CA1088816A - Heat resistant paperboard product - Google Patents
Heat resistant paperboard productInfo
- Publication number
- CA1088816A CA1088816A CA238,778A CA238778A CA1088816A CA 1088816 A CA1088816 A CA 1088816A CA 238778 A CA238778 A CA 238778A CA 1088816 A CA1088816 A CA 1088816A
- Authority
- CA
- Canada
- Prior art keywords
- paperboard
- water
- permeable
- substrate
- impermeable
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B65—CONVEYING; PACKING; STORING; HANDLING THIN OR FILAMENTARY MATERIAL
- B65D—CONTAINERS FOR STORAGE OR TRANSPORT OF ARTICLES OR MATERIALS, e.g. BAGS, BARRELS, BOTTLES, BOXES, CANS, CARTONS, CRATES, DRUMS, JARS, TANKS, HOPPERS, FORWARDING CONTAINERS; ACCESSORIES, CLOSURES, OR FITTINGS THEREFOR; PACKAGING ELEMENTS; PACKAGES
- B65D81/00—Containers, packaging elements, or packages, for contents presenting particular transport or storage problems, or adapted to be used for non-packaging purposes after removal of contents
- B65D81/34—Containers, packaging elements, or packages, for contents presenting particular transport or storage problems, or adapted to be used for non-packaging purposes after removal of contents for packaging foodstuffs or other articles intended to be cooked or heated within the package
- B65D81/3446—Containers, packaging elements, or packages, for contents presenting particular transport or storage problems, or adapted to be used for non-packaging purposes after removal of contents for packaging foodstuffs or other articles intended to be cooked or heated within the package specially adapted to be heated by microwaves
-
- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
- D21H19/00—Coated paper; Coating material
- D21H19/36—Coatings with pigments
- D21H19/44—Coatings with pigments characterised by the other ingredients, e.g. the binder or dispersing agent
- D21H19/62—Macromolecular organic compounds or oligomers thereof obtained otherwise than by reactions only involving carbon-to-carbon unsaturated bonds
Landscapes
- Engineering & Computer Science (AREA)
- Chemical & Material Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Life Sciences & Earth Sciences (AREA)
- Food Science & Technology (AREA)
- Mechanical Engineering (AREA)
- Paper (AREA)
- Laminated Bodies (AREA)
- Cookers (AREA)
- Package Specialized In Special Use (AREA)
- General Preparation And Processing Of Foods (AREA)
Abstract
Abstract of the Disclosure A paperboard product resistant to discoloration and otherwise stable upon heating, coated on the first surface thereof with n pigmented water impermeable layer and on the second surface thereof with a pigmented water permeable layer. The paperboard product is desirably used as the material employed in containers for food that is to be cooked in conventional or microwave ovens. The container is con-structed so that the food in the container is in contact with the water impermeable layer.
Description
Back~round of the Invention This invention xelates to a heat resistant paperboard product. More specifically, this invention relates to a coated heat resistant paperboard product which may be constructed into a container for food to be used in either conventional or micro-wave ovens.
In the past, containers for food to be cooked there-in have generally been manufactured from aluminum. However, with the increasing cost of aluminum raw material and the increasing use of microwave ovens in which food material lying directly against the aluminum cannot be heated, such containers have become increasingly impractical.
In considering alternative materials for containers ~-in which food may be cooked, several characteristics are dasired. First, the part of the container which is in contact with the food should provide a good barrler to the constituents of the food such as water and grease. Second, for aesthetic rèasons the container should retain its bright~
ness upon heating. Third, the material should have little tendency to blister or explode under cooking conditions and ~` ;
otherwise should be stable. Additionally, the material should be suitable for cooking in both conventional and microwave ovens. Finally, the alternative material should not affect the taste of the food cooked therein.
The heat resistant paperboard product of our .~ . . .
invention has the above characteristics and therefore, is a desirable material to be employed in containers for T.V.
dinners and the like.
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Summary of the Invention Broadly, the heat resistant paperboard product of
In the past, containers for food to be cooked there-in have generally been manufactured from aluminum. However, with the increasing cost of aluminum raw material and the increasing use of microwave ovens in which food material lying directly against the aluminum cannot be heated, such containers have become increasingly impractical.
In considering alternative materials for containers ~-in which food may be cooked, several characteristics are dasired. First, the part of the container which is in contact with the food should provide a good barrler to the constituents of the food such as water and grease. Second, for aesthetic rèasons the container should retain its bright~
ness upon heating. Third, the material should have little tendency to blister or explode under cooking conditions and ~` ;
otherwise should be stable. Additionally, the material should be suitable for cooking in both conventional and microwave ovens. Finally, the alternative material should not affect the taste of the food cooked therein.
The heat resistant paperboard product of our .~ . . .
invention has the above characteristics and therefore, is a desirable material to be employed in containers for T.V.
dinners and the like.
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Summary of the Invention Broadly, the heat resistant paperboard product of
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our invention comprises a pap~rboard substrate coated on one side with an impermeable la~er containing a binder and an opaque pigment, and coated on its oppos.ite side with a wa-ter permeable layer containing a binder and an opaque pigment.
The paperboard product of the preferred embodiment of the present invention has a brightness of a-t least 70% on its permeable side and at least 50% on its impermeable side after exposure to 400F. for 30 minutes.
The paperboard product of the present invention is desirably construc-ted by coating an aqueous slurry of binder ~ .
and opaque pigment onto a first surface of paperboard substra-te and then drying the subtrate -to provide a permeable layer of binder and opaque pigment on the first surface of .;~
the paperboard. Thereafter a mixture of binder and opaque pigment may be applied to the second surface of the paperboard :~
by extrusion coating and chilling the coated paperboard to provide an impermeable layer of binder and opaque pigment on the second surface of the paperboard.
The heat resistant paper product of our invention may be constructed into a container for cooking all types of food in both conventional and microwave ovens. The container ~ .
is constructed so that in use the food is in contact with the impermeable layer of the paperboard substrate, thereby insuring -that Eood constituen-ts do not seep into the paperboard. Further~ ~ :
as a result of the opaque, preferably white, pigment contained in -the layers, the container retains much of its brightness and shows very little evidence of discoloration or scorching caused by pyrolosis and oxidation of the cellulose in the paperboard substrate. Addi-tionally, the steam produced from the mois-ture present in the paperboard during cooking may escape through ~J~ :
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the permeable layer thereby avoiding blisterincJ, puffing or exploding of the paperboard. Finally, in our preferred embodiments, the taste of food is substantially unaffected when cooked in the containers of our invention.
Brief Description oE the Drawings Fig. 1 shows in cross section -the heat resistant paperboard of our invention.
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Fig. 2 shows a flow sheet o~ the preferred process by which the permeable coating is applied to the paperboard substrate.
Fig. 3 shows a flow sheet of the preferxed process - -by ~hich the impermeable coating is applied to the paperboard ;
substrate. -.., ~ ., .
Description of the Preferred Embodiments . .
Referring to Fig. 1, there is shown in cross section the heat resistant paperboard o~ oùr invention. More specif~
ically,there is shown paperboard substrate 12 coated on one side by impermeable layer 11 and on its other side by permeable ~ ;~
layer 13.
The paperboard substrate 12 of our invention may be made from any paper base stock which m Q be folded or formed into a container by techniques well known in the~art. Since it is preferred that the containers made from our heat resistant paperboard product are white, the paper base stock is preferably bleached. The prefexred base stock is bleached sulfate stoc~
but okher types o~ stock, e.g., bleached sulphite may be employed. The thickness of the substrate may also be varied widely and is not critical to our invention. The substrate, , of course, must be sufficiently thick to provide a container capable of holdin~ food but not so thick that containers for foo~ may not be madè therefrom. Thickness of the substrate will be dependent on size and shape of the container, weight of the food product, etc. For examplej~a .015 inch thick paper substrate is suitable for the purposes of our invention.
The impermeable layer 11 of the invention comprises a binder containing an opaque pigment represented by the dots ~ -~Q shown in Fig. l; The impermeable layer must be impermeable to 4.
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~ood constituents such as ~ater and preferably both water and grease. Thus, contain~rs produced from the paperboard product of our invention will permit substantially no permeation of water into its paperboard substrate when wa~er is poured into the container at 70F. and stored for a period of five minutes.
Additionally, the most preferred containers produced from the paperboard product of our invention will permit substantially no permeation of bacon ~rease into its paperboard substrate when grease at 300F. is poured into the container arld stored therei~ at an ambient temperature of 70F. until the grease solidifies.
The impermeable layer, o~ course, must be able to withstand oven temperatures, e.g., 350F., wlthout melting or degradation and must be capable of being applied as a layer to ,~, the paper substrate. Additionally, it is preferred that'the layer be sufficiently impermeable so as to prevent the loss of , ` ,' aroma into the paper substrate and,to prevent excessive inclusion of ambient aromas or gases into the food product. The preferred materials to be used in this aspect of our'invention are poly- ~-tetramethylene terephthalate (PTMT) or polycyclohexalene di-methylene terephthalate (PCDT), but other materials, e.g., poly-c,yclohexalene dimethylene terephthalate-phthalic acid copolymer, nylon 6, nylon 66, nylon 6/66 copolymers may desirably be used.
~he preferred materials have good extrusion co,ating character~
istics, and are relatively inexpensive.
The opaque pigment that is used in the impermeable layer of our invention is defined as any pigment with a refrac-tive index greater than 1.5 and preferably greater than about 1.9. ' The pigment must also be able to withstand oven temperatures and be capable of b,eing processed with the impermeable binder. The 5. ,~
. ~ : ,:,, pi~3ment mus~ ~C OL>;lq~C` ';O that (~ cont:aincr ~etains its bricJht:ness, whic~l otllcrw.i. .e would }~e losl: due to scoxching or discoloration of the paper sub.stl-ate during coo~iiny. For aesthetic reasons, it is preferred that the pigment be whlte, but it is contemplated that other colors may be employed within the scope of our invention.
The most preferred opaque pigrnents employed in the impermeable layer of our invention are titanium dioxides of either the rutile or anatase type. With titanium dioxide pigment, the preferred particle size is .l to .5 microns.
While titanium dioxicle has the highest refractive index of any white pigment of which we are aware, it is relatively expensive, and therefore it may be desired to replace titanium dioxide in ~7hole or in part by other opaque white pigments, e.g., kaolin clay, barium sulfate, amorphous silicon dioxide, zinc oxide, zir.c sulfide, calcium carbonate, calcium silicate, ;~
calcium sulfate, satin white, flux-calcined diatomaceous ~;
silica, talc, or hydrated alumina. However, for our present puxposes ~e prefer to use titanium dioxide alone in the impermeable layer of the paper substrate.
Broadly, it is contemplated that 2.5~ to 20~ by weight of the impermeabIe pigmented layer ll may be pi~ment.
The most preferred range is 5~O to 10o by weight pigment ~ith 7.5~ by weight the most preferred amount. Further, it is broadly contemplated that the impermeable pigmented layer be applied to the paper substrate in a thic~ness of from .0005 to .002 inches, with the most preferred range being from .00075 to .OOl inches.
It should be stressed, however, that the amounts of pigment and layer thic~ness may be variec~ widely both ~7ithil1 s 6.
and without the above ranges. If greater brightness retention is desired, the concentration of pigment or the thickness of the layer may be increased or, alternatively, if the product stored in the container requires low cooking temperature, or time, the concentration of pigment or the thickness of the l~yer may be decreased. It is therefore contemplated that a wide variety of impermeable layers may be provided according ~ ~
to the present invention. ~ -The permea~le layer 13 comprises at least a binder with an opaque pigment dispersed therein. The opaque pigment is represented by the dots in Fig. 1. Permeabl~e layer 13 must -be sufficiently permeable to permit the escape of steam which is vaporized from the paperboard substrate during heating.
Whether a particular layer is permeable is readily determined since products that are coated with layers that are not permeable will puff and blister when placed in an oven heated to 350F. for lS minutes.
The permeable layer in our invention must also be able to withstand oven temperatures, e.g., 350~F., without ~0 degradation and must be capable of being applied as a coating to the paperboard substrate.
The preferred binders employed in the impermeable layer are polymeric binders. The most preferred binder is `
polyvinyl acetate but other binders such as polyvinyl alcohol ~
or styrene butadiene may be employed. Polyvinyl acetate is ;- -preferred because it is easily coated onto the paper and does not darken excessively at high temperatures.
The opaque pigments that are employed in the permeable layer 13 of our invention are governed essentially by the same considerations described above for the impermeable 7.
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la)~er 11. ~n ol)aqu~ pix;lr,en~ is defi.llcd as any pi~m~n~ wi~h a l~Lracti~e in~ex ~Jr~a~er ~:hclr) 1.5 ~nd ~re~elc~ r is ~hite in color. Ho~evcr, sinc~ ~leStlle~iC COnSiClCratiOJlS are met by a mixturc of lcss cos~ly pig~ents havinc3 ~ refrac~ive ind~
c3reatcr than 1.5 bu~ l~ss than 1.9 ~ h more costly pig..ents having a refrac~ive index ahove 1.9, it i`s preferred that th~
opaque pl~ment in the permeahle layer of our invention com?rise a mi~:ture of ~tanium dioxide and kaolin clay.
In addition to the blnder and opa~ue pigment, ot~er constituents may also be employed ~.~ our permeable layer. .~.s will be described in more detail ~elo~, the binder and pigment of the permeable layer are preferably first slurried in ater ~:
and applied as a slurry to the paper substrate. In order to ; aid dispersion of the suspended pigment particles in the slur~t, tetra sodium pyrophosphate, sodium hexametaphosphate, or com~ercial anionic pol.yelectrolytes such as Tamol 850, produced by Roh~ and Haas, Dispex ~-40 produced by Allied Colloi~s, ~um~erlll pro~uced by Colloids, Inc., or Daxad 30 produced by l~. R. Grace Co~ may be employed.* The preferred dispersants are dispersin~ agents such as tetra sodium p~rophosphate and Tamol 850, a sodium salt of a carboxy~a~ed polyelectrolyte, or mi~tures thereof. The amount of dispersant may be varied id~ly, but is preferably about 0.1 to 0.17~ by weight of ~he ~icJmen~
Once thç slurr~t is applied to the paperboard substrate it,is o~ten desired to meter ofE excess coating ~ith applic2tion equipment. In order to retain enough water within the coating ~:
film during thc time lnterval between applica~ion ancl meterinc;
o~f and to pre~rent coating strea~s durinc3 met~xincJ o~f, ~e preer ~;~
.3~ to ada to the slurry s~all a~ounts o~ viscosit~ con~rol agcnts .
, * Tamol 850, Dispex N-40, and Daxad 30 are Trac~emarks. Each comprises a sodium salt of a polymeric carboxylic acid.
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such as sodium a]cJinate. Otller viscosi~y con~rol agcnts tha~
may be used for ~is purpose include sodiwn c?rboxymethyl cellulose, sodium polyacylate emulsions, and hydroxyethyl cellulose. Again, the amount of viscosity control agent may be varied widely, but the amount is preferably bet~een about 0.2 to 0.4~ by wei~ht of the pigment.
As will be described in more detail below, after the desired amount of permeable layer has been applied to the paperboard substrate,the composite is dried and preferably calendered and gloss calendered. In order that the composite may be more easily calendered, it is desirable to enhance the plasticity and slipperiness of the applied permeable layer.
To accomplish this end, small amounts of a lubricant, e.g., calci~n stearate,are preferably added to the coating slurry. ~ ~ ~
Other well Xnown lubricants, which may replace calcium -~
stearate, ~r ~Ihole or in part, include polyo~:ethy1z'ed ~thers, zinc stearate, alkoxylated triols, polyethylene emulsion, poly-oxyethylene ethex, ammonium stearate, polyalkylene glycol `-deriva~ives and mixtures thereof. The amount of lubricant may be varie~ widely, but preferably is between about 0.1 ~ -and 2% by weigh~ of the pi~nent.
It may sometimes ~e desired to print with ink the pe~neable layer of our invention. As is appreciated ~y those ;
skilled in the art, many offset printing inks require longer dryin~ times on acid coacings than on alkaline Goatings.
However, 1~ the coating is too alkaline, good ink coverage may be impeded under certain ofset printing condi~ions. It is thereore broadly preferred that the pH of layer 13 be between 7.0 and 10.5 at room temperature. The pref~rred pH range is 8.5 ~o 9.2,wit~ 9.0 belng the most preerred p~. To establish , `~ - .
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the preferred pH values it is sometimes required that an alkaline material be added to the ~ater slurry of permeable layer material in amounts suE~icient to raise the pH to the range of 7.0 to 10.5. The preferred alkaline material is ammonium hydroxide, but sodium or potassium hydroxide can also be used.
The concentration of the constituents and the thick-ness of the applied permeable layer may be varied widely by those skilled in the art for the same reasons that the same parameters can be widely varied ~or the impermeable lay~r.
The permeable layer preferably is applied to the substrate layer 12 at a loading of from 8 lbs. to 30 lbs. per 3000 sq.ft.
and more preferably is from 17 lbs. to 23 lbs. per 3000 sq.ft.
Further, the amounts of constituents by weight are preferably varied as shown in Tables 1 to 5 below:
Table 1 Component broad narrow preferred range range amount Opa~ue pigment 100 100 100 Permeable binder 10-30 18-22 20 Table 2 Component broad narrow preerred range range amount Titanium dioxide 15-80 30-50 45 Kaolin clay 20-85 50-70 55 Polyvinyl acetate 10-30 18-22 20 Table 3 Component broad narrow preferred range range amount Opaque pigment 100 100 100 Permeable binder 12-30 18-22 20 Viscosity control agent .05-.5 .2-.4 .33 Dispersant .02-.30 .10-.17 .14 Lubrlcant 0-3.0 .5-1.5 1.0 10. , , , rrab:Le 4 Component broad narrow pre~erred ranye range amount Titanium dioxide 15-80 30-50 45 Kaolin clay 20-85 50-70 55 polyvinyl acetate 12-30 18-22 20 viscosity control agent .05-.5 .2-.4 0.33 Dispersant .02-.30 .10-.17 .14 Lubricant 0-3.0 .5-1.5 .1.0 Table 5 Component broad narrow preferred range range amount Titanium dioxide 15-80 30-50 45 Kaolin clay 20-85 50-70 55 ~ :
Polyvinyl acetate 12-30 18-44 20 ~.
Sodium alginate .05-.5 .2-.4 0.33 . :
Tamol 850 .01-.15 .. 07-.11 0:09 Tetra sodium pyro- .01-.15 .03-.07 0.05 phosphate Calcium stearate 0-3 ,5-1.5 1.0 .
Alkali In amounts as needed to maintain pH of water slurry. .
One way of defining layers 11 and 13 of our paperboard ~
product is by measuring the brightness of the heat resistant . ;
paperboard product upon exposuxe to heat. The brightness of the heat resistant paperboard products.of our invention have been measured with a General Electric Brightness Meter by conventional .. ~ .
technique after heating two inch squares in a conventional oven at 400F. for 30 minutes. We have found that the side coated .`
with the permeable layer maintained a brightness above 70% and preferably above 75% while samples of uncoated paperboard main~
tained a brightness of below 50% under similar conditions. The side coated with the impermeable layer maintained a brightness above 50% while samples with conventional polyethylene or poly- :
propylene polymer coatings maintained a brightness below 30%. ~:
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Referrin~J no~J to Fi~ th~re is shown a schematic flow sheet of the preferred proccss by ~hich the permeable layer 13 is affixed to the paperboard substrate. As shown in Fig. 2 a suhstrate of paper is supplied to a first coating station 21 via roller 22. At the first coating station an aqueous slurry of the water permeable coating is applied to the paper substrate by conventional means such as puddle coater 23. Other conventional means by which the aqueous slurry of water permeable coating may be applied include flooded nip trailing blade coaters, rod coaters, reverse roll coaters, Massey coaters, air knife coaters and Chamflex coaters.
In order to minimize drying costs!the amount of water in the slurry is desirably maintained at the minimum amount required to maintain the mixture as a slurry. While the amount of water will vary somewhat depending on the water permeable coating formulation and application method,it is generally preferred to employ about 0.54 to l.0 parts by weight water per l part by weighk of water permeable coating mixture. In practice, the water permeable coating mixture is dispersed in water in an agitated tan~.
After the wet coating is applied to the paper substrate in first coating station 21, the applied water must be evaporated therefrom. As shown 1n Fig. 2, this is accomplished by passing the coated paperboard substrate via roller 24 through infra red driex 26 and then via roller 25 through two hot air driers 27 and 28 in series. It will be appreciated, however, that any type of dri~r or combination of driers may be employed and that the arrangement shown in Fig. 2 is for purposes of illustration only.
The temperatures and forced air velocities in the 12, .
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driers are maintaine~ to remove wa-t~r added t~ the paperboard substrate by the coating slurry and to obtain a product with a moisture level of 3% to 10~ water by weight.
Next, in our preferred embodiment, the coating process is repeated by passing the once coated paperboard substrate through a second coating station 31 containing a second puddle coater 33. After coating, the twice coated substrate is passed through a second drying system which, for purposes of illustr~tion, is shown as infra-red drier 35 fed b~ roller 34 and two hot air driers 37 and 38 in series fed -by roller 36.
Again the t~mperatures and forced air velocities in the driers are maintained to remove water added to the paper~
board substrate by the coating slurry and to obtain a product with a moisture level between 3% and 10~ water by weight.
Two coating stations are employed in the preferred process since at times it is difficult to control the thicker wet coating which would be required if only a single stage were employed. However, it is to be understood that the permeable layer 13 may be applied in any number of stages.
After the second coating has been dried, the coated substrate may optionally be passed via roIl~~44 to 46 to a --conventional gloss calender 39 wherein by application of pressure and heat, e.g., 200 to 350F. and preferably 250-300F., the coated product is glossed by the smooth polished surface of the gloss calender. Finally, the glossed coated paper substrate is optionally passed through a conventional calender stack 30 wherein through pressure imposed by opposing cylinders the product is smoothed and ~;
maintained at uniform thickness.
Referrin~ now to E g.3, there is shown a schematic flow ;'': ' - - ., . .. : . , , : ~, -sheet of the prcferred E~rocess for affixing th~ impermeable layer 11 to the paperboard substrate. It is preferred that the paperboard substrate supplied via supply roll 50 and roll 51 be already coated on one side with permeable layer 13.
The reason for this is that we prefer to produce the paper substrate in combination with coating the substrate with the permeable layer. Thus, the substrate introduced via rol~ 22 in Fig. 2 comes directly from the paper machine for producing the paper substrate. It is to be understood, however, that there is nothing critical in the order of coating and that the impermeable layer may be applied prior to the application of the permeable layer.
The polymer-pigment mixture which is used for the impermeable layer is preferably blended and then pelletized by the polymer manufacturer. Alternatively, a polymer-pigment concentrate is prepared by the polymer manufacturer or a processor and then the concentrate pellets are blended with "
natural polymer pellets to produce the impermeable mixturé.
The impermeable layer mixture is preferably applied to the paperboard substrate by a conventional process such as extrusion coating~ Referring again to Fig. 3 there is shown extruder 52 with die 53 arranged and constructed so that the impermeable layer mixture is applied by ex~rusion coating onto the paperboard substrate and is then passed through pressure roll 54 and chill roll 55. For a polytetramethylene terephthalate-titanium dioxide mixture, the chill roll is preferably maintained at about 60F. to 100F. The functions of the chill roll are: (1) to form a nip with the pressure roll for joining the paperboard substrate and the molten polymer layer under pressure~ (2) to remove heat from the ~t~ 3 L~
impermeable layer and l:he paperhoard substrate, and (3) to impart the desired surface finish to the impermeable layer.
Preferably the nip pressure applied to the coated substrate by chill roll 55 and pressure roll 5~ is about 50 to 350 lb.
per linear inch of web width. Finally, the heat resistant board product is passed from the chill roll 55 via roll 56 to storage roll 57.
The following example is provided to further illustrate the invention.
Example A mixture was prepared by dispersing into 77 parts water, 0.14 parts Tamol 850, 0.06 parts ~etra sodium pryophos-phate, 45 parts titanium dioxide, 55 parts Kaolin clay, 1 part calcium stearate, 20 parts polyvinyl acetate, a sufficient ~ ~
amount of alkali to maintain the pH at ~.0, and 0.29 parts sodium alginate, all parts by weight. The dispersed mixture ;~
was then applied to .015 inch thick bleached sulfate paper- ;
board in two stages to obtain a permeable layer coated onto ~-the paper in the amount of 20.9 lbs. per 3000 sq. ft. About equal amounts of coating were applied in each stage.
Next, the paperboard substrate was extrusion coated on its other side as described above in connection with Fig. 3, with a polymer mixture of 92 5 parts by weight polytetramethylene tere.phthalate and 7.5 parts by weight titanium dioxide. The thickness of the applied coating was 0.001 inches, the tempera-ture o~ the chill roll was 70F., and the applied pressure was lS0 pounds per lineal inch of web width. ~-~
The resulting coated product could be formed into ~ -containers for food by conventional techniques and was ' ' : . ; ~ ,, impermeable ~o water and grease on one side ~ut yet permeable to water on the other side. The initial G.E. brightness was 88.6% on the permeable side and 84.2~ on the impermeable side, while the average G.E. brightness after heating a two inch square piece of coated product at 400F. for 30 minutes was 77.1% on the permeable side and 55Ø% on the impermeable side.
From the above example, it is apparent that there are obtained coated paperboard substrates which may be formed into containers for food by conventional techniques. The resulting containers are impermeable to food constituents on the inside surface thereo. Further, the containers do n~t blister or explode but do retain their brig.htness upon heating. It is to be understood, however, that while the invention has been described with respect to preferred embodiments, variations and equivalents thereof may be perceived by those skilled in the art while nevertheless not departing from the scope of our invention as described by the claims appended hereto.
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our invention comprises a pap~rboard substrate coated on one side with an impermeable la~er containing a binder and an opaque pigment, and coated on its oppos.ite side with a wa-ter permeable layer containing a binder and an opaque pigment.
The paperboard product of the preferred embodiment of the present invention has a brightness of a-t least 70% on its permeable side and at least 50% on its impermeable side after exposure to 400F. for 30 minutes.
The paperboard product of the present invention is desirably construc-ted by coating an aqueous slurry of binder ~ .
and opaque pigment onto a first surface of paperboard substra-te and then drying the subtrate -to provide a permeable layer of binder and opaque pigment on the first surface of .;~
the paperboard. Thereafter a mixture of binder and opaque pigment may be applied to the second surface of the paperboard :~
by extrusion coating and chilling the coated paperboard to provide an impermeable layer of binder and opaque pigment on the second surface of the paperboard.
The heat resistant paper product of our invention may be constructed into a container for cooking all types of food in both conventional and microwave ovens. The container ~ .
is constructed so that in use the food is in contact with the impermeable layer of the paperboard substrate, thereby insuring -that Eood constituen-ts do not seep into the paperboard. Further~ ~ :
as a result of the opaque, preferably white, pigment contained in -the layers, the container retains much of its brightness and shows very little evidence of discoloration or scorching caused by pyrolosis and oxidation of the cellulose in the paperboard substrate. Addi-tionally, the steam produced from the mois-ture present in the paperboard during cooking may escape through ~J~ :
.. . .
the permeable layer thereby avoiding blisterincJ, puffing or exploding of the paperboard. Finally, in our preferred embodiments, the taste of food is substantially unaffected when cooked in the containers of our invention.
Brief Description oE the Drawings Fig. 1 shows in cross section -the heat resistant paperboard of our invention.
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Fig. 2 shows a flow sheet o~ the preferred process by which the permeable coating is applied to the paperboard substrate.
Fig. 3 shows a flow sheet of the preferxed process - -by ~hich the impermeable coating is applied to the paperboard ;
substrate. -.., ~ ., .
Description of the Preferred Embodiments . .
Referring to Fig. 1, there is shown in cross section the heat resistant paperboard o~ oùr invention. More specif~
ically,there is shown paperboard substrate 12 coated on one side by impermeable layer 11 and on its other side by permeable ~ ;~
layer 13.
The paperboard substrate 12 of our invention may be made from any paper base stock which m Q be folded or formed into a container by techniques well known in the~art. Since it is preferred that the containers made from our heat resistant paperboard product are white, the paper base stock is preferably bleached. The prefexred base stock is bleached sulfate stoc~
but okher types o~ stock, e.g., bleached sulphite may be employed. The thickness of the substrate may also be varied widely and is not critical to our invention. The substrate, , of course, must be sufficiently thick to provide a container capable of holdin~ food but not so thick that containers for foo~ may not be madè therefrom. Thickness of the substrate will be dependent on size and shape of the container, weight of the food product, etc. For examplej~a .015 inch thick paper substrate is suitable for the purposes of our invention.
The impermeable layer 11 of the invention comprises a binder containing an opaque pigment represented by the dots ~ -~Q shown in Fig. l; The impermeable layer must be impermeable to 4.
'` "'`' .
~ood constituents such as ~ater and preferably both water and grease. Thus, contain~rs produced from the paperboard product of our invention will permit substantially no permeation of water into its paperboard substrate when wa~er is poured into the container at 70F. and stored for a period of five minutes.
Additionally, the most preferred containers produced from the paperboard product of our invention will permit substantially no permeation of bacon ~rease into its paperboard substrate when grease at 300F. is poured into the container arld stored therei~ at an ambient temperature of 70F. until the grease solidifies.
The impermeable layer, o~ course, must be able to withstand oven temperatures, e.g., 350F., wlthout melting or degradation and must be capable of being applied as a layer to ,~, the paper substrate. Additionally, it is preferred that'the layer be sufficiently impermeable so as to prevent the loss of , ` ,' aroma into the paper substrate and,to prevent excessive inclusion of ambient aromas or gases into the food product. The preferred materials to be used in this aspect of our'invention are poly- ~-tetramethylene terephthalate (PTMT) or polycyclohexalene di-methylene terephthalate (PCDT), but other materials, e.g., poly-c,yclohexalene dimethylene terephthalate-phthalic acid copolymer, nylon 6, nylon 66, nylon 6/66 copolymers may desirably be used.
~he preferred materials have good extrusion co,ating character~
istics, and are relatively inexpensive.
The opaque pigment that is used in the impermeable layer of our invention is defined as any pigment with a refrac-tive index greater than 1.5 and preferably greater than about 1.9. ' The pigment must also be able to withstand oven temperatures and be capable of b,eing processed with the impermeable binder. The 5. ,~
. ~ : ,:,, pi~3ment mus~ ~C OL>;lq~C` ';O that (~ cont:aincr ~etains its bricJht:ness, whic~l otllcrw.i. .e would }~e losl: due to scoxching or discoloration of the paper sub.stl-ate during coo~iiny. For aesthetic reasons, it is preferred that the pigment be whlte, but it is contemplated that other colors may be employed within the scope of our invention.
The most preferred opaque pigrnents employed in the impermeable layer of our invention are titanium dioxides of either the rutile or anatase type. With titanium dioxide pigment, the preferred particle size is .l to .5 microns.
While titanium dioxicle has the highest refractive index of any white pigment of which we are aware, it is relatively expensive, and therefore it may be desired to replace titanium dioxide in ~7hole or in part by other opaque white pigments, e.g., kaolin clay, barium sulfate, amorphous silicon dioxide, zinc oxide, zir.c sulfide, calcium carbonate, calcium silicate, ;~
calcium sulfate, satin white, flux-calcined diatomaceous ~;
silica, talc, or hydrated alumina. However, for our present puxposes ~e prefer to use titanium dioxide alone in the impermeable layer of the paper substrate.
Broadly, it is contemplated that 2.5~ to 20~ by weight of the impermeabIe pigmented layer ll may be pi~ment.
The most preferred range is 5~O to 10o by weight pigment ~ith 7.5~ by weight the most preferred amount. Further, it is broadly contemplated that the impermeable pigmented layer be applied to the paper substrate in a thic~ness of from .0005 to .002 inches, with the most preferred range being from .00075 to .OOl inches.
It should be stressed, however, that the amounts of pigment and layer thic~ness may be variec~ widely both ~7ithil1 s 6.
and without the above ranges. If greater brightness retention is desired, the concentration of pigment or the thickness of the layer may be increased or, alternatively, if the product stored in the container requires low cooking temperature, or time, the concentration of pigment or the thickness of the l~yer may be decreased. It is therefore contemplated that a wide variety of impermeable layers may be provided according ~ ~
to the present invention. ~ -The permea~le layer 13 comprises at least a binder with an opaque pigment dispersed therein. The opaque pigment is represented by the dots in Fig. 1. Permeabl~e layer 13 must -be sufficiently permeable to permit the escape of steam which is vaporized from the paperboard substrate during heating.
Whether a particular layer is permeable is readily determined since products that are coated with layers that are not permeable will puff and blister when placed in an oven heated to 350F. for lS minutes.
The permeable layer in our invention must also be able to withstand oven temperatures, e.g., 350~F., without ~0 degradation and must be capable of being applied as a coating to the paperboard substrate.
The preferred binders employed in the impermeable layer are polymeric binders. The most preferred binder is `
polyvinyl acetate but other binders such as polyvinyl alcohol ~
or styrene butadiene may be employed. Polyvinyl acetate is ;- -preferred because it is easily coated onto the paper and does not darken excessively at high temperatures.
The opaque pigments that are employed in the permeable layer 13 of our invention are governed essentially by the same considerations described above for the impermeable 7.
. . - . . . - .
la)~er 11. ~n ol)aqu~ pix;lr,en~ is defi.llcd as any pi~m~n~ wi~h a l~Lracti~e in~ex ~Jr~a~er ~:hclr) 1.5 ~nd ~re~elc~ r is ~hite in color. Ho~evcr, sinc~ ~leStlle~iC COnSiClCratiOJlS are met by a mixturc of lcss cos~ly pig~ents havinc3 ~ refrac~ive ind~
c3reatcr than 1.5 bu~ l~ss than 1.9 ~ h more costly pig..ents having a refrac~ive index ahove 1.9, it i`s preferred that th~
opaque pl~ment in the permeahle layer of our invention com?rise a mi~:ture of ~tanium dioxide and kaolin clay.
In addition to the blnder and opa~ue pigment, ot~er constituents may also be employed ~.~ our permeable layer. .~.s will be described in more detail ~elo~, the binder and pigment of the permeable layer are preferably first slurried in ater ~:
and applied as a slurry to the paper substrate. In order to ; aid dispersion of the suspended pigment particles in the slur~t, tetra sodium pyrophosphate, sodium hexametaphosphate, or com~ercial anionic pol.yelectrolytes such as Tamol 850, produced by Roh~ and Haas, Dispex ~-40 produced by Allied Colloi~s, ~um~erlll pro~uced by Colloids, Inc., or Daxad 30 produced by l~. R. Grace Co~ may be employed.* The preferred dispersants are dispersin~ agents such as tetra sodium p~rophosphate and Tamol 850, a sodium salt of a carboxy~a~ed polyelectrolyte, or mi~tures thereof. The amount of dispersant may be varied id~ly, but is preferably about 0.1 to 0.17~ by weight of ~he ~icJmen~
Once thç slurr~t is applied to the paperboard substrate it,is o~ten desired to meter ofE excess coating ~ith applic2tion equipment. In order to retain enough water within the coating ~:
film during thc time lnterval between applica~ion ancl meterinc;
o~f and to pre~rent coating strea~s durinc3 met~xincJ o~f, ~e preer ~;~
.3~ to ada to the slurry s~all a~ounts o~ viscosit~ con~rol agcnts .
, * Tamol 850, Dispex N-40, and Daxad 30 are Trac~emarks. Each comprises a sodium salt of a polymeric carboxylic acid.
8. : .
such as sodium a]cJinate. Otller viscosi~y con~rol agcnts tha~
may be used for ~is purpose include sodiwn c?rboxymethyl cellulose, sodium polyacylate emulsions, and hydroxyethyl cellulose. Again, the amount of viscosity control agent may be varied widely, but the amount is preferably bet~een about 0.2 to 0.4~ by wei~ht of the pigment.
As will be described in more detail below, after the desired amount of permeable layer has been applied to the paperboard substrate,the composite is dried and preferably calendered and gloss calendered. In order that the composite may be more easily calendered, it is desirable to enhance the plasticity and slipperiness of the applied permeable layer.
To accomplish this end, small amounts of a lubricant, e.g., calci~n stearate,are preferably added to the coating slurry. ~ ~ ~
Other well Xnown lubricants, which may replace calcium -~
stearate, ~r ~Ihole or in part, include polyo~:ethy1z'ed ~thers, zinc stearate, alkoxylated triols, polyethylene emulsion, poly-oxyethylene ethex, ammonium stearate, polyalkylene glycol `-deriva~ives and mixtures thereof. The amount of lubricant may be varie~ widely, but preferably is between about 0.1 ~ -and 2% by weigh~ of the pi~nent.
It may sometimes ~e desired to print with ink the pe~neable layer of our invention. As is appreciated ~y those ;
skilled in the art, many offset printing inks require longer dryin~ times on acid coacings than on alkaline Goatings.
However, 1~ the coating is too alkaline, good ink coverage may be impeded under certain ofset printing condi~ions. It is thereore broadly preferred that the pH of layer 13 be between 7.0 and 10.5 at room temperature. The pref~rred pH range is 8.5 ~o 9.2,wit~ 9.0 belng the most preerred p~. To establish , `~ - .
.. : , ' ~
~:........ . . ~ . . . . . . . ..
- . - . . .
the preferred pH values it is sometimes required that an alkaline material be added to the ~ater slurry of permeable layer material in amounts suE~icient to raise the pH to the range of 7.0 to 10.5. The preferred alkaline material is ammonium hydroxide, but sodium or potassium hydroxide can also be used.
The concentration of the constituents and the thick-ness of the applied permeable layer may be varied widely by those skilled in the art for the same reasons that the same parameters can be widely varied ~or the impermeable lay~r.
The permeable layer preferably is applied to the substrate layer 12 at a loading of from 8 lbs. to 30 lbs. per 3000 sq.ft.
and more preferably is from 17 lbs. to 23 lbs. per 3000 sq.ft.
Further, the amounts of constituents by weight are preferably varied as shown in Tables 1 to 5 below:
Table 1 Component broad narrow preferred range range amount Opa~ue pigment 100 100 100 Permeable binder 10-30 18-22 20 Table 2 Component broad narrow preerred range range amount Titanium dioxide 15-80 30-50 45 Kaolin clay 20-85 50-70 55 Polyvinyl acetate 10-30 18-22 20 Table 3 Component broad narrow preferred range range amount Opaque pigment 100 100 100 Permeable binder 12-30 18-22 20 Viscosity control agent .05-.5 .2-.4 .33 Dispersant .02-.30 .10-.17 .14 Lubrlcant 0-3.0 .5-1.5 1.0 10. , , , rrab:Le 4 Component broad narrow pre~erred ranye range amount Titanium dioxide 15-80 30-50 45 Kaolin clay 20-85 50-70 55 polyvinyl acetate 12-30 18-22 20 viscosity control agent .05-.5 .2-.4 0.33 Dispersant .02-.30 .10-.17 .14 Lubricant 0-3.0 .5-1.5 .1.0 Table 5 Component broad narrow preferred range range amount Titanium dioxide 15-80 30-50 45 Kaolin clay 20-85 50-70 55 ~ :
Polyvinyl acetate 12-30 18-44 20 ~.
Sodium alginate .05-.5 .2-.4 0.33 . :
Tamol 850 .01-.15 .. 07-.11 0:09 Tetra sodium pyro- .01-.15 .03-.07 0.05 phosphate Calcium stearate 0-3 ,5-1.5 1.0 .
Alkali In amounts as needed to maintain pH of water slurry. .
One way of defining layers 11 and 13 of our paperboard ~
product is by measuring the brightness of the heat resistant . ;
paperboard product upon exposuxe to heat. The brightness of the heat resistant paperboard products.of our invention have been measured with a General Electric Brightness Meter by conventional .. ~ .
technique after heating two inch squares in a conventional oven at 400F. for 30 minutes. We have found that the side coated .`
with the permeable layer maintained a brightness above 70% and preferably above 75% while samples of uncoated paperboard main~
tained a brightness of below 50% under similar conditions. The side coated with the impermeable layer maintained a brightness above 50% while samples with conventional polyethylene or poly- :
propylene polymer coatings maintained a brightness below 30%. ~:
11. ~
;
Referrin~J no~J to Fi~ th~re is shown a schematic flow sheet of the preferred proccss by ~hich the permeable layer 13 is affixed to the paperboard substrate. As shown in Fig. 2 a suhstrate of paper is supplied to a first coating station 21 via roller 22. At the first coating station an aqueous slurry of the water permeable coating is applied to the paper substrate by conventional means such as puddle coater 23. Other conventional means by which the aqueous slurry of water permeable coating may be applied include flooded nip trailing blade coaters, rod coaters, reverse roll coaters, Massey coaters, air knife coaters and Chamflex coaters.
In order to minimize drying costs!the amount of water in the slurry is desirably maintained at the minimum amount required to maintain the mixture as a slurry. While the amount of water will vary somewhat depending on the water permeable coating formulation and application method,it is generally preferred to employ about 0.54 to l.0 parts by weight water per l part by weighk of water permeable coating mixture. In practice, the water permeable coating mixture is dispersed in water in an agitated tan~.
After the wet coating is applied to the paper substrate in first coating station 21, the applied water must be evaporated therefrom. As shown 1n Fig. 2, this is accomplished by passing the coated paperboard substrate via roller 24 through infra red driex 26 and then via roller 25 through two hot air driers 27 and 28 in series. It will be appreciated, however, that any type of dri~r or combination of driers may be employed and that the arrangement shown in Fig. 2 is for purposes of illustration only.
The temperatures and forced air velocities in the 12, .
,, , -:. : , . ,: :
lS18~1~
driers are maintaine~ to remove wa-t~r added t~ the paperboard substrate by the coating slurry and to obtain a product with a moisture level of 3% to 10~ water by weight.
Next, in our preferred embodiment, the coating process is repeated by passing the once coated paperboard substrate through a second coating station 31 containing a second puddle coater 33. After coating, the twice coated substrate is passed through a second drying system which, for purposes of illustr~tion, is shown as infra-red drier 35 fed b~ roller 34 and two hot air driers 37 and 38 in series fed -by roller 36.
Again the t~mperatures and forced air velocities in the driers are maintained to remove water added to the paper~
board substrate by the coating slurry and to obtain a product with a moisture level between 3% and 10~ water by weight.
Two coating stations are employed in the preferred process since at times it is difficult to control the thicker wet coating which would be required if only a single stage were employed. However, it is to be understood that the permeable layer 13 may be applied in any number of stages.
After the second coating has been dried, the coated substrate may optionally be passed via roIl~~44 to 46 to a --conventional gloss calender 39 wherein by application of pressure and heat, e.g., 200 to 350F. and preferably 250-300F., the coated product is glossed by the smooth polished surface of the gloss calender. Finally, the glossed coated paper substrate is optionally passed through a conventional calender stack 30 wherein through pressure imposed by opposing cylinders the product is smoothed and ~;
maintained at uniform thickness.
Referrin~ now to E g.3, there is shown a schematic flow ;'': ' - - ., . .. : . , , : ~, -sheet of the prcferred E~rocess for affixing th~ impermeable layer 11 to the paperboard substrate. It is preferred that the paperboard substrate supplied via supply roll 50 and roll 51 be already coated on one side with permeable layer 13.
The reason for this is that we prefer to produce the paper substrate in combination with coating the substrate with the permeable layer. Thus, the substrate introduced via rol~ 22 in Fig. 2 comes directly from the paper machine for producing the paper substrate. It is to be understood, however, that there is nothing critical in the order of coating and that the impermeable layer may be applied prior to the application of the permeable layer.
The polymer-pigment mixture which is used for the impermeable layer is preferably blended and then pelletized by the polymer manufacturer. Alternatively, a polymer-pigment concentrate is prepared by the polymer manufacturer or a processor and then the concentrate pellets are blended with "
natural polymer pellets to produce the impermeable mixturé.
The impermeable layer mixture is preferably applied to the paperboard substrate by a conventional process such as extrusion coating~ Referring again to Fig. 3 there is shown extruder 52 with die 53 arranged and constructed so that the impermeable layer mixture is applied by ex~rusion coating onto the paperboard substrate and is then passed through pressure roll 54 and chill roll 55. For a polytetramethylene terephthalate-titanium dioxide mixture, the chill roll is preferably maintained at about 60F. to 100F. The functions of the chill roll are: (1) to form a nip with the pressure roll for joining the paperboard substrate and the molten polymer layer under pressure~ (2) to remove heat from the ~t~ 3 L~
impermeable layer and l:he paperhoard substrate, and (3) to impart the desired surface finish to the impermeable layer.
Preferably the nip pressure applied to the coated substrate by chill roll 55 and pressure roll 5~ is about 50 to 350 lb.
per linear inch of web width. Finally, the heat resistant board product is passed from the chill roll 55 via roll 56 to storage roll 57.
The following example is provided to further illustrate the invention.
Example A mixture was prepared by dispersing into 77 parts water, 0.14 parts Tamol 850, 0.06 parts ~etra sodium pryophos-phate, 45 parts titanium dioxide, 55 parts Kaolin clay, 1 part calcium stearate, 20 parts polyvinyl acetate, a sufficient ~ ~
amount of alkali to maintain the pH at ~.0, and 0.29 parts sodium alginate, all parts by weight. The dispersed mixture ;~
was then applied to .015 inch thick bleached sulfate paper- ;
board in two stages to obtain a permeable layer coated onto ~-the paper in the amount of 20.9 lbs. per 3000 sq. ft. About equal amounts of coating were applied in each stage.
Next, the paperboard substrate was extrusion coated on its other side as described above in connection with Fig. 3, with a polymer mixture of 92 5 parts by weight polytetramethylene tere.phthalate and 7.5 parts by weight titanium dioxide. The thickness of the applied coating was 0.001 inches, the tempera-ture o~ the chill roll was 70F., and the applied pressure was lS0 pounds per lineal inch of web width. ~-~
The resulting coated product could be formed into ~ -containers for food by conventional techniques and was ' ' : . ; ~ ,, impermeable ~o water and grease on one side ~ut yet permeable to water on the other side. The initial G.E. brightness was 88.6% on the permeable side and 84.2~ on the impermeable side, while the average G.E. brightness after heating a two inch square piece of coated product at 400F. for 30 minutes was 77.1% on the permeable side and 55Ø% on the impermeable side.
From the above example, it is apparent that there are obtained coated paperboard substrates which may be formed into containers for food by conventional techniques. The resulting containers are impermeable to food constituents on the inside surface thereo. Further, the containers do n~t blister or explode but do retain their brig.htness upon heating. It is to be understood, however, that while the invention has been described with respect to preferred embodiments, variations and equivalents thereof may be perceived by those skilled in the art while nevertheless not departing from the scope of our invention as described by the claims appended hereto.
, ,::
' 16.
'~. '
Claims (18)
1. A paperboard product comprising:
a) a paperboard substrate having affixed to its first surface a water impermeable layer, said water impermeable layer com-prising a binder with opaque pigment dispersed therein; and b) a continuous water permeable layer affixed to the second surface of said paperboard substrate, said water permeable layer com-prising a binder with opaque pigment dis-persed therein, said paperboard product characterized by the facts that i) it retains a brightness of at least 70% on its permeable side and at least 50% on its impermeable side after exposure to 400°F. for 30 minutes, and ii) it will not puff or blister when placed in an oven heated to 350°F. for 15 minutes.
a) a paperboard substrate having affixed to its first surface a water impermeable layer, said water impermeable layer com-prising a binder with opaque pigment dispersed therein; and b) a continuous water permeable layer affixed to the second surface of said paperboard substrate, said water permeable layer com-prising a binder with opaque pigment dis-persed therein, said paperboard product characterized by the facts that i) it retains a brightness of at least 70% on its permeable side and at least 50% on its impermeable side after exposure to 400°F. for 30 minutes, and ii) it will not puff or blister when placed in an oven heated to 350°F. for 15 minutes.
2. The product of claim 1 wherein the pigment in the impermeable layer comprises titanium dioxide.
3. The product of claim 1 wherein the pigment in the permeable layer comprises a mixture of titanium dioxide and kaolin clay.
4. The product of claim 1 wherein the impermeable layer binder comprises polytetramethylene terephthalate, poly-cyclohexalene dimethylene terephthalate or polycyclohexalene dimethylene terephthalate-phthalic acid copolymer.
5. The product of claim 4 wherein the permeable layer binder comprises polyvinyl acetate.
17.
17.
6. The product of claim 1 wherein the impermeable layer comprises from about 2.5% to about 20% by weight titanium dioxide and the permeable layer comprises about 15 to 80 parts by weight titanium dioxide, about 20 to 85 parts by weight kaolin clay and about 10 to 30 parts by weight polyvinyl acetate.
7. The product of claim 1 wherein the water impermeable layer is also grease impermeable.
8. The product of claim 1 wherein the product has a water content of about 3% to about 10% by weight.
9. A paperboard container for cooking food comprising a coated paperboard substrate formed into the shape of a container, said container comprising:
a) an inside surface comprising a water impermeable layer affixed to said paperboard substrate, said water impermeable layer com-prising a binder with opaque pigment dispersed therein; and b) an outside surface comprising a continuous water permeable layer affixed to said paper-board substrate, said water permeable layer comprising a binder with opaque pigment dis-persed therein, said paperboard container being characterized by the facts that i) it retains a brightness of at least 70% on its permeable side and at least 50% on its im-permeable side after exposure to 400°F. for 30 minutes; and ii) it will not puff or blister when placed in an oven heated to 350°F. for 15 minutes.
18.
a) an inside surface comprising a water impermeable layer affixed to said paperboard substrate, said water impermeable layer com-prising a binder with opaque pigment dispersed therein; and b) an outside surface comprising a continuous water permeable layer affixed to said paper-board substrate, said water permeable layer comprising a binder with opaque pigment dis-persed therein, said paperboard container being characterized by the facts that i) it retains a brightness of at least 70% on its permeable side and at least 50% on its im-permeable side after exposure to 400°F. for 30 minutes; and ii) it will not puff or blister when placed in an oven heated to 350°F. for 15 minutes.
18.
10. A paperboard container for cooking food comprising a coated paperboard substrate formed into the shape of a container, said container comprising:
a) an inside surface comprising a water and grease impermeable layer affixed to said paperboard substrate, said water and grease impermeable layer comprising a binder with opaque white pigment dispersed therein;
and b) an outside surface comprising a continuous water permeable layer affixed to said paper-board substrate, said water permeable layer comprising a binder with opaque white pigment dispersed therein, said paperboard container being characterized by the facts that i) it retains a brightness of at least 70% on its permeable side and at least 50% on its im-permeable side after exposure to 400°F. for 30 minutes; and ii) it will not puff or blister when placed in an oven heated to 350°F. for 15 minutes.
a) an inside surface comprising a water and grease impermeable layer affixed to said paperboard substrate, said water and grease impermeable layer comprising a binder with opaque white pigment dispersed therein;
and b) an outside surface comprising a continuous water permeable layer affixed to said paper-board substrate, said water permeable layer comprising a binder with opaque white pigment dispersed therein, said paperboard container being characterized by the facts that i) it retains a brightness of at least 70% on its permeable side and at least 50% on its im-permeable side after exposure to 400°F. for 30 minutes; and ii) it will not puff or blister when placed in an oven heated to 350°F. for 15 minutes.
11. The container of claim 10 wherein the impermeable layer comprises titanium dioxide and polytetramethylene terephtha-late and the permeable layer comprises polyvinyl acetate, titanium dioxide and kaolin clay.
12. The container of claim 10 wherein the container has a water content of about 3% to about 10% by weight.
13. A process for cooking food in a paperboard con-tainer comprising heating food in the container defined by claim 9.
19.
19.
14. A process for producing a paperboard product comprising:
a) affixing a continuous water permeable layer comprising a mixture of binder and opaque pigment to a first surface of a paperboard substrate; and b) affixing a water impermeable layer comprising a binder and opaque pigment to a second surface of said paperboard substrate.
a) affixing a continuous water permeable layer comprising a mixture of binder and opaque pigment to a first surface of a paperboard substrate; and b) affixing a water impermeable layer comprising a binder and opaque pigment to a second surface of said paperboard substrate.
15. The process of claim 14 wherein the water im-permeable layer is affixed onto the second surface of the paper substrate by extruding the impermeable mixture onto the second surface and then chilling the coated substrate to harden and set the impermeable layer extruded thereon.
16. The process of claim 14 wherein the permeable layer is affixed to the paperboard substrate by first coating an aqueous slurry of the permeable layer onto the paperboard sub-strate and then drying the coated substrate.
17. The process of claim 16 wherein after the permeable layer is dried a second coating of aqueous slurry is coated onto the once coated substrate and subsequently dried.
20.
20.
18. The process of claim 14 wherein the permeable layers and impermeable layers are applied to the paperboard substrate so that the resulting product is characterized by the facts that: (a) it retains a brightness of at least 70%
on its permeable side and at least 50% on its impermeable side after exposure to 400° F. for 30 minutes, and (b) it will not puff or blister when placed in an oven heated to 350° F. for 15 minutes.
on its permeable side and at least 50% on its impermeable side after exposure to 400° F. for 30 minutes, and (b) it will not puff or blister when placed in an oven heated to 350° F. for 15 minutes.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US61044875A | 1975-09-04 | 1975-09-04 | |
| US610,448 | 1984-05-15 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1088816A true CA1088816A (en) | 1980-11-04 |
Family
ID=24445050
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA238,778A Expired CA1088816A (en) | 1975-09-04 | 1975-10-31 | Heat resistant paperboard product |
Country Status (7)
| Country | Link |
|---|---|
| JP (1) | JPS5234009A (en) |
| CA (1) | CA1088816A (en) |
| DE (1) | DE2626656A1 (en) |
| FR (1) | FR2322974A1 (en) |
| GB (1) | GB1546607A (en) |
| NL (1) | NL7606410A (en) |
| SE (1) | SE7606747L (en) |
Families Citing this family (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| ZA803457B (en) * | 1979-08-28 | 1981-06-24 | Keyes Fibre Co | Contoured molded pulp container with polyester liner |
| US4335181A (en) * | 1980-07-01 | 1982-06-15 | Mobil Oil Corporation | Microwaveable heat and grease resistant containers |
| DE3206341A1 (en) * | 1982-02-22 | 1983-09-01 | Compagnie Française de Raffinage S.A., Paris | Container, in particular for receiving milk or other foodstuffs |
| JPS6228772U (en) * | 1985-08-01 | 1987-02-21 | ||
| US7265176B2 (en) * | 2005-01-31 | 2007-09-04 | E. I. Du Pont De Nemours And Company | Composition comprising nanoparticle TiO2 and ethylene copolymer |
| DE602005004645T2 (en) | 2005-02-04 | 2009-01-29 | E.I. Dupont De Nemours And Co., Wilmington | Compositions comprising fluorocarbon-grafted polysiloxanes |
| WO2007002896A2 (en) * | 2005-06-29 | 2007-01-04 | Graphic Packaging International, Inc. | Packaging material for food items containing permeating oils |
| US8753012B2 (en) | 2006-06-29 | 2014-06-17 | Graphic Flexible Packaging, Llc | High strength packages and packaging materials |
| EP2032358A2 (en) * | 2006-06-29 | 2009-03-11 | Graphic Packaging International, Inc. | Packaging material for food items containing permeating oils |
| US8826959B2 (en) | 2006-06-29 | 2014-09-09 | Graphic Packaging International, Inc. | Heat sealing systems and methods, and related articles and materials |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2889299A (en) * | 1957-07-19 | 1959-06-02 | American Cyanamid Co | Grease resistant cellulosic webs coated with a linear anionic thermoplastic ethyl acrylate-acrylonitrile-methacrylic acid polymer containing a hydrophilic inorganic pigment as extender and composition for manufacture thereof |
| GB1386635A (en) * | 1972-05-19 | 1975-03-12 | Mardon Son Hall Ltd | Disposable heating containers |
| US3863832A (en) * | 1972-12-20 | 1975-02-04 | Int Paper Co | Food container |
-
1975
- 1975-10-31 CA CA238,778A patent/CA1088816A/en not_active Expired
-
1976
- 1976-05-13 GB GB19728/76A patent/GB1546607A/en not_active Expired
- 1976-06-10 JP JP51068186A patent/JPS5234009A/en active Pending
- 1976-06-14 NL NL7606410A patent/NL7606410A/en not_active Application Discontinuation
- 1976-06-14 SE SE7606747A patent/SE7606747L/en unknown
- 1976-06-15 DE DE19762626656 patent/DE2626656A1/en not_active Ceased
- 1976-06-15 FR FR7618137A patent/FR2322974A1/en active Granted
Also Published As
| Publication number | Publication date |
|---|---|
| SE7606747L (en) | 1977-03-05 |
| DE2626656A1 (en) | 1977-03-17 |
| FR2322974A1 (en) | 1977-04-01 |
| GB1546607A (en) | 1979-05-23 |
| NL7606410A (en) | 1977-03-08 |
| FR2322974B1 (en) | 1982-08-06 |
| JPS5234009A (en) | 1977-03-15 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |