Note: Descriptions are shown in the official language in which they were submitted.
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Preform ~or Blow Molding Spherical Contalners
Field oE Invention
This inventlon relates to injection ~olded, test tube shaped,
thermoplastic pol~ner preEorms useful in the blow molding of plastic
containers. Additionally, this invention relates to a method of blow
molding containers uslng a preform adapted to produce spherical containers
particularly useful for holding beverageR such as carbonated soft drinks
or beer.
Background
Blow molded plastic contalners (e.~. bottles) for holding food
and beverages are well known in the art. Generally such contalners have
a cylindrical body, however, in some cases they have a rectangular body.
Thcse containers are required to have VariOUS properties suitable to
their commercial use for packaging ~arious materials including foods and
beverages. Among such properties impact resistance, creep resistance and
the resistance to the passage of various substances (e.g. water, carbon
dioxide and oxygen) through the walls of the container (i.e. barrier
properties) are of particular importance. To achieve such properties it
is required not only to choose the appropriate plastic for making the
container but lt is important to achieve the neeessary cross sectional
structure, configuration and uniEormity from container to container.
Poor impact resistance renders the container susceptible to fracture
failure when dropped. Poor creep re~istance causes the container to
change shape with time and may even cause the container to be unable to
stand upright. Poor barrier propertles result in the loss of essential
cornponellts from the contents of the container or allows the penetration
of sul~taslces (e.g. oxygen) into tlle contailler with ~he su~sc~ ent
deterloration oE the containerts corltents. ~lolecular orientation of the
plas~ic forming the container, in particular uniaxial and biaxial orlen ~tion
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of the plastic-formin~ the walls of the container is known to significantly
impro~e the barrier properties, impact resistance and creep resistance
of these containers. Such orientation is achleved by stretching the
plastic during the formation (i.e. blow molding) of the container.
Blow molded uniaxially or biaxially oriented containers are
generally made from plastic preforms. These preforms are usually prepared
from thermoplastlc pol~ners by various techniques including for example
by injection molding and by the thermoshaping (i.e. heating in a mold)
of an extruded tube. Quite often the preforms wlll have a test t~lbe
shape (i.e. an elon~ated tubular or cylindrical shape open at one end
and closed at the other end), although other shapes are also known and
usedO
In known method~ for making blow molded containers there may
be used a reheated previously molded preform. The heated preform, at
the appropriate temperature is inserted into a mold, the mold halves
closed around the body of the preform and blowing fluid (e.g. air)
introduced into the preform to expand it against the cavity walls of the
mold. The cooled blow molded container is then removed from the mold.
The blow molding of con~ercially acceptable containers (i.e.
containers having the required shape and properties with respect to the
intended end use) is, once the polymeric material is selected, a function
of various factors. For example factors such as temperat~re9 blow rate
and blow pressure have to be considered. Along with these factors
consideration is to be given to the degree of extension of the preform,
the amount of orientation achieved in the plastic, the shape of the
container and the distribution of material in the container walls. Poor
or impropèr distribution of plastic material in the container walls n~ay
lead to weak spots in the container, an improperly shaped container and
premature failure of the container. Too l~ttle or too much orientation
may result in reduced barrier properties, impact resistance and creep
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re6istance. Most, if not all, of these Iactors ma~y be tr aceable back
to tlle preform as tlle source of contr ol. Thus appropriate preiorm
coilstruction and configuration is necessary and important to achieve
Lhe desired blow molded container.
Sumnlary of lnventiorl
There has now been discovered a thermoplastic polymer
pr erorm having a cor~iguration and cross section particularly adapted
to the ~low molding of a spherical container Ior packaging beverages,
more especially l~eer.
It is, therelore, an object of this invention to provide
an injection molded, thernloplastic polymer, essentially test tube shaped
preforrrl .
It is another object of this invention to provide an
injectioll molded, thermoplastic polyrrler, essentially test tube shaped
preform for blow rnolding a spherical container.
These and other objects, as will be apparent to one
skilled in the art from the following description, are achieved by an
injection molded, essentially test tube shaped, polyethylene
terephthalate preform for blow molding a spherical container, said
preform having an open end and a curved closed end and comprising a
neck portion at said open end, l~aving a continuous flange for positioning
said preform in a mold for blow molding the container and having an
acljoining elongated, cylindrical body portion containing said closed end
wherein the body portion comprises a) a tapered wall section adjoining
sclid neck portion and tapering toward and abutting said flange, said
tapered wall section constituting a minor segment of the length of the
overall body portion, b) adjoining the tapered wall section (a) a
sul~stanlicllly constant thickness wall section and c) a curved closed end
~`OIItainillg 'I ('Ul'V((] tapere(l wall sectioll joining the constant thickness
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wall section (b) to a curve(l substantillly conslanl lhickness closed
secliorl, said (~urved substarltially constant thiclu~ess elosed section
havitlg a thickncss less thall the thickness of the constant thiekness
wall section (b), but at least one halt the thickness of the constant
tllickness wall seclion (b), said curved closed end having at its bottorn
a flat spot approximately 1/~ lo 1/4 inch in diameter.
Brief Description of Drawings
In the following description of this invention referenee
will be made lo the accompanying drawings wherein:
Figure 1 is a front view, partly in seetion, of a preform
aceording to this invelltion;
I~'igure 2 is a front view, partly in section, of a spherieal
container obtained from a preform aceording to this invention, shown in
phantom in the intel ior of the spherical container.
Description of the Invention
There is now provided in aeeordanee with an aspeet of
this invention an injeetion molded, essentially test tube shaped,
thernloplastic molecularly orientable polymer preform for blow molding
a spherical container, said preform having an open end and a eurved
closed end and eomprising a neek portion, at said open end, having a
locating means for positioning said preform in a mold for blow molding
the container and an adjoining elongated eylindrical body portion
containing saicl closed end wherein the body portion eomprises a) a
tal)ered wall section adjoining said neek portion, b) adjoining the tapered
wall section (a) a substantially constant thickness wall seetion and e) a
curvecl closed end containing a curved tapered wall seetion joining the
constant thiclilless wall section (b) to a curved substantially constant
~hi(kl-less closed section, said curved substantially constant thickness
k)sed section having a thickness less than the thiclcness of the
ol~sLant thic~klless ~ all sectioll (b) but
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at least one half the thic~ness of thè constant thickncss wall sectlon
(b). Additionally, there is provided in accordance with this invention
a method for blow molding a spherical container comprising the steps of
I) positioning a heated preform according to the afore description in an
open mold having a spherical cavity9 II~ closing ~he mold, III) lntroducing
a blowing fluid into the lnterior of said preform, IV) expanding said
preform to and against the walls of said savity, V) opening said mold
and VI) removing the blown container from the mold.
In a particular aspect there i~ provided in accordance with
this invention an injection molded, essent-lally test tube shaped, polyethylene
terephthalate preform according to the above description and the method,
as described above, of blow molding a polyethylene terephthalate spherical
container. A further aspect of this invention provides the preform in
accordance with the above description wherein the tapered wall section
(a) adioining the neck portion of ~he preform tapers toward (i.e. narrows
toward) and abuts the locating means of the neck portion of the preform.
This aspect is particularly applicable to the afore described polyethylene
terephthate preform of this invention. ~s a still further aspèct of
this invention there i6 provided a preform according to the above description
wherein the thermoplastic polymer is a stretch orientable thermoplastic
polymer more particularly a blow stretch biaxially orientable thermoplastic
polymer. Another aspect of this lnvention provides a preform according
to the above description wherein the tapered wall section (a~ adjoining
the neck portion is a minor segment of the wall length of the body
portion of the preform. In a even further aspect of this invention
there is provided a preform according to the above description wherein
the locating means is a segmented or a continuous r;ng or Elange~ more
particularly a contilluous ring or flange.
The injection molding of the preform according to this invention
often produces a gate pro~ection (15 of Fig. 2~ at the bottom of the
curved closed end of the preform. Such a gate projection when removed
from the preform for subscqucnt blow molding operations may create a
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small flat spot at the bottom of the closed end of the preform. Therefore,
an aspect of the preform accordin~ to ~his inventlon includes ~he afore
described preform wherein the curved closed end contains a small, for
example about 1/~ to 1j4 inch diameter, flat spot at ~he bottom of the
curved closed end.
The neck portion of the prefo~m of this invention may be
conventional in configura~ion and cross section e~cept that in accordance
w$th this invention there iR required that the neck portlon contai~ a
locating means. Such locatlng means serves to position the preform in
the blow mold for blow molding the spherical container. This neck portion
remains substantially unchanged in configuration during the blowing of
the preform to form the spherical shaped container and forms the neck of
the container which engages a closure for retaining the contents of the
container. The body portion of the preform of this invention, containing
the closed end~ i6 the portion of the preform that exapands in the mold
to form the spherical shaped container.
By virtue of its shape the blow molding of a spherical container
is markedly different from the blow molding of a conventional bottle
and, therefore, re~uires special considerations in the cross sectional
structure and configuration of the preform for producing the spherical
container as compaLed to a preform for producing a bottle. Generally
bottles taught in the prior art have a cylindrical shape and in that
respect bear some resemblence to many of the prior art preforms that are
used to produce them. However; the preform of this invention bears very
llttle geometric resemblence to the spherical container ~hich is produced
therefrom. Because of many self-evident geometric distinctions between
bottles taught in the prior ar; and the spherical container produced in
accordance with this invention there is established the need for a
preform not only to produce a sp~lerical contain~r, but also to produce a
plleriCal CODtaiOe~ h~ving a unilo~ all structure (e. g. thickn2ss~ an~
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provide molecular orlentation in the contalner wall needed to obtain
commercially acceptable physical properties ~e.g. impact strength,
tensile strength and barrier properties). The preform of this invention
has the configuration to meet those needs (i.e. to produce a spherical
container having commercially acceptable structure and properties).
The preform according to this invention and described herein
is made by the in~ection molding method commonly known in the art for
molding thermoplastic articles.
In the practice of this invention the preform disclosed herein
i5 especially useful for making a hollow spherical container. Such
container is useful for packaging beverages, such as for example beer.
A variety of thermoplastic polymers may be used for the practice
of the preform and method of thls lnvention. Such thermoplastic polymers
include, but are not limited to, for example, homopolymers and copolymers
of vinyl monomers (e.g. polyvinyl chloride, polyvinylidene chloride,
vinyl chloride/vinyl acetate copolymer and ethylene/vinyl chloride
copolymer)~ homopolymers and copolymers of acrylonitrile (e.g. polyacrylonltril
and acrylonitrile/styrene copolymer), homopolymers and copolymers of
mono~olefin monomers (e.g. polyethylene, polypropylene, ethylene/vinyl
acetate copolymer and ethylene/propylene copolymer), linear thermoplastic
satllrated polyesters (e.g. polyethylene terephthalate and polybutylene
terephthalate),homopolymers and copolymers of acrylic acid esters or
lower alkyl substituted acrylic acid esters (e.g. polymethyl acrylate
and polymethyl methacrylate), polystyrene and polycarbonate. Physical
mix~ureff of thermoplastic polymers may also be used. In the practice of
the preform and method of this lnvention there is preferably used a
stretch orientable thermoplastic polymer, more preferably a thermoplastic
linear saturated polyester and most preferably polyethylene terephthalate.
There also is conte~plated in the practice of this invention a
preforin, as disclosed herein, and the metllod of making a spherical
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conta~ner wherein the preform has à barrier coating on the outside
surface or the ins-lde surface or both the outside surface and inside
surface thereof. Further, there is contemplated in the practice of this
invention a preform, as disclosed herein, and the method of making a
spherical container wherein the preform is a multi-layer wall preform
having two or ~ore layers of different the~oplastic polymers forming
the walls of ~he prefor~ and spherlcal container.
Thi8 invention is further described with reference to the non-
li~iting figures 1 and 2.
In Fig. l iB shown a preform 3, according to this invention
for producing a spherical container as shown in Fig. 2, having a neck
portion 4 with ring locating means 7 and a body portion 5 containing a
curved closed end section 6. The body portion 5 comprise~ a tapered
wall section 8 tapered toward and abutting the ring locating means 7
from the axially straight, substantially constant thickness wall section
9 The substantially constant thickness wall section 9 in turn joins and
leads into the curved, tapered wall section lO tapering toward and
blending into the curvedJ substantially constant thickness closed end
wall section 11. Curved substantially constant thickness, closed end
wall section ll has a thickness less than the thickness of the constant
thickness wall section 9 but at least one half the thickness of the
constant thickness wall section 9. Ring locating means 7 of neck portion
4 is used to position preform 3 in the spherical cavity of a blow mold
for blowing a spherical container shown in Fig. 2. Tapered wall sections
8 and lO in combination with the axially straight substantially constant
thic~ness wall section 9 and the curved substantially constant thickness
closed end~sectlon 11 provide the configuration in preform 3 for producing
a uniform spherical wall 17 in spherical container 13 of Fig. 2. The
neck port on 14 of the spherical container 13 of Fig. Z is substantially
the same as the neck portion 4 of prefon~ 3 of Fig. l. ~ase 16 of
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spherical container 13 i8 C0}2figUred ~0 allow container 13 to stand
unsupported on a flat surface. In Fig. 2 a preform according to this
invention for producing spherical container 13 is shown in phantom in the
interior of the container to depict a b~fore and after condition (i.e.
the condition prior to and after the blow molding operation)
In the preferred practice of this invention the preform as
disclosed herein is a stretch orientable thermoplastic polymer preform
more preferably a polyethylene terephthalate preform.
There ls ~ow provided i~ accordance with this invention a
Method Eor producing a spherical container`comprising the steps of I)
positioning a heated preform in an open blow mold having a spherical
cavity, II) clo.slng the blow mold around the body of the preform, III)
introducing a blowing fluid lnto the inside of the preform, IV) expanding
the body of the preform to and against the walls of the cavity, V)
op~ning the mold and VI) removing the spherical container from tle mold,
wherein said preform is an injection molded, essentially test tube
shaped, thermoplastic poly~ler preform having an open end and a curved
closed end and comprising a nec~ portion, at said open end, having a
locating means for positioning said preform in the mold and an adjoining
elongated cylindrical body portion containing said closed end wherein
the body portion comprises a) a tapered wall section adjoining said neck
portlon, b) adjoining the tapered wall section ta) a substantially
constant thickness wall section and c) a curved closed end containing a
curved tapered wall section ~oining the constant thickness wall section
(b) to a curved constant thickness wall closed section, said curved
constant thickness wall closed section having a thickness less than the
thickness of the constant thickness wall scction (b) but at least one
half the thickness of the constant thickness wall section (b).
In the practice of the mcthod of this invention tlle hcated
preform may be a heate~ preform resulting from a heating step wherein a
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cold previously inJection rnolded preform is heated to a predetermined
(i.e. desired~ temperature or temper~ture profile ~i.e. speclfic varlatlon
of temperatures over the configuration of the preform). Durlng the
heating of the preform the neck portion thereof is maintained at a
temperature substantially below the softening or glass transition temperature
of the thermoplastic polymer, preferably below 150F. The positioning
step of the afore described process may be accomplished by well known
methods such as, for example, by the use of a collar that grasps the
exterior neck of the preform and may become part of the blow ~old or a
mandrel which grasps the interior of the neck of the preform. Preferably
the positioning step is accomplished by a metllod us;ng a collar to ~rasp
the exterior of the neck of the preform. There may be used as the
blowing fluid in the practice of the step of lntroducing a blowing fluid
into the preform, a liquid or a gas. Preferably there is used a gas,
more preferably air, as the blowing fluid.
Various thermoplastic polymer~ usable in the practice of the
afore described method of this invention include, for example, those
thermoplastic polymers exemplified herein with respect to the preform of
this invention. Preferably the thennoplastic polymers used in the
practice of the method of this invention are molecularly orientable
thermoplastic polymers9 more preEerably a polyethylene terephthalate
polymer.
In the preferred practice of the method of this invention a
heated polyethylene terephthalate preform having a temperature profile
is positioned in the biow mold, the mold closed, air under pressure
introduced into the ;nside of the preform, the preform expanded to and
against the cavity walls of the blow mold, the mold opcned and the
spherical container removed. rne spherical container produced by the
~netllod of this invention is useful for the packaging of bevera~es,
partic~larly beer.
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As used in this di6closure the phrase spherical container
denotes a container having substantially a ball shape.
While this invent~on has been described above with rPspect to
various embodiments, which are intended to be non-limiting, it is recognized
that those skill~d in the art may practice further embodlments of this
invention wlthout departing from the splrlt and scope of the inventlon
as set forth and claimed herein.
