WO2000050186A1

WO2000050186A1 - No-bake ester cured molding mixes

Info

Publication number: WO2000050186A1
Application number: PCT/US2000/004254
Authority: WO
Inventors: Gary R. Hysell; James T. Schneider; Thomas E. Dando
Original assignee: Ashland Inc.
Priority date: 1999-02-22
Filing date: 2000-02-18
Publication date: 2000-08-31
Also published as: AU3002300A

Abstract

The subject invention relates to no-bake molding mixes comprising (a) an aggregate, particularly a briquetting aggregate; (b) an aqueous basic solution of an alkaline phenolic resole resin; (c) a liquid co-reactant composition comprising (1) a liquid ester curing catalyst, and (2) a tar selected from the group consisting of resorcinol pitch, bisphenol A tar, and mixtures thereof.

Description

NO-BAKE ESTER CURED MOLDING MIXES

TECHNICAL FIELD The subject invention relates to no-bake ester cured molding mixes comprising (a) an aggregate, particularly a briquetting aggregate; (b) an aqueous basic solution of an alkaline phenolic resole resin; (c) a liquid co-reactant composition comprising (1) a liquid ester curing catalyst, and (2) a tar selected from the group consisting of resorcinol pitch, bisphenol A tar, and mixtures thereof .

BACKGROUND OF THE INVENTION Aqueous basic solutions of phenolic resins are known in the art . They are used in making foundry mixes that are made into foundry shapes . The shapes are cured with an ester co-reactant by a no-bake or cold-box process depending upon whether a volatile ester is used for curing.

Although these processes have advantages from an environmental standpoint, they also have limitations. One of the primary limitations is that the tensile strengths and scratch hardness are lower than for some of the other no-bake and cold-box processes used for preparing workable foundry shapes such as amine catalyzed phenolic urethane or acid catalyzed furan binder systems. To overcome the lower strengths, additives are usually added to the ester cured alkaline phenolic resole binder system.

Examples of such additives are glycols, methanol, pyrrolidone, and oxyanions such as borates. See for instance EP 503 759 where pyrrolidone is the additive, EP 508 566 where a phenyl ethylene glycol ether is the additive, U.K. Patent Application GB 2 253 627 where an aliphatic glycol ether is the additive, and EP 323 096 where an oxyanion such as borate is the additive. It is also known to add benzylic ether resins (U.S. Patent 4,988,745) and novolak resins (U.S. Patent 5,043,412) to the ester portion of alkaline phenolic resole resin binder in order to improve the tensile strength of foundry shapes. The draw back to this method is that water and wastes are generated, such as unreacted phenol and/or formaldehyde, and must be removed by a stripping operation during the manufacturing of the benzylic ether resins and novolak resins. Consequently, this adds to the cost of binders that use benzylic ether resins and novolak resins in aqueous alkaline phenolic resole binders, and creates additional stress to the environment.

SUMMARY OF THE INVENTION

The subject invention relates to no-bake molding mixes comprising:

(a) an aggregate, particularly a briquetting aggregate;

(b) an aqueous basic solution of an alkaline phenolic resole resin;

(c) a liquid co-reactant composition comprising:

(1) a liquid ester curing catalyst, and

(2) a tar selected from the group consisting of resorcinol pitch, bisphenol A tar, and mixtures thereof .

The invention also relates to a process for preparing shapes from the molding mixes, including foundry molds and core, and briquettes. The invention also relates to the shapes prepared with the molding mixes. The invention also relates to a process for preparing metal castings with the foundry shapes, and the castings prepared thereby.

The subject molding mixes produce shapes with improved tensile strengths when compared to shapes prepared with binders that do not contain bisphenol A tar or resorcinol pitch in the co-reactant. Also, additives such as benzylic ether resins or novolak resins contain unreacted phenol and or formaldehyde, whereas, the bisphenol A tar and resorcinol pitch do not .

BEST MODE AND OTHER MODES FOR

CARRYING OUT THE INVENTION

The aqueous basic solutions of phenolic resole resins used in the subject binder compositions are prepared by methods well known in the foundry art. The general procedure involves reacting an excess of an aldehyde with a phenolic compound in the presence of a basic catalyst at temperatures of about 50°C to 120°C to prepare a phenolic resole resin. Generally the reaction will also be carried out in the presence of water. The resulting phenolic resole resin is diluted with a base and/or water so that an aqueous basic solution of the phenolic resole resin results having the following characteristics :

a viscosity of less than about 850 centipoise, preferably less than about 450 centipoise at 25°C as measured with a Brookfield viscometer, spindle number 3 at number 12 setting; 2. a solids content of 35 percent by weight to 75 percent by weight, preferably 50 percent by weight to 60 percent by weight, based upon the total weight of the aqueous basic solution, as measured by a weight loss method by diluting

0.5 gram of aqueous resole solution with one milliliter of methanol and then heating on a hotplate at 150°C for 15 minutes; and

3. an equivalent ratio of base to phenol of from 0.2:1.0 to 1.1:1.0, preferably from 0.3:1.0 to 0.95:1.0.

Although these ranges have been specified, it is not claimed that these aqueous basic solutions are novel products, or that the ranges are critical. The ranges are set forth to provide guidelines for those who want to make and use the invention. Obviously, the invention will usually be practiced more effectively in the preferred ranges specified. With this in mind, more specific procedures will be set forth for preparing phenolic resole resins.

The phenolic compounds used to prepare the phenolic resole resins are represented by the following structural formula:

wherein A, B, and C are hydrogen, or hydrocarbon radicals or halogen, preferably phenol. See, for instance, U.S. Patent 4,780,489 which is incorporated by reference into this specification. The aldehyde used in preparing the phenolic resole resin may also vary widely. Suitable aldehydes include aldehydes such as formaldehyde, acetaldehyde, propionaldehyde, furfuraldehyde, and benzaldehyde . In general, the aldehydes used have the formula RCHO, where R is a hydrogen or a hydrocarbon radical of 1 to 8 carbon atoms . The most preferred aldehyde is formaldehyde .

The basic catalysts used in preparing the phenolic resole resin include basic catalysts such as alkali or alkaline earth hydroxides, and organic amines. The amount of catalyst used will vary depending upon the specific purposes. Those skilled in the art are familiar with the levels needed.

It is possible to add compounds such as lignin and urea when preparing the phenol-formaldehyde resole resins as long as the amount is such that it will not detract from achieving the desired properties of the aqueous basic solutions. Urea is added as a scavenger to react with unreacted formaldehyde and decrease the odor caused by it .

The phenolic resole resins used in the practice of this invention are generally made from phenol and formaldehyde at a mole ratio of formaldehyde to phenol in the range of from about 1.1:1.0 to about 3.0:1.0. The most preferred mole ratio of formaldehyde to phenol is a mole ratio in the range of from about 1.4:1.0 to about 2.2:1.0. As was mentioned previously, the phenolic resole resin is either formed in the aqueous basic solution, or it is diluted with an aqueous basic solution. The base used in the aqueous basic solution is usually an alkali or alkaline earth metal hydroxide such as potassium hydroxide, sodium hydroxide, calcium hydroxide, or barium hydroxide, preferably potassium hydroxide.

It should again be mentioned that the aqueous basic solutions described herein are not novel products, nor is their method of preparation. The parameters set forth pertaining to their preparations are merely guidelines for those who want to make the aqueous basic solutions. There may be other effective ways to make them, which are not described herein.

The tars used in this invention are the by-products from the manufacture of bisphenol A and resorcinol. Bisphenol A tar is defined as the highly viscous product, which remains on the bottom of the reaction vessel after bisphenol A, or resorcinol pitch is produced and distilled from the reaction vessel. The bisphenol A tar and resorcinol pitch are solid at room temperature and has a melting point of about 70°C to 80°C. They are mostly dimers, trimers, and polymeric bisphenol A, but may also contain substituted materials. A typical and preferred bisphenol A tar (BPAT) is set forth below:

BISPHENOL A TAR (BPAT)

Component Amount p, p-bisphenol A 10-40% o, p-bisphenol A 0-1%

BPX (trisphenol) 10-25% chroman-L 0-3% phenol 0-0.5% other phenol-acetone 45-75% products

A typical and preferred resorcinol pitch (RP) is shown below where each component is given as a percent by weight :

RESORCINOL PITCH (RP)

Chemical Name Concentration resorcinol 5-10% dihydroxydiphenols 10-20% mostly 3 ' , 4-dihyroxydiphenyl) trihydroxydiphenols 30-50% mostly 2,4,3'-trihydroxydiphenyl )

1, 3-benzenediol (homopolymer) 20-55%

Mixtures of bisphenol A tar and resorcinol pitch can be used to modify the binder in an amount such that the ratio of bisphenol A tar to resorcinol pitch is from 3:1 to 1:3, most preferably about 1:1. Bisphenol A tar and resorcinol pitch are generally soluble in the liquid esters used in to cure the alkaline phenolic resole resins by the no-bake process. The liquid ester curing catalysts used in the subject foundry binder system are well known in the art, for instance, ethylene carbonate, propylene carbonate, g- butyrolactone, ethylene glycol diacetate, glycerol diacetate, gylceryl triacetate, dimethyl glutarate, dimethyl adipate and dimethyl succinate. See U.S. Patents 4,474,904 which is incorporated by reference into this specification.

The amount and method for using the specific co- reactant composition are known in the art and need no further elaboration. Generally from 5 to 50 weight percent of co-reactant is used, preferably from 15 to 35 weight percent, where said weight percent based upon the weight of the binder.

Generally from 1 to 50 parts by weight of bisphenol A tar and/or resorcinol pitch is used in the co-reactant composition, preferably from 5 to 30 parts by weight, where said parts by weight are based upon the weight of the total co-reactant composition. In terms of a weight ratio, the weight ratio of bisphenol A tar and/or resorcinol pitch to liquid ester catalyst is from 0.01:1.0 to 0.5:1.0, preferably 0.05:1.0 to 0.45:1.0.

Typically where foundry shapes are prepared by the no-bake process, the tar is preferably combined with the mixture with the liquid ester before adding to the aggregate . The binder may contain several optional components.

For instance, the binder may contain a source of oxyanions including borate, stannate and aluminate ions, preferably borate ions . The oxyanion improves the tensile strength of foundry shapes made from the binder and aggregate, and may be introduced into the binder composition by the addition of for example alkali metal oxyanion salts such as sodium tetraborate decahydrate, potassium tetraborate tetrahydrate, sodium metaborate, sodium pentaborate, sodium stannate trihydrate or sodium aluminate, or an ammonium oxyanion salt such as ammonium borate . The mole ratio of oxyanions (expressed as boron, tin, etc.) to phenol is preferably in the range of from 0.1:1 to 1:1. When the oxyanion is borate the mole ratio of boron to phenol is more preferably in the range of from 0.1:1 to 0.5:1. Other optional constituents a silane such as those having the general formula:

wherein R' is a hydrocarbon radical and preferably an alkyl radical of 1 to 6 carbon atoms and R is an alkyl radical, an alkoxy substituted alkyl radical, or an alkyl amine substituted alkyl radical in which the alkyl groups have from 1 to 6 carbon atoms. Such silanes, when employed in concentrations of 0.1% to 2%, based on the phenolic binder and hardener, improve the humidity resistance of the system. Examples of some commercially available silanes are Dow Corning Z6040 and Union Carbide A-187 (gamma glycidoxy propyltrimethoxy silane) ; Union Carbide A-1100 (gamma aminopropyltriethoxy silane) ; Union Carbide A- 1120 (N-beta (aminoethyl) -gamma-amino-propyltrimethoxy silane) ; and Union Carbide A-1160 (Ureido-silane) .

The binders may also contain optional components such as glycols, methanol, and pyrrolidone in an amount of 1-15 percent by weight based upon the weight of the resin. See for instance European Patent Applications 0 503 759 A2 where pyrrolidone is the additive, 0 508 566 A2 where a phenyl ethylene glycol ether is the additive, and U.K. Patent Application GB 2 253 627 where an aliphatic glycol ether is the additive.

Although any typical aggregate can be used to prepare the molding mix, the preferred aggregate is a foundry aggregate or briquetting fines. For purposes of this describing this invention, "briquettes" includes tablets or other like shapes. Any foundry aggregate can be used to prepare the foundry mix. Generally the aggregate will be sand which contains at least 70 percent by weight silica. Other suitable sand includes zircon, olivine, alumina-silicate sand, chromite sand, and the like.

Briquetting aggregates can be any fine solid particles which can be used for make briquettes and generate heat when burned. Examples of briquetting fines include coal fines, iron slag, cupola ash, graphite, mineral fines (for instance quartz, calcium silicate, alumino-silicate) , cellulose (for instance wood fines), plastic fines, and mixtures of fines. Briquetting fines will normally have a maximum size such that they will pass through a mesh of having a 5 millimeter square aperture, preferably a mesh having a 3 millimeter square aperture. The fines preferably contain a range of particle sizes of up to 10 the maximum noted. More preferably the fines have a maximum size range of from 150 to 200 mesh. Generally, the particle size of the foundry aggregate is such that at least 80 percent by weight of the aggregate has an average particle size between 50 and 150 mesh (Tyler Screen Mesh) .

Briquettes are made according to a process such as that described in WO 97/13827 or U.S. Patent 4,802, 890 which are hereby incorporated by reference into this specification. One typical method of forming briquettes is to form ovoid shapes by cold roll -press operation.

For instance, fines can be mixed without the binder and squeezed at pressures of 2.1 X 106 kg/m² (about 3,000 psi) between two metal rolls each having half-ovoid depressions. The briquettes so formed fall from the press to a conveyor belt for transfer to storage and subsequent packaging.

In making shapes, the aggregate constitutes the major (more than 50 percent by weight of the total weight of the foundry shape) constituent and the binder system constitutes a relatively minor amount. The amount of binder system is generally no greater than about fifteen percent by weight and frequently within the range of about 0.5 to about 7 percent by weight based upon the weight of the aggregate. Most often, the binder content ranges from 0.6 to about 5.0 percent by weight based upon the weight of the aggregate in most foundry shapes. When making briquettes, the binder level is from 3 to 10 % percent by weight based upon the weight of the aggregate. Foundry shapes are prepared with the foundry mixes by introducing them into a corebox, pattern mold, or other shaping device according to techniques well known in the art . A workable foundry shape is one which can be handled without breaking when it leaves the corebox or pattern mold. Curing is carried out according to techniques well known in the art.

Metal castings are produced from the workable foundry shapes in a conventional manner. Essentially, molten metal (ferrous or non-ferrous) is poured into and around the workable foundry shape and allowed to harden. The workable foundry shape is then removed.

In the Examples, the aqueous basic solution of a phenolic resole resin (hereinafter referred to as the resin component) used was CHEM REZ^® 400 binder sold by Ashland Chemical Company.

The examples which follow will illustrate specific embodiments of the invention. They are not intended to imply that the invention is limited to these embodiments. In the Examples the following abbreviations will be used:

% B.O.S. = percent of binder added Based On the weight of sand.

% B.O.B. = percent of ester Part II added Based On the weight of Binder used. BPAT = bisphenol A tar.

CR 450 = CHEM REZ^® 450 binder is a phenol - formaldehyde base catalyzed resole condensate prepared by reacting a phenol, paraformaldehyde, and water in the presence of dilute alkali hydroxide bases at elevated temperatures. CHEM REZ^® 450 binder has solids content of 50-55%, a viscosity of about 300-700 Cps @ 25 deg.°C, and an average (molecular weight of 400-1200) as determined by C_X3 NMR spectroscopy.

GTA = glyceryl triacetate, a liquid ester curing catalyst .

RES = resorcinol .

RH = relative humidity.

RP = resorcinol pitch as described in the specification.

EXAMPLES Foundry mixes were prepared as set forth in the Examples using 1.75 weight percent binder BOS. In all of these examples the same components and amounts were used unless otherwise specified.

CONTROL

In a N-50 Hobart laboratory mixer, 13.1 grams of glyceryl triacetate (GTA) were added to 3 kgm of Badger 5574 silica sand and mixed for 2 minutes. Then 52.5 grams of CR-400 were added and mixed with the sand coated with GTA for 2 minutes. The resulting mixture was then hand rammed into a 12 gang tensile specimen box to form AFS tensile test cores. The time to strip the cured cores from the box was determined by a measurement of 90 mold hardness using a Green Hardness "B" Scale gauge. Tensile strengths were measured at 1, 3, 24 hours and 24 hours + 1 hour at 100% R.H. at 25° C. The tensile tester used was a Thwing-Albert Model #1265-100 QC-1000, equipped with a 1,000 lb. load cell, using the #1 setting. The conditions of the sand lab were 52% R.H. at 24 °C. The conditions of the constant temperature room were 50% R.H. at 25°C.

EXAMPLE 1

The procedure for the Control was followed except co-reactant blend was formed by mixing 20 grams of bisphenol A tar (BPAT) with 80 grams of GTA. Then 13.1 grams of the GTA/BPAT co-reactant blend were added to 3 kgm of Badger 5574 silica sand and mixed for 2 minutes in a N-50 Hobart laboratory mixer. Thereafter, 52.5- grams of CR-400 were added to the sand mixture. This was mixed with the sand coated with GTA/BPAT for 2 minutes on the same mixer, and then tensile test cores were made.

The data for the Control and Example 1 are shown in Table I.

TABLE I TENSILE STRENGTHS OF FOUNDRY SHAPES CONTAINING BPAT

The data in Table I show the benefits of adding BPAT to the ester (GTA) catalyst. The addition of the BPAT causes an increase in tensile strengths. CONTROL B

The procedure used to carry out Control A was followed to form another test core.

COMPARISON EXAMPLE C (USING RESORCINOL)

The procedure of Control B was followed except five grams of resorcinol were dissolved in 95 grams of GTA to form a co-reactant blend. Then 13.1 grams of this

GTA/RES co-reactant blend were mixed with Badger sand.

Thereafter the procedure of Control B was followed to make test cores .

EXAMPLES 2-3

Control B was followed, except in Example 2 five grams of resorcinol pitch (RP) were dissolved in 95 grams of GTA to form a co-reactant blend of GTA/RES.

Then 13.1 grams of this GTA/RES co-reactant blend were mixed with Badger sand. Thereafter the procedure of Control B was followed to make test cores.

For Example 3, 20 grams of the resorcinol bottoms RP were dissolved in 80 grams of GTA to form a co- reactant blend of GTA/RP. Then 13.1 grams of this GTA/RES co-reactant blend were mixed with Badger sand. Thereafter the procedure of Control B was followed to make test cores . The data for Control B, Comparison A, and Examples 2-3 are shown in Table II. TABLE II TENSILE STRENGTHS OF FOUNDRY SHAPES CONTAINING BPAT

The data in Table I show the benefits of adding RP to the ester (GTA) catalyst. The addition of the RP causes an increase in tensile strengths in the test cores. Example 3 shows that increasing the amount of RP in the co-reactant composition provides even more benefit.

Claims

CLAIMSWe claim:

1. A no-bake molding mix comprising:

(a) an aggregate;

(b) an aqueous basic solution of an alkaline phenolic resole resin;

(c) an effective amount of a liquid ester co- reactant comprising:

(1) a liquid ester catalyst, and

2. The molding mix of claim 1 wherein the aqueous basic solution of phenolic resole resin has

(a) a viscosity of less than about 850 centipoise at 25°C;

(b) a solids content of about 35 to about 75 percent by weight, said weight based upon the total weight of the basic solution; and

(c) equivalent ratio of base to phenol of 2:1.0 to 1.1:1.0.

3. The molding mix of claim 2 wherein the aqueous alkaline phenolic resole resin is prepared by reacting formaldehyde and phenol in a mole ratio of formaldehyde to phenol of about 1.1:1.0 to about 2.2 : 1.0 in the presence of an effective amount of a basic catalyst at elevated temperatures of about 50°C to about 120°C.

4. The molding mix of claim 3 wherein the equivalent ratio of base to phenol used in preparing the aqueous basic solution is from 0.3:1.0 to 0.95:1.0.

5. The molding mix of claim 4 wherein the base is selected from the group consisting of sodium hydroxide, potassium hydroxide, and mixtures thereof .

6. The molding mix of claim 5 where the viscosity of the phenolic resin is from less than about 450 centipoise at 25°C.

7. The molding mix of claim 6 wherein the amount of co-reactant is from 5 weight percent to 50 weight percent based upon the weight of the aggregate.

8. The molding mix of claim 7 wherein the weight ratio of component (c) (1) to component (C) (2) of the co- reactant is from 0.01:1.0 to 0.5:1.0.

9. A process for preparing a shape by a no-bake process comprising: A. shaping the molding mix of claims 1, 2, 3, 4, 5, 6, 7, or 8 by compressing it into pattern;

B. allowing said mix to cure until a workable shape is formed; and

C . removing the workable shape from the pattern.

10. A process for forming a briquette comprising:

A. forming a shape according to claim 9 wherein said aggregate is a briquetting aggregate and said shape is a briquette;

B. allowing said briquette to cure; and

C. removing the briquette from the pattern.

11. A briquette formed by the process of claim 10.

12. A process for forming a foundry shape comprising:

A. forming a foundry shape according to claim 9 wherein said aggregate is a foundry aggregate and said shape is a mold or core;

B. allowing said foundry shape to cure; and

C. removing the foundry shape from the pattern.

13. A shape formed by the process of claim 12.

14. A process for casting a metal comprising:

A. forming a workable foundry shape according to claim 12;

B. pouring molten metal into or around said shape ;

C. allowing said metal to cool and solidify; and

D. removing the metal casting.

15. A metal casting prepared in accordance with claim

14.