how to limit the rotation of a gameobject in unity 2d code example
Example: 2d rotation unity
// Rotation scripting with Euler angles correctly.
// Store the Euler angle in a class variable, and only use it to
// apply it as a Euler angle, but never rely on reading the Euler back.
float x;
void Update ()
{
x += Time.deltaTime * 10;
transform.rotation = Quaternion.Euler(x,0,0);
}