GB Patent 1150508 - Rigid Polyurethane Plastics

Description

COMPLETE SPECIFICATION

Rigid Polyurethane Plastics

We, THE UPJOHN COMPANY, a corporation organized and existing under the laws of the

State of Delaware, United States of America, of 301 Henrietta Street, Kalamazoo, State of Michigan, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which; it is to be performed, to be particularly described in and by the followingstatement:

This invention relates to novel rigid plastics and to processes for the preparation thereof and is more particularly concerned with novel polyurethane rigid plastics having high impact strength and with processes for their preparation.

According to the invention there is provided afibre-reinforced synthetic resin product characterized by high tensile strength and impact resistance which comprises a fibrous reinforcing material (as defined herein) of a kind inert to polyurethane reactants having bonded thereto a rigid, non-cellular polyurethane comprising the reaction product of an aromatic polyisocyanate and at least one aromatic polyol as defined herein having an hydroxyl number substantiallywithin the range of 75 to75G, the polyiscyanat and the polyol being employed in proportions such that the overallNCO:OH ratio is substantially within the range 0.9:1 to 1.2:1.

The preparation of noncellular polyurethanes by reaction of a polyisocyanate and a polyol iswell-known in the art; see, for example, Saunders et al. Polyurethanes,

Chemistry and Technology, Part II, Interscience Publishers, New York, 1964. A wide variety of polyisocyanates and polyols are currently available and/or have been used to prepare such polyurethanes. The properties of the polyurethanes obtained vary widely depending upon the nature of the reactants employed.

Various attempts have been made hitherto to produce polyurethanes which are rigid and which possess a sufficiently high impact strength to be useful, for example, as structural members for constructional use and in the fabrication of automobile and truck bodies, marine vessels, and the like. Accordingly an extensive market for rigid plastic materials, currently dominated by thermoset resins particularly fiber-reinforced thermoset resins derived from unsaturated polyesters, phenolics, epoxies, melamines and the like resinifying materials, has so far been closed tothe polyurethanes because of deficient strength.

We have now found that, using the process of the present invention, there can be prepared polyurethane rigid plastics having physical properties, particularly in regard to impact shock resistance, superior to those of polyurethane rigid plastics hitherto available, and of such a nature that the rigid plastics, produced in accordance with this invention, can be used for a variety of structural applications for which it has not hitherto been possible to use polyurethanes.

The polyurethanes used in accordance with this invention, are obtained by interaction of one or more of a particular class of polyisocyanates, as hereinafter exemplified with one or more of a particular class of polyols, as hereinafter exemplified, and the resulting polyurethanes are found unexpectedly to possess markedly superior properties, particularly in regard to structural strength, to those of polyurethanes made from closely re lated combinationscf reactants. This

difference in properties is even more prpounced when there are incorporated into

the reaction system fibrous reinforcing materials such as glass fibers, synthetic fibers

and the like materials as hereinafter exempli

fied.

Thepolyisocyanates which are employed

in the preparation of the reaction products

of the invention are aromatic polyisocyanates

i.e. isocyanates containing 2 or more iso

cyslnate groups which are attached directly to

the same aromatic nucleus or to two or more

different aromatic nuclei present in the same

molecule. Examples of aromatic polyiso

cyanates are 2,4 - tolylenedilsocyanate, 2,6

tolylene diisocyanate or mixtures thereof such

as the 80/20 and 65/35 percent mixtures of

these isomers commonly available commer

cially, and dimeric forms of same as well as

crude mixtures thereof, 4,4' - methylenebis

(phenyl - isocyanate), tolidine diisocyanate

4,4'- diisozyanato - 3,3' -dimathyldiphenyl),

dianisidinediisocyanate(4,! - diisocyanato

3,3' -dimethoxydiphenyl), 4,4' - diiso

cyanatodiphenyl, m - phenylenediiso

cyarate, p -p:lenylencdiisocyanate, <RTI 4A',4"

triisocyanato - diphenyl ether, isocyanato

terminated isocyanuratesobtained by tri

merisation of diisocyanates such as tolylene

diisocyanate, and also the polyisocyanate

adducts obtained by treating triols, tetrols,

and higher polyols with excess polyiso

cyanates, for example thetrilsocyanate ad

ducts obtained by reacting 1 mole of a triol

such as glycerol, trimethylolpropane or 1,2,6

hexanetriol, with 3moles of a diisocyanate

such as 4,4' -meth-glenebis(p31enyl iso

cyanate), 2,4 - tolylene diisocyanate, 2,6

tolylene diisocyanate and mixtures thereof.

Mixtures of two or more of the above poly

isocyanates can be employed if desired.

A particularly useful aromatic polyiso

cyanate for employment in accordance with

the invention is that form of methylene bis

(phenyl isocyanate) which comprises a mix

ture of polymethylene polyphenyl iso

cyanates containing from about35 % to

about 85 %, ofmethylenebis(phenyi iso

cyanate) the remainder of said mixture being

polymethylene polyphenyl isocyanates having

a functionality greater than 2.0. Such polymethylene polyphenyl isocyanates are wellknown in the art and are generally obtained by phosgenation of mixtures of methylenebridged polyphenyl polyamines obtained by interactioncf formaldehyde, hydrochloric acid, and a primary aromatic amine such as aniline,o-chloroaniline and o-toluidine, see, for example, U.S. Patents2,683,73G, 2,5of,76 and3,C12,GG8, Canadian Patent7cm,026 and German Specification 1,131,877.

Preferred polyisocyanates of this type are those containing approximately 50 percent by weight ofmethylenebis(phenyl iso cyanate) and having an overall functionality of about 2.7 and those containing approximately0 percent by weight of methylenebis(phenyl isocyanate) and having an overall average functionality of about 2.2.

The aromatic polyisocyanates which can be employed in accordance with the invention also include those wherein a proportion, generally less than 33% by weight of the diisocyanate, has been converted to the correspondingisocyanato-terminated carbodiimide, for example by heating the polyisocyanate in the presence of acarbodiamide-forming catalyst such as triethyl phosphate or by treating the polyisocyanate with a carbodlimide in accordance with the procedure diclosed in British Patent 918,454.

The term "aromatic polyol" as it is employed throughout this specification and claims means a polyol wherein the hydroxy group or groups are attached indirectly to an aromatic nucleus via a linking group such asalkylene, azaalkylene, oxaalkylene and caboxyaRylene. Examples of aromatic polyols are:

(a) hydroxy terminated polyesters derived from aromatic polycarboxylic acids such as phthalic acid, terephthalic acid and isphthalic add, or the corresponding acid anhydrides, byesterification with an excess of a polyol preferably an aliphatic glycol such as ethylene glycol, propylene glycol, 1,4 butanediol and 1,2 - hexanediol or a polyol of higher functionality such as trimethylolethane, trimethylolpropane, mannitol, hexanetriol, glycol, andpentaeryiritol. Also included in this class are mixed polyesters derived in part from an aromatic polycarboxylic acid ofthe above type and in part from an aliphatic polycarboxylic acid such as adipic acid and glutaric acid. Such esters are prepared, for example, by reacting two moles of a glycol with one mole of a dicarboxylic acid to give the correspondingbis(liydroxaikyl)ester, reacting 1 mole of the latter with 2 moles of the arhydride of a second dicarboxylic acid followed finally byesterification of the resulting dicarboxylic acid with an appropriate glycol or polyol.

(b) Adducts ofalkylene oxides such as ethylene oxide, 1,2 - propylene oxide, 2,3 butylene oxide and 1,2 - hexylene oxide with primary aromatic amines such as aniline, toluidine,phloroariliue, p-bromoaniline,naphthylamine, ss - naphthylamine, and mixtures of polyamines obtained by acid condensation of aldehydes or ketones or formaldehyde and a primary aromatic amine such as those enumerated above.Q3 - naphthylamine is a prohibited product under the Carcingenic Substances Regulations 1967). Exemplary of the latter type of adduct are those obtained by mixing under hydroxyalkylation conditions from 2 to 20 molecular equivalents of ethylene oxide, propylene oxide

or 1,2 - butylene oxide, or mixtures thereof, and one amine equivalent of a polyamine mixture,101 parts of said polyamine mixture containing from 35 to 90 parts of methylenedianilines, the remaining parts being tri amines and polyamines of higher molecular weight, said methylenedianilines, triamines, and polyamines of higher molecular weight having been formed by acid condensation of aniline and formaldehyde. Such products and methods for their preparation are described in detail in Belgian Patent 657,763;

(c) Polyether polyols prepared by reacting ethylene oxide, propylene oxide and 1,2 butylene oxide with mono- and polynuclear polyhydric phenols such as catechol, resorcinol, hydroquinone, orcinol, 2,2, - bis (p - hydroxyphenyl)propane [Bisphenol A], bis(p - hydroxyphenyl)methane, 2,2 - bis (4 - hydroxyphenyl)butane [Bisphenol B], 4,4' - dihydroxydiphenyl ether, 2,4' di hydroxydiphenyl ether and 1,1,3 - tris (hydroxyphenyl) ethane.

(d) Mannich base polyols i.e. those obtained by condensation of an alkanolamine, formaldehyde, and a phenol, and the adducts of said Mannich base polyols withalkylene oxides such as ethylene oxide, propylene oxide and 1,2 - butylene oxide. The above type Mannich base polyols are generally prepared by reacting an alkanolamine such as monoethanolamine, diethanolamine, iso propanolamine, diisopropanolamine, N hydroxyethyl - piperazine and N - hydroxypropylpiperazine and formaldehyde with a phenolic compound such as phenol itself,o-, m- or p-cresol,ethylphenol, nonylphenol, pphenylphenol,,8-naphthol, p-chlorophenol and o-bromophenol under conditions such as those described in British Patent 1,002,272.

The polyols so obtained are characterized by having at least one tertiary-amino-methyl group attached directly to an aromatic nucleus, the nitrogen atom of said teritaryaminomethyl group having at least onehydroxydkyl substituent thereon. The formation of alkylene oxide adducts of the Mannich base polyols is carried out under conditions well-known in the art for the hydroxyalkylation of polyols e.g. in accordance with the procedure described in the aforesaid

British Patent.

The above dry aromatic polyols can be employed either singly or in combination. Preferably the polyol component consists exclusively of one or more of the above aromatic polyols However, minor amounts of dry nonaromauc polyols can be any of the polyesters and polyether polyols conventionally employed in the art in the formation of rigid cellular polyurethanes, see, for example,

Saunders et al. ibid. When using mixtures of non-aromatic and aromatic polyols in accordance with the invention it is generally desirable that the amount of aromatic polyol present be such that the % aromaticity (i.e. the proportion of phenyl nuclei expressed as a percentage by weight of the total weight of polyol) be greater than about5% and is preferably within the range of about 10% to about 40%.

In preparing the reaction product of the invention the aromatic polyisocyanate and aromatic polyol may be brought together and reacted in accordance with procedures wellknown in the arr. Advantageously the reactants are brought together at a temperature of about100C to about109 C and preferably at a temperature of about20"C to about50"C. Preferably the aromatic polyol or polyol mixture is pretreated, if necessary, in order to remove any water which may be entrained therein. Advantageously, the drying procedure is effected by heating the polyol under reduced pressure at a temperature above that of the boiling point of water under the pressure conditions employed. Advantageously the drying is continued until the polyol contains less than about0.05 % by weight of water.

Where the aromatic polyol employed is a tertiary amine-containing polyol such as the

Mannich base polyols, the reaction between the polyisocyanate and the aromatic polyol is generally self-catalyzed and it is unnecessary to add additional catalysts to the reaction mixture. In the case of all other aromatic polyols, however, it is desirable to add a catalyst to the mixture of polyisocyanate and polyol obtained above. Preferably the catalyst is a tertiary amine such astrimethylamme, triethylamine, triisopropylamine, trihexylgamine,triethylene-diamine, N,N,N',N' tetramethyl - 1,3 - butanediamine, N,N dimethyl - aniline, N - methylpiperidine,

N,N' -dimethylpiperazine, N - methyl morpholine, N - ethylmorpholine, 1,1,3,3 tetramethylguanidine,N,N - dimethyl ethanolamine and 2 - methyl - 4 - ethylimidazole.

If desired, the tertiary amine catalyst can be replaced by or used in combination with other catalysts known in the art, see, for example, Saunders et al. ibid, Vol. 1, pages228-232. In general, however, it is necessary to select a catalyst which controls the reaction between the polyol and the polyiso

cyanate at a rate sufficiently slow to enable the reaction mixture to flow after mixing or otherwise be worked for a reasonable period of time after mixing the ingredients. In general, a catalyst is chosen which gives a pot life (i.e. the interval between the time of initiating the reaction and the time at which the reaction product gels and becomes unworkable) of from about 1/30 minute to

about 5 minutes. The preferred catalysts

are:-- triethylamine or dimethylethanol amine for slow reactions and triethylene diamine for fast reactions.

After concomitant or sequential addition of catalyst, if any, to the mixture of polyisocyanate and aromatic polyol at the temperature set forth above it is generally unnecessary to apply external heat to the reaction mixture since the reaction is generally exothermic.. After the reactants have been brought together, with the aid of vigorous agitation, the reaction mixture is forced into an appropriate mould or it may be sprayed on a form the size and shape of which depend on the purpose for which the rigid plastic is to be used.

A particular filler may be incorporated into the reaction mixture used to prepare the rigid plastic. Generally speaking the filler is employed for additional reinforcing purposes, that is for giving additional strength to the resulting rigid plastic, but in certain cases the filler is employed as an inert diluent designed to reduce the overall cost of the resulting plastic without detractingsigrufi- cantly from the desired properties thereof.

"Fibrous reinforcing material" means any fibrous or filamentary reinforcing material which is inert to the reactants including glass fiber, asbestos fiber, mineral fiber (including metal fiber such as wire), fibers prepared by extrusion or spinning of synthetic materials such as polyester and fibers prepared from materials such as boron, carbon, graphite and beryllium which are particularly useful where the end product is to be subjected to high temperatures.

Fibrous materials of the above type can be incorporated into the rigid plastics of the invention by any of the means known in the art. For example, the fibers can be added in short pieces, or chopped form, to the reaction mixture prior to the addition of the catalyst. Preferably, however, the fibers are employed in the form of nonwoven mat or a woven fabric or mesh which is cut to the approximate size and shape of the article to be cast. The reinforcing fibrous material is placed in the mold, for example edge sealed matched diemolds, and the reaction mixture (aromatic polyisocyanate and polyol with catalyst, if used) is forced into the mold where it wets, surrounds and envelopes the reinforcing material. In the resulting product the polyurethane plastic is tightly bonded to the reinforcing material whether the latter be glass, metal, synthetic fibre or any other material set forth above.

A particularly useful low cost reinforcing material which is employed for the preparation of panels, car and truck bodies and the like is fiber glass mat which has been lightly precoated with a phenolic resin binder and which is normally supplied in the form ofbatts for insulating purposes. These can be cut to any desired shape prior to use for the purposes of this invention.

Where a filler is added as an inert diluent, it preferably takes the form of an inert solid having an average particle size advantageously less than about1001 microns and preferably less than about 50 microns. By inert solid material is meant material which will not enter into chemical reaction with any of the other components of the rigid plastic reaction mixture and is resistant to attack upon exposure to acids, alkalies, atmospheric conditions, soil microorganisms and the like.

Examples of such fillers are carbon black, including the various grades of channel black and furnace black, polystyrene, polyvinyl chloride, gypsum, natural clays including the various hard clays, kaolin and china clay, natural silica and asbestos. Such fillers are preferably dried, if necessary, before incorporation into the reaction mixture.

The reaction products of the invention are cured in or on the mold where they are formed in from 1 to 60 minutes and removal therefrom can take place when cured. Further curing can be carried out by heating at from about50 C to about1500C. The curing of the rigid plastics of the invention at fromICO"C to the latter upper temperature range has the additional advantage that the material so obtained has improved heat distortion properties as compared with the material cured at a temperature lower than that set forth above.

The products prepared in accordance with the invention are, in general, very dark brown to black solids which are characterized by a very low degree of shrinkage in the mold, high tensile strength, high compressive strength, high flexural strength, high impact resistance as measured by the Izod impact test, high shore D hardness, high heat distortion point and resistance to distortion when hot and high resistance to deterioration on exposure to boiling water and polar and nonpolar solvents, acids, alkalies and the like.

The above properties enable the products of the invention to be employed for a variety of purposes including panels for structural purposes, for example for walls, ceilings, partitions, floors, and the like on both the interior and exterior of buildings, as housing for machinery and the like, as panels or shapes for car bodies, furniture trucks, railroad cars, aircraft, ships, submarines and the like, and as ducts, pipes, storage tanks and the like. The products of the invention can also be cut, punched, sawed, drilled, tapped and machined in any of the processing opertions normally employed in metal or wood working. Accordingly the products of the invention can be used to prepare a variety of mechanical components normally fabricated from metals such as sprockets, gear wheels, drive mechanisms and the like.

The following examples illustrate the manner and process of making and using the reaction products which may be used to produce the reinforced products of the invention, Examples 4 and 5 showing how the products may be combined with fibrous reinforcements, and the remaining Examples illustrating the properties of preferred reaction products in the unreinforced condition.

EXAMPLE 1

A mixture of66 g. (0.49 equiv.) ofPAPS'2' (a polymethylene polyphenyl isocyanate, equiv.wit.=133; The UpjohnCom- pany, Polymer Chemicals Division) and 79 g. of CarwinolCBP-4 (0.51 equiv.; a mixture of propoxylated aniline and an adduct of propylene oxide and a polyamine mixture derived by acid condensation of aniline and formaldehyde; equiv. wt.= 158; previously dried by heating at130i"C under a pressure of 5 mm. of mercury) was prepared with stirring at40 C. The mixture was maintained under a pressure of 5 mm. of mercury for 5 minutes. At the end of this time the temperature of the mixture was54"C. The resulting mixture was cast in a tray and cured at900C overnight. The polyurethane so obtained was a tough, clear, dark brown solid having high tensile strength and impact resistance and could be removed from the tray without distorting after it cooled.

EXAMPLE 2

A blend of 154 g. (1 equiv.) of a polymethylene polyphenyl amine-propylene oxide adduct (equivalent weight 154; viscosity27,0001 cps at25"C) and 1.5 g. of 2-ethyl4-methylimidazole was heated at100"C under a pressure of 3 to 8 mm. of mercury for 0.5 hour. The dried blend was then mixed thoroughly with 146 g. (1.1 equiv.) ofPAPS'' and the mixture was cast in a pipe mold. The casting was cured in the mold at158"F for 30 minutes followed by curing at1010 to105"C for 1 hour. There was thus obtained a rigid polyurethane pipe section having an external diameter of 2.5 inches, an internal diameter of about 1.9 inches and a length of about 6 inches. Said section of pipe exhibited high tensile strength andim- pact resistance.

Using the above procedure, but replacing the pipe mold by a series of circular disc molds there was obtained a series of circular discs of diameter 2 inches and thickness 1/8 inches. The discs were cured as described above. One of said discs was clamped to a baffle confined within a chemical processing tank employed in a chemical manufacturing process such that twice a day for a period of 30 days said disc was exposed to the action of the following solutions :

Aqueous sulfuric acid(2025 %) at0 to60"C.

Benzene at0 to60"C.

Aqueous sodium hydroxide solution (10%) at circa35"C.

A solution of dichlorobenzidine disulfate in 25 to30% aqueous sulfuric acid.

A benzene solution of hydrazochlorobenzene.

The disc was weighed before and after treatment and found to have undergone no significant change in weight; weight beforeexposure=12.8440 g., weight after exposure followed by cleaning and vacuum drying =12.9316 g.

EXAMPLE 3

A mixture of1(PO parts by weight(o.94 equiv.) of Thanol (Registered TradeMarl:) R35()X (a Mannich base polyol believed to be the propylene oxide capped derivative of a

Mannich product obtained from phenol, diethanolamine and formaldehyde in the molar ratio1 :3:3; equiv. wt. 106; Jefferson Chemical Company Inc.) and 125 parts by weight (0.94 equiv) ofPAPI R' was prepared with stirring at about200 C. The resulting mixture was cast on a Teflon (Registered Trade

Mark) coated sheet and curedwithin 5 minutes without external heat. There was thus obtained a clear, dark brown, rigid polyurethane having high impact resistance, high abrasive resistance and high tensile strength.

EXAMPLE 4

A mixture of 100 parts by weight (0.94 equiv.) of ThanolR35OX and 122 parts by weight ofCarwinate'R' 390P (a polymethylene polyphenyl isocyanate, equiv. wt.

= 13C; The Upjohn Company, Polymer

Chemicals Division) was prepared with stirring at about20i"C. The resulting mixture was poured on to a piece of 20 mesh (20 holes per linear inch) aluminium wire screen supported on a Teflon coated tray. The resulting wire mesh reinforced rigid plastic cured in two minutes without external heating. The rigid plastic so obtained had very high impact strength and tensile strength and the polyurethane resin was found to beuni- formly and tightly bonded to the wire screen.

The above process was repeated using a thin (1/8 inch) sheet cut from a phenolic resin coated fiber glass insulation batt(Owens-Corning). The liquid polyurethane forming mix flowed evenly and freely over the fiber glass and the resulting reinforced rigid plastic, after curing as described above, had outstanding tensile and impact resistant strength.

EXAMPLE 5

Using the procedure described in Example 4, but replacing the Thanol R350X by an equivalent amount of Niax (Registered

Trade Mark) T222 (an aromatic based polyol, believed to be a propylene oxide capped nearly trifunctional A-stage phenol formalde hyde condensate equiv.wit.=140; Union

Clrbide Chemicals) there was obtained a reinforced rigid polyurethane plastic having high tensile strength and impact resistance.

Polyurethane rigid plastics, including reinforced andunreinforced rigid plastics, of the invention are also prepared using the procedures described above but replacing the polymethylene polyphenyl isocyanate by other aromatic polyisocyanates such as distilled or crude 2,4-tolylene diisocyanate, 2,tolylenediisocyanate and o-tolidinediiso- cyanate.

EXAMPLE 6

A batch of 524 g. (4.0 equivs) of Carwinol 151 (a modified polymethylene polyphenyl polyamine-propylene oxide adduct; equivalent weight 131; The Upjohn Company,

Polymer Chemicals Division) was heated at1200C for 0.5 hr. with stirring at a pressure of 1 mm. of mercury. The resulting degassed polyol was cooled to40"C and to the cooled polyol was added with stirring 506 g. (4.8 equivs) of Nacconate 4040 (crude tolylene diisocyanate; Allied Chemical). The resulting mixture was stirred for 3 to 4 minutes at a pressure of 1 mm. of mercury beforebeing poured into a6" x 6" X -" mold. The cast polymer was cured in the mold at 70 to80"C for 1 hour and the mold and contents were allowed to cool to room temperature before removing the polymer from the mold. The hard rigid plastic so obtained was a clear, dark brown solid having a specific gravity of 1.216, high tensile strength and high impact resistance.

Using the above procedure, but replacing

Nacconate41)40 by an 80/20 mixture of2,4 and2,Stolylene diisocyanate, there is obtained a rigid pol