Does "Zihar" occur when a man says to his wife, "You are to me as the back of my mother," if he intends prohibition (of sexual intimacy) and not divorce, especially when there is a need to go to the market?

Your statement to your wife: "You are to me as the back of my mother if you go to the market" is considered a suspended ẓihār. If the wife does not go to the market, then nothing is incumbent upon you. However, if she does go, then the expiation for ẓihār becomes obligatory upon you, even if your intention was to prevent her and not to divorce. The occurrence of the suspended ẓihār depends on the fulfillment of the condition, and the expiation for ẓihār is obligatory before conjugal relations with the wife.