INACTIVATED POLYURETHANE AND METHOD FOR PREPARING IT

Abstract: The polyurethane is inactivated by being coated with a layer of a polymer which contains e.g. hydroxyl groups. These hydroxyl groups react with free isocyanate molecules in the polyurethane material and a chemical bonding occurs which prevents noxious isocyanate molecules from coming into contact with the ambient atmosphere. The inactivated polyurethane will thereby be useful in products where it comes into direct contact with the skin or the mucous membranes.

Description: INACTIVATED POLYURETHANE AND A METHOD FOR PREPARING IT * The present invention relates to an inactivated polyurethane and a method, for preparing it, Polyurethane (PUR) is generally manufactured by a reaction between polyfunctional isocyanates and al- 5 cohols. The finished product then has a certain residual isocyanate content. It has long been known that isocya¬ nate molecules are toxic, this having restricted the use of polyurethane to fields where a certain isocyanate content has not been considered harmful. 10 An indication of the toxicity of isocyanate is that the hygienic limit value for its presence in the atmosphere (for instance in a workshop) is at present 2 (in Sweden) as low as 0.01 ppm [ml (gas)/m (air)]. However, there is no limit value for the residual con- 15 tent of isocyanate monomers..in completely cured poly¬ urethane material, which may be attributable to the fact that no suitable method of analysis for detecting so low contents of isocyanate molecules as here con¬ templated has been elaborated. 20 The commonest symptom of exposure to isocyanate are allergic troubles in the form of irritations of the mucous membranes and the skin. Since the residual isocyanate monomer content of completely cured poly¬ urethane is very low, it is possible nevertheless in 25 many instances to use polyurethane in cases where the human body comes into contact with the material, if an air gap can be provided between the polyurethane and the body. One example of this is the use as padding in mattresses which are covered with a fabric. 30 Considering the other properties of polyurethane, it would also serve well in other products, but its use has hitherto been hampered to a great extent by its noxiousness to the skin and the mucous membranes. The object of the present invention therefore is to provide an inactivated polyurethane which can also be used in such products as will come into direct con¬ tact with the skin, suc as ear protectors or dressing materials, e.g. plaster. This object is achieved by coating polyurethane with a layer of a polymer which contains functional groups capable of reacting v/ith isocyanate. Free iso¬ cyanate groups leaving the polyurethane material will then be prevented not only mechanically from escaping out into the ambient atmosphere but will react with the alcohol groups in the polymer layer and be chemi¬ cally bound therein. Examples of preferred functional groups which are capable of reacting with isocyanate are hydroxyl groups. The coating of the polyurethane can be carried out in various ways. Thus, the polyurethane can first be molded to the desired shape and thereafter be coated with a thin layer of a suitable polymer v/hich then reacts with isocyanate groups in the polyurethane. Another mode of producing the coating is first to apply a thin layer of a suitable polymer to the inner side of the mold in v/hich the polyurethane is to be shaped, and then form the polyurethane in the mold. Functional groups in the polymer will then react with isocyanate groups in the polyurethane, whereby the layer of polymer is chemically bonded to the polyurethane. A suitable hydroxyl group containing polymer is e.g. polyvinyl alcohol, but other hydroxyl group con¬ taining polymers mav also be used, such as partly hydrolyzed polyvinyl acetate or copolymers containing vinyl alcohol or hydrolyzed polyvinyl acetate, polymers prepared from vinyl and acrylate monomers containing hydroxyl groups, or hydroxyl group-terminated low mole¬ cular polyesters. For a more detailed illustration of the invention, reference is now had to the following Example v/hich is however not meant in any way to restrict the scope of the present invention. EXAMPLE Since the isocyanate content of polyurethane is so low that it cannot be analyzed by conventional methods a model test has been conducted in order to illustrate the penetration of the isocyanate molecule through poly¬ vinyl alcohol. A mixture of toluene-2,4-diisocyanate (2,4-TDI) and toluene-2,6-diisocyanate (2,6-TDI) , which are common starting materials for the preparation of polyurethane, was batched in a test tube over which the sheeting to be examined was stretched. Over the sheeting was placed a sealing flask having two taps. The polymer sheeting and the TDI were heated to 65-?70°C. 20 1 of air were blown for 20 min. through one tap of the flask and were collect ed at the other tap. The amount of isocyanate which had penetrated through the sheeting and been entrained by the current of air was determined by a gas chromatographi standard method. Tests were performed with sheetings of polyethy- lene, polyvinyl alcohol and polyvinyl alcohol treated with a catalyst (DABCO 33 LV) . The catalyst used is of the type employed in the production of polyurethane, and residues of spent catalyst are always present in the finished material. It was found that the amount of isocyanate that had penetrated through the sheeting of polyvinyl alcohol (not treated by catalyst) was about 50 times less than the a- ount that had penetrated through the polyethylene sheet¬ ing. The permeability of the catalyst-treated polyvΛnyl alcohol sheeting to isocyanate molecules was still less. A lesser amount of 2,4-TDI than of 2,6-TDI initial¬ ly penetrates through the polyvinyl alcohol sheeting. Since 2,4-TDI is far more reactive than 2,6-TDI, this is indicatxve of a reaction taking place between the isocyanate molucules and the alcohol groups. The more reactive molecule is thus barred to a greater extent by the reactive protective film.

Claims: CLAIMS 1. Inactivated polyurethane coated with a protec¬ tive layer, c h a r a c t e r i s e d in that it is coated with a layer of a hydroxyl group containing poly¬ mer the hydroxyl groups of which are capable of react- ing with free isocyanate groups in the polyurethane, said polymer comprising polyvinyl alcohol, partly hydro¬ lyzed polyvinyl acetate or a copolymer containing vinyl alcohol or hydrolyzed polyvinyl acetate, a polymer pre¬ pared from vinyl and acrylate monomers containing hy- droxyl groups, or a hydroxyl group-terminated low mole¬ cular polyester. 2. A method for preparing an inactivated polyure¬ thane, c h a r a c t e r i s e d by coating the poly¬ urethane with a protective layer of a hydroxyl group containing polymer the hydroxyl groups of which are capable of reacting v/ith free isocyanate groups in the polyurethane, said polymer comprising polyvinyl alcohol, partly hydrolyzed polyvinyl acetate or a copolymer con¬ taining vinyl alcohol or hydrolyzed polyvinyl acetate, a polymer prepared from vinyl and acrylate monomers containing hydroxyl groups, or a hydroxyl group-terminat¬ ed low molecular polyester. 3. Method as claimed in claim 2, c h a r a c ¬ t e r i s e d in that the coating is effected by coat- ing the polyurethane with the protective layer after molding the polyurethane to the desired shape. 4. Method as claimed in claim 2, c h a r a c ¬ t e r i s e d in that the coating is effected by apply- ing a layer of the polymer to the inner side of a mold in which the polyurethane is to be shaped, and there¬ after molding the polyurethane. 5. The use of the inactivated polyurethane as claim¬ ed in claim 1 in ear protectors or dressing materials. OA-PI

Inventors: UUSTALU JAAN M, UUSTALU, JAAN, M.
Applicants: PROTECTOR AGENTUR AB
Application year: 1983
Main classification: C08J7
IPC codes: A61L15, C08G18, C08J7