The Eastern Company Notes to Consolidated Financial Statements (continued) 5. INTANGIBLES Trademarks are not amortized as their lives are deemed to be indefinite. Total amortization expense for each of the next five years is estimated to be as follows: 2020 - $4,082,000; 2021 - $4,062,000; 2022 - $4,055,000; 2023 - $4,055,000 and 2024 - $3,372,000. 42 Industrial Hardware Segment Security Products Segment Metal Products Segment Total Weighted- Average Amortization Period (Years) 2019 Gross Amount Patents and developed technology $ 5,375,680 $ 1,618,950 $ — $ 6,994,630 10.2 Customer relationships 22,899,000 1,139,381 — 24,038,381  9.6 Non-compete agreements 12,000 459,570 — 471,570 1.9 Intellectual property — 307,370 — 307,370 2.0 Total Gross Intangibles $ 28,286,680 $ 3,525,271 $ — $ 31,811,951  9.5 2019 Accumulated Amortization Patents and developed technology $ 1,505,097 $ 789,056 $ — $ 2,294,153 Customer relationships 1,751,225 581,262 — 2,332,487 Non-compete agreements 800 417,032 — 417,832 Intellectual property — 307,369 — 307,369 Accumulated Amortization $ 3,257,122 $ 2,094,719 $ — $ 5,351,841 Net 2019 per Balance Sheet $ 25,029,558 $ 1,430,552 $ — $ 26,460,110 2018 Gross Amount Patents and developed technology $ 7,884,498 $ 1,648,731 $ — $ 9,533,229 10.2 Customer relationships 3,650,000 1,139,381 — 4,789,381 8.1 Non-compete agreements — 459,570 — 459,570 4.4 Intellectual property — 307,370 — 307,370 5.0 Total Gross Intangibles $ 11,534,498 $ 3,555,052 $ — $ 15,089,550  9.2 2018 Accumulated Amortization Patents and developed technology $ 2,448,380 $ 737,276 $ — $ 3,185,656 Customer relationships 638,750 408,233 — 1,046,983 Non-compete agreements — 329,296 — 329,296 Intellectual property — 245,895 — 245,895 Accumulated Amortization $ 3,087,130 $ 1,720,700 $ — $ 4,807,830 Net 2018 per Balance Sheet $ 8,447,368 $ 1,834,352 $ — $ 10,281,720