JP6984593B2 - Polypropylene resin multilayer film and packaging using it - Google Patents

Description

The present invention relates to a polypropylene-based resin multilayer film and a package using the same, and in particular, a fresh product made of plants such as vegetables, fruits, and flowers, which have a heat-sealing property and an antifogging effect, and which require high freshness. It relates to a polypropylene-based resin multilayer film suitable for packaging (hereinafter, these are referred to as fruits and vegetables in the present specification) and a package using the polypropylene-based resin multilayer film.

Conventionally, polypropylene-based resin films have been widely used in the packaging field such as food packaging and fiber packaging because they are excellent in optical properties, mechanical properties, packaging suitability, and the like. In particular, anti-fog films are widely used for packaging fruits and vegetables such as vegetables.

In fruit and vegetable packaging, labor saving in agricultural work is required due to the recent decline in the agricultural population, and automatic packaging equipment is becoming widespread. A so-called pillow packaging method is adopted as an automatic packaging device for fruits and vegetables, and a bag making process by heat sealing and a filling process of contents can be performed at the same time.

As a material that can be used for automatic packaging by pillow packaging, it is composed of an outer layer made of a biaxially stretched film containing crystalline polypropylene as a main component and an olefin polymer having a melting point 10 to 90 ° C lower than the melting point of the outer layer. A laminated film for packaging raw vegetables made of a film-like material is disclosed (see, for example, Patent Document 1).
However, since the film disclosed in Patent Document 1 uses a propylene / ethylene / butene-1 copolymer for the heat-sealing layer, there is a problem in terms of both low-temperature sealing property and sealing strength.
Further, two or more layers having a base layer mainly composed of a polypropylene resin and a heat seal layer mainly composed of a polyolefin resin using a propylene / butene-1 copolymer and a propylene / ethylene / butene-1 copolymer. A packaging film made of the laminate of the above is disclosed (see, for example, Patent Document 2).
However, there is a problem that the seal strength is not sufficient.

On the other hand, there are still many fruits and vegetables that are not automatically wrapped, and there are also uses for bag making and filling separately. In that case, most of the bag making processes are carried out by the fusing sealing method.
If it is possible to use both pillow packaging and fusing seal packaging as a film for packaging fruits and vegetables, there is an advantage in terms of inventory management from the standpoint of consumers such as farmers and converters.
However, none of the conventional pillow-wrappable films can be used for fusing and sealing.

Japanese Patent No. 3104166 Japanese Patent No. 4385443

We aim to provide a polypropylene-based resin multilayer film that can be used in a wide range of packaging fields by combining good automatic packaging suitability due to its low-temperature sealing properties and high heat-sealing strength, and fusing sealing properties at a lower cost than before. It is an issue.

That is, the present invention has the following configuration.
1. 1. Mainly polypropylene-based resin, consisting of a group consisting of a propylene / ethylene / butene-1 copolymer, a propylene / butene-1 copolymer, and a propylene / ethylene copolymer on one side of the base layer (A) and the base layer (A). It has a surface layer (B) mainly composed of a polypropylene-based resin composition composed of at least one selected copolymer, and has a propylene / ethylene / butene-1 copolymer weight on the opposite surface of the surface layer (B). Polypropylene having a seal layer (C) mainly composed of a polypropylene-based resin composition composed of at least one copolymer selected from the group consisting of a coalescence, a propylene / butene-1 copolymer and a propylene / ethylene copolymer. A polypropylene-based resin multilayer film, which is a polymer-based resin multilayer film and is characterized by satisfying the following a) to c).
a) The heat seal rising temperature of the seal layer (C) is 115 ° C. or higher and 125 ° C. or lower, and the heat seal ultimate strength is 3.0 N / 15 mm or higher.
b) The thickness of the seal layer (C) has a range of 1.5% or more and 5% or less with respect to the entire film layer. c) At least the anti-fog agent is contained in the seal layer (C).
2. 2. The temperature of the melting point of the resin having the lowest melting point among the copolymers constituting the seal layer (C) is in the range of 120 to 130 ° C., and the content thereof is 50% by weight or more and 85% by weight or less. The polypropylene-based resin multilayer film according to item 1.
3. 3. The copolymer having the highest melting point among the copolymers constituting the seal layer (C) has a melting point of 130 ° C. or higher and 140 ° C. or lower, and the content thereof is 15% by weight or more and 50% by weight or less. The polypropylene-based resin multilayer film described in the section.
4. The temperature of the melting point of the copolymer constituting the seal layer (C) is in the range of 120 to 140 ° C., and the content of the copolymer at 120 to 130 ° C. is 50% by weight or more and 85% by weight or less, 130. The polypropylene-based resin multilayer film according to the above item 1, wherein the content of the copolymer at ~ 140 ° C. is 15% by weight or more and 50% by weight or less.
5. The base layer (A) is selected from the group consisting of isotactic polypropylene, propylene / ethylene copolymer, propylene / butene-1 copolymer, propylene / ethylene / butene-1 copolymer and propylene / penten copolymer. The polypropylene-based resin multilayer film according to the above item 1, which is mainly composed of a polypropylene-based resin composed of at least one copolymer and contains an antifogging agent.
6. A package using the polypropylene-based resin multilayer film according to any one of the above items 1 to 5.

By optimizing the seal thickness and composition, the polypropylene-based resin multilayer film of the present invention can impart good pillow packaging suitability at a lower cost than before, and can also have fusing seal characteristics. ..

1. 1. Characteristics of the polypropylene-based resin multilayer film of the present invention 1-1. Base layer (A)
In the present invention, the base layer (A) is composed of isotactic polypropylene, a propylene / ethylene copolymer, a propylene / butene-1 copolymer, a propylene / ethylene / butene-1 copolymer and a propylene / penten copolymer. It is necessary to mainly use a polypropylene-based resin composition composed of at least one polymer selected from the group. The melting point of the entire base layer is preferably 145 ° C. or higher, more preferably 150 ° C. or higher. If the temperature is lower than 145 ° C., the heat resistance of the film as a whole is poor, and the appearance of the package may be impaired when the film is automatically packaged. Further, the melt flow rate (MFR) can be exemplified in the range of 0.1 to 100 g / 10 min, preferably 0.5 to 20 g / 10 min, and more preferably 1.0 to 10 g / 10 min.

It is necessary to add an anti-fog agent to the resin forming the base layer (A). If the anti-fog agent is not added, the inside becomes cloudy when the fruits and vegetables are packaged, and the putrefaction tends to proceed, so that the commercial value is lowered.
The mechanism for developing the anti-fog property of the polypropylene-based resin multilayer film of the present invention is to add an anti-fog agent to the resin forming the base layer (A) to prevent anti-fog during film production and storage after film formation. The agent sequentially shifts to the surface layer (B) and the seal layer (C), and the film surface becomes anti-fog. The effect can be exhibited when fruits and vegetables, which are characterized by maintaining their physiological action even after harvesting, are targeted for packaging.
In order to maintain excellent anti-fog properties over the long term in the distribution process, it is desirable that the package be stored in a room temperature atmosphere rather than frozen storage, so considering the temperature changes during storage and distribution. It is preferable to select an anti-fog agent that continuously exhibits anti-fog properties during the course of repeated temperature changes between 5 and 30 ° C.

Examples of the antifogging agent added to the resin forming the base layer (A) of the polypropylene-based resin multilayer film of the present invention include fatty acid esters of polyvalent alcohol, amines of higher fatty acids, and amides of higher fatty acids. , Amin of higher fatty acid, ethylene oxide adduct of amide, etc. can be mentioned as typical examples. The abundance of the anti-fog agent in the film is preferably 0.1 to 10% by weight, particularly 0.2 to 5% by weight, in terms of all layers.

Further, as long as the effect of the present invention is not impaired, various additives for improving quality such as slipperiness and antistatic property, for example, lubricants such as wax and metal soap for improving productivity, and plasticizers. It is also possible to add known heat stabilizers, antioxidants, antistatic agents, ultraviolet absorbers and the like which are usually added to agents, processing aids and polypropylene films.

1-2. Surface layer (B)
In the present invention, the surface layer (B) has at least one copolymer weight selected from the group consisting of a propylene / ethylene / butene-1 copolymer, a propylene / butene-1 copolymer and a propylene / ethylene copolymer. It is preferable that the heat seal rise temperature is 130 ° C. or higher and 140 ° C. or lower, mainly composed of a copolymerized polypropylene-based resin. In order to set the heat seal rise temperature of the surface layer (B) to 130 to 140 ° C., it is preferable to select the copolymer so as to contain the propylene / ethylene / butene-1 copolymer.
The heat seal rising temperature of the surface layer (B) is the heat seal when the surfaces of the surface layer (B) of the film of the present invention face each other, the heat seal pressure is 1 kg / cm2, and the time is 1 second. The temperature is such that the strength is 1 N / 15 mm. When the heat seal rise temperature of the surface layer (B) is 130 ° C. or higher, the surface layer (B) is difficult to fuse with the sealer during heat sealing of pillow packaging, and it is easy to make a bag. Further, when the temperature is 140 ° C. or lower, the back-pasted portion easily fuses with the exterior portion of the package during pillow packaging and has a good appearance, and the back-pasted portion does not get caught when the packages are stacked, so that the seal does not peel off.

The thickness of the surface layer (B) is preferably in the range of 1 to 10% with respect to the entire film layer. When it is 10% or less, the fused resin portion called a poly pool at the time of fusing and sealing does not become too large, and the fusing and sealing strength is further improved. When it is 1% or more, it tends to exhibit a function as a surface layer.

The surface of the surface layer (B) preferably has anti-fog properties. When packaging fruits and vegetables and displaying them at supermarkets, the appearance will improve if the surface becomes cloudy due to condensation.

Further, as long as the effect of the present invention is not impaired, various additives for improving quality such as slipperiness and antistatic property, for example, lubricants such as wax and metal soap for improving productivity, and plasticizers. It is also possible to add known heat stabilizers, antioxidants, antistatic agents, ultraviolet absorbers and the like which are usually added to agents, processing aids and polypropylene films. It is also possible to add inorganic or organic fine particles to ensure the blocking resistance and slipperiness of the film.

Examples of the inorganic fine particles include silicon dioxide, calcium carbonate, titanium dioxide, talc, kaolin, mica, and zeolite, and these shapes are not limited to spherical, elliptical, conical, and amorphous. As for the particle size, a desired particle size can be used and blended depending on the intended use and usage of the film. Further, as the organic fine particles, crosslinked particles such as acrylic, methyl acrylate, and styrene-butadiene can be used, and various particles such as inorganic fine particles can be used in terms of shape and size. It is possible. Further, it is possible to apply various surface treatments to the surface of these inorganic or organic fine particles, and these can be used alone or in combination of two or more. The above is also compatible with the seal layer (C) described later.

1-3. Seal layer (C)
In the present invention, the seal layer (C) has at least one copolymer weight selected from the group consisting of a propylene / ethylene / butene-1 copolymer, a propylene / butene-1 copolymer and a propylene / ethylene copolymer. It is necessary that the heat seal rise temperature of the seal layer (C) is 115 ° C. or higher and 125 ° C. or lower, mainly made of a polypropylene-based resin made of a coalescence. The heat seal rising temperature of the surface layer (C) is the heat seal when the surfaces of the surface layer (C) of the film of the present invention face each other, the heat seal pressure is 1 kg / cm2, and the time is 1 second. The temperature is such that the strength is 1 N / 15 mm.
When the heat seal rise temperature of the seal layer (C) is 125 ° C or lower, it is possible to maintain sufficient strength and heat seal even if the heat seal temperature is low, so that it can be operated at high speed during automatic packaging. In addition, the sealing portion is excellent in sealing property, and therefore, the freshness of the fresh product is maintained in combination with the antifogging property, the contents are good in appearance, and the handling of the package is excellent.
When the heat seal rise temperature of the seal layer (C) exceeds 125 ° C., the difference in melting point from the base layer (A) mainly composed of polypropylene resin becomes small, and the operation speed of automatic packaging cannot be sufficiently increased. Further, if the set temperature is raised in order to increase the heat-sealing strength, the entire laminated film shrinks during heat-sealing, which causes wrinkles in the heat-sealing portion and causes poor sealing of the heat-sealing portion.
When the heat seal rise temperature of the seal layer (C) is less than 115 ° C., the difference in melting point from the base layer (A) becomes too large, causing delamination, making it impossible to secure sufficient seal strength for automatic packaging. It also leads to a decrease in the strength of the fusing seal. In order to set the heat seal rise temperature of the heat seal layer (C) to 115 to 125 ° C., a combination of a propylene / ethylene / butene-1 copolymer and a propylene / butene-1 copolymer is preferable.

The heat seal reaching strength of the seal layer (C) needs to be 3.0 N / 15 mm or more. If it is less than 3.0 N / 15 mm, it is insufficient as an automatic package to prevent the contents from falling off.

The melting point temperature of the resin having the lowest melting point among the propylene / ethylene / butene-1 copolymer, the propylene / butene-1 copolymer and the propylene / ethylene copolymer constituting the seal layer (C) is 120 to 120. It is preferable that the resin having the lowest melting point in the range of 130 ° C. is added in the range of 50% by weight or more and 85% by weight or less.
When it is 85% by weight or less, the interlayer strength with the base layer (A) increases, so that the sealing strength becomes sufficient, and when it is 50% by weight or more, the sealing strength at a low temperature becomes sufficient.
In the prior art, a propylene-butene copolymer having a low melting point is added to the seal layer resin in order to develop low-temperature seal strength. However, since the propylene-butene copolymer contains a large amount of butene component and ethylene component, the core layer Poor compatibility with homopolypropylene resin causes interfacial peeling. Further, since the thickness of the seal layer is increased, the tendency is increased, and the seal strength of the original resin cannot be exhibited.

The melting point of the resin having the highest melting point among the propylene / ethylene / butene-1 copolymer, the propylene / butene-1 copolymer, and the propylene / ethylene copolymer constituting the seal layer (C) is preferably 130 ° C. As mentioned above, the temperature is 140 ° C. or lower, and the content thereof is preferably 15% by weight or more and 50% by weight or less. More preferably, it is 130 ° C. or higher and 135 ° C. or lower. At 140 ° C. or lower, the heat seal strength at a low temperature becomes sufficient and the reliability as a package is increased, and at 125 ° C. or higher, the interlayer strength with the base layer (A) increases and the seal strength becomes sufficient.
At this time, the temperature of the melting point of the copolymer constituting the seal layer (C) is in the range of 120 to 140 ° C., and the content of the copolymer at 120 to 130 ° C. is 50% by weight or more and 85% by weight or less. It is more preferable that the content of the copolymer at 130 to 140 ° C. is 15% by weight or more and 50% by weight or less.
At this time, the temperature of the melting point of the copolymer constituting the seal layer (C) is in the range of 120 to 140 ° C., and the content of the copolymer at 120 to 130 ° C. is 60% by weight or more and 85% by weight or less. It is more preferable that the content of the copolymer at 130 to 140 ° C. is 15% by weight or more and 40% by weight or less.

The thickness of the seal layer (C) needs to be in the range of 1.5 to 5% with respect to the entire film layer. If it is less than 1.5%, the heat seal strength becomes insufficient, and if it is thicker than 5%, the fusing seal strength becomes insufficient.

The surface of the seal layer (C) needs to have anti-fog properties. This is to prevent the inside from becoming cloudy due to the physiological action of the contents when packaging fruits and vegetables and displaying or distributing them at a supermarket or the like as described above.

1-4. Film Thickness The film thickness of the polypropylene-based resin multilayer film of the present invention varies depending on its use and usage, but the polypropylene-based film as a packaging film is generally about 10 to 100 μm, and has mechanical strength and transparency. More preferably, it is about 15 to 50 μm.

2. 2. Method for forming a polypropylene-based resin multilayer film of the present invention The polypropylene-based resin multilayer film of the present invention can be produced by the methods shown below, but the present invention is not limited thereto.
For example, after melt-laminating by the T-die method or the inflation method using an extruder suitable for the number of layers, it is cooled by the cooling roll method, the water-cooled method or the air-cooled method to form a laminated film, which is sequentially biaxially stretched and simultaneously biaxially stretched. A method of stretching by a stretching method, a tube stretching method, or the like can be exemplified.
Here, exemplifying the conditions for manufacturing by the sequential biaxial stretching method, a resin melt-extruded from a T-shaped die is cooled and solidified by a casting machine to prepare a raw sheet.
The temperature at the time of melt laminating is preferably set in the range of 240 ° C. to 300 ° C. with the melting point of the raw material resin used for each layer as a guide. Further, the roll temperature for casting is preferably set between 15 ° C. and 40 ° C. for the purpose of suppressing the crystallization of the resin and improving the transparency.
Next, after heating the raw sheet to a temperature suitable for stretching, the sheet is stretched in the flow direction of the sheet by utilizing the speed difference between the stretching rolls. At this time, the stretching ratio at this time is stable and stable. Considering what to do, it is preferable to set it between 3 times and 6 times. It is preferable to set the stretching temperature between 100 ° C. and 150 ° C. in consideration of stable production without uneven stretching.
Next, both ears of the vertically stretched sheet are grasped by a tenter clip, and the sheet is stretched while being sequentially expanded in a direction perpendicular to the flow of the sheet while being heated to a temperature suitable for stretching with hot air. The lateral stretching ratio at this time is preferably set between 7 times and 10 times in consideration of thickness variation and productivity. It is preferable to set the stretching temperature between 130 ° C. and 180 ° C. in consideration of stable production without uneven stretching.
Finally, it is preferable to perform the heat fixing treatment in the range of 150 ° C to 200 ° C.

The polypropylene-based resin multilayer film of the present invention can be surface-treated in order to improve printability, laminateability and the like. Examples of the surface treatment method include corona discharge treatment, plasma treatment, flame treatment, acid treatment, and the like, and are not particularly limited. It is preferable to perform corona discharge treatment, plasma treatment, and flame treatment, which can be continuously treated and can be easily carried out before the winding step of the film manufacturing process.

Hereinafter, specific examples of the present invention will be further described with reference to Examples, but the present invention is not limited to the following Examples as long as the gist of the present invention is not deviated. The characteristics in the present specification were evaluated by the following method.

(1) Layer thickness A polypropylene-based resin multilayer film that can be automatically packaged was cut into a size of 1 cm × 1 cm, embedded in a UV curable resin, and irradiated with UV for 5 minutes to solidify. Then, a cross-sectional sample was prepared by a microtome, observed with a differential interference microscope, and the thicknesses of the surface layer (B) and the seal layer (C) were measured. The sample was measured at 5 points and the average value was calculated.

(2) Heat-seal rise temperature Heat-seal layers of a polypropylene-based resin multilayer film that can be automatically packaged are stacked facing each other, and a heat-seal pressure tester (manufactured by Toyo Seiki Co., Ltd.) is used to heat-seal pressure 1 kg / cm ² , time. Is the temperature at which the heat seal strength becomes 1 N / 15 mm when heat-sealed in 1 second, and the heat-seal layer surfaces of the 5 cm × 20 cm film face each other and the temperature is set at a pitch of 5 ° C. (1 cm x 3 cm) 5 pieces are heat-sealed at the same time, the central part is cut to a width of 15 mm, attached to the upper and lower chucks of a tensile tester, and the strength of each when pulled at a tensile speed of 200 mm / min is measured. The heat seal strength was calculated (unit: N / 15 mm). A linear graph was drawn with the temperature on the horizontal axis and the heat seal strength on the vertical axis, and the temperature at which the heat seal strength exceeded 1 N / 15 mm was defined as the heat seal rise temperature.

(3) Reached heat seal strength The heat seal layers of the polypropylene resin multilayer film that can be automatically packaged are stacked facing each other, and using a heat gradient tester (manufactured by Toyo Seiki Co., Ltd.), the heat seal pressure is 1 kg / cm ² , time. Heat-sealed in 1 second, cut the central part to a width of 15 mm, attached to the upper and lower chucks of the tensile tester, and calculated from the heat-sealed strength when pulled at a tensile speed of 200 mm / min (unit: N / 15 mm). ).
The upper limit of the sealing temperature was set to 150 ° C., and the value at which the maximum strength was reached was defined as the reached heat sealing strength.

(4) Anti-fog property Put 300 cc of hot water at 50 ° C in a 1.500 cc upper opening container.
2. 2. Seal the container opening with the film with the anti-fog measurement surface of the film inside.
Leave in a cold room at 3.5 ° C.
4. With the hot water in the container completely cooled to the atmospheric temperature, the dew adhesion state on the film surface was evaluated on a 5-point scale.
Evaluation 1st grade: No dew on the entire surface (adhesion area 0)
Evaluation 2nd grade: Some dew adhesion (up to 1/4 of the adhesion area)
Evaluation grade 3: Dew adhesion of about 1/2 (adhesion area up to 2/4)
Evaluation 4th grade: Almost dew adhesion (up to 3/4 adhesion area)
Evaluation 5th grade: Full surface dew adhesion (adhesion area 3/4 or more)

(5) Suitability for automatic packaging Heat-seal layers of polypropylene-based resin multilayer films that can be automatically packaged are stacked facing each other, and a heat-seal tester (manufactured by Toyo Seiki Co., Ltd.) is used to heat-seal pressure 1 kg / cm ² , for a period of time. Heat-sealed in 1 second.
At that time, the presence or absence of fusion of the surface layer (B) to the seal bar and the heat seal rise temperature were evaluated according to the following criteria.
◯: No fusion to the seal bar ・ Rise temperature 115 ℃ or more and 125 ℃ or less △: No fusion to the seal bar ・ Rise temperature less than 115 ℃ or higher than 125 ℃ ×: Fusion to the seal bar

(6) Fusing Seal Strength Using a fusing sealing machine (manufactured by Kyoei Printing Machinery Co., Ltd .: PP500 type), a fusing sealing bag of a polypropylene-based resin multilayer film that can be automatically packaged was prepared.
Condition: Fusing blade; Cutting edge angle 60 °
Seal temperature; 370 ° C
Number of shots; 120 bags / minute The fusing seal part of the above fusing seal bag is cut to a width of 15 mm, and both ends are gripped by the gripping part of the tensile tester (grasping interval: 200 mm) with the looseness removed, and the tensile speed is 200 mm. Tensile at / min, the fusing seal strength (N / 15 mm) was calculated from the strength when the seal portion was broken. The number of measurements was 5 times and averaged. It was judged that the fusing seal suitability was good at 20 N / 15 mm or more.

(Example 1)
(1) Resins used The resins constituting each layer used in the following production examples are as follows.
[PP-1]: Propylene homopolymer: "FS2011DG3" manufactured by Sumitomo Chemical Co., Ltd., MFR: 2.5 g / 10 minutes, melting point: 158 ° C.
[PP-2]: Propylene / ethylene / butene-1 random copolymer: "FSX66E8" manufactured by Sumitomo Chemical Co., Ltd., ethylene content: 2.5 mol%, butene content: 7 mol%, MFR: 3 .1 g / 10 minutes, melting point: 133 ° C.
[PP-3]: Propylene-butene-1 copolymer: "SPX38F4" manufactured by Sumitomo Chemical Industries, Ltd., butene content: 25 mol%, MFR: 8.5 g / 10 minutes, melting point: 128 ° C.

(2) Glycerin monostearate (Matsumoto Yushi Seiyaku Co., Ltd., TB-123) as an antifogging agent was added to the base layer (A) resin composition [PP-1] at 0.16% by weight, and polyoxyethylene (2) stearyl. Amine (Matsumoto Yushi Pharmaceutical Co., Ltd., TB-12) was added in an amount of 0.2% by weight, and polyoxyethylene (2) stearylamine monostearate (Matsumoto Yushi Pharmaceutical Co., Ltd., Elex 334) was added in an amount of 0.6% by weight. As [PP-4], 100% by weight was used as the base layer (A) forming resin.

(3) Surface layer (B) Resin composition [PP-2], organic polymer fine particles (CS30: Sumitomo Chemical Industry Co., Ltd .: particle diameter 3.5 μm) 1.5% by weight, glycerin monostearate as anti-fog agent (Matsumoto Yushi Seiyaku Co., Ltd., TB-123) was melt-mixed at 0.45% by weight so as to have a resin temperature of 240 ° C. to form pellets.
This raw material was used as [PP-5] in an amount of 100% by weight as a resin for forming the surface layer (B).

(4) Resin composition of seal layer (C) A mixture of 20% by weight of [PP-2] and 80% by weight of [PP-3] was used as the resin for forming the seal layer (C).

The base layer (A) is melt-extruded from the first extruder at a resin temperature of 280 ° C. using three melt extruders, and the surface layer (B) forming resin is brought to a resin temperature of 250 ° C. by the second extruder. The seal layer (C) forming resin is melt-extruded from the third extruder at a resin temperature of 250 ° C., and the surface layer (B) / base layer (A) / seal layer (C) is melt-extruded from the chill roll contact surface. In this order, they are laminated and extruded in the T-die so that the thickness ratio is surface layer (B) / base layer (A) / seal layer (C) = 0.6 / 18.7 / 0.7, and 30 An unstretched sheet was obtained by cooling and solidifying with a cooling roll at ° C.
Subsequently, the metal rolls heated to 130 ° C. were stretched 4.5 times in the vertical direction by utilizing the difference in peripheral speed, further introduced into a tenter stretching machine, and stretched 9.5 times in the horizontal direction. .. The temperature of the preheated portion of the tenter stretching machine was 168 ° C, and the temperature of the stretched portion was 155 ° C.

Further, in the latter half of the tenter stretching machine, heat fixing is carried out at 163 ° C., and then a corona discharge treatment is carried out on the surface of the surface layer (B) by a corona discharge treatment machine manufactured by Kasuga Electric Co., Ltd., and then a seal layer (C) is carried out. ) Was similarly subjected to a corona discharge treatment, and the film was wound up with a film winder to obtain a polypropylene-based resin multilayer film that could be automatically packaged. The final film thickness was 20 μm.
The obtained multilayer film satisfies the requirements of the present invention, has sufficient heat-sealing strength and ultimate strength at low temperatures, and has both suitability for automatic packaging and fusing seal. In addition, the anti-fog property has reached a level where there is no problem in packaging fruits and vegetables. The film composition and physical characteristics are shown in Table 1.

(Example 2)
Example 1 except that the thickness of the base layer (A) is increased so that the film thickness is 30 μm, the thickness ratio of the seal layer (C) is 2.3%, and the thickness ratio of the surface layer is 2.0%. A laminated film was obtained in the same manner. The obtained laminated film has both the suitability for automatic packaging and the suitability for fusing and sealing as in Example 1. In addition, the anti-fog property has reached a level where there is no problem in packaging fruits and vegetables. The film composition and physical characteristics are shown in Table 1.

(Example 3)
By increasing the thickness of the base layer (A), the film thickness is 40 μm, the thickness ratio of the seal layer (C) is 1.8%, and the thickness ratio of the surface layer is 1.5%. A laminated film was obtained in the same manner. The obtained laminated film has both the suitability for automatic packaging and the suitability for fusing and sealing as in Example 1. In addition, the anti-fog property has reached a level where there is no problem in packaging fruits and vegetables. The film composition and physical characteristics are shown in Table 1.

(Example 4)
A laminated film was obtained in the same manner as in Example 3 except that the thickness ratio of the seal layer (C) was 3.0% and the thickness ratio of the surface layer was 1.5%. The obtained laminated film has both the suitability for automatic packaging and the suitability for fusing and sealing as in Example 1. In addition, the anti-fog property has reached a level where there is no problem in packaging fruits and vegetables. The film composition and physical characteristics are shown in Table 1.

(Example 5)
A laminated film was obtained in the same manner as in Example 1 except that the amount of [PP-3] added to the seal layer (C) was 70% by weight. The obtained laminated film has both the suitability for automatic packaging and the suitability for fusing and sealing as in Example 1. In addition, the anti-fog property has reached a level where there is no problem in packaging fruits and vegetables. The film composition and physical characteristics are shown in Table 1.

(Example 6)
A laminated film was obtained in the same manner as in Example 1 except that the amount of [PP-3] added to the seal layer (C) was 50% by weight. The obtained laminated film has both the suitability for automatic packaging and the suitability for fusing and sealing as in Example 1. In addition, the anti-fog property has reached a level where there is no problem in packaging fruits and vegetables. The film composition and physical characteristics are shown in Table 1.

(Comparative Example 1)
A laminated film was obtained in the same manner as in Example 1 except that the thickness ratio of the seal layer (C) was set to 10%. The obtained laminated film was inferior in fusing and sealing properties.
The film composition and physical characteristics are shown in Table 2.

(Comparative Example 2)
The same as in Example 1 except that the thickness of the base layer (A) is increased so that the film thickness is 40 μm, the thickness ratio of the seal layer (C) is 1%, and the thickness ratio of the surface layer is 1.5%. Obtained a laminated film. The obtained laminated film had a high seal rising temperature and was inferior in automatic packaging suitability. The film composition and physical characteristics are shown in Table 2.

(Comparative Example 3)
A laminated film was obtained in the same manner as in Example 1 except that the amount of [PP-3] added to the seal layer (C) was 40% by weight. The obtained laminated film had a high seal rising temperature and was inferior in automatic packaging suitability. The film composition and physical characteristics are shown in Table 2.

(Comparative Example 4)
A laminated film was obtained in the same manner as in Example 1 except that the amount of [PP-3] added to the seal layer (C) was 100% by weight. The obtained laminated film was inferior in fusing and sealing properties. The film composition and physical characteristics are shown in Table 2.

(Comparative Example 5)
A laminated film was obtained in the same manner as in Example 1 except that the addition of [PP-2] to the seal layer (C) was changed to [PP-4]. The obtained laminated film had a high seal rising temperature and was inferior in automatic packaging suitability. The film composition and physical characteristics are shown in Table 2.

(Comparative Example 6)
A laminated film was obtained in the same manner as in Example 1 except that the thickness ratio of the seal layer (C) was changed to 6.0% and the thickness ratio of the surface layer was changed to 3.0%. The obtained laminated film had a low seal reaching strength, a high rising temperature, and was inferior in automatic packaging suitability. Further, the fusing sealing property is also inferior. The film composition and physical characteristics are shown in Table 2.

By optimizing the seal thickness and composition, the polypropylene-based resin multilayer film that can be automatically packaged in the present invention can impart good pillow packaging suitability at a lower cost than before, and also has fusing sealing characteristics. It has become possible. It also has anti-fog properties, so it is particularly suitable for packaging fruits and vegetables.

Claims (6)

At least one weight selected from the group consisting of isotactic polypropylene, propylene / ethylene copolymer, propylene / butene-1 copolymer, propylene / ethylene / butene-1 copolymer and propylene / penten copolymer. A base layer (A) mainly composed of a composite polypropylene-based resin composition, and a propylene / ethylene / butene-1 copolymer, a propylene / butene-1 copolymer, and a propylene / ethylene compound on one side of the base layer (A). A surface having a surface layer (B) mainly composed of a polypropylene-based resin composition composed of at least one copolymer selected from the group consisting of polymers, and a surface in contact with the surface layer (B) of the base layer (A). polypropylene on the opposite side, consisting of propylene-ethylene-butene-1 copolymer, at least one copolymer was exposed, depend from the group consisting of propylene-butene-1 copolymer and propylene-ethylene copolymer A polypropylene-based resin multilayer film having a seal layer (C) mainly composed of a based resin composition, wherein the following a) to d) are satisfied.
a) The heat seal rising temperature of the seal layer (C) is 115 ° C. or higher and 125 ° C. or lower, and the heat seal ultimate strength is 3.0 N / 15 mm or higher.
b) The thickness of the seal layer (C) has a range of 1.5% or more and 5% or less with respect to the entire film layer.
c) At least the anti-fog agent is contained in the seal layer (C).
d) The thickness of the surface layer (B) has a range of 1% or more and 10% or less with respect to the entire film layer (however, 10% is not included). The melting point temperature of the resin having the lowest melting point among the copolymers constituting the seal layer (C) is in the range of 120 to 130 ° C., and the content thereof is in the range of 50% by weight or more and 85% by weight or less. The polypropylene-based resin multilayer film according to claim 1. The first aspect of the present invention, wherein the resin having the highest melting point among the copolymers constituting the seal layer (C) has a melting point of 130 ° C. or higher and 140 ° C. or lower, and the content thereof is in the range of 15 to 50% by weight. Polypropylene resin multilayer film. The melting point temperature of the copolymer constituting the seal layer (C) is in the range of 120 to 140 ° C., and the content of the copolymer at 120 to 130 ° C. is 50% by weight or more and 85% by weight.
The polypropylene-based resin multilayer film according to claim 1, wherein the content of the copolymer at a temperature of more than 130 ° C. to 140 ° C. is 50% by weight or less. The polypropylene-based resin multilayer film according to claim 1, wherein the base layer (A) contains an anti-fog agent. Use the polypropylene-based resin multilayer film according to any one of claims 1 to 5. A package using the polypropylene-based resin multilayer film according to any one of claims 1 to 5.