Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Radiation sensitive composition or product or process of making
Reexamination Certificate
2002-11-22
2004-04-27
Hamilton, Cynthia (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Radiation sensitive composition or product or process of making
C430S269000, C522S011000, C522S090000, C522S100000, C522S170000, C522S103000
Reexamination Certificate
active
06727043
ABSTRACT:
FIELD OF THE INVENTION
This invention discloses compositions adapted to produce, through solid imaging means, excellent quality objects having material properties that simulate the look and feel of polyethylene articles.
BACKGROUND OF INVENTION
In the field of liquid-based solid imaging, alternatively known as stereolithography, compositions have been developed which are capable of generating solid objects having the properties of epoxies and/or acrylates. Solid imaging generated objects made from previous epoxy and/or acrylate compositions provided a prototypical representation of the physical shape of plastic articles made on a production basis out of materials such as ABS, nylon, polyethylene, polypropylene, etc. However, such compositions lack the material properties that give users of the prototypes a sense of look and feel for the object when produced in the production material. Such a lack of look and feel accuracy in product prototyping is not just an aesthetic issue. The look and feel of a prototype also has significant engineering, design, packaging, labeling, and advertising implications.
For example, squeeze bottles, such as those used for dispensing dish soap, are designed to be attractive in shape, easy to grasp, and easy to squeeze. Typically such bottles are made from polyethylene type polymers. Previous epoxy and/or acrylate compositions used in solid imaging were capable of producing articles that have the same attractive shape. However, the stiffness of the prototyped articles made from these materials was likely to mislead the designer and evaluator of the article relative to such issues as, for example, wall thickness and surface radius design. For example, a commercial solid imaging resin, Somos® 2100 (E. I. DuPont De Nemours, Inc., Wilmington, Del.), produces articles having lower stiffness than polyethylene. Bottles made from this material do not provide adequate resistance to squeezing such that enough friction occurs between a person's fingers and the bottle. A person holding a Somos® 2100 prototype bottle of liquid soap is likely to squeeze too hard in order to generate enough friction to keep the bottle from slipping. As a consequence, the soap is likely to be dispensed prematurely. The designer of the bottle might then be misled into making the wall thickness of the bottle greater in order to improve its stiffness. But such a design change would lead to a bottle that is too stiff when manufactured with polyethylene. Similar problems are generated when other much stiffer epoxy and/or acrylate compositions are used to prototype articles such as bottles. A designer might be led to decrease the wall thickness of the bottle due to the stiffness. Or for example, since sharper radii may not feel as comfortable during squeezing when stiffer materials are used, the designer may be misled into re-designing the bottle with greater radii. This may affect the bottle squeezability when manufactured in polyethylene or may reduce the aesthetic appeal of the bottle shape.
Other examples may be made regarding the importance of appearance of an article when made out of certain materials. For example, use of a transparent prototype composition or an overly opaque composition may mislead those viewing the article into incorrect assumptions regarding appropriate packaging, labeling, coloring, and advertising of a product.
Other considerations when trying to utilize solid imaging for prototyping include photospeed, resistance to humidity, low potential for hydrolysis, similar coefficient of friction, dimensional accuracy, ability to span without supports during fabrication, and wide process latitude.
Japanese Patent Application Hei 2-75618 describes epoxy and acrylate compositions for use in optical molding. The compositions contain at least 40 wt % of alicyclic epoxy resin with at least two epoxy groups in each molecule.
U.S. Pat. No. 5,476,784 describes cationic epoxy and acrylate compositions for use in solid imaging. The compositions may comprise from 5-40% by weight of at least one OH-terminated polyether, polyester or polyurethane. In the examples given, the polyether polyols formulations provide lower elongation at break properties that the elongation at yield properties of most low-density polyethylenes. Additionally, the patent teaches that the epoxy content is to be from 40 to 80% of the formulation by weight. Compositions made with this epoxy content are likely to produce cured articles having a higher modulus than that of polyethylene.
SUMMARY OF INVENTION
This invention discloses photosensitive compositions comprising;
(a) about 20-40% by weight of an epoxide-containing material;
(b) about 5-40% by weight of acrylic material selected from aromatic acrylic material, cycloaliphatic acrylic material, or combinations thereof;
(c) about 5-50% by weight of a reactive hydroxyl-containing material;
(d) at least one cationic photoinitiator; and
(e) at least one free-radical photoinitiator;
with the proviso that upon exposure to actinic radiation an article is produced having the following properties:
(i) a tensile break before yield stress or a tensile yield stress greater than 13 N/mm2;
(ii) a tensile modulus in the range of about 180 to about 850 N/mm2;
(iii) a tensile break elongation before yield or a tensile yield elongation greater than 6%; and
(iv) a notched Izod :impact strength greater than 50 J/m.
The invention also relates to a process for forming a three-dimensional article, said process comprising the steps:
(1) coating a thin layer of a composition onto a surface;
(2) exposing said thin layer imagewise to actinic radiation to form an imaged cross-section, wherein the radiation is of sufficient intensity to cause substantial curing of the thin layer in the exposed areas;
(3) coating a thin layer of the composition onto the previously exposed imaged cross-section;
(4) exposing said thin layer from step (3) imagewise to actinic radiation to form an additional imaged cross-section, wherein the radiation is of sufficient intensity to cause substantial curing of the thin layer in the exposed areas and to cause adhesion to the previously exposed imaged cross-section;
(5) repeating steps (3) and (4) a sufficient number of times in order to build up the three-dimensional article;
with the proviso the three-dimensional article has the following properties:
(i) a tensile break before yield stress or a tensile yield stress greater than 13 N/mm2;
(ii) a tensile modulus in the range of about 180 to about 850 N/mm2;
(iii) a tensile break elongation before yield or a tensile yield elongation greater than 6%; and
(iv) a notched Izod impact strength greater than 50 J/m.
The invention also relates to the above process wherein the composition comprises:
(a) about 20-40% by weight of an epoxide-containing material;
(b) about 5-40% by weight of an aromatic or cycloaliphatic acrylic material;
(c) about 5-50% by weight of a reactive hydroxyl-containing material;
(d) at least one cationic photoinitiator; and
(e) at least one free-radical photoinitiator.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Liquid based Solid Imaging is a process wherein a photoformable liquid is coated into a thin layer upon a surface and exposed imagewise to actinic radiation such that the liquid solidifies imagewise. Subsequently, new thin layers of photoformable liquids are coated onto previous layers of liquid or previously solidified sections. Then the new layer is exposed imagewise in order to solidify portions imagewise and in order to induce adhesion between portions of the new hardened region and portions of the previously hardened region. Each imagewise exposure is of a shape that relates to a pertinent cross-section of a photohardened object such that when all the layers have been coated and all the exposures have been completed, an integral photohardened object can be removed from the surrounding liquid composition.
One of the most important advantages of the solid imaging process is the ability to rapidly produce actual objects that have been designed by computer aided design.
DSM Desotech Inc.
Hamilton Cynthia
Pillsbury & Winthrop LLP
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