GB2078228A - Phenolic-formaldehyde Foams - Google Patents

Abstract

A foam is made by foaming a phenol-formaldehyde resole having a molar ratio of phenol to formaldehyde from 1:1.9 to 1:2.4, a solids content from 70 to 80%, a free phenol content of less than 5% and a low reactivity, using pentane as the blowing agent, a hydrochloric acid-based hardener and a non-ionic surfactant having a HLB value of at least 13. Preferably the resole has a viscosity from 3,000 to 5,000 cps and a specific gravity from 1.20 to 1.30 g/cc and the surfactant has a HBL value of at least 15.

Description

SPECIFICATION Improvements in Insulating Foams This invention concerns improvements in insulating foams, and more particularly concerns foams of the phenol-formaldehyde type. The manufacture of phenolic foams from phenolformaldehyde resins is well known in the art and is carried out commercially by a number of manufacturers. The product is relatively expensive compared to other plastics insulating foams such as polystyrene, but phenolic foams exhibit excellent fire resistant properties. A defect of phenolic foams, however, is rather low structural strength with the result that products in board or sheet form are often laminated with sheets or webs capable of giving greater structural strength to the composite. The known phenolic foams also exhibit friability as a by-product of low structural strength.

Phenol-formaldehyde resoles are commercially available for the production of phenolic foams. A blowing agent, such as a low boiling point hydrocarbon or a "Freon" blowing agent is conventionally used, as is an acid hardener and a surfactant such as a silicone oil surfactant.

The present inventors have now discovered a method of making phenolic foams of significantly improved quality, in particular having increased strength and reduced friability.

The present invention provides a method for the production of phenolic foams which comprises foaming a phenol-formaldehyde resole having a molar ratio of phenol to formaldehyde from 1:1.9 to 1 :2.4, a solids content from 70 to 80%, a free phenol content of less than 5% and a low reactivity, using pentane as the blowing agent, a hydrochloric acid-based hardner and a non-ionic surfactant having a HLB value of at least 13.

Preferably the resole has a viscosity of 3,000 to 5,000 cps and a specific gravity of 1.20 to 1.30 g/cc.

The processing conditions are suitably conventional, by blending the resole and the surfactant, mixing in the pentane and then thoroughly mixing in the hardner before heating the mass to about 500C for about two hours.

The resole must have a low reactivity. This can be established by a test devised by the inventors in which 1 50 g of resole in a polystyrene cup is brought to 200C and 20 g of 50% sulphuric acid is rigorously mixed in for 1 5 seconds. A thermocouple is positioned in the centre of the resin mass and the cup is placed in an insulated container, conveniently a box of foamed plastics.

After five minutes the temperature of the resin is measured; to be classed as "low reactivity" the temperature should not exceed 75CC and is preferably not more than 700C.

A particularly suitable resole is available in the United Kingdom from Synthetic Resins Ltd. and from their associated company Sheby, under the designation Uravar 76/016. In France it is sold under the designation Alveophen 76/008.

Hardeners based on hydrochloric acid have been found in tests to be essential to yield high strength phenolic foams and is more effective than commonly used hardeners based on other acids. Preferably the hydrochloric acid is used in admixture with an agent which raises its viscosity close to that of the resole chosen. A suitable agent is ethylene glycol.

Preferably the surfactant has a HLB value of at least 1 5. The HLB value of a surfactant is its Hydrophilic/Lipophilic Balance. This is described along with methods for its determination in a paper by William C. Griffin published in the Journal of the Society of Cosmetic Chemistry, Volume 1, pages 311-326, 1949. The scale for HLB values ranges from 0 to 20. Surfactants suitable for the present invention must therefore have a high HLB value.

Preferred surfactants are those based on ethoxylated sorbitan monolaurate and an especially preferred surfactant has 1 5-25 ethylene oxide units per molecule of sorbitan monolaurate. A commercially available surfactant is "TWEEN" 20, which has 20 units of ethylene oxide per molecule of sorbitan monolaurate. This has a HLB value of 16.7.

Other surfactants which can be used in the present invention include "ETOCAS" 40 HLB 13.1, which is an ethoxylated castor oil, and "VOLPO" 020, HLB 15.5, which is an oleyl polyglycol ether.

Suitable proportions for the resole mix to be foamed are 40 to 100 g of pentane, to 50 9 of conc. hydrochloric acid, and 5-20 g of non-ionic surfactant per kg. of resole. Preferably the hydrochloric acid is present together with an approximately equal amount of ethylene glycol.

The foams prepared according to the invention are suitably prepared according to known technology in the form of boards or sheets.

Because of their increased strength over known foams, lamination may be dispensed with or thinner boards with lamination may be made. The foams of the invention also exhibit improvements in fire resistance and equivalent k-values compared with conventional foams.

The present invention which also includes the mixture to be foamed and the foamed and hardened material, will now be described by way of example only.

Example 2 kg of phenol formaldehyde foam resole (Uravar 76/016) having a molar ratio of phenol to formaldehyde of 1:2.04, a specific gravity of 1.27 g/cc, a viscosity at 200C of 41 60 cps, free phenol content of 4.1%, a total solids content of 77% and reactivity as measured in the test described above, of 69"C at 5 min. (purchased from Synthetic Resin Ltd.) was mixed in a vessel with 20 g of "TWEEN" 20 non-ionic surfactant. 120 g of pentane was then mixed in, and finally 120 g of 1:1 mix of concentrated hydrochloric acid and ethylene glycol was thoroughly stirred into the resole mixture.

The mixture was poured into a mould and heated in an oven at 500C for 2 hours, whereupon foaming and hardening took place.

The resulting foam was of good appearance and had an exceptionally fine cell structure. At a density of 38 kg/m3 the compressive strength was 39x 104 N.m-2 whereas a foam made with a comparable conventional commercial resole manufactured according to "good practice", had a compressive strength of approximately 20x104 N.m-2. Commercial resoles used for the foaming had a molar ratio of phenol to formaldehyde of about 1 :1.5, although in some cases this was a little higher, up to 1 :1.8. In a water absorption test involving seven days total immersion, the foam of the invention exhibited a water absorption of 6% v/v.

The foam made according to the invention was also subjected to conventional fire resistance tests. In particular, the foam exhibited good resistence to flame penetration, and in general showed a 3-4% improvement over the commercial foam in fire tests.

Claims (11)

Claims

1. A method for the production of phenolic foams which comprises foaming a phenol formaldehyde resole having a molar ratio of phenol to formaldehyde from 1:1.9 to 1:2.4, a solids content from 70 to 80%, a free phenol content of less than 5% and a low reactivity, using pentane as the blowing agent, a hydrochloric acid-based hardener and a non-ionic surfactant having a HLB value of at least 13.

2. A method according toclaim 1, wherein the resole has a viscosity from 3,000 to 5,000 cps and a specific gravity from 1.20 to 1.30 g/cc.

3. A method according to either one of claims 1 and 2, wherein the resole has a reactivity of less than 700C after 5 minutes.

4. A method according to any one of the preceding claims, wherein the hardener is used in admixture with a viscosity-raising agent.

5. A method according to claim 4, in which the agent is ethylene glycol.

6. A method according to any one of the preceding claims, wherein the surfactant has a HLB value of at least 1 5.

7. A method for the production of phenolic foams substantially as hereinbefore described.

8. A phenolic foam when made according to the method of any one of claims 1 to 7.

9. A mixture to be used to produce a phenolic foam comprising 1,000 parts of a phenolformaldehyde resole, from 40 to 100 parts of pentane, from 1 5 to 50 parts of a hydrochloric acid-based hardener, and from 5 to 20 parts of a non-ionic surfactant having a HLB value of at least 13, the resole having a molar-ratio of phenol to formaldehyde from 1:1.9 to 1:2.4, a solids content from 70 to 80% a free phenol content of less than 5% and a low reactivity.

10. A mixture according to claim 9, and inciuding an amount of a viscosity-raising agent approximately equal to the amount of hardener present.

11. A mixture to be used to produce a phenolic foam substantially as hereinbefore described.