JPH0224656B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to laminated sheet-like products reinforced with composite plastic strands having (in whole, in part or in part) a layer or coating of a heat-sealable adhesive material, preferably a thermoplastic polymer, and a method for making the same. This strand can be made of plastic film; foil such as aluminum foil;
It is sandwiched between layers of outer covering material, which can be paper, such as filled or coated paper, kraft paper, tissue paper (various weights), or various absorbent sheet materials. In a preferred form, the present invention provides an improved reinforced absorbent towel. The plastic strands used to strengthen the product consist of a relatively high strength core polymer such as polypropylene or polyester. The strand has a layer or coating of heat-sealable adhesive material, such as a polymer, which at least partially covers the strand. Preferably, the strands are produced by coextrusion or triple extrusion of the composite material in a special extrusion die. The strands may be arranged in any form of reinforcing fabric conventionally used in the art. Most preferably, however, they are extruded in the form of plastic nets. The present invention will be described in particular detail below with respect to the most preferred embodiment of a continuous absorbent towel comprising multiple tissues reinforced by a continuous three-extrusion plastic net. The net is sandwiched between papers and by means of heat bonding and pressure sealing.
Towels are manufactured in laminated sheet form. Continuous extrusion of plastic nets began in approximately 1956 using the process described in Mercer US Pat. No. 2,919,467.
Since this time, numerous patents have been filed in the United States and other countries describing improvements and improvements in continuous extrusion processes. Early extrusion methods developed along two basic lines: first, a plastic sheet was extruded and holes were formed in it to give a net-like structure; The plastic strands are extruded in an interconnected network to give a net-like structure.
The invention particularly relates to a variant of the latter of the two means. Methods for implementing the latter technique are well known. For example, U.S. Patent No. 3700521
No. 3767353; No. 3723218; No. 3723218;
No. 4,123,491; No. 4,152,479 and No. 4,190,692 disclose apparatus and methods for forming nets by continuous extrusion of strands. The disclosures of the above patents are all of the patents mentioned in the details of the invention below and are included in the description herein. In all of these patents, at least one set of strands is extruded through a number of regularly spaced individual orifices. The second set of strands in the net-like structure may be extruded through a second set of regularly spaced individual orifices, or the second set of strands may be extruded through a series of annular orifice slits. Preferably, the extrusion is carried out periodically. In all cases, the two sets of strands are extruded such that the individual strands intersect at an angle and form an integral bond in the extruded plastic net. The extruded planar sheet obtained by one process or the tube of plastic net obtained by another process is cooled, for example in a water bath, in order to solidify the plastic in the strands, and the net is then stretched with nip rolls or other suitable stretching means. Stretched from an extrusion orifice. It will be clear that the spacing between the strands can be varied as desired. If the net tube is extruded,
This is usually drawn over a cylindrical mandrel that can extend the strands and widen the mouth of the net-like structure. Such stretching of the strands covering the mandrel favorably orients the plastic, but in reality the net is characterized by an "unoriented" state. In many applications, it is desirable to further draw the net-like strands to more fully orient the plastic, and in the case of extruded net tubes, draw the tubes by heating and then further stretching them in the longitudinal direction. This can be done by then orienting the strands. Stretching the tube causes the tube to collapse as it is stretched lengthwise. If the tubes are cut and formed into a planar sheet of stretch net, the planar sheet is heated and one set of strands is drawn and oriented in one direction, and then the strands are separated in a second separation step. A second set of strands may be drawn to orient the strands in a second direction. Some plastic nets can be oriented at room temperature, but in practice the net is heated to accelerate and facilitate its orientation. It has been unexpectedly found that individual interconnected strands that are extruded to form a net-like structure can be co-extruded in the form of composite laminated strands even under shear conditions. It has been found that laminar flow of multiple polymers from coextrusion dies to form individual strands unexpectedly yields extruded composite strands with a laminated structure. vice versa,
Laminar extrusion through the relatively small strand orifice of the die is subjected to mechanical shear effects that occur when forming cross-linked strands, resulting in laminar flow turbulence and mixing of large numbers of polymers, resulting in separation of laminate structures. It was fully expected that this would give strands of mixed polymer that were not mixed. In one preferred form, the present invention provides a laminated sheet product having a net-like structure of individual extruded strands, each strand originating from a three-layer die and thus having a relatively low softening temperature. It is formed from a high strength polymer coated or sandwiched between an outer layer of a heat sealable type polymeric material. Three-layer strands and nets are referred to in the text as "three extrusions." Typical high strength resins for the core include polypropylene, high density polyethylene, low density polyethylene, linear low density polyethylene and polyesters and copolymers. Polypropylene is a preferred high temperature resin because it is relatively inexpensive and has a low orientation temperature. Polypropylene or the like, heat sealable resins such as ethylene-methyl acrylate copolymer (EMA), ethylene-vinyl acetate copolymer (EVA) or ionomeric resins such as Surlyn [Surlyn, E. Ai. EIDupont
de Nemours Co.) and the like.
When sandwiched between outer coverings, the composites together provide a composite reinforcement material that can be used to heat bond and pressure seal the composite to form a sheet laminate. Coextrusion and especially triple extrusion of net-like products in film form are known and described in US Pat. No. 4,410,587. However, there is no discussion in this patent that coextrusion or laminar flow of polymer through a three extrusion slot die can provide composite laminated extruded strands. Details of the invention may be more easily understood from the following description and drawings, in which FIG. 1 represents a three-dimensional cross-sectional view along the vertical axis of a portion of an extrusion die; FIG. 1 represents an enlarged partial sectional view of a portion of the extrusion die of FIG. 1 taken at the area indicated at 2 in FIG. 1; FIG. 3 shows how the tubular net is cut and opened into planar sheets of net; 4 depicts a perspective view of a preferred product of tubular extruded net with a small portion of the net cut along the long axis to show how the net is cut; FIG. 4 shows an enlarged partial perspective view of a portion of the flattened net shown in FIG. FIG. 5 shows an enlarged cross-sectional view of the strand of the net along line 5--5 of FIG. 4; FIG. 6 shows an illustration of a portion of the die head plate with only the extrusion head; FIG. 8 represents an enlarged cross-sectional view of a portion of FIG. 1 taken at the area indicated at 7 in FIG. 1 with the die striker in a lower position; FIG. 8 except that the striker is in a raised position; represents a partial view similar to FIG. 1; and FIG. 9 represents a perspective view of a form of netting of the invention used as a reinforcing material clamped to a portion of a reinforcing tissue. Typically, in the present invention, the plastic machine direction strand is continuously extruded through a number of regularly spaced orifice ports arranged annularly relative to the extrusion die head. Adjacent continuous orifices extending annularly relative to the die head are alternately closed and unclosed, so that each time they are not closed, an interconnected lateral strand is provided. The mechanism that alternately closes and uncloses the continuous annular orifice is referred to in the text as a striker. The extrudates produced by the above construction usually consist of a plastic net with a rectangular opening extending along the length of the tube. As is also known in the prior art, longitudinal splitting of the tube at the end remote from the extrusion die flattens the net-like product into a sheet-like form and then undergoes orienting operations and other treatments according to known techniques. It can be carried out. As particularly shown in the described drawings, the method of manufacturing a preferred embodiment of the present invention comprises a net of composite strands each consisting of a laminated extruded structure representing a different inner layer sandwiched between oppositely disposed outer layers of polymeric material. It will be described in detail as involving three extrusions of the workpiece. Referring to FIG. 1, an annular extrusion die 10 is partially shown as including an annular extrusion die head 12. As shown in FIG. Die 10 is of conventional conventional type and has standard features such as support bolts and known and common adjustment structures (not shown). However, this die differs in one important respect.
In die 10, polymer materials 18a, 20a
and 22a (shown in FIG. 2) are each held under pressure and placed in a die by an extrusion system (not shown), and the individual polymer material streams are The die 10 is fed as shown in annularly arranged reservoirs 18, 20 and 22. All of these reservoirs are connected and flow directly into a conventional annular reservoir 24. Reservoir 24 receives three separate streams of polymeric material 18a, 20a and 22a, respectively, which combine in annular reservoir 24 into a three-layer laminar flow condition;
It exits the reservoir 24 and enters a conventional annular feed channel 26. This is best illustrated in Figure 2, which shows a triple stack of flowing polymeric materials 18a, 20a and 22a. The three-layer flow passes through a die lip, generally indicated at 28, forming a composite three-layer strand as an interconnected network, as shown in Figures 1-3.
The tubular net-like structure 50 shown in the figure is provided. For the purpose of extruding machine direction strands 30 and cross direction strands 32, die lip 28 is preferably formed as shown and includes a series of raised and regularly spaced holes on upper die head plate surface 14. Land 34 placed in
6, forming a series of annularly disposed lower die orifices 36 therebetween, through which the machine direction strands 30 are continuously extruded from the die, as best shown in FIG. . As best shown in FIG. 1, the lands 34 on the die head plate 14 are spaced apart over a portion 38 of the die 10 so that the lands 34 form a continuous annular orifice surrounding the die.
4 provides an upper passage 40. Associated with the upper passageway 40 is a vertically movable striker 42 (FIG. ). Striker 42 contacts the upper surface of land 34 on its downward stroke as shown. When the striker 42 is in a lower position (best shown in FIG. 7), the passageway 40 is closed and has a number of regularly spaced rings distributed annularly as shown in FIGS. 1-3. Only continuous extrusion of the machine direction strands 30 occurs through the lower orifice 36 which is always open for continuous extrusion of the machine direction strands 30 disposed.
When the striker 42 is raised to its upper position (best shown in FIG. 8), the passageway 40
is not closed and extrusion of an annular transverse strand 32 occurs. The up and down movement of the striker 42 is relatively rapid and causes the extrusion of regular intervals of transverse strands 32 interlocking with the continuously extruded machine direction strands 30, thereby causing the extrusion shown in FIGS. 1-3. A tubular net-like structure 50 is formed. The resulting net tube, indicated generally at 50, passes through an extrusion die head 12, preferably over a cylindrical mandrel (not shown), and then over a water bath (not shown), as is already known in the art. ) and preferably through a pair of nip rolls (not shown). After the plastic strands have been placed, the tubular net is preferably cut lengthwise by conventional cutting means, indicated generally at 52 in FIG.
It is then opened into a flat sheet 54, a portion of which is shown in FIG. This sheet can be wound onto a take-up roll (not shown) by known means. In accordance with the present invention, the strands extruded using the die of FIG. 1 are composite and have a laminated multilayer structure as shown in FIG. 5 when polymer 20a is different from polymers 18a and 22a. The illustrated multilayer structure consists of a core polymer 2
The preferred three-layer three-extrusion structure is such that Oa is sandwiched between a first outer layer 18a and a second outer layer 22a, which are generally arranged opposite each other and both are adhesive materials. An unexpected advantage obtained is that the composite laminate structure created by the three-layer flow within the die body is relatively weak when formed within the extrusion head 12 with the shearing action provided by the striker 42. It resides in the fact that it is retained and emerges even when extrusion is carried out through a small strand-forming orifice. In accordance with a preferred embodiment of the present invention, the outer polymer layers 18a and 22a are relatively stable, heat-sealable types of adhesive polymers and adhesive resins, and other heat-sealable adhesives, which may be selected from the group consisting of adhesive polymers and adhesive resins, and the like. It can be an adhesive material. These materials are of the type that, when in polymeric form, have a lower softening temperature than the core polymer, such as ethylene-methyl acrylate copolymer (EMA), ethylene-vinyl acetate copolymer (EVA) and thermoplastic polyvinyl chloride,
Contains polyamide. In other forms, these include hot melt adhesives, ionomer resins such as Surlyn, E. Ai. Modified polyethylene, commercially available from EIDupont de Nemours Co., thermoplastic rubbers such as Kraton, Shell Chemical Co., Hyuston, Texas.
Chemical Co.) and the like. The expression "polymer" is generally used in the text to include copolymers. The most preferred resin polymer is ethylene-methyl acrylate copolymer (EMA). Core polymeric material 20a may be selected from the polymers generally described herein as high strength polymers, and may be selected from the group consisting of polypropylene, polyethylene, polybutylene, polyester, nylon, and the like. The present invention is not limited to the above-mentioned group of materials, but in other words includes a considerable number of polymers, copolymers and the like falling within the categories of cores and heat-sealable adhesives. 3. The most preferred combination in extrusion is a core layer 20a of polypropylene and ethylene-methyl acrylate copolymer (EMA) or ethylene-
two outer layers 18a and 22 of vinyl acetate copolymer (EVA), the former being most preferred;
Consists of a. In the case of biaxial stretching, this particular combination of materials
The present invention provides a three-extrusion reinforcing material, schematically shown in FIG. 9, which is useful for strengthening tissue and other sheet products when sandwiched between two external fabric layers such as paper, tissue, foil, or the like. The outer fabric layers are shown at 60 and 62. The reinforcing net structure is shown at 64. Ethylene-methyl acrylate copolymer (EMA) or other materials used as 18a and 22a are heat melt adhesives that when heat and pressure are applied to the composite bond the heat-reinforced net-like structure to the outer fabric layers 60 and 62. It has the advantage of providing functionality. Material 18
a and 22a do not need to be the same. As already mentioned, any flexible outer covering material can be used as the outer covering of the laminate, such as aluminum foil, polyester film, nylon film, cellophane paper, oriented polypropylene, acetate film, and the like. Absorbent papers are preferred for the purpose of providing reinforced towels. Preferred Teitshu materials for this purpose are 2, 3 and 4 ply 9-19
Scott Paper Company with a weight of lbs./3000 sq. ft.
Company) products are available. Another absorbent material for use in the present invention is U.S. Pat. No. 4,296,161.
It is listed in the issue. The most preferred heat-sealable material is EMA, several types of which are manufactured by Gulf Oil Chemicals, such as 2205,
2255 and 2207T etc. can be used. Some types of EVA are manufactured by E.I. Dupont de Nemours and Corporation.
Nemous & Co.) 3180, 3175, and 3190 are available. Conventional thermal bonding and pressure sealing are satisfactory in the preparation of the laminates of the present invention. Generally, this can be done by various means, such as by contacting heated plates or rolls on both sides of the laminate assembly or composite. Example 1 A strand network in which the core layer is made of polypropylene and the two outer layers are made of Dupont EVA #3180, produced by the above three extrusion operations, is sandwiched between the two layers of the above-mentioned Scott Tissue material. , hot-roll these at a temperature of 200-250
〓 was heat-bonded and pressure-sealed to form a laminate. Example 2 Dupont as the outer layer of the strand network
A laminate was produced by repeating the same procedure as in Example 1, except that Dupont EVA #3175 was used instead of EVA #3180. Example 3 Dupont as the outer layer of the strand network
A laminate was produced by repeating the same procedure as in Example 1, except that Dupont EVA #3190 was used instead of EVA #3180. Example 4 A strand network produced by the three extrusion operations described above, in which the core layer is made of polypropylene and the two outer layers are made of Gulf Oil Chemicals EMA2205, is sandwiched between the two layers of the above-described Scott tissue material. These were then thermally bonded and pressure sealed at a hot roll temperature of 220-250° to form a laminate. Peel Test: The peel test data described herein was obtained by separating the layers of the test laminate and measuring the force required to effect separation. This force is measured in grams and is shown below, normalized to strand count and adhesive coat weight for comparison.

[Table] These peel tests were performed on standard absorbent towels using the same paper, latex adhesive and conventional single layer plastic net reinforcement (typical results in peel tests of 10 grams/strand/resin bond/ 1000 square feet). It will be understood that the claims cover all changes and improvements in the preferred embodiments of the invention that are chosen for purposes of illustration in the text.

[Brief explanation of drawings]

1 is a three-dimensional sectional view along the vertical axis of a portion of the extrusion die; FIG. 2 is an enlarged partial sectional view of the portion of the extrusion die of FIG. 1 taken at the area indicated by 2 in FIG. 1; Figure 4 is a perspective view of a preferred product of tubular extruded nets with a small section of net cutting along the long axis showing how the tubular nets are cut and opened into planar sheets of nets; The figure is an enlarged partial perspective view of a portion of the flattened net shown in Figure 3, and Figure 5 is an enlarged partial perspective view of the flattened net shown in Figure 4.
6 is an explanatory view of a portion of the die head plate with only the extrusion head; FIG. 7 is a portion of the portion of FIG. 1 taken at the area indicated by 7 in FIG. 1; FIG. 8 is a partial view similar to FIG. 1 except that the striker is in a raised position; FIG. FIG. 3 is a perspective view of a net configuration of the present invention used as a clamped reinforcing material; In the figure, 10...Die, 12...Die head, 1
8a, 20a, 22a...polymer material, 28...
...Die lip, 30...Device direction strand, 3
2... Horizontal strand, 34... Land, 36
...Die orifice, 42...Striker.

Claims (1)

Claims: 1. A reinforcing network of interconnected thermoplastic strands sandwiched between an outer cladding, the strands forming an inner reinforcing core of polymeric material and an outer heat sealable mold. extrudable materials, wherein the inner and outer materials are coextruded by successive extrusions in a layered manner to form a strand network, the extrusion forming bonding the strands together; The inner cores are integrally connected to each other,
An outer reinforced laminate consisting of a combination produced by thermally bonding and pressure sealing a composite structure between outer sheathings. 2. A laminate according to claim 1, wherein the strand network comprises an extruded oriented network. 3. The structure of the strands is extruded in three parts in a stack and consists of at least two different polymers, the inner core polymer has a higher softening temperature than the outer polymer, and the outer polymers are usually arranged oppositely on the core. Claim 1 forming a layer part
Laminate as described in section. 4. A laminate according to claim 3, wherein the core polymer consists of polypropylene and the outer polymer is ethylene methyl acrylate copolymer (EMA). 5. The laminate according to claim 3, wherein the outer covering material is an absorbent material. 6. The laminate according to claim 3, wherein the outer sheathing material is made of a Teitshu material. 7. A laminate according to claim 6, wherein the core polymer consists of polypropylene and the outer polymer is ethylene methyl acrylate copolymer (EMA). 8. The laminate according to claim 1, wherein the core polymer comprises polypropylene. 9. A laminate according to claim 1, wherein the external material is an ethylene methyl acrylate copolymer (EMA). 10 The core polymer is made of polypropylene,
A laminate according to claim 1, wherein the external material is ethylene methyl acrylate copolymer (EMA).