DE19730330A1 - Injection moulded toilet seat and/or cover and moulding process - Google Patents

Abstract

In an injection moulding process for producing thick wall mouldings a core (6) comprising wood particles in a thermoplastic matrix, is injection moulded first and a thermoplastic outer layer(8) is injected around the core. A toilet seat and/or cover (1) made by the process is also claimed.

Description

The invention relates to an injection molding process for the manufacture make a thick-walled molded part according to the preamble of claim 1 and one after such Ver drive manufactured toilet seat and / or toilet lid.

Such toilet seat arrangements are in usually relatively massive, heavy items that one some have sufficient strength and others hand must be designed so that they the user convey a feeling of high quality and solidity. These requirements place a certain weight on the Seat arrangement ahead, which is usually only by ent speaking thick-walled design of the components lets. Experience has shown that weight-opt Mated toilet seat arrangements with minimal material consumption and correspondingly low weight for end users find no appeal.

The thick-walled toilet seats / lids are predominant made of thermosets in the pressing process, so that Molded part with a high density and with high precision can be produced. Such pressing methods are gone visually the material preparation and the device technical effort very expensive, so that one strives is, the toilet seat assemblies by injection molding put.

In European patent application EP 0 673 743 A1 It is suggested that a toilet seat first have a core to spray with a thermoplastic mixed with propellant and this core in subsequent injection molding processes to surround an envelope. Such a process at which the molded part by injection molding from several components  is manufactured in practice as a multi-component or 3-phase or color injection molding. The The core material is usually a foamed with propellant Plastic (TSG), the high-quality casing that fer term outer surface of the toilet seat assembly is from high quality material.

Such an injection molded part meets the requirements mentioned criteria, however, it has been shown that due to the very thick-walled core, the cycle times are very high are, because the core only moves towards one before demolding temperature must be cooled. Furthermore, must this molded part consisting of several types of plastic when disposing first with comparatively complex Processes to be recycled or recycled to enable other use.

In contrast, the invention is based on the object a method for producing a thick-walled molded part and a mold made by such a method to create part that is an injection molding with minimal cycle time and is easily recyclable.

This task is accomplished with regard to the procedure the features of claim 1 and in terms of Molding by the features of claim 10 ge solves.

By taking the core out of one material make a comparatively large proportion of wood contains particles, the cycle time during injection molding core compared to conventional solutions Third are reduced because the ver with wood particles set Kern even at a comparatively high demolding temperature temperature has sufficient dimensional stability. There through the core at comparatively high temperatures  removed from the injection mold and the other Processing step for overmolding are supplied.

A manufactured according to the inventive method Molding with the best of wood particles core can be disposed of in a simple manner because the the entire molded part is only shredded and the recyclate again the manufacturing process for injection molding a molded part core can be fed.

Initial tests have shown that the core material be standing out of wood particles and one that acts as a binder Thermoplastic very densely by the injection molding process tet is so that the core is present with high density and the desired high weight of the molded part sets.

Another positive aspect of the innovation is likely to be found in it can be seen that essentially made of wood particles manufactured toilet seat in the course of the current eco-movement should be very well marketable, since it is a big hit partly consists of biodegradable components.

By the injection molding process, it is also ge ensures that the molded part quality both in terms of dimensional accuracy and uniformity the surface of the previous thermosetting solutions is at least equal.

The molding can be optima with a short cycle time Produce molded part quality if the proportion of wood particles in the core more than 50% by weight, preferably 70% by weight and / or the particle diameter is between 0.1 and 1.0 mm. Since the wood particles are usually made of sawdust wood chips or chip-like residues, the particle diameter corresponds essentially to that Chip length.  

Preliminary tests have shown that egg ner relative residual moisture of the wood used by weni less than 10%, preferably less than 5% optimal Get results. Because of the residual moisture, which Locks must escape during the injection molding process force of the injection mold compared to raw materials very low residual moisture can be designed higher, so that due to the high locking forces and the outgassing what steam and the associated pressure a high Ver Sealing of the core material takes place, which the molding weight increased in the desired manner. Add to that on due to the high mold pressure the emergence of Sink marks reducing surface quality on a Minimum is reducible.

The cycle time of the method according to the invention can be reduce to a minimum if the core is at temperatures of more than 80 ° C, preferably between 95 ° C and 120 ° C is removed from the mold. Since conventional molded parts are made without wood part usually not ent at such high temperatures can be shaped, the cooling time and thus the cycle time compared to conventional solutions.

A flexible from a manufacturing point of view easy-to-use manufacturing unit has two sprays casting machines, one of which is only cores and the other only the coating is injected.

The flow front when the coating is sprayed can be designed particularly uniformly if the melt is injected through recesses in the core. The back can also be filled by so-called core pulling after spraying on the front if a distance holding according to FIG. 2 is not sufficient.

This recess can ver with a centering section Be seen so that the core through the spray nozzle Injection molding machine is centered in this centering section immersed.

In an alternative injection molding process, next one side of the wrapper and after withdrawing one Core of a tool in a further operation Rear trained. With this core pull technology, the Molded core reliably in during the injection molding process fixes its desired position so that asymmetries can be avoided.

In a preferred variant, the toilet seat is over four injection points, so that a uniform The tool cavity can be filled.

The core material is preferably made from a mixture from wood and polyolefins, for example polypropylene posed; the casing can also be made of polyolefins, ABS, nylon, etc. can be manufactured.

The wall thickness of the molded parts according to the invention is usually at least 8 mm.

Other advantageous developments of the invention are the subject of further subclaims.

The following is a preferred embodiment the invention with reference to schematic drawings tert. Show it:

Figure 1 is a partially sectioned illustration of a toilet seat arrangement.

Fig. 2 is a detailed view of an injection molding tool and

FIGS. 3 and 4, a flow simulation during encapsulation of a core of the toilet seat assembly in FIG. 1.

The illustrated in Fig. 1 toilet seat assembly 1 has ei NEN usually formed in annular toilet seat 2 and a pivotally connected to this toilet cover 4. The toilet seat assembly 1 is BEFE via a hinge device, not shown, via which the lid 4 is hinged to the seat 2 on a toilet bowl, not shown.

As can be seen from the sectional views of the seat 2 and the cover 4 , these consist of two components, each having a core 6 made of a core material that contains wood particles that are mixed with a thermoplastic. This wood-containing core 6 is surrounded by a wrapping 8 made of a thermoplastic.

As a thermoplastic material for the core 6 and for the sheath 8 , polyolefins, in particular polypropylene and other high-strength plastics such as ABS, nylon, etc. and their reinforced variants can be used.

In the application shown in FIG. 1, wood shavings are used for the core material in woodworking, which preferably have a particle size distribution that can be found in Table 1 below.

Table 1

The table 1 removable fraction can for example wise by sieving. The middle lies accordingly Particle size approximately at 0.4 mm, being the maximum particle size is about 8 mm and the fine fraction with particles less than 0.2 mm is about 6%. Because in the sieving process usually the chip length is decisive, have the use wooden rods corresponding to a maximum length of 8 mm. In principle, however, other particle sizes are also used bar, whereby it should be noted that a longer chip length gives the molding better strength, all of it However, there is a risk that long chips (<8 mm) during the processing process from the core area to the envelope penetration area.

The chip fraction is used with a polyolefin, for example wise polypropylene (PP) mixed, the proportion of Wood chips should be about 60 to 75, preferably 70%.

The wood shavings or wood flour is passed on a agreed relative residual moisture dried, which in the be written embodiment is about 5%.

The casing 8 formed in the following operation consists of the materials mentioned at the outset, ie PP, nylon, ABS, etc.

The manufacture of the components shown in FIG. 1 of the toilet seat assembly takes place in the injection molding process in the method according to the invention.

For the component - ie seat 2 or cover 4 - there are at least two injection molding machines with one tool each, the core 6 being formed in the tool of the first injection molding machine and the overmolding of the core 6 in the tool of the second injection molding machine to form the casing 8 is carried out.

Due to the different specific densities of the Wood chips and the plastic mixed with them the mixture with the mixture proportion described above (70 wt .-% wood chips and 30 wt .-% plastic) immediately the machine via dosing belt scales, so that by a Transport process no segregation between the silo and the injection molding machine can occur.

The processing of the mixed with wood particles Plastic granules are made with an essentially han usual injection molding machine, the melt temperature is about 140 ° C to 160 ° C. This melt temperature is et which is lower than when processing pure Polypro pylene to prevent thermal decomposition of the wood prevent. However, the mass must not be in the cylinder for too long which remain because then even at low melt temperatures decomposition cannot be prevented.

When the wood-containing mass is injected into the mold cavity of the first injection molding machine, the water contained in the wood chips is evaporated and attempts to escape from the injection mold as water vapor. As a result, an additional pressure builds up in the injection mold, which has to be compensated for via a corresponding locking pressure. The pressure to be built up in addition to compensating for the gas pressure can be 50% above that which would be required when processing a completely dried material. Due to the increased locking pressure and the corresponding mass pressure in the cavity, the formation of sink marks in the edge region of the core 6 is counteracted, so that the molded part quality can be positively influenced by suitable adjustment of the residual moisture.

After the cavity has been completely filled, the mold becomes part cooled by the tool cooling until the molded part has reached a temperature of about 95 ° C. Preliminary tests ha ben shown that the molded part at this temperature has sufficient dimensional stability so that it is without distortion can be removed from the mold of the first injection molding machine is. The corresponding demolding temperatures at Processing of pure polypropylene would be significantly lower riger. The good demoldability at higher temperatures right results from the wood content, which is a fiber carpet structure forms a certain inherent stability of the molded part borrows.

Compared to pure thermoplastic molded parts, the holzhal term core the advantage that it has a higher elasticity mo dul, reduced shrinkage, better mold release speed, a shorter cooling time and a higher specific Has weight.

The cooled to 95 ° C core 6 is then inserted by hand or a suitable handling device into the tool of the second injection molding machine and then the coating 8 injected ge from the aforementioned materials.

In FIG. 2 shows a section through the tool 10 of the second injection molding machine. It is a tool 10 with single or multiple use, which in the usual design has an ejector-side tool half 12 and a nozzle-side tool half 14 , which together form a cavity 16 in the closed state of the tool 10 . In the nozzle-side tool half 14 , a spray nozzle 18 is provided, which can be designed as a hot runner or cold runner nozzle. In the embodiment shown in FIG. 2, the core 6 produced as described above is inserted into the center of the cavity 16 , the centering and holding of the core 6 using suitable holding elements and a centering step 20 which takes place in a centering bore 22 of the core 6 immersed so that the centering of the core 6 also takes place through the nozzle 18 itself. Of course, in addition to the centering projection 20 , further holding elements must also be provided in the cavity 16 .

Alternatively, the cavity 16 on the back of the centering pins 18 can be reached by so-called core pulling, the centering pins should not absorb the spray pressure in the cavity 16 .

In the core 6 of the further still Durchtrittsbohrun are provided gene 22 for the melt which trier bore in the area of Zen are formed 22nd

Since both the seat 2 and the cover 4 are very large components, the component is generally not sprayed on via a nozzle 18 , but rather via several nozzles. In the formation of the seat 2 one has brought about optimal results for example by injecting the melt over four injection points.

As can be seen in FIG. 2, the material for forming the sheath 8 is injected through the center hole 22 and thus through the core 6 through to the ejector-side surface of the seat 2 , so that the melt initially surrounds the area of the cavity 16 adjacent to the center hole 22 fills and then fills the other circumferential walls by order to flow through the core 6 and flow through the Durchgangsboh 24 .

FIGS. 3 and 4 show the filling of the cavity 16 after 0.5 sec. Filling time from the bottom (Fig. 3) and viewed from the top (Fig. 4) of the seat 2 ago. In the present case, the underside of the ejector side of the tool would face.

As is apparent from Fig. 3, first of all four areas of the cavity in the region of the nozzle 18 on the seat bottom are in this exporting approximately example four injection points with one of the control orifices selected 18, so that the melt after 0.5 sec. Fills. The top of the seat (nozzle side of the tool) is only flowed around after flowing around the core 6 and flowing through the through bores 24 , so that, as shown in FIG. 4, this area is filled later.

After approximately one second, the flow fronts 26 , 28 converge in the central region of the seat and the edge regions 30 , 32 of the covering 8 of the seat 2 are completely filled after a little more than two seconds, the flow fronts moving towards one another in the direction of the arrow. After the cavity 16 has been completely filled and a suitable holding pressure has been applied to prevent sink marks, the injection-molded toilet seat 2 is cooled to its demolding temperature, which is substantially lower than the demolding temperature of the previously manufactured core.

The cooling time for cooling the casing 8 to the Ent molding temperature corresponds, however, due to the small wall thickness essentially the cooling time for cooling the thick-walled core to the demolding temperature of about 90 ° C, so that the cycle times of the two injection molding machines are approximately matched.

After cooling and removal of the finished toilet seat is a molded part with the highest mold quality, with high specific weight, which can be easily traced back to the raw material process, since the materials used are thermally decomposable, compostable and as recycled lat for the production of the core 6 can be used.

Of course, the use of the fiction The procedure does not apply to the manufacture of toilet seats  Arrangements limited, but other thick wall components, such as doors, window sills ter, toilet bowl, etc. are manufactured.

Of course, the method according to the invention can also by appropriate tool design on one zigen injection molding machine are carried out, with for example, rotary tables, multi-level or moving tools can be used. Appropriate technologies are state of the art Technology and need no further description.

In the above-described method, the prefabricated core 6 of the molded part is held in the cavity 16 of the tool 10 by means of retaining pins. Under unfavorable operating conditions (depending on the melt temperature, the plastic used, the pressure etc.) it can happen that the core 6 placed on the pins is deformed by the melt front or moved away from the predetermined position. To avoid such asymmetries, in According to an advantageous development of the method according to the invention, initially only the front of the molded part (the side facing the spray nozzle) is formed, the cavity on the back being inaccessible to the melt front by moving a core into an advanced position , so that the rear part of the cavity 16 is accessible to the melting front and is formed in a subsequent step .. In this procedure, the core 6 is initially reliably fixed in its symmetrical position by the displaceable tool core Tool cores remain - similar to the procedure described above - pins in contact with the prefabricated, not yet overmolded part of the core 6 , the previously sprayed-out front part of the molded part (toilet lid 4 ) also contributing to the fixation.

An injection molding process for manufacturing is disclosed a thick-walled molded part and one after such Process produced molded part, wherein a core of the mold part is made from a wood-containing core material, which is overmolded with a thermoplastic.

Claims (14)

1. Injection molding process for producing a thick-walled molded part, a core ( 6 ) first being produced by injection molding or pressing and then being encapsulated with a thermoplastic sheath ( 8 ), characterized by the steps:

• - Providing a fraction of wood particles with a predetermined size distribution and residual moisture;
• - Mixing a core material from a portion of the Frakti and a portion of thermoplastic;
• - Injection molding of a wood-containing core ( 6 ).

2. Injection molding process according to claim 1, characterized ge indicates that the proportion of wood particles at least 50% by weight, preferably 70% by weight. 3. Injection molding process according to claim 1 or 2, characterized characterized in that the average particle diameter between between 0.1 and 1.0 mm. 4. Injection molding process according to one of the preceding patents Claims, characterized in that the residual moisture is less than 15%, preferably 5%. 5. Injection molding process according to one of claims 1 to 4, characterized in that the demolding temperature of the core ( 6 ) is greater than 80 ° C, preferably 95 ° C to 120 ° C. 6. Injection molding process according to one of the preceding patent claims, characterized in that the injection-molded core ( 6 ) is removed from the mold and is inserted into the tool ( 10 ) of another injection molding machine for overmolding. 7. Injection molding process according to one of the preceding claims, characterized in that the sheath ( 8 ) is sprayed through at least one recess ( 22 ) of the core ( 6 ). 8. Injection molding method according to claim 7, characterized in that when spraying the sheath ( 8 ) an injection nozzle ( 18 ) of the injection molding machine with a Zen trier projection ( 20 ) is immersed in the recess ( 22 ) of the core ( 6 ). 9. Injection molding process according to one of the preceding claims, characterized in that the molded part has an approximately annular, elliptical structure and the envelope ( 8 ) is injection molded over four injection points. 10. Injection molding process according to one of the preceding Pa claims, characterized in that first a spray nozzle-side section of the core ( 6 ) is overmolded, and that in a subsequent operation after withdrawing a tool core covering the rear side, an ejector-side part of the envelope ( 8 ) forms out becomes. 11. toilet seat and / or toilet lid with a core ( 6 ) which is surrounded by a thermoplastic sheath ( 8 ), produced by the method according to one of the preceding claims. 12. toilet seat and / or toilet lid according to claim 11, characterized in that the core ( 6 ) has at least one center hole ( 22 ) which is surrounded by at least two through holes ( 24 ) for the melt. 13. toilet seat and / or toilet lid according to claim 11 or 12, characterized in that the core of wood and Po lypropylene and the covering made of polypropylene, ABS or Nylon is made. 14. Toilet seat and / or toilet lid according to one of the claims che 11 to 13, characterized in that the wall thickness is at least 8 mm.