METHOD OF PRODUCING AN OBJECT HAVING A FLUORINATED POLYMER COATING

Abstract

The invention relates to a method of producing an object having a fluorinated polymer coating free of per- and polyfluorinated acids and salts thereof, wherein the method comprises a step DF of depositing a fluorinated polymer coating on the object by means of plasma polymerization of a fluorinated precursor monomer and a step IG of exposing the object to an inhibiting gas which inhibits the formation of per- and polyfluorinated acids and salts thereof in or on the deposited fluorinated coating. Thereby step IG is carried out after step DF, and from the start of step DF until the end of step IG the object is treated in a substantially oxygen free atmosphere.

Claims

1. A method of producing an object having a fluorinated polymer coating free of per- and polyfluorinated acids and salts thereof, wherein the method comprises: performing a step DF of depositing a fluorinated polymer coating on the object by means of plasma polymerization of a fluorinated precursor monomer; performing a step IG of exposing the object to an inhibiting gas which inhibits the formation of per- and polyfluorinated acids and salts thereof in or on the deposited fluorinated coating, wherein the step IG is carried out after the step DF, and wherein from the start of the step DF until the end of the step IG the object is treated in a substantially oxygen free atmosphere.

2. The method according to claim 1, wherein in the step IG while exposing the object to an inhibiting gas no plasma, a plasma with a plasma power less than half of the plasma power of the step DF, or a plasma with a maximum plasma power equal to the plasma power of the step DF, is present.

3. The method according to claim 1, further comprising a step DNF of depositing a non-fluorinated polymer coating on the object by means of plasma polymerization of a non-fluorinated precursor monomer, wherein the step DNF is carried out before and/or after the step DF.

4. The method according to claim 1, wherein the plasma deposition processes for depositing the fluorinated polymer coating in the step DF and/or plasma deposition processes for depositing the non-fluorinated polymer coating in the step DNF are low-pressure plasma processes and/or atmospheric plasma processes under protective atmosphere.

5. The method according to claim 1, wherein the inhibiting gas in the step IG is hydrogen, nitrogen, hydrocarbon, a mixture thereof and/or a gaseous mixture containing any of the before mentioned gases.

6. The method according to claim 1, wherein the fluorinated plasma coating in the step DF is performed using perfluorocarbon or perfluorinated hydrocarbon.

7. The method according to claim 3, wherein the non-fluorinated plasma coating in the step DNF is performed using organosilane, siloxane and/or hydrocarbon precursors.

8. The method according to claim 1, further comprising the step PT of performing a pre-treatment of the object by means of an atmospheric or low-pressure plasma using an inert gas and/or a reactive gas; and wherein the step PT is carried out before the step DNF and/or the step DF, as a first step.

9. The method according to claim 1, wherein the step IG is carried out every time, directly, after the step DF, the step PT and/or the step DNF is carried out, to inactivate reactive plasma based species formed on the coated object surface during previous plasma depositions of the steps DF, PT and/or DNF.

10. The method according to claim 1, wherein in the step DF a fluorinated polymer coating is deposited on the object having a thickness from 5 nm to 300 nm; and/or in the step DNF a non-fluorinated polymer coating is deposited on the object having a thickness from 30 nm to 700 nm.

11. The method according to claim 1, wherein a plasma power during the step DF and/or the step DNF is lower than 1 W/cm.sup.2 of an electrode surface, lower than 500 mW/cm.sup.2 of the electrode surface or lower than 200 mW/cm.sup.2 of the electrode surface.

12. The method according to claim 1, wherein the object comprises polymeric materials of woven mesh, woven fabrics, knitted fabrics, nonwoven, nonwoven meltblown, nonwoven spunbond fabric, membranes, composite membranes and combinations thereof.

13. The method according to claim 1, wherein the fluorinated coating is free from per- and polyfluorinated acids and salts thereof according to Standard 100 by OEKO-TEX and/or DIN CEN/TS 15968:2010.

14. The method according to claim 1, wherein the step PT is carried out first, the step DNF is carried out second, the step DF is carried out third, the step IG is carried out fourth, and then optionally the step DNF is carried out again.

15. An object comprising a fluorinated polymer coating free of per- and polyfluorinated acids and salts thereof formed thereon by the method according to claim 1.

Description

DRAWINGS

[0040] In the following the invention is described further by way of a preferred exemplary embodiment illustrated schematically in the accompanying drawings, wherein show:

[0041] FIG. 1 a combination of a schematic flow chart of the inventive method including an illustration of the different deposited films on an object;

[0042] FIG. 2 a schematic drawing of a method to produce a polymeric composite fabric; and

[0043] FIG. 3 a diagram showing a comparison of contact angles on DF/DNF-coated and C6-coated articles.

DETAILED DESCRIPTION

[0044] On the left side of FIG. 1 a schematic flow diagram is shown, comprising several steps according to the invention. The right side of FIG. 1 illustrates the deposited layers on an object.

[0045] According to this embodiment, first a step PT is carried out. In this step, a plasma pre-treatment of the surfaces of an object, which should be a substrate to deposit the different following layers on, is carried out. The plasma treatment is preferably performed in a closed chamber with a low-pressure atmosphere. The aim of the treatment is to clean the surface of the substrate or object, so to better deposit the following polymers. Due to the plasma treatment, depending on the used power, it is also possible to roughen the surface of the substrate, so that the following layers can adhere better. Sometime this roughening is seen as creating micro grooves into the material of the substrate.

[0046] Following the PT step, a DNF step is carried out to deposit a non-fluorinated polymer coating on the object. Preferably, the object to be coated is kept in the chamber with the low pressure or with the vacuum during the entire treatment process.

[0047] The non-fluorinated polymer coating can be based on organosilanes (trimethyl silane etc.), siloxans (hexamethyldisiloxane, tetramethylsilane etc.), hydrocarbon (methane, ethane, acetylene etc.) and a mixture of thereof.

[0048] As can be seen on the right side, after the cleaning of step PT, a first deposition layer DNF is applied onto the substrate.

[0049] Following the DNF step, a step DF is executed wherein a fluorinated polymer coating is deposited onto the previous DNF layer. Due to the combination of these two layers, shown on the right side only in a very simplified manner, it can be ensured that the whole surface of the substrate is coated. Normally the deposition of the layers may not be this constant.

[0050] The fluorinated polymer coating of the DF step can be based on ultrashort-chain perfluorocarbons (hexafluoropropene, octafluoropropene, trifluoropropene, pentafluoropropene etc.), fluorsurfactants, acrylic monomer with C1/C2/C3 carbonfluorid based, fluorinated acrylates (perfluorodimethylcyclohexane).

[0051] Following the DF step, a step IG is executed, wherein the previously double coated substrate and therefore also the two coatings are exposed to an inhibiting gas. The aim of this exposure is to inhibit the formation of per- and polyfluorinated acids and their salts, should the coated object be brought into contact with oxygen.

[0052] The post-treatment during inhibition step using i.e., hydrogen, nitrogen, hydrocarbon and or mixture thereof can deactivate with the remaining reactive intermediates formed in the deposited coating as described above and thus, a chemically inactive coating via propagation, saturation etc. can be produced.

[0053] According to the invention it may be essential that, until the step IG is carried out, the treated and coated object is handled in an essentially oxygen-free atmosphere. According to the invention, this can be understood in a way that all the treatment and the deposition is done in a chamber which has a vacuum atmosphere, a low-pressure atmosphere or an atmosphere without external oxygen as is present in air. If in the chamber a vacuum is present, outgassing of water vapour comprising oxygenated substances out of the substrate may occur, hence it is hard to achieve a 100% oxygen-free atmosphere. However, these small amounts of oxygenated substances do not have any negative effect to inhibit the formation of per- and polyfluorinated acids and salts thereof.

[0054] After the step IG is executed, in principle the coated object can be used or delivered to further processing.

[0055] However, in this embodiment, to further improve the characteristics of the object, an additional DNF step is foreseen to provide a further coating. In this connection, it can be underlined that due to the use of non-fluorinated polymers during this step, the creation of critical radicals and active substances which may lead to pre- and polyfluorinated acids and salts thereof in combination with oxygen, does not occur, so that this step can also be carried out under atmospheric pressure including oxygen.

[0056] As can be seen on the right side in a simplified manner, the object to be coated in this way is provided with a fluorinated polymer coating which is sandwiched by two non-fluorinated polymer coatings.

[0057] Generally, the object to be coated can be of any kind. Preferably, the inventive method is used to coat composite membranes made of one or more carrying layers and a one or more membrane layers. For this a further example is explained in the following figures.

[0058] The scheme of FIG. 2 shows an example for a manufacturing process for a polymeric fabric like a composite comprising a carrier layer. A collection substrate (top picture) is provided on which an electrospinning membrane is formed (first production step). The electrospinning membrane is formed according to generally known concepts and further described in the following.

[0059] In a second step the formed membrane is transferred and bonded (Bond 1) onto a carrier layer and the original collection substrate on which the electrospinning membrane has been formed can be optionally removed (collection substrate removal). According to the above provided to diagram the carrier layer can be a mesh or fabric.

[0060] Optionally their second bonding (Bond 2) can take place after introduction of the second outer layer followed by an optional calendering process. Thus, the membrane can be optionally arranged between two equal or different layers forming a sandwich structure. The second outer layer can be provided for example as a mesh, lining or nonwoven material. Finally, the inventive plasma coating is applied to at least one carrier layer and the membrane.

[0061] A first layer providing hydrophobic characteristics only and a following layer providing hydrophobic and oleophobic characteristics may be deposited. The first layer may be a pp-HMDSO, a fluorine doped HMDSO, a DLC or a fluorine doped DLC layer. The further, outer layer may be a layer based on PFAS comprising only one, two or three C-atoms and/or based on PFPE.

Electrospinning

[0062] The processes for making the nanofiber web are illustrated in WO 2006/131081, WO 2008/106903.

[0063] Briefly, in the electrospinning process a high voltage is used to create an electrically charged jet of polymer solution or melt out of the pipette. Before reaching the collecting screen, the solution jet evaporates or solidifies and is collected as an interconnected web of small fibers. One electrode is placed into the spinning solution/melt and the other attached to the collector. In most cases the collector is simply grounded. The electric field is subjected to the end of the capillary tube that contains the solution fluid held by its surface tension. This induces a charge on the surface of the liquid. Mutual charge repulsion and the contraction of the surface charges to the counter electrode cause a force directly opposite to the surface tension. As the intensity of the electric field is increased, the hemispherical surface of the fluid at the tip of the capillary tube elongates to form a conical shape known as the Taylor cone. Further increasing the electric field, a critical value is attained with which the repulsive electrostatic force overcomes the surface tension and the charged jet of the fluid is ejected from the tip of the Taylor cone. The discharged polymer solution jet undergoes an instability and elongation process, which allows the jet to become very long and thin. Meanwhile, the solvent evaporates, leaving behind a charged polymer fiber. In the case of the melt, the discharged jet solidifies when it travels in the air.

Bonding Methods

[0064] There are different bonding techniques available such as hotmelt gravure lamination technology, ultrasonic bonding technology, dipping bonding technology, UFD fiberized spray technology (hotmelt) and spun-web bonding technology.

[0065] Hotmelt gravure lamination technology is industrially established for an in line process. Thus, two steps bonding can also be done in one line for a sandwich type membrane. It uses a multi-purpose hotmelt laminating and coating system which consists of a gravure roller for dot coating, a revolver dosing head (pos/pos or neg/neg) and application roller and a laminating roller and counter pressure roller.

[0066] The gravure roller is used to dot coating with adhesive, whereby two different reactive PU based adhesives (one for PU e-spinning membrane and the other for PA6 membrane) can be used. A high bond strength can be obtained by about 15-25% air permeability loss. The adhesive must be carefully chosen to avoid problems during end application of the membrane (conformity, physical & chemical suitability, medical & food grade etc.). A stiffening of the materials is observed because of adhesives.

[0067] The dipping bonding technology (chemical bonding) can be used for the pre-treatment of a carrier prior to the electrospinning process, which is sometimes preferable. Also, an additional process step for bonding can be eliminated, which is a major advantage. The two layer laminate can then be used for second bonding e.g., hotmelt, spun-web, UFD etc. to form a multilayer vent.

[0068] The UFD is a fiberized spray technology and the most advanced technology for hot melt adhesive applicators. The laminated plate technology (LPT) is applied to produce filament strands of adhesive. Heated air is used to elongate those strands and lay them down in random or ordered patterns. In many cases, by using UFD technology, one can cut adhesive usage by 20-50% without negatively influencing the bond strength or durability by a high precision application of adhesives. A non-contact mode is available which yields in less chance for damages of e-spun fibers during lamination. The UFD technology is a cleaner process than hotmelt gravure lamination.

[0069] The spun-web bonding technology yields rather a three-dimensional structure than a film with a closed surface. The open structure makes the resultant laminate more flexible and with high air permeability. Webs are made of different materials: co-polyamide, co-polyester, co-polyolefins, polyurethanes etc. The spun-web technology is a very simple process. Three major parameters to be considered during lamination are temperature, pressure and time.

Calendering

[0070] Calendering is used on materials such as fabric, mesh, laminate vent to obtain a smoother and thinner material, whereby the material is passed between or under rollers at raised temperatures and pressures. The size and shape of the pores can be affected depending on the calendering conditions.

Plasma PECVD

[0071] The plasma treatment of textile or other materials can be applied as a textile finishing process, i.e., for technical and medical textiles as well as for composite materials, to improve their surface properties like water and oil repellency. This is also possible for other materials and compact objects. Compared to conventional wet-chemical textile finishing, plasma technology shows advantages regarding environmental issues. With the PECVD treatment, e.g., improvement of adhesion characteristics, increasing hydrophilicity, introducing special functional groups on the surface, or modifying the surface morphology can be obtained.

[0072] In plasma deposition, which is commonly known as plasma polymerization or PECVD, a very thin polymer layer (nano-scaled) can be deposited on the substrate surface. The layer is formed through polymerization of an organic precursor gas which is directly polymerized on the substrate surface. In contrast to classic polymerization, plasma polymerization can use every monomer gas or vapor which is not limited to their reactivity. The plasma polymer shows unconventional polymerization behavior with branched and randomly terminated chains and a high degree of crosslinking.

[0073] The bulk structure of plasma polymers is completely irregular, far from that of conventional polymers. Plasma polymer coating (nanothin film) differs from conventional polymer by a high density of functional groups per volume, a highly cross-linked and branched plasma polymer network, a nanometer thick coating, a high adhesion of coating to the substrate and with no change of bulk properties of the substrate, which can be a polymeric fabric.

[0074] The plasma treatment can be performed in a plasma chamber, in case of a fabric having a plurality of rollers and/or expanders in a roll-to-roll system, which may operate with a radiofrequency, preferably of about 13 MHz to 14 MHZ, preferably of about 13.5 MHz or with a direct current (DC) power supply. Preferably all previously explained steps DF, DNF, PT and IG are carried out in this plasma chamber.

PERFORMANCE EXAMPLES

[0075] Below the performance and properties of fabrics being coated according to the inventions including DF coatings based on C3 fluorinated chemistries are shown.

Example 1

[0076] A contact angle of three liquids has been measured according to DIN 55660-2 on two different articles which on the one hand have been coated with a combined C3-based coating (DF), DNF coating and an IG step and on the other hand a C6-based FC coating (benchmark). As can be seen in FIG. 3, a similar hydro- and oleophobicity has been achieved even with the ultra-short chain eco-friendly C3-based coating (DF) compared to the C6-based coating. In addition, a little increase in contact angles for article 3A07-0019-115-XX were found compared to article 3A07-0025-158-XX. This can be explained as follows: higher fabric density (lower mesh opening) and finer filaments of 3A07-0019-115-XX contributes to better repellence effects.

Example 2

[0077] In order to make sure that the plasma coating (DN, DNF and IG steps) adheres well with the substrate, an internal washing test has been performed at 40? C. temperature for 47 min. Table 3 reveals a significant washing resistance of the coating. There is a little decrease in contact angles with three liquids which was measured according to DIN 55660-2, demonstrating high coating adhesion to the object. The oil repellency of the washed object has also been evaluated according to AATCC? 118 using 8 different liquid oils and the results show no changes in oil repellency after washing. Therefore, based on the invention it is possible to obtain a robust and reliable coating on polymeric fabric with excellent hydro- and oleophobic characteristics.

TABLE-US-00003 TABLE 3 Comparative example contact angles of three liquids on C3- coated polyester mesh article # 3A07-0025-158-XX Oil drop test according Contact angle [?] according to DIN 55660-2 to AATCC? 118 Water Diiodmethane Pentandiol [grade 1-8] (top/ (top/ (top/ (top/ Coating type bottom side) bottom side) bottom side) bottom side) DF/DNF coating before 138.5/140.5 128.4/128.0 137.5/135.3 7 washing DF/DNF coating after 138.1/136.3 127.8/128.0 136.6/133.4 7 washing

Example 3

[0078] In order to evaluate water separation efficiency, the test has been performed according to ISO/TS 16332 standard on a DNF and DF coated polyester article. It can be seen in the table 4 that a comparable result with water separation efficiency greater than 90% was obtained even with C3-based environmentally friendly coating as compared to a C6-based coating (benchmark).

TABLE-US-00004 TABLE 4 The developed coating shows excellent water separation efficiency Water separation Water separation Coating type Article top side [%] bottom side [%] DNF + DF coating 3A07-0019- 90.7 90.6 115-XX Benchmark: C6 3A07-0019- 90 90 based flourinated 115-XX coating

[0079] Besides a performance test, also endotoxin and hemocompatibility testing of fabrics coated according to the invention were performed.

[0080] Endotoxin testing is performed to determine the accessibility of the product for medical applications. The endotoxin limit is calculated according to Pharmacopoeia (EP 10, January 2020 and USP 42, May 1, 2019<85>). Both DF and DNF coated articles contain less than the endotoxin limit concentration and have passed the test.

[0081] Hemocompatibility of blood-contacting materials is also one of the most important criteria for medical applications. The interactions between newly developed coated materials and blood has been extensively analyzed, in accordance with ISO 10993-4 and ISO 10993-12, to prevent activation and destruction of blood components in applications. The hemocompatibility analysis of the coated articles are summarized in the below table 5 and all coated articles passed the test.

TABLE-US-00005 TABLE 5 The limulus amoebocyte lysate (LAL, according to Pharmacopoeia EP 10 and USP 42 <85>) and hemolysis (ISO 10993-4 and ISO 10993-12) shows the coating compliance for medical applications Test Tested Specification Pass/ Coaing type Article type parameter Results (limit value) Fail DF-based 3A07- LAL Endotox 0.063 ?0.125 PASS fluorinated 0019-055- in [EU/ml] coating XX PPC 108 50-200 PASS (positive product control) [%] DF-based 3A07- Hemolysis OD 0.008 ?0.03 PASS fluorinated 0019-055- (optical coating XX density) DNF-based 3A07- LAL Endotox 0.063 ?0.125 PASS coating 0025-158- in [EU/ml] XX PPC 99 50-200 PASS (positive product control) [%] DNF-based 3A07- Hemolysis OD 0.002 ?0.03 PASS coating 0025-158- (optical XX density)

[0082] In order to fulfil biocompatibility requirements in medical applications, the cytotoxicity test has been performed on a DNF and DF coated polyester article according ISO 10993-5 to determine how much the coated articles can damage, or even cause the death of human cells. The optical evaluation of the cell morphology and cell viability have been presented in the table 6. It was found that the coating almost don't inhibit the cell growth. The cell viability for the coating is also very good, and thus the coating meets the requirements of ISO 10993-5.

TABLE-US-00006 TABLE 6 Cytotoxicity results on coated articles Cell Viability Coating type Article morphology Reactivity [%] DNF + DF 3A07-0019- 10-20% growth 1/1/0 76 055-XX inhibition

[0083] Based on the invention it is possible to provide a method of producing an object having a fluorinated polymer coating deposited by a plasm deposition process, which is free of per- and polyfluorinated acids and salts thereof as well as an object comprising a fluorinated polymer coating which is free of per- and polyfluorinated acids and salts thereof.