EA043289B1 - CO-EXTRUDED MULTILAYER STRUCTURE AND METHOD FOR ITS PRODUCTION - Google Patents

Description

Technical field

The present invention relates to the field of extrusion, in particular to the extrusion of polymer melts.

The present invention relates to a new coextruded multilayer structure, as well as to a method for producing a coextruded multilayer structure.

The present invention also relates to a co-extruded multilayer structure for use as a coating. This cover may be the outer layer of the diaper or the cover of the flexible package.

State of the art

Polymer extrusion processes such as flat slot film extrusion, extrusion coating, blown film, profile extrusion, or filament spinning are subject to severe limitations in either speed and film thickness thinning or fiber diameter due to process instabilities associated with extrusion speed and draw.

Extrusion rate limitations are due to shear flow instabilities. Ultimate shear stress leads to well-known disadvantages: melt shark skin or cheek sticking and finally melt failure. Under shear flow conditions, extrusion rate limitation is caused by the shear stress on the die gap; in addition to the rheology of the polymer itself, the presence of lubricants and process conditions, the shear stress is highly dependent on the cross-sectional area of the die gap and the melt velocity at the outlet of the die or die capillary.

Draw restrictions are due to stretch flow instabilities. These instabilities are well-known disadvantages: melt-drawn resonance and complete collapse of the melt. The stretch flow properties of a polymer melt depend on its stretching viscosity.

The stretch ratio can be defined as the dimensionless ratio of the cross-sectional area of the die gap to the final cross-sectional area of the film divided by the blowing speed in the case of blown film, or the ratio of the cross-sectional area of the spinneret capillary to the final cross-sectional area of the filament yarn in the case of filament spinning. threads. The stretch ratio can also be defined as the ratio of the speed at the final removal position to the speed at the exit of the die.

In the case of tensile flow, the properties of polymer melts differ sharply from those in shear flow due to the nature of the stresses associated with the interaction of molecular chains during deformation.

The extrusion of polymer melts is primarily determined by their tensile flow properties rather than their shear flow properties, so melt instabilities during extrusion are mainly related to the tensile properties of the melt.

The tensile flow properties of a polymer melt depend on its tensile viscosity, and the tensile viscosity λ (also known as the tensile viscosity, tensile, tensile, or tensile viscosity) is determined by the ratio of the tensile stress to the tensile rate λ=σ/(dε/dt), where σ is the tensile stress and ε is the tensile strain or draw ratio, defined as the ratio of length increase to initial length

Δε=Δl/l ₀ , and for instantaneous deformation dε=dl/l

In stationary states of the flow, ε is constant.

Due to experimental and physical limitations, it is difficult to achieve steady-state conditions in tensile viscosity measurements; instead, there is usually a transient data plot showing the change in stretch viscosity over time for various strain rates.

Industrial tensile rheometers are available in the art based on either a constant or variable velocity of the molten polymer. Stretch measuring devices using shear rheometers are also very common. See, for example, Polymer Melt Rheology and the Rheotens Test by Anka Bernnat, Institut fur Kunststofftechnologie, Universit at Stuttgart, 2001. The rheological strain gauge experiment is a quasi-isothermal fiber spinning experiment. The polymer melt, previously cut in a capillary spinneret, is drawn out under the action of a constant drawing force until the filament yarn breaks. The result of the experiment is a stretch diagram that describes the elongation properties of a polymer melt and is therefore relevant to many processes in polymers such as blow molding, film blowing, and fiber spinning. The breaking stress of the polymer melt can also be calculated, which is important for these industrial applications. In general, melt strength and drawability depend on the properties of the melt material and on the conditions

- 1 043289 processing of the experiment. The presence of rheological-tensometric generalized curves makes it possible to separate the properties of the polymer melt from the processing conditions and, thus, simplifies the description of the elongation properties in the case of deformation with a constant force. The generalized rheological-tensometric curve reflects structural differences in polymer melts.

For an example of polymer tensile viscosity determination, see Determination of elongational viscosity of polymer melts by RME and Rheotens experiments by Manfred H. Wagner, Rheol. Acta (2002), 41:316-325, DOI: 10.1007/s00397-002-0228-0 attached to this application.

Three types of pure elongation flow properties can be observed.

1. The tensile viscosity is independent of the tensile stress at elongation, these materials are called Trutonian materials, and the viscosity is often referred to as the Trutonian viscosity.

2. Tensile viscosity increases continuously with increasing tensile stress. This property is known as tension stiffening, deformation thickening, tensile thickening, or elongation thickening. This is analogous to dilatancy in shear flow.

3. Tensile viscosity reaches a maximum value and then decreases with increasing tensile stress. This property is known as tensile thinning, strain thinning, tensile thinning, or elongation thinning. This is analogous to pseudoplasticity or shear thinning.

Trutonian materials, i.e. tensile viscosity is generally independent of flow rate. These include polymethyl methacrylate (PMMA), polystyrene (PS), polyethylene terephthalate (PETE), polycarbonate (PC) and polysulfone (PES), as well as all Newtonian fluids.

Tensile thickening has been observed for substantially long branched polymer structures such as low density polyethylene (LDPE), high melt strength polypropylene (HMSPP), ethylene vinyl acetate (EVA).

Linear or substantially short branched polymers such as high density polyethylene (HDPE) and polypropylene (PP) exhibit tensile thinning when subjected to a stretch flow.

Thus, depending on the tensile viscosity properties of polymer melts, the aforementioned disadvantages of instability in the case of tensile flow are

1) resonance during drawing from the melt;

2) complete destruction of the melt.

Resonance during drawing from the melt.

This phenomenon was first described by Christensen (1962) when discussing extrusion coating with polypropylene as draw oscillation or resonance; then, among many other works, in U.S. Pat. No. 4,339,507 to Kurt et al. and in U.S. Pat. occurs between the head and the doffing position when the boundary conditions are a fixed speed at the exit of the head and a fixed speed at the doffing position. Draw resonance occurs for stretchable polymer melts when the draw ratio exceeds the limit value of the removal rate for the particular polymer. Draw resonance is the instability of the melt flow under stretch flow conditions, which manifests itself as inhomogeneities in the final dimensions of the film or fiber. Further drawing above the critical speed causes the destruction of the melt.

Stretch thinning polymers exhibit draw resonance at their ultimate draw ratio.

Polymers that are substantially linear or short chain branched have the property of stretch thinning. Some common examples are linear low density polyethylene, high density polyethylene, polypropylene homo- and copolymers, thermoplastic polyurethanes, polyester-ether copolymers, linear polyamides, polyamide ester copolymers, or polylactic acid-based polymers.

Limiting stretch ratios for common commercial stretch thinning polymers range from 20 to 40.

Complete destruction of the melt.

Under tensile flow conditions, tensile-thickening and Trutonian polymer melts exhibit sudden complete melt failure at their ultimate draw ratio. Complete melt failure occurs at a specific stretch limit for each polymer and is highly dependent on local stress, defect distribution, crack size, and crack growth. In highly entangled molten polymers, the force of attraction between a single molecule and its neighbors is very strong due to the enormous length of the molecules. In addition, during deformation, polymer molecules are oriented and often stretched depending on the deformation field. This induced anisotropy leads to large normal stress differences as well as material inhomogeneities,

- 2 043289 depending on these voltage differences.

Polymers having a structure of essentially long branched chains, as a rule, have the property of thickening when stretched. Examples are low density polyethylene and its copolymers such as ethylene vinyl acetate or acrylate, or polystyrene; polyolefin elastomers and plastomers; polypropylene with high melt strength; linear low density polyethylene, partially crosslinked with peroxides; ionomers; copolymers of acrylic or methacrylic acid; or extended chain branched polyesters, polylactic acid polymers and polyamides.

Polymers exhibiting tensile-thickening properties under tensile flow conditions typically have a limiting draw ratio of 30 to 80.

The role of material defects or inhomogeneities as nucleation centers for cavities and cracks is important for fracture mechanics. Chen et al. in Shear fracture of polystyrene melts and solutions, Rheol. Acta, 1994, investigated the possible role of nucleation sites in melt fracture, supporting the hypothesis that cavity growth is necessary for fracture. They also observed that the addition of a solvent lowered the ultimate fracture stress. They concluded that defect size is an inherent property of a polymer melt or solution at a given temperature. The internal size of the defect was also noted by Kinlock and Young (Kinlock, Young) in Fracture behavior of polymers, New York, Elsevier, 1983, to explain the failure of rubbers and glassy polymers.

US 5,688,457 explains the effect of boron nitride in the extrusion of fluoropolymers and polyolefins. The boron nitride particles provide many nucleation sites for many very small cracks, thus reducing the stresses that cause a large scale fracture to a limiting value.

The general conclusion is that complete melt failure occurs at a specific stretch limit for each polymer and is highly dependent on local stress, defect distribution, crack size, and crack growth.

The most accurate study for predicting the tensile properties of polymer melts was developed by Dow Chemical for ethylene polymers only using DRI (Dow Rheological Index) presented in Antec reports in 1993. DRI is independent of shear viscosity and must be calculated for each specific polymer by non-linear regression of experimental data using the general equation

DRI = (3.65 * 10 ⁶ * - 1) / 10

Where το is the characteristic relaxation time, η ₀ is the viscosity at zero shear.

The index ranges from 0 (polymers without long chain branching) to 30.

Despite all these studies, the tensile properties of a polymer melt cannot be predicted for a particular polymer and must still be measured with an elongation viscometer (RME rheometrics) or with a Gottfert rheological strain gauge system, which is a common setup available in the field. equipment for a qualified specialist in the field of extrusion.

Draw instability also affects performance in extrusion coating processes where the substrate provides the desired mechanical performance of the product, in this case high speed and low coating weight are required. The extremely narrow die gaps required to achieve the desired low coating weight significantly increase the shear stress in the polymer, requiring the extrusion line to operate at low speed if it cannot operate at higher draw ratios.

Significant developments in process, equipment, or melt compositions have also been disclosed to improve limiting resonant draw ratios for linear polymers, also by mechanical means on extrusion equipment; see, for example, US 4668463, US 4608221 or US 4626574; overheating or rapid cooling of the melt in US 4859379 and US 4486377; encapsulation of linear low density polyethylene along the edge with low density polyethylene in US 4348346 or encapsulation across the entire width in Tension in multilayer film casting of polymer melts, Baigui B., 1998; polymer degradation in US 3247290 and US 4378451; melt blends of linear low density polyethylene with low density polyethylene, US 4339507, US 5582923, US 4780264, US 5773155, US 5674342, US 4339507, US 5395471, US 7846551 US 33836694A and US 5863665.

J.Z Liang in Melt elongation strength and drawability of LDPE/LLDPE blends, Institute of plastics machinery and plastics engineering, Beijing University of chemical technology, discloses improvements in melt drawability for 60% LDPE content in LLDPE and LDPE melt blends.

Joo Sung Lee in Stabilization of film casting by an encapsulation method, Department of Chemical and Biological Engineering, Applied rheology center, Korea University, February 2003, reveals some of the improvement in drawdown and constriction by encapsulating HDPE melt edges with LDPE in an encapsulation method extrusion.

-3 043289

Although the prior art has disclosed an improvement in drawdown ratios over individual property drawdown ratios of the components, there is still a need for a practical method that can substantially improve the drawdown ratio in multilayer structures over the individual property drawdown ratio of the polymers forming the layers. extruded multilayer material, and this method should be suitable for many polymers in a simple, safe and reproducible manner.

Brief description of the invention

The present invention has been made in view of the prior art described above, and the object of the present invention is to provide a co-extruded multilayer structure having an improved stretch limit compared to the stretch limit of each of the layer polymers present in the laminate and extruded separately. Thus, the present invention provides a co-extruded multilayer structure that, under conditions of stretch flow, is capable of greater elongation or stretching without causing elongation flow instabilities.

To solve the above problem posed by the invention, in the first aspect, the present invention provides a co-extruded multilayer structure containing a first composite layer located above the second composite layer, and additionally containing an intermediate layer located between the first and second composite layers, and the first composite layer contains the first polymer , the second composite layer contains the second polymer, and the intermediate layer chemically or physically interacts with the first polymer and the second polymer, gluing both layers either in the molten state or after the polymers have solidified, while the first polymer and the second polymer differ from each other by at least , its tensile viscosity, one polymer maintains or increases its tensile viscosity at its ultimate tensile stress draw ratio, and the other polymer decreases its tensile viscosity at its ultimate tensile stress draw ratio, and the intermediate layer can be obtained by the method co-extrusion using one common head, the method includes the following steps:

supply of the first and second composite layers to one common die under the influence of temperature for simultaneous co-extrusion of the molten layers, and the intermediate layer is formed as a result of chemical interaction between the first and second polymers or, optionally, the intermediate layer is formed as a result of physical interaction between the first and second polymers, if simultaneously serves the third adhesive layer between the first and second composite layers to one common head;

after the exit of the co-extruded layers from the die, stretching the molten co-extruded layers under tensile stress, whereby the resulting co-extruded multilayer structure has a draw ratio greater than the limiting stretch ratio of each of the first and second polymers extruded separately, thus reducing the cross-sectional area of the co-extruded multilayer structures to a lower value;

cooling the co-extruded multilayer structure to room temperature; and optionally performing stretching and cooling steps, isolating the co-extruded laminate from ambient air.

According to the present invention, the co-extruded laminate structure may be flat, tubular, or shaped, depending on whether a flat die, a tubular die, or a selected shaped die is used as one common die in a conventional extrusion technique.

Those. the inventors of the present invention have found that selecting first and second polymers with different tensile viscosity properties, provided that at their separate limiting draw ratios, one polymer decreases its tensile viscosity and the other polymer increases its tensile viscosity, results in a molten co-extruded multilayer structure with a greater amount of stretch/elongation under tensile stress.

In one embodiment, the first and/or second polymers may independently be a mixture of a polymer.

According to the present invention, the mixture of the first and/or second polymers has the same properties as the first and/or second polymers, respectively.

Therefore, it is within the scope of the present invention to replace the first polymer with a first polymer blend and/or replace the second polymer with a second polymer blend, provided that the polymer blend has the properties of the corresponding replaced first and/or second polymer.

In a preferred embodiment, the resulting co-extruded multilayer structure has an ultimate stretch ratio that is 10%, 20%, 50%, 90%, 100%, 150%, 200%, 250%, 275%, or 300% greater than the ultimate drawdown ratio of each of the first and second polymers extruded along the separately.

The fact that the resulting coextruded multilayer structure has an improved limiting stretch ratio is based on the various properties of the selected layers present in the coextruded multilayer structure thus formed. With these properties, the tensile-thinning layer is supported by the tensile-thinning layer at its resonant drawdown ratio due to the strength of its melt, and the tensile-thickening layer is supported by the tensile-thinning layer at its drawdown ratio due to the fact that small cracks formed in at the beginning of the melt fracture, do not grow due to the support of the tensile-thinning layer, which leads to the weakening of the stresses of the tensile-thickening layer instead of causing the fracture to propagate through the layer and completely destroy this melt. As a consequence, the limiting stretching for the complete destruction of the melt is significantly improved due to the presence of an tensile thinning layer in the set of selected layer properties.

In a first aspect, the present invention relates to a co-extruded laminate having the advantage of thinner thickness or smaller diameters as well as lighter weight, making the co-extruded laminate suitable for thinner coating and therefore lighter weight.

Polymers that reduce their tensile viscosity at their ultimate draw ratio under tensile stress are polymers whose structure is substantially linear or contains short branched chains such that when subjected to tensile stress their molecular chains become generally oriented in the direction shear, after which the molecular chains are unraveled to a certain extent, which reduces their resistance to flow.

Polymers with tensile thinning properties can be selected, without being limited to this list, from linear low density polyethylene; polyethylene and polybutylene terephthalate; polyester-ether block copolymers; polyesteramide block copolymers; thermoplastic polyurethanes; homo- and copolymers of polypropylene; high density polyethylene; linear polyamides of medium density polyethylene; polymers of polylactic acid, and their copolymers or mixtures and mixtures thereof with mineral fillers.

Polymers that increase their tensile viscosity at their ultimate draw ratio under tensile stress are polymers whose structure is essentially a long branched chain, so that when subjected to tensile stress, their molecular chains become entangled, thus preventing relative movement between molecular chains, which increases their resistance to flow.

Melts of Truton polymers show a sudden melt break at their ultimate drawdown under tensile stress, so a Truton polymer can be used as the stretchable polymer in the present invention.

Polymers with tensile-thickening properties or Trutonian polymers can be selected, without being limited to this list, from low density polyethylene; copolymers of ethylene vinyl acetate and acrylate; polystyrene; polyolefin plastomers and elastomers; polypropylene with high melt strength; cross-linked polypropylene with a peroxide or zinc catalyst (for example, dymalink 9200 from Cray Valley); partially crosslinked linear low density polyethylene and its copolymers; a polyolefinic acid copolymer; ionomers; branched polyamides, polylactic acid polymers and polyesters with chain extenders; and their copolymers or mixtures and their mixtures with mineral fillers.

Preferably the first polymer and/or the second polymer are selected to have a water vapor transmission rate equal to or greater than 1 g mm/m ² day.

In one embodiment, the co-extruded multilayer structure is a film with a thickness of not more than 1 micron.

In another embodiment, the co-extruded multilayer structure is a filament thread with a diameter of not more than 1 micron.

In an embodiment, the coextruded multilayer structure has a water vapor transmission rate in the range of 1000 to 20000 g/m ² day.

The co-extruded multilayer structure obtained by the method described in this application makes it possible to obtain films, filaments or melt-spun nonwovens with low weight at high speed using conventional extrusion equipment.

The co-extrusion process described herein may be selected from any one of the following: flat slot extrusion, blown film extrusion, extrusion coating, extrusion lamination, liquid coating extrusion, profile extrusion, filament spinning, or nonwoven extrusion. obtained by spinning from the melt.

- 5 043289

In a second aspect, the present invention provides a method by which a co-extruded multilayer structure according to the first aspect of the invention can be obtained.

Thus, in a second aspect, the present invention provides a method for producing a co-extruded multilayer structure comprising a first composite layer positioned over a second composite layer and further comprising an intermediate layer positioned between the first and second composite layers, using a conventional single die co-extrusion technique, wherein the method includes the following steps:

selection of the first polymer and the second polymer, provided that the first polymer and the second polymer differ from each other in at least their tensile viscosity, wherein one polymer increases its tensile viscosity at its ultimate elongation under tensile stress, and the other the polymer reduces its tensile viscosity at its ultimate draw ratio under tensile stress, the tensile viscosity being defined as the ratio of the tensile stress to the tensile rate in a conventional extrusion technique;

supply of the first and second composite layers to one common die under the influence of temperature for simultaneous co-extrusion of the molten layers, and the intermediate layer is formed as a result of chemical interaction between the first and second polymers or, optionally, the intermediate layer is formed as a result of physical interaction between the first and second polymers, if simultaneously serves the third adhesive layer between the first and second composite layers to one common head;

after the exit of the co-extruded layers from the die, stretching the molten co-extruded layers under tensile stress, whereby the resulting co-extruded multilayer structure has a draw ratio greater than the limiting stretch ratio of each of the first and second polymers extruded separately, thus reducing the cross-sectional area of the co-extruded multilayer structures to a lower value;

cooling the co-extruded multilayer structure to room temperature; and optionally performing stretching and cooling steps, isolating the co-extruded laminate from ambient air.

The method defined in the second aspect of the present invention provides the advantage of saving on the cost of raw materials, reducing the weight of both processed raw materials, which can be smaller, and finished materials, usually rolled, and, in addition, produces less waste from - because, in general, instabilities in the flow of stretching are prevented, so that a smaller amount of rejected extrudable polymers is formed.

The ultimate stretch ratio of molten co-extruded layers can be defined as the maximum stretch/elongation under tensile stress without causing elongation flow instabilities.

In a third aspect, the invention provides a co-extruded multilayer structure as defined in the first and/or second aspects of the invention for use as a coating on a substrate, the substrate being selected from the group consisting of polymer, paper, textile, nonwoven or metal film, wherein the substrate is coated with a co-extruded multilayer structure using a conventional extrusion method selected from extrusion coating, liquid coating extrusion, extrusion lamination, flat slot extrusion, blown film extrusion, profile extrusion, filament yarn spinning, and extrusion of nonwoven fabrics obtained melt spinning.

The present invention also relates to an outer layer of a diaper containing a co-extruded multilayer structure.

The present application also contemplates packaging covers containing the co-extruded multilayer structure described in the present invention, such as non-woven bags or cartons.

The method described in the present application for producing a co-extruded multilayer structure is particularly suitable for obtaining a thickness of 1 to 14 microns for films, filaments and low weight melt-spun nonwovens. Thus, the resulting polymeric coating with a thickness or diameter of 1 to 14 microns is suitable for use as a coating on substrates selected from cellulose, polymeric films, nonwovens, metals or textiles.

Brief description of the drawings

In FIG. 1 shows a cross-sectional view of a co-extruded multilayer structure obtained according to example 1 of the invention, which has a total thickness of 2.5 μm and is applied to a polypropylene non-woven substrate obtained by melt spinning, with a density of 15 g/m ² .

In FIG. 2 shows a sectional view of a co-extruded multilayer structure obtained according to example 2 of the invention, which has a total thickness of 1.5 μm and is applied to a non-woven substrate of

- 6 043289 polypropylene obtained by spinning from the melt, with a density of 15 g/m ² .

In FIG. 3 is a schematic view of conventional extrusion coating equipment. In this embodiment, conventional extrusion coating equipment has a common die (D) from which a co-extruded multilayer structure (1) emerges, which is then drawn and cooled in an air gap (A), and thereafter applied as a substrate coating (S ), then the coated substrate is rolled in a chill roller (C-R).

In FIG. 4 is a schematic view of the conventional extrusion coating equipment shown in FIG. 3, which additionally has a vacuum chamber (V). The vacuum chamber (V) isolates the molten co-extruded laminate (1) from the ambient air for stability purposes. In this embodiment, the molten coextruded multilayer structure (1) is cooled in contact with a chill roller (C-R). Thereafter, the co-extruded multilayer structure (1) is used as the coating of the substrate (S), then the coated substrate is rolled in a chill roller (C-R).

Implementation of the invention

Good adhesion of the intermediate layer to the first and second composite layers is obtained when the intermediate layer is bonded to the first and second composite layers both in the molten state and after the sandwich structure has solidified. The adhesive strength of the intermediate layer should be at least at the level of the melt strength of the strongest layer; an insufficient level of adhesion can provide only small improvements in stretching and quickly create surface instabilities due to partial or complete delamination of the layers caused by a significant difference in rheological properties between the layers.

The intermediate layer can be obtained in three different ways.

The intermediate layer may be formed as a result of chemical interaction between the first and second polymers. In this embodiment, the first and second polymers are chosen to be compatible polymers with each other, i.e. polymers, which together form a continuous phase in the molten state and after, when the multilayer structure has solidified. At extrusion temperatures, both the first and second polymers form the matrix of the mixture; thus, the intermediate layer is formed during the implementation of the extrusion process, in particular when they are contacted under the action of temperature in one common head.

The intermediate layer may be formed as a result of chemical interaction between the first and second polymers, provided that the first composite layer and/or the second composite layer additionally contain an adhesive material dispersed therein. At extrusion temperatures, the adhesive material is mixed with the first polymer and/or with the second polymer. The adhesive material dispersed in the first composite layer and/or in the second composite layer improves the compatibility between the first and second polymers. Depending on the degree of compatibility between the first and second polymers, the adhesive material may be added in an amount of 0.5 to 10% by weight of the total weight of the polymer, if the first and second polymers tend to mix uniformly with each other upon contact in the molten state. , or at a concentration of from 10 to 60% by weight of the total weight of the polymer, if the first and second polymers do not mix uniformly with each other in contact in the molten state.

The intermediate layer may be formed as a result of physical interaction between the first and second polymers. In this embodiment, an additional layer, which is an adhesive layer, is simultaneously fed between the first and second composite layers to one common head. The adhesive layer may be an adhesive layer made from an adhesive material. In the case of dissimilar incompatible polymers, it is preferable to use this additional tie layer. The tie layer must be chosen so that it has strong adhesion properties to both composite layers.

Preferably, the adhesive layer is a tie layer made from an adhesive material.

In one embodiment, the co-extruded multilayer film is extruded onto a substrate using extrusion coating, liquid coating, or extrusion laminating equipment. It is preferable to allow the co-extruded multilayer film to cool to room temperature before contacting the substrate to avoid excessive consumption of polymer when roughening the substrate.

The co-extruded multilayer film comprises two layers, one of a polymer with tensile thinning properties optionally containing an adhesive material dispersed therein, and the other of a polymer with tensile thickening properties optionally containing an adhesive material dispersed therein. Preferably, the same adhesive material can also be used to bond the co-extruded multilayer film to the substrate, thus preventing the use of a second adhesive material to bond the coating to the substrate.

In another embodiment, the co-extruded multilayer film contains three layers, one

- 7 043289 of a polymer with tensile thinning properties, another of a polymer with tensile thickening properties and a third layer of an adhesive material. Preferably, the same adhesive material can also be used to bond the co-extruded multilayer film to the substrate, thus preventing the second adhesive material from being used as a layer to bond the coating to the substrate.

In one embodiment, the combination of polymers and layers can result in a limiting draw ratio of 260 in the extrusion process, thus providing an overall film thickness of less than 3 microns at equipment removal rates of over 500 m/min.

Coating thickness of cross sections of coated samples can be measured using an optical microscope equipped with a lens scale.

Preferably, the stretchable layer is not positioned between the adhesive layer and the equipment rollers to prevent the adhesive layer from coming into direct contact with the roller, which could wrap around it and cause the equipment to stop.

In one embodiment, a cast coating method is used to coat the substrate (S) with the coextruded multilayer structure (1) and simultaneously with the formation of the coextruded multilayer structure (1) (FIG. 3). When the thickness of the melt curtain is less than 2 µm, it is disturbed by the air currents formed around the cooling roller (C-R). To improve the stability of the melt curtain, a vacuum chamber (V) can be used to support the melt curtain on the surface of the chill roller (C-R) (FIG. 4).

Preferred compositions for obtaining a co-extruded multilayer structure may be as follows.

Composition 1.

Base polymer: polyethylene.

Tensile-thinning layer: linear low density polyethylene, MFI (melt flow index) preferably from 2 to 30; layer thickness from 0.5 to 6 microns.

Stretch layer: low density polyethylene, MFI 2 to 30, blended with a hydrocarbon tackifier that is fully compatible with the blended polymer. The hydrocarbon tackifier is preferably selected from the group with an average molecular weight of 600 to 3000 in an amount of 15 to 60% by weight, preferably 20 to 40% by weight of the total weight of the stretchable layer; the layer thickness is from 0.1 to 6 µm.

Composition 2.

Base polymer: polypropylene.

Tensile thin layer: PP homopolymer or copolymer, MFI 2 to 30; layer thickness from 0.5 to 6 microns.

Stretch thickened layer: long branched high melt strength polypropylene or long polypropylene branched in situ by crosslinking, MFI 2 to 30; mixed with a hydrocarbon tackifier that is fully compatible with the base polymer. The hydrocarbon tackifier is preferably selected from the group with an average molecular weight of 1000 to 3000 in an amount of 15 to 60% by weight, preferably 20 to 40% by weight of the total weight of the stretchable layer; the layer thickness is from 0.1 to 6 µm.

This second composition is particularly suitable for coated substrates for the manufacture of airtight outer layers for diapers, when the substrate is a non-woven material or complex package covers. The support may be cellulose paper, a metal layer, in particular aluminum, or a polymeric layer and a bag wrapping material, when the support is a textile material, in particular woven raffia fibre.

Preferred compositions for producing a coated water vapor permeable polypropylene nonwoven fabric with extrusion of a co-extruded multilayer film in extrusion coating, flow coating or extrusion laminating equipment on a polypropylene nonwoven substrate can be:

an tensile thinning layer, optionally containing an adhesive material dispersed therein, selected from the group having a water vapor permeability value measured by ASTM E96B method greater than 1 g mm/m ² day, and based on an absorption-desorption mechanism (lack of porosity), for example ( but not exclusively) a polyester-ether block copolymer elastomer (commercially known as Hytrel from Dupont or Arnitel from DSM); styrene block copolymers; polyamides 6 or 6.6; polyethylene and polybutylene terephthalate; block copolymers of polyethylene oxide; ABS; thermoplastic polyurethanes; polyester blockamides (eg Pebax from Arkema); biopolymers such as PLA; acrylic copolymers; or mixtures or copolymers thereof; layer thickness is from 0.5 to 6 microns; and a stretchable layer optionally containing an adhesive material dispersed therein, selected from the group of low density polyethylene methyl or ethyl acrylate copolymers or the same anhydride or acid modified copolymers; the layer thickness is from 0.1 to 2 µm;

an acrylic or methacrylic acid copolymer polyolefin; layer thickness is from

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0.1 to 2 µm;

monomer; the layer thickness is from 0.1 to 2 µm;

an ethylene-vinyl acetate copolymer having a vinyl acetate content of more than 18% mixed with a compatible tackifier in a weight ratio of 20-60% by weight of the tackifier; the layer thickness is from 0.1 to 2 µm.

This combination of polymers and layers can achieve stretch ratios above 150, and the water vapor permeability of Mocon ASTM 1249 is between 3000 and 20000 g/m ² day.

In another embodiment, the polyolefin fibers are extruded in a bicomponent core and sheath filament extrusion equipment or melt spinning nonwoven fabrication equipment with the following compositions.

Composition 3.

The core of the filament thread: from 10 to 90% by weight of the total section of the filament thread.

Stretch thickening polyolefin (high melt strength polypropylene or low density polyethylene) 40 to 90% by weight; MFI from 2 to 30; a hydrocarbon compatible tackifier, preferably with an average molecular weight of from 1000 to 3000, from 10 to 60% by weight.

Sheath of the filament yarn: 10 to 90% by weight of the total section of the filament yarn.

Tensile-thinning polyolefin, polypropylene homopolymer or copolymer, or linear low density polyethylene, MFI from 2 to 30.

A similar implementation is performed by using the extrusion of a simple filament yarn (instead of a bicomponent filament yarn) and a higher viscosity polymer with a lower core volume percentage than the polymer viscosity and sheath volume percentage.

Composition 4.

The composition of the filament thread.

Tensile-thickening polyolefin, high melt strength polypropylene or low density polyethylene, MFI from 2 to 10; from 10 to 30% of the total weight.

Tensile-thinning polyolefin, homo- or copolymer of polypropylene or linear low density polyethylene, MFI from 10 to 30; from 60 to 85% of the total weight; compatible tackifier 5 to 10% by weight.

In the case of this composition, in a single component extrusion equipment, the lower volume percent, higher viscosity component passes to the core, and the higher volume percent, lower viscosity component passes to the sheath, allowing the core and sheath filament to self-structure.

In another embodiment, three layers were extruded simultaneously to form a co-blown multilayer film with improved high draw bubble resistance.

In this embodiment, the layer composition comprises an inner layer made of: the aforementioned stretchable layer such as low density polyethylene or high melt strength polypropylene or linear polymers branched in situ by 90 to 50% crosslinking blended with a hydrocarbon enhancer stickiness from 10 to 50%; and an outer layer made from the aforementioned stretch thinning layer such as linear low density polyethylene, polypropylene homo- and copolymers.

Examples

Example 1 (see sectional view in Fig. 1).

Product: breathable outer layer for diapers.

Equipment: 1.5 m wide extrusion coating plant.

Backing: 15 g/m ² polypropylene homopolymer spunbond nonwoven.

Layer structure: A-B substrate.

Layer A composition: Dowlex 2552E MFI 25 LLDPE stretch thinning polymer.

Layer B composition (tie layer): stretch thinning polymer 75% w/w Dow LDPE PG7008 MFI 7, 7; hydrocarbon tackifier molecular weight 1200 Eastman Regalite R1125, 25% by weight.

Technological settings for stable operation:

extrusion temperature of both layers 220°C;

head clearance (hot) 0.4 mm;

output speed 400 m/min;

air gap 345 mm;

total coating thickness (Fig. 1) 2.5 μm;

layer thickness A 1.5 µm;

layer thickness B 1 µm;

hood 160.

- 9 043289

Example 2 (see sectional view in Fig. 2).

The same product and composition as in example 1, but using a vacuum chamber and cooling on the surface of the rolling roll (Fig. 4).

Output speed 550 m/min;

total coating thickness (Fig. 2) 1.5 µm;

layer thickness A 0.9 µm;

layer thickness B 0.6 µm;

hood 266.

Example 3

Product: breathable outer layer for diapers.

The same equipment as in example 1.

Backing: 15 g/m ² polypropylene homopolymer spunbond nonwoven.

Layer structure: A-B substrate.

Layer composition A: stretch thinning polymer, polyester-ether block copolymer Dupont Hytrel DYM350 NC010 MFI 15.

Composition of layer B - tie layer: tensile thinning polymer copolymer resin of low density polyethylene-ethylene and acrylic acid Dupont Bynel 22E804.

Technological settings for stable operation:

extrusion temperature of both layers 270°C;

head clearance (hot) 0.4 mm;

vacuum chamber (cooling on the rolling roll);

total coating thickness 3 µm;

layer thickness A 2 µm;

layer thickness B 1 µm;

linear speed 550 m/min;

hood 133;

breathability (test Mocon ASTM1249) 5200 g/m ² day.

Example 4

Product: breathable outer layer for diapers.

The same equipment as in example 1.

Backing: 15 g/m ² polypropylene homopolymer spunbond nonwoven.

Layer structure: A-B substrate.

Layer composition A: stretch thinning polymer, polyamide 6 Zytel ST7301 NC010.

The composition of layer B - tie layer: stretchable polymer low density copolymer resin of polyethylene-anhydride-modified ethylene and Dupont Bynel 21E830 acrylic acid.

Technological settings for stable operation:

extrusion temperature of both layers 265°C;

head clearance (hot) 0.4 mm;

vacuum chamber (cooling on the rolling roll);

total coating thickness 2.5 µm;

layer thickness A 1.5 µm;

layer thickness B 1 µm;

linear speed 550 m/min;

hood 160;

breathability (test Mocon ASTM1249) 4200 g/m ² day.

Example 5

Product: PP-coated raffia fiber for bags.

The same equipment as in example 1.

Backing: woven raffia with PP 220 g/m ² .

Structure: substrate A-B.

Layer composition A: stretch thinning polymer, polypropylene homopolymer Repsol Isplen PP086Y3E MFI 25.

Layer B composition: 89.5% by weight Repsol Isplen PP086Y3E MFI 25 stretchable polymer; cross-linked with 0.5% by weight Cray valley Dymalink 9200 and 10% by weight Eastman Regalite R1125 tackifier.

Technological settings for stable operation:

extrusion temperature of both layers 260°C;

head clearance (hot) 0.4 mm;

air gap 400 mm;

total coating thickness 3 µm;

layer thickness A 2 µm;

- 10 043289 layer thickness B 1 µm;

linear speed 550 m/min;

hood 133.

Example 6

Product: PP spunbond nonwoven.

Equipment: installation of bonding two components by spinning using Reicofil technology.

Layer structure: A/B filament yarn with core/sheath.

Core Layer A: 90% by weight high melt strength polypropylene Daploy WS420 HMS MFI 22+ 10% by weight Eastman Plastolyn R1140 tackifier.

Sheath layer B: Repsol Isplen PP086Y3E MFI 25 polypropylene homopolymer.

Technological settings for stable operation:

extrusion temperature 260°C;

the diameter of the shell of the capillary die is 0.6 mm;

the diameter of the core of the capillary die is 0.3 mm;

linear speed 300 m/min;

weight number of the resulting filament yarn 0.35;

drawing ratio: 105.

Claims (18)

1. A method for producing a co-extruded multilayer structure containing a first composite layer located above the second composite layer, and additionally containing an intermediate layer located between the first and second composite layers, where the first composite layer contains the first polymer, the second composite layer contains the second polymer and the intermediate layer interacts with the first polymer and the second polymer, using the usual technique of co-extrusion with one common die, and the method includes the following steps: selection of the first polymer and the second polymer, provided that the first polymer and the second polymer differ from each other in at least their tensile viscosity, wherein one polymer increases its tensile viscosity at its ultimate elongation under tensile stress, and the other the polymer reduces its tensile viscosity at its ultimate draw ratio under tensile stress, the tensile viscosity being defined as the ratio of the tensile stress to the tensile rate in a conventional co-extrusion technique; supply of the first and second composite layers to one common head under the action of temperature for simultaneous co-extrusion of the molten layers; after the exit of the co-extruded layers from the die, stretching the molten co-extruded layers under tensile stress, whereby the resulting co-extruded multilayer structure has a draw ratio greater than the limiting stretch ratio of each of the first and second polymers extruded separately, thus reducing the cross-sectional area of the co-extruded multilayer structures to a lower value; cooling the co-extruded multilayer structure to room temperature. 2. The method according to claim 1, where the first composite layer and/or the second composite layer contains an adhesive material dispersed in the first polymer and/or in the second polymer, respectively, where the adhesive materials are present either in a concentration of from 0.5 to 10% by weight if the first and second polymers tend to be homogeneously miscible with each other upon contact in the molten state, or at a concentration of 10 to 60% by weight if the first and second polymers are not homogeneously miscible with each other upon contact in the molten state. 3. The method according to claim 1, where between the first and second composite layers, a third adhesive layer is simultaneously fed to one common head. 4. The method of claim 3, wherein the adhesive layer is a tie layer made from an adhesive material. 5. Method according to any one of claims 1 to 4, wherein the stretching and cooling steps are performed by isolating the co-extruded laminate from ambient air using a vacuum chamber. 6. The method according to any one of claims 1 to 5, wherein the draw ratio is 10% greater than the limit draw ratio of each of the first polymer and the second polymer individually extruded. 7. The method according to any one of claims 1 to 6, wherein the co-extrusion technique comprises flat slot extrusion, blown film extrusion, extrusion coating, extrusion lamination, liquid coating extrusion, profile extrusion, filament spinning, and nonwoven extrusion, obtained by spinning from the melt. 8. A co-extruded multilayer structure having an improved ultimate extrusion draw ratio compared to the ultimate stretch ratio of each of the polymers of the layer, - 11 043289 present in the multilayer material and extruded separately, while the structure contains the first composite layer located above the second composite layer, and additionally contains an intermediate layer located between the first and second composite layers, the first composite layer contains the first polymer, the second composite the layer contains the second polymer, and the intermediate layer interacts with the first polymer and the second polymer, while the first polymer and the second polymer differ from each other, at least in their tensile viscosity, one polymer increases its tensile viscosity at its limiting draw ratio under tensile stress, and the other polymer reduces its tensile viscosity at its ultimate elongation under tensile stress, the tensile viscosity being defined as the ratio of the tensile stress to the tensile rate in a conventional co-extrusion technique, wherein the interlayer is obtained by the method of any one of claims .1-7. 9. Co-extruded multilayer structure according to claim 8, in which these polymers, which reduce their viscosity when stretched, are selected from linear low density polyethylene; polyethylene and polybutylene terephthalate; polyester-ether block copolymers; polyesteramide block copolymers; thermoplastic polyurethanes; homo- and copolymers of polypropylene; high density polyethylene; linear polyamides of medium density polyethylene; polylactic acid polymers; and their copolymers or mixtures and their mixtures with mineral fillers. 10. Co-extruded multilayer structure according to claim 8 or 9, in which these polymers, which increase their viscosity when stretched, are selected from low density polyethylene; copolymers of ethylene vinyl acetate and acrylate; polystyrene; polyolefin plastomers and elastomers; polypropylene with high melt strength; cross-linked polypropylene with a peroxide or zinc catalyst; partially crosslinked linear low density polyethylene and its copolymers; a polyolefinic acid copolymer; ionomers; branched polyamides, polylactic acid polymers and polyesters with chain extenders; and their copolymers or mixtures and their mixtures with mineral fillers. 11. A co-extruded multilayer structure according to any one of claims 8 to 10, wherein at least one of the first polymer and the second polymer has a water vapor transmission rate equal to or greater than 1 g mm/m ² day, measured in accordance with ASTM E96B. 12. A co-extruded multilayer structure according to any one of claims 8 to 11, having a water vapor transmission rate in the range of 1000 to 20000 g/m ² day, measured in accordance with ASTM 1249. 13. A co-extruded multilayer structure according to any one of claims 8 to 11, wherein the co-extruded multilayer structure is a film with a thickness of at most 1 µm. 14. A coextruded multilayer structure according to any one of claims 8 to 11, wherein the coextruded multilayer structure is a filament yarn with a thickness of at most 1 µm. 15. The co-extruded multilayer structure of claim 8, wherein the polymers which reduce their tensile toughness at their own ultimate draw ratio under tensile stress are polymers whose structure is substantially linear or contains short branched chains such that, when subjected to upon them under tensile stress, their molecular chains become generally oriented in the direction of shear, after which the molecular chains are untangled to a certain extent, which reduces their resistance to flow. 16. The co-extruded multilayer structure of claim 8, wherein the polymers which increase their tensile toughness at their own limiting draw ratio under tensile stress are polymers whose structure is essentially a long branched chain such that when subjected to tensile stress stress, their molecular chains become entangled, which prevents relative movement between molecular chains, which increases their resistance to flow. 17. Use of a co-extruded multilayer structure according to any one of claims 8 to 16 as a coating on a substrate. 18. The outer layer of the diaper, containing the co-extruded multilayer structure according to any one of claims 8 to 16.