JP4528566B2 - Polyolefin stretch film - Google Patents

Description

  The present invention relates to a polyolefin-based stretch film used for food packaging.

  BACKGROUND ART Stretch films for food packaging are used by overlapping foods such as fruits and vegetables, fresh fish, meat, and prepared dishes directly or by placing the films on a lightweight plastic tray such as polystyrene paper (PSP). As for the type of film, it is suitable for automatic wrapping by automatic packaging machines (hereinafter referred to as "automatic"). "For hands") There is a film.

  Auto film uses an automatic wrapping machine. For example, the film is fed out by a conveyor belt, a saw-shaped cutting blade installed between the conveyor belts is projected, perforated, and cut while transporting the film. . Thereafter, the film is pushed up and stretched by a tray on which food is placed at the center of the cut film, and the film is folded and overlapped by a folding plate. For this reason, it is particularly required that the perforation enters the film cleanly, that the film is not broken when it is stretched and folded, and that it is not easily peeled off after the films are stacked.

  On the other hand, the film for a hand is manually performed by a packaging operator using a handler upper. For example, the end of the film placed on the feeding roll is grasped with both hands, and the entire tray on which the food on the workbench is placed is placed. Roll out the length of film needed to cover and cover the entire tray, then cut the film with heat rays, then stretch the covered film laterally and wrap the films together at the bottom of the tray . When done manually, the film can be drawn out smoothly, and it is easy for the operator to stretch, so that it will not get tired even if it is wrapped for a long time, it will not tear when stretched, and it will not peel easily when it is stacked. The performance different from the film is required.

  Polyvinyl chloride-based stretch films for hands used in food packaging have been mainly used. However, in recent years, PVC-based stretch films, such as hydrogen chloride gas generated during incineration and elution of contained plasticizers, have been found. As an alternative, stretch films based on resins other than vinyl chloride have been used as an alternative.

  As a stretch film for hands, a multilayer film in which an ethylene-vinyl acetate copolymer is laminated to provide adhesion to a layer mainly composed of a thermoplastic elastomer is provided. Is excellent and the productivity is excellent, and therefore, a stretch film having a single-layer structure comprising polyolefin as a main component (hereinafter abbreviated as “PO-based”) is provided.

  Examples of the stretch film composed of this PO-type single layer include those using resins such as high-pressure polyethylene, ethylene / α-olefin copolymer resin, and ethylene-vinyl acetate copolymer. Compared with the above-mentioned vinyl chloride-based stretch film, when used for hands, there is a problem that the elongation is low, the finish of the package remains wrinkles, and the adhesiveness is not sufficient. Many films that have improved the above point have been proposed (see, for example, Patent Documents 1 to 3).

Patent Document 3 improves the tackiness by adding a small amount of petroleum resin or the like as a tackifier to a film composed of a single layer, and the film of the present invention has good transparency, especially hand wrap packaging. It is excellent for hand wrap packaging in that it has elongation and tackiness suitable for. However, when the tackifier is added to such an extent that a necessary degree of adhesive strength can be obtained at the time of wrap packaging, the tackifier migrates to the surface of the film over time, and when the film is fed out by hand wrap packaging. There is a problem that resistance becomes large and workability is lowered, transparency of the film is lowered, and design properties of the product are lowered.
JP-A-52-27451 JP 52-107043 A JP 2001-323114 A

  The present invention has appropriate elongation and adhesiveness in hand wrap packaging, has resistance when unwinding an appropriate film, excessive increase in resistance over time, and decrease in transparency. It is an object to provide a suppressed PO-based stretch film.

That is, the present invention contains linear low-density polyethylene (A) having a density exceeding 910 kg / m ³ , linear low-density polyethylene (B) having a density of 910 kg / m ³ or less, and high-pressure polyethylene (C). And (A) 90 to 20% by mass, (B) 5 to 40% by mass, and (C) 5 to 40% by mass with respect to a total of 100 of (A), (B) and (C) (D) 0.5 to 10 parts by mass of petroleum resin, terpene, terpene derivative, rosin, rosin derivative as component, and 1 to 15 parts by mass of ethylene-vinyl acetate copolymer as component (E) It is a stretch film to which coalescence is added. And it is preferable that (A) component is a C6-C8 alpha-olefin and ethylene copolymer. (B) It is preferable that a component is a C3-C12 alpha-olefin and ethylene copolymer. In addition, it is preferable that the component (D) is a resin that is partially or completely hydrogenated. Furthermore, it is preferable that the vinyl acetate in (E) component is 5-20 mol%. On the other hand, the film of the present invention is preferably a stretch film produced by a T-die method.

  The present invention is easy to recycle scrap, has good transparency, has elongation and tackiness particularly suitable for hand wrap packaging, has resistance when unwinding an appropriate film, and over time This is a PO-based stretch film in which the excessive increase in resistance and the decrease in transparency are suppressed.

The present invention will be described in detail below. Linear low density polyethylenes used in the present invention (A) a density of 910 kg / ^{m 3,} preferably those of more than 915 kg / ^{m 3,} in general is what is referred to as LLDPE. Among these, a copolymer of ethylene and α-olefin is preferable. Examples of the α-olefin include propylene, butene-1, hexene-1, 4-methylpentene-1, hexene-1, heptene-1, octene-1, nonene-1, decene-1, dodecene-1, and the like. Preferably, the α-olefin has 6 to 8 carbon atoms. The ethylene / α-olefin copolymer film having 6 to 8 carbon atoms has high tensile strength and is not easily broken when the film is stretched. Commercially available linear low density polyethylene (A) can be used.

  The amount of (A) is 90 to 20% by mass with respect to the total 100 of (A), (B) and (C). When it exceeds 90% by mass, the transparency of the film is deteriorated. In addition, the film becomes hard and cannot be stretched with an appropriate strength, so that the worker is easily fatigued. On the other hand, if it is less than 20% by mass, the tensile strength of the stretch film is low, and it tends to be broken during film stretching.

Linear low density polyethylenes used in the present invention (B) a density of 910 kg / ^{m 3} or less, preferably of 880 kg / ^{m 3} or more 910 kg / ^{m 3} or less, generally what is referred to as VLDPE is there. Among them, a copolymer having 3 to 12 carbon atoms of ethylene and α-olefin is preferable. Specific examples of the α-olefin include propylene, butene-1, hexene-1, 4-methylpentene-1, hexene-1, heptene-1, octene-1, nonene-1, decene-1, dodecene-1, and the like. Is mentioned. Commercially available linear low density polyethylene (B) can be used.

  The amount of (B) is 5 to 40% by mass with respect to a total of 100 of (A), (B) and (C). If it is less than 5% by mass, the adhesiveness of the film is weakened, and the unwinding of the film becomes too light. In addition, before the portion where the films are overlapped at the bottom of the tray is heat-sealed, the stretched film is peeled off and returned to its original state, so heat sealing cannot be performed. On the other hand, if it exceeds 40% by mass, the adhesiveness of the film becomes too strong, causing a so-called “blocking” in which the film sticks and does not peel when it is made into a roll, and it becomes difficult to feed out when using the film, In some cases, it cannot be paid out. In the present invention, it is preferable that the amount of (A) is larger than that of (B) in order to give the film a waist.

  The high-pressure polyethylene (C) of the present invention is produced by a high-pressure radical polymerization method, and commercially available products can be used. The amount of (C) added is 5 to 40% by mass with respect to the total 100 of (A), (B) and (C). If it is less than 5% by mass, the melt tension becomes low and the film width fluctuates, so that the ear cut cannot be stably performed. On the other hand, if it exceeds 40% by mass, the film strength is reduced and the film is easily broken during stretching.

  The film of the present invention comprises, as component (D), a commercially available C5 (aliphatic), C9 (aromatic), C5 and C9 copolymer or cyclopentadiene petroleum resin, terpene, terpene derivative, rosin And at least one of rosin derivatives. As the component (D), a plurality of components selected from the above can be added. Inclusion of these makes it possible to increase the strength during film stretching and to impart adhesiveness to the film, and to easily satisfy several required performances as a hand stretch film at the same time. As the component (D), it is preferable to use a partially or completely hydrogenated resin among the above-mentioned resins, since the compatibility with other resin components is good and the transparency of the film becomes high. (D) The addition amount of a component is 0.5-10 mass parts with respect to the total 100 of (A), (B), and (C). When the amount is less than 0.5 parts by mass, the effect of improving the ease of tearing during film stretching is hardly observed. On the other hand, when the amount exceeds 10 parts by mass, when the resin raw material is charged into the extruder during film formation, the resin bite is poor and it is difficult to stably produce a film. On the other hand, the film formed becomes too sticky and blocking occurs.

  It is important that the film of the present invention contains an ethylene-vinyl acetate copolymer as the component (E). Since the component (E) has not only an effect as a tackifier but also a good compatibility with the component (D), the component (D) can be prevented from migrating to the surface over time, and blocking does not occur. . (E) As for the ratio of vinyl acetate in a component, 5-20 mol% is preferable. If it is less than 5 mol%, the above-mentioned effect is difficult to obtain. If it exceeds 20 mol%, the tackiness becomes too strong and blocking may occur. (E) The addition amount of a component is 1-15 mass parts with respect to the total 100 of (A), (B), and (C). The said effect is not acquired as it is less than 1 mass part. If it exceeds 15 parts by mass, the tackiness becomes too strong and blocking occurs. The effect of the present invention is obtained for the first time as a synergistic effect by adding the components (D) and (E) to the components (A), (B) and (C). is there.

It is preferable to add an antifogging agent to the stretch film of the present invention. The addition amount is 1 to 5 parts by mass, more preferably 1.5 to 4 parts by mass. Examples of antifogging agents include surfactants conforming to the PL standard (food additive list), glycerin fatty acid (C8-22) ester, sorbitan fatty acid (C8-22) ester, propylene glycol fatty acid (C8-22) ester, Sugar fatty acid (C8-22) ester, citric acid mono (di or tri) stearic acid ester, pentaerythritol fatty acid (C8-22) ester, polyglycerol fatty acid (C8-22) ester, polyoxyethylene (20) glycerol fatty acid (C8-22) ester, polyethylene glycol fatty acid (C8-22) ester, polypropylene glycol fatty acid (C8-22) ester, polyoxyethylene (9.5) dodecyl ether, polyoxyethylene (4-14.30-50) Alkyl (C4, 9, 12 Condensation products of phenyl ether, N, N-bis (2) -hydroxyethyl fatty acid (C12-18) and diethanolamine, polyoxypropylene polyoxyethylene block copolymer, polyethylene glycol (molecular weight 200-9500), polypropylene glycol, etc. One or more of the above can be added.

  If necessary, a propylene copolymer can be added to the stretch film of the present invention. For example, a propylene-ethylene copolymer can be added to adjust the strength of the film.

  If necessary, a stabilizer, an antistatic agent, and a processability improving agent can be added to the stretch film of the present invention. For example, 2,6-di-t-butyl-p-cresol (BHT), tetrakis [methylene-3- (3,5-di-tbutyl-4-hydroxyphenyl) propionate] methane, n-octadecyl-3- ( 4'-hydroxy-3,5'-di-t-butylphenyl) propionate represented by phenolic stabilizers, bis (2,4-di-t-butylphenyl) pentaerythritol diphosphite and tris (2, Phosphite stabilizers such as 4-di-t-butylphenyl) phosphite, glycerin esters of fatty acids having 8 to 22 carbon atoms, sorbitan acid esters, antistatic agents such as polyethylene glycol esters, calcium stearate, etc. A processability improver represented by a fatty acid metal salt can be added.

  The thickness of the stretch film of the present invention is a range used as a normal stretch film, that is, about 5 to 30 μm, preferably about 8 to 20 μm.

  It does not specifically limit to the manufacturing method of the stretch film for hands of this invention. A known method can be used, but the T-die method is preferred. The T-die method can suppress the crystallinity of the film and improve the transparency because the molten resin can be rapidly cooled by a cooling roll, compared to the inflation method. In addition, the film thickness accuracy is high, and the production rate is superior to the inflation method. The stretch film of the present invention can return scraps such as ears generated during film formation without any trouble. This is because scrap does not contain anything other than the ingredients used. Even if the scrap is returned, the transparency and strength of the film are not lowered, and the occurrence of gel or the like is not a problem.

The following examples further illustrate the present invention. The properties and properties of the raw materials used and the stretch film were measured and evaluated by the following methods.
(Evaluation methods)
1) Density The density was measured according to JIS K6760.
2) Melt flow rate (MFR)
The measurement was performed according to JIS K6760. It is a value of 190 ° C. and a load of 2.16 kg.
3) Transparency (Haze%)
The measurement was performed according to ASTM-D1003.
4) Hand wrapping property A film having a width of 300 mm is passed through a handler top (ARC Co., Ltd. POLYWRAPPER 40), and then the film edge is grasped with both hands and the film is fed out. Cover the entire tray with food on the workbench with the unrolled film, and cut the film with heat rays. The covered film is stretched in the horizontal direction and the films are stacked on the bottom of the tray. Based on the judgment criteria shown in Table 3, elongation, tearing, adhesiveness, and wrinkles at the time of packaging finish were evaluated.
4) Unwinding resistance force The resistance force when unrolling a film with a width of 300 mm and a length of 500 m wound around a paper tube with an outer diameter of 85 mm was measured with a tensile tester at a speed of 500 mm / min. The measured value is shown. Moreover, the result evaluated based on the criteria shown in Table 3 is also shown.
5) The aging film was stored for 1 month in an environment of 30 ° C., and the feeding resistance and transparency were evaluated based on the judgment criteria shown in Table 3.

Example 1
Ethylene / α-olefin copolymer (MFR = 2.0 (190 ° C., 2.16 kg)) having a density of 913 kg / m ³ as a linear low density polyethylene (A) and an α-olefin having 6 carbon atoms ) 50% by mass, a linear low density polyethylene (B) having a density of 900 kg / m ³ and an α-olefin having 4 carbon atoms, an ethylene / α-olefin copolymer (MFR = 2.0 (190 C., 2.16 kg)) 25% by mass and a high-pressure polyethylene (C) (MFR = 2.0 (190 ° C., 2.16 kg)) having a density of 924 kg / m ³ and hydrogenated petroleum resin (softening point) 125 ° C) (D) 2 parts by weight, ethylene acetate vinyl acetate copolymer (E) 3 parts by weight of vinyl acetate content 15 mol% and 2 parts by weight of diglycerin monooleate as an antifogging agent Things To produce a stretch film having a thickness of 12μm at molding by die method.

  For film formation, (A), (B), (C), (D) and (E) are dry blended, and a full flight screw with L / D = 28 is used with a 65 mm single screw extruder manufactured by Toshiba Machine. Then, using a T-die having a die width of 550 mm and a die lip of 0.7 mm, the temperature was set at 180 ° C. to 230 ° C. and the take-up speed was 60 m / min.

(Examples 2 to 5)
The same raw material resin as Example 1 was used, the ratio was changed as Table 1, and the stretch film was produced.
(Example 6)
A film was produced in the same manner as in Example 1 except that the vinyl acetate content of the ethylene-vinyl acetate copolymer of Example 1 was changed to 10 mol%.
The evaluation results of the films of Examples 1 to 6 are summarized in Table 1. All the films had no problem in transparency and hand wrapping properties, and the change over time in the feeding resistance was within an acceptable range.

(Comparative Examples 1-4)
The same raw material resin as Example 1 was used, the ratio was changed as shown in Table 2, and the stretch film was produced.
(Comparative Example 6)
The same resin as in Example 6 was used, and the ratio was changed as shown in Table 2 to prepare a stretch film.
The evaluation results of the films of Comparative Examples 1 to 6 are summarized in Table 2. In Comparative Examples 1 to 3 and 6, the feeding resistance force after the lapse of time was large, and the feeding could not be performed or was difficult to feed. Comparative Examples 4 and 5 were inferior in hand wrapping itself.

Claims (6)

A linear low-density polyethylene (A) having a density exceeding 910 kg / m ³ , a linear low-density polyethylene (B) having a density of 910 kg / m ³ or less, and a high-pressure polyethylene (C); ), (B) and (C) with respect to a total of 100 (A) 90 to 20% by mass, (B) 5 to 40% by mass and (C) 5 to 40% by mass as component (D) Stretch in which at least one of 0.5 to 10 parts by mass of petroleum resin, terpene, terpene derivative, rosin and rosin derivative and 1 to 15 parts by mass of ethylene-vinyl acetate copolymer as component (E) are added. the film.   The stretch film according to claim 1, wherein the component (A) is a copolymer of an α-olefin having 6 to 8 carbon atoms and ethylene.   (B) The stretch film of Claim 1 or Claim 2 whose component is a C3-C12 alpha-olefin and ethylene copolymer. The stretch film according to any one of claims 1 to 3, wherein the component (D) is a partially or completely hydrogenated resin.   (E) The vinyl acetate in a component is 5-20 mol%, The stretch film of any one of Claims 1-4.   The stretch film described in any one of claims 1 to 5 manufactured by a T-die method.