WET STRENGTH IMPROVED FIBROUS NON-WOVEN FABRICS, IN PARTICULAR PAPER, USES OF THESE WET STRENGTH FABRICS AS WELL AS PRODUCTION METHODS OF THE SAME

Abstract

Novel environmentally friendly, wet strength improved fibrous non-woven fabrics, optionally paper, impregnated with a mixture including a silicon component, further including water and/or an alcohol and/or a surfactant and a catalyst. Also encompassed are methods for production and uses of such wet strength improved fibrous non-woven fabrics.

Claims

1. A wet strength improved fibrous non-woven fabric with an air-dry silica-content of at least 0.1 wt.-%, wherein the silica is distributed in the wet strength fibrous non-woven fabric in so far that the silica-content on one side of the wet strength fibrous non-woven fabric and the silica-content on another side of the wet strength fibrous non-woven fabric is a ratio about 1:1, and wherein a Cobb.sub.60-value is less than 20% reduced as compared to the untreated fibrous non-woven fabric.

2. The wet strength improved fibrous non-woven fabric according to claim 1, wherein the fibrous non-woven fabric is selected from the group consisting of paper and cotton fleece.

3. The wet strength improved fibrous non-woven fabric according to claim 1, wherein a wet tensile strength according to DIN ISO 3781 of the fibrous non-woven fabric is between at least 5 times and up to 50 times higher than the wet tensile strength according to DIN ISO 3781 of a fibrous non-woven fabric without silica-content.

4. The wet strength improved fibrous non-woven fabric according to claim 1, wherein the wet tensile strength according to DIN ISO 3781 (1994-10) is between 1 and 50 N/15 mm.

5. The wet strength improved fibrous non-woven fabric according to claim 1, wherein the air-dry silica content is between at least 0.1 wt.-% and up to 30 wt.-%.

6. The wet strength improved fibrous non-woven fabric according to claim 1, wherein a contact angle on all surfaces of the wet strength improved fibrous non-woven fabric according to the present invention is less than 90.

7. The wet strength improved fibrous non-woven fabric according to claim 1, wherein the silica coated paper wet strength improved fibrous non-woven fabric has a water absorption capacity according to DIN EN ISO 535 (2014) is between 10 g/m.sup.2 and 300 g/m.sup.2.

8. The wet strength improved fibrous non-woven fabric according to claim 1, obtained by impregnating the fibrous non-woven fabric with a mixture comprising a silicon component, water, a surfactant and an acidic catalyst.

9. A mixture comprising the following compounds in weight-%: TABLE-US-00025 Compound wt.-% silicone compound (e.g., tetraethyl orthosilicate, (TEOS)) 3.5-15 surfactant 0.2-1.5 H.sub.2O 80-95 acidic catalyst 0.06-0.05.

10. The mixture of claim 9, wherein the surfactant is a cationic surfactant.

11. A mixture comprising the following compounds in weight-%: TABLE-US-00026 Compound wt.-% silicone compound (e.g., tetraethyl orthosilicate, (TEOS)) 2-20 H.sub.2O 6-10 alcohol (e.g., EtOH) 75-90 acidic catalyst 0.01-0.05.

12. The wet strength improved fibrous non-woven fabric according to claim 1, obtained by impregnating the fibrous non-woven fabric with a mixture comprising the following compounds in weight-%; TABLE-US-00027 Compound wt.-% silicone compound (e.g., tetraethyl orthosilicate, (TEOS)) 3.5-15 surfactant 0.2-1.5 H.sub.2O 80-95 acidic catalyst 0.06-0.05.

13. A method for producing a wet-strength improved fibrous non-woven fabric, optionally paper, comprising the steps of: a. obtaining a fibrous non-woven fabric; b. applying an impregnation solution according to claim 9 evenly to both sides of the paper with a size press with a speed of between 1 to 15 m/min at a roll pressure of between 0.25-3.0 bar; c. heating the paper from between 18-25 C. to between 60-200 C. with a heating rate of between 5-15 K/min under constant air flow of between 15-50 mL/min; d. thereby obtaining the wet-strength improved fibrous non-woven fabric, optionally paper.

14. A method for producing a wet-strength improved fibrous non-woven fabric, optionally paper, comprising the steps of: a. mixing the impregnation solution according to claim 9 in a bath with fibres for the fibrous non-woven fabric; b. extracting the fibrous non-woven fabric from said bath; c. heating the paper from between 18-25 C. to between 60-200 C. with a heating rate of between 5-15 K/min under constant air flow of between 15-50 mL/min; d. thereby obtaining the wet-strength improved fibrous non-woven fabric, optionally paper.

15. A method, comprising the steps of: 1) using the wet-strength improved fibrous non-woven fabric of any of claim 1 or 2) using an impregnation solution comprising the following compounds in weight-%: TABLE-US-00028 Compound wt.-% silicone compound (e.g., tetraethyl orthosilicate, (TEOS)) 3.5-15 surfactant 0.2-1.5 H.sub.2O 80-95 acidic catalyst 0.06-0.05 on a fibrous non-woven fabric for producing an article with improved wet tensile strength selected from the group comprising tea bags, kitchen paper, cardboard, map paper, security paper for bank notes, coffee or tea filters, wrapping paper, toilet paper, paper towels, cooking paper, paper labels, display boards, promotional poster, drinking straws, packaging papers, corrugated boards, paper bags, and cloths.

16. The wet strength improved fibrous non-woven fabric according to claim 2, wherein the wet tensile strength according to DIN ISO 3781 of the fibrous non-woven fabric is between at least 5 times and up to 50 times higher than the wet tensile strength according to DIN ISO 3781 of a fibrous non-woven fabric without silica-content, and wherein the wet tensile strength according to DIN ISO 3781 (1994-10) is between 1 and 50 N/15 mm.

17. The wet strength improved fibrous non-woven fabric according to claim 16, wherein the air-dry silica content is between at least 0.1 wt.-% and up to 30 wt.-%, and wherein the contact angle on all surfaces of the wet strength improved fibrous non-woven fabric according to the present invention is less than 90.

18. The wet strength improved fibrous non-woven fabric according to claim 17, wherein the wet strength improved fibrous non-woven fabric has a water absorption capacity according to DIN EN ISO 535 (2014) is between 10 g/m.sup.2 and 300 g/m.sup.2, and obtained by impregnating the fibrous non-woven fabric with a mixture comprising a silicon component, water, a surfactant and an acidic catalyst.

19. The wet strength improved fibrous non-woven fabric according to claim 18, obtained by impregnating the fibrous non-woven fabric with a comprising the following compounds in weight-%: TABLE-US-00029 Compound wt.-% silicone compound (e.g., tetraethyl orthosilicate, (TEOS)) 3.5-15 surfactant 0.2-1.5 H.sub.2O 80-95 acidic catalyst 0.06-0.05.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0155] FIG. 1: Depicted is the schematic illustration of the bilateral coating process using a size press.

[0156] FIG. 2: Depicted is the thermogravimetric analysis of a) model paper sheets with various composition of long fibres (LF; NBSK) and short fibres (SF; eucalyptus), namely 20LF80SF (black line), 50LF50SF (dashed line), and 80LF20SF (dotted line), coated with silica via option I and b) coated with silica via option II.

[0157] FIG. 3: SEM micrographs of eucalyptus paper sheets are shown before (left) and after silica coating via option I (mid) and option II (right) at a magnification of 2000 respectively. Scale bar: 10 m.

[0158] FIG. 4: a) Wet tensile strength of unmodified (black) and silica coated model paper sheets with various composition of long fibres (LF; NBSK) and short fibres (SF; eucalyptus) using coating option I (grey). b) Wet tensile strength of unmodified (black) and silica coated model paper sheets via coating option II (grey), and a reference that was proceeded without the silica source in the coating solution (white).

DETAILED DESCRIPTION OF THE INVENTION

EXAMPLES

Reagents

[0159] All chemicals and solvents were purchased from Merck Millipore and Thermo Fisher Scientific and used as received unless otherwise stated.

Example 1. Preparation of Paper Sheets

[0160] Lab-engineered paper sheets were prepared using bleached eucalyptus sulfate pulp and Northern bleached softwood kraft (NBSK; pine and spruce) pulp. The pulp was refined in a Voith LR 40 laboratory refiner at 75000 revolutions. Lab-engineered paper sheets with a grammage of 801.6 g/m2 were prepared using a Rapid-Kthen sheet former according to DIN 54358 and ISO 5269/2. No additives or fillers were used. Model paper sheets with different fibre ratios of long fibres (LF; NBSK) and short fibres (SF; Eucalyptus) of 100LF:0SF (Eucalyptus), 20LF:80SF, 50LF50SF, and 80LF20SF were prepared.

[0161] In one embodiment paper was made from mixing the paper fibre pulp suspension with the impregnation solution and drying the paper afterwards. For use in the fibre suspension, a wet strength was achieved of 1.580.1 N/15 mm for 20LF80SF with a silica content of 1.28% oven dry and 1.22% air dry.

Example 2. Silica Coating

Option I: Impregnating Sol

[0162] For silica coating of paper sheets, a coating sol (option I) with following compositions were prepared.

[0163] Very good results with respect to wet-strength were achieved with:

TABLE-US-00012 molar volume (50 mL)/ Compound amount mL mass/g wt % TEOS 1 152.30 140.302356 17.07 H.sub.2O 5 60.66 60.6620971 7.38 EtOH 20 786.47 620.527963 75.51 HCl 0.01 0.56 0.24554428 0.03

[0164] Also very good results with respect to wet-strength were achieved with:

TABLE-US-00013 molar volume (50 mL)/ Compound amount mL mass/g wt % TEOS 1 82.43 75.9336755 9.33 H.sub.2O 10 65.66 65.6624185 8.07 EtOH 40 851.30 671.677517 82.56 HCl 0.02 0.61 0.26578427 0.03

[0165] Still good results with respect to wet-strength were achieved with:

TABLE-US-00014 molar volume Compound amount (50 mL)/mL mass/g wt % TEOS 1 43.01 39.617674 4.90 H.sub.2O 20 68.52 68.5174864 8.47 EtOH 80 888.32 700.882731 86.63 HCl 0.01 0.16 0.06933521 0.009

[0166] Still mediocre results with respect to wet-strength were achieved with:

TABLE-US-00015 molar volume Compound amount (50 mL)/mL mass/g wt % TEOS 1 21.98 20.2466071 2.50 H.sub.2O 40 70.03 70.0317049 8.66 EtOH 160 907.95 716.372055 88.54 HCl 0.005 0.04 0.01771687 0.002

[0167] The components of the sol were mixed, stirred for 24 h at room temperature, and used for silica coating of paper sheets using a size press (FIG. 1) for bilateral coating with a speed of 5 m/min at a roll pressure of 0.5-1.0 bar. Freshly coated paper sheets were placed in a pre-heated oven at 160 C. for 5-15 min at atmospheric pressure before cooling down to ambient temperature.

Option II: impregnation Emulsion

[0168] For silica coating of paper sheets, a coating emulsion (option II) was prepared as follows.

[0169] Very good results with respect to wet-strength were achieved with:

TABLE-US-00016 Compound V/mL m/g n/mol molar ratios wt % TEOS 15.2 14.288 0.06721183 1.00 14.29 H.sub.2O 84.8 84.6304 4.69777408 69.90 84.67 HCl 0.028 0.03318 0.00033671 0.01 0.03 SDS NA 1 0.00350208 0.05 1.00

[0170] Good results with respect to wet-strength were achieved with:

TABLE-US-00017 Compound V/mL m/g n/mol molar ratios wt % TEOS 15.2 14.288 0.06721183 1.00 7.15 H.sub.2O 184.8 184.4304 10.237602 152.32 92.33 HCl 0.028 0.03318 0.00033671 0.01 0.02 SDS NA 1 0.00350208 0.05 0.50

[0171] Mediocre results with respect to wet-strength were achieved with:

TABLE-US-00018 Compound V/mL m/g n/mol molar ratios wt % TEOS 15.2 14.288 0.06721183 1.00 3.58 H.sub.2O 384.8 384.0304 21.3172578 317.17 96.16 HCl 0.028 0.03318 0.00033671 0.005 0.01 SDS NA 1 0.00350208 0.05 0.25

[0172] TEOS was mixed with HCl (37 wt %) and stirred for 24 h at room temperature. Then, water and sodium dodecyl sulfate (SDS) were added and the mixture is rigorously stirred for 1 h at room temperature, before applying the obtained emulsion for coating with a size press with a speed of 5 m/min at a roll pressure of 0.5-1.0 bar. Freshly coated paper sheets were placed in a pre-heated oven at 160 C. for 5-15 min at atmospheric pressure before cooling down to ambient temperature.

[0173] Surprisingly, when the paper was treated with a mixture according to option II comprising as surfactant the cationic surfactant cetrimonium bromide, the wet-strength of model paper sheets with different fibre ratios of long fibres (LFSF 20/80%; NBSK 100%) was 234 N/15 mm, i.e. much higher than with other impregnations.

[0174] Surprisingly it was found that TEOS can be brought into solution as emulsion without the use of ethanol. Thus, option II shows some advantages as compared to option I. For example, is EtOH (or alcohol in general) a security risk (alcohol fumes, explosivity) and it is more expensive than water. Thus, option II is the preferred mixture for impregnation.

Example 3. Thermogravimetric Analysis (TGA)

[0175] TGA was performed using a TGA 1 Mettler-Toledo. The samples were heated from 25 C. to 600 C. with a heating rate of 10 K/min under constant air flow of 30 mL/min.

Example 4. Scanning Electron Microscopy (SEM)

[0176] SEM micrographs were recorded using a Zeiss EVO 10 SEM operated at an acceleration voltage of 10 kV. Prior to measurements, the samples were sputter coated with a platinum/palladium layer of 10 nm.

Example 5. Determination of Wet Tensile Strength

[0177] Wet tensile strength was determined as an average of 10 samples according to DIN ISO 3781 with a Zwick Z1.0 with a 1 kN load cell using the software testXpert II V3.71 from ZwickRoell GmbH & Co. Kg in a controlled environment with 23 C. and 50 rH %. Thereby, the paper samples were immersed in water for at least 1 h prior to measurements.

Example 6. Determination of Silica Content

[0178] The silica content of silica coated paper sheets is determined via TGA. Thereby, the silica content can be determined from the plateau of the TGA curves at 550 C., since silica is stable up to 1700 C., whereas natural organic fibres are totally combusted. Comparing the values between 550 C. and 600 C. before and after silica coating allows to take the natural ash content of the substrates into account. Furthermore, the weight loss occurring till 150 C. can be assigned to physically adsorbed water and is considered in the calculation to determine the silica content with respect to oven-dry samples. TGA curves of model paper sheets coated with silica via option I and eucalyptus paper sheets coated with silica via option II are depicted in FIG. 2, whereas the calculated silica contents are illustrated in Table 1.

TABLE-US-00019 TABLE 1 Calculated silica contents derived from TGA. Coating Option II Coating Option II (cetrimonium Coating Option I (SDS) bromide) Silica Silica Silica Silica Silica Silica content content content content content content air-dry/ oven-dry/ air-dry/ oven-dry/ air-dry/ oven-dry/ Sample % % % % % % 20LF80SF 1.3 1.38 5.05 5.27 2.23 2.36 50LF50SF 1.61 1.72 4.77 4.98 80LF20SF 2.17 2.3 2.72 2.84

Example 7. Morphological Analysis

[0179] Eucalyptus paper sheets were investigated with respect to their morphology before and after silica coating using SEM (FIG. 3). Silica coated paper sheets coated with option I and option II do not show morphological differences on the micrometer scale compared to uncoated paper sheets. This can be explained due to the low silica amount as deduced from TGA.

Example 8. Determination of Wet Tensile Strength

[0180] The wet tensile strength of paper sheets before and after coating with silica was determined according to DIN ISO 3781. Thereby, paper samples of 15 mm width and approximately 120 mm length are immersed in water for 1 h before measurement. The determined values of wet tensile strength are depicted in FIG. 4. Comparing the wet tensile strength before and after silica coating, higher values are obtained due to silica coating for both option I and option II. Thereby, the wet tensile strength of model paper coated with silica via option I show higher values as compared to eucalyptus paper sheets coated with silica via option II. Furthermore, comparing the model paper sheets with different composition of long and short fibres, the wet tensile strength increases more with higher number of short fibres (eucalyptus).

Example 9: Wet Strength Features of Different Papers and Impregnations Mixtures

[0181] The wet strength was compared for different papers and different mixtures. As comparative paper (asymmetric impregnated with-type TEOS) paper was used, i.e., with a silica content on one side at least 2 times higher than on the other side.

[0182] In case of the impregnations with the mixtures according to options I and II a homogeneous silica-distribution was applied with a silica content on one side about 2 times or less higher than on the other side.

[0183] The silica content is depicted in example 6, table 1.

TABLE-US-00020 TABLE 2 Comparison of wet-strength. Option II w. Option II w. cationic Comparative anionic surfactant paper surfactant (cetrimonium (asymmetric Option I (SDS) bromide) Untreated impregnated) (cf. example 2) (cf. example 2) (cf. example 2) Paper wet strength in N/15 mm, determined according to DIN ISO 3781 20LF80SF 0.3 6.2 2 10.2 0.6 7.3 1 24.3 1.3 50LF50SF 0.6 4.1 1 8.3 0.5 12.8 1.5 80LF20SF 1.0 3.5 1 7.7 0.4 7.6 0.9

Example 10: Contact Angle Measurements

[0184] Contact angle measurements were performed with the model TBU90E from DataPhysics Instruments GmbH and the SCA software. All samples were measured at five positions and the mean value and standard deviation were calculated. A drop volume of 2 l was used for static contact angle measurements (application rate: 0.5 l/s) (at 23 C. with 50% relative humidity).

Example 11: Comparison with Prior Art Impregnations

[0185] Paper from eucalyptus fibres with a grammage of 80 gsm were prepared in the laboratory. The paper sheets were coated using a size press and an ethanolic solution according to US 2022/034041 as well as an aqueous emulsion and ethanolic solution according to the disclosure.

TABLE-US-00021 TABLE 3 Formulation for the aqueous emulsion according to the present disclosure. Compound V/mL M/g TEOS 15 14.1 H.sub.2O 385 385 HCl 0.028 0.033 CTAB NA 1

TABLE-US-00022 TABLE 4 Formulation for the ethanolic solution according to the present disclosure. Compound V/mL m/g TEOS 2.2 2.1 H.sub.2O 7 7 EtOH 90.8 71.6 HCl 0.004 0.005

TABLE-US-00023 TABLE 5 Formulation for the ethanolic solution according to US 2022/034041 Compound V/mL M/g TEOS 33 31 H.sub.2O 26 26 EtOH 340 268.3 HCl 0.24 0.284

[0186] The paper sheets were coated via size press and subsequently dried in an oven. For the preparation according to US '041, the coated paper sheets were placed in a preheated oven at 130 C. for 15 minutes. For the preparation of wet-strength paper due to silica coating according to the present disclosure, the coated paper sheets were placed in a preheated oven at 160 C. for 15 minutes.

[0187] The paper sheets were equilibrated at 50% relative humidity and 23 C. after coating. Then, Cobbeo values of the two main sides of the coated paper sheets were determined according to DIN EN ISO 535. Uncoated paper made from eucalyptus fibres with a grammage of 80 g/m.sup.2 have an initial water absorption capacity of 31037 g/m.sup.2.

TABLE-US-00024 TABLE 6 Water adsorption capacities of sponge cloths coated with various silica content. Cobb.sub.60 Cobb.sub.60 Reduction top/ bottom/ of Cobb.sub.60 Process gm.sup.2 gm.sup.2 vs. untreated Comment Ethanolic coating 17 2 76 18 >20% Inhomogeneous solution on both sides, according to high Cobb.sub.60 US041 reduction Ethanolic coating 275 10 270 19 <20% Homogeneous solution on both sides according to and low present disclosure Cobb.sub.60 reduction Water based 286 66 301 70 <20% Homogeneous emulsion on both sides according to and even less present disclosure Cobb.sub.60 reduction