Note: Descriptions are shown in the official language in which they were submitted.
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I~PROVEMENTS IN OR REL~TING TO T~E BONDING
0~ PLASTICS ~T~RIALS AND APPARAT~S FOR USE
IN T~E PREPARATION OF PLASTICS ~ATERIALS
~OR BONDING
This inventio~ relates to the bonding of plastics
materials a~d more particularly to the preparation of
plastics materials for bonding to like or different
plastics material or to non-plastics material using an
adhesive.
Polypropylene can generally be bonded to itself, or
even to other plastics materials or to non-plastics
materiaIs, with a bond strength ~hich is adequate for
many purposes using an adhesive. This bonding can gener-
~lly be improved if the surfaces of the plastics materialsto be bonded are initially subjected to oxidation by
exposure to a hot, blue gas flame ~or a few seconds until
a dull finish is produced on the plastics materials.
However, despite such oxidative pre-treatments of the
plastics surfaces to be adhesively bonded, it has not
hither.bo been possible to produce a truly adequate bond
capable of withstanding substaDtial stress so that plas-
tics products 1ncorporating the bond can be employed for
structural purposes.
According to the present invention, there is provided
a method for thepre-treatment of plastics surfaces prior
to bonding o~ the plastics surfaces to other surfaces by
use of an adhesive, which comprises exposing the plastics
surface to a hot blue gas flame, the gas flame having an
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oxygen content as little in excess as possible of that which
produces the maximum ionisation of gases within the blue
zone of the gas flame whereby a dull adhesive compatible
finish is produced on the surface of the plastics material,
the oxygen content of the gas at which the maximum ionisation
of gases within the blue zone occurs being determined by
inserting into the flame a pair of electrically connected
curren-t conductors having a gap therebetween, monitoring
the minute current produced in the flame and setting the
oxygen content of the gas flame to a value as li-ttle as
possible in excess of that at which the maximum current or
voltage is produced in the flame and conducted therefrom
by said current conductors.
According to a second aspect of the invention,
there is provided apparatus for use in the preparation
of the surface of plastics material to be bonded using
adhesive, which comprises a burner for producing a
flame for rendering dull the surface of a plastics article
to be bonded, the burner having gas inlet means~ gas
outlet means, current collector means for posi-tioning
within the flame produced by the burner, an amplifier
for amplifying the current or voltage produced as a
result of ionisation within the flame and means for
reading or recording the current or voltage thereby produced.
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The method of this irventio-n is particularly ~ell suited
to the pre-treatment of polypropyIene surfaces'to be bonded
to like or different plas~ics materials. Nevertheless, the
method is generally applicable'to: the bonding of piastics
materials which benefit from subjecting to surface oxidation
and hence dulling before undergoing bonding. The method of
the invention has been foun'd to give good results when applied
to the pre-treatment of fluorine-containing polymers such
as polytetrafluo~thylene, polycarbonates, silicon resins,
and melamine-formaldehyde resins. In the case of the
last identified plastics,it has been found that the method
of the invention places them in a condition in which they
can be bonded by means of cyanoacrylate resins which it has
not hitherto been possible to employ with such plastics.
In addition to preparing plastics materials for plastics-
bonding, plastics materials pre'-trea-ted by the method of
the invention may be bonded to 'other materials such as
properly degreased me~tals usïng, for example, such silicon
adhesives as Silcoset 152 and 153 and Dow Corning RTV
adhesives. Bonding'to brickwork can be achieved using
silicon~based sealing compounds which are currently avail-
able in the building trade.
When carrying out the method of'the invention, the
extent of exposure of a plastics surface'to the blue zone
of a flame will depend upon'the particular material being
treated and will need to be determined by trial for each
particular material. Whilst'the best test of the success
of the pre-treatment will lie in sophisticated methods of
struckural testing, in pra'ctice,'in fact,'the quality of
'30 preparation can generally be evaluated by viewing the
appearance of the trea~ed area'~ see`that it has a high
degree of dullness and by carrying out simple wetting tests.
In general, it has been foun'd'that'the method of this
invention ~produces particularly good results when an
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organosilicon adhesive which cur'es''to a resilient mass is
produced from the adhesive. '
The ionisation which occurs'in'the blue oxidising zone
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- of the treatment flame can'convenien-tly-be determined by
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electronic amplification of the minute current produced
in the flame when a suitable heat resistant gauze or
even a pair of electrically connected wires with a gap
therebetween is inserted into the flame to produce a
current of the order usually of a few nano amps but
which may amount to a few micro amps, depending on the
current collector used. Insofar as a gauze may be used,
the word "gau~e" is used herein to denote any electric-
ally conductive and usually metal structure which ~ever-
theless possesses a large open surface area to allow theflame to penetrate therethrough to act on the plastics
material being treated. Thus, although gauzes in the
conventional sense may be employed, it is also possible
to employ perforated or expanded metal sheet structures.
~or a better understanding of the invention and to
show how the same may be carried into effect, reference
will now be made, by way of example only, to the accompany-
ing drawings, in which:-
~igure 1 in an elevation, partly in section of a burner
embodying this invention; and
~ igure 2 is a transverse cross-section through
Figure 1 at A-A.
Referring to the drawings, a burner embodying this
invention comprises an angled meta:L, for example copper,
tube 1 h~ving an inlet tube 2 for gas and air passing
through one end thereof and being closed at the opposite
end 3. The inlet tube 2 is closed at its inner end and
formed with a plurality of circumferentially disposed
outlets 4 thereby ensuring an even distribution of combus-
tion mixture within the tube 1 and helping to ensure thatan even distribution of combustion mixlure within the tube
1 and helping to ensure that an even fiame height is
achieved. Be~-ond an angle 5 provided in the tube 1, the
tube 1 is surrounded by a copper tube 6. Over a portion
o~ its length and width at which it is covered by the
copper tube 6, the inner tube 1 is formed with an opening
7 which is matched by an opening 10 in the copper tube 6
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and over which double thickness openin~ is la;id a stain-
less steel ~ine mesh gæuze 8. The gauze is held iD
position by an outer tube 9 around the cop~er tube 6 aDd
pre~erablY made of aluminium the high thermal conduc~ g
of which prevents the setting up of excessive temperature
along the edge o~ the flame. As can be seen from ~igure
2, the opening 7 in the inner tube 6.is narrower tha~ the
corresponding opening lO in *he copper tube 6.
Spæc.ed aPart ~rom the gau2e 8 is a suitable supported
lG met~ gauze 11 ~ ch will g~nerally be much~oarser than the gauze
8 ?nd from which exte~d~ a lead l, to 2 current amplifier
13 fitted with a microammeter 14. ~ne amplifier 13 is
additionælly connected through a lead 15 to the copper
Lube 1.
i~ U7hen the gas burner is in use, ~ 7'~ture of gas
and ~ir is ~ed into the angled copper tube l through the
inlet lube 2 and outlets 4. As it emerges from the
an~led copper tube through the openings 7 and lO and is
ignited, æ flame 16 whose configuration is shown be~ter
~C~ iD Figure 2 is produced. This elongate flame is pla~ed.
over the sur~ace of a sheet of plas~ics material which is
to undergo.adhesive bonding to achieve dulling of tne
surface. The metal gauze lO is posi*ioned in the flame
produced, preferably in the blue p~rt thereof, and ionisa-
2~ tion which *akes place i~ the flame and whi~h is at a
ma~imNm in the b.lue.part thereof is conducted *o the -
amplifier 13 ~nd.~h~.:amplifier current thereby pro~uced
is re-ad o~f by means of the micro~mmeter 14. In ~ccord-
`ance with this inventioD, cont~ol of the flame is e~fec+ed
~C uDtil, for a particular combination of gas for exam?le
~ropane or butane, and oxidising gas, generall~- air or
ox~gen, ionisation is at a maximum and hence optimum
pre-treatment of the plastics materi~l is obtained.
A machine may be constrllcted for the flame trea.men~
of zones along the edges of sheet plastics material, for
example sheet pol~7prop~7lene~ according to this inventioD.
~or this purpose, two of the burners shown iD the accompan~-
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ing drawings may be disposed on a carriage having areversible drive mechanism to carry them at a substantially
uniform rate along the edge to be treated. When the
carriage is in its normal rest position, the burner flames
play upon the respective ion collector gauzes and the
minute current generated is electronically amplified as
~forementioned to enable the optimum flame conditions
to be established prior to setting the carriage in motion
to effect pre-treatment of the sheet plastics material.
10~lthough reference has been made herein in connection
with the drawings to the detection of a current as such,
since a voltage is concomitantly set up~ it is equally
. possible to use a voltage amplifier and a voltmeter to
eslablish when maximum ionisation of gases takes place in
1~ the flame and set the o~ygen content of the combustible
gases accordingly.
