Apparatus for protecting the surface of freshly printed sheets

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BACKGROUND OF THE INVENTION

FIELD OF THE INVENTION

The invention relates to an apparatus for protecting the surface of freshly printed sheets, which are deposited stacked on one another to form a sheet pile, the respective sheets having applied thereto by an applicator a separating-agent layer formed of solid particles of separating agent.

Heretofore known apparatuses of this general type, such as a dust applicator device in accordance with the German Patent Document DE 38 19 203 A1, blow separating-agent particles in the form of a powder onto a freshly printed surface of a respective sheet with the aid of compressed air.

As indispensible as a layer of separating agent formed by a powder often is, it can, nevertheless, have a deleterious effect on a final product passing through a printing process. One example is the urgent recommendation that powdered printed products be sanitized before being lined with foil. Any possible scratches in the printed image, for example, caused by joggers in delivery pile apparatuses in cooperation with the powder, remain irreparable.

Types of powder that are supposed to come loose under the influence of the moisture of the printing ink have indeed already been offered. However, tests have demonstrated, for example, in W. Walenski, "Die Bestaubung im Offsetdruck" (Powder Application in Offset Printing), Z. Druckindustrie (Printing Industry Journal), No. 21, Oct. 3, 1993, pp. 21-24, that suitable loosening does not occur even after what must certainly be called an adequate length of time.

SUMMARY OF THE INVENTION

Proceeding from this state of the prior art, it is an object of the invention to provide an apparatus for protecting the surface of freshly printed sheets, with which an initially adequately effective layer of separating agent can be produced in such a manner that in practical use it undergoes a structural change in the sense of a decreasing layer thickness.

With the foregoing and other objects in view, there is provided, in accordance with the invention, an apparatus for protecting the surface of freshly printed sheets which are deposited upon one another to form a sheet pile, comprising an applicator for applying to the respective sheets a separating-agent layer formed of solid particles of separating agent, the layer of separating agent being formed of a mixture including at least one degradable separating agent substance, an aqueous vehicle liquid, and at least one mixture component which degrades the separating agent substance upon simultaneous contact with the separating agent substance and the vehicle liquid.

In accordance with another feature of the invention, the mixture is formed of a natural thermoplastic substance which is degradable under the influence of microorganisms, and the microorganisms.

In accordance with another feature of the invention, the mixture includes a mixture component belonging to the substance group of polypeptides.

In accordance with a further feature of the invention, the vehicle liquid is a nutrient solution inoculated with bacteria.

In accordance with an added feature of the invention, the vehicle liquid includes a degrading mixture component in the form of a solvent which dissolves the separating agent substance.

In accordance with an additional feature of the invention, the mixture of the separating agent layer comprises a mixture of separating-agent particles moistened with the vehicle liquid, and first separating agent particles of the mixture of separating-agent particles are formed of the separating agent substance, and second separating agent particles of the mixture of separating-agent particles are formed of the degrading mixture component.

In accordance with an alternative feature of the invention, the mixture of the separating agent layer is formed from mixed particles moistened with the vehicle liquid, and the mixed particles have a core formed of the separating agent substance and a sheath surrounding the core and formed of the degrading mixture component.

In accordance with yet another feature of the invention, the separating agent particles are formed as microcapsules, respectively, having a capsule envelope formed of the separating agent substance, the capsule envelopes, respectively, being filled with a fractional amount of the vehicle liquid, the vehicle liquid being mixed with at least one degrading mixture component having degrading action reinforceable by energetic irradiation of the degrading mixture component, and the microcapsules being exposed to the energetic irradiation during the application of the separating agent layer to the respective sheets.

In accordance with yet a further feature of the invention, the separating agent particles are formed as microcapsules, and the microcapsules, respectively, have a capsule envelope formed of the separating agent substance, the capsule envelopes, respectively, being filled with a fluid which is free of a degrading mixture component and, during the application of the separating agent layer to the respective sheets, the microcapsules being exposed to moistening by means of the vehicle liquid mixed with at least one degrading mixture component.

In accordance with an alternative feature of the invention, the separating agent particles include first separating agent particles in the form of a granulate of a first separating agent substance and second separating agent particles in the form of microcapsules; the microcapsules, respectively, having a capsule envelope filled with a fractional amount of the vehicle liquid and formed of a second separating agent substance; the fractional amounts of vehicle liquid being mixed with at least one degrading mixture component; the at least one degrading mixture component and the first and the second separating agent substances being adapted to one another so that only the first separating agent substance is degradable by means of the at least one degrading mixture component; and including means for exposing the layer of separating agent at least temporarily to an external force which bursts the microcapsules.

In accordance with yet an added feature of the invention, the applicator has first spray nozzles for applying the mixture-forming separating agent particles, and second spray nozzles for applying a moistening agent for moistening the separating agent particles.

In accordance with yet an additional feature of the invention, the applicator includes a support roller rotatable in a first rotational direction during operation, and a contact roller rotatable during operation in a second direction of rotation opposite the first rotational direction, the support roller and the contact roller being positioned against one another in a contact zone and, respectively, contacting one side of a respective sheet passing through the contact zone in a sheet travel direction; the first spray nozzles, on the one hand, and the second spray nozzles, on the other hand, being directed towards a common target area on one side of the respective sheet, the target area being located before the contact zone in the sheet travel direction.

In accordance with one alternative feature of the invention, the applicator includes a support roller rotatable in a first rotational direction during operation, and an applicator roller rotatable during operation in a second direction of rotation opposite the first rotational direction, the support roller and the applicator roller being positioned against one another in a contact zone and, respectively, contacting one side of a respective sheet in the contact zone; the first spray nozzles, on the one hand, and the second spray nozzles, on the other hand, being directed towards a common target

area on a free region of a jacket face of the applicator roller.

In accordance with another alternative feature of the invention, the applicator has a support roller rotatable in a first direction of rotation during operation and a pair of rollers, respectively, extending parallel to the support roller, positioned against or in engagement with one another and rotatable in opposite directions during operation; one roller of the pair of rollers being positioned against the support roller and having a second direction of rotation opposite that of the first direction of rotation; the support roller and the one roller of the pair of rollers which is positioned against the support roller, respectively, contacting one side of a respective sheet; the first spray nozzles, on the one hand, and the second spray nozzles, on the other hand, being directed towards a common target area on a free region of a jacket face of one of the rollers of the pair of rollers.

In accordance with another aspect of the invention, there is provided an apparatus for protecting the surface of freshly printed sheets which are deposited upon one another to form a sheet pile, comprising an applicator for applying to the respective sheets a separating-agent layer formed of solid particles of separating agent, the layer of separating agent being formed of a mixture of substances having the separating agent particles in the form of microcapsules; the microcapsules, respectively, having a colorless capsule envelope formed of a polypeptide and filled with a colorless fluid which is inert with respect to the polypeptide.

The objective of the invention of the instant application is thus attained by two different embodiments; in a first embodiment, an apparatus of the foregoing general type is distinguished by the fact that the layer of separating agent is formed of a mixture which has at least one degradable separating agent substance, an aqueous vehicle liquid, and at least one mixture component which degrades the separating agent substance upon simultaneous contact with the separating agent substance and the vehicle liquid, and in a second embodiment, an apparatus of the foregoing general type is distinguished by the fact that the separating agent layer is formed of a substance mixture having the separating agent particles in the form of microcapsules; the respective microcapsules having a colorless capsule envelope of a polypeptide and being filled with a colorless fluid which is inert with respect to the polypeptide.

The decrease in layer thickness in the case of the first embodiment occurs due to the degradation of the separating agent substance, so that after it has fully broken down, the initially fully effective layer of separating agent has entirely disappeared.

In practical use, the layer of separating agent present between adjacent sheets of a sheet pile is exposed to the weight of all the sheets resting on top of it, so that in the second embodiment, the particles of separating agent, in the form of microcapsules, burst under this weight, at least in a lower region of the pile. The same effect can be attained for an upper region of the sheet pile by turning the pile over. If a basic wall thickness of the capsule envelopes of these microcapsules is in the order of magnitude of approximately 0.1 to 0.5 .mu.m, compared with a diameter of the microcapsules in the order of magnitude of up to approximately 300 .mu.m, the effect even in the case of the second embodiment, in practical use, is a marked reduction in an initially adequately effective layer thickness of the separating agent layer.

In a preferred form of the first embodiment of the invention, the mixture is made up of a natural thermoplastic substance which is degradable under the influence of microorganisms, and the aforementioned microorganisms themselves.

A further preferred feature of the aforementioned first embodiment of the invention is that the mixture includes a mixture component belonging to the substance group of polypeptides, and includes a mixture component belonging to the substance group of peptide hydrolases. Gelatin, for example, is preferable as the polypeptide.

A further preferred feature of the aforementioned first embodiment is that the vehicle liquid is a nutrient solution inoculated with bacteria.

In a further preferred feature of the aforementioned first embodiment, the vehicle liquid includes a degrading mixture component in the form of a solvent which dissolves the separating agent substance.

With respect to the structural makeup of a separating agent layer according to the invention, the degrading mixture is formed of a mixture of separating agent particles moistened with the vehicle liquid, and first separating agent particles of the moistened particle mixture are formed of the separating agent substance, and second separating agent particles of the moistened particle mixture are formed of the degrading mixture component.

In a further feature, in terms of the structural makeup of a separating agent layer according to the invention, the mixture is formed from mixed particles moistened with the vehicle liquid, and the mixed particles, respectively, have a core formed of the separating agent substance and a sheath surrounding the core and formed of the degrading mixture component.

Another preferred feature of the structural makeup of a separating agent layer according to the invention is that the separating agent particles are in the form of microcapsules, and the microcapsules, respectively, have a capsule envelope formed of the separating agent substance, the capsule envelopes, respectively, being filled with a fractional amount of the vehicle liquid, which is mixed with at least one degrading mixture component having a degrading action which is reinforceable by being energetically irradiated, the microcapsules being exposed to the energetic irradiation during the application of the separating agent layer to a respective sheet.

With a view to the structural makeup of a separating agent layer according to the invention, a further preferred feature calls for the separating agent particles to be in the form of microcapsules, the respective microcapsules having a capsule envelope formed of the separating agent substance, the respective capsule envelopes being filled with a fluid which is free of a degrading mixture component and, during the application of the separating agent layer to a respective sheet, the microcapsules are exposed to moistening by means of the vehicle liquid mixed with at least one degrading mixture component.

Also with reference to the structural makeup of a separating agent layer according to the invention, the first separating agent particles are in the form of a granulate of a first separating agent subs