JPS5912544B2 - film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a film for food packaging, and particularly to a film made of polyethylene terephthalate suitable for packaging confectionery such as rice crackers, drops, and candy.

Cellophane has conventionally been used for packaging confectionery, but the present invention provides a polyethylene terephthalate film that is superior in material quality to cellophane.

A film of polyethylene terephthalate, which is a synthetic resin, is melt-formed under heating and has the advantage of being essentially cleaner than cellophane.

Moreover, it has significantly lower hygroscopicity than cellophane, making it suitable for packaging confectionery that requires a moisture-proofing effect. Furthermore, even though it is a thin film, it is stronger than cellophane and is preferable in terms of resource saving, and the packaging process is simple and low cost. The present invention is a uniaxially or biaxially stretched film made of polyethylene terephthalate, which has a density at 25°C of 1.
5 in the range of 350 to 1.375 fl/cil, 1
Dry heat shrinkage at 20°C is at least 10%, preferably 20%
and the thickness of the film is 6-30 microns, preferably 12-25 microns,
A food packaging film that wraps food by twisting both ends.

10 The present invention will be explained.

A film suitable for wrapping foods, especially confectionery, and twisting both ends must have the property of not recovering from mechanical twisting deformation.

As for specific properties, there are 15 that are easily plastically deformed.
It must be thin and must not tear during the packaging process. Polyethylene terephthalate in the present invention is a polymer blend containing a small amount of other synthetic resins, if the main component is polyethylene terephthalate, and a small amount (15
It may also be polyethylene terephthalate containing other copolymerizable components (up to ml%) and non-toxic additives such as lubricants and pigments commonly used by those skilled in the art.

The No. 25 film is formed by the well-known inflation method or T-die method, and can be uniaxially or biaxially stretched as necessary to exhibit predetermined performance.

In particular, during film formation, air or a cooling drum is used to heat the film from room temperature to 6 ℃.
If rapidly cooled to a temperature range of 0℃, the density will be 1.331 to 301.3.
A substantially amorphous film in the range 381/Cd is obtained. By stretching this unstretched amorphous film, the film can be made thin and have high strength and low elongation. At this time, the density of the film increases from approximately 1.350 to 351.375 g/Clit depending on the stretching ratio and temperature. If necessary, the density can be increased to about 1.42θ/Cd by heating the stretched film. Similarly, the dry heat shrinkage rate and film thickness can be adjusted.
Therefore, engineers who are skilled in film manufacturing can suitably combine film forming and stretching heat treatments to meet the specified requirements for the density, dry heat shrinkage rate, and film thickness of polyethylene terephthalate based on the results of trial-and-error experiments. Can be designed. The density of the film of the present invention must be in the range of 1.35 to 1.3759/(:!l. If the density is less than 1.35f!/Cd, especially less than 1.3359/ml, it is difficult to wrap confectionery etc. The twisted part of the film becomes cloudy and loses its aesthetic appearance.It also tends to break during packaging, resulting in poor process stability.The preferred density is 1.359/Cd or higher, and a sufficiently stretched and strong film will not exceed this density. On the other hand, the twisting effect decreases as the density increases.A film with a high density can easily recover from twisting deformation.A film suitable for packaging is one in which confectionery (candy) is wrapped in the film and the edges are tied together. The rotation (return angle of twist after 360 twists (hereinafter referred to as recovery angle) must be within 1400 degrees, particularly preferably less than 120 degrees).
This condition corresponds to a film density of 1.389/d or less, particularly 1.3759/Cd or less. Since the torsional recovery is preferably as small as possible, a film having a recovery angle of 60 degrees or less has a density of 1.3759/d or less. Actually, 120
If the recovery angle is within 300 degrees, it is suitable for packaging confectionery. Therefore, the density of polyethylene terephthalate (homopolymer) is 1.35 to 1.375f! /Crlt range. Polyethylene terephthalate films with a relatively low degree of crystallinity are usually stretched and often do not require heat treatment (heat setting). As a result, films suitable for packaging have a relatively high dry heat shrinkage rate. A dry heat shrinkage rate of at least 10% is required. This dry heat shrinkage rate represents the shrinkage value after shrinkage with respect to the original length measured by exposing a film specimen to dry air at 120° C. for 1 minute under no tension. A preferable dry heat shrinkage rate is 20% or more, and there is a correspondence between the dry heat shrinkage rate and the recovery angle after twisting, and a film exhibiting a higher shrinkage rate has a smaller recovery angle and is suitable as a packaging film. A film having a shrinkage rate of usually 10 to 70%, particularly 20 to 60% is preferred. Curiously, the recovery angle does not have a direct correlation with the film's elongation at break, but it does have a correlation with the dry heat shrinkage rate, and this correlation holds true regardless of the film thickness in the range of 6 to 30 microns. . However, if the thickness of the film is too thin, it will easily break and the film will not be fed smoothly during the packaging process.

If the film is too thick, it will become hard and rigid, resulting in a poor appearance after packaging, and this is also undesirable since it requires a large amount of packaging material. As a result, the appropriate film thickness is in the range of 6 to 30 microns, and a versatile film with a thickness of 12 to 25 microns is preferred. The packaged confectionery needs to have a luxurious feel and bulk, and for bulk, a somewhat thick and hard film is preferable. A particularly preferred embodiment of the present invention is a uniaxially or biaxially stretched film made of polyethylene terephthalate, which has a density in the range of 1.35 to 1.3759/Cflt at 25°C;
The dry heat shrinkage rate at 20°C is 20% or more, and the film thickness is 12 to 25 microns.

Another embodiment of the present invention is a confectionery package with a film thickness of 12 to 25 microns, which has a twist angle (recovery angle) of 1200 or less when left after wrapping the confectionery in the film and twisting the end once. polyethylene terephthalate film.

In the present invention, the density of the film is measured at 25 DEG C. by a density gradient tube method (for example, using a mixed solution of carbon tetrachloride and n-heptane), a float-sink method, or the like.

The present invention will be further explained below with reference to Examples.

Example Polyethylene terephthalate with an intrinsic viscosity of 0.64 was melt-extruded in a conventional manner (melting temperature 286°C), rapidly cooled on a cooling roll, and then extruded in the machine direction at 82-88°C (temperature change) to 3.0-368°C. (stretching ratio change), then stretched 3.1 to 3.8 times in the width direction at 105 to 110°C, and then passed through a heat setting chamber (temperature changed from 70 to 230°C) to obtain a thickness of 4 with various densities. Table 1 shows an example in which a Tani-tane film with a thickness of ~40μ was produced and the heat shrinkage rate (120°C) and recovery angle were measured.

From the table, the diameter of the film with a thickness of 4.1 μ is approximately 1811 mm.
When packaging spherical candy, the film was easily torn, and when it had a low density (low crystallinity), it was too thin and unsuitable as a food packaging material. Films with a thickness in the range of 6 to 30 microns are susceptible to plastic deformation unless the density is high, so the recovery angle is small and they have properties suitable as food packaging materials. When the film becomes thick, about 40 μm, the plastic deformability slightly decreases (the recovery angle increases), and the packaging processability becomes unfavorable. Furthermore, the transparency of the film and the aesthetic appearance after packaging are also not good. As a result, it is found that the film thickness is preferably 6 to 30 microns. If the recovery angle of the film is 120 degrees or less, there will be no problem in packaging processability, but if the recovery angle is in the range of 120 to 140 degrees, there is a risk that the film will return after packaging and result in defective packaging.
It has been found that if it exceeds 14', it loses its practicality.

Claims (1)

[Claims] 1 A film made of polyethylene terephthalate, which has a density at 25°C of 1.35 to 1.375 g/
cm^3 range, has a dry heat shrinkage rate of at least 10% at 120°C, and has a film thickness of 6 to 30 microns, wrapping food with twisting at both ends. Food packaging film.