Technical Field

The technical field to which the present invention relates is furan resin compositions containing aromatic polyester polyols and their use as binder compositions for foundry aggregates.

Background Art

Thermosetting resins are those resins cured by sub- jecting the resin to elevated temperature, either to initiate the cure or to cause curing of the resin. When used as binders to make foundry cores and molds, these thermosetting resins are referred to as "hot box binders". They are use¬ ful as foundry sand binders because the resin/sand mix is capable of being cured rapidly in heated patterns at temper¬ atures of about 225°F to about 500OF. In addition, foundry cores and molds can be made with such resins by baking at similar temperatures.

One class of hot box binders known in the foundry art are furan binders, which are those binders containing fur- fury1 alcohol. Such binders include furfuryl alcohol resins, furfuryl alcohol-formaldehyde resins, urea-formaldehyde- furfuryl alcohol resins, and phenol-formaldehyde-furfuryl alcohol resins. These binders are usually cured by appli- cation of heat and their cure may be accelerated by the presence of an acid catalyst curing agent such as NH4NO3, NH.C1, FeCl ₃ , HCl, AlCl^, and other acids or acid salts generally known as latent catalysts in the foundry art. These binders are generally used in amounts of about 0.5% to about 5% by weight based on the weight of the sand.

Disclosure of Invention

An object of this invention is to provide an improve furan hot box binder. More particularly, an object of thi invention is to provide a furan hot box binder which has improved strength properties, humidity resistance, and pattern release characteristics, as well as good shake-out properties.

The above objects and others are accomplished by in- corporating in the furan binder an aromatic polyester poly derived from pol carbomethoxy-substituted diphenyl, poly- phenyl and benzyl esters of the toluate family. The aroma polyester polyols generally useful in this invention are t higher molecular weight polyesters having relatively high viscosities. These polyesters can be prepared as the tran esterification product of a dialkyl terephthalate and an aliphatic glycol, such as dimethyl terephthalate (DMT) and diethylene glycol or ethylene glycol. The preferred poly¬ ester is the transesterification product of DMT esterified oxidate residue and diethylene glycol. Such aromatic poly ester polyols are available commercially from Hercules Incorporated under the trademark "TERATE" polyols, series 100, 200 and 300. For example, Terate 203 resin polyol is an aromatic polyester polyol typically having about 9% hyd oxyl content, less than about 1% methoxyl content, an acid number of 4.2, a moisture content of about 0.2%, free di¬ ethylene glycol content of about 9%, an average functional of 2.3 and viscosities of 30,000 cps at 25°C, 7,000 cps at 40°C and 90 cps at lOOOC.

Best Mode of Carrying Out the Invention and Industrial Applicability

The aromatic polyester polyol can be used with the furan binder as a cold blend, or it can be mixed with fur¬ furyl alcohol, then blended with the furan binder. When desired, the aromatic polyester polyol may be prereacted t some extent with the furfuryl alcohol or the furan binder, or both. The aromatic polyester polyol may be used in amounts up to about 30% by weight based on the furan re _£ r

The preferred amount of aromatic polyester polyol is from about 2% to about 10%.

Example 1 illustrates the preparation of a furan resin while Examples 2 and 3 illustrate the use of the resin of Example 1 as a foundry sand binder both alone and in varying combinations with aromatic polyester polyols as shown in Tables I and II, respectively, where the improved properties of the sand- cores obtained in accordance with the present invention are demonstrated.

Example 1

To a three liter reaction flask equipped with a con¬ denser 119 grams of ethanol, 253 grams of urea, 0.5 grams of caustic solution (50% NaOH) , and 324 grams of paraform- aldehyde (91%) were charged. The mixture was then heated to 90OC and the pH of the mixture was about 7.5 to 8.0.

After all paraformaldehyde went into solution, the mixture was acidified to a pH of about 5.0 to 5.5 with acetic acid (30%) . The reaction was continued at 90° to 5θC until viscosity reached about 4.5 to 5.0 stokes, then 300 grams of furfuryl alcohol was added and mixed for 15 minutes.

The reaction mixture was cooled and 0.15% (by weight based on weight of the reaction mixture) silane (A1120 from Union Carbide) was added.

Example 2

The resin of Example 1 was used as a foundry hot box binder to form standard dog bone specimens for tensile strength tests. The pattern temperature was 425° to 450°F. A catalyst comprising a mixture of 39.1 parts of 50% NH ₄ 0 ₃ , 21.1 parts water, 38.5 parts urea, 0.8 parts NH ₄ OH, and 0.5 parts silane (A1120, Union Carbide) was added to the sand, mixed for 2 minutes, then resin was added and mixed for 2 additional minutes.

TABLE I

Wedron 5010 Sand (parts by wt) 100 100 100 100

Catalyst (parts by weight based on 100 parts resin) 20 20 20 20

Resin (parts by weight based on weight of sand) 1.85 1.85 1.85 1.85

Content by wt% 100% resin 95% resin 70% resin 95% resin 5% diethylene 25% furfuryl alcohol 5% Terate glycol 5% 50/50 blend of 203 furfuryl alcohol and Terate 203

Hot Tensile Strength Dwell Time in Seconds

10 10 38 43

20 43 73 78

30 72 70 88 95

40 115 95 110 145

60 185 170 238 260

Tensile Strength

30 Second Dwell, 5 minute Cool 245 307 415 383

Cold Tensile Strengths Dwell Time in Seconds

5 438 338 290 327

Example 3

Example 2 was repeated using the resin of Example 1, except that the catalyst for Tests No. 1 and 2 was pre¬ pared from a mixture of 100 parts of the catalyst mixture from Example 2, 15 parts urea and 2 parts hexa ethylene- tetramine. The catalyst for Tests No. 3, 4 and 5 was the same as in Example 2.

TABLE II

TEST NO. 1_ 4 5_

Wedrom Sand 5010 (parts by weight) 100 100 100 100 100

Catalyst (parts by weight based on 100 parts resin) 20 20 20 20 20

Resin (parts by weight based on weight of sand) 2

Content by wt% 100% resin 90% resin % resin 95% resin 90% resin

10% Terate 203 5% Terate 10% Terate 203 203

Hot Tensile Strengths Dwell T me in Seconds

¹

30 93 120 93 85 115

60 " 192 283 247 260 250

Cold Tensile Strengths Dwell Time in Seconds

5 312 303 530 543 570

10 508 695 242 582 667

20 475 822 272 562 . 623

30 412 668 293 542 667

40 468 603 308 488 482