METHOD FOR FORMING LAMINATED PRODUCTS

This invention relates to methods for forming laminated products comprising at least one flexible layer and a laminant layer of a polymer resin. In addition, this invention relates to such laminated products.

Laminates are used as facings for building materials and in particular in panel and board insulations, flexible duct wrap, pipe sections, coverings for resin bonded slabs and in joining tapes for, for example, foil vapour barriers. Such laminates typically comprise a laminant layer of a polyolefin, usually polyethylene, sandwiched between layers of flexible materials such as aluminium foil, kraft paper, fabrics, glass tissues and other materials. Such laminates may also be reinforced with scrim and contain further layers of laminants and other layers of various flexible materials.

When used in building materials, such laminates may be exposed to a variety of conditions including moisture at both relatively high and relatively low temperature. Laminates may also cojne into contact with condensation (i.e. with liquid water). In some circumstances, de-lamination of, for example, the aluminium foil layer from the polyolefin layer may occur. Such de- lamination is clearly disadvantageous and a need therefore exists for an improved laminate which is less prone to such de-lamination.

The present invention aims to address this problem.

The present invention accordingly provides, in a first aspect, a method for forming a laminated product, the method comprising slot die extruding a laminant layer of slot die extrudable cross-linkable polymer resin on to a first web of a first flexible material.

Preferably the slot die extrudable cross-linkable polymer resin comprises an organosilane grafted polymer resin. More preferably, the slot die extrudable cross-linkable polymer resin comprises a polymer resin on which is grafted a compound of formula R _t R ₂ SiX ₂ , where R ₁ is a monovalent olefinically unsaturated hydrocarbon group (preferably C ₂ -Ce alkene), each X is a hydrolysable group, and R ₂ is an X group, an R-i group, H, or a C ₁ -C ₄ alkyl group. The hydrolysable group may be, inter alia, an alkoxy or acetoxy group

(preferably C ₁ to C ₄ groups). A preferred compound of the formula is vinyltriethoxysilane although other vinyl trial koxysilanes may also be used. The most preferred compound is vinyltrimethoxysilane.

Preferably, the polymer resin comprises (or is) a polyolefin, more preferably polyethylene although other polyolefins (e.g. polypropylene) may be used. Alternatively the polymer may comprise a polystyrene polymer, an epoxy resin, an acrylic polymer, a cellulosic polymer, a polyester polymer, a polyurethane polymer, or mixtures or copolymers of these polymers.

The proportion of organosilane in the slot die extrudable cross-linkable polymer resin is preferably in the range of 0.2 wt % to 3 wt % organosilane, more preferably 0.3 wt % to 1.6 wt % organosilane.

If there is too high a proportion of organosilane in the polymer resin, this may lead to rapid gel formation and sharp viscosity increases during slot die extrusion. This is especially detrimental in a slot die extrusion when very thin laminant films are being produced because gel formation can lead to voids and even parting of the sheet during extrusion. The viscosity increase is also detrimental because it can lead to a rapid increase in barrel pressure during the extrusion process. Too low a proportion of organosilane in the polymer resin does enable the product to be readily extrudable but the final cross- linking and e.g. water resistant properties of the laminate may be reduced.

The cross-linkable polymer resin should be slot die extrudable in order to be operable in the method of the present invention.

The properties of a polymer resin which is slot die extrudable are significantly different from those required in, for example, injection moulding or tube extrusion of polymer resin. As mentioned above, slot die extrusion produces a very thin film of material (of, typically, less than 50μm thickness) with a high surface to volume ratio and which is susceptible to gelling and void formation unless the properties of the polymer resin are suitable.

Preferably, therefore, the slot die extrudable cross-linkable polymer resin has a melt flow index (as determined according to ASTM D-1238 at 190°C 2.16 kg) in the range 3 to 20g/10 minutes, more preferably 3 to 15g/10

minutes, and most preferably 3 to 12g/10 minutes. The polymer resin preferably has a density in the range of 0.9 to 0.97g/cm ² .

If the melt flow index of the polymer resin is significantly lower than the range indicated above, difficulties can start to arise in slot die extruding a polymer resin. Alternatively, if the melt flow index is significantly higher than the range indicated above, difficulties may arise because the polymer resin will have too low a viscosity.

The slot die extrudable cross-linkable polymer resin will normally comprise an organosilane grafted polymer resin compounded with a compatible polymer. Suitable polymer systems both for grafting the organosilane and for compounding with the organosilane grafted polymer resin are polyolefin polymer systems.

Thus, preferably, the slot die extrudable cross-linkable polymer resin comprises a compounded (i.e. mixed in the molten phase) mixture of an organosilane grafted polyolefin and a compatible polyolefin. Compounded mixtures are advantageous because they provide more consistent properties through more intimate mixing. Alternatively, the slot die extrudable cross- linkable polymer resin may comprise a blended (i.e. mixed in the solid phase) mixture of the organosilane grafted polyolefin and a compatible polyolefin.

The preferred polyolefins are polyethylenes, although other polyolefins (for example polypropylenes) may also be used.

The slot die extrudable properties of the cross-linkable polymer resin may be achieved by suitable selection of the proportion of organosilane in the grafted polymer resin, and also by selecting suitable properties of both the polymer resin on which the organosilane is grafted and also any compounding polymer which is blended with the organosilane grafted polymer resin.

In a preferred embodiment, the first flexible material is an aluminium foil. Typical thicknesses of the aluminium foil are above 6μm and preferably below 50μm, more preferably below 30μm.

It is an advantage. of the present invention that the adhesion of a cross- linkable polymer resin on to an aluminium foil is surprisingly enhanced over that of a conventional polymer resin (for example polyethylene) on an

aluminium foil. This is especially true in moist conditions (in particular where the laminate is in contact with liquid water e.g. through condensation) where in the past de-lamination could occur.

The adhesion may become even more improved after the laminate is aged under ambient conditions. It is thought that atmospheric moisture permeates through the outer layers of the laminate (and some moisture is, of course, present during extrusion) and causes cross-linking of the cross- linkable polymer resin. In the case of organosilane grafted polymer resin, the cross-linking may be related to hydrolysis of the hydrolysable groups of the organosilane.

Thus, ageing of the laminate improves adhesion still further. Cross-linking is normally substantially complete by 24 hours after extrusion. However, final cross-linking may only occur after a few days (e.g. 3 or more) or up to several weeks depending upon ambient moisture (relative humidity) and temperature.

A further surprising advantage of the use of slot die extrudable cross- linkable polymer resin is an improved heat and fire resistance of the laminate. Ageing further improves the temperature and fire resistance of the laminate, possibly by increasing the effective molecular weight of the laminant.

Although the laminates produced may comprise two layers of the laminant material and, for example aluminium foil, more preferably the method will comprise slot die extruding a laminant layer of the slot die extrudable cross- linkable polymer resin between the first web of the first flexible material and a second web of a second flexible material. The second flexible material may be, for example, kraft paper, plastics film, metallised film, glass tissue, scrim, non-woven polymeric web, fabric or aluminium foil.

There may also be a further layer of polymer adjacent to the laminant layer of slot die extrudabie cross-linkable polymer resin.

Thus, preferably the method may further comprise co-extruding a layer of a co-extrusion polymer with a slot die extrudable cross-linkable polymer resin layer. It is preferred if the co-extruded polymer comprises a polyolefin, more preferably polypropylene or polyethylene.

In order to ensure acceptable properties in the co-extruded polymers, it is preferred if the slot die extrudable cross-linkable polymer resin and the co- extrusion polymer are co-extrusion compatible (having compatible rheological properties, for example, a melt flow index of one polymer no more than three times that of the other, and/or similar chemical properties).

. Multi layer laminates comprising 4, 5, 6 or more layers may also be produced using further laminant layers, further flexible materials, additional (i.e. 3, 4, 5 or more layers) co-extrusion layers and/or additional or .sequential extrusion lamination stages.

It is most preferred if a method according to the present invention is performed such that the laminant layer is extruded so that it is, at least partially, in direct contact with the first flexible layer. This is advantageous because the enhanced adhesion properties of the cross-linkable polymer resin are thereby made use of in bonding to the first flexible layer.

If it is desired, for example, to reinforce the structure of the laminate a layer of scrim (i.e. an open web) may be situated between the laminant layer and the first flexible layer (or elsewhere in the laminate). However, because of the open nature of the scrim web, in this case the laminant layer would still be in direct contact, at least partially, with the first flexible layer.

Preferably, the method is performed at an extrusion melt temperature of 330 ⁰ C or less. Temperatures much higher than this may lead to charring of the extruded polymer or premature cross-linking.

It is also preferred if the moisture content of the cross-linkable polymer resin is kept below 0.2%, preferably 0.1 % (by weight) prior to extrusion.

In a second aspect, the present invention also provides a laminated product comprising a first flexible layer comprising a first flexible material and a laminant layer comprising a slot die extruded cross-linkable or cross-linked polymer resin.

The features of the first aspect of the invention are also preferred and beneficial features, with the corresponding advantages, of this second aspect of the invention. Each feature (in particular, each preferred feature) discussed

herein may be combined with any other feature unless clearly indicated to the contrary.

A laminant layer in a two layer laminate is also often referred to in the art as a coating layer.

The laminated product finds use in building materials, in particular panels, including insulating panels, although there are a number of other possible applications of the laminated product according to the present invention.

The invention will now be described, by way of example only, with reference to the following drawings, in which:

Figure 1 a is a schematic drawing showing a process for producing a laminated mono-extruded product of the invention with two flexible layers sandwiching a laminant layer; and

Figure 1 b is a schematic drawing showing a process for producing a laminated co-extruded product of the invention with the laminant and co- extruded polymer layers sandwiched between two flexible layers;

Figure 2a is a schematic cross-section of a laminated product according to the invention having a laminant layer and a single flexible layer;

Figure 2b is a schematic cross-section of a laminated product according to the invention, and produced by a process as illustrated in Figure 1a, having a laminant layer sandwiched between two flexible layers;

Figure 2c is a schematic cross-section of a laminated product according to the invention produced by the process as illustrated in Figure 1b;

Figure 2d is a schematic cross-section of a laminated product according to the invention having a laminant layer sandwiched between two flexible layers with a scrim layer between the laminant and one of the flexible layers;

Figure 2e is a schematic cross-section of a laminated product according to the invention having a laminant layer sandwiched between a flexible layer and a scrim layer; and

Figure 2f is a schematic cross-section of a laminated product according to the invention having a laminant layer, a co-extruded layer and a co-extruded tie layer sandwiched between two flexible layers.

Figure 1 a shows how a laminate according to the present invention may be produced. Hopper 2 is fed with a slot die extrudable cross-linkable polymer resin containing organosilane grafted polyethylene. This is slot die extruded through an extruder 4 to form a uniform layer of a thickness of less than 50μm.

The final step in the formation of the laminate is the adhesion of the extruded laminant layer 6 to a web of glass tissue 7 on one side and a web of aluminium foil 8 on the other side with the aid of rollers 9 and 10. Both the glass tissue 7 and the aluminium foil 8 webs are bonded to the laminant layer 6.

The laminant layer 6 is, therefore, used as a bonding layer between the flexible layers. After extrusion, within 24 hours, the polymer resin cross-links due to contact with external atmospheric moisture which also ensures that the chemical bond to the aluminium foil layer 8 develops. Additionally, the cross- linking increases the molecular weight of the polymer layer and hence, in turn, the temperature resistance.

Figure 1 b illustrates a similar process to that illustrated in Figure 1a. However, in Figure 1 b a second hopper 1 is fed with polyethylene. Polyethylene is co-extruded through slot die extruder 3 with the laminant layer 6 to form a co-extruded structure with laminant layer 6 and a polyethylene layer 5.

The laminate is formed by adhering the co-extruded structure to a web of glass tissue 7 on one side and a web of aluminium foil 8 on the other side with the aid of rollers 9 and 10. The glass tissue 7 is bonded to the polyethylene layer 5 and the aluminium foil 8 is bonded to the laminant layer 6.

Figure 2 illustrates a series of laminated products according to the invention.

Figure 2a shows a two layer laminate with an aluminium foil web 8 having a laminant layer 6 adhered to it. A laminate such as illustrated in Figure 2a may alternatively be referred to, in the art, as an aluminium foil substrate 8 coated with a coating layer 6.

Figure 2b shows a laminated product as produced by the process illustrated in Figure 1a having a laminant layer 6 of slot die extruded cross- linkable polymer resin sandwiched between an aluminium foil layer 8 and a glass tissue layer 7.

Figure 2c shows a laminated product as produced by a process illustrated in Figure 1 b having co-extruded layers of laminant 6 and polyethylene 5 sandwiched between an aluminium foil layer 8 (in contact with the laminant layer 6) and a glass tissue layer 7.

Figure 2d shows a laminated product generally as illustrated in Figure 2b but with a layer of scrim 14 for reinforcement between the laminant layer 6 and the aluminium foil layer 8. The scrim layer 14 has an open structure and so the laminant layer 6 is still in at least partial contact with the aluminium layer 8.

Figure 2e shows a laminated product generally as illustrated in Figure 2a but with a reinforcing scrim layer 14 adhering to the face of the laminant layer 6 not in contact with the aluminium layer 8.

Tissue or other materials having a generally open structure may be used in place of the scrim layer 14 in any embodiment of the present invention depending on the intended use of the laminated product.

Figure 2f shows a five-layer laminate generally as illustrated in Figure 2c but with an additional co-extruded polyethylene tie layer 16 between the glass tissue layer 7 and the polyethylene layer 5.

Laminates according to the invention are particularly suitable for bonding to foam panels, preferably with the aluminium foil layer positioned outermost to be used as an insulation facing.

The present invention is further illustrated by the following Examples.

Examples

In the Examples, laminated products were prepared by slot die extrusion of a laminant layer between a layer of aluminium foil and a layer of glass fibre tissue.

Details of each Example are as described in Table 1.

In each Example the laminant layer was a compounded mixture (i.e. mixed in the molten phase) of an organosilane grafted polyethylene and a polyethylene.

In each Example, the organosilane grafted polyethylene was prepared by dispersing 2 wt% vinyltrimethoxysilane into molten polyethylene with a peroxide initiator. After dispersion, the temperature of the melt was raised to split the initiator, and generate free radicals. The organosilane grafts on to the polyethylene in a free radical process.

Extrusion was performed using a conventional slot die extruder with barrel pressures in the range of about 790 psi (5.4 MPa) to about 3300 psi (22.8 MPa) and a melt temperature (as detailed in Table 1 ) of between 277°C and 335 ⁰ C. To prevent or reduce premature cross-linking, it is important to maintain relatively dry conditions during compounding of the cross-linkable polymer resin and during extrusion. Therefore, during compounding and extrusion, steps were taken to exclude as much moisture as possible.

The maximum extrusion width was about 1700 mm, deckled down to an extrusion width of about 1350 mm.

In Example 6 the laminant material was mono-extruded. In Examples 1 to 5 the laminant material was co-extruded with a layer as indicated in Table 1. In Examples 4 and 5, the laminant material consisted of two co-extruded layers of the same material. In each case, the laminant layer was laminated so as to be in direct contact with the dull side of the aluminium foil.

The line speed of lamination was in the range of about 80 to 120 m/min, with laminant coating weight of about 30 to 42 g/m ² (corresponding to an approximate thickness of about 27 to 36 μm). The laminants used in the Examples enabled a very consistent coating weight to be produced across the width of the laminated product web.

The cross-linkable polymer materials were surprisingly good in extrusion, with little gelling and little void formation.

Table 1

The materials used in the Examples were as follows:-

P-Si a polyethylene grafted with 2 wt% vinyltrimethoxysilane, density of 0.964 g/cm ³ and melt flow index 2 g/10min.

G a polyethylene, density of 0.923 g/cm ³ (23°C), MFI 4.

G-Si polyethylene G grafted with 2 wt% vinyltrimethoxysilane.

HDPE High density polyethylene, density 0.96 g/cm ³ , MFI 8 or 11 g / 10min.

Melt flow index (MFI) refers to MFI as determined in accordance with ASTM D-1238 at 190°C, 2.16kg.

Results

Each of the laminated products produced in the Examples exhibited improved adhesion over laminates produced using conventional polyethylene as laminant (i.e. not cross-linkable polyethylene) to aluminium foil as shown by a much reduced tendency to de-laminate in an immersion test.

In the immersion test, samples of the laminated product were immersed in water at room temperature. Samples according to Examples 1 to 6 showed no delamination after at least 2 months immersion. In contrast, conventional laminated products delaminated in less than 1 week.

It has been discovered that (possibly owing to the thinness of the laminant layer) it is sufficient to allow cross-linking merely by using ambient, atmospheric moisture. Thus, aging the laminates after production appears to result in much improved cross-linking and results in improved adhesion ^• between the laminant and foil layers. Complete cross-linking depends on relative humidity and temperature, but is usually complete after 24 hours, sometimes up to 3 days, and in dry and cold conditions even longer (e.g.

several weeks). To speed cross-linking, the moisture content of the air may be increased.