EP0625171A1 - Electrically dissipative composite - Google Patents

Electrically dissipative composite

Info

Publication number
EP0625171A1
EP0625171A1 EP92918535A EP92918535A EP0625171A1 EP 0625171 A1 EP0625171 A1 EP 0625171A1 EP 92918535 A EP92918535 A EP 92918535A EP 92918535 A EP92918535 A EP 92918535A EP 0625171 A1 EP0625171 A1 EP 0625171A1
Authority
EP
European Patent Office
Prior art keywords
package
composite
heat
film
metal foil
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP92918535A
Other languages
German (de)
French (fr)
Inventor
Hua-Feng Huang
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
EIDP Inc
Original Assignee
EI Du Pont de Nemours and Co
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from US07/873,178 external-priority patent/US5376446A/en
Application filed by EI Du Pont de Nemours and Co filed Critical EI Du Pont de Nemours and Co
Publication of EP0625171A1 publication Critical patent/EP0625171A1/en
Withdrawn legal-status Critical Current

Links

Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B15/00—Layered products comprising a layer of metal
    • B32B15/04—Layered products comprising a layer of metal comprising metal as the main or only constituent of a layer, which is next to another layer of the same or of a different material
    • B32B15/08—Layered products comprising a layer of metal comprising metal as the main or only constituent of a layer, which is next to another layer of the same or of a different material of synthetic resin
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B27/00—Layered products comprising a layer of synthetic resin
    • B32B27/12—Layered products comprising a layer of synthetic resin next to a fibrous or filamentary layer
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B27/00—Layered products comprising a layer of synthetic resin
    • B32B27/18—Layered products comprising a layer of synthetic resin characterised by the use of special additives
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B5/00—Layered products characterised by the non- homogeneity or physical structure, i.e. comprising a fibrous, filamentary, particulate or foam layer; Layered products characterised by having a layer differing constitutionally or physically in different parts
    • B32B5/02—Layered products characterised by the non- homogeneity or physical structure, i.e. comprising a fibrous, filamentary, particulate or foam layer; Layered products characterised by having a layer differing constitutionally or physically in different parts characterised by structural features of a fibrous or filamentary layer
    • B32B5/022—Non-woven fabric
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B7/00—Layered products characterised by the relation between layers; Layered products characterised by the relative orientation of features between layers, or by the relative values of a measurable parameter between layers, i.e. products comprising layers having different physical, chemical or physicochemical properties; Layered products characterised by the interconnection of layers
    • B32B7/04—Interconnection of layers
    • B32B7/12—Interconnection of layers using interposed adhesives or interposed materials with bonding properties
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B65—CONVEYING; PACKING; STORING; HANDLING THIN OR FILAMENTARY MATERIAL
    • B65D—CONTAINERS FOR STORAGE OR TRANSPORT OF ARTICLES OR MATERIALS, e.g. BAGS, BARRELS, BOTTLES, BOXES, CANS, CARTONS, CRATES, DRUMS, JARS, TANKS, HOPPERS, FORWARDING CONTAINERS; ACCESSORIES, CLOSURES, OR FITTINGS THEREFOR; PACKAGING ELEMENTS; PACKAGES
    • B65D65/00—Wrappers or flexible covers; Packaging materials of special type or form
    • B65D65/38—Packaging materials of special type or form
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K3/00—Use of inorganic substances as compounding ingredients
    • C08K3/02—Elements
    • C08K3/04—Carbon
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
    • H01B1/00—Conductors or conductive bodies characterised by the conductive materials; Selection of materials as conductors
    • H01B1/20—Conductive material dispersed in non-conductive organic material
    • H01B1/24—Conductive material dispersed in non-conductive organic material the conductive material comprising carbon-silicon compounds, carbon or silicon
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L23/00—Details of semiconductor or other solid state devices
    • H01L23/58—Structural electrical arrangements for semiconductor devices not otherwise provided for, e.g. in combination with batteries
    • H01L23/60—Protection against electrostatic charges or discharges, e.g. Faraday shields
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K9/00—Screening of apparatus or components against electric or magnetic fields
    • H05K9/0073—Shielding materials
    • H05K9/0079—Electrostatic discharge protection, e.g. ESD treated surface for rapid dissipation of charges
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2307/00—Properties of the layers or laminate
    • B32B2307/20—Properties of the layers or laminate having particular electrical or magnetic properties, e.g. piezoelectric
    • B32B2307/21—Anti-static
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2307/00—Properties of the layers or laminate
    • B32B2307/30—Properties of the layers or laminate having particular thermal properties
    • B32B2307/31—Heat sealable
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2307/00—Properties of the layers or laminate
    • B32B2307/70—Other properties
    • B32B2307/714—Inert, i.e. inert to chemical degradation, corrosion
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2553/00—Packaging equipment or accessories not otherwise provided for
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
    • H01L2924/0001—Technical content checked by a classifier
    • H01L2924/0002—Not covered by any one of groups H01L24/00, H01L24/00 and H01L2224/00

Definitions

  • This invention relates to composites useful as electrostatic-dissipative, flexible barrier materials.
  • An aluminum foil moisture barrier, a heat-sealable carbon- filled polyethylene inner layer and a nonwoven protective outer layer are laminated together to form the Mondano packaging material.
  • the carbon-filled polyethylene inner layer will delaminate from the aluminum foil and absorb oil when contacted by oil. Additionally, excessive carbon will contaminate the parts enclosed in the package by carbon transfer and will degrade the heat seal seam strength if the layer contains carbon sufficient to achieve static-dissipative electrical surface resistivity of between 10 5 and 10 12 ohms per square. If the carbon loading in the polyethylene is reduced to obtain sufficient heat seal seam strength, the surface resistivity exceeds 10 12 ohms per square and the inner surface of the package is no longer static-dissipative.
  • an oil-resistant, heat sealable, humidity insensitive, electrostatic- dissipative material for packaging electronic devices and systems. It is an object of the invention to provide composites useful as heat-sealable, oil- resistant, low contamination, humidity insensitive, electrostatic-dissipative, flexible materials for packaging electrostatic discharge sensitive (ESDS) items such as microcircuits, sensitive semiconductor devices, sensitive resistors and associated higher assemblies.
  • ESDS electrostatic discharge sensitive
  • the invention relates to an electrically dissipative composite free of any blowing agent and consisting essentially of 97.5-95.5 wt % ionically cross-linked thermoplastic polymer and 2.5-4.5 wt % electroconductive carbon powder having a surface area of 1000-1500 m 2 /gm and a pore volume of 480-510 ml/100 gm.
  • the invention relates to an electrically dissipative package comprising a continuous, heat-sealable, flexible sheet of the above composite and optionally, a continuous layer of metal foil. In packages comprising a composite layer and a metal foil layer, the composite layer is adhered to the face of the metal foil layer that constitutes the inner surface of the package.
  • Ionically cross-linked thermoplastic polymers or ionomers are the substrate polymer used in this invention.
  • Preferred ionomers are ethylene organic acid copolymers partly neutralized with metallic ions such as potassium, lithium, sodium and zinc.
  • Particularly preferred ionomers are disclosed by Rees in U.S. Patent 3,264,272 and sold under the name Surlyn® by E. I. du Pont de Nemours and Company (Wilmington, DE) .
  • the electroconductive carbon powder used in the invention has a surface area of 1000-1500 m 2 /gm and a pore volume of 480-510 ml/100 gm.
  • the carbon powder has a surface area of about 1250 m 2 /gm and a pore volume of about 495 ml/100 gm.
  • Ketjenblack® EC600JD marketed by Akzo Chemie America (Chicago, IL) .
  • a carbon weight percent in the composite of less than 5 likewise has a surface resistivity greater than the 10 5 to lO 1 ⁇ ohms per square range.
  • an ionomer resin is compounded with 2.5-4.5 wt % of the carbon powder of this invention, particularly Ketjenblack® EC600 D
  • the two components work together to enable better control of the surface resistivity of the final-blend non-foamed film (e.g., 0.5 mil-5 mils) to within the static dissipative range (e.g., 10 5 to 10 12 ohms per square, more preferably 10 ⁇ to lO 1 ⁇ ohms per square at or below an ambient humidity of 12%) .
  • Carbon particle emission and transfer when rubbed against a clean surface is also substantially reduced. It was surprising that the ionomer/carbon compositions of the invention had such advantageous properties in the absence of element
  • the ionomer resin and carbon powder can be compounded by blending with a twin-screw extruder, a continuous mixer, or a batch mixer to achieve thorough mixing at a melt temperature of 160°-195°C.
  • a low blending melt temperature tends to yield poor dispersion of carbon into the ionomer resin resulting in slightly higher volume resistivity.
  • the melt index of the ionomer resin should be selected so that the melt index of the blended resin/carbon falls in the range of 1-20 decigrams/min.
  • Monolayer packaging material comprising a resin and carbon powder film can be produced by extruding a resin/carbon blend into a film.
  • the blend is extruded at a melt temperature of 180°-240°C.
  • Extrusion at melt temperatures higher than 240°C can overheat the carbon particles causing blisters or streaks in the film surface.
  • Extrusion at temperatures lower than 180°C produces films having unsatisfactorily high electrical resistivities.
  • the resultant film has oil resistance, humidity insensitivity, low contamination, permanent electrostatic-dissipative functional performance and superior heat-sealability.
  • Perfect electrostatic dissipative functional performance means that films of this invention do not lose their static dissipative performance, as compared to films which have volatile organic antistatic additives.
  • Superior heat-sealability is characterized by a wider range of heat seal temperatures (e.g., 160°-200°C) and a seam strength of greater than 1590 grams/inch.
  • Multilayer packaging material can be produced by a number of different methods.
  • an intermediate or adhesive layer of ionomer resin is extruded at a melt temperature of 240°-300°C between an ionomer/carbon blend film and a metal foil or metal foil laminate using an extrusion laminator.
  • An extrusion melt temperature lower than 2 0°C will result in inadequate bond strength between the foil and the film.
  • An extrusion melt temperature above 300°C will cause resin degradation.
  • multilayer packaging material can be produced by laminating at a lamination interface temperature of 80°-160°C an ionomer/carbon film with an intermediate layer of ionomer film onto a surface of a metal foil or a metal foil laminate by passing the webs through a heated nip in a thermal laminator.
  • a lamination interface temperature of less than 80°C results in inadequate bond strength between the foil and the film.
  • a lamination interface temperature of greater than 160°C causes the preblended ionomer/carbon film to melt thereby deteriorating the surface resistivity of the film.
  • a third method produces multilayer packaging material by the sequential appplication of the ionomer adhesive layer and the ionomer/carbon blend composite.
  • An adhesive layer of the ionomer resin at a melt temperature of 240 - 300°C can be extruded directly on to a metal foil or metal foil laminate followed by the extrusion of a surface layer of ionomer/carbon blend composite at a melt temperature of 180 - 240°C.
  • multilayer packaging material can be produced by coextruding a coating of ionomer/carbon blend composite with an adhesive layer of ionomer resin directly on to a metal foil or metal foil laminate, using sufficient temperature and pressure to adhere the coating without degrading the surface resistivity of the resultant laminate.
  • multilayer packaging material can be produced by extrusion coating an ionomer/carbon blend composite directly on to a metal foil or metal foil laminate, using sufficient temperature and pressure to adhere the composite directly to the foil without the need for an intermediate or adhesive layer.
  • a metal foil laminate comprises a metal foil layer having secured to one face a layer of protective material which ultimately forms the outside of the package.
  • the layer of protective material may be any material suitable for protecting the metal layer and giving strength and body to the packaging laminate. Examples of protective material include woven, knitted, extruded or nonwoven sheets such as Kraft paper, nylon films, polyester films, and coated and uncoated bonded nonwoven sheets of polyolefin film-fibrils of the type disclosed in
  • Tyvek® bonded nonwoven polyethylene film-fibril sheets are lightweight and have outstanding mechanical properties such as puncture and tear strength, while also having good tolerance to ordinary weather conditions. Ionomer/carbon monolayer films and multilayer laminates can be used as a wrapping material or formed into packages, such as bags.
  • two sheets of the multilayer laminate having their respective ionomer/carbon layers facing and contacting each other can be heat sealed together to form a bag by applying heat and pressure along their marginal edges using any of the procedures well known in the art.
  • the resultant bag has an ionomer/carbon blend film inner surface that exhibits a broad heat-seal temperature window, high heat seal seam strength, oil resistance, humidity insensitivity, low contamination, and permanent electrostatic- dissipative functional performance.
  • Ketjenblack® EC600JD Seven percent by weight of Ketjenblack® EC600JD was melt-blended into 93% by weight of Surlyn® 1702 resin (a zinc ionomer derived from ethylene/methacrylic acid copolymers partially neutralized with zinc cations, having a melt index 16.2 decigrams/min., a density of 0.94 gms/cc, and melting point of 86°C (manufactured by E. I. du Pont de Nemours & Company, Inc., Wilmington, DE) , with a 28 millimeter twin-screw extruder (Werner & Pfleiderer,
  • the pellets were subsequently melt-extruded in a 1" Wayne table-top single-screw extruder (Wayne Machine and Die Company, Totowa, NJ) and cast into a film with a 6" horizontal film die. The cast film was quenched on a 3- roll finisher. The resultant film was tested for surface resistivity per ASTM D-257 at 12% ambient relative humidity.
  • Packaging laminates with a carbon/ionomer blend inner surface were made by laminating a carbon/ionomer blend film with an intermediate layer of an ionomer film onto the inner surface of an aluminum foil of an EMI shielding and moisture-barrier laminate.
  • An Inta-Roto 24" film-laminator (Inta-Roto Machine Company, Model LCL18, Richmond, VA) was used for thermal lamination.
  • a 2-mil MD230 O-dry (“A" wettable) aluminum foil made by Reynolds Metals Company, Richmond, VA was first preheated in the drying tunnel at 100°F (37.8°C).
  • the preheated foil was further heated by the chrome- surface hot-roll (heated by 190°F (87.8°C) circulating oil) and laminated with a 2-mil ionomeric film manufactured by Flex-0-glass, Inc., Chicago, Illinois prepared from Surlyn® 1605 ionomer resin (a sodium ionomer derived from ethylene/methacrylic acid copolymers partially neurtralized with sodium cations, having a melt index of 2.8 decigrams/min., a density of 0.95 gms/cc, and melting point of 86 C, manufactured by E. I. du Pont de Nemours & Co., Inc.
  • Surlyn® 1605 ionomer resin a sodium ionomer derived from ethylene/methacrylic acid copolymers partially neurtralized with sodium cations, having a melt index of 2.8 decigrams/min., a density of 0.95 gms/cc, and melting point of 86 C
  • the ionomer/foil laminate was fed through the laminator a second time and preheated in the drying tunnel at 100°F (37.8°C).
  • the preheated laminate was further heated by the chrome-surface hot-roll (heated by 190°F (87.8°C) circulating oil) with the foil side contacting the hot-roll and laminated with the carbon/ionomer blended film made in Example I on the Teflon®-covered rubber nip roll side.
  • the nip pressure used was 100 psi.
  • the laminate was then chilled (45°F (7.2 C) chill roll temperature) and wound-up.
  • the film and laminate speed was 25 feet per minute. The web tension was again kept low.
  • the laminates were tested for Surface Resistivity at 12% ambient relative humidity (ASTM D-257), Oil- Resistance (FTM 3015.1), and Heat Seal Strength.
  • the resultant inner surface of the film/aluminum foil laminates were static dissipative as shown by their surface resistivity values which were within the range of 10 ⁇ to 10 ⁇ 2 ohms/square. Further, the laminates demonstrate good oil resistance and have very good heat-seal seam strength ( i.e., all having values much greater than the industry standard of 1,590 grams/inch which is also required to meet Military Specification MIL-B-81705C (25 January 1989)). Contamination properties of the film were tested by rubbing the inner surface of the resultant laminate to a white Xerox paper surface showed no carbon transfer.
  • the hot feed extruder portion received the continuous discharge from the mixer and extruded each blend through a die into four 1/8-inch diameter strands. The four strands were subsequently water-quenched and pelletized. Mixing conditions are listed in the table below. Mixing Conditions
  • the pellets were subsequently melt extruded in a 1" Wayne table-top single screw extruder (Wayne Machine and Die Company, Totowa, NJ) and cast into a film with a 6" horizontal film die.
  • the cast film was quenched on a 3-roll finisher. Film casting conditions are listed in the table below:
  • the surface resistivity was measured using ASTM D-257 after the resultant films were conditioned for 24 hours in 5%, 12%, and 50% ambient relative humidity at room temperature (22.2°C).
  • Blend #IIIB 3.5% Ketjenblack® EC600JD and 96.5% Surlyn® 1702
  • the pellets of Blend #IIIB were melt-extruded with a 2.5" single screw extruder, (manufactured by Sterling Extruder Corporation, Linden, NJ) and cast into a 60-inch wide, and 2- il thick film with a coat-hanger-design film die.
  • the film takeoff and windup system was manufactured by Johnson Plastics Machinery, Chippewa Falls, WI. Extrusion conditions are as follows:
  • Example IV The center 23 inch portion of the film of Example IV was slit into a new 23 inch wide film roll.
  • Fresh resin of Surlyn® 1702 was melt extruded into 19-inch wide, 1.0 mil thick adhesive layer between the 23 inch wide 2-mil thick Ketjenblack® EC600JD/Surlyn® 1702 blen film of Example IV on the water-cooled chilled roll side and a 24-inch wide, 2 mil thick O-dry surface aluminum foil on the nip-roll side.
  • the laminating conditions of the two 100- feet laminate samples made were:
  • the two laminate samples were edge-trimmed to produce a 19-inch width center.
  • Three 4-inch diameter circular samples (left-edge, center, and right-edge) were taken from each of the two laminate samples. After conditioning for 24 hours in a 12% ambient relative humidity at room temperature, the surface resistivity of the carbon/ionomer blend film surface of the six 4-inch diameter circular laminate samples were measured.
  • the surface resistivity was between 10 6 * 7 to 10 9 * 1 ohms/square before lamination; and between 10 7 « ° to 10 8 * 4 ohms/square after extrusion lamination. These results showed that the surface resistivity was not affected significantly by the extrusion lamination condition used in this experiment. They are all within the static dissipative range of 10 5 to 10 12 ohms/square.
  • Heat seal seam strength of the two laminate samples were measured to show the superior heat seal performance of the film-laminate of this invention.
  • the sealing conditions are 4 second dwell time, bar temperature as noted, 40 psi bar pressure, 1-inch wide hot bar.
  • a heat-seal seam strength of 1,590 grams/inch is considered good by industrial packaging standards and is required by Military Specifications (MIL-B-81705C (25 Jan 1989)). These data show that film-laminates of this invention have a very wide window (200 to 400 degrees F or 93.3 to 204.4 degrees C) of heat seal temperature and a very high heat seal seam strength.
  • An extrusion-lamination temperature of 475 degrees F (246.1 degrees C) provided sufficient adhesion to pass the Federal Test Method 3015 ASTM #3 Oil Delamination Test when one-mil thick Surlyn® 1702 is used as the adhesive layer between carbon/ionomer blend film and aluminum foil.
  • the lower lamination temperature of 218.3 °C used to produce laminate sample V-B provided inadequate bond strength between the foil and adhesive layer.

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Physics & Mathematics (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Power Engineering (AREA)
  • Dispersion Chemistry (AREA)
  • Mechanical Engineering (AREA)
  • Polymers & Plastics (AREA)
  • Organic Chemistry (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Health & Medical Sciences (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • Medicinal Chemistry (AREA)
  • Textile Engineering (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
  • General Physics & Mathematics (AREA)
  • Computer Hardware Design (AREA)
  • Laminated Bodies (AREA)
  • Wrappers (AREA)
  • Extrusion Moulding Of Plastics Or The Like (AREA)

Abstract

L'invention se rapporte à un composite d'emballage dissipant l'électricité statique, résistant à l'huile et thermoscellable, qui se compose essentiellement de 95,5 à 97,5 % en poids d'ionomères et de 4,5 à 2,5 % en poids de poudre de carbone électroconductrice ayant une surface de 1000 à 1500 m2/g et un volume de pore de 480 à 510 ml/100 g. Le composite est utile dans les emballages de protection de composants et d'ensembles électroniques sensibles, électrostatiques.The invention relates to a static-dissipating, oil-resistant and heat-sealable packaging composite which consists essentially of 95.5 to 97.5% by weight of ionomers and 4.5 to 2 , 5% by weight of electroconductive carbon powder having a surface of 1000 to 1500 m2 / g and a pore volume of 480 to 510 ml / 100 g. The composite is useful in protective packaging for sensitive, electrostatic electronic components and assemblies.

Description

ELECTRICALLY DISSIPATI E COMPOSITE
CROSS REFERENCE TO RELATED APPLICATION
This application is a continuation-in-part of copending U.S. Application, Serial No. 07/649,109, filed February 1, 1991.
FIELD PF THE INVENTION
This invention relates to composites useful as electrostatic-dissipative, flexible barrier materials.
BACKGROUND OF THE INVENTION
Functional failures or manufacturability impairments of electronic components or assemblies are often attributable to damage caused by electrostatic discharge, electrostatic field force, electromagnetic radiation, moisture, oil and/or corrosive gases encountered during storage, shipment and/or processing. The problem has increased in severity in recent years, and will continue to worsen. The current trend in electronic devices and systems is towards miniaturization like VLSI (Very Large Scale Integration) chip technology. These smaller devices are more sensitive to corrosion and electrostatic damage. Yet, the demand for greater reliability is increasing. Accordingly, protection of electronic devices and systems is needed to preserve their functionality during storage, shipment and processing. A packaging material for electrostatic discharge, electromagnetic radiation, and moisture-proof protection is disclosed by Mondano in U.S. Patent 3,572,499. An aluminum foil moisture barrier, a heat-sealable carbon- filled polyethylene inner layer and a nonwoven protective outer layer are laminated together to form the Mondano packaging material. The carbon-filled polyethylene inner layer, however, will delaminate from the aluminum foil and absorb oil when contacted by oil. Additionally, excessive carbon will contaminate the parts enclosed in the package by carbon transfer and will degrade the heat seal seam strength if the layer contains carbon sufficient to achieve static-dissipative electrical surface resistivity of between 105 and 1012 ohms per square. If the carbon loading in the polyethylene is reduced to obtain sufficient heat seal seam strength, the surface resistivity exceeds 1012 ohms per square and the inner surface of the package is no longer static-dissipative. Thus, there is a need for an oil-resistant, heat sealable, humidity insensitive, electrostatic- dissipative material for packaging electronic devices and systems. It is an object of the invention to provide composites useful as heat-sealable, oil- resistant, low contamination, humidity insensitive, electrostatic-dissipative, flexible materials for packaging electrostatic discharge sensitive (ESDS) items such as microcircuits, sensitive semiconductor devices, sensitive resistors and associated higher assemblies.
SUMMARY OF THE INVENTION
The invention relates to an electrically dissipative composite free of any blowing agent and consisting essentially of 97.5-95.5 wt % ionically cross-linked thermoplastic polymer and 2.5-4.5 wt % electroconductive carbon powder having a surface area of 1000-1500 m2/gm and a pore volume of 480-510 ml/100 gm. In a further aspect, the invention relates to an electrically dissipative package comprising a continuous, heat-sealable, flexible sheet of the above composite and optionally, a continuous layer of metal foil. In packages comprising a composite layer and a metal foil layer, the composite layer is adhered to the face of the metal foil layer that constitutes the inner surface of the package.
DETAILED DESCRIPTION OF THE INVENTION
Ionically cross-linked thermoplastic polymers or ionomers are the substrate polymer used in this invention. Preferred ionomers are ethylene organic acid copolymers partly neutralized with metallic ions such as potassium, lithium, sodium and zinc. Particularly preferred ionomers are disclosed by Rees in U.S. Patent 3,264,272 and sold under the name Surlyn® by E. I. du Pont de Nemours and Company (Wilmington, DE) . These Rees ionomers comprise a polymer of an α-olefin having the general formula RCH=CH2 where R is a radical selected from the class consisting of hydrogen and alkyl radicals having from 1 to 8 carbon atoms, the olefin content of said polymer being at least 50 mol percent based on the polymer, and an α,β-ethylenically unsaturated carboxylic acid having 1 or 2 carboxylic acid groups, the acid monomer content of said polymer being from 0.2 to 25 mol percent based on the polymer, said carboxylic-acid containing polymer containing uniformly distributed throughout the polymer, one or more metal ions having ionized valences of 1 to 3 inclusive where the acid comonomer is monocarboxylic, and an ionized valence of one where the acid comonomer is dicarboxylic, the quantity of the metal ion being sufficient to neutralize at least 10 percent of the carboxylic acid.
The electroconductive carbon powder used in the invention has a surface area of 1000-1500 m2/gm and a pore volume of 480-510 ml/100 gm. Preferably, the carbon powder has a surface area of about 1250 m2/gm and a pore volume of about 495 ml/100 gm. Particularly preferred is Ketjenblack® EC600JD, marketed by Akzo Chemie America (Chicago, IL) .
When the weight percent loading-.of the carbon powders used in this invention falls below 5 in common base polymers such as EVA (ethylene-vinyl acetate) , ABS (acrylonitrile-butadiene-styrene) , HDPE (high density polyethylene) , LDPE (low density polyethylene) , and SBR (styrene-rubber) , the electrical volume resistivity rises steeply. Therefore, these carbon powders have not been used in static-dissipative thermoplastic materials which require a thin film (i.e., 0.5 mil-5 mils) surface resistivity in the range of 10s to 1012 ohms per square. Also, when a blowing agent is present in the composite, the final structure being a foam, a carbon weight percent in the composite of less than 5 likewise has a surface resistivity greater than the 105 to lO1^ ohms per square range. Nonetheless, applicants have found that when an ionomer resin is compounded with 2.5-4.5 wt % of the carbon powder of this invention, particularly Ketjenblack® EC600 D, the two components work together to enable better control of the surface resistivity of the final-blend non-foamed film (e.g., 0.5 mil-5 mils) to within the static dissipative range (e.g., 105 to 1012 ohms per square, more preferably 10^ to lO1^ ohms per square at or below an ambient humidity of 12%) . Carbon particle emission and transfer when rubbed against a clean surface is also substantially reduced. It was surprising that the ionomer/carbon compositions of the invention had such advantageous properties in the absence of elemental metal, such as copper.
The ionomer resin and carbon powder can be compounded by blending with a twin-screw extruder, a continuous mixer, or a batch mixer to achieve thorough mixing at a melt temperature of 160°-195°C. A low blending melt temperature tends to yield poor dispersion of carbon into the ionomer resin resulting in slightly higher volume resistivity. The melt index of the ionomer resin should be selected so that the melt index of the blended resin/carbon falls in the range of 1-20 decigrams/min.
Monolayer packaging material comprising a resin and carbon powder film can be produced by extruding a resin/carbon blend into a film. Typically, the blend is extruded at a melt temperature of 180°-240°C. Extrusion at melt temperatures higher than 240°C can overheat the carbon particles causing blisters or streaks in the film surface. Extrusion at temperatures lower than 180°C produces films having unsatisfactorily high electrical resistivities. The resultant film has oil resistance, humidity insensitivity, low contamination, permanent electrostatic-dissipative functional performance and superior heat-sealability. "Permanent electrostatic dissipative functional performance" means that films of this invention do not lose their static dissipative performance, as compared to films which have volatile organic antistatic additives. Superior heat-sealability is characterized by a wider range of heat seal temperatures (e.g., 160°-200°C) and a seam strength of greater than 1590 grams/inch.
Multilayer packaging material can be produced by a number of different methods. In one method an intermediate or adhesive layer of ionomer resin is extruded at a melt temperature of 240°-300°C between an ionomer/carbon blend film and a metal foil or metal foil laminate using an extrusion laminator. An extrusion melt temperature lower than 2 0°C will result in inadequate bond strength between the foil and the film. An extrusion melt temperature above 300°C will cause resin degradation.
In another method, multilayer packaging material can be produced by laminating at a lamination interface temperature of 80°-160°C an ionomer/carbon film with an intermediate layer of ionomer film onto a surface of a metal foil or a metal foil laminate by passing the webs through a heated nip in a thermal laminator. A lamination interface temperature of less than 80°C results in inadequate bond strength between the foil and the film. A lamination interface temperature of greater than 160°C causes the preblended ionomer/carbon film to melt thereby deteriorating the surface resistivity of the film. A third method produces multilayer packaging material by the sequential appplication of the ionomer adhesive layer and the ionomer/carbon blend composite. An adhesive layer of the ionomer resin at a melt temperature of 240 - 300°C can be extruded directly on to a metal foil or metal foil laminate followed by the extrusion of a surface layer of ionomer/carbon blend composite at a melt temperature of 180 - 240°C.
In a fourth method, multilayer packaging material can be produced by coextruding a coating of ionomer/carbon blend composite with an adhesive layer of ionomer resin directly on to a metal foil or metal foil laminate, using sufficient temperature and pressure to adhere the coating without degrading the surface resistivity of the resultant laminate.
And in yet another method, multilayer packaging material can be produced by extrusion coating an ionomer/carbon blend composite directly on to a metal foil or metal foil laminate, using sufficient temperature and pressure to adhere the composite directly to the foil without the need for an intermediate or adhesive layer.
The metal foil imparts to the packaging laminate EMI (electromagnetic interference) shielding and moisture vapor barrier properties. A metal foil laminate comprises a metal foil layer having secured to one face a layer of protective material which ultimately forms the outside of the package. The layer of protective material may be any material suitable for protecting the metal layer and giving strength and body to the packaging laminate. Examples of protective material include woven, knitted, extruded or nonwoven sheets such as Kraft paper, nylon films, polyester films, and coated and uncoated bonded nonwoven sheets of polyolefin film-fibrils of the type disclosed in
Steuber, U.S. 3,169,899. A commercial polyethylene film-fibril sheet product sold by E.I du Pont de Nemours and Company (Wilmington, DE) under the name Tyvek®, organic anti-stat coated Tyvek®, and vacuum metallized Tyvek® are particularly suitable. Tyvek® bonded nonwoven polyethylene film-fibril sheets are lightweight and have outstanding mechanical properties such as puncture and tear strength, while also having good tolerance to ordinary weather conditions. Ionomer/carbon monolayer films and multilayer laminates can be used as a wrapping material or formed into packages, such as bags. For example, two sheets of the multilayer laminate having their respective ionomer/carbon layers facing and contacting each other can be heat sealed together to form a bag by applying heat and pressure along their marginal edges using any of the procedures well known in the art. In addition to the EMI-shielding and moisture barrier properties of the metal foil layer, the resultant bag has an ionomer/carbon blend film inner surface that exhibits a broad heat-seal temperature window, high heat seal seam strength, oil resistance, humidity insensitivity, low contamination, and permanent electrostatic- dissipative functional performance. The following examples further illustrate the production and performance of the composites and packaging material of the invention. Unless otherwise specified, amounts are in weight percent. Properties measured and measurement methods are listed below:
Pro er y Measurement Method
Surface Resistivity ASTM D-257
Sample films are conditioned in a glove box maintained at specified ambient relative humidities at room temperature for 24 hours before measurement. Heat-Seal Strength 1" Flat Bar Sealer
400°F (204°C) bar temperature. 4-seconds dwell time
40 psi bar pressure The seam strength was measured with an Instron. The reported value is the average of three measurements.
Oil-Resistance Federal Test Method 3015.1 and Military Specification MIL-B-81705C of 25 January 1989
Melt Index ASTM D-1238. The melt-flow- index at 190°C is reported.
QMPt.R__TIVE EXAMPLE
Seven percent by weight of Ketjenblack® EC600JD was melt-blended into 93% by weight of Surlyn® 1702 resin (a zinc ionomer derived from ethylene/methacrylic acid copolymers partially neutralized with zinc cations, having a melt index 16.2 decigrams/min., a density of 0.94 gms/cc, and melting point of 86°C (manufactured by E. I. du Pont de Nemours & Company, Inc., Wilmington, DE) , with a 28 millimeter twin-screw extruder (Werner & Pfleiderer,
Stuttgart, Germany) at a melt temperature of 191°C. The melt-blend was extruded into a 1/8" diameter strand and water-quenched and pelletized (melt-index •= 0.3 decigrams/min.) . The pellets were subsequently melt-extruded in a 1" Wayne table-top single-screw extruder (Wayne Machine and Die Company, Totowa, NJ) and cast into a film with a 6" horizontal film die. The cast film was quenched on a 3- roll finisher. The resultant film was tested for surface resistivity per ASTM D-257 at 12% ambient relative humidity.
1
1
2
speed were adjusted to control the resultant film
25 thickness. The resultant films were tested for Surface
the resultant film to a white Xerox paper surface and the films showed no carbon transfer.
EXAMPLE I I
Packaging laminates with a carbon/ionomer blend inner surface were made by laminating a carbon/ionomer blend film with an intermediate layer of an ionomer film onto the inner surface of an aluminum foil of an EMI shielding and moisture-barrier laminate. An Inta-Roto 24" film-laminator (Inta-Roto Machine Company, Model LCL18, Richmond, VA) was used for thermal lamination. A 2-mil MD230 O-dry ("A" wettable) aluminum foil (made by Reynolds Metals Company, Richmond, VA) was first preheated in the drying tunnel at 100°F (37.8°C). The preheated foil was further heated by the chrome- surface hot-roll (heated by 190°F (87.8°C) circulating oil) and laminated with a 2-mil ionomeric film manufactured by Flex-0-glass, Inc., Chicago, Illinois prepared from Surlyn® 1605 ionomer resin (a sodium ionomer derived from ethylene/methacrylic acid copolymers partially neurtralized with sodium cations, having a melt index of 2.8 decigrams/min., a density of 0.95 gms/cc, and melting point of 86 C, manufactured by E. I. du Pont de Nemours & Co., Inc. Wilmington, DE) on the Teflon®-covered rubber nip roll side at the combining roll section. The nip pressure used was 100 psi. The laminate was then chilled (45 F (7.2 C) chill roll temperature) and wound-up. The film and laminate speed was 25 feet per minute. The web tension was kept low to prevent film stretching.
The ionomer/foil laminate was fed through the laminator a second time and preheated in the drying tunnel at 100°F (37.8°C). The preheated laminate was further heated by the chrome-surface hot-roll (heated by 190°F (87.8°C) circulating oil) with the foil side contacting the hot-roll and laminated with the carbon/ionomer blended film made in Example I on the Teflon®-covered rubber nip roll side. The nip pressure used was 100 psi. The laminate was then chilled (45°F (7.2 C) chill roll temperature) and wound-up. The film and laminate speed was 25 feet per minute. The web tension was again kept low.
The laminates were tested for Surface Resistivity at 12% ambient relative humidity (ASTM D-257), Oil- Resistance (FTM 3015.1), and Heat Seal Strength.
After-Lamination
The resultant inner surface of the film/aluminum foil laminates were static dissipative as shown by their surface resistivity values which were within the range of 10^ to 10^2 ohms/square. Further, the laminates demonstrate good oil resistance and have very good heat-seal seam strength ( i.e., all having values much greater than the industry standard of 1,590 grams/inch which is also required to meet Military Specification MIL-B-81705C (25 January 1989)). Contamination properties of the film were tested by rubbing the inner surface of the resultant laminate to a white Xerox paper surface showed no carbon transfer.
EXAMPLE III
Three ionomer/Ketjenblack® EC600JD carbon blends (3.0 % carbon/97 % Surlyn® 1702, 3.5 % carbon/96.5 % Surlyn® 1702, and 4.0 % carbon/96 % Surlyn® 1702) were made by feeding
Ketjenblack® EC600JD volumetrically from a K-Tron Twin-Screw Feeder (K-Tron Corporation, Pitman, NJ) and feeding Surlyn® 1702 from a K-Tron Weight-In-Loss Single Screw Feeder (K-Tron Corporation, Pitman, NJ) into the continuous mixer portion of a Farrel Compact Processor (using #7 blades) (Model CP-23
Farrel Machine Company, Ansonia, CT) . The hot feed extruder portion received the continuous discharge from the mixer and extruded each blend through a die into four 1/8-inch diameter strands. The four strands were subsequently water-quenched and pelletized. Mixing conditions are listed in the table below. Mixing Conditions
The pellets were subsequently melt extruded in a 1" Wayne table-top single screw extruder (Wayne Machine and Die Company, Totowa, NJ) and cast into a film with a 6" horizontal film die. The cast film was quenched on a 3-roll finisher. Film casting conditions are listed in the table below:
The surface resistivity was measured using ASTM D-257 after the resultant films were conditioned for 24 hours in 5%, 12%, and 50% ambient relative humidity at room temperature (22.2°C).
The surface resistivity of the static dissipative film of this invention did not change significantly with ambient relative humidity. Thus, these materials will function over a wide range of ambient relative humidity (i.e., they are humidity insensitive). EXAMPLE IV
The pellets of Blend #IIIB (3.5% Ketjenblack® EC600JD and 96.5% Surlyn® 1702) were melt-extruded with a 2.5" single screw extruder, (manufactured by Sterling Extruder Corporation, Linden, NJ) and cast into a 60-inch wide, and 2- il thick film with a coat-hanger-design film die. The film takeoff and windup system was manufactured by Johnson Plastics Machinery, Chippewa Falls, WI. Extrusion conditions are as follows:
EXTRUDER-ZONES DIE-ZONES TEMP (°C) TEMP (°C)
1 2 3 4 1 2 3 4 5 198198204200185182181185183180 180 30 10 65 60
Nine 4-inch diameter circular samples were taken across the 60 inch width of the last feet of the film. The nine 4-inch diameter circular samples were conditioned 24 hours at 12% ambient relative humidity and room temperature and their surface resistivity and film thickness profiles were measured using the test methods stated above.
POSITIONS OF THE CENTER OF 4" DIA SAMPLES FROM LEFT 4" 11.5" 18" 25" 31" 37" 43.5" 49" 54" LOG (OF)
SURFACE
RESISTIVITY
IN OHMS/SQUARE .
SIDE #1 13.1 14.3 8.6 6.9
SIDE #2 15.0 15.9 8.3 6.7
THICKNESS 2.0 2.4 2.2 2.3 (mil)
The center 23-inch width portion of the film was static dissipative as shown by the surface resistivity values which were between lO***7 to lO^' ohms/square after 24 hour conditioning in a 12% ambient relative humidity at room temperature. EXAMPLE V '
The center 23 inch portion of the film of Example IV was slit into a new 23 inch wide film roll. A 24-inch wide flat coextrusion line custom built by SANO Inc (A subsidiary of Cincinnati Milacron, Inc. Cincinnati, OH) was used for extrusion-lamination. For this experiment, only one layer- slot of the multilayer coextrusion die was left open.
Fresh resin of Surlyn® 1702 was melt extruded into 19-inch wide, 1.0 mil thick adhesive layer between the 23 inch wide 2-mil thick Ketjenblack® EC600JD/Surlyn® 1702 blen film of Example IV on the water-cooled chilled roll side and a 24-inch wide, 2 mil thick O-dry surface aluminum foil on the nip-roll side. The laminating conditions of the two 100- feet laminate samples made were:
The two laminate samples were edge-trimmed to produce a 19-inch width center. Three 4-inch diameter circular samples (left-edge, center, and right-edge) were taken from each of the two laminate samples. After conditioning for 24 hours in a 12% ambient relative humidity at room temperature, the surface resistivity of the carbon/ionomer blend film surface of the six 4-inch diameter circular laminate samples were measured. LAMINATE LOG OF SURFACE RESISTIVITY IN OHMS/SQUARE SAMPLE # LEFT-EDGE CENTER RIGHT-EDGE
V-A 8.4 7.2 7.7
V-B 7.2 7.0 8.3
The surface resistivity was between 106*7 to 109*1 ohms/square before lamination; and between 107«° to 108*4 ohms/square after extrusion lamination. These results showed that the surface resistivity was not affected significantly by the extrusion lamination condition used in this experiment. They are all within the static dissipative range of 105 to 1012 ohms/square.
Heat seal seam strength of the two laminate samples were measured to show the superior heat seal performance of the film-laminate of this invention. The sealing conditions are 4 second dwell time, bar temperature as noted, 40 psi bar pressure, 1-inch wide hot bar.
A heat-seal seam strength of 1,590 grams/inch is considered good by industrial packaging standards and is required by Military Specifications (MIL-B-81705C (25 Jan 1989)). These data show that film-laminates of this invention have a very wide window (200 to 400 degrees F or 93.3 to 204.4 degrees C) of heat seal temperature and a very high heat seal seam strength.
The resistance to ASTM #3 oil of the two laminate samples were also tested in accordance with the Federal Test Method 3015. The results are shown below:
LAMINATE Lamination Melt Pass or Observations
SAMPLE # Temperature Fail
V^A 475F (246.1C) Pass
V-B 425F (218.3C) Fail Blisters
An extrusion-lamination temperature of 475 degrees F (246.1 degrees C) provided sufficient adhesion to pass the Federal Test Method 3015 ASTM #3 Oil Delamination Test when one-mil thick Surlyn® 1702 is used as the adhesive layer between carbon/ionomer blend film and aluminum foil. The lower lamination temperature of 218.3 °C used to produce laminate sample V-B provided inadequate bond strength between the foil and adhesive layer.

Claims

CLAIMS We claim:
1. An electrically dissipative composite consisting essentially of 97.5-95.5 wt % ionomer, and 2.5-4.5 wt % electroconductive carbon powder having a surface area of 1000-1500 m /gm and a pore volume of 480-510 ml/100 gm.
2. The composite of claim 1 wherein the ionomer comprises ethylene-acid polymer partly neutralized with metallic ions.
3. The composite of claim 2 wherein the carbon powder has a surface area of about 1250 m2/gm and a pore volume of about 495 ml/100 gm.
4. An electrically dissipative package for protecting electrostatic-discharge sensitive items, said package comprising a continuous, heat-sealable, flexible sheet of the composite of claim 1.
5. An electrically dissipative package for protecting electrostatic-discharge sensitive items, said package comprising a continuous, heat-sealable, flexible sheet of the composite of claim 2.
6. An electrically dissipative package for protecting electrostatic-discharge sensitive items, said package comprising a continuous, heat-sealable, flexible sheet of the composite of claim 3.
7. An electrically dissipative package for protecting electrostatic-discharge sensitive items, said package comprising a continuous layer of metal foil and a heat-sealable, flexible sheet of claim 1 adhered to one face of the metal foil layer, which face constitutes the inside of the package.
8. An electrically dissipative package for protecting electrostatic-discharge sensitive items, said package comprising a continuous layer of metal foil and a heat-sealable, flexible sheet of claim 2 adhered to one face of the metal foil layer, which face constitutes the inside of the package.
9. An electrically dissipative package for protecting electrostatic-discharge sensitive items, said package comprising a continuous layer of metal foil and a heat-sealable, flexible sheet of claim 3 adhered to one face of the metal foil layer, which face constitutes the inside of the package.
10. An electrically dissipative package for protecting electrostatic-discharge sensitive items, said package comprising a continuous protective layer of a bonded nonwoven polyethylene film-fibril and a heat- sealable, flexible sheet of claim 1 adhered to one face of the protective layer, which face constitutes the inside of the package.
EP92918535A 1992-02-03 1992-08-20 Electrically dissipative composite Withdrawn EP0625171A1 (en)

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US9200830 1992-02-03
US873178 1992-04-24
US07/873,178 US5376446A (en) 1991-02-01 1992-04-24 Electrically dissipative composite
US920830 1992-07-28
PCT/US1992/006805 WO1993015142A1 (en) 1992-02-03 1992-08-20 Electrically dissipative composite

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