysis and condensation of organically modified silanes with traditional alkoxide precursors. The use of precursors containing non- hydrolyzable Si-C bonds allows introduction of organic groups directly bonded to the polymer-like silica network. In the uncured solution; monomers, silanols, alcohols and or other solvents, water and siloxanes are coexistent. Catalyst such as citric acid, nitric acid, sodium hydroxide; temperature; solvent concentration and water concentration; all affects the reaction direction, i.e., more silanols or more siloxanes remain in the solution. When the component is withdrawn from coating solution, a film of coextruded coating is formed.

The coextruded coating contains water and solvent (e.g. alcohols) which must be eliminated by heating. The heating temperature should below the boiling point of alcohols and water so that the coating molecules have enough relaxation time to relocate and further cross link. Best temperature in practice is around 70°C. Secondary heating is to form 3D crosslinks and which form the dimensional network. The temperature for the secondary heating is in the range of 120-200°C. Above 200°C curing temperature a quality degradation of the 3D crosslinks can be measured.

The currently defined sol-gel chemistry and coating processes are not optimal for hard disk components as they have "high stress" areas in the coatings formed during the hydrolysis reaction. The "high stress" areas are identified due to the resulting cracks when the coated surface is exposed to a humid environment or are when the cracking is accelerated in boiling water environments and other Highly Accelerated Stress (HAS) testing. Furthermore, typical dipping materials for coatings are known to have poor adhesion to the substrate and poor resistance to corrosion.

Given the disadvantages of using conventional coating systems for the hard disk drive components, there is a need to provide a coating material formed with an associated coating process that overcomes or at least ameliorates one or more of the disadvantages described above. In particular, a coating material associated with a coating process that eliminates cracks at the high stress areas on the coated surfaces. Summary of the invention

In accordance with a first aspect of the invention, there is provided a process for coating a hard disk drive component having one or more exposed surfaces within the hard disk drive, the process comprising the steps of: (a) applying a curable coating onto the surface of the component; (b) forming a first barrier layer on the surface of the coating adjacent the atmosphere, wherein the properties of the first barrier layer prevents external water molecules from diffusing through the first barrier layer; and (c) forming of a second barrier layer within the coating and below the first barrier layer.

Preferably, the barrier layer is a dense cross-linked polymer. More preferably, the polymer is siloxane.

Preferably, the curable coating includes a polymer forming additive. Such additives are typically known to the skilled person in the art.

Preferably, the first barrier is formed by heating the coated component in a humidity chamber. More preferably, the coated component is heated at temperatures above 70°C in a humidity chamber at 20% to 50% relative humidity. Still more preferably, the coated component is heated in the humidity chamber for between 3 to 10 minutes.

Preferably, the second barrier layer is formed by further heating the coated component at temperatures between 120°C to 200°C. Alternatively, the coated component may be incubated in a high temperature chamber at curing temperature of about between 120°C to 180°C to form the most advantageous hydrophobic polymer layer on the free surface and to have the most advantageous water molecule concentration within the coating interior. Preferably, the curable coating bath is a sol-gel composition comprising silane-based compounds selected from the group of tetraalkoxysilanes, alkylsilanes, and an alkylalkoxysilane. Preferably, the process is carried out in a clean room environment. Such clean room environments are known in the art and are achieved with filters that are described in this document.

Preferably, the coating is applied by any one of dipping or spraying. More preferably, the component is dipped in the curable coating bath at a temperature between 20°C to 100°C.

In accordance with a second aspect of the invention, there is provided a hard disk housing component comprising a coating formed according to the first aspect of the present invention.

The present invention allows for polymer cross linking on the free surface of the coating as well as internal polymer cross linking in a sequential manner. Advantageously, the cross linking at the free surface forms a barrier to external water molecules going inside the coating for further hydrolysis reaction. Concurrently, the internal water molecules that are generated during internal cross linking process squeeze out through the free surface network. The invention allows for the formation of a well-defined hydrophobic polymer layer which acts as a barrier preventing water molecules from entering the coating; and therefore, preventing further internal hydrolysis in the coating which is the cause of the high stress and the resulting in the cracks in the coating.

Most preferably, the curing process includes the two steps described below: Solvent evaporation and water molecule concentration control during low temperature cure.

The solvent and water within the coating bath act as carriers of the coating molecules. Too high of a temperature during the low temperature cure phase will result in a fast evaporation and generate porosity at the coating free surface. Correct cure temperature for this step is around 60-80 °C which is below the water boiling point at atmospheric pressure. Most importantly, it is necessary to provide the correct percentage of water molecules (%RH) at the free surface of the uncured coating material, first for hydrolysis reaction and then second for correct condensation on the surface to form the polymer cross linking. Too high of a %RH of water molecules at the surface will lead to a reaction more towards the hydrolysis direction. Then the condensation will be too high and the polymer cross linking at the surface will be adversely affected. On the other hand, too low of a %RH of water molecules at the surface will not provide sufficient water molecules for the hydrolysis reaction; and, the polymer cross linking at the surface will be adversely affected. The optimal %RH of water molecule is typically in the range of 20-50%RH.

2. Cross linking during cure at high temperature.

During the high temperature curing stage, the internal coating molecules form the polymer cross linking by a condensation reaction which releases water molecules. The released water molecules subsequently react with the remaining un-cross linked molecules. The number of available water molecules within the coating material provides the catalyst for the hydrolysis reactions resulting in the polymer cross linking to form 3D network. The properly formed surface, as described in section 1 above, on the coating allows any excessive water molecules to pass though the surface. Similarly, the properly formed surface prevents excessive water molecules to enter the coating interior. If the water molecules are more than the required number, the reaction will move forward to hydrolysis and therefore internal stress will be increased. Sudden changes during curing must be avoided during the high temperature curing process step. Any sudden temperature changes once the high temperature cure is initiated would enhance the internal, sub-surface tensile stress particularly at the high stress area such as edge and small holes. In either the first or second steps above, if the resulting internal stresses are large enough, cracks will be generated or the micro cracks propagation is facilitated till cracks are visible in the coating.

Preferably, the present invention involves the preparation of a coating material consisting of silane sol-gel compositions by adding an organoalkoxysilane into an aqueous alumina sol prepared from a hydrolyzable aluminum alkoxide. The organoalkoxysilane hydrolyzes and condenses with the hydrolyzed aluminum alkoxide to form a siloxane/alumina copolymer with an organic constituent.

Various organoalkoxysilanes may be used in accordance with the present invention. Organoalkoxysilanes of the general formula is below: wherein, x is less than 4 and preferably is one, R is an organic radical and R' is a low molecular weight alkyl radical is preferred.

R _x Si (OR') ₄ .x

R is preferably a low molecular weight, preferably from one to six carbon, alkyl or vinyl, methoxyethyl, phenyl, γ-glycidoxypropyl or γ-methacryloxypropyl. R' is preferably a two to four carbon alkyl group. Particularly preferred organoalkoxysilanes are those wherein R is methyl and R' is ethyl; a most preferred organoalkoxysilane is methyl trimethoxysilane.

The transparent, colorless organoalkoxysilane/alumina composition that is formed may be applied to a substrate by any of a variety of methods such as dipping, spraying, or spinning to form a continuous coating. Upon drying and curing at about 120°C, a durable, glassy coating is formed which improves the surface properties of the substrate. Preferred coating thickness is in the range of about 100 to 5000 nanometer. A coating about 1 micron thick provides a protective surface comparable to a glass surface in abrasion resistance. The preparation of a coating material is further defined as follows:

R SiR' _a wherein the radicals R' and R are the same or different, R' represents a hydrolysable radical, R represents a group selected from an alkyl group, an alkenyl group, a hydrocarbon group, an epoxide group, a glycidyloxy group, a mercapto group and a methacryloxy group; and, a and b independently of one another have a value from 1 to 3, provided that the sum of a and b is 4. M(R') _n wherein M is an element selected from the group consisting of Al, Ti or Zr; R' is as defined above; and n is an integer from 2 to 4; and optionally, at least one compound represented by general formula (I), wherein the hydrolysis occurs in the presence of at least 0.6 moles of water for every mole of hydrolysable radical R'

A preferred sol for making the sol coating on the substrate includes an organoaluminium compound (such as isopropoxyaluminium) to covalently bond to the substrate through Al and an organosilane (such as 3- glycidoxypropyltrimethoxysilane) to covalently bond to the organic primer, or resin.

In our preferred sol coating, bond strength and durability is increased by including organosilanes and organoaluminium compounds. The organosilanes have covalent bond to or otherwise associate with the organic resin or primer. Ideally, covalent bonding also occurs at the interface between the sol-gel and substrate surface. Mechanical interactions may also play a role depending on the internal crosslink design (i.e., porosity, microstructure) of the sol coating. Durability of the sol-gel film in humid conditions depends on whether the film rehydrates. If the film is too thick, it becomes glassy. In an alternate sol coating, organically modified silicates (organoalkoxysilanes) can be used. Organoalkoxysilanes are hybrid organic-inorganic materials formed through the hydrolysis and condensation of organically modified silanes with traditional alkoxide precursors. The use of precursors containing non-hydrolyzable Si-C bonds allows introduction of organic groups directly bonded to the polymer-like silica network.

The coating process begins by preparing a coating composition product by hydrolysing: R SiR' _a equation I wherein the radicals R' and R are the same or different, R' represents a hydrolysable radical, R represents a group selected from an alkyl group, an alkenyl group, a hydrocarbon group, an epoxide group, a glycidyloxy group, a mercapto group and a : methacryloxy group, and a and b independently of one another have a value from 1 to 3, provided that the sum of a and b is 4. M(R') n equation II wherein M is an element selected from the group consisting of Al, Ti or Zr, R' is as defined above, and n is an integer from 2 to 4; and optionally at least one compound represented by general formula I, wherein the hydrolysis occurs in the presence of at least 0.6 moles of water for every mole of hydrolysable radical R'.

Various organoalkoxysilanes may be used in accordance with the present invention. Organoalkoxysilanes of the general formula is below,

R _x Si(OR') ₄ .x, equation III wherein, x is less than 4 and preferably is one, R is an organic radical, and R' is a low molecular weight alkyl radical are preferred. R is preferably a low molecular weight, preferably from one to six carbon, alkyl or vinyl, methoxyethyl, phenyl, y- glycidoxypropyl or y-methacryloxypropyl. R' is preferably a two to four carbon alkyl group. Particularly preferred organoalkoxysilanes are those wherein R is methyl and R' is ethyl; a most preferred organoalkoxysilane is methyl trimethoxysilane.

With this alternate sol coating, the transparent, colorless organoalkoxysilane/alumina composition that is formed may be applied to a substrate by any of a variety of methods such as dipping, spraying, or spinning to form a continuous coating. Upon drying and curing at about 120°C, a durable, glassy coating is formed which improves the surface properties of the substrate. Preferred coating thickness is in the range of about 100 to 5000 nanometer. A coating about 1 micron thick provides a protective surface comparable to a glass surface in abrasion resistance

Another alternative sol coating uses a polymer forming additive. After the coating deposition, there is a substantial volume contraction and internal stress accumulation due to the large amount of evaporation of solvents and water. In order to reduce the internal stress of coatings, a polymer to sol-gel system is needed to modify the coatings. Polyvinylpyrolidone (PVP) is soluble in water made from the monomer N- Vinylpyrrolidone. In solution, it has excellent wetting properties and readily forms coatings. This makes it good as a coating or an additive to coatings. The polymer may be a single polymer or a mixture of a plurality of polymers. As long as the effect of the present invention is not adversely affected, the polymer may optionally comprise a polymer chain having recurring units other than the above- mentioned recurring units. Further, the main chain of the polymer may optionally have a functional group at terminals thereof. Usually, in a polyether, in polyester, and in a polycarbonate, the terminal groups are comprised of a hydroxyl group and/or a carboxyl group. However, the terminal groups of the main chain of the polymer are not particularly limited to hydroxyl and carboxyl groups. As long as the effect of the present invention is not adversely affected, the terminal groups of the main chain of the organic polymer may optionally be modified with other functional groups, such as Polyvinylpyrolidone, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, polypentamethylene glycol, polyhexamethylene glycol or similar materials.

It is preferred that the polymer has a number average molecular weight of from 200 to 100,000. It should be noted that the pore size of the hybrid coating of the present invention is very small and has only a small dependency on the molecular weight of the organic polymer. This is a great difference between the present invention and the conventional technique. In the preferred method of applying the sol coating, a clean and chemically active metal surface is preferred to bond a sol-gel film from the sol by dipping, spraying or spinning. Cleaning is a key factor toward obtaining good adhesion. If the surface is dirty, bonding is blocked by the dirt or occurs between the sol and the dirt rather than between the sol and the surface,

The sol coating contains water and solvents (e.g. alcohols) which must be eliminated by heating. The preheating temperature should below the boiling point of solvent and water so that the coating molecules have enough relaxation time to relocate and further cross link. In the preferred method, the preheat temperature is around 70°C. Secondary heating is to spacial crosslink and form dimensional network. In the preferred method, the temperature for the secondary heating is in the range of 120- 200°C.

During the preheating, solvent and water molecules are evaporated from the coating free surface into the adjacent atmosphere. Solvent and water molecules diffuse to the coating free surface due to concentration gradients within the coating. Simultaneously, crosslinks are forming both at the coating free surface and also in the coating interior. Non-hydrolyzed components will not be able to form the crosslinks. To form ideal crosslinks, the preferred method purposely provides water molecules onto surface to hydrolyze the coating components and then condensation to form the crosslink. However, if the amount of water molecules is insufficient, this hydrolyzing process will not be completed. On the other hand, if the number of water molecules is excessive, it will lead to the reversed reaction, i.e. more non-hydrolyzed component will be formed. Take the alkoxysilanes as example, from the previous equations (1) - (3), more water molecules will generate more silanols or silane which will create which will result in a less hydrophobic film with more opened entrances for diffusion of external water molecules. Since the internal crosslink cannot be perfect, there will be more in the coating able to react with the water molecules. Long term water molecules interaction under humidity chamber or hot water, those sites will be decomposed and create tensile stress and eventually cause coating crack.

The reaction can be occurred and completed in a few minute. Typically the preheating time is 3-10 min. after preheating treatment; a dense cross linked layer is formed. This layer will be a barrier to the external water molecules. In the secondary heating, it is for internal crosslink reaction to form dimensional network. The residue solvent and water molecules including crosslink reaction generated water molecules will be extruded by the inside pressure. While the external water molecules will be blocked by the dense cross linked coating surface.

In the present invention, preheating was carried out in a well control humidity chamber to provide certain water molecules onto the coating surface. The typical humidity is 20-50%RH. The best result for alkoxysilanes case is achieved at 30% at 70°C for 5min. After this treatment, the anti cracking property of the coating is significantly improved, as measured with the boiling water test passing from 2hour to 3 hour and higher with no observed cracking of the coating film.

Through the in situ formation using an enhanced, aqueous sol-gel process, the functionalized silica nanoparticles could cross-link with each other to form a dense, elastic thin coatings well covered and adhered onto metal for the substrate surface, for example a stainless steel or aluminium alloy substrate surface. In an organic/inorganic hybrid coating, a network combining the weathering stability and structural strength with the flexibility and low temperature cure of the resins is formed. Brief Description of Figure 1

In order that the present invention may be fully understood and readily put into practical effect, there shall now be described by way of non-limitative examples only preferred embodiments of the present invention, the description being with reference to the accompanying illustrative figure.

In the figure:

Figure 1 shows a schematic drawing of a coated hard disk drive according with an embodiment of the present invention. Item (10) represents the substrate material. Item (20) represents the coating layer consisting of the coating to air interface region of the polymer Item (30) and the interior regions of the polymer Item (40).

Detailed description of a preferred embodiment

In order that the present invention may be fully understood and readily put into practical effect, there shall now be described, by way of non-limitative examples, only preferred embodiments of the present invention. Prior to the coating or dipping step, the hard disk housings or components may be cleaned in order to substantially remove contaminants such as foreign particles, dust or grease that may be attached to the surfaces. The hard disk parts thereof may be cleaned by using an alkaline detergent in an aqueous medium. Cleaning is a key factor toward obtaining good adhesion. If the surface is dirty, bonding is blocked by the dirt or occurs between the sol and the dirt rather than between the sol and the surface.

The cleaning step may be carried out which includes loading of a basket containing the hard disk housings or components onto a loading conveyor which further transfers the basket to an auto transfer station. The basket containing the housings or components then goes through an ultrasonic washing step wherein the parts are cleaned with a 3% to 10% solution of of a commercially available alkaline detergent, Hvdrocleanse. which removes any grease or oil that may be present thereon.

The washing step takes place in a 316-litre electro-polished and passivized stainless steel tank with a 4-sided weir overflow design. The heater capacity is 6kW. Circulation of the cleaning solution occurs at 30 liters/min. Temperature in the tank may range from 45°C to 60°C. Ultrasonic rating is set at 40 kHz and 500W. Level control is achieved via float switches which act as protective level alarms.

Following the washing step, the hard disk housings or components are then rinsed to remove remaining residue. The ultrasonic rinsing step takes place in a similar tank filled with Dl water wherein the temperature is now maintained at around 50°C, before the parts move on to a subsequent pre-treatment step.

In the chemical pre-treatment step, the hard disk housings or components are soaked in 0.03% acidic acid concentration in Dl water chemical bath which chemically activates the surfaces. A chemically active metal surface is preferred to bond a sol-gel film from the sol. Chemical activation is a key factor toward obtaining good adhesion. If the surface is dirty, bonding is blocked by the dirt or occurs between the sol and the dirt rather than between the sol and the surface.

The parts are moved to a rinse bath of Dl water before moving on to the drying step.

In the drying step, an oven is used as the dryer. At this point the hard disk drive housings or components are free from organic and particulate contaminations, and have an activated surface. The oven drying station consists of clean, high pressure air supply with 0.5μιη filter and a pre-dry facility operating at 6 bar and 170 CFM. Drying takes place in a stainless steel oven. The heater capacity is 6 kW and blower capacity is 800 CFM. Slow velocity high air flow is achieved in drying step. The temperature in the oven is maintained at 90°C wherein the temperature is digitally monitored and controlled. An auto sliding door and thermal controller with oven heat alarm maintains the temperature. The oven is also well insulated by a double-walled 2" thick insulating material. Drying takes place via full width air inlets which direct air flow and air outlets at the base which is connected to a recirculation blower. The dip coating step follows sequentially from the above cleaning, activation, and drying steps.

The hard disk housings or components are dipped into a curable coating bath at a preferred temperature between 15°C and 25°C. The preferred control of the bulk temperature of the bath is +/2°C which is required to control coating uniformity at the edges, corners, and uneven surfaces. A preferred sol for making the sol coating (also called a sol-gel film) on the metal includes an organoaluminium compound (such as isopropoxyaluminium) to covalently bond to the metal through Al and an organosilane (such as 3- glycidoxypropyltrimethoxysilane) to covalently bond to the organic primer, or resin. The curable coating bath may be a sol-gel composition prepared using any of the preferred silane-based compounds: tetraalkoxysilane, for example, tetraethoxysilane; an orgartoalkylsilane, for example, tetraethyl orthosilane; or an alkylalkoxysilane, for example, dimethyldiethoxysilane or methyltrimethoxysilane.

In an embodiment of the present invention, silane/alumina sol-gel compositions for coating are prepared by adding an organoalkoxysilane into an aqueous alumina sol prepared from a hydrolyzable aluminium alkoxide. The organoalkoxysilane hydrolyses and condenses with the hydrolyzed aluminium alkoxide to form a siloxane / alumina copolymer with an organic constituent. As shown in Figure 1 , there is provided a hard disk drive component 10 having a coating 20 applied to its one or more exposed surface. The coating is carried out by a process described above. In the coating process of the present invention, the coating 20 comprises first 30 and second 40 barrier layers. From Figure 1 , it can be seen that the first barrier layer 30 is formed on the surface of the coating 20 adjacent the exposed surface that is adjacent the atmosphere. The second barrier layer 40 is formed within the coating 20 interior and below the first barrier layer 30. The barrier layers 30, 40 are comprised of cross-linked polymers. In the present process, first barrier layer 30 is formed before the second barrier layer 40.

The first formed first barrier layer 30 prevents water molecules from entering the coating interior while allowing excessive water molecules to pass though the surface from the coating interior. The first barrier 30 is formed by heating the coated component in a humidity chamber at temperatures above 70°C in a humidity chamber at 20% to 50% relative humidity for about between 3 to 10 minutes. Preferably, the heating takes place for about 5 minutes.

In order to form the internal crosslink dimensional network second barrier layer 40, secondary heating is carried out at temperatures between 120°C to 200°C The residue solvent and water molecules including crosslink reaction generated water molecules will be extruded by the inside pressure. While the external water molecules will be blocked by the dense cross linked coating surface.

Whilst there has been described in the foregoing description preferred embodiments of the present invention, it will be understood by those skilled in the technology concerned that many variations or modifications in details of design or construction may be made without departing from the present invention.