JP2010181109A - Heat treatment method of heat treated object - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a heat treatment method capable of more securely and efficiently drying adhesive paste while suppressing variation of contraction of a ceramic green sheet. <P>SOLUTION: For heat treatment of a heat treated object formed by applying, to a ceramic green sheet, the adhesive paste for bonding to the other ceramic green sheet, a first temperature rising process of raising the temperature of the heat treated object to ≥55°C and ≤65°C of an intermediate holding temperature, an intermediate maintaining process of maintaining the temperature of the heat treated object at the intermediate holding temperature, a second temperature rising process of raising the temperature of the heat treated object to ≥80°C and ≤90°C of a final holding temperature, and a final maintaining process of maintaining the temperature of the heat treated object at the final holding temperature are performed in this order. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a heat treatment method for an object to be heat treated by applying an adhesive paste to a ceramic green sheet.

Conventionally, as a method for producing a NOx sensor, an oxygen sensor, and the like, various electrode patterns and the like are printed and formed on a plurality of ceramic green sheets whose main component is ceramics such as zirconia (ZrO ₂ ). A method of laminating sheets to form a laminate and firing the laminate is known. When forming a laminated body, a method is generally used in which an adhesive paste is applied to each ceramic green sheet and dried, and then the ceramic green sheets are brought into close contact with each other to be integrated. .

  The drying of the adhesive paste applied to the ceramic green sheet is generally performed by heat treatment. As an apparatus used for such heat treatment, a continuous heat treatment apparatus that performs heating and cooling while conveying a ceramic green sheet by a conveying means is known (for example, see Patent Document 1).

JP-A-5-319893

  It is necessary to dry the adhesive paste by the heat treatment under such a condition that a sufficient adhesion can be obtained when the ceramic green sheets are brought into close contact with each other to form a laminate. Further, when forming a laminated body, if variation occurs in the degree of shrinkage due to heat treatment among a plurality of ceramic green sheets to be laminated, it causes a deviation during lamination. Furthermore, from the viewpoint of improving manufacturing efficiency, there is a demand for drying by heat treatment in as short a time as possible.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a heat treatment method capable of drying an adhesive paste more reliably and efficiently while suppressing variation in shrinkage of ceramic green sheets. And

  In order to solve the above-mentioned problems, the invention of claim 1 is a method for heat-treating a heat-treated material obtained by applying an adhesive paste for bonding to a ceramic green sheet to another ceramic green sheet, the intermediate holding A first temperature raising step for raising the temperature of the workpiece to a temperature and a second temperature raising step for raising the temperature of the workpiece to a final holding temperature are performed in this order.

  Invention of Claim 2 is the heat processing method of Claim 1, Comprising: The intermediate maintenance process which maintains the temperature of the said to-be-processed object at the said intermediate | middle holding temperature after the said 1st temperature rising process, The said 2nd raise And a final maintaining step of maintaining the temperature of the object to be heat-treated at the final holding temperature after the temperature step.

  A third aspect of the invention is the heat treatment method according to the first or second aspect, wherein the final holding temperature is higher than the intermediate holding temperature.

  Invention of Claim 4 is the heat processing method in any one of Claim 1 thru | or 3, Comprising: The said intermediate | middle holding temperature is 50 degreeC or more and 70 degrees C or less, The said final holding temperature is 75 degreeC or more and 100 degreeC. It is characterized by the following.

  Invention of Claim 5 is the heat processing method of Claim 4, Comprising: The said intermediate | middle holding temperature is 55 degreeC or more and 65 degrees C or less, The said final holding temperature is 80 degreeC or more and 90 degrees C or less, It is characterized by the above-mentioned. To do.

  Invention of Claim 6 is the heat processing method in any one of Claim 1 thru | or 5, Comprising: The temperature rising rate in the said 2nd temperature rising process is more than the temperature rising speed in the said 1st temperature rising process. It is large.

  A seventh aspect of the present invention is the heat treatment method according to any one of the first to sixth aspects, wherein the object to be heat treated is sequentially conveyed between a plurality of heating chambers capable of independently controlling the atmospheric temperature. While using each of the plurality of heating chambers, the first temperature raising step, the intermediate maintenance step, the second temperature raising step, and the final maintenance step using a heat treatment apparatus capable of heating the object to be heat-treated in an atmosphere. It is characterized by performing.

  Invention of Claim 8 is the heat processing method of Claim 7, Comprising: In the case of the said atmosphere heating, the horizontal direction which goes to the conveyance position of the said to-be-processed object from upper direction in each internal space of these heating chambers An atmospheric flow having a substantially uniform flow rate is generated.

  The invention of claim 9 is the heat treatment method according to claim 8, wherein the atmosphere flow is formed by circulating the atmosphere of the internal space by a predetermined circulation means, and the rectifying means is provided above the transfer position. By providing, the flow velocity of the atmosphere flow is made substantially uniform in the horizontal direction.

  According to the first to ninth aspects of the present invention, the thermal load on the ceramic green sheet can be reduced and the bonding can be achieved by holding the object to be heat-treated at two different temperature regions during the heat treatment. A heat treatment that can dry the paste with high uniformity can be realized efficiently. Specifically, it is possible to suppress the occurrence of cracks in the ceramic green sheet, reduce the variation in shrinkage of the ceramic sheet, and stabilize the weight reduction rate of the solvent in the adhesive paste. Thereby, the favorable drying process of the paste for adhesion | attachment which has few dispersion | variation in the dry state in the same ceramic green sheet or between different ceramic green sheets is implement | achieved stably.

  According to the invention of claim 6, it is possible to suppress an increase in heat treatment time while suppressing a thermal load applied to the object to be heat treated in the first temperature raising step.

  Further, according to the invention of claim 7 to claim 9, by continuously transporting a plurality of heat-treated objects to a heating chamber in which the heat treatment atmosphere is kept uniform, the plurality of heat-treated objects are subjected to the same conditions. It can be heat treated. Therefore, it is possible to reliably and efficiently perform a good drying process of the adhesive paste that does not cause variation in shrinkage or drying unevenness of the ceramic green sheet with respect to a large number of sheets.

  Moreover, according to the invention of Claim 8 and Claim 9, the favorable drying process of the adhesive paste in which the variation in the drying state within the same ceramic green sheet or between different ceramic green sheets is further reduced is stable. To be realized.

It is a figure which shows the heat processing profile P1 used with the method which concerns on this invention. 1 is a side view schematically showing an overall configuration of a continuous heat treatment apparatus 100. FIG. 3 is a schematic cross-sectional view schematically showing the configuration of a heating chamber 3. FIG. It is a figure which shows the heat processing profile P3 and P4 which concern on a comparative example.

<Heat treatment method>
In the present embodiment, for example, in a manufacturing process such as a ceramic gas sensor, a bonding paste applied to a ceramic green sheet is performed prior to bonding and stacking a plurality of ceramic green sheets to form a laminate. A drying process (hereinafter also simply referred to as a heat treatment or drying) will be described. Specifically, ceramic green sheets containing zirconia (ZrO ₂ ) as the main component of ceramics, ceramics, binder (organic matter) and solvent (organic matter), which also contain zirconia as the main component, plasticizer, dispersant, and sintering aid A heat treatment in which a paste to which an adhesive paste, which is a mixture containing an agent, is applied (hereinafter also simply referred to as a sheet) will be described. The size of the ceramic green sheet is, for example, about 150 mm × 114 mm, and the thickness is, for example, about several hundred μm.

  The drying of the bonding paste is performed for the purpose of adjusting the state of the bonding paste applied to the ceramic green sheet so that the subsequent bonding and lamination of the ceramic green sheet are good.

  When the green sheets are bonded and stacked, if the bonding paste is not sufficiently dried, a sufficient adhesive force cannot be obtained when the sheets are stacked. Here, that the drying is not sufficient corresponds to a small amount of solvent scattering in the adhesive paste, that is, a small weight reduction rate of the solvent during drying. On the other hand, if the scattering amount of the solvent is too large, that is, if the weight reduction rate of the solvent is too large, the adhesive between the green sheets becomes weak because the binder becomes difficult to dissolve in the solvent when the green sheets are brought into close contact with each other. It will be.

Table 1 shows the quality of the laminated state in the case where laminated bodies were produced by varying the weight reduction rate of the solvent of the adhesive paste. The temperature during the lamination 90 ° C., the pressure (gauge pressure) was set to 85 kgf / cm ^2. These conditions are conditions within a range normally used for bonding and laminating sheets with the above-described sheet.

  From the results shown in Table 1, it can be said that the weight reduction rate of the binder solvent in the adhesive paste is preferably 80% or more and 90% or less. More preferably, it is 85%.

  Further, in order to reliably and efficiently realize the solvent reduction within the range of the weight reduction rate, heat treatment is performed so as to have a process in which the temperature of the sheet is maintained at about 80 ° C. to 90 ° C. (around 85 ° C.). It is confirmed by the inventor of the present invention that it is preferable to perform the above. If the sheet is not heated to such a temperature range, drying is insufficient, and sufficient adhesion cannot be obtained at the time of lamination, and it takes time to dry and the efficiency is low. Will occur.

  FIG. 1 is a diagram showing a heat treatment profile P1 representing the relationship between the elapsed time from the start of heat treatment and the sheet temperature in the heat treatment according to the present embodiment, determined in consideration of the above points. In FIG. 1, the vertical axis indicates the temperature of the sheet when the room temperature T0 (about 23 ± 3 ° C.) is the origin position. The horizontal axis represents time t (elapsed time from the temperature rise start time) when the temperature rise start time of the sheet is the origin (t = 0). FIG. 1 shows an ideal profile. When the profile is produced by actually measuring the sheet temperature, some temperature fluctuations, overshoot, and the like may occur. However, there is no problem even if the temperature changes as long as it is within a range that is acceptable for explaining the present invention. The temperature of the sheet can be measured by, for example, a thermocouple.

  First, during a time Δt1 from t = 0 to t = t1, the sheet is heated from the room temperature T0 to the intermediate holding temperature T1 (first temperature raising step). For example, the time Δt1 is preferably 1.5 minutes or more and 2.5 minutes or less. The intermediate holding temperature T1 is preferably in the range of 50 ° C to 70 ° C, and more preferably 55 ° C to 65 ° C.

  Next, the sheet is held at the intermediate holding temperature T1 for a time Δt2 from t = t1 to t = t2 (first holding step). The time Δt2 is preferably 2.5 minutes or more and 3.5 minutes or less.

  Subsequently, during the time Δt3 from t = t2 to t = t3, the sheet is heated from the intermediate holding temperature T1 to the final holding temperature T2 (second heating step). The time Δt3 is preferably not less than 0.5 minutes and not more than 1.5 minutes. The final holding temperature T2 is preferably in the range of 75 ° C to 100 ° C, more preferably 80 ° C to 90 ° C.

  Further, the sheet is maintained at the final holding temperature T2 for a time Δt4 from t = t3 to t = t4 (second holding step). The time Δt4 is preferably 2.5 minutes or more and 3.5 minutes or less.

  Finally, during the time Δt5 from t = t4 to t = t5, the temperature of the sheet is lowered from the final holding temperature T2 to the room temperature T0 (temperature lowering step). The time Δt5 is preferably 0.5 minutes or more and 1.5 minutes or less. Thus, the heat treatment for drying the sheet is completed.

  As shown in FIG. 1, in the heat treatment profile P1 according to the present embodiment, the sheet is not suddenly heated to the final holding temperature T2 and held, but the temperature rising process is divided into two stages, and once the intermediate holding temperature T1 is reached. The temperature is raised to a predetermined holding temperature T2, and then held at that temperature for a while. Hereinafter, the heat treatment profile P1 in the present embodiment is also referred to as a two-stage profile.

  If it is only necessary to have a process of simply maintaining the temperature of the sheet at the final holding temperature T2, for example, the sheet is directly heated from near room temperature to the final holding temperature, and then at the final holding temperature for a certain period of time. A mode in which the simplest profile of maintaining and lowering the temperature to room temperature (hereinafter referred to as a simple profile) is also conceivable.

  By heating up to a certain temperature and holding at that temperature, the sheet is soaked and the uniformity of the dry state of the sheet becomes high, but in the case of a simple profile, there is an opportunity for the sheet to be soaked. Since only the holding process at the final holding temperature is performed, it is not always easy to set a profile for suitably realizing soaking and further drying of the sheet. For example, if the retention time at the final retention temperature is increased with the intention of achieving sufficient soaking, the solvent will be excessively reduced. On the other hand, if the holding time at the final holding temperature is too short, temperature variations easily occur in the same sheet or between different sheets, and unevenness occurs in the degree of drying, which must be avoided. In addition, when the holding time is set as a process condition when a large number of sheets are continuously dried, the majority of the sheets (preferably all the sheets) are dried well by holding at the set holding time. However, there are variations in the sheet composition, shrinkage rate, dryness, etc. between individual sheets or lots, as well as variations in the viscosity and thickness of the applied adhesive paste. Depending on the degree, the optimum holding time varies depending on the sheet, and it may be difficult to appropriately perform such setting.

  On the other hand, in the present embodiment, by adopting the above-described two-stage profile, once holding at the intermediate holding temperature T1 lower than the final holding temperature T2, the degree of drying (reduction in the weight of the solvent) However, the sheet is held at the final holding temperature T2, after which the sheet is held at the final holding temperature T2, so that the sheet can be dried more reliably. It has become so.

  In addition, in the simple profile, while maintaining the final holding temperature T2 as short as possible without causing unevenness in drying, it is possible to increase the temperature while suppressing temperature variation as much as possible by reducing the temperature increase rate. However, such an embodiment increases the heat treatment time, and is not a preferable embodiment in terms of processing efficiency.

  Increasing the initial heating rate for the purpose of shortening the heat treatment time increases the thermal load on the sheet and causes cracks on the sheet surface, and increases the variation in sheet shrinkage. As a result, since lamination after drying cannot be performed satisfactorily, it is not preferable.

  After all, heat treatment with a simple profile is not necessarily sufficient to achieve uniform drying stably and efficiently.

  On the other hand, when the two-stage profile is adopted as in the present embodiment, even if the heating rate in the first heating process is reduced for the purpose of reducing the thermal load on the sheet, the second heating process is performed. It is possible to set the heating rate higher than this. Since the temperature rise is from the intermediate holding temperature T1, not the temperature rise from room temperature, in such a case, if the rate of temperature rise in the second temperature raising step is applied at the time of temperature rise from room temperature, the sheet will crack. Even if the speed is set so that cracks occur, cracks do not occur. Therefore, the occurrence of cracks and the like can be suppressed while minimizing the increase in the overall processing time.

  That is, according to the heat treatment method with the two-stage profile according to the present embodiment, the thermal load on the sheet is reduced and the adhesive paste is dried with high uniformity as compared with the simple profile. The heat treatment that can be performed can be realized efficiently. Specifically, it is possible to suppress the occurrence of cracks and the like in the sheet, reduce the variation in shrinkage, and stabilize the weight reduction rate of the solvent in the adhesive paste. As a result, it is possible to achieve a favorable bonding paste drying process in which there is little variation in the drying state within the same sheet or between different sheets.

<Continuous heat treatment equipment>
Next, a heat treatment apparatus suitable for carrying out the heat treatment method according to the present embodiment described above will be described. FIG. 2 is a schematic side view schematically showing the entire configuration of the continuous heat treatment apparatus 100 as an example of the heat treatment apparatus. The continuous heat treatment apparatus 100 includes a conveying means 2 for conveying the object to be heat treated 1, four heating chambers 3 (3 a to 3 d) for heating and keeping the heat treated object 1, and cooling for cooling the object to be heat treated 1. The chamber 4 is mainly provided. Moreover, each heating chamber 3a-3d is divided by the partition 14, The damper 5 (5a-5d) and the exhaust path 11 (11a-11d) are provided in the upper part of each heating chamber 3a-3d, respectively. The heating chamber 3a is also referred to as a first heating chamber 3a, the heating chamber 3b as a second heating chamber 3b, the heating chamber 3c as a third heating chamber 3c, and the heating chamber 3d as a fourth heating chamber 3d.

  The continuous heat treatment apparatus 100 heats and cools the object to be heat-treated 1 by conveying the object to be heat-treated 1 to the heating chambers 3 a to 3 d and the cooling chamber 4 in this order while being held by the conveying means 2. . That is, in the continuous heat treatment apparatus 100, the heating chamber 3a side (the right side in the drawing in FIG. 2) is the upstream side in the transport direction of the workpiece 1 and the cooling chamber 4 side (the left side in the drawing in FIG. 2) is the downstream side in the transport direction. It has become.

  The conveying means 2 is a mesh type belt conveyor made of a material such as Teflon (registered trademark). The conveyance means 2 conveys to the heating chambers 3 a to 3 d and the cooling chamber 4 while holding the object to be heat treated 1. In addition to the mesh type belt conveyor, a roller conveyor, a walking beam, or the like may be used as the conveying means 2. In the continuous heat treatment apparatus 100, conveyance by a so-called continuous feed method in which the conveyance unit 2 sequentially conveys a plurality of objects to be heat-treated 1 is realized.

  Although a detailed configuration of the heating chamber 3 will be described later, a partition wall 14 is provided between the adjacent heating chamber 3 and cooling chamber 4 perpendicular to the transport direction. That is, the heating chambers 3 a to 3 d are partitioned by the partition wall 14. However, each partition wall 14 is provided with a penetrating portion to the extent that the heat treatment object 1 can be conveyed by the conveying means 2. By providing the partition wall 14, the atmosphere in each of the heating chambers 3 a to 3 d can be maintained at a desired atmosphere temperature without being substantially affected by the atmosphere temperature of the other heating chamber 3.

  The cooling chamber 4 includes a cooling unit that cools the workpiece 1 that has been transferred from the heating chamber 3 by the transfer unit 2. Although it is a suitable example to use air cooling means, such as a fan, as a cooling means, the aspect provided with another cooling means may be sufficient.

<Detailed configuration of heating chamber>
Next, the structure of the heating chamber 3 (3a-3d) is demonstrated in detail. FIG. 3 is a schematic cross-sectional view when the heating chamber 3 is viewed from the downstream side in the conveyance direction of the object to be heat treated 1 (the left side in the drawing in FIG. 2). The inside of the heating chamber 3 includes a heating space 15, a side flow passage 13 a provided in a side portion of the heating space 15 (left side in the drawing in FIG. 3), and an upper flow passage 13 b provided in an upper portion of the heating space 15. It is divided into.

  The heating space 15 is a space in which the atmosphere of the workpiece 1 is heated. In the heating space 15, the object to be heat-treated 1 is conveyed by the conveying means 2 that traverses in the direction from the back to the front of the drawing. A heater 6 as a heating unit is disposed below the transfer unit 2 (that is, below the transfer position of the workpiece 1). As the heater 6, it is preferable to use an electric heater that can be easily temperature-controlled. In the heat treatment method according to the present embodiment, since the atmospheric temperature in the heating chamber required for drying is in the range of about 60 to 90 ° C., as the heater 6, the atmospheric temperature in the heating chamber is in the temperature range. What has the heating ability of the grade hold | maintained should just be used.

  Control of heating by the heater 6 is performed by a temperature control unit 8 provided outside the heating space 15. The temperature control unit 8 controls the heating of the heater 6 based on a preset heating condition while referring to a measurement value obtained by the temperature sensor 7 provided in the heating space 15. Preferably, the temperature sensor 7 is provided in the vicinity of the transfer position of the workpiece 1 (that is, in the vicinity of the transfer means 2). As a heating control method, for example, PID control or the like is used.

  The side flow passages 13 a are provided in the side portion of the heating chamber 3 in a manner adjacent to the heating space 15. The side flow passage 13a communicates with the heating space 15 only at the lowermost end thereof. A fan 9 is provided in the heating chamber 3 and below the side flow passage 13a. The fan 9 generates airflow from the bottom to the top of the side flow passage 13a while taking in the external atmosphere and taking it into the heating chamber 3. Is provided. In addition, although illustration is abbreviate | omitted in FIG. 3, the aspect controlled together by the temperature control part 8 also about the operation | movement of the fan 9 may be sufficient. Furthermore, a damper 5 is provided above the side flow passage 13a.

  The upper flow passage 13 b is provided at the upper end of the heating chamber 3 in a manner adjacent to the heating space 15. The upper flow passage 13b communicates with the side flow passage 13a at one end thereof. In other words, it can be said that the side flow passage 13a and the upper flow passage 13b form a single L-shaped flow passage in the drawing. Further, the upper flow passage 13 b communicates with the heating space 15 via the filter 12. The filter 12 is provided for the purpose of removing impurities such as particles mixed in the atmosphere introduced into the heating space 15.

  On the other hand, a rectifying plate 10 is provided at the upper end of the heating space 15 and below the filter 12. The rectifying plate 10 adjusts the flow of the atmosphere flowing from above the filter to adjust the atmospheric temperature in the heating space 15 and the flow velocity of the atmosphere in the vicinity of the conveying means 2 (that is, in the vicinity of the heat-treated object 1 to be conveyed). It is provided for the purpose of homogenization. Specifically, when the rectifying plate 10 is provided, if the rectifying plate 10 is not provided, the atmosphere that should be directed vertically downward in the central portion in the horizontal direction of the heating space 15 is once changed to the side flow passage 13a. Will be headed towards. The effect of providing the current plate 10 in this way will be described later.

  In the heating chamber 3 having the above-described configuration, the fan 9 is also operated when the atmosphere is heated by the heater 6. Thereby, the flow of the atmosphere upwards as shown by arrow AR1 arises in the side part circulation part 13a. At that time, as indicated by an arrow AR2, the atmosphere below the internal space 15 heated by the heater 6 is also taken in and carried upward.

  The atmosphere reaching the upper end of the side circulation portion 13a is partly exhausted from the exhaust path 11 through the damper 5 as indicated by an arrow AR3a, but the rest is indicated by an arrow AR3b. Then, it flows to the upper circulation part 13b.

  Furthermore, the atmosphere that has reached the upper circulation portion 13 b flows into the heating space 15 through the filter 12.

  That is, in the continuous heat treatment apparatus 100, the heat treatment object 1 is heated while the atmosphere heated by the heater 6 is circulated in the heating chamber 3 in such a manner.

  However, the present embodiment is characteristic in that the atmosphere passing through the filter 12 is subjected to the rectifying action by the rectifying plate 10 when the atmosphere is heated and circulated in such a manner. .

  In the upper circulation portion 3b, the flow velocity decreases as the distance from the side flow passage 13a increases as indicated by the arrows AR4a to AR4c. Therefore, when the rectifying plate 10 is not provided, the flow velocity of the atmosphere toward the workpiece 1 is increased. The smaller the right side of the drawing, the smaller. Such non-uniformity is not preferable because unevenness of drying occurs in the object to be heat treated 1.

  However, in the continuous heat treatment apparatus 100, by providing the rectifying plate 10 in the above-described manner, an atmosphere passing through the filter 12 downward in the space between the side flow passage 13a and the rectifying plate 10 is provided. Once converged as indicated by arrows AR5a to AR5c, it is supplied downward to the heating space 15 where the conveying means 2 is present (that is, the object to be heat treated 1 is present). Thereby, the state where the non-uniformity in the horizontal direction of the flow rate of the atmosphere is suppressed is realized below the rectifying plate 10 as compared with the case where the rectifying plate 10 is not provided. Note that, on the right end side of the heating space 15, the flow passing through the filter 12 joins without being subjected to the rectifying action by the rectifying plate 10 as indicated by the arrow AR <b> 7. As a result, as indicated by arrows AR6a to AR6c, a state in which the non-uniformity in the horizontal direction of the flow velocity of the atmosphere is suppressed in the vicinity of the surface of the object to be heat treated 1 is realized.

  As a result, in the heating chamber 3 of the continuous heat treatment apparatus 100, the object to be heat-treated 1 conveyed by the conveying means 2 is heated under a substantially uniform atmosphere flow vertically downward. That is, the object to be heat treated 1 can be heated uniformly.

  For example, when the fan 9 is actuated to form an atmospheric flow having a flow velocity of 2.0 m / s in the side flow passage 13a, the heating space 15 is formed at the center left side, the center center, and the center right side. The flow rates of the atmosphere are about 0.52 m / s, 0.45 m / s, and 0.55 m / s, respectively.

<Execution of 2-stage profile heat treatment by continuous heat treatment equipment>
Next, in the continuous heat treatment apparatus 100, a case where the adhesive paste is heat treated and dried according to the heat treatment profile P1 (two-stage profile) shown in FIG. 1 while conveying the sheets continuously will be described. . In addition, it can be said that the continuous heat processing apparatus 100 which can heat the to-be-processed object 1 uniformly as mentioned above is an apparatus suitable for heat-drying many sheets on the same conditions (heat processing profile P1).

  FIG. 1 shows a set temperature profile P2 set in the continuous heat treatment apparatus 100 when the sheet is to be heat treated with the heat treatment profile P1 together with the heat treatment profile P1. In addition, the conveyance means 2 shall convey the sheet | seat which is to-be-heated material 1 at constant speed, and a sheet shall pass the one heating chamber 3 for every time (tau). In this case, as long as the conveying unit 2 is being driven, the drying process is performed under the same conditions regardless of the timing when the sheet is placed on the conveying unit 2. However, in order to satisfy the heat treatment profile P1, it is necessary to satisfy the following relationship.

    τ> t1, τ <t2 / 2, τ> t3 / 3, τ ≦ t4 (Formula 1)

  Furthermore, the atmosphere setting temperatures in the heating chamber 3a, the heating chamber 3b, the heating chamber 3c, and the heating chamber 3d are respectively Z1, Z2, Z3, and Z4. As described above, in the heat treatment profile P1, the intermediate holding temperature T1 is set in the range of 55 ° C. to 65 ° C., and the final holding temperature T2 is set in the range of 80 ° C. to 90 ° C. The atmosphere set temperatures Z1 to Z4 are set so as to satisfy at least the following relationship.

    T1 ≦ Z2 <Z1 <T2 <Z3 <Z4 (Formula 2)

  Hereinafter, the progress of the heat treatment by the continuous heat treatment apparatus 100 will be specifically described.

  First, the time point when the conveying unit 2 starts conveying the sheet to the first heating chamber 3a is time t = 0. While being conveyed in the first heating chamber 3a, the temperature of the sheet rises according to the heat treatment profile P1 aiming at the atmosphere setting temperature Z1 of the first heating chamber 3a. The atmosphere setting temperature Z1 is set to be about several degrees C. higher than the intermediate holding temperature T1.

  However, the temperature rise of the sheet slows in the vicinity of the intermediate holding temperature T1 at a time point t = t1 slightly before the sheet leaves the first heating chamber 3a. Then, after t = t1, the sheet temperature is practically constant at the intermediate holding temperature T1.

  Thereafter, when t = τ, the sheet is conveyed to the second heating chamber 3b. Although the atmosphere setting temperature Z2 of the second heating chamber 3b is lower than the atmosphere setting temperature Z1 of the first heating chamber 3a as expressed by Equation 2, it is slightly higher than the intermediate holding temperature T1 (about 1 to 2 ° C. at most). ), The sheet is substantially held at the intermediate holding temperature T1 while passing through the second heating chamber 3b.

  When t = 2τ, the sheet is conveyed to the third heating chamber 3c. The atmosphere setting temperature Z3 of the third heating chamber 3c is set to be about several degrees Celsius higher than the final holding temperature T2 (by this, about 20 ° C. higher than the atmosphere setting temperature Z2 of the second heating chamber 3b). At the time t = t2, which is shortly after being conveyed to the heating chamber 3c, the sheet temperature begins to rise again.

  However, the temperature rise of the sheet slows down near the final holding temperature T2 at time t = t3 while the sheet is conveyed through the third heating chamber 3c. Then, after t = t3, the sheet temperature is practically constant at the final holding temperature T3. Alternatively, it can be said that the atmosphere setting temperature Z1 is set so that such a state is realized.

  Thereafter, when t = 3τ, the sheet is conveyed to the fourth heating chamber 3d. The atmosphere setting temperature Z4 of the fourth heating chamber 3d is set slightly higher ((at most about 1 to 2 ° C. higher)) than the atmosphere setting temperature Z3 of the third heating chamber 3c, and therefore passes through the fourth heating chamber 3c. Meanwhile, the sheet is substantially held at the final holding temperature T4.

  When t = 4τ, the sheet is conveyed to the cooling chamber 4 and cooled by cooling means such as a blower.

  As described above, by appropriately adjusting the atmosphere set temperatures Z1 to Z4 in the respective heating chambers 3 of the continuous heat treatment apparatus 100 as shown in the set temperature profile P2, the sheet according to the heat treatment profile P1 is heat treated and dried. Can be realized. In addition, by using the continuous heat treatment apparatus 100, it is possible to heat the sheet by continuously conveying the sheet to a heating chamber in which the heat treatment atmosphere is kept uniform. Therefore, it is possible to reliably and efficiently perform a good sheet drying process without causing sheet shrinkage variation and drying unevenness.

<Modification>
In the above-described embodiment, the heat treatment of the ceramic green sheet coated with the adhesive paste has been described as an example, but the application of the present invention is not limited to this. For example, the present invention can be applied to heat treatment of an electrode pattern formed by screen printing or the like on a ceramic green sheet.

  Moreover, in the above-mentioned embodiment, the case where it is what is called a continuous feed system which the conveyance means 2 conveys to the to-be-processed material 1 to each heating chamber 3 and the cooling chamber 4 is demonstrated. However, if the heating conditions in each heating chamber 3 are set so that a desired heat treatment profile is realized, for example, the object to be heat-treated 1 is stopped at a predetermined position in the heating chamber 3a and the heat treatment is performed for a predetermined time. After performing, it may be a mode using a so-called intermittent feeding method in which the heat treatment object 1 is quickly moved to the next heating chamber 3b and stopped at a predetermined position and heat treatment is repeated.

  Further, for example, both the heat treatment object 1 is conveyed using a continuous feed method for conveyance in a heating chamber, and the intermittent feed method is conveyed for conveyance in another heating chamber. May be used separately.

  Moreover, in the above-mentioned embodiment, although the case where the continuous heat processing apparatus provided with four heating chambers is used is demonstrated, if uniform drying can be achieved by performing heat treatment according to the heat treatment profile P1, The configuration of the continuous heat treatment apparatus is not limited to this, and an apparatus having more heating chambers may be used.

  Or the aspect which performs heat processing, conveying a sheet | seat like the above-mentioned continuous heat processing apparatus is not essential, What kind of thing will be sufficient if it can implement | achieve uniform drying by performing heat processing according to heat processing profile P1? An embodiment using a heating device may be used.

(Example)
Prepare 100 sheets of zirconia-based ceramic green sheet coated with (zirconia + binder) as an adhesive paste, and use these as sheets 1 to be heat-treated by a continuous heat treatment apparatus 100 to perform heat treatment profile. A heat treatment according to P1 was performed. As the ceramic green sheet, one having a size of 150 mm × 114 mm and a thickness of 200 μm was used. The heat treatment was performed by continuous feeding.

  The heat treatment profile P1 was as follows: intermediate holding temperature T1 = about 60 ° C., final holding temperature T2 = about 85 ° C., Δt1 = 2 minutes, Δt2 = 3 minutes, Δt3 = 1 minute, Δt4 = 3 minutes, Δt5 = 1 minute. And the setting profile P2 was defined so that the heat processing profile P1 might be implement | achieved. Specifically, τ = 10 minutes, Z1 = 66 ° C., Z2 = 60 ° C., Z3 = 88 ° C., and Z4 = 92 ° C.

  For each sheet, the dry state of the adhesive paste and the state of the ceramic green sheet were evaluated according to the following four items.

  Evaluation item (1) Measurement of weight reduction rate of solvent: Using weights w1, w2, and w3 measured with an electronic balance before, after application of the adhesive to the ceramic green sheet, and before and after heat treatment. The weight reduction rate Δ of the solvent accompanying the heat treatment was determined by the following formula.

      Δ = (w2-w3) / (w2-w1) × 100 (Formula 3)

  The obtained sheet having a weight reduction rate Δ of 80% or more and 90% or less was determined to be satisfactorily dried. Those having a weight reduction rate Δ outside the above range were determined to be defective in drying because sufficient adhesive strength could not be obtained when laminated with other sheets in a subsequent step.

  Evaluation item (2) Determination of surface dryness: The degree of drying of the surface of the adhesive paste in the sheet after heat treatment was determined. The surface state was confirmed using a microscope, and in the case of a wet shape, it was determined that the surface was not sufficiently dried to the extent that adhesion to other sheets could be secured at the time of lamination.

  Evaluation item (3) Crack inspection: It was confirmed whether or not cracks were generated on the surface of the ceramic green sheet on which the adhesive paste was printed. The surface state was confirmed using a microscope, and when a crack was generated on the sheet surface, the sheet was determined to be poorly dried.

  Evaluation item (4) Measurement of sheet shrinkage: Before and after heat treatment, the distance between holes formed in the vicinity of the edge of the ceramic green sheet was measured using a microscope, and the difference between the two was measured by drying. The amount of shrinkage was determined. Similarly, when the difference from the measured shrinkage amount of other sheets exceeded 0.24 mm, it was determined that the drying was poor.

(Comparative Example 1 and Comparative Example 2)
As Comparative Example 1 and Comparative Example 2, 100 sheets manufactured under the same conditions as in the Examples were subjected to heat treatment with two simple profiles with different final holding temperatures using the continuous heat treatment apparatus 100. went. FIG. 4 is a diagram showing a heat treatment profile P3 according to Comparative Example 1 and a heat treatment profile P4 according to Comparative Example 2.

  As shown in FIG. 4, in the heat treatment profile P3 according to Comparative Example 1, the final holding temperature was about 85 ° C., which is the same as the final holding temperature of the example. In the heat treatment profile P4 according to Comparative Example 2, the final holding temperature was set to about 60 ° C., which is the same as the intermediate holding temperature of the example. In both Comparative Example 1 and Comparative Example 2, the sheet temperature reaches the final holding temperature in 1 minute after the start of the heat treatment, and the holding is performed for 8 minutes at the final holding temperature. The heating conditions and the conveyance speed in each heating chamber 3 of the continuous heat treatment apparatus 100 were set so that the temperature was lowered to room temperature.

  Specifically, in Comparative Example 1, Z1 = 86 ° C., Z2 = 85 ° C., Z3 = 85 ° C., Z4 = 85 ° C., and τ = 10 minutes.

  In Comparative Example 2, Z1 = 66 ° C., Z2 = 60 ° C., Z3 = 60 ° C., Z4 = 60 ° C., and τ = 10 minutes.

  About the sheet | seat after heat processing, evaluation similar to an Example was performed.

(Comparison of Example and Comparative Example)
Table 2 shows the results of evaluation performed in Examples, Comparative Example 1, and Comparative Example 2. In Table 2, for each evaluation item, the ratio of the number of sheets determined to be defective is shown as a percentage.

  As shown in Table 2, in the example, there was no sheet determined to be defective, but in Comparative Example 1 and Comparative Example 2, there was a sheet determined to be defective in any item.

  Although not directly appearing in the results of Table 2, in Comparative Example 1, the weight reduction rate of the solvent exceeded 90% in any of the sheets determined to be poor with respect to the evaluation item (1). That is, the solvent was often reduced excessively. On the other hand, in Comparative Example 2, on the other hand, the weight reduction rate of the solvent did not reach 80% in any of the sheets judged to be poor for the evaluation item (1). Further, only in Comparative Example 2, a defect occurred in the evaluation item (2). These results show that if the holding at 85 ° C. is long as in Comparative Example 1, drying proceeds too much, and if the holding temperature is as low as 60 ° C. as in Comparative Example 2, it is sufficient to hold for the same time. While drying does not proceed, it indicates that good drying can be achieved when two-step heat treatment is performed with 60 ° C. as the intermediate holding temperature and 85 ° C. as the final holding temperature as in the examples. .

  Further, only in Comparative Example 1, defects in the evaluation items (3) and (4) occurred. This is considered to be caused by a fast heating rate of raising the temperature to the final holding temperature of 85 ° C. in 1 minute. Such a result is considered to mean that it is not preferable to rapidly increase the sheet temperature after the start of the heat treatment, because it causes deterioration of the sheet state such as generation of cracks and increase in shrinkage variation.

  On the other hand, in the example, no defect occurred in any of the evaluation items. Therefore, when the adhesive paste applied on the ceramic green sheet was dried, the heat treatment profile according to the example was used for the sheet. It can be said that heat treatment is preferable.

DESCRIPTION OF SYMBOLS 1 Heat processing object 2 Conveying means 3 (3a-3d) Heating chamber 4 Cooling chamber 5 (5a-5d) Damper 6 Heater 7 Temperature sensor 8 Temperature control part 9 Fan 10 Rectification plate 11 (11a-11d) Exhaust path 12 Filter 13a Side flow passage 13b Upper flow passage 14 Bulkhead 15 Heating space 100 Continuous heat treatment apparatus

Claims (9)

A method for heat-treating an object to be heat-treated by applying a bonding paste for bonding to a ceramic green sheet to another ceramic green sheet,
A first temperature raising step for raising the temperature of the object to be heat-treated to an intermediate holding temperature;
A second temperature raising step for raising the temperature of the object to be heat-treated to a final holding temperature;
The heat processing method of the to-be-processed object characterized by performing these in this order. The heat treatment method according to claim 1,
An intermediate maintaining step of maintaining the temperature of the object to be heat treated at the intermediate holding temperature after the first temperature raising step;
A final maintaining step of maintaining the temperature of the object to be heat treated at the final holding temperature after the second temperature raising step;
A method for heat-treating an object to be heat-treated, comprising: The heat treatment method according to claim 1 or 2,
A heat treatment method for an object to be heat treated, wherein the final holding temperature is higher than the intermediate holding temperature. A heat treatment method according to any one of claims 1 to 3,
The intermediate holding temperature is 50 ° C. or higher and 70 ° C. or lower,
The method for heat-treating an object to be heat-treated, wherein the final holding temperature is 75 ° C. or higher and 100 ° C. or lower. The heat treatment method according to claim 4,
The intermediate holding temperature is 55 ° C or higher and 65 ° C or lower,
The heat treatment method for an object to be heat treated, wherein the final holding temperature is 80 ° C. or higher and 90 ° C. or lower. A heat treatment method according to any one of claims 1 to 5,
A heat treatment method for an object to be heat-treated, wherein a temperature increase rate in the second temperature increase step is larger than a temperature increase rate in the first temperature increase step. A heat treatment method according to any one of claims 1 to 6,
Using a heat treatment apparatus capable of heating the object to be heat-treated in each of the plurality of heating chambers while transporting the object to be heat-treated sequentially between a plurality of heating chambers capable of independently controlling the atmospheric temperature, A heat treatment method for an object to be heat-treated, comprising performing a first temperature raising step, the intermediate maintaining step, the second temperature raising step, and the final maintaining step. The heat treatment method according to claim 7,
During the atmosphere heating, in each internal space of the plurality of heating chambers, an atmosphere flow having a substantially uniform flow rate in the horizontal direction from above to the transfer position of the object to be heat-treated is generated.
A heat treatment method for an object to be heat treated. The heat treatment method according to claim 8,
The atmosphere flow is formed by circulating the atmosphere of the internal space by a predetermined circulation means, and the flow rate of the atmosphere flow is made substantially uniform in the horizontal direction by providing a rectifying means above the transfer position.
A heat treatment method for an object to be heat treated.

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