PRINTED ARTICLE AND A FEEDSTOCK

Abstract

The invention relates to a printed article and a feedstock for printing comprising a matrix forming material, in particular a polymeric material, and a filler material dispersed within the matrix forming material, in which the filler material comprises glass flakes. Glass flakes are characterised as having an aspect ratio of average diameter divided by average thickness greater than or equal to three. Selecting aspect ratio of glass flakes controls an orientation of glass flakes angled relative to a printed layer and formation of a depletion layer in a printed article. Technical effects of angled flakes include better adhesion between successive printed layers in 3D printing and a crack-stopping function. In a preferred embodiment the glass flakes comprise a conductive coating such that a printed article functions as a moisture sensor. Technical effects of a depletion layer include high moisture permeability and so a fast rate of change in electrical resistance due to moisture. A process of manufacturing a feedstock and a process of printing comprising a step of providing glass flakes are also disclosed.

Claims

1.-22. (canceled)

23. A printed article, comprising: a matrix forming material, and a filler material, dispersed within the matrix forming material, wherein the filler material comprises glass flakes, having an aspect ratio of average diameter divided by average thickness greater than or equal to three.

24. The printed article according to claim 23, wherein the matrix forming material (1) is a polymer selected from high density polyethylene (HDPE), polycarbonate (PC), polyphenylene ether (PPE), acrylonitrile butadiene styrene (ABS), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), poly(butylene adipate) (PBA), polypropylene (PP), polyurethane (PU), poly(lactic acid) (PLA), polyamide (PA) and UV-cured resins.

25. The printed article according to claim 24, wherein the glass flakes are coated with silane.

26. The printed article according to claim 23, wherein the glass flakes have average diameter in a range from 10 um to 500 um, more preferably from 15 um to 400 um, most preferably from 20 um to 300 um.

27. The printed article according to claim 23, wherein the glass flakes have average thickness in a range from 0.1 um to 5 um, more preferably 0.2 um to 3.5 um, most preferably 0.4 um to 2 um.

28. The printed article according to claim 23, wherein the glass flakes have an aspect ratio of average diameter divided by average thickness greater than or equal to 10, more preferably 15, most preferably 20.

29. The printed article according to claim 23, wherein a proportion of the glass flakes is angled relative to a printed layer.

30. The printed article according to claim 23, wherein a proportion of the glass flakes in the printed article is in a range 5 weight % to 30 weight %, more preferably 10 weight % to 20 weight %.

31. The printed article according to claim 23, comprising a depletion layer having a lower concentration of glass flakes than in the rest of the printed article.

32. The printed article according to claim 23, wherein a proportion of the filler material is glass flakes coated with an electrically conductive coating, preferably silver.

33. The printed article according to claim 32, wherein electrical resistance of the printed article is moisture-dependent, so as to function as a moisture sensor.

34. The printed article according to claim 33, wherein a change in electrical resistance of the printed article due to a change in moisture is faster than 10 seconds.

35. A feedstock for a printing apparatus, comprising: a matrix forming material, and a filler material, dispersed within the matrix forming material to provide a mixture, wherein the filler material comprises glass flakes, having an aspect ratio of average diameter divided by average thickness greater than or equal to three.

36. The feedstock according to claim 35, wherein the matrix forming material is a polymer selected from high density polyethylene (HDPE), polycarbonate (PC), polyphenylene ether (PPE), acrylonitrile butadiene styrene (ABS), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), poly(butylene adipate) (PBA), polypropylene (PP), polyurethane (PU), poly(lactic acid) (PLA), polyamide (PA) and UV-cured resins.

37. The feedstock according to claim 35, wherein the feedstock is configured as a filament.

38. The feedstock according to 35, wherein the glass flakes have average thickness in a range from 0.1 um to 5 um, more preferably from 0.2 um to 3.5 um, most preferably from 0.4 um to 2 um.

39. The feedstock according to claim 35, wherein the glass flakes have an aspect ratio of average diameter divided by average thickness greater than or equal to 10, more preferably 15, most preferably 20.

40. The feedstock according to claim 35, wherein a concentration of glass flakes in the feedstock is in a range from 5 weight % to 30 weight %, more preferably from 10 weight % to 20 weight %.

41. A process of manufacturing a feedstock for a printing apparatus, comprising: providing a matrix forming material, providing a filler material, and dispersing the filler material within the matrix forming material to provide a mixture, wherein the filler material comprises glass flakes, having an aspect ratio of average diameter divided by average thickness greater than or equal to three.

42. The process of manufacturing a feedstock according to claim 41, wherein the glass flakes are provided in granular form, preferably having average granular particle size in a range from 0.1 mm to 2 mm, more preferably from 0.5 mm to 1 mm.

43. A process of printing, comprising: providing a feedstock, comprising: a matrix forming material, and a filler material, dispersed within the matrix forming material, and feeding the feedstock into a printing apparatus, wherein the filler material comprises glass flakes, having an aspect ratio of average diameter divided by average thickness greater than or equal to three.

44. The process of printing according to claim 43, wherein a depletion layer having a lower concentration of glass flakes than in the rest of the printed article is formed during printing and wherein a proportion of the glass flakes is angled relative to a printed layer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0047] The invention will now be described by means of non-limiting examples with reference to the attached figures:

[0048] FIG. 1a shows a cross-section of a filament of feedstock comprising glass flakes according to the invention.

[0049] FIG. 1b shows a granule of the glass flakes of FIG. 1a for a process of manufacturing a feedstock according to the invention.

[0050] FIG. 2a shows an embodiment of the invention with a depletion layer.

[0051] FIG. 2b shows an embodiment of the invention with high permeation resistance.

[0052] FIG. 3 shows an embodiment of the invention with stitching between layers.

[0053] FIG. 4a shows an embodiment of the invention with glass flake oriented at an angle.

[0054] FIG. 4b shows prior art in which glass flake is oriented parallel to a direction of extrusion.

[0055] FIG. 5 is a chart of electrical conductivity (y) against weight percent glass flake (x)

[0056] FIG. 6 is a chart of resistance (R) against time (t) showing a change due to moisture.

DETAILED DESCRIPTION OF THE INVENTION

[0057] FIG. 1a shows a cross-section of a filament of feedstock according to the invention. A matrix forming material 1 has glass flakes dispersed within it as a filler material 2. The glass flakes may overlap each other. For clarity, glass flakes are shown oriented parallel with a diameter of the filament, but glass flakes may also be oriented parallel with a direction of formation of the filament, i.e. perpendicular to the diameter, or oriented randomly. The filament may also comprise a depletion layer adjacent to a surface of the filament.

[0058] FIG. 1b shows a granule of glass flakes 2, which are bound together with a binder material. Glass flakes 2 in this granule added to a matrix forming material disperse to form the filament cross-section shown in FIG. 1a. A flake diameter “d” is defined as a longest dimension of the glass flake 2. A granular diameter “D” is defined as a longest dimension of the granule of glass flakes 2.

[0059] FIG. 2a shows a single layer printed article according to the invention. A depletion layer 3 has a lower concentration of filler material 2 dispersed within the matrix forming material 1 than in the rest of the printed article. Permeation of moisture occurs along a path 4. The path 4 deviates from a straight line between top and bottom surfaces of the matrix forming material 1 due to the presence of impervious filler material 2. In the depletion layer 3, because there are no obstacles, the path 4 is a straight line.

[0060] FIG. 2b shows a single layer printed article according to the invention with high moisture permeation resistance. Permeation of moisture occurs along a path 5, which has a longer path length than FIG. 2a, due to the larger average diameter of the glass flakes. An advantage of the invention is that glass flakes reduce water absorption. The larger the average diameter, the higher the permeation resistance. For a predetermined average thickness of glass flakes, the aspect ratio should be selected to be as high as possible, for maximum moisture permeation resistance. For clarity, FIG. 2a and FIG. 2b omit any flakes angled relative to a printed layer.

[0061] FIG. 3 shows an embodiment of the invention with stitches between layers. A 3D printed article 10, formed by additive depositing of feedstock using a 3D printer, comprises layers 11, 12, 13 and interfaces 21, 22 between them. Each layer comprises a matrix forming material 1 and a filler material 2 within the layer. Depletion layers 31, 32, 33 have a lower concentration of filler material 2 dispersed within the matrix forming material 1 than in the rest of the layers 11, 12 and 13 respectively. Stitches 6 are filler material particles which straddle across interfaces 21, 22 partly embedded in each adjacent layer 11, 12 and 12, 13 respectively. Orientation of glass flakes 2 is measured as an angle “a” relative to a printed surface. For a larger stitching effect, larger average thickness is preferred. Larger average thickness provides stronger stitches 6. For larger crack stopping effect, larger average diameter is preferred. Larger average diameter provides larger stitches 6. For both a larger stitching effect and larger crack stopping effect, larger aspect ratio is preferred. Silane coating on the filler material 2 increases adhesion to the matrix forming material 1, so improves a breaking strength of the stitches 6. A larger concentration of filler material 2 in the matrix forming material 1 provides more stitches 6, so provides improved durability. For clarity, FIG. 3 and FIG. 4a omit any flakes angled relative to a printed layer at the top surface.

[0062] FIG. 4a shows an embodiment of the invention in which orientation of glass flakes 2 is measured as an angle “a” relative to a printed surface and controlled so as to optimise adhesion between printed layers. By contrast, FIG. 4b shows prior art for extrusion, showing a forming material 1 being extruded through an extrusion die 7, causing filler material 2 to be aligned substantially parallel with the direction of formation.

[0063] FIG. 5 is a chart of electrical conductivity “y” against weight percent filler material “x” in a printed article. The curve shows that electrical conductivity is approximately zero at concentrations of filler material below a threshold value “x1”. At this threshold it is believed that adjacent conductive coatings touch providing pathways for electrical current. Above the threshold value “x1” electrical conductivity increases approximately linearly.

[0064] FIG. 6 is a chart of electrical resistance “R” of a printed article against time “t”. At time “t1” moisture in the air around the printed article increases from ambient to maximum and then returns to zero. Resistance of the printed article changes over time at a rate dependent on the permeation resistance of the printed article, until it reaches a maximum at time “t2” and then returns to normal. A sensor response time is (t2−t1).

EXAMPLES OF THE INVENTION

Example 1

[0065] A printed article according to the invention comprises glass flakes having average thickness 5 um and average diameter 600 um, i.e. aspect ratio 120. Glass flakes such as Microglas® Glass Flake type REF-600, composition E-Glass, no surface treatment, supplied by NGF Europe Limited, St Helens, UK are suitable. E-Glass composition is selected because it is mechanically stronger than C-Glass, and is suitable for situations without risk of acid corrosion.

Example 2

[0066] A printed article according to the invention comprises glass flakes having average thickness 5 um and average diameter 160 um, i.e. aspect ratio 32. Glass flakes such as Microglas® Glass Flake type RCF160, composition C-Glass, no surface treatment, supplied by NGF Europe Limited, St Helens, UK are suitable. C-Glass is selected because it has better resistance to acid corrosion than E-Glass.

[0067] Printed articles of Example 1 and Example 2 are formed by additive depositing of layers, to form a 3D object. The printed article of Example 1 is mechanically stronger than Example 2. Higher mechanical strength is believed to be due to improved stitching and crack stopping capability, due to glass flakes of higher aspect ratio.

[0068] In a printing process to manufacture both Example 1 and Example 2, a 3D printer known in the art is set to a suitable temperature for a desired matrix forming material. The 3D printer is optimised to achieve the alignment of glass flakes and a depletion layer shown in FIG. 3. In particular, a temperature of printing is reduced so that the matrix forming material is more viscous, thereby forming a thicker deposit, i.e. a blob. A thicker deposit is found to have more angled glass flakes. Routine experimentation is required to select a printer head nozzle diameter and print speed suitable for a selected resin composition.

Example 3

[0069] A feedstock for 3D printing according to the invention comprises glass flakes having average thickness 2 um and average diameter 300 um, i.e. aspect ratio 150. Glass flakes such as Microglas® Glass Flake type RCF-2300, composition C-Glass, no surface treatment, supplied by NGF Europe Limited, St Helens, UK are suitable.

[0070] Printed articles made with a feedstock of Example 3 have higher moisture permeation resistance than similar printed articles made with a feedstock of Example 2. It is believed that flakes having a larger average diameter provide better moisture permeation resistance because of a longer path length for moisture, as shown in FIG. 2b, in contrast with FIG. 2a.

Example 4

[0071] A feedstock for 3D printing according to the invention comprises glass flakes in granular form. Glass flake average thickness is 5 um and average diameter is 600 um, i.e. aspect ratio 120. Glass flakes are bound together with a binder material. Average granular particle size is 1.0 mm, binder type is epoxy and coupling agent is amino silane and/or epoxy silane. Glass composition is E-Glass. Glass flakes such as Microglas® Fleka type REFG-101 supplied by NGF Europe Limited, St Helens, UK, are suitable.

Example 5

[0072] A feedstock for 3D printing according to the invention comprises smaller glass flakes in granular form. Glass flake average thickness is 0.7 um and average diameter is 160 um, i.e. aspect ratio 230. Glass flakes are bound together with a binder material. Average granular particle size is 0.7 mm, binder type is epoxy and coupling agent is amino silane. Glass composition is E-Glass. Glass flakes such as Microglas® Fleka type MEG-160-FYM01 supplied by NGF Europe Limited, St Helens, UK, are suitable.

[0073] Pellets of PBT under the name Crastin®, obtained from Du Pont, Wilmington, Del., USA, are mixed with the granular glass flakes in a master compounder apparatus, known in the art, and extruded to form a filament. The filament is wound on a reel suitable for use as a feedstock for a 3D printer known in the art.

Example 6

[0074] A two dimensional electrically conductive printed article according to the invention comprises glass flakes having average thickness 5 um and average diameter 90 um, i.e. aspect ratio 18. Glass flakes such as Microglas® Metashine type MC-5090PS, composition C-Glass, having a silver coating, supplied by NGF Europe Limited, St Helens, UK are suitable. A matrix forming material capable of absorbing moisture is selected from moisture sensitive polymers known in the art, for example a nylon, i.e. a hygroscopic polyamide (PA).

[0075] The printed article, dimensions 0.75 cm by 0.75 cm and thickness 0.3 cm, is printed on a circuit board and connected to a resistance measurement apparatus. Moisture in the air around the printed article is increased momentarily, and the change in electrical resistance is shown in FIG. 4. At time “t1” moisture in the air around the printed article increases from zero to 100% relative humidity and then returns to zero. Electrical resistance of the printed article changed from 0.8 ohm at “t1” to 1.0 ohm at “t2”. A sensor according to the invention responds in a time (t2−t1) of ten seconds.

Example 7

[0076] A printed article according to the invention comprises glass flakes having average thickness 2 um and average diameter 40 um, i.e. aspect ratio 20. Glass flakes such as Microglas® Glass Flake type RCF-2015, composition C-Glass, surface treatment silane, supplied by NGF Europe Limited, St Helens, UK are suitable.

Example 8

[0077] A printed article according to the invention comprises glass flakes having average thickness 0.4 um and average diameter 40 um, i.e. aspect ratio 100. Glass flakes such as Microglas® Glass Flake type RCFD015, composition E-Glass, surface treatment silane, supplied by NGF Europe Limited, St Helens, UK are suitable.

Example 9

[0078] A printed article according to the invention comprises glass flakes having average thickness 0.2 um and average diameter 30 um, i.e. aspect ratio 150. Glass flakes such as Microglas® Glass Flake type RCFB-030, composition E-Glass, surface treatment silane, supplied by NGF Europe Limited, St Helens, UK are suitable.

Example 10

[0079] A printed article according to the invention comprises glass flakes having average thickness 0.1 um and average diameter 20 um, i.e. aspect ratio 200. Glass flakes such as Microglas® Glass Flake type RCFA-020, composition C-Glass, surface treatment silane, supplied by NGF Europe Limited, St Helens, UK are suitable.

Example 11

[0080] A printed article according to the invention comprises glass flakes having average thickness 1 um and average diameter 10 um, i.e. aspect ratio 10. Glass flakes such as Microglas® Glass Flake type RCFA-010, composition C-Glass, surface treatment silane, supplied by NGF Europe Limited, St Helens, UK are suitable.

Example 12

[0081] A printed article according to the invention comprises glass flakes having average thickness 5 um and average diameter 15 um, i.e. aspect ratio 20. Glass flakes such as Microglas® Glass Flake type REF-015, composition E-Glass, surface treatment silane, supplied by NGF Europe Limited, St Helens, UK are suitable.

[0082] Examples 7 to 11 are provided from an improved process of manufacturing glass flakes whereby average thickness is in a range from 0.1 um to 2 um and average diameter is in a range from 10 um to 40 um. Glass flakes from the improved process are substantially without breaks or holes, i.e. have structural integrity. Combining these glass flakes with the selection of aspect ratio in a range from 10 to 200 provides printed articles with glass flakes angled relative to the printed layer and having a depletion layer.

[0083] Example 12 comprises glass flakes having a small average diameter and a large average thickness, such that the aspect ratio is three. Glass flakes with an aspect ratio significantly less than three resemble spheres, whose orientation is difficult to control.

[0084] Table 1 lists the Examples described above, showing selection of glass flakes by average diameter in um and average thickness in um so as to control aspect ratio of glass flakes in a printed article and in a feedstock for a printing apparatus.

TABLE-US-00001 TABLE 1 Average Average Diameter/ Thickness/ Aspect Ex. Flake Granular Treated um um Ratio 1 REF-600 No No 600 5 120 2 RCF-160 No No 160 5 32 3 RCF-2300 No No 300 2 150 4 REFG-101 Yes Yes 600 5 120 5 MEG-160FY Yes Yes 160 0.7 230 6 MC-5090PS No Silver 90 5 18 7 RCF-2015 No Yes 40 2 20 8 RCFD-015 No Yes 40 0.4 100 9 RCFB-030 No Yes 30 0.2 150 10 RCFA-020 No Yes 20 0.1 200 11 RCFA-010 No Yes 10 1 10 12 REF-015 No Yes 15 5 3

INDUSTRIAL USE

[0085] A printed article comprising glass flake dispersed in a polymer has improved properties due to orientation of the glass flakes during printing. In an advantageous embodiment of the invention, glass flakes are provided in granular form to facilitate manufacture of a feedstock.

[0086] An advantage of glass flakes over glass spheres is the formation of a depletion layer at a surface of a printed article thus providing a smoother surface and better shape definition, whilst simultaneously providing some glass flakes angled relative to a printed layer to provide a stitching effect between adjacent printed layers. Formation of a depletion layer at a surface is believed to be result of movement of glass flakes towards each other during printing. The inventors have found that this movement can be controlled by selection of glass flake diameter, aspect ratio and concentration in a resin composition.

[0087] Such a depletion layer is also advantageous in a two dimensional printed article according to the invention wherein the glass flakes are coated with silver and are at least 12 weight % of the resin composition. In this embodiment, the printed article has moisture dependent electrical resistance so as to be capable of functioning as a moisture sensor. The depletion layer is believed to result in fast response of the moisture sensor to a rise in moisture level. The rest of the printed article has high moisture permeation resistance, so the moisture sensor has a fast response to a fall in moisture level because little moisture is absorbed in the device. Thus a low hysteresis moisture sensor is provided.