AU693224B2 - Coating for paperboard - Google Patents

Description

WO 96100815 PCT/AU95/00385 TITLE: COATING FOR PAPERBOARD The present invention relates to a coated paperboard, to products, especially containers and blanks therefor, made from coated paperboard and to a method of applying a coating to paperboard.

Paper and paperboard are widely used in the manufacture of containers, such as boxes, for storage and transport of produce. -For convenience, the word "paperboard" will be used hereinafter to denote both paper and paperboard that is suitable for the manufacture of boxes and other containers. The term "boxboard" will also be used to denote a material that is used in the manufacture of boxes, such as cardboard boxes. Although generally possessing satisfactory properties for the manufacture and use of such containers, paperboard will absorb moisture if the container is exposed to a wet or humid environment. Moisture exposure may result from the weather, by splashing of the container, by storage in a high humidity environment, by emission of moisture from product stored in the container fruit and vegetables) or by breakage of produce inside the container. Once the paperboard has absorbed moisture, its strength decreases iite dramatically.

This problem is particularly acute in respect of produce boxes destined for storage of produce (possible for many days or weeks) in cool rooms. Humidity levels in cool rooms can approach 100%, which leids to relatively high levels of moisture absorption in untreated paperboard containers.

To overcome this problem, a number of treatments have been proposed to attempt to increase the water resistance of the paperboard. These treatments include a variety of polymer coatings that are applied to the paperboard. Commercially, the most common treatment involves applying a wax coating to the paperboard. The wax, which is a petroleum-based product having a mixture of long chain molecules, is applied by passing the paperboard through a bath of molten wax or under a shower of molten wax, The molten wax penetrates into the paperboard and forms a layer on top of the paperboard. If corrugated paperboard, which consists of a corrugated layer sandwiched between two facing sheets, is used, the coating treatment generally results in both the corrugated layers and the facing sheets becoming coated with wax.

-2- The purpose of applying the wax is to give the paperboard sufficient strength under wet conditions that would otherwise lead to softening of untreated paperboard and consequent collapse under moderate compression load. The wax acts as a water resistant layer to decrease water permeability into the paperboard. The wax coating also has a strength associated with it and this also adds to the strength of the paperboard. Wax levels currently used to coat paperboard destined for storage and transport containers typically result in the wax comprising from 50 to 60% of final container weight, with wax thickness of from 0.05 to 0.1 mm on exposed faces of the container and much thicker elsewhere.

Although wax coatings allow the manufacture of paperboard containers to have acceptable performance under humid and cool room conditions, it has been found that wax-coated containers are difficult to recycle. It will be appreciated that there is a worldwide trend to increase the amount of recycled paper and paperboard material used in paperboard products, for both economic and environmental reasons.

At present, wax-coated containers cannot be recycled. Disposal of such containers can also be a problem, and in some markets, especially in Europe, such nonrecyclable packaging is becoming increasingly unacceptable. Furthermore, the wax products used to coat the containers are obtained from a non-renewable resource.

The present inventors have now developed alternative coatings for paperboard 20 that can replace the wax coatings that are currently used.

In a first aspect, the present invention provides a paperboard having a coating applied thereto, said coating being substantially petroleum wax free and comprising at least one triglyceride compound.

In another aspect, the present invention provides a paperboard having a coating applied thereto, said coating being substantially petroleum wax free and comprising at least one triglyceride compound present in an amount of 90 99% by weight of said coating and one or more plasticisers present in an amount of 1 to by weight of said coating.

Triglycerides have a glycerol backbone and it is expected that this would result in the triglycerides taking up appreciable amounts of water. Compounds that take up appreciable quantities of water would be considered to be unsuitable for use GN:NB:#15940.RES 29 April 1998 Pc/AU 9 b U U .o a RECEIVED 2 2 APR 1996 -3as coatings for paperboard, The present inventors have discovered that the triglyceride coating do, in fact, take up significant quantities of water. However, it has also been surprisingly found that paperboard coated with the triglyceridecontaining coating of the present invention retains strength even after taking up water.

It has been found that applying a coating that includes at least one triglyceride compound to paperboard produces a coated paperboard that has sufficient water resistant and crush strength in moist conditions to enable the paperboard to be suitable for the manufacture of containers for storing produce in cool rooms.

Indeed, the paperboard of the present invention is suitable for fabricating containers that may be used in all applications in which present wax-coated containers are used.

In a further aspect, the present invention provides a paperboard product r characterised in that the paperboard product has a coating applied thereto, which coating includes at least one triglyceride compound.

The paperboard product is preferably a sheet of paperboard or a container blank.

In yet another aspect, the present invention provides a method for applying a coating to paperboard which comprises providing a molten coating composition including at least one triglyceride compound, applying said molten coating composition to the paperboard and allowing said molten coating composition to solidify to form said coating on the paperboard.

The molten coating composition may be applied to the paperboard by any convenient method known to those skilled in the art. Examples of suitable methods of application include passing the paperboard through a bath or pool of the molten coating composition or passing the paperboard under a shower of the molten coating composition.

Triglycerides are triesters of glycerol. The hydroxyl groups of glycerol may be esterified with the same acid to form a simple triglyceride. In mixed triglycerides, glycerol is esterified with two or three different acids. The general formula for triglycerides is shown below: GN:AM:07:15940.RES 19 April 1996 o'x AMENDED SHEET Y, IPEAIAU WO 96100815 PCT/AU95/00385 -4- 0 CH 0 C-R'

I

CH

2 0 C R"

I

0 where R, R' and R" may be the same or different and are usually C Ca hydrocarbon chains. The hydrocarbon chains may be saturated or unsaturated.

In a preferred embodiment, the coating including at least one triglyceride compound is applied to the paperboard such that the weight of the coating is up to 100% of the weight of the paperboard to which it is applied. It is preferred that the minimum amount of coating that is able to achieve that desired water permeability and crush strength parameters be applied to the paperboard. Using the minimum amount of coating will clearly minimise raw material costs. The coating is more preferably applied in an amount of 30 to 70%, based upon the weight of paperboard.

Any triglyceride that is solid under ambient conditions is suitable for use in the present invention. In general, saturated triglycerides fulfil this criterion. A number of unsaturated glycerides are also solid at room temperature (although these generally have only a small degree of unsaturation) and such unsaturated triglycerides may also be used in the present invention. A mixture containing liquid triglyceride(s) and solid triglyceride(s) may aso be suitable for use.

The coating may include a single triglyceride or a mixture of two or more triglycerides. If a mixture of two or mnre different triglycerides are used the different triglycerides may have similar molec-iar weights or different molecular weights.

Example of triglycerides that may be used in the present invention include lard (a mixture of C 1 4

C

1 saturated and unsaturated hydrocarbon chains), trimyristin (saturated tri-C 1 4 hydrocarbon chains), tristearin (saturated tri-C 8 hydrocarbon chains), hardened vegetable r1, hardened tallow, hardened fish oil, animal fats and e M WO 96/00815 PCT/AU95/00385 dripping (beef tallow). It will be appreciated that this list is not exhaustive and many others triglycerides may be used in the present invention.

One or more plasticisers may also be added to the coating in order to improve the flexibility of the coating composition. The addition of plasticizers can impart improved flexibility, increased water resistance, reduced brittleness, and affect tackiness and blocking properties. Addition of one or more plasticisers to the coating will act to reduce brittleness of the coating and hence reduce the risk of the coating flaking off the paperboard during use. The plasticiser is preferably added in an amount such that the plasticiser comprises 1-10% by weight of the total weight of the coating, with 3-5% by weight plasticisers being more preferred.

Examples of plasticisers that may be used on the present invention include low molecular weight polyester plasticisers, low density polyethylene, polyethylene wax methyl oleate, ethylene vinyl acetate (EVA) copolymers, cetosteoryl stearate, butyl stearate and beeswax. Low density polyethylene and EVA copolymers are preferred. This list of plasticisers is not exhaustive and a number of other plasticisers that are compatible with triglycerides may also be used. A mixture of different plasticisers may also be used.

Preferably, the plasticiser(s) used in the present invention are non-toxic and readily biodegradable.

To apply the coating to the paperboard, the coating composition must first be placed in the molten state. The coating composition is preferably heated to a temperature of 5-30°C above its melting point by any known heating method. For most coating compositions used in the present invention, this temperature is below 100°C and often in the range of 40 to 90°C. The actual temperature to which the coating composition is heated should be sufficiently high to ensure that the composition is molten whilst avoiding changes to the triglycerides due to elevated temperatures. In some cases where plasticisers are added to the triglyceride(s), the mixed composition goes through a gel phase as the temperature is increased, and it passes through the gel phase to a completely molten, liquid phase at higher temperatures. To ensure adequate coverage by the coating, it is important that the coating composition be heated to a temperature above that at which the gel phase WO 96/00815 PCT/AU951/00385 -6exists. Preferably, the coating composition is heated to a temperature above its cloud point. The cloud point is the temperature at which visible opacity first appears during cooling of the molten coating. The molten coating composition is then applied to the paperboard. A proportion of the applied coating is absorbed into the paperboard and the remainder coats the surface of the paperboard to form the coating. If corrugated paperboard is used, the coating preferably coats both facing sheets of the paperboard and also coats the fluted layer sandwiched between the facing sheets. The coating is then cooled to solidify the coating composition.

Cooling may take place under controlled conditions. Alternatively, the coating may be allowed to cool by placing the paperboard in ambient conditions.

The molten coating composition can be applied to the paperboard by any method known to a skilled person. Preferred methods includes dipping or otherwise passing the paperboard through a bath or pool of molten coating composition, or by passing the paperboard under a shower of molten coating composition. Preferably, the coating process is controlled to saturate all surfaces of the board (including within the fluted core of corrugated board).

The coated paperboard product produced by the present invention is especially suitable for use as storage and transport containers or boxes. Preferably, the paperboard is pre-cut to a container blank prior to coating the paperboard.

The triglyceride compounds used in the present invention may be edible, are readily biodegradable and can be obtained from renewable resources, such as animal fat, fish oil and vegetable oil. In addition to producing a coated paperboard that has properties suitable for commercial applications, use of triglyceride-containing coatings allows for potentially better recyclability than current petroleum-wax coated products. Triglycerides will melt in hot water and agitation of used paperboard in hot water will remove at least some of the triglycerides from the paperboard. The triglycerides, in being less dense than water, will float and can be recovered from the surface of the water.

There are at least four other potential methods for removal of triglycerides from paperboard: detergency/emulsification, WO 96/00815 PCT/AU95/00385 -7- (ii) saponification under alkaline conditions, (iii) enzyme mediated degradation, and (iv) repulping, optionally with flotation.

The first method is a non-destructive method and offers the possibility of separating the triglycerides from the surfactant/detergent and to recycle the triglyceride. Methods (ii) and (iii) above are destructive to the triglyceride. Method (iv) is non-destructive and offers the possibility of separating the triglycerides and recycling the triglyceride.

The invention will now be described in more detail with reference to the following Examples.

Example 1: The water uptake of three triglyceride films in both cool room conditions and cold water immersion was investigated. The triglycerides were lard, trimyristin and tristearin. Sessile drop water contact angles for each triglyceride coating were determined to be as follows: lard 111 trimyristin: 118 tristearin 112 t Samples of coated paperboard were prepared by placing 230 Liner (paperboard) in an oven at 60*C until ready for use. 230 Liner is a commercial grade paperboard/boxboard used in the manufacture of containers and blanks therefor. This removed any water from the liner. The triglycerides were heated to approximately 20*C above their melting points and the liner was dipped in the liquid medium for about 5 seconds, after which it was removed and allowed to drain on an absorbent piece of paper. All coated materials were allowed to cool at room temperature for at least one hour before undergoing any tests. The mass of the triglyceride coatings was 0.8 to 1 times that of the original weight of the native paper.

In the water immersion tests, the native or coated samples of paper were totally immersed in a beaker of water at 4 0 C. At various time intervals they were removed and placed to drain on an absorbent tissue for one minute before weighing WO 96/00815 PCT/AU95/00385 -8after which they were re-immersed until next removed for re-weighing.

In the cool room tests, the native or coated samples of paper were left hanging in the humidified and temperature controlled storage unit. The cool room environment was maintained at 92% relative humidity and 2*C. At various time intervals, the paper samples were removed and placed to drain on an absorbent tissue for one minute before weighing, after which they were returned to the unit until the next weighing.

The results of the water uptake experiments are shown in Figures 1 and 2.

Figure 1 shows the coolroom tests, Figure 2 shows the cold water immersion tests.

As can be seen from Figures 1 and 2, all the triglyceride coatings significantly reduce the water permeation into the paperboard. For comparison purposes, similar tests were conducted for paper coated with a commercially used wax coating. These results are also shown in Figures 1 and 2.

Example 2: Five samples of triglycerides were obtained and investigated. The samples were: hardened vegetable oil (fully refined); hardened tallow (semi-refined); hardened tallow (fully refined); hardened fish oil (semi-refined); and hardened fish oil (fully refined).

In the solid state triglycerides are crystalline and display polymorphism. In other words, they undergo transitions where the ordering of the crystalline hydrocarbon chains changes. There are 3 polymorphic forms and B).

Rapid cooling from the melt may lead to the a-form. This form is thermodynamically unfavourable. Consequently, the a-form will eventually transform to another polymorphic form that has better chain packing. The usual sequence is a- B'-B1. For high melting point triglycerides these transformations can take weeks at room temperature and months under cool room conditions. These transformations will also take place instantaneously at well defined polymorph transition temperatures.

I I, WO 96/00815 PCT/AU95/00385 -9- Coated liners using the samples mentioned above were prepared by melting the samples once then dipping the paper for ca. 2 seconds. Sessile drop water contact angles on the cooled coatings are given below.

Sample Water Contact Angle A) hardened vegetable oil (fully refined) 107 B) hardened tallow (semi-refined) 108 C) hardened tallow (fully refined) 106 D) hardened fish oil (semi-refined) 102 E) hardened fish oil (fully-refined) 109 Despite the fact that these triglyceride coatings take up moisture, it has been found that the surface of all these triglyceride coatings are very hydrophobic. Water uptake experiments show that the above triglycerides are very similar to the pure tristearin.

Edge-wise crush tests were performed on corrugated board that had been saturated coated with a commercially available wax product and the above triglycerides (samples The wax product is a petroleum wax product currently used to coat paperboard and has been included for comparison purposes. The results are given in Table 1. It is clear that in dry conditions, triglyceride coatings are stronger than both the untreated board and the board that has been treated with the wax product. The results for the samples of board that have been in the cool room for 65 hours show that the triglyceride coatings (samples A-E) do impart "wet strength" to the paperboard.

Example 3: The coating used in Example 1 and 2 were applied to paperboard that had been dried prior to coating. In commercial application, coating would be applied to paperboard that will be in equilibrium with the ambient humidity and hence will contain absorbed water. To determine if this would adversely affect the coating a series of experiments were carried out in which triglyceride coatings were applied to paperboard that had been allowed to equilibrate at ambient temperature (21"C) and humidity The coatings applied included these used in Examples 1 and 2, together with Dripping (beef tallow) and Supafry (a blended animal and vegetable WO 96/00815 PCT/AU95/00385 oil). For comparison purposes, similar tests were carried out using pre-dried paperboard.

Results of water uptake tests are shown in Figure 3 (pre-dried paperboard) and Figure 4 (equilibrated paper board). In the case where the paperboard had not been pre-dried, the maximum water uptake is about 30% less than that for a predried liner. A general observation was that the coatings on the moisture equilibrated paperboard showed less cracking than coating on a pre-dried paperboard.

Example 4: The experimental results obtained in Example 1 to 3 included coatings that comprised a single triglyceride. It was observed that some of these coatings were somewhat hard and brittle. Although the hardness of the coating contributed to the dry strength and the wet strength of the coated paperboard, the coatings were observed to flake off in some instances. In order to try to decrease the brittleness of the coating, an experiment was run in which small amounts of low molecular weight polyethylene (plasticiser) were added to hardened tallow (semi-refined). The results are shown in Figure 5 and reveal that small amounts (up to of low molecular weight polyethylene improved the water resistance properties of the coated paperboard.

Example A series of coatings were prepared on a boxboard substrate such that the uptake of coating on the boxboard was about 58% w/w the coating weight was about 58% of the weight of the uncoated boxboard). The coatings used included hardened tallow, a hardened tallow/polyethylene plasticiser mix, and a commercially available wax coating. Figure 6 shows edge-wise crush strength versus water uptake after 48 hours in cool room conditions. On average, the results show that the hardened tallow and the hardened tallow/polyethylene plasticiser mixture appears to take up 2 to 3 times more water than boxboard coated with the commercially available wax coating. However, the hardened tallow and hardened tallow/polyethylene plasticiser mixture coatings impart significantly greater wet strength to the boxboard than the commercially available wax coatings.

Example 6:

I

WO 96/00815 PCT/AU95/00385 11 Boxboard was coated with a series of coating compositions under conditions such that a coating thickness corresponding to 30% w/w was obtained. The coating method included dipping the boxboard into molten triglyceride, allowing the coating to cool and subsequently dipping into a hexane solution to remove some of the coating. The coated sample was then oven dried to remove volatile hexane.

Figure 7 shows edgewise crush strength versus water uptake for various coatingr at 30% w/w after 48 hours in coo: Jm conditions. These results show that the hardened tallow and hardened tallom/polyethylene plasticiser mixture had very similar water uptake to the commercially available wax coating and once again the commercially available wax coating had significantly smaller wet strength than the hardened tallow-based coatings.

Example 7: To test the effectiveness of other plasticisers in the triglyceride-based coatings, a series of coatings comprising a mixture of hardened tallow and various amounts of ethylene-vinyl acetate (EVA) copolymer resin were prepared. These coatings had about 100% w/w pick-up on the paperboard substrate. As shown in Figure 7, the addition of EVA resin did not deleteriously affect the properties of the hardened tallow-based coatings. The addition of 3% and 5% EVA, by weight of the coating, to the hardened tallow, provided a water barrier equivalent to that of the commercially available wax coating.

Edge-wise crush strength versus water uptake following 48 hours in cool room conditions for hardened tallow/EVA resin coatings (comprising 97% hardened tallow and 3% EVA resin) are shown in Figures 6 and 7 for coatings having about 58% w/w and 30% w/w uptake. These coatings are thinner than the 100% w/w uptake coatings used to obtain the results shown in Figure 10. As can be seen by reference to Figures 6 and 7, the hardened tallow/EVA resin coatings had similar properties to the hardened tallow/polyethylene plasticiser coatings.

Example 8: To assess the coating performance of triglyceride-based coatings on produce cardboard boxes, a number of boxes were coated by dipping into a pool of molten coating then removed and allowed to stand to allow the excess coating to drain off WO 96/00815 PCT/AU95/00385 12the box.

The boxes were coated with a hardened tallow coating or a hardened tallow (97%)/polyethylene plasticiser coating and coating uptakes varied between approximately 50% w/w to 70% w/w. Boxes coated with the commercially available wax coating and prepared by normal plant procedures were also investigated for comparison.

Some of the coated produce boxes were left at ordinary ambient conditions while others were placed in cool room conditions (2oC and 95% relative humidity) for 6 days. All the boxes containing hardened tallow based coatings were weighed before and after coating. Additionally, the coated boxes were weighed after they had been conditioned. After the conditioning period, the boxes were assembled and box crush tests performed. The results of these measurements are given in Table 2.

For the boxes left at ordinary ambient conditions, the triglyceride coated boxes displayed significantly greater crush strength than the commercially available wax-coated boxes; approximately 7.5 kN, irrespective of coating uptake, for the triglyceride boxes compared with approximately 5.5 kN for the commercially available wax-coated boxes.

Boxes coated with hardened tallow (ca. 50% w/w) and left in the cool room conditions had an average total moisture uptake of about 9% and a box crush strength of about 3.8 kN. Boxes coated with hardened tallow/polyethylene plasticiser (ca. 50% w/w) and left in the cool room conditions had an average total moisture uptake of about 7% and a box crush strength of about 3.8 kN. Hence, there was not much difference in the behaviour of these ca. 50% w/v coatings with or without the polyethylene additive. Boxes coated with hardened tallow/polyethylene plasticiser (ca. 70% w/w) and left in the cool room conditions had an average total moisture uptake of about 3% and a box crush strength of about 5.4 kN. Boxes coated with the commercially available wax coating and left in the cool room conditions had an average total moisture uptake of about 1% and a box crush strength of about 5.7 kN. Hence, the hardened tallow/polyethylene plasticiser coated boxes, had similar crush strength to the wax coated boxes but the moisture uptake of the triglyceride based coatings was about 3 times more.

WO 96/00815 PCI/AU95/00385 13- Example 9: The hardened tallow used as the basis for most of the previous Examples consists mainly of Cs 1 and C 16 hydrocarbon chains. In order to investigate triglyceride blends of different chain length material, hardened coconut oil (mainly

(C

12 and C 1 4 and partially hardened fish oil (mainly C, and C2 were used for further trials. Figure 8 shows the water uptake in cool room conditions of paperboard coated with pure hardened coconut oil and various mixtures of tallow and hardened coconut oil. The addition of the hardened coconut oil slightly Increased the water resistance of the hardened tallow-based coating. The coating of pure coconut oil increases the water resistance substantially.

Figure 9 shows the water uptake of paperboard coated with hardened tallow doped with partially hardened fish oil when placed in cool room conditions. The addition of partially hardened fish oil increases the water resistance of hardened tallow more than the fully hardened coconut oil. The coating of pure partially hardened fish oil increases the water resistance substantially. These trends probably reflect the longer alkyl chain length of the partially hardened fish oil and the fluidity of the unsaturated components. Although the water resistance of both the hardened coconut oil and the partially hardened fish oil appear to be superior to the hardened tallow, their melting point behaviour and mechanical strength would be inappropriate for them to be the major component of a commercial coating.

Example Hardened tallow was mixed with various additives in order to investigate the properties of the resulting mixture. The additives included tributyrin, dodecanol, beeswax, butyl stearate, cetostearyl stearate, lanolin and methyl stearate. All of these additives improved the relative flexibility/flaking of the hardened tallow, with some of the fatty acid ester materials (butyl stearate, cetostearyl stearate and lanolin) having the best effect.

Water uptake tests showed that coatings of hardened tallow doped with from 1 to 5% of butyl stearate, or cetostearyl stearate had similar water resistance properties to pure hardened tallow. The addition of 1 to 5% beeswax to the hardened tallow increased the water resistance properties of the hardened tallow- II I I WO 96/00815 PCT/AU95/00385 14based coating.

Figures 6 and 7 also contain edgewise crush strength versus water uptake for boxboard for hardened tallow-based coatings containing 3% of either butyl stearate or cetostearyl stearate, after 48 hours in cool room conditions. The coatings have similar properties to the hardened tallow/polyethylene plasticiser coatings.

Example 11 The previous Examples detailed investigations of paperboard coated by dipping the paperboard into molten coating material. It is believed that this coating method does not result in ideal coatings. Therefore, a pilot scale cascade coater was constructed to enable coating to take place under controlled conditions whilst using a process similar to that used on the commercial scale. The cascade coater comprises a heated lower reservoir for holding a pool of molten coating material.

A pump is used to raise the molten coating material to an upper reservoir having a weir. Overflow from the upper reservoir cascades over the weir and a box blank can be moved back and forwards through the falling cascade to coat the blank. The pilot scale cascade coater allows for accurate control of the temperature of the molten coating material, flow of the molten coating material and air flow. Variable coating thicknesses can be obtained using the cascade coater.

A series of trials were conducted using the pilot scale cascade coater in which cardboard box blanks were coated. After the coating had hardened, the box blanks were folded into boxes and box crush tests were conducted on the boxes, after the boxes had been exposed to ambient conditions (23*C, 50% relative humidity) or cool room conditions 95% relative humidity, 72 hours). The trials were conducted using a commercially available wax coating and a triglyceride coating comprising 97% hardened tallow and 3% polyethylene plasticiser. Both coatings were applied at variable coating pick-up. The boxes used had dimensions of 570 x 370 x 300 mm (approximately) and were made from corrugated boxboard. The results of these trials are given in Tables 3 to 11. Table 12 shows a 50% w/w coating comprising hardened Tallow and 5% polyester plasticiser.

Comparison of the results for the commercially available wax coating and the triglyceride-based coating show that the boxes coated with the triglyceride-based WO 96/00815 PCT/AU95/00385 coating have superior dry strength to the wax coated boxes, but exhibit slightly lower wet strength than the wax coated boxes. Strength increased with increasing coating uptake. Table 13 shows dry strength and wet strength properties of uncoated paperboards. The results of Table 13 clearly show that the coating of the present invention improves the dry strength of the boxes and markedly increases the wet strength of the boxes.

The triglyceride-based coatings of the present invention produce coated paperboard articles that exhibit satisfactory wet strength properties. The coatings are transparent, made from a non-solvent base and are sourced from renewable resources.

A very important feature of the triglyceride-based coating of the present invention is that they allow for recycling of the paperboard. Initial trials using boxboard coated with a coating comprising 97% hardened tallow and 3% polyethylene plasticiser were conducted using a laboratory scale repulper in order to assess the recyclability of the paperboard. It was found that the triglyceride coated boxes defibred quite readily. Hand drawn sheets were made from the repulped material and the quality of the material so-produced was similar to that of recycled uncoated boxboard. It was noted that more beating/repulping time was required to recycle the triglyceride-coated boxes.

As a further advantage of the present invention, the triglyceride materials used in the coatings are readily hydrolysed to form fatty acids which are readily biodegradable under both aerobic and anaerobic conditions. Thus, the coating material is unlikely to persist in the environment if coated boxes are disposed of as waste rather than being recycled.

Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically disclosed.

It is to be understood that the invention is considered to encompass all such variations and modifications that are all within its spirit and scope.

List of Chemicals: The following chemicals were used in the Examples listed in this specification: ,j i I WO 96/00815 PCT/AU95100385 16- 1) All triglyceride compounds obtained from Unichema Australia: Hardened vegetable oil fully refined; Unichema Prifat 9834 Hardened tallow semi-refined; Unichema Prifat 9813 Hardened tallow fully refined; Unichema Prifat 9833 Hardened fish oil semi-refined; Unichema Prifat 9811 Hardened fish oil fully refined; Unichema Prifat 9832 2) Polyethylene plasticizer Polywax 500 (Dusek Campbell) 3) Commercially available wax coating Surfowax 7111 4) Dripping (beef tallow) Wik Industries Australia 5) Supafry (blended animal and vegetable oil) Meadow Lea 6) Lard "Dandy" brand Metro Quality Foods 7) Tristearin 99% pure) Sigma 8) Trimyristin (2 99% pure) Kodak 9) Cetostearyl stearate Unichema 10) Butyl stearate BDH 11) Fully hardened coconut oil Swift Co.

12) Partially hardened fish oil Swift Co.

0l ~0 TA BL E EDGEWISE CRUSH TEST BOQARD GRAD)E: 220 EC.W/1501225 K 'Cl TIME IN HUMID ENVIRONMEN'!' (2*C 92% R1H): 65 HOURS UNTR D) WAX SAMPLE A SAMPLE B SAMPLE C SAMPLE 1) 7 A PLn 1 DR Y WEIGH T OF~ 7 SAMPLES 12.05 22.64 19.91 22.68 21.05 20.62 22 64 HIUMID WEIGHT (o)OF 7SAMPLES 13.52 22.94 21.11 23.88 22.33 21.88 23.72 MOISTURE CONTENT UNTREATED 18.670 E.C.T. (KNIM DRY 9.19 11.86 15.29 12.74 13.62 14.20 13.55 9.27 11.83 14.28 13.18 13.80 14.34 14.36 8.94 11.65 14.52 12.29 13.80 13.67 14.15 8.98 11.67 14.69 12.40 13.79 13.99 13.67 9.14 11.96 14.53 12.92 14.27 14.29 13.52 9.33 12.03 14.55 12.21 14.04 13.60 14.29 7.93 12.11 14.46 12.54 14.01 13.76 14.10 AV: 8.97 _t 0.44 11.87:t 0.16 14.62 ±t 0.23 12.61 13.90 :r 0.20 13.98: R 028 13.95 ;r 0133 HIUMID) 2.55 9.05 7.26 6.18 6,65 6.49 7.50 2.34 8.46 7.78 5.98 6.90 6.96 7:28 2.44 895 7.40 6.25 6.70 6.55 7T39 2.49 7.99 7.54 6.43 6.78 6 65 7.29 2.49 7.78 7.45 5.98 7.00 6.94 6.93 2.29 7.31 7.31 6.37 7.20 6.72 7.75 2.39 7.13 7.21 6.46 6.91 7.70 AV: 2.43 ;t 0.09 8.04 ±r 0.70 7.42.r 0.18 6.23 x 0.19 6.87 :t 0. 19 6.75 0. 18 7.41 _t 0.26 TABLE 2 HARDENED TALLOW Codle Calloni Weight Dipped Weighl Oven Died wt wiw Pick Up Hlumid Room wI iicr Miti 6 days 2'C495% 1 8410 1410 1220 45 1340 4.13 9.8 2 840 1430 1266 *50 1365 3.89 78 3 841 1413 1250 49 1370 3.73 9,6 43 842 1390 1300 54 Ambient 7.59 837 1330 58 1445 369 86 6 837 1350 61 Ambient 7.31 7 842 1225 46 1350 3-64 102 8 842 1250 49 Aniblent 7.45 9 842 1278 52, 1395 3.89 9-2 842 1287 53 Amablent 7.41 It 828 1290 56 1406 3.61 12 842 1295 54 1400 4.15 8.2 JIARDENEI) TALLOW 3% POLYETHYLENE PLASTIICISER Cutde Carlon weight Dipped Weight Oven Dried wi wlw Pick Up Ifumid Roomt wt 1cr Muisutle 6 days (LN) 2'Q95%RI A 827 1425 no oven drying 72 1460 5.50 24 B1 827 14501 1225 48 1335 3118 82 C 827 1446 1265 53 Amblent 7.47 1) 827 1435 1217 47 Ambient '7.14 Ei 827 1428 rno oven drying 713 1473 5.33 32 F 827 1451 1278 54 1365 3.41 68 G 827 1433 1243 50 Amnblent 7.62 827 1432 no oven drying 72 Ambient 7.44 1830 1433 1283 55 Amblent 771 830 1439 1230 48 1325 3.99 j 7.7 K 831 1432 1310 57 1385 4.65 5.7 L 838 1432 1250 50 Amblent 7.74 TA BL E CoatiIng Wax tcnip 40% wlw wax coating 87 Deg. C 180 cs Ciii No. Weight of C1ii Weight of 0iii. Pick-Upl Weight of C111. BCI' (MN) 1Cr (kN) (inlitial) (Ireated) (I Iuiiid) Ambient Humnid T6-1 738 1053 413 1082 6,29 T62736 1054 43 1083 6111 1'6-3 738 1055 43 1081 5.98 1'6-4 739 1053 '13 1083 6.2 742 1(059 43 1089 5.77 *T6-6 740 1058 43 10191 5.51, Tr6-7 7441 1057 42 1092 5,55 T'6-8 745 1053 411 1081 6,02 T16-9 747 1055 41 1087 5.49 '176-10 738 1056 43 1083 5.45 Average 741 1055 43 1085 5.83 T6-11 739 1056 43 -5.78 T16-12 737 1052 43 -5.94 T6-13 739 1051 42 -6,17 T6-14 7-10 1059 43 -6.00 *16-15 742 1059 43 -6.28 T6-16 743 16157 42 6.11 T16-17 744 10161 43 5.97 T6.-18 743 10161 43 6.16 T6-19 745 1062 43 6.18 T'6-20 477 1064 43 5.98- Average 742 15436.06 TABLE 4 Cmaling Wax temp slanding il Cabin ten p 50% wlw wax 87 Deg., C 60 secs.

87 Deg. C Cim No. Weight of Otn Weight of On. Pick-Up Weight of Oni. 13Cr (kN) I3Cr (MN) (iiiilial) (Uleattd) (Humid) Ambient Humid T5.-1 743 1032 52 1154 6.23 T5-2 741 1118 51 1142 6.05 T5-3 742 1116 50 1143 -5.71 T5-4 '738 1102 49 1131 5.87 735 1122 53 1143 6.08 T5-6 735 1115 52 1138 6.19 -7 735 1109 51 1137 6.07 T15-8 734 1120 53 1137 5.89 T5-9 741 1115 50 1138 6.08 T5-10 740 1116 51, 1141 5.92 Average 738 1117 51 1140 6.01 T5-11 740 1118 51 -5.64 T6-12 738 '1119 52 -5.91 T5-13 738 1113 51 -5.68 TS-14 7132 1111 52 -5.99 747 1112 49 -5.37 TS- 16 747 1120 50 -5.33 T5-17 746 1119 50 -5.36 T5-18 743 1111 50 -5.87 TS-19 741 1114 50 -5.85 T5-20 1 740 1113 50 5.52 Avrgi4 1115 51 5.63 TABLE CO(I&iiu Wax ten p stanldingjIle Cain Temp~ 40% wlw wax 87 Deg. C 0 87 Deg. C Cuti No. Weight of On Weight of Cmt. %Pick-Up Weight of COn. BCl' 13CT (k-N) (initial) (treated) Ambient Humid 'r4-1 737 1189 61 1213 -6.34 T4-2 739 1178 59 1203 6,1 1 '4-3 739 1163 57 1189 6.12 '1'4-4 743 1197 61 1216 602 '174-5 743 1171 58 1198 6.91 T[4-6 737 1193 62 1217 6.03 T[4-7 734 1187 62 1210 6.17 T4-8 733 1189 62 1212 1.18 T4-9 735 1191 62 1214 5.93 T4-10 734 1196 63 1218 5.98 Average 737 1185 61 1209 6.18 T4-11 733 1191 62 6.19 T14- 12 732 1191 63 -6.02 T4-13 729 1188 63 -5.92 T[4-14 733 118? 62 -601 T4 -15 734 1189 62 -5.99 T4-16 744 1193 60 -5.83 T4-17 740 1199 62 -6.00 T4-18 739 1179 60 -5.52 T-19 739 1192 61 -5.86 T[4-20 748 1204 61 15.90 Aeae737 1191 62 5.92 TABLE 6 Coating Wax lenip Staing~jims Cabin ten p 70% wlw wax 75 Deg. C 15 secs.

75 Deg. C Oin No. Weight of Oin Weight of Ci11. Pick-Up Weight of Cn. BCI' QiN) IlCr (MN) (inlitial) (Irealett) Ambtient Itumid 735 1259 71 1272 6.55 T7-2 736 1276 73 1292 6.31 1-7-3 738 1257 70 1275 6.83 '17-4 738 1285 74 1301 6.79 '17-5 737 1244 69 1278 7.17 1-7-6 74l0 1258 70 1273 6.04 T17-7 741 1280 73 1295 6.55 T7-8 741 1255 69 1271 6.54 T17-9 739 1281 73 1298 6.62 '[-0739 1266 71 1282 6.40 Average 738 1266 71 1284 6.58 17-11 745 1308 76 -5.81 1 7-12 747 1256 68 -5.91 1-7-13 749 1289 72 -6.23 '17-14 751 1268 69 -6.09 T7-15 751 1268 69 -5.86 T17-17 733 1260 72 6.19 1-7-18 735 1251 70 5.95 '1-9736 1255 71 5.77 17-20 734 1269 73 6.04 L Average 1 742 1268 71 5.98 TA BL E CoaIg Wax tenmp SiAW!dii lme 80% wlw Wax 75 Deg. C 70 Deg. C Cin No. Weight of Cli Weight of Ciii. Pick-Up Weight of COn. 3Cr (kN) Bcr (MN) (initial) (Irealed) (hiumid) Ambientl Ittmid 1,8-I 749 1356 81 1365 -6.87 "8-2 747 1344 80 1355 -6.62 T8-3 744 1324 78 1336 -6.67 T8-4 742 1321 78 1333 6.53 741 1326 Average 745 1334 79 1347 6.67 T8-6 740 1329 80 6.76 TE-7 738 1331 80 6.67 TS-8 739 1339 81 6.42 "8-9 736 1335 81 6.47 T810 738 1344 82 6.64 Average 738 1336 81 6.59 TABLE 8 Standing lime Cabin tempi wlw 97% hardened tallowI3%polycihylenc plasticiser 87 Deg. C 60 secs, 87 Deg. C Cmn No. Weighti of Oin Weight of Oin. Pick-Up Weight of Ginl. BCT (MN) 13Cr (kN) (initial) (treated) (Humid) Ambient Hlumid TI1-1 740 1126 52 -7.48 TII1-2 754 1149 52 -7.40 TI 1-3 749 1146 53 -7.68 TI1-4 751 1151 53 -7.60 749 1149 53 -7.39 TII1-6 747 1146 53 -7.51 TI 1-7 748 1149 54 -7.86 T11-8 748 1140 53 -7,66 TII1-9 742 1142 54 -7.47 TI 1-10 739 1138 54 -7.64 Average 747 1144 53 7.57 T1I-11 738 1165 58 1196 -5.54 TI 1-12 741 1147 55 1193 5.27 TI1-13 739 1146 55 1197 4.90 TII1-14 764 1155 51 1205 5.16 748 1145 53 1191 -4.84 TII-16 746 1146 54 1203 -5.40 TII1-17 743 1145 54 1200 -4.79 TI -18 742 1145 54 1205 -5.09 TI1-19 743 1143 54 1196 -5.44 744 1146 154 1195 Average 745 1148 54 1198 5.16 TABLE 9 Cating Wax lemii Cabin tenmp 60%/ w/w 97% hardened tallow/3% polyethylene plasticiser 87 Deg. C 0 87 Deg. C Oni No. Weight of COn Weight of On. Pick-Up Weight of Oni. BCl' (kN) 13C1 (kN) (inlitial) (treated) (hlumid) Ambhient t1unid TIO-1 759 1217 60 1259 -49 TIO-2 749 1208 61 1255 5.66 TIO-3 747 1202 61 1246 5.46 TIO-4 747 1194 60 1243 5.08 745 1189 60 1236 5.24 TIO-6 745 1180 58 1240 3.95 Tlfl-7 743 1198 61 1249 5.23 TIO-8 744 1197 61 1237 5.57 TIO-9 750 1214 62 1259 5.57 753 1219 62 1257 5.49 Average 748 1202 61 1248 5.2 TIO-11 751 1202 60 -7.79 TIO-12 752 1224 63 -8.09 TI0-13 756 1220 61 -7.48 TIO-14 759 1228 62 -7.88 746 1215 63 -7.51 TIO-16 742 1182 59 -7.59 TIO-17 745 1208 62 -7.44 TIO-13 747 1207 62 -7.47 TIO-19 744 1213 63 -7.68 743 1213 63 -7.62 Average 749 1211 62 11 7.66 TABLE Wax IC P_ Standi glim CAdttjjma wlw 97% hardened taIlowI3% polyethylene plasticiser 75 Deg. C 15 sccs.

75 Deg. C Ctzi No. Weight of On Weight of On. Pick-Up Weight of COn. 11Cr (MN) I3CT (kN) (inmitial) (IteatcA) (HUMIdl) Ambient Humid T12-1 750 1256 67 1279 5-82 T12-2 754 1240 64 1263 5,84 T12-3 747 1250 67 1275 586 T12-4 749 1233 65 1258 5.97 T12-5 747 1243 66 1271 5,61 T12-6 743 1228 65 1255 5.73 T12-7 744 1245 67 1272 5.72 T12-8 748 1237 65 1266 6.09 T12-9 745 1249 68 1274 6,10 '*P12-10 745 1237 66 1263 Average 747 1242 66 1268 5.86 T12-11 746 1251 68 -7.A7 T12-12 748 1241 66 -7A49 TI2-13 737 1256 70 8.B05 T12-14 738 1244 69 -7-55 T12-15 743 1241 67 -8.10 T12-16 743 1259 69 -7.76 T12-17 742 1245 68 -7.98 T12-18 745 1238 66 -7.85 T12-19 747 1242 66 -7.31 T12-20 750 1248 66 -7.79 JL_ Average 744 1247 68 7174 TA B LE Coaldng 45% wlw; 97% 1Iardeaited TaIlu/31%t Polyclliylene Platiclztr C111 No. Weighi of C111 Weight of ClIi. Pick--Up Weight of Oni. BC? (LN) Bcr kN (iliial) (tratd)(umid) Ambient hlunld 1*13-1 754 11147 1161 5.43 '113-2 750 1015 43 1165 3.16 T'13-3 748 1082 45 1153 4.38 T113-4 747 1088 46 1185 3.76 T13-5 749 1090 46 1178 3,93 '13-6 750 1091 45 1167 4. 69 T13-7 751 1091 45 1152 5.95 T13-8 751 1087 45 1163 4.941 T13-9 753 1098 46 1159 5.13 T13- 10 753 1105 47 1157 5,65 Averapm- 751 1092 48 1164 4.76 T[13-11 753 1100 46 7.29 TB3-2 752 1098 46 -7.81 1r13-13 751 1108 47 -7.49 11l3-14 753 1102 46 7.54 T13-15 756 1113 47 7.14 T13-16 752 1098 46 -7.65 ,r13-17 752 1101 46 -7.49 T13-18 752 1102 47 -7.49 T13-19 755 1105 46 -7.84 '[13-20 755 1099 46 Average 1 753 1103 46 7.53 TA BL E Coaling: 4S% wlw; 95% H~ardened TullowIS% Polyethylene, Plasticizer Otn No. Weight of Cn Weight of Ct. %Pick-Up Weight of CtnI. 11CT (kN) 11Cr (mN) (initial) (Ilealed) (1 tumid) Amibient Hlumid '114-1 760 1166 53 -6.97 T14-2 758 1162 53 -7.32 T14-3 754 1159 54 -7.45 T14-4 755 1157 53 -6.89 T14-5 757 1155 53 -7.31 T14-6 755 1155 53 -7.22 T14-7 752 1151 53 -7.32 T14-8 753 1144 52 -7.17 '114-9 753 1145 52 -6.94 T14-10 750 1141 52 -7.32 Average 755 1154 53 7.19 T14-11 751 1139 52 1186 -5.26 1*14-12 753 1138 51 1195 -5.24 T14-13 752 1148 53 1187 -5M9 T14-14 757 1156 53 1199 -5.60 T14-15 754 1146 52 1196 -5.38 T14-16 755 1152 53 1198 -5.51 T14-17 749 1145 53 1205 T14-18 750 1150 53 1198 5.61 T14-19 753 1154 53 1194 T14-20 753 1169 55 1203 5.855 Average 753 1150 53 1196 5.55 TABLE 13 Uncoated Properties Ciii No. BC-r OkN) DCr (kN) Moist. Cant IAmbient Humid M% 1 4.86 7.92 2 4.85 7.99 3 4.63 7.86 4 5.01 8.09 4.71 8.26 6 4.92 8.17 7 5.09 7.91 8 4.74 8.11 9 4.99 8.14 Average 4.87 8.05 11 -1.57 20.2 12 -1.87 20.1 13 -1.62 2(1,6 14 -1.57 21.2 -1.77 20.2 16 -1.74 21.8 17 -1.62 20.5 18 1.71 20.0 Average 20.61

Claims (19)

1. Paperboard having a coating applied thereto, said coating being substantially petroleum wax free and comprising at least one triglyceride compound.

2. Paperboard having a coating applied thereto, said coating being substantially petroleum wax free and comprising at least one triglyceride compound present in an amount of 90 99% by weight of said coating and one or more plasticisers present in an amount of 1 to 10% by weight of said coating.

3. Paperboard as claimed in claim 1 or claim 2 wherein the coating is applied in an amount of up to 100% of the weight of the paperboard.

4. Paperboard as claimed in claim 3 wherein the coating is applied in an amount of from about 30% to about 80% w/w of the weight of the paperboard.

5. Paperboard as claimed in any one of claims 1 to 4 wherein the coating includes a single triglyceride compound.

6. Paperboard as claimed in any one of claims 1 to 4 wherein the coating S 15 includes two or more triglyceride compounds.

7. Paperboard as claimed in claim 6 wherein the mixture of two or more triglyceride compounds comprises at least one triglyceride compound that is a solid at ambient temperature and at least one triglyceride compound that is a liquid at ambient temperature, the mixture being solid at ambient temperature. 20

8. Paperboard as claimed in claim 1 or claim 2 wherein the at least one triglyceride compound is selected from lard, trimyristin, tristearin, hardened vegetable oil, hardened tallow, hardened fish oil, dripping or mixtures thereof.

9. Paperboard as claimed in any one of claims 2 to 9 wherein the one or more plasticisers is/are present in an amount of from about 3% to about 5% by weight of the weight of the coating.

Paperboard as claimed in any one of claims 2 to 9 wherein the one or more plasticisers is selected from low molecular weight polyester plasticisers, low density polyethylene, polyethylene wax, methyl oleate, ethylene vinyl acetate (EVA) copolymers, butyl stearate, cetostearyl stearate, beeswax and mixtures thereof.

11. A paperboard product made from paperboard in accordance with any A one of claims 1 to GN:NB:#15940.RES 29 April 1998 I -31

12. A paperboard product as claimed in claim 11 wherein the paperboard product is a box or a box blank,

13. A method of applying a coating to a paperboard product which coating is substantially petroleum wax free and comprises at least one triglyceride compound, which method comprises heating the at least one triglyceride compound to a temperature above its melting point to thereby melt the at least one triglyceride compound, applying the molten at least one triglyceride compound to the paperboard product and allowing the coating to harden.

14. A method as claimed in claim 13 wherein the at least one triglyceride compound is heated to a temperature above the cloud point thereof.

15. A method as claimed in claim 13 wherein the at least one triglyceride compound is heated to a temperature 5 to 30 0 C above its melting temperature.

016. A method as claimed in claim 13 wherein one or more plasticisers are present in the molten at least one triglyceride compound.

17. A method as claimed in any one of claims 13 to 16 wherein the molten at least one triglyceride compound is applied to the paperboard product by passing the paperboard product through a curtain or cascade of the molten at least one triglyceride compound.

18. A method as claimed in claim 16 wherein the coating comprises at Y: 20 least one triglyceride compound present in an amount of 90-99% by weight of the coating and one or more plasticisers present in an amount of from 1 to 10% by weight of the coating.

19. Paperboard having a coating applied thereto substantially as hereinbefore described with reference to the Examples. 29 April 1998