JP2003191407A - Low temperature easily peelable polyolefin based multilayered film and its bag body - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polyolefin based bag for a packaging bag which is abound in a peelable property and a non-destructive property which are stabilized even at a very low temperature (for example, at about -20°C) and to provide the packaging bag thereby. <P>SOLUTION: A low temperature easily peelable polyolefin based multilayered film is provided wherein respective layers (A), (B), (C) and (D) have relations of the following (1) and (2) at each vicat softening temperature for a polyolefin based multilayered film by successively laminating a first intermediate layer (B) by a polyolefin based resin, a specific second intermediate layer (C) and a heat-sealing layer (HS layer) (D) by a polyolefin based resin on a side face of a polypropylene substrate layer (A). (1) The substrate layer (A) VST > the first intermediate layer (B) VST > the second intermediate layer (C) VST, and (2) the substrate layer (A) VST > the HS layer (D) VST > the second intermediate layer (C) VST. Further, the layer (B) VST > the layer (D) VST is preferable. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention, when used as a bag for food packaging, for example, has a low temperature at which it can be peeled and opened smoothly without damaging the substrate layer even in a subzero temperature region, and thus can be easily resealed and stored. The present invention relates to an easily peelable polyolefin-based multilayer film.

[0002]

2. Description of the Related Art Generally, a biaxially stretched polypropylene film is used as a substrate layer, and a low melting point resin capable of heat sealing (generally, a soft polyolefin resin mainly containing polyethylene as a main component) is laminated on the substrate layer. A two-layer heat seal polypropylene film is known and is also used as a packaging bag. A major drawback of a food packaging bag made of the film composed of two layers including the base layer is that when the package is generally opened, the polypropylene base layer is torn (without being opened only at the heat seal portion). It often happens. That is, it is lacking in easy peeling property. This means that it is not possible to use part of the food and re-encapsulate the rest and keep it properly sanitized. It is also said that when the heat seal layer is made of a more flexible polyolefin-based resin, the problem of blocking tends to occur and the workability is adversely affected.

[0003]

The applicant of the present invention has already found a solution to the above-mentioned two problems and found it.
It was also made public by the publication of -202958. This is achieved by laminating two layers of a polypropylene base layer, a seal fracture stress relaxation layer (made of a specific polyolefin resin) and a seal layer (made of a specific polyolefin resin). . As a result, the above-mentioned problem was greatly improved and it became easier to use. Therefore, the present inventors further tried to use it as a packaging bag for frozen food. As a result, surprisingly, the following two things were confirmed again. One of the cases is that the polypropylene base layer may be torn when the bag in which foods and the like are enclosed and frozen is opened at an extremely low temperature (in a frozen state). That is, it was found that the easy peeling property changes depending on the temperature at the time of opening.
The other two were the cases in which the body of the bag was torn due to a sudden shock when the frozen food packaging bag was thrown or dropped.

According to the present invention, even at an opening temperature such as an extremely low temperature (for example, -10 to -30 ° C) in the frozen state,
The main object was to find a packaging film that has stable and easy peelability (independent of the opening temperature) and does not break the bag body even when thrown or dropped. The solution is as follows.

[0005]

That is, the present invention has the above-mentioned claim 1 as a main invention, which is a polypropylene substrate layer (A).
A first intermediate layer (B) and a second intermediate layer (C) made of a polyolefin resin and a heat seal layer (D) made of a polyolefin resin, which are sequentially laminated on one side of , And (A), (B),
(C), (D) each layer has a Vicat softening temperature and has the relationship described in the following (1), (2) is a low temperature easily peelable polyolefin-based multilayer film. (1) Vicat softening temperature of base layer (A)> Vicat softening temperature of first intermediate layer (B)> Vicat softening temperature of second intermediate layer (C), (2) Vicat softening temperature of base layer (A)>
Vicat softening temperature of heat seal layer (D)> Vicat softening temperature of second intermediate layer (C). Hereinafter, the low-temperature, easily peelable polyolefin-based multilayer film will be referred to as the main multilayer film, the Vicat softening temperature will be referred to as VST, and the heat seal layer will be referred to as the HS layer.

Dependent on claim 1, claims 2 to 5 are also provided as preferred invention forms, and in addition, the invention of claim 6 is also provided as an effective use of the main body multilayer film. Hereinafter, each of the inventions will be described in detail with reference to the following embodiments.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION First, a substrate layer (A) which constitutes the main body multilayer film will be described. Needless to say, the base layer itself for a food packaging bag needs to firmly support the whole, but in addition, cold resistance, heat resistance, transparency, stress cracking (impact) resistance, moisture resistance, In addition to hygiene, it is also necessary to make it easy to separate after use, and not to incinerate pollution. In the present invention, it is made of polypropylene in particular. In other words, the polypropylene has an overall balance of these properties, and in terms of this balance, it has properties that other PET resins, nylon resins, etc. do not have. Is.

The above-mentioned polypropylene refers to a generally known (isotactic) polypropylene having a molecular weight of about 40,000 or more, but within a range that does not change the essence of the polypropylene as long as it has improved properties. It is said that alteration of is allowed. Examples of the modification means include a method by copolymerization with other vinyl monomers, a blending method with other compatible vinyl polymers, and a grafting method with vinyl monomers (for example, ethylene as a vinyl monomer, (iso ) Impact resistance is improved by using butylene). Of course, addition of a small amount of generally added inorganic or organic additives is also acceptable.

Although referred to as the polypropylene, there is a more preferable range among them, and as it is provided in claim 2, it has a VST of 145 to 165 ° C, preferably 148 to 160 ° C. It is a thing. Further, when this is used as the base layer (A), it is preferably a stretched layer. This is VST 145-165
The reason is that by selecting a material having a temperature range of 0 ° C., the overall balance of the above various properties can be more preferably taken, and by being a stretched layer, improvements can be seen in terms of transparency, strength and the like. Here, the stretching is more preferably biaxial stretching in the longitudinal and transverse directions. The degree of stretching is preferably 2 to 6 times in the length (longitudinal direction) and 5 to 12 times in the width (width direction). From the viewpoint of VST, it is determined by the structure of polypropylene itself (isotactic ratio, presence or absence of modification), molecular weight, molecular weight distribution, and the like. It also slightly changes depending on the presence or absence of stretching. 145 to 165 to be a preferred range
C is also the VST set with these factors.

The layer thickness of the base layer (A) is such that
It is decided considering waist, mechanical strength, application, etc.,
In many cases, it can be dealt with by setting it to 10 to 100 μm.

Next, the first intermediate layer (B), the second intermediate layer (C) and the HS layer (D) which are sequentially laminated on one surface of the polypropylene base layer (A) will be described. First, the present invention is composed of at least four layers of a polyolefin resin, and each layer needs to have a VST relationship shown in the following (1) and (2) with respect to the VST of the polypropylene base layer (A). . (1) VST of base layer (A)> VS of first intermediate layer (B)
T> VST of the second intermediate layer (C), (2) VST of the base layer (A)> VST of the HS layer (D)> VST of the second intermediate layer (C)
ST.

In the above description, each layer laminated on the polypropylene base layer (A) is basically composed of a polyolefin resin except for the second intermediate layer (C).

Each layer is made of a polyolefin resin except the second intermediate layer (C) as described above, but the object of the present invention cannot be achieved unless the following two points are satisfied. One of them is to provide two different intermediate layers between the polypropylene substrate layer (A) and the HS layer (D), and stack them in the substrate layer (A), firstly the first intermediate layer (B). , The (B)
Of the second intermediate layer (C) and the HS layer (D) on the upper surface of the (C). By adopting this stacking order, the peeling action mainly occurs around the second intermediate layer (C), and the polypropylene base layer (A) is not destroyed even when peeling at an extremely low temperature. Therefore, when the stacking order is changed, the peeling position becomes unstable, and the polypropylene base layer (A) may be broken.

Even in the order of stacking the layers, the above object cannot be completely achieved unless the resin of each layer forming the layers is specific. The basis of the condition is
It is the relationship of VST described in (1) and (2) above. First, in the relationship of (1), the first intermediate layer (B) that directly adheres to the base layer (A) needs to have a VST lower than that of the base layer (A). As a result, even in the case of peeling at a very low temperature, it is possible to exert a supporting action for suppressing the destruction of the base layer (A). That is, it is said that the action of suppressing the destruction is more effectively exerted on the suppression or the stop. Here, the VST of the (B) layer is premised to be low, but it can be said that the temperature is lower. That is the point of the adhesion to the base layer (A), which leads to a decrease. The layer is preferably required to have stronger adhesion than the other two layers, otherwise the three layers themselves will adhere to the substrate layer (A) and will not be laminated. Considering this point as well, it is preferable to keep the temperature within the VST range which is lower than the VST of the substrate layer (A) by 10 to 80 ° C., preferably 15 to 65 ° C.

The VST of the second intermediate layer (C) needs to have a VST relationship at a lower temperature than that of the first intermediate layer (B). As a result, even if the opening operation is performed violently at an extremely low temperature, the base layer (A) will not be broken at all (that is, when the opening operation is performed, the base layer (A) will be broken rather than the other two layers). Peeling occurs mainly in the two intermediate layers or near the interface with the other two layers). In addition, it is possible to contribute to the action of suppressing the destruction of the bag body against the throwing and dropping operation of the food packaging bag (under extremely low temperature). In other words, the second intermediate layer (C) can be said to be a central action layer that completely achieves the object of the present invention. Here, the VST of the layer (C)
Is presumed to be lower than that of the first intermediate layer (B), but the low temperature has a certain degree. In this case as well, between the layers of the first intermediate layer (B) and the HS layer (D) (though not necessary for the adhesive strength between the layer (B) and the base layer (A)).
This is because proper adhesion is also required. This too low VST means that there is a high risk that the VST of the layer (C) will be opened by itself during handling in a temperature environment of room temperature or higher (this means that the VST of the layer (C) has a lower temperature). If so, there is likely to be a cause for the softer layer to exist). Considering this point, VST of the layer (C)
Should be kept in a temperature range lower than VST of the layer (B) by 60 to 70 ° C., preferably 75 to 85 ° C. (from the viewpoint of the polypropylene substrate layer (A), 80 to 1).
It is said that it is better to be in the low temperature VST range of 40 ° C., preferably 90 to 130 ° C.).

On the other hand, regarding the VST relationship described in (2) above, first, the HS layer (D) provided as the outermost layer via the first intermediate layer (B) and the second intermediate layer (C) is The VST should be higher than the VST of the layer (C) but lower than that of the polypropylene substrate layer (A). This HS layer (D) is basically a seal layer (necessary for bag making), and this seal is heated (heated).
G)). It can be said that this is a VST condition for rapidly and surely performing this at a lower seal temperature. In addition, the layer (D) also has a slight assisting function for suppressing the breakage of the base layer (A) even at a very low temperature peeling. As described above, it is premised that the VST of the HS layer (D) is lower than that of the base layer (A), but it can be said that the temperature is low. This is because the heat seal function cannot be effectively expressed. From this fact, it is about 10 to 90 ° C., preferably 20 to 8 ° C., than the base layer (A).
It is better to stay in the low temperature range of 0 ° C. Both the first intermediate layer (B) and the second intermediate layer (C) also have a heat seal function, and if the HS layer (D) has unevenness in thickness and the like, a sufficient heat seal is obtained. If this is not possible, these layers can also supplement the seal.

Further, regarding the VST relationship between the first intermediate layer (B) and the HS layer (D), the same polypropylene base layer as that of the layer (B), which is seen by cryogenic peeling, is also present in the layer (D). (A)
Since there is also a supporting effect on the suppression of the destruction of the VST, both VSTs may be the same in that respect. However, the layer (B) needs to be sufficiently adhered to the base layer (A), and the HS layer (D) needs to have a more effective heat seal function preferentially. , The first intermediate layer (B)> HS layer (D). This VST difference is in the range of about 5 to 50 ° C. higher than that of the HS layer (D). In addition, in terms of a preferable VST relationship as a whole from the above, polypropylene base layer (A)> first intermediate layer (B)
> HS layer (D)> second intermediate layer (C), and the temperature ranges thereof are different with the upper limit of 165 ° C. of the base layer (A) and the lower limit of 20 ° C. of the second intermediate layer (C). It can be said that it is composed of VST polyolefin resin.

The VST relation of each layer is as described above,
A specific example of a polyolefin resin suitable for this is as follows.

The polyolefin resin of the first intermediate layer (B) is exemplified. First, as provided in claim 3, VST
The resin containing propylene as a main component and having a temperature of 85 to 140 ° C., and more preferably 110 to 130 ° C. is preferable.
Specifically, this is a combination of 2 to 20% by weight of ethylene copolymerized binary propylene resin, 1 to 10% by weight of ethylene and 1 to 10% by weight of C _{4 to} C ₆ α-olefin monomer. An example is a propylene resin that is a former copolymer. still,
A small amount of additives (antioxidants, antistatic agents, lubricants, antiblocking agents, nucleating agents, etc.) that are generally added to olefin resins are allowed in the resin (depending on need).

Next, the resin for the second intermediate layer (C) will be described.
First, as provided in claim 4, the VST20-
80 ° C, preferably 23-70 ° C, more preferably 23
It has a temperature of -60 ° C. An example of this is the resin described in (3) or (4) above.

First, as one of them, at least one C ₃ -C ₈ α containing ethylene as a main component described in (3) is used.
・ It is a copolymer with olefin, but this is 55-98
The main component is ethylene in an amount of 2% by weight, and 2 to 45% by weight of at least one C _{3 to} C ₈ α-olefin is copolymerized with the ethylene (any bond structure is acceptable). VST varies mainly depending on the type of α-olefin and its content. Since the VST of the HS layer (C) needs to be the lowest than that of the other layers, it can be said that the smaller the crystallinity, the better. As the α-olefin, at least one of propylene, butene-1, hexene-1, and octene-1 is preferably used.

On the other hand, the styrene type thermoplastic elastomer (hereinafter styrene TPE) or the olefin type thermoplastic elastomer (hereinafter olefin TPE) described in (4) is as follows. First, styrene TPE is a thermoplastic resin in which a styrene polymer block containing styrene as a main component is used as a hard phase, and a diene polymer block containing a diene such as butadiene and isoprene as a main component and a copolymer block of ethylene and butene as a soft phase. Is a block polymer. Of course, styrene TPE in which the remaining double bond in the diene polymer block is hydrogenated may be used. Incidentally, whether it is a styrene polymer block or a diene polymer block, for example, α-olefin is copolymerized with each other as long as the functions of the hard phase and the soft phase are not lost. It may be each block.

In the olefin TPE, a polymer block of ethylene or propylene containing ethylene or propylene as a main component is used as a hard phase, and as a soft phase, for example, a ternary polymer block of ethylene, propylene and a diene monomer such as butadiene or isoprene, A thermoplastic block polymer composed of a copolymer block of propylene containing 50 to 80% by weight of ethylene, a copolymer block of ethylene and butene, and the like. Here, in the polymer block of ethylene or propylene as a hard phase, for example, about 10
It may be a copolymer block obtained by copolymerizing styrene in an amount of not more than wt%. Also, an olefin TPE in which the double bond remaining in the diene polymer block is hydrogenated may be used.

The above-mentioned (3) or (4) is not limited to the above, and both may be blended, or the styrene TPE and the olefin TPE of (4) may be blended. Further, another polyolefin resin may be blended with (3) or (4) as long as the essence of the HS layer (C) is not lost. Among these blend resins, the blend of (3) and (4) is effective because it leads to further improvement of easy peeling property.

The above-mentioned styrene TPE and olefin TP
E does not show vulcanized rubber-like properties at the processing temperature (melted state), but shows vulcanized rubber-like properties when returned to the use temperature. However, since the processing temperature and the properties similar to vulcanized rubber change to some extent depending on the composition, it cannot be said that all the ranges described above can be applied. In this, further select by VST, 20 ~ 80 ℃,
It can be said that it is optimal to select the one having a temperature of 23 to 60 ° C. more preferably.

Next, the polyolefin resin of the HS layer (D) as the outermost layer will be described. First, as provided in claim 5, VST 75 to 135 ° C., more preferably 8
It is selected from the resins having a temperature of 5 to 125 ° C., and the following can be specifically exemplified. First, as described above, the same resin as that of the first intermediate layer (B) may be used. Therefore, when the same resin is used, VST in the example of the layer (B) is used.
The resin at 75 to 135 ° C. may be selected. But,
An HS layer (D) having a VST lower than that of the (preferred) layer (B) is, for example:

One of them is the VST adjustment (that is, 75%) for the polyolefin resin exemplified in the first intermediate layer (B).
To 135 ° C.), for example, petroleum resin, terpene resin, rosin and the like.

The second is a blend of at least two kinds of polyolefin resins having different VSTs and a temperature of 75 to 135 ° C.
Is the use of a blended resin. One of the polyolefin-based resins composed of two or more kinds is 75-
If the temperature is out of 135 ° C., the others are blended with those in this VST range and the VST is adjusted so as to fall within the range. Specifically, for example, a blended resin of a propylene copolymer in which propylene is copolymerized with 3 to 10% by weight of ethylene and a propylene copolymer in which propylene is copolymerized with 3 to 40% by weight of butene can be mentioned. Incidentally, H
The specific examples of the polyolefin-based resin in the S layer (D) are the above-mentioned two examples. For example, a ternary polyolefin resin obtained by copolymerizing three or more olefin monomers is also included.
At least heat sealability, VST 75-135
This is because all polyolefin resins in the range of 0 ° C. are effectively and effectively used as the HS layer (D).

The polyolefin resin exemplified in the HS layer (D) may be added with a small amount of generally used antioxidants, antistatic agents, antiblocking agents, lubricants and the like.

The layer thickness distribution of the first intermediate layer (B), the second intermediate layer (C) and the HS layer (D) is basically set to be thinner than that of the polypropylene base layer (A). ,
Among them, it may be appropriately determined so that the function of each layer is sufficiently expressed. Preferably, the layer (B) is 0.5 to 1
5 μm, the layer (C) 1 to 25 μm, HS layer (D) 0.5
Although it is about 15 μm, it is more preferable to set the layer (C) to the maximum thickness and to set the other two layers to the same degree.

The structure of the main body multilayer film of the present invention is as described above, but it will be illustrated and clarified for reference. This is shown in the sectional view of FIG. (A) is a polypropylene base layer, (B) is a first intermediate layer, (C) is a second intermediate layer,
(D) is the HS layer (D).

Next, the means for manufacturing the main body multilayer film will be described. Although not limited to the manufacturing means, the following method can be preferably exemplified. First, the polypropylene to be the base layer (A) is separately melt-extruded and molded so as to have a predetermined thickness, cooled, and taken out. This stretching may be carried out before it is taken out, but it is more robust to carry out continuously in the subsequent series of steps of coextrusion of HS three layers and lamination.
It is more preferable to take up the film in a substantially non-stretched state here, since it can also be adhered and the three layers (B) / (C) / (D) can be stretched.

Next, a first intermediate layer (B), a second intermediate layer (C) and an HS layer (D) are sequentially laminated on one side of the obtained (substantially unstretched) polypropylene film. The following method is good for. First, each of the polyolefin resins corresponding to the layer (B), the layer (C) and the HS layer (D) is supplied to a hopper of a three-layer co- (T type die) extruder and simultaneously melt-extruded. Arrange the device so that three layers are formed. On the other hand, while heating the film, first prepare a (heating) stretching apparatus for continuously stretching in the longitudinal direction (first stage stretching step) and then in the transverse direction (second stage stretching step). The three layers (T type die) are installed under the extruder.

Stretching / lamination is performed by the above-mentioned apparatus configuration, and it is performed in the following order. First, the (substantially unstretched) polypropylene film itself is sent to the first stage stretching step, where it is first roll-stretched in the longitudinal direction. Then, the film is continuously sent to the second-stage stretching process, and the film that has undergone the first-stage stretching process is extruded from the three-layer co- (T-die) extruder before entering the second-stage stretching process using a tenter. It merges with the layer and is laminated. Then, this laminated film is sent to the second stage stretching step, where it is stretched and cooled in the transverse direction while being heated and wound up to finish (the polypropylene film of the substrate is stretched in the longitudinal and transverse directions, The HS three layers are in a stretched state only in the lateral direction).

According to the above method, (B),
The three layers (C) and (D) are laminated in a state of being stretched in the lateral direction, but at least the HS (D) layer may be a substantially non-stretched layer. This is because it is more effective for ensuring a perfect heat seal (particularly in the case where the bag-making means described later is attached to the palm). This substantially unstretched HS
The layer (D) can be formed by laminating the layer on the surface (C) of the second intermediate layer by, for example, extrusion lamination or thermal lamination, or by forming it on the stretched HS (D) layer and then by laminating the extrusion lamination. Or thermal lamination to form an unstretched layer. The resin used for extrusion lamination or thermal lamination here is, of course, the same resin as the HS layer (D), but inorganic particles (for example, fine powder of silica, feldspar, mica, etc.) rather than this alone. Is preferably added (for example, 2 to 7% by weight). This is
This is because the tensile rupture elongation of the layer itself is reduced without affecting the to sealability and the easy-open property is further improved.
When a non-stretched HS layer is further laminated on the (stretched) HS layer (D), the layer thickness of the HS layer (D) is preferably thin.

The polypropylene film is subjected to a surface pretreatment (for example, by corona discharge) for improving the adhesiveness before laminating the three layers (B), (C) and (D). However, the first intermediate layer (B), which is in direct contact with the film, is in good contact even without any treatment, so that it is not necessary. However, the non-laminated surface of the film (HS
Since the surface opposite to the layer) is generally a printing-compatible surface, in this case, it is preferable to perform the treatment as a pre-process. For this printing, either direct printing or indirect printing,
The former is a method of directly printing on the surface and laminating an OPP film on the surface if necessary, while the latter is a method of laminating the separately printed film on the surface. Here, with respect to the laminated film, the use of nylon film, PET film or the like cannot be avoided. Regarding this printing, printing may be performed on the HS layer (D) surface. Of course, not only in the case of the printing, it is better to perform the surface pretreatment when the resin coating is necessary (for other purposes).

Various uses of the obtained main body multilayer film can be considered. For example, if it is in the form of a web, it may be attached / adhered to a certain object, for example, a film-like material whose surface is coated with the polyolefin resin used for the HS layer (D) (separately), or various containers. It can be used for protection. Further, it is also effective to use it as a bag body, which is processed into a packaging bag and used. There are various usage forms as a bag, and there is no limitation,
As described above, it is more effective to use as a bag for frozen foods because it has excellent properties at low temperatures. In addition, since the base layer (A) is not destroyed by opening in the bag and the bag can be re-sealed repeatedly, it is convenient to preliminarily adhere an adhesive seal label (which can be repeatedly used).

The following can be said regarding bag making. Because the main body multi-layer film has excellent low-temperature peelability and is easy to open (mouth), it is attached to the palm (that is, H
There are many cases in which the S layer (D) is combined with each other and heat-sealed.
Of course, envelope sticking (that is, polypropylene base layer (A)
The surface layer of the base layer (A) and the edge of the HS layer (D) are heat-sealed together, but in this case, the HS layer (D) is added to the heat-sealed portion of the base layer (A). ) Is recommended. Of course, in the case of mass production, insertion of the packaged object (into the bag) together with the bag making may be automatically performed in a series of automatic packaging systems.

Further, the main body multilayer film (B),
The three layers (C) and (D) are basically provided on one side,
Depending on the purpose and use, the film may be provided on the other side in the same manner to form a multi-layered film, and the film is not limited to this one side.

[0040]

EXAMPLES Next, the present invention will be described in more detail by way of examples together with comparative examples. The VST (Vicat softening temperature) referred to in the present invention
Is the temperature measured by the measuring method described in JIS K7206: 1999. (Measuring machine: H.D.T. & V.S.P.T.TESTER manufactured by Toyo Seiki Seisakusho Co., Ltd.) In addition, when a temperature load of less than room temperature (23 ° C.) was applied in this measurement, it was already The VST of itself when a given deformation occurs is shown as about 23 ° C.

Example 1 First, the following resins were prepared for the base layer (A), the first intermediate layer (B), the second intermediate layer (C) and the HS layer (D). <For base layer (A)> Crystalline polypropylene having a VST of 152 ° C (melting point of 162 ° C). Hereinafter referred to as a base resin. <For the first intermediate layer (B)> 7% by weight of ethylene / 2% by weight
Butene-1 / 91 wt% propylene of three components of VST 110 ° C polypropylene resin (melting point 132
C). It should be noted that 0.1% by weight of an anti-blocking agent (amorphous silica) and 0.4% by weight of an antioxidant (0.2% by weight of each of two types of phosphorus type and phenol type) with respect to the resin. Was added. Hereinafter referred to as B resin. <For Second Intermediate Layer (C)> VST about 23 ° C. Copolymer with propylene containing ethylene as a main component (TAFMA-P0180 manufactured by Mitsui Chemicals, Inc.). Hereinafter referred to as C resin. <For HS layer (D)> VST123 ° C. Copolymer with ethylene containing propylene as a main component (melting point 138 ° C.)
Of 50% by weight and a butene-1 having a VST of 83 ° C. and 50% by weight of a copolymer containing butene-1 containing 36% by weight of butene-1. Incidentally, 0.2% by weight of an anti-blocking agent (amorphous silica) and 0.1% by weight of a lubricant (erucic acid amide) were added to the resin. Hereinafter referred to as D resin.

First, the base resin A was melt-extruded at 260 ° C. by a (T-type nozzle) extruder, cooled, molded into a substantially unstretched polypropylene film (thickness 1250 μm), and taken out.

Next, the unstretched polypropylene film was fed into a stretching device at a speed of 20 m / min, and 130
The mixture was supplied to a first stage heated drawing zone (a method based on the difference in rotation speed of two pairs of nip rollers) adjusted to 0 ° C., where it was drawn 5 times in the longitudinal direction. The stretched film is continuously fed to a second stage heat-stretching zone (a method using a uniaxial stretching apparatus having a transverse tenter section), but before entering the zone, a three-layer coextrusion is conducted. The machine is arranged so as to be positioned before the first-stage heating and stretching (uniaxial) of the heating and stretching device is completed and before the second-stage heating and stretching (biaxial) is performed, and the B resin, C resin and D resin is co-melt extruded,
After cooling, the driving of the extruder was started so that the film was merged with the film to be laminated and adhered thereto. Here, the B resin is 220
C., C resin was adjusted to 200.degree. C., and D resin was adjusted to 220.degree. C., and melt-extruded from each extruder to one T-shaped nozzle. At this time, the layer surface of the B resin is extruded so as to be in contact with the film surface, cooled, and then pressure-bonded by a nipple roller (using the residual heat in the first-stage heating / drawing zone) while the second step of the second layer is performed. It was sent out to a heat drawing zone. The zone is 155
The temperature is adjusted to ℃ and the lateral tenter section stretches it laterally 10 times.
The desired body multilayer film was obtained.

The total thickness of the main body multi-layer film which has undergone all the above-mentioned steps is 30 μm, and the breakdown of each layer is polypropylene substrate layer (A) / first intermediate layer (B) / second intermediate layer (C) / HS layer (D). = 25 / 1.5 / 2 / 1.5 (each μm). A part of the (wound) main body multilayer film was rewound after one week to check the blocking state, but no blocking was observed at all.

(Example 2) (When the second intermediate layer (C) is made of the blended resin of the above (3) and (4)) First, the resin of the second intermediate layer (C) of Example 1 was used. VS
T about 23 ° C styrene TPE (styrene-based hard phase,
Block copolymer made of ethylene / butylene as a soft phase (Dialon P46 manufactured by JSR Co., Ltd.)
00) 30% by weight and 70% by weight of VST of about 23 ° C. and 70% by weight of a propylene copolymer (Tufuma-P0180 manufactured by Mitsui Chemicals, Inc.) containing ethylene as a main component,
Others prepared the same resin. This blend resin is called blend C resin. The extrusion temperature of the blend C resin is 200
℃ was made.

Then, in the same manner as in Example 1 except that the thickness was as follows, the total thickness of the main body multilayer film was 40 μm.
m, the breakdown of each layer is polypropylene base layer (A) / first intermediate layer (B) / second intermediate layer (C) / HS layer (D) = 32.
A film of 5/2 / 3.5 / 2 (each μm) was obtained.

(Comparative Example 1) (without second intermediate layer (C)) In Example 1, the base layer (A) was used under the same conditions except that the C resin was not used as the second intermediate layer (C). The first intermediate layer (B) and the resin used in HS (D) were laminated on the polypropylene film (1) to obtain a two-layer polypropylene film for comparison. The total thickness of the film obtained here is 3
0 μm, the breakdown of which is the base layer (A) / first intermediate layer (B)
/ HS layer (D) = 25 / 3.5 / 1.5 (each μm).

(Comparative Example 2) (VST of second intermediate layer (C))
Is larger than that of the other layers) First, the following resins were prepared for the base layer (A), the first intermediate layer (B), the second intermediate layer (C) and the HS layer (D). . <For Base Layer (A)> The same crystalline polypropylene ( VST152 ° C. ) as in Example 1 and hereinafter referred to as base resin. <For the first intermediate layer (B)> Polybutene- 1 having a VST of 65 ° C
A polypropylene resin in which 2.0 wt% of amorphous silica is mixed and dispersed in (melting point of 75 ° C.), and hereinafter referred to as B2 resin. <For the second intermediate layer (C)> 7% by weight of ethylene / 2% by weight
Butene-1 / 91 wt% propylene of three components of VST 110 ° C polypropylene resin (melting point 132
C). It should be noted that 0.1% by weight of an anti-blocking agent (amorphous silica) and 0.4% by weight of an antioxidant (0.2% by weight of each of two types of phosphorus type and phenol type) with respect to the resin. Was added. Hereinafter referred to as C2 resin <for HS layer (D)> same blend resin as in Example 1 ( VS
T123 ° C ) and is referred to as Blend D2 resin.

Then, in the same manner as in Example 1, the total thickness of the multilayer film was 30 μm, and the breakdown of each layer was polypropylene substrate layer (A) / first intermediate layer (B) / second intermediate layer (C) / HS.
Layer (D) = 25 / 1.5 / 2 / 1.5 (each μm). The extrusion temperature of the B2 resin from the three-layer coextruder is 2
25 ° C, 200 ° C for C2 resin, 22 for blended D2 resin
It was set to 0 ° C.

Reference Example 1 (Bag Making and Opening Test) The (main body) (comparative) multilayer film obtained in Examples 1 and 2 and Comparative Examples 1 and 2 was slit, and a bag making machine was used. To obtain a pouch with a length of 285 mm and a width of 160 mm. Hereinafter, the bags from Examples 1 and 2 will be referred to as main bags 1 and 2, and the bags from Comparative Examples 1 and 2 will be referred to as comparative bags 1 and 2.

Next, 20 bags of each of the bag 1 and 2 and the comparative bags 1 and 2 produced above were taken out, rapidly cooled at −20 ° C., and left standing for 5 hours. Then, in the cooled state, each bag was opened by hand, and the opened state of the heat seal portion was visually observed. As a result, the polypropylene base layer (A) was broken in all 20 bags of this bag 1 and 2,
There is no phenomenon such as cracks, and the first intermediate layer (B) and the HS layer (D) are centered around the second intermediate layer (C).
It was observed that peeling occurred only within the boundary between and. On the other hand, in Comparative bag 1, 7 to 20 bags were cracked or torn in the substrate layer (A), and in Comparative bag 1, 5 to 20 bags were cracked.

Regarding the opening test with the bag, the peel strength at room temperature and low temperature was actually measured as follows. The results are summarized in Table 1.
The measurement conditions were as follows. Samples: Examples 1 and 2 and Comparative Examples 1 and 2
Each of the (main body) (comparative) multi-layer films obtained in step 1 was cut into two pieces with a width of 15 mm, and both were combined (HS
Layer D (compared with each other), pressurized at 130 ° C. and 2 kg / cm ² for 0.5 seconds and heat-sealed to prepare 6 samples each. , ● Measuring device ・ ・ R200 type strograph manufactured by Toyo Seiki Seisakusho Co., Ltd. ・ Measuring temperature ・ ・ 23 ℃ and -20 ℃ ・ ● Peeling speed and angle ・ ・ 200mm / min, 180 °. Under the above measurement conditions, 3 samples at 23 ° C, 3 samples at -20 ° C
The sample was measured.

The results are shown in Table 1 (unit: N / c
In m, the results for each of the three samples are shown as a range). It can also be seen that in each of the example samples, even if the peeling temperature (use temperature) changes greatly, the peeling strength does not change much and the variation is small. On the other hand, in each of the samples of Comparative Examples, it is found that the peeling strength greatly changes depending on the peeling temperature (use temperature) and there is variation. This change in each comparative sample
It is considered that since the second intermediate layer (C) which should act as the intermediate layer does not exist, the peeling action was directly transmitted to the base layer (A), which resulted in cracking or tearing.

The heat seal was changed to 130 ° C.,
At 120 ° C. and 140 ° C. as well, samples were similarly heat-sealed to perform a peel test under the same conditions, and the peel strength at each peel temperature was determined, but there was no substantial difference. Also, when these peeled portions were observed with a magnifying microscope, it was observed that the second intermediate layer (C) portion was mainly peeled off in the example sample as at 130 ° C. In particular, the base layer (A) was partially cracked or broken at the peeling at −20 ° C. (It is considered that the peeling strength and variation in the comparative example are due to this crack or break).

[0055]

(Reference Example 2) (Drop Test) Using each of the 20 sheets obtained in Reference Example 1, 500 g of a frozen dessert with a stick was put into each of them, and the upper portion (corresponding to the mouth portion) of 7 mm width was HS. Layer (D) surface, heat seal (130 ℃, 2
kg / cm ² , 0.5 seconds). And each filling bag-
It was rapidly frozen at 20 ° C., and it was naturally dropped onto the concrete from a position of 1 m in height to check the rupture condition of the bag body.

As a result of the drop, in the filling bags according to the respective examples, neither the heat seal portion nor the bag body was cracked or torn at all. On the other hand, in the filling bag according to each comparative example, Comparative Example 1
It was broken by 6 out of 20 bags. And in the heat seal part, cracks were found in 4 bags. In Comparative Example 2, 4 out of 20 bags were torn and 6 at the heat seal portion were cracked.

[0058]

EFFECTS OF THE INVENTION The present invention, which is configured as described above, can provide the following effects.

In particular, it has become possible to obtain a main body multilayer film in which the easy peeling property and the peeling strength at extremely low temperatures are further improved. As a result, even when used as a packaging bag for frozen foods, there is no cracking or tearing even when opened in the frozen state, so that it is possible to safely and sanitize the frozen food again.

Further, even if the food packaging bag in the frozen state is dropped or thrown during handling, there is no risk of the bag body being torn or cracked, and a great improvement can be made.

[Brief description of drawings]

FIG. 1 is a sectional view showing a structure of a main body multilayer film.

[Explanation of symbols]

(A) ... Polypropylene base layer, (B) ... First intermediate layer, (C) ... Second intermediate layer, (D) ... (outermost) HS layer.

Continued front page    F-term (reference) 3E064 BA24 BB03 BC03 BC15 BC18                       EA12 FA01 HN05                 3E086 AA23 AC07 AD01 BA04 BA15                       BA33 BB42 BB85 BB90 CA01                       DA08                 4F100 AB10D AK03B AK03C AK03D                       AK07A AK07B AK62C AK64                       AK67 AK80 AL05 AL09C                       BA04 BA07 BA10A CA06                       CA17 CA19 CB03D EJ38A                       GB15 GB23 JA04A JA04B                       JA04C JA04D JB16C JK06                       JL12D YY00A YY00B YY00C                       YY00D

Claims (6)

[Claims] 1. A first intermediate layer (B) and a second intermediate layer (C) made of a polyolefin resin and a heat seal layer (D) made of a polyolefin resin on one surface of a polypropylene base layer (A). A polyolefin-based multi-layer film that is sequentially laminated, wherein each of the layers (A), (B), (C), and (D) has a Vicat softening temperature and has the following relationships (1) and (2). A low temperature easily peelable polyolefin-based multi-layer film. (1) Vicat softening temperature of base layer (A)> Vicat softening temperature of first intermediate layer (B)> Vicat softening temperature of second intermediate layer (C), (2) Vicat softening temperature of base layer (A)> Vicat softening temperature of heat seal layer (D)> Vicat softening temperature of second intermediate layer (C). 2. The low-temperature easily peelable polyolefin-based multilayer film according to claim 1, wherein the polypropylene base layer (A) is formed by biaxially stretching a polypropylene resin having a Vicat softening temperature of 145 to 165 ° C. 3. The low-temperature easily peelable polyolefin-based multilayer film according to claim 1, wherein the first intermediate layer (B) comprises a polyolefin-based resin containing propylene as a main component and having a Vicat softening temperature of 85 to 140 ° C. . 4. The first intermediate layer (C) is mainly composed of any one of the following (3) and (4) having a Vicat softening temperature of 20 to 80 ° C. The low temperature easily peelable polyolefin-based multilayer film according to any one of 3 above. (3) At least one C ₃ -containing ethylene as a main component
Copolymers of alpha · olefin C _8, (4) a styrene-based thermoplastic elastomer - or olefinic thermoplastic elastomer -. 5. The low-temperature easily peelable polyolefin-based material according to claim 1, wherein the heat-sealing layer (D) is made of a polyolefin-based resin having a Vicat softening temperature of 75-135 ° C. Multi-layer film. 6. A food packaging bag comprising the low-temperature easily peelable polyolefin-based multilayer film according to claim 1.