AU600349B2

AU600349B2 - Plastic, trough-shaped sanitary article, in particular, bathtub

Info

Publication number: AU600349B2
Application number: AU13816/88A
Authority: AU
Inventors: Karl Schock
Original assignee: Schock and Co GmbH
Current assignee: Schock and Co GmbH
Priority date: 1987-04-02
Filing date: 1988-03-29
Publication date: 1990-08-09
Anticipated expiration: 2008-03-29
Also published as: DE3712959A1; DE3712959C2; AU1381688A; CA1310796C; DE3884249D1; JPS6445610A; EP0285046A2; EP0285046B1; EP0285046A3

Description

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AUSTRALIA

PATENTS ACT 1952 COMPLETE SPECIFICATION Form

(ORIGINAL)

FOR OFFICE USE 60(349 Short Title: Int. Cl: Application Number: Lodged: If Ir I~ C t Complete Specification-Lodged: Accepted: Lapsed: Published: Priority: 1-T T-i*n rt, Related Art: TO BE COMPLETED BY APPLICANT Name of Applicant: SCHOCK CO. GmbH Address of Applicant: C t Actual Inventor: GMUNDER STRASSE 7060 SCHORNDORF, FEDERAL REPUBLIC OF GERMANY CLEMENT HACK CO., 601 St. Kilda Road, Melbourne, Victoria 3004, Australia.

t Address for Service: Complete Specification for the invention entitled: PLASTIC, TROUGH-SHAPED SANITARY ARTICLE, IN PARTICULAR, BATHTUB The following statement is a full description of this invention including the best method of performing it known to me:- 11

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Plastic, Trough-Shaped Sanitary Article, in particular, Bathtub The invention relates to a plastic, trough-shaped sanitary article such as a bathtub or shower tub, a basin, in particular, a washbasin or the like, comprising a plastic int ner layer forming that side which is used and a plastic outer layer which is substantially thicker than the inner layer and is materially joined to the inner layer, thereby f reinforcing the inner layer.

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Sanitary articles such as bathtubs, shower basins or shower tubs, washbasins and also wash tables with a basin formed therein, are being manufactured in ever increasing numbers from plastics containing, if required, fillers and reinforcing elements, because the plastics can be produced in many different colors and have lower thermal conductivity *t than, for example, enamelled steel tubs. Also, a surface showing traces of wear can, in many cases, be made attractive again by polishing. According to an article in the magazine "Plastics and Rubber International", October 1985 edition, Volume 10, No. 5, page 6, reporting on the state of the art of bathtubs, the state of the art is to manufacture in a vacuum-forming method from an acrylic resin sheet an inner shell constituting the innler layer within the meaning of the above definition and to then place this in a closed mold in which in a reaction injection molding method an outer layer of polyurethane foam for reinforcement of the inner shell is produced on the rearside of the inner shell. This procedure has quite a number of disadvantages: During thermoforming of the acrylic resin sheet to produce a 2 Vtrough-shaped inner shell, serious differences in the wall thickness are basically unavoidable. More specifically, in the manufacture of a bathtub, the thinnest points of the inner shell occur at the four "inside corners" at the bottom of the tub and the wall thickness of the inner shell can in certain regions be so small that the outer layer of polyurethane foam being of a different color shines through at that point. The inner shell which does not have particularly good form stability, is also quite difficult to handle when being placed in the mold to manufacture the outer layer. Finally, only those inner shells can be used which are accurate enough in size to adapt properly to the mold for manufacturing the outer layer, which, as experience shows, results in a considerable number of rejects.

Also known are plastic sanitary articles such as bathtubs and washbasins or wash table plates with a washbasin formed therein which are made of so-called cultured marble (polymer concrete) and are manufactured in the following way: A gel coat which later forms the inner layer of the sanitary article is first sprayed onto a convex mold designed in accordance with the used side of the sanitary article. In this case, a back side mold is not used. A plastic substance with which the rearside of the gel coat is to be coated is then introduced into a concave mold designed in accordance with the back side of the sanitary article. This plastic substance is generally polyester resin mixed with fillers. After the convex mold carrying the gel coat is dipped into the concave mold and the two molds are driven together, they are shaken and the plastic substance forming the outer layer

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Ii 3 is cured. As is customary with gel coats, the wall thickness of the inner layer is less than 1 mm and it is hardly possible to manufacture it with uniform thickness, which results in the same disadvantage as with a thermoformed inner shell, quite apart from the fact that the slight thickness of the wall seriously limits removal of surface damage to the used side of the sanitary article by polishing.

The object underlying the invention is to suggest a sanitary article of the kind mentioned at the beginning which is inexpensive to manufacture and has a top or used side which can be easily touched up by the user and from which scratches and the like can be removed by polishing.

This object is accomplished, in accordance with the invention, by the inner layer having a wall thickness of at least 1 mm and being in the form of a reaction molded part and by the outer layer also being in the form of a reaction molded part.

The wall thickness of the inner layer is preferably approximately 2 to 3 mm and that of the outer layer 8 to 10 mm.

The inner layer could also be a thermoformed shell, but a wall thickness of at least 1 mm permits the unproblematic manufacture of the inner layer as molded part and so nonthermoplastic material such as cross-linked acrylic resin or unsaturated polyester can be used for the inner layer, these being chemically more resistant than the thermoformable plastics which to a certain extent must possess thermoplastic properties. In addition, inner shells manu-

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factured as reaction molded parts are of higher dimensional accuracy than thermoformed shells, which reduces the number of rejects.

The outer layer may consist of foamed plastic,i.e.,foamed e polyurethane resin can, for example, be cast around the o rearside of the inner shell. However, better mechanical o properties are achieved with an embodiment in which at least half of the volume of the outer layer consists of filler particles having a diameter of at least 500 pm and o~aa: containing cavities. The high proportion by volume of the filler particles in the material of the outer layer enables a manufacture of a sanitary article whose outer layer shrinks S to a small extent during curing and leads to a high resisa aa tance on the part of screws .r other attaching elements to being torn out. Accordingly, parts such as attaching elements, handles, whirlpool nozzles, etc. can be fixed so as to hold reliably. As a result of the cavities of the filler particles or of the foam plastic, the outer layer has a low weight and also a high thermal insulating capacity and, therefore, the a Swall of a bathtub does, for example, not have a cold feel.

In addition, the material costs for the outer layer are much lower than, for example, in the case of an outer layer made of glass fiber reinforced polyester. However, the advantages gained from the type of the outer layer can only be achieved at acceptable cost for the manufacture by the outer layer being cast in a reaction molding method, by it being in the form of a reaction molded part, which also permits use of a chemically highly resistant plastics material such as PMMA or polyester.

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r! Since the color fastness of PMMA is better than that of polyester and PMMA produces an extremely attractive exterior on the inventive sanitary article, in a preferred embodiment, the plastic of the inner layer is cross-linked polymethyl methacrylate which is sufficiently resistant to chemical influences.

The inner layer may consist of pure resin, but, for cost reasons, it may be recommendable to choose an embodiment in which the inner layer contains filler particles with a diameter of 100 pm at the most. To ensure that the used side of the inner layer can be repolished, the filler particles of the inner layer must then consist of a material Ki which permits polishing of the inner layer, in particular, of aluminum hydroxide and/or magnesium hydroxide.

As pointed out above, it is particularly recommendable to use as plastics for the inner and outer layers, casting resins which after polymerization are fully cross-linked and, therefore, have an extremely high resistance to chemical influences. Different casting resins could be used for i! the inner and outer layers, but to enable a particularly good and firm bond between inner and outer layers, embodiments are recommended in which the plastic of the two layers is the same, fully cross-linked PMMA being preferred, but other casting resins also being usable, for example, polyester.

In a particularly advantageous embodiment of the invention, the filler particles of the outer layer are at least pre- -6dominantly of hollow configuration because this results not only in a particularly good improvement in the thermal insulating capacity but also in a substantial reduction in the weight of the sanitary article. In this case, the invention provides a particularly inexpensive, light and yet *resistant product. Closed hollow particles are preferred, above all, microglass beads which can be made at moderate cost from waste glass or separated off from power plant flue gases and, therefore, constitute a particularly inexpensive filler.

The invention further relates to a method for manufacturing a trough-shaped sanitary article, and, in this connection, the object underlying the invention is to simplify manufacture and reduce manufacturing costs. Proceeding from the second known method explained above, from a method in which a plastic inner layer is first manufactured with freeflowing plastics material on a convex mold designed in accordance with the used side of the sanitary article and then a plastic outer layer which firmly adheres to the inner layer is made with free-flowing plastics material on its outer side by means of a concave mold designed in accordance with the back side of the sanitary article, this object is accomplished, in accordance with the invention, by the inner layer being produced between the convex mold and a first t concave mold corresponding to the design of the inner layer, by the first concave mold then b-ing removed and the inner layer together with the convex mold dipping into a second concave mold designed in accordance with the back side of the sanitary article, and by the outer layer being produced between -7 i the second concave mold and the inner laver. Therefore, only i, three molds or mold halves are required for performing the inventive method, namely one convex mold and two concave molds, and the inner layer need not be handled as such, but rather remains on the convex mold and is driven into the second concave mold with it.

To enable the air to escape from the mold cavity as the free-flowing plastics material is filled into the mold cavity formed by the convex and the first concave mold or the inner layer and the second concave mold, it is recommended to arrange the convex mold and the respective concave mold during filling of the mold cavity formed by these two molds with plastics material such that only one point of the mold S cavity wall formed by the concave mold forms a zone enclosed by lower lying points of this mold cavity wall, and to then evacuate the mold cavity through a channel opening at this zone into the mold cavity. For the curing of the plastics material, the molds should, however, be arranged such that the trough bottom of the sanitary article points upwardly so that during the curing, any air bubbles present in the plastics material cannot collect at that side of the sanitary article which is used or at the boundary surface between inner and outer layers. In the former case, the appearance of the sanitary article would be seriously impaired or the latter would even be made unusable. In the latter case, the air bubbles would impair the bond between inner and outer layers or even be visible through the relatively thin inner layer.

-1 8 Since a certain shrinkage is unavoidable during curing of the plastics material, it is recommended that the two molds forming a mold cavity be made to approach each other during curing of the plastics material in accordance with the shrinkage of the plastics material in order to prevent it r from shrinking away from one or both molds and thereby acquiring a surface which no longer complies with the required S shape. This may be achieved with an appropriate gearing of a mold closing device, but it is simpler and less expensive to provide elastic mold closing elements which bias one mold Sin the direction towards the other.

In the manufacture of the outer layer, the large filler component may lead to problems concerning the flowabili, I of the plastics material. It is, therefore, recommended that one or Sseveral suitable silanes, as known in the prior art for improvement of the flow properties of plastic substances, be admixed to the plastics material for the outer layer before it is introduced between the molds.

iL It is particularly advantageous to use as plastics material for the outer layer the plastics material which is marketed under the protected trademark THERMASSIV by the firm Schock Co. GmbH as this material is particularly inexpensive and Slight and provides especially good resistance and thermal insulation.

Finally, the invention also relates to an apparatus for performing the inventive manufacturing method. Proceeding from an apparatus comprising a convex mold designed in accordance 9 with the side of the sanitary article which is used, a concave mold designed in accordance with the back side of the sanitary article and a mold closing device, the inventive apparatus is characterized in that it is provided with a first and a second concave mold, the first concave mold being designed in accordance with the rearside of the inner layer and the second concave mold in accordance with the OV rearside of the outer layer, and in that the convex mold can be driven by the mold closing device into both the first V concave mold and together with the inner layer into the se- O qao cond concave mold. In this connection, it is again pointed out that the inventive apparatus requires only three molds or mold halves and that the inner layer as such need not be Go handled but rather only the convex mold to which the inner d 1.

"o layer remains adhered on account of shrinkage of the curing plastics material.

TO enable filling of the respective mold cavity with plastics material in an optimal manner and, on the other hand, AD prevent air bubbles contained in the plastics material from a travelling to that side of the sanitary article which is used or to the boundary surface between the inner and outer layers during curing of the plastics material, a preferred embodiment of the inventive apparatus comprises a mold closing device with a pivot device for turning the convex mold jointly with at least the second concave mold about a horizontal pivot axis. For, while in the manufacture of the inner layer, the plastics material of relatively low viscosity used for this enables the mold cavity formed by the convex and the first concave mold to be filled with the trough bottom pointing upt 10 wards and evacuated through a venting channel opening into the trough bottom, in the manufacture of tle outer layer from a casting resin containing a high filler component, the highly viscous plastics material should be able to be introduced into the still open second concave mold. For the above stated reasons, it is, therefore, recommended to subsequently pivot the convex mold and the second concave mold jointly so that the trough bottom then points upwards.

In order that only the convex mold need be moved, that o as few drives as possible be required, the mold closing deo vice, in a particularly preferred embodiment, has a holding 0 device for releasably connecting the convex mold to one of a* the two concave molds so that only a pivot device connected to the convex mold is required, and it is only necessary to displace the convex mold in order to drive it into one of S the concave molds which is then secured to the convex mold o o n and held thereon by means of the holding device.

0C 00a So As mentioned above, it is recommended in view of the shrinkage of the plastics materials during curing, to decrease the mold cavity by one mold being made to follow up in the direction ooca of the other mold in accordance with the shrinkage. This is oo o: particularly easily achieved by the mold closing device comprising a support on which the convex mold is held so as to be movable in the mold closing direction, and for a readjustment device to be provided between support and convex mold to displace the convex mold relative to the support in the mold closing direction. The readjustment device may, as mentioned above, be in the form of gear means, but it is simpler to 11 provide one or several springs which, more particularly, may be in the form of a flexible hollow element which is arranged between support and convex mold and can be supplied with a fluid as pressure medium.

K To enable the wall thickness of the inner and outer layers i to be specified, an embodiment is recommended in which the holding device has adjustment means for adjusting the gap width of the mold cavity. In an embodiment with a readjustj ment device, it may also be recommendable to provide the holding device with an adjustable lift delimiting device for delimiting displacement of the concave mold in the dij rection of an increasing spacing from the support.

I A particularly space-saving and simply constructed embodi- :ij ment of the inventive apparatus is characterized in that the mold closing device comprises a lifting frame on which the convex mold is guided and displaceable by means of a lifting device, and in that one of the two concave molds is located above and the other below the convex mold in the lifting frame.

:l It has been mentioned that acrylic resin is preferred for the inner layer because it exhibits excellent color fastness properties and is not brittle. Above all, on account of its color fastness, acrylic resin will be preferred to polyester although polyester is less expensive and has higher resistance than acrylic resin to both chemical attacks and high temperatures. On account of the good bond produced between the inner and outer layers, it is recom- 1 r 12 mended to use the same resin for both layers, but pclyester and polyurethane could, for example, also be used as plastic for the outer layer.

Further features, advantages and details of the invention are to be found in the following description of a preferred embodiment of the invention and an advantageous embodiment of the inventive apparatus illustrated in the appended drawings, in which: Figure 1 is a perspective illustration c- the apparatus for manufacturing bathtubs of inventive design; Figure 2 is a plan view of this apparatus; Figure 3 Figures 4A to 4D is a side view of the convex mold and its support means; and are illustrations of the various steps in the manufacture of a bathtub, in which the molds are shown in longitudinal section.

aC-C'O(-Am 0 ke- Pre FeF-reA 3-n.\rYeAt The innen-r ve apparatus shown in its entirety, but in a highly simplified form, in Figure 1 comprises a base plate and a top plate 12 which are fixedly connected to each other by guide columns 14 and thereby form a frame for the apparatus. A bottom concave mold 16 which within the meaning of the Claims constitutes the second concave mold and comprises a mold cavity 16a stands on base plate 10. Mold cavity 13 16a is designed in accordance with the bottom or back side of the bathtub which is to be manufactured. On its upper side, mold 16 has register holes 18 which are formed by short bushings of spherical configuration on the inside and cooperate with register pins 68 referred to below. Holding pockets whose purpose will likewise be explained below are provided on the opposite longitudinal side walls of mold 16.

Two holding arms 21 are secured to the underside of top plate 12. A top concave mold 22 which within the meaning of the Claims constitutes the first concave mold is arranged between holding arms 21. Concave mold 22 comprises a mold cavity 22a which is designed in accordance with the rearside of the inner layer of the bathtub which is to be manufactured.

Each of the holding arms 21 has two holding recesses 23, each of which receives one holding bolt 24 of mold 22 to thereby suspend mold 22 on top plate 12.

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Like bottom mold 16, top mold 22 is also provided with holding pockets 20 and register holes 18.

qn- nt1- a oa i -u S The frame of the apparatus)comprises four threaded spindles 30 which are rotatably mounted in base plate 10 and top plate 12 and extend through top plate 12. A drive chain wheel 32 is attached to the upper end of each of threaded spindles 30. Over the four chain wheels 32 there runs a drive chain 34 driven by an electric motor 36 which is mounted on top plate 12 and has a chain wheel 38 seated on its shaft. In 14 this way, all four threaded spindles can be driven in the same direction and in synchronization. They serve to raise and lower a convex mold 40 which is designed in accordance with that side of the bathtub which is used.

A carriage 42 is displaceably held on two neighboring guide columns 14, in each case. Carriage 42 comprises two threaded i bores in which the two threaded spindles 30 extend in this region. Hence the carriage is raised or lowered when the threaded spindles are driven. The carriage comprises I bearing housing 44 with an integrated angular gear and a pivot pin 46 of a support arm 48 mounted for rotation therein, more particularly, about a horizontally extending pivot axis Finally, a pivot motor 52 by means of which support arm 48 is pivotable about axis 50 is flanged on bearing housing 44.

to the narrow sides of a support plate 54. Support plate 54, Sin turn, serves to hold convex mold 40. For this purpose, four stud bolts 40b are secured to a base 40a of mold I Stud bolts 40b pass through guide bores 56 of support plate 54 with play and are provided at their free ends with heads which fix the largest distance of base 40a from support plate 54. A number of pressure elements 58 formed by closed, flexible hoses whose interior can be supplied with a pressure 9 medium, preferably a compressible pressure medium such as compressed air, are located between these two plates 40a, 54.

Several pairs of bearing eyelets 60 with holding brackets 62 pivotably mounted between them are arranged at the two longi-

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3 Il lli i i i C 4tudinai sides of suopport plate 54. For this purpose, a shaft 64 with the holding brackets 62 secured thereto is rotatably mounted in the bearing eyelets on each longitudinal side of support plate 54. The holding brackets comprise angled free ends for engagement in the holding pockets 20 of bottom mold 16 or top mold 22. Arranged in these free ends of holding brackets 62 are threaded bores, not illustrated in greater detail, for holding one adjusting screw 66 each. This adjusting screw is of such dimensions that it can be inserted with play in its longitudinal direction into one of the holding pockets 20, the length of the adjusting screw is smaller than the height of the holding pockets. In this way, the maximum spacing of a mold 16, 22 held by support plate 54 by way of holding brackets 62 from the support plate can be adjusted.

Short register pins 68 which have a rounded-off free end and, for reasons of clarity, have been omitted in Figure 1 are secured to the underside, in accordance with Figure 1, of base 40a of convex mold 40. These register pins 68 are to engage register holes 18 of the bottom mold 16 or the top mold 22 and thereby hold the respectively cooperating molds r: in a precisely fitting manner (within the meaning of the S i statements below) relative to each other.

i Finally, filling and venting channels 70 and 72 are provided in each of the concave molds 16, 22 and are connectable to filling and venting pipes 73b and 73c, respectively, which are provided with valves 73a. Also connected to molds 16, 22 and 40 are power supply lines 74. By means of these

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16 and of channels 76 in the molds, the latter can be heated or cooled.

Scomputer control system for controlling the manufacturing sequence is designated in its entirety by reference numeral i ii Further details of the various molds will be explained with reference to Figure 4A which shows how the convex mold i after rotation through 180 degrees about pivot axis 50 cooperates with the top concave mold 22. It is assumed that the two concave molds 16 and 22 are of essentially identical I design, with the exception of the configuration of the mold K cavity 16a and 22a, respectively, but this need not be the case.

An actuating arm 82 which is pivotable by means of a pressure medium cylinder 84 is attached to each of the shafts 64 carrying holding brackets 62. These pressure medium cylinders iare articulated, on the one hand, at the free ends of the actuating arms 82 and, on the other hand, at bearing eyelets 86 attached to support plate 54. They, therefore, enable the I holding brackets 62 to swivel outwardly from the operative Iposition shown in Figure 4A into an inoperative position.

Arranged at the transition point between base 40a and convex area of mold 40 is a self-contained seal 88 which extends around this convex area and against which a likewise ringshaped area of the top or bottom concave mold 22 or 16 bordering on the free edge of mold cavity 22a or 16a can be V 17 pressed in order to seal a mold cavity 90 or 92 formed by mold 40 with mold 22 or 16. When the pressure elements 58 are pressureless and convex mold 40 is pivoted upwards, it rests on spacers 94 which are arranged between support plate I i 54 and mold 40 and serve to protect pressure elements 58 from damage by mold In accordance with the invention, means are provided for S, fixing a minimum spacing of convex mold 40 from support plate 54 while the mold cavity is being filled. This task could also be performed by spacers 94 if the pressure in Spressure elements 58 is appropriately reduced or they are 1 made pressureless so that mold 40 sinks back onto spacers 94 under its own weight or under the effect of pull-back springs, not illustrated, which engage mold 40 and support plate 54. However, it is more advantageous to provide the mechanism shown in Figures 4A to 4D for fixing the minimum spacing of mold 40 from support plate 54. This consists essentially of mountings 96 attached to the sides of base and spring-mounted pawls 98 which are carried by support plate 54 in the illustrated embodiment by holding brackets 62 articulated at support plate 54 and can be swivelled Sabout axes 100. Springs 102 serve to bias pawls 98 in the direction of mountings 96. The only essential feature of mountings 96 is that they form shoulders underneath which pawls 98 can drop in under the action of springs 102.

The sequence in which an inventivce bathtub)is manufactured will now be explained with reference to Figures 4A to 4D: Av.,IV iq L- A 18 Proceeding from the state of the inventive apparatus shown in Figure 1, support plate 54 and convex mold 40 are first pivoted jointly through 180 degrees about axis 50 and then raised by means of threaded spindles 30 until convex mold dios as far into top concave mold 22 as is shown in Figure 4A. In this case, pressure elements 58 are pressureless and so mold 40 rests on spacers 94 and pawls 98 do not engage behind mountings 96. Holding brackets 62 are then pivoted into holding pockets 20 of top mold 22, as shown in Figure 4A. In this case, it is essential that the adjusting screws 66 lie with play in the vertical direction in holding pockets I A relatively low pressure is then applied to pressure elements 58 so that these raise convex mold 40 and, by way of seal 88, top concave mold 22 until the bottom, in accordance with Figure 4A, edges of holding pockets 20 strike adjusting screws 66. By means of this raising of convex mold pawls 98 can swivel under mountings 96. The various dimensions of the parts of the inventive appooaratus shown in Figures 4A to 4D and the stiffness of seal 88 are so selected, in accordance with the invention, that concave mold 22 (or 16) is also held against adjusting screws 66 by seal 88 if the pressure in the pressure elements 58 is somewhat reduced again to allow convex mold 40 or its mountings 96 I to sink back onto pawls 98. As is evident from this, spacer means 66, 20, 62, 96 and 98 determine the maximum width or gap width of mold cavity 90 formed by the two molds.

Once pawls 98 have dropped in underneath mountings 96, 19 i the two molds 40, 22 which are joined by holding brackets V 62 (pressure elements 58 being in the pressurized state) V are slightly raised by means of threaded spindles 30 so that by slight pivoting of both molds about pivot axis Sholding bolts 24 can be moved out of holding recesses 23 the space required for this pivoting must, of course, be i available between top plate 12 and mold 22. Both molds i 22 can then be lowered by means of threaded spindles 30 to below holding arms 21.

Molds 40 and 22 are now rotated about pivot axis 50 through i 90 degrees into the position shown in Figure 4B in which venting channel 72 points upwards. In this position, mold cavity 90 is filled through filling channel 70 with the plastics material 110 which will later form the inner layer of the bathtub to be manufactured. In this case, valve 73a of venting pipe 73c is open. When the two molds 40, 22 are in this position, the opening of venting channel 72 into mold cavity 90 lies at the highest point of the mold cavity and so the air is completely expelled from the mold cavity by the plastics material being pressed into it, with the exception of possible air pockets in the plastics material, air bubbles in the plastics material. Valves 73a are then closed and molds 40, 22 pivoted back through degrees into the position shown in Figure 4A. In this position, any air bubbles contained in the plastics material rise to the wall of mold cavity 22a of top concave mold 22.

The plastics material is allowed to polymerize in this position, the polymerization being initiated by heating the two molds through channels 76. To enable convex mold 40 to r follow the plastics material which shrinks during polymerization and to prevent the plastics material from shrinking away from the walls of mold cavity 90, the pressure in pressure elements 58 is increased before the polymerization siarts. As a result of the transverse play of stud bolts in guide bores 56 of support plate 54, the short register pins 68 rounded-off at their ends and the register holes 18 formed by short bushings of spherical configuration on the inside, convex mold 40 is held floatingly between support plate 54 and concave mold 22. The convex mold is, therefore, also able to follow a reaction molded part which shrinks to a different degree owing to different wall thick- Snesses in different regions (in this connection, attention is also called to the fact that seal 88 is elastically deformable in all regions) The polymerized plastics material 110 forms an inner shell 112, shown in Figure 4C, of the bathtub which is to be manufactured. Air bubbles present in the plastics material do not lie on that side of the bathtub which is later the used side but on the rearside of inner shell 112 where they do not have a disturbing effect. Convex mold 40 can, of course, only be pressed further into mold 22 by pressure elements 58 if seal 88 allows this. The seal must, therefore, be made sufficiently elastically deformable. In principle, however, it is also conceivable to arrange a seal at a point other than that shown in the drawings, namely in a region in which the mold surfaces delimiting the mold cavity extend parallel to or approximately in the direction of stud bolts 40b so that the seal seals the mold cavity in the manner of a piston

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21 ring of a piston engine.

After polymerization, polyaddition or polycondensation of plastics material 110 has started, it may, in certain circumstances, be expedient to cool the mold cavity in order to remove heat produced during the curing. Channels 76 may also be used for this purpose.

After curing of the plastics material 110 and formation of the inner shell 112 illustrated in Figure 4C, the two molds t 9 40, 22 are slightly pivoted in the clockwise direction out of the position shown in Figure 4A about pivot axis 50 and then raised by means of threaded spindles 30 until pivoting v back into the position shown in Figure 4A enables the holding bolts 24 to be pivoted into holding recesses 23. The pressure elements 58 are then made pressureless to enable holding brackets 62 to be pivoted outwardly, whereupon convex mold 40 is lowered by means of threaded spindles and inner shell 112 remains on this mold. The top concave mold 22 remains suspended in holding arms 21.

Plastics material which will later form the outer layer or the outer shell of the bathtub to be manufactured is then introduced from above into mold cavity 16a of bottom concave mold 16. Although this plastics material is likewise a free-flowing substance, this is easier than to introduce this plastics material through a filling channel 70 because the plastics material for the outer layer has a substantially higher viscosity than the plastics material for the L li' 22 inner layer. After convex mold 40 has been swivelled out of the position shown in Figure 4A through 180 degrees about pivot axis 50 into the position shown in Figure 4C, Sit is lowered tcgether with the inner shell 112 into mold cavity 16a of bottom concave mold 16 and by means of threaded spindles 30 driven down until the inner shell 112 ipresses the free-flowing plastics material 114 upwardly along the walls of mold cavity 92 formed by bottom mold 16 j and inner shell 112. The plastics material expels the air from the mold cavity after seal 88 has come to rest against i bottom mold 16, the air escapes through venting channel 72 Sof bottom mold 16 and ventinQ pipe 73c connected to the f venting channel, valve 73a being in the open state. Excessi ive plastics material can be expelled from cavity 92 through i i channels 70 and 72, but it is also possible for plastics material to be additionally pressed through filling channel into the mold cavity in order to fill this out completely.

I The pressure elements 58, the holding brackets 62 and the j pawls 98 are handled in the same way during manufacture of the outer layer or outer shell as in the manufacture of the i inner layer or inner shell 112.

i: After mold cavity 92 has been filled in the position of the !i two molds 40, 16 shown in Figure 4C, the molds which are joined together by holding brackets 62 are raised by means E of threaded spindles 30 until the two molds can be rotated about pivot axis 50 through 180 degrees into the position shown in Figure 4D. In this position, any air bubbles still present in plastics material 114 can travel away from the boundary layer between the plastics material and the inner -e i i i 23 shell 112, more particularly, to the upwardly located outer side or back side of the outer layer or outer shell to be manufactured. Curing of plastics material 114 is then initiated by heating molds 40, 16 and, if required, the molds are cooled thereafter. In this case, too, the effect of the pressure elements 58 supplied with pressure medium is that plastics material 114 cannot shrink away from the wall of mold 16 or from inner shell 112 during the curing, which ensures good bonding between the inner shell od the outer layer or outer shell formed by plastics material 114. After plastics material 114 has cured, molds 40, 16 are pivoted back through 180 degrees, the bottom mold is set down on base plate 10, pressure elements 58 made pressureless and holding brackets 62 released from mold 16, whereupon mold 40 can be raised and the bathtub removed from the apparatus.

In accordance with the invention, the wall thickness of the sanitary article to be manufactured can be determined and reproduced in yet another way which will be explained with reference to manufacture of inner shell 112: The two molds 22 are first driven together to an extent allowed by spacers, not shown in the drawings, arranged between the two molds, and the mold cavity 90 is then filled with the plastics material used for manufacturing the inner shell.

In this case, the pressure elements 58 are pressurized and hold the two molds against the spacers. With the venting pipe 73a in the closed state, a quantitatively regulated volume of the plastics material is pressed through filling channel 70 into mold cavity 90 in order to push molds 22 apart to a specified gap width determined by the speci- 1- 24 fled volume of the additionally introduced plastics material, in which case, seal 88 must, of course, expand so far that it still seals the mold cavity. In this case, the pressure K of the plastics material which is additionally forced in Sovercomes the mold closing forces generated by pressure Selements 58. Accordingly, in accordance with the invention, after the mold cavity has been filled with the venting pipe i in the open state and the molds held at the minimum distance i from each other, the venLing pipe is closed and, against the action of the forces holding the molds closed, the two At molds are pressed so far apart by forcing in an additional, measured volume of plastics material that the desired wall I thickness is obtained.

In the case of sanitary articles of relatively simple de-

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I sign this may also apply to a bathtub the mold cavity Scould also be filled with plastics material in a position i as shown in Figures 4A and 4D if a venting channel were Sarranged on the bottom of the respective concave mold, thereby eliminating the pivoting into the position shown in Figure 4B.

Spacers provided between the convex mold and the respective concave mold also have the advantage that the seal, in this case, seal 88, cannot be crushed when the two molds are driven together. On the other hand, in the preferred embodiment of the inventive apparatus, this seal assumes the function of always holding the respective concave mold against the adjusting screws 66.

I

It may be expedient to hold register pins 68 on mold 40 by means of a kind of ball-and-socket joint.

It will be noted that the valves by way of which pressure elements 58 are filled with compressed air and likewise the structure of the plastics material which is used have not I been illustrated and, therefore, the drawings do, for example, not show the hollow glass beads in plastics material 114. Also not shown are parts of the molds required, for example, for initially forming an outflow opening of a bathtub in the reaction molded part.

As mentioned above, a plastics material 114 which is a foamable plastics material containing a blowing agent, in particular, methyl methacrylate may also be used for manufacturing Sthe outer shell. It is, however, also possible for an outer shell made of PU resin to be foamed onto the back side of the inner shell. Since this plastics material consisting of 3 resin and blowing agent and possibly a filler such as fine kaolin is of relatively low viscosity, exactly the same procedure may be used in filling mold cavity 92 as in the manufacture of the inner shell 112.

The density of the foamed plastics material should lie between approximately 300 and approximately 4009 but must at all events be greater than approximately 200 9 /1.

Claims

2. A sanitary article as defined in claim 1, characterized in that at least half of the volume of said outer layer consists of filler particles containing cavities and having a diameter of at least 500 pm.
3. A sanitary article as defined in claim 2, characterized in that the plastic of said inner layer is cross-linked polymethyl methacrylate.
4. A sanitary article as defined in claim 1, 4 characterized in that said inner layer contains filler particles having a diameter of 100 pm at the most. A sanitary article as defined in claim 4, characterized in that said filler particles of said inner 4layer consist of a material which permits polishing or grinding of said inner layer. 27
6. A sanitary article as defined in Claim 5, characterized in that said inner layer contains aluminum hydroxide and/or magnesium hydroxide as filler.
7. A sanitary article as defined in Claim 1, characterized in that the plastic of said inner and outer layers.4(2- Sis the same, more particularly, cross-linked PMMA.
8. A sanitary article as defined in Claim 1, characterized in i that the filler particles of said outer layer 14 are at least predominantly hollow particles.
9. A sanitary article as defined in Claim 8, characterized in that said hollow particles are closed hollow particles. A sanitary article as defined in Claim 9, characterized in that said hollow particles are microglass beads.
11. A sanitary article as defined in Claim 1, characterized in that said outer layer (114) consists of a foamed plastic. i
12. A sanitary article as defined in Claim 11, characterized in that the foamed plastic has a density of more than 200 9
13. A sanitary article as defined in Claims 11 or 12, characterized in that the foamed plastic is foamed PMMA or polyurethane foam.
14. A sanitary article as defined in Claim 11, characterized in that the foamed plastic contains fine kaolin as filler. :sf s F 28 A method for manufacturing a plastic, trough-shaped sanitary article such as a bath tub or shower tub, a basin or the like wherein a plastic inner layer is first produced with flowable plastics material on a convex mold designed in accordance with a user side of the sanitary article and then a plastic outer layer is produced with flowable plastics material on the outer side of said inner layer by means of a concave mold designed in accordance with the backside of the sanitary article, said outer layer adhering firmly to said inner layer, wherein said inner layer is produced by casting a flowable plastics material comprising a polymerizable resin between said convex mold and a first concave mold corresponding to the shape of the rear side of said inner layer, said first concave mold is then removed and said inner S layer together with said convex mold is dipped into a second concave mold designed in accordance with the backside of the sanitary article, and wherein said outer layer is produced by casting a flowable plastics material comprising a polymerizable resin between said second concave mold and said inner layer.
16. A method as defined in claim 15, characterized in that said convex mold and said respective concave mold are arranged while the mold cavity formed by said two molds is being filled with plastics material such that only one point of the mold cavity wall formed by the concave mold forms a zone enclosed by lower lying points of this mold cavity wall, and in that air is removed from the mold cavity through a channel opening into the mold cavity at this zone.
17. A method as defined in claim 15 or 16, characterized in that said molds are arranged for curing of the plastics material such that the trough bottom of the sanitary article points upwards.
18. A method as defined in claim 15, characterized in that said two molds forming a mold cavity are made to approach each other during the curing of the plastics material in accordance with its shrinkage. 29
19. A method as defined in claim 15, characterized in that the plastics material for the outer layer is introduced into the trough bottom of said second concave mold with its opening pointing upwards, and said convex mold together with said inner layer is then pressed from above into said second concave mold so that said plastics material for said outer layer rises up in the thus formed mold cavity. An apparatus for performing the method as defined in claim 15 comprising a convex mold designed in accordance with the used side of the sanitary article, a concave mold designed in accordance with the back side of the sanitary article and a mold closing device, characterized in that a first and a second concave mold are provided, said first o concave mold being designed in accordance with the rearside 00 of the inner layer and said second concave mold in accordance 0 oo with the rearside of the outer layer, and in that said convex mold can be driven both into said first concave mold and 9 o together with said inner layer into said second concave mold by said mold closing device.
21. An apparatus as defined in claim 20, characterized in that said mold closing device comprises a pivot device for S turning said convex mold jointly with at least said second po°t S concave mold about a horizontal pivot axis.
22. An apparatus as defined in claim 21, characterized in that said mold closing device comprises a holding device for releasably connecting said convex mold to each one of said concave molds, and in that said pivot device is So connected to said convex mold. o 23. An apparatus as defined in claim 20, characterized in that said mold closing device has a support on which said convex mold is held so as to be movable in the mold closing direction, and in that a readjustment device for displacement of said convex mold relative to said support in the mold closing direction is provided between support and convex mold. Kb 30
24. An apparatus as defined in claim 23, characterized in that said readjustment device comprises at least one flexible hollow element which is arranged between support and convex mold and is supplid raue with a fluid as pressre medium. An apparatus as defined in claims 23 or 24, characterized in that said holding device comprises an adjustable lift delimiting device for delimiting displacement of said concave mold in the direction of an increasing spacing from said support.
26. An apparatus as defined in claim 20, characterized in that said mold closing device comprises a lifting frame on which said convex mold is guided and displaceable by means of a lifting device, and in that said first concave mold is located above and said second concave mold below said convex mold in said lifting frame. L DATED THIS 25th DAY OF May 1990 SCHOCK CO. GmbH By Its Patent Attorneys GRIFFITH HACK CO. Fellows Institute of Patent I Attorneys of Australia i s r II; Q4.