JP7721072B2 - Firing unit laminate and firing method - Google Patents

Description

The present invention relates to a firing unit laminate and a firing method.

A conventional technique for firing objects such as semiconductor chips and multilayer ceramic capacitors (MLCCs) is to place the object on a flat setter placed on a firing rack and then fire the object.

In addition, to increase the baking efficiency of the above-mentioned baked items, a technology has been proposed in which multiple baking units, each consisting of a baking rack and a flat setter, are stacked and baked, allowing the baked items placed on the setters of each baking unit to be baked all at once (see, for example, Patent Document 1).

As shown in Figure 16, Patent Document 1 proposes a firing unit U that employs a plate-shaped firing jig (firing rack) 1 with an opening, and places a flat setter 20 on the firing rack 1. As shown in Figure 17, the document also proposes a technology in which multiple firing units U are stacked (with an object to be fired A placed on each setter) to form a firing unit stack, which is then fired in a kiln (firing furnace).

International Publication No. 2015/008503

As shown in Figures 16 and 17, Patent Document 1 proposes a baking rack 1 with support parts (legs) 13 on the underside of the frame 11. These support parts 13 allow furnace gas to flow between each baking unit U, U, allowing the objects A placed on each setter 20 to be separated from each other and baked all at once.

However, after investigations by the inventors, it was found that the method described in Patent Document 1 makes it difficult to uniformly bake the object to be baked.

This is thought to be because, during firing, the furnace gas generates an air current that rises from the bottom to the top of the furnace. However, when firing is performed with multiple firing units U stacked on top of each other, the flat setters 20 that make up the firing units U impede the flow of the furnace gas, making it difficult to achieve a uniform firing process in each firing unit U.

The inventors therefore came up with the idea of using mesh-shaped setters instead of flat ones to make up the firing units, thereby improving the flow of gas inside the furnace from the lower to the upper sides of each firing unit.

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

According to the inventors' investigations, as shown in Figure 18(a), the baking racks r that make up a baking unit are typically arranged in the same orientation and have the same opening pattern and shape. When the baking units are stacked and baked, observing only the baking racks r, as shown in the perspective view in Figure 18(b) and the side cross-sectional view in Figure 18(c) (a cross-sectional view of the side taken vertically along line Z-Z' in Figure 18(b)), when the in-furnace gas flow F rises from the bottom to the top of the baking furnace, it rises without coming into contact with any of the bridges (indicated by arrows in the figure) that define the opening pattern of each baking rack r. This is thought to be because, as shown in Figure 18(a), the air permeability is reduced, particularly in the baking units stacked at the top, reducing the contact efficiency between the in-furnace gas flow F and the baked material.

In light of these circumstances, the present invention aims to provide a baking unit stack and a baking method that can bake the object to be baked uniformly and efficiently.

After extensive research to solve the above technical problems, the inventors of the present application discovered that the above objectives can be achieved by a baking unit stack consisting of multiple 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 are observed vertically upward from below, the overlapping area of the bridge portion calculated by the formula (overlapping area of the bridge portion of the lower baking rack with the bridge portion and frame of the upper baking rack / area of the bridge portion of the lower baking rack) x 100 is 0 to 80%. Based on this finding, the inventors have completed the present invention.

That is, the present invention is
(1) A baking unit stack 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 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)
A firing unit stack, characterized in that the firing units are stacked so that the crosslinking area overlap ratio calculated 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,
The baking unit stack according to (1) above, wherein the baking racks constituting adjacent baking units are arranged so that the cross-linked portions of the baking racks do not completely overlap when only the baking racks constituting the adjacent baking units are observed vertically upward from the lower side;
(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,
The baking unit stack according to (1) above, wherein the baking racks constituting adjacent baking units are arranged so that the cross-linked portions of the baking racks do not completely overlap when only the baking racks constituting the adjacent baking units are observed vertically upward from the lower side;
(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 firing unit laminate according to any one of (1) to (3), wherein the crosslinked portion area ratio calculated by
(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 firing unit laminate according to any one of (1) to (4), wherein the crosslinked portion width ratio calculated by
(6) The baking rack constituting the baking unit is a baking unit laminate according to any one of (1) to (5), wherein the thickness of the cross-linking portion is 2 mm to 4 mm and the width of the cross-linking portion is 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) a thermal shock resistance strength according to JIS R 1648:R2002 of 400°C or more, the firing unit laminate according to any one of (1) to (6) above,
(8) A firing method is provided, which comprises firing an object to be fired in a firing furnace using the firing unit laminate according to any one of (1) to (7) above.

According to the present invention, when multiple stacked baking units are used, the cross-linking area overlap ratio, which is an indicator of the degree of overlap between the cross-linking sections on the baking racks, is reduced when the baking racks constituting adjacent baking units are observed vertically upward from the bottom. This promotes the flow of furnace gases that rise from the bottom to the top of the oven during baking. This makes it possible to provide a baking unit stack that can bake the object to be baked uniformly and efficiently, as well as a baking method using such a baking unit stack.

1A and 1B are diagrams showing examples of the configuration of a firing unit constituting a firing unit laminate according to the present invention. 1 is a diagram (top view) showing a schematic example of a baking rack that can be used in the present invention. FIG. 1 is a diagram (top view) showing a schematic example of a baking rack that can be used in the present invention. FIG. 1 is a diagram showing a schematic diagram of an example of a baking rack that can be used in the present invention. FIG. 1 is a diagram showing a schematic diagram of an example of a baking rack that can be used in the present invention. FIG. FIG. 10 is a diagram for explaining a method for calculating the cross-linked area ratio (%) of a baking rack. 10A and 10B are diagrams for explaining examples of the configuration of a bridging portion of a baking rack. 10A and 10B are diagrams for explaining examples of the configuration of a support part of a baking rack. 1A and 1B are diagrams illustrating examples of the shape of a mesh-shaped setter that can be used in the present invention. 1A and 1B are diagrams showing examples of firing unit laminates according to the present invention; 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. 1 is a diagram for explaining a firing mechanism using a firing unit laminate according to the present invention. FIG. FIG. 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. 1 is a perspective view of only the baking rack r constituting each baking unit in a baking unit stack produced in an example of the present invention, observed obliquely from above. FIG. FIG. 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. 1 is a perspective view of only the baking rack r constituting each baking unit in a baking unit stack produced in an example of the present invention, observed obliquely from above. FIG. 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. FIG. 10 is a diagram showing an example of the configuration of a firing unit constituting a conventional firing unit laminate. FIG. 10 is a diagram showing an example of the configuration of a conventional firing unit laminate. 10A and 10B are diagrams for explaining a firing mechanism using a conventional firing unit stack.

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 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 the above formula is 0 to 80%.

FIG. 1 is a diagram showing a schematic diagram of an example of a baking unit constituting the baking 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 arranged on the baking rack r.

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 bridge portion b provided inside the frame f.

As shown 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 portions b are provided within the frame body so as to connect the frame materials that make up the frame body f, and define a predetermined opening pattern within the frame body.

In the baking rack r shown 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 be rectangular, particularly approximately square or approximately rectangular, but it may also be oval, circular, etc., and the shape is not particularly limited.

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 within the frame body f.

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 within the frame body 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 baked effectively.

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 bridging portion that forms a roughly 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.

In the baking unit stack of the present invention, the baking racks that make up each baking unit may have different or identical shapes defined by the frame and bridging portions.

When the baking racks constituting each baking unit in at least some of the adjacent baking units that make up the baking unit stack according to the present invention have the same external shape, it is preferable that the baking racks have the same rectangular (i.e., oblong or square) external shape 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.

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 of the baking rack r 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).

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.
FIG. 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 FIG. 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 of the baking rack r 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 of the baking rack r as the axis of rotation, 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).

In this way, by using baking racks that are rectangular in shape and that 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, and by arranging them as baking racks for adjacent baking units in the pre- and post-rotation states, it is possible to install baking racks of the same shape so that the bridges 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.

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 the baking rack r is 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, it retains the same shape as before rotation, whether it is rotated 90° clockwise or 180° clockwise.
For this reason, 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.

When the baking racks constituting each baking unit in at least some of the adjacent baking units constituting the baking unit stack according to the present invention 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 portions of the baking racks have different pattern shapes (different opening shapes) when the baking racks are turned over and the front and back surfaces are reversed.

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, when only the baking racks that make up adjacent baking units are observed vertically upward from the bottom, it is possible to install them so that the bridging portions b of each baking rack do not completely overlap each other.

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.
For this reason, 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.

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):
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 the above formula is preferably 1 to 40%, more preferably 1 to 30%, and even more preferably 1 to 20%.

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) corresponds to the area _Sb of the bridge portion b, and the area of the shaded portion in FIG. 6(b) corresponds to the area S _i inside the frame body f that constitutes the baking rack r.
Therefore, in the baking rack r shown in FIG. 6, the crosslinked portion area ratio (%) is calculated by (S _b /S _i )×100.

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 corresponds to the area S i inside the outline of the opening shown in FIG. 6(b), which is defined when an exterior line L ₁ (shown by a thick line in the figure) is drawn around the frame body f, assuming that the baking rack r shown in FIG. 6(a) does not have the bridging portion _b .

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 Figure 6, the area of the bridge portion b constituting the baking rack r corresponds to the area Sb of the bridge portion b defined within the frame _f when an extrapolation line _L1 (shown by the thick line in the figure) is drawn on the baking rack r shown in Figure 6(a).

In the baking unit stack of the present invention, by ensuring that the cross-linked area ratio of the baking racks that make up each baking unit is within the above range, the flow of gas within the oven during baking is not impeded, and the baked material can be baked homogeneously and efficiently with ease.

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%.

7(a) shows a top view of the baking rack r corresponding to FIG. 2. In FIG. 7(a), the width _Wb of the bridge portion can be considered to be uniform in the longitudinal direction of the bridge portion, and therefore this can be taken as the average width of the bridge portion. Also, in FIG. 7(a), the vertical and horizontal lengths of the baking rack are the same, and therefore the horizontal length can be taken as the longitudinal length W _all of the baking rack.
Therefore, in the baking rack r shown in FIG. 7( a ), the crosslinked portion width ratio (%) is calculated by (W _b /W _all )×100.

In the baking unit stack of the present invention, by ensuring that the cross-linked portion width ratio of the baking racks that make up each baking unit is within the above range, the flow of gas within the oven during baking is not impeded, and the baked material can be baked homogeneously and efficiently with ease.

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 _Wb corresponds to the width of the bridge portion b.

In the baking unit stack of the present invention, by ensuring that the width of the cross-linking portion of the baking rack that makes up each baking unit is within the above range, the flow of gas within the oven during baking is not impeded, and the baked material can be baked homogeneously and efficiently with ease.

In the baking unit stack according to the present invention, the thickness of the cross-linked portion of the baking rack that constitutes 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.

In the baking unit stack of the present invention, the baking racks that make up each baking unit have a cross-linked portion with a thickness within the above range, which provides sufficient strength for handling during and after baking and effectively improves thermal efficiency during baking.

Figure 7(b) is a diagram showing the cross section of the baking rack r shown in Figure 7(a) taken along line Y-Y', where width T corresponds to the thickness of the cross-linked portion b.

In the baking unit stack of the present invention, it is preferable that the baking racks constituting each baking unit have a cross-sectional shape perpendicular to the longitudinal direction of the cross-linking portion that is roughly oval.

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

In the baking unit stack of the present invention, the cross-sectional shape of the bridging portion of the baking rack is roughly oval, and as shown in Figure 7(c), both ends are rounded. Therefore, when a mesh-shaped setter is placed on the baking rack, the contact area between the bridging portion and the setter can be reduced compared to a bridging portion with a square cross-sectional shape. As a result, the flow of gas inside the oven during baking is not impeded, and the baked material can be baked uniformly and efficiently with ease.

In the baking unit stack according to the present invention, the baking rack comprises:
(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;
It is preferable that the material satisfies one or more of the following conditions: (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.

In the baking unit stack according to the present invention, the baking rack satisfies one or more conditions selected from (i), (iv), and (v) above, making it possible to easily prevent damage to the baking rack due to thermal shock when baking the object to be treated.

Furthermore, in the baking unit stack according to the present invention, by the baking rack satisfying one or more conditions selected from (i), (ii), and (iii) above, the mass and heat capacity of the baking rack can be reduced, making it possible to easily bake the objects to be treated while saving energy.

In the firing unit stack according to the present invention, the firing rack satisfies one or more of the conditions (i) to (v) above, making it suitable for use in place of conventional ceramic firing racks, particularly during firing processes in continuous heat treatment furnaces where improved productivity is required, rapid heating and cooling processes are required, or increased loads of materials to be fired are required.

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.

Figures 8(a) to 8(d) each show an example of a baking rack r having a support portion l.

Figure 8(a) is a diagram showing an example of a baking rack r in which support parts (legs) 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 (arms) 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.

In the baking unit stack of the present invention, the baking racks have support parts, which allows the frames f of the baking racks r that make up each baking unit to be spaced apart, allowing furnace gas to circulate effectively between each baking unit when the baking units are stacked to form a stack.

In the baking unit stack of the present invention, each baking unit has a baking rack and a mesh setter placed on the baking rack.

In the firing unit laminate of the present invention, the setter is made of a mesh-like material, i.e., a network of multiple intersecting linear members.

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.

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

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 quadrilateral shape, with a square shape being preferred.

In the baking unit laminate of the present invention, the linear elements constituting the knitted material, the spacing between the linear elements in the knitted material, the size of the knitted material, etc. can be selected as appropriate within the scope that achieves the objectives of the present invention.

In the firing unit laminate according to the present invention, it is preferable that at least the surface of the mesh-shaped setter be formed from a heat-resistant material that melts during firing and adheres to the fired object or prevents reaction with the fired object.

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.

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 rises from the lower side to the upper side of the furnace during firing.
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.

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 arranged 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.

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 1000° C. or less is determined by 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 the above formula is 0 to 80%.

Figure 11 is a diagram illustrating how to calculate the cross-linking area overlap ratio when only the baking racks that make up adjacent baking units are observed vertically upward from the bottom.

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).

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 portion where the bridge portion b' of the baking rack r' located at the lower side and the bridge portion b of the baking rack r located at the upper side and the frame body overlap (in the example shown in Figure 11, only the bridge portion b' of the baking rack r' located at the lower side and the bridge portion b of the baking rack r located at the upper side overlap, so area _A2 indicates the area of the portion where both bridge portions overlap).

In addition, in the present application documents, the area of the bridge portion of the baking rack located at the bottom (area A ₁ 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.

In the example shown in FIG. 11, the crosslinking area overlap ratio (%) is
(Area A ₂ where the cross-linked portion b' of the lower baking rack r' and the cross-linked portion b of the upper baking rack overlap / Area A ₁ of the cross-linked portion b' of the lower baking rack) × 100
It is calculated as follows.

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

For each firing unit constituting the firing unit stack of the present invention, the crosslinking area overlap ratio between adjacent firing units needs to be within the specified range above. As long as it is within the specified range above, the crosslinking area overlap ratio calculated between each firing unit and its adjacent firing unit may be the same or different.

As mentioned above, in conventional stacks of baking units, 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 bridges 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 baking furnace, the in-furnace gas rises without coming into contact with any of the bridges that define the opening pattern of each baking rack. This reduces air permeability, particularly in the baking units stacked at the top, and reduces the contact efficiency between the in-furnace gas flow and the baked goods.

On the other hand, in the baking unit stack of the present invention, the baking racks in adjacent baking units are selected and arranged so that, when the baking racks are observed vertically upward from the bottom, the bridges that define the opening patterns of each baking rack do not completely overlap. This promotes the flow of in-furnace gases that rise from the bottom to the top of the furnace during baking.

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 upper 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, which, when turned over and placed with the front and back sides reversed, results in a different pattern shape formed by the cross-linking portions within the frame body, and is placed as the baking rack of adjacent baking units in the states before and after the above-mentioned turning over.

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 only the baking racks r constituting adjacent baking units are observed, 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 baking 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 baking racks, is reduced, thereby promoting the circulation of the in-furnace gas flow F (indicated by the arrow in the figure) that rises from the lower side to the upper side of the furnace during baking.

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 using a roller hearth furnace or 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, allowing multiple items to be fired (objects to be fired) to be fired simultaneously.

The present invention provides a baking unit stack that can bake the object to be baked uniformly and efficiently.

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.

Details of the firing unit laminate according to the present invention are as described above.

In the firing method according to the present invention, the temperature at which the fired material is fired can be set appropriately depending on the material, and is not particularly limited. However, a temperature of 800 to 1400°C is appropriate, and a temperature of 1000 to 1300°C is more appropriate.

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

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

The present invention will be explained in more detail below using examples and comparative examples, but the present invention is not limited to these examples in any way.

(Example 1) <Example in which baking racks are alternately arranged upside down in adjacent baking units>
(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 FIG. 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 within 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 so that 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, which has a different pattern shape when turned upside down with the front and back surfaces reversed.
The firing rack r used in this example was (i) made of atmospheric sintered SiC plate material having 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.

(2) Setter A mesh-shaped 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.

(3) Baking Unit Laminate Ten baking units were formed by placing the mesh setters on the baking racks.
At this time, five sets of the mesh-shaped setter were formed on the upper surface of the baking rack r shown in FIG. 13-1(a) (baking unit a), and
Five sets were formed, each of which had the mesh 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 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 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.
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, in the baking unit stack, when only the baking rack r constituting the adjacent baking unit a and the baking rack r constituting the baking unit b are observed vertically upward from the bottom side, the bridge portions b, b of both are observed to partially overlap, as shown in Figure 13-1 (c). At this time, the area of the part shown by the colored part in Figure 13-1 (c) indicates the area of the overlapping part between the bridge portion b of the baking rack r constituting the baking unit b located on the lower side and the bridge portion b and frame of the baking rack r constituting the baking unit a located on the upper side (in the example shown in Figure 13, only the bridge portion b of the baking rack r located on the lower side and the bridge portion b of the baking rack r located on the upper side overlap, so the colored part in Figure 13-1 (c) corresponds to the area of the overlapping part 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)
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 crosslinked area overlap ratios calculated by the above formula were all 67% (the crosslinked area overlap ratios defined between the lower and upper rows, such as the crosslinked area overlap ratio between the first and second rows, the crosslinked area overlap ratio between the second and third rows, etc., were all 67%).

(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 fired material placed thereon was placed on a 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 constituting the firing unit laminate was calculated using the following formula. The results are shown in Table 1.
Rate of non-defective products (%) = {(number of non-defective products per layer) / (number of baked products arranged per layer)} × 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: Cracks or discoloration are observed when visually inspected.

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 FIG. 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 within 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 having 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.

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

(3) Baking Unit Laminate Ten 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 setter was arranged 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 setter was arranged 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 disposing SiC cylindrical spacers at the four corners of each firing unit, each 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.
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, in the baking unit stack, when only the baking rack r constituting the adjacent baking unit a and the baking rack r constituting the baking unit b are observed vertically upward from the bottom side, the bridge portions b, b of both are observed to partially overlap, as shown in Figure 14-1 (c). At this time, the area of the part shown by the colored part in Figure 14-1 (c) indicates the area of the overlapping part between the bridge portion b of the baking rack r constituting the baking unit b located on the lower side and the bridge portion b and frame of the baking rack r constituting the baking unit a located on the upper side (in the example shown in Figure 14, only the bridge portion b of the baking rack r located on the lower side and the bridge portion b of the baking rack r located on the upper side overlap, so the colored part in Figure 14-1 (c) corresponds to the area of the overlapping part 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)
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 crosslinked area overlap ratios calculated by the above formula were all 9% (the crosslinked area overlap ratios defined between the lower and upper rows, such as the crosslinked area overlap ratio between the first and second rows, the crosslinked area overlap ratio between the second and third rows, etc., were all 9%).

(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 firing material 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 FIG. 14-2).
At this time, the yield of the fired products in the first, fifth and tenth firing unit laminates constituting the firing unit laminate was calculated in the same manner as in Example 1. The results are shown in Table 1.

(Comparative Example 1)
<Example of arrangement where the bridges of the baking racks that make up adjacent baking units are completely overlapped when only the baking racks that make up the adjacent baking units are observed vertically upward from below>
(1) Baking rack The same baking rack as used in Example 1 was prepared.
That is, a baking rack having 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 within the frame f.

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

(3) Baking Unit Laminate Ten baking units were formed by placing the mesh setters on the baking racks.
At this time, ten 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 having a diameter of 8 mm and a height of 10 mm were placed at the four corners of each firing unit, and the spacers (i) were made of atmospheric sintered SiC with a SiC purity of 99% by mass or more, (ii) had a bulk specific gravity of 3.10 or more, (iii) had an open porosity of 1% or less, (iv) had a three-point bending strength according to JIS R 1601 of 450 MPa or more, and (v) had 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, as viewed 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)
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 crosslinked area overlap ratios calculated by the above formula were all 100% (the crosslinked area overlap ratios defined between the lower and upper rows, such as the crosslinked area overlap ratio between the first and second rows, the crosslinked area overlap ratio between the second and third rows, etc., were all "100%").

(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 base 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 of the fired products in the first, fifth and tenth firing unit laminates constituting the firing unit laminate was calculated in the same manner as in Example 1. The results are shown in Table 1.

Table 1 shows that in Examples 1 and 2, when multiple stacked baking units are used and the baking racks constituting adjacent baking units are observed vertically upward from the bottom, the crosslinked area overlap ratio, which is an indicator of the degree of overlap between the crosslinked sections on the baking racks, is kept to 0-80%. This promotes the flow of furnace gases that rise from the bottom to the top of the furnace during baking, and therefore enables the baking materials on the first through tenth tiers to be baked uniformly and efficiently.

Table 1 shows that in Comparative Example 1, when multiple stacked baking units are used and the baking racks making up adjacent baking units are observed vertically upward from the bottom, the crosslinked area overlap ratio, which is an indicator of the degree of overlap between the crosslinked sections on the baking racks, is outside the range of 0 to 80% (it is 100%). This blocks the flow of furnace gas that rises from the bottom to the top of the furnace during baking, and as a result, the baked products, particularly on the tenth tier, cannot be baked uniformly and efficiently, resulting in a poor yield rate.

The present invention provides a baking unit laminate that can bake an object to be baked uniformly and efficiently, and also provides a baking method using such a baking unit laminate.

1: Firing unit laminate U: Firing unit r: Firing rack f: Frame b: Bridge c: Center l: Support s: Setter F: Furnace gas flow

Claims (8)

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 unit stack is characterized in that the firing units are stacked so that the crosslinking area overlap ratio calculated by the above formula is 0 to 80%. 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,
A baking unit stack as described in claim 1, wherein the baking racks constituting adjacent baking units are arranged so that the bridge portions of each baking rack do not completely overlap when observed vertically upward from the bottom side. 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,
A baking unit stack as described in claim 1, wherein the baking racks constituting adjacent baking units are arranged so that the bridge portions of each baking rack do not completely overlap when observed vertically upward from the bottom side. 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)
2. The firing unit laminate according to claim 1, wherein the crosslinked portion area ratio calculated by the above formula is 1 to 40%. 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)
2. The firing unit laminate according to claim 1, wherein the crosslinked portion width ratio calculated by the above formula is 1 to 10%. The baking unit stack described in claim 1, wherein the thickness of the cross-linking portion of each of the baking racks constituting the baking unit is 2 mm to 4 mm and the width of the cross-linking portion is 2 mm to 8 mm. 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;
The firing unit laminate according to claim 1, which satisfies one or more conditions selected from (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. 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.