Chemical Watermarking Paper

Chemical Watermarking Paper-43
The design of the mark in relief on the band is brought into contact with the wet paper web at the wet presses beyond the Fourdrinier wire. 3,293,062 describes the use of a curable hexamethoxymethyl melamine and a sulfonic acid derivative as a curing agent in the formation of chemical watermarks.At that point the paper is still plastic and compresses readily. The watermark products of this invention generally require 5 to 15 days aging at ambient temperatures in order to render the watermark insoluble in water, ethanol or other common solvents.

The design of the mark in relief on the band is brought into contact with the wet paper web at the wet presses beyond the Fourdrinier wire. 3,293,062 describes the use of a curable hexamethoxymethyl melamine and a sulfonic acid derivative as a curing agent in the formation of chemical watermarks.

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The fibers in the web are displaced in the horizontal direction and the paper is rendered thinner and consequently denser and more transparent in the area of the watermark when viewed under transmitted light.

Thus, the embossed rolls form a configuration or design of the mark in the damp or wet paper which remains permanent upon drying.

The chemical watermark of the present invention is formed by replacing air entrained in a paper sheet with a material having an index of refraction reasonably close to that of cellulosic fibers.

The chemical watermarks of the present invention are substantially insoluble, do not have excessive gloss, are colorless, can survive under long-term aging, have good ink receptivity and the like, and do not damage the finished paper.

Compositions and method for producing chemical watermarks in finished paper products, the watermarks being produced by applying to the surface of the paper a synthetic resin composition having a chemical grouping therein capable of being insolubilized upon exposure to high frequency radiation, and thereafter exposing the resin composition to such high frequency radiation to insolubilize the resin. A chemically watermarked product comprising a paper sheet having a watermark of preselected design applied to a portion thereof, said watermark having a refractive index approximating that of the paper and being an insoluble reaction product produced by irradiation of a synthetic resin with high frequency radiation above the visible spectrum. The product of claim 1 in which said resin composition includes a free radical polymerizable polyethylenically unsaturated monomer or prepolymer. The product of claim 2 in which said synthetic resin is an ester of an aliphatic polyhydric alcohol with at least 2 mols of an unsaturated carboxylic acid containing up to five carbon atoms per molecule. The product of claim 3 in which said acid is acrylic acid. The product of claim 3 in which said acid is methacrylic acid. The product of claim 3 in which said acid is itaconic acid. The product of claim 3 in which said composition also includes a photoinitiator. The method of applying a chemical watermark to paper which comprises applying to the surface of a finished paper a synthetic resin composition having a chemical grouping thereon capable of being insolubilized upon exposure to high frequency radiation, said resin composition being applied in the form of a preselected design in a preselected small area of the paper, said resin composition having a viscosity suitable for such coating and being insufficiently cross-linked to be chemically set, and thereafter exposing said resin composition to high frequency radiation above the visible spectrum to thereby insolubilize said resin composition. The method of claim 8 in which said high frequency radiation is rich in ultraviolet light. The method of claim 8 in which said composition also includes a photoinitiator. The method of claim 8 in which said composition is applied as a solvent solution. The method of claim 8 in which said synthetic resin composition includes a free radical polymerizable polyethylenically unsaturated monomer or a prepolymer. The method of claim 12 in which said synthetic resin is an ester of an aliphatic polyhydric alcohol with at least 2 mols of an unsaturated carboxylic acid containing up to 5 carbon atoms per molecule. The method of claim 13 in which said acid is acrylic acid. The method of claim 13 in which said acid is methacrylic acid. The method of claim 13 in which said acid is itaconic acid. Field of the Invention This invention is in the field of chemical watermarks, i.e., marks that are laid down upon paper products to provide a characteristic design to convey intelligence. DESCRIPTION OF THE PRIOR ART In the office operations of commercial enterprises, it is often desirable to have writing stationery and other forms of business and professional papers provided with a watermark.

These watermarks are sometimes business trandemarks used to identify the manufacturer of the paper product or they may contain coded information that relates to dates of manufacture or composition.The method and composition of the present invention make watermark paper economically available in large or small quantities.The process of the present invention can be carried out substantially at room temperature to thereby eliminate any necessity of involved procedural steps or elevated temperature cures.THERM-O-TYPE will not guarantee the performance of Aegis chemistry used on non-THERM-O-TYPE equipment.THERM-O-TYPE will not be held liable for any loss of income or damage to equipment caused by customers using watermark chemistry on non-THERM-O-TYPE equipment.The second method uses a polymer relief plate to apply a chemical that makes a faint image into the paper.True watermarking is for large quantities of paper, and for smaller runs of 10,000 sheets and up the second method makes a "watermark" available to a wide range of end users.The solvent may be removed by evaporation or normal drying at ambient temperatures or by forced drying with the application of heat or forced air streams. The present invention provides chemical watermarks which are substantially insoluble and colorless.One of the earliest of such disclosures appears in Livingstone U. It provides a method for making chemical watermarks which involves applying a liquid chemical composition to the surface of otherwise finished paper and then curing the composition in the paper to render it insoluble to water and common solvents.Secondly, the cost of the embossed or banded rolls for the papermaking machine is obviously extremely high and could not, therefore, be afforded by smaller industrial users. In one embodiment of the invention, up to 60% by weight of curing agents for the thermosettable resin are employed to render the resin insoluble in water and common solvents. In some instances, the curing agents are vesicants and skin sensitizing agents which must be handled with extreme care to avoid chemical burns or contact dermatitis.Third, the cost of setting up the embossed or banded rolls involves both labor as well as the loss of production on the papermaking machinery and would have to be included in the net cost to the purchaser. In another embodiment of the invention, prehardened synthetic thermosetting resins in solution in volatile organic solvents are utilized to form the chemical watermark. In other cases, the compositions require excessively long periods of time for the curing reaction to occur so that the chemical watermark so produced would not be undesirably altered by contact with water or common organic solvents.

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