Ink composition for a meltable ink

Abstract: An ink composition for a meltable ink, usable in printing devices in which ink droplets are ejected from ducts, which composition contains a meltable base material, wherein the ink composition also contains an amorphously setting monomer compound and an amorphous polymer or oligomer binder and the base material is a crystalline-setting monomer compound. The flow and setting properties and the stiffness of the ink is adjusted by the choice and relative proportion of the constituents.

Description: This invention relates to an ink composition for a meltable ink, usable in printing devices in which ink droplets are ejected from ducts, which composition contains a meltable base material. The base materials may be synthetic and natural waxes, alcohols, carboxylic acid and sulphonic acid amides and the like. Suitable materials are indicated, for example, in US 5 122 187. The prior art ink compositions in the set state generally yield on receiving materials printed ink layers which are too brittle or just too soft, with the result that the gum, scratch and fold resistance, particularly of double layers, i.e. different ink layers of, for example, different colours on one another, is not up to standard. To toughen ink formulations which are too brittle, or make too soft crystalline materials stiffer, the addition of an amorphous binder is necessary, with or without the combination of a monomer plasticiser. However, as a result of the considerable viscosity increase in the melted state, caused by such an addition, only a low concentration (up to about 20% by weight) of amorphous polymer or oligomer binder can be used. The viscosity increase in the melted state is undesirable because the resulting inks generally penetrate unsatisfactorily into the receiving material (e.g. paper), with the result that thick layers form on the receiving material which are mechanically vulnerable. With a viscosity increase the ink is also no longer reliably sprayed, certainly if spray heads having nozzle diameters below 45 µm are used. In the case of a low concentration of amorphous polymer, inadequate stiffness and/or excessive brittleness of the ink compositions in the set state occurs. There is therefore a dilemma with the existing ink compositions: the required stiffness in the set state versus a desirable relatively low viscosity at the working temperature. It has also been found in practice that ink formulations in which two or more materials are present are frequently unstable over time, even if the ink has already been sprayed on a receiving material. Thus with mixtures of crystalline and amorphous materials there is frequently a disturbing after-crystallisation, as a result of which colour changes may occur and prints may become opaque, this being an obstacle, for example, if these ink compositions are used on an overhead sheet. What is required, therefore, is an ink composition in which a considerable quantity of amorphous binder can be dissolved so that the stiffness after the setting of the ink composition is increased while the viscosity of the resulting ink composition has a value at 120 - 130°C such that the ink compositions can be used in printing devices having a nozzle with a diameter of less than 45 µm. In addition, the ink composition must have a good jet stability and gum, scratch and fold resistance and not exhibit any disturbing after-crystallisation. The ink composition according to the present invention as indicated in the preamble is characterised in that the ink composition also contains an amorphously setting monomer compound and an amorphous polymer or oligomer binder and the base material is a crystalline-setting monomer compound. According to the present invention, it is now possible, by the combination of these three constituents, to adjust the flow and setting characteristics by optimal choice of the relative proportions of the above-mentioned constituents. The amorphously setting monomer compound preferably has a glass transition temperature (Tg) of 10 - 50°C, a viscosity less than 100 mPa.s at 150°C and has a molecular weight lower than 1000 g/mol. If an amorphously setting monomer compound having a Tg value higher than 50°C is used in the ink composition, the resulting ink is too brittle and too highly viscous. A Tg value lower than 10°C leads to an ink composition which at ambient temperature has a setting characteristic such that, for example, paper printed with such an ink sticks together. A viscosity higher than 100 mPa.s at 150°C results in an unsatisfactory spray behaviour in the printing devices. If the molecular weight is more than 1000 g/mol, the viscosity will be outside the said range and the ink will be hardly processable, if at all. Amorphously setting monomer compounds are, for example, compounds which have the property that they set mainly amorphously even at cooling rates of about 50°C/min, which are relatively low in comparison with the cooling rate of ink droplets on a receiving material. By the combination of the three constituents it is possible to increase drastically to 40% by weight the amorphous fraction (amorphously setting monomer and amorphous polymer or oligomer binder) in the ink composition while the low viscosity is retained. Even a 75% amorphous fraction is possible if the lowest viscous monomer compounds are used having a viscosity of less than 50 mPa.s at 150°C. The amorphously setting monomer compound is preferably a compound selected from the group of bis-urethanes, esters of pentaerythritol and dipentaerythritol, carbonates of dipentaerythritol, reaction products of epoxides and alcohols, bis-amides, bis-sulphonamides, or mixtures of these compounds. Bis-urethanes preferably used are the reaction product of isophorone diisocyanate with methyl alcohol or the reaction product of 4,4' dicyclohexyl methane diisocyanate with benzyl alcohol. The esters of pentaerythritol and dipentaerythritol are preferably the benzoate, toluate and anisilate esters. The carbonates of dipentaerythritol are preferably phenyl carbonates or substituted phenyl carbonates. The reaction products of epoxides and alcohols are preferably reaction products of the diglycidyl ether of bis-phenol A with alkyl or cycloalkyl substituted phenols. It is also possible to select compounds from the group of asymmetrical bis-amides as given in US Patent US-5 421 868 and from the symmetrical bis-amides and bis-sulphonamides. It is possible to use mixtures of the above compounds. Although the above amorphously setting compounds are usable on their own as ink, they are in practice too highly viscous at the working temperature of about 130°C, and this gives rise to problems when small nozzles are used. Also, the printed images are frequently unstable in time. Ultimately crystallisation mostly occurs, so that brittleness increases and transparency decreases. The amorphously setting monomer compound does not simply function as a plasticiser, but as a stiffening binder with a low viscosity, without a drastic Tg reduction of the complete ink composition. If the same Tg reduction of the oligomer or polymer binder is obtained by an effective oily plasticiser, such as, for example, dioctyl phthalate instead of by an amorphously setting monomer compound, the result obtained is not good. In that case the product is more coarsely crystalline, being more opaque and less stiff. The amorphous polymer or oligomer binder has a glass transition temperature (Tg) preferably between 25 and 120°C, a weight-averaged molecular weight of between 1000 and 15000 g/mol, measured on the basis of polystyrene standards, and a viscosity greater than 1000 mPa.s at 150°C. A viscosity lower than 1000 mPa.s gives an insufficiently stiff binder which will generally be too brittle and will tend to crystallise. If the Tg value is less than 25°C, the ink composition obtained is too tacky and at a Tg value of above 120°C the viscosity will be too high. The amorphous polymer or oligomer binder used may be reaction products of hydrogenated rosins with, for example, glycerol and pentaerythritol or the condensation product of acetophenone and formaldehyde such as Kunstharz SK or AP (™ Hüls) are used or cyclohexanone condensation resins such as Kunstharz CA (™ Hüls), copolymers of styrene, acrylate and methacrylate, allyl alcohol, and the like and various (co)polyesters such as Dynacol 7130 and 7150 (™ Hüls) or polyethylene phthalate (Crystalbond 509, ™ Printlas) and mixtures of these compounds. The Tg value of the above-mentioned condensation product Kunstharz SK is 88°C and the weight-averaged molecular weight is about 1350 (measured on the basis of polystyrene standards). In addition to the strongly stiffening effect of the polymer or oligomer material on the ink, it also suppresses any occurrence of crystallisation of the amorphously setting monomer constituent in the course of time. The base material, which is a crystalline-setting monomer, preferably has a melting point lower than 110°C and a viscosity of 1-10 mPa.s at 150°C. Preferably, crystalline base materials are possibly selected from the group of aliphatic alcohols, such as dodecane diol and hexadecane diol, or aromatic compounds such as 1-0-para-anisyl glycerol, meta-toluamide, para-n-butylbenzene sulphonamide and mixtures of these compounds. In the case of predominantly crystalline inks, the ink composition according to the present invention preferably consists of a quantity of crystalline setting monomer compound between 60% by weight and 90% by weight, a quantity of amorphously setting monomer compound between 5% by weight and 20% by weight, and a quantity of amorphous polymer or oligomer binder between 5% by weight and 20% by weight, based on the total ink composition. Crystalline-setting monomers having a difference between the melting temperature and the crystallisation temperature (Tm-Tc) of less than 50°C (DSC, 20°C per minute) are most suitable in these inks. If the quantity of amorphously setting monomer compound used is more than 20% by weight, then the ink composition obtained is generally too soft, certainly if the crystalline material has naturally an ample crystallisation retardation so that it takes various seconds before the image is solid. If the quantity of amorphously setting monomer used is less than 5% by weight, then the ink composition obtained is not sufficiently stiff. The quantity of amorphous polymer or oligomer binder must be less than 20% by weight since otherwise the viscosity of the ink composition becomes too high. Nevertheless, according to the invention, predominantly amorphous inks can be prepared in which the amorphous fraction (the amorphously setting monomer and the amorphous polymer or oligomer together) constitutes more than 50% by weight. In that case, the crystalline-setting monomer should be a compound which naturaily crystallises rapidly, since otherwise the ink remains oily on the paper for too long. In addition, the viscosity of the amorphous fraction should not be too high. Crystalline-setting monomers with a difference between the melting temperature and the crystallisation temperature (Tm-Tc) of less than 25°C (DSC, 20°C per minute) are excellent for this purpose. The predominantly amorphous ink according to the invention preferably has the following composition: Rapidly setting crystalline monomer (25 - 45% by weight), e.g. 1,12-dodecane diol), amorphously setting monomer (45 - 65% by weight, e.g. pentaerythritol tetrabenzoate) and 5 10% by weight of amorphous polymer or oligomer binder, e.g. Kunstharz SK (™ Hüls). This composition is sufficiently stiff and has a sufficiently low viscosity at the jet temperature. The viscosity of the finally obtained ink composition at 130°C is preferably less than 25 mPa.s. If the viscosity of the finally obtained ink compositions at 130°C is greater than 25 mPa.s, the ink composition cannot be satisfactorily used in printing devices provided with ink ducts of a diameter less than 45 µm, since droplets can no longer be formed satisfactorily. Also, a thick layer forms on the receiving material. The ink then penetrates inadequately into the receiving material. The spreading behaviour and penetration behaviour of the ink accordingly leave much to be desired. The present invention will be explained in detail with reference to the following examples. Table 1 gives a selection of amorphously setting monomer resins. Table 2 is a survey of some amorphous oligomer or polymer materials. Table 3 is a selection of crystalline-setting monomers (base materials). Table 4 is a survey of ink formulations. Table 1 Part A of Table 1 gives compounds of pentaerythritol: I pentaerythritol tetra-acetate, II pentaerythritol tetra-benzoate, III, IV, V respectively the ortho, meta and para-toluate esters, VI is a statistically synthetic mixture of the ortho and para-toluate compounds. VII is the tetra-anisilate compound, VIII is the tetra-carbonate compound. The compounds IX to XV are the similar di-pentaerythritol compounds. These a given in Part B of Table 1. The esters and carbonates respectively of pentaerythritol and dipentaerythritol (Table 1A and 1B) are easily synthesised by reacting the said tetra and hexa hydroxy compounds with benzoylchlorides and phenyl chloroformate respectively, which may or may not be substituted. Part C of Table 1 gives compounds of isophorone diisocyanate with an aliphatic alcohol (e.g. isopropyl alcohol, methyl alcohol, ethyl alcohol) or aromatic alcohol (e.g. benzyl alcohol). The compounds of 4, dicyclohexylmethane diisocyanate with an alcohol (e.g. benzyl alcohol, methyl ethylene glycol and phenyl ethyl alcohol) are given in Part D of Table 1. Part E of this Table gives details of some other bis-urethanes based on diphenyl methane diisocyanate an an alcohol. Part F gives the details of some reaction products of dyglycidyl ether of bis-phen A with respectively phenol (XXVI), cyclohexyl phenol (XXVII) and tert.-amyl phenol (XXVIII). - The Table indicates whether the materials are usable as amorphously setting monomer in the ink according to the invention. Table 2 Table 2 clearly shows that the amorphous oligomer, for optimum functioning, preferably has a weight-averaged molecular weight of above 1000 measured on the basis of polystyrene standards and a viscosity at 150°C of more than 1000 mPa.s. Table 3 Table 3 is a survey of crystalline-setting monomers, including a number of crystalline bis-urethanes (reaction products of hexamethylene diisocyanate and respectively methyl ethylene glycol, ethyl ethylene glycol, hexanol and phenyl ethyl alcohol). In addition there are a number of sulphonamides (respectively para-toluene sulphonamide, a mixture of ortho and para-toluene sulphonamide, para-ethyl benzene sulphonamide and a mixture of para-toluene sulphonamide and para-ethyl benzene sulphonamide and para-n-butyl benzene sulphonamide. Details of some (di)-alcohols and some other compounds are also given. A crystalline-setting monomer compound suitable for use as a base material according to the present invention has a melting point lower than 110°C and forms a finely crystalline material after crystallisation. Table 4 Table 4 gives details of various ink formulations, wherein CM stands for crystalline monomer, ASM stands for amorphously setting monomer and AOP for amorphous oligomer or polymer, Tm and Tc respectively stand for melting and crystallisation temperature (both measured at cooling/heating rates of 20°C/min) and h 130°C stands for the viscosity (mPa.s) measured at 130°C of the total ink formulation. Inks 1, 2, 3, 5, 6, 9, 13, 15, 17-19, 24, 25, 27-30, 36, 37, 40, 44, 45 and 48 are not formulations according to the invention. These inks are either too brittle or insufficiently stiff directly after printing or within a few hours after printing. Although composition 4 has a reasonable flow on the receiving material, the resulting image is not very stiff because of the low viscosity of the AOP (the amorphous oligomer or polymer). The compositions 7, 8, 10-12, 14 and 16 are all inks based on 1,12-dodecane diol as the base material, and they are in accordance with the invention. Although these compositions have little flow on the receiving material the resulting images are sufficiently stiff. The inks 20-23 and 26 based on HMDI-MEG as the base material have a good flow and are stiff as printed images. The inks based on para-n-butyl benzene sulphonamide (inks 31 - 35) also give good results. The other inks according to the invention 38, 39, 41-43, 46 and 47 flow sufficiently well and are stiff. Ink composition 49 has too great a crystallisation retardation for practical use. Of course the conventional additions can be made to the inks, e.g. dyes, colour pigments, pigments, anti-oxidants such as Vanox 1005 (Vanderbilt™) and surfactants. Selection of amorphous oligomer/polymer (AOP) No. Name (trade name) (Abbreviation) Chemical description TG (°C) Mw (g/mol) η 150°C (mPa.s) Assessment A Foral 85E (Hercules™) (F85E) Glycerol ester of hydrogenated rosin 37 1000 250 Little stiffening action B Foralyn 110 (Hercules™) (F110) Pentaerythrito ester of hydrogenated rosin 54 1300 500 Little stiffening action C Uratak 68520 (DSM™) (U68520) Phenolic poly-α-methyl styrene 37 880 350 Little stiffening action D Crystalbond 509 (Printlas™) (CB509) Polyethylene phthalate 30 4000 1000 Usable E (Aldrich) (PSAA) Styrene allyl alcohol copolymer 59 1600 3000 Usable F Dynacoll 7130 (Hüls™) (D7130) Copolyester 27 7100 3400 Usable G Dynacoll 7150 (Hüls™) (D7150) Copolyester 46 6100 7500 Usable H Kunstharz AP (Hüls™) (KHAP) Acetophenone formaldehyde condensation product 47 1100 500 Little stiffening action I Kunstharz SK (Hüls™) (KHSK) Reduced acetophenone formaldehyde condensation product 89 1350 25000 Usable J Kunsthatrz CA (Hüls™) (KHCA) Cyclohexanone aldehyde condensation product 69 1050 5000 Usable K Kunstharz EP-TC (Hüls™) (KHEP) Ketone aldehyde condensation product 28 750 140 Litle stiffening action Selection of inks No % by wt. CM % by wt. ASM % by wt AOP Tm °C Tc °C Tm-Tc °C η 150°C (mPa.s) Assessment of print result, particularly directly after printing 1 80 1,12-DDD - - 20 F85E 86 65 21 6 Little flow, not stiff 2 70 1,12-DDD - - 30 F85E 85 63 22 8 Little flow, not stiff 3 80 1,12-DDD - - 20 F110 84 64 20 6 Little flow, not stiff 4 70 1,12-DDD 10 PETB 20 F110 80 52 28 7 Reasonable flow, not stiff 5 90 1,12-DDD - - 10 KHSK 83 60 23 6 Little flow, somewhat brittle 6 80 1,12-DDD - - 20 KHSK 81 55 26 7 Little flow, somewhat brittle 7 60 1,12-DDD 20 PETB 20 KHSK 82 54 26 9 Little flow, reasonably stiff 8 60 1,12-DDD 20 IPDI-MA 20 KHSK 79 52 27 9 Little flow, reasonably stiff 9 30 1,12-DDD 70 PETB - - 80 65 15 10 Little flow, too soft 10 30 1,12-DDD 60 PETB 10 KHSK 82 62 20 13 Little flow, reasonably stiff 11 30 1,12-DDD 45 10 10 PETB PET4T PET3T 5 KHSK 82 59 23 10 Little flow, reasonably stiff 12 60 1,12-DDD 20 10 PETB PBPA-PP 10 KHSK 82 58 24 11 Little flow, stiff 13 85 1,12-DDD - - 15 PSAA 84 63 21 8 Little flow, too brittle 14 75 1,12-DDD 10 IPDI-MA 15 PSAA 82 60 22 10 Reasonable flow, reasonably stiff 15 80 1,12-DDD - - 20 KHCA 86 62 24 7 Little flow, not stiff 16 70 1,12-DDD 10 IPDI-MA 20 KHCA 83 57 26 9 Reasonable flow, reasonably stiff 17 90 HMDI-MEG - - 10 KHSK 74 43 31 8 Reasonable flow, not stiff enough 18 85 HMDI-MEG - - 15 KHSK 72 17 55 10 Reasonable flow, not stiff enough 19 75 HMDI-MEG - - 25 KHSK 69 8 61 16 Reasonable flow, remains soft too long 20 85 HMDI-MEG 5 IPDI-MA 10 KHSK 72 39 33 9 Good flow, stiff 21 80 HMDI-MEG 10 IPDI-MA 10 KHSK 71 20 51 11 Good flow, stiff 22 80 HMDI-MEG 10 CMDI-BA 10 KHSK 72 27 45 11 Good flow, stiff 23 80 HMDI-MEG 10 PBPA-AP 10 KHSK 73 35 38 12 Good flow, stiff 24 80 HMDI-MEG - - 20 CB509 73 25 48 13 Reasonable flow, not stiff enough 25 85 HMDI-MEG - - 15 CB509 75 29 46 11 Reasonable flow. not stiff enough 26 80 HMDI-MEG 5 PETB 15 CB509 75 22 53 12 Good flow. stiff 27 90 p-BuBSA - - 10 CB509 93 54 39 8 Reasonable flow, to brittle 28 80 p-BuBSA - - 20 CB509 92 48 44 13 Reasonable flow, becomes too brittle after a few minutes 29 80 p-BuBSA - - 20 D7130 92 42 50 23 Reasonable flow. becomes too brittle after a few minutes 30 80 p-BuBSA - - 20 D7150 91 40 51 25 Reasonable flow, becomes too brittle after a few minutes 31 80 p-BuBSA 10 PETB 10 CB509 90 49 41 10 Good flow, reasonably stiff 32 70 p-BuBSA 20 PETB 10 CB509 89 43 46 12 Good flow, stiff 33 70 p-BuBSA 10 PETB 20 CB509 88 38 50 19 Good flow, very stiff 34 70 p-BuBSA 20 PETB 10 D7130 86 31 55 15 Good flow, stiff 35 70 p-BuBSA 20 PETB 10 D7150 87 30 57 17 Good flow, stiff 36 70 p-BuBSA 30 PETB - - 83 29 54 8 Good flow, too soft 37 40 40 p-TSA p-EBSA - - 20 CB509 98 77 21 14 Little flow, reasonably stiff 38 35 35 p-TSA p-EBSA 20 PETB 10 CB509 97 74 23 10 Reasonable flow, stiff 39 35 35 p-TSA p-EBSA 20 PET4T 10 CB509 99 73 26 11 Reasonable flow, stiff 40 80 ANGLY - - 20 KHSK 77 47 30 11 Reasonable flow, to brittle 41 70 ANGLY 10 PETB 20 KHSK 76 45 31 12 Reasonable flow, stiff 42 50 ANGLY 40 PETB 10 KHSK 74 38 36 18 Good flow, stiff 43 50 ANGLY 25 10 10 PETB PET4T PET3T 5 KHSK 78 44 34 9 Good flow, stiff 44 80 HQHE - - 20 KHSK 104 81 23 9 Little flow, too brittle, not very transparent 45 20 HQHE 80 PETB - - 99 65 34 11 Reasonable flow, too soft 46 30 HQHE 60 PETB 10 KHSK 100 60 40 16 Reasonable flow, reasonably stiff 47 30 HQHE 45 10 10 PETB PET4T PET3T 5 KHSK 103 69 34 15 Reasonable flow, reasonably stiff 48 85 PETA - - 15 PSAA 82 10 72 7 Flow excessive, crystallisation retardation excessive 49 80 PETA 10 IPDI-MA 10 PSAA 79 <5 >74 5 Flow excessive, crystallisation retardation excessive

Claims: An ink composition for a meltable ink, usable in printing devices in which ink droplets are ejected from ducts, which composition contains a meltable base material, characterised in that the ink composition also contains a monomer compound that sets amorphously at a cooling rate of 50°C/min and an amorphous polymer or oligomer binder and the base material is a crystalline-setting monomer compound, wherein the amorphously setting monomer compound has a glass transition temperature (Tg) of 10 - 50°C, a viscosity less than 100 mPa.s at 150°C and has a molecular weight lower than 1000, the amorphous polymer or oligomer binder has a Tg between 25 and 120°C, a weight-averaged molecular weight of between 1000 and 15000 and a viscosity greater than 1000 mPa.s at 150°C and the crystalline-setting monomer compound has a melting point lower than 110°C and a viscosity at 150°C of 1 - 10 mPa.s. An ink composition according to claim 1, characterised in that the amorphously setting monomer compound is selected from the group of bis-urethanes, esters of pentaerythritol and dipentaerythritol, carbonates of dipentaerythritol, bis-amides, bis-sulphonamides and reaction products of epoxides and alcohols. An ink composition according to claim 1, characterised in that the quantity of crystalline-setting monomer compound is between 60% by weight and 90% by weight, the quantity of amorphously setting monomer compound is between 5% by weight and 20% by weight, and the quantity of the amorphous polymer or oligomer binder is between 5% by weight and 20% by weight, based on the total ink composition, the difference between the melting temperature and the crystallisation temperature of the crystalline-setting monomer being less than 50°C. An ink composition according to claim 1, characterised in that the quantity of crystalline-setting monomer compound is between 25 and 45% by weight, the quantity of amorphously setting monomer compound is between 45% by weight and 65% by weight, and the quantity of the amorphous polymer or oligomer binder is between 5% by weight and 10% by weight, based on the total ink composition, the difference between the melting temperature and the crystallisation temperature of the crystalline-setting monomer being less than 25°C. An ink composition according to any one of the preceding claims 1 and 2 characterised in that the amorphously setting compound is selected from the group: the reaction product of isophorone diisocyanate with methyl alcohol or the reaction product of 4,4'-dicyclohexylmethane diisocyanate with benzyl alcohol, the benzoate, toluate and anisilate esters of penta-erythritol and dipentaerythritol, phenyl carbonates or substituted phenyl carbonates of dipentaerythritol, reaction products of the diglycidyl ether of bis-phenol A with alkyl or cycloalkyl substituted phenols. An ink composition according to any one of the preceding claims 1 and 2, characterised in that the crystalline-setting monomer compound is selected from the group: alcohols, sulphonamides, bis-urethanes and amides. An ink composition according to claim 6, characterised in that the crystalline-setting monomer compound is selected from the group: dodecanediol, hexadecanediol, para-toluene sulphonamide, para-ethylbenzene sulphonamide, para-n-butylbenzene sulphonamide, 1-O-para-anisyl glycerol, meta-toluamide, the reaction product of hexamethylene diisocyanate and 2-methoxyethanol or is a mixture of these compounds. An ink composition according to any one of the preceding claims, characterised in that the viscosity of the total ink composition is lower than 25 mPa.s at 130°C.

Inventors: EVERHARDUS ROELOF HENDRIK, GROOTHUIJSE RONALD, KELDERMAN ERIK, WEIJKAMP CLEMENS THEODORUS, EVERHARDUS, ROELOF HENDRIK, GROOTHUIJSE, RONALD, KELDERMAN, ERIK, WEIJKAMP, CLEMENS THEODORUS
Applicants: OCE TECH BV, OCE-TECHNOLOGIES B.V.
Application year: 1998
Main classification: C09D11
IPC codes: C09D11