The invention is in the field of the packaging industry and relates to a film material according to the generic part of the independent claim, which packaging material is applicable in particular for making pouches for flowable or pumpable, liquid, pasty or solid, light sensitive goods such as e.g. milk. The invention also relates to pouches made from such film material.

For packing the above named goods into pouches, usually so called vertical form and fill machines are used. In such machines the pouches are formed from quasi endless film material and filled immediately. For this purpose flat film material is made into a tube by joining its longitudinal edges preferably by heat sealing or seamless tubular film material is manufactured to start with. The tubular film material with or without longitudinal seam or seams is processed into filled pouches by transverse heat sealing (top seam of previous pouch and bottom seam of next pouch as two parallel seams or as one single seam), transverse cutting (between the two transverse seams or through the single seam), filling-in of a predetermined portion of the goods to be packed and advancing the filled-in portion together with the tube of film material downward by a predetermined distance. These four steps (sealing - cutting - filling - advancing) are repeated for each pouch to be formed and filled.

The transverse seams of the pouches are fin seams, the longitudinal seams, if any, are either lap seams or fin seams according to the film material used and according to the machine used. If both surfaces of the material are heat sealable, lap or fin seams are possible, if the material is heat sealable only on its inside surface, only fin seams are possible.

In addition to the required sealability, the film material has to have a sufficient mechanical strength, determined by the application (size of pouch, characteristics of goods to be filled in) and a satisfactory compatibility with the goods to be packed (at least the inside surface of the pouch). Furthermore according to the application it may have to be able to keep air or other gases in or out (gas barrier), it may have to preserve aroma components of the goods to be packed (aroma barrier) or it may have to preserve light sensitive goods to be packed from being impaired by light (light barrier). Last but not least, the film material or at least its outside surface should look nice and/or should be able to be further decorated e.g. by printing.

For making film materials with light barrier properties usually pigments or other optically active particles are added to originally transparent materials rendering them opaque. Pigments may be added also for giving a specific colour to the film material.

Film materials used for producing pouches with a content between ca. 0.25 to 2 liters are usually about 80μm thick and consist of one or several layers of thermoplastic polymers, e.g polyethylene, ethylene-copolymers or blends thereof. Film materials for pouches with a higher content of e.g. four liters are thicker. These larger, so called stand-up pouches are fabricated in the same

manner but through different design of the transversal seams they can have a handle on the top and a flat bottom on which they are able to stand.

The multilayer films are fabricated e.g. by coextrusion, lamination and/or coating.

According to the state of the art, pouches for milk are e.g. made from a two- layer film with an inside layer (light barrier) containing a black pigment and an outside layer (outside esthetic masking or colouring layer) containing e.g. a white pigment. Such materials may also have a third layer covering the inside surface of the black layer and serving as an inside esthetic masking or colouring layer.

It is the aim of further development of materials for pouch fabrication to decrease the necessary amount of material by decreasing the thickness of the film and to decrease the price of the film material and at the same time to maintain or even improve the quality of the pouch and its compatibility with the goods to be packed in the pouches. Furthermore, development is aimed at improving the material regarding its processability such that the form and fill process can be facilitated and in particular can be sped up.

Experience shows that one problem area of the pouch fabrication is the sealing, in particular the transverse sealing steps of the form and fill process. As the film material is very thin and in most cases highly heat sensitive, a very accurate heat control is necessary for these sealing steps in order to keep the ratio of pouches with faulty seams or with pin holes in the vicinity of the seams acceptably low. However, very precise heat control of such sealing steps

is difficult, in particular because not only the film material and parts of the sealing apparatus but also the goods which are filled into each pouch immediately after sealing the bottom seam, have to be taken into consideration as better or worse cooling medium. In order to achieve satisfactory seam qualities at high production rates and still with reasonable means for heat control, a lot of effort has been put into developing materials for sealing layers, which materials are to facilitate sealing.

In the publication CA- 1205052 a polymer blend applicable for film material for pouches or for sealing layers of such film materials is described. The polymer blend consists of a linear copolymer of ethylene and a C ₆ - C ₁₀ α- olefin to which is added a linear copolymer of ethylene and a C ₄ - C ₁₀ α- olefine and/or a high pressure polyethylene. If film materials with sealing layers made from this blend are to be used for fabricating non-transparent milk pouches as mentioned above, the sealing layer contains a white pigment (e.g. titanium dioxide) if inside masking of the black (barrier layer) is wished for.

The above mentioned publication (CA- 1205052) names as a special advantage of a sealing layer made of the named polymer blend, that very good seam qualities can be achieved regardless whether the sealing layer contains a pigment or not (mentioned pigment concentrations 4, 8 and up to 15 parts by weight of titanium dioxide) whereas with a sealing layer made from a polymer blend of an ethylene/butene copolymer and a high pressure polyethylene seam qualities decrease considerably with pigment concentration (same range and same pigment).

In the publication WO93/02859 a further polymer blend for the sealing layer of a film material to be made into pouches is described. This material is basically a linear ultralow density polyethylene which is described as having a temperature range for sealing from 70 to 140°C and sealing characteristics independent from pigment concentration.

The publication US-5360648 describes sealing layers made from a homogeneously branched, substantially linear ethylene/α-olefin interpolymer which seems to have similar characteristics.

The object of the invention is to create a multilayer film material applicable for pouch fabrication which film material is to contain one pigment or several different pigments and therefore possesses light barrier properties and/or is coloured. The film material is to show good sealability, the polymer materials used are to be easily available on the market. The film material is to be producible with a process well introduced in the industry.

The object is achieved by the inventive multilayer film material which shows a pigment concentration gradient near its at least one surface (sealing surface), i.e. it shows a pigment concentration which is lower in a surface layer than in a layer below this surface layer. For a film material with two sealing surfaces this applies to both surfaces. The inventive film material contains at least two layers wherein the first layer (pigment layer) is thicker and contains a pigment or a pigment mixture in a concentration high enough for its function in the pouch (light barrier, colouring, masking) and the second layer (sealing layer) is thinner, constitutes the inner surface in the finished pouch and contains no pigment at all or of the same pigment a considerably lower concentration than the pigment layer. It can be shown, that keeping the sealing layer substantially

free from pigment, excellent sealing qualities can be achieved with sealing layers of widely known polymers such as polyethylene (homopolymer or copolymers such as e.g. low density polyethylene (LDPE), linear low density polyethylene (LLDPE), high density polyethylene (HDPE) or blends thereof) or of polypropylene (homopolymer or copolymers) which sealing layers have a thickness of at least 6μm. In particular, according to the invention it is not necessary to make the sealing film from polymers well known as sealant materials such as e.g. very low density polyethylene (VLDPE), ultra low density polyethylene (ULDPE) or other copolymers of polyethylene with similar sealant characteristics nor is it necessary to add such materials to the sealing film material and still, the speed of sealing can be increased without loosing seal quality.

The inventive film material is preferably produced by coextrusion.

Two exemplified embodiments of the inventive film material are described in connection with the following Figures, wherein:

Figure 1 shows the cross section of a five-layer embodiment of the inventive film material which is applicable in particular for packing milk.

Figure 2 shows the cross section of a very simple two-layer embodiment of the inventive film material.

Figure 3 shows a pouch made from the inventive film material.

Figure 1 shows in cross section a five-layer film material as an exemplified embodiment of the inventive film material. This five-layer material is in particular applicable for packing milk.

As milk is a light sensitive product, the five layer film material contains a central light barrier layer 3 (inner pigment layer) containing preferably a black pigment, e.g. carbon black. As the black colour of the light barrier layer 3 is not estheticly favourable, it is masked on both sides with a masking layer 2 and 4 (outer pigment layers) containing a not black pigment, e.g. titanium dioxide with a concentration high enough to satisfactorily mask the blackness of the light barrier layer 3. The film surface facing to the inside of the pouch shows as the innermost layer a thin sealing layer 1 containing no pigment or the same pigment as the inner masking layer but in a substantially smaller concentration.

The outermost layer 5 may be a sealing layer also and therefore contain the same pigment as the outer masking layer in a substantially smaller concentration or no pigment at all. The advantage of such an outside sealing layer is not only that the variety of seams possible is increased, but also that there is no or at least less pigment deposition on the sealing jaws as there is when the masking layer 4 is the outermost layer. With less such deposition, sealing is easier controllable and the jaws need less maintenance.

If the outside of the pouch is to be decorated by printing, it is advantageous to cover it with an outermost layer 5 containing e.g. calcium carbonate or magnesia-calcium carbonate (dolomite) because such a layer is more favourable for printing than the masking layer 4, in particular if this one contains titanium oxide in a concentration higher than 10%.

Examples for the five layers of film materials as shown in Figure 1 are as follows:

Film material for pouches with 0.25 to 2 liters content has e.g. five layers all consisting of blends of LLDPE (linear low density ethylene/butene copolymer) and LDPE (low density homo-polyethylene) with the following ranges of thicknesses and polymer concentrations: sealing layer 1 : at least 6μm and 0 - 5% TiO,, masking layers 2 and 4 : 14 to 25μm and 10 to 20% Ti0 ₂ , light barrier layer 3: 10 to 20μm and 1 to 2,5% carbon black and outermost layer (printing layer) 5: at least 6μm and 0 - 11% Ti0 ₂ and/or 5 to 40% of CaC0 ₃ .

Two specific examples for such film materials are as follows:

layer thickness pigment μm type concentration %

1 10 TiO, 1.5

2 18 τio; 15

3 14 carbon black 1.5

4 18 Ti0 ₂ 15

5 10 CaCO, 25

layer thickness pigment μm type concentration %

1 10 no pigment 0

2 20 TiO, 12,6

3 20 carbon black 1.3

4 15 TiO, 14

5 15 TiO ^~ 10,5

. 0 .

Film material for stand-up pouches with e.g. four liters content, has e.g. five layers, the middle one consisting of polypropylene (PP, homo- or copolymer), the outer ones of polyethylene (PE, homo- or copolymer) and inbetween layers of polymers, copolymers or blends thereof known as being applicable for adhesive layers between PP and PE layers (e.g. blends of polyethylene and copolymers of polypropylene or ethylene-vinyl acetate copolymer), wherein the layers have the following ranges of thicknesses and pigment concentrations: sealing layer 1 : at least 6μm and 0 - 5% TiO,, - masking layers 2 and 4 : 40 to 60μm and 5 to 20% Ti0 ₂ , light barrier layer 3: 15 to 40μm and 1 to 2.5 carbon black and outermost layer (printing layer) 5: at least 6μm and 0 - 11% of Ti0 ₂ and/or 5 - 40% of CaCO ₃ .

A specific example of such a film material is as follows:

layer thickness polymer pigment μm type concentration

1 10 LDPE TiO, 1.5

2 50 adhesive TiOO 7

3 30 PP c.b. 1

4 50 adhesive TiO, 7

5 10 LDPE CaCO, 25

Further exemplified embodiments of the inventive film material still applicable for packing liquid food such as a.g. milk and showing good sealability, are deduced from the material according to Figure 1 by omitting layers 5, 4 and/or 2 and/or by introducing further layers such as e.g a thin aroma barrier layer of ethylene vinyl alcohol copolymer (EVOH).

Figure 2 shows in cross section the most simple embodiment of the inventive film material. It consists of a thin sealing layer 1 with a thickness of 6 to 20μm and of a thicker pigment layer 2' (thickness e.g 20 to 70 μm).

Figure 3 shows an example of a pouch 6 made from the inventive material with a longitudinal seam 7 and two transverse seams 8.1 and 8.2. The above description names pouch fabrication as application for the inventive material. This is not limitative. Obviously the inventive film material can be used for fabricating different packaging items by heat sealing.