KR20070057854A - Method of forming barrier rib microstructures with a mold - Google Patents

Abstract

In one embodiment the present invention relates to microstructured articles (e.g., barrier ribs formed by a method that comprises providing at least one discrete coating of slurry on a transfer sheet).

Description

METHOD OF FORMING BARRIER RIB MICROSTRUCTURES WITH A MOLD}

FIELD OF THE INVENTION The present invention relates to methods of forming microstructures on substrates using molds and articles formed using these methods, and more particularly to methods of forming inorganic microstructures on substrates using molds.

Advances in display technology, including the development of plasma display panels (PDPs) and plasma addressed liquid crystal (PALC) displays, are of interest in forming electrically-insulating inorganic barriers on glass substrates. Induced. The partition wall separates cells in which an inert gas can be excited by an electric field applied between opposing electrodes. The gas discharge emits ultraviolet (UV) radiation in the cell. In the case of PDPs, the inside of the cell is coated with phosphorus which emits red, green or blue visible light when excited by UV radiation. The size of the cell determines the size of the picture element (pixel) in the display. PDP and PALC displays can be used, for example, as displays for high definition television (HDTV) or other digital electronic display devices.

One way in which the partitions can be formed on a glass substrate is by direct molding. This involved laminating a planar rigid mold onto a substrate with a glass- or ceramic-forming composition disposed therebetween. The glass- or ceramic-forming composition is then solidified and the mold is removed. Finally, the partition wall is dissolved and sintered by firing at a temperature of about 550 ° C to about 1600 ° C. The glass- or ceramic-forming composition has a glass frit of μm-sized particles dispersed in an organic binder. The use of an organic binder causes the partition to solidify in the green state so that firing dissolves the glass particles at a predetermined location on the substrate.

While various methods of forming microstructures, such as bulkheads, have been described, the industry will find advantages in alternative methods.

In one aspect, the present invention provides a method of providing a transfer sheet, coating at least one release coating of the curable composition to a transfer sheet, transferring the release coating onto a substrate, and a microstructured surface (eg, a septum). Having a microstructured surface (eg, a septum for a plasma display panel) comprising contacting a mold having a mold with a release coating with a release coating, curing the curable composition, and removing the mold. A method of forming a product or a component of a product.

The transfer sheet is preferably coated with at least two separate coatings. The transfer sheet may be a substantially planar substrate or may be provided on a roll. Each separate coating may have an area (eg, in the range of about 1 cm 2 to about 2 m 2) corresponding to a single plasma display panel. The transfer sheet may comprise a flexible film and a rigid support layer. The flexible film can be removed at the same time as removing the rigid support layer. The detachable coating can be provided by the use of a template. The mold is typically flexible and permeable. The curable material can be cured through a mold, through a glass panel, or through a combination thereof. This method (s) is preferably at least semi-automated.

1 is a schematic diagram of a plasma display panel assembly.

Fig. 2 is a cross sectional view of an illustrative meaning of the implemented rigid support layer of the transfer sheet.

3A to 3C are side views showing the practiced method of employing the transfer sheet.

4A-4D are schematic diagrams of an illustrative meaning of transferring a coating from a transfer sheet to a substrate in a rotating structure.

It is contemplated that the present invention is applicable to methods of forming microstructures on substrates using molds and articles formed using these methods. In particular, the present invention relates to the formation of inorganic microstructures on substrates using molds. Plasma display panels (PDPs) can be formed using these methods and provide useful examples of these methods. It will be appreciated that other devices and articles may be formed using these methods, including, for example, electrophoresis plates with capillary channels and the field of illumination. In particular, devices and articles that can utilize molded ceramic microstructures can be formed using the methods described herein. While the present invention is not limited in this manner, an understanding of various aspects of the invention will be gained through the discussion of the examples provided below.

The plasma display panel PDP has various components as shown in FIG. The rear substrate oriented away from the viewer has independently addressable parallel electrodes 23. The back substrate 21 can be formed from various compositions such as glass. The ceramic microstructure 25 is formed on the rear substrate 21, and the ceramic microstructure 25 includes the partition portion 32 positioned between the electrodes 23 and red (R), green (G) and Blue (B) includes a separate region to which phosphorus is deposited. The front substrate comprises a glass substrate 51 and a set of independently addressable parallel electrodes 53. These front electrodes 53, also referred to as support electrodes, are oriented at right angles to the rear electrodes 23, also referred to as address electrodes. In the finished display, the area between the front and rear substrate elements is filled with an inert gas. To illuminate the pixel, an electric field is applied therebetween with sufficient intensity to excite the inert gas atoms between the crossed support and address electrodes 53, 23. The excited inert gas atoms emit ultraviolet (UV) radiation that causes phosphorus to emit red, green or blue visible light.

The rear substrate 21 is preferably a transparent glass substrate. Typically, for the PDP field, the back substrate 21 is optionally made of soda lime glass that is substantially free of alkali metal. The temperature reached during processing can cause the movement of the electrode material in the presence of alkali metal in the substrate. This movement can lead to conductive paths between the electrodes, thereby shorting adjacent electrodes or causing undesirable electrical interference between the electrodes known as "crosstalk". The front substrate 51 is typically a transparent glass substrate which preferably has a coefficient of thermal expansion that is about the same or about the same as the rear substrate 21.

Electrodes 23 and 53 are strips of conductive material. The electrode 23 is formed of a conductive material such as copper, aluminum or silver-containing conductive frit. The electrode may also be a transmissive conductive material such as indium tin oxide, in particular when it is desired to have a transmissive display panel. The electrodes are patterned on the back substrate 21 and the front substrate 51. For example, the electrodes may be spaced between about 120 μm and 350 μm and span the entire active display area, which may be within a range of about 50 μm to 75 μm, a thickness of about 2 μm to 15 μm and a few cm to several tens of centimeters. It can be formed as a parallel strip having a length. In some cases, the width of the electrodes 23, 53 may be less than 50 μm or more than 75 μm, depending on the configuration of the microstructure 25.

The height, pitch, and width of the microstructured partition portion 32 in the PDP may vary depending on the desired final product. The pitch of the partition (number per unit length) is preferably matched to the pitch of the electrode. The height of the partition is generally at least 100 μm and typically at least 150 μm. Furthermore, the height is typically below 500 μm and typically below 300 μm. The pitch of the partition pattern may be different in the longitudinal direction than in the width direction. The pitch is generally at least 100 μm and typically at least 200 μm. The pitch is typically below 600 μm and typically below 400 μm. The width of the barrier rib pattern may be different between the upper surface and the lower surface, especially when the barrier ribs thus formed are tapered. The width is generally at least 10 μm and typically at least 50 μm. Furthermore, the width is generally less than 100 μm and typically less than 80 μm.

When using the method of the invention to form microstructures (such as partitions for PDPs) on a substrate, the coating material from which the microstructures are formed is preferably a slurry or paste containing a mixture of at least three components. The first component is glass or ceramic which forms a particulate inorganic material (typically, ceramic powder). Generally, the particulate inorganic material of the slurry or paste is dissolved or sintered by firing to form microstructures with the desired physical properties that are finally attached to the patterned substrate. The second component is a binder (eg, a fugitive binder) that can be shaped and subsequently cured by curing or cooling. The binder causes the slurry or paste to be shaped into a microstructure in a semi-rigid green state that adheres to the substrate. The third component is a diluent that can promote alignment of the binder material and release from the mold after curing treatment and can promote rapid and complete burning of the binder during debinding prior to firing the ceramic material of the microstructures. The diluent preferably remains liquid after the binder has been cured such that the diluent is phase-separated from the binder during the binder curing treatment. The slurry preferably has a viscosity of less than 20,000 cps and more preferably less than 5,000 cps to uniformly fill all microstructured groove portions of the flexible mold without trapping air.

The amount of curable organic binder in the curable paste composition is typically at least 2% by weight, more typically at least 5% by weight and more typically at least 10% by weight. The amount of diluent in the barrier precursor composition is typically at least 2% by weight, more typically at least 5% by weight and more typically at least 10% by weight. The total amount of organic components is typically at least 10% by weight, at least 15% by weight or at least 20% by weight. Furthermore, the total amount of organic compound is typically up to 50% by weight. The amount of inorganic particulate material is typically at least 40% by weight, at least 50% by weight or at least 60% by weight. The amount of the inorganic particulate material is 95% by weight or less. The amount of additive is generally less than 10% by weight.

In one embodiment, the present invention is directed to a partition formed by a method comprising providing at least one separate coating of a slurry on a transfer sheet.

The transfer sheet is typically a thin flexible film layer supported by a rigid (eg movable) support layer. The flexible film may be peeled from the slurry at an acute angle defined by the edge of the rigid movable support that is retracted across the surface of the glass panel. Suitable flexible films include polyethylene terephthalate, polycarbonate film, cellulose acetate butyrate, cellulose acetate propionate, polyether sulfone, polymethyl methacrylate, polyurethane, polyester, polyvinyl chloride, polyimide, polyolefin, polypropylene And polycyclo-olefins.

The transfer sheet typically includes a release coating that allows it to peel off leaving almost all the slurry on the glass panel. Release coatings typically used on plastic films include low-surface-energy organic materials including hydrocarbons, silicon, and fluorocarbons. Hydrocarbons may include polymers such as oils, waxes, polyolefins and polyacrylates or polyurethanes with pendant alkyl segments. Silicones can include polydimethylsiloxanes having no functional groups as well as polydimethylsiloxanes having cross-linked silanol- or vinyl-functional groups, respectively, by condensation or silicon hydride addition reactions. Fluorocarbon is fluorine-based oil; Perfluoropolyethers; Fluoropolymers prepared by the co-polymerization of tetrafluoroethylene, vinylidene fluoride and hexafluoropropylene; And polymers such as polyacrylates, polyurethanes, or polyepoxides having pendant fluorine-substituted alkyl functional groups. In particular, perfluorine having curable functional groups such as acrylates, silanes or epoxy functional groups, which can be crosslinked with a strong coating with good surface release properties and good release properties for a wide range of organic materials such as resins and adhesives. Ropolyether.

2 shows a cross section of an example suitable rigid support 200. For example, the rigid support may be formed from an aluminum plate 210 of a suitable size (eg, 25 mm thick) that is machined to a depth of 10 mm on both sides leaving a grid of support ribs 220. A pair of aluminum plates (eg, 5 mm thick) can be coupled to the support ribs 220 thereby creating flat surfaces 230 and 240 on the top and bottom, respectively. The edge 260 of the rigid support (ie, at the position where the transfer film slides) is preferably inclined to a size of at least 30 ° and typically 90 ° or less, with a 45 ° taper being typically good. Furthermore, this edge of the rigid support typically has a radius of 0 to 10 mm with a radius of 0.50 mm being good.

The rigid support is provided with means for holding the transfer film in close proximity to the surface and means for releasing the transfer film surface. One suitable means includes providing a hole 250 (eg, 100 μm diameter) in the top and bottom surfaces of the rigid support operably connected to a vacuum (not shown). Since a fitting (not shown) can be provided at the edge of the rigid support, the transfer film can be selectively pulled by vacuum to the top or bottom surface of the support. A valve (not shown) alternately introduces compressed air into the fitting so that the transfer film can be easily moved across one or both surfaces.

Coating the transfer sheet with one or more separate coatings may be accomplished by the use of a template as described in US Patent Application No. 60/604557, filed August 26, 2004. In the alternative, the detachable coating may be prepared by screen printing, transfer printing or other conventional method capable of placing the slurry within a specified area. Appropriate methods can be combined with appropriate edge definitions to coat the curable material with the correct thickness. Regardless of the scheme employed, the slurry is coated in a manner that minimizes air entrapment.

The glass panel with the patterned electrode is brought into contact with the coated transfer sheet such that the electrode facing the slurry is aligned with the final partition area. This can be accomplished in a number of different ways.

In one aspect, the transfer sheet may remain horizontal while the glass panel is inverted thereon (ie, with the electrode facing down). Then, the glass panel and the transfer sheet are rotated together so that the glass panel is on the bottom. Referring to FIGS. 3A-3C, FIG. 3A shows a cross-sectional view of a coating area having a flat surface 310 (eg, a table), a suitable rigid support 320, and a transfer film 330. A detachable patch of slurry 340 is provided on the transfer film surface. Glass panel 350 is then placed on a separate patch of slurry (not shown) (ie, with the electrode facing down). Next, the glass panel and the transfer sheet are rotated together as shown in FIG. 3B so that the glass panel is under the transfer sheet. The transfer sheet is then removed from the slurry of the slurry by simultaneously pulling the rigid support 320 in a direction substantially parallel to the glass panel while removing the transfer sheet at an angle as shown in FIG. 3C. The angle formed during removal of the transfer sheet is typically at least 5 degrees and about 90 degrees or less.

In another aspect, the transfer sheet can be rotated and positioned on the top of the glass panel (ie, with the slurry side of the transfer sheet facing down). The transfer sheet is then removed with the slurry left on the glass panel. This can be accomplished by means of transferring the coating from the transfer sheet to the patterned substrate (eg, glass panel) in the rotating structure.

4A-4D, the transfer film 405 traverses the top surface of the rigid movable support 415 from the roll 410, around the bottom surface around one edge 420 of the rigid movable support 415. It may be a continuous web that is traversed and transferred onto another roll 425. The rolls 410, 425 holding the transfer film may be mounted to the ground and may be oriented such that the rolls may pull the film across the rigid movable support. Rolls 410 and 425 can both be driven by a servomotor system (not shown) having an encoder for feedback on the rotation of the roll and a sensor for monitoring the tension in the flexible film.

Rigid movable supports may be provided in the translational movement structure 450 that can slide the transfer sheet in any range of motion (eg, 2-3 m). The translational movement can be accomplished by a servomotor (not shown) that drives the ball screw actuator in contact with the hard stop at two extreme positions. The translational movement structure may be mounted inside the rotating structure 460 with a fully continuous 360 ° movement. The rotating structure rotates the transfer sheet from the coating area with the coated surface of the transfer film upward to the laminated area (such as flat granite surface) within the plane of the coating area with the coated surface of the transfer film facing downward. Can be.

A robotic component handling system (not shown) may provide a glass substrate 440 with an electrode-patterning area on the flat surface 435 in the stacking area with the electrode facing up. The vision system guides the movement of the robot and thereby orients the patch and electrode regions of the slurry when the glass panel is positioned. The rotating structure rotates the transfer sheet and slurry onto a glass substrate on the flat surface 435 (eg, granite) of the laminated area.

Referring to Figure 4b, a constant tension can be maintained on the transfer film, thereby carrying the film to enable this movement of the transfer sheet. 4C and 4D, after the slurry is in contact with the glass panel, the vacuum portion is replaced with low pressure compressed air (20-30 psi), and the translational moving structure slides the transfer sheet horizontally back into the coating area. While the translating moving structure is sliding, the lower film roll maintains its position, while the upper film roll exerts a constant tension to pull the transfer film across both surfaces of the rigid movable support. When the transfer film reaches the coating area, there will be some uncoated length film on the top surface prepared for coating.

Alternatively, the glass substrate 440 may be positioned with the electrode facing down on the coated slurry. A clamp mounted to the translational movement structure can hold the glass substrate on the transfer sheet while the rotating structure rotates the stack of transfer sheet, slurry and glass substrate on the flat surface 345 of the lamination area.

Regardless of how the slurry was transferred from the transfer sheet onto the glass substrate, the microstructured surface of the mold (e.g., suitable for forming the septum) is then aligned so that the electrode pattern of the glass panel is aligned with the microstructure pattern of the mold. Contact with a patch of slurry. The slurry is sufficiently cured (eg by exposure to a light source through the mold) before removal of the mold. The final cured partition wall disposed on the glass substrate is then sintered. After the slurry is transferred onto the glass, the slurry can be contacted with the mold, cured, the mold can be removed, and sintered as described above. The transfer sheet station can be employed to coat another glass substrate while the subsequent molding step is being applied to the just coated glass substrate.

The inorganic particulate material of the slurry or paste is selected based on the final field of the microstructure and the nature of the substrate to which the microstructure is to be attached. One consideration is the coefficient of thermal expansion (CTE) of the substrate material. Preferably, the CTE of the inorganic material of the slurry differs from the CTE of the substrate material by about 10% or less when fired. When the substrate material has a CTE that is much smaller than or much larger than the CTE of the inorganic material of the microstructure, the microstructure will not bend, crack, break, reposition, or cut completely during processing or use. Can be. Furthermore, the substrate may bend due to the high difference of CTE between the substrate and the microstructure.

The substrate can typically withstand the temperatures required to process the inorganic material of the slurry or paste. The inorganic material suitable for use in the slurry or paste preferably has a softening temperature in the range of about 600 ° C. or less and usually in the range of about 400 ° C. to 600 ° C. As such, a good choice for the substrate is another rigid material having a higher softening temperature than the inorganic material of glass, ceramic, metal, or slurry. Preferably, the substrate has a softening temperature higher than the temperature at which the microstructures should be fired. If the material will not be fired, the substrate can also be made of a material such as plastic. Inorganic materials suitable for use in slurries or pastes preferably have a coefficient of thermal expansion of about 5 × 10 ⁻⁶ / ° C. to 13 × 10 ⁻⁶ / ° C. As such, the substrate also preferably has a CTE within this range.

Choosing an inorganic material with a low softening temperature allows the use of a substrate that also has a relatively low softening temperature. In the case of glass substrates, soda lime float glass with low softening temperatures is typically less expensive than glass with higher softening temperatures. As such, the use of inorganic materials of low softening temperatures enables the use of less expensive glass substrates. The ability to fire the bulkhead in the green state at lower temperatures can reduce the amount of stress relaxation required during thermal expansion and heating, thereby avoiding excessive substrate torsion, bulkhead warpage and bulkhead peeling.

Lower softening temperature ceramic materials can be obtained by incorporating any amount of alkali metal, lead or bismuth into the material. However, for PDP barrier ribs, the presence of alkali metals in the microstructured barrier ribs can cause the material from the electrode to move across the substrate during elevated temperature processing. Diffusion of electrode material can cause short circuits between adjacent electrodes as well as interference or "crosstalk", thereby degrading device performance. As such, for the field of PDPs, the ceramic powder of the slurry is preferably substantially free of alkali metals. When a combination of lead or bismuth is employed, a low softening temperature ceramic material can be obtained using phosphorus or B ₂ O ₃ -containing compositions. One such composition comprises ZnO and B ₂ O ₃ . Another such composition includes BaO and B ₂ O ₃ . Another such composition includes ZnO, BaO and B ₂ O ₃ . Another such composition includes La ₂ O ₃ and B ₂ O ₃ . Another such composition includes Al ₂ O ₃ , ZnO and P ₂ O ₅ .

Other fully soluble, insoluble or partially soluble components may be incorporated into the ceramic material of the slurry to achieve or modify various properties. For example, Al ₂ O ₃ or La ₂ O ₃ may be added to increase the chemical durability of the composition and reduce the corrosiveness. MgO may be added to increase the glass transition temperature or to increase the CTE of the composition. TiO ₂ may be added to provide a higher degree of optical opacity, whiteness and reflectivity to the ceramic material. Other components or metal oxides may be added to modify or adjust other properties of the ceramic material such as CTE, softening temperature, optical properties, physical properties such as brittleness.

Another means of preparing a composition that can be calcined at relatively low temperatures includes coating a layer of low temperature melting material to core particles in the composition. Examples of suitable core particles include ZrO ₂ , Al ₂ O ₃ , ZrO ₂ -SiO ₂ and TiO ₂ . Examples of suitable low temperature dissolution coating materials include B ₂ O ₃ , P ₂ O ₅ and glass based on one or more of B ₂ O ₃ , P ₂ O _5, and SiO ₂ . These coatings can be applied by various methods. A sol-gel process in which the core particles are dispersed in the wet chemical precursor of the coating material is a preferred method. The mixture is then dried and comminuted to separate the coated particles (if necessary). These particles may be dispersed in the glass or ceramic powder of the slurry or paste, or may be used alone for the glass powder of the slurry or paste.

The inorganic material in the slurry or paste is preferably provided in the form of particles dispersed throughout the slurry or paste. The preferred size of the particles depends on the size of the microstructures to be formed and aligned on the patterned substrate. Preferably, the average size or diameter of the particles in the inorganic material of the slurry or paste is about 10% to 15% or less of the size of the critical minimum characteristic dimension of the microstructure to be formed and aligned. For example, the PDP bulkhead may have a width of about 20 μm, which width is an important minimum feature dimension. For PDP bulkheads of this size, the average particle size in the inorganic material is preferably about 2 or 3 μm or less. By using particles smaller than this size, there is a high possibility that the microstructures will be replicated with the desired fidelity and that the surface of the inorganic microstructures will be relatively smooth. As the average particle size approaches the size of the microstructures, the slurry or paste containing the particles may no longer follow the microstructured profile. In addition, the maximum surface roughness may vary based in part on the inorganic particle size. As such, it is easier to form smoother structures using smaller particles.

The binder of the slurry or paste is capable of bonding to the inorganic material of the slurry or paste, the ability to be cured or otherwise cured to retain the molded microstructures, the ability to attach to the patterned substrate, and the green state. Organic binders selected based on such factors as their ability to volatilize (or burn) at a temperature at least slightly lower than those used to fire the microstructures of. The binder helps to bind the particles of inorganic material to each other when the binder is cured or cured so that the mold can be removed to risk leaving the microstructures in the rigid green state attached to and left aligned with the patterned substrate. The binder may be referred to as a "leaving binder" because, if desired, the binder material may be burned out of the microstructure at elevated temperatures before dissolving or sintering the ceramic material in the microstructure. Preferably, the firing substantially burns the leaving binder and the resulting microstructures left on the patterned surface of the substrate are dissolved inorganic microstructures substantially free of carbon residues. In applications where the microstructures used, such as in PDP, are dielectric bulkheads, the binder is preferably at a temperature at least slightly below the temperature desired for firing without leaving a significant amount of carbon that may degrade the dielectric properties of the microstructured bulkheads. It is a material that can be degreased. For example, binder materials containing significant proportions of aromatic hydrocarbons, such as phenolic resin materials, may leave graphite carbon particles during degreasing, which may require significantly higher temperatures to completely remove them.

The binder is preferably an organic material that is radiation or heat curable. Preferred types of materials include acrylates and epoxies. In the alternative, the binder may be a thermoplastic material that is heated to a liquid state to conform to the mold and then cooled to a hardened state to form a microstructure that is then attached to the substrate. When precise placement and alignment of the microstructures on the substrate is desired, the binder is preferably radiation curable so that it can be cured under isothermal conditions. Under isothermal conditions (no change in temperature), the mold or slurry or paste in the mold can then be held in a fixed position relative to the pattern of the substrate during the curing treatment of the binder material. This reduces the risk of displacement or expansion of the mold or the substrate, in particular due to the differential thermal expansion properties of the mold and the substrate, as a result of which the precise placement and alignment of the mold can be maintained while the slurry or paste is cured.

When using a radiation curable binder, it is preferred to use a curing initiator in which the substrate is activated by substantially permeable radiation such that the slurry or paste can be cured by exposure through the substrate. For example, when the substrate is glass, the binder is preferably visible light curable. By curing the binder through the substrate, the slurry or paste is first attached to the substrate, and any shrinkage of the binder material during curing will tend to occur away from the mold and toward the surface of the substrate. This aids in microstructure demolding and helps to maintain the position and accuracy of microstructure placement relative to the pattern of the substrate.

In addition, the choice of curing initiator may depend on which material is used for the inorganic material of the slurry or paste. For example, in fields where it is desirable to form an impermeable and diffusely reflective ceramic microstructure, it may be advantageous to include any amount of titania (TiO ₂ ) in the ceramic material of the slurry or paste. While titania may be useful for increasing the reflectivity of microstructures, titania may also make it difficult to cure with visible light, which is a curing initiator for the reflection of visible light by titania in a slurry or paste to effectively cure the binder. This is because the sufficient absorption of the light by the light source can be prevented. However, by selecting a curing initiator that is activated by radiation that can propagate simultaneously through the substrate and titania particles, effective curing of the binder can occur. One example of such a curing initiator is bis (2,4,6-trimethylbenzoyl) -phenylphosphine, a photoinitiator commercially available from Ciba Specialty Chemicals, Hodon, NY, under the trade designation "Irgacure ^TM 819". Oxide. Another example is a ternary photoinitiator system as described in US Pat. No. 5,545,670, which comprises, for example, a mixture of ethyl dimethylaminobenzoate, camphorquinone and diphenyl iodonium hexafluorophosphate. Both of these examples are valid within the blue region of the visible light spectrum close to the edge of the ultraviolet in a relatively narrow region where radiation can pass through both the glass substrate and the titania particles in the slurry or paste. Other curing systems may be selected for use in the process of the present invention based on, for example, the components of the inorganic material in the binder, slurry or paste, and the material of the mold or substrate through which curing should occur.

Diluents of slurries or pastes generally have the ability to improve the mold release properties of the slurry, for example after the step of curing the release binder and the ability to improve the degreasing properties of the green state structure formed using the slurry or paste. The material is selected based on such factors. The diluent is preferably a material that is soluble in the binder prior to curing and remains liquid after curing the binder. By remaining liquid when the binder is cured, the diluent reduces the risk of the cured binder material sticking to the mold. Furthermore, by remaining as a liquid when the binder is cured, the diluent phase separates from the binder material, thereby forming an interpenetrating network of small pockets or droplets of diluent that are dispersed throughout the cured binder matrix.

Various organic diluents can be employed depending on the selection of the curable organic binder. In general, suitable dilutions include various alcohols and alkylene glycols (eg ethylene glycol, propylene glycol, tripropylene glycol), alkyl diols (eg 1,3 butanediol) and alkoxy alcohols [eg 2-hexyloxyethanol, 2 Glycols such as-(2-hexyloxy) ethanol and 2-ethylhexyloxyethanol]; Ethers such as dialkylene glycol alkyl ethers (eg, diethylene glycol monomethyl ether, dipropylene glycol monopropyl ether, tripropylene glycol monomethyl ether); Esters such as lactates and acetates and in particular dialkyl glycol alkyl ether acetates (eg diethylene glycol monoethyl ether acetate); And alkyl succinates (eg diethyl succinate), alkyl glutarates (eg diethyl glutarate) and alkyl adipates (eg diethyl adipate).

For many fields, such as PDP bulkheads, it is desirable that degreasing of the microstructures in the green state is substantially completed before firing. In addition, degreasing is often the longest and highest temperature stage in thermal processing. As such, it is desirable that the slurry or paste can be degreased relatively quickly and completely and at relatively low temperatures.

While not wishing to be bound by any theory, degreasing can be thought of as being limited mechanically and thermodynamically by two temperature-dependent processes: diffusion and volatilization. Volatilization is a process that leaves a porous network for release in order to allow the degraded binder molecules to evaporate from the surface of the green structure and to proceed in a less disturbed manner. In single-phase resin binders, internally trapped gaseous decomposition products can foam and / or rupture the structure. This is more effective in binder systems that leave decomposition products containing high levels of carbon at the surface that can form an impermeable skin layer to stop the release of binder decomposition gases. In some cases where single-phase binders are successful, the cross-sectional area is relatively small and the binder decomposition heating rate takes long enough to prevent the epidermal layer from forming.

The rate at which volatilization occurs depends on the temperature, the activation energy for volatilization and the frequency or sampling rate. Since volatilization mainly occurs at or near the surface, the sampling rate is typically proportional to the total surface area of the structure. Diffusion is the process by which binder molecules migrate from the bulk of the structure to the surface. Due to the volatilization of the binder material from the surface, there is a concentration gradient that tends to move the binder material towards the surface with the lower concentration. The rate of diffusion depends, for example, on temperature, activation energy for diffusion and concentration.

Since volatilization is limited by the surface area, if the surface area is small for the bulk of the microstructure, excessively rapid heating may cause volatile species to be trapped. When the internal pressure becomes sufficiently large, the structure can swell, rupture or break. To reduce this effect, it can be achieved by a relatively gradual temperature increase until degreasing is complete. Lack of open channels for degreasing or excessively rapid degreasing can also lead to a higher tendency for residual carbon formation. This may later require higher degreasing temperatures to ensure substantially complete degreasing. When degreasing is completed, the temperature can be raised more quickly to the firing temperature and maintained at that temperature until the firing is completed. At this point, the product can then be cooled.

Diluents improve degreasing by providing a shorter path for diffusion and increased surface area. The diluent preferably remains liquid and phase separates from the binder when the binder is cured or otherwise cured. This creates an interpenetrating network of pockets of diluent dispersed in a matrix of cured binder material. The faster the curing or curing treatment of the binder material occurs, the smaller the pocket of diluent will be. Preferably, after curing of the binder, a relatively large number of relatively small pockets of diluent are dispersed throughout the structure throughout the green state. During degreasing, the low molecular weight dilution can evaporate rapidly at relatively low temperatures before decomposition of other high molecular weight organic components. Evaporation of the diluent leaves a slightly porous structure, thereby increasing the surface area over which remaining binder material may volatilize and decreasing the average path length that the binder material must diffuse to reach these surfaces. Therefore, by including the diluent, the volatilization rate during binder degradation is increased by increasing the available surface area, thereby increasing the volatilization rate for the same temperature. This lowers the likelihood of pressure build up due to limited diffusion rates. Furthermore, relatively porous structures allow the accumulated pressure to be released more easily and at lower thresholds. As a result, degreasing can typically be performed at a faster rate of temperature increase while lowering the risk of microstructure destruction. In addition, because of the increased surface area and the reduced diffusion length, degreasing is completed at lower temperatures.

The diluent is not just a solvent compound for the binder. The diluent is preferably sufficiently soluble to coalesce into the binder in the uncured state. Upon curing the binder of the slurry or paste, the diluent must be phase separated from the monomers and / or oligomers involved in the cross-linking process. Preferably, the diluent is phase separated to form discrete pockets of liquid material in a continuous matrix of cured binder, wherein the cured binder binds particles of glass frit or ceramic material of the slurry or paste. In this way, the physical integrity of the cured green microstructure is not significantly impaired even if a fairly high level of diluent (a diluent to resin ratio greater than about 1: 3) is used.

Preferably, the diluent has an affinity for bonding an inorganic material of a slurry or paste that is lower than the affinity for bonding an inorganic material and a binder. When cured, the binder must bond with particles of the inorganic material. This in particular increases the structural integrity of the structure in the green state after evaporation of the diluent. Other desired properties for the diluent will depend on the choice of inorganic material, the choice of binder material, the choice of curing initiator (if any), the choice of substrate, and other additives (if any). Preferred diluents include glycols and polyhydroxyls, examples of which include butanediol, ethylene glycol and other polyols.

In addition to the inorganic powders, binders, and diluents, the slurry or paste may optionally include other materials. For example, the slurry or paste may include an adhesion promoter that promotes adhesion to the substrate. For glass substrates or other substrates having silicon oxide or metal oxide surfaces, silane coupling agents are a good choice as adhesion promoters. Preferred silane coupling agents are silane coupling agents having three alkoxy functional groups. Such silane may optionally be pre-hydrolyzed to promote adhesion to a better glass substrate. Particularly preferred silane coupling agents are silano primers such as those sold by 3M Company, St. Paul, Minn., Under the trade designation “Scotchbond Ceramic Primer”. Other optional additives may include materials such as dispersants to help mix the inorganic material with other components of the slurry or paste. Optional additives may also include surfactants, catalysts, anti-aging components, release enhancers, and the like.

In general, the method of the present invention typically uses a mold to form a microstructure. The mold is preferably a flexible polymer sheet having a smooth surface and an opposing microstructured surface. Molds can be made by compression molding of thermoplastic materials using a master tool having a microstructured pattern. The mold may also be made of a curable material that is cast and cured onto a thin flexible polymer film. The mold may have a curved surface that connects the barrier and land regions, such as those described in US Patent Application Publication No. 2003 / 0100192-A1. Furthermore, the material of the land portion may be continuous with the material of the barrier portion.

The microstructured mold can be formed according to processes such as, for example, those disclosed in US Pat. No. 5,175,030 (Ru et al.) And US Pat. No. 5,183,597 (Ru). The forming process comprises the following steps: (a) preparing the oligomer resin composition; (b) depositing the oligomer resin composition onto the master negative microstructured tool surface in an amount sufficient to fill the cavity of the master; (c) filling the cavity by moving the beads of the composition between the master and at least one preformed substrate that is flexible; (d) curing the oligomer composition. A good master is a metal tool. If the temperature of the curing and optional simultaneous heat treatment steps is not excessively large, the master can also be constructed from thermoplastic materials such as laminates of polyethylene and polypropylene.

The oligomer resin composition of step (a) is preferably an integral, solventless radiation-polymerizable and crosslinkable organic oligomer composition, but other suitable materials may be used. The oligomer composition is preferably curable to form a flexible and dimensionally stable cured polymer. Curing of the oligomer resin preferably occurs with low shrinkage.

The oligomer resin composition of step (a) is preferably an integral, solventless (eg, radiation-polymerizable) crosslinkable organic oligomer composition. The oligomer composition is preferably curable to form a flexible and dimensionally stable cured polymer. Curing of the oligomer resin preferably occurs with low shrinkage. Brookfield viscosity of the oligomer resin is typically at least 10 cps and typically 35,000 cps, more preferably has a viscosity in the range of 50 cps to 10,000 cps.

Preferred oligomer compositions include at least one acrylic oligomer and at least one acrylic monomer. As used herein, acrylics include species (meth) acryl. The acrylic monomer (s) and urethane acrylate oligomer (s) preferably each have a glass transition temperature (Tg) of about -80 to about 0 ° C., which means that the single polymer has such glass transition temperature. do.

Examples of acrylic monomers having glass transition temperatures of about −80 to about 0 ° C. include, for example, polyether acrylates, polyester acrylates, acrylamides, acrylonitriles, acrylic acids, acrylic acid esters, and the like. Acrylic oligomers having glass transition temperatures of about −80 to about 0 ° C. include, for example, urethane acrylate oligomers, polyether acrylate oligomers, polyester acrylate oligomers, and epoxy acrylate oligomers. For example, the urethane acrylate oligomer and acrylic monomer may each be combined in an amount of about 10 to about 90 weight percent and more preferably in an amount of about 20 to about 80 weight percent. Preferred oligomer resin compositions are disclosed in PCT Publication WO2005 / 021260; PCT Publication WO2005 / 021260; And US patent application Ser. No. 11/107554, filed April 15, 2005.

The polymerization can be accomplished by conventional means such as heating in the presence of free radical initiators, irradiation with ultraviolet or visible light in the presence of a suitable photoinitiator and irradiation with an electron beam. One method of polymerization is by irradiation with ultraviolet or visible light in the presence of a photoinitiator at a concentration of about 0.1% to about 1% by weight oligomer composition. Higher concentrations may be used but are typically not necessary to obtain the desired cured resin properties.

Various materials can be used for the base (substrate) of the patterned mold. Typically, the material is substantially optically transmissive to cure radiation and has sufficient strength to allow handling during casting of the microstructures. In addition, the material used for the base may be selected to have sufficient thermal stability during processing and use of the mold. Polyethylene terephthalate or polycarbonate films are preferred for use as substrates in step (c) because the materials are economical, optically transmissive to the cure radiation and have good tensile strength. The substrate thickness of 0.025 mm to 0.5 mm is good, and the thickness of 0.075 mm to 0.175 mm is particularly good. Other useful substrates for microstructured molds include cellulose acetate butyrate, cellulose acetate propionate, polyether sulfone, polymethyl methacrylate, polyurethane, polyester and polyvinyl chloride. The surface of the substrate may also be treated to promote adhesion to the oligomer composition.

Examples of suitable polyethylene terephthalate-based materials include photograde polyethylene terephthalate; And polyethylene terephthalate (PET) having a surface formed according to the method described in US Pat. No. 4,340,276.

Various other aspects that may be utilized in the invention described herein are described in each of the following patents: US Pat. No. 6,247,986; US Patent No. 6,537,645; US Patent No. 6,713,526; WO 00/58990; U.S. 6,306,948; WO 99/60446; WO 2004/062870; WO 2004/007166; WO 03/032354; WO 03/032353; WO 2004/010452; WO 2004/064104; US Patent No. 6,761,607; US Patent No. 6,821,178; WO 2004/043664; WO 2004/062870; PCT Application US04 / 33170, filed Oct. 8, 2004; PCT Application US04 / 26701, filed August 17, 2004; PCT Application US04 / 26845, filed August 18, 2004; PCT Application US04 / 23472, filed July 21, 2004; PCT Application US04 / 32801, filed October 6, 2004; PCT Application US04 / 43471, filed December 22, 2004; And US patent applications 60/604556, 60/604557, 60/604558, and 60/604559, filed August 26, 2004, respectively, are known in the art. .

The advantages of the invention are further illustrated by the following examples, but the specific materials and amounts recited in the examples as well as other conditions and details should not be construed to unduly limit the invention. All percentages and ratios herein are by weight unless otherwise specified.

Yes

Glass frit slurry compositions suitable for use in these examples are commercially available from Asahi Glass Company, Tokyo, Japan under the trade designation “RFWW030” containing lead borosilicate glass frits with refractory fillers such as TiO ₂ and Al ₂ O ₃ . 80 parts by weight of glass powder. Glass powders include 8.034 parts by weight of BisGMA (bisphenol-a diglycidyl ether dimethacrylate) available from Sartomer Company, Exton, Pa., Inc., and Gyoisha Chemical Company, Japan. 4.326 parts by weight of TEGDMA (triethylene glycol dimethacrylate), available from USA, is added thereby forming a curable leaving binder. As the diluent, 7 parts by weight of 1,3 butanediol (Aldrich Chemical Company, Milwaukee, Wisconsin, USA) is used. In addition, 0.12 parts by weight of POCAII (phosphorus polyoxyalkyl polyol) obtained from 3M Company, St. Paul, Minn., USA, is added as a dispersant and 0.16 parts by weight of A174 silane (Aldrich Chemical Company, Milwaukee, Wisconsin, USA) As a coupling agent, 0.16 parts by weight of a curing initiator, available from Ciba Specialty Chemicals, Basel, Switzerland, under the trade designation "Irgacure 819", is added. In addition, 0.20 parts by weight of a defoamer, available from BYK Chemie USA, Wallingford, Connecticut, under the trade designation “BYK A555” is added.

All liquid raw materials and photoinitiators are combined in a stainless steel mixing vessel. The raw materials are mixed using a Coles blade (VWR Scientific Products, West Chester, Pennsylvania, USA) driven by a pneumatic motor. While the mixing blade is in operation, the solid raw material is slowly added. After all the raw materials are coalesced, the mixture is mixed for an additional 5 minutes. The slurry is delivered to a high density polyethylene vessel filled with 1/2 inch cylindrical high density aluminum oxide milling media. Milling is performed using a paint conditioner (Red Devil Model 5100, Union, New Jersey, USA) for 30 minutes. The slurry is then discharged from the ball mill. Finally, the slurry is milled at 60 ° C. using a 3-roll mill (Model 2.5 × 5 TRM, Charles Ross & Sun Company, Hopose, NJ, USA).

Example 1

There is provided a transfer sheet having two separable layers. The first layer is a rigid support and the second layer is a flexible film.

Referring to Figure 2, the rigid support is a 1.5 mm x 2.5 m, 25 mm thick aluminum plate machined to a depth of 10 mm on both sides, leaving a lattice of support ribs. A 5 mm thick aluminum plate was bonded to the support ribs thereby creating a flat surface on the top and bottom. The edge of the rigid support on which the film slides has a sharp 500 μm radius and a 45 ° taper.

There is a 100 μm diameter hole provided on top of the rigid support and on its surface. The fitting is attached to the edge of the support so that the flexible film can be selectively pulled by vacuum to the top or bottom surface of the support. The valve alternately introduces compressed air into the fitting so that the flexible film can be easily moved across one or both surfaces.

Five mils of polyethylene with a release coating on one side are employed as the flexible film in the device of FIGS. 4A-4D.

The coating system locates four separate patches of slurry, each 523 mm × 930 mm (a suitable size for making a 42 inch plasma display panel) with a uniform thickness of 165 μm at a predetermined location on the top surface of the transfer sheet. Used to.

The apparatus of FIGS. 4A-4D can be used to transfer separate patches of slurry onto an electrode patterned glass panel as described above.

Four molds (eg, flexible polymers) are then pressed into a patch of slurry so that the partition structure is aligned with the electrode pattern. After molding, the coated substrate is exposed to a blue light source to cure the glass frit slurry. Curing is performed using a blue light source that is about 3.8 cm (1.5 inches) above the sample surface. The light source is ten super-actinic fluorescent lamps (model TLDK 30W / 03, Philips) spaced at about 5.1 cm (2 inches) capable of providing light in the wavelength range of about 400 to 500 nm. Electronics NV, Einhoven, The Netherlands). Cure time is typically 30 seconds.

Four mold tools are removed. The substrate is moved to a component handling system. The glass substrate with the cured structure will be sintered in air at 3 ° C./minute up to 300 ° C. and 5 ° C./minute up to 560 ° C., immersed for 20 minutes, and subjected to 2 to 3 atmospheres, according to the following thermal cycles. Will cool to 3 ° C / min.

Claims (20)

In the method of forming a partition for a plasma display panel, Providing a transfer sheet; Coating at least one separable coating of the curable composition comprising at least one inorganic particulate material, at least one curable organic binder and at least one diluent; Transferring the separate coating onto the substrate; Contacting the release coating with a mold suitable for forming the partition; Curing the curable composition; Step to remove the mold How to include. The method of claim 1, wherein the transfer sheet is coated with at least two separate coatings. The method of claim 1, wherein the transfer sheet is provided on a substantially planar rigid support. The method of claim 1, wherein the transfer sheet is provided on a roll. The method of claim 1, wherein transferring the separate coating comprises contacting the coated transfer sheet with the substrate while the transfer sheet remains horizontal and rotating the coated transfer sheet with the substrate such that the substrate is under the transfer sheet. Method comprising the steps. The method of claim 1, wherein transferring the separate coating comprises transferring the coating from the transfer sheet to the substrate in the rotating structure. The method of claim 1, wherein each separate coating is a region corresponding to a single plasma display panel. The method of claim 1, wherein each separate coating has an area in the range of about 1 cm 2 to about 2 m 2. The method of claim 1, wherein the transfer sheet comprises a flexible film and a rigid support layer. The method of claim 1, wherein the flexible film is removed simultaneously with removing the rigid support layer. The method of claim 1, wherein the substrate is a glass panel optionally comprising an electrode pattern. The method of claim 1, wherein the detachable coating is provided with a template. The method of claim 1 wherein the mold is permeable. The method of claim 1, wherein the curable composition is cured through the mold, through the substrate, or through a combination thereof. The method of claim 1 wherein the mold is flexible. The method of claim 1, wherein the method is at least semi-automated. The method of claim 1, wherein the curable composition comprises the diluent in an amount of at least 2%, at least 5%, or at least 10% by weight. The method of claim 1, wherein the slurry has a viscosity of less than 20,000 cps or less than 5,000 cps. The method of claim 1, wherein the two or more separate coatings are transferred onto a single glass panel. In the method of forming a product, Providing a transfer sheet; Coating at least one separate coating of the curable material to the transfer sheet; Transferring the separate coating onto the substrate; Contacting the microstructured mold surface with the detachable coating; Curing the curable material; Step to remove the mold How to include.

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