In Situ Blown Foams

This invention relates to the low density microcellular, rigid foams made from low water content or waterless resins such as phenolic resin (resole or novalac). We make the in situ blown, closed cell foams without an external blowing agent.

Insulating synthetic foams have found various application in contemporary society. One of the most voluminous applications of these foams is in the construction field, as insulators for walls, roofs, basements, etc. More Specialized applications for these foams include appliances (refrigeration), pipes, ducting, auto, aerospace and marine industries.

Despite expanding applications and ever increasing production of insulating foams, their thermal insulating properties especially their long term insulating properties did not improve in the last decade, but have somewhat suffered due to the switch to environmentally friendly blowing agents. Improvements in the insulating properties of these foams, especially their low density variety will save a lot of energy, reduce the consumption of fossil fuels and improve the environment due to the reduction in greenhouse gases formed by the combustion of fossil fuels.

This invention forms in situ carbon dioxide blown closed cell insulating foams in which blowing is achieved by the evolution of carbon dioxide resulting from partial hydrolysis of isocyanates such as methyl diphenyl diisocyanate (MDI) by water in the resole. The invention uses no additional blowing agent. The reaction is fast and the resulting product has small, closed cells that exhibit long term thermal performance.

Preferably, the composition comprises the following ingredients:

(1) Low water content resole, which is the reaction product of formaldehyde and phenol;

(2) Surface active agent, .such as ethylene oxide-propylene oxide block copolymer;

(3) Mixture of isomers of methyl diphenyl diisocyanate (MDI); and

(4) Catalysts, such as stannous octoate.

The process for producing the closed cell insulating foam of the invention comprises mixing the resole, the surface active agent and the MDI at room temperature. Next, the catalyst is added and stirred vigorously. The prefoam thus formed is placed in a release paper lined steel closed mold preheated at 60.degree. C., and the mold is maintained at this temperature for one minute. Finally, the foam bun thus produced is removed from the mold and allowed to cure at room temperature.

When producing a phenolic resin, we use well known methods having phenol:formaldehyde ratios of 1.1:1 to 1:3.0. We then dewater the reaction product to 0.1%-7.5% water and to viscosity of liquid resin from 2,000-20,000 cps at 40.degree. C. Next, we add a surfactant in an amount at 2% to 7% by mass of resin solids.

We then combine this with MDI in a mol ratio of 0.45:1 to 1.35:1 with respect to the average number of methylol groups of phenolic, as measured by NMR. This is reacted by addition of 0.1% to 1.0% by mass of catalyst. The catalyst is one or a mixture of dibutyltin dilaurate, N,N,N',N'-tetramethyl-1,3-butanediamine, stannous octoate acetate or triethylene diamine. After vigorous mixing for 15 seconds, the mixture is transferred to a closed mold at 25.degree.-90.degree. C. After 0.5 to 5 minutes of cure time, the product is removed from the mold.

In the case of waterless phenolics, we obtain only a microcellular structure since relatively small quantities of water are evolved from the phenolic polycondensation reaction which partially hydrolize the MDI and lead to CO.sub.2 evolution. In the case of water containing phenolic, the initial water promotes the formation of larger cells (.apprxeq.80 .mu.k) and the water of polycondensation gives rise to microcells (<1 .mu.k) in the struts of the cellular structure.

The following formula represents the resol: ##STR1## where X is H or --CH.sub.2 OH and n.dbd.0, 1, 2, 3, or higher.

When the phenol is used in molar excess, the novalac product has little or no hydroxymethyl substitution and has the following formula: ##STR2## where X is hydrogen and n.dbd.0, 1, 2, 3, or higher.

The --NCO containing compounds include the following: 2,4-tolylene diisocyanate; 2,6-tolylene diisocyanate; p-phenylene diisocyanate; polymethylene polyphenylisocyanate; diphenyl-methane diisocyanate; m-phenylene diisocyanate; hexamethylene diisocyanate; butylene-1,4-diisocyanate; octamethylene diisocyanate; 3,3'-dimethoxy 4,4-biphenylene diisocyanate; 1,18-octadecamethylene diisocyanate; polymethylene diisocyanate; benzene triisocyanate; naphthylene-2,4-diisocyanate, 3,3'-dimethyl-4,4'-biphenylene diisocyanate; 4,4'-diisocyanate; diphenylether; naphthylene-1,5-diisocyanate;diisocyanate-dicyclohexyl-methane; p-xylylene diisocyanate; xylylene diisocyanate; hydrogenareal dipehnylene diisocyanate; hydrogenated diphenyl methane diisocyanate; toluene-2,4,6-triisocyanate; 3-methyl-4,6,4'-triisocyanate diphenylmethane; 2,4,4'-triisocyanate diphenyimethane; 2,4,4'-triisocyanate diphenyl; 2,4,4'-triisocyanate diphenyl ether; long chain hydrocarbons; and substituted hydrocarbons terminated with --NCO radicals and mixtures thereof.

Other catalysts used for polyurethane formation are those known in the art and consist of tertiary amines, metal salts, or mixtures thereof. Examples of such suitable catalytic compounds are triethylamine, dimethylaminoethanol, N,N,N',N'-tetraethylethylenediamine, N,N,N',N'-tetramethyl-1,3-butanediamine, bis(-dimethylaminoethyl)ether, 1,4-diazol[2.2.2]-bicyclooctane, N-methyl- or ethylmorpholine, stannous oleate, stannous 2-ethylhexanoate, dibutyltin dilaurate, dibutyl-tin dilauryl mercaptide, dibutyltin diacetate, lead naphthenate, zinc stearate, or mixtures thereof.

The preferred catalysts for our invention are non-acidic organotin catalysts. The particular organic structure for the organotin catalyst is not critical; it is only necessary that tin be present since the tin is the basic catalytic agent. Examples of suitable organotin catalysts are stannous oxalate, stannous oleate, stannous chloride, stannous formate, etc. Any organotin compound which is not volatile or subject to decomposition at the initial reaction temperature (which is not higher than 90.degree. F.) and which is soluble in the reaction mixture will suffice. Preferred catalysts are reaction products of stannous oxide (SnO) or dibutyltin oxide with a carboxylic acid having 1 to 20 carbon atoms. A preferred catalyst is stannous octoate (stannous 2-ethylhexoate) Sn(C.sub.8 H.sub.12 O.sub.2).sub.2 -- which is a reaction product of stannous oxide and 2-ethylhexoic acid. Examples of catalysts derived from dibutyltin oxide are dibutyltin diacetate, dibutyltin di(2,ethylhexoate) and dibutyltin dilaurate.

Since low density foams are desired, we employ a surface active agent of an alkylene glycol of 2 to 10 carbon atoms such as ethylene glycol, butylene glycol and propylene glycol or an ether of an alkylene glycol of 2 to 10 carbon atoms such as diethylene glycol and dipropylene glycol, or mixture thereof. The preferred surface active agent is a alkylene glycol-polyoxyalkylene block copolymer.

The key to this invention is a waterless or low water phenolic resin. The resulting foam has a particular microcellular structure which provides high strength and interrupts crack migration.

The following examples further demonstrate our invention.

We prepared a resol resin by mixing 52% formaldehyde and 99% phenol to produce a formaldehyde: phenol ratio of 2.3:1. This blend was basicified to a pH of 8.6 by the addition of a 50% caustic solution and the temperature was elevated to start the reaction. The reaction was cooled and then neutralized with 50% aqueous aromatic sulphonic acid. We then added 8.3 parts of urea per 100 parts of resol.

Next, we then stripped water from the resulting mixture using a thin film evaporator. We reduced the water content from 31% to 5.4%. The final viscosity of the resin was 5,000 cps measured at 40.degree. C.

This resol was analyzed by NMR and found to have 1.57 methylol groups per phenol.

We used the resol of Example I to produce a low density closed cell structured foam having a small cell size and a rapid demolding time. We used the following ingredients and amounts.

The surface active agent used was an ethylene oxide propylene oxide block copolymer with a molecular weight greater than 5,000.

No blowing agent was added to the mixture. The only blowing agent present was the 5.4% water from the resol reaction.

The resulting foam has the following advantages: no blowing agent used (environmentally friendly); closed cell structure-long term thermal performance; economical--due to use of resol chemistry; fast urethane-type reaction; small cell size -80/.mu.k; microcellular structure in the struts; superior physicals at low density; and low flammability.