JPH03253339A - Polypropylene film for heat-resistant shrinkable packaging - Google Patents

Abstract

PURPOSE:To provide strong nerve and slip properties by applying heat-resistant transparent ink on at least one surface of a heat-shrinkable film composed of crystalline ethylene/propylene copolymer as a main component. CONSTITUTION:The surface of an ethylene/propylene film coated with heat- resistant transparent ink is cured by films, for example, of chlorinated polypropylene resin, cured polyurethane or the like as the main component of the heat-resistant transparent ink, and also its nerve strength and slip properties are provided. As for the heat-resistant transparent ink, chlorinated polypropylene ink and two-part reaction type ink composed of a mixture of polyurethane resin and a copolymer of vinyl chloride and vinyl acetate reacted with an isocyanate curing agent can be used as an example, and such inks can provide curing properties to an ethylene.propylene copolymer and are desirable to be used.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a polypropylene film for shrink wrapping that has excellent heat resistance.

(Prior art) Conventionally known polypropylene films for heat-resistant shrink packaging have the drawbacks of being weak and having poor lubricity with the walls of containers; for example, they cannot be used as shrink labels for containers that undergo retort processing. In this case, in the heat shrink packaging process, poor lubricity causes the film to shrink unevenly in areas where it contacts the wall of the container and areas where it does not, resulting in wrinkles.

In such a retort processing process, secondary shrinkage during retort processing causes the container to shrink in the axial direction, shorten the axial length of the container, move it out of its predetermined position, and also shrink in the circumferential direction, causing slippage. This has caused problems such as wrinkles due to poor quality, peeling of seals, and melt pores, which may lead to poor shrinkage finish.

(Problems to be Solved by the Invention) Conventionally, as heat-shrinkable films, in addition to the above-mentioned polypropylene films, polyvinyl chloride films,
Polyethylene films and polyethylene terephthalate films are known, but polyvinyl chloride films and polystyrene films have poor heat resistance and will melt and decompose during retort processing, for example, while polyethylene terephthalate films may crack due to impact. Because of this, polypropylene films are generally used, but such films also have the drawback of poor finish due to non-uniform shrinkage because they do not have sufficient stiffness. Under these circumstances, there is a demand in the industry for a polypropylene film for shrink wrapping that has a stiffness comparable to that of polyvinyl chloride films, which are said to have good stiffness, and smoothness.

In view of this point, the present inventors conducted extensive research and arrived at the present invention.

(Means for Solving the Problems) The present invention provides a heat-resistant shrink packaging polypropylene film made by coating a heat-resistant transparent ink on at least one side of a heat-shrinkable film mainly composed of a crystalline ethylene-propylene copolymer. It's about film.

Examples of the heat-resistant transparent ink include various types, but there are no particular limitations.2 Inks suitable for the present invention include chlorinated polypropylene inks and mixtures of polyurethane resins and vinyl chloride/vinyl acetate copolymers. An example is a two-component reaction type ink made by reacting an isocyanate curing agent, and such an ink can also impart curability to an ethylene-propylene copolymer film, making it desirable.

Chlorinated polypropylene ink has chlorinated polypropylene as its main component, and silicon or fatty acid amide, such as stearamide, oleic acid amide, erucic acid amide, etc., is added thereto as necessary and dissolved in a solvent.

Chlorinated polypropylene, which is generally used as a solid binder for printing inks, has excellent adhesion to ethylene-propylene copolymer films, heat resistance, and lubricity. In addition, fatty acid amide, silicone, etc. may be added in appropriate amounts as necessary to impart lubricity.

Polyurethane-based two-component reactive ink is a mixture of polyurethane resin and vinyl chloride/vinyl acetate copolymer.
This is dissolved in a solvent, and when used as a printing ink, by adding an isocyanate curing agent, it reacts with the curing agent and improves adhesion, heat resistance, and slipperiness with ethylene/propylene films. will be granted.

At this time, the vinyl chloride/vinyl acetate copolymer has the role of increasing the curing strength of the polyurethane resin and improving the heat resistance. Further, wax, silicone, etc. may be added as a lubricant if necessary.

The surface of the ethylene-propylene film coated with these heat-resistant transparent inks is hardened by a coating film made of the main component of the heat-resistant transparent ink, such as the aforementioned chlorinated polypropylene or reaction-cured polyurethane resin. is strengthened, and lubricity is imparted to the ethylene-propylene film either by its own lubricity or by the action of the added lubricant. With this coating, ethylene and
The propylene film has excellent lubricity and can provide a package with a good shrink finish due to the cured coating applied to the surface. Of course, it is possible to use heat-resistant transparent ink other than the curable type, and there are no particular limitations. It is desirable that such a heat-resistant transparent ink be applied to the entire surface of the film, but it may be applied only partially as long as it is effective.

Furthermore, it is possible to perform ordinary printing such as pictures and letters on the shrinkable polypropylene film using general printing ink, and by applying the above-mentioned heat-resistant transparent ink on top of such ordinary printing, the two-component ink described above can be used as the printing ink for pictures and letters. In some cases, it is desirable to improve the efficiency of printing operations without the need to use a type of printer.

At this time, the amount of heat-resistant transparent ink applied is 0°5g/d~3
The g/d and film thickness are preferably lu to 6u, but are not limited to these values. When the film thickness becomes 6u or more, the thermal shrinkage rate tends to decrease, and if it is less than 1u, the desired purpose may not be achieved, but these values are not particularly limited and values other than the above may be used as necessary. Possible.

Further, the lubricity is desirably within the range of 0.05 to 0.05 in terms of friction coefficient, but is not limited to this value. This 11!
i! If it is less than 0.05, the slipperiness is too good and the label shrink-wrapped the container tends to rotate or fall off.
If it is 05 or higher, the slipperiness is insufficient and shrinkage wrinkles tend to occur, so care may be required.

Lower back strength is Young's modulus: 2.0XIO'~40xlO'k
g/rrl'' is preferable, but it is not necessarily limited to this range, and as long as the waist is good from a sensual point of view, this is sufficient.

However, if the Young's modulus is 4.0×10'kg/crn'' or more, it may become too hard and the shrinkage rate may decrease;
If the amount is less than IO' kg/Crnt, the intended purpose may not be achieved, so care must be taken.

The crystalline ethylene/propylene copolymer of the present invention refers to an ethylene/propylene random copolymer with an ethylene content of 1 to 10% by weight, a crystalline ethylene/propylene random copolymer containing 0.2 to 10 mol% of ethylene monomer units, Examples include ethylene-propylene copolymers, but the above-mentioned values are not particularly limited. In this case, a composition based on an ethylene-propylene copolymer mixed with a butene-based copolymer is also effective, and there is no problem in adding such a third component as appropriate. Moreover, the MFR of the above-mentioned ethylene-propylene copolymer is preferably 1 to 4, but is not limited to this value.

At this time, if the ethylene content is less than the above-mentioned value, low-temperature stretching is difficult, low-temperature shrinkage is difficult, and low-temperature shrinkage tends to be insufficient. Even if the shrinkage rate is increased, the shrinkage rate does not improve, and the film tends to become stiffer, so caution may be required. For example, it is often impossible to apply it to shrink label packaging.

If the MFR is less than 1, it is difficult to stretch and the low-temperature shrinkage tends to be insufficient.On the other hand, if the MFR is 4 or more, the stiffness tends to be weak, so the amount of heat-resistant transparent ink applied is increased. This may also tend to reduce the shrinkage rate, so care must be taken.

In the present invention, a film-like original fabric is formed using the above-mentioned crystalline ethylene-propylene copolymer as a main component, and this is stretched along the -axis or two or more wheels.

At this time, as an example of longitudinal-axial stretching, the film is generally passed between a roll rotating at a low speed at the front end and a roll rotating at a high speed at the rear end, and the film is stretched according to the rotational speed ratio of both rolls. At this time, the stretching temperature is preferably 80° C. to 110° C., and the stretching ratio is preferably 2 to 10 times, preferably about 3 to 6 times. Of course, the stretching temperature, stretching ratio, and stretching means are not limited to the above.

On the other hand, as an example of horizontal uniaxial stretching, it is preferable to carry out using a tenter uniaxial method, at which time the stretching temperature is 60 to 100°C,
The stretching ratio is 3 to 10 times, preferably 5 to 8 times,
Of course, it is not limited to these numerical values.

Furthermore, sequential biaxial stretching in the longitudinal and transverse directions, simultaneous biaxial stretching, etc. are also possible under the conditions shown above.

The above is a flat case, but in addition to this, it is also possible to perform vertical-axis, horizontal-uniaxial, simultaneous two-wheel stretching, etc. on a tube-shaped original fabric by an inflation method.

In this case, there are no particular restrictions, but the raw material, for example 60-11
It is sufficient to heat the tubular film to 0°C (not particularly limited), send pressurized air into the tubular film, and stretch it uniaxially in the longitudinal or transverse directions, or simultaneously stretch it in the longitudinal and transverse directions, for example, by 1 to 5 times in the longitudinal direction. , 1 to 5 times in the horizontal direction, but the present invention is not limited to these values.

Next, if necessary, corona discharge treatment or the like may be performed.

The heat-resistant transparent ink may be applied using an appropriate method such as a normal gravure printing machine or a normal roll coating, but it is preferable to use a multicolor gravure printing machine that can print at the same time as regular printing such as pattern and letter printing. However, the method is not limited to this, and any suitable method may be used.

The gravure plate for gravure printing can have a depth of about 25u x 175 lines/inch, but usually it can be selected appropriately depending on the amount of coating and is not limited to the above values.

To apply heat-resistant transparent ink, first print pictures and letters using a multicolor gravure printing machine, and then apply heat-resistant transparent ink on the printed side of pictures and letters or on both the printed and non-printed sides. Although it is preferable to apply ink, it is of course possible to print pictures and letters and then apply heat-resistant transparent ink in a separate process, but this is of course not particularly limited.

In addition, normal printing can be performed on the surface coated with heat-resistant transparent ink, and you can do it at any time even if you do not perform normal printing at all.

The film of the present invention is most suitable for use as a shrink wrap for containers such as retort processing bottles and cans, but it is also applicable to all other uses including general shrink packaging, and is not particularly limited.

More specific examples of the present invention will be described below along with comparative examples.

(Example) MFRI-2, an ethylene-propylene random copolymer containing 4.7% by weight of ethylene, was produced using a T-die in an extruder with a screw of 45 mm in diameter to a thickness of 300 u and a width of 2
A 50 mm unstretched film was made, and the film was
℃, stretched 6 times in the transverse direction and subjected to corona discharge treatment to obtain a stretched film with a wetting tension of 38 dynes/cm and a thickness of 50 u.

The stretched film is printed with regular printing such as cypress pattern characters using a multicolor gravure printing machine, and then polyurethane resin, vinyl chloride/vinyl acetate copolymer,
2 u of a two-component heat-resistant transparent ink consisting of wax, silicone, and an isocyanate hardener was applied.

The heat shrinkage rate of the film is 100”c for 30 seconds in a glycerin bath.
420%, 50% at 120℃, lubricity is 0.08 to 0.12 in friction coefficient, Young's modulus is 2.5 x 10'
kg/cm".

(Comparative example) Polyvinyl chloride film (PVC), polystyrene film (PS), polyethylene terephthalate film (PET), ethylene propylene film, etc. were prepared in the same manner as in the example except for applying heat-resistant transparent ink. Polymer Film (PP) Obtained 6 The heat shrinkage rate, lubricity, and Young's modulus of the stretched films in the above Examples and Comparative Examples are as shown in Table 1.

Table 1 On the other hand, the films of Examples and Comparative Examples were slit to a width of 188 mm, then center-sealed and formed into tubing with a fold diameter of 9.
A cylindrical film of 0 mm was obtained, and this was cut into a shrink shell of 120 mm. (At this time, Rahel's vertical direction (
The axial direction) is the MD direction of the film, and the transverse direction (circular direction)
was taken as the TD direction of the film. ) Then the corresponding Rahel is 6
Cover the bottle container preheated to 0'C and heat the hot air at a temperature of 180℃.
After passing through the tunnel for 5 seconds, it was filled with 180 g of coffee and subjected to steam and hot water retort treatment at 130° C. for 30 minutes. Table 2 shows the comparison results of the finished state.

It was found that there was no vertical shrinkage due to the second table shrinkage, no uneven horizontal shrinkage, no shrinkage defects such as wrinkles, and the packaging suitability was 6 better than that of the comparative example.

(Effects of the invention) By applying a heat-resistant transparent ink to at least one surface of a heat-shrinkable film made of a crystalline ethylene-propylene copolymer, packaging suitability is improved, and the application can be used, for example, as a shrink label for retort-packed products. We can expect expansion.

○Good shrinkage finish with no wrinkles or vertical shrinkage.

Δ There are slight wrinkles and vertical shrinkage, and the shrinkage finish is poor.

The X label melts and decomposes, rendering it useless as a label.

Patent application A

Claims (1)

[Claims] A polypropylene film for heat-resistant shrink packaging made by applying a heat-resistant transparent ink to at least one side of a heat-shrinkable film containing a crystalline ethylene-propylene copolymer as a main component.