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Description  |
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BACKGROUND OF THE INVENTION
(1) Field of the Invention
This invention relates to a curable composition comprising a specific
aromatic dibasic acid having an ethylenically unsaturated group, such as
4-methacryloxyethyltrimellitate or its anhydride, an ethylenically
unsaturated monomer other than said aromatic dibasic acid and a catalyst.
More particularly, the invention relates to a curable composition valuable
as a dental adhesive or cement or as an undercoating agent for an adhesive
or paint.
(2) Description of the Prior Art
Curable compositions comprising an acrylic or methacrylic monomer such as
methyl methacrylate,
2,2-bis(p-2'-hydroxy-3'-methacryloxypropoxyphenyl)propane or the like and
a free-radical initiator have been proposed and used as dental adhesives
or cements.
These conventional compositions, however, are still insufficient in the
bonding force to enamel of teeth. Accordingly, when teeth are treated with
these compositions, it is necessary to treat enamel of the teeth in
advance with a strong acid and then conduct the bonding operation.
Therefore, the tooth treatment becomes troublesome and enamel on the
surface of a tooth is worn away by the acid treatment. It has been desired
to eliminate these disadvantages involved in the conventional
compositions.
BRIEF SUMMARY OF THE INVENTION
We found that when a curable composition comprising a specific aromatic
dibasic acid having an ethylenically unsaturated group such as
4-methacryloxyethyltrimellitate, an ethylenically unsaturated monomer
other than said aromatic dibasic acid and a catalyst is used as a dental
adhesive, the composition has a strong adhesiveness to either enamel or
dentin of a tooth and the resulting bonded structure is prominently
excellent in such properties as water resistance and durability.
It is therefore a primary object of this invention to provide a curable
composition which has an excellent adhesiveness to the tooth tissue or a
substrate such as a metal and can give a bonded structure excellent in the
water resistance and durability.
Another object of the present invention is to provide a curable composition
which can be applied to the tooth tissue or a substrate metal without use
of a solvent and can be polymerized and cured in situ to form an adhesive
layer or undercoat layer.
In accordance with the present invention, there is provided a curable
composition comprising (A) an ethylenically unsaturated carboxylic acid
represented by the following general formula:
##STR1##
wherein R.sub.1 is a hydrogen atom or a methyl group,
R.sub.2 is an alkylene group having 2 to 4 carbon atoms, and in the benzene
ring A two carboxyl groups are bonded to carbon atoms other than the
carbon atoms adjacent to the carbon atoms to which the ester group is
bonded,
or an acid anhydride thereof, (B) at least one ethylenically unsaturated
monomer other than said monomer (A), said ethylenically unsaturated
monomer (B) being copolymerizable with said monomer (A), and (C) at least
one catalyst selected from the group consisting of free radical initiators
and photosensitizers.
DETAILED DESCRIPTION OF THE INVENTION
In the ethylenically unsaturated carboxylic acid or its anhydride (A) that
is used in the present invention, it is important that two carboxyl groups
or one acid anhydride group should be present on the benzene ring, and
that in the benzene ring, two carboxyl groups or one acid anhydride group
should be bonded to carbon atoms other than the carbon atoms adjacent to
the carbon atom to which the ester group is bonded.
A curable composition comprising an ethylenically unsaturated carboxylic
acid or its anhydride having the above-mentioned chemical structure has a
prominently excellent adhesiveness over a curable composition comprising
an ethylenically unsaturated carboxylic acid having one carboxyl group on
the benzene ring or an ethylenically unsaturated carboxylic acid having in
the benzene ring a carboxyl group bonded to the carbon atom adjacent to
the carbon atom to which the ester group is bonded.
An ethylenically unsaturated carboxylic acid or its anhydride most
preferred for attaining the objects of the present invention is
4-methacryloxyethyltrimellitate (melting point=119.5.degree. to
120.0.degree. C.) having the following formula:
##STR2##
or its anhydride (melting point=95.0.degree. to 95.8.degree. C.) having
the following formula:
##STR3##
The monomer of the formula (3) may be prepared by dehydrochlorination
reaction between hydroxyethyl methacrylate and anhydrous trimellitic acid
chloride or by dehydration reaction between hydroxyethyl methacrylate and
trimellitic anhydride. 4-Methacryloxyethyltrimmellitate of the formula (2)
can easily be prepared by hydration of 4-methacryloxyethyltrimellitate
anhydride.
These acid and acid anhydride may be used singly or in the form of a
mixture thereof.
As examples of other ethylenically unsaturated carboxylic acids and acid
anhydrides that can be used in the present invention, there can be
mentioned 4-methacryloxy-3'-propyltrimellitate and its anhydride,
4-acryloxyethyltrimellitate and its anhydride,
4-methacryloxy-4'-butyltrimellitate and its anhydride, and
5-methacryloxyethyltrimesic acid.
As the ethylenically unsaturated monomer (B) that is used in combination
with the ethylenically unsaturated carboxylic acid or its anhydride (A) in
the present invention, there can be mentioned at least one monomer
copolymerizable with said monomer (A). It is preferred that the monomer
(B) or at least one of the monomers (B) be liquid in the normal conditions
and be capable of dissolving the monomer (A) therein.
As preferred examples of the monomer (B), there can be mentioned acrylic
monomers represented by the following general formula:
##STR4##
wherein R.sub.1 is a hydrogen atom or a methyl group
and R.sub.3 is an alkyl group having up to 8 carbon atoms, such as methyl
acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate, butyl
methacrylate and 2-ethylhexyl acrylate, and monomers represented by the
following general formula:
##STR5##
wherein R.sub.1 is a hydrogen atom or a methyl group and
R.sub.4 is a divalent organic group.
As the group R.sub.4 in the formula (5), there can be mentioned, for
example, residues derived from glycols such as ethylene glycol, propylene
glycol, tetramethylene glycol, diethylene glycol, triethylene glycol,
dipropylene glycol, tripropylene glycol, polyethylene glycol and
polypropylene glycol, residues derived from bis-epoxy compounds such as
2,2-bis(p-glycidyloxyphenyl)propane, and residues derived from
2,2-bis(p-hydroxyphenyl)propane/ethylene oxide adduct and the like. As
specific examples of the monomer represented by the formula (5), there can
be mentioned polyethylene glycol dimethacrylate, polypropylene glycol
diacrylate and 2,2-bis(p-2'-hydroxy-3'-methacryloxypropoxyphenyl)propane.
In addition, as the monomer (B), there can be used vinyl esters such as
vinyl formate, vinyl acetate and vinyl propionate, aromatic vinyl
compounds such as styrene, .alpha.-methylstyrene, vinyl-toluene and
divinyl-benzene, ethylenically unsaturated nitriles such as acrylonitrile,
methacrylonitrile and .alpha.-cyanoacrylic acid esters, vinyl ethers such
as butylvinyl ether and octylvinyl ether, vinyl ketones such as ethylvinyl
ketone and methylisopropenyl ketone, allyl esters such as diallyl
phthalate, and other ethylenically unsaturated carboxylic acids such as
itaconic acid and (.beta.-methacryloxy) ethyl maleate.
Among these monomers, an acrylic monomer of the formula (4), especially
methyl methacrylate, is preferably used singly or in combination with
other monomer.
The content of the above-mentioned ethylenically unsaturated dicarboxylic
acid or its acid anhydride (A) can be changed in a broad range according
to the intended use of the curable composition of the present invention,
namely depending on whether the composition is used as an adhesive or
undercoating composition. In general, however, it is preferred that the
amount of the monomer (A) be 0.1 to 20 mole %, especially 1 to 10 mole %,
based on the sum of the amounts of the monomers (A) and (B). When the
content of the monomer (A) is below the above range, it is often difficult
to increase the adhesiveness to a desirable level, and when the content of
the monomer (A) is above the above range, no particular improvement of the
adhesiveness can be expected and the use of such a large amount of the
monomer (A) is not preferred from the economical viewpoint.
In the present invention, a free radical initiator or photosensitizer is
incorporated in a mixture of the monomers (A) and (B) as the catalyst (C).
As the free radical initiator, peroxides and peracids such as benzoyl
peroxide, dicumyl peroxide, cumene hydroperoxide and t-butyl perbenzoate
and azo compounds such as azobisisobutyronitrile are ordinarily used, if
desired, in combination with polymerization promoters such as organic acid
amides and organic acid imides. When the curing is conducted at room
temperature, it is preferred to use partially oxidized tri-n-butylborane
or a mixture of cobalt naphthenate and methylethyl ketone peroxide.
Any of known photosensitizers can be used in the present invention. For
example, there can be used benzoin methyl ether, benzoin ethyl ether,
benzoin isopropyl ether, acetophenone, benzophenone and anthraquinone.
The catalyst is used in a so-called catalytic amount, namely 0.01 to 10% by
weight, especially 0.1 to 5% by weight, based on the sum of the amounts of
the monomers (A) and (B).
The curable composition of the present invention may further comprise
various additives. As additives that can be used in the present invention,
there can be mentioned inorganic powdery fillers such as kaolin, talc,
clay, calcium carbonate, silica, alumina, silica-alumina, calcium
phosphate and glass, pigments such as titanium oxide, tackifying agents
such as waxes and ethylene/vinyl acetate copolymers, curing promotors,
polymerization regulators and polymerization inhibitors such as
hydroquinone.
The curing composition of the present invention is used as an adhesive, an
undercoating agent or the like in the form of a homogeneous liquid formed
by homogeneously dissolving the ethylenically unsaturated carboxylic acid
or its anhydride (A) into the liquid ethylenically unsaturated monomer (B)
and adding the catalyst (C) to the resulting solution.
The curable composition of the present invention can be cured to form a
cured resin layer when it is allowed to stand at room temperature or it is
heated if necessary. When a photosensitizer is incorporated as the
catalyst (C), the composition of the present invention is cured under
irradiation of ultraviolet rays to form a cured resin layer.
When a powder of an acrylic or methacrylic resin, for example, a polymethyl
methacrylate powder, is present in the curable composition at the curing
step, a cured resin layer is formed in a relatively short time.
Accordingly, this feature is preferred when the composition of the present
invention is used as an adhesive. It is preferred that such resin powder
be made present in an amount of 0.1 to 2 parts by weight per part by by
weight of the sum of the monomers (A) and (B).
According to a preferred embodiment of the application of the curable
composition of the present invention, 4-methacryloxyethyltrimellitate
anhydride (A) is mixed with partially oxidized tri-n-butylborane (C) and
methyl methacrylate (B) at room temperature to form a cured resin.
Further, 4-methacryloxyethyltrimellitate anhydride (A) is mixed with a
small amount of benzoin methyl ether (C) and methyl methacrylate (B) and
the mixture is irradiated with ultraviolet rays, whereby a cured resin can
easily be formed.
When the curable composition of the present invention is used as an
adhesive, the composition is applied to at least one of the surfaces of
articles to be bonded, for example, teeth, metals and resins, then the
articles are bonded together before the composition is cured thoroughly,
so it can be obtained a high adhesive strength.
The curable composition of the present invention can be used especially
valuable as dental materials, for example, a pit and fissure sealant, an
orthodontic adhesive, a filling composite resin, a resin for veneered
crown, a metallic denture base resin or an adhesive for bonding a metal or
the like to teeth.
When the curable composition of the present invention is used as an
undercoating composition for an adhesive or paint, the composition of the
present invention is applied to a substrate and cured, and a known
adhesive is applied to the resulting cured resin layer and bonding is
effected or a paint is applied to the cured resin layer to form a coated
structure. When the composition of the present invention is used as an
undercoating composition, the adhesion or bonding strength can be
remarkably improved over the adhesion or bonding strength attained when
the composition of the present invention is not used.
The curable composition of the present invention can be applied to usage as
an adhesive, an undercoating composition and the like in the form of a
single composition formed by preliminarily mixing the three ingredients.
Further, the respective ingredients are applied to the surface of a
substrate to be bonded or coated to form the composition of the present
invention thereon and the composition is thus applied to the
above-mentioned uses.
For example, there may be adopted a method in which
4-methacryloxyethyltrimellitate or its anhydride (A) is dissolved in a
solvent such as a ketone or an alcohol, the resulting solution is coated
on a substrate, the solvent is evaporated from the coating, and an
ethylenically unsaturated compound (B) with a free radical initiator
and/or a photosensitizer (C) is applied to the coating to effect curing
and form a cured resin layer.
Since the above-mentioned specific ethylenically unsaturated dicarboxylic
acid or its anhydride is contained in the curable composition of the
present invention, the composition has a very high adhesiveness or bonding
strength to the surfaces of various substrates, especially the surface of
enamel or dentin of a tooth or the surface of a metal, and provides a
bonding especially excellent in the water resistance and durability.
As the tooth adhesive, there has been known a methyl methacrylate polymer
or a copolymer of methyl methacrylate with a vinyl compound such as
2,2-bis(p-2'-hydroxy-3'-methacryloxypropoxyphenyl)propane. However, since
these known adhesives are still insufficient in the bondability to teeth,
they are applied to teeth after the teeth have been treated with strong
acids. In contrast, the curable composition of the present invention
containing an ethylenically unsaturated carboxylic acid such as
4-methacryloxyethyltrimellitate or its anhydride has a sufficiently high
bondability to teeth. Accordingly, the acid treatment indispensable in the
conventional techniques need not be conducted, and therefore, the dental
treatment can be remarkably facilitated and the loss of the surface
portion of a tooth by the acid treatment can be completely prevented.
Therefore, the present invention makes great contributions to the art.
The present invention will now be described in detail by reference to the
following Examples that by no means limit the scope of the invention.
EXAMPLE 1
The flat labial enamel surface of fresh borine upper incisal tooth was
obtained by polishing with emery papers (up to No. 6/0). A cellophane tape
having a size of 13 mm.times.13 mm with a circular hole of a diameter of
5.4 mm in the center was fixed to the enamel surface. A 5% acetone
solution of 4-methacryloxyethyltrimellitate anhydride was coated to the
hole two times by using a small brush. Then, a mixture of a methyl
methacrylate monomer containing 4% of partially oxidized tri-n-butylborane
as a polymerization initiator and powdery polymethyl methacrylate in an
amount of 20% based on monomer was coated by using another small brush.
Next a polymethylmethacrylate rod having a diameter of 5 mm was placed on
the curing mass at room temperature. After one hour had passed, the bonded
sample was dipped in water maintained at 37.degree. C. for 24 hours. The
sample was taken out from water and polymethylmethacrylate rod was pulled
from the borine enamel at a loading speed of 2 mm/min by using a Universal
Testing Machine Model IM-500 (Shimazu Seisakusho Kyoto, Japan). It was
found that the tensile adhesive strength was 34.6 Kg/cm.sup.2.
COMPARATIVE EXAMPLE 1
The procedures of Example 1 were repeated in the same manner except that
coating with the 5% acetone solution of 4-methacryloxyethyltrimellitate
anhydride was omitted. The tensile adhesive strength was 0 Kg/cm.sup.2.
COMPARATIVE EXAMPLE 2
The procedures of Example 1 were repeated in the same manner except that a
5% acetone solution of methacryloxyethyl phthalate was used instead of the
5% acetone solution of 4-methacryloxyethyltrimellitate anhydride. The
tensile adhesive strength was 9.1 Kg/cm.sup.2.
COMPARATIVE EXAMPLE 3
The procedures of Example 1 were repeated in the same manner except that a
5% acetone solution of N-acryloyl-.gamma.-aminosalicylic acid was used
instead of the 5% acetone solution of 4-methacryloxyethyltrimellitate
anhydride. The tensile adhesive strength was 6.3 Kg/cm.sup.2
COMPARATIVE EXAMPLE 4
The procedures of Example 1 were repeated in the same manner except that a
5% acetone solution of N-methacryloylaspargic anhydride was used instead
of the 5% acetone solution of 4-methacryloxyethyltrimellitate. The tensile
adhesive strength was 2.7 Kg/cm.sup.2.
EXAMPLE 2
A flat labial enamel surface of fresh borine upper incisal tooth was
obtained by polishing with emery papers up to (No. 6/0). A cellophane tape
having size of 13 mm.times.13 mm with a circular hole of a diameter of 5.4
mm in the center was fixed to the enamel surface. Then, a mixture of
monomer solution made from 95% by weight of methyl methacrylate and 5%
4-methacryloxyethyltrimellitate anhydride, partially oxidized
tri-n-butylborane as a polymerization initiator in an amount of 4% based
on monomer solution and powdery polymethyl methacrylate in an amount of
20% based on monomer solution was coated by using a small brush. Next a
polymethylmethacrylate rod having a diameter of 5 mm was placed on the
curing mass at room temperature. After one hour had passed, the bonded
sample was dipped in water maintained at 37.degree. C. for 24 hours. The
sample was taken out from water and the polymethylmethacrylate rod was
pulled from the borine enamel at a loading speed of 2 mm/min by using a
Universal Test Machine Model IM-500. It was found that the tensile
adhesive strength was 56.8 Kg/cm.sup.2.
COMPARATIVE EXAMPLES 5 TO 7
The procedures of Example 2 were repeated in the same manner except that a
monomer or mixture indicated in Table 1 was used instead of the mixture of
95% by weight of methyl methacrylate and 5% by weight of
4-methacryloxyethyltrimellitate anhydride. In each run, the tensile
adhesive strength was 0 Kg/cm.sup.2.
Table 1
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Composition (% by weight) of
Tensile Adhesive Strength
monomers in Adhesive
(Kg/cm.sup.2)
______________________________________
Example 2
4-methacryloxyethyltri-
56.8
mellitate anhydride, 5
methyl methacrylate, 95
Compara-
methyl methacrylate, 100
0
tive
Example 5
Compara-
Bis-GMA*, 5 0
tive methyl methacrylate, 95
Example 6
Compara-
HNPM**, 5 0
tive methyl methacrylate, 95
Example 7
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Note
*2,2-bis(p-2'-hydroxy-3'-methacryloxypropoxyphenyl)propane
**2-hydroxy-3-.beta.-naphthoxypropyl methacrylate
EXAMPLE 3
The procedures of Example 1 were repeated in the same manner except that a
5% acetone solution of 4-methacryloxyethyltrimellitate was used instead of
the 5% acetone solution of 4-methacryloxyethyltrimellitate anhydride. The
tensile adhesive strength was 30.8 Kg/cm.sup.2.
EXAMPLE 4
The procedures of Example 2 were repeated in the same manner except that a
mixture of 95% by weight of methyl methacrylate and 5% by weight of
4-methacryloxyethyltrimellitate was used instead of the mixture of 95% by
weight of methyl methacrylate and 5% by weight of
4-methacryloxyethyltrimellitate anhydride. The tensile adhesive strength
was 40.6 Kg/cm.sup.2.
EXAMPLE 5
When the tensile adhesive strength was determined according to the method
described in Example 1, a 2/1 weight ratio mixture of Bis-GMA/triethylene
glycol dimethacrylate was used as the ethylenically unsaturated monomer
(B) and 0.5% by weight of benzoin methyl ether was incorporated and
sufficiently dissolved in the mixture. The so formed viscous liquid was
thinly coated on the surface of a bovine tooth exposed through a circular
hole formed on a cellophane tape in the same manner as described in
Example 1. Then, ultraviolet rays were applied to the coated surface for 1
minute by using an ultraviolet ray irradiator (Nuva Lite manufactured by
L. D. Calk Co.) to effect curing. Then, an acrylic resin rod was bonded to
the cured resin layer by using a methyl methacrylate type adhesive. The
rod-bonded bovine tooth was dipped in water maintained at 37.degree. C.
for 24 hours, and the tensile adhesive strength was measured in the same
manner as described in Example 1. It was found that the tensile adhesive
strength was 45.8 Kg/cm.sup.2.
COMPARATIVE EXAMPLE 8
The procedures of Example 5 were repeated in the same manner except that
coating with the 5% acetone solution of 4-methacryloxyethyltrimellitate
anhydride was omitted. The tensile adhesive strength was 3.2 Kg/cm.sup.2.
EXAMPLE 6
A cubic having a size of 1 cm.times.1 cm.times.1 cm was cut from wetted
ivory, and in the same manner as described in Example 2, an acrylic resin
rod was bonded to one surface of this ivory cubic. The acrylic resin
rod-bonded ivory cubic was dipped in water maintained at 37.degree. C. for
7 days. Then, the ivory cubic was dipped in water maintained at 4.degree.
C. for 1 minute and in hot water maintained at 60.degree. C. for 1 minute,
and this alternate dipping was repeated 800 times. The acrylic resin rod
was not pulled from the ivory cubic even if a pulling force of 40
Kg/cm.sup.2 was applied.
COMPARATIVE EXAMPLE 9
The procedures of Example 6 were repeated in the same manner except that
methyl methacrylate was used instead of the mixture of 95% by weight of
methyl methacrylate and 5% by weight of 4-methacryloxyethyltrimellitate
anhydride. The alternating dipping in water maintained at 4.degree. C. for
1 minute and in hot water maintained at 60.degree. C. for 1 minute was
repeated 300 times. The acrylic resin rod was pulled off from the ivory
cubic when a pulling force of 8 Kg/cm.sup.2 was applied.
EXAMPLE 7 AND COMPARATIVE EXAMPLE 10
The flat surface of a metal piece having a size of 1 cm.times.1 cm was
sufficiently ground by an emery paper No. 1 to attain a certain smoothness
on the surface. A cellophane tape having a size of 1 cm.times.1 cm and a
circular hole having a diameter of 5.4 mm was applied to the ground
surface of the metal piece. Partially oxidized tri-n-butylbornae was
incorporated as the free radical initiator in an amount of 8% by weight
into a monomer mixture comprising 95% by weight of methyl methacrylate and
5% by weight of 4-methacryloxyethyltrimellitate anhydride, and a small
amount of powdery polymethyl methacrylate was added to the mixture to form
an adhesive composition. The composition was coated on the metal piece
surface exposed through the circular hole of the cellophane tape and an
acrylic resin rod having a diameter of 5 mm was vertically held and fixed
on the coated surface of the metal piece. After one hour had passed, the
cellophane tape was peeled off, and the acrylic resin rod-bonded metal
piece was dipped in water maintained at 37.degree. C. for a predetermined
time. Then, the metal piece was taken out from water and the acrylic resin
rod was pulled from the metal piece at a loading speed of 2 mm/min by
using universal testing machine (Model IM-500) to determine the tensile
adhesive strength.
For comparison, the above procedures were repeated in the same manner
except that 4-methacryloxyethyltrimellitate anhydride was not used but
methyl methacrylate alone was used. The tensile adhesive strength was
determined in the same manner as described above.
Obtained results are shown in Table 2.
Table 2
______________________________________
Tensile
Dipping Time
Adhesive Strength
Metal Piece (days) (Kg/cm.sup.2)
______________________________________
Example 7
Suncolium 2 above 145.9*
" 30 above 185.6*
Sunilium 6 above 103.1*
Brass 4 121.4
Gold-silver-palladium
30 76.9
Silver alloy 1 above 190.0*
Comparative Example 10
Suncolium 2 22.8
Sunilium 6 67.7
______________________________________
Note
Suncolium: cobalt-chromium alloy for dental casting (manufactured by
Sankin Kogyo)
Sunilium: nickel-chromium alloy for dental casting (manufactured by Sanki
Kogyo)
Gold-silver-palladium: 12 % of gold, 20 % of palladium, 57.8 % of silver
and 9.9 % of copper
Silver alloy: 60 % of silver, 25 % of tin, 10 % of copper and 1 % of
palladium
*the adhesive layer of the acrylic resin rod was destroyed at the
measurement of the tensile adhesive strength
EXAMPLE 8 AND COMPARATIVE EXAMPLE 11
An acrylic resin rod was bonded to a copper piece according to the
procedures of Example 7. The copper piece was dipped in water maintained
at 37.degree. C. for 1 day, and it was then dipped in water maintained at
4.degree. C. for 1 minute and in water maintained at 60.degree. C. for 1
minute alternately. This alternate dipping was conducted 60 times, namely
for 2 hours as a whole. At the measurement of the tensile adhesive
strength, the acrylic resin rod was destroyed when a pulling force of
149.3 Kg/cm.sup.2 was applied.
For comparison, the above procedures were repeated in the same manner
except that 4-methacryloxyethyltrimellitate anhydride was not used but
methyl methacrylate alone was used. The tensile adhesive strength was 37.6
Kg/cm.sup.2.
EXAMPLE 9 AND COMPARATIVE EXAMPLE 12
In the same manner as described in Example 8 or Comparative Example 11, a
stainless steel piece (SUS 304) and an acrylic resin rod were bonded
together. It was found that the tensile adhesive strength was 105
Kg/cm.sup.2 when 4-methacryloxyethyltrimellitate anhydride was used in
combination with methyl methacrylate (Example 9) and the tensile adhesive
strength was 10 Kg/cm.sup.2 when methyl methacrylate alone was used
(Comparative Example 12).
EXAMPLE 10
A liquid mixture comprising 63 parts by weight of Bis-GMA, 32 parts by
weight of triethylene glycol dimethacrylate and 5 parts by weight of
4-methacryloxyethyltrimellitate anhydride was prepared, and 0.5% by weight
of benzoin peroxide was added to the liquid mixture to form a homogeneous
solution. The viscous liquid was coated on the surface of a stainless
steel sheet (SUS 304) having a thickness of 1 mm, a width of 10 mm and a
length of 100 mm, and the coated surface was lightly covered with a
cellophane paper. The coated steel sheet was maintained in a thermostat
tank maintained at 70.degree. C. for 3 hours to form an adhesive layer.
The, a methylene chloride solution of polymethyl methacrylate containing a
small amount of a dye (Oil Red) was coated on the adhesive layer.
Methylene chloride was evaporated to form a colored layer. The so treated
SUS 304 sheet was dipped in water maintained at 50.degree. C. for 1 month.
The sheet was taken out from water and water was wiped away from the
sheet. Then, an adhesive cellophane tape was applied to the colored layer,
and the cellophane tape was violently peeled off while the SUS sheet was
being firmly fixed. The colored layer was not peeled off but was held on
the SUS sheet.
COMPARATIVE EXAMPLE 13
The procedures of Example 10 were repeated in the same manner except that
formation of the adhesive layer was omitted. The colored layer-bonded SUS
sheet was dipped in water maintained at 50.degree. C. only for one day.
When the cellophane tape was peeled from the SUS sheet, the colored layer
was readily peeled off from the SUS sheet together with the cellophane
tape.
* * * * *
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