Patent Application
20090085235
This application claims the priority of German Patent Application, Serial No. 10 2005 013 974.4-16, filed Mar. 26, 2005, pursuant to 35 U.S.C. 119(a)-(d), the content of which is incorporated herein by reference.
The present invention relates to a method and apparatus for making articles having a microstructure or nanostructure, in particular a microstructure or nanostructure on a surface of the article.
Nothing in the following discussion of the state of the art is to be construed as an admission of prior art.
Plastic materials having a surface formed with a microstructure or nanostructure are used to impart certain physical effects, e.g. the lotus effect, resulting in a less soiled or self-cleaning surface and realized by applying the surface with a nanostructure. Reflection of optical articles can also be reduced by applying a microstructure or nanostructure on the surface. Microstructured or nanostructured elements can be made through an injection molding process which requires however a particular configuration of mold cavities and process conditions. Microstructures may be made through removal of microscopic material or laser application. Other methods include LIGA-technique (lithographic galvanic process) and special PVD-process (Physical Vapor Deposition). Such small structures can also be reproduced on thermoplastic material, and hot compression-molded, structured films may also be produced through back injection.
Fabrication of such products which are made of thermoplastic materials encounter a problem because they are not stable enough during use. In particular, these thermoplastic products are not sufficiently scratch-resistant. For example, in case of a fully transparent covering pane for a dashboard of a vehicle, reflection should be reduced as far as possible. This can be realized by providing the back and front sides of the pane with a nanostructure. While the backside faces the panel instruments and is separated from the surroundings so as to be inaccessible and thus not prone to soil or scratch, the front side is exposed to the vehicle interior space and thus can become dirty or scratched.
It would therefore be desirable and advantageous to provide an improved method and apparatus for making a product with a microstructure or nanostructure, to obviate prior art shortcomings and to remain useful over an extended period.
According to one aspect of the present invention, a method of making a product with a microstructure or nanostructure includes the steps of using an injection molding process or an injection-compression molding process to produce a substrate with a microstructure or nanostructure applied upon a surface of the substrate, and inundating the substrate with a cross-linking, curing material.
According to another feature of the present invention, the substrate may be placed in a cavity of a mold, and forming a cavity gap on the surface to be inundated, when the mold is closed, wherein the inundating step includes the step of filling the cavity gap with the cross-linking material.
The present invention resolves prior art problems by inundating a substrate in a cavity with a cross-linking material to thereby form a thin top layer. The material to inundate the substrate is hereby selected to satisfy, after cross-linkage and curing, the demanded requirements such as scratch resistance and long-term stability. The microstructure or nanostructure may also be provided on the material being inundated, i.e. substrate. This structure may however also be applied upon the surface of the cross-linking materials during the inundating process.
In order to enable the microstructure or nanostructure between the substrate and the top layer to impart an effective antireflection effect, the selected materials for the substrate and the top layer may have a different refractive index after being cured.
According to another feature of the present invention, the cross-linking material may be selected from the group consisting of polyurethane material, clear lacquer material, e.g. UV curable clear lacquer, acrylic paint, and epoxy resin. The material is of low viscosity when being introduced in order to assure a complete filling of the thin cavity gap. When cured, the product has a hard top layer which in particular is optically transparent to enable a long-term use of the product. Although the afore-described materials are currently preferred, any other material that is low in viscosity is conceivable so long as the material is able to cure and especially result in an optically transparent form.
The substrate may typically be made by an injection molding process or injection compression molding process in order to provide one or more sides of the substrate with a microstructure or nanostructure. In the event the microstructure or nanostructure should not be applied onto the substrate as such but merely upon the top layer, a respective cavity surface in configured with the desired microstructure or nanostructure which is duplicated upon the surface of the top layer as the material is introduced into the cavity gap. Of course, the substrate surface as well as the top layer may be provided with a microstructure or nanostructure. It is even possible to inundate various areas of the substrate on or to repeatedly inundate the substrate in order to develop multiple layers. In addition, it is also conceivable to inundate various sides of the substrate with cross-linking material so that, e.g., both sides of the substrate can be made scratch-resistant and useful for long-term application.
According to another feature of the present invention, the substrate may be made in another cavity though injection of plastic material before undergoing the inundating step with the cross-linking top coating material in the respective cavity. As an alternative, it is also conceivable to fabricate the substrate outside a cavity before undergoing the inundating process with the coating material. Suitably, a surface of the cavity or cavities may be heated and/or cooled by a heating and/or cooling device may be provided for.
According to another aspect of the present invention, an apparatus for making an article with a microstructure or nanostructure includes a mold having a cavity for positioning a substrate, wherein the mold is constructed to form a cavity gap on at least one side of the substrate and has a cavity surface which is provided with a microstructure or nanostructure, and a feeding device for introducing into the cavity gap a cross-linking material of low viscosity before curing to thereby allow formation of a top layer with reproduction of the microstructure or nanostructure.
By providing a cavity gap between the substrate and the cavity surface, the top layer is provided with a precisely defined layer thickness, when the coating material is filled into the cavity gap, whereby the application of a respective microstructure or nanostructure is easily possible on the top layer.
According to another feature of the present invention, an injection device may be provided for introducing plastic material into the cavity of the mold for producing the substrate. As an alternative, the substrate may be made in a separate mold whose cavity is filled with plastic material from an injection device. Suitably, the molds, the feeding device, and the injection device are disposed such that the introduction of the curing coating material and the introduction of the plastic material are executed in a same cycle.
According to another feature of the present invention, the mold may be arranged in a clamping unit, e.g. a swivel platen clamping unit, sliding table clamping unit, or rotary table clamping unit.
According to another feature of the present invention, the mold may be accommodated in a clamping unit such that after formation of the substrate the mold cavity can be expanded for realizing the cavity gap for subsequently inundating the substrate with the cross-linking material.
According to another feature of the present invention, a heating unit may be provided for heating the cavity surface.
According to another feature of the present invention, the injection molding and injection compression molding processes may be combined with a polyurethane reaction injection molding (PUR-RIM) process.
According to another feature of the present invention, a heating unit may be provided for heating the mold or at least a cavity surface. In this way, the accuracy of the reproduction of the microstructure and nanostructure is enhanced, the free flow property in particular with respect to longer flow paths is improved, and the cross-linkage reaction is promoted. This would also enable execution of a hot compression molding process in an injection mold. Heating may be provided during production of the substrate as well as during inundation of the substrate. Of course, a cooling system may also be provided to ensure, for example, a more rapid expulsion of the product. Such a cooling system may be integrated in a mold, e.g. in the form of cooling channels.
Other features and advantages of the present invention will be more readily apparent upon reading the following description of currently preferred exemplified embodiments of the invention with reference to the accompanying drawing, in which:
a is a schematic sectional view of one embodiment of a mold being closed and filled with substrate material;
b is a schematic sectional view of the mold slightly opened and filled with coating material to inundate a substrate surface;
a is a schematic sectional view of another embodiment of a mold filled with substrate material; and
b is a schematic sectional view of the mold of
Throughout all the Figures, same or corresponding elements are generally indicated by same reference numerals. These depicted embodiments are to be understood as illustrative of the invention and not as limiting in any way. It should also be understood that the drawings are not necessarily to scale and that the embodiments are sometimes illustrated by graphic symbols, phantom lines, diagrammatic representations and fragmentary views. In certain instances, details which are not necessary for an understanding of the present invention or which render other details difficult to perceive may have been omitted.
Turning now to the drawing, and in particular to
The mold 10 has two half-molds 12, 14 which jointly define a cavity, when the mold 10 is closed, as shown in
As indicated by reference numeral 17, an inside surface of the half-mold 14 is constructed with a microstructure or nanostructure.
The mode of operation is as follows: In a first process step, as shown in
As a consequence of the microstructure or nanostructure 17 on the top layer, the finished product exhibits an antireflection effect. Of course, the substrate 15 as well as the introduced coating material must exhibit optically transparent characteristics. Suitably, in order to render the microstructure or nanostructure 17 between the substrate 15 and the top layer effective, the substrate material and the coating material for the top layer should have different refractive index.
Referring now to
The mold 30 is further provided with a heating unit 44 in close proximity of the cavity surface 46 of the half-mold 34. The heating unit 44 may be realized, e.g., by means of an electrically conductive ceramic or by means of a heating coil immediately adjacent to the cavity surface 46. Of course, a corresponding heating unit, although not shown here, may be arranged in analogous manner in the other half-mold 32. Furthermore, both half-molds 32, 34 may be formed with cooling channels (not shown) in close proximity to the cavity surfaces 42, 46.
The mode of operation is as follows: Substrate material is introduced via sprue 36 into the cavity of the mold 30 which is closed to compression-mold the substrate material to thereby form the substrate 40. In other words, the substrate material is injected into a slightly enlarged volume of the cavity in the mold 30. Then, as the clamping force is increased to move the half-molds 32, 34 of the mold 30 toward one another to the final cavity size, the injected material is compression-molded. The cavity surface 46 (and/or cavity surface 42) is hereby heated to assist the reproduction of the microstructure or nanostructure on the surface of the substrate 40. During production of the substrate 40, the feed channel 38 is sealed by the half-mold 34 so as to prevent thermoplastic material from migrating or escaping through the feed channel 38.
After the substrate 40 has cured, the half-mold 34 is slightly opened to form a cavity gap 50 as the substrate 40 disengages from the half-mold 34. Thereafter, cross-linking and curing coating material, e.g. polyurethane material, which in particular is optically highly transparent, is introduced into the cavity gap 50. During the subsequent compression molding step, the microstructure or nanostructure is again reproduced on the top layer formed by the coating material on the substrate 40. The heating unit 44 hereby assists to enhance accuracy of the reproduction, to improve the flow capability, and to promote cross-linkage. When the top layer has cured, the substrate has a highly transparent surface which is hard and scratch-resistant.
In the event, both sides of the finished product should be made scratch-resistant, it is, of course, possible to engulf both sides of the substrate with coating material. In this case, the mold and the process sequence need to be adapted accordingly.
In the afore-described embodiments, a single mold is used to produce the substrate and to produce a top layer on one or more sides of the substrate. It is, of course, also feasible, to carry out the substrate producing and inundating steps in different molds. In other words, the substrate can be made in a separate mold through an injection-molding or injection-compression molding process, and then transferred into a cavity of another mold, whereby the cavity of this mold is sized larger than the substrate to form the cavity gap, when the mold is closed, for realizing the subsequent inundating step.
Although not shown in detail, it is, of course, possible to add further components or materials, such as light guides, glass fibers or electronic components, to realize visual effects that render these components visible, in particular when the coating material and the substrate are transparent. For example, these components can be placed in the cavity gap upon the substrate before the substrate is inundated with the cross-linking, curing material. As a result, all structures of and on the substrate can be made visible.
While the invention has been illustrated and described in connection with currently preferred embodiments shown and described in detail, it is not intended to be limited to the details shown since various modifications and structural changes may be made without departing in any way from the spirit of the present invention. The embodiments were chosen and described in order to best explain the principles of the invention and practical application to thereby enable a person skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated.
What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims and includes equivalents of the elements recited therein:
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2005 013 974.4 | Mar 2005 | DE | national |
