ULTRAFINE SURFACE-TREATED FILLERS FOR THIN BREATHABLE FILMS

Abstract

The present invention relates to a breathable film having a basis weight from 1 to 15 g/m.sup.2 comprising at least one thermoplastic polymer and a surface-treated filler material comprising calcium carbonate. The surface-treated filler material has a specific particle size distribution and a specific surface-treatment layer. The present invention further relates to a process for producing the breathable film, the use of a surface-treated filler material comprising calcium carbonate as a filler in a breathable film, an article comprising the breathable film and uses of the breathable film.

Claims

1.-16. (canceled)

17. A breathable film with a basis weight from 1 to 15 g/m.sup.2, the breathable film comprising at least one thermoplastic polymer and a surface-treated filler material, wherein the surface-treated filler material comprises A) at least one calcium carbonate-comprising filler material having a weight median particle size d.sub.50 in the range from 0.1 m to 7 m, a top cut particle size d.sub.98 of 15 m, a fineness (<0.5 m) such that at least 15 wt.-% of all particles have a particle size of <0.5 m, and a residual total moisture content of 1 wt.-%, based on the total dry weight of the at least one calcium carbonate-comprising filler material, and B) a treatment layer on the surface of the at least one calcium carbonate-comprising filler material comprising at least one mono-substituted succinic anhydride and/or at least one mono-substituted succinic acid and/or salty reaction product(s) thereof in an amount of from 0.1 to 3 wt.-%, based on the total dry weight of the at least one calcium carbonate-comprising filler material.

18. The breathable film of claim 17, wherein the at least one calcium carbonate-comprising filler material is natural ground calcium carbonate, precipitated calcium carbonate, surface-reacted calcium carbonate, or a mixture thereof.

19. The breathable film of claim 17, wherein the at least one thermoplastic polymer is a polyolefin.

20. The breathable film of claim 17, wherein the at least one thermoplastic polymer is selected from the group consisting of high density polyethylene (HDPE), linear low density polyethylene (LLDPE), low density polyethylene (LDPE), ultra-low density polyethylene (ULDPE), very low density polyethylene (VLDPE), and mixtures thereof.

21. The breathable film of claim 17, wherein the breathable film comprises the surface-treated filler material in an amount from 1 to 85 wt.-%, based on the total weight of the breathable film.

22. The breathable film of claim 17, wherein the breathable film comprises the surface-treated filler material in an amount from 15 wt.-% to 60 wt.-%, based on the total weight of the breathable film.

23. The breathable film of claim 17, wherein the at least one calcium carbonate-comprising filler material has a) a weight median particle size d.sub.50 from 0.25 m to 5 m, and/or b) a top cut particle size d.sub.98 of 12.5 m, and/or c) a fineness (<1 m) such that at least 70 wt.-% of all particles have a particle size of <1 m, and/or d) a fineness (<0.5 m) such that at least 20 wt.-% of all particles have a particle size of <0.5 m.

24. The breathable film of claim 17, wherein the at least one calcium carbonate-comprising filler material has i) a fineness (<1 m) such that at least 80 wt.-% of all particles have a particle size of <1 m, and/or ii) a fineness (<0.5 m) such that at least 30 wt.-% of all particles have a particle size of <0.5 m.

25. The breathable film of claim 17, wherein the at least one calcium carbonate-comprising filler material has a specific surface area (BET) of from 0.5 to 150 m.sup.2/g, as measured using nitrogen and the BET method according to ISO 9277:2010.

26. The breathable film of claim 17, wherein the at least one calcium carbonate-comprising filler material has a residual total moisture content of from 0.01 to 0.2 wt.-%, based on the total dry weight of the at least one calcium carbonate-comprising filler material.

27. The breathable film of claim 17, wherein the surface-treated filler material has a moisture pick-up from 0.1 to 1 mg/g, at a temperature of 23 C. (2 C.).

28. The breathable film of claim 17, wherein the surface-treated filler material has a moisture pick-up from 0.2 to 0.8 mg/g, at a temperature of 23 C. (2 C.).

29. The breathable film of claim 17, wherein the at least one mono-substituted succinic anhydride consists of succinic anhydride mono-substituted with a group selected from a linear, branched, aliphatic or cyclic group having a total amount of carbon atoms from C2 to C30 in the substituent.

30. The breathable film of claim 17, wherein the film has a basis weight from 4 to 13 g/m.sup.2.

31. The breathable film of claim 17, wherein the film has a basis weight of about 8 g/m.sup.2.

32. The breathable film of claim 17, wherein the water vapour retention rate and/or the hydrostatic pressure and/or the machinability of the breathable film is increased, compared to the same breathable film comprising a surface-treated filler material, which comprises the at least one calcium carbonate-comprising filler material and a treatment layer on the surface of the at least one calcium carbonate-comprising filler material comprising at least one saturated aliphatic linear or branched monocarboxylic acid and salty reaction products thereof, wherein the water vapour retention rate is determined according to ASTM E398-20, the hydrostatic pressure is determined according to AATCC Test Method 127-2013, WSP 80.6 or DIN EN ISO 811:2018-08, and the machinability is measured as a pressure increase observed in an extruder when producing the breathable film for 1 h and 5 min, wherein the pressure increase is measured by producing the breathable film by extruding a composition comprising the surface-treated filler material and the at least one thermoplastic polymer in a single screw extruder having a temperature profile of 195 C.-210 C.-230 C.-230 C., a screw diameter of 30 mm, a rotation speed of the extruder screw of 35 rpm and a die gap of 0.85 mm, wherein the pressure increase is defined as the difference of the initial pressure and the final pressure, measured in the extruder before the melt filter, wherein the initial pressure is measured 5 minutes after a melt filter with 42 micron mesh size is placed against the breaker plate between the extruder screw tip and the die, and wherein the final pressure is measured after 1 h and 5 min of producing the breathable film.

33. The breathable film of claim 17, wherein the water vapour retention rate is increased by at least 5%, compared to the same breathable film comprising a surface-treated filler material, which comprises the at least one calcium carbonate-comprising filler material and a treatment layer on the surface of the at least one calcium carbonate-comprising filler material comprising at least one saturated aliphatic linear or branched monocarboxylic acid and salty reaction products thereof, wherein the water vapour retention rate is determined according to ASTM E398-20.

34. The breathable film of claim 17, wherein the hydrostatic pressure of the breathable film is increased by at least 5%, compared to the same breathable film comprising a surface-treated filler material, which comprises the at least one calcium carbonate-comprising filler material and a treatment layer on the surface of the at least one calcium carbonate-comprising filler material comprising at least one saturated aliphatic linear or branched monocarboxylic acid and salty reaction products thereof, wherein the hydrostatic pressure is determined according to AATCC Test Method 127-2013, WSP 80.6 or DIN EN ISO 811:2018-08.

35. An article comprising a breathable film with a basis weight from 1 to 15 g/m.sup.2 according to claim 17, wherein the article is selected from the group consisting of hygiene products, medical products, healthcare products, filter products, geotextile products, agriculture products, horticulture products, clothing, footwear products, baggage products, household products, industrial products, packaging products, building products, and construction products.

36. A process for producing a breathable film with a basis weight from 1 to 15 g/m.sup.2 according to claim 17, comprising the steps of: a) providing a composition comprising at least one thermoplastic polymer and a surface-treated filler material, and b) forming a film from the composition of step a), and c) stretching the film obtained in step b) in at least one direction, wherein the surface-treated filler material comprises A) at least one calcium carbonate-comprising filler material having a weight median particle size d.sub.50 in the range from 0.1 m to 7 m, a top cut particle size d.sub.98 of 15 m, a fineness (<0.5 m) such that at least 15 wt.-% of all particles have a particle size of <0.5 m, and a residual total moisture content of 1 wt.-%, based on the total dry weight of the at least one calcium carbonate-comprising filler material, and B) a treatment layer on the surface of the at least one calcium carbonate-comprising filler material comprising at least one mono-substituted succinic anhydride and/or at least one mono-substituted succinic acid and/or salty reaction product(s) thereof in an amount of from 0.1 to 3 wt.-%, based on the total dry weight of the at least one calcium carbonate-comprising filler material.

37. The process of claim 36, wherein the composition provided in step a) is a masterbatch or a compound obtained by mixing and/or kneading the at least one thermoplastic polymer and the surface-treated filler material to form a mixture and continuously pelletizing the obtained mixture under water.

Description

EXAMPLES

1 Measurement Methods and Materials

[0366] In the following, measurement methods and materials implemented in the examples are described.

[0367] Particle Size

[0368] The particle distribution of the untreated ground calcium carbonate-comprising filler material was measured using a Sedigraph 5120 from the company Micromeritics, USA. The method and the instruments are known to the skilled person and are commonly used to determine grain size of fillers and pigments. The measurement was carried out in an aqueous solution comprising 0.1 wt.-% Na.sub.4P.sub.2O.sub.7. The samples were dispersed using a high speed stirrer and supersonics.

[0369] Specific Surface Area (BET)

[0370] The specific surface area was measured using nitrogen and the BET method according to ISO 9277:2010.

[0371] Ash Content

[0372] The ash content in [%] of the masterbatches was determined by incineration of a sample in an incineration crucible which is put into an incineration furnace at 570 C. for 2 hours. The ash content is measured as the total amount of remaining inorganic residues.

[0373] Melt Flow Rate (MFR)

[0374] Melt flow rate of the masterbatches has been determined according to ISO 1133:2011 (190 C., 2.16 kg).

[0375] Moisture Aquatrac

[0376] Moisture of pellets was determined with a BrabenderAquatrac+ equipment at 190 C. The polymer pellets were preconditioned in a Motan dry air drier MDE 40 for 2 hours at 80 C. Before the measurement in Aquatrac. The Aquatrac equipment measures the pressure caused by the reaction of the evaporated water of the pellets with calcium hydride agent. With the resulting pressure the moisture will be calculated by the equipment. For the measurement the procedure given by the manual was followed.

[0377] Film Grammage

[0378] Film grammage (also termed gauge or basis weight) was tested by punching out a round 100 cm.sup.2 specimen from the film and weigh the specimen. Therefrom, the weight per area (in g/m.sup.2, i.e., gsm) can be calculated.

[0379] Tensile Properties of the Film

[0380] Force at 2% elongation, Force at 5% elongation, maximum tensile force and elongation at break were determined according to ISO 527-3:2018. The width of the film specimen was of 15 mm and the testing length was 5 cm. The specimen were prepared in machine direction and cross direction and the tensile properties were measured in both directions.

[0381] Visual Evaluation of the Film

[0382] Film samples have been put under a light microscope. Calcium carbonate agglomerates appear black upon illumination from below and white upon illumination from above.

[0383] Water Vapour Transmission Rate (WVTR)

[0384] The WVTR value of the breathable films was measured with a Lyssy L80-5000 (PBI-Dansensor A/S, Denmark) measuring device according to ASTM E398-20.

[0385] Hydrostatic Pressure Test (Water Column)

[0386] The hydrostatic pressure test has been carried out according to a procedure which is equivalent to AATCC Test Method 127-2013, WSP 80.6 and ISO 811:2018. A film sample (test area=10 cm.sup.2) was mounted to form a cover on the test head reservoir. This film sample was subjected to a standardized water pressure, increased at a constant rate until leakage appears on the outer surface of the film, or water burst occured as a result of film failure (pressure rate gradient=100 mbar/min.). Water pressure was measured as the hydrostatic head height reached at the first sign of leakage in three separate areas of the film sample or when burst occurs. The head height results were recorded in centimetres or millibars of water pressure on the specimen. A higher value indicated greater resistance to water penetration. The TEXTEST FX-3000, Hydrostatic Head Tester (Textest AG, Switzerland), was used for the hydrostatic pressure measurements.

2 Materials

[0387] CC1 (comparative): Natural ground calcium carbonate, commercially available from Omya International AG, Switzerland (d.sub.50: 1.7 m; d.sub.98: 6 m, content of particles <0.5 m=12%), surface-treated with 1.0 wt.-% stearic acid (commercially available from Sigma-Aldrich, Croda) based on the total weight of the natural ground calcium carbonate. BET: 3.4 m.sup.2/g.

[0388] CC2 (comparative): Natural ground calcium carbonate, commercially available from Omya International AG, Switzerland (d.sub.50: 1.7 m; d.sub.98: 6 m, content of particles <0.5 m=12%), surface-treated with 0.7 wt.-% alkenyl succinic anhydride (CAS [68784-12-3], concentration >93%) based on the total weight of the natural ground calcium carbonate. BET: 3.4 m.sup.2/g

[0389] CC3 (comparative): Natural ground calcium carbonate, commercially available from Omya International AG, Switzerland (d.sub.50: 0.7 m; d.sub.98: 3 m, content of particles <0.5 m=34%), surface-treated with 1.4 wt.-% stearic acid (commercially available from Sigma-Aldrich, Croda) based on the total weight of the natural ground calcium carbonate. BET: 7.3 m.sup.2/g

[0390] CC4 (inventive): Natural ground calcium carbonate, commercially available from Omya International AG, Switzerland (d.sub.50: 0.7 m; d.sub.98: 3 m, content of particles <0.5 m=34%), surface-treated with 1.7 wt.-% alkenyl succinic anhydride (CAS [68784-12-3], concentration >93%) based on the total weight of the natural ground calcium carbonate. BET: 7.3 m.sup.2/g

[0391] P1: LLDPE Dowlex 2035G (MFR: 6 g/10 min (190 C., 2.16 kg), density: 0.919 g/cm.sup.3 according to technical data sheet), commercially available from The Dow Chemical Company, USA.

[0392] P2: LDPE Dow SC 7641 (MFR: 2 g/10 min (190 C., 2.16 kg), density: 0.923 g/cm.sup.3 according to technical data sheet), commercially available from The Dow Chemical Company, USA.

3 Examples

Example 1Preparation of Compounds (CO)

[0393] Compounds containing 50 wt.-% CC1 or CC2, respectively, were continuously prepared on a lab scale Buss kneader (PR46 from Buss AG, Switzerland). The obtained compounds were pelletized on a spring load pelletizer, model SLC (Gala, USA) in a water bath having a starting temperature between 20 and 25 C. The compositions and filler contents of the prepared compounds are compiled in Table 1 below. The precise filler content was determined by the ash content.

TABLE-US-00001 TABLE 1 Compositions and properties of prepared compounds. Melt flow Moisture rate Aquatrac ash (190 C., at P1 P2 content 2.16 kg) 190 C. Compound Filler [wt.-%] [wt.-%] [wt.-%] [g/10 min] [ppm] CO1 CC1 45 5 49.2 3.7 179 CO2 CC2 45 5 49.1 4.1 200 CO3 CC3 45 5 49.4 4.2 326 CO4 CC4 45 5 49.0 4.5 327

[0394] The results shown in Table 1 confirm that compounds with good quality and correct dosing of the calcium carbonate fillers were produced.

Example 2Preparation of Breathable Films

[0395] Breathable films were produced by a pilot-extrusion cast-film line with integrated MDO-II unit (Dr. Collin GmbH, Germany). The polymer compounds were dried for 2 hours at 80 C. in a Motan dry air dryer MD40 before extrusion. The extruder temperature settings were 195 C.-210 C.-230 C.-230 C., and the rotation speed of the extruder screw was 35 rpm, using the compounds of Example 1. The die gap was set at 0.85 mm. When changing the compound sample, the extrusion was run for 15 minutes to purge the former compound. After that a fresh melt filter with 42 micron mesh size was installed and after further 5 minutes the initial pressure before the filter was monitored. The film extrusion was then run for 1 hour and the pressure was measured again. The pressure difference is an indication for the dispersion quality of the compound, and for the machinability, i.e., whether the production process can be considered stable. The chill roll was at 45 C. The speed of the chill roll was at 3 to 5 m/min. It was adjusted to match the desired film grammage. The stretching roll temperature was at 60 C. The stretching ratio of the stretching unit was increased and until a homogeneously stretched film was achieved. The stretching ratio (also termed stretching factor or stretching magnification) is defined as the ratio of the speed of the final roll of the stretching unit of the Dr. Collin MDO-II line versus the speed of the first roll.

[0396] The film quality of the obtained breathable films was inspected visually and the films were tested regarding their tensile properties, their water vapor transmission rate (WVTR) and their hydrostatic pressure. The results are shown in Table 2, 3 and 4 below.

TABLE-US-00002 TABLE 2 Compositions and properties of prepared breathable films. Pressure Film Hydrostatic Stretching increase grammage Film WVTR pressure Sample Compound factor 1 h [bar] [g/m.sup.2] quality [g/(m.sup.2 day)] [mbar] 1 CO1 6.2 4 12 ok 3853 244 2 CO2 6.2 0 12 ok 4190 203 3 CO3 7.3 18 12 SA* 4177 267 4 CO4 7.3 2 12 ok 4637 308 5 CO4 7.3 2 11 ok 4702 240 6 CO4 7.3 2 10 ok 4926 208 *SA means Some agglomerates

[0397] The results shown in Table 2 confirm that the inventive breathable films 4 to 8 show a good quality and breathability. Film 1 to 4 were produced with 12 gsm basis weight. Film 1 and 2 had lower hydrostatic pressure which is an important parameter for hygiene applications. Film 3 and 4 contain finer carbonate which leads to higher hydrostatic pressure. Film 3 with the fine carbonate and stearic acid coating contained in CO3 showed some unwanted agglomerates and lead to a fast increase in extruder pressure. It was further tried with CO3 to produce films with slightly thinner gauge of 11.5 gsm, but the film broke twice. This may have been caused by void formation at agglomerates. Therefore the film trials with CO3 have been stopped. It was concluded that CO3 does not allow to produce thinner films than 12 gsm. In industrial film extrusion the fast extruder pressure increase would additionally lead to short and instable production runs with CO3, as the production may have to be stopped due to exceeding pressure and a new filter would have to be installed. Surprisingly, Film 4, using CO4 with finer carbonate but the inventive coating, did not show this phenomenon. It would therefore allow long production runs and high hydrostatic pressure at the same time. The good quality allowed to reduce the grammage of the breathable films from 12 gsm subsequently down to 10 gsm and still matching the hydrostatic pressure of the comparative film 2 with 12 gsm. This allows to reduce raw material cost and environmental impact.

TABLE-US-00003 TABLE 3 Compositions and mechanical properties of prepared breathable films. Film samples taken in machine direction (MD). Film Force Force Max. Max. grammage at 2% at 5% Force Elongation Sample [g/m.sup.2] [N] [N] [N] [%] 1 12 1.2 2.7 9.1 13.7 2 12 1.2 2.5 7.4 13.6 3 12 1.7 3.6 9.6 12.3 4 12 1.7 3.9 10.0 11.8 5 11 1.5 3.3 11.7 14.6 6 10 1.6 3.6 12.4 14.8

TABLE-US-00004 TABLE 4 Compositions and mechanical properties of prepared breathable films. Film samples taken in cross direction (CD). Film Force Force Max. Max. grammage at 2% at 5% Force Elongation Sample [g/m.sup.2] [N] [N] [N] [%] 1 12 0.24 0.37 0.56 323 2 12 0.23 0.36 0.58 334 3 12 0.28 0.44 0.64 323 4 12 0.27 0.44 0.70 316 5 11 0.27 0.44 0.72 328 6 10 0.29 0.43 0.63 323

[0398] The mechanical properties of the obtained breathable films, such as force at 2% elongation, force at 5% elongation, maximum tensile force and elongation at break in machine and cross direction, are outlined in Tables 3 and 4.

[0399] The mechanical properties are important for processing, for example for the subsequent processing steps, such as printing. Tensile properties in MD are important for film winding. Reasonable properties in CD direction are important to prevent slicing. As can be seen in table 3 and 4 the tensile forces of film 3 but even more of film 4 are higher than those of films 1 and 2. As CO4 allows easy processing the films could be made thinner by reducing the film grammage of films 6, 7 and 8 subsequently from 12 gsm down to 10 gsm. Surprisingly even the thinner films still exceeded the force at 2% elongation, force at 5% elongation and maximum tensile force of the comparative films 1 and 2. Even more surprisingly the thinner but stronger films 6, 7 and 8 did not provide distinctively lower elongation at break, as these films had even higher elongation at break in MD direction and elongations at break in CD direction above 300%.

Example 3Preparation of Breathable Films

[0400] Breathable films were produced by a pilot-extrusion cast-film line with integrated MDO-II unit (Dr. Collin GmbH, Germany) in the same way as in example 2

[0401] The film quality of the obtained breathable films was inspected visually and the films were tested regarding their tensile properties and their water vapor transmission rate (WVTR). The results are shown in Table 5, 6 and 7 below.

TABLE-US-00005 TABLE 5 Compositions and properties of prepared breathable films. Pressure Film Stretching increase grammage Film WVTR Sample Compound factor 1 h [bar] [g/m.sup.2] quality [g/(m.sup.2 day)] 7 CO2 5.5 0 12.5 ok 3766 8 CO4 5.5 0 12.4 ok 3485 9 CO4 6.4 2 9.8 ok 3160 10 CO4 6.4 2 9.1 ok 2792 11 CO4 6.4 2 7.7 ok 3176

[0402] The results shown in Table 2 confirm that the inventive breathable films 8 to 11 show a good quality and breathability. Film 7 to 8 were produced with around 12 gsm basis weight. Film 9 to 11 were produced with lower basis weight. All films had good breathability suitable for hygiene applications.

TABLE-US-00006 TABLE 6 Compositions and mechanical properties of prepared breathable films. Film samples taken in machine direction (MD). Film grammage Force at 2% Force at 5% Max. Force Sample [g/m.sup.2] [N] [N] [N] 7 12.5 1.8 3.8 10.4 8 12.4 2.7 6.2 13.6 9 9.8 2.2 5.1 10.5 10 9.1 1.9 4.7 9.4 11 7.7 1.9 4.5 9.3

TABLE-US-00007 TABLE 7 Compositions and mechanical properties of prepared breathable films. Film samples taken in cross direction (CD). Film grammage Force at 2% Force at 5% Max. Force Sample [g/m.sup.2] [N] [N] [N] 7 12.5 0.41 0.58 0.97 8 12.4 0.79 0.98 0.99 9 9.8 0.67 0.68 0.80 10 9.1 0.74 0.71 0.89 11 7.7 0.51 0.51 0.68

[0403] The mechanical properties of the obtained breathable films, such as force at 2% elongation, force at 5% elongation and maximum tensile force in machine and cross direction, are outlined in Tables 6 and 7.

[0404] The mechanical properties are important for processing, for example for the subsequent processing steps, such as printing. Tensile properties in MD are important for film winding. Reasonable properties in CD direction are important to prevent slicing. As can be seen in table 6 and 7 the tensile forces of film 8 are higher than those of film 7. As CO4 allows easy processing the films could be made thinner by reducing the film grammage of films 9, 10 and 11 subsequently from 12 gsm down to 8 gsm. Surprisingly even the thinner films still exceeded the force at 2% elongation and force at 5% elongation and maximum tensile force of the comparative film 7. This kind of stiffness is important for the further processing of the film. The maximum force stayed on a comparable level even at very low grammage.