JPS587445B2 - stretch film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to stretch films used primarily for food packaging, and more particularly for packaging fresh foods.

Generally, in order for this kind of stretch film for packaging to be used without any problems in industry, it must have the following properties.

That is, (a) less springback;

(The repellency of the film and the fact that there is little return when the film is stretched and folded into the bottom of the container.)

) (B) Self-adhesive strength (C) Slipperiness (d) Film MD/TD strength/elongation balance (E) Drop-free property (F) Antistatic property The following items will be explained in detail. .

Regarding the springback property mentioned above, when wrapping stretch film, regardless of whether it is done manually or with an automatic wrapping machine,
A container containing the packaged contents (hereinafter referred to as a tray).

), hold the film edge and pull it (hereinafter referred to as "stretch").

)Also, while the film is being stretched, it is folded into the bottom of the tray and thrown onto a hot plate, and the overlapping part of the film at the bottom of the tray is heated and sealed. There was a problem in that the polymerized portion of the film would open upon restoration, making effective heat fusion impossible.

In addition, the self-adhesive strength (b) is such that when the film is stretched and folded onto the bottom of the tray, it takes a very short time until the overlapping parts of the film are fused using a hot plate (main adhesion).
, is necessary for temporary adhesion to prevent the overlapping parts of the films from opening.

The following slipperiness (c) is required during stretch wrapping work, whether manual or automatic wrapping machines are used.

That is, when the film is unrolled smoothly, passed between rolls, and passed between belts, if the film does not have sliding properties, it will get caught on the rolls and tear, making it impossible to package it.

Performance (d) is when packaging with a manual or automatic packaging machine, the former stretches the film by hand, brings the film into close contact with the food placed on the tray, and then wraps the film at the bottom of the tray. If the film MD/TD has inappropriate strength and elongation characteristics when packaging the films by stacking them and bonding them together, or in the latter case by mechanically stretching the film, the film will tear and the packaging will not be possible.

Therefore, the strength/elongation balance of MD/TD of the film is extremely important.

Furthermore, performance (e) is an inconvenient problem in that when fresh foods are packaged, stored in a freezer, or taken out to room temperature for display, moisture condenses and the film surface turns white and cloudy, making it impossible to see the contents of the package. .

Therefore, there is a need to eliminate such inconvenience by imparting drip-free properties to the film.

Finally, performance (f) is due to residual static electricity generated during film forming, or even if the film is smoothly pulled out or fed out during packaging with an automatic packaging machine, the surface of the metal roll may be damaged during the process. There is a problem in that the film becomes electrically charged due to frictional contact with the metal plate surface, making efficient packaging operations difficult.

To solve this problem, it is necessary to provide the film with (f) antistatic properties.

As mentioned above, the above six performances are necessary for use as a stretch film for packaging without any problems.
Of course, other required performances include transparency of the film through which the contents of the package can be seen and economical cost.

The present invention focuses on the above-mentioned required performance and provides a stretch film that can satisfy both the resin compound composition and the film molding method.

That is, as a base resin, an ethylene vinyl acetate copolymer resin having a vinyl acetate content of 12 to 20% by weight is 93 to 98% by weight.
The reason for this limitation is the transparency of the film, the springback property, and the formability of the film.

Furthermore, this ethylene vinyl acetate copolymer resin has an MI of 0.
．． 5 to 20, preferably 1 to 5.

The adhesive resin is 1.0 to 4.0w, which is a copolymer of vinyltoluene and indene that is nuclear-hydrogenated to 80% or more.
The reason why it is limited to t% is because of the balance between transparency, springback properties, self-adhesion and slipperiness of the film.

This vinyltoluene may contain a small amount of α-methylstyrene or sterene.

With the advent of stretch films that have the above-mentioned performance characteristics, along with recent advances in the food distribution system, stretch packaging for hygienically supplying fresh foods in large quantities has become more popular in production areas, food manufacturers, and Widely used in supermarkets, retail stores, etc.

However, since the films currently in use are made of polyvinyl chloride, the phthalate ester plasticizers and heavy metal stabilizers added to these films bleed onto the surface of the film and can be used in foods that come in contact with the film. Not only is there a concern that it may have a harmful effect, but also harmful hydrogen chloride gas, chlorine gas, etc. may be released as decomposition products during film forming, when cutting film using added heat in packaging, and when used film is incinerated. It is well known that the toxicity of PVC resin products has become a social problem, including cancer caused by residual monomers, especially in hard PVC products.

Despite this, vinyl chloride resin is used as stretch film because the resin is amorphous and has polar groups, so various additives such as plasticizers, lubricants, and tackifiers can be used freely. This is because it can be mixed with other materials, and therefore various desired properties can be imparted to stretch films.

Furthermore, since it has no springback properties, it has the excellent advantage that the overlapping portion of the film at the bottom of the tray can be bonded almost solely by the self-adhesive force of the film surface, making it relatively easy to impart slipperiness to the film surface. be.

In terms of function, the present invention has the same physical effects as conventional PVC resins, but on the other hand, it completely eliminates many of the defects in use of PVC resins, and is a so-called harmless and chemically stable stretch. The purpose is to provide film.

That is, the stretch film of the present invention can be used industrially in the same way as the currently used soft PVC stretch film, and also satisfies the performance that a film must have, and also has no inferiority in appearance such as transparency. It concerns a processed molded product based on a new ethylene vinyl acetate copolymer that poses no health and safety problems.

The gist of the present invention is an ethylene-vinyl acetate copolymer resin with a vinyl acetate content of 12 to 20% by weight, 93 to 98% by weight, and a copolymer of vinyltoluene and indene in an amount of 80%.
1.0 to 4.0% by weight of the above nuclear hydrogenated adhesive resin and 1.0 to 3.0% by weight of 20 mole adducts of ethylene oxide of diglycerin oleate and sorbitan oleate, either alone or in mixture. The present invention relates to a stretch film obtained by inflation-molding a resin composition consisting of the following at a blow ratio of 4.0 to 7.0.

Therefore, in the present invention, the vinyl acetate content of the ethylene-vinyl acetate copolymer resin is set at 12% by weight or more because below this value, the transparency and self-adhesive strength of the film deteriorate and springback occurs. On the other hand, setting the vinyl acetate content at 20% by weight or less and not exceeding that value is because
If the value exceeds this value, the self-adhesive force of the film increases and the slipperiness deteriorates, and inflation molding at a blow ratio of 4.0 to 7.0 cannot be carried out efficiently.

In addition, the reason why we limited the nuclear hydrogenation rate of the adhesive resin to 80% or more of the copolymer of vinyltoluene and indene by nuclear hydrogenation of 80% or more is that when mixed with the base resin ethylene-vinyl acetate copolymer resin, This is because of the transparency of the film, and if the nuclear hydrogenation rate is less than 80%, the transparency of the film deteriorates.

Furthermore, the fatty acid of the diglycerin fatty acid ester of the non-droplet agent of the present invention preferably contains 60% or more of oleic acid, and other fatty acids of C8 to C22 are mixed.

Furthermore, it is preferable that the base is 70% or more of diglycerin.

The above reasons are due to the film's transparency, balance of self-adhesiveness and slipperiness, drop-free property, antistatic property, and other properties, as well as film formability.

The general formula of the 20 mol ethylene oxide adduct of sorbitan monooleate is (R, l, m are 0 to 2
R+l+m=20 with an integer of 0.

)or (x, y are integers from 0 to 20, and x+y=20.

), and its content is preferably 0.3% by weight or less in the resin composition of the present invention, and the reason for its addition is to further improve the slipperiness of the film, and to improve the non-droplet and antistatic properties. This is due to the reason why the prevention property is good.

On the other hand, adhesive resin 1.0 in which 80% or more of the copolymer of vinyltoluene and intene in the resin composition of the present invention is nuclear hydrogenated
If the amount is less than % by weight, the film will have a large springback property and will also have a lower self-adhesive strength, making trench packaging difficult.

On the other hand, if the amount of the adhesive resin exceeds 4.0% by weight, the self-adhesive strength of the film increases, resulting in a decrease in slipperiness and making stretch packaging difficult. Addition of 4.0% by weight or more is practically meaningless, as properties may deteriorate.

Therefore, the most appropriate range for the above-mentioned adhesive resin is 1.0 to 4.0% by weight.

Further, in the resin composition of the present invention, the adduct of digcerin fatty acid ester and sorbitan oleate ester with 20 moles of ethylene oxide alone or as a mixture is 1.0% by weight.
If it is less than 3.0% by weight, the slipperiness of the film deteriorates, making it difficult to package, and if it exceeds 3.0% by weight, the self-adhesion of the film decreases, making packaging difficult. It becomes inefficient.

(preferably 4.5 to 6.0) Therefore, the adduct of diglycerin fatty acid ester and sorbitan oleate ester with 20 moles of ethylene oxide alone or in a mixture is 1
．． A range of 0 to 3.0% by weight is preferable.

The above-mentioned adhesive resin 1.0~93~98 wt% ethylene vinyl acetate copolymer resin having a vinyl acetate content of 12~20 wt% and 80% or more nuclear hydrogenated copolymer of vinyltoluene and indene. 4.0% by weight and 20 moles of ethylene oxide adducts of diglycerin fatty acid ester and sorbitan oleate, either alone or as a mixture.
The reason why the composition consisting of 0 to 3.0% by weight was limited to inflation molding within a specific range, that is, at a blowing ratio of 4.0 to 7.0, is that the blowing ratio is 4.0 or less (ethylene-vinyl acetate copolymer The common knowledge in the industry for the blow ratio in inflation molding is that if the blow ratio is less than 2.0, the strength in the TD direction of the film will decrease, and when the film is stretched during packaging, the film will tear, making it impossible to package. This is because stable inflation film formation cannot be performed.

In other words, high blow ratio (4.0 or more) is achieved by inflation molding.
In order to perform molding, the frost line must be lowered by air cooling immediately after the molten resin exits the die lip, and the tube must be stabilized while being pulled under constant negative pressure in the air ring chamber. The resin composition of the present invention has the characteristics of being capable of stable high blow inflation molding.

Example 1 At least 80% nuclear hydrogenation of 94.5% by weight of an ethylene-vinyl acetate copolymer resin with a vinyl acetate content of 17.5% and a copolymer of α-methylstyrene and/or styrene, vinyltoluene, and indene. A resin composition consisting of 4.0% by weight of the adhesive resin and 1.5% by weight of diglycerin oleate was formed into a stretch film with a thickness of 0.018 mm by inflation molding at a die temperature of 170°C and a blow ratio of 5.0. was molded.

Using this film, the bottom squeeze mold (Fuji Kikai Auto
omac-22) Pillow type (Ibaraki Seiki SP-600)
An automatic packaging machine is used to place various fruits and vegetables and other foods on a tray of 190mm width x 90mm width x 15mm height (No. 3 tray), and a bottom squeeze type automatic packaging machine produces 30 pieces per minute, and a pillow type automatic packaging machine produces 35 pieces per minute.
Film cutting to standard length, film sliding, and packaging speed per minute
The packaging was completed without any problems such as film breakage or heat fusion of the overlapped film at the bottom of the tray.

In addition, the physical properties of the stretch film based on this example are shown in the following table in comparison with commercially available conventional PVC film.

Example 2 The physical properties of a film made by inflation molding the same resin composition as in Example 1 at a die temperature of 170°C and a winding speed of 20 M/min with different B, U, and R, and suitability for packaging with a bottom drawing type packaging machine. are shown in the table below.

Note that the thickness of the film is 0.018 mmt.

Next, regarding the present invention, the reason for limiting the various chemical components constituting the resin composition to a specific range will be explained based on experimental results.

A. Reason for limiting the three-component composition ratio of base resin, adhesive resin, and non-drop agent Material No. 1 to 8 indicate stretch films processed by changing the blending ratio to various values shown in the table.

In addition, each stretch film has a blow ratio of 5.0 at 170°C.
It was formed by inflation molding.

B. Reasons for limiting the base resin, adhesive resin, and non-droplet agent (a) Reasons for limiting the base resin and adhesive resin (b) Reasons for limiting the non-droplet agent As mentioned above, the present invention has a vinyl acetate content of 12% by weight or more. 20
Adhesive resin 1.0 to 4.0% by weight of 93 to 98% by weight of ethylene-vinyl acetate copolymer resin and 80% or more nuclear hydrogenated copolymer of α-methylsterene and/or sterene, vinyltoluene, and indene. % and a 20 mol adduct of ethylene oxide of diglycerol oleate and sorpitan oleate, singly or as a mixture (
In this case, sorbitan oleate E. The content of the O20 mole adduct in the resin composition is preferably 0.3% by weight or less.

) is defined as a resin composition containing 1.5 to 3.0% by weight, and resin compositions outside this range are currently used in the majority (almost 100%) of the market. A film that can be used in place of PVC stretch film is not provided, and on the other hand, the resin composition of the present invention alone cannot be practically used as a substitute for PVC stretch film currently used industrially in the market. It is something.

That is, only by inflation-molding the resin composition of the present invention at a blow ratio within the range of 4.0 to 7.0 can a film that is practical as a stretch film in the current industry be obtained. The benefits of this stretch film are enormous, as it completely eliminates sanitary hazards and has almost all of the functions necessary for packaging.

Claims (1)

[Claims] 1 Adhesive resin 1.0 to 4.0 which is obtained by nuclear hydrogenating 80% or more of an ethylene-vinyl acetate copolymer resin with a vinyl acetate content of 12 to 20% by weight and 93 to 98% by weight and a copolymer of vinyltoluene and indene. 0% by weight, and 1.0 to 3.0% of ethylene oxide adducts of diglycerol oleate and sorbitan oleate alone or as a mixture.
% by weight, at a blowing ratio of 4.0 to 7.
．． A stretch film obtained by inflation molding.