MXPA94001059A - Coextruded multilayer sheet, apparatus for manufacturing the same, and tube made therefrom - Google Patents

Abstract

Se describe una hoja o lámina termoplástica, coextruida, de capas múltiples, que consiste de una primera capa (121) que incluye al menos una banda (126) de una primera composición polimérica termoplástica alternativa con al menos una banda (127) de una segunda composición polimérica termoplástica, y una segunda capa (128) que consiste de la primera composición polimérica termoplástica, la segunda capa estácontigua a la primera capa. Tales hojas o láminas, que se pueden formar mediante la coextrusión de las diversas capas poliméricas, son, por ejemplo, para observar los contenidos de los tubos. Si la hoja o lámina incluye más de una de cada una de las bandas (126, 127),ésta se puede cortar de varias maneras para formar tubos con una variedad de arreglos de franjas.

Description

£ & "LEAF OR THERMOPLASTIC SHEET, COEXTRUIDA OF MULTIPLE LAYERS, METHOD AND APPARATUS FOR ITS MANUFACTURE AND TUBES MADE FROM THE SAME" Inventor: JOHN GERARD CUNNINGHAM, British, domiciled at 80 Broadway, Chilton Polden, Somerset, TA7 9EQ, England.

Causaire: SIDLA FLEXIBLE PACKAGING LIMITED, British company, domiciled in Plumtree Court, London EC4A 4HT, England.

SUMMARY OF THE INVENTION A multilayer, co-extruded thermoplastic sheet or sheet is described, consisting of a first layer (121) including at least one band (126) of a first alternative thermoplastic polymer composition with at least one band (127) of a second one. thermoplastic polymer composition, and a second layer (128) consisting of the first poly¬ composition # thermoplastic metal, the second layer is contiguous with the first layer. Such sheets or sheets, which can be formed by co-extruding the various polymeric layers, are, for example, to observe the contents of the tubes. If the sheet or sheet includes more than one of each of the bands (126, 127), it can be cut in various ways to form tubes with a variety of fringe arrangements. • DESCRIPTION OF THE INVENTION The present invention relates to a multi-layered, co-extruded thermoplastic sheet or sheet, to methods for making tubes from such a sheet or sheet, and to tubes made in this manner, and to the apparatus for use in the coextrusion of such sheet or sheet. A method of manufacturing multiple layer, co-extruded, thermoplastic sheets or sheets is described in U.S. Patent No. 3,557,265, the contents of which are incorporated herein by reference. This method is commonly known as the single feed / distributor block method, in which the feed block is commonly called the Dow power block. The streams of polymeric molten material are supplied from a supply head to a distribution block, which contains a plurality of passages. A programming section can be provided between the supply head and the distribution block, which section serves to subdivide the streams of molten material and to arrange the streams of molten material in the desired order, at the entrances to the passages. The passages serve to provide the desired order of layers and to provide the desired proportions of polymers in these layers. The streams of molten material leave the passages in a transition channel, where they combine in a stream of individual layered fused material. The layered stream passes through the transition channel under laminar flow conditions, and exits through an extrusion die to form the co-extruded, multilayer, composite thermoplastic sheet or sheet. The layered stream at the p of combination is relatively deep and narrow, compared to the shallow and wide extrusion die. The transition channel is generally tetrahedral in shape, and serves to convert the cross section of the stream of molten material into layers, to correspond to the cross section of the extrusion die. The layered current is combined at one edge of the general tetrahedron, the layers are arranged transversely to this edge and parallel to the opposite edge. The layered stream then passes through the body of the tetrahedron, whereby the layers become progressively wider and shallower, and is then extruded through the extrusion die located at the opposite edge of the tetrahedron. The co-extruded multi-layer thermoplastic sheet or sheet is used commercially in applications of packaging. The individual layers in such sheets or # sheets, each one is formed of a selected material to perform a specific function. The material of the layers of the surface, can be selected for its protective and decorative effect. The printed and decorative descriptions commonly apply to the outer surface of the multilayer thermoplastic container, by means of methods such as hot stamping or dry printing. The one or preferably preferred material, both of the surface layers, is commonly a heat-sealable thermoplastic polymer, so that the sheet can easily be formed into containers such as tubes. Examples of known heat-sealable thermoplastic polymers include polyolefins such as polyethylene and polypropylene. At least one of the surface layers can be pigmented, for example, with a white pigment such as titanium dioxide. It has been found advantageous, generally, to include within said sheet or sheet, one or more inner layers having barrier properties, for example having low oxygen permeability. This type of barrier layer serves to protect the packaged material, from effects such as discoloration or taste change caused by oxidation, and from loss by diffusion, through of the leaf, of essential oils and similar substances.

• Examples of known barrier materials include ethylene / vinyl alcohol copolymer (EVOH), poly (vinylidene dichloride) (PVDC), and poly (acrylonitrile) (PAN) . A known type of co-extruded, multilayer thermoplastic sheet or sheet consists of five layers, specifically the two surface layers, the barrier layer, and an adhesive layer on each side of the barrier layer. The adhesive layer provides good adhesion between the barrier layer and the respective surface layer. Another known type of multi-layer, co-extruded thermoplastic sheet or sheet consists of three layers, specifically the two surface layers and the barrier layer. This mode of construction can be used when the materials of the surface layers adhere sufficiently well to the material of the barrier layer, without the use of adhesive. Multilayer thermoplastic tubes are known, and have been used commercially to package materials, such as toothpaste, shampoo, cosmetics and food materials. Such tubes are manufactured from the same materials, and have the same arrangement of layers as the multilayer thermoplastic sheet or sheet, described above. In a Known method of manufacturing such tubes, the thermoplastic materials are coextruded through an annular die to form a multilayer thermoplastic cylinder. In another known manner of manufacturing such tubes, a multilayer thermoplastic sheet or sheet strip is thermally sealed along the composite edges to form a cylinder. In any case, the cylinder is then cut to length, to form tube preforms. One end of the tube preform is then fixed, for example, by heat sealing, with a head pierced by a hole. The head has a means for releasably securing a cover for covering the hole, for example a threaded neck. The partially finished tube is then filled, generally, with the desired contents from the other open end, which is then sealed, for example, by thermal sealing, to form the entire tube. Such tubes are generally elastic, and tend to recover their original shape after deformation, for example after being compressed to extrude their contents. The known multilayer thermoplastic packaging material in the form of sheet or tubes consists of layers of uniform thickness, so that the packaging material has the same visual appearance «Faith in its total surface. It is desirable that the printed or decorative matter in the package must be legible and distinctive. It is also desirable for the user to be able to see the amount of remaining contents in the package, especially after partial use. This is especially true in the case of an elastic tube that recovers its original shape after squeezing or compression. When the packaging material is opaque, the readability of the printed or decorative material is generally satisfactory, but the user can not see the packaged contents. When the packaging material is clear, ie transparent or translucent, the packaged contents are visible to the user, but the readability of the printed or decorative material may be less than desired, due to the light background. In addition, a transparent or full, translucent container exhibits the same color as its contents, which is not desirable «In many cases, for example, for aesthetic reasons. It is known to print solid color blocks or to apply color film on part of the surface of the clear packaging material, and to apply printed or decorative matter on the solid blocks. This provides packaging material that achieves both readability and visibility goals, but requires an additional manufacturing step.

The invention provides, in a first aspect, # a multilayer, co-extruded, thermoplastic sheet or sheet, comprising: (1) a first layer consisting of at least one band of a first polymeric, thermoplastic, alternative composition with at least one band of a second polymeric, thermoplastic composition, * Y (2) a second layer consisting of the first polymeric, thermoplastic composition, the second layer being contiguous with the first layer.

"Adjacent" means that the first and second layers are directly adhered to and adjoin each other, and that there is no adhesive or other layer between them. The first and second polymeric, thermoplastic compositions are preferably heat sealable both to themselves and to each other. The first and second polymeric, thermoplastic composition must adhere well to each other on a sheet or sheet co-extruded, to ensure good adhesion between # alternative bands and between the first and second layers. The first and second polymeric, thermoplastic composition, preferably, consist mainly of the same thermoplastic polymer. Such a thermoplastic polymer can be, in general, any of those known in the art, for example polyolefins such as polyethylene and polypropylene, polyamides and polycarbonates. * It is essential that the first and second thermoplastic polymer composition have a different visual appearance, and that the different visual appearance of the alternative bands, can be observed from at least one surface of the sheet or sheet. In a preferred embodiment of the first aspect of the invention, the first thermoplastic polymer composition l is clear and the second thermoplastic polymer composition is opaque, whereby the sheet or sheet exhibits alternative clear and opaque bands. The first polymer composition, in general form, is unpigmented. The second thermoplastic polymer composition, preferably, is pigmented, for example with a white pigment such as titanium dioxide. Alternatively, the second thermoplastic polymer composition may be a naturally opaque material, for example a mixture of polyethylene and polypropylene. In a modality »Alternative of the first aspect of the invention, the first and second polymeric composition, both are opaque and are of different color, so that the outside of the sheet or sheet exhibits alternative bands of different color. The invention is not limited by the absolute or relative widths of the alternative bands. In a preferred embodiment of the first aspect of the invention * tion, the opaque bands are relatively broad compared to the clear bands. For example, the minimum ratio of the width of an opaque band to that of a clear band may be 70:30 or greater, preferentially 80:20 or greater, and the maximum ratio may be 95: 5 or less, preferably 90:10 or less. The width of a clear band can be, for example, in the range of 5 to 40 mm or 10 to 20 mm. A preferred type of sheet or sheet according to the first aspect of the invention, consists of six layers arranged in the following order: (1) Alternative bands of a first (clear) and a second (opaque) polymeric, thermoplastic composition; (2) First (clear) polymer composition # thermoplastic (3) Adhesive (4) Barrier polymer; (5) Adhesive; Y (6) Thermoplastic polymer composition, clear.

A particularly preferred type of sheet or sheet, according to the first aspect of the invention, consists of six layers arranged in the following order: (1) Alternative bands of (a) clear polyethylene and (b) polyethylene pigmented with 2 to 10%, preferably about 4% by weight of titanium dioxide, the layer is 50-250 microns, preferably 100- 150 microns thick; (2) Clear polyethylene, 30-150 microns, preferably 75-150 microns thick; (3) Adhesive, 5-20 microns, preferably 10-20 microns thick; (4) EVOH barrier layer, 5-40 microns, preferably 15-40 microns • thickness; (5) Adhesive, 5-20 microns, preferably 10-20 microns thick; Y (6) Clear polyethylene, 50-250 microns, preferably 100-150 microns thick. # Another type of sheet or sheet according to the first aspect of the invention, consists of six layers arranged in the following order: (1) First thermoplastic polymer composition (clear); (2) Alternative bands of the first (clear) and the second (opaque) polymeric, thermoplastic composition; (3) Adhesive; (4) Barrier polymer; (5) Adhesive; Y (6) Thermoplastic polymer composition, clear.

The clear, thermoplastic polymer composition of layer (6) is preferably the same composition as the first polymer composition of layers (1) and (2). One or both layers of adhesives can be omitted, if the barrier polymer adheres sufficiently well to the adjoining polymer composition. A sheet or sheet according to the first aspect of the invention, in general, exhibits a plurality of alternative bands. This is cut, in general, in strips for further processing. These strips are particularly suitable for manufacture of multilayer thermoplastic tubes, whose outer surface exhibits alternative bands, which are visibly different in appearance. Accordingly, the invention provides in a second aspect, a method of manufacturing a tube, which includes the step of heat sealing, together the opposite edges, to form the tube, of a thermoplastic, co-extruded sheet or sheet, of multiple layers , which comprises: (1) a first layer consisting of at least one band of the first polymeric, thermoplastic, alternative composition with at least one band of a second polymeric, thermoplastic composition, and (2) a second layer consisting of the first polymeric, thermoplastic composition, the second layer being contiguous with the first layer.

The opposite edges of the sheet or sheet, preferably, overlap first and then heat sealed. The method may additionally include the Subsequent step of fixing a head at one end of the tube, the head has a hole through it and a means therein, to releasably secure a closure or cap to it. The head can be made of plastic material, fixed to the tube by the known method of thermal sealing. After fixing the head on one end of the tube, the tube can be filled with the desired contents, through the other open end, and the open end can be sealed to provide a tube • finished . The method may further include the step of cutting a wider sheet or sheet into a narrower sheet or sheet, or strips, before the thermal sealing step. The invention provides in a third aspect, a tube having a cylindrical body of sheet or thermoplastic sheet, composite, multilayer, comprising: (1) a first layer consisting of at least one band of the first polymeric, thermoplastic, alternative composition with at least one band of a second polymeric, thermoplastic composition, and (2) a second layer consisting of the jß ^ first polymeric, thermoplastic composition, the second layer is contiguous with the first layer, the body shows a thermal, axial sealing line. The tube according to this third aspect of the invention is manufactured according to the second aspect of the invention. The tube may additionally comprise a head fixed to one end of the body of the tube, the head has a hole therethrough and a means therein to releasably secure a closure or cap thereto. The head can be fixed, for example, with a threaded section capable of receiving a screw cap. Alternative bands are aligned, preferably axially along the tube. '• The alternative bands are visible from the outside of the tube and are of different visual appearance. In a preferred embodiment of the third aspect of the invention, a single band of each of the first and second polymeric composition is visible from the outside of the tube. The exterior of the tube, preferably, exhibits a single clear band surrounded by a wider band of opaque material, for example pigments. mentioned with white color. The width of the clear band • can be, for example, in the range of 5 to 20 mm. The diameter of the tube can be, for example and without limitation, in the range of 20 mm to 50 mm. When the tube shows a single band of each of the first and the second polymer, the strip used to manufacture the tube may contain either a single band of each of the first and the second polymer composition or contain two bands of one composition. ¬ * & polymeric partition divided by an individual band of the other polymer composition. A sheet or sheet containing a plurality of alternative bands, can be cut to form such strips in a variety of ways, as will be described more particularly later. The invention provides in a fourth aspect, a feed block for the manufacture of the sheet, or coextruded, multilayer thermoplastic sheet, comprising a distribution block, which serves to provide a stream of layered melt material, comprising: (1) a first stream layer of molten material, consisting of at least one band of the first polymer composition, ter- moplastic, alternative with at least one band of a second polymeric, thermoplastic composition, and (2) a second stream layer of molten material, consisting of the first polymeric, thermoplastic composition, the second layer being contiguous with the first layer.

The feeding block according to the fourth aspect of the invention is particularly suitable for the manufacture of the sheet or sheet according to the first aspect of the invention. In use, the distribution block according to the fourth aspect of the invention is attached to a supply head, which serves to supply a plurality of streams of molten material to the block, generally, through a section of interposed programming. The streams of molten material flow through a plurality of passages in the block, and combine upon leaving the block, through its outlet face in a stream of individual layered melt material. Each layer in the stream of molten material in layers, may correspond to the stream of molten material flowing through a single passage or may result from the combination of streams of molten material, which flow through two or more adjacent passages. For example, in a known type of distribution block, the thicker, outer, molten material layers of thermoplastic polymer are formed by the combination of streams of molten material flowing through two or more, commonly from three to five, adjacent passages separated by metal lamellae, and the inner, thinner, layers of melt stream of adhesive or barrier material correspond to a stream of individual molten material exiting a passageway individual. In an embodiment of the fourth aspect of the invention, the block contains a plurality of passages corresponding to the bands in the first stream layer of molten material, and one or more passages corresponding to the second stream layer of molten material. The passages are substantially parallel and are of substantially constant cross section through the distribution block. The passages are fed from a properly designed distributor feed hole in the supply head or the programming section. In an alternative modality of the first aspect of the invention, which may be preferred, the first thermoplastic polymer composition, (which may be clear) is supplied to one or more passages, which correspond generally, to the second stream layer of molten material, and second thermoplastic polymer, (which may be opaque) is supplied to one or more passages corresponding generally to the first stream layer of molten material. These passages are separated by deviators for example % metal lamellae These passages do not have constant cross sections throughout the distribution block. The internal channels within the distribution block, serve to divert a proportion of the clear composition in the first stage, to divide it into alternative bands of clear and opaque compositions, so that the stream of molten material in layers, combined, leaving the block, comprises the required combination of the first and second layers. Streams of molten, clear and opaque material are kept separate, preferably, by appropriately designed deflectors or deflectors, all the way through the distribution block. The invention is now described more particularly, with reference to the accompanying drawings, in which like reference numerals are used to refer to similar characteristics: Figure 1 shows a view of the separate, and partially sectioned, parts of a modular feed block form and the individual distributor die, designed according to the prior art, to produce a coextrusion of five layers, of three polymers.

Figure 2 shows a view of the separate parts, in an alternative form of the modular feed block, designed according to the prior art, to produce a coextrusion of five layers, of three polymers.

Figure 3 represents the cross section of a type of sheet, or coextruded, multilayer thermoplastic sheet, according to the prior art.

Figure 4 represents an embodiment of a coextruded, multilayer thermoplastic sheet or sheet according to the invention.

Figure 5 represents an alternative embodiment of a co-extruded, multilayer thermoplastic sheet or sheet, according to the invention.

Figures 6 to 9 represent four alternative ways of cutting the sheet of Figure 4 into strips.

§ Figure 10 shows the opposite edges of a strip cut of a sheet, according to Figure 9, superimposed on the preparation for heat sealing to form a tube.

Figure 11 shows a side view of a thermoplastic tube, longitudinally sealed, composite, multilayer, according to the invention.

Figure 12 shows a cross-sectional view of the tube of Figure 11, along line XII-XII.

With reference to Figure 1, a supply head 101 is supplied with material streams melting of a thermoplastic polymer T, a polymer • of barrier B and an adhesive A as indicated by arrows 102, 103 and 104 (respectively in an unnecessary way). The molten material streams are fed individually in a programming section 105, which serves to subdivide the streams of thermoplastic polymer T and adhesive A, each in two streams, and which arranges the resulting total of five streams of molten material in the desired order TABAT on its supply front 106. The five streams of molten material pass from the programming section 105 through the supply front 106, in an array of five generally rectangular channels, generally indicated as 107 in the distribution block 108. The streams of molten material arranged after passage through the channels 107, exit through the outlet front 109 of the block 108, whereby they are combined in a single layered stream in the combination channel 110. The layered stream passes from the combination channel 110 through a hanger section die 111, under laminar flow conditions , and is extruded between the edges 112 of the die, in the direction generally indicated by the arrows 113, to form a coextrusion of five layers, in which the layers remain unchanged. nece arranged in the order T-A-B-A-T mentioned above. The cross section of each layer within the coextrusion, observed in the direction of the arrows 113, has the shape of a wide and shallow rectangle. The layered stream is deformed by passing through the die 111, so that each layer within the stream becomes uniformly wider and thinner, corresponding to the dimensions of the rectangle defined by the edges 112 of the die. For example, the ratio of the width of a layer at the edges 112 of the die, to that of the same layer on the output front 109, may be in the range of 10: 1 to 20: 1, and correspondingly, the ratio of the thickness of a layer to the edges 112 of the die that of the same layer on the output front 109, may be in the range of 1:10 to 1:20.

With reference to Figure 2, a supply head 101 is supplied with melt flow streams of a thermoplastic polymer T, a barrier polymer B and an adhesive A. The molten material streams are fed individually into a programming section 105, which serves to subdivide and arrange streams of molten material in a total of seven streams of molten material, in ^^^^^ Fi the order T-T-A-B-A-T-T to a supply front 106. The seven streams of molten material pass from the programming section 105 through the supply front 106, in. an arrangement of the seven generally rectangular channels, generally injected, 107 in the distribution block 108. The channels 107 are separated by metal lamellae 114. The streams of molten material are arranged after passage through the channels 107, they come out through * output front 109 of block 108, after which they are combined into an individual layered stream. The outermost pairs of layers on both sides of this stream consist of the same material T, and each pair is combined at the outlet through the outlet front 109, so that the individual layered stream consists of five layers arranged in the TABAT order. This arrangement takes into account the good control of the cut and the flow of the molten material streams when, as is common, the outer layers (thermoplastic polymer composition) are the thickest layers in a coextruded sheet or sheet. Variations of this arrangement are known. For example, the programming section 105, can subdivide and arrange the currents of molten material, in a total of seven streams of molten material, in the order of T-T-T-T-A-B-A-T-T-T-T, streams of molten material that combine in the • outlet through the outlet front 109, to form a stream of individual layered melt, consisting as before of the five layers T-A-B-A-T. With reference to Figure 3, a co-extruded, multilayer thermoplastic sheet or sheet, according to the prior art, consists of five layers of uniform thickness, arranged in the following order: (1) Top layer 121 of polyethylene, pigmented with titanium dioxide, 50-250 microns, commonly 100-150 microns thick; (2) Adhesive layer 122, of 5-20 microns, commonly 10-20 microns thick; (3) Internal barrier layer 123 of EVOH, 5-40 microns, commonly 15-40 microns thick; (4) Layer 124 of adhesive, 5-20 microns, commonly 10-20 microns thick; Y > Ükdií -_ ^ d-a (5) Lower layer 125 of clear polyethylene, • 50-250 microns, commonly 100-150 microns thick.

With reference to Figure 4, a coextruded multi-layer thermoplastic sheet or sheet, according to one embodiment of the invention, consists of six layers of uniform thickness, arranged in the following order: (1) Top layer 121, consisting of clear bands 126 of clear polyethylene, alternatives with opaque bands 127 of pigmented polyethylene (containing up to 4% by weight of titanium dioxide), the layer is 50-250 microns, in the form preferably 100-150 microns thick; (2) Implicit layer 128 of clear polyethylene, 30-150 microns, preferably 75-150 microns thick; (3) Adhesive layer 122, 5-20 microns, preferably 10-20 microns thick; (4) Internal barrier layer 123 of EVOH, 5-40 microns, preferably 15-40 microns thick; (5) Layer 124 of adhesive, in 5-20 microns, preferably 10-20 microns in thickness; Y (6) Lower layer 125 of clear polyethylene, 50-250 microns, preferably 100-150 microns thick » With reference to Figure 5, a multi-layer thermoplastic sheet or sheet, co-extruded, according to an alternative embodiment of the invention, consists of six layers of uniform thickness, arranged in the following order: (1) Top layer 121 of clear polyethylene, 75-100 microns thick; (2) Implicit layer 128 consisting of clear bands 126 of clear polyethylene, alternatives with opaque bands 127 of pigmented polyethylene (containing up to 4% of titanium dioxide weight), 100-150 F microns thick; (3) Adhesive layer 122, 10 to 20 microns thick; (4) Internal barrier layer 123 of EVOH, 15 to 40 microns thick; F (5) Layer 124 of adhesive, 10 to 20 microns thick; Y (6) Interior layer 125 of clear polyethylene, 100 to 150 microns thick.

The visual appearance of the sheets or sheets of both Figures 4 and 5 is narrower, 126 narrower bands, alternatives with broader opaque strips 127 The visual appearance of the modality shown in Figure 4 may be superior to that shown in the Figure 5, due to the presence of pigment in the upper layer, and therefore, may be preferred. The sheet or thermoplastic multilayer sheet, co-extruded, according to the invention, in general form, contains a plurality of alternating bands.

- * - '^ J-He-WM ^ natives of clear and opaque appearance, as shown in Figures 4 and 5. Such sheet or sheet can be cut longitudinally into strips, suitable for the manufacture of tubes containing a single clear band and an individual opaque band. Figures 6 to 9 show a number of ways, in which this can be done. In Figure 6, the sheet or sheet is cut in the middle of the wider opaque strips 127, as indicated by the dashed lines 130-130. This method allows the manufacture of a tube, which exhibits a clear strip, free of any line of thermal sealing. In Figure 7, the sheet is cut at the alternate between the wider opaque bands 127 and the narrower narrow bands 126, as indicated by lines 131-131. This method allows the arrangement of both the opaque and clear portions of a cut strip, to a desired width. In Figure 8, the sheet is cut in the middle of the narrower narrow bands 126, as indicated by the dashed lines 132-132. This method allows the arrangement of the light portions of a strip cut to a desired width, and allows the manufacture of a tube that exhibits a clear strip containing a thermal seal line. In Figure 9, the sheet is cut in half -J "8» * - from both the wider opaque bands 127, as indicated by the dashed lines 130-130, and from the narrower narrow bands 126, as indicated by dashed lines 132-132. This method allows the arrangement of both the opaque and clear portions of a strip cut to a desired width. This method has the particular advantage that the width of the clear bands 126 in the sheet or sheet is at least twice the width of the clear band in the cut strip, and a tube formed therefrom. As mentioned above, the ratio of the width of the current layer of molten material in the extrusion, through the edges of the die, to that of the same layer at the point of combining the stream of layered material, commonly It is in the range of 10: 1 to 22: 1. This can cause engineering or production difficulties when it is desired to manufacture a tube containing a narrow clear band, for example 5 or 10 mm wide. The cutting method shown in Figure 9, lessens these difficulties, while minimizing the amount of arrangement required, and therefore, is a preferred method. Figure 10 shows the opposite edges of a strip cut according to the method shown in Figure 9, in which the strip has been rolled into a cylinder and the opposite edges of the strip have been rolled. > ? ^ i ^^ Wte ^^^^ & superimposed on the preparation for thermal sealing. The first edge portion 135 corresponds to a cut through an opaque band, as indicated in Figure 9 by the dashed lines 130-130. The second edge portion 136 corresponds to a cut through a clear band as indicated in Figure 9 by the dashed lines 132-132. The first edge portion 135 and the second edge portion 136 overlap, so that the lower layer of the first edge portion 135, is in contact with the upper layer of the second edge portion 136. The upper layer of the sheet having edge portions 135 and 136, forms the exterior of the cylinder . The outermost region 137 of the clear band 126 in the second edge portion 136, therefore, is superimposed by the first edge portion 135 opaque, and consequently, the width of the clear band in the cylinder and in the tube formed by heat sealing, it is narrower than the width of the clear band 126 on the cut strip. This method of sealing is of particular advantage when it is desired to manufacture a tube containing a narrow clear band. For example, the clear band on the extruded sheet can be 20 mm wide. The clear band on the cut strip will be half this width, specifically 10 mm. The edge portions of the strip can be overlapped by 5 mm. Consequently, the clear band in the tube will be 5 mm wide. Figure 11 shows a side view of a thermoplastic tube, longitudinally sealed, composite, multilayer, according to the invention. In general, the cylindrical tube 140 consists of the body 141 of the tube and the head 142. Body 141 and head 142 are heat sealed together, along the circumferential line 143. The diameter of the body 141 is approximately 35 mm. The body 141 shows a clear band or strip 144. longitudinal, 3 mm wide. The contents of the tube can be observed through the clear strip 144 and the implicit clear layers. The rest of the exterior of the body 141, indicated as 145, is opaque. The head 142 has an axial hole therethrough (not shown) and carries a threaded portion 146 for the application of a screw cap (not shown) to seal the hole. Figure 12 shows a cross-sectional view of the multi-layer tube body 141, shown in Figure 11, along the line XII-XII. The innermost layer 155 is a clear polyethylene ring 125 microns thick. The innermost layer 155 is covered by, and is contiguous with the first 154 antrial adhesive layer, which is 15 microns thick. The first adhesive layer 154 is directly covered by, and is contiguous with, the inner barrier layer 153, which is an EVOH ring 25 microns thick. The adhesive layer 154 serves to join the innermost layer 155 to the barrier layer 153. The barrier layer 153 is directly covered by, and is contiguous with the second annular adhesive layer 152, which is 15 microns thick. The second adhesive layer 152 is directly covered by, and is contiguous with the implicit annular layer 158, which consists of clear polyethylene. The adhesive layer 152 serves to join the barrier layer 153 to the implicit layer 158. The implicit layer 158 is directly covered by, and is contiguous with the outer layer 151, which is 100 microns thick. The outer layer 151 is a ring consisting of an opaque band 157 of polyethylene pigmented with up to 4% by weight of titanium dioxide, extending about 350 ° of the arc, and a clear band 156 of polyethylene extending over the rest of the ring. The tube body 141 exhibits a heat sealing line 159, which extends radially through the tube and axially along the tube in one of the two interfaces between the opaque band 157 and the clear band 156. The sealing line thermal ; - 36 - is shown schematically, and is, preferably, an overlapping thermal seal, of the type described above, with respect to Figure 10.

It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Having described the invention as above, property is claimed as contained in the following: «Ju" at-.A.-

Claims (20)

1. A multi-layer, co-extruded, thermoplastic sheet or sheet, characterized in that it comprises: (I) a first layer consisting of at least one band of a first polymeric, thermoplastic, alternative composition with at least one band of a second polymeric, thermoplastic composition, and (II) a second layer consisting of the first polymeric, thermoplastic composition, the second layer being contiguous with the first layer.

2. A sheet or sheet according to claim 1, characterized in that the first and second polymeric, thermoplastic composition can be sealed with heat, both with themselves and each other.

3. A sheet or sheet according to claim 1 or claim 2, characterized because the first and the second polymeric, thermoplastic composition consists mainly of the same thermoplastic polymer.

4. A sheet or sheet according to any preceding claim, characterized in that the first polymeric, thermoplastic composition is clear, and the second polymeric, thermoplastic composition is opaque.

5. A sheet or sheet according to claim 5, characterized in that the second polymeric composition, Lermoplastic, is pigmented.

6. A sheet or sheet according to claim 4 or claim 5, characterized in that each of at least one band of the first polymeric, thermoplastic composition, is relatively narrow compared to each, of at least one band of the second composition polymeric, thermoplastic.

7. A sheet or sheet according to any preceding claim, characterized in that it consists of six layers, arranged in the following order: (a) alternative bands of a first and a second polymeric, thermoplastic composition; (b) first thermoplastic polymer composition; (c) adhesive; (d) barrier polymer; (e) adhesive; Y (f) polymeric, thermoplastic, clear composition.

8. A sheet or sheet according to claim 7, characterized in that it consists of six layers arranged in the following order: (a) alternative bands of (i) clear polyethylene and (ii) polyethylene pigmented with 2 to 10 weight percent titanium dioxide, the layer being 50 to 250 microns thick; ^^^^ (b) clear polyethylene, 30 to 150 microns thick; (c) adhesive, 5 to 20 microns thick; (d) EVOH barrier layer, 5 to 40 microns thick; (e) adhesive, 5 to 20 microns thick; Y (f) clear polyethylene, 50 to 250 microns thick.

9. A method for manufacturing a tube, characterized in that it includes the step of heat sealing together, to form the tube, the opposite edges of a multi-layer, co-extruded thermoplastic sheet or sheet, comprising: (I) a first layer consisting of at least one band of a first polymeric, thermoplastic, alternative composition with at least one band of a second polymeric, thermoplastic composition, and (II) a second layer consisting of the first polymeric, thermoplastic composition, the second layer being contiguous with the first layer.

10. A method according to claim 9, characterized in that it additionally includes the previous step of cutting a wider sheet or sheet containing a plurality of bands on a narrower sheet containing a smaller number of bands, the thermal sealing step is then takes place at the edges of the narrowest sheet or sheet.

11. A method according to claim 10, characterized in that the wider sheet is cut through each band of the first thermoplastic polymer composition, and through each band of a second thermoplastic polymer composition, to provide a narrower sheet The first layer comprises an individual band of each of the first and second thermoplastic polymer compositions.

12. A method according to claim 11, characterized in that the sealing step thermal, is carried out on the opposite, superimposed edges of the sheet or sheet, whereby the first and second polymeric, thermoplastic composition, each forms a portion of the circumference of the tube without overlapping.

13. A method according to any of claims 9 to 12, characterized in that it additionally includes the subsequent step of fixing a head on one end of the tube, the head has a hole therethrough and a means therein, to secure releasably a closure or cover to it.

14. A tube, characterized in that it has a cylindrical body of sheet or thermoplastic sheet, composed, of multiple layers, comprising: (I) a first layer consisting of at least one band of the first polymeric composition, Lermop latic, alternative with at least one band of a second polymeric, thermoplastic composition, and (II) a second layer consisting of the first In the polymeric, thermoplastic composition, the second layer is contiguous with the first layer, the body shows a thermal seal line, axial

15. A tube according to claim 14, characterized in that an individual band of each of the first and second polymeric composition is visible from the outside of the tube.

16. A tube according to claim 14 or claim 15, characterized in that each band is axially aligned along the length of the tube.

17. A feed block for the manufacture of the co-extruded, multilayer thermoplastic sheet, characterized in that it comprises a distribution block that serves to provide a stream of layered melt material, comprising: (I) a first layer of molten material stream, consisting of at least one band of the first polymeric, thermoplastic, alternative composition with gjg ^ ¡jjg ^^^ g * at least one band of a second polymeric, thermoplastic composition, and (II) a second stream layer of molten material, consisting of the first polymeric, thermoplastic composition, the second layer being contiguous with the first layer,

18. A multi-layer, coextruded thermoplastic sheet or sheet, according to claim 1, characterized in that it is substantially as described and illustrated with respect to the accompanying figures.

19. A method for manufacturing a multilayer thermoplastic tube, according to claim 9, characterized in that it is substantially as described and illustrated with respect to the appended figures.

20. A multilayer thermoplastic tube according to claim 14, characterized because it is substantially as described and illustrated with respect to the appended figures. In testimony of which I sign the present in this City of Mexico, D.F., on February 10, 1994,