CA1266342A - Plastic bags of blends of linear ethylene polymers and aromatic polymers - Google Patents
Plastic bags of blends of linear ethylene polymers and aromatic polymersInfo
- Publication number
- CA1266342A CA1266342A CA000516702A CA516702A CA1266342A CA 1266342 A CA1266342 A CA 1266342A CA 000516702 A CA000516702 A CA 000516702A CA 516702 A CA516702 A CA 516702A CA 1266342 A CA1266342 A CA 1266342A
- Authority
- CA
- Canada
- Prior art keywords
- polymer
- bag
- film
- aromatic hydrocarbon
- ethylene
- 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
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- Compositions Of Macromolecular Compounds (AREA)
- Manufacture Of Macromolecular Shaped Articles (AREA)
Abstract
PLASTIC BAGS OF BLENDS OF LINEAR ETHYLENE
POLYMERS AND AROMATIC POLYMERS
ABSTRACT OF THE DISCLOSURE
Plastic bags are made from linear ethylene homopolymer or linear low density copolymers (LLDPE) blended with up to about 10 weight percent of an aromatic polymer, e.g., polystyrene or poly(para-methylstyrene), to improve the ease of opening the bags by reducing the blocking tendency of the film. Although ease of opening is improved the aromatic polymer does not adversely affect the other physical properties of the bag, such as machine direction (MD) tear strength and stiffness, but improves them.
POLYMERS AND AROMATIC POLYMERS
ABSTRACT OF THE DISCLOSURE
Plastic bags are made from linear ethylene homopolymer or linear low density copolymers (LLDPE) blended with up to about 10 weight percent of an aromatic polymer, e.g., polystyrene or poly(para-methylstyrene), to improve the ease of opening the bags by reducing the blocking tendency of the film. Although ease of opening is improved the aromatic polymer does not adversely affect the other physical properties of the bag, such as machine direction (MD) tear strength and stiffness, but improves them.
Description
3~æ
PLASTIC BAGS OF BLE~DS OF LINEAR ETHYLENE
POLYMERS AND AROMATIC POLYMERS
Compositions suitable for making the bags of this invention are disclosed in U.S. Patent 4,579,912.
~ inear low and medium density polyethylene copolymers (LLDPE), and linear high density polyethylene (HDPE) are known materials which are widely commercially available. LL~PE is also described in U.S. Patent 4,076,698. A commercially important use of LLDPE and o~ HDPE is in making bags which are conventionally prepared from films by blown film extrusion. Because of the availability of polymers having excellent physical properties~ such as tensile strength, the trend has been to reduce the gauge o~ the film used for economic reasons. Such bags even in film gauge of less than O.OZ5 mm ~1 mil) have generally satisfactory properties but often are difficult to open, particularly with the thinner gauge films. In accordance with this invention, bag opening characteristics can be improved by blending HDPE or LLDPE with aromatic polymers such as polystyrene or poly(para-methylstyrene).
It has been found that the aromatic polymer acts unexpectedly as an antiblocking agent and that blocking is one o~ the factors which contributes to difficulty in opening thin gauge bags.
This invention provides thermoplastic bags made from a film comprising, as a major const~tuent, a linear homopolymer of ethylene or a linear copolymer of ethylene and a higher olefin having at least 4 carbon atoms, and 0.1 to 15 weight percent of a thermoplastic polymer of an aromatic hydrocarbon in an amount sufficient to improve the ease of opening of the bag compared to the ease of opening of a ba~ containing no aromatic hydrocarbon polymer. This invention also~provides an improved method of making bags from a linear ethylene polymer film comprising including in the , ;
~ ~k , 3~
film 0.1 to 15 weight percent of a thermoplasic polymer of an aromatic hydrocarbon in an amount sufficient to improve anti-blocking characteristics of the film.
In accordance with this invention, the characteristics of bags made from ethylene polymers, particularly ~rom HDPE, LLDPE or mixtures thereof can be improved by blending up to about 10 weight percent, preferably up to about 8 weight percent, and most preferably between about 3 and 8 weight percent of a thermoplastic aromatic polymer.
The linear ethylene polymers which are suitable for use in this invention are those now conventionall~ prepared by low pressure techniques. But development is active in the preparation of linear copolymers under high pressure with coordination catalysts and the like. Such linear polymers are also suitable ~or use in this invention. Many suitable linear ethylene polymers are commercially available. Particularly suitable are LLCPE resins which are copolymers of ethylene and higher olefins, particularly l-butene, l-hexene, and l-octene. These LLDPE copolymers generally have a density of between û.90 and 0.94, preferably between 0.91 and 0.93.
Polystyrene and poly~para-methylstyrene) resins are particularly suitable as the aromatic polymer which is blended with the ethylene polymer. Polymers in which the aromatic monomer is the predominant constituent, such as high impact polystyrene and styrene copolymers are also suitable. The best tear strength is obtained with blends in which the linear ethylene polymer itself has good tear properties. Such blends result in films with good tear and impact properties, and the higher modulus characteristic of a higher density LLDPE film.
The linear ethylene polymer can be blended with other compatible polymers~providing that the linear polymer is the major constituent of the blend. For example9 LDPE high pressure polymer is suitable in such blends Compatibilizers can be used in small amounts up to about 2 weight percent of the composition but are not necessary. Suitable : ,, : :
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compatibilizers include block copolymers of styrene-ethylene propylene-styrene (~Kraton G~*), block copolymers of styrene and ethylene ('Shelvis~**) and ethylene propylene copolymers ('Vistal~n 3707***). Fo~ purposes of ease of blending and control on a chemical scale it is preferred that the LLDPE and the aromatic polymer be the sole polymeric components.
The resin blends and bags are made in the conventional manner. Preferably, the bags are made ~rom films obtained by blown film extrusion using conventional techniques to obtain films which are generally from about û.Oû5 to 0.13 mm (0.2 to 5 mils) in thickness.
This invention finds particular utility in the production o~ bags having a thin gauge which are commonly dispensed from rolls in supermarket produce sections, for example. It is a common experience to find these bags di~icult to open and this difficulty is reduced by using the polymer blends of this invention. But the invention is by no means limited to bags supplied on rolls. It is also advantageous in the production o~ the larger bags usually having handles and gussetts which are in widespread use at supermarket checkout counters. These bags are commonly supplied in packs of 50 or more bags attached to a tear-off tab fitted to a dispenser device for holding the bag open during loading. Bags of this type are disclosed in U.S. Patent 4,165,832.
As previously indicated blending o~ the LLDPE resin and the aromatic polymer is done in the conventional manner. Blending can be accomplished by melting the polymers into pellets for future extrusion or by ~eeding a mixture of the two polymers directly to the extruder. The latter may be preferable in commercial operations because the separate operation of melt blending and its attendant expense is eliminated.
Antiblock agents such as diatomaceous earth (silica) are commonly used in bag compositions. These agents often have deleterious e~fects on the physical properties of bag films. It is an anticipated advantage of this invention that conventional * Trademark ** Trademark *** Trademark ` '' . ~ : .
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anti-block agent can be reduced or eliminated and replaced in whole or in part with the aromatic polymer. The aromatic polymer, when used in proper amounts has a beneficial effect on important physical properties such as machine direction (MD) tear strength and stiffness, and provides the unexpected improvement in anti-block characteristics contributing to easier opening.
In addition to the improvements apparent in the final bags due to the incorporating of aromatic polymer, improvements in processing have been noted. For example, in post-gussetting nperations in which a tube blown film is flattened and reblown to introduce gussets difficulty is often encountered in the reblowing step due to blocking of the films causing non-uniform gussets and other problems. These problems are reduced by using the blends of this invention.
The following non-limiting examples are illustrative of this invention. Unless otherwise noted all parts are by weight.
.
A compounded blend of 95% LLDPE (ethylene-l-hexene copolymer, Melt Index 0.7, density û.922) and 5% polystyrene ~Mobil PS 124û) was produced by feeding both materials into an intensive mixer (Bolling Mill3 at the correct ratio, melting and mixing both polymers together such that an intimate mixture was obtained, then feeding the molten mass to a pelletizer, thus producing pellets.
These pellets were cooled and stored several weeks- The pellets were subsequently made into film suitable for producing grocery sacks by the blown film process. Similarly produced pellets of the LLDPE without polystyrene were also made into film in an identical ; ` ~ manner.
In a second run pellets o~ the identical polystyrene were blerlded with pellets of the LL3PE in the blown film extruder hopper in the proper ratio and immediately made into film suitable for grocery sacks. Films from both experiments were tested for 1%
:
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secant modulus (stiffness) and for tensile impact (spittiness).
Blend MD læ Secant TD Tensile Example Film Method Modulus (psi) Impact (ft-la) C-l. lûû% LLDPE Melt 37ûO0 0.46 1. 95% LLDPE/5% PS1240 Melt 48500 0.52 % increase (1) vs (C-l) - 31 15 C-2. 100% LLDPE Dry 462ûû 0.27
PLASTIC BAGS OF BLE~DS OF LINEAR ETHYLENE
POLYMERS AND AROMATIC POLYMERS
Compositions suitable for making the bags of this invention are disclosed in U.S. Patent 4,579,912.
~ inear low and medium density polyethylene copolymers (LLDPE), and linear high density polyethylene (HDPE) are known materials which are widely commercially available. LL~PE is also described in U.S. Patent 4,076,698. A commercially important use of LLDPE and o~ HDPE is in making bags which are conventionally prepared from films by blown film extrusion. Because of the availability of polymers having excellent physical properties~ such as tensile strength, the trend has been to reduce the gauge o~ the film used for economic reasons. Such bags even in film gauge of less than O.OZ5 mm ~1 mil) have generally satisfactory properties but often are difficult to open, particularly with the thinner gauge films. In accordance with this invention, bag opening characteristics can be improved by blending HDPE or LLDPE with aromatic polymers such as polystyrene or poly(para-methylstyrene).
It has been found that the aromatic polymer acts unexpectedly as an antiblocking agent and that blocking is one o~ the factors which contributes to difficulty in opening thin gauge bags.
This invention provides thermoplastic bags made from a film comprising, as a major const~tuent, a linear homopolymer of ethylene or a linear copolymer of ethylene and a higher olefin having at least 4 carbon atoms, and 0.1 to 15 weight percent of a thermoplastic polymer of an aromatic hydrocarbon in an amount sufficient to improve the ease of opening of the bag compared to the ease of opening of a ba~ containing no aromatic hydrocarbon polymer. This invention also~provides an improved method of making bags from a linear ethylene polymer film comprising including in the , ;
~ ~k , 3~
film 0.1 to 15 weight percent of a thermoplasic polymer of an aromatic hydrocarbon in an amount sufficient to improve anti-blocking characteristics of the film.
In accordance with this invention, the characteristics of bags made from ethylene polymers, particularly ~rom HDPE, LLDPE or mixtures thereof can be improved by blending up to about 10 weight percent, preferably up to about 8 weight percent, and most preferably between about 3 and 8 weight percent of a thermoplastic aromatic polymer.
The linear ethylene polymers which are suitable for use in this invention are those now conventionall~ prepared by low pressure techniques. But development is active in the preparation of linear copolymers under high pressure with coordination catalysts and the like. Such linear polymers are also suitable ~or use in this invention. Many suitable linear ethylene polymers are commercially available. Particularly suitable are LLCPE resins which are copolymers of ethylene and higher olefins, particularly l-butene, l-hexene, and l-octene. These LLDPE copolymers generally have a density of between û.90 and 0.94, preferably between 0.91 and 0.93.
Polystyrene and poly~para-methylstyrene) resins are particularly suitable as the aromatic polymer which is blended with the ethylene polymer. Polymers in which the aromatic monomer is the predominant constituent, such as high impact polystyrene and styrene copolymers are also suitable. The best tear strength is obtained with blends in which the linear ethylene polymer itself has good tear properties. Such blends result in films with good tear and impact properties, and the higher modulus characteristic of a higher density LLDPE film.
The linear ethylene polymer can be blended with other compatible polymers~providing that the linear polymer is the major constituent of the blend. For example9 LDPE high pressure polymer is suitable in such blends Compatibilizers can be used in small amounts up to about 2 weight percent of the composition but are not necessary. Suitable : ,, : :
.
.. . .
;. .,.,: :
~ .
.
~ . .,.. , . ::
~6~;3-~
F~3332 - 3 ~
compatibilizers include block copolymers of styrene-ethylene propylene-styrene (~Kraton G~*), block copolymers of styrene and ethylene ('Shelvis~**) and ethylene propylene copolymers ('Vistal~n 3707***). Fo~ purposes of ease of blending and control on a chemical scale it is preferred that the LLDPE and the aromatic polymer be the sole polymeric components.
The resin blends and bags are made in the conventional manner. Preferably, the bags are made ~rom films obtained by blown film extrusion using conventional techniques to obtain films which are generally from about û.Oû5 to 0.13 mm (0.2 to 5 mils) in thickness.
This invention finds particular utility in the production o~ bags having a thin gauge which are commonly dispensed from rolls in supermarket produce sections, for example. It is a common experience to find these bags di~icult to open and this difficulty is reduced by using the polymer blends of this invention. But the invention is by no means limited to bags supplied on rolls. It is also advantageous in the production o~ the larger bags usually having handles and gussetts which are in widespread use at supermarket checkout counters. These bags are commonly supplied in packs of 50 or more bags attached to a tear-off tab fitted to a dispenser device for holding the bag open during loading. Bags of this type are disclosed in U.S. Patent 4,165,832.
As previously indicated blending o~ the LLDPE resin and the aromatic polymer is done in the conventional manner. Blending can be accomplished by melting the polymers into pellets for future extrusion or by ~eeding a mixture of the two polymers directly to the extruder. The latter may be preferable in commercial operations because the separate operation of melt blending and its attendant expense is eliminated.
Antiblock agents such as diatomaceous earth (silica) are commonly used in bag compositions. These agents often have deleterious e~fects on the physical properties of bag films. It is an anticipated advantage of this invention that conventional * Trademark ** Trademark *** Trademark ` '' . ~ : .
,"': ",', ' ` . " :.
~6~
anti-block agent can be reduced or eliminated and replaced in whole or in part with the aromatic polymer. The aromatic polymer, when used in proper amounts has a beneficial effect on important physical properties such as machine direction (MD) tear strength and stiffness, and provides the unexpected improvement in anti-block characteristics contributing to easier opening.
In addition to the improvements apparent in the final bags due to the incorporating of aromatic polymer, improvements in processing have been noted. For example, in post-gussetting nperations in which a tube blown film is flattened and reblown to introduce gussets difficulty is often encountered in the reblowing step due to blocking of the films causing non-uniform gussets and other problems. These problems are reduced by using the blends of this invention.
The following non-limiting examples are illustrative of this invention. Unless otherwise noted all parts are by weight.
.
A compounded blend of 95% LLDPE (ethylene-l-hexene copolymer, Melt Index 0.7, density û.922) and 5% polystyrene ~Mobil PS 124û) was produced by feeding both materials into an intensive mixer (Bolling Mill3 at the correct ratio, melting and mixing both polymers together such that an intimate mixture was obtained, then feeding the molten mass to a pelletizer, thus producing pellets.
These pellets were cooled and stored several weeks- The pellets were subsequently made into film suitable for producing grocery sacks by the blown film process. Similarly produced pellets of the LLDPE without polystyrene were also made into film in an identical ; ` ~ manner.
In a second run pellets o~ the identical polystyrene were blerlded with pellets of the LL3PE in the blown film extruder hopper in the proper ratio and immediately made into film suitable for grocery sacks. Films from both experiments were tested for 1%
:
, .
....
" ~
.
-::
: ., . ~ .; , ., .:, ~L2~63'~
secant modulus (stiffness) and for tensile impact (spittiness).
Blend MD læ Secant TD Tensile Example Film Method Modulus (psi) Impact (ft-la) C-l. lûû% LLDPE Melt 37ûO0 0.46 1. 95% LLDPE/5% PS1240 Melt 48500 0.52 % increase (1) vs (C-l) - 31 15 C-2. 100% LLDPE Dry 462ûû 0.27
2. 95% LLDPE/5% PS1240 Dry 55000 0.47 % increase (2) vs (C-2) 19 76 The film produced according to Example 1 was tested for blocking as follows. Rectangles were cut through the tubular film to obtain two (2) 10.2 cm x 17.8 cm (4" x 7") film swatches each with an inner and an outer side (with respect to the original film tube). These samples were separated from each other to eliminate processing variations and placed back into contact inner side to inner side. The samples were then placed in a Carver press and conditioned at the listed pressure at room temperature for 24 hours. A~ter conditioning, the ~orce required to separate the two films (blocking force? was measured using a Kayeness Blocking Tester.
BlockinQ Force (~rams) Film Conditionin~ Pressure~kPa (psi) ~69 ~10) 17~ (25-r 345 (50) 690 (100) C-3 100% LLDPE 40 53 61 83
BlockinQ Force (~rams) Film Conditionin~ Pressure~kPa (psi) ~69 ~10) 17~ (25-r 345 (50) 690 (100) C-3 100% LLDPE 40 53 61 83
3 ~ 95% LLDPE/5~ PS 1240 22 29 42 55 % decrease (3) vs (C-3) 45 45 31 34 :
:
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3 ~
Films were produced and tested in an identical manner to Example 3 with the following exceptions:
The LLDPE utilized was an ethylene-l-octene copolymer, 0.75 MI, 0.923 density.
Pellets o~ -the LLDPE and pellets of PS 1240 were dry blended together in the proper ratio and made into film suitable for grocery sacks without other prior prucessing.
~locking Force (grams) '' Example Film ~
- 59 ~--r r72-~5~ 345 (50) 690 (100) C-4 100% LLDPE 24 30 43 54
:
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Films were produced and tested in an identical manner to Example 3 with the following exceptions:
The LLDPE utilized was an ethylene-l-octene copolymer, 0.75 MI, 0.923 density.
Pellets o~ -the LLDPE and pellets of PS 1240 were dry blended together in the proper ratio and made into film suitable for grocery sacks without other prior prucessing.
~locking Force (grams) '' Example Film ~
- 59 ~--r r72-~5~ 345 (50) 690 (100) C-4 100% LLDPE 24 30 43 54
4 95% LLDPE/5% PS 1240 13 18 26 27 % decrease (4) vs (C-4) 46 40 40 50 The bags made in accordance with this invention are demonstrably easier to open than the corresponding bags containing no aromatic polymer. ~The~ease of opening has been associated at least~in~part to a reduced~tendency~to block in standard~
quantitative blocking tests. lhe increased stiffness of the blends is also believed to contribute to the ease of opening.
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quantitative blocking tests. lhe increased stiffness of the blends is also believed to contribute to the ease of opening.
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Claims (10)
1. A thermoplastic bag made from a film comprising, as a major constituent, a linear homopolymer of ethylene or a linear copolymer of ethylene and a higher olefin having at least 4 carbon atoms, and 0.1 to about 15 weight percent of a thermoplastic polymer of an aromatic hydrocarbon in an amount sufficient to improve the ease of opening of the bag compared to the ease of opening a bag absent the polymer of an aromatic hydrocarbon.
2. The bag of claim 1 in which the thermoplastic polymer of an aromatic hydrocarbon is a polymer of styrene containing polymerized styrene as its predominant constituent.
3. The bag of claim 1 in which the thermoplastic polymer of an aromatic hydrocarbon is polystyrene.
4. The bag of claim 1 in which the thermoplastic polymer of an aromatic hydrocarbon is a polymer of para-methylstyrene containing polymerized para-methylstyrene as its predominant constituent.
5. The bag of claim 1 in which the low pressure linear ethylene polymer is a copolymer of ethylene and a higher olefin having 4-8 carbon atoms and a density of less than 0.94.
6. The bag of claim 1 in which the linear ethylene polymer is a copolymer of ethylene and a higher olefin having 4-8 carbon atoms and a density of less than 0.94 and the polymer of an aromatic hydrocarbon is polystyrene.
7. The bag of claim 1 in which the linear ethylene polymer is a copolymer of ethylene and a higher olefin having 4-8 carbon atoms and a density of less than 0.94 and the polymer of an aromatic hydrocarbon is poly(para-methyl styrene).
8. The bag of claim 1 in which the polymer of an aromatic hydrocarbon comprises up to 10 percent by weight of the film.
9. The bag of claim 1 in which the polymer of an aromatic hydrocarbon comprises up to 8 percent by weight of the film.
10. In a process for forming a bag from a linear ethylene polymer film the improvement comprising including in the film 0.1 to 15 weight percent of a thermoplastic polymer of an aromatic hydrocarbon in an amount sufficient to improve anti-blocking characteristics of the film.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US77196585A | 1985-09-03 | 1985-09-03 | |
| US771,965 | 1985-09-03 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1266342A true CA1266342A (en) | 1990-02-27 |
Family
ID=25093484
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000516702A Expired CA1266342A (en) | 1985-09-03 | 1986-08-25 | Plastic bags of blends of linear ethylene polymers and aromatic polymers |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1266342A (en) |
-
1986
- 1986-08-25 CA CA000516702A patent/CA1266342A/en not_active Expired
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKLA | Lapsed | ||
| MKEC | Expiry (correction) |
Effective date: 20121205 |