Title of Invention

SECURITY ELEMENT FOR A SECURITY DOCUMENT AND METHOD OF PRODUCING IT.

Abstract

There is disclosed a security element (9) for a security document (1) having at least two layers of reaction lacquers between which diffraction structures, in particular halographic structures, are present in the form of relief structure and which are combined with a reflective layer (3), a first layer of lacquer bordering directly on the document, on the one hand, and directly on the reflective layer, lon lthe other hand, characterised in that the said first layer is a layer of reaction lacquer from the group of cationically curing lacquers, blue light-curing lacquers or chemically curing multicomponent lacquers.

Full Text

The present invention relates to security element for a security document and method of producing it, and, in particular to security element for security documents such as bank notes, identity cards or the like, with multi-layer security elements having a layer in which diffraction structures, in particular holographic structures, are embossed in the form of a relief structure and which are combined with a reflective layer. This application is divided out of Indian Patent Application No.106/Cal/94 (hereinafter referred to the "parent application"). Optically variable elements such as holograms, diffraction grids or interference layer elements have been preferably used for some time as protection against forgery or copying due to their optical properties that vary with the viewing angle. For mass production of such elements it is customary to produce so-called master holograms which have the particular phase information in the form of a three- dimensional relief structure. Starting with the master hologram one produces by duplication so-called press dies for embossing the required holograms in large numbers of units. The embossing can also be done directly on the document material as described in EP-A 0 338 378. In a continuous process bank note paper in a roll form is first printed on both sides and then provided in certain areas with a holographic structure. The lacquer to be embossed and the relief structure are simultaneously transferred to the paper by covering the surface structure of the press die with a radiation-curable lacquer. As soon as paper and press die are brought in contact the lacquer is cured. The lacquer now adheres to the paper surface and has the holographic relief structure. Then the embossed structure is given a thin vacuum metalized layer that permits the holographic information to be observed in reflection. Since paper is virtually impermeable to UV radiation the curing of the lacquer can in this case only take place with the aid of electron radiation, a very elaborate and expensive method that furthermore damages the paper. For this reason the production of embossed holograms directly on the document material has not become accepted in practice, although this procedure has great advantages with respect to resistance to forgery since the hologram is connected vir- tually undetachably with the substrate. Due to the much more cost-effective production and more versatile applicability embossed holograms are therefore usually prepared as multi- layer elements on a separate carrier and transferred to the document by means of an adhesive layer. The layer structure is dimensioned, or prepared by additional measures, in such a way that the hologram can be removed from the carrier layer after being glued to the document. The multilayer element applied to the carrier material can be produced e.g. by the method known from US-C 4.758.296. A matrix in web form circulating on rolls is provided with a liquid resin and brought in contact with a plastic carrier material. The liquid resin is simultaneously cured by UV or electron radiation. In a further step the relief structure is provided with a thin metal layer so that the hologram can be observed in reflection. To be trans- ferred to a document the layer structure is finally provided with a hot-melt adhesive layer that is activated under the action of heat and pressure. However this security element has the disadvantage that the hologram element might be detached from the document by reheatinq the hot-melt adhesive, and transferred to another. In general, so-called transfer embossing foils have more than the layers described in US-C 4.758.296. For exam- ple EP-A 0 170 832 describes a transfer embossing foil com- prising a carrier material, a first layer of lacquer per- mitting subsequent detachment of the carrier material, a second layer of lacquer in which the diffraction structures are embossed, a metal layer and a layer of bonding agent. Such a foil can be glued to a document by the method known from EP-A- 0 433 5715. The embossing foil in which the hologram structure is embedded is applied to a document locally in the form of a marking. For this purpose the document is printed at a certain place with an adhesive which only becomes viscous and sticky through UV, gamma or electron radiation. This activation takes place either before or after the transfer foil and document are brought together. Although this security element offers irreversible adhesion to the document since the cured adhesive is not reactivable, the embossed structure can be exposed if the layer bordering the relief structure or the metal layer has a different chemical base. Interestingly enough, the prior art also contains proposals for preventing embossed layers from being exposed by using chemically homogeneous materials or permeable metal layers. 3ut r.ince these elements are applied with reversibly activable adhesives in all such proposals these elements are still detachable from the substrate and thus insufficiently protected from manipulation. according to the parent application The Invention,/ is therefore based on the problems of providing a security document with an embossed hologram, whereby the embossed hologram has a simple layer structure with a good laminar compound that is cost-effective and simple to produce, and the hologram is furthermore connected with the document irreversibly. This problem is solved by the features of the present invention. The present invention provides a security element for a security document such no bank note, identity card or the like having at least two plastic layers consisting of reaction lacquers between which diffraction structures, in particular holographic structures, are present in the form of a relief structure and which are combined with a reflective layer, a first plastic layer bordering directly on the document, on the one hand, and directly on the reflective layer, on the other hand, characterized in that the first plastic layer is a layer of reaction lacquer from the group of cationically curing lacquers, blue light-curing lacquers or chemically curing multicomponent lacquers. The present invention also provides a method for producing the security element/ as herein described, comprising the steps of embossing the diffraction structures in a first layer of reaction lacquer or layer of reaction adhesive, providing the embossed layer of reaction lacquer with the reflective layer, and applying a further layer of reaction lacquer to the reflective layer. The invention offers multilayered advantages involving both the production of embossed holograms directly on the document material and the production and application of transferred embossed holograms. For example it is possible to produce embossed holograms directly on the antifalsification paper with the aid of light-curing substances in very uncomplicated fashion. Such substances are e.g. blue liqht-curing or delayed-curing lacqueis. These substances can of course be used just as advan- tageously for producing or applying transferred embossed holograms. Along with this simple production or transfer, the in- ventive security documents also offer the crucial advantage that the security elements have a simple layer structure and an intensive laminar compound within the element or between element and document. This is because the materials selected for plastic layers adjacent in the element layer structure are chemi- cally homogeneous and therefore ensure a much more intensive compound in the boundary\layers than chemically different substances. The firm compound with the document arises from the use of reaction lacquers or adhesives which adhere ir- reversibly to the document. To obtain a layer structure as simple as possible even in the case of the transferred embossed holograms, the metal layer disposed above the embossed layer is not covered with an additional foil layer which is then equipped with an ad- hesive layer but, according to the invention, coated di- rectly with the adhesive, the adhesive being selected so as to have a foil-like character in the cured state (on the substrate). These requirements are met by all reaction ad- hesives that polymerize by physical and/or chemical activa- tion. To counteract manipulation of all kinds the embossed layer of the transfer element and the adhesive layer are formed according to the invention as chemically homogeneous layers. The metal layer located between these layers is de- signed so thin that it already has microcracks or pores with normal handling so that the embossed layer and adhesive layer are in contact through these randomly present openings and form a largely inseparable compound at these places. Exposure of the relief structure or detachment of the secu- rity element therefore leads inevitably to destruction of the stated layer structure. Alternatively or additionally the metal layer can also be provided with openings system- atically . In a preferred embodiment the transfer element com- prises a carrier material preferably bearing a UV-curable layer of lacquer in which the hologram structure is em- bossed, and a metal layer whose thickness is much smaller than 1 micron, preferably in the range of 0.01 microns. Transfer to the document takes place by means of a UV-acti- vable adhesive having a chemical composition similar to that of the UV-curable lacquer, whereby the adhesive and layer of lacquer are in direct contact with each other in some areas. This security element has a simple layer structure in which the layers themselves adhere in optimal fashion. Depending on the case of application the inventive layer structure can be varied. The above-described transfer structure is particularly useful when extremely thin secu- rity elements are required that add as little buildup as possible on the later substrate or paper of value and also have low inherent stability after the carrier foil is re- moved, thereby additionally preventing removal of the secu- rity element. If the security element is to be mechanically stable itself the invention offers two alternatives, namely to use a mechanically stressable foil in which the relief structure is embossed, or a carrier foil remaining on the later secu- rity element together with the embossed layer of lacquer or a foil layer bearing the embossing. Such a structure is to be equipped according to the invention with a permeable metal layer and with a curing adhesive layer. Such embodi- ments are of special interest in particular when the secu- rity element is designed as a strip and applied to the paper as a safeguarding thread. Further advantages and variants will be explained with reference to the figures. It is pointed out that the figures do not offer a true-to-scale representation of the invention but are only for the sake of illustration. The term "reaction adhesives" used in the following text includes all types of adhesive that cure irreversibly under specific physical or chemical action. Both UV-curable and two- component adhesives are thus referred to here as reaction adhesives. In the accompanying drawings, Fig. 1 shows an inventive security document; Fig. 2 shows a transfer embossing foil according to the invention; Fig. 3 shows a method for producing the inventive security document of Fig. 1; Figs. 4-7 show four variants of the production mothod of Fig. 3; Fig. n shows a variant of the inventive security document; Fig. 9 shows a method for producing the inventive security document of Fig. 8; Fig. 10 shows a variant of the production method of Fig. 9. Fig. 1 shows a cross section through a security document according to the invention. Security element 9 is disposed on security document 1 in a predetermined area. Depending on the requirements, element 9 can have the form of a thread or band or be formed as a mark with certain contour shapes. It comprises UV-curable or chemically curable layer of lacquer 2 in which diffraction structures are embossed in the form of a relief, and thin reflective layer 3, preferably a metal layer. Element 9. is inseparably connected with security document 1 via adhesive layer 4. Adhesive layer 4 consists of a material that is largely homogeneous chemically with the material of embossed layer) 2. This has the advantage that a very firm compound arises in areas where the metal layer contains pores or microcracks (which is un- avoidabLe with layer thicknesses in the range of about 1 micron) and where layer of lacquer 2 and adhesive layer 4 thus adjoin directly. This is very desirable with respect to protection against forgery by reembossing the relief struc- ture, and to resistance to wear. Since uv-curable or chemi- cally curable layers of lacquer and adhesive are irreversi- bly curable it is impossible to detach the layers later. In case of thermal or chemical attacks both layers are fur- thermore always affected so that such measures necessarily destroy the total security element. In this embodiment of the invention security element 9 is produced separately as transfer embossing foil 10 whose structure is shown in Fig. 2. Carrier material 5 is expedi- ently designed as an endless plastic band to which lacquer 2 is applied in a continuous process. A matrix whose surface structure corresponds to the interference stripe pattern of any desired diffraction structure is used to emboss the re- lief structure in lacquer 2, which is cured e.g. by UV ra- diation during the embossing process. Such a method is de- scribed for example in the abovementioned US-C 4.758.296. Alternatively one can of course also use a delayed- curing Lacquer, i.e. a lacquer in which polymerization is initiated, by irradiation with suitable light and then takes place with a time lag, or a blue Light-curing lacquer. More detailed information about such lacquers can be found else- where . After this the embossed structure in layer 2 is pro- vided with an either uninterrupted or screened reflective layer 3, preferably a metal layer. Screening offers the ad- vantage that the compound between adhesive layer 4 and em- bossed layer 2 can be made even firmer. The size of the metal-free areas can be selected as one chooses; it is thus conceivable to make the metal-free areas so small that they cannot be resolved by the eye and thus do not impair the general impression of the information shown. Alternatively the metal-free areas could be used as desiqn elements so that the diffraction information is observable visually within the security element area only at certain places. Metalizing methods to be used may be e.g. the customary vacuum metalizing method or else a photolytic method. The metalized layer can optionally be provided with a protective layer, whereby the latter should be made of a material chemically homogeneous with-embossed layer 2. The finished transfer embossing band 10 can be stored on rolls as a semifinished product and used on call-in a production method as described in the following with refer- ence to Figs. 3 to 5. Fig. 3 shows part of a continuous method for producing security documents according to the invention. Security document material 1, preferably bank note paper already printed, exists here in web form and is coated locally with a special adhesive in printing unit 6. This adhesive is for example a cationically reacting UV. adhesive that can be treated like an ink before activation. Unlike customary radically reacting UV adhesives which only cure during irradiation, so-called cationically curing ad- hesives have the property of being only activated by irra- diation with UV light and curing further after irradiation. Such cationically curing UV lacquer systems are sold e.g. by Herberts under type designation ISS 1202. After adhesive 4 has been transferred to substrate 1 in printing unit 6 it is irradiated in the next unit with UV lamp 7, as shown in Fig. 3, to activate its bonding ability. In the following step transfer embossing foil 10 is fed from supply roll 11 according to Fig. 2. Element 9 (Fig. 2) ad- heres to the adhesive layer and is removed from carrier band 5 in the form of the adhesive coating. Carrier band 5 and the non-transferred remains of element layer structure 9 are wound onto transfer band roll 12. In a last method step not shown, substrate 1 provided with security elements 9 is cut up into suitable formats, e.q. individual bank notes. In a variant, adhesive 4 can also be printed on trans- fer embossing foil 10 and activated there. This possibility is shown in Fig. 4. Before embossing foil 10 removed from roll 11 is brought together with substrate 1, UV-initiable adhesive 4 is applied to metal layer 3 of embossing foil 10 in any desired patterning in printing unit 6 and then acti- vated with UV lamp 7. In this case too carrier band 5 is removed from substrate 1 via roll 12 directly after gluing. Instead of delayed-curing adhesives one can of course also use the abovementioned blue light-curing adhesives. This method variant is shown in Fig. 5. Paper web 1 is pro- vided with the blue light-curing adhesive in printing unit 6. This adhesive is e.g. an acrylate from Imperial Chemical Industries PCL with the desicmation LCR 0603B. In the area of pressing cylinder 16 transfer material 10 and paper web 1 are brought in contact and irradiated with blue light 17. The adhesive thereby cures within sec- onds since the paper is permeable to blue light. The trans- fer foil can then be removed from the hologram-paper com- pound in the usual way. Departing from the embodiments shown in Figs. 3 to 5 it is also possible to leave carrier foil 5 on substrate 1 temporarily or permanently. This may be useful as additional protection from mechanical loads temporarily, e.g. for a period of storage or transport, or for the entire life e.g. of safeguarding threads. It is important in this connection that the protective layer function performed by carrier foil 5 should in this case be regarded only as additional to the protective layer function of layer of lacquer 2. Removal of carrier film 5 opens up no possibilities of manipulation since it doe 3 not yet make the relief structure accessible. The methods shown in Figs. 3 to 5 are wonderfully sim- ple and require no elaborate protective measures, as are necessary for example when eloctron-beam curing or solvent- containing adhesives are used. Furthermore one thus obtains both a firm laminar compound within the security element and firm adhesion to the document, so that it is not possible either to separate the embossed structure from the element layer structure or to detach the element from the document. Although it is preferable to use radiation-curing ad- hesives for reasons of process engineering, in particular due to their simple and extremely fast curing, one can al- ternatively use mixed adhesives which are related chemically with the embossed layer. According to the invention the em- bossed layer need not necessarily be a radiation-curable layer of lacquer, it can also be a chemically curing layer that has the same chemical base as the adhesive layer. This variant is shown in Fig. 6. One component of the adhesive is applied in printing unit 13 directly to transfer embossing foil 10 removed from roll 11, while the second component is applied in printing unit 14 to substrate 1. When substrate 1 and transfer embossing foil 10 are brought together a self-curing layer arises in the area of the ad- hesive components to ensure the compound between substrate 1 and embossed layer 2. Carrier material 5 can of course here too be removed directly after gluing, as shown in the fig- ure , or else be left on substrate 1 as a temporary protec- tive layer. The separate application of the adhesive components shown in Fig. 6 makes the functional principle particularly clear. However this procedure is not permissible with any two-component adhesive since these adhesives generally de- velop their adhesive properties only when intimately mixed. Departing from the principle shown in Fig. 6 one can, if necessary, replace pair of rolls 13 or 14 by a mixing appa- ratus (not shown) for first mixing the two components and then applying them jointly in the way customary for the ex- pert. The other pair of rolls is then omitted in this em- bodiment . Fig. 7 shows a further possibility for producing the inventive security element. This method corresponds sub- stantially to the production method of Fig. 4 only that se- curity element band 10 brought by roll 11 is completely fixed to substrate 1 here, i.e. no transfer band is removed. As already mentioned at the outset such an embodiment is useful in cases where the security elements have sufficient inherent stability (stable relief foil), or one desires in- creased protection from mechanical loads by providing an additional protective layer (additional protective layer instead of transfer carrier foil). Fig. 8 shows a variant of inventive security document 1. In this case security element 9 comprises layer of lac- quer 20 in which the diffraction structures are embossed in the form of a relief, thin reflective layer 3, preferably a metal layer, and layer of protective lacquer 21. Here too element 9 can have the form of a thread or band or else be formed as a mark with certain contour shapes, depending on the requirements. Embossed layer of lacquer 20 consists ac- cording to the invention of a reaction lacquer, in particu- lar a UV-initiated delayed-curing or a blue light-curing lacquer, as were already explained. Layer of protective lacquer 21 protects the sensitive embossed structure and metal layer 3 from outside environmental influences and me- chanical impairment. It is preferably made of a material chemically homogeneous with layer of lacquer 20 to form a firm compound with layer of lacquer 20 in the area of mi- crocracks or pores in the metal layer. In contrast to the security document shown in Fig. 1 security element 9 is produced directly on the document ,in this embodiment. The various procedures permitting simple and cost-effective production of this security document will be explained in more detail with reference to Figs. 9 and 10. In Fig. 9 a blue light-curing adhesive, e.g. the abovementioned acrylate LCR-0603B, is applied by means of printing unit 18 to paper substrate 1 in the desired form of later security element 9, possibly all over. The pretreated paper is then fed to an embossing unit, here embossing cyl- inder 22. The surface of the embossing cylinder has holo- graphic relief structure 23 which is transferred upon con- tact with the layer of lacquer. During the embossing process the lacquer is cured within seconds through the paper layer with the aid of blue light 17. In following method steps not shown in the figure the metalizing or protective lacquer coating is performed. Alternatively the embossing roll can be provided with the lacquer instead of paper web 1. After irradiation with blue light the cured layer adheres to the paper and is re- moved from the embossing roll. Fig. 10 shows a similar method in which a delayed-cur- ing lacquer is used for the layer to be embossed. In this case the layer of lacquer applied to the paper is irradiated shortly before the embossing unit. The exposure to UV light only initiates polymerization and does not cause complete curing. The still formable layer of lacquer is then provided with relief structure 23 by being brought in contact with embossing cylinder 22. When substrate web 1 leaves the em- bossing unit the layer of lacquer is completely crosslinked and can be processed further in the conventional way. It is of course also possible in this embodiment exam- ple to apply the lacquer to the embossing roll, activate it there and finally bring it in contact with the paper during the curing process. The described methods thus permit simple production of a security element very resistant to forgery having a mini- mum of element layers and thus requiring very few method steps for its production, and can furthermore dispense with complicated, cost-intensive techniques. A further method variant is to provide the embossing roll as shown in Figs. 9 and 10 with a metalized layer be- fore it is brought in contact with the layer of lacquer. More details of this procedure can be found in EP-A 0 563 992. Since particularly antifalsification papers frequently have great surface roughness which might impair the effec- tiveness of the diffraction structures the paper can, if necessary, be glazed in the area of the security element before lacquering by additional measures, as are described in EP-A 0 440 045. On the basis of the invention it is not absolutely necessary for reflective metal layer 3 to be provided be- tween the two plastic layers 2, 4, 20, 21. If one uses only adjacent plastic layers in contrast to the examples shown in Figs. 1, 2 and 8 they must of course have optically differ- ent properties, in particular different calculation indices, so that the diffraction structures remain recognizable. These layers are always reaction lacquers or reaction adhe- sives according to the invention. It is also evident that any desired combinations of reaction adhesives can be used for the embossed layer and the adhesive layer in the case of the transferred embossed hologram. The same holds for the embossed, or protective layer of the hologram produced directly on the document. WE CLAIM: 1. A security element for a security document such as bank note, identity card or the like having at least two plastic layers (2,4,20,21) consisting of reaction lacquers between which (diffraction structures) in particular holographic structures, are present in the form of a relief structure and which are combined with a reflective layer (3), a first plastic layer (4,20) bordering directly on the document, on the one hand, and directly on the reflective layer (3), on the other hand, characterized in that the first plastic layer (4,20) is a Layer of reaction lacquer from the group of cationically curing lacquers, blue light-curing lacquersor chemically curing multicomponent-lacquers. 2. The security element as claimed in claim 1, wherein the second plastic layer (2,21) is likewise a reaction lacquer from the group of cationically curing lacquers, blue-light curing lacquers or chemically curing multicomponent lacquers. 3. The security element as claimed in claim 1, wherein the first plastic layer (4,20) is formed as a cationically curing UV lacquer and the second plastic layer as a radically curing UV lacquer. 4. The security element as claimed in claim 1, wherein each of the first plastic layer (4,20) and the second plastic layer (2,21) is a chemically curing multicomponent lacquer. 5. The security element as claimed in any one of claims 1 to 4, wherein the reflective layer (3) has a thickness smaller than 1 micron. 6. The security element as claimed in claim 5, wherein the thickness is in the range of 0.01 microns. 7. The security element as claimed in any one of claims 1 to 6, wherein the reflective layer (3) contains openings. 8. The security element as claimed in claim 7, wherein the openings are microcracks or micropores in the reflective-layer (3). 9. The security element as claimed in claim 7, wherein the openings in the reflective layer (3) are present systematically in a predetermined pattern. 10. The security element as claimed in any one of claims 1 to 9, wherein the reflective layer (3) is a metal layer. 11. The security element as claimed in claim 1, wherein the security element (9) is designed in the form of a thread or band. 12. Security document such as bank note or identity card comprising a security element as claimed in any one of claims 1 to 11. 13. A method for producing the security element as claimed in claim 1 comprising the steps of embossing the diffraction structures in a first layer of reaction lacquer or layer of reaction adhesive, providing the embossed layer of reaction lacquer with the reflective layer, and applying a further layer of reaction lacquer to the reflective layer. 14. The method as claimed in claim 13 comprising the steps of providing a one-or multilayered foil with the first layer of reaction lacquer and embossing the relief structure in this layer, then providing the foil with a thin reflective layer, providing a security document material and/or the reflective layer at least in some areas with a further layer of reaction lacquer or layer of reaction adhesive, bringing the security document and the foil in contact and interconnecting them inseparably by the reaction adhesive activated shortly before or during contacting and removing the transfer layer in cases where the foil has a transfer foil. 15. The method as claimed in claim 13 or 14, wherein chemically homogeneous materials are used for the embossed layer and the adhesive layer. 16. The method as claimed in any one of claims 13-15, wherein the embossed layer is provided only partly with the reflective layer so that the embossed layer and the adhesive layer are in direct contact with each other in the areas free from reflective layer. 17. The method as claimed in claim 16, wherein the embossed layer and the adhesive layer are crosslinked with each other in the areas free from reflective layer. 18. The method as claimed in any one of claims 13-17, wherein a metal layer is applied as the reflective layer by the vacuum metalizing technique or by the photolytic metalizing technique. 19. The method as claimed in any one of claims 13-18, wherein the security element is applied to a security document material in the form of a thread or band. 20. The method as claimed in claim 13, wherein the first layer of reaction lacquer is applied directly to a security document material at least in some areas and embossed there. 21. The method as claimed in claim 20, wherein a blue light-curing lacquer is applied directly to the paper, provided with the embossing there and irradiated with blue light through the paper during the embossing process and thereby cured. 22. The method as claimed in claim 20, wherein a delayed-curing lacquer is applied directly to the paper and provided with the embossing there. 23. The method as claimed in claim 22, wherein a UV- initiable lacquer is used which is irradiated with UV light shortly before embossing and then cures with a delay within seconds. 24. The method as claimed in claim 13, wherein the first layer of reaction lacquer is applied directly to the embossing tool and transferred directly to a security document material with the embossing. 25. The method as claimed in claim 24, wherein a blue light-curing lacquer is applied to the embossing tool and, while the embossing tool is in contact with the paper, irradiated with blue light through the paper and thus cured, and finally the embossed layer adhering to the paper is removed from the embossing tool. 26. The method as claimed in claim 24, wherein a delayed-curing lacquer is applied to the embossing tool and activated before it comes in contact with the paper so that is cures during contact of the embossing tool with the paper, and the embossed layer adhering to the paper is removed from the embossing tool. 27. The method as claimed in any one of claims 20 to 26, wherein the embossing tool is first provided with a metalized layer and the layer of reaction lacquer only then applied to this metallized layer. 28. A security element for a security document substantially as herein described, particularly with reference to the accompanying drawings. 29. A method for producing a security element for a security document substantially as herein described. There is disclosed a security element (9) for a security document (1) having at least two layers of reaction lacquers between which diffraction structures, in particular halographic structures, are present in the form of relief structure and which are combined with a reflective layer (3), a first layer of lacquer bordering directly on the document, on the one hand, and directly on the reflective layer, on the other hand, characterised in that the said first layer is a layer of reaction lacquer from the group of cationically curing lacquers, blue light- curing lacquers or chemically curing multicomponent lacquers.

Documents:

74-cal-1998-granted-abstract.pdf

74-cal-1998-granted-assignment.pdf

74-cal-1998-granted-claims.pdf

74-cal-1998-granted-correspondence.pdf

74-cal-1998-granted-description (complete).pdf

74-cal-1998-granted-drawings.pdf

74-cal-1998-granted-form 1.pdf

74-cal-1998-granted-form 18.pdf

74-cal-1998-granted-form 2.pdf

74-cal-1998-granted-form 3.pdf

74-cal-1998-granted-gpa.pdf

74-cal-1998-granted-letter patent.pdf

74-cal-1998-granted-others.pdf

74-cal-1998-granted-reply to examination report.pdf

74-cal-1998-granted-specification.pdf