HK1069800B - Polyolefin film, tape or yarn - Google Patents

Description

Polyolefin films, tapes or yarns

Technical Field

The present invention relates to a polyolefin multilayer film, tape or yarn suitable for the preparation of reinforced textile materials or non-textile type materials, in particular for reinforcing and/or stiffening products. The single or multilayer banded polyolefin films are typically prepared by blown film or cast film extrusion. The material may be stretched at some stage of the manufacturing process in order to increase the strength and stiffness of the material.

Background

Polyolefin tapes and yarns are typically prepared from polyolefin films of the monolayer or multilayer type by cutting the film to the desired width. The material may be stretched at some stage of the manufacturing process in order to increase the strength and stiffness of the material.

US-a 5,578,370 discloses a thermoplastic composite formed from a polypropylene film coated with a layer of an ethylene copolymer further comprising propylene units. The coated layer has a lower softening point than the polypropylene core. This document discloses stretching the material in a hot oven to a stretch ratio of 20: 1. The examples illustrate that the composite material can have a tensile modulus of elasticity of up to 2.5 GPa.

JP-a 2000-8244 discloses a flat scrim for reinforcing sheet-like layers, made of an ABA-type composite yarn, wherein the B layer is polypropylene and the a layer is based on an ethylene- α -olefin copolymer or a blend of two ethylene- α -olefin copolymers. The yarn is prepared by extruding the two materials, slitting the film and stretching it to a draw ratio of 3-12. After weaving, the material is heat treated to bond the yarns together.

EP-A366,210 discloses a three-layer stretched polyolefin laminate comprising a core layer of polypropylene and/or LLDPE and a skin layer made of a butene-1 polymer. The material can be used in the field of packaging. This material has very poor mechanical properties.

EP-A776,762 discloses polyolefin tapes or yarns based on coextruded polyolefin materials having a draw ratio of from 6 to 10. This material is described as being suitable for use in making various cloths, belt materials, and the like.

Disclosure of Invention

Although the properties of the materials in the above documents are good, further improvements are required, especially in terms of tensile strength. A first object of the invention is to provide a belt or yarn with improved mechanical properties.

In composites, yarns or cloth are often used for reinforcement. Most commonly used are fiberglass materials. However, glass fiber materials have the following disadvantages: they make it extremely difficult to recover the material in which they are doped. It would be very useful if the glass fibers could be replaced by polymeric fibers or other polymeric reinforcing components, thereby making it easier to recycle the composite. One of the main advantages of glass fibers is their stiffness, which is often the weak point of polymeric fibers or other reinforcing components. It is therefore a further object of the present invention to provide a polymeric material having sufficient stiffness to be able to replace glass fibres in a composite material.

With respect to recycling products made from polyolefin films, tapes and yarns, it would be advantageous if all components of the material could be classified as the same material such as polypropylene or polyethylene (including copolymers thereof, wherein propylene and ethylene form the major monomer units, respectively), with the advantage that the resulting recycled material is still one material, rather than a mixture of components (non-contaminating).

The invention relates to a uniaxially stretched polyolefin multilayer film, tape or yarn of the AB or ABA type having a stretch ratio higher than 12 and an E-modulus of at least 10GPa, consisting essentially of an intermediate layer (B) of a polyolefin selected from polyethylene and polypropylene and one or two further layers (A) of a polyolefin selected from the same class as the material of the intermediate layer (B), the DSC melting point of the material of said further layers (A) being lower than the DSC melting point of the material of said intermediate layer (B), wherein the intermediate layer (B) constitutes from 50 to 99% by weight of the material and the further layers constitute from 1 to 50%.

It has surprisingly been found that such a multilayer material (also referred to as laminate) has excellent properties with respect to mechanical strength, stiffness, etc. Due to its composition, either polyethylene or polypropylene may be suitable as a one-component material, which is advantageous in recycling. More specifically, production waste that is part of the interlayer component can be recovered. In addition, with respect to recycling components after the useful life of the product, it is important to make the components consist of only one type of material in view of the needs of the producers of consumer products such as automobiles and the like.

The E-modulus used herein is a value measured by ISO 527.

By having a very high total draw ratio of the material components of the laminate (film/tape/yarn): above 12, preferably above 15, for example at least 20 and even up to 50 or more, the resulting material can be advantageously used in various reinforcing applications, can replace for example glass fibres in various reinforcing applications, can be used in various high temperature fields, for example in the automotive or aeronautical field. In general, the materials according to the invention are particularly suitable for use in the (lightweight) construction sector, in the high-pressure sector and in the medical sector. The material can be used in the construction of houses, ships, automobiles, etc., but also as a reinforcement layer in high pressure parts such as pipes (for oil extraction, etc.) or in the manufacture of ortheses.

In the context of the present invention, a material has been defined to meet the lowest level of Total Stretch Ratio (TSR). TSR is defined as the degree of drawing from the anisotropic melt to the final tape or yarn. This is defined at least in part by the difference in speed between the dancer rolls. The actual value of TSR may be determined by the birefringence and/or E-modulus (in the direction of stretching) of the final film, tape or yarn. The TSR is particularly useful for use in intermediate layers, which are preferably highly crystalline materials. The material of the other layers is generally less crystalline. The function of the other layer is to provide in particular the possibility of bonding films, tapes, fibres or yarns when heat treating a fabric, nonwoven or fibre (stack)/stack of material.

The base material used to prepare the film, tape or yarn of the present invention is polypropylene or polyethylene.

When polypropylene is used as the base material for the preparation of the film, tape or yarn, the material for the intermediate or core layer B is preferably homopolypropylene, preferably having a relatively high molecular weight, e.g. a weight average Molecular Weight (MW) of at least 250000g/mol, as determined by Gel Permeation Chromatography (GPC), and a melting temperature of at least 160 ℃. It should be noted that while the intermediate layer is preferably composed of only one material, minor amounts of other layer materials may also be present in the core layer when recycling production waste. This usually does not exceed 10 wt.%.

In one embodiment the core layer (B) is polypropylene and in this embodiment the outer layer material is also polypropylene as described above, preferably a copolymer of propylene with ethylene or another alpha-olefin. An important aspect is that the material softening point, which is generally indicated by the DSC softening point as defined in ISO 11357-3, is lower than the softening point of the intermediate layer by at least 10 ℃. The maximum difference between the softening points of layer B and layer a is not particularly critical. For reasons of production practice, this difference is generally below about 70 ℃. Especially excellent results have been achieved with films, tapes or yarns having a difference in softening point in the range of 15-40 ℃.

Excellent results have been achieved using a random copolymer such as a propylene-ethylene random copolymer as the outer layer a. Polyolefins, preferably polypropylene homopolymers or polypropylene copolymers, prepared using metallocene catalysts are used as outer layer a instead of or in combination with the copolymers. Particularly good results have been achieved using such metallocene-based statistical polymers. Suitable examples of metallocenes are rac- [ Me2Si (2-Me-4- (1-naphthyl) indenyl) 2] ZrCl2H (disclosed in H.Brintzinger, D.Fischer, R.Muelhaupt, B.Rieger, R.Waymouth, Angew.chem.107(1995)1255 and W.Kaminsky, Macromol.chem.Phys.197(1996) 3907).

Since the products of the invention are generally used in the form of films, tapes or fibres angled to one another (woven, non-woven materials), the outer layer enables the heat treatment of woven, piled or stapled (staple) materials, thereby binding together the individual films/fibres/yarns or tapes, resulting in a very high structural integrity composite (e.g. woven material). By selecting the softening point of the intermediate layer within a sufficiently large range from the softening point, heat treatment can be performed without impairing the properties of the material itself.

In one embodiment of the invention, the outer layer a consists at least of an ethylene propylene copolymer with an ethylene content of 75 to 99 mol% and a propylene content of 1 to 25 mol%. In embodiments where the intermediate layer B is polyethylene, good results have been achieved with such outer layers.

As the material of the outer layer A, particularly in the case of polypropylene as the intermediate layer, a propylene-ethylene copolymer having an ethylene content of 1 to 25 mol% and a propylene content of 75 to 99 mol% is preferably used. Such copolymers (as outer layer a), in particular such random copolymers, have been found to adhere highly satisfactorily to the intermediate layer. It has further been found that composites comprising tapes, yarns or films of such copolymers have excellent strength, impact resistance and abrasion resistance. Mixtures of two of these materials may also be used.

In the case of using polyethylene, basically the same measures are taken. As intermediate layer, preference is given to using HDPE, i.e. having a density of at least 950kg/m³The polyethylene of (1). The weight average Molecular Weight (MW) as determined by GPC is preferably at least 250000g/mol, and the melting point is 130 ℃ or higher. It should be noted that while the intermediate layer is preferably composed of only one material, minor amounts of other layer materials may also be present in the core layer when recycling production waste. This usually does not exceed 10 wt.%.

The material of the other layer is characterized in that it is also polypropylene, but here has a lower melting point, the difference being at least 10 ℃. Suitable polyethylenes are random or block ethylene copolymers, LLDPE, LDPE, VLDPE and the like.

For both types of layer materials, it should be noted that they typically contain conventional additives including, but not limited to, dyes and pigments, flame retardants, UV-stabilizers, antioxidants, carbon black, and the like.

In a less preferred general method of the invention, each outer layer itself is composed of two or more further layers. In a three-layer construction (ABA), the composition of the two outer layers may differ slightly.

The main part of the product of the invention consists of the intermediate layer (B). In a preferred embodiment, the amount of the intermediate layer is 50-99 wt.%, preferably 60-90 wt.%. The balance of the material consists of the outer layer (a).

In practice, the thickness of the tape, film or yarn is generally up to 300. mu.m, preferably 25 to 300. mu.m. This is controlled by the original film thickness and the draw ratio, in this case the speed ratio of the take-up rolls. The width of the tape may vary widely, for example from 25 μm to 50 μm or more. The width of the film may also vary widely, for example from 1cm to 150cm or more.

As indicated above, the material of the present invention has very good mechanical properties. For example, the E-modulus is at least 10GPa, preferably at least 12.5 GPa. The tensile strength can easily be at least 0.25GPa, even up to at least 0.4GPa (value measured by ISO 527). The upper limit of the strength obtainable in the material of the invention is about half of the theoretical value. This means that the upper limit is typically 1GPa for polypropylene and 5GPa for polyethylene.

The films, tapes or yarns of the present invention can be used to make a variety of materials, such as those described in the background.

One embodiment of the use of the film of the invention is to prepare a reinforcing material, for example by winding or stapling/stacking from the film, and/or compacting the material. Preferably the material is subsequently heat treated and pressed. By this heat treatment, the individual fibers are bonded together. In this way the regularity of the hook/pile material is ensured. The heat treatment is carried out at a temperature between the softening points of the material of the outer layer (a) and the material of the intermediate layer (B). The surprising properties of the heat-treated material are improved abrasion resistance and suppression of delamination of the individual films.

During the heat treatment, pressure is preferably applied, especially if the plate-like material or the shaped article is heat treated to a temperature at which the material of the intermediate layer (B) has a tendency to shrink (due to the deformation of the polymer chains into a more random configuration). For example, polypropylene tends to shrink at temperatures above 100-. Preferably, the pressure is at least 5X 10⁵And (6) handkerchief. By at 2X 10⁶-7×10⁶Compacting the material under pressure in pascals gives good results already in terms of the mechanical properties of the material obtained.

Alternatively or in combination with the application of pressure, the material may be clamped during the heat treatment in order to avoid shrinkage.

One of the preferred embodiments of the use of the tapes or yarns of the present invention is to prepare a (reinforcing) cloth, for example by weaving, winding, cutting, stapling, and/or compacting the cloth from the tapes, fibres or yarns. Preferably the material is subsequently heat treated and pressed. By this heat treatment, the individual fibers are bonded together. In this way, the regularity of the cloth is ensured. The heat treatment is carried out at a temperature between the softening points of the material of the outer layer (a) and the material of the intermediate layer (B). The surprising properties of the heat-treated material are improved abrasion resistance and suppression of delamination of the individual films.

The preparation of the material of the invention is generally carried out by coextrusion of the individual layers. Cast extrusion is typically used, where the extruder has a flat dye plate, without a profile. When making a film, the material may be stretched after coextrusion and cooling. In making the tapes or yarns, the material can be cut into individual strands of the desired width (after coextrusion and cooling) and subsequently drawn.

The stretching may be single stage or multi-stage stretching. The draw ratio in each step is from 1.1 to 50, preferably from 2 to 10, more preferably from 3 to 8, the overall draw ratio being important for determining the TSR as defined herein. Good results have been achieved in terms of the mechanical properties of the drawn tapes, yarns or films in a multistage drawing process with a draw ratio of 4-5 in the first drawing stage of the tapes, films or yarns.

The material is preferably stretched at a temperature of 20-250 c. Preferably at a temperature below the DSC melting point of the material used for the intermediate layer B (hereinafter referred to as "cold drawing". good results have been achieved using a cold drawing process in which at least one of the drawing stages is carried out at a temperature below the DSC melting point of the outer layers, said temperature being between 25 and 75 ℃, more preferably between 30 and 60 ℃.

In the case of multistage stretching, the first stretching is preferably carried out at a relatively low temperature, more preferably at 30-60 ℃, and the subsequent stretching stage or stages are preferably carried out at a relatively high temperature, for example at a temperature between 60 ℃ and the DSC melting point of the outer layer. This achieves the highest possible elongation. Subsequent stretching at a temperature of at least 100 ℃ gives good results. The subsequent stretching is preferably carried out at a temperature at which the stretching ratio is substantially maximized up to the break (during stretching). It has been found that the film, tape or yarn produced has very good mechanical properties, such as a very high E-modulus, at temperatures relatively close to the temperature at which stretching is maximised. The temperature at which stretching is maximized can be determined by one skilled in the art in a conventional manner.

An annealing step may be included between the two stretching steps. This may be done after the final stretching.

The materials of the present invention, including individual films, tapes, yarns/fibers or cloth or hook and loop/pile materials made therefrom, may suitably be used for incorporation into a matrix material, for example as a reinforcing material. Examples thereof are various composite fiber-reinforced plastics, applications in the automotive field such as bumpers, instrument panels, engine covers, etc., applications in the aeronautical industry such as structural materials for aircraft, etc. Other applications have been discussed above.

Detailed Description

The invention will now be illustrated on the basis of the following examples, which are not to be construed as limiting the invention.

Example 1

Using a co-extruded tube, a film was prepared consisting of a polypropylene core layer B with a DSC softening temperature of 152 ℃ and two propylene random copolymer skin layers a with a DSC softening temperature of 135 ℃ (ABA structure). The weight ratio of A to B to A is 5: 90: 50.

The film was stretched at 55 ℃ in a ratio of 1: 5, followed by stretching at 128 ℃ in a ratio of 1: 3.4, thereby producing a stretched film having a stretch ratio of 1: 17 and a thickness of 70 μm.

The stretched film had an elastic modulus of 15.8GPa and a strength of 585 MPa.

Example 2

Some of the films in the examples were processed into yarns having a width of 2.1 mm. The yarn was woven to prepare a textile material (woven material) which was subsequently heat treated at 150 ℃ to consolidate the structure. The final material had a quasi-isotropic stiffness of 7GPa (determined by ASTM 3039-76) and a tensile strength of over 270MPa (determined by ISO 527).

Example 3

Some of the films in the examples were stapled or stacked and then heat treated at 150 ℃ to consolidate the structure. The final material has quasi-isotropic stiffness of 7GPa and tensile strength over 270 MPa.

Example 4

A film was prepared as described in example 1, except that the stretching stage was carried out at a temperature of 128 ℃. The material (tensile ratio 1: 14, thickness 70 μm) had an elastic modulus of 11.5GPa and a tensile strength of 450 MPa.

Claims (24)

1. A uniaxially stretched multi-layer film, tape or yarn of the AB or ABA type having a stretch ratio higher than 12 and an E-modulus of at least 10GPa, consisting of an intermediate layer B of a polyolefin selected from the group consisting of polyethylene and polypropylene and one or two further layers A of a polyolefin selected from the same class as the material of the intermediate layer B, said multi-layer film, tape or yarn being a single-component material of polyethylene or polypropylene, comprising a copolymer in which propylene and ethylene each form the majority of monomer units, said further layer A material having a DSC melting point lower than the DSC melting point of the material of said intermediate layer B, wherein said intermediate layer B constitutes between 50 and 99% by weight of the material and said further layer A between 1 and 50%.

2. The film, tape or yarn of claim 1 wherein said draw ratio is at least 15.

3. The film, tape or yarn of claim 1 or 2 wherein said draw ratio is at least 20.

4. The film, tape or yarn according to claim 1 or 2, wherein the draw ratio is at most 50.

5. A film, tape or yarn according to claim 1 or 2 wherein the material of the intermediate and further layers is based on polypropylene.

6. A film, tape or yarn according to claim 1 or 2 wherein the material of the intermediate and further layers is based on polyethylene.

7. The film, tape or yarn of claim 1 or 2, wherein the material of said intermediate layer is a crystalline polymer having a weight average molecular weight of at least 250000 g/mol.

8. The film, tape or yarn according to claim 1 or 2, wherein the outer layer a consists at least of a random copolymer.

9. The film, tape or yarn of claim 1 or 2 wherein the outer layer a comprises a metallocene-based homopolymer or a metallocene-based copolymer.

10. Film, tape or yarn according to claim 1 or 2, wherein said outer layer a consists at least of a propylene ethylene copolymer having an ethylene content of 1 to 25 mol% and a propylene content of 75 to 99 mol%.

11. Film, tape or yarn according to claim 1 or 2, wherein said outer layer a consists at least of a propylene ethylene copolymer having an ethylene content of 75 to 99 mol% and a propylene content of 1 to 25 mol%.

12. Film, tape or yarn according to claim 1 or 2, having a thickness of 25 to 300 μm.

13. Film, tape or yarn according to claim 1 or 2, having an E-modulus of at least 12.5 GPa.

14. A woven or non-woven composite material prepared from a film, tape or yarn according to any one of claims 1 to 13.

15. The woven or non-woven composite material according to claim 14, which is heat treated.

16. Composite material comprising a composite material reinforced with a film, tape or yarn according to one of claims 1 to 13 or a woven or non-woven composite material according to claim 14.

17. A process for the preparation of a monoaxially drawn polyolefin multilayer film, tape or yarn of the AB or ABA type with a draw ratio of more than 12, in which,

(i) providing by co-extrusion a polyolefin multilayer film, tape or yarn of the AB or ABA type consisting of an intermediate layer B of a polyolefin selected from polyethylene and polypropylene and one or two further layers A of a polyolefin selected from the same class as the material of the intermediate layer B, said multilayer film, tape or yarn being a single component material of polyethylene or polypropylene comprising a copolymer in which propylene and ethylene respectively form the majority of the monomer units, said further layer A material having a DSC melting point lower than the DSC melting point of the material of said intermediate layer (B), and said intermediate layer (B) constituting from 50 to 99% by weight of the material, said further layers constituting from 1 to 50%, and

(ii) stretching the coextruded film, tape or yarn in a single or multiple stages at a temperature below the melting point of the intermediate layer B.

18. A process for the production of a uniaxially stretched polyolefin multilayer film, tape or yarn according to claim 17, said film, tape or yarn having an E-modulus of at least 10 GPa.

19. A process according to claim 17 or 18, wherein at least one of the stretching stages is carried out at a temperature of 25-70 ℃.

20. The process of claim 19 wherein said film, tape or yarn is first stretched at a temperature of 25-70 ℃ and then stretched at a temperature above 70 ℃.

21. The process of claim 17 or 18, wherein the tape, film or yarn is stretched to a total draw ratio of at least 15.

22. The process of claim 21 wherein said tape, film or yarn is stretched to a total draw ratio of at least 20.

23. The process of claim 22 wherein said tape, film or yarn is stretched to a total draw ratio of at most 50.

24. A process according to claim 17 or 18, wherein a tape, film or yarn according to any one of claims 2 to 13 is prepared.