JPH01133737A - Polyethylene composite film - Google Patents

Abstract

PURPOSE:To contrive improvements in moisture resistance, flexocrack resistance, cutting properties and heat-sealing properties, by a method wherein a kind of a laminating material having a specific shrinkage factor is laminated to one side of a polyethylene stretched film whose degree of crosslinking has been deteriorated inward in the direction of a thickness. CONSTITUTION:A BOPE film which becomes a base material layer is of a polyethylene biaxially stretched film whose degree of crosslinking has been deteriorated inward in the direction of a film thickness. It is preferable that the inside lowest gel content rate is 0%, gel content rate of an outside crosslinked layer falls within a range of 20-70% both sides of which are crosslinked identically, a crosslinked layer/an uncrosslinked layer/the crosslinked layer are constituted in the direction of the film thickness and a constituted ratio among layers each falls within a range of the uncrosslinked layer : both the side crosslinked layers = 1:0.1-10. Then paper or Al foil or cellophane or heat-resistant resin film whose heat shrinkage factor at 140 deg.C is less than 5% is made a laminating material. A thickness of a composite film obtained by laminating the BOPE film of the base material and at least a kind of the above-mentioned laminating material together is selected appropriately according to the purpose and use of packaging and it is normally about 20-200mum.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a polyethylene composite film suitable for packaging, which has excellent moisture resistance, flexible crack resistance, cuttability, and heat sealability.

Conventional technology Conventionally, general packaging films include paper, heat-resistant base materials such as polyethylene terephthalate film (PKTF), biaxially oriented polypropylene film (OPp), cellophane, oriented polyamide film (OPA), etc. A three-layer structure is known in which the intermediate base material is a film of saponified ethylene-vinyl acetate copolymer (saponified BVA), a gas barrier layer such as aluminum (HT) foil, and a seal base material. However, these front base materials have a problem in that they do not have sufficient flexo crack resistance, moisture resistance, cuttability, etc., and cannot sufficiently compensate for the performance of the intermediate base material. or,
The above-mentioned front base material does not have sealing performance in applications such as gusset bags that require sealing performance between the front base materials, and furthermore, it is necessary to provide a cool base material, which leads to cost increase.

On the other hand, a polyethylene composite film consisting of a cross-linked polyethylene stretched film with excellent moisture resistance and transparency with a specific cross-linking degree in the film thickness direction and a sealant layer such as low-density polyethylene has already been proposed (Japanese Unexamined Patent Application Publication No. 1989-1999). -1
71149). However, this polyethylene composite film also has a problem in heat sealability between stretched crosslinked polyethylene films.

The present invention has been made to solve the above-mentioned conventional problems, and provides a polyethylene composite film suitable for packaging applications that has excellent moisture resistance, flake resistance, cuttability, and heat sealability. The purpose is to

Means for Solving the Problems The present invention achieves the above-mentioned objects by using a stretched polyethylene film (hereinafter simply referred to as BOPE film A/A) having a polyethylene stretched film (hereinafter simply referred to as BOPE film A/A) whose degree of crosslinking decreases inward in the thickness direction of the film.
The gist of the present invention is a polyethylene composite film that is formed by laminating at least one type of laminate material (hereinafter simply referred to as laminate material) having a heat shrinkage rate of less than 5 at 140°C.

The BOPB film serving as the base layer in the present invention is a biaxially stretched polyethylene film in which the degree of crosslinking decreases inward in the thickness direction of the film. The degree of crosslinking is expressed by the gel fraction (ratio of insoluble portion by boiling p-oxygen extraction), and the lowest inner gel fraction is less than 5% and the outer crosslinked layer gel fraction is 5% or more. In particular, the inner minimum gel fraction is O
qb, the gel fraction of the outer crosslinked layer is in the range of 20 to 70cm, and both sides are crosslinked in the same manner, and the thickness direction of the film constitutes a crosslinked layer/uncrosslinked layer/crosslinked layer, and the composition ratio of each layer is uncrosslinked. Layer: both side crosslinked layer=1: It is preferable that it is in the range of 0.1-10. Further, it is biaxially stretched at a stretching ratio of 3 times or more in one direction and at a stretching ratio of 9 times or more in an area. The type of BOPK film mentioned above may be selected depending on the intended use.

For example, high-density polyethylene paste with a density Q of 935v/α3 or more is preferred from the standpoint of requiring moisture resistance, cutability, and bending pinhole resistance. Particularly preferable physical properties include a moisture permeability (y) of not more than a value determined by the following formula, and a haze of 5% or less.

7=17X-rod [However, yU moisture permeability (17m”/24 hrs),
X represents the thickness (μ) ft of the stretched film. ] When used as a sealant layer, a laminated film based on linear low-density polyethylene, which has less curl and can be heat-sealed at low temperatures, may be used.

The thickness of the BOHD film is appropriately selected depending on the intended use, but is usually about 10 to 50 μm.

The above-mentioned OPB film is, for example, JP-A-59-
It can be manufactured by the methods disclosed in JP-A No. 17432'2, JP-A No. 61-'74819, and the like. For example, from the standpoint of improving moisture resistance, polyethylene of various densities, density 193517 cm or more, melt index (K6760 from J, temperature 190 ° C, load 2.
Measured at 16 to 9, hereafter M-work) [L5 to 202/10 minutes,
High Road Melt Index (J Engineering 8K 6760
, temperature: 190° C., load: 21.6 boiling measurements, hereinafter referred to as HLM work)/M work: Preferably, polyethylene having a rating of 40 to 200 is used. Furthermore, it is preferable to add a hydrogenated petroleum resin to these. However, polyethylene may be used in mixtures. A sheet-like or tube-like original fabric formed by melt extrusion using this polyethylene is cross-linked from both sides by electron beam irradiation, etc. so that the degree of cross-linking decreases toward the inside in the thickness direction, and then An example is a method of biaxially stretching at temperature.

The laminate material in the present invention has a heat shrinkage rate of less than 5% at 140°C. Heat shrinkage rate at 140℃ is 5
If it exceeds %, thermal shrinkage occurs during heat cooling of the EOPIC films, and sufficient heat sealing cannot be achieved. Specific examples of the laminated material include paper, HT foil, cellophane, heat-resistant resin film, and the like. Examples of the paper include coated paper, double-sided wrapping paper, tissue paper, processed base paper for decorative boards, food containers, and the like. Further, as the At foil, one having a thickness of about 7 to 12 μm is used. Examples of heat-resistant resin films include those made of polyester, polyamide, polyimide, polyparabanic acid, and ethylene/polyvinyl alcohol copolymer. The thickness of these heat-resistant resin films is usually about 12 to 50 microns. Cellophane of approximately 300 count is used.

Polyethylene composite film of the present invention, EOPB as base material
The basic structure is a laminated film consisting of a film and at least one type of laminated material such as paper, a film or a heat-resistant resin film,
Furthermore, a sealant layer may be provided on the paper, HT foil, or heat-resistant resin film side of the laminated film.

Examples of the sealant include low density polyethylene, linear low density polyethylene, ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate, ionomer, polypropylene (unstretched), and the like.

In the present invention, paper, A
The method of laminating T-foil or heat-resistant resin film is as follows:
Any of the following methods may be used: (1) wet lamination, (2) hot melt lamination, (3) dry lamination, and (4) extrusion coating lamination.

The thickness of the laminated composite film is appropriately selected depending on the purpose and use, but is usually about 20 to 200 microns.

EXAMPLES Hereinafter, the present invention will be explained in detail using examples. The following general rules apply to the test methods used in the examples.

(1) Moisture permeability: JIS Z 0208, temperature 40℃
, relative humidity 90% compliant (2) Haze: JIS K 6714 compliant (3)
Heat sealing strength 2 J engineering S Z 025B (4) Heat shrinkage rate: A test piece with a marked line at length 10 and 310+m (width 101 x length 3
50 days) (taken in the longitudinal and transverse directions) for 10 minutes, the heat shrinkage rate of each test piece was determined from the length before heating, and the length after heating Ll.

Heat shrinkage rate "" (L6 Ll / Lo) X 1
00 (5) Gel fraction: A8TM D 2765, compliant with A method (6) Number of pinholes after flexo crank: 4 using Gelpo Flex Tester manufactured by Rigaku Kogyo Co., Ltd.
The number of pinholes in the test piece was counted after it was bent 100 times at 40° angle reciprocation/cycle and 40 cycles/min.

(Cutability: Type 1 notches are cut by hand and cut in a straight line as ○, others are marked as ×. Cutting edges that are clear when cut are marked as ○, and those that are slightly jagged are marked as △.
Other items were marked as ×.

(1) High-density polyethylene (density: 0.957f1 country,
M process: tor/io min, melting point: 154° C.) A sheet-like original fabric with a thickness of 480 μm was entirely molded using an iT die extrusion sheet molding machine. Using this original sheet laminated beam irradiation equipment (manufactured by ES'I), 150K was applied to each of the front and back sides in a nitrogen gas atmosphere.
20 Megaland irradiation was performed under the condition of V-'8 mA.

The degree of crosslinking on the irradiated surface of this raw sheet and inside the sheet in the thickness direction was determined by stacking 24 thin films of 20μ thick to form a 480μ thick test piece and irradiating each thin film under the same conditions. When the degree of crosslinking was investigated, the degree of crosslinking of the thin films on both sides of the irradiated surface was 50% gel fraction each, and the lowest degree of crosslinking inside the thickness direction was 0% gel fraction. Further, the composition ratio of the thicknesses of the crosslinked layer and the uncrosslinked layer was crosslinked layer:uncrosslinked layer:crosslinked layer=1:t75:1.

After heating this crosslinked raw sheet 1-' to 1127°C,
A stretched film having a thickness of 20 μm was obtained by sequentially stretching 4 times in the machine direction and 6 times in the transverse direction using a tenter type biaxial stretching machine. The complete characteristics table-1rc of this film (BOHD-1) is shown.

A stretched film was obtained in the same manner as in the production of the above film (BOHD-1), except that the electron beam irradiation dose was changed to 15 Megaland. The characteristics of this film (BOHD-2) are also listed in Table-1.

(3) In the production of the above film (BOHD-1), linear low density polyethylene (
A stretched film was obtained by using a density Q of 9242/Tan 3, M engineering zot/10 min) ft, and an electron beam irradiation amount ft 10 Mrad. Full table of characteristics of this film (EOIIL)-1
Also listed.

Examples 1 to 12, Comparative Examples 1 to 6 Base layer: (1) BOHD-1 film, (2) EO
HD-2 film, (3) BOLL film laminated material: (1) High quality paper (50?/rn''), (2)
At foil (9μ), (3) EvAL-F (15μ, manufactured by Kuraray Co., Ltd., trade name), (4) P, FTP film (12μ)
, (5) Cellophane (300 count), (6) At-deposited ITP film (1
2μ), (Power LDPF! Film (30μ), (8)
LLDPI film (30μ), (g) DP
P film (20μ) The above laminate materials (1) to (6) c) had a heat shrinkage rate of less than 5% at 140°C.

The base material layer and the laminated material have the layer configuration shown in Table 2,
]! Each was adhesively laminated by a wet lamination method using an iVA emulsion type adhesive or an acrylic adhesive, a dry lamination method using a urethane adhesive, or an extrusion coating lamination method. The characteristics of each composite film are shown in Table-2.

Effects of the Invention The composite film ij of the present invention allows for heat sealing of the BOPK film surfaces, and has excellent moisture proofing properties, flexing crank resistance, and straight cutability. In addition, its functionality can be further enhanced by combining it with other laminated materials.

For example, combining film with foil completely compensates for pinhole resistance and further increases moisture resistance, and combining film with paper improves the moisture resistance of paper and makes it suitable for adhesive bonding between BOPIIC film and paper. In addition, when combined with a laminate material having gas barrier properties such as ethylene-polyvinyl alcohol copolymer, gas barrier properties at high temperatures and high humidity can be improved, and [PET
When combined with P or cellophane, it is possible to add functional improvements such as improving the optical properties of a laminated film.

Due to the above-mentioned excellent properties, the composite film of the present invention can be used as a variety of packaging materials, but in particular, it can be used in gusseted bags, box materials, or 1JB with the BOPK film surface as the surface layer.
It is suitable for bags etc. in which the OPK film surface is the sea layer.

Claims (1)

[Scope of Claims] (1) At least one type of laminate material having a heat shrinkage rate of less than 5% at 140°C is laminated on one side of a stretched polyethylene film whose degree of crosslinking decreases inward in the thickness direction of the film. A polyethylene composite film characterized by: (2) The degree of crosslinking is the crosslinked layer /
It constitutes an uncrosslinked layer/crosslinked layer, and the gel fraction of the crosslinked layer is 20~
70%, the gel fraction of the uncrosslinked layer is 0%, and the uncrosslinked layer:
The polyethylene composite film according to claim 1, wherein the crosslinked layer has a ratio of 1:0.1 to 10. (3) Claim 1 in which the laminated material is selected from paper, aluminum foil, cellophane, and heat-resistant resin film.
The polyethylene composite film according to item 1 or 2.