EP0753028A1

EP0753028A1 - Radiation curable molding compositions

Info

Publication number: EP0753028A1
Application number: EP95938945A
Authority: EP
Inventors: Duncan E. Waller
Original assignee: Kerr Corp
Current assignee: Kerr Corp
Priority date: 1994-11-04
Filing date: 1995-10-24
Publication date: 1997-01-15
Also published as: WO1996015179A2; DE753028T1; JPH09504572A; WO1996015179A3

Abstract

The invention relates to radiation curable compositions for molding both rigid and flexible medical, orthodontic and other articles. The present invention broadly encompasses pourable liquid compositions which are radiation curable to form rigid or flexible articles. Uses of the compositions include medical devices, flexible or rigid prostheses, dental and orthodontic applications, model-making, and even industrial parts. In its broadest aspects, the compositions of the present invention include as the primary component acrylic-functional polyurethane resin(s), diluent monomers to dilute the composition to the desired consistency, photosensitizers, synergistic reducing agents, lubricants, thickeners, reinforcing fillers and pigments, as needed for the particular application. These components are present in suitable proportions so as to achieve the desired results in terms of physical properties (i.e., strength, hardness, etc.).

Description

RADIAΗON CURABLE MOLDING COMPOSITIONS Field of the Invention

The invention relates to molding compositions, and more particularly to radiation curable compositions for molding both rigid and flexible medical, orthodontic and other articles. Background of the Invention

In the field of custom-fitted medical devices (e.g. , custom fitted hearing aids) there is a recognized need for molding compositions which are biocompatible, permit safe and expeditious processing, accurate reproduction of intricate shapes, and can be custom pigmented as desired. Additionally, there are similar needs in the context of orthodontic appliances, and other moldable articles. The compositions of the present invention, as described fully hereinbelow, meet these requirements, provide significant advantages and have a wide variety of uses. Summary of the Invention

The present invention broadly encompasses pourable liquid compositions which are radiation curable to form rigid or flexible articles. Uses of the compositions include medical devices, flexible or rigid prostheses, dental and orthodontic applications, model-making, and even industrial parts.

In its broadest aspects, the compositions of the present invention include as the primary component acrylic-functional polyurethane resin(s), diluent monomers to dilute the composition to the desired consistency, photosensitizers, synergistic reducing agents, lubricants, thickeners, reinforcing fillers and pigments, as needed for the particular application. These components are present in suitable proportions, as described in more detail hereinbelow, so as to achieve the desired results in terms of physical properties (i.e., strength, hardness, etc.).

In one set of embodiments the compositions of the invention form a rigid polymeric material upon radiation curing. In these embodiments, the compositions include the following components in the stated weight percentages:

Table 1

COMPONENT WEIGHT PERCENT RANGE

Urethane Dimethacrylate Resin (Resin 10-70% A)¹

Urethane Dimethacrylate Resin (Resin B)¹ 15-65%

Urethane Diacrylate Resin (Resin C)¹ 15-70%

Polyfunctional Diluent Monomer 10-25%

Light Cure Photosensitizer 0.05-0.5%

Synergistic Reducing Agent 0.05-1.0%

Lubricant (Optional) 0-0.25%

¹ Details as to structure and/or sources of these components is found in the Detailed Description section hereof. COMPONENT WEIGHT PERCENT RANGE

Sub-Micron Sized Thickener 0-2.5%

Reinforcing Filler 0-30%

Pigments 0-1.0%

In a more preferred set of compositional ranges wherein the molding compositions form rigid articles upon radiation curing, the following components in the listed weight percentages are contemplated:

Table 2

COMPONENT WEIGHT PERCENT RANGE

Urethane Dimethacrylate Resin (Resin A) 30-55%

Urethane Dimethacrylate Resin (Resin B) 20-40%

Urethane Diacrylate Resin (Resin C) 30-50%

Polyfunctional Diluent Monomer 12-20%

Light Cure Photosensitizer 0.10-0.3%

Synergistic Reducing Agent 0.1-0.5%

Lubricant (Optional) 0.05-0.15%

Sub-Micron Sized Thickener 0.25-1.0%

Reinforcing Filler 5-15%

Pigments 0.1-0.5%

In an alternative set of embodiments of the invention, the molding compositions form flexible polymeric material upon radiation curing. These embodiments contemplate the following compositions: Table 3

COMPONENT WEIGHT PERCENT RANGE

Urethane Dimethacrylate Resin (Resin 35-55% D)²

Urethane Dimethacrylate Resin (Resin 25-50% E)²

Urethane Dimethacrylate Resin (Resin 30-55% F)²

Monofunctional Diluent Monomer 5-30%

Light Cure Photosensitizer 0.05-0.5%

Synergistic Reducing Agent 0.05-1.0%

Lubricant (Optional) 1.5-6.5%

Sub-Micron Sized Thickener 0-6.0%

Reinforcing Filler 0-15.0%

Pigments 0.05-0.5%

In a more preferred set of compositional ranges wherein the molding compositions form flexible articles upon radiation curing, the following components in the listed weight percentages are contemplated:

Table 4

COMPONENT WEIGHT PERCENT RANGE

Urethane Dimethacrylate Resin (Resin 60-75% D)

Urethane Dimethacrylate Resin (Resin 40-60% E)

Urethane Dimethacrylate Resin (Resin 40-70% F)

Monofunctional Diluent Monomer 10-30%

² Details as to structure and sources of these components is found in the Detailed Description section hereof. COMPONENT WEIGHT PERCENT RANGE

Light Cure Photosensitizer 0.05-0.25%

Synergistic Reducing Agent 0.1-0.5%

Lubricant (Optional) 1.0-3.0%

Sub-Micron Sized Thickener 1.0-3.0%

Reinforcing Filler 0-10%

Pigments 0.1-0.25%

With respect to the flexible compositions given in the above Table 4, it is contemplated in the invention that one, two or all three of Resins D, E and F, and mixtures thereof in suitable proportions can be utilized so as to achieve the desired degree of flexibility in the final article.

One common component in each of the compositions of the present invention is a polyurethane resin having methacrylate or acrylate functionality, of the following general formula: _s-O-C-N-R₄-N-C-O-R₂-O-R,-O-R₃-O-C-N-R₅-N-C-O-R₇,

II I I II II I I II

O H H O O H H o wherein R, is an aromatic hydrocarbon (for rigid compositions) or an aliphatic hydrocarbon (for flexible compositions), or a combination aliphatic/aromatic to obtain intermediate properties. R₂ and R₃ are aliphatic hydrocarbons of relatively short chain length (C₃.₅) when rigidity is desired, and of relatively longer chain length (C₁₅-₂₀) when maximum flexibility is desired. The R, and R_$ components in the diisocyanate units are preferably aliphatic hydrocarbons for flexible polymers and aromatic hydrocarbons for rigid polymers. Lastly, the I^ and R₇ components are methacrylate or acrylate ester groups which provide the ethylenic unsaturation necessary for the resins to be polymerized, so as to form the desired molded shapes upon application of radiant energy.

The acrylic-functional resins of the type described above (with either aliphatic or aromatic hydrocarbon backbone structure) are combined with diluent monomers and other additives, including photosensitizers, synergistic reducing agents, lubricants, thickeners, reinforcing fillers and pigments to achieve the desired molding composition. The radiation curable compositions can be advantageously utilized to form rigid articles or flexible articles, depending upon the specific nature of the formulation.

The optional lubricant component is utilized in the composition when the molded form or part is to be in insertion/removal contact with the human body, particularly in contact with dry or hair-covered skin as in the case of a rigid or flexible hearing aid shell. A photosensitizer or photoinitiator is used if the material is to be cured by radiant energy of wavelengths within the ultraviolet or visible regions of the spectrum. The synergistic tertiary amine component is added to function as a reducing agent, which lowers the intensity and duration of the radiation exposure necessary for polymerization to occur and proceed to completion. Additionally, minor proportions of one or more paniculate sub-micron sized thickeners, typically surface treated for hydrophobicity, easier resin and monomer wetting, and increased physical properties of the resultant polymer, are utilized. Reinforcing fillers, which are also optional, may be added to maximize the strength properties of the resulting material, particularly where rigidity is desired. Such fillers are generally utilized in larger proportions when the resulting materials are to be used as "solid" forms or shapes, as opposed to hollow forms or shells with relatively thin walls. Lastly, suitable pigments of the soluble, insoluble and "Lake "-type are used to achieve the desired color in the final product, except in applications where the final product is to be colorless or "clear. " It is believed that the sub-micron sized thickeners serve to prevent the sedimentation of the pigments and reinforcing fillers. Detailed Description of the Invention

Further advantages and features of the present invention will become readily discernible to persons skilled in the art in light of the following working examples, which represent illustrative embodiments of the present invention. All percentages and parts are by weight, unless otherwise stated; these examples are included for exemplary purposes only and the invention is not to be construed as limited to the specific compositions disclosed.

EXAMPLE 1

This composition, which is unpigmented, is suitable for molding rigid articles, including orthodontic appliances, rigid prostheses, and hearing aid shells. Although the composition is unpigmented and thus cures to a clear material, pastels or other color additives could be included if desired. COMPONENT COMPONENT TYPE WEIGHT PERCENT

Urethane Diacrylate Resin Polymerizable Resin 69.78% (Resin C)

Triethylene Glycol Diluent Monomer 16.58% Dimethacrylate

Dimethylamino Synergistic Reducing Agent 0.11 % ethylmethacrylate

2,3-bornanedione Photoinitiator 0.09%

Polymethylmethacrylate Reinforcing filler 13.44% (MW 50,000) (benzoyl peroxide-free)

The above composition can be molded to form an article of any desired shape, such as a molded orthodontic appliance. In this example, an impression is taken of the appropriate area of the mouth with dental impression material, from which a positive model is then made utilizing low- expansion die stone. The composition of the invention is then used to mold the orthodontic appliance by coating the model and curing with high intensity visible radiation in the 400-500 nanometer wavelength range, such as by using a commercial visible light-curing unit. Alternatively, the above composition, but without the photoinitiator and synergistic reducing agent components, may be utilized and cured with microwave radiation or heat curing in the 100' -120^* C range. It will be appreciated that this composition may be used in the fabrication of a wide variety of medical, dental/orthodontic, industrial, etc. articles where accurate, intricate shapes are required in a rigid molded polymer material. EXAMPLE 2

The following composition has been found to be suitable for the molding of rigid, hollow hearing aid shells. This material can be pigmented to a desired flesh color to match white, African-American, or Asian skin tones. The composition includes the following:

COMPONENT COMPONENT TYPE WEIGHT PERCENT

Urethane Dimethacrylate Polymerizable Resin 74.53% Resin (Resin A)

Triethylene Glycol Diluent Monomer 15.70% Dimethacrylate

Dimethylamino Synergistic Reducing Agent 0.28% ethylmethacrylate

2,3-Bornanedione Photoinitiator 0.16%

Liquid Paraffin Lubricant 0.07%

Titanium Dioxide Pigment 0.14%

Red Iron Dioxide Pigment 0.03%

Yellow Iron Oxide Pigment 0.013%

Surface treated³, sub- Thickener 0.32% micron silica particles

Surface treated³ micronized Reinforcing filler 8.75% silica

The above composition is curable by exposure to visible light radiation. In a modified version without the photoinitiator and reducing agent components, microwave radiation curing can be utilized. It will be appreciated by persons

³ Contemplated surface treatment is silanation (treatment with organofunctional silane) to convert the surface of the particles from hydrophilic to hydrophobic; this enables better wetting with the resin matrix and stronger bonding to the particles upon polymerization. skilled in the art that pigment changes may be made without departing from the physical properties of the composition to achieve desired coloration. Furthermore, the above composition is suitable for the fabrication of solid or hollow molded articles for medical, dental, industrial, or hobby craft applications.

EXAMPLE 3 The following example is a specific formulation which has been found to be suitable for rigid hearing aid shells.

COMPONENT COMPONENT SOURCE/ WEIGHT

TYPE/ MANUFACTURER PERCENT PURPOSE DESIGNATION

Urethane Primary Esschem X8500000 36.95% Dimethacrylate polymerizable Resin (Resin A) resin

Acrylic Polymerizable Kerr Dental 18.00% terminated modifying resin Materials Center polyurethane ATPU⁴ resin (Resin C)

Triethylene Viscosity Esschem 943X7469 11.37% glycol reducing dimethacrylate monomer

Urethane Aliphatic high Caschem 52223^s 3.37% dimethacrylate MW prepolymer prepolymer to reduce (Resin D) brittleness

Hydroxyethyl Hydrophilic Rohm & Haas 0.58% methacrylate monomer BM910

⁴ This material is the subject of U.S. Patent No. 4,554,336, owned by Sybron Corporation.

⁵ This component is custom synthesized by Caschem and is an adduct of polyester polyol(aliphatic), hexamethylene diisocyanate and hydroxypropyl methacrylate. COMPONENT COMPONENT SOURCE/ WEIGHT

TYPE/ MANUFACTURER PERCENT

PURPOSE DESIGNATION

Dimethylamino Synergistic Eastman P7073 0.50% ethyl tertiary amine methacrylate reducing agent

Mineral oil 9NF Internal/ Amoco B4750O 0.16% external lubricant

Camphorquinone Photoinitiator Aldrich 12489-3 0.29%

Pigment blend: Flesh pink 0.19%

-Titanium pigment blend -NL Industries dioxide (75.5%) RA2020

-Red iron oxide -BASF F4299R

(17.75%)

-Yellow iron -Citco MAPICO oxide (6.75%) 3100

TFA Filler Reinforcing filler Kerr Dental 27.64%

(barium Materials Center aluminum T3000A borosilicate)

Urethane Copolymerizable Rohm & Haas 0.95%

Dimethacrylate matrix- 6661-0 resin (Resin B)⁶ toughening resin

EXAMPLE 4 The following is a flesh pigmented composition, specifically pigmented for matching Asian complexions believed to be suitable for molding flexible, hollow hearing aid shells, or other flexible articles.

COMPONENT COMPONENT TYPE WEIGHT PERCENT

Urethane Dimethacrylate Polymerizable resin 68.6% resin (Resin D)

Hydroxyethylmethacrylate Diluent monomer 27.21 %

A preferred resin is a polymethyl hexamethylene diisocyanatoethyl methacrylate. COMPONENT COMPONENT TYPE WEIGHT PERCENT

Dimethylamino- Synergistic Reducing Agent 0.20% ethylmethacrylate

2,3-Bornanedione Photoinitiator 0.05%

Mineral Oil Lubricant 1.63%

White Petrolatum USP Lubricant 0.81 %

Titanium Dioxide Pigment 0.13%

Brown Iron Oxide Pigment 0.15%

Red Iron Oxide Pigment 0.13%

Yellow Iron Oxide Pigment 0.12%

Surface treated sub-micron Thickener 1.3% silica

As an alternative to the above, the same composition may advantageously utilize an ultraviolet photoinitiator such as benzoin methyl ether, in place of the noted photoinitiator, to permit curing using high intensity ultraviolet radiation in the range of 320-400 nanometer wavelength, in a commercial ultraviolet light curing unit.

EXAMPLE 5 An example of a preferred formulation which has been found to be suitable for molding flexible articles, such as flexible hearing aid shells is given below.

COMPONENT COMPONENT SOURCE/ WEIGHT

TYPE/ MANUFACTURER PERCENT

PURPOSE DESIGNATION

Urethane Primary Caschem 52223 71.5%

Dimethacrylate polymerizable

Prepolymer resin

(Resin D) COMPONENT COMPONENT SOURCE/ WEIGHT

TYPE/ MANUFACTURER PERCENT PURPOSE DESIGNATION

Hydroxypropyl Hydrophilic Polyscience 26.2% methacrylate monomer

Dimethylamino Synergistic Rohm & Haas 0.5% ethyl tertiary amine methacrylate reducing agent

Camphorquinone Photoinitiator Aldrich 12489-3 0.1%

Mineral oil 9NF Lubricant Amoco B47500 0.25%

Titanium Pigment National Lead 0.148% dioxide

Red iron oxide Pigment Plϋss-Stauffer 0.036% R4299

Yellow iron Pigment Citco Y3100 0.016% oxide

Surface treated Thickener Degussa R202 1.25% sub-micron silica

The custom synthesized resins, such as Resin E and Resin F available from Kerr Dental Materials Center may be produced utilizing the following general procedure. X moles of medium molecular weight (350- 650) polyol are placed in a glass polymer kettle fitted with stirrer, thermometer and inlet port. Dropwise, through the inlet port, 2X moles of diisocyanate are added at a rate such that an exotherm temperature of 40 ^*C is never exceeded. The following reaction proceeds:

Step 1

HO-R₂-O-R,-O-R₃-OH + OCN-R^NCO + OCN-R₅-NCO →

OCN-R₄-N-C-O-R₂-O-R,-O-R₃-O-C-N-R₅-NCO

I II II I

H O O H Following essential completion of this reaction (approximately 4 hrs.), 2X moles of a hydroxy-functional ester of acrylic or methacrylic acid, such as 2- hydroxyethylacrylate, are added dropwise, with stirring, at such a rate that an exotherm temperature of 40^* C is never exceeded during formation of the urethane diacrylate resin. The reaction proceeds according to the following equation:

Step 2 OCN-R^N-C-O-R O-R O-Rj-O-C-N-Rj-NCO + 2 HO-CH₂-CH₂-0-C-CH - i n i i i n

H O OH O CH₂

HC-C-0-CH_rCH_rO-C-N-R₄-N-C-0-R₂-0-R₁-0-R₃-0-C-N-R₅-N-C-0-CH_rCH₂-C-CH

H I I I I I I I I I I I

CH₂0 O H H O O H H O O CH₂

If allowed sufficient time (approximately 15 hrs.), these isocyanate reactions proceed to virtual completion, particularly in the presence of a very slight excess of polyol in step 1 and hydroxy functional ester in step 2. Typically, no free isocyanate remains after the reaction and thus no purification is generally required. In the molding compositions which utilize resins as described above and disclosed herein, a diluent monomer is also utilized and is selected for functionality and molecular weight, usually it is monofunctional when flexibility is desired, and poly functional when rigidity is desired in the final product. By way of example, the monomer may be methacry late-functional when the final material is intended for medical or dental applications, and of either acrylate or methacrylate-functionality for industrial applications when biocompatibility is not such an important issue.

In particular, Resin E is preferably an adduct of aliphatic polyester polyol, hexamethylene diisocyanate and hydroxymethyl methacrylate. Resin F is preferably an adduct of aliphatic polyether polyol, hexamethylene diisocyanate and hydroxypropyl methacrylate.

By way of further example, but not limitation, a typical application for the moldable liquid compositions of the present invention is the formation of rigid or flexible hearing aid shells. Compositions of the type disclosed hereinabove are suitable for producing such products according to the following procedure. Initially, a cotton plug is carefully placed in the ear canal to serve as a barrier to the inner ear. An impression of the outer ear is taken using a suitable dental impression material. A transparent mold is then made from this impression, using either pourable, unpigmented translucent dental impression material, or a suitable pourable reversible transparent Agar-Agar impression material. This mold is then filled in a filtered light environment with the desired composition of the present invention, covered with a cellophane, mylar or polyethylene film and an opaque metal or plastic disc. This arrangement is then placed in a suitable visible light curing cabinet for 12-15 seconds, or for a sufficient time to allow a polymer shell of approximately one millimeter thickness to form around the exposed surfaces of the liquid. All unpolymerized liquid is allowed to drain out of the mold and the mold is then filled with a suitable air barrier liquid (such as aqueous 1,2,3-propane triol), to prevent air inhibition of the surface. The uncovered mold is returned to the visible light curing cabinet for a full cure of approximately two minutes duration. The air barrier liquid is then poured out of the mold, the mold is rinsed with water to remove any residual traces of air barrier liquid, and a cured shell is pried from the mold, using dry warm air. Thereafter, the shell is trimmed and fitted with a base plate carrying the necessary electronic/acoustical components for the hearing aid, and the two sections are affixed together. The above procedure permits the completion, after one visit, of a custom- fitted hearing aid device.

It will be appreciated that other useful applications for the materials and compositions of this invention include rigid or flexible prostheses, dental/orthodontic appliances, model-making, industrial parts, etc. The scope of the present invention is not intended to be limited by the specific examples and compositions recited herein, but is defined by the scope of the appended claims.

What is claimed is:

Claims

1. A pourable molding composition which cures to a rigid polymeric material, comprising: a first urethane dimethacrylate resin component present in the range of about 10% -70% by weight; a second urethane dimethacrylate resin component present in the range of about 15%-65% by weight; a urethane diacrylate resin component present in the range of about 15%-70% by weight; a polyfunctional diluent monomer component present in the range of about 10%-25% by weight; a photosensitizer; a synergistic reducing agent; thickeners; and fillers.

2. The molding compositions of claim 1 wherein said first urethane dimethacrylate resin component is present in the range of about 30%-55% by weight.

3. The molding compositions of claim 1 wherein said second urethane dimethacrylate resin component is present in the range of about 20%-40% by weight.

4. The molding compositions of claim 1 wherein said urethane diacrylate resin component is present in the range of about 30% -50% by weight.

5. The molding compositions of claim 1 wherein said poly functional diluent monomer is present in the range of about 12%-20% by weight.

6. The molding compositions of claim 1 further including pigments.

7. A pourable molding composition which cures to a flexible polymeric material, comprising: a first urethane dimethacrylate resin component present in the range of about 35%-55% by weight; a second urethane dimethacrylate resin component present in the range of about 25%-50% by weight; a third urethane dimethacrylate resin component present in the range of about 30% -55% by weight; a monofunctional diluent monomer component present in the range of about 5% -30% by weight; a photosensitizer; a synergistic reducing agent; thickeners; and fillers.

8. The molding compositions of claim 7 wherein said first urethane dimethacrylate resin component is present in the range of about 60%-75% by weight.

9. The molding compositions of claim 7 wherein said second urethane dimethacrylate resin component is present in the range of about 40%-60% by weight.

10. The molding compositions of claim 7 wherein said third urethane dimethacrylate resin component is present in the range of about 40%-70% by weight.

11. The molding compositions of claim 7 wherein said monofunctional diluent monomer is present in the range of about 10%-30% by weight.

12. The molding compositions of claim 7 further including pigments.

13. A polymerizable urethane methacrylate resin according to the following formula:

-R₆-O-C-N--R₄-N-C-O-R₂-O-R₁-O-R₃-O-C-N-R₅-N-C-O-R₇,

II I I II II I I II

O H H O O H H O wherein R, is selected from aromatic and aliphatic hydrocarbons, R₂ and R₃ are selected from aliphatic hydrocarbons in the C₃._s range and the C₁₅.₂₀ range, R₄ and R₅ are selected from aliphatic and aromatic hydrocarbons, and R^ and R₇ are selected from acrylate and methacrylate esters.