JPH0220392A - Manufacture of compressive blanket for printing and compressive blanket for printing manufactured through said manufacture - Google Patents

Abstract

PURPOSE: To obtain a closed-cell cellular structure wherein voids having uniform dimensions are not mutually connected, by forming a support layer and a surface layer and inserting a compressive intermediate layer formed by adding microcapsules into an elastomer material between both layers. CONSTITUTION: An adhesive layer 34 is applied to the upper surface of a support layer 26 and a compressive layer 24 is formed by coating a fabric support layer 26 with a mixture prepared by mixing microcapsules and an accelerator with an elastomer compd. The fabric layer 22 is bonded to the layer 24 by an adhesive layer 32. This assembly is initially vulcanized to a degree sufficient to cure a polymer matrix structure in such a state that microcapsules are fixed within the structure. After curing, a second support fabric layer 27 is laminated on the under surface of the layer 26 by using an adhesive layer 36. An acting surface layer 20 is bonded to the upper surface of the reinforcing fabric layer 22 by using an adhesive layer 30 and the obtained assembly is subjected to final vulcanization treatment. At this time, the destruction of voids formed by microcapsules is avoided by the already cured intermediate layer.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method of curing a printing blanket and a printing blanket produced thereby;
It particularly relates to printing compressible blankets of the type used in offset printing processes.

BACKGROUND OF THE INVENTION The use of blankets in offset printing is well known, and their primary function is to transfer ink from the printing plate to the paper. Printing blankets are carefully designed to ensure that the surface of the blanket is not damaged by mechanical contact between the blanket and parts of the printing press or by chemical reactions with the components of the ink.・Ru. Repeated mechanical contact causes some compression of the blanket. This amount of compression must be within acceptable limits for proper reproduction of the image. Also.

The blanket should be resilient.

That is, it is also important that the material eventually returns to its original thickness and that it transfers a constant image regardless of the extent to which it is used.

Printing blankets typically consist of a substrate that provides bonding properties to the blanket. Woven fabric is preferred as this substrate. The substrate may consist of 1.2.3 or more layers of fabric. The active surface - by which we mean the surface that actually comes into contact with the ink - is usually a layer of elastomeric material, for example rubber. Conveniently, the blanket is manufactured by calendering or applying the rubber in layers until the desired thickness of rubber is deposited and then curing or vulcanizing this assembly to form the final blanket. While this type of blanket is acceptable for many applications, it often lacks the compressibility and resilience necessary for other applications. It is therefore desirable to produce blankets with improved resiliency and higher compressibility.

It is difficult to improve the compressibility factor by the above standard manufacturing methods. This is because rubber-based materials, although highly elastic, are not compressible and cannot be compressed in a direction perpendicular to their surface without causing distortion or stretching of the blanket in the area near the point of compression. irregularities in the printing plate, printing press or paper
If there is, the compression imparted to the blanket will vary during the printing operation and irregularities in the printing plate, press or paper will be magnified by the lack of compressibility of the printing blanket.

A means of providing a printing blanketer with the desired compressibility and resilience is to provide it with a compressible layer. In particular, by having the printing blanket contain at least one layer of material consisting of a compressible layer of an elastic polymer.

Printing problems such as those mentioned above and "bleeding"
small standing waves (sta-waves) on the blanket print surface close to the press nip, such as
nding waves) are avoided. Similarly, the compressible layer is
This is due to a temporary increase in the thickness of the material being printed, for example due to the accidental insertion of more than one sheet of paper during the printing operation. It is a deformation.

By inserting a compressible layer into the blanket.

The "smash" is absorbed without permanent damage to the blanket and without compromising the quality of the print on the blanket. In addition, the resilient compressible layer restores the normal thickness of the blanket after being compressed in the press nip, thereby improving the flatness and thickness uniformity of the printed surface of the blanket during printing operations. Helps maintain.

Many means are known in the art for forming compressible layers within printing blankets. For example, compressible layers can be created by mixing granular salts with the polymer used to form the compressible layer, and then leaching the salts from the polymer to form the pores (
void) 'l formed by forming. Pores in the compressible layer allow for volumetric displacement of the surface layer without deformation of the surface layer.
t) becomes possible. This is because the compression and displacement of volume occurs substantially perpendicular to the impact of the printing press. This type of method is described in Haren et al., U.S. Pat.
No. 25,685. Other methods have been used in the past to form compressible layers, such as compressible fibrous structures. An example is Duc!;ett
U.S. Pat. No. 3,887,750 and U.S. Pat.
, 093,764. Rodriguez (
U.S. Patent No. 4,303,72 to Rodríguez)
No. 1 teaches a compressible blanket made with a blowing agent to create pores within the compressible layer. U.S. Pat. No. 3,795.56 to Rhodarmer describes the use of rubber particles to form pores.
No. 8 specification.

The use of blowing agents to form pores has the disadvantage that the size of the pores formed and the interconnection of the pores cannot be easily controlled. Pores that are too large and interconnected can cause areas of the printing blanket to be more compressible and less resilient than adjacent areas of the printing blanket, thereby causing deformation during printing.

Leaching of salts from polymer matrices has the disadvantage that the particle size used is limited and the leaching process is difficult, time consuming and expensive.

More recently, it has been found preferable to produce printing blankets with a compressible layer consisting of a cellular elastic polymer with cells or pores in the form of independent microcells in the compressible layer. . It has been found to be particularly advantageous to form a compressible layer by incorporating hollow microcapsules into the polymer. This is US Pat. No. 3.7 of Shrimpton et al.
0 CI, 541 and (1) and the corresponding British Patent No. 1,327,758; and Larson, US Pat. No. 4,04.
No. 2,743.

In prior art methods of using microcapsules to form compressible layers for printing blankets, the microcapsules that are highly suitable for this application are produced at temperatures lower than the vulcanization temperatures employed for the vulcanization of printing blankets. It was observed that the thickness of the compressible layer formed was not easily controlled as it appeared to melt. The microcapsules formed by the microcapsules melt before the vulcanization is complete and before the compressible layer achieves the hardened structure.
Agglomeration of pores occurs, and variations in pore size also occur. This can affect the blanket's overall performance characteristics. Variations in pore size can also weaken the printing blanket and cause it to wear out prematurely.

SUMMARY OF THE INVENTION It is an object of the present invention to overcome the drawbacks of printing plankerats according to the prior art mentioned above.

The invention relies on forming a support layer and a surface layer and inserting therebetween a compressible intermediate layer formed by microencapsulation in an elastomeric material.

A method for manufacturing a laminated blanket for printing is provided.

According to one aspect of the method of the invention, at least one fabric support layer is applied. A compressible intermediate layer of elastomeric material is formed over this. The elastomeric material has a substantially uniform thickness and the microcapsules are contained therein and are substantially uniformly distributed throughout the compressible layer. The compressible layer is maintained at a temperature below the melting point of the microcapsules for a sufficient period of time for the elastomeric material to be vulcanized to a degree sufficient to substantially fix the position of the microcapsules within the compressible layer. . A surface layer is applied on top of the compressible layer.

A printing blanket structure is formed. The structure is cured in all layers and vulcanized to provide a compressible layer with a substantially uniform distribution of pores of substantially uniform size. In a preferred form, the elastomeric material containing the microcapsules is first heated to a temperature of 46-77°C (110-77°C) by addition of an accelerator that enables vulcanization of the elastomeric material.
170'F) for 1-12 hours. These temperature conditions below the melting point of the microcapsules result in initial vulcanization of the elastomeric formulation and formation of the intermediate layer. A final vulcanization of this assembly under controlled heat and pressure then laminates all the layers to form the imaged printing blanket. The final product consists of a printing laminate blanket comprising at least one support layer, one surface layer, and a compressible intermediate layer disposed between them. The intermediate layer has a substantially uniform thickness; A substantially uniform distribution of pores of substantially uniform size, with the pores having a non-interconnected, closed cell structure, including an additional reinforcing fabric layer. You may lie down.

Other details, features, objects, uses and advantages of the invention will become apparent from the following detailed description, the appended drawings, and the form specifically presented in the claims. Probably.

BRIEF DESCRIPTION OF THE DRAWINGS In order to better understand the present invention, it will be described with reference to the accompanying drawings.

FIG. 1 is a cross-sectional view of one embodiment of the printing blanket of the present invention, showing the relationship between the layers.

FIG. 2 is a flow diagram showing each step constituting one form of the method of the present invention.

Reference is now made to FIG. 1, which shows a printing blanket formed in accordance with the present invention. The printing blanket 10 has a surface layer 20. Reinforcing fabric layer 22, compressible layer 24. and at least one additional layer of fabric as a support. Two fabric support layers 26 and 27 are shown in the figures for illustrative purposes.

Those skilled in the art will recognize that the number and type of layers employed may vary depending on the intended application. Adhesive layer 6
0°32, 34 and 36 are preferred to ensure sufficient bonding between the different layers within the blanket. compressible layer 2
The pores 28 in 4 allow the surface layer 20 to be removed without deformation under operating conditions.

As shown in this figure, the pores 28 within compressible layer 24 are substantially uniform in size, substantially uniformly distributed, and non-interconnected. Pores 28 formed within compressible layer 24
The dimensions of the microcapsules were generally found to be within the same range as those of the microcapsules used to form the pores. Generally the pores are 10-125 microns in diameter, preferably 20-125 microns in diameter.
It is 60 microns.

Compressible layer 24 is formed from an elastomeric material containing conventional processing, stabilizing, reinforcing and hardening additives and formulated with reference to its particular application. This formulation is different from that used for surface layer 20, as is known in the art. Any suitable polymeric material that is considered a curable or vulcanizable material can be used, such as: Natural rubber, styrene-butadiene rubber (SBR), EPOM (ethylene/propylene/non-conjugated diene-terpolymer rubber), butyl rubber.

Butadiene-acrylonitrile rubber (NBR), polyurethane, etc. Elastomers that are resistant to solvents and inks are preferred.

(J6) Adhesive layers 30, 32, 34 and 66 may be any suitable elastomeric additive known in the art. Preferably the adhesive is rubber cement. Fabric layers 22, 26 and 27 should be made of a plain weave with relatively low elongation in the warp direction (longitudinal to the machining of the blanket) and are generally free from slubs and knots, weaving defects.

Made of high quality cotton thread that does not contain seeds. The fabric may be rayon, nylon, polyester or mixtures thereof. When applying adhesive to any of the fabric layers,
This is usually applied by means of a rolling knife spray. The adhesive is applied in layers until the desired thickness is achieved. Generally, the fabric layer has a thickness of about 0.076-0.41 mm (
0.003 to 0.016 inches).

Compressible layer 24 is formed by applying the elastomeric formulation containing microcapsules, as described above, to fabric support layer 26, also by roll knife spraying. The elastomeric formulation is brought to the desired consistency for application by the addition of a solvent. Generally, multiple layer formulations are required to form the intermediate layer 24 of a desired thickness. After each layer is applied, evaporation of the solvent causes it to cure, but not crosslink. Generally, the compressible layer can be about 0.20 to 0.38 inches (0.008 to 0.015 inches) thick. This layer has a thickness of approximately 0.28~
Preferably, it is 0.30 m+a (0.011 to 0.012 inch).

Surface layer 20 is formed by the same method as described in forming the intermediate layer using an elastomer formulation suitable for the working surface of printing blanket 100. Generally, multiple layer formulations are required to form a surface layer 20 of a desired thickness.

Generally, the surface layer has a thickness of about 0.13 to 6.4 mm (0.005 mm).
~0.25 inch), preferably about 0.25 to 0.68
mm (0.010 to 0.015 inch). Thickness approximately 0.60~0.68 dragon (0,012~0.
It is highly preferred to apply a surface layer of 0.015 inch).

According to the invention, resin microcapsules known in the art can be used in the intermediate layer. Any L microcapsule with the properties described herein is suitable for the present invention. Melting point approximately 74-132°C (165-2
70°F) can be used. Preferably, the microcapsules melt at about 180'F. Certain materials suitable for use in microcapsules are phenolic resins and thermoplastic materials such as polyvinylidene chloride. Preferably, the material used to make the microcapsules is a thermoplastic material. Examples of materials of this type are polyvinylidene chloride, polymethyl methacrylate, polyvinyl chloride, polyacrylonitrile and copolymers thereof. Preferably, a copolymer of acrylonitrile and vinylidene chloride can be used. Mixtures of different types of thermoplastic microcapsules may be used if desired.

Furthermore, it has the properties described herein. U.S. Patent No. 2,
Any of the resins described in No. 797,201 may be used. Of course, it should be understood that these materials listed by name are merely examples, and the present invention is not limited thereto.

(J9) The microcapsules used in the method of the invention are approximately spherical, with a diameter of 10-100 microns, and an average particle size of about 60-50 microns. These capsules are
For example, it is formed by a thin elastic thermoplastic shell made of vinylidene chloride/acrylonitrile copolymer or a similar material.

These capsules are generally described in U.S. Patent No. 2.797,20.
No. 1 or No. 3,615,972. These capsules may contain an inert gas to maintain their shape.

These capsules are prepared by conventional methods, for example by dispersing them in an elastomeric dough.

Can be mixed with an elastomeric matrix. These capsules are dispersed by uniformly mixing them throughout the elastomeric matrix for a certain period of time. Since the mixing operation generates a certain amount of heat, it is preferable not to mix for more than 60 minutes. Detailed studies have been carried out on the preferred form using electron microscopy and show that according to the method of the present invention substantially all, if not all, of the microcapsules used to form the compressible layer are present in the final printing planter; This suggests that it is recognized within the site.

The amount and size of individual capsules used is based on the desired compressibility of the blanket. For example to obtain a compressible layer with 50% porosity.

Microcapsules with an average diameter of 40 microns can be used in a ratio of 50% of the elastomeric material used in the compressible layer.

It is preferred to avoid the presence of water when incorporating microcapsules into the elastomer to avoid the introduction of water vapor during subsequent heating of the polymer. For this reason, it is preferable to dry the microcapsules before mixing with the elastomer.

Next, referring to FIG. 2, this is a flow diagram illustrating each step in one embodiment of the printing blanket manufacturing method of the present invention. The reference numbers used in FIG. 2 are the same as those used in FIG. 1 where the same elements are described. As illustrated in this flow diagram, an adhesive layer 64 is applied to the top surface of the support layer 26.

Compressible layer 24 is formed by mixing the microcapsules and active agent or accelerator with an elastomer formulation for about 30 minutes and applying this formulation onto fabric support layer 26 . Generally, multiple layer formulations are required to obtain a compressible layer of desired thickness. An adhesive layer 62 is then applied to the top surface of layer 24 to adhere fabric layer 22 to layer 24. The resulting assembly is then subjected to sufficient heat to pre-vulcanize the polymer matrix structure sufficiently to cure with the microcapsules secured therein. This vulcanization is made possible by the addition of accelerators that promote vulcanization at low temperatures. Vulcanization for 8 hours at 66°C (150'F) is preferred, but 46-77°C (110-170 below)
Temperatures of 1 to 12 hours can also be employed. In theory, longer periods at ambient temperature are also possible. The preferred accelerators mentioned in this example are dithiocarbamates, such as those commercially available under the trademark "Buty 1-Eight" (available from R.T. Panderbilt). Another example of an accelerator used in the present invention is piperidinium pentamethylene dithiocarbamate (Accel 55).
Zinc dibenzyldithiocarbamate (Araza)
te) (obtained from Uniroyal), zinc dibutyldithiocarbamate (butyl diram (Bu
tyl Ziram) (Trademark), available from Pennwald Company). This low temperature vulcanization creates a permanent cell structure that does not change throughout the rest of the manufacturing process.

In a preferred form of the invention, a low temperature initial vulcanization using an accelerator will provide optimal final vulcanization of the compressible layer. That is, all highly crosslinkable sites in the polymer are crosslinked in this step, and this crosslinking provides the desired modulus and resilience as well as other elastomer properties. Of course, those skilled in the art will recognize that crosslinking in rubber products is an intermittent process and no rubber material is completely crosslinked. Therefore, one skilled in the art knows that the elastomeric matrix containing the microcapsules freezes the microcapsules in place at 6°.

It will be appreciated that vulcanization in the cold cure of the compressible layer may be interrupted before optimal vulcanization is reached, as long as the cure is sufficient to yield an acceptable product.

Thus, a "partially vulcanized compressible layer can better crosslink with the support layer and the printing surface. However, it will be appreciated by those skilled in the art that a substantially fully vulcanized compressible layer can be used for this purpose." It will also be appreciated that the support and surface layers may be crosslinked by specially formulated rt,y,-adhesives.

After curing of the compressible layer 24, the second supporting fabric layer 27'l [
26f7') Laminate the adhesive layer 66 on the lower surface using a laminating pinch roll. After this step, a working surface layer 20 formulated according to the above is applied to the top surface of the reinforcing fabric layer 22;
At that time, the adhesive layer 60 is used for adhesion. The resulting assembly was then heated at 132-160°C (270-320'P
), preferably 146-149°C (290-300°F
) at a temperature of 5.2 bar (75 psi) from atmospheric pressure
A final vulcanization treatment is carried out under a pressure of up to 16 hours, known from the time bombardment technique (24). These variables depend on the exact formulation.

In the final vulcanization step, the paper with the fine finish along with the fine talc is brought into contact with the surface of the printing blanket before being placed in the Blankeratra vulcanization oven. The paper in contact with the surface of the printing blanket ensures the smoothness of the printing blanket. This is because the smoothness of paper is imparted to the printing blanket. For most applications the finish thus imparted to the printing blanket will be sufficient for that application and polishing of one surface will be unnecessary.

It has been observed that the process of partially vulcanizing or semi-curing the intermediate layer traps the microcapsules in the elastomer matrix, in a stationary or cured position. Since the position of the microcapsules is set in the matrix,
The position of the pores formed by the microcapsules is predetermined by the position of the microcapsules in the matrix. When the assembled blanket undergoes the final vulcanization step, the structure of the already cured intermediate layer maintains its shape and pore agglomeration or pore destruction within one layer is avoided. This fixed position will not change during final processing of the blanket.

It was noted that the melting temperature of the microcapsules was lower than the final vulcanization temperature. It is likely that some, but certainly most, of the microcapsules melt, but since they are retained within closed cells they reform and act as coatings on the pore walls. The material may also partially contact the elastomer to form a new coating material.

Electron microscopy studies confirmed that the thermoplastic material forming the microcapsules remained within the pores of the finished printing blanket. Of course, as long as the pores are formed in the compressible layer as described above, the presence of microcapsule material within the pores will not affect the performance of the haplankt.

Regardless of what happens, the previously fixed pore structure remains unchanged.

The exact construction of the blanket will vary according to its end use. For example, a single fabric support layer 2 without layer 27
6 or a sixth or more similar layer may be included. It may also be desirable to provide additional reinforcing fabric layers similar to layer 22.

For manufacturing, a compressible layer is produced on site to be used as an intermediate layer within the printing blanket.

The compressed column layer itself forms a separate feature of the invention, since it is also possible to transport this compressible layer to another location for processing of the blanket. The compressible intermediate layer can be manufactured by the same method as the rc one described in the previous description of printing blanket manufacturing.

Generally have the same parameters regarding pore size and distribution. In such cases, it is preferable to apply at least one fabric support layer to the compressible layer prior to vulcanization and transport. It is also possible to peel off the sexual layers, in which case these layers will be added later.

We also prepared a completed blanket structure containing a compressible layer containing microcapsules and a dithiocarbamate promoter, and applied a low temperature to this structure to fix the microcapsules within the compressible layer as described above. A vulcanization step can also be applied before the blanket structure is subjected to a final vulcanization.

It should be noted that the above description is only illustrative of the invention, and other parameters and configurations may be adopted without departing from the inventive idea presented herein. Figure 1 is a cross-sectional view of one form of the printing blanket of the invention, showing the relationship between the layers.

FIG. 2 is a flow diagram showing each step constituting one form of the method of the present invention.

In these figures, each symbol represents the following.

10: Printing blanket 20: Surface layer 22: Reinforcing fabric layer 24: Compressible layer 26.27: Support layer 2
8: Stomata 30, 32.34.36: Adhesive layer

Claims (1)

Claims: 1. Providing at least one fabric support layer and forming thereon a compressible intermediate layer of elastomeric material, the compressible intermediate layer having a substantially uniform thickness; and encapsulating microcapsules, these microcapsules being substantially uniformly distributed throughout the compressible intermediate layer; holding the elastomeric material for a period sufficient to vulcanize the elastomeric material to a degree sufficient to substantially fix the position of the microcapsules, and applying a surface layer over the compressible intermediate layer to form a printing blanket structure. and vulcanizing the structure to cure each layer and provide the interlayer with substantially uniformly distributed and substantially uniformly sized pores. How to make things. 2 adding an accelerator to the compressible intermediate layer during its formation, the accelerator having a
2. A method according to claim 1, which is capable of promoting vulcanization of the compressible intermediate layer within 12 hours. 3. The step of forming a compressible intermediate layer involves preparing an elastomeric material, incorporating microcapsules therein to form a mixture, applying the mixture onto a fabric support layer, and applying fabric reinforcement to the top surface of the compressible intermediate layer. 2. A method according to claim 1, comprising the step of applying a layer. 4. the structure is vulcanized at a temperature of about 132-160°C;
A method according to claim 1. 5. The method of claim 2, wherein the accelerator is a dithiocarbamate. 6. The method according to claim 1, wherein the microcapsules are formed from a thermoplastic resin. 7. The method of claim 2, wherein the accelerator is a dithiocarbamate and the microcapsules consist of a copolymer of acrylonitrile and vinylidecy chloride. 8 consisting of at least one support layer, a surface layer, and a compressible intermediate layer having a substantially uniform thickness, the compressible intermediate layer being of an elastomeric material and containing a number of closed cells forming pores. having a cellular structure, the pores being substantially uniform in size and substantially uniformly distributed throughout the compressible intermediate layer, these pores are microcapsules, and the elastomeric material is distributing an accelerator within the compressible intermediate layer that is vulcanizable at a temperature below the melting point of the capsules, and placing the compressible intermediate layer at a temperature below the melting temperature of the microcapsules; A printed laminated blanket structure formed by holding an elastomeric material for a period sufficient to vulcanize it to a degree sufficient to substantially fix the elastomeric material. 9. The printing blanket of claim 8, wherein the pores have a diameter within the range of about 10-125 microns. 10. The printing blanket according to claim 8, wherein the microcapsules are formed from a thermoplastic resin. 11 consisting of an elastomeric material having a substantially uniform thickness and a cellular structure comprising a large number of closed cells forming pores, the pores being substantially uniform in size and extending throughout the compressible layer. These pores distribute within the compressible layer the microcapsules and an accelerator capable of vulcanizing the elastomeric material at a temperature below the melting point of the microcapsules, and by holding the elastic layer at a temperature below the melting temperature of the microcapsules for a period sufficient to vulcanize the elastomeric material to a degree sufficient to substantially fix the position of the microcapsules within the compressible layer. A compressible layer for a printed laminated blanket structure is formed. 12. The compressible layer of claim 11, wherein the pores have a diameter within the range of about 10-125 microns. 13. The compressible layer according to claim 11, wherein the microcapsules are formed from a thermoplastic resin. 14 Forming a compressible layer of elastomeric material, mixing the microcapsules with the elastomeric material such that the microcapsules are substantially uniformly distributed therein, and bringing the compressible layer to a temperature below the melting point of the microcapsules. ,
holding the elastomeric material for a sufficient period of time to vulcanize the elastomeric material to a sufficient extent to substantially fix the position of the microcapsules within the compressible layer, thereby having a substantially uniform thickness; and forming a compressible layer in which the microcapsules are substantially uniformly distributed throughout the compressible layer. 15 adding an accelerator to the compressible layer during its formation, the accelerator containing about 4
15. The method of claim 14, wherein the method is capable of promoting vulcanization of the compressible layer within about 1 to 12 hours at a temperature of 3 to 77<0>C. 16 Claim 1, wherein the accelerator is a dithiocarbamate
The method described in Section 5. 17. The method according to claim 14, wherein the microcapsules are formed from a thermoplastic resin. 18. The method of claim 14, wherein the step of maintaining the compressible layer at a temperature below the melting point of the microcapsules is carried out at a temperature of about 43-77<0>C. 19. The method of claim 15, wherein the accelerator is a dithiocarbamate and the microcapsules are a copolymer of acrylonitrile and vinylidene chloride.