Independent thermoformed diaphragm

Abstract

Improved membrane compositions, methods, and systems for producing thermoformed dental appliances are disclosed.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of U.S. Provisional Application No. 62 / 791,798, filed January 12, 2019, which is incorporated herein by reference in its entirety. Technical Field

[0003] Improved membrane compositions, methods, and systems for producing thermoformed articles. Background Art

[0004] Thermoforming is a process in which a heated thermoplastic sheet material is formed over a mold, which may be male or female, to impart the desired shape to the sheet and then cooled to lock in that shape, thereby producing a thermoformed article.

[0005] It is necessary that the thermoformable sheet material does not adhere to the mold, is easily demoldable, has no material transfer or chemical reaction between the mold and the thermoformable sheet material, and that defects in the mold are not transferred to the thermoformed part.

[0006] One area of ​​particular interest is the production of dental or orthodontic appliances, including but not limited to braces, retainers, splints, sports mouthguards, indirectly bonded appliances, and bleaching trays. These dental and orthodontic appliances can be custom-made to fit the patient using a model of the patient’s dentition as a thermoforming mold.

[0007] To facilitate the forming and removal of the thermoformed article from the model, a diaphragm (also called a "release membrane") may be used. Such diaphragms are typically applied as a liquid by spraying, dipping, or brushing a film-forming material onto the model. It is therefore typically necessary to allow the release material to dry or cure before it can be thermoformed thereon. Examples of commercial diaphragm products include: Co-Sep Liquid Spacer sold by CG America and Triad Mold Release Agent sold by Dentsply. U.S. Patent No. 2,432,688 describes an alginate-based release film (or diaphragm) that can be applied to a model. Other commercial dental release materials may be polymer solutions or emulsions, dispersed waxes, dispersed silicone polymers, surfactants, or other agents.

[0008] Separators, used to prevent chemical reactions or material transfer between the pattern and the thermoformed article, include various barrier materials such as wax or putty, which may be applied to the pattern to cover undercut areas or make other modifications.

[0009] Some dental thermoformable sheet materials, such as polyester, acrylic, or polycarbonate, may be covered with a protective film on one or more surfaces to prevent scratching or surface abrasion during shipping and handling. These films are typically polyolefins, such as polyethylene, with a low-tack adhesive used to secure them to the film. Typically, the adhesive is an acrylic pressure-sensitive adhesive, a rubber-based material, or a soft polymer. In addition to providing handling protection, some of these films can also act as a separator, provided that they are compatible with thermoforming and do not permanently bond or stick to the model during the thermoforming process. These films must be carefully selected and pre-applied to the thermoformable material, usually by heat or pressure lamination, which adds an extra step to the production process. An example of a dental thermoformable sheet with an integrated separator is the "Track A and Track B" material sold by Forestadent in Germany, which is a copolyester thermoformable sheet with a polyethylene protective film.

[0010] If the model (or mold) onto which the thermoforming is to be performed is not smooth, such as when manufactured by 3D printing or cast from plaster or dental stone, an unsatisfactory optical finish may be transferred to the thermoformed article. This is particularly problematic in the manufacture of orthodontic appliances. An unsatisfactory surface finish may cause the appliance to appear hazy or gray. Furthermore, a rough surface may promote the deposition of calcium deposits from saliva and provide a difficult-to-clean surface where bacteria may accumulate.

[0011] Some types of thermoformable sheet materials cannot be provided with a protective liner due to their resistance to adhesion, or they may be chemically incompatible with the liner material or the adhesive used to attach the liner. Applying a protective film to a thermoformable sheet can be time-consuming and expensive, and the process often requires specialized equipment.

[0012] While there are many diaphragms on the market, there remains a need for a diaphragm that is cost-effective, has improved surface quality, does not require time-consuming additional manufacturing steps, and can be used with a variety of molds and thermoformable materials. Such a diaphragm is particularly needed for use in the manufacture of dental appliances. Summary of the Invention

[0013] The present invention provides a separate peelable membrane for use in thermoforming dental appliances.

[0014] The separate peelable membrane may comprise a polyolefin having an average thickness of about 37 to 75 microns; a minimum X or Y dimension of about 110 mm; a maximum X or Y dimension of about 150 mm; a melting point of about 80°C to about 160°C; a modulus of about 50 to 700 MPa; and MD and XD orientations less than 100%.

[0015] The separate peelable membrane may include a single layer; two or more layers wherein one layer has a higher melting point than another layer; or three or more layers wherein an inner layer has a higher melting point than any of the outer layers.

[0016] The separate peelable membrane may also include one or more of the following features: a trouser tear strength greater than 20 N / mm (Newtons / mm); two or more radial slits, each radial slit having a length greater than about 10 mm; two or more triangular cuts, occupying about 5% to about 50% of the total area; a conical or spherical shape, wherein the height of the Z axis is greater than about 10 mm; a slip agent or release agent selected from amides, esters and silicones; or 0.1% to 2% of an anti-sticking additive selected from silica, diatomaceous earth, talc and calcium carbonate.

[0017] The separate peelable membrane may comprise polyethylene and have a melt index of less than 10, preferably less than 5 or less than 1 according to ASTM D1238 at a temperature of 230° C. and a load of 2.16 Kg.

[0018] The separate peelable membrane may be provided as a "laminate" or as a plurality of separate membranes disposed between aligner materials, which may be the same or different.

[0019] The present invention also provides methods and systems for producing thermoformed articles using the separate peelable membranes described herein.

[0020] According to one embodiment, the present invention provides a separate peelable membrane for use in thermoforming of dental appliances, comprising (a) a material having a melt index of less than 10 according to ASTM D1238 at a temperature of 230°C and a load of 2.16 kg; and (b) a trouser tear strength greater than 20 N / mm.

[0021] According to another embodiment, the present invention provides a separate peelable membrane for use in thermoforming of dental appliances, comprising (a) a material having a melt index of about 2 to 50 according to ASTM D1238 at a temperature of 150°C and a load of 2.16 kg; and (b) a trouser tear strength greater than 20 N / mm.

[0022] According to another embodiment, the present invention provides a method for producing a thermoformed article. The method comprises the steps of placing a separate peelable membrane on a male or female dental mold or model; heating a thermoformable sheet material to a temperature above the melting point of the separate peelable membrane; thermoforming the heated sheet material on the separate peelable membrane and the mold or model in a thermoforming apparatus; separating the thermoformed article from the mold or model; and removing the separate peelable membrane from the thermoformed article and the mold or model, thereby producing the thermoformed article.

[0023] According to another embodiment, the present invention provides a system for producing thermoformed dental appliances, the system comprising a positive or negative mold or pattern; a thermoformable sheet material; a separate peelable membrane comprising (i) a material having a melting point lower than the thermoforming temperature of the thermoformable sheet material and (ii) a trouser tear strength greater than 20 N / mm; and a thermoforming apparatus.

[0024] Other features and advantages of the present invention will be realized by reference to the remainder of the specification, including the drawings and claims. Other features and advantages of the present invention, as well as the structure and operation of various embodiments of the present invention, are described in detail below with reference to the accompanying drawings. In the drawings, the same reference numerals indicate identical or functionally similar elements. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1A is a schematic diagram of a prior art thermoformable sheet having a protective film laminated to or adhered to one side.

[0026] Figure 1B is a schematic diagram of a thermoforming mold (mold) coated with a release material.

[0027] Figure 1C is a schematic side view of a free-standing diaphragm placed on a thermoforming mold (form) prior to thermoforming.

[0028] Figure 1D is a schematic diagram of the separator after thermoforming, showing areas where the membrane is folded (exemplified by dark triangles).

[0029] Figure 2A is a schematic diagram of an exemplary diaphragm with four radial slits.

[0030] Figure 2B is a schematic diagram of an exemplary diaphragm with four triangular portions removed.

[0031] Figure 2C is a schematic side view of an exemplary circular diaphragm having a conical shape.

[0032] Figure 2Dis a schematic side view of an exemplary diaphragm having a hemispherical shape.

[0033] Figure 2E is a schematic top view of an exemplary membrane having creases to facilitate controlled folding.

[0034] Figure 3A is a schematic top view of an exemplary diaphragm and mold on a thermoforming platform.

[0035] Figure 3B is a schematic top view of an exemplary diaphragm and mold on a thermoforming platform.

[0036] Figure 4A is a schematic diagram of a single-layer diaphragm.

[0037] Figure 4B Schematic diagram of a two-layer membrane. The "A" layer of the two-layer membrane can be the same as or different from the "B" layer of the two-layer membrane, and the B layer can have a higher melt flow than the A layer.

[0038] Figure 4C Schematic diagram of a three-layer or more-layer separator. One layer of the three-layer or more-layer separator can be the same as or different from the other layers of the separator. DETAILED DESCRIPTION

[0039] All patents, publications, and patent applications cited in this specification are herein incorporated by reference to the same extent as if each individual patent, publication, or patent application was specifically and individually indicated to be incorporated by reference in its entirety for all purposes.

[0040] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the invention belongs. Other methods and materials similar or equivalent to those described herein can be used in the practice of the present invention.

[0041] In describing and claiming the present invention, the following terminology will be used in accordance with the definitions set out below.

[0042] As used in this specification and claims, in the context of describing the disclosed embodiments (especially in the context of the claims), the use of the terms "a" and "an" and "the" and similar referents should be interpreted as covering both the singular and the plural, unless otherwise stated herein or clearly contradicted by the context. Unless otherwise stated, the terms "comprising", "having", "including" and "containing" should be interpreted as open terms (i.e., meaning "including but not limited to"). The term "connected" should be interpreted as being partially or completely contained within, attached to or joined together, even if something is inserted. The phrase "based on" should be understood to be open, without being limited in any way, and is intended to be interpreted or otherwise interpreted as "based at least in part on" where appropriate. Unless otherwise stated herein, references to numerical ranges herein are only intended to be used as a shorthand way of referring to each individual value falling within the range individually, and each individual value is incorporated into the specification as if it were quoted separately herein. Unless otherwise stated herein or clearly contradicted by the context, all methods described herein can be performed in any suitable order. Unless otherwise stated, the use of any and all examples or exemplary language (e.g., "such as") provided herein is intended merely to better illustrate embodiments of the present disclosure and does not limit the scope of the present disclosure. No language in the specification should be construed as indicating any non-claimed element is essential to the practice of the present disclosure.

[0043] The term "braces" is used to refer to the close-fitting, custom-made shells that are fitted over the teeth and used for orthodontic treatment.

[0044] The term "dental appliance" is used herein to refer to any device that is placed in or on the teeth or gums of a subject. Dental appliances include, but are not limited to, orthodontic, restorative, retaining, snoring / airway, cosmetic, denture, therapeutic, and habit change devices.

[0045] The terms "modulus," "Young's modulus," and "elastic modulus" are used herein to refer to a material's stiffness and / or its resistance to stretching. The higher the modulus of a material, the stiffer it is. For polymers, mechanical properties, including elastic modulus and other properties, can be measured according to ASTM D638 or, for softer materials, the 1% secant modulus can be measured according to ASTM D882.

[0046] The term "flexural modulus" is used herein to refer to the stiffness of a material and / or its resistance to bending deformation. The higher the flexural modulus of a material, the more resistant it is to bending. For isotropic materials, the flexural modulus and elastic modulus are nearly identical. Flexural modulus can be measured using the test outlined in ASTM D790, and the units used are force per unit area. Unless otherwise specified, "modulus" refers to the elastic modulus.

[0047] The terms "mold," "form," and "substrate" are used interchangeably herein to refer to an object used to impart a desired shape to a material during a forming operation such as thermoforming or compression or injection molding.

[0048] The term "polymer sheet" is used herein interchangeably with the term "plastic sheet."

[0049] As used herein, the term "peelable film" refers to a film that, after being applied to a substrate, can be substantially removed without damaging the substrate or the film itself.

[0050] The term "retainer" is used herein to refer to a dental appliance used to hold teeth in their correct position, particularly after orthodontic treatment.

[0051] As used herein, the term "membrane" refers to a material that forms a physical barrier between a form and one or more materials formed on the form.

[0052] The term "shell" is used herein to refer to a polymeric shell that fits over a tooth and is removably placed over the tooth.

[0053] As used herein, the term "thermoforming temperature" refers to the temperature of a polymer sheet when it is thermoformed.

[0054] The term "thermoplastic polymer" is used herein to refer to a polymer that is relatively stiff at lower temperatures, becomes pliable or moldable when subjected to heat and pressure, and becomes relatively stiff again when cooled, as long as the heat and pressure do not chemically change the polymer.

[0055] The term "thermosetting polymer" is used herein to refer to a polymer composition that is a solid or viscous material at relatively low temperatures and that irreversibly changes to a non-fusible polymer network when subjected to heat and / or suitable radiation, and / or when the material undergoes one or more chemical reactions. The term thermoset polymer is used to refer to a cured thermosetting polymer.

[0056] The term "tooth" includes natural teeth, including natural teeth modified by fillings or by crowns, implants, artificial teeth that are part of a bridge or other fitting affixed to one or more natural teeth or implants, and artificial teeth that may be permanent or part of a removable fitting.

[0057] The improved compositions, methods, and systems described herein provide solutions to unmet needs in the thermoforming and dental appliance manufacturing industries. Currently, thermoplastic sheets are placed on a mold and thermoformed to produce thermoformed articles. It is difficult to produce clean thermoformed parts that are free of surface defects and clean. Typically, when removing the thermoformed article from the mold, wax or other materials are transferred to the thermoformed article and / or defects such as ridges are present in the thermoformed article, resulting in undesirable cosmetic and / or optical properties. In addition, due to adhesion or topological factors caused by heat and pressure, it is usually difficult to remove the thermoformed article from the mold.

[0058] The compositions, methods, and systems disclosed herein are cost-effective and provide (1) improved surface quality and optical clarity of thermoformed articles; (2) ease of removal from the mold and thermoformed article; (3) physical and or chemical isolation between the mold and the thermoformed article; (4) good tear and crack resistance; (5) no need for time-consuming additional manufacturing steps; and (6) compatibility with a variety of molds and thermoformable materials.

[0059] Currently, when a membrane is useful or desired in a thermoforming process and is not provided on the thermoformable sheet used, the user must resort to one of two methods that require additional steps and costs.

[0060] Users can thermoform a thin, inert plastic sheet over a pattern, allow it to cool, and then thermoform a second time on top with the desired thermoformable material.

[0061] In the dental appliance field, an example of such a sheet is Isofolan TM , a 0.1 mm thick polyethylene sheet available from Great Lakes Orthodontics and Scheu Dental. US Pat. No. 7,758,346 B1 provides a description of a process for thermoforming a thin, inert plastic sheet onto a model. It is well known in the art of thermoforming dental appliances that plastic films, such as Isofolan, must be heated above their melting point to be formed onto a model, and acceptable conformation requires pressure or vacuum forming. Tests evaluating this method are described in Example 1, and the results indicate that the process is not effective.

[0062] Alternatively, users can apply a liquid release material, such as Triad Mold Release Agent, available from Dentsply, to the mold and allow it to dry before thermoforming. Many liquid release films are available on the market, but they often require time-consuming drying before molding and meticulous cleaning after thermoforming to remove residue. Furthermore, most liquid release materials cannot address optical defects in the mold or thermoformed piece.

[0063] The compositions, methods, and systems disclosed herein allow users to quickly complete the thermoforming process in a single step, producing clean thermoformed articles with few or no surface defects that are easily removed from the mold after thermoforming. These compositions, methods, and systems rely on the use of the membranes detailed herein, allowing users to simply place the membrane on top of the mold prior to thermoforming.

[0064] Common defects in the prior art include lack of optical clarity (cloudiness) of the thermoformed part, lack of ready (easy) removal from the mold and / or thermoformed article, and the presence of crease lines on the thermoformed article.

[0065] Crease lines are typically the result of folding of the membrane resulting in different thicknesses, thereby creating crease lines where the folding occurs. The amount of folding needs to be limited. As disclosed herein, folding is minimized by using membranes that, for example: (1) have slits radially on the exterior of the membrane; (2) have scalloped portions removed; (3) have radial creases; (4) have triangular portions removed, which convert to a conical shape; (5) are concave in shape to better fit the mold; and (6) are grooved and conform to the mold better. See, e.g. Figure 2A 、 Figure 2B 、 Figure 2C 、 Figure 2D and Figure 2E .

[0066] The diaphragm may be circular, rectangular, square, or other shapes and may be smaller or larger than the thermoformed thermoplastic sheet.

[0067] The present disclosure is based on the discovery that many of the deficiencies in prior art membranes can be reduced or eliminated by the improved membranes described herein.

[0068] In one embodiment, the separator is a split peelable separator, such as a split peelable polyolefin separator.

[0069] In one embodiment, the separate peelable membrane has a melting point below the thermoforming temperature.

[0070] In one embodiment, the melting point below the thermoforming temperature is about 60°C to about 200°C, about 70°C to about 160°C, about 80°C to about 150°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C, 100°C, 105°C, 100°C, 115°C, 120°C or 125°C.

[0071] In one embodiment, the film comprises a polypropylene copolymer having a melting point of about 120°C to about 160°C and a melt index less than 10, less than 5, less than 1 according to ASTM D 1238 (at 230°C, 2.16 Kg load).

[0072] In one embodiment, the split peelable membrane has a melt index measured according to ASTM D1238 (at 150°C, load 2.16 Kg) of about 1 to 50, 2 to 50, or 5 to 30. The split peelable membrane melt index may be greater than 10, greater than 20, or greater than 30.

[0073] In one embodiment, the discrete peelable separator has a melt index less than 10, preferably less than 5, and preferably less than 1, measured according to ASTM D1238 (at 230° C., load 2.16 Kg).

[0074] In one embodiment, the separating peelable membrane comprises polyethylene (PE), such as high density polyethylene, low density polyethylene, linear low density polyethylene including very low density polyethylene, ethylene copolymers including polyethylene and one or more comonomers including but not limited to vinyl acetate, acrylic acid, methacrylic acid, methyl acrylate, ethyl acrylate and butyl acrylate.

[0075] In one embodiment, the split peelable membrane comprises an ethylene, alpha olefin copolymer wherein the comonomer is one or more of propylene, butene, hexene, or octane.

[0076] In one embodiment, the discrete peelable membrane comprises polypropylene, for example, a random copolymer or a block copolymer, having a melting point of about 60°C to about 150°C.

[0077] In one embodiment, the separating peelable membrane is a polyolefin film comprising polyethylene or a polyethylene copolymer wherein the comonomer is one or more of vinyl acetate, methyl acrylate, ethyl acrylate or butyl acrylate, acrylic acid or methacrylic acid, propylene, butene, hexene or octene.

[0078] In one embodiment, the discrete peelable membrane has a modulus of about 50 to 700 MPa, such as 100 MPa, 150 MPa, 200 MPa, 250 MPa, 300 MPa, 400 MPa, or 500 MPa.

[0079] In one embodiment, the discrete peelable separator has less than about 100%, 50%, or 25% MD ("machine direction") and TD ("transverse direction") orientation.

[0080] In one embodiment, the discrete, peelable membrane has a trouser tear strength greater than 20 N / mm (Newtons / mm).

[0081] In one embodiment, the split peelable membrane comprises a single layer.

[0082] In one embodiment, the separate peelable membrane is a polyolefin having an average thickness of about 37 to 75 micrometers (μ).

[0083] In one embodiment, the discrete peelable polyolefin separator has one or more of: a melting point of about 80°C to about 125°C, a modulus of about 50 to 700 MPa, and MD and TD orientation of less than 100%, and in some cases less than about 50%.

[0084] In one embodiment, the separate peelable membrane has a minimum X or Y dimension of about 110 mm and a maximum X or Y dimension of about 150 mm.

[0085] In one embodiment, the split peelable membrane comprises two or more layers and one layer has a higher melting point than another layer. In one example of this embodiment, one of the layers has a melt index greater than 10.

[0086] In one embodiment, the split peelable membrane comprises three layers and the melting point of the inner layer is higher than the melting point of any of the outer layers.

[0087] In one embodiment, the split peelable membrane comprises two or more radial slits, for example, slits having a length greater than about 10 mm.

[0088] In one embodiment, the split peelable membrane includes two or more triangular cutouts, for example, cutouts that comprise about 5% to about 50% of the total area.

[0089] In one embodiment, the separate peelable membrane comprises a conical or spherical shape and the Z-axis may have a height greater than about 10 mm.

[0090] In one embodiment, the split peelable membrane comprises a slip agent or release agent selected from the group consisting of amides, esters, and silicones.

[0091] In one embodiment, the discrete peelable membrane comprises 0.1% to 2% of an anti-sticking additive selected from silica, diatomaceous earth, talc, or calcium carbonate.

[0092] The split peelable membrane disclosed herein has one or more of the features described in the embodiments listed above.

[0093] In one embodiment, a separate peelable membrane for a thermoformed dental appliance comprises a polyolefin having an average thickness of about 37 to 75 microns, a minimum X or Y dimension of about 110 mm, a maximum X or Y dimension of about 150 mm, a melting point of about 80°C to about 160°C, a modulus of about 50 to 700 MPa, and MD and XD orientations of less than 100% and in some cases less than about 50%.

[0094] In one embodiment, a separate peelable membrane having one or more of the features described in the above listed embodiments is used in a method of producing a thermoformed article, such as a dental appliance.

[0095] In one embodiment of the method, a separate peelable membrane is placed on a male or female dental mold or model, and a thermoformable sheet material is heated to a temperature above the melting point of the peelable membrane in a pressure or vacuum thermoforming apparatus and placed over the peelable membrane and mold or model to produce a thermoformed article. After thermoforming, the membrane is removed from the thermoformed article and from the model.

[0096] In one embodiment of the method, the separate peelable membrane is removed from the thermoformed article and the former without a chemical reaction occurring between the thermoformable sheet material and the former.

[0097] In one embodiment of the method, the separate peelable membrane is removed from the thermoformed article and the former without transferring material from the former to the thermoformable thermoformed article.

[0098] In one embodiment of the method, a separate peelable membrane is removed from the thermoformed article and the former, wherein the surface roughness of the thermoformed part is reduced relative to the former.

[0099] In one embodiment of the method, the separate peelable membrane is removed from the thermoformed article and the former, wherein the gloss of the thermoformed part is increased relative to a thermoformed part formed without the membrane.

[0100] In one embodiment, a separate peelable membrane having one or more of the features described in the above listed embodiments is a component of a system for producing thermoformed articles, such as dental appliances.

[0101] In one embodiment, the system includes (a) a male or female mold or former; a separate peelable polyolefin separator; a thermoformable polymer sheet material; and a thermoforming apparatus.

[0102] Dental appliances can be constructed by thermoforming a thermoformable polymeric sheet material onto a model of one or more teeth. The thermoformable polymeric sheet material can include one or more layers. The thermoforming process can be performed using a pressure thermoforming device ("thermoformer") or a vacuum thermoforming device or a combination of vacuum and pressure.

[0103] Thermoforming of sheets to produce test specimens or dental appliances can be performed using, for example, a "Biostar" pressure thermoformer available from Great Lakes Orthodontics and using procedures commonly used in the industry.

[0104] Examples of commonly used thermoformable sheet materials include Zendura A (rigid polyurethane available from Bay Materials, LLC), Essix Ace (polyester available from Dentsply), Duran (polyester available from Schue Dental), and Imprelon (polystyrene available from Scheu Dental).

[0105] Exemplary materials for constructing the separate peelable membrane disclosed herein include, but are not limited to, polyethylene (PE), including high-density polyethylene, low-density polyethylene, linear low-density polyethylene including very low-density polyethylene, ethylene copolymers including polyethylene and one or more comonomers, including but not limited to vinyl acetate, acrylic acid, methacrylic acid, methyl acrylate, ethyl acrylate and butyl acrylate, α-olefins including propylene, butene, hexene and octene; and polypropylene, including random copolymers and block copolymers, including ethylene or α-olefin and propylene copolymers having a melting point of about 60°C to about 160°C.

[0106] Utility Evaluation. To function as a stand-alone separator, numerous conflicting requirements must be met simultaneously. After thermoforming, the film must be completely removed from the substrate and the former, the thermoformed article must have a smooth surface and good optical appearance, and the thermoformed article must closely conform to the dimensions of the former. The improved separator disclosed herein is a separate, peelable separator that meets these requirements.

[0107] Exemplary Materials and Methods

[0108] Materials, methods, systems, and examples for making dental appliances are provided herein to illustrate features of the improved release liner compositions, methods, and systems disclosed herein.

[0109] The model used for thermoforming can be, for example, a plaster or 3D printed model, or any model known to use a membrane. In one illustrative embodiment, a dental model is created by casting dental stone using a silicone dental impression according to standard methods commonly used in the art. The cast model is trimmed and defects repaired. Alternatively, the model is produced by 3D printing or stereolithography (SLA).

[0110] Thermoformable sheets may include one or more layers. Single-layer thermoformable sheets, such as rigid polyurethane or polyester sheets, may be prepared by extrusion or molding. Multilayer thermoformable sheets may be prepared in a variety of ways, including but not limited to hot or cold lamination, adhesive lamination, melt lamination, coextrusion, or other known methods. The sheet may be completely prepared prior to being formed into an orthodontic appliance, or the appliance may be manufactured using a series of separate thermoforming steps to form multiple layers.

[0111] Thermoforming Process. Unless otherwise noted, thermoforming of sheets to produce test specimens or dental appliances was performed using a "Biostar" (Scheu Dental) pressure thermoformer available from Great Lakes Orthodontics using procedures commonly used in the industry and 0.76 mm thick Zendura A polyurethane as the thermoformable material (available from Bay Materials, LLC).

[0112] Thermoforming can be performed using different conditions, forms, or molds to vary the stretch ratio and part thickness. Multi-layer dental appliances can be manufactured in multiple steps using single or multiple layers of thermoformable sheet or in a single step using multiple layers of thermoformable sheet or by one or more 3D printing processes or by sequential dip coating, spray coating, powder coating, or similar processes known for producing films, sheets, and 3D structures.

[0113] Orthodontic or geometric models are 3D printed, cast using thermosetting polyester resins, epoxy casting resins, or machined from polyacetal or aluminum.

[0114] Melt index (MI) is a measure of the viscous flow of a polymer at elevated temperatures and can be measured according to ASTM D1238. Melt index can be measured under different conditions depending on the melting point or softening point and viscosity of the material. Unless otherwise stated, melt index values ​​are measured at 190°C and a 2.16 kg load (Condition E).

[0115] Melting Point. Thermal properties were measured using a differential scanning calorimeter at 10°C per minute and the onset of melting (Mp) and heat of fusion (J / g) were reported for the second heat results.

[0116] Mechanical Properties. Unless otherwise stated, mechanical properties were measured using an Instron Materials tester.

[0117] Applicable test methods include: tensile properties (ASTM D638), tear strength (ASTM D1938), and 90-degree peel adhesion strength using an Instron materials tester at a speed of 5 cm / min. It should be understood that test modifications may be necessary or desirable depending on the geometry or characteristics of the test specimen, and some reported tests may not be based on ASTM standards.

[0118] Film orientation was determined by measuring the sheet dimensions in the machine and transverse directions before (Li) and after (La) heat treatment at a temperature slightly below the melting point and calculating the percent reduction in length (shrinkage). Shrinkage (%) = 100 X [Li-La] / Li.

[0119] The optical and surface properties of the materials before and after thermoforming on models with and without a peelable film were judged visually and reported or measured using a BYK colorimeter and glossmeter or surface roughness meter.

[0120] The force required to remove the thermoformed article from the former can be judged by hand or can be measured with the aid of a tensile testing machine and suitable grips.

[0121] Candidate diaphragms were obtained whenever possible from commercial suppliers, such as Isofolan from Schue Dental, Densilk from Reliance Orthodontics, by removing the protective film from commercial thermoformable sheets such as Essix Ace, or plastic film suppliers. If the supplier did not report the material composition, their properties and composition were determined using infrared spectroscopy and measurements of thermal properties (melting point).

[0122] Additional films are prepared by melt pressing known commercial polymer resins or by extruding or coextruding the materials, for example by blown film coextrusion using a multilayer die.

[0123] Example

[0124] The present disclosure is further illustrated by the following examples. These examples are provided for illustrative purposes only. They should not be construed as limiting the scope or content of the present invention in any way.

[0125] Comparative Example

[0126] Example 1A

[0127] The printed dental arch model, approximately 20 mm high, was placed on the thermoforming platform of a Biostar compression molder (available from Great Lakes Orthodontics). Next, a 125 mm round sheet of Isofolan (polyethylene) 100 microns (μ) thick was placed on top of the model. A sheet of Zendura thermoformable material having a diameter of 125 mm and a thickness of 0.76 mm was heated and thermoformed onto the model. The model was removed from the thermoformed sheet and the Isofolan was removed from the thermoformed sheet. Upon inspection, it was observed that the Isofolan sheet had folded over itself in multiple locations over the teeth and gum areas of the thermoformed appliance (article). The thermoformed appliance was unacceptable because there were multiple crease lines on the areas covering the teeth. When the thermoformed appliance was placed back on the model, it fit loosely, rather than snugly as required.

[0128] In contrast, using a more time-consuming process, an Isofolan sheet is first pressure-formed onto a mold and allowed to cool. A 0.76mm sheet of Zendura is then thermoformed onto it, resulting in a smooth, crease-free, and more tightly fitting device. The tight fit is attributed to the fact that the Isofolan stretches and becomes significantly thinner during thermoforming.

[0129] This evaluation showed that simply placing a thermoplastic film designed for thermoforming onto a former and then thermoforming on top of it produced poor and unacceptable results.

[0130] Example 1B

[0131] A second test was conducted using Densilk, a commercial product available from Reliance Orthodontics. This material is a 25-micron-thick LDPE film marketed for use in the production of dentures by heat-curing acrylic paste, where it is necessary to prevent the acrylic resin from bonding to the dental plaque. This material is not marketed or reported to have been used for thermoforming.

[0132] Densilk film was placed over the printed model and evaluated in the same manner as Isofolan. After removing the printed model, the Densilk film tore and was difficult to remove from the thermoformable sheet. Furthermore, the dental appliance displayed numerous ridges on its interior that matched the 3D printed build lines of the model. From this evaluation, it is clear that simply placing a thermoplastic film designed for casting acrylic resin into a plaster model as a septum for thermoforming onto a printed dental appliance is unacceptable.

[0133] Example 2. Preparation of membrane samples.

[0134] The sources or preparation and characterization of the experimental membranes are listed in Table 1.

[0135] Table 1:

[0136]

[0137] Additional films were prepared by compression molding commercial pellets of polyethylene and ethylene vinyl acetate (EVA) copolymers having known compositions and melt index values.

[0138] Example 3. Effect of membrane thickness on glossiness

[0139] A smooth polyacetal block was fabricated having L x W x H dimensions of approximately 80mm x 50mmm x 10mm. A Zendura A polyurethane sheet was thermoformed over the block, cooled, and removed. The gloss values ​​of the surface formed relative to the block were measured. Next, a polyester mesh fabric was placed over the block and thermoformed thereon and the resulting surface gloss was measured. The candidate membrane was then placed on top of the polyester fabric and thermoformed onto the fabric as previously described. The membranes were separated, the separation force recorded, and the gloss level of the thermoformed sheet measured. The results, shown in Table 2, indicate that: films less than about 30 microns thick may not provide a smooth surface and high gloss; moderate (<18%) levels of vinyl acetate improved flow and gloss; higher levels of vinyl acetate caused the film to adhere to the polyester fabric and the thermoformed sheet; and the multilayer films exhibited improved strength and removability while maintaining good optical properties.

[0140] Table 2.

[0141]

[0142] Example 4. Effect of film size and shape on crease lines.

[0143] If the film is folded or creased during thermoforming, the crease line pattern may be transferred to the thermoformed article, which is undesirable. The size of the film is not expected to have a significant effect, as it does not change any of the inherent properties of the film. Films of various shapes, sizes, and configurations were prepared from a 50-micron multilayer film (FT 2004) and tested by thermoforming onto trapezoidal cylinders with a height of 24 mm, a base of 44 mm, and a top of 41 mm. The distance, number, and depth of the crease marks on the thermoformed parts are listed in Table 3.

[0144] Table 3.

[0145]

[0146]

[0147] Surprisingly, the results showed that the size and even the shape of the membrane had a strong impact on its performance. Specifically, performance was better when the membrane was increased from 110 mm to 125 mm, but membranes larger than approximately 125 mm tended to block airflow. Furthermore, the inventors discovered that cutting the perimeter of the membrane reduced the amount and number of surface defects. Further improvements were observed when triangular sections were removed from the perimeter of the membrane.

[0148] Additional advantageous results were obtained by pleating the film to form a cone or bowl with a Z-axis height > about 10 mm. Other related geometric modifications can be prepared by those skilled in the art to make the sheet more easily conform to the mold used.

[0149] Example 5. Effect of membrane on ease of separation

[0150] Testing was conducted to measure the ability of the films to facilitate separation of thermoformable sheets from polyester fabric. As reported in Table 4, various thermoformable sheets were thermoformed onto polyester fabric placed on acetal blocks with and without the test membranes.

[0151] Table 4

[0152]

[0153] The low polarity level of the membrane produced a glossier surface and significantly reduced the force required to separate the mold from the thermoformed article. Multilayer films with relatively polar outer layers and nonpolar inner layers performed particularly well.

[0154] Example 6. Dual-function membrane.

[0155] The utility of the separator as a protective film was evaluated by applying it directly to the thermoformable sheet prior to thermoforming.

[0156] A three-layer film was prepared having layers A and C composed of 93% EVA (containing 18% vinyl acetate) with a melt index of 2.5, 5% LLDPE with a melt index of 2 and a melting point of 97°C, 0.5% erucamide as a slip agent, and 1.5% silica as an anti-blocking agent (COEX 18). Layer B was LLDPE with a melting point of 107°C, an MI of 2, and 0.5% erucamide. Each of the A, B, and C layers was 25 μm, providing a total thickness of 75 μm.

[0157] Two further films were prepared, adjusting the ratio of 18% EVA to LLDPE so that the outer layers contained 12% and 9% VA. These materials were designated COEX 18, COEX 12 and COEX 9.

[0158] Two commercial protective films, 9026 and 9884, are available from Novacel. Novacell 9026 is a polyethylene film with a very low-tack adhesive, and its FTIR spectrum is consistent with polyethylene. Novacel 9884 is a polyethylene film with a low-tack acrylic adhesive. Both films are marketed for protecting thermoformable sheets.

[0159] 50 micron thick films were made from Elvax 240, EVA with 28% VA, melt index 43 and melting point 74°C, designated EVA 28. Films were made from Elax 460, 18% VA, MI 2.5 and melting point 84°C, designated EVA 18.

[0160] Films were made from the above-described Elvax 240 and Elvax 460 with the addition of 0.5% Incroslip SL (a proprietary slip additive manufactured by Croda) and 5% of Dow Corning HMB-6301 masterbatch (a non-migratory silicone slip additive).

[0161] The prepared films were heat laminated to Zendura polyurethane and tested for removal force before and after thermoforming. To be useful, the films must adhere well enough to the thermoformable sheet to withstand handling, and must be removed cleanly after thermoforming without tearing or leaving residue. The preferred initial adhesion level after lamination is about 10 grams per inch. Lower levels of adhesion are insufficient to keep the film attached during handling. Values ​​greater than about 50 g / cm are too high because they can be difficult to remove. Ideally, the adhesion level should not change after thermoforming, but values ​​less than about 100 g / cm are acceptable. Higher values ​​are unacceptable and often result in the film tearing or cracking during removal. The results are shown in Table 5.

[0162] Table 5

[0163]

[0164] The results demonstrate the undesirability of high levels of polar monomers and the advantages of multilayer films in achieving a balance between adequate adhesion and clean removability. Furthermore, they show that the addition of a slip agent can maintain controlled levels of adhesion after lamination and thermoforming, even in the presence of polar monomers.

Claims

1. A method for producing a thermoformed article, the method comprising: (a) placing a separate peelable membrane having an average thickness of 37 to 75 microns on a positive or negative dental mold or model; (b) heating the thermoformable sheet material to a temperature above the melting point of the separate peelable membrane; (c) thermoforming the heated sheet material onto the separate peelable membrane and the mold or former in a thermoforming apparatus; (d) separating the thermoformed article from the mold or former; and (e) removing the separate peelable membrane from the thermoformed article, thereby producing a thermoformed article. 2 . The method of claim 1 , wherein the separate peelable membrane has a peel adhesion level of less than 100 g / cm after thermoforming.

3. The method of claim 1, wherein the separate peelable membrane comprises a material having a melting point lower than a thermoforming temperature of the thermoformable sheet material.

4. The method of claim 1, wherein the separate peelable membrane has a trouser tear strength greater than 20 N / mm.

5. The method of claim 1, wherein the discrete peelable membrane has a machine direction (MD) and cross direction (XD) orientation of less than 100%.

6. The method of claim 1 , wherein the separate peelable membrane further comprises: The minimum X or Y dimension is 110 mm, and the maximum X or Y dimension is 150 mm.

7. The method of claim 1, wherein the separate peelable membrane is a polypropylene copolymer. The method according to claim 1 , wherein the separate peelable membrane material is a polyolefin.

9. The method of claim 1, wherein the separate peelable membrane comprises a single layer.

10. The method of claim 1, wherein the separate peelable membrane comprises two or more layers, wherein a melting point of one layer is higher than a melting point of another layer.

11. The method of claim 1, wherein the split peelable membrane comprises three layers, wherein the melting point of the inner layer is higher than the melting point of any of the outer layers.

12. The method of claim 1, wherein the separate peelable membrane comprises one or more of: (a) two or more radial slits, each of which is greater than 10 mm in length; (b) two or more triangular cuts, covering 5% to 50% of the total area; (c) conical or spherical, where the height of the Z axis is greater than 10 mm; (d) a slip agent or release agent selected from amides, esters and silicones; and (e) 0.1% to 2% of an anti-caking additive selected from silica, diatomaceous earth, talc and calcium carbonate.

13. The method of claim 1, wherein the separate peelable membrane: (a) having a melt index of less than 10 at a temperature of 230° C. and a load of 2.16 kg according to ASTM D1238; (b) having a melt index of 2 to 50 at a temperature of 150° C. and a load of 2.16 kg according to ASTM D1238; or (c) having a melt index of 2 to 35 at a temperature of 190° C. and a load of 2.16 Kg according to ASTM D1238.

14. A system for producing a thermoformed dental appliance, the system comprising (a) a positive or negative mould or model; (b) thermoformable sheet materials; (c) a separate, peelable membrane having X and Y dimensions and comprising (i) an average thickness of 37 to 75 microns; (ii) a melting point below the thermoforming temperature of the thermoformable sheet material; and (ii) a trouser tear strength greater than 20 N / mm, wherein the separate, peelable membrane comprises a) two or more radial slits formed along the perimeter of the separate, peelable membrane, or b) two or more triangular cuts formed along the perimeter of the separate, peelable membrane, or c) radial creases, or d) a conical or hemispherical shape, wherein the Z axis of the conical or hemispherical shape has a height greater than 10 mm; and (d) Thermoforming device.

15. The system of claim 14, wherein the discrete peelable membrane has a machine direction (MD) and cross direction (XD) orientation of less than 100%.

16. The system of claim 14, wherein the separate peelable membrane has a minimum X or Y dimension of 110 mm and a maximum X or Y dimension of 150 mm.

17. The system of claim 14, wherein the split peelable membrane comprises a polypropylene copolymer or a polyolefin.

18. The system of claim 14, wherein the separable peelable membrane comprises a single layer; two or more layers wherein one layer has a higher melting point than another layer; or three layers wherein an inner layer has a higher melting point than any outer layer.

19. The system of claim 14, wherein (a) the length of each of the two or more radial slits is greater than 10 mm; and (b) The two or more triangular cutouts occupy 5% to 50% of the total area.

20. The system of claim 14, wherein the detachable peelable membrane: (a) having a melt index of less than 10 at a temperature of 230° C. and a load of 2.16 kg according to ASTM D1238; (b) having a melt index of 2 to 50 at a temperature of 150° C. and a load of 2.16 kg according to ASTM D1238; or (c) having a melt index of 2 to 35 at a temperature of 190° C. and a load of 2.16 Kg according to ASTM D1238.

21. The system of claim 14, wherein the separate peelable membrane comprises a) a slip or release agent selected from amides, esters, and silicones, or b) 0.1% to 2% of an anti-sticking additive selected from silica, diatomaceous earth, talc, and calcium carbonate.

22. The system of claim 14, wherein the separate peelable membrane has a peel adhesion level of less than 100 g / cm after thermoforming.

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