FR3095772A1 - Process for manufacturing movable objects or parts of movable objects in optionally biodegradable polymer - Google Patents

Abstract

Process for the manufacture of movable objects or parts of movable objects in optionally biodegradable polymer. The process allows the production of parts or whole movable objects in plastic polymer, with a saving of materials, equipment and production energy compared to conventional processes such as thermal rotomoulding of plastic polymers such as polyamide or polyethene, either the semi-rigid RIM full-skin polyurethane molding, or the laminates with a plastic foam core injected inside the shell of the object. The process makes use of the high mechanical properties and the possibility of use by simple cold casting machines, in a fast time, without the use of large tools required for thermal processes or for full skin RIMs. The production is done by cold rotational molding, without the use of an oven which involves long heating and without the use of expensive cooking systems by circulating a fluid in a rotational molding mold. Polyurethane polyurea elastomers, allowing, cold, in liquid form, in a rotomoulded mold, to obtain, even in very thin layers, skins and surface membranes which, associated with a semi-rigid PU foam filling of low density, have very high resistance to tearing, static stress and static bending. In addition, the use, in these systems, of polyester polyols of the poly-adipate family makes these systems hydrolyzable under the prolonged action of humidity. Especially when they are linear, they hydrolyze in a few months in the form of acids and diols, which are biodegradable.

Description

Process for manufacturing movable objects or parts of movable objects in optionally biodegradable polymer.

The object of the present invention is to obtain an economic cost in the production of movable objects or parts of movable objects in plastic polymer (plastic material) with the additional option of making them biodegradable once crushed and buried or once unfortunately landing in the sea.

The invention constitutes progress and an economic reduction compared to the 3 processes commonly used today:

- The rotational molding of thermo-plastics such as propylene or polyamide which require either that the micro roto-molder is located in the oven with a long duration of obtaining the temperature and a high thermal cost or a very expensive mold associating a tubular heating circuit, integrated in the mold which makes it extremely expensive.

Compared to this system, the present invention proposes rotational molding at room temperature, in molds which can be simply produced by combination of laminated silicone or by simple boilermaking, without a circuit, the molding being completed by the injection of semi-finished PU foams. rigid low density or flexible foams depending on the choice of use.

The method of the present invention uses PU polyureas to which it is possible to impart very high properties of resistance to tearing, puncturing, repeated static stress or repeated static bending.

- The method of the present invention also differs from the flexible or semi-rigid RIM system with integral skin which is used for seats, backrests or armrests of economic furniture but whose system requires not only high densities but above all produces a skin of mechanical resistance much lower than the resistance of polyurea membranes in the ratio of 1/10, making it possible only for furniture or very inexpensive, low-stress and short-term uses.

Also, RIM without additional paint can only result in brown, black or very dark colors.

For example, the resistance-rupture of the micro-cellular skin of the RIM is less than 4 MPA with a low tear resistance while a polyurea elastomer can easily reach or exceed 30 MPA with a tear resistance of 20 times greater than that of RIM skin.

- The 3rd common process that the present invention can replace is the execution of an evaluation by extrusion + Blow molding, followed by a plasma treatment and an injection of PU foam, the equipment being a very heavy investment such as, for example, surfboards.

The method for executing an object or a component in accordance with the present invention is as follows:

It takes into account the fact that the curing speed of a 2-component liquid PU polyurea can be adjusted at will, by the choice of the amines of the hardener component incorporated in the prepolymer component, so as to be able to fill the mold before rotation with the liquid then distribute it and harden it in a few minutes by the operation of double rotation on 2 axes as is conventionally practiced in rotational molding, without cooking and without long waits, i.e. 3 to 10 minutes.

It is then possible to fill the mold with a PU foam chosen as flexible, semi-rigid or rigid-flexible depending on the chosen use of the object and to unmold after a few tens of minutes, or even less depending on the choice of foam. injected as does, after cooling, a classic rotational molding.

In summary, the outer membrane with high resistance and low thickness necessary given its resistance, is poured in the liquid state into the mold, roto-moulded and self-hardened then filled with the type of PU foam adapted and chosen.

As an option and standard formulas are described below, it is possible to choose, for the PU polyurea and for the PU foam, polyester polyols from the poly-adipate family, which are known to be slowly hydrolisable by permanent contact with water for periods of less than one year.

After hydrolysis, we find glycol acids and ureas which are bio-degradable.

In conclusion, the choice of this type of formulation makes it possible to produce objects that are subsequently biodegradable after destruction and therefore non-polluting plastic objects in the medium term.

Flexible, semi-rigid or rigid low-density (30 to 50 kg/m3) injected PU foams are known products both in the non-hydrolyzable polyester version and in the hydrolyzable polyester version. It is therefore useless to recall the formulations.

Example of formulations of polyurea PU membranes allowing the production of the high-strength membranous outer part of an object according to the present invention.

The prepolymer component, i.e. part "A", can be produced by condensation at 80°C with the following formula:

Polyol diol of molecular weight 2000 – OH index 56 200 games TDI (Toluene di-isocyanate) 100 games Dipropylene glycol 27 games Rutasolv DI type plasticizer 73 games

Gradual incorporation of the Di Propylene glycol/Rutasolv mixture into the reactor to control the exotherm below the 70°C temperature of the mixture. Functional isocyanate content of the prepolymer, after reaction: 6.5% Nco + 0.3

Component “B” hardener:

Ethacure 300 from HUNSTMANN 40 games Oleic acid 4 parts Bi-oxazolidine OZ.4 from BAYER 20 games

Potlife of the mix 5 minutes Curing time in the mold after rotational molding, before injection of the PU foam 12 minutes Rotational molding duration 12 minutes after mixing the components

The 4th process, for hard or semi-hard objects is the rigid foam with integral skin, that is to say the rigid RIM as it was established for the 1st small series of the famous "PANTON CHAIR". This process makes it possible to economically produce a rigid shape but does not allow either color or, above all, good surface conditions and therefore must be completed by surface preparation and painting as was the case for the PANTON CHAIR, which, in terms of labor and operation, is expensive and does not allow flexibility or semi-rigidity.

On the other hand, the rotational molding of a Pu polyurea skin, in a closed mould, with a thin joint, with the ease of demolding after opening by temporary deformation of the molded object for the series of the mould, makes it possible to obtain directly a aesthetic surface in the present invention.

Claims (2)

Process for obtaining economical movable objects, without the use of thermal means and thermal mold by the following process: Cold roto-moulding in a closed mould, with double axial roto-moulding, of polyurethane polyurea self-hardening at room temperature in a few minutes after mixing and incorporation, in a roto-moulding system. Then injection, after polymerization for a few minutes, of PU foam inside the roto-moulded skin. Process according to claim 1, in which the rotomolded skin is composed of poly-adipate polyols, acid-hydrolyzable glycol and biodegradable glycol. The process then includes the injection of poly-adipate polyester foam, which becomes, in the same way, hydrolyzable as poly-adipate and biodegradable after acid and glycol hydrolysis.