Sandwich structure including a VIP and method for producing the same

Abstract

The present invention relates to a process for the production of composite elements comprising a first and a second outer layer, a vacuum insulation panel between the two outer layers, rigid polyurethane foam in contact with the first outer layer and the underside of the vacuum insulation panel, and also rigid polyurethane foam in contact with the second outer layer and the upper side of the vacuum insulation panel, comprising application of a reaction mixture (R1) for the production of a rigid polyurethane foam onto the first outer layer, bringing the lower side of a vacuum insulation panel into contact with the unhardened reaction mixture (R1), application of a reaction mixture (R2) for the production of a rigid polyurethane foam to the upper side of the vacuum insulation panel, bringing the second outer layer into contact with the layer of the unhardened reaction mixture (R2), and finally hardening of the two rigid polyurethane foam systems (R1) and (R2) to give the composite element. The present invention further relates to composite elements thus obtainable, and also to the use of a composite element of the invention or of a composite element obtainable by a process of the invention, as component for refrigeration equipment or as construction material.

Claims

1. A process for production of composite elements comprising a first and a second outer layer, a vacuum insulation panel between the first and second outer layers, rigid polyurethane foam in contact with the first outer layer and an underside of the vacuum insulation panel, and also rigid polyurethane foam in contact with the second outer layer and an upper side of the vacuum insulation panel, comprising the following steps: (i) applying a first unhardened reaction mixture (R.sub.1) for the production of a rigid polyurethane foam onto the first outer layer, (ii) bringing the underside of a vacuum insulation panel into contact with the first unhardened reaction mixture (R.sub.1), (iii) applying a second unhardened reaction mixture (R.sub.2) for the production of a rigid polyurethane foam to the upper side of the vacuum insulation panel, (iv) bringing the second outer layer into contact with the layer of the second unhardened reaction mixture (R.sub.2), (v) hardening of the first and second unhardened reaction mixtures (R.sub.1) and (R.sub.2) to give the composite element, wherein the first and second unhardened reaction mixtures (R.sub.1) and (R.sub.2) comprise the following components: A) at least one polvisocyanate, B) at least one polyfunctional compound reactive toward isocyanates, C) at least one blowing agent, D) at least one catalyst, E) optionally foam stabilizers and F) optionally further auxiliaries and/or additional substances, wherein the composition of the first unhardened reaction mixture (R.sub.1) and of the second unhardened reaction mixture (R.sub.2) differ in relation to at least one of the components B) to F).

2. The process according to claim 1, wherein the second unhardened reaction mixture (R.sub.2) is applied while the first unhardened reaction mixture (R.sub.1) is unhardened.

3. The process according to claim 1, wherein components A) to F) are selected to give a closed-cell polyurethane foam with free-foamed envelope density in accordance with DIN 53420 in the range from 30 to 400 g/l and with compressive strength in accordance with DIN ISO 844 EN DE (2014-11) of greater than 140 kPa.

4. The process according to claim 1, wherein water is used as sole blowing agent C).

5. The process according to claim 4, wherein the quantity of water used, based on the total weight of components B) to F), is in the range from 0.05 to 4% by weight.

6. The process according to claim 3, wherein the free-foamed envelope density in accordance with DIN 53420 of the rigid polyurethane foam obtained from the first unhardened reaction mixture (R.sub.1) or of the rigid polyurethane foam obtained from the second unhardened reaction mixture (R.sub.2) in the composite element or of the rigid polyurethane foam obtained from the first unhardened reaction mixture (R.sub.1) and the second unhardened reaction mixture (R.sub.2) is in the range from 30 to 400 g/l.

7. The process according to claim 1, wherein component B) comprises at least one polyether polyol with functionality from 3 to 6 and with hydroxy number in the range from 300 to 500.

8. The process according to claim 1, wherein the first unhardened reaction mixture (R.sub.1) is applied into a device designed to prevent flow of the components away from a region of the first outer layer.

9. The process according to claim 8, wherein the device is a press.

10. The process according to claim 1, wherein step (v) is carried out at a temperature in the range from 35 to 80 C.

11. The process according to claim 1, wherein step (v) is carried out in a press.

12. The process according to claim 1, wherein the composite element is a refrigerator component or a sandwich element.

13. A composite element or obtained by a process according to claim 1.

14. A refrigeration equipment or construction material, comprising a composite element according to claim 13.

Description

EXAMPLES

1. Experimental Description

(1) TABLE-US-00001 TABLE 1 Details of foam systems Cream Fiber Free envelope Density of Foam time time density Compaction molding system [s] [s] [g/l] factor [g/l] R1 25 115 80 1.96 158 R2 5 50 32 1.10 35 R3 6 50 80 1.20 96 A plastics inliner is first inserted into a mold. The first reaction mixture (R1) for the production of a polyurethane foam is then applied to the first outer layer. The quantity of R1 introduced here was sufficient to fill a volume of 12 l and to obtain a density of 158 g/l of the molding with foam thickness about 5 mm. Immediately after introduction of R1 ends (introduction time T.sub.E1, see table 2), a silica VIP measuring 1300560015 mm is brought into contact with the reaction mixture R1, which has not yet reached its fiber time. At the juncture T.sub.S, as stated in table 2, a second reaction mixture (R2 or R3) is introduced, the quantity introduced here being sufficient to fill a volume of 71 l. Immediately after introduction of the second reaction mixture ends (introduction time T.sub.E2 or T.sub.E3, see table 2), a metal outer layer is superposed, and the mold is closed. Mold temperature during the entire experiment was 43 C. toward the bottom and 41 C. toward the top. After 20 min, the mold is opened, the component is removed, and the quality of the surface is evaluated optically. Where the component is evaluated optically as good, this means that the quality of the surface is high.

(2) TABLE-US-00002 TABLE 2 Experimental details Inventive Inventive Comparative example 1 example 2 example First foam system R1 R1 R1 Introduction time T.sub.E1 6 6 6 [in s] Second foam system R2 R3 R2 Juncture at which 42 44 85 second foam system is introduced T.sub.S [in s] Introduction time T.sub.E2 6 6 [in s] Introduction time T.sub.E3 10 [in s] Optical evaluation of + + component

2. Results

(3) In inventive examples 1 and 2, the second foam system (R2 or R3) is introduced at the juncture T.sub.S (42 s or 44 s). The fiber time of R2 and R3 is 50 s. The sum of fiber time of second foam system (R2 or R3) and introduction time T.sub.S is therefore in both cases smaller than the fiber time of R1 (115 s, see table 1). A composite element was obtained which in optical evaluation revealed no defects. In the comparative example, R2 is introduced at the juncture T.sub.S=85 s. The fiber time of R2 is 50 s. The sum of fiber time of R2 and introduction time T.sub.S is therefore 135 s. This is 20 s longer than the fiber time of R1 (115 s, see table 1). A composite element with defects, and therefore poor surfaces, was obtained.

3. Definitions

3.1 Cream Time [s]

(4) The cream time is defined as interval between start of stirring or start of shot and the beginning of volume expansion of the reaction mixture due to formation of foam.

3.2 Fiber Time [s]

(5) The time from the start of mixing to the juncture during progress of the reaction at which fibers can be drawn by a glass rod from the foam composition.

3.3 Full Rise Time [s]

(6) The full rise time is defined as interval between start of stirring and the end of volume expansion. It is determined by observing the height to which the top of the foam rises.