JP5784399B2 - Molding agent composition for sand casting - Google Patents

Description

  The present invention relates to a coating composition used for casting of cast steel, cast iron, aluminum, copper and alloys thereof.

  As a casting coating agent, one that protects the surface of a mold by coating on the surface of a sand mold (mold) in contact with a molten metal and coating a coating film is known. Such a casting mold agent is used to prevent the chemical reaction between the molten metal and the sand mold surface and the occurrence of casting defects in the casting.

  As a conventional sand mold casting coating composition, for example, the following Patent Document 1 contains a refractory aggregate and a binder, and as a binder, acrylic acid and / or methacrylic acid and an acrylic ester and A sand mold casting composition using an alkali metal salt, an ammonium salt or an amine salt of a copolymer (/ (meth) acrylic acid ester copolymer) with a methacrylate ester is described. Patent Document 2 listed below describes a sand casting casting composition containing a fireproof aggregate, a binder and an organic solvent as essential components, and further containing a predetermined amount of a polyvalent carboxylic acid or a derivative thereof. Yes. The following Patent Document 3 discloses a method for drying an aqueous coating composition, in which a) an aqueous coating composition is prepared, and b) the aqueous coating composition is applied to at least a part of the surface of a casting mold. And c) a portion of the carrier liquid of the coating formulation penetrates the substrate over time, optionally partially or fully matting the applied aqueous coating formulation; d) A method for drying an aqueous coating formulation is described, comprising applying a flammable liquid to an optionally matted layer of the aqueous coating formulation; and e) completely burning the flammable liquid. ing.

JP-A-4-342778 JP-A-4-75745 Special table 2009-525872 gazette

  However, in the conventional mold casting composition for sand mold casting, after application to the surface of the sand mold, streaks may occur on the coated surface, and it takes a long time to repair this dripping. Moreover, in the conventional coating agent composition for sand mold casting, it was difficult to suppress sagging while keeping the thickness of the coating film in an appropriate range. That is, when no dripping is observed, the coating agent penetrates into the sand mold, and there is a problem that a coating film having a sufficient thickness cannot be obtained. With regard to such problems, conventional sand mold casting coating compositions have not been sufficiently studied.

  The present invention provides a coating agent composition for sand casting that reduces dripping and obtains a coating film having an appropriate thickness. That is, in other words, an object of the present invention is to achieve both the suppression of sagging and the suppression of the thickness reduction of the coating film.

  As a result of intensive studies to solve the above problems, the present inventor contains a specific amount of a dispersant composed of a polymer having a specific structural unit with respect to the refractory aggregate, and a specific bentonite, It has been found that the above-mentioned problems can be solved by a sand casting casting composition containing a specific amount with respect to the synthetic aggregate.

  That is, the coating composition for sand casting according to the present invention comprises a fireproof aggregate, a binder, a sintering agent other than sodium bentonite (hereinafter also simply referred to as “sintering agent”), water, a dispersing agent and sodium. A coating composition for sand casting, containing bentonite, wherein the dispersant has a structural unit derived from acrylic acid and / or maleic acid, and is composed of acrylic acid and maleic acid in all the structural units The polymer has a total content of 90 mol% or more, the content of the dispersant is 0.04 to 1.2 parts by weight with respect to 100 parts by weight of the refractory aggregate, and the sodium bentonite This relates to a coating agent composition for sand casting, in which the content of is 1.5 to 15 parts by weight with respect to 100 parts by weight of the refractory aggregate.

  The mold casting composition for sand casting of the present invention contains structural units derived from acrylic acid and / or maleic acid, and the total content of structural units derived from acrylic acid and maleic acid in all the structural units is 90 mol% or more. Is contained as a dispersant, the dispersant is contained in an amount of 0.04 to 1.2 parts by weight with respect to 100 parts by weight of the refractory aggregate, and the sodium bentonite is added to 100 parts by weight of the refractory aggregate. On the other hand, by containing 1.5 to 15 parts by weight, dripping is reduced and a coating film having an appropriate thickness is obtained.

  The reason for manifesting the above effects is not clear, but by containing a specific amount of sodium bentonite and a polymer or alkali metal salt of acrylic acid and / or maleic acid as a dispersant, each of them is positively mixed in the coating composition. Even with ion exchange, there is little effect on the action of ensuring the thickness of the coating film of sodium bentonite, and if the ratio of the dispersant to sodium bentonite is within a certain range, it acts to suppress sagging of the dispersant It is speculated that the work of securing the thickness of the sodium bentonite coating can be achieved in an extremely balanced manner.

  The mold casting composition for sand casting of the present invention (hereinafter also simply referred to as “coating composition”) contains a refractory aggregate, a binder, a sintering agent, water, a dispersant, and sodium bentonite. .

  Hereinafter, each component contained in the coating composition of the present invention will be described.

<Dispersant>
The dispersant comprises a polymer containing structural units derived from acrylic acid and / or maleic acid, and the total content of structural units derived from acrylic acid and maleic acid in all the structural units is 90 mol% or more.
The structural unit derived from acrylic acid is represented by the following formula (1).

(In the formula, M represents H or an alkali metal salt.)

Moreover, the structural unit derived from maleic acid or maleic anhydride is represented by the following formula (2) or the following formula (3), respectively.

(In the formula, X and Y are the same or different and represent H and an alkali metal salt.)

  The neutralization rate of acrylic acid and / or maleic acid can be arbitrarily adjusted between 0 and 100%. The neutralization rate is preferably 30 to 100%, more preferably 50 to 100%, and still more preferably 80 to 100% from the viewpoint of reducing sagging and increasing the penetration depth. M in the above formula (1) and X and Y in the above formula (2) are a hydrogen atom and an alkali metal salt, respectively. From the viewpoint of reducing dripping, the alkali metal salt is preferably lithium, sodium and potassium, more preferably sodium and potassium, and still more preferably sodium.

  From the viewpoint of reducing dripping and obtaining a coating film with an appropriate thickness, the dispersant of the present invention is a structural unit derived from acrylic acid represented by the above formula (1) and a maleate represented by the above formula (2). What has only the structural unit derived from an acid is preferable, and what has only the structural unit derived from acrylic acid represented by the said Formula (1) is more preferable. 1000-100000 are preferable from a similar viewpoint, as for a weight average molecular weight, 2000-70000 are more preferable, and 3000-50000 are still more preferable.

  In the case of copolymerizing acrylic acid and maleic acid (including maleic anhydride), the content of acrylic acid is preferably 20 mol% or more, and more preferably 50 mol% or more. The molar ratio of acrylic acid to maleic acid and / or maleic anhydride is preferably maintained from the viewpoint of maintaining the fluidity of the coating composition and reducing dripping more reliably. Or maleic anhydride) = 40 / 60-100 / 0 is preferable, and 50 / 50-100 / 0 is more preferable.

  In order to favorably maintain the fluidity of the coating composition and more reliably reduce dripping, the total content of the structural units derived from acrylic acid and maleic acid in all the structural units is 90 mol% or more, and 95 mol % Or more, more preferably 98 mol% or more, and even more preferably 100 mol%. Examples of structural units other than the structural units derived from acrylic acid and maleic acid constituting the polymer include structural units derived from methacrylic acid, itaconic acid, and fumaric acid.

  In the coating composition of the present invention, the content of the dispersant is 0.04 to 1.2 parts by weight, preferably 0.08 to 1.0 parts by weight, more preferably 0 to 100 parts by weight of the refractory aggregate. By setting the content to 0.1 to 1.0 part by weight, the fluidity of the coating composition can be maintained in an appropriate range, and dripping can be reduced. When the content of the dispersant exceeds 1.2 parts by weight with respect to 100 parts by weight of the refractory aggregate, the amount of penetration of the coating composition into the sand mold becomes excessive, and an appropriate coating film thickness is obtained. It is not preferable because it is not possible.

  Since the coating agent composition of the present invention contains water as a solvent, the dispersant is preferably water-soluble. In the present invention, “water-soluble” means that 1 g or more of the dispersant is dissolved in 100 g of water at 20 ° C.

<Bentonite>
The mold agent composition of the present invention contains sodium bentonite in which the exchangeable cation of bentonite is sodium ion. By using sodium bentonite and a dispersant (alkali metal salt) having a specific structure, even if the sodium ion of the bentonite and the cation of the alkali metal ion are ion-exchanged, a smooth interaction is possible without causing any adverse effect. As a result, while maintaining the blending stability of the coating composition, the rheology of the coating composition is controlled, and the effects of suppressing sagging and reducing the thickness of the coating film are exhibited. When calcium is used as the cation, since the divalent cation has a strong electrical attraction and the swelling property is low, there is a problem in storage stability such as sedimentation, and an appropriate viscosity cannot be obtained. Sagging worsens. The content of sodium bentonite in the composition of the present invention is 1.5 to 15 parts by weight with respect to 100 parts by weight of the refractory aggregate from the viewpoint of maintaining the thickness of the coating film in an appropriate range and reducing sagging. However, 2.0 to 12 parts by weight is preferable, 2.5 to 8.0 parts by weight is more preferable, and 3.0 to 5.5 parts by weight is still more preferable.

  In the present invention, the weight ratio of sodium bentonite to the dispersant (sodium bentonite / dispersant) is preferably 4 to 150, more preferably 4 to 50 from the viewpoint of reducing dripping and obtaining a coating film having an appropriate thickness. .

  Hereinafter, each component contained in the coating composition of the present invention will be described.

<Fireproof aggregate>
The refractory aggregate used in the present invention is not particularly limited, but from the viewpoint of fire resistance, economy, and reaction resistance with molten metal, mullite, silica, alumina, magnesia, zircon, alumina silicate, graphite, It is preferably at least one selected from the group consisting of obsidian, olivine, talc and mica, and at least one selected from the group consisting of silica, obsidian, mica, mullite, and graphite (especially scaly graphite). It is more preferable that it is at least one selected from the group consisting of silica, obsidian, and mica.

From the viewpoint of improving application workability, the fireproof aggregate used in the present invention preferably has an average particle size of 0.5 to 100 μm, more preferably 1 to 50 μm, and 5 to 40 μm. More preferably it is. In the case of using a mixture of two or more refractory aggregates, the average particle size as a mixture of refractory aggregates is preferably 0.5 to 100 μm from the viewpoint of improving the coating workability. More preferably, it is -50 micrometers, and it is still more preferable that it is 5-40 micrometers. Here, the average particle diameter of the refractory aggregate is a volume-median particle diameter (D50) measured using a laser diffraction particle size distribution analyzer (LA-920 manufactured by Horiba, Ltd.). The analysis conditions are as follows.
Measurement method: Flow method Dispersion medium: Solvent dispersion method in which sodium hexametaphosphate (0.1% by weight) is added to ion-exchanged water: Stirring, built-in ultrasonic irradiation (3 minutes)
Sample concentration: 2 mg / 100 ml

<Binder>
In the coating composition of the present invention, as a binder, gum arabic that can form a strong coating film at room temperature, sugars such as polysaccharides, organic binders such as phenol, rosin, petroleum resin, and casting Sometimes an inorganic binder such as ethyl silicate or sodium silicate for increasing the hot strength of the coating film may be contained. These binders may be used in combination depending on conditions. The content of the binder in the coating composition is refractory aggregate (spherical refractory aggregate and non-spherical refractory aggregate) from the viewpoint of improving the coating film strength and reducing the amount of pyrolysis gas. 0.5 to 10 parts by weight is preferable, and 1 to 5 parts by weight is more preferable with respect to a total of 100 parts by weight.

<Sintering agent>
In the coating composition of the present invention, as a sintering agent, chain clay minerals such as attapulgite and sepiolite that can maintain a strong coating film even at high heat, kaolinite, talc, chlorite, montmorillonite, hectorite, etc. The layered clay mineral may be contained. From the viewpoint of fire resistance, economy, and workability as well as strength during high heat, it is preferably at least one selected from the group consisting of attapulgite, sepiolite, montmorillonite, and hectorite, and more preferably attapulgite. The content of the sintering agent of the coating composition of the present invention is 1 to 10 with respect to 100 parts by weight of the refractory aggregate from the viewpoint of maintaining the thickness of the coating film in an appropriate range and from the viewpoint of reducing sagging. Part by weight is preferable, and 1 to 5 parts by weight is more preferable.

<Solvent>
The coating composition of the present invention contains water as a solvent. A solvent other than water may be contained, but from the viewpoint of safety and economy, the content of water in the solvent is preferably 98% by weight or more, more preferably 99% by weight or more, More preferably, it is substantially 100% by weight. Examples of the solvent other than water include alcohols such as methanol, ethanol, propanol, butanol, and hexanol. Among these, ethanol is preferable from the viewpoint of cost and coating workability. The content of the solvent in the coating composition is 10 to 500 parts by weight with respect to 100 parts by weight of the refractory aggregate from the viewpoint of maintaining the thickness of the coating film in an appropriate range and reducing sagging. 10 to 100 parts by weight is more preferable.

<Other ingredients>
As other components that can be incorporated into the coating composition of the present invention, additives such as colorants such as pigments and dyes, rheology modifiers that improve coating workability, anti-settling agents, and surfactants can be used. In addition, additives such as thickeners and preservatives such as cellulose derivatives such as hydroxyalkylated cellulose, polyvinyl alcohol and sodium alginate can also be used.

  The mold agent composition of the present invention is suitable for a casting production method using a casting sand mold formed by applying a mold agent composition to a sand mold surface. That is, the casting manufacturing method of the present invention is a casting manufacturing method using a casting sand mold formed by applying the above-described coating agent composition of the present invention to a sand mold surface.

  The method for applying the coating composition of the present invention to the sand mold (mold) is not particularly limited, and is conventionally known, for example, flow coating (bukkake method), dipping (dipping method), brush coating, spray coating, and the like. The method you can use is available. Especially, it is preferable to apply the coating composition of the present invention by flow coating because the effect of the present invention (reduction of sagging muscles) is effectively exhibited. Moreover, as the foundry sand used for the sand mold, new sand such as zircon sand, chromite sand, synthetic mullite sand, or regenerated sand thereof is used in addition to quartz sand mainly composed of quartz. Foundry sand can also be used without the addition of a binder, in which case the filling property is good, but when high sand mold strength is required, a binder is added and a hardener is used. It is preferable to cure.

  In addition, the above sand molds are generally mixed with molding binders such as organic binders such as furan resins and alkali phenol resins and inorganic binders such as water glass. After being filled in, it is obtained by curing and die cutting.

  In general, the coating agent composition is kept as a composition (preservation composition) in a state where the solvent concentration is low (solid content concentration is high) during storage so that an appropriate viscosity can be obtained during use. And diluted with a solvent. The composition having a high solid content (preservation composition) may be adjusted to the amount of solvent and the like, usually with a penetration of about 200. The appropriate specific gravity at the time of use is 30 to 80 baume. Note that the specific gravity expressed in Baume units can express the viscosity and concentration factors of the coating agent in a lump, and serves as a standard when the coating agent is applied to the sand mold.

  The thickness of the coating film is preferably 50 to 300 μm, more preferably 75 to 150 μm, and still more preferably 80 to 120 μm, from the viewpoint of exerting the original function of the coating agent.

<Coating method of coating agent composition>
The blending composition at the time of storage is preferably 3 or more by weight ratio of the refractory aggregate to water from the viewpoints of cost, transportability and storage stability. Half of a predetermined amount of water, sodium bentonite and a thickener are added to the kneader and kneaded. To the kneaded product, the remaining components other than sodium bentonite, thickener, water and refractory aggregate, for example, a binder, a sintering agent and a preservative are added and kneaded. Further, the refractory aggregate and the remaining water are added to the kneaded product and kneaded. The moisture concentration of the obtained coating agent composition is preferably 25% by weight or less.

  When a casting is produced using the mold composition of the present invention, a casting having a small number of seizure defects and a beautiful casting surface is obtained, so that a complicated structure or a beautiful casting surface is required. It is suitable for. Specific examples of castings include members, parts and the like used for hydraulic valves, motors, molds, engine frames, machine tools, construction members, and the like of construction machines.

  Hereinafter, examples and the like specifically showing the present invention will be described.

<Preparation of coating agent composition>
100 parts by weight of refractory aggregate, 4.5 parts by weight of thickener, 1.2 parts by weight of binder, 19.7 parts by weight of water, 2.2 parts by weight of additive, dispersant having the content shown in Table 1 And the bentonite was kneaded by the blending method shown below. That is, in the blending method, sodium bentonite and a thickener were added to 9.85 parts by weight of water (half of a predetermined amount of water). Thereafter, the mixture was kneaded at 25 ° C. with a single-screw mixer at 300 rpm for 5 minutes. Other additives were mixed into the mixture and kneaded for 2 minutes at the same temperature and the same speed. To this mixture, refractory aggregate was added and all remaining water was added, and kneaded at the same temperature and the same speed for 10 minutes to obtain a paste-form coating composition.
All of the above refractory aggregates are composed of silica (average particle size 4 μm), obsidian (average particle size 91 μm), mica (average particle size 80 μm), silica: obsidian: mica = 67: 25: 8. What was mixed by weight ratio was used. The average particle diameter of the refractory aggregate after mixing was 34 μm.
The thickening agent is a polyamine cationic surfactant (manufactured by Kitahiro Chemical Co., Ltd., Softex K-370), the binder is gum arabic, and the additive is a sintering agent ( Attapulgite) and a bromine-based preservative (manufactured by Kay Kasei Co., Ltd., Biohope) were mixed at a weight ratio of sintering agent: bromine-based preservative = 92.15: 7.85. When the obtained coating agent composition was measured with a needle penetration measuring device 800S-01 manufactured by Koiso Co., Ltd., the penetration was 200 in all cases.
The dispersants in Table 1 used in the present invention are shown below.
Dispersant A: neutralized product of acrylic polymer partial Na; in formula (1), M = Na is 90%, M = H is 10%; weight average molecular weight Mw = 30000; neutralization degree 90%; Poise 530, manufactured by
Dispersant B: Acrylic acid polymer partial Na neutralized product; In the formula (1), M = Na is 35%, M = H is 65%; weight average molecular weight Mw = 30000; neutralization degree 35%; Synthetic Co., Ltd., Aronbis AH-106X]
Dispersant C: Neutralized product of acrylic acid polymer Na; in formula (1), M = Na is 100%; weight average molecular weight Mw = 3000; neutralization degree 100%; (Aldrich, sodium polyacrylate)
Dispersant D: acrylic acid polymer; in formula (1), M = H is 100%; weight average molecular weight Mw = 25000; neutralization degree 0%; (Aldrich, polycarboxylic acid)
Dispersant E: A copolymer of acrylic acid and maleic anhydride (molar ratio 1: 1) represented by the formula (1) and (3) or (2): neutralized Na; M = Na, X = Na and Y = Na; weight average molecular weight Mw = 20000; degree of neutralization 100%; [Pois 520, manufactured by Kao Corporation]
Dispersant F: Naphthalenesulfonic acid Na condensate; weight average molecular weight Mw = 100000; neutralization degree 100%; [Kao Co., Ltd., Demol RN]
Dispersant G: Acrylic acid polymer ammonium salt; in formula (1), M = NH ₄ is 100%; weight average molecular weight Mw = 30000; neutralization degree 100%; [Pois 532A manufactured by Kao Corporation]
Dispersant H: copolymer of diisobutylene and maleic acid (molar ratio 1: 1) Na neutralized product; weight average molecular weight Mw = 20000; neutralization degree 100%; [Demol EP, manufactured by Kao Corporation]

<Sagging test>
To 100 parts by weight of furan regenerated sand (AFS45), 0.8 part by weight of Kao Quaker furan resin (340B) is added, and further, Kao Quaker curing agent (TK-3) is added to 100 parts by weight of furan resin. 40 parts by weight was added and the kneaded sand obtained by kneading was cast to prepare a plate-shaped test piece having a height of 300 mm × width of 200 mm × thickness of 30 mm provided with a groove of 15 mm width × 5 mm depth. This test piece is leaned against an inclined wall of 75 degrees, diluted with water to a specific gravity (40 to 44 Baume) that can be applied by pouring each coating composition, and then washed with water (about 50% by weight of water in the diluted composition). Painted. Then, after 30 seconds passed immediately after the flow coating, the test piece was tilted 135 degrees, and the degree of dripping generated at that time was visually evaluated in the following four stages. The results are shown in Table 1.
(Sag test evaluation criteria)
1: A lot of sagging occurs. (Visually there are obvious irregularities, and if it is cast as it is, the streaks are clearly transferred.)
2: Some dripping occurs. (It is difficult to see the unevenness by visual inspection, but if it is cast as it is, the streaks are transferred.)
3: Sag is slightly generated. (It is almost smooth visually, and when it is cast as it is, the streaks are not transferred.)
4: No sagging occurs. (When cast as it is, no transfer is seen)

<Thickness of coating film>
The measurement was performed using a rotary wet film film pressure gauge (model number: ELCOMTER 3230) manufactured by Elcometer. Rotate the membrane pressure gauge over the wet coating and read the scale where the center wheel touched the membrane. This value is the thickness (μm) of the film. The results are shown in Table 1.

<Penetration depth>
After applying the coating agent to the sand mold, it was cut in the vertical direction, and the depth (mm) at which the coating agent penetrated the cross section was measured. The results are shown in Table 2.

  From the results of Table 1, it can be seen that in the coating composition according to Examples 1 to 14, sagging streaks are reduced and a coating film having an appropriate thickness can be obtained. On the other hand, in the coating agent compositions according to Comparative Examples 1-2 and 5-8, the occurrence of sagging is observed, and the sagging property is deteriorated as compared with the coating agent compositions according to Examples 1-14. Recognize. In addition, in the coating composition which concerns on the comparative example 3 with much content of a dispersing agent, and the comparative example 4 with little content of sodium bentonite, it is equivalent to the coating composition which concerns on Examples 1-9 about sagging property. However, when the applied coating composition soaks into the sand mold, the coating film becomes thin and there is a possibility that seizure occurs.

From the results in Table 2, the higher the degree of neutralization, the greater the penetration depth and the better the seizure resistance.

Claims (6)

A sand casting casting composition comprising a refractory aggregate, a binder, a sintering agent, water, a dispersant, and sodium bentonite,
The polymer in which the dispersant has a structural unit derived from acrylic acid and / or maleic acid, and the total content of the structural units derived from acrylic acid and maleic acid in all the structural units is 98 mol% or more, or an alkali thereof A metal salt,
The content of the dispersant is 0.04 to 1.2 parts by weight with respect to 100 parts by weight of the refractory aggregate,
A coating composition for sand casting, wherein the content of sodium bentonite is 2.5 to 15 parts by weight with respect to 100 parts by weight of the refractory aggregate.   The coating composition for sand mold casting according to claim 1, wherein the weight ratio of sodium bentonite to the dispersant (sodium bentonite / dispersant) is 4 to 150. The sand mold casting coating composition according to claim 1 or 2, wherein the dispersant has a neutralization rate of 80 to 100%.   The sand-casting coating composition according to any one of claims 1 to 3, wherein the dispersant is water-soluble.   The refractory aggregate is at least one selected from the group consisting of mullite, silica, alumina, magnesia, zircon, alumina silicate, graphite, obsidian, olivine, talc and mica. The coating composition for sand casting as described. The sand mold casting coating composition according to any one of claims 1 to 5, wherein the binder is at least one selected from the group consisting of saccharides, phenol, rosin and petroleum resin.