WO1996022883A1

WO1996022883A1 - Precision imaging components and methods for their formation

Info

Publication number: WO1996022883A1
Application number: PCT/US1996/000496
Authority: WO
Inventors: Alain R. E. Carre; Bernard Eid; Robert D. Shoup; Jean-Pierre Themont
Original assignee: Corning Incorporated
Priority date: 1995-01-24
Filing date: 1996-01-11
Publication date: 1996-08-01

Abstract

High precision image forming surfaces for printing applications such as, for example, gravure or typographic printing applications are formed by selectively growing or depositing metal or other materials onto a suitable substrate. In a preferred method, nickel metal is deposited by electroless deposition onto a low CTE substrate.

Description

PRECISION IMAGING COMPONENTS AND METHODS FOR THEIR FORMATION

BACKGROUND This invention relates to high precision image forming surfaces for printing applications such as, for example, gravure or typographic printing applications, and methods for making such high precision image forming surfaces. The imaging surfaces of the present invention are especially useful for printing color filters for liquid crystal flat panel displays. Previously, printing surfaces such as those used in gravure, typographic, or intaglio printing applications were manufactured by mechanically machining the metal imaging surface from a block of metal. These mechanical machining techniques were suitable for making imaging surfaces for applications such as the printing of decorations or printed letters. However, printing components manufactured using such mechanical machining techniques were not sufficiently accurate for high precision printing, such as is needed to deposit the black matrix pattern and color pixels for color filter arrays.

The lines which form the black matrix in such devices typically are about 10-25 microns wide and about 0.5 to 2 microns thick. The red, green, and blue color cells are typically on the order of about 70-100 microns in width by 200 to 300 microns in length. The printed color cells are typically less than about 10 microns thick, and preferably less than 5 microns thick, and must be evenly applied and accurately registered within the pattern formed by the black matrix. Whereas the black matrix pattern to some extent hides imperfections in the printing of the color pixels, any imperfections in the printing of the black matrix pattern will be apparent from an inspection of the color filter. Consequently, while precision imaging plates are needed for printing the color pixels for color filter arrays, the need is especially evident for the printing of black matrix patterns. In fact, because current printing techniques are so inaccurate, most manufacturers of color filters utilize photolithographic techniques, rather than ink printing techniques, to deposit the black matrix pattern. Another problem with conventional imaging surfaces is that metal printing surfaces are heavy and, because of their relatively large coefficient of thermal expansion (CTE), are very sensitive to temperature changes.

It would be desirable to develop a method for producing more accurate imaging surfaces which can be used in gravure, intaglio, typographic and other printing applications. Preferably, such imaging surfaces would be capable of printing even the black matrix patterns of color filter arrays. Further, these printing surfaces should preferably be constructed of light-weight materials which are not adversely affected by temperature changes in the surrounding environment.

SUMMARY OF THE INVENTION

In the present invention, extremely accurate imaging surfaces are formed by selectively depositing metal or other materials onto a suitable substrate. By selectively depositing, it is meant that the materials are selectively deposited or grown on the substrate, as opposed to being milled or machined away, as was the case with prior art methods. One such method for depositing metal materials is electroless or chemical metallization. This simple and inexpensive method can be used to deposit metal layers on substrates such as glass, ceramic, glass-ceramic, and synthetic resins. One aspect of the present invention relates to a method for forming an imaging plate which may be used in gravure, intaglio, or typographic printing applications. Using photoresist masking and electroless deposition techniques, a suitable material is deposited onto a suitable substrate.

In one preferred embodiment, a glass ceramic substrate is etched using an acid solution, such as, for example, hydrofluoric acid. A thin conductive coating is then deposited on the roughened surface of the glass ceramic material. The conductive coating can be, for example, tin oxide, such an indium tin oxide or fluorine doped tin oxide. One preferred conductive coating is nickel. The conductive coating can be deposited, for example, by electroless deposition, in which case the etched glass ceramic surface preferably is first treated with a palladium containing solution to catalyze the roughened surface for improved deposition of the nickel. After the conductive coating is deposited on the surface of the glass ceramic material, a photoresist coating is applied over the conductive coating. A mask is then positioned over the surface of the photoresist and the photoresist is exposed to radiant energy through the mask to produce the desired polymerized pattern. Portions of the photoresist are then removed to selectively expose the conductive coating (the portion removed depends on whether the photoresist is a positive or negative photoresist). Then, using an electrolytic nickel flash, a small quantity of nickel (less than 0.1 micron) is deposited on the conductive coating where the photoresist was removed. Using electroless deposition techniques, nickel is then deposited over the electrolytic deposited nickel. After the nickel has been built up to a suitable thickness, (for example, in the case of a black matrix imaging plate, about 5 microns) the remaining photoresist material is removed, leaving the selectively deposited nickel protruding from the substrate. The techniques of the present invention are very useful for forming high precision imaging plates, such as the typographic or intaglio variety. For example, these techniques may be utilized to grow typographic pins for typographic printing applications. Alternatively, these pins can form the recesses of an intaglio plate. Further, these techniques may be utilized to manufacture a master forming surface against which suitable materials may be pressed and embossed therewith to form a suitable intaglio or typographic imaging plate.

The imaging components and the methods used to form them in accordance with the present invention have several advantages over prior art components and methods. First, using the techniques of the present invention, very high precision imaging plates can be manufactured, to within tenths of microns if desired.

In addition to being more accurate, the methods of the present invention are considerably less expensive than direct mechanical machining of metal blocks. In addition, the methods of the present invention are particularly advantageous for many imaging surfaces for use in printing black matrix patterns and color filter patterns for liquid crystal displays. In such displays, the black matrix pattern is typically printed in about 5-20 micron width lines about 3-10 microns deep, more preferably about 10 -15 microns wide and about 3-5 microns deep. The color pixels for such patterns are typically printed in about 70 by 200 micron rectangles, more preferably about 50 by 180 microns, which are typically about 5-15 microns deep, more preferably about 8-10 microns deep. Ultimately, it could be desirable to print these color filter pattern and black matrix pattern as thin as 3-4 microns. Utilizing the techniques of the present invention, imaged patterns as narrow as 0.5 microns, deposited as thick (high) as 0.1 microns to one millimeter, separated by grooves as narrow as 0.5 microns, are achievable. Consequently, the techniques of the present invention are very useful for manufacturing imaging surfaces for use in the printing of black matrix patterns or color pixels for color filters, either of which generally employ dimensions larger than this. These imagining plates may be utilized on flat surface as well as cylindrical printing drums.

The methods of the present invention are preferably carried out on substrates made of low CTE materials such as glass, ceramic, glass-ceramic, or a low CTE metal. An example of a low CTE metal is Invar metal, an iron/nickel alloy ranging in composition from about 35-50% nickel, the remainder being iron. These compositional variations produce CTE variations between about 6-10x10^"7/° C at 100° C. Consequently, the resultant imaging plates will not be adversely effected by movements in temperature within the printing room. As a result, such materials can be utilized on larger area imaging plates without distortion occurring in the plate due to fluctuations in temperature. Consequently, less work is needed to control the temperature of such rooms. Materials such as glass, ceramic, and glass ceramic are also generally lighter in weight than metals.

BRIEF DESCRIPTION OF THE DRAWINGS

Figures 1a-1 i illustrate a method in accordance with the present invention for making an imaging surface.

Figures 2a and 2b illustrates an alternative method involving an embossing operation for making imaging surfaces in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

In the present invention, extremely accurate imaging surfaces are formed by selectively depositing metal or other materials onto a suitable substrate. The materials to be selectively built up or deposited on the substrate can be materials such as electrolytic metal deposits, electroless metal deposits, gel deposits, materials exuded from the substrate, or materials deposited using physical deposition, chemical vapor deposition, or any other technique suitable for selectively depositing a material on a substrate. The imaging surface could even be formed from a physically or electrophoretically deposited photoresist polymer, as long as the resultant polymer consists of a sufficiently rugged material. Preferably, the process should be selected to result in uniform deposition rates, in order to achieve accurate formation of the imaging surface. One preferred method, especially for depositing metal materials such as nickel or nickel based alloys, is electroless deposition. This simple and inexpensive method can be used to deposit metal layers on substrates such as glass, ceramic, glass-ceramic, and synthetic resin materials

Preferred substrates include materials having low coefficients of thermal expansion, such as ceramic, glass, or glass ceramic materials. One preferred material is fused silica. However, the invention is not limited to these materials, but could also include metals, particularly those metals and their alloys having relatively low coefficients of thermal expansion (CTE's). Preferred low CTE metals are those having a CTE between about 6-10x10^* ⁷/° C, or lower, in temperature range of about 0 to 100° C (especially at room temperature, where the print operation will most likely occur). One such family of metals are the iron/nickel alloys, ranging from about 35-50 percent nickel, the remainder being primarily iron. By utilizing a material having a low CTE for the substrate, the resultant imaging plates will not be adversely effected by movements in temperature within the printing room. Consequently, such materials can be utilized on larger area imaging plates without worrying about distortion from end to end of the plate. In addition, less work is needed to control the temperature of such rooms. Materials such as glass, ceramic, and glass ceramic based materials are also lower in weight compared to many metals.

Figures 1a through 1i illustrate a preferred embodiment of the present invention, in which nickel is deposited onto a glass ceramic substrate. Glass ceramic substrate 10 is first etched with a suitable acid to roughen its surface, as illustrated in Figure 1b. After etching, the etched surface is treated with palladium layer 12, such as by contacting the etched surface with a Pd sol, as illustrated in Fig. 1c. The Pd promotes adhesion of the nickel conductive layer, as well as a high selectivity for the metallization of the Pd exposed areas relative to the unexposed areas. In this connection, it is especially desirable for deposition onto glass, ceramics or glass ceramics. "Sol", as used herein, means a colloidal dispersion of Pd in water. The Pd sol is preferably stabilized with a water-soluble polymer. This Pd sol can be prepared by adding a suitable reducing agent, such as H₃PO₂ and dimethyl aminoborane, to an aqueous HCI-containing solution of Pd salt, such as PdCI₂, Pd nitrate and Pd acetate, causing metallic Pd to be formed. The solution also comprises a water-soluble polymer which stabilizes the sol. Stearic hindrance of the polymer chains on the Pd particles precludes flocculation of the particles.

Suitable water-soluble polymers are polyvinyl alcohol (PVA) and polyvinyl pyrolidone (PVP).

The Pd serves as a catalyst for forming conductive base coating 14. A preferred material for conductive base coating 14, illustrated in Fig. 1d, is a thin layer (approximately .2 microns, for example) of electroless deposited Ni.

Other suitable materials for base coating 14 include, for example, a doped tin oxide film, silver, or electrolytically deposited nickel.

After conductive layer 14 is applied, photoresist layer 16 is applied, as illustrated in Fig. 1e. Photoresist layer 16 may be any suitable material capable of protecting the conductive layer effectively during subsequent processing steps. Suitable photoresist materials include any of the materials well known in the photoresist art, such as those which are applied by physical, chemical or electrophoretic deposition techniques. These chemical materials, most often light-sensitive polymers, are typically exposed to visible or near UV radiation through a patterned mask (e.g. a pattern of vapor deposited chrome on glass) to render either the exposed or the unexposed portion insoluble to subsequent washing with solvents.

Using this exposure and removal technique, a portion of photoresist layer 16 is selectively removed to form mask 18, illustrated in Fig. 1f. In the preferred embodiment, illustrated in Fig. 1e, photoresist layer 16 is selectively exposed to radiation from UV light 19 on one side of a protective template 20. The UV radiation may cause the photoresist to remain soluble, or to polymerize and become insoluble, depending on whether a positive or negative photoresist is employed. One example of a commercially available positive photoresist is Shippley's Microposit 1620, while a commercially available negative photoresist is Shippley's Eagle 2100 ED. Of course, other methods of locally removing the photoresist layer 16 could alternatively be used, for example, a method employing an oxygen plasma or by local exposure using a laser light beam as generated by, for example, an ArF excimer laser (wavelength 1098nm). In Fig. 1e, a positive photoresist is selectively protected from the radiation emitted from UV light 19 by template 20. Template 20 may be, for example, patterned chrome deposited on glass or a stainless steel foil which is provided with apertures having the desired pattern. In the exposed parts of the glass surface, which correspond to the apertures in the foil, the positive type photoresist layer 16 is selectively removed down to the glass, leaving mask areas 18 on the glass, as illustrated in Fig. 1f. In regions where mask 18 remains, no nucleation takes place in the subsequent process steps and consequently these regions are not metallized.

After the mask 18 has been formed, metal material is deposited on the Ni base layer 14 in the area in which the photoresist material has been removed. In a preferred embodiment, an electrolytic flash is used to accomplish an initial deposition of conductive material 22, as illustrated in Fig. 1g. The purpose of the electrolytic flash is to form a catalytic layer to facilitate electroless deposition. After the electrolytic flash 22, metal material 24 is deposited, as illustrated in Fig. 1 h. A preferred material for metal layer 24 is a

NiP metal alloy (e.g., 92% Ni, 8% P) deposited by electroless deposition. Any known electroless nickel baths can be used for the electroless deposition of the NiP. One example of a commercially available bath is Shippley 54Tm, manufactured by Shippley, USA. After metal layer 24 has been deposited, the imaging device 26 is completed by removing or stripping the remaining photoresist material, resulting in the finished imaging surface illustrated in Fig. 1 i. The resultant imaging device 26 may be used as a gravure imaging plate, in which case ink will be deposited between the resultant metal pins 28 formed by the deposited metal 24, or as a typographic imaging plate, in which case ink would be deposited onto the ends of the pins 28. Alternatively, imaging device 26 can be used as an imaging master, against which another imaging plate can be embossed.

Such an embodiment is illustrated in Figs. 2a and 2b, in which imaging device 26, which was formed using the process illustrated in Figs. 1a-1i, is used as an imaging master against which another imaging plate is formed by embossing. Thus, as illustrated in Fig. 2a, imaging device 26 (the imaging master) is moved in the direction indicated by directional arrow A and contacted against substrate 30, which carries an embossable material 28 thereon. After the embossing operation is complete, the imaging device 26 is removed in the direction indicated by arrow B. As a result of the embossing operation, the resultant imaging device 31 comprises a plurality of pins 32 protruding from substrate 30. Like imaging device 26, imaging device 31 may be used as a gravure imaging plate, in which case ink will be deposited between the metal pins 32, or as a typographic imaging plate, in which case ink would be deposited onto the ends of the pins 32.

Preferred embossable materials include any polymer or gel like material capable of being molded against the master imaging plate for creating an impression of that master in its surface. For example, the embossable material 28 could be a liquid capable of filling channels of the master plate and then hardening by polymerization or other chemical means or by cooling from a melt. Another alternative is to heat a thermoplastic sheet while being compressed between a flat plate and the master plate and holding the material 28 in position until cool. Preferred embossable materials include fluorocarbons such as, for example, polytetrafluoroethylene (PTFE), fluorinated ethylene propylene copolymer (FEP), perfluoroalkoxy resin (PFA), ethylene-chlorotrifluoroethylene copolymer (ECTFE), ethylene- tetrafluoroethylene copolymer (ETFE), as well as poly(ethylene terephthalate) (PET).

If desired, various combinations of materials can be co-deposited to form the imaging surface. Such co-deposition can be achieved, for example, by adding the desired material in particulate form to the nickel bath and keeping the low CTE particulate material dispersed in the solution by stirring or by colloidal stabilization. There are various reasons for wanting to co- deposit materials.

For example, it may be desirable to form portions of the imaging pins 28 from wettable materials and other portions of the pins 28 from materials having non-wetting properties. In this way, the ink can be made to stick to areas of high wetability, while the ink is repelled in areas having non-wetting properties.

It may also be desirable to co-deposit different materials in order to reduce the stress caused by differences in CTE of different materials. Thus, it may be desirable to deposit intermediate coatings of intermediate CTE materials between materials having greatly different CTE's. For example, NiP deposited directly onto a low CTE substrate could produce high stresses at the coating/substrate interface, especially if relatively thick imaging pins are to be produced (greater than 3 microns). To reduce the stresses caused by the different CTEs, the metal can be co-deposited simultaneously with another low

CTE particulate material, such as alumina, silica, titania, or zirconia.

Similarly, a metal-ceramic composite structure having a roughened surface finish can be obtained by employing particulate ceramic materials in the metal bath. The size of the particulate material could vary, for example, from about one nanometer to about 10 microns. By adding large ceramic particles, the surface of the resultant deposit material can be roughened considerably to increase wettability.

The invention is further illustrated by the following examples, which are meant to be illustrative, and not in any way limiting, to the claimed invention.

EXAMPLE 1

An A4 size (about 8.27 x 11.69 inches) imaging plate suitable for high precision printing (HPP) was prepared using a zero thermal expansion beta quartz type glass ceramic known as Eclair (manufactured by Keraglass of Bagneaux, France) was utilized for substrate 10. On this substrate 10 a layer of silver enamel (70% silver, 30% glass) about 10 μm thick was applied and fired at 750° C. A nickel layer about 10μm thick was then deposited by electrolytic plating to complete conductive base layer 14.

Then, using a classical nickel coating and photoresist combination, NiP imaging pins about 5 m thick were formed using electroless deposition techniques, as described above. The NiP bath was a commercially available bath sold under the trade name Duraposit S2, from Shippley of Marlborough, MA, U.S.A. The photoresist employed was selectively removed and the NiP bath successfully utilized to result in the formation of two sets of imaging pins, one set about 10μm wide and the other set about 5mm wide, both of which were about 5_/-<m thick (high).

EXAMPLE 2

An A4 size imaging plate was prepared using the print process and materials in Example 1 , except that the glass-ceramic had its surface acid etched and catalyzed by Pd to improve NiP adhesion, and the silver layer was replaced by a layer of electroless deposited NiP about 1-2 μm thick.

EXAMPLE 3

This example illustrates the use of low-CTE metals as a substrate material. An A4 size imaging plate was prepared using a process similar to

Example 2, except that the base material was a low CTE Fe/Ni alloy containing about 30% Ni. The Fe/Ni alloy (about 1.5 mm thick) was attached to a glass- ceramic base material about 4mm thick using an epoxy adhesive. The metal alloy substrate was coated with a photoresist material. Portions of the photoresist were then selectively removed, and NiP imaging pins about 10μm wide and 5 m thick were deposited in these exposed areas by electroless plating using a Duraposit S2 NiP bath.

EXAMPLE 4 This example illustrates the deposition of different materials to differentially affect the wetting of the imaging pins. The method was similar to Example 1 except that a Ni-PTFE composite (about 6-9% PTFE by weight) about 10μm thick was deposited prior to a 1-2μm NiP top coating, both by electroless deposition.

The resulting imaging pattern was ink non-wettable on the vertical (Ni- PTFE) walls and wettable on the top (NiP) surface. Such a combination would be valuable as a typographic imaging plate, where ink would resist filling the free spaces between pins, but wet the top imaging surface. This would result in easier cleaning and better patterning accuracy, and help to avoid a condition known as shadowing or ghosting, which is produced by a build up of ink flowing over the top surface and down the side walls of the imaging pins.

EXAMPLE 5

This example illustrates the addition of ceramic particles to increase the roughness of the imaging pins. The method was similar to Example 4, except that a 1 -2μm topcoat of a NiP/particulate Al₂0₃ (about 10% by volume of Al₂0₃ particles about 0.5mm in diameter) mixture was deposited on top of the 10μm NiVPTFE imaging pins to increase the top surface roughness of the imaging plate. This resulted in Al₂0₃ particles approximately .5mm in diameter adhered to the NiP top surfaces, thereby roughening the imaging surface. Other materials could also be used for the particles, including, for example, silica, titanium, alumina or zirconia.

EXAMPLE S

This example illustrates the deposition of a midrange CTE buffer coating to reduce the stresses caused by the difference between CTE's of the substrate and the imaging pin material. This example was similar to Example 2, except that the pins were formed by first depositing five microns of a NiP\ZrO₂ particulate composite by electroless deposition, followed by 5 microns of a NiP top coat by electroless deposition. The ZrO₂ particles were about 0.06 microns in diameter and represented about 10% by volume of the NiP\ZrO₂ bath. This composite pin structure was deposited in order to limit stress and avoid inter layer delamination.

Among low CTE particles, silica, titanium, alumina, zirconia are preferred. The particulate size can be, for example, between a few nanometers to a few microns.

Although the invention has been described in detail for the purpose of illustration, it is understood that such detail is solely for that purpose and variations can be made therein by those skilled in the art without departing from the spirit and scope of the invention which is defined by the following claims.

Claims

What is claimed is:

1. A method for making imaging surfaces for use in depositing ink, comprising: selectively depositing material onto a substrate to form a plurality of imaging surfaces.

2. The method of claim 1 , wherein said selectively depositing step comprises depositing a material, selected from the group consisting of metals, oxides, and mixtures thereof, on said substrate.

3. The method of claim 2, wherein said selectively depositing step comprise depositing said material using a deposition method selected from the group consisting of electroless chemical, electrolytic, chemical vapor deposition, physical vapor deposition, exudation from the substrate and gel coating.

4. The method of claim 3, wherein prior to said depositing step, said substrate is selectively masked to form a protected and an unprotected area on said substrate and said depositing step comp ses depositing said material on said substrate within said unprotected areas.

5. The method of claim 1 , wherein said selectively depositing step comprises depositing said material on a substrate selected from the group consisting of glass, metal, ceramic, glass ceramic, and mixtures thereof.

6. The method of claim 5, wherein said depositing said material step comp ses electroless depositing a material selected from the group consisting of metals, oxides, polymers and mixtures thereof.

7. The method of claim 1 , wherein said selectively depositing step comphses selectively depositing said matehal on a substrate having a coefficient of thermal expansion below about 15 x 10^*7/° C.

8. The method of claim 1 , wherein said selectively depositing step comphses selectively depositing said material on a substrate having a coefficient of thermal expansion below about 10 x 10^"7/°C.

9. The method of claim 1 , further comprising, prior to said selectively depositing step, depositing an intermediate matehal having a coefficient of thermal expansion in between that of the substrate and selectively deposited material.

10. The method of claim 1 , wherein said selectively depositing step comphses selectively depositing a matehal comphsing a particulate material therein.

11. The method of claim 1 , wherein said selectively depositing step comphses selectively depositing a matehal comprising a particulate matehal therein, said particulate matehal selected from the group consisting of glass and ceramic materials, said particulate matehal comphsing a particle size between about 1 nanometer to about 10 microns in diameter.

12. An imaging device for applying ink images comphsing: a substrate; and a material selectively deposited on said substrate, said material selected from the group consisting of metals, oxides, polymers and mixtures thereof.

13. The imaging device of claim 12, wherein said substrate is a matehal having a coefficient of thermal expansion below about 15 x 10^'7/°C.

14. The imaging device of claim 12, wherein said substrate comprises a coefficient of thermal expansion below about 10x10^"7/^cC.

15. The imaging device of claim 13, further comphsing, between said substrate and said selectively deposed material, an intermediate material having a coefficient of thermal expansion in between that of the substrate and selectively deposited matehal.

16. The imaging device of claim 12, wherein said selectively deposited matehal further comphses a particulate material therein.

17. The imaging device of claim 16, wherein said particulate matehal is selected from the group consisting of glass and ceramic materials.

18. The imaging device of claim 16, wherein said particulate material comprises a particle size between about 1 nanometer to about 10 microns in diameter.

19. A method for making imaging surfaces, comphsing: selectively depositing matehal onto a substrate at least 5 microns thick to form a plurality of permanent imaging surfaces.