Patent Publication Number: US-2007116311-A1

Title: High strength curable compositions for the solid freeform fabrication of hearing aids

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to curable compositions and methods for producing high strength in-the-ear products using solid freeform fabrication (“SFF”) techniques. In particular, the present invention relates to curable compositions and methods for the production of hearing aid components using stereolithography.  
     BRIEF DESCRIPTION OF RELATED TECHNOLOGY  
      Hearing aids need to be durable, comfortable and reliable. Otherwise, end users may oftentimes resist their use. Durability focuses on the integrity of the material, long lasting, and integrity of the bonding of the components. Comfortability implies that the device is soft when placed in the ear canal. Reliability implies superior acoustic quality throughout the life of the device, which requires adequate sealing within the ear canal. The challenges to satisfy the comfort and reliability objectives are due to the dynamic nature of the ear canal, and the geometric alterations of the ear canal due to natural anatomical movement. The dynamic nature of the ear canal varies from person to person, and even the anatomical shape varies from ear to ear of the same person. The canal shape is geometrically altered by motion from the head and the mandible, usually causing elliptical elongation. These differences in canal shape and changes due to body movement make it difficult to achieve a comfortable and true acoustic seal.  
      Challenges in meeting comfort as well as durability are due to the nature of the ear canal and materials able to use. In the past, hearing aids were made from hard acrylic materials which have proven to be durable but uncomfortable. And when the device was displaced by motion, a leakage of sound pressure occurred. Attempts were made to use rubber instead of the hard acrylic materials, such as in U.S. Pat. No. 3,527,901 to Geib. Rubber is softer and more resilient than hard acrylic but it is not very comfortable and still lacks a true acoustic seal upon motion.  
      Attempt to use soft vinyl materials have also not been entirely successful in meeting the aforementioned characteristics. Although vinyl may be softer than rubber and offers a better acoustic seal, soft vinyl lacks durability, and in fact, after a relatively short period of time it shrinks, turns yellow and becomes hard or brittle. It is recommended in the hearing aid industry to replace vinyl components for behind-the-ear ear molds at least annually.  
      Silicone materials have also been used as the housing material, such as disclosed in U.S. Pat. No. 6,022,311 to Juneau et al. The &#39;311 patent discloses a two layer silicone housing bonded with an adhesive to the plastic faceplate of the device. Although silicone has a longer wear life than vinyl materials, it lacks strong bonding properties to the plastics commonly used in hearing aid instrumentality.  
      Polyurethanes have in the past been used for hearing aid components. For example, U.S. Pat. No. 5,763,503 to Cowperthwaite et al. discloses a housing for an in-the-ear hearing aid made from a solid and stiff polyurethane, polyesters or polyether to support the instrumentality.  
      Alternatively, instead of focusing on the housing material, attempts have been made to supply an attachment to the housing such as a covering or sleeve. This preserves the durability of the original housing material, while adding a comfort factor. For instance, U.S. Pat. No. 4,870,688 to Voroba et al. discloses a soft, resilient covering which is affixed to the rigid bonding of the ear shell. U.S. Pat. No. 5,002,151 to Oliveira et al. discloses a disposable sleeve made of a soft polyurethane retarded recovery foam attached to the ear piece by mating of screw threads on the sleeve and the ear piece. Unfortunately, a sleeve concept would lack durability and require continual replacement.  
      Further, hearing aid components, such as hearing aid housings, typically have been prepared by molding techniques. In general, a translucent mold representing the area of application in the individual&#39;s ear is formed. The composition is poured into the mold and cured therein to form the hearing aid component.  
      Therefore, there is a need for high-strength hearing aid components, which are durable and provide superior acoustics.  
     SUMMARY OF THE INVENTION  
      The present invention provides high-strength hearing aid components prepared by SFF techniques, which accurately use digital representations of the area of application in the individual&#39;s ear to additively form the three-dimensional hearing aid component. An added advantage is that the three-dimensional data may be stored for future use, such as, for example, hearing aid repairs.  
      In some embodiments, there is provided a curable composition including: at least one acrylate oligomer selected from urethane acrylate oligomers, epoxy acrylate oligomers, metallic acrylate oligomers and combinations thereof; at least one reactive diluent; and a cure system, wherein the composition when cured produces one or more properties selected from: Shore D hardness of at least about 85; tensile modulus of at least about 300,000 psi; and flexural modulus of at least about 300,000 psi.  
      Some embodiments provide a curable composition including: an aliphatic urethane acrylate present in amounts of about 10% to about 70% by weight of the composition; at least one reactive diluent selected from ethoxylated bisphenol A dimethacrylate, propoxylated neopentyl glycol diacrylate, dipentaerythritol monohydroxy pentaacrylate, isobornyl acrylate and combinations thereof, present in amounts of about 30% to about 90% by weight of the composition; a photoinitiator selected from methylbenzoylformate, diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide and combinations thereof, present in amounts of about 1% to about 10% by weight of the composition; and an antioxidant present in amounts of about 0.1% to about 1% by weight of the composition.  
      Some embodiments provide a hearing aid component, which includes the reaction product of: at least one acrylate oligomer selected from urethane acrylate oligomers, epoxy acrylate oligomers, metallic acrylate oligomers and combinations thereof; and at least one reactive diluent, wherein the composition when cured produces one or more properties selected from: Shore D hardness of at least about 85; tensile modulus of at least about 300,000 psi; and flexural modulus of at least about 300,000 psi.  
      In some embodiments, there is provided a method of making a hearing aid component including the steps of: (a) providing data of the three-dimensional size and shape of a region in an individual&#39;s ear, wherein the region corresponds to the hearing aid component to be made; (b) providing a first amount of a curable composition including: (i) at least one acrylate oligomer selected from urethane acrylate oligomers, epoxy acrylate oligomers, metallic acrylate oligomers and combinations thereof; (ii) at least one reactive diluent selected from ethoxylated bisphenol A dimethacrylate, propoxylated neopentyl glycol diacrylate, dipentaerythritol monohydroxy pentaacrylate, isobornyl acrylate and combinations thereof; and (iii) a cure system including at least one photoinitiator; (c) exposing the composition to photo-radiation for a time and intensity sufficient to cure a layer on the surface of the composition which corresponds to a cross-section of the hearing aid component; (d) providing a second amount of a curable composition; (e) applying the second amount to the cured layer to form a new layer and exposing the new layer to photo-radiation for a time and intensity sufficent to cure the new layer; and (f) repeating steps (d) and (e) until the hearing aid component is formed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  shows a perspective view of a hearing aid housing attached to a tip in accordance with an embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      As shown in  FIG. 1 , a hearing aid housing  12  (also commonly referred to as a shell) of hearing aid assembly  10  is constructed to fit within the outer ear of the wearer. Adhesively mated to the housing  12  is a tip  14  which projects through the concha and into the auditory canal area. The outer wall  16  of tip  14  forms a seal at the opening and in the auditory canal.  
      The hearing aid housing  12  typically contains amplifier means, volume adjustment control and battery access door, all of which are not shown. In operation, the amplifier means for receiving and amplifying unamplified sound is connected to a sound tube adapted for conveying sound from the amplifier means to the end of the tube inside the ear canal. The tip  14  encloses the tube for conveying sound and may contain other ports for various uses such as vent apertures. The end of the sound tube is positioned to deliver sound energy generally along the axis of the ear canal when inserted.  
      To provide a comfortable fit and an acoustic seal in the wearer&#39;s ear, hearing aid housing  12  is formed of a curable composition, which exhibits high strength yet is sufficiently deformable to provide an acoustic seal and be comfortable to the user. The sealing and comfort properties are important for commercial viability. Additionally, tip  14  may be mated to the hearing aid housing  12 . The tip  14  may be formed of the same curable composition as the hearing aid housing or alternatively the curable compositions disclosed in Applicants&#39; U.S. Pat. No. 6,829,362, entitled “Soft Molding Compound,” or Applicants&#39; U.S. patent application Ser. No. 10/922,458, entitled “Deformable Soft Molding Compositions” and filed on Aug. 20, 2004, both of which are incorporated herein by reference in their entirety.  
      The inventive curable compositions of the present invention exhibit high strength when cured allowing formation of hearing aid components using SFF techniques. The curable compositions include the reaction product of at least one acrylate oligomer and at least one reactive diluent, designed to provide a Shore D hardness of at least about 85, as well as high tensile modulus and flexural modulus. Desirably, the tensile modulus and flexural modulus both are at least about 300,000 psi. Curing is initiated by a cure system, which may include a photoinitiator, as well as other optional components.  
      Acrylate Oligomers  
      The curable compositions of the present invention contain at least one acrylate oligomer. The acrylate oligomer may be a urethane acrylate oligomer, an epoxy acrylate oligomer, a metallic acrylate oligomer or combinations thereof.  
      The urethane acrylate oligomer may be selected from a variety of materials, most desirably aliphatic urethane acrylates. Useful urethane acrylates include di- or tri-functionalized aliphatic urethane acrylates, which are capable of cross-linking during cure.  
      Representative commercially available urethane acrylate oligomers useful in the compositions of the present invention include EBECRYL 8402 (available from UCB Group), PHOTOMER 6008, 6019 and 6210 (available from Cognis, Corp.) and BR-582 (available from Bomar Specialties Co.).  
      EBECRYL 8402 is a low viscosity aliphatic urethane diacrylate. The viscosity of EBECRYL 8402 (neat) is about 500 cps at 65.5° C. EBECRYL 8402 typically exhibits the following properties: tensile strength of about 3300 psi and tensile elongation percent of about 90.  
      PHOTOMER 6008 and 6019 are aliphatic urethane triacrylates. PHOTOMER 6008 is a high viscosity acrylate resin. The viscosity range for PHOTOMER 6008 (neat) is about 12,000-20,000 cps at 60° C. PHOTOMER 6008 (homopolymer) exhibits the following properties: tensile strength of about 4800 psi and elongation percent of about 10. PHOTOMER 6019 is a medium viscosity acrylate resin. The viscosity range for PHOTOMER 6019 (neat) is about 2,500-4,000 cps at 60° C. PHOTOMER 6019 (UV-cured neat film) exhibits the following properties: tensile strength of about 8200 psi and elongation percent of about 8.  
      PHOTOMER 6210 is a low viscosity aliphatic urethane diacrylate. The viscosity range for PHOTOMER 6210 (neat) is about 8,500 to 15,000 cps at 25° C. PHOTOMER 6210 (with 33% tripropylene glycol diacrylate) exhibits the following properties: tensile strength of about 1400 psi and elongation percent of about 40.  
      BR-582 is an aliphatic linear polyether urethane acrylate. The viscosity of BR-582 (neat) is about 300,000 cps at 50° C. BR-582 (formulated with 30% isobornyl acrylate and Irgacure 184) exhibits the following properties: tensile strength of about 3300 psi and elongation percent of about 214.  
      Representative commercially available epoxy acrylate oligomers useful in the compositions of the present invention include PHOTOMER 3016 (available from Cognis, Corp.). PHOTOMER 3016 is bisphenol A epoxy diacrylate. The viscosity of PHOTOMER 3016 is about 4000 mPa.s at 60° C.  
      Representative commercially available metallic acrylate oligomers useful in the compositions of the present invention include CN 2400 series metallic acrylates (available from Sartomer Company, Inc., Exton, Pa.).  
      In accordance with the present invention, the acrylate oligomers may be employed in amounts of about 10% to about 70% by weight of the total composition, more desirably about 15% to about 50% by weight of the total composition.  
      Reactive Diluents  
      The compositions of the present invention also may contain at least one reactive diluent. Reactive diluents may be selected from those materials known in the art, and may be straight-chained, branched or cyclic, and may be at least partially aliphatic. The reactive diluent may soften the acrylate composition, for example, to exhibit a Shore D hardness of at least about 85 once cured.  
      Desirable reactive diluents for use in the present invention include monomers such as alkyl acrylates, methacrylates or alkoxylated alkyl (meth)acrylates, having about 6-18 carbon atoms in the alkyl moiety of the molecule. A variety of reactive diluents may be used, such as, for example, ethoxylated bisphenol A dimethacrylate, propoxylated neopentyl glycol diacrylate, dipentaerythritol monohydroxy pentaacrylate (“DIPETA”), isobornyl acrylate and combinations thereof.  
      Representative commercially available ethoxylated bisphenol A dimethacrylate reactive diluents include SR348, SR9036, CD 540, CD 542, SR101, SR150 and SR 541, available from Sartomer Company, Inc., Exton, Pa. Representative commercially available propoxylated neopentyl glycol diacrylate diluents include SR9003 and SR 9003IJ, available from Sartomer Company, Inc., Exton, Pa. Representative commercially available DIPETA reactive diluents include SR399E, also available from Sartomer Company, Inc., Exton, Pa.  
      Reactive diluents may be introduced independently in the overall composition or in a pre-mix of the urethane acrylate oligomer. In accordance with the present invention, reactive diluents may be employed in amounts of about 30% to about 90% by weight of the total composition, more desirably about 50% to about 85% by weight of the total composition.  
      Some embodiments of the present invention contain several reactive diluents, such as, for example, ethoxylated bisphenol A dimethacrylate in amounts of about 15-65%, propoxylated neopentyl glycol diacrylate in amounts of about 10-20%, dipentaerythritol monohydroxy pentaacrylate in amounts of about 1 -10% and isobornyl acrylate in amounts of about 15-40% by weight of the total composition.  
      Cure System  
      In applications where hearing aid components are to be made, the cure system is desirably one which is initiated by electromagnetic radiation. Photoradiation is desirable for its ability to produce a well-controlled cure and high quality parts efficiently. Various photoinitiators, such as UV, visible and infrared may be employed.  
      UV photoinitiators are generally effective in the 200 to 400 nm range, and particularly in the portion of the spectrum that borders on the invisible light and the visible portion just beyond this, e.g. &gt;200 nm to about 390 nm.  
      A variety of UV photoinitiators may be employed. Photoinitiators, those that will respond to UV radiation to initiate and induce curing of the (meth)acryl functionalized curable component, which are useful in the present invention include benzophenone and substituted benzophenones, acetophenone and substituted acetophenones, benzoin and its alkyl esters, xanthone and substituted xanthones, diethoxy-acetophenone, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, diethoxyxanthone, chloro-thio-xanthone, N-methyl diethanol-amine-benzophenone, 2-hydroxy-2-methyl-1-phenyl-propan-1-one, 2-benzyl-2-(dimethylamino)-1-[4-(4-morpholinyl)phenyl]-1-butanone, bisacyl phosphine oxides and mixtures thereof. Photoinitiators suitable for use in the present invention that will respond to visible light to initiate and induce curing include camphoroquinone peroxyester initiators and 9-fluorene carboxylic acid peroxyesters. Thermal initiators include 2,2′-azobisisobutyronitrile. The initiators set forth above are for the purposes of illustration only and are in no way meant to limit the initiators that may be used in the present invention.  
      Examples of such UV initiators include, but are not limited to: methylbenzoylforrnate (commercially available as DAROCUR MBF from Ciba Specialty Chemicals Inc.), diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (commercially available as LUCIRIN TPO from BASF Corp.), 1-benzoyl cyclohexanol (commercially available as IRGACURE 184 from Ciba Specialty Chemicals Inc.), phenyl bis(2,4,6-trimethylbenzoyl)phosphine oxide (commercially available as IRGACURE 819 from Ciba Specialty Chemical, Inc.) and combinations thereof.  
      Photoinitiators may be employed in amounts of about 1% to about 10% by weight of the total composition. More desirably, the photoinitiator is present in amounts of about 2% to about 6% by weight of the total composition.  
      The cure system also may include stabilizers and inhibitors, as well as chelating agents to control and prevent premature peroxide decomposition and polymerization. Among those useful inhibitors include phenols such as hydroquinone and quinones. Chelating agents may be used to remove trace amounts of metal contaminants. An example of a useful chelating agent is the tetrasodium salt of ethylenediamine tetraacetic acid (“EDTA”).  
      Optional Additives  
      A variety of optional additives also may be included in the compositions of the present invention. For instance, agents such as antioxidants, thickeners, plasticizers, fillers, elastomers, thermoplastics, dispersion stabilizers, hindered amine light stabilizers, UV absorbers, additional monomers and other well-known additives may be incorporated where functionally desirable.  
      Example of suitable antioxidants for use in the compositions of the present invention include thiodiethylene bis(3,5-di-tert-butyl-4-hydroxyhydrocinnamate) (commercially available as IRGANOX 1035 from Ciba Specialty Chemicals Inc.), tetrakis-(methylene-(3,5-di-terbutyl-4-hydrocinnamate)methane (commercially available as IRGANOX 1010 from Ciba Specialty Chemicals Inc.) and combinations thereof. Antioxidants may be present in amounts of about 0.1% to about 1% by weight of the total composition, more desirably about 0.1% to about 0.5% by weight of the total composition.  
      An example of a suitable hindered amine light stabilizer (“HALS”) is TINUVIN 292 (commercially available from Ciba Specialty Chemicals Inc.). Examples of suitable UV absorbers include TINUVIN 900 and TINUVIN 400 (both commercially available from Ciba Specialty Chemicals Inc.).  
      Additional monomers may include, for example, cyclic trimethylolpropane formal acrylate (commercially available as SR531 from Sartomer Company, Inc., Exton, Pa.), dimethylacrylamide, phenoxyethyl acrylate, alkoxylated hexanediol diacrylate (commercially available as SR564 from Sartomer Company, Inc., Exton, Pa.) and combinations thereof.  
      Various colorants also may be included in the inventive compositions. The term “colorants” is used to include dyes, pigments and other materials which can be used to impart color to the composition. Dyes are generally water-soluble organics, which often become water-insoluble once cured. Pigments may be organic or inorganic materials and are generally in the solid form.  
      Examples of useful pigments include, without limitation: white pigments, such as titanium oxide, zinc phosphate, zinc sulfide, zinc oxide and lithopone; red and red-orange pigments, such as iron oxide (maroon, red, light red), iron/chrome oxide, cadmium sulfoselenide and cadmium mercury (maroon, red, orange); ultramarine (blue, pink and violet), chrome-tin (pink) manganese (violet), cobalt (violet); orange, yellow and buff pigments such as barium titanate, cadmium sulfide (yellow), chrome (orange, yellow), molybdate (orange), zinc chromate (yellow), nickel titanate (yellow), iron oxide (yellow), nickel tungsten titanium, zinc ferrite and chrome titanate; brown pigments such as iron oxide (buff, brown), manganese/antimony/titanium oxide, manganese titanate, natural siennas (umbers), titanium tungsten manganese; blue-green pigments, such as chrome aluminate (blue), chrome cobolt-alumina (turquoise), iron blue (blue), manganese (blue), chrome and chrome oxide (green) and titanium green; as well as black pigments, such as iron oxide black and carbon black.  
      Combinations of pigments are generally used to achieve the desired color tone in the cured composition. Titanium and iron oxides, in combination, are particularly useful in creating flesh tones for hearing aids, and tips.  
      The colorants may be present in the compositions of the present invention in amounts sufficient to render the desired color. Colorants may be present, for example, in amounts of about 0.1 to about 10.0%, desirably about 0.2 to about 2.0% and more desirably in amounts of about 0.2 to about 0.6% by weight of the total composition. Insoluble pigments are the desired form of colorant useful in the compositions of the present invention.  
      Fillers may include inorganic fillers. At least a portion of the filler component may include filler particles in the 1-1,000 nanometer (“nm”) range. The inorganic filler may be colloidal silica nanoparticle dispersions in acrylate resins, in amounts of up to about 50% by weight. A commercially available example of such filler particles is sold under the tradename NANOCRYL, such as NANOCRYL C 150, by Hans Chemie, Germany. NANOCRYL fillers are colloidal silica sols in unsaturated (meth)acrylates. In particular, NANOCRYL is a silica reinforced trifunctional acrylate monomer having a silica content of about 50% by weight. The silica component is surface-modified, synthetic SiO 2  nanospheres with a particle size of less than about 50 nm and a narrow particle size distribution. NANOCRYL is a colloidal dispersion of the silica nanoparticles in the (meth)acrylate.  
      Another commercially available example of filler particles is sold under the tradename NANOPOX, such as NANOPOX XP 22, by Hans Chemie, Germany. NANOPOX fillers are monodisperse silica filler dispersions in epoxy resins, at a level of up to about 50% by weight. NANOPOX fillers ordinarily are believed to have a particle size of about 5 nm to about 80 nm. And NANOPOX XP 22 is reported to contain 40 weight percent of silica particles having a particle size of about 15 to 20 nm in the diglycidyl ether of bisphenol-F epoxy resin.  
      Tensile Properties  
      Standard measurements of the tensile properties of various substances are currently performed using tensile test procedures, such as those set forth in ASTM D882 herein incorporated by reference. These tensile test procedures are used for determining tensile properties of plastics in the form of thin sheeting, including film. These test methods measure the force required to break a specimen and the extent to which the material stretches or elongates to that breaking point. A stress to strain diagram is produced from these tests, which is then used to determine tensile modulus.  
      Tensile property measurements use a constant rate-of-grip separation machine, in which the test specimen is held between two grips (one fixed and one movable) in accordance with ASTM D882. A drive member separates the two grips at a controlled velocity. The force required to elongate the test specimen is measured (with the corresponding amount of material that has elongated) until the specimen breaks. A stress-strain curve may be produced, from which modulus of elasticity is calculated. The modulus of elasticity is the ratio between the stress per unit area to the amount of deformation resulting from that stress. A high tensile modulus generally means that the material is more rigid, i.e., more stress is necessary to produce a given amount of strain.  
      The curable compositions of the present invention, for example, may have a tensile modulus of at least about 300,000 psi (pounds per square inch).  
      Flexural Properties  
      Standard measurement of the flexural properties of various substances are currently performed using flexural test procedures, such as those set forth in ASTM D790 (“Flexural Properties of Un-Reinforced and Reinforced Plastics”) herein incorporated by reference.  
      Flexural modulus provides an indication of the stiffness of cured non-elastomeric adhesive materials. More specifically, the test procedures may measure the force required to bend a material under three-point loading conditions.  
      The curable compositions of the present invention, for example, may have a flexural modulus of at least about 300,000 psi (pounds per square inch).  
      Hardness  
      Standard measurements of the hardness of various substances are currently performed using durometer hardness test procedures, such as those set forth in ASTM D2240 herein incorporated by reference. The durometer hardness procedures are used for determining indentation hardness of various substances, and are particularly useful for elastomeric materials. These test methods measure the depression force of a specific type of indentor as it is forced under specific conditions against the material&#39;s surface. Due to the various parameters which influence hardness determinations, different durometer scales have been established. A particular scale is chosen depending on the type of material to be measured. For example, materials which are relatively soft, such as elastomeric materials, are measured on a Shore A scale. Slightly harder materials are measured on a Shore D scale. Shore D scale measurements use a steel rod indentor shaped with a pointed end, and a calibrated spring force, as shown in  FIG. 1  and Table 1, respectively of ASTM D2240. The indentor descends at a controlled rate against the specimen surface and a reading is recorded within a specified time period. This procedure is repeated multiple times at different positions on the specimen and the arithmetic mean of the results yields the Shore D measurement.  
      Durometer scales which are used for durometer hardness measurements include Shore A, B, C, D, DO, O, OO, and M. Each of theses scales has units from 0 to 100. There is no overlap between the scales, although certain materials may be suitable for testing on both scales. The geometry of the indentor and calibrated spring force scales influence the measurements, such that no simple relationship exists between the measurements obtained between different types of durometers. For example, the test for Shore D, which is designed for harder materials, is distinct from Shore A in that the indentor is shaped with a pointed tip and the calibrated spring force has a higher force scale then Shore A.  
      The curable compositions of the present invention, for example, may have a Shore D hardness of at least about 85 once cured.  
      Process of Making Hearing Aid Components  
      The present invention also is directed to methods of making hearing aid components. The hearing aid component may include a hearing aid housing and a hearing aid tip, which may be mated to the hearing aid housing. In some embodiments, the hearing aid component may be a single unit forming both the hearing aid housing and tip.  
      In accordance with the present invention, SFF techniques, particularly stereolithography and Inkjet processes, are employed to make the hearing aid components. Stereolithograpy uses an additive, built-up process to form a three-dimensional article, which is commonly referred to as rapid prototyping. In particular, stereolithography uses photo-radiation to cure additive layers of a composition to form a polymeric article, e.g., a hearing aid component.  
      More specifically, stereolithography uses data of the three-dimensional shape of the area of application in an individual&#39;s ear to control the layer by layer process of forming the article. In accordance with the present invention, data of the three-dimensional size and shape of a region in an individual&#39;s ear, which corresponds to the hearing aid component being made, may first be provided. The three-dimensional data may be provided by obtaining digital representations of the region in the individual&#39;s ear. The region may be, for example, the outer ear, ear canal or a combination thereof.  
      According to the present invention, a curable composition may be prepared by combining at least one acrylate oligomer, at least one reactive diluent and a cure system including a photoinitiator. The acrylate oligomer may be a urethane acrylate, epoxy acrylate, metallic acrylate or any combination thereof. The reactive diluent may be selected from ethoxylated bisphenol A dimethacrylate, propoxylated neopentyl glycol diacrylate, dipentaerythritol monohydroxy pentaacrylate and combinations thereof.  
      Once the components are combined, the curable composition may be exposed to photo-radiation for a time and intensity sufficient to solidify (cure) a layer at the surface of the composition. A UV laser may be used for curing. Desirably, this layer corresponds to a cross-section of the hearing aid component being made. This may be achieved by controlling the UV laser with the digitized three-dimensional data of the region in the individual&#39;s ear. Once the first layer is cured, a new layer of the curable composition may be applied to the first cured layer and similarly cured by photo-radiation. The new layer may be applied by lowering the first cured layer into the curable composition and covering it with a new layer of the composition. Layers may be repeatedly added and solidified in this manner until the hearing aid component having the desired three-dimensional shape is formed.  
      Desirably, each layer of the curable composition is cured to produce one or more of the following properties: Shore D hardness of at least about 85; tensile modulus of at least about 300,000 psi; and flexural modulus of at least about 300,000 psi.  
      Stereolithography techniques are described in detail in U.S. Pat. Nos. 6,540,045, 6,533,062, 6,413,697, and 6,136,497, each of which is incorporated herein by reference.  
      In some embodiments, Inkjet processes may be used to make the hearing aid component. Inkjet processes include both thermal phase change systems and photopolymer phase change systems. In thermal phase change systems, the polymer composition is first melted by heating. The molten polymer composition is jetted from one or more nozzles and the composition solidifies (cures) upon impact. The nozzles may be controlled by a computer program, which prescribes the configuration of each layer forming the three-dimensional object. The process is continued to add layers of the composition until the final three-dimensional object, i.e., hearing aid component, is formed. Thermal phase change techniques are described in detail in U.S. Pat. Nos. 6,132,665, 6,406,531, 6,133,353, 6,395,811, 6,528,613 and 6,476,122, each of which is incorporated herein by reference.  
      In photopolymer phase change systems, the photopolymer composition is ejected from inkjet heads and cured with UV flood lamps. The inkjet heads may be controlled by a computer program, which prescribes the configuration of each layer forming the three-dimensional object. The process is continued to add and cure layers of the composition until the final three-dimensional object, i.e., hearing aid component, is formed. Photopolymer phase change techniques are described in detail in U.S. Pat. Nos. 6,534,128, 6,467,897 and 6,259,962 and U.S. Patent Application Publication No. 2003/0032692, each of which is incorporated herein by reference.  
      The above-described SFF processes may be used to form a hearing aid housing, hearing aid tip or combination thereof. The hearing aid housing and tip may be formed separately and mated together. Alternatively, the hearing aid component may be a single unit including the housing and tip.  
      In some embodiments, the above-described processes may be used to prepare a hearing aid housing. The hearing aid housing may be mated to a tip component to form a hearing aid assembly. The tip component may be prepared in accordance with the curable composition and process described herein, or alternatively, the tip may be prepared in accordance with the disclosure of U.S. Pat. No. 6,829,362 or U.S. patent application Ser. No. 10/922,458, both referred to above.  
      For instance, a method of making the tip component may include pouring the curable composition disclosed in U.S. Pat. No. 6,829,362 or U.S. patent application Ser. No. 10/922,458 into the lower portion of a mold cavity, which is the tip cavity, of a light-penetrable mold, the mold having an exposed, generally upward-facing surface. The composition covers a major amount of the generally upward-facing surface of the tip cavity of the mold and fills the majority of the tip cavity. The surface is exposed to ultra-violet radiation through the transparent mold surface for a time and intensity sufficient to cure the composition. Once the tip is cured, it may be mated or adhered to the hearing aid housing by crosslinkage.  
      In accordance with the methods of the present invention, the resulting hearing aid components are self-supporting, free from surface blemishes and uniform in color. They can be pigmented to match a variety of skin tones and are ideally suited for hearing aid components, such as hearing aid housings and tips.  
      The following examples are intended to be non-limiting illustrations of compositions of the present invention.  
     EXAMPLES  
      Example 1  
      A curable composition was prepared in accordance with the present invention and tested for various physical properties. Table 1 below lists the weight percents for each component contained in the curable composition.  
                   TABLE 1                       COMPONENT   WEIGHT %                                        Ethoxylated Bisphenol A Dimethacrylate   59.75       Propoxylated Neopentyl Glycol Diacrylate   17.00       Aliphatic Urethane Diacrylate   15.00       Dipentaerythritol Monohydroxy Pentaacrylate   5.00       Methylbenzoylformate   3.00       Diphenyl (2,4,6-Trimethylbenzoyl) Phosphine Oxide   0.25       Antioxidant 1     0.20                   1 Thiodiethylene bis (3,5-di-tert-butyl-4-hydroxyhydrocinnamate) (IRGANOX 1035)             
 
      Once cured, the composition was tested for: yellowness index (determined in accordance with ASTM E313); tensile properties (determined in accordance with ASTM D882); flexural properties (determined in accordance with ASTM D790); hardness (determined in accordance with ASTM D2240); and shrinkage. The results of the tests with respect to each property are provided in Table 2 below.  
                           TABLE 2                                   PHYSICAL PROPERTY   RESULTS                                                    Yellowness               Initial   11.42           Post-cure   11.00           Delta   0.42           Tensile Properties           Modulus (psi)   315,000           Stress at break (psi)   7,400           Strain at break (%)   4.0           Flexural Properties           Modulus (psi)   346,000           Stress at max load (psi)   10,800           Strain at max load (in/in)   0.05           Hardness (Shore D)   85           Shrinkage           Volume (%)   7.3           Linear (%)   2.5                      
 
     Examples 2-17  
      Curable compositions were prepared in accordance with the present invention and tested for various physical properties. Tables 3-5 depict the weight percents for each component contained in the curable compositions of Examples 2-17.  
                       TABLE 3                                      EXAMPLE NO. (WEIGHT %)                                     COMPONENT   2   3   4   5   6                                             Aliphatic urethane triacrylate 1                     15.00       Acrylated urethane 2         15.00   15.00   15.00       Aliphatic urethane triacrylate 1  (50%), Triethylene   97.75       glycol dimethacrylate (25%), Hydroxypropyl       methacrylate &amp; Hydroxyethyl methacrylate (11%)       Ethoxylated Bisphenol A Dimethacrylate       59.50   59.75   57.55   57.55       Dipentaerythritol Monohydroxy Pentaacrylate       5.00   5.00   5.00   5.00       Neopentylglycol Propoxylate Diacrylate       17.00   17.00   17.00   17.00       1-Benzoyl Cyclohexanol 3     2.00   3.00   3.00       Diphenyl (2,4,6-Trimethylbenzoyl) Phosphine   0.25   0.50   0.25   0.25   0.25       Oxide       Thioethylene bis-(3,5-di-tert-butyl-4-hydroxy)               0.20   0.20       hydrocinnamate       Methylbenzoylformate               5.00   5.00                   1 PHOTOMER 6008 (available from Cognis, Corp.)              2 RSX 89462 (available from UCB Group)              3 IRGACURE 184 (available from Ciba Specialty Chemicals)             
 
     
       
         
           
               
               
             
               
                   
                 TABLE 4 
               
             
            
               
                   
                   
               
               
                   
                   
               
               
                   
                 EXAMPLE NO. 
               
               
                   
                 (WEIGHT %) 
               
            
           
           
               
               
               
               
               
            
               
                 COMPONENT 
                 7 
                 8 
                 9 
                 10 
               
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 Bisphenol A Epoxy Diacrylate 1   
                 25.00 
                 25.00 
                 25.00 
                 20.00 
               
               
                 Metallic Acrylate Oligomer 2  + Isobornyl 
                 40.00 
               
               
                 acrylate 
               
               
                 Metallic Acrylate Oligomer 2   
                   
                 40.00 
               
               
                 Metallic Acrylate Oligomer 2   
                   
                   
                 40.00 
               
               
                 Metallic Acrylate Oligomer 2   
                   
                   
                   
                 30.00 
               
               
                 Neopentylglycol Propoxylate Diacrylate 
                 32.75 
                 32.75 
                 32.75 
                 47.75 
               
               
                 l-Benzoyl Cyclohexanol 3   
                 2.00 
                 2.00 
                 2.00 
                 2.00 
               
               
                 Diphenyl (2,4,6-Trimethylbenzoyl) 
                 0.25 
                 0.25 
                 0.25 
                 0.25 
               
               
                 Phosphine Oxide 
               
               
                   
               
               
                     1 PHOTOMER 3016 (available from Cognis, Corp.)    
               
               
                     2 CN 2402 (available from Sartomer)    
               
               
                     3 IRGACURE 184 (available from Ciba Specialty Chemicals)    
               
            
           
         
       
     
     
       
         
           
               
               
             
               
                   
                 TABLE 5 
               
             
            
               
                   
                   
               
               
                   
                   
               
               
                   
                 EXAMPLE (WEIGHT %) 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 COMPONENT 
                 11 
                 12 
                 13 
                 14 
                 15 
                 16 
                 17 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 Acrylated urethane 1   
                   
                   
                   
                 40.00 
                   
                   
                   
               
               
                 Aliphatic Urethane Oligomer 
                   
                   
                 20.00 
                   
                   
                   
                   
               
               
                 Bisphenol A Epoxy Diacrylate 2   
                 20.00 
                   
                 20.00 
                 25.00 
                 20.00 
                 20.00 
                 25.00 
               
               
                 Metallic Acrylate Oligomer 3  + 
                   
                   
                   
                   
                   
                   
                 40.00 
               
               
                 Isobornyl acrylate 
               
               
                 Aliphatic Urethane Oligomer and 
                 35.00 
                 40.00 
                   
                   
                 35.00 
                 35.00 
                   
               
               
                 Cyclic Trimethylolpropane Formal 
               
               
                 Acrylate (25%) 4   
               
               
                 Ethoxylated Bisphenol A 
                   
                 25.00 
                   
                   
                   
                   
                   
               
               
                 Dimethacrylate 
               
               
                 Neopentylglycol Propoxylate 
                 42.75 
                 32.75 
                 57.75 
                 32.75 
                 32.75 
                 32.75 
                 32.75 
               
               
                 Diacrylate 
               
               
                 Cyclic Trimethylolpropane Formal 
                   
                   
                   
                   
                 10.00 
                 10.00 
                   
               
               
                 Acrylate 
               
               
                 1-Benzoyl Cyclohexanol 5   
                 2.00 
                 2.00 
                 2.00 
                 2.00 
                 2.00 
                 2.00 
                 2.00 
               
               
                 Diphenyl (2,4,6-Trimethylbenzoyl) 
                 0.25 
                 0.25 
                 0.25 
                 0.25 
                 0.25 
                 0.25 
                 0.25 
               
               
                 Phosphine Oxide 
               
               
                 Hindered Amine Light Stabilizer 6   
                   
                   
                   
                   
                   
                 1.00 
                 1.00 
               
               
                 Hydroxybenzotriazole 7   
                   
                   
                   
                   
                   
                 1.00 
                 1.00 
               
               
                   
               
               
                     1 RSX 89462 (available from UCB Group)    
               
               
                     2 PHOTOMER 3016 (available from Cognis, Corp.)    
               
               
                     3 CN 2402 (available from Sartomer)    
               
               
                     4 PRO-7157 (available from Sartomer Company, Inc.)    
               
               
                     5 IRGACURE 184 (available from Ciba Specialty Chemicals)    
               
               
                     6 TINUVIN 292 (available from Ciba Specialty Chemicals)    
               
               
                     7 TINUVIN 900 (available from Ciba Specialty Chemicals)    
               
            
           
         
       
     
      Once cured, compositions 2-17 were tested for: yellowness index (determined in accordance with ASTM E313); tensile properties (determined in accordance with ASTM D882); flexural properties (determined in accordance with ASTM D790); and/or hardness (determined in accordance with ASTM D2240). The results of the tests with respect to each property for the indicated compositions are provided in Tables 6-9 below.  
                       TABLE 6                                      EXAMPLE NO.                             TENSILE PROPERTIES   2   3   4                                     Modulus (PSI)   301,000   317,000   297,000       Stress @ Max Load (PSI)   7,690   7,430   5,970       Strain @ Max Load (%)   5   4   3       Stress @ Break (PSI)   6,360   7,430   5,970                  
 
     
       
         
           
               
               
             
               
                 TABLE 7 
               
             
            
               
                   
               
               
                   
               
               
                 FLEXURAL 
                 EXAMPLE NO. 
               
            
           
           
               
               
               
               
               
            
               
                 PROPERTIES 
                 2 
                 4 
                 5 
                 6 
               
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 Modulus (PSI) 
                 326,000 
                 346,000 
                 270,000 
                 320,000 
               
               
                 Stress @ Max Load 
                 11,370 
                 10,820 
                 7,960 
                 10,250 
               
               
                 (PSI) 
               
               
                 Strain @ Max Load 
                 0.05 
                 0.04 
                 0.04 
                 0.05 
               
               
                 (%) 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
             
               
                   
                 TABLE 8 
               
             
            
               
                   
                   
               
               
                   
                   
               
               
                   
                 EXAMPLE NO. 
               
            
           
           
               
               
               
               
               
               
               
            
               
                   
                 HARDNESS 
                 2 
                 3 
                 4 
                 5 
                 6 
               
               
                   
                   
               
               
                   
                 ShoreD 
                 83 
                 85 
                 84 
                 83 
                 82 
               
               
                   
                   
               
            
           
         
       
     
     
       
         
           
               
               
             
               
                   
                 TABLE 9 
               
             
            
               
                   
                   
               
               
                   
                   
               
               
                   
                 EXAMPLE NO. 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 YELLOWNESS 
                 4 
                 5 
                 7 
                 15 
                 16 
                 17 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Initial 
                 9.25 
                 12.28 
                 7.37 
                 4.84 
                 6.65 
                 8.07 
               
               
                 120″ Post Cure 
                 18.22 
                 11.58 
                 13.53 
                 7.75 
                 7.18 
                 9.88 
               
               
                 Delta 
                 8.97 
                 −0.70 
                 6.16 
                 2.91 
                 0.54 
                 1.81 
               
               
                   
               
            
           
         
       
     
     Examples 18-34  
      Curable compositions were prepared in accordance with the present invention and tested for cure through depth. Tables 10-11 depict the weight percents for each component contained in the curable compositions of Examples 18-34. The cure through depth of the compositions was measured by exposure to a 550 mW/cm 2  UV lamp for 3, 7 and 10 second intervals. These results also are provided in Tables 10-11.  
                       TABLE 10                                      EXAMPLE NO. (WEIGHT %)                                                     18   19   20   21   22   23   24   25                             COMPONENT                                                 Bisphenol A Epoxy Diacrylate 1     20.00   20.00   20.00   20.00   20.00   20.00   20.00   30.00       Aliphatic urethane triacrylate 2     20.00   20.00   20.00   20.00   20.00       50% Nanosilica and 50% Trimethylol   50.00   50.00   50.00   50.00   50.00       30.00       Propane Triacrylate 3         Aliphatic Urethane Oligomer and Cyclic                       35.00       Trimethylolpropane Formal Acrylate       (25%) 4         Aliphatic Urethane Oligomer 5                             20.00       Aliphatic Urethane Oligomer 6                                 37.60       Neopentylglycol Propoxylate Diacrylate                       42.60       Dimethylacrylamide   8.50   9.50   8.60   8.60   7.60       Phenoxyethylacrylate                           27.60       Cyclic Trimethylolpropane Formal                               10.00       Acrylate 7         Alkoxylated Hexanediol Diacrylate 8                                 20.00       Camphorquinone   0.50           0.50   0.50   0.50   0.50   0.50       N,N-dimethyl-p-toluidine (“DMpT”)   0.50           0.50   0.50   0.50   0.50   0.50       Bisacyl Phosphine Oxide   0.10   0.10   1.00       1.00   1.00   1.00   1.00       Pigment   0.40   0.40   0.40   0.40   0.40   0.40   0.40   0.40       CURE THROUGH DEPTH (mm)        3 second cure   0.00   0.00   0.00   0.00   0.24   0.00   0.35   0.00        7 second cure   0.45   0.00   0.24   0.35   0.61   0.53   0.55   0.39       10 second cure   0.59   0.00   0.32   0.48   0.68   0.64   0.74   0.61                   1 PHOTOMER 3016 (available from Cognis, Corp.)              2 PHOTOMER 6008 (available from Cognis, Corp.)              3 NANOCRYL C-150 (available from Hanse Chemie)              4 PRO 7157 (available from Sartomer Company, Inc.)              5 BR-582E (available from Bomar Specialties Co.)              6 PHOTOMER 6019 (available from Cognis, Corp.)              7 SR531 (available from Sartomer Company, Inc.)              8 SR564 (available from Sartomer Company, Inc.)             
 
     
       
         
           
               
               
             
               
                   
                 TABLE 11 
               
             
            
               
                   
                   
               
               
                   
                   
               
               
                   
                 EXAMPLE NO. (WEIGHT %) 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
            
               
                   
                 26 
                 27 
                 28 
                 29 
                 30 
                 31 
                 32 
                 33 
                 34 
               
               
                   
                   
               
            
           
           
               
            
               
                 COMPONENT 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
            
               
                 Bisphenol A Epoxy Diacrylate 1   
                   
                   
                   
                 15.00 
                   
                 15.00 
                 15.00 
                 12.00 
                 12.00 
               
               
                 Aliphatic urethane triacrylate 2   
                   
                 15.00 
                 27.60 
                   
                 15.00 
               
               
                 Acrylated urethane 3   
                 50.00 
               
               
                 50% Nanosilica and 50% 
                 12.60 
                 17.60 
                   
                   
                 17.60 
               
               
                 Trimethylol Propane Triacrylate 4   
               
               
                 Aliphatic Urethane Oligomer 
                   
                 30.00 
                 15.00 
                 30.00 
                 30.00 
                 30.00 
                 30.00 
                 25.00 
                 25.00 
               
               
                 Isobornyl Acrylate 
                 30.00 
                 35.00 
                 35.00 
                 35.00 
                 35.00 
                 35.00 
                 45.00 
                 40.00 
                 42.00 
               
               
                 Dipentaerythritol Monohydroxy 
                 5.00 
                   
                 5.00 
                 5.00 
                   
                 5.00 
                 5.00 
                 5.00 
                 5.00 
               
               
                 Pentaacrylate 
               
               
                 Neopentylglycol Propoxylate 
                   
                   
                 15.00 
                 12.60 
                   
                 12.60 
                 12.60 
                 13.60 
                 13.60 
               
               
                 Diacrylate 
               
               
                 Camphorquinone 
                 0.50 
                 0.50 
                 0.50 
                 0.50 
               
               
                 DMpT 
                 0.50 
                 0.50 
                 0.50 
                 0.50 
               
               
                 Bisacyl Phosphine Oxide 
                 1.00 
                 1.00 
                 1.00 
                 1.00 
                 2.00 
                 2.00 
                 2.00 
                 4.00 
                 2.00 
               
               
                 Pigment 
                 0.40 
                 0.40 
                 0.40 
                 0.40 
                 0.40 
                 0.40 
                 0.40 
                 0.40 
                 0.40 
               
               
                 CURE THROUGH DEPTH (mm) 
               
               
                  3 second cure 
                 0.00 
                 0.00 
                 0.00 
                 0.22 
                 0.15 
                 0.15 
                   
                   
                 0.00 
               
               
                  7 second cure 
                 0.54 
                 0.60 
                 0.45 
                 0.54 
                 0.39 
                 0.43 
                 0.32 
                   
                 0.33 
               
               
                 10 second cure 
                 0.68 
                 0.80 
                 0.80 
                 0.72 
                 0.50 
                 0.54 
                 0.45 
                   
                 0.45 
               
               
                   
               
               
                     1 PHOTOMER 3016 (available from Cognis, Corp.)    
               
               
                     2 PHOTOMER 6008 (available from Cognis, Corp.)    
               
               
                     3 RSX 89462 (available from UCB Group)    
               
               
                     4 NANOCRYL C-150 (available from Hanse Chemie)    
               
            
           
         
       
     
     Examples 35-37  
      Curable compositions were prepared in accordance with the present invention. Table 12 depicts the weight percents for each component contained in the curable compositions of Examples 35-37.  
                       TABLE 12                                      EXAMPLE NO.           (WEIGHT %)                             COMPONENT   35   36   37                                     Aliphatic Urethane Oligomer and Cyclic   29.00   35.00   40.00       Trimethylolpropane Formal Acrylate (25%)       Bisphenol A Epoxy Diacrylate   11.00   17.00       Ethoxylated Bisphenol A Dimethacrylate           19.00       Isobornyl Acrylate   37.00   25.00   18.00       Dipentaerythritol Monohydroxy   5.00   5.00   5.00       Pentaacrylate       Neopentylglycol Propoxylate Diacrylate   14.025   14.025   14.025       1-benzoyl cyclohexanol 1     3.00   3.00   3.00       Phenyl bis (2,4,6-trimethylbenzoyl)   0.50   0.50   0.50       phosphine oxide 2         Hindered Amine Light Stabilizer 3     0.10   0.10   0.10       UV Absorber 4     0.10   0.10   0.10       Pigment   0.275   0.275   0.275                   1 IRGACURE 184 (available from Ciba Geigy Specialty Chemicals)              2 IRGACURE 819 (available from Ciba Geigy Specialty Chemicals)              3 TINUVIN 292 (available from Ciba Geigy Specialty Chemicals)              4 TINUVIN 400 (available from Ciba Geigy Specialty Chemicals)