JPH02251549A - Film for shrink package - Google Patents

Abstract

PURPOSE:To obtain the subject film for shrink package by film forming a resin composition containing a specific propylene-alpha-olefin copolymer and a hydrocarbon resin having a specific softening point and subsequently stretching the resultant film at least monoaxially. CONSTITUTION:With (A) a propylene copolymer consisting of a copolymer alone composed of propylene, 8-35mol%, preferably 10-30mol% >=4C alpha-olefin (preferably butene-1) and arbitrarily <=5mol%, preferably <=3mol% ethylene and containing 10 to 70wt.%, preferably 12 to 65wt.% cold xylene-soluble part or a polymer mixture containing >=20wt.% above mentioned copolymer, (B) 10 to 60 pts.wt., preferably 10 to 55 pts.wt. hydrocarbon resin with >=120 deg.C, preferably 130 deg.C softening point and preferably having no polar group and >=95% hydration ration is blended. The resultant composition is film formed and subsequently stretched at least monoaxially, thus obtaining the objective film.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a shrink packaging film that exhibits high shrinkage (despite this, little natural shrinkage over time), excellent transparency, and firmness.

<Prior art> Currently, polyvinyl chloride, polystyrene, and PET are used as materials for shrink-wrapping films for cylindrical objects such as bottles.
, poly20pyrene, etc. are known, but each has its advantages and
It has shortcomings and is not satisfactory in all aspects.

Although polyvinyl chloride has excellent properties as a shrink packaging film, it poses waste disposal problems.

Polystyrene has problems such as poor weather resistance and large natural shrinkage over time.

PET has the problem of high raw material costs.

Therefore, shrink packaging films made of inexpensive polypropylene resin compositions have been studied for some time.

JP-A-49-99645, JP-A-62-4735
The publication discloses a method of blending approximately 20% by weight of petroleum resin with a propylene copolymer, but although it does show high shrinkage, the film naturally shrinks over time. , is undesirable.

JP-A No. 63-113059 by the inventors of the present application discloses a method of blending 10 parts by weight or less of petroleum resin into a specific propylene resin composition; For example, there is a problem that the film becomes stiff.

<Problems to be Solved by the Invention> In view of the above circumstances, the present inventors have attempted to develop a sealic packaging film that exhibits high shrinkage, less natural shrinkage over time, excellent transparency, and firmness. We have carefully considered this.

As a result, a resin composition in which a specific amount of a specific hydrocarbon resin is blended with a propylene copolymer (composition) containing a specific amount or more of a specific propylene-a-olefin copolymer. The present invention was completed based on the discovery that a shrink packaging film having all of the above properties can be obtained by stretching the film in at least one axis after forming the film.

That is, the present invention provides a copolymer of propylene and an a-olefin having 4 or more carbon atoms, or a copolymer of propylene, an α-olefin having 4 or more carbon atoms, and ethylene, comprising: (1) an a-olefin having 4 or more carbon atoms in the copolymer; A propylene-α-olefin copolymer having an olefin content of 8 to 35 mol%, ■ an ethylene content of the copolymer of 5 mol% or less, and a cold xylene soluble portion of the copolymer of 10 to 70 wt%. After forming a resin composition in which a hydrocarbon resin having a softening point temperature of 120° C. or higher is blended with lθ to 60 parts by weight of a propylene copolymer containing % by weight or more, stretching treatment is performed in at least one axis direction. This is a characteristic shrink packaging film.

The first characteristic of the film obtained by the present invention is that, despite its extremely high shrinkage rate during heat shrinkage, natural shrinkage occurs over time during storage from the time the film is produced until heat shrinkage is performed. This means that there are few This characteristic is surprising because it has been thought that conventional methods of blending petroleum resins with propylene resins achieve a high shrinkage rate, but increase natural shrinkage over time.

The second feature is that the film has excellent stiffness, so when shrink-wrapping bottles etc. with labels, the film does not buckle and is easy to operate.

The present invention will be explained in detail below.

The propylene-a-olefin copolymer used in the present invention uses a so-called Ziegler-Natsuta catalyst, which is a known catalyst for stereoregular polymerization of α-olefins, as a catalyst system.
That is, a compound consisting of a transition metal compound of Groups I to II of the Periodic Table, a classical typical metal organic compound of Groups I to I of the Periodic Table, and a third component, preferably an electron-donating compound, is used; As the polymerization method, it can be produced by any method such as a solvent polymerization method in which polymerization is carried out in a solvent or a gas phase polymerization method in which polymerization is carried out in a gas phase.

For example, it can be obtained by the method of polymerizing copolymer (1) described in Japanese Patent Application No. 164505/1982, but any propylene-〇-olefin copolymer that satisfies the conditions specified below may be used.

The propylene-α-olefin copolymer used in the present invention uses a small amount of a-olefin having 4 or more carbon atoms or ethylene as a comonomer. As α-olefins having 4 or more carbon atoms, butene-1, pentene-1
, hexene-1,4-methyl-pentene-1 alone or in combination. For example, when performing gas phase polymerization, butene is difficult to liquefy and can maintain a high partial pressure.
1 is preferred.

The content of α-olefin having 4 or more carbon atoms in the propylene-a-olefin copolymer used in the present invention is 8 to 35 mol%, preferably 10 to 30 mol%. When the content of α-olefin having 4 or more carbon atoms is below the lower limit, the resin composition obtained by blending the present propylene-α-olefin copolymer cannot reduce the natural shrinkage of the film over time. I don't like it. If the content of the a-olefin having 4 or more carbon atoms is below the upper limit, the stiffness of the film will decrease, which is undesirable.

The ethylene content of the propylene-α-olefin copolymer used in the present invention is 5 mol% or less, preferably 3 mol% or less. If the ethylene content is below the upper limit, the transparency of the film may deteriorate over time, which is undesirable.

The cold xylene soluble portion (CXS) of the propylene-a-olefin copolymer used in the present invention is 10 to 70 wt%, preferably 12 to 65 wt%, and 15 to 60 wt%.
is more preferable. If the CXS is below the lower limit, the resin composition obtained by blending the present propylene-a-olefin copolymer cannot reduce the natural shrinkage of the film over time, which is not preferable. When CXS falls below the upper limit,
The stiffness of the film decreases, which is undesirable.

The propylene copolymer (composition) used in the present invention can be obtained by the above-mentioned propylene-α-olefin copolymer itself or by blending it with the propylene random copolymer described below. The copolymer is a well-known crystalline ethylene-propylene random copolymer, or a crystalline ethylene-propylene-butene-1 terpolymer, and has a comonomer content of 1 to 5 wt%. Yes. Also,
CXS is 15 wt% or less. The blending ratio of the propylene-α-olefin comonomer is 20% by weight or more, preferably 30% by weight or more. The propylene
If the blending ratio of the α-olefin copolymer is below the lower limit, the natural shrinkage of the film over time cannot be reduced, which is undesirable.

The hydrocarbon resins used in the present invention include petroleum resins, terpene resins, and cyclopentadiene resins.

Examples include coumaron indene resin. Among these resins, those having no polar group or those having hydrogen added thereto to have a hydrogenation rate of 1 or more of 95% are preferred.

The softening point (ring and ball method) of the hydrocarbon resin used in the present invention is 1
The temperature is 20°C or higher, preferably 130°C or higher. If the softening point is less than 120°C, the natural shrinkage of the film over time will be reduced (difficult), and the heat shrinkability will also be poor.Note that a petroleum resin with a softening point of less than 120°C may be used in combination. It is sufficient if the overall softening point is 120°C or higher.

The resin composition used for film formation of the present invention includes the above-mentioned propylene copolymer (composition) and the above-mentioned hydrocarbon resin in an amount of 10 to 6
0 parts by weight, preferably 10 to 55 parts by weight, more preferably 11 to 50 parts by weight. If the blending ratio of the hydrocarbon resin falls below the lower limit, the propylene copolymer (composition) must be made softer than necessary in order to achieve high shrinkage of the film, and as a result, the film deteriorates. My lower back is poor and I don't like it. If the blending ratio of the hydrocarbon resin is below the upper limit, the film will become sticky, which is not preferable.

The melt index (f/10 minutes) of the resin composition used for film formation of the present invention is preferably from 0.3 to 302/10 minutes. When the melt index is below the lower limit, processability deteriorates, which is undesirable. When the melt index falls below the upper limit, the film becomes too sticky during film formation, which is undesirable.

In the present invention, the resin composition can be obtained by uniformly dispersing it by any known method. For example, extrusion melt blending.

Examples include the Banbury blend method.

In the present invention, the resin composition (hereinafter referred to as an antistatic agent,
Additives such as antiblocking agents, lubricants, antifogging agents, stabilizers and nucleating agents can be added.

In the present invention, the film forming method includes T
Known processing methods such as a die casting method and a water-cooled inflation method can be employed. In addition, methods for performing the stretching treatment include known l-axis stretching methods such as roll stretching, roll rolling, and tenter transverse uniaxial stretching, as well as known biaxial stretching methods such as tenter biaxial stretching and Cheapler biaxial stretching. can be adopted. The stretching temperature ranges from room temperature to a temperature below the melting point of the resin composition, but in order to improve the heat shrinkability of the resulting film, it is preferably as low as possible within a range that allows uniform stretching. The surface stretching ratio is preferably 2 to 50 times. In this case, the stretching ratios in MD and TD do not necessarily need to be balanced and can be arbitrarily selected depending on each application.

In a preferred embodiment of the present invention, in order to apply it to shrink labels for bottles and the like, it is preferably oriented mainly in a uniaxial direction. Also, heat setting may be performed.

<Example> Data and evaluation in Examples and Comparative Examples were performed according to the following method.

(1) Content of a-olefin in copolymer Determined from mass balance during polymerization. Further, the content of butene-1 was further determined using an infrared spectrophotometer using a conventional method based on the characteristic absorption of 770. In addition, measurements using an infrared spectrophotometer are for fluoropylene-butene-1 copolymer.
A calibration curve was created from the quantitative values obtained by C-NMR, and quantification was performed.

(2) Ethylene content of the copolymer: 732 cm-', 720 cm-' using an infrared spectrophotometer
It was quantified using a conventional method based on the characteristic absorption in cm-'. In addition,
For measurement using an infrared spectrophotometer, a calibration curve was created using quantitative values determined by radiation measurement of an ethylene copolymer labeled with +4.

(3) Chilled xylene soluble part (CXS) Polymer 52 is dissolved in xylene 500- and then slowly cooled to room temperature. The solution was then left in a bath at 20°C for 4 hours, filtered, and concentrated.

Weigh to dryness.

(4) Melt index (Ml) ASTM-D1
238 (5) Haze ASTM-D] 003 (6) Film Young's modulus ASTM-D882 (7) Heating shrinkage rate: 5011 square film specimens are heated to glycerin bath i
When immersed for 10 seconds, the shrinkage rates of MD and TD are measured.

(8) Natural shrinkage rate over time Measure the shrinkage rate when a 5 cIN square film specimen is left at 40°C for 7 days. The calculation method is the same as (7).

Hereinafter, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to the Examples unless the gist thereof is exceeded.

Example 1 50% by weight of propylene-α-olefin copolymer (butene-1 content 17.5 mol%, CXS 18.5wt%, Nord index 4.5F/10 min) and propylene-random copolymer (Sumiman Chemical Co., Ltd.) Sumitomo Noprene manufactured by Kogyo ■, ethylene content 6.2 wt%, CX 58.1 wt%,
100 parts by weight of a propylene copolymer composition consisting of 50% by weight (melt index 0.4f/10min), hydrogenated petroleum resin (Alcon P-140 manufactured by Arayo Kagaku, softening point (ring and ball method) 140°C) ) and 1 part of BITo as a stabilizer were melt-blended using a 40φ extruder to obtain a resin composition. The melt index of this was 2.5y/10 minutes.

This resin composition number is two, press method number trowel, 360μ
A 90 square sheet was prepared, and a uniaxially stretched film was obtained under the following conditions.

Stretching machine: Tabletop stretching machine manufactured by Toyo Seiki Temperature near 0°C Preheating time: 1 minute Stretching ratio: 5 times MD (1 times TD) Stretching speed: 5 m/min The physical properties of the film with a thickness of approximately 60 μm obtained above were Shown in the table. Regarding film physical properties, MD force direction values are shown. Although this stretched film has excellent heat shrinkability, natural shrinkage over time is unlikely to occur, and it is also highly transparent and stiff, making it an excellent film for label shrinkage. There was.

Example 2. Example 3 In Example 1, a stretched film was prepared in the same manner as in Example 1, except that the blending ratios of the propylene-α-olefin copolymer and the propylene-random copolymer were changed to the values shown in Table 1. I got it.

The physical properties of the film are shown in Table 1, and like the film of Example 1, it was very excellent as a film for label shrinkage.

Example 4 In Example 1, as a propylene-random copolymer, Tennorgren (ethylene content 5.0 wt%, CX
S 4.1wt%, melt index 1.39/10
A stretched film was obtained in the same manner as in Example 1, except that the amount of petroleum resin added was changed to 35 parts by weight. The physical properties of the film are shown in Table 1, and like the film of Example 1, it was very excellent as a film for label shrinkage.

Example 5 Propylene-α-olefin copolymer (edge-1 content 1
2.8 mol%, ethylene content 1.8 mol%.

CXS 20.1 wt %, / l) inch 7
A stretched film was obtained in the same manner as in Example 1, except that a resin composition in which 30 parts by weight of Alcon P-140 was added to a propylene copolymer consisting of 7.2.2 f/10 minutes) was used. . The physical properties of the film are shown in Table 1, and like the film of Example 1, it was very excellent as a film for label shrinkage.

Example 6 Propylene-α-olefin copolymer (buty-1 content 2
A propylene copolymer composition consisting of 4.5 mol%, CXS 31.0 wt%, melt index 3.5 f/10 min) and 80 wt% of the propylene-random copolymer of Example 1 was used Otherwise, a stretched film was obtained in the same manner as in Example 1. The physical properties of the film are shown in Table 1, and like the film of Example 1, it was very excellent as a film for label shrinkage.

Comparative Example 1 On the day of the example, the amount of Alcon P-140 added was 5
A stretched film was obtained in the same manner as in Example 1 except that the parts by weight were changed. The physical properties of the film are shown in Table 1, and this film was undesirable as it had poor heat shrinkage and stiffness.

Comparative Example 2 A stretched film was obtained in the same manner as in Example 1, except that the propylene copolymer made solely of the propylene-random copolymer used in Example 1 was used. Film properties first
As shown in the table, this film has a very large natural shrinkage rate over time.

It was undesirable.

Comparative Example 3 In Example 1, the petroleum resin to be added was Alcon P-1.
A stretched film was obtained in the same manner as in Example 1, except that the temperature was changed to 15 (softening point: 115° C.).

The physical properties of the film are shown in Table 1. Compared to the film of Example 1, this film had a somewhat lower heat shrinkage rate and a higher natural rate over time.

Comparative Example 4 A stretched film was obtained in the same manner as in Example 1, except that only the propylene-〇-olefin copolymer used in Example 1 was used and no petroleum resin was added.

The physical properties of the film are shown in Table 1, and this film was undesirable as it had poor heat shrinkage and stiffness.

Comparative Example 5 Propylene copolymer Alcon P - consisting of the glopylene-a-olefins polymer used in Example 6 alone
A stretched film was obtained in the same manner as in Example 1, except that 5 parts by weight of 140 was added and the stretching temperature was changed to 60°C.

The physical properties of the film are shown in Table 1, and the film had poor stiffness, which was not desirable.

<Effects of the Invention> Although the shrink packaging film produced by the method of the present invention has extremely excellent heat shrinkability,
After film production, it undergoes little natural shrinkage over time, which occurs during storage before heat shrinkage, and it also has some stiffness, so when shrink-wrapping labels for bottles, for example, the film may buckle. It is very easy to operate. Furthermore, unlike polyvinyl chloride, it does not have disposal problems and can be manufactured at low cost, so it has extremely great practical value.

Claims (2)

[Claims] (1) A copolymer of propylene and an α-olefin having 4 or more carbon atoms, or a copolymer of propylene, an α-olefin having 4 or more carbon atoms, and ethylene, [1] an α-olefin having 4 or more carbon atoms in the copolymer. The content is 8 to 35 mol% [2] The ethylene content of the copolymer is 5 mol% or less [3]
A propylene copolymer containing 20% by weight or more of a propylene-α-olefin copolymer in which the cold xylene soluble portion of the copolymer is 10 to 70% by weight, and a hydrocarbon resin having a softening point temperature of 120°C or higher is added to the copolymer. A film for shrink packaging, characterized in that the resin composition containing 60 parts by weight is formed into a film and then stretched in at least one direction. (2) The shrink packaging film according to claim 1, wherein the α-olefin having 4 or more carbon atoms is butene-1.