GB2089288A - Printing blankets - Google Patents

Abstract

A multilayer printing blanket comprises a printing surface layer (11) less than 50 microns thick, e.g. 5 to 15 microns thick, adapted to receive a printing ink, a compressible layer (12) of microporous polymer, preferably elastomeric polymer, at least 0.3 mms thick and preferably of a density of 0.3 to 0.5 gr/cc., contiguous to the said thin layer, and at least one fabric base ply (16) spaced from the printing surface (11) by the said compressible layer (12), to which the base ply (16) may be adhered by a layer of adhesive (14). A less compressible layer (13) may be interposed between the compressible layer (12) and the adhesive (14). Further fabric base plies (18) and (20) may be attached to the base ply (16) by layers of adhesive (17) and (19). The product is capable of producing prints with very good dot definition and has very good recovery characteristics from deformation after repeated loading. <IMAGE>

Description

SPECIFICATION Printing blankets The present invention relates to printing blankets and provides an improved compressible blanket.

According to the present invention a multi-layer printing blanket comprises a printing surface layer less than 50 microns thick, adapted to receive a printing ink, a compressible layer of microporous thermoplastic polymer at least 0.3 mms thick contiguous to the said printing layer and at least one fabric base ply spaced from the printing surface by the said compressible layer.

The surface layer is very thin compared with blankets conventionally used in the printing industry especially in high speed rotary printing such as offset letter press and offset litho printing. Such blankets usually have a rubber printing surface 200 to 400 microns thick built of many layers of rubber composition laid down one on top of the other and then cured to a solid layer. In our preferred embodiments the printing layer is substantially thinner than 50 microns or even 40, 30 or 30 microns and is generally less than 15 microns thick and is preferably in the range 3 to 15 microns.

Proposals for compressible blankets in the 1960's suggested that the compressible layer could be a latex impregnated paper or felt with a printing surface layer of 50 to 100 microns. However these blankets did not meet with acceptance in the printing industry and since then the normal structure has been to include a heavy thick rubber printing surface.

It is therefore not to be expected that blankets in accordance with our invention having such very thin surface layers will find ready acceptance in the industry.

We have done laboratory tests comparing dot definition with conventional printing blankets having a thick rubber printing surface layer and with our blanket having a very thin printing surface layer and we find that very substantially improved dot definition is achievable with our blanket.

The compressible layer as mentioned above is at least 0.3 mms thick and is preferably in excess of 0.4 mms e.g. 0.5 to 0.8 mms thick, the remainder of the thickness of the blanket (which is typically 1.0 to 2.0 mms e.g. 1.8 mms total thickness) being provided by an appropriate fabric base. The compressible layer being microporous has open intercommunicating pores and voids and preferably has an apparent density in the range 0.25 to 0.6 e.g. 0.3 to 0.5 gr/cc. Thus the blanket must be able to accomodate the normal interference fit settings and relatively high pressures used nowadays in high speed rotary printing without distortion in the surface direction of the printing surface and this the compressible layer can readily achieve with the very thin surface layer which is located contiguous to it.

The compressible layer may be adhered to the fabric base ply by being formed in situ on the base ply as a support or more conventionally by being adhered to it by appropriate adhesive means such as conventional cements or rubber adhesives such as neoprene, or by hot melt adhesives, or two-component reactive adhesives or flame lamination.

One or more additional fabric plies may be adhered to the fabric base ply by similar such adhesive means.

The face of the blanket remote from the printing surface may be provided with a layer of adhesive, e.g.

pressure sensitive adhesive, adapted to removably secure the blanket to the pressure applying surface e.g.

the cylinder of the printing machine.

Prior to use such an adhesive would be protected by a release surface e.g. of paper.

In a preferred form of the invention a second less compressible layer of microporous polymer is disposed between the compressible layer and the fabric base ply. In this arrangement the second compressible layer preferably has a density of 0.5 to 0.6 gr/cc and the compressible layer has a lower density.

The second compressible layer may be thinner or thicker than the first compressible layer.

The interior of the microporous compressible layer has a regular microporous structure right up to the thin printing surface. Thus at least 50% and preferably at least 90% of the void volume of the microporous compressible layer is made up of voids having a maximum dimension of less than 50 microns, the said maximum dimension being measured in the plane of a vertical cross-section cut through the material. The pores or voids within the microporous layer are generally compact through irregular in shape varying mainly from 5 to 50 microns across and most being about 10 to 30 microns across. The pores or voids are defined or surrounded by thin walls about 1 to 5 or 10 microns thick and entry pores penetrating these thin walls connect adjacent voids.

The second less compressible layer if present will have a more dense structure the walls surrounding or defining the pores and voids being thicker and thus affording denser regions having fewer or small voids and pores.

The microporous compressible layer or layers is preferably free of fibrous reinforcement and as an unsupported sheet has an elongation at break in excess of 200%. The material whilst thus extremely tough and resilient should however not be deformed too easily.

Thus in a preferred form of the invention the compressible layer when tested as an unsupported sheet nominally 0.5 mm thick before application of the printing surface had an optically measured thickness of 0.49 mm and had a thickness of 0.48 mm using a dead weight loaded dial micrometer having a foot of 11 mm diameter under a load of 375 grams and when the load was increased to 5375 grams without moving the foot a thickness of 0.29 mm. The reduction in thickness as a percentage of the value at 375 grams when the load is increased to 5375 grams will be referred to herein as the compressibility percentage. The compressibility percentage is thus preferred to be of the order of 40% or more broadly in the range of 30% to 50%.

When a second less compressible layer is also present the ratio of the compressibility percentages of the compressible layer to the second layer is preferably at least 1.1:1 e.g. at least 2:1 or at least 3:1 and preferably in the range 2:1 to 8:1. The compressibility percentage of the second less compressible layer is preferably of the order of 10% or more broadly in the range 5 to 15%.

The polymer from which the compressible layer is formed can be any thermoplastic organic resin material which fulfils the conditions described above and preferably is one which is capable of forming a film on coagulation from an emulsion, a colloidal dispersion, a gel or a solution.

The polymer must also be capable of undergoing the various processes specified in the methods described herein and is preferably elastomeric. The particular strength and wear characteristics required for the particular printing use of the printing blanket may influence the choice of the particular polymer to be used.

Any thermoplastic polymers used in printing blankets which can undergo the various processes described herein can be used but elastomeric polyurethanes are preferred. Clearly compatible blends of these materials with minor proportions, say up to 49% preferably less than 20% of the other polymers and copolymers such as nitrile rubbers including solid copolymers of butadiene and acrylonitrile, may also be used.

The preferred polymers however are elastomeric polyurethanes having recovery properties intermediate between pure rubbers and pure thermoplastic materials at room temperature.

The article by Schollenberger Scott and Moore in "Rubber Chemistry and Technology" Vol. XXXV, No.3, 1962 pages 742 to 752, at page 743 and in Figure 3 indicates the long so-called half lives of the polyester urethanes made from adipic acid, 1,4 butane diol and diphenyl methane-p,p'-diisocyanate by the methods disclosed in U.S. Patent Specification No. 2871218 and sold under the Trade mark ESTANE 5740. These two disclosures are incorporated herein by reference.

Polyurethanes may be based on a wide variety of precursors which may be reacted with a wide variety of polyols and polyamines and polyisocyanates. As is well known the particular properties of the resulting polyurethanes to a large extent can be tailored by suitable choice of the reactants, reaction sequence and reaction conditions.

The preferred polymers are elastomeric polyurethanes based on a linear, hydroxyl terminated polyester (although a polyether or a polyether/polyester blend may be used) and a diisocyanate, with a small addition of a difunctional low molecular weight reactant. The last mentioned component may be added either with the other reactants at the start of a one-step polymerisation or at a later stage when it will act primarily as a chain extender.

This type of polyurethane having thermoplastic properties is particularly preferred for use in producing these compressible layers. Particularly preferred polyurethanes are those derived from polyesters by reaction with diols and diisocyanates. As is known from United States Patent Specification No.2871218, mentioned above, many different polyesters, diols and diisocyanates can be used, but a particularly suitable polyurethane system is one in which a polyester made from ethylene glycol and adipic acid is reacted with 1,4-butylene glycol and with 4,4'-diphenylmethane diisocyanate.

In the system in accordance with the above specification the mole ratios of polyester and diol can vary between quite wide limits but the combined mole ratio of polyester and diol is arranged to be essentially equivalent to the mole ratio of diisocyanate so that the resultant polymer is essentially free of unreacted hydroxyl or isocyanate groups.

Polymers of this type but having an improved Shore hardness can be made by using a slight excess of diisocyanate, and also by using a copolyester as by replacing part of the ethylene glycol in the above system by 1,4-butylene glycol.

The polymers may be produced by a bulk polymerisation process and subsequently dissolved in suitable solvents or may be prepared directly in solution by a solution polymerisation process.

A particularly preferred polyurethane is that made by the novel solution polymerisation process disclosed in British Patent Specification Serial Number 1294450, the disclosure of which is incorporated herein by reference.

A further alternative polyurethane system which has been found particularly suitable uses polyester derived from caprolactones. Such polyurethanes are described in British Patent Specification No. 859640, the disclosure of which is incorporated herein by reference.

The preferred polyurethanes are characterised by having intrinsic viscosities in the range of 0.7 to 1.4 dl/g.

The intrinsic viscosity is determined in highiy dilute solution in analyticai grade DMF which has been thoroughly dried by storage under a nitrogen atmosphere over a molecular sieve (Linde 5A). Four measurements at 25"C corresponding to four, approximately equally spaced, concentrations are made and intrinsic viscosity and polymer-solvent interaction parameter are determined by the Huggins equation: nsp C = [n] +K1 [n]2C C where nSF is the specific viscosity and C is concentration expressed in 9/100 ml, and [n] is the intrinsic viscosity.

For use in making compressible layers the preferred polyurethanes have melting points of at least 100 C preferably above 130"C (e.g. about 70 to 200"C, as measured by differential thermal analysis or differential scanning calorimetry).When formed into a smooth void-free thin film 0.2-0.4 mm in thickness (by carefully casting a degassed solution in dimethyl-formamide and then carefully evaporating off the solvent in a dry atmosphere) they have the properties described below: a tensile strength of at least 210 kilograms per square centimeter (preferably at least 300, e.g. about 420 to 560), a percent elongation at break of at least 300% (preferably at least 400%, e.g. about 500 to 700%), a 100% modulus (stress divided by strain at 100% elongation) of at least 28 kilograms per square centimeter (preferably at least 60, e.g. about 110 to 134).

These mechanical properties are measured by ASTM D882-67.

The preferred polyurethane (again, tested as a thin film made as described above) recovers completely from a 5% elongation at room temperature (23"C).

Preferably the material has a Shore hardness of at least 75A (more preferably about 90A or 60D), measured byASTM D1706-67.

The preferred technique for making the microporous compressible layer is by casting a thick layer of a suspension of microscopic salt particles in a dimethylformamide (DMF) solution of the polyurethane, coagulating the solution and leaching out the salt. The thickness of the coagulated sheet, after leaching and drying is desirably at least 0.5 mm but it can be made up to any desired thickness, e.g. up to 1.5 mm or more thick.

When a second compressible layer is to be provided the process conveniently involves codepositing another thick layer of such a suspension, which in order to provide the more dense less compressible layer may contain less salt or larger salt particles or more polymer or any combination of two or more of these three variations.

The particle size of the microscopic particulate material for example sodium chloride is below 100 microns, preferably less than 50 microns and greater than about one micron, more preferably in the range of about 3 to 30 microns. The ratio of the total volume of the microscopic particulate void forming material and the total volume of polyurethane in solution may be, for instance, in the range of about 0.5:1 to 5:1, preferably in the range of about 1:1 to 3:1, thus 178 grams of the sodium chloride particles may be mixed with 333 grams of a 30% solution of the polyurethane in dimethylformamide, giving a volumetric salt; polymer ratio of 1:1.

The suspension used for making the compressible layer preferably contains 3 parts by weight of salt to each part by weight of the polymer, that used for making the second compressible layer preferably contains 1:8 parts by weight of salt to each part by weight of polymer.

The microporous compressible layer as mentioned above preferably has an apparent density in the range of about 0.25 to 0.6 grams/cm3 more preferably in the range of about 0.3 to 0.5 grams/cm3. Typically the density of the polyurethane itself is about 1.2 gr/cm it will therefore be apparent that in the neighbourhood of 2 to 4 of the volume of the microporous material is air. The layer as an unsupported sheet preferably has a percent elongation at break of above 50% (e.g. in the range of about 300 to 400% or more); a tensile strength above 35 kg/cm2 (e.g. in the range of about 60 to 100); an elastic modulus at 10% extension above 2 kg/cm2 (e.g. in the range of about 3 to 9).

The preferred microporous compressible layers have a very high resistance to taking on a permanent deformation after repeated loading and this makes the printing blankets of the invention most advantageous. Thus the preferred microporous polyurethane compressible layers generally recover with negligible permanent set (under standard dry conditions at room temperature) even after being compressed down to half of their original volume.

All measurements referred to herein are made at room temperature (e.g. 23'C) unless the test method specifies otherwise.

The printing surface layer is preferably made by depositing a polymer solution on the surface of the compressible layer the solvent for which includes an active solvent for the polymer of the compressible layer, and then heating the surface rapidly to evaporate off the active solvent so that the solvent attack or fusion of the surface of the compressible layer is controlled and the thin sealed ink-receiving surface is produced.

The deposited polymer may be any of those conventionally used in the production of printing surfaces for printing blankets. However, the preferred polymers are elastomeric thermoplastic polyurethanes for example elastomeric polyurethanes essentially free of unreacted hydroxyl or isocyanate groups.

Any solvent having a good solvent action e.g. one from which a 30% by weight solution of the polymer of the compressible layer at 25"C can be made can be used but polar organic solvents are especially effective and a particularly good example is N,N-dimethylformamide (referred to hereafter as dimethylformamide or DMF). The solvent may be diluted with less active or even inactive liquids which may be more or less volatile.

Useful diluents for dimethylformamide include cyclohexanone and acetone either separately or together, for example blends of 20-50 parts DMF, 55-20 parts cyclohexanone and 15-30 parts acetone such as 50 DMF, 20 cyclohexanone, 30 acetone, and 25 DMF, 55 cyclohexanone, 20 acetone may be used. Other suitable solvent mixtures are DMF with up to 75% cyclohexanone and DMFwith up to 50% acetone.

The dissolved polymer which is to be deposited is preferably the same as that in the compressible layer and may also contain a proportion of dispersed pigment (which is preferably white to assist colour registration on the blanket) or dye (provided it is stable at the temperatures involved in the process and insoluble in solvents conventionally used in printing inks).

The dissolved polymer in the solvent composition being deposited is generally below about 15% by weight, e.g. 1,2,3, 5, 8, or 10%. The amount of pigment or dye (if used) is usually above about 0.1% based on the total composition but less than 2% or perhaps 4%. The ratio of dispersed pigment to dissolved polymer in the solvent composition being deposited is usually within the range 1:50 to 1:1 preferably about 1:20 to 1:3 or 1:10 to 1:3.

The pigment may be any one suitable to impart the desired colour and should be in very finely divided form and evenly dispersed in the composition.

The solvent polymer composition is preferably deposited as a thin layer by a coating technique. An oven or heating stage, e.g. at 80"C to 150"C is used to ensure complete removal of the solvent.

The amount of active solvent, e.g. dimethyl-formamide actually deposited on the sheet is preferably at least 10 grams per square metre though higher amounts such as 25,50, 100 or 200 grams per square metre can be deposited. However, care must be taken that the amount of solvent deposited is not such as to produce pitting of the surface visible to the unaided eye.

When the solvent composition contains a dissolved polymer and/or pigment or dye the increase in weight of the material is preferably at least 4 grams per square metre and may be as high as 7, 13, 15 or more grams per square metre. Higher applications of solids such as 20 or more grams per square metre could also be used.

The invention may be put into practice in various ways and one specific embodiment will be described by way of example with reference to the accompanying drawing which is: A cross-section view taken with a scanning electron microscope at 90 to the cut face showing a printing surface 11, a compressible layer 12, a second less compressible layer 13, and a layer of adhesive 14 bonding the microporous layer 13 to the carcass 15. The carcass comprises a woven cotton fabric 16, a layer of neoprene adhesive 17, bonding the cotton fabric to a woven glass fibre fabric 18, and another layer of neoprene adhesive 19, bonding the glass fibre fabric to a final layer of woven cotton fabric 20.

The figure carries a scale beside it. The photomicrograph was prepared by cutting a smooth perpendicular cross-section through the material and then directing a stream of electrons on to the surface at 45" and collecting the electrons reflected from the surface also at 459.

The surface was first coated with a thin metallic reflecting layer as is conventional in preparing samples for electron photomicrography. It will be appreciated that the depth of focus of such photographs is very much greater than optical photography and thus that in effect one is able to see into the voids and cavities.

The polyurethane used to make the material described in the Example is as follows: 880 kgs of pure N,N-dimethylformamide were placed in a 1500 kg reactor flushed with dry nitrogen. 0.027 kgs of paratoluene sulphonic acid and 0.020 kgs of dibutyltin dilaurate were dissolved in the dimethyl formamide. 205.0 kgs of Desmophen 2001 polyester (a hydroxyl terminated polyester of 2000 molecular weight, having a hydroxyl number of about 55.5 mg KOH per g. made from about 1 mol butane diol - 1,4, 1.13 mol ethylene glycol and 2 mols adipic acid) and 48 kgs of butane diol - 1,4 were then added and dissolved in the mixture and the temperature of the mixture adjusted to 250C.

171.6 kgs of 4,4-diphenylmethanedi-isocyanate were then added bit by bit care being taken to keep the temperature from rising above 50"C. Once the addition was complete the mixture was heated to 60"C and maintained at that temperature for 12 hours with stirring. The excess unreated isocyanate content was then determined by titration of an aliquot.

Sufficient butane diol (3.0 kgs) was then added to react essentially stoichiometrically with the unreacted isocyanate. The mixture was then maintained at 600C with stirring and the viscosity measured periodically until it had risen to a value of 3500 poise (Brookfield 5 or 6 spindle) as corrected to 240C. 4.1 kgs of butane diol-1,4 were then added as capping agent to terminate the reaction dissolved in 3.5 kgs of N,Ndimethylformamide. The resultant solution had a polyurethane solids content of 32.5%.

Example A white pigmented microporous elastomeric polyurethane sheet about 1.0 mm thick and weighing about 460 grams per square metre was made first to provide a free smooth surface, the compressible layer and the second less compressible layer, the former layer being less dense than the latter.

The material was made by depositing a 32% solution of polyurethane in dimethylformamide having dispersed through it about 1.8 parts of microscopic sodium chloride particles per part of polyurethane as a substrate layer about 1.5 mm thick on a finely porous woven belt. A thinner top coat layer of the same solution but containing 3 parts (per part by weight of polyurethane) of sodium chloride (having a smaller particle size) was then immediately deposited on the previous layer before any solvent was removed. The total thickness of the two layers was about 20 mm. The belt was then carefully passed at room temperature into an aqueous coagulating bath, which in continuous operation may contain about 5 to 10% DMF and about5to 10% sodium chloride.

Each portion of the belt remained in the bath for about 35 to 40 minutes after which the material was self-supporting and could be stripped from the belt. The bath was fed with water heated to about 45"C at the output end so that there was a temperature gradient through the bath.

The unsupported coagulated layer which had shrunk in thickness to nearly its final thickness and by about 5% in length still contained quite a large amount of salt and this was reduced to an acceptable level, e.g. 1000 milligrams or less per square metre, by leaching in water at 60"C, e.g. for3 hours, using pressure nip rolls and then dried at 90"C. Thereafter it was relaxed by being heated in an unconstrained state as on a steel belt conveyor at 160"C for 5 minutes during which time it shrunk in area by about 5%. The compressible layer had a thickness at this stage of about 0.4 mm, the second compressible layer having a thickness of about 0.6 mm.

At this stage the surface of the material which was the free surface remote from the belt has a smooth faintly glossy appearance. When examined microscopically it is found to have small pores 1 to 10 microns across in its surface. The free dry surface of this material was then coated with a solvent mixture containing dimethylformamide, a solvent for the polyurethane of the microporous sheet material, dissolved polyurethane and dispersed white pigment and the coated material was then passed through a drying zone to ensure removal of the solvent. The coating was such as to increase the dry weight of the material by 8 grams per square metre. The coating composition contained the same elastomeric polyurethane as was used in the microporous material. The solids content of the coating composition was 10% and the ratio of polyurethane to pigment was 3 to 1.The liquid part of the composition was a blend of 60 parts dimethylformamide and 40 parts cyclohexanone (Sextone), i.e. for each 10 grams increase in weight of the material 100 grams of the total composition are applied.

Directly after the material has been coated it enters a multi-zone over with a temperature gradient from 100 to 150"C, the sheet being fed into the oven so soon after the coating step that the coated surface still contains a large amount of solvent, the solvent containing surface layer being substantially fused by the heat and acquiring a sheen.

The coated surface had a smooth surface substantially free of pores and the printing surface layer was 5 to 15 microns thick. The surface of the sheet which was in contact with the belt reflected the belt pattern and was sanded to remove about 0.4 mm and give the sheet a flatter surface through nubs of polymer derived from the belt pattern may be left to assist keying to the adhesive used to attach the microporous layers to the fabric plies.

The sanded lower surface was then laminated to the woven fibre glass ply shown in the Figure with a conventional rubber adhesive.

The compressible layer, the second less compressible layer, the carcass and the complete blanket (sample 4) were separately tested for compressibility percentage, initial modulus at varying elongations (corrected to constant area), tensile strength, and elongation at break. The results are given in the table below.

The compressible layer (sample 1) was tested as an unsupported sheet 0.49 mm thick (measured optically), the second less compressible layer (sample 2) was tested as an unsupported sheet 0.98 mm thick (measured optically). The carcass (sample 3) did not have its thickness measured optically because the surfaces are difficult to define at high magnification.

Compressibility percentage was measured as described above.

Sample 1 2 3 4 Dead weight gauge thickness at load 375 grams A 0.48 1.02 1.28 1.90 at load 5375 grams B 0.29 0.95 1.18 1.67 Compressibility percentage 41 7 8 12 A-B/A Initial modulus 5% L 0.06 0.50 5.5 7.0 kg/cm width X 0.06 0.50 - kg/cmwidth 7% L 0.12 0.87 10.0 11.7 kg/cm width X 0.12 0.80 - kg/cmwidth 10% L 0.20 1.20 13.0 18.3 kg/cm width X 0.17 1.12 - Tensile strength L 3.35 9.0 13.0 22.3 kg/cm width X 2.94 9.2 - Elongation at break /O L 297 332 10 13 X 324 381 - The blanket was cut so that its length was in the L direction thus utilising the low extensibility of the fabric in that direction.

The initial modulus is the value at the quoted extension, and initial modulus, ultimate tensile strength and elongation at break are all measured on a single test piece. The method is as described in British Standard Specification No. 3144:1968 using an INSTRON (Trade Mark) tensile test machine. The sample length between the jaws of the machine is 10 cms and the specimen is subjected to an increasing load so that the jaws separate at a constant rate of 100 cms per minute, i.e. 1000% per minute.

Claims (11)

1. A multilayer printing blanket comprising, a thin printing surface layer less than 50 microns thick adapted to receive printing ink, a compressible layer of microporous polymer at least 0.3 mms thick contiguous to the said thin layer and at least one fabric base ply spaced from the printing surface by the said compressible layer.

2. A multilayer printing blanket as claimed in Claim 1 in which the printing surface layer is less than 15 microns thick.

3. A multilayer printing blanket as claimed in Claim 1 or Claim 2 in which the compressible layer is at least 0.4 mms thick.

4. A multilayer printing blanket as claimed in Claim 1,2 or 3 in which the compressible layer has open intercommunicating pores and voids and has a density in the range 0.3 to 0.5 gr/cc.

5. A multilayer printing blanket as claimed in Claim 1,2,3 or4 in which the compressible layer is adhered to the fabric base ply by being formed in situ on the base ply as a support.

6. A multilayer printing blanket as claimed in any one of Claims 1 to 4 in which the compressible layer is adhered to the fabric base ply by adhesive means.

7. A multilayer printing blanket as claimed in any one of Claims 1 to 6 in which an additional fabric ply is adhered to the fabric base ply by adhesive means.

8. A multilayer printing blanket as claimed in any one of Claims 1 to 7 in which the face of the blanket remote from the printing surface is provided with a layer of adhesive adapted to removably secure the blanket to the pressure applying surface of the printing machine.

9. A multilayer printing blanket as claimed in any one of Claims 1 to 8 in which a second less compressible layer of microporous polymer is disposed between the compressible layer and the fabric base ply.

10. A multilayer printing blanket as claimed in Claim 9 in which the second compressible layer has a density in the range of 0.5 to 0.6 gr/cc.

11. A multilayer printing blanket as claimed in Claim 1 substantially as specifically described herein with reference to the accompanying drawing.