WO2021065744A1 - Ceramic article assessment method and ceramic article production method - Google Patents

Abstract

The present invention pertains to a ceramic article production method that comprises: a step for obtaining a molded body by injecting raw material slurry prepared in the form of ceramic raw material into a forming mold and letting said raw material slurry harden, demolding said molded body from the forming mold, and creating a ceramic article by subjecting the molded body to a drying treatment, a degreasing treatment, and a firing treatment in this sequence; a step for obtaining a columnar molded body by injecting raw material slurry into a specimen-forming mold and letting said raw material slurry harden, demolding said columnar molded body from the specimen-forming mold, and creating a ceramic specimen by subjecting the columnar molded body to a drying treatment, a degreasing treatment, and a firing treatment in this sequence; and a step for performing a prescribed ceramic article assessment method to the ceramic specimen so as to determine whether the production of the ceramic article is to be continued or not.

Description

Evaluation method and manufacturing method of ceramic articles

The present invention relates to an evaluation method and a manufacturing method for ceramic articles.

For the molding of ceramic parts, various moldings such as pressure molding, cold hydrostatic molding (CIP), hot hydrostatic molding (HIP), injection molding, casting molding, extrusion molding, etc. are performed using ceramic powder as a raw material to be used. The method can be used to produce ceramic products of various shapes. And, in order to make the obtained ceramic parts have better characteristics, various measures have been taken here as well. For example, a ceramic molded product containing a curable resin and a solvent is made into a cured product by heat treatment or the like, and ceramics with few cracks, high shape retention, excellent dimensional accuracy, and excellent physical properties when made into a sintered body. A method for producing a molded product is known.

In addition, ceramic balls used for rolling bearings (ball bearings) are required to have high strength and extremely high sphericity. In general, in order to manufacture such ceramic balls, a molding process of compacting the ceramic raw material powder, a primary firing process of firing at a high temperature, and high temperature / high pressure such as HIP (hot hydrostatic press) or gas pressure firing are performed. A ceramic element sphere is produced through a secondary firing process in which the ceramic element is fired below, and the obtained ceramic element ball is further polished and finished to have a high sphericity by mechanical polishing or the like.

For quality control of such spherical ceramic balls, for example, as shown in FIG. 7, the strength of such spherical ceramic balls can be confirmed by a so-called crushing test in which two product balls are arranged and crushed by applying a compressive load. It is done (see, for example, Patent Document 1 and Non-Patent Document 1). Here, conventionally, the test apparatus 50 for a crushing test is composed of a lower member 51, an upper member 52, and an auxiliary member 53 that can hold two ceramic balls 100A and 100B in an overlapping manner. The lower member 51 and the upper member 52 each have a conical recess so that the ceramic balls 100A and 100B can be stably held. Here, the test apparatus 50 is shown in cross section.

Japanese Patent Application Laid-Open No. 5-294728

In such a crushing test, one test data (n = 1) is usually obtained from two test samples (hereinafter, also referred to as ceramic specimens). Generally, the intensity data needs to be at least n = 5, and in this case, at least 10 test samples are required. In addition, the Weibull distribution is usually used to evaluate the variability. The evaluation of the Weibull distribution requires at least n = 20, preferably n = 30. In this case, the number of test samples used is as high as 60.

It takes a lot of effort to prepare this number of spherical samples for testing. In the case of a spherical sample, if the shape accuracy is not good, it may be difficult to properly carry out the crushing test, so that a certain degree of shape accuracy is required to prepare the spherical sample. If there is a test method that can be evaluated more easily and can be replaced by using a test sample that has a lower shape accuracy level required than a spherical sample and has a shape that can be easily manufactured, cost reduction of product manufacturing, etc. It is also preferable.

There is also a method of performing a bending test by cutting out a plurality of 3-point bending test pieces or 4-point bending test pieces from the fired product for the purpose of strength evaluation. However, in these bending tests, the portion where the maximum stress is generated is the lower surface of the test piece, unlike the crushing test inside the test piece. Therefore, in the crushing test, it is considered that the material itself of the test sample can be evaluated, but in the bending test, it is affected by the processing state of the sample surface, so that it cannot be essentially replaced with the crushing test.

In addition, in order to produce a test sample for a bending test, it is necessary to process the test sample from the product, which causes a problem that a great deal of labor and cost are required.

In view of the above points, one aspect of the present invention is to provide a novel method for evaluating a ceramic article that can be replaced with a crushing test using a spherical sample in order to evaluate the strength of the ceramic article. .. Another object of the present invention is to provide a method for manufacturing a ceramic article, which efficiently manufactures a ceramic article having desired characteristics by using such an evaluation method.

As a result of diligent studies by the present inventors in order to solve the above problems, it has been found that the strength of a ceramic article can be evaluated by substituting for a spherical sample by using a cylindrical ceramic specimen as a test sample. ..

That is, in the method for evaluating a ceramic article according to one aspect of the present invention, a cylindrical ceramic specimen is produced by using a ceramic raw material for forming the ceramic article, and the two sides of the ceramic specimen are brought into contact with each other. The ceramic article is subjected to a crushing test, and the strength of the ceramic article is evaluated based on the result of the crushing test.

Further, in the method for producing a ceramic article according to one aspect of the present invention, a raw material slurry in which a ceramic powder, a resin, a curing agent and a solvent are mixed is prepared as a ceramic raw material, and the raw material slurry is injected into a molding die to form the molding die. The resin in the raw material slurry injected into is cured to prepare a molded body having a desired shape, the molded body is demolded from the molding die, and then the molded body is dried, degreased, and degreased. Each process of firing was performed in this order to prepare a ceramic article, and the raw material slurry was injected into a specimen molding die for forming a cylindrical ceramic specimen, and then injected into the specimen molding die. The resin in the raw material slurry is cured to prepare a cylindrical molded body, the cylindrical molded body is demolded from the sample molding die, and then dried with respect to the cylindrical molded body. , Degreasing and firing are performed in this order to prepare a ceramic specimen, and the ceramic article of the present invention is evaluated on the ceramic specimen to determine whether or not the production of the ceramic article can be continued. , Characterized by that.

According to the evaluation method for ceramic articles according to one aspect of the present invention, since the maximum stress is generated inside, the original strength of the material can be evaluated regardless of the processing quality of the surface as in the evaluation sample for bending test. It is possible, and it is possible to evaluate the proper manufacturing process and product characteristics.
Further, in one aspect of the present invention, since the sample shape to be used is a cylindrical shape, the shape accuracy required is not strict as compared with the conventional spherical sample for crushing test, and labor for preparing the same number of samples, Costs and the like can be greatly reduced as compared with spherical samples. Therefore, the time and cost required for evaluation can be significantly reduced from the conventional crushing test.
Further, since it is easy to prepare a cylindrical sample according to one aspect of the present invention, for example, in a ceramics manufacturing process using a slurry, it is easy to prepare a sample reflecting the state of the process in the middle of the process, and the process It can also be applied to determine the quality of the condition.

According to the method for producing a ceramic article according to one aspect of the present invention, it is possible to confirm whether or not the characteristics of the ceramic article to be produced are sufficient to produce the ceramic article. Therefore, when the characteristics are not sufficient, the manufacturing conditions can be reviewed, and the production and shipment of the product having the desired characteristics can be efficiently performed.

FIG. 1 is a perspective view showing an arrangement example of ceramic specimens in the evaluation method for ceramic articles of the present invention. FIG. 2 is a diagram showing an example of support for the ceramic specimen of FIG. FIG. 3 is a diagram showing another example of supporting the ceramic specimen of FIG. FIG. 4 is a diagram showing still another example of the support of the ceramic specimen of FIG. FIG. 5 is a diagram showing still another example of the support of the ceramic specimen of FIG. FIG. 6 is a flowchart showing an example of a method for manufacturing a ceramic article of the present invention. FIG. 7 is a diagram showing an example of supporting a specimen (product) for a crushing test using a conventional ceramic ball.

Hereinafter, a method for evaluating a ceramic article and a method for manufacturing a ceramic article, which is an embodiment of the present invention, will be described in detail.

[Evaluation method for ceramic articles]
In the method for evaluating a ceramic article according to an embodiment of the present invention, a cylindrical ceramic specimen is produced using a ceramic raw material for forming the ceramic article, and the two sides of the ceramic specimen are brought into contact with each other. A crushing test is carried out, and the strength of the ceramic article is evaluated based on the result of the crushing test.

Hereinafter, each of these processes will be described.

(Preparation of ceramic specimen)
The ceramic specimen in this embodiment is a cylindrical ceramic specimen. This ceramic specimen is a cylindrical ceramic body (sintered body) obtained by processing the same ceramic raw material as the ceramic article to be evaluated under the same conditions.

The ceramic raw material used here includes ceramic powder and an auxiliary material suitable for ceramic molding used for shape imparting. For example, those containing ceramic powder, additives such as organic substances, and solvents such as water are exemplified. In the present invention, any ceramic raw material suitable for a known ceramic molding method may be used, and the present invention is not particularly limited. For example, for press molding, the ceramic powder to which an organic binder is added may be powdered as it is, or may be granulated into granules. Further, in the case of slip casting molding or gel casting molding method, the ceramic powder may be formed into a slurry together with a resin and a dispersant or a curable resin and a curing agent. For injection molding and extrusion molding, it may be in the form of a kneaded product obtained by kneading ceramic powder with a fluidity-imparting material such as resin.

Further, in order to form such a ceramic raw material into a cylindrical shape, the molding method is not particularly limited, and the above-mentioned molding method may be appropriately adopted. As the cylindrical specimen molding die, for example, a molding die having a cylindrical cavity or a cylindrical syringe is used. A ceramic raw material may be injected into a cylindrical specimen molding die to obtain a cylindrical molded body. In a molding method using a slurry such as a gel cast method, a part of the slurry transport pipe may be opened and closed and used as it is as a production mold for a cylindrical shape. Alternatively, a part of the pipe may be made of a disposable material such as resin, and the pipe in that part may be removed and used as a sample as it is. Alternatively, a part of the pipe may be branched and a jig or the like for preparing a sample may be attached to the branch. That is, any mold such as a syringe, a pipe, and a jig that can give a shape other than a general mold can be used as a mold for a specimen of the present embodiment.
Further, it is also possible to obtain a cylindrical ceramic body (sintered body) by cutting out from a molded body or a sintered body once produced in a block shape and performing processing such as grinding.

The size of the ceramic specimen used at this time is not particularly limited, but if it is large, the amount of raw materials used for producing the ceramic specimen is large, and it takes time during processing such as molding and firing. For example, the diameter of the ceramic specimen is preferably 2 mm to 50 mm, more preferably 5 mm to 20 mm, and even more preferably 8 mm to 15 mm. The axial length of the ceramic specimen is preferably 5 mm to 100 mm, more preferably 10 mm to 50 mm, still more preferably 15 mm to 30 mm.

By doing so, it is possible to easily evaluate the composition and preparation of raw materials. For example, in the case of ceramic powder obtained by mixing nitride ceramics such as silicon nitride and oxide ceramics which is a sintering agent for silicon nitride ceramics, evaluation of the homogeneity of the mixture of nitride ceramics and oxide ceramics and ceramics Evaluation of the homogeneity of the mixture of the powder and the ceramic powder in the ceramic raw material containing additives such as resin, and the slurry when the ceramic powder, curable resin, hardener, water, etc. are gel-cast into a mold as a slurry. Property evaluation, etc. are exemplified, but the present invention is not limited to these.

The same can be applied to the evaluation of processing conditions after the preparation of raw materials. Examples of the treatment conditions include curing conditions, demolding conditions, drying conditions, degreasing conditions, firing conditions, and the like. Further, when evaluating the processing conditions, the manufacturing conditions of the ceramic article of the final product and the conditions of sufficiently treating the inside of the cylindrical ceramic specimen are equal to each other (with the deepest part of the ceramic article). The processing conditions can also be evaluated by adjusting the size of the ceramic specimen (so that the firing near the axis of the ceramic specimen can be evaluated equally).

Here, also in this evaluation method, since two specimens are required for one test as in the conventional crushing test, [number of tests (n) × 2] are prepared. To do.

(Crushing test)
Next, a crushing test is performed on the cylindrical ceramic specimen prepared as described above. The crushing test can be carried out by using two ceramic specimens, bringing their side surfaces into contact with each other, and applying a compressive load until the ceramic specimens are crushed. In this respect, the same operation may be performed except for the shape of the ceramic specimen used, which is different from that of the spherical ceramic specimen.

Further, in this crushing test, the side surfaces of the ceramic specimens are brought into contact with each other, and at that time, it is preferable to bring the ceramic specimens into contact with each other so that the contact points are one point. That is, by arranging the ceramic specimens so as not to be parallel to each other, the ceramic specimens can be brought into contact with each other at one point. The ceramic specimens are preferably arranged so that the axes of the ceramic specimens are orthogonal to each other. By doing so, the load at the time of the test is concentrated on the contact point, so that an appropriate strength evaluation can be performed. FIG. 1 shows a schematic view when the axes of the ceramic specimens 1A and 1B are orthogonal to each other and stacked vertically.

Hereinafter, the crushing test will be described with reference to the drawings.
FIG. 2 shows a schematic configuration of a test apparatus for a crushing test capable of holding a ceramic specimen as shown in FIG. 1 above. The test apparatus 10 shown in FIG. 2 compresses the lower member 11 that supports the lower ceramic specimen 1A from the lower part and the upper ceramic specimen 1B from the upper part, and applies a compressive load to the ceramic specimens 1A and 1B. It is composed of an upper member 12 and an auxiliary member 13 that assists the ceramic specimens 1A and 1B in a predetermined arrangement. FIG. 2 shows a front view of the test device 10 as (a) and a side view of the test device 10 as (b). In these figures, only the auxiliary member 13 is shown in a cross-sectional view in order to show the holding states of the ceramic specimens 1A and 1B inside the test apparatus 10.

Here, in order to perform an appropriate strength evaluation of the lower member 11 and the upper member 12, the contact portions with the ceramic specimens 1A and 1B are supported (contacted) by point contact, respectively. .. FIG. 2 shows an example in which the pedestal forming the contact portion is a ball pedestal. Further, the sphere pedestal has a curvature larger than the curvature of the circles (cross sections) of the ceramic specimens 1A and 1B so that the maximum stress is generated near the contact surface between the ceramic specimens in this test.

Further, the auxiliary member 13 has a support portion extending in the horizontal direction inside the ceramic specimens 1A and 1B so as to support the ceramic specimens 1A and 1B from the side surface so that their axes are orthogonal to each other.

Further, the material of the test apparatus 10 is not particularly limited as long as it can perform a crushing test well. As the support portion that comes into contact with the lower member 11, the upper member 12, and particularly the ceramic specimen, it is preferable that the Young's modulus of the constituent material is formed of a material having a Young's modulus smaller than that of the ceramic specimen. This makes it possible to properly carry out a crushing test of the ceramic specimen and evaluate the strength of the ceramic article itself.

This crushing test can be performed in the same operation as the test using a conventional ceramic ball, except that the specimen is different. That is, when the test apparatus 10 is used, the ceramic specimens 1A and 1B are held so as to have the arrangement shown in FIG. 1, and the upper member 12 applies a compressive load from above to below to make the ceramic specimens. The load is gradually increased until 1A and 1B are crushed, and the compressive load at the time of crushing can be evaluated as the crushing strength.

In this test, as with conventional ceramic balls, the maximum tensile stress is generated inside the contact points of the ceramic specimens 1A and 1B, causing median cracks, which trigger macroscopic fracture. Conceivable. In fact, from the ceramic specimens 1A and 1B that were fractured after the test, it was confirmed that the maximum tensile stress (starting point of fracture) was generated inside rather than on the surface.

As the test device, instead of the test device 10 in which the pedestal is a ball pedestal, the test device 20 shown in FIG. 3 in which the pedestal is an inclined cylindrical pedestal, and FIG. 4 in which the pedestal is a two-point ball pedestal. The test device 30 shown and the test device 40 shown in FIG. 5 in which the pedestal is a cylindrical pedestal without inclination can also be used.

These test devices 20, 30, 40 are basically composed of lower members 21, 31, 41, upper members 22, 32, 42, and auxiliary members 23, 33, 43, similarly to the test device 10. The axes of the ceramic specimens 1A and 1B are orthogonal to each other and can be brought into contact with each other and held. Here, the lower members 21, 31, 41 and the upper members 22, 32, 42 differ only in the shape (the shape of the pedestal) for holding the ceramic specimen. In the test apparatus 20, the two cylindrical support portions are inclined and extended. In the test device 30, two spherical supports are projected. In the test apparatus 40, one cylindrical support portion extends without inclination. Each of the test devices 20, 30 and 40 has a structure of being supported from below and above the ceramic specimen. In these test devices 20 and 30, two contact portions between the support portion and the ceramic specimen are arranged in a direction orthogonal to the axis of the ceramic specimen.

This crushing test is carried out with a plurality of sets of ceramic specimens, and the crushing strength of the ceramic article obtained by using the above ceramic raw materials is measured. For this crushing strength, the load value when the ceramic specimen is crushed is used as it is as the crushing strength. Weibull distribution is also considered in addition to the calculation of crushing strength. The Weibull distribution is understood as a fracture model of ceramic articles (weakest link model). Here, as an example, it is calculated by the Weibull statistical analysis method of the strength data of JIS R 1625: 2010 fine ceramics.

(Evaluation of strength)
Next, the ceramic article is evaluated based on the result obtained by the above crushing test. The evaluation of the ceramic article can be evaluated based on whether or not the strength required for the ceramic article is satisfied. That is, when a ceramic article is produced using the ceramic raw material of the ceramic specimen used in the test, it can be confirmed whether or not the ceramic article has the required strength.

The criteria for this evaluation can be set arbitrarily from the viewpoint of application and quality assurance. For example, in the case of a general industrial silicon nitride ball used for a ceramic bearing, the crushing strength of a cylinder having a diameter of 10 mm may be set to 20 kN or more. In the case of a silicon nitride sphere for a special purpose that requires high strength and high durability, the crushing strength may be set to 25 kN or more. The Weibull coefficient is preferably 10 or more, and more preferably 15 or more.

Then, it can be evaluated that the ceramic specimen satisfying this evaluation standard is a ceramic article in which the raw material slurry used is good and the ceramic body obtained by the same treatment also satisfies the required quality. Further, in addition to the good raw material slurry, it can be evaluated that the treatment was good in each of the subsequent steps of molding, demolding, drying, degreasing, and firing.

[Manufacturing method of ceramic articles]
The method for manufacturing a ceramic article according to an embodiment of the present invention includes a ceramic article manufacturing step, a ceramic specimen manufacturing step, and a determination step. Then, in both the ceramic article manufacturing step and the ceramic specimen manufacturing step, a ceramic raw material is prepared, the ceramic raw material is molded into a desired shape by a molding die, and the obtained molded body is dried, degreased, and subjected to drying and degreasing. Each process of firing is performed in this order (FIG. 6). Hereinafter, each of these operations will be described in detail.

(Raw material preparation process)
In the above operation, first, a ceramic raw material as a raw material for the ceramic article and the ceramic specimen is prepared (S1).

The ceramic raw material used here is not particularly limited as long as it can produce a ceramic article. Specific examples thereof include ceramic raw materials exemplified in the above-mentioned evaluation method for ceramic articles.

Among the ceramic raw materials, a slurry-like ceramic raw material (hereinafter referred to as a raw material slurry) obtained by mixing a ceramic powder with a resin, a curing agent and a solvent is preferable. In the ceramic raw material obtained by containing the resin in this way, the curing action at the time of molding is obtained by the function of the resin, so that the size and shape of the molded body have little influence on the density of the molded body, and thus the molding is performed. This is because there is little fluctuation in body density and the like, and the characteristics between the article as a product and the specimen can be equated as they are. That is, even if the size of the ceramic specimen for testing is reduced for a large-sized ceramic article (final product), the fluctuation of the result is small. Since the size of the ceramic specimen can be reduced, the consumption of the raw material slurry for the crushing test can be suppressed to a very low level. In this case, the influence on the cost on the amount of raw materials used can be reduced.

Hereinafter, a method for manufacturing a ceramic article will be described by taking the case of using this raw material slurry as an example.

First, the ceramic powder used here is not particularly limited as long as it becomes ceramics by sintering, and known ceramic powders can be mentioned. Examples of the ceramic powder include oxide ceramics such as aluminum oxide (alumina), zirconium oxide (zirconia), silicon oxide (silica) and cordierite, and nitrides such as silicon nitride, aluminum nitride and sialon (also referred to as SiAlON). Examples thereof include ceramics and carbide ceramics such as silicon carbide. One of these may be used alone, or two or more thereof may be mixed and used.

_{Further, the ceramic powder preferably has a 50% particle size D 50} of less than 1.0 μm so that a stable sintered body can be obtained in the sintering step described later. If the 50% particle size D ₅₀ is 1.0 μm or more, molding defects may occur due to particle sedimentation in the slurry, which may lead to a decrease in sintering density. The 50% particle size D ₅₀ is more preferably 0.8 μm or less, still more preferably 0.6 μm or less. Further, when the particle size D _{50 of the} ceramic powder is 0.1 μm or more, it is preferable because it is easy to prevent scattering, clogging and procurement during handling. In the present specification, 50% particle size D ₅₀ refers to a value measured by a laser diffraction type particle size distribution device.

When silicon nitride (component; Si ₃ N ₄ ) is used as the ceramic powder, the structure obtained by sintering is such that the main phase crystal particles containing silicon nitride as a main component are bonded to glassy and / or crystalline materials. It will be in a phase-bonded form.

At this time, as the silicon nitride powder, a powder having a silicon nitride pregelatinization rate of 70% or more is preferable, and the pregelatinization rate is more preferably 80% or more, further preferably 90% or more. If the powder has an pregelatinization rate of less than 70%, the effect of incorporating the needle-like structure during the phase transition from α to β during sintering cannot be sufficiently obtained, and the strength is lowered. If the powder has a pregelatinization rate of 90% or more, a sufficient incorporation effect can be obtained and a sintered body having high strength, particularly toughness, can be obtained. The silicon nitride powder preferably contains 85% by mass or more of silicon nitride having a pregelatinization rate of 70% or more, and more preferably 92% by mass or more.

In addition, as a sintering aid, Group 2 (alkaline earth metal), Group 3 (rare earth (carbon group)), Group 4 (titanium), Group 5 (metal acid metal (vanadium)), 1% by mass to 15% by mass of a sintering aid containing at least one selected from the group 13 (boron group (earth metal)) and 14th group (carbon group) element groups based on the oxide. It is preferably contained, and more preferably 2% by mass to 8% by mass. In order to obtain a uniform and high-strength sintered body, it is preferable that the content of the sintering aid is small, but if it is less than 1% by mass, it may be difficult to obtain a sintered body.

The resin is a component for molding a ceramic raw material into a desired shape in a curing step described later, and examples thereof include known curable resins. As the resin used in this embodiment, a resin that is required to have good shape retention by a curing step and forms a three-dimensional network structure by a polymerization reaction is used. At this time, it is preferable that the mixture is liquid in that the fluidity of the mixture is increased and the filling property into the molding die is good.

It is also required that the resin can be easily removed from the ceramic molded product in the degreasing operation after curing and before sintering. Examples of such resins include epoxy resins, phenol resins, melamine resins, acrylic acid resins, urethane resins and the like. Among them, epoxy resin is preferably used because it has good shape retention. Examples of the epoxy resin include glycidyl ether type epoxy resin of bisphenols such as bisphenol A type and bisphenol F type, phenol novolac type epoxy resin, cresol novolac type epoxy resin, glycidylamine type epoxy resin, and glycidyl such as aliphatic epoxy resin. Examples thereof include ether type epoxy resin, glycidyl ester type epoxy resin, methyl glycidyl ether type epoxy resin, cyclohexene oxide type epoxy resin, and rubber-modified epoxy resin.

The number average molecular weight of the epoxy resin is preferably 20,000 to 30,000. The number average molecular weight of the epoxy resin is more preferably 50 to 3000, still more preferably 50 to 2500, because it is easy to mix with the powder and a constant mechanical strength can be obtained.

The curing agent cures the resin and is selected according to the resin to be used. Examples of this curing agent include amine-based curing agents, acid anhydride-based curing agents, and polyamide-based curing agents. The amine-based curing agent is preferable in that the reaction is quick, and the acid anhydride-based curing agent is preferable in that a cured product having excellent thermal shock resistance can be obtained.

Examples of the amine-based curing agent include aliphatic amines, alicyclic amines, and aromatic amines, and any of monoamine, diamine, triamine, and polyamine can be used. Examples of the acid anhydride-based curing agent include methyltetrahydrophthalic anhydride and dibasic acid polyanhydride.

The solvent adjusts the viscosity of the mixture of raw materials to be used to form a slurry, which facilitates filling of the raw material slurry into the molding die. As the solvent used here, for example, water, alcohols, and other organic solvents can be used. Among them, water or a water system containing water as a main component is preferable from the viewpoint of manufacturing cost and environmental load.

At this time, in order to facilitate the removal of the resin in the degreasing operation described later, the combination of the resin and the solvent has a good affinity. If the affinity is poor, it may separate and segregate inside the molded product, which may cause defects such as pores during sintering.

The above-mentioned ceramic powder, resin, curing agent and solvent are mixed to prepare a raw material slurry. At this time, mixing may be performed by a known method, for example, a dissolver, a homomixer, a kneader, a roll mill, a sand mill, a ball mill, a bead mill, a vibrator mill, a high-speed impeller mill, an ultrasonic homogenizer, a shaker, a planetary mill, and a self-revolution. Examples include mixers and in-line mixers.

Further, in the case of the reaction curing type, since the reaction starts when the resin and the curing agent are mixed, the slurry containing the resin and the slurry containing the curing agent are separately prepared and used. Sometimes these may be mixed. At this time, the ceramic powder may be mixed with either slurry, may be mixed with both slurries, and a slurry containing the ceramic powder may be prepared separately. Above all, it is preferable to mix the ceramic powder with both slurries containing each of the resin and the curing agent and prepare them at the same concentration because the concentration fluctuation and the like are small when mixed and stable operation is possible. ..

First, the above-mentioned raw materials are mixed and stirred to prepare a raw material slurry.
The viscosity of the raw material slurry obtained here may be any viscosity as long as it can be easily filled in the slurry injection described later. For example, the viscosity at a shear rate of 10 [1 / s] is preferably 50 Pa · s or less, and 20 Pa · s. The following is more preferable. Considering the handleability after filling, the viscosity of the raw material slurry is more preferably in the range of 0.1 Pa · s to 10 Pa · s. This viscosity can be easily adjusted by adjusting the amount of solvent used and the amount of resin added in the raw materials used.

In addition, air or the like may be entrained by the mixing in the raw material mixing, and gas may be contained in the obtained raw material slurry. Therefore, it is preferable to perform a defoaming treatment in order to remove the gas contained in the raw material slurry before the next slurry injection. If gas is contained in the raw material slurry, pores due to air bubbles may be generated inside in the curing process and may remain in the ceramic article obtained by firing.

For this defoaming treatment, the raw material slurry may be defoamed in a reduced pressure state, and a defoaming pump (vacuum pump), a defoaming mixer, or the like can be used. Defoaming may be performed, for example, for 1 minute to 5 minutes under a reduced pressure of 0.6 kPa to 10 kPa. When a defoaming mixer is used, the raw material mixing treatment and the defoaming treatment can be performed at the same time. Examples of the defoaming mixer used here include a rotation / revolution mixer equipped with a vacuum pump, a planetary mixer, and the like.

After preparing the ceramic raw material, the ceramic article and the ceramic specimen are prepared respectively. These fabrication operations will be described in detail below.

<Ceramic article manufacturing process>
The above-mentioned raw material slurry is used for producing the ceramic article, but the slurry injection into the molding die, the demolding, the drying, the degreasing, and the firing may be carried out in order in the same manner as in the production of the known ceramic article.

(Slurry injection)
Slurry injection is a step of injecting the raw material slurry obtained through the above-mentioned raw material mixing and defoaming into a molding die (S2). The molding die used here has a predetermined shape for producing a product shape, and a conventionally known molding die or an arbitrary molding die can be used. As the molding mold, various molds such as a mold, a resin mold, a styrofoam mold, a rubber mold, and an elastic container can be used.

In order to inject the slurry into such a mold, a device capable of sending the raw material slurry and supplying it into the mold may be used. For example, pumps such as a diaphragm pump, a tube pump, and a syringe pump are generally mentioned. In particular, a rotary positive displacement diaphragm pump equipped with a precision constant velocity cam having a structure that does not generate pulsation is preferable. Further, an in-line mixer or the like that can send a liquid while mixing raw materials to prepare a raw material slurry can also be used. When an in-line mixer is used, the raw material mixing step and the slurry injection step can be carried out at the same time. Further, when the in-line mixer prepares and molds a slurry containing a resin as a raw material slurry and a slurry containing a curing agent as described above, both slurries are mixed and immediately sent to a molding mold for filling. It is possible and preferable.

(Curing)
In the curing treatment, after the raw material slurry is injected into the molding die, the resin component in the raw material slurry is cured to form the ceramic raw material into a desired shape (S3). In this curing treatment, desired curing conditions are appropriately selected and cured according to the characteristics of the raw material slurry.

For example, in the case of a reaction-curing type raw material slurry, the reaction starts from the time when the slurry containing the resin component and the slurry containing the curing agent component are mixed and cured, so that the slurry may be left for a predetermined time. At this time, the curing time is about 1 hour to 3 days, preferably 1 hour to 24 hours, and more preferably 1 hour to 12 hours from the viewpoint of production efficiency.

Further, in the case of a heat-curing type raw material slurry, it is sufficient to heat it to a desired temperature and secure a sufficient curing time. For example, it may be heat-cured at 80 ° C. to 150 ° C. for 5 minutes to 120 minutes. Considering the production conditions, production efficiency, etc., 80 ° C. to 100 ° C. for 5 minutes to 90 minutes is preferable, and 80 ° C. to 100 ° C. for 5 minutes to 60 minutes is more preferable.

(Demolding)
The demolding treatment is a treatment for taking out the molded product of the ceramic raw material cured by the curing treatment from the molding mold (S4). This demolding process may be performed by a conventionally known method, for example, disassembling the split mold, extruding the molded product from the mold to the outside, or destroying the mold in some cases. , The inner molded body may be taken out and removed from the mold.

(Dry)
The drying treatment is a treatment of removing water, a volatile solvent, and the like from the molded product obtained by the demolding treatment and drying the molded product (S5). In this drying treatment, the molded product is gently dried so as not to cause cracks or the like. That is, the molded product is dried while preventing the occurrence of cracks and the like due to shrinkage stress due to the difference in drying speed between the surface and the inside of the molded product.

The conditions of this drying treatment include, for example, 25 ° C. to 30 ° C., relative humidity of 60% to 95%, relatively mild conditions such as 48 hours to 7 days, and moisture contained in the molded product over a long period of time. There are conditions for removing. Here, the drying is preferably performed so that the water content of the molded product is 20% or less with respect to the mass at the time of absolute drying.

(Solvent degreasing)
The degreasing treatment is a treatment for removing the resin, the non-volatile solvent, etc. from the molded product obtained by the drying treatment (S6). In this treatment, it is preferable to almost completely remove the components that inhibit sintering in the next sintering treatment. If a large amount of such a component remains, pores may be generated in the sintered body during sintering, or carbides may be generated as by-products, and the characteristics required for the final product may not be obtained. There is.

Examples of the conditions for this degreasing treatment include conditions for removing the resin component and the like contained in the molded product at 400 ° C. to 800 ° C. over a relatively long time such as 2 days to 14 days. Here, particularly in the degreasing treatment of silicon nitride, the amount of residual carbon in the molded product is preferably 200 ppm or less. This does not apply to carbides such as silicon carbide.

(Baking)
The firing treatment is a treatment of sintering a ceramic raw material into a ceramic article by firing the molded product that has undergone the degreasing treatment (S7). In the firing in this firing process, the mixed powder is sintered to obtain ceramics, which may be produced by a known firing method.

The firing conditions in the firing process are not particularly limited as long as the ceramic body can be obtained by firing. For example, when firing silicon nitride, an atmosphere having an oxygen concentration of 50 ppm or less is preferable under a nitrogen atmosphere. At this time, the maximum firing temperature in this treatment is 1800 ° C. or lower at which silicon nitride begins to thermally decompose, and the maximum temperature is preferably in the range of 1650 ° C. to 1750 ° C. The firing time is preferably in the range of 4 hours to 12 hours.

(Secondary firing process)
A secondary firing treatment may be performed in order to further obtain a sintered body having desired characteristics from the fired body obtained by the firing treatment. In this secondary firing treatment, the fired body obtained by the firing treatment (primary firing) is further subjected to a high-pressure firing treatment to densify the structure of the fired body.

As the high-pressure firing process in this secondary firing process, a hot isotropic press (HIP), a gas pressure firing, a hot press, or the like can be used. Generally, in order to obtain a high-strength sintered body, it is preferable to treat it with HIP in the range of 1500 ° C. to 1700 ° C. and 50 MPa to 200 MPa.

<Ceramics specimen manufacturing process>
In the production of the ceramic specimen, the slurry injection into the molding mold, the demolding, the drying, the degreasing, and the firing may be performed in order in the same manner as in the production of the ceramic article. It should be noted that this step is the same as the above description except that the molding die used for producing the cylindrical specimen is of a predetermined shape.

(Slurry injection)
As described above, the slurry injection is a step of injecting the raw material slurry obtained through the above-mentioned raw material mixing and defoaming into a molding die (S8). The molding die used here has a predetermined shape such as a cylindrical cavity in order to produce a cylindrical ceramic specimen, and this ceramic specimen is used in the evaluation method of the ceramic article. It is a ceramic specimen. Therefore, the ceramic specimen may be a molding mold for obtaining the specimen described in the above evaluation method. The molding die used here does not have to be the shape of the ceramic specimen itself, unlike the molding die when the obtained molded body is processed into a ceramic specimen.

Then, the obtained molded product for the ceramic specimen is subjected to each of curing (S9), demolding (S10), drying (S11), degreasing (S12), and firing (S13) as described above. Do. Since each of these processes has the same contents as each process in the ceramic article manufacturing step described above, the description thereof will be omitted.

It is preferable that the ceramic specimen is manufactured under the same conditions at the same time as the production of the ceramic article. That is, it is preferable that the processing conditions are the same in the ceramic article manufacturing step and the ceramic specimen manufacturing step. Further, the ceramic article manufacturing step and the ceramic specimen manufacturing step may be performed as separate processes, but it is more preferable to perform the same process in parallel, and the ceramic article and the ceramic specimen are processed in the same processing device. Is the most preferable.

Further, it is preferable to make the volume of the ceramic specimen smaller than the volume of the ceramic article because the amount used as a test piece is smaller than the total amount of the raw material used and the production efficiency of the ceramic article is improved. This is particularly effective when the volume of the ceramic article as a product is large or when the number of products produced is small. At this time, the volume of the ceramic specimen is preferably 1/4 or less, more preferably 1/15 or less, and further preferably 1/100 or less with respect to the volume of the ceramic article.

<Judgment process>
Next, the ceramic article evaluation method described first is carried out on the ceramic specimen obtained by the above-mentioned ceramic specimen manufacturing method (S14), and it is determined whether or not the obtained evaluation result is good. (S15).

If this evaluation result is good, the manufacturing process of the ceramic article is continued (S16). Then, the produced ceramic article is shipped as a final product.

On the other hand, if this evaluation result is not good, the process returns to the raw material preparation (S1), and the method for manufacturing the ceramic article is repeated again. In this case, it is considered that the cause is any of the processes from raw material preparation (S1) to firing (S7), and at least one of the conditions is changed so that the evaluation result becomes good. As an example, it is preferable to confirm and examine the quality of the raw materials used, the blending of the mixed raw materials, the mixing of the raw materials, the defoaming conditions, and the like, and change some conditions for the defects in the raw material adjustment stage.

For the judgment of quality, the standard may be set according to the strength required for the product. As this standard, the standard described in the above-mentioned evaluation method for ceramic articles may be used.

Hereinafter, the present invention will be described in more detail based on Examples and Comparative Examples, but the present invention is not construed as being limited to these Examples. Here, an example in which silicon nitride is used as the ceramics will be described, but ceramics other than silicon nitride can be used in the same manner.

[Example 1 (Example)]
(Preparation of slurry SN)
Silicon nitride powder (manufactured by Denka Co., Ltd., trade name SN-9FWS) 73.11 parts by mass, spinel powder 2.09 parts by mass as sintering aid, 23.19 parts by mass of water as solvent, fourth grade as dispersant 1.61 parts by mass of ammonium salt (manufactured by Seichem) was mixed by a ball mill to prepare a silicon nitride slurry (slurry SN) as a base of the raw material slurry.
In the above ball mill, a silicon nitride ball (manufactured by Nikkato Corporation, diameter 5 mm) was used as the pulverizing medium.

(Preparation and defoaming of slurry SN1)
90.10 parts by mass of the above slurry SN and 9.90 parts by mass of a water-soluble epoxy resin (manufactured by Nagase ChemteX Corporation) are mixed by a rotating and revolving mixer equipped with a vacuum pump, and the epoxy resin-containing silicon nitride slurry (slurry SN1). Was prepared.
By reducing the pressure (0.6 kPa), the slurry SN1 did not contain bubbles of 10 μm or more.

(Preparation and defoaming of slurry SN2)
Vacuum 98.4 parts by mass of the above slurry SN and 1.6 parts by mass of a resin curing agent (a mixture of triethylenetetramine and 2,4,6-tris (dimethylaminomethyl) phenol in a mass ratio of 2: 1). A silicon nitride slurry (slurry SN2) containing a resin curing agent was prepared by mixing with a pump-mounted rotating and revolving mixer.
By reducing the pressure (0.6 kPa), the slurry SN2 did not contain bubbles of 10 μm or more.

(Slurry injection)
The slurry SN1 was filled in the slurry tank 1 and the slurry SN2 was filled in the slurry tank 2 so as to have the same volume. Next, using two rotary positive displacement diaphragm pumps manufactured by Takumina Co., Ltd. equipped with a precision constant velocity cam that does not generate pulsation and does not generate air entrainment, slurry SN1 from slurry tank 1 and slurry tank 2, respectively. And the slurry SN2 was sucked and discharged. The liquid was sent to an in-line mixer (trade name: static mixer) manufactured by Noritake Company via a pipe for merging the slurry SN1 and the slurry SN2.

It was mixed with an in-line mixer to obtain a raw material slurry 1 containing an epoxy resin and a resin curing agent. At the same time as obtaining the raw material slurry 1, the raw material slurry 1 was supplied to a product molding mold connected to the outlet side of the in-line mixer.

Subsequently, the raw material slurry 1 was supplied to a Saint-Gobain Tygon tube 2375 (outer diameter 19.0 mm, inner diameter 12.7 mm), which is a tube for a specimen. This was carried out by reconnecting a tube for a specimen to the outlet side of the in-line mixer after supplying the molded product for the above product.
(Curing)
The tube filled with the raw material slurry 1 was allowed to stand at room temperature of 25 ° C. overnight to react the epoxy resin with the resin curing agent and cure it.

(Demolding)
A columnar molded product was obtained by carefully cutting the tube and the molded product cured in the tube with a cutter. The length was trimmed to 25 mm. The number was 40.

(Dry)
The columnar molded product was allowed to stand in a constant temperature / humidity bath controlled at a temperature of 25 ° C. and a relative humidity of 90% for 1 week to dry.

(Solvent degreasing)
The dried columnar molded product was heated from room temperature to 700 ° C. for 1 week in an air atmosphere and kept at 700 ° C. for 1 day to burn off the contained cured resin component and degreas it.

(Baking)
The degreased columnar molded product was fired in a nitrogen atmosphere at 1700 ° C. and a holding time of 12 hours. After this firing, a columnar silicon nitride sintered body was obtained.

(HIP)
Further, the columnar silicon nitride sintered body was subjected to HIP (hot isostatic pressing) at 1700 ° C. under a pressure of 100 MPa using nitrogen gas as a pressure medium. After HIP, 40 dense columnar silicon nitride specimens 1 having a density of 3.2 g / cm ³ and a diameter of about 10 mm and a length of 20 mm were obtained.

Using 40 columnar silicon nitride specimens 1 obtained, they were laminated so that their axes were orthogonal to each other using the test equipment for the crushing test shown in FIG. 2, and a load was applied to them from above until they were crushed. The load at the time of crushing (= crushing strength) was measured. This crushing test was carried out 20 times, and a crushing strength (average value) of 30 kN and a Weibull coefficient of 17 were obtained. The columnar silicon nitride specimen used here has a straightness of less than 2 mm and a roundness of less than 0.5 mm.

In addition, the fracture surface after the completion of the crushing test was observed using an Olympus stereomicroscope (trade name: SZX16) with an eyepiece lens magnification of 10 times and an objective lens magnification of 1 to 2.5 times. As a result of observation, it was confirmed that the fracture progressed from a depth of about 1 mm from the contact surface, that is, the maximum stress was generated inside the cylindrical silicon nitride specimen 1.

[Example 2 (Comparative example)]
Using the same raw material slurry 1 as in Example 1, a cylindrical ceramic molded product having a diameter of 12 mm was obtained. Subsequently, the cylindrical ceramic molded body was subjected to spherical raw processing, degreasing, and firing to obtain a spherical silicon nitride specimen having a diameter of about 10 mm.

The obtained spherical silicon nitride specimen was subjected to a load (= crushing strength) test at the time of crushing 20 times using the conventional crushing test test apparatus shown in FIG. As a result, a crushing strength (average value) of 16 kN and a Weibull coefficient of 16 were obtained.

Further, the fracture surface of the spherical silicon nitride specimen after the completion of the crushing test was observed using an Olympus stereomicroscope (trade name: SZX16) with an eyepiece lens magnification of 10 times and an objective lens magnification of 1 to 2.5 times. As a result of observation, it was confirmed that the fracture progressed from a depth of 1 mm to 2 mm from the contact surface, that is, the maximum stress was generated inside the spherical silicon nitride specimen.

Comparing Example 1 and Example 2, it was found that the Weibull coefficient indicating the degree of strength variation was as large as 17 (Example 1) and 16 (Example 2), and the intensity variation was small in both methods. Therefore, it was confirmed that the crushing test using the cylindrical silicon nitride specimen in the present embodiment can be evaluated in the same manner as the crushing test using the conventional spherical silicon nitride specimen. Therefore, in the evaluation of the ceramic article, it was confirmed that the crushing test using the columnar specimen according to the present invention can be replaced with the crushing test using the conventional spherical specimen.

[Example 3 (Example)]
Same as Example 1 except that the slurry SN of Example 1 contains 69.19 parts by mass of silicon nitride powder, 3.76 parts by mass of itria powder and 2.25 parts by mass of alumina powder instead of spinel powder as a sintering aid. The raw material slurry 2 was prepared.

A columnar silicon nitride specimen 2 was prepared under the same conditions as in Example 1 except that the obtained raw material slurry 2 was used, and a crushing test was performed. As a result, the crushing strength (average value) was 25 kN, and it was confirmed that the strength was different due to the difference in the slurry raw materials.

[Example 4 (Example)]
A columnar silicon nitride specimen 3 was prepared under the same conditions as in Example 1 except for the firing conditions, and a crushing test was carried out. Here, the firing was carried out at normal pressure at 1700 ° C. for 12 hours, and then at 10 MPa and 1700 ° C. at high pressure. As a result of the crushing test, the crushing strength (average value) was 20 kN, and the difference in strength due to the difference in firing conditions could be confirmed.

[Example 5 (Example)]
Among the cylindrical silicon nitride specimens prepared by the same operation as in Example 1, those having a straightness of 2 mm or more and a roundness of less than 0.5 mm were selected and used as the cylindrical silicon nitride specimen 4. A crushing test was carried out in the same manner as in Example 1 using the cylindrical silicon nitride specimen 4. As a result, a result not significantly different from that of Example 1 was obtained.

[Example 6 (Example)]
Among the cylindrical silicon nitride specimens prepared by the same operation as in Example 1, those having a straightness of less than 2 mm and a roundness of 0.5 mm or more were selected and used as the cylindrical silicon nitride specimen 5. A crushing test was carried out in the same manner as in Example 1 using the cylindrical silicon nitride specimen 5. As a result, a result not significantly different from that of Example 1 was obtained.

[Example 7 (Comparative example)]
Using the same raw material slurry 1 as in Example 1, a ceramic article was prepared, and a test piece for a 3-point bending sample was cut out from this and processed so that the surface roughness Ra on the four surfaces was 0.5 μm to prepare the test piece. Obtained. As a result of performing a three-point bending test using these test pieces, the average strength was 720 MPa. At this time, when observing the fracture surface after the test, it was found that there were many test pieces in which fracture progressed starting from the defective part of the surface and corners that were on the lower side at the time of the test, and the maximum stress was tested. It was found to be the lower surface, not the inside of one piece.

From the above, according to the method for evaluating a ceramic article and the method for manufacturing a ceramic article of the present invention, the original strength of the material of the ceramic article can be measured and evaluated in place of the conventional crushing test, and further, the final product, the ceramic article. Can be manufactured efficiently.
At this time, according to the evaluation method of the ceramic article of the present invention, the shape and surface roughness of the ceramic specimen can be evaluated without being affected so much, and the evaluation is carried out without being bound by the processing conditions of the specimen. I found that I could do it.

The method for evaluating a ceramic article and the method for producing a ceramic article of the present invention can evaluate a ceramic article having a desired shape, and can efficiently produce a ceramic article while performing this evaluation. The ceramic article to be targeted here is not particularly limited as long as the raw material is a ceramic raw material, and can be widely used.

Although the preferred embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications to the above-described embodiments are made without departing from the scope of the present invention. And substitutions can be made.
This application is based on Japanese Patent Application No. 2019-18093 filed on September 30, 2019, the contents of which are incorporated herein by reference.

1A, 1B ... Ceramic specimens 10, 20, 30, 40 ... Test equipment 11, 21, 31, 41 ... Lower member, 12, 22, 32, 42 ... Upper member, 13, 23, 33, 43 ... Auxiliary Element

Claims (9)

1. Using the ceramic raw material for forming the ceramic article, a cylindrical ceramic specimen was prepared.
   A crushing test was carried out by bringing the two sides of the ceramic specimen into contact with each other.
   The strength of the ceramic article is evaluated based on the result of the crushing test.
   A method for evaluating ceramic articles.
2. The method for evaluating a ceramic article according to claim 1, wherein in the crushing test, the two ceramic specimens are arranged so that their axes are orthogonal to each other.
3. The method for evaluating a ceramic article according to claim 1 or 2, wherein in the crushing test, the ceramic specimen is supported by a ball pedestal or a cylindrical pedestal.
4. Prepare a raw material slurry in which ceramic powder, resin, curing agent and solvent are mixed as a ceramic raw material.
   The raw material slurry is injected into a molding die, the resin in the raw material slurry injected into the molding die is cured to produce a molded body having a desired shape, and the molded body is removed from the molding die. After that, the molded product was subjected to each treatment of drying, degreasing and firing in this order to prepare a ceramic article.
   The raw material slurry is injected into a specimen molding mold for forming a cylindrical ceramic specimen, and the resin in the raw material slurry injected into the specimen molding mold is cured to form a cylindrical shape. A body is produced, the columnar molded body is demolded from the test piece molding die, and then the columnar molded body is subjected to drying, degreasing, and firing in this order to perform ceramic specimens. To make,
   The ceramic article evaluation method according to any one of claims 1 to 3 is performed on the ceramic specimen, and it is determined whether or not the production of the ceramic article can be continued.
   A method for manufacturing a ceramic article.
5. The method for producing a ceramic article according to claim 4, wherein the ceramic specimen is produced in the same process as the production of the ceramic article except for a molding die for injecting the raw material slurry.
6. The method for producing a ceramic article according to claim 5, wherein the ceramic specimen is produced under the same conditions at the same time as the production of the ceramic article.
7. The method for manufacturing a ceramic article according to any one of claims 4 to 6, wherein the ceramic specimen is produced by injecting it into a cylindrical specimen molding mold.
8. The method for producing a ceramic article according to any one of claims 4 to 7, wherein the volume of the ceramic specimen is 1/4 or less of the volume of the ceramic article.
9. The ceramic powder contains silicon nitride having a pregelatinization rate of 70% or more in an amount of 85% by mass or more, and is selected from at least an element group of Group 2, Group 3, Group 4, Group 5, Group 13, and Group 14. The method for producing a ceramic article according to any one of claims 4 to 8, which contains 1% by mass to 15% by mass of a sintering aid containing one kind in terms of mass% based on oxides.

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