Note: Descriptions are shown in the official language in which they were submitted.
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The present invention relates to a method of provid-
ing a sheet of glass with a splinter -resistant coating
on at least one surface thereoE.
Sheets of glass have previously been rendered
spli~ter-resistant by combining them with an elastic film
to which the splinters of glass adhere upon breakage.
Films of this kind can be applied to the sheet of glass
by means of, for example, an adhesive but this process
is generally expensive. When multilayer glass sheets are
required 9 a film of for example, polyvinylbutyral, may
be applied to glass sheets under the effect of pressure
and heat. This method is not, however, generally suitable
for coating one side of a single sheet of glass, since
the film cannot be pressed onto the glass pane.
Proposals have been made for the use of hardenable
polymerisable mixtures, which are suitable for sticking
several sheets of glass together, to form a splinter-
resistant film on the sheets of glass. Although clear
hardened layers can be obtained, they have proved
impractical owing to their lack of optical homogeneity.
This lack of optical homogeneity can be traced to slight
differences in the thickness of the film which in turn
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result from small local differences in the course of
polymerisation. Thus,if polymerisation proceeds faster
at a certain site than in the surrounding area, for
example 9 as a result of small accidental irregularities,
S this site tends to have a lower concentration oE poly-
merisable monomer than the surrounding area. As a result
of this drop in concentration, monomer may diffuse from
the surrounding area into this zone so that its volume
increàses and the volume of the surrounding area decreases.
~ven if the differences in thickness thus produced are only
fractions ofmillimetres, they may still distort vision
through the sheet of glass.
It is an object of the present invention to provide
a new and advantageous method of providing a sheet of glass
with a splinter-resistant coating.
According to the present invention we provide a
method of providing a sheet of glass with a splinter-
resistant coating on at least one surface thereof which
comprises forming a coating on the said surface by poly-
merising thereon a monomer composition at a temperature of
0 Cto 40C, the constitution of the said monomer composition
being selected to pro~ide, after polymerisation, a
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polymer having a dynamic second order transition tem-
perature of from -40Cto 40C.
From experiments which we have carried out we have
surprisingly found that in the temperature range between 0
and 40 C, particularly under the effect oE a redox
initiator system or with W light radiation, polymerisation
proceeds so uniformLy that local differences in the rate
of polymerisation do not occur or, if they do occur, they
do not lead to an appreciable diffusion of the monomer
and variations in thickness resulting therefrom. We have
th~s obtained totally uniform, colourless sheets as clear
as glass and which do not suffer from optical distortion.
The method according to the present invention provides a
technically simple way of producing such materials.
In order to obtain a completely uniform layer, a very
even starting temperature over the entire area of the
coating within the range from 0 to 40C is desirable.
The monomers or mixtures of monomers to be poly-
merised should be selected from those which yield films
of a strength and elasticity suitable for t4e intended
purpose. For example a mixtures of monomers which produce
hard homopolymers and monomers which produce soft
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homopolymers may be used ln a mixing ratio such that
the dynamic second order transition temperature of the
polymer f~rmed from the mixture is between -40 and 40 C.
However, it is also possible to use mo,nomers or mixture,s
S of pol~mers which, in the absence of other ingredierlts,
would form polymers with a dynamic second order transi-
tion temperature above 40C, if a quantity of plasticiser
is added to the monomer composition such that the result-
ing polymer has a dynamic second order transition tempera-
ture in the specified range. The dynamic second order
transition temperature is the temperature of maximum
attenuation in the torsional oscillation test according
to DIN 53445 and is termed T~ x Exc~nples of monomers
which produce hard homopolymers include methyl, ethyl
or propyl methacrylate, styrene, vinyl toluene, acrylo-
nitrile and vinyl acetate, whilst examples of monomers
yielding- soft homopolymers include the higher alkyl esters
of methacrylic acid and the alkyl esters of acrylic acid.
Alkyl esters of acrylic or methacrylic acid or mixtures
thereof are particularly advantageous for use in the
present invention. In order to improve the adhesive
strength of the coating on the glass~ the co-use of polar
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monomers, preferably in quantities of between 1 and 5%
by weight, is advantageous; these include in particular
po]ymerisable mono- and dicarboxylic acids, such as
acrylic or methacrylic acid, maleic acid, fumaric acid
S or itaconic acid. Monomers with hydrox~l, amino or amido
~roups also have the effect of improving adhesion, but
are inferior to monomers containing carboxyl groups.
Preferably, acrylic or methacrylic acid is used.
The monomers or mixtures of monomers may be used as
such or in a partially polymerised form. If desired, W
absorbers or solubl`e dyes may be added to the monomer
composition.
The monomer composltion is preferably hardened by
means of redox initiators which may for example be
composed of peroxides and amines or heavy metal mercaptides,
such as benzoyl peroxide and dimethyl-p-toluidine or tert-
butyl permaleate and cadmium thioglycolic acid mercaptide.
These initiators are convenientIy mixed into the monomer
composition shortly before application. If hardening is
effected by UV light, photoinitiators such as e.g. benzoin,
may be added to the monomer composition. It is generally
advantageous to effect polymerisation under an oxygen-free
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protecting gas.
The coating formed upon polymerisation adheres
firmly to the sheet of glass so that, upon breakage, large
splinters tend to remain bonded, whilst only small
splinters~ which are less likely to cause injury, fly o~f
from the uncoated side.
The polymerised coating is substantially softer than
the glass to which it is bonded and may therefore be prone
to scratches and other damage in use. Sheets of glass
produced according to the invention are therefore advanta-
geously used in the preparation of multilayer insulating
glass units wherein the polymerised coating on each sheet
of glass is on the inside of the unit where it is pro-
tected from mechanical damage. The sheets may be coated
individually and then assembled to form a unit of insula-
ting glass. However, it is also possible to carry out
polymerisation in the interior of the insulating glass
unit already assembled, provided that at least one opening
is left, when it is produced for introducing the monomer
composition. The two inner sid~s of a unit of insulating
glass consisting of two sheets can be coated one after the
other. The filling openings may be hermetically sealed
after the final polymerisation step an~ after a dry gas
has been introduced. 7
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The following Examples illustrate the present
invention.
Exam~e 1
.
3 g of tert~butylpermaleate and 2 g of cadmium thioglycolic
acid mercaptide are dissolved, as redox catalysts, in 500 g
of a mixture of me-thyl methacrylate, dibutyl phthalate and
some acrylic acid. The clear solution is poured onto a
horizontal sheet of glass (approx. 0.25 m ). The edge of
the sheet of glass is bounded by a relatively thick beading
of silicon rubber. Hàrdening takes place at room tempera-
ture over about 8 hours under a protecting gas. After
ha~dening, the finished sheet can be used to form an
insulating glass unit with the polymerised coating on the
inside.
Example 2
2.~ g of benzoin butyl ether are dissolved in 500g of the
mixture specified in Example 1. The solution is poured
onto a flat sheet of glass as in Example 1. Hardening is
carried out by irradiation for 4 hours with a fluorescent
lamp, of the type used for blueprints, under protective
gas. At the same tLme, the film temperature is not allowed
to rise above 35 C. A clear, colourless, soft elàstic
film i~ obtained. ~ 8 -
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Example 3 and 4
Examples 1 and 2 are repeated except that a monomer mixture
of 5 parts of methyl methacrylate, 20 parts of 2-ethylhexyl
acrylate, 30 parts of butyl acrylate and 5 parts of acrylic
acid is used.
Exam~le 5
Example 1 is repeated except that a commercial insulating
glass unit is coated on one or both of its interior surfaces.
Subsequently, dried air is introduced into the inner space
and the filling openings are sealed.
