US3748684A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Blackboard eraser
Assignee: Individual
•
Filing: 1971-12-09
•
Granted: 1973-07-31
•
Expires: 1991-12-09
Abstract
Abstract An eraser for removing chalk marks from blackboards, consisting of a block of non-reticulated, flexible, polyester urethane foam having inter-connected air cells and from about 70 to about 100 pores per linear inch, the block being supported by a channelshaped holder.
Inventors
- 👤 R Fraser
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-04 07:22
CPC Classifications
B; B43; B43L; B43L21/00
Claims Analysis
Total Claims: 4
Claim 1
Independent Claim
45 words
A chalk eraser as claimed in claim 1, in which the said block has a rectangular cross-section of which the width is approximately twice the depth, the channel-shaped holder spanning the width and the depending side walls reaching part-way down the depth of the block.
Claim 2
Dependent Claim
23 words
A chalk eraser as claimed in claim 1, in which the polyester urethane foam has between 75 and 85 pores per linear inch.
Claim 3
Dependent Claim
22 words
A chalk eraser as claimed in claim 1, in which the block of polyester urethane foam is glued within the channel-shaped holder.
Claim 4
Dependent Claim
39 words
A chalk eraser as claimed in claim 2, in which the depth of said block is between 1 1/2 inches and 2 inches, thereby enabling the block to absorb and retain chalk from several day''s use before necessitating cleaning.
References Cited (Backward Citations)
US2249912A
Cited
FR1115369A
Cited
US3081479A
Cited
US3377643A
Cited
US3262145A
Cited
US3257679A
Cited
US3447181A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1976-07-30 | 1977-01-29 | 1977-07-31 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1980-07-30 | 1981-01-29 | 1981-07-31 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1984-07-30 | 1985-01-29 | 1985-07-31 | $7700.00 | Window Closed / Lapsed |