US20140238628A1

US20140238628A1 - Method for Manufacturing a Security Paper and Microlens Thread

Info

Publication number: US20140238628A1
Application number: US14/342,861
Authority: US
Inventors: Rudolf Seidler; Manfred Heim; Bernhard Wiedner; Michael Rahm
Original assignee: Giesecke and Devrient GmbH
Current assignee: Giesecke and Devrient GmbH
Priority date: 2011-09-06
Filing date: 2012-09-04
Publication date: 2014-08-28
Also published as: EP2753754B1; WO2013034279A2; EP2753754B2; EP2753754A2; DE102011112554A1; WO2013034279A3

Abstract

A method for manufacturing a security paper includes an endless microlens thread having a top and an opposing bottom with the top provided at least in fractional regions with microlenses. A paper web having a predetermined ridge pattern is produced and defines ridge regions in which the microlens is embedded in the interior of the paper, and that exhibits, lying between the ridge regions, window regions in which the microlens thread emerges at the surface of the paper web. The microlens thread is introduced into the paper web and, at the same time, is joined on its bottom and, in the ridge regions, also on its top with the paper web. The paper web with the microlens thread forms the security paper.

Description

The present invention relates to a method for manufacturing a security paper, as well as a microlens thread for introduction into a paper web with such a method.
For protection, value documents, such as banknotes, stocks, bonds, certificates, vouchers, checks, valuable admission tickets and other papers that are at risk of counterfeiting, such as passports or other identification documents, are often provided with security elements that permit the authenticity of the value document to be verified, and that simultaneously serve as protection against unauthorized reproduction. The security elements can be developed, for example, in the form of a security thread that is completely or partially embedded in a banknote.
In recent years, security threads having microlenses have come into use on the banknote market. These microlens threads differ significantly from metalized threads and offer attractive optical properties. The microlens threads are furnished, on the side facing the viewer, with microlenses whose focusing effect is created by light refraction on an approximately spherically curved surface. In the focal plane of the microlenses, micropatterns are located that are arranged such that, through the coaction of the microlenses and the micropatterns, it is possible to depict for the viewer a magnified image having special motion effects.
In order not to impair the focusing effect of the microlenses and thus the optical effect of the microlens thread, the lens side of the thread is not provided with adhesive before the embedding in a paper web, as is the case in conventional security threads, such as hologram threads. However, the dispensation with adhesive on the top of the thread (lens side) often leads to a reduced stability of the banknotes produced, and in some cases even to a wrinkling on the banknote back.
Proceeding from this, the object of the present invention is to avoid the disadvantages of the background art and especially to specify a method for manufacturing a security paper that facilitates a secure embedding of a microlens thread in the paper, and that simultaneously ensures, in the window regions in which the microlens thread emerges at the surface of the paper, an attractive visual appearance of the microlens thread.
This object is solved by the features of the independent claims. Developments of the present invention are the subject of the dependent claims.
According to the present invention, in a generic method, it is provided that

- M) an endless microlens thread is provided that exhibits a top and an opposing bottom, the top being provided, at least in fractional regions, with microlenses,
- P) a paper web is produced having a predetermined ridge pattern that exhibits ridge regions in which the microlens thread is embedded in the interior of the paper web, and that exhibits, lying between the ridge regions, window regions in which the microlens thread emerges at the surface of the paper web, and
- E) the microlens thread is introduced into the paper web and, at the same time, is joined on its bottom and, in the ridge regions, also on its top, with the paper web, the paper web with the introduced microlens thread forming the security paper.

In a preferred method variant, it is provided that

- before the introduction into the paper web, the microlens thread is provided on its top with an adhesive layer in the form of the ridge pattern and
- in step E), the microlens thread is introduced into the paper web in register, such that the adhesive-coated regions of the microlens thread coincide with the ridge regions of the paper web.

A registered introduction of the microlens thread can especially occur according to one of the methods described in document WO 2004/050991 A1. In this respect the disclosure of this document is incorporated in the present application by reference.
In some designs, the microlens thread can include a motif having a motif jump. As described in greater detail in document WO 2008/145333 A2, in manufacturing a microlens thread, normally an endless security element foil is first manufactured as roll material, wherein, when conventional manufacturing methods are used, breaking points always occur, especially gaps or a misalignment in the appearance of the security elements. These breaking points come from the fact that the pre-products for the embossing dies used in manufacturing are generally manufactured as flat plates that are fitted on an impression or embossing cylinder. The image patterns that adjoin on both sides do not, as a general rule, match at the junctions and, after printing or embossing, lead, in the appearance of the finished security elements, to a motif jump of the kind cited. According to an advantageous embodiment of the present invention, a microlens thread that includes a motif having a motif jump is introduced into the paper web in register, such that the motif jump comes to lie in one of the ridge regions of the paper web. The motif jump then remains hidden from the viewer.
Motif jumps potentially also occur multiple times within an embossing cylinder. For example, in the event that the patterns are composed from small segments by means of recombination, seams having motif jumps result. In general, due to the method, motif jumps are created both in the grid of the micropatterns and in the grid of the microlenses. Here, it is usually attempted to bring the two seams into overlap at manufacture, such that the impression of only one motif jump is created for the viewer.
In a modification of the described method, immediately before entering into the paper web, the microlens thread is selectively printed on with an adhesive layer in those regions of its top that, at sheet formation, come to lie below ridge regions of the paper web.
In a further preferred method variant, it is provided that

- before the introduction into the paper web, the microlens thread is provided in an opening region with a plurality of openings in the form of the ridge pattern, and
- in step E), the microlens thread is introduced into the paper web in register, such that the regions of the microlens thread that are provided with openings coincide with the ridge regions of the paper web.

Also in this variant, the microlens thread can include a motif having a motif jump, and the microlens thread be introduced in register, such that the motif jump comes to lie in one of the ridge regions of the paper web and is thus hidden for the viewer.
According to a modification of the method, immediately before entering into the paper web, the microlens thread is selectively provided with openings in those regions of its top that, at sheet formation, come to lie below ridge regions of the paper web.
The openings are advantageously produced by punching or laser cutting. If the openings are produced only immediately before the entry of the microlens thread into the paper web, then they are preferably produced by laser cutting.
In all designs, the paper web is expediently formed having the predetermined ridge pattern in a paper machine, and the endless microlens thread enters into the paper machine.
According to a further preferred method variant, it is provided that, in step M), a microlens thread is provided whose top exhibits fractional regions having microlenses and microlens-free fractional regions, the microlens-free fractional regions being smaller than the width of the ridge regions of the ridge pattern in the paper web, and the microlens-free fractional regions being coated with adhesive before the introduction into the paper web. The microlens thread is especially introduced into the paper web not in register such that, in every window region, microlenses can be seen at least in some regions, and a portion of the adhesive-coated fractional regions always come to lie below ridge regions of the paper web.
According to a further preferred method variant, it is provided that, in step M), a microlens thread is provided that, on the one hand, exhibits fractional regions having microlenses, which fractional regions are coated with adhesive before the introduction into the paper web, and which are smaller than the width of the ridge regions of the ridge pattern in the paper web, and on the other hand, exhibits fractional regions having microlenses that are not coated with adhesive before the introduction into the paper web. The microlens thread is especially introduced into the paper web not in register, such that, in every window region, microlenses that exhibit no adhesive coating can be seen at least in some regions, and a portion of the adhesive-coated fractional regions always come to lie below ridge regions of the paper web.
In all described method variants, the microlens thread is advantageously contiguously provided on its bottom with an adhesive layer before the introduction into the paper web.
The present invention also includes a microlens thread for introduction into a paper web, especially with the method just described. The microlens thread includes a top and an opposing bottom, the top exhibiting fractional regions having microlenses, and exhibiting microlens-free fractional regions that are coated with adhesive.
The fractional regions having microlenses and the microlens-free fractional regions advantageously form, on the top of the thread, alternating strips that each completely occupy the width of the microlens thread, and that each exhibit, in the longitudinal direction of the microlens thread, a dimension between 1 mm and 30 mm, preferably between 3 mm and 12 mm.
The fractional regions having microlenses and the microlens-free fractional regions can usually be present in the form of rectangles. However, it would also be possible for the fractional regions having microlenses and the microlens-free fractional regions to be present in the form of diagonals. Especially in wider threads, it is possible to produce diagonal paper ridges.
The bottom of the microlens thread is preferably contiguously coated with adhesive.

Further exemplary embodiments and advantages of the present invention are explained below by reference to the drawings, in which a depiction to scale and proportion was dispensed with in order to improve their clarity.

Shown are:

FIG. 1 a schematic diagram of a banknote having an embedded microlens thread, manufactured according to the present invention,

FIG. 2 schematically, the layer structure of a microlens thread before the embedding in the security paper,

FIG. 3 a cross-section of a security paper having an embedded microlens thread according to FIG. 2,

FIG. 4 a top view of the microlens thread in FIG. 2,

FIG. 5 a top view of a further microlens thread before the embedding in a security paper,

FIG. 6 a cross-section of the microlens thread in FIG. 5,

FIG. 7 a cross-section of a security paper having an embedded microlens thread according to FIGS. 5 and 6,

FIG. 8 a cross-section of the microlens thread according to the present invention; and

FIG. 9 a cross-section of a security paper having an embedded microlens thread according to FIG. 8.

The invention will now be explained using a banknote as an example. For this, FIG. 1 shows a schematic diagram of a banknote 10 manufactured according to the present invention, having a microoptical window security thread 12 that, in the following, is also referred to as microlens thread for short. The microlens thread 12 emerges at the surface of the banknote 10 in window regions 14, while it is embedded in the interior of the banknote 10 in the ridge regions 16 lying therebetween.
In a first exemplary embodiment of the present invention, the microlens thread 12 illustrated in FIGS. 2 and 4 is used for the manufacture of a security paper. FIG. 3 shows a cross-section of the security paper 50 with the already embedded microlens thread 12. Here, at the manufacture of security paper, the microlens thread enters, for example in endless form, into a paper machine and is embedded there in a paper web forming on a cylinder mold. The paper web together with the embedded microlens thread is referred to in this description as security paper. From such a security paper is created, after further processing steps and separation of the ups of a paper web or a paper sheet, a banknote 10 as shown in FIG. 1.
FIG. 2 shows, schematically, the layer structure of the microlens thread 12 before the embedding in the security paper, with only those portions of the layer structure that are required to explain the functional principle being depicted. FIG. 4 shows a top view of the microlens thread 12 in FIG. 2.
The microlens thread 12 includes a support 20 in the form of a transparent plastic foil, for example a PET foil about 20 μm thick. The top 30 of the microlens thread 12 exhibits a grid-shaped arrangement of microlenses 22 that form, on the surface of the support foil, a lattice having a prechosen symmetry. The spherically or aspherically designed microlenses 22 preferably exhibit a diameter between 5 μm and 50 μm, and especially a diameter between merely 10 μm and 35 μm, and are thus not perceptible with the naked eye. It is understood that, in other designs, also larger or smaller dimensions may be considered. Also the use of cylindrical lenses is similarly possible.
On the bottom 32 of the microlens thread 12 is arranged a motif layer 26 that includes a likewise grid-shaped arrangement of micromotif elements 28. Also the arrangement of the micromotif elements 28 forms a lattice having a prechosen symmetry, with a desired magnification effect, characteristic motion effects and/or tilt effects being produced due to the coordination of the lattice of the microlenses 22 and the arrangement of the micromotif elements 28. The micromotif elements are not perceptible with the naked eye. Now, reference is additionally made to WO 2009/000528 A1, in which it is explained that the micropatterns can also consist of image fragments that are not arranged repeatingly. The microlens thread 12 typically includes further layers 24, such as protective, cover or further functional layers, which, however, are not significant for the present invention and are thus not described in greater detail.
Due to the manufacture with embossing cylinders, the motif perceived by the viewer will usually exhibit a motif jump, as described in greater detail in document WO 2008/145333 A2.
Now, to manufacture a security paper, a paper web 50 having a predetermined ridge pattern 18 (FIG. 1) is produced on the cylinder mold of a paper machine. The ridge pattern 18 exhibits ridge regions 16 in which the microlens thread 12 is later embedded in the interior of the finished paper web 50. Between the ridge regions 16 lie window regions 14 in which the microlens thread 12 emerges at the surface of the finished paper web 50.
As schematically depicted in FIGS. 2 and 4, before the introduction into the paper web 50, the microlens thread 12 is provided on its top 30 with an adhesive layer 40 in the form of the ridge pattern 18, such that the adhesive layer 40 forms an adhesive pattern 48 whose sequence of uncoated regions 44 and coated regions 46 corresponds to the sequence of the window regions 14 and ridge regions 16 of the ridge pattern 18. The bottom 32 of the microlens thread 12 is provided with a contiguous adhesive layer 42.
Said microlens thread 12 coated in this way with adhesive 40, 42 is now introduced in register into the paper web 50, such that the adhesive-coated regions 46 of the microlens thread coincide with the ridge regions 16 of the paper web 50, as shown in FIG. 3.
Such an introduction in register can especially occur according to one of the methods described in document WO 2004/050991 A1. For example, the microlens thread 12 can be introduced into the paper web by means of a biased coil. A first sensor detects the position of the coated regions 46 shortly before the introduction into the paper web, a second sensor the position of the ridges 16 formed in the paper web immediately after sheet formation. The positions detected by the two sensors are analyzed and used to control the magnitude of the bias. When the bias is increased, the microlens thread 12 is stretched more strongly, and when the bias is lowered, the stretching is reduced. In this way, the microlens thread 12, with its coated and uncoated regions 44, 46, can be aligned in perfect register with the window and ridge regions 14, 16.
For the registered thread embedding, the procedure is preferably such that the thread bears a register mark that is recognized particularly well by a detection system. The thread embedding is then controlled at the thread by means of tensile stress in such a way that the register mark of the thread has a fixed local reference to the register mark of the paper, usually a watermark. Here, the regions in which the thread exhibits adhesive on the top then have a fixed, known local reference to the register mark of the thread. Similarly, the ridge regions in the paper have a fixed local relationship to the register mark in the paper.
Through said approach it is ensured that the ridge regions 16 of the paper web 50 are glued to the microlens thread 12, such that a secure embedding of the microlens thread 12, without wrinkling and without lifting up or tearing out the paper ridges at manufacture, is ensured. Likewise, stability of the paper ridges to circulation stresses is significantly improved. At the same time, the microlenses 22 of the uncoated regions 44 that are visible in the window regions 14 remain free of adhesive, such that the optical properties of the microlenses 22 are not impaired. The microlens thread 12 thus displays, after its embedding in the paper web 50, the desired clear visual appearance in the window regions 14.
In advantageous embodiments, the uncoated regions 44 and the coated regions 46 exhibit the same size as the window regions 14 and the ridge regions 16, respectively. In some embodiments, it is also provided that the coated regions 46 are smaller, for example no more than 10% or no more than 50% smaller, than the ridge regions 16. How much shorter the glue-coated portion should be compared with the paper ridges of the thread also depends strongly on the register tolerance when embedding the thread in register. With, for example, ±1 mm register tolerance when introducing the thread in register, the glue-free regions of the thread should be 2 mm shorter than the paper ridges. Even if, in each case, only a portion of the microlens thread 12 is glued to the ridge regions 16, a significantly improved embedding results compared with the background art.
Also designs in which the uncoated regions 44 are somewhat smaller than the window regions 14 may be considered. However, the focusing effect of adhesive-coated microlenses 22 in the window regions 14 is reduced or canceled, such that the uncoated regions 44 are preferably not more than 10%, particularly preferably not more than 5% smaller than the window regions 14.
A further advantage of the introduction of the microlens thread 12 in register consists in that any motif jumps 34 in the motif image can be hidden under a paper ridge 16 of the security paper 50, as shown in FIG. 3. In this way, the uniformity of the visual appearance of the microlens thread 12 is further increased.
In a modification of the described method sequence, the microlens thread 12 is not introduced into the paper web 50 in register, but rather is, immediately before the entry into the paper machine, printed on with an adhesive pattern 48 in such a way that the coated regions 46 come to lie in the depressed sections of the cylinder mold, in which the paper ridges 16 form. For this, a sensor, for example, can detect the position of the ridges 16 formed in the paper web at sheet formation, and the detected position can be used to control the printing positions for the adhesive pattern 48. Also in this way, the uncoated and coated regions 44, 46 can be aligned in perfect register with the window and ridge regions 14, 16.
A further variant of the present invention will now be explained with reference to FIGS. 5 to 7. Here, FIGS. 5 and 6 show a top view and a cross-section, respectively, of the microlens thread 60 before the embedding in the security paper, and FIG. 7 shows a cross-section of the security paper 50 having the embedded microlens thread 60.
In the variant in FIGS. 5 to 7, the microlens thread 60 is not coated on its top 30 with adhesive, but rather, before the introduction into the paper web 50, it is provided with an opening pattern 68 in the form of the ridge pattern 18. The opening pattern 68 consists of a sequence of regions 66, having openings 62 and regions 64 without openings, that corresponds to the sequence of the ridge regions 16 and window regions 14 of the ridge pattern 18. The bottom 32 of the microlens thread 60 is preferably provided with a contiguous adhesive layer 42.
The microlens thread 60 is now introduced into the paper web 50 in register, such that the regions 66 of the microlens thread 60 that are provided with openings coincide with the ridge regions 16 of the paper web 50, as already described in principle in connection with FIGS. 2 to 4. In this case, the first sensor detects the position of the openings 62 shortly before the introduction of the microlens thread 12 into the paper web. In this way, the microlens thread 60 with its opening pattern 68 can be aligned in perfect register with the window and ridge regions 14, 16.
In this variant of the present invention, due to the provision of the openings 62, it is achieved that, at paper formation, under the ridge regions 16, paper fibers or other components of the substrate 50 can penetrate through the openings 62 to create a connection between the ridge regions 16 and the substrate material 52 under the microlens thread 60 (FIG. 7). In this way, also a close connection between the paper web 50 and the microlens thread 60 is achieved, and thus a secure embedding without wrinkling Since the top 30 of the microlens thread 60 remains adhesive-free, the optical properties of the microlenses 22 are not impaired.
The openings 62 can, for example, be punched or produced through laser cutting. Every region 66 can include one or also multiple openings 62. For illustration, FIGS. 6 and 7 show a design having, in each case, only one opening 62 per region 66, while FIG. 5 illustrates a design having three openings 62 per region 66.
In a modification of the described method sequence, the microlens thread 60 is not introduced into the paper web 50 in register, but rather, it is provided only immediately before the entry into the paper machine, through laser impingement, with the opening pattern 68, in such a way that the regions 66 having openings 62 come to lie in the depressed sections of the cylinder mold, in which the paper ridges 16 form. For this, for example, a sensor can detect the position of the ridges 16 formed in the paper web, and the detected position can be used to control the laser beam. Also in this way, the opening pattern 68 can be aligned in perfect register with the window and ridge regions 14, 16.
In a further variant of the present invention that is illustrated in FIGS. 8 and 9, a microlens thread 70 is used that exhibits, on its top 30, a sequence of fractional regions 74 having microlenses 22 and microlens-free fractional regions 76. The motif layer and any further layers of the microlens thread 70 are, for the sake of clarity, not shown in FIGS. 8 and 9. The microlens-free fractional regions 76 of the top 30 are coated with adhesive 40, and also the bottom of the microlens thread 70 is contiguously coated with adhesive 42.
Here, the adhesive-coated, microlens-free fractional regions 76 are developed to be smaller than the width of the window regions 14 of the ridge pattern 18. In this way, it is ensured that, when the microlens thread 70 is not introduced into a security paper 50 in register, microlenses 22 can be seen in every window region 14, at least in some regions (FIG. 9).
In this way, on the one hand, a visually attractive appearance is obtained, and on the other hand, an embedding that is improved over the background art can be achieved also without an introduction of the microlens thread 70 in register, since a portion of the adhesive-coated fractional regions 76 will always come to lie below ridge regions 16 of the paper web, as illustrated in FIG. 9.
According to a modification of the above-mentioned variant of the present invention illustrated in FIGS. 8 and 9, the adhesive-coated regions can definitely also exhibit microlenses. Indeed, said microlenses would become optically ineffective due to the adhesive coating, but they permit a uniform design of the thread with microlenses.
According to a further modification of the above-mentioned variant of the present invention illustrated in FIGS. 8 and 9, especially in wider threads, it is appropriate to arrange the microlens-free regions diagonally or in strip form alongside the thread and thus, if applicable, to provide, across the entire length of the thread, regions that can be coated with glue.
The adhesive or glue used in the present invention can be, for example, a heat seal coating. Furthermore, the adhesive can exhibit security features, for example dyes or color pigments and luminescent substances.

LIST OF REFERENCE SIGNS

10 Banknote
12 Microlens thread
14 Window regions
16 Ridge regions
18 Ridge pattern
20 Support
22 Microlenses
24 Further layers
26 Motif layer
28 Micromotif elements
30 Top
32 Bottom
34 Motif jump
40 Adhesive layer top
42 Adhesive layer bottom
44 Uncoated regions
46 Coated regions
48 Adhesive pattern
50 Paper web
52 Substrate material
60 Microlens thread
62 Openings
64 Regions without openings
66 Regions with openings
68 Opening pattern
70 Microlens thread
74 Fractional regions with microlenses
76 Microlens-free fractional regions

Claims

1-16. (canceled)

17. A method for manufacturing a security paper, comprising:

(A) providing an endless microlens thread defining a top and an opposing bottom, the top being provided with microlenses at least in fractional regions;

(B) producing a paper web having a predetermined ridge pattern defining ridge regions in which the microlens thread is embedded in the interior of the paper web, and that exhibits, lying between the ridge regions, window regions in which the microlens thread emerges at the surface of the paper web; and

(C) introducing the microlens thread into the paper web and, at the same time, joining on its bottom and, in the ridge regions, also on its top, with the paper web, the paper web with the introduced microlens thread forming the security paper.

18. The method according to claim 17, wherein

before the introduction into the paper web, the microlens thread is provided on its top with an adhesive layer in the form of the ridge pattern; and

wherein in step C), the microlens thread is introduced into the paper web in register, such that the adhesive-coated regions of the microlens thread coincide with the ridge regions of the paper web.

19. The method according to claim 18, wherein the microlens thread includes a motif having a motif jump, the microlens thread being introduced in register, such that the motif jump comes to lie in one of the ridge regions of the paper web.

20. The method according to claim 17, wherein the adhesive layer forms an adhesive pattern having a sequence of uncoated regions and adhesive-coated regions, the adhesive-coated regions each having an up to 50% smaller dimension than the ridge regions of the paper web.

21. The method according to claim 17, wherein, immediately before entering into the paper web, the microlens thread is selectively coated with adhesive in those regions of its top that, at sheet formation, come to lie below ridge regions of the paper web.

22. The method according to claim 17, wherein

before the introduction into the paper web, the microlens thread is provided in an opening region with a plurality of openings in the form of the ridge pattern; and

wherein in step C), the microlens thread is introduced into the paper web in register, such that the regions of the microlens thread that are provided with openings coincide with the ridge regions of the paper web.

23. The method according to claim 22, wherein the microlens thread includes a motif having a motif jump, the microlens thread being introduced in register, such that the motif jump comes to lie in one of the ridge regions of the paper web.

24. The method according to claim 17, wherein, immediately before entering into the paper web, the microlens thread is selectively provided with openings in those regions of its top that, at sheet formation, come to lie below ridge regions of the paper web.

25. The method according to claim 22, wherein the openings are produced by punching or laser cutting.

26. The method according to claim 17, wherein the paper web having the predetermined ridge pattern is formed in a paper machine, and the endless microlens thread enters into the paper machine.

27. The method according to claim 17, wherein, in step A), a microlens thread is provided whose surface exhibits fractional regions having microlenses, said fractional regions are coated with adhesive before introduction into the paper web, and are smaller than the width of the ridge regions of the ridge pattern in the paper web.

28. The method according to claim 17, wherein, in step A), a microlens thread is provided whose surface exhibits fractional regions having microlenses that are not coated with adhesive before the introduction into the paper web

29. The method according to claim 17, wherein, in step A), a microlens thread is provided whose top exhibits fractional regions having microlenses and microlens-free fractional regions, the microlens-free fractional regions being smaller than the width of the ridge regions of the ridge pattern in the paper web, and the microlens-free fractional regions being coated with adhesive before the introduction into the paper web.

30. The method according to claim 17, wherein the microlens thread is provided contiguously on its bottom with an adhesive layer before the introduction into the paper web.

31. A microlens thread for introduction into a paper web, according to the method of claim 29, having a top and an opposing bottom, wherein the top exhibits fractional regions having microlenses, and exhibits microlens-free fractional regions that are coated with adhesive.

32. The microlens thread according to claim 31, wherein the fractional regions having microlenses and the microlens-free fractional regions on the top form alternating strips that each completely occupy the width of the microlens thread and that each exhibit, in the longitudinal direction of the microlens thread, a dimension between 1 mm and 30 mm.

33. The microlens thread according to claim 31, wherein the bottom of the microlens thread is coated contiguously with adhesive.