Phenolic resins

Abstract

This invention relates to a phenolic resin composition R based on phenolic resins P made by reaction of hydroxyaromatic compounds H having at least one hydroxyl group -OH in its molecule, and (cyclo)aliphatic aldehydes A having at least one aldehyde group -C(H)=O in its molecule, which phenolic resin composition R further comprises a formaldehyde scavenger S which comprises at least one cyclic urea UC which is selected from the group consisting of alkylene ureas, in mixture with at least one of aliphatic aminocarboxylic acids AA having from two to twelve carbon atoms, to a process of its preparation, and to its application preferably in coated abrasives.

Description

Phenolic ResinsField of the InventionThis invention relates to phenolic resins with low propensity to form blisters, voids and / or bubbles during curing, to a method of preparation thereof, and to their application, preferably in abrasive materials such as coated abrasives.Background of the InventionThe use of phenolic resins made from phenol or its homologues, such as cresols and xylenols, and formaldehyde in abrasive compositions for grinding wheels or coated abrasives has been described by Leo Baekeland in the patent US 942,808 A issued on December 07, 1909. Blisters, voids and / or bubbles may be formed during curing, due to dissolved gases which can be liberated during the resinification or curing steps, or can be present already in the educts used for preparation of the resins and the compositions made therefrom. Formaldehyde is regarded as one of the gases which cause the formation of voids. Ever since the introduction of phenolic resins, the tolerable concentrations of formaldehyde in the air have been gradually and steadily reduced, most recently to 0.008 mg / m3or less, as decided by the EU commission on July 14, 2023 in the amendment of Annex XVII to Regulation (EC) 1907 / 2006. This limit is difficult to meet with formaldehyde scavengers having been in use before, such as those described in US patent 5,270,434 A issued on December 14, 1993 (phenol-formaldehyde- condensates with alkanolamines or cyclic amines), and US patent 5,358,748 A issued on October 25, 1994 (nitrogen heterocyclic compounds having replaceable hydrogen atoms attached to the nitrogen atom of an amine, such as melamine and alkanoguanamines, or a guanidine compound such as guanidine itself, and 2-cyanoguanidine).Other formaldehyde scavenger systems have been described in US patent application 2021 / 0087327 Al, where the formaldehyde scavenger comprises (a) at least one beta-di- carbonyl compound (I) comprising the group of formula R1C(O)-CH2-C(O)-O-, where R1is selected from the group consisting of a hydrogen atom, a Crto C]2- hydrocarbyl group, and a group -CH2-X, where X is a group comprising, along with hydrogen atoms, one to eleven carbon atoms, and one to three oxygen atoms, or a conversion product of the said betadicarbonyl compound (I) with formaldehyde, or both of these, and (b), an alpha-carbonyl- carboxyl compound (II) with the structure R3- O - C(O) - C(O) - R4, wherein each of R3and R4, independently of one another, are selected from the group consisting of a hydrogen atom, and a Cj- to C6- hydrocarbyl group, or a conversion product of the said alpha-carbonyl-carboxyl compound (II) with at least one of the further constituents of the phenolic resin, or both of these, see claim 1 thereof. It is further mentioned in page 5, paragraph

[0044] , that "other formaldehyde scavengers (III) may be used in accordance with the invention which contain nitrogen [atoms, added] in the molecule, preferred compounds being urea, and particularly preferred, ethylene urea and / or propylene urea, which can be used in addition to the beta- dicarbonyl compound (I)". The next paragraph

[0045] distinctly states that combinations are possible for the classes of named formaldehyde scavengers (I to III) within a class and / or between classes as long as at least one beta-dicarbonyl compound (I) is used. This statement clearly teaches away from using alkylene ureas without the presence of a beta-dicarbonyl compound (I) in the mixture. The only embodiment in this patent application US 2021 / 0087327 Al showing the use of a cylic alkyleneurea (in this case, an aqueous solution of ethyleneurea) is example B6; according to table I in page 9, the benzyl ether resin 1 is mixed with DBE (dimethylester mixture of C4- to C6- dicarboxylic acids, supplied by DuPont) and FSE (Fatty acid ester such as distilled rapeseed oil fatty acid methyl ester or isopropyl laurate, supplied by Oleon Americas Inc.), and next, ethyl acetoacetate, a beta-dicarbonyl compound of class I, and "Synthro Stab TF 501 " (a compound of class III, supplied by Protex International), which is a solution of ethylene urea in water with a mass fraction of solute of 50 %, are added.In the international patent application WO 97 / 24385 Al, the use of formaldehyde scavengers is discussed beginning in page 23, line 3. It is stated that nitrogen-containing additives having -NH groups function as in-situ formaldehyde scavengers upon heating, as well as post in-situ neutralisation agents of acid via hydrolysis of an amide or a Schiff base by liberating ammonia or an organic amine. Typical compounds are mentioned as formamide, N-methyl 2- pyrrolidinone, and N-2-vinyI pyrrolidinone. In lines 16 to 18 of the same page, urea, ethylene urea, and primary nitroparaffins are mentioned as further formaldehyde scavengers. Tests for the reduction of level of free formaldehyde are only reported for nitroethane / nitropropane, see page 26, lines 3 to 5, where a reduction of the initial level of free formaldehyde ofuntreated resin A of 2.5 % (see page 25, lines 24 to 28) was noted by treatment with nitroethane I nitropropane reduced this value to about 1.4 %.In the US patent application 2022 / 0364283 Al, binder compositions are described which include at least one formaldehyde-containing compound FC, a cyclic urea-dialdehyde compound CUD, and a polyamine compound PAC. The ratio mFC / ( mCUD+ mPAC) of the mass mFCof the at least one formaldehyde-containing compound FC to the sum mCUD+ mPACof the mass mCUDof the cyclic urea-dialdehyde compound CUD and the mass mPACof the polyamine compound PAC is greater than, or about equal to, 1:1, see claim 1 thereof. The formaldehyde- containing compound may be selected from the group consisting of phenol-formaldehyde (PF) resins, urea-formaldehyde (UF) resins, phenolurea-formaldehyde (PUF) resins, mel- amine-formaldehyde (MF) resins, melamine-urea-formaldehyde (MUF) resins, and resorcinol- formaldehyde resins. See claim 2 thereof.The cyclic urea-dialdehyde compounds CUD are formed as reaction products of a urea compound (i) and an aldehyde and / or ketone containing compound (ii), see paragraph

[0037] . The urea compound (i) has the formula 1where R1, R2, R3, and R4are independently chosen from a hydrogen moiety (H), an alkyl group, an aromatic group, an alcohol group, an aldehyde group, a ketone group, a carboxylic acid group, and an alkoxy group.The aldehyde reactant (ii) may include dialdehyde and / or diketone containing compounds, or may include polyaldehydes (e.g., dialdehydes), polyketones (e.g., diketones), and compounds that have at least two aldehyde groups or at least two ketone groups. Examples include alpha, beta-dicarbonyl compounds (ii-1 ) where carbonyl carbon atoms are directly bonded as illustrated in the following formula 2:where R5and R6are independently chosen from a hydrogen moiety (H), an alkyl group, or an aromatic group. Exemplary alpha, beta-carbonyl compounds (ii-1) include glyoxal, diacetyl, and benzil (i.e., 1 ,2-diphenylethane-l ,2-dione). See paragraph

[0038] .According to paragraph

[0039] , further examples include alpha, gamma-dicarbonyl compounds (ii-2) where the carbonyl carbons are separated by one aliphatic carbon atom as illustrated in the following formula 3:wherein R7and R8are independently chosen from a hydrogen moiety (H), an alkyl group, or an aromatic group. Exemplary alpha, gamma-dicarbonyl compounds include malonaldehyde and acetylacetone.In further alpha, gamma-dicarbonyl compounds (ii-3), R7and R8may also represent alkoxide groups -O-R, where R is an alkyl group, or amine groups -N (R')-R", where R' and R” independently represent a hydrogen atom or an alkyl group. Examples of compounds (ii-3) may include dialkyl malonates.Due to the nature of the reaction between dicarbonyl compounds and urea, hydroxyfunctional cyclic or bicylic compounds are formed, such as 4,5-dihydroxyimidazolidin-2-one from glyoxal and urea (paragraph

[0043] ), and with excess of glyoxal, 2,3,5,6-tetrahydroxy-l,4- diazabicyclo[2.2.1]heptan-2-one (paragraph

[0045] ). With an excess of urea, glycoluril (also known as acetylene urea) is formed from the same reactants.The polyamine compounds PAC are not specifically described in the said patent application, the only individual compounds mentioned both in the claims and the specification are melamine and dicyandiamide (also known as 2-cy anoguanidine).Object of the InventionIt has been found in the experiments that have been the basis for the present invention that formaldehyde or other gaseous substances generated during the curing process of phenolic resins give rise to formation of blisters, bubbles, and voids within the cured resin. Suchinclusions within the cured resin may impair its physical properties, and therefore also its usability in technical applications. For instance, in the application as make coat in coated abrasives, the adhesive layer between the abrasive particles and the backing would be weakened by such blisters, bubbles, and voids within the cured resin. These inclusions are also prone to lower the mechanical stability of the matrix formed by the moulded and cured resin in a bonded abrasive, in addition to those pores which are intentionally created to capture the grinding dust. None of the documents cited supra mentions such problems caused by such blisters, bubbles, and voids within the cured resin.It is therefore the object of the present invention to provide a phenolic resin composition that does not form undesired blisters, bubbles, and voids within the cured resin. Further, the mass fraction w(FFA) of free formaldehyde as measured according to DIN EN ISO 11402 (hydroxylamine hydrochloride procedure) is to be reduced below 0.1 %, where w(FFA) = m(FFA) / m(TPPF), m(FFA) standing for the mass of free formaldehyde found in the test portion of phenolic resin composition, and m(TPPF) standing for the mass of the test portion of phenolic resin composition.Summary of the InventionThese objects have been realised by providing a phenolic resin composition R based on phenolic resins P made by reaction of hydroxyaromatic compounds H having at least one hydroxyl group -OH bound to an aromatic carbon atom in its molecule, and (cyclo)aliphatic aldehydes A having at least one aldehyde group -C(H)=O in its molecule, which phenolic resin composition R further comprises a formaldehyde scavenger composition S which comprises at least one urea derivative U comprising at least one cyclic urea UC which is selected from the group consisting of alkylene ureas of formula Iwhere X1and X2are selected, independently from each other, from the group consisting ofhydrogen atoms H, and linear or branched alkyl groups having from one to ten carbon atoms, preferably, methyl, ethyl, butyl, hexyl, octyl, and nonyl, which linear or branched alkyl groups may be additionally substituted by hydroxy or hydroxyalkyl groups, and Y is an optionally substituted alkanediyl group, or alkenediyl group, or cycloalkanediyl group having from two to ten, preferably from two to six, carbon atoms. The substituents of Y may also be selected from the group consisting of hydroxy or hydroxyalkyl groups. At least one of X1and X2in UC is a hydrogen atom if only one kind of cyclic urea UC is present in the formaldehyde scavenger composition S. If more than one kind of cyclic ureas UC is present in the formaldehyde scavenger composition S, at least an amount of substance-fraction xHof 0.1 mol / mol, preferably at least 0.2 mol / mol, and preferably not more than 0.9 mol / mol, particularly not more than 0.5 mol / mol, of the sum of the amounts of substance of substituents XI and X2 are hydrogen atoms, where xH= nH / ( nH+ nx) is calculated as the ratio of nHwhich is the amount of substance of hydrogen atoms in positions XI and X2 in the said cyclic urea UC, and the sum (nH+ nx) of the amount of substance nHof hydrogen atoms and the amount of substance nxof groups XI and X2 which are different from hydrogen atoms in Formula I. Unsubstituted divalent groups Y are preferably selected from the group consisting of ethane- 1,2-diyl, propane-1, 2-diyl, propane-1, 3-diyl, butane-l,2-diyl, butane-1, 3-diyl, butane-2, 3-diyl, butane-1, 4-diyl, and cyclohexane-2, 3-diyl. One or more of the hydrogen atoms of the divalent group Y in formula I may also be substituted, preferably, by an alkyl or an alkoxy group having from one to four carbon atoms, and optionally, by one or more hydroxyl groups, such as in 4-hydroxyimidazolidin-2-one, 4,5-dihydroxyimidazolidin-2-one, and 5,6-dihydroxy-l,3- diazepan-2-one, or by a hydroxyethyl group such as in 4-(2-hydroxyethyl)imidazolidin-2-one. It is, however, more preferred to have no hydroxyl substituents in the divalent group Y of UC. It has further been found in the experiments which have led to the present invention that the additional presence in the formaldehyde scavenger composition S of small amounts of linear or branched aliphatic amino acids AA having one carboxyl group and at least one amino group, and a number of carbon atoms of from two to twelve, such as glycine (aminoacetic acid), sarcosine (N-methylamino acetic acid), alanine (alpha-aminopropionic acid), [3-alanine (beta-aminopropionic acid), valine (ct-aminoisovaleric acid), and omithin (a,b-diaminovaleric acid). It has been found mixtures of small amounts of linear or branched aliphatic amino acidsAA in mixture with the said cyclic ureas UC lead to the best results regarding suppression of blisters, bubbles, and voids in the cured resin. In these mixtures, the ratio n(AA) / n(UC) of the amount of substance n(AA) of aliphatic amino acids AA to the amount of substance n(UC) of cyclic ureas UC is preferably 0.01 mol : 0.99 mol ≤ n(AA) / n(UC) ≤ 0.10 mol : 0.90 mol; particularly preferably 0.03 mol : 0.97 mol ≤ n(AA) / n(UC) ≤ 0.08 mol : 0.92 mol; and most preferred, 0.04 mol : 0.96 mol ≤ n(AA) / n(UC) ≤ 0.07 mol : 0.93 mol.The formaldehyde scavenger S may also comprise at least one of a cyclic thiourea UCT which is selected from the group consisting of alkylene thioureas of formula IIwhere X3and X4are selected, independently from each other, from the group consisting of hydrogen atoms H, alkyl groups having from one to ten carbon atoms, preferably, methyl, ethyl, butyl, n-hexyl, octyl, and nonyl, and Y is an optionally substituted alkanediyl or cycloalkanediyl group having from two to ten, preferably from two to six, carbon atoms, and at least one of X3and X4is a hydrogen atom. One or more of the hydrogen atoms of the divalent group Y' in formula II may also be substituted, preferably by a hydroxyl group, or by a methoxy group, such as in 4-hydroxyimidazoIidin-2-one, 4,5-dihydroxyimidazolidin-2-one, and 5,6-dihydroxy-l,3-diazepan-2-one, or by a hydroxyethyl group such as in 4-(2- hydroxyethyl)imidazolidin-2-one. It is, however, more preferred to have no hydroxyl substituents in the divalent group Y' of UCT. Preferably, from 0.5 % to 50 % of the mass of the cyclic urea UC in the formaldehyde scavenger composition S may be replaced by a cyclic thiourea UCT.Other urea derivatives U useful as additional formaldehyde scavengers, together with the cyclic ureas UC of formula I, and / or the cylic ureas UCT of formula II, include cyclic ureides UC derived from organic dicarboxylic acids and urea or thiourea, such as parabanic acid, barbituric acid, uric acid, and their thio analogues, and bisureas BU derived from oligomericor polymeric primary diamines, preferably oligo- or poly-oxyalkylene amines D having at least two primary amino groups in their molecule, by reaction thereof with urea or thiourea, where the primary diamine D of formula IIIH2N - Z -NH2(Formula III), wherein Z is a polymeric or oligomeric oxyalkylene group of formula IV- CH2- CHR -( O - CH2- CHR' - )n-, (Formula IV) wherein n is at least one, and up to fifteen, and R and any of R’ are selected, independently from each other, from -H and -CH3, and wherein the ratio n(U) I n(D) of the amount of substance of urea n(U) and the amount of substance n(D) of the primary diamine D in the reaction of both is at least 1 mol / mol, and not more than 2 mol / mol.Further useful additives in the in the formaldehyde scavenger composition S are aliphatic aminoureido acids AU, such as citrullin [2-amino-5-ureidovaleric acid H2N-CO-N(H)-(-CH2)3- CH(NH2)-C(O)-OH], and aliphatic aminoguanido acids AG such as arginine (a-amino-b- guanidyl-valeric acid). These aminoacids AU and / or AG can replace at least partly, the amino acids AA in mixtures with cyclic ureas UC and / or cyclic thioureas UCT. A particularly preferred combination is glycine as AA, in combination with ethylene urea as UC.The mass fraction of these further additives UCT, UC, BU, AA, AG, and AU in the formaldehyde scavenger composition S, each of which additives may, or may not be present in the formaldehyde scavenger composition S, together with the cyclic urea UC, in the phenolic resin composition R, is(m(UCT) + m(UC') + m(BU) + m(AA) + m(AG) + m(AU)] / m(S), where the symbol m(XXX) in this formula stands for the sum of the mass of all of the further additives XXX (where XXX stands for any of the said further additives UCT, UC, BU, AA, and AU which may be present in a formaldehyde scavenger composition S), together with the cyclic urea UC, is preferably up to 0.5, more preferred, from 0.01 to 0.4, and most preferred, from 0.05 to 0.3. Accordingly, the mass fraction of cyclic ureas UC in the formaldehyde scavenger composition S is, for these cases, from 0.99 to 0.5, from 0.98 to 0.6, and from 0.95 to0.5. The best results have been obtained by using a mass fraction w(AA) = ra(AA) / m(S) of at least 0.1 and not more than 0.8, of linear or branched aliphatic amino acids AA having one carboxyl group and at least one amino group, and a number of carbon atoms of from two to twelve, where m(AA) is the mass of amino acids AA and m(S) is the total mass of the formaldehyde scavenger composition S.Detailed Discussion of the Preferred EmbodimentsThe phenolic resin composition comprises at least one phenolic resin P made by reaction of hydroxyaromatic compounds H having at least one hydroxyl group -OH in its molecule, and (cyclo)aliphatic aldehydes A having at least one aldehyde group -C(H) = O in its molecule.In the synthesis of phenolic resins P, the ratio n(A') / n(H) of the amount of substance n(A') of aldehyde groups -C(H)=O in the (cyclo)aliphatic aldehydes A to the amount of substance H(H) of hydroxyaromatic compounds H preferably obeys the relation1.1 mol / mol ≤ n(A') / rz(H) ≤ 3.0 mol / mol.It is also possible, within the scope of the present invention, to replace all, or a part of, the hydroxyaromatic compounds H by lignins isolated from lignocellulosic biomass such as hardwood pulp, softwood pulp, or nonwood pulp, such as from cotton, hemp, or jute, wheat straw, pine straw, alfalfa, kenaf, and flax fibre. For these cases, the amount of substance of reactive hydrogen atoms H* bound to an aromatic ring is usually lower than that calculated from the stoichiometry, due to sterical effects.The cyclic ureas UC according to formula I can easily be prepared, e. g., by the reaction of carbon dioxide and diamines with cerium dioxide catalysis as detailed by M. Tamura et al, Green Chemistry 15, 2013, pages 1567 to 1577.The mass fraction w(S) of the formaldehyde scavenger composition S in the mixture R of S and P is calculated as the ratio of the mass m(S) of the formaldehyde scavenger S, divided by the mass m(R) of the phenolic resin composition R which is the sum of the mass m(P) of thephenolic resin P and the mass m(S) of the formaldehyde scavenger S composition: m(R) = m(P) + m(S), w(S) = m(S) / [ m(P) + m(S) ].Preferably, w(S) is selected in such way to ensure that the ratio n(S') / n(A") of the amount of substance n(S') of N-H groups in the formaldehyde scavenger composition S to the amount of substance n(A") of free aldehyde groups -C(H)=O in the phenolic resin P obeys the relation 0.9 mol / mol ≤ ri(S') I M(A") ≤ 1.5 mol / mol, and preferably, 0.95 mol / mol ≤ n(S') / n(A") ≤ 1.30 mol / mol.As it has to be ensured that the above relation 0.9 mol / mol ≤ n(S') / n(A") ≤ 1.5 mol / mol is maintained in the phenolic resin composition R, the optimum ratio m(S) / m(P) of the mass m(S) of the scavenger composition S and the mass m(P) of the phenolic resin P has to be chosen depending on the ratio n(CHO) I n(H*) of the amount of substance n(CHO) of aldehyde groups in the (cyclo)aliphatic aldehydes A having at least one aldehyde group - C(H)=O in its molecule, to the amount of substance n(H*) of reactive hydrogen atoms H*- in ortho or para-position to a phenolic hydroxyl group in the hydroxyaromatic compounds H having at least one hydroxyl group - OH bound to an aromatic carbon atom in its molecule, in the synthesis of the phenolic resin P. In a phenolic resin made from formaldehyde and (unsubstituted) phenol, with a stoichiometric ratio n(FA) / n(phenol) of the amount of substance n(FA) of formaldehyde to the amount of substance n(phenol) of phenol, of 1.5, in the reaction, which corresponds to zi(CHO) / H(H*) = 0.5, the optimum ratio m(S) / m(P) is from 0.01 to 0.1, preferably, from 0.02 to 0.06. For a stoichiometric ratio H(FA) / n(phenol) of 2.2, the optimum ratio m(S) / m(P) has been found to be between 0.05 and 0.4, preferably, from 0.1 to 0.3.Preferred cyclic ureas UC are ethyleneurea, propylene urea, and mixtures of both, preferably in combination with at least one aminocarboxylic acid AA.The phenolic resin composition R of the present invention can be used in all applications where phenolic resins are used, such as adhesives, foams, mineral wool insulation binders, forlaminates, composites, friction materials, sand mould and core binders in metal casting, and as binders for refractories. A preferred application is in abrasives, particularly, as make coat in coated abrasives. It has been shown that voids and bubbles usually formed between the grains and the backing or support layer can be at least partially, and mostly, completely avoided. This leads to longer life and consistent quality of coated abrasives.Coated abrasives are usually provided in the form of sheets, belts, discs, and drums; they have a backing layer, also referred to as carrier or carrier material, which is usually selected from paper, special papers made from fibres which are impregnated and / or vulcanised, cloth made from cotton or synthetic fibres, fabrics including non-woven fabrics made from cotton or synthetic fibres, composite materials made from any of these, and polymer films. The backing layer is coated with a layer of the first coat ("make coat") and the wet coating is then sprinkled with abrasives grains, usually in a static electric field which supports the vertical alignment of the grains. The make coat solution usually contains a filler, in most cases, calcium carbonate. The grain size usually ranges, in the FEPA (Federation of European Producers of Abrasives) classification, for Macrogrit on paper (coarse-grained grit) from P12 to P220 (according to FEPA standard 43-1: 2006, mean diameter: 1815 pm to 68 pm), and for Microgrit on paper (fine-grained grit) from P240 to P5000 (according to FEPA standard 43-2: 2017, mean diameter: (58.5 ± 2) pm to 5 pm). During the next step which is the curing process of the make coat, the grains are fixed to the backing. A second coat ("size coat") is then applied which covers make coat and grains. The thickness of the size coat layer is frequently larger than that of the make coat.The following experiments serve to illustrate the invention, and do not limit the scope of protection.ExamplesExample 1 Preparation of a Phenolic Resin with a ratio n(FA) I n (phenol) of 1.5To a reactor equipped for distillation, 20.0 g of deionised water were added together with 630.4 g of phenol (100 %) and 18.5 g of an aqueous solution of sodium hydroxide NaOH [witha mass fraction m(NaOH) / (m(NaOH) + m(H2O)) = 45 %; m(NaOH) standing for the mass of sodium hydroxide, and m(H2O) standing for the mass of water in this solution] and heated to a temperature between 55 °C and 60 °C, preferably 58 °C. Then, 616.0 g of an aqueous solution of formaldehyde [with a mass fraction m(FA) / (m(FA) + m(H2O)) = 49 %; m(FA) standing for the mass of form aldehyde, and m(H2O) standing for the mass of water in this solution] was slowly added over ninety minutes at a temperature of 60 °C. The mixture was then heated to 70 °C and was stirred at this temperature until the water miscibility, measured at 23 °C, was between 1 ml / 3.5 g and 1 mL / 4.0 g. Samples were taken for characterisation, see table 1 below.Table 1 Unmodified Resin Characteristics - F / P ratio of 1.5Example 2 Preparation of a Phenolic Resin with a ratio n(FA) / n(phenol) of 2.2To a reactor equipped for distillation, 20.0 g of deionised water were added together with 485.2 g of phenol (100 %) and 19.5 g of an aqueous solution of sodium hydroxide NaOH [with a mass fraction m(NaOH) / (m(NaOH) + m(H2O)) = 45 %; m(NaOH) standing for the mass of sodium hydroxide, and m(H2O) standing for the mass of water in this solution] and heated to a a temperature between 55 °C and 60 °C, preferably 58 °C. Then, 685.65 g of an aqueous solution of formaldehyde [with a mass fraction m(FA) / (m(FA) + m(H2O)) = 49 %; m(FA) standing for the mass of form aldehyde, and m(H2O) standing for the mass of water in this solution] was slowly added over ninety minutes at a temperature of 60 °C. The mixture was then heated to 70 °C and was stirred at this temperature until the water miscibility, measuredat 23 °C, was between 1 mL / 2.5 g and 1 mL / 3.0 g. Samples were taken for characterisation, see table 2 below.Table 2 Unmodified Resin Characteristics - F / P ratio of 2.2Example 3 Mixtures of Phenolic Resins with Formaldehyde ScavengersMixtures of the phenolic resins of Example 1 with formaldehyde scavengers were prepared by admixing the formaldehyde scavengers according to the data in the following table 3. Five mixtures (3.1 through 3.5) were prepared, with mass fractions of the formaldehyde scavengers w(S) = m(S) / [m(S) + m(P)], where m(S) is the mass of (the solute of) the amine or amide used as formaldehyde scavenger, and m(P) is the mass of the solids of the phenolic resin solution used.Table 3 Mass Fractions of w(S) of Formaldehyde Scavengers in %The mass of added formaldehyde scavengers was calculated stoichiometrically for each mixture. The resulting mixtures were subjected to distillation under reduced pressure at a temperature not exceeding 55 °C until a viscosity within the range of from 2700 mPa s to 3200 mPa s, measured at 20 °C, was reached. When the desired viscosity was reached, the mixture was cooled down to a temperature below 18 °C for further use.The following characteristic data were measured on samples of mixtures 3.1 through 3.5, using the procedures according to the standards mentioned in Tables 1 and 2:Table 4 Data of phenolic resin compositionsExample 4 Mixtures of Phenolic Resins with Formaldehyde ScavengersMixtures of the phenolic resins of Example 2 with formaldehyde scavengers were prepared by admixing the formaldehyde scavengers according to the data in the following table 5. Three mixtures (4.1 through 4.3) were prepared, with mass fractions of the formaldehyde scavengers w(S) = m(S) I [m(S) + m(P)], where m(S) is the mass of (the solute of) the amine or amide used as formaldehyde scavenger, and m(P) is the mass of the solids of the phenolic resin solution used.Table 5 Mass Fractions of w(S) of Formaldehyde Scavengers in %The mass of added formaldehyde scavengers was calculated stoichiometrically for each mixture. The resulting mixtures were subjected to distillation under reduced pressure at a temperature not exceeding 55 °C until a viscosity within the range of from 2700 mPa-s to 3200 mPa-s, measured at 20 °C, was reached. When the desired viscosity was reached, the mixture was cooled down to a temperature below 18 °C for further use.The following characteristic data were measured on samples of mixtures 4.1 through 4.3, using the procedures according to the standards mentioned in Tables 1 and 2:Table 6 Data of phenolic resin compositionsExample 5 Mixtures of Phenolic Resins with Mixtures of Formaldehyde Scavengers Mixtures of the phenolic resins of Example 1 with mixtures of formaldehyde scavengers were prepared by admixing the formaldehyde scavenger mixtures according to the data in the following table 7. Two mixtures (5.1 and 5.2) were prepared, with mass fractions of the mixtures of formaldehyde scavengers w(S) = m(S) I [m(S) + m(P)], where m(S) is the sum of the masses of the formaldehyde scavengers used, and m(P) is the mass of the solids of the phenolic resin solution used.Table 7 Mass Fractions of w(S) of Formaldehyde Scavengers in %The resulting mixtures were subjected to distillation under reduced pressure at a temperature not exceeding 55 °C until a viscosity within the range of from 2500 mPa s to 3200 mPa s, measured at 20 °C, was reached. When the desired viscosity was reached, the mixture was cooled down to a temperature below 18 °C for further use.The following characteristic data were measured on samples of mixtures 5.1 and 5.2, using the procedures according to the standards mentioned in Tables 1 and 2:Table 8 Data of phenolic resin compositions 5.1 and 5.2Example 6 Application Testing - Evaluation of Bubble FormationA resin film with a wet thickness of 200 pm was applied with an adjustable film applicator on a transparent polyester film as backing. It was cured together with abrasive grain (Type Semi-friable Fused Aluminium Oxide, bluefired ALODUR® BFRPLCC, from Imerys Fused Minerals GmbH, 9523 Villach, Austria) which was applied gravimetrically and cured at 105 °Cfor sixty minutes in a ventilated lab oven. The visual evaluation and comparison was done with a digital, reflective light microscope (TOMLOV 16MP 7" LCD, RaySmart VMS 700). Pictures were taken with a view from the uncoated side of the transparent film backing, and are shown in Figures 3.1 through 3.5, 4.1, 4.3, 5.1 and 5.2 as attached.From inspection of these photographs, the following comments are given for the phenolic resin compositions of the Examples:The best results for suppression of bubble formation in the region between the backing surface and the grains have been obtained in the 3.4, 4.3, and 5.1, where ethyleneurea as cyclic urea UC is used as constituent in the formaldehyde scavenger S. Likewise, low values below 0.1 % have been obtained for the mass fraction of free formaldehyde.

Claims

Claims1. A phenolic resin composition R based on phenolic resins P made by reaction of hydroxyaromatic compounds H having at least one hydroxyl group -OH in its molecule, and (cyclo) aliphatic aldehydes A having at least one aldehyde group -C(H)=O in its molecule, which phenolic resin composition R further comprises a formaldehyde scavenger S which comprises at least one cyclic urea UC which is selected from the group consisting of alkylene ureas of formula Iwhere X1and X2are selected, independently from each other, from the group consisting of hydrogen atoms H, and alkyl groups having from one to ten carbon atoms, preferably, methyl, ethyl, butyl, n-hexyl, octyl, and nonyl, and Y is an optionally substituted alkanediyl or cycloalkanediyl group having from two to ten, preferably from two to six, carbon atoms, and at least one of X1and X2is a hydrogen atom, in mixture with at least one of aliphatic aminocarboxylic acids AA having from two to twelve carbon atoms, wherein the ratio n(AA) / n(UC) of the amount of substance n(AA) of aliphatic amino acids AA to the amount of substance w(UC) of cyclic ureas UC is0.01 mol : 0.99 mol ≤ n(AA) / n(UC) ≤ 0.10 mol : 0.90 mol.

2. The phenolic resin composition R of claim 1 wherein the formaldehyde scavenger S further comprises at least one of a cyclic urea UCT which is selected from the group consisting of alkylene thioureas of formula IIwhere X3and X4are selected, independently from each other, from the group consisting of hydrogen atoms H, alkyl groups having from one to ten carbon atoms, preferably, methyl, ethyl, butyl, n-hexyl, octyl, and nonyl, and Y is an optionally substituted alkanediyl or cycloalkanediyl group having from two to ten, preferably from two to six, carbon atoms, and at least one of X3and X4is a hydrogen atom.

3. The phenolic resin composition R of claim 1 or of claim 2 wherein at least 1 % of the mass of the least one of aliphatic aminocarboxylic acids AA having from two to twelve carbon atoms is replaced by aliphatic aminoureido acids AU and / or aliphatic aminoguanido acids AG.

4. The phenolic resin composition R of claim 1 or of claim 2 or of claim 3 wherein the formaldehyde scavenger S further comprises at least one of aliphatic bisureas BU made by reaction of urea with a primary diamine D of formula IIIH2N - Z -NH2(Formula III), wherein Z is a polymeric or oligomeric oxyalkylene group of formula IV - CH2- CHR -( O - CH2- CHR' - )n-, (Formula IV) wherein n is at least one, and up to fifteen, and R and any of R' are selected, independently from each other, from -H and -CH3, and wherein the ratio n(U) / n(D) of the amount of substance of urea n(U) and the amount of substance n(D) of the primary diamine D in the reaction of both is at least 1 mol / mol, and not more than 2 mol / mol.

5. The phenolic resin composition R of claim 1 or of claim 2 or of claim 3 or of claim 4 wherein the ratio n(A') / n(H) of the amount of substance n(A') of aldehyde groups -C(H)=O in the (cyclo)aliphatic aldehydes A to the amount of substance n(H) of hydroxyaromaticcompounds H in the synthesis of the phenolic resins P obeys the relation1.1 mol / mol ≤ n(A') I n(H) ≤ 3.0 mol / mol.

6. The phenolic resin composition R of any one of claim 1 or of claim 2 or of claim 3 or of claim 5 made by admixing the formaldehyde scavenger S to the phenolic resin P, wherein the ratio n(S') / n(A") of the amount of substance n(S') of N-H groups in the formaldehyde scavenger composition S to the amount of substance n(A") of free aldehyde groups -C(H)=O in the phenolic resin P obeys the relation 0.9 mol / mol ≤ n(S') I n(A") ≤ 1.5 mol / mol, preferably, 0.95 mol / mol ≤ n(S') / n(A") ≤ 1.30 mol / mol.

7. The phenolic resin composition R of any one of claim 1 or of claim 2 or of claim 3 or of claim 4 or of claim 5 or of claim 6 wherein the cyclic urea UC is ethyleneurea or propyleneurea, or a mixture of both.

8. The phenolic resin composition R of any one of claim 1 or of claim 2 or of claim 3 or of claim 4 or of claim 5 or of claim 6 or of claim 7 where the formaldehyde scavenger composition S additionally comprises at least one aliphatic aminocarboxylic acid AA, preferably, glycine.

9. The phenolic resin composition R of claim 8 where the ratio m(AA) / m(UC) of the mass m(AA) of the aminocarboxylic acid to the mass m(UC) of cyclic ureas present in the composition obeys the relation 3 g / g ≤ m(AA / m(CU) ≤ 10 g / g.

10. A method of use of the phenolic resin composition R of any one of claim 1 or of claim 2 or of claim 3 or of claim 4 or of claim 5 or of claim 6 or of claim 7 or of claim 8 or of claim 9 as resin for make coat in coated abrasives, wherein a backing preferably selected from the group consisting of paper, Kraft paper, paper modified with rubber, acrylic resin, or other polymers, woven cotton, linen, synthetic fibres, or vulcanised fibres is coated with a make coat comprising the phenolic resins composition R and at least one filler, and the coating is at least partially cured before applying the grain.

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