Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41M—PRINTING, DUPLICATING, MARKING, OR COPYING PROCESSES; COLOUR PRINTING
  • B41M5/00—Duplicating or marking methods; Sheet materials for use therein
  • B41M5/26—Thermography ; Marking by high energetic means, e.g. laser otherwise than by burning, and characterised by the material used
  • B41M5/40—Thermography ; Marking by high energetic means, e.g. laser otherwise than by burning, and characterised by the material used characterised by the base backcoat, intermediate, or covering layers, e.g. for thermal transfer dye-donor or dye-receiver sheets; Heat, radiation filtering or absorbing means or layers; combined with other image registration layers or compositions; Special originals for reproduction by thermography
  • B41M5/42—Intermediate, backcoat, or covering layers
  • B41M5/44—Intermediate, backcoat, or covering layers characterised by the macromolecular compounds
  • B41M5/443—Silicon-containing polymers, e.g. silicones, siloxanes
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41M—PRINTING, DUPLICATING, MARKING, OR COPYING PROCESSES; COLOUR PRINTING
  • B41M5/00—Duplicating or marking methods; Sheet materials for use therein
  • B41M5/26—Thermography ; Marking by high energetic means, e.g. laser otherwise than by burning, and characterised by the material used
  • B41M5/40—Thermography ; Marking by high energetic means, e.g. laser otherwise than by burning, and characterised by the material used characterised by the base backcoat, intermediate, or covering layers, e.g. for thermal transfer dye-donor or dye-receiver sheets; Heat, radiation filtering or absorbing means or layers; combined with other image registration layers or compositions; Special originals for reproduction by thermography
  • B41M5/42—Intermediate, backcoat, or covering layers
  • B41M5/426—Intermediate, backcoat, or covering layers characterised by inorganic compounds, e.g. metals, metal salts, metal complexes

Definitions

• This invention relates to thermally imageable films, and to a release coating for such films.
• Infrared imaging is a form of thermal imaging that involves the use of a focused infrared lamp to heat an infrared absorbing image, commonly referred to as the "original", which image is in contact with a substrate, e.g., a transparent polymeric film, having thermally sensitive imaging chemicals applied to a major surface thereof.
• a substrate e.g., a transparent polymeric film
• thermally sensitive imaging chemicals applied to a major surface thereof.
• projection transparencies e.g. transparencies for overhead projectors
• the electrostatic latent image on such a plain paper copy is developed by the application and fixing of toner powder to the plain paper copy.
• Toner powder is generally a blend of polymer having low melting point, and carbon.
• toner powder from the original is likely to be removed from said original and simultaneously transferred to the surface of the thus-formed projection transparency.
• This transfer of toner powder reduces the optical density of the image on the original and may, in effect, destroy the quality of the image.
• the original can be damaged when a projection transparency is made from it.
• the adherence of the toner powder to the projection transparency may also result in undesirable effects on the surface of the transparency itself.
• the image formed on the surface of the transparency is black, the toner powder does not harm the image itself, but the powder may be rubbed off the transparency and transfer to surfaces which subsequently come in contact with the transparency.
• the toner powder can cause the colored image to have irregular black spots in the colored image area.
• a barrier film interposed between the imageable layer of the transparency and the original can prevent toner power from being picked up and retained by the transparency.
• a film containing an acid does serve as such a barrier.
• U.S. Patent No. 3,955,035 discloses a trialkoxy silane coating which imparts abrasion resistance, hardness, and release properties to plastics. This coating, however, is brittle and will crack if applied to a flexible polyester substrate of the type commonly used for preparing transparencies. Clark, U.S. Patent No. 3,986,997 discloses a coating formed from a dispersion of colloidal silica in a condensate of methyl trihydroxy silane. This coating is also brittle, and, thus, it is unsuitable for flexible sheeting. Baney, et al, U.S. Patent No. 4,223,072 discloses a coating formed of phenyl trihydroxy silane.
• Patent 3,936,581 discloses a release coating containing vinyl siloxanes in mixture with alkyl hydrogen siloxanes and a platinum catalyst.
• the optimum cure temperatures are in excess of 100°C, a temperature which would bring about premature reaction of the temperature sensitive coatings of infrared imageable films.
• This invention involves a film suitable for thermal imaging which comprises (1) a substrate formed from a flexible material, (2) a layer of thermally imageable material applied to at least one major surface of the substrate, and (3) a cured organopolysiloxane release coating overlying the layer of imageable material.
• the release coating is a cured silicone polymer prepared from a composition comprising (1) at least one curable polysiloxane or epoxypolysiloxane, and (2) a catalyst.
• the preferred release coating is prepared from a composition comprising (1) a curable polysiloxane, (2) a catalyst, (3) a cross-linking agent, (4) a fast-cure additive, and (5) an anchorage additive.
• the release coating composition can be applied to the imaging film by conventional means and cured at temperatures sufficiently low so as to prevent adverse effects upon the layer of imageable material.
• the release coating is also sufficiently permeable so as to allow moisture to escape from the imageable layer, thereby reducing the "halo" effect.
• the coating is sufficiently flexible so that the film bearing it can be imaged in commercially available infrared copying machines, e.g., 3M Model 45 infrared copier. Toner powder from plain paper copies will not stick to this coating when the imaging film is processed in a conventional thermal imaging apparatus, e.g., an infrared copier.
• the type of film contemplated for use in the present invention is any imaging film which can be imaged by being exposed to thermal energy, e.g. infrared radiation, while in surface-to-surface contact with an original.
• thermal energy e.g. infrared radiation
• thermally imageable film contemplated for use in the present invention is described in Isbrandt, et al, U.S. Patent Application 352,053, filed February 24, 1982, incorporated herein by reference.
• This film can be imaged by means of infrared radiation.
• This film comprises a polymeric film substrate transparent to visible light, bearing an imageable layer on at least one surface thereof.
• Substrate materials which are suitable for this invention include polycarbonates, polyesters, polyacrylates, polystyrene, and polypropylene.
• a preferred substrate is polyvinylidene chloride primed polyester film.
• the preferred polyester is polyethylene terephthalate.
• the imageable layer comprises a nitrate salt, e.g., nickel nitrate, at least one leuco dye, e.g., 3,7-di(N,N-diethylamino)10-benzoyl phenoxazine, and a binder, e.g., cellulose acetate butyrate, one or more aromatic compounds which form quinones, diimines, or quinonimes upon oxidation, e.g., catechol, and I-phenyl-3-pyrazolidinone or derivatives thereof.
• the layer can also contain a material which supplies hydrogen ions, e.g., an acidic material such as phthalic acid. Upon the application of a sufficient amount of thermal energy, the nitrate salt will oxidize the leuco dye, resulting in a change in color.
• thermally imageable films that are suitable for use in the present invention are described in Owen, U.S. Patent No. 2,910,277; Grant, U.S. Patent No. 3,080,254; and Newman et al, U.S. Patent No. 3,682,684, all of which are incorporated herein by reference.
• Owen describes a heat-sensitive chemically reactive copy-sheet comprising a thin flexible carrier web coated with a visibly heat-sensitive coating comprising (1) a film-forming binder, (2) a noble metal salt of an organic acid, and (3) a cyclic organic reducing agent for the noble metal ions, having an active hydrogen atom attached to an atom which is selected from the class of oxygen, nitrogen and carbon atoms and is directly attached to an atom of the cyclic ring.
• Grant describes a heat-sensitive copy sheet comprising the same ingredients as contained in Owen and further including a sufficient amount of phthalazine to cause observable darkening of the thermographic image.
• the preferred film-forming binder is polystyrene resin
• the preferred noble metal salts of organic acid are silver behenate and silver stearate
• the preferred reducing agents are 3,4-dihydroxybenzoic acid and methyl gallate.
• Newman et al describes a heat-sensitive sheet material including a thin visibly heat-sensitive layer having wide exposure latitude and comprising a mixture of ferric and silver soaps of long chain fatty acids, a toner for the silver image, and a phenolic co-reactant for the soaps.
• ferric and silver soap mixture is forric stearate and silver behenate.
• An example of a toner is phthalazinone, and examples of phenolic co-reactants for the soaps are pyrogallic acid, catechol, 3,4-dihydroxybenzoic acid, methyl gallate, and behenoyl pyrogallol.
• compositions for preparing the organopolysiloxane coatings suitable for the present invention must be curable at temperatures under 70°C with an exposure time of under 3 minutes. Longer cure times or higher curing temperatures or both would be detrimental to the imaging chemistry of the thermal imaging system.
• Organopolysiloxanes suitable for the present invention include hydroxy-terminated or alkoxy-terminated polyalkylsiloxanes, for example, organopolysiloxane obtained by curing a mixture of siloxanes consisting essentially of from .1 to 3% by weight of methylhydrogenpolysiloxane and from 97 to 99.9% by weight of a siloxane of the formula in which x has a value from 1.9 to 2 inclusive and in which siloxane substantially all of the molecules have attached thereto at least a total of two silicon-bonded hydroxyl groups and/or alkoxy groups of less than 5 carbon atoms, as described in U.S. Patent No.
• organopolysiloxanes of the type disclosed in U.S. Patent No. 3,061,567 can be prepared from compositions comprising (1) a silicone resin, (2) a catalyst, (3) a cross-linking agent, and, optionally, a fast-cure additive, and an anchorage additive.
• a commercially available silicone resin which has been found to be useful for this invention is Syl-off O 294 which is available from Dow Corning Corporation.
• Catalysts are desirable for reducing the time required and heat input necessary to cure the aforementioned silicone resins.
• Catalysts useful in the practice of this invention include dialkyltin salts, wherein the alkyl groups contain from 1 to 6 carbon atoms.
• Catalysts that are preferred are represented by the following general formula: wherein R is -CH(C 2 H 5 )(CH 2 ) 3 CH 3 , -CH 3 , or -(CH 2 ) 10 CH 3 .
• Cross-linking agents can advantageously be employed for promoting cure.
• Cross-linking agents suitable for the aforementioned silicone resins include orthosilicates, for example, tetramethoxyethoxyethylsilicate.
• Dow Corning® C4-2117 available from Dow Corning Corporation, tetraethoxysilane, available from Alfa Products, tetrapropoxysilane, available from PCR Research Chemicals.
• Dow Carning® C4-2117 has the following formula:
• An anchorage additive can also be added to the silicone resin-containing composition to improve the adhesion of the coating to the substrate.
• a commercially available anchorage additive is Syl-off O 297, available from Dow Corning Corporation. This additive also is useful for increasing the pot life of the catalyzed coating composition formulation.
• Other pot-life extenders include anhydrous alcohols, ketones, and acetic acid. Representative examples of anhydrous alcohols are methanol, ethanol, and isopropanol. Representative examples of ketones are methyl ethyl ketone and methyl isopropyl ketone.
• the concentration of each ingredient can vary, the particular amount of each depending upon the combination of properties needed, as explained hereinafter.
• the resin be dissolved in an aliphatic or aromatic solvent, such as, for example, heptane, VM & P naphtha, toluene, and blends of toluene and heptane.
• an aliphatic or aromatic solvent such as, for example, heptane, VM & P naphtha, toluene, and blends of toluene and heptane.
• Some surfaces such as polyethylene may call for high levels of aliphatic solvents to obtain uniform wetting.
• the coating composition formulation hereinafter alternatively referred to as coating bath, contain from 2 to 10 percent by weight silicone.
• the level of catalyst can vary, depending upon the curing temperature and time desired.
• the concentration of catalyst be from 10 to 30 percent by weight, more preferably 10 to 18 percent by weight, based on weight of silicone solids; when Dow Corning° XY-176 catalyst is used with Syl-off® 294 resin, it is preferred that 5 to 15 percent by weight catalyst, based on weight of silicone solids, be employed.
• Dow Corning@ C4-2117 fast cure additive can be used at a level of 5 to 20 percent by weight, preferably 8 to 17 percent by weight, based on weight of silicone solids.
• Dow Corning® C4-2117 fast cure additive either 3 to 8 percent by weight, based on weight of silicone solids, of Syl-off O 297 anchorage additive or 1 to 5 percent by weight anhydrous alcohol, based on weight of total coating solution, should be used as a potlife extender.
• the ingredients for preparing the curable silicone polymer composition can be combined by introducing them into a vessel, and mixing them by any suitable method, such as, for example, stirring. Because of possible too rapid reaction of fast-cure additive, e.g. Dow Corning® C4-2117, with catalyst, e.g. Dow Corning® XY-176, the fast-cure additive should be added and mixed well before addition of catalyst.
• fast-cure additive e.g. Dow Corning® C4-2117
• catalyst e.g. Dow Corning® XY-176
• the composition can be applied to the surface of the imaging film by any of the techniques known in the art, such as, for example, knife coating, Mayer rod coating, curtain coating, extrusion bar coating, and rotogravure coating.
• the composition is coated over the surface of the film bearing the imageable layer formulation, thus acting as a top coat.
• the composition is preferably applied to the surface of the imaging film by coating from an organic solvent.
• solventless coating is an acceptable method when using the squeeze roll coating technique.
• Catalyst and cross-linking agents are critical in that proper selection thereof will permit coating by means of efficient methods, such as, for example rotogravure and reverse roll.
• Phthalic acid and catechol present in the imaging chemistry tend to inhibit the cure of the release coating. Generally, a long dry time for the imaging chemistry allows for adequate cure, but a short dry time for that layer reduces the likelihood of adequate cure.
• the additives employed with the formulation for preparing the release coating help to promote a faster cure and improved anchorage.
• Epoxysiloxane polymers of the type disclosed in U.S. Patent No. 4,313,988 are represented by the formula, wherein R 2 is a lower alkyl group of one to three carbon atoms, R 3 is a monovalent hydrocarbon radical of 4 to 20 carbon atoms, E is a monovalent epoxy-containing hydrocarbon radical, M is a silyl group R 2 Si ⁇ , R 2 R 3 Si or R 2 ESi ⁇ , where R 2 , R 3 , and E are defined above, a is 5 to 200, b is 0 or up to 20% of a, a+b is 5 to 200, c may be 0 when M is R2ESi- or greater than 0 but less than 20% of the value of a (a+b) when M is R 2 Si ⁇ , R2R3Si- or R 2 ESi ⁇ , and n is 1 to 75.
• the preferred R group is methyl
• the preferred M group is R 2 ESi ⁇ when c is 0, and R 2 Si ⁇ when c is greater than 0.
• n is 1 to 5, and preferably n is 1 or 2.
• the preferred b is 0.
• R 3 in the above formula are alkyl radicals such as butyl, isobutyl, tert-butyl, hexyl, octyl and octadecyl; aryl radicals such as phenyl, naphthyl and bisphenylyl; alkaryl radicals such as tolyl and xylyl; aralkyl radicals such as phenylmethyl, phenylpropyl and phenylhexyl; and cycloaliphatic radicals such as cyclopentyl, cyclohexyl and 3-cyclohexylpropyl; and ether oxygen- or ester oxygen-containing radicals such as ethoxypropyl, butoxybutyl, and ethoxycarbonylpropyl and the like.
• the preferred R 3 is alkyl of 4-8 carbon atoms.
• the epoxy group is preferably located at the terminal position of the radical, but it need not be a terminal group.
• Epoxy-terminated silanes can be used optionally with the epoxypolysiloxanes in the coating formulation of this invention. Use of such epoxy-terminated silanes enables the release performance of the coating to be varied.
• These epoxy-terminated silanes are compounds or materials having polymerizable epoxy group(s) and a polymerizable silane group, the bridging of these groups being through a non-hydrolyzable aliphatic, aromatic or aromatic and aliphatic divalent hydrocarbon linkage which may contain ether or carbonyl oxygen linking groups.
• the epoxy-terminated silane is represented by the formula, wherein E is an epoxy-containing monovalent hydrocarbon radical defined above, p is 1 to 3 (preferably 3) and R 4 can be an aliphatic hydrocarbon radical of less than 10 carbon atoms such as alkyl (methyl, ethyl, isopropyl, butyl), an alkenyl such a allyl or vinyl, or an acyl radical such as formyl, acetyl, or propionyl. Because of availability and performance, the preferred R 4 is a lower alkyl such as methyl or ethyl. Many illustrative examples are described in U.S. Patent No. 4,049,861.
• any hydrolyzate of the above silanes can be used.
• the hydrolyzate is formed by partial or complete hydrolysis of the silane OR 4 groups as described further in U.S. Patent No. 4,049,861.
• the amount of the epoxy-terminated silane or hydrolyzate can range from 0 to about 98% of the epoxypolysiloxane used, the amount being determined by the release performance desired. Generally, the higher amounts give the higher release values.
• Curing of the epoxypolysiloxane-containing compositions of this invention can be effected by mixing with conventional epoxy curing catalysts and may additionally require heat or radiation.
• epoxy curing catalysts are tertiary amines, Lewis acids and their complexes, such as BF 3 and complexes with ethers and amines; antimony halide-phosphorus containing ester complexes, such as with organophosphonates, mentioned below; polyaromatic iodonium and sulfonium complex salts (e.g., having SbF 6 , SbF 5 OH, PF 6 , BF 4 , or AsF 6 anions, as disclosed in U .S. Patent No.
• the epoxypolysiloxane, catalyst, and optionally, the epoxy-terminated silane are mixed in a solvent or, where possible, without solvent.
• the amount of catalyst used is about 1. to 5% by weight of the epoxy composition.
• the resultant material is coated on the imageable layer and cured at ambient temperatures or, where necessary, heated to bring about cure.
• Solvents which can be used include ethyl acetate, isopropyl acetate, acetone, methyl ethyl ketone, heptane, toluene, and mixtures thereof. The exact coating technique is not especially critical and any-of several well known procedures can be used.
• Wirewound rods such as a Mayer bar, or a rotogravure applicator roll having, for example, 80 lines per in, provide uniform coatings.
• a mixing spray nozzle having a line for the epoxypolysiloxane fluid or solution and a separate line for the catalyst solution cnn be used.
• the coating thickness of the organopolysiloxane release coating can be controlled to obtain optimum performance. Coating weights in excess of 2.1 g/m 2 tend to become soft and to deform upon exposure to heat. This deformation can lead to irregularities in image areas, resulting in light scattering, which in turn can produce dark spots in the projected image.
• the preferred range of coating weight is from about 0.108 g/m 2 to about 1.076 g/m 2 . The most preferred range is from about 0.108 g/m 2 to about 0.538 g/m 2 .
• a barrier coat must be interposed between the layer bearing the imaging chemicals and the release coating in order to permit the release coating to cure.
• An examples of a suitable substance for barrier coats is chlorinated polyisoprene (e.g., Parlon® S-20, commercially available from Hercules, Inc.).
• the composition of this invention is superior to those in conventional use for the following reasons:
• the imaging film of the present invention is also quite useful in thermal printing devices, such as the Hewlett-Packard 9800 series.
• the thermal print heads are extremely hot, e.g., greater than 100°C, and they have a tendency of picking off the thermally imageable materials from the substrate, resulting in fouled print heads.
• the cohesive strength of the coating combined with its low coefficient of friction, render it useful for separating the print head from the thermally imageable materials.
• a composition for preparing a silicone polymer release coating was prepared from a formulation containing the following ingredients in the amounts indicated: The composition was coated over the imageable layer of a sheet of transparent infrared imageable film by means of knife coating. The wet coating thickness was 2 mils (50.8 m). The coating was dried at a temperature of 140°F (60°C) for 3 minutes.
• the transparent infrared imageable film was 4 mil (100 m) thick polyethylene terephthalate sheet bearing on one major surface thereof an imageable layer coated from a formulation containing the following ingredients in the amounts indicated: Prior to coating, the above formulation was scaled-up 1500X and rotogravure coated with a 79.4 lines/in. knurl at 125 ft/min, with an oven dwell time of 68 seconds at a temperature of 180°F (82°C).
• Untreated infrared imageable film i.e., film not having a release coating
• the toner which adheres to the untreated film will block light and thereby raise the transmission optical density readings.
• Untreated imageable film and treated imageable film should give the same optical density readings when the image is prepared from a printed original, i.e. an original having no removable toner, assuming that the films are selected from the same lot. This was indeed true (See Sample A, Table I).
• a transparency prepared from a toned original and an infrared imageable film treated with an effective toner release coating should exhibit a lower optical density reading than a transparency prepared from a toned original and an untreated infrared imageable film from the same lot, solely due to the absence of adhering toner material on the treated film. This was shown to be true in Samples B, C, D, and E of Table I. Furthermore, because toner deposition on the untreated film was not uniform, the standard deviation of the average image density readings was greater for the untreated films than for the treated films. (See Samples B, C, D, and E of Table I). In contrast, standard deviations calculated for transparencies prepared from printed originals were approximately the same for both treated and untreated films (See Sample A, Table 1).
• a composition for preparing an epoxysiloxane release coating was prepared from a formulation containing the following ingredients in the amounts indicated: The composition was coated over the imageable layer of a sheet of infrared imageable film by means of knife coating. The wet coating thickness was 2 mils (50.8 m). The coating was dried at a temperature of 150°F (66°C) for 1-1/2 minutes.
• the transparent thermally imageable film was 4 mil (0.102 mm) thick polyethylene terephthalate sheet bearing on one major surface thereof an imageable layer prepared according to the procedure described below. All parts are parts by weight unless indicated otherwise.
• a first solution containing (a) 5 parts silver behenate, (b) 40 parts acetone, and (c) 5 parts methyl ethyl ketone was ball milled for 24 hours.
• a second solution containing (a) 13.00 parts polyvinyl acetate resin, (b) 83.20 parts acetone, (c) 0.20 parts benzotriazole, (d) 0.60 parts tetrachlorophthalic anhydride, and (e) 3.00 parts methyl gallate was stirred until the resin had dissolved. Twenty parts of the first solution was combined with ten parts of the second solution, and the combination was stirred for 5 minutes with an air mixer.
• the imageable composition was coated over the polyethylene terephthalate sheet with a flat bed knife coater at 3.0 mil orifice and was dried in an oven at 82°C for 2 minutes.
• a third solution containing 5 parts cellulose acetate butyrate resin and 95 parts acetone was stirred until the resin had dissolved.
• This solution was coated over the dried imageable composition with a knife coater at 2.0 mil orifice and was dried in an oven at 82°C for 2 minutes.
• a fourth solution containing 7.5 parts polyvinyl butyral and 92.5 parts ethanol was coated over the cellulose acetate butyrate resin layer with a knife coater at 2.0 mil orifice and was dried in an oven at 82°C for 2 minutes.
• a composition for preparing a silicone polymer release coating was prepared from a formulation containing the following ingredients in the amounts indicated: Heptane and methyl ethyl ketone were blended, and then, in order, were added the resin, the fast-cure additive, the anchorage additive, and the catalyst.
• the release coating composition was coated over the polyvinyl butyral layer by means of a knife coater at a 2 mil orifice. The coating was dried in an oven at 82°C for 2 minutes.
• the effectiveness of the release coating was determined through the measurement and comparison of the optical density of the image on the paper original prior to making a transparency, after making a transparency with thermally imageable film not treated with a silicone release coating, and after making a transparency with thermally imageable film treated with a silicone release coating.
• Originals were made on a Kodak Model 150 copier.
• Transparencies were made on a prewarmed 3M Model 45 Transparency Maker.
• the optical densities were measured with a MacHeth Model TR924 densitometer. The results in the following table represent the average of four samples. Loss of optical density and increase in standard deviation is observed when comparing the images on originals before and after imaging with untreated film.

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• 1984
  • 1984-07-09 CA CA000458436A patent/CA1227636A/fr not_active Expired
  • 1984-07-09 AU AU30395/84A patent/AU572525B2/en not_active Ceased
  • 1984-07-23 JP JP59152744A patent/JPS6044393A/ja active Granted
  • 1984-07-30 BR BR8403790A patent/BR8403790A/pt not_active IP Right Cessation
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