SE516028C2 - Transparent laminate of thermochromic material with UV light filter and gas impermeable layer - Google Patents

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

25 30 516 028 2.

Ternochrome pigments are pigments that go from one state to another when heated.

Thus, they normally show a color at ambient temperature and become transparent when heated, ie become colorless. This effect can be used in signs where the sign shows e.g. a text or other data at ambient temperature while the text disappears when the sign is heated. This can be used at a cash register to inform people that tickets are available when the sign is heated, and when you cool the sign, or turn off the heat, it informs you that no tickets are left.

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

Thermochromic pigments suffer from the disadvantage of being UV-sensitive and sensitive to oxidation in the presence of fi -it oxygen. It has been proposed (WO 94/27336) to protect a UV sensitive material by applying a UV light protective coating over the plate to protect the temperature sensitive material. Furthermore, the same document proposes the incorporation of an antioxidant with the thermochromic material and / or the encapsulation of materials containing tin chromium material.

However, the addition of additives to the encapsulating material is negative with respect to the effectiveness of the tin chromic material in expressing its brilliance, contrast and color. Thus, such encapsulation creates opacity of the colors and reduces their readability.

The use of a UV protective barrier that forms part of a sign increases the costs due to the aging of the UV protective agents. Thus, a UV protective coating of a laminate according to the present invention minimizes costs and provides a basis for a replacement in a simpler and more efficient manner.

Furthermore, JP7205547 discloses the use of a UV reflective material on reversible, heat-sensitive sign material which reflective material has a reflectance of less than 50% UV of the wavelength 350 nm. This means that more than 50% of the UV light with 350 nm will pass through, and will thus have detrimental effects on the tin chromium layer.

Although many patents have been granted for terinochrome signs, such signs have not yet reached commercial levels, due to the sensitive ternochrome materials used, and the problem of solving this disadvantage.

Summary of the present invention It has now surprisingly been found possible to solve this problem by the present invention which is characterized in that it comprises at least one layer comprising one or more thermochromic materials, and at least one, mainly UV light-transmissive layer.

Thus, the invention relates to transparent laminates comprising one or more thermochromic materials. A further aspect of the invention relates to heatable plates comprising at least one such transparent laminate, and in general to other objects comprising such a transparent laminate.

Additional characteristics will be apparent from the appended claims.

The laminate of the present invention is primarily intended to provide a physical contact between the thermochromic material and the protective layer (s).

By means of the present invention it is possible to significantly increase the life of a thermochromic plate and thereby obtain a commercially acceptable product by avoiding degradation with UV light and short-wave visible blue light, as well as degradation by oxidation while maintaining the brilliance and contrast of thermochromic data such as given e.g. on a sign.

In the following, the present invention will be explained in more detail with reference to some exemplary teachings, some of the embodiments being shown with reference to the accompanying drawing, however, without being limited thereto. Brief Description of the Drawing FIG. 1 shows an illustrative example of a transparent laminate according to 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 sign utilizing the present invention.

Detailed description In the drawing, the reference numerals used refer to the same type of layer used to build the laminate. l indicates a base substrate consisting of e.g. a polyester (PET) film with a thickness of about 250 μm to which a thermochromic ink 2 has been applied. The base substrate may be either transparent or non-transparent but is preferably non-transparent to form a background to the chromatic layer and to hide any equipment placed behind the substrate in an application thereof. On top of the substrate there is a layer 3 consisting of a UV-protective material, an optical filter, arranged. The filter prevents light with a wavelength of up to 420 nm from penetrating the layer, and thus reaching the tennochrome layer. Said layer has a thickness of about 10 μm.

Fig. 1 illustrates a basic design of a protected tin chromium layer. In Fig. 2, the protection has been further increased by adding an oxygen-blocking film 4, said mlm having been applied on both sides to prevent oxygen from reaching the tennochrome layer from either side.

Fig. 3 illustrates a further embodiment where the oxygen-blocking layer has been applied between the thermochromic layer 2 and the UV-protective layer 3 on the transparent side of the substrate.

Fig. 4 shows a sign on which a substrate according to Fig. 3 has been applied, the sign comprising a heating surface for heating the surface covered by the tin chromic printing material.

The substrate is removable from the plate to make changing substrate / laminate easier.

The UV protective layer consists of polymers with a UV protective agent therein, such as COURTGUARDR. UV absorbers are often of the type used in sunscreen lotions.

Other UV and light-protecting agents are angle barriers, ie reflective barriers that allow the right to react from one angle but not from others. Other means are layers which only allow polarized light thereby. A photochromic material can also be used to provide light protection and / or enhance the readability of a plate provided with such a laminate.

The oxygen-blocking layer consists of one or fl era of the following substances, namely poly-aInid polymers (NYLONR), polyvinyl diene chloride polymers (PVDC), hydrolyzed ethylene vinyl acetate polymers (EVOH), SiOZ, AIZOL which all act as oxygen-blocking material. Even polyester (PET) resists oxygen penetration to some extent. Another oxygen blocking material is metallic aluminum which can preferably be applied to the back of the substrate when it is a non-transparent material.

Other oxygen blocking materials are the so-called oxygen consumers, which are available, whereby such oxygen consumers can be obtained as thin films or as granules which can later be included and extruded together with each oxygen safe layer.

SiO 2, and Al 2 O 3 can be obtained and used as thin, transparent glass films with a thickness of 0.5 to 10 μm, preferably 5 μm, and can be laminated to the base substrate with the thermochromic layer thereon.

PVDC can be applied as a pure coating, while PET and polyamide are preferably applied as films, with an adhesive material being used to attach them to the underlying layers. 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, ie applied as a solution and then dried, or as an adhesive, the thickness of the resulting layer is about 0.5 to 10 μm. Furthermore, the layers can be applied to one side of a substrate or to both. The pressure mixture, normally an aqueous dispersion of the encapsulated thermochromic dye material, can be applied between two substrate layers, such as layers comprising UV light impermeable compounds and / or oxidation protective materials, the aqueous dispersion being hardened between said layers.

The adhesives used to attach the elements to each other or to the substrate are any adhesives which are compatible with the pressure mixture, i.e. the thermochromic material and its encapsulation, which give a good adhesion, and which retain their properties when heated and irradiated as such. it is in a sign.

The adhesive is preferably selected from the group consisting of polyurethane-based adhesives, silicone-based adhesives, polyvinyl acetate-based adhesives, and acrylate-based adhesives, the choice of adhesives being very dependent on them.

The oxygen permeability is as follows with respect to the materials mentioned above as preferred substances forming an oxygen-blocking layer, namely PET 80 cm 3 / (m2 x day x bar) PVDC ~ 8 cm 3 / (m2 x day x bar), coating EVOH ~ 2 cm3 / (m2 x day x bar), extruded in polyethylene SiO2, Al2 O, ~ O.2 cmJ / (mz x day x bar), coating polyamide ~ 8 cms / (mz x day x bar) Al ~ 0. l5 cmS / (mz x day x bar), metal fi lm The thermochromic material can consist of materials that are optically controlled by heat and in particular microencapsulated fl surface crystals, Polymer Dispersed Liquid Crystals (PDLC), and microencapsulated leukodye based thermochromic colors which all may change light absorption when heated. PDLC and microencapsulated leukodye based thermochromic dyes which can all change light absorption when heated are preferred, while microencapsulated leukodye based dyes are most preferred. The invention will be further illustrated in the following examples.

EXAMPLE A five-layer laminate was prepared according to the following. An oxygen layer is coated on a white PET film which forms a white background for a print. The oxygen banner consists of a Rayopp RXF or UCB fi ch. It has a thickness of 25 μm and is a bio-oriented polypropylene film with PVDC coatings on both sides. This film is laminated to the PET film using a 2 μm polyurethane adhesive. As such, the white PET film is not a 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 screen printing techniques to obtain the correct thickness of 20 to 30 microns of pressure. On top of the pressure, an additional oxygen bairier is laminated using the same polyurethane adhesive. Finally, on top of the second oxygen barrier, a UV filter consisting of a polyester base of 50 μm with a UV absorbing coating of 2 μm is laminated. The UV absorbing film is sold under the Tinuvin brand by Ciba-Geigy.

The coating consists of hindered amines (HALS) which are capable of absorbing most of the UV light and converting it into heat.

Other laminated transparent films with UV absorbing properties and oxygen protective properties have been investigated in a Xenotest solar accelerator, 500 W / mz, black body temperature 45 + 2 ° C, dry temperature 22 + 2 ° C with a dry filter that simulates window glass.

Color measurements were performed using a Minolta portable spectrophotometer CM-508d, which measures on a CIE Lab scale.

The laminate used a COURTGUARDR UV filter and the PET film was coated on its back using a 9 μm aluminum foil and the front of the 12 μm thick PET film was coated with 2 μm PVDC. The thermochromic pressure was a UV cured thermochrome dye 25 μm thick with a conversion temperature of 62 ° C. The original color was blue. Comparison was made with a printed pure PET film. Three different laminates were produced, namely: oxygen barriers on both sides + UV filters; oxygen barrier only; UV filters only.

The following results were obtained: 516 028 8 PROTECTION DURATION * (m) No protection 50 UV filter 300 Oxygen barrier 300 UV filter + oxygen barrier 800 lThe duration is defined as when the thermochromic material reaches an AE = 15 (CIE Lab scale).

Claims (18)

10 15 20 25 30 516 028 (f PATENTKRAV Transparent laminate comprising one or fl your ternochrome materials provided with a UV light filter, characterized in that it comprises at least one layer comprising one or fl your tennochrome materials, and at least one, substantially gas-impermeable layer. Laminate according to claim 1, characterized in that a substantially UV light impenetrable layer is present. Laminate according to claim 1-2, prevents light with a wavelength of less than 400 nm from penetrating the layer. characterized in that the substantially UV-light impermeable layer prevents light having a wavelength of less than 400 nm from penetrating the layer. Laminate according to Claim 1, characterized in that the substantially UV-light impermeable layer prevents light with a wavelength of less than 420 nm from penetrating the layer. Laminate according to claim 1, characterized in that the substantially UV light-impermeable layer prevents light with a wavelength of less than 450 nm from penetrating the layer. Laminate according to claim 1, characterized in that it further comprises at least one further substantially gas-impermeable layer. Laminate according to claims 1-6, characterized in that the layer comprising the thermochromic material is provided on its one side with a substantially gas-impermeable layer, and on its other side is provided with a substantially UV light-impermeable layer and a gas-impermeable layer in any order. 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 the gas phase. Laminate according to Claims 1 to 8, characterized in that the different layers have substantially the same coefficient of thermal expansion. Laminate according to claims 1-8, characterized in that the substantially UV light protective layer comprises benzophenones, benzotriazones, hindered amines or combinations thereof. Laminate according to Claims 1 to 9, characterized in that the substantially gas-protective layer comprises polyamide polymers, polyvinylidiene chloride polymers (PVDC), hydrolysed ethylene vinyl acetate polymers (EVOH), Al 2 O 3 and / or SiO 2. Laminate according to claims 1-9, characterized in that the substantially gas-protective layer comprises an oxygen consumer. Laminate according to claim 7, characterized in that the substantially gas-protective layer is located closest to the layer comprising the thermochromic material. Laminate according to claim 7, characterized in that the substantially light protective layer is placed closest to the layer comprising the thermochromic material. Laminate according to claim 6, characterized in that the substantially gas protective layer comprises a polymer substrate with a gas impermeable layer on one or two sides. An article carrying tin-variable information, characterized in that it comprises a substrate applied thereto, a laminate according to claims 1-15 and a heating source. Sign bearing tin-variable information, characterized in that it comprises a substrate with applied thereon, a laminate according to claims 1-15 and a heating source. Method for producing a laminate according to claims 1-15, characterized in that a transparent substrate (1, 4) comprising a UV filter and / or gas barrier is provided with a thermochromic material (2) on which a background color is applied and on which later a second gas barrier is optionally arranged, the tin chromium material being printed directly on the transparent substrate.