GB2296895A

GB2296895A - Printing blanket and method for use with platelet-like pigments

Info

Publication number: GB2296895A
Application number: GB9600526A
Authority: GB
Inventors: Francesco Castellie; Giampietro Invernizzi
Original assignee: Reeves Brothers Inc
Current assignee: Reeves Brothers Inc
Priority date: 1995-01-11
Filing date: 1996-01-11
Publication date: 1996-07-17
Anticipated expiration: 2016-01-11
Also published as: ITMI960028A0; GB2296895B; FR2729100B1; GB9600526D0; DE19600736C2; FR2729100A1; IT1281605B1; ITMI960028A1; DE19600736A1; JPH08230304A

Description

1 PRINTING BLANKET AND METHOD FOR USE WITH PLATELET-LIKE PIGMENTS 2296895

This invention relates to a printing system and blanket for transferring platelet-like pigments such as metallic ef f ect inks onto an article to be printed and a method for using the same.

Printing machines used for offset printing, waterless offset printing, coldset-heatset sheetfed metal decorating and other types of printing used in the graphic arts industry, usually include a plurality of cylinders for performing a variety of functions. In particular, most cylinders are arranged to act in direct contact with the paper or other surface to be printed upon, either to transfer ink thereto (impression cylinders) or perform other functions including paper conveyance, feed-in functions (transport cylinders) or counteraction of the pressure from the impression cylinders (pressure cylinders).

Although the above mentioned cylinders perform different functions, they may each be lined with the same type of blanket to provide similar mechanical and dynamic characteristics (e.g. deformability and peripheral velocity retention) to all of the cylinder pairs, thereby ensuring the highest possible paper handling and printing accuracy.

2 A number of printing blanket designs are known. For example, US Patent No. 2792321 discloses a resilient printer's blanket comprising a hard, smooth top surface which is moisture-proof and able to be readily cleaned.

US Patent No. 3881045 discloses an offset printing blanket comprising a void-free printing layer, a polyester film layer, a highly resilient backing layer and a fibrous backing sheet which does not compress under intended use. US Patent No. 4015046 discloses a printing blanket comprising a base, a fluorocarbon surface layer, and a polychloroprene binder, which can be used with a variety of inks and cleaning solutions. Japanese Patent No. 56-144196 discloses a printing blanket, comprising a rubber base and a lipophilic surface, which gives uniform and reproducible ink transfer from a printing plate. US Patent No. 4471011 discloses a multi-layer printing blanket comprising a reinforcing section composed of fabric layers with rubberised layers disposed therebetween, a cover and a rubberised coating, which offers increased durability and life expectancy.

German Patent No. 2227485 relates to an offset printing or duplicating machine comprising an offset cylinder having a cylindrical surface of a polymer with a low critical surface tension and a pressure cylinder to cooperate therewith. This document does not address the problems of paper handling and printing accuracy coupled with the demands of productivity.

French Patent No. 2061062 relates to a coating of a polyamide foil for the pressure cylinder to be used in a printing system. German No. 2718224 relates to a process for preparing a printing blanket wherein a fluororesin is used as the outer layer. However, neither addresses the aforesaid problem.

is Japanese Patent No. 57-117999 discloses an offset printing blanket that includes laminates of a surface elastomeric layer of PVC or PVDC and a polyester type plasticizer having a molecular weight of 1450 to 6000. The blanket has the necessary rubber elasticity, surface roughness, ink transfer and chemical resistance properties, and is easy to wash.

PCT application W091/11330 discloses a non-printing blanket which includes a base, an elastomeric layer and an outer film over the elastomeric layer. The film has a low affinity for printing ink and is formed from PVC, polyester, polyethylene, PTFE or PVF. In operation, the blanket can handle printed materials with much less incidence of ink particles or paper fibrous matter from sticking to the blanket.

None of these prior art documents disclose blankets which can be used to print inks that contain platelet-like pigments. When conventional printing blankets are used for printing inks that contain platelet-like pigments, their performance is not acceptable. Specifically, such printing blankets, as a result of ink and paper f ibre build-up thereon, require washing for removal of such build-ups after a relatively short printing time. This necessity disrupts the printing process and requires the reallocation of time, energy and manpower. Thus, there remains a need for a printing blanket which can be used for printing applications involving inks of such platelet-like pigments which avoids or minimizes the problem of ink build-up on the blanket to extend the useful operating time of the blanket.

According to one aspect of the invention, there is provided a method for increasing the number of articles that may be printed using inks containing platelet-like pigments comprising the steps of:

a) providing a printing blanket having a base, an elastomeric layer and an outer film formed of a polymeric thermoplastic material that has a low affinity for ink- containing platelet-like pigments; b) applying the ink to the blanket; and c) transferring the ink from the blanket to the article to be printed while reducing the rate of ink build-up on the blanket, thus increasing the service time of the blanket before it requires cleaning.

According to another aspect of the invention, there is provided a printing blanket comprising a base, an elastomeric layer and an outer film formed of a polymeric thermoplastic material that has a low affinity for inkcontaining platelet-like pigments.

The article to be printed may be paper and at least about 8,000 to as high as 15,000 to 20,000 sheets or more can be printed before it is necessary to shutdown for cleaning the blanket.

In the preferred method of the invention, the ink is preferably applied onto the blanket by an offset printing process prior to transferring the ink to the article. The blanket providing step may include forming a printing blanket having an outer film of the polymeric thermoplastic material, wherein the printing blanket is formed by attaching the outer film to the blanket. The outer film may be attached to the blanket by an adhesive or by cold rolling prior to subjecting the blanket to vulcanization.

The platelet-like pigment of the ink generally comprises a flat inorganic material such as mica coated with one or more metal oxide layers. The metal oxide layers may be transition metal oxides or mixtures thereof. Also, the elastomeric layer of the printing blanket preferably comprises a compressible layer having a microporous structure of a plurality of closed or open cells. The base preferably comprises a plurality of plies interleaved with a plurality of layers one of which is said compressible layer. Advantageously, the outer film is poly(vinyl chloride), poly(vinylidene chloride), poly(ethylene terephthalate), poly(butylene terephthalate), poly(ethylene), poly(vinyl fluoride), poly(vinylidene fluoride) or poly(tetrafluoroethylene).

Preferably, the outer film is of a polymeric material that contains a fluoride constituent or component or of a fluoropolymer.

The present invention will now be described, by way of example only, with reference to the accompanying drawing in which:

FIGURE 1 is a sectional view of a preferred offset printing blanket construction of the invention.

The present invention to be described hereafter allows improved performance to be achieved in the transfer of inks containing plateletlike pigments from a printing blanket onto an article such as paper, cardboard, metal or other media commonly used in printing. The ink is transferred using a printing system which includes a plurality of cylinders for performing different functions in the handling of the article to be printed, both before and after printing of the article.

In a preferred method of the invention, printing blankets are affixed to the cylinders of a printing system. The cylinders can include, but are not limited to impression cylinders, which transfer the ink to the article to be printed, and pressure cylinders, which interact with one or more impression cylinders to exert a print pressure on the article being printed which is fed between the impression cylinders and the pressure cylinders.

The printing blankets generally comprise a base which includes a compressible layer having a microporous structure with closed or open cells and an elastomeric layer or sublayer. These features are generally known in the art and are fully described in US Patent No. 5364683 and PCT published application PCT/US92/02973, the content of each of which is expressly incorporated herein by reference thereto for further details regarding the construction of the blanket. The use of the high melting thermoplastic microspheres disclosed in the PCT application is particularly preferred for the compressible layer.

The elastomeric layer may have adhered thereto an outer film which has a low affinity for the platelet-like pigments of the ink. By "low affinity,, is meant that the outer film of the printing blanket will provide high release of the platelet-like pigments such that the printing blanket can be used in the printing of 15,00020,000 articles or more prior to washing. The film does is not effect the elasticity or pliability characteristics of the printing blanket, each of which depend on the nature of the base and elastomeric layer. In addition, the film drastically reduces adhesion of pigment and printing article particles, such as paper fibre and fabric lint, to the printing blanket, insuring that high printing article handling and printing accuracy are maintained. Moreover, because the film deters the adhesion of debris, the printing blankets require fewer cleanings per unit of printer system operating time, keeping productivity high.

poly(ethylene The film can be formed from a polymeric material including, but not limited to poly(vinyl chloride); poly(vinylidene chloride); polyesters such as terephthalate) and poly(butylene terephthalate); polyethylene; fluoropolymers such as poly(vinyl fluoride), poly(vinylidene fluoride) and poly (tetrafluoroethylene), and mixtures thereof, since these polymers have a low affinity toward metal oxidecoated mica. Preferably, a fluorine containing polymer, such as poly(vinyl fluoride), is used for best results. A commercially available poly(vinyl fluoride) polymer is TEDLAR manufactured by DuPont. The film has a thickness of between about 10-10OAm and preferably between about 30-SOAm.

The f ilm can be af f ixed to the elastomeric layer by a cold rolling process prior to subjecting the elastomeric layer to vulcanization. Using the latter method, excellent adhesion of the film on the underlying elastomeric layer can be achieved. Alternatively, the film may be structurally independent of the assembly composed by the base and the elastomeric layer, and be simply combined with the assembly during the preparation and assembly stage of the pressure cylinder. In this case, the film may be affixed to the elastomeric layer 10 via an adhesive layer which is interposed therebetween.

When a separate f ilm layer is to be vulcanized to the carcass, it is preferably to use a multilayer structure which includes a rubber layer and the film. Compared to is rubber layers which are conventionally used, the thickness of the rubber layer of the laminate is reduced to allow for the inclusion of the film while maintaining the thickness at the same level as a conventional layer.

Preferably, the printing blankets lining each impression cylinder comprise a base and an elastomeric layer, and the printing blankets lining each pressure cylinder further include an outer film layer.

The pigments to be used in the printing method of the present invention are platelet-like pigments. Such platelet-like pigments advantageously comprise a nonpigment core of a flat or sheet-like inorganic material.

- 10 The f lat core is coated with one or more metal oxide layers. Typically, transition metal oxides are used.

The non-pigment core serves as a carrier f or the metal oxide layer (s) which give (s) a lustering ef f ect to the printing article upon which the pigment is imparted. Non-pigment cores suitable for such use include, but are not limited to, mica, talc, kaolinite and other phyllosilicates. Preferably, the non-pigment core is mica, and the metal oxide layers include titanium dioxide, iron oxide and mixtures thereof. The diameter of such platelet-like pigments ranges from 1-50OAm, preferably from 5-20OAm. One commercially available series of platelet-like pigments is sold under the name IRIODIN by Merck. These pigments, which are sold under the 100, 200, 300 and 500 series, are capable of providing gold, silver and other metal lustre effects, as well as interference effects.

Alternatively, organic or non-metal ion-containing pigments can be used in the printing method of the present invention. Such pigments are known to those of ordinary skill in the printing art and are preferably dispersed in a carrier such as clay, cellulosics such a starch, and the like.

The pigments are dispersed in an appropriate vehicle to obtain an inklike product which is transferred to the 11 paper from the support according to a traditional offset printing process.

Figure 1 shows schematically in section a blanket 1 of the present invention which comprises a base or printing carcass 2 and an elastomeric layer 3. The base 2 has a plurality of plies including a bottom ply 4, two fabric plies 5 and a compressible layer 6 which includes a microporous structure with closed or open cells. High melting point thermoplastic microspheres of EXPANCEL 091 are preferred for this layer. Above the compressible layer is another fabric ply 7.

The upper elastomeric layer 3 is generally made of is nitrile rubber alone or combinations of layers of nitrile rubber and polysulfide or other rubber materials. In the construction shown, a layer of nitrile rubber 8 contacts the carcass and supports an outer film 10, which is applied onto the elastomeric layer 4 and is preferably formed from poly(vinyl fluoride) (PVF).

For optimum adhesion, a layer 9 of an adhesive thermoplastic material is interposed between the elastomeric layer 3 and the outer f ilm 10 in order to ensure sufficient bonding. One preferred commercially available material is chlorosulfonated polyethylene, such as that sold under the name HYPALON by DuPont. Also, other halogenated thermoplastic materials can be used.

When included, the total thickness of layers 8, 9 and 10 is advantageously maintained at the same thickness as the upper elastomeric layer of a convention blanket.

When manufacturing the blanket 1, use is made, at an initial stage, of a conventional method whereby the base 2 and the overlying elastomeric layer 3 are formed using sequential steps for coating the plies with elastomeric material, and the coupling of further plies together by a cold rolling process.

Prior to subjecting the base 2 and elastomeric layer 3 to vulcanization in order to stabilize the elastomeric layer 3, the film 10 is preferably cold rolled thereon. Thereafter, the pre-vulcanized or green blanket 1 is subjected to vulcanization, thereby accomplishing in one step stabilization of the elastomeric layer 3 and the anchoring of the film 10 thereon. Such vulcanization comprises heating the green blanket 1 at a temperature of 120OC-1600C, preferably about 135-1500C, at 130-190 psi, preferably about 145-175 psi.

The blanket 1 so obtained has an outward surface 10 which has an extremely low affinity toward platelet-like pigment ink and can be readily washed clean, preferably using an aqueous detergent solution. In addition, the film 10 provides excellent resistance to surface abrasion, as well as excellent chemical resistance to the - 13 action of the solvents usually employed with printing systems.

EXAMPLE

The performance of a blanket of the present invention comprising a base or carcass 2 made of a bottom ply 4, two fabric layers 5, a closed cell compressible layer 6, another fabric layer 7, and a top elastomeric layer 3 comprising in combination a layer of nitrile rubber 8, a layer of hypalon 9, and a poly(vinyl fluoride) outer layer 10 was compared to a conventional blanket of the same construction but which did not include the outer film 10 of poly(vinyl fluoride). The blankets were placed on the impression cylinder of a printing system and were used for the offset printing of paper using IRIODIN inks. After the printing of only about 4000-5000 copies, the conventional blanket required washing to remove a significant build-up of ink and paper fibre which was affecting the quality of the print on the paper. By comparison, the blanket of the present invention was able to print between about 15, 000 and 20,000 copies before the quality of the print was affected. Also, due to the low af f inity of the ink to the blanket, the build-up was easily removed by washing, so the blanket could be quickly returned to service.

Claims

- 14 CLAIMS

A method for increasing the number of articles that may be printed using inks containing platelet-like pigments comprising the steps of:

a) providing a printing blanket having a base, an elastomeric layer and an outer film formed of a polymeric thermoplastic material that has a low affinity for inkcontaining platelet-like pigments; b) applying the ink to the blanket; and c) transferring the ink from the blanket to the article to be printed while reducing the rate of ink build-up on the blanket, thus increasing the service time of the blanket before it requires cleaning.
2. The method of claim 1 wherein the outer f ilm is formed of the polymeric thermoplastic material.
3. The method of claim 2 wherein the outer f ilm is attached to a conventional printing blanket.
4. The method of claim 3 wherein the outer f ilm is attached to the printing blanket using an adhesive.
5. The method of claim 3 wherein the outer f ilm is attached to the printing blanket by a cold rolling process.
6. The method of claim 5 wherein the film is applied to - is - the elastomeric layer and the blanket is subsequently subjected to vulcanization.
7. The method of claim 3 wherein a layer of a halogenated thermoplastic is interposed between the printing blanket and the outer film.
8. The method of claim 1 wherein the platelet-like pigment of the ink comprises a flat or sheet-like inorganic material coated with one or more metal oxide layers, and the ink is applied onto the blanket by an offset printing process.
9. The method of claim 8 further comprising the step of is selecting the inorganic pigment from the group consisting of mica, talc, kaolinite and other phyllosilicates and selecting the metal oxide layers to be transition metal oxides or mixtures thereof.
10. The method of claim 9 wherein the inorganic pigment is mica.
11. The method of any preceding claim wherein the elastomeric layer of the printing blanket comprises a compressible layer having a microporous structure having a plurality of closed or open cells.
12. The method of any preceding claim wherein the outer film is poly(vinyl chloride) or poly(vinylidene chloride), or poly(ethylene terephthalate) or poly(butylene terephthalate) or poly (ethylene) or poly(vinyl fluoride) or poly(vinylidene fluoride) or poly(tetrafluoroethylene).
13. The method of any preceding claim wherein the outer film is of a polymeric material that contains a fluoride constituent or component or a fluoropolymer.

is
14. The method of any preceding claim wherein the base comprises a plurality of plies interleaved with a plurality of layers, one of which is said compressible layer.
15. The method of any preceding claim wherein the article to be printed is paper and wherein at least about 8,000 sheets can be printed without cleaning the blanket.
16. A printing blanket comprising a base, an elastomeric layer and an outer film formed of a polymeric thermoplastic material that has a low affinity for inkcontaining platelet-like pigments.
17. The printing blanket of claim 16 wherein the outer film is attached to the blanket by an adhesive.
18. The printing blanket of claim 16 wherein the outer - 17 film is attached to the blanket by cold rolling.
19. The printing blanket of any of claims 16-18 wherein the f ilm is applied to the elastomeric layer prior to 5 subjecting the blanket to vulcanization.
20. The printing blanket of any of claims 16-19 wherein a layer of a halogenated thermoplastic is interposed between the blanket and the outer film.

is
21. The printing blanket of any of claims 16-20 wherein the elastomeric layer of said printing blanket comprises a compressible layer having a microporous structure having a plurality of closed or open cells.
22. The printing blanket of any of claims 16-21 wherein the outer layer is a f ilm of poly (vinyl chloride) or poly (vinylidene chloride) or poly (ethylene terephthalate) or poly (butylene terephthalate) or poly (ethylene) or 20 poly(vinyl fluoride) or poly(vinylidene fluoride) or poly(tetrafluoroethylene).
23. The printing blanket of claim 16 wherein the polymeric material of the outer film contains a fluoride constituent or component or a fluoropolymer.
24. The printing blanket of any preceding claim wherein the base comprises a plurality of plies interleaved with - 18 a plurality of layers one of which is said compressible layer.
25. A printing blanket substantially as herein described 5 and illustrated in the accompanying drawing.