IE43622B1 - Process for the manufacture of phenolic resins - Google Patents

Abstract

1489737 Phenolic resins SAINT-GOBAIN INDUSTRIES 7 April 1976 [30 April 1975] 14119/76 Heading C3R A process for the manufacture of phenolic resins intended for the production of foams comprises condensing a mixture of formaldehyde and phenol, generally in a molar ratio of from 1À0 to 1À7, in at least 2 successive stages, the HCHO generally being added in 2 stages, in the presence of an alkaline catalyst, e.g. NaOH, characterized in that after cooling of the reaction mixture at the end of the last stage of condensation, preferably to a temperature of from 30‹ to 35‹ C., a quantity of acid, e.g. HCl, sufficient to lower the pH to from 3 to 4 is added to the reaction mixture and the resinous phase is removed from the aqueous medium. The phenolic resins obtained generally have solids contents of from 70 to 74% wt. and viscosities from 1500 to 2000 cP. at 20‹ C.

Description

SCIENCE REFERENCE UBRAKT PAIINT APPI.ICATION BY (71) SAINT-GOBAIN INDUSTRIES, A FRENCH BODY CORPORA! OF 62 BOULEVARD VICTOR HUGO, NEUILLY-SUR-SEINE, FRANCE.

Pnct 12ip Ια French Patent No.· 2 147 766 has been disclosed a process- for the manufacture cf phenolic resin foams from resols obtained by condensation of phenol and formaldehyde, which process is characterised, by the fact that the condensation reaction is carried out in two successive stages.

/ After this condensation, the reaction mixture is neutralised to· a pH of between 7 and 7«5 and the resin is separated by decantation,and concentrated by removal of J water, for example1by distillation under vacuum.

In order to obtain foamed sheets in which the cells are fine and homogeneous throughout the thickness of the sheet, it is essential to prepare the foamable dispersions from resins which have a sufficiently high viscosity.

If the viscosity of the resol is not sufficiently high, the foamable dispersions obtained after incorporation of a blowing agent, surface active agent and hardening catalyst are also of insufficiently high viscosity.

As a result, the bubbles of vapour produced from the blowing agent in the course of its evaporation under the influence of the heat of the hardening reaction at the beginning have a tendency to coalesce and rise inside the cream.

The cells produced are therefore coarse and heterogeneous within the thickness of the sheet, the cells being coarsest ahd most numerous near the upper surface.

The resins obtained by the process according tc French Patent No. 2 147 766 after neutralisation of the reaction mixture have viscosities of between 700 and 900 cP at 20°C when their solid contents are between 64 and 66% by weight.

With these viscosities, one would encounter the disadvantages mentioned above in the course of manufacture of 3 6 2 2 the foams.

It was therefore necessary to increase the viscosity of these resins by increasing theix· solid content by an additional, very long operation of concentration under vacuum before prepax-ation of the foam able dispersions.

However, it was impossible, even by distilling at a low temperature and very low pressure, to prevent condensation of the resin in the course of this operation of concentration, with the result that an excessive increase in viscosity occurred. Values of 40C0 to 8000 cP at 20°G were reached with solid contents of from 70% to 75% respectively.

Such high viscosities interfere with the preparation of foamable dispersions. Not only is a large quantity of energy used up by the mixing apparatus but also the mixing operation must be greatly prolonged to obtain a sufficiently fine dispersion. It is therefore difficult to obtain foams with a low unit weight.

Attempts have also been made to increase the viscosity by removalof water by centrifuging. However, the resin was found to retain the water very powerfully and even with vigorous centrifuging it was impossible to obtain a solid content as high as 70% by weight.

It -has now been found that these disadvantages can be overcome, particularly the loss of time and energy required for concentration by distillation. Moreover, the dry content and hence viscosity of the resin can be adjusted very easily as desired, a factor which greatly facilitates the manufacitux— ing process.

The invention thus concerns a process for the manufacture of phenol resins intended in particular for the production of foams from a mixture of phenol and formaldehyde by condensation 43633 in at least two successive stages in the presence of an alkaline catalyst, characterised in that after cooling of the reaction mixture at the end of the last stage of condensation, a quantity of acid sufficient to lower the pH to between about 3.0 and 4.0, preferably between 3.4 and 3.6 is added and the resinous phase is removed from the aqueous medium for its subsequent use.

According to a preferred feature of the invention, the reaction mixture is cooled to a temperature of between 30°C and 35°C before addition of the acid.

The molar ratio of formaldehyde to phenol in the reaction mixture is preferably from 1.0:1 to 1.7:1, more preferably 1.0:1 to 1.6:1.

In the prior process described in French Patent No. 2 147 756, the reaction mixture is cooled after the second addition of formaldehyde. This mixture contains an excess of NaOH.

According to this, prior process, 35% hydrochloric acid is then added to neutralise NaOH and the pH is adjusted to about 7.

According to the present invention, instead of stopping the addition of hydrochloric acid when the pH reaches about 7, the addition of hydrochloric acid is continued to a pH of between 3.0 and 4.0. It has been found that a pH of 3.5 is obtained when the quantity of acid added corresponds stoichiometrically to the total quantity of sodium hydroxide used as catalyst.

This means that- at this. pH all the phenolic OH groups present in the resin and previously present in the form of water-soluble alkali phenolates are liberated.

It is obvious therefore that at pH values of between 3.0 and 4.0, the removal of water from the resin by decantation will be more complete and the solid content of the separated resin higher than in the case of neutralisation to pH 7.0 to 7.5. 42622 It has also been found that when the reaction mixture is neutralised to pH ?.O, the quantity of acid added corresponds substantially to only 58% of the total quantity of sodium hydroxide used as catalyst. The sodium phenolate groups remaining in the resin hence retain water and prevent h high solid content being obtained in the resin after it has been drawn off, even after centrifuging.

The pH range of acidification used in the present process » constitutes an optimum region. If acidification is continued to pH values below 5.0, the viscosities of the resins obtained after separation are much too high. It appears that this increase in viscosity is due to the fact that the excess acid introduced catalyses the condensation of the resin even at the low operating temperature employed. Conversely, if the pH is above 4.0, the viscosities and solid contents obtained are no longer sufficiently high to produce fine cells homogeneously distributed throughout the thickness of the foam sheet.

The invention is described in more detail in the nonlimiting Examples given below. 43632 Example 1 The reaction mixture oi a resin prepared by the twostage process according to French Patent No. 2 147 766 having a total molar ratio of formaldehyde to phenol of 1.4 and a total sodium hydroxide content of 2% by weight, based on the phenol, is acidified in accordance with the invention. The following values for the dry contents and viscosities are obtained: pH of acidification of the resin 5.0 5.4 3.6 4.0 Solid content of the decanted and drawn off resin in % hy weight 74.0 72.5 71.5 70.0 Viscosity in cP at 20°C of the decanted and drawn off resin 4000 2000 1500 1100 Example 2 6J.45 kg .(675 mol) of phenol and 67-50 kg of formaldehyde in the form of a 56% by weight aqueous solution (810 mol) are introduced into a stainless steel reaction vessel having a capacity of 150 litres equipped with heating and cooling jacket and high speed stirrer. The temperature of the mixture is raised to 50°C and 1268 g of a 50% by weight sodium hydroxide solution is added gradually at this temperature .

The mixture is heated to about 70°C and the temperature then rises spontaneously to 1OO°C. The reaction mixture is kept at this temperature for one hour by slight cooling.

The mixture is then cooled to 8O°C and 11.25 kg of a 36% by weight aqueous formaldehyde solution (135 mol) are added. The temperature of the mixture is kept at 80°C 2 6 3 3 while 1268 g of a 50% hy weight sodium hydroxide solution is added. The mixture is kept at this temperature for 30 minutes.

The resin is cooled to 30°C and divided into eight 5 equal portions. These samples of resin are acidified separately, in each case hy the addition of an 18% by weight hydrochloric acid with stirring until the pH attains different values for the different samples, ranging from 2.0 to 7.4.

After acidification, the samples are left to stand for hours so that the resin settles, and the resin layer is then separated from the aqueous layer. The characteristics indicated in the Table below are then measured on all these layers. In addition, the resins separated after neutralis15 ation to pH 5·0, 7·0 and 7·4, are concentrated at reduced pressure to a solid content of 72% and their viscosity is then again measured.

The results are summarized in the Table below. pH of acidification of the resin 2.0 3.0 3.4 3.6 4.0 5.0 7.0 7.4 solid content of the separated resin in % by weight (X) 74.0 72.5 7K5 70.0 68.2 66.3 64.5 viscosity in cP at 2Q°C of the separated resin measured after 24 hours >20000 4000 2000 1500 1100 1040 9co 810 viscosity in cP at 20°C of the reain aftei separation and concentration at reduced pressure to a solid content of 7255 3200 4100 56C0 (X) The resin is obtained in the form of a flocculate of very high viscosity which is unusable and difficult to separate· 6 32

Claims (10)

1. CLAIMS:1. A process for the manufacture of phenolic resins for the production of foams from a mixture of phenol and formaldehyde by condensation in at Least two successive stages in the presence of an alkaline catalyst, wherein after cooling of the reaction mixture at the end of the last stage of the condensation, a quantity of acid sufficient to lower the pH to from 3.0 to 4.0 is added to the reaction mixture, and the resin phase is separated from the aqueous medium.

2. A process according to Claim 1, wherein in the phenol formaldehyde reaction mixture the molar ratio of formaldehyde to phenol is from 1.0:1 to 1.7:1.

3. A process according to Claim 1 or 2, wherein the reaction mixture is cooled to a temperature of from 3θθΟ to 35θε before addition of the acid.

4. A process according to any one of Claims 1, 2 or 3, wherein the acidification is carried out using concentrated hydrochloric acid. 5. K. A phenolic resin according to Claim 7, wherein ihe sol ids content is from 71.5% to 72.5. by weight, and the viscosity is from 1500 to 2000 cP at 20%.

5. A process according to any preceding Claim, wherein a quantity of acid is added which is sufficient to lower the pH to from 3.4 to 3.6.

6. A process according to Claim 2, wherein the molar ratio of formaldehyde to phenol is from 1.0:1 to 1.6:1.

7. A phenolic resin obtained by the process of any of Claims 1 to 3, and having a solids content from 7θ·0% to 74.0% by weight, and a viscosity from 1100 to 4000 cP at 2O°C.

8. - 8 4 2 6 2 2

9. A process for the manufacture of a phenolic resin according to Claim 1, substantially as herein described.

10. 10. A phenolic resin wherever prepared by a process according to any of Claims 1 to 6 and 9.