JPS645979B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a new and useful binder for foundry sand, and more particularly, the present invention relates to a new and useful binder for foundry sand, and more particularly, for use in sand molds for light metals or light alloys cast at low temperatures, such as aluminum alloys, which are made by combining a specific solid resin and a liquid resin. It relates to a binder (binding agent) used in molding. Castings such as aluminum alloys, which are cast at a relatively low temperature of around 700°C, do not undergo a thermal cycle that sufficiently decomposes the phenolic resin binder, so sand removal is difficult. For this purpose, a great deal of effort and energy is expended, including the special mold-baking process. To this end, methods have been developed to date, including the use of polyester resin binders other than phenolic resins, which have slightly lower heat resistance, methods of adding decomposition aids to phenolic resins, and even methods of using easily decomposable compositions for phenolic resins. Although methods have been proposed to denature the mold, none of these methods meet the work standards and cause trouble or reduce the strength of the mold, or compensate for this decrease in mold strength. Therefore, increasing the amount used may increase gas defects, and the current situation is that a binder that is fully satisfactory for practical use has not been found. However, in view of the above-mentioned circumstances, the inventors of the present invention have developed a method that, without making any changes to the current working standards of the shell molding method, can sufficiently decompose even when cast at low temperatures, such as aluminum alloys, and prevent sand removal. As a result of intensive research aimed at finding a phenolic resin that can greatly omit processes such as mold baking, we first determined the ease of disassembly (disintegration) of the mold. 1. Making a mold by reducing the amount of binder (caking agent) added, 2. Decreasing the crosslinking density of the phenolic resin to lower the heat resistance, 3. Modifying it with an easily decomposable composition, 4. Bonding that is easy to decompose. 5. There are methods such as using auxiliary agents such as oxygen-containing substances, pyrogenic substances, or decomposition accelerating substances, and each of them has been found to be effective, but when using these methods,
As long as a single method is used, not only is it beyond the state of the art, but it also cannot meet the working standards of the shell molding method, resulting in slow curing and a decrease in strength. On the other hand, it has been further found that the more methods 1 to 5 listed above are combined, the more satisfactory easily disintegrating products can be obtained. On the other hand, it is necessary to keep the strength high since the strength decreases significantly.
If a modified formulation is adopted to meet these needs, it may result in slow curing and a decrease in strength, which is still unsatisfactory from an overall standpoint. However, the present inventors have gone further and found that when coating is performed not only with a solid resin but also with the same type of liquid resin, not only the curing speed and strength are significantly improved, but also the easily degradable (easily disintegrating) was also found to be effective.
The present invention has now been completed. That is, the present invention provides the following for phenolic resin:
A solid modified phenolic resin (A) obtained by reacting a brominated epoxy resin with a solid content weight of 3 to 20%, a liquid phenolic resin (B), and a solid content weight of the phenolic resin. The purpose of the present invention is to provide a particularly two-component molding sand binder comprising as an essential component a liquid modified phenolic resin (C) obtained by reacting 20% or less of a brominated epoxy resin. be. Here, as the above-mentioned phenolic resin, any commercially available phenol resin, either a novolak type or a resol type synthesized from phenol and formaldehyde, can be used, but in particular, free phenol resins can be used. The lowest possible amount of phenolic monomer is suitable. This is because when the phenol resin reacts with the brominated epoxy resin, the brominated epoxy resin reacts with the free phenol monomer, and that part becomes a mere contaminant and its performance is reduced. This is to reduce the Furthermore, since the phenolic resin has a high melting point and an increased viscosity due to the reaction with the brominated epoxy resin, it is preferable to use a phenolic resin that reacts slowly and has a slightly low melting point as the base. When preparing the solid modified phenolic resin (A), the melting point after modification is 65
It is necessary to keep the temperature within a range of ~100℃. This is because when the melting point of the solid modified phenolic resin (A) is low, the coated sand tends to block, and when the melting point is high, it becomes difficult to dissolve into the heated sand, making it difficult to mix uniformly. Because it will disappear. Furthermore, during the reaction between these phenolic resins and brominated epoxy resins, the ether bonds generated by the reaction between the phenolic hydroxyl groups and the epoxy groups are easier to decompose than the methylene bonds of the phenolic resins, and are less likely to participate in such reactions. The phenol nucleus reduces the reactivity of the active site, resulting in a lower crosslinking density. Next, as the above-mentioned brominated epoxy resin, bisphenol A type epoxy resin is particularly preferable. The rate of modification by the brominated epoxy resin is determined based on the amount of bonding parts that are easily decomposed, the crosslinking density, the apparent curing speed and strength, and the effect of the decomposed bromine decomposition gas auxiliary agent. Although determined, it is usually 3 to 20%, preferably 5% based on the solid content weight of the phenolic resin.
A range of ~15% is appropriate because it provides a good balance in terms of performance. Therefore, in order to obtain the solid modified phenolic resin (A) described above, which can also be referred to as the main ingredient in the present invention, it is necessary and desirable to first modify the solid phenolic resin, but the liquid resin itself cannot be modified. Even without any modification, the effects of the present invention can be fully expressed. If the degree of modification (denaturation rate) is too small, the effect will be small, and if it is too large, the bromine molecules themselves are large, so steric hindrance may occur, resulting in extremely slow curing. , the strength also becomes inferior. This is considered to be because the crosslinking density is low, and although this is highly desirable from the viewpoint of easy disintegration, it cannot be said to be desirable from the viewpoint of working conditions. As described above, by modifying the phenolic resin with the brominated epoxy resin, the crosslink density is reduced, and bonds that are easily decomposed are also introduced.
In addition, although the presence of this brominated epoxy resin has a flame retardant effect, the brominated epoxy resin itself is easily decomposed, and
When it is decomposed, it has the effect of promoting the decomposition of the resin and, ultimately, the collapse of the mold, so the modification of phenolic resin with brominated phenolic resin makes the resin more easily decomposed (easily disintegrated) as a whole. That's why. However, using only the aforementioned solid modified phenolic resin (A), which is the main ingredient in the present invention, results in slow curing and a decrease in strength.
In the present invention, in addition to this component (A), it is necessary to use either the above-mentioned liquid phenolic resin (B), which is a liquid resin, or the above-mentioned liquid modified phenolic resin (C). be. In fact, if only the solid modified phenolic resin (A) is used, it will harden slowly and the apparent strength will decrease, so the preferred method for producing coated sand is to melt-coat the resin (A). Practically satisfactory effects can be expected if the layer is further coated with a liquid phenolic resin (B) or a liquid modified phenolic resin (C). Moreover, dry coated sand
In order to achieve this, if a large amount of low melting point liquid resin is blended, the coated sand will easily block, and even if the solvent remains, it will be easy to block, so these components (A) and (B) should be used. Ratio or component (A)
The usage ratio of component (C) and component (C) is preferably in the range of 95:5 to 70:30 by weight in terms of solid content. At this time, the liquid resin dissolved in a solvent is
It should have as high a solids content as possible and a viscosity that is easy to handle, that is, usually 1000 cps/25°C or less. In order to further enhance the effects of the present invention, among the known and commonly used additives, particularly effective additives,
Silane coupling agent, strength imparting agent, organic acid
Additives such as a hexamethylenetetramine-based decomposition accelerating fast curing agent, a melt viscosity lowering agent such as waxes or amides, or a strength imparting agent may be added to the binder for foundry sand of the present invention, thereby preventing any damage. Without detracting from the effects of the present invention, the binder of the present invention obtained in this way can be applied particularly to the preparation of resin-coated sand grains, and the phenol used for ordinary hot marling or shell molding It can be used in almost the same way as resin. Next, the present invention will be specifically explained using reference examples, examples, and comparative examples, and all parts and percentages are based on weight unless otherwise specified. Reference Example 1 [Preparation example of solid modified phenolic resin (A)] 940 parts of phenol, 450 parts of 40% formalin, and 9 parts of oxalic acid were charged into a reactor equipped with a condenser and reacted for 4 hours with reflux. , immediately start vacuum distillation and reduce the vacuum to 40mm.
Dehydration and dephenolization were performed with Hg up to 160°C. The phenolic resin thus obtained had a melting point of 80° C. (the same applies hereinafter) as measured by the ring and ball method, and a free phenol content of 2%. Then, for 500 parts of this phenolic resin,
50 parts of "Epiclon 152" [brominated epoxy resin manufactured by Dainippon Ink and Chemicals Co., Ltd.; bromine content = 48%, melting point = 61°C] was added and reacted at 160 to 170°C for 2 hours, and the melting point A solid modified phenolic resin with a temperature of 88°C was obtained. Hereinafter, this will be abbreviated as resin (A-1). Reference Example 2 [Preparation example of liquid modified phenolic resin (C)] The resin (A-1) obtained in Reference Example 1 was dissolved in methanol to make a 60% concentration solution, and the solution was heated at 25°C.
The viscosity measured by the BM type viscometer (hereinafter the same) is
It was 65cps. Next, 9% hexamethylenetetramine and 9% water were added to this solution to obtain a liquid modified phenolic resin (C). Hereinafter, this will be referred to as resin (C-1).
It is abbreviated as Reference Example 3 [Preparation example of liquid modified phenolic resin (C)] 600 parts of "Pryoven TD-2040" [solid resol type phenolic resin manufactured by Dainippon Ink and Chemicals Co., Ltd.; melting point = 60°C] , "Epicron 152"
60 parts and 440 parts of methanol were charged so that the solid content was 60%, and the mixture was reacted for 5 hours while being dissolved at a reflux temperature (approximately 70°C).
A liquid modified phenolic resin (C) with a viscosity of 130 cps was obtained. Hereinafter, this will be abbreviated as resin (C-2). Example 1 10 pieces of flattery sand preheated to 140°C
Kg, 135 g of resin (A-1) and kneaded for 1 minute, then 25 g of resin (C-1) and 120 g of 16.9% hexamethylenetetramine aqueous solution were added and kneaded for 1 minute, and then 10 g of calcium stearate was added. The mixture was then kneaded for 20 seconds and then taken out to obtain resin-coated sand. Example 2 Same amount of resin (C-2) instead of resin (C-1)
Resin-coated sand was obtained in the same manner as in Example 1, except that the resin-coated sand was changed to use. Example 3 Instead of resin (C-1), the same amount of "Plyoven DG-307" [unmodified water-soluble resol type phenolic resin manufactured by Dainippon Ink and Chemicals Co., Ltd.; solid content = 60%, Viscosity = 200 cps] as liquid phenolic resin (B)
Resin-coated sand was obtained in the same manner as in Example 1, except that the sand was used as a resin. Comparative Example 1 Absent any use of resin (C-1) and using resin (A
- Change the usage amount of 1) to 150g and 18.7%
Resin-coated sand was obtained in the same manner as in Example 1, except that 123 g of the hexamethylenetetramine aqueous solution was used. Comparative Example 2 Instead of resin (A-1), the same amount of "Fandretsu TD-304-B" [unmodified solid novolac type resin for hot marling and shell molding manufactured by Dainippon Ink and Chemicals Co., Ltd.; melting point Resin-coated sand was obtained in the same manner as in Comparative Example 1, except that the temperature was changed to 85°C]. Comparative Example 3 The same amount of "Fandretsu TD-304-B" was used instead of resin (A-1), while resin (C-1)
Instead of the same amount of "Pryoven DG-307"
Resin-coated sand was obtained in the same manner as in Example 1, except that the resin-coated sand was changed to use. The performance evaluation of the resin-coated sand obtained in each of the above Examples and Comparative Examples is summarized in Table 1. It was set at 15%. The test methods for each performance test shown in the table are as follows. Melting point: Compliant with JACT (Casting Technology Promotion Association) test method C-1. Bending strength: Compliant with JIS K-6910. Curing speed (deflection)...The test sand was charged at 250℃ in the mold, fired for 20 seconds, and then 10 seconds after the mold was removed, a test piece (size: 50×
A load of 200 g is applied to the sample (150 x 5 mm, span width: 110 mm) and the amount of "deflection" is read with a dial gauge. The smaller the value, the less "deflection" and therefore the faster curing. Collapse property: The mold was heated to 230℃, the test sand was charged and held for 20 minutes, and then fired in a furnace at 300℃ for 1 minute to obtain a test piece (cylindrical object of 85mmφ x 10mm). This test piece was wrapped twice in aluminum foil, then baked in a furnace at 450℃ for 20 minutes, and the heat-treated test piece was passed through a 10-mesh sieve using a rotorp sieve to remove sand. The time (number of seconds) until no test piece remains on the sieve is measured as "disintegrability" data, or if sand remains as a result of sand removal, further sand removal is performed. The ratio (%) of the amount of sand falling 2 minutes after the start of the sand removal to the weight of the test piece before the start of sand removal is measured and used as "disintegration" data.

[Table] As shown above, the solid phenolic resin modified with a brominated epoxy resin, that is, the solid modified phenolic resin (A) described above, is itself extremely easily disintegrated, but the curing speed is It is somewhat unsatisfactory in terms of strength and strength. Therefore, by further coating with liquid resin, performance such as curing speed and strength can be significantly improved. ), it is possible to make excellent resin-coated sand that not only satisfies the criteria (2), but also shows almost no change in collapsibility even though the strength is improved.

Claims (1)

[Scope of Claims] 1 (A) A solid modified phenolic resin having a melting point of 65 to 100°C obtained by reacting a phenolic resin with 3 to 20% by solid weight of a brominated epoxy resin. and (B) liquid phenolic resin, or (C) phenolic resin, by its solid weight.
A two-component molding sand binder comprising as an essential component a liquid modified phenolic resin obtained by reacting 20% or less of a brominated epoxy resin. 2 The ratio of the solid modified phenolic resin (A) and the liquid phenolic resin (B) is 95 in terms of solid content weight ratio.
70:5-30. 3. Claim No. 3, characterized in that the ratio of the solid modified phenolic resin (A) and the liquid modified phenolic resin (C) is 95 to 70:5 to 30 in solid weight ratio. A binder as described in paragraph 1.