U.S. patent application number 10/815791 was filed with the patent office on 2004-09-23 for disposable food contact compatible microwaveable containers having at least one micronodular surface and process for their manufacture.
This patent application is currently assigned to Fort James Corporation. Invention is credited to Littlejohn, Mark B., Neculescu, Cristian M., Rogers, Richard J., Swiontek, Anthony J..
Application Number | 20040185200 10/815791 |
Document ID | / |
Family ID | 27112580 |
Filed Date | 2004-09-23 |
United States Patent
Application |
20040185200 |
Kind Code |
A1 |
Neculescu, Cristian M. ; et
al. |
September 23, 2004 |
Disposable food contact compatible microwaveable containers having
at least one micronodular surface and process for their
manufacture
Abstract
Disposable food contact compatible microwaveable containers
having one or more micronodular surface are disclosed. These
containers, including plates, bowls, cups, trays, buckets, souffl
dishes, and lids are prepared from a polyolefin selected from the
group consisting of polypropylene, polypropylene polyethylene
copolymer or blends, and mixtures of these, mica, and pigment and
are thermoformed into the shape of a the aforementioned containers
exhibiting (a) a micronodular surface on at least one side of the
surface; (b) a melting point of not less than about 250.degree. F.;
said containers being dimensionally stable and resistant to grease,
sugar, and water at temperatures up to at least 250.degree. F. and
being of sufficient toughness to resist cutting by serrated
polystyrene flatware.
Inventors: |
Neculescu, Cristian M.;
(Neenah, WI) ; Rogers, Richard J.; (Neenah,
WI) ; Littlejohn, Mark B.; (Appleton, WI) ;
Swiontek, Anthony J.; (Neenah, WI) |
Correspondence
Address: |
FINNEGAN, HENDERSON, FARABOW, GARRETT & DUNNER
LLP
1300 I STREET, NW
WASHINGTON
DC
20005
US
|
Assignee: |
Fort James Corporation
|
Family ID: |
27112580 |
Appl. No.: |
10/815791 |
Filed: |
April 2, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10815791 |
Apr 2, 2004 |
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09572967 |
May 18, 2000 |
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6719943 |
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09572967 |
May 18, 2000 |
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08947025 |
Oct 8, 1997 |
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6120863 |
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08947025 |
Oct 8, 1997 |
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08733463 |
Oct 18, 1996 |
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Current U.S.
Class: |
428/35.7 ;
264/211; 428/454; 428/500 |
Current CPC
Class: |
B29C 48/0021 20190201;
B29C 48/495 20190201; B29C 48/0019 20190201; B29C 48/0022 20190201;
B29C 48/0018 20190201; B29C 2948/92904 20190201; B29C 48/07
20190201; B29C 48/001 20190201; Y10T 428/1352 20150115; B29C 48/17
20190201; B29C 48/08 20190201; Y10T 428/1324 20150115; B29C 48/397
20190201; Y10T 428/31855 20150401; B29C 48/92 20190201; B29D 7/01
20130101; B29C 2948/926 20190201; B65D 1/34 20130101; B29C
2948/92923 20190201; B29C 48/625 20190201; B29C 2948/92704
20190201; Y10T 428/251 20150115; B29C 48/0017 20190201; B29C 48/21
20190201; B29K 2105/16 20130101; B29C 48/12 20190201 |
Class at
Publication: |
428/035.7 ;
264/211; 428/454; 428/500 |
International
Class: |
H05B 006/80; D01F
001/02 |
Claims
We claim:
1. A microwaveable, food contact compatible, disposable, rigid and
strong container comprising an extruded sheet consisting
essentially of an admixture of a polyolefin selected from the group
consisting of polypropylene and polypropylene polyethylene
copolymer or a blend, and mixtures of these, mica, and pigment
thermoformed by application of vacuum into the shape of a
container; said container further exhibiting: (a) a micronodular
surface on at least one side of the container surface; and (b) a
melting point of no less than about 250.degree. F.; said container
being dimensionally stable and resistant to grease, sugar, and
water at temperatures up to about 220.degree. F. and of sufficient
toughness to be resistant to cutting by serrated polystyrene
flatware.
2. The microwaveable container of claim 1 wherein the polyolefin
component of the extruded sheet is a propylene ethylene copolymer
or blend wherein the ethylene moiety comprises less than ten mole
percent of the total copolymer.
3. The container of claim 1 wherein the polypropylene in the sheet
is isotactic polypropylene homopolymer having a melt flow rate of
about 0.1 to about 5.0.
4. The container of claim 1 wherein the coupling agent comprises
the maleic anhydride modified polypropylene or acrylic modified
polypropylene in a concentration of about 0.5 to about 3 weight
percent based on the total weight of the container.
5. The container of claim 1 wherein the pigment is titanium
dioxide.
6. The container of claim 1 wherein the pigment is carbon
black.
7. The container of claim 1 wherein the container exhibits a
melting point of about 250 to about 330.degree. F.
8. The container of claim 2 or claim 3 wherein the polypropylene
moiety or propylene-ethylene copolymer or blend comprises about 40
to 90 percent by weight, the mica comprises about 7 to 59 percent
by weight, and the pigment comprises about 0.5 to 8 percent by
weight.
9. The container of claim 8 wherein the pigment comprises about 2.5
to 6.5 percent by weight.
10. The container of claim 8 wherein the mica content comprises
about 20 to 35 weight percent.
11. A microwaveable, food contact compatible, disposable, rigid and
strong container comprising an extruded sheet consisting
essentially of an admixture of a polyolefin selected from the group
consisting of polypropylene, polypropylene polyethylene copolymer
or blend, and mixtures of these and a coupling agent for promoting
adherence between the polyolefin and platy inorganic mineral
thermoformed by application of vacuum into the shape of a
container; said container exhibiting: (a) a micronodular surface on
at least one side; and (b) a melting point of no less than about
250.degree. F.; and (c) a basis weight of at least 130 lbs. per
3000 square foot ream; said container being dimensionally stable
and resistant to grease, sugar, and water at temperatures up to at
least 220.degree. F. and of sufficient toughness to be resistant to
cutting by serrated polystyrene flatware.
12. A microwaveable, food contact compatible, disposable, rigid and
strong container comprising an extruded sheet consisting
essentially of an admixture of a polyolefin selected from the group
consisting of polypropylene, polypropylene polyethylene copolymer
or blend, and mixtures of these, mica, a coupling agent for
promoting adherence between the polyolefin and mica, and pigment,
formed or thermoformed into the shape of a container; said
container exhibiting: (a) a basis weight of at least 130 pounds per
3000 square foot ream; and (b) a melting point of no less than
about 250.degree. F.; said container being dimensionally stable and
resistant to grease, sugar, and water at temperatures up to at
least 220.degree. F. and of sufficient toughness to be resistant to
cutting by serrated polystyrene flatware.
13. The container of claim 12 wherein the polyolefin component of
the extruded sheet is a polypropylene or a polypropylene
polyethylene copolymer or blend wherein the ethylene moiety
comprises less than ten mole percent of the total copolymer.
14. The container of claim 13 wherein the mica content is about 20
to 40 weight percent.
15. A microwaveable, food contact compatible, disposable, rigid and
strong container comprising an extruded sheet consisting
essentially of a polypropylene or polypropylene polyethylene
copolymer or blend, and mixtures of these, mica, and a coupling
agent for promoting adherence between the polypropylene or
polypropylene polyethylene copolymer or blend and mica,
thermoformed by application of vacuum into the shape of a
container; said container exhibiting: (a) a micronodular surface on
at least one side; and (b) a melting point of no less than about
250.degree. F.; and (c) a basis weight of at least 130 lbs. per
3000 square foot ream; said container being dimensionally stable
and resistant to grease, sugar, and water at temperatures up to at
least 220.degree. F. and of sufficient toughness to be resistant to
cutting by serrated polystyrene flatware.
16. A microwaveable, food contact compatible, disposable, rigid and
strong tray comprising an extruded sheet consisting essentially of
an admixture of a polyolefin selected from the group consisting of
polypropylene, polypropylene polyethylene copolymer or blend, and
mixtures of these, mica, a coupling agent for promoting adherence
between the polyolefin and mica, and pigment, formed or
thermoformed into; the shape of a tray; said tray exhibiting: (a) a
basis weight of at least 130 pounds per 3000 square foot ream; and
(b) a melting point of no less than about 250.degree. F.; said tray
being dimensionally stable and resistant to grease, sugar, and
water at temperatures up to at least 220.degree. F. and of
sufficient toughness to be resistant to cutting by serrated
polystyrene flatware.
17. A microwaveable, food contact compatible, disposable, rigid and
strong bowl comprising an extruded sheet consisting essentially of
an admixture of a polyolefin selected from the group consisting of
polypropylene, polypropylene polyethylene copolymer or blend, and
mixtures of these, mica, a coupling agent, a pigment for promoting
adherence between the polyolefin and mica, and pigment formed or
thermoformed into the shape of a bowl; said bowl exhibiting: (a) a
micronodular surface on one side; and (b) a melting point of no
less than about 250.degree. F.; said bowl being dimensionally
stable and resistant to grease, sugar, and water at temperatures up
to at least 220.degree. F. and of sufficient toughness to be
resistant to cutting by serrated polystyrene flatware.
18. A microwaveable, food contact compatible, disposable, rigid and
strong plate comprising an extruded sheet consisting essentially of
an admixture of a polypropylene or polypropylene polyethylene
copolymer or blend, mica, a coupling agent for promoting adherence
between the polypropylene or polypropylene polyethylene copolymer
or blend, mica, and pigment, formed, thermoformed, or thermoformed
by application of vacuum into the shape of a plate; said plate
exhibiting: (a) a micronodular surface on at least one side; (b) a
melting point of no less than about 250.degree. F.; and (c)
thickness uniformity characterized by a thickness coefficient
variation of less than five percent; said plate being dimensionally
stable and resistant to grease, sugar, and water at temperatures up
to at least 220.degree. F. and of sufficient toughness to be
resistant to cutting by serrated polystyrene flatware.
19. The microwaveable plate of claim 18 wherein the extruded sheet
is a polypropylene or a propylene-ethylene copolymer or blend and
mixtures of these wherein the ethylene moiety comprises less than
ten mole percent of the total copolymer.
20. The plate of claim 18 having a diameter in the range of about
8.75 inches to 11 inches.
21. The plate of claim 18 having a diameter of 10.25 inches.
22. The plate of claim 18 wherein the coupling agent comprises the
maleic anhydride or acrylic modified polypropylene.
23. The plate of claim 18 wherein the pigment is titanium
dioxide.
24. The plate of claim 18 wherein the pigment is carbon black.
25. The plate of claim 18 wherein the plate exhibits a melting
point of about 250 to about 330.degree. F.
26. The plate of claim 18 wherein the polypropylene moiety
comprises about 40 to 90 percent by weight, the mica comprises
about 7 to 59 percent by weight, and the pigment comprises about
0.5 to 8 percent by weight.
27. The plate of claim 18 wherein the mica comprises about 20 to 40
weight percent and the pigment comprises 2.5 to 6.5 weight
percent.
28. The plate of claim 27 wherein at a polyolefin basis weight of
at least 175 pounds per 3000 square foot ream, the plate exhibits a
SSI rigidity of at least 250 grams per 0.5 inch.
29. The plate of claim 28 wherein at the basis weight of at least
about 280 pounds per 3000 square foot ream, the plate exhibits a
SSI rigidity of at least 400 grams per 0.5 inch.
30. A microwaveable, food contact compatible, disposable, rigid and
strong container comprising an extruded sheet consisting
essentially of an admixture of a polyolefin selected from the group
consisting of polypropylene, polypropylene polyethylene copolymer
or blend, and a mixture of these, mica, a coupling agent for
promoting adherence between the polyolefin and mica, and pigment,
formed, thermoformed, or thermoformed by application of vacuum into
the shape of a container; said container exhibiting: (a) a
micronodular surface on at least one side; and (b) a melting point
of no less than about 250.degree. F.; said container being
dimensionally stable and resistant to grease, sugar, and water at
temperatures up to about 220.degree. F. and of sufficient toughness
to be resistant to cutting by serrated polystyrene flatware, the
container including a base portion and a lid portion comprising: I
(a) a bottom; (b) an upwardly extending peripheral wall joined to
said bottom, said upwardly extending peripheral wall having an
inwardly tapering frusto-conical base seal area formed therein; and
(c) a downwardly and outwardly extending brim joined to said
upwardly extending peripheral wall, said brim having an undercut
secondary seal ridge formed therein; and a unitary lid comprising:
II (a) a top joined to; (b) a downwardly extending peripheral wall
to; (c) an upwardly extending wall having a frusto-conical lid seal
area formed therein, said frusto conical lid seal area being
mateable with the frusto-conical base seal area; (d) a downwardly
extending wall having a secondary seal furrow mateable with said
secondary seal ridge; and (e) resilient lid realignment means
located between said secondary seal furrow and said frusto-conical
lid seal area for simultaneously urging said frusto-conical base
seal area into close engagement with said frusto-conical lid seal
area while urging said secondary seal ridge into engagement with
said secondary seal furrow.
31. The microwaveable container of claim 30 wherein the polyolefin
component of the extruded sheet is a polypropylene or
propylene-ethylene copolymer or blend wherein the ethylene moiety
comprises less than ten mole percent of the total copolymer.
32. The container of claim 30 wherein the coupling agent is
selected from the maleic anhydride modified polypropylene and
acrylic modified polypropylene.
33. The container of claim 30 wherein the pigment is titanium
dioxide.
34. The container of claim 30 wherein the pigment is carbon
black.
35. The container of claim 30 wherein the container exhibits a
melting point of about 250 to about 330.degree. F.
36. The container of claim 30 wherein the polyolefin moiety
comprises about 40 to 80 percent by weight, the mica comprises
about 19 to 59 percent by weight, and the pigment comprises about
0.5 to 8 percent by weight and wherein the container has a basis
weight of about 130 pounds to 950 pounds per 3000 square foot
ream,
37. The container of claim 36 wherein mica comprises about 20 to 40
percent by weight and the pigment comprises 2.5 to 6.5 by
weight.
38. The container of claim 1 in the form of a cup.
39. The container of claim 1 in the form of a bowl.
40. The container of claim 1 in the form of a tray.
41. The container of claim 1 in the form of a bucket.
42. The container of claim 1 in the form of a souffl dish.
43. A microwaveable, food contact compatible, disposable, rigid and
strong lid comprising an extruded sheet consisting essentially of
an admixture of a polyolefin selected from the group consisting of
polypropylene, polypropylene polyethylene copolymer or blend, or
mixtures of these, mica, and pigment, formed, thermoformed, or
thermoformed by application of vacuum into the shape of a lid; said
lid exhibiting: (a) a micronodular surface on at least one side;
and (b) a melting point of no less than about 250.degree. F.; said
lid being dimensionally stable and resistant to grease, sugar, and
water at temperatures up to about 220.degree. F.
44. The lid of claim 43 wherein the micronodular surface of the lid
is not in contact with the food.
45. A microwaveable, food contact compatible, disposable, rigid and
strong extruded sheet consisting essentially of an admixture of a
polyolefin selected from the group consisting of polypropylene,
polypropylene polyethylene copolymer or blend, and mixtures of
these, mica, a coupling agent for promoting adherence between the
polyolefin and mica, and pigment thermoformed by application of
vacuum into the shape of a container; said sheet exhibiting a
softening point of no less than about 250.degree. F.; said sheet
being dimensionally stable and resistant to grease, sugar, and
water at temperatures of about 220.degree. F. and of sufficient
toughness to be resistant to cutting by serrated polystyrene
flatware; said sheet being capable of forming a micronodular
surface on one side when subjected to vacuum forming.
46. The sheet of claim 45 wherein the polyolefin component of the
extruded sheet is a polypropylene ethylene copolymer or blend
wherein the ethylene content is not more than ten mole percent.
47. A microwaveable, food contact compatible, disposable, rigid and
strong, extruded and matted on one side, sheet consisting
essentially of an admixture of a polyolefin selected from the group
consisting of polypropylene, polypropylene polyethylene copolymer
or blend, and mixtures of these, mica, a coupling agent for
promoting adherence between the polyolefin and mica, and pigment
thermoformed by application of vacuum into the shape of a
container; said sheet exhibiting (a) at least one matted surface,
and (b) a softening point of no less than about 250.degree. F.;
said sheet being dimensionally stable and resistant to grease,
sugar, and water at temperatures of about 220.degree. F. and of
sufficient toughness to be resistant to cutting by serrated
polystyrene flatware; said sheet being capable of forming a
micronodular surface on one side when subjected to vacuum
forming.
48. The sheet of claim 47 wherein the polyolefin component of the
sheet is a polypropylene ethylene copolymer or blend, and mixtures
of these wherein the polyethylene content does not exceed about ten
mole percent.
49. A process for the manufacture of the sheet of claim 45
comprising the step of mixing the polyolefin selected from the
group consisting of polypropylene, polypropylene polyethylene
copolymer or blend, and mixtures of these, mica, coupling agent,
and pigment, and converting the mixture at a temperature of about
380.degree. F. to 480.degree. F. into a sheet and recovering the
sheet having a caliper in the range of about 5 to 50 units.
50. A process for the manufacture of the container of claim 1
comprising the steps of (a) heat softening the sheet of claim 45 at
a temperature of at least 260.degree. F.; and (b) vacuum forming
the container in a mold controlled to form a micronodular surface
of the container not in contact with the mold surface.
51. The process of claim 50 wherein the heat softening of the sheet
is conducted at a temperature of at least 330.degree. F.
52. A process for the manufacture of the plate of claim 18
comprising the steps of (a) heat softening the sheet of claim 45 at
a temperature of at least 260.degree. F.; (b) vacuum forming the
container in a mold controlled to form a micronodular surface of
the plate not in contact with the mold surface.
53. The sheet of claim 45 having a basis weight of about 200-950
lbs. per 3000-square foot ream.
54. The sheet of claim 45 wherein the mica flake aspect ratio is
about 30 to 300 at a particle size of about 50 to about 500
microns.
55. A process for the manufacture of the sheet of claim 45
comprising the step of mixing the polyolefin selected from the
group consisting of polypropylene, polypropylene polyethylene
copolymer or blend, and mixtures of these, mica, coupling agent,
and pigment, and converting the mixture at a temperature of about
380.degree. F. to 480.degree. F. into a sheet, matting the sheet on
one side, and recovering the sheet having a caliper in the range of
about 5 to 50 units and exhibiting a matted surface on one
side.
56. A process for the manufacture of the container of claim 1
comprising the steps of (a) heat softening the sheet of claim 45 or
claim 47 at a temperature of at least 260.degree. F.; and (b)
vacuum forming the container in a mold controlled to form a
micronodular surface of the container not in contact with the mold
surface.
57. The process of claim 55 wherein the heat softening of the sheet
is conducted at a temperature of at least 330.degree. F.
58. The sheet of claim 45 or claim 47 wherein the mica flake aspect
ratio is about 80 to 120 at a particle size of about 50 to 500
microns.
59. The plate of claim 18 having a caliper coefficient of variation
in the flange of less than 5.
60. The plate of claim 20 or claim 21 having a SSI plate rigidity
value of at least 250 grams per 0.5 inches at a basis weight of 170
lbs. per 3000 square foot ream.
61. The plate of claim 18 having a Parker Roughness of at least
about 10 microns.
62. The plate of claim 61 having a caliper coefficient of variation
in the flange of less than about 3.
63. The plate of claim 18 having a gloss surface below about 30
gloss units on the side in contact with food as measured by TAPPI
Standard Method T480-OM 92.
64. The plate of claim 18 having a caliper coefficient of variation
in the sidewall of less than about 7.
65. The plate of claim 64 having a caliper coefficient of variation
in the sidewall of less than about 5.
66. A process for forming a microwaveable, food contact compatible,
disposable, rigid and strong, mica-filled polyolefin container
wherein the polyolefin is selected from the group consisting of
polypropylene and polypropylene polyethylene copolymer or blend,
and a mixture of these comprising the steps of: (a) forming an
extrudable admixture of the polyolefin resin and mica; (b)
extruding said extrudable admixture of the polyolefin resin and
mica at elevated temperature; (c) passing the resulting extruded
admixture of the polyolefin resin and mica through a multiple roll
stack of rolls, at least one roll of said stack having a matte
finish; (d) passing said extruded admixture of the polyolefin resin
and mica at least partially around said roll having a matte finish;
(e) controlling the speed of said extrusion process, the size,
temperature- and configuration of said roll stack such that the
surface of said extruded admixture of the polyolefin resin and mica
in contact with said matte roll has a matted structure; (f)
thermoforming said extruded admixture of the polyolefin, resin, and
mica; and (g) recovering a container having a micronodular surface
and a coarse surface.
67. The process of claim 66 wherein the container is a plate.
68. A process for forming a microwaveable, food contact compatible,
disposable, rigid and strong, mica-filled polyolefin container
selected from the group consisting of polypropylene and
polypropylene polyethylene copolymer or blend, and a mixture of
these comprising the steps of: (a) forming an extrudable admixture
of the polyolefin resin and mica; (b) extruding said extrudable
admixture of the polyolefin resin and mica at elevated temperature;
(c) passing the resulting extruded admixture of the polyolefin
resin and mica through a multiple roll stack, at least one roll of
said stack having a matte finish; (d) passing said extruded
admixture of the polyolefin resin and mica at least partially
around said roll having a matte finish; (e) controlling the speed
of said extrusion process, the size, temperature and configuration
of said roll stack such that the surface of said extruded admixture
of the polyolefin resin and mica not in contact with said matte
roll has a coarse-grained structure; (f) thermoforming said
extruded admixture of the polyolefin, resin, and mica; and (g)
recovering a container having a micronodular surface and a rough
surface and exhibiting a melting point of no less than 250.degree.
F., said container being dimensionally stable and resistant to
grease, sugar, and water at temperatures up to about 220.degree. F.
and having sufficient toughness to be resistant to cutting by
serrated flatware.
69. The process of claim 68 wherein the coarse-grained structure of
the surface of said extruded admixture of the polyolefin resin and
mica not in contact with said matte roll is formed by transversing
the extruded admixture of the polyolefin resin and mica through a
curvilinear path and at least partially solidifying the surface of
said extruded admixture of polyolefin resin and mica not contacting
said matte roll while that surface is in tension relative to the
surface contacting said matte roll.
70. The process of claim 68 wherein the container is a plate.
71. The process of claim 68 wherein the container is a cup.
72. The process of claim 68 wherein the container is a bowl.
73. The process of claim 68 wherein the container is a tray.
74. The process of claim 68 wherein the container is a bucket.
75. The process of claim 68 wherein the container is a souffl
dish.
76. A container prepared according to the process of claim 68.
77. A plate prepared according to the process of claim 68.
78. A cup prepared according to the process of claim 68.
79. A bowl prepared according to the process of claim 68.
80. A tray prepared according to the process of claim 68.
81. A bucket prepared according to the process of claim 68.
82. A souffl dish prepared according to the process of claim
68.
83. The process of claim 66 or claim 68 wherein the thermoforming
is conducted at a temperature of about 260.degree. F. to
310.degree. F.
84. The process of claim 83 wherein the thermoforming is conducted
a temperature of about 270.degree. F. to 290.degree. F.
85. A process for forming a mica-filled polyolefin extruded sheet
wherein the polyolefin is selected from the group consisting of
polypropylene and polypropylene polyethylene copolymer or blend,
and a mixture of these comprising the steps of: (a) forming an
extrudable admixture of the polyolefin resin and mica; (b)
extruding said extrudable admixture of the polyolefin resin and
mica at elevated temperature; (c) passing the resulting extruded
admixture of the polyolefin resin and mica through a multiple roll
stack, at least one roll of said roll stack having a matte finish;
(d) passing said extruded admixture of the polyolefin resin and
mica at least partially around said roll having a matte finish; (e)
controlling the speed of said extrusion process, the size
temperature and configuration of said roll stack such that the
surface of said extruded admixture of the polyolefin resin and
mica-not in contact with said matte roll has a matted structure;
and (f) recovering a sheet comprising polyolefin and mica moieties,
said sheet having a matted surface and a rough surface.
86. The process of claim 85 wherein the coarse-grained structure of
the surface of said extruded admixture of the polyolefin resin and
mica not in contact with said matte roll is formed by traversing
the extruded admixture of the polyolefin resin and mica through a
curvilinear path and at least partially solidifying the surface of
said extruded admixture of polyolefin resin and mica not contacting
said matte roll while that surface is in tension relative to the
surface contacting said matte roll.
87. A process for forming a mica-filled polypropylene or
polypropylene polyethylene copolymer or blend extruded sheet
comprising the steps of: (a) forming an extrudable admixture of
polypropylene or polypropylene polyethylene copolymer or blend
resin and mica; (b) extruding said extrudable admixture of
polypropylene or polypropylene polyethylene copolymer or blend
resin and mica at elevated temperature; (c) passing the resulting
extruded admixture of polypropylene, polypropylene polyethylene
copolymer, or blend resin and mica through a multiple roll stack,
at least one roll of said stack having a matte finish; (d) passing
said extruded admixture of polypropylene, polypropylene
polyethylene copolymer, or blend resin and mica at least partially
around said roll having a matte finish; and (e) controlling the
speed of said extrusion process, the size temperature and
configuration of said roll stack such that the surface of said
extruded admixture of polypropylene, polypropylene polyethylene
copolymer, or blend resin and mica in contact with said matte roll
has a matted structure; and (f) recovering an extruded sheet
comprising a polypropylene or polypropylene polyethylene copolymer
or blend and mica moiety, said sheet having a matted surface.
88. The extruded sheet prepared according to the process of claim
85 or claim 87.
Description
RELATED APPLICATIONS
[0001] This application is a continuation in part application of
Ser. No. 08/733,463 filed on Oct. 18, 1996.
BACKGROUND OF THE INVENTION
[0002] This invention relates to disposable food contact compatible
microwaveable containers having at least one micronodular surface
including cups, trays, souffl dishes, lids, plates, bowls, and
related articles of manufacture useful for preparation, storage,
delivery, and serving of food, wherein convenience and low cost are
of paramount importance. Nevertheless, appearance and tactile
characteristics of the plate, container, etc., are important for
consumer preference. The suitability of these disposable articles
of manufacture for microwave cooking, or heating of food, has an
important place in today's marketplace. Both the commercial and
retail market components need an aesthetically pleasing
microwaveable, disposable, rigid and strong container, plate, or
cup, and related article of manufacture. This invention is directed
to economically meeting that need and provides a container or plate
comprising an extruded sheet of a polyolefin selected from the
group consisting of polypropylene, polypropylene polyethylene
copolymer or blend, or a mixture of these coupled with mica or a
similar platy inorganic mineral.
[0003] These disposable microwaveable containers and plates exhibit
(a) a micronodular surface on the food contact side of the plate or
container, and (b) a melting point of no less than about
250.degree. F., said container or plate being dimensionally stable
and resistant to grease, sugar, and water at temperatures up to at
least 220.degree. F. and exhibiting sufficient toughness to be
resistant to cutting by serrated polystyrene flatware.
Microwaveable and disposable containers and plates having all the
aforementioned properties are not known in the prior art. In U.S.
Pat. No. 5,377,860, assigned to assignee of the present patent
application, a double shell food container is disclosed. The
composition and properties of the container differ from the present
invention since a polyolefin/mica composition is not suggested or
disclosed and the container does not have the thermal properties or
the micronodular surface of the containers disclosed herein. The
containers disclosed in European Patent Application D544,429A1 do
not suggest or disclose a container which can meet the thermal
properties and have the desirable micronodular surface of the
container of the present invention.
SUMMARY OF THE INVENTION
[0004] Microwaveable, disposable, rigid, strong and food contact
compatible containers and plates have been prepared. These
disposable and microwaveable articles of manufacture exhibit (a) a
micronodular surface on the side coming in contact with the food;
and (b) a melting point of not less than 250.degree. F., suitably
250.degree. F. to 330.degree. F. These microwaveable, food contact
compatible containers and plates are dimensionally stable and
resistant to grease, sugar, and water at temperatures of at least
220.degree. F. and are of sufficient toughness to be resistant to
cutting by serrated polystyrene flatware. These containers, in the
form of disposable lunch (8.75 inch) and dinner plates (10.25
inch), exhibit a SSI rigidity of at least 200 grams per 0.5 inch at
a basis weight of about 130 lbs. per 3000 square foot ream. At a
basis weight of about 200, SSI rigidity is about 300 grams per 0.5
inches; and at a basis weight of about 360, SSI rigidity is about
700 grams. The containers and plates of this invention answer a
long felt need for products which can withstand the severe
conditions of a microwave oven when common foods such as beans and
pork, pancakes with syrup, pepperoni pizza, and broccoli with
cheese are microwaved during food cooking and reconstituting
processes. When the polyolefin is combined with mica, these
containers and plates exhibit a micronodular surface on one or both
sides usually on the side coming in contact with the food.
[0005] As shown in Example 9 and Table 12, competing commercial
polystyrene type plates cannot withstand the high temperatures
generated in the microwave oven during food contact and either
significantly warped or deformed when the aforementioned food
products were placed on them. Under the usual microwaving
conditions with high grease content foods, the prior art plates
tend to deform and flow to the point where parts of the plate
became adhered to the inside of the microwave oven. For disposable
plates and containers, appearance and feel are important
attributes. The micronodular surface of the plates and containers
of this invention where mica is used in combination with
polypropylene or polypropylene polyethylene copolymers or blends
tend to give these products the pleasing appearance and feel of
stoneware or a pottery-like look. Another significant property of
the containers and plates of this invention is their cut
resistance. These rigid articles of manufacture are of sufficient
toughness to be resistant to cutting by serrated polystyrene
flatware. In normal usage they are also resistant to cutting by
regular metal flatware.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] The present invention will become more fully understood from
the detailed description given herein below and the accompanying
drawings, which are given by way of illustration only, and thus,
are not limitative of the present invention and wherein:
[0007] FIG. 1 is a schematic flow diagram of the sheet extrusion
process.
[0008] FIG. 2 is a schematic flow diagram of the thermoforming
process for the manufacture of plates and containers having the
micronodular surface.
[0009] FIG. 3 is a graph comparing the rigidity of the plates of
this invention with prior art commercial products in the context of
current material costs.
[0010] FIG. 4 is a bar graph comparing the heat resistance of the
plates of this invention with prior art commercial products.
[0011] FIG. 5 is a drawing of a plate of this invention.
[0012] FIG. 6 is a cross sectional view of the plate shown in FIG.
5.
[0013] FIG. 7 is a radial cross-section of the plate shown in FIG.
5.
[0014] FIG. 8 is a schematic profile of the plate shown in FIG. 5,
beginning from the center line of the plate, formed in accordance
with the present invention.
[0015] FIG. 9 is a drawing of a plate of this invention.
[0016] FIG. 10 is a cross sectional view of the plate shown in FIG.
9
[0017] FIG. 11 is a radical cross section of the plate shown in
FIG. 9.
[0018] FIG. 12 is a schematic profile of the plate shown in FIG. 9
beginning from the center line.
[0019] FIG. 13 is a drawing of a tray included in this
invention.
[0020] FIG. 14 is a cross sectional view of the tray shown in FIG.
13.
[0021] FIG. 15 is a radical cross section of the tray shown in FIG.
13.
[0022] FIG. 16 is a schematic profile of the tray shown in FIG. 13
beginning from the center line.
[0023] FIG. 17 is a drawing of a bowl of this invention.
[0024] FIG. 18 is a cross-sectional view of the bowl shown in FIG.
17.
[0025] FIG. 19 is a radical cross section of the bowl shown in FIG.
17.
[0026] FIG. 20 is a schematic profile of the bowl shown in FIG. 17
beginning from the center line.
[0027] FIG. 21 is a drawing of a take-out food container included
in this invention.
[0028] FIG. 22 is a scanning electron photomicrograph of a plate
(upper picture) and a sheet (lower picture) of this invention
showing the micronodular food contact surface of the plate but not
so for the neat extruded sheet.
[0029] FIG. 23 is a graph plotting gloss versus mica level.
[0030] FIG. 24 is a graph plotting the plate rigidity versus mica
level.
[0031] FIG. 25 is a scanning electron photomicrograph of a sheet of
this invention showing a matted surface and a nonmatted
surface.
[0032] FIG. 26 is a scanning electron photomicrograph of a sheet of
this invention showing two high gloss sides.
DETAILED DESCRIPTION OF THE INVENTION
[0033] The aesthetically pleasing microwaveable disposable, rigid
and strong containers including plates, bowls, cups, trays,
buckets, souffl dishes and lids comprise isotactic polypropylene,
propylene-ethylene copolymer, or blends of isotactic polypropylene
and propylene-ethylene copolymer coupled with a mixture of a platy
inorganic mineral such as mica. Suitably coupling agents and
pigments are utilized. To form suitable containers, bowls, trays
and plates having excellent thermal, mechanical, and other physical
properties and also exhibiting a micronodular surface, coupling
agents should be utilized in conjunction with mica. The function of
the coupling agent is to promote the adherence of the polypropylene
moiety to mica. In the absence of a coupling agent, mica may not
adhere well to the polymer matrix and so may not be integrated into
the sheet from which the containers, bowls, trays and plates are
thermoformed. Maleic anhydride and acrylic modified polypropylenes
are suitable coupling agents.
[0034] The containers, bowls, trays and plates of this invention
are preferably formed from a sheet which has been extruded as shown
in FIG. 1 and then thermoformed as shown in FIG. 2.
[0035] Advantageously, the sheet is formed by an extrusion process
utilizing the compounded polymer/mica mixtures. The final extrusion
process renders a sheet with excellent thermal properties and cut
resistance. Generally, injection molding is inherently not suitable
for the manufacture of self-texturized micronodular containers,
bowls, trays and plates since injection molded products are smooth
plastic like articles which do not exhibit a micronodular surface
or have a feel of stoneware or pottery-like look.
[0036] The aesthetically pleasing disposable microwaveable
containers, trays, bowls and plates exhibit (a) at least one
micronodular surface, this surface is usually on the food contact
side of the plate or container, and (b) a melting point of at least
250.degree. F. In addition, the container or plate is dimensionally
stable and resistant to grease, sugar, and water at temperatures of
at least 220.degree. F. and is of sufficient toughness to be
resistant to cutting by serrated polystyrene flatware. The mica
filled polypropylene plates also exhibit a thickness uniformity
characterized by a thickness coefficient of variation of less than
about five percent.
[0037] Mica is a common name for naturally occurring inert mineral
of the phyllosilicate chemical family, specifically potassium
aluminosilicate whereby the aluminum ions may be partially replaced
by iron and magnesium and part of the chemically bound water may be
substituted by fluorine.
[0038] Mica is easily cleaved into thin, relatively regular,
flexible yet strong sheets (leaf-like flakes) with thickness in the
range of half a micron and aspect ratio as high as 300. Mica is
much softer than other inorganic fillers (calcium carbonate,
wollastonite, glass) yet only slightly harder than talc. Mica has a
slippery tactile feel and low abrasiveness relative to other common
inorganic fillers.
[0039] The reinforcement effect at 40 weight percent mica is
equivalent to that of 30 weight percent glass fiber. But hard
inorganic fibrous fillers such as glass (various lengths) and
wollastonite (acicular structures) have serious drawbacks such as
abrasiveness and are prone to fracture degradation during
conventional melt processing. Other fibrous (organic) fillers are
derived from wood and vegetable sources and are not suitable for
use in the manufacture of the containers of this invention since
the organic fillers tend to degrade during processing and they are
also moisture sensitive. In our process we prefer to use about 20
to 35 weight percent mica.
[0040] Extenders such as calcium carbonate and clay have been
traditionally used in disposable plastic foodservice articles with
low cost as the primary concern, i.e., these fillers are usually
selected for cost reduction rather than reinforcement. For example,
calcium carbonate is a cheap, hard, and abrasive filler which
delivers moderately low reinforcement (even when coupled) due to
its low aspect ratio and highly irregular particle structure. In
the case where microwaveability is desired for the plastic
disposable foodservice article, the not so perfect solution has
been the use of relatively expensive high heat polystyrene based
materials (e.g., unfilled PPO and SMA engineering resins), where
PPO refers to polyphenylene oxide and SMA refers to styrene-maleic
anhydride copolymer.
[0041] The mica filled polypropylene containers, bowls, trays and
plates of this invention have overcome the disadvantages of the
prior art type containers, bowls, trays and plates and are
significantly superior to them.
[0042] Platy mineral filled polypropylene is compounded by
pre-blending the polypropylene in pellet or flake form with mica
powder and other additives (coupling agents, color concentrates,
pigments, antioxidants, lubricants, nucleating agents, antistatic
agents, etc. This mixture is conveyed into the feed section
addition point of a twin screw compounding extruder. Alternatively,
the components are advantageously fed separately into the same or
at different points of addition, using combinations of volumetric
and/or gravimetric (i.e., loss in weight type) feeders.
[0043] For white pigmentation, titanium dioxide is preferred due to
combination of brightness, and opacity, as well as stability during
processing and final use. Surface treatment may be optionally used
to further enhance wetting, dispersion, compatibility with matrix
resins whereas the titanium dioxide forms may be of the rutile or
anatase type. Alternate white pigments may also consist of calcined
clay or blends of calcined clay with titanium dioxide. For black
pigmentation, carbon black is preferred due to a combination of
desirable characteristics such as blackness, and dispersibility,
the latter of which can be carefully controlled by choice of
particle size and surface chemistry. Carbon black is amorphous
carbon in finely divided form which is made by either the
incomplete combustion of natural gas (channel black) or by
reduction of liquid hydrocarbons in refractory chambers (furnace
black).
[0044] The twin screw extruder provides sufficient mixing action to
effectively cause the wetting and dispersion of the filler into the
polymer matrix. The twin screw extruder may be of the co-rotating
or counter-rotating type, where each type is equipped with
different screw flight elements which are appropriate for the feed,
mixing, and melt metering zones. The discharge zone normally
consists of a strand die where the exiting molten material strands
are quenched in a circulating water bath followed by knife cutting
into pellets.
[0045] Low molecular weight additives such as waxes, fluorinated
polymers, and other specialty lubricants are suitably used as
process aids to reduce the melt viscosity and improve throughput.
Other additives may include nucleating agents and antistatic
agents. Antioxidants may be added in small amounts, generally less
than one weight percent, to minimize shear and thermal degradation
of the polypropylene during the extrusion and forming processes as
well as to promote the chemical stability of the sheet prior to and
during final article use. Suitable antioxidants are advantageously
selected from the group of phenolics and phosphites and blends
thereof. These are produced by Ciba-Geigy and General Electric
Corporation.
[0046] Coupling agents such as silanes (azido functional or amido
styryl functional), organofunctional silicone compounds,
chlorinated hydrocarbons with and without silane, in situ
polymerization of monomers, or modified polyolefins are often used.
For certain applications, the mica particle surfaces may be
pretreated with the coupling agents. For the polymeric coupling
agents or compatibilizers, in particular, such agents may be
conveniently added directly during the formulation compounding
step. Polymeric compatibilizers are preferred for ease of handling
and also for the avoidance of toxic residual monomers and solvents.
In particular, maleic anhydride or acrylic modified polypropylene
can be used as coupling agents. They promote the adherence between
the polypropylene and the mica filler and serve to minimize the
embrittlement effect of the filler, and also promote toughness at
ambient conditions and dimensional stability at elevated
temperatures for the platy mineral filled sheets and the containers
made therefrom. The use of maleic anhydride modified polypropylene,
whereby the maleic anhydride is in the range of 0.5-5.0 mole
percent, is preferred. The use of coupling agents promotes good
interfacial bonding between the platy mineral filler and the matrix
resin interface resulting in good solid state mechanical properties
of the containers and plates. The coupling agents also maximize the
melt strength enhancing features of the platy mica filler. Melt
strength of the sheets is further improved when the mica mixtures
are used as a filler since said filler serves to provide
"inter-particle connectivity" or physical crosslinking.
[0047] SSI rigidity is measured with the Single Service Institute
Plate Rigidity Tester originally available through Single Service
Institute, 1025 Connecticut Ave. NW, Washington D.C. This test is
designed to measure the rigidity (i.e. resistance to buckling and
bending) of single service paper and plastic plates, bowls, dishes,
and trays by measuring the force required to deflect the rim of
these products a distance of 0.5 inch while the product is
supported at its geometric center. Specifically, the plate specimen
is held by a spring loaded clamp on one side and is center fulcrum
supported. The rim or flange side opposite to the clamped side is
subjected to 0.5 inch deflection by means of a motorized cam
assembly equipped with a load cell, and the force (grams) is
recorded. SSI rigidity is expressed as grams per 0.5 inch
deflection. A higher SSI value is desirable since this indicates a
more rigid product. All measurements were done at room temperature
and geometric mean averages for the machine and cross machine
direction are reported. As shown in FIG. 3, Fort James's containers
and plates of this invention (designation J) have a higher SSI
rigidity than commercial plates manufactured by Solo Cup Company
(designation S) at equal or lower cost.
[0048] Plastic cast sheet extrusion equipment is suitable for the
manufacture of multilayered or single layered mica filled sheets of
a polyolefin selected from the group consisting of polypropylene,
polypropylene polyethylene copolymer or blend, and mixtures of
these.
[0049] The use of coupling agents promotes good interfacial bonding
between the platy mineral filler and the matrix resin interface
resulting in good solid state mechanical properties of the
containers and plates. The containers in the form of a 8.75-inch
plate at a basis weight of about at least 175 pounds per 3000
square foot ream have a SSI rigidity of at least 250 grams per 0.5
inches. For 10.25-inch plates at a basis weight of about 280 pounds
per 3000 square foot ream, the SSI rigidity is at least about 400
grams per 0.5 inches. In plates of this invention, the basis weight
is determined from the micronodular surface. At a basis weight of
about 130, the SSI rigidity is about 200 grams per 0.5 inch and at
a basis weight of about 360 the SSI rigidity is about 700 grams per
0.5 inch. The coupling agents also maximize the melt strength
enhancing effect of the platy inorganic mineral filler. Melt
strength of the sheets is further improved when mica is used as a
filler since geometry of the mineral in the form of high aspect
ratio flakes serves to provide "inter-particle connectivity" or
physical crosslinking.
[0050] In FIG. 1 a process is shown for the manufacture of a single
layer mica filled polypropylene sheet. Previously compounded and
pelletized mixtures of polypropylene, mica, and other additives are
gravity fed by a hopper (10) into the feed zone of a single screw
extruder system. Primary extruder (11) has a 2 inch diameter screw
with a 24/1 length to diameter ratio. Optionally, multilayer
coextruded sheet can be produced by utilizing at least one
additional single screw extruder (12, 13, 14) in conjunction with a
combining feedblock with proper melt piping and manifold
arrangements. Suitably one to seven screw extruders are employed,
preferably three. A flexible lip flat sheet die (15) having a width
of 31 inches was used.
[0051] The sheet of this invention (16) enters the sheet takeoff
portion (i.e., after the molten material exits the die) comprising
a three-roll polishing/casing unit (17) with individually
temperature controlled rolls, a two-rubber roll sheet pull unit
(18), and a dual turret, dual shaft winder, whereby only one shaft
winder roll (19) may be used. The three takeoff units were
mechanically tied together, were on a common track, and can be
automatically traversed from close die lip proximity to about 36
inch distant. During the extrusion process, the distance between
the die exit and the casting unit were maintained at 2 inches.
These three chrome rolls comprising the sheet casting unit are
individually temperature controlled by integral oil circulating
pumps and heat exchangers and nip gaps are adjustable. A speed
differential between cast rolls and pull rolls is normally
maintained such that pull roll speed is approximately within ten
percent (10%) of cast roll speed. Achievable line speeds are in the
range of 1-12.5 feet per minute, while for a sheet on the order of
20 mil thick, the line speed is about 5-6 feet per minute. The
sheet is wound on a roll (19). Table 1 shows the sheet process
conditions employed for the sheet extrusion of mica filled
polypropylene and the unfilled polypropylene control. These sheets
suitably have a basis weight of about 200 to 950, per 3000 square
foot ream preferably about 200 to 400 per 3000 square foot
ream.
[0052] Thermoforming is the pressing or squeezing of pliable
material into final shape. In the simplest form, thermoforming is
the draping of a softened sheet over a shaped mold. In the more
advanced form, thermoforming is the automatic, high speed
positioning of a sheet having an accurately controlled temperature
into a pneumatically actuated forming station whereby the article's
shape is defined by the mold, followed by trimming and regrind
collection.
[0053] Forming techniques other than conventional thermoforming are
also suitable for the manufacture of articles described in the
present invention. These include variations such as presoftening
the extruded sheet to temperatures below the final melting
temperature, cutting flat regions (i.e., blanks) from the sheet,
transfer of blanks by gravity or mechanical means into matched
molds whereby the blanks are shaped into the article by heat and
pressure. The sheet from which the blanks have been cut out is
collected as regrind and is recyclable. Conventional paperboard
pressing equipment and corresponding forming tooling is optionally
modified to produce articles of this invention.
[0054] The extruded sheet used in the suitable forming, and
thermoforming process, or the preferred thermoforming process as
shown in FIG. 2 has a thickness of about 0.010 to 0.080 inches,
suitably 0.010 to 0.050 inches. For plates the preferred thickness
is about 0.015 to 0.025 inches. Suitable mica filler loading level
in the extruded sheet is in the range of 10 to 60 weight percent,
more preferably 20-50 weight percent, most preferably 20 to 35
weight percent. The mica flake aspect ratio is in the range of
30-300, more preferably 15-250, with particle size range of about
10 to 500 microns. The extruded sheet comprises isotactic
polypropylene homopolymer or polypropylene polyethylene copolymer
or blend or a mixture of these as base resin, preferably having a
melt flow index in the range 0.1-5.0, more preferably 0.2-2.0.
Propylene copolymers or blends with ethylene levels in the range of
1-10 mole percent, more preferably 2-5 mole percent, are optionally
used.
[0055] The preferred type of mica is muscovite, which is the most
common form in commerce. Optionally other less common mica types
such as phlogopite, biotite, and fluorphlogopite are used. Although
there are an infinite number of compositions possible for these
four generic types due to isomorphous substitution which are mine
specific, the selection of particular grades is driven by particle
aspect ratio, particle size, price, and availability.
[0056] The melt flow rate (MFR) or melt index is a common and
simple method for determining the flow properties of molten
polymers. Resin is introduced and melted in a cylindrical space.
After temperature equilibration is reached, a weight is used to
push a plunger vertically downward whereby the resin is extruded
through a narrow orifice. The usual test temperature for
polypropylene is 230.degree. C. and the load is 2.16 Kg. Extruded
material is collected and weighed and the time required to extrude
a specific weight is recorded. MFR is expressed as grams per 10
minutes, which is the weight of material extruded in a 10 minute
time period. MFR is inversely proportional to both polymer
viscosity and polymer molecular weight.
[0057] The extruded sheet comprises coupling agents, preferably
modified polypropylene, suitable modifiers are maleic anhydride or
acrylic modified polypropylene. The maleic anhydride or acrylic
modified polypropylene comprises about 0.5 to 3 weight percent of
total sheet composition.
[0058] Suitably the extruded sheet comprises coloring agents for
aesthetic appeal, preferably titanium dioxide, carbon black, and
other opacifying agents in the range of 0.5-8 weight percent based
on total composition, preferably 2.5 to 6.5 weight percent. The
extruded sheet comprises minor amounts of other additives such as
lubricants and antioxidants. These articles of manufacture may be
suitably colored with pigments or dyes. Pigments are defined as
small insoluble organic or inorganic particles dispersed in the
resin medium to promote opacity or translucency. Usual pigments
include carbon black, titanium dioxide, zinc oxide, iron oxides,
and mixed metal oxides. Dyes are organic and soluble in the
plastic, and may be used alone or in combination with pigments to
brighten up pigment based colors. All such colorants may be used in
a variety of modes which include dry color, conventional color
concentrates, liquid color and precolored resin.
[0059] Mica filled polypropylene sheets are suitably formed into
plates, bowls, cups, trays, buckets, souffl dishes, and containers
using a forming or thermoforming process disclosed herein. In the
preferred process, these articles of manufacture and containers are
made using the Comet Starlett Thermoformer Unit. This machine is
capable of vacuum forming products from heat softened thermoplastic
materials and is schematically depicted in FIG. 2. Sheet portions
(23) having dimensions of 17.5 inches by 16.25 inches were clamped
on two opposing sides and inserted into an oven (22) equipped with
upper (20) and lower (21) heaters, whereby heater input settings
were in the range of 20-30 percent and hold times were on the order
of 60-80 seconds. Under these conditions, the oven air temperature
as recorded by a digital thermocouple was in the range of
221.degree. F. to 225.degree. F., while the sheet surface
temperature, as recorded by adhering indicator thermocouples, was
approximately 330.degree. F. to 340.degree. F.
[0060] When the clamped and heat softened sheet (23) exits the oven
(22), it may be vacuum formed by either procedure (A) or (B), both
of which utilize only one mold which is fabricated from epoxy
thermoset materials. Mode (A) uses a male mold (24) whereby the
sheet is sucked up to conform to it by means of vacuum where the
vacuum ports are present on the mold base as well as on the
periphery side of the container (i.e., flange area). Mode (B)
arrangement is such that the vacuum direction is opposite to mode
(A), where again vacuum holes are located around the base and
periphery. In the case of mode (B), a female mold (25) is used, and
this arrangement is preferred since the air side of the sheet
corresponds to the food contact side. The food contact side
undergoes a beneficial texturizing effect as a result of the heat
treatment, whereby the resin flows around and outward from the mica
particles close to the surface causing the mineral to become more
exposed which creates a micronodular surface as manifested by
decreased gloss and increased surface roughness. The micronodular
surface gives the container a stoneware or pottery-like appearance.
This feature can be reasonably seen by reviewing FIG. 22 where the
micronodular structure of the plate is clearly shown in the black
and white scanning electron photomicrograph while the neat extruded
sheet exhibits no such micronodular surface. The photomicrograph
was obtained from a 10.times.15 mm piece cut out of the plate
bottom. The sheet sample was mounted with surface of interest up on
a specimen stub, and coated with gold/palladium. The stub was
placed in a JEOL 840A Scanning Electron Microscope (SEM).
Photomicrographs of the samples were taken at 75.times.
magnification, 30 degree tift, 39 mm working distance at 3 kv.
[0061] Suitably a process for forming a microwaveable, food contact
compatible, disposable, rigid and strong, mica-filled polyolefin
container, plate, bucket, etc., wherein the polyolefin is selected
from polypropylene, polypropylene polyethylene copolymer or blend
comprise the steps of:
[0062] (a) forming an extrudable admixture of the polyolefin resin
and mica;
[0063] (b) extruding said extrudable admixture of the polyolefin
resin and mica at elevated temperature;
[0064] (c) passing the resulting extruded admixture of the
polyolefin resin and mica through a multiple roll stack, at least
one roll of said roll stack having a matte finish;
[0065] (d) passing said extruded admixture of the polyolefin resin
and mica at least partially around said roll having a matte
finish;
[0066] (e) controlling the speed of said extrusion process, the
size, temperature and configuration of said roll stack such that
the surface of said extruded admixture of polyolefin resin and mica
not in contact with said matte roll has a coarse-grained structure;
and
[0067] (f) thermoforming said extruded admixture of polyolefin,
resin, and mica and recovering a container, plate, bucket, etc.,
having a micronodular surface and a rough surface, exhibiting a
melting point of no less than about 250.degree. F.; said container,
plate, bucket, etc., being dimensionally stable and resistant to
grease, sugar, and water at temperatures up to about 220.degree. F.
and having sufficient toughness to be resistant to cutting by
serrated flatware.
[0068] Advantageously, the coarse-grained structure of the surface
of said extruded admixture of polyolefin resin and mica not in
contact with said matte roll is formed by transversing the extruded
admixture of the polyolefin resin and mica through a curvilinear
path and at least partially solidifying the surface of said
extruded admixture of polyolefin resin and mica not contacting said
matte roll while that surface is in tension relative to the surface
contacting said matte roll.
[0069] Preferably a process for forming a mica-filled polypropylene
container, plate, bucket, tray, bowl, etc., comprises the steps
of:
[0070] (a) forming an extrudable admixture of the polypropylene
resin and mica;
[0071] (b) extruding said extrudable admixture of the polypropylene
resin and mica at elevated temperature;
[0072] (c) passing the resulting extruded admixture of the
polypropylene resin and mica through a multiple roll stack, at
least one roll of said roll stack having a matte finish;
[0073] (d) passing said extruded admixture of the polypropylene
resin and mica at least partially around said roll having a matte
finish;
[0074] (e) controlling the speed of said extrusion process, the
size, temperature and configuration of said roll stack such that
the surface of said extruded admixture of the polypropylene resin
and mica in contact with said matte roll has a matted structure;
and
[0075] (f) thermoforming said extruded admixture of polypropylene,
resin, and the mica and recovering a container, plate, bucket,
etc., having a micronodular surface and exhibiting a melting point
of no less than 250.degree. F., said container, plate, bucket, etc.
being dimensionally stable and resistant to grease, sugar, and
water at temperatures up to about 220.degree. F. and having
sufficient toughness to be resistant to cutting by serrated
flatware.
[0076] A process for forming a mica-filled polypropylene sheet
suitable for thermoforming micronodular containers and plates
comprises the steps of:
[0077] (a) forming an extrudable admixture of the polypropylene
resin and mica;
[0078] (b) extruding said extrudable admixture of the polypropylene
resin and mica at elevated temperature;
[0079] (c) passing the resulting extruded admixture of the
polypropylene resin and mica through a multiple roll stack, at
least one roll of said roll stack having a matte finish;
[0080] (d) passing said extruded admixture of the polypropylene
resin and mica at least partially around said roll having a matte
finish;
[0081] (e) controlling the speed of said extrusion process, the
size, temperature and configuration of said roll stack such that
the surface of said extruded admixture of the polypropylene resin
and mica not in contact with said matte roll has a coarse
structure; and
[0082] (f) the surface in contact with the matte roll has a matted
surface; and
[0083] (g) recovering a sheet having a matted surface and a coarse
surface said sheet comprising polypropylene and mica moieties. In
this process the polypropylene may be partially replaced with
polypropylene polyethylene copolymer or blend. Usually the
copolymer compresses less than ten mole percent of the total
polyolefin content of the sheet.
[0084] Advantageously, other thermoforming arrangements are
suitable and may be preferred in conventional sheet and web feed
thermoforming commercial production operations. Alternative
arrangements include the use of drape, vacuum, pressure, free
blowing, matched die, billow drape, vacuum snap-back, billow
vacuum, plug assist vacuum, plug assist pressure, pressure reverse
draw with plug assist vacuum, reverse draw with plug assist,
pressure bubble immersion, trapped sheet, slip, diaphragm,
twin-sheet cut sheet, twin-sheet rollfed forming or any suitable
combinations of the above. Details are provided in J. L. Throne's
book, Thermoforming, published in 1987 by Coulthard. Pages 21
through 29 of that book are incorporated herein by reference.
Suitable alternate arrangements also include a pillow forming
technique which creates a positive air pressure between two heat
softened sheets to inflate them against a clamped male/female mold
system to produce a hollow product. Metal molds are etched with
patterns ranging from fine to coarse in order to simulate a natural
or grain like texturized look. Suitably formed articles are trimmed
in line with a cutting die and regrind is optionally reused since
the material is thermoplastic in nature. Other arrangements for
productivity enhancements include the simultaneous forming of
multiple articles with multiple dies in order to maximize
throughput and minimize scrap.
[0085] The sheet of the present invention is suitably formed into
plates or bowls having a circular configuration. These articles of
manufacture may also be square or rectangular in shape having
angular corners, such as found in a tray. Further, additional
shapes such as triangular, multi-sided, polyhexal, etc., are
contemplated including compartmented trays and plates as well as
oval platters. In each contemplated embodiment, all corners are
rounded or curved with the preferred embodiment of the present
invention being depicted in FIGS. 5 through 21.
[0086] The description of FIGS. 5 through 21 is illustrative of the
present invention, but it should be understood that these figures
are not intended to limit the invention and that various changes
may be made by those skilled in the art without changing the
essential characteristics and basic concept of the invention. In
one embodiment of this invention the plates have the DIXIE.RTM.
Superstrong profile as illustrated in FIGS. 5 through 8 and also
described in U.S. Pat. No. 5,326,020 assigned to the assignee of
the present invention and incorporated herein by reference into
this application. These containers also may have other features
such as ridges, emboss, and deboss patterns suitable for enhancing
the properties of the containers of this invention.
[0087] Throughout the following description, each of the dimensions
are referenced with respect to a given diameter D which in,
accordance with the present invention as illustrated in FIGS. 6 and
7, is approximately 8.75 inches. However, the particular diameter
of the container is not a critical limitation and is only set forth
herein by way of example. It is the relationship between the
various portions of the rim configuration which are essential.
[0088] The planar inner region (61) in accordance with the
illustrated embodiment in FIGS. 5 through 8 has a radius X1 which
is equal to approximately 0.3 D-0.4 D and preferably 0.348 D.
Adjoining an outer periphery of the planar inner region (61) is a
sidewall portion (60) including annular region (63) having a radius
of curvature equal to approximately 0.05 D-0.06 D and preferably
0.0572 D with the center point thereof being positioned a distance
Y1 from the planar inner region (61). Included angle (70) of the
annular region (63) is from about 40.degree. to about 70.degree.
and preferably about 60.degree.-65.degree. or approximately
62.degree.. Adjoining the periphery of the annular region (63) is
the first frusto-conical region (64) which slopes upwardly at an
angle A1 with respect to the vertical from about 20.degree. to
about 35.degree. and preferably about 25.degree.-30.degree. or
approximately 27.5.degree.. Additionally, the frusto-conical region
(64) is of a length greater than about 0.015 D, preferably from
about 0.025 D to 0.05 D and more preferably approximately 0.036 D.
Further, adjoining the first frusto-conical region (64) is the
arcuate annular region (65) which includes a radius of curvature in
the range of 0.015 D to 0.03 D and preferably approximately 0.024 D
with the center point thereof being positioned a distance Y2 from
the planar inner region (61). The included angle (71) of the
arcuate annular region (65) may range from about 61.degree. to
about 82.degree. and is preferably 66.degree. to 77.degree. or
about 73.degree.. The second portion (67) of the arcuate annular
region (65), that is the distal portion of the arcuate annular
region (65), is positioned such that a line tangent to the
curvature of the arcuate annular region (65) at the second portion
(67) slopes downwardly and outwardly at an angle of approximately
0.degree. to 12.degree..
[0089] The combination of the annular region (63) and arcuate
annular region (65) should combine to position the second portion
(67) of the arcuate annular region (65) in the manner set forth
herein above. That is, the included angle (70) of the annular
region (63) when combined with the included angle (71) of the
arcuate annular region (65) with the first frusto-conical region
(64) spanning therebetween, positions the second portion (67) of
the arcuate annular region (65) in a manner such that the second
frusto-conical region (68), which extends substantially
tangentially from the distal end of the second portion (67) of the
arcuate annular region (65) extends outwardly and downwardly at an
angle of about 0.degree. to 12.degree.. The second frusto-conical
region (68) is of a length in a range from about 0.03 D to about
0.05 D and is preferably 0.04 D. Because the second frusto-conical
region (68) extends substantially tangentially from the second
portion (67) of the arcuate annular region (65), the second
frusto-conical region (68) extends outwardly and downwardly at an
angle A3 in the range from approximately 0.degree. to 12.degree.
with respect to a horizontal plane formed by the planar inner
region (61).
[0090] Adjoining an outer periphery of the second frusto-conical
region (68) is the lip (69) which is in the form of yet another
frusto-conical region which extends outwardly and downwardly from
the second frusto-conical region (68). The lip (69) is of a length
of at least 0.005 D and is preferably approximately 0.010 D.
Further, the lip (69) extends at an angle A2 of no more than 450
from vertical, preferably approximately 15.degree. to 30.degree.
with respect to the vertical plane.
[0091] At the transition between the second frusto-conical region
(68) and the lip (69) is a transition region (72). The transition
region (72) includes a radius of curvature R3 which is in the range
of about 0.008 D and 0.01 D and is preferably approximately 0.0092
D with the center point thereof being positioned a distance Y3 from
the planar inner region (61). Additionally, the transition region
(72) has an included angle A4 of approximately 48.degree. to
70.degree.. The plates disclosed in FIGS. 9 through 12 have the
dimensions of the plates disclosed in U.S. Pat. No. 5,088,040 and
incorporated herein by reference in its entirety. These containers
may have other features such as ridges, emboss, and deboss patterns
suitable for enhancing the properties of the containers of this
invention.
[0092] The description of FIGS. 13 through 16 is illustrative of
the present invention, but it should be understood that these
figures are not intended to limit the invention and that various
changes may be made by those skilled in the art without changing
the essential characteristics and basic concept of the invention.
In one embodiment of this invention the trays have either the
DIXIE.RTM. Superstrong profile as illustrated in FIGS. 13 through
16 and also described in U.S. Pat. No. 5,326,020 assigned to the
assignee of the present invention and incorporated herein by
reference into this application. These trays may have other
features such as ridges, emboss, and deboss patterns suitable for
enhancing the properties of the trays of this invention. A
representative tray is illustrated in FIGS. 13 through 16.
Throughout the following description, each of the dimensions are
referenced to either the length D1 or the width D2, which in
accordance with the present invention as illustrated in FIGS. 13
through 16 are approximately 10.90 and 8.00 inches respectively. D1
is larger than or equal to D2. However, the particular length and
width of these containers is not a critical limitation and is only
set forth herein by way of example. It is the relationship between
the various portions of the rim configurations which are essential.
The planar inner region (101) in accordance with the illustrated
embodiment in FIGS. 13 and 14, has a length X1 which is equal to
approximately 0.3 D1 to 0.4 D1 and 0.3 D2 to 0.4 D2 and preferably
0.354 D1 and preferably 0.342 D2. Adjoining an outer periphery of
the planar inner region (101) is a sidewall portion (100) including
annular region (103) having a radius of curvature equal to
approximately 0.02 D1 to 0.03 D1 and 0.025 D2 to 0.035 D2 and
preferably 0.023 D1 and 0.031 D2 with the center point thereof
being positioned a distance Y1 from the planar inner region (101).
Included angle (110) of the annular region (103) is from about 400
to about 800 and preferably about 65.degree. to 75.degree. or
approximately 69.degree.. Adjoining the periphery of the annular
region (103) is the first frusto-conical region (104) which slopes
upwardly at an angle A1 with respect to the vertical from about
10.degree. to about 50.degree. and preferably about 15.degree. to
25.degree. or approximately 21.degree.. Additionally, the
frusto-conical region (104) is of a length greater than about 0.05
D1 and 0.055 D2, preferably from about 0.1 D1 to 0.2 D1 and 0.15 D2
to 0.25 D2 and more preferably approximately 0.15 D1 and 0.19 D2.
Further, adjoining the first frusto-conical region (104) is the
arcuate annular region (105) which includes a radius of curvature
in the range of 0.005 D1 to 0.007 D1 and 0.007 D2 to 0.009 D2 and
preferably approximately 0.006 D1 and 0.008 D2 with the center
point thereof being positioned a distance Y2 from the planar inner
region (101). The included angle (111) of the arcuate annular
region (105) may range from about 40.degree. to about 92.degree.
and is preferably 65.degree. to 87.degree.. The second portion
(107) of the arcuate annular region (105), that is the distal
portion of the arcuate annular region (105) is positioned such that
a line tangent to the curvature of the arcuate annular region (105)
at the second portion (107) slopes downwardly and outwardly at an
angle of approximately 0.degree. to 12.degree..
[0093] The combination of the annular region (103) and arcuate
annular region (105); should combine to position the second portion
(107) of the arcuate annular region (105) in the manner set forth
herein above. That is, the included angle (110) of the annular
region (103) when combined with the included angle (111) of the
arcuate annular region (105) with the first frusto-conical region
(124) spanning therebetween, positions the second portion (107) of
the arcuate annular region (105) in a manner such that the second
frusto-conical region (108), which extends substantially
tangentially from the distal end of the second portion (107) of the
arcuate annular region (105) extends outwardly and downwardly at an
angle of about 0.degree. to 12.degree.. The second frusto-conical
region (108) is of a length in a range from about 0.045 D1 to about
0.055 D1 and 0.030 D2 to about 0.040 D2 and is preferably 0.052 D1
and 0.034 D2. Because the second frusto-conical region (108)
extends substantially tangentially from the second portion (107) of
the arcuate annular region (105), the second frusto-conical region
(108) extends outwardly and downwardly at an angle A3 in the range
from approximately 0.degree. to 12.degree. with respect to a
horizontal plane formed by the planar inner region (161).
[0094] Adjoining an outer periphery of the second frusto-conical
region (104) is the lip (109) which is in the form of yet another
frusto-conical region which extends outwardly and downwardly from
the second frusto-conical region (108). The lip (109) is of a
length of at least 0.006 D1 and 0.009 D2 and is preferably
approximately 0.010 D1 and 0.013 D2. Further, the lip (109) extends
at an angle A2 of no more than 450 from vertical, preferably
approximately 10.degree. to 30.degree. with respect to the vertical
plane and more preferably approximately 20.degree..
[0095] At the transition between the second frusto-conical region
(108) and the lip (109) is a transition region (112). The
transition region (112) includes a radius of curvature R3 which is
in the range of about 0.005 D1 to 0.007 D1 and 0.007 D2 to 0.009 D2
and is preferably approximately 0.006 D1 and 0.008 D2 with the
center point thereof being positioned a distance Y3 from the planar
inner region (21). Additionally, the transition region (112) has an
included angle A4 of approximately 48.degree. to 80.degree..
[0096] The description of FIGS. 17 through 20 is illustrative of
the present invention, but it should be understood that these
figures are not intended to limit the invention and that various
changes may be made by those skilled in the art without changing
the essential characteristics and basic concept of the invention.
In one embodiment of this invention the bowl is illustrated in
FIGS. 17 through 20. These containers may have other features such
as ridges, emboss, and deboss patterns suitable for enhancing the
properties of the containers of this invention. Throughout the
following description, each of the dimensions are referenced with
respect to a given diameter D which, in accordance with the present
invention as illustrated in FIGS. 17 through 20, is approximately
7.5 inches. However, the particular diameter of the containers is
not a critical limitation and is only set forth herein by way of
example. It is the relationship between the various portions of the
rim configuration which are essential. The planar inner region
(131) in accordance with the illustrated embodiment in FIGS. 17
through 20, has a radius X1 which is equal to approximately 0.2 D
to 0.3 D and preferably 0.25 D. Adjoining an outer periphery of the
planar inner region (131) is a sidewall portion (130) including
annular region (133) having a radius of curvature equal to
approximately 0.05 D to 0.15 D and preferably 0.11 D with the
center point thereof being positioned a distance Y1 from the planar
inner region (131). Included angle (141) of the annular region
(133) is from about 45.degree. to about 75.degree. and preferably
about 60.degree. to 70.degree. or approximately 65.degree..
Adjoining the periphery of the annular region (133) is the first
frusto-conical region (134) which slopes upwardly at an angle A1
with respect to the vertical from about 15.degree. to about
45.degree. and preferably about 20.degree. to 30.degree. or
approximately 25.degree.. Additionally, the frusto-conical region
(134) is of a length greater than about 0.1 D, preferably from
about 0.17 D to 0.19 D and more preferably approximately 0.18 D.
Further, adjoining the first frusto-conical region (134) is the
arcuate annular region (135) which includes a radius of curvature
in the range of 0.015 D to 0.030 D and preferably approximately
0.023 D with the center point thereof being positioned a distance
Y2 from the planar inner region (131). The included angle (142) of
the arcuate annular region (135) may range from about 45.degree. to
about 87.degree. and is preferably 60.degree. to 77.degree.. The
second portion (137) of the arcuate annular region (135), that is
the distal portion of the arcuate annular region (135) is
positioned such that a line tangent to the curvature of the arcuate
annular region (135) at the second portion (137) slopes downwardly
and outwardly at an angle of approximately 0.degree. to
12.degree..
[0097] The combination of the annular region (133) and arcuate
annular region (135) should combine to position the second portion
(137) of the arcuate annular region (131) in the manner set forth
herein above. That is, the included angle (130) of the annular
region (133) when combined with the included angle (131) of the
arcuate annular region (135) with the first frusto-conical region
(134) spanning therebetween, positions the second portion (137) of
the arcuate annular region (135) in a manner such that the second
frusto-conical region (138), which extends substantially
tangentially from the distal end of the second portion (137) of the
arcuate annular region (135) extends outwardly and downwardly at an
angle of about 0.degree. to 12.degree.. The second frusto-conical
region (138) is of a length in a range from about 0.02 D to about
0.04 D and is preferably 0.03 D. Because the second frusto-conical
region (138) extends substantially tangentially from the second
portion (137) of the arcuate annular region (135), the second
frusto-conical region (138) extends outwardly and downwardly at an
angle A3 in the range from approximately 0.degree. to 12.degree.
with respect to a horizontal plane formed by the planar inner
region (131).
[0098] Adjoining an outer periphery of the second frusto-conical
region (134) is the lip (139) which is in the form of yet another
frusto-conical region which extends outwardly and downwardly from
the second frusto-conical region (138). The lip (139) is of a
length of at least 0.01 D and is preferably approximately 0.017 D.
Further, the lip (139) extends at an angle A2 of no more than
45.degree. from vertical, preferably approximately 10.degree. to
30.degree. with respect to the vertical plane and more preferably
approximately 25.degree..
[0099] At the transition between the second frusto-conical region
(138) and the lip (139) is a transition region (143). The
transition region (143) includes a radius of curvature R3 which is
in the range of about 0.007 D and 0.012 D and is preferably
approximately 0.009D with the center point thereof being positioned
a distance Y3 from the planar inner region (131). Additionally, the
transition region (142) has an included angle A4 of approximately
48.degree. to 80.degree..
[0100] The description of FIG. 21 is illustrative of the present
invention, but it should be understood that this figure is not
intended to limit the invention and that various changes may be
made by those skilled in the art without changing the essential
characteristics and basic concept of the invention. The containers
of this invention may be formed as take-out containers, and as a
representative embodiment, a suitable take-out container, will now
be described in general with respect to FIG. 21 wherein the lid and
base formed as described in U.S. Pat. No. 5,377,860 and
incorporated herein by reference is illustrated. While the
container illustrated in FIG. 21 is oblong in configuration, the
container may be round, oval, substantially rectangular or square
as dictated by the contents which are to be placed within the
container. The container (30) is formed of a base or bottom portion
(31) and a lid (32). The lid (32) includes radially extending
opening tabs (33) which cooperate with the radially extending
opening tabs (34) of the base (31) in order to allow the consumer
to readily open the sealed container. The base (31) of the
container (30) includes a substantially planar bottom (35) and a
substantially vertically extending peripheral sidewall (36).
Integrally connected to the upstanding sidewall (31) is a sealing
brim (37) which is received within a cooperating sealing brim (38)
of the lid (32).
[0101] The lid (32) includes a substantially planar top portion
(39) and a rim (40) extending about a periphery of the top portion
(39). The rim (40) is provided in order to enhance the strength of
an extended volume portion (41) of the lid (32). The rim (40) also
serves to locate the base (31) on the lid when the lid is used as a
stand.
[0102] The extended volume portion (41) is formed by extension wall
(42) positioned about the perimeter of the rim (40) and extending
downwardly therefrom. The extension wall (42) is integrally formed
with a horizontal lid reinforcing ring (43) which is substantially
parallel to the top portion (39) of the lid (32). The outer
perimeter of the lid reinforcing ring (43) is further integrally
formed with the sealing brim (38). Also, extending radially outward
from the sealing brim (38) is a second horizontal lid reinforcing
ring (44) which extends substantially parallel to the top portion
(39) as well.
[0103] Similarly, the base (31) includes a horizontal lid
reinforcing ring (45) which extends from the periphery of the
sealing brim (37) for aiding in and maintaining the structural
integrity of the sealing brim (37) as well as the container (30) as
a whole. In addition to the reinforcing ring (45), a step (46) may
be provided about an upper portion of the peripheral sidewall (36)
for preventing nested units from becoming jammed together due to
excessive interpenetration when stacked and nested. Also, formed in
an upper portion of the sidewall (36) are undercuts (47) which
cooperate with detents (48), only one of which is illustrated in
FIG. 21 at the integral connection between a brim (38) and lid
reinforcing ring (43). The detents, when engaged in the undercuts
(47), provide an audible indication that the container is in fact
sealed. Additionally, undercuts (49) may be provided in an outer
periphery of the brim (37) for receiving detents (50) formed in an
outer portion of the brim (38) for again providing an audible
indication that the container is sealed. While the container
illustrated in FIG. 21 shows detents and undercuts formed in both
the inner and outer portions of the brims (47) and (38),
respectively, it may be desired to provide respective detents and
undercuts on only one side of the brim or to provide no undercuts
and detents on either side of the brim.
[0104] The Parker Roughness method was used to determine roughness
using the Messmer Parker Print-Surf Roughness. Operation procedure
details are referenced in the Messmer Instruments Ltd. user manual
for the instrument (Model No. ME-90) which is distributed by Huygen
Corporation. The flat specimen is clamped under 1 Mpa pressure
against a narrow annular surface by a soft backing and the
resistance of air flow of the gap between the specimen and the
annulus is measured. The air flow is proportional to the cube of
the gap width and the roughness is expressed as the root mean cube
gap in units of micrometers. Higher Parker roughness values
indicate higher degrees of surface roughness. Gloss is reported as
"gloss units at 75 or 60 degrees." Gloss measurements were
conducted following TAPPI Standard Method T-480-OM 92.
[0105] Hunter color L, a, and b parameters were measured using
TAPPI Method T 524 OM-94. The symbols L, a, b designate color
values as follows: L denotes lightness increasing from zero for
black to 100 for perfect white; a shows redness when plus,
greenness when minus, and zero for gray; and b represents
yellowness when plus, blueness when minus, and zero for gray.
[0106] Whiteness index was measured according to procedures
outlined in the publication "Measurement and Control of the Optical
Properties of Paper" by Technidyne Corporation, New Albany,
Ind.
[0107] The following examples are illustrative of the present
invention. It should be understood that the examples are not
intended to limit the invention and that various changes may be
made by those skilled in the art without changing the essential
characteristics and the basic concept of the invention.
EXAMPLE 1
[0108] Mica filled polypropylene sheets (20 mil) and unfilled
polypropylene sheets (22 mil) were extruded, as shown in FIG. 1,
with conditions specified in Table 1. These extrusion process
conditions may be varied as necessary to produce sheets which are
of acceptable quality. Specifically, the operable temperature
ranges for barrel zones 1, 2, and 3 are about respectively, 350 to
425.degree. F., 400 to 450.degree. F., and 450 to 500.degree. F.
The adaptor, feedblock, and die temperatures can all be in about
the range of 450 to 500.degree. F. The range of values for extruder
drive amperes, extruder speed, meft pressure, die pressure, chill
roll temperature, and line speed are about respectively, 12 to 20
amp., 60 to 100 RPM, 1500 to 2500 psi, 450 to 650 psi, 120 to
140.degree. F., and 3 to 8 FPM. Sheets were subsequently vacuum
thermoformed into plates and other containers and lids as set forth
in FIGS. 5 through 21. Tables 2 and 3 show, respectively, rigidity
values and caliper data for the sidewall, bottom, and flange (rim)
areas of vacuum formed plates using condition (B) of FIG. 2 and
having a dimension of 10.25 or 8.75 inches. In each table,
individual rigidity values are shown for each specimen. In
addition, the caliper uniformity for sidewall, bottom, and flange
areas are reported for each specimen, along with the summary
statistics. Specifically, the caliper of each plate specimen in
Tables 2 and 3 was measured ten times using a Fowler gauge for each
of the three regions of interest consisting of the sidewall,
bottom, and flange areas, and the average value for each plate
specimen is reported along with the corresponding standard
deviation (i.e., individual plate statistics). In the case of the
three plates of Table 2, the caliper summary statistics (expressed
in the average properties row) were obtained on the basis of
averaging 30 measurements, wherein the standard deviation is
reported for each of the three regions of interest. In the case of
the five plates of Table 3, the caliper summary statistics were
calculated on the basis of averaging 50 measurements where again
the standard deviation is reported for each of the three regions of
interest. Therefore, the caliper data of Tables 2 and 3 located in
the average property rows pertain to global statistics rather than
individual plate statistics. The caliper uniformity parameter
consists of the coefficient of variation (COV) which is calculated
as the standard deviation of caliper divided by the mean caliper,
whereas the ratio is multiplied by 100, whereas the above described
global averages and associated standard deviations are employed. A
lower COV value is desirable since it signifies improved caliper
uniformity for mica filled polypropylene plates with respect to
unfilled polypropylene plates. Tables 2 and 3 show that mica
reduces COV of polypropylene from 9.9 to 4.3 in sidewall and from
9.6 to 2.0 in the flange area. Therefore, caliper uniformity in
sidewall improved by more than a factor of 2 and caliper uniformity
in the flange improved by over a factor of 4. The improvement of
caliper uniformity is critical for promoting plate dimensional
stability during food transport and microwave cooking operations.
In great contrast to mica filled polypropylene plates, the unfilled
polypropylene plates exhibited poor quality as evidenced by poorly
defined rim area, and sharkskin, very rough surface. These data
demonstrate that mica greatly improves the drawability of
polypropylene as evidenced by improved caliper uniformity, as well
as improved thermoformability, both of which are due to enhanced
melt strength relative to unfilled polypropylene. Mica is the
preferred reinforcing mineral filler for enhancing the melt
strength because of its highly regular, high aspect ratio
morphology which can be thought of as resulting in "inter-particle
connectivity" or "physical crosslinking." The significant
reinforcing effect of mica is also evidenced by a SSI plate
rigidity value of 671 grams per 0.5 inches for PP/mica at a basis
weight of about 350 lbs. per 3000 square foot ream versus 342 grams
per 0.5 inches for unfilled PP at a basis weight of about 280 lbs.
per 3000 square foot ream.
1TABLE 1 Sheet Extrusion Conditions for Mica Filled Polypropylene
and Unfilled Polypropylene CONDITION PP/MICA UNFILLED PP Barrel
zone 1 (.degree. F.) 395 395 Barrel zone 2 (.degree. F.) 425 425
Barrel zone 3 (.degree. F.) 475 475 Adaptor (.degree. F.) 470 450
Feed block (.degree. F.) 470 460 Die zones 1-3 (.degree. F.) 470
475 Extruder RPM 80 70 Drive amperes 16 19 Melt pressure (psi) 1700
1780 Die pressure (psi) 550 825 Line speed (FPM) 6.1 5.0 Chill roll
temp. (.degree. F.) 130 137
[0109]
2TABLE 2 Caliper and SSI Rigidity Data for 101/4 Inch Plates
Thermoformed From Unfilled Polypropylene Sheet Plate SSI Rigidity
Sidewall Bottom Flange Specimen ID (g/0.5 in.) Caliper (mil)
Caliper (mil) Caliper (mil) 72-6 364 18.7 .+-. 1.9 20.7 .+-. 0.8
22.9 .+-. 2.8 (COV)* 10.1 3.9 12.2 72-7 382 19.2 .+-. 2.0 20.6 .+-.
0.4 23.3 .+-. 0.8 (COV) 10.4 1.9 3.4 72-8 280 19.6 .+-. 1.9 20.6
.+-. 0.5 23.3 .+-. 2.8 (COV) 9.7 2.4 12.0 Average 342 .+-. 54.4
19.19 .+-. 1.89 20.64 .+-. 0.58 23.15 .+-. 2.21 Properties (COV)
15.9 9.85 2.81 9.55 *COV = Coefficient of Variation
[0110]
3TABLE 3 Caliper and SSI Rigidity Data for 101/4 inch Plates
Thermoformed From Polypropylene/Mica/TiO.sub.2 Sheet Plate SSI
Rigidity Sidewall Bottom Flange Caliper Specimen ID (g/0.5 in.)
Caliper (mil) Caliper (mil) (mil) 72-1 705 18.3 .+-. 1.1 17.4 .+-.
0.5 18.2 .+-. 1.0 (COV)* 6.0 2.9 5.5 72-2 659 17.0 .+-. 1.5 17.9
.+-. 0.7 18.4 .+-. 0.5 (COV) 8.8 3.9 2.7 72-3 654 17.3 .+-. 1.6
17.0 .+-. 0.6 18.2 .+-. 0.7 (COV) 9.2 3.5 3.8 72-4 669 16.9 .+-.
1.2 16.7 .+-. 1.1 18.9 .+-. 0.8 (COV) 7.1 6.6 4.2 72-5 668 16.3
.+-. 1.0 16.3 .+-. 0.9 19.0 .+-. 0.9 (COV) 6.1 5.5 4.7 Average 671
.+-. 20 17.3 .+-. 0.76 17.1 .+-. 0.6 18.5 .+-. 0.38 Properties
(COV) 2.98 4.3 3.5 2.0 *COV = Coefficient of Variation
EXAMPLE 2
[0111] Extruded mica filled polypropylene sheets prepared as
described in Example 1 were characterized with respect to surface
gloss and roughness. Table 4 shows 75 degree gloss and Parker
Roughness (airflow method) data for an extruded mica filled
polypropylene sheet versus same properties for the food contact
(air) side of vacuum formed 10.25 inch plates produced according to
condition (B) of FIG. 2 using the same sheet formulation. The
unique thermally induced micronodular surface is characterized by
significant decrease in gloss and significant increase in roughness
as shown in the two photomicrographs in FIG. 22, which results in a
stoneware or pottery like appearance with aesthetic appeal. The
Parker Roughness method has been described in this specification
prior to the Example section.
4TABLE 4 GLOSS AND ROUGHNESS PROPERTIES OF THE FOOD CONTACT SIDE OF
POLYPROPYLENE/ MICA/TIO.sub.2 PLATE SURFACE VERSUS NEAT EXTRUDED
SHEET GLOSS PARKER ROUGHNESS SAMPLE ID (75 DEGREES)* (MICRONS) 72-1
(Plate) 22.4 13.41 72-2 (Plate) 30.6 14.05 72-3 (Plate) 24.8 14.89
72-4 (Plate) 24.3 14.24 72-5 (Plate) 24.5 12.48 PLATE AVERAGE 25.3
.+-. 3.1 13.8 .+-. 0.9 72-12-1 (Sheet) 45.7 5.92 72-12-2 (Sheet)
47.2 7.43 72-12-3 (Sheet) -- 5.89 72-12-4 (Sheet) -- 6.35 72-12-5
(Sheet) -- 5.84 72-12-6 (Sheet) -- 8.15 SHEET AVERAGE 46.5 6.6 .+-.
0.97 *= Average of Machine and Cross Machine Directions
[0112] As shown in Table 4, the food contact side is rougher as
evidenced by increased roughness and decreased gloss relative to
the neat extruded sheet. The rough appearance is desirable for
purpose of creating the micronodular surface giving the container
and plate a stoneware look.
EXAMPLE 3
[0113] Mica filled polypropylene sheets were successfully vacuum
thermoformed into 12 oz. oval microwave containers, whereby the
base was produced using mode (B) of FIG. 2 and the lid was produced
using mode (A) of FIG. 2. In contrast, attempts to form unfilled
polypropylene sheet into the same container were not
successful.
EXAMPLE 4
[0114] Sheet rolls (17.5 inch wide), at three calipers were
extruded as described in Example 1 and FIG. 1. Table 5 summarizes
the PP/40% mica material and process conditions. Table 6 summarizes
the PP/40% mica sheet properties.
5TABLE 5 PP/Mica Extrusion Process Conditions Summary Barrel Barrel
Barrel Feed Zone 1 Zone 2 Zone 3 Adaptor Block Die Temp. (F.) Temp.
(F.) Temp. (F.) Temp. (F.) Temp. Line Zone 1 Plate Size Actual/
Actual/ Actual/ Actual/ Actual/ Speed Temp. (F.) (in.) Set Set Set
Set Set (fpm) Actual/Set 11 395/395 452/425 475/475 470/470 470/470
9.27 470/470 10 376/375 410/410 431/430 430/430 430/430 8.32
430/430 9 375/376 410/410 434/430 430/430 430/430 8.07 430/430 Die
Die Zone 2 Zone 3 Screw Melt Die Chill Roll Plate Size Temp. (F.)
Temp. (F.) RPM Drive Pressure Pressure Temp. (F.) (in.) Actual/Set
Actual/Set Actual/Set Amperes (psi) (psi) Actual/Set 11 469/470
470/470 125 18.3 1387 694 130/130 10 430/430 430/430 130 19.3 2012
737 130/130 9 430/430 430/430 132 24.2 2112 686 130/130
[0115]
6TABLE 6 PP/Mica Sheet Property Summary Plate Size Overall Basis
Weight - Avg. (in.) Overall Caliper - Avg. (mil) (lb./3000
ft.{circumflex over ( )}2) 11 18.46 +/- 0.36 308.07 +/- 13.72 10
17.20 +/- 0.10 288.80 +/- 9.89 9 16.94 +/- 0.10 268.11 +/- 7.50
EXAMPLE 5
[0116] Plates from sheet specifications set forth in Example 4 were
produced using 1-up water cooled female molds (with pressure
box/vacuum assembly), followed by matched metal punch trimming.
Mold temperature was 70.degree. F., while sheet temperatures for
the 9, 10, and 11 inch plate runs were respectively 300.degree. F.,
310.degree. F., and 295.degree. F. The 9 and 10 inch plates were
produced at 20 cycles/minute while the bulk of the 11 inch plates
were made at 25 cycles/minute.
[0117] Oven temperature control on the commercial machine was good
due to the combination of top glass heaters and bottom calrod
heaters with proper zoning. In general, higher temperatures produce
more micronodularity at the expense of more pronounced sheet sag
and wrinkling while low temperatures tend to reduce sag at the
expense of diminished stoneware appearance.
[0118] Best results (i.e., micronodular matte eating surface
without "webbing" or wrinkling) were obtained by increasing the top
oven temperature by 3-5.degree. F. and decreasing the bottom by a
corresponding amount. This ability to selectively control oven
temperature in effect facilitated determination of the preferred
process temperature window of PP/mica sheets.
[0119] Set forth in Table 7 are the physical properties of plates
having the shape set forth in FIGS. 9 through 12 and having a
diameter of 9, 10, and 11 inches.
7TABLE 7 Plate Physical Property Data Product Size 9 inch plate 10
inch plate 11 inch plate Plates Produced 15,000 10,000 10,000 Plate
Weight Avg. 18.31 24.40 32.02 g. Std. Dev. 0.27 1.01 0.86 Basis
Weight Avg. 248.28 266.97 288.18 #/ream Std. Dev. 3.80 9.67 7.09
Caliper Avg. 15.89 16.41 17.32 mils Std. Dev. 0.48 0.49 0.86 Dry
Rigidity MD Avg. 300.2 341.6 411.9 gms/0.5 inches Std. Dev. 56.0
56.0 30.0 Dry Rigidity CD Avg. 307.5 345.9 417.4 gms/0.5 inches
Std. Dev. 57.0 50.0 29.0 Dry Rigidity GM Avg. 303.4 343.4 414.4
gms/0.5 inches Std. Dev. 54.0 52.0 26.0 Gloss 60.degree. 3.7 .+-.
0.6 3.7 .+-. 0.6 5.5 .+-. 1.2 75.degree. 9.0 .+-. 1.7 9.5 .+-. 2.1
15.6 .+-. 3.4 Color L* 80.5 .+-. 2.8 81.3 .+-. 0.9 80.7 .+-. 0.3
Hunter a* 0.67 .+-. 0.007 0.77 .+-. 0.07 1.2 .+-. 0.1 b* 6.3 .+-.
0.005 6.2 .+-. 0.05 6.7 .+-. 0.1 Whiteness % 33.5 .+-. 0.7 33.9
.+-. 0.8 31.1 .+-. 0.4 Index Parker Print microns 16.3 .+-. 1.63
15.9 .+-. 1.78 14.8 .+-. 1.86 Roughness
EXAMPLE 6
[0120] The sheets and plates were prepared as illustrated in
Example 1 and FIGS. 1 and 2. Table 8 shows sheet extrusion and
forming conditions. Table 9 contains formulation composition
information. Table 9 shows the plate physical test results. FIGS.
23 and 24 show respectively, gloss and plate rigidity versus mica
level (at constant mica/TiO.sub.2 ratio).
8TABLE 8 Extrusion/Forming Conditions Barrel Zone 1 375.degree. F.
Barrel Zone 2 410.degree. F. Barrel Zone 3 430.degree. F. Adaptor
430.degree. F. Feedblock 430.degree. F. Die Zones 1/2/3 430.degree.
F. RPM 130 Chill Roll 130.degree. F. Target Sheet Caliper 18.3 mil
Sheet Width 18.0 inches Comet Former Top Heater 20% Comet Former
Bottom Heater 35% Comet Former Time 50-60 seconds Plate Design 11
inch (having shape set forth in FIGS. 9-12)
[0121]
9TABLE 9 Physical Test Properties Run Plate Weight Basis Weight
Caliper Dry Rigidity - MD Dry Rigidity - CD Dry Rigidity - GM Mica
No. (g) (#/ream) (mU) (gm/0.5 in) (gm/0.5 in) (gm/0.5 in) (Wt %)
TiO.sub.2 (Wt %) 1 33.52 .+-. 0.17 294.92 .+-. 2.24 16.91 .+-. 0.08
543.0 .+-. 12.0 543.4 .+-. 11.7 543.2 .+-. 11.6 40 2.5 2 30.10 .+-.
0.39 259.13 .+-. 5.04 16.12 .+-. 0.26 363.6 .+-. 15.3 363.2 .+-.
16.2 363.4 .+-. 15.4 40 2.5 3 31.20 .+-. 0.17 271.34 .+-. 2.24
16.26 .+-. 0.08 468.4 .+-. 14.4 464.8 .+-. 16.5 466.6 .+-. 15.4 40
0 4 32.81 .+-. 0.69 288.66 .+-. 8.48 17.40 .+-. 0.31 480.4 .+-.
38.2 482.0 .+-. 37.6 481.2 .+-. 37.9 30 1.88 5 29.47 .+-. 0.09
254.82 .+-. 3.77 17.26 .+-. 0.32 338.4 .+-. 8.6 339.6 .+-. 12.2
339.0 .+-. 9.7 20 1.25 6 30.17 .+-. 0.30 263.73 .+-. 2.20 17.32
.+-. 0.32 334.7 .+-. 9.1 326.3 .+-. 5.0 330.5 .+-. 6.8 25 1.56 7
36.02 .+-. 1.00 313.87 .+-. 10.98 18.26 .+-. 0.52 473.3 .+-. 48.4
479.7 .+-. 59.7 476.5 .+-. 54.0 40 2.5 8 33.15 .+-. 0.37 289.62
.+-. 2.49 17.39 .+-. 0.34 440.3 .+-. 4.0 428.0 .+-. 10.4 434.1 .+-.
4.6 40 2.5 9 34.74 .+-. 0.50 305.79 .+-. 2.51 17.69 .+-. 0.24 440.3
.+-. 18.6 449.3 .+-. 11.0 444.8 .+-. 14.6 40 1.75 10 33.24 .+-.
0.20 291.79 .+-. 3.18 17.07 .+-. 0.20 407.3 .+-. 4.0 409.0 .+-. 8.5
408.2 .+-. 5.2 40 1.75 11 36.07 .+-. 0.30 316.39 .+-. 2.09 18.15
.+-. 0.11 501.0 .+-. 17.3 489.7 .+-. 8.5 495.3 .+-. 12.3 40 1.0 12
33.84 .+-. 0.55 293.84 .+-. 4.37 17.70 .+-. 0.28 413.0 .+-. 18.0
402.3 .+-. 19.7 407.6 .+-. 18.6 40 1.0 13 31.00 .+-. 0.38 271.53
.+-. 5.09 17.81 .+-. 0.32 413.7 .+-. 45.1 405.3 .+-. 44.4 409.4
.+-. 44.2 27.5 1.72 14 31.77 265.64 17.37 .+-. 0.80 384.0 372.0
378.0 25 1.56 15 31.02 269.00 17.41 .+-. 0.01 335.0 364.0 359.5 30
1.87 16 30.09 256.85 16.87 .+-. 0.57 325.0 328.0 326.5 30 1.87 17
30.36 261.41 16.70 .+-. 0.17 334.0 346.0 339.9 30 1.87 Parker Print
Run No. Gloss 60* Gloss 75* Color Hunter L* Color Hunter A* Color
Hunter B* Whiteness Index (%) Roughness (micron) 1 4.5 .+-. 0.3
11.2 .+-. 1.0 78.29 .+-. 0.5 0.99 .+-. 0.14 7.13 .+-. 0.14 26.72
.+-. 0.36 15.44 .+-. 3.19 2 4.8 .+-. 0.4 14.9 .+-. 0.3 80.99 .+-.
0.2 0.70 .+-. 0.04 6.40 .+-. 0.02 32.62 .+-. 0.18 15.28 .+-. 2.08 3
4.3 .+-. 0.3 11.8 .+-. 1.0 52.45 .+-. 0.5 3.17 .+-. 0.14 14.77 .+-.
0.14 -6.65 .+-. 0.36 13.86 .+-. 1.68 4 5.4 .+-. 0.5 16.0 .+-. 4.5
78.85 .+-. 0.1 0.93 .+-. 0.06 7.41 .+-. 0.05 26.34 .+-. 0.19 15.01
.+-. 1.81 5 7.3 .+-. 0.1 24.3 .+-. 0.3 78.83 .+-. 0.1 1.33 .+-.
0.05 8.10 .+-. 0.03 23.75 .+-. 0.16 13.62 .+-. 0.13 6 5.9 .+-. 0.1
18.3 .+-. 0.3 78.32 .+-. 0.1 0.83 .+-. 0.03 7.55 .+-. 0.03 25.26
.+-. 0.13 15.67 .+-. 2.17 7 4.4 .+-. 0.1 11.6 .+-. 0.5 81.04 .+-.
0.4 0.91 .+-. 0.03 7.29 .+-. 0.07 28.55 .+-. 0.88 16.07 .+-. 0.93 8
4.2 .+-. 0.1 11.7 .+-. 0.5 75.30 .+-. 0.8 1.22 .+-. 0.10 8.36 .+-.
0.17 19.05 .+-. 0.72 14.86 .+-. 1.40 9 4.4 .+-. 0.2 11.9 .+-. 0.4
76.77 .+-. 0.4 1.02 .+-. 0.04 8.19 .+-. 0.06 21.21 .+-. 0.51 14.91
.+-. 1.83 10 4.1 .+-. 0.1 11.5 .+-. 0.3 72.74 .+-. 0.4 1.31 .+-.
0.10 9.17 .+-. 0.10 14.49 .+-. 0.49 15.15 .+-. 0.50 11 4.0 .+-. 0.1
11.3 .+-. 0.3 70.35 .+-. 0.20 1.43 .+-. 0.04 9.62 .+-. 0.09 11.25
.+-. 0.38 16.12 .+-. 1.76 12 4.4 .+-. 0 13.2 .+-. 0.4 68.70 .+-.
0.62 1.62 .+-. 0.09 9.72 .+-. 0.11 9.83 .+-. 0.72 14.93 .+-. 1.14
13 5.0 .+-. 0.1 15.0 .+-. 0.7 78.87 .+-. 0.12 0.64 .+-. 0.03 7.40
.+-. 0.03 26.40 .+-. 0.16 15.90 .+-. 1.41 14 6.7 .+-. 0.2 20.9 .+-.
0.7 78.95 .+-. 0.03 0.89 .+-. 0.04 6.78 .+-. 0.01 28.76 .+-. 0.55
15.75 .+-. 1.74 15 6.1 .+-. 0.1 19.0 .+-. 0.6 79.38 .+-. 0.03 0.92
.+-. 0.03 6.81 .+-. 0.01 28.83 .+-. 1.15 13.97 .+-. 0.33 16 5.6
.+-. 0.2 18.9 .+-. 0.6 71.22 .+-. 0.08 -10.47 .+-. 0.08 -6.36 .+-.
0.06 64.16 .+-. 0.61 -- 17 6.0 .+-. 0.1 20.5 .+-. 0.5 55.98 .+-.
0.04 -11.16 .+-. 0.03 -28.54 .+-. 0.07 16.70 .+-. 0.17 16.09 .+-.
2.19
EXAMPLE 7
[0122] Table 10 shows the sheet process conditions employed for a
commercial sheet extrusion run of several mica filled polypropylene
formulations. These sheets suitably have a basis weight of about
200 to 950, per 3000 square foot ream, preferably about 200 to 400
per 3000 square foot ream. These mica filled polypropylene sheets
had a mica content in the range of 25 to 35 weight percent.
[0123] The extrusion of coupled mica and polypropylene blends was
conducted on a 6" commercial extruder line. The extruder was an
Egan 24/1 L/D with a general purpose screw. The die was an
Extrusion Die Inc. 52" coat hanger type. The stack conditioning
rolls were top polished chrome, middle matte (40 RA surface), and
bottom polished chrome. Extrusion conditions are set forth in Table
10. The matte chill roll assisted with the formation of the
micronodular surface during thermoforming of the sheet with
beneficially improving breadth of forming temperature window in
contrast with non matted smooth sheets of prior art depicted in
FIG. 26.
10TABLE 10 Sheet Extrusion Run Conditions For Mica Filled
Polypropylene Run Point Set Point PP/25% wt PP/30% wt PP/25% wt
PP/30% wt Mica Mica Mica Mica Barrel Zone 1 Temp (F.) 352 350 350
350 Barrel Zone 2 Temp (F.) 385 375 375 375 Barrel Zone 3 Temp (F.)
404 400 400 400 Barrel Zone 4 Temp (F.) 422 421 420 420 Barrel Zone
5 Temp (F.) 435 430 430 430 Adaptor Temperature (F.) 431 430 430
430 Melt Temperature (F.) 485 482 -- -- Die Zone 1 Temp (F.) 430
430 430 430 Die Zone 2 Temp (F.) 430 430 430 430 Die Zone 3 Temp
(F.) 431 430 430 430 Die Zone 4 Temp (F.) 431 430 430 430 Die Zone
5 Temp (F.) 430 430 430 430 Screw RPM 55 54 Drive Amperes -- 432
Melt Pressure (psi) 1704 1705-1760* Top Roll Temp (F.) 132 133
Middle Roll Temp (F.) 97 98 Line Speed (fpm) 42 37 Roll Gap top
(mil) 17 17 Roll Gap Bottom (mil) 21 21 Die Gap (mil) -- 19 - side
of die, 13 - middle of die Die - Full Width (in) 52 52 Die to Roll
Distance (in) .about.6.0 4.5 Full Sheet Width (in) 50.5 51.5 Trim
Width (each side) (in) 1.75 1.75 Final Split Roll Width (in) 16 16
Screen Pack 20 mesh 20 mesh Throughput (lb./hr.) -- 924 Back
Pressure (psi) 1830 1830 Sheet Caliper (mil) -- 17.3 Roll Weight
(lb.) 400 430 Roll Diameter (in) 45 40 Roll Footage (ft) -- 6,240
*No screen pack change
[0124] The sheets produced with conditions set forth in Table 10
were matte finished. The photomicrographs of the sheets produced
according to the process of Table 10 as contrasted to those
produced under conditions similar to Example 1 are set forth in
photomicrographs of FIGS. 25 and 26.
11TABLE 11 Roughness and Gloss Properties of PP/30% Mica Extruded
Sheets and Thermoformed Plates Sheet Thermoforming Parker Surface
Temperature (.degree. F.) Roughness (microns) Gloss (75.degree.) A
-- 8.56 .+-. 0.39 4.99 .+-. 0.14 B -- 15.82 .+-. 0.74 8.05 .+-.
0.30 C 305 13.14 .+-. 0.74 14.3 .+-. 1.0 D 300 11.74 .+-. 0.86 11.6
.+-. 1.0 E 292 12.10 .+-. 0.82 11.7 .+-. 1.0 F 265 10.63 .+-. 0.68
8.20 .+-. 0.6 G -- 6.17 82.10 H -- 5.14 80.75 (A) Matte extruded
sheet having top matte side. (B) Extruded sheet (A) - bottom side
opposite to matte side (C, D, E, F.) Plate - eating side
corresponding to top matte side of (A) (G) Non-matte extruded sheet
- top side (no matte roll) (H) Non-matte extruded sheet - bottom
side (no matte roll)
[0125] For a non-matte extruded sheet, usually plate gloss and
plate roughness are inversely related (e.g., high gloss corresponds
to low roughness and vice versa as demonstrated in prior art data
generally obtained). In that case, achieving desirable micronodular
texture is within a temperature range (about 295.degree. F. to
305.degree. F.) where above this range the forming process is sag
limited while below this range the plate exhibits poor micronodular
character as manifested by high gloss and low roughness.
[0126] The use of a matte roll in the chill roll stack portion of
the extrusion process effectively broadens the commercially
attractive thermoforming process temperature range (about
265.degree. F. to 305.degree. F.). Specifically, plates having
acceptable surface micronodularity can be formed at lower
temperatures, whereby the decrease in plate roughness is
compensated by an unexpected decrease in plate gloss using sheet
surface (A). This beneficial increase in plate forming temperature
window from about 10.degree. F. to about 40.degree. F. is brought
about by imparting a matte surface finish to the extruded
sheet.
[0127] Thermoforming is the pressing or squeezing of pliable
material into final shape. In the simplest form, thermoforming is
draping of a softened sheet over a shaped mold. In the more
advanced form, thermoforming is automatic, high speed positioning
of a sheet having an accurately controlled temperature into a
pneumatically actuated forming station.
[0128] The extruded sheet used in the suitable forming and
thermoforming process, or the preferred thermoforming process as
shown in FIG. 2 has a thickness of about 0.010 to 0.080 inches,
suitably 0.010 to 0.030 inches, and preferably 0.015 to 0.025
inches. Suitable mica filler loading level in the extruded sheet is
in the range of 25-30 weight percent, whereby mica flake aspect
ratio is in the range of 30-300, more preferably 80-120, with
particle size range of about 50 to 500 microns.
[0129] By matte finishing one side of the sheet using matte roll,
the commercial thermoforming was suitably conducted at a broader
temperature window of about 265.degree. F. to 305.degree. F. while
without matte finishing, the thermoforming using the same
commercial equipment was conducted at a temperature of about
295.degree. F. to 305.degree. F.
[0130] The runs on commercial equipment using PP/30% mica and
PP/25% mica formulations showed that the thermoforming temperature
window range has been expanded from about 10.degree. F. (previous
trial) to as high as about 35.degree. F. This is primarily due to
the fact that we beneficially used a matte roll in the chill roll
stack during the extrusion process. This gave a smooth matte finish
for the air side of the sheet (i.e., plate eating surface) while
the rougher bottom side was in contact with the sandblasted mold
side during the forming process. Use of matte sheet in turn enabled
forming at lower temperatures (which is good for sag avoidance)
without much loss in micronodularity. Specifically, the forming
window was in the range of 265.degree. F. to about 300.degree. F.
to 305.degree. F. where best balance of process stability and
product appearance/texture was seen at about 280.degree. F. to
290.degree. F.
EXAMPLE 8
[0131] FIG. 3 shows rigidity versus current plate material cost
comparisons for mica filled polypropylene plates versus competitor
plastic disposable plates. "J" refers to mica filled polypropylene
plate of this invention and "S" refers to polystyrene based plates
such as those currently manufactured by Solo Cup Company. Average
plate calipers are indicated for each plate type and size. The left
side of the diagram shows data for 8.75 inch plates whereby the J
plate rigidity is about three times higher than S at significantly
reduced caliper and cost. The right side of the diagram shows data
for 10.25 inch plates whereby J plate rigidity is more than seven
times higher than S at the same caliper. The open circle point
corresponds to an estimated rigidity for the 10.25 inch J plate
that is scaled down in caliper so that plate material costs are
equivalent to S.
[0132] The scaled J caliper X is calculated as X=(19 mil)(2.9
cents/3.8 cents). The theoretical rigidity R1 at equivalent cost
for the downscaled caliper is calculated as:
(R1/R2).dbd.(14.5 mil/9 mil)exp N
[0133] where R2 is the experimental rigidity at 19 mil and N=1.816
is the caliper exponent value for the Dixie Superstrong 10.25 inch
plate design which is obtained from the general equation for
rigidity:
R=(KE) TexpN
[0134] where E is Young's modulus, K is a shape constant, and T is
caliper. The data set forth it FIG. 3 demonstrate that the rigidity
of the J plate of this invention is significantly higher at
equivalent or lower material cost than commercial polystyrene
polymer based plates.
EXAMPLE 9
[0135] In FIG. 4, the heat resistance performance for mica filled
polypropylene 10.25 in plates (J), having an average caliper of 19
mil (J) is compared with (S) polystyrene based plates (S) of the
same size and caliper. A measure of heat resistance is dynamic
flexural storage modulus E', as measured with the Rheometrics
Solids analyzer at 10 rad/sec. Higher E' values indicate increased
stiffness and improved dimensional stability. Dynamic mechanical
spectroscopy is a common technique used for evaluation of
viscoelastic properties of polymeric materials with respect to
temperature and input frequency (deformation time scale). Dynamic
mechanical properties of flat rectangular specimens of S plate
material and PP/mica sheet of this invention were subjected to
flexural deformation at 10 rad/sec, using the Rheometrics Solids
Analyzer RSAII instrument, manufactured by Rheometric Scientific,
and equipped with a dual cantilever bending fixture. Temperature
scans were conducted at 0.05% strain using 2.degree. C. temperature
steps with a 0.5 minute soak time at each temperature. From the
time lag between input strain delivered by the driver motor and the
stress output measured by the transducer, values of material
complex modulus E* are obtained. The parameter E* is formally
expressed as E*=E'+iE", where E' is the storage modulus (purely
elastic term) and E" is the loss modulus (purely viscous term). The
storage modulus E' is defined as the stress in phase with the
strain divided by the strain, which gives a measure of the energy
stored and recovered per cycle. The loss modulus E" is defined as
the stress 90 degrees out of phase with the strain divided by the
strain, which gives a measure of the energy dissipated per cycle.
The ratio of loss modulus to storage modulus is commonly known as
the damping (tan delta) where delta is the phase angle between
stress and strain. The dynamic storage flexural modulus E' is the
operative measure of heat resistance performance, where higher
values mean higher performance. At ambient conditions (77.degree.
F.), E' for mica filled polypropylene plates of this invention is
appreciably higher than for S. At 250.degree. F., which corresponds
to aggressive temperatures which are commonly encountered in the
microwave heating or cooking of greasy foods, the heat resistance
of J plates of this invention is significantly superior to the
plates manufactured by S.
[0136] The superior heat resistance of the plates of this invention
J versus the plates sold by S as characterized by E' strongly
correlates with actual microwave cook test results for the two
plates, as shown in Table 12. The S plate warps and loses
dimensional stability with many types of foods as well as undergoes
undesirable changes when coming in contact with food as evidenced
by some staining and sticking. On the other hand, the J plate of
this invention is a superior plate since it has excellent
dimensional stability as well as excellent heat resistance when
food is cooked and/or reconstituted on it.
12TABLE 12 MICROWAVE COOKING TEST RESULTS FOR PLATES J AND S PLATE
TYPE FOOD TYPE J S donut pass sugar glazing sticks broccoli/cheese
pass significantly deforms pepperoni pizza pass moderate
deformation, staining barbecue pork slight stain significant
stain/warpage pancake/syrup pass significant warpage beans &
pork pass significant warpage butter slight warpage significant
warpage bacon moderate warpage, localized significant warpage,
melting, no leak rubbery plate flows and sticks to glass tray
[0137] Fort James Corporation (J) plate specimens of this invention
and plates manufactured by Solo Cup Company (S) were tested in the
microwave (Samsung model MW 8690) with a variety of foods. The
highest power setting (10) was used in all cases and
cooking/heating times and procedures corresponded food manufacturer
instructions on the packages. Most tested foods were of the frozen
microwaveable type and were placed in a semi-thawed state directly
on plates prior to cooking. When appropriate, a loose covering of
wax paper was employed during the cooking process. After cooking,
the plates were gently washed with warm water and inspected. The
following are the detailed test results which are also summarized
in Table 12.
[0138] Test #1 Results--Sugar Glazed Donut
[0139] J A large, oval shaped sugar glazed plain donut was
microwaved on the plate of this invention for 60 seconds. The sugar
glazing melted, bubbled, and flowed on the plate. The boiling sugar
and grease mixture caused the bottom of the plate to feel very warm
but the plate exhibited no warping, no straining, no softening, and
no soak-through. The plate was cool enough to be safely handled.
The residue of the donut was easily washed off and the appearance
of the used plate was excellent.
[0140] S The bottom of the plate got hot and slightly deformed with
no soak-through, however, sugar stuck to the plate.
[0141] Test #2 Results--Broccoli With Cheese Sauce
[0142] J Green Giant 10 oz. broccoli with cheese sauce was removed
from the flexible pouch and heated for five minutes in the
microwave on the plate with loose covering of wax paper. The cheese
melted and bubbled on the plate without sticking. The plate bottom
was warm, but no soak-through and no loss of dimensional stability
was observed. After washing, no staining was observed and the
appearance of the used plate was excellent.
[0143] S The plate bottom got hot and significantly deformed with
no soak-through.
[0144] Test #3 Results--Pepperoni Pizza
[0145] J Tombstone 7 oz. Pepperoni pizza was cooked on an uncovered
plate for 4 minutes. The cheese melted and started bubbling about
halfway through the test. The molten cheese mingled with the hot
liquid fat exuded from the pepperoni and dripped on the sides of
the crust onto the plate. No sticking, no soak-through, no
staining, and no loss in plate dimensional stability was observed
and the appearance of the used plate was excellent.
[0146] S The plate bottom got hot and moderately deformed with no
soak-through. The greasy reddish stain from oil in pepperoni could
not be completely washed off.
[0147] Test #4 Results--Microwave Kid Meal:
[0148] Pork Rib Patties, Barbecue Sauce, Fries, Honey Corn
Bread
[0149] J A quick meal preparation simulation test was conducted
using a Swanson 7.2 oz. microwave kids' meal with ingredients
consisting of partially cooked boneless pork rib patties, barbecue
sauce, fries, and honey corn bread. The food was transferred from
the compartmented tray onto the plate. Sauce was spooned on top of
the pork meat and was allowed to drip on the sides of the patties
and onto the plate. The cornbread batter was spooned out and was
placed on the plate next to the fries. The food was loosely covered
with wax paper and cooked for 3.5 minutes. Examination after
microwaving showed that the cornbread was fully cooked and there
was no sticking or damage to the plate. The fries and pork meat
with sauce caused no soak-through and no loss in plate dimensional
stability. Washing of plate revealed the presence of slight
staining from barbecue sauce. Overall, the appearance of the used
plate was very good.
[0150] S The plate bottom deformed mainly from pork meat with
considerable staining from the barbecue sauce without
soak-through.
[0151] Test #5 Results--Beans With Pork and Tomato Sauce
[0152] J Beans with pork and tomato sauce (8 oz can) were placed on
the plate, covered with wax paper and heated for 2 minutes to near
boiling. The bottom of plate got hot, but the rim was cool to
touch. The hot plate bottom exhibited no bulging and also, when the
hot food plate was handled by the rim there was no perceived loss
in dimensional stability. No soak-through, no warping, and no
staining was observed. The appearance of the plate was
excellent.
[0153] S The plate bottom became very hot and severely deformed
with no soak-through and when handled by the rim, the plate felt
like it had low rigidity.
[0154] Test #6 Results--Pancakes With Syrup And Precooked Bacon
[0155] J In this test, Swanson microwave pancakes and bacon
breakfast (4.5 oz. size) were used. The semi-thawed meal consisted
of three pancakes and three partially precooked bacon strips. The
pancakes and bacon were removed from the tray in carton and placed
on plate. Approximately 5 teaspoons of pancake syrup was spooned
over the pancakes and the assembled meal was covered with wax paper
and microwaved for 2 minutes. Although the bottom of the plate got
hot, the overall plate performance was excellent, i.e. no warpage,
no soak-through, no loss in dimensional stability, and no staining.
Some hot grease was exuded by the bacon during crisping but there
was no observed damage to the plate. The appearance of the used
plate was excellent.
[0156] S The plate bottom became hot and significantly deformed
(especially in areas where bacon was placed), but no soak-through
was observed and when handled by the rim, the plate felt soft.
[0157] Test #7 Results--Butter
[0158] J Butter (5 tsp. chunk) was placed the on plate and was
loosely covered with wax paper and was microwaved for 3 minutes.
The butter melted completely and covered the whole plate bottom.
The butter began boiling toward the end of the test. The plate
bottom got very hot and became slightly warped but no soak-through.
The rim of the plate felt cool to touch enabling safe removal of
the plate from the microwave oven. A small portion of the butter
became charred but was easily washed off the plate. Overall plate
performance was good.
[0159] S The plate bottom became very hot and was significantly
warped but no soak-through was observed and the greasy film residue
could not be washed off completely. Plate felt soft and rubbery
when handled by the rim.
[0160] Test #8 Results--Bacon
[0161] J Three strips of raw, cured bacon were wrapped in three
sheets of paper towel and cooked for 5 min. All of the bacon became
crispy and about 20% of it was charred. The bottom of plate got
very hot but most of rim area was relatively cool to touch. Grease
exuded from bacon and soaked through the towel. The grease pooled
on the plate bottom, side and on some rim areas. The grease which
pooled in some rim regions caused localized melting of the plate
but no holes were formed. The hot grease which pooled on plate
bottom caused significant warpage but no soak-through. Overall
plate performance for Test #8 was less satisfactory than Test
#7.
[0162] S When the raw bacon was wrapped in paper toweling and
cooked on the S plate, the bottom became very soft and stuck to the
glass tray in the microwave. Under such hot grease conditions, the
adhering polymer regions underwent localized melting and stretched
when the plate was lifted off the glass tray. The plate was
severely warped but no holes formed and no soak-through was
noticed.
[0163] With the possible exception of raw bacon, the behavior of
the J plate of this invention in the microwave oven is considered
excellent with a variety of aqueous, greasy/fatty, sugary food
combinations. No unusual or off odors were detected during and
after cooking for each type of food directly on the plate. The
foregoing data demonstrates the superior properties of the plates
of this invention.
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