WO2007034199A1

WO2007034199A1 - Dispersant

Info

Publication number: WO2007034199A1
Application number: PCT/GB2006/003528
Authority: WO
Inventors: Katharine Vincent Hill; Trevor Graham Blease; Wilhelmus Jacobus Adrianus Honcoop
Original assignee: Croda International Plc
Priority date: 2005-09-26
Filing date: 2006-09-21
Publication date: 2007-03-29
Also published as: GB0519551D0; TW200744746A

Abstract

Dispersions having at least one trimer fatty triamine and/or higher oligomeric amine dispersant to aid dispersion of a solid in an organic solvent with which the dispersant is compatible are disclosed. Their use in making plasma display panels and multi- layer ceramic capacitors are also described.

Description

Dispersant Field of Invention

The present invention relates to use of a dispersant comprising a trimer fatty triamine and/or higher oligomeric amine to aid dispersion of a solid in an organic solvent. The application includes use of the dispersant to disperse solids in rib paste, phosphor paste and dielectric layers for plasma display panels, for dielectric solid and conductive solid dispersion in multi-layer ceramic capacitors and for pigment dispersion, specifically inorganic pigments.

Background A plasma display panel (PDP) is known as a self-luminescent type flat display having excellent properties of being lightweight and thin whilst also having the capability of a large screen surface for display. A typical PDP has a front glass plate on which a plurality of electrodes are disposed for generating plasma discharge by cooperation with electrodes deposited on a rear glass plate facing, and separated from, the front glass plate. A dielectric layer is positioned on the electrodes on both the front and back plate of the PDP. The space between the plates is charged with mixed rare gases. A plurality of barrier ribs and phosphors are formed in this space between the front and rear glass plates. The phosphors emit light in respective colours of red, green and blue. The ribs partition the respective cells of red, green and blue (ie separate the phosphors of respective colours and inhibit the discharge interference between pixels) and serve to maintain the space between the front and rear panels.

A range of methods are available for manufacture of the ribs, which methods include screen printing, sand blasting and photolithography methods. Each rib is formed by firing a mixture of glass powder with ceramic powders as fillers with binder, solvent and plasticiser which is in the form of a paste. The organic material present in the paste is removed by the firing process. Therefore the type of organic material must be chosen so that it can be efficiently removed during the firing process.

Some instances of the use of dispersing agents in the formation of the rib paste has been disclosed. For example, use of a dispersing agent is mentioned in a paper in Bull. Chem Soc. Jpn, 77, 1613-1625 (2004) entitled "Technology for forming of barrier ribs on a plasma display panel by applying a photosensitive glass paste." Section 4, pages 1618 to 1619 describes the design of the paste for a photolithography method of rib manufacture which mentions that a dispersant may be included. There is no disclosure of any chemistry of the dispersant or any advantages that it brings to the rib paste.

It is disclosed in JP2003257314 A that dispersibility of the rib paste must be effective and uniform for the following reasons. Typically, when, using a paste, filtration of the paste is carried out to remove dust and other foreign matter. If the paste has low dispersibility, the filter can be blocked, not only with the foreign matter but also with aggregates from the paste. This results in filters having to be replaced with increased frequency with a consequent reduction of production efficiency. If a screen printing method for manufacture of ribs is used, a low paste dispersibility can lead to the screen being blocked; and, if a direct coating method is used, there could be nozzle hole blockage. Bonding between inorganic powder surfaces owing to surface static charges on the inorganic powder and hydrogen bonding is also cited as a cause of low paste dispersibility. In particular, in the case where two or more types of inorganic powder are used mixed together, aggregation is facilitated. If, at this time, two of the two or more types of inorganic powder possess different positive or negative charges, electrostatic attraction acts between the powders in the paste and aggregation of the powder particles readily occurs. Moreover, aggregation of the powder particles is readily brought about in the case where hydroxyl groups present at the surface of an inorganic powder, either directly, or indirectly via, for example, water undergo hydrogen bonding with hydroxyl groups at the surface of some other inorganic powder. To suppress the aggregation brought about by the surface static charges on the inorganic particles and/or by hydrogen bonding, JP2003257314 discloses the use as a dispersant of a material of molecular weight 200-3500 which must contain a carboxyl functional group.

Therefore, the dispersant for a rib paste must be selected so that it enables formation of an effective and uniform dispersion but also can be burnt off during the firing process.

The phosphors are typically inorganic oxides mixed with binder and solvent to form a paste which is then fired to remove the organic solvent. The dispersant for a phosphor must be selected so that it enables formation of an effective and uniform dispersion but also can be burnt off during the firing process. It is important that the paste is uniform whereby uniform colour may be emitted from the phosphors. It is also important that the viscosity of the dispersion is low for ease of use in the manufacture of the phosphors. The dielectric layer of the PDP is made of a glass and/or ceramic material. The unfired dielectric layer paste also contains a binder and solvent. To obtain a PDP of high quality it is important for the dielectric layer to possess uniform thickness and have a smooth surface. If the thickness of the dielectric layer is not uniform and the surface smoothness of it is insufficient, the insulating property of the dielectric layer may decline. Use of a dispersing agent in the formation of such layers to enhance these properties has been disclosed. For example, JP2004002164 A discloses a polycarboxylic acid polymeric compound as a dispersant for a PDP dielectric layer. In common with the dispersant disclosed in the prior art for barrier ribs, this dispersant for a dielectric layer paste has a carboxyl functional group as an essential feature.

Application of a finely divided dielectric material to a substrate and superimposing thereon a layer of finely divided conductive material in a desired pattern forms a capacitor or capacitor plate. Multi-layer ceramic capacitors (MLCC) are then formed from alternating layers of the dielectric material and the conductive material with the two outermost layers of the MLCC being dielectric material. This composite sandwich of alternating layers is then fired at the fusing or sintering temperature of the dielectric material to form a monolithic capacitor structure. The dielectric material and the conductive material are each generally prepared from dispersions of dielectric material and conductive material in an organic solvent. The dispersant must be selected such that for each alternative layer of dielectric and conducting material the material is uniformly dispersed in the organic solvent. The dispersant is removed either by being "burnt out" during the fusing or sintering process or removed during the drying process. Therefore, the dispersant must also be chosen such that it can be efficiently removed during the fusing, sintering or drying processes. WO04078333 A1 discloses use of a dispersant which is preferably a plurality of polyester chains attached to a polyamine or polyimine group to disperse dielectric material and conductive material, suitable for capacitors and printed circuit boards, in a carrier solvent. In common with the dispersants disclosed in the prior art for barrier ribs and dielectric layer for PDP, this dispersant for use in making capacitors has a carboxyl functional group as an essential feature.

Recently, there has been an increased trend towards miniaturisation of electronic components in general; and miniaturisation of MLCC has been actively pursued. Already the thickness of the dielectric material has been reduced to about 2 μm, with the potential for layers of about 1 μm under investigation. Therefore, this exacerbates the problem of selecting suitable dispersants for use in MLCC pastes to obtain a uniform dispersion which is stable over time.

Therefore, the dispersant for MLCC applications must be selected so that it enables formation of an effective and uniform dispersion but also can be burnt off during the firing process. It is also important that the viscosity of the dispersion is low for ease of use thereof in the manufacture of the solids for MLCC applications.

Pigments, particularly for paints and solvent inks, such as described in the Colour Index (3rd Ed 1971), can be dispersed in organic solvents. Many examples of polymeric dispersants have been disclosed for use in dispersing pigments. For example, in US3996059, US4224212, US4861380, US4797440 and US5300255 where in all cases the polymeric dispersant has a carboxyl functional group in its structure.

Therefore, the dispersant must be effective at dispersing pigments in an organic solvent.

Summary of the Invention

Surprisingly it has been found that a dispersant that does not have a carboxyl functional group in its structure can meet the above defined dispersant requirements for solids in barrier ribs, phosphors and dielectric layers in a PDP, dielectric material and conductive solids in MLCC applications and for dispersancy of pigments in an organic solvent.

Detailed Description of the Invention

Accordingly, the present invention provides the use of at least one trimer fatty triamine and/or higher oligomeric amine dispersant to aid dispersion of a solid in an organic solvent with which the dispersant is compatible.

The invention further provides a dispersion of a solid in an organic solvent which includes as a dispersant at least one trimer fatty triamine and/or higher oligomeric amine.

The trimer fatty triamine dispersant used in the present invention is preferably formed from the corresponding trimer fatty acid.

The terms trimer fatty acid and dimer fatty acid are well known in the art, and refer to the trimerisation/dimerisation products of mono- or polyunsaturated fatty acids and/or esters thereof. They are described in T.E. Breuer, 'Dimer Acids', in J.I. Kroschwitz (ed.), Kirk-Othmer Encyclopedia of Chemical Technology, 4th Ed., Wiley, New York, 1993, Vol. 8, pp. 223-237. They are prepared by polymerizing fatty acids under pressure, and then removing most of the unreacted fatty acid starting materials by distillation. The final product usually contains some mono fatty acid, mostly dimer fatty acids, and trimer fatty acids and some higher or oligomeric fatty acids. The resultant product can be prepared with various levels of the different fatty acids. The ratio of dimer fatty acids to trimer fatty acids can be varied, by modifying the processing conditions and/or the unsaturated acid feedstock. The trimer fatty acid may be isolated in substantially pure form from the product mixture, using purification techniques known in the art, or alternatively a mixture of trimer fatty acid and dimer fatty acid may be employed to produce the corresponding amines. The trimer fatty triamine and optional dimer fatty diamine may be produced from the corresponding trimer fatty acid and optional dimer fatty acid by standard chemical methods known in the art, for example by reacting with ammonia followed by hydrogenation, as described in EP-530696-A.

The dispersant used in the present invention preferably has a trimer fatty triamine (or trimer) content of greater than 5%, more preferably in the range from 10 to 90%, particularly 30 to 70%, and especially 40 to 50% by weight. In addition, particularly preferred dispersants have a dimer fatty diamine (or dimer) content of less than 95%, more preferably in the range from 10 to 90%, particularly 30 to 70%, and especially 50 to 60% by weight. Further, the dispersant preferably comprises less than 10%, more preferably in the range from 1 to 6%, particularly 2 to 4%, and especially 2.5 to 3.5% by weight of mono fatty monoamine (or monomer). All of the above % by weight values are based on the total weight of trimer, dimer and monomer amine present in the dispersant.

Preferred trimer fatty triamines are trimers of Ci₀ to C₃₀, more preferably C₁₂ to C₂₄, particularly Ci₄ to C₂₂, and especially C₁₈ alkyl chains. Thus, preferred trimer fatty triamines contain in the range from 30 to 90, more preferably 36 to 72, particularly 42 to 66, and especially 54 carbon atoms. The molecular weight (weight average) of the trimer fatty triamine is preferably in the range from 750 to 950, more preferably 790 to 910, particularly 810 to 890, and especially 830 to 870.

Suitable trimer fatty triamines are preferably derived from (i.e. are amine equivalents of) the trimerisation products of oleic acid, linoleic acid, linolenic acid, palmitoleic acid, and elaidic acid, and particularly of oleic acid. The trimer fatty triamines may also be derived from the trimerisation products of the unsaturated fatty acid mixtures obtained in the hydrolysis of natural fats and oils, e.g. of sunflower oil, soybean oil, olive oil, rapeseed oil, cottonseed oil and tall oil. Hydrogenated, for example by using a nickel catalyst, trimer fatty acids may also be employed to produce the corresponding trimer fatty triamines.

Similarly, the optional dimer fatty diamines are preferably derived from the dimerisation products of the materials mentioned in the above paragraph, and are preferably dimers of C₁₀ to C₃₀, more preferably C₁₂ to C₂₄, particularly C₁₄ to C₂₂, and especially C₁₈ alkyl chains. Thus, the dimer fatty diamines preferably contain in the range from 20 to 60, more preferably 24 to 48, particularly 28 to 44, and especially 36 carbon atoms. The molecular weight (weight average) of the dimer fatty diamine is preferably in the range from 450 to 69O₁₁ more preferably 500 to 640, particularly 530 to 610, and especially 550 to 590.

In one embodiment of the present invention, tetramer fatty tetraamines and higher oligomers (hereinafter both referred to as oligomeric amines) are formed during production of the amine from the trimer fatty acid and/or dimer fatty acid and/or mono fatty acid. Preferably the oligomeric amines are formed during production of the amine from a combination of trimer fatly acid with dimer fatty acid and mono fatty acid. Such oligomeric amines can also be used as a dispersant according to the present invention, either alone (by isolating from the amine reaction product mixture) or in combination with trimer fatty triamiraes and/or dimer fatty diamines and/or mono fatty monoamines. Preferably such oligomeric amines are used in combination with trimer fatty triamines and dimer fatty diamines and mono fatty monoamines. The oligomeric amines are preferably oligomers, containing 4 or more units, of C₁₀ to C₃₀, more preferably Ci₂ to C₂₄, particularly C₁₄ to C₂₂, and especially C₁₈ alkyl chains. The molecular weight (weight average) of the oligomeric amine is suitably greater than 1 ,000, preferably in the range from 1 ,200 to 1 ,800, more preferably 1 ,300 to 1 ,700, particularly 1 ,400 to 1 ,600, and especially 1 ,400 to 1,550.

For this embodiment, the dispersant suitably comprises up to 100%, preferably in the range from 1 to 50%, more preferably 5 to 35%, particularly 11 to 25%, and especially 13 to 20% by weight of oligomeric amines. When the oligomeric amine is present together with trimer fatty triamine and/or dimer fatty diamine and/or monomer fatty monoamine: (i) the amount of trimer fatty triamine is preferably in the range from 5 to 70%, more preferably 10 to 55%, particularly 15 to 45%, and especially 20 to 35% by weight; and/or

(ii) the amount of dimer fatty diamine is preferably in the range from 10 to 95%, more preferably 25 to 90%, particularly 40 to 75%, and especially 50 to 60% by weight; and/or

(iii) the amount of monomer fatty monoamine is preferably in the range from 0 to 10%, more preferably 1 to 7% and particularly 1 to 5% by weight.

All of the above % by weight values are based on the total weight of oligomer, trimer, dimer and monoamine present in the dispersant.

The solid to be dispersed is any material which it is desired to stabilise, preferably in a finely divided state, in an organic solvent. Preferably the solid to be dispersed is an inorganic solid or a metal.

In one embodiment for barrier ribs and dielectric layers in PDP, the solid to be dispersed comprises a mixture of glass powders and/or ceramic powders. The ratio of glass powder to ceramic powder is preferably 25 to 90 weight % glass to 75 to 10% ceramic.

Examples of glass powder include metal oxides and non metallic oxides; for example lead oxide, barium oxide, zinc oxide, boron oxide, silicon dioxide, aluminium oxide, sodium oxide, phosphorus oxide, strontium oxide, lithium oxide and calcium oxide. In one example the glass powder is a mixture of lead oxide, boron oxide and silicon dioxide where an especially preferred rib paste or dielectric layer contains a mixture of 30 to 55 weight % lead oxide, 0.5 to 10% boron oxide and 5 to 25% silicon dioxide as the glass powder component. In a second example the glass powder excludes the presence of lead oxide. Such a mixture can be, for example, a mixture of barium oxide, zinc oxide, boron oxide and silicon dioxide or a mixture of phosphorus oxide, zinc oxide and an alkaline metal oxide.

Examples of ceramic powder include metal oxides and non metallic oxides; for example silicon dioxide, aluminium oxide, titanium dioxide, zirconium oxide, chromium oxide, copper oxide, manganese oxide and zinc oxide. Preferably, the ceramic powder is a mixture of aluminium oxide, titanium dioxide, zirconium oxide, chromium oxide, copper oxide and manganese oxide. An especially preferred rib paste or dielectric layer contains a mixture of 5 to 25% aluminium oxide, 0.5 to 10% titanium dioxide, 0.5 to 10% chromium oxide, 0.5 to 10% copper oxide and 0.5 to 10% manganese oxide as the ceramic powder component.

The glass powder and/or ceramic powder each preferably has a particle size of less than 20 μm, especially 0.1 to 5 μm.

In another embodiment for dispersion of phosphors in PDP, the solid to be dispersed comprises an inorganic oxide. The inorganic oxide is activated by a metal. Examples include oxides of yttrium activated by europium (for example Y₂O₃:Eu), oxides of yttrium and boron activated by europium (for example YBO₃:Eu), oxides of zinc and silicon activated by manganese (for example Zn₂SiO₄:Mn), oxides of barium and aluminium activated by manganese (for example BaO. 6 AI₂O₃:Mn), oxides of barium, magnesium and aluminium activated by europium (for example BaMg₂Ah₆O₂₇: Eu). Other chemical elements that can be part of an inorganic oxide include vanadium and strontium. The solid to be dispersed preferably has a particle size of less than 10μm, especially less than 5μm.

In another embodiment for dispersion of a dielectric material in MLCC, the solid to be dispersed comprises a metal oxide and/or an inorganic metal derivative containing oxygen. Examples include glass, barium titanate, lead zirconate, bismuth stannate, titanium dioxide, lead-magnesium niobate, lead oxide, potassium carbonate, magnesium carbonate, lithium carbonate, strontium nitrate, barium-strontium-titanate, bismuth oxide, aluminium oxide and mixtures thereof. A particularly preferred dielectric material is ceramic, preferably barium titanate, especially doped barium titanate. Compounds suitable for doping of the barium titanate include barium carbonate, dysprosium oxide, magnesium oxide, manganese oxide, vanadium oxide, silicon oxide, aluminium oxide and mixtures thereof. The dielectric material to be dispersed preferably has a particle size of less than 300 nm, more preferably less than 200 nm, particularly less than 100 nm and especially less than 75 nm.

In another embodiment for dispersion of a conductive solid in MLCC, the solid to be dispersed is preferably a solid with a particle size of not more than 3 μm, particularly not more than 1 μm. Examples include copper, silver, gold, palladium, platinum, ruthenium, rhodium, osmium, iridium and nickel and alloys and mixtures thereof. Preferred metals are nickel and silver. In another embodiment, the solid to be dispersed is a pigment, preferably an inorganic pigment. Examples of inorganic pigment are titanium dioxide, zinc oxide, Prussian blue, cadmium sulphide, iron oxides, vermillion, ultramarine and the chrome pigments, including chromates, molybdates and mixed chromates and sulphates of lead, zinc, barium, calcium, and mixtures and modifications thereof which are commercially available as greenish-yellow to red pigments under the names primrose, lemon, middle, orange, scarlet and red chromes. The pigment preferably has a particle size of less than 10 μm, more preferably less than 5 μm.

When the dispersant is used to disperse solids in rib pastes, phosphor pastes, dielectric layers in PDP and dielectric and conductive solids in MLCC, the weight % of dispersant, as a % of the weight of solid to be dispersed, is preferably between 0.01 to 10%, more preferably 0.1 to 7%, particularly 0.5 to 4% and especially 1 to 2.5%.

When the dispersant is used to disperse pigment, the weight % of dispersant, as a % of the weight of pigment, is preferably between 1 to 100%, more preferably 1 to 30%.

The organic solvent may be any organic solvent in which it is desired to disperse the solid and with which the dispersant is compatible and at least partially soluble. It is preferably liquid at normal ambient temperatures.

In embodiments for barrier ribs and dielectric layers in PDP, the organic solvent is preferably present at between 1 to 55 weight % of the total weight of the barrier rib or dielectric layer dispersion.

The organic solvent is preferably at least one of butyl carbitol acetate, α-terpineol, diethylene glycol monobutyl ether acetate, ethyleneglycol monobutyl ether alcohol, 2,2,4-trimethyl-1 ,3-pentanediolmonoisobutyrate, diethylene glycol monobutyl ether, trimethylene glycol mono butyl ether, ethylene glycol mono-2-ethylhexyl ether, di- ethylene glycol mono 2-ethylhexyl ether, 2,2,4-trimethyl-1 , 3-pentanediol diiso butyrate , 2-ethyl-1 ,3-hexanediol , methylethyl ketone , dioxane , acetone , cyclo- hexanone , cyclopentanone , isobutyl alcohol , isopropyl alcohol, toluene, benzyl alcohol, ethyl acetate and tetrahydrofuran. More preferably the organic solvent is at least one of butyl carbitol acetate, α-terpineol and 2,2,4-trimethyl-1 ,3-pentanediol- monoisobutyrate, especially α-terpineol. A particularly preferred rib paste or dielectric layer contains a mixture of 1-15% butyl carbitol acetate, 1-15% α-terpineol and 1-15% 2,2,4-trimethyl-1 ,3- pentanediolmonoisobutyrate.

In embodiments for phosphors, the organic solvent is preferably present at between 40 to 80 weight %, more preferably 60 to 70 weight % of the total weight of the phosphor dispersion.

Examples of organic solvent include decalin, liquid paraffin, octanol, decanol, dodecanol, tetradecanol, terpineol, diethylglycol mono alkyl ethers, butyl carbitol acetate, α-terpineol, diethylene glycol monobutyl ether acetate, ethyleneglycol mono- butyl ether alcohol, 2,2,4-trimethyl-1 ,3-pentanediolmonoisobutyrate, diethylene glycol monobutyl ether, trimethylene glycol mono butyl ether, ethylene glycol mono-2-ethyl- hexyl ether, diethylene glycol mono-2-ethylhexyl ether, 2,2,4-trimethyl-1 ,3-pentanediol diiso butyrate, 2-ethyl-1 ,3-hexanediol, methylethyl ketone, dioxane, acetone, cyclohexanone, cyclopentanone, isobutyl alcohol, isopropyl alcohol, toluene, benzyl alcohol, ethyl acetate and tetrahydrofuran. The organic solvent is preferably at least one of decalin, liquid paraffin, octanol, decanol, dodecanol, tetradecanol, terpineol and diethylglycol mono alkyl ethers. More preferably the organic solvent is a mixture of decalin and liquid paraffin.

In embodiments for dispersion of either a dielectric material or a conducting solid in a MLCC, the organic solvent is preferably present at between 20 to 70 weight % of the total weight of the dielectric material or conductive solid dispersion.

Examples of organic solvent include decalin, liquid paraffin, octanol, decanol, dodecanol, tetradecanol, terpineol, diethylglycol mono alkyl ethers, butyl carbitol acetate, α-terpineol, diethylene glycol monobutyl ether acetate, ethyleneglycol monobutyl ether alcohol, 2,2,4-trimethyl-1 ,3-pentanediolmonoisobutyrate, diethylene glycol monobutyl ether, trimethylene glycol mono butyl ether, ethyleneglycol mono-2- ethylhexyl ether, diethylene glycol mono-2-ethylhexyl ether, 2,2,4-trimethyl-1 ,3- pentanediol diiso butyrate , 2-ethyl-1 ,3-hexanediol, methylethyl ketone, dioxane, acetone, cyclohexanone, cyclopentanone, isobutyl alcohol, isopropyl alcohol, toluene, benzyl alcohol, ethyl acetate and tetrahydrofuran. The organic solvent is preferably at least one of decalin, liquid paraffin, octanol, decanol, dodecanol, tetradecanol, terpineol and diethylglycol mono alkyl ethers. More preferably the organic solvent is a mixture of decalin and liquid paraffin. In embodiments for dispersion of a pigment, the organic solvent is preferably present at between 5 to 55% based on the total weight of the dispersion. The organic solvent is preferably at least one of hydrocarbons and chlorinated hydrocarbons such as aliphatic petroleum fractions, chloroform, carbon tetrachloride, perchloroethylene, benzene, toluene, xylene and chlorobenzene, alcohols such as n-butanol, ethers such as dialkyl ethers and tetrahydrofuran, ketones such as methyl-ethyl-ketone, methyl-i-butyl ketone and cyclohexanone and esters such as butylo acetate and 2- ethoxyacetate.

Other ingredients may be present in the dispersion, for example plasticisers and/or binders.

In embodiments for barrier ribs and dielectric layers in PDP, examples of binders include at least one of ethylcellulose, methylcellulose, hydroxy cellulose, methyl hydroxy cellulose, poly butyl methacrylate, poly vinyl butyral, poly methyl methacrylate, poly ethyl methacrylate, poly vinyl acetate, poly vinyl alcohol, polyethylene, silicon polymer such as poly methyl siloxane, poly methylphenyl siloxane, polystyrene, butadiene/styrene copolymer, poly vinyl pyrrolidone, polyamide, high molecular weight polyether, ethylene oxide and copolymer polyacrylamide and various acrylic polymers of propylene oxide. Ethylcellulose is a preferably preferred binder. The binder is preferably present at between 0.1 to 30%, more preferably 0.5 to 15% based on the total weight of the dispersion.

In this embodiment, examples of plasticisers include at least one of butyl benzyl phthalate, dioctyl phthalate, di-isooctyl phthalate, dicapryl phthalate and dibutyl phthalate. The plasticiser is preferably present at between 0 to 10% based on the total weight of the dispersion.

In embodiments for phosphors, examples of binders include at least one of ethylcellulose, methylcellulose, hydroxy cellulose, methyl hydroxy cellulose, poly butyl methacrylate, poly vinyl butyral, poly methyl methacrylate, poly ethyl methacrylate, poly vinyl acetate, poly vinyl alcohol, polyethylene, silicon polymer such as poly methyl siloxane, poly methylphenyl siloxane, polystyrene, butadiene/styrene copolymer, poly vinyl pyrrolidone, polyamide, high molecular weight polyether, ethylene oxide and copolymer polyacrylamide and various acrylic polymers of propylene oxide. Ethylcellulose is a preferably preferred binder. The binder is preferably present at between 0.05 to 15%, more preferably 0.1 to 10%, especially 0.5 to 5% based on the total weight of the dispersion.

In embodiments for dispersion of either a dielectric material or a conductive solid for use in MLCC, an example of a binder include polyvinyl butyral binder. In this embodiment, examples of a plasticiser includes diesters and polyesters of phthalic acid, for example dioctyl phthalate and diisodecyl phthalate, diesters and polyesters of adipic acid, for example dioctyl adipate, diesters and polyesters of azeleic acid, for example dioctyl azelate, and trimellitate. Preferably the plasticiser is present at between 0.1 to 10%, more preferably 1 to 5% based on the total weight of the dispersion.

In embodiments for dispersion of a pigment, an example of a plasticiser include substituted ammonium salts of coloured acids as disclosed in US 4507436 and disazo compounds as disclosed in US 4461647.

In all embodiments, it is important that the dispersion is uniform and stable over time. For use in barrier ribs for PDP, dispersibility of the rib paste must be effective and uniform. Typically, when using a paste, filtration is carried out to remove dust and other foreign matter. If the paste has low dispersibility, the filter can be blocked, not only with the foreign matter but also with aggregates from the paste. This means an increase in filter replacements and hence reduction of production efficiency.

If a screen printing method for manufacture of ribs is used, a low paste dispersibility can lead to the screen being blocked and if a direct coating method is used there may be nozzle hole blockage. An inhomogeneous dispersion could lead to cracking of the ribs and hence loss of screen resolution for the PDP.

For use in dielectric layers for PDP, if the thickness of the dielectric layer is not uniform and the surface smoothness insufficient the insulating property of the dielectric layer can decline. For use in dispersing dielectric solids in MLCC, the thickness of the dielectric material has been reduced to about 2 μm, with the potential for layers of about 1 μm under investigation. Therefore, this exacerbates the problem of selecting suitable dispersants for use in MLCC pastes to obtain a uniform dispersion which is stable over time. An inhomogeneous dispersed layer in MLCC could lead to reduction of the breakdown voltage. Preferably the dispersion is stable for up to six months, more preferably between a month and six months, even more preferably two weeks and especially one week.

In dispersion of a dielectric solid for use in MLCC and dispersion of phosphors in PDP, it is important that the viscosity of the dispersion is low for ease of use in the manufacture of the dielectric solid. For example a typical process for formation of the dielectric solid involves mixing together of the glass and ceramic powder in the organic solvent with addition of dispersant, binder and plasticiser to form a slurry. The slurry is passed through a homogenising unit and then poured into a hopper and spread over a doctor blade bed in a layer. The dispersion requires a low viscosity so that it can be poured into the hopper easily and will readily flow through the hopper and spread over the doctor blade bed in a uniform layer. It is also important, for the manufacturing process, that there is a low degree of change in the viscosity over time. If the viscosity gradually thickens over time the flow properties of the slurry will change necessitating changes in the settings of the doctor blade machine to accommodate the reduction in flow of the slurry. Therefore, the dispersion preferably has an initial viscosity of less than 400 Cp, preferably less than 350 Cp, more preferably less than 300 Cp.

The invention includes methods of making plasma display panels and multi-layer ceramic capacitors using dispersions according to the invention.

More particularly, the invention includes a method of making a plasma display panel which comprises forming at least one dielectric layer and/or at least one barrier rib from at least one dispersion as herein defined, said at least one dispersion comprising at least one dielectric powder component.

The invention also includes a method of making a plasma display panel which comprises depositing at least one dispersion as herein defined in interstices between barrier ribs, said dispersion comprising a phosphor powder.

The invention includes a method of making a multi-layer ceramic capacitor which comprises forming at least two dielectric layers separated by a conducting layer by alternatively depositing at least one dispersion containing dielectric powder and at least one dispersion containing conducting powder, said dispersions being as hereinbefore defined.

The invention is illustrated by the following non-limiting examples Examples

Example 1

To mimic the dispersion of a dielectric solid for use in a MLCC, 0.208g various dispersants were mixed with an organic solvent containing 6.19g of liquid paraffin and 9.52g of decalin. 10.338g of 100 nm particle size barium titanate (BT-01 available ex Sakai Chemical) solid was added to this mixture at room temperature. The dispersant was present at a level of 2% by weight with respect to the barium titanate solid. 7ml of glass beads (2mm diameter) were added and the mixture milled for 50 minutes by high energy mixing using a Red Devil mixer at temperatures up to 40⁰C. The mixture was then sieved to remove the glass beads and the viscosity measured using a Brookfield Viscometer. Further viscosity measurements were taken over a seven day period. The results are illustrated in Table 1.

Example 2

The stability of the dispersions prepared in Example 1 was visually monitored over a one week period. The results are illustrated in Table 2.

Use of the dispersant according to the invention provides a uniform dispersion of low viscosity which maintains its viscosity over a time period of seven days. The dispersion is stable by visual analysis for a seven day period. Comparative products LP4 and LP6 have much higher viscosities which are not desirable, although the dispersion is seen to be stable by visual analysis over a seven day period. LP1 has a low viscosity but the supernatant is cloudy when monitored visually over a seven day period.

Example 3

To mimic the dispersion of barrier rib paste for use in a PDP, in a 30ml vial 0.3g dispersant (1% by weight of solid) was firstly dissolved in an organic solvent (12g,

40%). Silicon dioxide (4.5g, 15%, Min-U-Sil 10 ex US-Silica), aluminium oxide (4.5g,

15% ex Aldrich) and lead oxide (9g, 30% ex Aldrich) were then added with shaking after each addition. 7ml of glass beads (2mm diameter) were added and the mixture milled for 50 minutes by high energy mixing using a Red Devil mixer at temperatures up to 40⁰C. The mixture was then sieved to remove the glass beads and the dispersion monitored visually .Further visual measurements were taken over seven day period. The results are illustrated in Table 3. Use of the dispersant according to the invention provides a dispersion which is stable over a seven day period as compared to the comparative dispersant and no dispersant.

Table 1

Trimer fatty triamine dispersant of the invention contains 2% monomer fatty monoamine, 53% dimer fatty diamine, 27% trimer fatty triamine and 18% oligomer as measured by gas chromatographic analysis.

Hypermer™ LP6, Hypermer™ LP4 and Hypermer™ LP1 are all polymeric dispersants available from Uniqema Ltd, which contain carboxyl functionality.

Table 2

In the Table 2, 3/40mm means 3mm in a vial of 40mm in height etc.

Table 3

BCA is butyl carbitol acetate available ex Dow

Terpineol is α -terpineol available ex Univar

Flowlen G-700 is a polycarboxylic acid polymeric compound ex Kyoeisha which is disclosed in JP2004002164 A.

Claims

1. Use of at least one trimer fatty triamine and/or higher oligomeric amine dispersant to aid dispersion of a solid in an organic solvent with which the dispersant is compatible.

2. Use of an amine dispersant according to claim 1 wherein said amine dispersant consists essentially of trimer fatty triamine.

3. Use of an amine dispersant according to claim 1 wherein said amine dispersant consists essentially of oligomeric fatty triamine.

4. Use of an amine dispersant according to claim 1 wherein said amine dispersant comprises at least one trimer fatty triamine, at least one dimer fatty diamine and, optionally, at least one mono fatty diamine.

5. Use of an amine dispersant according to claim 4 wherein said amine dispersant has a trimer fatty triamine content of greater than 5% and more preferably has a trimer fatty triamine content in the range from 10 to 90%, more particularly in the range 30 to 70%, and especially in the range 40 to 50% by weight based on the total weight of trimer, dimer and monomer present in said amine dispersant.

6. Use of an amine dispersant according to claim 4 or claim 5 wherein said amine dispersant has a dimer fatty diamine content of less than 95% and more preferably has a dimer fatty diamine content in the range from 10 to 90%, more particularly 30 to 70%, and especially 50 to 60% by weight based on the total weight of trimer, dimer and monomer present in said amine dispersant.

7. Use of an amine dispersant according to any one of claims 4 to 6 wherein said amine dispersant has a mono fatty monoamine content of less than 10% and more preferably has a mono fatty monoamine content in the range from 1 to 6%, more particularly 2 to 4%, and especially 2.5 to 3.5% by weight based on the total weight of trimer, dimer and monomer present in said amine dispersant.

8. Use of an amine dispersant according to any one of the preceding claims wherein said at least one trimer fatty triamine, and when present, said at least one oligomeric amine, and when present said at least one dimer fatty diamine and said at least one mono fatty monoamine, comprise respectively, trimers, dimers and monomers of C₁₀ to C₃₀, more preferably of C₁₂ to C₂₄, particularly of Cu to C₂₂, and especially of Ciβ alkyl chains.

9. Use of an amine dispersant according to any one of the preceding claims wherein said at least one trimer fatty triamine, and when present, said at least one oligomeric amine, and when present, said at least one dimer fatty diamine, are derived, respectively, from the trimerisation and dimerisation products of oleic acid, linoleic acid, linolenic acid, palmitoleic acid and elaidic acid, and particularly of oleic acid and, when present, said at least one mono fatty monoamine is also derived from said acids.

10. Use of an amine dispersant according to any one of the preceding claims wherein said at least one trimer fatty triamine, and when present, said at least one oligomeric amine, and when present, said at least one dimer fatty diamine, are derived, respectively, from the trimerisation, oligomerisation and dimerisation products of unsaturated fatty acid mixtures obtained in the hydrolysis of natural fats and oils and, when present, said at least one mono fatty monoamine is also derived from said acids.

11. Use of an amine dispersant according to claim 1 wherein said amine dispersant comprises in the range from 1 to 50%, more preferably in the range from 5 to 35%, more particularly in the range from 11 to 25%, and especially in the range from 13 to 20% by weight of oligomeric amines.

12. Use of an amine dispersant according to claim 1 or claim 11 wherein said amine dispersant comprises at least one oligomeric amine and at least one other amine selected from the group consisting of trimer fatty triamine, dimer fatty diamine and monomer fatty monoamine and mixtures thereof.

13. Use of an amine dispersant according to claim 12 wherein, when present:

(i) the amount of trimer fatty triamine is in the range from 5 to 70%, more preferably in the range from 10 to 55%, more particularly in the range from 15 to 45%, and especially in the range from 20 to 35% by weight; and

(ii) the amount of dimer fatty diamine is in the range from 10 to 95%, more preferably in the range from 25 to 90%, more particularly in the range from 40 to 75%, and especially in the range from 50 to 60% by weight; and

(iii) the amount of monomer fatty monoamine is in the range from 0 to 10%, more preferably in the range from 1 to 7% and more particularly in the range from 1 to 5% by weight;

based on the total weight of oligomer, trimer, dimer and monomer present in said amine dispersant.

14. A dispersion of a solid in an organic solvent which includes as a dispersant at least one trimer fatty triamine and/or higher oligomeric amine.

15. The dispersion according to claim 14 wherein said amine dispersant consists essentially of trimer fatty triamine.

16. The dispersion according to claim 14 wherein said amine dispersant consists essentially of oligomeric fatty triamine.

17. The dispersion according to claim 14 wherein said amine dispersant comprises at least one trimer fatty triamine, at least one dimer fatty diamine and, optionally, at least one mono fatty diamine.

18. The dispersion according to claim 17 wherein said amine dispersant has a trimer fatty triamine content of greater than 5% and more preferably has a trimer fatty triamine content in the range from 10 to 90%, more particularly in the range 30 to 70%, and especially in the range 40 to 50% by weight based on the total weight of trimer, dimer and monomer present in said amine dispersant.

19. The dispersion according to claim 17 or claim 18 wherein said amine dispersant has a dimer fatty diamine content of less than 95% and more preferably has a dimer fatty diamine content in the range from 10 to 90%, more particularly 30 to 70%, and especially 50 to 60% by weight based on the total weight of trimer, dimer and monomer present in said amine dispersant.

20. The dispersion according to any one of claims 17 to 19 wherein said amine dispersant has a mono fatty monoamine content of less than 10% and more preferably has a mono fatty monoamine content in the range from 1 to 6%, more particularly 2 to 4%, and especially 2.5 to 3.5% by weight based on the total weight of trimer, dimer and monomer present in said amine dispersant.

21. The dispersion according to any one of claims 14 to 20 wherein said at least one trimer fatty triamine, and when present, said at least one oligomeric amine, and when present said at least one dimer fatty diamine and said at least one mono fatty monoamine, comprise respectively, trimers, dimers and monomers of C₁₀ to C₃₀, more preferably of C₁₂ to C₂₄, particularly of C₁₄ to C₂₂, and especially of Ci₈ alkyl chains.

22. The dispersion according to any one of claims 14 to 21 wherein said at least one trimer fatty triamine, and when present, said at least one oligomeric amine, and when present, said at least one dimer fatty diamine, are derived, respectively, from the trimerisation and dimerisation products of oleic acid, linoleic acid, linolenic acid, palmitoleic acid and elaidic acid, and particularly of oleic acid and, when present, said at least one mono fatty monoamine is also derived from said acids.

23. The dispersion according to any one of claims 14 to 22 wherein said at least one trimer fatty triamine, and when present, said at least one oligomeric amine, and when present, said at least one dimer fatty diamine, are derived, respectively, from the trimerisation, oligomerisation and dimerisation products of unsaturated fatty acid mixtures obtained in the hydrolysis of natural fats and oils and, when present, said at least one mono fatty monoamine is also derived from said acids.

24. The dispersion according to claim 14 wherein said amine dispersant comprises in the range from 1 to 50%, more preferably in the range from 5 to 35%, more particularly in the range from 11 to 25%, and especially in the range from 13 to

20% by weight of oligomeric amines.

25. The dispersion according to claim 14 or claim 24 wherein said amine dispersant comprises at least one oligomeric amine and at least one other amine selected from the group consisting of trimer fatty triamine, dimer fatty diamine and monomer fatty monoamine and mixtures thereof.

26. The dispersion according to claim 25 wherein, when present: (iv) the amount of trimer fatty triamine is in the range from 5 to 70%, more preferably in the range from 10 to 55%, more particularly in the range from 15 to 45%, and especially in the range from 20 to 35% by weight; and

(v) the amount of dimer fatty diamine is in the range from 10 to 95%, more preferably in the range from 25 to 90%, more particularly in the range from 40 to 75%, and especially in the range from 50 to 60% by weight; and

(vi) the amount of monomer fatty monoamine is in the range from 0 to 10%, more preferably in the range from 1 to 7% and more particularly in the range from 1 to 5% by weight;

27. The dispersion according to any one of claims 14 to 43 wherein the dispersant is at least partially soluble in the organic solvent which is liquid at normal ambient temperatures.

28. The dispersion according to any one of claims 14 to 27 wherein said solid comprises a powder selected from the group consisting of a finely-divided inorganic solid and a finely-divided metal.

29. The dispersion according to any one of claims 14 to 28 wherein said solid comprises at least one powder selected from the group consisting of glass powders and ceramic powders and mixtures thereof.

30. The dispersion according to claim 29 wherein said solid comprises a mixture of at least one glass powder and at least one ceramic powder and wherein the ratio of glass powder to ceramic powder is 25 to 90 weight % glass to 75 to

10% ceramic powder.

31. The dispersion according to claim 29 or claim 30 wherein said solid comprises at least one lead-containing glass powder.

32. The dispersion according to claim 31 wherein said solid comprises a mixture of 30 to 55 weight % lead oxide, 0.5 to 10% boron oxide and 5 to 25% silicon dioxide as the glass powder component.

33. The dispersion according to claim 29 or claim 30 wherein said solid is essentially free from lead-containing glass powders.

34. The dispersion according to any one of claims 29 to 33 wherein said solid comprises a mixture of by weight 5 to 25% aluminium oxide, 0.5 to 10% titanium dioxide, 0.5 to 10% chromium oxide, 0.5 to 10% copper oxide and 0.5 to 10% manganese oxide as the ceramic powder component.

35. The dispersion according to any one of claims 29 to 34 wherein the powders have a particle size of less than 20 μm, preferably in the range 0.1 to 5 μm.

36. The dispersion according to any one of claims 29 to 35 wherein the organic solvent comprises a mixture of by weight 1-15% butyl carbitol acetate, 1-15% α- terpineol and 1-15% 2,2,4-trimethyl-1 ,3-pentanediolmonoisobutyrate.

37. The dispersion according to any one of claims 14 to 28 wherein said solid comprises at least one powder selected from the group consisting of a metal oxide powder and a powder of inorganic metal derivative containing oxygen and mixtures thereof.

38. The dispersion according to claim 37 wherein the powder has a particle size of less than 300 nm, more preferably less than 200 nm, more particularly less than 100 nm and especially less than 75 nm.

39. The dispersion according to claim 38 wherein the powder has a particle size of of not more than 3 μm, particularly not more than 1μm.

40. The dispersion according to any one of claims 27 to 39 wherein the weight % of dispersant, as a % of the weight of solid to be dispersed, is preferably between

0.01 to 10%, more preferably is 0.1 to 7%, more particularly is 0.5 to 4% and especially is 1 to 2.5%.

41. The dispersion according to any one of claims 27 to 40 wherein the organic solvent of said dispersion is present at between 1 to 55 weight % of the total weight of the dispersion.

42. The dispersion according to any one of claims 27 to 40 wherein the organic solvent of said dispersion is present at between 20 to 70 weight % of the total weight of a dielectric powder dispersion or a conductive powder dispersion.

43. The dispersion according to any one of claims 14 to 28 wherein said solid comprises at least one phosphor powder comprising an inorganic pigment.

44. The dispersion according to claim 43 wherein said at least one phosphor powder comprises at least one metal-activated inorganic oxide powder.

45. The dispersion according to claim 43 or claim 44 wherein the powder has a particle size of less than 10μm, especially less than 5μm.

46. The dispersion according to any one of claims 43 to 45 wherein the weight % of dispersant, as a % of the weight of solid to be dispersed, is preferably between 0.01 to 10%, more preferably is 0.1 to 7%, more particularly is 0.5 to 4% and especially is 1 to 2.5%.

47. The dispersion according to any one of claims 43 to 46 wherein the organic solvent comprises a mixture of decalin and liquid paraffin.

48. The dispersion according to any one of claims 43 to 47 wherein the organic solvent of said dispersion is present at between 40 to 80 weight %, more preferably 60 to 70 weight % of the total weight of the phosphor dispersion.

49. The dispersion according to any one of claims 14 to 28 wherein said solid comprises at least one inorganic pigment powder.

50. The dispersion according to claim 49 wherein the powder has a particle size of less than 10 μm, more preferably less than 5 μm.

51. The dispersion according to claim 49 or claim 50 wherein the weight % of dispersant, as a % of the weight of pigment, is preferably between 1 to 100%, more preferably 1 to 30%.

52. A method of making a plasma display panel comprising forming at least one dielectric layer and/or at least one barrier rib from at least one dispersion as defined in any one of claims 14 to 41 , said at least one dispersion comprising at least one dielectric powder component.

53. A method of making a plasma display panel comprising depositing at least one dispersion as defined in any one of claims 14 to 28 and in any one of claims 43 to 48 in interstices between barrier ribs, said dispersion comprising a phosphor powder.

54. A method of making a multi-layer ceramic capacitor comprises forming at least two dielectric layers separated by a conducting layer by alternatively depositing at least one dispersion containing dielectric powder and at least one dispersion containing conducting powder, said dispersions being as defined in any one of claims 14 to 40 and 42.