JP5013123B2 - Slurry production method - Google Patents

Description

The present invention relates to a method for producing a slurry .

  Slurries as a solid-liquid dispersion system in which solid particles are dispersed and mixed in a liquid are used not only in the field of fine ceramics but also in a wide range of industrial fields such as abrasive grains, cement, resins, and paints. The slurry is required to have not only characteristics as a solid-liquid dispersion system such as fluidity, coating characteristics and pot shell life but also various characteristics necessary for post-processing using the slurry as a material. This is the case when the slurry is used after being formed into a granular shape such as granules, a flat plate shape such as an extruded sheet, or a three-dimensional solid shape such as injection molding. This is because in such a case, the properties of the slurry itself have a great influence on the post-processability and the characteristics of the post-processed product.

  As described above, since the slurry has an important utility value in the industry, various studies have been accumulated on the slurry characteristics and various characteristics required when the slurry is post-processed. For example, a system (Patent Document 1) that enables continuous preparation of polishing slurry, a slurry (Patent Document 2) in which a polymer and inorganic particles are dispersed by adjusting the ζ potential, a toner for a copying machine (Patent Document 3), a dispersant Recent trends can be seen in the slurry (Patent Document 4) as a ceramic raw material containing the ceramic, the method of manufacturing the ceramic green sheet (Patent Document 5) and the like.

  Thus, the characteristics of the slurry are affected not only by the solvent as a solid-liquid dispersion system but also by chemical, physical, and electrochemical effects including the solid-liquid interface of solid particles (also referred to as primary particles).

  Furthermore, if ceramic is taken as an example, it will greatly affect the flowability and molding characteristics of the granules in the subsequent process such as forming the slurry after forming it into granules or green sheets and then sintering characteristics. Thus, various factors are intricately intertwined with the characteristics required for the slurry.

  Therefore, paying attention to the granule production process by the spray drying method, an example in which a binder and an emulsifier are used in combination (Patent Document 6) and a solvent that hardly dissolves the binder when granulating a rounded granule are added. There is an example (Patent Document 7), and there is a research (Non-Patent Document 1) that models the relationship between the pH adjustment condition of the slurry and the shape of the granule.

  In addition, techniques such as macro dispersion using additives and adjustment of ζ potential by a functional group of a polymer are also known (Patent Document 8, etc.).

  Furthermore, in the case of granulating granules using slurry as a raw material, a response (Patent Document 9 and the like) that attempts to manage the granulation work from the impeller resistance by paying attention to the bulk density of the granules and the particle diameter of the granules is also known. Yes.

  By the way, the most important matter required for granules is how to make solid spherical granules that are easy to mold.

However, in the above-described conventional method, even if the control parameters regarding the production of the slurry, the state of the slurry, the post-processing of the slurry, and the final product produced using the slurry are grasped for each process, the starting material In the process related to the whole process from the final product to the final product, the essential characteristic requirements that are the control parameters for making solid spherical granules are not clarified, and this causes the problem that the products are uneven and defective However, it was still unresolved.
JP 2000-308957 A JP 2000-273311 A JP 2001-31427 A JP 2001-48654 A Japanese Patent Laid-Open No. 2001-31474 Japanese Examined Patent Publication No. 63-27051 Kosho 63-29579 JP 2000-273111 A JP 2001-29769 A Journal of the Ceramic Society of Japan, Vol. 106, No. 12 (1998)

The subject of this invention is providing the manufacturing method of the slurry suitable for the production | generation of a spherical granule.

1. Slurry In order to solve the above-mentioned problems, first, the present invention provides a slurry in which solid component particles constitute a solid-liquid dispersion system in a liquid. The concentration of the particles is the average particle size of primary particles in the dispersed state of the particles. the diameter and D0, when the average particle diameter of the aggregated particles by agglomeration of the particles was D, (D / D0) and the aggregation degree represented by the spherical granules region obtained from the data showing the relationship between slurry viscosity and The non-spherical granule region is selected so as to fall within the spherical granule region.

  That is, in a slurry in which solid component particles form a solid-liquid dispersion in a liquid, for example, when a graph is created from experimental data indicating the relationship between the degree of aggregation (D / D0) and the slurry viscosity, this graph Was found to show spherical and non-spherical granule regions. Therefore, if the particle concentration or slurry viscosity of a slurry falls within the spherical granule region indicated by this graph, the slurry guarantees the production of spherical granules.

  The relationship between the degree of aggregation (D / D0) and the slurry viscosity is different for each particle material contained in the slurry, but in any case, when graphed, a spherical granule region and a non-spherical granule region are shown. Therefore, a slurry suitable for obtaining spherical granules for each particle material by experimentally collecting data on the relationship between the degree of aggregation (D / D0) and the slurry viscosity for each particle material contained in the slurry. Can be obtained.

  By the way, when the present invention is applied to the field of fine ceramics, the slurry includes ceramic powder, binder, dispersant, plasticizer, and the like, and may further include an antifoaming agent, an aggregating agent, and the like. . These components are mixed and stirred to produce a slurry.

  However, in accordance with the teaching of the present invention described above, even when the viscosity of the slurry and the concentration of the ceramic powder are selected so as to enter the spherical granule region, if the stirring is continued for a long time, the amount of the binder and the ceramic powder Depending on the concentration of the body, it may enter the non-spherical granule region from the spherical granule region. For example, in the process of granulating with a spray dryer etc., the slurry properties change, and initially the solid spherical granules become It was found that what was obtained might become a depressed granule.

  In order to solve the problem of the change with the passage of time, the present inventors have conducted intensive research. As a result, it was found that certain additives are extremely effective in suppressing the phenomenon of non-spherical granule region migration due to stirring. The additive has at least one hydroxyl group and is selected from the group consisting of carboxyl group, carboxylate, sulfonic acid, sulfonate, phosphoric acid, phosphate, amine, and quaternary amine salt. It is a non-polymeric organic compound having a group.

  For example, the organic compound is a hydroxyl group-containing carboxylic acid, a hydroxyl group-containing carboxylate, a hydroxyl group-containing sulfonic acid, a hydroxyl group-containing sulfonate, a hydroxyl group-containing phosphoric acid, a hydroxyl group-containing phosphate, a hydroxyl group-containing amine, and a hydroxyl group-containing quaternary ammonium. It can be selected from the group consisting of salts. More specifically, the organic compound is selected from the group consisting of citric acid, mesotartaric acid, hydroxyl group-containing lower carboxylic acid, hydroxyl group-containing lower alkenyl carboxylic acid, hydroxyl group-containing lower alkynyl carboxylic acid, hydroxyl group-containing aromatic carboxylic acid, and combinations thereof. Can be selected.

  In the application to the field of fine ceramics, as the research progresses further, the composition and manufacturing process are the same, but when using multiple types of ceramic powders with different production lots, a certain lot of ceramic powders Then, we faced the problem of entering into the non-spherical granule region in the ceramic powder of other lots, while entering into the spherical granule region. This problem has a direct influence on industrial mass production and must be solved.

  In order to solve this problem, the present inventors have further advanced research. As a result, it has been found that the addition of alkali is extremely effective in solving this problem. Specific examples include ammonia, sodium hydroxide, sodium carbonate, sodium hydrogen carbonate and the like.

2. Slurry management method In the slurry management method according to the present invention, the slurry is dropped onto a flat resin surface to form hemispherical droplets. Next, the droplet is heated to reduce the content of the liquid phase, and the property of the slurry is determined by the change in the shape of the hemispherical droplet during the drying process.

  According to the slurry management method of the present invention, it can be verified in a simulation whether or not the prepared slurry is suitable for obtaining spherical granules.

  Specifically, in the slurry management method, the degree to which the droplets are depressed by the drying is used as a criterion for determining the true sphericity and non-sphericity when the granules are formed. More specifically, when the droplets are recessed by the drying, it is determined that the true sphericity of the granules cannot be obtained, and when the droplets are not recessed, it is determined that the true sphericity is obtained.

3. Is hitting the preparation of the slurry according to a slurry of the production method the present invention, the average particle diameter D0 of the primary particles in the dispersed state of the particles, the ratio of the average particle diameter D of the agglomerated particles due to agglomeration of the particles (D / D0) Data showing the relationship between the degree of aggregation represented and the slurry viscosity is prepared.

  Next, the concentration of the particles in the solid-liquid dispersion is selected so as to fall within the spherical granule region out of the spherical granule region and the non-spherical granule region obtained using the data.

  According to the slurry manufacturing method of the present invention, the dispersed state of particles, the realization of the particle state, and the dispersed state required for the production of granules, which are the post-processing of the slurry, can be maintained. And the manufacturing method of the slurry which concerns on this invention is applicable to the solid-liquid dispersion system which is a composite_body | complex in which a solid-liquid is mixed in various aspects. In addition, the management parameters relating to the post-processing of the slurry and each of the final products produced using the slurry can be source-managed as the properties of the slurry.

  Data indicating the relationship between the degree of aggregation (D / D0) and the slurry viscosity is collected by conducting experiments for each particulate material constituting the slurry. Data indicating the relationship between the collected degree of aggregation (D / D0) and the slurry viscosity can be stored in a computer and displayed as a graph on the computer display. The graph on this display shows spherical and non-spherical granule regions.

  Therefore, the particle concentration or the slurry viscosity in the target slurry is set so as to fall within the spherical granule region of the spherical granule region and the non-spherical granule region shown on the graph. This makes it possible to create spherical granules.

Data indicating the relationship between the collected degree of aggregation (D / D0) and the slurry viscosity may be graphed on a paper surface and used as a data sheet.
Although a duplicate description is omitted, the method for producing a slurry according to the present invention includes all the steps for obtaining the slurry according to the present invention described above.

  Furthermore, the manufacturing method according to the present invention may include a step of stirring to form a floc-like or floc precursor aggregate after pulverizing from a state where the powder is agglomerated. In this case, the aggregation time can be controlled by adjusting the stirring time.

  As an alternative, the solvent properties may be adjusted to break up from agglomerated state into floc-like or floc precursor aggregates.

  As another means, it is also possible to employ a step of adjusting the average particle size distribution of the particles in order to obtain a floc-like or floc precursor aggregate after pulverizing from a state where the powder is agglomerated. it can.

  As yet another means, the ζ potential between particles may be adjusted in order to form a floc-like or floc precursor aggregate after crushing from a state where the powder is agglomerated.

  The properties of the slurry can be controlled by the degree of aggregation in which the particles form floc-like or aggregates of floc precursors in the solvent. The properties of the slurry may be controlled by at least one of the specific isoelectric point of the particles, the ζ potential (surface potential) of the interaction between the solvent and the powder, and the pH of the solvent.

4). Granule The granule according to the present invention is granulated from the slurry according to the present invention described above. These granules are spherical, and floc-like or aggregates of aggregated floc precursors form a skeleton inside.

  The granule according to the present invention described above is used for dry molding, injection molding, sheet molding and the like. Here, the granule according to the present invention is spherical, and is obtained by dry molding, injection molding, sheet molding, etc., because floc-like or aggregates of aggregated floc precursors form a skeleton inside. A final product having excellent characteristics can be obtained.

  In order to obtain solid spherical granules, the particles include fine particles and coarse particles, and the fine particles adhere to other fine particles or the coarse particles to form a floc-like or floc precursor. It is preferable to form an assembly of bodies. As another embodiment, the coarse particles may form floc-like aggregates of the fine particles or aggregates of floc precursors. In order to obtain solid spherical granules, it is preferable that the relative density difference between fine particles and coarse particles is small near the surface of the granules and near the center of the inside.

  Having a floc-like or aggregated floc precursor that leaves voids, having coarse particles that are sterically hindered, or having floc-like or floc precursor aggregates that are sterically hindered, specific shapes It is also an effective factor for obtaining solid spherical granules to contain a floc-like or aggregated form of aggregates of floc precursors and a porosity of 35% or more.

  As described above, according to the present invention, it is possible to provide a slurry suitable for producing spherical granules, a slurry management method, and a slurry production method.

1. Slurry In the slurry according to the present invention, solid component particles constitute a solid-liquid dispersion system in a liquid. The concentration of the particles is defined as (D / D0) when the average particle size of the primary particles in the dispersed state of the particles is D0 and the average particle size of the aggregated particles due to particle aggregation is D. The spherical granule region and the non-spherical granule region obtained from the data indicating the relationship with the viscosity are selected so as to fall within the spherical granule region.

  Therefore, according to the slurry concerning this invention, a spherical granule can be produced | generated reliably.

  FIG. 1 is a graph showing the relationship between the degree of aggregation (D / D0) of primary particles and slurry viscosity. In the figure, the horizontal axis represents slurry viscosity (Ps), and the vertical axis represents the degree of aggregation of primary particles (D / D0).

  The concentration is the volume concentration (vol%) of the powder in the slurry. The slurry includes a binder, a dispersant, a plasticizer, an antifoaming agent, and the like, and may further include a flocculant.

  Characteristics A11 to A13 indicate slurry viscosity-cohesion characteristics using the concentrations a11 to a13 (vol%) as parameters. The concentrations a11 to a13 (vol%) increase in the order of a11 <a12 <a13.

  In FIG. 1, the shaded area indicates the spherical granule area S1, and the white area defined by the straight line L0 from the spherical granule area S1 indicates the non-spherical granule area S2. As shown in FIG. 1, in a slurry in which solid component particles form a solid-liquid dispersion in a liquid, a graph obtained from experimental data indicating the relationship between the degree of aggregation (D / D0) and the slurry viscosity is spherical. A granule region S1 and a non-spherical granule region S2 are shown.

  Referring to FIG. 1, the concentration characteristics A11 to A13 indicate that the low viscosity is in the non-spherical granule region S2, but enters the spherical granule region S1 when the viscosity is high. Therefore, spherical granules can be obtained by preparing a slurry whose concentration or viscosity enters the spherical granule region S1 using the graph shown in FIG.

  Specifically, in a certain process, when the upper limit of the viscosity required for the slurry is PS1, spherical granules can be obtained if the slurry has a concentration of a12 (vol%).

  Assuming that a slurry having a concentration of a13 (vol%) is used, spherical granules can be obtained in any of the concentrations a13, a12, and a11 (vol%) if the viscosity is higher than PS2.

  As described above, the granule formed from the slurry according to the present invention has a spherical shape, the density in the vicinity of the surface and the inside is uniform, and there are innumerable pores, but the spherical shape has a high density. That is, being spherical is nothing but a high density and uniform granule.

  FIG. 2 is a graph showing the relationship between the degree of aggregation of primary particles (D / D0) and slurry viscosity for dielectric materials. In the figure, the horizontal axis represents slurry viscosity (Ps), and the vertical axis represents the degree of aggregation of primary particles (D / D0).

The dielectric material mentioned here is mainly composed of barium titanate, and has a dielectric constant of 93, a specific gravity of 5.8 (g / cm ³ ), and an average particle size (D50) of 1.9 μm. The slurry preparation conditions and the slurry physical property measuring method in this case are as follows.
(A) PVA
Polyvinyl alcohol (molecular weight 500) was used.
(B) Additive Dispersant: Synthetic polycarboxylic acid NH ₄ salt Plasticizer: DEG (diethylene glycol)
Antifoaming agent: Octyl alcohol (c) blending ratio The following amounts were added per 100 g of powder (primary primate) according to the mass production conditions.
PVA: 13cc / 100g of powder
Plasticizer: 1cc / 100g powder
Defoamer: 1cc / 100g powder
Dispersant: 0 to several cc / 100 g of powder
Pure water: remainder (amount depends on concentration)
(D) Slurry production method Using a homogenizer, a solvent (water, 10 PVA, 10 plasticizer, 10 antifoaming agent) was first prepared, and powder was gradually added while stirring. A dispersing agent was added when the powder did not dissolve or in order to obtain the target viscosity. Agitation was performed at 2000 r. p. m for 5-30 minutes.

(E) Measuring method of slurry physical properties The average particle diameter D0 of the primary particles of the particles was measured with a laser diffraction particle size distribution meter (SALD-2100) manufactured by Shimadzu Corporation. In the measurement, the dry powder of primary particles was diluted to a concentration of 0.2 wt%, a sodium hexametaphosphate dispersant was further added, and the average particle diameter was measured after irradiation with ultrasonic waves for 10 minutes.

The average particle diameter D of the aggregated particles due to the aggregation of the particles is the average particle diameter of the aggregated particles obtained by measuring the average particle diameter of the aggregated particles after slurrying with the laser diffraction particle size distribution analyzer (SALD-2100) described above. This is the value of the diameter (D50). The slurry viscosity (Ps) was measured using a Viscometer VM-10 manufactured by Lion Co., Ltd. and a B-type viscometer manufactured by Tokyo Koki Co., Ltd.

  In FIG. 2, when the viscosity requested | required of a slurry is lower than 1 (Ps), for example, a spherical granule cannot be obtained with the slurry of density | concentration a12 = 30 (vol%) and a13 = 35 (vol%). In order to obtain spherical granules, the concentration a11 = 25 (vol%) must be used.

  Assuming that a slurry having a concentration of a13 = 35 (vol%) is used, if the viscosity is higher than 3 (Ps), the concentration of a13 = 35 (vol%), a12 = 30 (vol%), a11 = In any case of 25 (vol%), spherical granules can be obtained.

FIG. 3 is a graph showing the relationship between the degree of primary particle aggregation (D / D0) and slurry viscosity for other dielectric materials. This graph is obtained by applying the same slurry preparation conditions and slurry physical property measuring method as the graph shown in FIG. The dielectric material mentioned here has a specific gravity of 5 (g / cm ³ ) and an average particle size (D50) of 1.1 μm.

  In FIG. 3, when the viscosity required for the slurry is lower than 1 (Ps), for example, the concentrations a11 = 20 (vol%), a12 = 25 (vol%), and a13 = a12 = 30 (vol%). In any of the slurries, spherical granules can be obtained, but at a concentration of a14 = 35 (vol%), spherical granules cannot be obtained.

  When using a slurry having a concentration of a14 = 35 (vol%), spherical granules can be obtained if the viscosity is higher than 2 (Ps). As a method of changing the viscosity under a constant concentration, there are adjustment of the primary particle size of the powder and adjustment of the pH of the slurry in addition to adjustment of the addition amount of the dispersant and the flocculant.

  As shown in FIG. 2 and FIG. 3, the relationship between the degree of aggregation (D / D0) and the slurry viscosity varies depending on the particle material contained in the slurry. A spherical granule region S1 and a non-spherical granule region S2 are shown. Therefore, a slurry suitable for obtaining spherical granules for each particle material by experimentally collecting data on the relationship between the degree of aggregation (D / D0) and the slurry viscosity for each particle material contained in the slurry. Can be obtained.

  In order to obtain a high density granule, it is necessary to increase the solid content (particle amount) of the slurry. As is clear from the characteristics A11 to A14 in FIGS. 1 to 3, spherical granules are formed if the slurry concentration is too high. It becomes difficult.

  Moreover, the above method was applied to several kinds of materials, and molding experiments were performed on a number of products using the obtained high-density spherical granules, and the effect that the molding weight variation was reduced to 1/2 to 1/4 was confirmed.

  The particles preferably form floc-like or aggregates as floc precursors in the liquid. A particularly preferable state of the aggregate is a state in which single particles or aggregate particles are discretely and aggregated in the liquid. A slurry containing such an aggregate is effective for obtaining solid spherical granules.

  FIG. 4 is a diagram schematically showing an aggregate of floc-like or floc precursors. A floc-like or floc precursor aggregate refers to an aggregate state in which particles 1 and 2 are gathered by a weak collective force. By the way, floc is generally defined as a flocculent aggregate with high particle density due to inorganic salt, electrolyte, or polymer flocculant, and the floc-like or floc precursor aggregate of the present invention is an additive. A state where particles are gathered with a force weaker than the cohesive force of.

  More preferably, the concentration of the powder in the slurry is set to be slightly before the concentration at which floc-like or aggregates of floc precursors are not formed. Thereby, a spherical granule can be obtained reliably. This point can also be explained using the graphs of FIGS. That is, in FIGS. 1 to 3, a floc-like or floc precursor aggregate is formed at the intersection of the straight line L0 serving as the boundary between the spherical granule region S1 and the non-spherical granule region S2 and the concentration characteristics A11 to A14. It can be considered that it is a boundary point that will not be performed, and if it is set at a slightly lower concentration than this boundary point, it will enter the spherical granule region S1.

  As shown in FIG. 4, the particles include fine particles 1 and coarse particles 2, and fine particles 1 adhere to other fine particles 1 or coarse particles 2 to form a floc-like or floc precursor. The slurry forming the aggregate is also effective for producing solid spherical granules. Alternatively, the particles may be floc-like in which the coarse particles 2 collect the fine particles 1 or a slurry forming an aggregate of floc precursors.

  When the particles include fine particles 1 and coarse particles 2, fine particles 1 mainly include particles having an average particle diameter d1 of 1 micron or less, and coarse particles 2 mainly include particles having an average particle diameter d2 of 1 micron or more. It is preferable that

  Next, the relationship between the average particle diameter, the viscosity, and the degree of aggregation will be described with reference to experimental data.

  The viscosity and the degree of aggregation of the slurry were investigated at an average particle diameter of 1.6 μm to 2.2 μm. The results are shown in FIG. In FIG. 5, the horizontal axis represents the average particle diameter (μm), the left vertical axis represents the viscosity (PS), and the right vertical axis represents the degree of aggregation. A characteristic L51 indicates a viscosity characteristic, and a characteristic L52 indicates a cohesion degree characteristic.

  As shown in FIG. 5, the viscosity of the slurry using primary particles having an average particle diameter of 2.2 μm was higher than that of the slurry using 1.6 μm primary particles, but the degree of aggregation was 2 on the contrary. Slurry with 2 μm primary particles was lower.

  From this, it can be considered that the degree of aggregation was higher than that of 2.2 μm because the smaller 1.6 μm of the electric double layer tends to aggregate. Moreover, regarding the viscosity, it is considered that the larger one became steric hindrance and the shear viscosity increased.

  However, since the floc-like aggregates may form larger steric hindrance at the viscosity at which aggregation is more likely, similar experiments and evaluations were performed on primary particles having a particle size of 1 μm or less. The results are shown in FIG.

  In FIG. 6, the horizontal axis represents the average particle diameter (μm), the left vertical axis represents the viscosity (PS), and the right vertical axis represents the degree of aggregation. A characteristic L61 indicates a viscosity characteristic, and a characteristic L62 indicates a cohesion degree characteristic.

  In the experiment, two kinds of particles pulverized so that the average particle diameter becomes 0.789 μm and 1.741 μm, respectively, were mixed at a ratio of 100: 0, 50:50, and 0: 100, respectively. Three types of samples were prepared.

  Referring to FIG. 6, it can be seen that the viscosity increases as the particle size decreases, unlike the results for the particle size of 1.6 to 2.2 μm illustrated in FIG. 5. This means that an inflection point at which the viscosity changes from a decreasing tendency to an increasing tendency exists between 0.8 μm and 1.6 μm. This is because the particle's Brownian motion increases with a particle size of about 1 μm as a boundary, and the cohesive force due to contact exceeds the particle peeling force due to the stirring of the slurry, and the primary particles are in the form of flocs. This time, however, is considered to be a steric hindrance and increase in viscosity.

  5 and FIG. 6 collectively, from the viewpoint of viscosity, the particles should include fine particles 1 and coarse particles 2 (see FIG. 4), and fine particles 1 have an average particle diameter d1 of 1 micron. It can be seen that the following particles are mainly used, and the coarse particles 2 are preferably particles having an average particle diameter d2 of 1 micron or more.

  Moreover, it is preferable that the average particle diameter d1 of the fine particles 1 and the average diameter df of the aggregate satisfy 0.01 <d1 / df <1.0. If (d1 / df) is 1.0 or more, in the subsequent granulation step using the slurry, a sufficient amount of floc-like or floc precursor to produce spherical granules is obtained. It will not be possible. Conversely, if (d1 / df) is 0.01 or less, the floc-like or floc precursor aggregate becomes too large, and problems such as clogging of piping occur in the subsequent granulation process. End up.

  The diameter df of the floc-like or floc precursor aggregate is preferably in a relationship of df ≧ d2 with respect to the average particle diameter d2 of the coarse particles 2. Furthermore, the diameter df of the aggregates of floc-like or aggregated floc precursors is in a relationship of df ≧ d2 with respect to the average particle diameter d2 of the coarse particles 2, which also gives a solid spherical granule. It is valid. When the average particle diameter d2 of the coarse particles 2 is larger than the diameter df of the aggregate, coarse particles are included in the granules produced in the subsequent process, and the density in the granules becomes non-uniform or coarse in the slurry. There is a possibility that the grains 2 will settle and the slurry concentration may vary.

  The particle size distribution of the particles in the slurry is preferably a binomial distribution of fine particles 1 and coarse particles 2. The smaller the average particle size of the primary particles, the easier it is to form a floc-like or floc precursor aggregate. Accordingly, if the primary particle size distribution is set in advance so as to have an appropriate binomial distribution in the volume particle size distribution, it becomes easier to produce a floc-like or floc precursor aggregate.

  Since the fine particles 1 mixed in the slurry liquid are smaller in weight than the coarse particles 2, the fine particles 1 easily move in the liquid (easy-moving state), and the fine particles 1 touch each other in the liquid, or the coarse particles 2 The fine particles 1 come into contact with the coarse particles 2 as the core, and the fine particles 1 or the coarse particles 2 and the fine particles 1 gather together by suction force or adsorption force to form a floc-like or floc precursor aggregate. Then, it becomes difficult to move.

  Since the floc-like or floc precursor aggregate or coarse particle 2 acts as a steric hindrance to the fine particles 1 in the liquid, the floc-like or floc precursor aggregate once locally When formed in the liquid, new fine particles 1 gather around the floc-like or floc precursor aggregate, and the floc-like or floc precursor aggregate grows in diameter. Then, the steric hindrance state develops.

  At this time, since the floc-like or floc precursor aggregate itself is not so strong, it may be repeatedly assembled. Then, floc-like or aggregates of floc precursors in the slurry as a solid-liquid dispersion system have a balanced and appropriate size, thereby reducing the number of independent fine particles 1 in the liquid. The movement of the fine particles 1 is suppressed. Thereby, the floc-like or floc precursor aggregate acts to make the solid-liquid dispersion state of the slurry homogeneous.

  In the slurry of the present invention, floc-like aggregates of fine particles 1 or aggregates of floc precursors act as steric hindrance in the liquid, so fine particles 1 and coarse particles 2 are biased, settled and separated in the slurry. And the slurry state in which the solid-liquid is dispersed is maintained for a long period of time.

  In addition, when obtaining slender bodies such as granules and green sheets using the slurry of the present invention, the fine particles 1 in the liquid are floc-like or floc precursor in the process of drying and reducing the liquid phase components. It is aggregated and restrained in a body aggregate, and the floc-like or floc precursor aggregate becomes a steric hindrance to prevent the fine particles 1 from moving from the inside of the rod-shaped body to the surface. Therefore, it works to prevent only fine particles 1 from collecting on the surface of the bowl. This prevents the so-called “skinning” from appearing on the bowl.

  In the process of reducing the liquid phase component contained in the floc-like or floc precursor aggregate, the aggregate composed of the fine grains 1 and the coarse grains 2 forms a skeleton, so that the cage is sparse throughout. A saddle shape will be formed. For this reason, the liquid phase component inside the saddle is easily exposed to the surface through the voids of the skeleton, so that the liquid phase component is not left inside the saddle, and the solid liquid is formed near and inside the saddle. The dispersed state becomes homogeneous.

  Furthermore, the slurry according to the present invention can contain second fine particles. The second fine particles are moved from the easy moving state in which the fine particles 1 are easy to move in the liquid to the difficult moving state in which the floc-like or floc precursor aggregates are difficult to move in the liquid. Change the mobility to increase the viscosity of the slurry.

  In the field of fine ceramics, which is the main application area of the invention, the slurry contains a binder. This slurry may be an aqueous solution containing no flocculant or a slurry containing no dispersant. On the contrary, a minute amount of a dispersant may be contained. Furthermore, a water sustained-release additive may be included.

  In the field of fine ceramics, even if the viscosity of the slurry and the concentration of the ceramic powder are selected so as to enter the spherical granule region, depending on the amount of the binder and the concentration of the ceramic powder, if stirring is continued for a long time, The non-spherical granule region may enter from the spherical granule region.

  The problem is that the functional group has at least one hydroxyl group and is selected from the group consisting of carboxyl group, carboxylate, sulfonic acid, sulfonate, phosphoric acid, phosphate, amine, and quaternary amine salt. This is solved by adding a non-polymeric organic compound having a group.

  For example, the organic compound is a hydroxyl group-containing carboxylic acid, a hydroxyl group-containing carboxylate, a hydroxyl group-containing sulfonic acid, a hydroxyl group-containing sulfonate, a hydroxyl group-containing phosphoric acid, a hydroxyl group-containing phosphate, a hydroxyl group-containing amine, and a hydroxyl group-containing quaternary ammonium. It can be selected from the group consisting of salts. More specifically, the organic compound is selected from the group consisting of citric acid, mesotartaric acid, hydroxyl group-containing lower carboxylic acid, hydroxyl group-containing lower alkenyl carboxylic acid, hydroxyl group-containing lower alkynyl carboxylic acid, hydroxyl group-containing aromatic carboxylic acid, and combinations thereof. Can be selected.

  Hereinafter, the case where citric acid is used as an additive will be described as an example. FIG. 7 is a diagram showing the viscosity-aggregation characteristics when citric acid (1 mol / l aqueous solution) is not added (0 ml). The amount of PVA was changed in five stages of 0 wt%, 0.5 wt%, 1.0 wt%, 1.5 wt%, and 2.34 wt%. In each amount of PVA, the characteristic indicated by the solid line of the double-pointed arrow is the initial viscosity-cohesion characteristic when the concentration of the ceramic powder in the slurry is changed in the range of 25 vol% to 34 vol%. A straight line L0 indicates the boundary between the spherical granule region S1 and the non-spherical granule region S2. Linear dotted arrows L71 to L74 indicate the viscosity-cohesion degree changing direction and the magnitude of change for each amount of PVA when stirring is continued for a long time (for example, about 24 hours). The viscosity-cohesion degree changing direction is indicated by the directions of dotted arrows L71 to L74, and the magnitude of the change is indicated by the length of the dotted line. This principle is similarly adopted in FIGS.

  First, as shown in FIG. 7, as the amount of PVA increases, both the viscosity and the degree of aggregation decrease. This is a common phenomenon in this type of slurry.

  In the slurry containing no citric acid in FIG. 7, if the amount of PVA is in the range of 0.5 to 1.5 wt%, it enters the spherical granule region S1 in the entire range of the ceramic powder concentration of 25 vov to 34 vol%. However, when the stirring is continued for a long time (for example, 24 hours), the viscosity-aggregation characteristic decreases as shown by the dotted arrow L72, and both the viscosity and the aggregation degree decrease, and the spherical granule region S1 and the non-spherical granule region S2 It changes in the direction which approaches the straight line L0 which shows the boundary. Moreover, changes in viscosity and cohesion are very large.

  When the amount of PVA is 1.5 wt%, the initial viscosity-aggregation characteristic when changing in the range of 25 vol% to 34 vol% is that part of the intermediate part enters the non-spherical granule region S2, and stirring is performed. When continuing for a long time, as indicated by a dotted arrow L73, the viscosity-aggregation characteristic changes in a direction in which both the viscosity and the aggregation degree decrease, and enters the non-spherical granule region S2 as a whole.

  When the amount of PVA is 2.34 wt%, the entire initial viscosity-aggregation characteristic when changing in the range of 25 vol% to 34 vol% enters the non-spherical granule region S2.

  If the amount of PVA is small, the granules granulated from this slurry become brittle. To avoid this, the amount of PVA is preferably set to a content of about 1 wt% to 3 wt%. However, in the slurry not containing citric acid, as shown in FIG. 7, the initial value may enter the non-spherical granule region S2 in the range where the PVA amount is 1.5 wt% to 2.34 wt%. Therefore, it is difficult to use.

  FIG. 8 is a graph showing the viscosity-aggregation characteristics when the citric acid content is 0.5 ml. The content of the PVA amount was changed in five steps as shown in FIG. In each amount of PVA, the characteristic indicated by the solid line of the double-pointed arrow is the initial viscosity-cohesion characteristic when the concentration of the ceramic powder in the slurry is changed in the range of 25 vol% to 34 vol%. A straight line L0 indicates the boundary between the spherical granule region S1 and the non-spherical granule region S2. A dotted line arrow L81 indicates the direction of change in viscosity-cohesion when a slurry having a PVA amount of 2.34 wt% and a ceramic powder concentration of 34 vol% is continuously stirred for a long time. This shows the direction of change in viscosity-cohesion degree when a slurry having an amount of 2.34 wt% and a ceramic powder concentration of about 30 vol% is continuously stirred for a long time.

  In the case where the citric acid content is 0.5 ml, the initial viscosity-cohesion property is as follows in the entire range of the ceramic powder concentration of 25 vov to 34 vol% in any case where the PVA amount is 0.5 to 2.34 wt%. Enter the spherical granule region S1.

  In the case of a slurry having a PVA amount of 2.34 wt%, if stirring is continued for a long time (for example, 24 hours), the viscosity and the cohesion degree both decrease in viscosity and cohesion degree as indicated by dotted arrows L81 and L82. However, the amount of change is smaller than that in the case of FIG. 7.

In addition, in the dotted arrows L81 and L82, there is a tendency that the amount of change in the degree of aggregation relative to the amount of change in viscosity tends to be smaller (in the direction of the arrow) than in the case of the dotted arrows L72 to L74 in FIG. It is done.
FIG. 9 is a graph showing the viscosity-aggregation characteristics when the citric acid content is 2.5 ml. The content of the PVA amount was changed in five steps as shown in FIG. In each amount of PVA, the characteristic indicated by the solid line of the double-sided arrow is the initial viscosity-cohesion characteristic when the concentration of the ceramic powder in the slurry is changed in the range of 25 vol% to 34 vol%. A dotted arrow L91 indicates the direction of change in viscosity-cohesion when a slurry having a PVA amount of 2.34 wt% and a ceramic powder concentration of 25 vol% is stirred for a long time.

  In the case where the citric acid content is 2.5 ml, the initial viscosity-cohesion property is as follows in the whole range of the ceramic powder concentration of 25 vov to 34 vol% in any case where the PVA amount is 0.5 to 2.34 wt%. Enter the spherical granule region S1. That is, spherical granules are easier to make than the example of FIG. 7 that does not contain citric acid. However, in order to prevent tube clogging in the mass production process, the viscosity is desirably 3 (Ps) or less. From this point of view, a slurry having a PVA amount in the range of 0.5 to 1.0 wt% with a viscosity exceeding 3 (Ps) is not suitable for mass production.

  A slurry having a PVA amount of 1.5 wt% to 2.3 wt% enters the spherical granule region S1 when the initial viscosity-cohesion property is in the range of a ceramic powder concentration of 25 vol% to about 28 vol%. That is, spherical granules are easier to make than the example of FIG. 7 containing no citric acid and the example of FIG. 8 containing 0.5 ml of citric acid.

  In the case of a slurry with a PVA amount of 2.34 wt%, the viscosity-cohesion property changes in a direction in which the coagulation degree decreases while maintaining a substantially constant viscosity as indicated by the dotted arrow L91 by long-time stirring. The amount of change is smaller than in the case of FIGS.

  Moreover, the directionality of the change indicated by the dotted arrow L91 is such that the amount of change in the degree of aggregation relative to the amount of change in viscosity is smaller than the case of the dotted arrows L81 and L82 in FIG. ) Shows a trend.

  FIG. 10 is a diagram showing the viscosity-aggregation characteristic when the citric acid content is 5 ml. The content of the PVA amount was changed in five steps as shown in FIG. In each amount of PVA, the characteristic indicated by the solid line of the double-pointed arrow is the initial viscosity-cohesion characteristic when the concentration of the ceramic powder in the slurry is changed in the range of 25 vol% to 34 vol%. A dotted arrow L101 indicates the direction of change in viscosity-cohesion when a slurry having a PVA amount of 2.34 wt% and a ceramic powder concentration of 25 vol% is stirred for a long time.

  When the citric acid content is 5 ml, the initial viscosity-cohesion characteristics are spherical granules in all ranges of the ceramic powder concentration of 25 vov to 34 vol% in any case where the PVA amount is 0.5 to 2.34 wt%. Enter region S1. That is, spherical granules are easier to make than the example of FIG. 7 that does not contain citric acid. Slurries with a PVA amount exceeding 3 (Ps) in the range of 0.5 wt% or more and less than 1.0 wt% are not suitable for mass production.

  A slurry having a PVA amount of 1.5 wt% to 2.3 wt% enters the spherical granule region S1 when the initial viscosity-cohesion property is in the range of a ceramic powder concentration of 25 vol% to about 28 vol%. That is, spherical granules are easier to make than the example of FIG. 7 containing no citric acid and the example of FIG. 8 containing 0.5 ml of citric acid.

  In the case of a slurry having a PVA amount of 2.34 wt%, the change in the viscosity-cohesion characteristic due to stirring is in the direction of decreasing the cohesion while maintaining a substantially constant viscosity, as indicated by the dotted arrow L101. The amount is smaller than in the case of FIGS. In addition, the change directionality indicated by the dotted arrow L101 indicates that the change amount of the cohesion degree with respect to the change amount of the viscosity is smaller than the case of the dotted line arrows L81 and L82 of FIG. It shows a trend.

  FIG. 11 is a diagram showing a changing tendency of the viscosity-aggregation characteristic when the ratio of citric acid and PVA is changed. The characteristics shown in FIG. 11 can also be read from the characteristic charts shown in FIGS. 7 to 10, but FIG. 11 is shown for understanding.

  Linear arrows L111 to L116 indicate the direction of viscosity-cohesion change when a slurry in which the PVA amount and the ceramic powder concentration are constant and the amount of citric acid is changed is stirred.

  As shown in FIG. 11, as the (citric acid / PVA) ratio increases (citric acid increase), the rate of change in the degree of aggregation with respect to the change in viscosity decreases, making it difficult to enter the non-spherical granule region S2. Is shown. That is, by controlling the citric acid content, it becomes possible to stably form spherical granules despite stirring.

  When the slurry is stirred, the reason why the slurry in the spherical granule region S1 enters the non-spherical granule region S2 and the reason why this problem can be solved by containing citric acid is speculative. However, it can be explained as follows.

  When considering an initial state before stirring for a slurry containing ceramic powder, water, PVA, and a dispersant, PVA is adsorbed on particles constituting the ceramic powder. Since lone electron pairs (lone pairs) of oxygen atoms exist on the surface of the oxide ceramic particles, the ceramic particles and the PVA adhering to them repel each other and are released by the electric repulsion. This electrical repulsion affects the viscosity and the degree of aggregation.

On the other hand, PVA releases protons (H ⁺ ). This release of protons (H ⁺ ) changes (decreases) the pH of the slurry. Changes in pH also affect viscosity and degree of aggregation.

  As described above, the slurry prepared according to the present invention, in the initial state, has the viscosity and the degree of aggregation affected by the repulsive force, pH and the like, and further the concentration is set in the spherical granule region. It is.

When the slurry system initially set as described above is stirred for a long time, among the protons (H ⁺ ) present in the slurry, those adsorbed to oxygen around the ceramic powder increase slightly. For this reason, although the pH of a slurry is very small, it raises and a viscosity and a cohesion degree fall.

  As a result, as shown in FIGS. 7 to 10, in the initial state, it is presumed that the slurry suitable for the spherical granule region S1 enters the non-spherical granule region S2 by stirring.

On the other hand, when citric acid is added to a slurry containing ceramic powder, water, PVA and a dispersant, the citric acid has (-C00H) and releases a large amount of protons (H ⁺ ). For this reason, pH of a slurry falls and a viscosity rises.

On the other hand, the released protons (H ⁺ ) are preferentially adsorbed around the ceramic particles constituting the ceramic powder and have a function of aggregating the ceramic particles by hydrogen bonding. That is, there is a function of reducing the particle dispersion effect caused by the adsorption of PVA to the ceramic particles.

  That is, by adding citric acid, the viscosity of the slurry and the degree of aggregation are increased. This means that in the viscosity-cohesion characteristics shown in FIGS. 1 to 10, the change with time indicated by the dotted arrow is cancelled.

  For this reason, it is presumed that by containing citric acid, the action and effect retained in the spherical granule region S1 can be obtained despite stirring.

The meaning of containing citric acid is to release a large amount of protons (H ⁺ ), and also to stabilize the pH buffering effect, that is, the amount of protons (H ⁺ ) in the liquid. Thus, it is clear that any organic compound having a similar function can be used in place of citric acid. Examples are the organic compounds mentioned above. Moreover, in the slurry of only ceramic powder and water, since the remarkable change with time is not seen, it can be considered that the above explanation in the slurry containing PVA is appropriate.

  Next, when a plurality of types of ceramic powders having the same composition and manufacturing process but different manufacturing lots are used, as shown in FIG. 12, in the slurry P1 using ceramic powders of a certain lot, spherical granules are used. In the slurry P2 using the ceramic powder of another lot when entering the region S1, there may be a problem that the slurry P2 enters the non-spherical granule region S2.

  In order to solve this problem, it is very effective to contain an alkali in the slurry. Specific examples include ammonia, sodium hydroxide, sodium carbonate, sodium hydrogen carbonate and the like.

  The effect by the addition of alkali can be explained as follows with reference to FIG. FIG. 13 is a graph showing the relationship between pH, viscosity (see the left vertical scale), and zeta potential (see the right vertical scale). Curve L131 is the pH-viscosity characteristic of the slurry before alkali addition, curve L132 is the pH-zeta potential characteristic before alkali addition, curve L133 is the pH-viscosity characteristic of the slurry after alkali addition, and curve L134 is pH- after the alkali addition. The zeta potential characteristics are shown.

  First, the pH-viscosity characteristic L131 and the pH-zeta potential characteristic L132 are examined for the slurry before alkali addition. When the pH decreases, the zeta potential approaches the equipotential point and the viscosity increases. Although the degree of aggregation is not shown in the figure, it changes almost in proportion to the viscosity. This is because as the pH decreases, the zeta potential due to the electric double layer formed on the surface of the ceramic particles in the slurry decreases, and the repulsive force acting between the ceramic particles decreases and agglomerates because it moves toward the equipotential point ζ01. It is presumed to be easier. Aggregation is maximized at the equipotential point ζ01 where the repulsive force acting between the ceramic particles is almost zero.

  On the other hand, as the pH increases, the zeta potential also increases and the viscosity decreases. This is presumed to be because the zeta potential of the ceramic particles in the slurry increases as the pH increases, and the repulsive force acting between the ceramic particles increases and becomes easier to disperse.

  When alkali is added to the slurry in the initial state as shown in FIG. 13, the pH becomes high. From the pH-viscosity characteristic L131 and the pH-zeta potential characteristic L132 in FIG. 13, it seems that the higher the pH, the easier the dispersion and the lower the viscosity and cohesion.

  However, in practice, the viscosity and the degree of aggregation increased by the addition of alkali, and as shown in FIG. 12, it was confirmed that the slurry P2 that had entered the non-spherical granule region S2 entered the spherical granule region S1.

  The reason for this is unconfirmed, but the equipotential point ζ01 of the initial zeta potential moves to the equipotential point ζ02 by the addition of alkali, and the initial pH-viscosity characteristic L131 and the pH-zeta potential characteristic L132 are indicated by arrows. It is presumed that the transition occurs as indicated by b1 and c1, and that the pH-viscosity characteristic L133 and the pH-zeta potential characteristic L134 are obtained.

2. Slurry management method Conventionally, when evaluating granules, there is only a method for confirming the granules obtained by a spray dryer. Therefore, much labor, time, and materials are required in examining the slurry conditions. It was.

  In the slurry management method according to the present invention, the slurry is dropped on a flat resin surface to form hemispherical droplets. Next, the droplet is heated to reduce the content of the liquid phase, and the property of the slurry is determined by the change in the shape of the hemispherical droplet during the drying process.

  According to the slurry management method of the present invention, it can be verified in a simulation whether or not the prepared slurry is suitable for obtaining spherical granules. Moreover, the slurry management method according to the present invention is an extremely effective means for the data collection shown in FIGS.

  Specifically, in the slurry management method according to the present invention, the degree to which the droplets are recessed by drying is used as a criterion for determining the true sphericity and non-sphericity when the granules are formed. More specifically, it is determined that the true sphericity of the granules cannot be obtained when the droplets are recessed by drying, and the true sphericity is obtained when the droplets are not recessed.

  FIG. 14 shows a specific example of the slurry management method. First, as shown in FIG. 14A, using a dispenser 32, the slurry is dropped onto the silicone sheet 31 to a size of about 500 μm, for example, to form droplets 33. Since the size of the droplet 33 affects the detection sensitivity, it is preferable to define it in advance.

  Next, as shown in FIG. 14B, the droplets 33 are dried by putting them into the dryer 34 at 150 ° C. within 10 seconds. Temperature conditions and the like are appropriately determined according to the granulation conditions.

  Next, as shown in FIG. 14 (c), when the shape of the dried product of the hemispherical droplet 33 when taken out from the dryer 34 is seen, it is depressed (FIG. 14 (C1)) or spherical (FIG. 14 (C2)). The granule shape by this method is in good agreement with the granule shape after spray drying.

  As the silicone sheet, Sircon (registered trademark) manufactured by Fuji Polymer Co., Ltd. is suitable. In this silicone sheet, an inorganic filler is kneaded, and the contact angle at the time of slurry dropping increases. For this reason, it can be brought closer to a granule shape produced by a spray dryer.

It is a graph which shows the relationship between the aggregation degree (D / D0) of a primary particle, and slurry viscosity. It is a graph which shows the relationship between the aggregation degree (D / D0) of a primary particle, and a slurry viscosity about a dielectric material. It is a graph which shows the relationship between the aggregation degree (D / D0) of a primary particle, and a slurry viscosity about another dielectric material. It is a figure which shows typically the aggregate | assembly of a flock-like or a flock precursor. It is a figure which shows the relationship between an average particle diameter (micrometer), a viscosity (PS), and a cohesion degree about a dielectric material. It is a figure which shows another relationship of an average particle diameter (micrometer), a viscosity (PS), and a cohesion degree about a dielectric material. It is a figure which shows the viscosity-cohesion property characteristic when a citric acid is not added (0 ml). It is a figure which shows the viscosity-aggregation degree characteristic when content of a citric acid shall be 0.5 ml. It is a figure which shows the viscosity-cohesion degree characteristic when content of a citric acid shall be 2.5 ml. It is a figure which shows the viscosity-cohesion degree characteristic when content of a citric acid shall be 5 ml. It is a figure which shows the change tendency of a viscosity-cohesion degree characteristic at the time of changing the ratio of a citric acid and PVA. It is a figure which shows the viscosity-cohesion degree characteristic of the slurry at the time of using the multiple types of ceramic powder from which a production lot differs. It is a figure which shows the relationship between pH, a viscosity, and a zeta potential. It is a figure which shows a specific example of the slurry management method which concerns on this invention.

Explanation of symbols

S1 Spherical granule region S2 Non-spherical granule region A11 to A13 Viscosity-aggregation characteristics using concentration as a parameter

Claims (4)

A method for producing a slurry in which solid component particles form a solid-liquid dispersion in liquid,
The relationship between the degree of aggregation represented by the ratio (D / D0) of the average particle diameter D0 of the primary particles in the dispersed state of the particles and the average particle diameter D of the aggregated particles due to the aggregation of the particles and the slurry viscosity is a graph. In the case of making use of the indication of the spherical granule region and the non-spherical granule region, for each particle material contained in the slurry, experimentally collecting the relationship data between the degree of aggregation and the slurry viscosity, Prepare in advance a graph or data specifying the spherical and non-spherical granule regions,
For the slurry having a predetermined particle concentration, the agglomeration degree or slurry viscosity is selected so as to fall within the spherical granule region among the spherical granule region and the non-spherical granule region obtained from the graph or data.
A method for producing a slurry comprising steps. It is a manufacturing method of the slurry described in Claim 1, Comprising:
The spherical granule region and the non-spherical granule region are
The slurry having a predetermined solid component concentration is dropped on a flat resin surface to form a hemispherical droplet,
The droplets are heated to reduce the liquid phase content,
The degree of depression of the droplets due to the drying due to the change in the shape of the hemispherical droplets during the drying process is used as a criterion for determining sphericity and nonsphericity when the granules are formed.
A method for producing a slurry identified through steps. It is a manufacturing method of the slurry described in Claim 1, Comprising:
The solid component is ceramic, and the liquid phase in the slurry includes PVA (polyvinyl alcohol) and an additive,
The spherical granule region and the non-spherical granule region are
First, on a flat silicone resin surface, the slurry is dropped so as to have a size of about 500 μm to form a hemispherical droplet of the slurry,
Next, the droplets are put into a dryer at 150 ° C. within 10 seconds, and dried to such an extent that the liquid phase exists in the droplets,
Furthermore, the shape of the granules obtained from the slurry is determined by the shape of the obtained droplets.
A method for producing a slurry identified through steps. It is a manufacturing method of the slurry described in Claim 2 or 3, Comprising: When the said droplet dents by the said drying, it determines with the true sphericity of a granule not being obtained, and not being able to obtain sphericity when not dented. ,
A method for producing a slurry comprising steps.

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