CN102785376B - Polyethylene surface treatment method - Google Patents
Polyethylene surface treatment method Download PDFInfo
- Publication number
- CN102785376B CN102785376B CN201210288369.8A CN201210288369A CN102785376B CN 102785376 B CN102785376 B CN 102785376B CN 201210288369 A CN201210288369 A CN 201210288369A CN 102785376 B CN102785376 B CN 102785376B
- Authority
- CN
- China
- Prior art keywords
- surface treatment
- treatment method
- polyethylene
- polyethylene surface
- compressed air
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Fee Related
Links
- 238000000034 method Methods 0.000 title claims abstract description 65
- 229920000573 polyethylene Polymers 0.000 title claims abstract description 64
- 239000004698 Polyethylene Substances 0.000 title claims abstract description 50
- -1 Polyethylene Polymers 0.000 title claims abstract description 49
- 238000004381 surface treatment Methods 0.000 title claims abstract description 27
- 238000000576 coating method Methods 0.000 claims abstract description 48
- 239000011248 coating agent Substances 0.000 claims abstract description 45
- 229920002635 polyurethane Polymers 0.000 claims abstract description 29
- 239000004814 polyurethane Substances 0.000 claims abstract description 29
- 239000011261 inert gas Substances 0.000 claims abstract description 20
- 238000009832 plasma treatment Methods 0.000 claims abstract description 18
- 239000000463 material Substances 0.000 claims abstract description 17
- 239000007789 gas Substances 0.000 claims abstract description 15
- 239000003595 mist Substances 0.000 claims abstract description 9
- 229910000831 Steel Inorganic materials 0.000 claims description 13
- 239000010959 steel Substances 0.000 claims description 13
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 claims description 12
- 239000007788 liquid Substances 0.000 claims description 7
- 229910052786 argon Inorganic materials 0.000 claims description 6
- 239000001307 helium Substances 0.000 claims description 6
- 229910052734 helium Inorganic materials 0.000 claims description 6
- SWQJXJOGLNCZEY-UHFFFAOYSA-N helium atom Chemical compound [He] SWQJXJOGLNCZEY-UHFFFAOYSA-N 0.000 claims description 6
- 239000004576 sand Substances 0.000 claims description 5
- 239000012948 isocyanate Substances 0.000 claims description 4
- 150000002513 isocyanates Chemical class 0.000 claims description 4
- 238000007788 roughening Methods 0.000 claims description 3
- 150000003077 polyols Chemical group 0.000 claims description 2
- 239000000523 sample Substances 0.000 description 24
- 229920001903 high density polyethylene Polymers 0.000 description 12
- 239000004700 high-density polyethylene Substances 0.000 description 12
- 239000000853 adhesive Substances 0.000 description 10
- 230000001070 adhesive effect Effects 0.000 description 10
- 230000000694 effects Effects 0.000 description 9
- 238000012360 testing method Methods 0.000 description 8
- 238000005516 engineering process Methods 0.000 description 6
- 238000009864 tensile test Methods 0.000 description 5
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 description 4
- 238000005498 polishing Methods 0.000 description 3
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 3
- 244000137852 Petrea volubilis Species 0.000 description 2
- 239000010242 baoji Substances 0.000 description 2
- 230000004888 barrier function Effects 0.000 description 2
- 239000003345 natural gas Substances 0.000 description 2
- 239000003973 paint Substances 0.000 description 2
- 239000003208 petroleum Substances 0.000 description 2
- 235000009781 Myrtillocactus geometrizans Nutrition 0.000 description 1
- 240000009125 Myrtillocactus geometrizans Species 0.000 description 1
- 238000005299 abrasion Methods 0.000 description 1
- 230000006835 compression Effects 0.000 description 1
- 238000007906 compression Methods 0.000 description 1
- 230000008878 coupling Effects 0.000 description 1
- 238000010168 coupling process Methods 0.000 description 1
- 238000005859 coupling reaction Methods 0.000 description 1
- 238000007599 discharging Methods 0.000 description 1
- 238000011156 evaluation Methods 0.000 description 1
- 230000014759 maintenance of location Effects 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 229920003023 plastic Polymers 0.000 description 1
- 239000004033 plastic Substances 0.000 description 1
- 238000012545 processing Methods 0.000 description 1
- 238000003672 processing method Methods 0.000 description 1
- 230000001681 protective effect Effects 0.000 description 1
- 238000007711 solidification Methods 0.000 description 1
- 230000008023 solidification Effects 0.000 description 1
- 238000010998 test method Methods 0.000 description 1
- 238000003466 welding Methods 0.000 description 1
Landscapes
- Application Of Or Painting With Fluid Materials (AREA)
- Treatments Of Macromolecular Shaped Articles (AREA)
Abstract
The present invention relates to a kind of polyethylene surface treatment method, for improving polythene material with the adhesion between polyurethanes coating, described method comprises: before polyurethanes coating contacts polythene material, with the surface of plasma treatment technique process polythene material, the process gas wherein used in plasma treatment is the mist of compressed air or compressed air and inert gas.According to the present invention, by adopting the plasma treatment of mist as process gas of compressed air or compressed air and inert gas, can improve polythene material significantly with the adhesion between polyurethanes coating, and the bond strength after process can keep for a long time.
Description
Technical field
The present invention relates to pipeline protection and technical field of surface, more specifically, relate to a kind of polyethylene surface treatment method.
Background technology
Current oil and gas pipeline generally uses 3LPE (3 layers of polyethylene) protective system, and high density polyethylene (HDPE) covers steel pipe surface, but in coupling welding position, needs to carry out field patch.Present novel solution uses polyurethanes coating, and polyurethanes coating has good adhesion with steel pipe, but bad with poly adhesion, mainly because polyethylene surface is difficult to bonding.Therefore, need to add the technology of strength polyethylene with the adhesion between polyurethanes coating.
Sanding is comprised, the mechanical processing methods such as sand papering and wire brush polishing with the conventional polyethylene surface treatment of adhesion between polyurethanes coating at present for improving polyethylene; And flame-treating process.But after mechanical treatment, polyurethanes coating is still lower with the adhesive force between polyethylene; Although flame treatment can strengthen adhesive force after sanding, there are differences between zones of different.
Plasma surface treatment technology is the new technique for the treatment of polyethylene surface, and especially vacuum plasma surface treatment greatly can improve polyethylene with the adhesion between polyurethanes coating.Plasma discharging teclmiques at present for polyethylene surface treatment mainly comprises: vacuum plasma technology, wherein in an airtight vacuum cavity, form plasma, and the pressure in cavity is significantly less than atmospheric pressure, usual pressure is 10Pa-1000Pa; And dielectric barrier discharge type plasma technique under atmospheric environment, as corona discharge.Although vacuum plasma surface treatment effect is very good, but it is too high that shortcoming is equipment investment, and due to Oil and Natural Gas Transportation Pipeline bulky, therefore applying vacuum plasma, to carry out surface treatment feasibility to Oil and Natural Gas Transportation Pipeline polyethylene layer very poor.In addition, use atmospheric air as the atmospheric pressure plasma jet treatment technology of main technique gas, as dielectric barrier discharge type plasma under atmospheric environment, such as corona discharge, although process petroleum pipeline polyethylene layer can be applied to more easily, but effect is far inferior to vacuum plasma surface treatment, gratifying degree can not be reached.
Summary of the invention
For above-mentioned problems of the prior art, the present invention proposes a kind of newly improve polyethylene with the method for adhesion between polyurethanes coating by plasma treatment technique, wherein adopt the mist of compressed air or compressed air and inert gas as the process gas of plasma treatment, achieve the very big raising of polyethylene with adhesion between polyurethanes coating with simple, practical technological means.
Specifically, the present invention relates to a kind of for improving the polyethylene surface treatment method of polythene material with the adhesion between polyurethanes coating, described method comprises: before polyurethanes coating contacts polythene material, with the surface of plasma treatment technique process polythene material, the process gas wherein used in plasma treatment is the mist of compressed air or compressed air and inert gas.
The compressed air used in plasma treatment of the present invention is the common oil removing compressed air that dewaters.Compressed-air actuated pressure is had no particular limits, the pressure in common compressed-air actuated pressure limit can be adopted, as 2atm to 10atm, preferred 4atm to 8atm, most preferably from about 6atm.
As the another kind of process gas in plasma treatment of the present invention, the mist of compressed air and inert gas refers to the compressed air mixing a certain proportion of inert gas, wherein inert gas comprises argon gas, helium etc., and its percent by volume of mixing is 0%-5%.Inert gas can improve treatment effect as argon gas, mixing of helium, as obtained higher adhesive bond intensity, can extend the retention time for the treatment of effect.If but the percent by volume of mixing is more than 5%, too much inert gas is not obvious to improving treatment effect further, and the problem that processing cost can be brought too high.Generally, under pure compression air can reach satisfied effect prerequisite, there is no need to add inert gas, now addition is 0%; When needing to obtain better treatment effect, a certain amount of inert gas can be added, be preferably 1-3%, most preferably be about 2%.
Polythene material of the present invention comprises the polyethylene anticorrosion layer material being applicable to steel pipe, as 2PE, 3PE etc., and preferred 3LPE (3 layers of polyethylene).
Polyurethanes coating of the present invention comprises conventional liquid two component polyurethane class coating, and one of them component contains polyol structure, and another component is that isocyanates is or/and isocyanate prepolymer.Preferred use has fast dry characteristic, the two component polyurethane class coating that the hard tactile dry time is less than 8 hours.In this respect, the 352HT polyurethane liquid coating of most preferably 3M company.
Plasma treatment of the present invention can use jet flow type atmospheric plasma apparatus to carry out, and it is simply portable that this discharge equipment has equipment, and the advantage that treatment effect is good, is applicable to very much process petroleum pipeline polyethylene surface.The plasma treatment process parameter of jet flow type atmospheric plasma apparatus, as voltage and current, to a certain degree can affect treatment effect, but impact is less.Ordinary circumstance is that 1-2 ampere-hour all can satisfy the demands preferably at discharge current.
In addition, before plasma treatment of the present invention, preferably mechanical surface roughening process is carried out to polyethylene surface, comprise sanding, sand papering and wire brush grinding process etc.
According to the present invention, by adopting the plasma treatment of mist as process gas of compressed air or compressed air and inert gas, can improve polythene material significantly with the adhesion between polyurethanes coating, and the bond strength after process can keep for a long time.
Accompanying drawing explanation
Fig. 1 shows the tensile test sample of inventive samples, and left figure is sample 7, and right figure is sample 8;
Fig. 2 is the figure of display coating adhesion test result, and wherein right figure is the partial enlarged drawing of sample 6.
Detailed description of the invention
Describe the present invention in more detail below by way of specific embodiment, these embodiments are only exemplary, and should not be construed as limitation of the scope of the invention.
The main material used in embodiment and equipment as follows.
Be coated with the steel plate of high density polyethylene (HDPE): the steel plate being attached with HDPE that the X70 steel pipe that Baoji steel tube factory produces intercepts, HDPE is the anticorrosion high density polyethylene (HDPE) of 3LPE that market is generally supplied, and typical supplier is Zibo Ou Qi.
Polyurethanes coating: the 352HT polyurethane liquid coating of 3M company.
Packaged type plasma processor: the JYS-B type plasma processor of Yantai Jin Ying Science and Technology Ltd., electric discharge operating voltage is 200-300V, preferred 250V.
Compressed air is the common oil removing compressed air that dewaters, and pressure is about 6atm.
The steel cylinder argon gas that argon gas, helium all adopt liquefied air company to produce, steel cylinder helium, purity is 99.99%.
Sand shaker: Shi Yong Mechanical Equipment Company SY9080.
Combustor: Qingdao Mount spins M601.
Sand paper, wire brush: the common coarse sandpaper that market is bought and wire brush.
The adhesion test method adopted in embodiment is as follows.
1. tensile test
Tensile tester: Elcometer106-3
Test program: in paint solidification process, be bonded in coating by measuring head (diameter 20mm), do tensile test with tensile tester, the unit of measurement result is Mpa.Manual rotation tensile tester, when measuring head arrives integer or 0.5Mpa value, stops 30s, if do not departed from, then thinks by this pulling force.
2. coating adhesion test (with reference to SY/T0315-annex G)
1) sample with polyurethanes paint coatings is placed in common plastics bucket, adds water logging and do not have sample;
2) regulate baking oven (HeraeusThermoT12) to 40 DEG C, bucket is put into baking oven;
3) within every 12 hours, use thermometer probe temperature, and ensure that the water surface is higher than sample;
4) soak after 40 days, take out sample;
5) to be cooled after room temperature, point of a knife is inserted below coating, with the power of horizontal direction sled stripping coating, continuously advance point of a knife until coating all prize from or coatings go out obvious anti-pick performance.
By following grade scale evaluation adhesive force grade:
1 grade---coating can not be peeled by sled significantly;
2 grades---by sled from coating be less than or equal to 50%;
3 grades---by sled from coating be greater than 50%, but coatings goes out obvious anti-pick performance;
4 grades---coating is easy to be prized stripping into strips or bulk chip;
5 grades---coating becomes whole piece to be stripped.
Embodiment 1
The steel plate being attached with HDPE that the X70 steel pipe selecting Baoji steel tube factory to produce intercepts, HDPE is the anticorrosion high density polyethylene (HDPE) of 3LPE of Zibo Ou Qi.Polyethylene surface carries out different disposal as described below, and subsequently by liquid two component polyurethane class coating, the 352HT polyurethane liquid coating of 3M company, mixes and brushes at polyethylene surface, normal temperature cure 7 days, thus prepares sample 1-8.According to above-mentioned tensile test program and adhesive force test program, carry out adhesive force test to sample 1-8, test result is in table 1 and table 2.
Surface treatment mode:
Sample 1: non-processor polyethylene surface;
Sample 2: the polyethylene surface of surperficial sanding process, surperficial depth of abrasion pattern 40 ~ 50 μm;
Sample 3: the polyethylene surface of sand paper process;
Sample 4: polyethylene surface sanding also with flame treatment surface, uses the process of flame blue-flame;
Sample 5: polyethylene surface wire brush process;
Sample 6: polyethylene surface uses wire brush process, and uses jet flow type plasma apparatus to process, and the medium of use is the common oil removing compressed air that dewaters, and pressure is 6atm.
Sample 7: polyethylene surface uses wire brush process, and uses jet flow type plasma apparatus to process, and the medium of use is the compressed air mixing 2% argon gas, and pressure is 6atm;
Sample 8: polyethylene surface uses wire brush process, and uses jet flow type plasma apparatus to process, and the medium of use is the compressed air mixing 2% helium, and pressure is 6atm.
In the left figure that the tensile test sample of sample 7 and sample 8 is shown in Fig. 1 and right figure.
Table 1. tensile test result
| Sample | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 |
| Mpa | ＜2 | 2.2 | 2.5 | 2.5～5 | 2.8 | Average 5 | Average 5 | Average 4.6 |
Pull test result shows: be-do not process separately at polyethylene surface treatment, sanding, when sand papering and wire brush are polished, coating with the adhesive force between polyethylene lower than 3Mpa; After sanding, flame treatment can strengthen adhesive force, but zones of different there are differences; Be suitable for jet flow type plasma apparatus after wire brush polishing to process, the medium of use is the compressed air of compressed air or mixed ratio inert gas, can significantly promote coating and poly pulling force, reach the level suitable with vacuum plasma treatment.
Table 2. adhesive force sled stripping test result
Fig. 2 shows the result of coating adhesion test, and wherein Reference numeral 5,6,7 represents sample 5,6 and 7 respectively.Coating adhesion result of the test as can be seen from table 2 and Fig. 2: be suitable for jet flow type plasma apparatus after wire brush polishing and process, the medium used is the compressed air of compressed air or mixed ratio inert gas, significantly can promote the adhesive force after coating and poly hot-water soak.
Claims (13)
1. one kind for improving the polyethylene surface treatment method of polythene material with the adhesion between polyurethanes coating, described method comprises: before polyurethanes coating contacts polythene material, with the surface of plasma treatment technique process polythene material, the process gas wherein used in plasma treatment is the mist of compressed air or compressed air and inert gas, and described compressed-air actuated pressure limit is 2atm to 10atm.
2. polyethylene surface treatment method according to claim 1, wherein said compressed air is the common oil removing compressed air that dewaters.
3. polyethylene surface treatment method according to claim 1, wherein said compressed-air actuated pressure limit is 4atm to 8atm.
4. polyethylene surface treatment method according to claim 1, wherein said inert gas comprises argon gas and helium.
5. polyethylene surface treatment method according to claim 1, the percent by volume of wherein said inert gas in the mist of compressed air and inert gas is less than 5%.
6. polyethylene surface treatment method according to claim 5, the percent by volume of wherein said inert gas in the mist of compressed air and inert gas is 1% to 3%.
7. polyethylene surface treatment method according to claim 1, wherein said polythene material is steel pipe polyethylene anticorrosive coating material.
8. polyethylene surface treatment method according to claim 7, wherein said polythene material is 3LPE, i.e. 3 layers of polyethylene.
9. polyethylene surface treatment method according to claim 1, wherein said polyurethanes coating is liquid two component polyurethane class coating, and one of them component contains polyol structure, and another component is that isocyanates is or/and isocyanate prepolymer.
10. polyethylene surface treatment method according to claim 9, wherein said polyurethanes coating is the 352HT polyurethane liquid coating of 3M company.
11. polyethylene surface treatment method according to claim 1, wherein said plasma treatment uses jet flow type atmospheric plasma apparatus to carry out.
12. polyethylene surface treatment method according to claim 1, before described method is also included in plasma treatment, carry out the step of mechanical surface roughening process to polyethylene surface.
13. polyethylene surface treatment method according to claim 12, described mechanical surface roughening process comprises sanding, at least one in sand papering and wire brush grinding process.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN201210288369.8A CN102785376B (en) | 2012-08-14 | 2012-08-14 | Polyethylene surface treatment method |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN201210288369.8A CN102785376B (en) | 2012-08-14 | 2012-08-14 | Polyethylene surface treatment method |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CN102785376A CN102785376A (en) | 2012-11-21 |
| CN102785376B true CN102785376B (en) | 2016-03-30 |
Family
ID=47151052
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CN201210288369.8A Expired - Fee Related CN102785376B (en) | 2012-08-14 | 2012-08-14 | Polyethylene surface treatment method |
Country Status (1)
| Country | Link |
|---|---|
| CN (1) | CN102785376B (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN104073175B (en) * | 2013-03-25 | 2016-03-09 | 中国石油天然气集团公司 | A kind of method that polyurethane coating and three-layer polyethylene coating chemical bond bond |
| US12433058B2 (en) | 2023-01-25 | 2025-09-30 | Google Llc | Electromagnetic radiation transmissive polymer substrates |
Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN1426889A (en) * | 2001-12-17 | 2003-07-02 | 中国科学院电子学研究所 | Method of surface modification of PTFE/ceramic composite medium material |
| CN1511333A (en) * | 2001-03-27 | 2004-07-07 | APIT�ɷ�����˾ | Method for plasma surface treatment and equipment for realizing the method |
| CN1640211A (en) * | 2002-09-13 | 2005-07-13 | 巴尔工业公司 | Plasma surface treating method and apparatus therefor |
| CN201243403Y (en) * | 2008-03-31 | 2009-05-20 | 中国石油天然气管道局 | Plasma surface processing device for pipe polyethylene anticorrosive coating |
Family Cites Families (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN87104425A (en) * | 1987-06-23 | 1988-04-06 | 哈尔滨工业大学 | Continuous Cold Plasma Treatment Technology of Fiber, Fabric and Film Surface |
| CN102009049A (en) * | 2010-09-29 | 2011-04-13 | 卓盈微电子（昆山）有限公司 | Surface processing process for flexible circuit boards |
-
2012
- 2012-08-14 CN CN201210288369.8A patent/CN102785376B/en not_active Expired - Fee Related
Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN1511333A (en) * | 2001-03-27 | 2004-07-07 | APIT�ɷ�����˾ | Method for plasma surface treatment and equipment for realizing the method |
| CN1426889A (en) * | 2001-12-17 | 2003-07-02 | 中国科学院电子学研究所 | Method of surface modification of PTFE/ceramic composite medium material |
| CN1640211A (en) * | 2002-09-13 | 2005-07-13 | 巴尔工业公司 | Plasma surface treating method and apparatus therefor |
| CN201243403Y (en) * | 2008-03-31 | 2009-05-20 | 中国石油天然气管道局 | Plasma surface processing device for pipe polyethylene anticorrosive coating |
Also Published As
| Publication number | Publication date |
|---|---|
| CN102785376A (en) | 2012-11-21 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| CN103056788B (en) | A kind of preparation method of sharp epoxy resin binder diamond grinding tool | |
| CN102785376B (en) | Polyethylene surface treatment method | |
| CN102464861B (en) | A carbon fiber composite material system for repairing pipelines and its application | |
| CN110468368B (en) | Manufacturing method of high-temperature-resistant wear-resistant insulating coating | |
| CN103757581B (en) | Middle high-temperature furnace roller surface supersonic flame spraying method | |
| CN103834259A (en) | Temperature-resistant wear-resistant coating and preparation method thereof | |
| CN102825519B (en) | Processing method of prism | |
| CN102391816B (en) | High-temperature repairing agent | |
| CN102481743A (en) | Tire retreading method and system | |
| CN204353153U (en) | Pipe interior uses the device of air force cleaning and coating | |
| CN104212323A (en) | Room-temperature self-setting corrosion protective coating and preparation method thereof | |
| CN102391815A (en) | Anticorrosive repair agent | |
| CN106011719A (en) | Repair method for aluminum coating of composite material | |
| CN102485426A (en) | Grinding pad finisher and grinding pad finishing method | |
| CN115257017B (en) | Composite material repairing method for crack of landing gear beam of airplane | |
| CN107899924B (en) | GIS shielding piece and silver-plated conductor paint spraying process | |
| CN105017954B (en) | Automobile coating bottom is made up the difference agent and automobile finish restorative procedure | |
| CN103949989B (en) | A kind of extra hard material grinding wheel abrasive material block and matrix consolidation device and method | |
| CN111531925A (en) | Method for repairing composite material by high-pressure abrasive particle water jet milling | |
| CN111320921A (en) | Amorphous igneous rock reinforced polyurea coating, wear-resistant anti-skid coating and preparation method thereof | |
| CN108057597B (en) | A repairing process for aluminum alloy fine wheel spraying defects | |
| CN101905539A (en) | Method for repairing breakage on surface of polyurethane rubber roller for cold rolling | |
| CN201848764U (en) | Locating ring for chemical mechanical polishing | |
| JP7565682B2 (en) | Method for manufacturing polishing pad and polished product | |
| CN212145853U (en) | Timber equipment of polishing |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| C06 | Publication | ||
| PB01 | Publication | ||
| C10 | Entry into substantive examination | ||
| SE01 | Entry into force of request for substantive examination | ||
| C14 | Grant of patent or utility model | ||
| GR01 | Patent grant | ||
| CF01 | Termination of patent right due to non-payment of annual fee |
Granted publication date: 20160330 Termination date: 20210814 |
|
| CF01 | Termination of patent right due to non-payment of annual fee |