EP4284654A1

EP4284654A1 - Book with an image and methods of production

Info

Publication number: EP4284654A1
Application number: EP22746362.7A
Authority: EP
Inventors: Alice VERMEULIN; Anthony ROUCH-PAULIN
Original assignee: Toppan Leefung Pte Ltd
Current assignee: Toppan Leefung Pte Ltd
Priority date: 2021-02-01
Filing date: 2022-01-28
Publication date: 2023-12-06
Also published as: WO2022164390A1

Abstract

A book with an image and methods of producing the book are described. The method includes providing a plurality of sheets, each sheet having a sheet side surface which combines to form a side surface of a book; and applying a laser beam to the side surface to modify at least a part of the side surface to form an image thereon, wherein removal of the sheet having a portion of it modified by the laser beam causes a distortion in the image. The book has a plurality of sheets, each sheet having a sheet side surface with at least one original region and at least one laser modified region, the plurality of sheet side surfaces combine to form a side surface of the book; and an image on the side surface of the book, formed by the combination of the adjacent original and laser modified regions.

Description

Book With An Image And Methods Of Production

The present invention relates to a book with an image and methods of producing the book.

Security features are provided on some documents to certify the authenticity of the document. In particular, security and identity documents are examples of a book (or booklet) having security features, some of these security features include having holograms, electronic chips, watermarks, and pictures viewable under ultraviolet light.

Most security features for identity documents, like a passport, are produced by printing (offset, silkscreen, inkjet, etc.). In an existing method, the security feature is printed (offset) on the page itself, at the border and not at the edge. The position of the printed pattern varies along the page’s border and creates a text when the booklet is viewed from the side. This is due to the ink used in the printing being absorbed into the paper substrate and becoming visible on the side surface. In offset and silkscreen printing, a screen with printing areas and non-printing areas is used to transfer an image onto a surface. However, in these printing methods the image is fixed and common to all produced books, in particular for a given production batch or a given project. It is difficult and expensive to provide a personalised image for each and every book.

In providing security features for documents, the laser has been used in several examples including changing the colour or aspect of the plastic raw material (for card or polycarbonate data page), or of a laser sensitive material embedded onto or printed on the document; by ablating / removing a laser sensitive material embedded into or printed on the document; or by perforating the document. Depending on the targeted applications I effects and the substrate material, different properties of the laser (e.g. wavelength, power) may be used. In particular for passports, the laser is applied for the perforation of the data page made of polycarbonate material, in other words a hole is created through the thickness of the data page. The laser power is quite high as it has to go through the whole plastic thickness (typically in the range of 400 to 800 microns) or even through the whole passport (at least 3 mm thick) and only dots or simple shapes (star, square, triangle, etc.) are producible to engraved a number which is formed by these shapes side by side. However, the existing use of laser modifications to the document is limited to the front or back page of each sheet, which is larger in area and may be worked on more easily. It is difficult to apply the existing methods and laser to a small area like the side surface of a book, where the thickness of each sheet and the whole book is much smaller than the front (or back) surface of the sheet or book. For example, typical dimensions for a 32 page passport are about 88 mm x 125 mm x 3 to 4 mm (if a rounded corner is used, it typically has a radius of 3.18 mm). For a 64 page passport, the thickness is approximately double at about 7 mm. As such, it may be seen that the “front” surface of the passport is much larger than the side surface, and different difficulties arises from these dimensions. In particular, with a typical passport thickness (or height) of 3 mm, there is difficulty in registration (i.e. visible to a person) and reproducibility of a modification to the side of the passport, which limits their use and application.

One of the most common passport forgeries is the substitution of the paper data page with a new data page containing the holder / forger data. In addition, visa pages featuring specific stamps (information on visited countries, on any refusal of entry, etc.) may be removed or substituted. At present, no feature is robust enough to prevent this page removal/substitution. Having something visible at first sight, without any need for specific equipment, and personalised (meaning which can be linked directly to the holder data and identity) ultimately reinforces security of the document, in particular for passports.

Hence, there is a continual need to constantly develop new security features to deter and stay ahead of forgers.

In an aspect of the invention, there is provided a method of creating an image on a side surface of a book, the method comprising providing a plurality of sheets, each sheet having a sheet side surface which combines to form a side surface of a book; and applying a laser beam to the side surface to modify at least a part of two adjacent sheet side surfaces to form an image on the side surface of the book, wherein removal of a modified sheet causes a distortion in the image. Advantageously, the image on the side surface of the book, in particular an exposed side surface, allows for easy visualisation and identification when a sheet in the book has been removed and/or substituted. This provides an improved security feature for books and documents.

As used herein, the term “sheet” is used to refer to a paper or material having two pages or faces, a piece of paper or material may be folded to produce two or more sheets, for example an A4 sized sheet of paper can be folded into two A5 sized sheets having four pages.

Preferably, applying the laser beam creates at least one original region and at least one laser modified region on each sheet side surface, which combines with the respective at least one original region and the at least one laser modified region of an adjacent sheet side surface to form the image on the side surface. The image itself may be either region, it is the combination of both regions that provides the visible image.

Preferably, the method further comprises coating at least part of the side surface of the book with a laser sensitive material prior to applying the laser beam, wherein applying the laser beam causes a physical modification and/or a chemical modification to the laser sensitive material. Advantageously, this improves the contrast of the image and makes the image more visible, especially when it is to be viewed with the naked eye. The laser sensitive material may be any one or more selected from an absorbent colour, a reflective element, a semi-reflective element, a metallic element, an optically variable element, and a fluorescent material.

In an embodiment, the physical modification is ablation of a portion of the laser sensitive material. In an embodiment, the chemical modification leads to a colour change in a portion of the laser sensitive material. The physical modification and chemical modification may occur together as well.

Preferably, the image is any one selected from an alphanumeric character, a symbol, and a pattern.

Preferably, providing the plurality of sheets comprises binding the plurality of sheets and at least one of the following: at least one unmodified sheet, a front cover, a back cover, a data page and a book spine. The binding may be permanent or temporary, and serves to assemble the sheets together for the application of the laser beam.

Preferably, the image represents a unique identifier associated with the book. Advantageously, the unique identifier may be provided in the data page or data chip in the document, in particular a passport to further create a link between the identifier and image, and increasing the security strength of the document. It may also be possible that the identifier is used for tracking and stock management purposes during production as well.

Preferably, the method further comprises providing a repellent coating on an interior of the plurality of sheets.

In another aspect of the invention, there is provided a book comprising a plurality of sheets, each sheet having a sheet side surface with at least one original region and at least one laser modified region, the plurality of sheet side surfaces combine to form a side surface of the book; and an image on the side surface of the book, the image formed by the combination of the at least one original region and the at least one laser modified region of each sheet side surface with the respective at least one original region and the at least one laser modified region of an adjacent sheet side surface. The image itself may be either region, it is the combination of both regions that provides the visible image.

Preferably, the at least one original region has a layer of laser sensitive material. Advantageously, this improves the contrast of the image and makes the image more visible, especially when it is to be viewed with the naked eye.

Preferably, the laser sensitive material is one or more selected from an absorbent colour, a reflective element, a semi-reflective element, a metallic element, an optically variable element, and a fluorescent material. In other words, more than one laser sensitive materials may be used on the side surface of the book, and the laser modified region contains two or more modified laser sensitive materials. Advantageously, this may allow for the provision of an image with more than one colour. As an example, two laser sensitive material may be used on all the sheet side surfaces, or each laser sensitive material is applied to different sheet side surfaces. This is similarly applicable to any number of laser sensitive materials.

Preferably, the laser modified region is physically modified and/or chemically modified.

Preferably, the physical modification is ablation of a portion of the laser sensitive material.

In an embodiment, a height difference between the at least one original region and the at least one laser modified region is at least 30 micrometres. In an embodiment, the difference between the at least one first region and the at least one second region is at least 200 micrometres. In an embodiment, the difference between the at least one first region and the at least one second region is at most 900 micrometres. In an embodiment, the difference between the at least one first region and the at least one second region is from 30 micrometres to 900 micrometres inclusive of both end points.

Preferably, the at least one original region has a different colour from the at least one laser modified region. Preferably, the image is any one selected from an alphanumeric character, a symbol, and a pattern.

Preferably, the plurality of sheets are made from any one of the following: cellulosic paper, synthetic paper, plastic materials, and combinations thereof.

Preferably, the book further comprises at least one of the following: at least one unmodified sheet, a front cover, a back cover, a data page and a book spine.

In an embodiment, the image is formed from the laser modified region surrounded by the original region. In an alternate embodiment, the image is formed from the original region surrounded by the laser modified region. Advantageously, this may make it more difificult to tamper with the image and hence enhance the security aspect of the image when used as a security feature.

The various aspects and embodiments described herein provide a new and improved security feature that is easily identified by authorities and provide a strengthened security for identity documents, like passports, and other important documents. Advantageously, the image may be readily viewed by a person without the need for specialised equipment or knowledge. The removal or substitution of a sheet may cause a distortion of the image which readily points towards the tampering of the book or document. Further, the embodiments described herein allow for the personalisation of each book in a cost effective manner, which is particularly advantageous for documents with high security requirements like passports.

In the Figures:

Figure 1 shows a side view of various embodiments;

Figure 2 shows a perspective view of various embodiments; and

Figure 3 shows a perspective view of an embodiment.

Unless defined otherwise, all technical and scientific terms used herein have the meaning commonly understood by a person skilled in the art to which this invention belongs.

In the following description, numerous specific details are set forth in order to provide a thorough understanding of various illustrative embodiments of the invention. It will be understood, however, to one skilled in the art, that embodiments of the invention may be practiced without some or all of these specific details. Embodiments described in the context of one of the methods or devices are analogously valid for the other methods or devices. Similarly, embodiments described in the context of a method are analogously valid for a device, and vice versa.

The phrase “at least one of A and B” means it requires only A alone, B alone, or A and B, i.e. only one of A or B is required.

As used herein, the articles “a”, “an” and “the” as used with regard to a feature or element include a reference to one or more of the features or elements. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. As used herein, the terms “first,” “second,” and “third,” etc. are used merely as labels, and are not intended to impose numerical requirements on their objects. As used herein, the terms “top”, “bottom”, “left”, “right”, “side”, “vertical” and “horizontal” are used to describe relative arrangements of the elements and features. As used herein, the term “each other” denotes a reciprocal relation between two or more objects, depending on the number of objects involved.

Ranges may be expressed herein as from "about" one particular value, and/or to "about" another particular value. When such a range is expressed, a further aspect includes from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by use of the antecedent "about," it will be understood that the particular value forms a further aspect. It will be further understood that the endpoints of each of the ranges are significant both in relation to the other endpoint, and independently of the other endpoint. It is also understood that there are a number of values disclosed herein, and that each value is also herein disclosed as "about" that particular value in addition to the value itself. For example, if the value "10" is disclosed, then "about 10" is also disclosed. It is also understood that each unit between two particular units are also disclosed. For example, if 10 and 15 are disclosed, then 11 , 12, 13, and 14 are also disclosed.

All publications mentioned herein are incorporated herein by reference to disclose and describe the methods and/or materials in connection with which the publications are cited. The publications discussed herein are provided solely for their disclosure prior to the filing date of the present application. Nothing herein is to be construed as an admission that the present invention is not entitled to antedate such publication by virtue of prior invention. Further, the dates of publication provided may be different from the actual publication dates, which may need to be independently confirmed. Figures 1 and 2 show examples of books 100, 200, 300, 400 with an image 40 formed on the book’s side surface 25. Each book 100, 200, 300, 400 may generally be made up of a front cover 10, a back cover 15, a plurality of sheets 22 between the front cover 10 and the back cover 15, and a book spine attached to the front cover 10, the back cover 15 and the plurality of sheets 22 placed between the front cover 10 and the back cover 15. The book spine is generally used to hold and bind the various components of the book together. In an embodiment, the book 100, 200, 300, 400 has a front surface, a back surface and four side surfaces for a conventional rectangular cuboid shaped book, of which one of the side surface is typically hidden by the book spine.

Each sheet 22 (may also be known as a paper substrate) generally has a front surface, a back surface and one or more side surfaces. For example, with a rectangular sized sheet there are typically four side surfaces and is essentially a rectangular cuboid. The front surface and back surface of the sheet may form opposing sides or pages when the sheets are bound into a book. In an example, the side surface for the image 40 is relatively flat or planar. The plurality of individual sheets are stacked to form the book 100, 200, 300, 400, such that the side surface/s of each sheet 22 combine to form a side surface 25 of the book. One of these side surfaces 25 is typically used to attach the plurality of sheets 22 to the book spine to hold (or bind) the book together. The image 40 may preferably be formed on any of the exposed side surfaces 25 of the book 100, 200, 300, 400 to make it readily visible to a third party. The corner/s of the book 100, 200, 300, 400 and/or sheet 22 may be rounded or right angled.

In another alternative embodiment, the book 100, 200, 300, 400 and/or the plurality of sheets 22 may have other shapes (for example circular, triangular and other regular and irregular shapes).

The books 100, 200, 300, 400 with the image 40 on the side surface 25 may be made by providing a plurality of sheets 22, each sheet having a sheet side surface 23, and the plurality of sheet side surfaces 23 combine to form a side surface 25 of the book 100, 200, 300, 400. A laser beam is applied or directed to the side surface 25 of the book 100, 200, 300, 400 to modify at least a part of a sheet side surface 23 to form an image 40 on the side surface 25. The laser beam may be applied to create (or form) an image 40 on the side surface 25 of the book 100, 200, 300, 400 and crosses a plurality of the sheet side surfaces 23 allowing the image 40 to serve as a visual link between the sheet side surfaces 23 and sheets 22, i.e. each sheet 22 may have a region that is modified by the lasser and a region that is original or unmodified by the laser. This may be called as positive personalisation. Alternatively, the laser beam may be used to remove parts of the sheet side surfaces 23 with the remaining parts forming the image 40 seen. This may be called as negative personalisation. The removal or substitution of one of these sheets 22 causes a distortion in the image 40 which may indicate that the book 100, 200, 300, 400 has been tampered with, and the image 40 may be used as a security feature for the book 100, 200, 300, 400. In Figure 3, book 500A is prior to the application of the laser beam. Book 500B shows a positive personalisation where the laser modifies a part of the side surface 25 or sheet side surface 23 to form the laser modified region 30 surrounded (totally or partially) by the original region 35, the image 40 is thus viewed as the laser modified region 30. Book 500C shows a negative personalisation where side surface 25 or sheet side surface 23 is removed leaving an original region 35 as the image 40, whereby the original region 35 is surrounded (totally or partially) by the laser modified region 30. The negative personalisation in book 500C may provide added security as it is difficult to further modify the image 40 subsequently by counterfeiters without compromising the image 40 and book 500C. In addition, if the laser sensitive material has some optical properties (for example visible under UV light or different colour is observed under UV light), this may provided added security as to whether the image 40 has been tampered with.

As indicated earlier, by modifying at least part (or some) of the sheet side surface 23 an image 40 may be formed by creating two distinct regions on the sheet side surface 23 - at least one original region 35 and at least one modified region 30. The combination of the respective distinct and different regions of adjacent sheet side surfaces 23 when stacked together create the image 40. Hence, there is at least one original (first) region 35 and at least one laser modified (second region) 30, which are different from each other. The at least one first region may be the original sheet side surface 23 unmodified by the laser beam. The original (first) regions 35 and laser modified (second) regions 30 of adjacent sheets combine to form the original (first) region and laser modified (second) region of the side surface 25 of the book 100, 200, 300, 400. The image 40 is formed when the plurality of sheets 22 are stacked or bound together, wherein the image 40 is formed by the combination of the respective regions put together.

The image 40 is formed on at least one side surface 25 of the book 100, 200, 300, 400. The side surface 25 is formed from the combination of the plurality of individual sheet (side) surfaces. Each sheet side surface 23 has at least one original or unmodified (first) region 35 and at least one modified (second) region 30. The image 40 is formed by the combination of the respective original (first) region 35 and laser modified (second) region 30 of adjacent sheet side surfaces 23. The combination of the adjacent first regions 35 and second regions 30 may be by alignment of the first regions 30 and second regions 35 of the plurality of individual sheet edges to form the image 40 on the book’s side surface 25 as shown in Figures 1 and 2. The alignment may be a straight line or a curve.

In an alternative embodiment, a layer of laser sensitive material is provided on the adjacent sheet side surfaces 23 to be modified. Hence at least part of the side surface 25 of the book 100, 200, 300, 400 has a layer of the laser sensitive material. A laser beam is applied or directed to the side surface 25 of the book 100, 200, 300, 400 to modify at least part of the laser sensitive material on at least two of the sheet side surfaces 23. Advantageously, the layer of laser sensitive material improves the contrast, visibility and quality of the image 40 formed from the application of the laser, i.e. between the modified laser sensitive material and the unmodified laser sensitive material and/or original sheet side surface 23.

By applying the laser to the layer of laser sensitive material, a layer of modified laser sensitive material is created and forms the modified second region. The region/s where the laser beam is applied to (or focussed on) causes a change in the laser sensitive material, and may be considered “worked on” by the laser beam to create the modified (or second) region 30. As a result, the laser modified region 30 may have a layer of modified laser sensitive material, which may be formed when the layer of laser sensitive material is completely or partly ablated (i.e. removed) by the laser.

The original region 35 may be a region unmodified by the laser. This could be due to several possibilities - the laser not being applied, the laser not being applied with sufficient power, the side surface may have a coating (or element) which is not sensitive to laser, or a combination of any of these factors. The at least one original region 35 may contain the layer of the laser sensitive material which is not worked on by the laser beam, i.e. the laser beam is not directed at these regions or the power of the laser is insufficient. The sheet side surface 23 need not be coated entirely with the laser sensitive material. Thus, the part of the sheet side surface 23 not provided with a layer of laser sensitive material may be considered part of the original (first) region 35 as well.

For each sheet side surface 23, there may be one or more modified (second) regions 30 and/or original (first) regions 35. The combination of the original regions (first region) 35 and modified regions (second region) of adjacent individual sheet edges together forms the image 40 which serves as the security feature. When one of the sheets 22 with the image 40 is removed or substituted, the image 40 becomes distorted and is easily seen by a person viewing the book 100, 200, 300, 400 without the need for any specialised equipment.

In an example, a laser sensitive material (for example an organic material) is coated on a part or whole of the sheet side surfaces 23. The laser is applied to heat the laser sensitive material modifying the laser sensitive material and removing or changing the colour of the laser sensitive material. As a result, a black or grey image (the modified laser sensitive material) may be formed on the sheet side surface 23 with the original side surface 23 as the background. It would be evident that the colour of the image itself is dependent on the laser sensitive material and the laser, and can be modified as required.

The extent of the laser sensitive material that may be worked on by the laser depends in part on the resolution of the laser beam, and how fine it can work on the sheet side surface 23. It is likely there would be laser sensitive material which is not worked on by the laser when viewed at the micro level, for example at a microscopic or nanoscopic scale, which may not be readily visible to the naked eye, but visible with other instruments.

The books 100, 200, 300, 400 may further contain at least one unmodified sheet. The unmodified sheet is a sheet having none of the sheet side surface 23 modified by the laser. The unmodified sheet may be provided (or place) within, at the top or bottom of the plurality of sheets 22. Thus, the image 40 may be only formed across a part of the side surface 25, and needs not include all the sheet surfaces that form the side surface 25. For example, the image 40 may be formed nearer the front cover 10 and the sheets nearer the back cover 15 are unmodified, or vice versa. In another example, the sheets in the middle of the book edge are left unmodified while an image is provided in the sheets near the front cover 10 and the back cover 15. The books 100, 200, 300, 400 may be further provided with a data page 20 which may be made of polycarbonate or other material.

The image 40 may serve as a security feature, in particular by creating a secure link between the sheets 22 of the book having the second (modified) region 30, any substitution or removal of a sheet 22 creates a defect in the image 40 which may be spotted, and thus protect the book 100, 200, 300, 400 from forgery attempts. In the examples shown, the image 40 is created on the side surface 25 opposite the book spine. However, the side surface 25 adjacent to the book spine may also be used either alone or in combinations thereof. Preferably, the side surface 25 with the image 40, is an exposed side surface to make it easily visible to a person. In the figures, the book 100, 200, 300, 400 is generally shown as a rectangular cuboid but need not be necessarily so as explained.

In an example, at least two sheets 22 are needed to form the image 40, although three or more sheets would make the distortion of the image 40 more easily visible. For the image 40 to be more easily visible, in particular when viewed by a person without any specialised equipment, the size of the image 40 may be varied by the number and thickness of the sheets to create an appropriately sized image that is visible. In an example, the resolution of the image is a minimum of 150 dpi (dots per inch). If the image 40 is to be viewed by specialised equipment, it may be possible for the image 40 to be smaller such that it may be visible under magnification or under special conditions, i.e. UV light.

As an example, when the book is a passport booklet, electronic information of the passport holder may be provided in the data page 20 (including a chip and an antenna). Alternatively, the chip and antenna may be provided in the cover or elsewhere in the passport booklet. The sheets 22 may be composed of cellulosic paper, synthetic paper, plastic materials, and mixing different types of the aforementioned substrates. In an example, when the document is used as a passport, the sheet 22 provides the pages which are stamped by the immigration official. For a passport, the sheet 22 is required by the International Civil Aviation Organisation (ICAO) regulations to have specific properties as detailed in the ICAO’s document Machine Readable Travel Documents, 7^th Edition, 2015, including UV dull (no reaction to UV light - most commercial paper turn blue under UV light), watermark comprising two or more grey levels, appropriate chemical sensitizers in the paper, paper with appropriate absorbency, roughness and weak surface tear. Other ICAO recommended requirements include a watermark in register with printed design, a cylinder mould watermark, invisible fluorescent fibres, visible fibres, security thread (embedded or windowed) containing additional security features such as micro print and fluorescence; a taggant designed for detection by special equipment; a laser-perforated security feature through the sheet and cotton content, usually 50%. The paper substrate may also be characterised to evaluate the contrast between exposed and non-exposed areas to the laser. The number of pages in a passport varies among different countries, and may be generally provided from 8 to 64 pages, with the lower range normally being for urgency passports. However, it is evident that the number of pages depend on the use of the document. For example, when the image 40 is to be easily visible, using a greater number of sheets 22 or a thicker sheet 22 may be needed. On the other hand, there may be situations where the image 40 is not needed to be easily visible, and in this scenario the number of sheets used may be less. The colour and/or contrast difference between the original substrate (the first region) and the modified regions (the second region) may have a greater visual effect on the image 40.

The image 40 may be personalised for each individual book 100, 200, 300, 400 and may be created using a laser beam to write a number, a text or create a simple design, symbol or pattern visible / readable from the book edge 25. The image 40 may be a unique identifier associated with the book 100, 200, 300, 400. The method for creating the image 40 on the side surface of the book may further comprise determining a unique identifier associated with the book, wherein the image 40 represents said unique identifier.

The image 40 may be composed of, for example but not limited to, variable data (the document holder’s own data), data stored on the document’s chip, and/or a fixed visual element. The variable data may thus be a unique identifier associated with the book 100, 200, 300, 400. For example, in Figures 1 and 2 the image 40 on the book 100 uses a country name “UTOPIA” and a serial number (e.g. a passport or identity number). In another example, the book 200 uses a symbol (e.g. a country flag) and a serial number as the image 40. In another example, the book 300 uses a name as the image 40. In another example, the book 400 uses a name and date of birth of the owner of the book 400. The serial number, document holder’s name, data of birth and other similar data may thus be considered examples of a unique identifier associated with the book. The country flag and country name may be considered examples of a fixed visual element.

To create the image 40 on the side surface 25 of the book 100, 200, 300, 400, a plurality of sheets 22 are provided, each sheet 22 having a sheet side surface 23 which combines to form the side surface 25. A laser beam is applied to the side surface 25 to modify at least a part of the side surface 25 to form the image 40 on the side surface 25. In particular, at least a part of two adjacent sheet side surfaces 23 are modified to create the image 40. The book 100, 200, 300, 400 may be created by binding (i.e. assembling) a plurality of sheets 22 together to provide the book 100, 200, 300, 400. This allows the image 40 to be created to complete the book. However, it may also be possible for the plurality of sheets to be bounded temporarily instead with the permanent binding or attachment done after the image 40 is created. For example, the temporary binding may be by clamping the ends or one side of the plurality of sheets.

The laser sensitive material may be provided as a layer on the side surface 23 of the sheet 22 that forms the side surface 25. The layer of laser sensitive material may be coated on before or after the plurality of sheets 22 are bounded. In an example, the layer of laser sensitive material has a minimum thickness of 1 micron (micrometre). In another example, the minimum thickness of the layer is 5 micron. In another example, the maximum thickness is 100 microns. In another example, the thickenss of the layer is from 10 to 100 microns. By applying a laser on to the laser sensitive material, a chemical modification and/or a physical modification to the laser sensitive material may occur thereby creating a modified region 30 in the sheet side surface 23. The regions where no laser sensitive material is present or the laser is not applied to remains as the original region 35, i.e. not modified by the application of the laser beam. Advantageously, the layer of laser sensitive material and modified laser sensitive material improves the contrast, visibility and quailit of the image 40.

In an example, the laser sensitive material may be selectively ablated by the laser beam to create a depression (or gap) in the layer of laser sensitive material, by removing in part or whole of the laser sensitive material at a point. In other words, the layer of laser sensitive material becomes a pitted layer. Similarly, in the absence of the layer of laser sensitive material, the sheet side surface 23 may be partly ablated by the laser to create a pitted sheet side surface with regions of depressions in the sheet side surface 23. The depressions thus form the modified region 30 while the untouched part of the laser sensitive material or paper substrate forms the original region 35. As the image 40 may be relatively small, to achieve a high resolution and a high contrast the height difference between the original region and ablated region should preferably be at least 30 microns (|im) to be detected by a human finger (sensitivity limit), more preferably 200 microns (regulated height for Braille dots) and even more preferably up to 900 microns. The height difference may also be considered as the depth of the image 40 in the side surface 25.

In an alternate example, the laser sensitive material may undergo a chemical modification when the laser is applied. The chemical modification may be a change in the chemical structure, chemical formula, or a chemical reaction occurring due to the energy provided by the laser beam. This chemical modification may cause a change in the electromagnetic radiation absorbed and reflected by the laser sensitive material, i.e. a change in the colour of the laser sensitive material is observed. For example, the original laser sensitive material may absorb only in the ultraviolet region, and is observed as white, while the modified laser sensitive material may absorb visible light in the blue wavelength region and thus appear yellow. Other examples are also possible and the present example is merely illustrative.

In another example, the laser sensitive material alone, or combination of two or more different materials, may be used to provide both a physical and a chemical modification occurring. The material of the sheet may aid in getting a contrast between the modified region 30 and the original region 35 to allow the image 40 to have sufficient contrast to be visually assessed. Combined together the image 40 is created by different depth and/or colour perception. The substrate or book edge 25 appears different visually after the ablation or engraving by the laser. The physical modification and chemical modification may occur together for certain laser sensitive materials. For example, a change in the chemical structure may be observed at the macro level as a physical change in the thickness of the layer of the laser sensitive material.

A suitable laser type for use may be a CO₂ laser, with a wavelength between 9 to 11 microns. Solid-state lasers (particularly YAG lasers and fiber lasers) operating at shorter wavelength in the 1 micrometre (pm) wavelength region may also be used. The laser power range for perforation is typically between 20 to 200 W and is likely to be too high for modifiying the surface edge. A laser power range below 20 W may be more suitable for modification of the sheet side surface 23 (or surface edge).

Existing methods to use a laser to modify a large surface is not suitable for modifying the side suface of a book due to the narrow edge of the book, in particular with passports which have a relatively small side surface (or thickness) compared to the front surface of a book

As an example to apply the laser to the side surface, the method may further include:

(a) finding a sensitivity range of the laser sensitive material including the minimum sensitivity threshold (the point when the laser sensitive material starts to be modified, react or change) and the maximum sensitivity threshold (the point when the laser sensitive material starts to be destroyed by the laser); (b) determining the reactivity of the laser sensitive material with respect to a laser parameter, for example power, frequency and speed; and

(c) setting up the laser paramters according to the requirements of the image 40 or book 100, 200, 300, 400.

The reactivity of the laser sensitive material may be measured differently for different laser sensitive materials, including a change in colour, opacity, thickness, reflectivity, etc. For the laser parameters of power, frequency and speed, power is typically the most influencing laser parameter while speed is the least influencing among the three parameters. Other laser parameters may also be important and tested to determine the reactivity of the laser sensitive material.

In an example, the frequency may be fixed in the microsecond or nanosecond range. The laser may be applied to engrave a test chart at various level of power and different speeds. The results may be visually assessed or measured with a a spectrophotometer to find the proper correspondence between laser parameters and results which may be used to adjust either the input data or the laser parameters.

Based on these measurements, the laser parameters may be set accordingly to achieve the requirements of the image 40 or the book 100, 200, 300, 400. For example, the requirements may be reproduction of colour gradation, max effect or max parameters etc. This allows the laser to be applied to modify only the side surface 25 of the book 100, 200, 300, 400 without affecting or damaging the rest of the sheet 22.

The laser sensitive element may be a colour for example but not limited to an absorbent colour, a reflective or semi-reflective element, a metallic element / colour, an optically variable element, a fluorescent material / ink (sensitive to infrared, ultraviolet, etc.). Laser sensitive materials / elements may be any organic ink. For example, with application of the laser, the ink will turn black. Other examples include speciality inks, thermochromic and photochromic inks, which would change colour. An example may be a silver (Ag) coating as the laser sensitive material, which may be ablated / removed by the laser beam.

Other metallic components may be formulated for use as the laser sensitive material. Examples include aluminium, copper, zinc, steal, titanium, chromium, gold, nickel and alloys. Examples of pigments which may be used are described in US patent 6,686,042 and incorporated herein by reference. Preferably, the average size of the metallic pigment is between 10 to 50 microns (inclusive of both ends) to allow the pigments to be used with conventional coating and printing techniques afer formulating the pigments in a suitable vehicle of solvent. Examples of the vehicle or solvent that may be used include water, volatile organic compounds like petroleum - alphatic, paraffinic, etc), modified rosin (a solid resin obtained from pines and other plants), oil based resins, or a polymer resin. For the polymer resin, it is typically the oligomer that determines the principal properties of the ink. The monomers are reactive diluents which enable the viscosity of the ink to be adjusted, and are polymerised. Photoinitiators are added to the ink mixture and exposure of the mixture to ultraviolet light (after coating or printing) causes polymerisation of the monomers to provide the oligomer. The concentration of metallic pigment is preferably between 5 and 50% in weight of the the final mixture. The mixture may contain other additives (fillers, waxes, drying agents, etc.) which may determine or influence specific properties such as rheology, abrasion resistance, drying, etc.

In an example, the laser radiation modifies the crystalline state of metallic pigment which becomes amorphous, and then more transparent. A NdYAG laser may be used for this modification. The NdYAG laser generates locally a high temperature allowing the changes of states to occur. When the laser radiation stops, the metallic pigment comes almost immediately back to room temperature, which allow the material to be fixed in this at least partially amorphous state.

An example of a laser system that may be used may include the following properties: a. Laser type: diode pumped solid state laser Nd YAG 1064 air cooled b. Wavelength: 1064 nm c. Nominal laser power: up to 12 W max +/-5% (at laser aperture), system may be typically set up at 6 W d. Modulation: up to 200kHz e. One or more reflecting mirrors to adjust the laser beam incidence angle f. Scanning head: 160mm F-Theta lens g. 256 shades of grey - 600 dpi

Thus, the laser modifies the laser sensitive material to create the modified region 30 by either physically or chemically altering the laser sensitive material in the original region 35 to create the image 40. The image 40 may be personalised for each document and/or be a general image for all similar documents. It may be possible to ablate the laser sensitive element to create an additional grey or colour level that may help achieve better contrast or colour difference for some parts or component of the image 40. In the absence of the laser sensitive material, the sheet 22 may be directly ablated by the laser beam. The extent of ablation or depth of the sheet side surface 23 removed would be a function of the accumulated energy in the laser dot. For example, higher power provides larger depth. Higher speed or frequency allows a lower amount of amount energy to be accumulated locally providing smaller depth. Thus, this allows for control of the extent of ablation of the sheet side surface 23. The laser beam may be done at an angle for this, which may ablate the material at an angle to create a diagonal or slope surface which may provide additional 3D effects when viewed.

When directing the laser beam to the plurality of sheet side surfaces 23 (side surface 25 of the book), the book 100, 200, 300, 400 needs to be positioned with the side surface 25 facing the laser beam perpendicularly to avoid any laser image distortion. If the front cover 10 and back cover 15 is present, the covers 10, 15 may be pushed away from the sheets 22 to avoid applying the laser to the covers 10, 15. Alternatively, the input image could be modified / adjusted to compensate the potential distortion.

The deposition of the laser sensitive material on the individual sheet edges may need to be controlled to deposit the laser sensitive material evenly and/or avoid spilling or bleeding on the interior of the sheet 22. This may be done by reducing the deposition speed. Alternatively, the interior of the sheet may be protected with a repellent coating, either a temporary or a permanent coat. Further, to manage the deposition of the laser sensitive material on round corners a non-contact printing/coating technic may be used. For example, using spray and inkjet printing/coating. In another example, the use of a soft printing plate such as tampography may be employed. In an example, a rounded edge may be printed in steps, printing on the “flat” or straight part of the side surface, printing the rounded corner, and managing the interface between the straight and rounded parts to make the connection consistent and generally uniform. A hot stamping method as described in EP 3031615 (incorprated by reference herein) may be used to print at round corners.

Each laser sensitive material and paper substrate may have a different response to laser beam. The modification or ablation of the laser sensitive material and paper substrate may not vary linearly with the laser parameters. In other words, doubling the laser power does not mean ablating twice the amount of material. Before directing the laser beam to the side surface 25, the parameters of the laser may need to be pre-calibrated to adapt to each laser sensitive material, and may be performed at a regular basis. As an example, the frequency may be fixed to the microsecond or nanosecond region. For determining the suitable laser power for the laser sensitive material, the minimum power for which the material remains unchanged and the maximum power for which start damaging either the laser sensitive element or the substrate is determined. After which trial runs are done by laser engraving a test chart with various levels of power and speed parameters. The results are visually assessed or measured with a spectrophotometer to find the correspondence or relation between the laser parameters and result to determine the optimal or suitable laser parameters. Other measuring device/s may also be used depending which change needs to be assessed after laser irradiation. Examples include in the measurement of thickness difference where ablation has occurred and a UV spectrophotometer to assess a color change in the UV spectrum, etc.

The laser beam may cause ablation of the sheet side surface 23, or a physical and/or chemical change to the laser sensitive covering on the sheet side surfaces 23. A common symbol could also be created using the laser, for example as shown in Figure 1 the country name or flag. In another example, for a laser sensitive element, a generic/common pattern may be coated or printed on the edges of all or part of the sheets 22.

It may be possible for the individual sheet edges to be modified by the laser beam first before binding of the plurality of sheets, and may be suitable for certain documents where the alignment is simpler.

Depending on the nature of the laser sensitive element, the number of side surfaces 25 to be covered and pattern to reproduce, different technics may be used, for example but not limited to, spray, silk screen, hot stamping, etc. All the sheet surfaces or side surfaces 25 could be covered by the same laser sensitive element or each edge could have a different element or only one edge is covered. A specific multicolour or multi-element design may also be created and reproduced on one or several of the book edges 25 as shown in the book 400 in Figure 2. In this book 400, there are three original regions 35, 45, 50 each having a unique laser sensitive material. In book 400, the laser sensitive material is placed next to each other, but it could also be stacked to create different visual effects and images 40.

The image 40 may feature at least one of the following: variable data (data belonging to the document holder - name or date of birth for instance), data stored on the document’s chip (chip’s serial number for instance) and a fixed visual element. The image 40 may be unique for every book 100, 200, 300, 400 or have a common feature (for example a country’s name or flag) and a unique feature.

The laser beam is adjusted to remove only an adequate amount or layer and not to damage the substrate of the sheets 22. The angle the laser impacts the sheet side surface 23 may be varied to create other optical effects. The laser engraving step may be performed on the booklet form factor, during the serialization or during final booklet personalization.

When the book 100, 200, 300, 400 is closed, the image 40 may be seen on the side surface 25. For example, the image 40 may appear “white”, or slightly lighter than the surrounding region, on a “coloured” background. The colour may be due to the sheet 22 itself or due to the laser sensitive material.

If the book 100, 200, 300, 400 has a data page 20, the book 100, 200, 300, 400 may be opened during the laser treatment so that the image is created only on the side surface of the sheets 22. In the example of the passport, these sheets 22 may be the pages where the immigration stamps and visas are placed.

Thus, when there is removal or substitution of a sheet 22, the image 40 is modified or distorted and the forgery attempt may be detected without the need for specialised equipment. When the image 40 is visible and intact, it provides evidence that the book 100, 200, 300, 400 (in particular a passport) has not been tampered or disassembled in a way that some sheets 22 of the book 100, 200, 300, 400 have been replaced or removed, and is authentic.

In Figures 1 and 2, the image 40 formed is shown as the laser modified region 30, but the original region 35 could also be the image, in other words the area surrounding the original region is modified by the laser. It is the combination of both regions 30, 35 that produces the image 40.

In Figure 3, the book 500A shows an example of the book 500 before the application of the laser beam. The books 500B and 500C show examples of the image 40 formed on the side surface 25 after the application of the laser beam. In book 500B, the laser modified region 30 is the image 40 shown in the form of a number with the original region 35 surrounding the number, this may also be called a positive personalisation as the original region 35 surrounds the laser modified region. In book 500C, the original region 35 is the image 40 shown in the form of a number with the laser modified region 30 surrounding the number, this may also be called a negative personalisation as the surrounding area is removed to leave behind the original region 35 as the image 40.

The book 100, 200, 300, 400, in particular a passport, may be further provided with existing security features to complement the embodiments described herein. The methods described allows each book 100, 200, 300, 400 to be personalised accordingly and provides a versatile and cost effective manner to generate a book 100, 200, 300, 400 with enhanced security features. Whilst there has been described in the foregoing description preferred embodiments of the invention, it will be understood by those skilled in the field concerned that many variations or modifications in details of design or construction may be made without departing from the present invention.

Claims

1. A method of creating an image on a side surface of a book, the method comprising providing a plurality of sheets, each sheet having a sheet side surface which combines to form a side surface of a book; and applying a laser beam to the side surface to modify at least a part of the side surface to form an image thereon, wherein removal of the sheet having a portion of it modified by the laser beam causes a distortion in the image.

2. The method according to claim 1 , wherein applying the laser beam creates at least one original region and at least one laser modified region on each sheet side surface, which combines with the respective at least one original region and the at least one laser modified region of an adjacent sheet side surface to form the image on the side surface.

3. The method according to any one of claims 1 to 2, further comprising coating at least part of the side surface of the book with a laser sensitive material prior to applying the laser beam, wherein applying the laser beam causes a physical modification and/or a chemical modification to the laser sensitive material.

4. The method according to claim 3, wherein the laser sensitive material is any one or more selected from an absorbent colour, a reflective element, a semi-reflective element, a metallic element, an optically variable element, and a fluorescent material.

5. The method according to any one of claims 3 to 4, wherein the physical modification is ablation of a portion of the laser sensitive material.

6. The method according to any one of claims 3 to 5, wherein the chemical modification leads to a colour change in a portion of the laser sensitive material.

7. The method according to any one of claims 1 to 6, wherein the image is any one selected from an alphanumeric character, a symbol, and a pattern.

8. The method according to any one of claims 1 to 7, wherein providing the plurality of sheets comprises binding the plurality of sheets and at least one of the following: at least one unmodified sheet, a front cover, a back cover, a data page and a book spine.

9. The method according to any one of claims 1 to 8, wherein the image represents a unique identifier associated with the book.

10. The method according to any one of claims 1 to 9, further comprising providing a repellent coating on an interior of the plurality of sheets.

11. A book comprising a plurality of sheets, each sheet having a sheet side surface with at least one original region and at least one laser modified region, the plurality of sheet side surfaces combine to form a side surface of the book; and an image on the side surface of the book, the image formed by the combination of the at least one original region and the at least one laser modified region of each sheet side surface with the respective at least one original region and the at least one laser modified region of an adjacent sheet side surface.

12. The book according to claim 11 , wherein the at least one original region has a layer of laser sensitive material.

13. The book according to any one of claims 11 to 12, wherein the laser sensitive material is one or more selected from an absorbent colour, a reflective element, a semi-reflective element, a metallic element, an optically variable element, and a fluorescent material.

14. The book according to any one of claims 11 to 13, wherein the laser modified region is physically modified and/or chemically modified.

15. The book according to claim 14, wherein the physical modification is ablation of a portion of the laser sensitive material.

16. The book according to claim 15, wherein a height difference between the at least one original region and the at least one laser modified region is at least 30 micrometres.

17. The book according to any one of claims 11 to 16, wherein the at least one original region has a different colour from the at least one laser modified region.

18. The book according to any one of claims 11 to 17, wherein the image is any one selected from an alphanumeric character, a symbol, and a pattern.

19. The book according to any one of claims 11 to 18, wherein the plurality of sheets are made from any one of the following: cellulosic paper, synthetic paper, plastic materials, and combinations thereof.

20. The book according to any one of claims 11 to 19, further comprising at least one of the following: at least one unmodified sheet, a front cover, a back cover, a data page and a book spine.

21. The book according to any one of claims 11 to 20, wherein the image is formed from the laser modified region surrounded by the original region.

22. The book according to any one of claims 11 to 20, wherein the image is formed from the original region surrounded by the laser modified region.