JP3312443B2 - Self-adhesive packaging film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a self-adhesive packaging film comprising a polypropylene resin and a polyethylene resin, and more particularly, to a film having improved adhesiveness, microwave oven suitability, cutability, and moderate flexibility. The present invention relates to a self-adhesive packaging film.

[0002]

2. Description of the Related Art Self-adhesive packaging films of this kind are:
It is often used in households, restaurants, hotels, etc. to seal food, preventing drying when stored in a refrigerator, preventing drying when heating in a microwave oven, or reducing flavor or odor during storage. It has the effect of preventing the emission or adhesion of other odors, and the prevention of the adhesion of dust when used for business use. In particular, with the spread of microwave ovens in recent years, the demand for this use has increased significantly. That is, it is used for hermetically packaging a container (generally made of ceramics or glass) containing foods in order to prevent moisture from evaporating in a microwave oven and impairing the flavor.

[0003] The packaging film used in such applications has a property that it has a small heat shrinkage in a microwave oven and does not cause heat melting or whitening, in addition to having close contact with the container or the same adhesiveness as the film. Hereinafter, it is required to have “suitability for microwave oven”.

[0004] As a conventional self-adhesive packaging film, those using polyvinylidene chloride, polyethylene, or polyvinyl chloride as a main raw material are known.

However, a polyvinylidene chloride film is disadvantageous in that it has a large shrinkage upon heating, and is more expensive than the other two. In addition, a film made of polyethylene has a disadvantage that the film is perforated when it comes into contact with oily substances (eg, meat or tempura) and becomes hot, and a film made of polyvinyl chloride has a drawback when it comes into contact with boiling hot water. There is a problem that causes whitening. Therefore, at present, none of these conventional self-adhesive films are sufficient as microwave oven suitability.

[0006] On the other hand, most of the usage forms of such self-adhesive packaging films include, for example, a film having a width of 20 to 45 cm and a thickness of 10 to 20 µ wound on a core material such as a paper tube.
It is stored in a case such as a paper box and used, and the film is cut off to an appropriate length by applying it to a cutting blade called a `` saw blade '' attached to this case, and by the adhesiveness of the film, It seals the opening of food storage containers and the cut end of food.

[0007] As the above-mentioned "saw blade" used for cutting a film, a simple blade which is generally obtained by punching an iron plate having a thickness of about 0.2 mm into a saw shape is used. For cases that support
A coated cardboard paper box of about 00 g / m ² is used, and the rigidity is extremely low.

[0008] This kind of film is required to be easily cut by such a simple cutting mechanism. However, in actuality, cutting occurs at a position off the case or "saw blade". Or may be.

More specifically, conventionally, a film mainly composed of polyvinylidene chloride, polyvinyl chloride, or polyethylene is used, and a film made of polyvinylidene chloride has a rupture in a part of the film when cut. If possible, the rift will spread and cut diagonally without being cut along the "saw blade". Further, a film made of polyvinyl chloride or polyethylene has a large elongation at the time of cutting, and the film is not only sharp but also deformed.

[0010] Furthermore, a film made of polyvinylidene chloride or polyvinyl chloride as a main raw material has a moderate flexibility (flexibility: in this specification, represented by Young's modulus). Although they are suitably used as household wrap films, since these films contain a large amount of chlorine, chlorine gas is generated at the time of incineration, and the harmfulness of the plasticizer contained in a large amount poses a problem. Yes,
Environmental suitability is not sufficient.

For this reason, as a self-adhesive packaging film mainly composed of polypropylene, for example, Japanese Patent Publication No. Sho 58
JP-A-46216 discloses a film obtained by blending a specific amount of polyethylene, and JP-B-63-63578 discloses a film obtained by blending a specific amount of a nucleating agent and atactic polypropylene or rosin. 4-
Japanese Patent Publication No. 328144 discloses a biaxially stretched film obtained by blending a specific amount of a surfactant with a polypropylene copolymer, and Japanese Patent Publication No. 2-14935 discloses a stretched resin composition containing a tackifier. Methods for producing self-adhesive packaging films have been proposed. However, a self-adhesive packaging film that satisfies all of adhesiveness, microwave oven suitability, and “saw blade” cutability and has appropriate flexibility has not yet been obtained.

[0012]

SUMMARY OF THE INVENTION An object of the present invention is to provide an inexpensive self-adhesive packaging film having excellent adhesiveness, microwave oven suitability, "saw blade" cutability, and moderate flexibility. is there.

[0013]

SUMMARY OF THE INVENTION In view of the above problems, the present inventors have intensively studied a self-adhesive packaging film which is excellent in microwave oven suitability and "saw blade" cutability and has moderate flexibility. Has been continued. As a result, both surface layers are made of a polyethylene resin, and a film having at least one polypropylene resin layer having a melting point of 140 ° C. or more between the two surface layers, and having a melting point of at least 2 The present inventors have found that a film stretched at least twice in the film take-off direction at a temperature of from 20 ° C. to 20 ° C. below the melting point satisfies the above performance, and have completed the present invention.

That is, the present invention relates to a film having both surface layers made of polyethylene resin and having at least one polypropylene resin layer having a melting point of 140 ° C. or more between both surface layers. Melting point
The present invention relates to a self-adhesive packaging film, which is stretched at least twice in the film take-up direction in the range of 2 ° C. to 20 ° C. below the melting point.

Hereinafter, the present invention will be described in detail. Examples of the polyethylene resin used in the present invention include low-density polyethylene, medium-density polyethylene, and high-density polyethylene, as well as ethylene-propylene copolymer, ethylene-butene-1 copolymer, and ethylene-4-methylpentene-1 copolymer. Coalescence, ethylene-hexene-1 copolymer, ethylene-
Ethylene-α olefin copolymers such as octene-1 copolymer and ethylene-decene-1 copolymer, and also unsaturated compounds such as conjugated diene and non-conjugated diene with ethylene, acrylic acid, methacrylic acid, and vinyl acetate And the like as a copolymer component. These polymers may be acid-modified, for example, polymers graft-modified with α, β-unsaturated carboxylic acids, alicyclic carboxylic acids, or derivatives thereof.

When low-density polyethylene, medium-density polyethylene, or high-density polyethylene is used as the polyethylene resin, considering that sufficient tackiness is obtained,
Those having a density of 0.93 g / cm ³ or less are preferred.

When an ethylene-α-olefin copolymer is used as the polyethylene resin, the density is from 0.88 g / cm ³ to 0.
It is preferably 94 g / cm ³ .

When a copolymer of ethylene and acrylic acid, methacrylic acid, vinyl acetate, or the like is used as the polyethylene-based resin, a copolymer having a comonomer content of 5 to 30% by weight is considered in consideration of obtaining an appropriate tackiness. preferable.

The polypropylene resin used in the present invention is mainly a propylene polymer having a melting point of 1%.
The type is not particularly limited as long as it is 40 ° C. or higher. The propylene homopolymer may, of course, be a copolymer containing one or more other α-olefins (eg, ethylene, butene, hexene, etc.),
The copolymer may be either a random copolymer or a block copolymer. Further, a mixture with these other components may be used. The use of a polypropylene resin having a melting point of less than 140 ° C. is not suitable because the heat resistance of the film is insufficient.

In producing a film from the polypropylene resin and the polyethylene resin of the present invention, additives generally used may be contained. For example, it is optional to include an antioxidant, a stabilizer, an antistatic agent, an antifogging agent, and the like.

In the present invention, a polyethylene film and a polypropylene resin are formed into a film by means of a co-extrusion T-die method, a co-extrusion inflation method or a heat bonding method to produce a raw film. Next, the obtained web is stretched by a method such as a tenter method or a tubular method. In the present invention, it is necessary to stretch the raw film at least twice in the take-off direction (MD), and it is preferable to stretch it three to eight times. Further, if necessary, stretching may be performed in a direction (TD) perpendicular to the take-up direction. The stretching ratio of MD and TD differs depending on the resin composition and the layer structure, and can be arbitrarily selected within a range satisfying appropriate flexibility. In this way, by stretching the raw film at least twice in the take-off direction, the "saw blade" cutability and strength are improved, and a film having a good surface condition can be obtained.

The stretching temperature is determined according to the appropriate stretching temperature of the polypropylene resin regardless of the type of the resin for both surface layers. That is, the stretching temperature of the polypropylene resin
The melting point is in the range of 2 ° C to 20 ° C, preferably 5 to 15 ° C. By stretching in such a temperature range, a film having a small shrinkage ratio during heating can be obtained.

The thickness of the film of the present invention is 50 μm or less, preferably in the range of 8 to 15 μm, and the thickness of the polypropylene resin layer is 20 to 80% of the total thickness of the film.
%. When the thickness of the entire film exceeds 50 μm, the resistance at the time of cutting becomes too large, which is not preferable. If the thickness of the polypropylene resin is less than 20% of the total thickness of the film, heat resistance during heating is insufficient, and if it exceeds 80%, the flexibility of the film is lost, which is not preferable.

The layer structure of the film of the present invention is basically composed of three layers of a polyethylene resin layer / polypropylene resin layer / polyethylene resin layer. And still another composition layer (for example,
Recycled resin layer or gas barrier resin layer)
It is also possible to have a configuration of four or more layers.

The thus obtained film according to the present invention is excellent in tackiness, microwave oven suitability, "saw blade" cutting property, and has appropriate flexibility. Moreover, since it is stretched and oriented, the strength is high, the transparency is excellent, and the appearance is good. In addition, the film can be thinned by the stretch orientation to save resources, and the environment suitability is extremely high as compared with a film mainly composed of polyvinylidene chloride or polyvinyl chloride. Therefore, the self-adhesive packaging film according to the present invention is useful as a packaging film for household wrap film, commercial wrap film and the like.

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples unless it exceeds the gist thereof. First, a method for measuring physical properties in the following examples will be described.

(1) Differential Scanning Calorimeter (DSC) The melting point of the polypropylene resin was measured using DSC-7 manufactured by PerkinElmer. Weight of about 10mg cut out from a sheet of about 0.5mm thickness created by hot press
Was placed in a sample pan for DSC measurement, heated to 230 ° C., cooled to 150 ° C., cooled from 150 ° C. to 40 ° C. at 5 ° C./min, held for 5 minutes, and then cooled at 5 ° C./min. 1
The temperature is raised to 80 ° C. to obtain a thermogram. The main peak temperature in the thermogram at the time of this temperature rise was defined as the melting point.

(2) Density The density of the polyethylene resin was determined according to the method specified in JIS K6760. After annealing for 1 hour in water at 100 ° C., the density was measured.

(3) Melt flow rate (MFR) The MFR of the polyethylene resin was measured by the method specified in JIS K6760.

(4) Comonomer content in the copolymer The comonomer content of the ethylene-vinyl acetate copolymer, ethylene-acrylate ester copolymer or ethylene-methacrylate ester copolymer is measured by an infrared spectrophotometer. 3480c which is the overtone of the carbonyl stretching vibration absorber
The absorbance at m ^-1 was measured and quantified from the calibration curve.

(5) Suitability for microwave oven According to Tokyo Metropolitan Ordinance No. 1072, “Quality display of wrap film”, a 2.5 cm vertical and a rectangular film sample of 3 cm width and 14 cm length are sandwiched between jigs, and the sample is inserted. 10g at the bottom
Lower the weight of In this state, the maximum ambient temperature at which the film does not break even after one hour has elapsed is displayed in increments of 10 ° C. The higher the temperature, the better the suitability for the microwave oven.

(6) Adhesive Strength A 10 cm wide, 15 cm long film sample piece is
Adhesion to glass plate of × 10cm, 23 ℃, 50% RH
After a load of 500 g is applied for 30 minutes in the atmosphere described above, one end in the longitudinal direction of the film is fixed to a jig and pulled up at a speed of 200 mm / min in a direction perpendicular to the glass plate. At this time, the force required for pulling up was measured and indicated as g / 10 cm as the adhesive force.

(7) Young's modulus MD, T according to the method specified in ASTM D882.
D was measured respectively. The smaller this value is, the higher the flexibility is. However, test specimen shape: strip type of 20 mm × 120 mm Distance between chucks: 50 mm Peeling speed: 5 mm / min

(8) Elongation at break Measured in accordance with the method specified in JIS K6781.

(9) Heat Shrinkage After clarifying the MD and TD, a film cut into a 9 cm square was immersed in a silicone oil bath maintained at 140 ° C. for 5 seconds, taken out, and measured for dimensions. The rate of shrinkage of the film at this time was expressed as a heat shrinkage%.

(10) Haze (Haze) The method specified in ASTM D1003 was followed. The smaller the value, the better the transparency.

(11) "Saw blade" cut property A film is wound around a core tube, and a case with a "saw blade" (0.2
Saw blade punched steel plate “mm saw blade”
g / m ² coated cardboard case)
And tried cutting with a “saw blade”. as a result,
A piece that is cut straight by just pulling it lightly against the "saw blade" is "good". It cuts diagonally, stretches the film greatly, deforms the "saw blade" case, or has a strong force to cut. Those that required were indicated as "poor".

[0038]

【Example】

Examples 1 to 6 A propylene-ethylene random copolymer (MFR = 2.6; melting point = 148 ° C .; ethylene content = 2.5 wt%; Noblen RH120B manufactured by Sumitomo Chemical Co., Ltd.) was used as a resin constituting the polypropylene resin layer. Further, each of the resins shown in Table 1 (all manufactured by Sumitomo Chemical Co., Ltd.) was prepared as a polyethylene resin constituting both surface layers, and these were shown in Examples 1 to 6 by a co-extrusion T-die method ( Table 1) An original sheet (300 μ thick) having a layer structure was processed. The extruder used for sheet processing had an intermediate layer of φ30 mm (manufactured by Tanabe Plastics) and both surface layers of φ40 mm (manufactured by IKG). The processing conditions were a die temperature of 230 ° C., a chill roll temperature of 25 ° C., and a processing speed of 3 m / min. Subsequently, this was sampled into a 9 cm square, and biaxially stretched under the following conditions to obtain a stretched film.

Stretching machine: Table-top biaxial stretching machine manufactured by Toyo Seiki Stretching temperature: 150 ° C. Preheating time: 3 minutes Stretching magnification: MD 6 times, TD 3 times (simultaneous method) Stretching speed: 5 m / min Heat treatment time: 5 seconds

The physical properties of the film having a thickness of about 11 μ obtained by the above method are shown in Tables 2 to 4. The films obtained in Examples 1 to 6 were excellent in adhesiveness, microwave oven suitability, "saw blade" cutability, and had appropriate flexibility, and were sufficient as wrap films.

Examples 7 and 8 In Examples 3 and 6, the polypropylene resin in the intermediate layer was replaced with a propylene homopolymer (MFR = 2.6; melting point =
161 ° C; Noblen FS201 manufactured by Sumitomo Chemical Co., Ltd.
A film was obtained as 1D). These films were excellent in adhesiveness, microwave oven suitability, "saw blade" cutability and moderate flexibility, and were sufficient as wrap films.

Comparative Example 1 In Example 4, the stretching temperature of the table-top biaxial stretching machine was set to 120
C. to obtain a film. This film had a large heat shrinkage and had unfavorable performance as a wrap film.

Comparative Example 2 A film having the layer constitution shown in Example 6 was obtained by a co-extrusion T-die method (unstretched film). Since this film was not subjected to a stretching treatment, the cut property was remarkably inferior, and cutting with a “saw blade” was impossible.

Comparative Example 3 The polypropylene resin used in Examples 1 to 6 was extruded in a single layer by a T-die method to produce a 300 μm thick raw sheet. This was stretched in the same manner as in Examples 1 to 6 to obtain a film. This film was not flexible and had no tackiness.

Comparative Examples 4 to 5 Table 4 shows the film properties of commercially available polyvinylidene chloride wrap film (Saran wrap manufactured by Asahi Kasei Corporation) and polyethylene wrap film (Clean wrap manufactured by Mitsubishi Aluminum Corporation). A vinylidene chloride film has a drawback of a large heat shrinkage, and a polyethylene wrap film is inferior in microwave oven suitability and "saw blade" cutability.

[0046]

[Table 1]

* 1 Polyethylene resin LD: Low density polyethylene (Sumikacene F200, manufactured by Sumitomo Chemical Co., Ltd., density 0.920 g / cm ³ , MFR 2.
LL: Ethylene-butene-1 copolymer (Sumikacene L FA201-0 manufactured by Sumitomo Chemical Co., Ltd., density 0.912 g)
/ Cm ³ , MFR 2.0 g / 10 min) VL: ethylene-butene-1 copolymer (Excellen VLVL102 manufactured by Sumitomo Chemical Co., Ltd., density 0.908 g / c)
^{m 3, MFR0.6g / 10min) EVA} : ethylene - vinyl acetate copolymer (manufactured by Sumitomo Chemical Co., Ltd. Ebateto H2011, density 0.936 g / cm
³ , MFR 3.0g / 10min, comonomer content 1
EMMA: ethylene-methyl methacrylate copolymer (Acriflift WH202 manufactured by Sumitomo Chemical Co., Ltd., density: 0.1%)
930 g / cm ³ , MFR 2.0 g / 10 min, comonomer content 20% by weight) EBM: Ethylene-butene copolymer (Splen SPO N0352 manufactured by Sumitomo Chemical Co., Ltd., density 0.905 g / c)
m ³ , MFR 2.0 g / 10 min) Polypropylene resin PP-1: propylene homopolymer (FS2011D,
PP-2: propylene-ethylene random copolymer (RH120B, melting point 148 ° C)

[0048]

Table 2 Table-top biaxially stretched film physical properties (two types and three layers) ------------------------------------ Example 1 2 3 4 5 6 Microwave oven characteristics ° C * 2 150 150 150 150 150 150 Adhesive strength g / 10cm * 3 7 8 28 25 30 21 Young's modulus MD kg / cm ² 9780 9830 9410 8970 9260 8860 TD kg / cm ² 7250 7210 7180 7260 6830 6620 Elongation at break MD% 58 63 61 71 52 48 Heat shrinkage MD / TD% * 4 6/3 8/5 7/6 6/7 10/5 6/4 Haze% 3.8 3.2 1.3 0.5 0.8 3.0 Saw blade cutability Good Good Good Good Good Good ---------------------------------------------------------

[0049]

[Table 3]

[0050]

Table 4 Table-top biaxially stretched film physical properties (two types and three layers) Comparative Example 1 Comparative Example 1 2 3 4 5 Microwave oven characteristics ° C * 2 150 150 160 140 110 Adhesive strength g / 10cm * 3 20 32 0 11 8 Young's modulus MD kg / cm ² 9020 2560 21800 5010 2100 TD kg / cm ² 7100 2310 13200 4260 2010 Break Elongation MD% 67 570 41 27 220 Heat shrinkage ratio MD / TD% * 4 46/28 7/3 6/4 51/42-Haze% 2.8 4.5 0.3 0.3 0.6 Saw blade cutability Good Bad Good Good Bad −−− −−−−−−−−−−−−−−−−−−−−−−−−−−−−−−

* 2 Microwave oven characteristics: Tokyo Metropolitan Ordinance No. 10
No. 27 compliant * 3 Adhesive strength: 90 ° peel test with glass plate * 4 Heat shrinkage: 140 ° C heating value

[0052]

As described above, according to the present invention, there is provided a self-adhesive packaging film having excellent adhesiveness, microwave oven suitability, "saw blade" cutability, and moderate flexibility. be able to.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-3-258542 (JP, A) JP-A-4-357029 (JP, A) JP-A 5-278179 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) B32B 1/00-35/00 B29C 55/00-55/30

Claims (4)

(57) [Claims] 1. A consists both surface layers is polyethylene resin, respectively, a multilayer film having a melting point has at least one layer of polypropylene-based resin layer above 140 ° C. between both surface layers, above the melting point of the polypropylene resin 2 ° C. or in the take-off direction at least the film at a temperature below the melting point 20 ° C., the self-adhesive wrapping film, characterized by comprising stretching at least twice. 2. The polyethylene resin has a density of 0.93 g.
/ Cm ³ or less, melt flow rate is 0.1 g / 10 m
The self-adhesive packaging film according to claim 1, which is a low-density polyethylene of in to 50 g / 10 min. 3. The polyethylene-based resin has a density of 0.88 g.
/ Cm ³ to 0.94 g / cm ^3, melt flow rate ethylene -α-olefin copolymer of 0.1 g / 10min to 50 g / 10min, according to claim 1, wherein α carbon atoms of the olefin is 10 from 4 Self-adhesive packaging film. 4. The polyethylene resin is an ethylene-vinyl acetate copolymer, an ethylene-acrylate copolymer or an ethylene-methacrylate copolymer, and the resin has a melt flow rate of 0.1. 1
The self-adhesive packaging film according to claim 1, wherein the film has a comonomer content of 5 to 30% by weight.