JPH0576723B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an antistatic film that is suitable for packaging articles that are susceptible to static electricity damage and whose interior can be seen through.

[Conventional technology and its problems]

Stores electronic components such as ICs that are susceptible to static electricity damage,
Conventionally, polyolefin film bags with antistatic agents incorporated into them are used as packaging materials that allow the interior to be seen through;
Laminated film bags made of a film coated with a thin metal layer to the extent that it can be seen through and a polyolefin film coated with an antistatic agent have been known [see Japanese Patent Application Laid-open No. 53-88953], but the former generally has poor antistatic performance. Also, since the latter is coated with a thin metal layer, it is possible to see through it, but due to the sharp reflection characteristic of metals, it becomes difficult to see the contents depending on the angle, and due to the characteristics of metals, chemical It has drawbacks such as being unstable and subject to significant deterioration over time due to oxidation, and relatively stable vapor-deposited thin films of metals such as noble metals and nickel being expensive. The inventors of the present invention have researched transparent conductive carbon thin films that are chemically stable, have little change in conductive performance due to humidity, and do not have sharp and unpleasant reflections, and have previously filed a patent application No. 59-46473.
The invention described in the publication was completed and a patent application was filed.

[Object of the present invention]

Using the invention of the above Japanese Patent Application No. 59-46473,
The present invention was completed after further research into the structure of an antistatic film that has sufficient strength as a container for contents with protrusions such as ICs, is easy to form into bags, and can provide bags with good abrasion resistance.

[Means to achieve the purpose]

The present invention comprises a transparent surface layer A having a thickness of 10 μm or less and a volume resistivity of 10 ¹³ Ωcm or less in the thickness direction, a transparent conductive layer B containing carbon black, a biaxially oriented polyester layer C, and a heat-sealable polyolefin layer D. , ABCD are laminated in this order, and the surface layer A is an acrylic resin containing polyethylene wax. This will be explained in more detail below.

For the biaxially stretched polyester layer C, a film having a thickness of 10 to 25 μm is used. Layer C serves as a base material in the production of this antistatic film, and provides the film with heat resistance and rigidity particularly suitable for bag-making processing and bag handling. It has the effect of increasing the puncture resistance, which is particularly required for protrusions such as lead wires of the packaged object. A conductive paint containing carbon black is applied and dried on layer C to form a transparent conductive layer B. The conductive paint contains carbon black as an essential component, and may also contain a binder, a solvent, or a dispersion medium as required. Carbon black is
It is best to choose one for conductive fillers. Although various brands are available, no criteria for selection has been found that necessarily determines particle size, dispersibility, degree of graphitization due to calcination, degree of structure development, etc. It is a good idea to test several types of conductive fillers and select a brand that is suitable for each process and has as good transparency as possible for the same conductivity. The binder should be selected from among those that have a high adhesive strength with the base material. Examples of the binder include latexes such as EVA latex, acrylic latex, and SB latex, PVA, cellulose derivatives, starch derivatives,
The resin is selected from resins that are dissolved in a solvent, such as acrylic resin, EVA resin, and styrene resin. Particular attention should be paid to the amount of binder, and it should not be too large. That is, the proportion of carbon black in the dried coating should be relatively large.

This may seem at first glance to contradict the purpose of obtaining a see-through paint film, but if the carbon black concentration in the dry paint film is relatively low, the mechanical strength of the paint film increases. , contamination due to desorption of carbon black is reduced, but the balance between conductivity and transparency deteriorates. That is, if the film thickness is increased to increase conductivity, the transparency becomes extremely poor. The concentration of carbon black in a coating film varies depending on the type of carbon black used, dispersion method, film formation method, etc., so it is difficult to specify a specific concentration range, but it is usually around 8% or higher. If the film formation method is selected, 100% carbon black may be used. That is, a coating film can be formed by agglomeration of carbon particles without using any binder.

However, if the carbon black concentration is 70% or more,
If it approaches 100%, the coating will become weaker and more likely to break before the next step, so care must be taken. Also,
When the carbon black concentration increases to over 70%,
Adhesive strength to the base material is also often insufficient. However, advantageously, as the concentration of carbon black increases, the thickness of the conductive layer of carbon black that can be seen through becomes thinner, and it is thought that the film becomes mechanically incomplete. When a synthetic resin liquid is applied on top of the carbon black to form the surface layer A, it is thought that the conductive layer B of the carbon black is not destroyed and allows the synthetic resin liquid to penetrate, and the synthetic resin of the surface layer A is Conductive layer B and base material C are selected from among materials that have good adhesion to material C.
can improve adhesion with The coverage of the transparent layer of carbon black must be determined to provide the desired light transmission and conductivity. Generally speaking, the higher the carbon black concentration and the lower the binder concentration, the smaller the amount of coating required to obtain the desired conductive performance, and the higher the light transmittance.
Since the strength of the intermediate coating film will be low, the formulation and application amount should be determined by considering the strength of the intermediate coating film that can be tolerated by the manufacturing process used. Since it is a spray coat that rarely comes into contact with the paint film, when applying a surface layer, you can use less binder and the amount of coating.

If you compare paints with a certain blend and dispersion,
The larger the amount of coating, the higher the conductivity and the lower the visibility, so the amount of coating should be determined to meet the required performance. If the coating amount is too small, the carbon black will form a layer and will no longer exhibit conductivity, making it impossible to obtain conductivity.

Examples of coating amounts and examples of conductive performance and transparency of the resulting products are shown in Examples. Regarding conductive performance, although a surface resistance of about 10 ¹⁰ Ω may be useful, the material of the present invention can have a resistance as low as about 10 ³ Ω. In addition, the see-through performance is such that even if the light transmission is about 10%, the contents can be confirmed in a bright place, but the material of the present invention can have much higher light transmission and lower haze. Conventional transparent paint films containing carbon black as a conductive component had drawbacks such as low light transmission, large haze, and poor transparency, and black staining when rubbed with white paper. By providing a see-through synthetic resin surface layer A with a volume resistivity of 1×10 ¹³ Ωcm or less and a thickness of 10 μ or less, haze is reduced, transparency is improved, and no contamination is detected even when rubbed with white paper. A good antistatic film can be obtained. This surface layer A can be provided by applying a transparent synthetic resin paint directly on top of the conductive paint film. This surface layer A should be selected to satisfy the various surface properties required for a bag material, ie, height, gloss, slipperiness, blocking resistance, etc. Since this surface layer A is related to electrical conductivity between the conductive layer B made of the conductive paint and the film surface, the layer must have a volume resistivity of 1×10 ¹³ Ωcm and a thickness of 10 μm or less. If the layer has a volume resistivity of 1×10 ¹³ Ωcm or more and a thickness of 10 μm or more, the antistatic performance of the packaging material will be insufficient. However, even if the volume resistivity of the resin itself used for this surface layer A is high, 10 ¹⁴ Ωcm or more, in many cases, the layer coated directly on the conductive layer B made of conductive paint has a resistance of 10 ¹³ Ωcm or more. Ω
It has been found that the material exhibits a low volume resistivity of less than cm. The cause of this is unknown, but some of the carbon black, which is a conductive component, moves during film formation, altering the newly formed surface layer A, and lowering the volume resistivity measured in the thickness direction of the surface layer A. Conceivable. Therefore, whether or not the plastic can be used as a material for the surface layer A should not be determined based on the normal volume resistance value of the plastic. This can be easily determined by contacting the obtained coated surface with an electrode and measuring its surface resistance. The relationship between this surface resistance and volume resistance is as follows.

Surface resistance value: Based on a method based on JIS K6911.
The measurement electrodes are a mercury electrode with a diameter of 5 cm and a donut-shaped mercury electrode with an inner diameter of 7 cm and an outer diameter of 8 cm placed concentrically with the mercury electrode.
11.8cm ² , and the circular pole is 19.6cm ² .

Calculation of the volume resistance of the surface layer Thickness of the surface layer T (cm) Resistance value measured on the coated surface of the conductive paint r ₁ (Ω) Resistance value measured on the surface layer layer layered on the coated film of the conductive paint r ₂ (Ω ) Surface layer volume resistance R (Ω·cm) Δr=(r ₂ −r ₁ )(Ω) R=Δr/0.136T (Ω·cm) However, 0.136 is a constant determined by the electrode. Calculation of surface resistance is based on the following formula.

Resistance value r (Ω) measured on the coating surface or surface layer surface Surface resistance (Ω) = 18.8r (Ω) However, 18.8 is a constant determined by the electrode.

As the surface layer A, acrylic resin containing polyethylene wax is particularly excellent. That is, the acrylic resin has the effect of firmly adhering the conductive layer B coated on the PET layer C to the layer C, and especially those containing polyethylene wax can provide very good abrasion resistance.

The polyolefin layer D serves as a heat-sealing layer for the antistatic film, and is made of polyethylene,
Made from EVA, polypropylene, etc. Layer D
If an antistatic agent is included, it has the effect of improving the antistatic effect of the surface of the layer D, so an antistatic agent may be included if desired. In the case where an antistatic agent is contained, a method of extrusion coating a polyolefin containing an antistatic agent or a method of laminating a polyolefin film containing an antistatic agent can be used.

This will be further explained below using examples.

The puncture strength in the examples was measured as follows.

Insert the film to be measured into a square frame with internal dimensions of 100 mm x 100 mm, hold the frame and film horizontally, and place an IC with 14 pins in the center of the film.
was placed on the IC from above at a speed of 50 mm/min, and the stress when the pin broke through the film was determined and expressed in kg.

Example 1 1.2 parts by weight of styrene-butadiene latex with a nonvolatile content of 50% and 1.4 parts by weight of carbon black were placed on the corona-treated surface of a biaxially stretched polyester film with a thickness of 12μ.
Water-based conductive paint containing 0.12 parts by weight on a dry basis
g/m ² coated and dried. The light transmittance of the coating is 52
%, haze is 19%, and when the paint film is rubbed against white paper, it easily stains the paper black and peels off. The surface resistance of the coated surface was 4×10 ⁵ Ω. On this coated surface, a 15% toluene solution of polymethyl methacrylate containing 2% polyethylene wax was applied in a dry amount of 1 g/m ² and dried. If the specific gravity of the solid material is 1, the thickness of the coating will be 1μ. The surface resistance of the coated surface was 6×10 ⁵ Ω. The volume resistivity of the coating layer in the thickness direction is calculated to be 8×10 ⁸ Ωcm. This metal polymethacrylate coating liquid was separately formed into a film, and the volume resistivity was measured to be 2×10 ¹⁴ Ωcm.

A 50 μm thick polyethylene film was laminated on the non-coated surface of this film with a 15 μm thick polyethylene melt extrusion layer to form an integral film. This film consists of a surface layer A of polymethyl methacrylate containing polyethylene wax with a thickness of 1μ, a transparent conductive layer B containing carbon black with a thickness of about 0.1μ, a stretched polyester layer C with a thickness of 12μ, and a polyethylene layer with a thickness of 65μ. It had a structure in which D was laminated.

When this film is vigorously rubbed 50 times with a polyethylene film and the charge is immediately measured using an electrostatic field measuring device model EA03 of Rion Co., Ltd., the surface layer A is 0 volt/cm, and the polyethylene layer D is 20 volt/cm.
cm, and was found to have excellent antistatic performance. When a bag was made from this film using layer D as the heat-sealing surface, a bag was obtained that had good bag-making processability, had a 0% incidence of defective bags, and was easy to handle. When we measured the penetration strength of the film, it was 1.5Kg.
It was shown that this value is large enough to be used as a packaging material for ICs, etc. In addition, using a JIS L 1048 Gakushin friction tester, a test film was placed on the friction element instead of white cloth, and a film-to-film friction test was performed.
The number of frictions until the surface resistance lost its initial value and rose again was measured. This film was rated 25,000 times. Since several bags of this type are often used at the same time, the abrasion resistance of the same film is important in practical use, and this film has been shown to have extremely excellent abrasion resistance. Ta.

Comparative Example 1 The 50μ thick polyethylene film used in Example 1 was rubbed with the polyethylene film 50 times and the charge was measured in the same manner as in Example 1.
It was 3000volt/cm.

Comparative Example 2 A commercially available IC packaging bag made of a 60 μm thick polyethylene film mixed with an antistatic agent was rubbed in the same manner as in Example 1 and Comparative Example 1, and the charge was measured to be 20 volt/cm.

Moreover, the breaking strength was 0.9 kg.

Comparative Example 3 Example 1 was repeated using a 20 μm thick biaxially stretched polypropylene film instead of the 12 μm thick biaxially stretched polyester film to obtain an antistatic film. The charging due to masatsu is 0 volt/cm on surface layer A and 20 volt/cm on polyethylene layer D.
However, this film was prone to wrinkles during the bag making process, and when used with the same bag making machine as Example 1, 7% of the bags were defective. In addition, the bags had no waist, making it difficult to work with the bags when tying the bags together. Also, the ease of opening the bag (ease of opening the bag with fingers)
It wasn't good either. The penetration strength was 1.1 kg.

Comparative Example 4 When the same friction test as in Example 1 was conducted using a laminate film bag whose surface was coated with metal to the extent that it could be seen through, which was commercially available as a packaging material for ICs, etc.
The friction resistance was 300 times. It was found that the film of Example 1 had extremely good abrasion resistance compared to the metal-coated film.

Example 2 Using a biaxially stretched polyester film with a thickness of 15μ, a conductive layer was applied in the same manner as in Example 1, and a 15% toluene solution of polystyrene was applied as the surface layer in Example 1.
It was applied in the same way. The surface resistance of the coated surface is 7×
It was 10 ⁵ Ωcm. The volume resistivity of the coating layer in the thickness direction is calculated to be 1.2×10 ⁹ Ωcm. When this polystyrene coating liquid was separately formed into a film and the volume resistance was measured, it was 1×.
It was 10 ¹⁵ Ωcm. A polyethylene heat-sealing layer was laminated on this film in the same manner as in Example 1 to obtain an antistatic film. This film was processed into a bag to obtain a bag that was easy to handle without any problems. The opening of the bag was good, and the puncture strength was 1.7 kg. The friction resistance times measured in the same manner as in Example 1 are as follows:
It was 4000 times.

〔Effect of the invention〕

As explained above, the film of the present invention combines materials with a special laminated structure, so that
Excellent product that satisfies antistatic properties, puncture strength, bag-making processability, ease of bag handling, ease of bag opening, and abrasion resistance, which are especially required for packaging products with protrusions such as ICs. You can get the same effect.

Claims (1)

[Claims] 1. Volume resistivity in the thickness direction is 10 ¹³ Ω when the thickness is 10 μ or less
cm transparent surface layer A, transparent conductive layer B containing carbon black, biaxially oriented polyester layer C, and heat-sealable polyolefin layer D.
An antistatic film with a laminated structure in the order of ABCD. 2. The antistatic film according to claim 1, wherein the surface layer A is an acrylic resin containing polyethylene wax.