Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J3/00—Processes of treating or compounding macromolecular substances
  • C08J3/20—Compounding polymers with additives, e.g. colouring
  • C08J3/22—Compounding polymers with additives, e.g. colouring using masterbatch techniques
  • C08J3/226—Compounding polymers with additives, e.g. colouring using masterbatch techniques using a polymer as a carrier
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C51/00—Shaping by thermoforming, i.e. shaping sheets or sheet like preforms after heating, e.g. shaping sheets in matched moulds or by deep-drawing; Apparatus therefor
  • B29C51/002—Shaping by thermoforming, i.e. shaping sheets or sheet like preforms after heating, e.g. shaping sheets in matched moulds or by deep-drawing; Apparatus therefor characterised by the choice of material
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J11/00—Recovery or working-up of waste materials
  • C08J11/04—Recovery or working-up of waste materials of polymers
  • C08J11/06—Recovery or working-up of waste materials of polymers without chemical reactions
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L23/00—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers
  • C08L23/02—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers not modified by chemical after-treatment
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L67/00—Compositions of polyesters obtained by reactions forming a carboxylic ester link in the main chain; Compositions of derivatives of such polymers
  • C08L67/02—Polyesters derived from dicarboxylic acids and dihydroxy compounds
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29K—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS OR TO MATERIALS FOR MOULDS, REINFORCEMENTS, FILLERS OR PREFORMED PARTS, e.g. INSERTS
  • B29K2067/00—Use of polyesters or derivatives thereof, as moulding material
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J2367/00—Characterised by the use of polyesters obtained by reactions forming a carboxylic ester link in the main chain; Derivatives of such polymers
  • C08J2367/02—Polyesters derived from dicarboxylic acids and dihydroxy compounds
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J2423/00—Characterised by the use of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Derivatives of such polymers
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
  • Y02P70/10—Greenhouse gas [GHG] capture, material saving, heat recovery or other energy efficient measures, e.g. motor control, characterised by manufacturing processes, e.g. for rolling metal or metal working
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
  • Y02W30/00—Technologies for solid waste management
  • Y02W30/50—Reuse, recycling or recovery technologies
  • Y02W30/62—Plastics recycling; Rubber recycling

Definitions

• This invention relates to a method of making a polyethylene terephthalate/polyolefin blend sheeting for use in thermoforming partially crystalline heat set articles.
• the invention describes a method for adding the antioxidant exclusively to the polyolefin prior to blending with the polyethylene terephthalate.
• the growing popularity of microwave ovens has created a general interest in production of lost cost, microwave transparent, disposable containers for packaging food.
• the precooked prepared food may be placed in the container and subsequently frozen.
• the consumer will finish cooking the frozen food package in a microwave oven or a conventional convection oven prior to its use.
• the requirements which this type of dual ovenable tray application places on the container to be utilized are many and varied. Firstly, the container must be capable of withstanding prolonged high temperature exposure without significant loss of impact strength or dimensional stability. Secondly, the container must maintain a uniform color and be resistant to any degradation which may alter the color during long term high temperature exposure in a microwave or conventional oven.
• 4,463,121 describes a method of manufacturing a partially crystalline polyester article consisting of a major component of polyethylene teraphthalate (PET) and a minor component of a polyolefin to produce an article which has a total crystallinity of about 10 to about 30%.
• PET polyethylene teraphthalate
• These articles are usable as containers and exhibit stable impact strength and dimensional stability due to the limitation on the degree of crystallinity achieved during thermoforming.
• This patent also teaches the desirability of adding from about 0.05 to about 2 weight percent of a heat stabilizer to the PET/polyolefin blend for the purpose of stabilizing the intrinsic viscosity of the article.
• U.S. Pat. No. 3,960,807 teaches a process for thermoforming articles from a composition having three essential components (1) a crystallizable polyester; (2) a crack stopping agent, preferably a polyolefin; (3) a nucleating agent.
• the process disclosed in this patent improved the impact resistant of the article and the rate of crystallization during thermoforming.
• An object of an aspect of this invention is to provide a method of manufacturing sheeting from polyethylene terephthalate and a polyolefin which is thermally stable during subsequent thermoforming operations on the sheeting.
• a derived benefit of the use of the method of this invention is the production of thin-walled articles or trays which resist discoloration or fingerprinting during high temperature thermal aging.
• An advantage of the invention is that a microwave or conventional oven tray manufactured from the method of this invention can withstand in excess of an hour at 200° C. with no discoloration, fingerprinting or substantial loss of intrinsic viscosity.
• a further advantage is that fractional levels of antioxidant will adequately protect the tray.
• Another aspect of the invention resides in a method of manufacturing a thermally stable, partially crystalline heat set, non-oriented article comprising the steps of:
• Yet another aspect of the invention is a method of manufacturing a recylable polyolefin modified polyethylene terephthalate sheet comprising the steps of:
• PET polyethylene terephthalate
• the polyethylene terephthalate polymer is obtained by known polymerization techniques from either terephthalate acid or its lower alkyl ester (dimethyl terephthalate) and ethylene glycol.
• the terephthalic acid or dimethyl terephthalate is esterified or transesterified and then polycondensed with ethylene glycol to a high molecular weight product.
• the polyester so produced should have an intrinsic viscosity ranging from about 0.65 to about 1.2 and preferably from about 0.80 to about 1.05 as measured in a 60/40 by volume mixed solvent of phenol/tetrachloroethane at 30° C.
• Known methods of solid state polymerization may be employed to achieve the higher intrinsic viscosities.
• nucleating agents may be added in order to increase the number of crystallites formed.
• Most known nucleating agents are inorganic materials having an average particle size of from 2 to 10 microns.
• Other known nucleating agents are carbonaceous materials such as carbon black and graphite.
• Common nucleating agents may be talc, gypsum, silica, calcium carbonate, alumina, titanium dioxide, pryophylite silicates, finely divided metals, powdered glass, carbon black, and graphite.
• the common feature shared by the foregoing list of known nucleating agents is that they exist in solid, form within the temperature range of 100° C. to 300° C. where polyesters are forming crystalline structures. Any of these particulate nucleating agents may be used to good advantage, although a leveling off of degree of crystallinity occurs if these particulate nucleating agents are reduced or eliminated.
• the second essential component of this invention is a polyolefin, which must be present with the polyethylene terephthalate.
• Polyolefins as used herein are those produced from olefin monomers having from 2 to 6 carbon atoms. The resulting polymer contains repeat units derived from the original monomer units. These repeat units differ from the monomers in that they no longer contain a carbon—carbon double bond.
• Such polymers include low density polyethylene, high density polyethylene, linear low density polyethylene, polypropylene, polyisopropylene, polybutene, polypentene, polymethylpentene.
• the polyolefin should be present in levels of from 0.5 to 15 weight percent of the total composition. The preferred range was found to be from 1 to 5 weight percent.
• a preferred class of polyolefins is the polyethylene with the most preferred type being linear low density polyethylene (LLDPE), as represented by products marketed by Dow Chemical under the tradenames DOWLEX 2045 and 2035.
• LLDPE linear low density polyethylene
• all the polyolefins provide improved impact strength in the finished article and improved mold release in the thermoforming process.
• the polyethylene and polypropylene have broader operating temperature ranges, faster rates of crystallization and lower temperatures for the onset of crystallinity. These improvements lead to faster cycle times, more parts per minute and a lower cost finished article.
• This method of incorporating the heat stabilizer prior to the blending of the PET and polyolefin provides a method for insuring (1) a minimal loss in intrinsic viscosity during processing and subsequent heat aging; (2) eliminating discoloration of the blend during high temperature exposure; and (3) elimination of the development of fingerprints or blotchy areas of discoloration during high temperature aging.
• Heat stabilizers as used herein are compounds which demonstrate antioxidant properties, the most important of which is the capability of inhibiting oxidation.
• An effective heat stabilizer in the practice of this invention must be capable of protecting the thermoformed, heat set polyester article during exposure to elevated temperatures.
• 3,644,482 disclose many examples of known heat stabilizers.
• the following compounds are representative of useful heat stabilizers in the practice of this invention: alkylated substituted phenols, bisphenols, substituted bis phenols, thiobisphenols, polyphenols, thiobisacrylates, aromatic amines, organic phosphites and polyphosphites.
• the particular aromatic amines which demonstrate specific heat stabilizing capabilities include: primary polyamines, diarylamines, bisdiarylamines, alkylated diarylamines, ketone-diarylamines condensation products, aldehyde-amine condensation products, and aldehyde amines.
• heat stabilizers for such severe high temperature applications particularly where any staining or discoloration from the heat stabilizer is undesirable are the polyphenols which have more than two phenol ring structures in the compound.
• Polyphenols which are useful include, but are not limited to: tetrakis(methylene 3-(3,5-ditertiarybutyl-4-hydroxyphenyl)-propionate) methane, and 1,3,5-trimethyl-2,4,6-tris(3,5-ditertiary butyl-4-hydroxybenzyl)benzene.
• the latter polyphenol is most preferred.
• the heat stabilizers may advantageously be added at levels up to 2 weight percent but more preferred are levels below 0.05 weight percent based on the total PET/polyolefin/stabilizer composition. The most preferred level is between 0.005 and 0.03 weight percent.
• the antioxidant is added by melt blending directly into the polyolefin component of the polymer blend.
• the polyolefin component will contain the appropriate larger weight percent of antioxidant appropriate for the finished ratio of PET to polyolefin.
• the particular level used is determined by the degree of protection required, the identity of the particular stabilizer chosen, the severity of the heat exposure and any solubility limitation in the polyolefin.
• the method of manufacturing a polyolefin modified polyethylene terephthalate sheet includes the steps of (1) melt blending a suitable heat stabilizer with a polyolefin derived from monoolefins having from 1 to 4 carbon atoms to form a stabilized polyolefin. (2) the polyethylene terephthalate having an intrinsic viscosity of from 0.65 to 1.2 must be heated above its glass transition temperature in a dry air or nitrogen atmosphere and maintained in that condition until a moisture level low enough to reduce hydrolytic degradation during subsequent method steps is attained. (3) The stabilized polyolefin and the dried polyethylene terephthalate resin is simultaneously conveyed in appropriate proportion to an extruder where the two components are melt blended to form a homogeneous molten blend thereof. (4) Forming a sheet from the homogeneous molten blend. (5) Quenching the sheet to form a substantially amorphous sheet.
• the melt blending of the heat stabilizer may be accomplished in the post-polymerization stage of the production of the polyolefin or it may be accomplished by the use of any conventional thermoplastic mixing extruder which will adequately disperse the antioxidant throughout the polyethylene which has been rendered molten in the barrel of the extruder.
• the process step wherein the polyethylene terephthalate resin is heated in a dehumidified atmosphere of nitrogen or air is necessary to maintain the intrinsic viscosity level of the resin. Any moisture level is suitable which maintains a sufficiently high intrinsic viscosity level during the remaining process steps of the method. Maintenance of the lowest practicable moisture level is advantageous. Generally levels below 0.02% are required. Mositure less than 0.005% is most preferred for high intrinsic viscosity PET.
• the mixing of the polyolefin containing the antioxidant with the dried PET may be accomplished in any conventionally known film extrusion technique where the polyolefin and PET are heated above their glass transition points and blended through shearing of the molten material to form a homogeneous blend of the two dissimilar plastics.
• the polyolefin is dispersed throughout the PET but maintains its identity in a separate phase.
• the forming of the sheet may be done by any conventional film forming technique.
• the sheets which are utilized in the examples which follow were produced on a Prodex film extruder where the molten sheet was extruded onto a chilled casting roll and immediately cooled to minimize crystallinity buildup.
• Table I shows the sheet extrusion conditions which were utilized to produce the amorphous sheeting used to make the trays in the examples of the Specification.
• the manufacture of heat set thin-walled trays which are made from the sheeting produced from stabilized polyolefin/PET can be made by using any of the known thermoforming methods including vacuum assist, air assist, mechanical plug assist or matched mold.
• the mold should be preheated to a temperature sufficient to achieve the degree of crystallinity desired. Selection of optimum mold temperature is dependent upon type of thermoforming equipment, configuration and wall thickness of articles being molded and other factors.
• the operable range of mold temperatures is 150-215° C.
• the preferred range is 170-190° C.
• Heatsetting is a term describing the process of thermally inducing partial crystallization of a polyester article without appreciable orientation being present.
• heatsetting is achieved by maintaining intimate contact of the film or sheet with the heated mold surface for a sufficient time to achieve a level of crystallinity which gives adequate physical properties to the finished part. It has been found that desirable levels of crystallinity should be about 10 to about 35 percent. For containers to be used in high temperature food application it was found that levels of crystallinity above 15 percent were necessary for adequate dimensional stability during demolding and during oven exposure.
• the heat set part can be stripped out of the mold cavity by known means for removal.
• One method, blow back, involves breaking the vacuum established between the mold and the formed sheet by the introduction of compressed air. Once the heat set part has been removed from the mold, the portion of the sheeting which remains in the original planar state is trimmed away to leave the finished tray. Since most commercial thermoforming molds will contain a plurality of cavities for production of many trays from a single sheet, the dinking out of the trays will leave a flat matrix of the original sheet which has the outline of the trays removed. Anywhere from 10 to 60% of the original sheet remains in the matrix and must be recycled in order to make the thermoforming operation economically feasible. This recycling of the matrix means that a very substantial amount of thermal heat history is built into the sheeting.
• Example 2 was a 97% PET/3% LLDPE sheet with no antioxidant added. It is clear from the results shown in Table II that PET alone or PET blended with a polyolefin such as linear low density polyethylene undergoes a substantial drop in intrinsic viscosity during high temperature aging when unprotected with an antioxidant or stabilizer system. This loss of intrinsic viscosity would be totally unacceptable in food trays for Example 3 would be characteristic of the articles produced having no antioxidant included according to the teachings of U.S. Pat. No. 4,463,121.
• the discoloration occurs typically on surfaces of the tray which have been touched by human hands. This sporadic blotchiness in Table II has either a yes or no value under the fingerprint category of aging effects. It is to be understood that if the entry is “yes” fingerprints appeared after aging. If the entry is “no” the tray retained its original uniform appearance; (2) Color—the term color designates the retention or lack of retention of the original color of the tray after one hour aging at 200° C. The appearance of discoloration is a uniform change in the hue of the tray. If the entry under the column color is “stable” it denotes that the color did not change after aging.
• Intrinsic Viscosity Intrinsic viscosity tends to decline when PET is subjected to high temperature. The original intrinsic viscosity is tested and compared to the intrinsic viscosity value after one hour at 200° C.
• the variables in Examples 3-7 include the level of AO, the component to which the AO is added and the method of adding the AO.
• Example 3 0.1% of AO was added to the PET in the melt phase during production of the polyethylene terephthalate polymer.
• the intrinsic viscosity was maintained satisfactorily but the relatively high level of AO in the PET contributed to discoloration of the PET polymer utilized in the blend.
• This discoloration was a general yellowing to brown from the normal milky white of the virgin PET resin. It is speculated that the high temperatures experienced during PET production and the prolonged high temperature maintenance during solid stating of the the base resin to a high intrinsic viscosity (1.04) all contribute to the overall discoloration. This discoloration is very objectionable in applications such as food trays. In addition, the aged samples showed fingerprinting which is also unsatisfactory.
• Example 4 is a blend identical in polymer composition to Example 3 but 0.19% antioxidant was added.
• the antioxidant was added both to the PET in the reactor and to the linear low density polyethylene in the master batch.
• the column under AO addition method which is designated as “master batch” indicates a procedure whereby an initial master batching step is taken in which a 77/23 weight percent PET/LLDPE were mechanically blended in particulate pellets to form a master batch.
• This master batch blend of PET and linear low density polyethylene was subsequently simultaneously fed to a Prodex film extruder along with PET resin in a ratio of 13 to 87 weight percent to yield a final LLDPE percentage of 3 and a PET percentage of 97.
• This master batch method achieves an improved dispersion of polyethylene throughout the PET in a circumstance when the hoppers feeding the film extruder are not accurately calibrated to handle resin percentages as low as 3%.
• the intrinsic viscosity was maintained and no fingerprinting was evident, however, discoloration of the tray was evident with this higher level of antioxidant.
• the antioxidant has a distinct tendency to yellow when relatively high levels are added to the PET/polyolefin blend.
• Film sheeting was prepared using a 97/3 weight percent ratio of PET/LLDPE along with varying in percentages of antioxidant.
• This series utilized the method of this invention in which the antioxidant was added to the linear low density polyethylene prior to any incorporation with the PET. No antioxidant is added to the PET and this method is described in the antioxidant addition method columns of Table III as the direct LLDPE.
• the antioxidant was added to the polyolefin by remelting the particulate polyolefin and homogeneously blending the desired level of antioxidant in the polyolefin and subsequently finishing the molten resin into the desired particulate form such as pellets, prilled beads or other desirable forms.
• Example 5 which uses a 0.009 weight percent of antioxidant shows evidence of fingerprinting while the Example 6 using a slightly higher level of antioxidant shows only a barely discernible trace of fingerprinting.
• Example 7 which uses 0.024 weight percent of AO shows no evidence of fingerprinting. This is in marked contrast to the Example 3 where nearly eight times the antioxidant level was required in order to eliminate fingerprinting and the resin displayed objectionable yellow color after aging.
• thermoforming process When manufacturing trays by thermoforming from flat sheeting, a typicaly thermoforming process will yield approximately 40% scrap sheeting after each forming and trim cycle. The sheeting must be reground and mixed with incoming virgin PET/polyolefin material for reuse. This recycle produces considerable thermal heat history on the polymeric blend leading to degradation problems of discoloration, fingerprinting, intrinsic viscosity loss, and changes in crytallinity. In order to produce acceptable thermoformed trays for food all of the foregoing properties must be stabilized or eliminated in a commercial process involving substantial percentages of regrind. A typical thermoforming process will regrind up to 40%.
• thermoforming system Simulation of the steady state operation of such a thermoforming system assumes that the regrind will mean that the same resin must proceed through the sheet making and tray thermoforming system appromately five times. Accordingly, the following experimental scheme simulates the 40% rework, 5 cycle system for evaluating thermal stability.
• the resin utilized was 97% PET (1.04 intrinsic viscosity), 3% linear low density polyethylene, Dowlex 2045 available from Dow Chemical Company and 0.015% Ethanox 330, available from Ethel Corporation.
• the antioxidant was melt blended into the LLDPE using a Sterling Transfermix extruder and then pelletized for subsequent blending into a 1.75 inch (45 mm) Prodex film extruder along with the PET. The steps of the process are the following:
• each sample was placed in a 100° vacuum oven to keep it dry and equilibrate the temperature at 100° C.

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• Chemical & Material Sciences (AREA)
• Polymers & Plastics (AREA)
• Health & Medical Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Medicinal Chemistry (AREA)
• Organic Chemistry (AREA)
• Sustainable Development (AREA)
• Life Sciences & Earth Sciences (AREA)
• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Compositions Of Macromolecular Compounds (AREA)
• Blow-Moulding Or Thermoforming Of Plastics Or The Like (AREA)
• Manufacture Of Macromolecular Shaped Articles (AREA)
• Processes Of Treating Macromolecular Substances (AREA)

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• 1986
  • 1986-01-07 IN IN21/DEL/86A patent/IN169503B/en unknown
  • 1986-02-25 CA CA000502602A patent/CA1266361A/en not_active Expired - Fee Related
  • 1986-03-04 FR FR8602984A patent/FR2578547B1/fr not_active Expired
  • 1986-03-04 BR BR8600935A patent/BR8600935A/pt not_active IP Right Cessation
  • 1986-03-05 SE SE8601012A patent/SE468854B/sv not_active IP Right Cessation
  • 1986-03-06 IT IT4772386A patent/IT1209973B/it active
  • 1986-03-06 DE DE3607412A patent/DE3607412C2/de not_active Expired - Fee Related
  • 1986-03-06 GB GB8605510A patent/GB2172601B/en not_active Expired
  • 1986-03-10 BE BE0/216386A patent/BE904379A/fr not_active IP Right Cessation
  • 1986-03-10 DK DK108486A patent/DK108486A/da unknown
  • 1986-03-10 KR KR1019860001668A patent/KR940002281B1/ko not_active IP Right Cessation
  • 1986-03-11 NL NL8600635A patent/NL193378C/nl not_active IP Right Cessation
  • 1986-03-11 JP JP5351086A patent/JPH0651810B2/ja not_active Expired - Lifetime
  • 1986-03-11 CN CN86101424A patent/CN1013450B/zh not_active Expired
• 1991
  • 1991-04-16 US US07/686,088 patent/USH2169H1/en not_active Abandoned

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