The ornamental design for a protectivecardboardcorner, as shown and described.
FIG. 1 is a perspective view of a protective cardboard corner showing our design.
FIG. 2 is a rear view of the protective cardboard corner of FIG. 1.
FIG. 3 is a front view of the protective cardboard corner of FIG. 1.
FIG. 4 is a right-side view of the protective cardboard corner of FIG. 1.
FIG. 5 is a left-side view of the protective cardboard corner of FIG. 1.
FIG. 6 is a top view of the protective cardboard corner of FIG. 1; and,
FIG. 7 is a view showing the underside of the protective cardboard corner of FIG. 1.
The protective cardboard corner is shown with a symbolic break in its length. The jagged break lines and the appearance of any portion of the article between the jagged break lines forms no part of the claimed design.