Hollow Plastic Object, Particularly Ribbed Preform for Container and Method of Overmoulding Thereof and Device Therefor

Abstract

Hollow injection molded article made of plastic material, esp. preform for blow molding a container, with a wall (17) extending along axis (I), which is composed of a layer of variable thickness (), being remarkable in that longitudinal ribs are provided in said axis direction, wherein the wall has a tooth profile of periodic nature varying periodically between a minimum and a maximum threshold value (m, resp. M) which is determined by a typical injection molding length (Ls) for said plastic material and/or characteristic ratio (max/min). A method of manufacturing thereof (10) by injection molding comprising forming inner and outer preforms (11, 12) with formation of an integrated composite preform (10), and apparatus for this purpose.

Claims

1-57. (canceled)

58. Hollow injection molded article made of plastic material comprising a wall portion (17) and a bottom portion (16) extending along an axis (l) thereof, wherein the wall portion is composed of at least one layer of variable thickness (), wherein a plurality of ribs (96) is provided in said axis direction (l), constituting a set of said longitudinal ribs, wherein said wall has a periodic tooth profile (95), thereby varying periodically between a minimum threshold value (m) and a maximum top value (M) determined by both material parameters being a typical injection mold length (Ls) and/or a typical thickness ratio .sub.max/.sub.min which are each characteristic for said plastic material.

59. Hollow article according to claim 58, wherein said wall has a square wave profile (95), particularly wherein said profile is a square-wave profile with steep flanks (94).

60. Hollow article according to claim 59, wherein said profile has a variable rib width, particularly wherein said profile has also a rate of variation that is periodic as well, more particularly wherein said articles (1;10) are equipped with vertical ribs (96) being injection-molded, wherein said articles have an increased wall thickness/injection mold length ratio, thereby providing thin-walled and light-weight articles (1;10) with an increased strength.

61. Hollow article according to claim 58, wherein it comprises a preform (10; 82) for blow molding to a container (91;92), comprising a neck portion (19) with its wall portion (17) adjacent thereto, extending along said axis (l), wherein said wall (17) is composed of at least one layer with variable thickness (), wherein a plurality of ribs (96) extending in said axis direction (l) are provided, thereby forming longitudinal ribs (96) at the surface thereof (10); particularly wherein it consists of an overmoulding preform (10; 82) comprising two different materials (a, b), with an inner preform and an outer preform, wherein the inner and outer preforms have contiguous vertical ribs (96), whereas the final product (91; 92) has no such longitudinal ribs remaining, visible; more particularly wherein the inner and outer preforms are composed of 2 different and non-complementary materials; yet more particularly wherein the inner and outer preforms have contiguous vertical ribs with an undercut (64), and in that a mechanical anchoring between the inner and outer preforms is established therewith; and/or in that the space between the ribs (96) is not greater than twice the width of a rib (96).

62. Hollow article according to claim 58, which is composed of a primary plastic base material and at least one additional secondary material, at least in a sub-area thereof, characterized in that the object (10, . . . , 81; 82) has at least two sub-areas (A, B) notably a primary and a secondary area respectively, which are adjacent by pair with their mutual contact sides (Z) and which have a mutually different coloration being continuous as a whole, particularly bicolor; more particularly wherein the sub-areas have an alternating profile of mutually substantially parallel separation lines (Z) extending according to the axis (l), thereby forming at least one vertical strip (A, B) with alternating color; yet more particularly wherein the sub-areas have a symmetrical alternating profile thereby forming a so-called zebra-like profile consisting of vertical strips with alternating color (A, B); and/or wherein at least one of the sub-areas (A, B) is opaque, and/or in that at least the other sub-area (B, A) is translucent; still more particularly wherein said at least opaque, resp. translucent sub-areas are colored; and/or wherein the sub-areas (A, B) have a mutually strongly contrasted coloration; and/or wherein at least the primary sub-area (A) is transparent.

63. Hollow article according to claim 61, wherein the inner and outer preforms have a different color, or wherein only the inner or outer preform is colored, in particular also including selective recesses in the inner preform with specific designs and variations in color, particularly two; or wherein the inner preform is colored opaque, wherein in the longitudinal axis (l) of the preform, a through-recess is provided, and a transparent outer preform, comprising a control window over the entire length of the preform, resp. container through which its filling level is perceptible; and/or wherein it consists of an overmoulding preform comprising two different materials, with the inner and the outer preform made of another injection molding material comprising a barrier, notably against gas, moisture or light; particularly wherein the outer preform is made from standard PET, and the inner preform from a high barrier material or hotfill material resp.; and/or wherein the inner preform is made of a polyolefin, and the outer preform of PET resp., wherein it combines the mechanical and gas barrier properties of PET with the chemical barrier, moisture barrier and thermal properties of polyolefins.

64. Hollow article according to claim 61, comprised as containers for dairy products, characterized in that it has a very high light barrier, comprising an inner preform made from a material which is light-tight, or opaque, and a corresponding outer preform which is transparent or has a color, wherein the produced milk bottle is white on the outside, while on the inside it has a black or gray layer of plastic as light barrier, under use of an overmoulding process consisting of making the preforms to start with the injection moulding of the gray inner layer, on which a 2.sup.nd white coat is further injected, which ensures the light barrier required at ultra-high temperature (UHT) milk bottles.

65. Method for manufacturing plastic hollow articles by injection moulding, as defined in claim 58, particularly preforms for containers, wherein primary raw material is injected into a mould (3) having a core side (31) and a cavity side (32), between which hollow articles (10) are formed, after which the mould (3) is opened into its two halves (31, 32), the cores (33) whereof each bear a hollow article, wherein composite preforms (10) are made as said hollow articles, which consist of sub-preforms (11, 12) and which are intended to be worked into plastics containers, in that secondary raw material for producing a secondary preform (12) conjugated to each preform (10) is injected into the injection mould (3), which is equipped with multicavities with an even number of at least 2 of cavities and cores (33, 34), and in that both sub-preforms (11) and (12) are injected at the same time, wherein in a 1.sup.st step (.sub.1) the injection mould (3) containing the injected composite preform (10) and secondary sub-preform (12) is closed, and a gripping member (4) provided with a set of receiving members (16) is set in a standby position (A) aside from the mould (3); in a 2.sup.nd step (.sub.2) the forming mould (3) is opened in its cavity side (32) and core side (31), which are driven apart from each other, wherein each primary core (33) bears an injected composite preform (10), and respectively the secondary core (33) bears a secondary inner preform (12); in a 3.sup.rd step (.sub.3), the gripping member (4) is set in motion, under the drive of a driving unit (5) according to a preset direction of movement between the set-aside standby position (A) and an active take-over operating position (B), which is directed to the core side (31) of the mould (3), wherein the injected composite preform (10) and the secondary sub-preform (12) are cooled and are taken over from the core side (31) by the gripping member (4) by means of suction means (6), wherein the composite preform (10) and the secondary sub-preform (12) are received in the corresponding receiving members (16); in a 4.sup.th step (.sub.4), the gripping member (4) is further moved into a further operating position (C), in which it places the received secondary inner preforms (12) onto the respective primary cores (33) and continues to hold said preforms (11) in place, with the formation of said integrated preform (10) composed of the primary preform (11) and its added secondary inner preform (12), after which the gripping member (4) is moved back into the set-aside standby position (A) in order to expel the so produced integrated composite preforms (10) to a discharge unit for further treatment, whereby one full cycle (O) is thus completed and whereupon the forming mould (3) is then closed again.

66. Method according to claim 65, wherein in said step (.sub.3) the one gripper arm (4) is moved (H) up to between both mould halves (31, 32) from which it receives the composite and secondary preforms (10, 12) for producing in said step (.sub.4) the integrated composite preform (10) by means of one overmoulding sequence (.sub.1, .sub.2, .sub.3, .sub.4) thereby accomplishing one cycle (O), yet starting again with a new set of simultaneously injected preforms (11, 12), wherein the production process is restarted in loop (O) for a new cycle (O) (.sub.1, .sub.2, .sub.3, .sub.4) in this prescribed order.

67. Method according to claim 65, wherein the injection moulded composite and secondary preforms (11, 12) are received in a vacuum plate (40) provided on the gripper arm (4), wherein the core side (31) forms the movable mould plate with a predetermined number of primary cores (33), and a corresponding number of secondary cores for the secondary inner preforms (12), each occupying substantially one half of the core side (31), wherein the opposite cavity side (32) forms the fixed side with a corresponding number of primary cavities (34) and a further set with a corresponding number of secondary cavities (34) for the secondary inner preforms (12), which occupy the other half of said cavity side (32); and/or in that both primary resp. secondary sub-fields (I, II, III, IV) of each mould side (31, 32) are divided into an even number of equally occupied sub-fields, in particular 2, of both mould plates (31; 32) being organized in a matrix pattern in an even number of rows and a predetermined number of columns respectively containing an equal number of elements, preferably according to a regular quadratic arrangement grid of the elements (33, 34), more particularly an even number of at least two cores (33) resp. cavities (34), preferably not less than 32 pieces as a power of 2 of at least 5.sup.th order exponent, up to 64 and more; yet more particularly wherein each said half (101, 101) of the core side (31), resp. (102, 102) of the cavity side (32) is split according to a staggered occupancy per row (110, 111), resp. column (120, 121), possibly grouped plural, esp. in pairs or more.

68. Method according to any one of the claim 65, wherein in the said 2.sup.nd step (.sub.2) the mould is opened, wherein the movable mould half (31) is removed in parallel respective the fixed mould half (32), wherein the top products (11) in the top half (101) form the outer preforms (11), and the inner preforms (12) are received therein, with the formation of a finished product (10) by the combination in each case of a top (11) and bottom product (12), possibly with a positive connection, wherein the bottom products (12) in the bottom half (102) form the inner preforms; and/or in that in the said third step (.sub.3) the gripping arm (4) is moved downward vertically with its vacuum plate (40), from the standby position (A) or deflected idle mode, into the active take-up working position (B) between both mould halves (31, 32) aligned therewith and in which the integrated composite preforms (10) and the secondary preforms (11, 12) are transferred from the resp. primary and secondary cores (33, 33) to the vacuum plate (40), in that in the fourth step (.sub.4) the gripping arm (4) is moved back in the opposite direction (H), vertically upward into alignment with the composite preforms (10) and the secondary preforms (12), wherein the secondary bottom preforms (12) are transferred on the primary top cores (33) at the primary top half; and/or in that the gripping arm (4) is then moved further upward vertically, thereby containing said integrated composite preforms (10), wherein the latter preforms (10) are expelled from the vacuum plate (40) and are thus ready to be further discharged to said discharge means; and/or in that as soon as the gripping arm (4) is removed from between both mould halves (31, 32), the mould (3) is closed again.

69. Method according to claim 65, wherein at least one second gripping member (42, . . . ) is operated, which is moved under drive from a second, resp. additional driving unit (52), wherein said gripping means (41), (42) are matched to each other for taking over and discharging the moulded preforms mutually sequentially, possibly alternately; or in mutual overlap, possibly in parallel; more particularly wherein in a parallel operation of overmoulding, several cycles (O, O) are proceeded at the same time, in particular under the action of yet one gripping element (41, 42) per cycle, which are matched to each other with a mutual phase shift (), wherein an integrated composite preform (10) is performed which consists of a primary preform (11) and secondary inner preform (12) resp., with actually one overmoulding sequence loop (.sub.1, .sub.2, .sub.3, .sub.4) per cycle (Oi).

70. Method according to claim 69 wherein the gripping members (41, 42) are moved in a to-and-fro motion (G, G) in the direction of their respective longitudinal axes (Y1, Y2), wherein the gripping members (41, 42) are initially arranged on top of the mould (3), and wherein their respective movement (X1, X2) relative to each other is shifted in time over (); and/or in that said at least two gripping members (41, 42) are arranged on a carrier (9), in a set-up plane which is substantially perpendicular relative to the ground of the supporting surface and are shifted in said set-up plane in accordance with a second direction under the drive of a further driving unit (5i), between a standby position (A) in idle mode and a take-over position (B) in operation mode; and/or in that said at least two gripping members (41, 42) are moved successively in accordance with two mutually substantially orthogonal directions, wherein said first direction of movement is selected substantially vertically relative to the ground, and both of the gripping means are moved between said take-over position (B) and operation mode (C); particularly wherein the latter movement of the two gripping members (41, 42) is proceeded simultaneously in said second direction (X) in which said carrier plate (9) is moved under the drive of a further motor that forms the further driving unit (5i).

71. Method according to claim 69, wherein a first cooling time is set for cooling the injected preforms (11) in the cavity side (32), in that at the end of the set first cooling time the cavity side (32) and the core side (31) of the mould (3) are separated from each other, to a distance between them which is sufficient for the insertion of one of said gripping members (41, 42) into a space (39) thus formed between cavity side and core side, wherein the reception side (44) of said one gripper element is directed towards the core side (31), said one gripper element is moved from the disconnected position (B) to said space (34), and said one gripper element is thus taken into said working position (C) relative to the core side, and the preforms (11) are cooled there in the yet corresponding reception elements (16) during a second set cooling time, wherein after expiry of said cooling time the preforms are passed from the core side to said one gripper element each into a reception element (16) corresponding to each core (33), following which said one gripper element is moved back into the disconnected position (B), both gripper elements are shifted crosswise until the further gripper element is driven in the disconnected position (B) and the one gripper element in said standby position (A), after which the movement executed by said one gripper element during the completed cycle is then carried out in the same way by the further gripper element, and a further set of preforms (11) is thus taken over by the latter (42) from the core side of the mould (3), and said further gripper element is then driven back to the disconnected position (B).

72. Method according to claim 70, wherein during a first cycle (O1) said mould opens at the end of a first cooling period, wherein injected preforms (11) are resting on said core side (31), wherein as soon as a space (34) is formed between core side (31) and cavity side (32) which is large enough to place therein the first gripper element (41), with a reliable transfer of the preforms, said first gripper element (41) is moved by being driven by a motor forming said drive unit (5) along the longitudinal axis (Y1) of said first gripper element (41) between said core side and cavity side until it is in the working position (C), wherein said first gripper element (41) then takes over a complete first set of preforms (81) from the core side (31), wherein after the preforms have been transferred, said first gripper element (41) is driven back along said longitudinal axis (Y1) to the disconnected position (B) in which the preforms (11) are held in respective sleeves forming said reception elements (16) of said first gripper element (41) during a subsequent cycle (O2) which starts from the moment that said first gripper element (41) is driven into said disconnected position (B), wherein the preforms (11) are accommodated in their respective sleeves (34), where they are subjected to an appropriate cooling, whereby in the meantime the preforms of said first cycle (O1) are still present in said second gripper element (42), wherein shortly before the end of the subsequent cycle (O2) said second gripper element (42) is moved from the standby position (A) into the disconnected position (B), while said first gripper element (41) is moved to a standby position (A) with a similar takeover process being carried out with the second gripper element (42), wherein after said first gripper element (41) has reached the disconnected position, its preforms (11) are removed, and wherein abovementioned steps are repeated for the next cycle (On) in a repeated process.

73. Method according to claim 69, wherein the primary and inner secondary outer preform (11, 12) are injected in a different color, in particular wherein only the inner or outer preform (11) or (12) is colored; more particularly wherein at least one selective recess (77) is made in the inner preform (12), through which certain specific aspects and variations (76) in colours of the final preform (10) are carried out, in particular by means of an opaquely coloured inner preform (12), more particularly wherein a complete longitudinal recess (77) is carried out in the longitudinal axis (l) of said inner preform (12), which is combined with a transparent outer preform (11), thereby yielding a transparent window (79) over the entire length of the preform (10) which is to be blown into a bottle (1), whereby the fill level (78) thereof becomes observable.

74. Method according to claim 1714, wherein for the manufacture of overmoulding preforms, two different materials (a, b) are added, wherein the inner and the outer preforms (12, 11) are injected in a different material, through which a blocking barrier (75), especially a gas barrier, moisture barrier or light barrier is incorporated in the final preform (10); particularly wherein the outer preform (11) is made from standard PET, and the inner preform (12) from a high barrier or hotfill material, in the case of use for hotfill applications; more particularly intended for containers for dairy products with a high light barrier, wherein the overmoulding process hereby used consists of producing preforms, which begins with the injection moulding of a gray inner layer, on which a 2.sup.nd white layer is further overmoulded, which perform ensures the light barrier which is required for ultra-high temperature (UHT) milk bottles, wherein the inner preform is made from a material that is light-tight, or opaque, and a corresponding outer preform which is transparent or has a color, wherein the relevant milk bottle becomes white outside after blowing the combined overmoulding preform (10), while being with a black or gray layer of plastic carried out as a light barrier at the inside.

75. Method according to claim 66 a primary preform (11) is coated by a secondary preform being applied as a coating on at least a portion of the primary plastic preform in which the latter preform (12) consists of at least one coating layer; particularly wherein a primary preform made of plastic, more specifically from a particularly biaxially stretchable material, for use in the manufacture of a plastic container, is coated, wherein it is partly covered with a secondary preform as coating, with at least one coating layer consisting of a polymer coating applied to at least a portion of the primary plastic preform (11); more particularly wherein the coating (98) has a glass transition temperature value T.sub.G which is lower or equal to that of the abovementioned stretchable material; even more particularly wherein PET is selected as said stretchable material, wherein the coating has a glass transition temperature value T.sub.G which is lower or equal to that of PET; yet more particularly wherein a barrier coating (99) is applied on the preform (11); still more particularly wherein said at least one coating layer (98) is provided on the outside of the preform, in particular in order to avoid contact of the coating (98) with foodstuffs.

76. An apparatus notably intended for carrying out a method according to claim 65, comprising a mould (3) to form preforms (11, 12), which has mutually releasable cavity (32) and core sides (31), in which a number of protruding cores (33) are provided for holding the preforms, a gripping member (4) is provided with a pair of receiving members (16) which can be directed at the cores (33) for cooling and receiving the preforms, wherein the gripping member (4) is movable under the drive of a driving unit (5) between a waiting position (B) and an operation mode (C), wherein the gripping member (4) is connected with the core side (31), wherein at least one hot-runner system is included in one injection mould (3); particularly wherein two independent hot runner systems are provided in one injection mould, in particular wherein the two hot runners for the primary and secondary materials (a, b) are completely separated, wherein both hot runners are adjustable at mutually independent processing temperatures (T.sub.a, T.sub.b); and/or wherein the insert overmoulding machine is composed of a 2K multicavities PET injection machine, esp. two cavities, wherein the hot-runner is mounted so that material (a) and material (b) are injectable individually in the upper cavity and in the lower cavity respectively, wherein the cavities (32) are mounted so that in the lower cavity (32) an inner preform (12) is producible without a screw thread, and in the upper cavity (32) an outer preform (11) with PCO screw-thread resp., wherein in the upper cavity a core (33) can be placed with a slightly smaller diameter than the core (33) in the lower cavity, esp. of about 0.6 mm less, wherein the take-off robot (4) is programmable so that, after one cycle the preform of the lower core (33) is removable and displaceable on the upper core (33), while the finished preform (10) of the upper core is removable and recoolable.

77. The apparatus according to claim 76, wherein at least one second gripping member (42) is provided with a further set of receiving means (16) with which the cores (33) of the core side (31) of the mould (3) can be aligned, wherein said at least second gripper means (42) is displaceable under the drive of a further drive unit (52) between the disconnected position (B) and the operating position (C), wherein the latter gripping member (42) is connected to the core side (31), and the latter movement is adjustable to the one of the first gripping member (41); particularly wherein each gripping member (41, 42) is formed by a gripper arm wherein the receiving elements 16) are formed by sleeves, wherein the cavity side (32) of the mould (30) is located on a fixed machine platform, wherein the core side (31) is fixed on a movable platform (37) of the machine, and herein a core puller (38) is provided having a retaining action on the preforms (11) which remain on the respective cores (33) of the core side (31) by way of a topically fitted clamping connection (39).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0073] FIG. 1 is a schematic linearly projected view of a main embodiment of a semi-finished product with a rib profile for an undercut resp. mechanical anchoring of a ribbed preform as an application of overmoulding for a container according to the invention.

[0074] FIG. 2 represents a variant of FIG. 1 with steep flanks.

[0075] FIGS. 3 and 4 are each a mixed representation of a composite preform according to the invention as semi-finished product, notably obtained by using the process as further presented below in FIG. 11.

[0076] FIGS. 5 to 10 show a series of different views of a further embodiment of a finished product as top portion of a pressurized container as an injection molded product according to the invention.

[0077] FIG. 11 is a general sequential representation of an overmoulding cycle of a main embodiment of the method according to the invention.

[0078] FIG. 12 shows step 1 of the method, wherein the mould is closed and the grab arm is in a standby position.

[0079] FIG. 13 is a cross section along the line D-D of the device represented in the previous FIG. 12.

[0080] FIG. 14 is an analogous representation to the previous FIG. 13, consisting of a cross-sectional view through the line A-A, though in this case with regard to the inner preform as the finished product.

[0081] FIG. 15 represents the following phase or step 2, wherein the mould is opened.

[0082] FIG. 16 represents a section along line E-E in FIG. 15, on which the topmost 32 products constitute the composite preforms, with inner preforms.

[0083] FIG. 17 is an analogous representation to FIG. 16, but of a section along line B-B representing the 32 bottom products only representing the 32 inner preforms.

[0084] FIG. 18 is a schematic representation of the finished product thus made, consisting of said composite preform in which the inner preform is accommodated.

[0085] FIG. 19 further shows the third phase of the method according to the invention, wherein the grab arm with the vacuum plate, coming from the standby position, now receives all products from the cores.

[0086] FIG. 20 is a sectional representation along line C-C in FIG. 19, showing a cross section, wherein the bottommost 32 products, being the inner preforms, are transferred into the vacuum plate.

[0087] FIG. 21 schematically represents the fourth step of the method according to the invention, wherein the grab arm moves upwards with the vacuum plate with the injection moulded products.

[0088] FIG. 22 further shows a cross section along line G-G in FIG. 21, wherein the injection moulded inner preforms are on the top cores.

[0089] FIG. 23 represents a 3D perspective view of a detail of the mould components.

[0090] FIG. 24 represents a front view of a detail of the mould components according to FIG. 23.

[0091] FIG. 25 represents a detail in enlarged view from FIGS. 11 & 12 respectively.

[0092] FIGS. 26-33 each represent a view of the robot components.

[0093] FIGS. 34 and 35 are a mixed representation of a composite preform according to the invention as a semi-finished product, especially obtained by applying the method as represented in FIG. 11.

[0094] FIGS. 36 and 37 show a combined application of overmoulding and coating on a preform, resp. the wall section thereof.

[0095] FIG. 38 et seq. show a combined application of overmoulding and coating on a preform, thereby including zebra configurations.

DESCRIPTION

[0096] Generally this invention relates to the injection molding of objects with vertical ribs 96 for injection-molding products having a higher wall thickness/injection length ratio than under normal limitation and providing thin-walled, light-weight products or semi-finished products with increased strength.

[0097] More specifically, a special application is described in the form of semi-finished products, such as for example a preform 10; 81, 82 in overmoulding, wherein an inner preform and an outer preform with contiguous vertical ribs are performed, in which surprisingly enough the final product shows no ribs however.

[0098] In a remarkable overmoulding application, the inner and outer preforms are executed in two different and not complementary materials. In this case, the inner and outer preform with contiguous vertical ribs can be made with an undercut, so that a mechanical anchoring is established between the inner and outer preform.

[0099] Different profiles of ribs 96 as well as different profiles 95 for undercut resp. mechanical anchoring are represented among which one is shown with steep flanks in FIG. 1, e.g. wherein the width of the space between longitudinal profiles represents maximum 2 times the width of a rib 96; and further a variant thereof with oblique flanks in FIG. 2.

[0100] Mainly products with vertical ribs 96 are injection molded for making products with a higher wall thickness/injection length ratio than under normal standards, on the one hand, and in order to achieve thin-walled and light-weight products with an increased strength, on the other hand, notably based on an overmolding process. In this way, one achieves remarkably to inject thinner-walled articles yet with an increased strength, which is not known in itself for preforms.

[0101] Next to ribbed preforms 10 forming injection molded products with vertical ribs, finished products 1 are also proposed yet with various views notably in FIGS. 5 to 10. The range is thus broader than just overmoulding products, and wider than only preforms as well, notably upper PV's as a pressurised chamber 1 in a pressure container shown in a cross-sectional view in FIG. 5. In short, it is a combination of light weight in any case, and strength and mechanical anchoring in the case of overmoulding.

[0102] More specifically, the product is injected with a higher wall thickness/injection length ratio than the one under normal limitation, by which is meant that when injecting PET, this goes along with a certain wall thickness, e.g. a product of 1 mm thick in a cold mold. PET material can typically be injected over a distance of 60 mm by 1 mm thick only, i.e. 6 cm against a thickness of 1 mm. E.g. with preforms of 3 mm thick, the longest PET preform to be achieved is thus up to 18 cm. Actually this simply consists of a ratio, wherein PET is thus characterized by an injecting/wall thickness of 60:1. In other words, it is possible to inject over a maximum distance up to 60 mm for each mm wall thickness, i.e. no more than 6 cm. Therefore, in case a little more is required such as up to 8 cm in height, this corresponds to a need of at least about 1.2 mm, in accordance with said ratio 60:1 rule, actually yielding 80:1.3 mm. However, if an injection is required with an average wall thickness of 1 mm on the basis of said ribs, thereby also injecting this entirely in PET, this would require at least such a wall thickness to an extent that it would make the final product far too heavy. Therefore, ribs are made in the preform, which need to have a certain thickness with regard to the wall thickness that is required, which is 1.3 mm. Between the ribs, merely 0.6 mm is made, whereby an average of 1 is thus yielded though. A non-uniform distribution is thus allowable, provided that the overall ratio is 1.3 mm. It needs to be continuous, and it must match said injection length. The configuration is in accordance with a rib, resp. tooth profile as shown in FIG. 1, resp. 2.

[0103] With a certain length, a flow path/wall thickness ratio of 60:1 must be satisfied, e.g., merely up to 100:1 or 120:1, in any case more than 60:1. It is not possible to make the whole product with that wall thickness, because it doesn't get fully injected then. Conversely, in case the product is made completely like this, it would be much too heavy.

[0104] For PET, the injection length/wall thickness ratio is 60:1. For having PET injected well, the corresponding ratio of L/c needs to be smaller than a certain value: the length L is fixed, e.g. 10 cm and the wall thickness is 1.5 mm, which yields 100:1.5=about 66.66 by 1. However 1.5 is too much. In case the requirement is to work at 1 mm, this yields a ratio of 100 to 1. So, the need here is of about 1.6 or 1.7, possibly even 2. If 2 mm is taken, this yields a ratio of 50:1, which is correct. The other parts then follow the ratio of 100:1. That is too much, since this corresponds to an average of 75:1. It is easier when taking it with 2 and 1 unit resp. So the injection length is 10 cm, the wall thickness here is 2 mm, and resp. 1 mm, thus yielding as ratio 50:1, respectively 100:1. This cannot be normally injected, since it is too heavy. This is the reason why it is done that way, thereby creating an average wall thickness of 1.5 mm, which is still in excess. Overweight means too expensive. So the aim is to work as thin as possible, but it is not possible to work below the actual limits being determined for the plastic. There is thus a need to inject products with a certain length and wall thickness, which cannot be injection molded in PET for example. PET can never reach a higher ratio than said 60:1, because PET is characterized by said 60:1 ratio, whereas polyethylene is characterized by a ratio of 300:1. The latter thus enables to inject much further.

[0105] However, the ratio 100:1 is not feasible either. So there are two states that cannot be realized separately, which is only achievable with an average however, whereas the only solution proposed to meet these two conditions consists of a ribbed preform according to the invention that is provided with a specific profile allowing an averaging.

[0106] For example, the profile may be smoothed instead of just a block shape. The purpose is that when injecting material, it will constantly follow a path. In the first phase, it will be affordable that these ribs get fully injected, whereas in a second step, the adjacent parts located between said ribs are getting full-injected starting from said ribs, because it is not possible to inject through completely in one time between the ribs.

[0107] With the ribbed preform, less PET material is needed, whereas a stronger preform is achieved with less PET than in the case of a preform with simply an equal mean wall thickness.

[0108] The first advantage is the ability of injecting lighter average, but this is not applicable for preforms, since they may cause restrictions due to warming, owing to some areas that are thicker thus heating up slower, whereas other areas are thinner thereby heating up quicker when blowing. Therefore, preforms can be made yet, but they cannot be blown, resulting in that it is not possible to get a bottle blown therefrom, so that such preforms are completely useless. Indeed, all preforms are merely intermediate injection molded products which are intended to be blown, since it is actually a semi-finished product.

[0109] Thanks to a specific application of the ribbed preform according to the invention in the case of overmoulding, there is both an inner and an outer preform with contiguous and interlocking vertical or longitudinal ribs: in said inner and outer preform the ribs hook into each other, whereas the final product remarkably shows no rib. Indeed, in the finished product, there are actually no ribs any more, with the great advantage that the inner and outer preform can be double injection molded in two times, each individually on its own, in the meaning that the inner and outer preform are injected separately.

[0110] By virtue thereof, the milk preform can be injected still lighter. Both the inner and the outer preform must meet the 60/1 rule, whereas there is advantageously no need therefor with those ribs. So, more weight is thus saved. Indeed, the final preform thus needs less PET material when thus double injected by separating in two times than in case the same preform would be injected in one single time.

[0111] Another aspect arises when the inner and the outer preform are not made both of the same PET material, but instead, the inner and the outer preform are injected from two non-complementary materials such as polypropylene and PET resp. Then those ribs offer extra added value if they are provided with an undercut. Indeed, polypropylene and PET do not normally adhere to one another. This causes delamination when blowing, which is thus prevented thanks to the invention, owing to a mechanical anchoring of the two layers.

[0112] Generally, in accordance with a preferred embodiment of the invention, in order to create a main barrier, the outside thereof is the one of PET, whereas polypropylene is provided on the inside, thereby maintaining both a visual and physical contact of a PET bottle. A polypropylene bottle has a completely different feeling indeed, is much heavier. Besides, PET is better formable as well.

[0113] In addition to preforms, the invention yet relates to injection molded products in general as well, in other words, not only semi-finished products, but also finished products, which no longer need to be blown though. An example of this is shown in FIGS. 5 to 10 with respect to injection molded products, such as so-called upper pv's that form a top component of a certain type of pressure container. In this case, a wall thickness of 1.5 mm e.g. is yet achievable even though it may provide insufficient resistance to pressure: it is injection molded but it expands too much in case a pressure of e.g. 8 bar is applied thereon. For a wall thickness of 1.5 mm, some parts can be made with a wall thickness of 2 mm and some other parts with 1 mm wall thickness, whereby the parts of 2 mm provide additional strength, whereas said added ribs provide additional strength without the need to thicken the whole product completely.

[0114] This second aspect thus aims an additional reinforcement without having to increase the thickness of the entire wall, notably the combination of both for a thin-walled light-weight product, wherein said increased strength is a result of the light weight and the added rib, and in subsidiary order said latter reinforcement mode.

[0115] FIG. 11 shows in partial views a to d a general sequential representation of overmoulding with, in .sub.1, an injection mould 3 which is closed; in .sub.2, the mould which is opened into its 2 mould halves, 31 as the core side and 32 as the cavity side; in .sub.3, a grab arm 4, which arrives therebetween and receives products 11, 12, and finally, in .sub.4 the grab arm 4, which places bottommost products 12 onto topmost cores 31.

[0116] FIG. 12 shows said one grab arm 4, which is provided with a vacuum plate 40 for the reception of injection moulded products 11, 12. Opposite thereto, the relevant mould plate 31 constituting the movable side, is represented, having e.g. 32 cores intended for the composite preforms 10 and 32 cores for the inner preforms 12, which each occupy virtually half of the plate surface, here on the top half.

[0117] The mould plate 32 constituting the fixed side, correspondingly has 32 cavities for the composite preform and a further set of 32 cavities intended for the inner preform, which occupy the other half of the plate surface, the bottom half here.

[0118] FIG. 13 shows the mould 3, closed in step 1 of the method, in the closed state, and the grab arm 4 in a standby position.

[0119] In FIG. 14, the mould plate is represented as the movable side 31 opposite the mould plate represented as the fixed side 32, in which the cavities for the composite preform 10 are also represented, in which the core is incorporated therefor, with there between the finished composite preform 10 with injected inner preform 12.

[0120] FIG. 15 is an analogous representation to the previous FIG. 14, consisting in a cross-sectional view through the line A-A, though in this case as the finished product with regard to the inner preform 12.

[0121] FIG. 16 represents the following phase 2, wherein the mould 3 is opened, in particular with a section along the line E-E in the previous Fig., on which the topmost 32 products constitute the composite preforms 10, with inner preforms.

[0122] FIG. 17 is an analogous representation to the previous Fig., though of a section along the line B-B, with representation of the bottommost 32 products, which represent only the 32 inner preforms.

[0123] FIG. 18 is a schematic representation of the so formed finished product consisting of said composite preform, in which the inner preform is accommodated.

[0124] FIG. 19 further shows the third phase of the method, wherein the grab arm 4 with the vacuum plate 40, coming from the standby position, presently receives all products from the cores 33.

[0125] FIG. 20 is a sectional representation along the line C-C in the previous Fig. showing a cross section, wherein the bottommost 32 products, being the inner preforms, are transferred into the vacuum plate 40.

[0126] FIG. 21 schematically represents the fourth step of the method according to the invention, wherein the grab arm moves upwards with the vacuum plate with the injection moulded products. The 32 bottom products being the inner preforms, are transferred herein onto the cores 33 of the 32 topmost composite preforms 10. Next, the topmost finished products are deposited onto a discharge conveyor 100.

[0127] FIG. 22 further shows a cross section along the line G-G in the previous Fig., wherein the injection moulded inner preforms 12 stand on the topmost cores 33.

[0128] The robot arm then moves further vertically, with the 32 topmost products therein being the composite preforms, wherein these are further expelled from the vacuum plate 40 and are thus ready for packing.

[0129] As soon as the robot arm 41 has disappeared from between the mould 3, the mould can reclose, just as in step 1. It is then ready to injection mould the following products consisting of 32 integrated preforms 10 at the top and 32 inner preforms 12 at the bottom.

[0130] It is to be understood that the method outlined above with the associated figures, is merely an example of embodiment, which is given only by way of non-limiting example, without that it may be considered that the present scope of protection is limited thereto.

[0131] The overmoulding method can be used to produce bicolour preforms. For this purpose, the inner and outer preforms 11 are injected with a different colour, or only the inner or outer preform is coloured. As a result of selective recesses in the inner preform 12, some specific designs and colour variations are obtainable.

[0132] For example, an opaquely coloured inner preform, wherein in the longitudinal axis of the preform a through-recess is provided, and a transparent outer preform 11. This generates a transparent window over the entire length of the preform and bottle, whereby the filling level of the bottle can be observed.

[0133] As far as the addition of two different materials is concerned, the described method for producing overmoulding preforms likewise allows the inner and the outer preform 11 to be injection moulded in another material. This can have special advantages for, e.g. gas barrier, moisture barrier or hot-fill applications. The outer preform 11 can be produced from standard PET, and the inner preform 12 from a high barrier material or a hot-fill material. If so desired, this allows the use of a higher proportion of secondary material for barrier applications compared with known multilayer preforms.

[0134] For hot-fill applications, wherein the complete bottle must standardly be made of expensive hot-fill material, the inner preform alone may consist in this case of secondary material.

[0135] For further applications, the inner preform could consist, e.g. of a polyolefin, and the outer preform of PET. This bottle combines the mechanical and gas barrier properties of PET with the chemical barrier, moisture barrier and thermal properties of polyolefins.

[0136] Even though this can call for a longer vertical movement between the primary and secondary injection step, it does ensure two completely separate hot runners for the primary and secondary material a, b. In addition to an extreme simplification of the hot runner systems, this ensures greater flexibility for the material, since both hot runners can be set at mutually independent processing temperatures.

[0137] Examples of insert-overmoulding with unitized machine:

[0138] Insert-overmoulding preforms were produced on a dual-cavity 2K PET injection machine. The hot runner was mounted such that the a material can be injected individually into the top cavity and the b material can be injected individually into the bottom cavity.

[0139] The cavities were mounted such that in the bottom cavity an inner preform was produced without screw thread, and in the top cavity an outer preform was produced with PCO screw thread. In the top cavity a core having a diameter of 0.6 mm less than the core in the bottom cavity has been placed.

[0140] The take-off robot was programmed such that, after one cycle, the preform has been taken off the bottom core and placed on the top core, whilst the finished preform has been removed from the top core and subsequently cooled.

[0141] Materials

[0142] Test 1: in a first test, an overmoulding preform was produced, the inner layer was coloured blue in order to be able to visually evaluate both layers.

[0143] Weight of inner preform 6.2 g; total weight 25.8 g

[0144] A material (outer preform): PET, not coloured.

[0145] B material (inner preform): PET, coloured blue.

[0146] From the produced preforms, bottles were blown and evaluated. Both layers were present in the expected ratio and there was good adhesion between the layers.

[0147] Test 2: In a second test, a milk preform having a highest possible light barrier was produced with overmoulding.

[0148] Weight of inner preform 6.5 g; total weight 26.3 g

[0149] A material (outer preform): coloured with 5% white dye.

[0150] B material (inner preform): coloured with 1% black dye.

[0151] From the produced preforms, bottles were blown and evaluated for light barrier with a spectrophotometer. The results indicated a markedly improved light barrier compared with only white coloured bottles.