Background
The use of blankets in printing techniques such as offset lithography is well known, wherein the main function of such blankets is to transfer ink from the plate to the paper. Such printing blankets are designed with great care so that the blanket is not damaged either by mechanical contact with the printing press or by chemical reaction with the ink components or other solvents used in the printing process. Repeated mechanical contact does result in some amount of compression of the blanket, however, the integrity of the blanket must be maintained within acceptable limits so that the image is properly reproduced. It is also important that the blanket have resilient properties so that it can eventually return to its original thickness and provide an image transfer of constant quality.
A multi-layer polymeric printing blanket can be broadly described as having two subassembly layers: a printing surface and a framework. The printing blanket is the portion of the blanket that transfers ink from the plate to the paper or the like. The skeleton is the whole structure that is located under the printing surface layer. To be able to create a skeleton that can withstand the stresses of the printing process, a large number of polymer coatings and textile layers are required. The carcass typically requires at least two layers of woven fabric to be pressed together to form a unit, with multiple layers of polymeric material coating on each of the layers. The polymeric material may include microspheres therein so that the structure is compressible. A topcoat or facestock as a substrate is applied to the uppermost layer of the fabric. This entire process may require 15 or 20 coating passes (pass) through the polymer laminator, plus 3 or 4 layers of fabric.
The key to achieving a printing blanket with the desired compressibility, stress and resiliency is to provide a compressible layer therein. In particular, it is generally known that: by including at least one layer of material in the printing blanket comprising a fabric-reinforced resilient polymer-compressible layer, printing problems such as those described above and "blurring" (i.e., lack of sharpness) caused by small standing waves (standing waves) on the printing surface of the blanket adjacent to the press nip or nip (nip) can be avoided. Such a compressible layer can also be used to absorb "breaks" (smash), i.e. large deformations of the blanket, for example due to temporary increases in the thickness of the material to be printed, caused by the accidental introduction of more than one sheet of paper during printing. By incorporating a compressible layer on the blanket, "breaks" can be absorbed without causing permanent damage to the blanket or compromising the print quality of the blanket. In addition, the resilient, compressible layer on the blanket helps maintain the flatness of the printing surface and the thickness of the blanket during printing by restoring the gauge thickness of the blanket after compression at the nip of the printing press.
Nevertheless, blankets of the above type have a number of disadvantages which adversely affect their service life and print quality. For example, blankets are susceptible to wicking of ink, water, and solvents commonly used in printing shops, either by exposed cut edges of the blanket, or, where these edges are protected by the application of a sealant, directly through cracks on the blanket or the bottom layer of the fabric. Water, solvents, and inks that penetrate to the lower layers of the blanket due to capillary action may react with or degrade the adhesive that bonds the blanket layers together. At best, this can cause the printing blanket to bubble, which can result in reduced print quality and reduced print speed due to imbalances created on the blanket. In the worst case, the capillary action can cause delamination of the blanket, which can lead to substantial damage and long downtime of the printing apparatus.
Therefore, it is highly desirable to produce a printing blanket that does not require as many polymer layers and laminations while also maintaining the required stress characteristics of the multi-layer blanket. It is also desirable that such blankets be resistant to solvents and other chemicals and thus resistant to delamination of the blanket. It is also desirable from an environmental standpoint to eliminate as much of the volatile solvent as possible. It is also desirable to be able to manufacture these blankets at a lower cost than the multi-layer blankets currently known in the art.
U.S. patent 6645601 to Serain et al describes a printing blanket that includes at least one layer of a thermoplastic elastomer. The layer may be made of polyurethane.
U.S. patent 6071620 to Kuczynski et al discloses a lithographic layer of a printing blanket. The lithographic layer (i.e., the printing surface) is a layer of thermoplastic material that ensures maximum transfer of printing ink from the blanket cylinder to the paper. The thermoplastic is preferably polyurethane or ethylene-propylene polarized by incorporation of additional ingredients such as ethylene vinyl acetate, mineral fillers, plasticizers, and pigments.
U.S. patent No. 6027789 to Canet al discloses the printing surface of a printing blanket. A primer layer beneath the printing surface is disclosed which may be made of a hydrophobic or hydrophilic elastomeric material such as a formulated polyolefin or polyurethane.
U.S. patent No. 5974974 to Agnew et al discloses a printing blanket in which the print layer is formed of an elastomeric polymer formed by photopolymerization. The polymer may be a polyurethane.
U.S. patent No. 554968 to Byers et al discloses a printing blanket in which the conventional compressible layer can be eliminated by incorporating an impregnated compressible fabric. The infusion fabric may be comprised of a thermoset polymer having microspheres therein.
U.S. patent No. 5487339 to Breventani et al discloses a method of attaching a fixing strip to a printing blanket in which a strip of thermoplastic or thermosetting hot melt material, such as polyurethane or nylon, is used to attach the fixing strip to the printing blanket.
U.S. patent No. 5389171 to Bartholmei et al discloses a method of making a printing blanket wherein the outer cover layer (i.e., the print layer) is preferably made of an elastomeric cured polymer such as polyurethane.
U.S. patent No. 5352507 to Bresson et al discloses a seamless multi-layer printing blanket in which the resiliently compressible layer comprises a foamed elastomeric material, such as polyurethane, which may be reinforced with fibers.
U.S. patent No. 4303721 to Rodriguez et al discloses a closed cell foam printing blanket in which the compressible layer may comprise polyurethane.
U.S. patent No. 4174244 to Tomas et al discloses a method of making a printing blanket wherein the blanket, or top printing layer, may comprise any material having resilient or compressive properties that will cure and optionally foam under molding conditions. Examples of acceptable materials include polyurethane.
U.S. patent No. 3983287 to Goosen et al discloses a printing blanket in which the elastic layer comprises polyurethane.
Additional objects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
Detailed Description
The fabric base 12 is comprised of at least one fabric ply (fabric) having warp fibers 14 and weft fibers (fill fibers) 16, the warp fibers 14 and weft fibers 16 being formed of natural or synthetic materials. These fibers are woven from spun or filament yarns of the desired length. Cotton, polyester, nylon, rayon, and the like are typical materials for the fibers or yarns used as the fabric base 12.
Preferably, warp fibers 14 are formed of a natural material such as cotton, but weft fibers 16 are comprised of a synthetic textile (e.g., polyester). Both the warp and weft fibers or yarns should have a tensile strength of at least 30 pounds per square inch (psi). The substrate preferably has a yarn count per inch in the range of about 55 to 61 for the warp yarns and about 57 to 63 for the weft yarns. The fabric substrate has a weight in the range of about 5.8 to 6.2 ounces per square yard (outer/sq.yd.) and a thickness (also referred to as a "gauge") in the range of 0.014 to 0.016 inches. The warp direction has a tensile strength of at least about 150 lbs/inch and the fill direction has a tensile strength of at least about 60 lbs/inch. Further, in preferred embodiments, the fabric substrate should be capable of having a residual elongation of no more than about 1.9%.
In general, the count of fibers or yarns per inch in either the warp or weft direction in the fabric plies used in the present invention can vary from 20 to 150, depending on the denier of the fibers or yarns. In addition, a fabric weight in the range of 2 to 8 ounces per square yard, preferably in the range of about 4 to 8 ounces per square yard, and a thickness in the range of 0.005 to 0.03 inches may be used as a specific application for the various fabric plies of the present invention.
In addition, the fabric substrate 12 is knife coated, calendered (calendared), dip coated, or otherwise contacted with the adhesive material 20 only on its upper surface. Suitable binder materials include thermoplastic resins, thermosetting resins, polyurethanes, and natural or synthetic elastomers. Polyvinyl chloride (PVC) and other polyolefins are suitable thermoplastic resins, with polyurethanes being preferred.
Suitable adhesives include those of the acrylonitrile, neoprene, acrylic series. Polysulfides may also be used alone or in combination with acrylonitrile or neoprene. Any natural or synthetic elastomer may be used if desired, and these materials are preferred for use in the present invention.
Preferably, the binder may be a thermosetting resin, most preferably a thermosetting polyurethane or polyurea. The preferred viscosity of the matrix material is in the range of about 10000 to 25000 centipoise (cps).
Moisture-curable polyurethanes are formed from resins having terminal isocyanate (NCO) groups in the molecule. They are usually single-component polyurethane prepolymers. With application, the prepolymer or isocyanate groups react with atmospheric moisture to form the final crosslinked coating.
These are generally low molecular weight, linear polymers with terminal isocyanate groups. Such isocyanate-terminated prepolymers can be prepared by reacting an excess of polyisocyanate with a high molecular weight hydroxy polyester or polyether polyol.
The isocyanate end groups are reacted with any active hydrogen containing compound such as alcohols, amines, or other polyurethane and urea compounds. For moisture curing systems, the active hydrogen is provided by atmospheric moisture. Thus, the relative humidity will affect the speed at which the system cures.
The reaction is in two steps, where water first reacts with isocyanate groups to produce amines and carbon dioxide. The amine will then react with other isocyanate groups to form urea until all available isocyanate is consumed. The carbon dioxide produced diffuses through the membrane and then volatilizes from the system. The reaction can be summarized as follows:
-NCO+H2O→-NH2+CO2
-NCO+-NH2→-NH-CO-NH
-NCO+-NH-CO-NH→-NH-CO-NH-CO-N
the adhesive material used with the fabric plies may additionally include a plurality of cells therein. These cells, either closed or open, are similar to the construction of the compressible layer, described below.
Located directly above and bonded to the adhesive 20 is a fabric 30 comprising at least one fabric ply. The fabric plies of the fabric 30 are similar in many respects to the fabric base 12 discussed above in that the fabric plies of the fabric 30 are composed of warp fibers 32 and weft fibers 34, the warp fibers 32 and weft fibers 34 being formed of natural or synthetic materials, respectively. These fibers, as in the case of base 12, comprise spun or filament yarns of the desired length and are machined. Preferably, the warp fibers are formed of a natural material such as cotton, while the weft fibers are comprised of a synthetic textile (e.g., polyester). Both the warp and weft fibers or yarns should have a tensile strength of at least about 30 psi.
In a preferred embodiment, the yarn counts per inch of the layers of fabric 30 are in the range of about 75-80 (warp) and 53-58 (weft). The weight of the fabric 30 is in the range of about 4.9 to 5.3 ounces per square yard. The thickness of the fabric 30, i.e., the gauge, is in the range between 0.0105 and 0.0115 inches. Warp fibers 32 have a tensile strength of at least about 150 lbs/inch. The tensile strength of the weft fibers 32 is at least about 40 lbs/inch. The fabric 30 should be capable of having a residual elongation of no greater than 2.2%.
Located above fabric 30 is compressible layer 40. Compressible layer 40 is made of a suitable elastomeric thermoset polymer matrix 42 into which a plurality of cell-forming materials or microspheres 44 are uniformly dispersed to form a compound. The polymer matrix can be a material similar to that used in adhesive layer 20, including acrylonitrile, neoprene, acrylic series, and polysulfides can also be used, either alone or in combination with acrylonitrile or neoprene. Preferably, the polymer matrix is a thermosetting resin, most preferably a thermosetting polyurethane or polyurea. The preferred viscosity of the matrix material is in the range of about 50000 to 60000 cps.
Typically, the microspheres are formed from materials such as thermoplastic resins, thermoset resins, and phenolic resins. The microspheres have a diameter in the range of about 1 to 200 microns, preferably in the range of 50 to 130 microns, with an average size of about 90 microns being most preferred. They are dispersed relatively uniformly throughout the matrix material so that they become thoroughly embedded in their interstices once the matrix is applied to the fabric ply. Thus, in use, the microsphere loaded material described herein will be infused into the fabric substrate substantially from the upper side thereof.
The microspheres are uniformly distributed throughout the elastomer to avoid any significant cracking of the microspheres. Furthermore, the microspheres are incorporated into the elastomeric material at about 1 to 20% by weight, preferably with a solids fraction of 1 to 10%. This percentage will vary based on such parameters as the size of the microspheres, the wall thickness, the degree of any cross-linking and the bulk density, or whether a blowing agent (blowing agent) is additionally incorporated into the matrix.
To form the cells in the above embodiments, various microspheres 44 may be added to the solution or dispersion of matrix 42. If a solvent solution is used, the selected microspheres must be resistant to chemical attack by the solvent.
Several acceptable thermoplastic microsphere types for use in the present invention are commercially available, for example, from Expancel and Dualite. Thermoplastic resin microspheres are preferred in this embodiment.
If desired, the microspheres may further include a coating thereon to prevent them from coalescing. Thus any of a variety of coatings may be used, such as talc, calcium carbonate, zinc oxide, titanium dioxide, mica, calcium sulfate, barium sulfate, antimony oxide, clay, silica, and aluminum trihydrate. The wrong choice of ball or coating may hinder the desired properties of the substrate and may adversely affect its polymerization.
Preferably, the polyurethane compressible layer 40 of the present invention is a hot melt, moisture curing system similar to adhesive 20 and does not use a solvent carrier. Therefore, the method can be applied without the need for a repeated layer process (layer pass) inherent in the prior art. Compressible layer 40 may be used as a single layer that may be applied in excess of 0.04 inches in a single process step. In typical blankets of the prior art, the compressible layer is formed by depositing thin layers of the layers onto the fabric, applied in succession to form the desired thickness, which is necessary for the solvent to evaporate efficiently from the coated elastomer without forming voids in the compressible layer. Thus, the preparation and curing time of the blanket is greatly reduced.
Compressible layer 40 may be bonded to fabric 30 with, for example, a suitable adhesive layer (not shown). The particular adhesive will depend on the particular elastomer used to form the layer. Preferably, compressible layer 40 is bonded directly to fabric 30 without the use of additional adhesives.
Located above compressible layer 40 is a top fabric 50, which top fabric 50 is comprised of at least one fabric ply. Fabric 50 can then be bonded to compressible layer 40 using a suitable adhesive such as those described above. Preferably, fabric 50 is extruded (nip) directly into compressible layer 40, avoiding the need for an adhesive.
The fabric plies of the top fabric 50 are similar in many respects to the fabric base 12 discussed above in that the fabric plies of the fabric 50 are comprised of warp fibers 52 and weft fibers 54, the warp fibers 52 and weft fibers 54 being formed of natural or synthetic materials, respectively. These fibers are woven and composed of staple or filament yarns of the desired length, as in the case of the base 12. Both the warp and weft fibers or yarns should have a tensile strength of at least about 30 psi.
In a preferred embodiment, the layers of the fabric 50 have a cotton count in the range of about 100 to 105 ends per inch in the warp direction and 77 to 82 ends in the weft direction. The weight of the fabric used to form the fabric 50 is in the range of about 3.7 to 3.9 ounces per square yard and the thickness, i.e., gauge, of the top layer 50 is in the range of 0.008 to 0.010 inches. The top layer 50 has a tensile strength of at least about 70 lb/in the warp direction. The top layer 50 has a tensile strength of at least about 60 lb/in the fill direction. In the top fabric ply 34, the fabric stretch may be in the range of between about 6 and 10%.
Bonded to the upper portion of the fabric 50 is an elastomeric bottom surface 60, which elastomeric bottom surface 60 is formed of a high durometer, high tensile, low elongation compound (i.e., as compared to the material forming the printing surface as described below), preferably a compounded nitrile rubber. Alternatively, however, various water and solvent based elastomeric compounds well known in the art may be used in place of nitrile rubber in forming the bottom surface. The bottom surface 60 is provided to reinforce the printing surface, thus improving the life of the blanket and resisting cutting in use.
The elastomeric printing surface 70 is adapted to receive a printed image from a printing plate and transfer it to, for example, a paper substrate, the elastomeric printing surface 70 being the uppermost layer on the stack/coating blanket 10. In prior art blankets, the application of the elastomeric printing surface is generally accomplished by the known method of knife over roll coating, wherein the solvated elastomeric compound is applied in a number of sequential steps, each by, for example, attaching a thickness of about 0.001 inch to the bottom or top fabric layer. Furthermore, as noted above, the elastomeric material used to form the printing surface has a low hardness and tensile strength and a high elongation compared to the material used to form the bottom surface.
Furthermore, such printing blankets as described above typically have a rough surface profile to maintain good release performance of the blanket while reducing dot gain. In the past, such rough contours were created either by shaping during curing or by polishing the cured surface using media or rough sandpaper, as is known in the art. The surface profile is thereafter measured by means of, for example, an apparatus known as a profilometer (manufactured by pershen corporation), which is also known in the art. The surface profile of the printing face of the prior art laminated blanket typically has an average roughness (i.e., RA) of 1.0 to 1.8 microns, while the casting blanket (castblanket) which does not have good release properties typically has an RA of 0.3 to 0.5 microns. In this regard, it is important to note that the higher the average roughness, the worse the print quality becomes because the dot uniformity is reduced.
However, in the blanket 10 of the present invention, the average roughness of the printing face 70 is adjusted to be above about 0.6 microns but below about 0.95 microns, and preferably between about 0.7 and 0.9 microns, by using fine sand paper. The advantage of this treatment is that it provides very good release properties to the blanket, while also leading to an improvement in the structure of the printing dots, thus providing improved print quality and improved release properties for the blanket of the invention. This effect can also be achieved by many alternative methods known in the art, such as molding.
Examples of the present invention
Example 1
The adhesive was conditioned for 2 hours in an oven at 85 ℃ prior to application.
The samples were prepared as follows: the samples shown were painted on S/4195 (bottom layer) with a 0.010 inch K/R gap setting. S/4200 (middle layer) is then pressed/laminated onto the coated base layer. The sample was cured for 24 hours.
The polyurethane composition was heated at 120 ℃ for two hours. The middle layer carcass was then coated with the PU composition shown in a 0.035 inch K/R gap setting. The top layer S/4232 is then laminated into the thermal adhesive. The sample was cured for 72 hours.
The following PUs are provided:
viscosity was measured using a Brookfield TT-100 on-line viscometer. The gauge length is measured by a Cady self-weight workbench micrometer or a Cady gauge. E130-095AD microspheres manufactured by Dualite are used in the compressible polyurethane layer. The next blanket carcass was made using the provided composition and the following results were obtained:
| skeleton # | Adhesive layer | Compressible layer | Gauge length | Stress (Kg/cm)2) |
| 1 | D(SGH 0005-3A) | A(SG 1516-31) | 0.049 | 50.1 |
| 1 | D(SGH 0005-3A) | A(SG 1516-31) | 0.051 | 40.6 |
| 2 | D(SGH 0005-3A) | B(SG 1516-32) | 0.051 | 45.1 |
| 2 | D(SGH 0005-3A) | B(SG 1516-32 | 0.050 | 39.0 |
| 3 | D(SGH 0005-3A) | C(SG 1516-33) | 0.051 | 35.3 |
| 3 | D(SGH 0005-3A) | C(SG 1516-33) | 0.051 | 34.3 |
Example 2
The adhesive was conditioned in an oven at 120 ℃ for 2 hours prior to application.
The samples were prepared as follows: the samples shown were painted on S/4195 (bottom layer) with a 0.010 inch K/R gap setting. S/4200 (middle layer) is then pressed/laminated onto the coated base layer. The sample was cured for 24 hours.
The polyurethane composition was heated at 120 ℃ for two hours. The middle layer carcass was then coated with the PU composition shown in a 0.045 inch K/R gap setting. The top layer S/4232 is then laminated into the thermal adhesive. The sample was cured for 96 hours.
The compressible layer PU includes Dualite E130-095AD microspheres.
The following PUs are provided:
| composition # | Viscosity (cps) @100 ℃. | Opening time (sec.) | % of microspheres (weight) |
| A(SG 1516-137) | 12200 | 24 | 0 |
| B(SG 1516-138) | 11270 | 55 | 0 |
| C(SG 1516-144) | 23950 | 60 | 0 |
| D(SG 1516-148) | 65000 | 10 | 6 |
| E(SG 1516-149) | 62800 | 30 | 6 |
Viscosity was measured using a Brookfield TT-100 on-line viscometer. The gauge length is measured by a Cady self-weight workbench micrometer or a Cady gauge. E130-095AD microspheres manufactured by Dualite are used in the compressible polyurethane layer.
The next blanket carcass was made using the provided composition and the following results were obtained:
| skeleton # | Adhesive layer | Compressible layer | Gauge length | Stress (Kg/cm)2) |
| 1 | A(SG 1516-137) | D(SG 1516-148) | 0.0555 | 29.69 |
| 2 | A(SG 1516-137) | E(SG 1516-149) | 0.0555 | 29.56 |
| 3 | B(SG 1516-138) | D(SG 1516-148) | 0.0555 | 28.64 |
| 4 | B(SG 1516-138) | E(SG 1516-149) | 0.0590 | 26.31 |
| 5 | C(SG 1516-144) | D(SG 1516-148) | 0.0540 | 25.21 |
| 6 | C(SG 1516-144) | E(SG 1516-149) | 0.0530 | 27.21 |
Example 3
The adhesive was placed in an oven set at 120 ℃ for 2 hours prior to coating. The samples were prepared as follows: the samples shown were painted on S/4195 (bottom layer) with a 0.010 inch K/R gap setting. S/4200 (middle layer) is then pressed/laminated onto the coated base layer. The sample was cured for 24 hours.
The polyurethane composition was heated at 120 ℃ for two hours. The middle layer carcass was then coated with the PU composition shown in a 0.045 inch K/R gap setting. The top layer S/4232 is then laminated into the thermal adhesive. The sample was cured for 96 hours.
The following PUs are provided:
| composition # | Viscosity (cps) @100 ℃. | Opening time (sec.) | % of microspheres (weight) |
| A(SG 1516-148) | 65000 | 10 | 6 |
| B(SG 1516-149) | 62800 | 30 | 6 |
Viscosity was measured using a Brookfield TT-100 on-line viscometer. The gauge length is measured by a Cady self-weight workbench micrometer or a Cady gauge. E130-095AD microspheres manufactured by Dualite are used in the compressible polyurethane layer. The next blanket carcass was made using the provided composition and the following results were obtained:
| skeleton # | Adhesive layer | Compressible layer | Gauge length | Stress (Kg/cm)2) |
| 1 | A(SG 1516-148) | A(SG 1516-148) | 0.055 | 20.28 |
| 2 | B(SG 1516-149) | B(SG 1516-149) | 0.055 | 22.89 |
Example 4
The adhesive was conditioned in an oven at 120 ℃ for 2 hours prior to coating. The samples were prepared as follows: the samples shown were painted on S/4195 (bottom layer) with a 0.010 inch K/R gap setting. S/4200 (middle layer) is then pressed/laminated onto the coated base layer. The sample was cured for 24 hours.
The polyurethane composition was heated at 120 ℃ for two hours. The middle layer carcass was then coated with the PU composition shown in a 0.045 inch K/R gap setting. The top layer S/4232 is then laminated into the thermal adhesive. The sample was cured for 96 hours.
The following PUs are provided:
| composition # | Viscosity (cps) @100 ℃. | Opening time (minutes) | % of microspheres (weight) |
| A(SG 1516-188) | 27400 | 3.0 to 6.0 minutes | 0 |
| B(SG 1516-189) | 27800 | 3.5 to 6.5 points | 0 |
| C(SG 1516-193) | 52800 | 3.5 to 6.0 minutes | 6 |
| D(SG 1516-194) | 50250 | 2.0 to 3.0 minutes | 6 |
Viscosity was measured using a Brookfield TT-100 on-line viscometer. The gauge length is measured by a Cady self-weight workbench micrometer or a Cady gauge. E130-095AD microspheres manufactured by Dualite are used in the compressible polyurethane layer. The next blanket carcass was made using the provided composition and the following results were obtained:
| skeleton # | Adhesive layer | Compressible layer | Gauge length | Stress |
| 1 | A(SG 1516-188) | D(SG 1516-194) | 0.054 | 20.02 |
| 2 | B(SG 1516-189) | C(SG 1516-193) | 0.059 | 20.07 |
In addition, carcass #1 shows an adhesion of 2.7 lbs/inch between the bottom and middle layers. Armature #1 also had an adhesion of 13.1 lbs/inch between the middle layer and the top layer.