why getting white patch export the file

Having issue with exporting. I have golden galaxy with black background. Added screen effect with 0 transparency which make the black background disappear. When i tried to export in Tiff CMYK file. why there is off white patch seen. Same i tried with RGB jpg there is no white patch seen. For offset printing i need CMYK Tiff file. I can convert RGB and CMYK but why there is issue with the cmyk. Any suggestion or help. Thanks