JPH0242066B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a laminate, and more particularly to a laminate having excellent physical properties such as strength and moisture resistance, which is obtained by laminating two types of high-density polyethylene layers having significantly different melt indexes and melt flow ratios. Conventionally, films made of high-density polyethylene or low-density polyethylene have been used in fields that require moisture resistance, such as food packaging bags and copy paper packaging bags. However, low-density polyethylene films do not have sufficient mechanical strength or moisture resistance, and have the disadvantage that they must be made thicker to improve these properties. For this reason, attempts have been made to reduce the thickness by using high-density polyethylene, which has excellent strength. However, ordinary high-density polyethylene for use in low-melt-index films, which has high impact resistance, has a large degree of directionality during molding and does not have sufficient tear strength. Moreover, it has insufficient moisture resistance and gloss, and its uses are limited. On the other hand, high-density polyethylene with a relatively large melt index has poor film formability and the resulting film has low impact strength and tear strength, making it unsuitable for film production. An object of the present invention is to eliminate the above-mentioned drawbacks of the prior art, and to provide a film or sheet-like laminate that has good strength balance even when the thickness is reduced, and has excellent moisture resistance. That is, the present invention provides a melt index (MI)
is 2.1~30g/10min, melt flow ratio (MFR)
layer (A) made of high-density polyethylene with a melt index of 15 or more and less than 50, and a melt index (M) of 0.01 to
0.5 g/10 minutes, and has a melt flow ratio (MFR) of 70 or more layer (B) made of high-density polyethylene, and the thickness ratio of the two layers is layer (A)/layer ( B)＝
9/1 to 4/6, and the difference in melt flow ratio (MFR) between the two layers is 30 or more. Here, as the layer (A), MI2.1-30g/10 minutes, preferably 3-30g/10 minutes
The layer is made of high-density polyethylene with a density of 10g/10min. Furthermore, the high density polyethylene constituting the layer (A) preferably has a density of 0.945 to 0.975 g/cm ² ,
Also, use one with an MFR of 15 to 50. In addition, this MFR is MI with a load of 21.6Kg and a load of 21.6Kg.
It is defined by the ratio of M _of 2.16 kg, that is, MFR=MI _21.6 Kg/ _{MI 2.16} Kg, and serves as an index of molecular weight distribution. Such high-density polyethylene includes not only ethylene homopolymers, but also copolymers of ethylene and other α-olefins (α-olefin unit content: 10 mol% or less), such as ethylene-propylene copolymers. , ethylene-butene-1 copolymer, etc. The layer (A) made of high-density polyethylene has excellent moisture resistance, but has rather poor moldability and extremely low mechanical strength, especially impact strength. Therefore, in the present invention, the layer (B) shown below and the layer (A) are used in a stacked manner to achieve the above-mentioned object. Layer (B) is a layer made of high density polyethylene having an MI of 0.01 to 0.5 g/10 min, preferably 0.02 to 0.2 g/10 min. Furthermore, the high-density polyethylene that makes up layer (B) usually has a density of 0.945~
0.970g/ ^cm3 , MFR is 70 or more, preferably
80 to 200 is used. The high-density polyethylene constituting such a layer (B) includes ethylene homopolymers, copolymers of ethylene and other α-olefins, such as ethylene-propylene copolymers, ethylene-butene-1 Examples include copolymers. This layer (B) made of high-density polyethylene has excellent mechanical strength such as tensile strength and tear strength, and by using a laminate of the above layer (A) and this layer (B), moisture proofing can be achieved. A laminate with an excellent balance of properties and strength can be obtained. Furthermore, the high-density polyethylene constituting the layer (B) has excellent moldability and has sufficient strength even when made thin. In the present invention, as described above, basically the above layer (A) and layer (B) are laminated to form a laminate, but if necessary, these layers may be further laminated to form three or more layers. It can also be a laminated film, and
A layer of low density polyethylene or the like may be provided as an outer layer or an intermediate layer of layers (A) and (B). Examples of the low-density polyethylene resin used for the outer layer or intermediate layer include ethylene homopolymers, copolymers of ethylene and α-olefin, and acrylic esters. As mentioned above, when layer (A), (B) or other layers are laminated, the difference in MFR between layers (A) and (B)
It is necessary to select 30 or more.
In particular, it is most preferable to set it to 50 or more. Furthermore, other resins and rubbers may be added to the high-density polyethylene constituting the layers (A) and (B) of the present invention, if desired, and pigments, dyes, stabilizers, slip agents, etc. may be added. It's okay. When producing the laminate of the present invention using the high-density polyethylene constituting the above layers (A) and (B), various methods can be applied. For example, a blow ratio of 1.5
Although coextrusion inflation molding was carried out using 5.0 to 5.0, film-like or sheet-like laminates can also be obtained by coextrusion T-die molding or the like. The thickness ratio of layer (A) and layer (B) in this laminate should normally be layer (A)/layer (B) = 9/1 to 4/6. Furthermore, when the laminate of the present invention is used as a packaging bag, either layer (A) or (B) may be used as an inner layer or an outer layer, but in general, layer (A) with excellent moisture resistance is used as an outer layer. used. As described above, since the laminate of the present invention is composed of two or more polyethylene layers having different physical properties, it has excellent moisture resistance and mechanical strength, such as impact strength and tear strength. In particular, a tear strength greater than that of either single layer film can be obtained. Moreover, this laminate also has excellent moldability. As described above, since it has sufficient mechanical strength, it can be made thinner and resource saving can be achieved. Therefore, the laminate of the present invention can be formed into a desired shape and effectively used for food packaging bags, copy paper packaging bags, and the like. Next, the present invention will be explained in more detail with reference to Examples. Examples 1 to 7 The predetermined raw material resins shown in Table 1 were melt-kneaded using an extruder, introduced into an in-die adhesion type circular die, and then inflation molded at a blow ratio of 2 to form a 40μ thick two-layer or A three-layer laminated film was obtained. The measurement results of various physical properties of the obtained film are shown in Table 1 along with the moldability. Comparative Examples 1 to 5 The same measurements as in Examples 1 to 7 were performed on films made of predetermined resins shown in Table 1. Results first
Shown in the table.

[Table] *1 Indicates the ratio of inner layer/outer layer or inner layer/middle layer/outer layer.
*2 Compliant with JIS Z 1702 *3 Film impact method (Film is fixed in a ring shape, and the film is punched with a pendulum with a 1-inch impact head, and the energy required for punching is calculated.
- was measured. (Using a film impact tester made by Toyo Seiki Seisakusho))
*4 Based on ASTM D 523 *5 JIS Z 0208 (40℃, 90%RH)
*6 MI 0.05g/10 minutes, density 0.955g/ ^cm3 , MFR
100
*7 MI 0.04g/10 minutes, density 0.960g/ ^cm3 , MFR
130
*8 MI 5.8g/10 minutes, density 0.967g/ ^cm3 , MFR
twenty five
*9 MI 5.0g/10 minutes, density 0.968g/ ^cm3 , MFR
30
*10 MI 0.3g/10min, density 0.920g/ ^cm3 ,
*11 MI 2.4g/10min, density 0.923g/ ^cm3 , (contains 8wt% of 4-methylpentene 1 as comonomer)
*12 MI 1.1g/10 minutes, density 0.954g/ ^cm3 , MFR
70
*13 MI 0.9g/10min, density 0.954g/ ^cm3 , MFR
twenty two
*14 MI 0.05g/10 minutes, density 0.951g/ ^cm3 , MFR
50
Here, MI, density, and MFR were based on JIS K 6760.

Claims (1)

[Claims] 1 A layer (A) made of high-density polyethylene with a melt index of 2.1 to 30 g/10 minutes and a melt flow ratio of 15 or more and less than 50;
0.01 to 0.5 g/10 minutes, and a layer (B) made of high-density polyethylene having a melt flow ratio of 70 or more is laminated, and the thickness ratio of the two layers is layer (A)/layer (B). )=9/
1 to 4/6, and the difference in melt flow ratio between the two layers is 30 or more.