Firing unit laminate and firing method

Abstract

To provide a stacked body of firing units capable of uniformly and efficiently firing a fired product.SOLUTION: A stacked body of firing units is formed by stacking plural firing units. The plural firing units have each a firing rack r and a mesh-like setter s disposed on the firing rack, the firing rack including a frame body f and a bridge part disposed in the frame body. The respective firing units are stacked over each other so that a bridge part area overlapping ratio becomes 0-80% when observing only firing racks that constitute adjacent firing units from a lower side in a vertically upper direction.SELECTED DRAWING: Figure 10

Description

[Technical Field]

[0001] The present invention relates to a firing unit laminate and a firing method. [Background technology]

[0002] Conventionally, a technique has been known for firing objects such as semiconductor chips and multilayer ceramic capacitors (MLCCs), in which a flat setter is placed on a firing rack, and the object is placed on the setter and fired.

[0003] Furthermore, in order to increase the efficiency of baking the baking objects, a technology has been proposed in which baking units each consisting of a baking rack and a flat setter are stacked together and baked, thereby baking the objects placed on the setters of each baking unit at once (see, for example, Patent Document 1).

[0004] In Patent Document 1, as shown in Figure 16, a plate-shaped firing jig (firing rack) 1 with an opening is used, and a firing unit U is proposed in which a flat setter 20 is placed on the firing rack 1. As shown in Figure 17, a technology is proposed in which multiple firing units U are stacked (with an object A to be fired placed on each setter) to form a firing unit stack, and then the stack is fired in a kiln (firing furnace). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2015 / 008503 DISCLOSURE OF THE INVENTION [Problem to be solved by the invention]

[0006] As shown in Figures 16 and 17, Patent Document 1 proposes a baking rack 1 having support parts (legs) 13 on the underside of a frame body 11, and it is said that these support parts 13 allow furnace gas to flow between each baking unit U, U, so that the objects A to be baked placed on each setter 20 can be baked at the same time while being spaced apart.

[0007] However, the inventors of the present invention have found that it is difficult to uniformly bake the object to be baked using the method described in Patent Document 1.

[0008] This is thought to be because, in the above-mentioned firing furnace, during firing, an air current is generated in which the gas inside the furnace rises from the lower side to the upper side of the furnace, and when firing is performed with multiple firing units U stacked on top of each other, the flat setter 20 that makes up the firing unit U obstructs the flow of the gas inside the furnace, making it difficult to perform a uniform firing process in each firing unit U.

[0009] Therefore, the inventor came up with the idea of improving the flow of gas inside the furnace from the lower side to the upper side of each firing unit by using a mesh-shaped setter instead of a flat one as the setter that makes up the firing unit.

[0010] However, after further investigation, the inventors found that even when a firing unit having a mesh setter is used in addition to a plate-shaped firing jig (firing rack) with openings as described above, it is not necessarily possible to efficiently obtain a uniform fired product.

[0011] According to the inventors' investigations, as shown in Figure 18(a), the firing racks r that make up a firing unit are usually multiple units with the same opening pattern and shape arranged in the same direction. Therefore, when the firing units are stacked and fired, when only the firing racks r are observed, as shown in the oblique view in Figure 18(b) and the side cross-sectional view in Figure 18(c) (a side cross-sectional view taken vertically along line Z-Z' in Figure 18(b)), when the in-furnace gas flow F rises from the lower side to the upper side of the furnace, the in-furnace gas flow F rises without coming into contact with any of the locations (indicated by arrows in the figure) where the bridging portions that define the opening pattern of each firing rack r are provided. This is thought to be because, particularly in the firing units stacked at the top, the air permeability is reduced, resulting in a decrease in the contact efficiency between the in-furnace gas flow F and the material to be fired.

[0012] Under these circumstances, an object of the present invention is to provide a firing unit laminate and a firing method that can uniformly and efficiently fire an object to be fired. [Means for solving the problem]

[0013] As a result of extensive research by the present inventors to solve the above technical problems, they discovered that the above objective can be achieved by a baking unit stack consisting of a plurality of stacked baking units, each of which has a baking rack and a mesh setter placed on the baking rack, and the baking rack has a frame and a bridge portion provided within the frame, and when only the baking racks constituting adjacent baking units in the stacked baking units are observed vertically upward from below, the bridge portion area overlap ratio, calculated by (the area over which the bridge portion of the baking rack located on the lower side overlaps with the bridge portion and frame of the baking rack located on the upper side / the area of the bridge portion of the baking rack located on the lower side) x 100, is 0 to 80%, and they have completed the present invention based on this finding.

[0014] That is, the present invention is (1) A firing unit stack formed by stacking a plurality of firing units, Each of the plurality of baking units has a baking rack and a mesh setter placed on the baking rack, The baking rack has a frame and a bridge portion provided within the frame, When only the baking racks constituting the adjacent baking units are observed vertically upward from the bottom side, the following formula (I) Cross-linking area overlap ratio (%) = (overlapping area of the cross-linking area of the lower baking rack and the cross-linking area and frame of the upper baking rack / area of the cross-linking area of the lower baking rack) × 100 (I) The firing units are stacked so that the cross-linking area overlap ratio calculated by is 0 to 80%. A firing unit laminate characterized by: (2) In at least some of the adjacent baking units, the baking racks constituting the baking units each have the same rectangular outer shape, The opening defined by the frame and the bridging portion of the baking rack has a shape that is not rotationally symmetric when rotated 90° or 180° clockwise around a vertical axis passing through the center of the top surface of the baking rack as the rotation axis, In the adjacent baking units, the baking rack constituting the baking unit arranged on the lower side is rotated 90° or 180° clockwise around a vertical axis passing through the center of the upper surface of the baking rack constituting the baking unit arranged on the upper side as the rotation axis, When only the baking racks constituting adjacent baking units are observed vertically upward from the bottom, the bridges of the baking racks are arranged so that they do not completely overlap. The firing unit laminate according to (1), (3) In at least some of the adjacent baking units, the baking racks constituting the baking units each have the same rectangular outer shape, The openings defined by the frame and the bridge portion of the baking rack have different pattern shapes when the baking rack is turned upside down and the front and back surfaces are reversed, In the adjacent baking units, the baking rack constituting the baking unit arranged on the lower side is arranged in a state where the baking rack constituting the baking unit arranged on the upper side is turned upside down, When only the baking racks constituting adjacent baking units are observed vertically upward from the bottom, the bridges of the baking racks are arranged so that they do not completely overlap. The firing unit laminate according to (1), (4) The baking racks constituting the baking unit each have the following formula (II): Cross-linked area ratio (%) = (area of the cross-linked part constituting the baking rack / inner area of the frame constituting the baking rack) × 100 (II) The crosslinked area ratio calculated by is 1 to 40%. The firing unit laminate according to any one of (1) to (3) above, (5) The baking racks constituting the baking unit each have the following formula (III): Crosslinked portion width ratio (%) = (average width of crosslinked portion / longitudinal length of baking rack) × 100 (III) The crosslinked portion width ratio calculated by is 1 to 10% The firing unit laminate according to any one of (1) to (4) above, (6) The baking unit laminate according to any one of (1) to (5), wherein the baking racks constituting the baking unit each have a thickness of 2 mm to 4 mm and a width of 2 mm to 8 mm at the cross-linked portion. (7) The baking racks constituting the baking unit are each made of the following materials: (i) The SiC is made of pressureless sintered SiC with a purity of 99% by mass or more, (ii) a bulk specific gravity of 3.10 or more; (iii) open porosity of 1% or less; (iv) A three-point bending strength according to JIS R 1601 of 450 MPa or more; and (v) Thermal shock resistance according to JIS R 1648:R2002 is 400°C or higher The firing unit laminate according to any one of (1) to (6) above, which satisfies one or more conditions selected from the following: (8) A firing method comprising firing an object to be fired in a firing furnace using the firing unit laminate according to any one of (1) to (7) above. This provides: [Effects of the Invention]

[0015] According to the present invention, in a plurality of stacked firing units, when the firing racks constituting adjacent firing units are observed vertically upward from the bottom, the cross-linking area overlap ratio, which is an indicator of the degree of overlap of the cross-linking portions provided on the firing racks, is reduced. This promotes the flow of furnace gas that rises from the bottom to the top of the furnace during firing, and therefore makes it possible to provide a firing unit stack that can uniformly and efficiently bake the material to be fired, as well as a firing method using such a firing unit stack. [Brief explanation of the drawings]

[0016] [Figure 1] 1A and 1B are diagrams showing examples of the configuration of a firing unit constituting a firing unit laminate according to the present invention. [Figure 2] FIG. 1 is a diagram (top view) schematically showing an example of the shape of a baking rack that can be used in the present invention. [Figure 3] FIG. 1 is a diagram (top view) schematically showing an example of the shape of a baking rack that can be used in the present invention. [Figure 4] 1 is a diagram showing a schematic diagram of an example of a baking rack that can be used in the present invention. FIG. [Figure 5] 1 is a diagram showing a schematic diagram of an example of a baking rack that can be used in the present invention. FIG. [Figure 6] FIG. 10 is a diagram for explaining a method for calculating the crosslinked area ratio (%) of a baking rack. [Figure 7]10A and 10B are diagrams for explaining examples of the configuration of a bridging portion of a baking rack. [Figure 8] 10A and 10B are diagrams for explaining examples of the configuration of a support part of a baking rack. [Figure 9] 1A and 1B are diagrams illustrating examples of the shape of a mesh-shaped setter that can be used in the present invention. [Figure 10] 1A and 1B are diagrams showing examples of firing unit laminates according to the present invention; [Figure 11] FIG. 10 is a diagram for explaining a method for calculating the crosslinking area overlap ratio when only the baking racks constituting adjacent baking units are observed vertically upward from the lower side. [Figure 12] 1 is a diagram for explaining a firing mechanism using a firing unit laminate according to the present invention. FIG. [Figure 13-1] 1 is a diagram showing a schematic view of the shape of the baking rack used in the examples of the present invention and the shape of only the baking rack constituting the adjacent baking unit when viewed vertically upward from the bottom side. FIG. [Figure 13-2] FIG. 2 is a perspective view of only the baking rack r constituting each baking unit in the baking unit stack produced in an example of the present invention, observed obliquely from above. [Figure 14-1] 1 is a diagram showing a schematic view of the shape of the baking rack used in the examples of the present invention and the shape of only the baking rack constituting the adjacent baking unit when viewed vertically upward from the bottom side. FIG. [Figure 14-2] FIG. 2 is a perspective view of only the baking rack r constituting each baking unit in the baking unit stack produced in an example of the present invention, observed obliquely from above. [Figure 15] FIG. 1 is a diagram showing a schematic view of the shape of a baking rack used in a comparative example of the present invention and the shape of only a baking rack constituting an adjacent baking unit. [Figure 16] FIG. 10 is a diagram showing an example of the configuration of a firing unit constituting a conventional firing unit laminate. [Figure 17] FIG. 10 is a diagram showing an example of the configuration of a conventional firing unit laminate. [Figure 18] 10A and 10B are diagrams for explaining a firing mechanism using a conventional firing unit stack. DETAILED DESCRIPTION OF THE INVENTION

[0017] First, the firing unit laminate according to the present invention will be described. The baking unit stack according to the present invention is formed by stacking a plurality of baking units, Each of the plurality of baking units has a baking rack and a mesh setter placed on the baking rack, The baking rack has a frame and a bridge portion provided within the frame, When only the baking racks constituting the adjacent baking units are observed vertically upward from the bottom side, the following formula (I) Cross-linking area overlap ratio (%) = (overlapping area of the cross-linking area of the lower baking rack and the cross-linking area and frame of the upper baking rack / area of the cross-linking area of the lower baking rack) × 100 (I) The firing units are stacked so that the cross-linking area overlap ratio calculated by is 0 to 80%. It is characterized by the following.

[0018] FIG. 1 is a diagram showing a schematic diagram of an example of a firing unit constituting the firing unit laminate according to the present invention. As shown in FIG. 1, a baking unit U constituting the baking unit stack according to the present invention has a baking rack r and a mesh-like setter s placed on the baking rack r.

[0019] FIG. 2 is a top view of the baking rack r illustrated in FIG. As shown in FIG. 2, in the baking unit stack according to the present invention, the baking rack r has a frame f and a bridging portion b provided inside the frame f.

[0020] As illustrated in Figure 2, in the baking unit stack of the present invention, the frame body f defines the outer peripheral shape of the baking rack r, and the bridging portion b is provided within the frame body so as to connect the frame materials that make up the frame body f, and defines a predetermined opening pattern within the frame body.

[0021] In the baking rack r illustrated in Figure 2, the outer shape of the frame body f is approximately rectangular, and it is preferable that the outer shape of the frame body f is rectangular, particularly approximately square or approximately rectangular, but it may also be elliptical or circular, and the shape is not particularly limited.

[0022] 3(a) to 3(e) are top views showing other examples of the baking rack r that can be used in the baking unit stack according to the present invention. Each baking rack r illustrated in Figures 3(a) to 3(e) also has a roughly rectangular frame body f and a bridging portion b provided inside the frame body f, and this bridging portion b defines a predetermined opening pattern inside the frame body f.

[0023] As illustrated in Figures 2 and 3(a) to 3(e), the baking rack r used in the baking unit stack of the present invention has an opening in the frame f, which allows the furnace gas to easily flow through the opening when the baking object is being baked, thereby enabling the baking object to be effectively baked.

[0024] As illustrated in Figures 2 and 3(a) to 3(e), the baking rack used in the baking unit stack of the present invention preferably has a trifurcated cross-section to form an approximately T-shaped intersection. In the baking unit stack of the present invention, by using a baking rack in which the bridging portions intersect in a triangular shape to form an intersection, when the baking object is baked, the gas inside the furnace is more likely to diffuse at the intersection, making it easier to bake the baking object uniformly.

[0025] In the baking unit stack of the present invention, the baking racks constituting each baking unit may have different shapes defined by the frame body and the bridging portion, or they may have the same shape.

[0026] In at least some of the adjacent baking units that make up the baking unit stack of the present invention, when the baking racks that make up each baking unit have the same external shape, it is preferable that the baking racks have the same rectangular external shape (i.e., oblong or square) and have a shape that is not rotationally symmetric when rotated 90° or 180° clockwise around a vertical axis passing through the center of the top surface of the baking rack as the rotation axis.

[0027] FIG. 4(a) is a view corresponding to FIG. 2, and shows a top view of the rectangular baking rack r exemplified in FIG. On the other hand, Figure 4(b) shows a top view of the baking rack r when rotated 90° clockwise around a vertical axis passing through the center c of the top surface of the baking rack r shown in Figure 4(a). The baking rack shown in Figure 4(a) and the baking rack r shown in Figure 4(b) are identical, but when the baking rack r is rotated 90 degrees clockwise around a vertical axis passing through the center c of the top surface as the rotation axis, the opening shape defined by the frame f and bridging portion b of the baking rack does not match before and after the rotation, and for this reason the baking rack shown in Figure 4 is not rotationally symmetric between the state shown in Figure 4(a) and the state shown in Figure 4(b).

[0028] FIG. 5(a) shows a top view of a rectangular baking rack r as another example of a baking rack that can be used in the baking unit stack according to the present invention. Also, Figure 5(b) shows a top view of the baking rack r when rotated 90° clockwise around a vertical axis passing through the center c of the top surface of the baking rack r shown in Figure 5(a). The baking rack shown in Figure 5(a) and the baking rack r shown in Figure 5(b) are the same, but when the baking rack r is rotated 90 degrees clockwise around a vertical axis passing through the center c of the top surface as the rotation axis, the opening shape defined by the frame f and bridging portion b of the baking rack does not match before and after the rotation, and for this reason the baking rack shown in Figure 5 is not rotationally symmetric between the state shown in Figure 5(a) and the state shown in Figure 5(b). Similarly, Figure 5(c) shows a top view of the baking rack r when rotated 180° clockwise around a vertical axis passing through the center c of the top surface of the baking rack r shown in Figure 5(a). The baking rack shown in Figure 5(a) and the baking rack r shown in Figure 5(c) are identical, but when the baking rack r is rotated 180 degrees clockwise around a vertical axis passing through the center c of the top surface as the rotation axis, the opening shape defined by the frame f and bridging portion b of the baking rack does not match before and after the rotation, and for this reason the baking rack shown in Figure 5 is not rotationally symmetric between the state shown in Figure 5(a) and the state shown in Figure 5(c).

[0029] In this way, baking racks are used that have a rectangular outer shape and do not exhibit rotational symmetry when rotated 90° or 180° clockwise around a vertical axis passing through the center of the top surface of the baking rack.By arranging them as baking racks for adjacent baking units in the pre- and post-rotation states, even though baking racks of the same shape are used, it is possible to install them so that the bridging portions of each baking rack do not completely overlap when only the baking racks that make up adjacent baking units are observed vertically upward from below, as described below.

[0030] On the other hand, for example, the conventional baking rack r shown in Figure 18(a) has a rectangular outer shape, but the opening defined by the frame and bridging portion of the baking rack exhibits rotational symmetry, meaning that when rotated 90° clockwise around a vertical axis passing through the center c of the top surface of the baking rack r as the rotation axis, the opening remains the same shape as before rotation, whether it is rotated 90° clockwise or 180° clockwise. Therefore, if the conventional baking rack r shown in Figure 18(a) is used as each baking rack that makes up the baking unit stack, even if they are arranged as baking racks for adjacent baking units in the pre- and post-rotation states, when only the baking racks that make up the adjacent baking units are observed vertically upward from the bottom, the bridging portions of each baking rack will completely overlap, and the baking unit stack of the present invention cannot be formed.

[0031] In at least some of the adjacent baking units that make up the baking unit stack of the present invention, when the baking racks that make up each baking unit have the same shape, it is preferable that the baking racks have the same rectangular outer shape, and that the openings defined by the frame and bridging portion of the baking rack have different pattern shapes (different opening shapes) when the baking rack is turned over and the front and back surfaces are reversed.

[0032] FIG. 4(c) shows a top view of the rectangular baking rack r shown in FIG. 4(a) when it is turned upside down and the front and back surfaces are reversed. The baking rack shown in Figure 4(a) and the baking rack r shown in Figure 4(c) are identical, but by arranging the baking rack r as the baking rack of adjacent baking units in the state before flipping (Figure 4(a)) and the state after flipping (Figure 4(c)), as described below, it is possible to install the baking racks so that the bridging portions b of each baking rack do not completely overlap when observing only the baking racks that make up adjacent baking units vertically upward from the bottom side.

[0033] On the other hand, for example, even if the conventional baking rack r shown in Figure 18(a) is turned upside down and the front and back sides are reversed, the openings defined by the frame and bridging portions of the baking rack have the same pattern shape (same opening shape) before and after turning it over. Therefore, if the conventional baking rack r shown in Figure 18(a) is used as each baking rack that makes up the baking unit stack, even if they are arranged as baking racks for adjacent baking units before and after being flipped, when only the baking racks that make up adjacent baking units are observed vertically upward from the bottom, the bridging portions of each baking rack will completely overlap, and the baking unit stack of the present invention cannot be formed.

[0034] In the baking unit stack according to the present invention, the baking racks constituting each baking unit are each represented by the following formula (II): Cross-linked area ratio (%) = (area of the cross-linked part constituting the baking rack / inner area of the frame constituting the baking rack) × 100 (II) The crosslinked area ratio calculated by the above formula is preferably 1 to 40%, more preferably 1 to 30%, and even more preferably 1 to 20%.

[0035] FIG. 6 shows a top view of the baking rack r corresponding to FIG. 2, and the area of the shaded portion in FIG. 6(a) is the area S of the cross-linked portion b. b The area of the shaded portion in FIG. 6(b) is the inner area S of the frame f that constitutes the baking rack r. i is equivalent to Therefore, in the baking rack r shown in Figure 6, the cross-linked area ratio (%) is (S b / S i ) × 100.

[0036] In this application document, the inner area of the frame that constitutes the baking rack used when calculating the crosslinked area ratio means the inner area of the outline of the opening defined when an exterior line is drawn around the frame, assuming that the baking rack does not have a crosslinked portion. In the example shown in FIG. 6, the area inside the frame body f constituting the baking rack r is determined by drawing an exterior line L1 (shown by a thick line in the figure) on the frame body f assuming that the baking rack r shown in FIG. 6(a) does not have the bridge portion b, and is calculated by multiplying the area S inside the outline of the opening shown in FIG. 6(b). iis equivalent to

[0037] In addition, in the present application documents, the area of the cross-linked portion constituting the baking rack used when calculating the cross-linked portion area ratio means the area of the cross-linked portion defined within the frame when the above-mentioned exterior wire is drawn within the frame. In the example shown in FIG. 6, the area of the bridge portion b constituting the baking rack r is calculated by drawing an extrapolation line L1 (shown by a thick line in the figure) on the baking rack r shown in FIG. 6(a), and then subtracting the area S of the bridge portion b defined within the frame f. b is equivalent to

[0038] In the baking unit stack of the present invention, since the cross-linking area ratio in the baking racks constituting each baking unit is within the above range, the material to be baked can be baked homogeneously and efficiently without interfering with the flow of gas inside the furnace during baking.

[0039] In the baking unit stack according to the present invention, the baking racks constituting each baking unit are each represented by the following formula (III): Crosslinked portion width ratio (%) = (average width of crosslinked portion / longitudinal length of baking rack) × 100 (III) The crosslinked portion width ratio calculated by the above formula is preferably 1 to 10%, more preferably 2 to 8%, and even more preferably 2 to 6%.

[0040] FIG. 7(a) shows a top view of the baking rack r corresponding to FIG. 2. In FIG. 7(a), the width W b Since the width of the crosslinked portion can be considered uniform in the longitudinal direction of the crosslinked portion, this can be taken as the average width of the crosslinked portion. In addition, since the length of the baking rack in the vertical and horizontal directions is the same in FIG. 7(a), the horizontal length can be taken as the longitudinal length W of the baking rack. all It can be said that: Therefore, in the baking rack r shown in FIG. 7(a), the crosslinked portion width ratio (%) is (W b / W all ) × 100.

[0041] In the baking unit stack of the present invention, by having the cross-linking portion width ratio in the baking racks constituting each baking unit within the above range, the material to be baked can be baked homogeneously and efficiently without interfering with the flow of gas inside the furnace during baking.

[0042] In the baking unit stack according to the present invention, the baking rack constituting each baking unit preferably has a width of the crosslinked portion of 2 mm to 8 mm, more preferably 2 mm to 6 mm, and even more preferably 2 mm to 4 mm. In the example shown in FIG. 7(a), the width W b corresponds to the width of the bridge portion b.

[0043] In the baking unit stack of the present invention, by having the width of the cross-linking portion in the baking rack that constitutes each baking unit within the above range, the material to be baked can be baked homogeneously and efficiently without interfering with the flow of gas inside the furnace during baking.

[0044] In the baking unit stack of the present invention, the thickness of the cross-linked portion of the baking rack constituting each baking unit is preferably 2 mm to 8 mm, more preferably 2 mm to 6 mm, and even more preferably 2 mm to 4 mm.

[0045] In the baking unit stack of the present invention, the baking racks constituting each baking unit have a thickness of the cross-linking portion within the above range, so that they have sufficient handling strength during and after baking and can effectively improve thermal efficiency during baking.

[0046] FIG. 7(b) is a diagram showing a cross section of the baking rack r shown in FIG. 7(a) taken along line YY', and the width T in the diagram corresponds to the thickness of the crosslinked portion b.

[0047] In the baking unit stack according to the present invention, it is preferable that the baking rack constituting each baking unit has a cross section perpendicular to the longitudinal direction of the cross-linking portion that is generally oval.

[0048] FIG. 7(c) is an enlarged view of the cross section of the cross-linked portion b taken along line XX' in the baking rack r shown in FIG. 7(a). It can be seen that the cross section of the cross-linked portion b of the baking rack r shown in FIG. 7(c) has a generally oval cross section perpendicular to the longitudinal direction.

[0049] In the firing unit stack of the present invention, the cross-sectional shape of the bridging part of the firing rack is roughly oval, and as shown in Figure 7(c), both ends are rounded.When a mesh-shaped setter is placed on the firing rack, the area of contact between the bridging part and the setter can be reduced compared to a bridging part with a square cross-sectional shape.As a result, the material to be fired can be easily fired uniformly and efficiently without interfering with the flow of gas inside the furnace during firing.

[0050] In the baking unit stack according to the present invention, the baking rack comprises: (i) The SiC is made of pressureless sintered SiC with a purity of 99% by mass or more, (ii) a bulk specific gravity of 3.10 or more; (iii) open porosity of 1% or less; (iv) A three-point bending strength according to JIS R 1601 of 450 MPa or more; and (v) Thermal shock resistance according to JIS R 1648:R2002 is 400°C or higher It is preferable that the material satisfies one or more conditions selected from the following:

[0051] In the baking unit stack of the present invention, the baking rack satisfies one or more conditions selected from (i), (iv), and (v) above, so that damage to the baking rack due to thermal shock can be easily suppressed when baking the object to be treated.

[0052] Furthermore, in the baking unit stack of the present invention, the baking rack satisfies one or more conditions selected from (i), (ii), and (iii) above, so that the mass and heat capacity of the baking rack are reduced, making it possible to easily bake the object to be treated while saving energy.

[0053] In the firing unit stack of the present invention, since the firing rack satisfies one or more conditions selected from the above (i) to (v), it can be suitably used in place of the ceramic firing racks that have been conventionally used, particularly during firing treatment in a continuous heat treatment furnace where improved productivity is required, rapid heating treatment or rapid cooling treatment is required, or an increased load capacity of the material to be fired is required.

[0054] In the baking unit stack according to the present invention, the baking rack preferably has a support portion. The form of the support portion is not particularly limited as long as it can separate the frames of the baking racks from each other.

[0055] 8(a) to 8(d) each show an example of the form of a baking rack r having a support portion l.

[0056] Figure 8(a) is a diagram showing an example of a baking rack r in which support parts (leg parts) l are provided on the underside of the frame body f, Figure 8(b) is a diagram showing an example of a baking rack r in which support parts (arm parts) l are provided on the upper side of the frame body f, Figure 8(c) is a diagram showing an example of a baking rack r in which rib-shaped support parts l are provided on the underside of the frame body f, and Figure 8(d) is a diagram showing an example of a baking rack r in which rib-shaped support parts l are provided on the upper side of the frame body f.

[0057] In the firing unit stack of the present invention, the firing rack has a support portion, so that the frame bodies f of the firing racks r that make up each firing unit can be spaced apart, and when the firing units are stacked to form a stack, furnace gas can be effectively circulated between each firing unit.

[0058] In the baking unit stack according to the present invention, each baking unit has a baking rack and a mesh setter placed on the baking rack.

[0059] In the firing unit laminate according to the present invention, the setter is made of a mesh-like material, that is, a net-like material in which a plurality of linear members intersect.

[0060] In this application document, a mesh-like object in which multiple linear members intersect means a lattice-like element formed by multiple first linear members arranged in parallel in one direction and multiple second linear members arranged in parallel in a direction intersecting the first linear members. In the firing unit laminate of the present invention, the mesh-like material may be formed by fixing and integrating the first linear member and the second linear member at the intersection of the first linear member and the second linear member, or by interweaving the first linear member and the second linear member in a mesh-like manner, with the first linear member and the second linear member moving up and down alternately.

[0061] An example of a mesh-like material in which linear members are woven alternately up and down to form a net is shown in Figures 9(a) and 9(b), in which vertical and horizontal lines each made of linear members are woven alternately up and down while maintaining a certain distance between them. Figure 9(a) shows an example of plain weave (a net-like weave in which warp and weft lines are alternately crossed one by one at a time, maintaining a fixed distance), and Figure 9(b) shows an example of twill weave (a net-like weave in which multiple warp and weft lines are alternately crossed one by one at a time, maintaining a fixed distance).

[0062] The grid-shaped pattern formed by intersecting the linear members may be a square (as exemplified in Figures 9(a) and 9(b)), as well as a rectangular, diamond, or other quadrangular shape, with a square shape being preferred.

[0063] In the firing unit laminate of the present invention, the linear members constituting the mesh-like material, the spacing between the linear members in the mesh-like material, the size of the mesh-like material, etc. can be appropriately selected within a range that can achieve the object of the present invention.

[0064] In the firing unit laminate of the present invention, it is preferable that at least the surface of the mesh-shaped setter is formed from a heat-resistant material that can melt during the firing process and adhere to the fired object or suppress reaction with the fired object.

[0065] In the firing unit laminate of the present invention, the mesh-shaped setter may be formed entirely from a heat-resistant material, or may have a coating layer of a heat-resistant material formed on the surface of the base material.

[0066] According to the firing unit laminate of the present invention, the setter is made of a mesh-like material, and therefore, compared to conventional plate-shaped setters, it can effectively promote the circulation of furnace gas that is generated during firing and rises from the lower side to the upper side of the furnace. In addition, the contact area with the object to be fired is reduced, thereby suppressing fusion and reaction between the two, and the heat capacity is reduced, thereby reducing the amount of energy used during firing processing in the firing chamber.

[0067] As shown in FIG. 1, in the baking unit stack according to the present invention, the baking unit U has a baking rack r and a mesh-like setter s placed on the baking rack r. As shown in Figure 10, the baking unit stack of the present invention is made up of multiple stacked baking units, each having the baking rack r and a mesh-like setter s placed on the baking rack r.

[0068] The baking unit stack according to the present invention has a structure in which, when only the baking racks constituting the adjacent baking units are observed vertically upward from the lower side, a temperature of the baking unit stack satisfies the following formula (I): Cross-linking area overlap ratio (%) = (overlapping area of the cross-linking area of the lower baking rack and the cross-linking area and frame of the upper baking rack / area of the cross-linking area of the lower baking rack) × 100 (I) The firing units are stacked so that the crosslinked area overlap ratio calculated by the above formula is 0 to 80%.

[0069] FIG. 11 is a diagram for explaining a method for calculating the crosslinking area overlap ratio when only the baking racks constituting adjacent baking units are observed vertically upward from the lower side.

[0070] Figures 11(a) and 11(b) show a bottom view of the upper baking rack r (Figure 11(a)) and a bottom view of the lower baking rack r' (Figure 11(b)), when only the baking racks constituting adjacent baking units are observed vertically upward from the bottom side, in an example of the baking unit stack of the present invention. In this case, when only the two baking racks r and r' are observed vertically upward from below, the bridges b and b' of both racks appear to partially overlap, as shown in FIG. 11(c).

[0071] In this case, the area A1 of the shaded portion in FIG. 11(d) corresponds to the area of the bridge portion b' of the baking rack r' located below. In addition, the area A2 of the shaded portion in Figure 11(e) indicates the area of the overlapping portion between the bridging portion b' of the baking rack r' located at the lower side and the bridging portion b and frame of the baking rack r located at the upper side (in the example shown in Figure 11, only the bridging portion b' of the baking rack r' located at the lower side and the bridging portion b of the baking rack r located at the upper side overlap, so area A2 indicates the area of the overlapping portion between the two bridging portions).

[0072] In the present application, the area of the bridge portion of the baking rack located at the bottom (area A1 in the example shown in Figure 11(d)) can be calculated in the same manner as the method for calculating the area of the bridge portion constituting the baking rack when calculating the bridge portion area ratio described above. Furthermore, in the present application documents, the area where the bridge portion of the lower baking rack overlaps with the bridge portion and frame of the upper baking rack (area A2 in the example shown in Figure 11(e)) can be calculated by determining the area of the portion of the bridge portion of the lower baking rack obtained by the above method that overlaps with the bridge portion and frame of the upper baking rack.

[0073] In the example shown in FIG. 11, the cross-linked area overlap ratio (%) is: (Area A2 where the bridge portion b' of the lower baking rack r' and the bridge portion b of the upper baking rack overlap / Area A1 of the bridge portion b' of the lower baking rack) × 100 It is calculated as follows.

[0074] In the baking unit laminate of the present invention, when only the baking racks constituting adjacent baking units are observed vertically upward from the bottom side, the crosslinking area overlap ratio calculated by the above formula (I) is 0 to 80%, preferably 1 to 45%, and more preferably 1 to 10%.

[0075] In each firing unit constituting the firing unit stack of the present invention, the cross-linking area overlap ratio in relation to adjacent firing units needs to be within the above-mentioned specified range, and as long as it is within the above-mentioned specified range, the cross-linking area overlap ratio calculated for each firing unit in relation to the adjacent firing unit may be the same or different.

[0076] As described above, in conventional baking unit stacks, when only the baking racks that make up adjacent baking units are observed vertically upward from the bottom, the baking racks are arranged so that their frames and bridging portions completely overlap each other.Therefore, when only adjacent baking racks are observed, when the in-furnace gas flow rises from the bottom to the top of the furnace, the in-furnace gas rises without coming into contact with any of the locations where the bridging portions that define the opening pattern of each baking rack are provided.As a result, air permeability is reduced, especially in the baking units stacked at the top, and the contact efficiency between the in-furnace gas flow and the baked material is reduced.

[0077] On the other hand, in the firing unit stack of the present invention, when the firing racks of adjacent firing units are observed vertically upward from the bottom, the firing racks are selected and arranged so that the bridging portions that define the opening pattern of each firing rack do not completely overlap, thereby promoting the circulation of furnace gases that are generated during firing and rise from the bottom to the top of the furnace.

[0078] In the baking unit stack of the present invention, it is preferable to select and arrange baking racks such as those shown below as the baking racks that constitute the adjacent baking units in at least some of the adjacent baking units. (1) Baking racks having different opening patterns are arranged as the baking racks of adjacent baking units. (2) (As illustrated in Figures 4(a) and 4(b)) A baking rack with a rectangular outer shape is used, which has a shape that is not rotationally symmetric when rotated 90° or 180° clockwise around a vertical axis passing through the center of the top surface as the rotation axis, and is arranged as the baking rack of adjacent baking units before and after the rotation. (3) (As illustrated in Figures 4(a) and 4(c)), a baking rack having a rectangular outer shape is used, so that when the baking rack is turned upside down and the front and back sides are reversed, the pattern shape formed by the crosslinking portion within the frame body will be different, and the baking racks are arranged in the states before and after the turning over as the baking racks of adjacent baking units.

[0079] FIG. 12(a) is a diagram showing an example of a baking rack r that can be used in the baking unit stack according to the present invention, corresponding to the diagram shown in FIG. 4(a). When the baking rack r shown in Figure 12(a) is turned upside down (as shown in Figure 4(c)) and the front and back surfaces are reversed, the pattern shape formed by the crosslinking portions within the frame body becomes a different crosslinking portion pattern shape. In one example of a baking unit stack according to the present invention, the baking racks of adjacent baking units have the shape shown in Figure 12(a), and as shown in Figure 12(b), inverted and non-inverted baking units are arranged alternately in the adjacent baking units. In this case, when observing only the firing racks r that constitute adjacent firing units, as shown in the oblique view in Figure 12(b) and the side cross-sectional view in Figure 12(c) (a side cross-sectional view when cut vertically along line Z-Z' in Figure 12(b)), the bridge portions of adjacent firing racks do not completely overlap, and the bridge portion area overlap ratio, which indicates the degree of overlap of the bridge portions provided on the firing racks, is reduced, thereby promoting the circulation of the in-furnace gas flow F that rises from the lower side to the upper side of the furnace during firing (as shown by the arrow in the figure).

[0080] The kiln (firing furnace) for firing the firing unit laminate according to the present invention is not particularly limited, but examples thereof include a roller hearth furnace and a tunnel furnace. By adopting a roller hearth furnace or a tunnel furnace as the kiln (firing furnace) for firing the firing unit laminate of the present invention, multiple firing unit laminates can be moved on multiple rollers installed in the furnace, or placed on a base plate and moved within the furnace, thereby allowing multiple items to be fired (objects to be fired) to be fired simultaneously.

[0081] According to the present invention, it is possible to provide a firing unit laminate that can uniformly and efficiently fire an object to be fired.

[0082] Next, the firing method according to the present invention will be described. The firing method according to the present invention is characterized in that an object to be fired is fired in a firing furnace using the firing unit laminate according to the present invention.

[0083] The details of the firing unit laminate according to the present invention are as described above.

[0084] In the firing method according to the present invention, the temperature at which the object to be fired is fired may be set appropriately depending on the object to be fired and is not particularly limited, but is suitably 800 to 1400°C, and more suitably 1000 to 1300°C.

[0085] In the firing method according to the present invention, the firing time for firing the object to be fired may be set appropriately depending on the object to be fired and is not particularly limited, but is suitably 0.5 to 20 hours, more suitably 2 to 5 hours.

[0086] According to the present invention, by using the baking unit laminate of the present invention, the baking object can be baked uniformly and efficiently.

[0087] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples in any way.

[0088] (Example 1) <Example in which baking racks are alternately arranged upside down in adjacent baking units> (1) Baking rack The baking rack used was a rectangular (square) rack measuring 170 mm in length and 170 mm in width, the bottom view of which is shown in Figure 13-1(a). As shown in FIG. 13-1(a), the baking rack r used in this example has a frame f and a bridge portion b provided inside the frame f. FIG. 13-1(b) shows a bottom view of the rectangular baking rack r shown in FIG. 13-1(a) when it is turned upside down and the front and back surfaces are reversed. As shown in Figures 13-1(a) and 13-1(b), the baking rack r used in this example has an opening defined by the frame body f and bridging portion b of the baking rack that has a different pattern shape when turned upside down with the front and back sides reversed. The firing rack r used in this example was (i) made of atmospheric sintered SiC plate material with a SiC purity of 99% by mass or more, and this atmospheric sintered SiC plate material had (ii) a bulk specific gravity of 3.10, (iii) an open porosity of 1% or less, (iv) a three-point bending strength according to JIS R 1601 of 450 MPa, and (v) a thermal shock resistance strength according to JIS R 1648:R2002 of 400°C. In addition, the baking rack r used in this example had a uniform width of 5 mm for the cross-linked portion and 14 mm for the frame, and the cross-linked portion area ratio calculated by formula (II) was 11%, the cross-linked portion width ratio calculated by formula (III) was 3%, the cross-linked portion thickness was 3 mm, and the frame thickness was 3 mm.

[0089] (2) Setter A mesh-type setter measuring 150 mm in length and 150 mm in width was prepared. The mesh setter is made up of a plurality of nickel wires arranged in parallel in one direction as first linear members, and a plurality of nickel wires arranged in parallel as second linear members in a direction perpendicular to the first linear members, and is made up of a plain weave fabric in which the first linear members and the second linear members are woven alternately up and down at the intersections of the two linear members in a mesh-like pattern.

[0090] (3) Firing unit laminate Ten sets of baking units were formed by placing the mesh setters on the baking racks. At this time, five sets of the mesh-shaped setter (baking unit a) were formed on the upper surface of the baking rack r shown in Figure 13-1 (a), and Five sets were formed, each of which had the mesh-like setter placed on the upper surface of the baking rack r shown in Figure 13-1(b) (the baking rack r shown in Figure 13-1(a) was turned upside down and the mesh-like setter placed on its main surface (baking unit b)). Then, by stacking each baking unit vertically so that the baking units a and b were alternately adjacent to each other (by arranging the baking racks so that the cross-linked portions of each baking rack do not completely overlap when only the baking racks constituting adjacent baking units are observed vertically upward from the bottom side), a baking unit stack was formed. At this time, the firing units were spaced 10 mm apart by placing cylindrical spacers made of SiC at the four corners of each firing unit, each measuring 8 mm in diameter and 10 mm in height, and having the following characteristics: (i) made of atmospheric sintered SiC with a SiC purity of 99% by mass or more, (ii) a bulk specific gravity of 3.10 or more, (iii) an open porosity of 1% or less, (iv) a three-point bending strength according to JIS R 1601 of 450 MPa or more, and (v) a thermal shock resistance strength according to JIS R 1648:R2002 of 400°C or more. Figure 13-2 is a perspective view of only the baking rack r constituting each baking unit in the baking unit stack produced in this example, in which baking units a and baking units b are stacked vertically so that they are alternately adjacent to each other, as observed from diagonally above. As shown in Figure 13-2, when only the firing racks that make up adjacent firing units are observed vertically upward from the bottom, the bridge portions of adjacent firing racks r do not completely overlap, and the bridge portion area overlap ratio, which indicates the degree of overlap of the bridge portions provided on the firing racks, is reduced, thereby promoting the circulation of the in-furnace gas flow F that rises from the bottom to the top of the furnace during firing (as shown by the arrow in the figure). In this case, when the baking rack r constituting the adjacent baking unit a and the baking rack r constituting the adjacent baking unit b are observed vertically upward from the bottom side in the baking unit stack, the bridge portions b, b of the two are observed to partially overlap, as shown in Figure 13-1(c). In this case, the area of the colored portion in Figure 13-1(c) indicates the area of the overlapping portion between the bridge portion b of the baking rack r constituting the lower baking unit b and the bridge portion b and frame of the baking rack r constituting the upper baking unit a (in the example shown in Figure 13, only the bridge portion b of the lower baking rack r and the bridge portion b of the upper baking rack r overlap, so the colored portion in Figure 13-1(c) corresponds to the area of the overlapping portion between the bridge portions of the baking racks r, r constituting the adjacent baking units a and b). In the baking unit stack, when only the baking racks constituting the adjacent baking units are observed vertically upward from the lower side, the following formula (I) Cross-linking area overlap ratio (%) = (overlapping area of the cross-linking area of the lower baking rack and the cross-linking area and frame of the upper baking rack / area of the cross-linking area of the lower baking rack) × 100 (I) The cross-linked area overlap ratios calculated by the above formula were all 67% (the cross-linked area overlap ratios defined between the lower and upper rows, such as the cross-linked area overlap ratios between the first and second rows, and the cross-linked area overlap ratios between the second and third rows, were all 67%).

[0091] (4) Firing treatment In the firing unit laminate obtained in (3) above, 200 multilayer ceramic capacitors were placed on the setter of each firing unit as the objects to be fired. The firing unit stack with the above-mentioned materials to be fired placed on a base plate was placed on the base plate and fired at 1200°C for 2 hours while moving through the tunnel furnace (in the furnace travel direction shown in Figure 13-2). At this time, the yield of the fired products in the first, fifth and tenth firing unit laminates that constitute the firing unit laminate was calculated using the following formula. The results are shown in Table 1. Good product rate (%) = {(Number of good products per layer) / (Number of baked items placed per layer)} x 100 The quality of the product was judged according to the following criteria. Good: No cracks or discoloration are visible when visually inspected. Defective product: When visually inspected, cracks or discoloration are observed.

[0092] Example 2: An example in which the baking racks of adjacent baking units are rotated 90° clockwise around a vertical axis passing through the center of their top surfaces. (1) Baking rack A baking rack with a rectangular (square) outer shape measuring 170 mm in length and 170 mm in width was prepared, as shown in the bottom view of Figure 14-1(a). As shown in FIG. 14-1(a), the baking rack r used in this example has a frame f and a bridge portion b provided inside the frame f. FIG. 14-1(b) shows a bottom view of the rectangular baking rack r shown in FIG. 14-1(a) rotated 90° clockwise around a vertical axis passing through the center of the top surface of the rack. As shown in Figures 14-1(a) and 14-1(b), the baking rack r used in this example has an opening defined by the frame body f and bridging portion b of the baking rack, which has a different pattern shape when rotated 90° clockwise around a vertical axis passing through the center of the top surface of the baking rack r. The firing rack r used in this example was (i) made of atmospheric sintered SiC plate material with a SiC purity of 99% by mass or more, and this atmospheric sintered SiC plate material had (ii) a bulk specific gravity of 3.10, (iii) an open porosity of 1% or less, (iv) a three-point bending strength according to JIS R 1601 of 450 MPa, and (v) a thermal shock resistance strength according to JIS R 1648:R2002 of 400°C. In addition, the baking rack r used in this example had a uniform width of 5 mm for the cross-linked portion and 14 mm for the frame, and the cross-linked portion area ratio calculated by formula (II) was 11%, the cross-linked portion width ratio calculated by formula (III) was 3%, the cross-linked portion thickness was 3 mm, and the frame thickness was 3 mm.

[0093] (2) Setter The same setter as that used in Example 1 was prepared.

[0094] (3) Firing unit laminate Ten sets of baking units were formed by placing the mesh setters on the baking racks. At this time, five sets (baking units a) were formed in which the mesh-like setter was placed on the upper surface of the baking rack r shown in Figure 14-1(a), and five sets (baking units b) in which the mesh-like setter was placed on the upper surface of the baking rack r shown in Figure 14(b) (the baking rack r shown in Figure 14-1(a) was rotated 90° clockwise around a vertical axis passing through the center of its upper surface as the rotation axis). Then, by stacking each baking unit vertically so that the baking units a and b were alternately adjacent to each other (when only the baking racks constituting adjacent baking units were observed vertically upward from the bottom side, each baking rack was rotated 90° around the vertical axis passing through the center of its upper surface as the axis of rotation, and the cross-linked portions of each baking rack were arranged so that they did not completely overlap), a baking unit stack was formed. At this time, the firing units were spaced 10 mm apart by placing cylindrical SiC spacers at the four corners of each firing unit, each spacer having a diameter of 8 mm and a height of 10 mm. The spacers had (i) dimensions of atmospheric sintered SiC with a SiC purity of 99% by mass or more, (ii) a bulk specific gravity of 3.10 or more, (iii) an open porosity of 1% or less, (iv) a three-point bending strength according to JIS R 1601 of 450 MPa or more, and (v) a thermal shock resistance strength according to JIS R 1648:R2002 of 400°C or more. Figure 14-2 is a perspective view of only the baking rack r constituting each baking unit in the baking unit stack produced in this example, in which baking units a and baking units b are stacked vertically so that they are alternately adjacent to each other, as observed from diagonally above. As shown in Figure 14-2, when only the firing racks that make up adjacent firing units are observed vertically upward from the bottom, the bridge portions of adjacent firing racks r do not completely overlap, and the bridge portion area overlap ratio, which indicates the degree of overlap of the bridge portions provided on the firing racks, is reduced, thereby promoting the circulation of the in-furnace gas flow F that rises from the bottom to the top of the furnace during firing (as shown by the arrow in the figure). In this case, when the baking rack r constituting the adjacent baking unit a and the baking rack r constituting the adjacent baking unit b are observed vertically upward from the bottom side in the baking unit stack, the bridge portions b, b of the two are observed to partially overlap, as shown in Figure 14-1(c). In this case, the area of the colored portion in Figure 14-1(c) indicates the area of the overlapping portion between the bridge portion b of the baking rack r constituting the lower baking unit b and the bridge portion b and frame of the baking rack r constituting the upper baking unit a (in the example shown in Figure 14, only the bridge portion b of the lower baking rack r and the bridge portion b of the upper baking rack r overlap, so the colored portion in Figure 14-1(c) corresponds to the area of the overlapping portion between the bridge portions of the baking racks r, r constituting the adjacent baking units a and b). In the baking unit stack, when only the baking racks constituting the adjacent baking units are observed vertically upward from the lower side, the following formula (I) Cross-linking area overlap ratio (%) = (overlapping area of the cross-linking area of the lower baking rack and the cross-linking area and frame of the upper baking rack / area of the cross-linking area of the lower baking rack) × 100 (I) The cross-linked area overlap ratios calculated by the above formula were all 9% (the cross-linked area overlap ratios defined between the lower and upper rows, such as the cross-linked area overlap ratio between the first and second rows, the cross-linked area overlap ratio between the second and third rows, etc., were all 9%).

[0095] (4) Firing treatment In the firing unit laminate obtained in (3) above, 200 multilayer ceramic capacitors were placed on the setter of each firing unit as the objects to be fired. The firing unit stack with the above-mentioned material to be fired placed thereon was placed on a plate and fired at 1200° C. for 2 hours while moving through the tunnel furnace (in the furnace moving direction shown in FIG. 14-2). At this time, the yield rates of the fired products in the first, fifth and tenth firing unit laminates constituting the firing unit laminate were calculated in the same manner as in Example 1. The results are shown in Table 1.

[0096] (Comparative Example 1) <An example of arranging the baking racks so that the bridges of each baking rack completely overlap when observing only the baking racks that make up adjacent baking units vertically upward from the bottom> (1) Baking rack The same baking rack as that used in Example 1 was prepared. That is, a baking rack with a rectangular (square) outer shape measuring 170 mm in length and 170 mm in width was prepared, as shown in a bottom view in FIG. 15(a). As shown in FIG. 15(a), the baking rack r used in this example has a frame f and a bridge portion b provided inside the frame f.

[0097] (2) Setter The same setter as that used in Example 1 was prepared.

[0098] (3) Firing unit laminate Ten sets of baking units were formed by placing the mesh setters on the baking racks. At this time, 10 sets (baking units a) each having the mesh-like setter arranged on one main surface of the baking rack were formed. Then, by stacking each baking unit vertically so that the baking units a were adjacent to each other (by arranging the baking racks so that the cross-linked portions of each baking rack completely overlap when only the baking racks constituting adjacent baking units were observed vertically upward from the bottom side), a baking unit stack was formed. At this time, cylindrical spacers made of silicon carbide were placed at the four corners of each firing unit, each spacer having a diameter of 8 mm and a height of 10 mm, and having (i) atmospheric sintered SiC with a SiC purity of 99% by mass or more, (ii) a bulk specific gravity of 3.10 or more, (iii) an open porosity of 1% or less, (iv) a three-point bending strength according to JIS R 1601 of 450 MPa or more, and (v) a thermal shock resistance strength according to JIS R 1648:R2002 of 400°C or more, so that the firing units were spaced apart by 10 mm. FIG. 15(b) is a perspective view of only the baking rack r constituting each baking unit in the baking unit stack produced in this comparative example, observed obliquely from above. As shown in Figure 15(b), when only the firing racks that make up adjacent firing units are observed vertically upward from the bottom, the bridging portions of adjacent firing racks r completely overlap, which suppresses the flow of furnace gas flow F (indicated by the arrow in the figure) that rises from the bottom to the top of the furnace during firing. In the baking unit stack, when only the baking racks constituting the adjacent baking units are observed vertically upward from the lower side, the following formula (I) Cross-linking area overlap ratio (%) = (overlapping area of the cross-linking area of the lower baking rack and the cross-linking area and frame of the upper baking rack / area of the cross-linking area of the lower baking rack) × 100 (I) The cross-linked area overlap ratios calculated by the above formula were all 100% (the cross-linked area overlap ratios defined between the lower and upper rows, such as the cross-linked area overlap ratio between the first and second rows, the cross-linked area overlap ratio between the second and third rows, etc., were all "100%").

[0099] (4) Firing treatment In the firing unit laminate obtained in (3) above, 200 multilayer ceramic capacitors were placed on the setter of each firing unit as the objects to be fired. The firing unit stack with the above-mentioned material to be fired placed thereon was placed on a plate and fired at 1200°C for 2 hours while moving through the tunnel furnace (in the furnace travel direction shown in Figure 15(b)). At this time, the yield rates of the fired products in the first, fifth and tenth firing unit laminates constituting the firing unit laminate were calculated in the same manner as in Example 1. The results are shown in Table 1.

[0100] [Table 1]

[0101] From Table 1, it can be seen that in Examples 1 and 2, when multiple stacked firing units are used and the firing racks constituting adjacent firing units are observed vertically upward from the bottom, the cross-linking area overlap ratio, which is an indicator of the degree of overlap of the cross-linking sections provided on the firing racks, is suppressed to 0 to 80%, thereby promoting the flow of furnace gas generated during firing and rising from the bottom to the top of the furnace, and therefore enabling the fired materials on the first to tenth tiers to be fired uniformly and efficiently.

[0102] From Table 1, it can be seen that in Comparative Example 1, when multiple stacked firing units are used and the firing racks constituting adjacent firing units are observed vertically upward from the bottom, the cross-linking area overlap ratio, which is an indicator of the degree of overlap of the cross-linking sections provided on the firing racks, is outside the range of 0 to 80% (it is 100%), and therefore the flow of furnace gas generated during firing and rising from the bottom to the top of the furnace is blocked, and as a result, the fired material, especially on the tenth tier, cannot be fired uniformly and efficiently, resulting in a poor yield rate. [Industrial Applicability]

[0103] According to the present invention, it is possible to provide a firing unit laminate that can uniformly and efficiently fire an object to be fired, and also to provide a firing method that uses such a firing unit laminate. [Explanation of symbols]

[0104] 1: Firing unit laminate U: Firing unit r: Baking rack f:Frame body b:Bridge part c:center l: Support part s:setter F: Gas flow in the furnace

Claims

1. A firing unit stack formed by stacking a plurality of firing units, Each of the plurality of baking units has a baking rack and a mesh setter placed on the baking rack, The baking rack has a frame and a bridge portion provided within the frame, When only the baking racks constituting the adjacent baking units are observed vertically upward from the lower side, the following formula (I) Crosslinked portion area overlap ratio (%) = (overlapping area of the crosslinked portion of the lower baking rack and the crosslinked portion and frame of the upper baking rack / area of the crosslinked portion of the lower baking rack) × 100 (I) The firing units are stacked so that the crosslinking area overlap ratio calculated by is 0 to 80%.

1. A firing unit laminate comprising:

2. In at least some of the adjacent baking units, the baking racks constituting the baking units each have the same rectangular outer shape, The opening defined by the frame and the bridging portion of the baking rack has a shape that is not rotationally symmetric when rotated 90° or 180° clockwise around a vertical axis passing through the center of the top surface of the baking rack as the rotation axis, In the adjacent baking units, the baking rack constituting the baking unit arranged on the lower side is rotated 90° or 180° clockwise around a vertical axis passing through the center of the upper surface of the baking rack constituting the baking unit arranged on the upper side as the rotation axis, When only the baking racks constituting adjacent baking units are observed vertically upward from the bottom, the bridges of the baking racks are arranged so that they do not completely overlap. The firing unit laminate according to claim 1 .

3. In at least some of the adjacent baking units, the baking racks constituting the baking units each have the same rectangular outer shape, The openings defined by the frame and the bridge portion of the baking rack have different pattern shapes when the baking rack is turned upside down and the front and back surfaces are reversed, In the adjacent baking units, the baking rack constituting the baking unit arranged on the lower side is arranged in a state where the baking rack constituting the baking unit arranged on the upper side is turned upside down, When only the baking racks constituting adjacent baking units are observed vertically upward from the bottom, the bridges of the baking racks are arranged so that they do not completely overlap. The firing unit laminate according to claim 1 .

4. The baking racks constituting the baking unit each have the following formula (II): Crosslinked portion area ratio (%) = (area of crosslinked portions constituting the baking rack / inner area of the frame constituting the baking rack) × 100 (II) The crosslinked area ratio calculated by is 1 to 40%. The firing unit laminate according to claim 1 .

5. The baking racks constituting the baking unit each have the following formula (III): Crosslinked portion width ratio (%) = (average width of crosslinked portion / longitudinal length of baking rack) × 100 (III) The crosslinked portion width ratio calculated by is 1 to 10% The firing unit laminate according to claim 1 .

6. The baking unit stack according to claim 1, wherein the baking racks constituting the baking unit each have a thickness of the cross-linking portion of 2 mm to 4 mm and a width of the cross-linking portion of 2 mm to 8 mm.

7. The baking racks constituting the baking unit are each made of the following materials: (i) The SiC is made of atmospheric sintered SiC having a SiC purity of 99% by mass or more; (ii) a bulk specific gravity of 3.10 or more; (iii) open porosity of 1% or less; (iv) a three-point bending strength according to JIS R 1601 of 450 MPa or more; and (v) Thermal shock resistance according to JIS R 1648: R2002 is 400°C or more 2. The firing unit laminate according to claim 1, which satisfies one or more conditions selected from the following:

8. A firing method comprising firing an object to be fired in a firing furnace using the firing unit laminate according to any one of claims 1 to 7.

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