Coating

Abstract

A method of applying a coating to a device which has one or more components housed in a housing. A liquid coating precursor is applied to at least part of the internal surface of the housing and/or at least part of the one or more components within the housing. Low pressure conditions are applied to the closed housing, sufficient to cause the liquid coating precursor to evaporate and initiation of the liquid coating precursor to thereby cause the coating to form on at least some of the internal surfaces of the device.

Claims

1. A method of applying a coating to an electronic or electrical device, the method comprising the steps of: (i) providing an electronic or electrical device comprising one or more components housed in a housing of the electronic or electrical device; (ii) applying liquid coating precursor to at least part of the internal surface of the housing and/or at least part of the one or more components while the housing is open or closed; (iii) closing the housing if the liquid coating precursor is applied while the housing is open in step (ii); (iv) evaporating the liquid coating precursor applied in step (ii) by applying below atmosphere pressure conditions to the closed housing, with the one or more components inside the closed housing of the electronic or electrical device in a processing chamber; and (v) initiation of the evaporated coating precursor, to thereby cause the coating to form from the coating precursor on at least some of the internal surfaces of the electronic or electrical device.

2. A method according to claim 1, wherein the initiation of the liquid coating precursor comprises an energizing and/or ionization field.

3. A method according to claim 1, wherein the initiation of the liquid coating precursor is selected from plasmas; penning ionization; laser; initiated and oxidative chemical vapour deposition; free radical initiators; and electromagnetic radiation including visible and infra-red light.

4. A method according to claim 1, wherein the coating is formed by plasma polymerization.

5. A method according to claim 4, wherein the coating is formed using a plasma chosen from a pulsed plasma, a continuous wave plasma, and combinations thereof.

6. A method according to claim 1, wherein the liquid coating precursor is applied in droplets at multiple locations.

7. A method according to claim 1, wherein the liquid coating precursor is applied at locations close to apertures in the housing.

8. A method according to claim 1, wherein the liquid coating precursor is applied at locations vulnerable to liquid damage.

9. A method according to claim 1, wherein the liquid coating precursor is applied at locations prone to corrosion.

10. A method according to claim 1, wherein the electronic or electrical device is selected from communication devices, sound and audio systems, computers or outdoor lighting systems.

11. A method according to claim 1, wherein the device comprises laboratory equipment.

12. A method according to claim 11, wherein the device comprises one or more articles of laboratory equipment, such as pipette tips, housed in a container.

13. A method according to claim 1 wherein step (ii) is chosen from applying the liquid coating precursor by spraying; applying the liquid coating precursor as multiple droplets; placing a material soaked in liquid coating precursor in the housing; and condensing the liquid coating precursor from the gas phase.

14. A method according to claim 1, wherein step (ii) comprises condensing the liquid coating precursor from the gas phase, and the gas phase of the liquid coating precursor is formed by evaporating it at below atmosphere pressure conditions.

15. A method according to claim 1, wherein step (ii) comprises condensing the liquid coating precursor from the gas phase, and the vapour of the liquid coating precursor is introduced through an aperture in the housing.

16. A method according to claim 1, wherein step (ii) is chosen from (a) applying the liquid coating precursor by spraying and (b) introducing the vapour of the liquid coating through an aperture in the housing and condensing the liquid coating precursor from the gas phase; wherein the liquid coating precursor is applied in step (ii) whilst the housing is closed.

17. A method according to claim 1, wherein the external surface of the housing is not exposed to the liquid coating precursor, except by diffusion from inside the housing.

18. A method according to claim 1, wherein liquid precursor is chosen from a compound of formula (I) ##STR00002## where R.sup.1, R.sup.2 and R.sup.3 are independently selected from hydrogen, alkyl, haloalkyl or aryl optionally substituted by halo; and R.sup.4 is a group XR.sup.5 where R.sup.5 is an alkyl or haloalkyl group and X is a bond; a group of formula C(O)O(CH.sub.2).sub.nY where n is an integer of from 1 to 10 and Y is a bond or a sulphonamide group; or a group (O).sub.pR.sup.6(O).sub.q(CH.sub.2).sub.t where R.sup.6 is aryl optionally substituted by halo, p is 0 or 1, q is 0 or 1 and t is 0 or an integer of from 1 to 10, provided that where q is 1, t is other than 0; a compound of formula (II)
CH.sub.2CR.sup.7C(O)O(CH.sub.2).sub.nR.sup.5(II) where n is an integer from 1 to 10, R.sup.5 is an alkyl or haloalkyl group and R.sup.7 is hydrogen, C.sub.1-10alkyl, or C.sub.1-10haloalkyl; 1H, 1H,2H,2H-Perfluorooctyl acrylate; 1H, 1H, 2H, 2H-heptadecafluorodecyl acrylate; and combinations thereof.

19. A method according to claim 1, wherein the coating is a liquid repellent coating.

20. A method according to claim 1, wherein the coating is a water and/or oil repellent coating.

21. A device which comprises a coating of a polymer which has been applied by a method according to claim 1.

22. An electronic or electrical device which comprises a coating which has been applied by a method according to claim 1.

23. A method according claim 3, wherein the plasmas comprise atmospheric based plasmas.

Description

(1) The present invention will now be further described with reference to the following non-limiting examples and the accompanying illustrative drawings, of which:

(2) FIG. 1 shows three different distribution patterns of monomer on cotton poplin placed onto the internal surface of an enclosure;

(3) FIG. 2 shows the values of the water repellency results on various locations of enclosures treated with monomer; 1 droplet of 15l (pattern I) and 3 droplets of 5l each (pattern II);

(4) FIG. 3 shows an enclosure with monomer droplets directly on the ABS surface in pattern III; and

(5) FIG. 4 shows two enclosures with aluminium samples inside and monomer droplets in pattern III.

EXAMPLE 1

(6) Monomer Deposited Inside Mobile Phone Coating

(7) Droplets of 1H, 1H, 2H, 2H-heptadecafluorodecyl acrylate (Apollo PC04389E, 95%+purity) were deposited onto the inside of mobile phone enclosures before subjected them to the plasma polymerization process. The mobile phone enclosures were made from ABS and had dimensions of 70mm135mm, with two circular apertures of 5mm diameter. A sheet of cotton poplin of dimensions 60mm130mm was placed inside each enclosure and droplets of monomer were applied to the cotton poplin using an adjustable micropipette in different volume and distribution patterns. The enclosures were then closed and subjected to the plasma polymerization process.

(8) The different distributions of monomer used in following examples are shown in FIG. 1, which shows enclosures 10 and monomer droplets 12; distributions patterns I,II and III have 1,3 and 5 droplets respectfully. In this example, 1 droplet of 15l (pattern I of FIG. 1) was compared to 3 droplets, each 5l (pattern II in FIG. 1) in order to determine any difference between application in a single area and multiple areas spread fairly evenly. The same total volume of monomer was used to allow potential differences caused by insufficient monomer to be ruled out.

(9) After the droplets of monomer were applied to the internal surfaces of the enclosures as described above, the enclosures were closed and placed inside a capacitive coupled plasma reactor vessel. The plasma reactor vessel used was rectangular, with a volume of 90l. The plasma reactor vessel had grounded reactors walls and RF powered electrodes made of the same material as the reactor. The enclosures were placed between the electrodes and the walls. The reactor was evacuated using a vacuum pump reaching base pressures lower than 4mTorr with the process pressure being sub-atmospheric. A cold plasma was generated by pulsed and continuous radio frequency of 13.56MHz applied between the electrodes and grounded walls. At the end of the process, the plasma reactor vessel was vented to atmospheric pressure in order to remove the treated materials.

(10) 1H, 1H, 2H, 2H-heptadecafluorodecyl acrylate (Apollo PC04389E, 95%+purity)is also placed in a monomer tube connected to the plasma reactor vessel.

(11) The enclosure is then subjected to either process A or process B outlined below. In example 1, process A is used.

(12) Process A:

(13) The processing chamber had a start pressure of 80mT and was then further pumped down for 20 sec to below 30mT at which a 30 sec outgas check was performed (OGR). A continuous plasma (CW) was then applied for 30s at a power of 300W, after 10 sec into the CW a first shot of monomer (128l) from the monomer tube was introduced into the chamber. Following application of the continuous wave plasma, a pre-shot of monomer (each 128l) from the monomer tube was applied to the chamber. The pulsed plasma was then ignited, followed by introducing a further shot of monomer (128l) from the monomer tube into the chamber under pulsed conditions (pressure=30mT, time=20s, power=400W and a pulse regime of 37s on and 10ms off). After the plasma treatment has finished, the chamber was cleared for 180 sec.

(14) Process B:

(15) The processing chamber had a start pressure of 80mT at which a continuous plasma (CW) was applied for 30s at a power of 300W whilst further pumping the chamber to 30mT. After 10 sec into the CW a first shot of monomer (12l) from the monomer tube was introduced into the chamber. Following application of the continuous wave plasma, a pre-shot of monomer (each 128l) from the monomer tube was applied to the chamber. The pulsed plasma was then ignited, followed by introducing a further shot of monomer (128l) from the monomer tube into the chamber under pulsed conditions (pressure=30mT, time=20s, power=400W and a pulse regime of 37us on and 10ms off). After the plasma treatment has finished, the chamber was cleared for 180 sec.

(16) Measurements

(17) The cotton in the ABS enclosures coated as described above were tested using a water repellency scale similar to the AATCC193-2003 method (Water/Alcohol Solution Resistance Test). The ratings used are reproduced in table 1.

(18) TABLE-US-00001 TABLE 1 % Deionised Surface Tension Water % Isopropanol at 22 C. with 3SD Rating (by volume) (by volume) tolerances (mN/m) W0 100 0 72.8 2.0 W1 90 10 42.1 2.3 W2 80 20 33.7 2.0 W3 70 30 28.4 1.4 W4 60 40 26.4 0.8 W5 50 50 25.0 0.5 W6 40 60 24.3 0.2 W7 30 70 23.8 0.3 W8 20 80 23.0 0.2 W9 10 90 22.4 0.3 W10 0 100 21.2 0.2

(19) An approximately 30l drop of deionized water/isopropanol (mixed according to table 1) is gently placed onto the cotton surface to be investigated. After 10 sec the drop is removed and the cotton observed for wetting. If wetting occurred then this counts as a fail. If there is no wetting, it is a pass and the procedure is repeated using the percentage mix in the next line of table 1 until the coating fails. The coating is given the highest rating it passes.

(20) This test method was applied to evaluate the cotton pieces treated inside the enclosures. The 1 droplet of 15l (pattern I in FIG. 1) was then compared to 3 droplets, each 5l, (pattern II in FIG. 1). The results of the water repellency test are shown in FIG. 2, which shows values 14 at different positions tested on the enclosure 10. It was found that a single droplet in the centre of the cotton led to a non-uniform coating with some areas performing worse than others, whilst the smaller droplets spread farther apart produced a uniformly well-performing coating.

EXAMPLE 2

(21) Control Enclosures

(22) A control enclosure which contained no monomer internally was treated under the same conditions as Example 1 (using process A). In this case, any coating being produced was entirely from the monomer introduced into the chamber during the CW and PW stages of the process.

(23) The results of the water repellency test show that the control enclosure had practically no coating internally with the exception of the two spots where there are holes in the ABS.

EXAMPLE 3

(24) Time StudyDispensing Monomer On Cotton

(25) A 3l drop of monomer was placed on the cotton and observed over 16 minutes. The drop was visually inspected and none observed to evaporate after this time had lapsed. Subsequent plasma treatment using process A of example 1 showed water repellency numbers of 9.

(26) Due to the high boiling point of 250 C., the monomer soaks into the cotton without losing too much to evaporation. This indicates that it is possible to dispense the monomer a reasonable time before exposure to the plasma, making it suitable for application in production.

(27) This example shows that a suitable soaking material allows the monomer to evaporate sufficiently after a defined period of soaking time.

EXAMPLE 4

(28) Depositing Monomer on ABS

(29) Monomer was dispensed directly on the ABS enclosure in distribution pattern III, as illustrated in FIG. 3. Cotton strips 16 were also placed in the enclosure as witness pieces. In a first experiment, the volume of each droplet was 1l whilst in a second experiment the volume of each droplet was 3l. The enclosures were left open for 23 minutes, after which the droplets were inspected.

(30) After a period of 23mins, there was no visible loss of monomer through evaporation. Subsequent plasma treatment using process A of example 1showed water repellency numbers of 9 for 3l and 4 for 1l showing a clear difference in evaporation rates during vacuuming to cotton doped enclosures. This shows that monomer can be applied to an ABS enclosure in production, with a time delay prior to plasma treatment, without significant loss of monomer.

EXAMPLE 5

(31) Treating Metal

(32) Aluminium samples 18 were placed in the enclosures 10, one with cotton 20 and one without cotton, as illustrated in FIG. 4. The 53l monomer drops 12 were placed as shown in the distribution pattern III and treated using the process of Example 1.

(33) After treatment with process A, no monomer was left behind. Contact angles of the treated enclosure were measured using the VCA Optima (by ACT Products Inc.). The contact angle measurements showed good results averaging 118 on the aluminium and 115 on the outside of the ABS.

EXAMPLE 6

(34) External Coating

(35) The external coating was characterized using colour-change measurements (E94, equipment: x-rite) and contact angle measurements for runs using Process A (described in Example 1). In total 3 runs were analysed and showed an average E94 of 0.23, (pass=<1) and an average contact angle of 117.0 (CV 1.3%) for the outside surface of the ABS enclosures. This demonstrates that an external coating is indeed being produced, and that the monomer that is introduced during the process is sufficient to pass both the discolouration and CAM tests.

EXAMPLE 7

(36) 301l droplets of 1H,1H,2H,2H-Perfluorooctyl acrylate were evenly placed into an ABS enclosure. The ABS enclosure contained a cotton poplin sheet for evaluation reasons. After dispensing the monomer, the ABS enclosure was closed and placed inside a 20 liter vacuum chamber, similar to the 9 l chamber used in examples 1-7. The pressure was reduced to 250mT, at which the plasma was struck using a 100W continuous wave radio frequency (13.56MHz). The pressure was then further lowered to 100mT and then quickly raised to 200mT process pressure. After 65 sec have passed the RF was switched off and the chamber evacuated for 30 sec, followed by venting. The total process time was 140 sec. This process resulted in water repellency values of up to W9 whilst no noticeable change to the visual appearance of the enclosure outside was observed.

EXAMPLE 8

(37) Mobile Phone Treatment

(38) The process of coating the internal surface of a mobile phone case was compared with a coating applied by conventional methods and with an untreated phone. In the conventional method, any coating of internal surfaces is via diffusion of the precursor from outside the housing.

(39) Processes:

(40) Internal Treatment of Phone:

(41) A mobile phone was treated using the below stated parameters for a modified version of the monomer dispensing method of process B in Example 1, conducted in a 90 liter machine.

(42) 171l droplets of 1H,1H,2H,2H-Perfluorooctyl acrylate were distributed around the phone surface inside the mobile phone housing prior to plasma treatment. During the plasma treatment an additional small quantity of monomer was delivered externally to achieve a technical effect on the phone outside. The following process parameters were used: Pressure: Start pressure 80mT (reached after 67 sec), process pressure 30mT, CW: 300W, 30 sec CW, 10 sec delay+1 shot (shot size=16l) PW: 1PW pre-shots, 400W; 35us on/10ms off, 19 sec PW, 1 shot Clearing: 300 sec Monomer: Total quantity used internal=17l and external=384l.

(43) Total process time: 7 min

(44) Conventional Phone Treatment:

(45) A mobile phone was treated using P2i Ltd's 4001standard process, with monomer applied into the reactor in its vaporized state. Activation of the monomer is achieved by plasma ionization using a 13.56MHz radio frequency generator. The polymerization process allows deep penetration of the coating into the enclosure, but takes about 90min

(46) Cotton Enclosures in Both Processes:

(47) ABS enclosures, including cotton sheets inside them (with monomer dispensed in the same volume and distribution pattern as the mobile phones), were placed next to the mobile phones inside the processing chamber.

(48) Evaluation Method Description:

(49) Shower Test

(50) The treated mobile phone was exposed to a shower test, described in more detail below.

(51) This test is similar to the IP-X1 test as stated in the Ingress Protection (IP) Rating: IEC60529: 2001 (Degrees of Protection Provided by Enclosures (IP code), 2001). The IP rating describes the level of protection a device has against solid and liquid objects. The IP rating is stated as IP-X1; the first digit after the dash stands for protection against solid objects and the second digit for protection against liquid objects. As the investigation was limited to protection against liquid objects, the first digit is replaced with an X.

(52) The phone is exposed to a drip box for a total of 30 min with a flow rate of 91.0mm/min IP-X1 specifies 10min and a flow of 1.00.5mm/min with the device checked for functionality after 10 minutes. In addition to the IP-X1, device checks similar to IP-X2 were performed. For the in-house shower test, general device functionality was checked (power button, volume button, speaker, screen functionalities (touch and display), front and back cameras) every 2 min until 10 min were reached. From this point onwards functionality was checked every 4 min until 30 minutes have passed. The phone's weight was taken before and after the shower test. The device functionality was also checked 24 hours after the test followed by investigation of corrosion on the internal components.

(53) CAM

(54) After shower test evaluation the phones were dismantled and contact angles measured on the internal surfaces using the same method as described in Example 5.

(55) Shower Test Results

(56) Untreated Phone:

(57) The untreated phone failed to pass the shower test with the phone not functioning after 4 minutes exposure. Water was allowed to penetrate into the phone causing short circuits stopping it from operating.

(58) Internal Treatment of Phone:

(59) Treating the phone with this method resulted in a good shower test performance. The test was stopped after 30 minutes as the phone survived the whole time with only minor issues to be reported from minute 22 onwards. These were power and volume button response issues. The button initially needed to be pressed twice for response, working as normal afterwards. The phone was fully functioning when inspected for corrosion the day after the shower test.

(60) Conventional Phone Treatment: The phone treated with standard process passed the shower test, but had some display problems due to electric shorts of components related to the touch screen. It was observed that after removing the phone from the shower tester and held horizontally the display showed menus being opened and closed making it impossible to operate the phone at all. The phone always returned to normal operation once held in a vertical orientation to allow water to drain out. After the shower test the phone was left to dry, a final check the following day indicated that all functions were still intact.

(61) CAM Results

(62) Water contact angle measurements after the shower test are shown in table 2.

(63) TABLE-US-00002 TABLE 2 Water contact angle measurements Phone Water contact angles Untreated 80-100 Internal treatment of phone 90-120 Conventional phone treatment 90-120

(64) Measured internal water contact angles show that both treated phone average 109 ranging from 90 to 120. The untreated mobile phone has average contact angles of 85. This shows that both processes deliver sufficient internal coating thickness. The contact angle positions show that polymerization of the monomer vapour is best closest to possible entry points of the phone. This is thought to be caused by active species created by the plasma ionization (such as nitrogen, oxygen, water and monomer related species) initiating polymerisation inside the mobile phone housing.

(65) Cotton Enclosures

(66) Table 3 lists water repellency results for the cotton enclosures for the 901 dispense study and P2is 4001 conventional process. The enclosure treated with the dispensed monomer in the 901 chamber achieved W10 all across the cotton produced in a 7 min process as described here in Example 8. All measured enclosures of the 4001standard process achieved W9 across the cotton as the vacuum stage is long enough (20 min) to remove moisture allowing optimum coating penetration.

(67) TABLE-US-00003 TABLE 3 Enclosure results conventional (400l) vs. dispensed monomer (90l) method Enclosure Top Bottom Hole l/enc 90l-Dispensed 10 10 10 10 10 10 22 400l-Conventional 9 9 9 9 9 9 10

(68) Conclusion

(69) This new method of treating electronic and electrical devices allows coating inside the device much faster than with conventional processes whilst giving good protection against liquids. The examples show that the method produces high internal contact angles, low discoloration and good shower test performance.

(70) By dispensing monomer locally inside the housing, a coating can be deposited despite high level of moisture inside the device, thus making a drying or degassing step unnecessary. For this reason, the method is significantly faster than prior art methods in which the monomer is introduced into the plasma chamber, externally to the device.

(71) The internal dispensing of monomer also reduced the risk of discoloration of the external surface because as monomer is being applied locally inside the device, low volumes can be used to treat the external surface.

(72) This new method of treating devices has produced a highly effective liquid repellent coating in a much faster time than prior art methods, which makes the process suitable for using in an in-line manufacturing process.

(73) The method of application allows for the precursor to be applied at critical locations, further improving the repellency in those areas. Small and multiple dispense volumes in a tightly packed enclosure, such as a phone, are beneficial for coating distribution.