By putting the comp into another way larger comp and scaling it up... the content gets pixalated. Despite the fact that there isn`t footage (videos or pictures) used.
Yes, you are scaling the result, not the source. No way around it. Such stuff needs to be adjusted. There is no continuous rasterization for this sort of thing.
The layers with masks, shape layers, vector layers (.ai files) will scale if you continuously rasterize as long as you haven't applied an effect to the layer that generates it's own pixels the way Particular does. Continuous Rasterization must be turned on in both compositions. If you have CR turned on in your Particular layer both comps then the Particular effect will now react to the pre-comp's scale transformation. I hope you understood that. If not, just throw the CR switch in both the main comp and the pre-comp and you'll see what I mean.
Right, but by switching on both the particular effect seems to be scaled down. The effects aren`t transfered correctly
That's what I was trying to say. Particular, and several other effects, generate the pixels rather than modifying existing ones. Those kind of effects will not scale when you continuously rasterize. They revert to their original size. Turn off CR and you scale the generated pixels.
If you want to resize your project and have things work out go to File>Scripts>Scale Composition and set a new comp width. Everything should be fine.