Note: Descriptions are shown in the official language in which they were submitted.
BACKGROUWD OF THE INVE~TIO~
Numerous ink systems are availablé in the
marketplace. These systems are often designed for
specific utilities.
S A ~airly recently ;ntroduced concept to
the packaging industry is the use of retort pouches
for medical implements, foodstuffs and the like.
These pouches are formed from a pair of laminaO
Each lamina comprises a pair of plastics resin film
layers sandwiching and adhered to a metallic foil
layer, such as alu~inum foil. Thus, the contents
within the pouch cannot be seen, and suitable
labeling is often required.
Many ink systems are available which
successfully print on plastics resin films, such as
polyester filmsO However, most ink systems ~hich
successfully print on plastic resin film layers
cannot withstand the heat of retort sterilization,
which normally takes place at approximately 250F
(121.1C) or higher, or if the ink system is able to
withstand the retort operation, the ink system
blocks severely when a printed roll of film is
stored. The term "blocking" refers t3 the tendency
for the ink to adhere to a surface against which it
` 25 comes into contact, other than the surface it was
printed onto. Thus, when a printed roll of film is
coiled, blocking refers to the tendency for the ink
to adhere to successive layers of the film which
have been coiled on top of the printed layerO
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THE PRESENT INVENTI0~
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By means o~ the present invention, an ink
system which can both withstand the retorting
process and which is nonblocking is provided.
S The ink system comprises a ~oft polyester resin, a
hard polyester resin, a polyisocyanate catalyst and
a pigment or pigments. The ink system of the
present invention may be reverse printed on plastics
resin film, such as polyester film, and laminated
between the plastics resin film and a metallic foil
layer in the production of a printed pouch.
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DETAILED DESCRIPTION OF THE PREFERRED EMBODI~IENTS
The ink system of the present inv~ntion is
based upon the combination of a hard polyester resin
and a soft polyester resin. As used herein, the
term "hard polyester resin" refers to a polyester
resin having a glass transition temperature of 32F
~OGC) and above, and the term "soft polyester resin"
refers to a polyester resin having a glass transition
- 20 temperature below 32~F (0C).
The hard polyester resin helps provide the
nonblocking properties to the finished ink at room
temperature. The soft polyester resin provides
adhesiveness and flexibility to the ink.
The ratios for the hard and soft polyester
resins may range from about 35% hard and 65~ soft to
about 45% hard and 55~ soft, solids by weight.
Preferably, this ratio is about 40~ hard polyester
resin and 60% soft polyester resin, solids by weight.
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Typical o~ the ~ard polyester resins which
may be employed is Bostik 7942, and typical of the
soft polyester resins which may be employed is
Bostik 72O0. Bosti~ 7942 i5 provided in a solid
form and has a melting point of about 248-284~F
(120-140C) using the ball~and-ring method while
Bostik 7260 is provided as 30% solids in methyl
ethyl ketone and has a glass transition temperature
,of 26.4F (~ C).
tO The third Key element of the ink system of
the present invention is a polyisocyanate catalyst.
This catalyst is provided in about 1-10~ by weight,
preferably 2-6% by weight, of the base ink. The
polyisocyanate catalys~ crosslinks with the
polyestersr providing improved adhesion and heat
resistance to the resulting ink system.
Typical of the polyisocyanate catalysts
which may be employed is Boscodur~ 1, which is
provided as 65-68.5% solids in toluol and ethyl
acetate and which includes 11.5-14% isocyanate in
the form of toluene diisocyanate.
, The polyester resin system is dissolved in
a solvent system. This solvent system is preferably
a combination of methyl ethyl ketone and toluol.
The methyl ethyl ketone reduces the viscosity of the
ink, while the toluol lowers the evaporation rate of
the ink and increases printability of the ink. The
toluol may be present in an amount from about 40-50%
by weight of the total solvent, and the methyl ethyl
ketone from about 50-60% by weight of the total
solvent.
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Additionally, methyl norrnal propyl ketone
may be employed as an addi~ional solverlt in an
amount up ~o about 50% by weiyht of the tot~l
~olvent. Me~hyl norm~l propyl ketone also improves
the printability of the ink system and lowers the
evaporation rate of the ink, while additionally
providing increased solubility for the polymers.
The ink color is provided by a pigment or
. . piymen~s which can be any pigment or pigments having
heat resistant properties to withstand retorting~
; Examples of suitable pigments include titanium
dioxide, carbon black, BON red, Red Lake C, Yellow HR,
phthalo blue, phthalo green and the like. ~ne pigment
. . or pigments may be provided in an amo~nt from about
~.5-60~ by weight on a solids basis depending upon the
intensity of the color required.
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- - EXAMPLE
: In accordance-with the present invention,
-- ~he-following in~ was prepared. . -..
2Q Ingredient :-- - - Parts by weight
pigments-BOllowdHR 3 3
soft polyester-Bostik i260 4507
- -30~ solids in methyl ehtyl ketone
25 hard polyester-Bostik 7942 9.2
-100~ solids
methyi ethyl ketone 12.0
toluol 29.4
. TOTAL . 100.0
_ -5
To 100 parts by weight uf the above ink
compvstion was then added 3 parts by weight of
toluene diisocyanate in the form of Bosccdur #1.
The above lnk was reverse printed onto a
S polyester film which was electrostatically treated
to 54~56 dynes per linear inch prior to coating.
- The printed film, when stored as a coil, showed no
tendency for the ink to block.
This film coil was then laminated by means
of a polyester adhesive on the printed side to an
aluminum foil, which foil was in turn laminated to a
polypropylene layer. ~ pair of these laminates were
then heat sealed to one another to form a pouch,
with the pouch being filled with foodstuffs, sealed
and retorted. The ink system withstood the retort
operation without degradation, running or other
failure.
From the foregoing, it is clear that the
present invention provides an ink system which is
both nonblocking and which can withstand the retort
sterilization process.
While presently prefPrred embodiments of
the invention have bèen illustrated and described,
it will be understood ~hat the invention may be
otherwise embodied and practiced within the scope of
tbe following claims.
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