An industrial loan company that has investment certificates outstanding shall not make any loan secured primarily by improved real property in a principal amount in excess of 20 percent of the company’s unimpaired capital stock and surplus not available for dividends as provided in Section 18319. An industrial loan company that has investment certificates outstanding shall not make any loan secured primarily by unimproved real property in a principal amount in excess of 10 percent of the company’s unimpaired capital stock and surplus not available for dividends as provided in Section 18319.