Ovenable coated paperboard

Details Ovenable coated paperboard Ovenable coated paperboard

2000-02-25

2001-09-18

Thomas, Alexander S. (Department: 1772)

Stock material or miscellaneous articles

Composite

Of silicon containing

C428S513000

Reexamination Certificate

active

06291075

ABSTRACT:

FIELD OF INVENTION
This invention relates to ovenable and dual-ovenable coated paperboard suitable for use in producing food trays. More particularly, the invention relates to paperboard substrates which have been coated with a water-based release coating composition. Food trays made from such paperboard have superior grease resistance, high temperature resistance, and excellent food release properties—characteristics which make these trays particularly suitable for use in baking applications.
BACKGROUND OF THE INVENTION
It has become a common practice to package convenience foods in disposable cooking or heating utensils made of coated paperboard. Due to the increased popularity of microwave cooking, substantial efforts have been made to provide dual-ovenable containers which are suitable for both conventional oven and microwave oven cooking. Accordingly, a number of polymeric plastic paperboard coatings have been developed to protect paperboard containers and their contents from the temperature extremes associated with cold storage and heating. For example, U.S. Pat. No. 3,813,256 discloses food heating utensils made of paperboard coated with polyphenylene oxide or polysulfones. The use of paperboard products coated with polypropylene or polyester are disclosed in U.S. Pat. Nos. 3,904,104 and 4,147,836. U.S. Pat. No. 4,421,825 discloses the use of titanium dioxide in coatings to give the paperboard resistance to browning.
There is a growing market demand for disposable paperboard for use in baking applications with food products such as cinnamon rolls, biscuits, and the like. However, these foods have proven to be difficult to successfully package in that they have a tendency to stick to the paperboard when baked. As sugar tends to caramelize upon heating, this adherence problem is particularly pronounced in those cases where the packaged food contains high levels of sugar.
Dual-ovenable food trays are disclosed in U.S. Pat. No. 5,494,716; while U.S. Pat. No. 5,002,833 discloses polymethylpentene (PMP) extusion-coated paperboard of the type currently utilized for ovenable baking applications. Although PMP paperboard can exhibit good grease resistance, heat resistance, and food release characteristics, the high material and processing costs associated with PMP paperboard makes this type of coated paperboard relatively expensive to use. Moreover, PMP paperboard may prove to be somewhat difficult to recycle.
Therefore, an object of this invention is to provide ovenable paperboard suitable for use in producing food trays for baking applications.
A further object of this invention is to solve the baking product adherence problem by providing ovenable coated paperboard which exhibits good grease resistance, high heat resistance and good food release characteristics.
Yet another object of this invention is to provide a dual-ovenable food tray coated with an aqueous coating composition that performs without grease seepage, browning, and emission of odors during cooking.
Additional objects, advantages, and novel features of the invention will be set forth in part in the description which follows.
SUMMARY OF THE INVENTION
These and other objects of the invention, as embodied and broadly described herein, are met by coating a paperboard substrate with an aqueous coating composition comprising at least one styrene-acrylic latex copolymer, a stearate, and, optionally, silicone.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The present invention relates to ovenable and dual-ovenable coated paperboard having good grease resistance, high heat resistance and good food release characteristics. More particularly, the present invention relates to an aqueous coating composition and its use in the fabrication of ovenable and dual-ovenable food trays. The aqueous coating composition may be applied to any conventional substrate, but preferably to a paperboard substrate. The aqueous coating composition may also be applied to the surface of other coatings.
Ovenable and dual-ovenable food trays suitable for use in the present invention comprise a paperboard substrate which is coated on at least one side thereof with an aqueous coating composition comprising:
A) from about 20 to about 50 wt. % (based on the total weight of the solids in the coating composition or BOS) of a member selected from the group consisting of the styrene-acrylic latex copolymer addition polymerization reaction products of
1) from about 60 to about 90 wt. % (based on the total weight of the polymer or BOP) of at least one nonionic free radical polymerizable monomer,
2) up to about 5 wt. % BOP of at least one acidic free radical polymerizable monomer, and
3) from about 40 to about 10 wt. % BOP of at least one alkali-soluble stabilizing resin having an acid number of at least 150 mg KOH/g, wherein said reaction products have a glass transition temperature in the range of from about −40° C. to about 10° C., and combinations thereof;
B) from about 80 to about 50 wt. % BOS of a member selected from the group consisting of calcium stearate, zinc stearate, and combinations thereof;
C) up to about 5 wt. % BOS of silicone; and
D) water.
Preferred aqueous coating compositions suitable for use in the present invention comprise those having:
A) from about 20 to about 50 wt. % BOS of a member selected from the group consisting of the styrene-acrylic latex copolymer addition polymerization reaction products of
1) from about 70 to about 80 wt. % BOP of at least one nonionic free radical polymerizable monomer,
2) up to about 5 wt. % BOP of at least one acidic free radical polymerizable monomer, and
3) from about 30 to about 20 wt. % BOP of at least one alkali-soluble stabilizing resin having an acid number of at least 150 mg KOH/g, wherein said reaction products have a glass transition temperature in the range of from about −40° C. to about 10° C., and combinations thereof;
B) from about 80 to about 50 wt. % BOS of a member selected from the group consisting of calcium stearate, zinc stearate, and combinations thereof;
C) up to about 5 wt. % BOS of silicone; and
D) water.
If desired, the aqueous coating compositions may contain one or more adjuvants for improving the physical and/or mechanical properties of the food trays on which the compositions are applied. Suitable adjuvants include, for example, thickening agents, coalescent solvents (such as polyols), defoaming/dispersing agents, and agents for improving other properties of the coated food trays. Other additives (such as aqueous ammonia) can be added to adjust the pH of the coating compositions.
The aqueous coating composition may also be employed as the top coating or food contact layer on multi-layer coated paperboard. That is, one or more coatings may be layered between the paperboard substrate and the present aqueous coating composition to impart desired characteristics to the food tray.
The styrene-acrylic latex copolymer should have a glass transition temperature (T
g
) of between about −40° C. and about 10° C.; with the preferred T
g
range being between about −20° C. and about 5° C.
Monomers which are suitable for use in the present invention include ethylenically unsaturated monomers such as olefins, monovinylaromatics, alpha, beta-ethylenically unsaturated carboxylic acids and esters thereof, ethylenically unsaturated dicarboxylic anhydrides (or acids) and esters thereof, and halo substituted olefmics. Specific examples of these monomers include, but are not limited to, the following: styrene, alpha-methylstyrene, acrylic acid, methacrylic acid, methyl methacrylate, butyl methacrylate, butyl acrylate, 2-ethylhexl acrylate, ethyl acrylate, hydroxyethyl acrylate, hydroxyethyl methacrylate, isobutyl methacrylate, itaconic acid, and combinations thereof. It is further preferred that the styrene-acrylic latex copolymer contain nonionic (meth)acrylate monomers. It is also further preferred that the alkali-soluble stabilizing resin be a styrene/maleic anhydride copolymer.
Addition polymerization reactions are well-known to those skilled in the art. The type of free-r

Affiliated with

Also associated with

Rating

Ovenable coated paperboard does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Ovenable coated paperboard, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Ovenable coated paperboard will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2515690