Composition

Abstract

A composition comprises a polymer, a wax, and a thermochromic material. The polymer may be a polyolefin, polylactic acid, polyamide (e.g. casein), ethylene-vinyl acetate, polyurethane, polyolefin, pol

Description

The present invention relates to a composition, which could be an adhesive composition or a coating composition, that is able to change colour when exposed to different temperature conditions. In one aspect of the invention, the composition is a hot melt adhesive composition. Compositions, such as hot melt adhesives, are well known for their uses in many commercial and industrial applications, such as woodworking, packaging, labelling, the bonding of laminates and personal hygiene products. A hot melt adhesive is an adhesive which is solid at room temperature and melts with heating. In use, hot melt adhesives are heated for conversion into a liquid state and applied to a substrate in order that it may adhere to another substrate. The adhesive then cools, causing it to create an adhesive bond, securing the surfaces of the substrates together. Typical application temperatures for such compositions are in the range of 80-200°C. The use of such temperatures means that there is a risk of bums with operators applying such adhesives. Many of the world’s products used in industry can be heat sensitive and require being stored at temperatures at which they will not perish or degrade, or be able to deteriorate in any way. It is therefore important that they are not stored or exposed to temperatures which may facilitate such deterioration. In such circumstances, it would be useful to have some sort of visual indicator which shows whether the packaging had been exposed to temperatures outside of the optimum range for the products, and whether the products have been exposed to any risk of deterioration. For example, certain perishable foodstuffs such as chocolate or frozen products would be ruined if exposed to temperatures which were too high during processing or transportation, and in the absence of a visual indicator of this, it would be impossible to know if this had happened until the packaging was opened, for example at destination or by the consumer. Thermochromic materials have been used as visual indicators previously. For example, they have been used in substances such as paints and inks. US 4,228,761 describes a thermochromic paint which is to be used in coating the exterior of a heat-deformable polymeric article, in order to indicate when the temperature to which the polymeric material has been exposed has reached a sufficient temperature to melt an adhesive located on an interior side of the polymeric article, while simultaneously not also degrading the polymeric article. US 6,413,305 describes a thermochromic ink composition for use on security documents such as checks (or cheques), which provides a reversible color change in response to heat. The ink composition includes a thermochromic aqueous slurry and an ink vehicle comprising either a phenolic modified rosin and a compatible oil, a styrene maleic anhydride resin and a glycol, or an acrylic resin varnish. Adhesives which change colour are also known; JP19940272799 describes a hot-melt adhesive which is transparent in a melt state and opaque at normal temperatures, the adhesive comprising at least 20 wt% of a propylene component, and a tackifier (e.g. a natural rosin), but does not use any thermochromic dye or pigment. EP 54,155 describes hot-melt thermoplastic adhesives containing a thermochrome dye, which displays a change in colour close to the melting point of the adhesive, in the temperature range between the temperature where a satisfactory moistening effect for the adhesive is present, in order that it may provide effective adhesion, and the temperature where it is no longer possible to assure the presence of the satisfactory moistening effect. The adhesive in this document is applied using a glue gun, rather than using an open tank vessel. Potential uses of the composition of the invention when used as an adhesive include being able to provide a visual indicator when it is exposed to an elevated or reduced temperature, for example, in order that it may be able to inform or warn a worker applying such adhesives that the adhesive is hot and therefore carries a risk of bums if touched. Another potential use of the composition of the invention when used as an adhesive is to provide a visual indicator of when packaged goods have been exposed to temperatures which may be detrimental to the quality of the goods. This can be done in such a way that it is hidden behind the packaging flap and therefore only visible to those in the know. A third potential use of the composition of the invention when used as an adhesive is to provide a visual indicator of when an adhesive used for security purposes has been exposed to hot or cold temperatures which may compromise the security of the packaging the adhesive is applied to. A fourth potential use of the composition of the invention is as a coating composition, where the composition is applied as a coating onto a surface, and is able to provide an indication of the temperature of the coating, or exposure of the coating to temperatures which are too high or too low which may compromise a product or the safety of workers nearby. Therefore, in accordance with the invention, there is provided a composition comprising a polymer, a wax and a thermochromic material. In one embodiment of the invention, the composition may be a hot melt adhesive. The composition may be in granulated form and used in open tanks, but is not limited to this form or type of usage. Existing compositions would not work with the present invention. The present invention utilises wax in the composition which gives a technical advantage in reducing the viscosity of the adhesive, which increases the setting speed of the adhesive. This allows the adhesive of the invention to be used on and support high speed automated production lines, where a faster setting time is critically important. The composition of the invention triggers a colour change at far lower temperatures in comparison to the prior art outlined in EP 54,155; and the colour change of the composition of the invention is in no way linked to the melt point of the adhesive, which is the case for EP 54,155. For example, the colour change of the composition could be triggered at about 25-35°C for chocolate, where blooming / deterioration of the product may occur, the colour change could trigger at about 1-20°C for ice-cream where the product spoils / deteriorates, and also for health and safety applications, the colour change could trigger at about >50°C to warn operators of the risk of injury through bums. Examples of polymers which may be used in the present invention include, but are not limited to, ethyl vinyl acetate (EVA), or a metallocene-processed polyolefin, or a polyvinyl hydroxide, or a polyvinyl alcohol, or a polyvinyl pyrrolidone (PVP), or an amorphous poly alpha olefin (APAO), or a polyamide, or a polyurethane or a polyolefin; or a water-dispersed polymer, such as an acrylic emulsion, or a casein, or a polysaccharide, such as starch, or a polylactic acid (PLA), or a polyvinyl acetate, or a vinyl acetate ethylene (VAE), or a combination of any two or more thereof. The composition may also be a water-based wax emulsion. The composition of the invention may be a non-pressure sensitive adhesive (PSA). As used herein, a metallocene processed polyolefin is a polyolefin elastomer, produced using a metallocene catalyst. The use of a metallocene polyolefin as a catalyst to process the polyolefin provides good thermal stability, which would not be the case for example with an ethyl vinyl acetate polymer, This is particularly important for a thermochromic application, as thermooxidation of the thermochromic dye can result in colour changes which are not as obvious to see, e.g. red to brown. The polymer may be present in the composition at an amount of between about 1 to about 99.99 wt%, by weight of the composition. For a water or solventbased composition, the polymer may typically be present in an amount of between about 1 to about 80.00 wt%, by weight of the composition. The wax used in the present invention may comprise a natural wax or a synthetic wax. The wax may be present in the composition at an amount of between about 0.01 to about 50 wt%, by weight of the composition; typically, between about 10 to about 40 wt%, or between about 15 to about 30 wt%, or between about 20 to about 25 wt%, by weight of the composition. According to one embodiment, a small amount of wax with a coloured (e.g. red) dye material may be used in addition to a second wax component, in order to support the appropriate colour change required with the thermochromic component. The wax may be selected from a petroleum derived wax such as paraffin wax, a microcrystalline wax, a Fischer-Tropsch wax (i.e. a synthetic wax produced from natural gas and air using the Fischer-Tropsch process), a polyolefin wax such as a polyethylene wax or a wax from natural sources, such as beeswax, a castor wax, a carnauba wax, soy based wax, rapeseed wax, palm wax, stearic acid vegetable wax, coconut wax, candelilla wax, sunflower wax, rice bran wax, or a combination thereof. Examples of the wax which may be used in the present invention include, but are not limited to, a paraffin wax with a melting point between about 50-70°C, a micro crystalline wax with a melting point between about 60-90°C and a Fischer-Tropsch wax with a melting point between about 50-130°C. In one embodiment of the invention, the wax may form a wax-based emulsion. The adhesive composition may also contain one or more further components selected from, but not limited to fillers such as CaCOs, an anti-oxidant, a viscosity modifier, and / or a resin / tackifier. In one embodiment, the thermochromic material may be made up in the form of a wax, or wax emulsion, containing a thermochromic pigment, dye or ink. In one embodiment of the invention, the adhesive composition does not contain a plasticiser. By “thermochromic material”, it is meant herein any ink, dye or pigment material which is temperature sensitive, which may or may not be micro encapsulated, that is able to change colour with exposure to different temperatures, both elevated temperatures and lower temperatures nearer freezing point. The colour change may be reversible or irreversible, and between any different colours as desired. However, a more extreme and distinct colour change, such as from a lighter colour to a stronger or darker colour - such as changing from blue at room temperature to red at an elevated temperature to indicate that the adhesive composition is hot - will provide a clearer visual indicator of the temperature change. By “elevated temperatures”, it is meant herein any temperature above about 20°C. By “reduced temperatures” or “lower temperatures”, it is meant herein any temperature below about 5°C. Different thermochromic materials are commercially available which change colour at specific temperatures. It is therefore possible to manufacture a bespoke composition for a particular purpose, which will change colour at any temperature which suits the desired purpose. One or more thermochromic materials may be present in the same composition, as desired. The thermochromic material used in the present invention may indicate a colour change at any temperature from about -50°C to about 250°C; from about 10°C to about -50°C for chilled / frozen goods, and about 10°C to about 250°C for other goods. The temperature range for the colour change can vary depending on the specific application, i.e. it may be different for each of, for example, chocolate, frozen goods and standard packaging, but the temperature of the colour change is not linked to the melt point of the adhesive. Potential uses of the composition of the invention include to provide a visual indicator when it has been exposed to an elevated temperature, in order to inform or warn a worker applying such adhesives that the adhesive is hot and therefore carries a risk of bums if touched. Alternatively, it can be used as an indicator to show if the final product has been subjected to lower temperatures, outside of its “working” temperature or outside the temperature such a product was designed for. This can be useful in items such as bank security bags, where adhesives can be frozen to make the adhesive brittle and fragile, with the purpose of compromising their security. Such lower temperature exposure can be indicated with an irreversible colour change, so it would be readily apparent that the product has been tampered or compromised. Alternatively, it is useful when the product it has been applied to has reached a certain temperature in its life time - such as a motor, or temperature perishable goods or to see if any breach of guarantees has occurred. A non-PSA (pressure-sensitive adhesive) composition used through open tank melt systems has never before been used for such an application. The colour change in the thermochromic material may be reversible or irreversible. When used for the purpose of a safety warning to a worker, it is desirable that the colour change is reversible, and the adhesive changes colour when it is hot, and then changes back to another colour as the adhesive cools down. In another aspect of the invention, however, it may be desirable for the colour change to be irreversible. An irreversible colour change provides a clear indicator if a package of goods has been exposed to temperatures which are too high or too low for the goods contained therein, as the colour of the adhesive will change colour upon such exposure and remain that colour. Similarly, if a security bag or package has been exposed to temperatures which are too high or too low and the adhesive may be compromised, an irreversible indication of this is also preferable. The thermochromic material may be present in the composition in an amount of between about 0.01 to about 25%, by weight of the composition. The thermochromic material will typically be present between about 0.01 to 10 wt%, better if between about 0.02 to 3 wt%, or best if between 0.10 to 0.80 wt%, by weight of the composition. According to a further aspect of the invention, there is provided a method of manufacturing a composition comprising a polymer, a wax and a thermochromic material, the method comprising combining the polymer, wax and thermochromic material together. The present invention also provides a method of providing a reversible or irreversible visual indication of when a composition has been exposed to elevated or reduced temperatures, the method comprising applying a composition comprising a polymer, a wax and a thermochromic material to a substrate, and exposing it to temperatures of between about -50°C to about 250°C. The invention will now be described further by way of example with reference to the following examples which are intended to be illustrative only and in no way limiting upon the scope of the invention. EXAMPLES Method The preparation of non-reactive Hot-Melt adhesive in a laboratory setting is a fairly simple process of heat and blend. The required components are weighed in a heat-proof container and the mixture is melted at high temperatures between 110-160° Celsius degrees typically in a heating mantle or laboratory oven. The preparation temperature depends on the molecular weight and softening point of the components used in the adhesive formula. The molten material is mixed either by hand using a glass rod or by mechanical stirrer until a homogenous mixture is achieved. Example 1 Metallocene processed Polyolefin 40.0 parts Hydrocarbon Resin 39.2 parts 5 Wax 20.0 parts Pentaerythritol tetrakis 0.40 parts Thermochromic dyes 0.35 parts Paraffin wax with Coloured Dye 0.05 parts 10 Example 2 Polylactic Acid 45.0 parts Hydrocarbon Resin 39.15 parts 15 Wax 15.0 parts Pentaerythritol tetrakis 0.40 parts Thermochromic dyes 0.40 parts Paraffin wax with Red Coloured Dye 0.05 parts 20 Example 3 Water 55.0 parts Defoamer 0.50 parts Wax emulsion 0.50 parts 25 Casein 15.6 parts Starch 10.0 parts Sodium Hydroxide 1.45 parts Urea 15.0 parts Biocide 0.15 parts 30 Aluminium Sulphate 17% 0.90 parts Thermochromic slurry 0.40 parts It is of course to be understood that the present invention is not intended to be 35 restricted to the foregoing examples which are described by way of example only. 19 1224

Claims

1. An adhesive composition comprising a polymer, a wax and a thermochromic material; wherein the polymer is selected from ethyl vinyl acetate (EVA), a metallocene processed polyolefin, a polyamide, a polyurethane or a polyolefin; a polysaccharide, polylactic acid, polyvinyl acetate, or vinyl acetate ethylene (VAE), poly vinyl alcohol, amorphous poly alpha olefin (APAO) or a combination of any two or more thereof; and wherein the wax is selected from a paraffin wax with a melting point between about 50-70°C, micro crystalline wax with a melting point between about 60-90°C and a Fischer-Tropsch wax with a melting point between about 50-130°C.

2. A composition according to claim 1, wherein the thermochromic material changes colour at a temperature from about minus 50°C to about +250°C.

3. A composition according to any preceding claim, wherein the thermochromic material is present in the adhesive composition in an amount of between about 0.01 to about 25 wt%.

4. A composition according to any preceding claim, wherein the colour change in the thermochromic material is reversible.

5. A composition according to any of claims 1-3, wherein the wherein the colour change in the thermochromic material is irreversible.

6. A composition according to any preceding claim, further comprising one or more further components selected from, but not limited to, an anti-oxidant, a viscosity modifier, and / or a resin / tackifier.

7. A composition according to any preceding claim, wherein the adhesive is a hot meltadhesive.CM8. A method of manufacturing a composition comprising a polymer, a wax and a thermochromic material as defined in any of claims 1-7, the method comprising combining the polymer, wax and thermochromic material together.

9. A method of providing a reversible or irreversible visual indication of when a composition has been exposed to elevated or reduced temperatures, the method comprising applying a composition comprising a polymer, a wax and a thermochromic material according to any of claims 1-7 to a substrate, and exposing it to temperatures of between about minus 50°C to about +250°C.