WO2001002168A1

WO2001002168A1 - Transparent laminate comprising colour changing materials, uv light filter and a gas impermeable layer

Info

Publication number: WO2001002168A1
Application number: PCT/SE2000/001363
Authority: WO
Inventors: Andreas Remling; Niklas Berg; Mattias BYSTRÖM; Henrik Fries
Original assignee: ARRAY DISPLAYS AB
Current assignee: ARRAY DISPLAYS AB
Priority date: 1999-07-05
Filing date: 2000-06-28
Publication date: 2001-01-11
Anticipated expiration: 2002-01-05
Also published as: SE9902563L; AU6038100A; SE9902563D0; SE516028C2

Abstract

The present invention relates to a transparent laminate comprising one or more colour changing materials, whereby it comprises at least one layer comprising one or more thermochromic materials, and at least one, substantially UV light impermeable layer or coating, and/or a gas impermeable layer or coating.

Description

TITLE

Transparent laminate comprising colour changing materials , υv light filter and a gas ijτpermeable layer.

DESCRIPTION Technical field

The present invention relates to a transparent laminate comprising one or more colour changing materials provided with an UV light filter, as well as objects, such as displays, provided with such a laminate.

The object of the present invention is to improve the lifetime of thermochromic, electro chromic and electrophoretic pigments in order to minimize the need for replacement and thereby reduction of costs for maintaining items containing such thermochromic pigments.

Within the framework of the present invention the term "laminate" is defined as a number of layers, either a number of different sheets, glued or otherwise adhered to each other; coatings, applied by solvent evaporation, sputtering, vapor evaporation or otherwise; or mixtures of coatings and sheets.

Background of the invention Reversible thermochromic materials are known (e.g., US-A-4,028, 118), and printing inks prepared from these materials have been applied to various articles to construct temperature indicators, ornamental objects and clothes and toys that reversibly change or develop colour at well defined, different temperatures. However, for these commercial products there has been a low demand for highly durable thermochromic materials exhibiting long life expectancy in outdoor conditions. The materials fade quickly due to sun light exposure, long time constant heating, and repeated switching. Development has been conducted within this technical field, as has been disclosed in US-A-4,425,161, where improved light fastness has been achieved by adding modifying chemical components within the thermochromic material. Further, US-A-5,281,570 discloses development leading to improve the long term stability by improving the chemical components and the chemical composition of the thermochromic material. Thermochromic pigments are pigments that go from one state to another when being heated. Thus they normally exhibit one colour at ambient temperature, and another when heated. This effect can be used in displays where the display shows e.g., a text or other data at ambient temperature, while that text disappears when the display is heated. One example of such a use is at a cashier to tell people that tickets are available when having the display heated, and when cooling the display, or turning the heat off, it informs that no there is no tickets left.

The thermochromic pigments are present in microcapsules as a dye compound, and is printed in the form of a printing composition onto a display, preferably on a substrate such as a polymer film which is applied on to a heatable backing, such as a printed circuit board or the like.

Thermochromic pigments suffer from the drawback of being UV-light sensitive and sensitive to oxidation. It has been proposed (WO 94/27336) to protect a UV sensitive material to apply a UV light protective shield to the top of a display to shield the temperature responsive material. Further, the same document proposes the incorporation of an anti-oxidant with the thermochromic material and/or to the encapsulating material containing the thermochromic material.

US-A-4,028,118 relates to a laminate of a film sheet, a thermochromic material and a protecting layer. An UV-absorbent is mixed into a polymer film comprising the thermochromic material or a UV-absorbent is mixed with a thermochromic ink.

EP-A-0 678 377 relates to a thermochromic laminate having a coating layer which may include a UV-absorbent, single oxygen quenchers, superoxide quenchers, ozone quenchers to improve light stability.

However, the addition of additives to the encapsulating material is negative with regard to the efficiency of the thermochromic materials to express their brightness, contrast, and colourfulness. Thus such encapsulation will cause opaqueness to the colours and reduce the readability thereof. Using a UV protecting shield forming a part of a display increases costs due to the fact that the UV protecting agent ages. Thus an UV protecting coating of the laminate of the present invention minimizes costs and provides for replacement in a more simple and efficient way.

Further, JP7205547 discloses the use of a UV reflecting material on reversible, heat sensitive display material, which reflecting material has a reflectance less than 50% of UV- light having a wavelength of 350 nm. This means that more than 50% of UV-light of 350 nm will pass through, and will cause detrimental effects to a thermochromic layer.

Although, several patents have been issued related to thermochromic displays, such displays have not yet obtained a commercial level due to the sensitive thermochromic materials used, and the problem solving this drawback thereof.

Summary of the present invention It has now been found possible to solve this problem by means of the present invention, which is characterized in it comprises at least one layer comprising one or more colour changing materials, and at least one, substantially UV light impermeable layer and/or gas impermeable layer.

Thus the invention applies to transparent laminates onto an object which laminates comprise one or more changeable, chromic material.

A further aspect of the invention relates to heatable displays comprising at least one such a transparent laminate, as well as in general, other objects comprising such a transparent laminate. These laminates serve to protect the sensitive thermochromic materials from UV light, and light near UV light, and/or gases found in the air as oxygen.

Further characteristics will be evident from the accompanying claims.

The laminate of the invention shall primarily provide a physical contact between the chromic material and the protecting layer(-s). By means of the present invention it is possible to increase, considerably, the lifetime of a chromic display, and thereby to obtain a commercially acceptable product, by avoiding degradation by UV-light and low wavelength visible blue light, as well as degradation by oxidation, while maintaining brightness and contrast to the chromic data provided on a product, e.g. a display.

In the following, the present invention will be further explained with reference to some exemplifying embodiments, some of the embodiments being disclosed with reference to the accompanying drawing, however, without being restricted thereto.

Brief description of the drawings

FIG. 1 shows an illustrative example of a transparent laminate of the present invention; FIG. 2 shows a further embodiment of the present invention; FIG. 3 shows another, further embodiment of the present invention; and FIG. 4 shows a display utilizing the present invention.

Detailed description

In the drawings the reference numerals used refer to the same type of layer used to build the laminate. 1 denotes a basic substrate consisting of a polymer film, e.g., a polyester (PET) sheet having a thickness of about 250 μm onto which a thermochromic print 2, such as thermochromic, electrochromic or electrophoretic dye has been applied. The basic substrate can be either transparent, or non-transparent, but is preferably non-transparent to form a background of the chromic layer, and to hide, any optional equipment placed behind the substrate in an application thereof. On top of the substrate, there is a layer 3 consisting of a UV protecting material, an optical filter, applied. The filter prevents light having a wavelength of up to about 420 nm to penetrate the layer, and thus reaching the thermochromic layer. Said layer has a thickness of about 10 μm.

Fig. 1 illustrates a basic design of protected thermochromic layer. In FIG. 2 the protection has been further increased by adding an oxygen blocking film 4, whereby said film has been applied on both sides to prevent oxygen to reach the thermochromic layer from either side. FIG. 3 illustrates a further embodiment wherein the oxygen blocking layer has been applied between the thermochromic layer 2 and the UV protecting layer 3 on the transparent side of the substrate.

FIG. 4 illustrates a further embodiment wherein different layers of contrasting dyes have been applied as well.

FIG. 5 shows a display 5 comprising heating zones 6 onto which display substrate 5 according to FIG. 3 has been applied. The display 5 comprises said heating zones 6 in form of electrically heated surfaces for heating the thermochromic print material 2.

The UV protecting layer consists of polymers having a UV absorbing agent therein, such as SENSITISERS^R, COURTGUARD^R. UV absorbing agents are often of the type used in suntanning protecting lotions. Suitable UV filtering agents are hindered amines (HALS), benzophenones, benzotriazones, or combinations thereof.

Other UV and light protecting means are angle barriers, i.e. reflecting barriers which allow reflectance from one angle and not from others. Other means are layers that only allow polarized light through. A photochromic material may also be used to provide light protection and/or enhance readability of a display provided with such a laminate.

A UV protecting layer in the form of a coating is usually applied in a thickness of 40 μm.

The oxygen blocking layer consists of one or more of the following substances, viz polyamide resins (NYLON^R), polyvinyldiene chloride resins (PVDC), hydrolyzed ethylene vinyl acetate resins (EVOH), Si0₂, A1₂0₃ which all works as oxygen blocking material. Even polyester (PET) resins resist oxygen permeability to some extent. Another oxygen blocking material is metallic aluminium which, preferably, can be applied onto the rear side of a substrate when of a non-transparent material. Other oxygen impermeable films are also available. The above mentioned have been given as examples only.

Other oxygen blocking materials, are the so called oxygen scavengers available, whereby such oxygen scavengers can be obtained as thin films, or as granulates, which latter can be included and extruded together with any oxygen proof layer.

SiO/Si0₂, and A1₂0₃ can be obtained and used as thin, transparent sheets having a thickness of 1 nm to 5 μm, preferably 10 nm to 1 μm, and will become laminated to the basic substrate with the thermochromic layer thereon. Normally any SiO/Si0₂ and A1₂0₃ sheet ia applied onto a polymer backing or substrate to enhance physical strength.

PVDC can be applied as a pure coating, while PET, and polyamide are preferably applied as films, whereby an adhesive material is used to attach them to the underlying layer. The adhesive used should not affect any of the layers, either directly or indirectly via gas transfer through any layer.

Whether or not the layers are applied as coatings, i.e., applied as solution and then dried, sputtered, or as films, the thickness of the resulting layer is about 1 nm to 1 μm. Further the layers can be applied on one side of a substrate or on both.

The printing mixture, normally a water or solvent dispersion of the encapsulated thermochromic dye material, or UV curable printing inks can be applied between two layers of substrates, such as layers comprising UV light impermeable compounds and/or oxidation protecting material, the water or solvent dispersion being hardened between said layers.

The adhesive agents used to affix the films onto each other or the substrate is any adhesive agent that is compatible with the printing mixture, i.e. the chromic material and its encapsulation, that provides a fair adhesion, and that maintains its properties while heated and subjected to light radiation, e.g., is non-yellowing, when present in a display or otherwise.

The adhesive agent is preferably selected from the group consisting of polyurethane based adhesives, silicon based adhesives, polyvinyl acetate based adhesives, and acrylate based adhesives, whereby the choice of adhesive very much depends on the chromic material used, and its encapsulation. Other chromic materials are electrochromic dyes, and electrophoretic dyes. The latter are subject to a change of colour by means of an electric field applied, while the former, e.g., consisting of wolfram oxide, are subject to a change when an electric current is allowed to pass through creating an ion conversion. Electrophoretic dyes are produced by E-Ink and MIT (Massachuset Institute of Technology). Electrochromic dyes are produced by COAT.

The permeability of oxygen is as follows with regard to the materials mentioned above as preferred substances forming an oxygen blocking layer, viz.

PET 80 cm³/(m² x days x bar) PVDC ~ 8 cm³/(m² x days x bar), coating

EVOH ~2 cm³/(m² x days x bar), extruded in polyethylene

Si0₂, A1₂0₃ -0.2 cm³/(m² x days x bar), coating polyamide ~ 8 cm³/(m² x days x bar)

Al -0.15 cm³/(m² x days x bar), metal film

The thermochromic material can consist of material which is optically controlled by heat, and in particular microencapsulated liquid crystals, Polymer Dispersed Liquid Crystals

(PDLC) (Hitachi Maxell; 3M), and microencapsulated leucodye based thermochromic inks which all can change absorption of light when they become heated. PDLC and microencapsulated leucodye based thermochromic inks which all can change absorption of light when they become heated are preferred.

The invention will be further illustrated in the following example.

EXAMPLE

A five layer laminate was prepared in accordance with the following. An oxygen barrier is coated onto a white PET film establishing a white background for a print. The oxygen barrier consists of a Rayopp RXF of UCB films. It has a thickness of 25 μm and is a bioriented polypropylene film with PVDC coatings on both sides. This film is laminated onto the PET film using a 2 μm polyurethane glue. The white PET film is as such no good oxygen barrier. The PET film has a thickness of 50 μm and is e.g. a Melinex polyester film from Dupont.

The PET film is then printed using sceen printing technique for establishing the right thickness of 20 to 30 μm of print. On top of the print another oxygen barrier is laminated using the same polyurethane glue. Finally, on top of the second oxygen barrier an UV filter is laminated consisting of a polyester base of 50μm having an UV absorbing coating of 2 μm. The UV absorbing film is sold under the trade mark Tinuvin by Ciba-Geigy. The coating consists of hindered amines (HALS) which are able to absorb most of the UV-light and convert it into heat.

Other laminated transparent films having UV absorbing properties and oxygen protecting properties have been examined in an sun-accelerator Xenotest, 550W/m², black-body temperature 45 + 2°C, dry temperature 22 + 2°C having a prefilter simulating window glassing. Colour measurements were carried out using a Minolta Portable spectrophotometer CM- 508d, measuring in CIE Lab scale.

The laminate used a COURTGUARD UV-filter and the PET film was coated on its backside using a 9 μm aluminum foil and the front side of the 12 μm PET was coated with 2 μm PVDC. The thermochromic printing was a UV cured thermochromic ink 25 μm thick having a switching temperature of 62°C. The original colour was blue. Comparison was made using a printed PET film only. Three different laminates were produced, viz: Oxygen barriers on both side + UV-filter; Oxygen barrier only; UV-filter only. The following results were obtained:

Protection Durability¹ (hrs)

No protection 50

UV filter 300

Oxygen barriers 300

UV filter + oxygen barriers 800 ' The durability is defined as when the thermochromic material reach a ΔE ~ 15 (CIE Lab scale). EXAMPLE 2

A leucodye ink was printed onto a transparent substrate consisting of a laminate of a UV filter having a thickness of 50 μm (SENSITISERSR) onto which an oxygen barrier (PET carrying SiO/Si0₂ coating of 10 nm) had been laminated by means of glue lamination. Onto the substrate surrounding colour containing polymer film had been affixed by means of heat lamination before printing the leucodye ink. The leucodye was applied in 2 to 3 applications and was then UV cured. Curing may take place after each application. Onto the leucodye (thermochromic) layer a background dye was applied in 1 to 3 layers. Finally, an oxygen barrier consisting of an Al-sheet was applied onto the background dye. The final layer can be applied using either a glue technique or a non-glueing technique. In the latter case, the final background dye layer is cured to the oxygen barrier, in particular if the oxygen barrier should consist of PET provided with a SiO/Si0₂ coating.

Other techniques for adhering the different layers to each other is by means of self-adhering sheets, or by means of an adhesive film having no backing substrate.

Claims

1. Transparent laminate comprising one or more colour changing materials provided with an UV light filter, characterized in that it comprises at least one layer comprising one or more colour changing materials, and at least one, substantially gas impermeable layer.

2. Laminate according to claim 1 , characterized in that a substantially UV light impermeable layer is present.

3. Laminate according to claim 1-2, characterized in that the substantially UV light impermeable layer prevents light having a wave length of less than 360 nm to penetrate the layer.

4. Laminate according to claim 1-2, characterized in that the substantially UV light impermeable layer prevents light having a wave length of less than 400 nm to penetrate the layer.

5. Laminate according to claim 1-2, characterized in that the substantially UV light impermeable layer prevents light having a wave length of less than 450 nm to penetrate the layer.

6. Laminate according to claim 1, characterized in that it further comprises at least one substantially gas impermeable layer.

7. Laminate according to claims 1-6, characterized in that the layer comprising the colour chaning material, on one side thereof is provided with a substantially gas impermeable layer, and on its other side is provided with a substantially UV light impermeable layer as well as a gas impermeable layer in arbitrary order.

8. Laminate according to claims 6-7, characterized in that the substantially gas impermeable layer is substantially impermeable to oxygen, ozone, carbon dioxide, water, lower alcohols and lower amines, including ammonia, in gas phase.

9. Laminate according to claims 1-9, characterized in that the different layers have substantially the same thermo coefficient of expansion.

10. Laminate according to claims 1-9, characterized in that the substantially UV light protecting layer comprises benzophenones, benzotriazones, hindred amines or combinations thereof.

11. Laminate according to claims 1-9, characterized in that the substantially gas protecting layer comprises polyamide resins, polyvinyldiene chloride resins (PVDC), hydrolyzed ethylene vinyl acetate resins (EVOH) A1₂0₃ and/or SiO/Si0₂.

12. Laminate according to claims 1-9, characterized in that the substantially gas protecting layer comprises an oxygen scavenger.

13. Laminate according to claim 7, characterized in that the substantially gas protecting layer is placed closest to the layer comprising the colour changing material.

14. Laminate according to claim 7, characterized in that the substantially light protecting layer is placed closest to the layer comprising the colour changing material.

15. Laminate according to claim 6, characterized in that the substantially gas protecting layer comprises a polymer substrate coated with a gas impermeable layer on one or two sides.

16. Laminate according to claim 15, characterized in that the colour changing material consists of thermochromic material.

17. Laminate according to claim 15, characterized in that the colour changing material consists of electrochromic material.

18. Laminate according to claim 15, characterized in that the colour changing material consists of electrophoretic material.

19. Method for preparing an laminate according to claims 1-18, characterized in that a transparent substrate (1 ; 4) comprising an UV filter and/or gas barrier is provided with a colour changing material (2) onto which a background dye is applied and onto which latter a second gas barrier is optionally applied, whereby the colour changing material is printed directly onto the transparent substrate.

20. Object carrying thermo variable information, characterized in that it comprises a substrate having applied thereon a laminate according to one or more of claims 1-18, as well as a heating and/or electric source.

21. Display carrying a variable infoonation, characterized in that it comprises a substrate having applied thereon a laminate according to one or more of claims 1-18, as well as a heating and/or electoc source.