JPS6368241A - Production of resin-coated sand for shell mold - Google Patents

Abstract

PURPOSE:To produce resin-coated sand for a shell mold having an excellent curing speed, mold strength and blocking property of the coated sand by coating heated sand with a layer consisting of specific novolak type phenolic resins and hexamine. CONSTITUTION:100pts.wt. raw material sand heated to 130-160 deg.C is put into a mixer and the solid novolak type phenolic resin (A) having <=60% ortho rate is added thereto and the mixture is kneaded. The novolak type phenolic resin (B) contg. <=10wt% phenol monomer, having >=60% ortho rate and contg. >=35wt% (phenol dikaryon + phenol trikaryon) component is added to and mixed with the mixture in such a manner that the ratio of A/B is in a 9/1-4/6 range and the total of the two resins is 0.5-4.0pts.wt. An aq. hexamine soln. is successively added as the hexamine at 0.10-0.75pts.wt. thereto an finally a lubricant such as calcium stearate is added at 0.5-5.0pts.wt. and the mixture is kneaded to coat the sand surface. The resin-coated sand for the shell mold having the excellent characteristics is thus obtd.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for producing resin-coated sand for shell molds, and in particular, the hardening speed of the resin-coated sand by hot marling is fast, mold strength, and The present invention relates to a method for producing resin-coated sand for shell molds that has excellent blocking properties.

[Conventional technology]

In the -S shell molding method, a novolac type phenol resin obtained by reacting phenol and formaldehyde with an acidic catalyst is used as a binder, and hexamine is used as a curing agent.

Recently, there has been a demand in the industry for so-called fast-curing type resin-coated sand for shell molds that can lower molding temperatures and shorten molding cycles from the viewpoint of energy conservation.

Generally, to increase the curing speed of a mold, a high ortho resin that reacts quickly with hexamine is used. High ortho resin is obtained by polymerizing phenol and formaldehyde using zinc acetate or cobalt acetate as a synthesis catalyst.

However, when such a high ortho resin is used alone, there is a drawback that fluidity deteriorates and mold strength decreases significantly. In addition, this method has its limitations because reducing the molecular weight to improve fluidity lowers the melting point and causes blocking of the resin-coated sand.

A satisfactory resin-coated sand for shell molds that has a fast curing speed and excellent mold strength has not yet been developed.

[Problem that the invention seeks to solve]

As mentioned above, in the conventional method, although the curing speed of the mold is improved, there are problems such as a significant decrease in mold strength and blocking of the resin-coated sand.

The present invention aims to provide a method for producing resin-coated sand for shell molds that is excellent in mold curing speed, mold strength, and blocking properties of resin-coated sand.

[Means for solving problems]

In order to obtain resin-coated sand for shell molds that has a fast mold curing speed and excellent mold strength and blocking properties of resin-coated sand, the present inventors investigated the mold curing mechanism and found that the hardening of the resin binder The flow characteristics of the resin binder, the novolak type phenol resin, have a large influence on the curing speed and mold strength.We also conducted a thorough study of the molecular weight and ortho ratio of the novolak type phenolic resin, which is a resin binder, and the curing properties and flow characteristics of hexazine. Low-molecular components such as phenol binuclear bodies and trinuclear bodies of resins have excellent fluidity, but they have the disadvantage of slow curing.
It has been found that polymeric components higher than the core have excellent curability but have a drawback of poor fluidity. Therefore, by reducing the ortho ratio of the high molecular weight component of the phenol resin, which is the binder for resin-coated sand, and increasing the ortho ratio of the low molecular weight component, resin-coated sand with good fluidity and curing properties can be obtained. The present inventors have discovered that the present invention has been completed.

That is, in the method for producing resin-coated sand for shell molds of the present invention, a solid novolac type phenolic resin (A) having an ortho rate of less than 60% and a solid novolac type phenol resin (A) having an ortho rate of 60% are added to heated sand.
It is characterized by adding and coating a novolak type phenol resin (B) and hexamine having a content of (phenol dinuclear body + phenol trinuclear body) component of 35% or more by weight.

The ortho rate of the phenolic resin in the present invention indicates O position/(O position + P position), and the infrared absorption spectrum of the phenol resin was measured by the KBr method using a model 270-30 manufactured by Hitachi, Ltd. A1), According to the method of Kamishin et al. (Reference: Relationship between bonding mode and curing rate of novolac type resins: Koka Yu, 93 (i956)), it was determined by the following formula. However, the transmittance of Hensen's nucleus appearing around 1600 cm-' was adjusted to 40 to 50%.

1ogD, 6o-to 1.44 x 1og
Dsz.

(1) Formula Drbo: Transmittance Dszo at 760 cm-'
: Transmittance of 820 cm-' The content of the phenol binuclear body + phenol trinuclear body component of the phenol resin was determined using high performance liquid chromatography HLC-802UR (solvent: THF, column Ni-TSK-GEL, G2000Hs).
: 3 pieces, G3000Hfi: 1 piece, Toyo Soda Kogyo Kagyun Co., Ltd. (trade name) were cut out and determined by gravimetric method. However, the content referred to in the present invention is the value for the resin excluding the phenol monomer from among the phenol resins.

The above HLC-802UR was used as the phenol monomer,
It was determined using a calibration curve.

Here, Fig. 1 is an example of an analysis chart of a solid novolak type phenol resin obtained by hydrochloric acid catalyst, and the symbols 1, 2, 3 and 4 in the figure are phenol monomer, phenol dinuclear, and phenol trinuclear, respectively. represents the region of high molecular weight components of 4-nuclear bodies and phenol tetranuclear bodies. A vertical line was drawn between each displacement point on the analysis chart of FIG. 1, and the area between each vertical line was regarded as the region of each polynuclear body to which it belonged. Then, the distance i from the center point of the phenol monomer peak to point X and point 7! 11Jx, y were measured. Hereinafter, in the present invention, vertical lines are drawn at distances x and y from the phenol monomer to divide the region into high molecular weight regions of phenol dinuclear, phenol trinuclear, and phenol tetranuclear, respectively. FIG. 2 is an example of an analysis chart of a novolak type phenolic resin obtained using a zinc acetate catalyst, and shows the above-mentioned method of division.

As the phenols used in the present invention, phenol, cresol, xylenol, bisphenol, etc. are used. Paraform, formalin, etc. are used as formaldehydes.

The method for producing the solid novolak-type phenol resin (A) used in the present invention is not particularly limited, but the following method is preferred.

0.6 formaldehyde per mole of phenols
~0.9 mol and an acidic catalyst such as hydrochloric acid, oxalic acid, phosphoric acid,
After adding a catalyst such as zinc chloride and reacting at a reflux temperature for 4 to 6 hours, dehydration and concentration are performed by a conventional method to reach a softening point of 80°C.

The ortho rate of solid novolac type phenolic resin (A) is 6
Less than 0%, preferably 40-50%. If the ortho rate is 60% or more, the mold strength will decrease significantly, which is not preferable.

The ortho ratio is adjusted by adjusting the type and amount of the catalyst.

Further, the method for producing the novolac type phenolic resin (13) used in the present invention is not particularly limited, but the following method is preferred.

Formaldehyde 0.3 to 1 mole of phenol
After adding 0.6 mol and a divalent metal salt catalyst such as cobalt acetate or zinc acetate and reacting at reflux temperature for 4 to 6 hours, dehydration and concentration are performed by a conventional method. 10% by weight of unreacted phenol
The synthesis is terminated when the amount becomes less than 100%, and if necessary, an organic solvent such as methanol is added to obtain a liquid novolac type phenol resin.

The ortho rate of novolak type phenolic resin (B) is 60%
The above shall apply. If the ortho rate is less than 60%, the effect of rapid curing will be small, which is not preferable.

Further, the content of the component (phenol dinuclear body↑phenol trinuclear body) of this resin (B) is 35 weight or more. 35
If it is less than the weight, the fluidity becomes poor and mold strength decreases, which is not preferable.

Furthermore, the phenol monomer content of the novolac type phenolic resin (B) is preferably less than 10% by weight. If the amount is 10% by weight or more, a large amount will remain in the resin-coated W sand, causing blocking of the resin-coated sand, which is not preferable. More preferably, it is 5% by weight or less.

However, in the present invention, since the content of the low molecular weight component (phenol dinuclear body + phenol trinuclear body) of the novolac type phenolic resin (B) is 35% or more, the softening point of the resin is low. , handling is often difficult due to resin blocking during storage. For this reason, it is preferable to add an organic solvent to the resin to make it liquid.

The organic solvent is not particularly limited, but methanol, acetone, methyl ethyl ketone, etc. are preferable.

Although the amount of the organic solvent to be added is not particularly determined by 1 ffl, it is preferable to add 10 to 100 parts by weight of the organic solvent to 100 parts by weight of the novolac type phenol resin (B). If it is less than 10 parts by weight, the viscosity becomes high and handling becomes difficult. On the other hand, if it exceeds 100 parts by weight, the viscosity decreases and it becomes easier to handle, but it is not necessary to add more than 100 parts by weight, which leads to cost increase, which is not preferable.

Solid novolac type phenolic resin (
The blending ratio of A)/novolac type phenolic resin (B) is:
Although not particularly limited, 9/1 to 4/6 is preferable. 9/
If it exceeds 1, there is little effect of increasing the curing speed, and
If it is less than 4/6, the fusion point of the resin-coated sand becomes low, which is undesirable because it causes blocking.

The blending amount of solid novolac type phenolic resin (A) and novolac type phenolic resin (B) with respect to sand is as follows:
00 parts by weight of solid novolank type phenolic resin (
The total amount of A) and novolac type phenolic resin (B) is 0
．． The amount is preferably 5 to 4.0 parts by weight. If it is less than 0.5 parts by weight, mold strength will be lowered, which is not preferable. Moreover, if it exceeds 4.0 parts by weight, the varnish becomes 1-amp, which is not preferable.

The amount of hexamine added to the sand is preferably 0.10 to 0.75 parts by weight per 100 ffi parts of sand. If it is less than 0.10 parts by weight, the hardenability of the mold will deteriorate,
On the other hand, if it exceeds 0.75 parts by weight, a large amount of ammonia gas etc. will be generated during mold forming, which is undesirable from the point of view of work 1 and 2.

The method of adding the solid novolac type phenolic resin (A) and novolac type phenolic resin (B) to the sand is not particularly limited. These resins may be added to the sand simultaneously or separately. Preferably, heated sand is put into a mixer, and when the temperature of the sand is 130°C to 160°C, solid novolac type phenolic resin (A) is added,
After kneading for 40 seconds, novolac type phenol resin (B)
It is preferable to add. After kneading for an additional 20 to 40 seconds, an aqueous hexamine solution is added according to a conventional method, and kneading is continued. When the resin-coated sand is loosened, a lubricant such as calcium stearate is added, kneaded for 10 to 60 seconds, and discharged from the mixer.

It is preferable to add a silane coupling agent to the phenolic resin used in the present invention in order to improve mold strength. As the silane coupling agent, γ-glycidoxypropyltrimethoxysilane, N-β(aminoethyl)T-aminopropyltrimethoxysilane, T-aminopropyltrimethoxysilane, etc. are used. The amount of the silane coupling agent added is preferably 0.05 to 3.0 parts by weight per 100 parts by weight of the phenol resin. If the amount is less than 0.05 parts by weight, the effect will be small, and if it exceeds 3.0 parts by weight, the cost will increase, which is not preferable.

Further, an aromatic organic acid can be added to the phenolic resin used in the present invention in order to further increase the curing speed of the mold. As the aromatic organic acid, salicylic acid, benzoic acid, etc. are used. The amount of the aromatic organic acid added is preferably 0.05 to 4.0 parts by weight per 100 parts by weight of the phenol resin. If it is less than 0.05 parts by weight, the effect is small;
If it exceeds 4.0 parts by weight, it is not preferable because it causes blocking of the resin-coated sand.

Furthermore, the phenolic resin used in the present invention can contain a lubricant that is normally used as a resin binder for shell molds. Acid amide, methylolamide, methylene bisstearamide, calcium stearate, polyethylene wax, paraffin wax, montan wax, carnauba wax, etc. are used. The amount of the lubricant added is not particularly limited, but it is 0.5 to 5.0 parts by weight per 100 parts by weight of the solid Novola 7-type phenolic resin (A).
Parts by weight are preferred. If it is less than 0.5 parts by weight, the effect will be small, and if it exceeds 5.0 parts by weight, it will cause a decrease in mold strength.
Undesirable.

[Effect]

In the method for producing resin-coated sand for shell molds of the present invention, the ortho rate of the solid novolac type phenolic resin (A) is less than 60%, thereby improving the fluidity of the resin. Further, by using a novolac type phenol resin (B) having an ortho ratio of 60% or more, fast curing properties were obtained. Furthermore, resin (B) (phenol dinuclear body +
By setting the content of the trinuclear phenol component to 35% by weight or more, the fluidity was improved. As a result, resin-coated sand was obtained which increased the curing speed of the mold and had excellent mold strength and blocking properties of the resin-coated sand.

〔Example〕

Hereinafter, the present invention will be explained in more detail with reference to examples, but the Z'A range of the present invention is not limited in any way by these examples.

Example 1 In a four-eye flask equipped with a stirrer, a reflux condenser, and a thermometer, 1880 g of phenol and 45 g of 80% paraform were added.
0g, 37% formalin and 4g of IN hydrochloric acid were weighed, heated on an oil bath without stirring, and reacted at reflux temperature for 4 hours, followed by dehydration and shrinkage in a conventional manner to obtain a softening point of 80°C. It was the end point. Add 40 g of ethylene bisstearamide at an internal temperature of 140 to 150°C, heat on a heating table for 30 minutes, and then add KBM-603 (N-β (aminoethyl) T-aminopropyltrimethoxysilane, Shin-Etsu Chemical Industry A product). name) was added. After heating on a heating stand for 30 minutes, the dish was taken out to obtain a solid novolac type phenol resin (a) with an ortho rate of 41%.

Also, in a four-eye flask equipped with a stirrer, a reflux condenser, and a thermometer, 1880 g of phenol, 300 g of 80% paraform, 80 g of 37% formalin, and 5 g of zinc acetate were added.
Weighed and heated on an oil bath with stirring, at reflux temperature for 4 hours.
Allowed time to react. Thereafter, concentration was performed at a reduced pressure of 700 mmHg, and the end point was reached when unreacted phenol reached 4% by weight.
) was obtained. The ortho rate of this resin (b) is 69%,
The content of the (phenol dinuclear body + phenol trinuclear body) component is 45%, and the content of phenol heptanium is 45%.
% by weight.

8 kg of flattery silica sand heated to 150'C in a speed mixer, 90 g of the above resin (a), and the above resin (b)
50g was added and kneaded for 30 seconds. Thereafter, 100 g of a 20% aqueous hexamine solution was added, and when the resin-coated sand was loosened, 8 g of calcium stearate was added, kneaded for 20 seconds, and discharged from the mixer to obtain resin-coated sand. Table 1 shows the properties of the resin-coated sand obtained.

Example 2 In a four-eye flask equipped with a stirrer, a reflux condenser, and a thermometer, 1880 g of phenol and 37 g of 80% paraform were added.
5g, 320g 37% formalin and 10g zinc chloride
Weigh out, heat on an oil bath without stirring, and boil at reflux temperature for 4 hours.
Allowed time to react. After that, dehydration and concentration were performed under normal pressure, and 1
When the temperature reached 20°C, the reaction was carried out again at reflux temperature for 3 hours, and then
Dehydration and concentration were carried out by a conventional method, and the softening point was set at 80° Cf: foggy point.

Ethylene bisstearamide and KBM-603 were added in the same manner as in Example 1 to obtain a solid novolac type phenol resin (c). The ortho rate was 55%. Also,
1 part of methanol was added to 500 g of the resin (b) obtained in Example 1.
25 g was added and mixed to obtain resin (d). 8 kg of flattery silica sand heated to 150°C in a speed mixer
100 g of the above resin (c) were added and kneaded for 20 seconds, and then 50 g of resin (d) was added and kneaded for 20 seconds. Thereafter, resin-coated sand was obtained in the same manner as in Example 1. Table 1 shows the properties of the resin-coated sand obtained.

Comparative Example 1 A solid novolak phenolic resin (e) was obtained in the same manner as in the method for producing solid novolak phenolic resin (a) of Example 1, except that 375 g of 80% paraform was used instead of 450 g of 80% paraform. . The ortho rate of this resin (e) was 54%.

Using 140 g of this resin (e), resin-coated sand was obtained in the same manner as in Example 1. Table 1 shows the properties of the resin-coated sand obtained.

Comparative Example 2 In a four-eye flask equipped with a stirrer, a reflux condenser, and a thermometer, 1880 g of phenol and 37 g of 80% paraform were added.
5g, 37% formalin 80g and zinc acetate 10g
Weigh out, heat on an oil bath without stirring, and boil at reflux temperature for 4 hours.
Allowed time to react. Thereafter, dehydration and concentration were performed under normal pressure, and when the internal temperature reached 170°C, it was considered as the end point. Ethylene bisstearamide and KBM-603 were added in the same manner as in Example 1 to obtain a solid novolac type phenol resin (f). The ortho rate of this resin (f) was 69%, the content of the (phenol binuclear body + phenol trinuclear body) component was 30% by weight, and the phenol monomer content was 15% by weight.

Resin-coated sand was obtained in the same manner as in Example 1 using 140 g of the resin (f) obtained above. Table 1 shows the properties of the resin-corrugated IW sand obtained.

Comparative Example 3 2 methanol was added to 100 g of the resin (f) obtained in Comparative Example 2.
5 g was added and mixed to obtain a resin (g).

Using 90 g of resin (a) and 62.5 g of the above resin (g),
Resin-coated sand was obtained in the same manner as in Example 2.

Table 1 shows the properties of the resin-coated sand obtained.

In addition, each characteristic in Table 1 was measured as follows.

Fusion point: Based on JACT shell work standards.

Strength: Based on JACT shell work standards.

Bend: Flat mold 70 x 1401 set at 230℃
A mold 50×120111 5 mm in height is placed on top of iI and filled with resin-coated sand. Thereafter, it was left in a furnace temperature of 350° C. for 40 seconds, then taken out, and 10 seconds later, it was placed on a jig with 100 fins between fulcrums, and the amount of deflection when a load of 500 g was applied was measured. It is shown that the smaller the amount of deflection, the faster the curing property.

(Margins below) Table 1 Conventionally, solid high ortho resins with an ortho rate of 60% or more have been used to increase the curing speed. Such resins have disadvantages such as poor fluidity, resulting in a significant drop in mold strength, and lowering the molecular weight to improve fluidity causes blocking of the resin-coated sand. Therefore, the ortho ratio of the solid novolac type phenol resin was set to less than 60% to improve fluidity. In addition, for quick curing,
゛In order to use a novolak type phenol resin with an ortho rate of 60% or more and to have good fluidity, the content of the components (phenol dinuclear body + phenol trinuclear body) was 35% by weight.
That's all. This will be explained using specific numerical values using Examples and Comparative Examples.

The resin-coated sand for shell molds obtained in Example 1.2 of the method of the present invention has the same strength and melting point as the conventional resin-coated sand for shell molds obtained in Comparative Example 1,
In addition, the bending was reduced to 3.5 mm-1.1, indicating rapid curing.

Comparative Example 2 Resin-coated sand according to Example 1.2 of the method of the invention
Compared to the conventional resin-coated sand using high-ortho resin, the curing speed is the same, and the mold strength is about 5% higher. Furthermore, the fusion point is 6°C higher and the blocking properties of resin-coated sand are also excellent.

In addition, when comparing Comparative Example 3, in which the solid novolac type phenolic resin (A) used in the present invention and a conventional high-ol resin was blended, and the resin-coated sand obtained in Example 1.2, it was found that the resin-coated sand obtained in Example 1.2 was The resin-coated sand obtained in Example 1.2 has a strength of 10
% higher.

Other characteristics are almost the same. This is a novolak type phenolic resin (phenol dinuclear body + phenol trinuclear body)
This is due to the influence of the content of the ingredients.

〔Effect of the invention〕

The resin-coated sand for shell molds obtained by the method of the present invention has excellent mold hardening speed, mold strength, and profking property of the resin-coated sand, and has great industrial value.

[Brief explanation of the drawing]

Figure 1 is an example of an analysis chart based on an infrared absorption spectrum of a solid novolac type phenolic resin obtained using a hydrochloric acid catalyst, and Figure 2 is an example of an analysis chart based on an infrared absorption spectrum of a novolac type phenolic resin obtained using a zinc acetate catalyst. This is an example.

Claims (1)

[Claims] 1. A solid novolac type phenolic resin (A) having an ortho rate of less than 60% and a component (phenol dinuclear body + phenol trinuclear body) having an ortho rate of 60% or more are added to heated sand. A method for producing resin-coated sand for shell molds, which comprises adding and coating a novolac type phenolic resin (B) and hexamine having a content of 35% by weight or more. 2. The method for producing resin-coated sand for shell molds according to claim 1, wherein the novolac type phenolic resin (B) has a phenol monomer content of less than 10% by weight. 3. The method for producing resin-coated sand for shell molds according to claim 1 or 2, wherein an organic solvent is added to the novolac type phenolic resin (B). 4. The shell mold according to claim 1, 2 or 3, wherein the blending ratio of solid novolac type phenolic resin (A)/novolac type phenolic resin (B) is 9/1 to 4/6. Method for producing resin-coated sand for use. 5. For 100 parts by weight of sand, the total amount of solid novolac type phenolic resin (A) and novolac type phenol resin (B) is 0.5 to 4.0 parts by weight, and hexamine is 0.10 to 4.0 parts by weight.
Claims 1 and 2 adding 0.75 parts by weight
The method for producing resin-coated sand for shell molds according to item 3, item 4, or item 4.