Detergent composition with low foam and high nickel solubility

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and incorporate by reference the provisional U.S. Patent Application Ser. No. 61/941,295, entitled “Detergent Solution For Nickel Removal With Low Foam and High Nickel Solubility,” filed on Feb. 18, 2014.

BACKGROUND

Hard disk drives generally incorporate stacked, commonly rotated rigid magnetic disks which are used for storage of data in magnetic form on the disk surfaces. The data is recorded in concentric, radially spaced data information tracks arrayed on the surfaces of the disks. Transducer heads are driven in a path toward and away from the drive axis in order to write data to the disks and read data from them.

The hard disks used in hard drives can comprise a substrate plated, for example, with nickel and phosphorus. Subsequent to plating, the disks are usually polished using chemical mechanical polishing, which exposes the disk to contaminants from the polish slurry, polish residue, manufacturing equipment, and/or the manufacturing environment. Nickel and phosphorus in the polishing slurry and/or derived from the surface of the disk, for instance, may bond back to the disk surface.

Contaminating particles on the surface of a hard disk, in particular nickel oxide (NiO) and nickel phosphorous (NiP) particles, can cause thermal asperities, i.e. local heating of the disk during operation due to the mechanical collision of the drive head with such particles protruding on the disk surface. If contaminating particles are not removed from the plated and polished disk, the operation and performance of a hard drive incorporating the disk may be negatively impacted, for instance due to head crash.

FIGURES

FIG. 1 is a graph showing the results of a test of the solubility of nickel in different concentrations of detergent solutions.

FIG. 2 is a graph showing the results of a test of the ability of detergent solutions to remove SiO.

FIG. 3 is a graph showing the results of a test of the foaming characteristics of detergent solutions.

FIG. 4 is a graph showing the results of a test of the rinse characteristics of detergent solutions.

DESCRIPTION

As used herein, the following terms and variations thereof have the meanings given below, unless a different meaning is clearly intended by the context in which such term is used.

“Cleaning” refers to the removal of unwanted materials. In regard to the surface of a hard disk drive, unwanted materials include particulates and other materials that would interfere with the proper or optimal operation of a hard disk drive.

“Contaminant” refers to an unwanted material as described above.

“Detergent” refers to a composition that combines with or chemically interacts with one or more contaminants of a material being cleaned in order to make the contaminants more soluble or otherwise to remove them from the material.

“Hard disk” refers to a rigid disk comprising a magnetic material used for storing computer data.

“Hard disk drive” and “disk drive” refer to a component of a computer or other system for storing data on a rotating hard disk fixed within the hard disk drive.

“Solution” refers to a homogeneous mixture of two or more substances. An “aqueous solution” is a solution in which one of the substances is water, and in which water is generally the solvent, i.e. the substance present in the greatest amount.

The term “comprise” and variations of the term, such as “comprising” and “comprises,” are not intended to exclude other additives, components, integers or steps. The terms “a,” “an,” and “the” and similar referents used herein are to be construed to cover both the singular and the plural unless their usage in context indicates otherwise.

Detergent Composition

There remains a need for improved detergent compositions for removing contaminants from the surfaces of hard disks, in particular disks plated or coated with nickel and/or phosphorous. The present detergent composition includes a combination of nonionic and amphoteric surfactants, chelating agents, and other formulation components which provide improved nickel removal from disk surfaces compared with prior detergents.

The surfactants of the present detergent preferably include an amphoteric surfactant, in particular sodium-2-ethylhexylimino dipropionate, which provides less foaming than other nonionic surfactants conventionally used to remove contaminants from hard disk surfaces. Ethylene oxide/propyleneoxide (EO/PO), a primary alcohol alkoxylate and nonionic surfactant, is also preferably used to provide hard surface cleaning with relatively low foaming. The detergent's foaming characteristics determine the degree of bubbles trapped in a cleaning tank. A higher bubble level causes more problems due to particles being trapped on container surfaces, and bubbles prevent particles from draining for filtration. The presence of fewer bubbles thus reduces contaminants and hence disk media defects.

The chelating agents used in the present detergent formulation preferably include diethylenetriamine penta (methylene phosphonic acid) (DTPMP), which provides high nickel solubility during disk cleaning due to its ability to form a complex bond with up to eight nickel ions, thereby allowing Ni ions to remain in solution and be rinsed away from the disk surface. The chelating agent hydroxyethylene diphosphonic acid (HEDP) is also preferably used in the present formulation.

The foregoing formulation components are preferably formulated in deionized water, preferably also together with potassium hydroxide (KOH), an inorganic salt, and oxalic acid, a reducing agent. The present detergent composition for removing contaminants from a hard disk surface thus preferably comprises ethylene oxide/propyleneoxide (EO/PO), sodium-2-ethylhexyliminodipropionate, potassium hydroxide (KOH), hydroxyethylene diphosphonic acid (HEDP), diethylenetriamine-penta(methylene phosphonic acid) (DTPMP), and oxalic acid.

In a preferred embodiment, the present detergent composition comprises the foregoing components in the following percentages by weight, in the absence of water or other solvent:

1%-5% ethylene oxide/propyleneoxide (EO/PO);

10%-15% sodium-2-ethylhexyliminodipropionate;

25%-30% potassium hydroxide (KOH);

20%-25% hydroxyethylene diphosphonic acid (HEDP);

30%-35% diethylenetriamine-penta(methylene phosphonic acid) (DTPMP); and

1%-5% oxalic acid.

The present detergent composition is preferably used as an aqueous solution when cleaning hard disk surfaces, and can be formulated as a concentrated solution prior to use as a cleaning agent. When applied to the surface of a hard disk, the detergent composition is preferably a solution diluted so that the detergent components, not including water, comprise between 1% and 10% of the solution, such as a solution comprising between 3% and 5% of the detergent components. Such a solution can thus comprise between 0.01% and 3.5% by weight of each of the following components: EO/PO, sodium-2-ethylhexyliminodipropionate, KOH, HEDP, DTPMP, and oxalic acid. More particularly, the solution can comprise, by weight:

0.01%-0.5% ethylene oxide/propyleneoxide (EO/PO);

0.1%-1.5% sodium-2-ethylhexyliminodipropionate;

0.25%-3.0% potassium hydroxide (KOH);

0.20%-2.5% hydroxyethylene diphosphonic acid (HEDP);

0.3%-3.5% diethylenetriamine-penta(methylene phosphonic acid) (DTPMP); and

0.01%-0.5% oxalic acid.

The foregoing solution preferably has a pH of between 11.3 and 12.3, such as a pH of 11.8, and a cloud point of >60° C. The surface tension of the solution is advantageously between 32.7 mN/m and 42.7 mN/m, for example about 37 mN/m.

Table 1 below summarizes preferred detergent compositions of the present invention.

TABLE 1
Detergent Compositions

	Amount*	Amount*	Amount*
	(without	(10%	(1%
Component	water)	dilution)	dilution)
Ethylene	1-5	0.1-0.5	0.01-0.05
oxide/propyleneoxide
(EO/PO)
Sodium-2-	10-15	1.0-1.5	0.1-0.15
ethylhexyliminodipropionate
Potassium hydroxide	25-30	2.5-3.0	0.25-0.30
(KOH)
Hydroxyethylene	20-25	2.0-2.5	0.2-0.25
diphosphonic acid (HEDP)
DTPMP	30-35	3.0-3.5	0.3-0.35
Diethylenetriamine-
penta(methylene phosphonic
acid)
Oxalic acid	1-5	0.1-0.5	0.01-0.05
Deionized (DI) water	0	(Balance)	(Balance)
*Amounts denote weight as a percent of the weight of the listed composition.

The present detergent can also be formulated as a more concentrated solution, either for direct application as a detergent or for further dilution to form a final solution, such as one of the solutions described above. Table 2 below describes the components of illustrative embodiments of such concentrated solutions.

TABLE 2
Concentrated Detergent Solutions

	Component	Amount*	Amount*
	Ethylene oxide/propyleneoxide	0.5-5.0	1-5
	Sodium-2-	3.0-5.0	1-5
	ethylhexyliminodipropionate
	Potassium hydroxide	4.0-7.0	2-6
	(KOH)
	Hydroxyethylene diphosphonic	3.0-6.0	3-10
	acid (HEDP)
	DTPMP	7.0-10.0	3-10
	Diethylenetriamine-
	penta(methylene phosphonic
	acid)
	Oxalic acid	0.5-1.0	<1
	Deionized (DI) water	(Balance)	(Balance)
	*Amounts denote weight as a percent of the weight of the listed composition.

The properties of an illustrative embodiment of the present detergent composition are shown in Table 3 below.

TABLE 3
Detergent Properties

	Property	Measurement
	Density	1.08 g/cm3
	pH (3% solution)	11.84
	Surface Tension	37.7 mN/m
	(3% solution)
	Cloud Point	>55
	(undiluted solution)

The present detergent composition is particularly effective at removing contaminants consisting of nickel, aluminum, silicon, oxygen and/or phosphorus, such as nickel oxide (NiO), nickel phosphorous (NiP), silica oxide (SiO), and AlSiO. Such contaminants can be present on the surface of a hard disk, especially when the surface of the hard disk is plated with nickel and/or phosphorous. The present detergent solution has numerous advantages, including:

improved nickel and NiP solubility, minimizing NiP re-deposition onto media surfaces;

lower foaming, which reduces stains and contaminants on media substrate surfaces after cleaning, and also helps prevent particles from becoming trapped and accumulating with bubbles on the top of tank surfaces;

good rinsability, to prevent detergent residue on substrates after cleaning;

better SiO removal;

better cleaning of organic and inorganic contaminants;

better chelating, reducing, and/or complexing of nickel;

no precipitation of metal ions which may remain on substrate after cleaning;

relatively low surface tension, improving wetting and cleaning;

good dispersibility (low agglomeration);

low chloride content to avoid corrosion;

thermal stability, i.e. a high cloud point (>60° C.), which prevents foaming of micelle particles; and

low nano-asperity.

Detergent Components

Ethylene Oxide/Propyleneoxide (EO/PO).

The EO/PO component of the present detergent is a nonionic surfactant polymer comprising ethylene oxide and/or propyleneoxide. It is preferably a branched ethoxylated linear alcohol containing 8 to 10 carbon atoms and having a propylene oxide cap. An example of such an EO/PO composition is available from Rhodia Inc. (Cranbury, N.J.) as ANTAROX LF-224 (CAS No. 37251-67-5). The EO/PO surfactant can also be a block copolymer, i.e. a polymer comprising two or more homopolymer subunits linked by covalent bonds, with the subunits being ethylene oxide and propyleneoxide, respectively. EO/PO provides hard surface cleaning with controlled foam and good rinsability.

Sodium-2-Ethylhexylimino Dipropionate.

Sodium-2-ethylhexylimino dipropionate is the sodium salt of 2-ethylhexylimino dipropionic acid. It is an amphoteric surfactant, sold for example as AMPHOTENSID EH, available from Zschimmer & Schwarz (Milledgeville, Ga.). Sodium-2-ethylhexylimino dipropionate has the following structure:

The use of this surfactant in predetermined quantities in the present composition reduces foaming compared with prior detergents used to remove impurities from hard disk surfaces.

Potassium Hydroxide (KOH).

Potassium hydroxide (CAS No. 1310-58-3) is an inorganic salt used in the present detergent solution.

Hydroxyethylene Diphosphonic Acid (HEDP).

HEDP, or (1-hydroxyethan-1,1-diyl)bis(phosphonic acid), acts as a chelating agent. It is also referred to as etidronic acid (CAS No. 2809-21-4) and has the following structure:

DTPMP.

DTPMP (CAS No. 22042-96-2), or diethylenetriamine penta(methylene phosphonic acid), is a chelating agent which has the following structure:

DTPMP is a phosphonate analog of EDTA, and can dissociate into 8 positive-negative ions, giving it the ability to chelate a number of metal ions, such as nickel ions. In addition, DTPMP can inhibit corrosion, in particular NiO formation, by sequestration of metal ions. It also inhibits the precipitation of sparingly soluble salts of alkaline-earth metals during media cleaning.

Oxalic Acid.

Oxalic acid (CAS No. 6153-56-5) is preferably included in the detergent formulation as a reducing agent.

The remainder of the present formulation can be water, preferably deionized (DI) water.

Method of Use

The present detergent compositions are used to clean the outer surface of a hard disk, in particular following a chemical and/or mechanical polishing step, when contaminants such as nickel, aluminum, silicon, oxygen and phosphorus compounds may become adhered, bonded, or otherwise associated with the surface of the disk. The present detergent composition is particularly useful in removing nickel oxide (NiO), nickel phosphorous (NiP), silica oxide (SiO), and AlSiO contaminants.

In order to clean the surface of a hard disk, the present detergent composition is first formed as an aqueous solution, as described above. A hard disk surface which has been exposed to processing conditions that are likely to result in the presence of contaminants on the surface of the hard disk is then contacted with the aqueous detergent solution. The hard disk surface can be placed into contact with the detergent solution in various ways known to the art, such as by dipping the disk into the detergent solution or by spraying the detergent solution onto the disk surface. At least some of the contaminants are thereby removed or dissociated from the surface of the hard disk and are transferred into the detergent solution.

The detergent solution is then removed from the surface of the hard disk by ways known to the art, depending in part on how it was applied to the surface. Following such removal, the surface of the hard disk can be rinsed with deionized water, in order to remove any remaining detergent solution from the surface of the hard disk. The deionized water or other solvent applied to the hard disk surface can then be removed by drying the surface, such as by allowing the solvent to evaporate.

EXAMPLES

Example 1

Solubility

The solubility of nickel in the present detergent formulation was compared with the nickel solubility of a prior formulation for cleaning plated hard disk surfaces. The prior formulation comprised nonionic surfactants, an inorganic salt, chelating agents, a reducing agent, and a dispersing agent (“Formulation 1”).

In this test, 1 g of nickel salt was mixed with a 2%, 7% and 10% solution of the present detergent composition in 100 ml. The precipitation of Ni²⁺ was observed. The current formulation was clear with no precipitation, while the prior formulation was turbid with some precipitation. FIG. 1 shows that at the concentrations tested, nickel was more soluble in the present detergent composition.

Example 2

Silica Oxide (SiO) Particle Removal

A test was run with a 10-20 nM SiO slurry, which was allowed to dry for 24 hours on disk surfaces. The surfaces were then cleaned with the prior detergent solution used in Example 1 and a 1%, 5%, and 10% solution of the present detergent composition. After drying, the surfaces were inspected. The results, shown in FIG. 2, demonstrate that the present detergent composition had a better SiO slurry residue removal rate compared to the prior detergent.

Example 3

Aluminum Silicate (AlSiO) Particle Removal

In a further study, a slurry containing AlSiO particles was dispensed in drops onto a NiP substrate surface and dried for 1 hour. The treated substrate was then soaked in a 3% and 5% solution of the present detergent composition for 10 minutes. Following this, the substrates were rinsed with deionized water for 10 seconds and spin dried at 3000 rpm. Substrates treated with the present detergent solutions had fewer AlSiO particles on their surfaces.

Example 4

Foaming Level Test

The detergent solutions tested in Examples 1-3 were tested for foaming alongside two additional prior detergent solutions. 30 mL of a 3% solution of each detergent was placed in a 100 mL graduated cylinder and shaken for 20 seconds. The foaming of each solution was then observed after 10 minutes. Results are shown in FIG. 3, where Formulation 1 comprises a solution of the present detergent. The present detergent solution exhibited comparable or better (lower) foaming characteristics compared with the other formulations.

Example 5

Rinsability Test

To test rinsability, test substrates were weighed and then soaked in the four detergent solutions of Example 3, undiluted, for 1 minute. The substrates were then individually transferred into a beaker containing deionized water and soaked for 10 seconds (i.e., rinsed). The substrates were then dried at 50° C. for 2-3 hours. After cooling, the substrates were weighed again, and the differences in weight were compared. The present solution had good rinsability, i.e. it did not substantially remain on the substrates, as shown in FIG. 4.

As used herein, the term “comprise” and variations of the term, such as “comprising” and “comprises,” are not intended to exclude other additives, components, integers or steps. The terms “a,” “an,” and “the” and similar referents used herein are to be construed to cover both the singular and the plural unless their usage in context indicates otherwise.

Although the present invention has been described in considerable detail with reference to certain preferred embodiments, other embodiments are possible. The steps disclosed for the present methods, for example, are not intended to be limiting nor are they intended to indicate that each step is necessarily essential to the method, but instead are exemplary steps only. Therefore, the scope of the appended claims should not be limited to the description of preferred embodiments contained in this disclosure.

Recitation of value ranges herein is merely intended to serve as a shorthand method for referring individually to each separate value falling within the range. Unless otherwise indicated herein, each individual value is incorporated into the specification as if it were individually recited herein. All references cited herein are incorporated by reference in their entirety.