DE102017108585A1 - Method for introducing image information into a volume hologram - Google Patents

Abstract

The present invention relates to a method for introducing image information, for example in the form of an image or in the form of personal data, into a volume hologram by applying a UV-deactivatable swelling agent to an inkjet printhead in the region intended to contain the image information. is printed on a pressure side of the volume hologram, so that the swelling agent can diffuse into the volume hologram for a defined period of time and increases the interplanar spacing of the Bragg net planes of the volume hologram, wherein the swelling agent cured by exposure to UV light after the defined period of time becomes. The invention provides that the swelling agent has a monomer content greater than 70% and a dynamic viscosity of 5 to 20 mPas and is printed with droplet sizes between 1 picoliter and 20 picoliters, wherein the defined period in which the swelling agent can diffuse into the volume hologram, at least 10 seconds and at most 8 minutes, so that the image information can then be read both under visible light and under infrared light

Description

The present invention relates to a method for introducing image information, for example in the form of an image or in the form of personal data, in a volume hologram according to the preamble of independent claim 1. In this method, a deactivatable by UV light swelling agent with an ink jet print head on a print page of the volume hologram, the imprint being in the area intended to contain the image information. The source means can diffuse into the volume hologram for a defined period of time, thereby increasing the interplanar spacing of the Bragg network planes of the volume hologram. After the defined period of time, the swelling agent is cured by exposure to UV light. This stops the diffusion of the swelling agent into the volume hologram.

The present invention also relates to a method for producing a forgery-proof document with a hologram produced in this way.

It is known from the prior art that the lattice plane spacing of the Bragg network planes of a volume hologram consisting of a photopolymer can be changed by contact with a monomer-containing swelling agent. By diffusing organic molecules into the volume hologram, a swelling is caused which leads to an increase in the interplanar spacing, resulting in a color shift towards a longer wavelength color range.

A method according to the preamble of independent claim 1 is, for example DE 10 2006 048768 A1 known.

The object of the present invention is to develop the method of the generic type to the effect that an improved image quality and an increased security against forgery of the resulting volume hologram results.

The object is achieved by the features of independent claim 1. Accordingly, in a method according to the preamble of independent claim 1 then an inventive solution to the problem, if the swelling agent preferably has a monomer content greater than 70% and preferably a dynamic viscosity of 5 to 20 mPas and is printed with droplet sizes between 1 picoliter and 20 picoliters, wherein the defined period of time in which the swelling agent can diffuse into the volume hologram is at least 10 seconds and at most 8 minutes, so that the image information then under both visible light and under Infrared light can be read.

By means of the method according to the invention, the interplanar spacing of the Bragg network planes in different layers of the volume hologram is changed in such a way that the image information introduced into the volume hologram is reconstructed both under visible light and under infrared light. This effect can serve as a security feature for determining the authenticity of a document provided with the hologram. With a corresponding infrared scanner can be checked whether the image information is actually present in the infrared range. Another advantage of the present invention is an improved image quality over the prior art.

The volume hologram used is preferably a reflection volume hologram. More preferably, the volume hologram is made of a photopolymer film. The thickness of this film is more preferably at least 8 microns and a maximum of 20 microns. More preferably, the thickness is about 10 microns. Although it is preferable to use a photopolymer volume hologram, the present invention is also basically applicable to a volume hologram made of a silver film. The Bragg network planes preferably do not run parallel to the plane of extent of the volume hologram, but they preferably enclose an angle to the plane of extent of the volume hologram which is at least 35 °.

The image information that is introduced into the volume hologram may be, for example, a passport photo or printed personal data. In principle, any type of image information can be introduced into a volume hologram with the method according to the invention.

The pressure preferably takes place under complete UV light exclusion to prevent unwanted premature curing of the swelling agent. The swelling agent is preferably colorless and transparent. It also preferably contains monomers that can diffuse into the photopolymer and thereby produce the desired swelling. Depending on how long the curing is delayed by exposure to UV light after printing, a different monomer concentration occurs within the hologram. The printing is analogous to a grayscale print. This means, depending on the desired wavelength shift, a certain droplet volume is selected, so that the swelling of the volume hologram in the individual pixels takes place differently depending on the applied volume of the swelling agent. As a swelling agent is particularly preferred transparent UV ink having a high diffusible monomer content of more than 70%, preferably more than 80%, and having a low dynamic viscosity, preferably in the range of 3 to 20 mPas. These swelling agent properties enable a fast diffusion and a strong broadening of the Bragg network planes in the adjacent hologram layer region, which can be detected well under infrared light, without impairing the visibility of the holographic information under white light viewing. The ink may for example consist of a blend of oligomer and acrylate monomer.

Advantageous embodiments of the present invention are the subject of the dependent claims.

According to a preferred embodiment of the present invention, the swelling agent is printed with droplet sizes between 1.3 picoliters and 10 picoliters. This results in a particularly high imaging quality.

Furthermore, it has proved to be advantageous if the defined period in which the swelling agent can diffuse into the volume hologram, according to another preferred embodiment of the present invention is at least 30 seconds.

According to another embodiment of the present invention, the defined period of time in which the swelling agent can diffuse into the volume hologram is at most 120 seconds, more preferably at most 1 minute. In this embodiment, the monomer concentration in the upper hologram layer is high, so that the lattice planes in this area are greatly expanded. This has the consequence that in this area, the network distances are so large that a shift in the infrared range is effected, the introduced image information in the visible range as a positive image and in the infrared range as a negative image. This effect can also be used as a security feature for determining the authenticity of a document provided with the hologram.

According to another alternative embodiment of the present invention, the defined period of time in which the swelling agent can diffuse into the volume hologram is at least 2 minutes and more preferably at most about 8 minutes, more preferably at most 3 minutes. In this embodiment, the image information is present both as a positive image both in the visible range and in the infrared range. Depending on the application, this effect can also be used as a security feature for determining the authenticity of a corresponding document.

According to another preferred embodiment of the present invention, the diffusion of the swelling agent into the volume hologram is carried out at an elevated temperature which is between 50 ° C and 80 ° C. More preferably, the elevated temperature is about 70 ° C. In this embodiment of the present invention, the diffusion period can be reduced by up to 50%. At the same time, a further improved imaging quality results.

According to a further preferred embodiment of the present invention, a volume hologram is used to carry out the method according to the invention, which reconstructs in the initial state in the visible green or blue region. In other words, the volume hologram used is a holographic ground glass that reflects green or blue over the entire area. The output wavelength may be, for example, 500 nm. If the starting color is more in the blue range, the shift to the longer wavelength range can cover a particularly wide color spectrum.

According to a further preferred embodiment of the present invention, the volume hologram is pretreated by surface application of a monomer-containing UV adhesive to one side of the volume hologram and subsequent curing of the UV adhesive after expiration of a period between 1 second and 20 seconds by exposure to UV light, so the lattice plane spacing of the Bragg network planes of the volume hologram is increased in a certain layer and thereby shifted in the direction of the infrared range. In this embodiment it is effectively prevented that in very bright image areas at certain viewing angles, dark green appearing artifacts occur due to solarization effects. The adhesive may for example consist of a blend of urethane oligomer and acrylate monomer.

The thickness of the layer in which the pretreatment acts is preferably at most 50% of the total thickness of the volume hologram. Further preferably, the displacement of the interplanar spacing in this layer takes place in the direction of the infrared region, but still in the visible region.

Further preferably, the monomer-containing UV adhesive is applied to the pre-treatment of the volume hologram on the side of the volume hologram, which is opposite to the side to be printed.

According to another preferred embodiment of the present invention, the Inkjet printhead a resolution of at least 300 dpi, preferably of at least 600 dpi. This achieves optimum imaging quality.

The present invention further provides a method of making a tamper-proof document with a hologram. According to the invention, a volume hologram is first glued onto a carrier layer of the forgery-proof document, with image information subsequently being introduced into the volume hologram in accordance with the method described above. Counterfeit-proof documents such as passports, ID cards, driving licenses or the like can be made particularly simple and inexpensive in this way. The forgery-proof document may contain additional layers in addition to the actual carrier layer. The carrier layer may preferably consist of polycarbonate.

According to a further preferred embodiment of the present invention is applied to the pressure side of the Volumenhologramms after introducing the image information, a protective cover layer of a polycarbonate film and at a temperature between 150 ° C and 180 ° C, preferably between 160 ° C and 180 ° C, and laminated to the volume hologram at a pressure between 1.5 bar and 2.5 bar. More preferably, the applied pressure is about 2 bar. In this embodiment, a particularly simple and inexpensive to produce protection of the volume hologram is produced. Alternatively, for example, a protective lacquer can be applied. The lacquer may further preferably be a UV lacquer.

Further preferably, the swelling agent printed in the form of personal data, for example as a portrait, is printed and cured in such a way that on the printing side a relief having a maximum height of at least 10 μm, preferably at least 15 μm, more preferably at least 20 μm, more preferably at least 25 microns results. The highest relief height is achieved in the dark areas of the portrait. The relief serves to relieve the brighter image areas during the lamination process or to protect it against undesired influence by the pressure required for lamination.

An example of the method according to the invention will be explained in more detail with reference to drawings.

• 1: ein Volumenhologramm im Ausgangszustand auf einem Filmträger,
• 2: das Volumenhologramm aus 1 nach dem Aufkleben des Volumenhologramms auf eine Trägerschicht eines fälschungssicheren Dokuments und Abziehen des Filmträgers,
• 3: das Volumenhologramm aus 2 mit bereichsweise aufgedrucktem Quellmittel nach Aushärtung des Quellmittels nach einer relativ kurzen Verzögerungszeit, und
• 4: das selbe Volumenhologramm aus 2 mit bereichsweise aufgedrucktem Quellmittel nach Aushärtung des Quellmittels nach einer etwas längeren Verzögerungszeit.

Show it:

• 1 : a volume hologram in the initial state on a film carrier,
• 2 : the volume hologram off 1 after sticking the volume hologram on a backing layer of a tamper-proof document and peeling off the film carrier,
• 3 : the volume hologram off 2 with partially printed swelling agent after curing of the swelling agent after a relatively short delay time, and
• 4 : the same volume hologram 2 with locally printed swelling agent after curing of the swelling agent after a slightly longer delay time.

For the following statements applies that the same parts are designated by the same reference numerals. If reference numbers are contained in a figure, which are not discussed in detail in the associated description of the figures, reference is made to preceding or subsequent description of the figures.

1 shows a volume hologram 1 in that it consists of a photopolymer and has a thickness of about 10 μm. On the top 3 of the volume hologram 1 is a movie carrier 8th applied. The illustration shows the volume hologram in the initial state. That means the Bragg network planes 4 have a uniform distance to each other. This distance corresponds to half the wavelength of the light with which the volume hologram was made. As can be seen in the illustration, the lattice planes do not run parallel to the plane of extent of the volume hologram. Instead, the lattice planes have an angle to the plane of extent of the volume hologram, which in the illustrated case corresponds to approximately 80 °.

As 2 shows, becomes the volume hologram 1 by means of a UV adhesive 5 that on the bottom 6 the volume hologram is applied, with a carrier layer 7 glued to a tamper-proof document. The carrier layer is preferably a polycarbonate layer or paper side. For example, the forgery-proof document may be a passport. Calculated from the date on which the glue 5 the bottom 6 of the volume hologram for the first time, a certain amount of time passes until the adhesive is cured by exposure to UV light. In this time span, between 1 Second and 20 Seconds, monomers from the UV adhesive diffuse into the lower layer 9 of the volume hologram causing swelling of the material and thereby increasing the distance between the Bragg lattice planes. This in turn leads to a shift the reconstruction wavelength in the longer wavelength range, thus in the direction of the infrared range. The swelling also changes the angle of the Bragg network planes. The change in the Bragg network planes is indicated by the reference numeral 4 ' highlighted. The thickness of the dashed lines symbolizes the prevailing monomer concentration.

After removal of the film carrier 8th can the top 3 of the volume hologram then with a monomer-containing swelling agent 2 be printed. The printing is done by means of an inkjet printhead. As 3 shows, becomes the volume hologram 1 not over the entire surface but only printed in the area in which image information is to be incorporated. In a manner similar to the adhesion of the volume hologram to the carrier layer of the tamper-proof document, the lattice planes are likewise altered by diffusion, resulting in a color shift. The degree of displacement depends on the one hand on the amount of the printed swelling agent, and on the other hand on the contact time of the swelling agent. The swelling agent is also cured by exposure to UV light after a certain period of time, whereby the swelling process or the change of the lattice planes is completed. Both factors are according to the invention coordinated so that the introduced into the volume hologram image information can be read both under visible light and under infrared light. In case of 3 For example, the time between printing the swelling agent and curing the swelling agent by exposure to UV light is about 2 minutes. 4 comparatively shows a condition after 6 minutes delay. The change of the Bragg network planes by diffusion of the swelling agent into the upper and middle layer of the volume hologram is shown in the illustrations of FIGS 3 and 4 by the reference numeral 4 ' highlighted

The amount of printed swelling agent and the delay time period between the application and the curing of the swelling agent are also coordinated so that the swelling agent is not completely absorbed by the material of the volume hologram but partially as a relief on the top 3 remains. This relief has a thickness of about 20 microns and serves to protect the brighter, holographic image areas from undesirable influence by the relatively high pressure required to laminate a polycarbonate protective overcoat (not shown).

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102006048768 A1 [0004]

Claims (15)

Method for introducing image information, for example in the form of an image or in the form of personal data, into a volume hologram (1) by applying a UV light-deactivatable swelling agent (2) to an inkjet printhead in the area intended to contain the image information , is printed on a printed side (3) of the volume hologram (1) so that the swelling means (2) can diffuse into the volume hologram (1) for a defined period of time and the interplanar spacing of the Bragg network planes (4, 4 ', 4 ") of the volume hologram thereby increased, wherein the swelling agent (2) is cured after expiration of the defined period by exposure to UV light, characterized in that the swelling agent (2) has a monomer content greater than 70% and a dynamic viscosity of 5 to 20 mPas and is printed with droplet sizes between 1 picoliter and 20 picoliters, wherein the defined period of time in which the swelling agent (2) in the Vo lumen hologram (1) can diffuse, at least 10 seconds and at most 8 minutes, so that the image information can then be read both under visible light and under infrared light. Method according to Claim 1 , characterized in that the swelling agent (2) is printed with droplet sizes between 1.3 picoliter and 10 picoliters. Method according to Claim 1 or 2 , characterized in that the defined period in which the swelling agent (2) can diffuse into the volume hologram (1) is at least 10 seconds and a negative image with IR light is detectable. Method according to one of Claims 1 to 3 , characterized in that the defined period in which the swelling agent (2) can diffuse into the volume hologram (1) is at most 120 seconds and a negative image with IR light is detectable. Method according to one of Claims 1 to 3 , characterized in that the defined period in which the swelling agent (2) can diffuse into the volume hologram (1) is at least two minutes, preferably at most about 3 minutes, and a positive image with IR light is detectable. Method according to one of the preceding claims, characterized in that the diffusion of the swelling agent (2) into the volume hologram (1) at an elevated temperature between 50 ° C and 80 ° C, preferably at an elevated temperature of about 70 ° C. Method according to one of the preceding claims, characterized in that a volume hologram (1) is used, which reconstructs in the initial state in the visible green or blue region. Method according to one of the preceding claims, characterized in that the volume hologram (1) by surface application of a monomer-containing UV adhesive (5) on one side (3, 6) of the volume hologram and subsequent curing of the UV adhesive (5) after expiration of a Time between 1 second and 20 seconds is pretreated by exposure to UV light, so that increases the interplanar spacing of the Bragg network planes (4, 4 ', 4 ") of the volume hologram (1) in a certain layer (9) and thereby is moved in the direction of the infrared range. Method according to Claim 8 , characterized in that the monomer-containing UV adhesive (5) for pretreating the Volumenhologramms (1) on the side (6) of the volume hologram is applied, which is opposite to the pressure side (3). Method according to one of the preceding claims, characterized in that the inkjet printhead has a resolution of at least 300 dpi, preferably of at least 600 dpi. A method for producing a tamper-proof document with a hologram, wherein a volume hologram (1) is first adhered to a carrier layer (7) of the tamper-proof document and then image information according to the method of any of Claims 1 to 10 is introduced into the volume hologram (1). Method according to Claim 11 , characterized in that the surface application of the monomer-containing UV adhesive (5) on one side (6) of the volume hologram (1) according to Claim 8 when gluing the volume hologram (1) on the carrier layer (7) of the forgery-proof document takes place. Method according to Claim 11 or 12 , characterized in that the carrier layer (7) of the forgery-proof document consists of polycarbonate. Method according to one of Claims 11 to 13 , characterized in that applied to the pressure side (3) of the volume hologram (1) after introduction of the image information, a protective cover layer of a polycarbonate film and at a temperature between 150 ° C and 180 ° C and a pressure between 1.5 and 2 5 bar is laminated to the volume hologram (1). Method according to Claim 14 , Characterized in that on the pressure side (3) printed source means (2) is printed in such a manner and cured, that on the pressure side (3) a relief with a maximum height of at least 10 microns, preferably at least 20 microns, more preferably at least 25 microns results.

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