JP2605114B2 - Laminated product of stretched polypropylene film and its use - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a laminate of a stretched polypropylene film and a pressure-sensitive adhesive tape having the laminate as a base material, and more particularly to a plurality of biaxially oriented tapes. A laminate in which a stretched polypropylene-based film (hereinafter referred to as an OPP film) is sandwich-laminated using a resin composition comprising a high-pressure low-density polyethylene and an ethylene / α-olefin copolymer, and the laminate as a base material Adhesive tape.

(Conventional technology and its problems) Many laminates in which various films of a synthetic resin are sandwich-laminated using an adhesive resin have been conventionally known.

On the other hand, it is well known that polypropylene films are generally excellent in heat resistance, rigidity, water resistance, and strength. However, the unstretched film has a drawback that the tensile strength is insufficient and the dimensional stability accompanying the elongation of the film is lacking. On the other hand, the OPP film obtained by biaxially stretching polypropylene usually has a thickness of 12 to 35μ depending on the stretching ratio, and the tensile strength of the OPP film alone is considerably improved, but the tear strength is significantly reduced. However, its use is currently limited to those used as composite films by lamination. And for the purpose of the present invention, mechanical strength is required rather than excellent in flexibility, for example, for applications such as adhesive tape base, unstretched polypropylene film and stretched OPP film alone, Aptitude is not enough.

On the other hand, as a base material of the adhesive tape, a synthetic resin film,
It is well known that cellophane, paper, cloth, metal foil and the like are used. Among them, a synthetic resin film is generally the most widely used material because of its relatively excellent water resistance and strength and easy handling. However, the use of these materials alone as the base material of the pressure-sensitive adhesive tape is limited only to the base material of the tape for electrical insulation and general applications that do not require large strength or flexibility. In addition, some adhesive tapes used for heavy packaging and for joining industrial articles require flexibility from the viewpoint of workability as well as mechanical strength. Often not. In this case, some proposals have been made to improve the mechanical strength, particularly the tensile strength and workability.

For example, JP-A-62-232476 discloses an adhesive tape provided with an adhesive layer on at least one surface of a biaxially stretched polyester film containing specific silicone resin fine particles in polyester. Describes that the tape has a strength that makes it difficult for the tape to be broken even when the tape is drawn in a state where a large pull-out angle is used and an impact force is applied at a high speed.

In addition, various adhesive tapes using a film laminate (hereinafter, referred to as a composite film) as a base material for improving the strength of the film have been proposed. For example, the OPP mentioned above
Since a film can be generally obtained only in a thin thickness by itself, for example, a composite film in which another synthetic resin film such as a styrene-based polymer is laminated on a polypropylene film via an adhesive resin is also known. ing.

However, in this case, since the adhesive resin used as the intermediate layer does not have sufficient adhesiveness to both the polypropylene and the polystyrene-based polymer, cracks are generated in the tape cut portion, and stringing occurs. It has the disadvantage that it causes phenomena and whitening and that the flexibility is not much improved.

As described above, the method of forming the composite film via the adhesive resin in the middle has advantages that the apparatus can be relatively simple and that the thickness of the laminate can be easily adjusted. As described above, it is actually difficult to find an adhesive resin having excellent adhesiveness to both films constituting the composite film, and many of them have the above-mentioned disadvantages after all.

As a method for forming a composite film, a method that does not use an adhesive resin is also known. For example, JP
No. 173251, a cross-linked high-density polyethylene, at least one side of a film biaxially stretched to a specific ratio or more such that the transverse stretching ratio and the longitudinal stretching ratio are in the longitudinal direction ≤ the transverse direction, the low-density An easy-cutting film provided with a layer of polyethylene or ethylene copolymer is described,
As a method of forming a composite film, a crosslinked unstretched film in the process of producing a crosslinked polyethylene stretched film, an intermediate process of a crosslinked uniaxial or biaxially stretched film, a uniaxial stretching process, and an intermediate process of a stretching process in a direction perpendicular thereto, or After the cross-linking biaxial stretching step, a low-density polyethylene or ethylene copolymer is melt-extruded and laminated on a cross-linked high-density polyethylene film as a substrate.

Since this invention does not use an adhesive in the middle, it can be said that this invention is significant in that a composite film having excellent cut properties can be obtained without causing a stringing phenomenon or a whitening phenomenon at the time of tearing the tape. This composite film has a considerably high tensile strength and excellent dimensional stability, lacks heat resistance, tear strength and flexibility, and is insufficient in suitability as a base material for an adhesive tape, for example. In addition, several steps are required from special raw materials, the equipment becomes large, and it is difficult to say that this method is always preferable in terms of economy.

By the way, it is an important requirement that the synthetic resin film as the base material for the adhesive tape has excellent heat resistance and dimensional stability in addition to the above-mentioned mechanical strength and flexibility. If the heat resistance and dimensional stability of the film are inferior, the film will shrink or curl at the heating temperature (usually about 100 to 180 ° C.) in the pressure-sensitive adhesive application step, and the yield of the product will be extremely poor. In other words, there is a problem in that the application of the adhesive cannot be performed efficiently.

In addition, conventional adhesive tapes are mainly used for packaging, industrial use, electrical insulation, joining of articles, and the like, and therefore should be sufficiently satisfied if they have the above-mentioned mechanical strength to some extent. Although it can be used, adhesive tapes have recently been supplied for quite a wide range of applications, and in applications where a part of the body may come into contact with the human body, for example, fastening tape for disposable diapers, It must be flexible enough to not hurt the skin.

Therefore, an object of the present invention is to provide a composite film which is extremely excellent in tensile strength and tear strength, excellent in heat resistance and flexibility, and a pressure-sensitive adhesive tape using the composite film as a base material.

(Means for Solving the Problems) The present invention has been made in order to achieve the above-mentioned object, and a plurality of OPP films are prepared by using a specific amount of a high pressure method low density polyethylene and an ethylene / α-olefin copolymer. It is characterized in that a composite film is formed using an adhesive resin composed of a blend composition having a specific ratio.

That is, according to the present invention, a plurality of polypropylene-based biaxially stretched films are prepared by mixing 90 to 60% by weight of a high-pressure low-density polyethylene with an ethylene / α-olefin copolymer 10 to 60% by weight.
A laminate of a biaxially stretched polypropylene film sandwich-laminated using an adhesive resin composition comprising 40% by weight, and an adhesive tape comprising the laminate as a base material and an adhesive layer laminated thereon are provided. .

In the present invention, a low-density polyethylene obtained by a high-pressure method having a density of 0.91 to 0.93 and a melt flow rate of 5 to 20, using a biaxially stretched thin polypropylene film as a polypropylene-based film and an adhesive resin, When a mixture with an ethylene-α-olefin copolymer is used, a composite film having the highest adhesive strength between the layers and the highest mechanical strength and heat resistance will be obtained. It is particularly suitably used as an adhesive tape which may be partially in contact with the human body during use, for example, a fastening tape for disposable diapers. At the same time, this adhesive resin is extremely flexible and has high tensile strength, so the composite film is rich in flexibility,
It has excellent tensile strength and has characteristics that do not damage the human body.

(Function) The present invention is to laminate a plurality of OPP films which are too hard on their own and do not have sufficient mechanical strength, and each layer is made of high-pressure low-density polyethylene and ethylene-α-
By sandwich lamination using a blend composition having a specific quantitative ratio with an olefin copolymer, the present inventors have obtained a composite film having excellent mechanical strength while retaining appropriate flexibility and heat resistance. Based on new findings, the above excellent properties are brought about by the excellent adhesiveness and flexibility of the OPP film constituting each layer and the above specific resin composition used as a joining resin.

In the present invention, the polypropylene-based biaxially stretched film refers to a polypropylene homopolymer, a copolymer of propylene and a small amount of another olefin, or a small amount of another olefin homopolymer or copolymer in polypropylene. It refers to a film obtained by biaxially stretching the mixed composition.

When the polypropylene-based biaxially stretched film is a copolymer, other olefins that can be copolymerized with propylene include ethylene, 1-butene, 1-pentene,
-Methyl-1-butene, 1-hexene, 4-methyl-1
Examples thereof include I-olefins having 10 or less carbon atoms, such as -pentene, 1-octene and 1-decene. Among them, copolymers with ethylene are preferably used.

Such a copolymer component is usually used in an amount of 15 mol% or less, preferably 10 mol% or less in a random copolymer, and in a block copolymer, the heat resistance of polypropylene is not impaired. Amount, usually 50 mol%
Below, preferably used in an amount of up to 40 mol%.

Further, as the olefin-based polymer to be blended with polypropylene, homopolymers or copolymers of the above-mentioned monomer components copolymerizable with propylene can be mentioned,
Among them, polyethylene is preferably used, and this copolymer component is usually 50 parts by weight or less based on polypropylene,
Preferably it is blended in an amount of up to 40 parts by weight. As described above, as the polypropylene polymer, a copolymer of propylene alone or with another olefin, or a blend of polypropylene with another olefin polymer is used. Flow rate (hereinafter referred to as MFR) is 0.5 to 10, preferably 0.5
It is recommended that the content be in the range of from 2.0 to 2.0 in order to improve the heat resistance and mechanical strength of the polypropylene film.

The production and biaxial stretching of the propylene-based copolymer film can be performed by a method known per se.

As a biaxially stretched film (OPP film), for example,
Using a 00 mm T die forming machine, a raw film having a film thickness of about 2 mm is obtained at a die temperature of 200 to 260 ° C. and a forming speed of 10 to 40 m / min.
A film having a film thickness of 5 to 50 μm, preferably 12 to 35 μm, obtained by stretching at a molding speed of 50 to 200 m / min by stretching the film 6 to 10 times in the horizontal direction by a tenter method and stretching at a molding speed of 50 to 200 m / min.

Known additives such as antioxidants, ultraviolet absorbers, lubricants, antiblocking agents, antistatic agents, and pigments can be added to the propylene-based polymer of the present invention, if necessary.

The blend composition of high-pressure low-density polyethylene and ethylene / α-olefin copolymer used as the adhesive resin in the present invention is a high-pressure low-density polyethylene of 90 to 60.
%, Preferably 75 to 65% by weight, and 10 to 40% by weight of the ethylene / α-olefin copolymer, preferably 25 to 65% by weight.
It is contained at a rate of 35% by weight.

As high-pressure low-density polyethylene, the density is 0.91 to
It is preferable to use one having a melt flow rate (MFR) of 0.93 and a melt flow rate of 5 to 20, particularly preferably 5 to 10.

As the α-olefin which is a copolymer component of the ethylene / α-olefin copolymer, propylene, 1-butene,
1-pentene can be exemplified. It is particularly preferable to use an ethylene / butene-1 / random copolymer as the ethylene / α-olefin copolymer.

Although the OPP film of the present invention varies depending on the stretching ratio, it usually has a thickness of 12 to 35 μ, and the composite film when used as the base material of the adhesive tape has a thickness of 20 μm.
It is standard to laminate two OPP films with a thickness of 30 μm to 35 μm so that the adhesive resin layer has a thickness of 30 μm, and to have a total thickness of about 70 to 100 μm, depending on other required physical properties. The thickness and number of OPP films can be appropriately selected, but in any case, the thickness of the adhesive resin is
It is preferable that the thickness per layer is about 30 μm in order to keep the flexibility and mechanical strength of the obtained composite film excellent.

As described above, the composite film of the present invention can have a laminated structure of three or more layers, but is excellent in mechanical strength, and yet has a degree of flexibility that does not damage the skin when it comes into contact with the human body. Has a three-layer structure, and the tear strength is best when it has a three-layer structure.

When using a composite Irumu of the present invention as a substrate for adhesive tape is the substrate for application by melt extrusion of adhesive approximately 70 g / m ² in solid weight, or in an organic solvent solution or emulsion was coated Then, the adhesive tape is wound into a roll through a heating and drying process. As the pressure-sensitive adhesive, for example, those known per se such as natural and / or synthetic rubbers, vinyl ethers, and acrylic urethanes are appropriately selected and used.

The thickness of the applied pressure-sensitive adhesive is preferably about 20 to 70 μm.If the adhesive layer is thin, not only the solvent resistance is lowered but also sufficient adhesiveness is often not obtained.
If it exceeds μ, the adhesive strength becomes unnecessarily high, and the re-sticking property, which is an important function of the adhesive tape, is reduced.

(Effect of the Invention) The laminate of the OPP film of the present invention, as an adhesive resin,
High-pressure low-density polyethylene of specific composition and ethylene α-
By using the blend composition with the olefin copolymer, each layer is firmly adhered, and flexibility is given by the interaction between the OPP film and the adhesive resin, compared with the case where other adhesive resins are used. More suitable flexibility is maintained and the mechanical strength is also excellent.

In addition, the laminate of the OPP film of the present invention exhibits excellent heat resistance and dimensional stability.When it is used as a base material for an adhesive tape, it is also resistant to heating during the adhesive application step. Since the base film does not shrink or curl, efficient application of the adhesive can be achieved, and the resulting adhesive tape has excellent tensile strength and tape cutability, and it comes into contact with the human body It is suitable for use as a fastening tape for disposable diapers because it has an appropriate degree of flexibility that does not damage the skin even when it is used.

(Examples) Hereinafter, the present invention will be described in detail based on examples.

 The evaluation in the examples was performed based on the following test methods.

<Test method> (1) Heat shrinkage rate (MPC method) Air oven: 140 ° C x 5 minutes (2) Curl (evaluation of sample appearance of (1)) ○ Good (No curl at all) △ Normal (Slight curl) × defective (severe curl) (3) flexibility (sensory evaluation) ○ good (soft) △ normal (slightly hard) × defective (hard) (4) tensile strength JIS-K-6781 (5) tear strength ( (Sensory evaluation) ○ Good (strong) △ Normal (slightly weak) × Poor (weak) (6) Peel strength JIS-P-8139 Example 1, Comparative Examples 1 to 4 Depending on the film and processing conditions shown below, Table 1 The films having various layer constitutions shown in Table 1 were obtained.

Table 1 shows the tape base aptitude and film properties of this film.

1. Film (resin) (1) OPP film Resin composition: Homopolymer (MFR = 1.0 / 10 min, density = 0.91 g / cm ³ ) Stretching ratio: Vertical 5 times / horizontal 10 times Film thickness: 25μ, 50μ (2) CPP film Resin composition: copolymer (MFR = 10 g / 10 min, density = 0.91 g / cm ³ ) Film thickness: 135 μ (3) HD-PE film Resin physical properties: (MFR = 0.4 / 10 min, density = 0.965 g / cm ³ ) Film thickness: 100μ 2. Adhesive resin (for sandwich lamination) Resin composition: LD-PE / ethylene / α-olefin copolymer blend composition, blend ratio = 70/30, LP-DE manufactured by Mitsui Petrochemical Industries, Ltd. Mirason ^{R MZ-11 MRF = 6.5g /} 10min, density = 0.917 g / cm ³ ethylene · alpha-olefin copolymer ethylene content 89 mol%, crystallinity of 15% by X- line, MFR = 3.6 g / 10min density = 0.88g / cm ³ 3. pressure-sensitive adhesive (hot-melt coating for the test) type: polyethylene-based hot melt Thailand (Ethylene / vinyl acetate copolymer) Processing: Roll coater Processing temperature 150 ° C Processing speed 3m / min Adhesive layer thickness: about 50μ 4. Laminating processing conditions (laminate) Processing temperature: 340 ° C Processing speed: 120m / min Lami layer (adhesive resin layer) thickness: 30μ Corona treated.

Claims (5)

(57) [Claims] 1. A plurality of biaxially oriented polypropylene-based films are prepared by using an adhesive resin composition comprising 90 to 60% by weight of a high-pressure low-density polyethylene and 10 to 40% by weight of an ethylene / α-olefin copolymer. A laminate of a sandwich-laminated polypropylene biaxially stretched film. 2. The adhesive resin composition has a density of 0.91 to 0.93,
The laminate according to claim 1, which is a mixture of a low-density polyethylene obtained by a high-pressure method with a melt flow rate of 5 to 20 and an ethylene / α-olefin copolymer. 3. The laminate according to claim 1, wherein the thickness of the laminate is in the range of 70 to 100 μm. 4. A sandwich laminating method wherein a plurality of biaxially stretched polypropylene-based films are formed by using an adhesive resin comprising 90 to 60% by weight of a high-pressure low-density polyethylene and 10 to 40% by weight of an ethylene / α-olefin copolymer. An adhesive tape obtained by further laminating an adhesive layer on at least one of the surface layers of a chilled polypropylene biaxially stretched film laminate. 5. The adhesive tape according to claim 4, wherein said tape is a fastening tape for a disposable diaper.