Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive...
Reexamination Certificate
1999-09-07
2001-06-26
Hamilton, Cynthia (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
C430S280100, C430S945000, C522S170000, C522S168000, C522S175000, C522S181000, C264S401000
Reexamination Certificate
active
06251557
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a photosensitive resin composition for use in rapid prototyping, and in particular, a resin made from both a cationic curable epoxy resin system and a radical-curable acrylate system.
BACKGROUND OF THE INVENTION
Rapid prototyping with the use of a photosensitive or radiation-curable resin compositions involves curing of well-defined areas of resin layers on top of each other to make a three-dimensional object. This object can be used either as a prototype or for making a prototype. A prototype, or model, is often used in the early preparation stages of new product manufacture.
The radiation-curable or photosensitive resin used in a prototype process must conform to many criteria, which can be a difficult challenge to the formulator. For example, the resin composition before cure must have a suitable viscosity. During cure, the resin composition must cure rapidly with a good through cure. Moreover, a sufficiently thick layer should be cured, preferably with a relatively low light intensity irradiation. Also, the cured resin composition should have good green strength mechanical properties, good final mechanical properties, and a relatively low shrink factor on cure. Such combinations of properties are difficult to achieve.
In order to achieve this balance of properties, various resin compositions have been proposed. For example, according to U.S. Pat. No. 5,418,112, a suitable resin system consists of an acrylate oligomer, acrylate functional diluents and a specific photoinitiator system for radical generation. However, radical-curable resin systems tend to shrink too much during cure, thereby causing difficulties with precision.
Other proposed resin compositions are dual systems and comprise both epoxy functional compounds and acrylate functional compounds. Here, the acrylates are cured using a radical generating photoinitiator, and the epoxy using a cation generating photoinitiator. Examples of these resin compositions are described in, for example, EP-A-535,828, U.S. Pat. No. 5,434,196, and EP-A-605,361.
According to EP-A-535,828, a suitable resin composition consists of a bisphenol-A based acrylate, an acrylate functional diluent, a cycloaliphatic epoxy functional component, and a suitable initiator system which is sensitive to light with a wavelength between 400 and 600 nm. According to U.S. Pat. No. 5,434,196, the cationically curable epoxy resin should be used in combination with a vinyl-ether compound. According to EP-A-605,361, a suitable composition consists of an epoxy resin, a cycloaliphatic or aromatic di-acrylate and an hydroxy functional polyether, polyester or polyurethane. The hydroxy functional polymer does react with the epoxy resin. Although these resin compositions have some favorable characteristics, further improvements are needed particularly with respect viscosity, post-cure mechanical properties, and accuracy of prototype parts.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a photosensitive resin composition suitable for rapid prototyping which has a good balance of mechanical properties together with other good properties such as viscosity.
It is a further object of the invention to provide a resin composition comprising both an epoxy resin and an acrylate functional compound together with cationic and radical generating photoinitiators that has a good stability in that it does not show phase separation on UV-cure.
It is yet another object of the invention to provide such a resin composition with appropriate photoinitiators which show homogeneous cure with relative low intensity UV-light (on comparison with laser light), good through-cure in at least resin layers of more than 200 &mgr;m thickness, which cured resin exhibits good mechanical properties.
It is yet another object of the invention to provide a method for manufacturing 3-dimensional objects in which the resin composition according to the present invention is used.
The photosensitive resin composition according to the invention for use in rapid prototyping comprises
a. about 30 wt. % to about 70 wt. % of at least two epoxy resins, wherein at least one of these resins is solid at room temperature and comprises aromatic groups, and at least one of these resins is liquid, having a viscosity at 25° C. lower than about 1,000 Pa.s,
b. about 15 wt. % to about 50 wt. % of at least one multifunctional acrylate compound,
c. about 5 wt. % to about 30 wt. % of a hydroxyfunctional compound,
d. about 1 wt. % to about 6 wt. % cationic photoinitiator,
e. about 1 wt. % to about 6 wt. % free radical photoinitiator.
Preferably, the amount of the solid epoxy resin(s) is about 10 wt. % to about 40 wt. %, and more preferably, about 15 wt. % to about 35 wt. %. Preferably, the amount of the liquid epoxy resin(s) is about 10 to about 40 wt. %.
The process of the present invention for the manufacturing of 3-dimensional objects comprises applying actinic radiation to a layer of photosensitive resin in order to cure a pre-determined well-defined area of the resin layer, which area forms a cross-section of the 3-dimensional form, introducing an uncured layer of resin on top of the cured layer and repeating the curing step, wherein the photosensitive resin composition comprises:
a. about 30 wt. % to about 70 wt. % of at least two epoxy resins, wherein at least one of these resins is solid at room temperature and comprises aromatic groups, and at least one of these resins is liquid, having a viscosity at 25° C. lower than about 1,000 Pa.s,
b. about 15 wt. % to about 50 wt. % of at least one multifunctional acrylate compound,
c. about 5 wt. % to about 30 wt. % of a hydroxyfunctional compound,
d. about 1 wt. % to about 6 wt. % cationic photoinitiator, and
e. about 1 wt. % to about 6 wt. % free radical photoinitiator.
The process of the present invention is advantageous in case the curing is performed with a laser, the laser is motion controlled with a computer, with the laser beam focused on a relatively tiny area of the pre-determined desired to-be-cured area, so as to have the laser scan over the to-be-cured area to at least substantially initiate the cure of the photosensitive resin composition. Presently preferred lasers are the helium/cadmium and the argon ion lasers.
Most preferred is a process which makes use of a photomask to define the to-be-cured area and in which the to-be-cured area is exposed to UV-light all at once.
DETAILED DESCRIPTION OF THE INVENTION
The first component of the resin composition according to the invention comprises at least two epoxy resins. One of these resins is solid at room temperature and comprises aromatic groups. The other resin is liquid, which means, throughout this specification, having a viscosity at 25° C. lower than about 1,000 Pa.s.
The solid epoxy resin generally is a substantially amorphous polymer, thus, such a resin has a melting range going from the solid to the liquid state.
The melting point of the solid resin preferably is higher than about 30° C. Solid epoxy resins with a melting point higher than about 40° C. are particularly preferred. Generally, these epoxy resins have a molecular weight (Mw) higher than about 600. Molecular weight, as used throughout this application, is the calculated molecular weight of the molecule concerned. In case of a polymer structure, it is the calculated molecular weight of the expected structure, based on the starting materials and reaction conditions. The molecular weight can also be determined using conventional techniques.
The liquid epoxy resin has a viscosity at 25° C. lower than about 1000 Pa.s, preferably lower than about 100 Pa.s. In general, the molecular weight of such a resin is lower than about 500.
The liquid epoxy resin can be aliphatic or aromatic. Preferably, the liquid epoxy resin comprises one or more cycloaliphatic groups, or comprises aromatic groups. Aliphatic epoxy resins give improved cure speed; aromatic epoxy resin results in better storage stability of the liquid resin. Both types of resins are very suitable as the liquid epo
Lapin Stephen C.
Sullivan Michael G.
DSM N.V.
Hamilton Cynthia
Pillsbury & Winthrop LLP
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