To answer this question, you first need to know what an IP69K package is.
The (IEC) developed its IEC 60529 rating system to define different degrees of protection (i.e., ingress protection (IP)) for enclosures. The most recent version is IEC 60529:1989+AMD1:1999+AMD2:2013 CSV, Consolidated version, Degrees of protection provided by enclosures (IP Code). It costs hundreds of dollars.
The National Electrical Manufacturers Association (NEMA) based its American National Standard for Degrees of Protection Provided by Enclosures (IP Code) (Identical National Adoption) (ANSI/IEC 60529-2004 – NEMA) on IEC 60529. It also costs hundreds of dollars.
Fortunately, several websites (including Wikipedia) explain the meaning of different IP codes,
The first digit of the IP rating indicates the sensor’s or other enclosure’s protection level against solids entering it. A 0 means no protection and a 6 indicates that the sensor is completely dust tight. Table 1 summarizes the different levels.
Table 1. IEC 60529 First Digit Decoder for Dust Protection Level
The second digit of the IP rating indicates the sensor’s water protection rating. Again, a 0 means no protection. Table 2 shows the key to understanding the second digit in the IEC rating.
Table 2. IEC 60529 Second Digit Decoder for Water Protection Level
In the IEC 60529 rating system, the highest rating a sensor can achieve is IP69K. Applications that require washdown, such as food processing, and those with harsh duty, such as off road vehicles that need frequent cleanings most likely require IP69K capability. This rating is frequently found in photoelectric sensors, proximity/position sensors. Suppliers who offer IP69K rated sensors and users who specify these types of sensors usually have a good understanding of the application requirements and need for this rating.