JP3126284B2 - Resin-coated aggregate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resin-coated aggregate suitable mainly as a material for producing a casting mold. More specifically, the present invention is dry and free-flowing at room temperature (hereinafter referred to as "dry-free flowing").
And at room temperature, optionally under heating (150 ° C
At a temperature of not more than 1) and a resin-coated aggregate (hereinafter, the resin-coated aggregate is referred to as “RCS”) that can be cured by contact with moisture and / or a curing agent.

[0002]

2. Description of the Related Art As a typical mold manufacturing process, a shell mold method is used as a typical example of a process using a thermosetting RCS.
A cold box method and an organic ester curing method are used as representatives of those using room temperature curable RCS.

Of these, R used in the shell mold method
CS is the only material that retains dryness at room temperature,
The RCS used in the latter two is a wet mold material.

[0004] The shell molding method uses the RCS
Although it is very widely used because of its storage stability and ease of use, since it is subjected to high-temperature molding at a temperature of 250 to 300 ° C. at the time of molding, it is important in terms of large energy consumption and the problem of deterioration of the working environment due to ammonia odor and the like. Has disadvantages. On the other hand, in the cold box method, although the RCS used for this is curable at room temperature, it has a problem of odor of amine gas and a problem that casting defects are apt to occur frequently due to a large amount of gas generated during pouring.

In order to solve these problems, a method of curing a water-soluble potassium-alkaline phenol formaldehyde resin with an organic ester has recently been proposed and spread (JP-B-61-37022, JP-B-61-43132). No.).

[0006]

However, the following problems remain in this process. The first point is that, as a basic property of this process, the strength of the mold tends to increase as the resin is a high molecular weight resin and the concentration of the resin liquid increases, but the handling of the resin liquid tends to increase. For reasons such as the above problem and uneven mixing at the time of mixing with the refractory aggregate, restrictions are imposed on the molecular weight, the resin concentration and the viscosity, so that the mold strength cannot be increased for the amount of the resin added.

The second point is that since the resin is a liquid resin, the amount of free aldehydes is increased and an irritating odor is generated, thereby deteriorating workability in molding. For example, in the case of formaldehyde, the cause is presumed to be the aldehyde odor due to the re-dissociation of polyoxymethylene and the like generated by the Cannizzaro reaction of the aldehyde with a strong alkali catalyst.

Third, there is a disadvantage that the resin must be stored in a cold place because of poor storage stability due to aging of the resin due to its water solubility and high pH.

An object of the present invention is to provide a high-temperature molding, heat, ammonia odor and the like without deteriorating the working environment unlike the shell mold method, and to contact with moisture and / or a curing agent at room temperature, and in some cases, at room temperature. To provide an RCS that can be molded under heating (within 150 ° C.) and that has dry body free-flowing properties at room temperature that is easy to handle. Even without using a high-viscosity (polymer) liquid resin,
To provide an RCS having a free-flowing dry body at room temperature including a polymerized resin capable of improving the working environment by improving the mold strength and reducing the generation of residual aldehydes,
There is no need to consider the aging of the liquid resin that affects the storage stability of RCS as in the past, and it provides a RCS that has dry storage fluidity at room temperature with significantly extended storage stability, etc. To provide a completely new RCS.

That is, the present invention relates to a refractory aggregate and the following (a),
It is a resin-coated aggregate containing an organic binder satisfying (b) and (c) and being dry at normal temperature. (A) a phenolic resin having a methylol group obtained by subjecting one or more moles of a compound having an active carbonyl group to one mole of a phenol to addition condensation, and (b) one gram equivalent of a phenolic hydroxyl group in the phenolic resin An organic binder containing 0.15 to 0.8 gram equivalents of alkali metal per weight, and (c) the amount of water in the organic binder is 20% by weight or less, and Water extraction amount of the organic binder is 40% by weight or more.

The most important points in the present invention are that the RCS in which the organic binder is coated on the refractory aggregate retains a dry-body free-flowing property at room temperature, that the binder has water solubility, The point is that the RCS is activated by contact with water and / or a curing agent at ordinary temperature, and in some cases, under heating to bind the aggregate.

The fire-resistant aggregate may be any aggregate having fire resistance and heat resistance that can withstand the use temperature. For example, besides silica sand, alumina, magnesia, zircon, chromite, olivine, slag, etc. And natural or artificial aggregates, or porous or hollow aggregates thereof, or recovered and recycled aggregates thereof. Of these, recovered and recycled aggregates are preferably used from the viewpoint of economy.

The outline of the requirements for the organic binder used in the present invention satisfies the above (a), (b) and (c), but it is also necessary to additionally use various additives in combination. Can also. The amount of the organic binder used in preparing the RCS is not particularly limited because it may be appropriately determined according to the purpose of use, but is generally 0.2 wt. % Or more, especially 0.2 to
It is selected in the range of 5% by weight.

There is no particular limitation on the phenols. For example, phenol, bisphenol A, bisphenol F, resorcinol, catechol, para-tert-butylphenol, cresols, xylenols, and by-products generated during the production of phenols are used alone or alone. Used mixed.

Examples of the compound having an active carbonyl group include formaldehyde, paraformaldehyde,
Glyoxal, dioxane, trioxane, tetraoxane, acetone, methyl ethyl ketone and the like are used alone or in combination, but aldehydes represented by formaldehyde are preferably used. The compound having an active carbonyl group is required to be at least 1 mol per mol of phenols, but does not exceed 6 mol for economic reasons. However, the preferred reaction molar ratio is 1.1 to 3 moles of a compound having an active carbonyl group per mole of phenols. Further, the methylol group in the phenolic resin obtained by the reaction of the phenols with a compound having an active carbonyl group is important for improving the heat resistance of the casting mold, or for the relationship with the curing speed during molding. Play a role.

In the present invention, for example, a resin obtained by reacting a compound having an active carbonyl group in less than 1 mol with respect to 1 mol of a phenol is reacted with a methylol group obtained by reacting a compound having an active carbonyl group in 1 mol or more. The resin adjusted to substantially 1 mol or more by combination with the resin having the above is also included in the range of the resin in the present invention.

The condition for maintaining the water solubility of the organic binder which is important in the present invention is that the alkali metal is contained in the range of 0.15 to 0.8 gram equivalent per 1 gram equivalent of phenolic hydroxyl group in the phenol resin. It is to include. That is, it is necessary to partially make the alkali phenolate,
If it is less than 0.15 gram equivalent, the water solubility becomes insufficient and the curing rate tends to be slow. If it exceeds 0.8 gram equivalent, the alkali metal is too much, for example, the heat resistance of the refractory aggregate may be reduced at high temperatures. is there. The alkali metal in the present invention is represented by Li, K, and Na, but specifically, K or Na is preferably used. These can be used alone or as a mixture, and can also be used in combination with other oxides or hydroxides such as alkaline earth metals.

Next, in the present invention, the water content in the coated organic binder must be maintained at 20% by weight or less. This is determined by the size of the molecular weight of the resin and the amount of the alkali metal. However, if the balance between the amount of water and the water is poor, RCS causes blocking. In general, the higher the molecular weight of a polymer, the more it can maintain a dry body at room temperature even if the amount of water is large, but the limit is 20% by weight. The amount of water in the organic binder in the present invention is expressed as a percentage on a weight basis obtained by dividing the amount of water measured by the Karl Fischer method for RCS by the amount (solid content) of the added organic binder.

In the present invention, the condition that the organic binder is water-soluble is a condition, and the degree of the water-solubility is determined by the amount of the organic binder in the RCS extracted with water, that is, the RCS is at least dissolved in water at room temperature. The amount of water (X / Y) expressed as a ratio of the amount of the organic binder (solid content X) extracted by the extraction treatment for 3 hours to the amount of the organic binder (solid content Y) used in the production of RCS. ,% By weight). If the amount of water extraction is less than 40% by weight, RCS
When trying to activate by contacting with water and / or a curing agent, the curing time becomes longer and the molding cycle becomes slower.

As a curing agent for curing the RCS according to the present invention, an organic ester-based curing agent or an acidic substance having a pKa of 9.82 or less in an aqueous solution at 25 ° C. (ie, an acidic substance having an acidity stronger than phenol). Acid-based curing agent such as an inorganic salt or the like, which generates the acidic substance upon contact with an alkali metal, or a combination thereof. As the organic ester-based curing agent, for example, methyl formate, ethyl formate, ethyl acetate, ethyl lactate, triethyl citrate, dimethyl succinate, dimethyl malonate, dimethyl sebacate, dimethyl oxalate, methyl acrylate, ethylene glycol Carboxylic esters such as diacetate, diacetin and triacetin, or lactones such as γ-butyrolactone, γ-caprolactone, δ-caprolactone, δ-valerolactone, β-propiolactone, ε-caprolactone, or ethylene carbonate, propylene Cyclic alkylene carbonates such as carbonate, 4-ethyldioxolone, 4-butyldioxolone, 4,4-dimethyldioxolone, and 4,5-dimethyldioxolone are used as a liquid or gas. Among them, methyl formate, ethylene glycol diacetate, triacetin, γ-butyrolactone, ethylene carbonate, propylene carbonate and the like are preferable.
Further, as the acid-based curing agent, for example, carbon dioxide gas, carbonated water, magnesium carbonate, aluminum phosphate, iron chloride,
Aluminum sulfate (sulfuric acid band), magnesium chloride,
Magnesium sulfate, divalent metal salts of organic sulfonic acids and the like are used. Among them, carbon dioxide, aluminum phosphate, aluminum sulfate (sulfuric acid band) and the like are preferable.

The amount of such a curing agent used is not specifically limited since it varies depending on the properties of the organic binder, the type of the curing agent and the molding method. It is selected in an amount of 5 parts by weight or more, preferably 10 to 200 parts by weight, more preferably 10 to 100 parts by weight with respect to parts by weight.

Next, one embodiment of the method for producing the RCS of the present invention will be described below.

(Step 1) A phenol and an aqueous formaldehyde solution are subjected to an addition condensation reaction in a prescribed molar ratio in the presence of a basic or acidic catalyst such as an alkali metal or alkaline earth metal compound, an amine compound or an acid compound. A liquid phenol resin having a methylol group (hereinafter, simply referred to as "liquid phenol resin") is synthesized, and a necessary gram equivalent number of an alkali metal hydroxide is added so that a higher molecular weight compound is obtained as required. To obtain a liquid phenol resin. At this time, a silane coupling agent, a release improver, or the like for improving strength may be included. Furthermore, it is also possible to previously dehydrate the liquid phenol resin by spray drying or the like to prepare a powdery resin, and to supply water so that it can be used as a medium during mixing with the refractory aggregate. Thus, an organic binder is obtained.

(Step 2) The heated refractory aggregate is charged into a batch-type and / or continuous-type mixer, if necessary, and the above-mentioned organic binder is blended while mixing is continued. Dry and free flowing RC at room temperature by removing water while blowing nitrogen
Get S. At this time, for example, a lubricant (such as calcium stearate), a curing accelerator (such as a hydroxide or oxide of an alkaline earth metal), a curing agent, or a compound containing water of crystallization that releases water by thermal decomposition may be used as necessary. May be latently blended. The dry RCS is preferably sealed so as not to touch the moisture or carbon dioxide in the air. Moisture solidifies the RCS, and carbon dioxide gas reacts with alkali to deteriorate water solubility.

(Step 3) In order to mold a mold using the obtained RCS, it is necessary to activate RCS by contacting water and / or a curing agent, and a typical molding method is as follows. Examples are given. (1) A method in which a mixture of water and a curing agent and RCS are mixed immediately before filling in a mold such as a wooden mold, and the mixture is filled in the mold and molded at normal temperature. (2) RCS is filled in a mold. A method in which a curing agent such as an organic ester containing water or carbon dioxide gas is contacted at the same time as blowing or sucking, (3) RC
A method in which S is sufficiently filled in a mold, and a gas or mist of moisture and a curing agent is blown or sucked into the mold, and (4)
A method in which a heating mold is filled with RCS, and then moisture or a decomposition gas serving as a curing agent is generated at a high temperature to make contact with an organic binder, (5) RCS containing substantially no moisture
A method in which a curing agent and a curing accelerator are latently mixed, and only water is contacted during molding.

[0026]

The present invention will be described in more detail with reference to the following examples.

(Example 1) (Preparation of organic binder) 1500 g of phenol (15.9)
Mol) and 1041 g of 92% by weight paraformaldehyde
(31.9 mol) and 1353 g of water were placed in a three-necked flask, and 150 g of a 50% by weight aqueous sodium hydroxide solution was added thereto.
After reacting at 80 ° C. for 1 hour, the mixture was further reacted at 80 ° C. for 1 hour and cooled. Then, the 50% by weight aqueous sodium hydroxide solution was added to 1
An additional 0.05 g was added so that the equivalent of 0.2 gram equivalent to 1 gram equivalent of the hydroxyl group of the phenol monomer was further raised and the temperature was maintained at 80 ° C.
The reaction was performed to obtain cP to obtain a resin. At this time, the solid concentration was 56% by weight, and neutralized with dilute sulfuric acid.
It was about 0 (hereinafter, this resin is referred to as “standard organic binder”). A 50% by weight aqueous solution of caustic soda or water is added to the organic binder of this standard at the ratio shown in Table 1,
Organic binders A to D were obtained.

[0028]

[Table 1]

(Manufacture of RCS) Mikawa silica sand V-6 was previously heated to 50 ° C., 100 ° C. and 150 ° C. as a refractory aggregate, and 4 kg each was put into an experimental mixer manufactured by Enshu Tekko. Under the conditions, the organic binders A to D were added to the refractory aggregate so as to have a solid content of 2.5% by weight, followed by blowing while mixing to dehydrate. At this time, the time required for the water to evaporate and disintegrate into a dry free-flowing RCS was as shown in Table 2. From Table 2, as expected, the higher the mixing temperature, the shorter the collapse time was. However, unexpectedly, the smaller the amount of alkali metal, the shorter the collapse time and the higher the productivity in this range. I understood that.

[0030]

[Table 2]

(Properties of RCS-1) Each RC obtained
The water content in S was measured by the Karl Fischer method, as shown in Table 3, and the value converted to the water content in the organic binder is shown in the lower row. However, a small amount of water adhering to the silica sand was ignored.

[0032]

[Table 3]

As shown in Table 3, the converted moisture content in the organic binder based on the actually measured moisture content is 20% by weight or less, and at least 3%.
The RCS had a dry-body free-flowing property at room temperature, despite the presence of nearly weight percent moisture. These facts indicate that the resin itself forms an alkali metal phenolate and has a substantially high melting point, though it has a water content that cannot be considered in the conventional RCS for shell molding.

(Properties of RCS-Part 2) Then, 50 g
Of the organic binder obtained by water-extraction of RCS at room temperature for 5 hours using a Soxhlet extractor (RC)
Table 4 shows the water extraction amount (% by weight) of the organic binder in the RCS, that is, the degree of water solubility of the organic binder, which was obtained as a ratio to the amount (solid content) of the organic binder used in preparing S. Shown in

[0035]

[Table 4]

According to the results shown in Table 4, the degree to which the organic binder is dissolved in water varies depending on the amount of the alkali metal and the temperature conditions for mixing. This is presumed to be due to the fact that the molecular weight of the resin increases during mixing and the water-soluble content decreases. This is the result of measuring the number average molecular weight of a resin obtained by neutralizing an organic binder extracted at room temperature with diluted sulfuric acid by liquid chromatography.
This was supported by the fact that all of them changed from 1.2 times to 2.8 times the resin (number average molecular weight was about 750) at the time of preparing the reference organic binder.

(Properties of RCS-Part 3) Each of the above RCSs
1000 g was taken into a Shinagawa mixer, 20 g of a 20% by weight lactone aqueous solution prepared from water and γ-butyrolactone was poured, mixed for 30 seconds, and then a cylindrical test piece having a diameter of 50 mm and a height of 50 mm was prepared and left standing (time Table 5 shows the results of measurement of the coercive pressure for each of the above cases.

[0038]

[Table 5]

(Comparative Example 1) An aqueous solution of the organic binder C was used as it was to prepare 1000 g of Mikawa silica sand V-6 at room temperature.
A wet resin sand was prepared by blending to a solid content of 2.5% by weight, and 20 g of the above-mentioned 20% by weight aqueous solution of γ-butyrolactone was poured into a Shinagawa mixer, and RC was added.
Properties of S-As in the case of No. 3, the strength of the mold was measured, and the results were as shown in the following table.

[0040]

[Table 6]

(Properties of RCS-Part 4) In the step of measuring each RCS in a Shinagawa mixer and mixing it with a curing agent,
The amount of formaldehyde generated was measured using a Kitagawa detector tube. Table 7 shows the results.

[0042]

[Table 7]

(Properties of RCS-Part 5) RCS prepared by mixing with organic binder C at 100 ° C. and organic binder C (aqueous solution) were stored in an atmosphere at 25 ° C. for 6 months. The degree of each time-dependent change was examined. An attempt was made to mix the organic binder C having increased viscosity with sand, but the performance of the mold could not be evaluated because it was semi-solidified. However, as for RCS, a 20% by weight aqueous solution of γ-butyrolactone was added, and the results of examining the mold performance were as shown in Table 8.

[0044]

[Table 8]

[0045]

The resin-coated aggregate of the present invention which is dry at normal temperature is
While having the same ease of handling as the resin-coated aggregate used in the shell mold method, it does not involve the deterioration of the working environment due to the conventional high-temperature molding, heat, ammonia odor, etc. Has the property of being cured at room temperature when contacted with it, and has improved mold strength, better storage stability, and better working environment than conventional wet resin-coated aggregates. In addition, since the resin-coated aggregate of the present invention can be stored as a dry body, it is necessary to take measures to ensure the storage stability of the organic binder (aqueous solution) which is liable to change with time as in the conventional case. There is no. In addition, it is a new mold material that enables a pressure molding method, that is, a physical molding method by reducing moisture in the molding method.

────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Yoshihisa Umikawa 26, Niitsu, Niizumi, Fuso-cho, Fuwa-cho, Niwa-gun, Aichi Prefecture Asahi Organic Materials Industry Co., Ltd. Aichi Factory (56) References JP-A-7-178507 , A) (58) Field surveyed (Int. Cl. ⁷ , DB name) B22C 1/22

Claims (1)

(57) [Claims] 1. A resin-coated aggregate comprising a refractory aggregate and an organic binder satisfying the following (a), (b) and (c), and being dry at room temperature. (A) a phenolic resin having a methylol group obtained by subjecting one or more moles of a compound having an active carbonyl group to one mole of a phenol to addition condensation, and (b) one gram equivalent of a phenolic hydroxyl group in the phenolic resin An organic binder containing 0.15 to 0.8 gram equivalents of alkali metal per weight, and (c) the amount of water in the organic binder is 20% by weight or less, and Water extraction amount of the organic binder is 40% by weight or more.