JP2005095933A - Novolak type phenolic resin for shell mold - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a novolak type phenolic resin for a shell mold which is good in working environmental characteristics and is excellent in workability and the strength of a casting mold. <P>SOLUTION: This novolak type phenolic resin for a shell mold is characterized in that (a) the content of unreacted phenols is ≤1 wt.%, (b) the content of the binuclear form components is ≤10 wt.%, (c) the degree of dispersion of molecular weight is ≤5 and (d) the number average molecular weight is 300 to 1,000. The novolak type phenolic resin is obtained by reacting phenols and aldehydes by using a phosphoric acid aqueous solution comprising phosphoric acids of ≥0.2 mol to 1 mol of the phenols. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a novolac type phenol resin for shell molding.

  Production of a mold by the shell mold method is performed by filling a resin-coated sand into a heated mold and curing it. In resin-coated sand, a binder is added to a preheated refractory aggregate, kneaded with a mixer, the surface of the refractory aggregate is coated with a molten binder, and the binder is a novolak type phenol resin. Is obtained by adding a curing agent such as hexamethylenetetramine and further cooling while kneading. Usually, as a binder, a novolac type phenol resin is used for reasons such as storage stability in resin-coated sand, high strength of the mold, high dimensional stability, mold disintegration property after pouring.

  The characteristics of the novolak type phenol resin required here include a low amount of low molecular weight components such as unreacted phenols and a high fluidity during heating. Unreacted phenols, etc., become a strongly irritating gas due to heat when using a novolak type phenolic resin as a binder for resin-coated sand to form a mold by a shell mold method, which causes problems in the working environment. In addition, if the fluidity during heating is low, the coating on the surface of the refractory aggregate when producing the resin-coated sand is insufficient, or the adhesion between the refractory aggregates is poor when molding the resin-coated sand into a mold. There is a problem that it becomes sufficient and the strength is lowered.

Various proposals have been made so far for methods for obtaining a novolak-type phenol resin in which unreacted phenols and the like are reduced. For example, when synthesizing a novolac type phenol resin by a usual method, a method of removing unreacted phenols by a method such as solvent fractionation or distillation of the resin can be mentioned.
However, in the case of solvent fractionation, there arises a problem that waste increases due to use of the solvent. In the case of distillation, it is disadvantageous in terms of cost due to an increase in processes and an increase in energy costs.
On the other hand, various proposals have been made for methods for obtaining novolak phenol resins having high fluidity during heating. For example, there is a method of adding a fluidizing agent such as acetanilide having an effect of lowering the molecular weight of the resin or increasing the fluidity of the resin (for example, see Patent Document 1).

  However, when lowering the molecular weight of the resin, the number of moles of phenols must be excessive with respect to the number of moles of formaldehyde during the reaction, and the content of unreacted phenols increases. For this reason, the reaction yield decreases, which is disadvantageous in terms of cost. In addition, when a fluidizing agent is added, the adhesion temperature of the resin-coated sand is lowered, and as a result, a blocking phenomenon of the resin-coated sand tends to occur, which causes a problem in storage stability.

  For this reason, the amount of unreacted phenols is reduced by reacting phenols with formaldehyde at a high reaction rate, instead of removing unreacted phenols, which are wasteful and costly. However, a novolac type phenolic resin for shell mold is desired which has high fluidity when heated and has good preservability of resin-coated sand.

JP 2002-34691 A

  The present invention has been made as a result of studies to solve various problems that have been a problem with conventional novolak type phenolic resins for shell molds, has good working environment, and excellent workability and mold strength. The present invention provides a novolac type phenolic resin for shell molding.

Such an object is achieved by the following present inventions (1) to (2).
(1) (a) The content of unreacted phenols is 1% by weight or less, (b) the content of binuclear components is 10% or less, (c) the degree of molecular weight dispersion is 5 or less, and (d) A novolac type phenol resin for shell mold having a number average molecular weight of 300 to 1,000, wherein the novolac type phenol resin contains phenols and aldehydes in an amount of 0.2 mol or more per 1 mol of the phenols. A novolak-type phenol resin for a shell mold, which is obtained by reacting with an aqueous phosphoric acid solution containing acids.
(2) The novolac phenol resin for shell mold according to (1), wherein the phosphoric acid is phosphoric acid.

The present invention comprises (a) a content of unreacted phenols of 1% by weight or less, (b) a content of dinuclear components of 10% or less, (c) a molecular weight dispersity of 5 or less, and (d ) A novolak type phenol resin for shell mold having a number average molecular weight of 300 to 1000, and this novolac type phenol resin contains phenol and aldehyde with 0.2 mol or more of phosphorus per mol of phenol. The reaction is carried out using a phosphoric acid aqueous solution containing acids.
By using the novolak type phenolic resin of the present invention for shell molding, it is excellent in the preservability of resin-coated sand, reduces the amount of irritating odor gas generated at the time of resin-coated sand production, and maintains the strength at the time of mold production. be able to.

Hereinafter, the novolak type phenol resin for shell mold of the present invention will be described in detail.
The novolak type phenolic resin for shell mold of the present invention (hereinafter sometimes simply referred to as “novolak type phenolic resin”) has (a) a content of unreacted phenols of 1% by weight or less, and (b) a binuclear component. Is a novolak type phenol resin for shell mold having a content of 10% or less, (c) a molecular weight dispersity of 5 or less, and (d) a number average molecular weight of 300 to 1000, The phenols and aldehydes are reacted using an aqueous phosphoric acid solution containing 0.2 mol or more of phosphoric acid with respect to 1 mol of the phenols.

Although it does not specifically limit as phenols used as a raw material of the novolak-type phenol resin of this invention, For example, phenol, o-cresol, m-cresol, p-cresol, xylenol, bisphenol A, p-tertiary butylphenol, p- Examples include octylphenol, p-nonylphenol, p-cumylphenol, other alkylphenols, catechol, resorcin, and bisphenols. Moreover, you may use these individually or in mixture of 2 or more types.
Usually, for shell molds, phenol, cresols, and bisphenol A are used because high strength is easily obtained when molded into a mold.

Moreover, although it does not specifically limit as aldehydes, For example, formaldehyde, paraformaldehyde, a benzaldehyde etc., the substance used as the generation | occurrence | production source of these aldehydes, or the solution of these aldehydes etc. are mentioned. Moreover, you may use these individually or in mixture of 2 or more types.
Usually, for shell molds, formaldehyde and paraformaldehyde are used because of high reactivity at the time of phenol resin production.

Although the reaction molar ratio (F / P) of aldehydes (F) and phenols (P) is not particularly limited, it is preferably 0.4 to 1.0, and more preferably 0.5 to 0.00. 8.
Thereby, the novolak-type phenol resin which has the molecular weight suitable for resin coated sand can be obtained. When the reaction is carried out under a condition where the reaction molar ratio is lower than the above lower limit, the yield tends to be low, and the resulting novolac phenolic resin also has a low molecular weight, which may result in a low softening point. On the other hand, when the reaction is carried out under conditions where the reaction molar ratio exceeds the above upper limit, the molecular weight of the novolak phenol resin tends to be high, the softening point is high, and sufficient fluidity may not be obtained during heating. . Moreover, it is sometimes difficult to control the molecular weight, and depending on the reaction conditions, gelation or partial gelation tends to occur.

  As a reaction method, the phenols and aldehydes may be charged all at once at the start of the reaction, and the reaction may be carried out by adding a catalyst. In order to suppress heat generation at the initial stage of the reaction, the phenols and the catalyst may be added. After charging, aldehydes may be sequentially added and reacted.

The content of unreacted phenols and dinuclear components in the novolak type phenolic resin of the present invention is preferably 1% by weight or less, more preferably 0.5% by weight or less of unreacted phenols. . The dinuclear component is preferably 10% or less, more preferably 7% or less.
If the content of unreacted phenols and dinuclear components is higher than the above upper limit, when resin-coated sand is molded into a mold, these components become strong irritating gases due to heat, leading to deterioration of the working environment. There is. In addition, the softening point of the novolak-type phenol resin is lowered, and the phenomenon of resin-coated sand blocking tends to occur, which may affect storage stability.

In the novolak type phenolic resin of the present invention, the molecular weight dispersity (hereinafter simply referred to as dispersity) is the number average molecular weight (Mn) in terms of polystyrene measured by liquid chromatography such as gel permeation chromatography (GPC). ) And the weight average molecular weight (Mw) ratio (Mw / Mn).
The degree of dispersion of the novolak type phenolic resin of the present invention is preferably 5 or less. More preferably, it is 3 or less. This is because a novolak type phenolic resin having such a degree of dispersion exhibits good fluidity in the vicinity of its softening point, and is therefore suitable for resin-coated sand applications.
If the degree of dispersion exceeds the above upper limit, the fluidity during heating of the resin will decrease, so when preparing the resin-coated sand, the coating of the refractory aggregate surface will be insufficient, or when molding the resin-coated sand into a mold In addition, the adhesion between the refractory aggregates may be reduced, and the mold strength may be insufficient.

  Moreover, as a number average molecular weight (Mn) of the novolak-type phenol resin of this invention, it is preferable that it is 300-1000, More preferably, it is 400-900. Thereby, the preservability as a resin coated sand and mold strength can be made compatible. If the number average molecular weight exceeds the above upper limit, the fluidity at the time of molding may decrease and the mold strength may decrease. On the other hand, if the number average molecular weight is less than the above lower limit, a blocking phenomenon may easily occur.

  The content of unreacted phenols in the novolak type phenolic resin of the present invention is a value measured by an internal standard method using 2,5-xylenol as an internal standard substance using a gas chromatography method in accordance with JIS K 0114. is there.

Moreover, GPC analysis was used for the measurement of the content of the binuclear component, the number average molecular weight, and the weight average molecular weight. GPC analysis was performed using tetrahydrofuran as an elution solvent under conditions of a flow rate of 1.0 ml / min and a column temperature of 40 ° C.
The apparatus used was: Main body: Tosoh Co., Ltd., HLC-8020, Analytical column: Tosoh Co., Ltd., TSKgel G1000HXL, and G3000HXL. In addition, the measured value of molecular weight uses the analytical curve created using the polystyrene standard substance, and obtained value is polystyrene conversion.

  Although the softening point of the novolak type phenol resin of the present invention is not particularly limited, it is preferably 85 ° C. or higher. When the softening point is less than 85 ° C., there may be a problem in storage stability, such as the resin-coated sand being easily blocked.

  The novolak-type phenol resin of the present invention is obtained by reacting the above phenols and aldehydes with an aqueous phosphoric acid solution containing 0.2 mol or more of phosphoric acid per mol of phenol. It is characterized by.

  Here, as the phosphoric acid, a phosphoric acid compound that can be dissolved in water to form a phosphoric acid aqueous solution can be used, and is not particularly limited. For example, phosphoric acid (orthophosphoric acid), diphosphoric acid, triphosphoric acid, etc. In addition to linear polyphosphoric acid, cyclic polyphosphoric acid, diphosphorus pentoxide, phosphorous acid, hypophosphorous acid and the like, various phosphoric acid ester compounds can be mentioned. These can be used alone or in combination of two or more.

  Of these phosphoric acids, phosphoric acid is preferred. Phosphoric acid can be easily adjusted in concentration and can be obtained at low cost.

  Although it does not specifically limit as a density | concentration of phosphoric acid in this phosphoric acid aqueous solution, It is preferable that it is 20 to 99 weight%, More preferably, it is 40 to 99 weight%. By setting the concentration of phosphoric acid in the phosphoric acid aqueous solution to the above lower limit or more, the reaction between phenols and aldehydes can be efficiently advanced.

The quantity of phosphoric acid used here is 0.2 mol or more with respect to 1 mol of phenols. Thereby, in the system which reacts phenols and aldehydes using phosphoric acid aqueous solution, distribution with the organic phase which has phenols as a main component, and the aqueous phase which consists of phosphoric acid aqueous solution can be stabilized.
The amount of the phosphoric acid is more preferably 0.3 to 1.0 mol, and particularly preferably 0.4 to 0.9 mol, with respect to 1 mol of phenols. Thereby, a novolak type phenol resin having a narrow molecular weight distribution and less unreacted phenols can be obtained efficiently.

  Increasing the amount of phosphoric acid tends to increase the effect of the present invention to obtain a high yield of novolak-type phenolic resin with a low content of unreacted phenols and a narrow molecular weight distribution. Even if an amount exceeding 1.0 mol is used for 1 mol, this effect may not be substantially changed, so that it may not be economical. On the other hand, if the amount is less than 0.2 mol, the phosphoric acid concentration in the aqueous phase is too low to stably distribute the organic phase and the aqueous phase, so that the reaction rate decreases.

  Although it does not specifically limit as a moisture content rate in the reaction system at the time of synthesize | combining the phenol resin of this invention, It is preferable to set it as 1 to 40 weight%. More preferably, it is 1 to 30% by weight.

  Here, the water content in the reaction system is the total amount of water present in the reaction system with respect to the total amount of phenols, aldehydes, phosphoric acid aqueous solution, novolac type phenol resin, etc. present in the reaction system. Refers to weight ratio. The water present in the reaction system includes water derived from the raw material to be added, such as water in an aqueous solution of phosphoric acid, water contained in aldehydes, and condensed water generated during the reaction.

  The water content in the reaction system can be calculated by taking the sum of the amount of water in the charged raw material and the amount of condensed water produced by the reaction as the amount of water in the reaction system and dividing this by the total amount charged. Also, when the reaction is carried out by distilling off water, the water content in the reaction system is reduced by subtracting the amount of water distilled off from the total amount of water content in the raw material and the amount of condensed water produced by the reaction. Can be calculated.

By carrying out the reaction with the water content preferably within the above range, a novolak-type phenol resin having a small content of unreacted phenols and a narrow molecular weight distribution can be obtained in a high yield.
By setting the water content in the reaction system to the above lower limit value or more, it is possible to prevent the phosphoric acids from becoming highly viscous or solidified. Moreover, since the fall of reaction rate can be suppressed by setting it as the said upper limit or less, reaction of phenols and aldehydes can be advanced efficiently.

The reason why the novolak-type phenol resin of the present invention has a small amount of unreacted phenols and binuclear components and a narrow molecular weight distribution is considered as follows.
Phosphoric acids are very water-soluble and have a property of being easily hydrated. The phenols have a low solubility, and the novolac type phenol resin has a property that the solubility is further reduced as the molecular weight is increased. For this reason, at the time of reaction, it will be in the state isolate | separated into the aqueous layer which contained the phosphoric acid which is a catalyst abundantly, and the organic layer in which the catalyst which consists of phenols and a novolak resin hardly exists. Low molecular components such as phenols and dinuclear substances are relatively easily eluted in the aqueous layer, and the eluted portion reacts with aldehydes, but the polymer component is hardly eluted and the reaction does not proceed. Moreover, the novolak type phenol resin eluted in the aqueous layer reacts with the aldehyde to increase the molecular weight and is quickly extracted into the organic layer, and the reaction does not proceed any further. In this way, there is a difference in the reaction rate between the low molecular component and the high molecular component, resulting in the production of a novolak type phenol resin with a low content of unreacted phenols and a narrow molecular weight distribution in a high yield. Is possible.

  In addition, it is possible to mix | blend a lubricant, a silane coupling agent, etc. as a modifier with the novolak-type phenol resin used by this invention as needed. As the lubricant, ethylene bis stearic acid amide, methylene bis stearic acid amide, oxystearic acid amide, stearic acid amide, methylol stearic acid amide, etc. can be used, and as the silane coupling agent, amino silane, epoxy silane, vinyl silane, etc. can be used. is there.

  As described above, the novolak-type phenolic resin used in the present invention has a low content of unreacted phenols, etc., so that when the resin-coated sand is molded into a mold, the amount of gas generated that worsens the working environment. Can be reduced. In addition, since the molecular weight distribution is narrowly dispersed and has a specific molecular weight, it has a moderate softening point and high fluidity in the vicinity of the softening point, so that the fire-resistant aggregate is sufficiently coated during the production of the resin-coated sand. And sufficient strength can be given to the mold.

  Hereinafter, the present invention will be specifically described with reference to examples. However, the present invention is not limited to the examples. “Parts” described herein indicate “parts by weight”, and “%” indicates “% by weight”. The content (%) of the binuclear component is based on the area ratio obtained by GPC measurement.

<Example 1>
To a reaction vessel equipped with a stirrer, a condenser and a thermometer, 1000 parts of phenol and 1000 parts of 85% phosphoric acid aqueous solution (corresponding to 0.82 mol of phosphoric acid per 1 mol of phenol) were added, and the internal temperature was adjusted. After the temperature was raised to 100 ° C., 690 parts of a 37% formaldehyde aqueous solution (molar ratio F / P = 0.80) was added successively over 30 minutes, and then refluxed for 1 hour. Thereafter, 500 parts of water was added and stirred at an internal temperature of 100 to 103 ° C. for 30 minutes, and then the internal temperature was cooled to 60 ° C. and allowed to stand for 30 minutes. After standing, the aqueous phase separated from the resin phase was removed. After performing such a water washing process 3 times, it switched to the dehydration piping again, performed normal pressure dehydration to the internal temperature of 130 ° C., and then depressurized dehydration until the desired water content was reached, thereby removing water in the system. Thereafter, 11 parts of ethylenebisstearic acid amide was added, and the resulting resin was taken out of the reaction vessel into a vat to obtain 1060 parts of a novolak type phenol resin A.
The molecular weight of the obtained resin by GPC measurement was Mn = 820, Mw = 1420, and the dispersity (Mw / Mn) = 1.73. Moreover, the unreacted phenol component was below the detection limit (0.1%), and the amount of dinuclear body was 2%. The softening point was 97 ° C.

<Example 2>
Add 600 parts of phenol, 400 parts of bisphenol A, and 900 parts of 85% aqueous phosphoric acid solution (equivalent to 0.96 moles of phosphoric acid per mole of phenol) to a reaction vessel equipped with a stirrer, a condenser and a thermometer. After raising the internal temperature to 100 ° C., 560 parts of a 37% formaldehyde aqueous solution (molar ratio F / P = 0.85) was added successively over 30 minutes, and then refluxed for 1 hour. Thereafter, 500 parts of water was added and the mixture was stirred at an internal temperature of 100 to 103 ° C. for 30 minutes, then the internal temperature was cooled to 60 ° C. and allowed to stand for 30 minutes. After standing, the aqueous phase separated from the resin phase was removed. After performing such a water washing process 3 times, it switched to the dehydration pipe again and performed normal pressure dehydration to the internal temperature of 130 degreeC, followed by depressurizing dehydration until it became the desired moisture content, and removed the water | moisture content in a system. Thereafter, 11 parts of ethylenebisstearic acid amide was added, and the resulting resin was taken out of the reaction vessel into a vat to obtain 1050 parts of a novolac type phenol resin B.
The molecular weight of the obtained resin as measured by GPC was Mn = 890, Mw = 1560, and the dispersity = 1.75. The unreacted phenol component was 0.3%, and the amount of dinuclear body was 7%. The softening point was 99 ° C.

<Comparative Example 1>
A reaction vessel equipped with a stirrer, a condenser tube and a thermometer was charged with 1000 parts of phenol and 10 parts of oxalic acid, heated to an internal temperature of 95 ° C. at normal pressure, and then added with 621 parts of 37% formalin over 1 hour. . After further refluxing reaction at 98-100 ° C. for 1 hour, heat dehydration is performed at atmospheric pressure, the internal temperature is raised to 140 ° C., dehydration is continuously performed until a desired water content is reached, and the internal temperature is further reduced. After heating to 180 ° C., 11 parts of ethylenebisstearic acid amide was added and taken out from the reaction vessel to obtain 1055 parts of a novolac type phenol resin C.
The molecular weight of the obtained resin by GPC measurement was Mn = 460, Mw = 986, and the dispersity = 2.14. The unreacted phenol component was 3.0%, and the amount of dinuclear body was 13%. The softening point was 94 ° C.

<Comparative example 2>
In a reaction vessel equipped with a stirrer, a condenser, and a thermometer, 1000 parts of phenol and 10 parts of oxalic acid were charged, and the temperature was raised to an internal temperature of 95 ° C. at normal pressure. Then, 720 parts of 37% formalin was added over 1 hour. . After further refluxing reaction at 98-100 ° C. for 1 hour, heat dehydration is performed at atmospheric pressure, the internal temperature is raised to 140 ° C., dehydration is continuously performed until a desired water content is reached, and the internal temperature is further reduced. After heating to 180 ° C., 11 parts of ethylenebisstearic acid amide was added and taken out from the reaction vessel to obtain 1065 parts of a novolac type phenol resin D.
The molecular weight of the obtained resin by GPC measurement was Mn = 676, Mw = 3412, and the degree of dispersion was 5.05. The unreacted phenol component was 2.5%, and the amount of dinuclear body was 11%. The softening point was 104 ° C.

<Preparation of resin-coated sand>
Using the novolak type phenol resins obtained in Examples 1 and 2 and Comparative Examples 1 and 2, resin coated sands were prepared for each.
After adding 8000 parts of the flattery sand heated to 130 ° C. to the mixer, 160 parts of a novolac type phenol resin was added and kneaded for 45 seconds. Next, an aqueous solution in which 30 parts of hexamethylenetetramine is dissolved in 88 parts of water in advance is added, and kneaded while cooling with air until the coated sand collapses. Further, 8 parts of calcium stearate is added and kneaded for 20 seconds. The resin-coated sand was obtained by discharging from the mixer. This was performed for four types of novolac type phenolic resins.

  Table 1 shows the molecular weight of the novolac type phenol resin, the degree of dispersion, the content of unreacted phenols, the content of the binuclear component, the softening point, and the resin-coated sand property measurement results.

<Method for measuring characteristics of resin-coated sand>
(1) Bending strength: The bending strength was measured according to JIS-K6910. (Baking conditions 250 ° C / 60 seconds)
(2) Irritating odor: 100 g of resin-coated sand was heated on a hot plate at 250 ° C. for 60 seconds, and the produced odor was confirmed. Based on Comparative Example 1, the case where there was a similar irritating odor was rated as x, and the case where it was small was marked as ○.
(3) Adhesion point: Resin coated sand was placed on a copper rod subjected to a temperature gradient (80 to 120 ° C.), and after 60 seconds, air was blown from a certain distance at a certain pressure. At this time, the lowest temperature at which the resin-coated sand remained on the copper rod was taken as the sticking point and used as an index of storage stability. The higher the adhesive point temperature, the harder the resin-coated sand is blocked and the better the storage stability.

From Table 1, the novolak-type phenolic resin used in Examples 1 and 2 was obtained by reacting phenol and formaldehyde at a preferred molar ratio using a phosphoric acid aqueous solution containing a predetermined amount of phosphoric acid as a catalyst. It is a thing. On the other hand, the novolak-type phenol resin used in Comparative Examples 1 and 2 uses oxalic acid as a catalyst instead of the phosphoric acid aqueous solution, and contains unreacted phenols and binuclear components as compared with the examples. The amount was large, and Comparative Example 2 had a high degree of dispersion.
As a result of using these for the resin-coated sand, Examples 1 and 2 were able to reduce the generation of an irritating odor during the production of the resin-coated sand while maintaining the storage stability of the resin-coated sand and sufficient mold strength. On the other hand, Comparative Examples 1 and 2 both had an irritating odor when resin-coated sand was produced, and Comparative Example 2 had a low dispersibility due to a high degree of dispersion, and a decrease in mold strength was also observed.

  The novolak type phenolic resin of the present invention, when used for a shell mold, is excellent in preservability of resin-coated sand, reduces the amount of irritating odor gas generated at the time of resin-coated sand production, and maintains the strength at the time of mold production. be able to. Therefore, the present invention can be suitably used for mold production by a shell mold method excellent in workability and environmental performance.

Claims (2)

(A) The content of unreacted phenols is 1% by weight or less, (b) the content of binuclear components is 10% or less, (c) the molecular weight dispersity is 5 or less, and (d) the number average molecular weight. Is a novolak-type phenol resin for shell molds, wherein the novolak-type phenol resin contains phenols and aldehydes in an amount of 0.2 mol or more per mol of the phenols. A novolac-type phenol resin for shell mold, which is obtained by reacting with an aqueous phosphoric acid solution. The novolac phenol resin for shell mold according to claim 1, wherein the phosphoric acid is phosphoric acid.