WO1996023015A1

WO1996023015A1 - Process for producing mouldings

Info

Publication number: WO1996023015A1
Application number: PCT/EP1996/000121
Authority: WO
Inventors: Andreas Ruckes; Jürgen GRÖNEN; Lutz Schmalstieg; Bruno Luckas; Manfred Schmidt
Original assignee: Bayer Aktiengesellschaft
Priority date: 1995-01-25
Filing date: 1996-01-12
Publication date: 1996-08-01
Also published as: DE19502198A1

Abstract

A process for producing possibly microcellular, elastic mouldings in the density range from 0.8 to 1.5 g/cm3 with a compact surface from polyurethanes possibly containing urea groups by reacting a reaction mixture producing such polyurethanes produced by the reaction injection moulding process in closed moulds, in which the polyisocyanate component of the reaction mixture is a polyisocyanate mixture liquid above 5 °C based on 4,4'-diphenyl methane diisocyanate with an NCO content of 14.5 to 24 wt.% and a content of allophant groups (calculated as C¿2?HN2O3, molecular weight = 101) of 7.7 to 14.5 wt.%.

Description

- 1 -

Process for the production of molded articles

The invention relates to a new process for the production of moldings from polyurethanes, optionally containing urea groups, by the reaction injection molding technique.

The production of polyurethane moldings by the reaction injection molding technique has been known for many years (cf. e.g. DE-AS 2,622,951, US Pat. No. 4,065,410 or US Pat. No. 4,218,543). For the production of highly stressed molded parts, such as those used for example in the automotive industry, a) organic polyisocyanates, b) higher molecular weight hydroxyl compounds, in particular polyether polyols, and c) low molecular weight chain extenders or crosslinking agents, optionally with the use of usual auxiliaries and additives, processed according to the principle of reaction injection molding technology in closed forms. As polyisocyanates a) there are in particular chemically modified polyisocyanates or polyisocyanate mixtures from the diphenylmethane series, as component b) in particular polyether polyols with a molecular weight in the range from 1800 to 12,000, predominantly those with predominantly primary hydroxyl groups and as component c) alcoholic chain extenders or crosslinking agents such as ethylene glycol, trimethylolpropane, triethanolamine or amine chain extenders such as, in particular, l-methyl-3,5-diethy 1-2,4-diaminobenzene or its technical mixtures with l-methyl-3,5-diethyl-2,6-diaminobenzene or Mixtures of the alcoholic and amine chain extenders mentioned are used.

The polyisocyanate component a) used is primarily 4,4'-diphenylmethane diisocyanate liquefied with the corresponding polypropylene glycols, in particular by partial carbodimidization of the isocyanate groups or by reaction with inferior amounts of aliphatic polyhydroxyl compounds of the molecular weight range 62 to 700. The disadvantage of these chemically modified polyisocyanates is their still unsatisfactory resistance to crystallization at temperatures below 15 ° C., which can lead to considerable processing problems. The crystallization stability can be improved by an increased carbodiimidization or by an increase in the urethanization with the aliphatic polyhydroxyl compounds, but this has considerable disadvantages, such as an increased viscosity and a loss in terms of mechanical properties of the moldings ultimately obtained are accepted

The raw materials are processed using the reaction injection molding process (RSG process). It is a filling technique in which the highly active, liquid starting components are introduced into the mold in the shortest possible time using dosing and mixing units up to 10 kg in weight, depending on the wall thickness, in 2 to 4 minutes.

For the applications mentioned, these moldings should be sufficiently stiff in the heat, but still flexible in the cold. The least possible dependence of the elastic modulus on the temperature is a prerequisite for this, but rapid hardening is also required for the moldings to be demolded quickly desired material (high "green strength")

One of the disadvantages of the previously used, chemically modified diisocyanates of the above-mentioned type can be seen in the fact that the achievement of the high-quality mechanical properties finally obtained is due to the structure of the flexural modulus being too slow and the hardening too slow This has the consequence that relatively long mold retention times are required before bending of the molded part or cracking in the surface of the molded part can be ruled out during removal from the mold. Although the hardening can be slightly improved by raising the mold temperature, this measure has again a negative influence on the rigidity of a molded part at the time of demolding

Surprisingly, it has now been found that these disadvantages can largely be overcome if, as polyisocyanate component a), AUophanate-modified 4,4'-diphenylmethane diisocyanate of the type described in more detail below is used. The moldings harden faster with the same recipe, while at the same time high-quality elastomer properties are achieved. A further advantage of using the allophanized diisocyanates described in more detail below is. in their excellent installation stability at low

See temperatures The invention relates to a process for the production of optionally microcellular, elastic molded bodies in the density range 0.8 to 1.5, preferably 0.9 to 1.3 g / cm ³ with a compact surface from polyurethanes which may have urea groups by reaction a reaction mixture prepared by the reaction injection molding process

a) organic polyisocyanates,

b) organic polyhydroxyl compounds in the molecular weight range from 1800 to 12,000,

c) low molecular weight compounds of the molecular weight range 62 to 400 with at least two reactive to isocyanate groups

Groups,

optionally with the use of auxiliaries and additives known per se from polyurethane chemistry,

in closed forms, characterized in that liquid polyisocyanate mixtures based on 4,4'- above 5 ° C are used as organic polyisocyanates a)

Diphenylmethane diisocyanate with an NCO content of 14.5 to 24% by weight and a content of allophanate groups (calculated as C ₂ HN ₂ O ₃ , molecular weight = 101) of 7.7 to 14.5% by weight was used.

Here and below, "4,4'-diphenylmethane diisocyanate" stands both for the pure 4,4'-isomer and for its mixtures with up to 1.9% by weight of 2,4'- and / or up to 0 , 5 wt .-% of 2,2'-diphenylmethane diisocyanate, these percentages each refer to the total mixture. Preferably, the "4,4'-diphenylmethane diisocyanate" used as the starting material consists at least 98.5% of the 4,4'-isomer.

The polyisocyanate component a) to be used in the process according to the invention has an NCO content of 14.5 to 24% by weight, a viscosity (23 ° C.) of 200 to 5000 mPa · s and a content of allophanate groups (calculated as C ₂ HN ₂ O ₃ , molecular weight = 101) from 7.7 to 14.5% by weight. One possibility for the preparation of these allophanate-modified diisocyanates is that 4,4'-diphenylmethane diisocyanate is formed with intermediate urethane formation with monohydric alcohols having 4 to 16 carbon atoms per molecule while maintaining an NCO / OH equivalent ratio of 5: 1 up to 8.5: 1 at temperatures of up to 160 ° C., the reaction being carried out at the latest after the formation of urethane in the presence of a catalyst which promotes the formation of allophanate.

Starting materials for the production of the allophanate-modified diisocyanates are, in addition to 4,4'-diphenylmethane diisocyanate, monohydric, preferably ether group-free alcohols having 4 to 16, preferably 4 to 10 carbon atoms per

Molecule. Linear, i.e. unbranched monohydric aliphatic alcohols with 4 to 10 carbon atoms that are liquid at room temperature and free of ether groups. Mixtures of different alcohols of this type can of course also be used.

Suitable alcohols are, for example, n-butanol, i-butanol, n-pentanol, n-hexanol, 2-ethylhexanol, n-octanol, n-decanol, n-dodecanol or n-hexadecanol. In principle, monohydric alcohols containing ether groups, such as those obtained by ethoxylation or propoxylation of the simple alkanols mentioned by way of example, such as e.g. Diethylene glycol monobutyl ether. However, the use of monoalcohols containing such ether groups is by no means preferred.

The reaction takes place at least after the intermediate urethane formation in the presence of allophanatization-promoting catalysts. Suitable catalysts are, for example, metal compounds of the 3rd and 4th main group soluble in the reaction mixture, as well as the 1st, 2nd, 6th, 7th and 8th subgroup of the type mentioned in US Pat. No. 3,769,318. Particular tin (II) octoate or zinc acetylacetonate are preferably used in amounts of 20 to 2000 ppm (weight), preferably 20 to 200 ppm (weight), based on the reaction mixture. In contrast to the recommendation of US Pat. No. 3,769,318, the presence of alkylating compounds during the reaction is not necessary. Surprisingly, the polyisocyanate mixtures contain only allophanate structures and no urethane, isocyanurate and / or carbodiimide structures. This is unequivocally proven by 13 C NMR spectroscopic investigations. The modification is carried out at temperatures of up to 160 ° C. The preferred temperature for the aliophanatization reaction is 80 to 120 ° C. According to a preferred procedure, the polyisocyanate mixtures are produced in a two-stage procedure. In a first process step, molten 4,4'-diphenylmethane diisocyanate is introduced and the monoalcohol is added dropwise at a temperature between 40 ° C. and 80 ° C., preferably 50 ° C. and 70 ° C. After the NCO content calculated for the formation of urethane has been reached, the catalyst is added in the second process step and the temperature is then increased to 80 to 160 ° C., preferably 80 to 120 ° C., the reaction when the NCO content calculated for the allophanate formation is reached is preferably terminated by adding a catalyst poison. Suitable catalyst poisons are, for example, alkylating or acylating compounds such as methyl p-toluenesulfonate, dimethyl sulfate, benzoyl chloride or isophthalic acid dichloride, which are preferably used in at least equimolar amounts, based on the amount of the catalyst used.

Component b) in the process according to the invention is in particular polyhydroxyl compounds as are recommended as component b) in US Pat. No. 4,218,543, column 7, line 29 - column 9, line 32. The polyhydroxyl compounds which can be considered as component b) preferably have (on a statistical average) 2 to 3 hydroxyl groups per molecule. The corresponding polyether polyols in the molecular weight range 3,000 to 7,000, the hydroxyl groups of which at least 50% consist of primary hydroxyl groups, are particularly preferred.

As component c) in the process (i) according to the invention there are low molecular weight polyhydroxyl compounds of the molecular weight range 62 to 400 as

Ethylene glycol, 1,4-butanediol, 1,6-hexanediol, glycerol, trimethylolpropane, diethylene glycol, triethylene glycol, dipropylene glycol, triethanolamine or mixtures of such polyhydric alcohols, (ii) aromatic diamines, especially those of US Pat. No. 4,218 543, column 9, line 60 - column 10, line 19 of the type mentioned by way of example, especially l-methyl-3,5-diethyl-2,4-diaminobenzene or its technical mixtures with l-methyl-3,5 -diethyl-2,6-diaminobenzene or (iii) mixtures of alcoholic or amine compounds of the type mentioned under (i) and (ii). When carrying out the process according to the invention, component c) is generally used in an amount of 3 to 40, preferably 5 to 25,% by weight, based on the total weight of components b) and c).

The usual auxiliaries and additives can be used. Catalysts are particularly worth mentioning here. Suitable catalysts are, for example, the compounds mentioned by way of example in US Pat. No. 4,218,543, column 10, line 26 - column 11, line 12. The tin catalysts mentioned there are particularly preferred. The catalysts are generally used in an amount of 0.01 to 10, preferably 0.05 to 1% by weight, based on the weight of component b).

Other auxiliaries and additives which may be used are reaction retarders, blowing agents, internal mold release agents, emulsifiers, stabilizers, fillers, reinforcing materials, flame retardants, plasticizers, dyes, fungicides or bactericides.

In the process according to the invention, the amount of the starting components a) - c) corresponds to an isocyanate index of 90 to 120, preferably 95 to 110. The isocyanate index here means the quotient of the number of isocyanate groups and the number of isocyanate-reactive groups, multiplied by 100 .

The process according to the invention is carried out using the known reaction injection molding technique (RSG process, English: RIM process). In this case, a "polyol component" is preferably first produced from components b) and c) and preferably the total amount of auxiliaries and additives d) used according to the principle of "one-shot process", which is based on the principle of reaction injection molding technology With the help of known mixing units such as working on the principle of countercurrent injection

Spraying machines, agitator machines or machines with a friction mixture are mixed with the polyisocyanate component a), whereupon the reaction mixture is injected into the metal tool. The temperature of the starting components is generally 15 to 60 ° C., preferably 20 to 40 ° C., the temperature of the metal tool before it is filled is 25 to

70 ° C. If desired, the inner walls of the metal tool can be coated with an external mold release agent known per se The mold life is generally 20 seconds to 5 minutes. Moldings with a high initial strength and excellent other mechanical properties result directly.

The density of the molded body depends on the degree of filling of the mold and on the type and amount of the fillers and reinforcing materials used.

A filling level of less than 100% by volume requires the use of blowing agents (eg water, n-pentane, cyclopentane) and / or an air load in the polyol component. The density of the shaped bodies is generally 0.8 to 1.5, preferably 0.9 to 1.3 g / cm ³ .

The method according to the invention is suitable e.g. for the production of flexible

Automotive body elements or for sheathing skis for the production of a flexible surface wear protection.

In the following examples, all percentages relate to the weight.

Example 1 (Preparation of a Polyisocyanate Component a))

1000 g of melted 4,4'-diphenylmethane diisocyanate are presented. 74 g of n-butanol (NCO / OH ratio 8: 1) are slowly added dropwise at a temperature of 60 ° C. and the mixture is stirred at this temperature until the NCO content calculated for urethane formation is 27.4%. Then 0.1 g is added

Zinc acetylacetonate and increases the temperature to 100 ° C. The mixture is stirred at this temperature until an NCO content of 22.5% is reached. The reaction is then ended by adding 0.1 g of benzoyl chloride. A liquid, pale yellow colored polyisocyanate mixture with a viscosity of 300 mPa-s (23 ° C.) is thus obtained. The product is stable to crystallization at a temperature of 5 ° C over a storage period of several weeks, when stored at 0 ° C the product becomes cloudy after approx. 5 days. The product contains a calculated proportion of allophanate groups of 9.4%. The 13 C-NMR spectrum only shows signals at 156 ppm and 151.5 ppm corresponding to allophanate structures and 120 ppm corresponding to isocyanate structures in the carbonyl range.

Example 2

Polyol component:

63.0 parts by weight of a polyether polyol of OH number 27, produced by

Propoxylation of trimethylolpropane and subsequent ethoxylation of the propoxylation product (PO: EO weight ratio = 78:22), 20.0 parts by weight of a polyether diol of OH number 28, produced by

Propoxylation of propylene glycol and subsequent ethoxylation of the propoxylation product (PO: EO weight ratio = 80.20),

3.0 parts by weight of a polyether polyol of OH number 630, produced by

Propoxylation of ethylenediamine, 6.0 parts by weight of ethylene glycol,

0.3 part by weight of a 33% solution of diazabicyclooctane in dipropylene glycol,

4.0 parts by weight of a black paste, consisting of 20% carbon black and 80% of a branched polyether of OH number 35, which by addition of 86.5% by weight of propylene oxide and subsequent Addition of 13.5% by weight of ethylene oxide to trimethylolpropane has been obtained, 0.2 part by weight of dimethyltin dilaurate,

0.2 part by weight of dibutyltin dilaurate,

Polyisocyanate component:

56.2 parts by weight of the allophanized diisocyanate prepared according to Example 1.

This processing ratio corresponds to an isocyanate index of 110.

Processing was carried out on a 2 K high-pressure metering machine with counter-current injection mixing. The raw material temperature was 28 ° C. The reaction mixture was introduced into a plate tool made of aluminum measuring 110 × 50 × 0.3 cm and heated to 60 ° C. PURA-1, a silicone-containing mold release agent from PURA, was used as the release agent. The mold life was 5 minutes. The plates showed excellent demolding rigidity and could be demolded without any problems. The plates produced in this way were used without further aftertreatment to test the mechanical properties. The results are summarized in Table 1.

Example 3 (comparative example)

A component: as example 2

B component:

55.0 parts by weight of a reaction product of tripropylene glycol and 4,4'-

Diphenylmethane diisocyanates with an NCO content of 23% by weight.

As in Example 2, this processing ratio corresponds to an isocyanate index of 110.

All details relating to the processing corresponded to Example 2. After a mold hold time of 5 minutes, the plates showed a significantly lower demolding stiffness than in Example 2. The plates produced in this way were without further Aftertreatment used to test the mechanical properties. The results are summarized in Table 1.

Table 1 Mechanical properties

Example 3 Example 2 (comparison) (according to the invention)

Sample thickness (mm) DIN 53 568 3 3

Bulk density (kg / m ³ ) DIN 53 420 998 985

Shore A at RT DIN 53 505 80 87

Tensile strength (MPa) DIN 53 504 8.5 8.9

Tear resistance DIN 53 504 15.8 24.6 (KN / m)

Elongation at break (%) DIN 53 504 207 216

Dynstat DIN 53 435 RT (kJ / m ² ) ngng -30 ° C (kJ / m ² ) ngng

n.g. = not broken

It can be seen in this comparison that with the isocyanate according to the invention

Material with higher tear strength and hardness with the same toughness is achieved. Example 4

A component:

A mixture of the following components was produced at room temperature:

42.25 parts by weight of a Polyetheφolyols OH number 28, produced by

Propoxylation of trimethylolpropane and subsequent

Ethoxylation of the propoxylation product (PO: EO weight ratio = 82.3: 17.7),

29.65 parts by weight of a Polyetheφolyols OH number 35, produced by

Propoxylation of trimethylolpropane and subsequent

Ethoxylation of the propoxylation product (PO: EO weight ratio = 86.5: 13.5),

3.65 parts by weight of a Polyetheφolyols OH number 810, produced by

Propoxylation of ethylenediamine,

13.59 parts by weight of ethylene glycol, 2.51 parts by weight of a mixture of 1.63 parts by weight of l-methyl-3,5-diethyl

2,4-diaminobenzene and 0.87 part by weight of l-methyl-3,5-di-ethyl-2,6-diaminobenzene,

5.04 parts by weight of black paste according to Example 2, 0.55 parts by weight of a Polyetheφolysiloxans (Polyurax SH 205 from Union

Carbides),

0.57 part by weight of a 33% solution of diazabicyclooctane in dipropylene glycol,

0.29 parts by weight of dimethyltin dilaurate

B component:

120 parts by weight of the allophanized diisocyanate prepared according to Example 1.

This processing ratio corresponds to an isocyanate index of 105.

Processing was carried out on a 2 K high-pressure metering machine with counter-current injection mixing. The raw material temperature was 28 ° C. The reaction The mixture was introduced into a plate tool made of aluminum measuring 100 x 50 x 0.4 cm and heated to 60 ° C. PURA-1, a silicone-containing mold release agent from PURA, was used as the release agent.

The mold life was 5 minutes. The plates showed excellent demolding rigidity and could be demolded without any problems.

The plates produced in this way were used without further post-treatment to test the mechanical properties. The results are summarized in Table 2.

Example 5 (comparative example)

A component: as example 4

B component

18.0 parts by weight of the reaction product of tripropylene glycol and 4,4'-diphenylmethane diisocyanate according to Example 3.

This processing ratio corresponds to an isocyanate index of 105.

All details relating to processing corresponded to Example 4. After a mold hold time of 5 minutes, the sheets showed a significantly lower stiffness than in Example 4.

Table 2 Mechanical properties

Example 4 Example 5 (according to the invention) (comparison)

Sample thickness (mm) DIN 53 568 4 4

Bulk density (kg / m ³ ) DIN 53 420 1 165 1172

Shore D at RT DIN 53 505 70 67

Bending modulus of elasticity (MPa) ASTM-D790 744 478

Tensile strength (MPa) DIN 53 571 i.A. 28.1 29.5

Tear resistance DIN 53 515 70.8 70.7 (KN / m)

Elongation at break (%) DIN 53 571 i.A. 152 163

Tensile modulus of elasticity (MPa) DIN 53 571 i.A. 669 550

Notched impact strength DIN 53 453 at 23 ° C (kJ / m ² ) 23 17.2 at -30 ° C (kJ / m ² ) 6.4 5.6 |

Despite the significantly higher rigidity, the notched impact strength is higher when the isocyanate according to the invention is used.

Example 6

A component:

A mixture of the following components was produced at room temperature:

25.30 parts by weight of the Polyetheφolyols OH number 27 according to Example 2,

50.50 parts by weight of a graft polyethylene polyol, produced by polymerizing 20 parts by weight of a mixture of 40% styrene and 60% acrylonitrile in 80 parts by weight of the polyether polyol of OH number 35 described in Example 4, 19.70 parts by weight of ethylene glycol, 0.30 parts by weight of a 33% solution of diazabicyclooctane in dipropylene glycol,

4.10 parts by weight of black paste according to Example 2, 0.02 parts by weight of dimethyltin dilaurate, 0.05 part by weight of dibutyltin dilaurate.

B component:

134.8 parts by weight of the allophanized diisocyanate prepared according to Example 1.

This processing ratio corresponds to an isocyanate index of 107.

All details relating to processing corresponded to Example 4. After a mold life of 5 minutes, the plates showed excellent demolding rigidity and could be demolded without any problems.

The plates produced in this way were annealed at 120 ° C. for 30 minutes and then used to test the mechanical properties. The results are summarized in Table 3.

Example 7 (comparative example)

A component: as example 6

B component:

131.8 parts by weight of the reaction product of tripropylene glycol and 4,4'-

Diphenylmethane diisocyanates according to Example 3.

This processing ratio corresponds to an isocyanate index of 107.

All details regarding the processing corresponded as in Example 6

Information in example 4. However, no usable plates could be removed from the mold become. Large skin solutions appeared on the plates. A mechanical test was not possible.

Table 3 Mechanical properties

Example 6

Sample thickness (mm) DIN 53 568 3

Bulk density (kg / m ³ ) DIN 53 420 1 1 10

Shore D at RT DIN 53 505 70

Bending modulus of elasticity (MPa) ASTM-D790 848

Tensile strength (MPa) DIN 53 504 32

Tear resistance (KN / m) DIN 53 515 132

Elongation at break (%) DIN 53 504 140

Dynstat -30 ° C (kJ / m ² ) DIN 53 435 10.6

This example clearly shows the processing advantages of the isocyanate according to the invention. The polyol formulation used here cannot be processed with the urethane-modified 4,4'-diisocyanatodiphenylmethane according to the prior art.

Claims

claims

1. A process for the production of optionally microcellular, elastic molded articles in the density range 0.8 to 1.5 g / m ³ with a compact surface made of polyurethanes which may have urea groups by reacting a one produced by the reaction injection molding process

Reaction mixture

a) organic polyisocyanates,

b) organic polyhydroxyl compounds of the molecular weight range from 1800 to 12,000,

c) low molecular weight compounds of the molecular weight range 62 to 400 with at least two groups which are reactive towards isocyanate groups,

in closed forms, characterized in that as organic

Polyisocyanates a) above 5 ° C liquid polyisocyanate mixtures based on 4,4'-diphenylmethane diisocyanate with an NCO content of 14.5 to 24% by weight and a content of allophanate groups (calculated as C ₂ HN ₂ O ₃ , molecular weight = 101) from 7.7 to 14.5% by weight.

2. The method according to claim 1, characterized in that one uses as component b) Polyetheφolyols of an (average) hydroxyl functionality of 2 to 3, the hydroxyl groups of which are at least 50% primary hydroxyl groups.

3. The method according to claim 1 and 2, characterized in that there is used as component c) ethylene glycol.

4. The method according to claim 1 and 2, characterized in that as component c) l-methyl-3,5-diethyl-2,4-diaminobenzene or its technical mixture with l-methyl-3,5-diethyl- 2,6-diaminobenzene used. 5. The method according to claim 1 and 2, characterized in that as component c) mixtures of (i) ethylene glycol and (ii) l-methyl-3,5-diethyl-2,4-diaminobenzene or its technical mixtures with 1- Methyl 3,

5-diethyl-2,6-diaminobenzene in the weight ratio (i) :( ii) 1: 5 to 5: 1 used.

6. The method according to claim 1 to 4, characterized in that the type and quantity ratios and the degree of filling of the mold used are chosen so that molded bodies of the density range 0.9 to 1.3 kg / m ³ result.