Silicon-based protective film for adhesive, method of production thereof and uses thereof

Abstract

Silicon-based protective film for adhesive or self-adhesive elements, characterized in that said protective film is based on silicone and has a level of extractible silicone less than or equal to 100 ng/cm.sup.2, preferably less than or equal to 50, preferably less than or equal to 20 ng/cm.sup.2, and even more preferably less than 10 ng/cm.sup.2, the method of production thereof and uses thereof.

Claims

1. A silicon-based protective film for adhesive or self-adhesive elements, wherein said protective film is based on silicone and has a level of extractible silicone less than or equal to 100 ng/cm.sup.2 being measured by the amount of silicone that is released in the form of monomers or oligomers, either non-volatile (IDEMA Standards M7-98 “Organic Contamination as Nonvolatile Residue (NVR)”, ECSS-Q-ST-70-05C “Detection of organic contamination of surfaces by infrared spectroscopy”, Seagate 20800032-001 Rev C. & 20800014-001 Rev G, Western Digital 2092-772141 Rev AD & 2092-771888 Rev AC), or volatile (IDEMA Standards M11-99 “General Outgas Test Procedure by Dynamic Headspace Analysis”, Seagate 20800020-001 Rev N, Western Digital 2092-001026 Rev AC & 2092-771888 Rev AC); wherein the silicon-based protective film has a level of nitrogen less than or equal to 1 at %, measured according to the XPS/ESCA technique.

2. The silicon-based protective film for adhesive or self-adhesive elements according to claim 1, further comprising a substrate of paper, woven or non-woven fabric or plastic.

3. The silicon-based protective film for adhesive or self-adhesive elements according to claim 1, having at least one of the following characteristics selected from a peeling force less than or equal to 2N/25 mm measured on a Tesa™ 7475 adhesive measured according to standard FTM10, having a residual adhesion greater than or equal to 80%, measured according to standard FTM11, a surface having a static contact angle of water greater than 90°, as measured on Krüss DSA25 apparatus, a surface energy less than 30 mN/metre as calculated from the measurements of contact angle of two liquids (water and diiodomethane) according to the model of Owens and Wendt.

4. An assembly comprising at least one silicon-based protective film for adhesive or self-adhesive elements according to claim 1, and an adhesive or self-adhesive element having a first face provided with adhesive or self-adhesive properties.

5. The assembly according to claim 4, wherein said adhesive element is a label, an adhesive tape, a double-sided adhesive, a protective film, in particular of electronic grade, an adhesive or self-adhesive medical device, such as an adhesive or self-adhesive medical dressing, for example siliconized, a patch, an adhesive electrode intended to be in contact with the skin, in particular of medical grade.

6. A method of producing a silicon-based protective film having a level of nitrogen less than or equal to 1 at %, measured according to the XPS/ESCA technique for adhesive or self-adhesive elements provided with at least one silicone-based coating layer intended to rest on a substrate of paper, woven or non-woven fabric or plastic comprising the following steps a) movement of said substrate from a source of substrate in a plasma coating cell for forming said protective film to a collection point of said protective film, b) exposure of a first face of said substrate to plasma deposition in a chamber in which there is an atmosphere consisting of at least one plasma gas with discharge controlled by dielectric barrier (DBD) of said plasma gas selected from the rare gases or mixtures thereof in the presence of at least one cyclic siloxanes precursor, c) formation of said silicone-based coating from said silicone precursor in said plasma and, d) collection of said protective film provided with said at least one silicone-based coating layer.

7. The method of producing a silicon-based protective film for adhesive or self-adhesive elements according to claim 6, wherein said gas atmosphere in the chamber has an oxygen content less than or equal to 50 ppmv.

8. The method according to claim 6, wherein said substrate moves at a substrate travel speed between 10 and 60 m/min and/or said gas atmosphere in the chamber is at atmospheric pressure ±100 Pa and/or said plasma deposition has a deposition time less than or equal to 4 seconds and/or said discharge is at radio frequency, the unit of area referring to the cumulative area of electrodes.

9. A method of using a protective film according to claim 1 with an adhesive element comprising a first face provided with adhesive or self-adhesive properties and eventually a second non-stick face, said protective film, said protective film being affixed on said first face provided with adhesive or self-adhesive properties and/or said second non-stick face.

10. The method of using a protective film according to claim 9, wherein said adhesive element is a label, an adhesive tape, a double-sided adhesive, a protective film, in particular of electronic grade, an adhesive or self-adhesive medical device, such as an adhesive or self-adhesive medical dressing, for example siliconized, a patch, an adhesive electrode intended to be in contact with the skin, in particular of medical grade.

11. The method of using a protective film according to claim 9, in a clean room.

12. A silicon-based protective film for adhesive or self-adhesive elements according to claim 1, wherein said protective film is based on silicone and has a level of extractible silicone less than or equal to 50 ng/cm2.

13. The silicon-based protective film for adhesive or self-adhesive elements according to claim 1, wherein said protective film is based on silicone and has a level of extractible silicone less than or equal to 10 ng/cm2.

14. The silicon-based protective film for adhesive or self-adhesive elements according to claim 1, wherein said protective film is based on silicone and has a level of extractible silicone less than or equal to 5 ng/cm2.

15. The silicon-based protective film for adhesive or self-adhesive elements according to claim 3, wherein the surface having a static contact angle of water greater than 95°.

16. The silicon-based protective film for adhesive or self-adhesive elements according to claim 3, wherein the surface energy is less than 25 mN/m.

17. The method according to claim 7, wherein the gas atmosphere in the chamber has an oxygen content less than or equal to 20 ppmv.

18. The method according to claim 7, wherein said substrate moves at a substrate travel speed between 10 and 50 m/min.

19. The method according to claim 6, wherein said plasma deposition has a deposition time less than or equal to 2 seconds.

Description

DESCRIPTION OF SPECIFIC EMBODIMENTS OF THE INVENTION

Brief Description of the Several View of the Drawings

(1) FIG. 1 is a graph which illustrates the peeling force of an adhesive on a protective film according to the invention compared with the peeling force of the same adhesive on a commercial protective film based on fluorosilicone.

(2) Other features, details and advantages of the invention will become clearer from the description given below, which is non-limiting, and referring to the examples and the appended figures.

(3) Unless stated otherwise, the concentrations of gases given in ppm (parts per million) are ppm by volume (ppmv).

(4) According to the invention, the substrate is exposed to a plasma at atmospheric pressure. The plasma is generated in a plasma gas (He, Ar) containing one or more siloxane precursors; this precursor will be specified below. Exposure of the substrate to the plasma and to the molecules of precursor causes formation of a thin deposit on the surface of the substrate. This thin deposit endows the protective film for adhesive elements with low adhesion and a very small amount of extractible silicone. Moreover, this deposit does not significantly reduce the subsequent adhesion of the adhesive to the protective film that comprises it.

(5) In the method of production of the protective film according to the present invention, plasma deposition at atmospheric pressure therefore makes it possible to produce a non-stick layer on a substrate to form a protective film (release liner).

(6) The method according to the invention may be carried out in a reactor, inside which a dielectric barrier discharge (DBD) takes place.

(7) Advantageously, the substrate travels through the treatment zone in roll-to-roll mode.

(8) In a preferred embodiment, the treatment reactor is of the roll-to-roll DBD type; it typically comprises the following elements: A treatment cylinder (for example with a diameter of 400 mm and a length of 800 mm) with a suitable dielectric coating. This cylinder propels the flexible film to be treated under the treatment electrodes at a speed selected in the range between 5 and 200 m/min. A treatment chamber located above the treatment cylinder and comprising electrodes and the devices for injecting gases; injection devices adjoining the electrodes make it possible to inject the gas or gases directly in front of the electrodes and on the surface of the film to be treated, namely: inerting gas, plasma gas, precursor, carrier gas, optional doping gas.

(9) The electrodes are connected to a low-frequency HV generator (typically one to some tens of kHz) of variable power (0.1 to 10 W/cm.sup.2). The power density is between 0.10 W/cm.sup.2 and 10 W/cm.sup.2, more preferably between 0.15 and 8 W/cm.sup.2, more particularly between 0.2 and 5 W/cm.sup.2, or even between 0.25 W/cm.sup.2 and 0.8 W/cm.sup.2, and even more preferably between 0.35 W/cm.sup.2 and 0.7 W/cm.sup.2, the unit of area referring to the cumulative area of the electrodes.

(10) An extraction system in the treatment chamber makes it possible to evacuate the plasma gas as well as any by-products created in the plasma and not transformed into deposit. The plasma gas generates the plasma, this is a specific feature of discharge at atmospheric pressure. The carrier gas is injected to accompany the precursor (monomer). The dopant may be injected in a small amount relative to the inerting gas, plasma gas and carrier gases. The inerting gas, plasma gas and/or carrier gas may be identical or different, and may be argon and/or helium.

(11) Advantageously, an inerted treatment atmosphere is maintained in the treatment reactor with a level of oxygen less than 50 ppm, preferably less than 20 ppm, and even more preferably less than 10 ppm.

(12) A reactor of this kind is described for example in patent application WO 2016/170242 in the applicant's name.

(13) The gap between the active surface of the electrodes and the film travelling along under them on the treatment roll must be adjusted very precisely in order to ensure stability and homogeneity of the plasma, two necessary conditions for obtaining a thin deposit with acceptable three-dimensional homogeneity. As an example, if the distance between the film and the active surface of the electrodes is set at 1 mm, this distance is advantageously stable with a standard deviation of ±0.2 mm.

(14) The precursor is advantageously injected directly into the discharge, this makes it possible to maximize the concentration of the latter between the electrodes. This is useful for making treatment possible in a single pass. A high concentration of precursor in the discharge generally leads to the formation of powder in the plasma; these powders make the product unusable and cause many problems in reactor maintenance. With a high gas velocity it is possible to reduce the residence time of the precursor molecules in the plasma; this avoids the formation of powder. Thus, it is possible to work at a high concentration of precursor, which makes it possible to carry out deposition in a single pass without forming powder.

(15) It should also be noted that exposure of the protective film formed to the plasma lowers the performance of the thin layer. Therefore deposition in several passes is not necessarily desirable.

(16) As an example, the following parameters were used in a reactor of the type described in WO 2016/170242:

(17) The flow rate of the precursor is preferably between 8 g/h and 14 g/h, more preferably between 8.5 g/h and 13 g/h; a good result is obtained with a value of 10 g/h, but the result is poorer with a value of 5 g/h or of 20 g/h. The speed of the substrate is preferably between 3 m/min and 8 m/min, preferably between 3.5 m/min and 8.5 m/min, but with a value of 2 m/min or of 10 m/min the result is poorer. The power is preferably between 450 W and 700 W, more preferably between 500 W and 650 W, but with a value of 300 W or of 900 W the result is poorer. The plasma gas is preferably argon.

(18) In the context of the present invention, the precursor should be a siloxane comprising a cyclic characteristic group, for example such as a cycloalkylsiloxane, preferably a cyclomethylsiloxane. The inventors discovered, surprisingly, that the linear alkylsiloxanes, therefore not comprising a cyclic characteristic group, do not give satisfactory results, whereas the use of siloxanes comprising a cyclic characteristic group, such as cycloalkylslioxanes, and in particular cyclomethylsiloxanes, makes it possible to solve the problem that the present invention tries to address.

(19) Advantageously, said silicone precursor is decamethylcyclopentasiloxane (CAS No. 541-02-6) or octamethylcyclotetrasiloxane (CAS No. 556-67-2), hexamethylcyclotrisiloxane (CAS No. 541-05-9), dodecamethylcyclohexasiloxane (CAS No. 540-97-6) or a mixture of two or more of these.

EXAMPLES

Example 1

(20) Surface treatments were carried out by depositing a thin layer in an argon plasma at atmospheric pressure. The plasma gas was argon. Table 1 below presents the best results obtained on a PET substrate for forming a protective film according to the invention. In particular, the peeling force and the residual adhesion of the adhesive were determined after removing the protective film of treated PET.

(21) Several types of organosiloxane monomers were used for producing the deposits of silicon-based release layers, in proportions of monomer ranging from 100 to 10 000 ppm (by volume): DMCPS=decamethylcyclopentasiloxane; CAS No. 541-02-6; OMCTS=octamethylcyclotetrasiloxane, CAS No. 556-67-2; OTES=triethoxy(octyl)silane, CAS No. 2943-75-1 HMDSO=hexamethyldisiloxane, CAS No. 107-46-0;

(22) Two types of OH or NH functionalized reactive silicone precursor monomers (Silmer™) were also used for making thin deposits based on silicone, in proportions of monomer ranging from 100 to 5000 ppm. The trade name of these monomers is: Silmer™ NH Di-8 and Silmer™ OH A0 UP (supplied by Siltech). They are linear polyalkylsiloxanes; more precisely, Silmer™ NH Di-8 is a linear amino polydimethylsiloxane (molecular weight about 860 to 940) comprising NH end groups, and Silmer™ OH A0 UP is a polydimethylsiloxane with a propylhydroxy terminal function (molecular weight about 280).

(23) For comparison, a non-silicone type of monomer (dodecyl vinyl ether, CAS No. 765-14-0) was investigated for making silicon-free release deposits, in a proportion of monomer of 100 ppm. A monomer of the fluorosilicone type was also tested.

(24) The best results were obtained on PET film with a width of 600 mm, treated at 20 m/min with a 600 W argon plasma, into which 60 g/h of DMCPS is introduced (sample called “DMCPS”), as can be seen, although pre-treatment can possibly be carried out, it was not necessary in this case while allowing excellent results. The same preferred method was carried out on paper and on BOPP film, with excellent results.

(25) Table 1 summarizes the characteristics of the protective film measured on the samples produced according to the present invention.

(26) TABLE-US-00001 TABLE 1 Fp MD15 AR Θ.sub.water Es Fp 7475 [N/25 Nitto Monomer [degrees] [mN/m] [N/25 mm] mm] 31b None  70 52.5 ± 0.5 22.6 ± 0.5  HMDSO (*) 102-104 25-30 5 ± 5 (Zippy) DMCPS (+) 112 ± 1 21 ± 2 1.0 ± 0.5 0.25 ± 0.10 95 Dodecylvinyl- 9.42 ± 0.73 ether (−) OTES (*) 11.01 ± 2.82  Silmer ™ NH 9.8 ± 6.1 Di-8 (*) Silmer ™ OH (*) 2.9 ± 2.sup.  OMCTS (+) 110 64  0.4 ± 0.03 0.11 ± 0.09 97 (+) Cyclosiloxane according to the invention. (*) Linear siloxane, not according to the invention. (−) not according to the invention
In this table: “Zippy” indicates that the adhesive detaches jerkily from the protective film; θ.sub.water water is the static contact angle of water measured on Krüss DSA25 apparatus; Es is the surface energy calculated from the measurements of contact angle of two liquids (water and diiodomethane) according to the model of Owens and Wendt; Fp 7475 is the peeling force of TESA 7475 adhesive measured according to standard FTM 10 with AR1000 apparatus; Fp MD15 is the peeling force of MD15 adhesive (ultra-pure acrylic adhesive for applications in the field of electronics), supplied by the company JDC (Tennessee, U.S.A.). AR Nitto 31b is the residual adhesion of the adhesive Nitto 31b measured on a glass plate cleaned according to standard FTM 11; This adhesive is used by those skilled in the art for the measurement of residual adhesion.

(27) Standards FTM 10 and FTM 11, familiar to a person skilled in the art, are published by FINAT (International Federation of Manufacturers and Processors of Adhesives and Heat-sealing Adhesives on paper and other substrates): FTM 10 “Quality of silicone coated substrates for self-adhesive laminates: release force (300 mm per minute)”, FTM 11 “Quality of silicone coated substrates for self-adhesive laminates: subsequent adhesion”

(28) Table 2 shows the results of determinations (in atomic percentages) of carbon, oxygen, silicon and nitrogen in three samples treated with plasma at atmospheric pressure. These values were determined from survey spectra with equipment of the Nova-Kratos™ type with a monochromatized Al-Kα source (225 W) on an area of 300μ×700 μm in normal detection (detection angle θ=0°). The depth of analysis in these conditions is less than 10 nm.

(29) TABLE-US-00002 TABLE 2 Carbon Oxygen Silicon Nitrogen Sample [at %] [at %] [at %] [at %] DMCPS Argon 1 50.7 25.8 25.0 — DMCPS 44.7 33.3 16.3 5.7 Nitrogen DMCPS Argon 2 60.9 30.4 8.7 —

(30) Note that the sample “DMCPS Argon 1” corresponds to the sample “DMCPS” in Table 1. The sample “DMCPS Nitrogen” was prepared with a nitrogen plasma comprising the precursor DMCPS: this layer comprises nitrogen. Its Fp value is too high. The sample “DMCPS Argon 2” was prepared in conditions similar to those for the sample “DMCPS Argon”, but it has a thickness of less than 10 nm: the XPS spectrum reveals a contribution to the signal due to the substrate, and the concentrations indicated therefore do not reflect the composition of the layer deposited by the method according to the invention.

(31) The content of extractible residual siloxane was determined for a sample of plastic film treated by the method according to the invention using the monomer DMCPS. For determining this content of residual siloxane, the 50 cm.sup.2 area treated was rinsed with n-hexane, and the liquid phase was concentrated on a ZnSe plate and analysed by Fourier transform infrared spectroscopy (FTIR) (resolution 4 cm.sup.−1, 8 scans, mirror speed 0.20 cm/s). The siloxane content was determined on the basis of the intensity of a spectral band characteristic of siloxane (between about 2800 and 300 cm.sup.−1 as indicated in the ECSS reference document “Space product assurance: Detection of organic contamination of surfaces by infrared spectroscopy” No. ECSS-Q-ST-70-05C dated 6 Mar. 2009 at point e. page 21 and Table 5.1), calibrated for intensity by a series of poly(dimethylsiloxane) standards, a commercial product from Aldrich, reference 378380 (CAS No. 63148-62-9). The results of this measurement are shown in Table 3. In another procedure the sample is heated under a constant gas stream. The identity and the quantity of the molecules emitted by the sample are determined by gas chromatography with detection by mass spectrometry (GC-MS) (see 4th column in Table 3).

(32) Table 3 shows the results of the measurements of extraction of silicone compounds on the samples treated according to the methods described above.

(33) TABLE-US-00003 TABLE 3 Extractible silicone (non- Extractible silicone volatile) (volatile) measured by Fp MD 15 measured by the degassing method Monomers (N/inch) FTIR (ng/cm.sup.2) DHS (ng/cm.sup.2) DMCPS 0.31 ± 0.21 4.15 0.24 DMCPS 0.29 ± 0.23 9.67 Not detected DMCPS 0.24 ± 0.19 9.46 0.67 DMCPS 0.19 ± 0.15 0.97 0.04

Example 2

(34) The peeling force (measurement according to standard FINAT 10) of an adhesive on a protective film according to the invention was compared with the peeling force of the same adhesive on a commercial protective film based on fluorosilicone after being in contact for 20 hours at a temperature of 70° C. and a moisture content of 50%. The results are shown in the FIG. 1. As can be seen, the peeling force of the protective film according to the present invention is lower than that of the protective film based on fluorosilicone.

(35) The average peeling force Fp of an adhesive on a protective film according to the invention is 0.9 N/25 mm.

(36) The average peeling force Fp of an adhesive on a commercial protective film (Fluorosilicone) is 1.0 N/25 mm.

(37) Of course, the present invention is not in any way limited to the embodiments described above, and many modifications may be made to it while remaining within the scope of the appended claims.