GB2401370A

GB2401370A - Polishing composition

Info

Publication number: GB2401370A
Application number: GB0410212A
Authority: GB
Inventors: Tomoaki Ishibashi; Toshiki Owaki
Original assignee: Fujimi Inc
Current assignee: Fujimi Inc
Priority date: 2003-05-09
Filing date: 2004-05-07
Publication date: 2004-11-10
Anticipated expiration: 2024-05-07
Also published as: CN1550531A; MY139093A; GB2401370B; JP4068499B2; CN100547045C; GB0410212D0; JP2004331887A

Abstract

The present invention relates to a polishing composition more suitable for use in polishing a substrate for a magnetic disk. The polishing composition contains an abrasive which contains at least one component selected from the group consisting of aluminum oxide, silicon dioxide, cerium oxide, zirconium oxide, titanium oxide; silicon carbide, and silicon nitride, a polishing accelerator which contains at least one component selected from the group consisting of carboxyethyl thiosuccinic acid and its salts, and water. The polishing accelerator may further contain other components e.g. malic acid, citric acid. Also shown is a method of polishing a substrate using the above polishing composition.

Description

POLISHING COMPOSITION

BACKGROUND OF THE INVENTION

The present invention relates to a polishing composition to be used for polishing a substrate for a magnetic disk and the like.

With respect to a magnetic disk for use as a hard disk serving as a memory device for a computer, there have been strong demands for high recording density. Therefore, a substrate for a magnetic disk is required to have superior surface characteristics.

Japanese Laid-Open Patent Publication No. 2000-1665 discloses polishing composition improved so as to satisfy such a requirement for a substrate. The polishing composition contains an abrasive such as aluminum oxide, succinic acid or its salt serving as a polishing accelerator, and water.

However:, the polishing composition has the problem that although succinic acid or its salt promotes polishing and prevents surface defects from occurring on the surface of polished substrate, succinic acid or its salt is little effective in reducing microwaviness of the substrate surface and cannot sufficiently improve the smoothness of the substrate surface.

SUMMARY OF THE INVENTION

Accordingly, it is an objective of the present invention to provide a polishing composition more suitable for use in polishing a substrate for a magnetic disk.

To achieve the foregoing and other objectives and in tIetre i:' tleeele. . :e Ite' accordance with the purpose of the present invention, a polishing composition is provided. The polishing composition contains an abrasive which contains at least one component selected from the group consisting of aluminum oxide, silicon dioxide, cerium oxide, zirconium oxide, titanium oxide, silicon carbide, and silicon nitride, a polishing accelerator which contains at least one component selected from the group consisting of carboxyethyl thiosuccinic acid and its salts, and water.

The present invention also provides a method for polishing an object. The method includes preparing the above polishing composition, and polishing the surface of the object by using the polishing composition.

Other aspects and advantages of the invention will become apparent from the following description, illustrating by way of example the principles of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

One embodiment of the present invention will now be described.

A polishing composition according to this embodiment contains (a) an abrasive which contains at least one component selected from the group consisting of aluminum oxide, silicon dioxide, cerium oxide, zirconium oxide, titanium oxide, silicon carbide, and silicon nitride, (b) a polishing accelerator which contains at least one component selected from the group consisting of carboxyethyl thiosuccinic acid and its salts, and (c) water.

The polishing composition is used for polishing, for example, a substrate for a magnetic disk. This substrate may ::e a.e À:e be a substrate formed by providing an electroless plating layer composed of nickel-phosphorus on a blank member composed of an aluminum alloy, or a substrate containing nickel-iron, boron carbide, or carbon.

The abrasive plays a role in mechanically polishing an object. The abrasive preferably contains at least one of aluminum oxide and silicon dioxide, and more preferably contains aluminum oxide. Aluminum oxide and silicon dioxide have great effect of reducing microwaviness of the surface of the polished object and aluminum oxide also has high mechanical polishing ability.

Aluminum oxide may be a-alumina, lo-alumina, O-alumina, ]5 K-alumina, or fumed alumina. Silicon dioxide may be colloidal silica or fumed silica. Cerium oxide may be cerium dioxide or dicerium trioxide, and may be in the hexagonal crystal system/ equiaxed crystal system, or face centered cubic crystal system.

Zirconium oxide may be in the monoclinic system or tetragonal system, and may be amorphous zirconia or fumed zirconia.

Titanium oxide may be titanium monoxide, dititanium trioxide, titanium dioxide, or fumed titania. Silicon carbide may be a- silicon carbide, p-silicon carbide, or amorphous silicon carbide. Silicon nitride may be a-silicon nitride, p-silicon nitride, or amorphous silicon nitride.

In a case where the abrasive is aluminum oxide, zirconium oxide, titanium ox-ice, silicon carbide, or silicon nitride, the average particle size of the abrasive determined by the laser diffraction and scattering method is preferably from 0.05 to 2.0,um inclusive, more preferably from 0.1 to 1.5 Am inclusive. In a case where the abrasive is silicon dioxide, the average primary particle size of the abrasive determined from the specific surface area measured by a BET method is preferably from 0.005 to 0.5,um inclusive, more preferably c: ee ee: e.e.e e.

from 0.01 to 0.3 Em inclusive. In a case where the abrasive is cerium oxide, the average particle size of the abrasive measured by a scanning electron microscope (SEM) is preferably from 0.01 to 0.5 Am inclusive, more preferably from 0.05 to 0.45 Am inclusive. If the average particle size of the abrasive is too small, the abrasive might have low mechanical polishing ability. If the average particle size of the abrasive is too large, the precipitation of the abrasive might occur in the polishing composition and scratches might occur on the surface of the polished object.

The content of the abrasive in the polishing composition is preferably from 0.1 to 40% by weight inclusive, more preferably from 1 to 25% by weight inclusive. If the content of the abrasive is less than 0.1% by weight, the polishing rate of the polishing composition might be reduced. If the content of the abrasive exceeds 40% by weight, stability of the polishing composition might be deteriorated due to the aggregation of the abrasive, with the result that sedimentation might occur in the polishing composition and at the same time the viscosity of the polishing composition might become high.

The polishing accelerator plays a role in accelerating the mechanical polishing by the abrasive and a role in reducing the microwaviness of the surface of the polished object. It might be thought that this is because the polishing accelerator removes the microwviness by its chemical polishing action. The term "microwaviness" used here means micro irregularities measured by use of a surface roughness measuring device with a given measuring wavelength, which are expressed by height (A). Various kinds of polishing accelerators are known other than carboxyethyl thiosuccinic acid and its salts. However, these hardly reduce the microwaviness of the surface of the polished object.

e: .. . À A. ee: Àe ae Carboxyethyl thiosuccinic acid is given by the following general formula 1. The salts of carboxyethyl thiosuccinic acid may be alkali metal salts such as potassium salt, ammonium salts, or amine salts such as monoethanolamine salt.

The polishing accelerator preferably contains carboxyethyl thiosuccinic acid, its potassium salt, or its monoethanolamine salt because they have a strong action of removing the microwaviness of the surface of the polished surface by their chemical polishing action.

General Formula 1 HOOD-CH2 CH2 S-CH-COOH CH2 COOH The content of the polishing accelerator in the polishing composition is preferably from 0. 001 to 10% by weight inclusive, more preferably from 0.003 to 5% by weight inclusive, and most preferably from 0.01 to 2% by weight inclusive. If the content of the polishing accelerator is less than 0.001% by weight, the microwaviness of -the surface of the polished surface is not removed much, with the result that the polishing rate of the polishing composition might be reduced. If the content of the polishing accelerator exceeds 10% by weight, surface defects such as microprotrusions and micropits might occur on the surface of the polished surface.

The water plays a role as a medium for dissolving and dispersing components other than water in the polishing composition. It is preferred that the water contains as little impurities as possible. More specifically, purified water, ultrapure water, or distilled water is preferable.

polishing composition according to this embodiment is À : : : . prepared by mixing an abrasive, a polishing accelerator, and water. During the mixing, the order of in which each component is added may be in any order, or all the components may be added at the same time.

When the surface of a substrate for a magnetic disk is polished using a polishing composition according to this embodiment, for example, the surface of the substrate is rubbed with a polishing pad while supplying the polishing l0 composition to the surface of the substrate.

A polishing composition according to this embodiment is preferably used in the first polishing step in a plurality of polishing steps commonly carried out during the manufacturing processes for a substrate. The first polishing step is generally performed to remove the waviness and surface defects such as large scratches and irregularities on the substrate which might not be capable of being removed in the following polishing step. On the other hand, the final polishing step is generally performed to make an adjustment to a desired surface roughness of the substrate and to remove surface defects which occurred in the previous polishing step and surface defects which could not be removed in the previous polishing step.

The present embodiment provides the following advantages.

A polishing composition according to this embodiment contains an abrasive for mechanically polishing an object and a polishing accelerator for accelerating the mechanical polishing by the abrasive. Therefore, the polishing composition has an ability to polish an object, in particular, to polish a substrate for a magnetic disk at a high speed. In other words, the polishing composition according to the embodiment has a high polishing rate for a substrate.

: Be. tee cee. it.: À. ,. .e ee cece Carboxyethyl thiosuccinic acid and its salts have an ability to reduce the microwaviness of the surface of the polished object. Therefore, a polishing composition containing carboxyethyl thiosuccinic acid or its salts improves the smoothness of the surface of the polished object.

It should be apparent to those skilled in the art that the present invention may be embodied in many other specific forms without departing from the spirit of scope of the invention. Particularly, it should be understood that the invention may be embodied in the following forms.

The polishing accelerator may further contain at least one component selected from the group consisting of organic acids, inorganic acids, or salts of these acids, together with the carboxyethyl thiosuccinic acid and its salts. The additional component to be contained in the polishing accelerator is preferably organic acids or inorganic acids because of its strong chemical polishing ability. The additional component to be contained in the polishing accelerator is more preferably malic acid, glycolic acid, succinic acid, citric acid, maleic acid, itaconic acid, malonic acid, imiondiacetic acid, gluconic acid, latic acid, mandelic acid, tartaric acid, crotonic acid, nicotinic acid, acetic acid, glycine, alanine, methane sulfonic acid, benzene sulfonic acid, toluene sulfonic acid, xylene sulfonic acid, thioacetic acid, mercaptosuccinic acid, aluminum nitrite, or aluminum sulfate, and most preferably malic acid, glycolic acid, succinic acid, citric acid, or imiondiacetic acid.

The content of the additional component to be contained in the polishing accelerator in the polishing composition is preferably from 0.001 to 0.5% by weight inclusive, more preferably from O.OOS to 0.3% by weight inclusive. If the :: '.. I: content is less than 0.001% by weight, the polishing rate of the polishing composition is not improved much. If the content exceeds 0.5% by weight, the surface of the polished object might be eroded by the additional component, with the result that the mierowaviness of the surface of the polished object might worsen and surface defects such as micropits might occur on the surface of the polished object.

The polishing composition may further contain a surfactant; alumina sold mol.ybdic acid; salts of molybdic acid such as sodium salt, potassium salt, and ammonium salt; a disinfectant such as sodium alginate and potassium hydrogencarbonate; a chelating agent such as nitrilo triacetic acid (NTA), ethylenediamine tetraacetic acid (EDTA), diethylenetriamine pentaaceti.c acid (DTPA), and triethyelnetetramine hexaacetic acid (TTHA) i water-soluble celluloses such as hydroxyl cellulose, hydroxylpropyl cellulose, and carboxymethyl cellulose; higher fatty amine; sulfonic acid; a rust inhibitor; an antifoaming agent; and working oils.

The surfactant improves the dispersibility of the polishing composition and has the effect of suppressing the occurrence of surface defects on a surface of the polished object. The surfactant may be a nonionic surfactant or anionic surfactant. The nonionic surfactant is preferably polyoxyeLhylene polyoxypropylene alkylether represented by the following general formula 2, a polyoxyethylene polyoxypropylene copolymer represented by the following general formulae 3 or 4, polynxyethylene sorbitan fatty acid ester, polyoxyethylene sorbit fatty acid ester, or urethane associated surfactanE represented by the following general formula 5. The anionic surfactant is preferably polycarboxylates such as sodium polyacrylate, or polymers, such as a copolymer of isoprene sulfonic acid and acrylic ac.id, :. ate. dee. et.; eere. .e including a monomer unit derived from isoprene sulfonic acid or its salts. When the polishing composition containing the above listed nonionic surfactant or the above listed anionic surfactant is used for polishing the surface of a substrate for a magnetic disk, the flatness of the surface of the substrate is improved because the surface droop of an outer peripheral portion of the substrate is suppressed.

General Formula 2 ICH3 R-O - (CH2CHO)(CH2CH2O)mH In the general formula 2, R denotes an alkyl group, and 1 and m each denote an integer.

General Formula 3

CH

HO(CH2CH2O)ntcHcH2O)ocH2cH2o)pH In the general formula 3, n, o and p each denote an integer.

General Formula 4 IH3 IHa HO(CHCH2O)q(CH2CH2O)r(CHCHzO)sH In the general formula 4, q, r and s each denote an integer.

General Formula 5

O O 11 11

X-(C-NH-Y-NH-C-(OCH2CH2)U-Z), In the general formula 5, X denotes a residue of polyether polyol which is derived from a compound having an active oxygen atom and alkylene oxide (however, the polye-ther chat contains 20 to 90% by weight of oxyethylene group), denotes an integer between 2 to 8 inclusive (= the number of hydroxyl groups in one molecule of the above-described polyether polyol), Y denotes a divalent hydrocarbon group, Z denotes a residue of a monovalent compound having an active oxygen atom, and u denotes an integer of 3 or more.

The content of the surfactant in the polishing composition is preferably from 0.001 to 0.5% by weight inclusive, more preferably from 0.005 to 0. 3% by weight inclusive. If the content of the surfactant is less than 0.001% by weight, the surface droop is not suppressed much.

If the content of the surfactant exceeds 0.5% by weight, the polishing rate of the polishing composition might be reduced because the polishing promoting effect is impaired, with the result that precipitating and foaming might occur.

The alumina sol suppresses surface defects, such as microprotrusions and micropits, on the surface of the polished object. It might be thought that this is because alumina sol adheres to the surface of the abrasive, thereby promoting mechanical polishing ability of the abrasive. Furthermore, because the alumina sol disperses in the polishing composition in a colloidal state, the alumina sol prevents the precipitation of the abrasive by improving the dispersibility of the abrasive and causes the abrasive to be easily held by a polishing pad during the polishing an object.

The alumina sol may contain at least one component selected from the group consisting of alumina hydrates and alumina hydroxide dispersed in a colloidal state in an acid aqueous solution. The alumina hydrates may be boehmite, pseudobochmite, diaspore, gibbsite, or bayerite. The acid aqueous solution is prepared by adjusting the pll of water to the acid side by use of organic acids, inorganic acids, or salts of these acids. The alumina sol may contain two or more # À À À c, kinds of alumina hydrates. Preferable alumina hydrate is boehmite or pseudobohmite because boehmite and pseudobohmite have relatively high abilities to suppress surface defects and to reduce the surface roughness of the polished object.

The polishing composition may be prepared by diluting a stock solution with water immediately before use.

The polishing of a substrate for a magnetic disk may be lO performed in a single polishing step. In such a case, the polishing composition may be used in the single polishing step.

The polishing composition may be used in the polishing step other than the first polishing step. For example, the polishing composition may be used in the final polishing step.

The polishing composition may be used in polishing an object other than a substrate for a magnetic disk. The object other than a substrate for a magnetic disk may be an object containing tungsten, copper, silicon, glass, or ceramic More specifically, the object may be a semiconductor wafer or an optical lens.

The present invention will now be described in more detail by referring to Examples and Comparative Examples.

In Examples l to 16, and Comparative Examples l to 8, polishing compositions were prepared by mixing an abrasive, a polishing accelerator, and water. The abrasive in each polishing composition is aluminum oxide having the average particle size of 0.8,um. The average particle size of aluminum oxide is determined by using a laser diffraction and scattering type grain size measuring machine (LS-230 made by Coulter). The content of aluminum oxide in each polishing composition is 6% by weight. Detailed compositions of the Àe B cee eee polishing accelerators in respective polishing compositions are shown in Table 1.

Using each of the polishing compositions, the surface of a substrate for a magnetic disk was polished under the following polishing conditions.

<Polishing conditions> Substrate to be polished: An electroless Ni-P substrate 3.5 inches in diameter Polishing machine: two-side polishing machine with fixed bases of 720 mm diameter Polishing pad: Polyurethane pad (BELLATRIX N0048, made by Kanebo LTD.) Polishing load: 100 g/cm2 Rotational number of top fixed base: 24 rpm Rotational number of bottom fixed base: 16 rpm Supply amount of polishing composition: 150 ml/minute Stock removal: 3 Em in terms of finishing allowance on both sides The size of microwaviness was measured on the substrate surface after polishing by use of a noncontact surface roughness measuring device (Micro XAM made by PhaseShift, objective lens: 10x, filter: Gaussian Bandpass), Ra values being measured at 80 to 450 um. The measured size of microwaviness was evaluated by three levels: Ra of less than 4.5 A (good), Ra of not less than 4.5 but less than 5.0 A (fair), Ra of not less than 5.0 A (poor). The results are shown in the column entitled "Microwaviness" in Table 1.

With respect to polishing processes carried out under the above-mentioned conditions, the polishing rate was calculated based on the following equation. The calculated polishing rate was evaluated by three levels: a polishing rate te cee Àe celllee of not less than 0.50,um/minute (good), a polishing rate of not less than 0.45 M/minute but less than 0.50 M/minute (fair), a polishing rate of less than 0.45,um/minute (poor).

The results are shown in the column entitled "Polishing rate" ;

S in Table 1.

<equation> Polishing rate [pm/minute] = reduced amount of substrate [g] due to polishing / (area [cm2] of substrate surface to be polished x density [g/cm3] of Ni-P plated layer x polishing time [minute]) x 104.

Table 1 1

Polishing accelerator K. Content Content Micro- Polishing _ wt%) Kind(wt%) waviness rate Ex.1A1 0.1 _ Good Fair Ex.2A1 0. 2 _ Good Fair Ex.3Al 0.5 _ Good Fai.r Ex.4Al. 1.0 Good Fair.

Ex.5A2 0.2 Good Fair i Ex.6A3 0.2 _ Good Poor Ex.-/A4 0.2._ Good Poor: Ex. 8A5 0.2 _ _ Good Poor Ex.9 A1 0.2 Citric acid 0.1 _ Good _ Good Ex. 10 A1 0.2 Succinic acid 0.1 Good Good Ex.ll A1 0.2 Malic acid O.l _ Good Good = Ex.12 _ A1 0.2 Iminodiacetic acid 0.1 Good Good; Ex.13 A1 0. 2 Glycolic acid 0.1 Good Good

_

Ex.14 A1 0.2 Glycine 0.1 Good Good Ex.15 A1 0.2 Methane sulfonic acid 0. 1 Good _ Good Ex.16 _ Al 0.2 Aluminum sulfate 0.1 Good Good.

C.Ex.1.. Citric acid 0.2 Poor Fair; C.Ex.2 Succinic acid 0.2 Fair Fair I C.Ex.3 _ _ Mal.ic acid 0.2 Poor Fair C.Ex.4 _ Iminodiacetic acid 0. 2 Fair Fair C.Ex.5 _ Glycolic acid 0.2 Poor _ Poor C.Ex.6 _ _ Glyci.ne 0. 2 Poor Poor C.Ex.7 Methane sulfonic acid 0.2 Fair Fair C.Ex.8 _. Aluminum sulfate 0.2 _ Poor Poor In Table l, carboxyethyl thiosuccinic acid is denoted by Al, monopotassium carboxyethyl thiosuccinate is denoted by A2, dipotassium carboxyethyl thiosuccinate is denoted by A3, and tripotassium carboxyethyl thiosuccinate is denoted by A4, : monoethanolamine carboxyethyl thiosuccinate is denoted by A5.

Ietete As shown in Table 1, Examples 1 to 16 are good in result of microwaviness. Moreover, Examples 9 to 16 are good in result of polishing rate because of the presence of organic S acids or salts of inorganic acid other than carboxyethyl thiosuccinic acid and its salts. In contrast, Comparative Examples 1 to a are not good in any of results of microwaviness and polishing rate.

The present examples and embodiments are to be considered as illustrative and not restrictive and the invention is not to be limited to the details given herein, but may be modified within the scope and equivalence of the appended claims. is 1 L

Claims

CLAIMS: 1. polishing composition characterized by: an abrasive which

contains at least one component selected from the group consisting of aluminum oxide, silicon dioxide, cerium oxide, zirconium oxide, titanium oxide, silicon carbide, and silicon nitride; a polishing accelerator which contains at least one component selected from the group consisting of carboxyethyl thiosuccinic acid and its salts; and water.
2. The polishing composition according to claim 1, characterized in that the abrasive contains at least one of aluminum oxide and silicon dioxide.
3. The polishing composition according to claim 1 or 2, characterized in that the abrasive contains aluminum oxide.
4. The polishing composition according to any one of claims 1 to 3, characterized in that average particle size of the aluminum oxide, zirconium oxide, titanium oxide, silicon carbide, and silicon nitride is from 0.05 to 2.0 Am inclusive.
5. The polishing composition according to any one of claims 1 to 4, characterized in that average primary particle size of the silicon dioxide is from 0.005 to 0.5 Am inclusive.
6. the polishing composition according to any one of claims 1 to 5, characterized in that average particle size of the cerium oxide is from 0.01 to 0.5 Am inclusive.
7. The polishing composition according to any one of claims 1 to 6, characterized in that the content of the abrasive in the polishing composition is from 0.1 to TOGO by weight #am, inclusive.
8. The polishing composition according to any one of claims 1 to 7, characterized in that the polishing accelerator contains at least one component selected from the group consisting of carboxyethyl thiosuccinic acid, its potassium salt, or its monoethanolamine salt.
9. The polishing composition according to any one of claims 1 to 8, characterized in that the polishing accelerator further contains at least one component selected from the group consisting of organic acids, inorganic acids, or salts of these acids other than carboxyethyl thiosuccinic acid and its salts.
10. The polishing composition according to any one of claims 1 to 9, characterized in that the polishing accelerator further contains at least one component selected from the group consisting of malic acid, glycolic acid, succinic acid, citric acid, maleic acid, itaconic acid, malonic acid, imiondiacetic acid, gluconic acid, latic acid, mandelic acid, tartaric acid, crotonic acid, nicotinic acid, acetic acid, glycine, alanine, methane sulfonic acid, benzene sulfonic acid, toluene sulfonic acid, xylene sulfonic acid, thioacetic acid, mercaptosuccinic acid, aluminum nitrite, and aluminum sulfate.
11. The polishing composition according to any one of claims 1 to 10, characterized in that the polishing accelerator further contains at least one component selected from the group consisting of malic acid, glycolic acid, succinic acid, citric acid, and imiondiacetic acid.
12. The polishing composition according to any one of claims 1 to 11, characterized in that the content of the polishing accelerator in the polishing composition is from 0.00] to 10% by weight inclusive.
13. The polishing composition according to any one of claims 1 to 12, characterized by alumina sol.
14. The polishing composition according to claim 13, characterized:i.n that the alumina sol contains at least one component selected from the group consisting of alumina hydrates and aluminum hydroxide dispersed in a colloidal state in an acid aqueous solution.
15. The polishing composition according to claim 14, characterized in that the alumina hydrates are boehmite or pseudobohmite.
16. The polishing composition according to any one of claims 1 to 15, characterized in that the polishing composition is used for polishing a substrate for a magnetic disk.
17. A method for polishing a substrate for a magnetic disk, the method characterized by: preparing the polishing composition according to any one of claims 1 to 15; polishing the surface of the substrate by using the polishing composition.
18. A polishing composition substantially as hereinbefore described with reference to

the examples.
19. A method for polishing a substrate substantially hereinbefore described with reference to th examples. -')

? . I INVESTOR IN PEOPLE Application No: GB0410212.5 Examiner: Dr Jonathan Corden Claims searched: 1-17 Date of search: 27 August 2004 Patents Act 1977: Search Report under Section 17 Documents considered to be relevant: Category Relevant Identity of document and passage or figure of particular relevance to claims X,P 1-10, 12, GB 2390370 A 13, 16, 17 (FUJIMI) see page 5 line 30 to page 6 line 13 and example 16 especially A,P GB 2384003 A (FUJIMI) whole document A,P GB 2383797 A (FUJIMI) whole document A GB 2338490 A (FUJIMI) whole document A US 5922910 A (ELF ATOCHEM) whole document Categones: X Document indicating lack of novelty or inventive A Document indicating technological background and/or state step of the art.

Y Document indicating lack of inventive step if P Document published on or after the declared priority date but combined with one or more other documents of before the filing date of this invention.

same category.

& Member of the same patent family E Patent document published on or after, but with priority date earlier than, the filing date of this application.

Field of Search:

Search of GB, EP, WO & US patent documents classified in the following areas of the UKC: C4V Worldwide search of patent documents classified in the following areas of the IPC07 | C09G; C09K I The following online and other databases have been used in the preparation of this search report l WPI, EPODOC, PAJ, STN: CAS Online l Anne-Stir Arn/^ftl-nnartmpntlfTlrlaunrilnAlt-/