JPS6410337B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to packaging materials that have antistatic properties, and include one side of a base material that is nonstatic, such as metal foil or paper, or that exhibits nonstatic properties because the charge quickly moves even if it is charged. Vinyl acetate content of ethylene-vinyl acetate copolymer is 5-20% by weight
and is characterized in that the ethylene-vinyl acetate copolymer resin layer is provided so as to have a thickness of 100 μm or less and 10 μm or more. As electronic products become more sophisticated and precise,
Integrated circuits (ICs) and large-scale integrated circuits (LSIs) have come into use, but these are easily damaged by static electricity due to minute amounts of static electricity, and photosensitive materials have also become more sensitive, such as X-ray film. etc. are also prone to a type of exposure phenomenon called static marks due to the generation of static electricity. In addition, powdered foods such as dried bonito flakes are easily charged with static electricity, which can easily cause problems with mechanical suitability during filling. When packaging these static-sensitive materials or parts, if general-purpose plastic films such as polyethylene, polypropylene, polyvinyl chloride, polyethylene terephthalate, and polyamide are used, since these general-purpose plastic films are insulating materials, , extremely easy to charge,
Due to static electricity generated during work or wheel transport,
It is prone to various electrostatic problems including electrostatic breakdown, and has had difficult problems as a packaging material. Conventionally, in order to prevent this kind of trouble, a general-purpose resin such as polyethylene was mixed with a conductive filler such as conductive carbon fine powder or metal fine powder and dispersed therein, or an ionic surfactant was mixed in. It is something that However, it is difficult to disperse these fine carbon powders and fine metal powders in resin completely uniformly and at regular intervals, and if the dispersion is incomplete, the desired conductivity cannot be obtained, and the antistatic properties may be uneven. Become something. Furthermore, since these conductive fillers are dispersed in the resin, they impair coloring or heat-sealability, impairing their functionality as packaging materials. On the other hand, when an ionic surfactant, a so-called antistatic agent, is mixed into a resin, its effectiveness is easily affected by humidity, and the effect is produced by bleeding onto the surface of the resin. Therefore, it is necessary for the resin and surfactant to be incompatible, and for the surfactant to have a low molecular weight to promote the mobility of the surfactant. The uniformity and sustainability of the effect may be affected by the separation and volatilization of the surfactant due to aging or shedding during transportation, the volatility of the surfactant due to the latter, or the thermal history during resin film formation. It is not desirable in such cases. The present invention relates to a packaging material having antistatic properties that does not have such drawbacks, and its composition is made of paper,
The vinyl acetate content of ethylene-vinyl acetate copolymer is 10 to 20% by weight on one side of a base sheet made of either metal foil or a laminate thereof, and
In addition, an ethylene-vinyl acetate copolymer resin layer is provided so that the thickness is 100 μm or less. Also, since it is used as a package, it needs to be at least 10 μm thick in terms of heat sealing strength. This makes it possible to obtain a packaging material having antistatic properties for packaging electronic equipment parts and the like that are prone to electrostatic damage, which is the object of the present invention. A method for numerically determining whether or not a packaging material has antistatic properties is to measure the surface resistivity of the material.General-purpose plastic films, such as polyethylene films, have surface resistivity It is about 10 ¹⁴ Ω and is an insulator, but when this becomes less than 10 ¹⁰ Ω, the charging phenomenon decreases rapidly. However, as a more practical method,
This is a method in which a constant voltage is applied to the material surface, the voltage application is stopped after a steady state is reached, and the elapsed time of the charged voltage is followed, and the evaluation is made by measuring the decay time (seconds) until the charged voltage is reduced by half. In the present invention, various constituent materials were investigated using this latter method. Further, in the present invention, the base sheet is also an important constituent material. The role of this base sheet is to strongly protect the ethylene-vinyl acetate copolymer resin film that serves as the inner layer, as well as to provide printability and light-shielding properties for the contents like photographic light-sensitive materials. In addition to using metal foil to achieve this effect, paper or metal foil such as aluminum (Al) foil can also be used to ensure that these materials themselves do not have static electricity. This is also necessary in terms of the structure of the packaging material. Metal foil is a highly conductive material, and paper is an insulating material, but its cellulose fibers have many OH groups in their molecules, which is the basis for their water absorption and hydrophilic properties, and they are susceptible to static electricity. It is considered a conductor. As a means of laminating an ethylene-vinyl acetate copolymer resin layer having a predetermined vinyl acetate content and a base sheet, the ethylene-vinyl acetate copolymer resin is directly extruded onto the base sheet using a T-die extruder to form a film. There are two methods: one method is to prepare a film in advance, and the other method is to bond the film to a base sheet, but any method may be used. It is also useful to use an adhesive to improve adhesion when laminating with the base sheet, but in this case, it is better to use an ethylene-vinyl acetate resin with a relatively high vinyl acetate content. It is preferable from the viewpoint of antistatic properties. The vinyl acetate content can be up to 100%, but considering suitability for film forming processing, a value of 20% or less is appropriate. In addition to ensuring that the vinyl acetate content of the ethylene-vinyl acetate copolymer resin film is a predetermined amount, the thickness is also important. That is, it has been found that the generated static electricity not only leaks from the surface but also leaks in the volume direction (thickness direction), and it is preferable that the thickness does not exceed 100μ. Examples of experimental data are shown below. Table 1 shows bleached kraft paper 65g/m ² / adhesive / Al
A laminate of 7μ foil/adhesive/resin film is used as a resin film with various vinyl acetate (VA) contents
It was made using a thick ethylene-vinyl acetate copolymer resin, and the charged voltage of this resin film layer was measured using a static honest meter manufactured by Shishido Shokai Co., Ltd., and the initial charged voltage and decay time were calculated. , and FIG. 3 of the drawings is a graph of this. The applied voltage was 10 KV, and the apparatus shown in Figure 1 of the drawings was used. The temperature was 25°C and the humidity was 50% RH.

[E ₀ = Potential t in equilibrium state: Time until E _t = E ₀ /2 R _c : Leakage resistance of the sample C: Capacitance of the sample]

It can be calculated using the formula. In the previous table, if the decay time is 300 seconds or more (300〈), there is actually almost no decay observed, and the charged state continues indefinitely, so anti-static measures are required. It is extremely inappropriate as a packaging material. those that show attenuation (e.g.
250 seconds or less), antistatic properties are observed, and the shorter the decay time, the more effective it is. Furthermore, the experiment was repeated while varying the vinyl acetate content of the ethylene-vinyl acetate copolymer resin film layer, and it was confirmed that the results correlated with the results shown in the table above. This change in decay time due to vinyl acetate content is as follows in ethylene-vinyl acetate copolymer resin.
It is thought that this effect is due to an increase in the number of polar groups that the vinyl acetate group has, or that the degree of crystallinity decreases as the vinyl acetate content increases, but the theory is not clear. We also investigated resins with other polar groups, such as ethylene-ethyl acrylate copolymer resins and ionomer resins, but it was difficult to change the content of polar groups as freely as the resins mentioned above, and no significant effects were found. I couldn't help it. As shown in the above data, the vinyl acetate content of the ethylene-vinyl acetate copolymer resin film layer is between 5% and 20%, and the thickness is
A value of 100μ or less is appropriate. These can be selected as appropriate depending on the antistatic property required depending on the contents, and they also have sufficient heat sealability, which is essential as a packaging material. It is also capable of printing and marking, and has sufficient strength to package various parts and materials. As described above, the packaging material having antistatic properties according to the present invention has many advantages and is unprecedented in the prior art. Examples of the present invention will be shown below. Example Paper (bleached kraft paper 60g/m ² , manufactured by Marusumi Paper Co., Ltd.)
An ethylene-vinyl acetate adhesive (manufactured by Toyo Morton Co., Ltd.) was applied to the Al surface of the base sheet, which was made by laminating 7 μm Al foil (Tokai Metal Co., Ltd.) with an adhesive (acrylic emulsion, 2 g/m ² ). PR-152) was applied at 2g/ ^m2 ,
On this surface, use a T-die extruder (film forming machine).
Ethylene-vinyl acetate copolymer resin with vinyl acetate content of 19% (Evaflex, Mitsui Polychemical Co., Ltd.)
P1905) was extruded into a film at 240°C. The thickness was 25μ. This thing is made with the resin film layer on the inside,
When the bag was made using a heat-sealing bar at 150°C, the surrounding heat-sealed area had a heat-sealing strength of 1.5 kg/15 mm or more, and the bag was able to support the packaging of heavy items. When the charging voltage decay time of this product was measured in the same manner as described above, it was found that the inner surface had excellent antistatic properties of 1000 V for 10 seconds and the outer surface for 250 V for 5 seconds. When IC parts were packaged in this bag, there was no influence of external charge on the packaging material during handling or transportation, and no dirt or dust was observed, indicating that an appropriate packaging material was obtained. . When this material was used as a packaging material for photographic film for photosensitive materials, it was found to be an excellent packaging material free from static electricity damage.

[Brief explanation of drawings]

The drawings all show embodiments of the present invention; Fig. 1 is a circuit diagram of the device, Fig. 2 is an explanatory diagram showing the relationship between time and voltage, and Fig. 3 is the relationship between decay time, vinyl acetate content, and thickness. This is a graph showing.

Claims (1)

[Claims] 1 One side of a base sheet made of paper, metal foil, or a laminate of these has a vinyl acetate content.
A packaging material with antistatic properties made of a 10-20% ethylene-vinyl acetate copolymer resin layer laminated to a thickness of 10-100μ.