Why do you want to use the Lazer printer to print negatives for exposure? You can make great boards, including doublesided using the lazer printed page itself as the etch resist. I have done it for long time, with excellent results. All you need is "Coated paper" i.e. for high resolution printing, some acetone and your etch, ferric chloride or hydrogen peroxide. Reason for coated paper is simple. It allows for better release of the toner on your copper board.
To use: Print your artwork. 600dpi resolution is more than enough.
For bottom copper no need to mirror artwork. For Top copper must mirror artwork. Clean Copper board with steelwool and rinse and dry. Take artwork placing printed surface face down on copper. Take some cotton wool and wet with acetone. Rub on back of printed artwork. Let acetone evaporate from the paper. Place board with printed artwork now stuck to board in warm water for some minutes. Peel of the paper and ther is your board ready for etching.
Reason for the acetone and not hot iron on, if you transfer the artwork with a hot clothes iron (Melting the toner onto the copper) the copper board expands with heat under the iron and leads to inconsistency especially if you make doublesided boards!
Whacko.