PLASTIC SPECTACLE FRAME

MONTURE PLASTIQUE POUR LUNETTES

English Abstract

\
Abstract of the Disclosure
In a spectacle frame made of plastic ma-
terial, each lens of the spectacle is adapted to be
held in a closed annular rim member by means of a bead
which is fitted in an annular groove. The thickness of
the rim member can be greatly reduced because the bead
constitutes a closed annulus, which surrounds the rim
member and has on at least one side of the rim member
an inclined ramp surface. The annular groove is formed
in each lens.

Claims

The embodiments of the invention in which
an exclusive property or privilege is claimed are de-
fined as follows:-
1. In a spectacle frame comprising a closed
annular rim member made of plastic material and adapted
to hold a lens by means of a joint comprising an annular
groove and a bead fitted in said annular groove,
the improvement residing in that
said rim member is designed to hold a lens
formed with said annular groove and
said bead is formed on said rim member and
constitutes a closed annulus extending around said rim
member and has at least on one side of s aid rim member
an inclined ramp surface.
The improvement set forth in claim 1, where-
in said bead has substantially the shape of an isosceles
triangle in cross-section.
3, The improvement set forth in claim 2, where-
in said bead has in cross-section a vertex angle of 60
to 90 degrees.
4. The improvement set forth in claim 5, where-
in said bead has in cross-section a vertex angle of 75
degrees.
5. The improvement set forth in claim 1, where-
in the thickness of said rim member measured in the di-
rection of the height of said bead is two to four times
the height of said bead.
6. The improvement set forth in claim 5, where-
in the thickness of said rim member measured in the di-
rection of the height of said bead is three times the
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height of said bead.
7. In a spectacle frame comprising two closed
annular rim members made of plastic material and adap-
ted to hold respective lenses by means of respective
joints comprising each an annular groove and a bead
fitted in said annular groove,
the improvement residing in that
each of said rim members is designed to
hold a lens formed with said annular groove and
each of said beads is formed on one of said
rim members and constitutes a closed annulus extending
around said rim member and has on at least one side of
said rim member an inclined ramp surface.
8. In a spectacle comprising a lens and a
closed rim member made of plastic material and adapted
to hold said lens by means of a joint comprising an annu-
lar groove and a bead fitted in said annular groove,
the improvement residing in that
said lens is formed with said annular groove
and
said bead is formed on said rim member and
constitutes a closed annulus extending around said rim
member and has at least on one side of said rim member
an inclined ramp surface.
9. The improvement set forth in claim 89 where-
in said bead has a base width exceeding the width of
said groove formed in said lens.
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Description

This invention relates to a spectacle frame
which is made of plastic material and comprises for each
lens a closed rim member ~hich is adapted to be connected
to the lens by a bead fitted into an annular groove.
Spectacle frames made of plastic material
comprise for each lens a closed annular rim member formed
with an annular groove for recEiving a bead formed on the
lsns. The resilience of the plastic material of the rim
member and the possibility to change the properties of
0 its material are utili~ed to secure the lenses in the
rim members. The rim members condining the lenses ensure
a reliable fixation of the lenses and the lat er impart
an adequate stiffness to the rim members and to the en-
tire spectacle frame. ~ut the cross-se~tiona~ area and the
chickness of the rim membsr made of plastic material must
be above respective lower limits so that spectacle
frames made of plastic material have a relatively large
thickness, which is undesirable as regards appearance
and weight in many cases.
To avoid the use of closed annular rim mem-
bers for holding lenses of spectacles~ it is known par-
ticularly in spectacles having metal frames to hold the
lenses in a half frame having no lower rim portion and
comprising a cord~ which replaces the lower rim portion
of th0 frameO That cord is substantially ~nvisible be-
cause it is insertad into a groove formed in each lensO
A disadvantage of that design resides in that it is dif-
ficult to tension the cord and that the cord, which is
connected to the half frame adjacent to the bridge and
atthe portion to which the bows are connected~ cannot
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contribute to the torsional streng~h of the frame so
that a distortion of the rim members must be expected
particularly where the bows are connected to the rim
members and as a result the lenses may be forced out
of the rim members. Whereas metal frames can be designed
to ha~e a reasonable bending strength7 this is hardly
possible with spectacle frames made of plastic material
owing to the properties of` said material so that com-
parable designs cannot possibly be adopted for spec-
0 tacle frames mada of plastic material.
In oroer to avoid ths occurrencs of rings
caused by reflection near the edges o~ th;ck lenses9
it has been proposed in British Patent Specification
739,493 to provide the bead in the rim member and to
form each lens with an annular groove~ ~ut for that pur-
pose the metal rim member must be split and the split
frame must be closed by clasing members and a closing
screw so that the design cannot be adopted for spectacle
frames made of plastic material because an adequate
strength cannot be obtained by means of the closing
members~
It is an object of the invention to avoid
these dlsadvantages and so to improve a spectacle frame
of` the kind descr~bed first hereinbefore that the thick-
ness of the rim member can be greatly reduced and that
this can bs accomplished with simple means, which do not
adversely affect the strength of the spectacle frame.
This object is accomplished in accordance
with ths invention in that the bead constltutes a closed
annulus extending around the rim member and has a ramP

surface on at least ons side of the rim member and that
the annular groove is formsd in each lens.
Because the rim member is formed with the
baad for holdin~ the lens and the bead cnnsists of a
closed annulusg the thickness of the rim member can be
greatly reduced but this will not involve a decrease in
the cross-sectional area of the rim member at any point
oF its periphery compared with a rim member having an
annular grooveO Because the shape proposed by the inven-
10 tion is more suitable for injection molding, the load-
carrying cross-section of the rim member may be reduced
to the minimum thickness required for the desired strength
and this will not result in a cross-sectiona1 dimension
which is too small for injection molding. For this reason
the meas~re which is proposed permits the use of a rim
member which is much thinner than the previously known
rim members of plastic material so that the spectacle
~rame is comparable to a metal frame in appearance and
evsn rimless spectacles can be simula-ted if transparent
plastic material is employed,~ But the relatively high
strength of such rim member would prevent ~ e insertion
of a lens into the rim member in spite of the resilience
of the p~stic material unless the bead has an inclined
ramp sur~ace at least on one side of the beadO A lens
which is forced into the rim member from that side will
slide on the ramp surface and will expand the rim member
until the bead snaps into the annular groove of the lens.
In a particularly desirable design, the bead has in
cross-section substantially the shape of an isosceles
triangle so that a symmetry is obtained9 which ensures

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more favorable conditions for the manufacture of the
spectacle frame and also for the insertion of the lensss~
The bead must have such a crossrsect;onal
shape that it has the required strength properties and
that the lenses can easily be insertedO These require-
ments will be met if the vertex angle of the bead which
is triangular in cross-section is 60 to 9o degrees and
preFerably 75 dsgrees, With such a vertex angle there
will be a ramp surface which will greatly facilitate
the forcing of the lenses into the rim member and will
ensure that the inserted lenses will be reliably hPld in
the rim member~
If the base width of the bead exceeds the
width of the groove in the inserted lens~ the ramp sur-
faces of the bead will bear on the edges of the groove
of a lens which has been inserted so that the lenses
will be held reliably and without play as the rim mRmber
surrounding the lenses bears on the latter under initial
stress~
If an appropriate plastic material is se-
lected~ adequake strength properties will be obtained
if the thickness of the rim member~ measured in the d.i-
rection of the height of the bead, is two to four times
and preferably three times the height o~ the bead~ With
usual proportions~ the rim member will then have a thick-
ness of an order of 1 mm.
The invention is illustrated by way of ex-
~mple on the drawing, which is an enlarged transverse
sectional view showing a spectacle frame which embodies
the invention~

~L2~51~~
The spect.acle frame comprises ~or each
lens 2 a closed annular rim member 1 ~hich consists of
plastic materialO That lens is held in the rim member 1
by means oF a bead 3~ which is formed on the rim member
on that inside surface which faces ths lens. The bead 3
constitutes a closed annulus and has in cross-section
substantially the shape of an isosceles triangle having
a vertex angle of about 75 degrees. The side faces of
this triangular bead 3 constitute inclined ramp sur~aces
10 4, which permit ~ e insertion of the lens 2 because the
latter can slide along these ramp ~ rfaces until the
bead 3 snaps into an annular groove 5 formed in the lens 2.
Because the base of the bead 3, which is
triangular in cross-section, is wider than the groove 5
and the groove 5 is substantially semicircular in cross-
seGtion9 the ramp sur~aces ~ of the bead 3 baar on the
longitudinal edges of the annular groo~e 5 and regardless
of any tolerancas which may occur the lenses 2 will be
held in the rim member 1 without play becausa the rim
member bears on the lens 2 under initial stressO
It is directly apparent from the drawing
that the rim member which has been shown can be much
thinner than a conventional spectacle rim member havinq
a comparable cross-sectional area and formed with an
annular groovs~ provided that a suitable plastic material
is selected and the thickness of the rim member 1 mea-
sured in the direction of the height of the bead is two
to three times the height o~ the bead.