IE43271B1 - Aqueous solutions of etherified melamine formaldehyde resins - Google Patents

Abstract

1501534 Non - woven fabric SAINTGOBAIN INDUSTRIES 6 April 1976 [30 April 1975] 13897/76 Heading D1R [Also in Division C3] A web of glass fibres is bonded by immersing it in a starch size containing a modified melamine - formaldehyde resin and polyvinyl acetate, draining it and drying it. The modified melamine - formaldehyde resin is obtained in the Examples by adding melamine over 12 minutes to a mixture of 36% formaldehyde, ethylene glycol and triethanolamine to give molar ratios of melamine to these ingredients of 1:6.75-10:4:0.33, the mixture is cooled to 35‹C when the turbidity point is 50‹C; H 2 SO 4 is added over 30 mins. and the mixture is kept for 90 mins. at pH 2 and 35‹C. the pH is adjusted to 7.2 with a further 0.33 moles (per mole of melamine) of triethanolamine, and NaOH as necessary and the mixture left at 70‹C for 5 hrs.; then 0.8 moles (per mole of melamine) of urea pellets are added. In further Examples there is used 1.2 moles of urea (Ex. 7); glycorol, di- or triethylene glycol, d - glucose or sucrose or sucrose/ethylene glycol mixture (Exs. 10 and 11): HCI, H 3 PO 4 , HNO 7 ,H - COOH or ClCH 2 COOH (Ex. 15).

Description

The present invention relates to aqueous solutions of melamine formaldehyde resins.

Processes for the preparation of such resins have already been disclosed, in particular in German Patent Application (DAS) No. 2005166 laid open to inspection on 5th February 1970. In this prior process, alkaline condensation of melamine with formaldehyde is carried out in the presence of a polyol. The formaldehyde is put into the process in the form of solid paraformaldehyde. One serious disadvantage of using paraformaldehyde is that the cost price of anhydrous formaldehyde per kg is 2 to 3 times higher in this form than in the form of the aqueous solution.

Etherified tetramethylolmelamines are obtained by this prior process in a practically anhydrous form or in alcoholic solution. .

For certain applications of etherified melamine formaldehyde resins, there is a demand for aqueous solutions of such resins with a long storage life and low free formaldehyde content.

According to the invention we provide a process for the preparation of etherified melamine formaldehyde resins, wherein in a first stage, melamine is reacted with formaldehyde by adding solid melamine with stirring to a solution containing: >5 a 30 to 50% by weight aqueous solution of formaldehyde, in a quantity corresponding to a final molar ratio of formaldehyde to melamine of from 5:1 to 1:1; - 2 43271 one or more aliphatic polyols containing only C, H and 0 atoms in a quantity corresponding to a molar ratio of polyol to melamine of from 3:1 to 5:1; and triethanolamine in a quantity corresponding to a molar ratio of triethanolamine to melamine of from 0.2:1 to 0.6:1; at a temperature of from r0 to 70°C the pH after the addition of the melamine being from 8.Ξ to 9.5, and the reaction is stopped by rapid cooling to a temperature of from 20 to 40°C when the turbidity point is from 40 to 65°C; In a second stage, etherification is carried out by lowering the pH of the reaction mixture obtained from the first stage to a value of from 1.5 to 3.0 by addition of a pure acid or of a concentrated aqueous solution of an acid while maintaining the temperature at the same level as at the end of the first stage, and the solution obtained at the end of the etherification reaction is neutralised by addition of base which includes at least one third mol of triethanolamine per mol of melamine; in a third stage, the solution obtained at the end of the second stage is ripened by keeping it for a length of time between 2 and 5 hours at a temperature of between 50 and 90°C; in a fourth stage, the proportion of free formaldehyde in the solution obtained at the end of the third stage is reduced by the addition of urea to a final free formaldehyde content not exceeding 6% by weight.

Preferably, the solution of formaldehyde which is reacted with the melamine in the first stage contains 36% by weight of formaldehyde. The final molar ratio of formaldehyde to melamine is preferably from 6.5:1 to 10:1, the molar ratio of polyol to melamine is preferably from 3.5:1 to 4:1, and the molar ratio of triethanolamine to melamine is preferably from 0.3:1 to 0.4:1. The temperature of the reaction between the melamine and the formaldehyde is preferably 63 to 68°C, and the pH after the addition of the melamine is preferably 8.8 to 9.2. Preferably, the reaction qf the melamine with the formaldehyde is stopped by cooling to 33 to 37°C.

Preferably, the solution obtained at the end of the second stage is ripened at 70 to 85°C.

The reaction time for etherification, calculated from the introduction of the acid to the beginning of neutralisation, is preferably from 105 to 135 minutes, and the turbidity point is preferably from 45 to 55°C.

In the fourth stage, the reduction in the formaldehyde content is preferably achieved by the addition of from 0.8 to 1.2 moles of solid urea per mole of melamine.

The resins obtained. according to the invention are distinguished by an exceptionally high molecular ratio of formaldehyde to melamine, hereinafter referred to as ratio, M by good dilutability with water, by a storage life at room temperature of at least 2 months and by a free formaldehyde content of less than 6% by weight.

By dilutability with water is meant the maximum quantity of water, in terms of volume per 100 volumes of aqueous solution of the resin, which can be added to the resin at a - 4 43271 temperature of 25°C with stirring before cloudiness appears.

By storage life at room temperature is meant the length of time after their manufacture during which aqueous solutions of the resins kept at a temperature of between 15°C and 25°C maintain a viscosity of below 800 centipoises measured at 25°C and a dilutability with water of at least 1200.

The respective limiting values of the two characteristics defined above refer to aqueous solutions of resins according to the invention for a storage life of at least two months, which is the minimum time liable to elapse before their industrial utilisation.

The resins are used mainly as binders for glass fibre sheets in combination with other products, the whole combination constituting a glue or size for the said fibres.

The present aqueous solutions of resins impart excellent tensile strength and suppleness to the glass fibre sheets.

The table below, which shows some of the differences 20 between the present process and the prior art process mentioned above, clearly indicates the advantages obtained by the process according to the invention. ~ 43271 •CT Ratio Present invention DAS KO.2005166 5 to 11 and preferably 6.5 to 10 2 to 6 Mols of diol/mols of melamine 5.0 to 5.0 and preferably 5.5 to 4.0 0.4 to 1.2 and preferably 0.7 to 1.1 Hols of triethanolamine/mols of melamine 0.2 to 0.6 and preferably 0.5 to 0.4 not indicated in the claims 0.057 (Example 5) Temperature of alkaline condensation 60 to ?0°C and preferably 65 to 68°0 80 to 140Ό and preferably 85 to 1OO°O It is clear from what has been.said that the resins according to the present invention contain a larger number of methylol groups per molecule of melamine and are much more highly etherified by a polyol since in the process according to DAS No. 2 005 166 only a small quantity of polyol is used at the stage of alkaline condensation while a large quantity of a lower monohydric alcohol, for example methanol, is added at the stage of etherification (more than 6 mols and particularly from 8 to 20 mols per mol Of melamine). It would thus appear that this lower monohydric alcohol and not the polyol is the true etherification agent in the said DAS.

In the process according to the present invention, on the other hand, the polyol is the major etherifying agent, the other hydroxyl compoundswhich may be present but in much smaller quantity being triethanolamine and methanol, of which a small quantity may be present in the aqueous formaldehyde solution. In particular no alcohol is added other than the polyol or polyols originally put into the - 6 43271 process.

Another distinguishing feature of the resins according to the present invention is that they contain a considerable quantity of triethanolamine which becomes attached to the methylolmelamines during the stage of etherification.

The presence of these residues of triethanolamine in the molecule of resin finally obtained increases its solubility in water. By contrast, the very small quantity of triethanolamine used in DAS No. 2 005 165 obviously serves only to obtain the necessary pH for the alkaline condensation reaction.

The addition of triethanolamine after etherification also increases the dilutability of the solution, as will be seen hereinafter.

According to the invention, the formaldehyde used as starting material is an approximately 56% aqueous solution which is obtainable commercially at a much lower cost than solid paraformaldehyde.

The operating conditions of the four stages of the process are described in more detail below. 1st Stage Commercial melamine may be used but it should contain at least 99% by weight of melamine and 99% by weight of the particles should have a diameter less than 160 μ.

If the particles are too large, they interfere with the pi'oeess of dissolving the melamine in the reaction mixture.

The formaldehyde should be used in the form of an aqueous solution having a concentration of 50 to 50% by weight. An aqueous 56% solution would preferably be employed - 7 43271 because it is so widely available. _ These solutions should net contain more than 10% by weight of methanol and should preferably contain less than V/, by weight thereof in order to prevent the presence of methoxy groups in the ebherified resin. In order to increase the dilutability with water as much as possible, it is in fact preferable to carry out etherification mainly with polyol or with triethanolamine.

The F/M ratio should be between 5 and 11 and preferably between 6.5 and 10. Values below 5 would have a deleterious effect oir the properties and particularly on the tensile strength of the glass fibre sheets. Moreover, the resins would then have too low a dilurability with water. Values higher than 10 would result in aqueous solutions having too low a solid content, which are of little interest industrially. F/M ratios of · 5, 6.5, 10 and 11, respectively, correspond substantially to solid contents of 52,5θι 44 and 41% if the formaldehyde used as starting material is an aqueous 36% by weight solution.

The alkaline condensation reaction is cari’ied out at a pH of between 8.5 and 9·5> preferably between 8.8 and 9·2.

This pll is adjusted by the addition of triethanolamine to the reaction mixture.

The quantity of triethanolamine should be between 0.2 and 0.6, preferably 0.3 to 0.4- mols pex· mol of melamine.

This ratio will be referred to below as TEA/H ratio. The quantities given are widely in excess of those strictly required for adjustment of the pH of the reaction to the values indicated. The reason for using such high ratios is, as already indicated above, to confer on the recins according to the invention a high solubility in water. - 8 43271 The reaction is carried out as follows: The required quantities of aqueous formaldehyde solution, polyol and triethanolamine are first mixed aid the mixture is heated to the reaction temperature of between 60°C and 70°G, preferably between 63°G and 68°G, with continued stirring. If temperatures below 60°C are employed, melamine dissolves too slowly in the reaction mixture.

Melamine is then added, preferably gradually over 10 to 15 minutes. The same temperature is maintained and stirring is then continued for a period which may vary from 30 to 90 minutes.

The reaction is then stopped by cooling to a temperature of between 20 and 40°C, preferably between 33 and 37°0.

It is stopped by rapid cooling at a precise moment 15 which is determined by the turbidity point of the reaction mixture, which is measured and followed in the course of the reaction.

This turbidity point is characteristic of the degree of alkaline condensation reached. It is measured by success20 ively removing samples of the reaction mixture at regular intervals, The samples are cooled and shaken at the same time and the temperature at which turbidity first appears is noted. This temperature, which is quite low at the beginning of the reaction, rises progressively as the reaction continues The alkaline condensation reaction is thus stopped by rapid cooling when the turbidity point is between 40°0 and 65°C, preferably between 45°C and 55°G. This takes from 30 to 90 minutes, as already indicated above. , If the reaction .is stopped when the turbidity point is - 9 43271 still below 4O°C, the reaction mixture has a high viscosity 4‘ when cooled, so that it is then very difficult to maintain its homogeneity by stirring. On the other hand; if the turbidity point is allowed to rise above the reaction temperature, the reaction mixture becomes opaque at the reaction temperature. Even if the reaction temperature were 70°C, it would be very difficult to measure a turbidity point higher than 65°C because it would be too close to the reaction temperature.

It should be noted that reaction temperatures above 70°C make it impossible to measure the turbidity point and to follow the high reaction velocity at these temperatures. 2nd Stage; Etherification This is the stage of etherification of methylolmelamines obtained in Stage 1 by means of the polyol or polyols already introduced into the reaction mixture. The following polyols for example may be used: Ethylene glycols, diethyleneglycol, triethylene glycol, glycerol, saccharose and d-glucose.

Ethylene glycol is preferred on account of its low cost and ready availability.

Certain mixtures of polyols are also of interest.

Thus, for example, the viscosity of the final resin can be controlled by using mixtures containing varying proportions of ethylene glycol and saccharose, an increase in the proportion of saccharose tending to increase the viscosity.

The total quantity of polyol or polyols used should be between 3.0 and 5.0 and preferably between 3.5 and 4.0 mols per mol of melamine. This ratio is referred to below as the P/M ratio. If insufficient polyol is used, the dilutability of the resin with water becomes too low. However, - 10 43271 there is no point in using an excess of polyol since one cannot thereby obtain a greater increase in dilutability.

The acid used for lowering the pH of Stage 1 to that of Stage 2 is pure acid or a concentrated aqueous solution so that the final solid content of the aqueous resin solution will not be unnecessarily reduced.

One of the following acids may, for example, be used: sulphuric, hydrochloric, orthophosphoric, nitric, formic and monoehloroacetic acid.

The reaction mixture is cooled immediately after alkaline condensation, as already mentioned above, and while maintaining the temperature constant the reaction mixture is acidified to the pH required for the given temperature. It is under these conditions of temperature and pH that the etherification reaction is then carried out.

The above conditions must be strictly observed. If etherification is carried out at too high a pH and/or temperature, the viscosity of the resin will be too high and above all it will increase too rapidly in storage so that in extreme cases it will not even be possible to use the resin immediately after its preparation. On the other hand, too low a pH and/or temperature of etherification will result in a resin which has a low viscosity and high dilutability with water but the glass fibre sheets produced will have insufficient tensile strength for practical purposes.

Preferably, etherification is carried out at 20°C at pH 1.5, or 40°C at pH 3.0, or at a temperature between from 20°C to 40°C and a pH 1.5 to pH 3, generally the higher the temperature within this range, the higher the pH. 4327 More preferably, the reaction is carried out at a temperature from 33 to 37°C at a pH 1.8 to 2.2.

After the addition of acid, it is found that the originally opaque reaction mixture becomes clear at the end of a period of time which varies according to the turbidity point. The etherification reaction is then continued for a certain length of time beyond this stage at the same temperature before it is stopped by neutralisation.

The terms opaque stage and clear stage of etherification will be Used hereinafter to denote respectively the periods of time before and after the moment when the reaction mixture becomes clear.

The following conditions should preferably be observed during the stage of etherification: The acid should be run in very evenly over a period of between 25 and 35 minutes and more preferably between 28 and 32 minutes.

It has been found that for a given total etherification time, a reduction in the time during which the acid is run in substantially increases the final viscosity of the aqueous resin solution.

Moreover, the acid must be added slowly in order to maintain a constant temperature in spite of the heat released by the addition of acid in the reaction mixture.

The total etherification time, measured from the beginning of the addition of acid to the moment of neutralisation, should be between 50 and 180 minutes, and it is preferably between 105 and 135 minutes for a turbidity point of between 45°C and 55°C.

It should be understood that these time limits are valid for the pH and temperature values given above.

It is found in practice that for the above values of turbidity point, pH and temperature, the minimum duration of the opaque phase is 50 minutes, measured from the onset of the inflow of acid.

If a total etherification time of 180 minutes is exceeded for the above values of turbidity point, pH and temperature, the viscosity of the resins is found to be too high and their dilutability with water substantially below 1200 immediately after their manufacture. It is also found that when such resins are kept at room temperature, their viscosity rapidly increases and their dilutability with water decreases equally rapidly.

Immediately after their manufacture, the resins according to the present invention have a viscosity of between about 30 and about 200 cP measured at 25°C, which is quite low.

It should be remembered that the minimum storage time of two months for these resins means that at the end of this time their viscosity should not be 'above 800 cPs and their dilutability with water not less than 1200. It is well ’•s. known that normal ageing of resins tends to increase their viscosity and reduce their dilutability with water.

The base used for neutralisation should, as in the first stage of the process consist entirely of triethanolamine or contain at least one third mol of triethanolamine per mol of melanin;·:, the remainder of the neutralising agent being another base, e.g. a 50% by weight solution of NaOH.

It is found that if neutralisation is carried out entirely with HaOH, the dilutability of the resins,with water becomes very low and in extreme cases the resins precipitate on neutralisation. The object of adding this fresh quantity of triethanolamine is again to promote solubil ity of the resin in water.

A pH of from 7.0 to 7.5 is thereby obtained, which corresponds substantially to neutrality. 3rd Stage.

This Sage of . ripening is important since it improves two of the properties of glass fibre sheets bonded with a binder prepared with the aid of the aqueous resin solutions according to the present invention.

It was found that an increase in the duration of this •’•ripening stage caused the., flexibility of the glass fibre sheets to change in the same direction as their tensile . strength.

Definition and measurement of the flexibility index A sheet of glass fibres is cut up into 60 samples measur ing 25 x 5 cm. 30 of these samples are used to measure the tensile strength, and the mean of the measurements is taken. once The 30 other samples are each folded up/under the follow ing conditions: A metal plate having a length of 25 cm, a *'S. width of 5 cm and a thickness of 2 mm has two hinges at its centre, enabling it to be folded into two half plates each measuring 12.5 cm in length. Each sample of glass sheet is placed flat ’on this plate without folding and two other plates measuring 12.5 cm x 5 cm are placed on the sheet.

With the sample thus held flat between the hinged plate and the two half plates, the whole arrangement is folded through 180° about the hinge. After folding, the distance between the two halves of the sample still held between the plates as described above is 10 mm.

The tensile strength of the JO samples folded as described above is measured and the mean value of these measurements is taken. The loss in tensile strength after folding is calculated as a percentage.

The flexibility index is a number between 0 and 10 as indicated in the following Table: Loss of tensile strength after Flexibility index folding in % 0 to 4 10 4 to 10 9 10 to 20 8 20 to 50 7 30 to 40 6 40 to 50 5 50 to 60 4 60 to 70 3 70 to 80 2 80 to 90 1 90 to 100 0 , It is found that a slight reduction in the free formaldehyde content of the aqueous resin solution and a gradual increase in viscosity occur during the stage of ripening.

This is why the following conditions must be observed during the ripening stage in order that the viscosity will not increase unduly to the detriment of the possible storage life of the resin solution finally obtained: At the end of Stage 2, after neutralisation, the reaction mixture should he heated to a temperature of between 50 and 90°G, preferably between 70 and 85°0, without change in pH; 32 71 this temperature should be maintained for between 2 and 5 hours.

Under these conditions, the aqueous solution of resin remains dilutable with water to an extent of at least 12 times its own volume.

If the ripening time exceeds 5 hours at the temperatures indicated above, the resin becomes excessively viscous.

If, on the other hand, ripening is stopped before 2 hours have passed, always using the same temperature range, no further improvement in the flexibility of the glass fibre sheet is obtained. 4th Stage: The higher the initial F/M ratio, the higher will be the free formaldehyde content of the aqueous resin solutions after the ripening stage. These formaldehyde contents are of the order of 6 to 12% or even higher.

Such free formaldehyde concentrations interfere with the utilisation of the solutions because the formaldehyde yapoucs are am irritant to the eyes and the respiratory tracts of the operators.

It is therefore the main object of this 4th stage of the process to reduce the free formaldehyde content of the aqueous resin solutions to below 6%. At these reduced concentrations, the irritant vapours are emitted into the air only in quantities tolerable to the operators.

This operation also has two other advantages: One is the increase in tensile strength of the glass fibre sheets; the other is the reduction iu the rate of increase in the viscosity of the aqueous resin solutions during storage and consequently an increase in the possible storage life.

This fourth and last stage consists of adding urea - 16 43371 to the aqueous resin solution at the temperature employed at the end of Stage 3 in amounts of 0.6 to 1.6 and preferably 0.8 to 1.2 mol per mol of melamine, the quantity depending on the initial F/M ratio and consequently on the concentration of free formaldehyde in the reaction mixture at the end of Stage 3· Thin molar ratio of urea to melamine will be referred to. hereinafter as the U/H ratio.

The urea is used in the solid form, as urea pellets, firstly because its endothermic solution in the reaction mixture lowers the reaction temperature and secondly because in this form it will not reduce the final solid content in the way that an aqueous urea solution would.

The product is then left to cool at room temperature for a period of from 12 to 24- hours before it is stored or put into use.

In the examples which follow, tho concentrations are given in percentages by weight, the viscosity is measured with a Brookfield viscosimeter at 25°0 and the dilutability is measured at 25°C and expressed in terms of volumes of water per 100 volumes of resin.

EXAMPLE 1 STAGE 1 562 g of an aqueous formaldehyde solution containing 36% of formaldehyde and 0.55’ of methanol, 248 g of ethylene glycol and 49-5 S of triethanolamine are introduced into a 1 litre reaction vessel equipped with reflux condenser, stirrer and thermometer. The reaction mixture is heated to 65°C with stirring. When this temperature is reached, 126 g of melamine are added in the course of 12 minutes.

Condensation is carried out at 65e0 until a turbidity point of 50°C is obtained. The temperature is then rapidly reduced to 35°C.

STAGE II g of concentrated sulphuric acid are added at a uniform rate over 30 minutes until the pH has been reduced to 2. Etherification is then continued for 1 hour and 30 minutes at 35°C.

STAGE III At the end of etherification, the pH of the reaction mixture is adjusted to 7-2 by the addition of 49.5 E of triethanolamine and 50 g of a 50% sodium hydroxide solution.

The temperature is then raised to 70°C and kept constant for 5 hours.

STAGE IV At the end of these 5 hours, 48 g of urea are introduced at a temperature of about 60°C while the iresin is cooled.

The resin obtained has the following characteristics: - 18 4327! F/M ratio = 6.75 P/M ratio = 4 TEA/M ratio = 0.35 number of mols of triethanolamine added after etherifi5 cation per mol of melamine: 0.35 U/M ratio = 0.8 Solid content: 50.1% viscosity: 94 cP free formaldehyde content: 1.9% dilutability: infinite ( >2,000) pH: 7.2 after 2 months storage: dilutability : infinite ( >2000) viscosity : 160 cPs.

Preparation of size Starch paste: An aqueous dispersion is prepared from a potato starch modified by treatment with ethylene oxide and having a concenti’ation of 8% calculated in the form of anhydrous starch. Steam is bubbled through this dispersion until the temperature is raised to 9S°C. The introduction of steam is continued for a further 20 minutes and the dispersion is then left to cool. When the temperature is down to 25-5O°O, the paste is ready for use. 110 kg of' the paste are mixed with a quantity of the above mentioned aqueous melamine formaldehyde resin solution corresponding to a dry weight of 1.2 kg.

In addition, 1.578 kg of an emulsion having a 58% solid content of polyvinyl acetate homopolymer plasticized with 50% of dibutyl phthalate, calculated on the quantity of polymer, are weighed out. The emulsion is thon diluted with its own weight of water.

The diluted, emulsion is added to the mixture described above. The whole mixture is then homogenised hy stirring for 10 minutes. It constitutes a concentrated size.

When ready for use, the concentrated size is diluted with the necessary quantity of water to reduce the solid content’ to 2.2%.

Preparation of the glass fibre sheet A non-bonded web of staple glass fibres is used, hereinafter referred to as primitive sheet. -This web was obtained by evenly distributing staple glass fibres over a conveyor belt made of sheet metal. The fibres had been obtained by steam drawing threads of molten glass extruded through the apertures in the lower part of a platinum spineret.. These glass fibres had a mean diameter of about 16 microns. The primitive sheet used weighs 80-5 · The primitive sheet is immersed in the previously prepared size in the form of a continuous hand placed between two metal conveyor belts.

Excess size retained by .the primitive sheet is removed continuously by extraction with the aid of a .vacuum box placed under the lower conveyor belt. The vacuum in the box is regulated so that after drying the sheet will contain 20% by weight of binder, measured as dry matter based on the total weight of tho glass and dry binder.

The sized and dried primitive sheet is then passed continuously for 2 minutes through a circulating air oven heated to 145°0.

The following properties are then measured on the finished shefet; 43371 tensile strength: 5·5 kg/em flexibility index: 7· EXAMPLE 2 A melamine formaldehyde resin is prepared by the method 5 described in Example 1, using the following quantities of substances: 36% formaldehyde 666 g ethylene glycol 248 g triethanolamine 49.5 g melamine .126 g concentrated sulphuric acid 56 g 50% aqueous sodium hydroxide solution 50 g urea 48 g tri ethanolamine 49.5 g The resin obtained has the following characteristics: F/M ratio: 8.0 Ρ/Il ratio: 4.0 TEA/M ratio: 0.33 number of mols of triethanolamine added after ether20 ification, per mol of melamine: 0.35 U/M ratio: 0.8 Solid content: 4-7.8% viscosity: 70 cP free formaldehyde content: 4-.0% dilutability:infinite ( >2000) pH: 7.2 After two months storage: dilutability: infinite (>2000) viscosity: 130 cP.

A size is prepared with this resin and applied to a '3271 primitive sheet v/hich is then stove dried by the method described in Example 1.

The following characteristics are measured on the finished sheet: Tensile strength: 5·θ kg/cm Flexibility index: 7 EXAMPLE 3 · .

A melamine formaldehyde resin is prepared by the method described in Example 1, using the following quantities of substances: 36% formaldehyde 750 g ethylene glycol 248 g triethanolamine 49.5 S melamine 126 g concentrated sulphuric acid 5θ g triethanolamine 49.5 S 50% aqueous sodium hydroxide solution 50 g urea 48, g This resin has the following characteristics: P/M ratio: 9.0 P/M rations 4 TEA/M ratio: 0.35 number of mols of triethanolamine added after etherification per mol of melamine: 0.35 U/M ratio: 0.8 solid content: 45.6% viscosity: 52 cP free formaldehyde content: 5·4% dilutability: infinite ( ^>2000) Λ : pH: 7.2 After two months storage: dilutability: viscosity: infinite ( ^2000) 100 cP This resin was used to prepare a sise which was applied to a primitive sheet and the sheet was then treated as described in Example 1.

The following characteristics were measured on the 5 finished sheet: Tensile strength: 5.9 kg/cm Flexibility index: 8 EXAMPLE 4 A melamine formaldehyde resin was prepared by the 10 method described in Example 1, using the following quantities of substances: 36% formaldehyde 666.5 E ethylene glycol 198.5 S triethanolamine 39.5 S melamine 101 g concentrated sulphuric acid 45 g triethanolamine 39·5 E 50% aqueous sodium hydroxide solution 40 g urea 3θ·3 E This resin has the following chai’acteristics: F/M ratio: 10.0 1-/M ratio: 4.0 TEA/ΓΙ ration: 0.33 number of mols of triethanolamine added after etherification per mol of melamine: 0.33 U/M ratio: 0.8 solid content: 43.2% viscosity: nt\ cP free formaldehyde content: 5·7% - 23 43271 dilutability: infinite ( /2000) pH: 7.2 After two months storage: dilutability: infinite ( /2000) viscosity: 92 cP A sise is prepared with the aid of the above resin and a sheet is manufactured by the method described in Example 1. This sheet is found to have the following characteristics: tensile strength: 6.2 kg/cm flexibility index: 7· If one compares the tensile strength of the sheets obtained in Examples 1,2, 3 and 4, it is found that this value increases with the P/M ratio.

Example No. P/M ratio Tensile strength of the sheets in kg/cm 1 6.75 5.5 2 ' 8.0 5.6 3 9.0 5.9 4 10.0 6.2 1 EXAMPLE 5 Alkaline condensation offormaldehyde and melamine is carried out at a temperature of 65¾ in a reactor equipped with high speed stirrer and heating means. The following quantities are used: ethylene glycol: 248 g (4 mol) triethanolamine: 49-5 S (0.33 mol) melamine: 126 g (1 mol) formaldehyde: quantity indicated below The 36% aqueous formaldehyde solution containing 0.5% of methanol is introduced into the reactor, glycol-’and triethanolamine are added and the mixture is heated to the - - ·’ reaction temperature. Melamine is then added in 12 minutes The following findings are obtained for increasing quantities'of aqueous formaldehyde solution: F/M ratio: 2.5: fhe reaction mixture remains turbid even after 5 hours -at 65ο0· When heating is continued beyond that, a solid mass of resin is finally obtained.

F/M ratio: 2.9: the reaction mixture is clear at the end of 90 minutes at 65°C. The operations corresponding to stages 2, 3 and 4 are carried out under the conditions indicated in Example 1. The resin finally obtained is not dilutable.

F/M ratio: 4.0: the reaction mixture of alkaline condensation becomes clear at the end of 50 minutes at 65°C. The proces of preparation is completed by the method ’described in Example 1. The resin obtained has a dilutability in water of only 1000.

This resin is used to prepare a size, and a'glass'fibre sheet is manufactured in accordance with the particulars I given in Example 1. ί The tensile strength of the sheet obtained is only 4.2 kg/cm.

This example shows the disadvantages of an F/M ratio of less than 5.0, namely insufficient dilutability of the resins with water and reduction in the pensile strength of the glass fibre sheets.

EXAMPLE 6 Three resins are prepared, observing all the conditions indicated in Example 1 except that the turbidity point is 12°0 in all these preparations. The temperature employed for alkaline condensation is varied from one preparation to another. The following results are obtained: · - 25 438*71 1st Preparation: Condensation temperature 6O°C. Condensation time 45 minutes. The resin obtained has a viscosity of 14 cP and a dilutability above 20C0. 2nd Preparation: Condensation temperature 65°C. Condensation time 35 minutes. The resin has a viscosity of 12 cP and a dilutability above 2000. , 3rd Preparation:, Condensation temperature 70°0· Condensation, time 23 minutes. The resin has a viscosity of 11 cP and a dilutability above 2000.

However, at the end of only 15 · days of storage, all these three resins have undergone such a high increase in viscosity that they have the consistency of a gel.

This example demonstrates the necessity of having a sufficiently high turbidity point for obtaining resins with a sufficiently long storage life. The. reduction in viscosity which results from lowering the turbidity point by comparison with Example 1 should also be noted.

\ EXAMPLE 7 A melamine formaldehyde resin is prepared by the method described in Example.4, using the following quantities of substances: 36% formaldehyde ethylene glycol triethanolamine melamine concentrated sulphuric acid triethanolamine 6^56.5 S 198.5 S 59.5 S 101 g *5 G 59-5 G 50% aqueous sodium hydroxide solution 40 g urea 57.5 g Λ The method of preparation employed, however, differs - 25 43271 from that of Example 4 in that alkaline condensation is continued to a turbidity point of 62°C instead of 50°C and the etherification time is 3 hours 10 minutes instead of 2 hours and the ripening stage is continued for 3 hours at a temperature of 85°C instead of 5 hours at 70°G.

The characteristics of this resin are the same as those of the resin from Example 4 except for the following features: U/H ratio: 1.2 Solid content: 43.3% viscosity: 80 cP free formaldehyde content: 4.9% dilutability: 1900 after two months storage: dilutability: 1400 viscosity: 210 cP.

Thin resin is used to prepare a size which is employed for manufacturing a sheet by the method described in Example 1 This sheet is found to have the following characteristics: Tensile strength: 6.7 kg/crfi Flexibility index: 6.

This example demonstrates’the possibility of preparing a resin according to the invention by stppping alkaline condensation at a turbidity point of 620¾. It also shows that the total etherification time must he adjusted according to the turbidity point. ΕλΛΗΕΕ 8 A rosin is prepared in accordance with, all the particular given in Example 4 except that a Ί.ΈΛ/Η ratio of only 0.1 is used for alkaline condensation instead of 0.53· The dilutability of the resulting resin is practically zero (< 50) and ios viscosity ia 275 cP.

This example illustrates clearly, by comparison with Example 4, the disadvantage of using too low a TEA/M ratio for alkaline condensation, that is to say the important function of triethanolamine, v/hich is to impart to the resin a high solubility in water and dilutability with water.

EXAMPLE 9 . < A resin is prepared by the method given, in Example 4 but using sodium hydroxide as catalyst for alkaline conden.sation instead of triethanolamine. The quantities of substances used are as follows: 36% formaldehyde ethylene glycol y 50% aqueous sodium hydroxide solution melamine concentrated sulphuric acid triethanolamine 50% aqueous sodium hydroxide solution The resin obtained after the stage of etherification and neutralisation has practically zero dilutability with water ( <( 100). If ripening is then carried out by heating under the conditions indicated in Example 4, the resin is converted to a gel.

This example shows, like the preceding Example 8, the important role of triethanolamine introduced at the stage of alkaline condensation, namely to confer on the resin the properties of high solubility in water and high dilutability v/ith water, properties v/hich in this case have not been obtained by means of sodium hydroxide.

EXAMPLE 10 666.5 g (8 mol) 198.5 g (5.2 mol) ml 101 g (0.8 mol) ml 39.5 S (0.264 mol) 7 ml.

This example illustrates the use of a certain number of - 28 43271 different polyols of ethylene glycol in the synthesis of the resins according to the present invention.

The preparations are carried out under all the conditions described in Example 1 except for the nature and quantities of polyols used ani certain particular characteristics of each glycol, which are indicated in the following table: Mature and quantities of polyols in gram mol Particular features | Results., and observations of pPGp^.2?(aC XOBS j Glycerol: 4 mol 3 hours of ripening at 75°O (Otago III) Dilutability: >2000 Viscosity: 90 cP Stable 2 months in storage Biethylene glycol: 4 mol d-glucose: 0.4 ethylene glycol: 3.0 Turbidity point 4?·'Ό obtained after 70 minutes at 65°C (Stage 1) Dilut ability: >2000 Viscosity: 94 cP Stable 2 months in storage Dilutability: >2000 Viscosity: 112 cP Stable 2 months in storage triethylene glycol: 4 mol Turbidity point 47° 0 obtained after 120 minutes at 65°C (Stage I) Dilutability: >2000 Viscosity: 98 cP Stable 2 months in storage EXAMPLE 11 ' Three melamine formaldehyde resins are prepared by the general method of preparation given in the previous examples and using the following quantifies of substances: 36% formaldehyde t ri et h an ο1amine melamine concentrated sulphuric acid tri cthanolamine 50% fiiuc-otip sodium hydroxide solution urea 583.3 g (7 mol) 49-5 5 (0.33 mol) 126 g (1 mol) g 4-9.5 g (0.33 mol) 50.0 g 48.0 g (0.:8 mol) Alkaline condensations are carried out at 65°0 and 43371 stopped when a turbidity point of 52°C is reached. The γ etherification reactions are carried out at pH 2.0 and at $ a temperature of JO’C. · The three preparations differ in the mixture of polyols used: Preparations A B C Mixture of polyols sucrose (saccharose) ' 342 g 171 S 86 g ethylene glycol 0 124 g 186 g Resin A was etherified for only 40 minutes because its viscosity was already very high by the end of that time; Rosins B and 0 were etherified foi? a total of 90 minutes. After neutralisation, the three prep.arations wore heated (ripening) for 5 hours at 70°0. ,,-95 E of water bad to be added-to resin A in the course of heating because of its progressive thickening.

The resins finally obtained have the following characteristics: A B C ratio 7.o 7.0 7.0 sucrose ar ratio melamine 1.0 0.5 0.25 ethylene glycol melamine 2.0 3.0 /M ratio 0.33 0.33 0.3? ber of mols of triethanolamine ed after etherification per mol aelamine 0,33 0.53 0.33 ratio 0.8 o.a . O.S id content in '/. 57.3 (X) 55» 6 54 .0 ios:i by in cP I 2100 I ;it ab l lit?,- ............... { 1 geo i 1100 > 2000 125 > 20-. 0 “'TO'”-43271 (X) Taking into account the water added in the course of ripening.

This example illustrates the possibility of obtaining resins in which the viscosities are very different from each other and adjustable as desired by varying the relative proportions of sucrose and ethylene glycol. In calculating the relative proportions of the two polyols in the three resins A, B and C indicated above, it was taken into account that since sucrose contains 8 alcoholic hydroxyl groups per molecule,, it should^be used in only one quarter of the molar quantity of diol. It is clear that only small proportions of sucrose can give rise to interesting resins for practical purposes.

EXAMPLE 12 Three preparations of resins/are carried out by the method described in Example 1 and using the quantities indicated In Example 1 except for the quantities of ethylene glycol.

In a first preparation, a F/M ratio of only 2.0 is employed. It is* found that the resin solidifies at the stage of etherification and cannot he redissolved by the addition of water.

A P/M ratio of 2.5 is used in a second preparation.

The resin does not solidify in the course of etherification but at the end it has a dilutability in water of only 1000.

A F/M ratio of 3.0 is employed in a third preparation. No difficulty is encountered in the preparation of this resin which finally has an infinite dilutability with water (>2000).

This example shows the necessity of using a F/M ratio of at lens!; 3.0 in order that the resins according to the - 31 43271 invention will have good dilutability with water.

EXAM1LE 15 Two resins are prepared under the same conditions as in Example 1 except the conditions governing the pH and j temperature of the etherification stage.

In·a first preparation, etherification is carried out at pH 4 and a temperature of 40°C. The resin obtained has a normal viscosity and dilutability the day after its manufacture. 20 Days later, however, the viscosity of the resin has increased so mu6h that the resin is more or less gel-like at room temperature.

In a second preparation, etherification is carried out at pH 1.5 and a temperature of 20°C. The day after its manufacture, the resin has a dilutability v/ith water above ; 2000 and a viscosity of 15 cP. At the end of two months storage, the dilutability with water is still above 2000 and the viscosity is 40 cP.

This second resin is used to prepare a size for the manufacture of a glass fibre sheet by the method given in ) Example 1. The sheet is found to have a tensile strength of only 4.0 kg/cm.

By comparison v/ith the results indicated in Example 1, the present example demonstrates the disadvantages encountered if the stage of etherification is carried out under ι conditions of pH and temperature outside the limits defined in the text of the present patent.

EXAMPLE 14 Two resins are prepared in accordance with all tho particulars given in Example 4 except for the duration of the etherification stage. - 32 43271 In the first preparation, the total etherification time including the time of inflow of acid is only 60 minutes for a turbidity point of 5θ°0 instead of 90 minutes for the same turbidity point. The final viscosity of this resin i3 only 23 cP and its dilutability with water i3 above 2000.

This re3in is used for the preparation of a size which in turn is used for the manufacture of a glass fibre sheet in accordance with the particulars given in Example 1.

The tensile strength determined on this sheet is found 10 to be only 4.9 kg/cm.

In the second preparation, etherification is prolonged to a total time of 180 minutes for a turbidity point of 50°C. The resin finally obtained has a viscosity Of 285 cP and a dilutability with water of 1500.

The resin is found to have the following properties after 2 months storage: dilutability: 600 viscosity: 1050 cP.

This example demonstrates, by comparison with the , results obtained in Example 4, the disadvantages encountered if etherification is carried out for a length of time outside the limits indicated for a given turbidity point.

EXAMPLE 15 A resin is prepared by the method of preparation 25 described in Example 4 except that 60 g of 35·5% aqueous hydrochloric acid solution are used instead of 45 g of concentrated sulphuric acid.

Apart from the molar ratios of the reactants, which are the same as in Example 4, this resin has the following chax'actoris tics.

J Solid content 43.3% Viscosity 35 cP Free formaldehyde content , 5.5% Dilutability infinite Viscosity 30 cP ( >2000) After 2 months storage; dilutability: infinite (>2000) viscosity: 55 cP This resin is used for the preparation of a size which in turn is used for the manufacture of a sheet in accordance with Example 1. This sheet is found to have the following properties: Tensile strength: 6.0 kg/cm Flexibility index: 7.

Similar results are obtained if the same method of operation and same stoichiometric proportions are used but hydrochloric acid is replaced by orthophosphoric acid, nitric acid, formic acid or monochloroacetic acid.

This example demonstrates that any of these various acids or sulphuric acid may equally well be used in the process according to the present invention.

EXAMPLE 16 A resin is prepared in accordance with all the particulars given in Example 4 except that neutralisation to pH 7.2 after etherification is carried out solely with a 50% aqueous sodium hydroxide solution instead of 0.33 mol of triethanolamine followed by 40 g of aqueous sodium hydroxide.

In the course of ripening at 70°C (Stage III) it is found that the resin solidifies at the end of 2 hours. This resin can no longer be redissolved by the addition of water.

This example illustrates the necessity of using at - 34 <13271 least a proportion of triethanolamine for neutralisation of the resin after the stage of etherification. It also shows, hy comparison with Examples δ and 9, that triethanolamine plays an essential role for the solubility of the resin in water not only in stage I (catalyst for alkaline condensation) but also at the end of stage II (etherification), during neutralisation.

EXAMPLE 17 This example illustrates the improvement obtained in the resins by ripening (Stage III).

Pour resins are prepared in accordance with all the particulars given in Example 1 except that the etherification temperature employed is 30°C instead of 35°G in all cases.

Ripening (Stage III) of these resins is then carried out for lengths of time which increase from one preparation to the other.

Each resin is used for preparing a size, and a glass fibre sheet is manufactured by the method described in Example 1.

The following results are obtained: Tensile strength of glass fibre sheets in kg/cm Resin with ripening time zero Resin with ripening time 1 hour Resin with ripening time 4 hours Resin with ripening time 5 hours 4.2 4.6 4.8 flexibility index of glass fibre sheets 5 6 8 Viscosity of aqueous resin solutions after manufacture in cP 4.1 53 115 245 This example also demonstrates the very rapid increase in viscosity after about 4 hours of ripening time. This operation must therefore be restricted to a time limit so that the resins can still be put to industrial use.

EXAMPLE 18 This example illustrates the improvement in properties obtained by the addition of urea to the resins'after the ripening stage.

A resin is prepared in accordance with all the particulars given -in Example 4 except that no urea is added at the end of the process.

A size is prepared from the resin obtained, and a glass fibre sheet is manufactured by the method of operation given in Example 1.

The following results are obtained by comparison with the resin from Example 4: Resin from Example 4 Same resin without the addition of urea Free formaldehyde content in % 5.7 11.0 Tensile strength of glass fibre sheet in kg/cm 6.2 5-7 Viscosity after manufacture in cP 44 55 Viscosity 2 months after manufacture in cP 92 185 The resins obtained according to the invention are advantageous for bonding thin glass fibre sheets, in particular sheets having a thickness of less than 4 ram, on which they confer good qualities of flexibility and tensile strength

Claims (26)

1. A process for the preparation of a solution of etherified melamine formaldehyde resins, wherein in a first stage, melamine is reacted with formaldehyde by adding solid melamine with stirring to a solution containing: a 30 to 50% by weight aqueous solution of formaldehyde, in a quantity corresponding to a final molar ratio of formaldehyde to melamine of from 5:1 to 11:1; one or more aliphatic polyols containing only C, H, and 0 atoms in a quantity corresponding to a molar ratio of polyol to melamine of from 3:1 to 5:1; and triethanolamine in a quantity corresponding to a molar ratio of triethanolamine to melamine of from 0.2:1 to 0.6:1; at a temperature of from 60 to 70°C, the pH after the addition of the melamine being from 8.5 to 9.5, and the reaction is stopped by rapid cooling to a temperature of from 20 to 40° C, when the turbidity point is from 40 to 65°C; in a second stage, etherification is carried out by lowering the pH of the reaction mixture obtained from the first stage to a value of from 1.5 to 3.0 by addition of a pure acid or of a concentrated aqueous solution of an acid while maintaining the temperature at the same level as at the end of the first stage, and the solution obtained at the end of the etherification reaction is neutralised by addition of base which includes at least one third of a mole of triethanolamine per mole of melamine; 37 438” in a third stage, the solution obtained at the end of the second stage is ripened by keeping it for a length of time between 2 and 5 hours at a temperature of between 50 and 90°C; in a fourth stage, the proportion of free formaldehyde in the solution obtained at the end of the third stage is reduced by the addition of urea to a final free formaldehyde content not exceeding 6¾ by weight.

2. A process according to Claim 1, wherein the solution of formaldehyde which is reacted with the melamine in the first stage contains 36% by weight of formaldehyde.

3. A process according to Claim 1 or Claim 2, wherein the final molar ratio of formaldehyde to melamine is from 6.5:1 to 10:1.

4. A process according to any preceding Claim, wherein the molar ratio of polyol to melamine is from 3.5:1 to 4:1.

5. A process according to any preceding Claim, wherein the molar ratio of triethanolamine to melamine is from 0.3:1 to 0.4:1.

6. A process according to any preceding Claim, wherein the temperature of the reaction between the melamine and the formaldehyde is 63 to 68°C.

7. A process according to any preceding Claim, wherein the pH after the addition of the melamine is 8.8 to 9.2.

8., A process according to any preceding Claim, wherein the reaction of the melamine with the formaldehyde is stopped by cooling to 33 to 37°C. 38 43271

9. A process according to any preceding Claim, wherein the solution obtained at the end of the second stage is ripened at 70 to 85°C.

10. A process according to Claim 1, wherein the first stage melamine is added over a period of between 10 and 15 minutes.

11. A process according to Claims 1 or 2, wherein the polyol used is ethylene glycol, diethylene glycol, triethylene glycol, glycerol, saccharose or d-glucose.

12. A process according to Claim 11, wherein a mixture of ethylene glycol and saccharose is used.

13. A process according to any preceding Claim, wherein in the second stage, the acid used for acidification is sulphuric, hydrochloric, orthophosphoric, nitric, formic or monochloroacetic acid.

14. A process according to any preceding Claim, wherein the acid is added over a period of between 25 and 35 minutes so as to maintain the temperature substantially constant.

15. A process according to any one of Claims 1 to 14, wherein the etherification is carried out at 20°C at a pH of 1.5, or at 40°C at a pH of 3, or at a temperature between 20 and 40°C at a pH between 1.5 and 3.

16. A process according to Claim 11, wherein the etherification step is carried out at from 33°C at pH 1.8 to 37°C at pH 2.2.

17. A process according to Claims 15 or 16, wherein the reaction time of etherification, calculated from the introduction of acid to the beginning of neutralisation, is between 50 and 180 minutes.

18. A process according to Claim 17, wherein the said reaction time is from 105 to 135 minutes and the turbidity point is from 45 to 55°C.

19. A process according to any one of Claims 1 to 18, wherein neutralisation is carried out partially with triethanolamine used in a proportion of one third mol per mol of melamine and neutralisation is completed with a 50% by weight solution of sodium hydroxide.

20. A process according to any preceding Claim, wherein in the fourth stage, reduction in the formaldehyde content is achieved by the addition of solid urea in a quantity of between 0.6 to 1.6 mol per mol of melamine used as starting material, depending on the initial quantity of formaldehyde.

21. A process according to Claim 20, wherein the quantity of solid urea is from 0.8 to 1.2 mols per mol of melamine.

22. Aqueous solutions of etherified melamine formaldehyde resins obtained by the process of any preceding Claim.

23. Aqueous solutions of etherified melamine formaldehyde resins prepared by the process of Claim 1, wherein the solids content is between 41 and 52% by weight, the formaldehyde/ melamine molar ratio is between 5 and 11, the polyol/melamine molar ratio is between 3 and 5, the urea/melamine molar ratio is between 0,6 and 1.6 and the free formaldehyde content is below 6%.

24. Aqueous solutions of melamine formaldehyde resins according to Claim 2, which, after being left to stand for a minimum of 2 months at room temperature, have a viscosity of at the most 800 cP and a dilutability with water of at least 1200, the viscosity and dilutability being measured at 25°C. 40 43271

25. Fibrous products impregnated with aqueous solutions according to any of Claims 22 to 24.

26. Fibre sheets having a thickness of less than 4 mm impregnated with aqueous solutions according to any of 5 Claims 22 to 24.