WO2007121934A1

WO2007121934A1 - Mould for thermally processing polymeric moulding materials, temperature controlled mould system and polymer processing system

Info

Publication number: WO2007121934A1
Application number: PCT/EP2007/003471
Authority: WO
Inventors: Bostjan Zagar; Janez Navodnik
Original assignee: Tecos, Slovenian Tool And Die Development Centre
Priority date: 2006-04-21
Filing date: 2007-04-20
Publication date: 2007-11-01

Abstract

A temperature controllable mould (10, 10') having a mould cavity (12, 12'), wherein a polymeric moulding material can be introduced and thermally processed, comprises at least one thermoelectric module (13) that is arranged in the mould (10, 10') in thermally conductive relation with a surface of the mould cavity.

Description

Mould for thermally processing polymeric moulding materials, temperature controlled mould system and polymer processing system

The present invention relates to a mould having a mould cavity wherein a polymeric moulding material can be introduced and thermally processed.

The present invention further relates to a temperature controlled mould system, comprising a mould.

The present invention further relates to a polymer processing system. The term "polymer processing system" as used herein is to be understood in that a polymeric plastic material is changed in form by applying varying temperatures to the material. Practical applications of such polymer processing systems are injection moulding, blow moulding, thermoforming, extrusion processes and machines. The polymeric material comprises thermoplastic materials, thermosetting materials, elastomers, rubber, silicon and the like.

One of the basic problems in the development of moulds for thermally processing polymeric moulding materials is the control of temperature conditions in the mould.

Nowadays temperature within a mould is controlled through a mould cooling system which comprises cooling fluid channels through which a cooling fluid flows as a heat exchange medium, thereby transporting the needed thermal energy to and from the mould. Such known systems control the heat exchange process through the entire mould, what in many cases leads to insufficient heat exchange results, particularly to insufficient cooling. Due to insufficient heat exchange between the moulding material and the mould the moulded parts may have reduced mechanical properties and/or poor aesthetic appearance including various kinds of deformation, and/or may suffer from demolding problems.

Another problem that is inherent to known temperature control systems of moulds is the difficulty in optimizing the moulding time cycle for achieving satisfying yields of moulded parts.

Further, the known cooling systems of polymer processing moulds are prone to general construction problems, since they require a lot of space within the mould. Further, moving parts of the mould, like sliders, are difficult to cool, the surface temperature of the mould cavity can hardly be controlled, and finally, it is impossible to run a predefined temperature profile across the moulding cycle. In order to give a better understanding of the problems of present polymer processing systems the thermal processes in injection moulding are now exemplarily explained in greater detail.

Plastic processing in moulds is based on heat transfer between plastic moulding material and a mould cavity. Within calculation of heat transfer one should consider two major facts: First is all used energy which is based on first law of thermodynamics - law of energy conservation, second is velocity of heat transfer.

The basic task in heat transfer analysis is temperature calculation over time and temperature distribution inside a studied system. The latter depends on velocity of heat transfer between the system and its environment and velocity of heat transfer inside the system. Heat transfer can occur as heat conduction, heat convection or heat radiation. The typical heat transfer system in an injection moulding system 1 is described in the block diagram shown in figure 1. The injection moulding system 1 comprises an injection moulding machine 4 to which plastic material P is fed, for instance in form of a granulate. The injection moulding machine 4 exerts pressure and heat on the plastic material, thereby generating a melt 2 of plastics which is injected under pressure into a moulding tool 3 (the mould). The moulding tool 3 is connected with a cooling device including cooling fluid channels 5 to control the temperature inside a cavity 6 of the moulding tool 3. Heat transfer to and from the moulding tool 3 occurs as heat conduction HC via a cooling fluid in the cooling fluid channels 5 and the thermally conductive walls of the moulding tool 3, as heat convection HCV or heat radiation RD from exterior surfaces of the moulding tool 3. Further, the melt when being injected into the moulding cavity 6 carries intrinsic heat energy HI, and, on the other hand, the moulded parts when being removed from the moulding tool 3 spread thermal energy HO to the environment.

A complete injection moulding process cycle comprises the mould closing phase, injection of melt into the mould cavity, packing pressure phase for compensating shrinkage effect, cooling phase, mould opening phase and part ejection phase. In most cases the longest time of all phases described above is the cooling time. When emphasise this fact through costs one can see why it is reasonable to explore this field.

Cooling time in injection moulding process is defined as the time needed to cool down the moulded plastic part down to a predefined ejection temperature and is described by the following equation: with /,, as cooling time, t_u as injection time, t_np as packing pressure time, t^ as plastification time, t_m as movement of injection time to zero position and t_d as additional cooling time.

The main aim of a cooling process is to lower t_d which is theoretically needless, but in practice takes up from 45% up to 67% of the whole cycle time.

Relationship between important temperatures in a process of injection moulding is experimentaly given with ratios:

AT₁₁ : AT_K : AT₁ = 6 : 5 : 1

with AT₁₁ as an ejection temperature, AT_K as mould temperature and AT_T as melt temperature. From this relation one can conclude that the mould temperature has enormous influence on the ejection time and therefore the cooling time.

Injection moulding process is a cyclic process wherein the mould cavity temperature varies. As shown in figure 2, the mould cavity temperature T_κ varies from average value through whole cycle time t_c. T,_z is defined as the temperature in the mould cavity at the time when the mould is opened to eject the moulded part.

Maximal mould cavity temperature T_KMAX = TD is defined as:

_ _ T_pb_k + T_rb_P

¹ KMAX ^{~ λ} O ^~ j , b_k + b_P

with T,, = T_KMIN as a starting mould cavity temperature (adjustable temperature), b_k as mould cavity heat conductivity, b_p as polymer heat conductivity, T_p as mould cavity start temperature and T₁ as polymer melt temperature. Numeral th denotes the time period between injecting the melt into the mould cavity and opening the mould for ejecting the moulded plastic part, and can be calculated by the formula:

T₁₁ - T_κϊ with: b₀ as characteristic dimension, a_ef as heat conduction coefficient of material, K₁₁ as shape coefficient, T₁- as melt temperature, T_κ as mould cavity temperature and T₁₁ as ejection temperature.

Thermodynamic processes in moulds of polymer processing technologies can be well described via modern finite elements analysis (FEA) tools. Outputs of those FEA tools are thermodynamic results that enable optimization of a cooling process which is needed to control parameters of the moulded plastic part, like:

• Surface appearance and quality

• Residual stress rate

• Crystallisation

• Thermal deformation

• Product dimension stability • Structure of material and orientation

On the other hand, the production costs are the second major fact that requires optimization of the cooling time. With the optimization of the cooling process, the following parameters can be controlled and reduced, respectively:

• Ejection temperature

• Cycle time of production

Up to now arranging cooling fluid channels in a mould has been used to achieve the necessary cooling effects in the mould. In practice, positioning of said cooling fluid channels is based on experience and available space inside the mould. Due to the limited space and other restrictions effective cooling zones 7 that are generated around cooling fluid channels 5 are unevenly distributed in the mould 3 what causes formation of "dead zones" 8 between the effective cooling zones 7, as can be seen in figures 3A and 3B. It will be appreciated that the surfaces of the tool cavity 6 are not evenly cooled due to the dead zones 8. While increasing the number of cooling fluid channels 5 and decreasing their diameters to reduce the necessary distance between adjacent cooling fluid channels 5, as has been done in the mould 3' depicted in figure 3B seems to mitigate the problem, since the dead zones 8 have been narrowed, such a measure results in potentially stuffing the cooling fluid channels 5 with water limestone (1 mm of water limestone has similar heat resistance as 50 mm of tool steel). The direct consequences of unevenly distributed cooling fluid channels 5, like corner effects are shown in figures 4A and 4B which depict temperature distribution diagrams of moulds 3" and 3'", respectively, comprising T-shaped mould cavities 6'. As can be seen in figure 4 A positioning the cooling fluid channels 5 too far away from the junction of the legs of the T-shaped mould cavity 6' results in strong corner effects at the junction, meaning that at these corners there is a high temperature variation. High temperature variation result in residual stress rate, thermal deformation and dimension instability. On the other hand, positioning cooling fluid channels 5 with small diameters close enough to the junction of the mould cavity 6\ as shown in the mould 3"' of figure 4B, involves the risk of stuffing the cooling fluid channels 5 with limestone.

It should be noted that although the problems inherent to present polymer processing systems have been exemplarily explained by way of an injection moulding system they also apply to other polymer processing systems like blow moulding, thermoforming, extrusion processes and machines.

Due to the above described drawbacks of the current moulding systems there is a strong need to develop moulds, temperature controlled mold systems and polymer processing systems having a temperature controlled injection mould system which will allow fast and precisely located temperature changes in defined mould locations.

In order to achieve the objects defined above, the present invention provides a mould having a mould cavity wherein a polymeric moulding material can be introduced and thermally processed, with the characterizing feature that at least one thermoelectric module (TEM) is arranged in the mould in thermally conductive relation with a surface of the mould cavity.

The mould according to the present invention provides the advantage that the temperature at the surface of the mould cavity can be exactly controlled within an accuracy of 0,1 K. Use to a thermoelectric module with its straightforward connection between the input and output relations represents a milestone in cooling problematic. The present invention allows not only for fast an precise cooling, but also for precise heating of the mould, wherein it is possible to switch very fast between cooling and heating. Thus, generally the invention enables precise temperature control within the mould cavity making it possible to run various predefined temperature cycles. Industrial problems such as uniform cooling of problematic A class surfaces of plastic parts and its consequence to plastic part appearance can be solved by the invention. Problems of introducing the moulding material into long thin recesses to form long walls can be solved with the invention by overheating some surfaces of the mould cavity when the moulding material is introduced. Furthermore, with the present invention control over rheological properties of plastic materials can be gained. The plastic materials to which the invention is applicable comprise thermoplastic materials, thermosetting materials, elastomers, rubber, silicon and. the like.

By configuring the thermoelectric modules as semiconductor type thermoelectric modules very fast and exact temperature control can be achieved.

In order to improve cooling of the mould cavity by the thermoelectric modules it is preferred that cooling means are provided in heat exchanging relation with the thermoelectric modules, so that the heat produced at the second surface of the TEMs when their first surface is cooled can be withdrawn from the TEMs. In other words, the cooling means provide the function of a heat sink to the TEMs. In embodiments of the inventions the cooling means comprise cooling fluid channels and/or forced air ventilation.

Very fast and effective cooling of the mould cavity can be achieved when the thermoelectric modules are arranged between the surface of the mould cavity and the cooling means. The first surfaces facing the surface of the mould cavity take up the heat from the mould cavity and pass it on to the cooling means via their second surface which faces the cooling means.

In order to reduce the volume of the material of the mould body that has to be cooled or heated by the TEMs advantageously a thermally insulating element encompasses at least the mould cavity and the thermoelectric modules. When the thermally insulating element is arranged between a mould body containing the mould cavity and a mould structure plate or around the mould thermal decoupling of the TEMs from the processing machine or the environment can be achieved.

The mould according to the invention can be thermally controlled by simply energizing the TEMs with direct current of a predefined polarity and current intensity, i.e. by controlling

(steering) them in a straight forward manner. However, in order to achieve a more exact control over the temperature within the mould cavity at least one temperature sensor should be arranged at or in the mould for sensing the temperature of the surface of the mould cavity.

In one embodiment of the invention at least one temperature sensor is arranged at the thermoelectric module. Such an embodiment can easily be assembled. In a variant of this embodiment temperature sensors are arranged at both the first and second surface of the thermoelectric module so that the temperature difference at the first and second surface of the thermoelectric module can be measured and used to control the thermoelectric module. The mentioned embodiments allow to operate the mould in various temperature control modes. In a first temperature control mode measuring the temperature at a first surface of the TEM and estimating the temperature at the surface of the mould cavity from the temperature of the first surface of the TEM can be sufficient for many applications. In practice, additionally measuring the temperature of additional cooling means, if any, will yield more precise results. In another temperature control mode the minimum and maximum temperatures at the two opposing surfaces of the TEMs are measured (can be carried out by non contacting measurements and also perhaps in several places) and from these min/max temperatures the maximum temperature difference at the TEM is calculated. With that information one can control whether the TEM is saturated and thus cannot transport heat any more.

In yet another embodiment of the invention the at least one temperature sensor is arranged to sense the temperature of the surface of the mould cavity in non-contacting manner. Such an embodiment enables many degrees of freedom in designing the mould.

The number of TEMs used in the present mould is not decisive. In simple embodiments only one TEM is used, while in more complicated embodiments a plurality of TEMs will be employed. The TEMs can be electrically connected in series or in parallel. They can be arranged in distances from each other adjacent to each other. However, in an embodiment that is particularly useful for heating/cooling thin parts of the mould, like protrusions or sliders, a plurality of thermoelectric modules are stacked one on the other, multiplying the heating/cooling effect.

The present invention further comprises a temperature controlled mould system, comprising a mould according to the present invention and an electric supply unit for energizing the thermoelectric modules with electric energy.

In order to allow high flexibility in operating the temperature controlled mould system it is preferred to provide it with a control unit being adapted to control the temperature of the surface of the mould cavity by controlling the electric energy fed to the thermoelectric modules.

Very precise control of the temperature within the mould cavity can be achieved when the control unit is adapted to control the electric energy fed to the thermoelectric modules in response to output signals provided by temperature sensors arranged to sense the temperature of the surface of the mould cavity. Of course, closed loop control enables highest accuracy, but for simpler applications working without closed loop (non regulating system) might be regarded as sufficient.

In order to enable the present temperature controlled mould system to run various temperature cycles it comprises a circuit for controllably energizing the thermoelectric modules. To achieve this purpose the control unit is adapted to control the temperature of the surface of the mould cavity according to a predefined temperature profile.

In order to enable the present temperature controlled mould system to cool and heat the mould cavity the circuit for controllably energizing the thermoelectric modules is adapted to reverse the polarity of the electric direct current fed to the thermoelectric modules.

The control unit must be able to control the temperature on all needed areas in the mould during the whole moulding cycle. Therefore, in a preferred embodiment of the invention the control unit is based on fuzzy logic, offering short response times and simplicity.

The present invention further comprises a polymer processing system that comprises at least one temperature controlled mould system according to the present invention. The polymer processing system achieves a change of form of a polymeric plastic material by applying varying temperatures to the material. Practical applications of such polymer processing systems are injection moulding, blow moulding, thermoforming, extrusion processes and machines, and the like.

The aspects defined above and further aspects of the invention are apparent from the exemplary embodiments to be described hereinafter and are explained with reference to these exemplary embodiments. However, the invention is not limited to these exemplary embodiments.

Fig. 1 shows a schematic representation of an injection moulding system according to prior art.

Fig. 2 shows a chart of an injection moulding cycle.

Fig. 3 A shows a mould according to prior art in cross section.

Fig. 3B shows another mould according to prior art in cross section. Fig. 4 A shows a temperature distribution diagram through a mould according to prior art.

Fig. 4B shows a temperature distribution diagram through another mould according to prior art. Fig. 5 shows a first embodiment of a mould according to the invention in cross section. Fig. 6 shows a second embodiment of a mould according to the invention in cross section. Fig. 9 shows a cross section of an evaluation prototype for the present invention. Fig. 10 shows a temperature distribution diagram according to finite elemente analysis through the evaluation prototype.

Fig. 1 1 is a temperature distribution diagram over the vertical cross section of the evaluation prototype as indicated in figure 10.

Fig. 12 shows the transient results of the evaluation prototype in form of a temperature over time chart.

A first embodiment of a mould 10 according to the invention is shown in fig. 5 in a cross sectional view. The mould 10 comprises a mould body 1 1 that defines a mould cavity 12 being adapted to receive a moulding material that is to be moulded into a part with a shape as defined by the moulding cavity. The moulded part - while still being kept in the mould cavity - is cured by thermal treatment (subjected to heat and/or cold according to predefined temperatures or a temperature profile). After curing the moulded part is ejected from the mould cavity 12. According to the invention the mould 10 comprises one or more thermoelectric modules (TEM) 13 that can be both heated and cooled, wherein the TEMs 13 are positioned in the mould body 1 1 close to the surface 14 of the mould cavity 12, thus enabling primarily heat transfer from or to the surface 14 of the mould cavity 12 in a temperature controllable manner. Additionally, cooling means 15 being configured as cooling fluid channels are arranged in the mould body 1 1. The cooling means 15 (cooling fluid channels) contribute to maintain constant temperature conditions inside the mould 10 by circulating a liquid or gaseous heat exchange medium, e.g. water or cooling air, through the cooling fluid channels, thus establishing secondary heat transfer means. Alternatively or additionally to cooling fluid channels the cooling means 15 may comprise forced air ventilation. In operation, the thermoelectric modules 13 act as heat pump and as such manipulate the moulding material inside the mould cavity 12 by applying the necessary temperatures to the surface 14 of the mould cavity 12. As will be explained in detail below the thermoelectric modules 13 have a first surface 13a that is hot or cold depending on the direction of direct current flowing through the TEM, and a second surface 13b opposite to the first surface 13a which second surface 13b is cold or hot in reverse manner as the first surface. Hence, when the TEMs 13 of the present embodiment of the mould 10 are energized by direct current such that the first surfaces 13a of the TEMs 13 that are located adjacent to the surface 14 of the mould cavity 12 are cold heat is dissipated at the second surfaces 13b of the TEMs. Since the cooling fluid channels 15 are located at the backside of the TEMs 13, i.e. adjacent to the second surfaces 13b of the TEMs 13, they cooperate with the TEMs 13 as heat exchanger carrying off the heat that is radiated from the second surfaces 13b of the TEMs 13. Further, a thermal insulation layer 16 is installed between the mould body 1 1 and mould structure plates 17.

Another mould 10' according to the invention is shown in fig. 6 in cross sectional view. The second mould 10' represents a variation of the first mould 10 seen at figure 5 and differs from the first mould 10 in that there is a central protrusion 20 having an inner hollow space 19. The central protrusion 20 extends into the mould cavity 12'. The central protrusion 20 can be a fixed part of the mould 10' but can also be a moveable part of the mould, e.g. an ejector pin. It is necessary that the outer surface of protrusion 20 is temperature controllable, which in practice is a demanding task due to small volume and difficulty to arrange cooling means 15 (cooling fluid channels) close enough to exhibit useful cooling effect. The present invention, however, solves this problem by stacking a plurality of thermoelectric modules 13 thermally in series (i.e. one over the other) so that their thermal effect (cooling or heating) is multiplied. The temperature produced by the stack of TEMs 13 is transferred through the space 19 and the walls of the protrusion 20. It should be noted that although not shown in Fig. 6 further TEMs can be arranged in the mould body 11 in the same way as in the mould 10 shown in fig. 5. While the thermoelectric modules 13 applied in series (for more effective heat manipulation) act as primary heat transfer means secondary heat transfer is enabled via the cooling means 15.

Now, with reference to Fig. 7, the function of a thermoelectric module 13 is explained. TEMs utilize an effect that was discovered by Jean Peltier. The basic idea behind the so called Peltier effect is that whenever DC passes through a circuit of heterogeneous conductors, heat is either released or absorbed at the conductors' junctions, which depends on the current's polarity. The amount of heat released or absorbed is proportional to the current that passes through the conductors. The TEM 13 comprises a plurality of basic TEM units which are thermocouples, which consists of a p-type (13f) and a n-type (13e) semiconductor elements, often called pellets. A copper commutation tab 13g is used to interconnect the p-type (13f) and n-type (13e) semiconductor elements that are traditionally made of Bismuth Telluride-based alloy. In the TEM 13 the plurality of basic TEM units (13e, 13f, 13g) are electrically connected in series and are sandwiched thermally in parallel between two Alumina ceramic plates 13c, 13d. The number of thermocouples may vary greatly - from several elements to hundred of units. This allows to construct a TEM 13 of a desirable cooling and heating capacity ranging from fractions of Watts to hundreds of Watts. When a direct durrent I_DC flows across the TEM 13, it causes a temperature differential Q between the first and second surfaces 13a, 13b opposite to each other.- As a result, one TEM surface, which is called "Cold", in the representation of fig. 7 the first surface 13a, will be cooled, while its opposite face, which is called "Hot", in the representation of fig. 7 the second surface 13b, will simultaneously be heated. If the heat generated on the TEM hot side is effectively dissipated into heat sinks and further into the surrounding environment, then the temperature on the TEM cold side will be much lower than that of the ambient by dozens of degrees. The TEM's cooling capacity is proportional to the current passing through it. TEM's cold side will consequently be heated and its hot side will be cooled once the direction of the direct durrent I_DC flowing through the TEM 13 has been reversed. Temperature sensors 18a, 18b are arranged at the first and second surface 13a, 13b, respectively, to measure and control the temperature difference at the first and second surface 13a, 13b.

The main idea of the present invention is to arrange TEMs in the walls of the mould cavity and to use them as primary heat transfer units. Fig. 8 shows a block circuit diagram of a temperature controlled mould system according to the invention. The temperature controlled mould system comprises a mould 10, 10' with TEMs 13, wherein the TEMs 13 are arranged close to the surface 14 of the mould cavity. In order to control the temperature of the surface 14 a temperature sensor 18 is, for instance, inserted into the surface 14. (Alternatively, the temperature sensors 18a, 18b at the TEM 13 can be used.) The TEMs 13 are sandwiched between the surface 14 and a heat exchanger which, for instance, consists of the cooling fluid channels 15 arranged in the mould body 11. The system further comprises an electronic circuit that controls the complete system.

The electronic circuit comprises a control unit 21 which is the central processing unit of the system and controls all other parts of the circuit. The control unit 21 is connected to an input unit 23 that functions as an input interface, and a supply unit 22 that provides electric power supply for both the electronic components and the power components of the system. Optionally, the control unit 21 has a temperature control loop 26 that is connected to the temperature sensor 18 so that a closed-loop control of the temperature of the surface 14 can be implemented. With closed-loop control an accuracy of control within 0.1 K can be achieved.

The control unit controls the direct current delivered from the supply unit 22 to the TEM 13 via a control driving unit 24 and a power driving unit 25. The power driving unit 25 may be configured as an H-bridge to reversibly deliver a direct current I_DC to the TEM 13. The control unit 21 acts as an execution unit imposing predefined temperatures or temperature profiles on the surface 14. The control unit 21 must be able to control the temperature on all needed areas in the mould during the whole moulding cycle. Therefore, in a preferred embodiment the control unit 21 is based on fuzzy logic due to nature of regulation system, short response times and simplicity. Although classical PID regulation can be used, too, it is not preferred on basis of fact that with fuzzy logic the required accuracy is gained within shorter regulation cycle times. There are more parameters to be calculated at PID regulation and therefore needed regulation cycle time is longer and further there is no need for accuracies below 0.1 K.

The temperature controlled mould system according to the invention can achieve heating as well as cooling operations. Secondary heat removal is realized via fluid cooling channels 15 acting as heat exchangers. Those fluid cooling channels 15 are operated according to current cooling technologies and serve as a heat sink. The invention enables complete control of processes in terms of temperature and times through the whole moulding cycle. Furthermore, it allows various temperature/time profiles within the moulding cycle also for starting and ending procedures.

The use of thermoelectric modules within moulds represents a milestone in temperature controlling of moulds. Particularly, its introduction into moulds for injection moulding with its problematic cooling construction and problematic processing of precise and high quality plastic parts represents high expectations.

With the mentioned functionality of a temperature profile run across the cycle time injection moulding process can be fully controlled. Industrial problems such as uniform cooling of problematic A class surfaces and its consequence of plastic part appearance can be solved. Problems of filling thin long walls can be solved with overheating some surfaces at injection time. Furthermore, with such application control over rheological properties of plastic materials can be gained.

In order to evaluate the approach of the present invention a prototype was constructed that is shown in cross section in fig. 9. The prototype comprises a heat exchanger comprising two aluminium plates that form a channel for circulating water. On the upper aluminium plate a thermoelectric module (TEM) was arranged in thermally conductive manner, and on the TEM a steel plate was arranged representing the surface of a mould cavity. The prototype was tested both in reality and virtually, the latter by using a special finite element analysis software. In the present example the TEM was operated in cooling operation. Surrounding air and the water were set at stable temperature of 20 deg C.

Fig. 10 shows a temperature distribution diagram according to finite elements analysis through the evaluation prototype. Figure 10 represents steady state analysis which was very accurate in comparison to prototype tests.

The temperature distribution over the vertical cross section as indicated in figure 10 can be seen in figure 11. Figure 11 shows that the highest temperature just below 200 deg C occurs at TEM hot side surface, while the cold side of the TEM cools to approximately 5 deg C; both ends of a curve converge to ambient temperature of 20 deg C. Such a high temperature difference in TEM results in high mechanical stress which requires correct mounting, choosing adequate TEM and applying intelligent electronic regulation.

Transient analyses and prototype test were also performed, as already described. Figure 12 shows transient response of temperature at controllable surface when driving TEM with unit pulse (at time 0 s full heating has been applied and starting conditions were set to 20 deg C).

Claims

Claims:

1 . A mould (10, 10') having a mould cavity (12, 12') wherein a polymeric moulding material can be introduced and thermally processed, characterized in that at least one thermoelectric module (13) is arranged in the mould (10, 10') in thermally conductive relation with a surface (14) of the mould cavity (12, 12').

2. The mould as claimed in claim I₅ wherein the thermoelectric modules (13) are configured as semiconductor type thermoelectric modules.

3. The mould as claimed in claim 1 or 2, wherein cooling means (15) are provided in heat exchanging relation with the thermoelectric modules (13).

4. The mould as claimed in claim 3, wherein the cooling means (15) comprise cooling fluid channels and/or forced air ventilation.

5. The mould as claimed in claim 3 or 4, wherein the thermoelectric modules (13) are arranged between the surface (14) of the mould cavity and the cooling means (15).

6. The mould as claimed in claims 1 to 5, wherein a thermally insulating element (16) encompasses at least the mould cavity (12, 12') and the thermoelectric modules (13).

7. The mould as claimed in claim 6, wherein the thermally insulating element (16) is arranged between a mould body (1 1) containing the mould cavity (12, 12') and a mould structure plate (17).

8. The mould as claimed in claims 1 to 7, wherein at least one temperature sensor (18, 18a, 18b) is arranged at or in the mould (10, 10') for sensing the temperature of the surface (14) of the mould cavity (12, 12').

9. The mould as claimed in claim 8, wherein at least one temperature sensor (18a, 18b) is arranged at the thermoelectric module.

10. The mould as claimed in claim 9, wherein temperature sensors (18a, 18b) are arranged at both the first (13a) and second (13b) surface of the thermoelectric module (13) so that the temperature difference at the first and second surface (13a, 13b) of the thermoelectric module can be measured and used to control the thermoelectric module (13).

1 1. The mould as claimed in claim 8, wherein the at least one temperature sensor is arranged to sense the temperature of the surface of the mould cavity in non-contacting manner.

12. The mould as claimed in claims 1 to 1 1, wherein a plurality of thermoelectric modules (13) are stacked one on the other.

13. A temperature controlled mould system, comprising a mould according to claims 1 to 12 and an electric supply unit (22) for energizing the thermoelectric modules (13) with electric energy.

14. The temperature controlled mould system according to claim 13, further comprising a control unit (21) being adapted to control the temperature of the surface (14) of the mould cavity (12, 12') by controlling the electric energy fed to the thermoelectric modules.

15. The temperature controlled mould system according to claim 13, wherein the control unit (21) is adapted to control the electric energy fed to the thermoelectric modules in response to output signals provided by temperature sensors (18) arranged to sense the temperature of the surface (14) of the mould cavity.

16. The temperature controlled mould system according to claims 13 to 15, comprising a circuit (24, 25) for controllably energizing the thermoelectric modules (13).

17. The temperature controlled mould system according to claim 16, wherein the circuit for controllably (24, 25) energizing the thermoelectric modules is adapted to reverse the polarity of the electric direct current fed to the thermoelectric modules.

18. The temperature controlled mould system according to one of claims 13 to 17, wherein the control unit (21) is adapted to control the temperature of the surface (14) of the mould cavity according to a predefined temperature profile.

19. The temperature controlled mould system according to one of claims 13 to 18, wherein the control unit (21) is operated on the basis of fuzzy logic.

20. A polymer processing system, comprising at least one temperature controlled mould system according to one of claims 13 to 19.