JPH1170625A - Multilayered film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To develop stable heat sealability at the time of both of area seal and fusing seal, especially, at the time of high speed packaging. SOLUTION: A multilayered film consisting of at least four layers is characterized by that the m.p. and MFR of a polypropylene resin used in a surface layer A and an inner layer C have specific relation and an inner layer B is composed of an ethylene/α-olefin copolymer having specific density and MFR and the thickness ratios of the surface layer A, the inner layer B and the inner layer C with respect to all of the layers A, B, C are respectively 10-60%, 20-80% and 5-60%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat-shrinkable multilayer film having good packaging machine aptitude, good transparency and gloss, and especially excellent heat sealability and high-speed packaging at high-speed packaging.

[0002]

2. Description of the Related Art Conventionally, shrink wrapping (synonymous with shrink wrapping) is capable of rapidly and tightly packaging a plurality of products regardless of the shape and size of an object to be packaged, resulting in a package obtained. It is used for packaging foods and sundries because of its beautiful appearance, display effect, enhancement of commercial value, keeping the contents sanitary, and easy visual quality control. Such shrink wrapping is generally carried out by first wrapping the contents by heat sealing with a little room for the film, and then heat shrinking the film with hot air from a shrink tunnel, etc., and a tight and beautiful finish is obtained. . At this time, as a method of heat sealing, a heat sealing method such as a bar sealing method, a heat roller method,
There are an impulse seal method, a fusing seal method, and the like. The above-mentioned is basically a face seal, and a so-called seal-and-cut method is adopted in which a cutter is cut immediately near the seal face and almost simultaneously with the seal. Further, the fusing-sealing method does not require a separate cutter as described above, and is a method in which a hot-blade instantaneously melts and cuts simultaneously with a melting seal, and is widely used as a simple method for various films for packaging. . As these packaging films, films capable of responding to recent automation and speeding of packaging machines and having satisfactory performance in any of the above sealing methods are required.

[0003] On the other hand, the properties required for a shrinkable packaging film include shrinkage properties, heat sealing properties, optical properties, mechanical strength, and the like. High shrinkage properties for tight finishing, particularly low temperature and high shrinkage properties, are required. In particular, there is little stringing phenomenon (a phenomenon in which the resin melted at the time of fusing draws a thread between the cutting blade and the film and / or between the films separated from each other by the fusing). And that it can be melt-sealed at as low a temperature as possible, especially regarding the transparency and gloss of the film after shrinkage, and the strength against various external loads including packaging and transportation and storage after packaging (tear, Piercing, etc.). In view of the above-mentioned required characteristics, a multilayer film in which a polypropylene resin is disposed on a surface layer has been conventionally known.

For example, Japanese Patent No. 2570359 discloses that both outermost layers made of a specific polypropylene resin are
A multilayer shrinkable film including a polypropylene-based soft resin layer and a layer made of linear ultra-low-density polyethylene is disclosed as a plurality of intermediate layers, and according to the publication, low-temperature shrinkage comparable to a polyvinyl chloride shrink film is disclosed. sex,
It is described that it has characteristics such as excellent blocking resistance, transparency, gloss, and preferably tear resistance. JP-B-3-42180 discloses a surface layer composed of an ethylene / propylene copolymer and a core layer containing a linear low-density polyethylene, a linear low-density polyethylene, an ethylene-vinyl acetate copolymer, an ionomer resin, and the like. Discloses a five-layer shrink film including an intermediate layer composed of a resin mixed layer appropriately selected from the group, and describes that the shrink tension, optical properties, sealing properties, and the like are improved, and that the film has a wide range of shrink temperatures. I have.

[0005]

However, among the above prior arts, the multilayer shrink film described in Japanese Patent No. 2570359 having a specific polypropylene resin in both outer layers has good transparency and gloss and low temperature. Although shrinkage can be exhibited, there is a problem in heat sealability, particularly in high-speed packaging. That is, in high-speed packaging (usually, a packaging speed of 50 packs / min or more), the sealing time itself is shortened. Therefore, a high-temperature sealing temperature is adopted. However, face sealing is performed due to the temperature characteristics of the resin constituting the film. In the case of, the middle layer, that is, the inner layer, is softer and easier to melt than both outer layers, so that the seal portion of the film is fused to the seal bar, or the seal portion is stretched at the time of seal and cut, and the seal portion is broken. Seal failures are likely to occur. Also, in the case of the fusing seal, although fusing can be performed for the time being, there is a problem that a stringing phenomenon easily occurs, the appearance of the package is deteriorated, and the merchantability is reduced. In addition, the film exemplified in Japanese Patent Publication No. 3-42180 has the same problems as the prior art described in the above-mentioned Japanese Patent No. 2570359, and also includes a sheet material such as a notebook or printing paper (and a bundle thereof). (Including the above-mentioned ones), there is a problem that the article to be packaged is easily deformed.

Accordingly, an object of the present invention is to provide a multi-layered film having a conventional polypropylene resin disposed on a surface layer in excellent packaging machine suitability (film waist and slip), mechanical strength such as tearing, and shrinkage characteristics. In addition, the heat-sealing property, which is a drawback of the conventional film, that is, stable heat-sealing property in both face-sealing and fusing-sealing, especially stable heat-sealing property in high-speed packaging, is developed for notebook and printing paper. Provided is a heat-shrinkable multilayer film capable of suppressing deformation of an object to be packaged, which has occurred when packaging a single sheet (and a bundle thereof), and significantly improving the packaging finish. It is.

[0007]

Means for Solving the Problems The present inventors have made intensive studies to achieve the above object, and as a result, have reached the present invention. That is, the present invention relates to a multilayer film comprising at least four layers having a surface layer (A) containing a polypropylene resin and a layer (B) containing an ethylene α-olefin copolymer in at least one of the inner layers. And a multilayer film characterized by the following (1) to (4). (1) As another internal layer (C), at least one layer containing a polypropylene resin or a resin composition of a polypropylene resin and a polybutene-1 resin is included. (2) Used for the surface layer (A) The melting point of the polypropylene resin used is not more than the melting point of the polypropylene resin used for the inner layer (C) and 155 ° C. or less, and the melting point of the polypropylene resin used for the surface layer (A) is 230 ° C.
2. The melt flow rate measured under the condition of 16 kgf is equal to or higher than the melt flow rate of the polypropylene resin used for the inner layer (C) and is 3 to 18 g / 10 minutes. (3) The inner layer (B) The density of the ethylene α-olefin copolymer used in the above is 0.870 to 0.930 g / cm ³
And the melt flow rate measured under the conditions of 190 ° C. and 2.16 kgf is 0.2 to 7 g / 10 min. (4) The ratio of the thickness of each layer to the total layer is the surface layer (A)
The present invention will be described in detail below with reference to 10 to 60%, the internal layer (B) 20 to 80%, and the internal layer (C) 5 to 60%.

First, the present invention differs from the prior art in that a surface layer (A) containing a specific polypropylene resin and at least one inner layer (B) containing a specific ethylene α-olefin copolymer are used. Further, as another internal layer, a layer containing a polypropylene resin having a specific relationship between a melting point and a melt flow rate with respect to a polypropylene resin used for the surface layer (A), or a polybutene-1 resin In that a layer containing the resin composition is added. Further, it is to specify the thickness ratio of each layer. The role of the constituent elements of the present invention, which is different from the above prior art, is that in addition to excellent packaging machine suitability, tear strength and shrinkage properties, heat sealing properties for both face seals and fusing seals, which were conventional problems, In particular, a stable heat sealing property in high-speed packaging can be sufficiently ensured, and a good finish can be realized by suppressing deformation of the article to be packaged during shrink packaging.

The most important requirements in the present invention are that the surface layer (A) and the inner layer (C) have a melting point (the highest temperature peak value measured by DSC) and a melt flow rate (hereinafter referred to as MFR). )) Is to use a polypropylene resin satisfying specific requirements. That is, the melting point of the polypropylene resin (hereinafter, referred to as PP-a) used for the surface layer (A) is the melting point of the polypropylene resin (hereinafter, referred to as PP-c) used for the inner layer (C). Not more than 155 ° C. and P
The MFR measured under the condition of 230 ° C. and 2.16 kgf of Pa (hereinafter, the same applies to the polypropylene-based resin) is equal to or more than the MFR of PP-c and 3 to 1
It is important to have a value of 8 g / 10 minutes. here,
The surface layer (A) means at least one of both surfaces of the multilayer film.

In the multilayer film of the present invention, at least one surface layer which is a sealing surface only has to satisfy the above-mentioned requirements. However, in order to sufficiently exert the effects of the present invention, both surface layers must satisfy the above-mentioned requirements. It is desirable to have. Here, the MFR in the present invention refers to a value measured according to JIS-K7210. If the melting point of PP-a exceeds the melting point of PP-c, defects are likely to occur in the seal portion of the face seal. Particularly in high-speed packaging, at least the entire film at the seal portion becomes a molten state or an extremely softened state. The fusion or adhesion of the film to the seal bar occurs, and troubles such as tearing of the seal portion easily occur. The melting point of PP-c with respect to PP-a is preferably the same or preferably higher, and the difference of the melting points is preferably 1 ° C. or more, more preferably 3 ° C. or more, and still more preferably 5 ° C. or more.
° C or higher. When the melting point of PP-a exceeds 155 ° C., the low-temperature sealing property is impaired, and in the case of face sealing under high-speed packaging conditions, poor sealing is likely to occur as described above. As a result, the stringing phenomenon easily occurs, and the appearance of the product deteriorates. The preferred melting point of PP-a is 150 ° C. or less, more preferably 145 ° C. or less, and the lower limit is usually 120 ° C. from the viewpoint of preventing the film from lowering in stiffness and preventing a decrease in packaging suitability due to a blocking phenomenon. Further, the upper limit of the melting point of PP-c is a melting point represented by an extremely high stereoregularity, usually a homotype, and is about 170 ° C.

If the MFR of PP-a used for the surface layer (A) is less than 3.0 g / 10 minutes, the fusion of the films in the face seal during high-speed packaging tends to be insufficient, If it exceeds 18 g / 10 minutes, fusion of the film to the seal bar, poor sealing, and stringing at the time of fusing and sealing tend to occur, and all of these phenomena become remarkable due to an increase in the packaging speed. M of PP-a
It is important that the FR has a value equal to or higher than the MFR of PP-c in addition to the range of 3.0 to 18 g / 10 minutes. That is, it is important that the MFR of PP-c is the same as or lower than the MFR of PP-a, and in this way, the fusing-sealing property particularly at the time of high-speed packaging is significantly improved. . PP-a MFR is PP-c MF
If the value is less than the value of R, the stringing phenomenon in the fusing seal is likely to occur, and the strength of the seal portion tends to vary widely. The preferred MFR of PP-a is 3.0 to 3.0.
15 g / 10 min, more preferably 4.0 to 12 g / 10
Minutes. Further, the value of the MFR of PP-a with respect to PP-c may be the same or larger.
2.0 or more, more preferably 3.0
Larger ones are better. Further, the lower limit of the MFR of PP-c is preferably about 0.2 mainly from the viewpoint of moldability.

The surface layer (A) and the inner layer (C) of the present invention
As the polypropylene resin used for
P, a copolymer of polypropylene having a propylene content of 70% by weight or more and one or more kinds of other α-olefins (other than ethylene, having 4 to 8 carbon atoms),
In addition to those polymerized with conventional catalysts such as Ziegler-Natta catalysts, the molecular weight distribution polymerized with a metallocene catalyst or the like is narrow (usually Mw (weight average molecular weight) / Mn (number average molecular weight) of 4 or less. Thing) Syndiotactic PP
And isotactic PP and the like, and a rubber component having a high concentration of up to 50% by weight may be evenly and finely dispersed, and at least one of these is used. When two or more types of PP are used as a mixture, the melting point, MF,
R should satisfy the above requirements.

In shrink wrapping, when the object to be wrapped is weak in rigidity (for example, sheets such as notebooks and printing paper and bundles thereof), the shrinkage of the film causes the shrinkage of the film. In such a case, the PP-c used for the inner layer (C) may be easily deformed to prevent deformation without impairing the above-mentioned excellent sealing suitability. It is extremely effective to mix a polybutene-1 resin (hereinafter referred to as PB). The ratio of PB to be usually mixed is 150 parts by weight or less with respect to 100 parts by weight of PP-c, and is appropriately used according to the degree of request for deformation suppression. PB ratio is 15
If the amount exceeds 0 parts by weight, the effect of improving the sealing properties of PP-c is difficult to exert, and furthermore, the shrinkage is reduced and the whole film is lowered to deteriorate the suitability for a packaging machine. A preferred mixing ratio of PB is 100 parts by weight or less, more preferably 80 parts by weight or less, based on 100 parts by weight of PP-c.

As the PB used in the present invention, one or two kinds of other monomers (olefins having 5 to 8 carbon atoms other than ethylene and propylene) having a butene-1 content of 70 mol% or more are used. Those having a high molecular weight including a copolymer of at least one kind are used. It differs from liquid and waxy molecular weights in that the MFR (190 ° C., 2.16 k
gf: Hereinafter, the same conditions are applied to PB. ) Is usually 0.1 ~
It is 10 g / 10 minutes. Among them, a copolymer having a Vicat softening point of 40 to 100 ° C. is more effective and preferable.
The Vicat softening point shown here is based on JIS-K7206-19
It is a value measured according to 82.

Next, the film of the present invention has, as at least one of the inner layers, an inner layer (B) containing a specific ethylene α-olefin copolymer. To ensure the properties, practically sufficient tear strength, impart strength properties such as piercing strength to the entire film,
It also plays a role in expressing low-temperature shrinkage. The density of the ethylene α-olefin copolymer used in the inner layer (B) of the present invention is 0.870 to 0.930 g / cm ³ , and the temperature is 190 ° C. and 2.16 kgf (hereinafter referred to as ethylene α). -The olefin copolymer has an MFR measured under the same conditions) of 0.2 to 7 g / 10 min. In addition, the density referred to in the present invention is a value at 23 ° C. measured according to JIS-K-7112. 0.930g density
If it exceeds / cm ³ , the stretching itself becomes difficult, the transparency of the obtained film is lowered, and the low-temperature shrinkability is hardly obtained.

On the other hand, if the density is less than 0.870 g / cm ³ , the difference in viscoelasticity with respect to PP-a and PP-c becomes too large. The effect is difficult to demonstrate. Preferred density 0.880~0.926g / cm ^3, more preferably 0.900~0.920g / cm ^3. Also, M
If the FR is more than 7, the stretching stability is lowered, the film is easily broken at the time of stretching, and uneven thickness is easily generated. Even if the film is obtained, only those having poor mechanical strength such as tear strength and piercing strength are obtained. I can't get it. When the MFR is less than 0.2, there arises a problem that the extrusion power at the time of extrusion molding increases, and a problem that the extrusion efficiency decreases and productivity decreases due to the increase of the extrusion power. Further, the extruded raw material may have an adverse effect on the surface smoothness. The preferred MFR is 0.
It is 5-5, more preferably 0.6-4.

The ethylene α used in the inner layer (B)
-Examples of the olefin copolymer include linear low-density polyethylene and ultra-low-density polyethylene. These are ethylene and propylene, butene-1, pentene-1, 4-methyl-pentene-1, hexene-1, octene-1. Is a copolymer with at least one monomer selected from α-olefins having 3 to 18 carbon atoms, such as mechanical strength such as impact resistance, tear strength and puncture strength, and stretch film formation. From the viewpoint of properties, α-olefin is 4-methyl-pentene-
1, pentene-1, hexene-1, and octene-1 are preferred.

The above-mentioned ethylene α-olefin copolymer is a polymer obtained by using a conventional multi-site catalyst such as a Ziegler catalyst or a molecular (comonomer distribution) polymerized by a single-site catalyst such as a metallocene catalyst. Etc.) and those which are more uniform than those polymerized by a conventional method in terms of molecular weight distribution (for example, those having a value represented by Mw / Mn of 1.5 to 3.5, more preferably 1. 5
~ 3.0), which may be a mixture of both,
At least one of them is used. The ethylene α-olefin copolymer polymerized by the single-site catalyst may have a controlled long-chain branch,
In addition to the α-olefin, other monomers such as a monomer having a polar group and a styrene-based monomer may be copolymerized.

Next, in the film of the present invention, the thickness ratio of each layer to the total layer is 10 to 60% for the surface layer (A), 20 to 80% for the inner layer (B), and 5% for the inner layer (C). It is important that the content is 〜60%, and it is important in satisfying the necessary properties as a shrink film such as mechanical strength, sealability, shrinkage (finished packaging), slipperiness and waist in a well-balanced manner. If the surface layer (A) is less than 10%, the sliding of the film utilizing the stiffness of the polypropylene resin and the suitability for the packaging machine are reduced. On the other hand, if it exceeds 60%, the mechanical strength against tearing or piercing decreases, and under high-speed packaging conditions, stringing tends to occur during fusing and sealing. When the thickness ratio of the inner layer (B) is less than 20%, mechanical strength such as tearing is insufficient, and the effect of imparting low-temperature shrinkage cannot be exhibited.

On the other hand, when the thickness ratio of the inner layer (B) exceeds 80%, the strength against tearing and piercing becomes excessive, the stiffness of the film decreases, and partial peeling occurs at the interface of the layers during shrinking. Also, the interface is deformed in a zigzag shape, and the transparency and gloss are deteriorated. If the thickness ratio of the inner layer (C) is less than 5%, the seal breakage in the face seal or the stringing phenomenon in the fusing seal is likely to occur at the time of high-speed packaging, and the PB blending effect of the packaged object at the time of shrinkage. It is difficult to exert the deformation suppressing effect. On the other hand, if the thickness ratio of the inner layer (C) exceeds 60%, the stretching stability tends to decrease, and the resulting film also has poor low-temperature shrinkage, and the shrinkage itself is at a low level. Cause problems in terms of The preferred layer composition ratio of each layer is 15 to 50% for the surface layer (A) and 30 to 70% for the inner layer (B).
%, And the internal layer (C) is 10 to 45%. More preferably, the layer composition ratio of each layer is 15 to 40% for the surface layer (A), 40 to 70% for the internal layer (B), and 15 to 40% for the internal layer (C).
It is.

The multilayer film of the present invention preferably has a heat shrinkage at 140 ° C. of at least 30% in at least one direction in the vertical and horizontal directions in order to sufficiently perform tight packaging during shrink packaging. If the heat shrinkage of the multilayer film at 140 ° C. in at least one direction is less than 30% in at least one direction, the shrinkage is poor, there is no tight feeling after packaging at the time of shrinkage packaging, and the commercial value of the product is reduced by wrinkles after packaging. It will significantly impair. More preferably, the heat shrinkage at 140 ° C. is 35% in at least one of the vertical and horizontal directions.
More preferably, it is 40% or more.

The surface layer (A), the inner layer (B) and the inner layer (C) each have a thickness within a range not impairing their original characteristics.
50% by weight or less, preferably 40% by weight or less, more preferably 30% by weight or less of other resins may be mixed. Other resins are not particularly limited, for example, ethylene-vinyl acetate copolymer and its partially saponified product, ethylene-aliphatic unsaturated carboxylic acid ester copolymer, ionomer resin, high-pressure low-density polyethylene, low-pressure high-density Highly branched ethylene polymer polymerized by polyethylene and transition metal catalyst (degree of branching: 5 to 110 groups / 100
0 carbon), styrene-conjugated diene copolymer (block,
Random) and those obtained by hydrogenating at least a part of the copolymer, those obtained by modifying these resins by acid modification, crystalline 1,2-polybutadiene, etc., hydrogenated polydicyclopentadiene, hydrogenated polyterpene, etc. Petroleum resin,
Examples of the amorphous polyolefin include propylene alone or an amorphous polyolefin polymer having a relatively low molecular weight obtained by copolymerizing propylene with ethylene or butene-1.
000 cps is a typical example. Also,
Resins and the like used for layers other than the layer to be mixed are exemplified.

Similarly, the surface layer (A), the inner layer (B) and the inner layer (C) of the present invention are provided with a plasticizer, an antioxidant, a surfactant and an ultraviolet ray as long as their original properties are not impaired. Absorbents, inorganic fillers, antifogging agents, antistatic agents, antiblocking agents, lubricants, crystal nucleating agents, coloring agents, etc., may be added directly to the target resin layer as a method of adding to the resin, In some cases, a master batch may be prepared in advance and diluted and added.

The film of the present invention comprises a total of at least four layers of the surface layer (A) and the inner layers (B) and (C). In some cases, the same resin as the surface layer (A) is used. Layers may be added as internal layers. The arrangement of the layers is, for example, A / B / C / A for four layers, A / C / B / C / A, A / B / C / B / A, and A / B for five layers.
/ A / C / A etc. for 7 layers: A / C / B / C / B / C
/ A, A / B / C / B / C / B / A and the like. In addition, it includes the case of six layers, eight layers and more.
In addition, the film of the present invention may further comprise, as an inner layer, (A) and (A) of the present invention as long as the original properties are not impaired.
In addition to the resin usable for each layer of (B) and (C), another layer composed of a known thermoplastic resin may be provided. This additional layer also includes, as a recovery layer, a mixed composition layer made of a resin used for each layer of the film.

The thickness of the heat-shrinkable multilayer film of the present invention is usually a thin region of 5 to 80 μm, preferably 6 to 60 μm, more preferably 7 to 40 μm. If it is less than 5 μm, the stiffness of the film decreases, and the sealing strength also decreases. In addition, there is a problem in workability during packaging. On the other hand, when the thickness exceeds 80 μm, the film becomes too stiff and the fit property is deteriorated, the response to shrinkage is deteriorated, and the performance such as mechanical strength becomes excessive.

Next, an example of a method for producing the heat-shrinkable multilayer film of the present invention will be described. First, each layer ((A),
(B), the resin constituting the (C) layer and other layers used as necessary) is melted by each extruder,
Coextrusion and rapid solidification with a multilayer die to obtain a raw multilayer film. As the extrusion method, a multi-layer T-die method, a multi-layer circular method, or the like can be used, and the latter is preferable. The thus obtained multilayer film raw material is heated and stretched under a temperature condition suitable for imparting orientation. The stretching temperature is usually 140 ° C. or lower, preferably 130 ° C. or lower as the surface temperature at the stretching start point of the film (in the case of the inflation method, the position where expansion as a bubble starts). However, the lower limit of the stretching temperature is preferably 40 ° C. from the viewpoint of the dimensional stability of the stretched film.

As the stretching method, there are a roll stretching method, a tenter method, an inflation method (including a double bubble method), and the like, and a method of forming a film by simultaneous biaxial stretching is preferable from the viewpoint of stretchability and other rationality. The stretching is performed in at least one direction at an area stretching ratio of 3 to 50 times, preferably 3.5 to 40 times, and more preferably 4 to 30 times, and is appropriately selected depending on the heat shrinkage required according to the application. You. Also, if necessary,
Post-processing, for example, heat setting for dimensional stability, surface treatment such as corona treatment or plasma treatment, printing treatment, lamination with other kinds of films and the like may be performed. Further, at least one layer of the film of the present invention may be cross-linked, and the cross-linking treatment may be performed by irradiating energy rays such as an electron beam (for example, an irradiation device having an acceleration voltage of 50 to 1000 kV), ultraviolet rays, and γ rays. A conventionally known method such as use of a peroxide is used.

[0028]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in more detail with reference to examples, but the measurement and evaluation method used in the present invention is as follows. (1) Melting point 6 to 8 mg of a measurement sample was sampled, packed in an aluminum pan, and heated at a rate of 10 ° C./min by a DSC method using a Perkin-Elmer differential scanning calorimeter (DSC-7) under a nitrogen stream. Once the temperature is raised to 200 ° C and held for 1 minute,
It was cooled to 0 ° C. at a rate of 10 ° C./min. Then 0
After maintaining the temperature at 1 ° C. for 1 minute, the temperature was raised again at 10 ° C./min, and the measurement was performed. The highest endothermic peak at that time was taken as the melting point. (2) Thermal shrinkage rate A 100 mm square film sample is placed in an air oven type constant temperature bath set at a predetermined temperature, treated for 30 minutes in a freely shrinkable state, and then the amount of shrinkage of the film is obtained and divided by the original dimension. Values are expressed as percentages. The measurement was performed in the vertical direction (M
D) and in the transverse direction (TD).

(3) Optical properties Haze is ASTM-D-1003 and gloss is ASTM-D
The measurement was performed according to each of D-2457. (4) Dynamic friction coefficient According to JIS-K-7125, the test speed is 700 mm /
The measurement was performed in minutes. At this time, the test table used was one in which a semi-rigid polyethylene foam sheet was fitted and fixed in a frame of an acrylic plate, and the sliding piece was a stainless steel plate with a matte finish surface (weight: 500 g). It was used. (5) Tear strength According to JIS-P-8116, using a light load tearing tester (manufactured by Toyo Seiki), longitudinal direction (MD) and transverse direction (TD).
It measured about each. The reading of the measured value here was made so that it would fall within the range of 20 to 60 on the scale. If there was a difference in the measured value depending on the measurement range, the higher value was measured.

(6) Fusing Sealability (6-1) Fusing Seal Starting Temperature TP701 heat seal tester manufactured by Tester Sangyo Co., Ltd.
An mR × 280 mmL fusing blade was attached, and air pressure was 3 kg / cm ² (air cylinder diameter:
50 mmφ) and the sealing time was 1 second, and the temperature was variously changed to perform the fusing sealing. At this time, the temperature at the tip of the fusing blade was actually measured with a contact-type thermometer, and the measured value was used as a value for each temperature condition. The above-mentioned test was performed with each of the measurement films in a state of being folded in two and being overlapped with each other with a width dimension having a margin for the fusing blade, and the minimum of 90% or more (252 mm or more) of the fusing blade was blown. The temperature was defined as the fusing seal starting temperature. It should be noted that the lower the fusing seal starting temperature, the more suitable for high-speed packaging conditions, and is also preferable from the viewpoint of energy saving.

(6-2) Finishing of the fusing seal For the case where the fusing seal was performed at a temperature higher by about 10 ° C. than the starting temperature of the fusing seal specified in the above (6-1), the finishing of the fusing seal was determined based on the following criteria. evaluated. ：: The seal is complete and has no defects, and there is almost no stringing and the finish of the melted surface is clean. Δ: The seal is almost complete, but slight stringing is observed, and there is a problem with the productability. X: A state in which obvious stringing is observed in several places, or there is a seal failure such as a local opening in the seal portion, and there is a problem as a product.

(7) Suitability for high-speed packaging Using a FP-280 universal automatic packaging machine manufactured by Ibaraki Seiki Co., Ltd., a rectangular parallelepiped wooden piece (approximate dimensions: 150 × 100 × 35 m)
m) was packed at a packing speed of 60 packs / min for 2 minutes, for a total of 120 pieces. The used packaging machine employs, as a sealing method, a face seal using a hot roller method at a center seal portion, and then a fusing seal at a cutter seal portion, and the following evaluation was performed. The shrinkage was performed by passing the package through a hot air shrink tunnel in about 5 seconds. In addition, appropriate conditions were changed so that the temperature of each seal portion and the hot air at the time of shrinkage became the optimum condition of each film. ：: There is no running trouble of the film due to fusion or adhesion in each seal part during packaging, and there is no defect such as tear in each seal part even in the package after shrinking, and the fusing seal part has good appearance and good merchantability Excellent. ○: There is no film running trouble due to fusion or adhesion at each seal part during packaging, and even after shrinking, there are no defects such as tears in each seal part, but more than half of the packages are blown seal parts. Some poor appearance due to the effect of stringing is observed. However, the range is acceptable as a product. Δ: Fusion and adhesion of the film to the sealer were observed in each seal portion during packaging, and the running property of the film was unstable. In addition, in most of the packages after shrinking, defective appearance due to stringing is observed in the fusing seal portion, or 1 to 10 defects having breakage or the like in the seal portion of the package are observed. ×: Trouble due to fusion and adhesion of the film to the sealer occurred at each seal portion of the package, making it difficult to run the film continuously. Alternatively, the shrink-wrapped package may have a defect such as a tear in the seal portion.
More than one month.

Next, the resins used in Examples and Comparative Examples are described below. LL1: ethylene α-olefin copolymer (MFR (1
90 ° C., 2.16 kgf) = 2.0 g / 10 min, density =
0.917 g / cm ³ , α-olefin = hexene-
1) LL2: ethylene α-olefin copolymer (MFR =
4.0 g / 10 min, density = 0.927 g / cm ³ , α-
Olefin = hexene-1) LL3: ethylene α-olefin copolymer (MFR =
2.0 g / 10 min, density = 0.912 g / cm ³ , α-
Olefin = hexene-1) LL4: ethylene α-olefin copolymer (MFR =
4.0 g / 10 min, density = 0.916 g / cm ³ , α-
Olefin = octene-1) LL5: ethylene α-olefin copolymer (MFR =
0.8 g / 10 min, density = 0.905 g / cm ³ , α-
Olefin = octene-1) LL6: ethylene α-olefin copolymer (polymerized with a single-site catalyst; MFR = 1.0 g / 10)
Min, density = 0.868 g / cm ³ , α-olefin = octene-1) LL7: ethylene α-olefin copolymer (MFR =
1.0 g / 10 min, density = 0.920 g / cm ³ , α-
Olefin = octene-1) LL8: ethylene α-olefin copolymer (MFR =
0.7 g / 10 min, density = 0.917 g / cm ³ , α-
Olefin = hexene-1) LL9: ethylene α-olefin copolymer (polymerized with a single-site catalyst; MFR = 1.6 g / 10)
Min), density = 0.895 g / cm ³ , α-olefin =
Octene-1) LL10: ethylene α-olefin copolymer (MFR =
1.0 g / 10 min, density = 0.884 g / cm ³ , α-
Olefin = butene-1)

LL11: ethylene α-olefin copolymer (MFR = 2.2 g / 10 min, density = 0.905 g /
cm ³ , α-olefin = 4-methyl-pentene-1) LL12: Ethylene α-olefin copolymer (polymerized with a single-site catalyst; MFR = 1.0 g / 10)
Min, density = 0.902 g / cm ^3, alpha-olefin = octene -1) LL13: ethylene alpha-olefin copolymer (as polymerized with a single site catalyst .MFR = 3.5g / 10
Min, density = 0.910 g / cm ³ , α-olefin = octene-1) LL14: ethylene α-olefin copolymer (MFR =
2.1 g / 10 min, density = 0.939 g / cm ³ , α-
Olefin = octene-1) LL15: ethylene α-olefin copolymer (MFR =
10.0 g / 10 min, density = 0.914 g / cm ³ , α
-Olefin = hexene-1) PP1: polypropylene-based resin (ethylene-propylene copolymer: MFR (230 ° C., 2.16 kgf) = 7.
0 g / 10 min, density = 0.900 g / cm ³ , melting point = 1
PP2: polypropylene resin (ethylene-propylene copolymer: MFR = 6.5 g / 10 min, density = 0.90)
0 g / cm ³ , melting point = 145 ° C.) PP3: polypropylene-based resin (ethylene-propylene copolymer: MFR = 1.0 g / 10 min, density = 0.90)
0 g / cm ³ , melting point = 148 ° C.) PP4: Polypropylene resin (homopolypropylene:
MFR = 4.0 g / 10 min, density = 0.900 g / cm
³ , melting point = 161 ° C.) PP5: polypropylene resin (ethylene-propylene copolymer: MFR = 18.0 g / 10 min, density = 0.9)
00g / cm ^3, melting point = 145 ° C.) PP6: Polypropylene resin (propylene - (ethylene - propylene rubber) copolymer: MFR = 8.7g / 1
0 min, density = 0.900 g / cm ³ , melting point = 130 ° C.) PP7: polypropylene resin (ethylene-propylene-butene copolymer: MFR = 5.5 g / 10 min, density =
0.890 g / cm ³ , melting point = 132 ° C.) PP8: polypropylene-based resin (ethylene-propylene-butene copolymer: MFR = 5.0 g / 10 min, density =
0.99 g / cm ³ , melting point = 120 ° C.) PP9: syndiotactic propylene polymerized with a metallocene catalyst: MFR = 2.5 g / 10 min, density = 0.
886 g / cm ³ , melting point = 149 ° C.) PP10: polypropylene resin (homopolypropylene: MFR = 8.0 g / 10 min, density = 0.900 g /
cm ³ , melting point = 161 ° C.)

PP11: polypropylene resin (ethylene-propylene copolymer: MFR = 5.0 g / 10 min,
(Density = 0.900 g / cm ³ , melting point = 126 ° C.) PP12: polypropylene resin (ethylene-propylene copolymer: MFR = 1.9 g / 10 min, density = 0.9)
PP13: polypropylene resin (ethylene-propylene copolymer: MFR = 20.0 g / 10 min, density = 0.00 g / cm ³ , melting point = 142 ° C.)
900 g / cm ³ , melting point = 135 ° C.) PP14: polypropylene-based resin (ethylene-propylene copolymer: MFR = 0.8 g / 10 min, density = 0.9)
00 g / cm ³ , melting point = 140 ° C.) PB1: polybutene-1 resin (copolymer using propylene as a comonomer, MFR (190 ° C., 2.16 kg)
f) = 2.0 g / 10 min, Vicat softening point = 61 ° C.) Mix 1: LL1 (57% by weight), PP1 (19% by weight), PP3 (24% by weight) Mix 2: LL1 ( 53% by weight), a mixture of PP1 (21% by weight) and PP3 (26% by weight) Mixing 3: a mixture of LL1 (32% by weight), PP1 (12% by weight), and PP3 (56% by weight) Mixture 4: Mixture of LL1 (28% by weight), PP1 (14% by weight), PP3 (58% by weight) Mixture 5: PP3 (50% by weight), PB1 (50% by weight)
6: PP3 (70% by weight), PB1 (30% by weight)
Mixture 7: PP3 (90% by weight), PB1 (10% by weight)
A mixture of

[0036]

Example 1 Ethylene-propylene copolymer: PP1 (MFR = 7.0 g / 10 min, melting point = 14) on the surface layer (A)
0 ° C.), and an ethylene α-olefin copolymer: LL1 (MFR = 2.0 g / 10 min, density =
0.917 g / cm ³ , α-olefin = hexene-
1), an ethylene-propylene copolymer: PP3 (MFR = 1.0 g / 10 min, melting point = 148 ° C.) was used for another inner layer (C), and the surface layer (A) was 32 mm in diameter.
Extruder (L / D = 22), 40 mm
m extruder (L / D = 24) and the inner layer (C)
mm extruder (L / D = 22), the layer arrangement is PP
It was extruded using a circular 5-layer die so as to have 5 layers of 1 / LL1 / PP3 / LL1 / PP1 (extrusion rate 20 kg /
h). Immediately after that, it is quenched and solidified with cold water and folded 200m in width.
Each of the layers having a thickness of 230 μm and a thickness of 230 μm formed a tubular raw material having uniform thickness accuracy. The thickness ratio (%) of each layer was adjusted to be 10 / 27.5 / 25 / 27.5 / 10 from the outside of the tube.

In the surface layer (A), 0.1% by weight of a finely ground feldspar product (average particle size: 4.5 μm: Shiraishi Kogyo “Minex7”) and 0.15% by weight of erucamide were used as antiblocking agents. % Was added. Next, the raw material is passed between two pairs of differential nip rolls, heated in a heating zone to a temperature at which stretching can be performed, air is injected into the tube in the stretching zone to form bubbles, and continuous stretching is performed. Simultaneous vertical and horizontal biaxial stretching was performed by blowing cold air in the zone. The obtained film had a thickness of 15 μm and the evaluation results of the film are shown in Table 1. The resulting film was excellent in fusing sealability, suitable for high-speed packaging, highly shrinkable, and excellent in physical properties such as optical properties and tear strength.

[0038]

Examples 2 to 10 Ethylene α used for the inner layer (B)
Example 1 except that each of the olefin copolymers was changed
A film was obtained in the same manner as in
And Tables 1 and 2 show the layer structure and evaluation results of the film. Each of the obtained films was excellent in fusing sealability, high-speed packaging suitability, high shrinkage, and also excellent in physical properties such as optical properties and tear strength as in Example 1.

[0039]

Examples 11 to 18 Films were obtained in the same manner as in Example 1 except that the inner layer (B) was kept as it was and the polypropylene resin of the surface layer (A) and the inner layer (C) was variously changed. The layer structure of the film and the evaluation results are shown in Tables 2 and 3, all of which have excellent fusing sealability, high-speed packaging suitability, high shrinkage, and excellent physical properties such as optical properties and tear strength. Met.

[0040]

Examples 19 to 21: Inner layer (B) and inner layer (C)
Example 1 and the resin used for each layer were variously changed.
A film was obtained in the same manner as described above. Table 4 shows the layer structure of the film and the evaluation results.

[0041]

Examples 22 to 24 Films were obtained in the same manner as in Example 1 except that the thickness ratio of each layer was variously changed. The layer composition ratio (%) of Example 22 was A / B / C / B / A = 20/2.
0/20/20/20, the layer composition ratio (%) of Example 23 is A / B / C / B / A = 10 / 32.5 / 15 / 32.5
/ 10, the layer composition ratio (%) of Example 24 is A / B / C / B
A film was formed at / A = 10/20/40/20/10.
Table 4 shows the evaluation results of the obtained films. The obtained film was excellent in fusing sealability and high-speed packaging suitability as in Example 1, and also excellent in physical properties such as high shrinkage, optical properties and tear strength.

[0042]

Examples 25 to 27 The same layer structure as in Example 1 except that the amount and type of additives added to the surface layer (A) were changed.
A tubular raw material having a layer ratio was prepared, and a film was obtained in the same manner as described below. In Example 25, a finely pulverized feldspar product (average particle size: 4.5 μm: Shiraishi Kogyo “Mine”) was used for the surface layer (A).
x7 ") of 0.25% by weight, erucamide 0.3% by weight and glycerin monostearate as main components (RIKEN vitamin" Likemar S-100 ") 1
In the same manner as in Example 26, 0.25% by weight of finely ground feldspar (Minex 7) and 0.3% by weight of methylphenyl silicone oil (having a viscosity of about 400 centistokes at 25 ° C.) were added. And 1% by weight of an antistatic agent (Likemar S-100), and in Example 27 1.5% by weight of a mixture of glycerin monooleate and diglycerin laurate in a weight ratio of 2: 1 was added.
Was added. Table 5 shows the physical properties of the obtained film. Each of the obtained films was excellent in fusing sealability and suitability for high-speed packaging, and the film obtained in Example 27 was excellent in antifogging property. (As an evaluation of anti-fog properties, cover the top open container filled with water at 20 ° C with a film and then store it in a refrigerated showcase at 5 ° C to observe the state of water droplets on the film surface. , The one with no water drop and good transparency has excellent anti-fog properties.)

[0043]

Examples 28 to 30 Using the resin raw materials used in Example 1, a ternary blend resin composition was appropriately disposed in the inner layers (B) and (C). To obtain a film. Table 5 shows the layer structure of the film and the evaluation results.
Shown in Each of the obtained films was excellent in fusing sealability and high-speed packaging suitability as in Example 1.

[0044]

Examples 31 to 33 Films were obtained in the same manner as in Example 1 except that the thickness of the tubular raw material was changed. Example 31
The thickness of the tubular raw material was 150 μm, and
2 was adjusted to 300 μm, Example 33 was adjusted to 350 μm, and the thickness of the obtained film was 10 μm from Example 31 in order.
20 μm and 25 μm. Table 6 shows the evaluation results of the obtained films. Each of the obtained films had excellent fusing sealability, high-speed packaging suitability, and also excellent physical properties such as shrinkage and optical characteristics.

[0045]

Examples 34 to 36 Films were obtained in the same manner as in Example 1 except that a resin composition in which a polybutene-1 resin (PB1) was blended for the inner layer (C) was used. Example 3 using a blend ratio of PB1 of 50% by weight
4. Example 35 also using the blend ratio of 30% by weight, and the blend ratio of 10% by weight
Example 36 was used as a sample. Table 7 shows the evaluation results of the obtained films. Each of the obtained films was excellent in fusing sealability and high-speed packaging suitability as in Example 1, and also excellent in physical properties such as shrinkage, optical properties and tear strength.

The obtained film was prepared in Example 1 (PB
4 notebooks (No. 6, 179 x 252 mm) were packaged together with the film obtained in Example). When the film of Example 1 was used, a slight warp was observed in the package, but in the films of Examples 34 to 36 having a layer in which PB was blended, the package had no deformation such as warpage and was tight. A good finish was obtained, and it was suitable for shrink wrapping of articles to be wrapped having poor rigidity.

[0047]

Embodiment 37 PP3 of the inner layer (C) of Embodiment 14 is replaced with P.
The composition was replaced with a blend of P14 and an amorphous polyolefin (melt viscosity at 190 ° C. = 8000 cps, softening point = 110 ° C.). The blend ratio of the amorphous polyolefin was 3 to 3 for PP14 used for the inner layer (C).
A resin composition blended with 0% by weight was used. The physical properties of the composition were as follows: MFR = 3.8 g / 10 min, density = 0.887 g
/ Cm ³ , melting point = 139 ° C. Otherwise, in the same manner as in Example 14, a film was obtained, and Example 34 was performed. The evaluation of the obtained film is shown in Table 7, which was excellent in fusing sealability, suitable for high-speed packaging, improved in shrinkage, and excellent in physical properties such as optical properties and tear strength.

[0048]

Example 38 A film was obtained in the same manner as in Example 37 except that the thickness ratio of each layer was changed. The layer composition ratio (%) of Example 38 was A / B / C / B / A = 10 / 32.5 /
A film was formed on 15 / 32.5 / 10. The evaluation of the resulting film is shown in Table 7, which was excellent in fusing sealability, high-speed packaging suitability, high shrinkage, and excellent physical properties such as optical properties and tear strength.

[0049]

Comparative Examples 1 to 3 Ethylene α- used for the inner layer (B)
A film was obtained in the same manner as in Example 1 except that the olefin copolymer was replaced with one outside the technical scope of the present invention, and this was used as Comparative Examples 1 to 3. LL6 of Comparative Example 1 (α
-Olefin: octene-1) and LL1 of Comparative Example 2
4 (comonomer: octene-1) is a resin having a density outside the range of the present invention, and LL15 (comonomer: hexene-1) of Comparative Example 3 has an MFR (190 ° C., 2.16 kgf) outside the range of the present invention. Resin.

Table 8 shows the evaluation results of the film. The film obtained in Comparative Example 1 was poor in shrinkage, poor in optical characteristics (transparency), and poor in tear strength. In Comparative Example 2, although the stretching itself was difficult, when the stretching ratio was lowered and a small piece sample barely obtained was evaluated, it was inferior in shrinkage and optical characteristics. In Comparative Example 3, the film was liable to break during stretching, and stable stretching was difficult. The tear strength of the obtained film was weak, and the suitability for high-speed packaging was poor.

[0051]

Comparative Examples 4 to 7 As those outside the technical scope of the present invention,
First, the surface layer (A) in Example 1 was replaced with PP10.
The melting point of Pa (and the relation with the melting point of PP-c) was out of the range of the present invention, as Comparative Example 4, and then the surface layer (A) of Example 1 was replaced with PP13. PP-
The sample whose a MFR was out of the range of the present invention was designated as Comparative Example 5. Further, the inner layer (C) of Example 1 was replaced with PP8, and those having a melting point relationship between PP-a and PP-c outside the range of the present invention were compared with Comparative Example 6 and the surface layer of Example 1 ( A)
Is replaced with PP3 and the inner layer (C) is replaced with PP4, and PP-a
Comparative Example 7 in which the relationship between the MFR of PP and PP-c was out of the range of the present invention. In each case, a film was obtained in the same manner as in Example 1, and the evaluation results are shown in Table 9.
Comparative Examples 4 and 7 were inferior in optical characteristics, and Comparative Example 5 was inferior in tear characteristics, and both were inferior in fusing sealability and high-speed packaging suitability.

[0052]

Comparative Examples 8 to 10 Except that the thickness composition ratio of the film was changed out of the range of the present invention, a tubular raw material was produced and stretched and formed. Table 10 shows the thickness composition ratios and the evaluation results of the films. First, in Comparative Example 8, a film lacking in stretching stability and having a large thickness variation (the thickness variation of the film over the entire circumference of the bubble was ± 42%. Incidentally, all the films obtained in Examples of the present invention were within ± 15%. The film did not run stably during high-speed packaging, resulting in frequent seal failures. Also, the optical characteristics were slightly inferior. In Comparative Example 9, at the time of high-speed packaging,
Film tearing frequently occurred, and a stringing phenomenon was also observed in the fusing seal, which was problematic. And, the film obtained in Comparative Example 10 is inferior in fusing sealability (occurrence of a stringing phenomenon).
In both the center seal portion and the cutter seal portion, troubles due to poor sealing occurred, and had problems.

[0053]

[Table 1]

[0054]

[Table 2]

[0055]

[Table 3]

[0056]

[Table 4]

[0057]

[Table 5]

[0058]

[Table 6]

[0059]

[Table 7]

[0060]

[Table 8]

[0061]

[Table 9]

[0062]

[Table 10]

[0063]

According to the present invention having the above-described structure, a high-performance heat-shrinkable film which is extremely well-balanced and which cannot be obtained by conventional shrink-wrapping films can be provided. That is, in addition to the excellent packaging machine aptitude (film waist and slip), mechanical strength such as tearing, and shrinkage properties of a conventional multilayer film in which a polypropylene-based resin is disposed on the surface layer, it is a disadvantage of the conventional film. Heat sealability, that is, stable heat sealability in both face seal and fusing seal is exhibited under high-speed packaging conditions. In addition, sheets of notebooks and printing paper (and bundles thereof) are also used. The present invention can provide a heat-shrinkable multilayer film capable of suppressing deformation of an article to be packaged, which is likely to occur when packaging (including), and significantly improving the packaging finish.

Continued on the front page (51) Int.Cl. ⁶ Identification code FI B29K 105: 02 B29L 9:00

Claims (2)

[Claims] 1. A method according to claim 1, wherein at least one of the surface layer (A) containing the polypropylene resin and the inner layer has ethylene α-
In a multilayer film comprising at least four layers having a layer (B) containing an olefin copolymer, the following (1)
To (4). (1) As another internal layer (C), at least one layer containing a polypropylene resin or a resin composition of a polypropylene resin and a polybutene-1 resin is included. (2) Used for the surface layer (A) The melting point of the polypropylene resin used is not more than the melting point of the polypropylene resin used for the inner layer (C) and 155 ° C. or less, and the melting point of the polypropylene resin used for the surface layer (A) is 230 ° C.
2. The melt flow rate measured under the condition of 16 kgf is equal to or higher than the melt flow rate of the polypropylene resin used for the inner layer (C) and 3 to 18 g / 10 minutes. (3) For the inner layer (B) The density of the ethylene α-olefin copolymer used is 0.870 to 0.930 g / cm ³
And the melt flow rate measured under the conditions of 190 ° C. and 2.16 kgf is 0.2 to 7 g / 10 min. (4) The ratio of the thickness of each layer to the total layer is the surface layer (A)
Is 10 to 60%, the internal layer (B) is 20 to 80%, and the internal layer (C) is 5 to 60%. 2. The multilayer film according to claim 1, wherein the heat shrinkage at 140 ° C. in at least one of the vertical and horizontal directions is 30% or more.