JPH0761703B2 - Method for producing antistatic sheet material - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing an antistatic sheet-like material suitable for packaging articles that are susceptible to electrostatic damage and allowing the inside to be seen through.

[Conventional technology and its problems] As a packaging material that can store electronic parts such as ICs, which are susceptible to electrostatic damage, and see through the inside, a bag of polyolefin film into which an antistatic agent has been kneaded and a metal thin film to the extent that can be seen through are conventionally used. A bag of a laminated film of a coated film and a polyolefin film in which an antistatic agent is kneaded is known (for those coated with a thin metal layer, U.S. Pat. No. 4,154,344, U.S. Pat. The former) has a low antistatic performance, and there is a drawback that the antistatic performance is extremely deteriorated particularly when the humidity is low. In addition, the latter has a sharp reflection peculiar to metal because it is coated with a thin metal layer, so it is difficult to see the contents depending on the angle.
As a characteristic of the metal, there are drawbacks such that it is chemically unstable and largely deteriorates with time due to oxidation, and that a relatively stable vapor-deposited thin film of a metal such as precious metal or nickel is expensive.

The present inventors have studied a transparent and conductive carbon thin film that is chemically stable, has little change in conductivity due to humidity, and has no sharp and unpleasant reflection, and has previously been disclosed in JP-A-58-4245.
The invention of No. 5 was completed and applied. The invention of JP-A-58-42455 has a technical means of applying a conductive coating material containing a conductive carbon black to obtain a transparent conductive thin film, and has a low relative humidity. Although a packaging material with low performance deterioration can be obtained even in dry air, the light transmittance is low and the haze is large, making it relatively difficult to check the contents, and the content of carbon black in the coating film is increased. When the surface was rubbed with a white paper, the carbon black was easily removed, and there was a defect that black contamination was found.

[Means and Actions for Solving Problems] An object of the present invention is to provide a carbon black which is chemically stable, has little deterioration for a long period of time, has little deterioration in conductive performance even when the relative humidity is low, and has no sharp and unpleasant reflection. Used as the main means of conductivity, improved transparency and lower haze,
Another object of the present invention is to make it possible to easily produce an improved see-through antistatic sheet material which is easier to see through and is prevented from being contaminated due to desorption of carbon black.

The object of the present invention is to provide a mixed solution containing water, methanol and a binder on one side of a base layer which is a transparent plastic,
Applying a conductive coating containing carbon black agglomerated particles together with carbon black dispersed, by drying, on one side of the base layer, to form a conductive layer containing 0.01 ~ 0.8 g / m ² carbon black, Furthermore, 0.2 on this conductive layer
This is achieved by providing a method for producing an antistatic sheet-like product, which comprises providing a surface layer which is a transparent plastic layer having a thickness of -10 μm.

The transparent plastic base layer used in the present invention is selected from those which are transparent and suitable as a packaging material. For example, a sheet-shaped material such as polystyrene, polyvinyl chloride, polyester, polypropylene, polyethylene, or fibrin-based plastic is used.

The sheet-like product produced by the present invention includes both those classified as a film having a thickness of less than 0.254 mm in the case of a soft plastic and those classified as a sheet having a thickness of 0.254 mm or more, and a hard plastic. In the case of, both those classified as a film having a thickness of less than 0.076 mm and those classified as a sheet having a thickness of 0.076 mm or more are included.

For applications requiring particularly high strength, biaxially stretched materials such as biaxially stretched polyester, biaxially stretched nylon and biaxially stretched polypropylene are desirable.

For applications requiring heat sealing, materials having good heat sealing properties such as polyethylene, EVA, and modified PP are preferable, and materials obtained by laminating these materials with other materials are also preferable.

A laminate of a biaxially stretched film having a high heat denaturation temperature and a material having a good heat-sealing property has high strength and is very useful because it can be easily heat-sealed such as a bag-making process.

As a film for making a bag for the purpose of accommodating many articles such as IC, a biaxially oriented polyester film is used as a base material, and a polyolefin layer is added as a heat-sealing layer for bag making. It is particularly superior in terms of strength against breakage due to protrusions, ease of bag making, and ease of handling work.

The polyolefin layer is made of polyethylene, EVA, polypropylene or the like. If the polyolefin layer is subjected to an antistatic treatment, it has the effect of improving the antistatic effect on this surface, so an antistatic treatment may be carried out if desired. The antistatic treatment can be carried out by extrusion coating a polyolefin containing an antistatic agent or laminating a polyolefin film containing an antistatic agent. For applications such as trays, cylindrical magazines, boxes, plates, etc., it is preferable to use a sheet material having a large rigidity, for example, a relatively thick sheet material such as hard polyvinyl chloride, polycarbonate, or biaxially oriented polystyrene. Good.

A conductive layer is formed on the surface of the base material used as the base layer.

The conductive layer uses opaque carbon black as the main conductive material, and must have a special structure so that the sheet-like material can be seen through and has good antistatic properties. In the present invention, a conductive coating is applied to one surface of the base layer and dried to form a conductive layer, and the conductive layer contains 0.8 to 0.01 g / m ² of carbon black with respect to the plane. Further, in the present invention, the structure is such that carbon black partially projects from the surface layer.

The conductive layer having such a structure is formed as described below.

First, a conductive coating material containing carbon black is applied on a base material to form a film. This conductive paint contains carbon black as a conductive component and additionally contains water, methanol and a binder.

The carbon black is preferably selected from those for conductive fillers. Various brands are available, but a selection scale that does not necessarily uniquely determine particle size, dispersibility, degree of graphitization by firing, degree of structure development, etc. has not been found. I tested several kinds for conductive filler,
It is good to select a brand with as high transparency as possible for the same conductivity.

The binder has good adhesiveness to the substrate,
It is good to choose one that will help disperse the carbon black as much as possible. As the binder, for example, latexes such as EVA latex, acrylic latex, SB latex and partially saponified vinyl acetate are used.

Special attention should be paid to the amount of binder and should not be too high. That is, the proportion of carbon black in the dry coating should be relatively high.

This seems to be contrary to the purpose of obtaining a transparent coating film, but when the carbon black concentration in the dry coating film is relatively low, the mechanical strength of the coating film increases and Contamination due to detachment of black is reduced, but the balance between conductivity and transparency is deteriorated. That is, if the film thickness is increased in order to obtain conductivity, the transparency becomes extremely poor. The concentration of carbon black in the conductive layer coating film is
Since it depends on the type of carbon black used, the method of dispersion, the method of film formation, etc., it is difficult to describe a certain concentration range.

A surfactant is optionally added as a dispersant.
Latexes usually contain some amount of surfactant, and in particular it may not be necessary to add a dispersant. or,
Since a binder dissolved in a solvent may also be used as the dispersant, whether or not to use the dispersant and the amount of the dispersant used may be determined by judging the necessity in each case.

The amount of carbon black applied as a conductive paint is
It is desirable that the conductivity be as low as possible in order to improve the see-through performance. This amount varies depending on the type of carbon black and the state of dispersion, but the upper limit is 0.8 g / m ² , and 0.1 g / m ² or less is desirable. The lower limit is 0.01 g / m ² . If it is more than the above upper limit, the fluoroscopic performance is inferior, and if it is less than the lower limit, it is usually difficult to develop the conductive performance. Further, the thickness of the conductive layer, that is, the average thickness of the layer in which carbon black is formed into a substantially continuous layer is 5 μm.
m to 0.01 μm, preferably 1 μm to 0.01 μm. As a characteristic of the conductive layer, it is necessary to have a structure in which carbon black partially protrudes from the surface layer.

Such a special structure can be obtained by including agglomerated particles of carbon black in the conductive paint. The particles in which carbon black is aggregated form a portion protruding from the conductive layer to the surface layer side. The protrusions shown in Example 1 are due to the aggregated particles.

In the present invention, methanol is added to the dispersion medium of carbon black in order to increase the drying rate as compared with water and to reduce the surface tension to facilitate the coating on the plastic surface and to improve the dispersion action of the dispersion medium. This is for facilitating formation of appropriate aggregated particles of carbon black by reducing the amount.

The size of the conductive particles for forming the protruding portion, which are formed by the aggregated particles of carbon black, must be larger than the average thickness of the conductive layer so that the conductive particles obviously protrude. The degree is about 1.3 times the average thickness of the conductive layer, that is, 1.3 μm in the case of the conductive layer having an average of 1 μm, and about 0.026 μm or more in the case of the average thickness of 0.02 μm. The amount of the protrusions is difficult to analyze and has not been quantified yet, but it is sufficient if the protrusions are included so that they can be easily detected by observation with a microscope.

By taking such a special structure, the surface resistance of the surface layer can be remarkably reduced. Although details of the cause of this effect are unknown, it is imagined that the protruding portion of the conductive layer on the surface layer is likely to cause the concentration of charges, so that the diffusion of the charge between the surface layer and the conductive layer mainly affects the protruding portion of the conductive layer. It can happen over time.

The conductive layer may be usually applied on the substrate to have a substantially uniform thickness, but the thickness can be intentionally increased or decreased if desired. Providing a continuous line-like and slightly thick part such as a fine mesh or parallel lines is effective for obtaining a product that is easy to see through and has a low surface resistivity in addition to the design effect. Further, even if the thickness is increased to such an extent that only a continuous linear portion cannot be seen through, or the carbon black concentration is increased, it is possible to see through as a whole and the surface resistivity can be improved to a very low level.

Such a continuous thin line thick part or a part where the concentration of carbon black per surface is high is prepared by a gravure printing method so that the plate can be formed in such a pattern, or it is thin and almost even over the entire surface. It can be prepared by a method of applying a conductive layer to the above and further applying the pattern as described above. In this case, it is preferable that the distance between the lines is small, and it should be 20 mm or less as much as possible. Also, the line width should be as thin as possible, preferably 2 mm or less. This is because if the line spacing is too large, the protection performance against electrostatic damage becomes insufficient, and if the line width is too large, it becomes conspicuous when seeing through.

When the concentration of carbon black in the non-volatile content of the conductive coating material is as high as 70% by weight or more, the adhesive strength with the base material often becomes insufficient. However, the higher the concentration of carbon black, the better the conductivity of carbon black, which is the conductive layer, even if the transparent layer of carbon black is thin. At this time, it seems that the coating film of this conductive paint is likely to penetrate the liquid, and when synthetic resin liquid is applied to form a surface layer directly on the conductive layer, the conductivity of the conductive layer of carbon black is almost Improving the adhesiveness of the conductive layer to the base material by allowing the synthetic resin solution to penetrate to the base material without lowering and selecting the surface synthetic resin from those with good adhesion to the base material. I found that I can do it.

Further, by coating the surface layer on the conductive layer, the light transmittance and haze are improved as a whole. That is, they have found that it becomes easy to see through an object through a film. The degree of improvement in light transmittance is usually 2% or more as compared with a film lacking a surface layer, and if good, 5% or more. Also, the haze improvement is particularly large, usually 2% or more, and 10% if good.
The above is also improved.

When applying a conductive coating to a substrate, pretreatment such as corona discharge treatment may be performed on the base material to improve wettability with the base material and improve adhesion with the base material. You can also do it.

The surface layer can be provided by directly overlaying a coating film of a conductive paint and applying a transparent synthetic resin paint. Since this surface layer forms the surface layer of the antistatic plastic film or sheet, a material satisfying various surface properties required for the packaging material, that is, hardness, gloss, slipperiness, blocking resistance, etc., is selected. Should be.

Since the surface layer serves as the surface layer of the antistatic plastic film, it is generally considered that a synthetic resin having a low electric resistance should be used, but this is not always necessary. That is, the volume resistivity of the resin itself is very high, even if a thermoplastic resin such as ordinary polyolefin is used, the surface layer directly coated on the conductive layer as described above has a very high surface resistivity. It was found that it can be lowered. This was a totally unexpected effect, but it seems to be understood to some extent by providing the conductive layer with a portion protruding from the surface layer.

Examples of the resin that can be used as the surface layer include polystyrene,
Fiber-based plastics such as polyvinyl chloride and nitrification cotton,
Thermoplastic resins and phenolic resins such as polyethylene, EVA, polyacrylic acid ester, polymethacrylic acid ester, polyvinylidene chloride, polyamide, polyester, etc.,
A thermosetting resin such as an epoxy resin can be used for application in the form of emulsion or solution. Alternatively, a method of applying a polymerizable monomer to form a polymerized film may be used. Acrylic resins such as polyacrylic acid ester and polymethacrylic acid ester are particularly preferable in terms of strength, adhesiveness, transparency and the like.

Additives such as various waxes can be added to the surface layer for the purpose of improving slipperiness and abrasion resistance.
Polyethylene wax is particularly preferable because it improves abrasion resistance and hardly pollutes other things. The surface layer has a thickness of 0.2 to 10 μm. A surface layer thicker than 10 μm causes insufficient antistatic effect, and a surface layer thinner than 0.2 μm causes insufficient mechanical strength of the coating film.

The antistatic sheet material obtained in the present invention is transparent, and a light transmittance of 20 or more can be sufficiently achieved.
Of course, 40 or more can be achieved, haze of 20 or less can be sufficiently achieved, and haze of 10 or less can be achieved.

As a laminate based on the basic antistatic sheet obtained in the present invention, a transparent plastic layer A having a thickness of 0.2 μm to 10 μm and a conductive layer B containing carbon black of 0.01 to 0.8 g / m ² are further added. (However, carbon black partially protrudes from the surface layer), base layer C of synthetic resin having a melting point of 180 ° C. or higher, and thermal fusion bonding of a vinylidene chloride-based copolymer having a drying loss of 0.01 to 2% by an emulsion polymerization method. Layer D and layer A, B, C, D
An antistatic sheet laminated in this order is also provided. The layer structure of this laminate is shown in FIG.

The base layer C supports the conductive layer B laminated on the surface of the base layer C, and also serves as a base material for imparting the overall strength and the like required when used for packaging to the film.

The base layer C needs to be a synthetic resin film having a melting point of 180 ° C. or higher. For example, when using a synthetic resin film with a melting point of less than 180 ° C, such as polyethylene and polypropylene,
When the present film is heat-sealed into a bag, the base layer C melts or shrinks, and the conductive layer B laminated on the surface is divided, so that a good antistatic effect cannot be obtained.

The base layer C has a sufficient role as a support and a base material for the conductive layer B, and the present film is easy to handle for packaging and has sufficient transparency.
It is preferable to use a transparent synthetic resin film having a thickness of 5 to 50 μm and excellent in smoothness and mechanical strength. Since articles to be packaged often have protrusions such as pins and burrs, it is preferable that they have sufficient puncture resistance required for the protrusions. Further, it is preferable that the smoothness, mechanical strength, and transparency are not impaired at a temperature of 140 ° C. or higher.

The base layer C preferably has a high adhesive force with other layers laminated on the base layer C. From this point, the wetting tension (JI
(According to SK-6768) is preferably 35 dyne / cm or more. Further, in order to increase the adhesive force, the surface of the synthetic resin film forming the base layer C may be subjected to corona discharge treatment.

Specific examples of the synthetic resin film constituting the base layer C include:
For example, films of polyester, nylon, polyimide, cellulose acetate, polyvinyl alcohol and the like can be mentioned.

The heat-sealing layer D has good heat-sealing strength during the bag-making process and prevents static electricity from being charged from the inner surface of the bag.

The heat-sealing layer D needs to be composed of a vinylidene chloride-based copolymer formed by an emulsion polymerization method.

The method for producing a vinylidene chloride-based copolymer includes a suspension polymerization method and an emulsion polymerization method using an emulsifier. However, the surface resistance of the vinylidene chloride-based copolymer film produced by the suspension polymerization method is 10 ¹⁶ Ω or more, and how the heat-sealing layer D is the inner surface of the bag, which has less cause of static electricity generation. However, it becomes impossible to achieve the necessary antistatic property. Also,
Synthetic resins other than vinylidene chloride copolymer that are produced by emulsion polymerization include polyvinyl chloride, polyvinyl alcohol, and tetrafluoroethylene, but they lack heat-sealing properties and are sticky or blocking. Prone to

The heat fusion layer D is formed by applying corona discharge treatment or providing an anchor coat layer on the base layer C, if necessary, and then coating and drying a vinylidene chloride copolymer latex produced by an emulsion polymerization method. can do. The vinylidene chloride-based copolymer is preferably one in which the copolymerization ratio of vinylidene chloride is 50 to 95% by weight, and the monomer to be copolymerized with vinylidene chloride is 5 to 50% by weight. As the monomer, for example, vinyl chloride, acrylonitrile,
One kind or two or more kinds can be selected from methyl methacrylate, methyl acrylate, ethyl acrylate, vinyl acetate and the like.

As the emulsifier used in the emulsion polymerization method, an anionic or nonionic surfactant is used, preferably an alkyl sulfonate, an alkyl aryl sulfonate having an alkyl group having 8 to 24 carbon atoms, or a polyethylene glycol alkyl ether. The alkylaryl sulfonate is most suitable because it is not hydrolyzed by a strong acid. More specifically, for example, polyoxyethylene lauryl ether, polyoxyethylene nonylphenyl ether, sodium dioctyl sulfosuccinate, sodium dodecylbenzene sulfonate, etc. can be used.

The surface resistance of the heat-sealing layer D varies in the range of about 10 ⁹ to 10 ¹⁴ Ω depending on the type and amount of the emulsifier in the polyvinylidene chloride latex.
It is preferable to select the grade by measuring the surface resistance after drying.

If the coating amount of the vinylidene chloride copolymer latex for forming the heat-sealing layer D is 1.0 g / m ² or more as the solid content, there is no problem with respect to the surface resistance. However, in order to obtain a good heat-sealing property with this heat-sealing layer D, the heat-sealing layer D obtained by coating and drying a vinylidene chloride copolymer latex is 3 μm or more, optimally 10 ~ 100μ
It is preferable to apply it so as to have a thickness of m. As a coating method of the vinylidene chloride-based copolymer latex, for example, air knife coating, gravure coating, roll coating, Mayer bar coating and the like can be used.

Examples of the anchor coating agent for improving the adhesive strength of the base layer C and the increase in D during heat fusion include isocyanate-based, imine-based, polyester-based, urethane-based, acrylic-based anchor coating agents and chlorinated polypropylene. Used. This coating amount may be 5 g / m ² or less in terms of solid content,
The thermal fusion bonding layer D may be formed after coating the base layer C and drying.

Between the base layer C and the heat fusion layer D, as shown in FIG.
The auxiliary heat sealing layer E can also be provided. Since the auxiliary heat-sealing layer E is hard to be thick until the heat-sealing layer D has a sufficient heat-sealing strength, a sufficient heat-sealing strength is obtained regardless of the thickness of the heat-sealing layer D. It is intended to be done.
Even if the auxiliary heat-sealing layer E is provided, its surface is covered with the above-mentioned heat-sealing layer D, so that the surface resistance is not increased, and stickiness or blocking does not occur.

The auxiliary heat-sealing layer E may be a synthetic resin excellent in transparency and heat-sealing property, but polyolefin is preferable in that it can play a reinforcing role of the present film. Among the polyolefins, polyethylene, EVA and polypropylene are preferable. When this auxiliary heat-sealing layer E is provided, the total thickness with the heat-sealing layer D is 3 μm or more, optimally 10 to 100 μm.
It is preferable to provide m. Auxiliary heat sealing layer E
As a method for laminating the above, for example, a dry laminating method, an extrusion coating method, a coextrusion coating method, or the like can be used.
When the auxiliary heat-sealing layer E is provided, the heat-sealing layer D is laminated on the auxiliary heat-sealing layer E in the same manner as described above, using a corona discharge treatment or an anchor coating agent if necessary. Then, in this case, even if the heat fusion layer D is thinned to about 1 μm, sufficient fusion strength can be obtained.

The laminate in which the layers A, B, C and D are laminated has the conductive layer B formed as an extremely thin film of a dry conductive paint film containing carbon black, and the haze is reduced by laminating the surface layer A. Together with this, it is possible to obtain the transparency necessary for practical use. Further, the conductive layer B can be formed by a simple method of coating and drying a coating material containing carbon black, and since it is firmly adhered to the base layer C together with the surface layer A, there is no fear of being damaged by bending or the like. .

On the other hand, it has been confirmed that the heat-fusion layer D can have a surface resistance of about 10 ⁹ to 10 ¹⁴ Ω, and it is hard to cause stickiness and blocking. The reason for this is not necessarily clear, but it is presumed that the water content of the heat-sealing layer D lowers the surface resistance and that the crystallinity of the vinylidene chloride-based copolymer hardly causes stickiness or blocking.

In addition, the layers A, B, and C of the above-described laminate are the same, and the D layer has a density of
It is also possible to use a buffering antistatic sheet in which the buffering plastic sheet (D ') of 05 to 0.50 g / cm ³ is replaced. The layer structure of this laminate is shown in FIG.

The cushioning plastic sheet D'has a good heat-sealing strength during bag-making process, has a sufficient cushioning property to protect the contents contained therein from cushioning, and is formed from the inner surface side when formed into a bag. This is to prevent electrostatic charge.

The cushioning plastic sheet D'has a density of 0.005 to 0.50 g / cm ³
It is necessary to be. When the density is less than 0.005 g / cm ³ , the retainability of the content to the article is lowered, and the mechanical strength such as heat fusion strength and breakthrough resistance is deteriorated. If the density exceeds 0.50 g / cm ³ , the shock absorbing property becomes insufficient. Here, the density is the apparent volume V of the cushioning plastic sheet.
And the weight M of the apparent volume of the buffer plastic sheet, the value obtained by the following equation.

The cushioning plastic sheet D'has a thickness of 0.2 mm in order to have good heat-sealing strength and sufficient cushioning property.
The above is suitable and is selected from, for example, a foamed plastic sheet, an air-filled plastic sheet, or the like, using a polyolefin-based resin or polystyrene-based resin having excellent heat fusion property as a raw material. Among the polyolefins, polyethylene and polypropylene are preferable.

The cushioning plastic sheet D needs to be transparent, and the number of bubbles in the thickness direction needs to be 10 or less, preferably 5 or less in the thickness direction, more preferably 3 or less, most preferably It is preferably one. When the number of bubbles in the thickness direction exceeds 10, the haze is large and the light transmittance is reduced, which makes it difficult to see through.

As a method for laminating the buffer plastic sheet D and the base layer C, for example, thermocompression bonding, dry laminating method, extrusion coating method, extrusion laminating method or the like may be used or used in combination.

The outer surface of the cushioning plastic sheet D'is preferably wrinkled and slack. When an article is put with the cushioning plastic sheet D'inside, even if there is some shaking or vibration due to the wrinkles and slacks in the layer D, the article is held down and the movement is made difficult to move. As a result, , The risk of static electricity due to friction between the article and the D'layer is reduced. If the D'layer is smooth without wrinkles or sagging, the effect of holding the article and making it hard to move becomes less.
A method for forming wrinkles or slack is, for example, heating the cushioning plastic sheet when laminating the cushioning plastic sheet D'and the base layer C, and then gradually cooling without rapid cooling, or by using D'and C. After laminating, the winding tension can be increased and the winding can be performed harder when winding into a roll.

As the buffer plastic sheet D ′, it is preferable to use one in which an antistatic agent is kneaded or applied, but as shown in FIG. 5, the buffer plastic sheet D ′ is charged. It is also possible to further laminate and provide a polyolefin film E kneaded with an inhibitor as an auxiliary heat-sealing layer. At this time, there is no particular problem even if the buffer plastic sheet D'is not provided with an antistatic property. This is because the antistatic agent in the auxiliary heat-sealing layer E migrates and the antistatic property is imparted to the buffer plastic sheet D. This auxiliary heat-sealing layer E is for ensuring sufficient heat-sealing strength when it is difficult to obtain sufficient heat-sealing strength for the buffer plastic sheet D. Further, even if the auxiliary heat-sealing layer E is provided, the cushioning property is not impaired, and the outer surface of the cushioning plastic sheet D does not have wrinkles or slack. When the auxiliary heat-sealing layer E is provided, the thickness is suitably 10 to 100 μm, and as a laminating method, for example, a dry laminating method, an extrusion coating method or the like can be used.

When the apparent volume resistivity of the surface layer was calculated from the measured surface resistance, it was improved to an extremely low value as shown in the examples. The measurement and calculation were performed as follows.

(1) Surface resistivity: According to JIS K6911.
Measuring electrode inner diameter 7cm disposed in the mercury electrode and concentric therewith diameter 5 cm, donut-shaped mercury electrodes having an outer diameter of 8 cm, the contact area is a donut-shaped electrode 11.8 cm ^2, poles of circular is a 19.6 cm ² .

The electrode is brought into contact with the measurement surface, the resistance value between both electrodes is measured, and the surface resistivity is determined by the following equation.

Resistance value between electrodes rp (Ω) Surface resistivity r (Ω) r = 18.8rp (Ω) where 18.8 is a constant determined by the electrode shape.

(2) Calculation of apparent volume resistivity of surface layer Thickness of surface layer T (cm) Resistance value between electrodes of conductive paint film rp ₁ (Ω) Resistance value between electrodes of surface layer overlaid on conductive paint film rp
₂ (Ω) Surface volume resistivity R (Ω · cm) However, 0.136 is a constant determined by the shape of the electrode.

A film with a conductive coating on one side of the base material and a surface layer on top of it has a fairly good antistatic ability even in a bag with the surface layer on the outside of the bag, but the surface layer on the inside of the bag It has been found that the provision thereof is effective for further protecting the contents. That is, it was confirmed that the bag having the surface layer on the outside of the bag had a larger accumulation of static electricity in the contents than the bag having the surface layer on the inside of the bag.

It is known that most of the failures such as IC due to static electricity are insulation damage of the insulating thin film that insulates the semiconductor part or conductor part inside the element, and most of this insulation damage is due to charged conductors (large Part is called the human body), and the discharge from the conductor part or semiconductor part in the device to the conductor part or semiconductor part in the charged element to the grounded conductor (human body etc.) occurs in the bag. It is a very important property not to store electricity in the conductor.

If the surface layer is provided on the inner surface of the bag, antistatic treatment is not necessarily required for the other outer surface, but it is desirable to perform antistatic treatment by kneading or applying an antistatic agent on the outer surface. It is also desirable to provide a surface layer on both sides of the conductive coating film.

Containers other than bags, such as boxes, trays, cylinders, and magazines, are suitable for being made of a sheet-like material using a thick substrate having high rigidity. These can be made by thermoforming a sheet. Also in the case of these types of containers, the contents can be better protected from electrostatic damage by forming the container with the inner surface side having a surface layer having a low surface resistivity.

[Examples] Examples will be further described below.

The break-through strength in the examples was measured as follows.

Insert the film to be measured into a square frame with an inner size of 100 mm × 100 mm, hold the film horizontally with the frame, place an IC with 14 pins in the center of the film, and place the IC at 50 mm / min from the top.
The pressure when the film was pierced by the pin was calculated by pressing at the speed of, and expressed in Kg.

The light transmittance and haze were measured by the method according to JIS K 7105.

Example 1 Ketjenblack EC manufactured by Lion Akzo Co., Ltd., which is a carbon black commercially available as a conductive filler.
A dispersion liquid containing 10% by weight, 8% by weight of a nonionic surfactant as a dispersant, and the balance water was prepared. Separately, as a binder, a solution was prepared by dissolving partially saponified vinyl acetate in a mixed solvent of methanol and water at a mixing weight ratio of 90:10 by 9.2% by weight.

While stirring 40 parts by weight of the carbon black dispersion, 60 parts by weight of the binder solution was added to carbon black 4
A conductive coating material was prepared containing 5 wt% of a surfactant, 3.2 wt% of a surfactant and 5.5 wt% of a binder, and the solvent was a mixed solvent of methanol and water at a mixing ratio of 56:44 by weight.

The non-volatile content of this conductive paint is 12.7% by weight.
31% by weight is carbon black.

When a mixed solvent of methanol and water is used as a solvent, the drying speed is increased as compared with water, and the surface tension is lowered to facilitate application on the plastic surface, and the dispersion action of the nonionic surfactant is reduced. It is possible to easily reduce the amount by which the carbon black is slightly aggregated.

One side of a biaxially stretched polyester film with a thickness of 12 μm is subjected to corona discharge treatment, and the surface of the surface is coated with the above conductive paint in a dry amount of 0.
2g / m ² Apply with a gravure coater, dry, and stack on top of this acrylic resin containing methyl methacrylate as the main component 14.7
A top coat paint using toluene as a solvent containing 1% by weight and 0.3% by weight of polyethylene wax was applied in a dry amount of 1 g / m ² and dried.

When the specific gravity of the solid material obtained by drying each paint is 1, the thickness of the conductive layer is about 0.2 μm and the thickness of the surface layer is about 1 μm. Carbon black is applied at a rate of 0.06 g / m ² .

0.7% by weight of a nonionic antistatic agent, Chemistat 1100 manufactured by Sanyo Kasei Co., Ltd., on the non-coated surface of this film
The heat-sealing layer was formed by laminating the contained polyethylene to a thickness of 65 μm by an extrusion coating method.

This film has a surface resistivity of 9 × 10 ⁵ Ω, a heat seal layer of 8 × 10 ¹¹ Ω, and a light transmittance of 40.
%, Haze 13%, and the object was easily seen through.

A micrograph of the cross section of the conductive layer and the surface layer side of this film is shown in FIG. As shown in FIG. 1, it was confirmed that carbon black partially protruded from the surface layer.

This film was rubbed violently 50 times with a polyethylene film and immediately subjected to electrostatic charge measurement with a ION03 electrostatic field meter manufactured by Rion Co., Ltd. The surface layer had 0 volt / cm and the polyethylene layer had 16 volt / cm, showing excellent antistatic performance. I found out. When this film was heat-sealed to form a bag, the bag-making processability was good, and the occurrence rate of defective bags was 0%, and the bags were easy to handle. The breaking strength of the film was measured and found to be 1.5 kg, which was a sufficiently large value as a packaging material for ICs and the like. In addition, a JIS L 1048 Gakushin-type friction tester was used to put a test film on the friction element instead of white cloth, and a film-to-film friction test was conducted to determine the number of frictions until the surface resistance lost its initial value and stood up. Was measured. This film was 25,000 times. Since this type of bag is often used at the same time more than once, the abrasion resistance of the same film is practically important, but this film has been shown to have very excellent abrasion resistance. . When the surface layer was rubbed with white paper, it was not contaminated at all. For comparison, the surface resistivity of the film coated with only the conductive layer without coating the surface layer was 6 × 10 ⁵ Ω.

It was observed that this coated surface stains the paper black when rubbed with white paper. The volume resistivity in the thickness direction of the surface layer is calculated to be 1 × 10 ⁹ Ω · cm.

Separately, when a coating solution for the surface layer is formed and the volume resistivity is measured, 2
It was × 10 ¹⁴ Ω · cm. It was found that the volume resistance of the surface layer was significantly reduced and improved.

Further, it was found that the film coated with only the conductive layer without coating the surface layer had a light transmittance of 42% and a haze of 18%, and the coating of the surface layer improved the transmittance by 3% and 5%, respectively.

Example 2 An antistatic film having a heat-sealing layer laminated was obtained in the same manner as in Example 1 except that a biaxially stretched polyester film having a thickness of 15 μm was used and a 15 wt% polystyrene solution in polystyrene was used as the surface layer.

The surface resistance of the surface layer was 9 × 10 ⁵ Ω, the surface resistance of the heat seal layer was 8 × 10 ¹¹ Ω, the light transmittance was 45%, and the haze was 13%, and the object was easily seen through.

When the cross sections of the surface layer and the conductive layer were observed with a microscope, it was confirmed that carbon black partially protruded from the surface layer as in Example 1.

The bag-making processability was good, there were no defective products, and the bag could be processed with good openability and easy handling. The breaking strength was 1.7 kg. The number of times of abrasion resistance was 4000 times. For comparison, when the liquid used for the surface layer was separately formed and the volume resistance was measured, it was 1 × 10 ¹⁵ Ω · cm.

The volume resistivity of the surface layer in the thickness direction was calculated to be 1 × 10 ⁹ Ω · cm, and it was found that the volume resistivity of the surface layer was significantly reduced.

Comparative Example 1 Carbon black used in Example 1 and non-volatile content 40% by weight
A styrene-butadiene latex containing styrene-butadiene latex was used to disperse carbon black in water to prepare a conductive paint. This coating material contained 20% by weight of nonvolatile components, and 7% by weight of the nonvolatile components was carbon black. Since this coating material has a low carbon black content, the dispersion of carbon black was easier and the dispersion state was better than that of the conductive coating material used in the above examples.

This coating was applied to the corona treated surface of a 15 μm biaxially oriented polyester film and dried to form a 6 μm coating film. Carbon black is applied at a rate of 0.42 g / m ² . The coating film was smooth and glossy, but almost opaque and colored black. The coated surface was pressed by a mirror-finished heating roller to finish it into a smooth and glossy surface, and the protrusion of carbon black was removed. The surface resistivity of this coating film surface was 8 × 10 ⁷ Ω. On top of this, the acrylic resin coating liquid used in Example 1 was applied and dried to form a coating film having a thickness of 13 μm. The surface resistivity of this coated surface was 2 × 10 ¹¹ Ω, which was an insufficient value as an antistatic film.

Comparative Example 2 0.8 parts by weight of the carbon black used in Example 1 was mixed with 100 parts by weight of the acrylic resin topcoat paint used in Example 1 to prepare a coating containing carbon black. The non-volatile content of this coating contains 5% by weight of carbon black, which is the same as the average concentration of carbon black in all coatings of Example 1.

The base film used in Example 1 was coated with 1.3 g of this coating material by dry weight.
The coating was applied and dried at a ratio of / m ² . The coated material had a coating film of 1.3 g / m ² as in Example 1, and carbon black was coated at a rate of 0.06 g / m ² as in Example 1, but the surface resistivity was measured. Then, it was 6 × 10 ¹³ Ω, and there was no antistatic effect. It was found that even if carbon black was applied at the same ratio as in Example 1, the one lacking the production of the special coating film as in Example 1 had no antistatic effect.

Comparative Example 3 When a commercially available IC packaging bag made of a polyethylene film having a thickness of 60 μm in which an antistatic agent was kneaded was rubbed in the same manner as in Example 1 to measure the charge, both the front surface and the back surface were 20 volt / cm. . This value was inferior to the bag of Example 1 on both the front surface and the back surface. The breaking strength was 0.9 kg, which was inferior to the bag of Example 1.

Comparative Example 4 When the same friction test as in Example 1 was carried out using a laminate film bag, which is commercially available as a packaging material for ICs and the like, the surface of which is coated with a metal so that it can be seen through, the number of times of abrasion resistance is 300 It was Example 1 compared to the metal coated film
It can be seen that the film No. 1 has extremely good abrasion resistance.

Comparative Example 5 5 cm × 5 cm, thickness, in a polyethylene bag specially made for packaging an IC etc. in which a commercially available antistatic agent is kneaded
Put a handle with a polystyrene stick on one end of a 0.3 mm aluminum plate, rub it 50 times with your hand and take it out immediately, and measure the electric field of the aluminum plate with an electrostatic field measuring instrument manufactured by Rion Co., Ltd. It was 1500 volt / cm. In a bag containing this kind of antistatic agent, the bag itself is less likely to be charged, but very high voltage electricity is generated in the internal conductor, so it was found to be dangerous when used for packaging ICs. .

[Effects of the Invention] The present invention is as described above, and has the following effects.

(1) In the antistatic sheet material obtained by the present invention, the surface layer of plastic is provided on the surface of the conductive layer containing carbon black, and the surface resistance of this surface layer is
The surface resistance of the conductive layer is not significantly increased as compared with the surface resistance of the conductive layer, thereby maintaining a practical antistatic effect. It is considered that this is because the agglomerated particles of carbon black contained in the conductive paint form a protrusion protruding toward the surface layer when the conductive layer is formed, and suppress the increase in the surface resistance of the surface layer. Further, in the present invention, by adding methanol to the dispersion medium of the conductive paint, it is possible to obtain appropriate aggregated particles of carbon black, and it is easy to obtain a special structure having the above-mentioned protruding portion. It is a thing.

(2) By providing the surface layer, not only the light transmittance and the haze degree can be improved, but also the surface layer can prevent the carbon black particles constituting the conductive layer from falling off.
It is possible to prevent the adverse effect of the fallen particles.

[Brief description of drawings]

FIG. 1 is a microscopic image of a cross section of the sheet-like article of Example 1 for illustrating the structure of the conductive layer of the sheet-like article obtained by the present invention. Reference numeral 1 is a conductive layer, 2 is a surface layer, and 3 is a base layer. It can be seen that the conductive layer partially protrudes from the surface layer. 2 to 5 show that each of the layers 1, 2 and 3 of the basic sheet material is composed of the selected material, that is, the conductive layer B, the surface layer A and the base layer C, and further another layer is laminated. FIG. 2 is a cross-sectional view showing the layer structure of the laminated body, wherein FIG. 2 shows the laminated body in which the heat-sealing layer D is laminated on the basic sheet-like material, and FIG. 3 is C of the laminated body of FIG. Fig. 4 shows a laminate in which an auxiliary heat-sealing layer is provided between C and D, Fig. 4 shows a laminate in which a cushioning plastic sheet D'is laminated on a basic sheet, and Fig. 5 shows Fig. 4. 3 shows a laminate in which an auxiliary heat sealing layer is provided on the D surface of the laminate.

Claims (1)

[Claims] 1. A transparent plastic base layer on one side,
In a mixed solution containing water, methanol and a binder, a conductive coating containing dispersed carbon black and containing agglomerated particles of carbon black is applied and dried, on one side of the base layer, 0.01 to 0.8 g / m 2. ² to form a conductive layer containing carbon black, further 0.2 ~ 10 on the conductive layer
A method for producing an antistatic sheet-like article, which comprises providing a surface layer which is a transparent plastic layer of μm.