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Description  |
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BACKGROUND OF THE INVENTION
This invention relates to a process for efficiently cast molding a
transparent polymeric product which is free from defects such as strain
and has improved properties, for example, of transparency, weather
resistance, impact resistance and heat resistance.
It is well known that transparent polymeric materials are substituting for
some applications of inorganic glass by virtue of their advantageous
properties such as light weight, improved fabricability (processability)
and impact resistance. Their importance as materials for safety glass has
also been recognized in recent years.
A transparent polymeric material that is currently most commonly used is
polymethylmethacrylate, which is less expensive and has improved
transparency, appearance, impact resistance, and weather resistance. For
these advantages, the polymethylmethacrylate is used in a wide variety of
applications such as interior decoration, displays, building materials
like ceilings or doors, window glass of passenger vehicles, and aquaria.
But in other respects, for example, surface hardness, heat resistance and
chemical resistance, the polymethylmethacrylate is not highly desirable.
The properties mentioned above can be improved by incorporating into the
polymethylmethacrylate those polyfunctional monomers which are capable of
providing polymers having high heat resistance or surface hardness, but
then in turn, the thus treated polymethylmethacrylate becomes less
thermoplastic and it is difficult to mold and process a copolymer from it.
This difficulty in molding requires cast polymerization, but to produce a
product free from such drawbacks as strain or bubbles, this process takes
a long polymerization time. The production, for example, of polymeric
product 1 cm thick in a plate glass form requires at least 24 hours. A
thicker product is cast polymerized only after a period ranging from some
50-60 hours up to about 500-600 hours. This is without doubt too
uneconomical for the commercial production of a desired cast molded
article.
It is therefore plain to see that the development of a cast polymerization
process for producing efficiently and rapidly those
polymethylmethacrylates, representative of polymers of lower alkyl
acrylates or methacrylates, which have improved heat resistance, chemical
resistance and surface hardness will be greatly advantageous and
contribute noticeably to commercial acceptance of transparent plastics
materials in the art concerned. As such technique, this invention provides
a process for cast polymerizing quickly as well as efficiently
polymethylmethacrylate having improved properties.
SUMMARY OF THE INVENTION
One object of this invention is to improve the heat resistance, chemical
resistance and surface hardness of the polymethylmethacrylate. In general,
polymeric materials, as they are polymerized, have increased heat
resistance and chemical resistance but their impact resistance is poor.
Improved heat resistance and chemical resistance are only compatible with
high impact resistance if two or more monomers of specified structures are
blended with each other at specified proportions.
DETAILED DESCRIPTION OF THE INVENTION
According to one aspect of this invention, the following components (A),
(B) and (C) are mixed and the mixture is poured into a cell or mold and
irradiated with light or an ionizing radiation at a temperature below room
temperature to produce a cast polymeric product. The components are
specified as follows:
(A) methyl methacrylate and/or its prepolymer;
(B) a monomer represented by the formula
##STR1##
wherein X is H or CH.sub.3 and R is alkyl having 2-6, preferably 4-6,
carbon atoms, or
##STR2##
wherein X is as defined above and n is an integer of 3-7, a mixture
thereof and/or prepolymer thereof, and
(C) a monomer represented by the formulae
##STR3##
wherein X is defined as above and m is an integer of from 2 to 4, a
mixture thereof and/or a prepolymer thereof.
The components (A), (B) and (C), each in an amount ranging from 20 to 50%
by weight, are mixed, the total amount of the components being 100% by
weight.
According to another aspect of the invention, a copolymerizable monomer (D)
in an amount less than 20% by weight based on the total amount of the
components is added in addition to the components to form a polymerizable
mixture which may be polymerized in a manner similar to that of the
mixture mentioned above to produce a transparent cast polymeric product.
Preferable examples of the monomer (D) will be specified hereinbelow.
According to a further aspect of this invention, a component (E) which is
one or more compounds represented by the formulae
##STR4##
wherein R.sup.1 is --OH, --OR.sup.4 or --OOCR.sup.4 in which R.sup.4 is
alkyl having carbon atoms of from 1-20; R.sup.2 is straight or branched
chain alkylene having carbon atoms of from 1 to 10 or
##STR5##
wherein l is an integer from 1 to 20 and R.sup.3 is a trivalent carbyl
radical having carbon atoms of from 1 to 20, is mixed with the components
(A), (B) and (C) in an amount of 3 to 30% by weight based on the total
amount of monomers (A), (B) and (C) to form a mixture which may be
polymerized in a manner similar to that of the first aspect of this
invention to produce a desirable transparent cast polymeric product.
According to a still further aspect of this invention, the component (E) is
mixed with the components (A), (B), (C) and (D) in an amount of from 3 to
30% by weight based on the total amount of the latter four components to
form a mixture which is adapted to use a polymerizable mixture in this
invention.
Among the components (E), the compounds represented by the formula R.sup.1
R.sup.2 OH wherein R.sup.1 and R.sup.2 are the same as defined above are
more advantageously used for the process of this invention.
A person skilled in the art should note that ethyl methacrylate, methyl
acrylate and ethyl acrylate may be used in each aspect of this invention
as a substitute for methyl methacrylate.
The inventors of this invention have found that methyl methacrylate and/or
its prepolymer are mixed with the components (B) and (C) in a proportion
mentioned above to produce a transparent cast polymeric product having
simultaneously heat resistance and chemical resistance as well as impact
resistance whereby the defects of a polymethylmethacrylate can be
dissolved.
By mixing methylmethacrylate with the components (B) and (C) in a manner
according to this invention, the mixture may maintain a high rate of
polymerization even at a considerably low temperature for example below
the melting point of methylmethacrylate (-48.degree. C.), and a product to
be produced has few defects such as strain and bubbles, whereby a cast
polymeric product may be efficiently obtained in a extremely short period
of time.
The reasons for this phenomenon are believed to be that the components (B)
and (C) and therefore a mixture containing the components have properties
such that they easily take a stable super-cooled state without
crystallization at a considerably low temperature. Under this state, the
system generally rapidly increases in viscosity as the temperature is
lowered whereby the rate of polymerization is significantly increased and
the change (decrease) in volume is low during polymerization to prevent
optical strain and strain at adhesion area from taking place. Further,
there is no expansion of entrained air nor vaporization of monomer to
produce bubbles because the polymerization temperature is low enough to
prevent the raise of temperature to an undesirable level.
Thus, the addition of the components (B) and (C) to the polymerizable
mixture according to this invention realizes significant improvement of
such properties as heat resistance, solvent resistance, surface hardness
of polymethyl methacrylate and highly efficient cast polymerization.
The component (B) which is useful in this invention includes ethyl
acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate,
isopropyl acrylate, isopropyl methacrylate, isobutyl acrylate, isobutyl
methacrylate, 1,3-butanediol monomethacrylate, 1,3-butanediol
monoacrylate, 1,4-propanediol monomethacrylate, 1,4-propanediol
monoacrylate, 1,5-pentanediol monomethacrylate, 1,5-pentanediol
monoacrylate, 1,6-hexanediol monomethacrylate, 1,6-hexanediol
monoacrylate, 1,7-heptanediol monomethacrylate, 1,7-heptanediol
monoacrylate and a prepolymer of the same.
The components (C) which are suitable for use in this invention include
glycidyl methacrylate, glycidyl acrylate, diethyleneglycol dimethacrylate,
diethyleneglycol diacrylate, triethyleneglycol dimethacrylate,
triethylene-glycol diacrylate, tetraethyleneglycol dimethacrylate,
tetraethyleneglycol diacrylate, pentaethyleneglycol dimethacrylate,
pentaethyleneglycol diacrylate, hexaethyleneglycol dimethacrylate,
hexaethyleneglycol diacrylate, polyethyleneglycol dimethacrylate,
polyethyleneglycol diacrylate, and a prepolymer of the same.
The term "prepolymer" used herein is regarded as a mixture of a monomer and
its polymer which is obtained by polymerizing a monomer to a level such
that the conversion is less than 30% or by mixing a monomer and its
polymer in an amount less than 30% of the polymer. The prepolymer is used
instead of all or a part of the monomer for the purpose of increasing the
viscosity of the polymerizable mixture and decreasing the polymerization
time of the monomer to be used. However, it should be noted that if a
prepolymer containing more than 30% of polymer is used, the fabricability
is reduced and the removal of entrained air becomes harder because of the
increase in viscosity.
Specific examples of the components (D) which are useful in this invention
are styrene, toluene, divinyl-benzene, .alpha.-methylstyrene, acrylic
acid, acrylamide, acrylonitrile, methacrylic acid, methacrylamide,
methacrylonitrile, vinyl acetate, vinyl propionate, vinyl butylate, vinyl
stearate, vinyl pyridine, vinyl pyrrolidone, vinyl carbazole, maleic
anhydride, itaconic acid, crotonic acid, diallyl phthalate, triallyl
cyanurate, allyl acetate, diallyl maleate,
diethyleneglycol-bis-allylcarbonate, trimethylolethane trimethacrylate,
trimethylolpropane trimethacrylate, trimethylolpropane triacrylate,
trimethylolethane triacrylate, glycelol monomethacrylate, neopentylglycol
dimethacrylate, neopentylglycol diacrylate, tribromomethacryloxy
phosphate, monobromomethacryloxy phosphate, benzyl methacrylate, toluyl
methacrylate, phenyl methacrylate, benzyl acrylate, cyclohexyl
methacrylate, 2-ethylhexyl methacrylate, lauryl methacrylate, cyclohexyl
acrylate, stearyl methacrylate, furfuryl methacrylate, ethyleneglycol
dimethacrylate and ethyleneglycol diacrylate.
Specific examples of the components (E) which are useful in this invention
are propyleneglycol, diethyleneglycol, butanediol, triethyleneglycol,
tetraethyleneglycol, pentanediol, hexanediol, nonanediol, decanediol,
heptanediol, 2-ethylhexanediol, octanediol, neopentyleneglycol,
ethyleneglycol monomethyl ether, ethyleneglycol monoethyl ether,
ethyleneglycol monobutyl ether, glycerin, glycerol monoacetate, glycerol
monobutylate, glycerol monopropionate, glycerol monolaurate, glycerol
diacetate, glycerol dibutylate, trimethylolpropane monoacetate,
trimethylolethane monoacetate, glycerol methyl ether, glycerol monobutyl
ether, glycerol dimethyl ether and glycerol dibutyl ether.
When a compound represented by the formulae for the components (B) or (C)
wherein n is an integer larger than that defined therein is used, the
polymeric product obtained tends to be soft and, therefore, is
undesirable.
If the compound used is represented by the formula for the component (E)
except that the number of carbon atoms for R.sup.2, R.sup.3 or R.sup.4 is
larger than that defined for (E), the compatibility of the compound with
other monomers becomes low and the product produced tends to be waxy.
The basic properties given for a transparent polymeric product, such as
resistance to heat, chemicals, impact and weather, are due to the
components (A), (B) and (C). However, in order to improve various
properties such as flame retardancy, machinability especially for cutting,
and antistatic property for specific use of the product, the component (D)
is incorporated into a polymerizable mixture thereby generalizing the use
of the product to be produced.
The component (E) is used for the purpose of further improving the impact
resistance of the product. However, it is used in an amount such that the
impact resistance is significantly improved without essentially reducing
the heat resistance, more particularly in an amount of from 3 to 30% by
weight, preferably 5 to 20% by weight based on the total amount of (A),
(B), (C) and (D) because too much of the component (E) lowers the heat
resistance.
According to the method of this invention, a mixture of (A), (B) and (C),
and, if necessary, (D) and/or (E) is poured into a cell or mold. The cell
or mold is designed to give a shaped product, such as plate, lens, tube,
cylinder or sphere and is made of glass or a metal. The poured mixture is
irradiated with light or an ionizing radiation to initiate the
polymerization. When the mold or cell is made of a metal, the use of
radiation is desired because light cannot generally penetrate the metal.
The kinds of light useful in this invention include strong natural light
condensed, for example, through a condensing lens, visible and ultraviolet
light from a high pressure or low pressure mercury lamp, laser, strong
light from photofactory, luminescence such as fluorescence or
phosphorescence and the like. On the other hand, the ionizing radiation
which may be used for the polymerization according to this invention
includes any radiation which ionizes substances, such as alpha-rays,
beta-rays, gamma-rays, X-rays, electron beams and mixed rays from a
nuclear reactor or a fission product. The dose and the dose rate should be
determined taking into consideration the other conditions for
polymerization and the composition of the polymerizable mixture, but are
usually in the range of from 10.sup.3 to 10.sup.9 preferably 10.sup.4 to
10.sup.7 roentgen/hr and in the range of from 10.sup.3 to 10.sup.7
preferably 10.sup.5 to 10.sup.7 roentgen, respectively.
An important feature of this invention resides in the cast polymerization
at a temperature lower than room temperature by irradiating a monomer
mixture of this invention with light or a kind of ionizing radiation. By
mixing the components (B) and (C) with methyl methacrylate, a cast
polymeric product with no or little defects such as strain and bubbles can
be produced at a high rate of polymerization even at a temperature below
room temperature, particularly at a considerably low temperature for a
very short polymerization time. Thus, the cast polymerization can be
advantageously and economically practiced according to this invention. The
polymerization temperature useful in this invention suitably ranges from
0.degree. C. to -100.degree. C., most preferably from -30.degree. to
80.degree. C.
This invention is further illustrated by the following Examples wherein all
"parts" and "percentages" are based on weight unless otherwise indicated.
EXAMPLE 1
Methyl methacrylate (30 parts), butyl acrylate (30 parts) and glycidyl
methacrylate (30 parts) were mixed and the mixture was poured into a glass
cell by which a sample 60 mm .times. 60 mm square and 10 mm thick can be
formed, cooled to -78.degree. C. and irradiated with gamma-rays from Co-60
at a dose rate of 1 .times. 10.sup.6 roentgen/hour for 3 hours. The
temperature of the sample was returned to room temperature, and an organic
glass plate free from any defects such as strain and bubbles was obtained.
It was found that in order to obtain a sample plate same as the above
mentioned sample from the mixture disclosed above, it was necessary to
carry out the polymerization using benzoylperoxide as a catalyst in an
amount less than 0.05% at 60.degree. C. for 73 hours, or alternatively, to
carry out the polymerization at 70.degree. C. for 65 hours by the use of
azobisbutylonitrile in an amount lower than 0.02%.
It was also found that when the mixture stated above is subjected to
polymerization by irradiation of gamma-rays at room temperature, a product
free from strain and bubbles could not be produced unless the mixture was
irradiated with gamma-rays at a dose rate of 2 .times. 10.sup.5
roentgen/hour for 10 hours. On the other hand, in case the polymerization
of the same mixture was carried out at a temperature above 40.degree. C.,
a product without the defects could be obtained only when the mixture was
irradiated with gamma-rays at a dose rate lower than 5 .times. 10.sup.4
roentgen/hour for 50 hours or longer.
The organic glass obtained according to the method of this Example had
improved mechanical strength, such as impact resistance and the like,
resistance to heat, and weather, surface hardness and transparency which
are comparable to a conventional acrylic resin and was superior to an
acrylic resin in resistance to solvents.
When methyl methacrylate was polymerized by pouring it into the glass cell
identical to that mentioned above, a polymeric cast product free from
strain and bubbles could be produced only when the polymerization was
carried out by the use of benzoyl peroxide as the catalyst at a
concentration up to 0.07% at 60.degree. C. for 72 hours, or alternatively,
by the use of azobisisobutylonitrile at a concentration lower than 0.03%
at 70.degree. C. for 65 hours.
EXAMPLE 2
Methyl methacrylate (50 parts), ethyl acrylate (30 parts) and
diethyleneglycol diacrylate (20 parts) were mixed and the mixture was
poured into a stainless steel mold by which a concave lens 60 cm in
diameter can be obtained, cooled to -30.degree. C. and irradiated with
gamma-rays from Co-60 at a dose rate of 3 .times. 10.sup.5 roentgen/hour
at that temperature for 4 hours. The thus obtained cast product was a lens
free from strain and bubbles.
It was found that in order to produce a lens free from strain and bubbles
from the mixture mentioned above by the use of the same mold as the above
without irradiation of gamma-rays, it was necessary to use a catalyst at a
concentration lower than 0.05% and to heat at 60.degree. C. for 59 hours
or longer when the catalyst is t-butylhydroxy-peroxide, or alternatively,
to use benzoylperoxide as a catalyst at a concentration lower than 0.05%
and to heat to 60.degree. C. for 55 hours or longer.
The copolymeric product obtained according to this Example had improved
mechanical strength such as impact resistance and the like, resistance to
heat, weather and solvents, surface hardness, light transmission and the
like which are comparative to those of an acrylic resin plate.
EXAMPLE 3
Methyl methacrylate (20 parts), isobutyl methacrylate (20 parts) and
tetraethyleneglycol diacrylate (30 parts) were mixed and the mixture was
poured into a metal mold by which a concave mirror 60 cm in diameter can
be formed, cooled to 0.degree. C. and irradiated with gamma-rays from
Co-60 at a dose rate of 2 .times. 10.sup.5 roentgen/hour at that
temperature for 5 hours to obtain a polymeric cast product free from
optical strain and bubbles.
It was found that in case the monomer mixture above was polymerized without
irradiation of gamma-rays, a polymeric cast product free from optical
strain and bubbles could be obtained only when the polymerization was
carried out by the use of benzoylperoxide at a concentration of 0.03% at
60.degree. C. for 56 hours or longer.
The copolymer prepared according to this Example had improved properties
superior to those of an acrylic resin plate, the properties being
mechanical strength such as impact resistance, resistance to heat, weather
and solvents, surface hardness, light trnasmission and the like.
EXAMPLE 4
Methyl methacrylate (30 parts), pentanediol monoacrylate (20 parts) and
diethyleneglycol diacrylate (50 parts) were mixed and the mixture was
poured into a glass cell adapted to form a polymeric plate 60 cm .times.
60 cm square and 15 mm thick. After sealing the cell with a
polyvinylchloride ring packing to prevent the mixture from leaking, the
mixture was irradiated with visible and ultraviolet light having maximum
energy at 3,600 A from a high pressure mercury arc lamp located 15 cm away
from the light source for 5 hours to obtain a polymeric cast product free
from any defects such as optical strain and bubbles.
It was found that in order to produce a cast polymeric product free from
strain and bubbles from the mixture specified above, without irradiation
by light, it is required to polymerize it at 60.degree. C. for 55 hours by
the use of benzoylperoxide as the catalyst in an amount of 0.05%.
The copolymeric product prepared according to this Example had improved
properties, for example, mechanical strength such as impact resistance,
resistance to heat, weather and solvents, surface hardness, light
transmission and the like which were comparable or superior to those of an
acrylic resin plate.
EXAMPLE 5
Methyl methacrylate (40 parts), hexanediol monoacrylate (40 parts),
tetraethyleneglycol diacrylate (20 parts) and hexanediol (15 parts) were
mixed and the mixture was poured into a glass cell adapted to form a
sample plate 100 cm .times. 100 cm square and 10 mm thick and irradiated
with gamma-rays from Co-60 at a dose rate of 2 .times. 10.sup.5
roentgen/hour at room temperature for 4 hours to obtain an organic glass
plate free from optical strain and bubbles and having good appearance.
When the mixture specified above was polymerized by a conventional method
without irradiation by gamma-rays, and the polymerization time was
reviewed, it was found that to polymerize it at 60.degree. C. for 58 hours
or longer when benzoyl peroxide was used as the catalyst in an amount
0.05%.
The copolymeric product prepared according to this Example had improved
properties, for example, resistance to heat, solvents and weather, surface
hardness, transparency and mechanical strength such as impact resistance
which were superior to those of an acrylic resin plate. In particular, the
impact resistance of the copolymeric product of this Example was 28.6
kg/cm.sup.2 as Izod value which was far superior to the 19.2 kg/cm.sup.2
of a conventional acrylic resin plate. A copolymeric product which was
prepared in a manner similar to this Example except that hexanediol was
omitted had an Izod value of 22.2 kg/cm.sup.2.
EXAMPLE 6
Methyl methacrylate (20 parts), butanediol monoacrylate (20 parts),
diethyleneglycol diacrylate (60 parts) and glycerol diacetate (20 parts)
were mixed and the mixture was poured into a cell made of thin glass
plates adapted to form a sample plate 35 cm .times. 35 cm square and 8 mm
thick, kept at a temperature of from -50.degree. to -78.degree. C. on dry
ice and irradiated with electron beams from a 2 MeV electron accelerator
at a dose of 5 .times. 10.sup.5 rad/sec. for 10 seconds. After the
completion of irradiation, the temperature of the mixture was returned to
room temperature to promote the polymerization to obtain a cast polymeric
product free from optical strain and bubbles.
When the mixture above was polymerized in a conventional way without
irradiation of ionizing radiation or light, a copolymeric product free
from strain and bubbles could be obtained only when the polymerization was
carried out at 70.degree. C. for 46 hours by the use of
azobisisobutylonitrile in an amount of 0.08% based on the mixture.
The copolymeric product obtained according to this Example had improved
properties, for example, resistance to heat, solvents and weather, surface
hardness, transparency and mechanical strength such as impact resistance
which were comparable or superior to those of a conventional acrylic resin
plate. Especially, it was found that the product produced according to
this Example had an Izod value of 29.9 kg/cm.sup.2 which was far higher
than the 19.7 kg/cm.sup.2 of a conventional acrylic resin plate. On the
other hand, a polymeric product polymerized from the mixture above except
that glycerol diacetate was omitted had an Izod value of 23.5 kg/cm.sup.2
which was also lower than that of the product according to this Example.
EXAMPLE 7
Methyl methacrylate (30 parts), propyl methacrylate (30 parts),
polyethyleneglycol dimethacrylate (30 parts) and trimethylolpropane
trimethacrylate (10 parts) were mixed and the mixture was poured into a
metal mold adapted to form a tube of 3.5 cm diameter and of 20 cm length,
cooled to -30.degree. C. and at that temperature irradiated with
gamma-rays from Co-60 at a dose rate of 5 .times. 10.sup.5 roentgen/hour
for 2 hours to obtain a tubular cast polymeric product free from strain
and bubbles.
It was found that if the mixture specified above was polymerized in the
same mold as mentioned above without irradiation, a cast polymeric product
free from strain and bubbles could be obtained only when
cumenehydroperoxide was incorporated into the mixture at a concentration
of 0.05% and polymerization was carried out at 60.degree. C. for 34 hours.
It was also found that the product obtained according to this Example was
significantly superior to a product in the same manner above from the
mixture containing no trimethylolpropane trimethacrylate in resistance to
solvents, chemicals and heat, characteristics being required in a
flowmeter.
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