Sintered glass and glass-ceramic structures and methods for producing

Priority claim

This application claims the priority of European Patent Application No. 06300471.7 filed on May 15, 2006, entitled "Sintered Glass and Glass Ceramic Structures and Manufacturing Methods".

Generally speaking, the present invention relates to sintered glass and glass-ceramic structures and methods for forming them, and particularly to glass and glass-ceramic structures formed on a solid substrate and methods for forming the same.

One useful method of making glass or glass-ceramic structures, such as glass or glass-ceramic structures used as fluid or microfluidic devices, is to form a mixture of glass frit and binder on a substrate to achieve relatively high purity. It is to form a three-dimensional structure. The substrate and glass frit are then stacked on one or more other substrates, each with its own patterned frit three-dimensional structure, and sintered together to form an integral or single device. Form. For the entire description of an example of a manufacturing method of this type, refer to Patent Document 1 assigned to the assignee of the present application.

<p><patcit num="1"><text>U.S. Pat. No. 6,769,444</text></patcit></p>

<p> However, there are challenges in imparting high strength to the final device over a range of element sizes of the patterned frit material. When the three-dimensional structure of the formed frit material is sintered, cracks can occur due to the physical constraints of the substrate. As a result, the final fully sintered product has weak spots, that is, potential breakage points. Therefore, a device or method for preventing such crack formation is desired.</p>

<p> According to one embodiment, the invention has two or more flat substrates integrally fused by sintered and patterned glass or glass-ceramic frit material placed in between. It has a single structure. The pattern of the sintered and patterned frit material defines a passage inside, and the sintered and patterned frit material has a first characteristic minimum element size in a direction parallel to the substrate. Have. The particles of the frit material have a polydisperse particle size distribution up to the maximum frit particle size in the maximum length dimension, and the first minimum element size of the sintered and patterned frit material is the maximum frit particle. It is larger than twice the size, preferably about 3 times or more, and less than 6.25 times the maximum frit particle size, preferably within about 5 times, and most preferably within about 4 times. Setting the minimum element size sufficiently smaller than the maximum frit particle size makes the structure stronger by preventing the formation of cracks, while keeping the minimum element size large is used in useful forming processes such as molding. Ensuring sufficient resolution facilitates the manufacture of the structure.</p><p> According to another embodiment, the invention also includes a method of forming a sintered structure with a desired pattern on a substrate. The method comprises providing a polydisperse frit consisting of a material that is viscous sintered and allowing the frit to be mixed with a sufficient amount of binder to form a frit-binder mixture. The method further comprises forming the frit-binder mixture on a single substrate with a desired pattern, which pattern has a first minimum element size in a direction parallel to the substrate and then the above. The formed mixture is sintered to form a sintered structure. According to this method, the polydisperse frit is 0.16 times, preferably about 0.2 times or more, most preferably about 0.25 times or more the first minimum element size, and 0.5 times the first minimum element size. It has a maximum particle size of less than, preferably within about 0.3 times. Choosing a large enough particle size can make the resulting structure stronger, but keeping it small enough facilitates the manufacture of this structure. This method provides a polydisperse frit by milling with a ball mill or a similar suitable step, then sieving the frit with a sieve sized 1.5 times the maximum particle size for the frit and passing through the sieve for the frit content. Includes the use of all the particles. The method of the present invention provides a very simple method for providing a high performance frit with a polydisperse particle size distribution.</p><p> Further features and effects of the present invention are described in the detailed description below, some of which are immediately apparent to those skilled in the art from the description, or which include the description, claims and accompanying drawings below. Will be recognized by the implementation of.</p><p> Both the above-mentioned summary description and the following detailed description present embodiments of the present invention, and provide an overview and a framework for understanding the properties and characteristics of the present invention described in the claims. It should be understood that it is intended. The drawings show various embodiments of the present invention, and contribute to the explanation of the principle and operation of the present invention together with the description contents.</p>

<figref num="1">It is the schematic sectional drawing of one Embodiment of the microfluidic device of this invention.</figref><figref num="2">FIGS. 2A-2E are photomicrographs of a part of the frit structure 20.</figref><figref num="3">It is a graph which shows the particle size distribution and the particle size distribution and the result of the frit used to make the structure of FIGS. 2A-2E.</figref><figref num="4">Layer 44 of three-dimensional frit structure after sintering showing cracks at the base of a raised oval structure when a 63 μm sieved frit is used for a structure with a minimum width in the 1000 μm range. It is a perspective micrograph.</figref><figref num="5">Similar to that of Fig. 4, but from the three-dimensional frit structure after sintering, which shows that there are no cracks at the root of the raised oval structure when a frit sieved at 125 μm is used. It is a perspective micrograph of the layer 44.</figref><figref num="6">FIG. 3 is a photomicrograph of a cross section of a portion of device 10 similar to FIG. 1 where first cut and then etched to reveal crystal boundaries in the sintered structural material 20.</figref>

Microfluidic devices such as device 10 in FIG. 1 include a three-dimensional (3D) sintered frit structure 20, which is a monolithic device 10 that is sintered and thereby has a fluid passage 70 inside. One layer 44, consisting of a 3D frit structure, fused between the two substrates 30 and 40 so as to define, as in device 10 shown in FIG. 1, preferably by molding, on one side. It is formed on a substrate and then sintered into another substrate having only a thin flat frit layer 50, resulting in a melt junction in the 3D frit structure 20 as shown by the broken line 46. Alternatively, in another device or part of the device, two three-dimensional frit structures initially formed on separate substrates may be sintered against each other.

In both cases, the resulting patterned sintered frit structure 20 has a characteristic minimum element size or dimension 60 in the direction parallel to the substrates 30, 40. Dimension 60 corresponds to the characteristic shortest distance between the free (unconstrained) surfaces of the frit structure 20 or the characteristic wall thickness of the passage 70.

The patterned and sintered frit structure 20 also has a characteristic minimum element size ie dimension 62 or 64 in the direction perpendicular to the substrates 30, 40. This dimension 62 or 64 is characteristic between the constrained surface of the frit structure 20 (constrained by the contact of the substrate 30 or 40) and the unconstrained surface of the frit structure 20 (such as the inner surface of the passage 70). Corresponds to the shortest distance. Dimension 62 is also referred to as the thickness of the residual layer, which is a substrate coating layer consisting of the frit generated on the substrate 30 as part of the layer 44 of the 3D frit structure. Dimension 64 may also be referred to as the thickness of the flat layer 50. Dimensions 62 and 64 are equal, but may be different, in which case the shorter of the two dimensions represents the characteristic minimum element size in the direction perpendicular to the substrates 30, 40.

According to the fracture cause analysis of the microfluidic device of the type shown in FIG. 1, the mechanical resistance of the final device is a crack, apparently shrinking, at the bottom of the frit wall structure, i.e. at or near the inner corner of the fluid passage 70. It has been shown that it can be changed by cracks. In addition, cracks are most frequent when the final device 10 undergoes a pressure test to measure the potential for internal pressure, whether the fracture occurred below or above the desired specifications. It was confirmed that it was the cause of the destruction.

A configuration similar to Figure 1 with a size of 60 of about 500 μm, made using a frit with a polydisperse particle size distribution (PSD) screened below 63 μm, shall not have any cracks. Was found as a result of the research. However, when a frit structure 20 with a minimum element size of 60 parallel to the substrate of about 1000 μm is produced with the same frit, cracks are observed in the final product, and the formation of these cracks is pre-sintered (incomplete sintering). Detected in and survived through the final sintering step. Heat treatments have been studied to try to solve the cracking problem, but their effects seem to play a secondary role at best.

In forming and sintering ceramic powders, minimum particle size and maximum particle uniformity are generally preferred. However, crack defects have been tested by frit testing with particles with smaller maximum particle size and higher uniformity of particle size, such as frit with all passing particles screened at 20 μm. Was found to increase dramatically. Testing of frit with particles with a larger polydisperse PSD, such as frit with all passing particles sieved at 125 μm and 160 μm, revealed no crack formation. Therefore, it has been found that a polydisperse frit with a larger maximum particle size works better than a polydisperse frit with a smaller maximum particle size. The formation of cracks was eliminated or clearly reduced, and the pressure resistance of the frit sieved at 125 μm was significantly improved from the 8% range to the 32% range compared to the frit sieved at 63 μm.

The results of these experiments are shown in FIGS. 2A-E, which are micrographs of cross sections of the incompletely sintered or "pre-sintered" frit structure 20. Such pre-sintering is utilized to impart physical strength and cohesive force to the formed frit structure prior to assembly of a large number of desired substrates for final sintering. desirable. The sizes of each sieve used to generate the frit used to form the frit structure 20 were 20 μm, 63 μm, 80 μm, 125 μm and 160 μm from left to right in FIGS. 2A-E. In the above micrograph, the crack 80 appears as a white region. As is clear from the figure, cracks are present for sieve sizes of 20 μm, 63 μm and 80 μm, but not for sieve sizes of 125 μm and 160 μm. These results are further summarized in Figure 3, showing PSD by cumulative volume percent as a function of equivalent particle size (μm) detected by a laser particle size meter. Curves 102, 104, 106, 108 and 110 show particle size distributions obtained from sieving to 20 μm, 63 μm, 80 μm, 125 μm and 160 μm or less, respectively.

The amount of binder used with the increased particle size of the frit sieved at 125 μm (from 20% by weight binder to 17.6% by weight in the same mixture) while keeping the viscosity of the mixture of frit and binder the same. In addition, it was possible to reduce it to 15.3% by weight in a sufficiently mixed state.

Compared to the method commonly practiced in the ceramic industry, where several monodisperse PSDs, individually prepared, must be mixed to improve the initial compactness of the particles mixed with the binder. Thus, the method of the present invention obtained the complete desired PSD by dry grinding and sieving very simply. Here, in contrast to conventional, an overall polydisperse PSD of less than one size value is obtained after sieving, resulting in good compactness, continuous PSD with very small particles by dry grinding itself. In essence generated.

Although not intended to be bound by a single theoretical expression, the inventor thus understands the effects of the present invention.

When a three-dimensionally shaped frit structure such as layer 44 is sintered on a substrate, the result is sintering under constraints, that is, under the constraints of fixed substrate dimensions. In the method of the present invention, the three-dimensional structure is such that the top of the layer 44 is very free at the initial stage of pre-sintering or final sintering, but the interface between the residual layer and the substrate 30 is constrained. Is preferably formed with the remaining flat frit layer having a thickness of 62. If the shrinkage is significant, high stress will occur, resulting in cracking.

Effective addition of larger particles to the PSD by sieving the very small particles provided by dry grinding and the larger size while maintaining a continuous particle size distribution requires less binder. become. This is because the voids between the particles that are replaced by the binder are essentially replaced by the material of the larger particles. A smaller amount of binder and associated smaller total void volume results in less shrinkage during sintering.

Although glass was used in this experiment, any material that can withstand viscous sintering, such as glass ceramics and possibly other ceramic materials, can be used as well.

The frit mixture is prepared as follows. The desired glass or glass ceramic is ground in a ball mill, then the particles smaller than the desired particle size are sieved (preferably a sieve of 125 μm is used here), and the particles smaller than the desired particle size are pasted (frit). And binder) used for preparation. Add a larger sieve to protect the sieve from the largest particles. To protect the sieve, for example, a 1 mm sieve may be used above the 125 μm sieve. There are no restrictions on the size of the ball mill, the initial amount of glass, the ball load, or the duration or speed of grinding, and the goal is to obtain the desired particle size distribution.

The particles generally obtained after grinding have an aspect ratio of approximately 1: 2, which means that the largest particles that can pass through the sieve during sieving have a length equal to about twice the size of the mesh of the sieve. .. As a result, the maximum size of the maximum particles in the PSD sieved to 63 μm or less is about 126 μm, and for the PSD sieved to 125 μm or less, it is about 250 μm. These values also correspond to the highest values measured on the PSD curve obtained by a laser particle size meter that characterizes all dimensions of the particles. The lowest value on the PSD curve corresponds to the size of the finest particles detected, which is approximately 1.3 μm in all cases described herein. If the PSD is characterized by using a device that employs particle precipitation in solution, then only the particle length is characterized, as the particle precipitation flows in the direction of the lowest resistance, and the PSD. The curve should be different from that obtained with the laser particle size meter. Therefore, care must be taken in interpreting the PSD curve, depending on the instrument used to characterize the PSD, especially if the particles are not significantly spherical.

2 and 3 show that when the minimum parallel element size dimension 60 in FIG. 1 is 1000 μm, there are few, but not all, crack problems in the frit sieved at 80 μm. .. Assuming a particle aspect ratio of 2: 1, a frit sieved at 80 μm has a maximum particle size of 160 μm in the maximum dimensional direction. Therefore, the minimum parallel element size is preferably within about 6.25 times the maximum particle size, and preferably within about 5 times the maximum particle size. As shown in FIGS. 2 and 3 and explained above, the frit sieved at 125 μm does not show cracks for the minimum parallel element size of 1000 μm, while the frit sieved at 63 μm No cracks were shown for a minimum parallel element size of 500 μm. Therefore, it is most desirable that the minimum parallel element size is within about 4 times the maximum particle size.

It has also been found that cracks occur when the vertical dimensions 62 and 64 are too large. In particular, the minimum element size in the vertical direction is preferably within 2.5 times the maximum particle size, preferably within 1.5 times the maximum particle size, if possible.

As described above, when the PSD sieved to 63 μm or less is advanced to the PSD sieved to 125 μm or less, the ratio of binders in the paste is increased while maintaining the same paste viscosity for the same mixing treatment. Reduced from 20% by weight to 17.6% by weight. By improving mixing by increasing the mixing time, the amount of binder may be reduced to 15.3% by weight while maintaining the same paste viscosity. Reducing the amount of binder is going in the right direction to stop the overall shrinkage from the molded or formed part to the sintered part, switching to a PSD sieved below 125 μm, This can be explained by the fact that there are fewer voids due to the presence of larger particles added.

Since the frit material used in this method and thus used in the resulting device is viscous sintered, sintering large particles into the structure is not as problematic as with ordinary ceramic powders. The sintering schedule may need to be adjusted by extending the time or increasing the temperature to ensure a fully complete sintering.

As mentioned above, it is desirable that the maximum size particles of the frit used are large particles, and sintering of large particles is the largest in PSD, even if it is feasible by using a viscous sintering material. If the particles are too large for the minimum element size of the three-dimensional structure to be formed, they lose resolution, i.e. small, during the molding process, which should be used to form the patterned structure. Or there is a risk of losing small elements. Experience has shown that the minimum parallel element size should be more than twice the maximum frit particle size and more than about three times the maximum frit particle size to avoid resolution problems. There is.

Figure 4 shows a crack at the base of a raised oval structure when a 63 μm sieved frit was used for a structure with a minimum width in the 1000 μm range, from a three-dimensional frit structure after sintering. It is a perspective micrograph of the layer 44.

FIG. 5 is similar to that of FIG. 4, but is tertiary after sintering, showing that there are no cracks at the root of the raised oval structure when a frit screened at 125 μm is used. It is a perspective micrograph of the layer 44 composed of the original frit structure. No cracks were formed during the presintering.

FIG. 6 is a photomicrograph of a portion of a device 10 similar to FIG. 1 in which the crystal boundaries in the sintered frit structure 20 were exposed by first cutting and then etching. Without etching, no crystal boundaries are seen and the cross-sectional structure looks uniform and smooth. Passages 70 are defined inside the sintered three-dimensional frit structure and are separated by these passages by a characteristic minimum parallel distance of about 1000 μm. As is clear from the figure, no cracks are found anywhere in the corners of these passages 70 after the final sintering of the structure 20. The long-dimensional orientation of 125 μm particles is such that the maximum particles in the 125 μm range are sufficiently rare and their orientations are sufficiently random, as noted by the size of the particles exposed by etching. Is not visible along this cross section. Many cross-sections are needed to observe the largest particles along the maximum dimensions.

10 Microfluidic device 20 frit structure 30,40 Substrate 44,50 frit layer 60,62,64 Minimum element size 80 cracks