CA2313986A1 - Flowable elastomer granules - Google Patents
Flowable elastomer granules Download PDFInfo
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- CA2313986A1 CA2313986A1 CA 2313986 CA2313986A CA2313986A1 CA 2313986 A1 CA2313986 A1 CA 2313986A1 CA 2313986 CA2313986 CA 2313986 CA 2313986 A CA2313986 A CA 2313986A CA 2313986 A1 CA2313986 A1 CA 2313986A1
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- process according
- powdering
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- granules
- powdering agent
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- 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
- C08J3/124—Treatment for improving the free-flowing characteristics
-
- 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
- C08J2321/00—Characterised by the use of unspecified rubbers
Abstract
This invention relates to a process for producing polar, flowable rubber granules with the aid of powdering agents, which are rendered hydrophobic at the surface.
Description
Le A 33 803-US SCJ/klu/NT
FLOWABLE ELASTOMER GRANULES
FIELD OF THE INVENTION
This invention relates to a process for producing polar, flowable rubber granules with the aid of powdering agents, which are rendered hydrophobic at the surface.
BACKGROUND OF THE INVENTION
The provision of elastomers or of polymers in general as granular material is very de-sirable, because this form of supply permits further processing in continuously operating machines. In most cases, higher throughputs are thus achieved. In many processing operations, only continuous mixers (extruders) are available, so that only those raw materials, which permit a continuous feed, can be processed.
In order that there can be elastomers available for these processing operations, it is necessary to provide granular material.
However, the problem arises in that sticky polymers can indeed be granulated by means of the known techniques, but that the granules rapidly agglutinate or become blocked. This problem occurs, in particular, with elastomers which, owing to their comparatively low or non-existent crystallinity and to low glass transition tempera-tures, are both sticky and may have a cold flow.
Typical representatives of such polymers are copolymers of ethylene and vinyl ace-tate or of ethylene and acrylates.
In the production of granules of these polymers, it is prior art, after or during the granulation process, to add powdering agents, which are intended to prevent the sub-sequent agglutination. These powdering agents are mostly inorganic substances or . , CA 02313986 2000-07-17 Le A 33 803-US
FLOWABLE ELASTOMER GRANULES
FIELD OF THE INVENTION
This invention relates to a process for producing polar, flowable rubber granules with the aid of powdering agents, which are rendered hydrophobic at the surface.
BACKGROUND OF THE INVENTION
The provision of elastomers or of polymers in general as granular material is very de-sirable, because this form of supply permits further processing in continuously operating machines. In most cases, higher throughputs are thus achieved. In many processing operations, only continuous mixers (extruders) are available, so that only those raw materials, which permit a continuous feed, can be processed.
In order that there can be elastomers available for these processing operations, it is necessary to provide granular material.
However, the problem arises in that sticky polymers can indeed be granulated by means of the known techniques, but that the granules rapidly agglutinate or become blocked. This problem occurs, in particular, with elastomers which, owing to their comparatively low or non-existent crystallinity and to low glass transition tempera-tures, are both sticky and may have a cold flow.
Typical representatives of such polymers are copolymers of ethylene and vinyl ace-tate or of ethylene and acrylates.
In the production of granules of these polymers, it is prior art, after or during the granulation process, to add powdering agents, which are intended to prevent the sub-sequent agglutination. These powdering agents are mostly inorganic substances or . , CA 02313986 2000-07-17 Le A 33 803-US
mineral powders such as silicas, talc and various silicates, such as wollastonite, kao-linite or mica or even finely-ground thermoplastics such as PE. The latter is de-scribed, for example, in EP-A 100,434.
EP 575,900 describes the use of micronized PE waxes for separating polyisobutylene granules.
WO 93/23458 describes the use of anti-sticking agents for ethylene-acrylate copoly mers containing at least 50% incorporated ethylene. These agents are low-molecular compounds having definite melting points.
It is also possible, prior to the granulation of the polymer melts, to add certain release agents which, after the granulation process, migrate to the surface and there form a film which prevents agglutination.
These agents are typically also used as slip agents in the production of films. Appar-ently, these substances only work within a narrow application range. U.S.
Patent 4,510,281 (Reissue 32,325), EP 68 148 claim, for example, the use of ethylene bisoleylamide only up to EVA copolymers having a VA content of 55%.
What is common to all these documents, however, is the fact that exclusively hydro-philic or untreated powdering agents are used.
Polar polymers, in particular, place high demands on the powdering agents and these demands are not satisfied by the disclosures in the prior art. The disadvantages of the known powdering agents include a high water absorption of the granular material, the large quantities of powdering agent which are required for an adequate release effect (more than 30 phr powdering agent in EP-A 100,434) and, in the case of organic powdering agents such as carbon black or polyethylene, either the impossibility to manufacture colored articles or handling problems due to dust explosion hazards.
, , CA 02313986 2000-07-17 Le A 33 803-US
EP 575,900 describes the use of micronized PE waxes for separating polyisobutylene granules.
WO 93/23458 describes the use of anti-sticking agents for ethylene-acrylate copoly mers containing at least 50% incorporated ethylene. These agents are low-molecular compounds having definite melting points.
It is also possible, prior to the granulation of the polymer melts, to add certain release agents which, after the granulation process, migrate to the surface and there form a film which prevents agglutination.
These agents are typically also used as slip agents in the production of films. Appar-ently, these substances only work within a narrow application range. U.S.
Patent 4,510,281 (Reissue 32,325), EP 68 148 claim, for example, the use of ethylene bisoleylamide only up to EVA copolymers having a VA content of 55%.
What is common to all these documents, however, is the fact that exclusively hydro-philic or untreated powdering agents are used.
Polar polymers, in particular, place high demands on the powdering agents and these demands are not satisfied by the disclosures in the prior art. The disadvantages of the known powdering agents include a high water absorption of the granular material, the large quantities of powdering agent which are required for an adequate release effect (more than 30 phr powdering agent in EP-A 100,434) and, in the case of organic powdering agents such as carbon black or polyethylene, either the impossibility to manufacture colored articles or handling problems due to dust explosion hazards.
, , CA 02313986 2000-07-17 Le A 33 803-US
Ensuring a flowability in the case of EVA, however, is a problem, particularly, where the VA content is high, that is, distinctly higher than 45% and up to 95%.
SUMMARY OF THE INVENTION
Accordingly, the object was to find powdering agents which exhibit a satisfactory activity in the case of polar polymers and copolymers.
A further object was to decrease the water absorption of the powdered granules.
A further object was to improve the dye receptivity of powdered polar polymers.
Another object was to avoid the disadvantages of the powdering agents known in prior art. Another object was to provide an alternative process to the processes known in prior art for the production of flowable granular materials.
These objects were completely or mainly achieved by a process for producing flow-able polar rubber granules, characterized in that a powdering agent which is rendered hydrophobic at the surface is used.
DETAILED DESCRIPTION OF THE INVENTION
Polar rubbers are defined as rubbers containing polar repeat units in the polymer chain. These induce a dipole moment in the repeat units. Typical polar monomers are chloroprene, acrylonitrile, vinyl chloride, vinylidene chloride, vinyl fluoride, acrylic acid and their analogues, such as methacrylic acid, methyl methacrylate, vinyl ace-tate, acrylamide, methacrylonitrile, as well as vinylpyrrolidone, and vinylcarbazole.
These monomers and other polar monomers are well known to the person skilled in the art. Polar and non-polar monomers are frequently copolymerized to form polar rubbers. Suitable non-polar monomers are, for example, a.-olefins such as ethylene, propylene, butene, hexene, octene, diolefins such as butadiene, pentadiene, hexadi-Le A 33 803-US
SUMMARY OF THE INVENTION
Accordingly, the object was to find powdering agents which exhibit a satisfactory activity in the case of polar polymers and copolymers.
A further object was to decrease the water absorption of the powdered granules.
A further object was to improve the dye receptivity of powdered polar polymers.
Another object was to avoid the disadvantages of the powdering agents known in prior art. Another object was to provide an alternative process to the processes known in prior art for the production of flowable granular materials.
These objects were completely or mainly achieved by a process for producing flow-able polar rubber granules, characterized in that a powdering agent which is rendered hydrophobic at the surface is used.
DETAILED DESCRIPTION OF THE INVENTION
Polar rubbers are defined as rubbers containing polar repeat units in the polymer chain. These induce a dipole moment in the repeat units. Typical polar monomers are chloroprene, acrylonitrile, vinyl chloride, vinylidene chloride, vinyl fluoride, acrylic acid and their analogues, such as methacrylic acid, methyl methacrylate, vinyl ace-tate, acrylamide, methacrylonitrile, as well as vinylpyrrolidone, and vinylcarbazole.
These monomers and other polar monomers are well known to the person skilled in the art. Polar and non-polar monomers are frequently copolymerized to form polar rubbers. Suitable non-polar monomers are, for example, a.-olefins such as ethylene, propylene, butene, hexene, octene, diolefins such as butadiene, pentadiene, hexadi-Le A 33 803-US
ene, octadiene, methyloctadiene or isoprene. Other non-polar comonomers are known to the person skilled in the art.
Preferred polar rubbers are polychloroprene, acrylonitrile-butadiene copolymers, styrene-acrylonitrile-butadiene copolymers, ethylene-vinyl acetate copolymers (such as LEVAPREN~) and ethylene-acrylate copolymers (such as VAMAC~) or mix-tures of these.
The polar rubbers are generally used in uncrosslinked or partially crosslinked form.
The person skilled in the art also refers to partially cross-linked rubbers as being pre-vulcanized, the degree of cross-linking being low enough not to impede the good processing properties.
All particulate materials which decrease or completely neutralize the stickiness of the rubber particles are suitable for use as powdering agents. These materials must not change in shape at the storage temperature; in particular, the melting point or the glass transition should be above the storage temperature. At the same time, the pow-dering agents must not interact adversely with the rubber particles during the further processing or the final application of the rubber.
Powdering agents can generally be classified as organic and mineral powdering agents. Within the scope of this invention, mineral powdering agents are preferred, as under adverse conditions organic powdering agents can give rise to dust explosions.
The chiefly preferred organic powdering agents are polyolefin powders, such as poly-ethylene or polypropylene, and carbon black.
The chiefly preferred mineral powdering agents are unreinforced and reinforced fill-ers known to the person skilled in the art, such as silica, in particular, precipitated silicas, talc, clays, mixed silicates, in particular aluminium-containing silicates, metal oxides, in particular ZnO, Mg0 and, optionally precipitated, carbonates, in particular Le A 33 803-US
Preferred polar rubbers are polychloroprene, acrylonitrile-butadiene copolymers, styrene-acrylonitrile-butadiene copolymers, ethylene-vinyl acetate copolymers (such as LEVAPREN~) and ethylene-acrylate copolymers (such as VAMAC~) or mix-tures of these.
The polar rubbers are generally used in uncrosslinked or partially crosslinked form.
The person skilled in the art also refers to partially cross-linked rubbers as being pre-vulcanized, the degree of cross-linking being low enough not to impede the good processing properties.
All particulate materials which decrease or completely neutralize the stickiness of the rubber particles are suitable for use as powdering agents. These materials must not change in shape at the storage temperature; in particular, the melting point or the glass transition should be above the storage temperature. At the same time, the pow-dering agents must not interact adversely with the rubber particles during the further processing or the final application of the rubber.
Powdering agents can generally be classified as organic and mineral powdering agents. Within the scope of this invention, mineral powdering agents are preferred, as under adverse conditions organic powdering agents can give rise to dust explosions.
The chiefly preferred organic powdering agents are polyolefin powders, such as poly-ethylene or polypropylene, and carbon black.
The chiefly preferred mineral powdering agents are unreinforced and reinforced fill-ers known to the person skilled in the art, such as silica, in particular, precipitated silicas, talc, clays, mixed silicates, in particular aluminium-containing silicates, metal oxides, in particular ZnO, Mg0 and, optionally precipitated, carbonates, in particular Le A 33 803-US
calcium carbonates. The above-mentioned organic and mineral powders may, of course, also be used in mixtures.
The powdering agents have to be rendered hydrophobic at the surface in order to achieve the significant improvement compared with prior art.
The person skilled in the art is acquainted with prior art processes for hydrophobing fillers. Conventional products which are suitable for the invention. are, for example, from the processes for the treatment of, in particular, siliceous fillers with polysul-fides of silyl ethers, in particular, bis(triethoxysilylpropyl) tetrasulfide, described in U.S. Patents 4,514,213 and 4,704,414. The processes for the treatment of silicas with alcohols disclosed in U.S. Patents 2,736,669 and 2,801,185 are also suitable.
Hydrophobic fillers, in particular, hydrophobic silicas, are also commercially avail-1 S able.
Suitable powdering agents are particulate and have average particle diameters in the range of 2 to 50 Vim, in particular, of 2 to 20 pm, in each case based on the so-called DSO value (ASTM C 690-1992, Multisizer 100 p.m capillary).
The required quantity of the hydrophobic powdering agent is clearly below the quan-tities of 30 to 100 phr (EP-A 100,434) given for the known powdering agents.
As a rule, a quantity of below 10 phr, or even less, of the hydrophobed powdering agent is sufficient. The precisely required quantity of hydrophobed powdering agent is deter-mined by the intended storage temperature, the size of the rubber particles, the inher-ent stickiness of the rubber and the intended use of the rubber granules.
Mineral powdering agents are preferred, as they lessen the hazard of dust explosions.
Moreo-ver, it is, of course, unnecessary that all the powdering agent present be localized on the rubber particles. Frequently, it can be advantageous to compensate for the cold flow of the rubber particles by means of additional free powdering agent.
Le A 33 803-US
The powdering agents have to be rendered hydrophobic at the surface in order to achieve the significant improvement compared with prior art.
The person skilled in the art is acquainted with prior art processes for hydrophobing fillers. Conventional products which are suitable for the invention. are, for example, from the processes for the treatment of, in particular, siliceous fillers with polysul-fides of silyl ethers, in particular, bis(triethoxysilylpropyl) tetrasulfide, described in U.S. Patents 4,514,213 and 4,704,414. The processes for the treatment of silicas with alcohols disclosed in U.S. Patents 2,736,669 and 2,801,185 are also suitable.
Hydrophobic fillers, in particular, hydrophobic silicas, are also commercially avail-1 S able.
Suitable powdering agents are particulate and have average particle diameters in the range of 2 to 50 Vim, in particular, of 2 to 20 pm, in each case based on the so-called DSO value (ASTM C 690-1992, Multisizer 100 p.m capillary).
The required quantity of the hydrophobic powdering agent is clearly below the quan-tities of 30 to 100 phr (EP-A 100,434) given for the known powdering agents.
As a rule, a quantity of below 10 phr, or even less, of the hydrophobed powdering agent is sufficient. The precisely required quantity of hydrophobed powdering agent is deter-mined by the intended storage temperature, the size of the rubber particles, the inher-ent stickiness of the rubber and the intended use of the rubber granules.
Mineral powdering agents are preferred, as they lessen the hazard of dust explosions.
Moreo-ver, it is, of course, unnecessary that all the powdering agent present be localized on the rubber particles. Frequently, it can be advantageous to compensate for the cold flow of the rubber particles by means of additional free powdering agent.
Le A 33 803-US
For many applications, it is advantageous to use a product which is white or capable of being dyed. For this reason, mineral powdering agents are often preferred to car-bon black or polyolefms, which have a poor dye receptivity.
S The person skilled in the art knows of numerous processes for producing rubber granules. At this point, reference may be made to the so-called underwater granula-tions. Here, a melt of the rubber to be granulated is pressed through a perforated plate and the granules are cut with a rotating knife. This is preferably.carned out under water, to ensure the rapid cooling of the granules and to avoid agglomeration.
It is also appropriate to use a bale of rubber granulated by means of a so-called Nielander mixer (U.S. 3,623,703). This process is described in EP-A2,100,434, page 9 ff., to which reference is made herewith. A portion of the powdering agent is pref erably added during the granulating step.
The advantages of the described process are mainly the clearly decreased quantity of powdering agent required, which minimizes the effect on subsequent processing steps. Rubber granules having improved flowability are produced. These rubber granules absorb significantly less water than do conventional granules and are emi-nently suitable for continuous processing, for example, in extruders. The rubber granules according to the present invention can easily be recognized by the fact that they float in water.
The rubber mixtures according to the present invention may, of course, contain still further rubber auxiliaries, such as reaction accelerators, antioxidants, heat stabilizers, light stabilizers, antiozonants, processing agents, plasticizers, tackifiers, blowing agents, dyes, pigments, waxes, extenders, organic acids, reaction retardants, metal oxides, as well as activators, such as triethanolamine, polyethylene glycol, hexane-triol, which are known and conventional in the rubber industry. The rubber auxilia-ries are admixed in conventional quantities and depend on the intended use in each Le A 33 803-US
case. Conventional quantities are, for example, quantities of from 0.1 to 50 wt.%, based on the total weight of the rubber used.
Besides the previously mentioned rubber auxiliaries, the known cross-linking agents, such as sulfur, sulfur donors or peroxides, may also be added to the rubber mixtures according to the present invention. The rubber mixtures according to the present in-vention may, in addition, contain vulcanization accelerators, such as mercapto-benzothiazoles, mercaptosulfenamides, guanidines, thiurams, dithiocarbamates, thio-ureas and/or thiocarbonates. The vulcanization accelerators and the cross-linking agents mentioned are conventionally used in quantities of from 0.1 to 10 wt.%, pref erably 0.1 to 5 wt.%, based on the total quantity of the rubber used in each case.
These cross-linkable rubber mixtures are also provided by the present invention.
The rubber mixtures according to the present invention can be vulcanized at conven-tional temperatures of 100°C to 200°C, preferably 130°C
to 180°C (optionally under a pressure of 10 to 200 bar).
The further mixing of the rubbers with the other rubber auxiliaries, cross-linking agents and accelerators mentioned can be carried out in a conventional manner by means of suitable mixing units, such as rolls, closed mixers and mixer-extruders.
The resulting mixtures may optionally be compounded and vulcanized in a conven-tional manner as described in more detail, for example, in Encyclopedia c~f p c-lymer Science and Engineering, Vol. 4, page 66 ff (compounding) and Vol. 17, page 666 ff (vulcanization). To improve the heat stability and the stability in storage, preferably the known phenolic, amine, sulfur-containing or phosphorus-containing antioxidants are added. These are described in more detail, for example, in Ullmanns En-zyklopadie der technischen Chemie, Volume 8, page 19 ff.
The following Examples serve to illustrate the invention.
Le A 33 803-US
_g_ F.1~ A MPI .F.C
The polar rubbers investigated were various ethylene-vinyl acetate copolymers which are commercially available under the trade name Levapren~ (Bayer AG).
S
In detail, the products used were:-Levapren~ S00 HV, an ethylene-vinyl acetate copolymer produced by Bayer AG, with a vinyl acetate content of 50%, Levapren~ 600 HV, an ethylene-vinyl acetate copolymer produced by Bayer AG, with a vinyl acetate content of 60%, Levapren~ 700 HV, an ethylene-vinyl acetate copolymer produced by Bayer AG, with a vinyl acetate content of 70%.
The following were used as powdering agents:-Wessalon S, a precipitated silica from Degussa AG, having an average diameter of 6 ~m (D50 value), as a hydrophilic powdering agent, Talc Luzenac No. 1 from Luzenac, likewise as an example of a hydrophilic powder-ing agent, having an average diameter of 15 pm (D50 value), Sipernat D 10, a precipitated and hydrophobically modified silica from Degussa AG, having an average particle diameter of 5 pm (D50 value), Sipernat D17, a precipitated and hydrophobically modified silica from Degussa AG, having an average particle diameter of approximately 10 um (D50 value), Le A 33 803-US
Coatylene HA 1681, a hydrophobic LDPE powder from Herberts, having an average particle diameter of 17 Vim, melting point 105°C.
To investigate the flowability, the corresponding products were each removed from the production process immediately after the powdering and various powdering agents were added in a simple powder mixer. In each case, 0.30 wt.% was added.
The samples taken were used in the form of dry granules of 4 mm in size and on their surfaces they still bore 0.1 % talc, which is used as a granulating aid during the un-derwater granulation process.
Description of the production conditions for Levapren (T, P, etc.) Ethylene-vinyl acetate copolymers with the trade name Levapren~ are produced by means of radical polymerization by a medium-pressure solution process. Further de-tails may be found in EP 341,499, EP 307,755, EP S 10,478 and EP 632,067.
The Levapren types used were produced as described above, freed from monomers and solvent via degassing steps and the melt was pressed through the holes in the plate of an extruder head. The material was granulated underwater into pellets of approximately 3 m in size by means of a rapidly-acting knife. The water contained approximately 2% talc as a granulating aid and was also used as a transporting me-dium for the granules. The water was centrifuged off, the granules were dried in an air current and then, in each case, various powdering agents were added.
The flowability was investigated in each case by putting 300 g of granules into a plastics cylinder of 10 cm in diameter with a movable bottom plate and loading the granules with a 5 kg weight. After storage for a given period of time at given tem-peratures, the weight and the bottom plate were removed and a determination was made of the quantity of granules which fell out freely.
Le A 33 803-US
Example 1 Various powdering agents were added to Levapren S00 HV as described above, the samples were stored for 6 days at 40°C and then the flowability was determined.
The granules containing Wessalon S and talc were firmly blocked and could be re-moved from the test cylinder only after vigorous shaking and finally scraping by hand. The two other samples fell unobstructed out of the cylinder. and were accord-ingly still flowable.
Wessalon S Talc Sipernat D10 Sipernat D17 after one minute:
10% free-flowingSO% free-flowingup to 100% free-flowing, free-90% blocked 50% blocked flowing some granules blocked Example 2 Various powdering agents were added to Levapren 600 HV as described above, the samples were stored for 3 days at 40°C and then the flowability was determined.
Wessalon S Talc Sipernat D10 Sipernat D17 after one minute:
had not fallen had not fallenup to 100% 80% free-flowing free-flowing after three minutes:
flowable after flowable afterup to 100% up to 100% free-free-shaking, but shaking, but flowing flowing partially blockedpartially blocked Le A 33 803-US
Example 3 Various powdering agents were added to Levapren 600 HV as described above, the samples were stored for 5 days at 40°C and the flowability was determined.
Wessalon S Talc Sipernat D10 Sipernat D17 immediately:
had not fallen 10% free-flowingup to 100% free-90% free-flowing flowing after three minutes:
very blocked flowable afterfree-flowing free-flowing shaking, but partially blocked The sample containing Wessalon fell as a coherent block. The sample containing talc fell out of the cylinder after vigorous shaking. The samples containing the Sipernat powdering agents were freely flowable. The sample containing Sipernat D 10 fell out of the cylinder somewhat more rapidly.
Example 4 Various powdering agents were added to Levapren 700 HV as described above, the samples were stored for 4 days at 40°C and then the flowability was determined.
Le A 33 803-US
Wessalon S Talc Sipernat D10 Sipernat D17 immediately:
had not fallenas Wessalon up to 80% 100% free-flow-S free-flowing ing after three minutes:
very blocked, as Wessalon free-flowing free-flowing S
partially flowable after vigorous shaking The samples powdered with Wessalon S and talc were definitely blocked. The sam-ples containing the Sipernat powdering agents remained flowable. The sample con-taming Sipernat D10 fell out of the cylinder somewhat more rapidly.
Example 5 (Comparison - similar to EP-A 068 148) During the production of Levapren 600 HV, ethylene bisoleylamide was metered into the screw-type processor, a solution in vinyl acetate at a concentration of 5%
first being added in order to achieve easier metering. The quantity of ethylene bi-soleylamide was so calculated that the end product contained 4000 to 5000 ppm.
The product was granulated under water and packed into 25 kg sacks and stacked onto pallets. These pallets were stored for 3 months at RT and the extent of the blocking was observed.
To this end, the pallets were repacked and the degree of blocking assessed on the basis of the sack in the lowest - that is, the most heavily loaded - position.
The sacks were partially blocked and no longer freely flowable.
Le A 33 803-US
Example 6 25 kg of Levapren 700 HV was powdered with 0.25 phr Wessalon S. A further 25 kg was additionally powdered with Coatylene 1681 and both samples were put into polyethylene sacks, packed in cardboard and both stored for 14 days in a hot cabinet at 40°C.
The product powdered with Wessalon S was completely baked and could not be fur-ther processed.
The subsequently powdered product remained flowable and was therefore suitable for further processing.
Example 7 Water absorption of the powdering agent:
Wessalon S had a water content of 4 to 5%, measured as loss on drying after 2h at 105°C.
Sipernat D17 had a water content of 2%, measured as loss on drying after 2h at 105°C.
Hydrophobic powdering agents are also advantageous, because these do not agglom erate in the presence of moisture. Agglomerated powdering agents can lead to defects and voids when used in thin layers.
Although the invention has been described in detail in the foregoing for the purpose of illustration, it is to be understood that such detail is solely for that purpose and that variations can be made therein by those skilled in the art without departing from the spirit and scope of the invention except as it may be limited by the claims.
S The person skilled in the art knows of numerous processes for producing rubber granules. At this point, reference may be made to the so-called underwater granula-tions. Here, a melt of the rubber to be granulated is pressed through a perforated plate and the granules are cut with a rotating knife. This is preferably.carned out under water, to ensure the rapid cooling of the granules and to avoid agglomeration.
It is also appropriate to use a bale of rubber granulated by means of a so-called Nielander mixer (U.S. 3,623,703). This process is described in EP-A2,100,434, page 9 ff., to which reference is made herewith. A portion of the powdering agent is pref erably added during the granulating step.
The advantages of the described process are mainly the clearly decreased quantity of powdering agent required, which minimizes the effect on subsequent processing steps. Rubber granules having improved flowability are produced. These rubber granules absorb significantly less water than do conventional granules and are emi-nently suitable for continuous processing, for example, in extruders. The rubber granules according to the present invention can easily be recognized by the fact that they float in water.
The rubber mixtures according to the present invention may, of course, contain still further rubber auxiliaries, such as reaction accelerators, antioxidants, heat stabilizers, light stabilizers, antiozonants, processing agents, plasticizers, tackifiers, blowing agents, dyes, pigments, waxes, extenders, organic acids, reaction retardants, metal oxides, as well as activators, such as triethanolamine, polyethylene glycol, hexane-triol, which are known and conventional in the rubber industry. The rubber auxilia-ries are admixed in conventional quantities and depend on the intended use in each Le A 33 803-US
case. Conventional quantities are, for example, quantities of from 0.1 to 50 wt.%, based on the total weight of the rubber used.
Besides the previously mentioned rubber auxiliaries, the known cross-linking agents, such as sulfur, sulfur donors or peroxides, may also be added to the rubber mixtures according to the present invention. The rubber mixtures according to the present in-vention may, in addition, contain vulcanization accelerators, such as mercapto-benzothiazoles, mercaptosulfenamides, guanidines, thiurams, dithiocarbamates, thio-ureas and/or thiocarbonates. The vulcanization accelerators and the cross-linking agents mentioned are conventionally used in quantities of from 0.1 to 10 wt.%, pref erably 0.1 to 5 wt.%, based on the total quantity of the rubber used in each case.
These cross-linkable rubber mixtures are also provided by the present invention.
The rubber mixtures according to the present invention can be vulcanized at conven-tional temperatures of 100°C to 200°C, preferably 130°C
to 180°C (optionally under a pressure of 10 to 200 bar).
The further mixing of the rubbers with the other rubber auxiliaries, cross-linking agents and accelerators mentioned can be carried out in a conventional manner by means of suitable mixing units, such as rolls, closed mixers and mixer-extruders.
The resulting mixtures may optionally be compounded and vulcanized in a conven-tional manner as described in more detail, for example, in Encyclopedia c~f p c-lymer Science and Engineering, Vol. 4, page 66 ff (compounding) and Vol. 17, page 666 ff (vulcanization). To improve the heat stability and the stability in storage, preferably the known phenolic, amine, sulfur-containing or phosphorus-containing antioxidants are added. These are described in more detail, for example, in Ullmanns En-zyklopadie der technischen Chemie, Volume 8, page 19 ff.
The following Examples serve to illustrate the invention.
Le A 33 803-US
_g_ F.1~ A MPI .F.C
The polar rubbers investigated were various ethylene-vinyl acetate copolymers which are commercially available under the trade name Levapren~ (Bayer AG).
S
In detail, the products used were:-Levapren~ S00 HV, an ethylene-vinyl acetate copolymer produced by Bayer AG, with a vinyl acetate content of 50%, Levapren~ 600 HV, an ethylene-vinyl acetate copolymer produced by Bayer AG, with a vinyl acetate content of 60%, Levapren~ 700 HV, an ethylene-vinyl acetate copolymer produced by Bayer AG, with a vinyl acetate content of 70%.
The following were used as powdering agents:-Wessalon S, a precipitated silica from Degussa AG, having an average diameter of 6 ~m (D50 value), as a hydrophilic powdering agent, Talc Luzenac No. 1 from Luzenac, likewise as an example of a hydrophilic powder-ing agent, having an average diameter of 15 pm (D50 value), Sipernat D 10, a precipitated and hydrophobically modified silica from Degussa AG, having an average particle diameter of 5 pm (D50 value), Sipernat D17, a precipitated and hydrophobically modified silica from Degussa AG, having an average particle diameter of approximately 10 um (D50 value), Le A 33 803-US
Coatylene HA 1681, a hydrophobic LDPE powder from Herberts, having an average particle diameter of 17 Vim, melting point 105°C.
To investigate the flowability, the corresponding products were each removed from the production process immediately after the powdering and various powdering agents were added in a simple powder mixer. In each case, 0.30 wt.% was added.
The samples taken were used in the form of dry granules of 4 mm in size and on their surfaces they still bore 0.1 % talc, which is used as a granulating aid during the un-derwater granulation process.
Description of the production conditions for Levapren (T, P, etc.) Ethylene-vinyl acetate copolymers with the trade name Levapren~ are produced by means of radical polymerization by a medium-pressure solution process. Further de-tails may be found in EP 341,499, EP 307,755, EP S 10,478 and EP 632,067.
The Levapren types used were produced as described above, freed from monomers and solvent via degassing steps and the melt was pressed through the holes in the plate of an extruder head. The material was granulated underwater into pellets of approximately 3 m in size by means of a rapidly-acting knife. The water contained approximately 2% talc as a granulating aid and was also used as a transporting me-dium for the granules. The water was centrifuged off, the granules were dried in an air current and then, in each case, various powdering agents were added.
The flowability was investigated in each case by putting 300 g of granules into a plastics cylinder of 10 cm in diameter with a movable bottom plate and loading the granules with a 5 kg weight. After storage for a given period of time at given tem-peratures, the weight and the bottom plate were removed and a determination was made of the quantity of granules which fell out freely.
Le A 33 803-US
Example 1 Various powdering agents were added to Levapren S00 HV as described above, the samples were stored for 6 days at 40°C and then the flowability was determined.
The granules containing Wessalon S and talc were firmly blocked and could be re-moved from the test cylinder only after vigorous shaking and finally scraping by hand. The two other samples fell unobstructed out of the cylinder. and were accord-ingly still flowable.
Wessalon S Talc Sipernat D10 Sipernat D17 after one minute:
10% free-flowingSO% free-flowingup to 100% free-flowing, free-90% blocked 50% blocked flowing some granules blocked Example 2 Various powdering agents were added to Levapren 600 HV as described above, the samples were stored for 3 days at 40°C and then the flowability was determined.
Wessalon S Talc Sipernat D10 Sipernat D17 after one minute:
had not fallen had not fallenup to 100% 80% free-flowing free-flowing after three minutes:
flowable after flowable afterup to 100% up to 100% free-free-shaking, but shaking, but flowing flowing partially blockedpartially blocked Le A 33 803-US
Example 3 Various powdering agents were added to Levapren 600 HV as described above, the samples were stored for 5 days at 40°C and the flowability was determined.
Wessalon S Talc Sipernat D10 Sipernat D17 immediately:
had not fallen 10% free-flowingup to 100% free-90% free-flowing flowing after three minutes:
very blocked flowable afterfree-flowing free-flowing shaking, but partially blocked The sample containing Wessalon fell as a coherent block. The sample containing talc fell out of the cylinder after vigorous shaking. The samples containing the Sipernat powdering agents were freely flowable. The sample containing Sipernat D 10 fell out of the cylinder somewhat more rapidly.
Example 4 Various powdering agents were added to Levapren 700 HV as described above, the samples were stored for 4 days at 40°C and then the flowability was determined.
Le A 33 803-US
Wessalon S Talc Sipernat D10 Sipernat D17 immediately:
had not fallenas Wessalon up to 80% 100% free-flow-S free-flowing ing after three minutes:
very blocked, as Wessalon free-flowing free-flowing S
partially flowable after vigorous shaking The samples powdered with Wessalon S and talc were definitely blocked. The sam-ples containing the Sipernat powdering agents remained flowable. The sample con-taming Sipernat D10 fell out of the cylinder somewhat more rapidly.
Example 5 (Comparison - similar to EP-A 068 148) During the production of Levapren 600 HV, ethylene bisoleylamide was metered into the screw-type processor, a solution in vinyl acetate at a concentration of 5%
first being added in order to achieve easier metering. The quantity of ethylene bi-soleylamide was so calculated that the end product contained 4000 to 5000 ppm.
The product was granulated under water and packed into 25 kg sacks and stacked onto pallets. These pallets were stored for 3 months at RT and the extent of the blocking was observed.
To this end, the pallets were repacked and the degree of blocking assessed on the basis of the sack in the lowest - that is, the most heavily loaded - position.
The sacks were partially blocked and no longer freely flowable.
Le A 33 803-US
Example 6 25 kg of Levapren 700 HV was powdered with 0.25 phr Wessalon S. A further 25 kg was additionally powdered with Coatylene 1681 and both samples were put into polyethylene sacks, packed in cardboard and both stored for 14 days in a hot cabinet at 40°C.
The product powdered with Wessalon S was completely baked and could not be fur-ther processed.
The subsequently powdered product remained flowable and was therefore suitable for further processing.
Example 7 Water absorption of the powdering agent:
Wessalon S had a water content of 4 to 5%, measured as loss on drying after 2h at 105°C.
Sipernat D17 had a water content of 2%, measured as loss on drying after 2h at 105°C.
Hydrophobic powdering agents are also advantageous, because these do not agglom erate in the presence of moisture. Agglomerated powdering agents can lead to defects and voids when used in thin layers.
Although the invention has been described in detail in the foregoing for the purpose of illustration, it is to be understood that such detail is solely for that purpose and that variations can be made therein by those skilled in the art without departing from the spirit and scope of the invention except as it may be limited by the claims.
Claims (16)
1. A process for producing flowable polar rubber granules, comprising the step of rendering the surface of a powdering agent hydrophobic.
2. A process according to Claim 1, wherein said powdering agents are mineral powdering agents.
3. A process according to Claim 1, wherein said polar rubbers are selected from the group consisting of polychloropene, acrylonitrile-butadiene copolymers, styrene-acrylonitrile-butadiene copolymers, ethylene-vinyl acetate copolymers, and ethylene-acrylate copolymers and a mixture of two or more of the abovementioned polymers.
4. Flowable polar rubber granules having a low water absorption, comprising a hydrophobic powdering agent.
5. Cross-linkable rubber mixtures comprising flowable polar rubber granules having a low water absorption, comprising a hydrophobic powdering agent.
6. A process for enhancing the flow properties of flowable polar rubber granules which comprises coating the granules with a powdering agent that has been rendered hydrophobic.
7. A process according to claim 6, wherein the quantity of powdering agent used is less than 30 phr.
8. A process according to claim 6 or 7, wherein the quantity of powdering agent used is less than l0 phr.
9. A process according to any one of claims 6 to 8, wherein the powdering agent has an average particle diameter of 2 to 50 µm.
10. A process according to any one of claims 6 to 9, wherein the powdering agent has an average particle diameter of 2 to 20 µm.
11. A process according to any one of claims 6 to 10, wherein the powdering agent is selected from the group consisting of silica, talc, clays, mixed silicates, metal oxides, and carbonates, and a mixture of two or more of the abovementioned powdering agents.
12. A process according to claim 11, wherein the silica is a precipitated silica.
13. A process according to claim 11 or 12, wherein the mixed silicates are aluminum-containing silicates.
14. A process according to any one of claims 11 to 13, wherein the metal oxides are ZnO or MgO.
15. A process according to any one of claims 11 to 14, wherein the carbonates are precipitated.
16. A process according to any one of claims 11 to 15, wherein the carbonates are calcium carbonates.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE1999133152 DE19933152A1 (en) | 1999-07-20 | 1999-07-20 | Free-flowing elastomer granules |
| DE19933152.9 | 1999-07-20 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2313986A1 true CA2313986A1 (en) | 2001-01-20 |
Family
ID=7914874
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2313986 Abandoned CA2313986A1 (en) | 1999-07-20 | 2000-07-17 | Flowable elastomer granules |
Country Status (4)
| Country | Link |
|---|---|
| EP (1) | EP1070735A1 (en) |
| JP (1) | JP2001055448A (en) |
| CA (1) | CA2313986A1 (en) |
| DE (1) | DE19933152A1 (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP4734313B2 (en) * | 2007-12-07 | 2011-07-27 | 株式会社カネカ | Method for preventing blocking of (meth) acrylic block copolymer pellets |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE3101413C2 (en) * | 1981-01-17 | 1983-10-20 | Hoechst Ag, 6230 Frankfurt | Powdered polymer composition, process for their preparation and their use |
| DE69126597T2 (en) * | 1990-11-20 | 1998-02-05 | Mitsubishi Rayon Co | Process for improving powder characteristics |
| JPH06166757A (en) * | 1992-10-30 | 1994-06-14 | Dainichiseika Color & Chem Mfg Co Ltd | Fine particulate polystyrene elastomer and its production |
| DE19732333A1 (en) * | 1997-07-28 | 1999-02-04 | Buna Sow Leuna Olefinverb Gmbh | Process for the preparation of redispersible powders with good "instant" behavior |
-
1999
- 1999-07-20 DE DE1999133152 patent/DE19933152A1/en not_active Ceased
-
2000
- 2000-07-07 EP EP00114076A patent/EP1070735A1/en not_active Withdrawn
- 2000-07-13 JP JP2000212703A patent/JP2001055448A/en active Pending
- 2000-07-17 CA CA 2313986 patent/CA2313986A1/en not_active Abandoned
Also Published As
| Publication number | Publication date |
|---|---|
| DE19933152A1 (en) | 2001-02-22 |
| EP1070735A1 (en) | 2001-01-24 |
| JP2001055448A (en) | 2001-02-27 |
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