Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
The present in~ention relates to the preparation
of a glass sealing surface for sealing to a thin mem-
brane capable o~ effecting a liquid-tight seal. The
method is especially useful for sealihg the mouth por-
tion of a glass container which has been treated tofacilitate durable and long term sealing preferably
by means of a laminate of aluminum ~oil and a thermo-
plastic polymer.
It i5 fairly common to form hea-t-activated seals
on plastic containers using thin membrane type sealing
materials. Generally, a membrane, which may be com
prised of a laminate of aluminum foil and a thermo
plastic polymer is forced against the mouth of the
plastic container under heat and pressure so that the
container and sealing laminate form polymer-to-polymer
adhesive contact. While the method is of considerable
bene~it in sealing plastic containers, it cannot be
used in sealihg glass containers since only short-term
seal li~e can be obtained unless a supplemental closure
2~ is employed. Poor adhesion between the polymer and
the glass results in leakage especially in packing many
types oE hot fill and acidic products.
The present invention provides a method of sealing
a container mouth, the mouth consisting of glass and
having an upper rim portion, which comprises the s-teps
of heating at least the container xim portion to an
elevated -temperature to oxidize any existent materials
thereon, applying a first thin coating of an organo
~uctional silane compound to the rim portion, applyiny
a second thin coating of an ethylene acrylic acid co-
polymer over the first thin coating of the silane
compound on the rim portion, pressing a thin imper-
iorate membrane comprising a thermoplastic sealingmaterial against the said second thin coating of
ethylene acrylic acid copolymer, and heating at least
the xim portion to a temperature above ~he softening
point temperature of the thermoplastic sealing material
to seal the thin membrane to the rim portion in liquid-
tight relation.
In a preferred embodiment of the present lnven-
tlon~ the sealing surface of the mouth portion of the
glass container is initially flame treated to oxidize
any and all surface coatings which may exist thexea-t.
Such coatings may be present where the exterior sur-
faces of the container body portion have been treated
with thin films of metal oxide and lubricou~ organic
materials for example. The mouth or rim portion of
the container is next treated with an organo-~unc-tional
silane compound applied over the heated rim sl~rface
in a fully annular pattern and then treated with a
second coating of an ethylene acrylic acid copolymer
which is applied over the cooled surface in a similar
annular pattern. The silane and copolymer treatmen-ts
are conducted successively in the stated order aEter
which the container is ready to be sealed with a thin
imperorate membrane.
-2
.
The seal is formed, after filling the container
with product, by pressing the thin imperforate membrane
comprising a film layer of thermoplastic ionomer
material such as Surlyn over the sealing surEace and
heating the thermoplastic ionomer material -to form a
strong glass to thermoplastic adhesive bond. The thin
membrane preferably is comprised o an aluminum foil/
thermoplastic film laminate although it may also be
comprised o~ paper~polymer laminate, a polymer sheet
or a laminate of two or more layers of polymers, metal
foil and/or paper. The only requirement is that the
polymeric material of the thermoplastic type face the
annular pattern of the preferred-ethylene acrylic acid
copolymer on the container sealing surface for heat
and pressure sealing compatible with the contained
product.
Thus, a specific ohject of the present invention
is to provlde an improved method of preparing the seal-
ing surace of a glass container to form a more durable
li~uid-tight seal. This may be effected by first heat-
ing the sealing surface such as by flame treatment to
oxidize the material existent thereon, coating the
sealing rim surface with a thin coating of an organo-
functional silane compound, and then applying a second
~5 thin coating of a thermoplastic ~thylene arcylic acid
copolymer. The sealing surface may then be sealed,
after filling the container, using a
-2a-
thin imperforate membrane having a ~hin coating of e~hyl~ne
acryl~c acid ~opolymer over ~t~ sealing ~urfacer the rim portion
of the container being h~ated ~bove the softening point
temperature of the ~atter thermopla3tl~ sealing mateial to
effect the va~uum-tight ~eal. Thus, a durable long-lived liquid~
tight v~cuum seal is achieved by ~he pla~tic to-glas~ bonding.
Preferably, a method of closing a glass container is
employed in which a dual-layer adhesive coating is placed
on the rim of the container and a thin metal foil having a
thermoplastic sealing layer thereon is pressed against th~
container rim employing heat and pressure to efect the
seal.
With regard to the ~ealing of glass containers it i5 known
to use metal foils such a~ aluminum h~ving a thermoplastic
coating thereon and applying same to the containex mouth
employin~ heat and pre~sure. I~ thi~ process the foil is
pressed against the container rim for a sufficient period of
time for the thermoplaskic coating to adhere to the oontainer
rim. Normally either conduction or induction heating is u~ed
for such ~ealing to ~oin the met~l oil to the glass; however~
such ~al~ are only practical for dry Gontents and not liquids
filled by hot-f~ll technigues. Further sealing materials must
be u~ed which are approved ~or such sealing purpose ln con~ac~
with a wide v~riety of ood~tuff~ and bev~rage~, While lt is
known to use a ~ilane material on the glass .rim for ~ealing
purpose~ to a metal foil, ~he adhe~ion a9entB prevlously
dlsclosed are eith~r not approved for food use, or present a
~ti~ky or t~Cky eondltion not readily storabl~ ~lthout ~pecial
care, or requirlng an undue t~me del~y for ag~ng beore
acceptable sealing. 5uch u3e of a silhne i6 broadly dl~closed
in Wes~ German Pa ent Document P 28 33 334.~23 publi~hed ~une
~ 15~15
23, 1979 to Gerre~heimer Glas A~Go
~rie~ cri~tion of the ~rawin~
Figure 1 is an exploded view of the metal foil/thermoplastic
film membrane and snap cap for sealing a glas~ container~
Figure 2 is a fragmentary ver~ical sectional ~iew of the
upper portion of a glass container illustrating the metal
oil~thermoplastic film membrane seale~ ~o the sealing surface
of the container with the snap cap in place.
This invention relates to the preparation of a ylass
container for use with a seal of the membrane-closure type
which is liquid-tight to erve as a replacement for the
conventional ~crew cap clo~ure for glass containersO A thin
strong membrane preferably consisting of a metal foil laminate
having a layer of thermoplas~ic polymex thereon i5 heat seal2d
to the sealing surface at the mo~th of the glass container.
Heat sealing is normally accomplished ater filling the
container by forcing the thin membrane against the glass sealing
surface or lip area at a temperature slightly above the
~o ~oftening point temperature of the thermoplastic material but
pr~erably b~low the melting point temperature. Either
conduction or induction heating may be employed to at~ain such
heat sealing u~ually within a ~hort period of time where a
heated platen is u~ed~ After effecting the final seal ~he
m~mbrane can be covered by a plastic snap cap for protective and
r~sealing purposesO
It has been found that in many common types of such sealing,
problems of ~eaka~e can occur e~p2cially ir ~he p~ckaging of hot~
fill and acldic type products partieularly s~ored in high
humidity condition~. Many dif erent types of coating materials
have been em~loyed ~o attempt to eliminate these problems
15515
however r vir~ually all have been unsuccessful until the advent
of the present proces~. Also various processes of treating the
glass surfaces using sulfur oxides or decomposable fluorine
compounds have been tried as disc~o ed in U.S. Patents 3,249,246
and 4,260,438. All of these method w~re directed at improving
the sealing surface of glass containers using fluorine or sulfur
oxide treatments to improve the strength and stability of the
glass to polymer bonding. All re~uire extensive processing
steps and exp~rience at least some leakage in providing liquid-
tight long-term seals.
In accordance with the present invention a vacuum and liquid-
tight seal capable of lsng-lasting storage can be provided to
the mouth portion of a glass bottle or jar using a thin sealing
membrane. The ~eal is formed by initial oxidizing treatment of
the gla~s sealing surface to oxidize or remove any exi~tent
materials thereon. Glass containers which have been surface
treated over the exterior surfaces of their body portion with
combinations of thin transparent coatings are 50 subjected to
oxidizing conditionq. Frequently such containers are previously
surface treated with combinations of tin or titanium oxides
applied in the form of so-called hot-end treatments while the .
containers possess considerable heat of formation, and
polyethylene, oleic acid or other organic coating materials
applied in the form of ~o-called cold~end treatments. The
containers, preferably wide mou h bott~es and ~ars, are
conducted under a lineal eries of ribbon-type gas ~urner~ which
produce an oxy~en rich gas flame to oxidize or burn off the
organic constituent~ of the afore~aid ~reatments on the upper
lip or so-called fi~i~h portion of the contain@rs thus making
them water receptiqe or e~sentially hydrophilic at ~uch area.
The con~aineEs are heated to a ~empera~ure of up to about
~ 9 L~ 15515
180F,, at the finish portion during ~his phase of the process
to accelerate the sxidation and hasten the drying of subsequent
coatings to be immediately applied. The gla55 containers may
have a finish area desi~ned wi~h a flat or crowned sealing
surface adapted to accep~ a hea~ sealO The flame treatment of
the finish area serves to modify and partially remove the
~urace treatment in that area.
The heated containers then pass under an overhead roller
coating device consi~ting of a cylindrical rubber or other
resilient material roller which is able to forc2fully contact
the container lip portion during its passage therebeneath. The
roller is mounted transversely of the direction of container
travel and i.~ a~apte~ to apply about a Ool to 2 percent -~olution
b~ wei~ht of an organo-functional silane compound in deionized
water. Two such rollers are used mounted in adjacent relation
over the container path. The containers are rotated through 90
degrees bet~een each application. Two applications are used ~o
ensure complete and thorough coverage of the l.ip area especially
in cases where the lip is not truly planar but possessive of
minor dips or valleys. The dual application is pre~erred
although a single application may suffice upon proper selection
of roller facing material and certain types of container
finishes.
A preferred ~ilane compound i5 Union-Carbide organo-
functional Sil~ne A-1120, N(beta-aminoethyl) ga~ma amino propyl-
trimethoxysilane, which is a diamino-functional ~ilane coupling
agent used over a broad range of adhesive application~O It is
manufactured and sold by Union-Carbide Corporation7 Silicone
Divi~ion, Danburys Connecticuk~ This product is solubl~ in
ethanol, methanol, benz~ne toluene, methyl oello~olve~ and in
water when hydrolysis oecur~. It i~ us~d as adhesion promoter
~ 15515
in cer~ain plastisol sealants and as an addi~ive to phenolic
binders and molding compounds. It is a straw-colored li~u.id
having a specific graYity of 1O03 (25/25C) t a refractive index
of 1.448 (nD25C1 and a flash point o~ 280F. The produc~ is
dissolved in deionized water to give a one-percent solution,
which is then delivered to the roll coa~ers. The silane
coupling agent is applied as a ~hin film over the lip sealing
surface, ~nion-Carbide A-1120 being preferred, although products
A-llO0 and A-174 are al o suitakle silanes for this purpose.
The containers are then force coole~ and dried at a
temperature of about 100~, and no~ in excess of abou~ 140F.
The initially-coated silane-bearing containers are then passed
under a second pair of overhe~d roller coaters which apply a
coating of bonding ayent over the ~ilane coating.
As in the ca~e of the application of the sil~ne the
containers are successively passed beneath the pair of roll
coaters mounted in tandem in close proximity. The containers
are again rotated 90 degrees between each application to ensure
that the bonding agent fully covers the first silane coating and
does not miss a low spot on the container lip area. The bonding
or adhe~ive agent preferably consists of an ethylene acryllc
acid copolymer in the form of a water emulsion. A Dow EAA
dispersion which is called Polyethylene No, 483 made and sold by
Dow Chemical CGmpany, Midland, Michigan, has most desirable
25 property pr~f iles . This ~AA coating combines the stren~th and
~bemical resistance of polyethylene and the high degree of
adhesion and fun~tionality of free carboxylic acid groups. The
dispersion offers ex~eptional performance advantages in priming
and laminating operation~. The EAA material as applied
comprises about a 25% by weight solids ~i~persion in water.
The material bonds and ~eals at relative1y low temperature~ and
15515
proYides flexible coatings high in tensile strength, clarity and
glo~s. The coating provides ~xcellent wa~er resistance and
outstanding adhes~on to me~al foil, paper, nylon and
polyethyleneO ~he material al~o complies with FDA regulations
for paperboard coatin~s and adhesives. In aadi~ion, the
material is an inherent fllm former requiring no supplemental
heating other than'that required ~o dry the applied coatings.
As stated, the heat-softenable Dow EAA product ~ethylene acrylic
acid) ethylene copolymer i~ applied as a sec~nd thin film over
the silane treated finish. Dow Polye~hylene 483 and similar
products are suitable adhesive materials~
The silane coating is ex~remely thin being applied from a
dilute ~queous dispersion. The second coating of EAA
dispersion is thicker having a thickne~s ranging from about 2 to
20 microns, although a narrower intermediate range of thickness
of about 5 to ll microns is preferred. The dual coating is
fully contiguous with and uninterrupted over ~he annular lip
area.
In addition to the use of the EAA dilute disper~ions as the
bonding agent/ a hot melt material ~uch as Product No. 3746 made
and sold by 3M Company, St. Paul, Minnesota may be similarly
employed as a coating over the silane material. While the EAA
material is pref~rred the hot melt material can be used as an
alteEnative ~o provide comparable results.
Th~ particular bonding agent may require a orced drying and
a cooling step before the container~ can be palletized or placed
in a carton for ~hipment. ~he u~e of a hot mel~ ive would
not re~uire a drying step as ~ay be ~he case with ~AA
di~persions.
The coated containers bearing the fir~t and seeond coa~ings
over their lip regions are then transported to the product
~8--
~ 15515
filling line for subsequent proce sins. The coated finish area
of the con~ainers do not require ~ny special handling or
protective covering techniques~ and may be stacked as
necessary or desired in conve~ional processing~
Either cold or hot filling ~echniques may be u~ed to fill
the containers with product. Al~o products which are
considered somewhat difficul~ to pack with liquid-tight seals
such as citric juices can be packed with the present proce~s
providing long~lasting storage life.
The containers are filled with the selected product which
may be at an elevated temperature ranging from about 190 to
210F., for example. A preshaped Surlyn-coated aluminum foil
laminated lid is preferably use~ to ~eal the containers. The
lid has a recessed central panel comparable in diameter to the
container mouth diameter, and a thermopla~tic 6ealing material
such as a Surlyn ionomer resin over i~s sealing surface.
The Surlyn material is preferably a duPont Surlyn Grade No.
1652 of the zinc type having a melt index of 5.0 and an
extru~ion melt temperature of 310C. (590F) which can be
applied to a paper or foil substrate. While there are many
varieties of Surlyn formulations, ~ubstrate adhesion is the key
factor governing the choice of Surlyn ionomer resin grade. All
of the zinc type ionomers show ~cellent aged adhesion to
unprimed foil as well a~ paper ~ubstrates. All grades of Surlyn
lonomer re~in are based on either zinc or sodium ionsO The zine
ionomers are most de~irable where products high in water or
alcohol content are to be packaged~ The ~odium ionomers
generally have a higher moisture content than zinc resins and
can exhibit a hazy film appearance on extended exposure to
water. All grades of Surlyn ionomer re~in have superior oil
resistance in eomparison to polyethylene and other common olefin
~ 34 15515
copolymersl 5urlyn Grade No. 1652 has good oil resistance and
excellent toughness and abrasion resistance for packaging many
types of aggressive productsO
The overall heat ~ealing properties of Surlyn ionomer resins
are outs~an~ing and are generally characterized by low
temperature sealability, high mel~ s~rength and ability to seal
through contamination, broad sealing range, and high seal
strength. Ionomers provide greater fusion seal strength than
most polyolefin materials. The Surlyn Grade No. 1652 provides a
Vicat so~tening point of 80C (176F) which is one measure of
low temperature sealability. This resin has a heat-~eal
interface temperature of 132C. (269F) and a melt viscosity at
shear rate of 0.1 sec ~1 of 10 lb. - sec/sq.in. Grade 1652 has
a low viscosity value and thus a high flow to assist
sealing through liquid-type contamination. As stated, the zinc
iono~ers provide higher seal strength at lower seal temperatures
than the sodium re~in~.
Surlyn Grade No. 1652 i~ an extrudable ionomer resin which
i~ a metal salt of an ethylene/or~anic acid copolymer of the
xinc type available in pellet form for use in conventional
extrusion equipment de~igned to process polyethylene resins.
5urlyn ionomer resins are approved under FDA regulations for use
in packaging food~ subjec~ to extraction ~pecifications on the
~inished food~contact article. While ~he Surlyn ~r~de No. 16S2
is preferred~ Grade ~aOs. 1702 and 1705 which are ionomer resins
for flexible packaging may ~l~o be used in the present
inventlon O
The aluminum foil/thermoplastic ionomer resin laminate is
employed to seal the container mouth using conduction or
induction heating to ~often the Surlyn ionomer resin sealing
layer and the bondin9 a9ent on the lip area so that ~hey f~se
--10--
15515
together in a Fusion type reaction. Sealing ~emperatures are
effected in the range of about 330 to 420F. using heat and
pressure on the lid lip area. A heated platen may be used ~o
apply uniform top pressure of a~out 40 to 90 psi gauge to the
~lexible coated oil lid during the fu~ion cycle for a brief
period of abou~ 1/2 to 1 1/2 second. The foil lid is preshaped
with a central recess to assist in aligning the lid and to
reduce stress on the bond as the seal and the contained product
cools in the case of hot packingn The top pressure can be
created by a capping machine supplying a combination of both
heat a~d pressure. Following sealing of th2 lid to the
container, the containers are cooled to ambient temperature
desirably using a cooling tunnel which sprays progressively
cooler w~ter onto the cor.tainers. The cool containers may then
be checked for any leakage and labeled as desired.
An aluminum foil lid, or a lid of other flexible material
with ~uitable barrier prop~rties such as Mylar film, coated on
the side contacting the treated finish area with a heat
sealable material~ maybe usea as the closure. A thin alumimum
foil, coated on one ~ide with one of the Surlyn materials
supplîed by duPont, is most desirable for the lidding
material. Preferably the foil ha~ a 1 1/2 ~o 2 1/2 mil
thickness. The foil can be also coated with an ~A bonding agent
~uch ~ the Polyethylene No. 483 applied OVeE the glass finish
as an exterior coating, providing two similar materials for
fusion bonding. The ~ubject ~ethod of sealing provides a
practical heat-sea~able clo~ure for glass container~ for use
with high moisture containing product5~ e~pe~ially product5
which are hGt-filled ~uch as citric fruits and juices.
Figure 1 illu6trate~ the var~ous components of the glas~
container sealing construction in disa5sembled relationO Figure
15515
2 illustrates the compone~ts o the ~ealed container . The f irst
layer or film 1 of silane compound is adhered to the lip area of
the glass container G . The second layer or f ilm 2 of EA~
di~persion is deposited over ~che f irs~ layer ~ Metal foil
membrane 3 has a Surlyn ionomer layer or film 4 which is fusion
sealed to film 2. The me~al oil may have a paper or other
coating 5 adhered to its exterior surface. The snap cap 6 may
be optionally used to cover the foil seal.
Samples of ~he sealed containers have been tested under
vacuum and been found to withstand more than 25 1/2 inches of
mercury vacuum without leakage. Such samples w~re sealed using
the aforesaid preferred sealing constituents as thin coatings
intermediate the glass finish and an aluminum foil lid. As
desired, the sealed container~ can be covered with a
thermoplastic snap cap, such as those commonly made of
polyethylene, which serves to protect the foil closure from
puncture or damage and to permit resealing of the container.
Extensive sealing test5 have been made usiny wide mouth
glass jars comprised of soda--lime-silica glass as ~he
containers. Pint jars havin9 16 ounce capacity and a rounded
crown~type lip ar~a were coa~ed s~ith the silane and EAA
dispersion coatingæ. The jars were first treated over the lip
area with the 1% A-1120 silane and then with the ~AA coating
having a 75 melt index . The jars were 'chen sealed using a 2 . 5
~11 Surlyn coated aluminum foil made by RJR Archer Company,
Winston-Salem, NC. The seals were made using a h~ate~ pla~en-
head capping apparatu~ at about 400F over ~ period of about 1.2
seconds and at 85 p~ig pre~6ureO As stated, the ~ealing
pressure can be varied from abouî 4Q to 90 psig.
Twelve of twelve jars which had been previou~ly filled with
210F. water passed test~ of 7 inches of mercury vacuum plus
~12-
15~15
26 1/2 in~he~ of mercury vacuum ~lthout leaksO Such te~ts were
conducted per iodically and successively and no leakage of the
containers was obser1lred over a sub~antial period of time.
El~ven of twelve jar~ which had beerl filled with 210F.
orange juice passed the 7 inche~ of mercury vacuum plus the 26
1/2 inches of mercury vacuum tests. One jar pas~ed the 7 inches
of mercury vacuum te~t but failed the 26 1/~ inches of mercury
vaouum test when leakage was obaerved.
Further, twenty-one of t~7enty-one samples of illed and
sealed glass jar~ coa~ed over ~heir lip area with silane and EAA
Product No. 483 having a 300 melt index which had been
previously filled with 190''F. water were stored 169 days
inverted in beakers in a 10ûF. room without leakage. Also no
leaks were observed af ter 7 inches of mercury vacuum was
applied.
The following water absorption results were obtained on
several adhesive materials which have been considered for glass
container sealing.
Glass slides were taken as the ~ub~trate for depositing
the adhesives and measuring their watee absorptlon. The two
materials compared were ethylene acrylic acid copolymer (EEA)
and polyvinyl butyral ~opolymer (PVB), the former being the
preferred ma~erial of ~his inven~ion.
Weight Gain
Condition Materia~ Wt
(1) Slides above water EAA 0.01
- 2 days ;~t 100F. PVB 0.6
~) Slides i~nmersed ir: EAA -0O4
deionized water PVB 6 . 3*
- 2 days at 10ûF.
* (PVB range 3~ to 8.3)
( 3 ) 51ide~ above wa~er El~ 0 . 5
- 2 days at 31;F. PVB 1.1
~].3--
15S15
~3~9~894~
Thus, very little water absorption by EAA
coatings was obs rved.
In another experiment, coa~ed slides were immersed in
denatured alcohol for 1 day a~ 100F. The PVB coa~ing was
completely dis~olved and the EAA coa~ing was softened~
The sealed foil closure may have a pull tab at one
peripheral region of its edge to acilita~e opening of the
container. Normally the closure can be fully or partially
removed by upward angular tensive force applied to the closure.
Various modifications may be resorted to wi~hin ~he spirit
and scope of the appended claims.
-14-
