WO1998008886A1

WO1998008886A1 - Polyurethane-isocyanurate casting systems with high heat deflection temperatures

Info

Publication number: WO1998008886A1
Application number: PCT/EP1997/004486
Authority: WO
Inventors: Teruko Uchimi Miyazaki
Original assignee: Ciba Specialty Chemicals Holding Inc.
Priority date: 1996-08-27
Filing date: 1997-08-16
Publication date: 1998-03-05
Also published as: KR20000035906A; EP0922063A1; ZA977654B; CA2261222A1; JP2000516975A; AU4380097A

Abstract

The present invention relates to a polyurethane-isocyanurate casting system including an isocyanate component or isocyanate terminated prepolymer and a hardener. The hardener includes a polyol component, at least one trimerization catalyst, and, optionally, a poly(oxyalkylene) polyamine. The isocyanate component and hardener are blended at a volumetric ratio of between 2.5:1 and 1:1. The blend of component a and component b has an isocyanate index of from about 1.5 to about 4.0. The present invention further relates to a process employing the casting system and articles resulting from the casting system having a high head deflection temperature.

Description

Polvurethane-lsocvanurate Casting Systems With High Heat Deflection Temperatures.

The invention relates to novel compositions and reaction mixtures for polyurethane- isocyanurate casting systems, a process for the production of polyurethane-isocyanurate shaped articles using the reaction mixtures described herein, and the polyurethane- isocyanurate shaped articles obtained from the reaction mixtures.

The chemistry of polyisocyanates and the production of polyurethane shaped articles using polyisocyanates and polyols are well-known Typically, the polyurethane shaped articles are based, in part, on polyisocyanates of the diphenylmethane series. The polyisocyanate resin component is combined with a hardener component that is usually made up of two or more different components. The mechanical or thermal properties of the resulting polyurethane shaped articles plus the processing time or the course of full curing or the viscosity of the mixture, may be controlled by varying the components making up the hardener component. Hardener compositions for the production of polyurethane shaped articles are shown in U.S. Pat. No. 5,340,900, which is incorporated herein by reference Polyol compositions for the production of polyurethane moldings are shown in U.S Pat. No. 5,237,036, which is incorporated herein by reference. Neither of the compositions shown in U S Pat Nos. 5,340,900 and 5,237,036 employ tπmeπzation catalysts in the production of the polyurethane shaped articles or moldings.

The use of tπmeπzation catalysts to promote the formation of isocyanurates in polyurethane systems for reaction injection molding operations is known, as shown in U.S. Pat. Nos. 4,126,741 and 4,530,941. In the polyurethane system shown in U.S. Pat. No. 4,530,941 , the NCX index, which is the ratio of the total number of NCO and/or NCS equivalents to the total number of hydrogen equivalents contained in the formulation, is from 0.7 to 1.5, with the proviso that with the addition of tπmeπzation catalysts, the NCX index may be as high as 5. The use of trimeπzation catalysts in polyurethane compositions for the production of non-foamed moldings is shown in U.S. Pat No. 4,182,826. The NCO index for the polyurethane system shown in U.S. Pat. No. 4,182,826 is most preferably between 5 and 33. Two part polyurethane casting systems for making prototypes and short-run production parts have gained wide-spread commercial application. Rapid prototyping systems have expanded the application of polyurethane casting systems by producing parts that are demoldable within 15 to 30 minutes. For many applications in rapid prototyping systems, it is desirable to produce a polyurethane shaped article having a very high heat deflection temperature (HDT). The currently available compositions for use in rapid prototyping systems produce polyurethane shaped articles having a HDT of 133°C when properly post- cured. There is a need for polyurethane shaped articles having a HDT in excess of 164°C, more preferably in excess of 170°C.

The present invention relates to a polyurethane-isocyanurate casting system comprising- a) an isocyanate component or isocyanate terminated prepolymer and b) a hardener. The hardener comprises a polyol component, at least one trimeπzation catalyst and, optionally, a poly(oxyalkylene) polyamine, wherein component a is blended with component b at a volumetric ratio of from about 2.5:1 to1 :1. More preferably, the volumetric ratio of component a to component b is from about 2.1 to 1 :1 , most preferably about 2:1

The isocyanate component is selected from the group consisting of monomeπc polyisocyanates, polymeric polyisocyanates and mixtures thereof The polymeric isocyanate may be represented by the formula

wherein n is 0 to 8. The isocyanate component preferably has a functionality of about 2.0 to about 2.4.

The polyol component in the hardener is a mixture of polyols and/or polyether-polyols that comprises a) a polyol having a hydroxyl equivalent weight of up to 150 and a functionality of 4 to 8, b) a polyol having a hydroxyl equivalent weight of more than 1900 and a functionality of 2 to 4, and c) a polypropylene glycol having a functionality of 2 to 3 or a polytetrahydrofuran, each of which has a hydroxyl equivalent weight of 150 to 500, or a mixture thereof. The poly(oxyalkylene) polyamine component has 2 to 4 ammo groups per molecule and an average molecular weight of between 1000 to 3000. The trimeπzation catalyst employed in the casting system is selected from 1 ,3,5-trιs[3-(dιmethylamιno)propyl] hexahydro-s-tπazine, potassium octoate, or mixtures thereof.

In the alternative embodiment, the present invention relates to a polyurethane-isocyanurate casting system comprising a) an isocyanate component or isocyanate terminated prepolymer and b) a hardener that comprises a polyol component, at least one tπmerization catalyst, and, optionally, a poly(oxyalkylene) polyamine, wherein a blended mixture of components a and b has an isocyanate index of from about 1.5 to about 4 0. More preferably, the isocyanate index is from about 2.0 to about 3.5, most preferably about 3.2

The present invention further relates to a process for making hardened polyurethane- isocyanurate compositions comprising a) blending an isocyanate component and hardener at a volumetric ratio of from about 2.5:1 and 1 :1 , more preferably from about 2.1 to about 1 1 , most preferably about 2.1 , to produce a polyurethane-isocyanurate composition; b) allowing the polyurethane-isocyanurate composition to gel; and c) subjecting the gelled polyurethane-isocyanurate composition to a thermal post-curing to produce a final cured composition The polyurethane-isocyanurate composition is allowed to gel for a period of time of from about 35 seconds to about 5 minutes The blend of isocyanate component and hardener preferably has an isocyanate index of from about 1.5 to about 4.0, more preferably from about 2 0 to about 3.5, most preferably about 3.2.

In a further embodiment, the present invention relates to a process for making hardened polyurethane-isocyanurate shaped articles comprising a) blending an isocyanate component and a hardener at a volumetric ratio of from 2.5:1 and 1.1, more preferably from about 2:1 to about 1 :1 , most preferably about 2:1 , to produce a polyurethane-isocyanurate composition; b) introducing the polyurethane-isocyanurate composition into a mold; c) allowing the polyurethane-isocyanurate composition to gel within the mold to produce a semi-cured shaped article; d) demoldmg the semi-cured shaped article from the mold; and e) subjecting the semi-cured shaped article to a thermal post-curing to produce a final shaped article The polyurethane-isocyanurate composition according to the instant invention is demoldable within about 5 minutes to about 1 hour The polyurethane- isocyanurate composition may be introduced into a mold maintained at a temperature of from about 80° to 100°C. The semi-cured shaped article should be thermally cured for about 1 hour at 100°C, followed by an additional cure for about 1 hour at 120°C and followed by a still further cure for about two hours at 140°C.

In a still further embodiment, the present invention relates to a hardened polyurethane- isocyanurate shaped article made by the process described above wherein the shaped article has a heat deflection temperature in excess of about 160°C, more preferably in excess of about 170°C.

The present invention relates to novel compositions for producing polyurethane- isocyanurate shaped articles having a high HDT, preferably in excess of 170°C. The polyurethane-isocyanurate compositions comprise an isocyanate component or isocyanate terminated prepolymer and a hardener. The hardener comprises a polyol component that includes a mixture of polyols and/or polyether-polyols comprising a) a polyol having a hydroxyl equivalent weight of up to 150 and a functionality of 4 to 8, b) a polyol having a hydroxyl equivalent weight of more than 1900 and a functionality of 2 to 4, and c) a polypropylene glycol having a functionality of 2 to 3 or a polytetrahydrofuran, each of which has a hydroxyl equivalent weight of 150 to 500, or a mixture thereof. The hardener further comprises at least one trimerization catalyst, and, optionally, a poly(oxyalkylene)polyamine component having 2 to 4 amino groups per molecule and an average molecular weight of between 1000 and 3000. The hardener may optionally further include additives, e.g., a plasticizer, fillers, defoamer, moisture scavenger, filler dispersing agent, flame retardants and pigments.

The isocyanate component is a liquid aromatic, aliphatic or cycloaliphatic polyisocyanate. Polyisocyanates of the diphenylmethane series or prepolymers of diphenylmethane are particularly preferred. Polyisocyanates of the diphenylmethane series is understood as meaning derivatives of diphenylmethane which contain on average at least two free isocyanate groups per molecule. Examples of acceptable compounds that can be used as the polyisocyanate component are monomeric diisocyanatodiphenylmethane isomers (MDI), such as 4,4-'diisocyanatodiphenylmethane, 2,4'-diisocyanatodiphenylmethane, or mixtures thereof, and polymeric MDI compounds (PMDI) ideally represented by the formula

in which n is 0 to 8.

Pure MDI may be represented by the formula:

Pure MDI, as used in this invention, is a thin liquid having a viscosity of about 5 to 15 centipoise at 20°C and containing approximately 50% of 2,4-MDI isomer. Commercial products are available from, among others, Dow under the tradename of Isonate 50 OP and from Bayer under the tradename of Mondur ML. A modified MDI can be prepared by a catalytic reaction in known fashion with pure MDI to produce a mixture containing a four membered ring MDI-compound. Modified MDI typically is a liquid at ambient conditions having an average functionality of about 2.1. Modified MDI is commercially available. Modified MDI is commercially available from BASF under the tradename of Lupranate MM- 103, from Dow under the tradename Isonate 2143, from Bayer under the tradename of Mondur CD, and from ICI under the tradename of Rubinate 1680. Polymeric MDI typically is a liquid at ambient conditions having an average functionality of about 2.7. Examples of PMDI commercial products having a functionality of about 2.7 are Papi 2027 from Dow, Mondur MR from Bayer, Rubinate M from ICI and Lupranate M20 from BASF. PMDI can be employed as a mixture with the monomeric or pure MDI, either modified or unmodified, to produce a formulated MDI. Modified PMDI mixtures are commercially available having a functionality of 2.4, such as Papi 2901 from Dow, Mondur MRS 10 from Bayer and Rubinate 1820 from ICI. Additives, such as benzoyl chloride may be added in the range of 100 to 440 ppm of the isocyanate component, if desired.

A preferred isocyanate-terminated prepolymer is a reaction product of a polyoxyalkylene glycol with a diisocyanate. Suitable polyoxyalkylene glycois include polyoxyethylene glycols, polyoxypropylene glycois, polyoxytetramethylene glycois, polyoxyalkylene glycois obtained by reacting diols such as 1 ,4-butanediol, neopentyl giycol or 1 ,6-hexanediol with ethylene oxide or propylene oxide, and mixtures of two or more thereof; polyoxyethylene glycois and polyoxypropylene glycois are preferred, especially those having a molecular weight of 1000 or more. Isocyanate terminated prepolymers are available from Ciba-Geigy Corporation, such as RP-6410 based on MDI and polyether polyol.

Particularly good results for the cured products are obtained by using a isocyanate component with a functionality of 2.0 to 2.4, particularly a formulated MDI containing a modified MDI having a functionality of about 2.1.

The polyol component of the hardener is preferably a mixture of polyols and/or polyether- polyols that comprises a) a polyol having a hydroxyl equivalent weight of up to 150 and a functionality of 4 to 8, b) a polyol having a hydroxyl equivalent weight of more than 1900 and a functionality of 2 to 4, and c) a polypropylene glycol having a functionality of 2 to 3 or a polytetrahydrofuran, each of which has a hydroxyl equivalent weight of 150 to 500, or a mixture thereof

Examples of the compounds that can be used as constituent a) of the polyol component are erythntol, pentaerythntol, pentitols, hexitols, such as simple sugars. Particularly preferred compounds are low molecular weight, generally less than about 150, reaction products of polyhydroxy compounds with ethylene oxide and/or propylene oxide and low molecular weight, generally less than about 150, reaction products of compounds capable of reacting with ethylene oxide and/or propylene oxide. For example, amines, such as, in particular, ethylenediamine, 1 ,4-dιamιnobenzene, 2,4-dιamιnotoluene, 2,4'-dιamιnodιphenylmethane, 4,4'-dιamιnodιphenylmethane, 1-methyl-3,5-dιethyl-2,4-dιamιnobenzene have a sufficient number of groups capable of reacting with ethylene oxide and propylene oxide.

Especially preferred compounds as constituent a) in the polyol component are the reaction products of propylene oxide with amines, in particular, ethylenediamine, and with polyhydroxy compounds, in particular, sugars. Such products are commercially available. The number average molecular weight per hydroxyl group of the polyol component is preferably at least about 60. Particularly good results are achieved when the number average molecular weight per hydroxyl group is at least about 70. Polyols that can be employed as constituent b) of the polyol component can be obtained by reaction of an initiator with alkylene oxides, for example with ethylene oxide, propylene oxide or butylene oxide, or tetrahydrofuran. Preferred initiators are usually suitable for the preparation of polyether-polyols having a functionality of 2 to 4, for example, aliphatic, cycloaliphatic or aromatic polyhydroxyl compounds having 2 to 4 hydroxyl groups, such as ethylene glycol, propylene glycol, butanediols, hexanediols, octanediols, dihydroxybenzenes, or bisphenols, hexanediols, octanediols, dihydroxylbenzenes, or bisphenols, for example bisphenol A, trimethylolpropane, or glycerol, erythritol or pentaerythritol, or corresponding polyamines, for example ethylenediamine or dianilines. Polyols based on ethylene oxide and/or propylene oxide are preferred, it being possible for the ethylene oxide/propylene oxide copolymers to be either random or block copolymers. The ratio of the ethylene oxide to propylene oxide can vary within wide limits.

The hydroxyl equivalent weight of the polyols for constituent b) should be more than 1900. The upper limit for the equivalent weight is preferably about 3000. The amount of constituent b) is, in general, about 3 to about 40, preferably about 5 to about 30% by weight, based on the total weight of the polyol component. Particularly preferred constituents b) are di- and tri-functional polyols, in particular polyols that are started with glycerol and are based on mixtures of ethylene oxide and propylene oxide.

Compounds suitable for constituent c) are accessible from di- and tri-functional initiators, such as propylene oxide. Polytetrahydrofurans are commercially available under the trade name, for example, Terathane® or Polymeg®. Constituent c) is, in general, present in the polyol component in an amount of from about 10 to about 30, more preferably about 10 to about 20% by weight, based on the total weight of the polyol component. Constituents a) and b) make up the balance of the polyol component such that the total weight percentages totals 100 percent.

The use of polytetrahydrofuran is in general preferred for mechanical production processes for polyurethane shaped articles because polytetrahydrofurans contain only primary hydroxyl groups. The use of polypropylene glycois is preferred for the production of polyurethane shaped articles by manual casting. The polyol component is preferably present in the hardener in an amount of from about 50% to about 99% by weight, based on the total weight of the hardener. More preferably, the polyol component is present in an amount of from about 66% to about 97% by weight.

The trimerization catalysts of the present invention promote trimerization of isocyanate groups to form isocyanurate rings. Isocyanurate rings are stable hydrolytically and thermally. The incorporation of isocyanurate rings into a polyurethane composition improves heat resistance and lowers combustibility. For purposes of the instant polyurethane casting system, an excess of isocyanate (a high isocyanate index) is employed in the polyurethane-isocyanurate composition relative to the polyol component. The isocyanate index is understood to mean a ratio between the equivalent weights of the isocyanate component to components having hydrogen groups reactive with the isocyanate component in the hardener. Suitable groups containing reactive hydrogen include OH, SH, NH and the like.

In conventional manner, the equivalent weights of the isocyanate component and polyol component are determined by dividing the respective molecular weights by the number of reactive sites on each component. In the alternative, the equivalent weight of a polyol is determined by dividing the atomic weight of a hydroxyl group (17) by the percent of hydroxyl groups in the polyol. The percent of hydroxyl groups in a polyol is determined by dividing the hydroxyl number by 33. The hydroxyl number is the number of milligrams of potassium hydroxide equivalent to hydroxyl content of one gram of the polyol.

For purposes of the instant casting system, the isocyanate index is preferably from about 1.5 to about 4.0, more preferably from about 2.0 to about 3.5, most preferably about 3.2. As the isocyanate index is increased above 4.0, the resulting polyurethane-isocyanurate compositions become brittle and unsuitable for rapid prototyping.

Trimerization catalysts and catalyst levels play an important role in balancing polyurethane and isocyanurate reactions. Examples of acceptable trimerization catalysts are quaternary ammonium carboxylates, e.g., DABCO® TMR, DABCO® TMR-2 and DABCO® TMR-5, tertiary amines, e.g., DMP-30 which is 2,4,6-tris(dimethylaminomethyl)phenol and Polycat® 41 which is 1 ,3,5-tris[3-(dimethylamino)propyl]hexahydro-s-triazine, and alkyl metal carboxylates, e.g., DABCO® K-15 (75% potassium octoate in diethylene glycol), KOSMOS 64 (sodium acetate), and Polycat® 46 (potassium acetate). Catalysts with low odor such as DABCO® K-15, Polycat® 41 and DABCO® TMR-5 are preferred. The trimerization catalysts are preferably present in the polyurethane-isocyanurate composition of from about 0.1 % to 1% by weight, based on the total polyurethane-isocyanurate composition.

The hardener may optionally further comprise a poly(oxyalkylene) polyamine component The poly(oxyalkylene)polyamιne component has on average 2 to 4 ammo groups per molecule and an average molecular weight of between 1000 and 3000, more preferably about 2000. The average molecular weight is determined by a theoretical estimation based on an analytical test method, a Total Acetylatable Test. Poly(oxyalkylene)polyamιnes are known and commercially available. Particularly preferred polyamines are commercially available under the trade name Jeffamine®. Examples are Jeffamine® D 2000, which is an ammo-terminated polypropylene glycol having an average molecular weight of about 2000, Jeffamine® ED 2001 ; Jeffamine® BUD 2000, a urea-terminated polypropylene ether having an average molecular weight of about 2075; and Jeffamine® T 3000, a poly(oxypropylene) tπamine started from glycerol having an average molecular weight of about 3000

The poly(oxyalkylene)polyamιne component is preferably present in an amount of from about 1% to about 20% by weight, based on the total weight of the hardener More preferably, the poly(oxyalkylene)polyamιne component is present in an amount of from about 10% to about 16% by weight

The hardener may optionally contain a plasticizer including phthalates, such as dialkyl phthalates, for example, dibutyl phthalate; alkyl benzyl phthalates, adipates, such as dialkyl adipates; dialkylene glycol benzoates; glutarates, epoxidized vegetable oils, phosphates, such as alkyl diaryl phosphates and triaryl phosphates; N-substituted pyrrolidones, and the like.

The compositions may further comprise customary additives in the field of polyurethane molding Customary additives include catalysts, such as tertiary amines, N-methyl- diethanolamine, triethanolamine, dibenzylmethylamtne, diazabicyclooctane, and the like, and organometallic compounds, for example organotin compounds, such as dibutyltin dilaurate Other additives include foam suppressants, for example, polysihcones, surface- active substances, such as castor oil, drying agents, for example molecular sieves based on zeolite, internal mold release agents, fillers, dyes, pigments, in particular, titanium dioxide, and flameproofing agents. The total quantity of customary additives in the hardener composition is typically from about 0 to about 30% by weight of the polyurethane- isocyanurate composition.

In order to prepare the polyurethane-isocyanurate compositions for use in the instant casting systems, the hardener and isocyanate components are prepared separately. The poly(oxyalkylene) polyamine, if present, and polyol components of the hardener mixture are introduced into a reaction vessel containing a mechanical stirrer and heating element The mixture is heated and stirred under a vacuum for approximately 1 to 3 hours. Once the moisture content of the mixture is below 0.05%, the mixture is cooled to approximately 50°C to 60°C and customary additives, such as molecular sieves, may be added. The resulting mixture is then stirred under vacuum until a uniform mixture is obtained. A trimerization catalyst is then thoroughly blended with the uniform mixture in a closed container to produce the hardener mixture.

The resulting hardener mixture and isocyanate component or isocyanate terminated prepolymer are mixed in a controlled fashion in a conventional dispensing machine, such as a metering mixer to produce the polyurethane-isocyanurate composition The volumetric ratio of hardener to isocyanate component is controlled. Preferably, the volumetric ratio of ιsocyanale--5orn onent to hardener is from about 2.5:1 to about 1 -1 , more preferably from about 2.1 to about 1 :1 , most preferably about 2:1 The polyurethane-isocyanurate composition begins to gel, with or without the application of heat, once the hardener mixture and isocyanate component or isocyanate terminated prepolymer are blended together The gel time typically ranges from 35 seconds to 5 minutes The polyurethane-isocyanurate composition may be introduced into a heated mold to produce a semi-cured molded article Semi-cured articles are demoldable within about 5 minutes to about 1 hour The gelled composition and semi-cured molded article are typically subjected to a thermal post-curing process to produce a final cured composition or molded article. For the production of shaped polyurethane-isocyanurate articles, the shaped articles should be subjected to a thermal post-curing process at elevated temperatures. A heat curing schedule of about 1 hour at 100°C, followed by an about 1 hour at 120°C and then an additional two hours at 140°C produces fully cured articles having good HDT and mechanical properties.

The practice of this invention will be better understood by reference to the following non- limiting illustrative examples. The following percentages or parts are expressed in percentages or parts by weight unless otherwise indicated.

Example 1 : Preparation of Hardener Ingredients Parts by weight

Ethylene oxide capped polypropylene ether glycol 295 (MW 6500)

N,N,N',N'-tetrakis(2-hydroxypropyl)ethylene diamine 345

Polyoxypropylene diamine (MW 2000) 147

Polyethylene ether glycol (MW 600) 138

Silicone 0.2

Silica 4.8

Molecular sieves 70

A one liter reaction flask with a four-neck flask head is equipped with a mechanical stirrer, thermometer, vacuum connection and heating mantle connected to a temperature regulator. All ingredients listed immediately above except the molecular sieves are charged to the reaction flask and stirred for one to three hours at 80 to 100°C under vacuum. When the moisture content is below 0.05%, the mixture is cooled to 50 to 60°C and the molecular sieves are added. The resulting mixture is stirred under vacuum until a uniform mixture is obtained.

Example 2: Preparation of Hardener II Ingredients Parts by weight

Hardener I 980

1 ,3,5-tris[3-(dimethylamino)propyl] hexahydro-s-triazine 20

Both of the ingredients listed above are blended thoroughly by stirring or shaking in a closed container. Example 3: Preparation of Hardener III Ingredients Parts by weight

N,N,N'.N'-tetrakιs(2-hydroxypropyl)ethylene diamine 323

Polytetrahydrofuran (MW 650) 142

Ethylene oxide capped polypropylene ether glycol (MW 4500) 163

Ethylene oxide capped polypropylene ether glycol (MW 6500) 290

Silicone 0.2

Silica 5

Molecular sieves 66.8

N-methyldiethanolamine 10

A one liter reaction flask with a four-neck flask head is equipped with a mechanical stirrer, thermometer, vacuum connection and heating mantle connected to a temperature regulator. The first six ingredients listed above are charged to the reaction flask and stirred for one to three hours at 80 to 100°C under vacuum. When the moisture content is below 0.05%, the mixture is cooled to 50 to 60°C and the rest of the ingredients are added The hardener mixture is stirred under vacuum until a uniform mixture is obtained.

Example 4: Preparation of Hardener IV Ingredients Parts by weight

Hardener III 996

1 ,3,5-trιs[3-(dιmethylamιno)propyl] hexahydro-s-tnazine 2

Potassium octoate in diethylene glycol 2

All of the ingredients listed above are blended thoroughly by stirring or shaking in a closed container

Example 5- Preparation of Formulated Modified Resin Ingredients Parts by weight

Modified MDI 500

Pure MDI 500 The Modified MDI is Lupranate® MM-103 commercially available from BASF. Lupranate MM-103 is an a carboiimide modified MDI containing MDI prepolymer, 4,4'-dιphenylmethane diisocyanate, and MDI mixed isomers having a specific gravity of 1.22 and a viscosity of 50 centipoise at 77°F. The Pure MDI is Isonate® 50 OP commercially available from the Dow Chemical Company composed of approximately 50% 4,4-diphenylmethane diisocyanate and 50% 2,4-diphenylmethane diisocyanate. Both of the ingredients listed above are charged into a container that is sealed with a nitrogen blanket. The mixture is stirred or shaken until a uniform blend is obtained. Benzoyl chloride (250 ppm) is added to the blend.

Example 6- Preparation of Polyurethane A

Hardener I (H) and polymeric MDI (R) with a functionality of 2.7 is mixed at a volumetric ratio of 67R/100H using a metering mix equipment and dispensed through a static mixer. The polyurethane composition is allowed to gel. The gelled material is thermally post-cured at 80°C for 4 hours and then at 120°C for 2 hours. The properties of the cured product is given in Table 1.

Example 7: Preparation of Polyurethane-isocyanurate A'

Hardener II (H) and Polymeric MDI (R) with a functionality of 2.4 is mixed at a volumetric ratio of 100R/67H and is poured into a metal mold heated to 100°C. The mixture is allowed to gel The gelled material is thermally post-cured for 2 hours each at 100°C, 120°C and 140°C The properties of the cured product are given in Table 1.

Table 1

Test Method Polyurethane A Polyurethane- ASTM (Example 6) isocyanurate A' (Example 7)

Mix ratio by volume 67R/100H 100R/67H

NCO index 1.08 2.39

Gel time (150g), seconds 50 35

Mold temperature, °C 25 100

Cure schedule 4 hrs @ 80°C 2 hrs @ and 2 hrs @ 100°, 120° and 120°C 140°C 14 -

Hardness, Shore D D-2240 80 85

Density, g/cm³ D-792 1.17 1.19

Heat deflection temperature, D-648 133 (271 ) 184 (364) @66 psi, °C(°F)

Tg , DMA, °C(°F) D-4065 147 (297) 215(419)

Izod impact, ft.lbs/in of notch D-256 0.56 0.36

Flexural strength, psi D-790 7,400^* 9,400

Flexural modulus, psi D-790 166,000 282,000

Tensile strength, psi D-638 4,800 5,500

Tensile modulus, psi D-638 151 ,000 289,000

Elongation, % D-638 7.0 2.3

Compressive strength, psi D-695 12,900 19,000

Compressive modulus, psi D-695 90,000 159,000

^* Samples did not break

The cured product resulting from the mixture containing Hardener II, a tnmenzation catalyst and a polymeric MDI having a functionality of 2.4 wherein the isocyanate index was 2.39 exhibited a significantly higher HDT relative to the mixture wherein the isocyanate index was 1.08. Polyurethane A product shown in Table 1 was further heat treated at 177°C for 3 hours to determine whether additional curing at higher temperatures would improve the HDT There was no improvement in the HDT for the Polyurethane A as a result of the additional heat treatment Further, Polyurethane A, as a result of the additional heat treatment, exhibited discoloration and blistering on the test samples, which indicated deterioration of the material. The gelled/cured product resulting from Polyurethane- isocyanurate A' composition did not crack during the thermal post-curing process or HDT testing

Example 8- Preparation of Polyurethane B

Hardener III (H) and polymeric MDI (R) with a functionality of 2 7 are mixed at a volumetric ratio of 67R/100H using a metering mix equipment and is dispensed into a mold through a static mixer The mixture is allowed to gel. The gelled material is thermally post-cured for 14 hours at 80°C. The properties of the cured product are given in Table 2 Example 9: Preparation of Polyurethane-isocyanurate B'

Hardener IV (H) and Resin I (R) are mixed at a volume ratio of 100R/67H and is poured into a metal mold heated to 100°C. The mixture is allowed to gel. The gelled material is thermally post-cured at 100°C and 120°C for one hour each and for two hours at 140°C. The properties of the cured product are given in Table 2.

Table 2

^* Samples did not break. The cured product resulting from the mixture containing Hardener IV with two trimerization catalysts and Resin I having an isocyanate index of 2.4 exhibited significantly higher HDT relative to a mixture wherein the isocyanate index was 1.11. The gelled/cured product resulting from Polyurethane-isocyanurate B' composition did not crack during the thermal post-curing process or HDT testing.

Hardener (IV) and resin (I) can be mixed in varying ratios. Cured products were made from mixtures based on resin to hardener volumetric ratios of 67/100, 100/100, 100/67, 100/50, 100/45; 100/40, 100/33 and 100/25. The properties of the resulting cured products are given in Table 3. The applicable test methods have been identified in preceding tables.

Example 10: Determination of NCO Index

Resin I has an equivalent weight of 136 as determined by titration. Hardener IV has an equivalent weight of 185 which is calculated from the equivalent weights of the ingredients that have a reactive hydrogen with the isocyanate. Wherein the weight ratio of resin to hardener is 80:100, the ratio of resin equivalents to hardener equivalents is 0.588 to 0.541 or 1.09.

Table 3

Flex.strength.psi 7,300^* 10,800^* 12,000 14,000

Flex.modulus.psi 156,000 227,000 241 ,000 309,000

Table 3 (continuation)

^** Samples expanded slightly.

While the invention has been illustrated by means of various examples, it will be apparent that further modifications and variations are possible without departing from the spirit and scope of the invention, which is defined by the appended claims.

Claims

Claims:

1. A polyurethane-isocyanurate casting system comprising a) an isocyanate component or isocyanate terminated prepolymer and b) a hardener that comprises a polyol component, at least one trimerization catalyst and, optionally, a poly(oxyalkylene) polyamine, wherein the components a and b are used in form of a blended mixture having an isocyanate index of from about 1.5 to about 4.0.

2. The casting system according to claim 1 wherein the isocyanate index is from about 2.0 to about 3.5.

3. The casting system according to claim 2 wherein component a is selected from the group consisting of monomeric polyisocyanates, polymeric polyisocyanates and mixtures thereof.

4. The casting system according to claim 3 wherein the polymeric isocyanate is a polymeric compound represented by the formula:

wherein n is 0 to 8.

5. The casting system according to claim 1 wherein the isocyanate component has an isocyanate index of about 3.2.

6. The casting system according to claim 1 wherein the isocyanate component has a functionality of about 2.0 to about 2.4.

7. The casting system according to claim 6 wherein the isocyanate component has a functionality of about 2.1.

8. The casting system according to claim 1 wherein the trimerization catalyst is 1 ,3,5-tris[3- (dimethylamino)propyl] hexahydro-s-triazine, potassium octoate, or mixtures thereof.

9. The casting system according to claim 1 wherein the polyol component comprises a mixture of: a) a polyol having a hydroxyl equivalent weight of up to 150 and a functionality of 4 to 8; b) a polyol having a hydroxyl equivalent weight of more than 1900 and a functionality of 2 to 4; and c) a polypropylene glycol having a functionality of 2 to 3 or a polytetrahydrofuran, each of which has a hydroxyl equivalent weight of 150 to 500, or a mixture thereof.

10. In a polyurethane-isocyanurate casting system for molding the reaction product of a composition containing a) an isocyanate component or isocyanate terminated prepolymer and b) a hardener that comprises a polyol component, at least one trimerization catalyst, and, optionally, a poly(oxyalkylene) polyamine, the improvement comprising blending component a with component b at a volumetric ratio of from about 2.5:1 to about 1 :1.

11. The casting system according to claim 10 where the volumetric ratio of component a to component b is from about 2:1 to about 1 :1.

12. The casting system according to claim 11 wherein component a is selected from the group consisting of monomeric polyisocyanates, polymeric polyisocyanates and mixtures thereof.

13. The casting system according to claim 12 wherein the polymeric isocyanate is a polymeric compound represented by the formula:

wherein n is 0 to 8.

14. The casting system according to claim 11 wherein the isocyanate component has a functionality of from about 2.0 to about 2.4.

15. The casting system according to claim 11 wherein the trimerization catalyst is 1 ,3,5- tris[3-(dimethylamino)propyl] hexahydro-s-triazine, potassium octoate, or mixtures thereof.

16. The casting system according to claim 10 wherein the polyol component is a mixture of: a) a polyol having a hydroxyl equivalent weight of up to 150 and a functionality of 4 to 8; b) a polyol having a hydroxyl equivalent weight of more than 1900 and a functionality of 2 to 4; and c) a polypropylene glycol having a functionality of 2 to 3 or a polytetrahydrofuran, each of which has a hydroxyl equivalent weight of 150 to 500, or a mixture thereof.

17. The casting system according to claim 16 wherein the composition contains the poly(oxyalkylene) polyamine component and the poly(oxyalkylene) polyamine component has 2 to 4 ammo groups per molecule and an average molecular weight of between 1000 to 3000.

18. In a process for making hardened polyurethane-isocyanurate articles by a) blending component a and component b of claim 1 to prepare a polyurethane-isocyanurate composition, b) allowing the polyurethane-isocyanurate composition to gel, and c) subjecting the gelled polyurethane-isocyanurate composition to a thermal post-curing to produce a final cured composition, the improvement comprising blending component a with component b at a volumetric ratio of from about 2.5:1 to about 1 :1.

19. The process according to claim 18 wherein the volumetric ratio is from about 2:1 to about 1 :1.

20. The process according to claim 18 wherein the blend of component a and component b has an isocyanate index of from about 1.5 to about 4.0.

21. In a process for making hardened polyurethane-isocyanurate shaped articles by a) blending component a and component b of claim 1 to produce a polyurethane-isocyanurate composition, b) introducing the polyurethane-isocyanurate composition into a mold, c) allowing the polyurethane-isocyanurate composition to gel within the mold to produce a semi-cured shaped article, d) demolding the semi-cured shaped article from the mold, and e) subjecting the semi-cured shaped article to a thermal post-curing to produce a final shaped article, the improvement comprising blending component a and component b at a volumetric ratio of from about 2.5:1 to about 1 :1

22. The process according to claim 21 wherein the volumetric ratio is from about 2:1 to about 1 :1.

23. The process according to claim 21 wherein the blend of component a and component b has an isocyanate index of from about 1.5 to about 4.0.

24. A hardened polyurethane-isocyanurate shaped article made by the process according to claim 21 wherein the shaped article has a heat deflection temperature in excess of about 170°C.