SK9122000A3 - Heat-shrinkable biaxially oriented polypropylene film for use as tobacco pack overwrap - Google Patents

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

Technical field

The invention relates to a tobacco heat-shrinkable biaxially oriented polypropylene film for packaging cigarette boxes and cigarette cartons. It falls within the field of packaging film production.

BACKGROUND OF THE INVENTION

Shrink films have the ability to shrink under a certain temperature, which is used to wrap different kinds of goods. The packaging devices are equipped with heating segments which allow the foil to be shrinked into which the respective goods are inserted, resulting in an aesthetic package adapted to the shape of the product.

Polyolefin films, which are also patent protected, form a significant number of compositions, predominantly for packaging. These include eg. EP 885121a WO 9825765 protected heat-shrinkable bilayer polyolefin film, consisting mainly of a low-density polyethylene layer A and a layer B made of a mixture of at least 73 to 73

%, Wt. % of a copolymer of ethylene with at least an alpha-olefin CH2 = CHR, wherein R is an alkyl radical having 1 to 10 carbon atoms, and 60 to 98 wt. propylene. The copolymer is characterized by an insoluble fraction of xylene greater than 70% by weight. Both the multilayer polyethylene film is protected by both EP 72983 and WO 729831. The intermediate layer consists of a mixture of specific linear low density polyethylene and the inner and outer layers mainly consist of a specified high pressure polyethylene mixture. copolymer of ethylene alpha-olefin and linear low density polyethylene. A surfactant mixture can be added to at least two layers to provide an excellent anti-haze effect. The multilayer film is also protected by EP 681914, an improved biaxially oriented heat shrinkable film suitable for vacuum packaging food. The improved shrinkable films of EP 662989 are directed to alloys or combinations containing precise, narrow, unambiguous, melting point polyethylene combinations. polyethylene having a higher (at least 10 ° C) melting point. Similarly, WO 9512490 protects a heat-shrink laminated polyethylene film, EP 562496 a biaxially oriented multilayer film suitable for poultry packaging. Another of the ethylene-based monolayer or multilayer films has a very good combination of physical properties and processability, including higher shrinkage and puncture resistance (EP 374783).

The targeted shrinkage property can be achieved by a number of manufacturing processes, the selection of which is conditioned by the application properties of the prepared films. Of these, the most important is the temperature at which the film shrinks. Packaging of cigarette boxes and cigarette cartons requires the use of films that shrink at relatively low temperatures.

This low temperature shrinkage is achieved with films containing certain additives that assist in such shrinkage and / or films that have been oriented under conditions that allow shrinkage to occur at low temperatures. The additives act as modifiers regulating the crystallinity of the polypropylene core, thus the process of crystallization of the core layer, and thus affect the resulting properties of the finished film. Such an additive may be hydrogen hydrocarbon resins whose drawback is migration during final application, the nucleating agents used to form beta-type polypropylene, atactic polypropylene, ethylene-propylene copolymer and others. As far as orientation at low temperatures is concerned, this causes difficulties in the production of the films themselves due to the greater forces required to achieve orientation. The degree of shrinkage may not be sufficient.

This drawback is overcome by the solution according to EP 865913, according to which the biaxially oriented heat-shrinking polyolefin film consists of a polypropylene-based resin with microscopic cavities formed by film orientation obtained by extruding the melt through a slit and subsequently cooling to form a non-oriented film consisting of beta-type polypropylene. The film has a shrinkage of at least 10% in at least one direction (at 130 ° C, 10 min.). The film of the cited invention may consist of one layer of polypropylene based microcavities, but often may contain one or more layers of another to impart some characteristic property to them, e.g. heat weldability, gloss and others. Preferably, the layers are polyolefins. They are made by extrusion or coextrusion through a melt die of the respective polymers to the desired layer (or layers), which is cooled and then gradually biaxially oriented, generally at length, in the machine direction, at a temperature of 70 to 110 ° C, preferably 80 to 95 ° C, wherein the orientation ratio is at least from 3: 1 to 3.5: 1 to 8: 1 and then wide, but at temperatures lower than those commonly used for transverse orientation.

These are temperatures below 160 ° C to 155 ° C, most preferably between 140 ° C to 152 ° C. The approximate ratio is from 3: 1 to 10: 1.

In recent years, metallocene isotactic and syndiotactic polypropylenes can be produced using new metallocene catalysts. Due to their specific properties, these new metallocene polymers have different applications in the packaging industry, in the production of packaging films with new utility properties.

Currently used tobacco biaxially oriented polypropylene films that are manufactured by standard technologies (i.e., a low degree of initial orientation and a high degree of doorientation, e.g., from 1.05 to 5.3) have a shrinkage of 3.0 to 5.0%. (at 135 ° C and 7 min. in an oven). The shrinkage parameter also depends on the polypropylene used (in particular its atactic value) as well as the technological conditions of production. The shrinkage of the tobacco film directly affects the quality of packaging of the finished cigarette pack, in particular the quality requirements for a good visual appearance of the pack of the cigarette pack. It is a requirement that the film be wrapped sufficiently around the box and that undesirable undulations of the film are not formed. By using the heat-shrinkable tobacco foil to which the present invention relates, these drawbacks are eliminated and hence the packaging of cigarette boxes is improved.

The quality of packaging of the finished cigarette box, in particular the quality requirements for a good visual appearance of the box packaging, can also be achieved by a suitable film size relative to the cigarette box, appropriate mechanical properties and material stiffness. A very good evaluation parameter (used in tobacco film processors) is to measure the tightness of cigarette packs in multilayer biaxially oriented polypropylene films that are used to pack cigarette boxes.

SUMMARY OF THE INVENTION

The present invention provides a tobacco-heat shrinkable biaxially oriented polypropylene film consisting of three layers, wherein the core layer comprises a mixture of isotactic and syndiotactic metallocene polypropylene and an antistatic masterbach, and the 2 outer heat-sealable layers comprise a terpolymer, slip and antistatic masterbach. The content of syndiotactic metallocene polypropylene is in the range of 1.0 to 5.0 wt. %. The two outer heat-sealable layers are either of the same composition, type of three-layer ABA film, without a Koran finish, or of different composition, type of three-layer AB-Cs one-sided Q-shaped treatment on side C. In this type of film oil and in the outer layer C arucamid. The tobacco-shrinkable biaxially oriented polypropylene film exhibits a shrinkage of 6.0-11.0% in the longitudinal and transverse directions at 135 ° C. The method of producing a tobacco-heat-shrinkable biaxially oriented polypropylene film according to these characteristics is carried out at increased orientation ratios for orientation in length and length respectively. for wide orientation and reduced temperatures in the wide orientation stabilization zones. The length orientation is 6.0 to 8.0 times depending on the final shrinkage requirement. The film, when oriented in width, is preheated with air at a temperature of 165 to 178 ° C and then sequentially oriented 8.0 to 10.0 times in width at an air temperature of 160 to 165 ° C. The temperature in the stabilization zones is reduced to 145 ° C and lower depending on the operational stability of the production. ·

The tobacco heat-shrinkable biaxially oriented polypropylene film of the present invention is produced such that the blended raw material mixture for the core layer and the two topsheets is plasticized by heating in a screw extruder to a melt temperature of about 265 ° C. After melt filtration from the main extruder and two additional coextruders, the resulting coextrudate is extruded through a flat die slot heated to 260 ° C. The melt from the die is cast and cooled on a cooling cylinder having a temperature of 32 ° C. On the other hand, the melt is cooled with 22 ° C hot water in a cooling bath. These melt cooling conditions provide the desired coarse film structure before entering the length orientation (MDO) portion. On the hot rollers of the lengthwise orientation, the coarse film is heated by heat from the coils that are heated to a temperature of 125-135 ° C (so that the coarse film does not stick to the surface of the coils, thereby disrupting the terpolymer layer). The heated coarse film is stretched to length on the orientation rolls (at different roll speeds). The final shrinkage value of the film also depends on the size of the orientation achieved. To achieve the desired shrinkage of the finished film min. 6.0 to 11.0% (in an oven at 135 ° C and 7 min), a two-stage longitudinal orientation of the coarse film is particularly preferred. Setting the orientation ratio to length is 6 x 1.1 to 6 x 1.3. The resulting degree of longitudinal orientation along it is thus 6.6 to 7.8 times. The use of syndiotactic polypropylene in the blend is particularly advantageous over other modifiers, since there is less stress on the electric motors in the MDO with such increased longitudinal orientation. After leaving the MDO film, it is then pulled into a wide orientation (TDO) by a chain. In preheat zones of TDO, the film is heated at about 172 ° C with warm air and is subsequently 8 to 10 times oriented in width by gradually extending the chain pitch at 165 ^° C. In the stabilization zones of TDO sections, the temperature should be reduced to 145 ° C. or lower if permitted by production reliability) and widening the chain spacing at its TDO exit, if permitted by the width of the rollers behind the TDO exit and in the winding section of the machine.

The finished film intended for one-sided printing can still be treated by coronating the surface of the films in the winding part. Finished films are produced in thicknesses from 14 to 40 pm (usually 16, 20, 21 pm). One of the target parameters of the finished film is shrinkage, respectively. dimensional stability of foil. The dimensions of the film sample before it is placed in the oven and removed from the oven are measured with a Hirlinger ruler at the locations indicated (for accuracy of measurement). The change in dimensions shall be measured in the transverse and longitudinal directions. The conditions in the oven are: temperature of 135 ° C and 7 minutes of sample residence in the oven. The shrinkage values of the tobacco sheet produced according to the invention range from 6.0% to 11.0% depending on the height of the orientation ratio. (Tobacco films produced to date have a shrinkage value of 3.0 to 5.0%). Tobacco foil with such shrinkage values better encircles the cigarette pack, respectively. cardboard and so the visual quality evaluation of the packaging is better.

Tobacco sheet produced by the process may be illustrated by the following examples in which the temperatures in the individual technological parts of the production line may be within plus / minus the temperatures given in the individual examples depending on the production line temperature, power and type of carrier isotactic polypropylene used. .

Examples of use

Example 1

A standard frame line is used to produce the film. Mixed raw material mixture for foil type A - B - A, namely core layer -B- of 98.6874 wt. % isotactic polypropylene, 1.0 wt. % of syndiotactic metallocene polypropylene and 0.3126 wt. an antistatic masterbach having a composition of 0.0700 wt. % glycerol monostearate, 0.2300 wt. % alkyl (C 12 -C 18) bis (2-hydroxyethyl) amine, 0.0072 wt. % bis- [3,3-bis- (4'-hydroxy-3-tert-butylphenyl) butanic acid] glycol ester, 0.0027 wt. % of tris (2,4-di-tert-butylphenyl) phosphite and two identical top heat-weldable terpolymer layers of 99.4115 wt. % terpolymer (C2 C3 C4), 0.5489 wt. % silicone oil, 0.0275 wt. % calcium stearate, 0.0088 wt. % tris (2,4-di-tert-butylphenyl) phosphite and 0.0033 wt. bis [3,3-bis- (4'-hydroxy-3-tert-butylphenyl) butanic acid] glycol ester is plasticized by heating in a screw extruder to a melt temperature of about 265 ° C. After melt filtration from the main extruder and two additional coextruders, the resulting coextrudate is extruded through a flat die slot heated to 260 ° C. The melt from the die is cast and cooled on a cooling cylinder having a temperature of 32 ° C. On the other hand, the melt is cooled with 22 ° C hot water in a cooling bath. On the hot rollers of the lengthwise orientation, the coarse film is heated by heat from the coils that are heated to a temperature of 125-135 ° C (so that the coarse film does not stick to the surface of the coils, thereby disrupting the terpolymic layer). The heated coarse film is stretched to length on the orientation rolls (at different roll speeds). The final shrinkage value of the film also depends on the size of the orientation achieved. To achieve the desired shrinkage of the finished film min. 6.0 to 11.0% (in an oven at 135 ° C and 7 min), a two-stage longitudinal orientation of the coarse film is particularly preferred. Setting the orientation ratio to length is 6 x 1.1 to 6 x 1.3. The resulting degree of longitudinal orientation along it is thus 6.6 to 7.8 times. The use of syndiotactic polypropylene in the blend is particularly advantageous over other modifiers, since there is less stress on the electric motors in the MDO with such increased longitudinal orientation. After leaving the MDO film, it is then pulled into a wide orientation (TDO) by a chain. In the preheat zones of TDO, the film is heated at about 172 ° C with warm air and subsequently 8 to 10 times oriented in width by gradually expanding the chain pitch at 165 ° C. In the stabilization zones of TDO parts, a reduction of the temperature to 145 ° C (or even lower if production reliability allows) and an extension of the chain spacing at its exit from the TDO is necessary if the roll width beyond the TDO exit and in the winding part of the machine permits.

The finished films are produced in thicknesses of 14 to 40 μηι (usually 16, 20, 21 pm). The shrinkage of the tobacco film produced according to this example is min. 6%.

Example 2

For the plasticization in the screw extruder, a mixture of raw materials for the type A-B-A foil is used, the core layer -B- consisting of a different ratio of isotactic and syndiotactic polypropylene as in Example 1, namely from 97.6874% by weight. % isotactic polypropylene and 2.0 wt. syndiotactic metallocene polypropylene, while maintaining the antistatic masterbach content and production method as in Example 1, similarly two identical top heat-weldable terpolymer layers are identical to Example 1. Shrinkage values from 6.0 to 11.0% depending on the current orientation ratio.

Example 3

For plasticization in a screw extruder, a blend of raw materials for type A-B-A foil is used, wherein the core layer -B- is composed of a different ratio of isotactic and syndiotactic polypropylene as in Examples 1 and 2, namely 96.6874% by weight. % isotactic polypropylene and 3.0 wt. % of syndiotactic metallocene polypropylene;

% glycerol stearate, 0.2300 wt. % alkyl (C 1 -C 18) bis (2-hydroxyethyl) amine, 0.0072 wt.

% bis- [3,3-bis- (4'-hydroxy-3-tert-butylphenyl) butanic acid] glycol ester, 0.0027 wt. tris (2,4-di-tert-butylphenyl) phosphite, but the two identical top heat-weldable terpolymer layers are identical to Example 1. Film production process similar to Example 1. When the resulting degree of orientation is 6.6 to 7.8 times, a shrinkage value of 6 is obtained. , 0 to 11.0% depending on the current orientation ratio.

Example 4

For the plasticization in the screw extruder, a mixture of raw materials for type A - B - A foil is used, wherein the core layer -B- is composed of a different ratio of isotactic and syndiotactic polypropylene than in Examples 1 to 3, namely 95.6874% by weight. % isotactic polypropylene and 4.0 wt. % of syndiotactic metallocene polypropylene;

% glycerol stearate, 0.2300 wt. % alkyl (C 12 -C 18) bis (2-hydroxyethyl) amine, 0.0072 wt.

% bis- [3,3-bis- (4'-hydroxy-3-tert-butylphenyl) butanic acid] glycol ester, 0.0027 wt. tris (2,4-di-tert-butylphenyl) phosphite, but the two identical top heat-weldable terpolymer layers are identical to Example 1. A film production process similar to Example 1. When a final degree of orientation of 6.6 to 7.8 times is reached, a shrinkage value of 6 , 0 to 11.0% depending on the current orientation ratio.

Example 5

For the plasticization in the screw extruder, a mixture of raw materials for the type A-B-A foil is used, wherein the core layer -B- is composed of a different ratio of isotactic and syndiotactic polypropylene than in Examples 1 to 4, namely 94.6874% by weight. % isotactic polypropylene and 5.0 wt. % of syndiotactic metallocene polypropylene;

% glycerol stearate, 0.2300 wt. % alkyl (C 11 -C 11) bis (2-hydroxyethyl) amine, 0.0072 wt.

% bis- [3,3-bis- (4'-hydroxy-3-tert-butylphenyl) butanic acid] glycol ester, 0.0027 wt. tris (2,4-di-tert-butylphenyl) phosphite, but the two identical top heat-weldable terpolymer layers are identical to Example 1. A film production process similar to Example 1. When a final degree of orientation of 6.6 to 7.8 times is reached, a shrinkage value of 6 , 0 to 11.0% depending on the current orientation ratio.

Example 6

For plasticization in a screw extruder, a blend of raw materials for type A-B-C foil is used, wherein the core layer -B- and the top terpolymer layer -A- are composed of the raw materials as described in Example 1 of the present invention. The second outer heat-sealable terpolymer layer -C consists of 99, 4115 wt. % terpolymer (C ₂ C 3 C ₄ ), 0.5489 wt. erucamide,

0.0275 wt. % calcium stearate, 0.0088 wt. % tris (2,4-di-tert-butylphenyl) phosphite; bis- [3,3-bis- (4'-hydroxy-3-tert-butylphenyl) butanic acid] glycol ester.

This layer is corona coated for printing. The film production process is similar to Example 1. The finished film intended for one-sided printing is treated by coronating the film surface in the winding section. The shrinkage is from 6.0% to 11.0% depending on the height of the orientation ratio.

Example 7

For plasticization in a screw extruder, a blend of raw materials for type A-B-C foil is used, wherein the core layer -B- and the top terpolymer layer -A- are composed of the raw materials as described in Example 2 of the present invention. The second outer heat-sealable terpolymer layer -C consists of the raw materials as in Example 6, and the manufacturing process including the corona treatment is similar to that in Example 6. The shrinkage is from 6.0% to 11.0% depending on the orientation ratio height.

Example 8

For plasticization in the screw extruder, a mixture of raw materials for the type A-B-C foil is used, wherein the core layer -B- and the top terpolymer layer -A- are composed of the raw materials as described in Example 3 of the invention. The second outer heat-sealable terpolymer layer -C consists of the raw materials as in Example 6, and the manufacturing process including the corona treatment is similar to that in Example 6. The shrinkage is from 6.0% to 11.0% depending on the orientation ratio height.

Example 9

For plasticization in a screw extruder, a blend of raw materials for type A-B-C foil is used, wherein the core layer -B- and the top terpolymer layer -A- are composed of the raw materials as described in Example 4 of the invention. The second outer heat-weldable terpolymer layer -C consists of the raw materials as in Example 6, and the manufacturing process including the Koran treatment is similar to that of Example 6. The shrinkage is from 6.0% to 11.0% depending on the orientation ratio height.

Example 10

For plasticization in a screw extruder, a blend of raw materials for type A-B-C foil is used, wherein the core layer -B- and the top terpolymer layer -A- are composed of the raw materials as set forth in Example 5 of the present invention. The second outer heat-sealable terpolymer layer -C consists of the raw materials as in Example 6, and the manufacturing process including the corona treatment is similar to that of Example 6. The shrinkage is from 6.0% to 11.0% depending on the orientation ratio height.

Industrial usability

This new tobacco film is sufficiently treated with antistatic and sliding additives, and therefore it can be used and processed on high-speed automatic machines with a packing speed of up to 600 boxes / min.

Claims (10)

PROTECTION REQUIREMENTS A heat-shrinkable biaxially oriented polypropylene film consisting of three layers, characterized in that the core layer comprises a mixture of isotactic and syndiotactic metallocene polypropylene and an antistatic masterbatch and the two outer heat-sealable layers comprise a terpolymer and a sliding masterbatch. The tobacco heat shrinkable biaxially oriented polypropylene film of claim 1, wherein the core layer is a mixture of isotactic and syndiotactic metallocene polypropylene, wherein the content of syndiotactic metallocene polypropylene in the core is in the range of 1.0 to 5.0% by weight. Tobacco heat-shrinkable biaxially oriented polypropylene film according to claim 1,2, characterized in that the two outer heat-sealable layers are of the same composition, type triple-layer film A-B-A, without corona finish. Tobacco heat-shrinkable biaxially oriented polypropylene film according to claim 1,2, characterized in that the two outer heat-sealable layers are of different composition, a three-layer film type A-B-C, with a one-sided corona finish on the C side. The tobacco-shrinkable biaxially briented polypropylene film according to claim 4, wherein the active lubricant additive in the outer layer A is silicone oil and in the outer layer C the active lubricant additive is erucamide. A tobacco-heat-shrinkable biaxially oriented polypropylene film according to claims 1 to 5, characterized in that the shrinkage of the produced film is 135 ° C, 7 min under defined measurement conditions. from 6.0 to 11.0% in the longitudinal and transverse directions Method for producing a tobacco-shrinkable biaxially oriented polypropylene film according to claims 1 to 6, characterized in that the production of said film is carried out at elevated orientation ratios in orientation to length or length. for wide orientation and reduced temperatures in the wide orientation stabilization zones. j A method for producing a tobacco-shrinkable biaxially oriented polypropylene film according to claim 7, characterized in that the length orientation is 6 to 8 times depending on the desired shrinkage value. The method of producing a tobacco heat shrinkable biaxially oriented polypropylene film according to claim 7, wherein the widthwise orientation film is preheated with warm air at a temperature of 165-178 ° C and then sequentially oriented 8-10 times widthwise at an air temperature of 160-178 ° C. 165 [deg.] C. Method for producing a tobacco-heat shrinkable biaxially oriented polypropylene film according to claims 7 and 9, characterized in that the temperature in the stabilization zones is reduced to 145 ° C and lower depending on the operational stability of the production.