JPH05280753A - Grease-absorbing pad and package for microwave cooking - Google Patents

Abstract

PURPOSE: To provide a pad which absorbs sufficiently liquefied grease, generated upon cooking a food stuff in a microwave oven, but which does not absorb moisture. CONSTITUTION: A pad 14, used by putting a food thereon upon cooking a piece of food 12 containing solidified grease, molten when the food is cooked by the irradiation of microwave, includes at least a web, formed of a mutli-layered micro-fiber having hydrophobic property and grease absorbing property, while the web forms an integrated flow, laminated together with at least two flows of fluidized materials. In this case, the integrated flow is extruded through a dye 40, having at least one set of orifice 41, while the extruded flow is changed into fine fibers by high-speed gas for manufacturing the fiber by forming the web, entangled after collecting the fibers on a collecting surface 49.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to an oil-absorptive pad for use in a microwave oven for cooking foods containing a large number of solidified grease and water, and such pad and cooking purpose. For packages containing food products sealed therein for.

[0002]

Foods containing large amounts of water and solidified fats and oils, especially precooked and hardened foods such as bacon, sausage, ham or bolognese, are
It can cause problems when cooked in the wave.
The water in such foods evaporates by contact with the heated and melted fats and oils as the food is cooked,
A small rupture occurs, which causes a piece of oil to splash around the oven. Furthermore, when food is cooked by microwave irradiation, the solidified fats and oils melt.
One attempt at addressing such concerns has been to place the food on a pan that collects the molten fat and cover the food with multiple layers of paper towels to limit spatter.

It is known to place a liquid absorbent pad within a package for absorbing food byproducts such as oils and moisture that exude from food during cooking in a microwave oven. Such pads must not only absorb enough of the food by-products produced during cooking, but also decompose to the elevated temperatures required to properly cook precooked or hardened food. Must endure without.

However, conventional absorbent pads absorb both water and various fats and oils from food products. This is not desirable. This is because if the portion of the absorption capacity of the pad is occupied by water, insufficient capacity will remain due to oil and fat. Alternatively, the pad capacitance must be increased by increasing the pad size and weight, which is more expensive.

[0005] In many cases, keeping the water that exudes from the food in the form of steam during cooking in the immediate vicinity of the food evenly distributes the heat within the package and reduces the cooking time for the food. Is also desirable. Further problems arise during long-term storage and shipping of packages containing food products with substantial amounts of water and fats. Pads that absorb water and grease will tend to gradually absorb water from food products. Therefore, the weight of the food is
It will be shown that the weight of the package is reduced compared to when it was sealed.

One attempt at addressing these concerns is Lar.
Son U.S. Pat. 4,865,854, which discloses a food package for a microwave oven for use in cooking a food containing a substantial amount of water and solidified fats and oils. The package includes a pad adjacent to the food product that is capable of retaining the total amount of oil and fat in the food product when it melts, formed from microwave permeable and generally hydrophobic, fat and oil absorbing microfibers. ..

The package further includes a pad and a vapor tight microwave permeable enclosure that encloses the food and has a vapor vent that opens while the food is being cooked. This patent is US Pat. 4,103,058 and N
o. Blown microfibres manufactured according to the teachings of 4,042,740.
from Bers; BMF), it teaches the manufacture of pads for said packages.

Pads formed as disclosed in the above-invented Larson patent have their own uses, but may be relatively expensive for purposes of commercial microwave food packaging. It is clear. Pads like this are entangled webs (ent
It is made from melt-blown microfibers formed in angled web). The polymer pellets were dry blended together to form a 50/50 mixture of polypropylene and poly 4-methylpentene-1 (a relatively expensive polymer). Polypropylene and poly 4-methylpentene-1 can be dry blended and extruded into useful products.

Therefore, it is used in a microwave oven package which has an increased oil absorption capacity, which reduces the pad size or thickness requirements and thereby the pad weight, and at the same time reduces manufacturing and material costs. It is desirable to develop a pad for doing this. In some applications, it is also desirable to bond a scrim or cover sheet of another material to the food-adjacent surface of the pad, and there is a need for a pad that readily maintains such bonding.

Furthermore, we have developed a fat absorbent pad for microwave food packaging from blends of polymeric materials that could not previously be blended by conventional extrusion techniques and still retain the increased absorbency and binding properties. It is desirable to produce satisfactorily blended microfibers and finished pad products for commercial use.

[0011]

SUMMARY OF THE INVENTION The present invention provides a fat absorbing pad for use in packaging food products to be cooked, for example in a microwave oven containing a substantial amount of water and solidified fat. The pad is generally formed from an intertwined web of multi-layer microfibers that are both hydrophobic and fat-absorbent.

In this web, at least two streams of fluent material are layered together to form one stream which is extruded through a die having at least one orifice, It is produced by refining the extruded stream with a high velocity gas stream to form fibers, and collecting the fibers on a collecting surface to form an entangled web. This pad can hold the total amount of fats and oils in the food when the fats and oils melt by cooking the food in a microwave oven.

In one embodiment, the pad is used in combination with a microwave food preparation package.
This package prevents oil and fat from scattering inside the microwave oven, and collects oil and fat during the cooking process.
It does not require special handling to prevent spills of oils and fats collected after food etc. has been cooked, and is easy to manufacture. According to the invention, a package for use in a microwave oven is a food product, especially a precooked or hardened food product containing a substantial amount of water and solidified fats (e.g. bacon, sausage, ham). , Or bollonia); a pad adjacent to a food product, comprising an entangled web of generally hydrophobic and fat-absorbent multilayer microfibers formed as described above; and surrounding the pad and the food product Vapor-tight
Tight) a microwave permeable enclosure.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Structure of the Package and Web of the Invention FIGS. 1-4 show a package of the food product of the invention that can be cooked in a microwave oven, which package is generally designated by the reference numeral 10. Shown. As best seen in FIGS. 1 and 2, the package 10 comprises a food product (eg, bacon pieces) 12 containing water and a substantial amount of solidified fat, and a pad 1 adjacent to the food product 12.
Including 4. The pad 14 is formed from a microwave-permeable, generally hydrophobic and fat-absorbing material capable of absorbing at least the entire amount of fats and oils in the food 12 when liquefied. Preferably, the pad comprises coextruded multi-layer blown microfibers produced according to the web-forming method described herein.

A generally rectangular vapor tight microwave permeable enclosure 16 surrounds the pad 14 and food 12 and heats the pad 14 and food 12 to provide a vapor tight seal 19 across the edges. With top and bottom rectangular sheets 17 and 18 of polymer film secured together by a seal. Providing suitable means for ventilating the enclosure 16 can facilitate the cooking of the food product 12 within the enclosure 16 in a microwave oven.

In one embodiment, as shown,
The ventilation means comprises a layer of microwave absorbent material in the form of a strip of metallized film 20 adhered by a suitable adhesive to a top sheet 17 of polymeric film forming enclosure 16. The vapor deposited film 20 and the portion of the top sheet 17 in contact therewith softens upon heating of the metal vapor deposited film to prevent flow or vapor pressure within enclosure 16 and / or contraction of films 17 and 18 during cooking of food 12 by microwave energy. Failure of the top sheet 16 of film and vapor deposited film 20 due to the difference will occur.

As illustrated in FIG. 3, the top sheet of film 17 and the vapor deposited film 20 leave excess vapor in enclosure 16 while leaving sufficient vapor in enclosure 16 to enhance the cooking of food product 12. It will allow the vapor pressure to diminish. In another aspect, the ventilation means is a weakened portion of the heat seal between the edges of the enclosure, which is due to the generation of flow or vapor pressure in the enclosure as the food is cooked (in a controlled manner). Tear, which controls the cooking and pressure of the food in the enclosure.

Package 10 also includes cooked food 1
It has a structure for easily opening the enclosure 16 by hand to facilitate the taking out of 2. Seal 1 between face-to-face layers of polymer film near edges 24 or corners of package 10.
A substantial distance between a portion of 9 and the edge 24 (ie,
3 cm or more, and preferably about 6 cm) is placed on the edge 2
Top and bottom sheets 17 and 1 of the film adjacent 4
8 is peeled off by pulling it by hand. This unpacking can be done without pushing the package 10 so that hot steam can be forced out of the package 10 through the ventilation openings formed in the vapor deposited film 20 as the package is opened. Absent.

Preferably, the pad material has about the same surface area as the food product supported on the pad. Therefore,
The pad can completely absorb or retain all the fats and oils contained in the food so that the enclosure and the pad do not drain the fat or oil even if the opening through which the food is taken out is in the lowest part of the enclosure (food After being cooked and removed from the enclosure). It has been found that a pad capable of holding at least 1-2 g of fat per square inch of surface area is suitable for packaging conventional bacon pieces.

FIG. 2 illustrates a pad selected to have approximately the same size and surface area as the food product it overlies. During cooking, some food products shrink in size (eg bacon pieces). FIG. 5 shows a pad 14a having a smaller surface dimension than the food product 12a placed thereon. Pad 14a
May have a smaller surface area than the food product, as long as it has sufficient oil absorption capacity to absorb oils that liquefy during cooking of the food product 12a. Such pads would need to be thicker to compensate for the smaller surface area.

According to one preferred embodiment, the pads are designed for use within enclosure 16 to form package 10, as shown in FIGS. 1-4, although such pads are generally hydrophobic. The lipophilic pad can also be used alone in a microwave oven for food cooking purposes. That is, the food is placed on the pad and a preformed vapor tight enclosure is not used.

The pad and food are placed in a pan or container (eg, designated by reference numeral 26 in FIG. 5) for holding liquefied fats and oils as the food is cooked and for handling the food after it is cooked. Is placed. The container may or may not include a lid or cover (e.g., indicated by reference numeral 28 in Figure 5) for containing spattered food during the cooking process.

Method of Forming Web As described above, the pad is formed of, for example, Wente, Van.
A. , "Superfine Thermoplast
ic Fibers ", IndustrialEngine
neering Chemistry , Vol. 48,
1342-1346 and Went, Van A .; Et al. "Manufacture of Superfine"
Organic Fibers ", Report N
o. 4364 the Naval Research
Laboratories (issued May 25, 1954), and US Pat. 3,849,241 (Bu
tin et al., No. 3,825,379 (Lohkam
p.), No. 4,818,463 (Buehnin
g), No. 4,986,743 (Buehing),
No. 4,295,809 (Mikami et al.) Or N
o. 4,375,718 (Wadsuorth et al.) Made of blown microfibers produced by a method that uses in part the device. These devices and methods are useful in the method of the present invention, in the portion shown schematically as die 6 in FIG. 6, which may be of any of these conventional designs.

Each microfiber is formed from two or more separate polymeric material components. The polymer components are introduced from a separate splitter, splitter area or mixing manifold 30 into the die cavity 42 of the die 40, and 3
2 and 34, for example, introduced into the splitter from an extruder. Gear pumps and / or purge blocks can also be used to precisely control the polymer flow rate. In the splitter or mixing manifold, separate polymer component streams are formed into a single laminar flow.
However, preferably the separate streams are kept out of contact for as long as possible before reaching the die 40.

The separate polymer streams from the extruder can also be split in a splitter (30). The split or separate streams are combined only just before reaching the die or die orifice. This minimizes the possibility of flow instability occurring in the separate streams after being laminarized, which tends to result in non-uniform and discontinuous longitudinal layers in the multilayer microfiber. Flow instability can also adversely affect the properties of the nonwoven web, such as strength, temperature stability, or other favorable properties obtained by the method of the present invention.

The separate streams are preferably laminar along closely parallel flow channels. These streams are then preferably brought together, such that at the point of joining the individual streams are layered and the channels and the channels of the resulting layered layers are substantially parallel. This again minimizes separate flow turbulence and lateral flow instability during or after the combining step. Suitable splitters for the above step of combining separate streams are described, for example, in US Pat. No. 3,557,265, which describes a manifold in which two or three polymer components are brought into one multi-layer rectiline melt flow.

The polymer streams from the separate extruders are fed into a plenum and then into one of three variable series ports or orifices. The port of each series is in flow communication with one of the charging chambers. Thus, each stream is divided into a plurality of separate streams by one of a series of ports, each having a height to width ratio of about 0.01-1. Separate streams from each of the three charge chambers are then extruded into a single channel so that they are simultaneously intersected by 3 series of ports, resulting in a multi-layer flow.

The multilayer flow combined in the channels is then deformed (eg, in a coat hanger transfer piece) such that each layer extruded from the manifold die has a substantially smaller height to width ratio. However, one layered combined flow is provided at a die orifice to provide a height of about 50 mils or less, preferably 15 to 30 mils or less. Other suitable devices for providing multi-layer flow are described, for example, in US Pat. 3,924,990 (Sch
renk), No. 3,687,589 (Schren
k), No. 3,759,647 (Schrenk
, Or No. 4,197,069 (Cloere
n), all but Cloeren disclose manifolds that bring diverse polymer streams into a single multi-layered stream, the single multi-layered stream prior to the exit of the film die. Delivered normally through the coat hanger transfer piece or neck down zone.

The Cloeren method has separate flow channels in the die cavity. Each flow channel in turn comprises a back pressure cavity and a flow restriction cavity, each preferably defined by an adjacent vane. The adjustable vane arrangement allows fine adjustment of the relative layer thickness of the combined laminar flow. The multilayer polymer stream from this arrangement does not necessarily have to have the proper length / width ratio. Because this can be done by vanes, and the combined flow can be fed directly to the die cavity 42.

The multi-layer polymer stream is generally fed to the die cavity 42 as a unitary stream. However, it is also possible to keep the laminar flow separate in the die cavity 42 by using a separating plate that allows the separate polymer flows to be brought together just before reaching the die orifice.

From die cavity 42, the multilayer polymer stream is extruded through a row of side-by-side orifices 41.
As discussed previously, prior to this extrusion, a cavity 4 was suitably prepared using a conventional coat hanger transfer piece.
In 2, the feed can be shaped appropriately. Air holes 48 are located on either side of the row of orifices 41 for directing high velocity, uniformly heated air to the extruded layered melt stream. The air temperature is generally about the same as that of the melt stream, but is preferably 20-30 ° C above the melt temperature.

This high temperature, high velocity air blows off and extrudes the extruded polymeric material, which then dies 4
It solidifies after moving a relatively short distance from zero. The solidified or partially solidified fibers are then formed into webs by known methods and collected on a collecting surface such as rotating drum 50. The collecting surface can be a fill or perforated surface in the form of a drum (as shown), or a flat surface, a moving belt or the like. If a perforated surface is used, US Pat. 4,103,058 (H
The back surface of the assembly surface can be exposed to a vacuum or low pressure to assist the attachment of the fibers, as disclosed in Umlickk). This low pressure region allows the formation of a web having low density regions with pillows formed therein.

The assembly surface distance is generally 3 to 3 from the die tip.
It is 50 inches. At closer distances to the assembly surface, the fibers are collected with high velocity and still sticky due to incomplete cooling. This is especially the case for thermoplastic materials that are inherently tacky, such as thermoplastic elastomeric materials. By moving the collecting surface closer to the die tip, for example, 3-12 inches, a web with stronger interfiber bonding and less softness will be obtained. A later offset of the assembly surface (eg, 20 inches) will generally result in a softer and less cohesive web.

The temperature of the polymer in the splitter region is generally about the same as the temperature of the higher melting point component as it exits the extruder. The splitter region and manifold are typically die-toe and are maintained at the same temperature. The temperature of the separate polymer streams can also be adjusted to bring the polymer closer to a more suitable relative viscosity. When the separate polymer streams are concentrated, they are generally 150-800 poise, preferably 200-40.
It has an apparent viscosity of 0 poise (as measured by a capillary rheometer). The relative viscosities of the separate polymer streams to be concentrated should generally be an exact match.

Empirically, this changes the temperature of the melt, and the crossweb of the assembled webs.
b) It can be determined by observing the sex. As the cross-web property becomes more uniform, the viscosities match well. The overall viscosity of the layered and combined polymer stream at the die tip should be between 150 and 800 poise. The difference in relative viscosities is preferably generally the same as when the polymer streams were first combined. The apparent viscosity of the polymer stream is, in this respect, US Pat. 3,849,
It can be adjusted by changing the temperature as in 241.

The size of the polymer fibers depends to a large extent on the velocity and temperature of the refined air stream, the orifice diameter, the temperature of the melt stream, and the overall flow rate per orifice. At high air volume velocities, about 1 fiber is formed.
A web having an average fiber diameter of less than 0 micrometer, but with increasing air flow velocity, becomes more difficult to obtain.

However, at milder air velocities, the polymer has a larger average diameter, making the fibers more prone to clinging to what is called a "rope".
Needless to say, this depends on the polymer flow rate,
Polymer flow rates in the range of 5 to 0.5 cjm / min / orifice are generally suitable. Coarse fibers, for example up to 25 micrometers, can be used in certain situations, such as webs with large pores or rough webs.

The multi-layer microfibers formed by this method can be mixed with other fibers or particles before being collected. For example, US Pat. 3,9
71, 373 or No. Adsorbent particles or fibers can be incorporated into the agglomerated web of blown multilayer fibers as described in 4,429,001. In these patents, separate streams of melt-blown fibers are achieved, and these streams are interlaced prior to assembly of the fibers or fibers are introduced into the air stream and the air carrying the particles is loaded. Is then directed to the intersection of the two microfiber streams.

A method of introducing particles or fibers, such as staple fibers, extender fibers or binding fibers, along with the method of the present invention for forming melt-blown microfiber webs is described, for example, in US Pat. 4,
118,531, No. 4,429,001 or No.
4,755,178, wherein particles or fibers are fed into a single stream of melt-blown fibers.

Before, during, or after collecting the fibers, other materials such as surfactants or binders can be introduced into the web using, for example, a spray jet. When applied prior to collection, the material is sprayed onto a stream of microfibers (with or without added fibers or particles) moving towards the collection surface.

The web forming method and the microfiber formed by the method of the present invention are the basis of the following patent application filed on the same date as this application. (1) Novel materials and material properties from multiphase blown microfibers; (2) Stretchable nonwoven webs based on multilayer blown microfibers; (3) Improved modulus based on multilayer blown microfibers. (4) High temperature stable nonwoven web based on multilayer blown microfibers; (5) Film material based on multilayer blown microfibers; and (6) Multilayer blown microfiber based wipes. material. All of these are incorporated herein by reference.

The microfiber forming method described is
It provides webs with unique properties and characteristics when compared to webs formed from homogeneous polymer melts of single polymers or blends of polymers (compatible or incompatible). For example, FIG. 7 shows an electron micrograph of a 50/50 blend preparation of polypropylene (PP) and polymethylpentene (TPX). These polymers were "dry blended" in pellet form prior to extrusion. In other words, the polymer is blended and then the conventional dry-
Extruded through a single extrusion orifice in the blend extrusion method. The extruded fiber was formed into a web on the collecting surface as described above.

For the example of FIG. 7, a sample of blown microfiber was first 0.25 g of RuCl ₃ : H ₃ O powder dissolved in 10 ml of 5.25 aqueous sodium chloride solution.
The solution was dyed. Add each sample to this solution
It was immersed at room temperature (about 20 ° C.) for 2.5 hours. Each sample was then removed, rinsed with deionized water, and air dried on filter paper for 24 hours.

Next, each sample was obtained from Minnesota Mining and Manufacturing Company, using a microtome embedding mold, "Socc".
h-Cast ”brand electric resin No. Embedded in 5,
The resin was then cured at room temperature for 24 hours. -45
Reichert Ultra at temperatures between ℃ and -50 ℃
A thin slice of 0.1 micrometer was cut from the sample using a diamond knife on a cut E / F D-4 cryo-ultra microtome.

Next, each section was picked up on a carbon-saturated grid and brought to room temperature and then operated at 100 kV JEOL.
It was examined with a 100 CX transmission electron microscope. The dark part of the electron micrograph in FIG. 7 is dyed polymethylpentene, which can be seen as irregularly dispersed in the fiber. As expected by observing FIG. 7, this results in fibers with non-uniform strength, blending properties and bonding properties.

As long as the viscosities of the particular polymers are adequately matched, generally uniform multi-layer microfibers from two (or more) otherwise incompatible polymers (eg polypropylene and polyethylene tetraphthalate). It is possible to form. Accordingly, it is possible to obtain microfiber nonwoven webs having some desirable properties that are not individually available or otherwise obtained from incompatible polymers.

For example, 100% heated to 350 ° F
Polyethylene tetraphthalate (PEF) blown microtiter pads are highly shrinkable and 350 °
Blown microfiber pads of 100% polypropylene (PP) heated to F will show visible melting. However, 50/50 of polyethylene terephthalate and polypropylene heated to 35 ° F
Blown microfiber pads formed by the microfiber forming method described herein, which are coextruded, show no visible signs of melting and no perceptible shrinkage.

Any amount of high temperature stable polymer (eg PE
The addition of T) improves the desirable properties of the binding polymer (eg PP) in such blown microfiber pads of coextruded microfibers. Such a combined stream of polymers, one of which constitutes 20-80% by weight of the stream, provides a useful web product. However, the preferred composition has one of the polymers that makes up 40-60% of the stream.

Surprisingly, the overall web properties of these novel webs formed from multilayer microfiber webs are generally different from the web properties of uniform webs formed from any of the constituent materials. In fact, multilayer microfibers often provide entirely new web properties and / or range of properties not available with any of the constituent polymeric materials.

Fibers and webs for a given combination of polymers, for example, by independently varying the relative ratios of the polymers, the order of layers in the microfibers, the number of layers, the distance of the assembly surface and other process variables. The modulus of can be adjusted over a wide range. Thus, this method of forming a web allows for precise adjustment of properties such as modulus and absorbency of the web by changing one or all of these variables.

In the formation of a web that is fat-absorbent and suitable for microwave cooking of food, the microfibers of the web are temperature stable at the temperature levels required for cooking food by microwave irradiation. It is necessary. The microfibers in the heat stable melt-blown webs of the present invention are formed from a combination of at least two different phase types. The first layer type is used in combination with the second layer type which is a relatively non-thermal stable but relatively good web forming layer material. Heat stable melt-comprising a blowable material.

The relatively heat stable material can be any heat stable polymeric material capable of melt-blowing (high melting point polymer). These materials are generally highly crystalline and have high melting points. However, a problem with these materials is that they exhibit a relatively low degree of self-bonding. Tackiness is the ability of individual fibers to bond to each other when assembled from a melt-blowing die to an assembly surface. These heat stable materials themselves form low strength webs that generally lack the integrity required for most typical applications of melt-blown web products unless post-embossed.

Typical examples of such heat stable materials include:
Polyester such as polyethylene terephthalate, polyolefin such as poly 4-methyl-1-pentene,
Or, a polyarylene sulfide such as poly (phenylene sulfide) is included. These materials exhibit relatively high individual fiber strengths, but very low interfiber bonding, and as such generally form low strength webs even when the assembly surface is relatively close to the die.

In general, these materials are characterized as melt-blown polymers having a glass transition temperature above room temperature or a melting point above 180 ° C. Preferably, the heat stable polymer is capable of producing a stable web above about 130 ° C, more preferably above 150 ° C.

The second layer material used in the microfibers and webs of the present invention is generally a material that exhibits significantly higher tack in melt-blowing conditions. Typically, these materials are below the softening point or melting point of high modulus materials, but at the melting point of high modulus materials of 150 ° C.
It will exhibit a softening point or melting point within. If the difference in melting point is too large, coextrusion of the polymer becomes difficult.

In general, the tackifying component will have a glass transition temperature below room temperature, preferably about 15 ° C below. A preferred material would be an amorphous or semi-crystalline material that exhibits relatively good bonding properties in melt-blowing conditions. Suitable materials include polyolefins such as polypropylene. The material comprising the relatively high tie layer material can also contain conventional additives.

Relatively low levels (eg, <50%) in combination with the second layer material as defined herein.
By using the relatively heat stable material of, the mechanical performance characteristics of the relatively heat stable material can be obtained.
The web will also exhibit the favorable properties of the second layer material at low temperatures.

Thermally stable webs formed from the multilayer microfibers described above have relatively high strength properties over a wide temperature range. The fiber and web modulus can also be extensively controlled for a given combination of polymers by varying the relative proportions of the polymers, the order of layers in the microfiber, the number of layers, the distance of the assembly surface and other process variables. It is possible. The present invention thus allows for precise adjustment of web strength by varying one or all of these variables.

At least a portion of the high binding component is on the fiber surface. The heat stable layer stabilizes the binder component layer, while the binder component material on the surface provides interfiber bonding. Theoretically, the relative volume percentages of the individual layers can vary within a very wide range, for example from 1 to 99% by volume for each individual layer component. The preferred amounts of the individual layer components will depend on the relative values of the modulus desired for the individual high temperature webs and the desired high temperature performance required.

In general, the outer layer should contribute significantly to the surface properties that occur in the web without significantly altering the bulk fiber properties such as tensile strength and modulus behavior when used at relatively low volume percentages. Let's see In this way, a relatively high bond material can be used as the thin outer layer so as to contribute to the web properties without substantially affecting the bulk fiber properties.

Using the web-forming method described herein, the web properties are further changed by changing the number of layers and the layer arrangement used in a given relative volume percent. As noted above, varying the number of layers in at least a few layers tends to significantly change the relative proportions of each polymer (assuming two polymeric materials) at the microfiber surface. This (assuming alternating layers of two polymeric materials) results in a change in web properties to which the surface properties of the microfiber contribute significantly.

That is, the web properties can vary depending on which polymer or composition constitutes the outer layer. However, as the number of layers increases,
Changes in web properties due to surface effects are small. At large numbers of layers, the thickness of the individual fiber layers tends to decrease, significantly reducing the surface effect of the individual layers. Preferably, the melt-blown microfibers are 20
It has an average diameter smaller than a micrometer.

The number of layers obtained by the method described is theoretically infinite. In practice, the manufacture of manifolds, etc., in which the polymer layers can be divided and / or put together in a very highly layered arrangement would be prohibitively complex and expensive. In addition, it may be difficult to form the layer and hold it through the appropriate transfer piece in order to obtain a properly sized flow for feeding the die orifice.
A practical limit of 1000 layers is expected, and in this respect process problems will outweigh the benefits of potential additional properties.

The web formed can have any suitable thickness for the desired end use. However, in general, 0.01-5 cm for most applications
Is appropriate. Further, for some applications, the web can be a composite multi-layer structure. For example, the other layer can be a nonwoven web. Other layers,
It can be applied to the layers of the melt-blown web of the present invention by conventional techniques such as heat bonding.

Suitable materials for such layers include other high temperature stable materials such as polyester or polycarbonate. The web or composite structure comprising the web formed by this method is further processed after assembly or assembly, for example by calendering, point embossing, to increase the strength of the web, patterning the surface, and The fibers are fused at the contact position of the web structure or the like, and the orientation (orientatio
n), a hole is formed with a needle, a heat or molding operation is performed, and for example, an adhesive is applied to obtain a tape structure.

Preferred foods for microwave cooking
Eb Properties The webs of the present invention which, as described above, form a pad for use in microwave cooking must be oil-absorptive (oleophilic) and generally hydrophobic. Since the pad is in direct contact with the food, it must be a neutral food grade material that does not leach any ingredients into the food. Furthermore, it must not absorb moisture from food products and dehydrate them while stored together in a sealed enclosure.

The pad must also be formed of a material that can withstand the high temperatures required to properly cook food by microwave irradiation. Furthermore, it goes without saying that it is preferable for the pad to absorb as much grease as possible, thereby reducing the size, thickness and weight of the pad, which in turn lowers the pad material requirements and pad price. In some applications it is desirable to bond the pad to other materials and there is a need for a pad of material that has good bonding properties.

The blown microfibers (BMF) that make up the pad can be formed from a multilayer blend of polymeric materials. In a preferred embodiment, the temperature stable polymer layer in each microfiber consists of polyethylene terephthalate (PET), which has a relatively high melting point (about 460 ° F). The other layer of microfibers is preferably formed from polypropylene (PP).
Polypropylene (PP) has excellent fat absorption properties and hydrophobicity for use in multi-layer microfiber blends.

Polypropylene only blown microfiber webs exhibit some meltability in microwave applications where fatty foods such as bacon are cooked. Polypropylene (PP) and polyethylene terephthalate (PE) formed from the web forming method described herein.
T) multilayer microfiber webs are conventional web structures (eg, polypropylene and poly 4-).
Shows improved absorption compared to dry blended microfiber webs with methylpentene-1),
And it does not show any significant melting at the temperatures required for microwave food preparation. It is believed that this is a result of the "strength enhancement" of the coextruded web structure of the present invention over prior art web structures of extruded structure.

Since polypropylene and polyethylene terephthalate are dissimilar polymers, they are useful as melt-melts by dry blending and extruding polymer pellets.
Forming blown microfibers is difficult. When extruding a dry blend of these polymers,
Polyethylene terephthalate forms excess "shots" or "sands" in the polyethylene melt stream.

For high-temperature or temperature-stable components, this material must have a high crystalline melting point above 200 ° C., for example polybutylene terephthalate (PBT) or polycyclohexane terephthalate (PCT),
Or a material having a high glass transition temperature higher than 60 ° C. such as polycarbonate (PC). In addition to the above polyesters (PET, PBT and PCT), other types of high temperature materials can be used. Polyamide (nylon 6
Or nylon 66), polyolefin (for example, poly 4-
Methylpentene-1 (PMP)) or polyphenylene sulfide (PPS) could be satisfactory. Of course, those skilled in the art will recognize that this list is not limiting and that other materials or properties are suitable for this application.

The surface treatment of the web is necessary to remove the stickiness of the food after cooking. One means for providing such surface treatment is to hot roll calender the web with a predetermined gap for a particular web thickness. Another means is to flame the surface of the web. Another means to achieve a non-stick web cooking surface is to attach a scrim to the food side surface of the web. The scrim may also be calendered as it is attached to the coextruded absorbent web. The use of PET in the blended microfibers also optionally provides the basis for thermally bonding the PET scrim to the web.

Multilayer blown microfibers can be made with two layers, three layers, or other number of layers within each fiber. The choice of number of layers is determined by the end use.
When the microfiber web is exposed to heat following formation of the web, for example in an embossing or calendering process, the bonding component can "film over" the high temperature component. In other words, the binding component (PP) can be melted and the high temperature component (PET) can be coated with a thin film of polypropylene.

Two-layer microfiber structure (one layer is PP
And one layer of PEP) provides a poor web for PET filmover opportunities during calendering,
The additional PET is then exposed for lamination of PEP to the web. 3-layer microfiber structure (1 layer is P
ET, and 2 layers PP) results in unexposed PET and further film over of polypropylene during calendering. This results in a less fluffy surface on the calendered side of the web, which may be preferred in some applications.

The following examples are provided to illustrate preferred and best modes of the invention and are not meant to limit the invention. Test Method Tensile Strength Tensile strength data for blown microfiber webs with multilayer BMF microfibers is 1
I with a chin spacing of 0.48 cm (2 inches) and a crosshead speed of 25.4 cm / minute (10 inches / minute)
nstron Tensile Tester (Mod
el 1122). Web sample is 2.
It has a width of 54 cm (1 inch), and samples are taken in the machine direction (MD) and cross direction (TD) of the web. Each sample was stretched until it broke and the breaking force at the breaking point was measured.

Mineral Oil Absorption This test shows the oil absorption of a fat absorption pad. 397 cm
^{A 2} (61.5 in ² ) pad was weighed and immersed in mineral oil for 30 seconds at room temperature (about 30 ° C.), the oil was stirred and left for another 30 seconds. The pad was then suspended for 2 minutes to drain excess oil from the pad and weighed to determine the amount (g) of mineral oil absorbed and retained by the pad.

Maximum Oil Absorption Under Cooking Conditions This test is used to determine the maximum amount of oil absorbed by a pad by cooking 12 strips of bacon. 1
A 6 inch by 10.25 inch pre-weighed pad of 5.2 cm x 26 cm is placed in the microwave cooking package as shown in Figures 1-3.

Bacon is placed on the pad and the bacon in the package is cooked in a 700 W microwave oven for 7.5 minutes. The pad is then removed from the package and suspended until the dripping of grease has substantially stopped (about 30-45 seconds). The pad is then weighed (compared to the pad's uncooked weight) and the amount of fat absorbed is determined.

Example 1. For example Wente, Van
A, "Superfine Thermoplasti
c Fibers ", Industrial Erge
neeringChemistry , Vol. 48,1
342, etc. (1956), or Naval Research
rch Laboratories, “Manufac
true of Superfine Organic
Fibers "Wente, Van A, Bone,
C. D. And Fluharty, EL. BMF apparatus using a meltblown process similar to that described in (May 25, 1954), but with two extruders, each of which controls the polymer melt flow. Gear pumps, each gear pump connected to a melt-blowing die having an annular surface smooth surface orifice (10 / cm) with a length to diameter ratio of 5: 1, US Pat. 3,480,802 (Chish
olm et al.), No. 3,487,505 (Schren
k) or No. A polypropylene / polyethylene terephthalate BMF web of the present invention was prepared using a 3-layer feedblock assembly feed similar to that described in 4,197,069 (Cheren).

The first extruder is a polypropylene (PP) resin (PP 3860X, FinaOil & Che.
m, available from Co.) was fed to a gear pump feeding a three-layer feedblock assembly heated to about 300 ° C. The second extruder held at about 300 ° C was a polyethylene terephthalate resin (PET,
Those having an intrinsic viscosity of 0.60 and a melting point of about 257 ° C., US Pat. 4,939,008, 2nd column, 6th
(Prepared as described in lines 3 to 3, line 20) was fed to a second gear pump which also feeds the feedblock assembly.

The polymer melt stream gathered in three layers upon exiting the feedblock. 50/50 wt% PP / P
The gear pump was adjusted so that the ET polymer melt was fed to the feedblock assembly and a polymer passage rate of 0.11 kg / hr / cm die width (0.61 b / hr / inch) was maintained in the BMF die. The primary air temperature was maintained at about 305 ° C and suitable pressure was used to produce a uniform web width with a gap width of 0.76 mm. The web was collected in a collector at a distance of 50.8 cm (20 inches) from the die. The resulting BMF web, comprising 3-layer microfibers having an average fiber diameter of less than 10 micrometers, had a thickness of about 0.150 inches and a basis weight of about 200 cJm / m ² .

An electron micrograph showing a layered uniform blend of PP and PET in the blown microfibers produced by the above method is shown in FIG. The photomicrograph of Figure 8 was prepared by the same method as previously described for Figure 7. The darker portion of each microfiber section shown in Figure 8 is the PET polymer, while the lighter portion is polypropylene.

The surface of the blown microfiber web was smoothed by calendering the web with one side of a calender roll heated to a temperature of about 260 ° F., with the other roll at ambient temperature or It is kept at room temperature. These rolls are shown in FIG. 6 as calender roll 52 and heated calender roll 54. Two 10 inch (25.4
cm) 0.0 between diameter calender rolls 52 and 54
The gap of 50 inches (1.27 mm) is about 0.
It provides an acceptable surface on a 150 inch (3.8 mm) thick web. The web is calendar rolls 52 and 54
The speed is 8 ft / min (2.4 m / min).

The web was then tested for mineral oil absorption and cooking of 12 pieces of bacon. No visible melting was observed in the pad after the cook test. The oil absorption and tensile strength test results are summarized in Table 1.

Example 2. BMF according to the method of Example 1
A web was formed. Non-woven polyester scrim (Reemy Corporation) during calendering
Reemy 2250) available from BMF, Inc. was laminated to a BMF web. Lamination was performed by placing the nonwoven scrim between a heated calender roll and a BMF web and heating the heated calender roll to a temperature of 160 ° C (320 ° F). No visible melting was observed in the pad after the cook test. The test results of oil absorption and tensile strength are shown in Table 1.

Example 3. A BMF web having a basis weight of 200 g / m ² was prepared according to the method of Example 1 except that a two-layer feedblock was used. Obtained 2
The layered microfibers had an average fiber diameter of less than 10 micrometers, and the web thickness was about 3.8 mm (0.150 inch).

An electron micrograph showing a layered and homogeneous blend of PP and PET in blown microfibers produced by the method described in Example 3 (using a bilayer feedblock) is shown in FIG. The electron micrograph of Figure 9 was prepared in the same manner as described above with respect to Figure 7. The dark portion of each microfiber section in FIG. 9 is PET polyester and the lighter portion is polypropylene. No visible melting was observed on the web after the cook test. The calendered web was tested for oil absorbency and tensile strength. The test results are shown in Table 1.

Example 4. 75/25 wt% PP / PE
A BMF web was prepared according to the method of Example 3 except that the gear pump was adjusted so that the T polymer melt was fed to the feedblock assembly. The resulting BMF web comprising bilayer microfibers having an average diameter of less than 10 micrometers was 3.8 mm (0.
It had a thickness of 150 inches) and a basis weight of about 200 g / m ² . The web was tested for oil absorbency and tensile strength. The test results are shown in Table 1. No visible melting was observed on the pad after the cook test.

Comparative Example C1. US Patent No. 4,873
BMF was formed according to the method described in No. 101 (incorporated herein by reference). The composition of the microfiber is 50/50 wt% polypropylene and 4-methylpentene-1 (Mitsui Petroch).
MX- from electricals America, LTD
007 TPX brand resin). 20 web
It had a basis weight of 0 g / m ² and was calendered by the method described in Example 1. The results of oil absorbency and tensile strength are shown in Table 1.

[0090]

[Table 1]

Table 1 shows the excellent oil absorbency and tensile strength of BMF webs of the present invention made with multilayer microfibers.

The water-absorbent microwave cooking web is a pad of a pad that does not dehydrate the food product during transport and storage and absorbs water from the food product, and absorbs fats and oils during cooking due to the water produced during the cooking of the food product. It should be hydrophobic so that ease is not compromised. (1) 15.2 cm x 26.0 cm (6 inches x 1
0.25 inch) and a tare-weighted BMF pad of Example 1 weighing about 9.6 g, or (2) a tare-weighted paper towel (Wyp A11) weighing about 7.0 g. Each is about 22.7 g (0.
Four pieces of bacon (8 ounces) were packed and the pads were tested for moisture or water absorption.

The sealed package is 0.005 cm
"0.002" thick "Scotchpak"
Branded film (Minnesota Mining and
30.5 cm (12 inches) x 25.4 cm (10 sold by Manufacturing Company)
(Inch) by heat sealing two sheets. Place sealed package at 4 ° C (40 ° F)
Hold for days. After 4 days the pad was removed and the moisture uptake determined.

The BMF pad weighs 11.4 g and absorbs about 18% by weight of water and fats, while Wyp A1
1 was 11.9 g and absorbed about 69% by weight of water and fats. 121 ° C (250 ° F) BMF pad
Dry for about 1 hour, and the actual moisture absorption is about 9%
Was decided to be. Although the present invention has been described with reference to preferred embodiments, those skilled in the art will recognize that many changes can be made without departing from the spirit and scope of the invention.

[Brief description of drawings]

FIG. 1 is a perspective view of a microwave food package of the present invention.

FIG. 2 is an enlarged cross-sectional view of the package shown in FIG.

3 is an enlarged cross-sectional view of the package of FIG. 1 while the food product therein is being cooked in a microwave oven.

FIG. 4 is an open perspective view of the package of FIG.

FIG. 5 is an enlarged cross-sectional view of the food cooking pad of the present invention with food thereon.

FIG. 6 is a schematic diagram of an apparatus useful for making a nonwoven web of longitudinally laminated meltblown microfibers that defines a pad useful for cooking food in a microwave oven. ..

FIG. 7 is an electron micrograph of a cross section of a blended fiber of polypropylene (PP) and polymethylpentene (TPX) blended by a prior art “dry-blend” technique, showing the shape of the fiber. It is a photo instead of.

FIG. 8 is a scanning electron micrograph of a cross section of a multi-layer blend fiber of polypropylene (PP) and polyethylene terephthalate (PET) blended by the web-forming method described herein, showing the shape of the fiber. It is a photograph instead of a drawing.

FIG. 9 is a scanning electron micrograph of a cross section of a multi-layer blend fiber of polypropylene (PP) and polyethylene terephthalate (PET) blended by the web-forming method described herein, showing the shape of the fiber. It is a photograph instead of a drawing.

[Explanation of symbols]

 10 ... Package 12 ... Food 14 ... Pad 16 ... Enclosure 17 ... Top sheet 20 ... Metal evaporated film 30 ... Manifold 32, 34 ... Extruder 40 ... Die 41 ... Orifice 42 ... Die cavity 48 ... Air hole 49 ... Assembly surface

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Internal reference number FI Technical display location D04H 3/03 Z 7199-3B H05B 6/64 J 8815-3K (72) Inventor Pierre Howard Reper USA , Minnesota 55144-1000, St Paul, 3M Center (No Address) (72) Inventor Daniel Edward Mayer United States, Minnesota 55144-1000, St Paul, 3M Center (No Address) (72) Inventor James Raymond Nelson United States, Minnesota 55144-1000, Saint Paul, 3M Center (No address)

Claims (7)

[Claims] 1. A pad (14) for use on cooking in a food product (12) containing a substantial amount of solidified fats and oils which melt when cooked by microwave irradiation. At least one generally hydrophobic and fat-absorbent multi-layer microfiber comprising an entangled web that combines at least two streams of flowable material. To form a layered combined stream and extruding the combined stream through a die having at least one orifice, the extruded stream being refined by a high velocity gas stream to form fibers. And the fibers are collected on a collection surface to form the entangled web, the pad comprising a microweave. Characterized in that it is capable of holding the amount of fats and oils in the food when the fats and oils are melted by cooking the food in an Ave oven,
Cooking pad. 2. The pad of claim 1, wherein the plurality of separate streams of fluent material comprises a polypropylene stream and a polyester stream. 3. The pad of claim 2, wherein the polyester is polyethylene terephthalate. 4. The pad of claim 1, wherein each microfiber comprises a plurality of alternating stacks of the flowable material in cross section. 5. The pad comprises first and second major surfaces facing in opposite directions, the first major surface calendered to form a relatively smooth surface thereon, and The pad of claim 1, wherein the first major surface is adjacent to the food product. 6. The pad comprises oppositely directed first and second major surfaces, and further comprising a web formed from a high temperature stable material, the web comprising oppositely directed first and second opposite surfaces. A second major surface, the first major surface of the web being bonded to the first major surface of the pad,
The pad of claim 1, wherein the second major surface of the web is adjacent to the food product. 7. The pad (14) further comprises a vapor-tight microwave permeable enclosure (16) that surrounds both the pad (14) and the food product (12) to be cooked with microwave energy. 1 and thus forming a package (10) for use in a microwave oven.
Pad described in.