Interactive coating for end printing

Abstract

Thermochromic coatings are improved by mixing thermochromic capsules with polymer resins in a manner that imparts shelf stability to flowable precursors that may be cured quickly using dodecylbenzenesulfonic acid and/or other acid catalysts to form relatively hard coatings that are capable of withstanding machine operations, such as the operations needed to make beverage can lids, bottle caps, pull tabs and the like.

Claims

1. A method of coating a substrate, said method comprising: providing a thermochromic pigment comprising an encapsulated thermochromic system including a leuco dye, a developer, and a solvent; providing a vehicle including a polymerizable resin; providing an acid catalyst which catalyzes curing of said polymerizable resin; applying said thermochromic pigment, said vehicle, and said acid catalyst to said substrate to form a thermochromic coating on said substrate; and curing said polymerizable resin in less than about 20 seconds to provide a cured thermochromic coating having a thickness of between about 1 mg/in.sup.2 and 5.5 mg/in.sup.2.

2. The method of claim 1, further comprising: (i) combining said thermochromic pigment and said vehicle to provide a combined thermochromic pigment and vehicle; (ii) next, applying said combined thermochromic pigment and vehicle to said substrate; (iii) next, applying said acid catalyst to said combined thermochromic pigment and vehicle on said substrate to foul said thermochromic coating on said substrate; and (iv) next, curing said polymerizable resin to provide said cured thermochromic coating.

3. The method of claim 1, further comprising combining said thermochromic pigment, said vehicle, and said acid catalyst prior to application to said substrate to form said thermochromic coating on said substrate.

4. The method of claim 1, further comprising providing said thermochromic pigment as a reversible thermochromic pigment which exhibits reversible thermochromic behavior.

5. The method of claim 1, further comprising providing said thermochromic pigment which achieves a color change between a temperature of about 5 Celsius to about 65 Celsius.

6. The method of claim 1, further comprising providing said polymerizable resin as one selected from the group consisting of: polyester, polyurethane, urethane, acrylic acid, and acrylate.

7. The method of claim 1, further comprising providing said acid catalyst in an amount of between about 1% to about 10% by weight of said thermochromic coating.

8. The method of claim 1, further comprising combining a conventional pigment with said thermochromic pigment.

9. The method of claim 1, further comprising providing said acid catalyst as a benezenesulfonic acid substituted with at least one alkyl group having between 1 and 20 carbons.

10. The method of claim 9, further comprising providing said acid catalyst as dodecylbenezenesulfonic acid.

11. The method of claim 1, further comprising forming said thermochromic coating on said substrate which comprises metal.

12. The method of claim 11, further comprising forming said thermochromic coating on said metal which comprises aluminum.

13. The method of claim 12, further comprising forming said thermochromic coating on said aluminum which comprises coil stock.

14. The method of claim 13, further comprising forming said thermochromic coating on said coil stock via a roller coating application.

15. The method of claim 13, further comprising coiling said coil stock into a roll following said curing of said polymerizable resin.

16. The method of claim 13, further comprising applying mechanical forces to said coil stock to form can ends, tabs, caps, and closures.

17. The method of claim 16, further comprising curing said polymerizable resin to provide said cured thermochromic coating prior to applying said mechanical forces to said coil stock to form said can ends, said tabs, said caps, and said closures.

18. The method of claim 16, further comprising providing said cured thermochromic coating on said can ends, said tabs, said caps, or said closures as a cold indicator.

19. The method of claim 16, further comprising topping a beverage can with said can ends, said tabs, said caps, or said closures.

20. The method of claim 19, further comprising filling said beverage can with a beverage prior to topping said beverage can with said can ends, said tabs, said caps, or said closures.

Description

BRIEF DESCRIPTION OF THE FIGURE

(1) The FIGURE shows a beverage can lid with a thermochromic coating.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

(2) Thermochromic ink coatings contain, in combination, a vehicle and a pigment including thermochromic microcapsules. The thermochromic microcapsules are preferably present in an amount ranging from 1% to 50% of the coating by weight on a sliding scale. The vehicle contains a solvent that is preferably present in an amount ranging from 25% to 75% by weight of the coating. The vehicle contains a dodecylbenzenesulfonic acid curing agent present in an amount ranging from about 1% to about 10% by weight of the coating.

(3) Pigment

(4) Careful preparation of encapsulated reversible thermochromic material enhances coating stability in the presence of low molecular weight polar solvents that are known to adversely affect thermochromic behavior. One skilled in the art of microencapsulation can utilize well-known processes to enhance the stability of the microcapsule. For example, it is understood that increasing the cross linking density will reduce the permeability of the capsule wall, and so also reduces the deleterious effects of low molecular weight solvents. It is also commonly understood that, under certain conditions, weak acids with a pK.sub.a greater than about 2 may catalyze microcapsule wall polymerization and increase the resulting cross linking density. It is presently the case that using formic acid as a catalyst enhances solvent stability of blue thermochromic microcapsules in the presence of low molecular weight ketones, diols, and aldehydes at room temperature. Further, it is well understood that increasing the diameter of the thermochromic microcapsule can result in enhanced solvent stability.

(5) The selection of material for use as the non-polar solvent for the thermochromic dye and color developer that is encapsulated within the thermochromic pigment determines the temperature at which color change is observed. For example, changing the solvent from a single component to a two component solvent system can shift the temperature at which full color is perceived almost 7 C. from just under 19 C. to 12 C. The present disclosure shows how to apply this knowledge in preparing resin-based vehicle coatings for use in can and coil coatings with full color temperatures, i.e., the temperature at which maximum color intensity is observed, as low as 5 C. and as high as 65 C. No adverse effects on the physical properties of the resulting coating were observed as the full color temperature was changed over the above range by the use of different straight chain alkyl esters, alcohols, ketones or amides.

(6) Thermochromic materials including encapsulated thermochromic systems with a variety of color properties may be purchased on commercial order from such companies as Chromatic Technologies, Inc., of Colorado Springs, Colo.

(7) Control over observed color intensity is demonstrated in several ways, generally by providing increased amounts of pigment. For a typical coating, material thickness ranges from 1 mg/in.sup.2 to 6 mg/in.sup.2. Very intense color is observed for coatings with thickness greater than about 3 mg/in.sup.2. Increasing thermochromic pigment solids can also result in a more intense observed color even when coating thickness is decreased. However, dried film properties such as flexibility and toughness may be compromised if too much thermochromic pigment is incorporated. The optimal range of thermochromic pigment solids is within 5 to 40% by weight of the coating.

(8) Vehicle

(9) Physical properties of the finished coating can be significantly affected by the selection of resin to be used. When no resin is used in formulating a reversible thermochromic coating, a matte finish is achieved that is able to be formed into can ends, tabs, caps and/or other closures. While this result may be desired, the inclusion of a low viscosity, relatively low molecular weight resin, monomer, oligomer, polymer, or combination thereof, can enhance gloss and affect other physical film properties such as hardness, flexibility and chemical resistance. The resin is designed to supplement the total solids deposited on the substrate, thus impacting the physical properties of the dried film. Any resin material, monomer, oligomer, polymer, or combination thereof that can be polymerized into the commercially available can and coil coating material is suitable for inclusion in the formulation of the current reversible thermochromic can and coil coating. Acceptable classes of resins include, but are not limited to polyester, polyurethane, urethane, acrylic acid and acrylate, or other types of resin systems with suitably high solids content.

(10) Final coating properties such as chemical resistance, hardness and flexibility can be manipulated by selection of cross linkers or curing agents. Materials that readily react with, and incorporate into, the selected resin system is suitable for inclusion as a cross linker or curing agent. Examples include, but are not limited to primary, secondary, tertiary, and cyclic aliphatic amines, blocked amines, amino resins with a range of alkylation, aromatic amines, polyamines, polyamides, amidoamines, ketimines, melamine resins, isocyanates or resins that can be cured using ultraviolet radiation and dodecylbenzenesulfonic acid. In one preferred embodiment, the curing agent is dodecylbenzenesulfonic acid. Care should be taken to balance reactivity needs with pot life and/or shelf life. For example, if the curing agent reacts too quickly with the resin, the reversible thermochromic coating may cure before the coating can be applied to the aluminum or steel substrate.

(11) In order to ensure the reversible thermochromic coating fully cures before the coil is re-wound, accelerators and/or catalysts may be added to the coating formulation. Examples of suitable materials for use as cure accelerators or catalysts include, but are not limited to; imidazoles, amidoamines, linear phenolics, blocked and unblocked acid catalysts, isocyanates, dihydrazides or photoinitiators and dodecylbenzenesulfonic acid. In one preferred embodiment, the curing agent is dodecylbenzenesulfonic acid. Curing agents that quicken the cure rate to less than about 20 seconds but do not permanently activate the thermochromic pigments include dodecylbenzenesulfonic acid. Dodecylbenzenesulfonic acid or other acid catalyst curing agents containing dodecylbenzenesulfonic acid include at least the following acid catalyst curing agents, for example: A 40S; ABS 100; Ambicat LE 4476; B 121; B 121 (surfactant); Bio-Soft S 100; Bio-Soft S 101; Biosoft S 126; Calsoft LAS 99; Cat 6000; Catalyst 600; Catalyst 6000; Cycat 600; DBS; Dobanic acid; Dodecylbenzenesulphonic acid; E 7256; Elfan WA Sulphonic Acid; LAS 99; Laurylbenzenesulfonic acid; Lipon LH 500; Maranil DBS; Marlon AS 3; Nacconol 98SA; Nacure 5074; Nacure 5076; Nansa 1042; Nansa 1042P; Nansa SSA; Neopelex FS; Neopelex GS; Neopelex GS-P; P 3 Vetralat; Pelex F 25; Polystep A 13; Rhodacal SSA/A; Richonic Acid B; S 100; Soft Osen 5S; Sulfosoft; Sulframin 1298; Sulframin Acid 1298; Taycacure AC 430; Taycapower L 120D; Taycapower L 121; Taycapower L 122; Ufacid K; Witco 1298; Witco 1298 Acid Soft; Witco 1298 Soft Acid; Witconic 1298 Hard Acid; Witconic 1298 Soft Acid; blocked or unblocked acid catalysts; Decotherm 255e, Nacure 2500, cycat 4040, cycat 4045, cycat 600, paratoluene sulfonic acid, amine blocked paratoluenesulfonic acid; and n-Dodecylbenzenesulfonic acid.

(12) Coating properties can also be manipulated with the inclusion of natural or synthetic waxes. For example, carnuba, polytetrafluoroethylene (PTFE), or a combination thereof may be included to affect physical film properties such as slip, coefficient of friction and abrasion resistance.

(13) Adequate dispersion of thermochromic pigment throughout the resin is an aspect of achieving high quality coatings for commercial use. The inclusion of additional molecular or polymeric dispersing aids, such as nonionic, anionic, cationic or zwitterionic surfactants, polymers or copolymers, can ensure adequate dispersion. Active diluents, in addition to reacting with the resin selected, may also function as a dispersing aid. Furthermore, active diluents can reduce the coating viscosity and affect film flexibility and impact resistance. Suitable materials to be included as an active diluent include but are not limited to, aliphatic or cycloaliphatic glycidyl ethers, monofunctional and polyfunctional glycidyl ethers.

(14) Final adjustments to coating rheology may be made by the addition of select solvents. A reversible thermochromic coating can be adjusted to meet rheological criteria established for use in a roller coating application. Many solvents are available for this purpose. Care should be exercised to select solvents most compatible with thermochromic pigment systems. Nonpolar solvents or solvents of low polarity are preferred. However, modifications to thermochromic pigment preparation initiated by the inventors as well as the different coating preparations available to the inventors increased the solvent options available to include low molecular weight polar solvents such as butyl carbitol acetate.

(15) The chemical stability and shelf life of the reversible thermochromic coating may be enhanced in various ways. In one aspect, this involves separating the thermochromic pigment from organic solvents. A two-part coating system containing thermochromic pigment and resin in Part A and commercially available coating material and other solvents in Part B is then mixed immediately prior to coating aluminum or steel alloys. The shelf life of the fully mixed coating material ranges from several days to many months depending on the identity of the other components selected.

(16) For those situations for which a two-part solution is not preferable, stability can be balanced with convenience by preparing a one-part reversible thermochromic coating. In this case, careful selection of formulation components is paramount. The use of water-based commercially available can and coil coating material enhances the shelf life stability by minimizing the amount of organic solvents in contact with the thermochromic pigment system. In one example, coating degradation was observed within 14 days when red thermochromic coatings were prepared using butyl carbitol acetate and stored at room temperature. Enhanced stability was observed when formulation components were modified as well as when stability enhanced thermochromic pigment systems were used.

(17) The non-limiting embodiments that follow teach by way of example and prophetic example and should not be construed as unduly limiting the scope of this disclosure.

Example 1Two Part Coating

(18) Part A (30%) Thermochromic pigment (any color)

(19) Part B (70%) Clear Coating

Example 2Two Part Coating

(20) Part A (60%) 45% Thermochromic Pigment (any color) 50% Polyester resin 3.3% Dispersing aid 1.7% Dodecylbenzenesulfonic acid.

(21) Part B (40%) 85% Clear Coating 15% Solvent to reduce viscosity

Example 3Two Part Coating

(22) Part A (60%) 45% Thermochromic Pigment (any color) 50% Polyurethane resin 3.3% Dispersing aid 1.7% Dodecylbenzenesulfonic acid.

(23) Part B (40%) 85% Clear Coating 15% Solvent to reduce viscosity

Example 4

(24) 30% thermochromic pigment

(25) 60% polyester resin Decotherm 290E

(26) 10% acid catalyst (Cycat 600)

Example 5

(27) 30% thermochromic pigment

(28) 60% polyurethane resin

(29) 10% acid catalyst (Cycat 600)

(30) The FIGURE depicts an end printing on an aluminum can using fast curing thermochromic ink formulations disclosed herein.

(31) As opposed to placing thermochromic ink on the entire lid, it is possible to coat selected elements of the can lids, such as the just the tabs, just the closures, or both the lids and the tabs without the closures. The same coating or one having a different color and/or color transition temperature may be selectively applied to any feature of a lid, such as a surface, closure, an area surrounding closure, and/or the rim.

(32) The tab of a can printing with thermochromic inks of the present disclosure may be manufactured from coil stock that is pre-coated with any of the coatings as described above before the tab is formed.

(33) In one embodiment, a method for applying the thermochromic ink coating disclosed herein to the coil stock of aluminum is disclosed. As the sheet aluminum unwinds from a roll, a roller coaster receives an uncured thermochromic coating material, as described above. This places a liquid coating or film on the aluminum sheet. This film is cured, for example by the application of dodecylbenzenesulfonic acid, at curing station, and the sheet including the dried film is coiled onto a roll. This roll may then be used to make beverage can components as discussed above. It will be appreciated that additional coating operations (not shown) may be performed on a sheet of metal and/or plastic or any other container material.

(34) Those skilled in the art will appreciate that the various embodiments described herein teach by way of example and not by limitation. These embodiments may be subjected to insubstantial changes without departing from the true scope and spirit of the invention. Accordingly, the inventors hereby state their intention to rely upon the Doctrine of Equivalents in protecting their rights in what is claimed.