JPH07205566A - Blanket used with blanket cylinder - Google Patents

Abstract

PURPOSE: To accurately register an image at each printing station by forming a blanket so as to change its section. CONSTITUTION: The blanket 18 mounted on the blanket cylinder 14 is made of an elastomer. For example, the blanket is made of a nitrile containing fiber- reinforced material. A composite material comprising a microporous elastic polymer layer B, a knitted woven fabric layer 3 and a solvent resistant elastomer layer D is formed of a layer A of a filament material 1 and a compressible layer. For example, as the layer A, rayon cords are embedded in a flexible polymer blend 2 of nitrile rubber or the like. The layer B is made of a miroporous nitrile rubber. The layer C is impregnated with a polymer mixture 4 such as the same nitrile rubber as that of the printing surface. The layer D is a veneer type printing surface of a nitrile rubber blend.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to problems in the field of printing, especially offset printing.

[0002]

During operation of an offset printing press, an ink pattern is transferred to a material at a printing station by a blanket mounted on a blanket cylinder. These patterns are transferred from the plate cylinder to the blanket. For full color printing, typically for lithographic printing, four such blankets and cylinders are used at four printing stations. They are for each process color and black plate.
A full color image is formed by overlaying four patterns on top of each other. In order to accurately form one image with four images transferred by four separate blankets, the images formed by each blanket at each printing station must be registered with each other.

The web (typically paper) on which the image is formed
Unexpectedly distorting the geometry of the will result in inaccurate image registration. Then, the more inaccurate, the greater the blurring of the composite image.

One cause of this distortion is that the web tends to absorb moisture as it traverses the printing station.
The source of this moisture is the dampening water that dampens the printing plate. The fountain solution dampens the plate surface portion to which the ink (which is hydrophobic) is not desired to adhere. If the web absorbs this dampening water sufficiently, a "fan-out" phenomenon of lateral spreading occurs. With each passing print station, this phenomenon progresses and the web's lateral geometry gradually expands,
The distortion increases as it passes through the press. The lateral distortion causes the above-mentioned misregistration of the image.

A commonly practiced solution to this problem is to compensate for the distortion before the web reaches the blanket portion of the printing station. The so-called "bustle wheel"
Are used for this purpose. The Basle Wheel is a rotating disk that impresses rubbing width-reducing webs in front of the printing station. The stretched web absorbed by the dampening water is compensated for by the shrinkage by the Basle wheel to correct the register. This bassle wheel can be viewed as a solution to a very specific type of distortion that occurs downstream of the printing unit.

Another common cause of web distortion lies in web wrinkles that occur during lithographic printing. Therefore, much attention has been paid to this type of distortion.

There are various causes of this wrinkle, some of which are due to vibration, some of which are due to mechanical misalignment, and the other of which is due to uneven manufacturing of the web itself.
One solution to this wrinkle problem is to remove it after it has developed. For example, it is often used to remove wrinkles by laterally stretching the web using a concave spreading roller. The web is wound around a rigid steel roller that is curved 90 ° to 180 ° with a concave cross section. By moving in cooperation with this concave steel roller, the web is stretched in the transverse direction. One variation of the concave spreading roller is a cylindrical roller that is rotated about a curved axis of rotation. Unfortunately, the spreading roller cannot be placed between the printing units. This is because the partially inked, flat web passes over a portion of the curving roller, which smears the image. Similarly, the use of a Basle wheel downstream of the printing station is impractical. This is because, when the use is not limited to the non-printed area on the peripheral surface, the ink on the web is also stained. Spreading rollers are also similar to bustle wheels in that they are thus limited to solving special problems upstream of the printing unit.

Moreover, neither of these solutions directly addresses what is happening at the printing station itself where web wrinkling actually occurs. Those solutions anticipate the occurrence of distortion and take counter measures to fan it out (such as the Basle wheel) or remove it after it has wrinkled and before the web reaches the printing station. It only takes measures (spreading roller).

[0009]

Wrinkles occur at the nip of a blanket cylinder as the web passes through the blanket cylinder. The result is an irregular velocity distribution of the web passing through the blanket cylinder. Due to the geometrical distortions that occur when the web passes over the deformable cylinder and the blanket, respectively, the effective speed of the web through the nip of the blanket cylinder varies along the linear extension of the nip itself. . For example, due to the bending effect of the barrel, and / or the effect of blanket stiffness and / or compressibility,
The velocity distribution of the web passing through the nip becomes non-uniform. That is, the center of the web is faster than the edges of the web, which causes wrinkling. This is an example of a problem that occurs at a print station, which is best solved at the print station without smearing the image.

This requires a mechanism for smoothing wrinkles at the blanket cylinders within the printing stations, which can be used at each printing station to provide accurate registration of images at each printing station. Matching is possible.

[0011]

The present invention solves the above problems by using a blanket cylinder having a blanket that is not uniform in cross section or contour. As used herein, the term "profile" is intended to include the meaning of changes in the blanket that can change with axial position. In particular, the term includes the meaning of changes in the blanket material properties, such as compressibility, stiffness, material thickness, etc., with axial position.

With respect to wrinkling due to fluctuations in the web speed along the nip, a cross section having a concave thickness is effective in preventing wrinkling. In contrast to blanket cylinders with flat, straight cross-sections, concave cross-section cylinders increase web edge velocity. This is because the edge of the concave cross section has a larger effective radius than the center (thus forming a longer arch for a given angular velocity). The combined effect of the use of a concave cross section and other elements that provide the opposite effect (eg, body bending, blanket compressibility and stiffness) is such that the two do not oppose each other and wrinkle. , Velocity distribution when passing through the nip, that is,
In this particular example, a constant velocity distribution is obtained.

Alternatively, when another factor is combined to produce a specific wrinkle generation pattern in the web, the development of a blanket having an appropriate cross section prevents the formation of wrinkles or the removal of already formed wrinkles. Is possible. In essence, by applying the basic principles of this mechanism, it is possible to determine the velocity distribution needed to give the web a modifying effect. Further, by overcompensating the variable speed distribution to make the web edges faster than the center, the web is laterally loaded so that the web is pulled laterally as by a spreading roller. can do. This particular embodiment is superior to the spreading roller solution in that it can be used within the printing station itself. This is because the spreading roller cannot be used in the printing station itself for the reasons already mentioned.

[0014]

In order to more fully understand the present invention, the following detailed description of the preferred embodiments is set forth in the accompanying drawings.

The present invention can be implemented in several different configurations and is also applicable to several different types of offset printing machines. In the illustrated embodiment, the present invention is applied to an offset lithographic double-sided printing machine 10.

The lithographic printing machine 10 prints on both sides of the web 12. Further, the printing machine 10 has blanket cylinders 14 and 16 which are vertically equal. Blanket 18, 20
Is attached to the cylinders 14 and 16 and transfers the ink pattern to both surfaces of the web 12. The plates stretched over the upper and lower plate cylinders 22 and 24 are placed at the nips 26 and 28 at the blanket 1
8 and 20 are in rotary contact. The ink pattern is the plate cylinder 22,
It is transferred to blankets 18, 20 at nips 26, 28 by the 24 plate. These ink patterns are also transferred from the blankets 18, 20 to both sides of the web 12.

The printing machine 10 has dampening water devices 30 and 32. The dampening water device applies dampening water to the plate surfaces of the plate cylinders 22 and 24. In addition, the upper and lower inking units 34 and 36 are attached to the plate cylinder 2.
Ink is supplied to 2, 24 plate surfaces. The drive device, indicated generally by the reference numeral 38 in FIG. 1, is a blanket cylinder 14, 16
And the plate cylinders 22 and 24 are rotated at the same peripheral speed. The drive unit 38 also includes dampening units 30, 32 and the inking unit 3.
It also supplies the power to drive 4, 36. The printing machine 10
It may have a different configuration from the one shown. For example,
The printing machine 10 may be configured to print only one side of the web 12.

The blanket itself is preferably made of elastomer, ie nitrile, and may contain fiber reinforcements. For a detailed discussion of blanket structure and composition, see US patent application Ser. No. 07 / 699,668,
Shrimpton U.S. Pat. No. 3,700,541, Rodriguez U.S. Pat. No. 4,303,721, and Larson U.S. Pat. No. 4,042,743. All of these contents are incorporated herein.

Briefly, as shown in FIG.
The blanket 18 is a composite material of A, B, C and D layers. Layer A is a flexible fiber filament material 1, for example rayon cord, partially embedded in a flexible polymer blend 2, for example a blend of nitrile rubber and polypropylene or nylon.

Layer B is a compressible layer, made of a microporous elastomeric polymer such as microporous nitrile rubber and containing uniformly distributed microvesicles produced incorporating hollow microspheres. I'm out.

Layer C is the woven fabric layer 3, about 40 per cm.
Made of material with warp ends. This material is
It is impregnated with the same polymer formulation 4 as the printed surface, for example nitrile rubber.

Layer D is the printing surface in the form of a veneer of a solvent resistant elastomer such as a nitrile rubber compound.

The composite structure of the blanket described above is for illustration purposes only and is not meant to limit the structure of the blanket that may be used in the present invention. For example, any of the blanket structures described in the references cited above can be effectively used in the present invention.

One form of blanket cross-section modification is to vary the thickness. For example, in FIGS. 2 and 3, blanket 18 is formed with a curved concave cross section 19. Due to this concave cross-sectional shape, the lateral edges of the blanket surface are located radially further from the axis of rotation of the blanket cylinder 14 than the central portion of the blanket. By doing so, unlike the case of the conventional cylindrical blanket, a velocity distribution is obtained in which the velocity of the edge portion of the blanket becomes faster than that of the central portion when passing through the nip.

The concave cross-section has a cylindrical blanket attached to a convex mandrel, the outer peripheral surface of the blanket is ground, and a flat and cylindrical side surface having a constant diameter when attached to the convex mandrel. Can be obtained by doing. It should be understood that it is within the scope of the invention that this or a similar grinding procedure can be performed on any of the layers that make up the composite layer blanket.
Other shapes may be obtained using other shapes of mandrels (eg, a blanket with a convex cross section may be attached to a concave mandrel and the blanket ground flat) or a different degree of material may be removed from the blanket. It can be obtained by removing.

By properly selecting the blanket cross-sectional geometry, a uniform blanket is obtained from the web surface velocity as it passes through the nip, thereby preventing wrinkling due to different velocity distributions. Alternatively, other strain producing effects can be compensated by obtaining a velocity distribution that produces a lateral load on the web. In that case, it does not matter whether this distortion effect occurs in the printing station or in front of or behind the printing station.

Section 1 of the blanket 18 shown in FIG.
9'has a uniform thickness, but differs in rigidity, compressibility, and coefficient of friction. For example, by making the rigidity of both edges higher than that of the central portion of the blanket, the velocity distribution when passing through the nip can be corrected, and a function similar to that of the concave section can be obtained.

Generally speaking, the velocity along the cylinder roll is a function of the effective radius which varies with the bending of the cylinder roll and the compressibility or stiffness of the surface of the cylinder roll. Therefore, the effective radius of the cylinder roll can be changed by changing the compressibility or the rigidity.

7 and 8 show another embodiment of the present invention. In the embodiment of Fig. 7, the blanket has a convex cross section 19 ". As already mentioned, depending on the desired effect, either this shape or another shape can be used.

In the case of the embodiment shown in FIG. 8, instead of changing the cross section of the blanket, the cross section of the blanket cylinder 18 'is changed. In this case, a flat blanket is used with a concave blanket cylinder (as opposed to the embodiment of FIG. 2, ie the blanket cylinder has a constant diameter and the blanket has a concave cross section). .

[Brief description of drawings]

FIG. 1 is a schematic view of an offset printing machine.

FIG. 2 is a plan view of a blanket and a blanket cylinder showing a concave profile of one possible embodiment of the blanket. The hidden contour of the torso is shown in phantom.

FIG. 3 is a partial view showing the outline of the blanket of FIG.

FIG. 4 is a side view of a pair of cooperating blanket cylinders for printing both sides of the web.

FIG. 5 is a partial enlarged cross-sectional view of a blanket used as part of the present invention.

FIG. 6 is a plan view of a blanket having a constant thickness with varying material properties as a function of axial position.

FIG. 7 is a plan view similar to FIG. 2 of another embodiment with a convex contour.

8 is a plan view similar to FIG. 2, showing another embodiment in which a flat blanket is attached to a concave blanket cylinder.

[Explanation of symbols]

 10 Flat plate printer 12 Web 14,16 Blanket cylinder 18,20 Blanket 22,24 Plate motion 26,28 Nip 30,32 Damper 34,36 Ink unit

Claims (31)

[Claims] 1. A blanket for use with a blanket cylinder, characterized in that it is made of an elastically deformable material and has a variable cross-section.
Blanket used with the blanket cylinder. 2. The blanket according to claim 1, wherein the thickness of the cross section changes in the axial direction. 3. A blanket as claimed in claim 1, characterized in that the material properties of the cross-section vary in the axial direction. 4. The blanket of claim 3, wherein the material property is blanket stiffness. 5. The blanket of claim 3, wherein the material property is blanket compressibility. 6. The blanket according to claim 1, wherein the blanket is made of a composite material. 7. The blanket according to claim 2, wherein the blanket has a concave cross section. 8. The blanket of claim 1, wherein the blanket comprises an elastomer. 9. The blanket of claim 1, wherein the blanket has a convex cross section. 10. The blanket according to claim 1, wherein the blanket has a seamless cylindrical structure. 11. The blanket according to claim 1, wherein the blanket is flat. 12. In a printing press, a rotatable blanket cylinder having an axis of rotation, blanket means mounted on the blanket cylinder for transferring an ink pattern to a material, and holding an image to be printed, said blanket means. A rotatable plate cylinder for transferring the ink pattern to the plate cylinder, the plate cylinder and the blanket means being arranged for rolling contact at a nip formed therebetween; Driving means for rotating the blanket cylinder and an inking device for supplying ink to the plate cylinder are provided, the blanket means being arranged in rolling contact with the plate cylinder at the nip, the blanket means being the blanket. Has an inner surface profile that matches the outer surface of the cylinder and also its axial direction relative to the blanket cylinder A printing machine comprising an outer surface having a cross-section that varies with position. 13. Blanket according to claim 12, characterized in that the thickness of the cross-section varies. 14. A blanket according to claim 12, characterized in that the material properties of the cross section change as a function of the axial position along the blanket. 15. The blanket of claim 14, wherein the material property is blanket stiffness. 16. The blanket of claim 14, wherein the material property is the compressibility of the blanket. 17. The blanket according to claim 13, wherein the blanket has a concave cross section. 18. The blanket according to claim 13, wherein the blanket has a convex cross section. 19. A method of correcting velocity changes occurring at a nip of a blanket cylinder web, comprising the following steps: sensing a velocity change across the nip that requires compensation and an effective change in effective blanket cylinder radius. By correcting the change to produce the desired velocity distribution and, if the blanket is wrapped around the blanket cylinder, a corresponding change in cross section with respect to its axis, and A method of correcting a velocity change occurring at a nip of a web of a blanket cylinder, the method comprising: mounting the blanket on the blanket cylinder. 20. The blanket according to claim 19, characterized in that the thickness of the cross section varies. 21. The blanket of claim 19, wherein the material properties of the cross section change as a function of axial position along the blanket. 22. The blanket of claim 21, wherein the material property is the blanket stiffness. 23. The blanket of claim 21, wherein the material property is the compressibility of the blanket. 24. The blanket of claim 20, wherein the blanket has a concave cross section. 25. The method of claim 20, wherein the blanket has a convex cross section. 26. The method of claim 19, wherein the blanket has a conical cross section. 27. The method of claim 21, wherein the material property is the coefficient of friction of the material. 28. A method of making a blanket of non-uniform thickness, wherein the blanket of uniform thickness is first
Is attached to a mandrel having a cross-section formed by the curved lines of the blanket, and then the mandrel is removed from the blanket such that the cross-section of the blanket is in the form of a second curved line taken while the blanket is attached to the mandrel. , A method of manufacturing a blanket of non-uniform thickness. 29. The mandrel has a convex cross section,
29. The method of claim 28, wherein the second curve is linear. 30. A blanket cylinder and blanket, wherein the blanket cylinder is formed with a varying outer contour. 31. In a printing press, a rotatable blanket cylinder having a rotation axis, a blanket means mounted on the blanket cylinder for transferring an ink pattern to a material, and a blanket means for holding an image to be printed. A rotatable plate cylinder for transferring an ink pattern to the printing plate, and the printing plate and the blanket means are arranged so as to be in rotational contact at a nip formed therebetween, and the plate cylinder and Means for driving a blanket cylinder and an inking device for supplying ink to the plate cylinder are provided, the blanket means being arranged for rolling contact at the nip, the blanket means being the outer surface of the blanket cylinder. Has an inner surface that conforms to the outer surface of the blanket cylinder A printing machine having a cross-section that changes with axial position.