CA2181388A1 - Multi-layer particles for rotational molding - Google Patents
Multi-layer particles for rotational moldingInfo
- Publication number
- CA2181388A1 CA2181388A1 CA 2181388 CA2181388A CA2181388A1 CA 2181388 A1 CA2181388 A1 CA 2181388A1 CA 2181388 CA2181388 CA 2181388 CA 2181388 A CA2181388 A CA 2181388A CA 2181388 A1 CA2181388 A1 CA 2181388A1
- Authority
- CA
- Canada
- Prior art keywords
- polymer
- core
- shell
- lldpe
- microns
- 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.)
- Abandoned
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
- C08J9/22—After-treatment of expandable particles; Forming foamed products
- C08J9/228—Forming foamed products
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29B—PREPARATION OR PRETREATMENT OF THE MATERIAL TO BE SHAPED; MAKING GRANULES OR PREFORMS; RECOVERY OF PLASTICS OR OTHER CONSTITUENTS OF WASTE MATERIAL CONTAINING PLASTICS
- B29B9/00—Making granules
- B29B9/12—Making granules characterised by structure or composition
-
- 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
- B29C41/00—Shaping by coating a mould, core or other substrate, i.e. by depositing material and stripping-off the shaped article; Apparatus therefor
- B29C41/02—Shaping by coating a mould, core or other substrate, i.e. by depositing material and stripping-off the shaped article; Apparatus therefor for making articles of definite length, i.e. discrete articles
- B29C41/04—Rotational or centrifugal casting, i.e. coating the inside of a mould by rotating the mould
-
- 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
- C08J3/12—Powdering or granulating
-
- 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
- C08J3/12—Powdering or granulating
- C08J3/126—Polymer particles coated by polymer, e.g. core shell structures
-
- 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
- B29K2023/00—Use of polyalkenes or derivatives thereof as moulding material
-
- 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
- B29K2077/00—Use of PA, i.e. polyamides, e.g. polyesteramides or derivatives thereof, as moulding material
-
- 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
- B29K2105/00—Condition, form or state of moulded material or of the material to be shaped
- B29K2105/25—Solid
- B29K2105/251—Particles, powder or granules
-
- 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
- C08J2323/00—Characterised by the use of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Derivatives of such polymers
- C08J2323/02—Characterised by the use of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; 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
- 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
- C08J2423/02—Characterised by the use of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Derivatives of such polymers not modified by chemical after treatment
Landscapes
- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Engineering & Computer Science (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Medicinal Chemistry (AREA)
- Polymers & Plastics (AREA)
- Health & Medical Sciences (AREA)
- Mechanical Engineering (AREA)
- Crystallography & Structural Chemistry (AREA)
- Materials Engineering (AREA)
- Compositions Of Macromolecular Compounds (AREA)
- Moulding By Coating Moulds (AREA)
- Manufacturing Of Micro-Capsules (AREA)
- Processes Of Treating Macromolecular Substances (AREA)
- Glanulating (AREA)
Abstract
Multi-layered, core and shell particles are used to rotationally mold articles. The core and shell materials may be thermoplastic polymers, the difference between the core and the shell will be at leat 0.5 melt index units, optionally, the core and shell may also differ by at least about 1 ~CTm. The core and shell particles produce a rotationally molded article with generally an outer layer (of the molded article) that fuses more easily, and an inner layer that may provide superior toughness.
Description
WO96/158~2 2 ~ 8 ~ Pcrluss5~l44 MULTI-LAYER pART~.F.!~ FOR ROTATIONAL MOLDING
TECE[NICAL FIELD
This invention relates generally to improved rotational molded articles.
More specifically, this mventi~n relates to polymer particles that y~ldl~ a corelayer and a shell layer, each layer exhibitmg different properties. A ., ".~, molded part made from such particles will exhibit improved physical propetties when compared to a part madc with ~. ' ' particles. Such particles can facilitate processing conditions more favorable to physical property . u BACKGROIJND
Many types of polymers have been used for r ' ' g artides by rotational molding where both the polymers and the process are well known in theart, polyolefins are the generally preferred polymer due largely to economics and ease of processing. The rotatio~nal molding process utilizes a cavity mold which is suspended on at least one axis, more often on at least two axes. A polymer or polymers to be molded into a hollow part are charged to the mold cavity with a particle size that permits ease of filling all cavities of a mold, as well as rapid melting. The mold is closed and rotation oiF the mold on at least one axis is begun, concurrent with heating of the mold either from the outside of the mold or from hot gases on the interior of the rnold, or both. As the softening point or melting point of the polymer or polymers is reached the polymers begin to fuse or sinterinto the shape of the mold cavitSr. After ! ' ' " "~ all of the polymer has fused, the mold still containing the mol~ed article is cooled until the polymer would not be deformed by handling, then the part is removed from the mold. A well executed'l "S~ molded part will be generally a hollow part or a part having a cavity such as a toy, a surf board, a small boat, a tank or other types of objects withgenerally uniform properties aro~:nd the molded part. A more detailed of description of I ~ , can b~: found in Modern Plastics E~oy~,lo~J.,d;~l, l 985-1986, pg 3 19.
I
~1V0 96/15~92 PCIIUS95114401 ~813~ ~
In order to improve rotational ob~ect molded physical properties such as impact strength, or ~ ;,, ' stress crack resistance (ESCR), weight average molecular weights (Mw) of the resins are generally increased. However, as with many such l~ ' ' . s, the increase in molecular weight can be beneficial for 5 some physical properties, but detrimental to others causing a trade-off. In this case, a trade-offmay be that while increased Mw gives a molded article with improved physical properties, the ~ J of a bigher molecular weight material (Mw) generally becomes more and more difficult with increasing molecular weights, due at least in part to its lower flowability at rotational molding 10 L~ ldLulca. The lower fiowability is ' ` 'l~ related to the resin's higher viscosity. This problem may be solved in l,~ lal extruder type melt fabrication processes by ;IlLluduc;l~ additional shear and heat to such a polymer via machine changes. However m a rotational molding process there is relatively little shear. Accordingly, creating properly fused or void free parts with 15 ;ll~ y higher molecular weight material becomes ~ ,I,h,lll~ . because of either economic ~u~ such as length of time for a molding cycle, or because of dynamics of the process or both. Such process dynamics might include heating the mold to a t~,l.lp~ Lul~i high enough to fuse the higher molecular weight materials, which might lead to -- ~ d~ ddl;~J-., oxidation and/or perhaps 20 charring of the innermost portions of the molded article.
Another factor affecting the ability of a resin or resins to fuse in a rotational mold, ~ , free of voids, is the variable heating of a mold. Molds can have hot spots and cold spots due to, for instance, location (near a door, or surroumded ~y other molds) or heat transfer differences (e.g. where additional heat conductors 25 or insulators inevitably touch the mold).
Attempts have been made in the past to make tougher rotational molded parts, for instance US Patent 5,260,38l, discloses a cross-linkable p~ ,;h~
based ~ ., for rotational molding. The cross-linking that takes place based on this disclosure delivers a tougher part from a p~ ,lh.~ 1~".6 resin than would be WO 96115892 2 ~i 8 1 3 ~ PCTIUS9~114401 attaiinable by the part in an un.ross-iiniced state. The difficuities with such an approach are that the recycling or reuse of scrap or off-~ products once they are cross-iiniced is more difficuit.
There is a need for a method of producing the ~ , molded parts 5 that are tougher and maybe l~ , molded without use of cross-linicing agents.
In US Patent 4,533,696 a method is disclosed for d;ffc. "~ depositing polymer layers in a rotationai rnold by control of the relative particle sizes of two or more different polymer layers. This approach is icnown as a salt arld pepper 10 blend, referring to a blend of hvo different, . In the document the two different ~ t are differently stabilized materiais to achieve a specific purpose, which is having a well stabilized outer layer for protection of the artide from exposure to the elements, while the inner layer is a sl~h "~, non polymer which is disclosed as oxidizing inside the mold providing a receptive 15 surface for a mold f lling such a s p~ , for example, for use in surf boards.An article entitied "Processing and Properties of R . ? "~, Molded Foam", R. L. Heck Journai of lCeliular Plastics, MarchlApril 1993, illustrates the use and h,~pical production of foamed resins via use of various foaming agents. The problems presented with this approach is that different foaming agents must be 20 chosen based on the L~ ulc profiie during rotationai molding. Often tt , ~Lu.c~ are different even within a given part causing uneven foarned structure or blistering on the molded part surface.
JP 84-145733 discloses the use of muitiiayer particles to aid sintering in a non-pressurized ~.~ owever ti~is is ~ l via p~l~ . r~.i~,dLiu.. in 25 an aqueous process to create la~ex polymers. This is cc,l.sid~,.~ly different firom a rotationai molding process.
Accordingly, there is a need to have a ..u ~ of properties that will permit a uL~lLio~all~ molded artiicle to have relatively easy processing polymer while still exhibiting improved physicai properties.
WO96/15892 ~ J8 1 38~ pcr/usgsll440l O
SUMMARY
With . ~ '` of the present invention, I have found that the above-mentioned di~u~-t~ associated with prior solutions to the problem of obtaining 8 rotational molding resin that processes rel$ively easily and has superior 5 toughness, can be solved by the use of particles containing at least two polymers, where at least a Srst polymer has a different fusing lw..~ lu-~ than a second polymer. The second polymer may will impart toughness generally unavailable by l,V~ .iu~l~l rotational moldmg methods or by use of the Srst polymer by itself.
The first polymer will form a shell b. '1~ covering the second polymer, the 10 second polymer forming a core.
A shell may contain one or more polymers7 and a core may contain one or more polymers. The differences discussed below between the melt index (M[) and/or peak melting point (Tm) will still be of importance.
Preferably the shell has a viscosity ~ by melt index, which is at 15 least O.5 (dg/min) higher than that of the core polymer, at typical test conditions.
If the viscosity of the shell polymer is too low (i.e. too a high melt index), the overall binder, which the shell layer becomes, may become too weak and superior part properties may not result. If the viscosity of the shell polyrner is too high, poor fusion and voids may result which again generally cause parts with weak 20 physical properties.
Rotationally molded parts made from such a h.,t~,lubs~,uu~ particle, ~u~ , show improved physical property p~lru~ over salt and pepper particle, pellet, or powder blends.
The l.~ ue,~ ,uu~ particles may be made up of an outer shell of a 25 relatively low Ir.~ polymer where the shell polymer is present in the range of rrom about 5 to about 70 percent of the total particle diameter. The interior or core of the particle made up of a more difflcult to fuse material ispresent in the range of from about 30 to about 95 percent based on total diameter of the particle. The optimum shell and core distribution is in the range of 70130 to ~ WO9C/~5892 ~ ~11 8 1 38~ Pcrlusssll44o~
30/70. Preferred particles can be as large as about 30 mils (762 microns) in diameter with an aspect ratio defined by the l~,..~"i~l;_...~..~. ratio of the particle in the range of firom about 2:1 to 1:2. The preferred aspect ratio is 1:1. Smaiier particles may be made by traditionai grinding processes or by extrusion. The 5 preferred diameter is less thar. about 20 rnils (508 microns) and the preferred method of production is extrusion.
The differences betwe~n the shell and core polymers may be further enhanced by a difference in peak melting point (T",) as measured by differentiaisca~rning ~iUI i~ tly (DSC), i~speciaily if greater tharl about 2 C.
Other . r~ '' may require different ~ , between the shell and core polymers, for instance in a foamed .~ molded part, the sheli polymer may desirably have a higher Ivlw than the core polymer. N....~ Ih 1. - ., the differences between the shell .und core materiai should stiil be at least 0.5 dglmin, optionally the Tm should still ~e at least about 1C different between the shell15 polymer or polymers and the ~,ore polymer or polymers.
BRIEF DESCRIPTION OF TEIE DRA,WINGS
These and other featules, aspects, and advantages of ~ - ' of the present invention will become better understood with regard to the following 20 I~crnrtic n. appended claims ~md - , , ;.lg drawings where: Figure I shows a~ at 10X ~, ~ ofthemoldedpartsfiromRuns I and2.
DESCRIPTIOI~
The present invention concerns certain polymer ~ .J~ and 25 ~" ' based onthese ~ u~ Thesepolymer~ have properties when used in a rotational molding which make them particularly well suited for,, ' that require superior toughness from a rotational molded part. The structure of the particles used to maiie the ~ "~/ molded articles WO96/1~892 ~ 18 ) 3 8g PCT/IJS95/14401 deliver a ' of ~ and toughness generally superior to previously available materials.
Following is a detailed description of certain preferred polymer ;.... - within the scope of the present invention, preferred methods of S producing these c ~ . ,, and preferred 4.1~ ' ~ ;r~ of these polymer ~ - -r Those skilled in the art wiD appreciate that numerous I ' ~
to these preferred ~,...~ " can be made without departing from the scope of this invention. For example, though the properties of the polymer: ~ are prr rrlrlifiPA in rotational molding ., ' , they will have numerous other uses.
To the extent our description is specific, it is solely for the purpose of illustrating preferred; ~ - " of my invention and should not be taken as limiting the present invention to these specific ~ ~ " Various values given in the te~ct and claims are determined and defined as follows:
Impact Strength, measured by Association of Rotational Molders (ARM) test using a 15 lb. (6.g Kg) weight dropped at various heights to give an impactenergy in ft - lb.F or Joules. Test done at -40 C.
Part Thickr~ess known as the average part thickness. Measured as rnils (1/1 000th of an inch), or millimeters using a Cure State can be described as a qualitative ~ ,~u~l of the absence of voids in the part cross-section. E ccellent cure has no voids, poor cure has many voids throughout the cross-section.
The Fle~ural Modulus, at 1% secant, in KPSI (MPa) measured using ASTM D-790.
te~' Impact Test (IIT) using a CEAST tester at -40C. Method follows ASTM D-3763-86.
~I~v;~ ' ' Stress Crack 1~ , (ESCR), using ASTM D-1693 Condition A, 10% Igepal solution, on luLaLio~.iL~ molded samples 136 mils (3.45 mm) thick. Reading in hours, is taken when 50% of the samples fail (Fso).
-~ W096/15892 ~! 1 8 1i388 PCII~IS95114401 Viscosity as measured by melt index using ASTM D-1238, Condition E
(2160 gm/190 C). Viscositi~s may also be measured by plate and cone rheometry at 102 sec-~. Flow units in pascal-sec.
P~ Molding Cure Time (minutes): Exxon method, using a clam S shell rotational molding macbine, Model lFSP M-60. The time necessary for a rotational molding 1'. " ", ~ , . typically in granular, micro-pellet, or powder form, to fuse into a void free part at a given l~ . Too little cure time will result in voids or air pockets, too ml~ch cure time will degrade the resin from which the part is formed. Resin d~ is ~ i by arl increase in resin viscosity 10 (drop in melt index), and/or s~vere color shifting towards a ~,llu . /bl u ' part.
Tbis may quantified by measuring carbonyl forrnation on the inside surface of the ., "~ molded part, or g~nerally in the industry by using the arm dart impact tests discussed above.
Melt Strength as defined by a method outlined by G. Meissner, Pure &
Applied Chemistry, Vol. 42, pg. 553, 1975.
Palrticle Size D;~t. ;- " , measured by the amount retained on a screen, as defined by ASTM D-1921 using a Rototap Model B, 100 gm sample, 10 minute shake.
Dry Flow of particles measured in seconds by a Funnel Flow Test, as defined by ASTM D- 1895, Method A on a 100 gm sample. E~gh values of dry flow or no flow denote poorer powder quality as the tumbling action of the powder wili not be uniform, and this part forming will be poorer.
Bulk Density in g/l 00 cc as defined by ASTM D-l ~95, Method A, using a minimum of a 200 gm sample.
Melt Inde~ is defined by ASTM D-123~ using 2160 grams at 190 C, units in gm/10 minutes, or dc.,;~;.~"l~/ , dg/min).
Density is defined by ASTM D-1505, units in gm/cc.
Differential Scanning ~ (DSC) by ASTM D-3417.
WO96115892 2 18 13g8 PCTIUS95/14401 ~
In an ' ' of the present invention for improved impact strength, a sheil amd core ~.~ ' of a particle is comprised of at le~st one polymer im the shell or outside layer of the particle and at least a second higher molecular weight, (optionaily) lower melting point, than the polymer of the sheii layer materiai in the S core. The more easily fused polymer (generaily the shell polymer) may melt amd fiii areas in a mold that are intricate or involve sharp angles (whereas a lower MI
materiai would be more difficult to fill in such areas). The shell polymer also as it fuses between the core polymer domains fiils in the voids between the particles thus becoming a binder or adhesive layer, creating a s ' '1~ void free part.
10 The more difficult to fuse (e.g., lower Ml or core) domains trapped and dispersed between and behind (or to the part interior) the binder layer, will have improved impact strength amd stress crack resistamce so the overall lllOl ~,llolu~y may be similar to l,UII. . " ' rubber modified polymers.
15 Sheil Materislc Among the polymers envisioned for the shell are lower viscosity materiais such as linear low density p~ .,h,.l~.S with melt indices above about 1.5 dg/min.
with densities above about û.915, preferably above or about 0.930g/cc high density pUI~ with a melt index above about 1.5 dg/min. and most preferred a 20 density above about 0.940 g/cc; ionomer materiais having a melt index greater than about 1.5 dg/min. preferably above about 2.0 dg/min, more preferably above about3.0 dg/min. and a cation content greater than about 0.5 wt% amd; p~ luy.~!c having a melt flow M i rate in the range of from about above about 1.0 dg/min.
preferably in the range of from about 3 to about 40 dg/min, more preferably from25 about 5 to about 40 dg/min; ethylene co-polymers of acrylic acid, l ~ acid or ester ~ such as acrylic acid, I~ , acid, methyl acrylate, vinyl acetate, ethyl acrylate, or butyl acrylate having melt indexes greater than about 1.5 dg/min. amd ~ ,.. contents greater than about 4 weight percent are generally preferred. More preferred above about :Z O Ml, most preferred above about 2.5.
-WO 96/15892 ~ ~ 8 ~ 3 ~ ~ ~CTrUS95114401 More preferred, I~vel above about 5 wt%, most preferred above about 8 wt%.
LDPE is also; , ' ' for the shell material. LDPE's with 1.5 dg/min.
are preferred, more preferabl)r greater than about 2 dg/min., and preferred densities greater than 0.915 g/cc, more preferably densities in the range of from about 0.915 to about 0.930 g/cc. LDPE's are generally pc.l~ 1 in the presence of free radical initiators.
The shell material ma~ be filled with talc, silicas, glass beads, .,.~
agents, or other materials to il~prove surface abrasion resistance of the finished article. The shell material may also be nylon, SELAR@) (DuPont) 5 PE, fluorinated or ~ ' ' polymers to improve chemical resistance, again having melt indexes of greatel. than about 1.5 dg/min. For impact . u._...~,..l~, most preferred for the shell layer will be lower melting point linear low density p~ s (LLDPE), high density ~UI~ YI~ ~DPE)s, IJOIJ~JIU
(PP), and ionomers.
For foamed ~, 1 ' the preferred shell material would have a higher viscosity (lower ~) than the core material by at least 0.5 MI units and more preferred by 2.0 Ml units. Ol)tionally this could be enhanced by using a higher melt strength material, to aid ,~ell stlucture formation.
For chemical resistance, the preferred shell material would be a SELAR
'` ' ' PE, or nylon, most preferred a nylon 6.
The LLDPEs, HDPEs, and PP can be made employing " -traditional Ziegler-Natta, and Chromium type catalysts, and catalyst systems. The LLlDPE will have a density in the range of from about 0. 85 to about 0.940 g/cc preferably in the range of frorn about 0.90 to about 0.940 g/cc, more preferablyfrom about 0 915 to about 0.940 g/cc. The HDPE will have a density in the ramge of from about 0.940 to about 0.965 g/cc. The PP will generally have a density about 0.90. The shell materials of an 1l .o.l - ~ of the present invention for impact forming illllul ~, . _.II.,.IL will be selected from the group consisting of LLDPE, g WO 96/15892 ~ I ~ 13 88 PCI~/US95114401 ~
HDPE, pul~p.u~"~lc..c, pc~ ,.u~,jlc~ ,ulJul~ ,.a, ethylene vinyl-acetates, ethylene cLl.J' '1~, 1 ' acrylic ester wl~ul~ , iûnûmers~ acid co amd L~ ul~ a.
S Core r r . I
Core materials for impact , u.. are those materials which will be higher molecular weight (M,v), optionally lower melting (than the shell materials), than the materials described for the shell. These will genera51y be resins that will yield tougher 1~ molded parts. The core materials may be linear low 10 density pol~ }l;lcll~, (ILDPE) having a melt index in the range of from about 0.5 to about 10 dg/min., and a density in the range of firom about 0.915 to 0.940 g/cc (preferably .915 - .930 glcc), more preferably the Ml will be in the rimge offrom about 0.5 to about 5 dg/min., and most preferably in the range of from about 0.8 to about 4 dglmin.; high density ~ol~ lcllw (IIDPE) having a melt index in the range of from about 0.05 to about 70 preferably in the range of from about 0.3 to about 5, more preferably in the range of fi om about 0.3 to about 4.0 dg/min. and densities in the r~mge of fi om about 0.940 to about 0.960 g/cc p~5~ ~,.u~ c l~u~ul~ul~ , pol ~,. u~lc..~. co and lcl l~ul~ a where ethylene andlor a-olefinshaving carbon numbers from 4-20 may be used; ~ol~ .;lc...,s or PUI.YI~UIJ~!C.
20 when not l.u...u~ul~ a~ can have co and lr~ a selected from the group consisting of a-olefins having 4-20 carbon atoms. The c. ~ . may be selected from the group consisting of butene-l, 4-methyl-1-pentene, pentene-l hexene-l, octene-l, or any ofthe alpha-olefins having from 4-20 carbon atoms. Inthe case of ~ . ul~ylc.~c, the ~ may be any of these alpha-olefins but 25 also includes ethylene as potentia5 ~ . In the case of ..u... _.~L;u~ 5 low density pol~cLhJ!c..c (LDPE) C~ can be selected from c~
acrylicacidesters. Nylonandother " - ., Lll~lllu~ aL;~a are also .-, ~ ..t~ as core materials. The pù~ ylc..~,s and pOI~ u~ .S can be catalyzed by traditional Ziegler-Natta Catalysts, M ~ rl alumoxane Catalysts, WO 96/15892 ~ 8~ PCIIUS ,5114401 chromium based cataiysts, certain free radicai initiated Low Density PEs or LDPEethylene carbon monoxide ,op~ and lel~Jul~ Preferably the ethyiene or propylene co or terpolymer wii~l have a ~ content in the range of from about 0.5 to 6 mole percent, m~re preferably in the range of from about 2 to about 5 6, most preferably in the range Df from about 4 to about 6 mole percent. Preferred c~-olef ns for both ethylene and propylene co and lel~Ju~ are 4-methyl-1-pentene, butene-l, pentene-l, h.exene-l, and octene-l.
Aiso as a core materiai, nylon is . . ' i, having the following properties: melt index greater 1han about 1.5 dg/min and about densities 1Øglcc.
Other preferred core materiais will be selected from the group consisting of linear low density pc,l~ }, ~ " high density pui~ ~,lt.yh",~ ., pu~ ul,yl-_,lc, pbl~JIu~J~ e l,UyUlJ , nylons, and ethylene elt.~ ester .u~cil~ ~ or ionomers. LLDPEs, E[DPEs, and PPs, and pul~t,.u~ ...c. and ,o~,u'.~ ~ thereof may be cataiyzed by the Cu..~ iullc i Ziegler-Natta cataiysts, chromium type Cuul i;l~iiull caitalysts, " ' ' ~' site catalysts, or in the case of high pressure i ibl~ ~.;11, !, .~ materials (IDPEs), through free radicai initiation p~ ,li~liui~. The ~ thylene an~i the propylene polymers may be made by a number of processes including high pressure, gas pbase fluidized bed, slurry, or solution processes.
2û In the selection of core amd shell materiais a difference in Mw as manifested in Ml of at least 0.5 melt index urlits wiii acbieve the melting and fusing differences of importance. Preferably this difference is at least 1, most preferably 2.5 melt index units. In addition to or in place of the melt index differentiai, a peak melting point diffe}ential (as measured i)y Differential Scanning t`-' (DSC)) of at least about 1 C, preferably at least about 2 C, most preferably at least about 5 C.
For foamed rr~' " the preferred core materiai would contain a foaming agent. Some foarning agents are hA~ ~ b~ , p-toluene sulfonyl sc..l;c~llb~ic, p-p-oxobis- (benzene-sulfonyl hydraxide), 'i~ ' ~!uAidc.-4, 4'-wo 96/15892 2 1 8 ) 3 88 PCT/US95/14401 ~
' .rJ~ , or p-toluene ''' ," ~J~d~,. The preferred agent is pp-oxybis (benzene-sulfonyl hydraxide) or ~ u,d~c ~, 4'-~ J.~i~.
The foaming agent can be added at 0.05 wt to 10% wt with a more preferred range of 0.2 to 6 wt % and the most preferred range of 0.3 to 5 wt %
The foaming agent can be ~,, ' by melt extrusion (single screw preferred method), Banbury mixers, 2-roll mills. Melt extrusion via extruders ispreferred with single screw extrusion most preferred.
MAKEUP OF CORE AND SHELL PARTICLES
A shell is defined and used hereinafter as a material that partially covers and is on the outside of a core material in the range of from about 5 to about 70 percent of the particle diameter, preferably in the range of from about 30-70 percent based on the total diameter of a h~.t~ .u~ particle. Preferably the shell material will cover ! ' ' " '1~ all of the core material. The core material will make up the balarlce of the particle and will be preferred ' "S covered by the shell material. If the shell material covers less than about 25% of the core material surface area, the same problems that would be c..~,.,~....~,.~l with anattempt to l~L~Iliu~dl ~ mold the core materials would be ~d, and the benefit the core and shell distribution on a particle may be lost.
METnODS OF MAKING A ~ETERQGENEOUS CORE AND S~ELL
PART~CLE
Methods of forrning core and shell polymers include, but are not limited to, C~ u~;vl1~ powder deposition, or cûp~ ,... The use of series reactors is 25 a well known way to combine two different poly~ner properties in the same particle. The size of pellets or particles are typically, 5-100 mils (127-2540 microns) preferred 5-50 mils (127-1270 microns), more preferred 5-30 mils (127-762 microns), most preferred 5-20 mils (127-50~ microns) in diarneter with and aspect ratio (the ratio of a particle's length to diameter) in the range of from about ~ WO96/15892 2~13~ PCTJUS95J14401 2:1 to about 1:2 preferred in tile range offrom about 1.5:1 to about 1:1.5, mostpreferred in the range of from ~bout 1:1. The pellets may then be ground to a size typically used in rotational molding, specifically in the range of from about 20 to 2.9 mils ~500 to 75 microns) al.so described as a maximum of 35 US mesh preferred in the range of from about 13 .8 to 2.9 mils (350-75 microns), more preferred in the range offrom about 11.7 to 2.9 mils (300-75 microns).
Another method of ~ u.luL~,Lul~ would be to use a ~,u~ u ~;Oll technique followed by a strand cutting pelletizing operation or an l ' ... pelletizing operation. If the pellets or particles are to be used in a rotational molding process they should not exceed about 30 mils (762 microns) preferably, 20 mils (508 microns) most preferably 8 mils (203 microns). Alternatively howeYer, particles of any size may be ground into a ,~owder finer than about 30 miis (762 microns) in diameter, preferably finer than about 20 miles (508 microns).
Whatever method of ,,,~,ur.l.,LIu- ~ is chosen for forming the shell and core materials, whatever the percentage of each particle is, ShelUcore, and however complete the ~ of ~he core by the shell, the particle should perform to advantage when compared to for instance salt and pepper blends, or melt blends.
Examples 1-9 ID/run numbers 1-9 combine a range of materials in a Killion ;u."~l- u:~;u apparatus. Polymer particles are pelletized and then ground in sn attrition mill, made by Wedco, USA. The p~lrticle Aictrihll~inn is outlined in Table 3. The material from each ofthe cc,~uu ,;~,.. tests is run in rotational molding evaluations.
These evaluations are carried out in an FSP Model 60 clam shell rotational molding machine, using a sheet mold, c~red at 600 F for 14 minutes. The molded polymer is allowed to cool 5 minutes with the top of the oven closed and then 5 minutes with the top of the oven open ~ith ambient air circulated by a fan, followed by 11 minutes of water spray onto the mold and part then a 3 minute period of drying.
Where a part was made, the thicknesses are ~ 240 mils (6.1 mm). The W096115892 2 ) 8 138g PCTIUS95/144~
physical properties of the parts molded are shown on Table 4. No physical property testing is done on runs 1-3, as runs 1-3 are only used to illustrate the Illol~ created. Run I illustrates that a 20/80 shell/core polymer structure when ground to a powder, creates a coarse p~._.. aL;II~ network where the 5 core polymer exhibits domain regions.
Run 2 illustrates that a 50/50 core/shell particle, when ground to 35 mesh particle size provides a continuous network. Comparing Runs I and 2, in photos leads us to believe that if a 30/70 structure was created a dense ;1l;~
network would be present.
Runs 4 and 4B are of most interest relative to improving impact strength.
Run 4 utilized a particle according to an l ~ ' of the present invention, specifically a shell polymer of LL-8460 at 3.3 melt index7 0.939 density, stabilized LLDPE available from Exxon Chemical Canada, with a core material of LL-5005 wbich is a 0.3 Ml, 0.960 density bigh density pûl~_Lh~ available from Dow 15 Chemical Canada. Whereas run 4B utilized a more traditional blend, specif cally a "salt and pepper" blend of the same two resins of example 4. The parts were cured identically. As can be seen the salt and pepper blend had less than half the impact strength of the }~.Ltl u~,_.._uu~ particle material at the same thickness. The }..,L~I U~,_.l.,~lU:i part also exhibited a better cured state. Additiûnally, the 20 II~L~,.U~,_.I_.JU~ particle molded article displayed well over 100% increase in ESCR
when compared to the salt and pepper blend.
Runs 6-9 show other ~ ' though none were optimized and none were ~aLi~L~,Luly.
25 FY~nlrl.~ 10 To create a ., "S~ molded part having relative ;IIl~J. ' "`S/ to solvents a SELAR (R) material is used in the shell. The "platelets" formed by the SELAR provide a difflcult or torturous path for a Solvent to traverse. Additionally a high ."y " 'S/ polymer such as nylon is also employed to provide relative ~ WO 96/15892 2 1 8 i 3'8 ~ PCrlUS95114401 , to solvent ppn~tr~tjnn When SELAR@) is used as the shell material and T T npE is used as a core Inaterial, a part having excellent solvent barrier, but good impact strength at reduced cost is produced.
5 Example 11 A dense ~....~h~L;..~ network especially containing conductive fiilers, is used in the shell to improve static charge dissipation. Relatively high Ml materials e.g. 5 MI LLDPE (density 0.930 g/cc) containing aiuminum flakes, carbon black and conductive fibers are used in the shell to provide a ' of 10 mter~ .l-dLu.p network Witil conductive fillers to more easily facilitate dissipation of static build. Tho core material used a LLDPE with a 0.5 MI lower than the shell materiai. The core materiai provides enhamced impact strength.
Compared to the filled polymer used by themselves in a .~ , molded palt, the parts made from the core Md shell does play superior impact resistance.
Aithough the present i]lvention has been described in ~ detail with reference to certain preferred versions thereof, other versions are possible.
For example, other means of fDrming h~t~,.uc_...,~,u~ particles, and other of polymers are . ' 1. Therefore, the spirit and scope of the 20 appended claims should not be limited to the description of the preferred versions contained herein.
.
WO96/15892 æ/813~ PCTIUS9~/14401 ~
1~ 1' ~, C
r~ r 1~; r z ~ æ ~ ~ O
TECE[NICAL FIELD
This invention relates generally to improved rotational molded articles.
More specifically, this mventi~n relates to polymer particles that y~ldl~ a corelayer and a shell layer, each layer exhibitmg different properties. A ., ".~, molded part made from such particles will exhibit improved physical propetties when compared to a part madc with ~. ' ' particles. Such particles can facilitate processing conditions more favorable to physical property . u BACKGROIJND
Many types of polymers have been used for r ' ' g artides by rotational molding where both the polymers and the process are well known in theart, polyolefins are the generally preferred polymer due largely to economics and ease of processing. The rotatio~nal molding process utilizes a cavity mold which is suspended on at least one axis, more often on at least two axes. A polymer or polymers to be molded into a hollow part are charged to the mold cavity with a particle size that permits ease of filling all cavities of a mold, as well as rapid melting. The mold is closed and rotation oiF the mold on at least one axis is begun, concurrent with heating of the mold either from the outside of the mold or from hot gases on the interior of the rnold, or both. As the softening point or melting point of the polymer or polymers is reached the polymers begin to fuse or sinterinto the shape of the mold cavitSr. After ! ' ' " "~ all of the polymer has fused, the mold still containing the mol~ed article is cooled until the polymer would not be deformed by handling, then the part is removed from the mold. A well executed'l "S~ molded part will be generally a hollow part or a part having a cavity such as a toy, a surf board, a small boat, a tank or other types of objects withgenerally uniform properties aro~:nd the molded part. A more detailed of description of I ~ , can b~: found in Modern Plastics E~oy~,lo~J.,d;~l, l 985-1986, pg 3 19.
I
~1V0 96/15~92 PCIIUS95114401 ~813~ ~
In order to improve rotational ob~ect molded physical properties such as impact strength, or ~ ;,, ' stress crack resistance (ESCR), weight average molecular weights (Mw) of the resins are generally increased. However, as with many such l~ ' ' . s, the increase in molecular weight can be beneficial for 5 some physical properties, but detrimental to others causing a trade-off. In this case, a trade-offmay be that while increased Mw gives a molded article with improved physical properties, the ~ J of a bigher molecular weight material (Mw) generally becomes more and more difficult with increasing molecular weights, due at least in part to its lower flowability at rotational molding 10 L~ ldLulca. The lower fiowability is ' ` 'l~ related to the resin's higher viscosity. This problem may be solved in l,~ lal extruder type melt fabrication processes by ;IlLluduc;l~ additional shear and heat to such a polymer via machine changes. However m a rotational molding process there is relatively little shear. Accordingly, creating properly fused or void free parts with 15 ;ll~ y higher molecular weight material becomes ~ ,I,h,lll~ . because of either economic ~u~ such as length of time for a molding cycle, or because of dynamics of the process or both. Such process dynamics might include heating the mold to a t~,l.lp~ Lul~i high enough to fuse the higher molecular weight materials, which might lead to -- ~ d~ ddl;~J-., oxidation and/or perhaps 20 charring of the innermost portions of the molded article.
Another factor affecting the ability of a resin or resins to fuse in a rotational mold, ~ , free of voids, is the variable heating of a mold. Molds can have hot spots and cold spots due to, for instance, location (near a door, or surroumded ~y other molds) or heat transfer differences (e.g. where additional heat conductors 25 or insulators inevitably touch the mold).
Attempts have been made in the past to make tougher rotational molded parts, for instance US Patent 5,260,38l, discloses a cross-linkable p~ ,;h~
based ~ ., for rotational molding. The cross-linking that takes place based on this disclosure delivers a tougher part from a p~ ,lh.~ 1~".6 resin than would be WO 96115892 2 ~i 8 1 3 ~ PCTIUS9~114401 attaiinable by the part in an un.ross-iiniced state. The difficuities with such an approach are that the recycling or reuse of scrap or off-~ products once they are cross-iiniced is more difficuit.
There is a need for a method of producing the ~ , molded parts 5 that are tougher and maybe l~ , molded without use of cross-linicing agents.
In US Patent 4,533,696 a method is disclosed for d;ffc. "~ depositing polymer layers in a rotationai rnold by control of the relative particle sizes of two or more different polymer layers. This approach is icnown as a salt arld pepper 10 blend, referring to a blend of hvo different, . In the document the two different ~ t are differently stabilized materiais to achieve a specific purpose, which is having a well stabilized outer layer for protection of the artide from exposure to the elements, while the inner layer is a sl~h "~, non polymer which is disclosed as oxidizing inside the mold providing a receptive 15 surface for a mold f lling such a s p~ , for example, for use in surf boards.An article entitied "Processing and Properties of R . ? "~, Molded Foam", R. L. Heck Journai of lCeliular Plastics, MarchlApril 1993, illustrates the use and h,~pical production of foamed resins via use of various foaming agents. The problems presented with this approach is that different foaming agents must be 20 chosen based on the L~ ulc profiie during rotationai molding. Often tt , ~Lu.c~ are different even within a given part causing uneven foarned structure or blistering on the molded part surface.
JP 84-145733 discloses the use of muitiiayer particles to aid sintering in a non-pressurized ~.~ owever ti~is is ~ l via p~l~ . r~.i~,dLiu.. in 25 an aqueous process to create la~ex polymers. This is cc,l.sid~,.~ly different firom a rotationai molding process.
Accordingly, there is a need to have a ..u ~ of properties that will permit a uL~lLio~all~ molded artiicle to have relatively easy processing polymer while still exhibiting improved physicai properties.
WO96/15892 ~ J8 1 38~ pcr/usgsll440l O
SUMMARY
With . ~ '` of the present invention, I have found that the above-mentioned di~u~-t~ associated with prior solutions to the problem of obtaining 8 rotational molding resin that processes rel$ively easily and has superior 5 toughness, can be solved by the use of particles containing at least two polymers, where at least a Srst polymer has a different fusing lw..~ lu-~ than a second polymer. The second polymer may will impart toughness generally unavailable by l,V~ .iu~l~l rotational moldmg methods or by use of the Srst polymer by itself.
The first polymer will form a shell b. '1~ covering the second polymer, the 10 second polymer forming a core.
A shell may contain one or more polymers7 and a core may contain one or more polymers. The differences discussed below between the melt index (M[) and/or peak melting point (Tm) will still be of importance.
Preferably the shell has a viscosity ~ by melt index, which is at 15 least O.5 (dg/min) higher than that of the core polymer, at typical test conditions.
If the viscosity of the shell polymer is too low (i.e. too a high melt index), the overall binder, which the shell layer becomes, may become too weak and superior part properties may not result. If the viscosity of the shell polyrner is too high, poor fusion and voids may result which again generally cause parts with weak 20 physical properties.
Rotationally molded parts made from such a h.,t~,lubs~,uu~ particle, ~u~ , show improved physical property p~lru~ over salt and pepper particle, pellet, or powder blends.
The l.~ ue,~ ,uu~ particles may be made up of an outer shell of a 25 relatively low Ir.~ polymer where the shell polymer is present in the range of rrom about 5 to about 70 percent of the total particle diameter. The interior or core of the particle made up of a more difflcult to fuse material ispresent in the range of from about 30 to about 95 percent based on total diameter of the particle. The optimum shell and core distribution is in the range of 70130 to ~ WO9C/~5892 ~ ~11 8 1 38~ Pcrlusssll44o~
30/70. Preferred particles can be as large as about 30 mils (762 microns) in diameter with an aspect ratio defined by the l~,..~"i~l;_...~..~. ratio of the particle in the range of firom about 2:1 to 1:2. The preferred aspect ratio is 1:1. Smaiier particles may be made by traditionai grinding processes or by extrusion. The 5 preferred diameter is less thar. about 20 rnils (508 microns) and the preferred method of production is extrusion.
The differences betwe~n the shell and core polymers may be further enhanced by a difference in peak melting point (T",) as measured by differentiaisca~rning ~iUI i~ tly (DSC), i~speciaily if greater tharl about 2 C.
Other . r~ '' may require different ~ , between the shell and core polymers, for instance in a foamed .~ molded part, the sheli polymer may desirably have a higher Ivlw than the core polymer. N....~ Ih 1. - ., the differences between the shell .und core materiai should stiil be at least 0.5 dglmin, optionally the Tm should still ~e at least about 1C different between the shell15 polymer or polymers and the ~,ore polymer or polymers.
BRIEF DESCRIPTION OF TEIE DRA,WINGS
These and other featules, aspects, and advantages of ~ - ' of the present invention will become better understood with regard to the following 20 I~crnrtic n. appended claims ~md - , , ;.lg drawings where: Figure I shows a~ at 10X ~, ~ ofthemoldedpartsfiromRuns I and2.
DESCRIPTIOI~
The present invention concerns certain polymer ~ .J~ and 25 ~" ' based onthese ~ u~ Thesepolymer~ have properties when used in a rotational molding which make them particularly well suited for,, ' that require superior toughness from a rotational molded part. The structure of the particles used to maiie the ~ "~/ molded articles WO96/1~892 ~ 18 ) 3 8g PCT/IJS95/14401 deliver a ' of ~ and toughness generally superior to previously available materials.
Following is a detailed description of certain preferred polymer ;.... - within the scope of the present invention, preferred methods of S producing these c ~ . ,, and preferred 4.1~ ' ~ ;r~ of these polymer ~ - -r Those skilled in the art wiD appreciate that numerous I ' ~
to these preferred ~,...~ " can be made without departing from the scope of this invention. For example, though the properties of the polymer: ~ are prr rrlrlifiPA in rotational molding ., ' , they will have numerous other uses.
To the extent our description is specific, it is solely for the purpose of illustrating preferred; ~ - " of my invention and should not be taken as limiting the present invention to these specific ~ ~ " Various values given in the te~ct and claims are determined and defined as follows:
Impact Strength, measured by Association of Rotational Molders (ARM) test using a 15 lb. (6.g Kg) weight dropped at various heights to give an impactenergy in ft - lb.F or Joules. Test done at -40 C.
Part Thickr~ess known as the average part thickness. Measured as rnils (1/1 000th of an inch), or millimeters using a Cure State can be described as a qualitative ~ ,~u~l of the absence of voids in the part cross-section. E ccellent cure has no voids, poor cure has many voids throughout the cross-section.
The Fle~ural Modulus, at 1% secant, in KPSI (MPa) measured using ASTM D-790.
te~' Impact Test (IIT) using a CEAST tester at -40C. Method follows ASTM D-3763-86.
~I~v;~ ' ' Stress Crack 1~ , (ESCR), using ASTM D-1693 Condition A, 10% Igepal solution, on luLaLio~.iL~ molded samples 136 mils (3.45 mm) thick. Reading in hours, is taken when 50% of the samples fail (Fso).
-~ W096/15892 ~! 1 8 1i388 PCII~IS95114401 Viscosity as measured by melt index using ASTM D-1238, Condition E
(2160 gm/190 C). Viscositi~s may also be measured by plate and cone rheometry at 102 sec-~. Flow units in pascal-sec.
P~ Molding Cure Time (minutes): Exxon method, using a clam S shell rotational molding macbine, Model lFSP M-60. The time necessary for a rotational molding 1'. " ", ~ , . typically in granular, micro-pellet, or powder form, to fuse into a void free part at a given l~ . Too little cure time will result in voids or air pockets, too ml~ch cure time will degrade the resin from which the part is formed. Resin d~ is ~ i by arl increase in resin viscosity 10 (drop in melt index), and/or s~vere color shifting towards a ~,llu . /bl u ' part.
Tbis may quantified by measuring carbonyl forrnation on the inside surface of the ., "~ molded part, or g~nerally in the industry by using the arm dart impact tests discussed above.
Melt Strength as defined by a method outlined by G. Meissner, Pure &
Applied Chemistry, Vol. 42, pg. 553, 1975.
Palrticle Size D;~t. ;- " , measured by the amount retained on a screen, as defined by ASTM D-1921 using a Rototap Model B, 100 gm sample, 10 minute shake.
Dry Flow of particles measured in seconds by a Funnel Flow Test, as defined by ASTM D- 1895, Method A on a 100 gm sample. E~gh values of dry flow or no flow denote poorer powder quality as the tumbling action of the powder wili not be uniform, and this part forming will be poorer.
Bulk Density in g/l 00 cc as defined by ASTM D-l ~95, Method A, using a minimum of a 200 gm sample.
Melt Inde~ is defined by ASTM D-123~ using 2160 grams at 190 C, units in gm/10 minutes, or dc.,;~;.~"l~/ , dg/min).
Density is defined by ASTM D-1505, units in gm/cc.
Differential Scanning ~ (DSC) by ASTM D-3417.
WO96115892 2 18 13g8 PCTIUS95/14401 ~
In an ' ' of the present invention for improved impact strength, a sheil amd core ~.~ ' of a particle is comprised of at le~st one polymer im the shell or outside layer of the particle and at least a second higher molecular weight, (optionaily) lower melting point, than the polymer of the sheii layer materiai in the S core. The more easily fused polymer (generaily the shell polymer) may melt amd fiii areas in a mold that are intricate or involve sharp angles (whereas a lower MI
materiai would be more difficult to fill in such areas). The shell polymer also as it fuses between the core polymer domains fiils in the voids between the particles thus becoming a binder or adhesive layer, creating a s ' '1~ void free part.
10 The more difficult to fuse (e.g., lower Ml or core) domains trapped and dispersed between and behind (or to the part interior) the binder layer, will have improved impact strength amd stress crack resistamce so the overall lllOl ~,llolu~y may be similar to l,UII. . " ' rubber modified polymers.
15 Sheil Materislc Among the polymers envisioned for the shell are lower viscosity materiais such as linear low density p~ .,h,.l~.S with melt indices above about 1.5 dg/min.
with densities above about û.915, preferably above or about 0.930g/cc high density pUI~ with a melt index above about 1.5 dg/min. and most preferred a 20 density above about 0.940 g/cc; ionomer materiais having a melt index greater than about 1.5 dg/min. preferably above about 2.0 dg/min, more preferably above about3.0 dg/min. and a cation content greater than about 0.5 wt% amd; p~ luy.~!c having a melt flow M i rate in the range of from about above about 1.0 dg/min.
preferably in the range of from about 3 to about 40 dg/min, more preferably from25 about 5 to about 40 dg/min; ethylene co-polymers of acrylic acid, l ~ acid or ester ~ such as acrylic acid, I~ , acid, methyl acrylate, vinyl acetate, ethyl acrylate, or butyl acrylate having melt indexes greater than about 1.5 dg/min. amd ~ ,.. contents greater than about 4 weight percent are generally preferred. More preferred above about :Z O Ml, most preferred above about 2.5.
-WO 96/15892 ~ ~ 8 ~ 3 ~ ~ ~CTrUS95114401 More preferred, I~vel above about 5 wt%, most preferred above about 8 wt%.
LDPE is also; , ' ' for the shell material. LDPE's with 1.5 dg/min.
are preferred, more preferabl)r greater than about 2 dg/min., and preferred densities greater than 0.915 g/cc, more preferably densities in the range of from about 0.915 to about 0.930 g/cc. LDPE's are generally pc.l~ 1 in the presence of free radical initiators.
The shell material ma~ be filled with talc, silicas, glass beads, .,.~
agents, or other materials to il~prove surface abrasion resistance of the finished article. The shell material may also be nylon, SELAR@) (DuPont) 5 PE, fluorinated or ~ ' ' polymers to improve chemical resistance, again having melt indexes of greatel. than about 1.5 dg/min. For impact . u._...~,..l~, most preferred for the shell layer will be lower melting point linear low density p~ s (LLDPE), high density ~UI~ YI~ ~DPE)s, IJOIJ~JIU
(PP), and ionomers.
For foamed ~, 1 ' the preferred shell material would have a higher viscosity (lower ~) than the core material by at least 0.5 MI units and more preferred by 2.0 Ml units. Ol)tionally this could be enhanced by using a higher melt strength material, to aid ,~ell stlucture formation.
For chemical resistance, the preferred shell material would be a SELAR
'` ' ' PE, or nylon, most preferred a nylon 6.
The LLDPEs, HDPEs, and PP can be made employing " -traditional Ziegler-Natta, and Chromium type catalysts, and catalyst systems. The LLlDPE will have a density in the range of from about 0. 85 to about 0.940 g/cc preferably in the range of frorn about 0.90 to about 0.940 g/cc, more preferablyfrom about 0 915 to about 0.940 g/cc. The HDPE will have a density in the ramge of from about 0.940 to about 0.965 g/cc. The PP will generally have a density about 0.90. The shell materials of an 1l .o.l - ~ of the present invention for impact forming illllul ~, . _.II.,.IL will be selected from the group consisting of LLDPE, g WO 96/15892 ~ I ~ 13 88 PCI~/US95114401 ~
HDPE, pul~p.u~"~lc..c, pc~ ,.u~,jlc~ ,ulJul~ ,.a, ethylene vinyl-acetates, ethylene cLl.J' '1~, 1 ' acrylic ester wl~ul~ , iûnûmers~ acid co amd L~ ul~ a.
S Core r r . I
Core materials for impact , u.. are those materials which will be higher molecular weight (M,v), optionally lower melting (than the shell materials), than the materials described for the shell. These will genera51y be resins that will yield tougher 1~ molded parts. The core materials may be linear low 10 density pol~ }l;lcll~, (ILDPE) having a melt index in the range of from about 0.5 to about 10 dg/min., and a density in the range of firom about 0.915 to 0.940 g/cc (preferably .915 - .930 glcc), more preferably the Ml will be in the rimge offrom about 0.5 to about 5 dg/min., and most preferably in the range of from about 0.8 to about 4 dglmin.; high density ~ol~ lcllw (IIDPE) having a melt index in the range of from about 0.05 to about 70 preferably in the range of from about 0.3 to about 5, more preferably in the range of fi om about 0.3 to about 4.0 dg/min. and densities in the r~mge of fi om about 0.940 to about 0.960 g/cc p~5~ ~,.u~ c l~u~ul~ul~ , pol ~,. u~lc..~. co and lcl l~ul~ a where ethylene andlor a-olefinshaving carbon numbers from 4-20 may be used; ~ol~ .;lc...,s or PUI.YI~UIJ~!C.
20 when not l.u...u~ul~ a~ can have co and lr~ a selected from the group consisting of a-olefins having 4-20 carbon atoms. The c. ~ . may be selected from the group consisting of butene-l, 4-methyl-1-pentene, pentene-l hexene-l, octene-l, or any ofthe alpha-olefins having from 4-20 carbon atoms. Inthe case of ~ . ul~ylc.~c, the ~ may be any of these alpha-olefins but 25 also includes ethylene as potentia5 ~ . In the case of ..u... _.~L;u~ 5 low density pol~cLhJ!c..c (LDPE) C~ can be selected from c~
acrylicacidesters. Nylonandother " - ., Lll~lllu~ aL;~a are also .-, ~ ..t~ as core materials. The pù~ ylc..~,s and pOI~ u~ .S can be catalyzed by traditional Ziegler-Natta Catalysts, M ~ rl alumoxane Catalysts, WO 96/15892 ~ 8~ PCIIUS ,5114401 chromium based cataiysts, certain free radicai initiated Low Density PEs or LDPEethylene carbon monoxide ,op~ and lel~Jul~ Preferably the ethyiene or propylene co or terpolymer wii~l have a ~ content in the range of from about 0.5 to 6 mole percent, m~re preferably in the range of from about 2 to about 5 6, most preferably in the range Df from about 4 to about 6 mole percent. Preferred c~-olef ns for both ethylene and propylene co and lel~Ju~ are 4-methyl-1-pentene, butene-l, pentene-l, h.exene-l, and octene-l.
Aiso as a core materiai, nylon is . . ' i, having the following properties: melt index greater 1han about 1.5 dg/min and about densities 1Øglcc.
Other preferred core materiais will be selected from the group consisting of linear low density pc,l~ }, ~ " high density pui~ ~,lt.yh",~ ., pu~ ul,yl-_,lc, pbl~JIu~J~ e l,UyUlJ , nylons, and ethylene elt.~ ester .u~cil~ ~ or ionomers. LLDPEs, E[DPEs, and PPs, and pul~t,.u~ ...c. and ,o~,u'.~ ~ thereof may be cataiyzed by the Cu..~ iullc i Ziegler-Natta cataiysts, chromium type Cuul i;l~iiull caitalysts, " ' ' ~' site catalysts, or in the case of high pressure i ibl~ ~.;11, !, .~ materials (IDPEs), through free radicai initiation p~ ,li~liui~. The ~ thylene an~i the propylene polymers may be made by a number of processes including high pressure, gas pbase fluidized bed, slurry, or solution processes.
2û In the selection of core amd shell materiais a difference in Mw as manifested in Ml of at least 0.5 melt index urlits wiii acbieve the melting and fusing differences of importance. Preferably this difference is at least 1, most preferably 2.5 melt index units. In addition to or in place of the melt index differentiai, a peak melting point diffe}ential (as measured i)y Differential Scanning t`-' (DSC)) of at least about 1 C, preferably at least about 2 C, most preferably at least about 5 C.
For foamed rr~' " the preferred core materiai would contain a foaming agent. Some foarning agents are hA~ ~ b~ , p-toluene sulfonyl sc..l;c~llb~ic, p-p-oxobis- (benzene-sulfonyl hydraxide), 'i~ ' ~!uAidc.-4, 4'-wo 96/15892 2 1 8 ) 3 88 PCT/US95/14401 ~
' .rJ~ , or p-toluene ''' ," ~J~d~,. The preferred agent is pp-oxybis (benzene-sulfonyl hydraxide) or ~ u,d~c ~, 4'-~ J.~i~.
The foaming agent can be added at 0.05 wt to 10% wt with a more preferred range of 0.2 to 6 wt % and the most preferred range of 0.3 to 5 wt %
The foaming agent can be ~,, ' by melt extrusion (single screw preferred method), Banbury mixers, 2-roll mills. Melt extrusion via extruders ispreferred with single screw extrusion most preferred.
MAKEUP OF CORE AND SHELL PARTICLES
A shell is defined and used hereinafter as a material that partially covers and is on the outside of a core material in the range of from about 5 to about 70 percent of the particle diameter, preferably in the range of from about 30-70 percent based on the total diameter of a h~.t~ .u~ particle. Preferably the shell material will cover ! ' ' " '1~ all of the core material. The core material will make up the balarlce of the particle and will be preferred ' "S covered by the shell material. If the shell material covers less than about 25% of the core material surface area, the same problems that would be c..~,.,~....~,.~l with anattempt to l~L~Iliu~dl ~ mold the core materials would be ~d, and the benefit the core and shell distribution on a particle may be lost.
METnODS OF MAKING A ~ETERQGENEOUS CORE AND S~ELL
PART~CLE
Methods of forrning core and shell polymers include, but are not limited to, C~ u~;vl1~ powder deposition, or cûp~ ,... The use of series reactors is 25 a well known way to combine two different poly~ner properties in the same particle. The size of pellets or particles are typically, 5-100 mils (127-2540 microns) preferred 5-50 mils (127-1270 microns), more preferred 5-30 mils (127-762 microns), most preferred 5-20 mils (127-50~ microns) in diarneter with and aspect ratio (the ratio of a particle's length to diameter) in the range of from about ~ WO96/15892 2~13~ PCTJUS95J14401 2:1 to about 1:2 preferred in tile range offrom about 1.5:1 to about 1:1.5, mostpreferred in the range of from ~bout 1:1. The pellets may then be ground to a size typically used in rotational molding, specifically in the range of from about 20 to 2.9 mils ~500 to 75 microns) al.so described as a maximum of 35 US mesh preferred in the range of from about 13 .8 to 2.9 mils (350-75 microns), more preferred in the range offrom about 11.7 to 2.9 mils (300-75 microns).
Another method of ~ u.luL~,Lul~ would be to use a ~,u~ u ~;Oll technique followed by a strand cutting pelletizing operation or an l ' ... pelletizing operation. If the pellets or particles are to be used in a rotational molding process they should not exceed about 30 mils (762 microns) preferably, 20 mils (508 microns) most preferably 8 mils (203 microns). Alternatively howeYer, particles of any size may be ground into a ,~owder finer than about 30 miis (762 microns) in diameter, preferably finer than about 20 miles (508 microns).
Whatever method of ,,,~,ur.l.,LIu- ~ is chosen for forming the shell and core materials, whatever the percentage of each particle is, ShelUcore, and however complete the ~ of ~he core by the shell, the particle should perform to advantage when compared to for instance salt and pepper blends, or melt blends.
Examples 1-9 ID/run numbers 1-9 combine a range of materials in a Killion ;u."~l- u:~;u apparatus. Polymer particles are pelletized and then ground in sn attrition mill, made by Wedco, USA. The p~lrticle Aictrihll~inn is outlined in Table 3. The material from each ofthe cc,~uu ,;~,.. tests is run in rotational molding evaluations.
These evaluations are carried out in an FSP Model 60 clam shell rotational molding machine, using a sheet mold, c~red at 600 F for 14 minutes. The molded polymer is allowed to cool 5 minutes with the top of the oven closed and then 5 minutes with the top of the oven open ~ith ambient air circulated by a fan, followed by 11 minutes of water spray onto the mold and part then a 3 minute period of drying.
Where a part was made, the thicknesses are ~ 240 mils (6.1 mm). The W096115892 2 ) 8 138g PCTIUS95/144~
physical properties of the parts molded are shown on Table 4. No physical property testing is done on runs 1-3, as runs 1-3 are only used to illustrate the Illol~ created. Run I illustrates that a 20/80 shell/core polymer structure when ground to a powder, creates a coarse p~._.. aL;II~ network where the 5 core polymer exhibits domain regions.
Run 2 illustrates that a 50/50 core/shell particle, when ground to 35 mesh particle size provides a continuous network. Comparing Runs I and 2, in photos leads us to believe that if a 30/70 structure was created a dense ;1l;~
network would be present.
Runs 4 and 4B are of most interest relative to improving impact strength.
Run 4 utilized a particle according to an l ~ ' of the present invention, specifically a shell polymer of LL-8460 at 3.3 melt index7 0.939 density, stabilized LLDPE available from Exxon Chemical Canada, with a core material of LL-5005 wbich is a 0.3 Ml, 0.960 density bigh density pûl~_Lh~ available from Dow 15 Chemical Canada. Whereas run 4B utilized a more traditional blend, specif cally a "salt and pepper" blend of the same two resins of example 4. The parts were cured identically. As can be seen the salt and pepper blend had less than half the impact strength of the }~.Ltl u~,_.._uu~ particle material at the same thickness. The }..,L~I U~,_.l.,~lU:i part also exhibited a better cured state. Additiûnally, the 20 II~L~,.U~,_.I_.JU~ particle molded article displayed well over 100% increase in ESCR
when compared to the salt and pepper blend.
Runs 6-9 show other ~ ' though none were optimized and none were ~aLi~L~,Luly.
25 FY~nlrl.~ 10 To create a ., "S~ molded part having relative ;IIl~J. ' "`S/ to solvents a SELAR (R) material is used in the shell. The "platelets" formed by the SELAR provide a difflcult or torturous path for a Solvent to traverse. Additionally a high ."y " 'S/ polymer such as nylon is also employed to provide relative ~ WO 96/15892 2 1 8 i 3'8 ~ PCrlUS95114401 , to solvent ppn~tr~tjnn When SELAR@) is used as the shell material and T T npE is used as a core Inaterial, a part having excellent solvent barrier, but good impact strength at reduced cost is produced.
5 Example 11 A dense ~....~h~L;..~ network especially containing conductive fiilers, is used in the shell to improve static charge dissipation. Relatively high Ml materials e.g. 5 MI LLDPE (density 0.930 g/cc) containing aiuminum flakes, carbon black and conductive fibers are used in the shell to provide a ' of 10 mter~ .l-dLu.p network Witil conductive fillers to more easily facilitate dissipation of static build. Tho core material used a LLDPE with a 0.5 MI lower than the shell materiai. The core materiai provides enhamced impact strength.
Compared to the filled polymer used by themselves in a .~ , molded palt, the parts made from the core Md shell does play superior impact resistance.
Aithough the present i]lvention has been described in ~ detail with reference to certain preferred versions thereof, other versions are possible.
For example, other means of fDrming h~t~,.uc_...,~,u~ particles, and other of polymers are . ' 1. Therefore, the spirit and scope of the 20 appended claims should not be limited to the description of the preferred versions contained herein.
.
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Claims (11)
1. A method of producing shaped articles by;
including in a rotational mold, polymer particles,characterized in that said polymer particles have a core and a shell, wherein a) said core includes a polymer selected from the group consisting of HDPE, LLDPE, LDPE, PP, polypropylene copolymer, ionomer, and nylon, preferably HDPE and LLDPE, more preferably LLDPE;
b) said shell includes a polymer selected from the group consisting of HDPE,LLDPE,LDPE,ethylene copolymers of ethylenically unsaturated carboxylic acid esters, and ionomers, preferably HDPE
and LLDPE, more preferably LLDPE;
wherein said core and shell polymers differ by at least 0.5 melt index units, preferably by at least 1 melt index unit, more preferably at least 2.5 melt index units;
wherein said core is at least partially encapsulated by said shell, preferably said shell polymer is present in said polymer particle in the range of from 5 to 70 percent, preferably 30 to 70 percent based on the total diameter of the polymer particle;
wherein said polymer particle size does not exceed 1016 microns, preferably 889 microns; and wherein said core and said shell polymers differ by at least 2°C in Tm, preferably 5°C.
including in a rotational mold, polymer particles,characterized in that said polymer particles have a core and a shell, wherein a) said core includes a polymer selected from the group consisting of HDPE, LLDPE, LDPE, PP, polypropylene copolymer, ionomer, and nylon, preferably HDPE and LLDPE, more preferably LLDPE;
b) said shell includes a polymer selected from the group consisting of HDPE,LLDPE,LDPE,ethylene copolymers of ethylenically unsaturated carboxylic acid esters, and ionomers, preferably HDPE
and LLDPE, more preferably LLDPE;
wherein said core and shell polymers differ by at least 0.5 melt index units, preferably by at least 1 melt index unit, more preferably at least 2.5 melt index units;
wherein said core is at least partially encapsulated by said shell, preferably said shell polymer is present in said polymer particle in the range of from 5 to 70 percent, preferably 30 to 70 percent based on the total diameter of the polymer particle;
wherein said polymer particle size does not exceed 1016 microns, preferably 889 microns; and wherein said core and said shell polymers differ by at least 2°C in Tm, preferably 5°C.
2. In rotational molding process, a molded article being formed by:
charging polymer particles to a mold, heating and rotating said mold;
characterized in that said polymer particles are multilayered particles wherein at least a first polymer is substantially by a second polymer;
wherein said first and said second polymer differ in melt index by at least 0.5 dg/min, preferably at least 1 dg/min, more preferably at least 2.5 dg/min;
wherein said polymer particles have a size between 127 and 1270 microns, preferably 127 to 762 microns, most preferably 127 to 508 microns; and wherein said polymer particles have an aspect ratio in the range of from 2:1 to 1:2, preferably 1.5:1 to 1:1.5, more preferably 1:1.
charging polymer particles to a mold, heating and rotating said mold;
characterized in that said polymer particles are multilayered particles wherein at least a first polymer is substantially by a second polymer;
wherein said first and said second polymer differ in melt index by at least 0.5 dg/min, preferably at least 1 dg/min, more preferably at least 2.5 dg/min;
wherein said polymer particles have a size between 127 and 1270 microns, preferably 127 to 762 microns, most preferably 127 to 508 microns; and wherein said polymer particles have an aspect ratio in the range of from 2:1 to 1:2, preferably 1.5:1 to 1:1.5, more preferably 1:1.
3. The process of claim 2 wherein said multilayered polymer particles are ground to a size between 75 to 500 microns, preferably 75 to 350 microns.
4. The process of claim 2 wherein said first polymer is selected from the group consisting of LLDPE, LDPE, HDPE, PP and ionomers;
wherein said second polymer is selected from the group consisting of LLDPE, HDPE, and polypropylene; and wherein said first and second polymers differ in melt index by at least 1, preferably 2.5 melt index; units, and wherein said first and second polymers differ in Tm by at least 1°C, preferably 2°C, more preferably 5°C.
wherein said second polymer is selected from the group consisting of LLDPE, HDPE, and polypropylene; and wherein said first and second polymers differ in melt index by at least 1, preferably 2.5 melt index; units, and wherein said first and second polymers differ in Tm by at least 1°C, preferably 2°C, more preferably 5°C.
5. The process of claim 2 wherein said first and said second polymers are the same or different, preferably wherein both said first and said second polymers are LLDPE.
6. The process or method of claims 1 or 2 wherein said core or first polymer contains a foaming agent;
said foaming agent being selected from the group consisting of p-toluene sulfonyl semicarbazide, p-p-oxobis- (benzene-sulfonyl hydraxide), diphenyloxide-4,4'-disulphohydraxide, or p-toluene sulfonylhydrazide;
wherein said foaming agent is present in the range of 0.2 to 6 weight percent, preferably in the range of 0.3 to 5 weight percent.
said foaming agent being selected from the group consisting of p-toluene sulfonyl semicarbazide, p-p-oxobis- (benzene-sulfonyl hydraxide), diphenyloxide-4,4'-disulphohydraxide, or p-toluene sulfonylhydrazide;
wherein said foaming agent is present in the range of 0.2 to 6 weight percent, preferably in the range of 0.3 to 5 weight percent.
7. The process or method of claims 1 or 2 wherein said shell or second polymer partially covers said core or first polymer in the range of 5 to 70 percent, preferably 30 to 70 percent, based on the total diameter of the polymer particle.
8. In a process for forming rotationally molded articles,characterized in that said articles are formed by:
placing a plurality of core and shell polymer particles in a mold, rotating said mold in at least one axis, and heating said mold containing said particles;
wherein said core and said shell polymers are selected from the group consisting of LLDPE, HDPE, LDPE and ionomer, wherein said core and shell polymers are the same or different, preferably where both said core and shell polymers are LLDPE;
wherein said shell polymer covers said core polymer in the range of 30 to 70 percent, based on the total diameter of the polymer particle;
wherein said core and shell polymer differ in melt index by at least 2.5 dg/min;
wherein said core and shell polymers differ in Tm by at least 5°C;
wherein said core and shell polymer particle have a size in the range of 127 to 508 microns; and wherein said particles have an aspect ratio of 1:1.
placing a plurality of core and shell polymer particles in a mold, rotating said mold in at least one axis, and heating said mold containing said particles;
wherein said core and said shell polymers are selected from the group consisting of LLDPE, HDPE, LDPE and ionomer, wherein said core and shell polymers are the same or different, preferably where both said core and shell polymers are LLDPE;
wherein said shell polymer covers said core polymer in the range of 30 to 70 percent, based on the total diameter of the polymer particle;
wherein said core and shell polymer differ in melt index by at least 2.5 dg/min;
wherein said core and shell polymers differ in Tm by at least 5°C;
wherein said core and shell polymer particle have a size in the range of 127 to 508 microns; and wherein said particles have an aspect ratio of 1:1.
9. The process of claim 8 wherein said core and shell polymer particles are ground to a size in the range of from 75 to 300 microns.
10. The process or method of claims 1, 2, or 8 wherein said shell or second polymer contains a filler selected from the group consisting of talc, silica, glass beads, cross linking agents and combination thereof.
11. Use of the processes of claims 2 or 8, or the method of claim 1, to make a toy, a surfboard, a small boat, or a tank.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US31504294A | 1994-11-17 | 1994-11-17 | |
| US08/315,042 | 1994-11-17 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2181388A1 true CA2181388A1 (en) | 1996-05-30 |
Family
ID=23222619
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2181388 Abandoned CA2181388A1 (en) | 1994-11-17 | 1995-11-17 | Multi-layer particles for rotational molding |
Country Status (4)
| Country | Link |
|---|---|
| EP (1) | EP0759841A1 (en) |
| AU (1) | AU4363696A (en) |
| CA (1) | CA2181388A1 (en) |
| WO (1) | WO1996015892A1 (en) |
Families Citing this family (11)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5970173A (en) * | 1995-10-05 | 1999-10-19 | Microsoft Corporation | Image compression and affine transformation for image motion compensation |
| GB9603969D0 (en) * | 1996-02-24 | 1996-04-24 | Rotec Chemicals Ltd | Rotational moulding |
| AUPN928196A0 (en) * | 1996-04-16 | 1996-05-09 | Linpac Polycast Pty Ltd | Rotational moulding process |
| US5922778A (en) * | 1996-05-24 | 1999-07-13 | Equistar Chemicals, Lp | Rotational molding compositions and process for producing foamed articles therefrom |
| US6027806A (en) * | 1997-01-16 | 2000-02-22 | Mitsubishi Chemical Basf Company Limited | Expanded resin beads |
| US6180203B1 (en) | 1997-04-09 | 2001-01-30 | Peter J. Unkles | Rotational moulding process |
| US6261490B1 (en) | 1998-09-15 | 2001-07-17 | Rotec Chemicals Limited | Rotational moulding |
| GB2413331B (en) * | 2004-03-19 | 2008-10-29 | Pvaxx Res & Dev Ltd | Load-carrying apparatus and methods of manufacture |
| GB2425506B (en) * | 2005-04-26 | 2010-11-10 | Pvaxx Res & Dev Ltd | Load carrying apparatus and method of manufacture |
| EP1736502A1 (en) * | 2005-06-22 | 2006-12-27 | Total Petrochemicals Research Feluy | Rotomoulded articles prepared from a blend of polyethylene powders |
| EP3768485B1 (en) | 2018-03-22 | 2023-11-22 | Dow Global Technologies LLC | Process for forming a rotational molded article and rotational molded article |
Family Cites Families (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB8517845D0 (en) * | 1985-07-15 | 1985-08-21 | Du Pont Canada | Polyethylene compositions |
| DE3906478A1 (en) * | 1989-03-01 | 1990-09-13 | Inventa Ag | Multilayer granular material, process for the preparation thereof, and the use thereof |
| DE4237637A1 (en) * | 1992-11-07 | 1994-05-11 | Basf Ag | Process for the production of polypropylene skins |
| JP3375684B2 (en) * | 1993-08-04 | 2003-02-10 | 三井・デュポンポリケミカル株式会社 | Powder processing composition |
| GB9401214D0 (en) * | 1994-01-22 | 1994-03-16 | Univ Belfast | A method of rotational moulding and rotationally moulded products |
| US5366675A (en) * | 1994-03-02 | 1994-11-22 | Needham Donald G | Foamable polyethylene-based composition for rotational molding |
-
1995
- 1995-11-17 CA CA 2181388 patent/CA2181388A1/en not_active Abandoned
- 1995-11-17 WO PCT/US1995/014401 patent/WO1996015892A1/en not_active Application Discontinuation
- 1995-11-17 AU AU43636/96A patent/AU4363696A/en not_active Abandoned
- 1995-11-17 EP EP95942403A patent/EP0759841A1/en not_active Withdrawn
Also Published As
| Publication number | Publication date |
|---|---|
| EP0759841A1 (en) | 1997-03-05 |
| AU4363696A (en) | 1996-06-17 |
| WO1996015892A1 (en) | 1996-05-30 |
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