GB2141022A - Improvements in mirrors - Google Patents

Abstract

A moulded plastics mirror for a vehicle sun visor has a flat, silvered central area and a rim of undulatory form which is shaped to minimise distortion of the central area during cooling of the moulding, and to present a rounded shape complying with the road vehicle safety regulations. <IMAGE>

Description

SPECIFICATION Improvements in mirrors This invention relates to mirrors particularly, but not exclusively, to vanity mirrors for mounting on a vehicle sun visor.

Plastics vanity mirrors have been in use for some years. They are conventionally moulded as a flat plate of plastics material which isthen 'silvered' on one side by a suitable process, and is subsequently welded to the plastics skin of a sun visor.

The European road vehicle safety regulations will make itcompulsory in 1984forthe edges of car components which could be involved in passenger collision to have a minimum radius of 3.2 mm. Since the thickness of conventional plastics mirrors is approximately 2mm their edges will contravene the new regulations.

One possible solution might be to increase the thickness ofthe mirror plate but this would add to the cost of the materials employed. In addition the mirror plates would take longer to cool after moulding, so thatthe production time would be increased, and optical distortion would be increased.

Another possible solution might be to provide the edge ofthe mirrorwith a thick bead but again production times would be increased and I consider thatwith such a construction there would be some distortion ofthe mirror plate produced on cooling of the moulding.

According to one aspect ofthe invention a moulded plastics mirror comprises a substantially flat mirror plate with a rim which in transverse cross-section is of substantiallyundulatoryshapeso arranged that portions ofthe rim lie above the upper surface of the plate, and other portions ofthe rim lie belowthe lower surface ofthe plate.

Thus the mirror is provided with a waved edge which need be of no greaterthickness at any point than the thickness of the mirror plate. The substantially uniform thickness ofthe rim can assist in preventing distortion ofthe mirror plate during cooling.

Another advantage of a rim of this shape is that, after 'silvering' with a suitable metallic coating, the silvered surface ofthe mirror, when the mirrors are stacked or placed on a flat surface, is protected from damage by the upwardly and downwardly projecting portions of rim.

The precise cross-sectional shape ofthe rim is preferably chosen such that during cooling ofthe rim any stresses developed in the section are balanced to minimum the stress which may be imparted to the mirror plate, therebyto minimise distortion of the mirror plate.

I believe that a substantially stress-balanced rim may be achieved by arranging the shape of the rim such thatthefirst moment of area of elements of the rim about the central plane of the mirror plate is balanced for parts of the rim above and below that plate.

The mirror plate may be 'silvered' on either side. When the back surface of the mirror plate is to be silvered, that surface which lies adjacent to the body of the sun visor in use, the main part of the mirror plate back surface is preferably surrounded by a marginal portion of the mirror plate which stands proud ofthe main part, to provide some protection to the silvering during assembly ofthe mirrorto a sun visor.

Preferably the marginal portion ofthe mirror plate blends gradually into the wave shape of the rim in orderto minimise any stresses in this region which may affectthe flatness ofthe silvered part ofthe mirror plate.

According to a second aspectofthe invention in a process for moulding a plastics mirror in accordance with the first aspect ofthe invention the injection gate to the mould cavity is connected to that part of the cavity in which the rim is formed, and the gate is elongated in the lengthwise direction ofthe rim cavity.

This arrangement ofthe gate reduces the residual stresses in the moulded rim to a minimum, as compared with existing designs where significant stresses are produced in the region ofthe gate. The spruelrunnermaythen be snapped off the mirror moulding without affecting the mirror surface.

Avanity mirror in accordance with the invention will now be described, by way of examply only, with reference to the accompanying drawings in which: Figure 1 is a transverse cross-section ofthe edge portions ofthe mirror; Figure 2 is a partial plan view of the mirror moulding with sprue and runner still attached; Figure3is a section on the line 3-3 of Figure 2; and Figure 4 is a section on the line 4-4 of Figure 2.

With reference to Figure 1,the main partofthe moulded plastics mirror comprises a flat plate 1 having a surrounded marginal planar portion 2 of slightly g reaterthickness, the increase in thickness being provided on the underside in the drawing to define a shallow recess 3for receiving the 'silvering' which may be any suitable metallic or other reflective thin film. The downwardly projecting surface of planar portion 2 helpsto protectthe lower surface 1 ' of plate 1 during the welding process. The marginal portion 2 blends tangentially into an upsweep 2' of a rim 4 which, as shown, is of substantially undulatory shape in transverse cross-section, and of constant crosssection throughout its length.The upsweep 2' is arcuate in shape having surfaces of radii t and 2t respectively, where t is the thickness of planar portion 2, and extends through an arc of substantially 25"to a point 5where it blendstangentiallyintoa second arcuate portion 6 of the rim of opposite curvature which portion 6then extends through an arc of substantially 1150 before terminating tangentially in a downwardly directed terminal leg 7, the leg 7 extending in a direction normal to the plane ofthe silvered surface.

It should be noted thatthe local thickness ofthe upsweep 2', second arcuate portion 6 and leg 7 are of substantially uniform thickness equal to that of marginal portion 2, apartfrom a chamfer 8 provided on the innerface of leg 7to assist in mould release. The drawings(s) originally filed was/were informal and the print here reproduced is taken from a later filed formal copy.

The crest 9 ofthe second arcuate portion 6, and the free end 10 of leg 7 provide upper and lower abutment surfaces in the event of stacking of the mirrors, and will in general protectthe main part ofthe mirror should the mirror be placed on a flat surface during handling. This enables omission of the usual paper backing employed to protect the silvered surface.

The radii of curvature ofthe inner and outer surfaces 6' and 6" respectively of the arcuate portion 6 are conveniently chosen to bet and 2t in this embodiment.

Thus, when t is made 1.6 mm the radius of curvature of surface 6", that surface which may be involved in collision with a vehicle occupant, is 3.2 mm to comply with the regulations previously mentioned.

Since the free end 10 ofthe leg 7 will be directed in use atthe body of the visor, it will be protected by the body in use from colliding with a vehicle occupant.

Acontinuous upwardly projecting rib 11 oftriangularcross-section is provided on the upper surface of marginal portion 2 forthe purpose of assisting in welding ofportion2tothe overlapping skin of a sun visor. The current practice is to weld the overlapping visor skin to the marginal planar portion of a mirror plate, butthe provision of a rib 11 attheweld line will enable a better and faster weld to be produced. A elongate welding head is proposed to be used as at present, the welding head being positioned in register with the rib 11 during welding.

In orderto help prevent distortion of the mirror plate 1 resulting from distortion ofthe rim 4 during cooling after moulding and due to subsequenttemperature changes, the cross-sectional shape of rim 4 has been arranged such that the first moment of area about the central plane Pofthe mirror plate 1 of elements of the rim 4above and below plane Pare balanced. The first moments of area ofthe elements identified in the drawing are y1x1 oy, and y2x2y̲2, and the section is designed such that fy1x1oy1 = fy2x26y2. Convenient ly,the integrals may be computed graphically, by counting graph squares, and the length of leg 7 may be adjusted as necessaryto balance the moments of area.

The design of the new mirror rim serves as a plastic injection barrierwhich deflects the "shot" along the rim wall at the outsetofthe moulding cycle. This ensures that the first part of the shot which often includes contamination does not go into the critical mirror section.

The design ofthe new mirror shape lends itselfto the repositioning ofthe injection "gate" which by extending its length along the rim wall reduces residual stress and strain to a minimum. With existing designs the residual stress and strain at the gate area is a major problem.

With reference to Figures 2 to 4, a sprue injection gate 12 is elongated in the direction along rim 4so as to be of substantia I ly fan-shape, tapering in crosssection in radial directions from runner 13. The sprue 12 is connected to the leg 7 ofthe rim 4 by a thin web 14 which after moulding may be snapped simply be bendingthemirrorwith respecttothe runner 13.

The sprue/runnercan be snapped offfrom the new mirrorwithout affecting the mirrorsurface. This is not possible on existing mirror designs.

The illustrated shape of mirror will reduce the tendencyforthe mirror to collect dust, as might happen with a rim having sharp internal corners.

Other benefits of the invention are as follows: (1) The injector pressure(s) required for moulding the new mirror are much less than for the existing mirrortypesand therefore dies can be made lighter and cheaper.

(2) The mirror and rim section thickness can be reduced below that used for existing mirrors, and mirrors made more cheaply.

(3) Press size, in terms of clamp pressure, is less, and therefore production cost are lower.

(4) Athinner mirror sets more quickly and will produce more mirrors per unit of time.

(5) Athinnermirrorwill "sink" less on the mirror surface, after cooling and will therefore retain better optical qualities with less rejects due to sink.

CLAIMS (Filed on 30/Aug/83) 1. A moulded plastics mirror comprising a substantiallyflat mirror plate with a rim which in transverse cross-section is of substantially undulatory shape so arranged that portions of the rim lie above the upper surface of the plate, and other portions of the rim lie below the lower surface of the plate 2. A mirror as claimed in claim 1 in which the rim is arranged to be substantially stress-balanced by arranging the shape ofthe rim such thatthefirst moment of area of elements of the rim aboutthe central plane of the mirror plate is substantially balanced for parts ofthe rim above and belowthat plane.

3. A mirror as claimed in claim 1 or claim 2 in which the back surface of the mirror plate is silvered, that surfacewhich liesadjacenttoa mounting in use, and the main part the mirror plate back surface is surrounded bya marginal portion ofthe mirror plate which stands proud ofthe main part.

4. A mirror as claimed in claim 3 in which the marginal portion ofthe mirror plate blends gradually intothewaveshapeofthe rim.

5. A mirror substantially as described with referenceto Figure 1 oftheaccompanying drawings.

6. Avehicle sun visor provided with a mirror in accordance with any ofthe preceding claims.

7. A processfor moulding a plastics mirror in accordance with any of claims 1 to 4 in which the injection gate to the mould cavity is connected to that part of the cavity in which the rim isformed, and the gate is elongated in the lengthwise direction ofthe rim cavity.

8. A process for moulding a plastics mirror as claimed in claim 7 and substantially as described with reference to Figures 2 to 4 of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (8)

**WARNING** start of CLMS field may overlap end of DESC **. The crest 9 ofthe second arcuate portion 6, and the free end 10 of leg 7 provide upper and lower abutment surfaces in the event of stacking of the mirrors, and will in general protectthe main part ofthe mirror should the mirror be placed on a flat surface during handling. This enables omission of the usual paper backing employed to protect the silvered surface. The radii of curvature ofthe inner and outer surfaces 6' and 6" respectively of the arcuate portion 6 are conveniently chosen to bet and 2t in this embodiment. Thus, when t is made 1.6 mm the radius of curvature of surface 6", that surface which may be involved in collision with a vehicle occupant, is 3.2 mm to comply with the regulations previously mentioned. Since the free end 10 ofthe leg 7 will be directed in use atthe body of the visor, it will be protected by the body in use from colliding with a vehicle occupant. Acontinuous upwardly projecting rib 11 oftriangularcross-section is provided on the upper surface of marginal portion 2 forthe purpose of assisting in welding ofportion2tothe overlapping skin of a sun visor. The current practice is to weld the overlapping visor skin to the marginal planar portion of a mirror plate, butthe provision of a rib 11 attheweld line will enable a better and faster weld to be produced. A elongate welding head is proposed to be used as at present, the welding head being positioned in register with the rib 11 during welding. In orderto help prevent distortion of the mirror plate

1 resulting from distortion ofthe rim 4 during cooling after moulding and due to subsequenttemperature changes, the cross-sectional shape of rim 4 has been arranged such that the first moment of area about the central plane Pofthe mirror plate 1 of elements of the rim 4above and below plane Pare balanced. The first moments of area ofthe elements identified in the drawing are y1x1 oy, and y2x2y̲2, and the section is designed such that fy1x1oy1 = fy2x26y2. Convenient ly,the integrals may be computed graphically, by counting graph squares, and the length of leg 7 may be adjusted as necessaryto balance the moments of area.

The design of the new mirror rim serves as a plastic injection barrierwhich deflects the "shot" along the rim wall at the outsetofthe moulding cycle. This ensures that the first part of the shot which often includes contamination does not go into the critical mirror section.

The design ofthe new mirror shape lends itselfto the repositioning ofthe injection "gate" which by extending its length along the rim wall reduces residual stress and strain to a minimum. With existing designs the residual stress and strain at the gate area is a major problem.

With reference to Figures

2 to 4, a sprue injection gate 12 is elongated in the direction along rim 4so as to be of substantia I ly fan-shape, tapering in crosssection in radial directions from runner 13. The sprue

12 is connected to the leg 7 ofthe rim 4 by a thin web 14 which after moulding may be snapped simply be bendingthemirrorwith respecttothe runner 13.

The sprue/runnercan be snapped offfrom the new mirrorwithout affecting the mirrorsurface. This is not possible on existing mirror designs.

The illustrated shape of mirror will reduce the tendencyforthe mirror to collect dust, as might happen with a rim having sharp internal corners.

Other benefits of the invention are as follows: (1) The injector pressure(s) required for moulding the new mirror are much less than for the existing mirrortypesand therefore dies can be made lighter and cheaper.

(2) The mirror and rim section thickness can be reduced below that used for existing mirrors, and mirrors made more cheaply.

(3) Press size, in terms of clamp pressure, is less, and therefore production cost are lower.

(4) Athinner mirror sets more quickly and will produce more mirrors per unit of time.

(5) Athinnermirrorwill "sink" less on the mirror surface, after cooling and will therefore retain better optical qualities with less rejects due to sink.

CLAIMS (Filed on 30/Aug/83) 1. A moulded plastics mirror comprising a substantiallyflat mirror plate with a rim which in transverse cross-section is of substantially undulatory shape so arranged that portions of the rim lie above the upper surface of the plate, and other portions of the rim lie below the lower surface of the plate 2. A mirror as claimed in claim 1 in which the rim is arranged to be substantially stress-balanced by arranging the shape ofthe rim such thatthefirst moment of area of elements of the rim aboutthe central plane of the mirror plate is substantially balanced for parts ofthe rim above and belowthat plane.

3. A mirror as claimed in claim 1 or claim 2 in which the back surface of the mirror plate is silvered, that surfacewhich liesadjacenttoa mounting in use, and the main part the mirror plate back surface is surrounded bya marginal portion ofthe mirror plate which stands proud ofthe main part.

4. A mirror as claimed in claim 3 in which the marginal portion ofthe mirror plate blends gradually intothewaveshapeofthe rim.

5. A mirror substantially as described with referenceto Figure 1 oftheaccompanying drawings.

6. Avehicle sun visor provided with a mirror in accordance with any ofthe preceding claims.

7. A processfor moulding a plastics mirror in accordance with any of claims 1 to 4 in which the injection gate to the mould cavity is connected to that part of the cavity in which the rim isformed, and the gate is elongated in the lengthwise direction ofthe rim cavity.

8. A process for moulding a plastics mirror as claimed in claim 7 and substantially as described with reference to Figures 2 to 4 of the accompanying drawings.