GB2053250A - Liquid novolak resin - Google Patents

Abstract

A method of manufacturing a novolak resin comprises the steps of reacting, at an elevated temperature, an excess of a phenol with aldehyde or ketone under acidic conditions, allowing the reaction to continue until substantially all the formaldehyde or ketone is reacted, stripping water from the reaction mixture after the presence of aldehyde or ketone has substantially disappeared, neutralizing the resulting novolak resin to provide a pH above 5.5, and adding to the resulting neutralized, novolak resin, either before or after stripping, while the resin is still liquid, a furan-containing solvent selected from furfuryl alcohol, furfural, or mixtures thereof, said solvent being added in an amount sufficient to maintain the resulting novolak resin solution as a liquid at ambient room temperatures. The resulting liquid novolak resin is storage stable. The invention also relates to a liquid novolak resin solution comprising an admixture of neutralized novolak resin and a solvent consisting essentially of a mixture of furfural and cyclohexanone. Uses: Binders, e.g. in the manufacture of particle board.

Description

SPECIFICATION Liquid novolak resin and products made therefrom The present invention relates to a method making novolak resins. Novolaks are well known thermoplastic phenol-aldehyde type and phenol-ketone type resins obtained primarily by the use of the acid catalyst and excess phenol. These resins are generally alcohol soluble, and typically require reaction with furfuryl alcohol, hexamethylenetetramine, para-formaldehyde, etc., for conversion to cured, crosslinked structures by heating, for example to 200-400 F. The result of the acid-catalyzed reaction between a phenol and an aldehyde or ketone when an excess of phenol is present, is a completed reaction in which the individual polymers have no ability to continue growing in molecular weight once the aldehyde or ketone in the batch has been consumed.

Consequently, because ofthis stability it has been regarded as of no importance that the catalyst which is used in the manufacture of novolak resins be allowed to remain unneutralized in the reaction mixture so that at the time that the water which is present in the reaction mixture is stripped off, the pH of the reaction mixture is between 2.5 and 4.0. Typically, upon stripping of the water from the reaction mixture and cooling of the resulting resin, a very high viscosity liquid or a solid novolak results. It has been well known to use these resins, for example, by grinding the resulting solid novolak resin and then mixing them with furfuryl alcohol for use as foundary binders, and the like. Such mixtures are well known to be acid-curable and provide the advantage of a "high-solids" resin mixture.

In addition, novolak resin, when cured, is recognized to provide high percentage of carbon residue so that it ranks approximately at the same level as cured furfuryl alcohol resin with respect to efficiency in generation of high carbon residue.

One of the disadvantages of one of the widely used methods of manufacture of novolak resins heretofore available has been the requirement of the intermediate step of converting the resin into a solid by cooling, e.g. in a flaking step, and then grinding the resulting solid and admixing the resulting powdered novolakwith a suitable solvent. In order to make the "solid" novolaks grindable the resins had to be stripped drastically during original manufacture to remove substantially all traces of unreacted phenol. It has been regarded as good commercial practice for stripping to continue until the melting point is elevated to at least 100 C. to facilitate grinding. Traces of phenol would render the powdery ground material fusable on storage, and the resulting fused or lumpy solid resins were difficult to work with.Such problems are only partially alleviated by an alternative method commonly using, methyl or ethyl alcohol, for example, to dissolve the stripped, but unneutralized novolak polymer in the reactive vessel. However, such a solution is not 100% reactive, and cannot normally be used unless or until the inert solvent is volatilized into the atmosphere at the point of use.

Another object of the present invention is the elimination of the manufacturing steps in the manufacture of novolak resins in which the novolak resin is converted into an intermediate solid and in which an intermediate grinding step is required.

The present invention provides a method of manufacturing a novolak resin comprising the steps of reacting, at an elevated reaction temperature, an excess of a phenol with aldehyde or ketone under acidic conditions, allowing the reaction to continue until substantially all the formaldehyde or ketone is reacted, stripping water from the reaction mixture after the presence of aldehyde or ketone has substantially disappeared, neutralizing the resulting novolak resin to provide a pH above 5.5, and adding to the resulting neutralized, novolak resin, either before or after stripping, while the resin is still liquid, a furan-containing solvent selected from furfuryl alcohol, furfural, or mixtures thereof, said solvent being added in an amount sufficient to maintain the resulting novolak resin solution as a liquid at ambient room temperatures.

In accordance with the present invention, a stream-lined method of the manufacture of a 100% reactive liquid novolak resin is provided, which method results in a novolak resin which is acid curable in addition to being curable in the conventional manner, e.g. with hydroxymethylaminetetramine, and in preferred embodiments is either acid or base curable, and which provides high carbon residues, and from which no inert organic solvent must be used at point of application or use.

An advantage flowing from the present invention is the fact that in the original manufacture reactor, the product of the invention has reduced viscosity thus speeding up and otherwise facilitating the removal of the resin from the novolak reactor, or other containers.

In carrying out the present invention of a furancontaining solvent selected from the group consisting of furfuryl alcohol and furfural and mixtures thereof is admixed with the freshly prepared novolak resin after it has been neutralized and either before or after it has been stripped, while it is still in the liquid condition. In accordance with a preferred embodiment of the present invention the quantity of furan-containing solvent which is admixed with the neutralized, stripped novolak resin is sufficient to provide a fluid novolak resin at room temperature such as for example a solution having a viscosity 100,000 cps or less at 20 C., when the hot novolak solution is cooled to ambient room temperature within 30 minutes of the time at which the furfuryl alcohol is first added.

When levels offurfuryl alcohol are admixed to provide the resulting novolak resin solution with approximately 10%furfuryl alcohol the resulting solution can be characterized as a gummy viscous mass. On the other hand, generally speaking, when levels of furfuryl alcohol are used that would provide between 25 and 30% monomeric furfuryl alcohol in the resulting novolak resin solution, viscosities less than 100,000, usually less than 50,000 cps at 20 C. are normally encountered. Generally speaking the amount of the furan-containing solvent which can be used in accordance with the present invention can be relatively high levels, e.g. upto 50% and higher. It is preferred that sufficient solvent be added to result in a solution which has at least 15% solvent, based on the weight of the solution.

Furthermore, it is highly desirable in order to achieve maximum benefit of the present invention to apply positive cooling means to quickly drop the temperature of the novokal solution as soon as it is formed, so that ambient room temperature conditions are quickly achieved. The furfuryl alcohol or furfural is added while the novolak resin is still hot enough to be in a liquid, readily mixed condition, although the temperature can be decreased substantially from the stripping temperature, e.g. by cooling, or by addition of incremented portion of the cold furfuryl alcohol or furfural, before the solution is completely formed by addition of the rest of the furan-containing solvent.

In the manufacture of novolak resins, a phenol, (this term is discussed more fully hereinafter), is allowed to react with an aldehyde, or ketone typically in the presence of water, at acid pH's, under reflux conditions. For example, oxalic acid is used in quantities sufficient to provide a pH of about 2.5-4.0 in the aqueous system. Typically the reactions are allowed to proceed at reflux conditions until the aldehyde or ketone is determined to be (by conventional titration) absent from the reaction mixture, and at least a slight excess of phenol is allowed to remain. Up to this pointthe methods bywhich novolak resins are produced are entirely conventional, and the method of the present invention relates to an improvement in the subsequent steps.

Consequently any conventional method for reacting phenol with an aldehyde in an acid medium with an excess of phenol are contemplated as within the purviewofthe practice improved by the present invention.

After the conventional manufacturing titrations have determined that the aldehyde or ketone level has been reduced substantially to zero, the reaction is regarded as "terminated". In typical conventional practice heretofore, the novolak-water mixture containing sufficient acid to provide a pH in the range of 2.0-4.0, for example, is immediately stripped usually under reduced pressure conditions with the result that the free unneutralized acid is typically allowed to remain in the novolak resin upon the completion of its manufacture.

However, in accordance with the practice of the present invention, the novolak is neutralized priorto further processing. This can be achieved, in accor dance with the present invention, for example, by addition to the reaction mixture of any suitable basic material such as, for example, a solution of sodium hydroxide. Alkali metal hydroxides, and carbonates.

and other non-reactive alkaline materials can be employed. The amount of sodium hydroxide which is added, or other basic neutralizing material, is an amount sufficient to bring the pH of the resulting resin to at least 5.5 and preferably substantially above 6.0. The preferred neutralized pH range is between 6.0 and 7. Neutralizing to a pH above 7 is permissible unless the furfural cyclohexanone mix ture is used as a solvent, in which case the pH should be below 7.0. The neutralization preferably takes place while there is a substantial amount of water still in the reaction mixture, although the novolak resin can be stripped to remove the water, either before orafterthe addition of the basic material to neutralize the reaction mixture.

The furan-containing solvent can be added either before or after the stripping is completed. However, it is preferred that it be added after stripping. Thus, in a preferred embodiment, after the stripping step has been completed and most of the water has been removed from the reaction mixture (for example up to 4% or so water can remain, typically) the furancontaining solvent is added. In a preferred embodiment the hot novolak resin is cooled substantially before addition of the furan-containing solvent, e.g.

to a temperature below 150 F. but at which the resin is still a liquid. Also, the furfuryl alcohol can be added incrementally so that the fluidity is maintained during cooling, with a large portion ofthe solvent being added near ambient temperature conditions. This is to maximize the effect of the solvent with respect to imparting fluidity. As used herein the term "cooling" is intended to denote a positive application of cooling means, such as, for example, contacting the liquid with a heat exchange surface maintained at temperatures substantially lowerthan the temperature of the liquid, resulting in a rapid reduction in temperature of the liquid. "Cooling" does not necessarily indicate that temperatures below ambient room temperatures are achieved.

Another positive application of cooling means includes the addition of "cold" furan-containing solvent, e.g. solvent at ambient room temperature.

Addition of a substantial quantity of cold solvent abruptly drops the temperature of the liquid, and because of increased fluidity, increased cooling efficiency at the heat exchange surfaces are achieved, as well. As used herein, "cold" is intended to refer to a temperature which is at least 50 F. below the temperature of the liquid to which the "cold" material is added. For example, ambient room temperature furan-containing solvent is "cold" as used herein for the purpose of addition of the solvent to the hot resin liquid resulting in abrupt drop of its temperature. The total amount of furan-containing solvent which is added is an amount sufficient to liquifythe resulting novolakresin attemperature, e.g. 20 C. The preferred levels of furfuryl alcohol or furfural solvent which are included, however, are at least 15% based on the weight of the resulting solution, and amounts sufficient to provide between 25 and 35% of furan-containing solvent is preferred.

Generally speaking, as used herein, the term "novolak" and "novolak resin" denote a condensation product such as is obtained by causing a phenol to condense with less than an equimolar portion of an aldehyde or a ketone, in an acidic environment.

Structurally the molecules of a novolak consist essentially of alkyt-substituted or unsubstituted phenylol nuclei connected together by methylene or substituted methylene links. Although phenol and formaldehyde are preferred condensation reactants, other substances may be used. For example, phenol may be substituted with cresol, xylenols, mixtures of cresols and xylenols, and epoxy resins such as the condensation products of bis-phenol with epich lorohydrin; and formaldehyde can be substituted with other water-soluble and phenol-reactive aldehydes such as acetaldehyde and propienealdehyde. In fact, the manufacture of any phenolic resin of the novolak type can be improved in accordance with the present invention.Such resins, for example, are produced by condensing phenol such as phenol itself, m-cresol, p-cresol, o-cresol, 3,5xylenol, 3,4-xylenol, 2,5-xylenol, p-ethylphenol, p-tert-butylphenol, p-tert-amylphenol, ptert-oxtylphenol, p-phenylphenol, 2,3,5trimethylphenol, resorcinol, and the like.

In the following examples, unless otherwise indicated, all percents are expressed in percent by weight, parts are parts by weight, and temperatures are expressed in F.

Example 1 A mixture of phenol and aqueous formaldehyde is prepared at a ratio of 1.15 phenol to 1.00 moles of formaldehyde. A sufficient quantity of oxalic acid is admixed therewith to provide a pH of about 3.0 and the reaction mixture is allowed to react under atmospheric reflux temperature conditions until all of the formaldehyde disappears. Thereafter, a sufficient quantity of aqueous sodium hydroxide is added to the reaction mixture to elevate the pH of the reaction mixture to approximately 6.3. Thereafter the refluxing condensor is removed and most of the water and unreacted phenol is allowed to be removed from the reaction mixture in the conventional reduced pressure distillation stripping step.

When the water removal, stripping step is substantially completed, sufficient furfuryl alcohol is added to the stripped novolak resin which is at an elevated temperature of about 100 C. to provide a resulting solution having about 20 percent of furfuryl alcohol.

Immediately after admixing the solution is cooled to room temperature within 30 minutes. The resulting neutralized solution is storage stable.

Example 2 The procedure of Example 1 is repeated, except that, instead of furfuryl alcohol, the same quantity of furfural is added to the hot, neutralized, stripped novolak liquid resin. Likewise a liquid solution result which has similar fluidity at ambient temperature conditions. This resulting novolak resin solution is storage stable.

Example 3 The procedure of Example 1 is repeated except that instead of furfuryl alcohol, the same amount of a solution of 66% furfural and 33% cyclohexanone is added to the hot novolak resin. Likewise a similarly fluid solution of novolak resin is obtained. The result ing resin solution is found to be readily curable under either acidic or basic conditions, but is storage stable, as produced in accordance with this invention.

Example 4 Relatively fine particulate carbon is admixed with a pre-catalyzed novolak resin mixture comprising catalyst and resin, the catalyst being a 50:50 mix of maleic anhydride and furfural, the resin being produced in accordance with Example 1. The catalyst and resin were used in respective amounts sufficient to provide about 4% maleic anhydride based on the weight of the resin and about 24% weight of resin based on the weight of the particulate carbond. The resulting admixture is shaped into the form of an electrode, and heated to about 200 F. Upon heating the binder cures into a solid, and a strong carbon form in the shape of an electrode is produced.

Example 5 Particle board ingredients comprising wood chips, saw dust, wood dust, and the like, are admixed with a precatalyzed novolak resin mixture comprising catalyst and resin, the catalyst being a 50:50 mix of maleic an hydroxide and furfural, the resin being produced in accordance with Example 1 the catalyst and resin were used in respective amounts sufficient to provide approximately 5% maleic an hydroxide based on the weight of the resin and 6% by weight of the resin solution based on the weight of the wood particulate ingredients. The resulting mass is pressed into the shape of a board and heated to 300 F. to trigger the curing of the resin. A high-strength particle board results from the curing step.

Example 6 Calcined magnesite is admixed with a pre mixture of triethanolamine, and the liquid novolak resin solution produced in Example 1 (in which furfuralcychlohexanone mixture was used instead of furfury alcohol). The triethanolamine catalyst is used in an amount sufficient to provide between 5-10% based on the weight of the resin, and the amount of resin solution which is used is sufficient to provide 6% by weight based on the weight of the basic magnesite. The resulting mixture is formed into a desired brick form, heated, and the resin cures into a solid. The resulting magnesite brick can be used under very high temperature conditions. At high temperatures the binder is carbonized and the carbon formed improves the performance and prolongs the life of the brick.

Example 7 Furfuryl alcohol, novolak resin, and the novolak resin solution produced in accordance with Example 1 and 3 are respectively tested to determine carbon residue using the Conradson Carbon Residue Test identified as follows: In this test a weighed quantity of the material, or solution to be tested, is admixed with a known quantity of catalyst, and placed in a crucible containing glass boiling beads. The assembly is then weighed and post cured by heating 2 hours at 180 F., 2 hours a- 200 F., and 16 hours at 300 F. The resulting post cured assembly is then placed in a Conradson apparatus which comprises a second crucible partially filled with a coke flour. The entire unit is heated to temperatures set forth in the ASTM Procedure, about 900 C. The cured material or solution then thermally disintergrates.The weight loss is finally determined and the residue (carbon) is calculated. The results of the test are summarized in Table TABLE I Material Tested Carbon Residue Straight Furfuryl Alcohol (acid cured 48 Novolak Resin (hexamethyltetramine acid cured 48 The product of Example 1 (acid cured) 48 The Product of Example 3 (base cured) 33 The Product of Example 3 (acid cured) 45 Example 8 The tests of Example 1 were repeated, except that in Example 8, sufficient furfuryl alcohol was used to provide about 20% by weight in the resulting novolak resin. The resulting solution was found to be acid curable, and had a stable viscosity of about 40,000 cps at room temperature.

Example 9 This example provides a comparison of the effect of pH, solvent concentration and effect of hotholding time on the viscosity of the novolak resin produced in accordance with the invention.

TESTA In a laboratory glassware kettle, the novolak resin was prepared in accordance with the general method described in Example 1. However, the novolakwas neutralized to a pH of 5.7 with a sodium hydroxide solution while refluxing, the resin was then stripped and furfuryl alcohol in an amount suf ficient to provide 30% furfuryl alcohol in the resulting solution was added. The furfuryl alcohol was added while cold, i.e. at ambient room temperature. The stirring was allowed to continue, and the temperature of the resulting solution was allowed to gradually achieve ambient room temperature condition without further cooling other than ambient air cool- ing. The viscosity of the resulting product was found to be 39,000 cps at 20"C.

TEST B In this test, the novolak resin was again prepared bythe identical procedure used in TestAabove, and in a pilot plant reactor equipped with a water cooling jacket. Afterthe phenol formaldehyde reaction was complete, the novolak was neutralized to a pH of 6.9, with a sodium hydroxide solution while refluxing, the resin was then stripped, and furfuryl alcohol in an amount sufficient to provide 30% furfuryl alcohol in the resulting solution was added. The furfuryl alcohol was added cold, and immediately upon completion ofthe addition of the furfuryl alcohol, cooling was applied rapidly by means of cold water in the water jacket. The resulting solution was found to have a viscosity of 3,500 cps at 20"C.

TEST C In this test, the procedure of producing the novolak resin of Tests A and B above was repeated in separate production runs, except that after stripping, the hot liquid neutralized resin was sampled and six separate samples of each respective resin batch were aliquoted into glass laboratory beakers which were placed on a laboratory hot plate and maintained at 200 F. Into each of the respective beakers of each series of samples, different quantities of furfuryl alcohol were added, to provide in the respective beakers resulting solutions having 20, 25, 30, 35, 40 and 45% furfuryl alcohol respectively for each series.The alcohol in this test, however, was added atthe same high temperature as the resin namely 200"F. Afterthoroughly stirring, the resins were allowed to gradually be cooled with ambient air cooling to ambient room temperature conditions.

The results of the two series of tests of Test C are reported on Table II.

TABLE II viscosity (cpslroom temp.) %FuffurylAlcohol pHS.9 pH 5. 7 20 5,000,000 7,C00,000 25 1,600,000 - 30 246,000 1,500,000 35 79,000 512,000 40 36,000 83,000 40 (100"C/8 hr.) 71,000 141,000 It is noted that in Test A and B, cold furfuryl alcohol was added, and this resulted in a substantial decrease in temperature immediately.In Test A, in which the resin was allowed to be maintained at elevated temperature prior to addition of the furancontaining solvent, and were maintained at elevated temperature for a long time as a result of inefficient ambient air cooling, however, the resulting vis cositieswere relatively high, e.g. almost 40,000 compared to the relatively low viscosity i.e. 3,500 cps at 20"C. which was achieved in Test B in which the mixture was cooled quickly to ambient temperature conditions. Also, it is apparent from Table II that neutralization to the pH of 5.7 produced viscosities which are generally speaking, almost twice that achieved by corresponding dilutions of novolak resin which had been neutralized to the pH of 6.9.

Nonetheless, in Test C in which hot furfuryl alcohol is added to the novolak resin, and in which the resulting solutions are not cooled quickly, the viscosities for corresponding levels of furfuryl alcohol are vastly higherthan the viscosities which are achieved with sudden cooling of the solution by addition of cold (ambient temperature) furan-containing solvent thereto.

We know of no chemical or physical explanation of this phenomenon atthistime.

Thus, it will be appreciated from the above disclosure that the method of manufacturing liquid novolak resin in accordance with this invention has been substantially streamlined with no significant adverse impact with respect to the production of high carbon-residue acid curable binders. Also this invention gives an alkaline curable binder, e.g. with furfural cyclohexanone solvent, which ranks very high among alkaline curable resins, with respect to relatively high carbon residues.

The convention of the novolak resin to an intermediate solid, with the inherent requirement of grinding and other processing ofthe solid material, has been eliminated, in accordance with the present invention. An easily handled, readily applied liquid novolak resin solution is produced.

Claims (10)

1. A method of manufacturing a novolak resin comprising the steps of reacting, at an elevated reac tion temperature, an excess of a phenol with aldehyde or ketone under acidic conditions, allowing the reaction to continue until substantially all the formaldehyde or ketone is reacted, stripping water from the reaction mixture after the presence of aidehyde or ketone has substantially disappeared, neutralizing the resulting novolak resin to provide a pH above 5.5, and adding to the resulting neutralized, novolak resin, either before or after stripping, while the resin is still liquid, a furan-containing solvent selected from furfuryl alcohol, furfural, or mixtures thereof, said solvent being added in an amount sufficient to maintain the resulting novolak resin solution as a liquid at ambient room temperatures.

Z The method according to Claim 1, in which the phenol is phenol itself, and in which the aldehyde is formaldehyde.

3. The method according to Claim 1 or 2, in which the reaction mixture is neutralized with a strong base and in which the solvent is furfuryl alcohol.

4. The method according to Claim 1 or 2, in which novolak resin is neutralized to a pH between 6.0 and 7.0, and in which the solvent is a solution of cyclohexanone and furfural.

5. The method according to any of the preceding claims, wherein the solvent is added while the resin is still at a sufficiently high temperature to remain in liquid condition.

6. The method according to any of the preceding claims wherein the solvent is cold when added to the novolak resin.

7. The method according to Claim 6, in which the mixture of novolak resin and furan-containing solvent is cooled rapidly to ambient room temperature conditions immediately after the addition of said furan-containing solvent thereto.

8. The method of manufacturing the novolak resin comprising the steps of reacting at an elevated reaction temperature an excess of phenol with aldehyde or ketone under acidic conditions, allowing the reaction to continue until substantially all of the aldehyde or ketone is reacted, stripping water from the reaction mixture after presence of aldehyde or ketone has substantially disappeared, neutralizing the resulting novolak resin to provide a pH above about 5.5; adding to the resulting stripped novolak resin a furan-containing solvent selected from the group comprising furfuryl alcohol, furfural, and mixtures thereof, said addition being made incrementally in which some ofthe furan-containing solvent is added to the neutralized stripped novolak resin while at an elevated temperature which is sufficiently high to maintain the resin in liquid condition; a first incremental portion of the added solvent being large enough, however, to maintain the resulting solution as a liquid at reduced temperatures, said resulting stripped novolak resin and/or solutions resulting therefrom being cooled rapidly; a final incremental portion of the solvent being added to the resulting initiaily prepared solution at substantially ambient room temperature condition in an amount sufficient to provide the desired viscosity at ambient room temperature.

9. A liquid novolak resin solution comprising admixture of neutralized novolak resin and a monomeric solvent consisting essentially of a mixture of furfural and cyclohexanone.

10. A method of manufacturing novolak resin substantially as herein described with reference to Example 1, Example 2 or Example 3.