The present invention relates to reaction injection moulding, and more particularly to the production of polyureas in such a moulding operation.

Reaction injection moulding (RIM) involves the intimate mixing of at least two streams of reactive liquids followed by their injection into a mould where polymerization and fabrication occur simultaneously. Production of polyurethanes and polyurethane-ureas by RIM is well documented and these polymers are typically formed by reaction of an organic polyisocyanate, a polyol and a chain extender

(usually a onomeric diol or dia ine) . The use of an aliphatic/aromatic diol as chain extender yields a polyurethane whilst an aromatic diamine chain extender gives a poly(urethane-urea) . Both types of polymeric material are generally phase-separated comprising hard and soft-segment phases. The soft-segment phase is derived from reaction of the polyol and the polyisocyanate whereas the hard-segment phase originates from reaction of the chain extender and the polyisocyanate.

Amine functionalized polyether prepolymers have been available for several years (see, for example, UK-A-2,175,910) and in the early 1980s their use as soft-segment precursors in polyurea elastomer RIM formulations was disclosed, see for example US-A- 4,433,067 and US-A-4,607,090. This work however has been restricted to the production of polyurea elastomers containing low hard segment contents (<50%), and their glass-filled composites. A typical patent by Texaco has an example based on a diphenyl methane diisocyanate (MDI) prepolymer reacted with Jeffamines D2000/T3000/T5000/T403 (Texaco amine

functionalized polyethers) alone, or in admixture, with diethyl toluene diamine (DEDTA) as chain extender.

DEDTA is a mixture of compounds of the formula

The hard segment level was ^- 0% and typical materials had Young's moduli of MPa, elongations of 200% and tensile strengths of /"*•—'27 MPa.

BASF, similarly, have disclosed in DE-A1-3215909 (see also Chem Abs 100:82146) polyurea elastomers produced by RIM. This German patent specification is based on amine functionalized polyethers, MDI prepolymers and aromatic amine chain extenders of general formula I and II.

The patent again relates to low hard segment materials and an Example cites a material containing

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ethylene bis-2,6-diisopropylaniline (MDIPA) (R ^IV ,R ^V ,R ^VI ,R ^VI1 = iPr in structure II).

This material had a hard segment content of

' -45%, a flexural modulus of-——580 MPa, a tensile strength of 27 MPa and an elongation at break of 350%.

The data shown above are typical for polyurea elastomers. In addition the following general observations may be made on patents which disclose polyurea elastomers.

(1) There are numerous patents disclosing polyurea elastomers formed from amino functionalized polyoxypropylenes in combination with an aromatic amine chain extender and an organic polyisocyanate. The hard segment contents are low, 50%, and the mould temperatures employed are less than 100°C (generally 50-70°C) .

(2) Most patents use DEDTA as the chain extender in their Examples, although one specific patent application (DE-A1-3215909) uses MDIPA.

(3) We are unaware of any patents specifically aimed at the production of rigid, high hard segment content polyureas via Reaction Injection Moulding.

It is an object of the present invention to provide a method of producing rigid polyureas of comparatively high hard segment content by Reaction Injection Moulding.

According to the present invention there is provided a method of producing a polyurea by reaction injection moulding comprising reacting in the mould

(i) a polyisocyanate compound

(ii) a polyamine chain extender having at least

two sterically hindered amino groups provided one on each of two ring systems connected directly or indirectly to each other.

(iii) a further amino compound having at least two amino groups connected by a flexible chain

wherein the HS% value (as herein defined) of the reactants is at least 60% and the initial temperature of the mould surface at the commencement of moulding is at least 90°C.

The HS% value (representative of hard segment composition) as used herein is calculated as follows

HS% = amount of chain extender + its stoichiometric equivalent of polyisocyanate x 100 Total mass of (i),(ii) and (iii)

= x [E _c +rE _x ] x 100

xE _c +yE _p +r(x+y)Eτ _.

where E = equivalent weight x = equivalents of chain extender (ii) y = equivalents of further amino compound (iii) subscripts c = chain extender, p = polyamine and I = isocyanate, and r is the ratio of the number of equivalents of the isocyanate compound to the total number of equivalents of the two amino compounds ((ii) and (iii)).

Generally r is greater than 1, e.g. 1.05.

The invention enables coherent polyurea materials having high moduli > lGPa with elongations

>100%, to be produced by increasing the hard segment content of the system and altering its structure.

of ultimate material's properties formed an important aspect of this work. The current view of those experienced in RIM is that production of materials having the properties described above is not feasible under the processing conditions used for DEDTA based polyureas. This arises because premature hard segment vitrification prevents the formation of hard segment sequences of sufficiently high molar mass to allow development of ultimate properties. Thus under the processing conditions employed in the prior art for polyurea elastomers, high hard segment content reactant systems yield incoherent particulate materials. Raising the mould temperature to 120°C for DEDTA-based systems also gives fragile materials which cannot be demoulded without damage (see Comparative Example 1 below) .

The problem has been overcome and materials with the desired properties have been formed by using as the chain extender a polyamine with sterically hindered amino groups provided on respective ring systems and ensuring that the initial temperature of the mould surface (i.e. at the commencement of the moulding operation) is at least 90°C.

In such chain extenders the number of amine groups/unit mass of the chain extender (and hence the concentration of urea groups in the final product) is reduced as compared to DETDA in which the amino groups are on the same aromatic nucleus. The steric hindrance of the amino groups reduces their reactivity to the isocyanate. The initial mould temperature of at least 90°C is closer to the vitrification temperature of the hard segment thus giving more chance for the hard segment to develop.

There are the following effects upon hard segment properties (which are described with specific reference to the use of one of the preferred chain

extenders, MDIPA, employed in the invention).

(a) The glass transition (TgH) ₀ f the hard segment is reduced relative to hard segments based on DEDTA (TgH i _s 185°C for MDIPA hard segments compared with 230°C for DEDTA hard segments) .

(b) The urea group concentration is reduced relative to that in DEDTA-based systems (3.5 mol m ^~ 3 for MDIPA compared with 5.6 mol m ^-3 for DEDTA) .

(c) The hydrogen bonding potential is reduced relative to the DEDTA-based system because of the reduction in urea group concentration and the steric hindrance afforded by the bulky isopropyl groups of the MDIPA.

These factors together with the increased mould temperature facilitate a greater conversion of amine groups to urea hard segment groups giving a higher sequence length prior to vitrification, thus allowing higher hard segment contents in the polyurea. This allows improvements in "as moulded" properties (green-strength) to be achieved. These improvements are also retained in the post-cured samples.

The properties of these polyurea materials are superior to those of reinforced polyurea elastomers and have significant potential as metal replacements in the automotive industry. They may be differentiated from polyurea elastomers reported in previous patents by their high hard segment contents, the high mould temperatures used in processing and their behaviour on tensile testing where a yield point is observed.

In accordance with the invention, polyureas are produced by RIM from a minimum of three reacting components. These reactants are (a) a polyamine

compound with a flexible chain connecting the amino groups (b) a chain extender with at least two sterically hindered amino groups on respective ring systems, preferably an aromatic diamine chain extender, and (c) a polyisocyanate, preferably an aromatic polyisocyanate. Typical reactants are described below.

(a) Polyamines

These include a flexible chain, i.e. one with a glass transition temperature (Tg) well below ambient temperature.

The preferred polyamines under this heading are high molecular weight amine functionalised (preferably amine terminated) polyether based materials and have a molecular weight of 200-12000. Their functionality is preferably in the range 2-8. The materials can be used in admixture, i.e. mixed functionalities and/or mixed molecular weights.

Other polyamines which may be used are based on silicones, butadienes, isobutylenes, and isoprenes as well as copoly ers thereof with other monomers, e.g. a copolymer of butadine and acrylonitrite.

(b) Chain Extenders

The chain extenders used have sterically hindered amino groups provided on ring systems which are connected directly or indirectly to each other, e.g. via a ethylene group. The attachment of the amino group to a ring as well as the steric shielding reduces its reactivity towards isocyanates as compared to aliphatic diamines.

Preferably the chain extender is a diamine.

Preferably there are two ring systems in the molecule. These ring systems may be the same or different and may be aromatic, quasi-aromatic, heterocyclic or alicyclic.

The steric shielding of the amino group is preferably provided by an alkyl group (e.g. a Cχ_4 alkyl group, more preferably a Cι_3 alkyl group) on at least one carbon atom adjacent to that to which the amino group is attached. The preferred shielding gropup is an iso-propyl group.

Typical aromatic diamines which may be used are represented by the general formula III or IV.

in which R1-R10 ^ma Y ^ ^e hydrogen, alkyl, aryl or araalkyl in any combination with the proviso that at least one of each of the pairs listed below is a group providing steric shielding of the adjacent

amine group, preferably an isopropy] group. R and R5 R3 and R4 R8 and R9 ι h< resence of a methylene grou:. betweer, the two aromatic nuclei in Formula (III) provides a limited amount of flexibility in the chain extender.

The analogous cycloaliphatic derivatives (i.e. in which the aromatic nuclei are hydrogenated ) may also be used.

The preferred compounds are MDIPA (methylene bis-2, 6-diisopropyl aniline) Rj,R3,R4,Rg = iPr; R2, ^R 5 = H; in structure (III), and M.MIPA (methylene bis 2-methyl-6-isopropyl aniline) ] _. , 3 = iPr; 12,^5 ^{= H} ' ^* and 4, β = Me in structure (III) together with their mixtures with DEDTA.

Other amino functional chemicals such as aliphatic diamines, napthalenic diamines liquid mixtures of the polyphenylene polymethylene polyamines of the type obtained from aniline formaldehyde condensation may also be used, (c) Polyisocyanate

This will most preferably be an aromatic diisocyanate particularly diphenyl methane diisocyanate (MDI) (V).

OC NN CH ₂ -Λ U /~" ^NC0 ( V )

and its derivatives conventionally used to obtain a liquid product.

The preferred derivative would be a uretonimine/carbodiimide modification of pure MDI for

example Isonate 143L (ex DOW) or their mixture with quasi prepolymers, e.g. Isonate RMA 400 (ex DOW).

Further aromatic polyisocyanates which may be used in the process of the invention are those exemplified in columns 3 and 4 of US-A-4,487 _; 908.

It should also be noted that the polyisocyanate and chain extender may be such that they react together to give a "rigid rod" structure for the hard segment. Polyureas formed with such rigid rod hard segement structures are high perfomance materials.

Still further examples of diisocyanates which may be used are alicyclic and heterocyclic diisocyanates, e.g. furan diisocyanates.

In addition to the three components described above, optional further species may be used, including a blowing agent to produce cellular materials, catalysts to equate reactivity of reactants, mould release agents to assist de oulding of fabricated materials and reinforcing fibres and fillers.

Typical blowing agents are low boiling fluorocarbons or azo compounds decomposing at the moulding temperature. Catalysts include organo tin compounds such as dibutyl tin dilaurate and tertiary amines such as diazabicyclo octane (DABCO) . Mould release agents may be organo siloxanes such as silicone fluids (Dow Corning Q2-7119 fluid) or soaps such as metal stearateε; typically the zinc salt.

Reinforcements used to form composite materials are inorganic or organic fillers and fibres such as glass (hammer milled and chopped strand), glass flakes, mica, wollastonite, calcium carbonate, Kevlar and C-fibres.

In general polyurea formation is a rapid process with reactants being converted from low viscosity

liquids to high modulus solids in less than 2 seconds. In order to fabricate such materials careful consideration must be given to part size and machine capacity. Reactants should be maintained between 10 and 80°C and optimally between 30 and 60°C. The mould surface should initially be maintained between 90 and 180OC and preferably between 100 and 180°C. The isocyanate index, defined as the ratio of functional groups (NCO/NH ₂ )xlOO should be maintained between 70-130 preferably in the range 90 to 110.

The amounts in which the components (a), (b), and (c) are to be reacted together may be readily calculated given their molar masses, their functionalities, the desired hard segment content, and isocyanate index.

Post-curing of moulded materials should be effected between 100 and 250°C and typical schedules were 200θc/lhr or 100°C/18hr dependent on product structure/stability. It is however envisaged that with the use of suitably high mould temperatures (although obviously not so high as to degrade the product) it may be possible to effect complete curing within the mould.

The density of as-moulded materials is ✓— _* ^1.2g cm ^~ 3 and this may be altered by addition of blowing agents.

The invention will be further described by way of example only with reference to the following Examples. The method by which the tensile test results described in the Examples were obtained is described at the end of the Examples.

Comparative Example 1

Materials code UD65 where U = polyurea, D = DEDTA and

65 = % HS. The formulation consisted of Jeff mine T,5000 (ex Texaco) 100 parts by weight, DEDTA (ex Lonza) 74.5 parts and RMA 400 (ex DOW) 147.6 parts. The reactant streams isocyanate (A) and mixed amine (DEDTA/T5000) (B) were maintained at 35°C. The materials were moulded using a mould initially at 120°C and a throughput (W β ) of the mixed amine of lSOgs" ¹ .

The physical properties of the as-prepared and post-cured samples are given in Table 1.

Table 1. Physical properties of UP 65.

(a) (b) (c) (d) (e) (f)

Sample E 0~ϋ~ Ut Tg ^ε Tg ^H pre-history (MPa) (%) (MPa) (MJm ^-3 ) (°C) (°C)

as-prepared 951 9 34 4 -40 230

post-cured

100°C/18h 1144 17 38 9 -40 236 200°C/lh 1130 2 19 .3 -38 234 (a) Youngs Modulus; (b) elongation to break; (c) tensile strength; (d) toughness; (e) glass transition temperature of the soft-segment (f) glass transition temperature of the hard segment.

This material was fragile and shattered in the mould. At lower mould temperatures the product was incoherent and particulate. The material is typical of polyureas produced from DEDTA-based reactants at high hard segment contents.

The materials can be tested and have high moduli approaching IGPa but elongations to break as-moulded are low. Post-curing whilst improving both moduli and elongation to break gives materials with

properties which fall significantly below that set out in the objectives of this study (required for non-reinforced metal replacement materials).

Example 1

Sample code UMD 65, where MD refers to MDIPA as chainextender. The formulation consisted of Jeffamine T5000, 5 parts; MDIPA 5.3 parts; RMA 400, 5.2 parts. The isocyanate stream (A) was maintained at 40°C and the mixed amine, stream (B), (T5000/MDIPA) was maintained at 50°C. Samples were moulded with the mould initially at 120°C and Wg, was 130gs ^-1 .

Material properties are presented in Table 2.

Table 2. Physical properties of UMD 65

Sample E > "u ^"" (J^ Tg ^ε Tg ^H pre-history (MPa) (%) (%) (MJirT ³ ) (°C) (°C)

as-prepared 1067 91 37 37 -25 181

post-cured

100°C/18h 1065 91 38 40

200°C/lh 1127 107 43 54

The properties of this material to that in Comparative Example 1 and it can be seen that changing the chain extender to MDIPA yields a material with a high modulus >lGPa and much improved elongation >- 100% and toughness is increased fivefold.

Example 2

Sample code UMD 70. The formulation consisted of Jeffamine T5000, 5 parts; MDIPA, 6.7 parts; RMA 400, 6 . 6 parts.

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The isocyanate stream (A) was maintained at 40°C and the mixed amine, stream (B) was maintained at 50°C. Samples were moulded with the mould initially at 120°C and We, was s*»-t 130gs ^_1 . The physical properties of the as-prepared and post-cured samples are given in Table 3.

Table 3. Physical properties of UMD 70

Sample E C (Tu ^"* |)^ Tg ⁶ Tg ^H pre-history (MPa) (%) (%) (MJπr ³ ) (°C) (°C)

as-prepared nt( ^a ) nt nt nt nt nt

post-cured

100°C/18h 1717 3 38 0.9 -30 214 200°C/lh 1630 47 54 25.4 -32 224 (a) nt = not tested because the material could not be converted into suitable test specimens.

Comparison of the properties of UMD 70 with UMD 65 shows that a 5% increase in HS content increases the modulus by 70% and the elongation and toughness are only reduced to 50% of the values observed for UMD 65 on post-curing at 200°C/lh.

This material shows properties which are superior to glass-filled polyurea elastomers.

Example 3

Sample code UD/MD 65. The formulation consisted of Jeffamine T5000, 100 parts; DEDTA, 56 parts; MDIPA, 28 parts; RMA 400, 137 parts.

The isocyanate stream (A) was maintained at 40°C and the mixed amine stream (B) was maintained at 50°C. Samples were moulded with the mould initially at 120°C and Wβ was -~*-' /304gs ^_1 . The physical

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properties of the as-prepared and post-cured samples are given in Table 4.

Table 4. Physical properties of UD/MD 65

^S am ^p le ^E &~ ( t- ^{TgS TgH} pre-history (GPa) (%) (MPa) (MJM ^-3 ) (°C) (°C)

as-prepared 0.85 18 30

post-cured

If this material is compared with the material UD 65 reported in Comparative Example 1 it can be seen that incorporation of MDIPA facilitates moulding and yields a material which can be demoulded. The moduli are similar but elongations and tensile strength should be superior to UD 65.

Example 4

Sample code UMM 65 where MM = MMIPA. The formulation used was Jeffamine T5000, 5 parts; MMIPA4.9 parts; RMA 400, 5.6 parts. The isocyanate stream (A) was maintained at 40°C and the mixed amine (B) was maintained at 50°C. Samples were moulded with the mould initially at 120°C and £ was /30gs~l. The physical properties of the as-prepared and post-cured samples are given in Table 5.

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Table 5. Physical properties of UMM 65 Sample E C pre-history (MPa) (%) (MPa) (MJπr ³ ) (oc) (oc)

as-prepared 1330 1 13 0.1 -20 212

post-cured

100 ^O C/18h 1280 4 36 1.1 -20 220

200 ^O C/lh 1050 32 38 15 -30 235

Comparison of UMM 65 with UD 65 shows that moulding is facilitated and coherent materials are obtained. Comparison of the data from UMM 65 and UMD 65 will show the effects of structural features on material's properties.

Tensile tests were performed according to ASTM D638-m which specifies methods of determining Young's Modulus (E), tensile strength (Ou) and elongation at break (Eu). The area under the stress-strain curve was measured by cutting and weighing and is conventionally taken as the "toughness".

The glass transition temperatures TgS and TgH were determined from peaks in the tan - temperature curves obtained by dynamic Mechanical Thermal Analysis. Specimens (10mm x 45mm x 3mm) were tested at 1Hz in a double cantilever mode at a heating rate at 5 ^θ Cmm ^_1 on a Polymer Laboratories DMTA.

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