阅读说明：本技术 用于将图像信息引入体积全息图的方法 (Method for introducing image information into a volume hologram ) 是由 金特·道斯曼 伊丽娜·门茨 奥利弗·埃梅里希 于 2018-04-17 设计创作，主要内容包括：本发明涉及一种用于通过涂敷能借助UV光失活的膨胀剂将例如形式为图像或形式为个人数据的图像信息引入到体积全息图中的方法,该膨胀剂用喷墨打印头在应当包含图像信息的区域中被打印到体积全息图的打印面上,因而膨胀剂能在限定的时间段内扩散到体积全息图中并且体积全息图的布拉格晶面的晶面间距因此变大,其中,膨胀剂在限定的时间段结束后通过UV光的光照而硬化。按照本发明规定,膨胀剂具有大于70％的单体份额和5至20mPas的动态粘度并且用在1皮升和20皮升之间的微滴大小打印,其中,膨胀剂可以扩散到体积全息图中的限定的时间段至少是10秒和最长是8分钟,因此图像信息紧接着既能在可见光下也能在红外光下读取。(The 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 swelling agent which can be deactivated by means of UV light, which is printed with an inkjet print head onto the printing surface of the volume hologram in the region which is intended to contain the image information, so that the swelling agent can diffuse into the volume hologram within a defined period of time and the interplanar spacing of the Bragg interplanar faces of the volume hologram is consequently enlarged, wherein the swelling agent is hardened by the illumination with UV light after the end of the defined period of time. According to the invention, the swelling agent has a monomer content of more than 70% and a dynamic viscosity of 5 to 20mPas and is printed with a droplet size of between 1 picoliter and 20 picoliters, wherein the defined time period during 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 can be read immediately both in the visible and in the infrared.)

1. 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 swelling agent (2) which can be deactivated by means of UV light, which is printed with an inkjet print head onto the printing surface (3) of the volume hologram (1) in the region which is intended to contain the image information, so that the swelling agent (2) can diffuse into the volume hologram (1) within a defined period of time and the interplanar spacing of the bragg interplanar faces (4, 4', 4 ") of the volume hologram (1) is thereby enlarged, wherein the swelling agent (2) hardens after the end of the defined period of time by means of illumination with UV light, characterized in that the swelling agent (2) has a monomer fraction of more than 70% and a dynamic viscosity of 5mPas to 20mPas and is printed with a droplet size of between 1 picoliter and 20 picoliters, wherein, the defined time period during which the swelling agent (2) can diffuse into the volume hologram (1) is at least 10 seconds and at most 8 minutes, so that the image information can be read immediately both in the visible and in the infrared.

2. The method according to claim 1, characterized in that the swelling agent (2) is printed with a droplet size of between 1.3 and 10 picoliters.

3. The method according to claim 1 or 2, characterized in that the swelling agent (2) can diffuse into the volume hologram (1) for a defined period of time of at least 10 seconds and can detect a negative image with infrared light.

4. A method as claimed in any one of claims 1 to 3, characterized in that the defined period of time during which the swelling agent (2) can diffuse into the volume hologram (1) is at least 120 seconds and a negative image can be detected with infrared light.

5. A method according to any one of claims 1 to 3, characterized in that the defined period of time for which the swelling agent (2) can diffuse into the volume hologram (1) is at least 2 minutes, preferably at most about 3 minutes, and a positive image can be detected with infrared light.

6. The method according to any of the preceding claims, characterized in that the diffusion of the swelling agent (2) into the volume hologram (1) is carried out at an elevated temperature between 50 ℃ and 80 ℃, preferably at an elevated temperature of about 70 ℃.

7. Method according to any of the preceding claims, characterized in that a volume hologram (1) is used which is reconstructed in the visible green or blue range in the initial state.

8. Method according to one of the preceding claims, characterized in that the volume hologram (1) is pre-treated by applying a monomer-containing UV glue (5) planarly onto one side (3, 6) of the volume hologram and hardening the UV glue (5) by irradiation with UV light immediately after the time period of between 1 and 20 seconds has elapsed, so that the interplanar spacing of the Bragg facets (4, 4') of the volume hologram (1) increases in a specific layer (9) and is thereby shifted in the direction of the infrared range.

9. Method according to claim 8, characterized in that the monomer-containing UV glue (5) is applied to the side (6) of the volume hologram opposite the printing side (3) in order to pretreat the volume hologram (1).

10. A method according to any preceding claim, wherein the inkjet printhead has a resolution of at least 300dpi, preferably at least 600 dpi.

11. Method for producing a security document with a hologram, wherein a volume hologram (1) is first glued to a carrier layer (7) of the security document and image information is subsequently introduced into the volume hologram (1) according to the method according to one of claims 1 to 10.

12. Method according to claim 11, characterized in that a monomer-containing UV glue (5) is applied planarly to one side (6) of the volume hologram (1) according to claim 8, when the volume hologram (1) is adhered to the carrier layer (7) of the security document.

13. Method according to claim 11 or 12, characterized in that the carrier layer (7) of the security document consists of polycarbonate.

14. Method according to any of claims 11 to 13, characterized in that after the introduction of the image information, a protective cover layer made of polycarbonate film is applied onto the printing side (3) of the volume hologram (1) and laminated onto the volume hologram (1) at a temperature between 150 ℃ and 180 ℃ and at a pressure between 1.5bar and 2.5 bar.

15. Method according to claim 14, characterized in that the swelling agent (2) printed onto the printing surface (3) is printed and hardened such that a relief with a maximum height of at least 10 μ ι η, preferably at least 20 μ ι η, further preferably at least 25 μ ι η, is produced on the printing surface (3).

Technical Field

The 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 according to the preamble of independent claim 1. In this method, the volume hologram is printed with an inkjet print head with the aid of a UV-light-deactivatable swelling agent, wherein the printing is carried out within the range in which the image information is to be contained. The expansion agent can diffuse into the volume hologram within a defined period of time, so that the interplanar spacing of the bragg facets of the volume hologram is consequently enlarged. After the end of the defined period of time, the expansion agent is hardened by irradiation with UV light. Thereby stopping the diffusion of the swelling agent into the volume hologram.

The invention also relates to a method for producing a security document having a hologram produced in this way.

Background

It is known from the prior art that the interplanar spacing of the bragg facets of volume holograms composed of photopolymers can be varied by contact with a monomer-containing expanding agent. Diffusion of organic molecules into the volume hologram causes an expansion which leads to a larger interplanar spacing, thereby producing a color shift towards a longer wavelength gamut.

A method according to the preamble of independent claim 1 is known, for example, from DE 102006048768 a 1.

Disclosure of Invention

The aim of the invention is to expand the design of a generic method in such a way that the imaging quality of the volume holograms produced is improved and the security thereof is increased.

This object is achieved by the features of independent claim 1. The solution according to the invention of the object is therefore achieved in a method according to the preamble of independent claim 1 when the swelling agent preferably has a monomer content of more than 70% and preferably has a dynamic viscosity of 5 to 20mPas and is printed with a droplet size of between 1 and 20 picoliters, wherein the swelling agent can diffuse into the volume hologram for a defined period of time, at least 10 seconds and up to 8 minutes, so that the image information can be read both in visible light and in infrared light.

The interplanar spacing of the Bragg facets is varied in different layers of the volume hologram by the method according to the invention in such a way that the image information introduced into the volume hologram is reconstructed both in the visible and in the infrared. This effect is used as a security feature for determining the authenticity of a document provided with a hologram. With a corresponding infrared scanner, it can be checked whether image information is actually present in the infrared range. Another advantage of the present invention is improved imaging quality over the prior art.

The hologram used preferably relates to a reflective volume hologram. The volume hologram is further preferably constituted by a photopolymer foil. The thickness of this foil is further preferably at least 8 μm and at most 20 μm. The thickness is more preferably about 10 μm. Although the use of photopolymer volume holograms is preferred, the invention can in principle also be applied to volume holograms consisting of silver foil. The bragg facets preferably do not extend parallel to the plane of extension of the volume hologram, but preferably enclose an angle of at least 35 ° with the plane of extension of the volume hologram.

The image information introduced into the volume hologram may for example relate to a certificate photograph or printed personal data. In principle, any type of image information can be introduced into the volume hologram by the method according to the invention.

Printing preferably takes place with complete exclusion of UV light in order to prevent undesired premature hardening of the expansion agent. The swelling agent is preferably colorless and transparent. The swelling agent further preferably contains monomers which can diffuse into the photopolymer and thus produce the desired swelling. Depending on how long the curing by irradiation with UV light is delayed after printing, different monomer concentrations are adjusted in the hologram. Printing is performed similarly to grayscale printing. This means that the particular droplet volume is selected depending on the desired wavelength shift, and thus the volume hologram expands differently at each image point depending on the volume of the applied swelling agent. Transparent UV inks having a high diffusible monomer fraction of more than 70%, preferably more than 80%, and a low dynamic viscosity, preferably in the range of 3 to 20mPas, are particularly preferably suitable as swelling agents. These expansion agent properties, which allow rapid and intense expansion of the bragg facets in the region of the adjacent hologram layer, can be detected well under infrared light without hindering the legibility of the hologram information under white light observation. The ink may, for example, be comprised of a mixture of oligomers and acrylate monomers.

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

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

It has furthermore proved advantageous if, according to a further preferred embodiment of the invention, the defined period of time over which the swelling agent can diffuse into the volume hologram is at least 30 seconds.

According to another embodiment of the invention, the swelling agent may diffuse into the volume hologram for a defined period of time of at most 120 seconds, further preferred at most 1 minute. In this embodiment, the monomer concentration in the upper hologram layer is high, so that the crystal planes in this region are strongly expanded. As a result of this, the interplanar spacings in this region are so large that a shift into the infrared range is caused, wherein the image information introduced is present as a positive image in the visible range and as a negative image in the infrared range. This effect can likewise be used as a security feature for determining the authenticity of a document provided with a hologram.

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

According to another preferred embodiment of the invention, the diffusion of the swelling agent into the volume hologram is carried out at an elevated temperature between 50 ℃ and 80 ℃. The elevated temperature is further preferably about 70 ℃. In this embodiment of the invention, the diffusion duration may be reduced by up to 50%. At the same time, a further improved imaging quality is obtained.

According to a further preferred embodiment of the invention, a volume hologram is used to carry out the method according to the invention, which volume hologram is reconstructed in the visible green or blue range in the initial state. In other words, the volume hologram used relates to a holographic frosted glass which reflects green or blue light over the entire area. The output wavelength may be, for example, 500 nm. If the initial color is in the blue range, a particularly large color spectrum can be covered by a shift to a longer wavelength range.

According to a further preferred embodiment of the invention, the volume hologram is pre-treated by applying a monomer-containing UV paste in a planar manner to one side of the volume hologram and hardening the UV paste by irradiation with UV light immediately after the time period of between 1 and 20 seconds has elapsed, so that the interplanar spacing of the bragg facets of the volume hologram increases in the specific layer and is thus shifted in the direction of the infrared range. In this embodiment, dark green artifacts due to the solarization effect are effectively prevented in the very bright areas at certain viewing angles. The glue may for example consist of a mixture of urethane oligomers and acrylate monomers.

The thickness of the layer in which the pretreatment is carried out is preferably at most 50% of the total thickness of the volume hologram. The shift in interplanar spacing occurs in this layer, preferably further towards the infrared range, but also in the visible range.

The UV glue containing the monomer is further preferably applied to the side of the volume hologram opposite the side to be printed in order to pretreat the volume hologram.

According to another preferred embodiment of the invention, the inkjet printhead has a resolution of at least 300dpi, preferably at least 600 dpi. Thereby achieving an optimal imaging quality.

The invention further provides a method for producing a security document with a hologram. According to the invention, the volume hologram is first bonded to the carrier layer of the security document, wherein the image information is subsequently introduced into the volume hologram in the manner described above. In this way, security documents such as travel passports, identity cards, driver licenses and the like can be produced particularly simply and cost-effectively. The security document contains further layers in addition to the original carrier layer. The support layer can preferably consist of polycarbonate.

According to a further preferred embodiment of the invention, after the introduction of the image information, a protective cover layer made of a polycarbonate film is applied to the printing side of the volume hologram and laminated to the volume hologram at a temperature of between 150 ℃ and 180 ℃, preferably at a temperature of between 160 ℃ and 180 ℃ and at a pressure of between 1.5bar and 2.5 bar. The pressure applied is further preferably about 2 bar. In this embodiment, a protection of the volume hologram is created that is to be particularly simple and cost-effective to create. Alternatively, a protective lacquer may be applied, for example. The lacquer can further preferably relate to a UV lacquer.

The swelling agent, which is printed in the form of personal data, for example as a portrait, is further preferably printed and hardened such that a relief with a maximum height of at least 10 μm, preferably at least 15 μm, further preferably at least 20 μm, further preferably at least 25 μm is produced on the printed side. Here, the maximum relief height is reached in the dark region of the portrait. The embossment serves to relieve or protect the brighter image areas from undesirable effects caused by the pressure required for lamination during the lamination process.

Drawings

An example of the method according to the invention is explained in detail below with the aid of the drawing.

In the figure:

fig. 1 shows a volume hologram on a film carrier in an initial state;

fig. 2 shows the volume hologram from fig. 1 after the volume hologram has been adhered to a carrier layer of a security document and the film carrier has been removed;

FIG. 3 shows the volume hologram from FIG. 2 with a partially printed swelling agent after the swelling agent has hardened after a relatively short delay time; and is

Fig. 4 shows the same volume hologram from fig. 2 with partially printed swelling agent after the swelling agent has hardened after a longer delay time.

Detailed Description

It is applicable to the following embodiments, in which like parts are denoted by like reference numerals. In case reference numerals are included in one figure, which are not discussed in detail in the related figure description, reference is made to the preceding or following figure description.

Fig. 1 shows a volume hologram 1, which is composed of a photopolymer and has a thickness of about 10 μm. A film carrier 8 is applied to the upper side 3 of the volume hologram 1. The diagram shows a volume hologram in an initial state. This means that the bragg facets 4 have a uniform spacing from one another. This pitch corresponds to half the wavelength of the light used to make the volume hologram. As can be seen in the illustration, the crystal planes do not extend parallel to the extension plane of the volume hologram. Instead, the crystal planes have an angle with respect to the plane of extension of the volume hologram, which in the case shown corresponds to about 80 °.

As can be seen from fig. 2, the volume hologram 1 is bonded to the carrier layer 7 of the security document by means of a UV glue 5 applied to the bottom side 6 of the volume hologram. The support layer preferably relates to a polycarbonate layer or a paper surface. The security document may be, for example, a travel passport. A certain period of time has elapsed since the point in time when the adhesive 5 first contacts the bottom surface 6 of the volume hologram until the glue is hardened by illumination with UV light. In this time period, which may be between 1 and 20 seconds, the monomer diffuses from the UV paste into the lower layer 9 of the volume hologram, thereby causing an expansion of the material and thus also an increase in the spacing between the bragg facets. This in turn results in a shift of the reconstruction wavelength into the longer wavelength range and thus into the infrared range. The angle of the bragg facets is also changed by the expansion. The variation of the bragg facets is highlighted in the figure by the reference numeral 4'. The thickness of the dashed line indicates the main monomer concentration.

After removal of the film carrier 8, the top side 3 of the volume hologram is printed with the monomer-containing swelling agent 2. Printing is accomplished with an inkjet printhead. As shown in fig. 3, the volume hologram 1 is not printed over the entire surface, but is printed only in the area where the image information should be introduced. In this case too, the crystal planes are changed by diffusion in a similar manner to that already when the volume hologram is bonded to the carrier layer of the security document, so that a color shift occurs. The extent of the displacement depends on the one hand on the amount of swelling agent printed and on the other hand on the action time of the swelling agent. The expansion agent is likewise hardened after a specific time duration by irradiation with UV light, thereby ending the expansion process or the change in crystal planes. The two factors are coordinated with one another according to the invention in such a way that the image information introduced into the volume hologram can be read both in the visible and in the infrared. In the case of fig. 3, the time duration between printing of the expansion agent and curing of the expansion agent by means of illumination with UV light is, for example, approximately 2 minutes. Fig. 4 similarly shows a state after a 6 minute delay. The change in the bragg facets which occurs by diffusion of the expansion agent into the upper and intermediate layers of the volume hologram is highlighted in the illustrations in fig. 3 and 4 by the reference numeral 4 ".

The amount of the applied expanding agent and the delay time between the application and curing of the expanding agent are also coordinated with one another in such a way that the expanding agent is not completely absorbed by the material of the volume hologram, but remains partially as a relief on the upper side 3. This relief has a thickness of about 20 μm and serves to protect the brighter holographic image area from the undesirable effects caused by the higher pressure required to laminate a protective cover layer (not shown) of polycarbonate.