METHOD FOR THE MANUFACTURE OF MINERAL WOOL PRODUCTS

Abstract

A method for the manufacture of mineral wool products is disclosed. In one example, the method comprises reacting an aqueous phenol-formaldehyde resole with free formaldehyde with a first amount of urea, thereby preparing a prereact. The prereact is contacted with a second amount of urea. The resulting mixture of prereact and second amount of urea, as part of a binder, optionally with additives is applied to the surface of mineral fibers. The binder is cured on the surface of the mineral fibers. A mineral wool product with reduced emissions of formaldehyde is also disclosed.

Claims

1-16. (canceled)

17. A method for the manufacture of mineral wool comprising the steps of: a) providing an aqueous phenol-formaldehyde resole with free formaldehyde, b) preparing a phenol-formaldehyde-urea prereact by contacting the resole with a first amount of urea and allowing the mixture to react; c) contacting the prereact with a second amount of urea, d) applying the resulting mixture of prereact and second amount of urea, as part of a binder, to the surface of mineral fibers; and e) curing the binder on the surface of the mineral fibers; wherein the total amount of urea is between 30 and 35 wt. % relative to the sum of the dry weight content of the phenol-formaldehyde resole and the total amount of urea, and the second amount of urea used in c) is between 20-35 wt. % of the total amount of urea.

18. The method according to claim 17, wherein the total amount of urea is 30-35 wt. % relative to the sum of the dry weight content of the phenol-formaldehyde resole and the total amount of urea, and U2 is 22-33 wt. %, preferably 25-30 wt. % of the total amount of urea.

19. The method according to claim 17, wherein the total amount of urea is between 30 and 35 wt. % relative to the sum of the dry weight content of the phenol-formaldehyde resole and the total amount of urea, and the second amount of urea used in c) is between 20-35 wt. % of the total amount of urea.

20. The method according to claim 17, provided that the addition of a resin apart from the aqueous phenol-formaldehyde resole of step a) is excluded.

21. The method according to claim 17, wherein the phenol-formaldehyde resole in step a) has a free formaldehyde content at most 10 wt. % related to the dry weight content of the resole, preferably at most 6 wt. %.

22. The method according to claim 17, wherein the phenol-formaldehyde resole has a water dilutability at 20 C. greater than 10 parts by weight, a viscosity of at most 50 mPa.Math.s at 20 C. and 45 wt. % dry weight content, a pH higher than 8, and a B-stage gel time ranging from 2-15 minutes at 130 C.

23. The method according to claim 17, wherein in step b), the phenol-formaldehyde resole and first amount of urea (U1) are allowed to react for at least 1 hour, preferably at a temperature between 10-60 C. to prepare the prereact.

24. The method according to claim 17, wherein in step c), the second amount of urea (U2) is added to the prereact at least 24 hours, preferably at least 72 hours, after the prereact has been formed.

25. The method according to claim 17, wherein the prereact and second amount of urea (U2) are contacted in step c) less than 48 hours before this mixture is applied to the surface of the fibers in step d).

26. The method according to claim 17, wherein in step d), the mixture of prereact and second amount of urea(U2) is applied to the mineral fibers as part of a binder comprising additives in a concentration of 1-30 wt. % related to the non-aqueous content of the binder.

27. The method according to claim 17, wherein the first amount of urea (U1) in step b) is selected to produce a prereact with a free formaldehyde content of 0.9 wt. % or less, preferably of 0.2 wt. % or less, related to the dry weight content of the prereact.

28. The method according to claim 17, wherein the phenol-formaldehyde resole in step a) has a total concentration of nitrogen lower than 1.0 wt. %, preferably lower than 0.6 wt. %, related to the dry weight content of the resole.

29. The method according to claim 17, wherein the phenol-formaldehyde resole in step b) is substantially free of formaldehyde scavengers selected from the group of amines, tannins, sulfite and bisulfite salts, compounds with methylene active groups, glycine, resorcinol and its derivatives, alkanolamines, and mixtures thereof

30. A mineral wool product obtained by the method of claim 17, wherein the emissions of formaldehyde of said mineral wool product are lower than 10 g/m.sup.3, preferably lower than 8 g/m.sup.3measured according to ISO 16000-3:2011.

31. The mineral wool product according to claim 30, wherein the mineral wool product further has a LOI of between 1.5 and 15 wt. %.

32. The use of the mineral wool product according to claim 30 for the insulation of buildings, transportation, airconducting ducts and/or appliances.

33. A method for the manufacture of mineral wool comprising the steps of: a) providing an aqueous phenol-formaldehyde resole with free formaldehyde, b) preparing a phenol-formaldehyde-urea prereact by contacting the resole with a first amount of urea and allowing the mixture to react; c) contacting the prereact with a second amount of urea, d) applying the resulting mixture of prereact and second amount of urea, as part of a binder, to the surface of mineral fibers; and e) curing the binder on the surface of the mineral fibers; wherein the total amount of urea is about 40 wt. % relative to the sum of the dry weight content of the phenol-formaldehyde resole and the total amount of urea, and the second amount of urea used in c) is about 25 wt. % of the total amount of urea.

34. A method for the manufacture of mineral wool comprising the steps of: a) providing an aqueous phenol-formaldehyde resole with free formaldehyde, b) preparing a phenol-formaldehyde-urea prereact by contacting the resole with a first amount of urea and allowing the mixture to react; c) contacting the prereact with a second amount of urea, d) applying the resulting mixture of prereact and second amount of urea, as part of a binder, to the surface of mineral fibers; and e) curing the binder on the surface of the mineral fibers; wherein the total amount of urea is between 42 and 50 wt. % relative to the sum of the dry weight content of the phenol-formaldehyde resole and the total amount of urea, and the second amount of urea used in c) is between 15-52 wt. % of the total amount of urea.

35. The method according to claim 33, wherein the total amount of urea is 42-50 wt. %, preferably 45-48 wt. % relative to the sum of the dry weight content of the phenol-formaldehyde resole and the total amount of urea, and U2 is 15-50 wt. %, of the total amount of urea.

36. The method according to claim 33, wherein the total amount of urea is between 42 and 50 wt. % relative to the sum of the dry weight content of the phenol-formaldehyde resole and the total amount of urea and the second amount of urea used in c) is between 63% and 66 wt. % of the total amount of urea.

37. A method for the manufacture of mineral wool comprising the steps of: a) providing an aqueous phenol-formaldehyde resole with free formaldehyde, b) preparing a phenol-formaldehyde-urea prereact by contacting the resole with a first amount of urea and allowing the mixture to react; c) contacting the prereact with a second amount of urea, d) applying the resulting mixture of prereact and second amount of urea, as part of a binder, to the surface of mineral fibers; and e) curing the binder on the surface of the mineral fibers; wherein the total amount of urea is between 42 and 50 wt. % relative to the sum of the dry weight content of the phenol-formaldehyde resole and the total amount of urea, and the second amount of urea used in c) is between 63% and 66 wt. % of the total amount of urea.

38. A method for the manufacture of mineral wool comprising the steps of: a) providing an aqueous phenol-formaldehyde resole with free formaldehyde, b) preparing a phenol-formaldehyde-urea prereact by contacting the resole with a first amount of urea and allowing the mixture to react; c) contacting the prereact with a second amount of urea, d) applying the resulting mixture of prereact and second amount of urea, as part of a binder, to the surface of mineral fibers; and e) curing the binder on the surface of the mineral fibers; wherein the total amount of urea is about 45 wt. % relative to the sum of the dry weight content of the phenol-formaldehyde resole and the total amount of urea, and the second amount of urea used in c) is about 56 wt. % of the total amount of urea.

Description

DETAILED DESCRIPTION OF THE EMBODIMENTS OF THE INVENTION

[0040] The aqueous phenol-formaldehyde resole suitable for the method of the present invention is a water soluble curable resole having free formaldehyde, resole which is produced by methylolation and condensation of a phenolic compound with formaldehyde in the presence of an alkaline catalyst by methods known in the art. In resoles, the molar ratio of phenol:formaldehyde is <1. Phenol-formaldehyde resoles are reactive mixtures with methylol functional groups, which undergo a self-curing reaction under influence of heat or acids. The resoles are thus partially reacted thermosets, also known as resins, prepolymers or precondensates, stable at low temperature and alkaline pH, and which can be further condensed to a thermoset in a curing reaction by application of heat and/or at acidic pH value. The skilled person is aware of how such resole is commonly manufactured and recognizes how to modify the different reaction phases and parameters to obtain the characteristics described in the preferred embodiments of the invention. Such parameters include e.g. the phenol:formaldehyde molar ratio, the catalyst type and amount, and the condensation reaction time and temperature.

[0041] The phenol:formaldehyde molar ratio for the preparation of the resole of the method of the invention is preferably in the range 1:2-1:6. The stoichiometric excess of formaldehyde assures the predominant formation of low molecular weight species from methylolation and condensation, lower solution viscosity and low free phenol content in the resole. The molar excess of formaldehyde also has the consequence that free, unreacted, formaldehyde is contained in the aqueous resole after reaction.

[0042] Although for the sake of clarity in this description the suitable resole is referred to as phenol-formaldehyde resole, it has to be understood that it is not implied that the resole might only comprise unsubstituted phenol and formaldehyde as components. Other components might be present in the resole without departing from the scope of the invention. Such components can be for instance substituted phenol derivatives such as alkylphenols, phenol esters, or resorcinol and its derivatives, or formaldehyde related compounds such as paraformaldehyde, or higher aldehydes such as butyraldehyde, acrolein or glyoxal. Other compounds having hydroxy or carboxy groups can be also reacted with phenol and formaldehyde, such as carbohydrates or alkanolamines, and even compounds having functional groups different than hydroxy or carboxy, such as hexamethylenetetramine, can included in the reaction. It is however preferred that the sum of the weights of unsubstituted phenol and formaldehyde in the resole totals at least 80 wt. %, preferably at least 90 wt. %, of the dry weight of the resole.

[0043] Advantageously, resoles with low free formaldehyde content, i.e. with free formaldehyde content of 10 wt. % or less in relation to the dry weight content of the resole, can be used in the method of the invention. According to certain embodiments of the invention, the free formaldehyde content in the resole is preferably 10 wt. % or less, more preferably 6 wt. % or less, also preferably at least 1 wt. %, related to the dry weight content of the resole, when measured according to the method ISO 9397:1995 (hydroxylamine hydrochloride method). A central advantage of using resole with these levels of free formaldehyde content in the method of the invention is that mineral wool products obtained by applying the method of these embodiments are satisfactory in mechanical performance, and additionally they have lower emissions of formaldehyde. In particular, sufficiently low free formaldehyde content in the resole allows the manufacture of mineral wool products with formaldehyde emissions lower than 10 g/ms, and more preferably lower than 8 g/ms. The formaldehyde emissions from mineral wool products relate to the emissions when the products are stored in a test chamber with air exchange and under controlled conditions for 28 days and then, the formaldehyde concentration in the air in the chamber is measured according to standard method ISO 16000-3:2011.

[0044] According to the method of certain embodiments, the preferred phenol-formaldehyde resole has a dry weight content of 40-60 wt. %. The content of unreacted free phenol in the resole is preferably at most 6 wt. %, more preferably at most 2 wt. %, with respect to the resole dry weight content. The water dilutability of the resole in demineralized water at 20 C. is suitably greater than 10 parts by weight (this is, at least 10 g of water can be added to 1 g of resole before permanent turbidity appears), preferably greater than 20 parts, and more preferably greater than 50 parts. The resole viscosity is preferably at most 50 mPa.Math.s at 20 C., more preferably at most 30 mPa.Math.s, when measured for the resole aqueous solution with 45 wt. % dry weight content. The pH of the resole solution is preferably higher than 8, more preferably higher than 8.5, and even more preferably higher than 8.9. The B-Stage gel time of the resole preferably ranges from 2 to 15 minutes at 130 C. The methods used to determine these values are known to the skilled person, and explained briefly with some level of detail below.

[0045] In preferred embodiments, the phenol-formaldehyde resole, before it is contacted with urea to form the phenol-formaldehyde-urea prereact, has a total concentration of nitrogen lower than 1.0 wt. %, preferably lower than 0.6 wt. %, related to the dry weight content of the resole. Preferably, this resole is substantially free of nitrogenated compounds (compounds comprising at least one nitrogen atom), particularly substantially free of a compound selected from urea, ammonia, ammonium inorganic or organic salts, alkanolamines, alkylamines and/or melamine.

[0046] The phenol-formaldehyde resole, according to certain embodiments of the invention, is substantially free of formaldehyde scavengers selected from the group of amines, tannins, sulfite and bisulfite salts, compounds with methylene active groups, glycine, resorcinol and its derivatives, alkanolamines, and mixtures thereof.

[0047] Resoles with the properties described in preferred embodiments herein are available from resole manufacturing companies such as Momentive Performance Materials or Prefere Resins.

[0048] The method according to the invention comprises a step(step b)) of contacting the phenol-formaldehyde resole with a first amount of urea (U1), and allowing the resole and urea mixture to react, in order to prepare a phenol-formaldehydeurea prereact. The contacting step can be done by adding the urea (both in solid or liquid form), normally under efficient stirring, to the aqueous resole composition. After the urea and the resole are contacted, they are vigorously mixed and allowed to react by leaving the mixture to evolve during at least 1 hour, preferably for at least 2 hours, either in the same reactor used for the preparation of the resole, or in a separated container. The temperature during this step b) including the contacting, the mixing and the reacting phases leading to the prereact formation, ranges between 10-100 C., preferably between 15-80 C., preferably between 18-70 C., preferably between 20-60 C., preferably between 30-50 C., more preferably between 35-45 C. In a preferred embodiment the temperature in step b) does not exceed 70 C., more preferably the temperature in step b) is between 20-60 C. Higher temperatures within the range 10-100 C. lead to accelerate the condensation reaction so that said reaction needs to be stopped sooner to avoid advancing the condensation beyond the desired point. In a preferred embodiment the phenol-formaldehyde resole and first amount of urea (U1) are allowed to react in step b) of the method of the invention for at least 1 hour at a temperature between 10-60 C. to prepare the prereact.

[0049] In preferred embodiments of the invention, the first amount of urea (U1) contacted with the phenol-formaldehyde resole in step b) is selected to be sufficient as to produce a phenol-formaldehyde-urea prereact with a free formaldehyde content of 0.9 wt. % or less related to the dry weight content of the prereact, preferably of 0.2 wt. % or less, as measured according to the ISO 11402:2004 (KCN method).

[0050] The first amount of urea (U1) preferably ranges from 34-85 wt. %, for example 44 wt. %, preferably from 48-85 wt. %, preferably from 65 to 80 wt. %, for example 75 wt. %, related to the total amount of urea (Ut).

[0051] Particularly good results of prereact stability, low free formaldehyde prereact content and low formaldehyde emissions have been achieved when using a resole with free formaldehyde content of less than 6 wt. % related to the dry weight content of the resole, contacted with a first amount of urea (U1) of at least 34 wt. %, more preferably at least 48 wt. %, more preferably at least 65 wt. %, relative to the total amount of urea (Ut).

[0052] In a subsequent step c), the phenol-formaldehyde-urea prereact formed in step b) is contacted with a second amount of urea (U2) to produce a mixture of prereact and urea. The start point of this step c) is separated in time from the end of step b), preferably at least for 24 hours, and more preferably at least for 72 hours. This step c) will usually be done by the mineral wool manufacturer at its facilities, shortly before the prereact and urea mixture is applied to the mineral fibers in the manufacture of mineral wool products. In contrast with this, the preparation of the phenol-formaldehyde-urea prereact will usually be done by the resole producer, who delivers the finished prereact to the mineral wool manufacturer.

[0053] In step c), the phenol-formaldehyde-urea prereact and the second amount of urea (U2) can be contacted and well mixed in a container adapted for this purpose, or alternatively, and currently less preferred, the contacting/mixing can be done continuously in-line in the mineral wool manufacturing line, as the mixture is transported to the binder application station. The prereact and second amount of urea (U2) mixture is preferably kept at a temperature lower than 50 C., preferably lower than 40 C., more preferably under 30 C. at all time, and more preferably between 20-25 C. until it is applied onto the surface of the mineral fibers, to avoid premature advance of the condensation reaction.

[0054] The phenol-formaldehyde-urea prereact and the second amount of urea (U2) are contacted and mixed shortly before the resulting mixture is applied to the surface of mineral fibers, preferably less than 48 h before, and more preferably less than 24 h before.

[0055] The method according to the invention foresees that the total amount of urea (Ut), this is, the sum of the first (U1) and second (U2) amounts of urea used in steps b) and c), relative to the sum of the dry weight of the phenol-formaldehyde resole and the total amount of urea(Ut), and the second amount of urea (U2), are used in the following ranges:

(i) when the total amount of urea (Ut) is between 30 and 35 wt. % relative to the sum of the dry weight content of the phenol-formaldehyde resole and the total amount of urea (Ut), the second amount of urea (U2) used in c) is between 20-35 wt. % of the total amount of urea (Ut); or
(ii) when the total amount of urea (Ut) is about 40 wt. % relative to the sum of the dry weight content of the phenol-formaldehyde resole and the total amount of urea (Ut), the second amount of urea (U2) used in c) is about 25 wt. % of the total amount of urea; or
(iii) when the total amount of urea (Ut) is between 42 and 50 wt. % relative to the sum of the dry weight content of the phenol-formaldehyde resole and the total amount of urea (Ut), the second amount of urea (U2) used in c) is between 15-52 wt. % of the total amount of urea (Ut); or
(iv) when the total amount of urea (Ut) is between 42 and 50 wt. % relative to the sum of the dry weight content of the phenol-formaldehyde resole and the total amount of urea (Ut), the second amount of urea (U2) used in c) is between 63% and 66 wt. % of the total amount of urea; or
(v) when the total amount of urea (Ut) is about 45 wt. % relative to the sum of the dry weight content of the phenol-formaldehyde resole and the total amount of urea (Ut), the second amount of urea (U2) used in c) is about 56 wt. % of the total amount of urea. The inventors surprisingly found that when this combination of features is used, the emissions of formaldehyde from the mineral wool products manufactured is significantly reduced compared with the case where the same total amount of urea is only used in the preparation of the prereact (without cold urea addition).

[0056] In order to manufacture mineral wool products according to the method of the invention, in a further step d), the mixture of phenol-formaldehyde-urea prereact and second amount of urea (U2) from step c) is applied to the surface of mineral fibers. The mixture of prereact and second amount urea (U2) is applied to the fibers as part of a binder. The binder optionally comprises additives employed either to assist in the manufacture of mineral wool products or to improve the mineral wool product properties. The binder is preferably an aqueous composition with a non-aqueous content in the range 4-15 wt. %, relative to the aqueous binder weight.

[0057] The optional additives comprised in the binder, in addition to the phenol-formaldehyde-urea prereact and the second amount of urea (U2), are preferably in a concentration of more than 1 wt. % and less than 30 wt. % related to the non-aqueous content of the binder, more preferably in a concentration of 5-25 wt. %, more preferably in a concentration of 10-20 wt. %, even more preferably in a concentration of 15-18 wt. %. The optional additives include at least one additive selected from the following groups of substances: i) curing catalysts, such as ammonium sulfate; ii) resin extenders different than urea, such as carbohydrates; iii) anti-dust agents such as mineral oil; iv) adhesion promoters such as silanes; and v) water repellent agents such as silicones, and more particularly reactive silicones. It is particularly preferred to include up to 10 wt. % of molasses and/or glucose as resin extender.

[0058] In certain embodiments, resins are excluded from the optional additives. In particular embodiments, the addition of sodium-silicate resins, polyester resins, melamine resins, novolac resins, epoxi resins, polyamide resins, furane-based resins, phosphate resins, or combinations thereof is excluded.

[0059] In preferred embodiments, the mixture of phenol-formaldehyde-urea prereact and second amount of urea (U2) will be largely diluted with fresh or process water, and optionally mixed with the additives in order to prepare the binder. Wherein no additives are used, the binder might comprise only the prereact and second amount of urea (U2) mixture, preferably diluted with water to the desired concentration.

[0060] The concentration of the different components in the binder preferably ranges from 40-90 wt. % of phenol-formaldehyde resole, 30-50 wt. % total urea (sum of first (U1) and second (U2) amounts of urea) and 1-20 wt. % of additives, based on the non-aqueous weight of the binder.

[0061] In preferred embodiments, the mixture of the phenol-formaldehyde-urea prereact and the second amount of urea (U2) is applied in atomized form to the attenuated individual fine mineral fibers being produced by a fiberizer from a hot molten mineral mixture. The atomization can be produced by spraying nozzles or similar devices oriented in a direction so that the sprayed mixture meets the surface of the attenuated fibers. The mixture contacts the surface of the mineral fibers when they are still warm. The impregnated fibers are collected on a foraminous conveyor in a forming chamber, where a primary uncured mat is formed. A significant part of the water comprised in the binder is evaporated at this stage.

[0062] Next, the primary mat is densified and transported by a series of conveyors to a heated curing oven. The binder is then cured at temperatures above 100 C., preferably at a temperature between 140-180 C., more preferably between 150-170 C., even more preferably between 155-165 C. The curing time preferably ranges from 2-5 min. The cured mineral wool mat is afterwards trimmed and shaped into its final dimensions, optionally rolled up, and packaged.

[0063] In certain embodiments, the phenol-formaldehyde-urea prereact and second amount of urea (U2) mixture is applied as part of a binder to the fibers in an amount to produce a content of solid binder related to the weight of the mineral fibers in the final mineral wool product after curing between 1.5 wt. % and 15 wt. %, preferably between 3 and 12 wt. %, even more preferably between 5 and 10 wt. %. The amount of cured binder relative to the mineral fiber weight in the mineral wool product is measured as LOI (loss on ignition) according to ISO 29771:2008.Thus, in a preferred embodiment the mineral wool product obtained by the method of the invention has a LOI of between 1.5 wt. % and 15 wt. %.

[0064] It has been found that when the phenol-formaldehyde resole has a free formaldehyde content lower than 6 wt. % related to the dry weight content of the resole, the second amount of urea (U2) ranges from 20-35 wt. % related to the total amount of urea (Ut); and the total amount of urea (Ut) adds up to 30-35 wt. % related to the sum of the dry weight of the resole and the total weight amount of urea (Ut), or when the second amount of urea (U2) ranges from 63-66 wt. % related to the total amount of urea (Ut); and the total amount of urea (Ut) adds up to 42-50 wt. % related to the sum of the dry weight of the resole and the total weight amount of urea (Ut), and without the need of using further formaldehyde scavengers, the mineral wool products manufactured according to this embodiment of the method of the invention, surprisingly exhibit formaldehyde emissions lower than 10 g/ms, and even lower than 8 g/ms, when measured according to ISO 16000-3:2011. Thus, in one aspect the present invention relates to a mineral wool product with formaldehyde emissions lower than 10 g/ms obtained by the method of the invention, preferably with formaldehyde emissions lower than lower than 8 g/ms when measured according to ISO 16000-3:2011. In a preferred embodiment, the mineral wool product obtained by the method of the invention further has a LOI of between 1.5 wt. % and 15 wt. %. The mineral wool product obtained by the method of the invention exhibits a non-acidic behavior in pH terms, namely when said mineral product is in contact with water, said water does not acquire an acid pH.

TESTING METHODS

[0065] The free formaldehyde content of the resole is measured for instance according to the international standard ISO 9397:1995, using the hydroxylamine hydrochloride procedure. This method involves the following general principle: The formaldehyde present in the resole is converted to the oxime with hydroxylamine hydrochloride. Then the hydrochloric acid formed during this reaction is determined by potentiometric back-titration, using a sodium hydroxide solution. The free formaldehyde content of the resole with respect to its dry content is then calculated from the amount of sodium hydroxide.

[0066] The free formaldehyde content of the phenol-formaldehyde-urea prereact is measured according to ISO 11402:2004, using the KCN method. Alternative methods for measuring the free formaldehyde content are HPLC or NMR.

[0067] The free or unreacted phenol content of the resole is measured for instance according to the international standard ISO 8974:2002. This international standard determines the free phenol content by gas chromatography using either a weighed amount of internal standard being added to the test portion or using a stock solution of internal standard. The internal standard used is 1-octanol. The free phenol content of the resole is then calculated with respect to its dry weight content.

[0068] The content of nitrogen in the phenol-formaldehyde resole is measured for instance with the Kjeldahl method.

[0069] The resole water dilutability (or miscibility) is measured with demineralized water and at 20 C. according to the international standard ISO 8989:1995 method. Resole dilutability is a measure of the mass of demineralized water relative to the mass of aqueous resole which results in permanent turbidity in the liquid resole. This method involves adding water to the resole until turbidity persists for a minimum of 30 seconds after agitation.

[0070] The viscosity of the resole is measured at 20 C. using a Brookfield viscometer, for example with the spindle 1 and r.p.m. The viscosity as referred to in the present invention is based on an aqueous resole having a dry weight content of 45 wt. %.

[0071] The B-Stage gel-time of the resole is measured at 130 C. according to the international standard ISO 8987:2005.

[0072] The content of cured binder in the mineral wool product (LOI) is measured according to the international standard ISO 29771:2008.

[0073] The amount of formaldehyde emissions from mineral wool products is measured from freshly manufactured samples, for instance, according to ISO 16000-3:2011. The method involves placing the fresh samples into a 212 1 acclimatized glass chamber equipped with a ventilator and set at a temperature 231 C., a relative humidity of 505%, air flow 0.20.1 m/s and an air exchange rate 0.5 h-15% for 28 days. Other settings are the loading factor of 1 m.sup.2 of sample surface per m.sup.3 of test chamber volume, and a specific area air exchange rate of 0.5 m.sup.3/m.sup.2 h. Emitted formaldehyde is determined in g/ms from air samples of the air in the chamber taken on to adsorbent cartridges coated with 2,4-dinitrophenylhydrazine (DNPH) at the time of the measurement (after 28 days in this case) and the hydrazones formed are subsequently analyzed by high performance liquid chromatography (HPLC) with detection by ultraviolet absorption.

EXAMPLES

[0074] A phenol-formaldehyde resole characterized by having a pH 9,6, viscosity 20 mPa.Math.s, dilutability in demineralized water >50, B-Stage gel-time of 3 min, 45 wt. % dry weight content supplied by a commercial provider, was employed for the manufacture of glass wool products. This resole was further characterized by a phenol content under 2 wt. %, nitrogen content <0.6 wt. %, and free formaldehyde content of 6 wt. %, all wt. % based on the resole dry weight content.

[0075] In inventive examples, two amounts of urea U1 and U2 were added to the phenol-formaldehyde resole in two separated steps. The first amount U1 was used to prepare a phenol-formaldehyde-urea prereact, and it was added to the same reactor where the resole had been prepared, once the condensation reaction was quenched. The mixture was allowed to react for several hours in the same reactor. One week later, the second amount of urea U2 was added to the prereact and mixed under agitation at approx. 25 C. for 1 hour, before it was employed for the manufacture of glass wool products.

[0076] A binder mixture was prepared by mixing the resulting mixture of prereact and second amount of urea U2, with water, ammonium sulfate, mineral oil and aminopropyltrimethoxysilane. The binder was applied to the surface of glass wool fibers, in form of small drops, by spraying rings, as the fibers from a disc fiberizer, attenuated by hot air blowers, fell down to a foraminous conveyor belt. The glass fibers bearing the binder were collected in the form of an uncured mat, densified and transported to a curing oven, where the binder was heated to a temperature between 140-180 C. for 3-5 minutes to produce its curing. After curing, the produced glass wool mat had a density of 29.5 kg/m3 and a thickness of 100 mm. The cured binder content measured as LOI was 6.5 wt. % related to the weight of the fibers.

[0077] In the comparative example, the same procedure was repeated, except that all the urea was added undivided, in one single step, for the formation of the prereact, and that no urea was subsequently added to the prereact.

[0078] Table 1 depicts the amounts of urea U1 and U2 as weight percentages relative to the total amount of urea, in inventive and comparative examples, as well as the results obtained of formaldehyde emissions after 28 days from the glass wool products manufactured.

TABLE-US-00001 TABLE 1 U1 First U2 Second Formaldehyde Urea amount of Urea amount of urea emissions Total (wt. % of Ut) (wt. % of Ut) (g/m.sup.3) Example 1 45% 66% 33% 7 PFU30 + U15 Example 2 35% 71% 29% 7 PFU25 + U10 Example 3: 45% 33% 66% 6 PFU15 + U30 Example 4: 30% 66% 33% 9 PFU20 + U10 Example 5: 40% 75% 25% 8 PFU20 + U10 Example 6: 45% 44% 56% 7 PFU20 + U10 Comparative 30% 100% 0% 12 Example (PFU30)

[0079] The phenol-formaldehyde-urea prereact of examples 1 to 6 had a free formaldehyde content of <0.2 wt. % related to the dry weight of the prereact.