LAMINATED GLAZING

Abstract

Methods of making a laminated glazing having reduced optical distortion when installed in a vehicle are described. The laminated glazing has first and second sheets of glazing material each separately shaped between a pair of shaping members that are then laminated together. The position for bending the first sheet of glazing material may be deliberately offset from the position for bending the second sheet of glazing material. During the lamination step, the first sheet of glazing material may be displaced relative to the second sheet of glazing material by a lateral and/or longitudinal positional displacement. The first and/or second sheet of glazing material may have been cut such that after lamination at least a portion of the peripheral edges thereof are aligned. Apparatus for shaping a sheet of glazing material for carrying out the aforementioned methods is also described, as is a resulting laminated glazing.

Claims

1. A method of making a laminated glazing for installing in a vehicle at an installation angle θ to the vertical, the laminated glazing having a thickness in millimetres of d and comprising a first sheet of glazing material laminated to a second sheet of glazing material via at least one adhesive sheet, the first and second sheets of glazing material each having a major surface with a respective geometric centre; the method comprising the steps: providing a complementary pair of moulding members comprising a first shaping member and a second shaping member, the first shaping member having a least one concave portion and being a ring mould or a full surface contact mould and the second shaping member being a full surface contact shaping member having a corresponding complementary convex portion; transporting a first sheet of glazing material in a first direction between the pair of moulding members; shaping the first sheet of glazing material between the pair of moulding members, wherein during shaping, the geometric centre of the first sheet of glazing material is aligned with a reference point on the second shaping member; transporting the first sheet of glazing material away from between the pair of moulding members; thereafter transporting a second sheet of glazing material between the pair of moulding members; shaping the second sheet of glazing material between the pair of moulding members, wherein during shaping the geometric centre of the second sheet of glazing material is offset from the same reference point on the second shaping member by a lateral displacement in a direction perpendicular to the first direction and/or by a longitudinal displacement in a direction parallel to the first direction; transporting the second sheet of glazing material away from between the pair of moulding members; and using suitable lamination conditions to laminate the first sheet of glazing material to the second sheet of glazing material via at least one adhesive sheet, wherein θ is between 20° and 80°, further wherein the lateral displacement and/or the longitudinal displacement is between $1/2\times d\times \tan \left({\sin }^{-1}\left(\frac{1}{1.52}\times \sin \theta \right)\right)$ $\mathrm{and}$ $3/2\times d\times \tan \left({\sin }^{-1}\left(\frac{1}{1.52}\times \sin \theta \right)\right).$

2. The method according to claim 1, wherein the lateral displacement is between 0.5 mm and 8.0 mm.

3. The method according to claim 1, wherein the longitudinal displacement is between 0.5 mm and 8.0 mm.

4. The method according to claim 1, wherein θ is between 50° and 70°.

5. The method according to claim 1, wherein the first and/or second sheet of glazing material is a glass sheet.

6. A method of making a laminated glazing for installing in a vehicle at an installation angle θ to the vertical, the laminated glazing having a thickness in millimetres of d and comprising a first sheet of glazing material laminated to a second sheet of glazing material via at least one adhesive sheet, the first and second sheets of glazing material each having a major surface with a respective geometric centre; the method comprising (i) transporting a first sheet of glazing material in a first direction between a complementary pair of moulding members comprising a first shaping member and a second shaping member, the first shaping member having a least one concave portion and being a ring mould or a full surface contact mould and the second shaping member being a full surface contact shaping member having a corresponding complementary convex portion; (ii) stopping the first sheet of glazing material such that the first sheet of glazing material is stopped at a first position for bending between the pair of moulding members, wherein the geometric centre of the first sheet of glazing material is aligned with a reference point on the second shaping member; (iii) shaping the first sheet of glazing material between the pair of moulding members; (iv) transporting the first sheet of glazing material away from between the pair of moulding members; (v) transporting a second sheet of glazing material between the pair of moulding members; (vi) stopping the second sheet of glazing material such that the second sheet of glazing material is stopped at a second position for bending between the pair of moulding members, wherein the geometric centre of the second sheet of glazing material is offset from the same reference point on the second shaping member, (vii) shaping the second sheet of glazing material between the pair of moulding members, (viii) transporting the second sheet of glazing material away from between the pair of moulding members; and (ix) using suitable lamination conditions to laminate the first sheet of glazing material to the second sheet of glazing material via at least one adhesive sheet; wherein steps (ii) and (iii) take place before steps (vi) and (vii), wherein in step (vi), the geometric centre of the second sheet of glazing material is offset from the same reference point on the second shaping member by a lateral displacement in a direction perpendicular to the first direction and/or by a longitudinal displacement in a direction parallel to the first direction, wherein θ is between 20° and 80°, further wherein the lateral displacement and/or the longitudinal displacement is between $1/2\times d\times \tan \left({\sin }^{-1}\left(\frac{1}{1.52}\times \sin \theta \right)\right)$ $\mathrm{and}$ $3/2\times d\times \tan \left({\sin }^{-1}\left(\frac{1}{1.52}\times \sin \theta \right)\right).$

7. The method according to claim 6, wherein the magnitude of the lateral tolerance is less than 2.0 mm.

8. The method according to claim 6, wherein the magnitude of the longitudinal tolerance is less than 2.0 mm.

9. The method according to claim 6, wherein the lateral displacement is between 0.5 mm and 8.0 mm.

10. The method according to claim 6, wherein the longitudinal displacement is between 0.5 mm and 8.0 mm.

11. The method according to claim 6, wherein θ is between 50° and 70°.

12. The method according to claim 6, wherein the first and/or second sheet of glazing material is a glass sheet.

13. A method of making a laminated glazing for installing in a vehicle at an installation angle θ to the vertical between 20° and 80°, the laminated glazing having a thickness in millimetres of d and comprising a first sheet of glazing material laminated to a second sheet of glazing material via at least one adhesive sheet, the first and second sheets of glazing material each having a major surface with a respective geometric centre; the method comprising (i) transporting a first sheet of glazing material in a first direction between a complementary pair of moulding members comprising a first shaping member and a second shaping member, the first shaping member having a least one concave portion and being a ring mould or a full surface contact mould and the second shaping member being a full surface contact shaping member having a corresponding complementary convex portion; (ii) stopping the first sheet of glazing material such that the first sheet of glazing material is stopped at a first position for bending between the pair of moulding members, wherein the geometric centre of the first sheet of glazing material is aligned with a reference point on the second shaping member; (iii) shaping the first sheet of glazing material between the pair of shaping members; (iv) transporting the first sheet of glazing material away from between the pair of moulding members; (v) transporting a second sheet of glazing material between the pair of moulding members; (vi) stopping the second sheet of glazing material such that the second sheet of glazing material is stopped at a second position for bending between the pair of moulding members, wherein the geometric centre of the second sheet of glazing material is offset from the same reference point on the second shaping member by a lateral displacement in a direction perpendicular to the first direction and/or by a longitudinal displacement in a direction parallel to the first direction, (vii) shaping the second sheet of glazing material between the pair of moulding members, (viii) transporting the second sheet of glazing material away from between the pair of moulding members; and (ix) using suitable lamination conditions to laminate the first sheet of glazing material to the second sheet of glazing material via at least one adhesive sheet; wherein steps (ii) and (iii) take place before steps (vi) and (vii); wherein in step (ii) stopping of the first sheet of glazing material at the first position for bending is performed with a longitudinal tolerance in a direction parallel to the first direction, such that when the first sheet of glazing material is stopped at the first position for bending, the geometric centre of the first sheet of glazing material is aligned with the reference point on the second shaping member to within the longitudinal tolerance; and wherein in step (ii) stopping of the first sheet of glazing material at the first position for bending is performed with a lateral tolerance in a direction perpendicular to the first direction, such that the first sheet of glazing material is stopped at the first position for bending, the geometric centre of the first sheet of glazing material is aligned with the reference point on the second shaping member to within the lateral tolerance; wherein the lateral displacement is greater than a magnitude of the lateral tolerance and/or the longitudinal displacement is greater than a magnitude of the longitudinal tolerance.

14. The method according to claim 13, wherein the magnitude of the lateral tolerance is less than 2.0 mm.

15. The method according to claim 13, wherein the magnitude of the longitudinal tolerance is less than 2.0 mm.

16. The method according to claim 13, wherein the lateral displacement is between 0.5 mm and 8.0 mm.

17. The method according to claim 13, wherein the longitudinal displacement is between 0.5 mm and 8.0 mm.

18. The method according to claim 13, wherein θ is between 50° and 70°.

19. The method according to claim 13, wherein the first and/or second sheet of glazing material is a glass sheet.

Description

[0121] Embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings, in which:

[0122] FIG. 1 shows a schematic plan view of a sheet of glazing material prior to being shaped;

[0123] FIG. 2 shows a cross-section of a curved laminated glazing;

[0124] FIG. 3 shows a plan view of two glass sheets prior to being shaped;

[0125] FIG. 4 shows a cross-sectional view of a laminated glazing using two curved sheets of glazing material that have the configuration shown in FIG. 3 prior to being shaped;

[0126] FIG. 5 shows a curvature measurement map of a glass sheet that has been press bent between a male die and a female support ring;

[0127] FIG. 6 show a schematic plan view of a conveyor of a press bending furnace;

[0128] FIG. 7 shows a side view of a portion of a press bending furnace;

[0129] FIG. 8 shows the positional variation of a locator used to position glass sheets between shaping members of a press bending furnace;

[0130] FIG. 9 shows the position of a locator at two positions;

[0131] FIG. 10 shows a plan view of how two plies of glass may be offset to improve optical quality in transmission;

[0132] FIG. 11 shows a cross-sectional view of a laminated glazing where the plies have been offset prior to lamination;

[0133] FIG. 12 shows how normalised optical power of a laminated glazing varies with misalignment between the inner and outer plies;

[0134] FIG. 13 shows how the optical quality in transmission (in millidioptres) varies with the amount of offset (in mm) between the inner and outer plies; and

[0135] FIG. 14 shows how the optical quality in transmission (in millidioptres) varies with rake angle (angle of inclination from the vertical).

[0136] FIG. 1 shows a plan view of a glass sheet of the type used for a ply of a vehicle windscreen. Depending upon the radius of curvature of the bent vehicle windscreen, each of the inner and outer plies may be cut to the same peripheral dimensions. If each ply 1, 3 has the same external dimensions, then when bent the edges of the glass sheets do not exactly align in the laminated glazing. This is shown in FIG. 2, where the glass sheet 3 is the outer ply and the glass sheet 1 is the inner ply. Glass ply 1 is joined to the glass ply 3 by an adhesive sheet 5 of polyvinyl butyral (PVB). The degree of misalignment may be acceptable to a customer, especially for low radius of curvature. Furthermore there may be a polyurethane gasket or the like around the peripheral edge of the curved windscreen so that the misalignment is not seen.

[0137] The geometric centre C is shown in the major surface of the glass ply 1, 3. When bending, the intention is to position the point C on each ply 1, 3 at the same position between press bending members. The axis A-A′ is suitably positioned and is parallel to the parallel edges of the glass ply 1, 3. The axis B-B′ is perpendicular to the axis A-A′ and is positioned mid-way between the upper and lower edges of the glass ply 1, 3.

[0138] FIG. 3 shows a plan view of glass sheets 11 and 13. Glass sheet 11 is the flat blank for the inner ply of the laminated vehicle glazing and glass sheet 13 is the flat blank for the outer ply of the laminated vehicle glazing. The external dimensions of the glass sheet 11 (shown as a dashed line) are smaller than the external dimensions of the glass sheet 13. The external dimensions of the glass sheet 11 are chosen such that the edges of the bent glass sheets align in the final laminated glazing.

[0139] The edges of the individual glass sheets 1, 3 of the laminated glazing 10 shown in FIG. 2 are not aligned, whereas the edges of the individual glass sheets 11, 13 of the laminated glazing 20 shown in FIG. 4 are aligned. In FIG. 4, glass ply 11 is joined to glass ply 13 by means of adhesive sheet 15, which in this example is PVB but may be EVA.

[0140] The point C′ lies at the geometric centre of each of the glass plies 11, 13. When bending, the intention is to position the point C′ on each ply 11, 13 at the same position between press bending members. The axis A-A′ is suitably positioned and is parallel to the parallel edges of the glass ply 1, 3. The axis B-B′ is perpendicular to the axis A-A′ and is positioned mid-way between the upper and lower edges of the glass ply 11, 13.

[0141] FIG. 5 shows a curvature measurement map 21 of a curved glass sheet that has been press bent between a male die and a female support ring. The male die has a convex shaping face covered with a woven stainless steel cloth which contacts the surface of the initially flat, heat softened glass sheet to impart a concave curvature thereto.

[0142] The curved glass sheet has a desired curvature as specified in a CAD drawing of the glazing. On the curvature measurement map 21, the deviation of actual curvature of the curved glass sheet at a given point from the desired curvature at that point (as specified by the CAD drawing) is specified by a pixel having a particular grey level i.e. a certain level of reference RGB values to indicate no deviation. That is, if there is no deviation from the desired curvature there would be a grey point having a particular shade (a reference shade) on the curvature measurement map 21. The greater the deviation of actual curvature of the curved glass sheet at a given point from the desired curvature at that point (as specified by the CAD drawing), the greater is the variation in the shade of grey for the pixel away from the shade of grey representing no deviation. Positive and negative deviations may be represented on the curvature measurement map. The area of the curvature measurement map 21 near the upper edge, as indicated by arrow 22, is almost entirely black indicating that part of the curved glass sheet has the greatest deviation from the desired curvature. In the region 22 the deviation is of the order of a few tenths of a micron.

[0143] The curvature measurement map 21 shows that instead of being smooth i.e. the curvature map is all one shade of grey, the surface of the curved glass sheet is covered with an imprint. This imprint is from the stainless steel woven cloth that covers the surface of the male die. The imprint on the glass surface may be enhanced if the male die is configured to use negative pressure reducing means capable of drawing the heat softened sheet towards the shaping surface of the male die. This type of male die is described in WO2005/033026A1. Given that the imprint is of the order of a few hundredths to a few tenths of a micron, to the human eye the surface of the curved glass sheet appears smooth.

[0144] The points a′, b′, c′ and d′ lie at the corners of a rectangle e′. At the centre of the rectangle e′ is the point C. The rectangle a′b′c′d′ may be particularly relevant since this is an important vision area for a vehicle windscreen.

[0145] A heat softened glass sheet that is pressed between a male die covered with a stainless steel woven cloth and the female support ring will have the imprint on the concave surface.

[0146] If the female shaping member is a full surface complementary shaping member instead of a support ring, there may be an imprint on both opposed major surfaces of the press bent glass sheet.

[0147] FIG. 6 shows a schematic plan view of part of a press bending furnace 30 and FIG. 7 shows a schematic side view of part of the furnace 30. The furnace 30 has a number of conveyor rolls 32 that define a longitudinal direction of travel, for example as shown by arrow 34. Each roller 32 rotates in a clockwise direction as shown for one roller by arrow 36. A glass sheet 31 is shown being transported on the rollers 32 in the direction of arrow 34 so as to position the glass sheet 31 between the male die 35 and the female support ring 37. The glass sheet 31 is transported by direct contact with the rollers i.e. the glass sheet 31 is not carried on a ring mould or the like prior to being positioned between the male die 35 and the female support ring 37.

[0148] The shaping surface of the male die 35 is covered with a stainless steel woven cloth. The male die 35 may be of the type described in WO2005/033026A1. The direction indicated by arrow 34 is perpendicular to the rollers 32 and parallel to the longitudinal axis of the bending furnace.

[0149] A pair of locators 38, 39 are raised when the glass sheet 31 is in the desired position between the shaping members for bending. The locators (often known as stops) are configured to act on the leading edge of the flat glass sheet 31.

[0150] Each locator 38, 39 is in electrical communication with a controller 40. The controller is used to actuate the locators at the correct time and may take inputs from suitable sensors such as photodiodes upstream thereof. Such sensors provide positional input of the glass sheet, or a portion thereof, such as an edge portion of the glass sheet, to the controller so that the controller actuates the locators to correctly position the glass sheet 31 in between the shaping members 35, 37.

[0151] Once the glass sheet 31 is supported on the female support ring 37 (by movement of the female support ring 37 relative to the rollers), the male die 35 moves relative to the female support ring 37 to press bend the glass sheet therebetween. For example, the male die 35 is moveable vertically relative to the female support ring 37 in the direction of arrow 35′. As is conventional in the art, the female support ring 37 may be segmented to permit displacement of the female support ring 37 above the level of the conveyor rolls 32, for example as described in U.S. Pat. No. 4,015,968.

[0152] After the glass sheet is bent, the glass sheet is suitably transported to a cooling furnace. For example the glass sheet may be transported by means known in the art, such as on rollers, by air flotation, or carried on a shuttle ring. In FIG. 6 and FIG. 7 the bent glass 31 is transported on rollers 42.

[0153] The locators 38, 39 have a positional accuracy which determines how consistent the bending operation is. When the control means actuates the locators ideally each locator 38, 39 should stop subsequent glass sheets 31 at the same position each time for bending between the male die 35 and the support ring 37. For example the imaginary reference point C on the glass sheet 31 should coincide with the imaginary reference point M located at the centre of the male die. The reference point C may be located at the geometric centre of the flat glass sheet 31. In practice each locator 38, 39 is able to be position to within a lateral tolerance and a longitudinal tolerance.

[0154] This is illustrated in FIG. 8. FIG. 8 shows a plan view of locator 38 positioned between roller 32 and roller 42. The locator 38 is shown as having a circular perimeter but other configuration of perimeter for each locator 38, 39 may be used.

[0155] The target longitudinal position for the locator 38 is X and the target lateral position for the locator 38 is Y. The target position X lies along lateral axis X′-X″ and the target position Y lies along longitudinal axis Y′-Y″. The position X, Y lies at the intersection of axis X′-X″ with the axis Y′-Y″. The axis X′-X′ is parallel to the lateral axis (or direction) of the furnace and the axis Y′-Y″ is parallel to the longitudinal axis (or direction) of the furnace. Typically the rollers 32, 42 are parallel to the lateral axis of the furnace.

[0156] The positions X, Y may be measured relative to a fixed point on the furnace, for example the position of the first conveyor roller, the entrance to the furnace, etc. The lateral tolerance is ±δx and the longitudinal tolerance is ±δy. Therefore the locator 38 may be positioned at the point X, Y to within ±δx and ±δy. Shown in phantom is the locator 38′ at position X+δx, Y+δy.

[0157] Note that in this example the centre point of the locator 38 is desired to be at the point X, Y but it may be some other fixed point on the locator. The dimensions of the locator may be taken into account when positioning the locator at a given point X, Y such that the reference point C on the flat glass sheet is correctly positioned between the shaping members.

[0158] In prior art systems for separately shaping two glass sheets for use as inner and outer plies in a laminated glazing such as a vehicle windscreen, the locators 38, 39 target for the same position for each ply, taking into account any dimensional change of the inner ply, as described in relation to FIGS. 3 and 4. Consequently the imprint on the surface of the glass sheets in contact with the stainless steel woven cloth covering the male die 35 is the same.

[0159] FIG. 9 shows how the locator 38 is used to position the glass sheets between the male die 35 and the female support ring 37 according to the first aspect of the present invention.

[0160] The locator 38 is shown at a first position 38 (1). This position of the locator is at the intersection of axis X1′-X1″ and Y1′-Y1″. The axis X1′-X1″ is parallel to the lateral axis of the furnace and the axis Y1′-Y1″ is parallel to the longitudinal axis of the furnace. The outer ply of a vehicle windscreen is positioned by the locator at position 38(1) such that the reference point C on the outer ply is in the correct position for bending between the shaping members.

[0161] In order to consistently achieve improved optical quality in transmission for laminated windscreens installed in a vehicle at a typical installation angle off-normal, the position for bending of the inner ply for the vehicle windscreen is deliberately offset with respect to the position for bending the outer ply. The locator 38 is moved from position 38(1) to position 38(2) which lies at the intersection of axis X2′-X2″ and Y2′-Y2″. The axis X2′-X2″ is parallel to the lateral axis of the furnace and the axis Y2′-Y2″ is parallel to the longitudinal axis of the furnace. The outer ply of a vehicle windscreen is positioned by the locator at position 38 (2). The position of the locator 38 is changed using the controller 40.

[0162] As described with reference to FIG. 8, the locator 38 may be positioned at position 38(1) to within ±δx and ±δy. Given that the same locator 38 is used to position both the glass sheets for the outer and inner plies of the vehicle windscreen, the locator 38 may be positioned at position 38(2) to within ±δx and ±δy.

[0163] The magnitude of the lateral separation between axis Y1′-Y1″ and axis Y2′-Y2″ is greater than the twice the magnitude of the lateral tolerance of the locator 38, that is |X1−X2|>2×|δx|.

[0164] The magnitude of the longitudinal separation between axis X1′-X1″ and axis X2′-X2″ is greater than the twice the magnitude of the longitudinal tolerance of the locator 38, that is |Y2−Y1|>2×|δy|.

[0165] In this example, δx is 0.5 mm, so the longitudinal tolerance is ±0.5 mm i.e. δx=±0.5 mm. Also, δy is 0.5 mm, so the lateral tolerance is ±0.5 mm i.e. δy=±0.5 mm. The lateral separation between axis Y1′-Y1″ and axis Y2′-Y2″ was 2.5 mm and the longitudinal separation between axis X1′-X1″ and axis X2′-X2″ was 2.5 mm.

[0166] The first glass sheet positioned by locator 38 at position 38(1) is shaped between the male die 35 and female support ring 37. A second glass sheet positioned by locator 38 at position 38(2) is shaped between the male die 35 and female support ring 37.

[0167] Once cooled, the first and second glass sheets are laminated together with a sheet of PVB.

[0168] The optical quality of the laminated glazing was found to have a higher quality when inclined at an angle of 60° to the vertical compared to when measured at normal incidence i.e. the laminated glazing is inclined at 0° to the vertical.

[0169] Since the locator 38 is at a first position to bend the outer ply and at a deliberately offset second position to bend the inner ply, the imprints on the major surfaces of the outer and inner plies are offset relative to each other when viewed at normal incidence.

[0170] In an alternative embodiment to that shown in FIG. 9, the longitudinal separation between axis X1′-X1″ and axis X2′-X2″ is less than or equal to twice the longitudinal tolerance of the locator 38 i.e. 2×δx. The axes X1′-X1″ and X2′-X2″ may be collinear.

[0171] In another alternative embodiment to that shown in FIG. 9, the lateral separation between axis Y1′-Y1″ and axis Y2′-Y2″ is less than or equal to twice the lateral tolerance of the locator 38 i.e. 2×δy. The axes Y1′-Y1″ and Y2′-Y2″ may be collinear.

[0172] In another alternative embodiment to that shown in FIG. 9, a first locator is used to position the first glass sheet at position 38(1) and a second different locator is used to position the second glass sheet at position 38(2).

[0173] Another way to achieve the offset between the outer and inner plies is described with reference to FIGS. 8, 10 and 11.

[0174] FIG. 10 shows two flat glass plies 51, 53. The outer glass ply 51 is positioned between the male die 35 and female support ring 37 by the locator 38 at position X, Y. The outer glass ply 51 is shaped and cooled and transported away on rollers 42.

[0175] As is conventional in the art, the inner glass ply 53 is also positioned between the male die 35 and female support ring 37 by the locator 38 at position X, Y. The inner glass ply 53 is also shaped and cooled and transported away on rollers 42.

[0176] In accordance with the second aspect of the present invention, and with particular reference to FIG. 11, prior to the lamination process, the shaped outer ply 51 is offset relative to the shaped inner ply 53 i.e. the outer ply 51 is first laid up, then a sheet of PVB 55 is placed on the shaped outer ply 51, followed by the shaped inner ply being placed on the sheet of PVB 55 but offset relative to the shaped outer ply 51. The amount of offset in relation to axis q-q′ and/or r-r′ should be more than twice the respective longitudinal/lateral tolerance of the locators to ensure consistently better optical quality in transmission.

[0177] The imaginary reference point M1 lies on the major surface of the outer ply 51 and is that point that was in contact with the male die 35 at imaginary point M on the surface of the male die. The imaginary reference point M2 lies on the surface of the inner ply and is that point that was in contact with the male die 35 at imaginary point M on the surface of the male die. The reference points M1, M2 are located at the geometric centre of the major surface of the inner and outer plies 51, 53.

[0178] In a conventional lamination process when the inner and outer plies are laid up for lamination the imaginary references points M1 and M2 are aligned. In this way, the resulting laminated glazing would have the edges aligned. However in accordance with the present invention the imaginary reference points M1 and M2 are deliberately offset by more than twice the magnitude of the lateral tolerance and/or longitudinal tolerance of the locators. In this way, the imprint on the major surface of the outer ply that was in contact with the male die 35 and the imprint on the major surface of the inner ply that was in contact with the male die 35 are offset relative to one another when viewed at normal incidence to the surface of the laminated glazing.

[0179] A consequence of this is that the edges of the laminated glazing 57 are not aligned, as shown in FIG. 11 and the inner ply 53 may have an overlap region 54 that extends beyond periphery of the outer ply 51 in one direction and is inboard the periphery of the outer ply in the opposite direction.

[0180] To avoid the overlap 54 the overlapping edges prior to laminating the two plies 51, 53 may be removed by cutting for example. Alternatively, the flat glass sheets prior to being shaped may be suitably cut such that when they are misaligned the edges are aligned in the resulting laminated glazing. It will be apparent that the shapes may be cut to have an outline defined by the degree of overlap between the outer and inner plies as shown in FIG. 10.

[0181] The laminated glazing may be encapsulated such that the peripheral edge of the laminate is covered with a gasket of suitable material such as polyurethane. Using encapsulation in this way hides the misaligned edges.

[0182] To illustrate the effect of misaligning the outer ply relative to the inner ply a number of laminated vehicle windscreens were made. Each windscreen has an inner ply of 2.1 mm float glass joined to an outer ply of 2.1 mm float glass via an adhesive sheet of PVB.

[0183] Each inner ply and a corresponding outer ply were made by press bending each individual glass ply between the same press bending members using substantially the same bending conditions. In particular the position of the inner ply and the outer ply between the press bending members was such that the surface imprint would align if laid up in a conventional manner during the lamination process. A suitable press bending furnace is described in WO2004/085324A1, in particular the figures and related description thereof. Other suitable press bending furnaces are known, for example as described in EP0398759A2.

[0184] Five windscreens were made where the inner ply was misaligned horizontally with respect to the outer ply. In this context, “horizontal” means the direction with respect to the windscreen in the installed position.

[0185] A test was designed to simulate the situation, where a driver looks “cross-car” through a vehicle windscreen, i.e. whilst sat in the driver's seat, the driver looks through the portion of the vehicle windscreen on the passenger side of the vehicle, as for example when observing traffic lights. When the driver looks through the glass in this way, the optical path of light has a horizontal angel of inclination to the normal of the glass surface of the order of 45°.

[0186] Each sample was tilted to 61° from the vertical to simulate an installation angle and then rotated about the vertical axis in a clockwise and anti-clockwise direction of 45°.

[0187] In order to assess the optical affects, the optical power in a region in the centre of the windscreen under test was measured, see for example the region abcd on FIG. 5. The region was approximately 300 mm×300 mm and the optical power in transmission was measured using a technique as described in WO2004/083835A1. A parameter ROC was used to define each windscreen under test. The parameter ROC is the difference between the maximum optical power and minimum optical power within a certain distance and is used to describe the observable distortions in the glass.

[0188] For each measurement angle +45° and −45°, the optical power characterised in terms of the parameter ROC in the test region of each respective windscreen was measured and an average calculated. For each angle of rotation the measured optical power characterised in terms of the parameter ROC was divided by the average optical power:

[00005]$\mathrm{Normalised}\mathrm{Optical}\mathrm{Power}\left(+45°\right)=\frac{\mathrm{Optical}\mathrm{Power}\left(+45°\right)}{1/2\left[\mathrm{Optical}\mathrm{Power}\left(-45°\right)+\mathrm{Optical}\mathrm{Power}\left(+45°\right)\right]}$$\mathrm{Normalised}\mathrm{Optical}\mathrm{Power}\left(-45°\right)=\frac{\mathrm{Optical}\mathrm{Power}\left(-45°\right)}{1/2\left[\mathrm{Optical}\mathrm{Power}\left(-45°\right)+\mathrm{Optical}\mathrm{Power}\left(+45°\right)\right]}$

[0189] This test was carried out on each of the five windscreens. The five windscreens were made with a different degree of misalignment between the inner ply and the outer ply when the plies were laid up for lamination:

TABLE-US-00001 TABLE 1 SAMPLE MISALIGNMENT (mm) A −2 B −1 C 0 D +1 E +2

[0190] The results are shown in FIG. 12 which shows how the normalised optical power (in the direction of arrow 60) varies as a function of misalignment (in mm) of the inner and outer plies (in the direction of arrow 62). For clockwise rotation (shown as line 64), the normalised optical power of the windscreen reduces when the misalignment increases in a positive direction. For anti-clockwise rotation (shown as line 66), the normalised optical power reduces when the misalignment increases in the negative direction.

[0191] It would therefore be expected that as the vertical misalignment increases the optical power will reduce in a similar way.

[0192] To determine the effect of vertical misalignment, ten windscreens were made where the inner 2.1 mm glass ply was moved upwards relative to the outer 2.1 mm glass ply prior to being laminated. A positive displacement represents an upwards misalignment. In this context, upwards means the upper portion of the windscreen in the installed position at an angle of about 61° from the vertical i.e. the portion of the windscreen nearest the vehicle roof is the upper part of the windscreen.

[0193] FIG. 13 shows how the ROC in millidioptres (axis 70) varies with the amount of offset in mm (axis 72) between the inner and outer plies with each windscreen installed at an angle of about 61° from the vertical. As the vertical misalignment increases, the ROC in a central zone of the windscreen is seen to vary. Samples having misalignment in the 2-3 mm region shown significantly lower distortion (30-40 millidioptres) compared to 70 millidioptres for a conventional windscreen where there is no misalignment between the inner and outer plies.

[0194] The line through the data points on FIG. 13 is a line of best fit.

[0195] To determine the effect of rake angle on optical quality a number of windscreens were made where the vertical misalignment between the inner and outer plies was changed. Four samples were made where the misalignment was −0.25 mm (line 85), +0.7 mm (line 86), +2.4 mm (line 87) and +2.6 mm (line 88) and the results are shown in FIG. 14.

[0196] In FIG. 14, the axis 80 denotes the rake angle in degrees (°), that is, the angle of inclination with respect to the vertical. The axis 82 denotes the measured ROC value (in millidioptres) in a central zone of the windscreen i.e. a region abcd as shown in FIG. 5. At a rake angle of 0° i.e. normal incidence, samples with an offset of +2.4 mm and +2.6 mm show higher values of ROC in the central zone compared to a windscreen manufactured in a conventional manner.

[0197] As the rake angle increases, the +2.4 mm (line 87) and +2.6 mm (line 88) samples exhibit a minimum in ROC at around 30° rake angle. At a rake angle of 70° the samples +2.4 mm (line 87) and +2.6 mm (line 88) have significantly lower ROC compared to the samples with little misalignment (80-100 millidioptres compared to >120 millidioptres).

[0198] Without being bound by theory, one explanation for the optical power not having a minimum at zero millidioptres is that there is still some optical distortion caused by the PVB adhesive sheet, in particular thickness variations of the PVB sheet.

[0199] The examples above demonstrate that when the inner and outer plies are bent using a conventional press bending furnace, by deliberately offsetting the bent plies when they are laid up for lamination can result in a laminated glazing having a better optical quality when measured at an installation angle (i.e. around 60° from the vertical) compared to when measured at normal incidence (i.e. at 0° from vertical).

[0200] It would be expected that similar behaviour would be observed if the inner and outer glass plies were offset with respect to each other when each ply was press bent between the shaping members. Consequently the inner and outer plies would be deliberately press bent at different position between the shaping members.

[0201] The present invention provides particular application for the production of vehicle windscreens, especially windows for cars. Such windows typically comply with the requirements of ECE R43.