JPS6114280A - Hygroscopic packing material - Google Patents

Abstract

PURPOSE:To provide a hygroscopic packing material having excellent moisture adsorption performance over a long period of time and useful as a container lid, consisting of a (foamed) molding of a uniform mixture of a polyolefin resin and an adsorbent having a specified particle size. CONSTITUTION:95-35wt% polyolefin resin (e.g. PE), 5-70wt% adsorbent having a particle size of 60 mesh or below (e.g silica gel) and optionally, a volatile or heat-decomposable blowing agent (e.g. azodicarbonamide) are kneaded together. The mixture is molded into a sheet. If desired, the sheet is expanded 1.2-2.5- fold by heating. The sheet is punched into the desired shape, thus obtaining a hygroscopic packing material of 0.5-5mm. in thickness.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to hygroscopic packing materials. More specifically, the present invention relates to a packing material for container lids that has moisture adsorption performance.

[Conventional technology]

Molded polyolefin resins, especially foam molded products, are widely used as packing materials for container lids because they satisfy the various properties required for packing materials, such as moldability, non-toxicity, cushioning properties, durability, and strength. It is being

However, if the product to be filled into the container is a product whose quality deteriorates over time due to moisture absorption, such as coffee, cocoa, powdered milk, or pharmaceuticals, the packaging material made from conventional polyolefin resin cannot be used to It cannot be said that the performance is necessarily sufficient in terms of the effect of blocking moisture from entering the room or the effect of protecting the contents.

In order to prevent such deterioration in the quality of products in containers due to moisture absorption in the atmosphere, packing materials with high moisture-proof performance have been developed. For example, Tokuko Sho 57-3074
No. 4 discloses a three-layer laminate made of saponified polyethylene terephthalate ethylene-vinyl acetate copolymer/foamed polyethylene. Furthermore, examples of inner sealing materials that are currently widely used include sealing materials having a five-layer structure such as (c) paperboard/wax/aluminum foil/glassine paper/adhesive.

However, even with such a multi-layered structure and the use of expensive sealing materials, the problem of product quality deterioration due to moisture entering the container from the outside when the container is opened is resolved. Can not.

In such a case, a method of inserting a desiccant or the like into the container may be considered, but this method cannot be used if the product inside is a powdered food or medicine.

[1. Problems to be solved by the invention] The present inventors have discovered that once moisture in the air enters the container,
As a result of various studies in search of countermeasures to prevent this from causing a deterioration in the quality of the product inside the container, we found that a polyolefin resin packing material blended with an adsorbent of a specific particle size effectively solves all of the above problems. I discovered that.

[Means for Solving the Problems] and [Operations] Accordingly, the present invention relates to a packing material, and this packing material comprises:
It consists of a homogeneous mixture molded product or a homogeneous mixture foamed molded product of a polyoleain resin and an adsorbent whose particle size is smaller than 60 mesh.

Examples of polyolefin resins that can be used as molding materials for banking materials include high-density polyethylene, low-density polyethylene, linear low-density polyethylene, polypropylene, ethylene-vinyl ester copolymers typified by ethylene-vinyl acetate copolymers, and ethylene-vinyl ester copolymers such as ethylene-vinyl acetate copolymers. Ethylene-α,β-unsaturated carboxylic acid ester copolymers represented by (meth)acrylic acid esters; ethylene-α-olefin copolymers represented by low-crystalline to non-crystalline ethylene-propylene copolymers These can be used alone or as a mixture. Other polymeric substances such as synthetic rubber, natural rubber, soft vinyl chloride resin, and polystyrene resin can also be added to these polyolefin resins.

One of the important functions required when these polyolefin resins are used as packing materials is cushioning properties. Excellent cushioning properties mean excellent adhesion to the container opening, and from this point of view, it is preferable that the polyolefin resin is used in the form of a foam molded product. The production of foam molded products requires a homogeneous mixture of polyolefin resin and adsorbent.
In the presence of volatile or thermally decomposable foams such as propane, freon, azodicarbonamide, etc.
This is done by foaming the foam to about twice its original size.

Polyolefin resin foam moldings generally have closed cells, but if a synthetic rubber such as styrene-butadiene copolymer rubber is added and foamed, an open-cell foam can be obtained. Foams are characterized by a higher moisture adsorption rate than closed-cell foams. Therefore, by taking advantage of these characteristics and adjusting the mixing ratio of polyolefin resin and synthetic rubber, it is possible to adjust the moisture adsorption rate. however,
When the packing material is an open cell, it is desirable to attach film layers to both sides in order to impart sealing performance to the parking material. As described above, one of the features of the present invention is that it is possible to manufacture a packing material having an appropriate moisture adsorption rate depending on the properties of the product in the container.

Adsorbents that exhibit such water adsorption properties include silica gel, activated alumina, acid clay, activated clay, zeolite, etc. If the particle size of these adsorbents is too large, unevenness will occur on the surface of the packing material, resulting in poor airtightness. It is necessary to use a particle size finer than about 60 mesh as this will result in a loss of particles.

The polyolefin resin and the adsorbent are about 95 to 3
0% by weight, preferably about 85 to 50% by weight, and about 5 to 70% by weight, preferably about 15 to 50% by weight. If the mixing ratio of the adsorbent is less than this, the moisture absorption capacity will be insufficient and the object of the present invention cannot be achieved, while if the adsorbent is used in a ratio higher than this, the surface smoothness of the packing material may be impaired. become.

Packing materials are produced by tri-blending or melt-blending polyolefin resin and adsorbent, and molding this using a molding method such as extrusion molding, press molding, in-shell molding, etc. using a plane, cast, or sheet. When a foaming agent is added, foam molding is performed, and in the case of an extrusion molded product or a press molded product, this is performed by punching into a desired mold. The packing material thus formed generally has a weight of about 0.5 to 5 mm, preferably about 1 mm.
It has a thickness of ~3 recommended.

The banking material of the present invention includes polyethylene, ethylene-
It is also possible to laminate at least one type of vinyl acetate copolymer, oriented polypropylene, polyethylene terephthalate, polyvinylidene tetralide, saponified ethylene-vinyl acetate copolymer, etc. by a known method.
If these laminated surfaces are placed facing the container lid side, it is extremely effective for blocking oxygen, carbon dioxide gas, water vapor, etc. from the outside. Conversely, if a thin film of paper, polyethylene, or other synthetic resin is laminated or coated on the side of the packing material that faces the filled product, this will prevent the adsorbent in the packing material from contaminating the product. be able to. Further, in order to further improve the cushioning properties, it can be used in a laminated manner with a foam sheet such as a low-density polyethylene crosslinked foam sheet or a polyurethane foam sheet.

〔Effect of the invention〕

In the packing material containing the adsorbent according to the present invention, not only moisture from the outside existing in the air is absorbed by the adsorbent on the surface of the packing material, but also air passing through the packing material layer or the container Moisture contained in the air that enters the container when the container is opened is also adsorbed by the adsorbent contained within the packing material. Therefore, the existence of an adsorbent that is completely retained inside the packing material and never dissipates not only provides sufficient adsorption performance, but also maintains its performance effects over a long period of time. let In addition, in the case of a foam packing material containing synthetic rubber, 1. Control the water adsorption speed!
It also makes I possible.

Therefore, the packing material of the present invention, which exhibits such effects, can be effectively used as a packing material for lids of containers filled with foods, medicines, etc., especially powdered products thereof.

〔Example〕

Next, the present invention will be described in detail with reference to examples.

Example Low density polyethylene (Mitsui Polychemical product Mirason M
53; density 0.9219 shoulder, melt flow rate 3
．． 3) or ethylene-vinyl acetate copolymer (Evaflex P-1405; dense & 0.939Ad)
, melt flow rate 3.5) and 70 parts by weight of silica gel (passed through a 60 mesh sieve, the average particle size was 150
μ) 30 parts by weight, and if necessary, 0.5 parts of azodicarbonamide as a blowing agent. I Okibe! : Both were dry-bred using a ribbon blender, and then fed to an extruder having a diameter of 65 layers. After melting and kneading this in an extruder, it is molded into a sheet using a T-die to form a non-foamed sheet or a foamed sheet (
Thickness 1.50 fin, foaming ratio 2. ．． 5 times) was produced. The sheet thus formed was used in the tests described below in 72 ways as follows.

Foamed sheet B: Foamed sheet membrane of ethylene-vinyl acetate copolymer/silica gel mixture (thickness: 70 μm) The following measurements were performed on each sheet of the size of a counterfeit bond layer or larger.

Latitude; weight of test piece/volume of test piece The results obtained are shown in the following table. Note that the value in parentheses for the hardness of foam sheet 0 is a value measured in a layer not containing silica of the 6-layer structure.

Thickness Latitude Hardness Leak test A 1.50 0.75 83 None
Some B 1.50 0.67 75
None None o 2.40 0.15 75 (4
7) None None D 2.50 -
75 Yes x 1.54 0.
73 79 None None 1F 1.5
0' 1.05 95 Somewhat YesG
1.57 0.85 78 None
Furthermore, the moisture absorption performance of these ANFs was measured. Measurements were carried out at a temperature of 25°C and a relative humidity of 90%.
, 50% or 20% of the atmosphere, and the rate of increase was measured to determine the water absorption rate characteristics. The results obtained under each of these relative humidity conditions are shown in the graphs of FIGS. 1-3. In addition, as a comparative example, the water absorption rate was measured against the number of days of equilibrium adsorption at 25°C and in various relative humidity atmospheres using silica gel powder with a particle size of 60 to 80 mesh, and the results are shown in the graph of Figure 4. I got deceptive results.

[Brief explanation of drawings]

1 to 3 are graphs showing the measurement results of the moisture absorption performance of the packing material according to the present invention. Moreover, FIG. 4 is a graph showing the measurement results of the moisture absorption performance of the packing material serving as a comparative example.

Claims (1)

[Scope of Claims] 1. A hygroscopic packing material comprising a molded homogeneous mixture of a polyolefin resin and an adsorbent having a particle size of less than 60 mesh. 2. The hygroscopic packing material according to claim 1, which comprises a molded homogeneous mixture of about 95 to 30% by weight of a polyolefin resin and about 5 to 70% by weight of an adsorbent. 3. A hygroscopic packing material made of a foam molded product of a homogeneous mixture of a polyolefin resin and an adsorbent with a particle size smaller than 60 mesh. 4. The hygroscopic packing material according to claim 3, which is made of a foamed homogeneous mixture of about 95 to 30% by weight of a polyolefin resin and about 5 to 70% by weight of an adsorbent.