CH417079A - Process for the production of foams from curable plastics - Google Patents

Description

  

  
 



  Process for the production of foams from curable plastics
Foam plastics, in particular those made from curable condensation products, are increasingly being used for insulation purposes. They are characterized by their flame retardancy, very low thermal conductivity and resistance to chemicals and higher temperatures.



   The basic substances of such foams are on the one hand condensates of phenol or phenoid derivatives and aldehydes and on the other hand condensation products of urea or melamines with aldehydes.



   The following processes, among others, are known for producing foams from condensates of the type mentioned above:
1. Resoles are mixed with propellants that split off gases either by decomposition under heat or in conjunction with the acid added for hardening. (For example hydrazides, azo compounds or alkali or alkaline earth carbonates.)
2. Instead of gas-releasing compounds, volatile organic solvents (ethers, ketones, gasoline fractions, aldehydes or



  Derivatives etc.) are added which, due to the heat supplied from the outside or the exothermic hardening reaction triggered by acids, change into the gaseous state and thus form the cell structure.



   3. First, a stable foam is formed from air, water and a surface-active substance, which also already contains the hardening agent or accelerator. On the lamellae of this foam you then bring z. B. the condensate of urea and formaldehyde. As soon as the curing, which has to take place quickly, has ended, the preformed foam has fulfilled its function and remains in the resin foam as water.



   The hardening of condensates made of phenol or



  Phenol derivatives and aldehydes can be carried out in the heat or by adding acids or paraformaldehyde at room temperature or slightly elevated temperature (40 to 800 C). Since the synchronization of foaming and hardening reactions is of great importance for the production of foams, normal, storable resols are usually foamed at elevated temperature and with the addition of acids and a blowing agent. It is also possible to let this process take place at room temperature if particularly reactive resins are used. Such reactive resins react immediately with the hardener acid and, when the appropriate agents are added, form a foam-like product within a short time, but are not economical on their own in terms of their low storage stability.



   It has now been found that even normal resins that are sufficiently stable in storage can be foamed and cured at room temperature if inorganic compounds are added which react with the water that is present or that is formed during the condensation.



   These compounds are substances that react with the water in the mixture to generate heat. This reaction serves on the one hand to generate a gaseous substance from the added propellant in order to form the desired foam structure, and on the other hand to accelerate the hardening process. If an acid anhydride is used as the heat-generating agent, the separate addition of the otherwise customary hardening acid may be unnecessary, since in this case the acid required for hardening is formed from its anhydride and the water present in the mixture.



   Inorganic compounds that can be used are, for example, acid anhydrides, hydrate-forming salts, hydrides and carbides. In detail, for. B. be used: boron dioxide, phosphorus pentoxide, calcium chloride, lithium chloride, zinc chloride, magnesium perchlorate, calcium hydride, aluminum carbide, calcium carbide.



   The abovementioned substances, which are added in amounts of 3 to 4% by weight, based on the condensation product, can also be slurried or dissolved in anhydrous inert liquids or mixtures thereof.



   Such liquids are e.g. B. gasoline fractions, n-pentane, carbon tetrachloride, dioctyl phthalate, dibutyl phthalate, tricresyl phosphate, trichloroethyl phosphate, glycol, glycerine and others. Liquid polymerization products of coumarone and / or indene are also suitable.



   If carbides or hydrides are added to the resols, there is no need to add a propellant, since the aforementioned compounds develop both the necessary heat and a gas that helps achieve the cell structure.



   The following examples serve to describe the process in more detail.



   Example I.
A. 1000 g of phenol and 1220 g of formaldehyde (37%) are refluxed for 30 minutes with the addition of 30 g of a 50% aqueous NaOH solution. Subsequently, dehydration is carried out under reduced pressure in the usual way until a viscosity of 2000 to 3000 cP is reached.



   B. 100 parts of the liquid phenolic resin obtained according to A are intimately mixed with 12 parts of petroleum ether and 4.5 parts of hydrochloric acid. A slurry of 8 parts of phosphorus pentoxide in 10 parts of tricresyl phosphate is then added. Immediately after the addition, the mixture foams and hardens.



   Example 2
100 parts of a phenol resol as described in Example 1 A are mixed with 10 parts of n-pentane and 10 parts of a mixture of hydrochloric acid and alcohol (1: 1). After adding 25 parts of boron trioxide alone or slurried in 10 parts of a liquid coumarone resin, the mixture foams and hardens in the required time.



   Example 3
100 parts of a phenokesol as described in Example 1A containing 25 parts of a mixture of hydrochloric acid and alcohol (1: 1) are mixed with a suspension of 4 parts of aluminum carbide in 5 parts of trichloroethyl phosphate Time is up.



   Example 4
A suspension of 25 parts of calcium chloride in 10 parts of trichloroethyl phosphate is added with vigorous stirring to a mixture of 100 parts of a phenol resol prepared according to Example 1A, 12 parts of n-pentane and 5 parts of hydrochloric acid. After a short period of time, the mixture foams up and hardens.



   Example 5
A. 1000 g of formaldehyde (37% in) are mixed with 6.4 g of a 47% solution of K3PO4 in water. A pH of about 4 is set by adding acids. A solution of 371 g of urea in 250 g of water is then added and the mixture is heated to 100 ° C. After 10 minutes, the mixture is adjusted to pH 7.5 to 8. The water is then distilled off in vacuo until a solid resin content of about 60% is reached.



   B. 100 parts of liquid urea resin prepared according to A with about 60% solid resin content, which contains 2 to 6% of a surface-active compound, are mixed with 10 cm3 of petroleum ether. 11 cm3 of a saturated aqueous oxalic acid solution are then added and 30 g of boron trioxide are then stirred in. The mixture foams up and hardens within a short time.

 

Claims (1)

PATENT CLAIM Process for the production of foams from curable plastics, in particular from condensation products of phenols and carbamides with aldehydes, characterized in that, after the condensation, inorganic compounds are added which react with the water present or during the condensation. SUBCLAIMS 1. Process according to claim, characterized in that 3 to 40 total% of the inorganic compound, based on the condensation product, is added. 2. The method according to claim, characterized in that inorganic acid anhydrides are added after the condensation. 3. The method according to claim, characterized in that hydrides and carbides are added after the condensation.