HUT65769A - Process for wrapping articles with stretch wrap films - Google Patents

Abstract

A process for wrapping articles, particularly large or heavy articles, with a stretch wrap film is disclosed. The film is at least 45 mu m thick and is made from a polymer blend, such blend comprising (i) from 1 to 20 wt.-% of at least one polybutene having a number average molecular weight of from 500 to 10,000 and (ii) a polyethylene selected from the group consisting of at least one linear ethylene/C4-C10 alpha -olefin copolymer having a density of from 0.915 to 0.940 g/cm<3> and blends of such copolymer with a second polymer, selected from a homopolymer of ethylene and a copolymer of ethylene and vinyl acetate, said second polymer having a density of from 0.910 to 0.940 g/cm<3>, said polyethylene having up to 70 wt.-% of said second polymer, and wherein said film has a low crystallinity.

Description

The present invention relates to a process for wrapping articles with stretch film, which is suitable for wrapping or wrapping piece goods. Piece goods include rolled or wrapped articles, such as paper, carpet, felted textiles, spools, which can be wound with stretch film.

Flexible stretched, rewindable films are already known. U.S. Pat. No. 4,657,982. U.S. Pat. elastic tensioned polybutene for packaging • ·

-2 describes a usable foil. DE 2,821,733, incorporated herein by reference. German Patent No. 6,308,198, issued November 30, 1978 to British Cellophane Limited, discloses a process for making a film for winding which can be used for spooling. The process involves extruding a mixture of polyethylene and 0.5-10% by weight polyisobutylene and applying a crown discharge to one surface of the film. This publication exemplifies the use of low density polyethylenes. U.S. Pat. No. 4,337,188. U.S. Patent No. 5,198, June 29, 1982 to Climenhage and Eadie, discloses high-adhesive films made of polyolefins, an elastomeric material, and Ν, Ν-bis (2-hydroxyethyl) alkylamine, mineral oil, liquid polyolefin and organic phosphate ester, polyethylene glycol, glycerol oleate and N- (3-alkoxy-2-hydroxypropyl) ethanolamine. Coil wrapping is already known for coating objects, in which the object is rotated about a vertical axis. The film used to coat such articles is generally made from low density polyethylene or a mixture of linear low density polyethylene and at least one polybutene by a conventional blown film forming process. The layer thickness is generally in the range of 20-30 micrometers. Unsuccessful attempts have been made to coat larger, generally horizontal, spools of rolled goods, such as paper, carpet, and similar materials, or heavy objects (such as bricks placed on pallets) with linear low density polyethylene film. The films were produced by conventional blasting and were about 51 micrometres thick. In such attempts, the film is unevenly deformed, especially when the prestress (prestress) is approximately 100%. Higher pre-stretching resulted in more frequent film rupture. Such procedures have therefore resulted in significant waste losses.

It is an object of the present invention to provide a coating process which is free of the drawbacks outlined above.

The present invention provides a process for wrapping an article with a stretch film having a layer thickness of at least 45 micrometres and

-3 wrapper is made of a polymer blend containing:

% polyethylene i) 1 to 20 weight of at least one, from 500 to 10,000 number average molecular weight of polybutene, and ii) at least one density linear ethylene / C ₄ -CiQ α-olefin copolymer is between 0.905 g / cm ³ and 0.940 g / cm ³ or a mixture of such a copolymer and a second polymer and said second polymer having a density of between 0.910 g / cm ³ and 0.940 g / cm ³ , or a copolymer of ethylene and vinyl acetate, and the latter in a mixture of polyethylene and second polymer up to 70% by weight;

furthermore, the film has a slightly crystalline structure.

The object to be packaged is preferably cylindrical and of circular cross-section.

In a preferred embodiment, the ratio of the length to height of the object is at least one and a half times.

In a preferred embodiment of the method, the film is pre-stretched at least 200%, preferably at least 250%, and most preferably at least 400% prior to wrapping the article.

In another embodiment, the ethylene / C ₄ -C 10 α-olefin copolymer is an ethylene / octene-1 copolymer or an ethylene / hexene-1 copolymer having a density in the range of 0.910-0.930 g / cm ³ .

In another embodiment, the polybutene has an average molecular weight of between 700 and 5000, preferably between 900 and 3000.

In a further embodiment, the polymer blend contains from 2 to 12% by weight, in particular from 3 to 10% by weight, of polybutene.

In another embodiment, the layer thickness is between 50 and 110 micrometers.

In another preferred embodiment, the layer has a luminance of at least 90% and is measured by the ASTM D-2457 method from a 20 ° reflection angle.

In another embodiment, the luminance is 90-120% ····· · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · ······

-4 in the middle.

In another embodiment, the layer opacity is between 4% and 6% as measured by ASTM D-1003.

The present invention is particularly suitable for packaging large or heavy objects.

In a preferred embodiment, the object is a roll of paper, fabric or carpet. The object is usually wrapped with a horizontal winding machine, since rotation about the horizontal axis is advantageous for the object. Of course, a vertical winding machine can also be used for coating.

Unless otherwise defined, the molecular weight of the referred polybutenes is as defined by ASTM D-2503-67.

As used herein, the term polybutene ¹ · refers to polymers having a predominantly N-butene or isobutylene backbone. Polybutenes, also known as polyisobutylene, are commercially available by the catalytic polymerization of isobutylene-rich mixtures wherein the 1- and 2-butenes are incorporated into lower weight polyisobutylenes rather than higher molecular weight polyisobutylenes. Polybutenes can also be synthesized by a low-temperature catalytic process from a gas stream from the refinery which contains polymerizable olefins, in particular isobutylene.

The components of the film-forming material may be mixed by methods known per se, for example, the ingredients may be premixed, incorporated into a main slurry concentrate, then left to mix with polyethylene, or added directly to the extruder. In either of these ways, polybutene must be well blended with the polyethylene to form as uniform a layer as possible. The blend can be directly extruded into a thin film form by a flat film blowing or blowing film process which results in the film having only a slightly crystalline material structure, as described in more detail below.

-59 99 • · ·

The crystal structure (crystallinity) of the films of the invention is not easy to measure, but the degree of crystallinity is also indicated by the purity of the film. Crystallinity refers to the brightness and opacity of the film. The luminance is measured by the ASTM D-2457 method from a reflection angle of 20 ° and the opacity is measured by the ASTM D-1003 method, in both cases the film thickness is 51 micrometers. According to the invention, at least 90% luminosity is desirable and the preferred range is between 90% and 120%. The preferred range of opacity is between 4% and 6%, and preferably between 4% and 5.5%. By comparison, films made by known methods have a brightness of between 35% and 70% and an opacity of between 7% and 15%.

The film used in the present invention is preferably made by a blow molding process. In the blow molding process, the polymer blend is extruded through a circular die hole. The tubular film exiting the tool is pulled forward by rotating clamping rollers and the material flattens between the rollers. The tubular film formed between the die and the die roller is often referred to as a bubble. The molten or ductile film is expanded by air or inert gas introduced from the center of the circular opening of the tool. The plastic film can be cooled from the outside by blowing air. Cooling should continue until the material solidifies. The faster the cooling, the lower the crystallinity. In the blown film production process, rapid cooling (hardening) can be accomplished by guiding the expanded film along a chilled mandrel within the bubble. Such a procedure using a chilled mandrel is known in CA 893 216. Canadian Patent (Feb. 15, 1972, to M. Bunga et al

C.V. Thomas). The rapid heat transfer between the foil and the mandrel can be improved by introducing a gas, such as helium, with good heat transfer properties between the mandrel and the bubble. This process is capable of providing the low degree of crystallinity required by the present invention. Conventional blown film forming processes are unable to achieve rapid cooling and therefore do not provide the required low crystallinity.

It will be appreciated that the film of the present invention may contain ultraviolet light stabilizing agents, dyes, oxidation inhibitors, and other known modifiers.

The invention will now be described in more detail by way of examples.

Example 1

On a horizontal stretching machine, a large roll of nonwoven fabric was attempted to be wound tightly (control) with a 51 micrometer stretch stretch wrap. This film is made from a blend of polybutene and linear low density polyethylene by a conventional blow molding process. The apparatus was suitable for prestressing the film in the range of 50% to 650%. The film expanded unevenly, was not sufficiently prestressed, and at 50% to 100% prestress, adhesion was not satisfactory. In some cases, the film was stretched and then stretched to form 2550 mm wide transverse sections having a thickness of 51 micrometers and then 1 micrometer. The stretches were blurred and the stretched sections were transparent. At tension ratios greater than 100%, the film was often torn, which reduced productivity. Similar properties were obtained for 51 micrometers of non-linear polyethylene stretch blown film made by conventional blow molding.

Starting material with a similar composition to that of the control was blown using a chilled mandrel and helium gas flowing around the inside of the film making bubble. The resulting film (labeled A) had a significantly smaller crystalline structure than the control film, which was also demonstrated by the fact that the purity of the A film was enhanced compared to the less pure control film and the haze of the A film was much less than that of the control film. control foil. Although the glossiness and opacity of the A film used in this example do not change the brightness and opacity of the film. ··

-7 measured, films of the same composition and similarly manufactured films had a brightness of 100.2% and a haze of 5.1% (mean value of 10 measurements). Layer A covered larger rolls of paper with 50, 100, 150, 200, 250, 300, 350, 400,450,

With 500, 550, 600 and 650% promotions. There was no film break anywhere in the entire pre-renewal range. The film expanded uniformly with all the protrusions and the adhesion remained good. After stretching, the film was crystal clear. This example clearly illustrates the surprisingly favorable properties of low-crystalline films.

Example 2

Eighteen spools of synthetic fiber were wrapped in a three-layered vertical winding machine. A second vertical tensioned winding machine was combined with two three-layer units. The film used for tension winding of spindles and units was a commercially available polyethylene film for tension winding of 30.5 micrometers. The prestress rate was around 120%. The foil wrapped around the spools and units was blurred and gave the impression of uneven stretching, often called zebra stripes in the art. Although the winding was generally well performed, a film break period was observed once.

The film was then replaced with film A as described in Example 1 and the coating was carried out at a pre-stretch ratio of 350% to 450%. Less than 450% pre-tension occurred, with no tear at 350, 375, and 425%. The film was evenly stretched and clean. Each package required about 125 g of foil. This example clearly illustrates the advantageous features of the present invention.

Claims (12)

Claims A method for wrapping an article with a stretch wrapping film, wherein the film is at least 45 micrometres thick and consists of a polymer blend, characterized in that the film is made from a polymer blend containing at least one polybutene and polyethylene having an average molecular weight of 50010000, which is at least one linear ethylene / C 4 -C 10 α-olefin copolymer having a density between 0.905 g / cm ³ and 0.940 g / cm ³ or a mixture of such copolymer and a second polymer, and this second, 0.910 g / cm ³ and 0.940 g a polymer having a density of between about ³ cm ³ and an ethylene homopolymer or a copolymer of ethylene and vinyl acetate, and the latter in a mixture of polyethylene and a second polymer of up to 70% by weight; furthermore, the film has a slightly crystalline structure. 2. The process of claim 1, wherein the film has a luminance of at least 90%. 3. The process of claim 1, wherein the film has a haze of between 4% and 6%. Method according to any one of claims 1 to 3, characterized in that the article to be covered is cylindrical and of circular cross-section. Method according to any one of claims 1 to 3, characterized in that the ratio of length to height of the object is at least 1.5. A method according to any one of claims 1 to 3, wherein the film is pre-collected at least 200% immediately prior to wrapping the article. • · «♦ 9 · * · Method according to any one of claims 1 to 3, characterized in that the film is pre-stretched at least 400% immediately before the article is wrapped. Process according to any one of claims 1 to 3, characterized in that the ethylene / C ₄ -C ₃ Q α-olefin copolymer is an ethylene / octene-1 copolymer or ethylene / hexene-1 copolymer and has a density of 0.910 and 0.930 g / cm ³ between. A process according to any one of claims 1 to 3 Tl · · ¹ characterized in that polybutene has an average molecular weight of between 700 and 5,000. The process according to any one of claims 1 to 3, wherein the polymer blend comprises 2 to 12 polybutenes. The process according to any one of claims 1 to 3, wherein the ethylene / C 4 -C 10 α-olefin copolymer is an ethylene / octene-1 copolymer or ethylene / hexene-1 copolymer and has a density of 0.910 and 0.930 g / cm ^3. and the polymer blend contains 2 polybutenes. The process according to any one of claims 1 to 3, wherein the film has a thickness of between 50 and 110 micrometers.