CA1310796C

CA1310796C - Plastic, trough-shaped sanitary article, in particular, bathtub

Info

Publication number: CA1310796C
Application number: CA000562826A
Authority: CA
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: 1992-12-01
Anticipated expiration: 2009-12-01
Also published as: DE3712959C2; DE3884249D1; AU600349B2; EP0285046A3; AU1381688A; DE3712959A1; JPS6445610A; EP0285046B1; EP0285046A2

Abstract

Abstract A plastic, trough-shaped sanitary article such as a bath-tub which can be manufactured in a simple manner by an inner layer with a wall thickness of at least 1 mm first being cast from a first plastics material between a con-vex mold and a first concave mold, by the first concave mold then being removed, but the inner layer remaining on the convey mold, and by an outer layer being cast from a second plastics material between the inner layer and a second concave mold.

Description

~ 7`~ 0 7qS

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 par-ticular, a washbasin or the like, comprising a plastic in-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 reinforcing the inner layer.

Sanitary articles such as bathtubs, shower basins or shower tubs, washbasins and also wash tables with a basin formed tharein, are being manufactured in ever increasing numbers from plastics containing, if requiredl fillers and rein-forcing elements, because the plastics can ba produced in many different colors and have lower thermal conductivity than, for e~ample, enamelled steel tubs. Also, a surface showing traces of wear can, in màny cases, be made attract-ive again by polishing. According to an article in the ma-gazine "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 manu-~acture in a vacuum-forming method from an acrylic res.in sheet an inner shell constituting the inner layer within the meaning of the above definition and to then place this in a closed mold in which in a reaction injection molding mathod an outer layer of polyurethane foam for reinforcement of the inner shell is produced on the rearside of the inner shell, ~his procedure has quite a number of disadvantages:
During thermoforming of the acrylic resin sheet to produce a 1 71 07 q ~

trough-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 poly-urethane 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. Fi-nally, 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 con-siderable 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 ar-ticle is first sprayed onto a convex mold designed in accor-dance 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 con-cave mold and the two molds are driven together, they are shaken and the plastic substance forming the outer layer ~ 3 7, ~

is cured. As is customary with gel coats, the wall thick-ness o the inner layer is less than 1 mm and it is hardly possible to manufacture it with uniform thickness7 which results in the same disadvantage as with a thermoformed in-ner shell, quite apart from the fact that the slight thick-ness of the wall seriously limits removal of surface damage to the used side of the sanitary article by polishing.

The object undarlying the invention is to suggest a sanitary article of the kind mentioned at the beginning which is in-e~pensive to manu actura and has a top or used side whi-h can be easily touched up by the user and from which scratches and the like can be removed by polishing.

~ha article provided by the invention comprises a plastic innar layer forming a first side of the article which is u~a~ and having a rear side opposite the first side, and a plastic outer layer, in which the inner layer is a reaction molded, cross-linked part with a thickness of at least 1 mm and the outer layer i~ a reaction molded, cross-linked plastic part formed in situ directly on the rear side of the inner layer and has a thickness substantially greater than that of the inner layer.

Tha ~11 thickness of the inner layer is preferably approxi-m~taly 2 to 3 mm and that of the outer layer 8 to 10 mm.
Tha innar layer could also be a thermoformed shell, but a ~all tllickness of at least 1 mm permits the unproblematic m~nu~actura of the inner layer as molded part and 50 non-th3rmoplastic material such as cross-linked acrylic resin ar unsaturated polyester can be used for the inner layer, thesa being chemically more resistant than the thermo-~rmable plastics which to a certain extent must possess tharmoplastic properties. In addition, inner shells manu-J~?

fac~ured as reac~ion moldad 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 polyurethane resin can, for example, be cast around the rearside of the inner shell. However, better mechanical 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 ~m and containing cavities. The hiah proportion by volume of the filler particles in the material of the outer layer enables manufacture of a sanitary article whose outer layer shrinks to a small extent during curing and leads to a high resis-tance on the part of screws or 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 tha foam plastic, the outer layer has a low weight and also a high thermal insulating capacity and, therefore, the wall 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, i.e., 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.

Since the color fastness of PM.~A is better trlan that of polye3t_r and P~A produces an extre~ely attractive ex-te~ior on the inventive sanitary article, in a preferred embodimant, the plastic of the inner layer is cross-linked polymethyl methacrylate which is sufficiently resistant to chemical influences.

Tha inner layer may consist of pure resin, but, for cost ~asons, it may be recommendable to choose an embodiment in which the inner layer contains filler particles with a diamete_ oF 1 oo ~m at the most. To ensure that the used 3ida of the inner layex can be repolished, the filler par-ticles of the inner layer must then consist of a material which permits polishing of the inner layer, in particular, o~ aluminum hydroxide and/or magnesium hydroxide.

~s pointed out above, it is particularly recommendable to use as plastics for the inner and outer layers, casting resins which after polymerization are ~ully cross-linked ~nd, therefore, have an extremely high resistance to chemi-cal influences. Different casting resins could be used for tha inner and outer layers, but to enable a particularly ~ood and firm bond between inner and outer layers, emhodi-mant3 are recommended in which the plastic of the two layers i3 tha same, fully cross-linked P~MA being preferred, but ~thar casting resins also being usable, for example, poly-a3tar.

In a particularly advantageous embodiment of the invention the filler particles of the outer layer are at least pre-~ 3 1 07q~

cQminan.ly of hollow con~^ guration because this resul~s notcnly in a particularly good improvement in the thermal in-~ulatin~ capacity but also in a substantial reduction in tha weight of the sanitary article. In this case, the in-vantion provides a particularly inexpensive, light and yet r~sistant 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 ~lua gasa3 and, therefo_e, constitute a particularly in-~ensiva ~illar.

~h~ invention further relates to a method for manufacturing ~ trouqh-shaped sanitary article, and, in this connection, tha object underlying the invention is to simplify manufac-tu~ and reduce manufacturing costs. Proceeding from the second known method explained above, i.e., from a method in which a plastic inner layer is first manufactured with free-~lowing plastics material on a convex mold designed in ac-cor~ance with thè used side of the sanitary article and than a plastic outer layer which firmly adheres to the inner l~yar is made with free-flowing plastics material on its ~utar sida by means of a concave mold designed in accordance with the back side of the sanitary article, this object is ~ocomplished, in accordance with the invention, by the in-sla~ laya~ baing produced between the convex mold and a first ~on~va mold corresponding to the design of the inner layer, by tha Eirst concave mold then being removed and the inner l~yer togathar with the convex mold dipping into a second ~on~ava mold designed in accordance with the back side of the sanitary article, and by the outer layer being produced between s __n_ co..cz i mo; -.. h~ aye~ ~-.a- r - o- y 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 rathe 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-fiowing plastics material is filled into the mo'd ca-vity 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 plas.ics 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 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 articIe points upwardly so that during the curing, any air bubbles present in the plastics material cannot collect at that side of the sani-tary article which is used or at the boundary surface be-twean inner and outer layers. In the former case, the ap-pearance of the sanitary article would be seriously im-paired 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 re-latively thin inner layer.

1 3 ~ 0 7 q 6 Si~_a a cartain shrinkage is unavoidab,e during curing of the ~lastics material, it is recommended that the two molds ~o-ming 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 from sh~inking away from one or both molds and thereby ac-~uiring a sur~ace which no longer complies with the required shape. This may be achieved with an appropriate gearing of a mold closins device, but it is simpler and less expensive to provide elastic mold closing elements which bias one mold in .ha diraction to~ards tha other.

In the manufacture of the outer layer, the large filler com-pon*nt may lead to problems concerning the flowability of the plastics material. It is, therefore, recommended that one or sevaral suitable silanes~ as known in the prior art for im-prov~mant of tha flow properties of plastic substances, be ~dmi~ad to the plastics material for the outer layer before it is introduced between the molds.

It is particularly advantageous to use as plastics material ~or the outer layer the plastics material which is marketed ~ndar tha protacted trademark THERMASSIV by the firm Schock .~ ~o. ~mbH as this material is particularly inexpensive and li~ht and provides especially good resistance and thermal in3ulation.

Finally, the invention also relates to an apparatus for per-~rming the inventive manufacturing method. Proceeding from ~n apparatus comprising a convex mold designed in accordance 1 31 07q6 wish the side of the sanitary article which is used, a con-cava mold designed in accordance with the bac~ 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 rearside of the outer layer, and in that the convex mold can be driven by the mold closing device into both the first concave mold and together with the inner layer into the se-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 handled but rather only the convex mold to which the inner layer remains adhered on account of shrinkage of the curing plastics material.

To enable filling of the respective mold cavity with plas-tics material in an optimal manner and, on the other hand, pravent air bubbles contained in the plastics material from 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 embodi-ment of the inventive apparatus comprises a mold closing de-vice with a pivot device for turning the convex mold jointly ~ith at least the second concave mold about a hori20ntal pivot a~is. 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 up-1 3 i 0 7 9 6 wa_~s and ev2cuated through a venting c.~annei open~ng into thetrough bottom, in the manufacture of the outer layer from a cas~ing 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, i.e., that as féw drives as possible be required, the mold closing de-vice, in a particularly preferred embodiment, has a holding device for releasably connecting the convex mold to one of the two concave molds so that only a pivot device connected to the convex mold is requirad, and it is only necessary to displace the convex mold in order to drive it into one of the concave molds which is then secured to the convex mold and held thereon by means of the holding device.

~s 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 of the other mold in accordance with the shrinkage. ~his is particularly easily achieved by the mold closing device com-prising a support on which the convex mold is held so as to be movable in the mold closing direction, and for a readjust-ment 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 ~ 2i Q79~

prcv~e ona or several sprincs w~ich, more par.icularly, may bP in the for~ of a flexibla hollow element which is arranged batwaen su~port and convex mold and can be supplied with a fluid ~s prassure medium.

To enable the wall thickness of the inner and outer layers 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 readjust-mant device, it may also be recommendable to provide the h~ldinq devic~ with an adjustable lift delimiting device ~or dalimiting displacement of the concave mold in the di-raotion of an increasing spacing from the support.

~ particularly space-saving and simply constructed embodi-mant of the inventive apparatus is characterized in that the mold closing device comprises a lifting frame on which tha 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 liftin~ frame.

~t ha3 bean mentioned that acrylic resin is preferred for tha innar layer because it exhibits excellent color fast-nas3 propertias and is not brittle. Above all, on account it3 color fastness, acrylic resin will be preferred to ~lyaster although polyester is less expensive and has hig2~ar rasistance than acrylic resin to both chemical at-tac~3 and high temperatures. On account of the good bond ~roducad between the inner and outer layers, it is recom-1 31 07~6 --. ~ u s ~ . a- l e ~ 2 a ;~ - - r ~ o ~ i ~ a ~ _; ~ O _ J _ a ~ _ ~
and polyu-ethane could, for e~amDle, also be used as plastic ~or the outer layer.

Furthe_ 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:
igure 1 is a perspective illustration of the apparatus for manufacturing bathtubs of inventive design;
igure 2 is a plan view of this apparatus;
igure 3 is a side view of the convex mold and its support means; and Fisures 4~ to 4D a_e illustrations of the various steps in the manu-facture of a bathtub, in which the molds are shown in longitudinal section.

~he inventive apparatus shown in its entirety, but in a highly simplified form, in Figure 1 compri~es a base plate lO and a top plate 12 which are fixedly connected to each othar 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 com-prises a mold cavity 16a stands on base plate 10. Mold cavity 1 31 07q6 16a is designed in accordance with ~he bottom or back slde o the bathtub which is to be manu~actured. On its upper side, mold 16 has register holes 18 which are formed by short bush-ings of spherical configuration on the inside and cooperats with register pins 68 referred to below. ~olding pockets 20 whose purpose will likewise be explained below are provided on the opposite longi~udinal side walls of mold 16.

Two holding arms 21 are secured to the underside of top plata 12. A top concave mold 22 which within the meaning o~ the ~laims constitutes the first concave mold is ar-ran~ad between holding arms 21. Concave mold 22 comprises a mold cavity 22a which is designed in accordance with the raarsi~e of the inner layer of the bathtub which is to be manu~actu-ed.

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.

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

Tha ~rame of the inventive apparatus comprises four threaded spindles 30 which are rotatably mounted in base plate io and top plate 12 and e~tend through top plate 12. A drive chain whaal 32 is attached to the upper end of each of threaded spindles 30, Over the four chain wheels 32 there runs a drive chain 3~ driven by an electric motor 36 which is mounted on top plate 12 and has a chain wheel 38 seated on its~shaft. In this way, all four threaded spindles can be driven in the same direction and in synchronization. They serve to raise and lo~er a convex mold 40 which is designed in accordance with that side of the bathtub which is used.

~ carriage 42 is displaceably held on two neighboring guide columns 14, in each case. Carriage 42 comprises two threaded boras in which the two threadad spindles 30 extend in this ra~ion. ~ance the carriage is raised or lowered when the t~raadad spindlas are driven. The carriage comprises a bear-~n~ hcusins 44 wi~h an integrated angular gear and a pivot pin 4~ o} a support arm 48 mounted for rotation therein, more particularly, about a horizontally extending pivot axis 50.
~inally, a pivot motor 52 by means of which support arm 48 is pivotable about axis 50 is flanged on bearing housing 44.

The suooort arms 48 held by the two carriages 42 a~e secured t~ tha narrow sides of a support plate 54. Support plate 54, in tnrn~ serves to hold convex mold 40. For this purpose, ~our stud bolts 40b are secured to a base 40a of mold 40.~
Stud bolts 40b pass through guide bores 56 of support plate 5~ t~ith play and are provided at their free ends with heads ~c t~hich }ix the largest distance of base 40a from support plata 54. A number of pressure elements 58 formed by closed, ~laxibla hosas whose interior can be supplied with a pressure m~ium, praferably a compressible pressure medium such~as camprassad air, are located between these two plates 40a, 54.

Savaral pairs of bearing eyelets 60 with holding brackets 62 pivotably mounted between them are arranged at the two longi-13107q~

~udinai sld_s o- s~poo_~ pla~e ~ . For this purposa, ~ sna~~
64 with the holding brac~ets 62 secured thereto is rotatably mounted in the bearing eyelets on each longitudinal side of s~pport plate 54~ The holding b~ackets comprise angled free ends for engagamen~ in the holding pockets 20 of bottom mold 16 or top mold 22. Arranged in these free ends of holding brRckets 62 a~e threaded bores, not illustrated in greater datail, for holding one adjusting screw 66 each. This ad-justing screw is of such dimen-ions that it can be inserted with play in its longitudinal direction into one of the h~lding poc~ets 20, i.e., the length of the adjusting screw is smaller than the height of the holding pockets. In this way, the ma~imum 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 ara secured to the underside, in accordance with Figure }, o~ basa 40a of conve2 mold 40. These register pins 68 are to engage reglster holes 18 of the bottom mold 16 or the to mold 22 and thereby hold the respectively cooperating molds in a precisely fitting manner (within the meaning of the 3t~taments below) relative to each other.

Finally, filling and venting channels 70 and 72 are pro-vidad in each o~ the concave molds 16, 22 and are connect-abla to ~illing and venting pipes 73b and 73c, respectively, which ara provided with valves 73a. Also connected to molds 16, 22 and 40 are power supply lines 74. By means of these :' `

1 3 ~ ~79~

and of channels 76 in the molàs, the latter can be hea_ea or cooleà.

computer control system for cont_olling the manufacturing sa~uence is designated in its entirety by reference numeral 30.

Furthar details of the various molds will be explained with rafarance to Figure 4A which shows how the convex mold ~0 a~t~r rotation through 180 degrees about pivot axis 50 co-o~arates with the top concave mold 22. It is assumed that tha two concave molds 16 and 22 are of essentially identical design, with the exception of the configuration of the mold cavity 16a and 22a, respectively, but this need not be the case~

~n actuating arm 82 which is pivotable by means of a pres-3ura madium cylinder 84 is attached to each of tha shafts 61 o~rrying holding bracXets 62. These pressure medium cylinders ara a-ticulated, on the one hand, at the free ends of the actuating arms 82 and, on the other hand, at bearing eyelets ~ attached to support plata 54. Theyj therefore, enable the holdin~g brackats 62 to swivel outwardly from the operative ~o~ition shown in Figure 4A into an inoperativè position.

~rxanged at the transition point between base 40a and con-va~ a~aa o~ mold 40 is a self-contained seal 88 which extends ~round this convex area and against which a likewise ring-shaped area of the top or bottom concave mold 22 or 16 bordering on the free edge of old cavity 22a or 16a ~an b~

-- : : '' t 3 1 0796 p-~sed ir o-~e- to seal a mola cavity 90 or 92 formed by mold 40 with mold 22 or 16. When the pressure ele~ents 58 a_a pressureless and conve~ mold 40 is pivoted upwards, it rests on spacers 94 which are arranged between support plate 54 2nd mold 40 and serve to protect pressure elements 58 from damage by mold 40.

In accordance with the invention~ means are provided for ~i~ing a minimum spaCing of Convex mold 40 from support plata 54 while the mold cavity is being filled. This task could also be performed by spacers 94 if the pressure in prassure elements 58 is appropriately reduced or they are made pre~suraless so that mold 40 sinks back onto spacers under its awn weight or under the effect of pull-back ~prings, not illustrated, which enyage mold 40 and support ol~te 54. ~owever, 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 o~ mountings 96 attached to the sides of base ~Oa and spring-mounted pawls 98 which are carried by support plata 54 ~ in the illustrated embodiment by holding brackets ~ articulated at support plate 54 - and can be swivelled a~oUt axes 100. Springs 102 serve to bia5 pawls 98 in the direction of mountings 96. The only essential feature of mountings 96 iS that they form shoulders underneath Which ~WlS 98 can drop in under the action of springs 102.

T~a sequence in Which an inventive bathtub is manufactured will now be e~plained with refere~nce to Fiqures 4A to~4D

:' ;

, 1 31 37~6 Proceedins 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 raisad by means of threaded spindles 30 until convex mold 40 dios as far into top concave mold 22 as is shown in Fi-gure ~A. In this case, pressure elements 58 are pressure-less and so mold 40 rests on spacers 94 and pawls 98 do not engage behind mountings 96. ~olding brackets 62 are then pivot~d into holding poc~ets 20 of top mold 22, as shown in Fiqura 4A. In this case, it is essential that the adjusting sc-aws 66 liq with play in the vsrtical direction in holding pockats 20.

~ relatively low pressure is then applied to pressure ele-ments 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 4~, edges of holding pockets 20 strike adjust-ing screws 66, By means of this raising of convex mold 40, pawls 98 can swivel under mountings 96. The various dimen-sions of the parts of the inventive apparatus shown in Fi-~uras 4A to 4D and the stiffness of seal 88 are so selected, in accordance with the invention, that concave mold 22 tor 16) is also held against adjusting screws 66 by seal 88 ic tha pressure in the pressure elements 58 is somewhat re-ducad again to allow convex mold 40 or its mountings 96 to sink back onto pawls 98. As is evident from this, spacer maans 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, ' ' , 131079&

tha ~o mol d3 40, 22 ~hich are jolned by holding bracke~s ~ t~ressur~ alaments 58 being in tne pressurized state) axe slightly raised by means of threaded spindles 30 so ~hat by sligh~ pivoting of both molds about pivot axis 50, holding bolts 2- can be moved out of holding recesses 23 -tha space required for this pivoting must, of course, be ~vailabla between top plate 12 and mold 22. Bo~h molds 40, c~n then be lowqred by means of threaded spindles 30 to balow holdin~ arms 21.

N~ld3 4~ ~nd ~2 are now rotated about ~ivot axis SO through ga dagraas into the position shown in Figure 4B in which vanting channel 72 points upwards. In this position, mold c~vity ~ is filled through filling channel 70 with the tics materi~l 110 which will later form the inner layer of th~ bathtub to be manufactured. In this case, valve 73a o~ vanting pipe 73c is open. When the two molds 40, 22 ~ra in this position, the opening of venting channel 72 i~t~ mold cavity 90 lies at the highest point of the mold ~vity and so the air is completely expelled from t~e mold c~vity by the plastics material being pressed into it, with tha a~caption of possible air pockets in the plastics ma-t~rial, i.e., air bubbles in the plastics material. Valves ~3~ ara then closed and molds 40, 22 pivoted back through ~0 daqraa3 into the position shown in Figure 4A. In this ~o~itlon, any air bubbles contained in the plastics material ~3a to tha wall of mold cavity 22a of top concave mold 22.
~hq plastics material is allowed to polymerize in;this po-3ition, the polymerization being initiated by heating the t~o molds through channels 76. To enable convex mold~40 to :: :

' ,' ~' ' ' ~

1 3 1 07 9 ~

~ollow the plastics material which shrin~s du~ing polymer-ization and to prevent the plastics material from shrin~ing awav from the walls of mold cavity 90, the pressure in pras-sure elemants 58 is increased before the polymeriza~ion starts. ~s a result of the transverse play of stud bolts 40b in guide bores 56 of support plate 54, the shart re-gistar pins ~8 rounded-off at their ends and the register holes 18 formed by short bushings of spherical configuration on the inside, convex mold ~0 is held floatingly between support plate 54 and concave mold 22. The convex mold is, therefors, also able to follow a reac~ion molded part which shrin~s to a different degree owing to different wall thick-nasses in different regions (in this connection, attention is also called to the fact that seal 88 is elastically de-formable in all regions).

The polymerized plastics material 110 forms an inner shell 112, shown in Figure 4C, of the bathtub which is to be manu-factured. ~ir 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 prassed further into mold 22 by pressure elements 58 if seal 38 allo~s this. The seal must, therefore, be made suffici-antly elastically deformable. In principle, however, it is also conceivable to arrange a seal at a point other than that shown in the drawinss, 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 13107~6 rinc of 2 pis~on engine.

~cter polymerization, polyaddition or polycondensation of plas~ics material 110 has started, it may, in certain cir-cu~s.ances, be expedient to cool the mold cavity in order to remove heat produced during the curing. Channels 76 may ~lso be used for this purpose.

A~tar curing of the plastics material 110 and formation of tha inner shell 112 illustrated in Figure 4C, the two molds ~, 2~ a~e slightly pivots in the cloc.~w-se dirsction out o~ the position shown in Figure 4A about pivot axis 50 and then raised by means of threaded spindles 30 until pivoting bac~ into the position shown in Figure 4A enables the hold-i~g 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 c~nva~ mold 40 is lowered by means of threaded spindle~s 30 and inna- shell 112 remains on this mold. The top con-cave mold 22 remains suspended in holding arms 21.

~la3tics material which will later form the outer layer or t~ outar shell of the bathtub to be manufactured is then lntroducad ~rom above into mold cavity 16a of bottom con-~ava mold 16. ~lthough this plastics material is likewise a ~raa-~lowing substance, this is easier than to introduce thls pla~tics material through a filling channel 70 because t~a plastics material for the outer layer has a substan-tially higher viscosity than the plast~cs ~ateri-l fo~ the :
' , inne- laye~. ~ t-r conve~ mold ~0 has been swivelled out o;~ tha position shown in Figure 4A through 180 degrees about pivot a~is 50 into the position shown in Figure 4C, it is lowered together with the inner shell 112 into mold cavity 16a of bottom concave mold 16 and by means of thraaded spindles 30 driven down until the inner shell 112 prasses tha free-flowing plastics material 114 upwardly alang tbe walls of mold cavity 92 formed by bottom mold 16 and ~nne- shell 112. The plastics material expels the air ~rom the mold cavi~y - after seal 88 has come to rest against bottom mold 16, the air escapes throuqh venting channel 72 o~ bottom mold 16 and venting pipe 73c connected to the vantin~ channel, valve 73a being in the open state. Excess-iva plastics material can be expelled from cavity 92 through ohannals 70 and 72, but it is also possible for plastics matarial to be additionally pressed through filling channel 70 into the mold cavity in order to fill this out completely.
The pressure elements 58, the holding brackets 62 and the pawls 98 are handled in the same way during manufacture of tha oute~ layer or outer shell as in the manufacture of the innar layer or inner shell 112.

~tar mold cavity 92 has been filled in the position of the two molds 40, 16 shown in Figure 4C, the molds which are ~ina~ together by holding brackets 62 are raised by means o~ thraadad spindles 30 until the two molds can be rotated ~baut pivot axis 50 through 180 degrees into the position 3~0wn in Fiqure 4D. In this position, any air bubbles still ~rasant in plastics material 114 can travel away from the undary layar between the plastics material and the inner she~ , mo~a pa~ticularlv, to the upwardly located outer side or back slde of the outer layer or outar shell to be manu-actured. Curing of plastics material 114 is then initi-ated by heating molds 40, 16 and, if required, the molds are cooled thereafter. In this case, too, the effect of the pres-sure elements 58 supplied with pressure medium is that plas-tics matarial 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 and 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 de-graes, the bottom mold is set down on base plate 10, pressure elements 58 made pressureless and holding brackets 62 re-leased 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 raproduced in yet another way which will be explained with reference to manufacture of inner shell 112: The two molds ~0, 22 are first driven together to an extent allowed by spacars, not shown in the drawings, arranged between the two molds, and the mold cavity 90 is then filled with the ~la~tics 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 pipa 73a in the closed state, a quantitatively regulated ~ol~me of the plastics material is pressed through filling channel 70 into mold cavity 90 in order to push molds 40, 2~ apart to a specified gap width determined by the speci-- 2~

fied voluma o~ t`na adcitionally introduced plastics material, in which case, seal 88 must, of course, expand so far that it still seals t~.e mold cavity. In this case! the pressure o~ tha ~lastics material which is additionally forced in ovarcomas the mold closing forces generated by pressure alaments 58. .~ccordingly, in accordance with the invention, a~tar the mold cavity has been filled with the venting pipe in tha opan state and the molds held at the minimum distance ~rom aach other, the venting pipe is closed and, against tha action of the forces holding the molds closed, the two molds ara pressed so far apart by forcing in an additional, maa3u~dd volume of plastics material that the desired wall thicknass is obtained.

~n tha case o~ sanitary articles of relatively simple de-siqn - this may also apply to a bathtub - the mo}d cavity could also be filled with plastics material in a position ~s shown in Fiqures 4~ and 4D if a venting channel were a-rangad on ths bottom of the respective concave mold, tha-aby eliminating the pivoting into the position shown in ~ig~ra 43.

S~cars providad between the convex mold and the respec-tiva concava mold also have the advantage that the seal, in thi~ case, seal 88, cannot be crushed when the two molds ~ra driven together. On the other hand, in the preferred ambodlmQnt of tha inventive apparatus, this seal assumes t~a ~unc~ion of always holding the respective concave mold ~y~inst tha adjusting screws 66.

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,, ' ~ :' ' 1 3 1 07q6 It may be e~ped ant to hoid register plns 68 on mol 40 by means Oc a kind of ball-and-soc~et joint.

It will be noted that the valves by way of which pressure elements 58 are filled wlth comprassed air and likewise the structure of the plastics material which is used have not been illustratsd and, therefore, the drawings do, for ex-ample, not show the hollow glass beads in plastics material il4. ~lso not shown are parts of the mclds requi ed, for e~ample, for initially forming an outflow openinq of a bath-tub in the raaction molded part.

As mentioned above, a plastics material 114 which is a foam-abla plastics material containing a blowing agent, in parti-cular, methyl methacrylate may also be used for manufacturing the outer shell. It is, however, also possible for an outsr shell made of PU resin to be foamed onto the back side of the inner shell. Since this plastics material consisting of rasin and blowing agent and possibly a filler such as fine kaolin is of relatively low viscosity, exactly the same pro-cadura may be used in fillinq mold cavity 92 as in the manu-~ctur~ of the inner shell 112.

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Th2 density of the foamed plastics material should lie be-twaan approximately 300 and approximately 4009 /l ~ but must at all events be greater than approximately 200 9/l .

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Claims

1. A plastic, trough-shaped sanitary article comprising a plastic inner layer forming a first side of the article which is used and having a rear side opposite said first side, and a plastic outer layer, wherein said inner layer is a reaction molded, cross-linked part with a thickness of at least 1 mm and said outer layer is a reaction molded, cross-linked plastic part formed in situ directly on the rear side of the inner layer and has a thickness substantially greater than that of the inner layer.

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 µm.

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, characterized in that said inner layer contains filler particles having a diameter of 100 µm at the most.

5. A sanitary article as defined in claim 4, characterized in that said filler particles of said inner layer consist of a material which permits polishing or grinding of said inner layer.

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 is the same, more particularly, cross-linked PMMA.

8. A sanitary article as defined in Claim 1, characterized in that the filler particles of said outer layer 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.

10. 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 consists of a foamed plastic.

12. A sanitary article as defined in claim 11, characterized in that the foamed plastic has a density of more than 200 g/1.

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.

15. A method for manufacturing a plastic, trough-shaped sanitary article such as a bathtub 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 the used 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 back side of the sanitary article, said outer layer adhering firmly to said inner layer, characterized in that said inner layer is produced between said convex mold and a first concave mold corresponding to the shape of the rearside of said inner layer, said first concave mold is then removed and said inner layer together with said convex mold dips into a second concave mold designed in accordance with the back side of the sanitary article, and said outer layer is produced 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.

19. A method as defined in Claim 15, characterized in that the plastics material for the outer layer is introduced onto 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.

20. 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 concave mold being designed in accordance with the rearside of the inner layer and said second concave mold in accordance with the rearside of the outer layer, and in that said convex mold can be driven both into said first concave mold and 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 turning said convex mold jointly with at least said second 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 connected to said convex mold.

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.

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 supplied with a fluid as pressure medium.

25. 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.