An aqueous alkaline developing system for alkaline-developable lithographic printing plates and a method for its use are disclosed. The developing system comprises one or more water-soluble suppressors of the following structure:

This invention relates to lithographic printing. In particular, this invention relates to a developing system for both positive-working and negative-working imageable elements useful as alkaline-developable lithographic printing plates and to a method for its use.
In lithographic printing, ink receptive regions, known as image areas, are generated on a hydrophilic surface. When the surface is moistened with water and ink is applied, the hydrophilic regions retain the water and repel the ink, and the ink receptive regions accept the ink and repel the water. The ink is transferred to the surface of a material upon which the image is to be reproduced. Typically, the ink is first transferred to an intermediate blanket, which in turn transfers the ink to the surface of the material upon which the image is to be reproduced.
Imageable elements useful as lithographic printing plates, sometimes called printing plate precursors or printing forms, typically comprise an imageable layer applied over the surface of a hydrophilic substrate. The imageable layer includes one or more radiation-sensitive components, which may be dispersed in a suitable binder. Alternatively, the radiation-sensitive component can also be the binder material.
To obtain a printing plate with imagewise distribution of printable regions, it is necessary to remove regions of an imaged imageable element. The most common method for removing the undesired regions is to contact the imaged element with a developer. If after exposure to radiation the exposed regions of the layer are removed by the developer revealing the underlying hydrophilic surface of the substrate, the element is a positive-working printing element. Conversely, if the unexposed regions are removed, the element is a negative-working element. In each instance, the regions of the imageable layer (i.e., the image areas) that remain after development are ink-receptive, and the regions of the hydrophilic surface revealed by the developing process accept water and aqueous solutions, typically a fountain solution, and repel ink.
Many alkaline-developable positive-working imageable elements comprise a light sensitive layer comprising a phenolic resin, such as a novolac resin, on a hydrophilic substrate, typically a specially treated aluminum sheet. In one type of element, for example, the light sensitive layer comprises a novolac resin and a radiation-sensitive o-diazoquinone or diazonaphthoquinone compound, such as a naphthoquinonediazide sulfonic acid ester of a novolac resin. Upon exposure to light, the radiation-sensitive diazonaphthoquinone is converted to the corresponding carboxylic acid. The developer penetrates and removes the exposed, or image regions of the imageable layer, revealing the underlying hydrophilic surface of the substrate, without substantially affecting the complimentary unexposed regions.
Certain negative-working printing plates contain novolac resins, a cross-linking agent, and a radiation-sensitive component that produces acid on exposure. Subsequent heating cures the exposed regions, so that only the unexposed areas can be removed by an alkaline developer. The exposed regions, which remain after development, are oleophilic and will accept ink.
In both types of printing plates, an alkaline developer can attack the imageable layer, front side (aluminum oxide) and/or the backside (aluminum) of the imageable element. Developers for imageable elements that contain phenolic or similar resins typically comprise components that suppress the attack of the high alkaline developer either on the substrate or on the imageable layer. Often there are problems of miscibility of these components in the alkaline developer. Typically, silicate solutions (either as meta silicate or water glass) are used to protect aluminum substrates. In practice, this leads to problems caused by silicate deposits on developed plates.
In addition, the activity of developers based on meta-silicates cannot be monitored by conductivity measurements. Therefore, a top-up mode is required leading to a high volume of wasted developer. In this mode, only the developer is used to keep the activity of the developer in the developing section of a processor constant. This requires about 150 to 250 mL of developer per square meter of plate treated, from which about 100 to 200 mL are removed by an overflow device of the processor.
Therefore, a need exists for a developing system that protects the substrate from attack by an alkaline developer, that does not cause undesirable deposits on the developed printing plate, that requires only a small number of components, and whose activity can be monitored by conductivity measurements.
The invention is a developing system for both positive-working and negative-working imageable elements useful as lithographic printing plates. The developing system comprises both a developer and a replenisher.
The developer comprises an aqueous alkaline solution of one of more water-soluble suppressors of the following structure:
R1(CHOH)nR2
in which n is 4 to 7; and
either (i) R1 is hydrogen, aryl, or CH2OH; and R2 is alkyl group having 1 to 4 carbon atoms, CH2OR3 in which R3 is an alkyl group having 1 to 4 carbon atoms, CH2N(R4R5) in which R4 and R5 are each independently hydrogen or an alkyl group having 1 to 4 carbon atoms, or CO2H; or (ii) R1 and R2 together form a carbon-carbon single bond. These suppressors prevent attack by the alkaline developer on both the image and on the aluminum substrate.
The aqueous alkaline solution has a pH of about 10.0, typically greater than about 11.0, to about 14.0; and the one or more suppressors together comprise about 10 wt % to about 30 wt % of the developer.
Although the developer may be used as its own replenisher, typically a specially formulated replenisher, which comprises all the ingredients of the developer but which has a higher concentration of base is used as the replenisher.
preferred positive-working imageable element for use with the developing system of the invention comprises an aluminum substrate and an imageable layer that comprises a phenolic resin, preferably a novolac resin. Preferred suppressors include N-methyl-glucamin, meso-inosit, gulonic acid gamma-lactone, and mixtures thereof.
In another aspect, the invention is a method for forming an image using the developing system. In another aspect, the invention is an image formed by the method of the invention.
Attack both on the imageable layer and on an aluminum or aluminum alloy substrate by a developer having a pH of greater than about 10 can be suppressed by water-soluble organic compounds, or suppressors, having the following structure:
R1(CHOH)nR2
in which n is 4 to 7; and
either (i) R1 is H, aryl, or CH2OH; and R2 is alkyl group having 1 to 4 carbon atoms, CH2OR3 in which R3 is an alkyl group having 1 to 4 carbon atoms, CH2N(R4R5) in which R4 and R5 are each independently H or an alkyl group having 1 to 4 carbon atoms, or CO2H; or (ii) R1 and R2 together form a carbon-carbon single bond.
Either a single suppressor or a mixture of suppressors may be used. The suppressor or the mixture of suppressors comprises about 10 wt % to about 30 wt % of the developer.
In one group of suppressors, R1 and R2 together form a carbon-carbon single bond. Included are carbocyclic compounds of the structure: (CHOH)n, in which n is 4 to 7. In a preferred group of suppressors, n is 5 or 6, more preferably 6. There are nine possible stereoisomers of 1,2,3,4,5,6-hexahydroxycyclohexane, several of which are naturally occurring. A preferred suppressor is meso-inosit (cis-1,2,3,5-trans-4,6-hexahydroxycyclohexane). meso-Inosit can be isolated from corn steep liquor.
In another group of suppressors, R1 is H, aryl, or CH2OH; and R2 is alkyl group having 1 to 4 carbon atoms, CH2OR3 in which R3 is an alkyl group having 1 to 4 carbon atoms, CH2N(R4R5) in which R4 and R5 are each independently H or an alkyl group having 1 to 4 carbon atoms, or CO2H.
In one preferred group of suppressors, R1 is H or CH2OH; and R is CO2H. More preferably, R1 is H and n is 4 or 5. This group includes suppressors of the structure H(CHOH)nCO2H, in which n is 4 or 5. Conceptually, these suppressors may be produced by oxidation of the aldehyde of the corresponding hexose or pentose sugar, i.e., oxidation of the aldehyde of a hexose sugar such as glucose, fructose, galactose, allose, mannose, etc, or oxidation of the aldehyde of a pentose sugar such as arabinose, ribose, xylose, etc. Gluconic acid [H(CHOH)5CO2H], for example, may be prepared by oxidation of glucose by, for example, microbiological oxidation. Preferred suppressors include ribonic acid, gluconic acid (dextronic acid), mannonic acid, and gulonic acid.
As is known to those skilled in the art, these suppressors may exit in a ring-closed lactone form. Ribonic acid may exist as ribonic acid gamma-lactone. Gluconic acid may exist as gluconic acid gamma-lactone. Mannonic acid may exist as mannonic acid gamma-lactone. Gulonic acid may exist as gulonic acid gamma-lactone. The lactone form of these suppressors is included is the definition given above.
Also, as it apparent to those skilled in the art, in alkaline solution the suppressor may exist as an anion [H(CHOH)nCO2] due to ionization of the carboxyl group (CO2H) to the carboxylate anion (COOxe2x88x92). Lactose are converted to salts of the corresponding ring-opened acids in alkaline solution. Or the compound may be supplied as a salt, especially as an alkali metal salt, such as a sodium salt [H(CHOH)nCO2xe2x88x92Na+], or a potassium salt [H(CHOH)nCO2xe2x88x92K+]. Anions and salts of these suppressors are included in the definition given above.
In another group of suppressors, R1 is hydrogen, and R2 is CH2N(R4R5) in which R4 and R5 are each independently hydrogen or an alkyl group having 1 to 4 carbon atoms. n is preferably 4 or 5, and R4 and R5 are preferably each independently hydrogen or an alkyl group having 1 to 2 carbon atoms. Preferred suppressors include glucamine, N-methyl-glucamine, and 1-desoxy-1-(methylamino)-galactit. A more preferred suppressor is N-methyl-glucamine.
The developer has a pH between about 10 and about 14.0, typically at least about 11, preferably at least about 12, and preferably less than about 13.5. The alkalinity of the developer can be achieved by any of the conventional alkaline systems; e.g. alkali metal hydroxides, silicates, phosphates, borates, amines etc. Alkali metal hydroxides are preferred. Silicates are not favored because silicate deposits can be formed on the exposed and developed image. Consequently, the developer preferably does not comprise a silicate.
The developer may additionally comprise materials that are conventional components of developers, such as, surfactants (wetting agents), biocides (antimicrobial and/or antifungal agents), antifoaming agents, such as certain silicones, buffers, chelating (complexing) agents, etc, in a suitable amount (for example up to 5 wt % based on the total composition weight). If the developer is used in combination with and/or diluted with hard water, the presence of a chelating agent is preferred. Salts of ethylenediamine tetraacetic acid, for example, can be used as both a buffer and a chelating agent.
The developer may be a wholly aqueous developer, i.e., one that do not comprise an organic solvent, or it may comprise a small amount of one or more organic solvents, such as are disclosed in Fiebag, U.S. Pat. No. 6,143,479, incorporated herein by reference. Polyglycol derivatives with the structure:
R6Oxe2x80x94(CH2CHR7O)yxe2x80x94R8
in which R6 is hydrogen or C1-C8 alkyl; R7 is hydrogen, methyl or ethyl; R8 is hydrogen or CH2COOH; and y is an integer from 10 to 20, may be included. Polycondensation products of C2-C4 alkylene oxides with ethylene diamine may also be included. Mixture of polyglycol derivatives may also be used. Preferred polyglycol derivatives are polypropylene glycol ether, polyethylene glycol ether, polybutylene glycol ether, derivatives thereof, and mixtures thereof.
Glycols with the structure:
R9xe2x80x94CH(OH)xe2x80x94(CH2)zxe2x80x94CH(OH)xe2x80x94R10
in which z is 0, 1, or 2; and R9 and R10 are each independently hydrogen or C1-C3 alkyl, may be included. Preferred glycols are ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, and mixtures thereof.
When present, the total amount of polyglycol derivative or derivatives present typically comprises about 0.0005 wt % to about 3 wt % of the developer, based on the total weight of the developer. When present, the total amount of glycol pr glycols present typically comprises about 3 wt % to about 8 wt % of the developer, based on the total weight of the developer.
The developer may be conveniently prepared by dissolving the components in water. It can be supplied in a form ready for use, or it can also be provided in the form of a concentrate, which is diluted with water by the user prior to use.
Although the developer can also be used as its own replenisher, preferably, a specially formulated replenisher is used. In the replenisher, the concentration of base is higher than the concentration of base in the developer to compensate for the base consumed in the development process. Thus, a balance between developer drag-out and developer feed-in is reached. There is a correlation between the value of the electric conductivity and the alkalinity of the total developer bath.
The replenisher comprises the same components as the developer. The only difference is that the electrical conductivity of the replenisher has to be higher than that of the corresponding developer (i.e., the conductivity of the developer is lower than that of the corresponding replenisher). This is can, for instance, be obtained by having a higher concentration of the alkali metal hydroxide in the replenisher. The replenisher typically has a pH of about 11.0 to about 14.
As soon as a reduction of developer efficiency is detected by a lower electrical conductivity in the developing bath, replenisher is added to the developer until the electrical conductivity of the developer reaches its original value. The developer preferably has a conductivity of about 40 to about 80 mS/cm at 20xc2x0 C. The conductivity of the replenisher is higher than that of the developer, typically from about 60 to about 120 mS/cm at 20xc2x0 C.
The imageable element comprises an imageable layer on a hydrophilic substrate.
Substrate
The hydrophilic substrate, i.e., the substrate that comprises at least one hydrophilic surface, comprises a support, which may be any material conventionally used to prepare imageable elements useful as lithographic printing plates. The support is preferably strong, stable and flexible. It should resist dimensional change under conditions of use so that color records will register in a full-color image. Typically, it can be any self-supporting material, including, for example, polymeric films such as polyethylene terephthalate film, ceramics, metals, or stiff papers, or a lamination of any of these materials. Metal supports include aluminum, zinc, titanium, and alloys thereof.
Although the developers may be used with imageable elements that comprise any type of substrate known in the art, they are particularly well adapted for use with those that comprise an aluminum or an aluminum alloy support. The surface of the aluminum support may be treated by techniques known in the art, including physical graining, electrochemical graining, chemical graining, and anodizing. The substrate should be of sufficient thickness to sustain the wear from printing and be thin enough to wrap around a printing form, typically from about 100 to about 600 xcexcm.
Typically, the substrate comprises an interayer between the aluminum support and the imageable layer. The interlayer may be formed by treatment of the support with, for example, silicate, dextrine, hexafluorosilicic acid, phosphate/fluoride, polyvinyl phosphonic acid (PVPA) or polyvinyl phosphonic acid copolymers.
Imageable Layer
The imageable layer comprises either a positive-working or a negative-working imageable composition. The composition may be sensitive to ultraviolet and/or visible radiation (i.e., photoimageable), and/or it may be thermally imageable.
Positive-working photoimageable compositions are well known. They are discussed, for example, in Chapter 5 of Photoreactive Polymers: the Science and Technology of Resists, A. Reiser, Wiley, New York, 1989, pp. 178-225. These compositions comprise a water insoluble, alkali soluble binder and a material that comprises a photosensitive moiety. The photosensitive moiety may be bonded to the binder and/or be present in a separate compound.
The binder may comprise a phenolic resin, such as a novolac resin. Novolac resins are commercially available and are well known. They are typically prepared by the condensation reaction of a phenol, such as phenol, m-cresol, o-cresol, p-cresol, etc, with an aldehyde, such as formaldehyde, paraformaldehyde, acetaldehyde, etc. or ketone, such as acetone, in the presence of an acid catalyst. The weight average molecular weight is typically about 1,000 to 15,000. Typical novolac resins include, for example, phenol-formaldehyde resins, cresol-formaldehyde resins, phenol-cresol-formaldehyde resins, p-t-butylphenol-formaldehyde resins, and pyrogallol-acetone resins. Particularly useful novolac resins are prepared by reacting m-cresol, mixtures of m-cresol and p-cresol, or phenol with formaldehyde using conventional conditions.
Other phenolic resins include polyvinyl compounds having phenolic hydroxyl groups. Such compounds include, for example, resole resins, polymers of hydroxy-styrene (vinyl phenol), such as poly(p-hydroxystyrene); copolymers containing recurring units of hydroxystyrene; and polymers and copolymers containing recurring units of substituted hydroxystyrenes, such as acrylate and methacrylate copolymers of hydroxystyrene.
The binder may also be a water insoluble, base soluble polymeric compound having pendent sulfonamide groups, such as is described in Aoshima, U.S. Pat. No. 5,141,838 (EP 330,239). Particularly useful polymeric materials comprise (1) a sulfonamide monomer unit, especially N-(p-aminosulfonylphenyl)methacrylamide, N-(m-aminosulfonylphenyl)methacrylamide N-(o-aminosulfonylphenyl)methacrylamide, and/or the corresponding acrylamide, more especially N-(p-aminosulfonylphenyl)methacrylamide; (2) acrylonitrile and/or methacrylonitrile; and (3) methyl methacrylate and/or methyl acrylate.
The photosensitive moiety is typically the o-diazonaphthoquinone moiety. Compounds that contain the odiazonaphthoquinone moiety (i.e., quinonediazides), preferably compounds that comprise an o-diazonaphthoquinone moiety attached to a ballasting moiety that has a molecular weight of at least 1500, but less than about 5000, are preferred. Typically, these compounds are prepared by the reaction of a 1,2-naphthoquinone diazide having a halogenosulfonyl group, typically a sulfonylchloride group, at the 4- or 5-position with a mono- or poly-hydroxyphenyl compound, such as mono- or poly-hydroxy benzophenone.
The phenolic resin may be derivatized with an o-diazonaphthoquinone moiety. Polymeric diazonaphthoquinone compounds include derivatized resins formed by the reaction of a reactive derivative that contains diazonaphthoquinone moiety and a polymeric material that contains a suitable reactive group, such as a hydroxyl or amino group. Suitable polymeric materials for forming these derivatized resins include the novolac resins, resole resins, polyvinyl phenols, acrylate and methacrylate copolymers of hydroxy-containing monomers such as hydroxystyrene. Representative reactive derivatives include sulfonic and carboxylic acid, ester, or amide derivatives of the diazonaphthoquinone moiety. Derivatization of phenolic resins with compounds that contain the diazonaphthoquinone moiety is well known in the art and is described, for example, in West, U.S. Pat. Nos. 5,705,308, and 5,705,322.
A mixture comprising one or more phenolic resins and/or one or more polymeric-compounds having pendent sulfonamide groups may also be used as the binder in the positive-working photosensitive compositions.
Positive-working thermally imageable layers comprise a binder, a dissolution suppressor, and optionally, a photothermal conversion material. Such systems are disclosed in, for example, Parsons, WO 97/39894; Nagasaka, EP 0 823 327; Miyake, EP 0 909 627; West, WO 98/42507; and Nguyen, WO 99/11458, all of which are incorporated herein by reference. The binder is typically a phenolic resin, such as a novolac resin, as discussed above. The dissolution suppressors are believed not to be sensitive, i.e. photoreactive, themselves to radiation in the range of about 600 nm to about 800 nm and radiation in the range of about 800 nm to about 1200 nm, the radiation typically used to image a thermally imageable element.
The dissolution suppressor may be a compound that comprises an o-diazo-naphthoquinone moiety, such as is discussed above. The derivatized resins that comprise an o-diazonaphthoquinone moiety can act as both the binder and the dissolution suppressor. They can be used alone, or they can be combined with other binders and/or dissolution suppressors. Other compounds useful as dissolution suppressors include, compounds that contain a positively charged (i.e., quaternized) nitrogen atom, for example, tetraalkyl ammonium compounds, quinolinium compounds, benzothiazolium compounds, pyridinium compounds, and imidazolium compounds. A preferred group of dissolution suppressor compounds includes those that are also dyes, especially triarylmethane dyes such as ethyl violet. These compounds can also act as contrast or coloration dyes, which distinguishes the unimaged regions from the imaged regions in the developed imageable element.
Alternatively, or additionally, the binder itself can comprise polar groups that act as acceptor sites for hydrogen bonding with the hydroxy groups present in the polymeric material and, thus, act as a dissolution suppressor. Using well-known methods, a portion of the hydroxyl groups of the binder can be derivatized to introduce polar groups, for example carboxylic acid esters, such as benzoate esters; phosphate esters; ethers, such as phenyl ethers; and sulfonic acid esters, such as methyl sulfonates, phenyl sulfonates, p-toluene sulfonates (tosylates), and p-bromophenyl sulfonates (brosylates).
Derivatization of the hydroxyl groups of the binder increases its molecular weight and reduces the number of hydroxyl groups, typically reducing both its solubility and rate of dissolution in the developer. Although it is important that the level of derivatization be high enough that the binder also acts as a dissolution suppressor, it should not be so high that, following thermal imaging the binder is not soluble in the developer. Although the degree of derivatization required will depend on the nature of the binder and the nature of the moiety containing the polar groups introduced into the binder, typically about 0.5 mol % to about 5 mol%, preferably about 1 mol % to about 3 mol %, of the hydroxyl groups will be derivatized. These derivatized binders can be used either alone or in combination with other polymeric materials and/or dissolution suppressors.
One preferred group of binders that comprise polar groups and function as dissolution suppressors are derivatized phenolic polymeric materials in which a portion of the phenolic hydroxyl groups have been converted to sulfonic acid esters, preferably phenyl sulfonates or p-toluene sulfonates. Derivatization can be carried by reaction of the polymeric material with, for example a sulfonyl chloride such as p-toluene sulfonyl chloride, in the presence of a base such as a tertiary amine. A preferred derivatized binder is a derivatized novolac resin in which about 1 mol % to 3 mol %, preferably about 1.5 mol % to about 2.5 mol %, of the hydroxyl groups have been converted to phenyl sulfonate or p-toluene sulfonate (tosyl) groups.
When a photothermal conversion material is present, it may comprise infrared absorber or dye bound to a phenolic material (i.e., a phenolic material derivatized with an infrared absorber or infrared absorbing dye). If an appropriate infrared absorber or dye is selected, the derivatized polymeric material can act as the binder, the dissolution suppressor, and/or the photothermal conversion material.
The imageable layer may also comprise dye to aid in the visual inspection of the exposed and/or developed element. Printout dyes are added to distinguish the exposed regions from the unexposed regions before and during processing. Contrast or coloration dyes are added to distinguish the unimaged regions from the imaged regions in the developed element.
If the imageable element is to be imaged with infrared or near infrared radiation, the imageable layer absorbs the imaging radiation, preferably radiation in the range of about 800 nm to 1200 nm, the radiation is commonly used for imaging thermally imageable elements. An absorber called a photothermal conversion material, which absorb radiation and convert it to heat, is typically present in the imageable layer. Photothermal conversion materials may absorb ultraviolet, visible, and/or infrared radiation and convert it to heat. Although the binder may itself comprise an absorbing moiety, i.e., be a photothermal conversion material, typically the photothermal conversion material is a separate compound.
The photothermal conversion material may be either a dye or pigment, such as a dye or pigment of the squarylium, cyanine, merocyanine, indolizine, pyrylium, or metal diothiolene class. Examples of absorbing pigments are Projet 900, Projet 860, and Projet 830 (all available from the Zeneca Corp.). Carbon black pigments may also be used. Because of their wide absorption bands, carbon black-based plates can be used with multiple infrared imaging devices having a wide range of peak emission wavelengths.
Dyes, especially dyes that are soluble in the aqueous alkaline developer, are preferred to prevent sludging of the developer by insoluble material. The dye may be, for example, an indoaniline dye, oxonol dye, porphyrin derivatives, anthraquinone dye, merostyryl dye, pyrylium compound, or a squarylium derivative. Absorbing dyes are disclosed in numerous disclosures and patent applications in the field, for example, Nagasaka, EP 0,823,327; Van Damme, EP 0,908,397; DeBoer, U.S. Pat. No. 4,973,572; Jandrue, U.S. Pat. No. 5,244,771; and Chapman, U.S. Pat. No. 5,401,618.
The amount of photothermal conversion material in the imageable layer is generally sufficient to provide an optical density of at least 0.05, and preferably, an optical density of from about 0.5 to about 2 at the imaging wavelength.
In another embodiment of this invention, a negative-working, alkaline developable printing plate, typically one containing a novolac resin and/or another phenolic resin, is imagewise exposed with a suitable light source and heated to harden the exposed regions. These materials are described, for example, in Haley, U.S. Pat. No. 5,372,907; Haley U.S. Pat. No. 5,466,557; and Nguyen, U.S. Pat. No. 5,919,601.
Haley ""907 discloses a radiation-sensitive composition that is sensitive to both ultraviolet and infrared radiation. The composition comprises (1) a resole resin, (2) a novolac resin, (3) a latent Brxc3x6nsted acid and (4) an infrared absorber. The solubility of the composition in an alkaline developer is both reduced in exposed areas and increased in unexposed areas by the steps of imagewise exposure to activating radiation and heating.
Latent Brxc3x6nsted acids are precursors that form a Brxc3x6nsted acid by thermally or photochemically initiated decomposition. The Brxc3x6nsted acid is believed to catalyze a matrix-forming reaction between the resole resin and the novolac resin. Latent Brxc3x6nsted acids include, for example, onium salts in which the onium cation is iodonium, sulphonium, phosphonium, oxysulphoxonium, oxysulphonium, sulphoxonium, ammonium, diazonium, selononium, or arsonium, and the anion is a non-nucleophilic anion selected from tetra-fluoroborate, hexafluorophosphate, hexafluoroarsenate, hexafluoroantimonate, triflate, tetrakis(pentafluoro-phenyl)borate, pentafluoroethyl sulfonate, p-methyl-benzyl sulfonate, ethyl sulfonate, trifluoromethyl acetate, and pentafluoroethyl acetate. Typical latent Brxc3x6nsted acids include, for example, diphenyliodonium hexafluorophosphate, diphenyl iodonium hexafluoroantimonate, bis-4-do-decylphenyliodonium hexafluoro antimonate, dicumyliodonium hexofluorophosphate, and triphenylsulfonium hexafluoroantimonate. Non-ionic latent Brxc3x6nsted acids include, for example, haloalkyl-substituted s-triazines, which are described, for example, in Smith, U.S. Pat. No. 3,779,778.
Nguyen discloses radiation-sensitive compositions imageable by infrared and ultraviolet/visible radiation. These compositions comprise a thermal-activated acid generator; a crosslinking resin; a binder resin comprising a polymer containing reactive pendant groups selected from hydroxy, carboxylic acid, sulfonamide, and alkoxymethylamides; an infrared absorber; and optionally an ultraviolet/visible radiation-activated acid generator for ultraviolet/visible sensitization. The thermal-activated acid generators are typically the same as the latent Brxc3x6nsted acids described above.
Conventional additives, such as dyes, pigments, plasticizers, sensitizers, stabilizers, surfactants, and components, such as leucodyes, that produce print-out images can be included in these negative-working, alkaline developable compositions.
Imaging may be carried out by well-known methods. When the element is xe2x80x9cpositive working,xe2x80x9d the exposed regions are removed to reveal the underlying hydrophilic surface of the substrate. When the element is xe2x80x9cnegative working,xe2x80x9d the unexposed regions are removed to reveal the underlying hydrophilic surface of the substrate.
If the element is a photoimageable element, it may be exposed to actinic radiation from a source of light that is absorbed by the photoreactive component or components present. Conventional exposure sources include, for example, carbon arc lamps, mercury lamps, xenon lamps, tungsten lamps, metal halide lamps, and lasers emitting at the appropriate wavelength. Diazonaphthoquinone compounds substituted in the 5-position typically absorb at 345 nm and 400 nm. Diazonaphthoquinone compounds substituted in the 4-position typically absorb at 310 nm and 380 nm. Imagewise exposure is typically carried out through a photomask, but direct digital exposure with a laser emitting at the appropriate wavelength is also possible.
If the element is a thermally imageable element, it may be imaged with a laser or an array of lasers emitting modulated near infrared or infrared radiation in a wavelength region that is absorbed by the element. Infrared radiation, especially infrared radiation in the range of about 800 nm to about 1200 nm, is typically used for imaging a thermally imageable element. Imaging is conveniently carried out with a laser emitting at about 830 nm or at about 1056 nm. Suitable commercially available imaging devices include image setters such as a Creo Trendsetter (CREO, British Columbia, Canada) and a Gerber Crescent 42T (Gerber).
Alternatively, the thermally imageable element may be imaged using a conventional apparatus containing a thermal printing head. An imaging apparatus suitable for use in conjunction with the imageable elements includes at least one thermal head but would usually include a thermal head array, such as a TDK Model No. LV5416 used in thermal fax machines and sublimation printers. When exposure is carried out with a thermal head, it is unnecessary that the element absorb infrared radiation. However, elements that absorb infrared radiation can be imaged with a thermal head.
Imaging produces an imaged element, which comprise a latent image of imaged and unimaged regions. Developing the imaged element to form a developed element converts the latent image to an image by removing the exposed, or imaged, regions and revealing the hydrophilic surface of the underlying substrate.
Typically, the developer is applied to the imaged element by rubbing or wiping the imageable layer with an applicator containing the developer. Alternatively, the imaged element may be brushed with the developer or the developer may be applied to the element by spraying the imageable layer with sufficient force to remove the exposed regions. In either instance, a developed element is produced. Development may be carried out in a commercially available processor, such as a Mercury Processor (Kodak Polychrome Graphics). The Mercury Processor is equipped with an immersion type developing bath, a section for rinsing with water, a gumming section, and a drying section. Additional, a conductivity-measuring unit can be incorporated into the processor.
Development of both positive-working and negative-working imaged elements is typically carried out at a temperature of from about 18xc2x0 C. to about 28xc2x0 C., for a period of from about 5 seconds to about 60 seconds.
After a certain number of imaged elements have been developed, the conductivity value falls below a predetermined level. Then the replenisher is added to the processor section that contains the developer. Usually about 30 mL to about 100 mL, typically about 50-80 mL, of replenisher per 1 m2 of imaged element processed is necessary to keep both the volume of developer and its conductivity value constant.
The developed element, typically a lithographic printing member or a printing plate, comprises regions in which imageable layer has been removed revealing the underlying surface of the hydrophilic substrate, and complimentary regions in which the imageable has not been removed. The regions in which the imageable layer has not been removed are ink receptive and correspond to the regions that were not exposed during imaging.
Following development, the developed element is rinsed with water and dried. Drying may be conveniently carried out by infrared radiators.
After drying, the developed element is treated with a gumming solution. A gumming solution comprises one or more water soluble polymers, for example polyvinylalcohol, poly(meth)acrylic acid, poly(meth)acrylamide, polyhydroxyethyl(meth)acrylate, polyvinylmethylether, gelatin, and polysaccharide such as dextran, pullulan, cellulose, gum arabic, and alginic acid. A preferred material is gum arabic.
A developed and gummed plate can also be baked to increase the run length of the plate. Baking can be carried out, for example at about 220xc2x0 C. to about 240xc2x0 C. for about 7 to 10 minutes, or at a temperature of 120xc2x0 C. for 30 min.
The developing system is especially suitable for developing imageable elements useful as positive-working lithographic printing plates. It is especially suited for use with elements in which (1) the imageable layer comprises at least one phenolic resin that is insoluble in water and removable by the aqueous alkaline developer and/or at least one polymeric compound having pendent sulfonamide groups that is insoluble in water and removable by the aqueous the aqueous alkaline developer, and (2) the substrate is aluminum or and an aluminum alloy.
In practice not every developer works well with every printing plate, especially with those that have different interlayers. The attack of a developer on the aluminum substrate depends on the composition of the developer. Therefore, printers who use printing plates with different interlayers must store and use a developer for each type of plate. Because the developer of the invention suppresses attack on aluminum substrates, it can be used with printing plates having a variety of interlayers. Because the developer does not contain a silicate solution (either as metasilicate or an alkali metal water glass), silicate deposits on developed plates are eliminated. Because the conductivity of the developer can be monitored, the invention provides a developing system that makes it relatively easy for an operator to work with a constant activity developer.
The advantageous properties of this invention can be observed by reference to the following examples, which illustrate but do not limit the invention. In the specification, examples, and claims, unless indicated otherwise, all percentages are percentages by weight based on the weight of the developer.
N-Methyl-D-glucamin, meso-inosit (cis-1,2,3,5-trans-4,6-hexahydroxycyclohexane), and L-gulonic acid gamma-lactone were obtained from Aldrich, Milwaukee, Wis., USA.
The following developers and repelenishers were prepared by stirring the components together:
Developer 1xe2x80x94839 g water, 140 g N-methyl-D-glucamin, and 21 g sodium hydroxide.
Developer 2xe2x80x94839 g water, 140 g meso-inosit, and 21 g sodium hydroxide.
Developer 3xe2x80x9484.6 kg water, 14.0 kg meso-inosit, 2.1 kg sodium hydroxide, and 0.24 kg SYNPERONIC(copyright) 304 T.
Developer 4xe2x80x94708.5 g water, 140 g L-gulonic acid gamma-lactone, 120 g sodium meta-silicate penta-hydrate, and 31.5 g sodium hydroxide.
Developer 5xe2x80x9481.7 9 water, 15 g, meso-inosit, 2.9 g potassium hydroxide. 0.2 g TRILON(copyright) B chelating agent B, and 0.2 g REWOTERIC(copyright) AM-V wetting agent.
Replenisher 1xe2x80x9483.3 kg water, 14.0 kg meso-inosit, 3.4 kg sodium hydroxide, and 0.24 kg SYNPERONIC(copyright) 304 T.
Comparative developers 14 were prepared by mixing the components given in Table 1.
The weight loss for 1 dm2 aluminum discs having different interlayers but no imageable layer was determined by treating the discs with developer containing different wt % of suppressor. Weight loss was measured by comparing the initial weight of the disc with the weight of the disc after it laid in the developer composition for 5 min at 20xc2x0 C. Comparative Developers 1 and 2 containing differing amounts of inventive suppressors were evaluated. A developer containing SYNPERONIC(copyright) 304-T (Comparative Examples 3 and 4), which is a suppressor for the imageable layer only, was also evaluated. The results are shown in Tables 2 and 3 below.
For all substrates there was little or no attack on the aluminum disc when an appropriate concentrations of suppressor was present in the developer. When only SYNPERONIC(copyright) 304-T was present, there was attack on all substrates.
EASYPRINT(copyright) and Virage(trademark) positive-working lithographic printing plates (Kodak Polychrome Graphics LLC) were cut into 790 mmxc3x97850 mm test samples and exposed with a metal halide lamp (MH-Burner, available from Sack) with 510 mJ/cm2 (EASYPRINT(copyright))) and 525 mJ/cm2 (Virage(trademark)) under a silver halide film half-step wedge (Fogra) with a density range of 0.15 to 1.95 increments as a positive copy.
A commercially available processor (Mercury 850; Kodak Polychrome Graphics LLC), equipped with an immersion type developing bath, a section for rinsing with water, a gumming section, and a drying section, was used to develop the exposed plates. The processor was filled with 60 L of the appropriate developer. If the processor contains more than the given 60 L, the excess is removed via an overflow. This excess can be collected in a container. Separately, a container for the replenisher was attached from which a predetermined amount of replenisher per square meter of exposed plate was added to the developing bath via a pump.
The activity of the developer was examined with the help of its conductivity and by titration of the amount of alkali. The conductivity of the developing bath was monitored by an incorporated SIPAN 3 conductivity measuring unit (Siemens). To determine the alkali content, 10 mL of the developer was removed from the developing bath, 90 mL deionized water was added, and the titration was carried out with 0.5 N HCl (Titrino DMS 716, Metrohm). The number of mL used to reach the first equivalence point is referred to as alkali value.
The temperature of the developing bath, (23xc2x11)xc2x0 C., and dwell time in the developer, 25 sec, were kept constant in all tests.
To evaluate the copies obtained after development, the following criteria were examined. (1) Number of steps after gray wedge exposure that do not retain coating after development (in the following referred to as GWxe2x80x94the lower the number the less image attack); (2) Microlines in a test pattern to assess resolution that have not been attacked (in the following referred to as MLxe2x80x94the lower the number the greater the resolution indicating less image attack); and (3) Behavior during the print proof or during restarting of the printing (ink acceptance problems of the image and non-image areasxe2x80x94i.e. xe2x80x9ctoningxe2x80x9d).
To obtain the latter test results, the exposed and developed plates were mounted in a sheet-fed offset press and proofed. The image areas accepted ink without any problems and the paper copies did not show any background (referred to as toning) in the non-image areas. After about 2000 copies, the press was stopped for about 45 minutes and then restarted (restarting test). The same results as at the beginning of the printing test were obtained. In particular the non-image areas did not show any toning, which indicates a good protection of the basis material by the developer.
The copying results with EASYPRINT(copyright) and Virage(trademark) plates and the developers of the invention are listed in Table 4 below.
EASYPRINT(copyright) plates exposed with the Fogra wedge in the same manner as described above were developed one after another at a rate of 140 plates per day for 25 days (plus 4 weekend interruptions) in the Mercury 850 processor. The quality of the resulting copies was evaluated in terms of the GW and the ML values. The activity of the developer was monitored at a throughput of 4 m2/L by conductivity measurements and by titration with 0.5 N HCl.
The results for developer 3 and the corresponding replenisher 1 are listed in Table 5. Titration and conductivity data show that the activity of the developer can be kept constant during long testing period by the addition of 80 mL/m2 of developed plate. This is apparent in the almost constant values for the copy parameters gray scale wedge and microlines after the development of 3500 m2 plates in the 60 L of developer in the processor. Throughout the course of the test, 175 L of overflow of used developer was collected which corresponds to a value of 50 mL/m2 of developed plate.
During the test period, the developing process was not affected by either the formation of foam or the precipitation of insoluble material on the bottom of the processor. After testing was completed, the processor could be easily cleaned by rinsing with water, and no residue remained.
After a throughput of 20, 40 and 58.3 m2/L, EASYPRINT(copyright) plates did not show any irregularities in the printing test. Neither ink acceptance nor toning problems occurred.
ELECTRA(copyright) positive-working thermal printing plates (Kodak Polychrome Graphics LLC) were cut into 515 mmxc3x97790 mm test samples. The test samples were exposed in a Trendsetter 3244 (Creo) infrared exposure unit at an energy of 10 W and a rotional speed of the drum of 180 rpm. The Kodak Professional COLORFLOW(copyright) Strip (Eastman Kodak), which contains different elements for evaluating the quality of the copies, was used for evaluation.
A commercially available processor (Sprinter; Kodak Polychrome Graphics LLC), equipped with an immersion type developing bath, a section for rinsing with water, and a gumming and drying section, was used to develop the imagewise exposed plates. The processor was filled with 20 L of the appropriate developer. Separately, a container for the replenisher was attached from which a predetermined amount of replenisher per square meter of exposed plate was added to the developing bath via a pump.
The temperature of the developing bath, (23xc2x11)xc2x0 C., and the dwell time in the developer, 45 sec, were kept constant in all tests.
The activity of the developer was examined with the help of its conductivity and by titration of the amount of alkali. The conductivity of the developing bath was monitored by a separately mounted conductivity measuring unit (Conductivity Monitor, Unigraph). To evaluate the copies obtained after development, the following criteria were examined: reproduction of the 1 and 2 pixel elements, optical density (OD) of the checkerboard dots of the pixel elements (measured with the apparatus D 19C/D196 from Gretag/Macbeth).
The tests using developers 3 and 4 provided the following results:
(1) The image areas were not attacked which follows from unchanged optical density of the image areas as compared with the non-treated areas.
(2) The 1 and 2 pixel elements were well reproduced.
(3) The optical density for 50% dot was measured to be OD=50 with developer 3 and OD=49 for developer 4.
For the stability and load test exposed ELECTRA(copyright) plates were developed in the manner described above one after another at a rate of 33 plates per day for 30 days (plus 5 weekend interruptions) in the Sprinter processor filled with developer 3. For replenishment the replenisher 1 was used. To determine the alkali content, 10 mL of the developer was removed from the developing bath, 90 mL deionized water was added, and titration was carried out with 0.5 N HCl (Titrino DMS 716, Metrohm). The number of mL used to reach the first equivalence point is referred to as alkali value. The quality of the resulting copies was evaluated in terms as above. At a throughput of 2 m2/L the electrical conductivity was measured as well as the developer activity.
Addition of 82 mL of replenisher kept the activity of the developer constant until the end of testing of 15 m2/L (electrical conductivity: 58.4 mS/cm; titration: 10.8 mL). The copy parameters of OD (optical density)=94 for 95% dot screen and OD=50 for 50% dot screen in the beginning only slightly changed to OD=95 and OD=51, respectively, at the end of the test. The reproduction of the 1 and 2 pixel elements did not change.
Plates developed with this developing system showed no problems in ink acceptance or toning during the printing test at the print proof and upon restart.
When positive-working thermal printing plate exposed as above were developed with the Comparative Developers 1 to 4, both the 1 and 2 pixel elements were not reproduced by the plates. With Comparative Examples 1 and 2, the 50% dots were also removed. In Comparative Examples 3 and 4, the 50% dots were highly attacked.

Developer for alkaline-developable lithographic printing plates

Abstract: R1 (CHOH)nR2

Abstract: in which:

Abstract: n is 4 to 7; and

Abstract: either (i) R1 is hydrogen, aryl, or CH2OH; and R2 is alkyl group having 1 to 4 carbon atoms, CH2OR3 in which R3 is an alkyl group having 1 to 4 carbon atoms, CH2N(R4R5) in which R4 and R5 are each independently hydrogen or an alkyl group having 1 to 4 carbon atoms, or CO2H; or (ii) R1 and R2 together form a carbon-carbon single bond. The developing system is especially suited for developing imageable elements useful as lithographic printing plates. The developing system is especially suited for use with elements in which (1) the imageable layer comprises at least one phenolic resin or at least one polymeric compound having pendent sulfonamide groups, and (2) the substrate is aluminum or and an aluminum alloy.


A metal free dental filling system is provided which prevents the transmission of destructive forces from the shrinking filling material to the sealed dental hard tissue. The system prevents the transmission of destructive forces by making the bond of the cured adhesive sealant to the dental hard tissue, i.e., the enamel, dentin, and root cement, substantially stronger than the bond of the cured adhesive sealant to the filling material. An intermediate layer material may be arranged between the dental filling material and the cured adhesive sealant. If an intermediate layer is used, the bond between the dental hard tissue and the cured adhesive sealant is much stronger than the bond between the cured adhesive sealant and the intermediate layer in order to ensure that substantially no destructive forces are transmitted from the shrinking filing material to the cured adhesive material on the dental hard tissue. The intermediate layer may be removed prior to application of the filling material.

The present invention relates to a metal-free dental filling system for filling therapy or root filling therapy, respectively, as well as to its use as a substitute for amalgam.
For tooth restoration in dentistry, three hierarchically ordered goals are pursued, whereby each higher standard is based on the fulfillment of the lower standard or the lower standards.
The partial goal of the lowest standard 1 consists in the conservation of the dental hard tissue and the protection of the pulpa.
Standard 2 is further aiming at restoring the tooth""s shape and function.
The purpose of standard 3 is to design the restoration in such a way that it is imperceptible at conversation distance and remain so throughout the stipulated service life.
Amalgams, i.e. mixtures of a silver-tin alloy with liquid mercury, have been used for more than 150 years as standard filling material, in particular for posterior, permanent teeth. When used with adequate operative techniques, amalgam restorations are able to protect the dental hard tissue for years and to restore the tooth""s shape as well it""s functionality. Thus, amalgam restorations fully satisfy standard 2. In filling therapy with amalgam, a comparatively simple operative technique has evolved that relies on steel matrices and wooden wedges for giving the filling its correct, preferably overhang-free contour at its outer surfaces. Occlusal shaping is carried out by carving. Amalgam fillings are furthermore comparatively cheap. The medium survival rate of amalgam fillings can be 10 years and more.
In recent years, however, amalgams have lost quite some ground as a standard restorative material. The main reasons of this decline are, among others, its controversial toxic and allergenic potential, its environmental impact and its lack of tooth color. As a consequence, it was necessary to search for materials or material systems that could be used to replace amalgam for posterior teeth, in particular for permanent teeth and stress-bearing restorations. This resulted in two material or system groups differing in their purpose, namely amalgam alternatives and amalgam substitutes.
Amalgam alternatives have to suffice standard 3 and not only have to guarantee the conservation of the dental hard tissue as well as shape and function of the restored tooth over a long time, but they also must be and remain imperceptible at normal conversation distance. This group of materials in particular comprises composite fillings and composite or ceramic work-pieces. This not only requires tooth color, but also a stress resistant, perfect marginal adaptation. With fillings, the latter is achieved by using a rather complex operative technique, with work-pieces by high accuracy in conjunction with efficient adhesive or combined adhesive/luting systems.
In contrast to this, an amalgam substitute has to satisfy standard 2 just as amalgam does; in addition to this, the operative technique should be simple for cost reasons and be as close as possible to the known amalgam technique, i.e. it should be possible to work with steel matrices and wooden wedges, to use a simple incremental technique and, if light curing materials are used, irradiation from an occlusal direction should suffice.
Various amalgam substitute systems are known:
DE-196 03 577 A1 relates to an adhesive system, wherein a gap free connection between the plastic filling material and the dental hard tissue is aimed at. In such a system, the bond between dental hard tissue and filling material is excellent, such that in case of adhesive failures, continuity fractures occur in the dental hard tissue or in the restorative material. This means that no caries protection is provided along these marginal openings if they run in the dental hard tissue.
DE 195 44 670 describes an adhesive system that does not harden by radical polymerization but rather as a product of condensation. In this way, an oxygen-inhibited surface layer is to be avoided. Thus, however, the adhesive may be better suited than usual, radically polymerizing sealants for sealing caries. In the application as an adhesive, where, according to the inventor, the prevention of margin gap formation is again aimed at, cohesive failure results in the dentin and in the enamel. Hence, this system is unable to reliably protect the dental hard tissue. With comparatively frequent adhesive failure, the enamel is not protected at all in the area of the marginal openings, which are therefore not desired at all. In dentin, a partial, erratic, unpredictable protection is to be expected where the bond happens to break between the adhesive and the filling material and adhesive islands remain on the dental hard tissue. The described system therefore provides no safe and complete protection of the enamel or dentin, and it also belongs to the category of the adhesive systems aiming at a total bond between the dental hard tissue and the restorative material.
EP 0 423 430 describes a dentin-adhesive system using a primer and a bond on dentin. Again, it is aimed at a total leakage-free bond between dental hard tissue and restorative material.
EP 0 088 527 describes an enamel conditioner designed to generate a better bond between the enamel and the restorative material than it used to be the case upon the usual etching process by means of phosphoric acid.
DE 34 14 163 relates on a dentin primer and describes a dentin bonding system working with a primer and a bond on dentin, wherein again a total leakage-free bond between dental hard tissue and restorative material is desired.
None of the adhesive systems according to the state of the art, however, uses enamel and dentin bonding selectively for protection and adhesive sealing of the dental hard tissue, while selectively eliminating the requirement of a bond between the shrinking restorative material and the sealed dental hard tissue.
The adhesive systems according to the state of the art are fully unsatisfactory when being used in combination with amalgam substitutes and the corresponding operative techniques, because unpredictably located fractures in the restorative material, the interface between restorative material and adhesive, within the adhesive, at the interface between the adhesive and the dental hard tissue and/or within the dental hard tissue can occur. Fractures at the interface between the adhesive and the dental hard tissue and within the dental hard tissue are particularly damaging. A reliable protection cannot be achieved using the required simple placement techniques and currently available adhesive systems.
Investigations have shown that fillings made of materials presently used as amalgam substitutes are visible after a short period of time especially when occlusally loaded. Such materials include amalgam substitutes in combination with an adhesive system such as composite-adhesive or compomer adhesive systems, i.e., polyacid-modified composites, as well as composite adhesive systems specifically developed as amalgam substitutes. Sometimes within months, from 60% to 95% of the total margin length of the filling is visible resulting in both marginal discoloration and a high risk for secondary caries in medium time range caries diagnostics.
While marginal discoloration may be acceptable within the requirements of operative standard 2, the high risk for secondary caries with fillings of the known material combinations mentioned above, cannot satisfy operative standard 1, i.e., tooth conservation can not be achieved over a medium time range. Thus, materials presently used as amalgam substitutes should only be used as temporary fillings.
The reason for the failure of the amalgam substitute materials according to the state of the art lies in the fact that such materials usually shrink by 2.5 to 4.5 volume percent during the curing process. The resulting stress build-up damages the bonds as generated by the adhesive systems according to the state of the art and exceeds the cohesive strength of the dental hard tissue, especially in the enamel, and of the filling material itself. Under stress, non-predictable continuity fractures occur, namely fissures in the enamel and, more rarely, in the dentin, a breaking of the bond between dental hard tissue and adhesive system, within the adhesive system, at the interface between adhesive system and filling, and within the filling. Even though an adhesive system is used, unprotected, adhesive free areas of dental hard tissue are exposed, either due to cohesive fractures within the dental hard tissue or due to a breaking of the bond between the adhesive system and the dental hard tissue.
Hence, it is a general object of the invention to provide a dental filling system that avoids at least part of the above disadvantages and problems.
In particular, it was an aim of the present invention to provide an amalgam substitute, which fulfills the above partial goals 1 and 2 as well as, possibly, 3.
This object is achieved according to claim 1. Preferred embodiments are described in the dependent claims.
The metal free, dental filling system for the filling therapy of cavities or for the filling therapy of root canals according to the present invention comprises
a) a dental filling material for cavities or root canals, as well as
b) an adhesive, curing or self-curing sealant for the dental hard tissue,
c) wherein the adhesive bond of the cured adhesive sealant to the dental hard tissue, i.e., the enamel dentin, and root cement, is substantially stronger than to the cured filling material such that substantially no destructive forces are transmitted from the shrinking filling material to the adhesive sealant.
In an especially preferred embodiment the filling system according to the invention comprises an intermediate layer material d), which is suitable to be arranged between the dental filling material a) and the sealant b), wherein the adhesive bond between the cured adhesive sealant b) to the dental hard tissue is much stronger than to the intermediate layer material d), such that substantially no destructive forces are transmitted from the shrinking filling material to the adhesive sealant.
Preferably, said intermediate layer material d) is removable before application of the filling material.
In an especially preferred embodiment, substantially no adhesive bond is formed between the cured sealant b) to the filling material a) or, if applicable, to the intermediate layer d), respectively, such that during the curing no destructive forces at all are transmitted from the shrinking filling material a) and/or the intermediate layer material d) to the adhesive sealant b).
Hence, in contrast to the known state of the art the present invention does not aim at protecting the dental hard tissue by a perfect bond to the filling material. The present invention rather provides an isolating, selective adhesive seal of the dental hard tissue, thereby generating the desired protection in the area of the margin gaps.
Preferably, the desired separation or, compared to the destructive stress build-up within the filling, the weak, no stress transferring bonds between the sealant and the filling material are achieved by making known adhesive coatings unable to co-polymerize or lock by a suitable choice of monomers, admixtures or curing methods. Alternatively, instead of using a known adhesive system, an adhesive system is used that adheres to the enamel and dentin, forms a coating, is chemically and physically resistant but does not form a mechanical or chemical bond to the filling system that might endanger its own bond to the hard dental material.
Using the system according to the invention, the dental hard tissue remains free of fractures and is protected against caries and erosive processes throughout the stipulated service life of the filling. The amalgam substitute according to the invention therefore meets standard 2 by a complete prevention of the risk of secondary caries and by preserving the dental hard tissue, while shape and function of the tooth are restored by the filling material.
The main object of the present invention is a dental filling system that that eliminates the need for a total bond from the sealant b) for the dental hard tissue to the filling material a) or the intermediate layer material d), respectively. An isolated, selective adhesive sealing of the dental hard tissue can be reached as follows:
A) A transmission of shrinking-forces can be avoided by preventing mechanical interlocking and homo or co-polymerization between the dental filling material a) and, if present, the intermediate layer material d) on the one hand, as well as the adhesive sealant b) for the dental hard tissue on the other hand. This can e.g. be achieved by entirely coating the sealant b) by a separation layer. For this purpose, painting materials, such as zinc oxide-Eugenol, said compound being known to those skilled in the art, barrier materials, such as powders or powder coatings, or glycerolacetate-based isolating gels, or primers, e.g., silicon-organic compounds.
B) The undesired transmission of the shrinking forces from the filling material to the adhesive sealant can be further prevented by a reduction of the free radicals at the surface of the radically polymerizing sealant. In a further preferred embodiment, the undesired transmission of the shrinking-forces is therefore prevented by the fact the hardened adhesive sealant b) has a low free radical content and is therefore not apt for co-polymerization.
It is especially preferred that the hardened sealant b) is even unable to undergo homo- and/or co-polymerization. The ability for co-polymerization of the components a), b) and d) can e.g. be affected and weakened by admixing of BisGMA (2,2-Bis[4-(2-hydroxy-3-methacryloxypropoxy)phenyl] propane) bicarbonate (of the Bayer Company) or photo-initiators in higher concentrations, or by coating the sealant b) with an arbitrary air blocker as known to the person skilled in the art before light curing for preventing the build-up of an oxygen-inhibited surface layer.
On the other hand, a reduction of the free radicals at the surface of a radically polymerizing sealant can also be reached by a suitable choice of the monomer systems.
C) In a further preferred embodiment a transmission of shrinking-forces is reduced or diminished by using filling materials d) and adhesive sealants b) of different polarity, notably for suppressing wetting. It is especially preferred to use a hydrophilic or amphiphilic sealant for the dental hard tissue and a strongly hydrophobic filling system. Particularly preferred is thereby a sealant b) being hydrophilic or amphiphilic, whereby the filling material a) is strongly hydrophobic, e.g., Etch and Prime 3.0 or Prime and Bond NT (of the Dentsply company) combined with Adaptic II (Johnson and Johnson) or Pertac (Espe company). Also preferred is a sealant b) being hydrophobic whereas the filling material is strongly hydrophilic, e.g. Visiobond (Espe company) in combination with PhotacFil (Espe company) or Ketac (Espe company) Bond.
D) Especially, if the dental filling material a) is a methacrylated substance, the adhesive sealant b) has a separating effect in respect to the filling material a) due to a different polymerization that does not allow a co- or homo-polymerisation of di- or polyacrylatesystems. This prevents a shrinking-force transmitting bond between the adhesive sealant and the filling material. Preferred sealants for the dental hard tissue are selected from the group comprising water glass, silica ester hydrolysates, polymerizable silane compounds, natural resin varnishes, cyanate based varnishes, epoxide resins, epoxidated soy oil or epoxy-modified silicones. They can preferably be selected as follows:
water glass: e.g. a water glass glue in colloidal solution of potassium or sodium silicate, wherein the setting takes place, e.g. through evaporation of the water share.
silica ester hydrolysates: Through the preparation of partial hydrolysates of silica ester hydrolysates, solid resin coatings can be achieved. The mode of preparation of such a coating could be e.g. vinyltriethoxysilane 12% per weight, silica ester TES (tetraethoxy silane) (Dynamit Nobel) 34% per weight, phosphoric acid 0.3% per weight dissolved in acetone. After the evaporation of the solvent, clear, hard, shining hydrophobic films are formed. The adhesion to substrates such as dentin and enamel can be adjusted by means of metal acetylacetonates.
polymerizable silane compounds: preferably silanes being modified with epoxide- or methacrylate groups. The mentioned reactive silane monomers could contain metal complexes having an affinity to the dentin or the enamel, e.g. compounds with calcium, fluorine or other halides;
epoxy resins: As an example the epoxide-modified vinylester resins, polyester resins, vinyletherresins or bisphenol-A-epoxid resin (Dow Corning) Dercane Oligomer; vectomer-vinylether oligomeres, ISP=vinylether (ISP company), CIBA Araldit types (Ciba-Geigy company); Union Carbide cycloaliphatic epoxides are to be mentioned. Depending on their modification, said raw materials could be polymerized through radical or ionic initiation, thus providing 2-component systems hardening chemically, e.g. following to the preparation comprising the component A: bisphenol-A-epoxy resins (D.E.R. 335 Dow Corning); Cumene hydroperoxide and component B: bisphenol-A-epoxyresin, silane Z-6020 (Dow Corning) and triethanolamine. Correspondingly the formulations that harden upon light exposure are conceivable with light in the visible or ultra-violet range, e.g. following to the preparation Vectomer 2010 urthan oligomer (of the Vectomer company) 45% per weight, monomer 4010 15% per weight, Rapicure CHVE (of the ISP company) monomer 39% by weight (1,4-cyclohexane-dimethanole-divinylether), cationic initiator UVI-6974 1% per weight.
natural resin varnishes: Through hydrophobic natural resin varnishes forming films, dense, hydrophobic coatings could be achieved, e.g. following the preparation of Cophonium 12% per weight, Shellac 25% per weight, gum arabic 8% per weight, Cellulose 5% per weight and Alkohol DAB (Deutsches Arzneibuch) to make 100%.
epoxidated soy oils: They are cross-linkable through cationic or radical initiation, e.g. Henkel Edenol types; further examples for reactive oligomers are cyracure oligomeres (Union Carbide), cycloaliphatic epoxide resins like UVR 61110 (Dow Corning), i.e. 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane-carboxylate, or UVR 6128 (Dow Corning), i.e. bis-(3,4 epoxycyclohexyl-adipate or UVR 6216 (Dow Corning), i.e. 1,2-epoxyhexadecane.
methacrylic or epoxy-modified silicones (e.g. of Goldschmidt, Wacker, Mitsubishi) as well as methacryl-modified gelatines and cellulose esters also display good film forming properties: they could also serve as film-forming carrier materials for a variety of active agent, like fluorides or antiseptic or bactericidal additives. The desired separation effect is notably achieved by employing 2 different synthesis forms. Said process could be achieved through different cross-linkage mechanisms, like the chemical hardening, the light-induced hardening, the radical- or cationic induced hardening, cross-linking through radical condensation etc.
The filling materials a) comprise plastics, composites, compomers, ormaceres, ceromers, polyglasses, glass ionomer cements, carboxylate cement, phosphate cement, EBA (ethoxybenzoic acid) cement (ESPE company) or guttapercha, or materials consisting thereof. These materials are preferably photo curing, chemically curing, dually curing, heat curing or thermoplastic.
The above mentioned compounds are commercially available and are generally known by persons skilled in the art.
The sealants b) for the dental hard tissue exhibit a good bond with the dental hard tissues. They form a leakage-free and gap-free, closed, mechanically and chemically resistive protective layer and, if possible, release (as a xe2x80x9csmart materialxe2x80x9d) caries protective agents, i.e. they release plaque-suppressing or caries-protective agents permanently or upon request, such as fluorides, chlorhexidine, triclosan, calcium or hydoxyl-ions. Preferably used sealants for the dental hard tissue are photo hardening, chemically hardening, dually curing, heat curing or thermoplastic or they cure using the principles of contact glues.
In a highly preferred embodiment the dental filling material a) is photo hardening (i.e. hardening upon exposure to light of a suitable wave-length) and the sealant b) for the dental hard tissue is chemically hardening.
In another preferred embodiment the dental filling material a) is chemically curing and the sealant b) for dental hard tissue is photo curing.
The adhesive sealant b) can further also be used as a base material, as a proximal sealant or as a fissure sealant.
Using the filling system presented here, it is possible to prepare fillings that are metal free and preferably tooth colored with a required simple, economical operative technique corresponding to the general skill of the dentist. Such filling systems are true amalgam substitutes because they not only restore the tooth""s shape and function but also protect the same against caries and erosion. Analogously, such systems can also be used for root fillings.
A further aspect of the present invention is a method for filling therapy of cavities or root canals by using one of the dental filling systems described above.

Metal-free dental filling system as a substitute for amalgam


A needle printing head comprising a support (11) able to axially guide a plurality of printing needles (15), each of which has one end attached to a mobile armature (16) of a corresponding actuation electromagnet (17) having a ferromagnetic core (18) provided with polar extensions. A separation element (30) is interposed between the mobile armatures (16) and the corresponding polar extensions. The separation element (30) is made of a metal material and comprises elements (33, 34) able to reduce the effects of the eddy currents which are generated by the energizing of every electromagnet (17).

The invention concerns a needle printing head comprising a plurality of electromagnetic actuators arranged in a circular crown, each one associated with a printing needle able to move axially to transfer, by impact, a particular quantity of ink from an inking element to a print support, such as a sheet of paper, a print-out or suchlike. The printing head is able to move serially along the line of writing to compose, in successive dots, any character or number, graphic symbol, code or image, either in black and white or in color, according to information arriving from a computerized control unit.
The state of the art includes impact printers which, as a printing device, use a head comprising a plurality of needles with one end able to cooperate with an inking element, normally consisting of a ribbon, and the other end connected to the mobile armature of an electromagnetic actuator.
By selectively energizing the individual electromagnets, the needles are displaced axially so that, by means of the inking element, they impress a programmed combination of dots onto the print support according to a pre-defined matrix; the print support can consist of a sheet or printout, made of paper, plastic material or other suitable material.
A printing head with needles is described in the European patent application EP-A-0.622.213.
The printing speed which can be obtained with a needle head is very high, in the range of 1,000-1,500 characters per second (cps), when sketch mode in used, and 200 cps when high definition/high quality writing mode is used; the speed is strictly connected to the actuation cycle of each electromagnet and more particularly to the movement of the mobile armature. The frequency of energizing of the electromagnets is in the range of 3000-3600 Hz.
With frequencies like this, one of the biggest problems in designing printing heads with needles is the reduction of the eddy currents (or Foucault currents) which are generated every time at least one of the coils of the electromagnets is energized.
Maxwell""s equation, which describes the distribution of the electromagnetic field, is as follows:
rot J=xe2x88x921/xcfx81dB/dt
given that:
J=current density
B=magnetic induction
xcfx81=resistivity that is, a relationship is established between a phenomenon of magnetic induction, which can vary in time, and the density of a current circulating in a conductor means.
The losses due to the Joule effect can be described by the following equation:
Pj=∫vxcfx81J2dV
On the contrary the losses due to eddy currents are proportional, in a first approximation, to the second power of the peak induction B, the second power of the thickness of the material affected d, the second power of the functioning frequency f. In the state of the art, the following expression is empirically adopted:
Pw≈K*f2*B2*d2
The coefficient K is specific to the material.
To reduce losses due to eddy currents, when there are variable magnetic fields, high resistivity materials (Fexe2x80x94Si etc.) are used, laminated materials, sintered materials (ferrites etc.) in the magnetic circuits or, where a magnetic material is not required, insulating material is used.
In the case of printing heads with needles, the separation element is located in the ferromagnetic gap of the main magnetic circuit, therefore the variation in the induction of the magnetic field is at the maximum value and, as a consequence, also the eddy currents are very high.
It is well-known that, to prevent the eddy currents from interacting with the armatures of the command electromagnets, a sheet of insulating plastic material, such as Mylar, Kapton or similar, with a thickness of some hundredths of a millimetre, is inserted as a separation element between the polar expansions and the mobile armatures.
This sheet of plastic material, which is easily subject to wear, especially in the points at which the mobile armatures pivot on the corresponding fixed polar expansions of the electromagnets, considerably reduces the duration, that is the life, of the printing head.
Moreover, another disadvantage of conventional printing heads, which use the sheet of plastic material, is that the frequency of energizing the electromagnets must necessarily be limited, to prevent the head from overheating too much and from reaching temperatures of around 100xc2x0 C., which could at least deform, if not melt, the sheet of plastic material.
From the EP-A-0.364.800 it is known a needle printing head wherein a multilayer element is interposed between the permanent magnet poles of the electromagnets and the armatures thereof. Such multilayer element comprises two thin sheets of magnetic steel between which a thin film of resilient material, such as polyester, is interposed. The sole scope of this multilayer element is to absorb the damping action of the armatures.
From the JP-A-11-320929 it is known a wire dot printer head wherein a film made of non-magnetic material is disposed between the movable armatures and the static electromagnetic core. In this embodiment the film of non-magnetic material is used firstly to prevent the abrasion of the fulcrum section of the movable armatures and secondly to reduce an influence caused by the residual magnetism generated between the core and the armature.
U.S. Pat. No. 4,396,304 discloses a wire printing apparatus wherein a non-magnetic member is provided, the member having a projecting ear corresponding to each coil position within a printing head, each ear being interposed between the ends of the yoke assemblies and the associated armature to provide a conventional residual non-magnetic gap spacer against which the armature bears in the closed position.
From the U.S. Pat. No. 4,561,790 it is known a wire matrix print head apparatus wherein a residual magnetism interrupter constituted by a thin non-magnetic or dielectric plastic material is disposed to separate the armatures from direct physical contact with the central electromagnetic cores of the actuation windings. Such residual magnetism interrupter has only the scope to prevent slight magnetism in the armatures from retarding the return thereof.
From the U.S. Pat. No. 5,209,585 it is known a print head for a dot matrix printer wherein a residual sheet, made of non-magnetic material, such as ferroalloy, is attached to the electromagnetic core. Such residual sheet has a minimum thickness necessary for preventing the plunger of the armatures from sticking to the core and for preventing the end portion of the armature from floating from the yoke even if the armature is deflected when the latter strikes a center ring of non-magnetic material.
None at all of the above-mentioned documents shows or suggests a needle or wire printing head provided with means able to prevent that the eddy currents have a negative influence on the actuation elements of the printing needles.
The invention is set forth and characterized in the main claim, while the secondary claims describe other innovative characteristics of the invention.
The main purpose of the invention is to achieve a printing head with needles which has a high energy yield, wherein the eddy currents do not have a negative influence on the actuation elements of the printing needles.
At the same time the printing head according to the invention must be able to improve performance in terms of functioning frequency, number of copies which can be printed and overall quantity of characters printed during its life, compared with printing heads which are on the market today, that is to say, more than 400-700 million characters or numbers.
In accordance with said purposes, the printing head according to the invention comprises a thin foil of metal material, suitably shaped, interposed between the mobile armatures and the polar expansions of the actuation electromagnets.
A generic metal separation element, however, without adequate means able to prevent the propagation of the eddy currents, would provide a performance inferior to the equivalent non-conductor and therefore would be practically unusable (high eddy currents downgrade the performance in terms of functioning frequency and repeatability of positioning of the print dots).
The technique used to drastically reduce the eddy currents consists of achieving a geometric conformation of the metal foil able to reduce the area affected by the eddy currents, that is, to increase the resistivity of the electric circuit affected by them. According to a preferential embodiment, a plurality of notches is made on the metal foil, in correspondence with the polar expansions of the actuation electromagnets.
The invention is able to guarantee, with regard to the physical and functioning aspects of the printing head, at least the following advantages:
a) an adequate ferromagnetic gap between the polar expansions of the electromagnets is provided;
b) the impact between the mobile armatures and the fixed ferromagnetic cores of the electromagnets is absorbed;
c) a reliable, wear-resistant and long-lasting fulcrum point is provided;
d) the eddy currents generated by the variation in the magnetic field are drastically reduced; and
e) it functions even at high temperatures (more than 100xc2x0 C.).
Using a metal separation element, with techniques to reduce the eddy currents, allows to improve the following features:
Energy yield (eddy currents have no function with regard to the printing);
Performance in terms of pages printed per hour (reduction in the heat generated by the eddy currents and therefore the device has a lower temperature);
Frequency performance (eddy currents introduce a delay in the movement of the armature).
An increase in the average life of the printing head, compared with those using a sheet of plastic material, is obtained because the metal material used as a separation element suffers practically no wear over time at the fulcrum point, so that the working life of the printing head in its entirety is no longer a function of the life of the material used as a separation element, which was the weak link in the chain.


An electric machine, includes a stator with a laminated stator body having winding end portions potted in a cast, and a rotor for interaction with the stator. In order to cope with the increased heat development in the zone of the winding end portions compared to the zone of the stator body, the cast of the winding end portions is formed with surface-enlarging structures in heat-conducting contact with a cooling jacket or with a cooling medium, and/or the cast is provided at least partially with a heat-conducting envelope which carries off heat.

This application claims the priority of German Patent Application, Serial No. 10114321.4, filed Mar. 23, 2001, the subject matter of which is incorporated herein by reference.
The present invention relates to an electric machine of a type having a stator with laminated stator body, rotor and potted winding end portions.
European Pat. No. EP 0 915 554 A2 describes an electric motor which includes a stator without housing and with a laminated stator body of rotation-symmetric configuration. The stator body has cooling slots which are located on the slot-distal side of the stator body and receive cooling conduits for conduction of a cooling medium. Winding end portions axially extend out of the stator, whereby a heat-conducting plastic material connects the cooling conduits with the stator body and the winding end portions.
This electric motor suffers shortcomings because the cooling conduits are connected with the winding end portions by a heat-conducting plastic casting material in a single operation. This has to be taken into account during fabrication. Before casting, the cooling conduits may be slightly damaged. Furthermore, the cooling device is used for cooling the laminated stator body as well as for the winding end portions. This lack of discrimination is disadvantageous because it fails to take into account the desired increased need for heat dissipation in the area of the winding end portions.
It would therefore be desirable and advantageous to provide an improved electric machine to obviate prior art shortcomings and to enhance a cooling of the winding end portions while yet simplifying fabrication.
According to one aspect of the present invention, an electric machine, includes a stator with a laminated stator body having winding end portions encased in a casting material that forms a cast, a rotor for interaction with the stator, and an arrangement for carrying away heat generated by the electric machine, with the arrangement including surface-enlarging structures formed on the surface of the cast and/or a heat-conducting envelope which is, at least partially, provided upon the cast.
Surface-enlarging structures in the cast material of the winding end portions enhance a cooling of the winding end portions and improve the heat dissipation. This is realized through passive cooling by means of convection and/or active cooling by means of gaseous or liquid cooling media, which carry off heat though their volume flow. In addition, enclosing the cast for the winding end portion with a heat-conducting envelope can further enhance cooling of the winding end portion.
Further advantageous configurations for providing an improved cooling of the winding end portion through a heat-conducting encasement may be realized through combination of surface-enlarging structures with a heat-conducting envelope of winding end portions. Heat-conducting envelopes of potted winding end portions bear at least partially upon the casting material. The heat-conducting envelope is made of a highly heat-conducting material which, unlike the heat-conducting casting material, may also be electrically conducting. Examples of highly heat-conducting material include in particular metals, such as copper, aluminum or iron, or metal alloys.
Heat-conducting envelopes are capable to direct heat from regions that are difficult to reach by active coolants, such as gases and/or liquid, to regions that are more accessible. For example, heat can be carried away from the zone of the inner radius area of the potted winding end portion or also from the region at the end face of the potted winding end portions. Establishing a contact of the envelope with a cooling fluid can optimize heat dissipation by means of a heat-conducting envelope. With air-cooling, the heat dissipation is suitably implemented by a combination of cooling air stream and cooling body. In the event, cooling with liquid is desired, the heat-conducting envelope should have contact with a liquid-cooled body.
Surface-enlarging structures should be so configured as to allow the fabrication of a negative mold as well as a positive moldxe2x80x94negative impression and positive impressionxe2x80x94that can easily be fabricated. Preferred are wavy, triangular, pyramid-like structures or combinations thereof. Mold design requirements should hereby be taken into account.
Suitably, the electric machine is provided with laminated stator body, rotor, potted winding end portions formed by conductors, and casting material with cooling channels for conduction of a coolant, whereby the cooling medium absorbs heat from the winding end portions, with the heat being carried away across surface-enlarging structures of the cast. The surface-enlarging structures may be of the macroscopic type as well as microscopic type. Crucial is only the heat-conducting contact area. In the event, cooling channels are disposed in a cooling jacket or in cooling slots of a laminated stator body, a surface-enlarging structure may be implemented by the cooling jacket itself or by the material which forms the cooling slots.
According to another feature of the present invention, the overall cooling system is so configured as to provide a higher degree of cooling of the winding end portions compared to the cooling of the stator body. Such a targeted or discriminating cooling action takes into account different temperature development in the winding end portions, i.e. in the zone, of the winding end portions, and in the zone of the stator body. In particular, when highly exploited indirect water-cooled machines are involved, the temperature at the winding end portions is substantially higher than the temperature in the stator body, thereby forming the basis for the recognition to provide a better cooling action in the area of the winding end portions. An enhanced cooling action may be realized through denser, i.e. closer, arrangement of cooling channels. Moreover, the cooling channels may not only be arranged two-dimensional in a plane in side-by-side disposition but can also be arranged three-dimensional in staggered disposition. As a consequence of the increased cooling action in the area of the winding end portions, an uneven heat distribution is offset and the motor can be better exploited according to the thermal classes. Example of cooling systems include air cooling, liquid cooling or gas cooling, which can each be suited to the requirements at hand.
Another feature of the present invention involves the utilization of heat-conducting envelopes for heat transport and improved cooling of the winding end portions. Heat-conducting envelopes of potted winding end portions bear at least partially upon the cast, and may be made of a highly heat-conducting material, which unlike the heat-conducting casting material may also be electrically conducting. Examples include in particular metals, such as copper, aluminum or iron, or metal alloys.
Heat-conducting envelopes are capable to guide heat from regions that are difficult to reach by active coolants, such as gases and/or liquid, to regions that are more accessible. For example, heat can be carried away from the zone of the inner radius area of the potted winding end portion or also from the region at the end face of the potted winding end portions. The heat conduction is routed to conventional cooling devices such as air-cooling or liquid cooling.
The heat transport by means of a heat-conducting envelope can be optimized through contact of the envelope with a cooling assembly. Examples of a cooling assembly include the cooling jacket or the formed part having the cooling slots in which the cooling channels, e.g. cooling conduits, are incorporated.
Just as the cast for encasing the winding end portions may have surface-enlarging structures, it is also conceivable to provide the heat-conducting envelope with surface-enlarging structures. The configuration of such surface-enlarging structures can be best suited to the type and scope of the cooling action and in particular can be shaped in dependence on the desired cooling action. In particular, when active cooling is involved, e.g., cooling air flow or cooling water, the heat-conducting envelope may be formed with surface-enlarging structures such as wavy profiles, wedged profiles or combinations thereof.
When taking into account the different heat fluxes to be carried away, the components for conducting the heat flow may have a cross section that is sized in dependence with the magnitude of the heat flow to be carried off. In the event, a heat-conducting envelope is routed across the inner radius of the casting material and contacts the end face of the cast, the heat flow to be carried off is increased.
Suitably, the heat flow to be carried off is guided in the enlarged cross section of the components to a cooling assembly. As a consequence of the greater cross sectional area, a greater contact area can be established with an active component of the cooling system or active component for cooling, such as a cooling jacket.

Electric machine with improved cooling feature