Roll of film including multilayer birefringent reflective polarizer having low pass axis variation

A method of forming a roll of film comprising:

• providing a polymeric multilayer web including alternating layers of a layer capable of developing birefringence including polyethylene naphthalate or a copolymer including polyethylene naphthalate and polyethylene terephthalate monomers, and an isotropic layer;
• heating the polymeric multilayer web beyond the glass transition temperature of the isotropic layer;
• tentering the polymeric multilayer web to form a multilayer birefringent reflective polarizer such that the layer capable of developing birefringence develops birefringence and becomes a birefringent layer;
• after tentering, controlling the instantaneous change in machine direction tension of the multilayer birefringent reflective polarizer such that the pass axis of the multilayer birefringent reflective polarizer varies by no more than about 1.5 degrees across a full crossweb width of the multilayer birefringent reflective polarizer, and the full crossweb width is greater than 27 inches;
• and
• winding the multilayer birefringent reflective polarizer into the roll of film;
• wherein the multilayer birefringent reflective polarizer includes at least two optical packets, each optical packet including a plurality of alternating layers of a birefringent layer and an isotropic layer, the alternating layers being alternating micro-layers,
• wherein the multilayer birefringent reflective polarizer is environmentally stable such that it has a contrast ratio of at least 200:1 after the roll of film is exposed to 90% relative humidity at 65° C. for 500 hours.