WO2006085342A1

WO2006085342A1 - A method for strengthening preformed plastic sanitaryware structures

Info

Publication number: WO2006085342A1
Application number: PCT/IT2005/000068
Authority: WO
Inventors: Fabrizio Storti
Original assignee: Sirtek S.R.L.
Priority date: 2005-02-11
Filing date: 2005-02-11
Publication date: 2006-08-17

Abstract

A method for strengthening preformed plastic sanitaryware structures which have at least an internal surface (4) and an eternal surface (9). The method comprises the operating steps of positioning a structure (1), resting at least part of its internal surface (4) on a supporting template (5) which is at least mainly shaped to match said part of the internal surface (4), and of applying at least one layer of polyurethane based resin (10) on at least part of the e:ternal surface (9) of the structure (1). In addition, the step of positioning the structure (1) on the template (5) involves creating a hermetic seal between the template (5) and the structure (1). This is followed by an operating step of creating a vacuum between the template (5) and the part of the internal surface (4) resting on it, to hold the internal surface (4) against the template (5) during the step of applying the resin (10).

Description

A method for strengthening preformed plastic sanitaryware structures

Technical Field

The present invention relates to a method for strengthening preformed plastic sanitaryware structures .

Background Art

In recent years there has been a spread in sanitaryware whose structure remains visible after fitting, made of plastic, such as methacrylic resins ( commonly known as acrylic sanitaryware) . In particular, plastics were used to made bath tubs , shower trays and wash basins (understood to mean both sinks and wash tubs) . The structures of such sanitaryware are normally obtained by thermoforming from a flat sheet of preselected plastic material . However, the thermoforming process has the disadvantage of significantly reducing the thickness of the structure at the most deformed zones . For example , in the case of bath tubs , whilst the edges substantially maintain the thickness of the original sheet (normally around 5 mm) , the part of the structure which will form the base of the tub may be less than l , mm thick . As a result, at least the thinner zones of the structures obtained in this way cannot guarantee sufficient strength to resist the normal stresses to which they are subj ected during daily use . For this reason methods for strengthening preformed plastic sanitaryware structures had to be devised . The traditional method involves applying a polyester and styrene based resin with added glass fibre to the outer surface of the structure . These are normally sprayed on then rolled by hand directly on the structure mounted ^' upside-down (with its convex part facing upwards ) on a supporting template . Moreover, to allow subsequent installation of the sanitaryware, in many cases pieces of wood (on which screws can then be screwed) may be incorporated in the resin .

However, this first known technology has several disadvantages . Firstly, polyester based resins and glass fibre release volatile particles , which are highly dangerous health risk. Consequently, to protect the health of operators who manufacture sanitaryware, they must wear protective clothing, and the premises used for said processing must be equipped with suitable extractor and air filtration systems .

Secondly, this type of processing requires relatively lengthy periods of time for the production of each item.

To overcome these disadvantages , over time other methods for the production of sanitaryware and for strengthening their preformed plastic structures have been developed .

Some examples of such methods are described in patents JP9109287 , JP2000301059, JP11169312, JP11151767 and JP11151175. In particular a method was developed which involves the strengthening application of a polyurethane based resin, with the use of a primer if required (patent JP11216075) .

Although the use of polyurethane avoids all of the health risks to operators linked to use of polyesters and glass fibre, said method did not become commercially widespread since it also has significant disadvantages . In particular, the Applicant has found that applying polyurethane resins on preformed plastic structures may cause unwanted permanent deformation of the structure, due to the different thermal expansions of the two materials of which the structure and the resin are made . In particular, once the polyurethane resin has solidified, the structure may have undulations . This problem mainly occurs in the thinner zones of the preformed structures , that is to say, where the structures have less mechanical strength ( for example the base of bath tubs ) . Obviously, this situation would be unacceptable if such technology were applied at industrial level .

Disclosure of the Invention In this situation the technical need which forms the basis of the present invention is to provide a method for strengthening preformed plastic sanitaryware structures which overcomes the above-mentioned disadvantages . In particular, the technical need of the present invention is to provide a method for strengthening preformed plastic sanitaryware structures which uses polyurethane based resins but which does not deform the preformed structures .

The technical need specified and the aims indicated are substantially achieved by a method for strengthening preformed plastic sanitaryware structures as described in the claims herein .

Brief Description of the Drawings

Further features and the advantages of the present invention are more clearly illustrated in the detailed description which follows , with reference to the accompanying drawings , which illustrate a preferred embodiment of a method for strengthening preformed plastic sanitaryware structures , without limiting the scope of the inventive concept, in which : Figure 1 is a schematic view of the sequence of steps for the production of a tub using the method according to the present invention;

Figure 2 is an enlarged view of a step in the sequence illustrated in Figure 1 ; Figure 3 is an exploded view of some of the parts illustrated in Figure 2 ;

Figure 4 is a side view in cross-section of a bath tub strengthened using the method according to the present invention;

Figure 5 is a top view of a supporting template used in the step illustrated in Figure 2 ; and

Figure 6 is an enlarged view of a detail illustrated in Figure 2.

Detailed Description of the Preferred Embodiments of the Invention With reference to the accompanying drawings , the numeral 1 denotes as a whole a preformed batch tub structure, made of plastic (this generic term being understood to mean any type of polymeric material ) . Although in the accompanying drawings a bath tub is illustrated as an example, the present invention may be applied to any type of sanitaryware, and in particular, as well as bath tubs , to shower trays and wash basins . Figure 1 schematically illustrates an entire process, divided into five steps , for the production of the sanitaryware 2

(bath tub - step V) from a flat sheet 3 of plastic material (step

D •

In this case, the preformed structure 1 ( step II ) is therefore obtained by thermoforming the flat sheet 3. The structure 1 is then subj ected to the strengthening method disclosed (which in the most complete version comprises steps III and IV) , to obtain the sanitaryware 2 in its almost finished state

( step V) . However, generally speaking, the method disclosed may be applied to preformed structures 1 obtained in any way, not just by thermoforming .

The present invention is particularly advantageously applied for structures 1 made of acrylic materials, such as polymethylmethacrylate ( PMMA) , or polystyrene ( PS ) . For example, the structures 1 may be made of cast acrylic material , extruded acrylic material , or acrylic material coextruded with ABS .

The fundamental step of the strengthening method disclosed is illustrated in Figure 2 ( step IV of Figure 1) . Figure 3 also provides an exploded view of the various parts of which Figure 2 is composed.

During this step, the preformed structure 1 is positioned on a supporting template 5, on which at least part of the internal surface 4 of the structure rests . The supporting template 5 has a connecting surface 6 at least mainly shaped to match the part of the internal surface 4 of the structure 1 resting on it .

During the step of positioning the structure 1 on the template 5 , a hermetic seal is also created between the template 5 and the structure 1. In the embodiment illustrated, the hermetic seal is created between an outer edge 7 of the template 5, fitted with a special seal 8 , and the internal surface 4 of the structure 1.

Once the hermetic seal has been created, a vacuum is created between the template 5 and the part of the internal surface 4 resting on it, to hold the internal surface 4 against the template 5 during the next operating step in which at least one layer of polyurethane based resin 10 is applied on at least part of the external surface 9 of the structure 1.

In the preferred embodiment, the resin 10 is applying by spraying it on . A plurality of layers of resin 10 are applied on top of one another with successive passes by the spray nozzle 11.

Moreover, depending on requirements , the resin 10 may be applied to the entire external surface 9 of the structure 1 (as illustrated in Figure 4 ) , or only to part of the structure 1

(normally the thinnest part which therefore is most in need of strengthening) .

As regards structure 1 positioning on the template 5 , the entire internal surface 4 of the structure 1 may rest on the template 5 (not illustrated) , or only part of the internal surface 4 of the structure 1 may rest on the template 5 ( Figure 2 ) . In the latter case, the part of the structure 1 resting on the template 5 corresponds to a thinner zone of the structure 1 ( for simplicity, in the accompanying drawings the structure 1 has constant thickness ) or a zone most in need of strengthening .

As regards the step of creating the vacuum between the template 5 and the structure 1 , in the embodiment illustrated the vacuum is generated by means of a suction system 20.

As illustrated in Figures 3 and 6, the suction system 20 comprises a plurality of suction outlets 12 on the connecting surface 6 of the template 5 and connected by connecting tubes 13 to a manifold 14 which is in turn connected to a suction pump 15. In the accompanying drawings , between the pump 15 and the manifold 14 there is also a rotary pneumatic j oint 16 connected to the rotary base 17 of the template 5.

To improve the adherence of the structure 1 to the template 5 , the vacuum is preferably created in such a way that it is distributed relative to the portion of the internal surface 4 of the structure 1 connected to the template 5. This result is achieved not j ust by distributing the suction outlets 12 over the entire template 5 ( Figure 5 ) , but also by shaping the connecting surface 6 of the template 5 so that, once the connection is made between the template 5 and the structure 1 , on the surface of the template 5 it is possible to identify alternated contact zones (not illustrated, where the template 5 is in contact with the internal surface 4 ) and detached zones 18 ( Figure 6 ) .

In this way, at the detached zones 18 the template 5 and the structure 1 form a plurality of micro-chambers 19 in fluid communication with one another (only one is illustrated in Figure 6) . Advantageously, these micro-chambers 19 are distributed at least on the portion of the internal surface 4 connected to the template 5 corresponding to the thinnest zone of the structure 1. Said shaping of the template 5 may be achieved in various ways . In particular, the dimensions of the detached zones 18 must be defined on each occasion based on the thickness of the structure 1 at that point and the material it is made of, to prevent deformation of the structure 1 by the vacuum created. Therefore, advantageously, shaping may involve , for example, surface grooves on the template 5, production of the connecting surface 6 with a predetermined roughness , etc .

Depending on the materials used (the plastic used to make the structure 1 and components of the strengthening resin 10 ) , another operating step may be necessary before application of the resin 10 (not illustrated) .

When the surface porosity of the tub is limited and the strengthening resin 10 cannot adhere to the structure 1 correctly, there may be a previous step of applying a primer at least on the part of the external surface 9 on which the polyurethane resin 10 will then be applied . Advantageously, the primer may be applied for example by nebulisation .

The primer is normally an adhesive which can adhere to the preformed plastic structure 1 and on which the polyurethane based resin 10 can easily cling .

For example, the primer may be a mixture of isocyanates . Depending on requirements and the type of resin 10 used, the method disclosed may also involve another operating step, of heating the structure 1 before application of the resin 10 ( schematically illustrated as step III in Figure 1 ) .

Although Figure 1 illustrates structure 1 heating before it is positioned on the template 5 , heating may also take place after positioning on the template 5.

The time for resin 10 solidification and hardening depends on the heat that the resin 10 can absorb . However, if the solidification time is prolonged, some resins may form foams , incorporating air bubbles in them. This situation, which may weaken the sanitaryware 2 , must therefore be avoided .

Consequently, the heating is designed to increase the resin 10 solidification speed at the start of the application step, to prevent or minimise the formation of foam on the external surface 9 of the structure 1.

In practice, for the choice of temperature to which the structure 1 must be heated, the upper limit is set by the softening temperature of the structure 1.

For example, in many applications , the heating temperature may be between 30⁰C and 8O ⁰C, or between 4 O ⁰C and 60 °C .

The present invention brings important advantages .

Thanks to the present invention it has been possible to provide a method for strengthening plastic sanitaryware structure using polyurethane based resins , without the risk of accidental deformation of the preformed sanitaryware structure .

The use of polyurethane resins avoids the health risks to operators linked to the use of conventional polyester and styrene based resins with added glass fibre .

It should also be noticed that the present invention is relatively easy to produce and that the cost linked to implementation of the invention is not high .

The invention described may be subj ect to modifications and variations without thereby departing from the scope of the inventive concept . All details of the invention may be substituted by other technically equivalent elements and in practice all materials used, as well as the shapes and dimensions of the various components, may be any according to requirements.

Claims

1. A method for strengthening preformed plastic sanitaryware structures with at least an internal surface ( 4 ) and an external surface ( 9 ) , comprising the operating steps of: positioning a structure ( 1 ) , resting at least part of its internal surface ( 4 ) on a supporting template (5 ) at least mainly- shaped to match said part of the internal surface ( 4 ) ; and applying, on at least part of the external surface ( 9) of the structure ( 1) , at least one layer of polyurethane based resin ( 10 ) ; characterised in that the step of positioning the structure

(1) on the template (5) involves creating a hermetic seal between the template ( 5 ) and the structure ( 1 ) , and also comprising the operating step of creating a vacuum between the template (5) and the part of the internal surface ( 4 ) resting on it, to hold the internal surface ( 4 ) against the template ( 5 ) during the step of applying the resin ( 10 ) .

2. The method according to claim 1, characterised in that before the step of applying the resin (10 ) , it involves a step of heating the structure ( 1 ) .

3. The method according to claim 2 , characterised in that the structure ( 1 ) is heated to a temperature of between 3O ⁰C and 80⁰C .

4. The method according to claim 2 or 3 , characterised in that the structure ( 1 ) is heated to a temperature of between 4O ⁰C and 6O ⁰C .

5. The method according to any of the foregoing claims , characterised in that the step of applying the resin ( 10 ) involves applying a plurality of layers of said resin ( 10 ) .

6. The method according to any of the foregoing claims , characterised in that the step of applying the resin ( 10 ) affects the entire external surface ( 9 ) of the structure ( 1 ) .

7. The method according to any of the foregoing claims , characterised in that the step of positioning the structure (1) involves resting at least part of the internal surface ( 4 ) of the structure ( 1 ) corresponding to a thinner zone of the structure ( 1 ) on the template (5) .

8. The method according to any of the foregoing claims , characterised in that the step of positioning the structure ( 1) involves resting the entire internal surface ( 4 ) of the structure ( 1 ) on the template (5 ) .

9. The method according to any of the foregoing claims , characterised in that the hermetic seal is created between an outer edge (7 ) of the template (5) and the internal surface (4 ) .

10. The method according to any of the foregoing claims , characterised in that it also involves , before the step of applying the resin ( 10 ) , a step of applying a primer at least on the part of the external surface ( 9 ) on which the resin ( 10 ) will subsequently be applied.

11. The method according to claim 10 , characterised in that the primer is applied by nebulisation .

12. The method according to any of the foregoing claims , characterised in that the vacuum is created using a suction system (20) .

13. The method according to any of the foregoing claims , characterised in that the vacuum is created in such a way that it is distributed relative to the internal surface ( 4 ) connected to the template ( 5) .

14. The method according to claim 13, characterised in that the distributed vacuum is obtained using a template (5) with a surface ( 6) for connection to the internal surface (4 ) of the preformed structure ( 1 ) which, once connected to the internal surface ( 4 ) , has alternated contact zones and detached zones (18 ) , the detached zones ( 18 ) forming, together with the internal 'surface ( 4 ) , a plurality of micro-chambers ( 19 ) in fluid communication with one another, distributed at least on a portion of the internal surface ( 4 ) connected to the template ( 5) .

15. The method according to any of the foregoing claims , characterised in that the step of applying the resin ( 10 ) takes place by spraying .

16. The method according to any of the foregoing claims , characterised in that it is applied to structures (1) made of methacrylate material .

17. The method according to claim 16, characterised in that it is applied to structures ( 1) made of cast acrylic material .

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18. The method according to claim 16 characterised in that it is applied to structures ( 1 ) made of extruded acrylic material .

19. The method according to claim 16, characterised in that it is applied to structures ( 1 ) made of acrylic material coextruded with ABS .

20. The method according to claim 16, 17 , 18 or 19, characterised in that it is applied to structures ( 1 ) made of polymethylmethacrylate .

21. The method according to any of the foregoing claims , characterised in that it is applied to structures ( 1 ) made of polystyrene .

22. The method according to any of the foregoing claims , characterised in that it is used to strengthen preformed sanitaryware structures ( 1 ) made using thermoforming .

23. The method according to any of the foregoing claims, characterised in that the sanitaryware consists of bath tubs , shower trays or wash basins .

24. A method for producing sanitaryware, comprising the operating steps of making a preformed plastic sanitaryware (2 ) structure ( 1 ) ; strengthening an external surface ( 9) of the preformed structure ( 1 ) , characterised in that the preformed structure ( 1 ) is strengthened with a method according to any of the foregoing claims .

25. The method according to claim 24 , characterised in that the preformed structure (1 ) is made using thermoforming starting with a flat sheet ( 3 ) of plastic material .