JPH0214935B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a packaging film, and more particularly to a method for producing a packaging film that has excellent self-adhesiveness (wrapping properties), heat resistance, and cutting properties. BACKGROUND ART Conventionally, so-called wrap films used for household and commercial purposes include films made from polyvinylidene chloride resin and high-pressure low-density polyethylene resin. In addition to self-adhesiveness, these wrap films are required to have various properties such as cuttability during use, strength, transparency, and heat resistance. However, since polyvinylidene chloride resins and polyvinyl chloride resins contain large amounts of chlorine, there are problems such as generation of chlorine gas when incinerated and the toxicity of the plasticizers contained in large amounts. For this reason, high-pressure low-density polyethylene resins are also used, which have fewer problems, but they have the disadvantage of having very low self-adhesiveness and the need to add various tackifiers. It has the disadvantage of poor cutability. Furthermore, polyvinylidene chloride resin wrap films are biaxially stretched, so they tend to tear diagonally when cut, and they also shrink significantly when heated in a microwave oven. On the other hand, wrap films made of high-pressure low-density polyethylene resin do not have sufficient heat resistance, so if they are used for cooking or heating in microwave ovens, which are becoming increasingly popular these days, the film may melt and break, or the film may become damaged. Because they have the drawback of being fused together and torn, or melting and adhering to containers, etc., their uses are severely limited. In order to solve these problems, it has also been proposed to use polypropylene resin.
However, when polypropylene resin is used, although it is satisfactory in terms of heat resistance, it cannot satisfy the most important performance requirements of wrap films, such as self-adhesiveness and cutability. Therefore, if a tackifier is added to impart self-adhesive properties, the self-adhesive properties will be improved, but the cutting properties will be poor and the product will not be usable. In addition, when the film is stretched for the purpose of improving cuttability, the tackifier may not bleed, or even if the orientation is relaxed and allowed to bleed, the tackifier that bleeds out aggregates into beads and gives the film a transparent appearance. It is not possible to obtain a film with excellent gloss and gloss, and furthermore, there are drawbacks such as interfacial destruction occurring when the stacked films are peeled off. Therefore, no wrap film made of a polypropylene resin that satisfies both self-adhesiveness and cuttability has so far been obtained. The object of the present invention is to eliminate these above-mentioned drawbacks and provide a method for producing a packaging film suitable as a wrap film. That is, the present invention consists of a resin composition in which a tackifier is blended with a polypropylene resin, and a film stretched at least in the transverse direction is subjected to surface oxidation treatment and heat treatment at a temperature below the crystal melting point and above 50°C. The present invention provides a method for producing a packaging film, which comprises post-winding and then aging the wound film at a temperature of 60 to 120°C for 30 minutes or more. The type of polypropylene resin used in the present invention is not particularly limited, and may be a propylene homopolymer or a copolymer of ethylene or the like and propylene. Further, the copolymer of propylene and other components such as ethylene may be either a random copolymer or a block copolymer. Note that the physical properties of this polypropylene resin may be selected appropriately depending on various uses and conditions, but usually it has a melt index (MI) of 6 to 11 and a density of 0.900.
~0.910g/10 minutes is preferred. Next, as the tackifier added to the polypropylene resin, a nonionic surfactant or a relatively low molecular weight resin of 3000 or less is used. Here, nonionic surfactants refer to esters of alcohol and fatty acids and their derivatives, and examples of alcohols used here include glycerin, polyglycerin, sorbitan, sorbitol, pentaerythritol, polyethylene glycol, and polypropylene glycol. Examples of fatty acids include linear unsaturated fatty acids with an alkyl group of 5 to 13 carbon atoms, and alkyl groups with 17 to 13 carbon atoms.
There are 21 straight chain unsaturated fatty acids. Furthermore, derivatives of the esters include ethylene oxide adducts and the like. Specific examples of this nonionic surfactant include polyoxyethylene alkyl ether, polyoxyethylene alkyl phenyl ether, polyoxyethylene alkyl ester, polyoxyethylene sorbitan alkyl ester,
Examples include polyoxyethylene alkylamine, glycerin fatty acid ester, sorbitan fatty acid ester, pentaerythritol fatty acid ester, propylene glycol fatty acid ester, trimethylolpropane fatty acid ester, and the like. The blending ratio of this nonionic surfactant and the above polypropylene resin is
1 to 5 parts of nonionic surfactant per 100 parts by weight
It is preferable to use within the range of parts by weight. When the amount of nonionic surfactant is less than 1 part by weight,
Sufficient self-adhesiveness cannot be obtained, and if the amount exceeds 5 parts by weight, the nonionic surfactant that bleeds onto the surface of the film will transfer to the surface of the packaged object, which is not preferable. Moreover, as the nonionic surfactant, one that is liquid at room temperature is preferable. In addition, examples of resins with a relatively molecular weight of 3000 or less include terpene resins, coumaron resins, coumaron-indene resins, xylene resins, mesitylene resins, petroleum resins, and low polymerization degree polyolefins (polyethylene, polybutene, polyisobutylene, etc.). can be mentioned. This molecular weight
The blending ratio of relatively low molecular weight resin of 3000 or less and the above polypropylene resin is 100 parts by weight of the latter,
The former is preferably used in a range of 1 to 10 parts by weight. In the present invention, first, a resin composition in which a tackifier consisting of a nonionic surfactant or a relatively low molecular weight resin with a molecular weight of 3,000 or less is blended with a polypropylene resin is prepared by a T-die method or an inflation process. A raw film is produced by melt extrusion film formation by a method such as a method. Next, the obtained original fabric is stretched by a tubular method, a tenter method, or the like. In the present invention, it is necessary to stretch the original film at least in the transverse direction using a biaxial stretching device or the like.
The stretching ratio is 2 times or more in the transverse direction, preferably 3 to 6
It's double. By stretching the raw tube at least in the transverse direction in this way, it is possible to obtain a film with improved cuttability and strength and a good surface condition. The thickness of the film is usually 6 to 60 microns, preferably 8 to 15 microns. Although the film thus obtained has improved cutting properties, it does not have self-adhesion and cannot necessarily be said to be fully satisfactory as a wrap film. Therefore, in the present invention, the film thus obtained is cut open with a slitter or the like, subjected to surface oxidation treatment and heat treatment, and then wound up, and then the wound up film is aged to produce a packaging film. In the present invention, either the surface oxidation treatment or the heat treatment may be performed first, but the surface oxidation treatment is usually performed under tension before winding.
Further, heat treatment is usually carried out in a relaxed state. There is no particular restriction on the method of surface oxidation treatment;
Corona discharge treatment, flame treatment, ozone treatment, ultraviolet treatment, oxidizing chemical treatment, etc. can be applied.
Particularly preferred is corona discharge treatment. The degree of oxidation on the surface varies depending on the surface oxidation treatment method, etc., and is difficult to determine unambiguously. In the case of corona discharge treatment, it is preferable to carry out the treatment so that the surface tension is usually 35 dyn/cm or more. Such surface oxidation treatment allows the tackifier to bleed uniformly onto the film surface. Further, the method of heat treatment is not particularly limited, and may be carried out by a heated roll method, an oven method, or the like. The heat treatment conditions are below the crystal melting point and 50
Perform at a temperature of ℃ or above. Further, the heat treatment time varies depending on the heat treatment temperature, the thickness of the film, etc., and is difficult to determine unambiguously, but is usually 2 to 20 seconds. Note that after the heat treatment, it is preferable to cool the film using a cooling roll or the like. The film subjected to the surface oxidation treatment and heat treatment is wound up into a paper tube or the like, and then the wound film is aged. Considering film productivity, etc., at a temperature of 60 to 120°C for 30 minutes or more, preferably
Maturing at 90-110℃ for 1-5 hours. In addition, in the present invention, in the resin composition,
Various additives can also be added as appropriate. Examples of additives include lubricants and anti-blocking agents, including metal soaps such as calcium stearate and barium stearate, fatty acid amides such as stearic acid amide and palmitic acid amide, stearic acid monoglyceride, powdered silica, Examples include diatomaceous earth, kaolin, and talc. According to the method of the present invention having such a configuration, it is possible to obtain a film that satisfies both properties of self-adhesiveness, heat resistance, and cuttability. Moreover, since the film obtained by the method of the present invention is stretched and oriented, it has high strength and also has excellent cuttability, and does not tear diagonally when cut. Furthermore, the thickness of the film can be reduced by stretching and orientation, resulting in resource savings. Furthermore, the film obtained by the method of the present invention has excellent transparency and good appearance. Moreover, it has excellent heat resistance, making it suitable for use when cooking and heating in a microwave oven.
Furthermore, when disposed of by incineration, it does not generate chlorine gas unlike polyvinylidene chloride resin or polyvinyl chloride resin, making it highly safe. Therefore, the present invention provides household wrapping film,
This method is useful as a method for producing packaging films such as wrap films for commercial use. Next, the present invention will be explained by examples. Examples 1 to 4 Films were manufactured using the apparatus shown in FIG. First, polypropylene resin (density 0.91g/cm ³ ,
A resin composition prepared by blending a predetermined amount (using a master batch) of the tackifier shown in Table 1 with MI7g/10 minutes) was extruded using a tube manufacturing extruder 1 at a resin temperature of 200°C using a water-cooled downward blowing method, and the diameter was 100mm. A raw tube 2 having a thickness of 100 μm was obtained. The obtained original fabric tube was then introduced into the tubular method biaxial stretching device 3,
Stretching machine entrance speed 2.2m/min, stretching machine exit speed 8.0
A film (thickness: 7 μm) with a stretching ratio of about 4 times in both the longitudinal and transverse directions was obtained under the stretching conditions of m/min. Next, the film was cut open with a slitter 4 and heated to 130°C.
Heat treatment was performed using a heating roll 5 for a contact time of 4 seconds, and after cooling with a cooling roll, the surface tension became 38 dyn/
A surface oxidation treatment was performed using a corona discharge device 6 so that the thickness was at least cm. Next, the film was wound up into a paper tube using the winding device 7, and the wound film was aged at 100° C. for 5 hours using the aging device 7 (heating furnace) to obtain a packaging film. Table 1 shows the physical properties of the obtained film and the evaluation results as a wrapped film. Comparative Example 1 A resin composition prepared by blending a predetermined amount of the tackifier shown in Table 1 with polypropylene resin (the same as used in Examples 1 to 4) was heated in a 50 mmφ die (rip opening degree 0.5).
A film with a diameter of 100 mm and a thickness of 10 μm was obtained by extrusion using a water-cooled downward blowing method at a resin temperature of 200°C. I got it. Table 1 shows the physical properties of the obtained film and the evaluation results as a wrapped film. Comparative Examples 2 to 6 Films were obtained in the same manner as in Example 3, except that only the treatment steps shown in Table 1 were carried out. Table 1 shows the physical properties of the obtained film and the evaluation results as a wrapped film. Comparative Example 7 High-pressure polyethylene resin (density 0.922 g/cm ³ ,
A resin composition containing 1% by weight of sorbitan monooleate (MI5g/10min) was molded using a T-die extruder at a temperature of 260°C to obtain a film with a thickness of 10μ. Table 1 shows the physical properties of the obtained film and the evaluation results as a wrapped film.

【table】

[Table] *4 Polyglycerin fatty acid ester
〓B:HLB6.2
In Comparative Example 6, the bleeding tackifier aggregated and a mottled pattern appeared on the film surface.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of the apparatus used in the method of the invention. DESCRIPTION OF SYMBOLS 1...Tube manufacturing extruder, 2... Raw tube, 3... Biaxial stretching device, 4... Slitter, 5
... Heating roll, 6 ... Corona discharge device, 7 ...
Winding device, 8... aging device.

Claims (1)

[Claims] 1. A film made of a resin composition containing a tackifier blended with a polypropylene resin and stretched at least in the transverse direction is surface oxidized and heated at a temperature below the crystal melting point and above 50°C. After heat treatment, the film is rolled up, and then the rolled film is heated for 60~
A method for producing a packaging film characterized by aging at a temperature of 120°C for 30 minutes or more. 2. The method according to claim 1, wherein the surface oxidation treatment is a corona discharge treatment.