WO2010083647A1

WO2010083647A1 - Method of changing the wettablility of plastic surfaces by solvent-induced precipitation or solvent-induced crystallization

Info

Publication number: WO2010083647A1
Application number: PCT/CN2009/070272
Authority: WO
Inventors: Yoong Kim; Szu Lui Tey; Andreas Fechtenkoetter; Alexander Traut; Liang Zhang; Jian Xu
Original assignee: Basf Se; Basf (China) Company Ltd.
Priority date: 2009-01-22
Filing date: 2009-01-22
Publication date: 2010-07-29
Also published as: CN102292382A

Abstract

A method for making an article comprises the following steps: providing a polyamide substrate; contacting a selected surface region of the polyamide substrate with a swelling agent having a high solubility limit for the polyamide substrate, whereby a surface part of the polyamide substrate is swollen and a part underneath the surface is non-swollen; contacting the swollen polyamide substrate with a coagulating agent having a low solubility limit for the polyamide and being miscible with the swelling agent, whereby the swollen part of the polyamide substrate is first precipitated and then crystallized back onto the non-swollen part. With the method, an article having a structured hydrophilic or superhydrophilic polyamide surface is obtained.

Description

Method of changing the wettability of plastic surfaces by solvent-induced precipitation or solvent-induced crystallization

Description

The present invention relates to a method for making an article from a polyamide substrate, the article having a structured surface, as well as an article prepared by said method, and the use of said article for outdoor and indoor applications.

There are many methods known in the art to modify the wettability of surfaces. It is known in the art that by increasing the surface roughness of a hydrophobic material the surface water repellency can be dramatically enhanced. This strategy is impeccably exhibited by the Lotus leaf, of which the surface is structured on two length scales by micron- and nanosized waxed protrusions. Inspired by the Lotus effect, researchers attempt to mimic the behaviour of the Lotus effect. Similarly, according to the Wenzel theory, the increase in surface roughness of a hydrophilic material can enhance surface hydrophilicity. Techniques known in the art for surface modification include for example plasma treatment, lithography, physical deposition/adsorption, or grafting. However, these techniques are usually time-consuming, difficult to control, expensive or suffer from poor durability of the coated films obtained. Therefore, a simple and economical procedure for obtaining suitably structured surfaces still remains.

The focus of most of the prior art documents concerning the wettability of surfaces is the provision of superhydrophobic surfaces. However, also hydrophilic and superhy- drophilic surfaces are of interest, because of the good wettability with water, demonstrated by a low contact angle. Hydrophilic and superhydrophilic surfaces are for example useful as anti-fogging equipment for mirrors, headlights, etc., or for providing surfaces which are easily cleaned, because a water film formed on the hydrophilic or superhydrophilic surface entraps dirt particles present on the surface.

US 2007/0009709 A1 relates to a method to modify the surface of an article so as to alter its wettability. The method according to US 2007/0009709 A1 comprises the steps of: (a) providing a substrate comprising a polymer; and (b) inducing a phase transformation at a selected surface region of the substrate, wherein the phase transformation forms a texture at the selected surface region; wherein the texture comprises a plurality of features having a largest characteristic dimension of up to about 50 microns. According to US 2007/0009709 A1 several different methods for inducing the phase transformation according to step (b) are disclosed. According to US 2007/0009709 A1 it is possible to make either hydrophobic/superhydrophobic or hydrophilic/superhydrophilic articles by the method mentioned in US 2007/0009709 A1. Examples of polymers that may be made superhydrophilic are according to US 2007/0009709 A1 poly(ethylene oxide), poly(hydroxy ethyl methacrylate, poly(acrylic acid), poly(acrylamide), poly(styrene sulphonic acid), poly(ethylene imine), polyvinyl pyrrolidone) and biopoly- mers like cellulose acetate. However, it is neither mentioned in US 2007/0009709 A1 whether or not a quenchant is used to obtain the superhydrophilic surfaces, nor which quenchants may be suitable. Further, polyamides are not mentioned in US 2007/0009709 A1 as appropriate polymers. According to the examples in US 2007/0009709 A1 polycarbonate and a copolymer of polycarbonate and siloxane are made superhydrophobic. US 2007/0009709 A1 therefore especially mentions the en- hancement of the hydrophobicity of surfaces of crystallizable polycarbonate.

It is an object of the present invention to provide articles having superhydrophilic surfaces, wherein a common and not expensive polymer is employed.

The present invention therefore provides a method as well as an article, wherein polyamides can be used as substrates to create hydrophilic and - preferably - superhydrophilic structured surfaces thereon.

The present invention therefore relates to a method for making an article comprising the steps of

(i) providing a polyamide substrate;

(ii) contacting a selected surface region of the polyamide substrate with a swelling agent, the swelling agent having a high solubility limit for the polyamide sub- strate, whereby a surface part of the polyamide substrate is swollen and a part underneath the surface of the polyamide substrate is non-swollen; (iii) contacting the polyamide substrate of step (ii), wherein a part of the polyamide surface substrate is swollen, with a coagulating agent, the coagulating agent having a low solubility limit for the polyamide and being miscible with the swelling agent, whereby the swollen part of the polyamide substrate is first precipitated and then further crystallized back onto the non-swollen part of the polyamide substrate, whereby an article having a structured hydrophilic or superhydrophilic polyamide surface is obtained.

In one embodiment the method of the present invention additionally comprises the incorporation of additives, especially nanoparticles, into the structured polyamide surface obtained in step (iii).

Step (i)

Types of polyamide substrate Suitable polyamide substrates may be all polyamides known in the art. Said polyam- ides may be classified as aliphatic polyamides, wherein the monomers employed for preparing the aliphatic polyamides are aliphatic monomers, for example PA6 made from caprolactam or PA66 made from hexamethylene diamine and adipic acid; semi- aromatic polyamides, wherein the monomers employed for preparing the semi- aromatic polyamides are aliphatic monomers as well as aromatic monomers, for example PA6T made from hexamethylene diamine and terephthalic acid, or aromatic poly- amides, wherein the monomers employed for preparing the aromatic polyamides are aromatic monomers, for example aramide made from para-phenylene diamine and terephthalic acid.

Further, suitable polyamide substrates classified as homopolyamides derived from an amino-carboxylic acid or a lactame or derived from a diamine and a dicarboxylic acid. Such polyamides are described by one repetition unit. Examples are the polyamide of caprolactam (PA6) [NH-(CH₂)_S-CO]_n or the polyamide of hexamethylene diamine and adipic acid (PA66) [NH-(CH₂)6-NH-CO-(CH₂)₄-CO]_n (which both are also classified as aliphatic polyamide). Alternatively, copolyamides derived from several different monomers are suitable polyamide substrates. Such copolyamides are described by more than one repetition unit. Examples are the polyamide of caprolactam, hexamethylene diamine and adipic acid (PA6/66) [NH-(CH₂)₆-NH-CO-(CH₂)₄-CO]_n-[NH-(CH₂)₅-CO]_m or the polyamide of hexamethylene diamine, adipic acid and sebacinic acid (PA66/610) [NH-(CH₂)₆-NH-CO-(CH₂)₄-CO]_n-[NH-(CH₂)₆-NH-CO-(CH₂)₈-CO]_m. The monomeric units of the copolyamides are usually statistically distributed over the polymer chain.

Further, suitable polyamide substrates may be classified as semi-crystalline polyam- ides or amorphous polyamides depending on the chemical nature of the polyamide and on the cooling conditions. Easily crystallizable polyamides are for example PA 46 (tetramethylene diamine/adipic acid) or PA66. Hardly crystallizable polyamides are for example the polyamide m XD6 made from m-Xylylendiamin and adipic acid or some copolyamides. Amorphous polyamides are for example the polyamide PA6I made from hexamethylene diamine and isophthalic acid and some copolyamides.

Suitable examples of polyamides useful as polyamide substrates according to the pre- sent invention are PA6, PA66, PA6T, Aramide, PA6/66, PA46, PAmXD6, PA6I, PA69 (hexamethylene diamine/acelaic acid), PA612 (hexamethylene diamine/dodecane dia- cid), PA11 (1 1-aminoundecanoic acid), PA12 (laurine lactame or omega aminode- canoic acid), PA1212, PA6/12 (caprolactame/laurine lactam and blends thereof. Preferred polyamides are PA6, PA66 and PA6/66. Most preferred is PA66. The polyamides mentioned before are known by a person skilled in the art and are commercially available or prepared by known methods.

The molecular weight of the polyamides mentioned before is not specifically limited. However, suitable molecular weights for specific applications are known by a person skilled in the art.

The polymer substrate may be in the form of a fiber, film, sheet or in form of a bulk shape.

It is possible to produce highly hydrophilic articles by the method of the present invention. For the case of highly hydrophilic articles, the static water contact angle of the original flat, untreated polyamide substrate should be 50 to 80°. In some preferred embodiments to achieve highly hydrophobic surfaces the static water contact angle of its original flat, untreated surface is 60 to 70°.

The static contact angle is the angle that a liquid droplet forms on the interphase of three phases, i.e. the angle made by the liquid/vapour interface from the liquid /solid interface. The contact angle of a liquid on a surface is governed by the Young relation and it is dependent on the interfacial tensions at a point on the three-phase contact line.

Generally, a hydrophilic material or surface is characterized by a static water contact angle of water of less than 90°. Some hydrophilic coatings are being referred to in the art as superhydrophilic coatings. Superhydrophilic coatings are generally defined by a static water contact angle below 5°.

For a highly hydrophilic surface, a 5μl_ deionized water droplet dispensed on such a given surface did not remain stable and would continually spread over a period of time. Consequently, as a measure of the degree of surface hydrophilicity, the time taken for a 5μl_ deionized water droplet to completely spread on the structured sample surface until it dries up was noted.

The time taken for a 5μl_ deionized water droplet to completely spread on the struc- tured surface of the articles prepared according to the method of the present invention is usually below 10 minutes, preferably 0 to 5 minutes, more preferably 0 to 1 minute.

The time taken for a 5μl_ deionized water droplet to completely spread on the structured surface was measured as described in the example part of the present applica- tion. It has been found that it is possible to prepare hydrophilic or superhydrophilic polyam- ide surfaces by the method of the present invention.

Step (ii)

Types of swelling agent (solvent)

The swelling agent used according to the method of the present invention has a high solubility limit for the polyamide substrate. Suitable swelling agents may comprise of liquid and/or gaseous fluids. A liquid fluid may be an acid, base, water, organic solvent or a suitable mixture thereof. Organic solvents that may be used include, but are not limited to alcohols like ethanol-or hexafluoroisopropanol as well as formic acid. The most generally used gaseous fluid may be moisture or humidity in the environment. Preferred swelling agents for the polyamide are selected from the group consisting of formic acid, hexafluoroisopropanol, alcohos like methanol, ethanol or isopropanol, water and mixtures of the swelling agents mentioned before. For PA6 and PA66 formic acid and hexafluoroisopropanol are particularly preferred. For amorphous polyamide copolymers mixtures of ethanol/water are particularly preferred. If the polyamide is PA 66, the most preferred swelling agent is formic acid.

According to the process of the present invention a part of the polyamide substrate surface is swollen and a part of the polyamide substrate underneath the surface is non- swollen. The part of the polyamide substrate which is swollen is usually the top surface of the polyamide substrate. The polyamide surface which is preferably swollen is usu- ally at the top 10 to 100 μm of the substrate surface. Preferred effective swelling of the polyamide substrate is indicated by softening of the top 10 to 100 μm of the substrate surface, which is usually achieved within at most 3 minutes, preferably at most 1 minute, more preferably at most 30 seconds (contact of the polyamide with the swelling agent).

According to step ii) of the method of the present invention a selected surface region of the substrate is contacted with the swelling agent. The term selected surface region as used in the present invention includes the surface and a region preferably from 10 to 100 μm below the surface of the polymer substrate.

The part of the polyamide substrate which is swollen is the selected surface region, which is the region comprising the surface of the polyamide substrate and the region from 10 to 100 μm below said surface. The part of the substrate which is non-swollen is the part of the substrate underneath the swollen surface region.

Method of introducing the swelling agent If a liquid swelling agent is used, step (ii) of the method of the present invention is carried out by introducing the liquid swelling agent onto the surface of the polyamide substrate by drop cast application, spray application, doctor blade application or dipping the substrate into the liquid swelling agent, or by any other methods, depending on the requirements of the intended application.

If a gaseous swelling agent is used, step (ii) of the method of the present invention is carried out by placing the polyamide substrate inside an enclosed environment that is filled in with the vapour of the particular gaseous fluid, which may be moisture or the humidity in the environment. Said fluid is usually fed to specific levels of vaporisation.

The choice of the introduction of the swelling agent onto the surface of the polyamide substrate depends on the intended application, especially on whether the process can fit into the current forming process for manufacturing of plastic components specific to the intended application.

Step (iii)

Types of coagulating agent (non solvent)

The coagulating agent has a low solubility limit for the polyamide substrate. According to the present invention the coagulating agent is miscible with the swelling agent in order to facilitate mass transfer, and therefore phase separation, of the polymer from the swelling agent into the coagulating agent. The coagulating agent used may comprise of liquids and/or gaseous fluids. A liquid fluid may be water, an organic solvent or a suitable mixture thereof. Organic solvents that may be used include but are not limited to alcohols like methanol, ethanol, isopropanol or petroleum ether. The most generally used gaseous fluid may be moisture or humidity in the environment.

The term "miscible with the swelling agent" means that at least 20 wt.-% of the coagulation agent are soluble in the swelling agent, preferably 50 to 100 wt-% are soluble in the swelling agent, more preferably 80 to 100 wt.-% are soluble in the swelling agent.

Preferred coagulating agents are selected from the group consisting of water, one or more alcohols, preferably ethanol, or mixtures of water with one or more alcohols like water and ethanol. If the polyamide is PA66, the coagulating agent is most preferably water.

In step (iii) of the method of the present invention the coagulation is carried out, whereby the swollen polyamide substrate is first precipitated and further crystallized back onto the non-swollen part of the polyamide substrate, whereby an article having a structured surface is obtained.

The structured surface is - in the case of crystallizable polyamides - in form of micro and nano-sized particles covered with grooves on the outer surface. In the case of amorphous polyamides the structured surface obtained is a coarse structure comprising of globule-like polymer spheres.

The coagulation of the swollen part of the polyamide substrate, i.e. the coagulation of the swollen surface polyamide chain of the substrate polyamide, onto the non-swollen part of the polyamide substrate occurs via precipitation and crystallization. This means, once the swollen part of the polyamide substrate surface is in contact with a coagulating agent in step (iii) of the method of the present invention, phase separation will involve precipitation and crystallization of the swollen part of the polyamide substrate, i.e. the swollen polyamide chains, back onto the non-swollen part of the polyamide substrate.

Effective coagulation in step (iii) is usually indicated by the appearance of a white precipitate within up to 10 minutes, preferably up to 5 minutes, more preferably up to 1 minute of contact between the part of the polyamide substrate which is swollen (polyamide substrate surface) and the coagulating agent. Thereafter, the entire polyamide substrate surface usually turns completely white and opaque within 60 minutes, preferably up to 20 minutes, more preferably within 5 minutes of contact between the swollen polymer substrate surface (swollen part of the polymer substrate) and the coagulat- ing agent. Preferably, a white precipitate is observed on the swollen polyamide substrate surface within 5 minutes and the entire substrate turns completely white and opaque within 20 minutes. More preferably, a white precipitate is observed on the swollen polyamide substrate surface within 1 minute and the entire substrate surface turns completely white and opaque within 5 minutes.

Method of introducing the coagulating agent

If a liquid coagulating agent is used in step (iii) of the method of the present invention, the liquid coagulating agent may be introduced onto the swollen part of the surface region of the polyamide substrate for example by immersion application, drop cast application, spray application or any other method, depending on the requirements of the intended application.

If a gaseous coagulation is used in step (iii) of the method of the present invention, the polyamide substrate is usually placed inside an enclosed environment that is filled with the vapour of a particular gaseous fluid. The gaseous fluid is usually fed to specific levels of vaporisation.

The choice of the method used for introducing the coagulating agent depends on the intended application, especially on whether the method can fit into the current forming process for manufacturing of plastic components specific to the intended application.

In a preferred embodiment of the present invention the swelling agent is formic acid or hexafluoroisopropanol and the coagulating agent is water, one or more alcohols, pref- erably ethanol, or mixtures of water and at least one alcohol, preferably mixtures of water and ethanol. Most preferably, the polyamide substrate is PA66 and the swelling agent and coagulating agent are preferred combinations of the swelling agent and coagulating agents mentioned before.

Environment temperature during the process

The temperature during the process of the present invention may be the same or different in steps (i), (ii), and (iii). In general, the temperature depends on the speed at which the surface polyamide chains of the substrate may be swollen or coagulated in respect to the swelling agent or coagulating agent used. Heating may for example be required to accelerate the swelling and/or coagulation step. In one embodiment the polyamide substrate alone is preheated to temperatures of 50 to 80°C, preferably 55 to 65°C. Preferably, the polyamide substrate is heated 5 to 20°C above its glass transition temperature (T_g). In a further embodiment (which may be combined with the first em- bodiment) the swelling agent and/or the coagulating agent having a flash point below 20°C, for example ethanol, are maintained at temperatures of at most 25°C; the swelling agent and/or coagulating agent having a flash point below 60°C are maintained at temperatures of 30 to 80°C, preferably 40 to 60°C. More preferably, the swelling agent and/or coagulation agent is maintained at not more than 10°C below its flash point dur- ing use. In a further preferred embodiment, no heating is required and the entire process comprising steps (i), (ii) and (iii) of the present invention is conducted at ambient temperature.

Incorporation of particles onto the structured surface

In a further embodiment of the present invention additional performance benefits, for example ultraviolet- or infrared-absorbents or antimicrobial effects, may be introduced onto the structured polyamide substrate surface by incorporating additives, especially particles, onto the structured surface obtained in step (iii). Preferably, the additional performance benefits are introduced via the incorporation of additives, which may be present in the form of particles, preferably organic or inorganic nanoparticles or organic small molecules. Examples for suitable additives are silica nanoparticles which may be non- or partially hydrophobized. The additives may be deposited in either an ordered or disordered manner, leading to partial or complete coverage of the polyamide substrate surface with said additives. Deposition methods may include, but are not limited to, drop cast application, spray application or doctor blade application. The incorporation of the additives may take place as an additional process step or one or more additive may be dispersed into the swelling agent and/or coagulation agent used. In a preferred embodiment of the method of the present invention the additives are homogeneously dispersed into the swelling agent and/or a coagulation agent. In a further preferred em- bodiment, the additives are homogenously dispersed into the swelling agent, where the additives can act as seeds for controlled precipitation and/or crystallisation to occur during phase separation with the coagulating agent. The amount of additives in the swelling agent and/or coagulating agent is in general of from 0.5 to 30 wt.%, preferably 1 to 20 wt.%, more preferably 1 to 10 wt.%.

The present invention further relates to an article prepared by the method according to the present invention. Said article has surface which is highly hydrophilic and may be superhydrophilic. The time taken for a 5μl_ deionized water droplet to completely spread on the structured surface of the article prepared according to the method of the present invention is in general of from 0 to 10 minutes, preferably 0 to 5 minutes, more preferably 0 to 1 minute. The surface of the articles prepared according to the method of the present invention comprises a precipitation and crystallization of the polyamide substrate employed. It has been found by the inventors that highly hydrophilic polyamide surfaces are obtained by the method of the present invention.

Suitable applications

The articles of the present invention are useful in indoor as well as in outdoor applications. The surfaces of the articles according to the present invention comprise a very good wettability with water, demonstrated by a low static water contact angle.

Such highly wettable surfaces can be used for indoor and outdoor applications to produce articles having anti-fogging properties, including, but not limited to mirrors, headlights. Further, the process of the present invention may be used for making articles more hydrophilic to increase and/or accelerate the water uptake. Polyamides are hydrophilic, but it takes some time for example after the injection molding until the molded article has reached its equilibrium concentration. The change in water concentration also results in a changing size of the article. So one has to wait some days or weeks until the article has reached its final size before the article can be integrated for exam- pie into cars or trucks. By the hydrophilization process of the present invention the water uptake can be accelerated by making the surface of the article more hydrophilic, so the waiting time until the article reaches its final size can be reduced.. Further, the highly hydrophilic articles are easily cleaned, because a water film formed on the highly hydrophilic surface entraps dirt particles present on the surface.

The following examples serve to illustrate the features and advantages offered by the present invention, and are not intended to limit the invention thereto.

Examples

1. Test methods for characterization

A. Rate of Spreading of Water Droplet

As a measure of the degree of surface hydrophilicity, the time taken for a 5μl_ de-ionized water droplet to completely spread on the structured sample surface until it dries up was noted. Measurements were taken from 5 different locations on each sample. The range of time taken for the water droplets to completely spread on surface and dry up was quoted as the rate of spreading.

S Field emission secondary electron microscopy (FE-SEM)

The surface morphology of the final solvent-treated sample was analyzed using field emission secondary electron microscopy on a JEOL JSM 6700 F equipment, where an accelerating voltage of 5 kV was used (see X. Li, G. Chen, Y. Ma, L. Feng, H. Zhao, L. Jiang and F. Wang, Polymer 47 (2006) 506-509).

2. Examples

i. Solvent-Induced Crystallization (SINC) on a Semi-crystalline Homopolymer Plastic Substrate to obtain Highly Hydrophilic Surface

Example on Polvamide 6

A piece of 3cm x 3cm translucent Ultramid^® B3 Polyamide 6 (PA6) substrate was first cleaned with isopropyl alcohol and left to dry under ambient conditions (23°C, 60%RH) for 5 minutes. A thin layer of formic acid solvent (0.5 - 1 mL) was uniformly spread across the entire PA6 surface and swelling of the substrate surface was allowed to take place under ambient room conditions (23°C, 60%RH) for 30 seconds. After which, the surface swollen PA6-substrate was immersed into a non-solvent bath comprising of a mixture of de-ionized water and ethanol at 9:1 volumetric ratio for 20 minutes. The water and ethanol mixture acts as a coagulating agent, which served to phase separate, precipitate and then crystallize the mobile swollen PA6 polymer chains on the surface. At the end of 20 minutes, the PA6 substrate surface appeared completely white and opaque, leaving the unswollen bulk PA6 still translucent. Finally, the surface treated PA6 substrate was placed inside a Petri dish and covered with perforated polyolefin Parafilm^®, then dried under ambient conditions in the fumehood for 24 hours. After which, the PA6 substrate was dried in a dessicator under vacuum for 8 hours to remove water, ethanol and formic acid completely.

The surface morphology of such PA6 substrate, treated via SINC, was investigated using FE-SEM. Representative images (Fig. 1 a and b) show loose clusters of spherical particles (500nm - 5μm) aggregated with one another, producing micro-pores that allow water to penetrate and spread quickly on surface to facilitate the desired highly hydro- philic effect. The nano-sized grooves (or folds) on the particle surface increase surface roughness and enhance the hydrophilic effect. The as-obtained highly hydrophilic sur- face was confirmed by measuring the rate of spreading of water droplet on the dried substrate surface. A 5μl_ droplet of de-ionized water spread and penetrated the substrate surface instantly and dried up between 30 and 60 seconds. In comparison, the original untreated PA6 substrate exhibits a static water contact angle of 70°.

Example on Polvamide 66

A piece of 3cm x 3cm translucent Ultramid^® A3 Polyamide 66 (PA66) substrate was first cleaned with isopropyl alcohol and left to dry under ambient conditions (23°C, 60%RH) for 5 minutes. A thin layer of formic acid solvent (0.5 - 1 mL) was uniformly spread across the entire PA66 surface and swelling of the substrate surface was allowed to take place under ambient room conditions (23°C, 60%RH) for 30 seconds. After which, the surface swollen PA66 substrate was immersed into a de-ionized water bath for 3 minutes. Water acts as a coagulating agent, which served to phase separate, precipitate and then crystallize the mobile swollen PA66 polymer chains on the surface. At the end of 3 minutes, the PA66 substrate surface appeared completely white and opaque, leaving the unswollen bulk PA66 still translucent. Finally, the surface treated PA66 substrate was placed inside a Petri dish and covered with perforated polyolefin Parafilm^®, then dried under ambient conditions in the fumehood for 24 hours. After which, the PA66 substrate was dried in a dessicator under vacuum for 8 hours to remove water and formic acid completely.

The surface morphology of such PA66 substrate, treated via SINC, was investigated using FE-SEM. Representative images (Fig. 2a and b) show loose clusters of spherical particles (500nm - 5μm) aggregated with one another, producing micro-pores that allow water to penetrate and spread quickly on surface to facilitate the desired highly hydro- philic effect. The nano-sized grooves (or folds) on the particle surface increase surface roughness and enhance the hydrophilic effect. The as-obtained highly hydrophilic surface was confirmed by measuring the rate of spreading of water droplet on the dried substrate surface. A 5μl_ droplet of de-ionized water spread and penetrated the substrate surface instantly and dried up between 30 and 60 seconds. In comparison, the original untreated PA66 substrate exhibits a static water contact angle of 70°.

Claims

1. A method for making an article comprising the steps of

i) providing a polyamide substrate; ii) contacting a selected surface region of the polyamide substrate with a swelling agent, the swelling agent having a high solubility limit for the polyamide substrate, whereby a surface part of the polyamide substrate is swol- len and a part underneath the surface of the polyamide substrate is non- swollen; iii) contacting the polyamide substrate of step (ii), wherein a part of the surface of the polyamide substrate is swollen, with a coagulating agent, the coagulating agent having a low solubility limit for the polyamide and being misci- ble with the swelling agent, whereby the swollen part of the polyamide substrate is first precipitated and then further crystallized back onto the non- swollen part of the polyamide substrate, whereby an article having a structured hydrophilic or superhydrophilic polyamide surface is obtained.

2. The method of claim 1 , wherein additives are incorporated into the structured surface obtained in step (iii).

3. The method according to claim 1 or 2, wherein the polyamide substrate is selected from the group consisting of PA6, PA66, PA6T, Aramid, PA6/66, PA46, PAmXD6, PA6I, PA69, PA612, PA11 , PA12, PA1212, PA6/12 and blends thereof.

4. The method according to claim 3, wherein the polymer substrate is selected from PA6, PA66 and PA6/66 and blends thereof.

5. The method according to any of claims 1 to 4, wherein the swelling agent is selected from water, ethanol, mixtures of water and ethanol, formic acid and hexafluoroisopropanol.

6. The method according to any of claims 1 to 5, wherein the coagulating agent is selected from the group consisting of water, alcohol, preferably methanol, ethanol, isopropylalcohol; petroleum ether and mixtures of said coagulating agents.

7. The method as claimed in any of claims 1 to 6, wherein the swelling agent is se- lected from formic acid and hexafluoroisopropanol and the coagulating agent is selected from water, one or more alcohols, preferably ethanol, or mixtures of water and at least one alcohol, preferably mixtures of water and ethanol.

8. An article prepared by the method as claimed in any of claims 1 to 7.

9. The article of claim 8 comprising a polyamide structured surface having a time taken for a 5μl_ deionized water droplet to completely spread on the structured surface from 0 to 10 minutes, preferably 0 to 5 minutes, more preferably 0 to 1 minute.

10. Use of an article according to claim 8 or 9 in indoor applications or outdoor applications.