Method for characterizing hiding of coating compositions and apparatus used therefor

A method of characterizing hiding of a coating composition, said method comprising:

• (i) applying a monotonic layer of said coating composition over a test pattern affixed to a hiding test panel to produce a monotonic coating thereon;
• (ii) sequentially uniformly illuminating target areas P1 to Pn of said monotonic coating, each said target area comprising a light portion and a dark portion;
• (iii) sequentially directing reflections of said target areas P1 to Pn to a photosensitive device for acquiring:
• (a) intensities lr1 to lrn, lg1 to lgn and lb1 to lbn of said light portions of said areas P1 to Pn, and
• (b) intensities dr1 to drn, dg1 to dgn and db1 to dbn of said dark portions said areas P1 to Pn;
• (iv) sequentially measuring applied measured thicknesses X1 to Xn of said monotonic coating at locations that respectively correspond to said target areas P1 to Pn;
• (v) sequentially computing measured Y1 to Yn at said target areas P1 to Pn by using the formula:
• [(lri−dri)2+(lgi−dgi)2+(lbi−dbi)2]0.5 (1)
• wherein i ranges from 1 to n, and said measured Y1 to Yn are measured ΔRGBs;
• (vi) storing on a computing device hiding data comprising said measured Y1 to Yn and said applied thicknesses X1 to Xn;
• (vii) determining a threshold measured Yth by using the formula:
• measured Yth=Loge(measured Ymax), (2)
• said measured Ymax being the maximum value within the range of said measured Y1 to Yn;
• (viii) sequentially comparing said measured Y1 through Yn to identify first measured Yq that is less than measured Yth wherein q falls within said range 1 to n;
• (ix) computing a ratio (q/n) to classify said hiding data, wherein said is classified as:
• (i) type 1 hiding data when said ratio is in the range of 0.01 to less than 0.25,
• (j) type 2 hiding data when said ratio is in the range of 0.25 to less 0.35,
• (k) type 3 hiding data when said ratio is in the range of 0.35 to less 0.50, or
• (l) type 4 hiding data when said ratio is in the range of 0.50 to 1.00;
• (x) selecting one or more fitting equations applicable for said type 1 hiding data, type 2 hiding data, type 3 hiding data or type 4 hiding data, wherein said fitting equations define a relationship between (y) and (x), said (y) being a fitted color difference that corresponds to said (x), which is a fitted thickness on a fitted curve generated by said one or more fitting equations;
• (xi) fitting said one or more selected fitting equations to match paired measured (X1, Y1) to paired measured (Xn, Yn), wherein said fitted curve has a fitted baseline value of yb at an asymptote of said fitted curve;
• (xii) selecting a fitted threshold value yth above said fitted baseline value yb, wherein said fitted threshold value yth is suited for said type 1 hiding data, type 2 hiding data, type 3 hiding data or type 4 hiding data;
• and
• (xiii) locating a hiding thickness xh of said coating composition that corresponds to said fitted threshold value yth on said fitted curve.