Patent Application
20080036114
Presently described are molds having a microstructured surface, methods of making microstructured articles by utilizing a mold, and methods of making molds. Hereinafter, the embodiments of the invention will be explained with reference to a flexible mold suitable for making microstructures such as barrier ribs. The flexible molds can be utilized to make other microstructured articles for (e.g. forming cells of) displays as well as other uses such as for example electrophoresis plates with capillary channels.
The flexible mold 100 of
The depth, pitch and width of the microstructured grooves 130 of the shape-imparting layer can vary depending on the desired finished article. The depth of the microstructures (e.g. groove corresponding to the barrier rib height) is generally at least 100 μm and typically at least 150 μm. Further, the depth is typically no greater than 500 μm and typically less than 300 μm. The pitch of the microstructured (e.g. groove) pattern may be different in the longitudinal direction in comparison to the transverse direction. The pitch is generally at least 100 μm and typically at least 200 μm. The pitch is typically no greater than 600 μm and preferably less than 400 μm. The width of the microstructured (e.g. groove) may be different between the upper surface and the lower surface, particularly when the barrier ribs thus formed are tapered. The width is generally at least 10 μm, and typically at least 50 μm. Further, the width is typically no greater than 100 μm and typically less than 80 μm.
The thickness of a representative shape-imparting layer is at least 5 μm, typically at least 10 μm, and more typically at least 50 μm. Further, the thickness of the shape-imparting layer is no greater than 1,000 μm, typically less than 800 μm and more typically less than 700 μm. When the thickness of the shape-imparting layer is below 5 μm, the desired rib height typically cannot be obtained. When the thickness of the shape-imparting layer is greater than 1,000 μm, warp and reduction of dimensional accuracy of the mold can result due to excessive shrinkage.
The mold includes a non-molding (e.g. non-rib) region 160 typically comprised of the same material as the microstructured molding region. The non-molding (e.g. non-rib) regions are provided for various reasons. With reference to
The non-molding (e.g. non-rib) regions are typically provided at the periphery of the mold on at least two opposing sides. In the case of quadrilateral shaped molds, opposing sides are generally parallel to each other. The entire periphery of the microstructured surface of a (e.g. sheet) mold may be bounded by non-molding regions.
The dimensions of the non-molding region can vary. For flexible molds suitably sized for the manufacture of a 30 to 60 inch plasma display back panel, the width of the non-molding regions between microstructured molding regions of adjacent discrete molds, i.e. d1 of
It has been found that a flexible mold having non-molding regions can be further improved by surface modifying the non-molding regions on at least two opposing sides. In general, the surface modification of the non-molding regions provides a non-molding region having a reduced contact area. The reduced contact area can reduce the adhesion of the non-molding regions of the mold with the substrate during molding, thereby reducing positional error of the molded barrier ribs.
During use of the mold, a coating of paste of uniform thickness is typically provided on an electrode patterned substrate, such as described in WO 03/032353. The width of this coating typically does not extend beyond the peripheral (e.g. groove 130a) recesses of the microstructured molding surface. When the mold contacts the uniform coating of paste, the planar surfaces of peripheral planar portions 145 contact the substrate. However, the uppermost surface of the surface modified non-molding regions 160 either do not contact the substrate at all, by virtue of having a substantially reduced thickness or have substantially reduced contact with the substrate by virtue of other physical or chemical surface modifications.
With reference to
The unmodified planar portion 145 typically has a relatively small contact area in comparison to the surface modified non-molding region 160, such as depicted in
Various approaches can be employed to physically and/or chemically modify the non-molding regions.
In one aspect, the contact area of the non-molding region can be reduced by reducing the thickness of at least portions of the non-molding region adjacent the unmodified peripheral planar portions 145. The thickness of the physically modified non-molding region is typically reduced by at least 10%, 20%, 30% or 40% relative to the adjacent peripheral planar portions 135a. In some embodiments, 100% of the physically modified non-molding region adjacent unmodified region 135a is removed such that only support 110 remains in such physically modified regions.
In another aspect, at least portions of the non-molding regions may comprise a roughened surface. The non-rib regions may be sanded or abraded by other means thereby providing a surface roughness Ra of at least 1 micron. Typically, the surface roughness is no greater than about 10 microns.
Another way of physically modifying at portion of the non-molding region is to microstructure the non-molding region. Such microstructures are generally substantially smaller than the microstructures (e.g. grooves) of the microstructured surface of the mold. For examples the microstructures of the non-rib regions may range in size from about 1 to about 10 percent of the size of the microstructures of the microstructured surface of the mold.
Alternatively, the non-molding regions can be chemically modified by coating the surface a fluorinated material or a silicone material as known in the art.
Any one or combination of the physical and/or chemical modifications described herein can be utilized.
The surface modifications can be incorporated into the flexible mold by first making the flexible mold having the non-molding regions by methods known in the art and then surface modifying a portion of the non-molding regions on at least two opposing sides of the flexible mold. Alternatively however, the physical modifications can be incorporated into the transfer mold from which the flexible mold is formed and/or be incorporated into the master mold from which the transfer mold is formed. The preparation of a transfer mold from a master mold is known such as described in U.S. Patent Publication 2005/0206034. Further, the preparation of a master mold is also known such as described in U.S. Publication No. 2006/0225463.
The preparation of a flexible mold from a transfer mold is known such as described in U.S. Publication No. 2006-0231728. In an embodied method of manufacture of a flexible mold, a polymerizable resin composition is provided at least in the recesses of the microstructured surface of a (e.g. polymeric) transfer mold having, a corresponding inverse microstructured surface pattern as the flexible mold,. This can be accomplished with known customary coating means such as a knife coater or a bar coater. A support comprising a flexible polymeric film is stacked onto the polymerizable resin filled mold such that the resin contacts the support. While stacked in this manner, the polymerizable resin composition is cured. Photocuring is typically preferred. For this embodiment, it is preferred that the support as well as the polymerizable composition are sufficiently optically transparent such that rays of light irradiated for curing can pass through the support. Once cured, the flexible mold, having the support film integrally bonded to the shape-imparting layer formed from the cured polymerizable resin, is separated from the transfer mold.
Suitable photocurable polymerizable resin compositions for preparation of the shape-imparting layer of the flexible mold are also known such as described in U.S. Publication No. 2006/0231728.
Prior to preparation of the flexible mold, the transfer mold and support film are typically conditioned in a humidity and temperature controlled chamber (e.g. 22° C./55% relative humidity) to minimize any dimensional changes thereof. It is also desirable to maintain a constant humidity and temperature during the method of making barrier ribs from the flexible mold. Such conditioning is further described in WO 2004/010452; WO 2004/043664 and JP Application No. 2004-108999, filed Apr. 1, 2004; incorporated herein by reference.
Although the support may optionally comprise the same material as the shape-imparting layer, for example by coating the polymerizable composition onto the transfer mold in an amount in excess of the amount needed to only fill the recesses, the support is typically a preformed polymeric film. The thickness of the polymeric support film is typically at least 0.025 millimeters, and more typically at least 0.075 millimeters. Further the thickness of the polymeric support film is generally less than 0.5 millimeters and typically less than 0.175 millimeters. The tensile strength of the polymeric support film is generally at least about 5 kg/mm2 and typically at least about 10 kg/mm2. The polymeric support film typically has a glass transition temperature (Tg) of about 60° C. to about 200° C. Various materials can be used for the support of the flexible mold including cellulose acetate butyrate, cellulose acetate propionate, polyether sulfone, polymethyl methacrylate, polyurethane, polyester, and polyvinyl chloride. The surface of the support may be treated to promote adhesion to the polymerizable resin composition. Examples of suitable polyethylene terephthalate based materials include photograde polyethylene terephthalate and polyethylene terephthalate (PET) having a surface that is formed according to the method described in U.S. Pat. No. 4,340,276; incorporated herein by reference.
Methods of making microstructured articles from flexible molds are also known such as described for example in U.S. Published Application No. 2006/0235107. In one embodied method, a flat transparent (e.g. glass) substrate, having an (e.g. striped) electrode pattern is provided. The flexible mold described herein is positioned for example by use of a sensor such as a charge coupled device camera, such that the barrier pattern of the mold is aligned with the patterned substrate. A curable ceramic paste can be provided between the substrate and the shape-imparting layer of the flexible mold in a variety of ways. The curable material can be placed directly in the pattern of the mold followed by placing the mold and material on the substrate, the material can be placed on the substrate followed by pressing the mold against the material on the substrate, or the material can be introduced into a gap between the mold and the substrate as the mold and substrate are brought together by mechanical or other means. For example a (e.g. rubber) roller may be employed to engage the flexible mold with the barrier rib precursor. The rib precursor spreads between the glass substrate and the shape-imparting surface of the mold filling the groove portions of the mold. In other words, the rib precursor sequentially replaces air of the groove portions. Subsequently, the rib precursor is cured. The rib precursor is preferably cured by radiation exposure to (e.g. UV) light rays through the transparent substrate and/or through the mold. The flexible mold is removed while the resulting cured ribs remain bonded to the substrate.
The curable rib precursor (also referred to as “slurry” or “paste”) comprises at least three components. The first component is a glass- or ceramic-forming particulate material (e.g. powder). The powder will ultimately be fused or sintered by firing to form microstructures. The second component is a curable organic binder capable of being shaped and subsequently hardened by curing, heating or cooling. The binder allows the slurry to be shaped into rigid or semi-rigid “green state” microstructures. The binder typically volatilizes during debinding and firing and thus may also be referred to as a “fugitive binder”. The third component is a diluent. The diluent typically promotes release from the mold after hardening of the binder material. Alternatively or in additional thereto, the diluent may promote fast and substantially complete burn out of the binder during debinding before firing the ceramic material of the microstructures. The diluent preferably remains a liquid after the binder is hardened so that the diluent phase-separates from the binder material during hardening. The rib precursor preferably has a viscosity of less than 20,000 cps and more preferably less than 5,000 cps to uniformly fill all the microstructured groove portions of the flexible mold without entrapping air. The rib precursor composition preferably has a viscosity of between about 20 to 600 Pa-S at a shear rate of 0.1/sec and between 1 to 20 Pa-S at a shear rate of 100/sec. Suitable ceramic paste compositions are known such as described in U.S. Publication No. 2006/0235107.
In some embodiment, the photoinitiator of the polymerizable composition of the shape-imparting layer is different that the photoinitiator of the ceramic paste as described in U.S. Publication No. 2006/0113713.
Various other aspects that may be utilized in the invention described herein are known in the art including, but not limited to each of the following patents that are incorporated herein by reference: U.S. Pat. Nos. 6,247,986; 6,537,645; 6,352,763; 6,843,952, 6,306,948; 6,761,607; 6,821,178; PCT Publications WO 99/60446; WO 2004/062870; WO 2004/007166; WO 03/032354; WO 03/032353; WO 2004/010452; WO2004/064104; WO 2004/043664; WO2005/042427; WO2005/019934; WO2005/021260; and WO2005/013308; WO2005/052974; WO2005/068148; WO2005/097449; U.S. Publication Nos. 2006/0043647; 2006/0043638; 2006/0043634 and U.S. PublicationNos. 2007/0018363; 2006/0231728; 2007/0018348; 2006/0235107; 2007/0071948.
The present invention is illustrated by the following non-limiting examples. The ingredients employed in the examples are described in Table 1 as follows:
A microstructured mold was prepared with a polymerizable composition containing 80 parts by weight (pbw) of Ebecryl 270 acrylated urethane oligomer and 20 pbw of POA and 1 pbw Darocure-1173 photoinitiator. The polymerizable composition was mixed at ambient temperature and coated onto the surface of a transfer mold having a lattice pattern (which is the same as the eventual barrier ribs). The dimensions of the microstructured molding surface and non-molding regions of the mold are shown in
21.0 gms of Epoxyester 3000M, 9.0 gms of TEGDMA, 30.0 gms of 1,3-butandiol, 3.0 gms of POCA II, 0.3 gms Irgacure 819, and 180 gms of glass frit RFW-030 were mixed with Conditioning Mixer AR-250 (manufactured by THINKY Corporation) at ambient temperature until homogeneous.
Five samples 0.15 mm by 0.15 mm in area were viewed through a 20× lense of a laser microscope VK9500 manufactured by KEYENCE Corp. The surface roughness was measured at a depth interval of 0.2 microns and the Average Arithmatic Mean Deviation of the Profile (Ra) and the standard deviation were calculated according to JIS B 0601-1994.
A point was selected on the mold and the corresponding point on the cured barrier rib pattern was located. The distance from this point to a reference mark was measured by use of a Coordination Measurement Machine (manufactured by Sokkia Fine Systems Co., Ltd.). Five measurements were made in both the long (1000 mm) and short (500 mm) dimension of the mold and cured barrier rib pattern. The maximum difference between the measured value of the point on the mold and the corresponding point on the cured rib was calculated.
Material was removed from the periphery of two opposing non-molding regions by cutting with a razor blade and removing portions of the cured non-molding region. With reference to
A glass substrate was primed by coating the surface with a 1 to 2% solution of A-174 diluted with IPA and dried at ambient conditions for 15 minutes.
The photocurable precursor paste was coated onto a primed glass substrate and the mold was laminated to the coated glass by use of a roller. The curable paste was cured with 0.16 mW/cm2 light by irradiating through the flexible mold for 30 seconds with a fluorescent lamp having a peak wavelength at 400-500 nm (Philips). The mold was then separated leaving the cured barrier ribs bonded to the glass substrate. The maximum microstructure positional error of the cured barrier ribs was determined to be 18 ppm.
With reference to
A mold was prepared according to the method described above except that the non-molding regions were not physically modified. The mold was used to mold barrier rib microstructures in the same manner as Example 1. The maximum microstructure positional error of the barrier ribs was determined to be 115 ppm.
This application claims the benefit of U.S. Provisional Application Ser. No. 60/822272, filed Aug. 14, 2006.
| Number | Date | Country | |
|---|---|---|---|
| 60822272 | Aug 2006 | US |
