Classifications

• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B5/00—Optical elements other than lenses
  • G02B5/30—Polarising elements
  • G02B5/3083—Birefringent or phase retarding elements
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B1/00—Instruments for performing medical examinations of the interior of cavities or tubes of the body by visual or photographical inspection, e.g. endoscopes; Illuminating arrangements therefor
  • A61B1/24—Instruments for performing medical examinations of the interior of cavities or tubes of the body by visual or photographical inspection, e.g. endoscopes; Illuminating arrangements therefor for the mouth, i.e. stomatoscopes, e.g. with tongue depressors; Instruments for opening or keeping open the mouth
  • A61B1/247—Instruments for performing medical examinations of the interior of cavities or tubes of the body by visual or photographical inspection, e.g. endoscopes; Illuminating arrangements therefor for the mouth, i.e. stomatoscopes, e.g. with tongue depressors; Instruments for opening or keeping open the mouth with means for viewing areas outside the direct line of sight, e.g. dentists' mirrors
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61C—DENTISTRY; APPARATUS OR METHODS FOR ORAL OR DENTAL HYGIENE
  • A61C19/00—Dental auxiliary appliances

Definitions

• dental implements as used in connection with the present invention includes devices having at least one optical surface that is designed for use in a dental procedure including, but not limited to: dental mirrors, light guides for use in connection with photo-curing dental materials, matrix bands for use in molding photo-curing dental restoratives, etc.
• the term “dental articles” encompasses devices used in connection with dental procedures.
• dental articles includes dental implements designed for use within a patient's mouth, as well as devices designed to assist dental professionals in dental procedures such as dental operatory lights, room lighting covers, etc.
• Dental articles also include at least one optical surface.
• Figure 3 A is an enlarged partial cross-sectional view of the post-formed multilayer optical film of Figure 3 taken along line 3A-3A.
• Figure 5 is an enlarged partial cross-sectional view of the multilayer optical film of Figure 4 taken along line 5-5 in Figure 4.
• Figure 6 is a partial cross-sectional view of another post-formed multilayer optical film according to the present invention.
• Figure 7 is a partial cross-sectional view of a dental operatory light assembly including post-formed multilayer optical film according to the present invention.
• Figures 13A-13C are cross-sectional views of alternate dental light guides.
• Figure 14 is a plan view of a dental matrix band manufactured with post-formed multilayer optical film according to the present invention.
• Figure 16 is a graph illustrating temperature (horizontal axis) versus crystallization rate (vertical axis) for an exemplary birefringent material.
• Figure 17 is a perspective view of an article including post-formed multilayer optical film with areas having different optical properties.
• Figure 18 is a cross-sectional view of a composite including an multilayer optical film and a substrate.
• the optical stack of the multilayer optical film 10 can include tens, hundreds or thousands of layers, and each layer can be made from any of a number of different materials, provided that at least one of the materials is birefringent.
• the characteristics which determine the choice of materials for a particular optical stack depend upon the desired optical performance of the film.
• the optical stack may contain as many materials as there are layers in the stack. For ease of manufacture, however, preferred optical thin film stacks contain only a few different materials.
• the preferred optical stack is comprised of low/high index pairs of film layers, wherein each low/high index pair of layers has a combined optical thickness of 1/2 the center wavelength of the band it is designed to reflect at normal incidence.
• the optical thickness is the physical layer thickness multiplied by the index of refraction of the material in the layer for a given wavelength and polarization plane cross-section. Stacks of such films are commonly referred to as quarterwave stacks.
• Post-forming involves further processing of the optical stacks in the multilayer optical films to obtain some permanent deformation in the optical stack.
• the deformation will preferably involve thinning of the optical stack and it may also involve deforming at least one surface of the film from the uniformly smooth, planar-surfaced film shape in which it is manufactured. Because the deformations may cause the planarity of the optical stack to be disrupted, it should be understood that, where discussed, the in-plane directions are considered to be relative to a localized area of the optical stack or a point on the optical stack. For a curved optical stack, the in-plane axes can be considered to lie in a plane defined by the tangent lines formed at a particular point on the optical stack. The z-axis would then be perpendicular to that plane.
• the optical stack 20 includes a first major side 24 and a second major side 26 (see Figure 2A). Also illustrated are selected areas 22 in which the optical stack 20 has been deformed. The selected areas 22 are depicted as being substantially uniform in size and arranged in regular, repeating pattern. It will however, be understood that the selected areas 22 may be non-uniform and/or provided in pattern that irregular/non-repeating. One of the selected areas 22 and the surrounding optical stack 20 is seen in the enlarged, partial cross-sectional view of Figure 2A. The result of the post-forming is that the thickness of the optical stack 20 varies.
• the multilayer optical film has sufficient structural integrity such that entire lamp cavity 44 is constructed of the multilayer optical film, it may be preferable that the multilayer optical film be transmissive for infrared energy to limit heat build-up within the light assembly 40.
• the multilayer optical film used for the inner surface 46 of the light assembly 40 may be transmissive for light in the photo-curing wavelength or wavelengths to reduce or prevent its delivery out of the lens 42. If the multilayer optical film used on the inner surface 46 of the lamp cavity 44 is attached to a substrate material, that material may absorb or transmit the photo-curing light such that it is not available for reflection through the lens 42 and into the patient's mouth.
• the expanded field illuminated by the light 273 can, e.g., assist dental professionals in viewing areas within a patient's mouth. It should be noted that both light guide 170 and 270 could be manufactured of multilayer optical film that is not post-formed in accordance with the teachings of EP Patent Application No. 835464 titled HIGH EFFICIENCY OPTICAL DEVICES.
• the degree of crystallinity (or total polarizability as described later) tolerable in this regime depends on the particular polymer, its quenching conditions and its pre-drawing post process conditions.
• the draw ratio at which the rate of crystallization of the birefringent material in the multilayer optical film begins to increase significantly and move into Regime II can be influenced by a number of factors including draw rate, temperature, etc. After the birefringent material has experienced sufficient strain-induced crystallization to enter Regime II, however, it will typically follow the crystallization curve defined by that initial drawing. In other words, the film cannot continue to be drawn without inducing crystallization in the birefringent materials at the increased rates associated with Regime II in the graph of Figure 15. As a result, the characteristics of the film will be subject to less variability when drawn further in post-forming processes because the crystallization rate of the birefringent materials is, in large part, set by the pre-stretching required to put the film into Regime II.
• underdrawn multilayer optical films may alternatively be characterized using what will be referred to herein as "total polarizability" of the layers including birefringent materials. Determination of total polarizability is based on the refractive indices of the layer or layers including birefringent materials within the multilayer optical film.
• n,, n 2 and n 3 are the refractive indices in the principal directions of a given layer within the multilayer optical film
• p is the density of the materials in that layer
• K is a volume polarizability per unit mass for the materials in that layer.
• Total polarizability is a function of wavelength due to the wavelength dependence of the indices of refraction. As a result, when referred to numerically herein, total polarizability will be determined with respect to light having a wavelength of 632.8 nanometers (e.g., as provided by a helium neon laser light source).
• each of the three principal indices in the equation is set equal to the simple average of the three measured principal indices.
• the total polarizability is then called a refractivity and an analogous refractivity difference may be defined.
• density and crystallinity may be calculated. These may vary from that calculated using the total polarizability. For discussion purposes, the total polarizability calculation is used in the examples that follow.
• a uniaxially drawn film will have a higher degree of underdrawing in the non-drawn direction at the point of Regime II onset.
• equal underdrawing in both directions may be preferred. This may be achieved by minimizing the in-plane birefringence.
• the in- plane birefringence is simply defined as the absolute value or magnitude of the difference between the maximum and minimum refractive index values in the plane on the film. In the case of a uniaxially drawn film, this is typically the difference between the indices of refraction in the draw and non-drawn directions.
• a large in- plane birefringence is desired within the constraints of the underdrawing required to obtain a desired level of extensibility in the post process.
• the total polarizability difference of the birefringent materials in underdrawn multilayer optical films including PEN (and, by the definitions provided below in the section regarding materials selection, predominantly PEN copolymers) as measured in the birefringent layers is preferably within a range of from about 0.002 up to about 0.018, more preferably within a range of from about 0.002 up to about 0.016.
• the maximum in-plane birefringence of reflective polarizing multilayer optical films is less than about 0.22, more preferably less than about 0.17, and, in some cases, still more preferably less than about 0.15. In the case of underdrawn mirror films, a maximum in-plane birefringence of less than about 0.14 is preferred in combination with either of the ranges for the total polarizability difference in the birefringent materials.
• total polarizability of the material(s) in a given layer of the optical stack of the multilayer optical film represents the product of density and the volume polarizability per unit mass of the material(s) in that layer.
• the volume polarizability per unit mass (K) is typically considered an invariant material property under draw according to the conservation of molecular polarizability assumption discussed above. Drawing of birefringent materials causes strain-induced crystallization as discussed above and, in most birefringent materials, the density of the material varies based on whether the material is crystallized or amorphous.
• the above discussions set out different approaches to characterizing underdrawn films according to the present invention.
• the strain-induced crystallinity of the birefringent materials is measured and used to define underdrawn multilayer optical films.
• the refractive indices of the birefringent materials can be used to determine the total polarizability of the birefringent materials which can also be used to define underdrawn multilayer optical films.
• the strain-induced crystallinity can be determined based, at least in part, on the refractive indices used to determine total polarizability.
• the total polarizabilities of amorphous cast webs of PET and PEN are found to be about 0.989 and 1.083, respectively, and the densities of the amorphous materials are measured using a standard density gradient column at about 1.336 and 1.329 grams per cubic centimeter, respectively.
• the resulting volume polarizabilities can be calculated at about 0.740 and 0.815 cubic centimeters per gram for PET and PEN, respectively.
• Densities of drawn films of PET and PEN may now be calculated by dividing the total polarizabilities by the respective volume polarizabilities.
• the crystallinity may be estimated given the density of the pure crystalline phase, estimated as 1.407 grams per cubic centimeter for the typical crystalline phase of PEN and 1.455 grams per cubic centimeter for the crystalline PET.
• the post-formed multilayer optical films used in connection with the present invention rely on birefringent materials that provide strain-induced refractive index differentials to obtain the desired optical properties, variations in deformation of the multilayer optical film during post-forming can be particularly problematic.
• the strain-induced crystallization and corresponding refractive indices can, however, be changed when the birefringent materials are subjected to heat during post-forming. For example, heating may result in increased crystallization due to the heat during post-forming or decreased crystallization as a result of melting or relaxation during post-forming. In either case, changes in the crystallization level of the birefringent materials can result in a change in the refractive index differentials in the film.
• the potential crystallization changes in the birefringent materials may be further exacerbated by the simultaneous post-forming deformation and heating of the film which, in combination, may cause greater changes in the recrystallization/refractive index of the birefringent materials than either action alone.
• one material used in some preferred multilayer optical films according to the present invention is polyethylene naphthalate (PEN), which has a peak melting point of about 270 degrees Celsius (520 degrees Fahrenheit) using standard differential scanning calorimetry (DSC).
• PEN polyethylene naphthalate
• DSC differential scanning calorimetry
• the onset of melting is, however, often seen at about 255 degrees Celsius (490 degrees Fahrenheit) or below.
• This onset of melting may be attributable to the melting of less well-developed crystals within the PEN with the peak melting temperature being that point at which all or nearly all of the crystals in the material have melted.
• Heating the birefringent materials in the multilayer optical film may also increase mobility within the microstmcture, thereby activating crystal slip and other deformation mechanisms that could enhance extensibility of the multilayer optical film.
• a way to improve uniformity in the multilayer optical film during post-forming is to include materials in the multilayer optical film that are subject to strain hardening during deformation.
• Strain hardening is a property of materials in which the stress required to achieve a particular level of strain increases as the material is strained (i.e., stretched). Essentially, strain hardening materials may provide self-regulation of the thinning process due to post-forming. In terms of molding, as the multilayer optical film is stretched during post-forming, unquenched sections of the film that have not yet made contact with a mold surface will tend to draw more uniformly after the onset of strain hardening.
• Strain-hardening can help to regulate the uniformity of the drawing process, thus potentially reducing variations in the amount of deformation experienced by the film during post-forming. If the bandwidth of the multilayer optical film as manufactured is specifically designed to the final biaxial draw ratio of the post-forming process, rather than the draw ratio at tear or fracture as discussed above, then strain hardening can allow the design of a multilayer optical film with a narrower, more reflective band for use in the post-forming process. The effect of strain hardening may also influence the degree to which vacuum- forming as one post-forming process will allow for adequate or desirable mold replication. Pressurized or plug assisted molding techniques may be needed for accurate post-forming processing of materials in which strain hardening potentially increases the resistance of the film to stretching during the molding process. The effect of strain hardening may be influenced by both the post-forming draw conditions and the degree of draw (strain- hardening) before post-forming is initiated.
• this heat setting preferably follows the last post- forming drawing step; e.g., further crystallization can now be encouraged with attendant refractive index difference increases without consideration of further extensibility after the final post-forming draw step.
• the underdrawn multilayer optical films can be provided with and post-formed according to all of the variations described above with respect to multilayer optical films in general. In other words, they can be provided as highly reflective films that retain their reflectivity after post-forming, etc. Furthermore, the modifications discussed above for thinning effects should also be considered when manufacturing and processing underdrawn multilayer optical films as well.
• strain-hardening Another mechanical property that may be supplied by the substrate 104 is strain- hardening during deformation as discussed above with respect to the multilayer optical film. That strain-hardening property may be used to limit the stresses placed on the attached multilayer optical film 102, thereby acting to distribute the stresses over the multilayer optical film 102 in a way that improves the post-formability of the composite 100 over the post-formability of the multilayer optical film 102 alone.
• the difference in the index of refraction of the first and second polymers in one film-plane direction is often advantageous for the difference in the index of refraction of the first and second polymers in one film-plane direction to differ significantly in the finished film, while the difference in the orthogonal film-plane index is minimized.
• the first polymer has a large refractive index when isotropic, and is positively birefringent (that is, its refractive index increases in the direction of stretching)
• the second polymer will typically be chosen to have a matching refractive index, after processing, in the planar direction orthogonal to the stretching direction, and a refractive index in the direction of stretching which is as low as possible.
• Tri- or polyfunctional comonomers which can serve to impart a branched stmcture to the polyester molecules, can also be used. They may be of either the carboxylic acid, ester, hydroxy or ether types. Examples include, but are not limited to, trimellitic acid and its esters, trimethylol propane, and pentaerythritol.
• One typical formulation employs as the dicarboxylic acid or ester components dimethyl naphthalate at from about 20 mole percent to about 80 mole percent and dimethyl terephthalate or dimethyl isophthalate at from about 20 mole percent to about 80 mole percent, and employs ethylene glycol as diol component.
• dicarboxylic acids may be used instead of the esters.
• the number of comonomers which can be employed in the formulation of a coPEN second polymer is not limited. Suitable comonomers for a coPEN second polymer include but are not limited to all of the comonomers listed above as suitable PEN comonomers, including the acid, ester, hydroxy, ether, tri- or polyfunctional, and mixed functionality types.
• syndiotactic vinyl aromatic polymers and copolymers referred to in this invention generally have syndiotacticity of higher than 75% or more, as determined by carbon- 13 nuclear magnetic resonance.
• the degree of syndiotacticity is higher than 85%) racemic diad, or higher than 30%, or more preferably, higher than 50%, racemic pentad.
• PEN/PETcoPBT where "PBT” refers to polybutylene terephthalate, "PETG” refers to a copolymer of PET employing a second glycol (usually cyclohexanedimethanol), and “PETcoPBT” refers to a copolyester of terephthalic acid or an ester thereof with a mixture of ethylene glycol and 1,4-butanediol.

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• Health & Medical Sciences (AREA)
• Life Sciences & Earth Sciences (AREA)
• Physics & Mathematics (AREA)
• Dentistry (AREA)
• Oral & Maxillofacial Surgery (AREA)
• Veterinary Medicine (AREA)
• Public Health (AREA)
• Optics & Photonics (AREA)
• General Health & Medical Sciences (AREA)
• Animal Behavior & Ethology (AREA)
• Surgery (AREA)
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• General Physics & Mathematics (AREA)
• Heart & Thoracic Surgery (AREA)
• Engineering & Computer Science (AREA)
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• Pathology (AREA)
• Nuclear Medicine, Radiotherapy & Molecular Imaging (AREA)
• Biophysics (AREA)
• Biomedical Technology (AREA)
• Epidemiology (AREA)
• Optical Elements Other Than Lenses (AREA)
• Optical Filters (AREA)
• Dental Tools And Instruments Or Auxiliary Dental Instruments (AREA)
• Polarising Elements (AREA)
• Surface Treatment Of Optical Elements (AREA)
• Laminated Bodies (AREA)

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• 1998
  • 1998-07-31 US US09/127,137 patent/US6749427B1/en not_active Expired - Fee Related
• 1999
  • 1999-06-11 JP JP2000562778A patent/JP2002521729A/ja active Pending
  • 1999-06-11 EP EP99928564A patent/EP1099131B1/en not_active Expired - Lifetime
  • 1999-06-11 AU AU45605/99A patent/AU4560599A/en not_active Abandoned
  • 1999-06-11 WO PCT/US1999/013156 patent/WO2000007044A1/en not_active Ceased
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  • 1999-06-11 DE DE69916068T patent/DE69916068T2/de not_active Expired - Lifetime
• 2004
  • 2004-06-15 US US10/868,572 patent/US7077649B2/en not_active Expired - Fee Related

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