Lithographic master base material

Abstract

 A lithographic printing plate comprising a polymeric base having one water or alcohol receptive surface forming the non-printing areas of said printing plate, and ink receptive printing areas bonded to said water or alcohol receptive surface of said polymeric base, said water or alcohol receptive surface being produced by graining or forming a water receptive reaction product on the base by reacting phenol, sodium hydroxide and sodium formaldehyde-sulfoxylate thereon, or laminating to said base a water or alcohol receptive polymeric material.

Description

[0001] This invention relates to a lithographic printing plate and more particularly to a lithographic printing plate comprising a polymeric base having one water or alcohol receptive surface forming the non-printing areas of the printing plate and ink receptive printing areas bonded to the water or alcohol receptive surface of the polymeric base.

[0002] Lithography is a well known printing process in which the printing surface of the master member is substantially planographic and contains printing areas which are ink accepting and non-printing areas which are water accepting or alcohol or aqueous alcohol solution accepting.

[0003] The lithographic master member is normally a relatively thin sheet of water accepting metal such as grained zinc or grained aluminium and the like and the ink accepting printing areas usually consist of photoresist which has been hardened by exposure and subsequently developed, as is well known in the art. Metal masters of the type commonly known as bi-metal or tri-metal plates containing on their printing surfaces successive layers of water accepting and ink accepting metals are also known in the art. It is also known to produce electrophotographic or electrostatic lithorgraphic masters by toning a charged and exposed photoconductor paper member with ink accepting electroscopic toner material where the deposits formed by such toner material may be fixed directly to the photococonductor paper surface which is then rendered hydrophilic in the non-printing areas by a subsequent chemical treatment commonly known as conversion, or alternatively the ink accepting toner deposits may be transferred to a water accepting metal surface such as for instance grained aluminium and fused thereto. Electrostatic transfer of the ink accepting toner deposits from the photoconductive member to the water accepting metal surface is also known.

[0004] The master member is normally wrapped around the so-called plate cylinder and clamped thereto. Roller systems are located adjacent to the plate cylinder to apply the so-called fountain solution to the printing surface to wet the non-printing or background areas prior to the application thereto of hydrophobic ink by a further set of rollers. Such fountain solution may comprise water, alcohol or aqueous alcohol solution and may also contain other materials to assist printing, as is well known in the art. The fountain solution contained on the non-printing areas of the printing surface prevents adherence of the hydrophobic ink thereto, the ink thus adhering to the printing areas only.

[0005] In so-called offset lithography the ink contained on the printing areas of the master is transferred to an offset member, commonly called the blanket cylinder, which contains on its surface a layer of resilient material such as synthetic rubber or the like and which cylinder rotates in contact with the plate cylinder surface. A further cylinder, known as the impression cylinder, rotates in contact with the blanket cylinder and the paper to be printed is fed into and through the nip between the blanket cylinder and the impression cylinder to cause transfer of the ink from the blanket to the paper. In so-called direct lithography the plate cylinder rotates in contact with the impression cylinder and the paper to be printed is fed into and through the nip between the plate cylinder and the impression cylinder to cause transfer of the ink from the printing surface of the master directly to the paper.

[0006] Lithographic printing presses may be web fed or sheet fed and may contain a multiplicity of printing stations to produce multicolour reproductions and be capable of printing one or both sides of the paper.

[0007] Prior art lithographic printing presses are constructed to operate with masters as previously described. Thus the plate cylinder includes clamping means which normally allow the master to be stretched and clamped around the cylinder. The end clamps require a gap in the plate cylinder and as such gap extends across the full printing width of the plate cylinder it defines the beginning and the end of the so-called repeat length which can be printed, where such repeat length itself is defined by the circumference of the plate cylinder. A printing press for publications printing such as book printing is normally constructed to allow printing of a fixed number of pages of a certain fixed size in one impression that is in one repeat length and thus at a given page size the number of pages which can be printed in one repeat length is fixed. It would be advantageous to be able to vary the number of pages which can be printed in one impression and also to be able to use a printing press for publications printing at different page sizes without being governed by the circumference of the plate cylinder. This may be obtained by making masters in the form of flexible continuous belts of larger circumference than that of the plate cylinder, which belts may be used on a press so constructed that a guide cylinder adjustably mounted in relation to the plate cylinder is provided whereby continuous belts of varying circumference may be mounted in the printing press to pass around the plate cylinder and the guide cylinder and be tensioned thereby to the correct degree for printing. Metal base masters are generally not suited to such operation as the constant change in belt curvature causes metal fatigue and premature breakdown.

DESCRIPTION OF THE INVENTION

[0008] The present invention discloses a flexible master base member which may be used in the form of a continuous belt if so desired without fatigue due to flexing and in addition may be clamped to a plate cylinder for operation in conventional prior art lithographic printing equipment.

[0009] Such flexible base member may be produced to be intrinsically water accepting yet capable of supporting ink accepting printing deposits.

[0010] The master base member in accordance with this invention comprises a polyester or the like flexible film having at least one side thereof rendered water or alcohol or aqueous alcohol solution accepting.

[0011] Polyester film possesses many desirable properties with regards use as a lithographic base member, such as dimensional stability, mechanical strength and fatigue resistance, however as normally produced it is water repellant. Certain surface treatments will render polyester film water accepting to a greater or lesser extent, and such treatments may include surface graining, chemical treatment such as disclosed for example in United States Patent No. 3,864,128 or laminating thereto a thin hydrophilic or alcohol accepting film.

[0012] The flexible lithographic master base member may be imaged by various known methods such as for instance by first coating the water or alcohol accepting surface thereof with a photopolymer, followed by exposure and development to form hardened ink accepting photopolymer deposits thereon corresponding to the information to be printed, or by electrostatic transfer thereto of ink accepting toner deposits from a photoconductive recording member as referred to in the foregoing.

DESCRIPTION OF THE PREFERRED EMBODIMENTS.

[0013] A preferred flexible base material for long run lithographic printing may be prepared by laminating a regenerated cellulose film to one surface of a polyester film. Such regenerated cellulose film may also contain on one or on both sides thereof a layer of nitrocellulose which may be solvent coated onto such regenerated cellulose film or may be bonded thereto with a suitable adhesive such as a urea-formaldehyde compound. Alternatively the regenerated cellulose film may contain on one or on both sides thereof a thin coating of polyvinylidene chloride which can be applied thereto from solution or from aqueous suspension or emulsion. A flexible base material for lithographic printing may also be prepared by laminating a cellulose acetate film or a nylon film preferably of the non-oriented type to one surface of a polyester film. Other water or alcohol wettable films can of course also be laminated to the polyester film or solution or emulsion coated thereon.

[0014] It should be noted that regenerated cellulose and cellulose acetate are water accepting whereas nitrocellulose, polyvinylidene chloride and nylon depending on their grade are alcohol and/or aqueous alcohol solution wettable.

[0015] The polyester base may be of a thickness within the range 0.1 - 0.5 mm, or more or less as desired. A thickness of 0.25 mm has been found adequate for most printing applications.

[0016] The regenerated cellulose film may advantageously be of the order of 0.024 mm in thickness, the cellulose acetate may be for instance of 0.15 mm thickness and the nylon may be in the thickness range of 0.01 to 0.1 mm, however the thickness of the regenerated cellulose, of the cellulose acetate and of the nylon may be greater or lesser depending on printing requirements.

[0017] The laminating adhesive is selected to provide adequate adhesion to each of the polyester base and the laminate. The adhesive may be of the permanently pressure sensitive type or may crosslink or otherwise cure to form a permanent bond and may be heat setting if desired. The adhesive may form a hard layer, or if desired may possess some elastomeric properties whereby the printing surface may more easily conform to irregularities in the paper web when printing in the direct lithographic mode. A solution of polyurethane or a polyurethane prepolymer in a solvent such as ethyl acetate has been found to be suitable and such an adhesive may be prepared by dissolving the polyurethane or polyurethane prepolymer in the solvent at a desired concentration such as 5 - 40% by weight and applying to the polyester surface with a wire wound rod or other metering means. The laminate may be formed by passing the components preferably after solvent evaporation through pressure rollers which may be heated if desired. Final curing in the temperature range of for instance 90 - 130°C. may be carried out to achieve maximum bond strength. Other suitable adhesives include solutions of linear polyester resins and solutions of nitrile resins.

[0018] We have also found that substantial increase in bond strength of the adhesive to the polyester film can be attained by mechanical graining of the polyester film surface prior to the application thereto of the adhesive material or of the solution or emulsion coating. Such mechanical graining can be carried out for instance by means of frictional application to the surface of an aqueous slurry of colloidal silica or similar mildly abrasive compound.

[0019] The laminated master base member previously described may be replaced by a surface treated polyester film, such as for example the drafting film manufactured by Du Pont under the trade name Cronaflex, or alternatively a hydrophobic film support such as a polyester film may be rendered water accepting by the application thereto for example of a layer containing vinylidene chloride or vinyl chloride in combination with an ethylenically unsaturated hydrophilic monomer as disclosed in United States Patent No. 3,864,128. An alternative process for rendering polyester film water accepting by treatment with a mixture containing phenol, sodium hydroxide and sodium formaldehyde - sulfoxylate as disclosed in United States Patent No. 3,394,023.

[0020] The water or alcohol accepting master base may be imaged in a variety of ways. For instance the base may be precoated with a photoresist such as the negative working photoresist disclosed in United States Patent No. 3,440,047 or a positive working photoresist such as is described for example in United States Patent No. 3,834,998. Proprietary so-called "wipe on" photoresist materials may also be used if desired.

[0021] A further method of imaging the water or alcohol accepting master base member of the present invention consists in the transfer of ink accepting toner deposits from a photoconductive recording member surface thereto. Such ink accepting toner deposits are preferably transferred to the water or alcohol accepting master base electrostatically as is well known in the art and fixed or fused thereto preferably by the application of heat. It will be realized that in such applications the toner materials and compositions need to be so selected that the toner deposit by its nature is compatible with the laminate in order that good interfacial bonding therebetween may be attained when such toner deposit is fixed or heat fused onto such laminate.

[0022] The following Examples will further illustrate the principles of this invention.

EXAMPLE 1.

[0023] A polyester film 0.25 mm in thickness was rendered water accepting by laminating thereto a regenerated cellulose film 0.024 mm thick containing on one surface thereof a thin nitrocellulose layer which was bonded thereto with urea-formaldehyde adhesive. The films were laminated together with an adhesive comprising polyurethane dissolved in ethyl acetate. The nitrocellulose layer formed the bonded surface of the laminate. The laminate was passed through pressure rollers at the temperature of 120°C.

[0024] The water accepting surface of the thus prepared master base was coated with a negative type photopolymer of the following composition:-

[0025] This mixture was flow coated to the regenerated cellulose surface of the master base and dried. The master member was subsequently exposed through a negative film to harden the photopolymer coating in the image areas. After exposure the master was dipped in a 1% aqueous hydrogen peroxide solution, after which the unexposed photopolymer was removed from the non-image areas with a soft cellulose sponge dipped in water at 40 - 45⁰C. The thus prepared flexible lithographic master was subsequently rinsed with water and dried with a warm air blast. The hardened photopolymer provided ink accepting printing areas bonded to the water accepting base surface.

EXAMPLE 2.

[0026] Example 1 was repeated, but in this instance the photopolymer was of the positive type comprising a mixture of diazoxide resin and a phenol resin prepared as described in British Patent No. 1,113,759.

EXAMPLE 3.

[0027] The laminated master base member of Example 1 was imaged by transfer thereto of ink accepting electroscopic toner deposits from a charged, exposed and toned photoconductive recording member of the zinc oxide/binder type. The electroscopic toner was of the following composition:-

[0028] These components were ball milled together for 72 hours and then diluted for use as a toner in the proportions of 20 mls. of concentrate to 1 litre isoparaffinic hydrocarbon dispersant.

[0029] The laminate was placed on the flat base member of a roller transfer device such as that disclosed in the co-pending Australian Patent Application No. 25,184 and the toned side of the photoconductive recording member was placed in contact with the regenerated cellulose layer of the laminate.

[0030] A potential of 1000V positive was applied to the core of the semi-conductive resilient roller as it passed in contact with the back surface of the photoconductive recording member to effect electrostatic transfer of the toner deposits to the regenerated cellulose layer. The toner deposits were dried and fused to the regenerated cellulose layer at a temperature of 14_{0 C}.

EXAMPLE 4.

[0031] Example 1 was repeated with the exception that the flexible water accepting lithographic master base comprised a 0.1 mm thick drafting film of the grained or surface treated type, supplied by Du Pont under the Trade Name Cronaflex.

EXAMPLE 5.

[0032] Example 2 was repeated with the water accepting lithographic master base of Example 4.

EXAMPLE 6.

[0033] Example 3 was repeated with the water accepting lithographic master base of Example 4. The transfer potential was 900 volts.

EXAMPLE 7.

[0034] Example 1 was repeated with the exception that the flexible water accepting lithographic master base comprised a 0.25 mm thick polyester film which had been rendered water accepting by the application thereto of a preparation containing phenol, sodium hydroxide and sodium formaldehyde - sulfoxylate as disclosed in United States Patent No. 3,394,023.

EXAMPLE 8.

[0035] Example 2 was repeated with the water accepting lithographic master base of Example 7.

EXAMPLE 9.

[0036] Example 3 was repeated with the water accepting lithographic master base of Example 7.

EXAMPLE 10.

[0037] A polyester film 0.25 mm in thickness was rendered alcohol accepting by laminating thereto a regenerated cellulose film 0.024 mm thick, containing on its upper surface an alcohol wettable nitrocellulose layer. The films were laminated together with an adhesive comprising a polyurethane crosslinking prepolymer dissolved in ethyl acetate solvent.

[0038] The thus prepared lithographic master base was used in accordance with Example 1 to produce a lithographic master, the non-printing areas of which were wettable with an alcohol containing fountain solution.

EXAMPLE 11.

[0039] The lithographic master base of Example 10 was used in accordance with Example 2 to produce a lithographic master, the non-printing areas of which were wettable with an . alcohol containing fountain solution.

EXAMPLE 12.

[0040] The lithographic master base of Example 10 was used in accordance with Example 3 to produce a lithographic master, the non-printing areas of which were wettable with an alcohol containing fountain solution.

EXAMPLES 13 - 15.

[0041] Examples 10 - 12 were repeated with the exception that the regenerated cellulose film contained on each surface thereof an alcohol wettable nitrocellulose layer.

EXAMPLES 16 - 18.

[0042] Examples 1 - 3 were repeated with the exception that the regenerated cellulose film was of the plain and uncoated type.

EXAMPLES 19 - 21.

[0043] Examples 1 - 3 were repeated with the exception that the regenerated cellulose film contained a coating of polyvinylidene chloride on its surface bonded to the polyester film.

EXAMPLES 22 - 24.

[0044] Examples 10 - 12 were repeated with the exception that the regenerated cellulose film contained on each surface thereof a polyvinylidene chloride coating.

EXAMPLES 25 - 27.

[0045] Examples 1 - 3 were repeated with the exception that the regenerated cellulose film containing on one side thereof a nitrocellulose layer was replaced by a non-oriented nylon film, 0.05 mm thick.

EXAMPLES 28 - 30.

[0046] Examples 10 - 12 were repeated with the nylon laminate of Examples 25 - 27.

EXAMPLES 31 - 33.

[0047] Examples 1 - 3 were repeated with the exception that the regenerated cellulose film containing on one side thereof a nitrocellulose layer was replaced by a cellulose acetate film, 0.15 mm thick.

[0048] There has been described a novel flexible lithographic master base with reference to the embodiments disclosed, however the details set forth in the foregoing should be construed as illustrative only without limiting the scope of the invention as changes and modifications may be made to the materials specifically disclosed as will be obvious to those skilled in the art without departing from the spirit of this invention.

Claims

1. A lithographic-printing plate comprising a polymeric base having one water or alcohol receptive surface forming the non-printing areas of said printing plate, and ink receptive printing areas bonded to said water or alcohol receptive surface of said polymeric base, characterised by said water or alcohol receptive surface being produced by one of the means selected from the group graining, forming a water receptive reaction product on said base by reacting phenol, sodium hydroxide and sodium formaldehyde-sulfoxylate thereon, or laminating to said base a water or alcohol receptive polymeric material.

2. A lithographic printing plate as disclosed in claim 1, further characterised by said water receptive polymeric material laminated to said base comprising a regenerated cellulose film.

3. A lithographic printing plate as disclosed in claim 1, further characterised by said alcohol receptive polymeric material laminated to said base comprising a nitrocellulose layer.

4. A lithographic printing plate as disclosed in claim l, further characterised by said water receptive polymeric material laminated to said base comprising a non-oriented nylon layer.

5. A lithographic printing plate as disclosed in claim 1, further characterised by said alcohol receptive polymeric material laminated to said base comprising a polyvinylidene chloride layer.

6. A lithographic printing plate as disclosed in claim 1, further characterised by said ink receptive printing areas comprising a photopolymer.

7. A lithographic printing plate as disclosed in claim 1, further characterised by said ink receptive printing areas comprising ink accepting electroscopic toner material transferred thereto.

8. A lithographic printing plate as disclosed in claim 1, further characterised by said polymeric base comprising a polyester film.