Electrically Conductive Paper

Abstract

The present invention relates to an electrically conductive paper structure and a method for its production, as well as the use of the electrically conductive paper structure, for example as a heating element.

Claims

1. An electrically conductive paper structure comprising a paper structure having electrodes formed from an electrically conducting ink, wherein the ink is substantially absorbed into the paper structure so that there is no substantial increase in the thickness of the paper structure, wherein the increase in the thickness of the paper structure due to the presence of the ink is less than 50 μm, a substantial part of the ink being located within the paper structure is greater than 50% of the ink, and the electrodes are embedded within the paper structure to a depth of 10 μm to 80 μm.

2. The electrically conductive paper structure of claim 1, wherein the paper structure has an air permeability of between about 50 and 300 l/m2/s.

3. (canceled)

4. (canceled)

5. (canceled)

6. The electrically conductive paper structure of claim 1, wherein the electrically conducting ink is solvent-free.

7. The electrically conductive paper structure of claim 1, wherein the electrodes are between 1 and 50 mm wide, and/or are embedded within the paper structure to a depth of 10 μm to 60 μm.

8. The electrically conductive paper structure of claim 1, wherein greater that 50% of the electrically conducting ink is located within the paper structure.

9. The electrically conductive paper structure of claim 1, wherein any increase in the thickness of the paper structure due to the presence of the electrically conducting ink is less than 50 μm.

10. The electrically conductive paper structure of claim 1, wherein any increase in the thickness of the paper structure due to the presence of the electrically conducting ink is less than 15 μm.

11. A method of forming electrodes on an electrically conductive paper structure comprising selecting electrically conductive paper and printing electrically conductive ink onto the electrically conductive paper, wherein the ink is substantially absorbed into the electrically conductive paper structure so that there is no substantial increase in the thickness of the paper structure, wherein the increase in the thickness of the paper structure due to the presence of the ink is less than 50 μm, a substantial part of the ink being located within the paper structure is greater than 50% of the ink, and the electrodes are embedded within the paper structure to a depth of 10 μm to 80 μm.

12. The method of claim 11, wherein the ink is applied to the paper structure using one of the following printing techniques: screen printing; pad printing; flexo printing; gravure printing; 3D printing; and offset printing.

13. (canceled)

14. The method of claim 11, wherein the electrically conducting ink has a viscosity between 1 and 100 Pa.Math.s.

15. The method of claim 11, wherein the electrically conducting ink has a viscosity between 5 to 60 Pa.Math.s.

16. A method of using electrically conductive paper structure, comprising selecting the electrically conductive paper structure according to claim 1 as a heating element, and passing electricity through the paper structure using the electrodes in order to generate heat.

Description

[0032] The following examples are set forth as being representative of the present disclosure. These examples are not to be construed as limiting the scope of the present disclosure as these and other equivalent embodiments will be apparent in view of the present disclosure, Figures and accompanying claims.

[0033] FIG. 1 shows a schematic image of a paper structure having electrodes formed from electrically conducting inks.

[0034] FIG. 2 shows a schematic image of a cross-section of the paper structure with the embedded electrodes.

[0035] FIG. 3 shows a schematic image of a cross-section of the paper structure with an electrical connector attached to an electrode.

[0036] FIG. 4 shows a microscope image of the surface of an electrically conductive paper on which an electrically conductive ink has been applied. FIG. 4A is at 50× magnification, and FIG. 4B is at 750× magnification.

[0037] FIG. 5 shows a microscope image at 250× of a cut section of electrically conductive paper on which an electrically conductive ink has been applied.

EXAMPLE 1

[0038] Electrically conducting paper was made using the method disclosed in EP 2 770 104 A1. Electrically conducting paper from a number of different producers (S, W and A) was obtained.

[0039] Electrically conducting paper comprising 10% (w/w) of carbon fibers having an average length of about 5 mm, and a paper weight of 75 g/m.sup.2, was obtained from three different producers, and is referred to as 10/05-75. The paper was sized by applying a styrene acrylate to the surface (on each side up and down wards) of the paper at a coverage of about 10 to 13 g/m.sup.2. Electrically conducting ink (e.g., DuPont® Solamet PV410) was applied to the paper using screen printing in order to form strips 20 mm wide along opposing edges of the paper.

[0040] Copper foil electrodes were also attached to the same electrically conductive paper using an adhesive.

[0041] In order to determine the additional thickness caused by forming the different types of electrode on the electrically conducting paper, measurements were taken using a laser microscope. The result are the average of 10 measurements (5 times for the paper thickness in the absence of the electrode, and 5 times for the thickness of the paper including the electrode) taken for each different electrode structure. The measurement scatter was in each case in the 1/100 range. The results are shown in Table 1.

TABLE-US-00001 TABLE 1 values given as mm. Test 1 2 3 4 5 Ø Δ Paper 0.20 0.20 0.20 0.20 0.20 0.200 with copper foil 0.32 0.27 0.30 0.29 0.29 0.294 0.094 Paper-S 0.17 0.18 0.19 0.18 0.18 0.180 with conducting ink 0.19 0.20 0.19 0.18 0.19 0.190 0.010 Paper-W 0.25 0.26 0.25 0.25 0.26 0.254 with conducting ink 0.28 0.27 0.28 0.28 0.28 0.278 0.024 Paper-A 0.19 0.19 0.19 0.19 0.18 0.188 with conducting ink 0.19 0.20 0.20 0.20 0.20 0.198 0.010

[0042] The table shows that the use of copper foil electrodes increases the thickness of the paper by 0.095 mm, whereas the use of electrically conducting ink to form the electrodes increases the thickness of the paper by 0.024 mm or 0.01 mm.

[0043] A variety of different electrically conducting papers have also been produced with the electrodes formed from electrically conducting ink, and tested. The results are set out in Table 2. The paper is defined using the following nomenclature XX/YY-ZZ-Q, wherein: [0044] XX indicates the percentage of carbon fibres present (w/w); [0045] YY indicates the average length of the carbon fibres (mm); [0046] ZZ indicates the weight of the paper (g/m.sup.2); and [0047] Q indicates the producer.

[0048] The results show that electrodes formed from the electrically conductive ink function effectively on a variety of papers.

TABLE-US-00002 TABLE 2 Test 1.1 1.2 2.1 2.2 3.1 3.2 4.1 4.2 5.1 5.2 6.1 6.2 Paper 10/05- 75-S 10/05- 75-S 10/10- 90-S 10/10- 90-S 35/10- 90-S 35/10- 90-S 35/10- 90-W 35/10- 90-W 10/05- 80-W 10/05- 80-W 10/05- 75-A 10/05- 75-A Specific  (Ω*m*10.sup.−6) 5.3 5.3 4.8 4.8 1.8 1.8 2.1 2.3 5.8 5.6 6.9 6.6 electrical resistance Electrical R (Ω) 17.8 17.7 11 11 4.3 4.3 4.7 5.3 16.5 15.8 19.5 30.3 resistance Thickness d (m*10.sup.−3) 0.18 0.18 0.26 0.26 0.25 0.25 0.25 0.25 0.2 0.2 0.2 0.2 Length l (m) 0.25 0.25 0.25 0.25 0.25 0.25 0.296 0.296 0.296 0.296 0.296 0.182 Width w (m) 0.15 0.15 0.15 0.15 0.15 0.15 0.167 0.167 0.167 0.167 0.168 0.168 Resistance Rsq (Ω) 0.030 0.030 0.018 0.018 0.007 0.007 0.008 0.009 0.029 0.028 0.034 0.033 square Electri. K (S*m.sup.−1) 187.27 188.32 209.79 209.79 558.14 558.14 480.16 425.80 170.97 178.54 145.53 152.32 conductivity

[0049] FIG. 1 shows a paper structure (1) having a first electrode (3) positioned on the left hand side of the paper structure, and a second electrode (5) positioned on the right hand side of the paper structure. FIG. 2 shows a section through the paper showing how the electrodes are embedded within the paper structure. FIG. 3 shows one way of connecting an electrode to an electrical source. In particular, an electrical cable (7) is connected using a clamp (9) which contacts one of the electrodes.

[0050] In one example, electrically conducting paper (type 10/05-75)—2 meters in length, 0.5 meters wide and 0.22 mm thick—has electrodes formed on opposing edges of the paper from electrically conducting ink, as described above. Electricity was then passed through the electrodes and heat generated. Details are as follows: [0051] Voltage 12V, 54 Watts—Ω 2.67, temperature 5.5° C. [0052] Voltage 24V, 216 Watts—Ω 2.67, temperature 22° C. [0053] Voltage 32V, 384 Watts—Ω 2.67, temperature 38° C. [0054] Voltage 48V, 864 Watts—Ω 2.67, temperature 86° C.

[0055] In each test the heat was generated in a consistent manner in the area of the paper between the electrodes, without any hotspots forming.

[0056] Microscope images were taken of the paper having the electrically conducting ink electrodes. In FIGS. 4A and 4B the presence of the electrically conducting ink on the surface of the paper can be seen. As the underlying fibers of the paper can be seen, it is apparent that the layer of ink on the surface of the paper is very thin and does not in any significant way add to the thickness of the paper.

[0057] In addition, a sectional view of the paper is shown in FIG. 5. It can be seen that the layer of electrically conducting ink penetrates the paper by about 40 μm (i.e., the ink has been substantially absorbed). It can further be seen that the fibers of the paper structure are embedded in the ink layer. A strong and robust connection between the ink and the fibers of the paper is therefore formed.

[0058] In contrast to the use of copper foils to form the electrodes, the use of the electrically conducting ink does not add significantly to the thickness of the paper, but still forms an electrode having substantially the same depth as the copper foil electrodes, i.e., a depth of about 30 μm to 40 μm. Accordingly, the electrodes function to provide consistent heat distribution across the paper because they are of sufficient size and have excellent connections with the carbon fibers present within the paper structure. In particular, there is no overheating of the material due to different “contact quality” at the contact edges, and no hotspots at the terminals because the applied energy is evenly dissipated due to the numerous contact points between the electrode ink layer and the carbon fibers.

[0059] In addition, the electrodes will not become detached from the paper even if bent because the ink layer is embedded within the paper. In addition, rolls of the paper in large diameter can be produced without any noticeable deformation of the paper as there is no substantial increase in the thickness of the paper caused by the presence of the electrodes.

[0060] The use of an electrically conducting ink to form the electrodes also enables simple cutting of the individual heating tracks from the parent roll. In addition, no additional covering layer or fixing of the electrodes is necessary. The paper structure can therefore be quickly and efficiently produced.

[0061] It is also noted that at high humidity the copper foils corrode and the corrosion shows up as “dirt particles” in the paper structure. Such corrosion is avoided by the use of the electrically conducting ink electrodes.

[0062] Although the invention has been described above with reference to one or more preferred embodiments, it will be appreciated that various changes or modifications may be made without departing from the scope of the invention as defined in the appended claims.