DE3729082A1 - Process for the production of mouldings from heat-distortion-resistant structural polyurethane foam - Google Patents

Abstract

The invention relates to a process for the production of mouldings from structural polyurethane foam, in particular body parts for the automobile industry, where, in the first process step, the polyol component (component A) is prepared, and in the second process step, component A is reacted with the isocyanate component (component B), for example by the RIM method. The essential feature of this invention is that the mouldings are subjected to thermal aftertreatment in a subsequent third process step at from 120 to 180@C for from 30 minutes to 3 hours, in the mould and/or after demoulding, (process variant I) or that component A contains nucleating agents, where the nucleated mouldings are not conditioned (process variant II) or are subjected to thermal aftertreatment, in a subsequent third process step, in the mould and/or after demoulding (process variant III).

Description

The invention relates to a method for producing 2. Shaped bodies according to the preamble of claim 1 or 2.

Regarding the production of this molded body from segmented There are numerous types of polyurethane (integral polyurethane foam) published works, now the previous ones Development work by the applicant in this area in As part of an overview.

DE-OS 24 61 521DE-PS 26 12 896 DE-OS 27 14 518DE-PS 28 19 037 DE-OS 27 18 173 DE-PS 32 26 818 DE-OS 29 22 769

Cross-linked and uncross-linked segmented polyurethanes different structures are used as materials Character of elastomer in a wide range of hardness (approx. 60 Shore A to 60 Shore D) can be displayed.

Your diverse Areas of application as solid or integral foam molded parts are well known (see e.g. plastic handbook, publisher G. W. Becker / D. Braun, Vol. 7: Polyurethane, publisher G. Oertel).  

This can also be assumed to be known outstanding property profile of this material group, the its usability as a construction material.

The high level of properties of segmented polyurethanes relies largely on their multi-phase structure. In the reaction of the diisocyanates with long and short chain multifunctional connections form block or Segment copolymers with flexible, soft sequences and such rigid, hard scaffold structure. They are usually not compatible with each other, so that it is used for phase separation Soft and hard components come. Generally forms the Soft phase the continuous phase, i.e. the matrix, during the hard phase represents the dispersed phase. Only with very high concentrations of hard segments in the framework chains one observes phase reversal. Then, however, they lose Polyurethanes also have an elastomeric character. Typical Soft phase images are the implementation products of Diisocyanates, for example with "macrodiols" such as linear ones Polyether or polyester diols. Hard phase formers are e.g. B. the reaction products of diisocyanates with "microdiols or diamines ", such as butanediol, ethanediol or or alkyl-substituted Arylene diamines. These low molecular weight reaction components are also called "chain extenders". As is well known can by varying the molar concentration of the reactants Hardness and degree of crosslinking of the polyurethane within wide limits can be varied.

For a phase separation of the soft and hard segments obviously under given reaction conditions Difference in the polarity of the underlying Structural units cheap; however there are limits here  because if the affinity difference is too extreme, heterogeneous "structural structures" can arise (example: Systems with polybutadiene diols as macrodiol) that the mechanical-technological property profile of the end product influence negatively if necessary.

An increase in the degree of networking is admittedly for the Advancement of the flow softening point advantageous, on the other hand, chemical cross-connections make it more difficult the formation of an optimal phase structure. So it's in important in this sense, of a suitable reaction system going out. However, this is not the subject of the present Invention. In this regard, reference is made to those mentioned at the beginning References printed.

The polyurethanes formed in the polyol isocyanate reaction have because of the generally very fast running Reaction, e.g. B. in the so-called RIM process, no sufficient Time to crystallize in an orderly way. It arises Mixture of amorphous and semi-crystalline, disordered Molecular ranges. So far, this has resulted in a medium one Resistance to heat. With the normal RIM Qualities arise at 120 ° C irreversible deformations, if, for example, body parts made of this material are not be supported well enough. Its own weight is enough then to form sink marks or markings.

The object of the invention is therefore to continue the method develop that the heat resistance of PU integral foam parts is improved, so that especially in the automotive industry polyurethane body parts in so-called online process can be painted. Solved this object is achieved by characterizing claim 1 or 2.  

The following are the three according to the invention Process variants I, II and III described in more detail, wherein the following overview is given:

Process variant I:
The A component contains no nucleating agents. The moldings are post-treated thermally.

Process variant II:
The A component contains nucleating agents. The nucleated molded articles are not post-treated thermally.

Process variant III:
The A component contains nucleating agents. The nucleated moldings are post-treated thermally.

Process variant I

The third method step according to the invention heats the beforehand after the first and second process steps manufactured article (e.g. in the RIM process) 30 minutes up to 3 hours at a temperature of 120 to 180 ° C (Annealing process). The disordered melt crystalline areas and can cool down slowly crystallize in an orderly manner. Crystalline Molecular areas accumulate to form larger crystallites together and thus cause an internal "reinforcement" of the Material that u. a. in the increased heat stability expresses. Due to the structure formed, these products stabilized, d. that is, they deform when renewed Thermal stress no longer in the same way as before.  

The annealing process is both in the choice of conditions as well also in the process to choose correctly to the desired one Realize heat resistance. So z. B. already part anticipated by higher mold temperatures and by post-heating the finished parts at higher temperatures be completed, taking the latter into account the painting conditions should expediently be 160 ° C. With a few exceptions, it has been found that the post-tempering immediately after the demolding of the Share the greatest effects in improving the Provides heat resistance. Generally there are times of 1 hour is sufficient, but it is clearly recognizable that longer times and / or higher temperatures further Allow optimizations. The temperature increase, however, are Limits because in temperature ranges <180 ° C increasingly irreversible chemical processes the polymer degradation initiate.

Two test series are listed below. In terms of the implementation of the sag test is based on the experimental Description referred. In order to interpret the Test series should only be noted that the The heat resistance of the molded body is greater, the lower the sag value.

Test series 1

Target:
Investigation of the influence of the tempering temperature on the sag value

Annealing conditions (Std./°C) sag (mm) a)

without tempering18 1/12012 1/130 9.5 1/140 8.5 1/150 8.0 1/160 7.5 1/170 5.5 1/180 2.5

a) Test specimens based on polyurethane quality grafted polyether diols, modified 4,4 'diphenplemethane diisocyanate (MDI) and Diethyl toluenediamine.

Result:
The heat resistance increases with increasing temperature.

Test series 2

Target:
Examination of the influence of tempering duration, the tempering type and the quality of the test specimen on the sag value

Result:
The heat resistance increases with both qualities with the annealing time. Step tempering is not as effective as tempering at the highest temperature step over the entire tempering time.

Test series 1 and 2 relate to plate tests, d. H. there were test plates in the for the sag test required dimensioning manufactured. In this regard reference is made to the experimental description. The Results of these plate tests can be viewed directly manufactured small body parts transferred easily will. However, if you put large body parts in a direct process and determines the sag value according to the thermal Aftertreatment, the mean sag value is 6.2 to 6.7 (1 hour / 160 ° C) or 3.7 to 5.6 (3 hours / 160 ° C), whereby after 3 hours / 160 ° C did not reach the level of plate tests becomes. The sag values relate here to the polyurethane quality according to a (see test series 1 and 2).  

Process variants II and III

In the manufacture of integral foam parts Polyurethane base, especially of voluminous large parts, as they are for exterior cladding in the rear of the car, bow and Side areas as protective parts, energy absorbers (bumpers) or spoilers are used, the training is more optimal Structural structures especially through the applied Process engineering difficult. The RIM (Reaction Injection Molding process injects the reaction components with high Speeds into the mold. The reaction mixture is because the economically necessary short cycle times highly reactive. Both process parameters together result in a high Flow rate with rapid solidification of the Material flow. Turbulence is particularly complicated molded parts inevitable. So all in all Conditions for extensive phase separation and a Phase growth of the hard segments is extremely unfavorable. Annealing processes in the train of production and after demolding of the parts are therefore inevitably a requirement for the Development of a sufficiently heat-resistant phase morphology. However, tempering processes are part of the production process Always, a not negligible cost factor, because they cause wasted time and require a higher one Use of energy and investments in the not inconsiderable Extent.

For large parts, the heat transport is also in the Material interior due to the low thermal conductivity of the Materials a fairly slow process, so the annealing times and / or temperatures at the expense of economy Manufacturing processes must be extended or increased a homogeneous structure formation can hardly be achieved unless you could use microwave heating realize.  

From this point of view is a modified process variant to strive for, the additional measure according to the invention therein exists that one uses nucleating agents which as Nucleating the training and growth of Accelerate hard segment structures in the polymer structure. By the use of nucleating agents will increase thermal stability the molded body improved. Whether for further improvement an additional thermal resistance Post-treatment depends on the Polyurethane quality, the type of nucleating agent, the Intended use of the molded body and its requirement profile with regard to heat resistance as well as depending on economic considerations.

The nucleation rate is strongly temperature-dependent. At a certain temperature it runs (depending on the substance) a maximum. At low temperatures there is nucleation energetically favored, but - in the opposite direction - with decreasing temperature due to the diffusion of the for nucleation, structural elements require their transport to the interface due to the increasing viscosity of the medium finally completely prevented.

The nucleating agents must meet the following requirements fulfill:

• - reduction of the interfacial energy.
• - Their melting point must be above that of the polymer.
• - Insolubility in the polymer.
• - You mustn't be volatile.
• - You should not react chemically with the polymer.

Two further test series are listed below.

Test series 3

Target:
Investigation of the influence of temperature in the absence and in the presence of different carbon blacks as nucleating agent N on the sag value.

Result:
The nucleation significantly increases the heat resistance.

Test series 4

Target:
Investigation of the influence of different nucleating agents N (amount 2% by weight) on the sag value under different tempering conditions

Result:
Immediate tempering is more effective than tempering with intermediate storage. The nucleating effect is relatively clearest with diphenylurea, followed by activated carbon black NAR 30.

The test series 3 and 4 relate to plate tests.  

Experimental description of process variants I to III

In a stirred tank, using a stirrer (e.g. Ultra-Turrax high-speed mixer) prepared the A component that in the case of process variants II and III nucleating agents contains. With the help of a foam dosing machine with a mixing head the A component with the B component in the corresponding Foamed shape. The usual conditions (column U) and the Test conditions underlying test series 1 to 4 (column V) are:

Regarding procedural details of the preparation and the foaming is at the level mentioned at the beginning referred to the technology.

Is carried out in the case of process variants I and III thermal aftertreatment (tempering) of the (nucleated) Polyurethane integral foam molded body, so the tempering in the form and / or after removal from the mold. The results on which the test series 1 to 4 are based are based on a thermal aftertreatment Demolding. The moldings are placed on a mold after demolding Edition and placed in a tempering furnace as part of a third Process step thermally post-treated.  

After the tempering process has ended, the shaped body is opened Cooled to room temperature. To determine the heat resistance the so-called sag test is used, which is as follows is carried out: A test rod as a test specimen 150 mm long, 25 mm wide and 3 to 4 mm thick is fixed on a base applied, so that 50 mm are firmly supported and the remaining area (100 mm) freely over the support area protrudes. The amount of reduction in mm is measured on End of the bar compared to the initial state after one Heating for 1 hour at 160 ° C. These parameters are also based on the test series 1 to 4. The smaller the sag value (Short name "sag"), the greater the heat resistance.

This effect is surprisingly high, what the test series 1 to 4 illustrate.

Claims (8)

1. A process for producing molded articles from integral polyurethane foam, in particular body parts for the automotive industry, the polyol component (A component) being prepared in the first process step and the A component being reacted with the isocyanate component (B component) in the second process step, for example According to the RIM method, characterized in that the moldings are thermally aftertreated in the form and / or after demolding in a subsequent third process step for 30 minutes to 3 hours at 120 to 180 ° C (process variant I). 2. Process for producing molded articles from polyurethane Integral foam, especially body parts for the Automotive industry, the first step in the Polyol component (A component) prepared and in the second Process step the A component with the isocyanate component (B component) is implemented, for example according to the RIM Method, characterized in that the A component Contains nucleating agents, the nucleated shaped body are not annealed (process variant II) or in the Form and / or following the demolding in the context of a subsequent third process step thermally be treated (process variant III).   3. The method according to claim 1, characterized in that the Shaped body at 130 to 170 ° C for 1 to 3 hours, in particular thermally treated at 160 ° C. 4. The method according to claim 2, characterized in that nucleating agents from the following classes of substances in concentrations of max. 5% by weight, based on the effective substance and the polyol component, are used individually or in combination:

• a) Color black
• b) furnace, canal and / or thermal soot
• c) Active silica and / or silicates
• d) metal oxides of the 2nd and 3rd main and subgroup of the periodic table
• e) metal carboxylates with melting points <160 ° C.
• f) low molecular weight or oligomeric derivatives of urea or thiourea with melting points <160 ° C.
• g) Low molecular weight or oligomeric compounds with urethane, allophanate, biuret or isocyanurate structures with melting points <160 ° C.
• h) metal halides of the 1st and 2nd main group of the periodic table with melting points <160 ° C

5. The method according to claims 2 or 4, characterized characterized in that the nucleated moldings for at least 30 minutes and at temperatures ≧ 110 ° C (upper Limit: 180 ° C) can be thermally treated.   6. The method according to claim 5, characterized in that the nucleated moldings thermally for 1 hour at 160 ° C. be treated. 7. Use of the method according to claim 1 for the production of small body parts. 8. Use of the method according to claim 2 for the production of small and large body parts.