TECHNICAL FIELD

The present invention relates to the high barrier anti-fog stretch film with elasticity that prevents contact of external oxygen, heat, dirt, dust, water, and water vapor with the industrial or food products contained therein; is cost-effective and easy to process, thereby allowing the user to save on time; also reduces the product storage costs; and is resistant to external pressures.

BACKGROUND ART

Importance of plastics have been increasing day by day as a material utilized in packaging of all kinds of food and beverage since the second half of the last century. There are many reasons as to why polymers have many application areas. Some of these reasons may be listed as follows: high level of durability and stiffness, high impact resistance, improved electrical properties, repetitive process cycles, low equipment and production cost. In addition, ensuring and providing high safety standards for consumers has increased the demand for this substance in the packaging industry and its product base has expanded.

Today, there are many types of materials used in packaging. The most practical, modem and quality is stretch film. Stretch film is employed as a packaging material for many products. It is utilized in pallet freight shipments to prevent the materials, by wrapping them, from falling or tumbling or being affected from external weather conditions. It can also be benefitted from in transportation and storage of products; for example, large carpet rolls, fabrics or the like may be wrapped in stretch film while being transported from the manufacturer to a desired location.

Various types of plastics are utilized in packaging due to their flexibility. Polyethylene is one of the most important of these materials. Polyethylene is a thermoplastic film that is produced by way pf the polymerization of the gaseous Ethylene monomer (CH2=CH2) at high pressure and temperature. Having transparent properties, these films are employed, at a higher rate, in packaging printing and in the production of layers for aseptic packaging boxes, compared to other films. They are preferred especially in fruit-vegetable, bakery products, and pharmaceutical packaging, as well as lamination and coextrusion because of their properties including durability, barrier, heat sealability, and low cost. They, however, do not ensure as much clarity as polypropylene (PP) film does.

Stretch films are produced by pre-stretching a film. Pre-stretching the film will increase the strength of the film. Additionally, the pre-stretching process creates a film memory so after being stretched further, the film remembers its previous state, in other words, the film shrinks back. Stretch films are used in the packaging of goods for shipment. They are especially utilized to secure the goods to each other and bind them together on a pallet or the like. For this purpose, the goods are stacked on a pallet and then completely wrapped in stretch film to keep them secured on the pallet.

Stretch films can easily tear at the edges while being wrapped around goods due to different tensions in the film and sharp edges of the goods. While the film has an inherent tension, any additional tension will cause the film to tear and thus the goods will have to be re-wrapped. It is known from EP 0 728 102 that the two outer edges of a longitudinal film are folded inward in order to reduce the risk of tearing at the outer edges of the stretch film. Moreover, the sharp edges or protruding edges of a cardboard can make holes in such a stretch film. Due to the tension in the longitudinal direction of the film, these holes will expand along the entire longitudinal axis of the film and therefore a secure containment of goods on the pallet will not be guaranteed.

Mostly, LDPE is utilized for the production of plastic packaging film. It is highly durable and transparent and has relatively low water vapor permeability. It is chemically very inert and practically odorless and tasteless. One of its most significant advantages is that it is easy to adhere. For this reason, it is also used as a binder for heat sealing in lamination applications. It has a high level of tear strength and is resistant to impact. In addition, it has a common usage temperature regulation feature of up to minimum -50 °C and maximum 70 °C.

Low-density polyethylene (LDPE): The properties of LDPE are the same as HDPE. However, LDPE is less resistant to solvents and mineral oils. Low density polyethylene (LDPE) film thickness varies from 9 microns (as a binding film) to 0.25 mm (as a compositional film). Their width may range from 100 mm to 1 ,000 mm. Among the crucial properties of films, we can mention brightness, resistance to various impacts, elongation, resistance to tear, tensile strength, heat sealability, processability in terms of printing and ease of use in a machine.

On the other hand, low density PE film has a relatively high level of permeability to gases such as oxygen and carbon dioxide. Therefore, it is not a quite suitable option for packaging that is effective against oxidation or for vacuum packaging directly as a film. It is also permeable to many types of oils. Certain products packaged with low density PE should be checked to see if they gradually lose their odor and taste. They can easily be coated on the surface of materials such as paper, cardboard, aluminum foil.

LDPE film can be printed with flexographic and silk screen printing methods. Pretreating the surface is not quite necessary. Low density polyethylene is used for packaged bread, frozen foods, skimmed milk, sausages, fresh-cut meat pieces, and packaging bags.

Ethylene Vinyl Alcohol (EVOH)

EVOH is a moisture sensitive polymer. The presence of water weakens the oxygen barrier property of the material. Therefore, EVOH is usually included in the package as an inner layer in coextrusion surrounded by polyolefins or other polymers that prevent the entry of water vapor. In these structures, the adhesive layer or binding layer between EVOH and polyolefin ensures that they sufficiently adhere to each other. Ethylene vinyl alcohol (EVOH) is manufactured by the controlled hydrolysis of ethylene vinyl acetate copolymer. While OH groups with strong polar properties increase intermolecular forces, ethylene groups provide and ensure molecular mobility. The polymer has randomly distributed units of ethylene and vinyl alcohol. The ratio of ethylene to vinyl alcohol determines the properties of the end product. Very strong barrier properties can be achieved by using the lowest ethylene or highest vinyl alcohol content. On the other hand, the highest ethylene content or the lowest vinyl alcohol content increases flexibility.

Manufacturers must decide on the desired processing properties in order to find the ethylene/vinyl ratio that suits their needs.

Stretch films, in the state of the art, are insufficient in many aspects. For example, when the targeted strength is not achieved, then the product has to be packaged several times, thereby increasing both the use of film, the cost and the packaging time.

In conclusion, the need to eliminate the above-mentioned shortcomings and disadvantages of the prior art has necessitated a development in the relevant technical field.

DESCRIPTION OF THE INVENTION

The present invention relates to a high barrier anti-fog stretch film developed in order to remove the above-mentioned disadvantages and provide new advantages to the relevant technical field.

The aim of the invention is to produce a transparent, lightweight, and economical film with high barrier and anti-fog properties.

Another aim of the invention is to obtain a dirt-resistant film structure on the exterior of the film, thanks to its bright and slippery surface. A further aim of the invention is to manufacture a stretch film whose barrier property has been improved and that can guarantee steady transportation of loads in a single piece, without being subject to any harm, until their arrival point.

Another aim of the invention is to obtain a film that tightly covers, clings onto and protects the relevant product around which it is wrapped, without being detached therefrom while it is carried from one point to another, thanks to its high adherence strength.

Another aim of the invention is to ensure that the film is sufficiently adherent and remains so after it is subject to stretching.

A further aim of the invention is to guarantee that the film acts like a hydrophobe without allowing the leakage of rain water or water from any other source.

A further aim of the invention is to obtain a film that remains durable under normal conditions from -40 °C to +80 °C.

Another aim of the invention is to present an economical and practical product accessible for everyone, instead of high-cost packaging material.

Another aim of the invention is to achieve a product that can be produced in desired thickness.

A further aim of the invention is to ensure that, considering for example the industrial use including placement of goods on pallets, the products on pallets remain intact and together by preventing the products from dispersing and the pallets from sticking to each other.

Another aim of the invention is to create a thin, easily transportable film with absorption property against impacts. A further aim of the invention is to further increase its oxygen barrier feature thanks to ethylene vinyl alcohol, EVOH, in its structure.

Another aim of the invention is to avoid leaving any unwanted and unfavorable odor in the related product as a result of its odorless nature.

A further aim of the invention is to guarantee the visibility of the product around which it is wrapped thanks to its transparent structure.

Another aim of the invention is to provide a film that can be easily applied and takes the shape of the related product thanks to its flexible structure.

A further aim of the invention is to enable production of films with any thickness between 8 microns-30 microns according to the customer’s demand.

DETAILED EXPLANATION OF THE INVENTION

Alternatives selected for this detailed description of the structure subject to the invention are described only to ensure a better understanding of the subject and in a way that will not create any limiting impact

The invention is that it is characterized by consisting 94-100% LDPE and 0-10% process additive in screw B, 0-10% LLDPE modified maleic anhydride and 92-100% LLDPE in screw A, 100% EVOH in screw D, 59-69% LLDPE, 30-40% additive anti-fog, and 0-10% process additive in screw C.

It is characterized in that a preferred exemplary structure of the invention includes

- 99% LLDPE and 1 % process additive in screw B;

- 3% LLDPE and modified maleic anhydride and 97% LLDPE in screw A;

- 100% EVOH in screw D; and

- 64% LLDPE, 35% additive anti-fog, and 1% process additive in screw C.

Barrier stretch film is drawn in stretch film manufacturing machine. Manufacturing method of the product:

- The products to be dosed are placed in Dosing chambers A, B, C, and D in the stretch film manufacturing machine. - Products in screw A is distributed into two channels since the utilized machine has a feed block system.

- Film is drawn from the machine, and as a result, a 5-layer film is obtained.

EVOH added to the invention acts as a barrier against the passage of oxygen and water vapor into the surface wrapped with stretch film. Anti-fog added to the invention prevents occurrence of fog on the surface of stretch film. The material used as additive anti-fog is a kind of masterbatch.

The operating principle of the stretch film manufacturing machine, as well as the temperatures of different parts are given below:

A: Between 170-265 °C

B: Between 170-265 °C

C: Between 170-265 °C D: Between 170-265 °C

Feed block at 265 °C

Head at 265 °C