JP2006176620A - Film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a film having characteristics of heat-sealable properties and tearable properties in good balance and uniaxially oriented in lateral one direction; and to provide a bag obtained by using the film, easily opened straightly and providing a beautiful cut face when opened. <P>SOLUTION: The film is obtained by uniaxially orienting a resin composition comprising a high-density polyethylene and a linear low-density polyethylene in the lateral direction. The resin composition comprises 100 pts.mass high-density polyethylene and 10-60 pts.mass linear low-density polyethylene. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention relates to a polyethylene-based laterally uniaxially stretched film and its use. In addition, unless otherwise indicated, the unit of "part" which shows the compounding composition of this invention is displayed on a mass basis.

Films made of polyethylene resin are widely used for packaging foods and various parts. When these films are used for packaging, these films are processed into a bag shape, and a part thereof is heat-sealed to be used as a packaging bag. The film used for such a packaging bag is required to have heat seal suitability in addition to the mechanical strength and impact resistance necessary to protect the contents during transportation and storage. On the other hand, in recent years, it has been required that these bags can be easily opened by hand without using scissors or knives. As one of the means, in order to give the film an appropriate tear property in a certain direction. There is a method of uniaxial stretching. However, in general, a film obtained by stretching a polyethylene resin film in a uniaxial direction has an appropriate tearing property in a specific direction. However, if the film is to be fused by heat sealing, the film is melted before being fused. Shrinkage occurred and it was difficult to obtain a good bag. In order to overcome such problems, for example, as described in Patent Document 1, a method of forming a sealant layer on the surface of a laminate of a base film and a longitudinally uniaxially stretched film has been performed. However, since such a film has a complicated structure and high cost, it is a single-layer film, is suitable for heat sealing, and is made of a polyethylene-based resin having appropriate tearability in a specific direction. Was demanded.
JP 2003-034008 A

It is an object of the present invention to provide a polyethylene film having a good balance between heat sealability and tearability.

As a result of intensive studies to achieve the above-mentioned problems, the present inventor has achieved heat sealability by stretching a film made of a resin composition in which linear low-density polyethylene is mixed with high-density polyethylene in the transverse uniaxial direction. The present invention has been completed by finding that a film having a good balance between tear properties and tearing properties can be obtained.

That is, the present invention is a film obtained by laterally uniaxially stretching a resin composition containing high-density polyethylene and linear low-density polyethylene. Furthermore, it is preferable that a resin composition contains 10-60 mass parts of linear low density polyethylene with respect to 100 mass parts of high density polyethylene. Moreover, it is a film which can be heat-sealed, and is a bag using the film.

According to the present invention, a resin composition containing high-density polyethylene and linear low-density polyethylene is laterally uniaxially stretched so that even a single-layer film has an excellent balance between heat sealability and tearability. And the bag for soft packaging which can be torn in the width direction can be obtained.

The film of the present invention comprises a polyethylene-based resin composition in which linear low-density polyethylene (hereinafter abbreviated as “LLDPE”) is mixed with high-density polyethylene (hereinafter abbreviated as “HDPE”). When HDPE is used alone, heat sealability becomes extremely difficult when a transversely stretched film described later is used. On the other hand, when LLDPE is used alone, the heat-sealability is good even when transversely stretched, but the tearability in the transversely-stretching direction is extremely poor.

In the present invention, the stretched film is transversely uniaxially stretched. For example, when the content is a long product, if it is a packaging bag of a longitudinally uniaxially stretched film, it can be torn only in the longitudinal direction, that is, in the longitudinal direction of the content. . In such a case, the contents jump out of the bag, which is inconvenient. However, in the case of a laterally uniaxially stretched film packaging bag, it can be used while pushing out the contents little by little even in a long packaging bag or by cutting the bag sideways little by little according to the rest of the contents It is possible and very convenient.

HDPE used in the present invention has a melting point in the range of 126 to 136 ° C. as measured by the DSC method, a melt flow rate (MFR) in the range of 0.93 to 0.97 g / cm ³ , and a JISK6922- 2 is preferably 0.03 to 5.0 (g / 10 min), more preferably 0.1 to 2.0 under the measurement conditions of a temperature of 190 ° C. and a load of 2.16 kg specified in 2. If the MFR is less than 0.03, the fluidity is hardly exhibited even when heated and melted, so the film formability may be deteriorated. On the contrary, if the MFR exceeds 2.0, the fluidity is too large and film formation is difficult. It may become.

LLDPE used in the present invention is a copolymer of ethylene and butene-1, hexene-1, octene-1, etc., and has a melting point of 115 to 125 ° C. as measured by DSC method and a density of 0.90. In the range of 0.95 g / cm ³ , the melt flow rate (MFR) is preferably 0.05 to 10.0 (g / kg) under the measurement conditions of a temperature of 190 ° C. and a load of 2.16 kg as defined in JISK6922-2. 10 minutes), and more preferably 0.05 to 5.0. If the MFR is less than 0.1, even if it is heated and melted, the fluidity is hardly exhibited, so that the film formability may be deteriorated. On the contrary, if the MFR exceeds 5.0, the fluidity is too large and film formation is difficult. It may become.

The mixing ratio of HDPE and LLDPE is preferably 10-60 parts by mass of LLDPE, more preferably 20-40 parts by mass with respect to 100 parts by mass of HDPE. If LLDPE is less than 10 parts by mass, sufficient heat sealability may not be obtained, and if it exceeds 60% by mass, sufficient tearability may not be obtained.

The film of the present invention can be obtained as follows. First, an unstretched film is formed using the resin composition. As a method for forming an unstretched film, the raw material resin mixture is supplied to an extruder, melted, extruded through a film die, and cooled by a molding machine, whereby the thickness is in the range of about 20 to 1400 microns. A stretched film is formed and transversely uniaxially stretched at a constant width at 100 to 140 ° C. In the present invention, a film excellent in tearing properties can be obtained by transversely uniaxially stretching a formed unstretched film.

The lateral uniaxial stretching ratio of the film of the present invention is in the range of 2 to 16 times, preferably 6 to 14 times. When the draw ratio is less than 2, sufficient molecular orientation cannot be obtained, and the film cannot be linearly torn in the drawing direction. On the other hand, if it exceeds 16 times, stretching becomes difficult. The stretched film has a thickness in the range of 5 to 100 microns, preferably 10 to 60 microns. If the thickness is less than 5 microns, the strength required for the film is lost, whereas if it exceeds 100 microns, it may be difficult to tear the film.

A conventionally well-known method can be used for the specific extending process. For example, it can be considered that the film is stretched by a tenter stretching method. In this case, the stretching temperature is 100 ° C. to 140 ° C., preferably 110 ° C. to 130 ° C., and is stretched in the range of the stretching ratio.

In order to stabilize the dimensions after the transverse stretching, for example, it is conceivable to perform heat treatment (heat setting) at 100 to 165 ° C. for 1 to 60 seconds. It is because the stretched film which has favorable heat-sealing property is obtained by performing heat processing.

Moreover, although it does not extend | stretch substantially in the vertical direction, you may extend | stretch longitudinally in the range of 1-3 times so that the directionality of tear may not be lost.

The film of the present invention is used as a bag by heat sealing as described above. As a method of heat sealing, for example, it can be performed by a known method such as bar seal, rotary roll seal, belt seal, impulse seal, high frequency seal, ultrasonic seal, etc. Particularly excellent heat sealability can be obtained. When the film of the present invention is used as a laterally stretched packaging bag, the heat seal strength is preferably 15 N / 15 mm or more.

The packaging bag of the laterally uniaxially stretched film obtained in this way is easy to open, especially when the contents are long, because it is easy to open in the width direction of the bag. That is, the bag can be cut little by little according to the remaining length of the contents. A longitudinally uniaxially stretched film is easy to open only in the length direction of the bag, and in such a case, the bag can be opened only in the vertical direction, and the contents jump out of the bag, which is inconvenient. Of course, the contents of the bag need not be long. Any content can be handled in the same way.

Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited to the examples.

In Table 1, “possible heat seal temperature” means a film uniaxially stretched using a heat seal tester (TP-701, manufactured by Tester Sangyo Co., Ltd.) with a seal pressure of 0.2 MPa, a seal width of 10 mm, and a seal time of 0.5. Each temperature was heat-sealed in seconds, and the film breaking condition when a film having a test piece width of 15 mm was pulled at a pulling speed of 300 mm / min was evaluated for each temperature according to the following criteria.
○ The film causes material destruction, and the maximum strength of the seal part is 15N / 15mm or more.
△ Material destruction was insufficient.
× Removed from the heat seal part without destroying the material.

In Table 1, “tearability” was determined by visually tearing the film by hand in the width direction and following the criteria below.
○ The film is easily cut in a straight line by the twist of the fingertip.
△ Cut off by placing a fingernail.
× Even if the fingernail is raised, the film stretches and does not cut, but can be cut by making a cut.

(Example 1) 100 parts by mass of high-density polyethylene (Novatec HD HF313, manufactured by Nippon Polyethylene Co., Ltd.) and 10 parts by mass of linear low-density polyethylene (Novatech LL UF421, manufactured by Nippon Polyethylene) were dry blended and supplied to an extruder. Then, it was melted, extruded through a film die, and cooled by a molding machine to form an unstretched film having a thickness of about 200 microns. This unstretched film was stretched 10 times in a 120 ° C. tenter to obtain a 20-micron lateral uniaxially stretched film.

(Example 2) A film was obtained in the same manner as in Example 1 except that 100 parts by mass of the high-density polyethylene was dry blended with 20 parts by mass of the linear low-density polyethylene.

(Example 3) A film was obtained in the same manner as in Example 1 except that 100 parts by mass of the high-density polyethylene was dry blended with 40 parts by mass of the linear low-density polyethylene.

(Example 4) A film was obtained in the same manner as in Example 1 except that 100 parts by mass of the high density polyethylene was dry blended with 60 parts by mass of the linear low density polyethylene.

Comparative Example 1 A film was obtained in the same manner as in Example 1 except that only the high density polyethylene was used.

(Comparative Example 2) A film was obtained in the same manner as in Example 1 except that only the above-mentioned linear low density polyethylene was used.

The transversely uniaxially stretched film of the present invention can be impulse-sealed or heat-sealed, and is excellent in tearing properties, for example, pharmaceuticals, juices, jelly-like beverages, energy drinks, drinking water, tea, coffee It can be preferably used for bags such as beverages, buns, dorayaki, cakes and other Western confectionery, snacks, rice balls, cup noodles, seasonings and the like.

Claims (4)

A film obtained by transversely uniaxially stretching a resin composition containing high-density polyethylene and linear low-density polyethylene. The film of Claim 1 in which a resin composition contains 10-60 mass parts of linear low density polyethylene with respect to 100 mass parts of high density polyethylene. The film according to claim 1 or 2, wherein heat sealing is possible. A bag using the film according to claim 3.