Patent Application
20080233404
The present invention relates to microreplication tools and methods to make them using laser induced thermal embossing (LITE) films and laser induced thermal imaging (LITI) methods.
Machining techniques, such as diamond turning and plunge electrical discharge machining, can be used to create a wide variety of work pieces such as microreplication tools. Microreplication tools are commonly used for extrusion processes, injection molding processes, embossing processes, casting processes, or the like, to create microstructures. The articles having microstructured surfaces may comprise optical films, abrasive films, adhesive films, mechanical fasteners having self-mating profiles, or any molded or extruded parts having microreplication features of relatively small dimensions, such as dimensions less than approximately 1000 microns.
The microstructured features can also be made by various other methods. For example, the structure of the master tool can be transferred onto other media, such as to a belt or web of polymeric material, by a cast and cure process from the master tool in order to form a production tool, which is then used to make the microstructures. Other methods such as electroforming can be used to copy the master tool. Other techniques of making tools include chemical etching, bead blasting, or other stochastic surface modification techniques.
A LITE film, consistent with the present invention, includes a substrate and a light-to-heat conversion layer overlaying the substrate. A surface of the LITE film is capable of bearing a microstructured surface selectively embossed thereon.
A method of fabricating a microreplication tool, consistent with the present invention includes the following steps: providing a LITE film comprising a substrate and a light-to-heat conversion layer overlaying the substrate; laminating the LITE film to a master tool comprising a pattern of microstructures with the light-to-heat conversion layer being in contact with the microstructures; pattern-wise imaging the LITE film to selectively expose the light-to-heat conversion layer; and removing the master tool to produce a microstructured pattern on the LITE film corresponding with the microstructures of the master tool.
The accompanying drawings are incorporated in and constitute a part of this specification and, together with the description, explain the advantages and principles of the invention. In the drawings,
a-2c are diagrams illustrating a process of embossing a LITE film to produce a microreplication tool, liner, or product such as LITI donor film;
a is a perspective diagram of a microreplication tool;
b is a perspective diagram of a LITE tool made using the microreplication tool shown in
a is a perspective diagram of three different microreplication tools;
b is a perspective diagram of a LITE tool made using the three microreplication tools shown in
a-7f are diagrams illustrating a process of embossing a LITE film, while using a structure on structure pattern in the film or a corresponding tool, to produce a microreplication tool, liner, or product such as LITI donor film;
a-8c are diagrams illustrating a LITI process of imaging an embossed a LITE film having a transfer layer in order to transfer a portion of the transfer layer to a permanent receptor;
a is a diagram illustrating a process for making a LITE tool using a 90° orientation of laser scanning;
b is an image of a sample LITE tool made using the scanning orientation shown in
a is a diagram illustrating a process for making a LITE tool using a 45° orientation of laser scanning; and
b is an image of a sample LITE tool made using the scanning orientation shown in
Embodiments of the present invention include methods to generate complex tools for micro- and nano-replication processes. The methods involve combining aspects of precision laser exposure and LITE with conventional microreplication tools such as those made using precision diamond machining, Excimer Laser Machining of Flats (ELMoF), photolithographic patterning, or other techniques. LITE can be performed using virtually any microreplication tool surface and a LITE sheet or film having sufficient heat stability. The film is laminated to the microreplication tool and then exposed from the back with a laser. The result is a three dimensional embossed pattern that corresponds with the pattern of the microreplication tool at the laser exposure area.
LITE can be used to create many different microstructured films. For example, LITE can provide for a rapid method to create customizable holographic patterns on film substrates for security applications using a single holographic master (e.g., laminates for drivers licenses or credit cards). LITE can also be used to create microstructured films having various other optical properties based upon, for example, their microstructured optical elements. In addition, LITE offers the ability to combine elements from different MS tooling methods into one LITE tool.
LITE can also be used to make products from a master tool. The LITE film, after embossing, can form a microstructured master tool having a microreplicated pattern corresponding with the embossing. The LITE film as a master tool can be used to microreplicate a product having the inverse pattern from the tool, for example a protrusion in the master tool corresponds with an indentation in the product. Alternatively, the LITE film as a master tool can be used to make a microreplicated mold, which can then be used to make a product having the same microreplicated pattern as the master tool, or to make a more robust (metal) tool, for example by nickel electroforming having the inverse pattern. Electroforming is described in, for example, U.S. Pat. Nos. 4,478,769 and 5,156,863, which are incorporated herein by reference. The LITE film as a master tool can thus be used to produce positive and negative replicated products of the microreplicated pattern of the master tool.
The term “microreplication tool” means a tool having microstructured features, nanostructured features, or a combination of microstructured and nanostructured features from which the features can be replicated. The term “microstructured” refers to features of a surface that have at least one dimension (e.g., height, length, width, or diameter), and typically at least two dimensions, of less than one millimeter. The term “nanostructured” refers to features of a surface that have at least one dimension (e.g., height, length, width, or diameter) of less than one micron.
The film substrate 102 provides support for the layers of the film 100. One suitable type of polymer film is a polyester film, for example, PET or polyethylene naphthalate (PEN) films. However, other films with sufficient optical properties can be used, if light is used for heating and embossing. The film substrate, in at least some instances, is flat so that uniform coatings can be formed. The film substrate is also typically selected from materials that remain substantially stable despite heating of any layers in the film (e.g., an LTHC layer). A suitable thickness for the film substrate ranges from, for example, 0.025 millimeters (mm) to 0.15 mm, preferably 0.05 mm to 0.1 mm, although thicker or thinner film substrates may be used.
The LTHC layer 104 typically includes a radiation absorber that absorbs incident radiation (e.g., laser light) and converts at least a portion of the incident radiation into heat to enable embossing of the LTHC layer. Alternatively, radiation absorbers can be included in one or more other layers of the LITE film in addition to or in place of the LTHC layer. Typically, the radiation absorber in the LTHC layer (or other layers) absorbs light in the infrared, visible, and/or ultraviolet regions of the electromagnetic spectrum. The radiation absorber is typically highly absorptive of the selected imaging radiation, providing an optical density at the wavelength of the imaging radiation in the range of 0.2 to 3, and preferably from 0.5 to 2. Suitable radiation absorbing materials can include, for example, dyes (e.g., visible dyes, ultraviolet dyes, infrared dyes, fluorescent dyes, and radiation-polarizing dyes), pigments, metals, metal compounds, metal films, and other suitable absorbing materials. Examples of other suitable radiation absorbers can include carbon black, metal oxides, and metal sulfides.
For imaging of the LITE film in order to emboss it, a variety of radiation-emitting sources can be used. For analog techniques (e.g., exposure through a mask), high-powered light sources (e.g., xenon flash lamps and lasers) are useful. For digital imaging techniques, infrared, visible, and ultraviolet lasers are particularly useful. Suitable lasers include, for example, high power (e.g. ≧100 mW) single mode laser diodes, fiber-coupled laser diodes, and diode-pumped solid state lasers (e.g., Nd:YAG and Nd:YLF). Laser exposure dwell times can be in the range from, for example, about 0.1 microsecond to 100 microseconds and laser fluences can be in the range from, for example, about 0.01 J/cm2 to about 1 J/cm2. In at least some instances, pressure or vacuum may be used to hold the LTHC layer in intimate contact with a microreplication tool. A radiation source may then be used to heat the LTHC layer or other layers containing radiation absorbers in an image-wise fashion (e.g., digitally or by analog exposure through a mask) to emboss the LTHC layer.
A microreplication tool can be used to generate LITE films by irradiating the films, when laminated to the microreplication tool, with an area of a laser exposure. The result is an embossed film with a structure corresponding with the microreplication structure of the tool in the areas of laser exposure. In addition, the process can be repeated with different tools, made from different MS techniques, to provide a single LITE tool with a number of different patterns.
a-2c are diagrams illustrating use of LITE to make a microreplication tool using a LITE film. As shown in
a is a perspective diagram of a microreplication tool 300 having microstructured prisms.
A variation of the LITE process involves the use of multiple microreplication tools having different microstructured patterns to create a more complex LITE tool.
LITE Film with Structure on Structure
Another variation of the LITE process enables the creation of structure on structure arrays or patterns comprising micron scale features, such as prisms, with nanostructured features on their surface. As an example, the nanostructured features can include one- or two-dimensional diffraction gratings.
d-7f illustrates alternatives to the structure on structure patterns.
a-8c are diagrams illustrating a LITI process of imaging an embossed LITE film 600 having a transfer layer 606 in order to transfer a portion of the transfer layer to a receptor 608. As shown in
Various layers of an exemplary LITI donor film, and methods to image it, are more fully described in U.S. Pat. Nos. 6,866,979; 6,586,153; 6,468,715; 6,284,425; and 5,725,989, all of which are incorporated herein by reference as if fully set forth.
Film 600 can have an optional interlayer between LTHC layer 606 and embossing layer 608. The optional interlayer may be used in the thermal donor to minimize damage and contamination of the transferred portion of the layer and may also reduce distortion in the transferred portion of the layer. The interlayer may also influence the adhesion of the transfer layer to the rest of the thermal transfer donor. Typically, the interlayer has high thermal resistance. Preferably, the interlayer does not distort or chemically decompose under the imaging conditions, particularly to an extent that renders the transferred image non-functional. The interlayer typically remains in contact with the LTHC layer during the transfer process and is not substantially transferred with the transfer layer. Suitable interlayers include, for example, polymer films, metal layers (e.g., vapor deposited metal layers), inorganic layers (e.g., sol-gel deposited layers and vapor deposited layers of inorganic oxides (e.g., silica, titania, and other metal oxides)), and organic/inorganic composite layers. Organic materials suitable as interlayer materials include both thermoset and thermoplastic materials. Suitable thermoset materials include resins that may be crosslinked by heat, radiation, or chemical treatment including, but not limited to, crosslinked or crosslinkable polyacrylates, polymethacrylates, polyesters, epoxies, and polyurethanes. The thermoset materials may be coated onto the LTHC layer as, for example, thermoplastic precursors and subsequently crosslinked to form a crosslinked interlayer. The interlayer may contain additives, including, for example, photoinitiators, surfactants, pigments, plasticizers, and coating aids.
The transfer layer 606 typically includes one or more layers for transfer to receptor 608. These one or more layers may be formed using organic, inorganic, organometallic, and other materials. Organic materials include, for example, small molecule materials, polymers, oligomers, dendrimers, and hyperbranched materials. The thermal transfer layer can include a transfer layer that can be used to form, for example, light emissive elements of a display device, electronic circuitry, resistors, capacitors, diodes, rectifiers, electroluminescent lamps, memory elements, field effect transistors, bipolar transistors, unijunction transistors, metal-oxide semiconductor (MOS) transistors, metal-insulator-semiconductor transistors, charge coupled devices, insulator-metal-insulator stacks, organic conductor-metal-organic conductor stacks, integrated circuits, photodetectors, lasers, lenses, waveguides, gratings, holographic elements, filters for signal processing (e.g., add-drop filters, gain-flattening filters, cut-off filters, and the like), optical filters, mirrors, splitters, couplers, combiners, modulators, sensors (e.g., evanescent sensors, phase modulation sensors, interferometric sensors, and the like), optical cavities, piezoelectric devices, ferroelectric devices, thin film batteries, or combinations thereof, for example the combination of field effect transistors and organic electroluminescent lamps as an active matrix array for an optical display. Other items may be formed by transferring a multi-component transfer assembly or a single layer.
Permanent receptor 608 for receiving at least a portion of transfer layer 606 may be any item suitable for a particular application including, but not limited to, transparent films, display black matrices, passive and active portions of electronic displays, metals, semiconductors, glass, various papers, and plastics. Examples of receptor substrates include anodized aluminum and other metals, plastic films (e.g., PET, polypropylene), indium tin oxide coated plastic films, glass, indium tin oxide coated glass, flexible circuitry, circuit boards, silicon or other semiconductors, and a variety of different types of paper (e.g., filled or unfilled, calendered, or coated).
a is a diagram illustrating a process for making a LITE tool using a 90° orientation of laser scanning, and
LITE Film 1, comprising two coated layers on PET film was prepared in the following manner. An LTHC was applied on 2.88 mil thick PET film substrate (M7Q film, DuPont Teijin Films, Hopewell Va.) by coating LTHC-1 (Table 1) using a reverse microgravure coater (Yasui Seiki CAG-150). The coating was dried in-line and photocured under ultraviolet radiation in order to achieve an LTHC dry thickness of approximately 2.7 microns. The cured coating had an optical density of approximately 1.18 at 1064 nanometers (nm).
A clear coat was applied to the LTHC layer by coating CC-1 (Table 2) using a reverse microgravure coater (Yasui Seiki CAG-150). The coating was dried in-line and photocured under ultraviolet radiation in order to achieve a dry clear coat thickness of approximately 1.1 microns.
LITE Film 2, comprising a single coated layer on PET film was prepared in the following manner. An LTHC layer was applied on 2.88 mil thick PET film substrate (M7Q film, DuPont Teijin Films, Hopewell Va.) by coating LTHC-2 (Table 3) using a reverse microgravure coater (Yasui Seiki CAG-150). The coating was dried in-line in order to achieve an LTHC dry thickness of approximately 3.7 microns. The dry coating had an optical density of approximately 3.2 at 808 nm.
The patterned silicon wafer master was fabricated on a standard orientation 4 inch silicon wafer which was coated with Shipley 1813 photoresist (Rohm and Haas Electronic Materials, Newark, Del.). The resist was patterned with small square arrays of 5 micron linear features by way of contact photolithography using a standard I-line mask aligner (Quintel, San Jose, Calif.) and an E-beam written chrome on glass phototool. Standard development techniques for Shipley resists were used, although no final hard bake was performed on the resist. The sample was then etched in a reactive ion etch tool equipped with an inductively coupled plasma generator (Oxford Instruments, Eynsham, England). The sample was etched for 2 minutes to an approximate etch depth of 0.5 micron using C4F8 and O2, an RF power of 70 W, an ICP power of 1600 W, and a pressure of 5.5 mTorr. The sample was then stripped of the resist using Shipley 1165 resist stripper in a heated ultrasonic photoresist stripper bath, yielding the master tool.
The master tool was plated with electrolytic nickel to a thickness of approximately 25 mils. Prior to nickel plating, 1000 Å of vapor coated nickel was deposited on the surface in order to make the wafers conductive. The nickel plating was performed in two steps consisting of a preplate of 6 hours with a low deposition rate to ensure that a uniform conductive layer of nickel was established, followed by a more rapid deposition to achieve the target thickness value of 25 mils. The electroforming yielded the nickel electroform tool with arrays of 5 micron wide linear features having a uniform height of approximately 1.29 microns (as determined by AFM analysis).
In order to create a LITE tool, a LITE film was brought into intimate contact with a structured tool. Air between the film and tool was removed with a vacuum chuck assembly, and the film-tool laminate was exposed to laser radiation through the support layer (substrate) of the film. For laser system A exposure (λ=1064 nm), the scan velocity was 0.635 m/s, spot power was 1 W in the image plane, and the dose was 0.85 J/cm2. For laser system B exposure (λ=808 nm), the scan velocity was 1.0 m/s, spot power was 1.3 W and dose was 1.3 J/cm2.
Atomic force microscopy (AFM) in tapping mode was used to characterize embossed features of LITE film 2 and corresponding features of the nickel electroform and IDF. The instrument used for analysis of TMF film and corresponding LITE film 2 was a Digital Instruments Dimension 3100 SPM. The instrument used for analysis of nanotool and corresponding LITE film 2 was a Digital Instruments Dimension 5000 SPM. The probes used were Olympus OTESP single crystal silicon levers with a force constant of ˜40 N/M. The setpoint value was set to 75% of the original free space amplitude (2.0 V).
