EP1513907A1

EP1513907A1 - Method of preparing a stable phenolic resin with low ph

Info

Publication number: EP1513907A1
Application number: EP03756024A
Authority: EP
Inventors: Kathleen H. Coventry-Saylor
Original assignee: Saint Gobain Isover SA France
Current assignee: Saint Gobain Isover SA France
Priority date: 2002-05-31
Filing date: 2003-05-28
Publication date: 2005-03-16
Also published as: WO2003102103A1; AU2003258780A1

Abstract

The invention relates to a method of preparing a stable phenolic resin with low pH. According to the invention, a phenol-formaldehyde resol resin, which is to be used as a binder for glass fibres, is acidified to a pH of 3 or less after resinification catalysed by a base. An increase in the effective concentration of solid substances is noted in relation to a neutralised resin. Phenol-formaldehyde-urea-ammonia resins are surprisingly stable at pH 3 and have desirable cure profiles.

Description

PROCESS FOR THE PREPARATION OF A STABLE PHENOLIC RESIN,

LOW PH

The present invention relates to the manufacture of insulation materials based on glass fibers and, more particularly, the preparation of phenolic resin for glass fibers.

Aqueous dispersions of resol phenol formaldehyde resins are often used in the manufacture of glass fiber-based insulation materials, such as insulating blankets for walls, in roofs and ceilings, insulating blankets for pipes, and the like. Typically, after the glass fiber has been formed, an aqueous sizing dispersion is sprayed onto the still hot fiber in a formation enclosure or under a hood, the fibers being collected on a conveyor belt in the form of a wool-like mass associated with sizing. In some cases, an aqueous dispersion is sprayed onto a sheet of glass fibers. Resol resins and urea modified resins have been used for this purpose, urea contributing to the punking resistance of the sizing (ie resistance to exothermic decomposition at high temperatures ), and reducing the volatiles released when the resin is hardened at high temperature.

An excess of formaldehyde over phenol is typically employed so as to minimize the amount of free phenol in the reaction product.

Therefore, other constituents (e.g. urea) can be incorporated to fix the free formaldehyde.

It is frequent, in the manufacture of insulation materials based on glass fibers, to prepare the aqueous resol resin before gluing, or to have it delivered by a manufacturer of resin and

COPY OF CONFIRFSAÏfcOSI store it until shortly before use. The resol is typically prepared by reaction of phenol and formaldehyde under basic conditions, the reaction mixture thus obtained being neutralized to a weakly basic pH by the addition of a strong acid, to provide a resol dilutable with water. Then, the sizing is prepared, by adding to the resol resin an acid catalyst for the curing of the resin, water to dilute the dispersion and, optionally, other constituents, such as an adhesion promoter. silane type glass, an emulsion lubricant in oil and urea, to reduce volatiles released during hardening. It is desirable to obtain the highest possible level of solids during the preparation of the resol resin. A high solids content corresponds to a reduced release of volatiles and to an increased yield. Resol resin can be prepared by a variety of specific methods, such as those described in US Patent 5,300,562. Often, a single step process is employed. The phenol and formaldehyde are mixed with a strongly basic catalyst, such as an alkali metal base, and the mixture is maintained at an elevated temperature until the desired degree of reaction has been reached, after which the reaction mixture is cooled and neutralized by addition of an appropriate acid. Alternatively, a multistage process can be employed such as a process which consists of an initial reaction step under acidic conditions and a subsequent reaction step under basic conditions, followed by neutralization. US Patent 5,362,842 describes a two-step process for manufacturing a urea-formaldehyde resin composition, comprising an initial step under basic conditions and a second step under acidic conditions, during which the pH is maintained in the range of 4.9 to 5.2.

US Patents 5,358,748 and 5,505,998 describe an acidic sizing composition for glass fibers. A strong acid soluble in an aqueous medium is used in the preparation of the sizing composition in order to reduce the proportion of alkylamine produced otherwise during curing. Alkylamines are said to be undesirable odorous compounds produced by the degradation of urea (the formaldehyde-fixing agent) during curing. A strong acid, in other words an acid having a pK _a of 4 or less, is added to the binder composition to lower the pH to a value between 4.5 and 6.5, preferably between 4.5 and 6. As suitable acids, there may be mentioned sulfamic acid, oxalic acid and sulfuric acid. The sizing contains a phenol-formaldehyde resin, preferably having a low content of free formaldehyde and a low content of free phenol. According to this patent, most of the commercially available phenol-formaldehyde resins have an alkaline pH range, such as between 9 and 9.6, and this makes the addition of the strong acid completely different to obtain a pH between 4.5 and 6.5. In US Patent 5,538,761, the phenol-formaldehyde condensation products prepared under acidic conditions or with low formaldehyde contents under basic conditions are generally not soluble in water, since significant amounts of insoluble dihydroxydiphenylmethanes are produced.

US Pat. No. 5,538,761 describes a process for the preparation of glass fibers treated with a sizing having lower formaldehyde and ammonia emissions thanks to the use of an acidifying hydrolysable salt, a mineral acid or a partial ester of carboxylic acid, to lower the instantaneous pH of the preaction sizing solution diluted with urea to less than 5.5, and preferably in the range of 3.0 to 5.0, and better still in the range of 4.0 to 5.0. The method also includes treating the glass fibers with the acidified solution and curing the sizing. The "pre-reaction" product is a sizing solution comprising a resol phenol-formaldehyde resin to which urea has been added and which has been reacted with free formaldehyde.

US Patent 5,864,003 describes a thermosetting resin composition containing a mixture of a resol phenol-formaldehyde resin and a latent hardening agent. The latent hardening agent acts in synergy with a strong acid catalyst of the type commonly used to harden resol phenolic resins. As strong acid catalysts of this type, mention may be made of mineral acids such as sulfuric acid, hydrochloric acid and phosphoric acid, and organic acids such as sulfamic acid, trichloroacetic acid, and acids. disulfonic and aromatic polysulfonic such as phenylsulfonic acid and other organosulfonic acids. US Patent 5,864,003 notes that the resol resin can be neutralized after alkaline reaction of phenol and formaldehyde using a conventional acid neutralizing agent such as methanesulfonic acid, hydrochloric acid, phosphoric acid or sulfuric acid. Neutralization is carried out by adding a sufficient amount of acid to obtain a pH between 6.5 and 7.5 in the aqueous resin, although a pH as low as 4.0 can lead to stable resin systems.

Given the large volume of resinous sizing compositions required in the production of glass fiber-based insulation and for other uses, and the need to minimize the smelly emissions of formaldehyde and other compounds during manufacture, there is a constant demand for phenol-formaldehyde resin compositions for use in sizing, which have low emissions during hardening and which have a high solids content.

The present invention provides a process for preparing a phenolic resin for use as a sizing for glass fibers and giving a higher solids content than the processes of the prior art. Higher solids compositions are highly desirable with a view to reducing emissions. This process provides more effective resin compositions by increasing the solids content of the resin composition, and reduced emissions during curing, while maintaining good storage stability, which is determined by the dilutability in water of the resin composition, and having good curing characteristics. The process can be used to prepare compositions containing either water-soluble phenol-formaldehyde resins or water-soluble phenol-formaldehyde resins modified with a nitrogen-containing reagent such as urea and / or ammonia. In the case of phenol-formaldehyde resins modified with urea, the present invention offers an unexpected improvement in the curing profiles of the sizing. The present process provides compositions which exhibit very good stability, even at low pH.

The method includes preparing a water-soluble phenol-formaldehyde resol resin which consists of first preparing an initial aqueous mixture containing formaldehyde and phenol, and adding a basic polymerization catalyst to the initial aqueous mixture. The aqueous mixture is then maintained at a predetermined temperature during the reaction of phenol and formaldehyde to form the water-soluble phenol-formaldehyde resol resin until the free formaldehyde content of the aqueous mixture drops to a preset level. Then, the aqueous mixture is cooled, then finally acidified to a pH not exceeding step 3. Preferably, the aqueous mixture containing the unmodified resol resin is acidified to a pH of about 2 to 3.

The acidified resol resin of the present process is stable at low pH. The acidified resol resin can be modified by then adding one or more modifying agents serving to alter or improve the properties of the resin thus obtained and / or of the size then prepared from the resol resin. Examples of suitable acid modifiers which can be used include latent catalysts such as ammonium sulfate, reactive diluents such as benzyl alcohols, weak acids such as boric acid, and fatty acids such as oleic acid and stearic acid, polycarboxylic acids such as polyacrylic acids, and esters such as diethyl phosphite.

If desired, the process can be employed to prepare a modified phenol-formaldehyde resin composition by preparing an aqueous reaction mixture containing the phenol-formaldehyde resol resin and a nitrogen reagent, such as urea, ammonia, or a mixture urea and ammonia, and reacting the nitrogen reagent with the resol phenol-formaldehyde resin to form a modified resin.

Then, the preparation of the sizing is completed by adding a resolving resin hardening catalyst. Preferably, the phenol-formaldehyde resin has a formaldehyde / phenol molar ratio of from about 2.5: 1 to 4.2: 1, and more preferably from about 3.2: 1 to 4.0: 1. It is also preferred that the predefined proportion is about 40 percent by weight of the free formaldehyde in the initial aqueous mixture.

Furthermore, the process of the present invention also provides, where appropriate, for adding ammonia and / or urea to the reaction mixture as a formaldehyde fixing agent. Preferably, the ammonia is added in sufficient amount to provide a weight ratio of the formaldehyde fixing agent to the unmodified resin solids of from about 1.0: 100 to 3.0: 100. When it is desired to have a sizing modified with urea or ammonia, it is preferred that the molar ratio between the urea or ammonia modifying agent and the free formaldehyde of the phenol-formaldehyde resin is approximately 1: 1 to 1 , 75: 1 and that the aqueous mixture is maintained at a temperature of about 5 ° C to 30 ° C, while reacting the modifier with the resol resin.

The present invention also provides a process for producing a sheet of glass fibers, which comprises preparing a sizing as described above and spraying the sizing on glass fibers to form a sheet, then curing the sizing at a high temperature to bond the fibers together. To complete the preparation of the aqueous sizing composition based on mineral fibers, it is possible to add to the aqueous mixture of the modified resol other other constituents of sizing, such as an acid catalyst for curing at high temperature, a lubricant of mineral oil type and an organosilane type adhesion promoter. Such constituents can be added to the aqueous mixture of modified resol resin shortly before applying the binder to the glass fibers. FIG. 1 shows the hardening profiles measured by calorimetric analysis with differential scanning for example 14.

FIG. 2 shows the hardening profiles measured by calorimetric analysis with differential scanning for example 15.

The phenol-formaldehyde resol resin used in the process of the present invention can be prepared by conventional methods known in the art, such as those which result in a soluble resol resin in water and which use commercial grade phenol and formaldehyde. For example, formaldehyde can be provided as an aqueous formaiin solution containing 30-50 percent by weight of formaldehyde, although other forms of formaldehyde known in the art can also be used. In addition to the phenol itself, other hydroxy-functional aromatics can be used, or used in addition to the phenol. As examples of substituted phenols which can be used, mention may be made of alkyl-substituted phenols, such as o-cresol, m-cresol and p-cresol, 3,5-xylenol, 3,4 -xylenol, 3,4,5-trimethylphenol, 3-ethylphenol, 3,5-diethylphenol, p-butylphenol, 3,5-dibutylphenol, p-amylphenol and p-octylphenol; cycloalkyl substituted phenols such as cyclohexylphenol and 3,5-dicyclohexylphenol; alkenyl substituted phenols; aryl substituted phenols such as p-phenylphenol; alkoxy-substituted phenols such as 3,5-dimethoxyphenol, p-ethoxyphenol, p-butoxyphenol and 3,4,5-trimethoxyphenol; aryl-oxyphenols such as p-phenoxyphenol; and halogen substituted phenols such as p-chlorophenol, as well as polycyclic phenols such as naphthol, anthranol and their substituted derivatives. Likewise, dihydroxylated phenols such as catechol, resorcinol, hydroquinone, bisphenol A and bisphenol F can be used. However, phenol itself is preferred. Mixtures of phenols can also be used, preferably mixtures which contain the phenol itself.

Likewise, formaldehyde may be replaced, in whole or in part, by other reactive aldehydes to produce the aqueous solution of water-soluble resol resin. Examples of other reactive aldehydes which can be used include acetaldehyde, propionaldehyde and benzaldehyde. Formaldehyde is very particularly preferred. The preparation of resins resins is reviewed and described in R.. Martin, The Che istry of Phenolic Resins (John iley and Sons, Inc., New York, 1956), at pages 88-97. The process of this invention relates to the preparation of a water-soluble phenol-formaldehyde resol resin. Conventionally used to prepare the resin is a condensation catalyzed by a base of phenol and aldehyde. The reaction, which is exothermic, is initiated, after mixing the phenol and the aldehyde, by addition of the catalyst. The proportion of phenol with respect to the aldehyde is chosen so as to give a resin of the resol type.

(stoichiometric excess of formaldehyde) if formaldehyde and phenol are used, the molar ratio between formaldehyde and phenol is preferably from approximately 2.5: 1 to 4.2: 1, and better still from approximately 3.2: 1 to 4.0: 1. Preferably, an aqueous mixture of formaldehyde and phenol is maintained at a first temperature, of about 40 ° C to 50 ° C, during the addition of a basic polymerization catalyst.

The catalyst used in the process for preparing the resol resin may contain at least one alkali metal or basic alkaline earth metal base. As examples of alkali metal bases which can be used, mention may be made of sodium, potassium and lithium hydroxides. As examples of alkaline earth metal bases which can be used, mention may be made of oxides and hydroxides of calcium, barium and strontium, such as calcium oxide and calcium hydroxide. Potassium hydroxide or sodium hydroxide is preferred over calcium hydroxide, since the alkali metal bases appear to impart greater stability than calcium hydroxide in the present process. Other strongly basic water-soluble substances which do not react with formaldehyde, such as tertiary amines such as triethylamine, tertiary amino function alcohols such as 2-dimethylamino-2-methyl-1-propanol and 2- (dimethylamino) -2- (hydroxymethyl) -1, 3-propanediol, and the like. The temperature is then preferably allowed to rise from the first temperature to a second temperature, preferably between around 60 ° C and 80 ° C, and better still 70 ° C. The time required for the temperature rise to occur depends on the scale on which the exothermic reaction is carried out. On the production scale, this temperature rise can take place over a period of about thirty minutes. If desired, the reactor can be cooled to slow the temperature rise. This second temperature is preferably maintained until the free formaldehyde content of the aqueous mixture drops by about 65 percent of the initial free formaldehyde content and, more preferably, about 60 percent of the initial formaldehyde content. free formaldehyde, by weight.

Then, the aqueous mixture is preferably cooled, preferably to a temperature between about 20 ° C and 30 ° C, and the aqueous mixture is acidified, preferably to a pH of about 3 or less, more preferably to a pH about 2.5 to 3.5. Unexpectedly, these resins neutralized at a pH of about 3 or less have an effective solids content greater than the theoretical solids content (based on non-neutralized solids).

According to a first embodiment, the aqueous mixture is acidified with a strong acid, such as a strong mineral acid. Examples of acids which can be used include mineral acids such as sulfuric acid, including a 25% solution of sulfuric acid, hydrochloric acid, nitric acid and acid. phosphoric, and organic acids such as acetic acid, trichloroacetic acid, and disulfonic acids and aromatic polysulfonic, especially phenylsulfonic acids such as p-toluenesulfonic acid, and other organosulfonic acids.

According to a second embodiment, the aqueous mixture is acidified with a weak acid, in particular an acid comprising at least one amino function. Examples of such acids include sulfamic acid and amino acids, in particular containing more than one carboxylic function such as aspartic acid and glutamic acid.

Typically, the method is chosen so as to give an aqueous resol resin having a total solids content of about 40 to 50 percent by weight. The aqueous resol resin may also contain small amounts of residual formaldehyde, up to about 15 percent by weight, and small amounts of residual phenol, up to about 2 percent by weight. In addition, the aqueous resol resin will typically contain small amounts of residual sodium, calcium or the like salts from the polymerization of the resin.

Since the acidified resol resin of the present process is stable at low pH, the acidified resol resin can be modified by the subsequent addition of one or more acid modifying agents serving to alter or improve the properties, such as the curing characteristics, of the resin thus obtained and / or of the binder then prepared from the resol resin. The amount of acid modifier used depends on the nature of the modifier and the degree of modification desired. As examples of suitable acid modifiers which can be used, mention may be made of latent catalysts such as aryl phosphites, salts of a primary or secondary amine and of a strong acid, partial phosphate esters; reactive diluents such as benzyl alcohols; weak acids such as boric acid, and fatty acids such as oleic acid and stearic acid; and polycarboxylic acids such than polyacrylic acids. Aryl phosphite type latent catalysts are described, for example, in US Pat. No. 5,317,050, as alternatives to strong acid type catalysts, for the rapid curing of phenolic resins at relatively low elevated temperatures. Amine salts of strong acids are described as effective latent catalysts for phenolic resins in US Patent 5,243,015, which also describes the synergistic combination of such latent catalyst with a minor amount of curing catalyst. classic strong acid type. US Patent 5,378,793 describes partial phosphate esters as latent catalysts for resol phenolic resins, the partial phosphate esters being prepared by reaction of condensed phosphoric acids with polyols under controlled conditions. US Pat. No. 6,133,403 describes benzylic alcohols, namely alkoxylated benzylic alcohols and dibenzyl ethers, as reactive diluents for phenolic resins curable with curing catalysts of strong acid type. The use of polyacrylic acids as an acid modifying agent for resol resins is described, for example, in US Patents 5,670,585 (reduction of ammonia emissions), 6,194,512 (preferred formulation of trimethylolphenol) and the US Patent 5,804,254 (flexibility additive).

At the end of the preparation of the aqueous resol resin, the aqueous resin can be packaged, for example in cans, and stored there until it is needed or until it is transferred to a transport vehicle such as a tank truck or tank car and shipped to another site where sizing for mineral fiber products is to be made.

The aqueous resol resin of the present invention has good stability, measured by its dilution capacity in water. Preferably, the aqueous resol resin can be diluted more than 2000 to 1, even after two weeks of storage at low temperature (5 ° C or 40 ° F).

The aqueous resol resin produced can be used to prepare an aqueous size for products formed by means of mineral fibers. Typically, in such products, mineral fibers, such as glass fibers, are initially formed into a nonwoven mat. An aqueous sizing containing the resol resin is typically sprayed on the still hot glass fibers which have just been formed, in a formation enclosure or the like, to give a mass comparable to wool containing the glass fibers bonded by resinous gluing. The characteristics and usefulness of the products are determined to some extent by the type of mineral fiber used, the length and diameter of the fibers, the density, oxidation and concentration of the fibers in the mat, and the like. For some applications, it may be desirable to weave the fibers or otherwise form a fabric of the fibers.

Alternatively, in one embodiment of the present invention, the aqueous resol resin can be modified at the resin manufacturing site by subsequently carrying out a reaction with one or more formaldehyde fixing agents to reduce the free formaldehyde content, before to package and ship the resin. Alternatively, formaldehyde fixing agents can be added later, after the resol resin reaches the site where it will be used. Typically, the resol resin is diluted with water, and a curing catalyst is added to form an aqueous size. The glue is applied to the fibrous material to be bonded; and the resol is hardened by the action of heat. The size can also contain other constituents, such as one or more formaldehyde fixing agents.

Typically, a nitrogen reagent such as urea is used as the formaldehyde-fixing agent for the resol phenol-formaldehyde resins. Other formaldehyde-fixing agents can also be used, in particular nitrogen-containing reagents such as ammonia, ammonium hydroxide, primary and secondary amines, thiourea, dicyandiamide, guanidine, aminotriazoles such as guanamine and benzoguanamine, melamine, melamine-formaldehyde resins and dicyandiamine-formaldehyde resins. Other types of formaldehyde fixing agents can also be used, such as sodium sulfite, sodium cyanide and resorcinol. Combinations of reagents can also be used, with preference here for a combination of urea and ammonia. Preferably, the formaldehyde-fixing agent is added in an amount sufficient to react with almost all of the residual formaldehyde in the resol resin. When urea is used as the formaldehyde fixing agent, the molar ratio between urea and free formaldehyde in the aqueous mixture containing the resol resin is preferably from about 1: 1 to 1.75: 1. By mixing the formaldehyde fixing agent with the aqueous resol resin, an increase in the pH of the aqueous mixture is observed, such as an increase in pH to a range of 7 to 9.

In one embodiment of the present process, urea and ammonia are added directly to the aqueous resol mixture, after acidifying the aqueous mixture, and preferably not more than about three days after the acidification of the mixture. reaction. Advantageously, urea and ammonia can be added immediately after acidification. Preferably, the reaction mixture thus obtained is stirred for a duration at least sufficient to guarantee a complete mixture of the resol resin, urea and ammonia, as for at least approximately 30 to 60 minutes, by means of a classic liquid mixing machine. If the acidified aqueous mixture containing the resol is stored for a certain period of time before adding nitrogen reagents, it is preferred that the aqueous mixture is stored at a temperature below room temperature, especially at about 4.4 to 12.8 ° C (40 to 55 ° F). The phenolic resin prepared by the process of the present invention has a storage stability of at least about two weeks at temperatures up to at least about 12.8 ° C (55 ° F).

The process of the present invention may further include further completing the preparation of the sizing by adding a catalyst, such as a latent acid catalyst, to cure the resol resin.

As examples of catalysts used to harden the resol resin, mention may be made of acid catalysts such as the salts, preferably the salts of ammonium or amine acids, such as ammonium sulphate, ammonium phosphate. , ammonium sulfamate, ammonium carbonate, ammonium acetate, ammonium maleate, and the like. The catalyst can be added in an amount of about 0.1 to 5 weight percent, based on the weight of the resolved resin, or based on the resolved resin and urea in the case of a modified resolved resin. through urea. If a latent catalyst is used as the acid modifier of the resin, the amount of curing catalyst may be reduced, or the curing catalyst may not be used at all, depending on the type and amount of the latent catalyst employed. The completion of the preparation of the sizing may also consist in adding a lubricant composition, such as a mineral oil emulsion, and a product promoting the adhesion of the modified resol resin to the glass fibers, such as a suitable silane. An example of an adhesion enhancing silane which can be added is 3-aminopropyltriethoxysilane. Other additives such as finely divided mineral fibers, resins can also be added to the aqueous sizing non-reactive organics such as VINSOL resin (trademark of Hercules) (derived from rosin), tall oil, surfactant compounds such as lignosulfonate salts, thickeners and rheology regulators, dyes, additives colored, water, and the like.

Before application, the sizing can be diluted by adding water to obtain a concentration suitable for application on hot mineral fibers or on the sheet or mat of hot mineral fibers. For example, water can be added to obtain a total solids content of about 1 to 80 percent by weight.

The aqueous sizing can be applied directly to the still hot glass fibers that have just been formed, or to a mat or fabric of mineral fibers, and then dried and hardened to form a product. The mineral fiber can be a glass fiber and the mat can be a non-woven mat. The mineral fibers can be continuous or discontinuous, or take the form of a mineral fiber wool. If fiberglass is used, it can be shaped by any conventional process such as stretching by flame or by steam, centrifugal fiberizing, or the like. The shape, density of fibers, length of fibers, orientation of fibers, and other characteristics of the fiber mat, depend on the intended application for the products formed. A particularly important application is thermal insulation. In this case, the fiber mats take the form of rolls or continuous sheets of non-woven glass fibers, randomly oriented. A similar mat is used in the production of glass fiber sheets for sound insulation. If thermal and acoustic insulation based on glass fibers is to be produced, it is typically sprayed onto still hot glass fibers that have just been formed, in a formation enclosure or under a hood, the aqueous sizing to distribute a sizing coating on the fibers, and in particular at the points of contact between the fibers. If the hot fibers do not have a sufficient calorific content to expel the water, the mat coated with the aqueous sizing solution can then be dried with heat to remove the water. In both cases, the resinous compounds containing the resol and the nitrogenous reagent are cured to form an infusible binder for the mineral fiber mat. The process of the present invention can also be used to prepare glues for other mineral fiber products such as battery separators, printed circuit boards and electrical insulation products, as well as for elaborate wooden products. such as chipboard, particle board, plywood and the like.

The following examples are illustrations of the methods, compositions and products of the present invention and will be useful to those skilled in the art in practicing the invention. However, the invention is in no way limited by these examples. Unless otherwise indicated, all percentages are given on a weight basis in the following examples. Examples 1 and 2

100 parts of commercial grade phenol and 255 parts of a 50% (w / w) aqueous solution of formaldehyde are introduced into a reactor. The reactor is heated and the contents are stirred until the temperature of the mixture stabilizes at 45 ° C. The temperature is maintained at a first temperature of 45 ° C. and 10 parts of 50% sodium hydroxide (w / w) are added at a constant rate over the course of thirty minutes. The temperature is then allowed to rise to a second temperature of 70 ° C over the course of thirty minutes, and this second temperature is maintained for 60 minutes. The reaction mixture is cooled. The pH of the resin is adjusted by adding sulfuric acid to 25% to obtain a pH of 2.7 (example 1). The solids content of the resin is measured and found to be 42.97% by weight, based on non-neutralized solids, and the calculation of the theoretical solids content gives a value of 42.66 %, calculated on the same basis.

The process is repeated, except that 25% sulfuric acid is added to obtain a pH of 7.2 (Comparative Example 1). The solids content of the resin is measured and found to be 40.96% by weight, based on the non-neutralized solids, and the calculation of the theoretical solids content gives a value of 42 , 79%, calculated on the same basis. The process is repeated, except that 25% sulfuric acid is added to obtain a pH of 5.1

(example 2). The solids content of the resin is measured and found to be 41.36% by weight, based on the non-neutralized solids, and the calculation of the theoretical solids content gives a value of 42 , 73%, calculated on the same basis.

Examples 1 and 2 and Comparative Example 1 show that acidification at a pH below 7 gives a higher effective solid content (compared to the theoretical value) than neutralization at a pH of 7. Examples 3-7 Example 1 is repeated, except that a different neutralizing acid is used, as indicated below, to neutralize the resin at an acidic pH or at a pH of approximately 7, the results being given in Table A below. Table A

Example 8

The process of Example 1 is repeated, except (a) that the resol phenol-formaldehyde resin is neutralized to the pH indicated in Table B below, and (b) that the resol resins are modified. thus obtained by adding 0.8 part of ammonia and 21 parts of urea, to obtain a resol phenol-formaldehyde resin modified with urea. The solids and free formaldehyde contents of the resins before neutralization, the solids content of the resins after neutralization, the theoretical solids content (relative to the solids content before neutralization) and the pH after modification are indicated in table B below. The effective solids contents after modification are indicated in table C below, as well as the theoretical solids contents, based on (a) the solids content before neutralization, (b) the theoretical solids content. solids after neutralization and (c) the effective solids content after neutralization, as well as the content of free formaldehyde and free phenol after modification, and the stability of the modified resin, determined by its dilution capacity. These results show that resins neutralized at pH 3 produce an equivalent, if not higher, measured solid content than resins neutralized at a conventional pH of 7.6. In addition, the level of free formaldehyde in the final product is slightly higher for the modified resins (0.72% versus 0.67%), which suggests a possible shift in the chemistry of the resin, giving a release of formaldehyde. (HCHO) resulting in higher solids content at lower pH. Table B

Table C

Example 9

The process of Example 1 is repeated, except (a) that urea and formaldehyde are reacted at 70 ° C. for 85 minutes instead of 60 minutes, (b) that the resins are resolved. phenol-formaldehyde up to the pH indicated in Table D below and (c) the resol resins thus obtained are divided into two samples, one remaining unmodified and the other sample being modified by adding 0 , 8 parts of ammonia and 21 parts of urea, to give a resol phenol-formaldehyde resin modified by urea. The solids and free formaldehyde contents of the resins before neutralization, the solids content of the resins after neutralization and the stability of the neutralized resins thus obtained, measured by the dilution capacity of the resins, are indicated in Table E below. .

These results show that resins neutralized to a pH of 3 produce an equivalent measured solids content, if not more than the resins neutralized at a conventional pH of 7.6, even with the longer reaction time of 85 minutes. The results also show that a modified resin with a reaction time of 85 minutes has a slightly lower stability (dilution capacity of 0 after 3 days).

Table D

Table E

Example 10

The process of Example 1 is repeated, except (a) that the resol phenol-formaldehyde resins are neutralized to the pH indicated in Table F below and (b) that the resol resins are thus divided obtained in two samples, one remaining unmodified and the other sample being modified by adding 0.8 part of ammonia and 21 parts of urea, to give a resol phenol-formaldehyde resin modified with urea. The resins thus obtained are stored at 4.4 ° C (40 ° F). Oven solids contents are measured on the day of neutralization.

After 24 hours, all samples are infinitely dilutable and show no signs of precipitation.

Table F

Example 11

A resol phenol-formaldehyde resin modified with urea is prepared as in Example 10 above and is divided into two samples, one of which is neutralized at a pH of 7.6, the other being neutralized at a pH of 3.12. Likewise, the base resin is divided and one of the samples is neutralized at a pH of 3. The percentage on the date of preparation and after storage at 4.4 ° C (40 ° F) is measured of formaldehyde, the percentage of phenol, the percentage of solid content, pH and dilution capacity. The results are shown in Table G below. Table G

Example 12

The process of Example 10 is repeated to obtain a resin modified with urea acidified to pH 3 and an unmodified resin. Sizes are prepared from the resins by adding 2.2 parts by weight of ammonium sulfate to the unmodified resin (no ammonium sulfate is added to the modified resin) and a tensile strength is measured. from 116.6 - 122.9 kg (257-271 lbs) after curing at 160 ° C or 180 ° C, after storing the resin for up to 2 weeks at 4.4 ° C (40 ° F), as indicated table H.

The results presented in Table H show that the size prepared with the modified resin at pH 3 has a lower tensile strength than the size prepared with the unmodified resin containing the hardening catalyst of ammonium sulfate type, but which is deemed acceptable for the purposes of product performance.

Table H

Example 13

The process of Example 12 is repeated, except that 1 part of ammonium sulphate is added to the binder as curing catalyst on the basis of the urea-modified resin, acidified to pH 3, and the the resins are stored for 3 weeks before measuring their tensile strength. The results indicated in Table I show that the addition of 1.0 part of ammonium sulfate significantly increases the tensile strength up to a level comparable to the control. Table I

Example 14

Figure 1 shows the results of a differential scanning calorimetric analysis (DSC) of the curing profiles of the two sizes based on urea-modified resins, one acidified to pH 3 and the other to pH 7.6 . No curing catalyst of the ammonium sulphate type is added to these sizes. The DSC curves show that the sizing prepared with the resin modified with acidified urea at pH 3 present, which is surprising, little pre-hardening and does not produce a marked increase in the exotherm phenol-formaldehyde compared to the binder prepared using the neutralized binder at pH 7.6. Example 15

Figure 2 shows the result of a differential scanning calorimetric analysis (DSC) of the two sizes based on urea-modified resins, one acidified to pH 3 and the other to pH 7.6. 2 parts by weight of hardening catalyst of the ammonium sulphate type are added to these sizes. The addition of ammonium sulphate considerably alters the curing profile of the glue based on the urea-modified resin at pH 3. The amplitude of the phenol-formaldehyde exotherm is significantly reduced and the exotherm urea -formaldehyde is also affected, which indicates the possibility of increased pre-hardening. Example 16

10 parts of commercial grade phenol and 255 parts of a 50% (w / w) aqueous solution of formaldehyde are introduced into a reactor. The reactor is heated and the contents are stirred until the temperature of the mixture stabilizes at 45 ° C. The temperature is maintained at a first temperature of 45 ° C. and 10 parts of 50% sodium hydroxide (weight / weight) are added at a constant rate over the course of 30 minutes. The temperature is then allowed to rise to a second temperature of 70 ° C over 30 minutes, and this second temperature is maintained for 60 minutes. The reaction mixture is cooled. The pH of the resin is adjusted by adding 3.1 parts of solid sulfamic acid (based on the total weight of liquid) to obtain a pH of 3

(example 16). The solids content of the resin is measured and found to be 48.74% by weight, based on the non-neutralized solids, and the calculation of the theoretical solids content gives a value of 45.25 %, calculated on the same basis.

The process is repeated, except that 2.8 parts of sulfamic acid are added to obtain a pH of 7 (comparative example 16). The solids content of the resin is measured and found to be 47.76% by weight, based on the non-neutralized solids, and the calculation of the theoretical solids content gives a value of 45.17 %, calculated on the same basis.

Example 16 and Comparative Example 16 show that acidification to a pH of 3 gives a higher solid content (compared to the theoretical value) than neutralization to a pH of 7.

Various modifications may be made to the details of the various embodiments of the methods, compositions and products of the present invention, all within the scope and in the spirit of the invention, as defined in the appended claims.

Claims

1. A process for preparing a phenolic sizing for glass fibers, comprising the steps consisting in a) preparing a water-soluble phenol-formaldehyde resol resin by:

1) preparing an initial aqueous mixture containing formaldehyde and phenol;

2) adding a basic polymerization catalyst to the initial aqueous mixture; 3) maintaining the aqueous mixture at a predetermined temperature to form the water-soluble phenol-formaldehyde resol resin until the free formaldehyde content of the aqueous mixture drops to a predefined level;

4) cooling the aqueous mixture; and

5) acidifying the aqueous mixture to a pH not exceeding 3; b) then to complete the preparation of the sizing by adding a catalyst for hardening the resol resin.

2. The method according to claim 1 further comprising the steps of a) preparing an aqueous reaction mixture containing the phenol-formaldehyde resol resin and a nitrogenous reagent and b) allowing the nitrogenous reagent to react with the phenol-formaldehyde resol resin to form a modified resin.

3. The method of claim 2 wherein the nitrogen reagent is urea, ammonia or a mixture of urea and ammonia.

4. Method according to one of claims 1 to 3 further comprising mixing an acid modifying agent with the aqueous mixture.

5. The method of claim 4 wherein the acid modifying agent is a latent catalyst or a reactive diluent.

6. Method according to one of claims 1 to 5 wherein the phenol-formaldehyde resin has a formaldehyde / phenol molar ratio of from 2.5: 1 to 4.2: 1.

7. The method of claim 6 wherein the phenol-formaldehyde resin has a formaldehyde / phenol molar ratio of from about 3.2: 1 to 4.0: 1.

8. Method according to one of claims 1 to 7 wherein the predefined level is about 40 percent by weight of the free formaldehyde in the initial aqueous medium.

9. Method according to one of claims 1 to 8 wherein the aqueous mixture is acidified with a strong acid.

10. The method of claim 9 wherein the acid is selected from mineral acids such as sulfuric acid, hydrochloric acid, nitric acid and phosphoric acid, and organic acids such as acetic acid , trichloroacetic acid, and aromatic disulfonic and polysulfonic acids.

11. Method according to one of claims 1 to 8, wherein the aqueous mixture is acidified with a weak acid, in particular an acid comprising at least one amino function.

12. The method of claim 11 wherein the acid is chosen from sulfamic acid and amino acids, in particular containing more than one carboxylic function.

13. The method of claim 1 wherein the aqueous mixture containing the unmodified resol resin is acidified to a pH of about 2 to 3.

14. The method of claim 2 wherein the molar ratio between the urea or ammonia modifying agent and the free formaldehyde of the phenol-formaldehyde resin is from about 1: 1 to 1.75: 1.

15. The method of claim 2 wherein the aqueous mixture is maintained at a temperature of about 5 ° C to 30 ° C, while allowing the nitrogen reagent to react with the resol resin.

16. The method of claim 2 wherein the ammonia is added to the reaction mixture in an amount sufficient to give a weight ratio of ammonia to unmodified resin solids of from about 1.0: 100 to 3.0: 100 .

17. Method according to one of claims 1 to 16 wherein the completion of the preparation of the binder further comprises adding to the aqueous mixture containing the resol resin a lubricant of mineral oil type and an adhesion promoter of organosilane type.

18. Improved sizing for glass fibers prepared according to the method of any one of claims 1 to 17.

19. A method for producing a sheet of glass fibers, the method comprising the steps consisting in: a) preparing a water-soluble phenol-formaldehyde resol resin by:

1) preparing an initial aqueous mixture containing formaldehyde and phenol;

2) adding a basic polymerization catalyst to the initial aqueous mixture;

3) maintaining the aqueous mixture at a predetermined temperature to form the water-soluble phenol-formaldehyde resol resin until the free formaldehyde content of the aqueous mixture drops to a predefined level;

4) cooling the aqueous mixture; and

5) acidifying the aqueous mixture to a pH not exceeding 3; b) preparing a binder for the glass fibers by then adding a curing catalyst for the resol resin, c) spraying the binder on the glass fibers to form a sheet; and d) hardening the binder at an elevated temperature.

20. The method of claim 19 further comprising the steps of a) preparing an aqueous reaction mixture containing the resol phenol-formaldehyde resin and a nitrogen reagent; and b) reacting the nitrogen reagent with the phenol-formaldehyde resol resin to form a modified resin.

21. The method of claim 20 wherein the nitrogen reagent is urea, ammonia or a mixture of urea and ammonia.

22. Method according to one of claims 19 to 21 further comprising mixing an acid modifying agent with the aqueous mixture.

23. Product prepared by the process according to any one of claims 19 to 22.