WO2001096465A1

WO2001096465A1 - Biaxially oriented polypropylene tobacco film heat shrinkable

Info

Publication number: WO2001096465A1
Application number: PCT/SK2001/000017
Authority: WO
Inventors: Jan Harman; Eva SÁMELOVÁ
Original assignee: Chemosvit, A.S.
Priority date: 2000-06-14
Filing date: 2001-06-08
Publication date: 2001-12-20
Also published as: LT5038B; PL353883A1; LV12876B; CZ2002840A3; SK9122000A3; HRP20020224A2; BG106498A; LT2002025A; HUP0204411A2

Abstract

Biaxially oriented polypropylene tabacco film heat shrinkable consists of three layers featuring isotactic and syndiotactic metallocene polypropylene mixture and antistatic masterbatch in the core layer and terpolymer and sliding masterbatch in the two outer heat sealable layers. The way of production of the biaxially oriented polypropylene heat shrinkable tobacco film features higher orientation ratios in the machine orientation, or transversal orientation and reduced temperatures in stabilising zones in the width orientation.

Description

Biaxially oriented polypropylene tobacco film heat shrinkable

Technical field

The invention relates to biaxially oriented polypropylene tobacco film heat shrinkable, intended for cigarette boxes and cigarette cartons wrapping. It falls within the packaging film productions.

Technical background

Shrink films feature good ability to shrink under certain temperature which is used at wrapping of various types of goods. Packaging appliances are equipped by heating segments enabling shrinking of film in which the product is put into. The final packaging is fully adapted to the shape of a product which results in its good aesthetic appearance.

Out of many mono or multilayer shrink films of different chemical composition used mostly for packaging applications, the polyolefm films which are well patent protected represent a rather big part. Among them there are for example EP 885121 and WO 9825765 protected two-layer polyolefm film heat shrinkable, compounded of low density polyethylene A layer and B mixture layer consisting of at least 73 up to 95 % ethylene copolymer weight with at least alfa-olefm CH₂ = CHR, with R alkyl radical having 1 - 10 carbon atoms and 60 - 98 % propylene weight. The copolymer is characterized by insoluble xylene fraction higher than 70 % weight. Multilayer polyethylene film is protected by EP 72983 and WO 729831. Interlayer consists of a mixture of specific linear low density polyethylene and internal and external layers are compounded mainly of specified high pressure polyethylene, alfa-olefm ethylene copolymer and linear low density polyethylene. A mixture of surface-active agent can be added into at least two layers which results in an excellent anti-fog effect. The multilayer film is also protected by EP 681914 which is an improved biaxially oriented heat shrinkable film suitable for vacuum packaging of foods. The improved shrink films according to EP 662989 are intended for alloys or compositions containing exact combinations of polyethylene "with narrow, unequivocal" melting point and polyethylene with higher melting point (at least by 10°). Similarly, WO 9512490 protects laminated polyethylene film heat shrinkable and EP 562496 biaxially oriented multilayer film suitable for poultry wrapping. Another one of single or multilayer films on ethylene basis has a very good combination of physical properties and machineability and features higher shrinkage and puncture resistance (EP 374783). The targeted property, shrinkage, can be reached by numerous production methods the selection of which is subject to application properties of the films developed. The most important of them is temperature at which the film shrinking occurs. Wrapping of cigarette boxes and cartons requires application of such film grades where shrinkage occurs at relatively low temperatures.

This low temperature shrinkage occurs at films containing certain additives supporting this shrinkage and/or at films oriented in conditions enabling occurring of shrinkage at low temperatures. The additives act as modifiers treating crystallinity of polypropylene core, e.g. the core layer crystallisation process and thus influence final properties of the ready-made film. The additives suitable can be hydrogen hydrocarbon resins, the disadvantage of which is migration in time of final application, nucleonic agents applied in order to produce a beta-type polypropylene, atactic polypropylene, ethylene propylene copolymer and others. As far as orientation at lower temperatures is concerned, this causes problems at the film production because of stronger efforts necessary to reach the orientation. The shrinkage values reached need not to be sufficient.

This shortcoming is removed based on EP 865913 solution, according to which the biaxially oriented heat shrinkable polyolefm film consists of polypropylene based resin with microscopic cavities originated while orienting the film produced by melt extrusion through a nozzle and following quenching while production of non-oriented film consisting of beta- type polypropylene. The film shrinkage is 10 % in at least one direction (at temperature 130°C. 10 min.). According to the invention cited, the film may consist of one polypropylene based resin with micro cavities, it may, however, often comprise one or more other layers providing them with a certain characteristic feature, e.g. heat sealability, gloss, etc. These layers are mostly made of polyolefins. They are produced by extrusion or co-extrusion of respective polymers melt through the nozzle orifice to a required layer (or layers), which is chilled and then gradually biaxially oriented, first in length, in a machine direction, at temperature from 70 to 110 °C, the best from 80 to 95°C, with orientation ratio ranging from at least 3:1 - 3,5:1 up to 8 : 1 and then in width, but at temperatures lower than usually applied for transversal orientation. The temperatures required are below 160°C to 155°C, the most suitable between 140 - 152°C. Orientation ratio is from 3J to 10:1.

In the last time, metallocene isotactic and syndiotactic polypropylenes can be produced by using new metallocene catalysts. Owing to their specific properties, these new metallocene polymers have different application range in packaging industry and in packaging films and new utility properties. Currently applied biaxially oriented polypropylene tobacco films produced by standard methods (for example low orientation degree at the beginning and high orientation degree in the end, e.g. 1,05 to 5,3), have shrinkage from 3,0 to 5,0 % (at 135°C and 7 min. drying time at least). Parameter of shrinkage depends on polypropylene used (mainly its atactic share value), as well as on technological conditions of production. Shrinkage of tobacco film directly influences quality of final cigarette box wrapping, mainly quality requirements on good visual appearance of cigarette box wrapped. The requirement is that the film was sufficiently tight all around the box and that no undesirable ripples were formed. Application of heat shrinkable tobacco film covered by this invention, eliminates these shortages and thus improves cigarette boxes wrapping.

Quality of cigarette box wrapping, mainly quality requirements for good visual appearance of a box wrapped can be reached by suitable dimension of the film fitted to cigarette box, suitable mechanical properties and material stiffness. A very good assessment parameter (used by tobacco film converters) is measurement of tightness at multilayer biaxially oriented polypropylene films applied for cigarette boxes wrapping.

Disclosure of Invention

Dissclosure of invention is biaxially oriented polypropylene tobacco film heat shrinkable consisting of three layers, with the core layer compounded of isotactic and syndiotactic metallocene polypropylene and antistatic masterbatch and of two outer heat sealable layers containing terpolymer, sliding and antistatic masterbatch. The content of syndiotactici metallocene polypropylene is within 1,0 to 5,0 % weight. Both outer heat sealable layers are either of the same composition, A-B-A, three layer type without corona treatment, or different composition, A-B-C, three layer type with one side C corona treatment. In this type of film the effective sliding additive on an outer A side is silicone oil and on an outer C side arucamide. The biaxially oriented heat sealable polypropylene tobacco film reaches 6,0 up to 11,0 % shrinkage in machine and transversal direction, at 135°C. The way of production the biaxially oriented heat sealable polypropylene tobacco film according to these characteristics is carried out at higher orientation ratios in machine, or transversal orientations and the reduced temperature in stabilising zones in the width orientation. The length orientation is 6,0 to 8,0 times depending on final shrinkage requirement. In the width orientation the film is air pre-heated to 165 - 178°C and then gradually oriented 8,0 to 10,0 times in width at 160 — 165°C air temperature. Temperature in stabilising zones is cut down to 145°C and lower, depending on operational stability of production. The biaxially oriented heat sealable polypropylene tobacco film is according to this invention produced in such a way that the raw materials mixture for the core layer and two upper layers are plasticized by heating in the worm extruder to the melt temperature of ca 265°C. After the melt filtration from the main extruder and two additional co-extruders, the resulting co-extrudate is ejected through the flat nozzle orifice heated on 260°C. The melt from the nozzle is cast and chilled on the chill roll with temperature 32°C. From the other side the melt is chilled by water with temperature 22°C in the chill bath. These melt chilling conditions ensure requested structure of the thick film before its entrance in the machine direction orientation part (MDO). The thick film is heated on heating rolls with 125 - 135°C in the machine orientation part (so that the thick film didn't stick to the rolls surface which would cause terpolymer layer impairment). The heated thick film is oriented in the length on orientation rolls (different speed of rolls). The final shrinkage value depends on the orientation value reached. In order to reach the requested shrinkage of the ready-made film, min. 6,0 - 11,0 % (in the drier at 135°C and 7 min.), the most suitable is the two-step machine orientation of the thick film. The length orientation ratio setting is 6 x 1,1 to 6 x 1,3. The resulting value is 6,6 to 7,8 times in length orientation. Using of syndiotactic polypropylene in mixture is more suitable than using other modifiers, because electric drives efforts in MDO are lower. After leaving MDO, the film is drawn by chain in the width orientation (TDO). The film is heated on 172°C by hot air in the pre-heated TDO zones and following it is 8 - 10 times width oriented by gradual chain distance increase at temperature 165°C. In the stabilising zones of TDO it is necessary to cut temperature down to 145°C (or lower, if production reliability allows it) and to increase chain distance in its outlet from TDO as far as the rolls width behind the TDO outlet and in the winding part of the machine allow it.

The final film intended for one-side printing can be surface corona treated in the winding part of the machine. The films are produced in thickness from 14 to 40 μm (usually 16, 20, 21 μm). One of the targeted parameters is the film shrinkage, or dimensional stability. The film sample is measured by the Hirlϊnger ruler in the marked points (because of the measurement accuracy) before putting into the drier and after taking out. The change in dimensions is measured in longitudinal and cross directions. The drier's conditions are as follows: temperature 135°C, 7 min. time in the drier. The values of the tobacco film shrinkage produced according to this invention are ranging from 6,0 to 11,0 % depending on orientation ratio. (Tobacco films produced so far used to reach shrinkage from 3,0 to 5,0 %). Tobacco film with such shrinkage values can wrap cigarette box, or carton perfectly which improves its visual quality. Tobacco film produced by the mentioned technological method can be illustrated on the following examples in which temperatures in particular technological part of manufacturing line can range in plus/minus tolerances compared to temperatures specified in particular examples in dependence on manufacturing line temperature, output and main isotactic polypropylene used.

Examples

Example 1

For the film manufacture, a standard frame line is used. The raw materials mixture for the A-B-A film type production is as follows: the core B layer made of 98,6874 % isotactic polypropylene weight, 1,0 % syndiotactic metallocene polypropylene weight and 0,3126 % antistatic masterbatch weight, the composition of which is 0,0700 % glycerol monostearate, 0,2300 % alkyl weight (C₁₂ - C₁₈) bis (2-hydroxy-ethyl)amine, 0,0072 % bis-[3,3-bis-(4'- hydroxy-3tercbutyl-phenyl(butanic acid]-glycolester weight, 0,0027 % tris (2,4-di-terc-butyl- phenyl) phosphite weight and two identical surface heat sealable terpolymer layers made of 99,4115 % terpolymer weight (C₂ C₃ C₄), 0,5489 % silicone oil weight, 0,0275 % calcium stearate, 0,0088 % tris(2,4-di-terc-butyl-phenyl)phosphite weight and 0,033 % bis-[3,3-bis- (4'-hydroxy-3-tercbutyl-phenyl)butanic acid]-glycolester weight plastified by heating in the worm extruder up to the melt temperature of ca 265°C. After the melt filtration from the main extruder and from two additional co-extruders, the final coextrudate is extruded through the plain nozzle orifice heated up to 260°C. The melt from nozzle is cast and chilled on the chill roll with 32°C temperature. From the other side the melt is chilled by 22°C temperature water in the chill bath. On MDO heating rolls the thick film is heated to 125 - 135°C (so that the thick film couldn't stick to the rolls surface which could impair the terpolymer layer). The heated thick film is oriented in length on the orientation rolls (different rolls speed). The final shrinkage value depends on the orientation reached. In order to reach the requested shrinkage value, min. 6,0 to 11,0 % (in the drier at 135°C and 7 min.), a two-step length orientation of the thick film is the most suitable. The length orientation ratio setting is 6 x 1,1 to 6 x 1,3. The resulting value of the longitudinal MD orientation is 6,6 to 7,8 times. Using of syndiotactic polypropylene in mixture is especially favourable compared to other modifiers since a lower electric drives effort in MDO is required for longitudinal orientation increased in this way. After leaving MDO, the film is drawn by a chain into the width orientation (TDO). In pre-heated zones of TDO the film is air-heated to ca 172°C and following 8 - 10 times oriented in width by gradual chain distance increase at 165°C. In stabilising zones of TDO the temperature reduction to 145°C (or lower, if the production reliability allows it) is necessary similarly as the chains distance increase in the TDO output, if the rolls width behind TDO output and the winding part of the machine allow it.

The ready-made films are produced in thickness ranging from 14 - 40 μm (usually 16, 20 and 21 μm). Shrinkage of tobacco film produced according to this example is 6 % minimally.

Example 2

For plastification in the worm extruder on the A-B-A film type production, the raw materials mixture is as follows: the core B layer compounded of a different ratio of isotactic and syndiotactic polypropylene than in the example 1, i.e. from 97,6874 % isotactic polypropylene weight and 2,0 % syndiotactic metallocene polypropylene weight while keeping the antistatic masterbatch content and the way of production as in the example 1, similarly two identical, surface heat sealable terpolymer layers complying with the example 1. The shrinkage values are from 6,0 to 11,0 %, depending on actual orientation ratio.

Example 3

For plastification in the worm extruder on the A-B-A film type production, the raw materials mixture is as follows: the core B layer compounded of a different ratio of isotactic and syndiotactic polypropylene than in the examples 1 and 2, i.e. from 96,6874 % isotactic polypropylene and 3,0 % syndiotactic metallocene polypropylene weight, of 0,0700 % glycerol stereate weight, 0,2300 % alkyl weight (C12 - C₁₈) bis (2-hydroxy-ethyl)amine, 0,0072 % bis-[3,3-bis-(4'-hydroxy-3-tercbutyl-phenyl)butanic acidj-glycolester weight, 0,0027 % tris (2,4-di-terc-butyl-phenyl) phosphite weight and two identical surface heat sealable terpolymer layers identical with the example 1. The film production proceeding is similar to the example 1. On reaching the resulting orientation values of 6,6 - 7,8 times, the shrinkage values are 6,0 - 11,0 %, depending on actual orientation ratio.

Example 4

For plastification in the worm extruder on the A-B-A film type production, the raw materials mixture is as follows: the core B layer compounded of a different ratio of isotactic and syndiotactic polypropylene than in the examples 1, 2 and 3, i.e. from 95,6874 % isotactic polypropylene and 4,0 % syndiotactic metallocene polypropylene weight, of 0,0700 % glycerol stearate weight, 0,2300 % alkyl weight (C₁₂ - C₁₈) bis (2-hydroxy-ethyl)amine, 0,0072 % bis-[3,3-bis-(4'-hydroxy-3-tercbutyl-phenyl)butanic acid]-glycolester weight, 0,0027 % tris (2,4-di-terc-butyl-phenyl) phosphite weight, but the two identical surface heat sealable terpolymer layers comply with the example 1. The film production proceeding is similar to the example 1. On reaching the resulting orientation values of 6,6 - 7,8 times, the shrinkage values are 6,0 - 11,0 %, depending on actual orientation ratio.

Example 5

For plastification in the worm extruder on the A-B-A film type production, the raw materials mixture is as follows: the core B layer compounded of a different ratio of isotactic and syndiotactic polypropylene than in the examples 1 to 4, i.e. from 94,6874 % isotactic polypropylene and 5,0 % syndiotactic metallocene polypropylene weight, of 0,0700 % glycerol stearate weight, 0,2300 % alkyl weight (Cι₂ - C₁₈) bis (2-hydroxy-ethyl)amine, 0,0072 % bis-[3,3-bis-(4'-hydroxy-3-tercbutyl-phenyl)butanic acid]-glycolester weight, 0,0027 % tris (2,4-di-terc-butyl-phenyl) phosphite weight, but the two identical surface heat sealable terpolymer layers comply with the example 1. The film production proceeding is similar to the example 1. On reaching the resulting orientation values of 6,6 - 7,8 times, the shrinkage values are 6,0 - 11,0 %, depending on actual orientation ratio.

Example 6

For plastification in the worm extruder on the A-B-C film type production, the raw materials mixture is as follows: the core B layer and the surface A terpolymer layer compounded of materials specified in the example 1 of this invention. The second outer heat sealable tepolymer C layer consists of 99,4115 % terpolymer weight (C₂ C₃ C₄). 0,5489 % erucamide weight, 0,0275 % calcium stearate weight, 0,0088 % tris(2,4-dϊ-terc-butyl- phenyl)phosphite weight and 0,0033 % bis-[3,3-bis-(4'-hydroxy-3-tercbutyl-phenyl)butanic acid]-glycolester weight. This layer is corona treated for printing applications. The film production proceeding is similar to the example 1. The ready-made film is intended for one- side printing and is corona treated in the winding part. The shrinkage values range from 6,0 - 11,0 %, depending on actual orientation ratio.

Example 7 For plastification in the worm extruder on the A-B-C film type production, the raw materials mixture is as follows: the core B layer and the surface A terpolymer layer compounded of materials specified in the example 2 of this invention. The second outer heat sealable terpolymer C layer is compounded of materials specified in the example 6, the production proceeding including corona treatment is similar to that in the example 6. The shrinkage values range from 6,0 to 11,0 %, depending on actual orientation ratio.

Example 8

For plastification in the worm extruder on the A-B-C film type production, the raw materials mixture is as follows: the core B layer and the surface A terpolymer layer compounded of materials specified in the example 3 of this invention. The second outer heat sealable terpolymer C layer is compounded of materials specified in the example 6, the production proceeding including corona treatment is similar to that in the example 6. The shrinkage values range from 6,0 to 11,0 %, depending on actual orientation ratio.

Example 9

For plastification in the worm extruder on the A-B-C film type production, the raw materials mixture is as follows: the core B layer and the surface A terpolymer layer compounded of materials specified in the example 4 of this invention. The second outer heat sealable terpolymer C layer is compounded of materials specified in the example 6, the production proceeding including corona treatment is similar to that in the example 6. The shrinkage values range from 6,0 to 11,0 %, depending on actual orientation ratio.

Example 10

For plastification in the worm extruder on the A-B-C film type production, the raw materials mixture is as follows: the core B layer and the surface A terpolymer layer compounded of materials specified in the example 5 of this invention. The second outer heat sealable terpolymer C layer is compounded of materials specified in the example 6, the production proceeding including corona treatment is similar to that in the example 6. The shrinkage values range from 6,0 to 11,0 %, depending on actual orientation ratio. Industrial Applicability

This new tobacco film is sufficiently treated by antistatic and sliding additives, that's why it is suitable for using on high-speed packaging machines with wrapping speed of up to 600 boxes/min.

Claims

1. Biaxially oriented polypropylene tobacco film heat shrinkable consists of three layers characterized by isotactic and syndiotactic metallocene polypropylene mixture and antistatic masterbatch in the core layer and terpolymer and sliding masterbatch in the two outer heat sealable layers.

2. Biaxially oriented polypropylene tobacco film heat shrinkable features according to the claim 1 characterized by isotactic and syndiotactic metallocene polypropylene mixture in the core layer, with the syndiotactic metallocene polypropylene content in the core ranging from 1,0 to 5,0 % weight.

3. Biaxially oriented polypropylene tobacco film heat shrinkable features according to the claims 1, 2 characterized by the same composition of both of the two outer heat sealable layers, A-B-A three-layer film type, without the surface corona treatment.

4. Biaxially oriented polypropylene tobacco film heat shrinkable features according to the claims 1, 2 characterized by the different composition of two outer heat sealable layers, A-B- C three-layer film type, with one-side C surface corona treated

5. Biaxially oriented polypropylene tobacco film heat shrinkable features according to the claim 4 an effective sliding additive in the outer A layer, the silicone oil and an effective sliding additive in the outer C layer, the erucamide.

6. Biaxially oriented polypropylene heat shrinkable tobacco film features according to the claims 1 to 5 characterized by the film shrinkage of 6,0 to 11,0 % in longitudinal and transversal directions under the defined measurement conditions of 135°C and 7 min. time.

7. The way of production of the biaxially oriented polypropylene tobacco film heat shrinkable according to claims 1 - 6 characterized by features higher orientation ratios in the machine orientation, or transversal orientation and reduced temperatures in stabilising zones in the width orientation.

8. The way of production of the biaxially oriented polypropylene tobacco film heat shrinkable according to the claim 7 characterized by features 6 - 8 time longitudinal orientation depending on the shrinkage value required.

9. The way of production of the biaxially oriented polypropylene tobacco film heat shrinkable according to the claim 7 characterized .by features Jhe hot air pre-heated width orientation, having 165 - 178°C and subsequent 8 - 10 times width orientation at 160 -

165°C.

10. The way of production of the biaxially oriented polypropylene tobacco film heat shrinkable according to the claims 7 and 9 characterized by features the reduced temperature in the stabilising zones of 145° and lower, depending on operational stability of production.