CA1285362C - Pelletization of saran - Google Patents
Pelletization of saranInfo
- Publication number
- CA1285362C CA1285362C CA000527302A CA527302A CA1285362C CA 1285362 C CA1285362 C CA 1285362C CA 000527302 A CA000527302 A CA 000527302A CA 527302 A CA527302 A CA 527302A CA 1285362 C CA1285362 C CA 1285362C
- Authority
- CA
- Canada
- Prior art keywords
- saran
- pellets
- resin
- cooled
- temperature
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
Links
Landscapes
- Processing And Handling Of Plastics And Other Materials For Molding In General (AREA)
- Processes Of Treating Macromolecular Substances (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
Saran pellets with high stability are produced by mixing a saran resin in a mixing means until the saran fuses at a temperature significantly below its crystalline melting point. The saran is formed into a sheet or strand, cooled, and divided into pellets.
Saran pellets with high stability are produced by mixing a saran resin in a mixing means until the saran fuses at a temperature significantly below its crystalline melting point. The saran is formed into a sheet or strand, cooled, and divided into pellets.
Description
i3~
PELLETIZATION OF SARAN
BACKGROUND OF THE INVENTION
This invention relates to packaging film, and more particularly to barrier materials useful in producing packaging films, bags, and laminates.
Copolymers of vinylidenè chloride, commonly known as saran, have been used in the past, and are presently used, in producing packaging material having high o~ygen barrier characteristics.
This barrier feature is especially critical in food packaging applica-tions such as fresh red meat, smoked and processed meats, cheeses, and other items sens1tive to an oxygen atmosphere.
Commercially, saran is often marketed as a powder, which is heat sensitive and ~ay result in a less stable and less consistent material in an extrusion process.
It is advantageous, therefore, to pelletize this saran by extruding molten saran resins through a die and chopping the emerging strands into pellets.
Saran pellets feed better than saran powder in extrusion operations, ~nd provide greater output rates with a more consistent product.
404/860414tl/1 -1 ~
' `
53~
However, pelletizing at melt temperatures, typically between about 300F and 320F for vinylidene chloride copolymers, adds to the heat his-tory of the resin. Because the heat sensitivity of the saran is cumulative, a lengthy thermal history will adversely affe~t the final product quality.
Saran exposed to elevated temperatures may turn brown and then car-bonize. Carbonization is not only detrimental for aesthetic reasons. It can also substantiall~ and adversely affect the processing of the saran, for example in processes where a cooled extruded tape containing the saran is subsequently inflated by for example a blown bubble process to produce an oriented film. The presence of carbon material in the saran makes pro-cessing under these conditions more difficult.
Pelletizing at melt temperatures for saran may also result in the production of other undesirable by-products such as hydrogen chloride in subsequent processing operations.
It is, therefore, an object of the present invention to provide a method for pelletizing a saran resin whereby improvements in extrusion operations are obtained.
It is also an object of the present invention to provide a method for pelletizing saran resin whereby the thermal history of the resin is minimized.
It is also an object of the present invention to provide such a process whereby carbonization problems and the production of undesirable by-products such as hydrogen chloride is minimized.
It is further an object of the present lnvention to provide a method for pelletizing saran resin whereby a saran pellet with more stable and consistent behavior in extrusion processes is obtained.
o2 ~
~ ~8~3~
SU~MARY OF_THE INVENTION
In accordance with the present invention, a method of producing a saran pellet comprises mixing a saran resin in a mixing means until the saran fuses at a temperature significantly below its crystalline melting point; forming the fused saran;
cooling the formed saran; and dividing the cooled saran into saran pellets.
In another aspect of the present invention, saran pellets useful in extrusion applications are :Eormed from a saran resin which has been mixed in a mixing means until it fuses at a temperature signiEicantly below its crystalline melting point.
The invention herein comprises a method of producing a saran pellet usefu:l in extrusion applications, and charac-terized by substantial absence of carbonization-derived carbon, comprising:
(a) mixing a saran resin in a mixing means until the saran fuses at a temperature between about 210F and 260F;
~b) forming the mixed saran into a sheet, strand or other shaped article;
(c) cooling the formed saran; and (d) dividing the cooled saran into saran pellets.
The inven-tion herein further comprises saran pellets useful in extrusion applications, and characterized by substantial absence of carbonization-derived carbon, said pellets formed from a saran resin which has been:
,, ~ .
..~, ., ~8~
(a) mixed by shearing in a mlxing means until the saran is brought to a temperature of between about 210F and 260F;
(b) formed into a sheet, strand or other shaped article;
(c) cooled; and ~d) divided into pellets.
DEFINITIONS
The term "sara~l" is used herein to include vinylidene chloride copolymers having as copolymerizable comonomers vinyl chloride, acrylonitrile, vinyl acetate, alkyl acrylates, etc.
Terpolymers such as vinylidene chloride, dimethyl maleate and vinyl chloride can also be employed. Generally, the vinylidene chloride is at least 50% of the material in the polymer.
The term "fuse" is used herein to describe the conversion of the saran resin from a solid to a partially molten state characterized by high viscosity, a whitish appearance, and a dough like consistency.
The term "forming" is used herein to describe the step of further processing the fused saran by any suitable means in order to produce a sheet, strand, or other shaped article.
The term "dividing" is used herein to mean granulating, dicing, chopping or other processiny of the Eormed saran in order to produce a pellet.
3a s~
DESCRIPTION OF THE PREFE~R~D EMBODIMENTS
Conventional pelletizing of saran powder typically includes melting the powder at between about 300F and 320F, the latter being the crystalline melting temperature of typical commercially available saran resins. This adversely affects the stability and qual1ty of the final product made from the saran pellets produced by this process. It has been found that saran which has been fused and partially but not totally melted at temperatures ranging from about 210F to 260F produces a high viscosity mass with a consistency and white appearance similar to bread dough. It is possible to form this viscous material into saran pellets. Because the rate of thermal decomposition of saran approximately doubles for every 20 degrees of Fahrenheit increase in temperature during the melting/pelletizing process, pelletizing the saran at temperatures of approximately 40F to 90~F lower than conventional techniques produces only a fraction of the thermal degradation that occurs in the conventional melt pelletizing process.
It is, therefore, a feature of the present invention that the saran feedstock, commonly in the form of a powder, is mixed, for example, by shearing in a suitable mixing means until the feedstock fuses, preferably at a temperature of between about 210F and 2~0F. More preferably, the feedstock is brought to a temperature of between about 240F and 250F.
These temperature ranges represent temperatures of approximately 40F to 90F less than in conventional pelletizing processes.
At these lower temperatures, the formation of hydrogen chloride and other undesirable by-products is minimized, and carbonization and browning problems associated with saran processing is also reduced. A saran pellet is produced characteriæed by high stability and good consistency in ex-trusion processing, and is especially useful in connection with the ex-trusion or coextrusion of multilayer films, and the production of laminates, in which a saran barrier layer is required.
_y _ ~.~8~3~:
~XAMPLE 1 In a small Banbury mixer, saran powder was sheared by blade action until the saran fused, taking on a bread dough consistency at between 240~F
and 250F. The resul~ing highly viscous melt was pressed into a sheet, cooled, and granulated to pelletize the saran.
The saran pellets were then extruded in a conventional extrusion process to produce an oriented film.
Saran powder was sheared as described in Example 1 in a larger, 100-pound Banbury mixer, with similar results, i.e. the production of a fusedhighly viscous melt having a whitish bread dough consistency and appearance.
Approximately 5,000 pounds of saran powder was pelletized during each of three separate tests on a Condux Pelletizing System. This system operates by utilizing an outer cone which revolves around a fixed concentric cone, causing the saran resin to fuse and form long, thin strands which are then ground into pellets. The equipment, produced by Condux Werk, is a commercial system presently used to reclaim scrap polyethylene, polypropylene, and other plastic materials.
The saran pellets thus made were used in subsequent extrusion operations and found to have an acceptable heat history without carbon speck contamination. Film was successfully oriented from the extruded tape by the blown bubb1e procesH we]l known in tho Mrt.
I u ~
~04/860414/1/S
Conventionally, the addition of p]asticizers to vinylidene chloride copolymers is necessary to allow for coextrusion of saran with other resins in a typical coextrusion process. The plasticizers reduce the saran melt viscosity so that lt can be extruded without surging, air entrapment, and resin degradation. Although plasticizers are, therefore, a valuable ex-trusion aid, they also drastically reduce the saran oxygen and moisture barrier properties. Por example, an unplasticized saran having an oxygen transmission rate (cc-mil/~n. /day) of 1 to 2 has, when plasticized, an increased oxygen transmission rate (and therefore a reduced barrier) of 8 to 12 cc-mil/m2/day. The moisture barrier property of the saran is also reduced, dropping from less than 0.1 grams-mil/100 in.2/day to a moisture vapor transmission rate of 0.2 to 0.4 grams-mil/100 in.2/day.
In the development of very high oxygen and moisture barrier films, it is therefore desirable to use unplasticized, low molecular weight saran resins to achieve the higher barrier levels required for more stringent end use applications.
Typical of such resins are PV858 and PV864 unplasticized saran manufactured by Solvay. These are similar resiris, with PV864 having a larg-er particle size than PV858.
Because of the greater difficulties in extrusion encountered in un-plasticized low molecular weight saran resins, and because of their erratic feed characteristics, it is advantageous to pelletize these materials.
It is, therefore, highly useful, in the use of such unplasticized sarans, as well as in the conventional plasticized materials, to pellet the sarans by the present invention.
The above described examples include-the production of a fused highly viscous melt which is then formed into a sheet or strand. Strands produced by tile pre~ent lnventlon may t~ke tlle ~orm Or thln ~p~hStti like stran~, and one skilled in the art would, after revlew of thi~ dlsclo~ure clearly find other suitable dimensions and shapes ln which to press or otherwl~e prepare the fused saran for pelletizing. The pelletizing step itself may be accomplished by any suitable means, includin~ granulatin~ or dicing of the sheet, strand, or other form of the fused, cooled and formed material.
This invention has been described in conjunction with preferred embodiments, but it should be understood that modifications and variations can be used without departing from the scope of the invention as those skilled in the art will readily understand. AccordinglyJ such modifications and variations may be practiced within the scope of the following claims.
PELLETIZATION OF SARAN
BACKGROUND OF THE INVENTION
This invention relates to packaging film, and more particularly to barrier materials useful in producing packaging films, bags, and laminates.
Copolymers of vinylidenè chloride, commonly known as saran, have been used in the past, and are presently used, in producing packaging material having high o~ygen barrier characteristics.
This barrier feature is especially critical in food packaging applica-tions such as fresh red meat, smoked and processed meats, cheeses, and other items sens1tive to an oxygen atmosphere.
Commercially, saran is often marketed as a powder, which is heat sensitive and ~ay result in a less stable and less consistent material in an extrusion process.
It is advantageous, therefore, to pelletize this saran by extruding molten saran resins through a die and chopping the emerging strands into pellets.
Saran pellets feed better than saran powder in extrusion operations, ~nd provide greater output rates with a more consistent product.
404/860414tl/1 -1 ~
' `
53~
However, pelletizing at melt temperatures, typically between about 300F and 320F for vinylidene chloride copolymers, adds to the heat his-tory of the resin. Because the heat sensitivity of the saran is cumulative, a lengthy thermal history will adversely affe~t the final product quality.
Saran exposed to elevated temperatures may turn brown and then car-bonize. Carbonization is not only detrimental for aesthetic reasons. It can also substantiall~ and adversely affect the processing of the saran, for example in processes where a cooled extruded tape containing the saran is subsequently inflated by for example a blown bubble process to produce an oriented film. The presence of carbon material in the saran makes pro-cessing under these conditions more difficult.
Pelletizing at melt temperatures for saran may also result in the production of other undesirable by-products such as hydrogen chloride in subsequent processing operations.
It is, therefore, an object of the present invention to provide a method for pelletizing a saran resin whereby improvements in extrusion operations are obtained.
It is also an object of the present invention to provide a method for pelletizing saran resin whereby the thermal history of the resin is minimized.
It is also an object of the present invention to provide such a process whereby carbonization problems and the production of undesirable by-products such as hydrogen chloride is minimized.
It is further an object of the present lnvention to provide a method for pelletizing saran resin whereby a saran pellet with more stable and consistent behavior in extrusion processes is obtained.
o2 ~
~ ~8~3~
SU~MARY OF_THE INVENTION
In accordance with the present invention, a method of producing a saran pellet comprises mixing a saran resin in a mixing means until the saran fuses at a temperature significantly below its crystalline melting point; forming the fused saran;
cooling the formed saran; and dividing the cooled saran into saran pellets.
In another aspect of the present invention, saran pellets useful in extrusion applications are :Eormed from a saran resin which has been mixed in a mixing means until it fuses at a temperature signiEicantly below its crystalline melting point.
The invention herein comprises a method of producing a saran pellet usefu:l in extrusion applications, and charac-terized by substantial absence of carbonization-derived carbon, comprising:
(a) mixing a saran resin in a mixing means until the saran fuses at a temperature between about 210F and 260F;
~b) forming the mixed saran into a sheet, strand or other shaped article;
(c) cooling the formed saran; and (d) dividing the cooled saran into saran pellets.
The inven-tion herein further comprises saran pellets useful in extrusion applications, and characterized by substantial absence of carbonization-derived carbon, said pellets formed from a saran resin which has been:
,, ~ .
..~, ., ~8~
(a) mixed by shearing in a mlxing means until the saran is brought to a temperature of between about 210F and 260F;
(b) formed into a sheet, strand or other shaped article;
(c) cooled; and ~d) divided into pellets.
DEFINITIONS
The term "sara~l" is used herein to include vinylidene chloride copolymers having as copolymerizable comonomers vinyl chloride, acrylonitrile, vinyl acetate, alkyl acrylates, etc.
Terpolymers such as vinylidene chloride, dimethyl maleate and vinyl chloride can also be employed. Generally, the vinylidene chloride is at least 50% of the material in the polymer.
The term "fuse" is used herein to describe the conversion of the saran resin from a solid to a partially molten state characterized by high viscosity, a whitish appearance, and a dough like consistency.
The term "forming" is used herein to describe the step of further processing the fused saran by any suitable means in order to produce a sheet, strand, or other shaped article.
The term "dividing" is used herein to mean granulating, dicing, chopping or other processiny of the Eormed saran in order to produce a pellet.
3a s~
DESCRIPTION OF THE PREFE~R~D EMBODIMENTS
Conventional pelletizing of saran powder typically includes melting the powder at between about 300F and 320F, the latter being the crystalline melting temperature of typical commercially available saran resins. This adversely affects the stability and qual1ty of the final product made from the saran pellets produced by this process. It has been found that saran which has been fused and partially but not totally melted at temperatures ranging from about 210F to 260F produces a high viscosity mass with a consistency and white appearance similar to bread dough. It is possible to form this viscous material into saran pellets. Because the rate of thermal decomposition of saran approximately doubles for every 20 degrees of Fahrenheit increase in temperature during the melting/pelletizing process, pelletizing the saran at temperatures of approximately 40F to 90~F lower than conventional techniques produces only a fraction of the thermal degradation that occurs in the conventional melt pelletizing process.
It is, therefore, a feature of the present invention that the saran feedstock, commonly in the form of a powder, is mixed, for example, by shearing in a suitable mixing means until the feedstock fuses, preferably at a temperature of between about 210F and 2~0F. More preferably, the feedstock is brought to a temperature of between about 240F and 250F.
These temperature ranges represent temperatures of approximately 40F to 90F less than in conventional pelletizing processes.
At these lower temperatures, the formation of hydrogen chloride and other undesirable by-products is minimized, and carbonization and browning problems associated with saran processing is also reduced. A saran pellet is produced characteriæed by high stability and good consistency in ex-trusion processing, and is especially useful in connection with the ex-trusion or coextrusion of multilayer films, and the production of laminates, in which a saran barrier layer is required.
_y _ ~.~8~3~:
~XAMPLE 1 In a small Banbury mixer, saran powder was sheared by blade action until the saran fused, taking on a bread dough consistency at between 240~F
and 250F. The resul~ing highly viscous melt was pressed into a sheet, cooled, and granulated to pelletize the saran.
The saran pellets were then extruded in a conventional extrusion process to produce an oriented film.
Saran powder was sheared as described in Example 1 in a larger, 100-pound Banbury mixer, with similar results, i.e. the production of a fusedhighly viscous melt having a whitish bread dough consistency and appearance.
Approximately 5,000 pounds of saran powder was pelletized during each of three separate tests on a Condux Pelletizing System. This system operates by utilizing an outer cone which revolves around a fixed concentric cone, causing the saran resin to fuse and form long, thin strands which are then ground into pellets. The equipment, produced by Condux Werk, is a commercial system presently used to reclaim scrap polyethylene, polypropylene, and other plastic materials.
The saran pellets thus made were used in subsequent extrusion operations and found to have an acceptable heat history without carbon speck contamination. Film was successfully oriented from the extruded tape by the blown bubb1e procesH we]l known in tho Mrt.
I u ~
~04/860414/1/S
Conventionally, the addition of p]asticizers to vinylidene chloride copolymers is necessary to allow for coextrusion of saran with other resins in a typical coextrusion process. The plasticizers reduce the saran melt viscosity so that lt can be extruded without surging, air entrapment, and resin degradation. Although plasticizers are, therefore, a valuable ex-trusion aid, they also drastically reduce the saran oxygen and moisture barrier properties. Por example, an unplasticized saran having an oxygen transmission rate (cc-mil/~n. /day) of 1 to 2 has, when plasticized, an increased oxygen transmission rate (and therefore a reduced barrier) of 8 to 12 cc-mil/m2/day. The moisture barrier property of the saran is also reduced, dropping from less than 0.1 grams-mil/100 in.2/day to a moisture vapor transmission rate of 0.2 to 0.4 grams-mil/100 in.2/day.
In the development of very high oxygen and moisture barrier films, it is therefore desirable to use unplasticized, low molecular weight saran resins to achieve the higher barrier levels required for more stringent end use applications.
Typical of such resins are PV858 and PV864 unplasticized saran manufactured by Solvay. These are similar resiris, with PV864 having a larg-er particle size than PV858.
Because of the greater difficulties in extrusion encountered in un-plasticized low molecular weight saran resins, and because of their erratic feed characteristics, it is advantageous to pelletize these materials.
It is, therefore, highly useful, in the use of such unplasticized sarans, as well as in the conventional plasticized materials, to pellet the sarans by the present invention.
The above described examples include-the production of a fused highly viscous melt which is then formed into a sheet or strand. Strands produced by tile pre~ent lnventlon may t~ke tlle ~orm Or thln ~p~hStti like stran~, and one skilled in the art would, after revlew of thi~ dlsclo~ure clearly find other suitable dimensions and shapes ln which to press or otherwl~e prepare the fused saran for pelletizing. The pelletizing step itself may be accomplished by any suitable means, includin~ granulatin~ or dicing of the sheet, strand, or other form of the fused, cooled and formed material.
This invention has been described in conjunction with preferred embodiments, but it should be understood that modifications and variations can be used without departing from the scope of the invention as those skilled in the art will readily understand. AccordinglyJ such modifications and variations may be practiced within the scope of the following claims.
Claims (9)
1. A method of producing a saran pellet useful in extrusion applications, and characterized by substantial absence of carbonization-derived carbon, comprising:
(a) mixing a saran resin in a mixing means until the saran fuses at a temperature between about 210°F and 260°F;
(b) forming the mixed saran into a sheet, strand or other shaped article;
(c) cooling the formed saran; and (d) dividing the cooled saran into saran pellets.
(a) mixing a saran resin in a mixing means until the saran fuses at a temperature between about 210°F and 260°F;
(b) forming the mixed saran into a sheet, strand or other shaped article;
(c) cooling the formed saran; and (d) dividing the cooled saran into saran pellets.
2. The method according to claim 1 wherein the saran resin is mixed until it reaches a fusion temperature between about 240°F
and 250°F.
and 250°F.
3. The method according to claim 1 wherein the saran resin is fused by a shearing action.
4. The method according to claim 1 wherein the formed saran is cooled to about room temperature.
5. The method according to claim 1 wherein the formed and cooled saran is divided by grinding to produce the saran pellets.
6. The method according to claim 1 wherein the formed and cooled saran is divided by dicing to produce the saran pellets.
7. Saran pellets useful in extrusion applications formed from a saran resin which has been mixed in a mixing means until it fuses at a temperature between about 210°F and 260°F.
8 The saran pellets according to claim 7 wherein the saran resin is a saran powder.
9. Saran pellets useful in extrusion applications, and characterized by substantial absence of carbonization-derived carbon, said pellets formed from a saran resin which has been:
(a) mixed by shearing in a mixing means until the saran is brought to a temperature of between about 210°F and 260°F;
(b) formed into a sheet, strand or other shaped article;
(c) cooled; and (d) divided into pellets.
(a) mixed by shearing in a mixing means until the saran is brought to a temperature of between about 210°F and 260°F;
(b) formed into a sheet, strand or other shaped article;
(c) cooled; and (d) divided into pellets.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US86663786A | 1986-05-22 | 1986-05-22 | |
| US866,637 | 1986-05-22 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1285362C true CA1285362C (en) | 1991-07-02 |
Family
ID=25348048
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000527302A Expired - Lifetime CA1285362C (en) | 1986-05-22 | 1987-01-14 | Pelletization of saran |
Country Status (6)
| Country | Link |
|---|---|
| JP (1) | JP2514969B2 (en) |
| AU (1) | AU7312887A (en) |
| BR (1) | BR8702586A (en) |
| CA (1) | CA1285362C (en) |
| NZ (1) | NZ219956A (en) |
| ZA (1) | ZA872802B (en) |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5323725B2 (en) * | 1974-06-24 | 1978-07-17 |
-
1987
- 1987-01-14 CA CA000527302A patent/CA1285362C/en not_active Expired - Lifetime
- 1987-04-13 NZ NZ21995687A patent/NZ219956A/en unknown
- 1987-04-21 ZA ZA872802A patent/ZA872802B/en unknown
- 1987-05-15 JP JP62117175A patent/JP2514969B2/en not_active Expired - Lifetime
- 1987-05-18 AU AU73128/87A patent/AU7312887A/en not_active Abandoned
- 1987-05-20 BR BR8702586A patent/BR8702586A/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| JP2514969B2 (en) | 1996-07-10 |
| ZA872802B (en) | 1987-11-25 |
| BR8702586A (en) | 1988-02-23 |
| JPS62286709A (en) | 1987-12-12 |
| AU7312887A (en) | 1987-11-26 |
| NZ219956A (en) | 1989-04-26 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKLA | Lapsed |