News Column

Researchers Submit Patent Application, "Method of Forming Printed Patterns", for Approval

August 27, 2014



By a News Reporter-Staff News Editor at Electronics Newsweekly -- From Washington, D.C., VerticalNews journalists report that a patent application by the inventors ZWADLO, Gregory Lloyd (River Falls, WI); FOHRENKAMM, Elsie Anderson (St. Paul, MN); SIMPSON, Charles W. (Lakeland, MN), filed on January 8, 2014, was made available online on August 14, 2014.

No assignee for this patent application has been made.

News editors obtained the following quote from the background information supplied by the inventors: "Relief images can be provided and used in various articles for many different purposes. For example, the electronics, display, and energy industries rely on the formation of coatings and patterns of conductive materials to form circuits on organic and inorganic substrates. Such coatings and patterns are often provided using relief imaging methods and relief image forming elements. There is also need for means to provide fine wiring in various articles.

"Microelectronic devices have been prepared by photolithographic processes to form necessary patterns. Photolithography, however, is a complex, multi-step process that is too costly for the printing of electronic devices on plastic substances.

"Contact printing is a flexible, non-lithographic method for forming patterned materials. Contact printing potentially provides a significant advance over conventional photolithographic techniques since contact printing can form relatively high resolution patterns for electronic parts assembly. Microcontact printing can be characterized as a high resolution technique that enables patterns of micrometer dimensions to be imparted onto a substrate surface. Contact printing is a possible replacement to photolithography in the fabrication of microelectronic devices, such as radio frequency tags (RFID), sensors, and memory and back panel displays. The capability of microcontact printing to transfer a self-assembled monolayer (SAM) forming molecular species to a substrate has also found application in patterned electroless deposition of metals. SAM printing is capable of creating high resolution patterns, but is generally limited to forming metal patterns of gold or silver for example using thiol chemistry. Although there are variations, in SAM printing a positive relief pattern provided on an element having a relief image is inked onto a substrate.

"Flexography is a one method of printing or pattern formation that is commonly used for high-volume printing runs. It is usually employed for printing on a variety of soft or easily deformed materials including but not limited to, paper, paperboard stock, corrugated board, polymeric films, fabrics, metal foils, glass, glass-coated materials, flexible glass materials, and laminates of multiple materials. Coarse surfaces and stretchable polymeric films are economically printed using flexography.

"Flexographic printing members are sometimes known as 'relief' printing members (for example, relief-containing printing plates, printing sleeves, or printing cylinders) and are provided with raised relief images onto which ink is applied for application to a printable material. While the raised relief images are inked, the relief 'floor' should remain free of ink. These flexographic printing precursors are generally supplied with one or more imageable layers that can be disposed over a backing layer or substrate. Flexographic printing also can be carried out using a flexographic printing cylinder or seamless sleeve having the desired relief image.

"A method for printing with a conductive ink using a relief printing plate at high print speed is described in U.S. Patent Application Publication 2004/0003734 (Shively et al.).

"U.S. Pat. No. 7,026,012 (Chen et al.) describes a method for transferring catalytic particles from a stamp to a substrate followed by plating the catalytic particles.

"U.S. Patent Application Publication 2008/0233280 (Blanchet et al.) describes the use of an elastomeric stamp having a relief structure with a raised surface that is treated with heat or by other means to enhance its wettability, and then application and transfer of a functional material to form a pattern on a substrate.

"While there are numerous methods described in the art to form patterns using relief images, there remains a need to find a way to consistently provide patterns with high resolution lines (for example, 10 .mu.m or less) and feature uniformity using various printable material compositions (or what are sometimes known as 'inks'). The industry has been pursuing these goals for many years with limited success and continued research is being done to achieve these goals using a wide variety of print materials. A number of problems must been addressed to achieve the desired high resolution lines.

"One problem is the spread of the viscous printable material composition (or ink) during compression contact between an elastomeric relief element and a substrate (receiver element). This results in a loss of resolution and uniformity of edge quality.

"A second problem that has been observed is the limited amount of print material composition that can be applied to and subsequently transferred from an elastomeric relief element to a substrate (receiver element). Typically, only about half of the printable material composition is transferred to the substrate when the printable material composition still contains volatile carrier liquid or is too viscous. Thus, in such instances, insufficient printable material composition is transferred to the substrate to meet performance requirements.

"Yet another problem that must be addressed is the potential incompatibility of the carrier liquid with an elastomeric relief element as well as the receiver material.

"Lastly, another problem to be addressed is the low impression pressure between the elastomeric relief element and the substrate that is typically needed to provide sufficient wet transfer of both fine features and large area features. Typically, multiple printing steps from multiple elastomeric relief elements are required to provide both fine features and large solid area features because of this problem.

"There is a desire to address as many of these problems using the same printing method."

As a supplement to the background information on this patent application, VerticalNews correspondents also obtained the inventors' summary information for this patent application: "The present invention provides a method for forming a pattern of a print material on a receiver element comprising a print material receptive layer, the method comprising:

"providing an elastomeric relief element that comprises a relief pattern comprising (1) an uppermost relief surface, and (2) an average relief image depth of at least 50 .mu.m relative to the uppermost relief surface and a shoulder angle greater than 25.degree. and up to and including 85.degree. from vertical, and (3) a modulus of elasticity of at least 2 megaPascals and up to and including 10 megaPascals,

"applying a printable material composition to the uppermost relief surface of the elastomeric relief element, the printable material composition comprising a print material and a carrier liquid, the printable material composition having a viscosity of at least 1 cps and up to and including 1500 cps,

"removing at least 50 weight % of the carrier liquid from the printable material composition that is disposed on the uppermost relief surface of the elastomeric relief element, leaving print material disposed on the uppermost relief surface,

"providing a receiver element comprising a print material receptive layer disposed on a substrate, wherein the print material receptive layer has a dry thickness of at least 0.05 .mu.m and up to and including 10 .mu.m when measured at 25.degree. C.,

"heating the receiver element to a heating temperature that is higher than the glass transition temperature (T.sub.gl) of the print material receptive layer, to form a heated receiver element,

"contacting the print material disposed on the uppermost relief surface and the heated receiver element such that the elastomeric relief element (not supporting means such as mounting tape) is compressed and the print material disposed on the uppermost relief surface is in contact with the heated receiver element, and

"separating the elastomeric relief element from the heated receiver element to leave a pattern of the print material on the heated receiver element, wherein at least 70 weight % of the print material originally disposed on the uppermost relief surface of the elastomeric relief element is transferred to the heated receiver element.

"In addition, in some embodiments of this invention, a method for forming a pattern of a print material on a receiver element comprising a print material receptive layer, comprises:

"providing an elastomeric relief element that comprises a relief pattern comprising (1) an uppermost relief surface, and (2) an average image depth of at least 50 .mu.m relative to the uppermost relief surface and a shoulder angle greater than 25.degree. and up to and including 85.degree. from vertical, and (3) a modulus of elasticity of at least 2 megaPascals and up to and including 10 megaPascals,

"applying a printable material composition to the uppermost relief surface of the elastomeric relief element, the printable material composition comprising a print material and a carrier liquid, the printable material composition having a viscosity of at least 1 cps and up to and including 1500 cps,

"removing at least 25 weight % of the carrier liquid from the printable material composition that is disposed on the uppermost relief surface of the elastomeric relief element, leaving print material disposed on the uppermost relief surface,

"repeating the preceding applying and removing steps together, in the noted sequence, at least once using additional amounts of the same printable material composition and the same elastomeric relief element, to provide an increased amount of print material disposed on the uppermost relief surface,

"providing a receiver element comprising a print material receptive layer disposed on a substrate, wherein the print material receptive layer has a dry thickness of at least 0.05 .mu.m and up to and including 10 .mu.m when measured at 25.degree. C.,

"heating the receiver element to a heating temperature that is higher than the glass transition temperature (T.sub.gl) of the print material receptive layer, to form a heated receiver element,

"contacting the print material disposed on the uppermost relief surface and the heated receiver element such that the elastomeric relief element (not mounting means such as mounting tape) is compressed by at least 10 .mu.m of its original thickness, and the increased amount of print material disposed on the uppermost relief surface is in contact with the heated receiver element, and

"separating the elastomeric relief element from the heated receiver element to leave a pattern of the print material on the heated receiver element, wherein at least 70 weight % of the print material originally disposed on the uppermost relief surface of the elastomeric relief element is transferred to the heated receiver element.

"In still other embodiments, the method of this invention comprises the following conditions, all of which are defined in more detail below:

"removing at least 75 weight % of the carrier liquid from the printable material composition on the uppermost relief surface of the elastomeric relief element,

"transferring at least 90 weight % of the print material originally disposed on the uppermost relief surface of the elastomeric relief element to the heated receiver element, and

"contacting the print material disposed on the uppermost relief surface and the heated receiver element,

"wherein the print material receptive layer has a dry thickness of at least 0.05 .mu.m and up to and including 3 .mu.m when measured at 20.degree. C.,

"wherein the flexographic printing member has a modulus of elasticity of at least 4 megaPascals to and including 8 megaPascals, and

"wherein the printable material composition comprises a print material that comprises nanoparticles of an electrically conductive material selected from the group consisting of silver, gold, copper, palladium, indium-tin oxide, or combinations thereof.

"The method of this invention provides a number of advantages for what is known as 'functional printing'. For example, the method provides a means for obtaining high resolution printed patterns on various substrate (or receiver elements) using print materials that are not previously useful to achieve such results. The high resolution line features in a printed pattern are obtained by a unique series of operations including removal of at least some of the liquid used to uniformly disperse and 'carry' the print material in a printable material composition on an elastomeric relief element that is used as the printing element. The more viscous or cohesive printable material composition is then transferred to a heated receiver element before the elastomeric relief element is separated from the heated receiver element. The elastomeric relief element used for this transfer can be provided in a variety of ways (described below) including but not limited to, the use of flexographic printing elements.

"In some embodiments, it is possible to build up the print material on the elastomeric relief element before the pattern is formed on the heated receiver element. This can be done by multiple applications of the printable material composition to the uppermost relief surface of the elastomeric relief element, and removal of at least some of the carrier liquid from the printable material composition. This drier or more viscous, cohesive, and increased amount of printable material composition can be applied to the heated receiver element to provide several advantages.

"For example, multiple applications of the printable material composition, with carrier liquid removal between applications, can increase conductivity or other properties of the eventual printed image beyond what can be obtained with a single application due to the additional quantity of print material. In some instances, the print material has limited dispersibility in the carrier liquid and thus multiple applications are needed to get sufficient density or thickness of the print material in the printed image on the heated receiver element.

"Inking systems such as high ink volume Anilox rollers cannot always be used to apply sufficient printable material composition without leaving residue of the composition on the sides of the elastomeric relief element due to spread of the printable material composition (or ink) onto the sides of the elastomeric relief element feature sides. This problem can be minimized by multiple applications of the printable material composition to the elastomeric relief element, such as by use of a low volume Anilox roller.

"In addition, compression contact of the elastomeric relief element and a heated receiver element can cause significant spread of the wet printable material composition away from the contact area between the two elements and a corresponding undesirable increase in image features (known as print gain). However, this problem can also be diminished by multiple applications of the printable material composition to the elastomeric relief element (with appropriate removal of carrier liquid between applications). Each application of the printable material composition can be relatively thin, but the multiple applications appropriately build up dry thickness on the elastomeric relief element, and the resulting printed image can have desired properties such as conductivity. The built-up dry and cohesive printable material composition on the elastomeric relief element does not spread during the subsequent compression contact between the two surfaces. The intervening drying steps can also provide desired registration of the printable material composition as sequential contact printing steps are not required to build up printable material composition thickness.

BRIEF DESCRIPTION OF THE DRAWING

"FIG. 1 is a schematic illustration of one embodiment of an equipment system for carrying out the present invention, as described in the Examples below."

For additional information on this patent application, see: ZWADLO, Gregory Lloyd; FOHRENKAMM, Elsie Anderson; SIMPSON, Charles W. Method of Forming Printed Patterns. Filed January 8, 2014 and posted August 14, 2014. Patent URL: http://appft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&u=%2Fnetahtml%2FPTO%2Fsearch-adv.html&r=7337&p=147&f=G&l=50&d=PG01&S1=20140807.PD.&OS=PD/20140807&RS=PD/20140807

Keywords for this news article include: Patents, Microelectronics, Photolithography.

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Source: Electronics Newsweekly


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