KR19980702528A - Security paper - Google Patents

Abstract

The present invention relates to a method of manufacturing a security paper comprising a security feature. The method includes the steps of: producing a paper in a wet state, the paper comprising at least one security pattern; Applying a calligant to the paper; And applying a coating comprising uncoloured polyurethane to one or both sides of the exfoliated paper. The uncoloured polyurethane may optionally comprise a functional additive if the functional additive does not increase the opacity of the paper by more than 1%. After the polyurethane is applied, the paper is dried. Said coating composition providing a film when cast on a glass surface, said film having a Konig hardness of 15-130 Seconds and comprising the following steps:

a) casting a total preparation to be used in said coating on a glass plate to produce a film having a dry weight of 80 g / m ² ;

b) initially drying the film at 23 占 폚 (once it has become sticky, it is continuously dried at 80 占 폚);

c) measuring the weight of the film, wetting it to measure the tensile strength (Young's modulus), and visually checking the change in the degree of film transparency;

d) the step of heating for 30 minutes in water containing 10 g / liter Na ₂ CO ₃ to the film sample;

e) subsequently rinsing the film with cooling water and then repeating steps b) -c) (drying and re-weighing the film)

[Among the above steps, when the film is dried and then weighed again, the following criteria are met.

i) the wet tensile strength and the Young's modulus of the heated film are at least 90% of the initial wet tensile strength and Young's modulus.

ii) the transparency of the film is reduced to an unrecognized extent.

iii) when the dry weight of the film is more than 98% of the original weight.

Pass water resistance test defined by

Description

Security paper

The present invention relates to security documents, more specifically, paper sheets such as banknotes and driver's licenses, which are handled in significant amounts. These security documents must be durable; I.e., resistance to heat, bending, and resistance to water. In handling, the paper may be physically damaged due to moisture and chemicals absorbed by such security documents. It is preferable that such a substrate for security documents has moisture-proof property and chemical resistance. Of course, the special requirements for such security documents are that, under extreme conditions, especially where mechanical abrasion or accidental washing has occurred, the substrate applied to the substrate must be well adhered.

The security document according to the present invention includes at least one visual security feature for preventing or suppressing forgery. Security patterns that may be used include watermarks and security seals that are present in the paper. The security room may be present in the paper itself or may be in a so-called window located between the areas where there is a seal between the sheets, such as, for example, England Series E Banknotes. Normally, in the security document, the quality of the substrate should be excellent as long as embossing can be obtained satisfactorily on the substrate and strong durability, such as embossing formed by the known Intaligo printing method.

BACKGROUND ART [0002] Conventionally, there has been proposed a technique related to the use of a coating composition comprising a fixing agent such as an elastomeric binder and a pigment as a method for producing a paper for security paper with good water-repellency and durability. In addition, it is generally known in the art that various polyurethane compositions can be used on a variety of substrates to provide a coating that generally has one or more protective effects; As an example of the use of the above-mentioned constitution, polyurethane is used as a varnish for wood or other substrates. In addition, it can be seen from EP-B-189945 that a polyurethane composition is used as a sizing material for the paper.

When a coating composition comprising a pigment is used to make a secure paper, as for example in PCT Application No. WO 91/12372, the pigment typically has microporosity which allows the ink to be adhered satisfactorily, Or roughness of the surface of the substrate. However, there is a problem that a serious problem due to the presence of a pigment, that is, a security pattern such as a watermark on a substrate or a windowed thread in a window becomes somewhat opaque.

The presence of the pigment results in the adhesion of the fixing agent to the substrate falling at a particular site, so that the colored coating has an inherently weak adhesion.

Normally, when a colored coating composition is used, there is a disadvantage that since the coating step is performed after the paper is produced, it is necessary to apply the coating composition after drying the paper. In the previous specification EP-B-189945 it is mentioned about sizing, which is to apply a polyurethane composition to a security paper after the paper is crimped with a natural sizing agent or synthetic primer, It will be noted from the point of view that the invention is concerned. Furthermore, it is an essential feature of the present invention that no security pattern is rendered opaque since no pigment is present. However, as will be described below, various functional additives may be added to polyurethane coatings unless the opacity of the paper is increased by more than 1%.

The present invention is based on the results of extensive research conducted by the inventors in various fields for the purpose of manufacturing a security document with enhanced durability and water repellency.

According to the present invention there is provided a method of making a security sheet comprising a security pattern, the method comprising the steps of: producing a wet state sheet comprising one or more security features; Applying an uncoloured polyurethane containing a functional additive on either or both sides of the exfoliated paper if the functional additive does not increase the opacity of the paper by more than 1% Wherein the coating composition has a Konig hardness of 15 to 130 Seconds and is further characterized by a water resistance test defined by the following steps: Is provided on the passed film.

a) casting a total preparation to be used in said coating on a glass plate to produce a film having a dry weight of 80 g / m ² ;

b) at the beginning, drying the film at 23 DEG C (once dried at 80 DEG C for an additional 1 hour if the stickiness is lost);

c) measuring the weight of the film and wetting it to measure the tensile strength (Young's Modulus), and then visually checking for any change in the film transparency;

d) the step of heating for 30 minutes in water containing 10 g / liter Na ₂ CO ₃ to the film sample;

e) subsequently rinsing said film with cooling water and then repeating steps b) -c) (drying said film and re-weighed);

If the tested film conforms to the following criteria, it is classified as being waterproof.

i) the wet tensile strength and Young's modulus of the heated film is at least 90% of the initial wet tensile strength and Young's modulus.

ii) the transparency of the film is reduced to an unrecognizable extent.

iii) the dry weight of the film is greater than 98% of its original weight.

According to the results of the study, the polyurethane coatings satisfactory for the purpose of the present invention were confirmed by the above test.

The aqueous polyurethane may be present in the form of an aqueous dispersion. The coating may comprise an extender such as polyacrylate and may therefore be present in the form of a urethane-acrylic blend; Such formulations will provide good waterproof coatings and chemical resistant coatings. In addition, the use of less expensive extender than polyurethane will result in a much lower cost than using only polyurethane.

The coating is a polyurethane dispersion in which one component pre-crossed-linked polyurethane is present, or is a single component, but is chemically bonded to the polymer chain, but generally at the final stage of the paper- May be a polyurethane dispersion in which there is a blocked polyurethane having isocyanate groups that are used and regenerated at high temperatures. In addition, the coating may be a polyurethane dispersion of a two-component product that can be crosslinked using a multi-functional reagent such as a melamine / formaldehyde precondensate. Crosslinking agents that may be used may include polyaziridines. The crosslinking agent improves the waterproofness, including the wash resistance of the unpigmented polyurethane coatings, thereby improving the quality of the finally produced security papers and security papers.

The polyurethane compositions used in the process of the present invention may comprise components known to those skilled in the art, including catalysts, co-solvents and emulsifiers or surfactants. However, care must be taken as emulsions can degrade the performance of the coating under wet or humid conditions. In addition, other known additives may be used including zwitterionic, flowable additives, extenders or viscosity modifiers. In general, the additives contained in the coating composition should be kept at a minimum because they can adversely affect important properties such as adhesion to the substrate.

The gist of the present invention is to provide a useful uncoloured coating for realizing the effects described herein, one of which is a paper of the present invention, without substantially sacrificing the general advantages realized by using an uncoloured polyurethane coating It is possible to use a plurality of functional additives in order to provide a specific effect of enhancing the security of the manufactured security sheet. It will be understood by those skilled in the art that pigments are added to the coating, especially the paper coating, to provide color or opacity. In contrast, the functional security additive that can be used according to the invention is not a pigment but a particulate material which meets the following criteria:

a) Once the coating is applied, the additive does not increase the opacity of the paper by more than 1%. This confirms that the addition maintains the general advantage of the uncoloured coating since it has little effect on the transparency of the coating;

b) The presence of additives in polyurethane coatings does not fail in tests to identify polyurethane coatings according to the invention, i.e. Koenig hardness test and waterproofness test.

The functional additive according to the present invention is preferably a fluorescent pigment or an iridescent pigment.

The security functional additive will provide a particular effect of enhancing the security or discrimination of the documents made with the paper according to the invention so that these additives will additionally include a security feature if present in the polyurethane coating. Generally, security functional additives are classified into the following three classes.

(a) a publicly identifiable security pattern, such as a pearlescent pigment

(b) a security pattern, such as a fluorescent pigment or magnetic particle, which provides a high level of security and can be detected by a security device

(c) For example, a perceived externally exposed security pattern using a sophisticated sensing device such as that used in a central bank, such as a phosphorescent pigment with a unique decay time

In general, the coating weight of the polyurethane coating will be between 0.05 and 20 g / m ² , preferably between 0.5 and 5 g / m ² .

The timing of applying the polyurethane coating is controlled immediately after the paper is passed through the size bath squeeze roll and before the introduction into the after-dryer, It is preferred to apply a urethane coating. Alternatively, however, the polyurethane may be applied to the dried paper after all of the usual papermaking steps have been carried out.

Preferably the polyurethane coating is applied to both sides of the paper.

The fibers present in the paper may be natural fibers or synthetic fibers or mixtures of natural fibers and synthetic fibers.

The polyurethane is preferably an aliphatic polyester type and may be used in a dispersion wherein the polyurethane content is in the range of 2-70 wt% and more preferably the polyurethane content is in the range of 5-30 wt% Aliphatic polyether types may optionally be used in the process of the present invention. In addition, the polyurethane may be an aliphatic polycarbonate polyurethane.

The paper used in the method is preferably a security feature, provided with a watermark or a windowed or windowed yarn in the paper that contains a visual element or a hidden security element.

In order to meet the essential requirements of the present invention, the coating comprising polyurethane should be substantially transparent as described herein, with a 100% modulus of at least 4.0 mPa. The maximum tear strength of the polyurethane coating is preferably 40 mPa or more, for example 40 to 80 mPa, and the Konig hardness is preferably 20 seconds or more, for example, 20 to 40 seconds.

The use of uncoloured polyurethane coatings as described herein is an innovative suggestion in making security papers such as banknote paper. The method of the present invention provides a number of useful properties above expectations:

a. The polyurethane coating with the extender removed is transparent; Therefore, this does not include a visible security pattern in the paper.

b. The coating reduces porosity and surface roughness of the surface and significantly increases the water repellency of the paper. This is important in extending the circulation life of banknotes.

c. In contrast to b), the coating significantly improves the adhesion of the paper surface print, which is evidenced by wet and dry wiping test, wet friction and laundry testing. This is most surprising in the sense that those skilled in the art will be able to overcome the adherence of low prints with the use of polyurethane coatings according to the present invention.

d. Unlike pigmented coatings, the polyurethane coatings described herein do not significantly change the feel or appearance of the paper. This is important because the unique visual and tactile characteristics of the banknote paper help the public identify counterfeit banknotes.

e. In addition, the coating enhances embossing and its clarity, which is a yaw angle print.

f. The coating will also prevent the optical brightener from being absorbed upon accidental washing. The intangibility of banknotes also helps detect counterfeit goods, which is very beneficial and can be said to be more than expected. The fluorescence of the optical brightener also prevents any elaborate fluorescent security pattern present in the banknote from becoming opaque.

g. The coating does not affect the efficiency of the papermaking process or the printing process. Specifically, it does not interfere.

The properties according to the process of the invention are due to the mechanical resistance and chemical and chemical properties of the polyurethane coatings, as defined above, according to waterproofness tests and Konig hardness. Materials that fail the above two tests do not meet specific requirements as banknotes.

Another aspect of the present invention provides a security document manufacturing method for manufacturing a security sheet by the method described herein, and then printing the manufactured security sheet and manufacturing the security sheet. Security documents are banknotes, identification documents, driver's licenses and passport sheets.

The following examples illustrate the invention. In the following examples, comparative reference material for testing described or defined herein is used. Parts are parts by weight.

a) dry crumple test

Roll the banknote with the glue on the printed paper sample by hand 10 times according to the standard technique. Then, the printed sample is observed to measure the ink loss.

b) The wet crumple test

The dry wiping test is performed in the same manner as in the dry wiping test except that the paper is first wetted each time it is rolled.

c) The sheen wet rub test.

The banknote with the sample of the printed paper is rubbed 300 times with 800 g of brush using a gloss tester. The degree of ink loss during the test is visually measured.

d) The severe laundry test

The banknote with the printed paper sample is heated for 30 minutes in a solution containing 5 parts of household detergent powder and 10 parts of sodium carbonate.

The sample was then rinsed with cold water. Then, the degree of ink loss is visually measured.

e) FIRA contamination test

At one end of the cylinder was placed a printed paper sample and at the other end a reference sample was placed and 20 felt cubes absorbing artificial sweat and colloidal graphite were placed inside. The cylinder was rotated while turning for 30 minutes. The change in the reflectance of the printed sample was measured, and the degree of relative contaminant absorption was measured while comparing the test results.

Example 1.

A paper sheet was prepared on a paper machine with an aqueous suspension of cellulosic fibers optionally blended with optical fibers or synthetic fibers or other additives used in the paper industry. After that, the paper was dried and fired, dried again, and wound.

The coating formulation is composed as follows:

Part 15: Aliphatic polyester polyurethane (Witocobond 785 ^TM ) manufactured by Baxenden Applied Chemicals Limited,

Part 85: Water

After the wound corrugated sheet was loosened, the coating was applied to both sides of the sheet using a Meyer bar coater and dried. Both sides of the sheet were covered with a coating of 2 g / m ² .

Thereafter, the coated paper was subjected to a finishing process by cutting it by a conventional method, that is, by a pressing roller.

Thereafter, the coated paper was printed by a four-angle printing method and an offset printing method.

The coating composition samples were tested using the waterproofness test and the Konig hardness test method described above. The Konig hardness of the coating was 100 Seconds. In addition, the coating was also waterproof.

All of the coated and uncoated printed papers were tested using a wet writhing test, a dry writhing test, an intensification point test, an FIRA contamination test and a wet gloss friction test. When compared to uncoated paper of the same paper batch, after each test the coated samples showed the following results:

Wet Wiping Test: Significantly reduced ink loss

Dry wisdom test: Significantly reduced ink loss

Strong Point Test: Inkless paper showed almost 80% loss of ink, whereas ink loss was almost unobservable.

Wet friction test: more than 50% of printed area of uncoated paper is lost; Polyurethane-coated paper, less than 10% of the printed area is lost.

FIRA contamination test: less than 30% of contamination absorption rate

Observation of the washed samples under UV light showed that unlike the uncoated samples which became significantly fluorescent after the washing process, the coated samples adsorbed a small amount of optical brightener I could.

The coated and uncoated samples were subjected to yamprinting and the results were observed. Characteristic feathering expected on banknote paper was observed on the uncoated paper. In the coated paper, feathering remarkably decreased.

Example 2.

A paper sheet was prepared on a paper machine with an aqueous suspension of cellulosic fibers optionally mixed with optical fibers, synthetic fibers or other additives used in the paper industry. Thereafter, the paper was dried, baked, dried and wound.

The coating formulation is made as follows:

7.5 part: aliphatic polyester polyurethane (Witocobond 785 ^TM ) manufactured by Baxenden Applied Chemicals Limited,

7.5 parts: Vinyl acetate-VeoVa copolymer (Vinamul 6975 ^TM ) manufactured by Vinamul Limited,

0.5 part: Zeneca Resins BV. The product polyaziridine (CX100 ^TM )

84.5 parts: water

After the rolled-up foil paper was re-sprinkled, the coated paper was coated on both sides of the paper using a Meyer bar coater and then dried. Both sides of the paper were covered with a coating of 2 g / m ² .

Thereafter, the sheet was calendered on the squeeze roller, and the coated sheet was cut in a usual manner.

Thereafter, the coated paper was printed by a four-angle printing method and an offset printing method.

The coating composition samples were tested using the waterproofness test and Konig hardness test described above. The Konig hardness of the coating was 120 Seconds. The waterproofness of the polyurethane coatings has been found to be good.

The coated and uncoated printed papers were tested using a wet wiping test, a dry wiping test, an intensive point test, an FIRA contamination test and a wet friction test. The resulting paper possessed essentially the same properties as those exhibited in the paper produced by the method of Example 1 for wet wiping test and the like.

Observation of the washed samples under UV light showed that unlike the uncoated samples which were remarkably fluorescent after the washing process, the coated samples absorbed a minute amount of optical brightener there was.

The results were observed on the coated and uncoated samples after the yaw angle printing. Characteristic feathering expected on banknote paper was observed on the uncoated paper. In the coated paper, feathering remarkably decreased.

Example 3.

A paper sheet was prepared on a paper machine with an aqueous suspension of cellulosic fibers optionally mixed with optical fibers, synthetic fibers or other additives used in the paper industry. Thereafter, the paper was dried, baked, dried and wound.

The coating formulation is made as follows:

10.5 parts: aliphatic polyester polyurethane (Witocobond 779 ^TM ) manufactured by Baxenden Applied Chemicals Limited,

4.5 parts: Anionic styrene-acrylate copolymer (Vinamul 7172 ^TM ) manufactured by Vinamul Limited,

0.5 part: Zeneca Resins BV. The product polyaziridine (CX100 ^TM )

84.5 parts: water

After the rolled-up foil paper was re-sprinkled, the coated paper was coated on both sides of the paper using a Meyer bar coater and then dried. Both sides of the paper were covered with a coating of 2 g / m ² .

Thereafter, the coated paper was hooked on a squeeze roller, and then the coated paper was cut in a usual manner.

Thereafter, the coated paper was printed by a four-angle printing method and an offset printing method.

The coating composition samples were tested using the waterproofness test and the Konig hardness test method described above. The Konig hardness of the coating was 80 Seconds. In addition, it has been found that the coating is also waterproof.

The coated and uncoated printed papers were tested using a wet wiping test, a dry wiping test, an intensive point test, an FIRA contamination test and a wet gloss friction test. The resulting paper possessed essentially the same properties as those exhibited in the paper produced by the method of Example 1 with respect to wet wiping test and the like.

Observation of the washed samples under UV light showed that unlike the uncoated samples which were remarkably fluorescent after the washing process, the coated samples absorbed a microscopic amount of optical brightener in an undetectable amount .

The results after the printing of the ridges on the coated and uncoated samples were observed. Characteristic feathering expected on banknote paper was observed on the uncoated paper. In the coated paper, feathering remarkably decreased.

Example 4.

A paper sheet was prepared on a paper machine with an aqueous suspension of cellulosic fibers optionally mixed with optical fibers, synthetic fibers or other additives used in the paper industry. Thereafter, the paper was dried, baked, dried and wound.

The coating formulation is made as follows:

Part 15: Aliphatic polyester-polycarbonate polyurethane (IR 140 ^TM ) manufactured by Industrial Copolymers Limited,

0.5 part: Zeneca Resins BV. The product polyaziridine (CX100 ^TM )

84.5 parts: water

After the rolled-up foil paper was re-sprinkled, the coated paper was coated on both sides of the paper using a Meyer bar coater and then dried. Both sides of the paper were covered with a coating of 2 g / m ² .

Thereafter, the coated paper was hooked on a squeeze roller, and then the coated paper was cut in a usual manner.

Thereafter, the coated paper was printed by a four-angle printing method and an offset printing method.

The coating composition samples were tested using the waterproofness test and Konig hardness test described above. The Konig hardness of the coating was 120 Seconds. In addition, it has been found that the coating is also waterproof.

The coated and uncoated printed papers were tested using a wet wiping test, a dry wiping test, an intensive point test, an FIRA contamination test and a wet gloss friction test. The resulting paper possessed essentially the same properties as those reported in the paper produced by the method of Example 1 for wet wiping test and the like.

Observation of the washed samples under UV light showed that unlike the uncoated samples which were remarkably fluorescent after the washing process, the coated samples absorbed a minute amount of optical brightener there was.

The results were observed on the coated and uncoated samples after the yaw angle printing. Characteristic feathering expected on banknote paper was observed on the uncoated paper. In the coated paper, feathering remarkably decreased.

Example 5.

A paper sheet was prepared on a paper machine with an aqueous suspension of cellulosic fibers optionally mixed with optical fibers, synthetic fibers or other additives used in the paper industry. Thereafter, the paper was dried, baked, dried and wound.

The coating formulation is made as follows:

Part 15: Aliphatic polyester-polycarbonate polyurethane (IR 140 ^TM ) manufactured by Industrial Copolymers Limited,

0.5 part: Zeneca Resins BV. The product polyaziridine (CX100 ^TM )

84.5 parts: water

After passing through a size bath squeeze roll, the coating was applied to the wet-laid paper using a Meyer bar coater and dried to form a coating of 2 g / m ² on both sides of the paper . The process provides an economic advantage in that the drying process is omitted.

Thereafter, the coated paper was dried and wound again.

Thereafter, the coated paper was cut in a usual manner after being put on a squeeze roller.

Thereafter, the coated paper was printed by a yaw angle printing method and an offset printing method.

The coating composition samples were tested using the waterproofness test and Konig hardness test described above. The Konig hardness of the coating was 120 Seconds. In addition, it has been found that the coating is also waterproof.

The coated and uncoated printed papers were tested using a wet wiping test, a dry wiping test, an intensive point test, an FIRA contamination test and a wet gloss friction test. The resulting paper possessed essentially the same properties as those exhibited in the paper produced by the method of Example 1 for wet wiping test and the like.

Observation of the washed samples under UV light showed that unlike the uncoated samples which were remarkably fluorescent after the washing process, the coated samples absorbed a minute amount of optical brightener there was.

The results were observed on the coated and uncoated samples after the yaw angle printing. Characteristic feathering expected on banknote paper was observed on the uncoated paper. When printing with ink to produce a security document such as a bank note, the coated paper has noticeably reduced feathering.

All of the papers produced by each of Examples 1 to 5 were coated with a waterproof coating as measured by the criteria (i), (ii) and (iii) set forth above. In particular, (i) the wet tensile strength and the Young's modulus were not reduced; (ii) the reduction in transparency was not visible, and (iii) the weight of the film did not change.

For purposes of comparison, an embodiment describing typical strengths for coatings where water resistance and mechanical strength are not suitable is presented.

Example A.

A paper sheet was prepared on a paper machine with an aqueous suspension of cellulosic fibers, optionally mixed with other additives used in the paper industry or optical fibers or synthetic fibers. Thereafter, the paper was dried, baked, dried and wound.

The coating formulation is made as follows:

Part 15: Aliphatic polyester polyurethane (Witocobond 290H ^TM ) available from Baxenden Applied Chemicals Limited,

84.5 parts: water

After the rolled-up foil paper was re-sprinkled, the coated paper was coated on both sides of the paper using a Meyer bar coater and then dried. Both sides of the paper were covered with a coating of 2 g / m ² .

Thereafter, the sheet was hooked on a squeezing roller, and then the coated sheet was cut in a usual manner.

Thereafter, the above-mentioned paper was printed by a yaw angle printing method and an offset printing method.

The coating composition samples were tested using the waterproofness test and Konig hardness test described above. The Konig hardness of the coating was 15 Seconds. In addition, it has been found that the coating is also poor in water resistance.

FIRA contamination test was used to test printed and uncoated printed papers. The resistance to contamination of the coated paper was noticeably better than that of the coated paper.

Wet wrinkle test, dry wrinkle test, stress point test, and wet gloss friction test were used to test printed and uncoated printed papers. When compared to uncoated paper of the same paper batch, the coated samples were noticeably inferior.

Thereafter, the coated paper was printed by a four-angle printing method and an offset printing method. Characteristic feathering expected on banknote paper was observed on the uncoated paper. In the coated paper, feathering remarkably decreased.

As shown above through a number of tests in Example 1 - Example 5, the papers produced by the method of the present invention have comparatively significantly improved characteristics over standard banknote paper.

Good print adhesion was determined by a wet crumple test, a dry crumple test, a wet rub test and a severe laundry test. In addition, the print sharpness of the paper according to the present invention was significantly better than in the case of using ordinary banknote paper. In addition, the sharpness of the printing was particularly good, and the effect of the embossing was further improved. Also, the excellent soil resistance means that the coated paper produced by the method of the present invention absorbed less than two-thirds of the contaminating media when compared to uncoated paper.

As noted above, an extender may be used in the coating formulation to reduce cost; The extender may also have useful properties, such as improving the adhesion of a paper surface to which a security pattern such as a hologram is applied.

The extenders that may be used in the present invention may typically be dispersions of water-insoluble binders, such as styrene / acrylic copolymers, acrylated vinyl acetate, vinyl chloride / ethylene copolymers, or vinyl acetate copolymers. In general, they could not withstand waterproofness and hardness tests.

Another extender is VA / VEOVA copolymer, for example, under the trade name Vinamul ^TM .

However, if the composition comprising the polyurethane and the extender has the Konig hardness and passes the waterproofness test, they have the function of meeting the criteria set forth above in combination with a suitable polyurethane.

The extender may be added at a level of up to 70 parts, preferably 15 to 50 parts, per 100 parts of the coating formulation. The strongest and most waterproof extender may be added to the above levels. Obviously, the properties described above with respect to the coating composition can not be added at such a level that a weaker, more water-resistant and more inferior extender can not be added at this level.

Crosslinking agents may be used to increase the water resistance and hardness of the polyurethane coatings. The crosslinking agent can be used to obtain the requisite properties from the polyurethane that can not be obtained if it is not present. In addition, the crosslinking agent improves the properties of the polyurethane component to make the extender more usable. Suitable crosslinking agents include polyaziridines, carbodiimides, isocyanates and zirconium salts. Other crosslinking systems such as epoxy resins can be used, but they are less practical because of higher curing temperatures and longer curing times.

In addition, further investigation revealed that the polyurethane coatings according to the invention additionally provide important properties. It has been found that the use of certain polyurethane coatings improves durability and optical effects such as flakes, holograms, and kinograms. Since the polyurethane coating considerably reduces the extent to which the adhesive used to fix the flake containing the hologram is adsorbed on the paper surface. The adhesive can be used more uniformly and as a result, the adhesion and gloss of the surface become better. As a result, the better the gloss of the surface formed, the more visually the image present in the hologram becomes clear to the viewer, which is particularly advantageous for holograms. As is widely known, holograms are generally expensive, and security documents such as banknotes are in place for a longer period of time when in circulation, which is a result of enhanced durability by the polyurethane coatings of the present invention It is worth mentioning that it is commercially useful.

Claims (18)

Fabricating a sheet of paper comprising one or more security features into a wet state; Applying a sizing agent to the paper; Applying a coating comprising an uncoloured polyurethane, optionally including a functional additive, on one or both sides of the corrugated paper, if the functional additive does not increase the opacity of the paper by more than 1% ; And drying the paper, wherein the coating composition provides a film when cast on a glass surface, the Konig hardness being 15-130 Seconds, the following steps: a) casting a total preparation to be used in said coating on a glass plate to produce a film having a dry weight of 80 g / m ² ; b) at first, drying the film at 23 ° C (once it has lost its stickiness, it continues to dry for an additional hour at 80 ° C); c) measuring the weight of the film, wetting it to measure the tensile strength (Young's modulus), and visually checking the change in the degree of film transparency; d) the step of heating for 30 minutes in water containing 10 g / liter Na ₂ CO ₃ to the film sample; e) subsequently rinsing the film with cooling water and then repeating steps b) -c) (drying and re-weighing the film) [Among the above steps, when the film is dried and then weighed again, the following criteria are met. i) the wet tensile strength and the Young's modulus of the heated film are at least 90% of the initial wet tensile strength and Young's modulus. ii) the transparency of the film is reduced to an unrecognized extent. iii) when the dry weight of the film is more than 98% of the original weight. Wherein the security pattern passes through a waterproofness test defined by the security pattern. The method of claim 1, wherein the polyurethane is in the form of an aqueous dispersion. 3. The method of claim 1 or 2, wherein the coating further comprises an extender. 4. The method of claim 3, wherein the extender is a polyacrylate. The method according to any one of the preceding claims, wherein the covering weight of the polyurethane-containing coating is from 0.05 to 20 g / m ² . The method of claim 5, wherein the coating weight of 0.5-in method 5 g / m ^2. 7. A method according to any one of the preceding claims, wherein a coating comprising polyurethane is applied to the paper immediately after sizing the paper when the paper is still wet. 7. A method according to any one of claims 1 to 6, wherein a coating comprising polyurethane is applied to the dry paper after completing a normal papermaking step. The method according to any one of the preceding claims, wherein the fibers present in the paper are natural fibers or synthetic fibers or blended fibers of natural and synthetic fibers. The method according to any one of the preceding claims, wherein the polyurethane is an aliphatic polyester type and the polyurethane content is in the range of 2-70 wt%. 11. The process according to claim 10, wherein the polyurethane content of the dispersion is in the range of 5 to 30% by weight. The method according to any one of the preceding claims, wherein the polyurethane can be crosslinked and cross-linked while the paper is being dried. 13. The method of claim 12, wherein cross-linking is performed using aziridine as a cross-linking agent. Method according to any one of the preceding claims, wherein the security pattern is a watermark or is embedded in a thread that may contain visual or covert security elements The method according to any one of the preceding claims, wherein the polyurethane is not colored. 15. The method according to any one of claims 1 to 14, wherein the polyurethane composition comprises a functional additive that is a fluorescent or a pearl light additive. 7. A method according to any one of the preceding claims, wherein a foil comprising a flat flake, hologram or kinogram before or after printing is attached to the secure paper. A method for manufacturing a security document, comprising the steps of: preparing a security sheet according to any one of the preceding claims, and then printing a resultant security sheet to produce a security document such as a bank note.