Sheet material and envelope for packaging electronic parts

The sheet material for packaging electronic parts consists of a laminated material which comprises a transparent plastic film layer and a thin metal film layer having a light transmittance of at least 25% and an electric resistance of less than 10.sup.8 ohms/cm.sup.2. The sheet material is heat-sealable at the surface of said metal film layer. An envelope for packaging electronic parts is made of the sheet material by heat-sealing in a state of disposing the plastic film layer outside.

BACKGROUND OF THE INVENTION 
This invention relates to a sheet material and an envelope for packaging 
electronic parts. 
Such electronic parts as semiconductors, which are vulnerable to static 
electricity, can be easily damaged by static electrification before and 
after they are attached to electronic circuits, presenting a serious 
problem. 
Thus, protection of electronic parts from static electricity has heretofore 
resorted to the use of metal foils and plastic films having electrically 
conductive materials, such as carbon and metal powders, incorporated 
therein as packaging materials for electronic parts. 
However, these materials, all of which are opaque, as such, do not allow 
visual inspection to ascertain whether the contents, or electronic parts, 
are present and whether they are damaged or to ascertain their type. On 
the other hand, plastic films having antistatic agents incorporated 
therein are available, but their electric resistance is so high that they 
are altogether unsuitable for protection of electronic parts, and 
depending upon the type of the antistatic agent used, they can be easily 
influenced by humidity, a lack of stability. 
An object of the invention is to provide a sheet material for packaging 
electronic parts, through which the contents or electronic parts can be 
seen and which is effective to protect electronic parts from static 
electricity. 
Another object of the invention is to provide an envelope for effectively 
protecting electronic parts. 
Other objects and advantages of the invention will be apparent from the 
following detailed description. 
SUMMARY OF THE INVENTION 
The sheet material for packaging electronic parts according to the 
invention consists of a laminated material which comprises a transparent 
plastic film layer and a thin metal film layer having a light 
transmittance of at least 25% and an electric resistance of less than 
10.sup.8 ohms/cm.sup.2. The sheet material is heat-sealable at the surface 
of said metal film layer. 
An envelope for packaging electronic parts is made of the sheet material by 
heat-sealing in a state of disposing the plastic film layer outside. 
The transparent plastic film layer may be per se heat-sealable. A 
heat-sealable resin film layer may be formed partially or wholly between 
the transparent plastic film layer and the thin metal layer or on the thin 
metal film layer coated on the transparent plastic film layer. 
DETAILED DESCRIPTION OF THE INVENTION 
The transparent plastic film layer may be made from polyester, acrylic 
resin, polyvinyl chloride, fluorine resin, polystyrene, polypropylene, 
polyethylene and any other material which can be used as packaging 
materials. 
The transparent plastic film layer desirably has a thickness of 4 to 100 
microns. If the thickness of the transparent plastic film layer is less 
than 4 microns, it is too thin and too weak to be used for a packaging 
material. On the other hand, the transparent plastic film having a 
thickness of more than 100 microns is so stiff and springy that handling 
operation during heat sealing and after formation of an envelope becomes 
inconvenient. 
The metal film layer in the invention may be produced in a conventional 
method such as vacuum plating, ion plating (chemical plating), 
electron-beam plating, sputtering and the like. 
As the thin metal film, there are included all thin films made of simple 
metal substances, alloys and metal compounds such as Cr, Al, Ni, Fe, In, 
Ag, Au, Cu, Sn, Ti, Ni-Cr, In.sub.2 O.sub.3, SnO.sub.2, In-Sn-O.sub.2 
series and the like. 
The thin metal film layer must meet the conditions that the light 
transmittance is at least 25% and the electric resistance is less than 
10.sup.8 ohms/cm.sup.2. These conditions are indispensable for the 
attainment of the objects of the invention. 
More particularly if the light transmittance is less than 25%, it becomes 
difficult to see the contents through the sheet material. Further, if the 
electric resistance is more than 10.sup.8 ohms/cm.sup.2, the electric 
conductibility is poor and insufficient to protect electronic parts from 
static electricity. 
An envelope for packaging and protecting electronic parts is made of the 
laminated material by heat-sealing in a state of disposing the plastic 
film layer outside. Accordingly, when the transparent plastic film layer 
is per se heat-sealable or a heat-sealable resin film layer is formed 
between the transparent plastic film layer and the thin metal film layer, 
it is important that the thin metal film layer is pervious to the 
heat-sealable plastic material or resin on heating. In this case, the 
thickness of the metal film layer is preferably within the range of 20 A 
to 250 A. 
When a heat-sealable resin film layer is formed wholly on the thin metal 
film layer laminated on the transparent plastic film layer or between the 
transparent plastic film layer and the metal film layer, the heat-sealable 
resin film layer should be transparent to see the contents through the 
laminated material. 
Further, a heat-sealable resin film layer may be partially formed in a 
given pattern on the metal film layer or between the transparent plastic 
film layer and the metal film layer. In this case, since the contents can 
be seen through the laminated material without an obstacle of the 
heat-sealable resin film layer, the heat-sealable resin film layer may be 
opaque or coloured. 
When the heat-sealable resin film layer is partially formed between the 
transparent plastic film layer and the thin metal film layer, the 
thickness of the metal film layer is also preferably within the range of 
20 A to 250 A. 
Among the heat-sealable resin film layer used in the invention, there are 
included those made from polyethylene, soft polyvinyl chloride, modified 
polyester, polypropylene, ionomer, EVA and other heat-sealable materials. 
The heat materials according to the present invention are mainly used for 
packaging electronic parts, but they may be used as a covering on a 
working desk or a box for electronic parts.

In FIG. 1, a metal film layer 2 is coated on a heat-sealable transparent 
plastic film 1. 
In FIG. 2, a heat-sealable resin film layer 3 is formed on a transparent 
plastic film 1 and a metal film layer 2 is coated on the heat-sealable 
resin film layer 3. 
In FIG. 3, a metal film layer 2 is coated on a transparent plastic film 1 
and a heat-sealable resin film layer 3 is formed on the metal film layer 
2. 
In FIG. 4, a metal film layer 2 is coated on transparent plastic film layer 
1 and a heat-sealable resin film layer 3 is formed partially on the metal 
film layer 2. 
In FIG. 5, a heat-sealable resin film layer 3 is formed partially on a 
transparent plastic film 1 and a metal film layer 2 is coated on the 
heat-sealable resin film layer 3 comprising surface of the transparent 
plastic film 1. 
Each of the heat-sealable resin film layers 3 in FIGS. 4 and 5 is located 
on the portion which will be actually heat-sealed to form an envelope for 
packaging electronic parts. 
The sheet materials in FIGS. 1 to 5 are useful for packaging electronic 
parts and used to form an envelope adapted to protect electronic parts. 
The envelope for enclosing electronic parts, as shown in FIGS. 6 and 7, is 
made of the sheet materials by heat-sealing in a state of disposing the 
transparent plastic film 1 outside. 
In the present invention, since electric resistance of the metal film layer 
2 is not more than 10.sup.8 ohms/cm.sup.2, electronic parts can be fully 
protected from static electricity produced inside and outside the 
envelope. Further, the envelope according to the present invention has a 
metal film layer 2 positioned inside the transparent plastic film 1 so 
that it is highly weather-resistant. 
The transparent plastic film 1 may contain an antistatic agent or may be 
formed on one or both surfaces thereof with a layer containing an 
antistatic agent. Further, an antistatic agent may be contained in the 
heat-sealable resin layer 3 or such layer containing an antistatic agent 
may be provided on any other suitable place. 
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
The following examples serve to illustrate the invention in more detail 
although the invention is not limited to the examples. 
EXAMPLE 1 
A polyethylene film of 40 microns was prepared as a base sheet. Chromium 
was deposited on a surface of the base sheet by a vacuum plating from a 
distance of 25 cm with a vacuum degree of 1.times.10.sup.-4 Torr for about 
20 seconds to form a chromium film layer of 50 A having a resistance of 
1.times.10.sup.5 ohms/cm.sup.2 and a light transmittance of 75%. 
An envelope was made of the resultant sheet material by heat-sealing in a 
state of disposing the polyethylene film outside. 
EXAMPLE 2 
A heat-sealable polyester film (Melinex type #850 manufactured by Imperial 
Chemical Industries Limited), which consists of a polyester film of 25 
microns and a modified polyester film layer coated thereon, was prepared 
as a base sheet. Chromium was deposited on the modified polyester coated 
surface of the base sheet in the same manner as in Example 1 to form a 
chromium film layer of 50 A having a resistance of 1.times.10.sup.5 
ohms/cm.sup.2 and a light transmittance of 75%. 
An envelope was made of the resultant sheet material by heat-sealing in a 
state of disposing to polyester film outside. 
EXAMPLE 3 
A transparent polyester film of 38 microns (Diafoil manufactured by Diafoil 
Company) was prepared as a base sheet. Chromium was deposited on a surface 
of the base sheet by a vacuum plating from a distance of 20 cm with a 
vacuum degree of 8.times.10.sup.-5 Torr to form a chromium film layer of 
220 A having a resistance of 4 ohms/cm.sup.2 area and a light 
transmittance of 27%. Further, a transparent polyethylene film was bonded 
to the chromium film layer. 
An envelope was made of the resultant sheet material by heat-sealing in a 
state of disposing the polyester film outside. 
EXAMPLE 4 
By the same manner as in Example 3, aluminum was deposited on a surface of 
a transparent polyester film of 16 microns (Diafoil manufactured by 
Diafoil Company) to form an aluminum film layer of 60 A having a 
resistance of 150 ohms/cm.sup.2 and a light transmittance of 67%. Then the 
aluminum film layer was coated with EVA (ethylene-vinylacetate copolymer). 
Further, the non-metallized surface of the polyester film was coated with 
a cation type antistatic electronic agent. 
An envelope was made of the resultant sheet material by heat-sealing in a 
state of disposing the non-metallized surface of the polyester film 
outside. 
EXAMPLE 5 
A surface of a transparent polyester film of 25 microns (Diafoil 
manufactured by Diafoil Company) was subjected to a magnetron spattering 
in an argon+oxygen mixed gas at a vacuum degree of 2.times.10.sup.-2 Torr 
using indium as a target with a discharge power of 0.5 KV.times.1.0 A. to 
form an indium oxide film layer of 300 A having a resistance of 
3.times.10.sup.6 ohms/cm.sup.2 and a light transmittance of 80%. Then only 
the necessary portion of the indium oxide film layer was partly coated 
with polyethylene. 
An envelope was made of the resultant sheet material by heat-sealing in a 
state of disposing the polyester film outside. 
EXAMPLE 6 
A coloured polyethylene was coated partially on a given portion of a 
transparent polyester film of 25 microns. Chromium was deposited on the 
polyethylene-coated surface of the polyester film, but the same manner as 
in Example 1, to form a chromium film layer of 50 A having a resistance of 
1.times.10.sup.5 ohms/cm.sup.2 and a light transmittance of 75%. 
An envelope was made of the resultant sheet material by heat-sealing in the 
state of disposing the polyester film outside. 
Control 1 
A heat-sealable antistatic polyethylene envelope (Pinkpoly Envelope 
manufactured by Tokyo Denki Kagaku Kabushiki Kaisha) was prepared. 
Control 2 
A laminated material which consists of a polyester film of 25 microns and a 
polyethylene film was used to form an envelope by heat-sealing in a state 
of disposing the polyester film outside. 
Liquid crystal boards were enclosed in the envelopes prepared in the above 
Examples and Controls. The envelopes having the liquid crystal boards 
enclosed therein were then irradiated with (+) and (-) ions directed 
thereto at a distance of 10 cm by a 8,000-10,000 V static electricity 
generator (Antistatic pistol manufactured by Zerostat Instrument Limited), 
and letters and numbers on the liquid crystal boards were examined for 
their disturbance. The seeing-through qualities of the envelopes were also 
compared. The results are as shown in Table below. 
______________________________________ 
Disturbance of letters 
and numbers on the 
Seeing-through 
liquid crystal boards 
qualities 
______________________________________ 
Example 1 O Good 
Example 2 O Good 
Example 3 O Good 
Example 4 O Good 
Example 5 O Good 
Example 6 O Good 
Control 1 X Good 
Control 2 X Good 
______________________________________ 
Note: 
O . . . Any disturbance was not found. 
X . . . A gross disturbance was found.