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CPC technology class · D21

D21G - Calenders

Calenders; accessories for paper-making machines. 371 US utility patents granted 2015–2025, with the leading assignees and year-by-year filing trajectory.

371
US patents granted
D21
Parent CPC class
20
Active assignees
+20%
5-yr velocity

The verdict

Calenders ranks #568 of 670 CPC technology areas - 371 US patents granted since 2015, with filing up 20% over five years.

#568
of 670 CPC technology areas
371
US patents granted, 2015–2025
Seiko Epson
leading assignee (51)
+20%
filing velocity, last 5 yrs
Top assignee: Seiko Epson Corporation (51 patents)

CPC subclass D21G - CALENDERS; ACCESSORIES FOR PAPER-MAKING MACHINES - covers 371 US utility patents granted between 2015 and 2025 according to USPTO PatentsView records, within the broader CPC class D21 (PAPER-MAKING; PRODUCTION OF CELLULOSE). See our CPC classification guide for how the system works.

The competitive landscape in D21G is shaped by 20 distinct companies actively filing in this space. Seiko Epson Corporation leads with 51 patents, followed by GPCP IP Holdings Llc at 18 grants and International Paper Company at 14.

Filing activity in D21G is up 20% over the past five years versus 2015-2019, a sharp acceleration suggesting an emerging or fast-moving technology area. All counts come directly from USPTO PatentsView and reflect US granted utility patents only.

Is D21G innovation accelerating?

US utility-patent grants per year in D21G, 2015–2025 - recent five years are up 20% versus 2015–2019.

20253035404550 20152016201720182019202020212022202320242025 25

Who leads D21G?

The 12 most active assignees in CALENDERS; ACCESSORIES FOR PAPER-MAKING MACHINES - wider bars mean more grants

patents

What this shows Seiko Epson is the most active filer in D21G, holding 51 of the 371 patents in this class. Concentration at the top signals how contestable this technology area is for new entrants.

Source USPTO PatentsView, granted utility patents As of 2015–2025 grant years
View data table
Top patent holders in CPC subclass D21G
Rank Company Patents in D21G
#1 Voith Patent Gmbh 22
#2 GPCP IP Holdings Llc 18
#3 International Paper Company 14
#4 Valmet Technologies, Inc. 11
#5 Andritz Inc. 9
#6 Valmet Technologies Oy 9
#7 Honeywell Limited 9
#8 Brunn Air Systems, Inc. 9
#9 Stowe Woodward Licensco Llc 8
#10 Georgia-pacific Consumer Products Lp 7
#11 Valmet Automation OY 6
#12 IBS Of America 6
#13 Andritz Kuesters Gmbh 6
#14 Kadant Inc. 6
#15 Procemex Oy 6
#16 Honeywell Asca 5
#17 Industrial Video Solutions Inc. 5
#18 Valmet Aktiebolag 4
#19 Buckman Laboratories International, Inc. 3
#20 Structured I, Llc 3

About This Class

CPC subclass D21G belongs to class D21.

371 patents were granted in this class between 2015 and 2025.

20 companies actively patent in this space.

Classification System

Cooperative Patent Classification (CPC) is a hierarchical patent classification system used by the USPTO and EPO.

← All Technology Classes Technology Rankings →

Footprint here vs. claim strategy

Each dot is a leading D21G 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 D21G assignees by class footprint. Bubble size = patents in D21G. Source: USPTO PatentsView (claim depth is company-wide across all classes).

Top 14 D21G assignees by class footprint. Bubble size = patents in D21G. Source: USPTO PatentsView (claim depth is company-wide across all classes). Scatter plot of 14 data points (bubble-sized by third dimension). 10152025 510152025 Patents in D21G Avg claims / patent (company-wide) Voith PatentGpcp Ip HoldingsInternational PaperValmetAndritzValmet OyHoneywellBrunn Air SystemsStowe Woodward Licens…Georgia-pacific Consu…Valmet Automation OyIbs of AmericaAndritz KuestersKadant
Top 14 D21G assignees by class footprint. Bubble size = patents in D21G. Source: USPTO PatentsView (claim depth is company-wide across all classes).

Frequently Asked Questions

What is CPC class D21G?
CPC subclass D21G covers CALENDERS; ACCESSORIES FOR PAPER-MAKING MACHINES. It belongs to CPC class D21 (PAPER-MAKING; PRODUCTION OF CELLULOSE), with 371 US utility patents granted since 2015.
How many patents have been filed in D21G?
371 US utility patents were granted in CPC subclass D21G between 2015 and 2025, based on USPTO PatentsView data.
Which company holds the most patents in D21G?
Seiko Epson Corporation leads D21G with 51 patents, making it the most active assignee in this technology area.
How is patent data for D21G collected?
Patent data comes from USPTO PatentsView, a public research dataset maintained by the United States Patent and Trademark Office. It covers all US granted utility patents and assigns CPC codes based on the technology described in each patent.
What is the difference between CPC class and subclass?
A CPC class (e.g., D21) is a broad technology category. Subclasses like D21G provide finer granularity within that category. PlainPatent organizes data at the subclass level (4-character codes) for the most useful view of technology domains.

Read our methodology - how this data is sourced, computed, and verified.

Data sourced from USPTO PatentsView - official U.S. government patent data. See our methodology for computation details. Retrieved and formatted by PlainPatent Editorial

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.