JP2001138453A - Stretch film for packaging food - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a stretch film for packaging a food at a low cost capable of finishing good packaging by incorporating excellent transparency, delayed stress developing characteristic and excellent packaging workability. SOLUTION: In the stretch film for packaging a food comprising at least three layers of a central layer and both outer surface layers, at least one of the central layer is formed of a resin composition containing a mixture of a crystalline polypropylene resin having a flexual modulus of 200 to 500 N/mm2 and a petroleum resin having a softening point of 130 deg.C or higher or its hydrogen-additive of 60 to 95:40 to 5 of weight ratio as a main body, a total layer thickness of 7 to 15 μm and a layer ratio of the central layer of 40 to 90%. In this case, the composition may contain an amorphous polypropylene resin having a flextural modulus of 500 N/mm2 or less.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a stretch film for food packaging. More specifically, the present invention relates to a stretch film for food packaging mainly composed of a polyolefin-based resin excellent in packaging workability and excellent in stretchability with good packaging finish.

[0002]

2. Description of the Related Art In supermarkets and the like, a method of putting foods such as fruits and vegetables, fresh fish, meat, and the like into trays, covering the trays with a packaging film (stretch film), and wrapping and selling them is often used. This packaging is performed by stretching the stretch film over the tray containing the food while stretching the film, overlapping the films on the outer surface of the bottom of the tray (so-called overlapping), and joining the portions. This packaging is done manually or with an automatic packaging machine.Whether or not this packaging work can be carried out smoothly and whether or not the finish is beautiful, especially in the case of automatic packaging, is to use stretch film. Depends on the nature of

Conventionally, a flexible polyvinyl chloride film having a flexural modulus of 80 to 180 N / mm ² has been frequently used as the stretch film. The polyvinyl chloride film generates hydrogen chloride gas during incineration and contains the same. There is a problem that the plasticizer may be eluted, and a resin film, especially a polyolefin resin film, which is a non-plasticizer and replaces the polyvinyl chloride film, is being developed. For example, a low-density polyethylene resin stretch film and an ethylene-vinyl acetate copolymer stretch film have been proposed. In addition, ethylene and / or propylene have been copolymerized with α-olefins such as butene-1, hexene-1, and 4-methylpentene-1. Improved stretch films have been proposed, such as those having a polymer as a central layer and an ethylene-vinyl acetate copolymer layer formed on both sides, but stretchability, transparency, flexibility, deformation recovery, cut However, there is a problem in terms of properties and the like, and the same excellent packaging workability and packaging finish as in the case of the polyvinyl chloride resin stretch film cannot be obtained.

Further, in recent years, it has been proposed to use a mixture of polypropylene and petroleum resin for a stretch film for food packaging. That is, the central layer is made of a resin composition containing a propylene-based polymer having a specific calorific value of crystallization and a petroleum resin, a terpene resin, a coumarone-indene resin, a rosin resin or a hydrogenated derivative thereof, and has a specific storage property. A multilayer stretch film for packaging having an elastic modulus and a loss tangent has been proposed (Japanese Patent Application Laid-Open No. 9-154479). Also, both outer layers are composed of an ethylene-based polymer,
A stretch film for food packaging has been proposed in which a center layer is formed of a resin composition containing a mixture of amorphous polypropylene and crystalline polypropylene, and a petroleum resin or a hydrogenated derivative thereof (Japanese Patent Application Laid-Open No. 11-115122). .

The standard homopolymer of propylene has a flexural modulus of about 1300 N / mm ² (measured according to JIS K7208). Polypropylene having a large flexural modulus is too hard as a material for a stretch film.
Even if petroleum resin is compounded, it cannot be stretched smoothly with an automatic packaging machine, thus hindering the packaging work.
The packaging finish is not enough. Therefore, in a stretch film for food packaging using a propylene-based polymer as a material, conventionally, 200 N /
Attention has been paid to propylene polymers having a flexural modulus of not more than mm ^2, and they have been adopted because they can be used as they are in stretch packaging machines adapted for flexible polyvinyl chloride. However, a propylene-based polymer having a flexural modulus of 200 N / mm ² or less has a large rubber elasticity. Therefore, even if a petroleum resin or the like is blended, it does not easily overlap when stretched on a stretch wrapping machine. (Returns to the original state before fusing) and is generally expensive. In addition, atactic polypropylene has a flexural modulus of 200 N / mm ² or less and is inexpensive, but contains a low molecular weight component. Therefore, when blended in a large amount, the low molecular weight component bleeds on the surface of the stretch film, and the film becomes cloudy. is there.

In a stretch film for food packaging, a propylene-based polymer serving as a central layer is blended with a petroleum resin or a hydrogenated product thereof to impart retardation elasticity to the film, to increase the glass transition temperature, It is known that it has the effect of lowering the crystallinity of the polymer or improving the extensibility at room temperature, but the problem that petroleum resin or its hydrogenated product bleeds on the surface of the stretch film and foggs the film. There is a point.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has an excellent transparency, a stress delay, an excellent packaging workability, and a good packaging finish. It is an object to provide a relatively inexpensive stretch film for food packaging that can be obtained.

[0008]

Means for Solving the Problems The present inventors have made a resin composition containing a propylene-based polymer and a petroleum resin or a hydrogenated product thereof a central layer, and provided an ethylene-based polymer layer on both outer sides thereof. As a result of various studies on a stretch film for food packaging, the flexural modulus was 200 to 500 N / mm ^2.
Propylene-based polymer as a material, which has a softening point of 1
The present invention has been found that when a relatively high petroleum resin having a temperature of 30 ° C. or higher or a hydrogenated product thereof is mixed, a stretch film having good transparency, excellent packaging workability, and excellent packaging finish can be obtained. Was completed.

That is, the present invention relates to a stretch film for food packaging comprising at least three layers of a central layer and both outer layers, wherein at least one of the central layers has crystallinity having a flexural modulus of 200 to 500 N / mm ² . A resin composition mainly comprising a mixture of a polypropylene resin and a petroleum resin having a softening point of 130 ° C. or higher or a hydrogenated product thereof in a weight ratio of 60 to 95:40 to 5; And a total layer thickness of 7 to 15 μm and a layer ratio of the central layer of 40 to 90%. Also, in the present invention, the above resin composition contains an amorphous polypropylene resin having a flexural modulus of 500 N / mm ² or less, and the compounding ratio of the amorphous polypropylene resin is such that the polypropylene resin and the petroleum resin or hydrogen gas Mixture of additives 100-60
The stretch film for food packaging has a weight ratio of 0 to 40 based on the weight of the stretch film. The amorphous polypropylene resin is a copolymer of propylene and butene-1, and is preferably an amorphous polypropylene resin having a copolymerization ratio of butene-1 of 20% by weight or less.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention is a stretch film for food packaging comprising at least three layers of a central layer and both outer layers. At least one of the center layers has a flexural modulus of 2
From a resin composition mainly composed of a mixture containing a crystalline polypropylene resin having a softening point of not less than 130 ° C. or a hydrogenated product thereof and a crystalline polypropylene resin having a softening point of not less than 100 to 500 N / mm ^2. Become. The weight ratio of the mixture of the crystalline polypropylene resin and the petroleum resin or a hydrogenated product thereof in the resin composition is 50% by weight or more, preferably 60% by weight or more. More preferably, the ratio of the crystalline polypropylene resin in the resin composition is 50% by weight or more. The flexural modulus is a value measured by a measuring method described in JIS K7208.

A crystalline polypropylene resin having a flexural modulus of 200 to 500 N / mm ² is generally obtained by crosslinking a hard segment composed of polypropylene and a soft segment obtained by copolymerizing propylene with ethylene or an α-olefin (excluding propylene). It was done. The hard segment and the soft segment may be separately polymerized and then cross-linked, or the hard segment and the soft segment may be polymerized and cross-linked by one polymerization process. Those manufactured by the former manufacturing method are inferior in transparency, but those manufactured by the latter manufacturing method have good transparency and are preferably used. This crystalline polypropylene-based resin is, for example, "Cataroy KS-221P" or "Cataalloy KS-081P" from Montel JP Corporation.
It is commercially available under the trademark name.

This flexural modulus is 200 to 500 N / mm ^2.
The crystalline polypropylene resin is suitable because it has excellent transparency and low cost. In addition, the flexural modulus 2
When a crystalline polypropylene resin of 00 N / mm ² or less is used, the softening point is 13
Even if a petroleum resin or its hydrogenated product of 0 ° C or more is added,
When packaging with an automatic packaging machine, the so-called overlap property is poor. When a crystalline polypropylene resin having a flexural modulus of 500 N / mm ² or more is used, even if a petroleum resin having a softening point of 130 ° C. or more or a hydrogenated product thereof is added to the automatic packaging machine, the resin is hard. When wrapped, it is difficult to overlap, wrinkles, and slips off the belt of the packaging machine. From the viewpoint of the overlap property, it is preferable to use a crystalline polypropylene resin having a flexural modulus of 200 to 300 N / mm ² .

The petroleum resin or its hydrogenated product used in the present invention is a thermoplastic resin obtained by polymerizing and solidifying a cracked oil fraction generated by thermal cracking of petroleum. C ₅ fractions as a raw material fat genus system, aromatic system a C ₉ fraction as a raw material, or both copolymeric, there is dicyclopentadiene-based. Further, those obtained by hydrogenating these are also used. This petroleum resin or a hydrogenated product thereof is commercially available under the trade names of Alcon (manufactured by Arakawa Chemical Industries, Ltd.), Heylets, Petrozine (all manufactured by Mitsui Chemicals, Inc.). Hydrogenated C ₉ petroleum resin is preferably used. Further, those having a softening point of 130 ° C. or higher, preferably 140 ° C. or higher are used. When a petroleum resin having a high softening point or a hydrogenated product thereof is used as described above, the stress delay manifestation is greater than when a resin having a softening point of less than 130 ° C. is used, and bleeding becomes more difficult, so that it is transparent. Good nature.

The flexural modulus is 200 to 500 N / mm.
The ratio between the crystalline polypropylene resin of No. ² and the petroleum resin or a hydrogenated product thereof is 60 to 95:40 to 5 by weight. When the proportion of the crystalline polypropylene-based resin is 60% by weight or less, the transparency deteriorates with time due to bleeding.
If the content is more than 10% by weight, the stress retarding property is insufficient, and the overlapping property is poor.

At least one of the center layers is formed by mixing the above-mentioned crystalline polypropylene resin having a flexural modulus of 200 to 500 N / mm ² with a petroleum resin having a softening point of 130 ° C. or more or a hydrogenated product thereof in an amount of 60 to 95:40. The resin composition mainly contains a mixture mixed at a weight ratio of 5. The resin composition may contain an amorphous polypropylene resin having a flexural modulus of 500 N / mm ² or less. The cost can be reduced by blending the amorphous polypropylene resin. The mixing ratio of the mixture of the crystalline polypropylene resin and the petroleum resin or the hydrogenated product thereof and the above-mentioned amorphous polypropylene resin is 100 to 60: 0 to 0.
40 (parts by weight).

The above-mentioned amorphous polypropylene resin is, for example, polypropylene, propylene-ethylene copolymer,
Propylene-butene-1 copolymer, propylene-butene-1-ethylene copolymer, propylene-hexene-1 copolymer and the like. Among them, an amorphous polypropylene resin which is a copolymer of propylene and butene-1 and has a copolymerization ratio of butene-1 of 20% by weight or less is preferable. These are provided by Ube Tex UT27
80, Ubetac UT2385, etc. marketed under the trade name are used.

In the present invention, a layer made of a polyethylene resin is provided as both outer layers of the central layer. This polyethylene-based resin is, for example, ethylene-propylene copolymer, ethylene-butene-1 copolymer, ethylene-pentene-1 copolymer, ethylene-hexene-1 copolymer, ethylene-vinyl acetate copolymer, ethylene -Methyl acrylate copolymer, ethylene-ethyl acrylate copolymer,
Ethylene-acrylic acid copolymer, ethylene-methyl methacrylate copolymer, ethylene-ethyl methacrylate copolymer, ethylene-methacrylic acid copolymer, ethylene-ethyl methacrylate copolymer, ionomer resin, Resin films of low-density polyethylene, linear low-density polyethylene, ultra-low-density polyethylene, medium-density polyethylene, and high-density polyethylene. In particular, an ethylene-vinyl acetate copolymer film is preferable because a stretch film for food packaging can be prepared without impairing the properties of the central layer described above.

The sum of the thickness of the center layer and the thickness of the layers on both sides thereof, that is, the total layer thickness of the stretch film is 7 to 15 μm.
m, preferably 8 to 12 μm. The layer ratio of the center layer, that is, the ratio of the thickness of the center layer to the total layer thickness is 40.
９０90%, preferably 50-80%. The thickness of both outer layers may be the same or different.

The film of the present invention may optionally have antifogging agents, antibacterial agents, antibacterial agents, antibacterial agents, antibacterial agents, antibacterial agents, antibacterial agents, etc. It is preferable to mix agents, lubricants, adhesives and the like. Examples of the anti-fog agent include mono- or diglycerin fatty acid esters, polyglycerin fatty acid esters, sorbitan fatty acid esters, sucrose fatty acid esters, ethylene oxide adducts thereof, and polyoxyalkylene ethers. As the tackifier, aliphatic hydrocarbon resin, rosin, aromatic petroleum resin and the like are used.

The stretch film for food packaging according to the present invention comprises a crystalline polypropylene resin having a flexural modulus of 200 to 500 N / mm ² and a petroleum resin having a softening point of 130 ° C. or higher or a hydrogenated product thereof, in the range of 60 to 95:40. The resin composition mainly containing a mixture mixed at a weight ratio of ~ 5 is made into a central layer, and an ethylene-based polymer is located on both sides of the resin composition, and is manufactured by inflation molding or extrusion molding using a T-die. . In the case of inflation molding, the obtained tubular molded product is cut open to form a film. Thereafter, the film is cut into a predetermined width and wound on a roll to obtain a product.

[0021]

EXAMPLES AND COMPARATIVE EXAMPLES Examples 1 to 7 and Comparative Examples 1 to 4 Stretch films for food packaging were manufactured with the respective composition ratios and respective layer thicknesses shown in Table 1. In Table 1, EVA is an ethylene-vinyl acetate copolymer containing 15.8% by weight of vinyl acetate units. Cataloy KS-221P (trade name) and Cataloy KS-081P (trade name) are crystalline polypropylenes manufactured by Montell JP Corporation, and have flexural moduli of 270 N / mm ² and 350 N / mm ² , respectively. PERT-310J (trade name) is a low-crystalline propylene polymer manufactured by Tokuyama Corporation, and is a block copolymer of propylene-ethylene-propylene type,
Its flexural modulus is 160 N / mm ² . Noblen WF732-1 (trade name) is a crystalline propylene polymer manufactured by Sumitomo Chemical Co., Ltd. and has a propylene unit content of 9%.
7% by weight of a propylene-ethylene random copolymer having a flexural modulus of 1200 N / mm ² . Ubetac UT2780 (trade name) is an amorphous polyolefin resin manufactured by Ube Lexen Co., Ltd., and is a propylene-butene-1 copolymer containing 65% by weight of propylene and 35% by weight of butene-1. Elastic modulus is 11
0 N / mm ² . Alcon P-140 (trade name) and Alcon P-125 (trade name) are alicyclic saturated hydrocarbon resins manufactured by Arakawa Chemical Industries, Ltd., and have softening points of 140 ° C. and 125 ° C., respectively.

A stretch film for food packaging was prepared using the resin composition shown in Table 1 for the central layer and an ethylene-vinyl acetate copolymer containing 2% by weight of an antifog agent glycerin oleate for the outer layer. That is, the above resin composition was used as a central layer, and extruded with a round die so that the outer layer of the ethylene-vinyl acetate copolymer was located on both sides of the resin layer, and inflation-molded. Was prepared and wound into a roll to obtain a product.

Each of the obtained stretch films was examined for bleeding, releasability, overlap property, wrinkling of the tray, tearing during packaging, and detachment from the belt during automatic packaging by the following methods. Table 1 shows the results. Bleed: Each stretch film was left at 50 ° C. for 14 days, and then measured with a haze according to JIS K7105. This is an examination of the transparency of the film. If it exceeds 5, the merchantability is inferior. Those having 5 or less, particularly 2.5 or less, are preferable. Reversibility: The roll-shaped stretch film product was left at 50 ° C. for 14 days, and then released from the roll by hand. The state of dissolution at this time was examined. ○ indicates that the solution is light, Δ indicates that the solution is heavy, and X indicates that the solution is very heavy.

Overlapping property: Using a stretch automatic wrapping machine AW-3600 manufactured by Teraoka Seiko Co., Ltd., a width of 35
Each stretch film of 0mm, length 23cm x width 33
A styrofoam tray measuring 3 cm in height and 3 cm in height was automatically packaged. At this time, the degree of film overlapping on the bottom of the tray was examined. ◎ indicates 5-7cm overlap, ○ indicates 3-5c
m has an overlap, △ has an overlap of 1 to 3 cm, ×
Indicates that there is no overlap. This indirectly evaluates the stress delay development of the film.

Wrinkling of tray: 350 m wide using a stretch automatic wrapping machine AW-3600 manufactured by Teraoka Seiko Co., Ltd.
m each stretch film, length 23cm x width 33cm
× A 3 cm high styrofoam tray was automatically packaged. At this time, wrinkles of the film on the upper surface of the tray were examined. ◎
Extremely good without wrinkles, very good, almost no wrinkles, poorly wrinkled, poor wrinkles throughout.

Film tearing during packaging: Using a stretch automatic packaging machine AW-3600 manufactured by Teraoka Seiko Co., Ltd.
Each stretch film with a width of 350mm, length 23cm ×
A 33 cm wide x 3 cm high styrofoam tray,
Each 100 packs were automatically packaged. The state of tearing of the film at this time was examined. ◎: No pack torn in 100 packs, ○: 1-2 packs torn in 100 packs
There are packs, △ means that there are 3 torn packs in 100 packs
There are 5 packs, × means 6 packs torn out of 100 packs
Indicates that there is more than a pack.

Film detachment during packaging: The test was performed using a stretch automatic packaging machine AW-3600 manufactured by Teraoka Seiko Co., Ltd. , A stretch film having a width of 350 mm is sandwiched between the holding belts of the automatic packaging machine and activated, and
The detachment of the film from the holding belt when stretched by 0% was examined. ○ indicates that the film did not come off the holding belt, Δ indicates that the film partially came off the holding belt, × indicates that the film completely came off the holding belt,
Is shown.

[0028]

[Table 1]

[0029]

According to the stretch film for food packaging of the present invention, a petroleum resin having a softening point of 130 ° C. or more or a petroleum resin having a softening point of at least 130 ° C. even when a crystalline polypropylene resin having a high flexural modulus of 200 to 500 N / mm ² is used. By adding a hydrogenated compound, transparency is good, stress delay is exhibited, packaging workability is excellent, and packaging finish is good. Further, a tray in which food is stored is covered with the film, and is excellent in finger restoring property. In addition, it has excellent cutability and sealing performance at the bottom at the time of tray packaging, and has a good stretch feeling.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C08L 57:02 C08L 57:02 23:14) 23:14) (72) Inventor Kazuhisa Fukui Haibara-gun, Shizuoka No. 1 Kobe, Yoshida-cho, Okamoto Shizuoka Plant (72) Inventor Kenichi Tsuruhashi No. 1, Kobe, Yoshida-cho, Haibara-gun, Shizuoka Prefecture Okamoto Shizuoka Plant Co., Ltd. F-term AA18 AA19 AA20 AA28X AA32X AA33X AA39 AA85 AF17Y AF61 AH04 BB06 BB09 BC01 BC12 4F100 AK02B AK04A AK04C AK07B AK67B AK68A AK68C BA03 BA06 BA10A BA10C BA15 GB23 JA04B JA11B01 J01B01 J01B01 J01B01

Claims (3)

[Claims] A stretch film for food packaging comprising at least three layers, a central layer and both outer layers, wherein at least one of the central layers has a flexural modulus of 200 to 500 N /.
mm ² crystalline polypropylene resin and softening point 130 ° C
60-95: 4 with the above petroleum resin or its hydrogenated product
A resin composition mainly composed of a mixture having a weight ratio of 0 to 5, both outer layers are made of a polyethylene resin, and the total layer thickness is 7 to 15 μm; Stretch film for food packaging characterized by being 90%. 2. A resin composition having a flexural modulus of 500 N / mm ^2.
The following amorphous polypropylene-based resin is contained, and the compounding ratio of the amorphous polypropylene-based resin is a mixture of a polypropylene-based resin and a petroleum resin or a hydrogenated product thereof of 100 to 6
The stretch film for food packaging according to claim 1, wherein the weight ratio is 0 to 40 with respect to 0. 3. The non-crystalline polypropylene resin according to claim 1, wherein the non-crystalline polypropylene resin is a copolymer of propylene and butene-1, and the copolymerization ratio of butene-1 is 20% by weight or less. The stretch film for food packaging according to claim 2, characterized in that: