Fiel d of i nvention

The invention relates to extrusion coating compositions , processes and uses of additives in such compositions and processes as well as to extrusion coated articles . The invention has particular application in packaging, especially of liquids e . g . drinks .

Background of the invention

Low density polyethylene (LDPE) is made by a high pressure process using free radical initiators. Its branching and broad molecular weight distribution permit high speed extrusion, for example in extrusion or coating processes. The LDPE is used to provide a seal layer in food or drink packages. LDPE is coated under severe conditions (e.g. high temperature) to aid adhesion. For this use, LDPE is conventionally, free of additives such as anti-oxidants because such additives are believed to have a negative impact on adhesion. More severe conditions improve adhesion but worsen off-taste.

In the invention, particular additives or combination of additives are used in circumscribed, low amounts to provide an improved balance of adhesion and off-taste under severe extrusion conditions. In extrusion coating, at least one layer is extruded downward into a nip between a substrate to which the extruded layer is to adhere and a chill roller. Adhesion is effected at high temperatures.

Where adhesion is not critical, anti-oxidants have been used to protect polyolefins against deterioration e.g. exposure to heat during melt processing etc. Hindered phenols have been used as primary antioxidants (AO) .

This has been used on its own for LDPE. Primary anti- oxidants in combination with secondary anti-oxidants such as phosphorus-containing compounds especially phosphites have been used for LLDPE (linear low density polyethylene) .

Conventionally, extrusion coating grades of LDPE contain no AO because of the reduction in adhesion; AO packages are used for blown-film extrusion of LDPE, LLDPE and PP (polypropylene) grades for which good adhesion is not as critical.

Prior art on additive packages for materials other than LDPE coating or cast-film extrusion grades include: GB 2156358; GB 2156359; GB 2156360; EP 551062; US 5026592. GB 803557 concerns a linear polyethylene.

Prior art on additive packages, which mention LDPE but not in coating or cast film extrusion applications, include US 4863983 and US 5219600.

US 4863983 generally relates to the extrusion of LLDPE materials and aims to improve melt fracture rather than the balance of adhesion and off-taste. Fluorocarbon polymers are an essential ingredient as are organophosphites or organophosphates or blends thereof. Hindered phenols are not essential nor should they be absent but (column 2, line 34) anti-oxidants may be added optionally. In the Examples, anti-oxidants are added in an amount of 300 ppm (column 6, line 16) . The hydrocarbon polymers are defined broadly and low density polyethylene is disclosed as a blend component (column 3, line 40) . However, US 4863983 does not teach specific anti-oxidant packages in combination with specific polyethylene type materials for the purpose of aiding

adhesion without unduly worsening off-taste under severe extrusion process conditions. It does not teach the use of a phosphorus containing compound in an amount of at least 25 ppm where phenolic anti-oxidants are used in an amount of from 0 to 150 ppm.

US 5219600 discloses a moulding composition. LDPE

(column 2, line 8) is one of a long list of polyolefin options. A hindered amine light stabilizer (HALS) is an essential ingredient. Substantially, no primary, phenol type AO should be used. From 0.01 to 0.5 parts of an aromatic phosphite or phosphonite AO additive should be used. The aim of the invention is to reduce discoloration. No mention is made of extrusion processes and adhesion and off-taste effects.

US 5026 592 in column 2 line 18 discusses a multilayer structure incorporating a polymer derived from ethylene. Column 3 line 17 discusses the addition of 0.2 to 0.8 wt % of a phosphite stabiliser ( from 2000 to 8000 ppm) . That specification does not disclose the use of less than 1500 of a phosphorus containing anti-oxidant. The polymer contains less than 50 wt % ethylene derived units. The layer with anti-oxidant or stabiliser contains more than 5 wt% of a hydrocarbon resin tackifier; while the invention essentially concerns less than 4 wt % of tackifier or a composition substantially free of tackifier. The US specification concerns a film which is biaxially oriented after extrusion and contains an opacifying agent when the invention is in the field of non-biaxially oriented coextrusions onto substrates which are essentally non-elastic or stretchable ( the elasticity is below 10 percent ) . The anti-oxidant poor layers extruded in the invention are preferably either the surface layer or at least sufficiently proximate to the surface to be a major determinant of adhesion

properties and organoleptic properties.

It has been found that the adhesion/off-tate balance can be improved by the selective use of AO in polyethylene based on materials for use in extrusion coating type processes .

It is further possible with the invention to achieve higher processing speeds ( because of the improved adhesion) without resorting to costly adhesion improving blend components such as ethylene-acryic acid copolymers . Preferably therefore the later discussed composition of the invention are substantially devoid of polymers derived from monomers having acid or ester groups to enhance adhesion and are comprised essentially of the copolymers derieved of ethylene and non-polar group containing comonomers .

It has been found that the adhesion/off -taste balance can be improved by the selective use of AO in polyethylene based materials for use in extrusion/coating type processes .

Summary of the invention

Most generally the invention provides a process for extruding an ethylene based polymer into a layer which comprises (1) extruding an ethylene derived polymer having a density of less than 0.94 and containing (A) at least 25, preferably less than 5000 ppm of a phosphorus containing anti-oxidant and (B) from 0 to 150 ppm of a phosphorus- free, phenolic anti-oxidant; and (2) applying and adhering the layer onto a substrate .

As a general principle, additives other than (A) and the optional component (B) can be added but only if no disturbing effect is encountered on adhesion or the off- taste. Preferably, the polymer contains only the anti-

oxidant (A) . At below 25 ppm, the AO becomes difficult to distribute evenly; at above 5000 ppm additional effects are hard to detect.

The invention differs from US 4863983 because the film or layer is extruded onto a substrate and adhered thereto. An additional layer may be used between the substrate and the film or layer to improve or optimise adhesion such as ethylene acrylic acid. In US 4863983 the film is extruded and is not adhered to a substrate following extrusion.

Ppm (parts per million) in this specification are parts per million of the total composition weight.

The layer in an extrusicr. coating process is applied to a substrate. In certain processes , the layer forms the exterior surface of the coated product; however, the extruded layer may be incorporated between another layer; .for forming the exterior surface and the substrate, referred to generally as extrusion lamination which is special form cf extrusion coating. In other processesses more than one layer may be simultaneously extrusion coated onto a substrate.

The substrate is preferably a non-thermoplastic surface, such as cellulose based paper or card or board or a metallic surface such as aluminum foil. However the invention is also applicable to substrates of thermoplastic materials such as polyester, polypropylene and polyamice.

The ethylene derived polymer may be a single polymer component or a blend. Overall preferably it contains at least 50 wt % of ethylene derived units. It has a

SUBSTTTUTE SHEET (RULE 26)

density of less than 0.94. Where melt strength is required (e.g. for a self-supporting film) preferably, the polymer has a molecular weight sufficient for that purpose.The polymer may have a density of at least 0.88, especially 0.89 or 0.90.

The comonomer, if used, may be a C3to Cι_2 non-polar monomer especially mono-olefin such as propylene; 1- butene; 1-pentene; 1-hexene; 1-heptene or 1-octene or a monomer, preferably having from 4 to 12 carbon atoms, which has a polar group such as an ethylenically unsaturated ester such as vinyl-acetate, methyl acrylate; ethylacrylate; propylacrylate equivalents or an ethylenically unsaturated carboxylic acid or anhydride such as acrylic acid or ethacryclic acid.

The polymer(s) may be mace by a variety of polymerization process e.g. gas phase or solution but are preferably- made using free radical initiators at elevated pressure to give a highly branched, broad molecular weight distribution material .

Overall the ethylene derived polymer may have a density preferably of from 0.900 to 0.940, and preferably a melt index of 1 to 100, especially 2 to 20.

If the ethylene based polymer is formed by a blend, LDPE is preferably present in amount of at least 10 wt %, preferably 20 wt % and especially at least 50 wt % and preferably such LDPE may be used in conjunction with more linear non-branched polymers such as LLDPE.

For the composition overall i.e. the combination of the ethylene based polymer and any accompanying polymeric component, the M /Mn is suitably at least 5, especially 6

or above .

The phosphorus containing anti-oxidant may have the formula:

R2

where a is 0 or 1, b is an integer of 1 to 4 and equal to the valence of R ¹ . R^-is a onovalent or polyvalent (e.g. 2 to 4) organic radical preferably derived from a phenol, alcohol, diphenol, diol, polyol (e.g. glycol), 2,4, -di- tert-butylphenol, pentaerythritol, 4-nonylphenol, benzylalcohol, 4 chlorophenol;

1, 1, 1 tri ethylolpropar.e; the R ² groups which can be the same or different are monovalent radicals having from 1 to 30 carbon atoms and can be selected from substituted or unsubstituted aryl , alkyl or combinations thereof such as aralkyl, and cycloalkyl groups. R ¹ and R ² can contain hetero-ato s such as O and N and can be substituted with non-interfering substituents such as chlorine, fluorine, cyano, alkyl (branched or straight chain) ; alkoxy, acyl and amidocarbonyl .

Many of the organophoshites and organophosphites useful in this invention are known compounds and are, respectively, esters of phoεhorous and phoshoric acids. Synthesis can be carried out by reaction of the desired organic hydroxy compound with phosphorus trichloride (for phosphite esters) , or with phosphorus oxychloride (for phosphate esters) . Many examples of both organophoshites and organophosphates are available commercially, and blends of such compounds can also be used.

Representative organophosphites and organophosphates include: tris(2, 4-di-tert, butylphenyl)phosphite, bis (2-, 4-di-tert,butylphenyl)pentaerythritol diphosphite, tris ( -nonylphenyl)phosphite, tris [4- (1-phenylethyl)phenyl]phosphite tetrakis (2, 4-di-tert-butylphenyl) -4,4' -bisphenylene diphoshite, tris (4-methylphenyl)phosphite, tris (4-chlophenyl)phosphite, decyl diphenyl phosphite, tris (2, -4-di-tert, -butylphenyl)phosphate, tris (4-methylphenyl)phosphate, tris (4-nonylphenyl)phosphate,

2-ethylhexyl diphenyl phosphate, and blends thereof.

Triarylphosphites of the general formula:

wherein R _j _, represents tert, -butyl, 1, 1-dimethylpropyl, cyclohexyl or phenyl, and one of R2 and R3 is hydrogen and the other is hydrogen, methyl, tert, -butyl, 1, 1- dimethyl, propyl, cyclohexyl or phenyl may be used.

Suitable compounds are ccmmercially available.

The term "anti-oxidant" is used to describe the principal conventional effect of the phosphorus containing compound. However this does not preclude the effect of the compound on other aspects of performance in

processing or in the end-use. It is surmised that the anti-oxidant (A) is principally effective in removing hydroperoxide functionalities.

Other components may be present as additives but in amounts so as to not interfere with the off-taste

(or/also known as a degree of organoleptic behaviour) and adhesion performance. In the case of food packaging, the preferred composition contains minimal amounts of such other additives.

The ethylene-derived polymer and the component (A) are preferably combined in an extruder downstream of the reactor in which the monomer is polymerised. This helps to minimise any negative impact on adhesion and off-taste and ensure that anti-cxidant (A) is present in the polymer and active to prevent thermal decomposition etc. as much as possible.

With reference now to components, which may be present optionally but are preferably not present the HALS is preferably present in an amount less than that used in US 5219600 e.g. less than 0.01 pph. Fluoroelastomer is preferably present in an amount less than that disclosed in US 4863S83 so as to produce a ratio of phosphorus containing anti-oxidant to fluoroelastomer of more than 5. Alternatively less than 100 ppm of the phosphorus containing compound may be present . The HALS and fluoroelastomer may in higher amounts have a negative impact on adhesion and/cr off-taste.

Preferably, no primary anti-oxidant is used such as a hindered phenol compound. Hindered phenols are characterised by the presence of ortho substituted phenols. Phenolic compounds, which can be used if

necessary in minor amounts include:

1. Single 2, 6-dialkylphenols, such as 2,6-di-tert, -butyl-4-methylphenyl, 2, 6-di- tert, -butyl-4-methoxymethylphenol or 2,6-di- ter , -butyl-4-methoxyphenyl .

2. Bisphenols, such as

2, 2' -methylene-bis- (6-tert-butyl-4-methylphenol) , 2,2' -methylene-bis- (6-tert-butyl-4-ethylphenol) , 2,2' -methylene-bis- [4-methyl-6- (α-methylcyclohexyl) phenol], 1, 1-bis- (5-tert-butyl-4-hydroxy-2- methylphenyl) -butane, 2, 2-bis-(3, 5-di-tert-butyl- 4-hydroxyphenyl) -propane, 1, 1, 3-tris- (5-tert- butyl-4-hydroxy-2-methylphenyl) -butane, 2, 2-bis-(5- tert-butyl-4-hydroxy-2-methylphenyl) -4-n- dodecylmercapto-butane, 1, 1, 5, 5-tetra- (5-tert- butyl-4-hydroxy-2-methylphenyl) -pentane, ethylene glycol-bis [3, 3-bis- (3 ' -tert-butyl-4 ' - hydroxyphenyl) -butyrate] , 1, l-bis-(3, 5-dimethyl-2- hydroxyphenyl) -3- (n-dodecylthio) -butane, or 4,4'- thio-bis- (6-tert-butyl-3-methylphenol) .

3. Hydroxybenzyl compounds, such as

1, 3, 5-tri- (3, 5-di-tert-butyl-4-hydroxybenzyl) -2 , 4, 6-trimethylbenzene, 2, 2-bis- (3, 5-di-tert-butyl-4- hydroxybenzyl) -malcnic acid-diocta-decyl ester, 1, 3, 5-tris- (3, 5-di-tert-butyl-4-hydroxybenzyl) -iso- cyanurate, or 3 , 5-di-tert-butyl-4-hydroxybenzyl- phosphonic acid-diethyl .

4. Amides of β- (3 , 5-di-tert-butyl-4-hydroxyphenyl) - propionic acid, such as 1, 3, 5-tris- (3, 5-di-tert- butyl-4-hydroxyphenyl-propionyl) -hexamethylenedine.

5. Esters of β- (3 , 5-di-tert butyl-4-hydroxyphenyl) -

propionic acid with mono- or polyvalent alcohols, such as with methanol octadecanol, 1, 6-hexanediol, ethylene glycol, thiodiethylene glyxol, neoperityl glycol, pentaerythritol, tris-hydroxyethyl- isocyanurate.

6. Spiro compounds, such as diphenolic spiro-diacetals or spiro-diketals, such as 2, 4, 8, 10-tetraoxaspiro- [5, 5] -undecane substituted in the 3- and 9-position with phenolic radicals, such as 3, 9-bis- (3 , 5-di-tert-butyl-4hydroxyphenyl) - 2,4,8, 10-tetraoxaspiro- [5,5] -undecane, 3, 9-bis- [1,1- dimethyl-2- (3, 5-ditert-butyl-4-hydroxyphenyl) - ethyl] -2,4,8, 10-tetroxaspiro- [5,5] -undecane.

In a preferred embodiment from 0 to 100 ppm especially less than 50 ppm of the phenol type stabiliser is used. It also preferred to use lower level of the phosphorus containing compound; suitably from 50 to 1000 ppm, preferably from 60 to 500 and especially from 75 to 200 ppm. Surpringly, lower amounts provide better adhesion.

The extrusion process is suitably performed under conditions similar to those conventionally practised for extrusion coating of a given polymer. For non-polar polymers higher temperatures are recommended to promote adhesion, e.g. at 295 to 330 °C and at a line speed of from 10 to 600; preferably from 300 to 550 m/min. For polar group containing polymers lower temperatures can be recommended e.g. 265 to 300°C.

The extruder layer passes unsupported through a gap during which period surface oxidation may take place and then passes between the substrate and a chill roll for adhesion and cooling.

The invention also provides a use of a ^p hosphorus containing anti-oxidant in an amount of 25 ppm with from 0 to 150 ppm hindered phenol type anti-oxidant in the process of extrusion coating of an ethylene based polymer for adhesion onto a substrate so as to provide high adhesion with low off-taste. The use may lead to or involve the same features as are indicated above in the process .

The invention furthermore provides a composition comprising:

(A) an ethylene-derived polymer having a density of less than 0.95 and containing at least 25 and preferably less than 5000 ppm of a phosphorus containing anti-oxidant and from 0 to 150 ppm of

(B) a phosphorus-free phenolic anti-oxidant, preferably with less than 0.01 pph of a hindered amine type light stabiliser and having a ratio of a phosphorus containing compound to a fluoroelastomer processing aid of above 5.

US 4863983 requires an amount of fluoroelastomer in excess to that given above. US 5219600 requires an amount of HALS in excess.

The invention also provides a composition comprising:

(A) at least 50 wt % of a LDPE having a density of less than 0.95 containing from 25 and preferably less than 5000 ppm of a phosphorus containing compound and from 0 to 150 ppm of

(B) a phosphorus-free phenolic anti-oxidant, said composition containing less than 0.01 pph of a hindered amine type stabiliser. US 4865983 does not teach a combination of LDPE with that specific additive package content. US 521S600 requires an amount of HALS in excess

of that stated.

Drawings

Figure 1 is a graph interrelating adhesion and antioxidant levels, referred to in the Examples;

Figure 2 is another graph interrelating adhesion and antioxidant levels, referred to in the Examples; Figure 3 is a graph indicating the influence on adhesion of light stabilisers or fluoroelastomer processing aids, referred to in the Examples; and

Figure 4 is a schematic drawing of a cast extrusion apparatus used in the Examples .

Examples

Blends were made and adhesion and off-taste tested in the examples .

Density is determined according to ASTM -D1505 and D 2839. Melt index is determined in accordance with ASTM-

D-1238 Condition E; 2.16 kg at 1S0°C-

Melting point is measured by Differential Scanning

Calorimetry.

Adhesion in N/15 mm is tested in a T-peel configuration. It is the force required to produce separation on a strip of 15 mm wide.

Off-taste is tested by a human panel which aims to rank off-taste relative to a standard. The positive values indicate an off-taste worse than the standard; a negative value would indicate an off-taste better than a standard.

Example 1

A polymer was made in a high pressure autoclave ^' using peroxide initiator. The material is available commercially for Exxon Chemical as an Escorene grade, having the following characteristics:

Table 1

Density 0.9185 Melt Index 7.9 Mw/Mn 6 Melting Point 106°C

Ccmonomer Type none

Additives none

Anti-oxidants were mixed into masterbatches using a powdered polyethylene available from Exxon Chemical as grade MP 652.35, having the follov.'ing characteristics.

Table 2

Density 0.923 Melt Index 6

Comonomer none

Additive none

Masterbatches were produced with the different additives set out in Table 3, containing an appropriate high level (e.g. 1 % of anti-oxidant)

Table 3

Masterbatch Anti-oxidant No

1 none comparative

2 Irganox 1010 comparative

3 Irgafos P-EPQ invention

Irganox and Irgafos are registered Trade Marks. The chemical composition follov; Table 6 hereafter. These masterbatches were added to the above mentioned Escorene grade (Table 1) to give

SUBSTTTUTE SHEET (RULE 26)

Table 4

Sample No Masterbatch No AO ppm

1 1 o (comparative)

2 2 and 3 500 Irganox 1010

1000 Irgafos P-EPQ

(comparative)

3 2 500 Irganox 1010 (comparative)

4 3 1000 Irgafos P-EPQ (invention)

The samples were extrusion coated on apparatus (see Figure 4) at 295°C at the die outlet 4 onto an aluminium foil 6 acting as the substrate which was corona treated for improved adhesion using ambient air in the airgap 8. The extruded polymer web is oriented and drawn towards the nip 10 between a pressure roll 12 and a chill roll 14.

The coated materials were evaluated

Table 5

Sample No Adhesion Sensory (off-taste) N/15 mm evaluation by human panel

1 1.23 strong off-taste (3.2)

2 0.04 (low) very low off-taste (not measurable)

3 0.04 (low) low off-taste (1.3)

₄ 1.53 low off-taste (1.1)

Using the invention ccoα adhesion can be obtained simultaneously with good organolεptic behaviour. Only where Irganox 1010 was absent, was good adhesion obtained. 1000 ppm of Irganofos P-EPQ improved off-taste without reducing, and in fact increasing, adhesion.

Example 2

In a similar manner further blends were prepared to shov/ the relative effects for lower levels of anti-oxidants added and the effect cf minor amounts of HALS and fluoroelastomer.

Table 6

Run No Irganox PEPQ Tinuvin B900 Fluoro¬ 662 elastomer

1010 (2) (3) (4) (5) (1) ppm ppm ppm ppm

1 with no 0 0 0 0 0 masterbatch

2 with 0 0 0 0 0 masterbatch 1

3 100 0 0 0 0

4 200 0 0 0 0

5 100 200 0 0 0

6 200 200 0 0 0

7 0 200 0 0 0

8 100 200 0 0 0

9 200 400 0 0 0

10 0 400 0 0 0

11 100 400 0 0 0

12 100 200 0 0 0

13 0 400 200 0 0

14 0 400 500 0 0

15 0 0 0 1000 0

16 0 400 0 0 200

17 0 400 0 0 500

(1) Registered Trade Mark; principal component

Benzenepropanoic acid, 3 , 5-bis (1, l-dimethylethyl) -4- hydroxy-,2,2-bis [ [3- [3, 5-bis (1, l-dimethylethyl ^' ) -4- hydroxyphenyl] -1-oxopropoxy] methyl] -1,3- propanediylester (Formula I)

(2) Irgafos P-EPQ, Registered Trade Mark; principal component phosphonous acid, [1, 1 ' -biphenyl] -4, 4 diylbis-,tetrakis- [2,4-bis (1,1- dimethylethyl)phenyl] ester (Formula II)

Registered Trade Mark

Butanedioic acid, polymer with 4-hydroxy-2, 2, 6, 6- tetramethyl-l-piperidine ethanol (Formula III)

- 21

(4) 20 % Irganox 1076 + 80 % Irgafos 168

Irganox 1076; Benzenepropanoic acid, 3,5-bis(1,1- dimethylethyl) -4-hydroxy-,octadecyl ester (Formula IV)

HO (Q) CH ₂ CH ₂ sCOC ₁₈ H ₃₇

Irgafos 168: Phenol 2,4-bis (1,Idimethylethyl) - phosphite (3:1) (Formula V)

(5) Polymer processing aid: fluorelastomer obtainable from DuPont or 3M or as masterbatch AMF 702 from Schulman (this was used here) .

The results are set out in Table 7

Table 7

Run No. Adhesion Off-taste Off-taste

N/15 mm (relative (relative versus versus control) run 10)

1 0.92 0

2 0.85 0.9

3 0.71 -2.6

4 0.12

5 0.88

6 0.18

7 1.63 -1.3 and -1.2

8 1.14 -1.6

9 0.23

10 1.43 -1.6 0

11 0.82

12 0.89

13 0.98

14 0.91 0.6

15 0.85 -1.9

16 1.09

17 0.96 -0.3

Some of the results are shown in graphs Figure 1 - 3.

HALS and fluoroelasto ers negate the positive effect on adhesion of the phosphorus containing compound on adhesion and should not be used or only to such extent as is unavoidably necessitated (Figure 3) . Only when the amount of fluoroelastomer is less than 80 ppm (l/5th of the amount (400 ppm) of the phosphorus containing compound) are good adhesion strenghts obtained. HALS caused marginal worsening of off-taste.

Over 150 ppm of the hindered phenol AO, the influence of the phosphorus containing compound on adhesion is difficult to detect. Below 150 ppm especially below 10 ppm (see Figure 1) the presence of low amounts of the phosphorus containing compounds improves adhesion significally, with the greatest improvement apparent at amounts of the phosphorus containing compound of less than 400 ppm especially 200 ppm.

The same effect is visible in Figure 2.

Blends of a phenol anti-oxidant (Irganox 1076) and a phosphorus containing compound (Irgafos 168) gave rise to high levels of the phenol anti-oxidant and relatively low adhesion.

It has been found that drawdown can be improved by the use of the anti-oxidant packages of the invention.

The coated materials may be used to package foods and solids or liquids and drinks. The invention hence also relates to packages made using the coated materials obtained by the process of the invention.

Using the invention both off-taste and adhesion can be improved compared to convential LDPE not containing any anti-oxidants by the selective use of a phosphorus containing anti-oxidant with no, or small amounts of other additives.

For purposes of U.S. Law, all documents, including all test methods, and priority documents, are incorporated by reference herein.

SUBSTTTUTE SHEET (RULE 26)