Appeal No. 1998-2077
Application 08/553,324
two oxygen stages after one another at the beginning of a bleaching sequence[,] . . . after an initial
oxygen treatment, it is difficult to use a repeated oxygen treatment to remove such amounts of lignin [sic]
that the high investment costs for such a stage are justified,” and that “a
first step with only a complexing agent being added under neutral conditions results in a considerable
reduction principally of the metals most detrimental to the decompositions of hydrogen peroxide” (col. 5,
lines 4-45). Lundgren also states that “in a bleaching process, the aim is a low kappa number, which
means a low content of undissolved lignin, and a high brightness of the pulp” (col. 5, lines 59-62).
I find that Lindberg also recognizes the problem that transition metal ions affect Z and P stages
and discloses a method to remove such metals from treatment fluids, the two steps of interest here being
“(a) [t]reating digested pulp in an acidic or neutral stage to dissolve transition metals” and “(b) [w]ashing
the pulp after step (a) to produce a filtrate containing dissolved transition metals” (e.g., col. 1, lines 7-20,
and col. 2, lines 14-17). The reference discloses that “[s]tep (a) may be an ozone stage, or a chelation
stage (such as an EDTA stage, an acid only stage, or a combination EDTA and acid stage)” (col. 2, lines
28-30), which would have taught one of ordinary skill in this art that the “an ozone stage” will dissolve
transition metals in the pulp and that the chelating agent EDTA can be used in acid or neutral conditions.
The position of the “step (a)” Z stage or Q stage in the process is shown by the disclosure that “[a]fter5
[wash] step (b) the pulp may be further treated in at least one Z bleach stage [sic] at least one P bleach
stage, and also preferably in at least one E stage” (col. 2, lines 30-33; see above note 1). Such a
sequence is shown in Lindberg FIG. 1 where QPZP has a washing step between each of the stages (col.
3, line 45, to col. 4, line 35). Lindberg discloses that “[a] number of modification may be made to the
bleaching sequence,” and provides such examples as ZEZP and QZEZP, that is, either a Z or a Q stage
is the initial stage following oxygen delignification, further stating that
“a wide variety of other bleaching sequences may be utilized” (col. 4, lines 4-10). Lindberg further
discloses that the method thereof can be used with “any (or more than one) acidic stages, such as shown
at 31´ in FIG. 1 (there associated with a Z stage)” (col. 4, lines 32-34; see also col. 6, lines 4-6). I find
that one of ordinary skill in this art would have readily distinguished the acidic Z bleach stage at a later
point in the process of Lindberg from the acidic Z stage or “ozone stage” disclosed to dissolve metal ions
from digested pulp in the initial stage or “step (a)” of the bleaching sequence, even though this person
For consistency, I refer to “T” in Lindberg as “Q” (see above note 1).
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