Polypropylene film with enhanced hydrophobicity and method of making and use thereof

Abstract

The present invention relates to a multilayer polypropylene film comprising: a polypropylene base layer (2); optionally, a tie layer (3) comprising a blend of polypropylene and a sacrificial thermoplastic engineering plastic; a top layer (1) comprising a film having a structured surface with a water contact angle (WCA) greater than 104.5°, preferably greater than 110°, more preferably greater than 120°, more preferably greater than 130°; wherein the top layer comprises a blend of 20-40 wt% polypropylene and 60-80 wt% of the thermoplastic engineering plastic, wherein the sacrificial thermoplastic engineering plastic has been selectively etched to produce the structured surface.

Description

TECHNICAL FIELD

[0001] The present invention relates to a polypropylene film, in particular a polypropylene film having a structured surface with a water contact angle greater than 104.5°. The present invention also relates to a process for obtaining said polypropylene film. TECHNICAL BACKGROUND

[0002] Materials are intrinsically hydrophilic when the water contact angle (WCA) is < 90° and hydrophobic when the WCA is > 90°. The hydrophobicity of a surface results in a self-cleaning property, where water droplets roll off the surface, taking with them any dirt particles. This self-cleaning property is more effective at high WCA. Achieving this self-cleaning property is of great value for different applications, from windows and windshields to road surfaces and clothing.

[0003] To achieve this property, various treatments, coatings, fabrics, etc. have been developed. These different approaches make it possible to render surfaces hydrophobic and even superhydrophobic.

[0004] However, in most cases such treatments are expensive, not durable and not fully transparent. The latter means that it cannot be used for example on applications such as windows, windshields and solar panels. Especially solar panels require high transparency and need to be cleaned regularly, otherwise they will lose efficiency over time as dirt builds up on the surface.

[0005] In the past decades, extensive research has been done on the patterning of polymer films in order to create a rough surface to increase the WCA of the material. Techniques such as (soft) lithography are difficult to use on large surface areas, because the production of the stamps is very difficult and expensive and they easily lose their surface structure when used at the high speeds required for mass production. Other techniques involve the use of exotic / toxic solvent / non-solvent combinations.

[0006] It is an object of the present invention to provide a simple, fast and cheap way to produce a polypropylene film having a structured surface with a water contact angle greater than 104.5° to have a better hydrophobicity than flat polypropylene. SUMMARY

[0007] The present invention achieves this object. In a first aspect, the present invention relates to a multilayer polypropylene film comprising:

[0008] a polypropylene base layer (2)

[0009] optionally a tie layer (3) comprising a blend of polypropylene and a thermoplastic engineering plastic;

[0010] a top layer (1) comprising a film having a structured surface with a water contact angle (WCA) greater than 104.5°, preferably greater than 110°, more preferably greater than 120°, more preferably greater than 130°;

[0011] wherein the top layer comprises a blend of 20-40 wt% of polypropylene and 60-80 wt% of the sacrificial thermoplastic engineering plastic, and wherein the thermoplastic engineering plastic has been selectively etched to produce the structured surface.

[0012] In some embodiments of the application, the top layer comprises a compatibilizer consisting of a PP block / grafted thermoplastic engineering plastic.

[0013] In some embodiments of the application, the thermoplastic engineering plastic is PBT or PC and the compatibilizer is PP-b / g-PBT or PP-b / g-PCL, respectively.

[0014] In some embodiments of the application, the amount of compatibilizer in the top layer is at most 15 wt%, preferably between 2 and 15 wt%, more preferably between 12 and 6 wt%.

[0015] In some embodiments of the application, the amount of polypropylene in the tie layer is between 90 and 60 wt%, preferably 70 wt%, and the amount of thermoplastic engineering plastic is between 10 and 40 wt%, preferably 30 wt%.

[0016] In some embodiments of the application, the thickness of the top layer is between 10 and 40 pm, preferably 20 pm.

[0017] In some embodiments of the application, the thickness of the tie layer is between 5 and 10 pm, preferably 5 pm.

[0018] In some embodiments of the application, the solvent used for selectively etching the sacrificial thermoplastic engineering plastic is hexafluoro-2-propanol (HF-PIP) in case of a PBT / PP top layer and dichloromethane (DCM) in case of a PC / PP top layer.

[0019] In some embodiments of the application, the viscosity ratio between PP and the sacrificial thermoplastic engineering plastic in the top layer is greater than 2, preferably greater than 5, more preferably greater than 10.

[0020] In another aspect, the present application relates to the use of the multilayer polypropylene film according to any of the preceding claims as a coated surface of a substrate, preferably the substrate is a panel, a transparent material, a window, a windshield or a solar panel.

[0021] In another aspect, the present application relates to a method of producing a hydrophobic polypropylene multilayer film, wherein the method comprises the following steps:

[0022] a. Immersion of a polypropylene multilayer film with a top layer comprising a blend of 20 to 40 wt% polypropylene and 60 to 80 wt% of a sacrificial thermoplastic engineering plastic selected from the group consisting of PBT and PC in an etching solvent selected from hexafluoro-2-propanol (HF-PIP) in case of a PBT / PP top layer and dichloromethane (DCM) in case of a PC / PP top layer for 30 minutes; optionally shaking, preferably with a shaking frequency of 100 Hz.

[0023] b. Drying of the polypropylene multilayer film in a fume hood for at least 24 hours.

[0024] It should be noted that the present application relates to all possible combinations of the features described herein, in particular preferably those combinations of features recited in the claims. It is therefore to be understood that all combinations of embodiments described herein, all combinations of features relating to the composition according to the present application, all combinations of features relating to the method according to the present application, and all combinations of features relating to the composition according to the present application and features relating to the method according to the present application are described.

[0025] It should also be noted that the terms "comprising", "comprise", "including", "include" do not exclude the presence of other elements. However, it should also be understood that descriptions according to products / compositions containing certain components also disclose products / compositions consisting of these components. Products / compositions consisting of these components can be advantageous, for example, because their manufacture is less costly or more economical. Similarly, it should be understood that descriptions according to methods containing certain steps also disclose methods consisting of these steps. Methods consisting of these steps can be advantageous, for example, because they are less costly or more economical.

[0026] When referring to a lower limit and an upper limit value of a parameter, it is also understood that the range formed by the combination of the lower limit value and the upper limit value is disclosed. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 a shows a comparative embodiment which is not part of the present application. In this embodiment the top layer consists for the most part of PP.

[0028] Figure 1 b and Figure 1 c shows an embodiment of the present application wherein the top layer consists for the most part of a sacrificial thermoplastic engineering plastic:

[0029] Figure 1 b shows an embodiment wherein no tie layer is present;

[0030] Figure 1 c shows an embodiment wherein a tie layer is present.

[0031] Figure 2 The microscopic analysis of the samples is shown, demonstrating the effects of different amounts of compatibilizer on PP fibrils. Detailed Implementation

[0032] The present invention preferably relates to a multilayer film prepared from a polypropylene (PP) base layer (2) and a top layer (1) comprising a blend of polypropylene and sacrificial thermoplastic engineering plastics.

[0033] The top layer is etched using a selective solvent to remove sacrificial thermoplastic engineering plastics. This leaves a structured surface with a water contact angle >104.5°, preferably >110°, more preferably >120°, and even more preferably >130°.

[0034] Preferably, the sacrificial thermoplastic engineering plastic is polybutylene terephthalate (PBT) or polycarbonate (PC).

[0035] To selectively etch only a single component of sacrificial thermoplastic engineering plastics, the solvent used should dissolve the sacrificial thermoplastic engineering plastic while preserving the integrity of the PP phase. For this purpose, the following sacrificial thermoplastic engineering plastic / solvent combinations are selected:

[0036] PBT / Hexafluoro-2-propanol (HF-PIP)

[0037] PC / Dichloromethane (DCM)

[0038] In addition, in order to obtain a higher WCA, the top layer of the blend must contain a majority of sacrificial thermoplastic engineering plastics in its composition.

[0039] In fact, an experiment has been conducted on a PP-rich blend film with a top layer containing 70% by weight of PP and 30% by weight of sacrificial thermoplastic engineering plastic.

[0040] Prior to etching, the WCA of the blend was only slightly lower than that of PP alone, indicating that the polarity only increased slightly after the sacrificial thermoplastic engineering plastic was added to PP.

[0041] After etching, as Figure 1 As shown in Figure A, WCA increases only slightly as the polar sacrificial thermoplastic engineering plastic is removed. However, WCA does not appear to increase due to surface roughness during etching.

[0042] This effect can be explained by the amount of PP in the blend. The surface of the top film is mainly covered by PP, which protects / shields the underlying dispersed sacrificial thermoplastic engineering plastics, allowing only a small amount of sacrificial thermoplastic engineering plastics to be removed, leaving an almost flat surface.

[0043] These results clearly show that the PP-rich top layer did not deliver the expected results.

[0044] As Figure 1 As shown in Figure B, the presence of only "negative" structures on the surface does not seem to be as effective as the presence of "positive" structures on the surface.

[0045] Through various tests, it has been shown that the maximum amount required to avoid the shielding effect of PP is 40-45 wt. %.

[0046] Furthermore, it has been shown that the minimum of PP required to have a structured pattern on the surface of the film is 20 wt. %. At lower concentrations, there is not enough PP and the solvent etches the entire top layer.

[0047] Therefore, a concentration of PP in the top layer of 20-40 wt. % achieves the highest contact angle.

[0048] At lower PP content (<20 wt. %), the PP fibrils can not form a network and can be completely removed from the surface upon etching. At higher PP content (>45 wt. %), the PP either becomes the dominant phase on the top surface or forms a very thick, non-penetrable layer, preventing proper etching, as in the case of a PP-rich top layer.

[0049] In some embodiments, a tie layer (2) comprising a blend of polypropylene and a sacrificial thermoplastic engineering plastic can be present between the top layer and the PP base layer.

[0050] In contrast to the top layer, the tie layer is mainly (>50 wt. %) composed of PP, preferably 60-90 wt. % of PP, more preferably 70-80 wt. % of PP, more preferably 70 wt. % of PP.

[0051] Due to the small amount of sacrificial thermoplastic engineering plastic contained in the tie layer, the tie layer is used to improve the adhesion of the top layer.

[0052] Furthermore, as shown in Figure C, the presence of the tie layer allows the surface of the film to have both "negative" and "positive" structures, allowing for a higher WCA. Figure 1

[0053] In some embodiments, the thickness of the tie layer can be between 5 and 10 pm, preferably 5 pm.

[0054] In some embodiments, to enhance the adhesion of the top layer as well as increase the WCA, a compatibilizer can be used in the top layer at a concentration of up to 15 wt. %.

[0055] In fact, due to the etched top layer that can lack mechanical integrity, especially since the sacrificial thermoplastic engineering plastic is used as the main phase of the top layer, the top layer will require a suitable carrier.

[0056] ​One difficulty in using PP films is that PP is immiscible, even incompatible, with most other polymers. Possibly, therefore, any blend would require a compatibilizer to adjust the morphology and thereby control the surface topography after etching.

[0057] The compatibilizer is specific to the sacrificial thermoplastic engineering plastic used. In the case of PP / PBT, it can consist of a block / graft copolymer of PP and PBT; or in the case of PP / PC, of polycaprolactone (PCL).

[0058] Those compatibilizers were produced starting from maleic anhydride grafted PP (PP-MAH (0.8 wt% of MAH)) using ethanolamine to convert it into PP-OH.

[0059] For the compatibilizer of PP / PBT blends, PP-b / g-PBT was prepared from PP-OH and PBT. The grafting of PBT was carried out in the presence of aluminium diethylphosphinate in a 67:33 ratio.

[0060] For the compatibilizer of PP / PC blends, PP-b / g-PCL was prepared from PP-OH and PCL. The grafting of PCL was carried out in the presence of stannous (II) 2-ethylhexanoate in a 33:67 ratio.

[0061] The compatibilizer content in the optimized top layer is between 2 and 15 wt%, more preferably 6-12 wt%, more preferably 6-10 wt%, more preferably 6 wt%.

[0062] Microscopic analysis of the samples showed that when the compatibilizer content increased, the PP fibril thickness increased, so the surface became "flatter" compared to surfaces with thin PP fibrils, as Figure 2 shown.

[0063] In some embodiments, the thickness of the top layer is between 10 and 40 pm, preferably 20 pm.

[0064] In some embodiments, the presence of a tie layer can prevent the top layer from being delaminated by the solvent, at low PP concentration, or when the thickness of the top layer is higher than 30 pm; or in the absence of a compatibilizer. However, the presence of such a tie layer is not essential in the present application.

[0065] In some embodiments, the viscosity ratio between PP and the sacrificial thermoplastic engineering plastic is higher than 2, preferably higher than 5, more preferably higher than 10. Indeed, it was surprisingly found that a higher viscosity ratio greatly increased the WCA of the film (see Example 7 and Example 11), allowing superhydrophobicity with a WCA > about 130°.

[0066] Note that the present invention relates to all possible combinations of embodiments described herein, and particularly preferred combinations of features present in the claims. Therefore, it should be understood that this document describes all combinations of embodiments, all combinations of features relating to compositions according to the invention, all combinations of features relating to methods according to the invention, and all combinations of features relating to compositions according to the invention and methods according to the invention.

[0067] Another aspect of the present invention is a method for producing hydrophobic polypropylene multilayer films, wherein the method includes the following steps:

[0068] a) Immersing a polypropylene multilayer film having a top layer in an etching solvent for 30 minutes, the top layer comprising 20 to 40 wt% polypropylene and 60 to 80 wt% a sacrificial thermoplastic engineering plastic selected from PBT and PC, the etching solvent being selected from hexafluoro-2-propanol (HF-PIP) in the case of a PBT / PP top layer and from dichloromethane (DCM) in the case of a PC / PP top layer; and

[0069] The earthquake motion can be selected, with a preferred vibration frequency of 100Hz.

[0070] b) Dry the polypropylene multilayer film in a fume hood for at least 24 hours.

[0071] Another aspect of the invention is the use of the multilayer polypropylene film according to the invention as a substrate, preferably a coating surface of a panel, transparent material, window, windshield, or solar panel.

[0072] Example

[0073] raw materials

[0074] The raw materials used in this report are listed in the table below:

[0075]

[0076] Membrane extrusion

[0077] All multilayer films are assembled in Labtech with an L / D ratio of 30 using a winding system. TM Extrusion was performed on an LCR300 25mm blown film co-extruder. The extruder was equipped with a 300mm wide multi-layer die with an A / B / C / B / A design and adjustable die gap. The extrusion distribution used was adjusted according to each composition, as shown in Section 4. PP and PBT reference films were extruded at 240°C and approximately 100 rpm.

[0078] Film etching

[0079] The membrane was cut into slices approximately 1 x 6 cm, immersed in a solvent, and vibrated at 100 Hz for 30 minutes. This process was repeated twice, after which the membrane was removed and dried in a fume hood for at least 24 hours. Hexafluoro-2-propanol was used as the solvent for PBT / PP samples, and dichloromethane (DCM) was used for PC / PP samples.

[0080] Membrane evaluation

[0081] 2 μL of demineralized water droplets were deposited using a special hydrophobic nozzle, and then... (The sentence is incomplete and requires more context to translate accurately.) TM The water contact angle (WCA) was measured using a THETA optical tensiometer. Temperature and relative humidity were recorded within the range of 22–23°C and 50–70% RH.

[0082] Table 1. Formulations used in multilayer polypropylene films containing a PC / PP top layer (including WCA data before and after etching).

[0083]

[0084] Table 1 Formulations used in multilayer polypropylene films containing a PC / PP top layer (including WCA data before and after etching) (continued)

[0085]

[0086] The blend of Example 11 was prepared based on high-viscosity PP (PP-2) and low-viscosity PC (PC-2).

[0087] Under the blending conditions used, the viscosity ratio of this blend is expected to be 1 to 2.

[0088] The blend of Example 7 was prepared based on medium viscosity PP (PP-1) and high viscosity PC (PC-1), and should have a viscosity ratio of 11 to 12 under the blending conditions used.

[0089] Both blends were used as top layers on PP multilayer films with connecting layers and were etched under the same conditions.

[0090] Before etching, the viscosity ratio was unaffected, which was expected because the surface polarity remained unchanged.

[0091] However, after etching, the high viscosity ratio WCA is much higher than that of the low viscosity ratio WCA.

[0092] Therefore, the best results are achieved when the viscosity ratio between PP and sacrificial thermoplastic engineering plastic is high.

[0093] Table 2 Formulations used in multilayer polypropylene films with a PBT / PP top layer (including WCA data before and after etching).

[0094]

[0095] The blend of Example 11 was prepared based on high-viscosity PP (PP-2) and low-viscosity PC (PC-2). Under the blending conditions used, this blend is expected to have a viscosity ratio of 1 to 2.

[0096] The blend of Example 7 was prepared based on medium viscosity PP (PP-1) and high viscosity PC (PC-1), and should have a viscosity ratio of 11 to 12 under the blending conditions used.

[0097] Both blends were used as top layers on PP multilayer films with connecting layers and were etched under the same conditions.

[0098] Before etching, the viscosity ratio was unaffected, which was expected because the surface polarity remained unchanged.

[0099] However, after etching, the high viscosity ratio WCA is much higher than that of the low viscosity ratio WCA.

[0100] Therefore, the best results are achieved when the viscosity ratio between PP and sacrificial thermoplastic engineering plastic is high.

Claims

1. A multilayer polypropylene film, comprising: Polypropylene base layer; The bonding layer comprises a blend of polypropylene and a sacrificial thermoplastic engineering plastic selected from polybutylene terephthalate or polycarbonate. The top layer contains a membrane with a structured surface having a water contact angle greater than 104.5°; The top layer comprises a blend of 20-40 wt% polypropylene and 60-80 wt% of the sacrificial thermoplastic engineering plastic, wherein the sacrificial thermoplastic engineering plastic has been selectively etched to produce the structured surface.

2. The multilayer polypropylene membrane according to claim 1, wherein the top layer comprises a membrane with a structured surface having a water contact angle greater than 110°.

3. The multilayer polypropylene membrane according to claim 1, wherein the top layer comprises a membrane with a structured surface having a water contact angle greater than 120°.

4. The multilayer polypropylene membrane according to claim 1, wherein the top layer comprises a membrane with a structured surface having a water contact angle greater than 130°.

5. The multilayer polypropylene film according to claim 1, wherein the top layer comprises a compatibilizer composed of polypropylene block / grafted thermoplastic engineering plastic.

6. The multilayer polypropylene film according to claim 5, wherein the compatibilizer is either a block / graft copolymer of polypropylene and polybutylene terephthalate (PP-b / g-PBT) or a block / graft copolymer of polypropylene and polycaprolactone (PP-b / g-PCL).

7. The multilayer polypropylene film according to any one of claims 5-6, wherein the amount of compatibilizer in the top layer is at most 15% by weight.

8. The multilayer polypropylene film according to any one of claims 5-6, wherein the amount of compatibilizer in the top layer is between 2 and 15% by weight.

9. The multilayer polypropylene film according to any one of claims 5-6, wherein the amount of compatibilizer in the top layer is between 6 and 12% by weight.

10. The multilayer polypropylene film according to any one of claims 1-6, wherein the amount of polypropylene in the connecting layer is between 60 and 90% by weight, and the amount of the sacrificial thermoplastic engineering plastic is between 10 and 40% by weight.

11. The multilayer polypropylene film according to any one of claims 1-6, wherein the amount of polypropylene in the bonding layer is 70% by weight and the amount of the sacrificial thermoplastic engineering plastic is 30% by weight.

12. The multilayer polypropylene film according to any one of claims 1-6, wherein the thickness of the top layer is between 10 and 40 μm.

13. The multilayer polypropylene film according to any one of claims 1-6, wherein the thickness of the top layer is 20 μm.

14. The multilayer polypropylene film according to any one of claims 1-6, wherein the thickness of the bonding layer is between 5 and 10 μm.

15. The multilayer polypropylene film according to any one of claims 1-6, wherein the thickness of the bonding layer is 5 μm.

16. The multilayer polypropylene film according to any one of claims 1-6, wherein the solvent used for selectively etching the sacrificial thermoplastic engineering plastic is hexafluoro-2-propanol in the case of a polybutylene terephthalate / polypropylene top layer, and dichloromethane in the case of a polycarbonate / polypropylene top layer.

17. The multilayer polypropylene film according to any one of claims 1-6, wherein the viscosity ratio between the polypropylene and the sacrificial thermoplastic engineering plastic in the top layer is greater than 2.

18. The multilayer polypropylene film according to any one of claims 1-6, wherein the viscosity ratio between the polypropylene and the sacrificial thermoplastic engineering plastic in the top layer is greater than 5.

19. The multilayer polypropylene film according to any one of claims 1-6, wherein the viscosity ratio between the polypropylene and the sacrificial thermoplastic engineering plastic in the top layer is greater than 10.

20. Use of the multilayer polypropylene film according to any one of claims 1-19, as a coating surface of a substrate.

21. The use according to claim 20, wherein the substrate is a panel, a transparent material, a window, a windshield, or a solar panel.

22. A method for producing a hydrophobic polypropylene multilayer film, wherein the method comprises the following steps: a. Immersing a polypropylene multilayer film having a polypropylene base layer, a connecting layer, and a top layer in an etching solvent for 30 minutes, wherein the top layer comprises a blend of 20 to 40 wt% polypropylene and 60 to 80 wt% a sacrificial thermoplastic engineering plastic selected from polybutylene terephthalate or polycarbonate; the connecting layer comprises a blend of polypropylene and the sacrificial thermoplastic engineering plastic; the etching solvent is selected from hexafluoro-2-propanol in the case of a polybutylene terephthalate / polypropylene top layer, and from dichloromethane in the case of a polycarbonate / polypropylene top layer; and b. Dry the polypropylene multilayer film in a fume hood for at least 24 hours.

23. The method of claim 22, wherein the polypropylene multilayer film having a polypropylene base layer, a connecting layer and a top layer is immersed in an etching solvent and vibrated for 30 minutes.

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