Note: Descriptions are shown in the official language in which they were submitted.
1051'~9~
It is known that high temperature resistant plastics
sheets, for example polyimide sheets coated with fluorinated
hydrocarbons which are solid at room temperature are capable
of being heat-sealed. m e layer of fluorinated hydrocarbons is
generally produced by laminating the temperature-resistant
sheet to a sheet of the fluorinated hydrocarbon at a tempera-
ture above the softening point of the fluorinated hydrocarbon.
Another method consists of applying the fluorinated hydrocar-
bon in the form o~ a powder to the temperature-resistant sheet
and then fixing the powder by sintering. Attempts have also
been made to dissolve the fluorinated hydrocarbon in high boi-
ling solvents, to apply the solution to the temperature-resi-
stant sheet and then evaporate the solvent. This method re-
quires high drying temperatures and long drying times and the
finished sheet must be finally tempered at temperatures above
200C. Furthermore, additives must be added to the solution of
fluorinated hydrocarbon to improve film-formation. These addi-
tives must be completely removed with the solvent or at the
tempering stage. me formation of a perfect coating by this
method is difficult and very complicated.
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- ~ This invention relates to a new process for producing
temperature-resistant sheet materials which are capable of
: being heat-sealed, using a coating of fluorinated hydrocarbons,
,
~ wherein a solution of a partially fluorinated, high-molecular
i
weight aliphatic hydrocarbon with a molecular weight of 1000 to
500,000 which is solid at room temperature, a solvent mixture
- of
a) 10 to 60 volumes percent of a chlorinated aliphatic hydro-
carbon containing 1 to 6 carbon atoms and having a boiling
point of 30 - 150C and
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b) 40 - 90 volumes percent of an alkyl ester of a polybasic
aromatic carboxylic acid or high boiling ketones is applied
to a temperature-resistant plastics sheet and the solvent
is removed.
Preferred solvent mixtures are those which at least at
their boiling point are capable of swelling the temperature-
resistant sheet and thus producing a firm bond between the
temperature-resistant sheet and the layer of fluorinated hydro-
carbon.
The solvent mixtures used for dissolving the fluorina-
ted hydrocarbons generally consist of 10 to 60 volumes percent
of a low-boiling chlorinated hydrocarbon which contains 1 to
6 carbon atoms and 40 to 90 volumes percent of an alkyl ester
~ of a polybasic aromatic carboxylic acid or high-boiling ke-
; 15 tones.
~; Low-boiling chlorinated hydrocarbons which have a boi-
; ling point between ~0 and 150C is 1,1,1-trichloroethane.
Suitable alkyl esters of polybasic aromatlc carboxylic
acids, preferably of di-, tri- or tetracarboxylic acids, are,
for example, C1 - C18 alkyl esters Or phthalic acid, trimel-
litic acid and benzene tetracarboxylic acid. Dimethyl phtha-
late, dioctyl phthalate and phorone are particularly suitable.
The solution of fluorinated hydrocarbons in such solvent mix-
tures generally contains 10 to 25~ of fluorinated hydrocarbons.
Suitable high boiling ketones are those having a boi-
ling point between 80 and 250C, such as aliphatic ketones
containing from 5 to 11 carbon atoms, pre~erably phorone,
~s~ aliphatic aromatic ketones containing from 7 to 1~ carbon
atoms, preferred phenoxy acetone, or aromatic ketones con-
~0 taining 7 to 13 carbon atoms, preferred diphenyl ketone.
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A most preferred solvent mixture consists of 10 to 60
volume percent of l,l,l-trichloroethane and of 40 to 90
volume percent of dimethylphthalate.
Fluorinated hydrocarbons which are particularly
suitable for the coating are high-molecular weight ali-
phatic compounds with molecular weights of about 1000 to
about 500,000. Preferably 25 - 75% of the hydrogen atoms
are replaced by fluorine. Up to 10% of the hydrogen atoms
which are capable of being substituted may also be sub-
stituted with other substituents which are stable at the
reaction temperature, for example chlorine. The
fluorinated hydrocarbons must be solid at room tempera-
ture.
Particularly suitable fluorinated hydrocarbons are
fluorinated ethylene-propylene copolymers with a molecular
weight of about 1000 to about 500,000 which are composed of
about 80 to 20% by weight of ethylene units and 20 to 80%
by weight of propylene units and in which 25 to 75% of
~ the hydrogen atoms are substituted with fluorine. Polyvinyli-
- 20 dene fluorides with a molecular weight of about 1000 to about
10,000 are also particularly suitable.
The basic material used may in principle be any high-
temperature resistant plastics sheet. Polyhydantoin
f sheets are particularly suitable. Polyhydantoins arealready known. They may be prepared, for example, by
reacting aromatic diglycine esters with diisocyanates.
A typical example is the reaction of N,N'-bis-carbethoxy-
methyl-4,4'-diamino-diphenylmethane with 4,4'-diisocyanato-
diphenylmethane. Polyhydantoins and methods of preparing
them have been described, for example, in U.S. Patent
Specification No. 3,397,253.
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To carry out the process, a sheet is produced from a
temperature-resistant synthetic resinJ preferably a poly-
hydantoin. The thickness of the sheet is generally about
5 to about 2001u . The solution of fluorinated hydrocarbon
in the above described solvent mixture is applied to this
sheet and the solvent is evaporated. The quantity of
solution applied is calculated to produce a coating with a
thickness of preferably 2 to 30~u. The solution of
fluorinated hydrocarbons may be applied by any known
methods, preferably by means of a roll coater or doctor
knife. Temperatures of about 120 - 200C are in most cases
required for evaporating the solvent.
Another object of this invention is a polyhydantoin
sheet with a thickness of about 5 to about 200/u which
carries a coating about 2 to about 30 ~ in thickness which
is firmly bonded to the sheet and which consists of a
partially fluorinated high-molecular weight aliphatic
hydrocarbon with a molecular weight of 1000 to 500,000.
This sheet material is suitable in particular for use as
an electro-insulating sheet. Coated sheets of other high-
temperature resistant plastics are also suitable for this
purpose but coated polyhydantoin sheets are preferred
because they have an exceptionally high electrical insula-
5 ~ tion value and exceptionally high break-down voltage. In
, addition, their mechanical strength is exceptionally high.
,! The polyhydantoin sheets coated with fluorinated hydro-
carbons according to the invention are used particularly
; for insulating flat copper conductors. They are wound
spirally round such conductors and then sealed by heat.
Flat copper conductors of this kind are used for the field
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winding Or high power electrlc motorsJ e.g. with outputs
o~ over 100 kilowatt.
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1051294
Exam~le 1
-
An ethylene-propylene copolymer with a molecular
weight of about 50,000 which i9 composed of 50~ ethylene
units and 50% propylene units and in which half the hydro-
gen atoms which are capable of being subst~tuted are re-
placed by fluorine atoms is dissolved in a mixture of 50
parts by ~olume of 1~ trichloroethane and 50 parts by
volume of dimethyl phthalate at temperatures of 50 - 60C
to form a 10% by weight ~olution~ The filtered solution
i~ coated by spreading on a polyhydantoin sheet 20 - 30
in thickne~s to form on it a layer with a thickness oi
about 100 p. The coated sheet is dried in hot air at
about 150C.
The coated polyhydantoin sheet obtained in this way
carries a fluorinated hydrocarbon layer 10 ~ in thickness
which adheres so firmly to the polyhydantoin æheet that
, the ~trength of the bond is greater than the tear resistance
- of the fluorinated hydrocarbon layerO
he coated ~heet i8 wound spirally round a flat copper
conductor and sealed by heating to 250 - 300C. ~he
insulated flat conductor obtained in this way can be twisted
~pirally without the insulating layer becoming detached.
Example 2
` ~xample 1 i~ repeated except that a polyvinylidene
r 25 fluoride with a molecular weight of about 1000 i8 used
~- instead of the fluorinated ethylene-propylene copolymer.
Here again the in~ulation obtained on the flat copper con-
ductor is not detached by twisting.
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