The present invention provides improved devices, systems and methods for repositioning teeth from an initial tooth arrangement to a final tooth arrangement. Repositioning is accomplished with a system comprising a series of polymeric shell appliances configured to receive the teeth and incrementally reposition individual teeth in a series of successive steps. The individual appliances may be formed from layers having different stiffnesses (elastic moduluses), and the stiffnesses of successive appliances may be different, or both.

This invention relates in general to a method of repositioning teeth for use in orthodontic treatment. Particularly, this invention relates to the use of orthodontic appliances for producing tooth movements. More particularly, this invention relates to the use of a plurality of elastic repositioning appliances for producing such tooth movements.
Orthodontic treatments involve repositioning misaligned teeth and improving bite configurations for improved cosmetic appearance and dental function. Repositioning teeth is accomplished by applying controlled forces to the teeth over an extended period of time. This is conventionally accomplished by wearing what are commonly referred to as xe2x80x9cbraces.xe2x80x9d Braces comprise a variety of appliances such as brackets, bands, archwires, ligatures, and O-rings. After they are bonded to the teeth, periodic meetings with the orthodontist are required to adjust the braces. This involves installing different archwires having different force-inducing properties or by replacing or tightening existing ligatures. Between meetings, the patient may be required to wear supplementary appliances, such as elastic bands or headgear, to supply additional or extraoral forces.
Although conventional braces are effective, they are often a tedious and time consuming process requiring many visits to the orthodontists office. Moreover, from a patient""s perspective, they are unsightly and uncomfortable. Consequently, alternative orthodontic treatments have developed. A particularly promising approach relies on the use of elastic positioning appliances for realigning teeth. Such appliances comprise a thin shell of elastic material that generally conforms to a patient""s teeth but is slightly out of alignment with the initial tooth configuration. Placement of the elastic positioner over the teeth applies controlled forces in specific locations to gradually move the teeth into the new configuration. Repetition of this process with successive appliances comprising new configurations eventually move the teeth through a series of intermediate configurations to a final desired configuration. A full description of an exemplary elastic polymeric positioning appliance is described in U.S. Pat. No. 5,975,893, and in published PCT application WO 98/58596 which designates the United States and which is assigned to the assignee of the present invention. Both documents are incorporated by reference for all purposes.
In addition to their ease of use, polymeric positioning appliances are generally transparent, providing an improved cosmetic appearance, and impart substantial force on the teeth, due to stiffness of the appliance. The stiffness of an elastic positioning appliance is a result of the modulus of the thermoformable polymer materials from which it is made. The higher the modulus of the materials, the higher the stiffness of the appliance. When a patient positions such an appliance over a prescribed group of teeth, one or more of the teeth will provide a base or anchor region for holding the positioning appliance in place while the stiffness of the polymeric material will impart a resilient repositioning force against one or a portion of the remaining teeth. However, the stiffer the appliance, the more difficult it is to slip the misaligned appliance over the teeth and fully engage the appropriate surfaces; the appliance often has the tendency to disengage or xe2x80x9cpop offxe2x80x9d. Likewise, once it is firmly seated, it is more difficult to remove. Further, a stiff appliance is less forgiving in cases of lowered patient compliance. If a patient were to remove the appliance for an unprescribed period of treatment time, the patient""s teeth may move slightly out of the planned tooth arrangement. When attempting to reapply the appliance, it may be too rigid to accommodate these slight differences and a new appliance may need to be created. Similarly, the tooth positions defined by the cavities in each successive appliance must not differ beyond a limiting dimension from those defined by the prior appliance or, again, it may be too rigid to accommodate the differences. Consequently, only small increments in tooth repositioning may be made with each appliance.
Thus, it would be desirable to provide tooth positioners, systems, and methods which apply adequate force to selected teeth yet overcome the inherent limitations of stiffness in the polymeric material. Likewise, it would be desirable to reduce the number of positioners required for a treatment plan by increasing the size of the repositioning increments throughout the plan. Further, it would be desirable to reduce the cost of lowered patient compliance by reducing the need for new appliances to be created for patient treatment resumption. At least some of these objectives will be met by the designs and methods of the present invention described hereinafter.
The present invention provides improved devices, systems and methods for repositioning teeth from an initial tooth arrangement to a final tooth arrangement. Repositioning is accomplished with a system comprising a series of polymeric appliances configured to receive the teeth in a cavity and incrementally reposition individual teeth in a series of successive steps. This is accomplished by applying force to specific surfaces of the teeth to cause directed movement. In order to apply such force, one or more of the teeth will provide a base or anchor region for holding the positioning appliance in place while the stiffness of the polymeric material will impart a resilient repositioning force against one or more of the remaining teeth. However, such stiffness creates limitations in ease of use, patient compliance, and overall cost in material, manufacturing labor and treatment time.
To overcome these limitations, the present invention utilizes polymeric or other material appliances with portions differing in rigidity, hardness, or stiffness. Portions of the appliance designed to apply specific forces may have different elastic moduluses (stiffnesses) and/or hardnesses than other portions. Alternatively, elastic moduluses and/or hardnesses may vary from one appliance to the next in a successive series to accomplish various treatment goals. Thus, the systems and methods of the present invention provide the design, production and use of such multiple stiffness positioning appliances in orthodontic treatment. Similarly, the devices of the present invention provide variable stiffness appliances which may be used independently for purposes other than repositioning, such as for retaining teeth in a desired position. Thus, reference hereinafter to repositioning appliances with portions having differing or varying stiffnesses or hardnesses is not intended to limit the scope of the present invention and is understood to include appliances of the described design for other purposes.
In a first aspect of the present invention, an elastic repositioning appliance may be comprised of portions with differing elastic moduluses. Elastic modulus may be used to express or describe the stiffness of a material or a material""s resistance to elastic deformation. Therefore, elastic modulus may be used hereinafter to refer to stiffness. The different portions of the appliances will also usually vary in hardness. More usually, stiffer portions will be harder while the less stiff portions will be softer. Hardness is usually measured as a xe2x80x9cdurometerxe2x80x9d reading on either the A or the D scale. In most instances, the present invention will be more concerned with the elastic modulus of the material since that will effect the force applied to the teeth for either moving the teeth or for gripping or anchoring the teeth. In other instances, however, the hardness of the material may be more important, e.g., to avoid trauma to soft tissue regions engaged by the appliance. The remaining description and claims generally refer to materials having greater and lesser sniffinesses. It will be appreciated that such terminology will also comprise materials having greater and lesser hardnesses.
The elastic modulus of a material is the ratio of the increment of unit stress to an increment of unit deformation within the elastic limit. When a material is deformed within the elastic limit, the bonds between adjacent atoms are stretched but not broken. The magnitude of the elastic modulus is indicative of the atomic and molecular bonding forces. When the stress is relieved, the material returns to its original shape and the deformation is nonpermanent. Different materials may have different elastic moduluses based on their molecular structures. Some materials, such as certain polymers, may be specially produced to have different elastic moduluses while retaining similar chemical compositions (and thus assuring compatibility of the different modulus materials in a single structure). Likewise, the elastic modulus of a polymer or other material may be enhanced or otherwise modified. This may be achieved by adding a powder, such as CaCO3, talc, TiO2, glass, diamond or a polymer powder, to name a few. In addition, this may be achieved by embedding structural reinforcements, such as metal pieces, strips, wires, mesh, lattices, networks, polymeric filaments, or the like. In addition, the elastic modulus may be altered by post-production methods, such as layering, coating, interpenetrating, treating with various chemical agents, and altering the temperature, to name a few. In the resulting appliance, the elastic moduluses of the varying portions will usually range from 0.5 to 5 GigaPascal (GPa), although in some instances portions of the appliance may fall outside of this range. The elastic modulus of one portion may differ from another portion by 25% to 600%, or more.
The differing elastic moduluses of different portions of the dental appliance shells of the present invention will exist while the device is present over teeth in a normal oral environment. Thus, different portions of the appliance shell will impart different forces to the immediately underlying teeth, where the level of the force depends both on the device geometry or tooth positions (relative to the underlying tooth or teeth, which may vary over time) and on the elastic modulus of that portion of the device (which will remain constant over time in the normal oral environment). The present invention should be distinguished from that described in copending application Ser. No. 09/250,962, where the stiffness of a dental appliance shell may change over time by expose to a non-oral environment, such as elevated temperature or changed osmolality. Of course, the dental appliance shells of the present invention which have different portions with differing stiffness may also incorporate regions (including the entire appliance) where a change in stiffness may be induced according to the teachings of application Ser. No. 09/250,962, the full disclosure of which is incorporated herein by reference.
In a first embodiment, portions of the shell of an elastic repositioning appliance may be composed of material(s) which differ in elastic moduluses and/or hardnesses along a mesial-distal axis. A mesial-distal axis may be defined as an axis following the gingival line or dental arch. Thus, the elastic repositioning appliance may be comprised of portions with a lower elastic modulus covering the molars, for example, and portions with a higher elastic modulus covering the remainder of the teeth. In this example, the portions may be relatively large so that a portion may receive one or more teeth, such as contiguous molars. This may be utilized when one or more teeth are to provide an anchor or base region for imparting repositioning force against another tooth or teeth. The portion of the appliance covering the anchor teeth may be of a relatively flexible nature with a lower elastic modulus than the portion covering the teeth to be repositioned. This is because the portions covering the anchor teeth may not need to apply repositioning forces to the teeth they cover; they may merely be designed to hold the appliance in place. Consequently, a high level of rigidity or stiffness may not be required. However, it may be appreciated that portions covering anchor teeth may in fact require a higher stiffness material than other portions, including portions which are designed to apply repositioning forces. Thus, any variation of stiffness or elastic modulus along a mesial-distal axis is included in this embodiment.
The introduction of such portions or regions with more flexibility provides utility in ease of use for the patient. The patient may find ease in positioning the appliance with the more flexible portions first which may guide the appliance in placement of the more rigid, slightly misfit portions designed for repositioning. This sequence may be reversed in removal of the appliance. Likewise, such flexibility may also allow for any slight differences in mold versus appliance versus dentition geometry which may otherwise make placement and removal of the appliance more difficult. In some cases, a generally misfit appliance may xe2x80x9cpop offxe2x80x9d or have a tendency to disengage even when properly positioned over the teeth. Increased flexibility may reduce these tendencies.
In further embodiments, portions of the elastic repositioning appliance may vary in elastic moduluses along different and/or additional axes. For example, moduluses may vary along a facial-lingual axis. Facial may be defined as next to or toward the lips or cheek, including terms labial and buccal. Lingual may be defined as next to or toward the tongue. Thus, a facial-lingual axis may be described as an axis following a radial or similar line from the tongue toward the lips or cheek and vice versa. Likewise, moduluses may vary along a gingival-crown axis. This may be described as a substantially vertical axis following a line from the top of the crown at the edge of the occlusal surface of a tooth toward the gingival line or root and vice versa. In a preferred embodiment, an appliance may have a portion with a lower elastic modulus covering the occlusal surfaces of the teeth and a portion with a higher elastic modulus covering the remaining surfaces of the teeth. Thus, the moduluses may vary along a facial-lingual axis and/or a gingival-crown axis, depending on the boundaries of the delineated portions. Such a design may incorporate added flexibility to the appliance while maintaining adequate repositioning forces in the most efficient areas.
In addition to varying in stiffness along the axes described above, the appliances of the present invention may vary in stiffness or hardness over the xe2x80x9cthicknessxe2x80x9d of the appliance. Usually, such variations and stiffness over the thickness will be accomplished by layering the device, i.e., with layers of differing stiffnesses or hardnesses being placed successively over the mold used to form the appliances, as described in more detail below. Thus, the appliances may comprise shells having first and second portions, as generally described above, where each of those portions comprise layers in a laminar structure. Usually, at least one of the first and second portions will comprise a continuous layer along the mesial-distal axis. The second and optionally additional layers may also be continuous along the mesial-distal axis, but will often be discontinuous, i.e., broken into two or more segments. Such layered devices can provide a variety of benefits. For example, layers formed from stiffer or harder materials can be used to more firmly engage teeth, while the less stiff or softer layers can be used to provide compliance and greater elasticity. In a particular preferred embodiment, the appliance comprises a discontinuous inner layer and a continuous outer layer. At least a portion of the inner layer is configured to engage individual teeth or groups of teeth and will be stiffer or harder than the outer layer. The outer layer, which is less stiff and therefore more compliant, provides the elasticity to move the teeth relative to one another, while the harder inner layer firmly engages the teeth to provide a better grip or anchor upon the teeth.
It may be appreciated that the elastic modulus of the appliance shells may vary over any number of delineated portions. Such portions may be of any size, shape, thickness, or dimension. Thus, such portions may receive entire teeth or they may be of the size to cover only a portion of a tooth or dental surface. When portions are relatively large, an appliance may be divided into, for example, two to five portions. Portions adjacent to one another differ in elastic moduluses, however not all portions of an appliance may differ from each other, such as in the case of an appliance with portions alternating between two moduluses. When portions are relatively small, an appliance may contain an unlimited number of portions, varying along any axis or combination of axes.
In a second aspect of the present invention, such appliances comprised of portions having differing stiffness may be used independently or in a series with similar or differing devices. When used independently, the appliance may be worn to achieve a specific goal with a single device. For example, the appliance may be used as a xe2x80x9cretainerxe2x80x9d to hold the teeth in a desired position. Or, the appliance may be used for a specific one-time repositioning movement, such as xe2x80x9cfinishingxe2x80x9d or correcting a slight misalignment. When used in a series, the appliances may comprise a system for repositioning teeth from an initial tooth arrangement to a final tooth arrangement. In this case, a plurality of incremental elastic position adjustment appliances comprising polymeric or other material shells are successively worn by a patient to move teeth from one arrangement to a successive arrangement. Individual appliances may be configured so that their tooth-receiving cavity has a shape or geometry corresponding to an intermediate or end tooth arrangement intended for that appliance. Thus, successive individual appliances may have a shape or geometry differing from that of the immediately prior appliance. According to the present invention, some or all of the individual appliances may also be comprised of a material stiffness differing from the stiffness of the immediately prior appliance. In addition, each individual appliance be comprised of portions with varying stiffnesses. In some cases, of course, individual appliances in the system may not vary in stiffness from prior or successive appliances, but only in geometry. In other cases, individual appliances may vary only in stiffness (and not in geometry) when compared to immediately prior or subsequent appliances. Thus, systems according to the present invention may be comprised of appliances having stiffness varying within the appliance and/or from one appliance to the next in the series.
In a specific embodiment, a system of elastic repositioning appliances may comprise individual appliances having uniform elastic moduluses over their entire tooth contact area where the moduluses will differ among successive appliances used in a course of treatment. The elastic modulus of a given appliance may be chosen to be most suitable for a specific type of tooth movement, such as translating, tipping, root uprighting, rotation, extrusion, intrusion or a combination of these. For example, translation may require 70-120 gm of force, whereas rotation may only require 35-60 gm of force. Therefore, an elastic positioning appliance designed for translating teeth may need to have a higher elastic modulus than one designed for purely rotating teeth. This is again due to the fact that stiffness of the appliance is a critical factor in imparting repositioning force. Consequently, a series of appliances may be produced for a treatment plan in which successive appliances designed for a specific tooth movement may all have substantially similar elastic moduluses. At the point in the treatment plan in which a different type of tooth movement is desired, further appliances designed for the new tooth movement may have substantially similar elastic moduluses to each other but different from the previous appliances. Such a sequence may be repeated at any time or may continue with new moduluses and tooth movements.
In an additional specific embodiment, one or more appliances may be produced with a suitably flexible elastic modulus to receive and resiliently reposition teeth from an unprescribed arrangement to a prescribed arrangement. This might be necessary in cases of lowered patient compliance. If a patient were to remove an appliance for an unintended and/or extended period of a prescribed treatment time, the patient""s teeth may move slightly out of the planned tooth progression. When attempting to reapply the appliance, an appliance which is too rigid may not be able to accommodate these slight differences. Thus, a more flexible appliance (but having an identical geometry) may be produced for this purpose and may be incorporated into the treatment plan at any given point in the series of successive appliances. The ability to return to the same geometry is an advantage because it minimizes the need to replan the treatment protocol.
In a third aspect of the present invention, systems for repositioning teeth from an initial tooth arrangement to a successive tooth arrangement comprise a plurality of incremental elastic position adjustment appliances in which at least one appliance has the same shape yet different elastic modulus as an immediately prior appliance. In a specific embodiment, a series of incremental appliances may be produced with differing elastic moduluses to reposition teeth from an initial tooth arrangement to the next successive tooth arrangement in a progression of arrangements to the final arrangement. Each of the appliances in the series from the first to the next successive tooth arrangement may have the same shape or geometry since the tooth movement represents one step in tooth movement. However, the variance in elastic moduluses may allow for a larger step or increment in tooth movement than may be obtainable with consistent, rigid appliances. For example, an appliance may be produced with a tooth arrangement which is substantially misaligned from the initial arrangement. High modulus appliances may not be flexible enough to allow the appliance to fit over the teeth in the initial arrangement. However, a series of appliances of the same shape may be produced with increasing elastic moduluses from relatively low to adequately high. The patient may begin with the lowest elastic modulus appliance which may be the most flexible to fit over the teeth. As the teeth are repositioned, the patient may successively utilize each appliance in increasing modulus until the teeth have conformed to the successive tooth arrangement. At that time, the patient may begin a new series of appliances with varying moduluses and a shape to reposition the teeth to the arrangement of the next step in the repositioning progression. The ability to reduce the number of different appliance geometries required for a single course of treatment can provide a significant reduction in planning effort and manufacturing costs.
In a fourth aspect of the present invention, the elastic modulus of an appliance or portions of an appliance may be modified in a number of different ways. To begin with, the elastic modulus may be determined by the choice of materials. For example, metals will generally have a higher elastic modulus than polymers due to atomic structure. For example, the modulus values for metals may range between 48 and 414 GPa, whereas the modulus for polymers may range from 0.5 to 35 GPa. Thus, it will be possible to form appliances having moduluses which differ greatly by forming different portions from metal(s) and polymer(s), or by forming successive appliances from metals and polymers. Usually, however, the appliances will comprise or consist of a polymeric shell formed from a single polymer, multiple polymers, copolymers, and the like, typically by thermoforming and/or lamination. Stiffness of a polymer may be varied within a range (typically 0.5 GPa to 5 GPa) by changing the molecular structure of the polymer chains. Polymer chains with hindered side-chains are unable to pack as closely as those with smaller side-chains. Thus, such a polymer may have more intermolecular motion and therefore a lower bulk elastic modulus. Stiffness can also be changed by controlling the degree of cross-linking as well as the cross-linking entity within a polymer or copolymer. Further, alternatively, differing elastic moduluses may be created within the same polymer shell by layering or laminating the same or different polymers. Two layers of a polymer material bonded together to form an integral appliance, i.e., an appliance having a monolithic shell structure where the layers are resistant to delamination, may have a higher elastic modulus than a single layer of such material. Thirdly, different elastic moduluses may be created with a single layer of one type of polymer material by production methods, such as coating, treating with various chemical agents, and altering the temperature, to name a few.
Further, different elastic moduluses may be produced by forming selectively reinforced and/or composite-type materials. For example, a polymer material may be reinforced with structures such as strips, wires, pieces, mesh, lattices, networks, and the like. These structures may be comprised of any suitable material, particularly metals and alloys but also including polymer filaments, wires, braids, and the like. Likewise, composite materials may be comprised of interpenetrating polymeric networks. An interpenetrating polymeric network is comprised of a base material and an additional material that interpenetrates the base material to alter its mechanical properties. For example, the base material (A) may be a solid polycarbonate. The added material (B) may be a liquid polymer, monomer or crosslinking agent which is allowed to interpenetrate and activate to form a composite network. The composite (A+B) may have a stiffness which is greater than the sum of its parts, (A) and (B). Further, another material (C) may also be allowed to interpenetrate and activate to form a new composite network. The composite (A+B+C) may also have a stiffness which is greater than the sum of its parts, (A), (B) and (C). With this method, any number of composites may be formed providing a wide range of mechanical properties, specifically stiffnesses. In addition, a number of these production methods may provide materials with gradual changes in elastic moduluses. For example, purposely irregular coating of a polymer material may provide higher stiffness in areas with thicker coating and lower stiffness in areas with thinner coating. This may be applied to a number of production methods.

Systems and methods for varying elastic modulus appliances


A candle having a selectively and reversibly variable color pattern. In one embodiment, the candle comprises a solid transparent gel with a thermochromic or photochromic pigment dispersed evenly throughout. The candle main body changes from a first color to a second color, or from colored to transparent, or from transparent to colored, in response to heat or light from the candle flame, and reverts to the original color or absence of color upon extinguishing the flame. The candle comprises (a) a solid combustible matrix, and (b) a reversible thermochromic or photochromic composition blended into said solid combustible matrix.

1. Field of the Invention
The present invention relates to a candle having a selectively and reversibly variable color pattern. The candle comprises a conventional wax or a solid transparent gel with a thermochromic or photochromic pigment dispersed evenly throughout the main body. The candle main body changes from a first color to a second color in response to heat or light from the candle flame, and reverts to the original color upon extinguishing the flame.
2. Description of the Related Art
Although electric lights have virtually eliminated the need for candles, candles continue to remain popular as a way to provide xe2x80x9catmospherexe2x80x9d. Candlelight is associated with romantic dinners, holidays, weddings, anniversaries, etc. However, aside from the addition of fragrances and colors, candles have remained virtually unchanged for hundreds of years, a simple combination of wick and wax.
It is difficult to improve upon the simple elegance of a traditional white candle. While many variations have been proposed over the years, they have not met with commercial success, the modifications often perceived as detracting or intrusive.
For example, U.S. Pat. No. 5,762,487 teaches candles with colored particles that swirl in a pool of molten wax near the flame. While this is interesting, it also detracts from the beauty of the candlelight.
U.S. Pat. No. 4,818,215 teaches a thermally color-changing candleholder. While this is an interesting effect, the candle itself, which is merely a conventional candle inserted into the candleholder, remains unchanged. The effect is not surprising.
U.S. Pat. No. 5,798,184 teaches a candle having a xe2x80x9ccoloration areaxe2x80x9d provided on the surface of the candle in the manner of a film by brushing, spraying, or the like. The xe2x80x9ccoloration areaxe2x80x9d may contain a pigment that generates fluorescent light upon being irradiated with ultraviolet light, or may contain a luminescent or phosphorescent agent that glows after being illuminated, or may contain organic photochromic compounds that change in color upon receiving light. In the figures, the xe2x80x9ccoloration areaxe2x80x9d is shown as intricately shaped flower petals far from the flame, with the main body of the candle being a wide body formed of a conventional wax. It does not appear that this candle can be shaped into a slender candle. It also appears that the coloration areas do not respond to temperature.
The present inventors, keeping in mind the overwhelming popularity of the simple common candle, considered that consumers may not be interested in candles that display complex patterns or images which detract from the simple beauty of a burning candle. The inventors considered that the same consumers may be more willing to accept a candle which changes in display after being lit in a manner which is simple and eloquent, yet subliminally amazing.
During the course of experimentation, the present inventors developed a new type of candle that has the appearance of a conventional candle, yet changes in display upon being lit in a simple yet intriguing way.
This new type of candle, upon being lit, changes in appearance in a manner which does not detract from the aesthetic beauty of a burning candle, but rather enhances it.
The invention concerns a candle wherein the main body comprises (a) a solid combustible matrix, which may be a conventional wax or a solid clear gel formulation, and (b) a reversible color changing composition, preferably a thermochromic or photochromic composition, the components (a) and (b) preferably forming a homogeneous mixture.
Upon lighting, the light or heat given off by the flame causes the reversible color changing composition contained in the main body to change in color, to loose color, or to become colored, at least in the area nearest the flame. For example, a wax candle with both a blue-to-white thermochromic pigment and a conventional red pigment homogeneously mixed into the main body would appear to have a solid purple body. Upon lighting the candle, the top two inches of the candle would turn red (the red pigment in the candle main body remaining unaffected while the thermochromic pigment transforms from blue to white). As the candle burns down inch by inch, the area of color change travels down along with the flame. Thus, the visual effect remains essentially constant, and can be said to work in tandem with the flame as the candle is being consumed by the flame. Upon extinction of the flame, the entire length of the candle again turns purple.
As mentioned above, the solid combustible material of the main body may be a clear self-supporting gel composition. A candle formed of such a material having a blue-to-clear thermochromic material compounded therein would initially appear to have a solid conventional candle body. After being lit, the top part of the candle may turn from blue to clear, giving the optical illusion of the top part of the candle disappearing. A candle having such a unique display would stand out in the marketplace.
The color change effect can be created by mixing into the candle main body either mixtures of conventional pigments and thermochromic or photochromic compositions, or mixtures of different thermochromic compositions, or mixtures of different photochromic compositions, or mixtures of thermochromic and photochromic compositions, or a pure single thermochromic or photochromic composition. Each of these may be incorporated into conventional wax candle materials or transparent materials. The color changing candle body is made of a composition that can be used by the amateur hobbyist, yet provides a completely unique candle display.
The foregoing has outlined rather broadly the more pertinent and important features of the present invention in order that the detailed description of the invention that follows may be better understood and so that the present contribution to the art can be more fully appreciated. Additional features of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and the specific embodiments disclosed may be readily utilized as a basis for modifying or designing other color changing candles for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent structures and the processes for forming them do not depart from the spirit and scope of the invention as set forth in the appended claims.
The present invention imparts to candles the property of reversible color change. The term xe2x80x9ccandlexe2x80x9d as used herein means any candle of any design as conventional in this art, and includes tapers (e.g., traditional dinner candles), filled or jar candles (candles formed by pouring melted wax into glass containers), votives (candles shaped to refill the glass containers after the original wax has been consumed), pillars (free-standing candles generally having a diameter of about three inches or more), etc.
The development of a color changing candle is more complex than merely mixing color changing compositions and waxes or transparent gels.
For correct burning, the radiant heat of the candle""s flame must melt a small pool of the candle body material around the base of the exposed portion of the wick. The molten candle body material must have a relatively low viscosity to insure that it will be capable of being drawn up through the wick by capillary action. The candle body material can not contain any materials that would clog the wick, or combust to give off smoke or unpleasant aromas or toxic fumes.
Generally, a one-to-one ratio of pigment to conventional dyes can be used in the present invention, and optimum concentrations for burning and affordability are 0.5-1.0%. Proportions and amounts can easily be selected by those working in this art. Obviously, if the concentration were too low the effects would not be noticeable, and if the concentration of thermochromics was too high the candle would probably not burn as well. Any of the FDandC or DandC pigments can be used as the conventional color.
Other factors to be taken into consideration are discussed in U.S. Pat. No. 5,591,255 (Small, et al.) entitled xe2x80x9cThermochromic ink formulations, nail lacquer and methods of usexe2x80x9d. This patent concerns overcoming the problems associated with formulations that destroy the color change properties of thermochromic encapsulated dyes, and teaches that (1) certain solvents destroy the dye, therefore any aldehydes, ketones, and diols, and most aromatic compounds should be removed from the formulation and if needed they should be replaced with solvents preferably having a large molecular weight (i.e. greater than 100 and low reactivity); and (2) the formulation should be adjusted to be neutral (i.e. 6.5-7.5 pH, using HCl or KOH to adjust the pH down or up) or have a low acid value (i.e. acid number below 20 according to ASTM Test Method D-1639-70). When the thermochromic dye is added to a, formulation that has a pH outside this range, the color change properties are almost always lost. This is an irreversible effect and therefore, it is important to adjust the pH prior to adding the thermochromic dye. These two adjustments will allow the thermochromic dyes to be added to the formulation without a loss of its color change properties.
The microcapsule is hard, non-polar, thermally very stable (it won""t melt), and relatively impermeable. For maximum shelf life, the infiltration of compounds such as solvent through the capsule must be stopped or slowed to the point that the characteristics of the dye are not effected. Aldehydes, ketones, diols and aromatic compounds should not be used when preparing products. The best solvents to use will be those that have low reactivity, are large molecular weight (i.e. over 100), and which are relatively non-polar. One preferred solvent is cyclohexane. It has low toxicity and works well.
Thermochromic and photochromic materials are well known, and any of these can be used in the present invention, so long as they meet the above requirements.
Photochromic compounds which can be used in the present invention include any reversible photochromic compounds as employed in the printing art and plastics art, including for example napthopyran compounds and other photochromic compounds as taught in U.S. Pat. Nos. 5,721,059; 5,558,700; 5,558,699; 5,514,635; 5,502,967; 5,458,815; 5,458,814; 5,466,398; 5,384,077; 5,451,344; 5,429,774; 5,411,679; 5,441,418; 5,405,958; 5,381,193; 5,369,158; 5,340,857; 5,274,132; 5,244,602; 5,223,958; 4,679,918; 4,556,605; and 4,498,919, the disclosures of these patents being incorporated herein by reference.
Specific examples of photochromic material which can be used in the present invention include organic photochromic substances such as azobenzene compounds, thioindigo compounds, dithizone metal complex compounds, spiropyran compounds, spirooxazine compounds, fulgide compounds, dihydropyrene compounds, spirothiopyran compounds, 1,4-2H-oxazine, triphenylmethane compounds, viologen compounds, naphthopyran compounds, benzopyran compounds and so on. Particularly preferred for purposes of the invention are spiropyran compounds, spirooxazine compounds, fulgide compounds, naphthopyran compounds and benzopyran compounds.
Among specific examples of said photochromic substance are 1,3,3-trimethylspiro[indoline-2,3xe2x80x2-(3H)naphtho(2,1-b)(1,4)-oxazine], 6xe2x80x2-indolino-1,3,3-trimethylspiro[indoline-2,3xe2x80x2-(3H)naphtho(2,1-b) (1,4)-oxazine],5-chloro-1,3,3-trimethylspiro[indoline-2,3xe2x80x2-(3H)naphtho(2,1-b)(1,4)-oxazine], 6xe2x80x2-piperidino-1,3,3-trimethylspiro[indoline-2,3xe2x80x2-(3H)naphtho(2,1-b)(1,4)-oxazine], 1-benzyl-3,3-dimethylspiro[indoline-2,3xe2x80x2-(3H)naphtho(2,1-b)(1,4)-oxazine], 1,3,5,6-tetramethyl-3-ethyl-spiro[indoline-2,3xe2x80x2-(3H)naphtho(2,1-b)(1,4)-oxazine], 1,3,3,5,6-pentamethylspiro[indoline-2,3xe2x80x2-(3H)naphtho(2,1-b)(1,4)-oxazine], 1,3,5,6-tetramethyl-3-ethylspiro[indoline-2,3xe2x80x2-(3H)pyrido(3,2-f)(1,4)-benzoxazine], 1,3xe2x80x2,3xe2x80x2-trimethylspiro(2H-2-benzopyran-2,2xe2x80x2-indoline), 1,3,3-triphenylspiro[indoline-2,3xe2x80x2-(3H)naphtho-(2,1-b)pyran], 1-(2,3,4,5,6-pentamethylbenzyl)-3,3-dimethyl-spiro[indoline-2,3xe2x80x2-(3H)naphtho(2,1-b)pyran], 1-(2-nitrobenzyl)-3,3-dimethylspiro[indoline-2,3xe2x80x2-(3H)naphtho(2,1-b)pyran], 2,2-diphenylnaphtho(2,1-b)pyran, 2,2-di(p-methoxyphenyl)naphtho(2,1-b)pyran, 2,5-dimethylfuryltrimethylfulgide, 2-methyl-5-chlorotrimethylfulgide, spiro[2H-chromen-2,2xe2x80x2-tricyclo[18.104.22.168.-sup.3.7]decane, spiro[2H-naphtho[1,2-b]pyran-2,2xe2x80x2-tricyclo-[220.127.116.11.sup.3.7]decane], 5,7-dimethylspiro[2H-chromene-2,2xe2x80x2-tricyclo[184.108.40.206.sup.3.7]decane], 6-(4-methoxyphenyl)-9-methoxyspiro[2H-naphtho[1,2-b]pyran-2,2xe2x80x2-tricyclo][126.96.36.199.-sup.3.7]decane], 6-chlorospiro[2H-naptho[1,2-b]pyran-2,2xe2x80x2-tricyclo[188.8.131.52.sup.3.7]decane and so on.
The photochromic substances can be used independently but for the purpose of improving the color changing function or the fastness to light, it is preferable to concomitantly use auxiliary agents such as high-boiling solvents, plasticizers, synthetic resins, hindered amines, hindered phenols and so on. These compounds are well known additives for use in combination with photochromic substances and their proportions can be selected from the known ranges. In the present invention, for the purpose of improving the light fastness of said organic photochromic substances, the use of a hindered amine compound or a combination of a hindered amine and other auxiliary agents is recommended.
Most thermochromic dyes undergo a color change from a specific color to colorless (i.e. clear). Therefore, background color pigments can be provided in combination with the thermochromic compounds, such that when the thermochromic compounds change to colorless, the conventional or background pigments define the color of the candle body. If a yellow pigment is mixed into the candle body in combination with a blue thermochromic dye, the visible color will appear to change from green to yellow, when what is really happening is that the blue thermochromic dye is changing to colorless.
On the other hand, U.S. Pat. No. 5,919,404 (Fujita, et al.) entitled xe2x80x9cReversible thermochromic compositionsxe2x80x9d teaches a reversible thermochromic composition that has a reversible metachromatic function, that is, it presents a color-developed state when heated in a color-extinguished state and presents the color-extinguished state when temperature-dropped or cooled in the color-developed state. The composition comprises as essential components (a) an electron-donating color-developing organic compound, (b) at least one electron-accepting compound selected from alkoxyphenol compounds represented by a given formula, and and (c) a compound such as paraffin wax serving as a reaction medium capable of reversibly causing electron-donating/accepting: reaction attributable to the components (a) and (b).
It should be understood that the term xe2x80x9cthermochromic materialxe2x80x9d is used herein to mean any and all thermochromic materials inclusive of pseudo-thermochromic materials which show a hysteresis of thermochromism.
Reversible thermochromic compositions are known which are constituted of a solubilized mixture containing essentially a reaction medium for causing reversible electron exchange between an electron-donating coloring organic compound and an electron-accepting organic compound in a specific temperature range as disclosed in U.S. Pat. Nos. 4,028,118; 4,732,810; 4,865,648; 4,720,301; 4,957,949; 4,554,565; 4,421,560; 4,425,161; and 4,421,560.
Additional examples of reversible thermochromic materials that can be used in the present invention include those disclosed in U.S. Pat. No. 5,281,570 (Hasegawa, et al.) entitled xe2x80x9cThermochromic materialsxe2x80x9d teaching a microencapsulated reversible thermochromic material comprising: (a) an electron donative color former; (b) a sulfide, sulfoxide or sulfone containing a hydroxy phenyl radical; and (c) a chemical compound selected from alcohols, esters, ethers, ketones, carboxylic acids or acid amides; U.S. Pat. No. 4,425,161 (Shibahashi, et al.) entitled xe2x80x9cThermochromic materialsxe2x80x9d teaching a thermochromic material comprising (a) an electron-donating, chromatic organic compound, (b) a compound capable of reversibly accepting an electron or electrons from the electron-donating, chromatic organic compound, (c) a compound controlling the temperature and sensitivity of coloration/decoloration of the thermochromic material and (d) a N-radical, P-radical, O-radical or S-radical cationic compound having an aromatic ring or rings which improves by light-fastness; U.S. Pat. No. 4,717,710 (Shimizu, et al.) entitled xe2x80x9cThermochromic compositionxe2x80x9d teaching a thermochromic composition comprising (1) an electron-donating chromogenic material, (2) a 1,2,3-triazole compound, (3) a weakly basic, sparingly soluble azomethine or carboxylic acid primary amine salt, and (4) an alcohol, amide or ester serving as a solvent; and U.S. Pat. No. 5,558,700 (Shibahashi, et al.) entitled xe2x80x9cReversible thermochromic compositionxe2x80x9d teaching a reversible thermochromic composition comprising a solubilized mixture of three components of (a) an electron-donating color-developing organic compound selected from pyridine types, quinazoline types, and bisquinazoline types of compound, (b) an electron-accepting compound for the electron-donating color-developing organic compound, and (c) a compound serving as a reaction medium for causing reversibly an electron exchange reaction between the components (a) and (b) within a specified temperature range, the composition developing a fluorescent color of yellow, yellowish orange, orange, reddish orange, or red with a high color density and high color brightness, yet gives no residual color under non-color-developing conditions, and has remarkably improved light resistance.
The acid-responsive chromogenic substance in said thermochromic material includes triphenylmethanephthalide compounds, phthalide compounds, phthalan compounds, acylleucomethylene blue compounds, fluoran compounds, triphenylmethane compounds, diphenylmethane compounds, spiropyran compounds and so on. Among species of such compounds are 3,6-dimethoxyfluoran, 3,6-dibutoxyfluoran, 3-diethylamino-6,8-dimethylfluoran, 3-chloro-6-phenylaminofluoran, 3-diethylamino-6-methyl-7-chlorofluoran, 3-diethylamino-7,8-benzofluoran, 2-anilino-3-methyl-6-diethylaminofluoran, 3,3xe2x80x2,3xe2x80x3-tris(p-dimethylaminophenyl)phthalide, 3,3xe2x80x2-bis(p-dimethylaminophenyl)-phthalide, 3-diethylamino-7-phenylaminofluoran, 3,3-bis(p-diethylaminophenyl)-6-dimethylaminophthalide, 3-(4-diethyl-aminophenyl)-3-(1-ethyl-2-methylindol-3-yl)phthalide, 3-(4-diethylamino-2-methyl)phenyl-3-(1,2-dimethylindol-3-yl)phthalide, 2xe2x80x2-(2-chloroanilino)-6xe2x80x2-dibutylaminospiro-[phthalido-3,9xe2x80x2-xanthene] and so on.
The acidic substance mentioned above includes 1,2,3-benzotriazole compounds, phenol compounds, thiourea compounds, oxo-aromatic carboxylic acids and so on. Among specific examples of such compounds are 5-butylbenzotriazole, bisbenzotriazole-5-methane, phenol, nonylphenol, bisphenol A, bisphenol F, 2,2xe2x80x2-biphenol, .beta.-naphthol, 1,5-dihydroxynaphthalene, alkyl p-hydroxybenzoates, phenol resin oligomer and so on.
The amount of the acidic substance may be in the range of about 0.1 to 50 parts by weight per part by weight of the acid-responsive chromogenic substance.
Any of the thermochromic materials each containing an acid-responsive chromogenic substance and an acidic substance are preferably diluted with a solvent before use. The use of a solvent renders the material responsive to change in temperature with greater sensitivity and definition. The solvent which can be used for the thermochromic material includes, among others, alcohols, alcohol-acrylonitrile adducts, azomethine compounds, esters and so on. Among specific examples of the solvent are decyl alcohol, lauryl alcohol, myristyl alcohol, cetyl alcohol, stearyl alcohol, behenyl alcohol, lauryl alcohol-acrylonitrile adduct, myristyl alcohol-acrylonitrile adduct, stearyl alcohol-acrylonitrile adduct, benzylidene-p-toluidine, benzylidene-butylamine, octyl caprate, decyl caprate, myristyl caprylate, decyl laurate, lauryl laurate, myristyl laurate, decyl myristate, lauryl myristate, cetyl myristate, lauryl palmitate, cetyl palmitate, stearyl palmitate, cetyl p-t-butylbenzoate, stearyl 4-methoxybenzoate, dilauryl thiodipropionate, dimyristyl thiodipropionate, stearyl benzoate, benzyl stearate, dibenzyl thiodipropionate, distearyl thiodipropionate, benzyl benzoate, glycerol trilaurate and so on.
The amount of the solvent may be in the range of 0 to 800 parts by weight, preferably 0.1 to 100 parts by weight, per part by weight of the acid-responsive chromogenic substance.
In the present invention, the reversibly variable color material can be directly blended with wax or can be microencapsulated beforehand. The microencapsulation can be carried out using the reversibly variable color material, a shell-forming polymer and, where necessary, a surfactant, protective colloid, pH control agent, electrolyte, etc., the desired microcapsules can be prepared in water by any of interfacial polymerization, in situ polymerization, coacervation, air suspension, interfacial precipitation and other techniques. By such processes, microcapsules including the reversibly variable color material and measuring about 1 to 50 xcexcm in diameter can be obtained. It is also possible to provide double-or multiple-walled microcapsules by using one, two or more of the microencapsulation techniques mentioned above. The preferred shell-forming material includes a polyamine and a carbonyl compound for forming a polyurea shell, a polybasic acid chloride and a polyamine for forming a polyamide shell, a polyisocyanate and a polyhydroxy compound for forming a polyurethane shell, a polybasic acid chloride and a polyhydroxy compound for forming a polyester shell, an epoxy compound and a polyamine for forming an epoxy resin shell, a melamine-formaldehyde prepolymer for forming a melamine resin shell and a urea-formaldehyde prepolymer for forming a urea resin shell, as well as ethylcellulose, polystyrene, polyvinyl acetate and so on. The shell of said microcapsules is preferably made of a thermosetting material which is superior in heat resistance.
When using a wax to form the matrix of as in a conventional wax candle main body, the wax is preferably mainly constituted of at least one type of wax selected from a group of waxes that includes animal waxes (e.g., whale oil wax, beef tallow hardened oil, fish oil hardened oil), bees waxes (e.g., as obtained from honey bees), plant waxes (e.g., repeseed hardened oil, montan wax, palm wax, sugar cane wax, carnauba wax, candelilla wax, calnoba wax, vegetable tallow, oliquy wax, Douglas Fir bark wax, rice bran wax, jojoba wax and bayberry wax), mineral waxes (e.g., ceresin wax, montan wax, peet wax and ozokerite wax) and petroleum wax (e.g., paraffin wax having a melting point of from 50 to 120xc2x0 C., microcrystalline wax, petrolatum, paraffin oxide wax and petrolatum oxide, microcrystalline wax and crystalline wax) and synthetic waxes (e.g., ethylene-vinyl acetate copolymer wax, ethylene-acrylate copolymer wax and vinyl ether wax polyethylene wax, Fischer-Tropsch wax, chemical modification hydrocarbon wax and substitution amido wax).
Any wax supplier can provide a wax suitable for use in a candle, and suppliers include Ross, Walnut Hill, More and Munger, and American Candle Corp.
Self supporting clear gel formulations useful for forming the candle main body are disclosed in U.S. Pat. Nos. 5,882,363 (Spaulding, et al.) entitled xe2x80x9cClear compositions for use in solid transparent candlesxe2x80x9d and 5,843,194 (Spaulding) entitled xe2x80x9cClear gel formulation for use in transparent candlesxe2x80x9d. These patents teach clear solid compositions that may be used as the base material of a transparent candle. In one form, the compositions comprise one or more polyamide resins, which may be present in a total amount of about 40-70% by weight of the composition; and one or more 12-hydroxystearic acid ester solvents, which may be present in a total amount of about 10-70% by weight of the composition. The compositions have a high degree of clarity, with little or no haze or cloudiness, even when fragrances or coloring agents have been added. The compositions can be formulated not darken or smoke when a candle made of the composition is burning, and so that candles made of the composition do not crack or split during burning, nor suffer from syneresis. Moreover, the transparent candles formed of the clear solid composition are self-supporting, and do not require a container or external support, unlike clear gel candles. The transparent candles also have other desirable aesthetic features, such as a waxy feel.
The composition includes a gellant and a solvent, mixed together. The gellant provides structure to the candle. The solvent binds to the gellant, and has a large effect on the burning characteristics of the candles, such as whether the candle smokes while burning, whether the pool darkens during burning, and the heat of the flame.
A preferred liquid base material of the present invention, hydrogenated polyisobutene, has the advantage of being readily available in commercial quantities as an ingredient that is listed in the Cosmetic Toiletry and Fragrance Associate Ingredient Dictionary, having a CAS number of 68937-10-0. The odorless, low volatility base materials of the present invention are, thus, recognized as toxicologically safe for use in the cosmetic arts. Furthermore, the base materials of the present invention have no tendency to auto-ignite. Such auto-ignition, which is caused by excessive fumes emanating from the surface, may occur with certain prior art transparent candle compositions, such as those which use kerosene, lamp oil or a mineral oil/styrene/rubber copolymer mix.
Isostearyl alcohol or dimethyl isosorbide could be added as a flame-enhancing agent, so as to produce whiter, hotter flames, they also provide improved gel clarity by reducing the haze that may sometimes be produced in the gel.
Two classes of polyamides are typically soluble in solvents of interest, and are preferred gellants for the present invention: (1) polyamides based on terpolymers of simple nylons (such as DuPont ELVAMIDE(trademark) 8061, which is a terpolymer of nylon 6, nylon 66, and nylon 610); and (2) polyamides based on complex fatty acids, such as the VERSAMID(trademark) series of Henkel Corp. or the UNIREZ(trademark) series of Union Camp Corp. U.S. Pat. No. 5,500,209 provides a more detailed description of these polyamides. The preferred gellant is the polyamide resin VERSAMID(trademark) 1655, available from the Henkel Corporation located in Ambler, Pa.
Go Suitable solvents include esters of 12-hydroxystearic acid with a monohydric or polyhydric alcohol, i.e., octylhydroxystearate and derivatives thereof. This class of solvents is referred to herein as xe2x80x9c12-hydroxystearic acid esters.xe2x80x9d More preferably, the solvent is octylhydroxystearate, available commercially as WICKENOL(trademark) 171 from Alzo, Inc., located in Matawan, N.J., or as CRODAMOL(trademark) OHS from Croda, Inc., located in Parsippany, N.J.
Clear candles made from a composition using VERSAMID(trademark) 1655 as the gellant and octylhydroxystearate as the solvent are hard to the touch and capable of self-support, and do not require a container. Also, such a candle does not significantly darken or smoke during burning.
Other transparent candle compositions include a thermoplastic polyamide resin and a flammable solvent for solubilizing the resin, such as described in U.S. Pat. Nos. 3,615,289 and 3,819,342; however, these are vulnerable to auto-ignition, and tend to sweat, produce black smoke, and darken during burning. Sweating is not only an aesthetic drawback, but can be a performance or safety problem as well. If a candle sweats, the oil on the surface is available to ignite, which can result in an uncontrolled or torch-like situation rather than a candle.
U.S. Pat. No. 5,578,089 describes a heterophase thermally reversible mineral oil gel formed by a system of physically crosslinked block copolymers which purportedly overcome the problem of sweating and syneresis by adjusting the ratio of diblock and triblock polymers so as to ensure that all the oil remains entrained: within a system of physically crosslinked copolymers. The thermoplastic rubber type polymers of U.S. Pat. No. 5,578,029 consist of block segments of styrene monomer units and rubber monomer units, wherein each block segment may consist of 100 monomer units or more. While such compositions are alleged to provide an improvement over the prior art transparent candle compositions, styrene/rubber-based candle compositions are susceptible to surface ignition, which may produce black smoke, and also have limited fragrance throw.
U.S. Pat. No. 5,578,089 (Elsamaloty) entitled xe2x80x9cClear candlexe2x80x9d teaches a clear candle made from a gel comprising mineral oil containing blends of diblock and triblock copolymers based on synthetic thermal plastic rubbers. The clear candle is stable, does not separate, and does not flash when burned. The candle, although free standing at room temperature, is preferably supplied in a container, and it may be colored and/or scented.