COMPOSITION AND USE

Abstract: A toner resin composition comprising a metal salt or complex of an optionally substituted 1-hydroxy-2-pyridinethione and use in electro-reprographic imaging processes. The preferred compound is the 2:1 zinc salt or complex or 3:1 iron salt or complex with 1-hydroxy-2-pyridinethione.

Description: COMPOSTTTON AND TISK The present invention relates to a composition comprising a toner resin and a l-hydroxy-2-pyridinethione or the metal salt or complex thereof and to its use as a negative charge control agent (hereinafter "CCA") in electro-reprographic image processes. US 2,809,971 discloses l-hydroxy-2-pyridinethione (hereinafter "HPT") and metal salts thereof including their use as industrial microbiocides. It has now been found that such salts and complexes are useful as CCA's and certain compounds exhibit very rapid and high tribocharge. According to the invention there is provided a toner composition comprising a toner resin and the metal salt or complex of l-hydroxy-2-pyridinethione of general formula 1: wherein R is C 1-12 -alkyl, C 1-12 -alkoxy or halogen; n is 0 to 4; M is a di- or tri-valent metal cation; and x is 2 or 3 When R is alkyl it can be linear or branched but is preferably linear. It is also preferred that R is C 1-10 -alkyl, more preferably C 1-6 -alkyl and especially C 1-4 -alkyl. When R is alkoxy it is preferably C 1-6 -alkoxy and especially C 1-4 -alkoxy. Halogen includes fluorine, bromine and especially chlorine. Preferably n is zero. The metal cation M is preferably one from group 2a, 3a, 4a, lb, 2b, 6b, 7b and 8 of the Periodic Table according to Mendeleef as illustrated on the inside rear cover of The Handbook of Chemistry and Physics published by The Chemical Rubber Co., Ohio, USA. The especially preferred metal cations include Mg, Ca, Ba, Cr, Mn, Fe, Co, Ni, Cu, Zn and Al. Metal salts or complexes derived from Mg(II), Ca(II), Ba(II), Zn(II) and Al(III) have the specific advantage that they are substantially colourless and such compounds may be used as CCA's for making coloured images whereas compounds derived from Cr(III) and Fe(III) tend to be strongly coloured and hence such CCA's are mainly of use for forming black images The metal salts or complexes of formula 1 are readily prepared by dissolving the l-hydroxy-2-pyridinethione in aqueous alkali and adding the appropriate metal in the form of a water-soluble salt. Preferred salts are chlorides, nitrates and sulphates. The molar ratio of the pyridinethione to metal salt is dependent on whether a 2:1 or 3:1 salt or complex of the metal is required. The reaction is very facile and the metal salt or complex generally separates from the aqueous alkaline media and is isolated by, for example, filtration. The metal salt or complex is preferably formed at temperatures below 100°C, more preferably below 70°C and especially below 40°C. Preferably the temperature is above 10°C and especially above 20°C. Suitable l-hydroxy-2-pyridinethiones from which the metal salt or complex is made include inter alia l-hydroxy-2-pyridinethione (HPT); 3-, 4-, 5- or 6-methyl, ethyl, butyl, methoxy or ethoxy HPT; 3-,5-bromo or chloro HPT; 4,6-, 3,6- or 5,6-dimethyl or diethyl HPT; 3-,4-, 5- or 6-ethyl-6-, 3-, 4- or 5-methyl HPT; 4,5-, 3,6- or 5,6- dimethoxy HPT; 3,5-dibromo or dichloro HPT, 4,5,6-trimethyl HPT and 2,4,5,6-tetramethyl HPT. The metal salt or complex may be derived from one or a mixture of HPT's and may contain more than one metal. Preferably the salt or complex contains the one metal and is derived from one HPT. The preparation of certain of the alkyl substituted HPT's are described in US 2,809,971. The toner resin is a thermoplastic resin suitable for use in the preparation of toner compositions. A preferred toner resin is a styrene or substituted styrene polymer or copolymer such as polystyrene or styrene-butadiene copolymer. It is especially preferred that the toner resin is a styrene- acrylic copolymer such as a styrene-butyl methacrylate copolymer. Other suitable toner resins are polyesters, especially alkoxylated bis-phenol based polyester resins such as those described in US 5,143,809, polyvinyl acetate, polyalkenes, poly(vinyl chloride), polyurethanes, polyamides, silicones, epoxy resins and phenolic resins. Further examples of these and other resins are given in the book "Electrophotography" by R.M. Shafert (Focal Press); UK 2,090,008, US 4,206,064 and US 4,407,924. The toner resin composition may contain more than one HPT. The HPT is present in the composition from 0.1 to 12%, preferably from 0.5 to 10% and especially from 1 to 3% by weight of the total composition. The toner resin composition may also contain a dyestuff or pigment as colourant. Thus, according to a further aspect of the invention there is provided a toner resin composition as hereinbefore defined which further comprises a colourant. The colourant is preferably a pigment such as carbon black, metallised phthalo-cyanine, quinacridone, perylene, benzidine, nigrosine, aniline, guinoline, anthraquinone, azo disperse dye, benzodifuranone, metallised lake or pigment toner or water insoluble salt of a basic dye. The colourant may also be a water soluble basic dye, especially a triphenylmethane dyestuff. The toner composition may contain up to 20% colourant and especially from 3 to 10% relative to the total weight of the toner resin composition. The toner resin composition may be prepared by any method known to the art which typically involves mixing the toner resin with the HPT and optionally the colourant by kneading in a ball mill above the melting point of the resin. Generally, this involves mixing the molten composition for several hours at temperatures from 120 to 200°C, in order to uniformly distribute the HPT and colourant (if present) throughout the toner resin. The toner resin is then cooled, crushed and micronised until the mean diameter of the particles is preferably below 20μ and, for high resolution electro-reprography, more preferably from 1 to lOμ. The powdered colour toner or toner-resin so obtained may be used directly or may be diluted with an inert solid diluent such as fine silica by mixing for example in a suitable blending machine. The toner resin composition may be mixed with a carrier to form a developer composition. Thus, according to a still further aspect of the invention there is provided a developer composition comprising a toner resin composition and a carrier. Preferred carriers are those which are capable of assuming a tribo-electrically opposite polarity to the toner resin composition itself. The carrier particles are those that render the toner resin negatively charged whilst acquiring a positive charge polarity themselves via frictional charging against the toner resin particles. Examples of suitable carriers are iron powder, steel, nickel, iron and ferrites such as zinc ferrites and nickel zinc ferrites. The carrier may optionally be coated with a polymer especially one derived from styrene, methylmethacrylate and silane. Preferably the silane is triethoxysilane. The coating on the carrier may also include a conductive material such as carbon black. The coating is preferably from 0.1 to 3% by weight based on the carrier and the conductive material is preferably present in an amount from 5 to 30% by weight of the coating. As noted hereinbefore the metal salts or complexes of the HPT can be used as a CCA. Thus, according to a further aspect of the invention there is provided the use of a metal salt or complex of a HPT as a CCA. Particularly useful effects have been obtained where the CCA is the 2:1 zinc salt or complex or 3:1 iron salt or complex of HPT itself. The invention is further illustrated by the following examples wherein all references are to parts by weight unless indicated to the contrary. Example 1 Preparation of the 2:1 zinc salt or complex of HPT A solution of zinc chloride (6.82 parts; 0.05M in 20mls water) was added to a stirred aqueous solution of the sodium salt of l-hydroxy-2-pyridinethione (37.25mls at 40% strength; 0.1M; ex FLUKA) and water (150mls) over 30 minutes at 20 to 25°C. A white precipitate formed immediately and was filtered, washed with water and dried. Yield = 13.92 parts (88% theory) . This is CCA 1. Elemental Analysis Found 37.6%C,2.5%H,8.8%N,20.1%S,19.0%Zn C 10 H 8 N 2 0 2 S 2 Zn Requires 37.85°C,2.52%H,8.83%N,20.19%S,20.5%Zn Example 2 Preparation of the 3:1 iron salt or complex of HPT This was prepared by the method described in Example 1 except that the aqueous solution of zinc chloride was replaced by a solution of ferric chloride hexahydrate (8.92 parts; 0.033M) in water (30 parts) . On addition of the ferric chloride solution to the solution of sodium HPT the ferric salt or complex separated immediately as a blue-black solid (13.8 parts; 96.5% theory). This CCA 2. Elemental Analysis Found 41.5%C,2.6%H,9.6%N,22.3%S and 12.86%Fe C 15 H 12 N 3 θ 3 S 3 Fe Requires 41.5%C,2,7%H,9.68%N,22.13%S and 12.86%Fe Example 3 Preparation of a toner resin composition A styrene/acrylic resin (300 parts; Amacryl B-1500 ex Image Polymers, Europe) and CCA (7.5 parts) were melt kneaded together at 160 to 180°C for 60 minutes in a Z-blade mixer. After cooling to 20 to 25°C, the resultant resin toner composition was crushed and finely ground in a ball-mill until the mean particle size of the toner was between 6 and 30/,. Example 4 Evaluation as a CCA The finely ground toner resin composition whose preparation is described in Example 3 (0.4 parts) and uncoated iron powder (19.6 parts; RAV-270; ex Powdertech Corp., Valparaiso, Indiana, USA) were mixed together in an aluminium tin on a roller mill for 20 minutes. The tribo-charge was then measured after 5, 10 and 20 minutes using a Toshiba TB200 Blow-off apparatus. The results are given in Table 1. below Table 1 Tribo-charge (μCg-1) after time (mins) CCA 5 10 20 30 CCA1 -24.4 -29.86 -37.06 CCA2 - -31.15 - -41

Claims: £MM≥ 1. A toner resin composition comprising a toner resin and a metal salt or complex of l-hydroxy-2-pyridinethione of formula 1: wherein: R is C 1-12 -alkyl, C 1-12 -alkoxy or halogen; n is 0 to 4; M is a di- or trivalent metal cation; and x is 2 or 3. 2. A toner resin composition as claimed in Claim 1 wherein n is zero. 3. A toner resin composition as claimed in either Claim 1 or Claim 2 which contains the 2:1 zinc salt or complex with l-hydroxy-2- pyridinethione. 4. A toner resin composition as claimed in either Claim 1 or Claim 2 which contains the 3:1 ferric salt or complex with l-hydroxy-2- pyridinethione. 5. A toner resin composition as claimed in any one of Claims 1 to 4 wherein the resin is a styrene-acrylic copolymer. 6. A toner resin composition as claimed in any one of Claims 1 to 5 which further comprises a colorant. 7. A developer composition comprising a carrier and a toner resin composition as claimed in any one of Claims 1 to 6. 8. The use of a metal salt or complex of l-hydroxy-2- pyridinethione of formula 1 as a charge control agent wherein: R is C 1-12 -alkyl, C 1-12 -alkoxy or halogen; n is 0 to 4 ; M is a di- or trivalent metal cation; and x is 2 or 3.

Inventors: CAMPBELL JAMES STANLEY, FAWKES DAVID MELVILLE, GREGORY PETER, CAMPBELL, JAMES, STANLEY, FAWKES, DAVID, MELVILLE, GREGORY, PETER
Applicants: CAMPBELL JAMES STANLEY, FAWKES DAVID MELVILLE, GREGORY PETER, ZENECA LTD, CAMPBELL, JAMES, STANLEY, FAWKES, DAVID, MELVILLE, GREGORY, PETER, ZENECA LIMITED
Application year: 1995
Main classification: G03G9
IPC codes: G03G9