Auto-retractable safety blood collection needle

An auto-retractable safety blood collection needle, comprising:

• a needle holder comprising a first tube, a second tube and a holder tail connected in sequence;
• a needle;
• a built-in sliding sleeve which is elongated and has a C-shaped cross section;
• a needle shield which is hollow and elongated;
• and
• a spring;
• wherein a diameter of the second tube is larger than a diameter of the first tube;
• a rear of the needle is mounted in the first tube;
• the first tube and the second tube both are installed in the built-in sliding sleeve;
• a built-in slider is provided on a peripheral surface of the second tube, and the second tube matches with the built-in slider to allow the second tube to slide back and forth;
• a holder tail of the needle holder is located outside a rear of the built-in sliding sleeve which is mounted in the needle shield and is capable of sliding back and forth;
• the holder tail is allowed to be locked at or unlocked from a rear of the needle shield;
• the spring is sheathed on the first tube;
• a front end of the spring abuts against an inner wall of the needle shield, and a rear of the spring abuts against a front end of the second tube;
• a first locking mechanism is provided between the needle holder and the built-in sliding sleeve and is configured for locking the second tube with the built-in sliding sleeve;
• a second locking mechanism is provided between the built-in sliding sleeve and the needle shield and is configured for locking the built-in sliding sleeve with the needle shield;
• a third locking mechanism is provided between the holder tail and the needle shield and is configured for locking the holder tail with the needle shield;
• when the holder tail is locked at the rear of the needle shield, the spring is in a compressed state, and a front end and the rear of the built-in sliding sleeve are respectively limited by the inner wall of the needle shield and the holder tail;
• when the holder tail is unlocked from the rear of the needle shield, the spring forces the second tube to slide rearward to a locking position of the first locking mechanism, so that the second tube is locked at the built-in sliding sleeve;
• the needle holder keeps sliding rearward, and the built-in sliding sleeve is driven to slide rearward to a locking position of the second locking mechanism, so that the built-in sliding sleeve is locked at the needle shield;
• at this time, the needle is fully covered by the needle shield, and a needle tip is not exposed.