Abstract: A film material according to the present disclosure includes an amorphous polymer (A) including a reversible bond which is reversibly dissociated and recombined in response to a temperature change. The polymer (A) has a glass transition temperature of higher than or equal to 40° C. The polymer (A) has a storage elastic modulus of greater than or equal to 0.2 MPa at a temperature higher than the glass transition temperature by 100° C. and a storage elastic modulus of less than or equal to 100 MPa at a temperature higher than the glass transition temperature by 50° C.

Abstract: A rock drill having a hydraulic system for controlling striking, rotating and advancing movements of a drilling rod. The advancing or forward feeding conduit for a feed actuator is provided with a relief valve which is responsive to the pressure in the positive rotating conduit for a rotary actuator so that the pressure in the forward feeding conduit is relieved to weaken the advancing force when the load on the rotary actuator is increased. A further relief valve is also provided for relieving the pressure in the striker conduit to weaken the striking force.