EP4028238A1

EP4028238A1 - Device for producing stretch film intermediates and a stretch film

Info

Publication number: EP4028238A1
Application number: EP21752148.3A
Authority: EP
Inventors: Tomasz Szalas; Robert Saczuk
Original assignee: Glopack Spolka Z Ograniczona Odpowiedzialnoscia
Current assignee: Glopack Spolka Z Ograniczona Odpowiedzialnoscia
Priority date: 2020-06-23
Filing date: 2021-06-20
Publication date: 2022-07-20
Also published as: PL237815B1; WO2021260513A1; PL434413A1

Abstract

Device for producing stretch film intermediates and a stretch film made using this device. The device is characterised in that it consists of multiple sets, preferably nine sets placed on strip guiding lines (2a). The line (2a) of each film strip (2) passes over a base (3) with rolls (4a, 4b, 4c, 4d) attached thereto. The axes of the rolls (4a, 4b, 4c, 4d) are parallel to each other and perpendicular to the film strip (2) guiding line (2a). Between the rolls (4a, 4b, 4c), in the base (3), there are pairs of holes (5), preferably four pairs of holes (5). Each pair of holes (5) is arranged on a single line perpendicular to the strip (2) line (2a) and the holes (5) of each pair are arranged symmetrically on both sides of the strip (2) guiding line (2a). Distances (c) between successive pairs of holes (5) decrease on the side of film insertion. In the pairs of holes (5), pins (6) are placed which wrap the strips (2). A stretch film made of linear low-density polyethylene - LLDPE, comprising a sheet of base film (1) on which parallel film strips (2) are rolled. It is notable that the multilayer film strips (2) made of LLDPE have a thickness (g) of 44 to 90 μm. The width of the film strips (2) ranges from 41.67 to 49.07 mm. Alternatively, the film strips are made of a material containing LLDPE re-granulate. Optionally, the film strips are made of a material containing a dye. Optionally, perforation holes (10) are provided on the surface between the film strips (2).

Description

Title of Invention: Device for Producing Stretch Film Intermediates and a Stretch Film

[0001] The object of the invention is a device for producing stretch film intermediates and a stretch film with increased tensile strength.

[0002] Stretch films are mainly made of polyethylene, the consumption of which for this type of film constitutes more than 50% of polyethylene consumption for the production of polyethylene films. Stretch films are produced by extrusion blow moulding as so- called sleeve films or by slit-head extrusion moulding as so-called flat films. Due to its much higher efficiency, the slit-head extrusion moulding method provides, despite the use of much more complex and expensive equipment constituting the process line, a more competitive film when used on a large scale, for example for pallet wrapping. In recent years, stretch film technology has been dominated by multilayer materials composed of several to dozens of layers made from different types of polyethylene copolymers, for example: linear low-density polyethylene, linear very low-density polyethylene, metallocene linear low-density polyethylene and the like. This ensures that the product retains a better mechanical strength despite the reduced film thickness.

[0003] Both the composition of stretch films and the technology for their production are the subject of numerous patents. From patent specification PL210951 (Bl) a five-layer biaxially-oriented polyethylene film is known which is characterised in that the basic raw material from which layers A, B, C, D and E are made is metallocene linear low- density polyethylene. Outer layer A is an activated layer with a thickness of 2.0 pm, in termediate layers B and D have a thickness of 2.5-3.5 pm, middle layer C has a thickness in the range 4.8-10.8 pm and layer E is an unactivated layer with a thickness of 2.0 pm. In addition, an antioxidant in the amount of 0.7-1.3% by weight is in troduced to all layers, an anti-bloking modifier in the form of Si0₂ in the amount of 0.2- 1.0% by weight is introduced to layers A and E, and layers B, C and D are treated with slip-antistatic agents in the amount of 0.5- 1.5% by weight. The method for producing a five-layer biaxially-oriented polyethylene stretch film, disclosed in this patent specification, comprises extruding metallocene linear low-density polyethylene heated to about 250°C, through a web-forming flat head, composed of five layers of film, cooling the web of film on a cooling roll at a temperature of 20-40°C, and then subjecting the web of film to a sequential orientation process.

[0004] From patent specification PL 182545 (Bl) a method for producing a multilayer polyethylene film is known which consists in the fact that individual layers of film consisting of a mixture of linear low-density polyethylene (LLDPE) with a density in the range of 915-935 kg/m³ and low-density polyethylene (LDPE) in the amount of 8-40% by weight in relation to LLDPE are co-extruded through a slit head, and then the film web is directed to a first cooling roll at a temperature of 10-25°C and in turn to a second cooling roll at the same temperature as the first one or in the range of 10-20°C, the rotation speed of the second roll being 10-40% higher than the rotation speed of the first cooling roll.

[0005] In turn, from patent application W02009/055316 (Al), multilayer films with a total thickness of 10-50 pm are known, each film layer being made of the same ther moplastic material selected from the following materials: polyethylene, polypropylene, polybutadiene, linear low- and medium-density polyethylene, polypropylene-ethylene interpolymer.

[0006] Patent specification US6153702 (A) discloses a composition composed of 85-99% by weight of polyethylene having a density not exceeding 0.94 g/cm³ and 1-15% by weight of a copolymer derived from 60-80% by weight of propylene and 20-40% by weight of olefinic comonomers, which composition can be used to produce multilayer stretch films.

[0007] From patent specification PL223808 (Bl), a polyolefin five-layer stretch film is known which is composed of five layers joined together. The first layer, representing 10 to 12% of the film thickness, is made of an ethylene-n-hexene copolymer with a melt flow rate (MFR) of 1.0 to 6.0 g/10 min. The second layer representing 28 to 32% of the film thickness is made of a mixture of an ethylene-n-hexene copolymer with a melt flow rate (MFR) of 1.0 to 6.0 g/10 min with a percentage of 20 to 80% by weight, preferably 50% by weight, the ethylene-n-hexene copolymer being obtained with the use of metallocene catalysts, with a melt flow rate (MFR) of 1.0 to 6.0 g/10 min. The third layer, representing 14 to 18% of the film thickness, is made of an ethylene- n-hexene copolymer with a melt flow rate (MFR) of 1.0 to 6.0 g/10 min, preferably 4.0 g/10 min. The fourth layer representing 28 to 32% of the film thickness is made from a mixture of ethylene-n-hexene copolymer having a melt flow rate (MFR) of 1.0 to 6.0 g/10 min, in an amount of 20 to 80% by weight, preferably 60% by weight, with polypropylene having a melt flow rate (MFR) of 2.0 to 6.0 g/10 min in an amount of 80 to 20% by weight, preferably 40% by weight. The fifth layer representing 10 to 12% of the film thickness is made of a mixture of an ethylene-n-hexene copolymer with a melt flow rate (MFR) of 1.0 to 6.0 g/10 min with a percentage of 40 to 95% by weight, preferably 80% by weight, the ethylene-n-hexene copolymer being obtained with the use of metallocene catalysts, with a melt flow rate (MFR) of 1.0 to 6.0 g/10 min and with a percentage of 60 to 5% by weight, preferably 20% by weight.

[0008] From patent application US2018072024 (Al), a method for producing reinforced stretch film is known which involves the following steps: [0009] 1) providing an elongated base sheet of plastic stretch film having a longitudinal axis;

[0010] 2) forming a plurality of elongated cord-like reinforcement members; positioning the plurality of reinforcement members into the base sheet, wherein the reinforcement members extend along the longitudinal axis of the base sheet;

[0011] 3) placing multiple plastic film overlays on each of the reinforcement members, the overlays being parallel and spaced apart;

[0012] 4) fixing the overlays to the reinforcement members and the base sheet to firmly arrange the reinforcement members between the base sheet and the overlays.

[0013] Thus, the reinforcement members contain parallel, longitudinal reinforcing strips defining elongated spaces between them.

[0014] From patent application WO2017189960 (Al), a reinforced stretch film is known which is obtained by a method comprising the following steps:

[0015] 1. providing an elongated base sheet of plastic stretch film having a longitudinal axis, forming a plurality of cord-like, elongated reinforcement members and a plurality of plastic film strip overlays,

2. positioning the plurality of elongated reinforcement members on the elongated base sheet,

3. positioning a single plastic film strip overlay over each of the elongated rein forcement members,

4. folding each edge of the elongated base sheet inward toward a centre of the elongated base sheet to further strengthen and reinforce each edge and attaching the plastic film strip overlays and the folded edges to the cord-like, elongated reinforcement members and to the elongated base sheet to fixedly sandwich the cord- like, elongated reinforcement members between the elongated base sheet and the narrow plastic film strip overlays.

[0016] From patent specification US8637134 (Bl), a vented plastic stretch film and a method of making thereof are known. In this solution, elongated reinforcement strips are applied to a base sheet, each reinforcement strip including a cord- like, rein forcement member formed from plastic film and a flat, narrow film strip covering the reinforcement member. Vent holes are formed from slits between the reinforcement members by applying tensional forces to the base sheet.

[0017] From patent specification PL430380 (Al), a stretch film, a device and a method for producing thereof are known. The stretch film is made of linear low-density polyethylene LLDPE and is composed of a sheet of basic film on which parallel film strips are applied. The thickness of the base film sheet is 0.023 mm and the thickness of the film strip is 0.03 mm. Optionally, perforation holes are provided on the surface between the film strips. The application also includes a device for producing the stretch film, which comprises a first unwinding shaft onto which a roll of base film is placed and a second unwinding shaft onto which a roll of overlay film is placed. Behind the second unwinding shaft in the overlay film unwinding line, there is a cutting and spreading unit containing knives, which cuts the overlay film into film strips and spreads them in the direction of the sheet width. Behind the cutting and spreading unit and the first unwinding shaft, there is a set of two backing rollers and between them, a pressure roller which has a spiral groove on its surface. The set of backing rollers and a pressure roller combines the base film and film strips. Behind the set of backing rollers and the pressure roller, there is a winding roller mounted on a mechanism that induces oscillatory motion in the direction of its axis. Optionally, the pressure roller is mounted on servomotors allowing its pressure force to be adjusted. The object of the application is also a method for producing a stretch film which consists in the fact that a base film is unwounded from a first unwinding shaft and an overlay film is simultaneously unwounded from a second unwinding shaft, the overlay film being then cut into strips, after which the strips are rolled with the base film and the combined film is wound onto a winding roller which is set in oscillatory motion towards its axis.

[0018] From patent application WO2011026954A2, a thermoplastic film is known which comprises: a base film, wherein the base film comprises a stretchable polyolefin material comprising one or more layers and a plurality of extruded fibrous elements, wherein the extruded fibrous elements are positioned on at least one surface of the base film. The extruded fibres form one or more projections in relation to the plane of the base film. At the location where the fibrous elements are placed on the base film, the domain of the material mixture comprising the base film material and the fibrous material is located between the domain of the pure base film material and the domain of the pure fibrous material. The average thickness of the base film is smaller than the average thickness of the projection.

[0019] From patent application WO02096634A1, a reinforced plastic film is known which comprises a section of plastic film and a reinforcing strip of plastic film which is connected to the former and extends along the length of the film and is spaced from opposite side edges thereof. The strip is designed to prevent propagation.

[0020] From patent application W 02016001107 A 1 , a non-perforated reinforced stretch film is known which comprises: a base film which has a thickness in the range of 3 pm to 18 pm, and 5 to 100 reinforcing strips attached to at least one surface of said base film, each reinforcing strip having a width independently ranging from 1 mm to 17 mm.

[0021] From patent application WO2011026953A1, a viscous stretchable polyolefin film is known which is suitable for flexible packaging, comprising a base film containing a stretchable polymeric material, having a plurality of perforations covering at least 25% of the total surface area of the base film and arranged in a series of columns along the longitudinal direction of the film, wherein the columns of perforations are separated by columns without perforations along the longitudinal direction of the film, and the per forations are shifted in a transverse direction across the film. It also has a plurality of reinforcing elements comprising a stretchable polymeric material, wherein the elements are fixed on the base film parallel to the longitudinal direction and at least one element is arranged in a column without perforations.

[0022] From patent application no. US2005123721A1, a stretch film for packaging goods is known, in particular for packaging goods stacked on a pallet. It consists of a pre stretched main film. The main film is reinforced with reinforcing strips extending in the longitudinal direction. Reinforcement tapes are made from strips of pre-stretched film that have been repeatedly bent in the longitudinal direction. The film strips are symmetrically folded preferably twice, and especially four times in the longitudinal direction.

[0023] The aim of the invention is to increase the strength of the stretch film with a minimum increase in its dimensions, especially with the use of recycled raw materials. An additional problem to be solved is to quickly determine the degree of tension in the film when wrapping it around the package.

[0024] An object of the invention is a device for producing stretch film intermediates, having a base and rolls. Its essence lies in the fact that it consists of multiple sets, preferably nine sets placed on strip guiding lines. The lines of every film strip passes over the base with the rolls attached thereto. The axes of these rolls are parallel to each other and perpendicular to the film strip guiding line. Between the rolls in the base, there are pairs of holes, preferably four pairs of holes. Each pair of holes is arranged on a single line perpendicular to the strip line and the holes of each pair are arranged sym metrically on both sides of the strip guiding line. The distances between successive pairs of holes decrease on the side of film insertion. In the pairs of holes, pins are placed which wrap the strips asymmetrically. The pins are located on the side of the strips.

[0025] Another object of the invention is a stretch film made of linear low-density polyethylene - LLDPE, comprising a base film sheet on which parallel film strips are rolled, made using the device according to the invention. The essence of the film according to the invention is that asymmetrically over its thickness, the multilayer film strips have a thickness ranging from 44 to 90 pm, and the width of the film strips ranges from 41.67 to 49.07 mm.

[0026] Optionally, the film strips are made of a material containing LLDPE regranulate.

[0027] Alternatively, the film strips are made of LLDPE, doped with a dye which may be: phthalocyanine blue BN, phthalocyanine green G, aniline black, monoase pigments, anthroquinone derivatives, isoindoline derivatives, di-azo pigments, perthenotete- tracuronic acid derivatives, isoindotizine derivatives, bicinchona violet, thioindigo derivatives, dioxazine pigments. Optionally, perforation holes are provided on the surface between the film strips.

[0028] The advantageous effect of the produced stretch film according to the invention is that it has a higher strength due to the use of layers with increased thickness and a smaller width pressed onto the film. This combination reduces the amount of material used. The pre-stretched film does not need to be stretched during the application process. This film provides three times lower wear than standard stretch film. This ensures less waste and a lower cost of disposal. The use of recycled waste makes this film more environmentally friendly than those produced so far. The use of dyed films helps to determine the safe tension of the film when packaging products.

[0029] The objects of the invention in an embodiment are illustrated in the drawing, wherein the individual figures show:

[0030] [Fig.1] - a section of the finished film in isometric view,

[0031] [Fig. la] - a detail of the film in isometric view,

[0032] [Fig.2] - a fragment of the finished perforated film in isometric view,

[0033] [Fig.3] - a device for increasing the thickness of film strips,

[0034] [Fig.4] - a diagram of a technological line for film production.

[0035] The device for increasing the thickness of film strips in the embodiment consists of nine sets placed on strip guiding lines 2a. Five sets are at one height, with four such sets below them. The line 2a of each film strip 2 passes over the base 3 with rolls 4a, 4b, 4c, 4d attached thereto. The axes of the rolls 4a, 4b, 4c, 4d are parallel to each other and perpendicular to the film strip 2 guiding line 2a. Between the rolls 4a and 4b and also 4b and 4c, in the base 3, there are four pairs of holes 5, symmetrically arranged on both sides of the film strip 2 guiding line 2a. Distances "c" between successive pairs of holes 5 decrease on the side of film insertion. In the pairs of holes 5, pins 6 are placed which wrap the strips 2.

[0036] The device for producing stretch film intermediates by increasing the thickness of the film strips 2 in the embodiment has been placed in a technological line for film production, the schematic diagram of which is shown in [Fig.4] of the drawing. It comprises a first unwinding shaft 7 onto which a roll of base film 1 is placed and a second unwinding shaft 8 onto which a roll of overlay film is placed. Behind the second unwinding shaft 8 in the overlay film unwinding line, there is a set of knives 9 cutting the overlay film into film strips 2. Behind it, a device for increasing the thickness of film strips is mounted, behind which there is a set of two backing rollers 10a, 10b and a pressure roller 11 between them which has a spiral groove on its surface. The set of backing rollers 10a, 10b and pressure roller 11 combines the base film 1 and the film strips 2. Behind the set of backing rollers 10a, 10b and pressure roller 11, there is a film perforating mechanism 12, a film stretching mechanism and an edge alignment mechanism, behind which there is a winding roller 13 mounted on a mechanism that induces an oscillatory motion in the direction of its axis.

[0037] The production of the stretch film in the embodiment consists in unrolling the base film 1 from the first unrolling shaft 7 and in parallel unrolling the overlay film from the second unrolling shaft 8, which is then cut by the set of knives 9 into nine strips 2. The film strips 2 are wrapped on the wrapping device, and their width and thickness depend on where the individual pegs 6 are fixed in the holes 5 located in the base 3 of the device. The base film 1 and the film strips 2 symmetrically distributed on it are directed to the rollers of the set of backing rollers 10a, 10b and pressure roller 11 and the strips 2 are rolled with the base film 1. The pressure roller 11 is pressed against the base film sheet 1 and the strips 2 located on the backing rollers with a force of 1.07 MPa. In a further step, the longitudinally connected film reinforced with the strips 2 is stretched, the edges are aligned and wound onto the winding roller 13 which moves in an oscillatory motion towards its axis. The winding speed is 400 m/min.

[0038] A stretch film made using the device according to the invention, in embodiments, comprises a sheet of the base film 1 on which there are nine strips 2 evenly distributed over its entire width. The sheet of the base film 1 was made from a jumbo transparent stretch film sheet by Star Pak sp. z o.o., which is made of linear low-density polyethylene LLDPE. The film has the following parameters: sheet width 500 mm +/- 5 mm, point measured thickness 0.023 mm (tol. +/- 5%), running metre weight - 10.75 g (tol. +/- 5%), weight per square metre 21.50 g (tol. +/- 5%), density 0.921 kg/ m³, low-slip value >0.4 and stretchability 300%.

[0039] In the first embodiment, a sheet of jumbo transparent stretch film from Star Pak sp. z o.o., which was made of linear low-density polyethylene (LLDPE), was used to produce the film strips 2. The film has the following parameters: sheet width 250 mm +/- 5 mm, point measured thickness 0.023 mm (tol. +/- 5%), running metre weight 6.92 g (tol. +/- 5%), weight per square metre 27.60 g (tol. +/- 5%), density 0.921 kg/m³ , low-slip value >0.4 and stretchability 300%.

[0040] In the second embodiment, a sheet of jumbo stretch film Stand. 500/0, 023/150 Eko black produced by TW PLAST Sp. z o.o., made from linear low-density polyethylene LLDPE with 80% addition of recycled materials, was used to produce the film strips 2. The film has the following parameters: sheet width 250 mm +/- 5 mm, point measured thickness 0.023 mm (tol. +/- 5%), running metre weight 10.6 g (tol. +/- 5%), weight per square metre 21.20 g (tol. +/- 5%), density 0.918 kg/m³ and stretchability 150%.

[0041] In the third embodiment, stretch film produced by Lood Pack Sp. z o.o., made from linear low-density polyethylene (LLDPE), was used to produce the film strips 2. The film has the following parameters: sheet width 250 mm +/- 5 mm, point measured thickness 0.023 mm (tol. +/- 5%), running metre weight 10.6 g (tol. +/- 5%), weight per square metre 21.20 g (tol. +/- 5%), density 0.92 kg/m³ and stretchability 150%. The LLDPE films used have the following dyes in their composition:

[0042] • dye (29 H 31 H -phthalocyaninato (2 -) - N 29 N 30 N 31 N 32) of copper (II),

• phthalocyanine green G,

• aniline black,

• monoase pigments,

• anthroquinone derivatives,

• isoindolin derivatives,

• di-azo pigments,

• perthenetetracarbonyl acid derivatives,

• isoindotis derivatives,

• bicinchona violet,

• thioindole derivatives,

• dioxazine pigments.

[0043] The type of dye additive has no measurable effect on the strength parameters of the sample, therefore separate values are not provided.

[0044] The obtained films are shown in the embodiment in [Fig.l], [Fig. la]. All of them have, asymmetrically on their thickness, multilayer film strips 2 and perforations in the basic film 1. The asymmetrical thickness was due to the passage of the film strips 2 through the decreasing space between the pins 6. The thickness of the film strips 2 was g. From each film, samples ([Fig.2]) containing two film strips 2 with the base foil 1 between them were cut out and subjected to a uniaxial tensile test on a Zwick Z010 testing machine. Test speed 50 mm/min and Young's modulus determination speed 5 mm/min. Measurement deviations were +/- 5%. Table 1 shows averaged test values.

[0045] Table 1. Results of the tensile test

[0046] g - thickness of the applied film strip

[0047] Et - Young's modulus

[0048] ox - conventional yield point

[0049] ec - deformation at the conventional yield point

[0050] List of designations:

[0051] 1 - base film

[0052] 2 - film strip

[0053] 2a - strip guiding line

[0054] 3 - base

[0055] 4a, 4b, 4c, 4d - roll

[0056] 5 - hole

[0057] 6 - pin

[0058] 7 - first unwinding shaft

[0059] 8 - second unwinding shaft

[0060] 9 - set of knives

[0061] 10a, 10b - backing rollers

[0062] 11 - pressure roller

[0063] 12 - perforating mechanism

[0064] 13 - winding roller

[0065] 14 - perforation hole

Claims

[Claim 1] A device for producing stretch film intermediates, having a base and rolls, characterised in that it consists of multiple sets, preferably nine sets placed on strip guiding lines (2a), wherein the line (2a) of each film strip (2) passes over the base (3) with rolls (4a, 4b, 4c, 4d) attached thereto, and the axes of these rolls (4a, 4b, 4c, 4d) are parallel to each other and perpendicular to the film strip (2) guiding line (2a), and between the rolls (4a, 4b, 4c), in the base (3), there are pairs of holes (5), preferably four pairs of holes (5), wherein each pair of holes (5) is arranged on a single line perpendicular to the strip (2) line (2a) and the holes (5) of each pair are arranged symmetrically on both sides of the strip (2) guiding line (2a), wherein distances (c) between successive pairs of holes (5) decrease on the side of film insertion, and in the pairs of holes (5), pins (6) are placed which asymmetrically wrap the strips (2).

[Claim 2] A stretch film made of linear low-density polyethylene - LLDPE, comprising a sheet of base film (1) on which parallel film strips (2) are rolled, made using the device according to claim 1 characterised in that asymmetrically over its thickness, the multilayer film strips (2) made of LLDPE have a thickness (g) of 44 to 90 pm, and the width between the film strips (2) ranges from 41.67 to 49.07 mm.

[Claim 3] The stretch film according to claim 2, characterised in that the film strips (2) are made of LLDPE with LLDPE regranulate.

[Claim 4] The stretch film according to claim 2, characterised in that the film strips (2) are made of LLDPE, with an admixture of a dye.

[Claim 5] The stretch film according to claim 4, characterised in that the dye is phthalocyanine blue BN.

[Claim 6] The stretch film according to claim 4, characterised in that the dye is phthalocyanine green G.

[Claim 7] The stretch film according to claim 4, characterised in that the dye is aniline black.

[Claim 8] The stretch film according to claim 4, characterised in that the dye is monoase pigments.

[Claim 9] The stretch film according to claim 4, characterised in that the dye is anthroquinone derivatives.

[Claim 10] The stretch film according to claim 4, characterised in that the dye is anthroquinone derivatives.

[Claim 11] The stretch film according to claim 4, characterised in that the dye is di-azo pigments.

[Claim 12] The stretch film according to claim 4, characterised in that the dye is perthenetetracarbonyl acid derivatives.

[Claim 13] The stretch film according to claim 4, characterised in that the dye is isoindotis derivatives.

[Claim 14] The stretch film according to claim 4, characterised in that the dye is bicinchona violet.

[Claim 15] The stretch film according to claim 4, characterised in that the dye is thioindole derivatives.

[Claim 16] The stretch film according to claim 4, characterised in that the dye is dioxazine pigments.

[Claim 17] The stretch film according to claim 2, characterised in that perforation holes (10) are provided on the surface between the film strips (2).