Radiation imagery chemistry: process – composition – or product th – Imaged product – Multilayer
Reexamination Certificate
2001-09-10
2004-07-13
Hamilton, Cynthia (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Imaged product
Multilayer
C430S280100, C430S269000, C264S401000, C522S100000, C522S170000
Reexamination Certificate
active
06762002
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 polypropylene 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 provide a prototypical representation of the physical shape of plastic articles made on a production basis out of materials such as ABS, nylon, polyethylene, propylene, 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.
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 275618 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.
SUMMARY OF INVENTION
This invention features photosensitive compositions that, upon exposure to actinic radiation, have one or more of the following polypropylene characteristics, specifically:
(i) an elongation at yield in the range of 7% to no yield;
(ii) a tensile modulus in the range of 1000 to 1600 N/mm
2
;
(iii) an average elongation at break of at least 10%; or
(iv) a yield stress of 28 to 40 kN/mm
2
.
The invention also relates to a three-dimensional article formed from a photosensitive composition including
(a) 30-70% by weight of an epoxide-containing material;
(b) 5-35% by weight of an acrylic material selected from aromatic acrylic material, cycloaliphatic acrylic material, or combinations thereof;
(c) 0-40% by weight of a hydroxyl-containing material;
(d) at least one cationic photoinitiator; and
(e) at least one free-radical photoinitiator.
In preferred embodiments, the photosensitive composition includes 35-69.9% by weight of an epoxide-containing material. Preferably, the epoxide-containing material can have a poly(tetramethylene oxide) backbone. The composition can include 10-20% by weight of an acrylic material. The composition can include 10-39% by weight of a hydroxyl-containing material. Preferably, the hydroxyl-containing material can be an aliphatic polycarbonate diol.
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 crosssection 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. A significant amount of progress has been made with compositions and processes that have been adapted to improve the accuracy of the objects produced. Also, composition developers have made significant progress toward improving individual properties such as the modulus or deflection temperature of the photohardened objects. However, attempts to simulate a particular set of physical properties of a common manufacturing material to such a degree that the material made could be easily mistaken for the material simulated, based upon look and feel properties, have been unsuccessful.
During the development of the compositions disclosed herein, it was noted that substantial changes in the look and feel of articles fabricated by the liquid solid imaging process could be attained by slight alterations in component concentration. Surprisingly it was found that by making these alterations in composition, articles could be made that had the look and feel of articles manufactured from polypropylene materials. Within the field of liquid solid imaging such a discovery is a first in that previous commercial compositions did not make articles that elicited a similar look and feel sense with regard to any other common plastic. It was then recognized that by tailoring the composition, the properties of polypropylene manufactured articles could be simulated. This potential therefore solved an oft expressed but unfilled need to produce prototypes that not only had the appearance of desired objects but also material properties that simulated the look and feel of the materials out of which production objects were destined to be manufactured.
In order to simulate a material in terms of look and feel, it is necessary to decide upon the appropriate appearance factors and physical properties. For example, in the field of liquid solid imaging the most commonly quoted fully cured part physical properties are the tensile stress, tensile modulus, elongation at break, average elongation at yield, flexural stress, flexural modulus, impact strength, hardness and deflection temperature. Some of these physical properties, such as, for example, elongation at break, are not something that can be “felt” unless the material is deformed. Such physical properties are therefore not indicative of a good simulation material property.
In some cases, the characteristics of a material that serve to define the look and feel properties of a particular material are difficult to define. This is especially so in the case of how a materials looks. However, in the case of the instant invention a deliberate compositional choice was made such that articles fabricated through solid imaging means, when given various amounts of exposure to actinic radiation, had a similar color and light scattering characteristic as various grades of polypropylene. It was also found that changing the actinic exposure can also modify the feel properties of the articles manufactured from the composition by the solid imaging process.
Tensile properties are best representative of how the articles feel. The “elongation at yield” is the percent elongation at the yield point. For the purposes of this invention, the yield point in a tensile stress-strain test is where a large increment of strain occurs at constant stress. Some samples may break prior to the yield point or at the yield point. All tensile properties as discussed herein were measured according to ASTM Test D638M, without humidity control.
By far, the most important property that relates to what is felt when handling a material, is the tensile modulus. This is representative of the feeling of stiffness.
A second important property is that of the elongation of the material. When a simulation of a material is handled and flexed, it should not break or permanently distort
Chawla Chander P.
Lawton John A.
DSM Desotech Inc.
Hamilton Cynthia
Pillsbury & Winthrop LLP
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