WO2008116575A1 - Method and device for producing insulating elements - Google Patents

Abstract

The invention relates to a method and a device for producing insulating elements consisting of polyurethane (PUR) foam or polyisocyanurate (PIR) foam. According to the invention, the foaming agent is mixed into at least one of the two reactive constituents in a circulation circuit.

Description

 Method and device for the production of insulating elements

The invention relates to a method and a device for producing insulating elements of polyurethane (PUR) or polyisocyanurate (PIR) foam, in which the blowing agent is mixed in a circulation in at least one of the two reactive components.

The production of insulating elements for thermal insulation of PUR or PIR foam is generally carried out in a continuous process. The insulation elements are produced endlessly on so-called contimates in thicknesses of generally about 20 to 200 mm. Thicknesses of less than 20 mm or over 200 mm are also possible. Such a Contimat usually consists of a circumferential upper belt for guiding the upper cover layer, a circumferential lower belt for guiding the lower cover layer, a feed device for the upper cover layer, a feed device for the lower cover layer, a molding section, within which the reaction mixture between the upper cover layer and the lower cover layer is foamed and reacted, a cutting device for the insulating elements to be produced and a dosing station with a mixing head for applying the reactive mixture to the lower cover layer. A Contimat according to the prior art is shown in FIG.

The reactive mixture is formed by mixing an A-reactive component with a B-reactive component, wherein the A-reactive component includes at least one polyether or a polyester polyol or mixtures of polyether and polyester polyols and the B-reactive component at least one isocyanate or Isocyanatabmischungen. Furthermore, in the A-reactive component or in the B-reactive component or proportionately in both the A and the B-reactive component nor a halogen-free blowing agent, e.g. Pentane, as well as PUR or PIR foam specific additives mixed.

In order to achieve fire class B2 in insulation elements made of PUR foam with flexible cover layers, a relatively large amount of flame retardants is required. However, these delay the curing time, so that the Contimat can be operated only with relatively low transport speed, which significantly affects the cost of production. An alternative would be a Contimat with a longer molding line, which in turn would increase the investment costs drastically.

Depending on the characteristic number, no or only very little flame retardant must be added so that insulation elements made of PIR foam with flexible cover layers achieve fire class B2, since a protective carbon layer forms when heat is applied to PIR foam. Furthermore, PIR compounds decompose only at higher temperatures than PUR compounds. PIR foams cure much faster than PUR foams, which enables significantly higher production speeds. On the other hand, they are more brittle than polyurethane foams, so that a high-precision tempering of at least 60 ⁰ C of both the upper and the lower band of Contimaten is required so that the foam adheres optimally to both outer layers.

PIR systems are highly reactive. This has the consequence that a traversing of the mixing head to apply the mixture is not possible because the individual webs no longer flow together. In order nevertheless to apply the reactive mixture uniformly over the entire bandwidth, it is possible to arrange either a plurality of stationary mixing heads in parallel (see also FIG. 2) or a stationary mixing head to connect a so-called "antler" as outlet system or a special distributor (see FIG. 3). Also combinations of these basic variants are possible.

PIR foams are extremely temperature critical. This requires an exact temperature control for the reactive components. In order to achieve an optimal process flow, therefore, amounts of heat introduced by process organs should, as far as possible, be removed directly behind the heat input point. This also means that process agents that introduce less heat into the reactive components than others that otherwise perform the same function are the more appropriate.

Polyurethane polyols are generally used in PUR systems and highly viscous polyester polyols in PIR systems, the viscosity of which can be up to 10,000 mPas.

The amounts of foaming agent required for the foaming process, based on the polyol, for example, about 16 to 25 parts by weight of pentane, but only go to a small proportion, namely only about 3 to 5 parts by weight in solution. The majority must be processed as an emulsion.

This always leads to problems in the systems used according to the prior art, since the polyol-pentane or isocyanate-pentane emulsions are not sufficiently stable and disintegrate in production breaks and especially after the end of the shift into their constituents.

Another serious problem is that the mixing ratio between the

Polyol or the isocyanate and the additives is extremely unfavorable. That is, the amounts of additive are very small compared to the amounts of polyol or isocyanate. In an online process, as it is the state of the art, this leads in principle to mixing problems. That's why so far disproportionately large or expensive mixers or mixing systems required. This problem applies equally to PUR and PIR systems.

As a rule, the metering streams of the additives are pulsating due to the small flow rates and the single- or two-cylinder pumps used. This also leads to inhomogeneities in the mixture. In order to obtain continuous, and above all, exact flow rates for the additives, relatively expensive multi-cylinder pumps would have to be used. This problem also applies to both PUR and PIR systems.

Furthermore, it should be taken into account in the production of insulating elements that the thickness of the insulating elements can be very different. It can be 20 mm but also 200 mm. This has the consequence that the Gemischaustragsmengen are variable in a corresponding bandwidth.

Another production criterion for insulation elements are recipe changes. That is, a change, e.g. of additives, during ongoing production must be possible.

It was therefore the task to find a simple and cost-effective method that meets the following criteria:

proper emulsification of the propellant, for example pentane, in the polyol or in the isocyanate to produce a homogeneous and above all stable polyol pentane or isocyanate pentane emulsion,

- perfect, i. homogeneous mixing of the additives in the polyol blowing agent or isocyanate blowing agent emulsion, and indeed for the entire product range of various

additives

minimized heat input into the process by the process organs used,

- minimal production losses when changing production parameters,

- reproducible quality, i. even after changes unchanged uniform cell in size and shape.

The invention relates to a process for the preparation of insulating elements comprising a layer of polyurethane or polyisocyanurate foam, in which

a) a halogen-free blowing agent in at least one premixer in a first reactive component A, containing at least one polyether or polyester polyol, is mixed and / or in a second reactive component B, containing at least one isocyanate, is mixed, and

b) then the first reactive component A is mixed with the second reactive component B in at least one mixing head, wherein a reactive mixture is obtained, and

c) the reactive mixture from step b) is discharged from the at least one mixing head and applied to a substrate, on which it reacts out and hardens,

characterized in that

d) the interference of the halogen-free blowing agent in the first reactive component A and / or in the second reactive component B in step a) is carried out such that

the reactive component and the halogen-free blowing agent are introduced into the premixer, and the reactive component and the halogen-free blowing agent are mixed in the premixer and discharged as a mixture stream, and separated from the mixture flow of reactive component and halogen-free blowing agent, a partial stream and fed back into the premixer with a homogenizing pump , And the remaining partial flow with at least one metering pump with the metering ^ D is conveyed to the at least one mixing head, wherein the

Flow ^ H of the homogenization pump in dependence on the metering flow 'D of the metering pump is set.

Suitable halogen-free blowing agents are e.g. n-pentane, iso-pentane and cyclo-pentane and mixtures of these.

Figures 2 and 3 show by way of example the solution for the described task. The described method fulfills all the criteria for an optimized process for the production of insulating elements for thermal insulation.

By repeated circulation of the mixture of the blowing agent, preferably pentane, polyol or isocyanate and optionally other substances such as additives and by the respective

Homogenizing pump via the corresponding premixer or the corresponding

Mixing system, a flawless, i. completely homogeneous mixing of the pentane and the

Additives in the polyol or in the isocyanate. The resulting emulsion is also stable because

Droplet sizes of about 2 to 80 microns, preferably from about 3 to 50 microns, more preferably from about 4 to 20 microns are achievable in this manner. What is new about this method is that the delivery flow Vn of the respective homogenization pump is adjustable as a function of the metering flow V _{D of} the at least one corresponding metering pump. _Namely, the maximum delivery _{flow Fmax of} the respective homogenization _pump must be designed for the maximum metering _{flow Fdmax of} the corresponding metering system. Since the dosing flows of the metering systems are varied by a factor of 10 for a bandwidth of the insulating element thickness of 20 mm to 200 mm, the number of revolutions would then increase by a factor of 10 if the metering currents were minimal, if the respective homogenizing pump were a constant pump. This would heat up the emulsion of the propellant, preferably pentane, and polyol or isocyanate and possibly additives enormously. The resulting heat energy would then have to be dissipated again. In addition, gaseous blowing agent components could thereby be formed, which would then be much more difficult to emulsify due to the high volume fraction of the gaseous blowing agent.

The essential step of this invention is thus that the flow rate V _{H of} the respective homogenization pump is adapted to the dosing flow V _{D of} the corresponding dosing system. In this way, an optimal operation for the process is possible:

- as many revolutions as necessary to achieve proper emulsification,

- as few revolutions as possible to avoid unnecessary heat input into the system.

The optimal operating point, i. the optimum number of revolutions must be determined empirically. It is recognizable by a uniform, fine cell structure of the PUR or PIR foam. The aim is cells of about 0.1 mm in diameter, because the smaller the cell is, the greater the insulating effect.

By minimizing the volume of liquid in the respective homogenization cycle, a reduction in production losses is possible even when changing production parameters.

Furthermore, even with production changes, a reproducible quality, i. ensures a consistent cell in size and shape. This can be achieved by adjusting the number of revolutions.

This new method is flexible applicable. Thus, the halogen-free blowing agent, for example pentane, and the additives may optionally be blended into either the polyol or the isocyanate component. It is particularly efficient when the interference of halogen-free blowing agent and Additives proportionally carried out both in the polyol and in the isocyanate component. This makes it possible, even higher propellant amounts of pentane than 16 parts by weight, namely up to 25 parts by weight and also beyond, in each case based on the polyol component to interfere in the entire raw material system. In this way, it is possible to achieve extremely low densities of up to 30 kg / m ³ in the insulating elements, which on the one hand results in a particularly good insulating effect, but on the other hand also lowers the raw material costs for polyol and isocyanate.

It has been found that the novel process meets all operating requirements if the reactive component A or B is circulated in the respective homogenization cycle one to twenty times, preferably two to ten times, particularly preferably two to five times.

In a further embodiment of this new method, the delivery flow Vw of the respective homogenization pump is adjusted by means of a control unit as a function of the corresponding metering flow V _D. The control can satisfy a function that is linearly proportional:

VH = A - VD

It can also correspond to an exponential function:

Namely, in an exponential function, the system can e.g. To adapt to mixer specific conditions, because if a mixer is designed for a maximum amount, it has a lower efficiency at lower levels, so that the number of passes must be increased disproportionately.

The factor A can be chosen in the order of 1 to 20. It is preferably in a range between 1.5 and 10 and more preferably in a range between 2 and 5.

The exponent B can be: 0.5 <B <1.5.

Surprisingly, it has further been found that the quality of the insulating foam, that is, the uniformity and fineness of the cell structure, correlates with the temperature of the emulsion flowing out of the respective homogenization circuit in cooperation with the adjustment of the delivery flow V _H as a function of the corresponding metering flow F _D. This provides the possibility of subsequent control of the flow rate fi _{H of} the respective homogenization pump as a function of the corresponding metering flow V _D , in which the temperature of the emulsion flowing out of the homogenization cycle is used as the controlled variable.

Such a variant is shown in FIG. The level of this temperature as a controlled variable is primarily dependent on the raw material system and must therefore be determined empirically in individual cases.

The control process and the control process are completely separated from each other and never at the same time.

First of all, the adjustment of the delivery flow P _{H of} the respective homogenization pump by the controller takes place as a function of the corresponding metering flow P _D. Subsequently, the control is switched off and the control of P _H in the absence of O takes over. Likewise, the control is turned off when a control operation is again performed.

The invention also relates to an apparatus for the production of insulating elements for thermal insulation comprising a layer of polyurethane or polyisocyanurate foam, comprising:

a) containers for the provision of the reactive components A and B,

b) at least one mixing head for mixing the reactive components A and B, and for discharging the reactive mixture onto a substrate,

c) at least one metering pump for the metering of the reactive component A to the mixing head,

d) at least one metering pump for the metering of the reactive component B to the mixing head,

e) connecting lines from the containers to the metering pumps and from the metering pumps to the mixing head,

characterized in that it further contains

f) at least one premixer for mixing the reactive component A or the reactive component B with a halogen-free blowing agent,

g) a pre-mixer circuit upstream charge pump for the promotion of the reactive component A or the reactive component B in the circulation and pressure generation and a biasing valve, through which a partial flow of the funded through the charge pump in the circulation reactive component A or reactive component B is discharged,

h) a connecting line between the premixer and the circuit comprising charge pump and biasing valve, and

i) a return line from the exit from the premixer back to the entrance to the premixer containing an adjustable homogenizing pump, and

j) a control unit with impulse lines from the at least one corresponding metering pump to the control unit and from the control unit to the adjustable homogenization pump.

New in this device is that parallel to the respective premixer or mixing system for the halogen-free blowing agent and optionally for the additives and the corresponding polyol or isocyanate a Homogenisierungskreislauf is arranged with an adjustable homogenization and this adjustable homogenization each with a control unit with impulse lines of the at least one corresponding metering unit (metering pump) is assigned to the control unit and from the control unit to the adjustable homogenization pump.

In the further embodiment of this new device, the respective control unit is combined with a control unit and the respective homogenization cycle is followed by a temperature measuring point θ, each of which leads a pulse line to the control part of the combined control-rule unit.

In this way, it is possible to first control the flow rate V _{H of} the respective homogenization pump as a function of the corresponding metering flow V _D and then, after switching off the control, to regulate the flow V _H as a function of θ.

With the concept of arranging heat exchangers wherever heat has been introduced into the system immediately before, ie behind pumps or mixing devices, it is possible to precisely and particularly for the required processing temperature for the reactive components of 20 to 22 ° C Raw materials "stress minimized" to adjust.

In a further embodiment of this new device, the reactive components are also assigned to gassing devices, by means of which, as a rule, nitrogen is dispersed in. This favors the mixing of the reactive component A with the reactive component B. As a mixing element for the halogen-free blowing agent, for example pentane, as well as for the additives in the polyol or isocyanate component static mixer, stirrer mixers, rotor-stator mixers or combinations of such mixers can be used.

When using static mixers, it is also possible to perform these two or more stages, then in the primary stage flow rates of about 0.5 to about 5 m / s and in the at least one subsequent stage flow rates of 5 to 50 m / s, preferably from 5 to 40 m / s, particularly preferably from 5 to 30 m / s are produced.

In this way, a particularly good emulsification of the propellant, preferably pentane and optionally the additives in the polyol or in the isocyanate is possible. For in the first stage, the uniform pre-distribution of the components to be mixed or emulsified takes place by shearing the pentane being divided into droplets. In the at least one subsequent stage, these drops of pentane and additives are then elongated so that they thereby disintegrate into microdroplets of 2 to 80 .mu.m, preferably from 3 to 50 .mu.m, particularly preferably from 4 to 20 .mu.m, so that then a completely homogeneous and especially stable emulsion is formed.

The invention also relates to the use of the insulating elements for thermal insulation produced by the process according to the invention.

The invention will be explained in more detail with reference to the following figures. Show it

1 shows schematically a device for the production of insulating panels according to the prior art.

Figure 2 schematically shows an inventive device for the production of insulation boards, in which the halogen-free blowing agent pentane and the additives are mixed into the polyol and the flow of the homogenization pump is adjusted by means of a control unit.

Figure 3 schematically a device according to the invention, in which the halogen-free propellant pentane and the additives are also mixed in the polyol and the flow of the homogenization pump is also controlled.

Figure 1 shows schematically a device 1 for the production of insulating elements 2 for the

Thermal insulation according to the prior art. In this case, a lower cover layer 3 and an upper cover layer 4 are continuously by corresponding feeders 5, 6 in the in Longitudinally extended gap between the circulating upper belt 8 and the circulating lower belt 7 of a so-called Contimaten 1 promoted.

The reactive component A (polyol) and the reactive component B (isocyanate) are conveyed via associated suction and pressure lines through the metering pumps 9, 10 to the mixing head 11, where mixed and applied the resulting PIR reaction mixture on the lower cover layer 3. The applied to the lower cover layer 3 PER reaction mixture begins to foam and is transported by the longitudinal movement of the lower cover layer 3 in the forming section, which is formed by the circulating upper belt 8 and the circulating lower belt 7.

In the forming section, the PIR reaction mixture foams up between the upper cover layer 4 and the lower cover layer 3 and reacts, so that after passing through the molding section, an endless insulation board is formed, from which individual insulation elements 2 are separated by means of the cutting device 12.

While the reactive component B contains only isocyanate, which passes from the associated tank 13 to a metering pump 10, the reactive component A polyester polyol, pentane and PER foams specific additives. Pentane and additives are conveyed from associated containers (not shown in the diagram) via associated metering units 14, 15a, 15b, 15c and lines to the stirred premixer 16 where they are mixed into the polyester polyol.

The exact dosage of the polyester polyol is carried out by the metering pump 9 for the reactive mixture A, which doses the total amount of polyester polyol, pentane and additives.

To ensure the suction-side supply of the metering pump 9 for the reactive component A, the polyester polyol recirculates by means of the charge pump 17 from the associated tank 18 via the biasing valve 19, through which the required for the metering pump 9 form is established. In this case, the flow rate of the charge pump 17 must be greater than the proportion of polyester polyol removed by the metering pump 9 and the pressure built up by the biasing valve 19 must be higher than the sum of all pressure losses that occur over the entire suction line between the recirculation of the charge pump 17 and the Suction side of the metering pump 9 result.

The incorporation of pentane and the additives in the polyester polyol by the stirred premixer 16 produces the reactive mixture A, in which still by means of

Gas Loading Device 20 Nitrogen is dispersed. After that it will be fumigated

Reactive mixture A through the heat exchanger 21 to the required operating temperature of approx. 18 ⁰ C brought to 20 ⁰ C, before the metering by the metering pump 9 and the mixing with the reactive component B in the mixing head 1 1 takes place.

Figure 2 shows schematically a special embodiment of the device according to the invention. Here, too, insulating elements for thermal insulation (not shown in the diagram) are produced by means of a contimates.

While in the scheme 1, the Contimat 1 is shown in side view, in the scheme 2, the Contimat 30 is shown with a view to the front, i. the transport direction for the produced insulating elements is perpendicular to the image plane, and indeed in this.

FIG. 2 also shows three stationary mixing heads 31, 32, 33, which apply PIR reaction mixture to the lower cover layer resting on the lower belt 34 (not shown in the diagram).

Three dosing pumps 35, 36, 37 for the reactive mixture A and three dosing pumps for the reactive component B are assigned to each of these three mixing heads. Furthermore, in each case a heat exchanger is arranged in the pressure lines of these metering pumps 35, 36, 37 to the associated mixing head 31, 32, 33 to set the required PIR process temperature of about 20 ⁰ C to 22 ⁰ C.

The metering pumps 35, 36, 37 of the reactive component B (isocyanate) are supplied by the associated tank 38 via corresponding suction lines.

The reactive mixture A consists in this example of polyester polyol, pentane and PIR foam specific additives, pentane and additives of associated containers and dosing (not shown in the diagram) via an injection block 39 to a special static mixer system comprising static mixers 49A, 49B and 49C promoted and mixed there into the polyester polyol.

Also in this example, the exact dosage of the polyester polyol via the associated metering pumps 35, 36, 37 for the reactive mixture A, again an associated tank 40 and a charge pump 41 and a biasing valve 42 ensure the necessary supply of throughput and to form with reactive component A. ,

In the suction-side line between recirculation of the charge pump 41 and the suction side of the metering pumps 35, 36, 37, in turn, a gas loading device 43 for the Eindispergierung of nitrogen and a heat exchanger 44 are arranged.

The novelty in this device according to the invention consists in the fact that parallel to the Einmischstrecke, ie in this example the static mixer system, for the pentane and the Additive a homogenization circuit with an adjustable homogenization pump 45 is arranged and this adjustable homogenization pump 45 is assigned a control unit 46, to which impulse lines from the adjustable metering pumps 35, 36, 37 of the reactive mixture A and a pulse line lead to the adjustable homogenization pump 45. In this way, it is possible to adjust the flow rate Vn of the homogenizing pump 45 as a function of the metering flow V _D removed by the metering pumps 35, 36, 37. Optimal process control is thus possible: The reactive mixture A is circulated through the static mixer system only as often in the homogenization cycle as is necessary in order to produce a perfect, ie homogeneous and stable polyester-pentane additive emulsion. Otherwise, namely, at low flow rates removed from the metering pumps 35, 36, 37, the reactive mixture A would be circulated too frequently, thereby unnecessarily wasting much pump energy and, in addition, introducing too much heat energy into the system, which would subsequently have to be dissipated costly again.

In this particular embodiment of the device according to the invention, further pulse lines lead from the control unit 46 to the valves 47 and 48.

Working the metering pumps 35, 36, 37 in the upper region, ie V _D is about 70% to 100% of the maximum amount, so valve 47 and valve 48 are opened and the corresponding maximum flow Vn of the homogenization pump 45 flows essentially through the large static mixer ie via static mixer 49A.

If the metering pumps 35, 36, 37 work in the middle range, ie V _D is about 35% to 70% of the maximum quantity, then valve 47 is closed as shown in the example, while valve 48 remains open.

Now the corresponding, i. the average flow Vn of the homogenizing pump 45 is first passed through the large static mixer, i. via static mixer 49A, and then substantially via the middle static mixer, i. via static mixer 49B.

If the dosing pumps 35, 36, 37 work in the lower region, ie V _D is about 10% to 35% of the maximum quantity, then valve 47 and valve 48 are closed.

Now, the corresponding, minimum flow Vn of the homogenization pump 45 flows over all now in series static mixers 49A, 49B, 49C.

This special arrangement of the static mixer has the advantage that not only over the entire volume range optimal mixing is ensured, but that always all three Static mixers are flushed through and no nests with too old material form, which would be the case if the three static mixer and the associated valves would be just arranged in parallel.

FIG. 3 shows schematically a further embodiment variant of the device according to the invention. Also in this example, insulating elements for thermal insulation (not shown in the diagram) are produced by means of a Contimaten 60.

While in the example shown in FIG. 2 the distribution of the PIR reactive mixture over the entire bandwidth takes place by means of three stationary mixing heads, in the example shown in FIG. 3 the mixture distribution over the entire bandwidth is achieved by means of a special distributor 61, which is a single distributor Mixing head 62 is connected downstream, so that only one metering pump 63, 64 and one arranged in the associated pressure line heat exchanger 65, 66 are required in this Ausflihrungs example for the two reactive components.

The metering pump 64 of the reactive component B (isocyanate) is supplied from the tank 67 via the suction line.

The reactive mixture A consists in these embodiments of polyester polyol, pentane and PIR foam specific additives, pentane and additives of associated containers and dosing (not shown in the diagram) are conveyed via an injection block 68 to a stirred premixer 69 and mixed there.

Also in this example, the exact dosage of the polyester polyol via the metering pump 63 for the reactive mixture A, in turn, an associated tank 70 and a charge pump 71 and a biasing valve 72 ensure the necessary supply of throughput and to form.

In the suction line between recirculation of the charge pump 71 and the suction side of the metering pump 63, in turn, a gas loading device 73 for the Eindispergierung of nitrogen and a heat exchanger 74 are arranged. Parallel to the interference path, i. In this example, parallel to the injection block 68 and the stirred pre-mixer 69 for the pentane and the additives in the polyester polyol, a homogenization circuit with adjustable homogenizing pump 75 is arranged.

The novelty in this embodiment with respect to the example shown in Figure 2 is that the adjustable homogenization pump 75 is associated with a combination of a control and a control unit 76. The control component is that in turn by means of pulse lines from the metering pump 63 to the control unit 76 and from the control unit 76 to the homogenizing 76 the flow rate V _{H of} the homogenization pump 75 in response to the dosing flow V _{D of} the metering pump 63 is adjusted.

The control component consists in the fact that a further impulse line leads from a homogenizing circuit downstream of the homogenization cycle to the combined control and regulating unit 76, so that the flow Vn of the homogenizing pump 75 is adjusted not only as a function of the metering flow V _D but virtually as Fine adjustment depending on θ is also regulated. The control process and the control process are completely separated from each other and never at the same time.

First, the adjustment of the flow rate V _{H of} the homogenization pump 75 by the controller in response to the dosing flow V _D ■ Subsequently, the controller is switched off and the control of V _H in response to θ takes over. Likewise, the control is turned off when a control operation is again performed.

Claims

claims A process for the preparation of insulating elements comprising a layer of polyurethane or polyisocyanurate foam, wherein a) a halogen-free blowing agent in at least one premixer (49 A, 49B, 49C, 69) in a first reactive component A, containing at least one polyether or polyester polyol, is mixed and / or mixed into a second reactive component B, containing at least one isocyanate will, and b) then the first reactive component A with the second reactive component B in at least one mixing head (31, 32, 33, 62) is mixed, wherein a Reactive mixture is obtained, and c) the reactive mixture from step b) is discharged from the at least one mixing head and applied to a substrate, on which it reacts out and hardens, characterized in that d) the interference of the halogen-free blowing agent in the first reactive component A and / or in the second reactive component B in step a) is carried out such that the reactive component and the halogen-free blowing agent are introduced into the premixer, and the reactive component and the halogen-free blowing agent are mixed in the premixer and discharged as a mixture stream, and separated from the mixture stream of reactive component and halogen-free blowing agent, a partial stream and with a Homogenizing pump (45, 75) is fed back into the pre-mixer, and the rest Partial flow with at least one metering pump (35, 36, 37, 63) with the metering ^ D to the at least one mixing head is conveyed, wherein the flow rate ^ H of the Homogenizing pump in response to the dosing flow 'D is set at least one metering pump. 2. The method according to claim 1, characterized in that the mixture flow of reactive component and halogen-free propellant through the homogenizer one to twenty times, preferably two to ten times, more preferably two to five times circulated. 3. The method according to claim 1 or 2, characterized in that the delivery stream V _{H of} the homogenization pump by means of a corresponding control unit (46, 76) is adjusted. 4. The method according to claim 3, characterized in that the control of the flow rate V _{H of} the homogenization pump, which takes place in dependence on the metering flow V _{D of} the at least one metering pump, a control is followed, in which the temperature of the flowing to the at least one mixing head Emulsion of polyol or isocyanate component and halogen-free blowing agent is used as a controlled variable. 5. A device for the production of insulating elements for thermal insulation comprising a layer of polyurethane or polyisocyanurate foam, comprising: a) containers (30, 40, 67, 70) for the provision of the reactive components A and B, b) at least one mixing head (31, 32, 33, 62) for mixing the reactive components A and B, and for discharging the reactive mixture onto a substrate (34), c) at least one metering pump (35, 36, 37, 63) for the metering of the reactive component A to the mixing head, d) at least one metering pump (64) for metering the reactive component B to the mixing head, e) connecting lines from the containers to the metering pumps and from the metering pumps to the mixing head, characterized in that it further contains f) at least one premixer (49A, 49B, 49C, 69) for mixing the reactive component A or the reactive component B with a halogen-free blowing agent, g) a pre-mixer circuit upstream charge pump (41, 71) for the promotion of the reactive component A or the reactive component B in the circulation and for pressure generation and a biasing valve (42, 72) through which a partial flow of the funded by the charge pump in the circulation reactive component A or reactive component B is discharged, h) a connecting line between the premixer and the circuit comprising charge pump and biasing valve, and i) a return line from the exit from the premixer back to the entrance to the premixer containing an adjustable homogenization pump (45, 75), and j) a control unit (46, 76) with impulse lines from the at least one corresponding metering pump (35, 36, 37, 63) to the control unit (46, 76) and from the control unit (46, 76) to the adjustable homogenization pump (45, 75). 6. Apparatus according to claim 5, characterized in that the control unit is combined with a control unit and that in the connecting line between the premixer and the mixing head, a temperature measuring point (θ) is arranged, of the one Pulse line leads to this control unit. 7. Apparatus according to claim 5 or 6, characterized in that both suction and pressure side of the metering pumps (35, 36, 37, 63, 64) heat exchangers are arranged. 8. Device according to one of claims 5 to 7, characterized in that arranged on the suction side of the metering pumps gassing. 9. Device according to one of claims 5 to 8, characterized in that the at least one premixer contains at least one static mixer or a stirrer mixer or a rotor-stator mixer or combinations of such mixer. 10. The device according to claim 9, characterized in that these two or more stages are executed when using static mixers.