THIS INVENTION relates to compostible laminates. Used packaging materials constitute a refuse disposal problem and it is desirable to be able to compost them. Also, in composting organic wastes, for example food or vegetation, it is convenient to transport the compostible material in a compostible container. Bags made of paper or other cellulosic material, for example cellulose film or boxes made of such materials, for example cardboard or the like may be used but are mechanically weak when wet.

This invention provides compostible laminates comprising cellulosic sheets, for example paper or board, of satisfactory strength which comprise substantially only compostible components and which comprise layers of a cellulose sheet, a polycaprolactone, a polylactic acid and/or a cellulose ester and a poly 3- or 4-hydroxy- alkanoic acid.

The invention preferably comprises a compostible laminate which comprises a cellulosic sheet directly coated on at least one surface with a layer of polycaprolactone, polylactic acid and/or a cellulose ester and a layer overlying the said directly coated layer of a poly 3 or 4-hydroxyalkanoic acid. We have found that laminates according to the invention have acceptable wet strength and resistance to cracking. Resistance to cracking is important if the paper or board is folded as any cracking along the fold will allow access to moisture and impairment of the wet strength along the fold.

The invention also comprises a compostible laminate as aforesaid in which the polyhydroxyalkanoic acid layer is covered with a readily removable sacrificial layer of optionally non-compostible polymer, for example polythene or polypropylene. The sacrificial layer is useful in improving the manufacture of the laminate, for example in preventing the sticking of the laminate to chill rolls in the course of manufacture. If desired it may be left in position to protect the laminate until it is to be used. The added layers may be applied to the cellulosic sheet simultaneously using known techniques, for example by the use of a multi manifold co-extruder. Temperatures of 150 to 300°C and preferably 150 to 250°C are suitably used for co-extrusion and polymers with melting points below the extrusion temperature should be used. After application of the added layers the laminate is suitably cooled for example to a temperature of 40 to 70 ^C C. This may be accomplished by contacting the laminate with a chill roller. It is preferred that the total weight of the coating layers after stripping the sacrificial layer from the product should be about 5 to 40 grammes per square metre and is preferably 10-25 grammes per square metre. The ratio of the polyhydroxyalkanoic acid to the polycapro- lactone, cellulose ester or polylactic acid layer may be 1:10 to 10:1 preferably 5:1 to 1:5 and more preferably 2:1 to 1:2 by weight

The polyhydroxyalkanoic acid may be a homo or co- polymer suitably of hydroxybutyric acid preferably together with hydroxyvaleric acid. Suitable polymers of

this type are described in our European Patents EP 52459 and EP 69497. The polyhydroxyalkanoic acid preferably has a molecular weight of 50,000 to 1 million and more preferably 100,000 to 800,000. The polylactic acid, cellulose ester or polycaprolactone preferably has a molecular weight of at least 40,000 for example 30,000 to 500,000.

The sacrificial layer may after it is stripped from the laminate be reused in the manufacturing process if it is a thermo-plastic.

A pilot line was used for the following work which comprises a roll of 110g/m ² brown Kraft paper feeding the paper to a unit for corona discharge onto the paper, a support roller supporting the paper emerging from the corona discharge chamber, a die for extruding three layers of polymer onto the paper beyond the support roller, a chill roller and a nip roller for pressing the laminate of paper and polymer together against the chill roller and a wind-up roller for collecting the laminate. The corona discharge was at a power of approximately

1.5 kw over a width of 350 mm, the paper being run through the discharge at a rate of 15 to 75 m per minute.

The die was fed by three extruders supplying polycaprolactone (a commercial product sold as "Tone" 767 by Union Carbide, estimated number average molecular weight 43,000 melt flow index of 30 at 190°C) , a copolymer comprising 92% hydroxybutyric acid units and 8% hydroxyvaleric acid units in a D-configuration of estimated weight average molecular weight 480,000 sold under the trade name "BIOPOL" by ZENECA Limited and low

density polyethylene sold by Borealis as grade NCPE 1515, MFI 15 at 190°C. The die was a Cloeren vane flat die of width 350 mm with adjustable vanes and equipped with breaker plates and screen packs and using a CCABB configuration plug.

This arrangement enabled the polymers to be extruded onto the paper in the order paper/polycaprolactone/- "BIOPOL" polyhydroxyalkanoate/polyethylene in the desired thicknesses set by the outputs from each extruder.

The chill roller was maintained at a temperature of 60°C.

The line was operated under the conditions shown below. For comparison a single layer consisting of "BIOPOL" polymer was coated onto the paper using only one of the extruders under the conditions shown below. The "Barrel Zone" temperatures indicate the successive increases in temperature in the barrel zones of the extruders which feed adaptors of the extruders which adjust the temperature of the polymer as shown. The temperature of the die itself was set at 185°C. Single Layer Extrueion

Sample Barrel Zones °C Adaptor Screw Line °C Speed speed 1 2 3 rpm m/min

#1 150 175 185 185 40 30

#2 150 175 185 185 40 20

#3 150 175 185 185 40 25

3 Layer Co-Extrusion

Sample Barrel Zones ° C Adap Screw Line

-tor speed speed

°C rpm m/min

1 2 3 4

#9 150 175 185 185 45 35

150 170 180 185 185 20

150 170 180 185 185 90

#10 150 175 185 185 32 35

150 170 185 185 185 32

150 170 185 185 185 90

#20 150 175 185 185 50 50

150 175 180 185 185 50

170 190 195 200 205 200

#21 150 175 185 185 50 75

150 170 180 185 185 50

170 190 195 200 205 200

The screw speeds in the preceding table are proportional to the approximate relative thickness of the layers.

The products were tested as follows:

Laminate from the wind-up roller was removed and any polyethylene layer stripped off. The coat weight (i.e. the total polymer remaining per square metre of laminate) was recorded.

Adhesion of the layers was tested by manual

stripping of the deposited polymer layers from the paper. Cracking of the polymer layer was tested by folding the laminate over so that the polymer layer contacted the polymer layer, the direction of folding being transverse to the line processing direction or parallel to the line processing direction as the case may be, and also so that the paper layer contacted the paper layer in the transverse and parallel directions as aforesaid.

The integrity of the polymer coating after folding was tested by laying the laminate flat, applying coloured turpentine to the crease from the polymer side of the laminate and after 10 minutes measuring the proportion of the crease in which colouring on the paper side was observed. 10 cm lengths of crease were tested. The results are reported as follows:

Sample Coat Adhesion Turpentine (Line Direction) Turpentine (Traverse Direction)

Weight Number Substrate to Coating to Substrate to Coating to g/m ² Substrate Coating Substrate Coating (%) (%) (%) (%)

#1 15 0 60 80 90 50 #3 20.5 0 20 70 50 50 #2 28 0 0 0 0 0

#21 12.1 5 5 0 5 1 #20 14.4 5 1 3 5 1 #10 18.6 3 1 0 5 0 #9 21.0 2 1 0 5 0

10 #1, #2 and #3 all single layer extrusion coating

#21. #20 and #10 are all 3 layer co extrusions with equal "BIOPOL" Polymer to PCL layers

#9 is a 3 layer co extrusion with a 9/4 ratio of "BIOPOL" Polymer to PCL

PCL means polycaprolactone. Adhesion numbers are assessed as follows:

15

Adhesion 0 Layers not bonded at all and both materials remain completely intact.

Adhesion 1 Layers come apart easily and both materials remain completely intact.

Adhesion 2 Some force needed to separate the layers and materials damaged slightly.

Adhesion 3 More force needed to separate the layers and both materials damaged.

Adhesion 4 Layers difficult to pull apart and both damaged almost totally.

Adhesion 5 Layers impossible to pull apart, both tear immediately.