These fast-curing and high-performance Isocyanate-Epoxy resins FPR are two-shot thermosetting systems based on liquid aromatic polyisocyanates of the MDI family (component A) + liquid, di- or multifunctional, glycidylether-type epoxies (component B). Upon mixing of the two components A + B in a 70:30 or 60:40 weight ratio, the resulting resins are odorless, low-viscosity liquids, with a pot-life at room temperature adjustable from 15 minutes to 6 hours.  The subsequent polymerization converts them into hard and high-softening materials, with a mixed isocyanurate-oxazolidone chemical structure.

Through their own specialty & proprietary polymerization catalysts FPC, the resin hardening time at temperatures from 25 to100° C may easily be varied at will within a broad interval from hours to a few minutes, and optionally made as short as 20-30 seconds at 80-100° C.  After appropriate post-curing, the solid products are turned into densely crosslinked and absolutely insoluble, amber-colored polymeric glasses, with a softening point optionally as high as 320°C.

By varying the catalyst type and concentration, hardening times can be adjusted to fulfil the wide range of processing requirements including those of the fast R-RIM, S-RIM, RTM, HS-RTM, and pultrusion technologies, to those of the relatively slow Bag Molding, Liquid Injection Molding, Vacuum Infusion Molding, and resin casting techniques.

These hard, moderate-cost thermosets are further characterized by:  1) a superior hydrolytic, solvent and chemical resistance;  2) an intrinsic flame resistance;  3) outstanding adhesion to mineral glasses, ceramics and metals.  Besides the above characteristics, durability at peak temperatures of 300°C, and at continuous service temperatures of up to 200°C, make these resins materials of choice as matrices for structural composites, for fabrication of parts and components, embedding or coating of electrical/electronic/electromechanical devices, and a variety of applications whenever a critical combination of heavy-duty performance, fast processing and competitive prices is a critical issue.

1.      Processability Characteristics

1.1     Pot-Life and Polymerization Rates

• Pot-life at temperatures up to 50°C:  perfect latency (stability of the initial viscosity) adjustable from 10-15 minutes to 1-1.5 hours, depending on temperature, FPC catalyst type and concentration.

• Gelation times at 60-100°C:  from 20 seconds to 2 hours, depending on the catalyst type & concentration.

• Vitrification times at 60-100°C:  from 40 seconds to 6 hours, depending on the catalyst type & concentration.

• The resin hardening must be completed by thermal after-treatments:  1 to 6 hours at temperatures from 150 to 240°C (typically, 1.5 ÷ 2 hours at 180 ÷ 240°C).  Plasticized FPR resins (with lower final Tg) require shorter post-curing treatments, and/or lower post-curing temperatures (150 ÷ 180°C).

1.2   Microwave Processability

Thanks to the peculiar physico-chemical properties and chemical mechanisms of action of their specialty catalysts, these isocyanate-epoxy resins are exceptionally-well suited to be cured and/or post-cured by microwave heating.  By means of such processing techniques, the curing and/or post-curing times can typically be reduced to 1/4 ÷ 1/10 of those required under conventional thermal conditions.  Novel proprietary catalysts, specifically developed for the microwave processing of FPR resins ( FPC W1  e  FPC W2 ), allow for the preparation of FPR resin compositions endowed with the following, extremely interesting combination of features:  a prolonged pot-life at room temperature (up to 4-6 hours), coupled with particularly short vitrification times under microwave irradiation, minimized to 1/8 - 1/10 of those under conventional thermal treatments, at the same resin temperature.

1.3  Rheological Properties

• Initial viscosity:  100 ÷ 600 cps at 23°C, depending on the resin formulation, i.e. (without any resin diluents) viscosity values 5-10 times lower than those of known epoxy resin formulations, and 2-4 times lower than those of unsaturated polyester, and conventional & multifunctional vinyl-ester resins.

• Chemorheology:  typical "snap-curing" profile, as required, e.g., by RTM and RIM technologies.

• Thixotropy::  the resins can easily be endowed with thixotropic properties, by addition of conventional thixotropic agents (e.g. 0.5 ÷ 1 % by weight of colloidal silica).

2.    Properties of Cured Resins

2.1  Distortion Temperature

Glass Transition Temperature ( Tg ~ HDT ).  Depending on the resin formulation:  Tg of standard Isocyanate-Epoxy FPR S resins = 250 ÷ 300 °C (typically:  270 ÷ 300°C);  Tg of specialty Isocyanate-Epoxy FPR H resins = 300 ÷ 320 °C.  Plasticized formulations possess a glass transition temperature lowered to180 ÷ 240 °C;  for partially plasticized grades, the Tg spans the 230 ÷ 270°C range.

2.2  Thermal and Thermo-Oxidative Resistance

Fully cured FPR resins possess an excellent thermal stability up to 280°C, being currently able to sustain continuous use temperatures  > 150°C (typically, of 160 ÷ 180, and up to 200°C), and peak temperatures up to 350-360 °C.  Their high-temperature aging, in both inert atmosphere and air, implies a smooth and slow weight loss, without any bulk and surface micro-structural damages (with the resin surface remaining in fact smooth and brilliant).  For example, the weight loss of neat resin specimens is of 5 - 6 % after 200 hours at 250°C in air; and that of glass fiber-reinforced or mineral powder-filled resins (i.e., quartz-, calcined clay-, silica-filled, etc.) [60 wt. % of fibers or mineral powder] spans the 2.5 ÷ 2.8 % interval after 2000 hours of continuous exposure at 200° C in air.

2.3   Fire Resistance

Fully-cured, neat FPR resins are inherently flame retardant (with respect to neat unsaturated polyester, vinyl-ester and conventional epoxy resins), and display a fire behavior not so much different from that of phenolic and imide resins.  Classification according to the UL 94 test method (Underwriters Laboratories), for 3.2 mm-thick specimens:

•  neat resins                                                                                                   V1

•  resins filled with common, inert mineral fillers  (talcs, micas, clays)                   V0

•  resins filled with commercial, mineral flame retardants (10-20% by weight)         better than V0

•  partially brominated resins                                                                             much better than V0

2.4     Water Uptake and Chemical Resistance

• In boiling water, as well as in saturated moist air, the fully-cued resins display water uptake levels remarkably below those exhibited by the best epoxy thermosets (maximum, equilibrium water uptake capacities of FPR thermosets = 0.9 ÷ 1.0 % by weight).  Such values indicate a superiority of FPR resins over the entire category of epoxy materials, and particularly with respect to the DDS-cured ones (with the highest Tg levels) for structural, aerospace-grade applications (whose hydrophilicity problems, hydration attitudes in moist air, and resulting remarkable rigidity losses, dimensional instability issues, etc. are well recognized and critically evaluated in the field of structural composite materials).

• Thanks to the absence of hydrolytically- and chemically-weak groupings (such as esters, amides and urethanes), as well as to the perfect chemical neutrality of their specialty FPC catalysts, the glass transition temperature and mechanical properties of FPR resins are unaffected (or just minimally affected) by aging in both moist environments and boiling water (even in the presence of surfactants).  By virtue of their chemical structure, the resistance to very aggressive chemicals is excellent as well.  Only concentrated, strong acids and bases can attack, and slowly degrade, the surface of the fully-cured resins, which sustain indeed, e.g., 12 hours in aqua regia at room temperature, or 24 hours in boiling aqueous (20 wt. %) caustic soda.

2.5  Mechanical Properties of the Neat, Cured Resins

• The overall spectrum of their mechanical and thermal-mechanical properties make these isocyanate-epoxy resins excellent matrices for structural composites, especially for high-temperature applications.

• From the standpoint of flexural, tensile and impact properties at room temperature, they are equivalent to the best unsaturated polyester and vinyl-ester resins, as well as to most conventional and specialty epoxy thermosets:

 flexural strength at 23° C (ASTM D790)  =   90 ÷ 110 MPa;

 flexural modulus at 23° C ( ASTM D790)  = 3 ÷ 4 GPa.

• As an important advantage over the aforementioned reference resins, this level of mechanical properties is well maintained over a broad interval from below room temperature up to about 50°C below the glass transition point of the particular isocyanate-epoxy resin composition considered.  Typically, in fact, flexural modulus decays of only 20 ÷ 25 % are shown over the -50 ÷ 200-220°C temperature range for the standard grade resins (FPR S resins), and over the -50 ÷ 260°C interval for the high-Tg ones (FPR H resins).  Obviously, proportionally smaller stiffness decreases are being displayed by glass or carbon fiber-reinforced materials.

 2.6  Mechanical Properties of Composites

• Short-term properties:  the mechanical properties of structural laminates fabricated by fast Liquid Injection Molding with these resins are equivalent to those of the best epoxy laminates obtained by pre-pregging + bag molding.

Typical mechanical properties of isocyanate-epoxy structural composites (reinforcement:  glass fiber woven roving;  overall fiber content: 70-75 % by weight, 55-59 % by volume) are the following:

quasi-isotropic 8-ply glass fiber-reinforced laminates  (0, 90, ± 45°, symmetrical);  @ 23°C

orthotropic 8-ply glass fiber-reinforced laminates  (0, 90°);  @ 23°C

The excellent mechanical properties of fiber-reinforced FPR thermosets are linked primarily to the high adhesion of such resins to reinforcing fibers, as evidenced by the SEM micrographs below, showing the fracture morphology of a glass fiber-reinforced FPR resin.  These micrographs exemplify the post-impact permanence of significant portions of the glassy polymeric matrix firmly linked to the fiber surfaces, despite the micro-morphology proper to a brittle fracturing of the composite.  Such strong FPR resin-fiber adhesion is further demonstrated by the values of the interlaminar shear strength (short-beam shear strength, according to ASTM D2344) of glass and carbon fiber-reinforced FPR resin orthotropic laminates (at 23°C):

• Post-impact mechanical properties:  as compared to commercial, aerospace-grade carbon fiber/epoxy composites, evaluations of the residual mechanical strength (tensile, flexural, and impact strength) of structural, carbon fiber-reinforced FPR laminates after non-destructive ball-drop impacts allowed for rating them as aerospace-grade materials, with the advantage of a 60-80°C-higher distortion temperature.

2.7   Electrical Properties

These resins are per se characterized by a spectrum of electrical properties (i.e., dielectric strength, dielectric constant and loss factor, surface and volume resistivity, as well as thermal endurance) similar to that of the best epoxy materials qualified on the market for heavy-duty, low and medium-voltage electrical applications (high-power electrical transformers, big capacitors and insulators, etc.).

Cast thermosets from quartz powder-filled (60 wt. %) FPR H-0 and H1 resins exhibit the following, typical properties:

3.  Main Grades of Isocyanate-Epoxy FPR Resin Systems Developed

3.1     FPR Resin Systems

• Resin System FPR S-1 :  Standard resin, with medium viscosity and medium thermal-mechanical properties (HDT > 250°C), flame resistance = V1 according to UL 94, transparent, pale amber color.  General purpose, high-temperature resin, and for manufacturing of composite materials with glass, carbon and/or Kevlar® fiber reinforcements of standard type.

• Resin System FPR S-1 FG  (food-grade):  Novel, food-grade, fast-curing and standard-performance resin, with medium viscosity and medium thermal-mechanical properties (HDT > 250°C), flame resistance = V1 according to UL 94, transparent, pale amber color.  High-temperature and strongly chemically-resistant resin for items in contact with foods and beverages;  this resin system implies the use of the special, food-grade Catalyst FPC FG-2.

• Resin  System FPR S-2 (experimental grade):  Standard resin, with medium viscosity and medium thermal-mechanical properties (HDT > 250°C), halogen-free flame-retardant (V0 according to UL 94), translucent, pale amber color.  Resin for standard high-temperature composite materials; high-temperature resin for general purposes requiring halogen-free flame retardancy.

• Resin System  FPR S-3 :  Standard resin, with medium viscosity and medium thermal-mechanical properties (HDT = 240-250°C), partially brominated flame-retardant (V0 according to UL 94), transparent, amber color.  High-temperature resin for standard composite materials, and general purposes, implying high flame retardancy requirements.

• Resin System  FPR S-1 LV :  Very low-viscosity resin, with medium thermal-mechanical properties (HDT = 220° C), flame resistance = V1 according to UL 94, transparent, pale amber color.  High-temperature resin ideal fo manufacturing of composite materials containing particularly high volume fractions of reinforcing fibers, and especially for structural composites with very high mechanical properties made by infiltration of densely packed preforms of glass, carbon and/or Kevlar® fibers.

• Resin System  FPR S-3 LV :  Resin similar to FPR S-1 LV, partially brominated flame-retardant (V0 according to UL 94).

• Resin System FPR H-0 :  Very high-performance, specialty resin, of dark brown color, with medium/high viscosity and outstanding thermal-mechanical and chemical properties (HDT = 300° C), flame resistance = V1-V0 according to UL 94.  Resin for highly-demanding, heavy-duty applications (high-temperature, structural composites complying with aerospace standards;  high-voltage electrical applications;  parts, components and protective coatings for chemically and biologically strongly aggressive environments).

• Resin System  FPR H-1 :  High-performance, specialty resin, similar to FPR H-0, of amber color, with medium viscosity and high thermal-mechanical and chemical properties (HDT = 280° C), flame resistance = V1-V0 according to UL 94.

• Resin System  FPR H-2 (experimental grade):  High-performance, specialty resin, similar to FPR H-1, with relatively-high viscosity, halogen-free flame-retardant (V0 according to UL 94).

• Resin System  FPR H-3 :  High-performance, specialty resin, similar to FPR H-1, with medium viscosity, partially brominated flame-retardant (V0 according to UL 94).

3.2     FPC Curing Catalysts

• Catalyst  FPC 1A :  "Pure catalyst".  Standard, medium/fast-curing catalyst, for the standard FPR S Resin Systems .  Clear, white to pale-straw oily liquid;  promptly soluble in resins at room temperature.  Low-cost, dual-function catalyst:  fast-hardening catalyst + fast wetting and impregnation promoter for reinforcing fibers in composites.  Best suited for RTM and LIM manufacturing of highly qualified commodity and structural composites for automotive, appliances and general construction uses.

• Catalyst  FPC 1B :  "Pure catalyst".  Standard, fast-curing catalyst, for the standard FPR S Resin Systems.  Clear, pale-straw oily liquid;  promptly soluble in resins at room temperature.  Convenient, dual-function catalyst:  rapid-hardening catalyst +  fast wetting and impregnation promoter for reinforcing fibers in composites.  Ideal for R-RIM, S-RIM, RTM & HS-RTM, LIM, as well as pultrusion, manufacturing of structural composites for automotive, appliances and general construction uses.

• Catalyst  FPC 2A :  "Pure catalyst".  Very fast-curing catalyst, designed for the high-performance FPR H Resin Systems .   Very fast-curing or low-dosage catalyst for the standard, FPR S Resin Systems.  Clear, refractive, honey-like, yellowish liquid;  readily soluble in resins at room temperature.  For applications requiring thermosets with a superior thermal and chemical performance level:  recommended for high continuous-service temperatures, uses in strongly oxidizing and/or chemically aggressive environments, implying stressing wet/dry and/or warm/cold cycles, etc.  Well suitable for heavy-duty electrical insulation purposes.

• Catalyst FPC CP-2A :  "Catalyst concentrate".  Masterbatch solution of the fast-curing catalyst FPC 2A in a liquid mixture of epoxy resins.  Clear, pale-yellow, honey-like liquid;  easily miscible with resins at room temperature.  Especially designed for a precise dosage of FPC 2A catalyst in small-scale or occasional manufacturing operations.

• Catalyst FPC FG-2 :  "Pure catalyst".  Special, food-grade fast-curing catalyst, especially designed for the food-grade Resin System FPR S-1 FG.  Clear, yellow, honey-like liquid.

• Catalyst  FPC 2B :  "Pure catalyst".  Superfast-curing catalyst, designed for the high-performance FPR H Resin Systems .  Ultrafast-curing or very low-dosage catalyst for the standard FPR S Resin Systems .  Clear, refractive, yellow, honey-like liquid;  easily soluble in resins at room temperature.  For applications requiring thermosets with a premium thermal, chemical and dielectric performance spectrum:  ideal for high-temperature structural composites for heavy-duty automotive parts, industrial constructions and appliances, aerospace-grade composites, high dielectric strength electric insulators for high-voltage/high-temperature uses, etc.

• Catalyst FPC CP-2B :  "Catalyst concentrate".  Masterbatch solution of the superfast-curing catalyst FPC 2B in a liquid mixture of epoxy resins.  Clear, yellowish, honey-like liquid;  easily miscible with resins at room temperature.  Especially designed for a precise dosage of the FPC 2B catalyst in small-scale or occasional manufacturing operations.

• Catalyst  FPC XF :  NEW!  "Pure catalyst".  Ultrafast-curing catalyst, for all the FPR H and FPR S Resin Systems .  Pale yellow, low-melting crystalline solid.  Designed to minimize (i.e. further decrease the already low) concentration of the FPC 2B catalyst.

•  Catalyst FPC W1  :  "Pure catalyst".  Specialty,  fast microwave-curing  catalyst for all the Resin Systems FPR S & H .  It enables a long pot-life and short curing and post-curing times under microwave irradiation.  Honey-like, light amber, refractive liquid;  promptly soluble in gently warmed resins.  It imparts to isocyanate-epoxy thermosets the same high-performance spectrum provided by Catalyst  FPC 2A.

•  Catalyst FPC W2  :  "Pure catalyst".  Specialty,  superfast microwave-curing  catalyst for all the Resin Systems FPR S & H.  It ensures a long pot-life and particularly short curing and post-curing times under microwave irradiation.  High-viscosity, amber-colored, refractive liquid;  easily miscible in gently warmed resins.  It provides isocyanate-epoxy thermosets with the same premium performance spectrum enabled by Catalyst  FPC 2B.