U.S. patent application number 12/575711 was filed with the patent office on 2010-04-15 for mold and method for manufacturing two-layered preforms by injection overmolding, and two-layered preform.
This patent application is currently assigned to MOLMASA APLICACIONES TECNICAS, S.L.. Invention is credited to Angel ATANCE ORDEN, Alain VIRON.
Application Number | 20100092711 12/575711 |
Document ID | / |
Family ID | 39863293 |
Filed Date | 2010-04-15 |
United States Patent
Application |
20100092711 |
Kind Code |
A1 |
ATANCE ORDEN; Angel ; et
al. |
April 15, 2010 |
MOLD AND METHOD FOR MANUFACTURING TWO-LAYERED PREFORMS BY INJECTION
OVERMOLDING, AND TWO-LAYERED PREFORM
Abstract
The mold includes a first molding cavity connected to a first
hot channel for supplying a primary molding material, a second
overmolding cavity connected to a second hot channel for supplying
an overmolding material; and a core configured to be first
introduced in the first cavity for a molding operation of a first
layer, and to then be introduced, with the first layer thereon, in
the second cavity for an overmolding operation of a second layer.
At least one supporting member is arranged to support the core with
respect to the first cavity during the entire molding operation of
the first layer. An opening left in the first layer by the
supporting member is filled and/or covered by the second layer.
Inventors: |
ATANCE ORDEN; Angel;
(Montcada I Reixac, ES) ; VIRON; Alain; (Desmont,
FR) |
Correspondence
Address: |
RATNERPRESTIA
P.O. BOX 980
VALLEY FORGE
PA
19482
US
|
Assignee: |
MOLMASA APLICACIONES TECNICAS,
S.L.
Montcada i Reixac
ES
|
Family ID: |
39863293 |
Appl. No.: |
12/575711 |
Filed: |
October 8, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
PCT/ES2008/000226 |
Apr 11, 2008 |
|
|
|
12575711 |
|
|
|
|
Current U.S.
Class: |
428/36.91 ;
264/328.15; 425/112; 425/588 |
Current CPC
Class: |
B29B 2911/14466
20130101; B29B 2911/141 20130101; B29C 49/06 20130101; B29B
2911/1408 20130101; Y10T 428/1352 20150115; B29B 2911/14026
20130101; B29K 2995/003 20130101; B29B 2911/14326 20130101; B29B
2911/14113 20130101; B29C 45/1625 20130101; B29C 45/1684 20130101;
B29B 11/14 20130101; B29B 2911/14486 20130101; B29K 2509/02
20130101; B29K 2105/258 20130101; B29K 2507/04 20130101; B29K
2995/0025 20130101; B29B 2911/1414 20130101; Y10T 428/1393
20150115; B29C 49/221 20130101; B29C 45/1615 20130101; B29B
2911/14086 20130101; B29K 2995/0055 20130101; B29C 45/36 20130101;
B29B 2911/1402 20130101; B29B 2911/144 20130101; B29B 2911/14066
20130101; B29B 2911/14333 20130101; B29K 2023/12 20130101; B29K
2105/253 20130101; B29C 45/2628 20130101; B29B 2911/1444 20130101;
B29B 11/08 20130101; B29K 2067/00 20130101 |
Class at
Publication: |
428/36.91 ;
264/328.15; 425/588 |
International
Class: |
B32B 3/20 20060101
B32B003/20; B29C 45/16 20060101 B29C045/16; B29C 45/12 20060101
B29C045/12 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 11, 2007 |
ES |
PCT/ES2007/000202 |
Claims
1. A method for manufacturing two-layered preforms by injection
overmolding, said two-layered preforms comprising a tubular body
with a mouth providing a neck at a first end and a closed bottom at
an opposite second end, at least part of said tubular body being
formed by a first layer of a primary molding material and a second
layer of an overmolding material, the method comprising the steps
of: first introducing a core in a primary molding cavity connected
to a first hot channel through which a primary molding material is
injected to perform a molding operation of said first layer; then
introducing said core with the first layer formed thereon in an
overmolding cavity connected to a second hot channel through which
an overmolding material is injected to perform an overmolding
operation of a second layer; forming the first layer with the
primary molding material covering a region of the preform including
said closed bottom and excluding said neck of the preform while
supporting a free end of the core with respect to said primary
molding cavity during the entire molding operation of the first
layer by means of at least one supporting member; and forming the
second layer with the overmolding material covering all the first
layer and forming the neck, thus filling and/or covering a
corresponding opening left by said supporting member in the first
layer with the overmolding material of the second layer.
2. The method according to claim 1, further comprising supporting
the core by means of at least one supporting member fixed to the
primary molding cavity and projecting from an inner surface thereof
to make contact with the core.
3. The method according to claim 2, further comprising supporting
the core by means of at least three of said supporting members
arranged in a closed bottom of the primary molding cavity around a
primary molding material injection nozzle.
4. The method according to claim 1, further comprising supporting
the core by means of at least one supporting member fixed to the
core and projecting from an outer surface thereof to make contact
with the primary molding cavity.
5. The method according to claim 4, further comprising forming a
bulge in a region of the second layer to cover the corresponding
opening in the first layer by means of a depression formed in the
overmolding cavity and facing the supporting member of the
core.
6. The method according to claim 5, further comprising supporting
the core by means of at least three of said supporting members
arranged at a free end of the core to be around a primary molding
material injection nozzle in the primary molding cavity, and
forming at least three of said corresponding bulges in the second
layer by means of at least three of said depressions arranged in a
closed bottom of the overmolding cavity around an overmolding
material injection nozzle.
7. The method according to claim 1, further comprising using a
synthetic polymer as common base material for both the first and
second layers, said synthetic polymer being mixed with one or more
coloring agents in each of the first and second layers, and at
least one of said coloring agents being common in both the first
and second layers.
8. The method according to claim 7, wherein said synthetic polymer
is selected from the group consisting of polyethylene terephthalate
(PET), polypropylene (PP), and high density poliethylene (HDPE),
and said coloring agents are selected from the group consisting of
titanium oxide (TiO.sub.2) in solid or liquid form, and carbon
black or activated carbon in solid, powder or liquid form.
9. A mold for manufacturing two-layered preforms by injection
overmolding, said two-layered preforms comprising a tubular body
with a mouth providing a neck at a first end and a closed bottom at
an opposite second end, at least part of said tubular body being
formed by a first layer of a primary molding material and a second
layer of an overmolding material, the mold comprising: a primary
molding cavity connected to a first hot channel for supplying a
primary molding material; an overmolding cavity connected to a
second hot channel for supplying an overmolding material; a core
configured to first be introduced in said primary molding cavity
for a molding operation of a first layer of said primary molding
material, and to then be introduced, with said first layer formed
thereon, in said overmolding cavity for an overmolding operation of
a second layer of said overmolding material; and a pair of neck
half-molds forming at least an external configuration of said neck,
wherein said core has a surface in a region corresponding to said
neck of the two-layered preform configured to make contact with a
corresponding surface of the primary molding cavity to form the
first layer with the primary molding material covering a region of
the preform including said closed bottom and excluding said neck of
the preform, said neck half-molds are associated with said
overmolding cavity to form the neck with the overmolding material
of the second layer not coated by the first layer, at least one
supporting member is arranged between a free end of said core and
the primary molding cavity to support the core in the primary
molding cavity during the entire mentioned molding operation of the
first layer, and said second cavity is configured to make the
overmolding material of the second layer fill and/or cover an
opening left in the region of the closed bottom of the first layer
by said supporting member.
10. The mold according to claim 9, wherein said supporting member
is fixed to the primary molding cavity and projects from an inner
surface thereof to make contact with the core.
11. The mold according to claim 10, wherein at least three of said
supporting members are arranged in a closed bottom of the primary
molding cavity around a primary molding material injection
nozzle.
12. The mold according to claim 9, wherein said supporting member
is fixed to the core and projects from an outer surface thereof to
make contact with an inner surface of the primary molding
cavity.
13. The mold according to claim 12, wherein a depression is formed
in an inner surface of the overmolding cavity facing the supporting
member of the core, said depression being configured to form a
bulge in a region of the second layer which covers the mentioned
opening in the first layer of the two-layered preform.
14. The mold according to claim 13, wherein at least three of said
supporting members are arranged at a free end of the core to make
contact with the primary molding cavity around a primary molding
material injection nozzle, and at least three of said depressions
are correspondingly arranged in a closed bottom of the overmolding
cavity around an overmolding material injection nozzle.
15. A two-layered preform obtained by injection overmolding,
comprising a tubular body with a mouth providing a neck at a first
end and a closed bottom at an opposite second end, at least part of
said tubular body being formed by a first layer of a primary
molding material and a second layer of an overmolding material,
wherein said first layer, or inner layer, is made of a material
providing a barrier effect against light by absorption, said second
layer, or outer layer, is made of a material providing a barrier
effect against light by reflection, and said neck is formed with
said overmolding material of the second layer not coated by the
first layer.
16. The preform according to claim 15, wherein said primary molding
material of the first layer is polyethylene terephthalate (PET),
polypropylene (PP) or high density poliethylene (HDPE) with from
0.01% to 2% by weight of carbon black or activated carbon and from
3% to 10% by weight of active ingredients of titanium oxide
(TiO.sub.2), and the overmolding material of the second layer is
polyethylene terephthalate (PET), polypropylene (PP) or high
density poliethylene (HDPE) with from 3% to 10% by weight of active
ingredients of titanium oxide (TiO.sub.2).
17. The preform according to claim 15, wherein the first layer
includes at least one opening in the region of said closed bottom
of the two-layered preform, and said second layer covers completely
the region of the closed bottom, with said at least one opening
being filled or covered with the overmolding material of the second
layer.
18. The preform according to claim 17, wherein the first layer
comprises three of said openings arranged at angular intervals of
120 degrees around the longitudinal central axis of the two-layered
preform.
19. A two-layered preform obtained by injection overmolding,
wherein said two-layered preform is obtainable by the method of
claim 1.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a Continuation-in-Part (CIP) Application
of PCT International Application No. PCT/ES2008/000226, filed Apr.
11, 2008, which claims benefit of priority from PCT International
Application No. PCT/ES2007/000202, filed Apr. 11, 2007. The
contents of these applications are incorporated herein by
reference.
TECHNICAL FIELD
[0002] The present invention relates to a mold and a method for
manufacturing two-layered preforms by plastic injection
overmolding, including means for stably supporting a mold core
inside a corresponding mold cavity while an injection step for
injecting a plastic material into said cavity is performed. The
present invention also relates to a two-layered preform provided
with an inner layer of a material capable of providing a barrier
effect against light by absorption and an outer layer of a material
capable of providing a barrier effect against light by reflection,
such two-layered preform being applicable, for example, to the
formation of bottles of milk.
BACKGROUND OF THE INVENTION
[0003] The use of preforms for manufacturing bottles and other
containers is well known. These preforms consist of tubular bodies
of plastic material, with a mouth at a first end, a closed bottom
at an opposite second end, and a neck adjacent to the mouth, which
optionally includes an outer thread and a perimetric annular
flange. The preforms are intended for the subsequent manufacture of
plastic bottles by blowing the blind tubular part of the preform
inside a mold without the neck and the mouth being altered.
Two-layered preforms in which at least part of said tubular body is
formed by two superimposed layers having different properties are
increasingly used. These two-layered preforms are especially
designed for packages requiring a layer with barrier property, for
example, barrier against light or against certain gases such as
O.sub.2 and CO.sub.2, packages in which an outer layer can be made
of a recycled plastic material and an inner layer of a quality
plastic material, or packages formed by two layers of plastic
materials of a different color for aesthetic purposes.
[0004] Two-layered preforms can be manufactured by several
techniques, among which injection overmolding is emphasized, which
basically consists of first introducing a core in a primary molding
cavity for molding a first layer of a primary molding material on
the core, and then introducing said core, with said first layer
arranged thereon, in an overmolding cavity for molding a second
layer of an overmolding material on the first layer to produce the
complete two-layered preform. The neck of the two-layered preform
can be formed with the material of the first layer or with the
material of the second layer by closing and opening a pair of neck
half-molds arranged next to the mouth of the primary molding cavity
or of the overmolding cavity, respectively. The molds for producing
two-layered preforms in many injection overmolding apparatuses
comprise multiple primary molding cavities, multiple overinjection
cavities, multiple pairs of neck half-molds and multiple grouped
cores which are operated together by the injection overmolding
apparatus for large productions.
[0005] There are different types of injection overmolding
apparatuses using different mechanisms and methods for performing
the alternate introduction and extraction of the cores from the
primary molding cavities and overinjection cavities, the closing
and opening of the neck half-molds, the ejection of the finished
two-layered preforms, etc. International patent application PCT/ES
2006/000047 describes an example of an apparatus for manufacturing
preforms by injection overmolding using multiple cores to be
alternately introduced in multiple primary molding cavities and
multiple overinjection cavities.
[0006] A common problem in the molds of any type of apparatus for
manufacturing two-layered preforms by injection overmolding is that
the cores, due to their slenderness and to their long cantilevered
portion, can be slightly deformed elastically inside the primary
molding cavities during the injection of the primary molding
material of the first layer due to the differences in the
temperature, and therefore in the fluidity, of the plastic material
injected in an initial phase and in a final phase of the injection
process, and to the random distribution of this material with
different degrees of fluidity inside the empty space defined
between the primary molding cavity and the core.
[0007] The injection nozzle is generally arranged in a closed
bottom of the primary molding cavity facing a free end of the core.
Thus, if the material injected in the initial phase, which is less
hot, and therefore less fluid, due to the time it has been retained
in the injection nozzle and adjacent conduit during the movements
of position change of the cores, is randomly directed towards a
side of the free end of the core, the hotter, and therefore more
fluid material injected next and coming from the hot channel will
flow more easily and quickly towards the opposite side of the core
and towards the area of the mouth of the cavity. The less fluid
material will exert a pressure on a first side of the core greater
than the pressure exerted by the less fluid material on an opposite
second side, and the core will experience a slight elastic
deformation towards this second side.
[0008] Given that the thicknesses of the layers of the two-layered
preform are subject to strict dimensional tolerances, a slight
deformation of the core during the injection operation of the first
layer results in variations in the thickness of both layers in
opposite sides of the two-layered preform which may be
unacceptable, taking into account that the thickness of the layers
is reduced to significantly small values during the subsequent blow
molding process to form the bottle or another container from the
two-layered preform.
[0009] U.S. Pat. No. 3,301,928 proposes supporting the core inside
the molding cavity by means of a supporting appendage extending
from a valve body of an injection valve for injecting molding
material arranged in the closed bottom of the cavity. The valve
body is axially movable in alignment with the axis of the cavity
and the core, and the mentioned supporting appendage has a conical
head which is coupled in a conical recess formed at the end of the
core whereas the valve is open to inject the molding material into
the cavity. During a final phase of the molding operation of the
preform, when a small portion of the cavity still has to be filled,
the valve body is retracted to allow completely filling the cavity
and to then close the passage of molding material into the cavity.
However, this arrangement has several drawbacks. On one hand, the
incorporation of the injection valve arranged in the closed bottom
of the cavity involves a relatively complex construction and
operation, and on the other hand, the fact that the core is no
longer supported during the final phase of the molding operation
does not ensure a perfect alignment of the core in the molding
cavity during the entire injection process of the preform.
[0010] U.S. Pat. No. 4,086,315 discloses an apparatus for producing
hollow plastic bodies by injection molding a preform on a core
introduced in an injection molding cavity and subsequent blowing
said preform inside a blow molding cavity. Supports projecting from
an area of the closed bottom of the injection cavity make contact
with the end of the core to coaxially support it during the entire
injection molding operation. These supports leave holes in the
preform. The injection molding cavity is furthermore configured to
form a protrusion at the axial end of the preform. The core is
extracted from the injection molding cavity and then introduced,
with the recently formed and still hot preform thereon, in the blow
molding cavity for the blow molding operation. In an area of the
bottom of the blow molding cavity there is arranged a cylinder with
an axially operated piston to press said protrusion of the preform
against the end of the core for the purpose of extruding the
material of said protrusion and thus close the holes existing in
the preform before the blow molding. A drawback of this arrangement
is that the incorporation of the cylinder and piston assembly at
the end of the blow molding cavity is complex and expensive.
Furthermore, if, as usual, the preforms are to be allowed to cool
in order to remove them from the core and store them for a
subsequent distribution and use in a plurality of blow molding
apparatuses, this would limit the use of such preforms with holes
to only those blow molding apparatuses which are equipped with the
mentioned cylinder and piston assembly to extrude the protrusion
and close the holes before the blow molding operation. Furthermore,
the apparatus is intended to manufacture monolayer preforms and in
the specification is not described nor suggested the way to use it
to manufacture two-layered preforms.
[0011] International patent application WO 89/07219 A describes a
process for injection molding a thin-walled, hollow plastic
product, wherein a first common mold part is combined with a first
complementary mold part to assemble a first mold cavity. Portions
of the first complementary mold part contact portions of the first
common mold part to rigidly secure mold parts in a position which
impedes movement of the mold parts in relation to each other during
injection of a first plastic material into the first mold cavity.
The first plastic material is shaped such that when it is contained
in a second mold cavity, which is formed by combining the first
common mold part with a second complementary mold part, it provides
stabilizing regions that rigidly secure the mold parts in a
position which impedes movement during injection of a second
plastic material. However, there is not described nor suggested
that the two-layered plastic product obtained by such process is
useful to be subsequently blow molded, and in fact the alternate
arrangement of monolayer regions of different materials in the
hollow plastic product is a serious drawback since the joining
areas therebetween are substantially parallel to the pressure
direction during a blow molding operation and this involves a risk
of said joining areas to be broken.
[0012] Patent EP-A-1681239 describes a multilayer preform obtained
by a sequential co-injection process and having inner and outer
layers made of PET colored with titanium dioxide to reflect light
and a layer made of PET colored with carbon black to absorb light
arranged between said inner and outer layers. A drawback related
with the sequential co-injection process in comparison with the
overmolding process I that the former is not suitable for injecting
only two layers forcing to inject an odd number thereof, in general
three or five. It neither permits to accurately control the extent
of the intermediate layer or layers nor the uniformity in the width
of the layers. A lack of precision in the preform can result in
irregularities in a container obtained by blow molding the preform,
and such irregularities will be the more accentuated the more
thinner are the layers of the preform.
[0013] WO 95/00325 discloses a multi-layer plastic preform for use
in plastic blow molding including an injection molded inner layer
of virgin plastic having an outwardly extending annular flange at
an open end of the preform. An injection molded outer layer of post
consumer recycled plastic covers the inner layer and has a thread
for securing a closure, and this thread is located toward the
closed end of the preform from the annular flange of the inner
layer to thereby provide a construction that allows increased use
of the recycled plastic. The preform may be provided with an
intermediate layer of a gas barrier material when the container to
be blow-molded from the preform is to be used to hold gas
pressurized liquids such as soft drinks. The need of the mentioned
annular flange in the inner layer at an open end of the preform
prevents the possibility of making the neck of the preform only
with the material of the outer layer.
DISCLOSURE OF THE INVENTION
[0014] According to a first aspect, the present invention
contributes to solving the previous and other problems by providing
a mold for manufacturing two-layered preforms by plastic injection
overmolding. The mold comprises a primary molding cavity connected
to a first hot channel for supplying a primary molding material, an
overmolding cavity connected to a second hot channel for supplying
an overmolding material, and a core configured to first be
introduced in said primary molding cavity for a molding operation
of a first layer of said primary molding material, and to then be
introduced, with said first layer arranged thereon, in said
overmolding cavity for an overmolding operation of a second layer
of said overmolding material. The mold of the present invention is
characterized in that it includes at least one supporting member
arranged between a free end of said core and the primary molding
cavity to support the core in the primary molding cavity during the
entire molding operation of the first layer. The mentioned
supporting member is configured to form a corresponding opening in
the first layer to be subsequently filled and/or covered by the
overmolding material of the second layer.
[0015] With this construction, the supporting member, which is at
least one in number, holds and stabilizes the core in a centered
position inside the primary molding cavity and prevents the elastic
deformation of the core during the injection operation of the first
layer, whereby the thickness of the first layer is substantially
uniform around the circumference thereof according to accepted
dimensional manufacturing tolerances. The fact that the first layer
has a uniform thickness contributes to the second layer,
subsequently obtained by injection overmolding in the overmolding
cavity, also being substantially uniform. On the other hand, the
problem of elastic deformation of the core during the overmolding
operation of the second layer is generally less pronounced, and in
many cases the second layer has a greater thickness than the first
layer and/or has a less relevant function, for example, as a
barrier material, whereby a small irregularity in the thickness of
the second layer is less relevant than in the first layer.
[0016] In a first embodiment of the mold, the supporting member is
fixed with respect to the primary molding cavity, whereas in a
second embodiment of the mold, the supporting member is fixed with
respect to the core. In any of the two embodiments of the mold, it
is preferable that three or more of said supporting members are
provided. Three supporting members angularly spaced at 120 degrees
around a longitudinal central axis of the primary molding cavity
and of the core are preferable, since they thus provide an
isostatic support, and it is also preferable that the supporting
members support the core close to the free end thereof.
[0017] Due to the fact that the supporting members are fixed, they
are obviously present during the entire injection operation of the
first layer and therefore they form openings in the material of the
first layer which are filled and/or covered with the material of
the second layer during the injection operation of the second layer
by overmolding. When the supporting members project from the
primary molding cavity, the openings in the first layer are empty
when the core with the first layer is introduced in the overmolding
cavity, and thus the overmolding material of the second layer fills
and at the same time covers the openings of the first layer. When
the supporting members project from the core, the openings in the
first layer are occupied by the supporting members when the core
with the first layer is introduced in the overmolding cavity, such
that the overmolding material of the second layer simply covers the
openings of the first layer without filling them. The overmolding
cavity is preferably configured to form bulges in those regions of
the second layer which cover the openings of the first layer.
[0018] The situation of the openings in the first layer filled
and/or covered by the second layer close to the closed bottom of
the two-layered preform determines that in the bottle or another
container obtained by blow molding from the two-layered preform
these openings are located in the base and very close to the center
of the bottle or another container, which is a place generally not
very exposed, and therefore not very critical. Furthermore, this
final area of the preform is deformed relatively little during the
blow molding process and the openings are stretched relatively
little.
[0019] According to a second aspect, the present invention provides
a method for manufacturing two-layered preforms by plastic
injection overmolding which comprises the steps of first
introducing a core in a primary molding cavity connected to a first
hot channel and supplying a primary molding material to perform a
molding operation of a first layer, and then introducing said core,
with said first layer arranged thereon, in an overmolding cavity
connected to a second hot channel and supplying an overmolding
material to perform an overmolding operation of a second layer. The
method of the present invention is characterized in that it
comprises supporting a free end of the core with respect to said
primary molding cavity during the entire mentioned molding
operation of the first layer by means of at least one supporting
member and filling and/or covering a corresponding opening left by
said supporting member in the first layer with the overmolding
material of the second layer.
[0020] In a first embodiment of the method, the core is supported
by means of one or more fixed supporting members projecting from an
inner surface of the primary molding cavity to make contact with
the core, and openings produced by the supporting members in the
first layer are filled and covered with the overmolding material
during the overmolding operation of the second layer. According to
a second embodiment of the method, the core is supported by means
of one or more fixed supporting members projecting from the core to
make contact with an inner surface of the primary molding cavity,
and openings produced by the supporting members in the first layer
are simply covered with the overmolding material during the
overmolding operation of the second layer. In this case, the method
preferably comprises forming bulges in the regions of the second
layer which cover the openings of the first layer by means of
depressions formed in the inner surface of the overmolding cavity
to provide the two-layered preform with a thickness in the regions
in which the openings of the first layer are located equivalent to
the thickness of the regions with a double layer.
[0021] The mold and/or the method of the first and second
embodiments can be used in a machine provided with two injection
units for injecting two different materials for the two layers of
the two-layered preform or two-component preform. A drawback
associated with the two-layered preforms of different components
obtained by injection overmolding of some synthetic polymers, and
especially of polyethylene terephthalate (PET) or polypropylene
(PP), according to the prior art, is that the bottles and other
containers obtained by blow molding such two-layered preforms show
a tendency towards exfoliation or separation of the two layers
forming them. This is due to the fact that a mixture of the
synthetic polymer with one or more different coloring agents is
used as molding material for each of the two layers, and in some
cases the different nature of the coloring agents makes the
adhesion between the two layers relatively weak even when the base
polymer is the same. To prevent this drawback, the method of the
present invention comprises using a synthetic polymer as common
base material for both layers, said synthetic polymer being mixed
with one or more coloring agents in each layer, at least one of
said coloring agents being common in the two layers.
[0022] In an embodiment, said synthetic polymer is polyethylene
terephthalate (PET), polypropylene (PP) or high density
poliethylene (HDPE), and among the coloring agents which can be
used there is titanium oxide (TiO.sub.2) (white colorant) in solid
or liquid form, and carbon black or carbon (black colorant) in
solid, powder or liquid form. In a more specific embodiment, the
method of the present invention comprises using polyethylene
terephthalate (PET), polypropylene (PP) or high density
poliethylene (HDPE) with from 0.01% to 2% by weight of carbon black
or activated carbon and from 3% to 10% by weight of active
ingredients of titanium oxide (TiO.sub.2) as primary molding
material of the first layer, or inner layer, and using polyethylene
terephthalate (PET), polypropylene (PP) or high density
poliethylene (HDPE) with from 3% to 10% by weight of active
ingredients of titanium oxide (TiO.sub.2) as overmolding material
of the second layer, or outer layer. This composition is suitable
for manufacturing two-layered preforms intended for obtaining
milk-containing bottles, in which the outer layer must provide a
barrier effect against light by reflection and furthermore offer a
final aesthetic appearance of the bottle in relation to its
content, i.e., a white appearance which is as pure as possible, and
in which the object of the inner layer is to provide a barrier
effect against light by absorption.
[0023] The use of a percentage of titanium oxide (TiO.sub.2) in
both the inner and outer layers has the dual interest of favoring
the adhesion of the two layers to one another and of mixing a
proportion of white in the black colorant of the inner layer to
cause a gray effect facilitating the optical coating by the outer
layer and thus give a deep white appearance to the bottle obtained
by blow molding the two-layered preform without this involving a
significant decrease in the capacity of the inner layer to offer an
efficient barrier against light by absorption. Nevertheless, it
must be indicated that the present invention is not limited to the
mentioned base materials and colorants, being it possible to use
any other plastic materials which are suitable for manufacturing
preforms and/or any other colorants.
[0024] Alternatively, the mold and/or the method of the present
invention can be applied to produce preforms with a very thin wall,
for example with a thickness of 2.1 mm or less. To that end, most
of the wall of the preform is of a single layer provided by the
first layer, whereas the second layer is reduced to the region of
the closed end of the preform just enough to fill and/or cover the
openings produced in the first layer by the supporting members. In
this case, the same plastic material, for example polyethylene
terephthalate (PET), polypropylene (PP) or high density
poliethylene (HDPE), can be used for the first and second layers,
such that the mold can be used with a standard injection machine,
i.e., with a single injection unit. As a result of the fact of
supporting the core in the primary molding cavity, the first layer
in the single-layer regions can have a thickness which is
sufficiently small, for example 2.1 mm or less, and uniform to
assure a very thin and uniform wall in the product subsequently
obtained by blow molding the preform.
[0025] The two-layered preform obtained by injection overmolding by
means of the mold and method of the present invention typically
comprises a tubular body with a mouth at a first end and a closed
bottom at an opposite second end. At least part of said tubular
body is formed by a first layer of a primary molding material and a
second layer of an overmolding material. In the closed bottom, the
mentioned first layer comprises one or more openings filled and/or
covered by the material of the second layer. As a result of the
first layer having been molded with the core supported inside the
primary molding cavity, the thickness of the first and second
layers of the two-layered preform is substantially uniform around
the perimeter of the two-layered preform.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] The previous and other features and advantages will be more
fully understood from the following detailed description of
exemplary embodiments with reference to the attached drawings, in
which:
[0027] FIG. 1 is a schematic cross-sectional depiction of several
parts forming a mold for manufacturing two-layered preforms by
injection overmolding according to a first embodiment of the
present invention, in a position prior to the start of a molding
injection operation according to a first embodiment of the method
of the present invention;
[0028] FIG. 1A is an enlarged detail of FIG. 1 to better show a
closed bottom of the primary molding cavity;
[0029] FIG. 2 is a schematic cross-sectional depiction of the parts
forming the mold of FIG. 1 in a position corresponding to a primary
molding step of the method of the present invention;
[0030] FIG. 2A is an enlarged detail of FIG. 2 to better show a
closed bottom of the primary molding cavity with the core supported
therein and the first layer of the two-layered preform between
both;
[0031] FIG. 3 is a schematic cross-sectional depiction of the parts
forming the mold of FIG. 1 in a position prior to an overmolding
step of the method of the present invention;
[0032] FIG. 3A is an enlarged detail of FIG. 3 to better show an
end of the core with the first layer of the two-layered preform
thereon;
[0033] FIG. 4 is a schematic cross-sectional depiction of the parts
forming the mold of FIG. 1 in a position corresponding to the
overmolding step of the method of the present invention;
[0034] FIG. 4A is an enlarged detail of FIG. 4 to better show a
closed bottom of the overmolding cavity with the core arranged
therein and the first and second layers of the two-layered preform
between both;
[0035] FIG. 5 is a cross-sectional view showing the inside of the
closed bottom of a two-layered preform according to an embodiment
of the present invention;
[0036] FIG. 6 is a perspective view sectioned through the planes
indicated as VI-VI in FIG. 5;
[0037] FIGS. 7 to 10 are sectioned views of several examples of
two-layered preform obtained with the mold and/or the method of the
first embodiment of the present invention;
[0038] FIG. 11 is a sectioned partial view of another example of
two-layered preform obtained with the mold and/or the method of the
first embodiment of the present invention;
[0039] FIG. 12A is a partial view showing a free end of a core
belonging to a mold according to a second embodiment of the present
invention;
[0040] FIG. 12B is a sectioned partial view showing the interaction
of the core with the primary molding cavity in the mold of the
second embodiment during a molding operation of the first layer of
the preform according to a second embodiment of the method of the
present invention;
[0041] FIG. 12C is a sectioned partial view showing the interaction
of the core with the overmolding cavity in the mold of the second
embodiment during an overmolding operation of the second layer of
the preform according to a second embodiment of the method of the
present invention;
[0042] FIG. 13 is a sectioned partial view of an example of
two-layered preform obtained with the mold and/or the method of the
second embodiment of the present invention; and
[0043] FIG. 14 is a sectioned partial view of another example of
two-layered preform obtained with the mold and/or the method of the
second embodiment of the present invention.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
[0044] Referring first to FIG. 1, there are shown the different
parts forming a mold for manufacturing two-layered preforms by
injection overmolding according to a first embodiment of the mold
and/or the method of the present invention. The mold comprises a
primary molding cavity 1, which is connected to a first hot channel
10 for supplying a primary molding material into said primary
molding cavity 1 through a first injection nozzle 15, and an
overmolding cavity 2 connected to a second hot channel 20 for
supplying an overmolding material into said overmolding cavity 2
through a second injection nozzle 25. In the embodiment shown, the
primary molding cavity 1 and overmolding cavity 2 are stationary,
although this is not essential for the present invention. The mold
further comprises a core 3 connected to a mobile plate 30 of an
injection molding apparatus (not shown) operated to alternately
introduce said core 3 into the primary molding cavity 1 and into
the overmolding cavity 2. In the embodiment shown in FIG. 1, the
mold is completed with a pair of neck half-molds 5a, 5b connected
to respective mobile elements, which are in turn assembled on a
mobile plate 50 of said injection molding apparatus (not shown),
which is controlled to close and open the neck half-molds 5a, 5b
next to the mouth of the overmolding cavity 2, in a well-known
manner.
[0045] In the first embodiment shown in FIGS. 1 to 4, the core 3
has an outer surface configured to cooperate with an inner surface
of the primary molding cavity 1 to form a first layer P1 of the
two-layered preform P, the mentioned first layer P1 of the
two-layered preform P has an outer surface which together with
another outer surface of the core 3 cooperates with an inner
surface of the overmolding cavity 2 to form a second layer P2 of
the two-layered preform P, and the neck half-molds 5a, 5b are
configured to form a neck 61 of said two-layered preform P together
with the second layer P2 (see FIGS. 7 and 9). In an alternative
embodiment (not shown), the neck half-molds 5a, 5b are arranged to
be closed and opened by the injection molding apparatus next to the
mouth of the primary molding cavity 1, such that the preforms
obtained have the neck 61 formed together with the first layer P1
of the two-layered preform P (see FIGS. 8 and 10).
[0046] The primary molding cavity 1 and overmolding cavity 2
generally have an elongated configuration with respect to a
longitudinal axis and have a closed bottom opposite to their mouth.
The first and second injection nozzles 15, 25 are opened in the
center of the mentioned closed bottom of the respective primary
molding cavity 1 and overmolding cavity 2. The core 3 generally has
an elongated configuration with respect to a longitudinal axis and
has a free end which is located adjacent to the closed bottom of
each of the primary molding cavity 1 and overmolding cavity 2 when
it is introduced therein. Three supporting members 4 (see also the
enlarged detail of FIG. 1A) project from the inner surface of the
primary molding cavity 1, said supporting members 4 being fixed
with respect to the primary molding cavity 1 and arranged to make
contact with the core 3 when the core 3 is introduced in the
primary molding cavity 1 (FIG. 2). The supporting members 4 have a
slightly conical configuration and are oriented in a direction
parallel to the longitudinal axis of the primary molding cavity 1
to facilitate the extraction of the first layer P1 from the mold in
a direction parallel to the direction of the movement of extraction
of the core 3.
[0047] The arrangement of three supporting members spaced at
angular intervals of 120 degrees around said first injection nozzle
15 in the closed bottom of the primary molding cavity 1 is
preferred, since they thus provide an isostatic support for the
core 3, close to the free end thereof, during a molding operation
of the first layer P1 by means of the primary molding material.
However, any number of fixed supporting members 4 arranged to
support the core 3 inside the primary molding cavity 1 will be
within the scope of the present invention.
[0048] FIG. 2 shows a first step of the method of the present
invention using the mold of FIG. 1. This first step comprises first
introducing the core 3 in the primary molding cavity 1 and
supplying the primary molding material through the first hot
channel 10 and the first injection nozzle 15 into the empty space
defined between the primary molding cavity 1 and the core 3 to
perform a molding operation of the first layer P1 of the
two-layered preform P. In this step, the method comprises
supporting the core 3 during the entire molding operation of the
first layer P1 of the primary molding material by means of the
supporting members 4 projecting from the inner surface of the
primary molding cavity 1 to make contact with the core 3. Due to
the fact that the core 3 is supported by the supporting members 4
during the molding operation of the first layer P1, the core 3 is
not deformed and the first layer P1 has a uniform thickness around
the perimeter of the two-layered preform P. The supporting members
4 which are in contact with the core 3 during the molding operation
form corresponding openings 60 in the first layer P1 as is better
seen in the enlarged detail of FIG. 2A.
[0049] FIG. 3 shows the core 3 once it has been extracted from the
primary molding cavity 1 after molding the first layer P1, where
the first layer P1 remains arranged on the core 3. The enlarged
detail of FIG. 3A shows a cross-sectional view of one of the
openings 60, which are empty when the core 3 is removed from the
primary molding cavity 1. It can be observed in FIG. 3 that the
core 3 has been aligned with the overmolding cavity 2 ready for the
performance of the following step.
[0050] FIG. 4 shows the following step of the method of the present
invention, which comprises introducing the core 3, together with
the first layer P1 arranged thereon, in the overmolding cavity 2
supplying the overmolding material through the second hot channel
20 and the second injection nozzle 25 to perform an overmolding
operation of a second layer P2, together with which the neck 61 of
the two-layered preform P is formed by means of the closed neck
half-molds 5a, 5b next to the mouth of the overmolding cavity 2.
During this overmolding operation, the overmolding material fills
and covers the openings 60 which had been formed by the supporting
members 4 in the first layer P1 during the molding operation in the
primary molding cavity 1. The enlarged detail of FIG. 4A shows a
cross-sectional view of one of the openings 60 in the first layer
P1 filled with the material of the second layer P2.
[0051] Finally, the core 3 is extracted from the overmolding cavity
2 with the two-layered preform P finished thereon, the two-layered
preform P is ejected from the core 3 by a conventional ejection
device (not shown) of the injection molding apparatus, and the bare
core 3 is again aligned with the primary molding cavity 1 (FIG. 1)
ready for starting a new cycle.
[0052] FIGS. 5 and 6 show the closed bottom of a two-layered
preform P obtained by means of the mold and/or the method of the
first embodiment of the present invention described above in
relation to FIGS. 1 to 4. The two-layered preform P is comprised of
a first layer P1 of a primary molding material and a second layer
P2 of an overmolding material. The first layer P1 includes openings
60 filled with the material of the second layer P2. The openings 60
are a result of the presence of the supporting members 4 in contact
with the core 3 during the molding operation of the first layer P1.
Furthermore, as a result of the action of supporting the core 3
during the molding operation of the first layer P1, the thickness
of both the first and second layers P1, P2 is substantially uniform
around the perimeter of the two-layered preform P.
[0053] FIG. 7 depicts an example of two-layered preform P obtained
by means of the mold and/or the method of the first embodiment of
the present invention, and especially designed for obtaining
bottles for containing milk by means of a subsequent blow molding
process. This two-layered preform P, as is usual, has the form of a
tubular body with a mouth 62 at a first end and a closed bottom at
an opposite second end. A part of said tubular body is formed by a
first layer P1 of a primary molding material and a second layer P2
of an overmolding material. The first layer P1 of the two-layered
preform P preferably has a thickness equal to or less than 1.8 mm
and is sufficiently uniform to produce a very thin and uniform
inner layer in a bottle subsequently obtained by blowing the
two-layered preform P.
[0054] The mentioned primary molding material forming the first
layer P1, which is the inner layer, is polyethylene terephthalate
(PET), polypropylene (PP) or high density poliethylene (HDPE) with
from 0.01% to 2% by weight of carbon black or activated carbon and
from 3% to 10% by weight of active ingredients of titanium oxide
(TiO.sub.2). The overmolding material forming the second layer,
which is the outer layer, is likewise polyethylene terephthalate
(PET), polypropylene (PP) or high density poliethylene (HDPE) but
only with from 3% to 10% by weight of active ingredients of
titanium oxide (TiO.sub.2). Thus, the first layer P1, or inner
layer, has an opaque dark gray color and performs a function of
barrier against light by absorption, whereas the second layer P2,
or outer layer, has an opaque intense white color and performs a
function of barrier against light by reflection. The fact that a
proportion of one and the same coloring agent, such as titanium
oxide (TiO.sub.2), is present in the material of both layers P1, P2
favors a suitable adhesion of the two layers P1, P2 to one another
and prevents exfoliation.
[0055] The first layer P1 comprises openings 60 filled with the
material of the second layer P2. The mentioned openings are located
in the closed bottom of the two-layered preform P, arranged at
angular spaces of 120 degrees around the longitudinal central axis
of the two-layered preform P and close to the center of said closed
bottom. The openings 60 in the first layer P1 are a result of the
presence of the supporting members 4 in contact with a core 3 in
the primary molding cavity 1 of the mold in which the molding
operation of said first layer P1 has been performed, and the fact
that the first layer P1 has been molded with the core 3 being
supported results in the thickness of said first and second layers
P1, P2 being substantially uniform around the perimeter of the
two-layered preform.
[0056] Furthermore, this two-layered preform P designed for
obtaining bottles for containing milk has a neck 61 integrally
formed from the overmolding material of the second layer P2, or
outer layer. This neck 61 is formed around said mouth 62 and
comprises an outer thread 63 for coupling a stopper and a
perimetric annular flange 64 performing an auxiliary function in
the handling and bottling lines. The neck 61 of the two-layered
preform P has the final dimensions required for the bottle since it
is unchanged during the blow molding process. The first layer P1
does not coat the inner surface of the mouth 62 in the neck 61,
such that the inner surface of the neck 61 visible from the outside
has the intense white color of the second layer P2. It must be
emphasized that the substantially uniform thickness of the first
and second layers P1, P2 as a result of the fact that the first
layer P1 has been molded with the supported core 3 facilitates a
precise demarcation of the extent of the first and second layers
P1, P2 in the longitudinal direction of the two-layered preform
P.
[0057] The two-layered preform P of FIG. 8 is, in relation to the
shape, completely similar to the two-layered preform P shown in
FIG. 7, except in that here the neck 61 is integrally formed from
the primary molding material of the first layer P1, or inner layer.
This two-layered preform P of FIG. 8 is obviously designed for
obtaining bottles or other containers intended for other uses and
as a result, the materials of the first and second layers P1, P2
are also different from those of the two-layered preform P of FIG.
7. For example, in the two-layered preform P of FIG. 8 the first
layer P1, which is the inner layer in contact with the contained
liquid, and which includes the neck 61, can be made of a quality
polyethylene terephthalate (PET), polypropylene (PP) or high
density poliethylene (HDPE), whereas the second layer P2, which is
the outer layer and will not be in contact with the contained
liquid, can be made of a recycled polyethylene terephthalate (PET),
polypropylene (PP) or high density poliethylene (HDPE).
[0058] FIG. 9 shows a two-layered preform P similar to the one
described above in relation to FIG. 7, although here the
two-layered preform P is designed for obtaining wide-mouthed
containers, for which the neck 21 and the mouth 62 are relatively
wider.
[0059] FIG. 10 shows a two-layered preform P similar to the one
described above in relation to FIG. 8, with the difference of the
second layer P2, which in this embodiment externally coats only the
closed bottom and a portion, approximately half, of the tubular
body of the two-layered preform P. An application of this
two-layered preform P of FIG. 10 is, for example, for obtaining
bottles of water or drinks with a visual effect of change or
combination of colors. To that end, for example, the first layer P1
can be made of a transparent polyethylene terephthalate (PET),
optionally containing a proportion of one or more transparent or
translucent coloring agents, and the second layer P2 can be made of
a polyethylene terephthalate (PET) containing a proportion of one
or more transparent, translucent or opaque coloring agents.
Furthermore, by playing with changes in the thicknesses of the
first and second layers P1, P2 in combination with the areas of the
two-layered preform P subjected to greater or lesser expansion
during the blow molding operation, multiple visual effects of
change and/or combination of colors, including color gradations can
be achieved.
[0060] FIG. 11 shows the end corresponding to the closed bottom of
a two-layered preform P with a thin wall made by means of the mold
and/or the method of the first embodiment of the present invention,
in which the first layer P1 provides a single layer for most of the
wall of the preform, optionally including a neck (not shown) at the
open end. The second layer P2 is very small and only covers the
region corresponding to the closed bottom of the first layer P1
filling the openings 60 left by the supporting members 4. Although
FIG. 11 shows the second layer P2 covering the entire closed bottom
with a thickness substantially equivalent to the thickness of the
first layer P1, the overmolding cavity 2 could alternatively be
configured to form the second layer P2 with a much smaller
thickness and/or with a smaller configuration just enough to assure
the flow of the molten overmolding material from the overmolding
material injection nozzle 25 to the openings 60 of the first layer
P1 in order to fill them during the overmolding operation. In the
two-layered preform P of FIG. 11, the first and second layers P1,
P2 can advantageously be made of the same material.
[0061] In relation to FIGS. 12A to 12C, a mold and a method
according to a second embodiment of the present invention are
described below. In this second embodiment, the supporting members
4 are fixed in the core 3, as shown in FIG. 12A, and project from
the free end thereof to make contact with the inner surface of the
primary molding cavity 1 (FIG. 12B). In the example shown, at the
free end of the core 3 there are arranged three of said supporting
members 4 to make contact with areas of the closed bottom of the
primary molding cavity 1 around a primary molding material
injection nozzle 15 located coaxially in the primary molding cavity
1.
[0062] When the core 3 is removed from the primary molding cavity 1
carrying the first layer P1, the openings 60 formed by the
supporting members 4 are occupied by the supporting members 4.
Thus, when the core 3 with the first layer P1 is then introduced in
the overmolding cavity 2 (FIG. 12C) and the overmolding material is
injected through the overmolding material injection nozzle 25 to
form the second layer P2, the latter will simply cover the openings
60 of the first layer P1 without filling them. Preferably, in the
closed bottom of the overmolding cavity 2 there are formed
depressions 6 arranged around the overmolding material injection
nozzle 25 in positions facing the supporting members 4 of the core
3 and openings 60 of the first layer P1. These depressions 6 are
configured to form bulges 65 in those regions of the second layer
P2 which cover the mentioned openings 60 of the first layer P1 of
the two-layered preform P.
[0063] Thus, when the two-layered preform 3 is ejected from the
core 3 (FIG. 13) the openings 60 of the first layer P1 are empty
but covered by the bulges 65 of the second layer P2, such that the
thickness of the wall of the two-layered preform P facing the
openings 60 is substantially equivalent to the thickness of the
wall in the regions provided with a double layer, which provides a
substantially uniformity in the stretching of the materials of the
first and second layers P1, P2 during a subsequent blow molding
operation of the two-layered preform P.
[0064] FIG. 14 shows another example of two-layered preform P which
can be produced by means of the mold and/or the method of the
second embodiment of the present invention. The two-layered preform
P of FIG. 14 is a preform with a very thin wall, for example of
less than 2.1 mm. The first layer P1 provides a single layer for
most of the wall of the preform, optionally including a neck (not
shown) at the open end. This first layer P1 has a thickness equal
to or less than 2.1 mm. The second layer P2 is very small and only
covers the region corresponding to the closed bottom of the first
layer P1, with the bulges 65 of the second layer P2 covering but
not filling the openings 60 left by the supporting members 4. It
must be indicated that it is not necessary for the second layer P2
to cover all the closed bottom of the preform with a thickness
substantially equivalent to the thickness of the first layer P1.
The overmolding cavity 2 can alternatively be configured to form
the second layer P2 with a much smaller thickness and/or with a
smaller configuration just enough to assure the flow of the molten
overmolding material from the overmolding material injection nozzle
25 to the bulges 65 of the second layer P2 in order to fill them
during the overmolding operation. In the two-layered preform P of
FIG. 14, the first and second layers P1, P2 can advantageously be
made of the same material.
[0065] A person skilled in the art will be able to carry out
modifications and variations to the embodiments shown and described
without departing from the scope of the present invention as it is
defined in the attached claims.
* * * * *