GB1581237A - Method of producing expandable thermoplastic polymer particles - Google Patents
Method of producing expandable thermoplastic polymer particles Download PDFInfo
- Publication number
- GB1581237A GB1581237A GB3594877A GB3594877A GB1581237A GB 1581237 A GB1581237 A GB 1581237A GB 3594877 A GB3594877 A GB 3594877A GB 3594877 A GB3594877 A GB 3594877A GB 1581237 A GB1581237 A GB 1581237A
- Authority
- GB
- United Kingdom
- Prior art keywords
- hardened
- oil
- polymer particles
- moulding
- filling
- 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.)
- Expired
Links
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
- C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
- C08J9/0061—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof characterized by the use of several polymeric components
-
- 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
- C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
- C08J9/22—After-treatment of expandable particles; Forming foamed products
- C08J9/224—Surface treatment
-
- 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
- C08J2491/00—Characterised by the use of oils, fats or waxes; Derivatives thereof
Landscapes
- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Health & Medical Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Medicinal Chemistry (AREA)
- Polymers & Plastics (AREA)
- Organic Chemistry (AREA)
- Manufacture Of Porous Articles, And Recovery And Treatment Of Waste Products (AREA)
Description
(54) A METHOD OF PRODUCING EXPANDABLE THERMOPLASTIC
POLYMER PARTICLES
(71) We, KANEGAFUCHI KAGAKU KOGYO KABUSHIKI KAISHA, organised under the laws of Japan, of 3-3 chome, Nakanoshima, Kita-ku, Osaka, Japan, do hereby declare the invention, for which we pray that a Patent may be granted to us, and the method by which it is to be performed to be particularly described in and by the following statement:
The present invention relates to a method of producing expandable thermoplastic polymer particles. More particularly, the present invention relates to a method of producing expandable thermoplastic polymer particles having goood interior unitability and filling up property at the time of moulding, by coating or impregnating the expandable thermoplastic polymer particles with at least one of the moulding additives of the invention.
As a method of production of expandable thermoplastic resins, it has been commonly known that the resinous discrete particles are pre-expanded with water vapor and the like, then the resulting pre-expanded particles are introduced into a closed mould which is provided with perforations permitting the escape of gases, thereafter being heated again with water vapor or the like to obtain the desired shaped articles. Expandable thermoplastic resins thus moulded include for example expandable polystyrene resin, expandable methyl methacrylate resin and modified polyethylene resin. These expandable thermoplastic resins are moulded at a temperature ranging from about 108"C to 1150C.However, under the moulding conditions in the vicinity of 108"C, referred to as "the region of lower temperature moulding", the discrete particles imperfectly unite together and the resulting shaped articles are substandard both in strength and appearance. On the other hand, in the vicinity of 11 5 C, referred to herein as "the region of higher temperature moulding", expanded polymer particles tend to agglomerate or the shaped articles obtained are liable to shrink, so that the commercial value of the products is decreased. Furthermore, the development of expandable thermoplastic resins capable of producing a quality shaped article over a wide range of the moulding temperatures is very desirable, since a wide variety of moulding machines are employed by process manufacturers.In addition, moisture contained in the pre-expanded particles or from other sources may bring about the deterioration of the particles when these are loaded into the cavity of the mould, which further reduces the chance of a satisfactory shaped article being manufactured.
It is already known to enhance molecular weight or increase cell diameter of expandable polymer particles by bridging or the like in order to suppress agglomeration or shrinkage of the shaped articles at the region of higher temperature moulding. These methods however, are accompanied by a lowering in the interior unitability at the region of lower temperature moulding.
As a method for eliminating these disadvantages, it is proposed in the Japanese Patent
Publication No. 53487/1975 that liquid organic compounds are introduced into the expandable polystyrene resin. In recent years, however, public health provisions with regard to food have come to the fore and the safety of plastic products used in the field of foods has been more and more strictly controlled. In view of these circumstances, it is undesirable to carry out the method disclosed in the aforesaid Japanese Patent Publication, especially when the products are to be used in conjunction with foods.
According to the present invention there is provided a method of producing expandable thermoplastic polymer particles, which comprises coating or impregnating expandable thermoplastic polymer particles containing a lower aliphatic hydrocarbon (as herein defined) as a blowing agent with at least one moulding additive consisting of hardened edible oils, har
dened castor oils, and esters of saturated higher fatty acids (as herein defined) and di- or
mono- hydric alcohols.
The term "lower aliphatic" means Cl to 7 aliphatic, and the term "higher fatty acids"
means at least C12 fatty acids.
Expandable thermoplastic polymer particles include polymer particles obtained by adding
a blowing agent in the course of polymerization, or by impregnating polymer particles with a
blowing agent. Thermoplastic polymers suitable for carrying out the invention include, for
example, polystyrene, copolymers of styrene and other copolymerizable vinyl monomers,
polymethyl methacrylate, copolymers of methyl methacrylate and other copolymerizable
vinyl monomers and polyethylene impregnated or graft- polymerized with a monomer mainly containing styrene or methyl methacrylate. These polymer particles may be previously
impregnated during polymerization with a liquid or gaseous blowing agent at room tempera
ture, so as to be able to expand or foam up when heated.
Hardened edible oils include hardened coconut oil, hardened palm-kernel oil, hardened
herring oil, hardened cod liver oil, hardened whale oil, hardened palm oil, hardened cotton
seed oil, hardened olive oil, hardened arachis oil, hardened soybean oil, and any other
hardened vegetable or animal oils.
Most of animal or vegetable oils have one or more double bonds in the molecule of their
own, at which spots they are likely to be oxidized. Oxidized oils result in degeneration in
quality and colour and sometimes, in their becoming poisonous. Hardening is carried out in
order to prevent such oxidation of oils. It is preferable to harden oils as low as possible in
iodine value. When hardening is carried out to such an extent that oils become solid at higher
than room temperature, they can be powdered with ease and mingled with the expandable
polymer particles using a mixer commonly employed, which is practically very convenient. It
was ascertained that powdery hardened oils especially and surprisingly improve the filling
property of the pre-expanded particles a loading into a mould.
Esters of saturated higher fatty acids and di- or mono- hydric alcohols include montanic
acid ester.
The quantity of these moulding additives employed is preferably within the range of from
0.005 to 1.0% by weight of expandable thermoplastic polymer particles. In cases where less
than 0.005%is used, the effect obtained diminishes. On the other hand, the amount less than 1.0% can give such a satisfactory effect that there is no need to employ the amounts exceeding
the upper limit. Some of the moulding additives have an unpleasant odour and thus it is
preferred to a proportion of 0.01 to 0.20 % by weight, where a greater effect can be obtained
with a less amount applied.
The polymer particles may be coated or impregnated with these moulding additives. The
coating or impregnation may be carried out by adding the moulding additives to a suspension
polymerization system, or dispersing the polymer particles in water in the presence of a
dispersing agent in which the moulding additives are added, or by direct mixing of the
polymer particles with these additives in a mixer. Polymer particles in the suspension
polymerization system may be formed when the polymerization ratio reach the order of 70%.
After the formation of particles, the moulding additives may be added, thus impregnation is
readily executed. The addition of the moulding additives in a mixer may be effected using a
blender provided with an agitator. A super mixer, a ribbon blender or any other mixers may
be used. Some kinds of additives are solid and they are preferably melted by heating before
use. In order to make an intimate and homogeneous coating or impregnation, it is recom
mended to dissolve the moulding additives in a suitable volatile solvent with which the
polymer particles are coated or impregnated, thereafter being dried.
Blowing agents with which the polymer particles are impregnated to be expandable
polymer particles may be liquid or gaseous lower aliphatic hydrocarbons. Examples are
propane, butane, and pentane and may also be applied in combination with hexane, heptane,
cyclohexane, methylene chloride, or a flourinated hydrocarbon (for example Firon; Regis
tered Trade Mark).
Blowing agents are preferably employed in the range of from 3.0 to 15.0%byweight of the
thermoplastic polymer particles. In the coating or impregnating, an antistatic agent, an
antiblocking agent or a dehydrating agent may be added concurrently or may be blended
before or after the coating or impregnating.
Following is a description by way of example only and with reference to the accompanying
drawings of methods of carrying the invention into effect. In the examples, "part(s)" and " %" mean "part(s) by weight per 100 parts of expandable thermoplastic polymer particles" and
"% by weight", respectively, unless otherwise indicated. The rate of interior unitability
stands for the unitability among expanded polymer particles on a broken surface of the
shaped articles and is represented by percent of particles torn off on the expanded particles
per se, not on the boundary faces of the particles, per total expanded particles on the broken
surface. Hence, the higher the rate of interior unitability becomes, the better is the unitability among the particles one another.
The filling up property is judged by whether or not the cavity of the mould is fully filled with the pre-expanded particles and ranked as follows:
A: adequate filling up
B: partly inadequate filling up
C: inadequate filling up
In Example 3, more precise experiments were carried out in order to prove the superiority in filling up property of the hardened oils over non-hardened oils.
In the drawings:
Figure 1 is a perspective view of the metallic mould employed.
Figure 2 is an enlarged view of the cavity of the mould, which is marked in Figure 1, wherein the shaded portion shows the filling up of the pre-expanded particles. The filling up property was calculated according to the following equation;
Filling up property (%) = B/A x 100
EXAMPLE 1
In an autoclave provided with an agitator and a temperature indicator, were charged 128 parts of water, 15 parts of tricalcium phosphate, 0.0045 part of a-olefine sodium sulfonate, 0.08 part of ethylene bis-stearylamide, 1.0 part of coconut oil, 0.13 part of benzoylperoxide and 0.2 part of tertiary butyl perbenzoate, then being well dispersed. Then 100 parts of styrene monomer were introduced into the system and heated up with stirring to 900C while pressed with nitrogen at 0.5 kg per square centimeter, then styrene was polymerized for 6 hours.Next, 1.5 parts of heptane were added and one hour after 8.5 parts of butane were further added to the polymerization system, then heated up to 1020C, thus impregnation of the polystyrene particles with a blowing agent being carried out for 6 hours. After the completion of polymerization and impregnation, the autoclave was cooled to room temperature and granular expandable polystyrene beads were taken out. Said polystyrene beads were passed through a screen to obtain beads of from 14 to 24 meshes. To expandable polystyrene beads thus obtained, an ethanol solution dissolving 0.1 part of montranic acid ester as a moulding additive was added and mixed with stirring for 10 min. The obtained mixture was then charged into a pre-expanding machine, then heated for one and a half min. to obtain pre-expanded beads having about 55 times the orginal apparent volume.The resulting pre-expanded beads were stored for 24 hours, then being moulded using "BELMO-90" automoulding machine (manufactured by Toyo Machinery and Metal Co., Ltd.) The moulding conditions were given as below;
Pre-heating: 10 sec.
Adjustment pressure: 0.6 kg/cm2
Primary heating pressure: 0.2 kg/cm2
Secondary heating time: 3 sec.
Tertiary heating time: 10 sec.
Water-cooling: 30 sec.
Air-cooling: 30 sec.
Interior temperature of the shaped article: 107"C The broken face of the shaped article thus obtained was observed and showed above 90% in the rate of interior unitability.
EXAMPLE 2
In accordance with the same manner as executed in Example 1, a variety of moulding additives were added to expandable polystyrene beads; 0.05 part of montanic acid ester, 0.10 part of montanic acid ester and 0.075 part of hardened castor oil, respectively. IN Table 1 were shown the rate of interior unitability and the filling up property of each article. The control was also shown for comparison. I No.Moulding additiies Part Rate of interior Filling UP
Unitability (%) Property 1 Montanic acid ester 0.05 about 80 A
2 Montanic acid ester 0.10 more than 90 A
3 hardened castor oil 0.075 more than 90 A
4 Control - less than 10 B-C
As is apparent from the results in Table 1, in cases where the moulding additive for the present invention were employed, the prominent improvement in both the rate of interior unitability and the filling up property could be seen.
EXAMPLE 3
Expandable polystyrene beads ("KANEPEARL KH-M" beads, manufactured by
Kanegafuchi Chemical Industry Co., Ltd.) were mixed for 10 minutes with a variety of the moulding additives set out in Table 3 using a ribbon blender.
The mixture thus obtained was heated for one and a half minutes in the pre-expanding machine to obtain pre-expanded particles having about 55 times the original apparent volume. The resulting pre-expanded particles were stored for 24 hours, then introduced into "BELMO-90" auto-moulding machine (manufactured by Toyo Machinery and Metal Co.
Ltd.) and moulded. The moulding conditions are the same as in Example 1.
The interior unitability and filling up property of the shaped articles were measured and the results were tabulated in Table 3.
Table 2 No. Moulding additives Part Rate of interior Filling up
unitability (%) property (%) 1 Hardened colza oil* o.075 more than 90 90
2 Hardened corn oil ** 0.06 90 90
Hardened palm oil
3 Hardened palm oil 0.08 80 90
4 Completely Hardened
caster oil**** 0.07 more than 90 100
5 Control - 40-50 less than 70
* "TP-9", manufactured by Nippon Oil and Fats Co., Ltd.
(Iodine value; less than 5)
** Corn oil (Hardened)/Palm oil (hardened)= 1/1
*** "NEOPOWDER-A", manufactured by Nippon Oil and Fats Co., Ltd.
**** "KAO-WAX 85" powder, manufactured by Kao Soap Co., Ltd.
It was understood from the foregoing results that hardened oils could produce an outstanding and surprising effect of improving the filling up property, in particular. Among hardened oils, hardened castor oil produced by far superior filling up property to any other hardened oils. The reason why it shows such a prominent effect is unknown, but it is surmised that hydroxy group contained in licinoleic group of castor oil possesses such an antistatic effect that the filling up property was surprisingly improved.
WHAT WE CLAIM IS:
1. A method of producing expandable thermoplastic polymer particles, which comprises coating or impregnating expandable thermoplastic polymer particles containing a lower aliphatic hydrocarbon (as defined) as a blowing agent with at least one moulding additive consisting of hardened edible oils, hardened castor oils, and esters of saturated higher fatty acids (as defined) and di- or mono- hydric alcohols.
2. A method as claimed in claim 1 wherein the expandable thermoplastic polymer particles are polystyrene particles.
3. A method as claimed in claim 1 or claim 2 wherein the hardened oil is at least one member selected from hardened coconut oil, hardened palm-kernel oil, hardened herring oil, hardened cod liver oil, hardened whate oil, hardened palm oil, hardened cotton seed oil, hardened olive lil, hardened arachis oil and hardened soybean oil.
4. A method as claimed in claim 1 or claim 2 wherein esters of higher fatty acid and di- or mono- hydric alcohols are employed in amounts ranging from 0.005 to 1.0% by weight based on the weight of the expandable polymer particles.
5. A method as claimed in claim 1 or claim 2 wherein hardened edible oils, and esters of saturated higher fatty acids and di- or mono-hydric alcohols are employed in amounts ranging from 0.005 to 1.0% by weight based on the weight of the expandable polymer particles.
6. A method as claimed in claim 5 wherein said hardened edible oils, and esters of higher
**WARNING** end of DESC field may overlap start of CLMS **.
Claims (10)
1 Hardened colza oil* o.075 more than 90 90
2 Hardened corn oil ** 0.06 90 90
Hardened palm oil
3 Hardened palm oil 0.08 80 90
4 Completely Hardened
caster oil**** 0.07 more than 90 100
5 Control - 40-50 less than 70
* "TP-9", manufactured by Nippon Oil and Fats Co., Ltd.
(Iodine value; less than 5)
** Corn oil (Hardened)/Palm oil (hardened)= 1/1
*** "NEOPOWDER-A", manufactured by Nippon Oil and Fats Co., Ltd.
**** "KAO-WAX 85" powder, manufactured by Kao Soap Co., Ltd.
It was understood from the foregoing results that hardened oils could produce an outstanding and surprising effect of improving the filling up property, in particular. Among hardened oils, hardened castor oil produced by far superior filling up property to any other hardened oils. The reason why it shows such a prominent effect is unknown, but it is surmised that hydroxy group contained in licinoleic group of castor oil possesses such an antistatic effect that the filling up property was surprisingly improved.
WHAT WE CLAIM IS:
1. A method of producing expandable thermoplastic polymer particles, which comprises coating or impregnating expandable thermoplastic polymer particles containing a lower aliphatic hydrocarbon (as defined) as a blowing agent with at least one moulding additive consisting of hardened edible oils, hardened castor oils, and esters of saturated higher fatty acids (as defined) and di- or mono- hydric alcohols.
2. A method as claimed in claim 1 wherein the expandable thermoplastic polymer particles are polystyrene particles.
3. A method as claimed in claim 1 or claim 2 wherein the hardened oil is at least one member selected from hardened coconut oil, hardened palm-kernel oil, hardened herring oil, hardened cod liver oil, hardened whate oil, hardened palm oil, hardened cotton seed oil, hardened olive lil, hardened arachis oil and hardened soybean oil.
4. A method as claimed in claim 1 or claim 2 wherein esters of higher fatty acid and di- or mono- hydric alcohols are employed in amounts ranging from 0.005 to 1.0% by weight based on the weight of the expandable polymer particles.
5. A method as claimed in claim 1 or claim 2 wherein hardened edible oils, and esters of saturated higher fatty acids and di- or mono-hydric alcohols are employed in amounts ranging from 0.005 to 1.0% by weight based on the weight of the expandable polymer particles.
6. A method as claimed in claim 5 wherein said hardened edible oils, and esters of higher
fatty acids and mono- hydric alcohols are employed in amounts ranging from 0.01 to 0.20% by weight based on the weight of expandable polymer particles.
7. A method as claimed in claim 1 and substantially as therein described with reference to the accompanying drawings.
8. A method as claimed in claim 1 and substantially as described in any one of the specific examples hereinbefore set forth.
9. Expandable thermoplastic polymer particles whenever produced by the method claimed in any one of the preceding claims.
10. Articles whenever produced from the particles claimed in claim 9.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP10304476A JPS5928339B2 (en) | 1976-08-27 | 1976-08-27 | Method for manufacturing expandable polystyrene resin particles |
| JP9683477A JPS5430260A (en) | 1977-08-11 | 1977-08-11 | Production of foaming granules of themoplastic resin |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| GB1581237A true GB1581237A (en) | 1980-12-10 |
Family
ID=26437996
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB3594877A Expired GB1581237A (en) | 1976-08-27 | 1977-08-26 | Method of producing expandable thermoplastic polymer particles |
Country Status (2)
| Country | Link |
|---|---|
| AU (1) | AU516267B2 (en) |
| GB (1) | GB1581237A (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2009019310A1 (en) * | 2007-08-09 | 2009-02-12 | Basf Se | Coating compound for expandable styrol polymer particles |
| WO2012130778A1 (en) | 2011-03-29 | 2012-10-04 | Basf Se | Method for producing expandable styrene polymer particles having reduced thermal conductivity |
-
1977
- 1977-08-17 AU AU28002/77A patent/AU516267B2/en not_active Expired
- 1977-08-26 GB GB3594877A patent/GB1581237A/en not_active Expired
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2009019310A1 (en) * | 2007-08-09 | 2009-02-12 | Basf Se | Coating compound for expandable styrol polymer particles |
| CN101778890B (en) * | 2007-08-09 | 2012-04-11 | 巴斯夫欧洲公司 | Coating compound for expandable styrol polymer particles |
| RU2475502C2 (en) * | 2007-08-09 | 2013-02-20 | Басф Се | Agent for coating spumescent particles of styrene polymerisate |
| WO2012130778A1 (en) | 2011-03-29 | 2012-10-04 | Basf Se | Method for producing expandable styrene polymer particles having reduced thermal conductivity |
Also Published As
| Publication number | Publication date |
|---|---|
| AU516267B2 (en) | 1981-05-28 |
| AU2800277A (en) | 1979-02-22 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| US3093599A (en) | Flameproofed synthetic thermoplastic polymer containing an organic polybromine compound and method of making same | |
| US4243717A (en) | Expandable polystyrene with stabilized cell structure | |
| EP0046494B1 (en) | Expandable-styrene polymer particles and their use | |
| US3056752A (en) | Method of coating heat-expansible resin particles with a solution of perfluorooctanoic acid and coated composition obtained thereby | |
| GB1581237A (en) | Method of producing expandable thermoplastic polymer particles | |
| DE1256888B (en) | Reduction of the minimum dwell time in the production of cell bodies from styrene polymers | |
| US3505253A (en) | Expandable alkenyl aromatic polymers containing incorporated expandable alkenyl aromatic polymers and polysiloxane | |
| EP0134414B1 (en) | Finely divided expandable styrene polymers useful in the production of easily demouldable foamed products | |
| DE3904370A1 (en) | PEARL-SHAPED EXPANDABLE MOLDS WITH HIGH THERMAL RESISTANCE AND METHOD FOR THEIR PRODUCTION | |
| DE1494934A1 (en) | Flame-resistant, finely divided, eypandable plastic compound | |
| JPS5928339B2 (en) | Method for manufacturing expandable polystyrene resin particles | |
| DE2659403A1 (en) | NON-CLUMBING SHEATHABLE STYRENE POLYMER | |
| US3637538A (en) | Foamable styrene polymer resins | |
| JPS5921341B2 (en) | Method for producing expandable thermoplastic polymer particles | |
| JP3456758B2 (en) | Pre-expanded polyolefin resin particles having antistatic properties and method for producing the same | |
| DE2226168A1 (en) | FINE PARTICLE EXPANDABLE STYRENE POLYMERIZED WITH GOOD PROCESSING PROPERTIES | |
| JPH047341A (en) | Production of expandable thermoplastic resin particle | |
| DE3640877A1 (en) | EXPANDABLE STYRENE POLYMERISATE AND STYRENE POLYMERISATE FOAM | |
| EP0027609B1 (en) | Particulate styrene polymers containing an expanding agent, and their use | |
| KR970010471B1 (en) | Novel particulate expandable styrene polymers having sheet minimum molding times and method for preparing the same | |
| US2808379A (en) | Process for foaming resins using furan adduct foaming agents and foamable compositions containing same | |
| DE2255397C3 (en) | Expandable styrene polymers that are suitable for the production of rapidly demoldable cell bodies | |
| DE2420298A1 (en) | STYRENE POLYMERISATE EXPANDABLE FOR LOW DENSITY FOAM | |
| JPS6368644A (en) | Expandable thermoplastic resin particle | |
| DE1794032C3 (en) | Process for making an expandable alkenyl aromatic polymer composition |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PS | Patent sealed | ||
| PCNP | Patent ceased through non-payment of renewal fee |
Effective date: 19950826 |