Bendable or foldable articles as well as methods for the production thereof

Abstract

An article of transparent and brittle material, such as glass, glass ceramic, ceramic or crystals. The article includes at least one exchange layer and at least one bulk layer. The at least one exchange layer includes at least one kind of cation ion.sub.I with an increased proportion compared to the at least one bulk layer and at least one kind of cation ion.sub.R with a reduced proportion compared to the at least one bulk layer. The article is in particularly used as a display cover for flexible displays or flexible protective foils, for example in smartphones or tablets or TV sets. The article can also be used as a substrate for an electronic component such as an OLED or LED.

Claims

1. An article of transparent and brittle material having an article surface, the article comprising: at least one exchange layer and at least one bulk layer, the at least one exchange layer includes at least one kind of cation ion.sub.I with an increased proportion compared to the at least one bulk layer and at least one kind of cation ion.sub.R with a reduced proportion compared to the at least one bulk layer, the article having a thickness d of at most 100 μm, wherein an ion radius of ion.sub.I is higher than an ion radius of ion.sub.R, a ratio c.sub.R,surface of the proportion of ion.sub.R at the article surface to the proportion of ion.sub.R in the at least one bulk layer and the ratio c.sub.R,inner of the proportion of ion.sub.R in a depth y of the at least one exchange layer to the proportion of ion.sub.R in the at least one bulk layer are such that $\frac{y (- \ln (\frac{4 - 3 .Math. c_{R, surface}}{4}))}{\ln (\frac{4 - 3 .Math. c_{R, surface}}{4 - 3 .Math. c_{R, inner}})}$ is higher than 5 μm, and wherein the ratio c.sub.R,surface of the proportion of ion.sub.R at the article surface to the proportion of ion.sub.R in the at least one bulk layer and the ratio c.sub.R,inner of the proportion of ion.sub.R in a depth y of the at least one exchange layer to the proportion of ion.sub.R in the at least one bulk layer are such that $\frac{y}{\ln (\frac{4 - 3 .Math. c_{R, surface}}{4 - 3 .Math. c_{R, inner}})}$ is higher than 12 μm.

2. The article of claim 1, wherein the transparent and brittle material is glass.

3. The article of claim 1, wherein ion.sub.R is Na.sup.+.

4. The article of claim 1, wherein the article includes exactly two exchange layers and one bulk layer lying in between.

5. The article of claim 1, wherein the article in a 2-point bending test shows a 63.2% bending strength of at least 1700 MPa.

6. The article of claim 1, wherein the article has an impact strength such that a mean drop height of an object which drops onto the article and at which the article breaks is at least 40 mm, wherein the object has a length of 130 to 150 mm, a weight of 4 to 7 g and a stiffness of 250 to 350 N/mm as well as a tip of tungsten carbide with a diameter of 0.5 to 0.75 mm, wherein the object with the tip of tungsten carbide ahead impinges on the article, wherein on a side of the article opposite to the object an adhesive PSA layer with a thickness of 2 to 10 μm and a polyethylene layer with a thickness of 200 to 300 μm are present and wherein the adhesive PSA layer is arranged between the article and the polyethylene layer.

7. The article of claim 1, wherein the article has a fracturing behavior in a fracturing test such that when an object falls onto the article from a fracturing height and thereby causes breakage of the article a number of cracks that are formed and that have a length of at least 1000 μm is at most 40, wherein the object has a length of 130 to 150 mm, a weight of 4 to 7 g and a stiffness of 250 to 350 N/mm as well as a tip of tungsten carbide with a diameter of 0.5 to 0.75 mm, wherein the object impinges with the tip of tungsten carbide ahead on the article, wherein on a side of the article being opposite to the object an adhesive PSA layer with a thickness of 2 to 10 μm and a polyethylene layer with a thickness of 200 to 300 μm are present and wherein the adhesive PSA layer is arranged between the article and the polyethylene layer.

8. An article of transparent and brittle material, the article comprising: at least one exchange layer and at least one bulk layer, the at least one exchange layer includes at least one kind of cation ion.sub.I with an increased proportion compared to the at least one bulk layer and at least one kind of cation ion.sub.R with a reduced proportion compared to the at least one bulk layer, the article having a thickness d of at most 100 μm, wherein the article has a fracturing behavior in a fracturing test such that when an object falls onto the article from a fracturing height and thereby causes breakage of the article a number of cracks that are formed and that have a length of at least 1000 μm is at most 40, wherein the object has a length of 130 to 150 mm, a weight of 4 to 7 g and a stiffness of 250 to 350 N/mm as well as a tip of tungsten carbide with a diameter of 0.5 to 0.75 mm, wherein the object impinges with the tip of tungsten carbide ahead on the article, wherein on the side of the article being opposite to the object an adhesive PSA layer with a thickness of 2 to 10 μm and a polyethylene layer with a thickness of 200 to 300 μm are present and wherein the adhesive PSA layer is arranged between the article and the polyethylene layer.

9. The article of claim 8, wherein the transparent and brittle material is a glass or a glass ceramic.

10. The article of claim 9, wherein the article is chemically hardened.

11. The article of claim 8, wherein the article has an impact strength such that a mean drop height of an object which drops onto the article and at which the article breaks is at least 40 mm, wherein the object has a length of 130 to 150 mm, a weight of 4 to 7 g and a stiffness of 250 to 350 N/mm as well as a tip of tungsten carbide with a diameter of 0.5 to 0.75 mm, wherein the object with the tip of tungsten carbide ahead impinges on the article, wherein on the side of the article opposite to the object an adhesive PSA layer with a thickness of 2 to 10 μm and a polyethylene layer with a thickness of 200 to 300 μm are present and wherein the adhesive PSA layer is arranged between the article and the polyethylene layer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein:

(2) FIG. 1 shows schematically a side view of a chemically tempered glass;

(3) FIG. 2 shows exemplarily the course (due to the exchange process) of the concentration of an ion ion.sub.I;

(4) FIG. 3 shows a simplified model of the stresses which occur;

(5) FIG. 4A shows the results of a 2-point bending test for glasses with a characteristic depth of penetration x.sub.c;

(6) FIG. 4B shows the results of a 2-point bending test for glasses with another characteristic depth of penetration x.sub.c;

(7) FIG. 5A shows a photograph of a fracturing test done with a sample type;

(8) FIG. 5B shows a photograph of a fracturing test done with another sample type;

(9) FIG. 6 is a graph showing the dependence of the number of cracks observed in the fracturing test (y-axis) on etching removal A (x-axis); and

(10) FIG. 7 shows the dependence of number of cracks (y-axis) on the 63.2% bending strength (x-axis).

(11) Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate embodiments of the invention and such exemplifications are not to be construed as limiting the scope of the invention in any manner.

DETAILED DESCRIPTION OF THE INVENTION

(12) FIG. 1 shows schematically a side view of a chemically tempered glass. The glass comprises three layers 1, 2 and 3, wherein the sum of the respective thicknesses thereof is the glass thickness d which is indicated by the reference sign 4. The layers 1 and 3 which are hatched are exchange layers. The layer 2 which is not hatched is the bulk glass layer.

(13) FIG. 2 shows exemplarily the course (due to the exchange process) of the concentration of an ion ion.sub.I, wherein the proportion thereof in the exchange layer in comparison to the bulk glass layer is increased (for example K.sup.+). On the y-axis the ion concentration is specified and on the x-axis the relative depth position in the glass is specified. A relative depth position in the glass of 0 corresponds to the surface of the glass. There, the concentration of the ion reaches a maximum (here shown as 100%). The x position is the distance from the glass surface. This distance can also be referred to as depth position y or depth y. It can be seen that the concentration of the ion from the surface into the direction of the center of the glass, following a complementary error function (erfc), decreases.

(14) Here, the depth position in the glass is specified relatively to x.sub.c, wherein x.sub.c according to the definition can be calculated from the parameters diffusion coefficient and prestressing time which are decisive for the prestressing process. Accordingly, the concentration profile shown in FIG. 2 describes the general course after a single-step prestressing process. In comparison to the complementary error function erfc (dotted line) also the exponential function used for approximation (continuous line) is shown.

(15) FIG. 3 shows a simplified model of the stresses which occur, when a glass is bent. In this model the total stress σ.sub.total (continuous line) is the sum of the tensile stress due to bending σ.sub.tensile, (dotted line), the compression stress being introduced by the chemical tempering σ.sub.CS (dotted-dashed line) and the tensile stress σ.sub.CT (dashed line) being directed against σ.sub.CS. Tensile stresses are illustrated positive and compression stresses are illustrated negative. The occurring stresses are shown as a function of the depth position x. The vertical dashed line (a0) highlights the depth position at which the total stress σ.sub.total is zero. The illustration shown in FIG. 3 is based on the assumption of an exchange layer with a characteristic depth of penetration x.sub.c=7 μm and a tensile stress due to the bending σ.sub.tensile of 200 MPa. For the sake of convenience, in this model the introduced compression stress σ.sub.CS was linearly approximated.

(16) FIGS. 4A and 4B shows the results of a 2-point bending test for glasses with different characteristic depth of penetration x.sub.c. For each point of measurement 30 single measurements were utilized. The shown values are the values of the Weibull distributions (1% strengths) which were fitted with the help of the 30 single measurements. In the case of the glasses shown in FIG. 4A the characteristic depth of penetration x.sub.c which has been achieved by the chemical tempering was 16 μm and in the case of the glasses shown in FIG. 4B this value was 24 μm. On the y-axis the determined 1% bending strength is shown in MPa. On the x-axis the extent of the removal by etching which has been conducted after the tempering is plotted, wherein the removal is shown in μm.

(17) FIGS. 5A-5B show photographs of a fracturing test done with two different sample types. The glasses shown were subjected to an etching step, wherein on each of both main side faces material was removed, prior to the fracturing test. The etching removal A was 4 μm on each of both main side faces for the glass shown in FIG. 5A. The etching removal A was 19 μm on each of both main side faces for the glass shown in FIG. 5B.

(18) FIG. 6 is a graph showing the dependence of the number of cracks observed in the fracturing test (y-axis) on etching removal A (x-axis). It can be seen that the number of cracks decreases with increasing removal A. FIG. 7 shows the dependence of number of cracks (y-axis) on the 63.2% bending strength (x-axis). It can be seen that the number of cracks decreases with increasing 63.2% bending strength.

EXAMPLES

(19) The following examples are provided for further explaining the present invention.

(20) 1. Provision of a Starting Glass

(21) With the help of a downdraw method a thinnest glass with a length of 600 mm, a width of 500 mm and with a thickness d of 100 μm was provided. The glass comprised the following components in % by weight:

(22) TABLE-US-00003 Component Proportion (% by weight) SiO.sub.2 61 Al.sub.2O.sub.3 17 Na.sub.2O 12 K.sub.2O 4 MgO 4 ZrO.sub.2 2

(23) The glass may have an elastic modulus of higher than 70,000 MPa, a Poisson number of 0.22 and a density of about 2500 kg/m.sup.3.

(24) On one of the main sides at defined sites the glass was scored with a diamond for being able to break the glass in a targeted manner for achieving the desired sample sizes. After the scoring step the glass was broken such that samples with a length l of 100 mm, a width b of 20 mm and a thickness d of 10 μm were achieved.

(25) 2. Chemical Tempering

(26) The glass was tempered on both sides in a KNO.sub.3 bath at a temperature of 380° C. over a period of time of 7.8 hours. On both sides of the glass the characteristic depth of penetration x.sub.c was 24 μm each and thus 24% of the starting thickness d.sub.A of the glass which was 100 μm such as described above.

(27) In a further test it was tempered in a KNO.sub.3 bath at a temperature of 380° C. over a period of time of 3.5 hours on both sides such that the characteristic depth of penetration x.sub.c on both sides of the glass was 16 μm each and thus 16% of the starting thickness d.sub.A of the glass.

(28) In a further test it was tempered in a KNO.sub.3 bath at a temperature of 380° C. over a period of time of 56 minutes on both sides such that the characteristic depth of penetration x.sub.c on both sides of the glass was 8 μm each and thus 8% of the starting thickness d.sub.A of the glass.

(29) 3. Etching Step

(30) After the chemical tempering the glass was subjected to an etching step. It was etched at room temperature in an etching bath with an etching solution which contained 2% (w/v) of ammonium bifluoride and 2% (w/v) of nitric acid.

(31) By the etching step on each of both main side faces material was removed. Depending on the duration of the etching step which was between 7 minutes and 39 minutes different amounts of material were removed. The results are summarized in the following table.

(32) TABLE-US-00004 Characteristic depth of penetration x.sub.c in μm Removal A in μm Ratio A/x.sub.c in % (rounded) 8 1.9 24 8 3.5 44 8 5.7 71 8 7.8 98 16 3.9 24 16 8.6 54 16 11.1 69 24 6.4 27 24 10 42

(33) Thus, for the glasses with a characteristic depth of penetration x.sub.c of 8 μm four different amounts of removal were realized. For the glasses with a characteristic depth of penetration x.sub.c of 16 μm three different removals were realized. For the glasses with a characteristic depth of penetration x.sub.c of 24 μm two different removals were realized. As control from the different tempered glasses also non-etched samples were retained.

(34) 4. 2-Point Bending Test

(35) The determination of the bending strength was achieved by way of a 2-point bending test such as described by Matthewson et al. (Journal of the American Ceramic Society, Vol. 69, No. 11, pages 815-821, November 1986). The bending strength was measured by inserting the tempered and etched glass between two parallel guide plates which were then moved towards each other, until the article broke. The tests were conducted such that one “main faces” of the glass panes—that which is curved in a convex manner—touched both guide plates. Here, the long edges of the samples were curved. The geometries of the samples were 20 mm×100 mm such as described above. For the determination of the Weibull distribution 30 samples each were tested.

(36) From the distance of the plates at the event of fracture the bending radius of the glass at the event of fracture was determined. From the bending radius at the event of fracture in turn the tensile stress at the event of fracture was determined, such as described by Matthewson et al. A Weibull distribution of the probability of fracture as a function of the tensile stress was obtained (not shown). In FIGS. 4A-4B the 1% bending strength for the samples with a characteristic depth of penetration x.sub.c of 16 μm and 24 μm is shown as the tensile stress at which the probability of failure in the Weibull distribution is 1%. For the samples with a characteristic depth of penetration x.sub.c of 8 μm no increase of the bending strength was obtained by the etching removal (not shown).

(37) Comparable results were also achieved with a glass of the following composition:

(38) TABLE-US-00005 Component Proportion (% by weight) SiO.sub.2 64 B.sub.2O.sub.3 9 Al.sub.2O.sub.3 4 Na.sub.2O 6 K.sub.2O 7 ZnO 6 TiO.sub.2 4

(39) Thus, the results are not limited to certain compositions.

(40) 5. Impact Strength

(41) A glass with a thickness of 100 μm was chemically tempered so that the characteristic depth of penetration x.sub.c on both sides of the glass was 24 μm each and thus 24% of the starting thickness d.sub.A of the glass, such as described in the examples 1 and 2. After the tempering the glass was subjected to an etching step, wherein on each of both main side faces material was removed, such as described in example 3. On each of both main side faces the removal A was 10 μm each which corresponds to about 42% of x.sub.c. Thus, after the etching step the glass had a final thickness d.sub.E of 80 μm. The glass corresponds to the glass shown in FIG. 4B with a removal of about 42%.

(42) The impact strength was tested according to the method described above. A defined object was dropped from a predetermined height vertically with the tip downwards onto the glass, wherein on the side of the glass opposite to the object a plastic has been laminated. The plastic film was a base polyethylene foil with a thickness of 245 μm and an adhesive PSA layer with a thickness of 5 μm. The adhesive layer was located between the polyethylene layer and the glass. The glass was glued onto the polyethylene foil with the help of the adhesive PSA layer. The polyethylene foil was tied with the glass via the adhesive PSA layer by at first providing a respective layer arrangement and then laminating it into the final layer composite by exerting pressure.

(43) For the test the glass was laid with the polyethylene layer downwards onto a block of stainless steel. Then the object was dropped from a defined height onto the non-coated side of the glass. The height from which the object was dropped was increased step by step, until the glass broke. The drop height of the object at which the fracture had taken place is the measured value via which the impact strength of the glass is evaluated. As starting height a height of 5 mm was chosen. The drop height is the distance between the tip of the object and the glass surface.

(44) For the test the defined object was clamped in a testing machine. The testing machine moved to the predetermined height of 5 mm. Then the glass was placed in the apparatus and the object was dropped onto the glass from a height of 5 mm. Since the glass was not broken, the drop height of the object was increased by 5 mm and the glass was shifted a bit for again testing a site at which before no impact has occurred. This was continued so long, until the article broke.

(45) The defined object which was dropped onto the glass was an oblong rod-shaped object with a tip of tungsten carbide. The tip had a diameter of 0.515 mm. The object was dropped onto the glass such that the object impinged on the glass with the tip of tungsten carbide ahead. The object had a length of 138.5 mm and a weight of 6.46 g. The stiffness of the object was preferably 300 N/mm.

(46) During the measurement the temperature was 23.5° C. and the relative air humidity was 40%.

(47) With respect to the adhesive layer, the polyethylene layer and the tip of tungsten carbide the following characteristic numbers applied:

(48) TABLE-US-00006 Material Elastic modulus Poisson number Density Adhesive layer 700 MPa 0.48 1,400 kg/m.sup.3 Polyethylene layer 1,000 MPa 0.48 940 kg/m.sup.3 Tungsten carbide 680 GPa 0.25 15,700 kg/m.sup.3

(49) In total 32 samples of the glass were tested for obtaining a statistical distribution. The following distribution was obtained:

(50) TABLE-US-00007 Drop height of the object at Number of the which the glass broke [mm] samples 35 1 40 3 45 3 50 6 55 15 60 4

(51) The drop height at which the glass broke was for 15 of 32 samples 55 mm. The average value was 51.7 mm and the standard deviation was 6.4 mm.

(52) On the other hand, in the case of other samples which were not subjected to the etching step according to the present invention the glass already broke at a mean drop height of 20 mm.

(53) 6. Fracturing Behavior

(54) Glasses with a thickness of 70 μm were chemically tempered so that the characteristic depth of penetration x.sub.c on both sides of the glass was 20 μm each and thus 28.6% of the starting thickness d.sub.A of the glasses, such as described in the examples 1 and 2. After the tempering the glasses were subjected to an etching step, wherein on each of both main side faces material was removed, such as described in example 3. Removal A was different for different sample types.

(55) In sample type 1, the etching step was omitted (removal A=0 μm). Sample type 1 served as a control. The 63.2% bending strength was determined to be about 500 MPa.

(56) In sample type 2, on each of both main side faces the removal A was 2 μm each which corresponds to about 10% of x.sub.c. Thus, after the etching step the glass had a final thickness d.sub.E of 66 μm. The 63.2% bending strength was determined to be about 900 MPa.

(57) In sample type 3, on each of both main side faces the removal A was 4 μm each which corresponds to about 20% of x.sub.c. Thus, after the etching step the glass had a final thickness d.sub.E of 62 μm. The 63.2% bending strength was determined to be about 1800 MPa.

(58) In sample type 4, on each of both main side faces the removal A was 7 μm each which corresponds to about 35% of x.sub.c. Thus, after the etching step the glass had a final thickness d.sub.E of 56 μm. The 63.2% bending strength was determined to be about 2500 MPa.

(59) In sample type 5, on each of both main side faces the removal A was 19 μm each which corresponds to about 95% of x.sub.c. Thus, after the etching step the glass had a final thickness d.sub.E of 32 μm. The 63.2% bending strength was determined to be about 2600 MPa.

(60) Sample types 1 to 3 are comparative examples. Sample types 4 and 5 are in accordance with the present invention.

(61) The fracturing behavior was tested according to the method described above. A defined object was dropped from a predetermined height vertically with the tip downwards onto the glass, wherein on the side of the glass opposite to the object a plastic has been laminated. The plastic film was a base polyethylene foil with a thickness of 245 μm and an adhesive PSA layer with a thickness of 5 μm. The adhesive layer was located between the polyethylene layer and the glass. The glass was glued onto the polyethylene foil with the help of the adhesive PSA layer. The polyethylene foil was tied with the glass via the adhesive PSA layer by at first providing a respective layer arrangement and then laminating it into the final layer composite by exerting pressure.

(62) For the test, the glass was laid with the polyethylene layer downwards onto a block of stainless steel. Then the object was dropped from a defined height onto the non-coated side of the glass. The height from which the object was dropped was increased step by step, until the fracturing height was reached and the glass broke. The fracturing height is thus the drop height of the object at which the fracture had taken place. As starting height a height of 5 mm was chosen. The drop height is the distance between the tip of the object and the glass surface.

(63) For the test, the defined object was clamped in a testing machine. The testing machine moved to the predetermined height of 5 mm. Then the glass was placed in the apparatus and the object was dropped onto the glass from a height of 5 mm. Since the glass was not broken, the drop height of the object was increased by 5 mm and the glass was shifted a bit for again testing a site at which before no impact has occurred. This was continued so long, until the article broke (fracturing height).

(64) The defined object which was dropped onto the glass was an oblong rod-shaped object with a tip of tungsten carbide. The tip had a diameter of 0.515 mm. The object was dropped onto the glass such that the object impinged on the glass with the tip of tungsten carbide ahead. The object had a length of 138.5 mm and a weight of 6.46 g. The stiffness of the object was preferably 300 N/mm.

(65) During the measurement the temperature was 23.5° C. and the relative air humidity was 40%.

(66) With respect to the adhesive layer, the polyethylene layer and the tip of tungsten carbide the following characteristic numbers applied:

(67) TABLE-US-00008 Material Elastic modulus Poisson number Density Adhesive layer 700 MPa 0.48 1,400 kg/m.sup.3 Polyethylene layer 1,000 MPa 0.48 940 kg/m.sup.3 Tungsten carbide 680 GPa 0.25 15,700 kg/m.sup.3

(68) The results of the experiments are shown in FIGS. 5 to 7. The experiments show that the number of cracks decreases with increasing removal A (FIG. 6). FIG. 5 shows photographs for exemplary comparison of the fracture behavior of sample types 3 and 5 having removal A of 4 μm and 19 μm, respectively.

(69) Particularly interesting is the comparison of sample types 4 and 5 with respect to the dependence of number of cracks on the 63.2% bending strength (FIG. 7). Even though the 63.2% bending strength of sample types 4 and 5 is very similar, the number of cracks is drastically reduced in sample type 5 as compared to sample type 4. Thus, the removal A appears to be more relevant with respect to determining the number of cracks (FIG. 6) as compared to the 63.2% bending strength (FIG. 7), at least for high 63.2% bending strengths above 2500 MPa.

(70) While this invention has been described with respect to at least one embodiment, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.

LIST OF REFERENCE SIGNS

(71) 1 exchange layer

(72) 2 bulk glass layer

(73) 3 exchange layer

(74) 4 glass thickness d

Bendable or foldable articles as well as methods for the production thereof

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C03C17/3405

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Abstract

Claims

Description