CPC technology class · D21

D21C - Production Of Cellulose By Removing Non-cellulose Substan…

Production of cellulose by removing non-cellulose substances from cellulose-containing materials; regeneration of pulping liquors; apparatus therefor. 1,427 US utility patents granted 2015–2025, with the leading assignees and year-by-year grant trajectory.

Compiled by PlainPatent · May 15, 2026

1,427
US patents granted: #2/7
in D21: 17.5%
D21 class share: -9%
5-yr velocity

The verdict

According to USPTO PatentsView, Production Of Cellulose By Removing Non-cellulose Substan… ranks #413 of 670 CPC technology areas - 1,427 US patents granted since 2015, with recorded grant volume down 9% over five years.

#413
of 670 CPC technology areas: 1,427
US patents granted, 2015–2025: Valmet Ab
leading assignee (58): -9%
grant velocity, last 5 yrs

How D21C's grant cadence moved

Between 2020–2024, D21C recorded 596 grants versus 658 in 2015–2019 (-9% equal-window velocity). Across complete years, output peaked in 2021 at 136 grants and bottomed in 2023 at 99 (+37% peak-over-trough). Lead assignee Valmet AB holds 4.1% of the class ; the top three share 10.2%.

Leaderboard read

D21C concentration, lead at 4.1%

Valmet AB leads this historical grant record at 4.1% of D21C - foreign corporation assignees hold 61% of class grants (540 of 884). Figures describe granted US utility patents in this CPC subclass, not current investment or legal strength.

Leader's share: 4.1%
Top three share: 10.2%
Lead over #2: 11

Where D21C sits inside D21

Among 7 subclasses in D21 (PAPER-MAKING; Production OF Cellulose), D21C ranks #2 and holds 17.5% of the parent class's 8,169 recorded grants. Sibling chips below are the other subclasses in the same parent class, not the nationwide volume/lead-share peers further down.

D21H 4,080 D21F 1,255 D21B 452 D21G 371 D21D 314 D21J 270

Rising assignees active in D21C

Company-wide grant multiples (2022–2024 vs 2019–2021) among assignees with ≥5 patents in this subclass. Growth is company-wide; class patent counts are subclass-specific.

#1 Sixring Inc. 14x 0 → 14 company-wide · 23 in D21C
#2 Qilu University of Technology 12x 2 → 23 company-wide · 6 in D21C
#3 Borregaard AS 10x 1 → 10 company-wide · 5 in D21C
#4 FPInnovations 2.00x 4 → 8 company-wide · 9 in D21C
#5 Inbicon A/S 2.00x 1 → 2 company-wide · 7 in D21C

D21C grants by year, peak 2021 (136)

US utility-patent grants per year in D21C, 2015–2025 - recent five years are down 9% versus 2015–2019.

Valmet Ab

58
Xyleco

47
Andritz

40
Gp Cellulose

33
International Paper

31
Upm-kymmene

31
Stora Enso Oyj

30
Andritz Oy

29
Unicharm

25
Shell Oil Compny

23
Sixring

23
Kemira Oyj

20

What this shows Valmet Ab is the most active filer in D21C, holding 58 of the 1,427 patents in this class. Concentration at the top signals how contestable this technology area is for new entrants.

View data table

Top patent holders in CPC subclass D21C
Rank	Company	Patents in D21C
#1	Valmet AB	58
#2	Xyleco, Inc.	47
#3	Andritz Inc.	40
#4	GP Cellulose GmbH	33
#5	International Paper Company	31
#6	Upm-kymmene Corporation	31
#7	Stora Enso OYJ	30
#8	Andritz OY	29
#9	Unicharm Corporation	25
#10	Shell OIL Compny	23
#11	Sixring Inc.	23
#12	Kemira OYJ	20
#13	Granbio Intellectual Property Holdings, LLC	20
#14	Fiberlean Technologies Limited	17
#15	Virdia, LLC	17
#16	Nippon Paper Industries Co., Ltd.	16
#17	Valmet Technologies Oy	16
#18	Solenis Technologies, L.P.	14
#19	Lenzing Aktiengesellschaft	11
#20	API Intellectual Property Holdings, LLC	11

Footprint here vs. claim strategy

Each dot is a leading D21C assignee, placed by how many patents it holds in this class (horizontal) against its company-wide average claims per patent (vertical) - a read on whether the class is led by broad-but-shallow filers or focused deep-claim players.

Top 14 D21C assignees by class footprint. Bubble size = patents in D21C. Source: USPTO PatentsView (claim depth is company-wide across all classes).

Classes near D21C's 1,427-grant footprint

Nationwide nearest neighbors for D21C (#413 of 670 by volume ; lead share 4.1%) - not the D21 parent-class siblings above.

Nearest by grant volume

B65F 1,429 B07B 1,431 G04F 1,418 D02G 1,439

Nearest by lead-assignee share

F04D 4.0% B44F 4.0% E04F 4.1% G08C 4.1%

Questions about D21C

Which company holds the most patents in D21C?

Valmet AB leads D21C with 58 patents (4.1% of the subclass). By PatentsView assignee type, foreign corporations account for 61% of class grants.

Which D21C assignees grew fastest recently?

Among assignees with ≥5 grants in D21C, Sixring Inc. shows the highest company-wide grant multiple (14x: 0 grants in 2019–2021 → 14 in 2022–2024) while holding 23 patents in this subclass. Growth is company-wide, not class-only.

How does D21C compare inside parent class D21?

Inside D21 (PAPER-MAKING; Production OF Cellulose), D21C ranks #2 of 7 subclasses by grant volume and holds 17.5% of the parent class total. The largest sibling is D21H (4,080 grants).

What to do with this data

D21C in context - here's where to go next.

Valmet AB leads D21C with 58 grants in this class. See full portfolio
D21C ranks #413 of 670 by grant volume among all tracked CPC technology areas. See the ranking
Inside parent class D21, the largest sibling subclass is D21H with 4,080 grants. Explore D21H

Figures reflect USPTO PatentsView grant data through 2026-05-15; pending applications not yet granted are not counted.

Methodology - D21C figures are USPTO PatentsView granted-utility totals for this subclass (1,427 grants in the tracked window).

Every figure on PlainPatent is rendered directly from USPTO source data, no number is typed in by an editor. This page draws directly on USPTO source data, no figure is typed in by an editor. See our editorial standards & corrections policy, the methodology behind these numbers, or report a data error.