Plastic and nonmetallic article shaping or treating: processes – Pore forming in situ – Composite article making
Patent
1993-12-03
1995-11-28
Kuhns, Allan R.
Plastic and nonmetallic article shaping or treating: processes
Pore forming in situ
Composite article making
264 469, 264255, B29C 4420, B29C 4432
Patent
active
054705150
DESCRIPTION:
BRIEF SUMMARY
The coating of pipes by application of several solid plastic layers by rotational molding is known (cf. EP-A 166 245).
The present invention relates to a process for insulating pipes. In the process according to the invention, a specially developed rigid polyurethane foam is used as the insulating layer while a specially developed solid polyurethane, more particularly an elastomeric polyurethane, is used as the surface layer.
At the present time, two processes are widely used, namely: layer to the rotating pipe. paths
The present invention avoids the disadvantages mentioned above.
Another advantage of the process according to the invention lies in its flexibility of application to pipes of various diameters with individual layers of variable thickness. Adaptation of the formulations of the solid polyurethane surface layer and the rigid polyurethane foam to the particular dimensions of the pipe in conjunction with variation of the machine parameters provides for any desired setting.
The present invention relates to a process for isolating pipes by application of at least one insulating layer and at least one outer surface layer by rotational molding, characterized in that a rigid polyurethane foam is used as the insulating layer while a solid polyurethane is used as the surface layer.
In a preferred embodiment of the invention, hydrogen atoms and containing molecular weight of 300 to 700 weight of 32 to 1,000 as crosslinking agent and molecular weight of 200 to 700 and having a molecular weight of 62 to 299 as chain-extending or crosslinking agent and polyisocyanates (crude MDI) is used as the aromatic polyisocyanate, obtainable by reaction of and 2,2'-isomers and 0 to 30% by weight components of higher functionality with 1,000 to 6,000 to which up to 30% by weight of a hydrophobicizing agent, preferably castor oil, has optionally been added having a molecular weight of 1,000 to 6,000, 122 to 400, molecular weight of 60 to 400, diamine, polyurethane are applied in a single operation, rigid polyurethane foam layer develops its final strength and are applied by means of mixing heads and casting nozzles, either the mixing heads being advanced at defined intervals parallel to the axis of rotation of the pipe or the pipe being axially advanced at a defined speed under fixedly positioned mixing heads.
The following starting components are used for the production of the rigid polyurethane foams:
Polyisocyanates of the type described, for example, by W. Siefken in Justus Liebigs Annalen der Chemie, 562, pages 75 to 136, for example those corresponding to the following formula to 13 carbon atoms, 10-11.
In general, it is particularly preferred to use the commercially readily obtainable polyisocyanates, for example 2,4- and 2,6-tolylene diisocyanate and mixtures of these isomers (TDI), mixtures of diphenyl methane diisocyanate and polyphenyl polymethylene polyisocyanates of the type obtained by phosgenation of aniline/formaldehyde condensates ("crude MDI") and polyisocyanates containing carbodiimide groups, urethane groups, allophanate groups, isocyanurate groups, urea groups or biuret groups ("modified polyisocyanates").
These polyisocyanates are reacted with the polyol component defined more closely hereinafter.
The polyol component contains (50 to 90% by weight) of a (short-chain) polyether containing at least two hydroxyl groups and having a molecular weight of 300 to 700 which has been produced by addition of propylene oxide and/or ethylene oxide onto starters, such as sorbitol, ethylene glycol, trimethylol propane, glycerol, pentaerythritol and/or sugar. The polyol component preferably has an OH value of 300 to 600.
In addition, the polyol component contains (0.5 to 20% by weight) an aliphatic, cycloaliphatic or aromatic polyamine having a molecular weight of 32 to 1,000 as cross-linking agent, for example tetraethylene pentamine, hexamethylenediamine or diethyl tolylenediamine.
In addition, a hydrophobicizing agent, preferably castor oil, may be present in quantities of 0 to 30% by weight.
The blowing agent (k
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Eisen Norbert
Grimm Wolfgang
Ruprecht Hans-Dieter
Bayer Aktiengesellschaft
Gil Joseph C.
Kuhns Allan R.
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