DE102011112554A1 - Method for producing a security paper and microlens thread - Google Patents

Abstract

The invention relates to a method for producing a security paper, in which M) an endless microlens thread (12) is provided, which has an upper side (30) and an opposite lower side (32), wherein the upper side (30) at least in partial areas with microlenses ( 22), P) a paper web (50) having a predetermined web pattern (18) is produced, which web portions (16), in which the microlens filament (12) is embedded in the interior of the paper web (50), and between the Having web portions (16) lying window areas (14) in which the microlens thread (12) on the surface of the paper web (50) emerges, and E) the microlens thread (12) introduced into the paper web (50) and thereby on its underside (32 ) and in the web areas (16) also on its upper side (30) with the paper web (50) is connected, wherein the paper web (50) with the introduced microlens thread (12) forms the security paper.

Description

The invention relates to a method for producing a security paper, as well as a microlens thread for introduction into a paper web with such a method.

Security documents, such as banknotes, stocks, bonds, certificates, vouchers, checks, high-quality admission tickets, but also other forgery-prone papers, such as passports or other identity documents, are often provided with security elements for security, which allow a verification of the authenticity of the value document and at the same time serve as protection against unauthorized reproduction. The security elements can be designed, for example, in the form of a security thread completely or partially embedded in a banknote.

In recent years, microlens security threads have become established on the banknote market. These microlens filaments differ significantly from metallized filaments and offer attractive optical properties. On the side facing the observer, the microlens threads are equipped with microlenses whose focusing effect is produced by refraction of light on an approximately spherically curved surface. In the focal plane of the microlenses are microstructures that are arranged so that the interaction of the microlenses and the microstructures for the viewer can represent an enlarged image with special motion effects.

In order not to affect 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 prior to embedding in a paper web, as is the case with conventional security threads, such as hologram threads. However, dispensing with adhesive on the top of the thread (lens side) often results in reduced durability of the produced banknotes and in part even wrinkling on the banknotes back.

Based on this, the present invention seeks to avoid the disadvantages of the prior art and in particular to provide a method for producing a security paper, which allows a secure embedding of a microlens thread in the paper and at the same time in the window areas in which the microlens thread on the Surface of the paper, ensuring an attractive visual appearance of the microlens thread.

This object is solved by the features of the independent claims. Further developments of the invention are the subject of the dependent claims.

• M) ein endloser Mikrolinsenfaden bereitgestellt wird, der eine Oberseite und eine gegenüberliegende Unterseite aufweist, wobei die Oberseite zumindest in Teilbereichen mit Mikrolinsen versehen ist,
• P) eine Papierbahn mit einem vorbestimmten Stegmuster erzeugt wird, welches Stegbereiche aufweist, in denen der Mikrolinsenfaden im Inneren der Papierbahn eingebettet ist, und das zwischen den Stegbereichen liegende Fensterbereiche aufweist, in denen der Mikrolinsenfaden an der Oberfläche der Papierbahn hervortritt, und
• E) der Mikrolinsenfaden in die Papierbahn eingebracht und dabei auf seiner Unterseite und in den Stegbereichen auch auf seiner Oberseite mit der Papierbahn verbunden wird, wobei die Papierbahn mit dem eingebrachten Mikrolinsenfaden das Sicherheitspapier bildet.

According to the invention, it is provided in a generic method that

• M) an endless microlens thread is provided, which has an upper side and an opposite lower side, wherein the upper side is provided with microlenses at least in partial areas,
• P) a paper web having a predetermined web pattern is produced, which has land regions in which the microlens thread is embedded in the interior of the paper web, and which has window regions lying between the web regions, in which the microlens thread protrudes on the surface of the paper web, and
• E) the microlens thread is introduced into the paper web and in this case is also joined on its underside and in the web areas on its upper side to the paper web, wherein the paper web forms the security paper with the introduced microlens thread.

• – der Mikrolinsenfaden vor der Einbringung in die Papierbahn auf seiner Oberseite mit einer Klebstoffschicht in Gestalt des Stegmusters versehen wird, und
• – der Mikrolinsenfaden in Schritt E) registriert in die Papierbahn eingebracht wird, so dass die mit Klebstoff beschichteten Bereiche des Mikrolinsenfadens mit den Stegbereichen der Papierbahn zusammenfallen.

In a preferred variant of the method it is provided that

• - The microlens thread is provided prior to introduction into the paper web on its upper side with an adhesive layer in the form of the web pattern, and
• - The microlens thread in step E) registered in the paper web is introduced so that the adhesive coated areas of the microlens thread coincide with the web portions of the paper web.

A registered introduction of the microlens thread can in particular according to one of the in the document WO 2004/050991 A1 described method. The disclosure of this document is included in the present application in this respect.

In some designs, the microlens thread may include a motif with a motif jump. As in the publication WO 2008/145333 A2 described in more detail, in the production of a microlens thread usually first an endless security element film is produced as a roll material, which always occur when using conventional manufacturing methods break points, especially gaps or an offset in the appearance of the security elements. These fractures are due to the fact that the precursors for the stamping tools used in the manufacture are generally manufactured as flat sheets which are mounted on a printing or embossing cylinder. At the seams, the mutually adjacent image patterns usually do not match and lead after printing or embossing in the appearance of the finished security elements to a scene jump of the type mentioned. According to an advantageous embodiment of the invention, a microlens thread, which contains a motif with a motif jump registered registered in the paper web, so that the jump in one of the motif Web areas of the paper web comes to rest. The subject jump then remains hidden from the viewer.

Under certain circumstances, subject jumps occur several times within an embossing cylinder. For example, if the patterns are composed by recombination of small segments, stitches with motif jumps result. In general, motive jumps occur due to the process both in the grid of the microstructures and in the grid of the microlenses. Usually, attempts are made to bring the two seams in the production in coverage, so that arises for the viewer the impression of only one jump in the subject.

In a modification of the method described, the microlens thread is printed directly before entering the paper web targeted in the areas of its upper side with an adhesive layer, which come to lie in the sheet formation below land areas of the paper web.

• – der Mikrolinsenfaden vor der Einbringung in die Papierbahn in einem Öffnungsbereich in Gestalt des Stegmusters mit einer Mehrzahl von Öffnungen versehen wird, und
• – der Mikrolinsenfaden in Schritt E) registriert in die Papierbahn eingebracht wird, so dass die mit Öffnungen versehenen Bereiche des Mikrolinsenfadens mit den Stegbereichen der Papierbahn zusammenfallen.

In a further preferred variant of the method it is provided that

• - The microlens thread is provided prior to introduction into the paper web in an opening region in the form of the web pattern with a plurality of openings, and
• - The microlens thread in step E) registered in the paper web is introduced, so that the apertured areas of the microlens thread coincide with the web portions of the paper web.

In this variant, too, the microlens thread can contain a motif with a motif jump and the microlens thread can be registered, so that the motif jump comes to rest in one of the web areas of the paper web and is therefore hidden from the viewer.

According to a modification of the method, the microlens thread is provided in the areas of its upper side with openings, which come to rest below the land areas of the paper web during sheet formation, immediately before entering the paper web.

The openings are advantageously produced by punching or laser cutting. If the openings are only produced immediately before the microlens thread enters the paper web, they are preferably produced by laser cutting.

In all configurations, the paper web is expediently formed with the predetermined web pattern in a paper machine and the endless microlens thread runs into the paper machine.

According to a further preferred variant of the method, it is provided that in step M) a microlens thread is provided whose upper side has partial areas with microlenses and microlens-free partial areas, wherein the microlens-free partial areas are smaller than the width of the web areas of the bridge pattern in the paper web, and wherein the microlens-free portions are coated with adhesive before being introduced into the paper web. In particular, the microlens thread is introduced into the paper web in an unregistered manner so that microlenses can be seen at least in certain areas in each window area and part of the adhesive-coated subareas always come to rest below web areas of the paper web.

According to a further preferred variant of the method, it is provided that in step M) a microlens thread is provided which on the one hand has partial regions with microlenses, which partial regions are coated with adhesive before being introduced into the paper web and which are smaller than the width of the web regions of the web pattern in the paper web on the other hand, have partial areas with microlenses which are not coated with adhesive before being introduced into the paper web. The microlens thread is introduced in particular unregistered in the paper web, so that in each window area at least partially microlenses that have no adhesive coating, can be seen and always come to lie part of the adhesive-coated portions below web portions of the paper web.

In all described variants of the method, the microlens thread is advantageously provided over its entire surface with an adhesive layer on its underside prior to introduction into the paper web.

The invention also includes a microlens thread for insertion into a paper web, in particular with the method just described. The microlens thread includes an upper side and an opposite lower side, the upper side having microlens sections and microlens-free sections coated with adhesive.

The microlens sections and the microlens-free sections advantageously form alternating strips on the upper side of the thread, each of which completely occupies the width of the microlens thread and in each case has an extension of between 1 mm and in the longitudinal direction of the microlens thread 30 mm, preferably between 3 mm and 12 mm.

The microlens sections and the microlens-free sections may usually be in the form of rectangles. However, it would also be possible for the partial areas with microlenses and the microlens-free partial areas to be present in the form of diagonals. It can be made especially for wider threads diagonal paper webs.

The underside of the microlens thread is preferably coated over the entire surface with adhesive.

Further exemplary embodiments and advantages of the invention are explained below with reference to the figures, in the representation of which a representation true to scale and proportion has been dispensed with in order to increase the clarity.

Show it:

1 a schematic representation of a banknote according to the invention with an embedded microlens thread,

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

3 a cross section of a security paper with an embedded microlens thread after 2 .

4 a top view of the microlens thread the 2 .

5 a view of another microlens thread before embedding in a security paper,

6 a cross section of the microlens thread of 5 .

7 a cross section of a security paper with an embedded microlens thread after the 5 and 6 .

8th a cross section of the microlens thread according to the invention; and

9 a cross section of a security paper with an embedded microlens thread after 8th ,

The invention will now be explained using the example of a banknote. 1 shows a schematic representation of a bill according to the invention 10 with a micro-optical window security thread 12 hereinafter also referred to as microlens thread for short. The microlens thread 12 occurs in window areas 14 on the surface of the banknote 10 while standing in the intervening land areas 16 inside the banknote 10 is embedded.

In a first embodiment of the invention is for the production of a security paper in the 2 and 4 illustrated microlens thread 12 used. 3 shows a cross section of the security paper 50 with the already embedded microlens thread 12 , In the production of security paper, the microlens thread runs, for example, in an endless form into a paper machine and is embedded there in a paper web which forms on a round screen. The paper web together with the embedded microlens thread is referred to in this specification as security paper. From such a security paper arises after further processing steps and separation of the benefits of a paper web or a sheet of paper a banknote 10 as in 1 shown.

2 schematically shows the layer structure of the microlens thread 12 before embedding in the security paper, wherein only the parts of the layer structure required for explaining the functional principle are shown. 4 shows a plan view of the microlens thread 12 of the 2 ,

The microlens thread 12 contains a carrier 20 in the form of a transparent plastic film, for example, an approximately 20 micron thick PET film. The top 30 of the microlens thread 12 has a grid-shaped arrangement of microlenses 22 on which form a grid with a preselected symmetry on the surface of the carrier film. The spherically or aspherically designed microlenses 22 preferably have a diameter between 5 microns and 50 microns and in particular a diameter between only 10 microns and 35 microns and are therefore not visible to the naked eye. It is understood that in other designs, larger or smaller dimensions come into question. The use of cylindrical lenses is possible in the same way.

On the bottom 32 of the microlens thread 12 is a motif layer 26 arranged, which also has a grid-like arrangement of micromotif elements 28 contains. The arrangement of the micromotif elements 28 forms a grating with a preselected symmetry, by tuning the grating of the microlenses 22 and the arrangement of micromotif elements 28 a desired magnification effect, characteristic motion effects, and / or tilt effects are generated. The micromotif elements are invisible to the naked eye. At this point, in addition to the WO 2009/000528 A1 in which it is stated that the microstructures may also consist of image fragments which are not arranged repetitively. The microlens thread 12 typically contains more layers 24 such as protective, covering or other functional layers, which are not essential to the present invention and are therefore not described in detail.

Due to the production with embossing cylinders, the motif perceived by the viewer usually has a motif jump, as in the publication WO 2008/145333 A2 described in more detail.

To produce a security paper is now on the round screen of a paper machine, a paper web 50 with a predetermined ridge pattern 18 ( 1 ) generated. The bridge pattern 18 has web areas 16 in which the microlens thread 12 later inside the finished paper web 50 is embedded. Between the bridge areas 16 are window areas 14 in which the microlens thread 12 on the surface of the finished paper web 50 emerges.

As in the 2 and 4 schematically shown, the Mikrolinssenfaden 12 before being introduced into the paper web 50 on its top 30 with an adhesive layer 40 in the form of the bridge pattern 18 provided so that the adhesive layer 40 an adhesive pattern 48 forms, whose sequence of uncoated areas 44 and coated areas 46 the sequence of window areas 14 and land areas 16 of the bridge pattern 18 equivalent. The bottom 32 of the microlens thread 12 comes with a full-surface adhesive layer 42 Mistake.

This way with glue 40 . 42 coated microlens thread 12 is now registered in the paper web 50 introduced so that the areas coated with adhesive 46 of the microlens thread with the land areas 16 the paper web 50 coincide, as in 3 shown.

Such a registered contribution can in particular according to one of the in the document WO 2004/050991 A1 described method. For example, the microlens thread 12 be introduced by means of a coil under bias in the paper web. A first sensor detects the position of the coated areas 46 shortly before the introduction into the paper web, a second sensor, the position of the webs formed in the paper web 16 immediately after the formation of leaves. The positions detected by the two sensors are evaluated and used to control the magnitude of the bias voltage. As the bias increases, the microlens thread becomes 12 more stretched, with reduction of the bias, the elongation is reduced. The microlens thread 12 can work this way with its coated and uncoated areas 44 . 46 register accurate on the window and web areas 14 . 16 be aligned.

Preferably, in the case of registered thread embedding, the method is such that the thread carries a register mark, which is recognized particularly well by a detection system. The thread embedding is then controlled by means of the tension on the thread so that the register mark of the thread is in fixed local reference to the register mark of the paper, usually a watermark. The areas in which the thread has adhesive on the top are then in a fixed, known local reference to the register mark of the thread. In an analogous manner, the land areas in the paper are in fixed local relation to the register mark in the paper.

This procedure ensures that the land areas 16 the paper web 50 with the microlens thread 12 be glued, so that a secure embedding of the microlens thread 12 is guaranteed without wrinkling and without lifting or tearing the paper webs during manufacture. Likewise, the stability of the paper webs against circulation stresses is significantly improved. At the same time, the microlenses remain 22 the one in the window areas 14 visible uncoated areas 44 free of adhesive, so that the optical properties of the microlenses 22 not be affected. The microlens thread 12 therefore shows after its embedding in the paper web 50 in the window areas 14 the desired clear visual appearance.

The uncoated areas 44 and the coated areas 46 have in advantageous embodiments the same size as the window areas 14 or the web areas 16 , In some embodiments, it is also provided that the coated areas 46 smaller, for example not more than 10% or not more than 50% smaller than the web areas 16 , Also, how much the adhesive-coated part should be shorter compared to the paper webs of the thread is also strongly related to the register tolerance of registered thread embedding. At z. For example, with ± 1 mm register tolerance in the registered filament feed, the non-adhesive areas of the filament should be 2 mm shorter than the paper webs. Even if only a part of the microlens thread at a time 12 with the bridge areas 16 glued, results over the prior art, a significantly improved embedding.

Even designs where the uncoated areas 44 a little smaller than the window areas 14 is being brought up for consideration. However, the focusing effect of adhesive-loaded microlenses 22 in the window areas 14 diminished or canceled, leaving the uncoated areas 44 preferably not more than 10%, more preferably not more than 5% smaller than the window areas 14 ,

Another advantage of the registered introduction of the microlens thread 12 is that any motive jumps 34 in the motif picture under a paper bridge 16 of the security paper 50 can be hidden, as in 3 shown. This will improve the uniformity of the visual appearance of the microlens thread 12 further increased.

In a modification of the described procedure, the microlens thread 12 not registered in the paper web 50 is introduced, but immediately before entering the paper machine so with an adhesive pattern 48 printed that the coated areas 46 in the recessed sections of the round screen, in which the paper webs 16 train, come to rest. For this purpose, for example, a sensor, the position of the webs formed in the sheet formation in the paper web 16 and the detected position can be used to control the print positions for the adhesive pattern 48 be used. Also in this way can the uncoated and coated areas 44 . 46 register accurate on the window and web areas 14 . 16 be aligned.

Another variant of the invention will now be described with reference to 5 to 7 explained. The show 5 and 6 a plan view and a cross section of the microlens thread 60 before embedding in the security paper and 7 shows a cross section of the security paper 50 with the embedded microlens thread 60 ,

In the variant of 5 to 7 becomes the microlens thread 60 on its top 30 not coated with adhesive, but he is before the introduction into the paper web 50 with an opening pattern 68 in the form of the bridge pattern 18 Mistake. The opening pattern 68 consists of a sequence of areas 66 with openings 62 and areas 64 without openings, the sequence of web areas 16 and window areas 14 of the bridge pattern 18 equivalent. The bottom 32 of the microlens thread 60 is preferably with a full-surface adhesive layer 42 Mistake.

The microlens thread 60 is now registered in the paper web 50 introduced so that the apertured areas 66 of the microlens thread 60 with the bridge areas 16 the paper web 50 coincide, as in principle already in connection with the 2 to 4 described. The first sensor detects the position of the openings in this case 62 just before the introduction of the microlens thread 12 in the paper web. The microlens thread 60 can do this with his opening pattern 68 register accurate on the window and web areas 14 . 16 be aligned.

In this variant of the invention, the provision of the openings 62 achieved that in the paper formation under the land areas 16 Paper fibers or other constituents of the substrate 50 through the openings 62 can penetrate to connect between the bridge areas 16 and the substrate material 52 under the microlens thread 60 manufacture ( 7 ). This also makes an intimate connection of paper web 50 and microlens thread 60 and thus achieved a secure embedding without wrinkling. Because the top 30 of the microlens thread 60 adhesive-free, the optical properties of the microlenses 22 not impaired.

The openings 62 For example, they can be stamped or produced by laser cutting. Every area 66 can have one or more openings 62 contain. For illustration, the show 6 and 7 a design with only one opening at a time 62 per area 66 , while 5 a design with three openings 62 per area 66 illustrated.

In a modification of the described procedure, the microlens thread 60 not registered in the paper web 50 introduced, but it is only immediately before entering the paper machine by laser exposure so with the opening pattern 68 provided that the areas 66 with openings 62 in the recessed sections of the round screen, in which the paper webs 16 train, come to rest. For this purpose, for example, a sensor, the position of the webs formed in the paper web 16 and the detected position can be used to control the laser beam. Also in this way can the opening pattern 68 register accurate on the window and web areas 14 . 16 be aligned.

In a further variant of the invention, in the 8th and 9 is illustrated, a microlens thread 70 inserted on its top 30 a sequence of subareas 74 with microlenses 22 and microlens-free portions 76 having. The motif layer and any further layers of the microlens thread 70 are in the 8th and 9 for the sake of clarity not shown. The microlens-free sections 76 the top 30 are with glue 40 coated and also the underside of the microlens thread 70 is full surface with adhesive 42 coated.

The adhesive-coated, microlens-free sections 76 are smaller than the width of the window areas 14 of the bridge pattern 18 educated. This ensures that during the unregistered introduction of the microlens thread 70 in a security paper 50 in every window area 14 at least partially microlenses 22 you can see ( 9 ).

In this way, on the one hand, a visually attractive appearance is obtained, on the other hand, even without a registered introduction of the microlens thread 70 a comparison with the prior art improved embedding can be achieved, since always a part of the adhesive-coated portions 76 below land areas 16 the paper web will come to rest, as in 9 illustrated.

According to a modification of the above, in the 8th and 9 In the illustrated variant of the invention, the areas coated with adhesive can certainly also have microlenses. Although these would be optically ineffective by the adhesive coating, but allow a uniform configuration of the thread with microlenses.

According to a further modification of the above, in the 8th and 9 illustrated variant of the invention is particularly suitable for wider threads to arrange the microlens-free areas diagonally or strip-shaped along the thread and thus optionally provide over the entire length of the thread areas that can be coated with adhesive.

LIST OF REFERENCE NUMBERS

10

bill

12

Microlens thread

14

panes

16

web regions

18

web patterns

20

carrier

22

microlenses

24

more layers

26

motif layer

28

Micromotif elements

30

top

32

bottom

34

motive jump

40

Adhesive layer top side

42

Adhesive layer underside

44

uncoated areas

46

coated areas

48

adhesive pattern

50

paper web

52

substrate material

60

Microlens thread

62

openings

64

Areas without openings

66

Areas with openings

68

opening pattern

70

Microlens thread

74

Subareas with microlenses

76

Microlens-free sections

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

• WO 2004/050991 A1 [0009, 0045]
• WO 2008/145333 A2 [0010, 0041]
• WO 2009/000528 A1 [0040]

Claims (16)

Method for producing a security paper, in which M) an endless microlens thread is provided, which has an upper side and an opposite lower side, wherein the upper side is provided with microlenses at least in partial areas, P) a paper web having a predetermined web pattern is produced, which has land regions in which the microlens thread is embedded in the interior of the paper web, and which has window regions lying between the web regions, in which the microlens thread protrudes on the surface of the paper web, and E) the microlens thread is introduced into the paper web and in this case is also joined on its underside and in the web areas on its upper side to the paper web, wherein the paper web forms the security paper with the introduced microlens thread. Method according to claim 1, characterized in that - The microlens thread is provided prior to introduction into the paper web on its upper side with an adhesive layer in the form of the web pattern, and - The microlens thread in step E) registered in the paper web is introduced so that the adhesive coated areas of the microlens thread coincide with the web portions of the paper web. A method according to claim 2, characterized in that the microlens filament contains a motif with a jump in the subject, wherein the microlens filament is registered registered, so that the motif jump comes to lie in one of the web portions of the paper web. Method according to one of claims 1 to 3, characterized in that the adhesive layer forms an adhesive pattern with a sequence of uncoated areas and adhesive-coated areas, wherein the adhesive-coated areas each up to 50%, preferably up to 10%, smaller Have dimension as the land areas of the paper web. A method according to claim 1, characterized in that the microlens thread is coated directly before entering the paper web targeted in the areas of its upper side with adhesive that come to lie in the sheet formation below land areas of the paper web. Method according to claim 1, characterized in that - The microlens thread is provided prior to introduction into the paper web in an opening region in the form of the web pattern with a plurality of openings, and - The microlens thread in step E) registered in the paper web is introduced, so that the apertured areas of the microlens thread coincide with the web portions of the paper web. A method according to claim 6, characterized in that the microlens thread contains a motif with a jump in the subject, wherein the microlens thread is registered registered, so that the jump in the subject comes to lie in one of the web portions of the paper web. A method according to claim 1, characterized in that the microlens thread is provided directly before entering the paper web targeted in the areas of its upper side with openings that come to lie in the sheet formation below land areas of the paper web. Method according to one of claims 6 to 8, characterized in that the openings are produced by punching or laser cutting. Method according to one of claims 1 to 9, characterized in that the paper web is formed with the predetermined ridge pattern in a paper machine, and the endless microlens thread enters the paper machine. A method according to claim 1, characterized in that in step M) a microlens thread is provided whose surface on the one hand has partial areas with microlenses, which partial areas are coated with adhesive before being introduced into the paper web and which are smaller than the width of the web areas of the web pattern in the Paper web, and on the other hand portions with microlenses, which are not coated with adhesive before being introduced into the paper web. A method according to claim 1, characterized in that in step M) a microlens thread is provided, the upper side having partial areas with microlenses and microlens-free portions, wherein the microlens-free portions are smaller than the width of the web portions of the ridge pattern in the paper web, and wherein the microlens-free portions are coated with adhesive before being introduced into the paper web. Method according to one of claims 1 to 12, characterized in that the microlens thread is provided over the entire surface with an adhesive layer on its underside prior to introduction into the paper web. Microlens thread for insertion into a paper web, in particular with a method according to claim 12 or 13, with a top side and an opposite bottom side, characterized in that the top part has microlens sections and microlens-free sections coated with adhesive. Microlens filament according to claim 14, characterized in that the partial regions with microlenses and the microlens-free partial regions form alternating strips on the upper side, which occupy completely the width of the microlens thread and which in the longitudinal direction of the microlens thread each have an extension between 1 mm and 30 mm, preferably between 3 mm and 12 mm. Microlens thread according to claim 14 or 15, characterized in that the underside of the microlens thread is coated over its entire surface with adhesive.

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