CA2133782A1

CA2133782A1 - Plyisocyanate compositions

Info

Publication number: CA2133782A1
Application number: CA002133782A
Authority: CA
Inventors: Eduard Mayer; Thomas Munzmay; Hartmut Nefzger; Werner Rasshofer
Original assignee: Individual
Current assignee: Bayer AG
Priority date: 1993-10-11
Filing date: 1994-10-06
Publication date: 1995-04-12
Also published as: JPH07149858A; ES2105457T3; EP0647666A1; EP0647666B1; DE59403371D1; DE4334549A1

Abstract

POLYISOCYANATE COMPOSITIONS
ABSTRACT OF THE DISCLOSURE
Polyisocyanate compositions which are liquid at room temperature and have a content of aromatically bound isocyanate groups of up to 43.5% by weight, a content of urea groups of up to 0.88 mol/kg and a content of urethane groups of up to 1.35 mol/kg are produced by heating a mixture of an aromatic polyisocyanate having an NCO content of up to 48.3% and a polyurethane polyurea present in size-reduced form until the mixture is fully homogenized. The polyurethane urea has a urea group content of up to 2.5 mol/kg and a urethane group content of up to 3.8 mol/kg. These polyisocyanate compositions are useful as polyisocyanate components in the production of polyurethane elastomers containing urea groups by reaction injection molding.

Description

~3'3782 ....
Mo-41 1 6 LeA 29,941 PC)LYISOCYANATE COMPOSITIONS
BACKGROUND OF THE INVENTION
This invention relates to a new process for the production of polyisocyanate compositions which are liquid at room temperature, to the polyisocyanate compositions produced by this process and to the use of these polyisocyanate compositions in the production of polyurethane elastomers by reaction injection molding. These polyisocyanate compositions are prepared by heating aromatic polyisocyanates in admixture with selected polyurethanes containing urea groups in size-reduced form.
The production of polyurethane elastomers having a density above o~9 g/cm3 by reaction injection molding is known (See, for example, DE-AS 2,622,951; EP-A 0,355,000; DE-OS 3,914,718; DE-OS 4,115,037 and US 4,374,210). The moldings obtained by such reaction injection molding processes are particularly useful for the production of flexible automobile fenders or bodywork elements.
The mechanical and thermomechanical properties o~ these moldings such as their hardness, rigidity and heat resistance, are determined by their content of urea segments. In practice, the urea se~ments are generally incorporated into the molding by using low molecular weight, sterically hindered aromatic diamines, such as in particular DETDA (i.e., 1-methyl-3,5-diethyl-2,4-diaminobenzene or technical mixtures thereofwith 1-methyl-3,5-diethyl-2,6-diaminobenzene)~ -as low molecular weight chain-extending agents; or by using an aminofunctional polyether as a relatively high molecular weight syn-kgb\AN41 16 Mo-41 16 . .

~133782 thesis component or as a chain-extending agent in the isocyanate polyaddition reaction.
In the well-known process disclosed in DE-AS 2,622,951, the DETDA content of the "polyol component" to be reacted with the 5 polyisocyanate cornponent is limited by the high reactivity of the diamine.
If the DETDA concentration is too high, mixing problems and, in extreme cases, premature solidification of the reaction mixture are the inevitable consequence. A major advantage over this old process is afforded by the process disclosed in EP-A 0,355,000. In the process described in EP-A 0,355,000, the polyisocyanate starting material is first reacted with a polyether polyol of the type commonly used to form NCO prepolymers.
This reaction product is then chain-extended with DETDA. In this way, the concentration of urea in the molding ultimately obtained can be considerably increased, enabling the mechanical and thermornechanical 15 properties to be improved.
The logical solution to the problem of incorporating more urea segments into the molded article would be to increase the diamine concentration in the reaction mixture by preliminary reacUon of the polyisocyanate component with diamines, more particularly DETDA.
20 Unfortunately, this solution is not practicable because the reaction of organic polyisocyanates, even with small quantities of diamines, leads to a dramatic increase in viscosity (in the most unfavorable case, solids can even precipitate). The resultant viscous or solid reaction products cannot be used as polyisocyanate components in a reaction inJection molding 25 process.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a process for the production of polyisocyanate compositions containing urea segments. ~ ' ,', ,:

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It is another object of the present invention to provide poly-isocyanate compositions containing urea segments which are liquid at room temperature.
It is a further object of the present invention to provide a process 5 for the production of polyurethane elastomers by a reaction injection molding process in which these polyisocyanates having urea groups present that are liquid at room temperah~re are employed.
These and other objects which will be apparent to those skilled in the art are accomplished by mixing one or more of the aromatic 10 polyisocyanates typically used in reaction injection molding processes with size-reduced polyurethane polyureas and homogenizing the resulting mixture at elevated temperatures.
The use of the polyisocyanate compositions of the present invention as the polyisocyanate component in a reaction injection molding 15 process leads to a number of remarkable advantages. These advantages include:
1. Higher contents of urea segments can be obtained in the elastomer without any increase in the reactivity of the components.

2. Elastomers with better heat resistance for comparable hardness can be obtained.

3. Longer flow paths can be obtained for a similar urea and urethane segment content, i.e. Iarger moldings ~an be produced.

4. The process enables the waste inevitably accumulating during production (in the form of sprues, flash, etc.) to be reused. This has a favorable effect on production costs.

5. The process also enables polyurethanes containing urea groups obtained by the reaction injection molding process to be recycled.

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~337~2 DETAILED DESCRIPTION OF THE PRESENT INVENTION
The present invention relates to a process for the production of polyisocyanate compositions which are liquid at room temperature and which have a content of aromatically bound isocyanate groups of up to 5 43.S% by weight. In this process, a) an aromatic polyisocyanate with an NCO content of up to 48.3%
by weight is mixed with b) up to 35% by weight, based on the total weight of components a) and b), of a polyurethane plastic present in size-reduced form which polyurethane plastic is a polyurethane containing urea ~ `
groups with a density above 0.9 glcm3, a urea group content of up to about 2.5 mol/kg and a urethane group content of up to about 3.8 mol/kg, pr~ferably size-reduced to a mean particle diameter of at most 10 mm.
and the mixturc is heated to temperatures above 160C until it is fully homogenized.
The content of urea and urethane groups in the polyisocyanate compositions obtained by the process of the present invention corresponds to the quantity of component b) and to the concentration of :
the urea and urethane groups in component b). ` `;
Accordingly, the present invention also relates to a corresponding polyisocyanate composition which is characterized by i) a content of aromatically bound isocyanate groups of up to about 43.5% by weight, ~`
ii) a urea group content of up to about 0.88 mol/kg and iii) a urethane group content of up to about 1.35 mol/kg, excluding fillers and reinforcing materials optionally introduced through component b).

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2~,33782 The present invention also relates tQ the use of the polyisocyanate compositions of the present invention as polyisocyanate components in the production of polyurethane elastomers containing urea groups by reaction injection molding.
Although the production of modified polyisocyanates by heating simple polyisocyanates with polyurethane plastics is disclosed in DE-OS 2,035,175 and EP-A-0,047,419, these prior publications are not concerned with polyisocyanates having increased urea group content much less their use as isocyanate components in the production of high-quality polyurethane elastomers by reaction injection molding.
Polyisocyanates a~ suitable for use as starting materials in the process of the present invention include the aromatic polyisocyanates known from polyurethane chemistry having an NCO content of up to 48.3% by weight, preferably from 25 to 33.6% by weight. Examples of such polyisocyanates are 2,4- and/or 2,6-diisocyanatotoluene and, more particularly, the known and optionally chemically modified polyisocyanate mixtures of the diphenylmethane series which are liquid at room temperature and which have an NCO content of from 23.6 to about 25%
by weight. Such modified polyisocyanate mixtures include mixtures of 4,4-diisocyanato-diphenylmethane with 2,4'- and optionally 2,2'-diiso-cyanato-diphenylmethane p~lyisocyanates which have been liquefied by partiai carbodiimidization and/or urethanization of the isocyanate groups and also polyisocyanate mixtures which are liquid at room temperature that, in addition to the diisocyanates mentioned, contain up to 20% by weight, based on the total weight of isocyana!e, of higher homologs of the diisocyanates mentioned.
Component b) used in the process of the present invention is a polyurethane polyurea in mechanically size-reduced form, preferably with a mean particle diameter of at most 10 mm. The polyurethane polyurea Mo-41 1 6 ~1337~2 --may be size-reduced, for example, in typical cutting mills.
Suitable polyurethane polyureas b) include solid or microcellular materials with a density above 0.9 g/cm3, preferably from about 0.95 to about 1.3 g/cm3, which may optionally contain fillers or reinforcing 5 materials in a quantity of up to 30% by weight, based on the total weight of component b). The polyurethane polyureas are generally characterized by a urea group content of up to 2.5 mol/kg, preferably from about 0.15 to about 2.2 mol/kg and by a urethane ~roup content of up to 3.8 mol/kg, preferably from about 0.15 to about 3~5 mol/kg, based 10 on the polymer matrix free from any reinforcing materials. Any polyurethane polyurea produced by a reaction injection molding process which has a density and urea group content within the above-given `- :
ranges is particularly suitable for use as component b) in the practice of the present invention.
To oarry out the process of the present invention, a mixture of polyisocyanate a) and size-reduced polyursthane polyurea b) is heated to at least 160C, preferably from about 180 to about 250C, more prcferably from about 180 to about 2204C until it is homogenized. Up to 35 parts by weight, preferably from about 10 to about 30 parts by weight 20 of component b) are used per 100 parts by weight of mixture. The heating time is, of course, determined to a large extent by variables such as the heating temperature, the type and quantity of components a) and b) used, and the degree of size-reduction of component b). The heating may therefore vary within the range of from about 1 to about 360 mins., 25 preferably from about 5 to about 60 mins.
The products obtained by the process of the present invention having the characteristic properties already mentioned are valuable starting materials for reaction injection molding processes.

Mo-4116 ~133782 Reactants for the polyisocyanate compositions of the present invention in a reaction injection molding prooess include: (1) polyether polyols with a molecular weight (caIculated from the hydroxyl group content and hydroxyl functionality) in the range of from about 1,800 to 5 about 12,000, preferably in the range of from about 3,000 to about 7,000 of th~ type disdosed in DE-AS 2,822,951; (2) amino-terminated polyethers with molecular weights in the range of from about 1,800 to about 12,000, preferably from about 3,000 to about 7,000 of the type described in EP-B-0,081,701; (3) polyhydric alcohols with molecular 10 weights in the range of from about 62 to 1,799, preferably from about 62 to about 300 such as ethylene glycol, propylene glycol, trimethylol propane, glycerol, dialkoxylation products of such aloohols with molecular weights in the specified range or mixtures of suoh polyhydric alcohols; (4) low molecular weight amino-terminated polyethers with molecular weights in the range of from about 230 to 1,799 and preferably in the range from about 350 to about 450; and/or (5) aromatic diamines, particularly sterically hindered aromatic diamines such as DETDA.
When a polyisocyanate composition produced in accordance with the present invention is used as a reactant to produce a polyurethane by 20 a reaction injection molding process, mixtures of a polyether polyol (1) described above with DETDA are preferably used. 10 to about 95% by weight of these mixtures is DETDA. In a particularly preferred ambodiment of the present invention, the polyisocyanate composition of the present invention and reactants of the type mentioned are used in 25 combinations such that the resulting moldings will have a urea group content of at least i.0, preferably from about 1.2 to about 2.5, more preferably from about 1.4 to about 2.35 mol/kg and a urethane group content of at least 0.05, preferably from about 0.1 to about 1.8, more Mo-41 1 6 ~1337~2 preferably ~rom about 0.3 to about 1.0 mol/kg, based on polyurethane -matrix free from reinforcing materials.
The auxiliaries and additives typically used in reaction injection molding (described, for example, in the publications identified above), may, of course, be used to produce polyurethanes in accordance with the present invention. The type of starting n aterials used, the quantities in which they are used and the degree of filling of the molds used are selected so that the molded products will have a density of at least 0.9 g/cm3, preferably from about 0.95 to about 1.3 9Icm3.
Molded materials produced in accordance with the present invention are distinguished in particular by excellent heat resistance (sag values) by virtue of their high content of urea groups. They are also particularly suitable for the production of automobile fenders and ;
bodywork parts.
Having thus described our invention, the following Examples are given as being illustrative thereof. All percentages and parts given in these Examples are percentages by weight and parts by weight, unless otherwise indicated.
EXAMPLES
~ . ~
The formulations described in the following Examples were :
processed by reaction injection molding.
Polyisocyanate compositions of the present invention (component r -A) and crosslinker mixture (component B) were delivered to a high- -pressure metering unit and, after intensive mixing in a positively con-trolled mixing head, were rapidly introduced under pressure into a heatable, hot matal mold. The inner walls of the mold were coated with a ready-to-use, soap-based commercial external mold release agent (RCTW 2006, a product of Chem Trend). The aluminum plate mold ~nabled test plates measuring 300 x 200 x 3 mm to be produced.

Mo-4116 ~133782 The elastomers were characterized by their Shore D (DIN 53 505) values and their sag test results (test specimen length 100 and 150 mm, thickness 3 mm, 1 h at 160C).
ComPonent b1):
A poiyurethane polyurea elastomer filled with approximately 22%
by weight of glass fibers which had been produced by reaction injection molding containing 1.9 mol urea groups and 0.7 mol urethane groups per k~ of polymer matrix.
Com~onent b2!
A polyurethane polyurea elastomer filled with approximately 22%
by weight of glass fibers which had been produced by reaction injection molding containin3 2.0 mol urea groups and 0.5 mol urethane gr~ups per kg of polymPr matrix.
ExamPle 1 In a 100 liter tank reactor with a jacket heating system and helical stirrer, 40 kg of a polyisocyanate mixture of th~ diphenylmethane series with an NCO content of 32.5%, a percentage content of diisocyanato~
diphenylmethane isomers of 90% (remainder higher polyisocyanates) of which about 90% was 4,4'-diisocyanatodiphenylmethane, and 10 kg of dried Component b1) in granular form (partide size < 10 mm diameter) were heated for 30 minutes to 200C and stirred for another 30 minutes at that temperature. After the mixture had been cooled to 50C, 0.12 kg of dry p-toluenesulfonic acid was added and dissolved. A polyisocyanate composition according to the present invention having an NCO content of 23.4% and a viscosity of 2,000 mPa-s at 25C and 300 mPa-s at 50C
was obtained. The polyisocyanate composition had a theoretical content of 0.31 mol of urea groups and 0.1 mol of urethane groups per kg of polyisocyanate composition, excluding filler.

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ExamPle 2 In a 100 liter tank reactor with a jacket heating system and helical stirrer, 30 kg of a polyisocyanate mixture of the diphenylmethane series having an NCO content of 32.5%, a percentage content of diisocyanato-5 diphenylmethane isomers of 90/0 (remainder higher polyisocyanates) ofwhich about 90% was 4,4'-diisocyanatocliphenylmethane, and 10 kg of Gomponent b1) granules (particle size < 1û mm diameter) were heated for 30 minutes to 200C and stirred for another 30 minutes at that temperature. After the mixture had been cooled to 50C, 0.05 kg of 10 propionyl chloride was added. A polyisocyanate composition according to the invention having an NCO content of 20.2% and a viscosity of 1,900 mPa-s at 50C was obtained. The polyisocyanate composition had a theoretical content of 0.41 mol of urea groups and 0.10 mol of urethane groups per kg of polyisocyanate composition, excluding filler.
15 Example 3 In a 100 liter tank reactor with a jacket heating system and helical stirrer, 40 kg of a polyisocyanate mixture of the diphenylmethane series having an NCO content of 32.5%, a percentage content of diisocyanato-diphenylmethane isomers of 90% (remainder higher polyisocyanates) of 20 which about 90% was 4,4'-diisocyanatodiphenylmethane, and 10 kg of dried Component b2) in granular form (particle size ~ 10 mm diameter) were heated for 30 minutes to 200C and stirred for another 30 minutes at that temperature. After the mixture had been cooled to 50G, 0.12 kg of dry p-toluenesulfonic acid was added and dissolved. A polyisocyanate 25 composition according to the invention with an NCO content of 23.3%
and a viscosity at 50C of 200 mPa-s W3S obtained. The polyisocyanate composition had a theoretical content of 0.33 mol of urea groups and 0.08 mol of urethane groups per kg of polyisocyanate composition, excluding filler.

Mo~1 16 ~133782 Example 4 (Comparison Example) In a 100 liter tank reactor equipped with jacket heating and a helicai stirrer, 40 kg of a polyisocyanate mixture of the diphenylmethane series with an NCO content of 32.5%, a percentage content of 5 diisocyanatodiphenylmethane isomers of ~0% (remainder higher polyisocyanates) of which about 90% was 4,4'-diisocyanatodiphenyl-methane and 5.5 kg of a polypropylene glycol mixture (OH value 515) were stirred for 3 hours at 80C. The polyisocyanate composition obtained had an NGO content of 23.8% and a urethane group content of 10 1.1 mol/kg.
Examples ~ - 8 In four parallel tests, 100 parts by weight of a polyol mixture containing auxiliaries and additives described in Table 1 were processed with the polyisocyanate compositions described in Table 2 by reaction 15 injection molding. A steel mold measuring 300 x 200 x 3 mm was used as the mold. Tha mold temperature was 70C and the residence time in the mold was 30 seconds. Moldings with satisfactory demolding behavior and appearanGe were obtained under these conditions.

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f Mo-4116 337~2 3 Polyether polyol having an OH value of 35 prepared by propoxylating trimethylol propane and subsequent ethoxylation of the propoxylation product (EO:PO ratio by weight = 82.5:17.5).
4 Ricinoleic acid/hexanediol polyester having an OH value of 35.
5 5 Polyether diarnine having a molecular weight of 400 which is commercially available under the name Jeffamine D 400 from Texaco.
8 33% solution of triethylene diamine in dipropylene glycol which is commercially available under the name Dabco 33 LV.
10 7 Commercially available under the name Fomrez UL 28.
Commercially available under the name Tegostab B 8404 from Goldschmidt, Essen.
Table 2: RIM formulations ~

Example 5 6 7 8 : .:
(Comparison .: ::
Example ~ ~:
Polyol mixture 1 1 2 3 NCO Exampte 4 Example 1 Example 1 Example 2 preparation ` .
(Parts by 71.3 72.5 79.3 85.5 - : ~:
wel~ht) :
Mol U/l~') 0.76 0.34 0.32 0.31 ~ ~1~ ~ ~ ~'';"
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1) Mols of urethane groups per kg of polymer matrix.
2) Mols of urea groups per kg o~ polymer matrix. ;~
ExamPles 9-12 Examples 5 to 8 were varied by incorporation of 22% by weight of ~:
glass fibers (based on total elastomer) on the polyol side.

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Table 3: Mechanical and thermomechanical data Ex. 5 Ex. 6 Ex. 7 Ex. 8 Ex. 9 Ex. 11 Ex. 12 (Comp.) (Comp. = (= Ex. 7 ~ = Ex. 8 Ex. 5 ~ 229~ 229 22b%s ghs~ ~las~
¦ Mol _ _ _ UM~) 0.76 0.34 0.32 0.3t 0.76 0.32 0.31 Hhg~ 1.76 1.87 2.01 2.13 1.76 2.01 2.13 Shore D 66 59 64 68 67 67 68 Imml') 2 1 22 1 4 8 1 2 6 2 [lm50 lmm 84 87 60 40 n.d.~ 31 16 ~ _ _ ~._ _ 1) Mols of ursthane groups per kg of polymer matrix.
2) Mols of urea groups per kg of polymer matrix.
15 3) Not deterrnined.
4) 1 hl160C, test specimen 100 mm in length.
5) 1 h/160C, test specimen 150 mm in length.
Comparison of Examples 5 (Comparative) and 6 shows that the isocyanate composition of Example 1 (according to the invention) 20 containing urea and urethane groups produces elastomers which, despite lower hardness, show oomparable heat resistance (sag values). In contrast, the elastomers produced in Examples 7 and 8 (produced from an isocyanate composition having urea and urethane groups prepared in accordance with the present invention) have a hardness comparable to 25 that of Comparal:ive Example 5 but have better heat resistance than the elastomer of Comparative Example 5. The same improved heat Mo~1 1 6 ~33~82 resistance without loss of hardness was found with respect to the glass-fiber-filled elastomers produced in Examples 9 to 12.
Although the invention has been described in detail in the foregoing for the purpose of illustration, it is to be understood that such S detail is solely for that purpose and that variations can be made therein by those skilled in the art without departing from the spirit and scope of the invention except as it may be limited by the claims.

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Claims

1. A process for the production of a polyisocyanate composition which is liquid at room temperature and which has up to 43.5% by weight of aromatically bound isocyanate groups comprising 1) mixing a) an aromatic polyisocyanate having an NCO content of up to 48.3% by weight with b) up to 35% by weight, based on the total weight of components a) and b), of a polyurethane plastic present in size-reduced form which polyurethane plastic has a density about 0.9 g/cm3, a urea group content of up to 2.5 mol/kg and a urethane group content of up to 3.8 mol/kg and

2) heating the mixture formed in 1) to a temperature above 160°C until the mixture is fully homogenized.
2. The process of Claim 1 in which component b) is size-reduced to a mean particle diameter of no more than 10 mm.

3. The process of Claim 1 in which a polyisocyanate mixture of the diphenylmethane series which is liquid at room temperature and has an NCO content of from about 25 to about 33.6% by weight is used component a).

4. The process of Claim 3 in which the polyisocyanate mixture is a chemically modified mixture of polyisocyanates of the diphenylmethane series.

5. The process of Claim 4 in which a polyurethane polyurea having a urea group content of from about 0.15 to about 2.2 mol/kg and a urethane group content of about 0.15 to about 3.5 mol/kg is used as component b).

6. The process of Claim 3 in which a polyurethane polyurea having a urea group content of from about 0.15 to about 2.2 mol/kg and a urethane group content of from about 0.15 to about 3.5 mol/kg is used as component b).

7. A polyisocyanate composition which is liquid at room temperature, characterized by i) is a content of aromatically bound isocyanate groups of up to 43.5%
by weight, ii) a urea group content of up to 0.88 mol/kg and iii) a urethane group content of up to 1.35 mol/kg.

8. A process for the production of a polyurethane elastomer comprising reacting the polyisocyanate composition of Claim 1 with an isocyanate-reactive material by a reaction injection molding process.

9. A process for the production of a polyurethane elastomer comprising reacting the polyisocyanate composition of Claim 5 with an isocyanate-reactive material by a reaction injection molding process.

10. A process for the production of a polyurethane elastomer comprising reacting the polyisocyanate composition of Claim 6 with an isocyanate-reactive material by a reaction injection molding process.

11. The product of the process of Claim 8.

12. The product of the process of Claim 9.

13. The product of the process of Claim 10.