A METHOD FOR MAKING A GLUED JOINT

Abstract: A glue is disclosed which comprises a solution of at least one water-insoluble synthetic organic polymer, such as PVC or ABS, in a solvent which essentially consists of one or several compounds selected from the group consisting of 5- or 6-membered water-miscible lactones or lactams having a melting point of at the most -10°C, a boiling point of at least 200°C and a flash point of at least 90°C, such as N-methyl-2-­ pyrrolidone or γ-butyrolactone. The polymer or polymers may be present in a concentration of between 0.5 and 50%, in particular about 10% by weight. The glue may be used at tropical temperatures without problems arising from solvent vapours and without fire risks. The glue is particularly useful for gluing soft PVC articles to hard PVC articles without loss of the sort character of the sort PVC, and for gluing different polymers, such as PVC on polycarbonate or polycarbonate on polyacrylate.

Description: The present invention relates to a method making a glued joint. The use of polymer materials in e.g. the building industry has had as a consequence that it is necessary to join, by gluing prefabricated or fitted articles mainly made from PVC or ABS. Examples of such components are roof gutters, roofings, window frames or PVC tubing for tap water or sewage junctions. The types of glue commonly used so far practically all consist of a 10-30% by weight solution of PVC in one or several of the following solvents: Butylacotate, cyclohexanone, dimethylformamide or tetrahydrofuran. These solvants all have a relatively low boiling point and/or flash point and are hazardous to the health when inhaled and, in varying degree: by skin contact. Thus, official safety demands dictated by the fire hazards involved and offical demands dictated by the occupational hazards involved are so strict that the compliance to such demands renders the use of such solvents costly and in some instances almost impossible. Futhermore, all directions for use of currently available glues demand at the very least a careful de-greasing of the components with a de-greasing agent, normally of the same type as the thinner recommented for the glue, thus furhter subjecting the user contact with a solvent and solvent vapours. Technically, the low boiling point of most of the currently used solvents leads to problems when gluing at elevated temperatures or in strong sunlight, such as the gluing of PVC tubes in subtropical or tropical regions where it is common that such gluing operations can only be carried out at night. The present invention obviates or substantially reduces the above-discussed disadvantages of the glues according to the prior art both as regards flammability, occupational hazards and environmental problems, and difficulties in connection with gluing at elevated temperatures. The invention relates to a method for making a glued joint between surfaces of articles made from a material comprising water-insoluble synthetic organic polymers, said method comprising applying a glue consisting of a solution of at least one water-insoluble synthetic organic polymer selected from the group consisting of PVC, ABS, polyacrylate, polycarbonate, cellulose acetate, polyacrylamide, polyamide and polystyrene in a solvent which consists of one or several compounds selected from the group consisting of 5- or 6-membered water-miscible lactones or lactams having a melting point of at the most -10°C, a boiling point of at least 200°C and a flash point of at least 90°C, on at least one of the surfaces to be joined, joining the surfaces and allowing the joint to develop. Among the lactams, N-alkylated lactams, in particular N-methylated lactams are preferred, since N-alkylated lactams have lower melting points than N-unsubstituted lactams. In the present context, the term "alkylated" designates substitution with a C₁₋₄ alkyl group which may be straight or branched, such as methyl, ethyl, propyl, isopropyl, butyl, and tert.butyl. Preferred lactones are lactones which are either unsubstituted or alkylated in the 4- or 5-position. The lactams may be unsubstituted on the ring carbon atoms or alkylated in the 4- or 5-position. As examples of 5- or 6-membered water-miscible lactones or lactams having a melting point at the most -10°C and a boiling point of at least 200°C may be mentioned N-methyl-2-pyrrolidone (also known as NMP), butyrolactone, N,5-dimethyl-2-pyrrolidone, γ-valerolactone, δ-valerolactone and γ-caprolactone. A preferred lactam is N-methyl-2-pyrrolidone, and a preferred lactone is γ-butyrolactone. Each of these preferred solvents may be used per se, or a mixture thereof may be used. N-methyl-2-pyrrolidone is especially preferred because of its low toxicity (LD₅₀≧7 g/kg in rats). Among the above listed polymers, PVC and ABS are especially important due to their widespread use in articles destined for the building, construction and plumbing fields, etc. The polymer or polymer mixture dissolved in the solvent to form the glue may be newly made polymer, or it may be polymer waste from the production of polymer articles. As a general rule, the polymer or polymers in a glue is/are preferably identical or substantially identical to the polymer or polymers which are to be joined by means of the glue in question. In other words, the polymer in a glue for gluing PVC is preferably PVC, the polymer in a glue for gluing ABS is preferably ABS, etc. However, it has also been found that two different polymer materials may be glued by means of a glue which comprises only one of the polymers. Thus, both soft and hard PVC may be glued onto polycarbonate by means of a 10% solution of polycarbonate in NMP, and polycarbonate may be glued onto polyacrylate by means of a 10% solution of polycarbonate in NMP. For use in the various applications the viscosity of the glue may be adjusted within a wide range by increasing or decreasing the concentration of the polymer or polymers in the glue. The polymer or polymers are preferably present in the glue in a concentration between 0.5 and 50% by weight, or preferably a concentration between 2 and 40% by weight, usually between 3 and 30% by weight. For most practical applications, a suitable glue will contain the polymer or polymers in a concentration of between 5 and 20%, in particular 8 and 16% such as about 10% by weight. If desired, a thixotropic agent such as colloidal silica may be incorporated in the glue in order to avoid dripping of the glue without resorting to an otherwise undesired high concentration of the polymer or polymers. The colloidal silica may, for example, be of the type sold under the trademarks "Aerosil®" (from Degussa, BRD) or "HDK" (from Wacker Chemie, BRD) and may be incorporated in any suitable amounts such as from about 0.1 to about 3% by weight. Also, a viscosity-adjusting agent may be incorporated, such as baryte in a concentration of from 1 to 10% by weight, a di-2-ethylhexylamine neutralized carboxyvinyl polymer (such as "Car bopol" 934 from Goodrich Chemicals) in a concentration of from about 0.5 to about 1% by weight, or a hydroxyethyl cellulose (such as "Cellosize" QP 100M from Union Carbide) in a concentration of from about 0.5 to about 2% by weight. One of the advantages of the glue is that it permits the gluing of components which were not, in the prior art, easily gluable by means of the known compositions. As examples of such systems which are now easily gluable may be mentioned gluing of soft or softened PVC to hard PVC where prior art glues based on conventional solvents often failed, probably due to undesired interaction with the plasticizers in the soft PVC. According to the invention this permits e.g. the easy gluing of soft PVC hoses to hard PVC fittings in connection with the installation of e.g. swimming pools, or in connection with the construction of laboratory apparatus (gluing of soft PVC hoses to hard PVC tubes, in dishwashers, washing machines, etc.). A further possibility is the gluing or repair of soft PVC articles where a glue may be constructed with a sufficient body and viscosity to fill cracks or fissures and other irregularities and join them to attain the original dense structure, with retention of the general soft character of the original article. This is ascribable to the characteristics of the glue to the effect that it does not interfere with or extract plasticizer from the PVC, in contrast to other glues, the solvents of which are also much more efficient solvents of the plasticizer. EP-A-0 046 957 describes polymer glue compositions in which part of the content of conventional solvents, with a view to reducing the concentration of solvent vapours, is replaced by a N-alkylated-pyrrolidone. It is, however, only attempted to add the N-alkylated-pyrrolidone in an amount of up to 20% by weight. U.S. Patent No. 4,152,313 described a laminating adhesive which contains a solvent mixture of toluene and a N-alkyl-pyrrolidone in a weight ratio of 2:1 to 1:2. The solvent mixture, however, only constitutes 5-15% of the total composition wherein the remainder is a polymer emulsion. In a textbook on NMP (cf. "NMP, N-methyl-2-pyrrolidone Handbook", GAF Corporation, N.Y. 1972, page 47), it is mentioned that NMP may improve performance in such applications as rubber and vinyl cements, and it is also suggested to use NMP as a solvent welding agent. The textbook, however, does not state or indicate that NMP may be used as the sole or substantially the sole solvent in glues, and the mention of NMP as a solvent welding agent does not anticipate the use of NMP as a glue solvent. The technology of gluing is distinct from welding of plastics in many regards: Firstly, gluing does not solely depend upon dissolution of the plastic parts to be joined. Secondly, gluing will serve to fill voids between the articles to be joined because of the body constituted by the solid contents of the glue itself. Thirdly, solvent welding cannot be used in practice in several applications because the solvent would tend to drip or spread over a too large area. Fourthly, solvent welding would tend to apply too much solvent at the junction with the result that the polymer material adjacent to the joint would soften to a too high degree and it would take a too long period before the full strength had been developed through migration of the solvent. Although the GAF Handbook on page 38 does indicate that various polymer resins are soluble in NMP, it does not in any way indicate or even hint at the possibility that such solutions containing NMP as sole solvent can serve as polymer glues. The invention is illustrated in the following examples. Example 1 Preparation of an NMP-based glue containing PVC. In a closed vessel 10% by weight of PVC granulate (trademark Vinnol® from Wacker Chemie, BRD) are added to NMP at room temperature under vigorous stirring until a homogeneous solution is obtained. Example 2 Preparation of an NMP-based glue containing PVC-waste In a closed vessel 10% by weight of PVC granulate (made from waste from the production of hard PVC articles) are added to NMP under vigorous stirring at room temperature until a homogeneous solution is obtained. Example 3 Preparation of an NMP-based glue containing ABS By following the procedure described in Examples 1 and 2, but substituting ABS granulate for PVC granulate, a solution of 10% by weight of ABS in NMP is prepared. Example 4 Preparation of an NMP-based glue containing PVC and ABS By following the procedure described in Examples 1 and 2 a solution of 5 parts by weight of PVC granulate and 5 parts by weight of ABS granulate in 90 parts by weight of NMP is prepared. Example 5 Pressure testing of glued joints From a length of PVC-tube with a nominal diameter of about 50 mm were cut two pieces with a length of about 50 cm. To each of the four ends of the two pieces of tubing were glued a closed tube sleeve with an inside diameter of about 50.5 mm. One of the sleeves of each length of tube was fitted with a pressure coupling and a manometer. The gluing was performed by means of a 10% by weight solution of PVC in N-methyl-2-pyrrolidone prepared as described in Example 1. The gluing was performed by applying a thin layer of glue to the outside surface of the tube end about 3 cm up the length of the tube, fitting the sleeve over the end of the tube, rotating the sleeve on the tube end to distribute the glue and leaving the joints to set. Tube No. 1 had a diameter at one end of between 50.0 mm and 50.2 mm and at the other end of between 50.0 mm end 50.2 mm, which ends were fitted with closed sleeves with an inside diameter of 50.5 mm and 50.4 mm, respectively, thus producing joints with a gap between the surfaces of 0.3-0.5 mm and 0.2-0.4 mm, respectively. After the glue had been applied and the sleeves fitted, the glue was allowed to set for 4 hours at room temperature. Thereafter, the gluing was pressure tested at 10 kg/cm² water pressure for 15 minutes and thereafter at 19-20 kg/cm² water pressure for 15 minutes. No leaks were obrserved. Tube No. 2 had end diameters of 49.9-50.3 mm and 49.9-50.3 mm, and the ends were fitted with closed sleeves with inside measures of 50.5 mm and 50.3-50.5 mm, respectively, thus producing joints with a gap between the surfaces of 0.2-0.6 mm and 0.2-0.6 mm, respectively. The sleeves were glued to the tube in the same manner as above, and the glue was allowed to set for 4 hours at room temperature. Pressure testing was performed at 8 kg/cm² water pressure for 15 minutes followed by 19-20 kg/cm² water pressure for 15 minutes. No leaks were observed. Example 6 Gluing of soft PVC onto hard PVC To the outside surface of the end of a piece of hard PVC tube (outside diameter of 16 mm) a glue prepared according to Example 1 was applied ca. 1 cm up the length of the tube. A piece of soft PVC hose (inside diameter 13 mm) was thereafter fitted over the end of the tube and rotated slightly to distribute the glue, whereafter the glue was allowed to set. The gluing showed no cracking or brittling of the hose, and it was not possible to pull the hose off.

Claims: 1. A method for making a glued joint between surfaces of articles made from a material comprising water-insoluble synthetic organic polymers, said method comprising applying a glue consisting of a solution of at least one water-insoluble synthetic organic polymer selected from the group consisting of PVC, ABS, polyacrylate, polycarbonate, cellulose acetate, polyacrylamide, polyamide and polystyrene in a solvent which consists of one or several compounds selected from the group consisting of 5- or 6-membered water-miscible lactones or lactams having a melting point of at the most -10°C, a boiling point of at least 200°C and a flash point of at least 90°C, on at least one of the surfaces to be joined, joining the surfaces and allowing the joint to develop. 2. A method as claimed in claim 1 in which the lactams are N-alkylated, in particular N-methylated. 3. A method as claimed in claim 1 in which the lactones are unsubstituted or alkylated in the 4- or 5-position. 4. A method as claimed in claim 2 in which the lactams are unsubstituted on the ring carbons or alkylated in the 4- or 5-position. 5. A method as claimed in claim 1 in which the solvent consists of N-methyl-2-pyrrolidone and/or γ-butyrolactone. 6. A method as claimed in claim 5 in which the solvent consists of N-methyl-2-pyrrolidone. 7. A method as claimed in claim 5 in which the solvent consists of γ-butyrolactone. 8. A method as claimed in claim 1 in which the polymer is PVC. 9. A method as claimed in claim 1 in which the polymer is ABS. 10. A method as claimed in claim 1 in which the polymer is a mixture of PVC and ABS. 11. A method as claimed in any of claims 1-10 in which the polymer or polymers in the glue is/are present in a concentration of between 0.1 and 50% by weight. 12. A method as claimed in claim 11 in which the polymer or polymers in the glue is/are present in a concentration of between 2 and 40% by weight. 13. A method as claimed in claim 12 in which the polymer or polymers in the glue is/are present in a concentration of between 3 and 30% by weight. 14. A method as claimed in claim 13 in which the polymer or polymers in the glue is/are present in a concentration of between 5 and 20% by weight. 15. A method as claimed in claim 14 in which the polymer or polymers in the glue is/are present in a concentration of between 8 and 16% by weight. 16. A method as claimed in claim 15 in which the polymer or polymers in the glue is/are present in a concentration of about 10% by weight. 17. A method as claimed in any of the preceding claims in which the glue contains a thixotropic agent. 18. A method as claimed in claim 17 in which the thixotropic agent is colloidal silica. 19. A method as claimed in claim 18 in which the colloidal silicia is present in the glue in an amount from about 0.1 to about 3% by weight. 20. A method as claimed in any of claims 1-16 in which the glue contains a viscosity-adjusting agent.

Inventors: SPERLING, BENT
Applicants: A/S F. HEIMANN & CO.
Application year: 1983
Main classification: C09J4
IPC codes: C08J3, C09J201, C09J11