JP4825031B2 - Laminated film - Google Patents

Description

The present invention relates to a laminated film obtained by laterally uniaxially stretching a laminated body including a base film layer and a heat-sealable film layer. In addition, unless otherwise indicated, the unit of "part" which shows the compounding composition of this invention is displayed on a mass basis.

Conventionally, a film including a base material layer and a heat seal layer is processed into a bag shape, a part of which is heat sealed, and is widely used for packaging foods, medical products, various parts, and the like. For this reason, the film used for such packaging is required to have proper heat sealing. 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.

In the case of producing a film having uniaxially stretched film and easy cutability in the stretching direction, polyolefin crystalline resin such as polypropylene and high density polyethylene are used as raw materials. As a film uniaxially stretched using polypropylene, three layers of two types of polypropylene resins having different melting points and a heat seal layer are laminated on the base film layer, and then a film having a three-layer structure (for example, patents) Document 1) has been proposed. As a film using polyethylene, a heat-sealable easily tearable film (for example, Patent Document 2) obtained by uniaxially stretching a linear low density ethylene resin having a density of 0.94 g / cm ³ or less uniaxially has been proposed. However, the resin is soft and the tensile modulus is low, and good tearability may not be obtained. In addition, as a low-density ethylene-based resin, a film that is uniaxially stretched in the flow direction, that is, in the longitudinal direction at a low magnification of 7 times or less by using the peripheral speed difference between rolls, and is easy to tear in the direction perpendicular to the stretching direction. (For example, Patent Document 3) has been proposed. However, when a low-density ethylene-based resin is stretched at a low magnification, the linear cut property and the easy cut property in the stretching direction may not be obtained. As a high-density polyethylene, a film having a transverse twist holding property and an anti-tear property by twisting, which is uniaxially stretched 4 to 10 times between metal rolls after laminating high-density polyethylene and linear low-density polyethylene (for example, patent documents) Although 4) has been proposed, there are cases in which the straight cut property and the easy cut property in the stretching direction cannot be obtained.
Japanese Patent Laid-Open No. 04-229251 JP 59-78817 A Japanese Examined Patent Publication No. 61-41732 Japanese Patent Laid-Open No. 02-127041

It is an object of the present invention to provide a laminated film having heat sealability that has a straight-cut property and an easy-cut property in a well-balanced direction in the stretching direction.

As a result of diligent studies to achieve the above-mentioned problems, the present inventors have obtained a laminated film obtained by stretching a laminated body including a base film layer and a heat-sealable film layer in a horizontal uniaxial direction at a high magnification. The inventors have found that the resistance during tearing can be greatly reduced, and that the properties of easy cutability are maintained in a well-balanced manner in the stretching direction while maintaining straight advance cutability, and the present invention has been completed.

That is, the present invention is a laminated film comprising the following (1) to (6) obtained by transversely uniaxially stretching a laminate comprising a base film layer and a heat-sealable film layer.
(1) The draw ratio of the laminated film is more than 10 times and 18 times or less.
(2) The tensile elastic modulus in the stretching direction of the laminated film is 2.5 to 6.0 GPa.
(3) The resin composition constituting the base film layer is a mixture containing 100 parts by weight of high-density polyethylene and 0 to 25 parts by weight of low-density polyethylene or linear low-density polyethylene.
(4) The melt flow rate of the high density polyethylene used for the substrate film layer is 0.05 to 10.0 g / 10 min.
(5) The thickness of the laminated film is in the range of 5 to 100 μm.
(6) The base film layer and the heat-sealable film layer are laminated by thermal lamination.

The resin composition constituting the base film layer is preferably high-density polyethylene alone or a mixture of high-density polyethylene and at least one of linear low-density polyethylene and low-density polyethylene. Furthermore, the resin composition constituting the heat-sealable film layer is preferably a polyolefin resin. Further, the density of the high-density polyethylene in the base film layer is preferably 0.94 g / cm ³ or more.
The laminated film can be used for bags.

ADVANTAGE OF THE INVENTION According to this invention, the lamination film with the heat-sealing property which has the characteristic of straight-cut property and easy-cut property in a good balance in the extending | stretching direction can be obtained.

The present invention specifies the stretching ratio of the transverse uniaxial stretching of the laminated film and the tensile elastic modulus in the stretching direction in the laminated film comprising the laminate including the base film layer and the heat-sealable film layer as described above. This is based on the finding that a heat-sealing laminated film having a balance between straight-cutting properties and easy-cutting properties in the stretching direction can be obtained.

The laminated film of the present invention is preferably uniaxially stretched in the transverse direction by a tenter stretching method, for example, at a stretching temperature of 80 ° C. to 140 ° C., for a laminate including a base film layer and a heat-sealable film layer.

The draw ratio of the laminated film of the present invention is more than 10 times and 18 times or less, preferably 12 to 16 times. When the draw ratio is 10 times or less, the obtained laminated film is not torn linearly or cannot be easily torn. On the other hand, when the draw ratio exceeds 18 times, it becomes difficult to stretch the resulting laminated film, resulting in a laminated film having large variations. The tensile modulus of the laminated film in the stretching direction is 2.5 to 6.0 GPa, preferably 3.0 to 6.0 GPa. The laminated film obtained when the tensile elastic modulus is less than 2.5 GPa does not provide a straight-cut property and an easy-cut property in the stretching direction. On the other hand, the laminated film obtained when the tensile elastic modulus exceeds 6.0 GPa has high rigidity (strength of waist) and requires attention for film forming and handling, so that workability is deteriorated.

“Tensile modulus” is measured in a standard atmosphere of JISK-7127, test piece type B1, test speed 5 mm / min, temperature 23 ° C., relative humidity 50%. The stretched laminated film has a thickness of 5 to 100 μm, preferably 10 to 60 μm. If the thickness of the laminated film is less than 5 μm, the strength required for the film is insufficient, while if it exceeds 100 μm, it may be difficult to tear.

As a method of controlling the value of the tensile elastic modulus in the stretching direction of the laminated film, there is a method of changing the density of HDPE or the amount of LLDPE or LDPE mixed with HDPE for the above-mentioned base film layer. For example, when the density of HDPE is increased, the tensile elastic modulus can be increased. As a method of adjusting the molding conditions at the time of molding the laminated film, it can be carried out by the stretching temperature, the stretching ratio, etc. during the stretching process step of the laminated film. As an example, the tensile modulus increases by lowering the stretching temperature. On the other hand, when the draw ratio is lowered, the tensile elastic modulus can be reduced.

The resin composition mainly composed of high-density polyethylene constituting the base film layer may be high-density polyethylene (hereinafter abbreviated as “HDPE”) alone, or high-density polyethylene and linear low-density polyethylene (hereinafter “LLDPE”). And a mixture of at least one of low density polyethylene (hereinafter abbreviated as “LDPE”). When LLDPE or LDPE is mixed with HDPE, 25 parts by mass or less is preferable with respect to 100 parts by mass of HDPE. When LLDPE or LDPE exceeds 25 parts by mass, the obtained laminated film may not have sufficient straight cut property or easy cut property.

The HDPE of the base film layer preferably has a density of 0.94 g / cm ³ or more. When the density of HDPE is 0.94 g / cm ³ or less, the obtained laminated film may not have sufficient tearability. The upper limit of the density is not particularly limited, but is preferably less than 0.97 g / cm ³ . The melting point of HDPE is preferably 126 to 136 ° C. as measured by the DSC method. Furthermore, the melt flow rate (MFR) of HDPE is preferably 0.05 to 10.0 g / 10 min under the measurement conditions of a temperature of 190 ° C. and a load of 2.16 kg as defined in JISK-6922-2, Preferably it is 0.05-5.0.

The LLDPE and LDPE of the base film layer preferably have a melting point of 90 to 125 ° C. as measured by the DSC method. Further, these densities are preferably 0.90 to 0.93 g / cm ³ . Furthermore, these melt flow rates (MFR) are preferably 0.05 to 20.0 g / 10 min under the measurement conditions of a temperature of 190 ° C. and a load of 2.16 kg as defined in JISK-6922-2, More preferably, it is 0.05-10.0.

There is no restriction | limiting in particular in the method of obtaining the said mixture, A well-known mixing method is used. For example, the method of mixing at room temperature or the temperature of the vicinity using well-known mixers, such as a Henschel mixer, a ribbon blender, a Banbury mixer, and a tumbler mixer, is mentioned. After mixing, the mixture may be kneaded and melted using a mixing roll, a single-screw or twin-screw extruder, etc., and then the obtained sheet or strand may be pulverized and cut to form a pellet. When each resin is already formed into a pellet, the resins may be mixed and used as they are.

The heat-sealable film layer is a layer composed of a heat-meltable synthetic resin, and the resin constituting the heat-sealable film layer requires heat-sealability, so that the melting point is 40 to 40 according to the DSC measurement. The polyolefin resin is not particularly limited as long as it is in the range of 160 ° C., preferably in the range of 80 to 140 ° C. For example, polyethylene, polypropylene, ethylene-vinyl acetate copolymer (hereinafter abbreviated as “EVA”), propylene-ethylene copolymer, ethylene-1-butene copolymer, propylene-1-butene copolymer, ethylene- Examples thereof include at least one selected from a propylene-butadiene copolymer and an ethylene-propylene-1-butene copolymer. Among these, polyethylene is preferable in that it has good adhesiveness without using HDPE, which is the main component of the base film layer, and an adhesive.

As a method for producing the laminated film of the present invention, a conventionally known method may be used, and a base film layer and a heat-sealable film layer are extruded from separate extruders to form a composite flow in a molten state, and then molded, There is a method in which the other film is melt-extruded and bonded to an unstretched film. Also, a thermal lamination method in which the base film layer and the heat-sealable film layer are bonded by pressing with a heating roll, a solvent-type adhesive is applied to the base film layer, and once dried, the heat-sealable film layer is applied. Examples of the method include a dry lamination method, a non-solvent lamination method, and a wet lamination method. Among these, the thermal lamination method is preferable because it does not use an adhesive and simplifies the process.

As a method for obtaining the base film layer, for example, there is a method of forming an unstretched film, but it is not limited thereto. As a method for forming an unstretched film, the resin composition or the resin mixture constituting the base film layer is supplied to an extruder, melted, extruded through a film die, and cooled by a molding machine to have a thickness of about An unstretched film of 20 to 1800 μm is formed.

As a method for obtaining a heat-sealable film layer, for example, there is a method of forming an unstretched film, but it is not limited thereto. As a method for forming an unstretched film, the resin or resin mixture constituting the heat-sealable film layer is supplied to an extruder, melted, extruded through a film die, and cooled by a molding machine to have a thickness of about 10 Form an unstretched film of ˜300 μm.

If necessary, additives such as heat stabilizers, antioxidants, UV absorbers, anti-blocking agents, lubricants, antistatic agents, pigments, dyes, etc. may be added to the resin of the base film layer and heat sealable film layer. May be added.

In order to stabilize the dimension of the laminated film after stretching, the film may be contracted by about 1 to 10% in the stretching direction and heat-treated (heat set) at 70 to 165 ° C. for 1 to 60 seconds. The surface of the laminated film may be subjected to surface treatment such as corona treatment.

The laminated film of the present invention is a film in which at least a base film layer and a heat-sealable film layer are laminated, and it is sufficient if it has a strength that can withstand distribution and storage. Within the range, in addition to the configuration of the laminated film, for example, a film such as biaxially stretched polypropylene, biaxially stretched nylon, or polyester can be laminated.

The thickness of the laminated film is in the range of 5 to 100 μm, preferably 10 to 60 μm. If the thickness is less than 5 μm, the strength required for the laminated film is insufficient. On the other hand, if the thickness exceeds 100 μm, it may be difficult to tear the laminated film.

Hereinafter, the present invention will be described in more detail with reference to Table 1 with reference to Examples and Comparative Examples. These are all illustrative and do not limit the contents of the present invention.

In Tables 1 and 2, “straight cut” refers to the tearing direction when the laminated film is torn, and the following standard superiority: almost in the stretching direction, with the laminated film being linearly cut Good: deviating from the stretching direction , Defect in which the laminated film was cut: There was almost no directionality, and the laminated film was cut and visually evaluated.

“Easy-cut” in Tables 1 and 2 indicates that the laminated film is torn in the stretching direction, and the following standard excellence: twisted fingertips, and the laminated film is easily cut in a straight line Good: fingernails are made According to the results, the laminated film was broken. Defects: Even if the fingernail was made, the laminated film was stretched, and scratches were caused and the film was cut and evaluated visually.

Example 1
HDPE (Novatec HD HB442R manufactured by Nippon Polyethylene Co., Ltd., melting point = 134 ° C., density = 0.957 g / cm ³ , MFR = 0.25 g / 10 min) was fed into the extruder, and the melted material was passed through a film die. A substrate film layer having a thickness of 300 μm was formed by extrusion and cooling with a molding machine. A laminate obtained by laminating an unstretched film (V-1 film manufactured by Tamapoly Co., Ltd.) having a thickness of 180 μm using LDPE as a heat-sealable film layer on this base film layer by a thermal lamination method in a tenter at 120 ° C. A laminated film having a thickness of 32 μm was obtained by uniaxially stretching 15 times.

(Example 2)
The horizontal uniaxial stretching ratio of Example 1 was changed to the values described in Table 1, and a laminated film having a thickness of 40 μm was obtained in the same manner as Example 1.

(Example 3)
The thickness of the heat-sealable film layer of Example 1 was the same as that of Example 1 except that a 160 μm-thick unstretched film using LLDPE (DS-2 manufactured by Tamapoly Co., Ltd.) was used and uniaxially stretched 18 times. A laminated film having a thickness of 26 μm was obtained.

Example 4
10 parts by mass of LDPE (Novatech LD LF125E manufactured by Nippon Polyethylene Co., Ltd., melting point = 111 ° C., density = 0.922 g / cm ³ , MFR = 0.4 g / 10 min) to 100 parts by mass of HDPE of the base film layer of Example 1 A laminated film having a thickness of 32 μm was obtained in the same manner as in Example 1 except that a dry blend was used.

(Example 5)
10 parts by mass of LLDPE (Novatec LL UE320, manufactured by Nippon Polyethylene Co., Ltd., melting point = 122 ° C., density = 0.922 g / cm ³ , MFR = 0.8 g / 10 min) to 100 parts by mass of HDPE of the base film layer of Example 1 A laminated film having a thickness of 32 μm was obtained in the same manner as in Example 1 except that a dry blend was used.

(Example 6)
A laminated film having a thickness of 31 μm was obtained in the same manner as in Example 1 except that a 160 μm-thick unstretched film using EVA (AV-51 manufactured by Tamapoly Co., Ltd.) was used for the heat-sealable film layer of Example 1. Obtained.

(Comparative Examples 1 and 2)
In Comparative Examples 1 and 2, the transverse uniaxial stretching ratio of Example 1 was changed to the values described in Table 2, and Comparative Example 1 was changed to 150 μm for the base film layer and 90 μm for the heat-sealable film layer, A laminated film having a thickness of 40 μm was obtained in the same manner as in Example 1. Since the laminate film of Comparative Example 2 having a thickness of 24 μm had a draw ratio of 20 times, the drawing process was not stable, and the characteristics shown in Table 1 had a large variation and were poor.

(Comparative Example 3)
Before laminating the base film layer and the heat-sealable film layer, only the base film layer formed in the same manner as in Example 1 was horizontally uniaxially stretched at a stretch ratio of 15 times, and then the LDPE was used as the heat-sealable film layer. An unstretched film (V-1 film manufactured by Tamapoly Co., Ltd.) having a thickness of 30 μm using a polyester adhesive (Takelac A-620 manufactured by Mitsui Takeda Chemical Co., Ltd.) and a curing agent (Takenate A- manufactured by Mitsui Takeda Chemical Co., Ltd.) The mixture of 65) was used as an adhesive and laminated by a dry lamination method to obtain a laminated film having a thickness of 50 μm.

(Comparative Example 4)
Before laminating the base film layer and the heat-sealable film layer, only the base film layer formed in the same manner as in Example 1 was horizontally uniaxially stretched at a stretch ratio of 15 times, and then the LDPE was used as the heat-sealable film layer. (UBE Kogyo Co., Ltd. UBE polyethylene L719) was used for lamination by an extrusion lamination method to obtain a laminated film having a thickness of 32 μm.

As can be seen from Tables 1 and 2, if the laminated film falls within the scope of the present invention, a laminated film having heat sealing properties with extremely good straight-cut properties and easy-cut properties in the stretching direction can be obtained. .

The laminated film of the present invention includes, for example, powdered or granular medicine packaging paper, juices, jelly-like beverages, drinking water, energy drinks, tea, coffee beverages, rice balls, manju, dorayaki, cakes and other Western confectionery, snack confectionery, cups It can be preferably used for soft packaging materials such as noodles, seasoning bags and sandwiches.

Claims (1)

A laminated film comprising the following (1) to (6) obtained by transversely uniaxially stretching a laminate comprising a base film layer and a heat-sealable film layer.
(1) The draw ratio of the laminated film is more than 10 times and 18 times or less.
(2) The tensile elastic modulus in the stretching direction of the laminated film is 2.5 to 6.0 GPa.
(3) The resin composition constituting the base film layer is a mixture containing 100 parts by weight of high-density polyethylene and 0 to 25 parts by weight of low-density polyethylene or linear low-density polyethylene.
(4) The melt flow rate of the high density polyethylene used for the substrate film layer is 0.05 to 10.0 g / 10 min.
(5) The thickness of the laminated film is in the range of 5 to 100 μm.
(6) The base film layer and the heat-sealable film layer are laminated by thermal lamination.