CA2271389A1

CA2271389A1 - Peel pack paper

Info

Publication number: CA2271389A1
Application number: CA002271389A
Authority: CA
Inventors: Robert Emil Weber; Bernard Cohen; Michael Joseph Scott; Rene Howard Kapik
Original assignee: Individual
Current assignee: Kimberly Clark Worldwide Inc
Priority date: 1996-12-06
Filing date: 1997-12-05
Publication date: 1998-06-11
Also published as: WO1998024970A1; AU5375598A

Abstract

Disclosed is a peel pack paper having a Gurley porosity of greater than 20 seconds/sheet. The paper includes a) from about 45 to about 65 %, by weight, of substantially fully bleached eucalyptus Kraft pulp fibers; b) from about 10 to about 45 %, by weight, of a blend of substantially fully bleached softwood Kraft pulp fibers and substantially fully bleached hardwood Kraft pulp fibers wherein the softwood Kraft pulp fibers comprise at least 90 %, by weight, of the blend; and c) from about 10 to about 30 %, by weight, of reinforcing fibers. Importantly, substantially all of the fibers of the paper are coated with a dielectric material with the coating having an average thickness of less than 1 micron. In some embodiments, the coated paper is subjected to an electret treatment to instill a charge in the dielectric material.

Description

WO 98/24970 PCT/L1S97/223d3 PEEL PACK PAPER
FIELD OF THE INVENTION
The field of the present invention is that of peel packs for use in the automated sterilization of, for example, hospital operating room instruments.
BACKGROUND OF THE INVENTION
Various medical instruments and supplies used in hospitals are subjected to sterilization treatments such as, for example, steam sterilization) ethylene oxide gas sterilization, radiation sterilization, and dry-heating sterilization before they are used in medical treatments. In many instances) the non-sterile instruments andlor supplies are first packaged in what is conventionally called a "peel pack" and then the pack and its contents are subjected to sterilizing conditions. One of the major functions of the peel pack is to maintain the supplieslinstruments in a sterile condition until such time as the pack is opened and the supplies/instruments are utilized.
Typically) there are at least three elements to a peel pack. First) the pack includes a layer of a material which is impervious to pathogens. Exemplary materials of this sort are poiyoiefinic films or plastics. In some instances the films or plastic materials are molded to provide a chamber for retention of the supplies/instruments. The second element of a peel pack is an adhesive which is usually applied around the outer periphery of the pathogen impervious layer. Lastly, peel packs include a layer of a material {typically paper) which allows entry of sterilizing gases into the chamber during a sterilization procedure but prohibits entry of pathogens into the chamber thereafter. This peel pack paper is joined to the pathogen impervious material by the adhesive.
The juncture of the peel pack paper with the pathogen impervious material forms the "peel pack". It should be noted that, in some instances, the peel pack paper can be heat sealed directly onto the pathogenic impervious material. These situations arise where the pathogenic impervious material has been especially formulated to form a heat seal with a peel pack paper. In such instances) naturally, the necessity of an adhesive is eliminated.

WO 98/24970 __ PCT/US97/22363 Conventionally, peel packs are opened by peeling the peel pack paper away from the pathogen impervious material so as to allow access to the chamber and the supplies/instruments contained therein.
One of the problems with which those of skill in the art have been confronted is that peel packs do not always easily and cleanly open. That is, the peel pack paper may resist separation from the adhesive/pathogen impervious material. In such situations, the peel pack paper may tear in a non-uniform, non-predictable manner. This can lead to two undesirable results. First, the peel pack paper may separate into a number of smaller parts which may then be inadvertently strewn about the operating field.
Secondly) the paper's resistance to uniform tearing/separation can be a general aggravant to operating room personnel. In those instances where an adhesive is utilized to join the peel pack paper to the pathogenic impervious material) another potentially complicating factor is that the act of sterilizing the peel pack and contents can) in some instances, lead to an increase in the bond strength of the bond formed by the adhesive between the peel pack paper and the pathogen impervious film or molded plastic material. See) for example, U.S. patent number 3,995,739 to Tasch et al. which issued on December 7, 1976.
Generally speaking, to overcome these problems a desirable peel pack paper will have to be strong enough to resist internal tearing up to and exceeding the amount of force that is necessary to promote separation of the peel pack paper from the adhesive/pathogen impervious material. That is, if the strength of the juncture/bond between the peel pack paper and the pathogen impervious material exceeds the strength of the peel pack paper) the paper will fail before separation with unsatisfactory results.
Accordingly, peel pack papers having sufficient strength to withstand the demands placed upon them during the opening or peeling operation are highly desirable.
Those of skill in the art have sought to strengthen peel pack papers by incorporating strengthening or reinforcing fibers into the paper. While incorporation of such reinforcing fibers did improve the strength of the resulting peel pack paper, it was found that the porosity of the strengthened peel pack paper had been increased with a subsequent and adverse decrease in the pathogenic barrier properties of the resulting strengthened paper. In other words, the peel pack paper was now of a satisfactory strength to peel (open) with reliability and consistency, but the paper no longer performed its primary function of maintaining a sterile filed within the peel pack.
Naturally, this result is undesirable.

OBJECTS OF THE INVENTION
Accordingly, it is a general object of the present invention to provide a peel pack paper which provides a satisfactory barrier to pathogens.
Another object of the present invention is to provide a peel pack paper which is of a satisfactory strength so that it easily delaminates from the other portions of a peel pack. That is, so that the peel pack can be easily and satisfactorily opened.
Yet a further object of the present invention is to provide a peel pack which has the peel pack paper incorporated therein.
Still another general object of the present invention is to provide a process for forming such a peel pack paper and for forming a peel pack having the peel pack paper incorporated therein.
Still further objects and the broad scope of applicability of the present invention will become apparent to those of skill in the art from the details given hereinafter. However, it should be understood that the detailed description of the presently preferred embodiment of the present invention is given only by way of illustration because various changes and modifications well within the spirit and scope of the invention will become apparent to those of skill in the art in view of the following description.
DEFINITIONS
As used herein, the term "reinforcing fibers" means fibers which are conventionally incorporated into cellulose-based papers to impart higher strength and/or higher endurance and/or increased resistance to, for example, heat, light, insects and/or bacteria. Examples of such fibers are polyester fibers, cotton fibers, rayon fibers and nylon fibers. Reinforcing fibers typically have an average fiber length of less than 25.4 millimeters. For example, in some cases, about 0.5 inch {'f 2.7 millimeters) and, in other instances, about 0.25 inch {6.3 millimeters).
As used herein, the term "hardwood fibers" means fibers obtained from an angiosperm. Angiosperms typically possess true vessels in the structure of the wood.
As used herein, the term "softwood fibers" means fibers obtained from a gymnosperm. Gymnosperms typically lack true vessels in the structure of the wood.
As used herein, the term "eucalyptus fibers" means any fibers obtained from a tree which is a member of the genus "eucalyptus". These trees are typically tall, aromatic evergreen trees of the myrtle family which bear pendent leaves and umbels of white, red, or pink flowers. Eucalyptus trees naturally occur in Austrafia,Tasmania and South America. However) they have been introduced into other geographic areas such as, for example, the United States) by man. The fibers typically have an average fiber length of from 0.55 to 0.65 millimeters (mm). For example, an average fiber length of about 0.59 millimeters.
As used herein, the term "dielectric material" refers to any material, such as a polymer, which is an electrical insulator or in which an electric field can be sustained with a minimum dissipation of power. A solid material is a dielectric if its valence band is full and is separated from the conduction band by at least 3 eV. This definition is adopted from the McGrav~i-Hill Encyclopedia of Science & Technoio~w, 7th Edition, Copyright 1992.
As used herein, the term "high density polyethylene" refers to any polyethylene material having a density measured in accordance with ASTM D 2839-93 in the range of from about 0.941 to about 0.959 grams per cubic centimeter.
Unless otherwise stated, Gurley porosity is to be determined in accordance with TAPPI test method T460-1988.
Unless otherwise stated, Elmendorf tear values are to be determined in accordance with TAPPI test method T414-1982.
Unless otherwise stated, the effectiveness of a peel pack paper in resisting pathogenic penetration is measured by a particulate filtration test conventionally known as the NaCI Filter Efficiency Test (hereinafter the NaCI Test). The NaCI Test is conducted using an automatic filter tester, CertitestTM Model # 8110, which is available from TSI
Inc., St. Paul, MN. The particulate filtration efficiency of the tested material is reported as percent (%) penetration. The percent penetration is calculated by the following formula:
100 X (downstream particles/upstream particles). The upstream particles represent the total quantity of approximately 0.1 micron NaCI aerosol particles which are introduced into the tester. The downstream particles are those particles which have been introduced into the tester and which have passed through the bulk of the test material.
Therefore, the percent penetration value reported is a percentage of the total quantity of particles introduced into a controlled air flow within the tester which pass through the test material.
In all cases the face velocity was 31 liters per minute. Unless otherwise stated percent penetration values are the average of three such tests.
Unless otherwise stated, delamination resistance values are to be determined by conducting a "Delamination Test". The Delamination Test is conducted as follows. One inch wide (cross-machine direction) by eight inch long (machine direction) samples of material to be tested are obtained. Starting at one end) seven inches of each sample is covered on both sides with black pressure tape (#A963-02-5 from Ideal Tape Co.
of Lowell, Mass.). The taped sample is placed on a hot plate (Thermolyne Model SP-A1025B from the Sybron Corp. of Dubuque) Iowa) which is maintained at a temperature in the range from 300 degrees F. to 325 degrees F. for 20 seconds. While on the hot plate, six inches of the sample, starting at the taped end, is subjected to pressure from a five (5) pound steel weight measuring 6 inches in length by 1.5 inches in width. Thus, the first six inches of sample are subjected to pressure and are taped, the next one inch of sample is just taped and the last inch of sample is not taped or subjected to pressure.
After its removal from the hot plate, each sample is allowed to cool for at least 30 minutes. The sample is then cut, lengthwise, into 15mm wide strips using a JDC Precision Sample Cutter (Thwing-Albert Instrument Co. of Philadelphia, Pa, Model JDC 15M-10).
Thereafter, the one inch long portion of the tape that was not subjected to pressure while the sample was on the hot plate is peeled back on both sides of the sample.
Each peeled back portion is placed in the jaws of an Instron Model 5500R instrument available from the Instron, Inc. of Canton) Mass. and the tape is pulled away from the sample.
The gauge length is one inch and the crosshead speed is 300 millimeters per minute (300mm/min).
As used herein, the terminology "electret treatment" or "electreting" refers to any process which places a charge in and/or on a dielectric material. One exemplary process for placing a charge on a dielectric material involves the application of a DC
corona discharge to the material. An exemplary conventional method of this type is described in detail in U.S. patent number 5,401,446 to Tsai et al. entitled "Method and Apparatus for the Electrostatic Charging of a Web or Film" which issued on March 28, 1995.
The entirety of this patent is hereby incorporated by reference.
As used herein, the term "Kraft" pulp or fibers refers to conventional Kraft pulping processes. This alkaline pulping process typically uses a combination of sodium hydroxide and sodium sulfide. The term Kraft is derived from the German word meaning "strong" because Kraft pulp is amongst the strongest chemical pulps. Those of skill in the art utilize the term "sulfate pulping" alternatively or as a synonym for Kraft pulping. The "Handbook For Puip & Paper Technologists" by Gary A. Smook (Angus Wilde Publications), copyright 1992, [ISBN 0-9694628-1-6] gives a detailed description of conventional Kraft pulping techniques at chapter 7, pages 74-83. The entirety of this book is hereby incorporated by reference.
As used herein, any given range is intended to include any and all lesser included ranges. For example, a range of from 45-90 would also include 50-90; 45-30; 46-89; etc.

In response to the foregoing problems and difficulties encountered by those of skill in the art, a peel pack paper has been discovered which can be utilized in making improved peel packs for use in automatic sterilization processes. The peel pack paper has a Gurley porosity of greater than 20 seconds/sheet. The paper includes (a) from about 45 to about 65%, by weight, of substantially fully bleached eucalyptus Kraft pulp fibers; (b) from about 10 to about 45%, by weight) of a blend of substantially fully bleached softwood Kraft pulp fibers and substantially fully bleached hardwood Kraft pulp fibers wherein the softwood Kraft pulp fibers comprise at least 90%) by weight, of the blend; and (c) from about 10 to about 30%, by weight, of reinforcing fibers. Importantly, substantially all of the fibers of the paper are coated with a dielectric material with the coating having an average thickness of less than 1 micron.
In some embodiments, the softwood fibers may be fir fibers. For example, the softwood fibers may be selected from the group including spruce fibers, pine fibers and cedar fibers.
In some embodiments, the hardwood fibers may be selected from the group including aspen fibers) maple fibers ash fibers, poplar fibers and beech fibers. Many combinations of softwood and hardwood fibers are possible.
A wide variety of physical characteristics and numerous combinations and permutations thereof are possible with the peel pack paper of the present invention. For example, the paper may have a Gurley porosity of greater than 25 seconds/sheet andlor a delamination resistance of at least 200 grams/15mm. In some instances the peel pack paper may have a delamination resistance of at least-900 grams/15mm.
In some embodiments the peel pack paper may have an Elmendorf tear of greater than 145 grams. For example, the peel pack paper may have an Elmendorf tear of greater than 180 grams.
One of the important aspects of the present invention is that the peel pack paper provides a satisfactory barrier to pathogens. This barrier capability is evidenced by the paper having an average 0.1 micron sodium chloride particulate penetration of less than 5 percent. For example, the paper may have an average 0.1 micron sodium chloride particulate penetration of less than 2 percent.
In some embodiments, the reinforcing fibers are selected from the group of polyester fibers, nylon fibers, cotton fibers and rayon fibers.
in some embodiments the dielectric coating is selected from the group of polyolefins and polyolefin copolymers. For example,the dielectric material is selected from the group of high density polyethylenes, natural rubbers, synthetic rubbers and ethylene acrylic acid copolymers.
In some embodiments, the peel pack paper includes: (a} from about 50 to about 60%, by weight, of eucalyptus fibers; (b) from about 10 to about 30%, by weight, of the blend of northern softwood and hardwood pulp fibers; and (c) from about 20 to about 30%, by weight, of the reinforcing fibers. For example, the peel pack paper can include:
(a) about 55%, by weight, of eucalyptus fibers; (b) about 20%, by weight, of the blend of northern softwood and hardwood pulp fibers; and (c) about 25%) by weight) of the reinforcing fibers.
__ 6 WO 98l24970 __ PCT/US97/22363 In some desirable embodiments) the coated peel pack paper may be subjected electreting. For example, to treatment with a DC corona charge apparatus(DC
corona discharge treatment). The present invention is also directed toward a method for forming the peel pack paper where the method includes the steps of: (a) providing a paper comprising ( 1 ) from about 45 to about 65°l°, by weight, of substantially fully bleached eucalyptus Kraft pulp fibers; {2) from about 10 to about 45%, by weight) of a blend of substantially fully bleached softwood Kraft pulp fibers and substantially fully bleached hardwood Kraft pulp fibers wherein the softwood fibers comprise at least 90%, by weight, of the blend; and (3) from about 10 to about 30%, by weight, of reinforcing fibers; and (b) coating substantially all of the fibers of the paper with a dielectric material wherein the average thickness of the coating is less than 1 micron.
In some embodiments, the dielectric coating may be applied by an emulsion coating process. In further embodiments the method may include the additional step of electreting the emulsion coated paper. An exemplary method of electreting the emulsion coated paper is to apply a DC corona charge to the coated fibers.
DETAILED DESCRIPTION OF THE INVENTION
Turning now to the drawings where like numerals represent like or equivalent structure or process steps, it can be seen that Fig.1 is a schematic representation of a process for forming a peel pack in accordance with the present invention.
Fig. 1 reveals that the first step in the process, step 10, is to form a liquid dispersion, desirably from water, containing the desired cellulosic component fibers.
Thereafter, as step 20 illustrated, a reinforcing fiber material is added to the dispersion.
At this point) the celluiosic fibrous portion of the dispersion will include (a) from about 45 to about 65%, by weight, of substantially fully bleached eucalyptus Kraft pulp fibers and (b) from about 10 to about 45%, by weight, of a blend of substantially fully bleached softwood Kraft pulp fibers and substantially fully bleached hardwood Kraft pulp fibers wherein the softwood Kraft pulp fibers comprise at least 90%, by weight, of the blend and (c) from about 10 to about 30°l°, by weight, of reinforcing fibers. For example, the celiulosic portion of the dispersion may include (a) from about 50 to about fi0%, by weight, of eucalyptus fibers; (b) from about 10 to about 30%, by weight) of the blend of softwood and hardwood pulp fibers and (c) from about 20 to about 30%, by weight, of the reinforcing fibers. More particularly, the cellulosic portion of the dispersion may include:
(a) about 55%, by weight, of eucalyptus fibers; (b) about 20%, by weight, of the blend of softwood and pulp fibers and (c) about 25%, by weight; of the reinforcing fibers. The amount of water or other appropriate liquid in the dispersion will vary with the amount and type of cellulosic fibers as is well known to those of skill in the paper making art.
While any eucalyptus pulp fibers may be utilized; one desirable source of such fibers is Aracruz Cellulose SA, Rio De Janerio, Brazil. Eucalyptus base sheet may be obtained from this source under the trade designation "Aracruz Eucalyptus".
Aracruz Eucalyptus is fully bleached Brazilian hardwood Kraft pulp (100%) with an average fiber length of about 0.59 millimeters.
In some embodiments) the softwood fibers may be fir fibers. For example, the softwood fibers may be selected from the group including spruce fibers, pine fibers and - cedar fibers.
in some embodiments, the hardwood fibers may be selected from the group including aspen fibers, maple fibers ash fibers, poplar fibers and beech fibers. Many combinations of softwood and hardwood fibers are possible.
One desirable blend of softwood and hardwood fibers can be obtained from the Kimberly-Clark Corporation of Dallas, Texas under the trade designation "Longloc-19"
(LL-19). LL-19 is fully bleached northern softwood Kraft pulp (approximately 95%, by weight spruce) with a trace amount of fully bleached northern hardwood (mainly aspen).
The average fiber length of LL-19 is approximately 1.07 millimeters.
In some embodiments, the reinforcing fibers may be selected from the group of polyester fibers, nylon fibers, cotton fibers and rayon fibers.
Fig. 1, at step 30) reveals that, after the reinforcing fibers and the cellulosic paper making fibers have been satisfactorily combined, the dispersion is formed into a paper product in any of a number of conventional and well known paper forming methods.
Step 40 illustrates that, after the paper has been formed, it is coated with a dielectric material. In some embodiments, the coating can be accomplished through use of conventional emulsion coating techniques. For example, the emulsion coating can be accomplished by passing the paper through a nip formed by nip rollers with the nip being flooded by the dielectric emulsion. Those of skill in the art will readily recognize that the amount of dielectric emulsion applied to the paper can be easily and readily varied by condensing or dilution of the emulsion. Additionally, this amount can be easily increased by passing the paper through the flooded nip two or more times since, with each passage, the paper tends to pick up more dielectric material. The amount of material picked up and retained by the peel pack paper (add-on) desirably is within the range of 25-200%, by weight, of the paper. For example the amount of dielectric add-on may vary within the range of from 50-150%, by weight) of the paper. More particularly, the amount of dielectric add-on may vary within the range of from 50-100%, by weight, of the paper.
The emulsion coating processes is carried out, in conventional fashion, so that substantially all of the fibers of the paper are coated with the dielectric material with the s coating having an average thickness of less than 1 micron. For example, the coating may have an average thickness of less than 0.5 microns.
In some embodiments the dielectric coating is selected from the group of polyolefins and polyolefin copolymers. For example, the dielectric material is selected from the group of high density poiyethyienes, natural rubbers, synthetic rubbers and ethylene acrylic acid copolymers. One particular dielectric emulsion coating may be obtained under the trade designation Michem Emulsion 93135 (Michelman, Inc.
Cincinnati Ohio). Michelman information states that Michem 93135 is a high density polyethylene emulsion which is a tan colored translucent liquid, having a pH of 10.0 - 11.5 and a specific gravity of 0.99 - 1.01. Another dielectric coating material may also be obtained from Michelman, Inc. under the trade designation Michem Prime 4983. Michelman information states that Michem 4983 is a dispersion of ethylene acrylic acid which is a translucent liquid having a pH of 8.3 - 10.
Fig. 1, at optional step 45, further illustrates that, in some desirable embodiments, the coated peel pack paper may desirably be subjected to electreting in order to instill a charge on the dielectric coating. Electreting may be accomplished by, for example, application of a DC corona charge (DC corona discharge treatment) in a conventional manner. The method described in U.S. patent number 5,401,446 is a conventional method for DC corona discharge treatment. The contents of this patent are hereby incorporated by reference.
The invention will now be described in mare detail with reference to specific examples and embodiments. However, in no way should the invention be taken to be limited to the specific examples disclosed 'and discussed below.
COMPARATIVE EXAMPLE A
This example was prepared in order to establish a baseline for conventional peel pack paper manufactured in a conventional matter from eucalyptus. pulp fibers and a blend of substantially fully bleached, northern softwood Kraft pulp with a trace amount of substantially fully bleached northern hardwood pulp.
Approximately 75%) by weight, of eucalyptus pulp fibers (Aracruz Eucalyptus Sheet from Aracruz Cellulose SA, Rio De Janeiro, Brazil) was combined with about 25%, by weight of a blend of substantially fully bleached northern softwood Kraft pulp fibers (about 95%, by weight, spruce) with a trace of substantially fully bleached northern hardwood (mainly aspen) pulp fibers (Kimberly-Clark Corporation Longloc 19 sheet) in a Valley Beater (Valley Laboratory Equipment Serial # 109-F-1461, V5-04649, Voith Inc., Appfeton, WL). The Beater was run for approximately one (1 ) minute with the roll off, then for about five (5) minutes with the roll on. Thereafter, the Beater was run for an additional five (5) minutes with a 12.3 pound weight on the bed plate.
At this point, the pulp slurry was diluted with water at least ten fold and stirred with a mixer (Model 1024 Faucett Co., RichField, OH.) to obtain a good dispersion.
Seven hundred {700) milliliters of the dispersion was then transferred to a Hand Sheet Mold and Wet Press (Williams Apparatus Co., Watertown, NY). A sheet of paper was formed in the press unit. The sheet was then pressed in a wet press at 200 pounds per square inch (psi) for five (5) minutes to remove water. The sheet was then dried on a drum which consists of a steam heated (about 7 psi steam pressure) Teflon cover drum which has a felt sheet press cloth. The thus formed paper was then conditioned for about twenty four (24) hours at 73.4 degrees F. ( 23 degrees C.) and 50% relative humidity before measuring its properties. The properties of this conventional peel pack paper are reported in Table I under "A".
COMPARATIVE EXAMPLE B
Comparative Example A was repeated with the exception that after the 700 milliliters of dispersion had been transferred to the Hand Sheet Mold and Wet Press, polyester (PET) reinforcing fibers having a denier of three and a length of about 0.25 inch (Mini Fiber, Inc. of Johnson City, TN.) were added until the composition of the dispersion was 56.25%, by weight, eucalyptus, 18,75%) by weight, LL-19 and 25%, by weight, PET. The properties of this reinforced conventional peel pack paper are reported under "B" in Table Comparative Example B was repeated with the exception that after the peel pack paper had been formed) the paper was emulsion coated with a dielectric polyethylene (Michem 93135). The emulsion was coated onto the peel pack paper by flooding a nip formed by two nip rollers and passing the peel pack paper through the flooded nip. fn this example one of the nip rolls was hard rubber and the other was steel. The amount of dielectric material coated onto the peel pack paper is measured as a percent of the dry weight of the paper. That is, the paper is weighed before its emulsion coating and after the coating. The percent add-on is the weight of the amount of dielectric material added to the paper divided by the uncoated weight of the paper. Those of skill in the art will recognize that the amount of add-on can be varied by (a) condensing or diluting the emulsion and/or (b) passing the paper through the flooded nip more than one time. In this example the paper was passed through the flooded nip once to achieve a 63%, by weight) to add-on of dielectric polyethylene. Percent add on in all cases is determined from the formula:
coated weight - uncoated weight x 100 = % add on uncoated weight Example 1 was repeated with the exception that the paper was passed through the flooded nip twice to achieve a 99%) by weight, add-on of dielectric polyethylene.

Example 2 was repeated with the exception that a different dielectric material, a dispersion of ethylene acrylic acid was utilized. In this example the dielectric ethylene acrylic acid used was Michem 4983. The paper was passed through the flooded nip twice to achieve a 80%, by weight, add-on of dielectric ethylene acrylic acid.

PHYSICAL PROPERTIES OF SHEETS

Basis Weight 23.69 23.86 39.63 47.52 43.16 T412-1983 (Ib/rm) Caliper 8.36 11.96 11.44 11.49 12.6 T411-1984 Dry Tensile 1.996 1.143 2.55 2.663 14.473 T494-1981 (kg/15 mm) Dry Stretch (%) 0.989 0.95 1.049 1.217 8.983 T494-1981 Elmendorf Tear 41 60 140 148 185 T414-1982 Delamination 31 26 160 242 916 See definition (grams) Sheffield Smoothness375 >400 >400 >400 >400 T538-1982 Gurley 0.75 0.23 2.12 20.85 27.9 T460-1988 Porosity (1 sheet) Opacity TAPPI 90 86 81 84 75 T425-1986 A. 75% Eucalyptus, 25% LL-19.
B. 56.25% Eucalyptus, 18.75% LL-19, 25% PET.
1. Same as B coated with 63% Michem Emulsion 93135 (1 pass).
2. Same as B coated with 99°Jo Michem Emulsion 93135 (2 passes).
3. Same as B coated with 80% Michem Prime 4983 (2 passes).

WO -98l24970 PCT/US97/2Z363 Table I demonstrates that the strength of the peel pack paper having the reinforcing fibers (Comparative Example B) improved, as evidenced by the increased Elmendorf Tear value as compared to the non-reinforced peel pack paper (Comparative Example A).
However, and as has been previously stated, the addition of such reinforcing fibers resulted in a deterioration of the pathogenic barrier properties of the peel pack paper as evidenced by the decreased Gurley Porosity of Comparative Example B as compared to Comparative Example A.
In stark contrast, the Example 1 peel pack paper has over three times the strength of Comparative Example A and over twice that of Comparative Example B (per Elmendorf values) and a Gurley porosity increase of almost three times that of Comparative Example A and about nine times that of Comparative Example B. Substantially equivalent or even superior improvement is noted in Examples 2 and 3 as compared to Comparative Examples A and B. Further evidence of the enhancement in strength of Example 1, 2 and 3 as compared to the Comparative Examples, can be noted by comparing the extraordinary improvement in deiamination resistance of the Examples.
In summary, the peel pack papers of Examples 1, 2 and 3 have clearly superior strength and pathogenic penetration resistance as compared to Comparative Examples A
and B.
ELECTRET TREATMENT EXAMPLES
Samples of each of the peel pack papers were subjected to DC corona discharge treatment. The corona discharge was produced by using a Model No. PIN 25A -120 volt, 50I60 Hz reversible polarity power unit (Simco Corp., Hatfield, PA.), which was connected to a RC-3 Charge Master charge bar (Simco Corp.), and a Model No. P16v 120 volt,. 25 A
50l60 Hz power unit (Simco Corp.) which was connected to a solid, three inch diameter, aluminum roller. The corona discharge environment was 72.8 degrees F. and 70%
relative humidity. As described in U.S. patent no 5,401,446, two sets of charge bars/rollers were used. The voltage applied to the first charge baNroller set was 20 Kv/0.0 Kv, respectively. The voltage applied to the second charge bar/roller set was 12 Kv/0.0 Kv, respectively.
The resistance to pathogenic penetration as indicated by NaCI particulate testing was determined for samples of each material both before and after a charge was instilled upon the dielectric material by electreting the material through application of DC corona discharge treatment. The results of these test are reported in Table 2.

WO 98/249?0 _ _ PCT/US97I22363 FILTRATION TESTING

(TSI, 0.1 micron NaCI) Sample Saturant Electret 0.1 micron NaCI

%Pick-Up) Penetration*

A None No 17.67 A None Yes 14.00 B None No 55.70 B None Yes 38.70 1 63% Michem No 25.7 1 63% Michem Yes 24.70 2 99% Michem No 1.84 2 99% Michem Yes 1.59 3 80% Michem No 2.55 3 80% Michem Yes 1.85 * - Average of three samples Table 2 demonstrates that even further improvement in resistance to pathogenic penetration is provided by application of an electret treatment to the dielectric emulsion coated peel pack papers.

FORMATION OF PEEL PACKS
In order to demonstrate the efficacy of the peel pack paper of the present invention, peel packs were formed in a conventional manner utilizing the present peel pack paper.
fn particular, pee! packs of approximately 23 centimeters by 14 centimeters in size were made from the peel pack paper of Example 3. The clear polyethylene portion of a Medi-Plus Self-Seal Pouch (Medi Plus Laboratories, Hargo Health Care Packaging, Chicago, Illinois) was used for the pathogenic impervious material.
Prior to formation of the peel packs, electron microscopy was conducted on the peel pack paper and the thickness of the polyethylene dielectric coating was found to be less than 0.5 microns. The eVectron microscopy was accomplished by cryomicrotoming the peel pack paper samples using a Reichert-Juung Ultra cryomicrotome at -110 degrees C. The samples were mounted on 600 mesh grids using a Gatan cold transfer stage. A
Jeo1 2000fx transmission electron microscope was used for the observations.
The accelerating voltage was 200Kv with a 10 micron condenser aperture and a condenser spot size of 8. A low dose MDD system was used to take the micrographs at very fast exposure speeds of about 0.3 seconds. This reduced the electron beam damage and overall_exposure of the samples to the electron beam. The samples were observed at various magnifications from 1000x to 20,000x.
The peel packs were formed by heat sealing the peel pack paper to the clear polyethylene with an indicator strip being located inside the thus formed peel pack.
Five (5) packs with indicator strips for steam sterilization (Tower Steam Indicator Strips, Baxter Health Care Corporation, Deerfield, Illinois) were steam sterilized in a conventional manner in an Amsco 2021 Gravity Sterilizer (American Sterilizer Co, Erie, PA.). In all packs the indicator turned from white to black indicating that sterilization had taken place.
An additional five (5) packs with indicator strips for peroxide plasma sterilization (Sterrad Chemical Strips, Code 14100 from Advanced Sterilization Products, Arlington, Texas) were peroxide plasma sterilized in a conventional manner in a Sterrad Plasma Sterilizer Model 100, from Advanced Sterilization Products, Irvine, California. Hydrogen peroxide was used as the chemical precursor of the active species in the plasma. In all packs the indicator turned from red to yellow indicating that sterilization had taken place.
Lastly, in order to determine whether the peel pack paper of the present invention could adversely affect the plasma sterilization apparatus, a sample size as large as 5,000 square centimeters was run without shutdown of the unit.
While the invention has been described in detail with respect to specific preferred embodiments thereof, it will be appreciated that those skilled in the art, upon attaining an W0:98/24970 PCT/US97/22363 understanding of the foregoing, may readily conceive of alterations to and variations of the preferred embodiments. Such alterations and variations are believed to fall within the scope and spirit of the invention and the appended claims.

Claims

WHAT IS CLAIMED IS:

1. A peel pack paper having a Gurley porosity of greater than 20 seconds/sheet, the paper comprising:
from about 45 to about 65%, by weight, of substantially fully bleached eucalyptus Kraft pulp fibers;
from about 10 to about 45%, by weight, of a blend of substantially fully bleached softwood Kraft pulp fibers and substantially fully bleached hardwood Kraft pulp fibers wherein the softwood Kraft pulp fibers comprise at least 90%, by weight, of the blend; and from about 10 to about 30%, by weight, of reinforcing fibers; and wherein substantially all of the fibers of the paper are coated with a dielectric material with the coating having an average thickness of less than 1 micron.

2. The peel pack paper of claim 1, wherein the softwood fibers are fir fibers.

3. The peel pack paper of claim 2, wherein the softwood fibers are selected from the group of spruce fibers, pine fibers and cedar fibers.

4. The peel pack paper of claim 1, wherein the hardwood fibers are selected from the group of aspen fibers, maple fibers ash fibers, poplar fibers and beech fibers.

5. The peel pack paper of claim 4, wherein the northern hardwood fibers are aspen fibers.

6. The peel pack paper of claim 1, wherein the paper has a Gurley porosity of greater than 25 seconds/sheet.

7. The peel pack paper of claim 1, wherein the paper has a delamination resistance of at least 200 grams/15mm.

8. The peel pack paper of claim 1, wherein the paper has a delamination resistance of at least 900 grams/15mm.

9. The peel pack paper of claim 1, wherein the paper has a Elmendorf tear of greater than 145 grams.

10. The peel pack paper of claim 1, wherein the paper has an Elmendorf tear of greater than 180 grams.

11. The peel pack paper of claim 1, wherein the paper has an average 0.1 micron sodium chloride particulate penetration of less than 5 percent.

12. The peel pack paper of claim 1, wherein the paper has an average 0.1 micron sodium chloride particulate penetration of less than 2 percent.

13. The peel pack paper of claim 1, wherein the reinforcing fibers are selected from the group of polyester fibers, nylon fibers, cotton fibers and rayon fibers.

14. The peel pack paper of claim 1, wherein the dielectric coating is selected from the group of polyolefins and polyolefin copolymers.

15. The peel pack paper of claim 14, wherein the dielectric material is selected from the group of high density polyethylenes, natural rubbers, synthetic rubbers and ethylene acrylic acid copolymers.

16. The peel pack paper of claim 1, wherein the paper comprises:
from about 50 to about 60%, by weight, of eucalyptus fibers;
from about 10 to about 30%, by weight, of the blend of northern softwood and hardwood pulp fibers; and from about 20 to about 30%, by weight, of the reinforcing fibers.

17. The peel pack paper of claim 1, wherein the paper comprises:
about 55%, by weight, of eucalyptus fibers;
about 20%, by weight, of the blend of northern softwood and hardwood pulp fibers; and about 25%, by weight, of the reinforcing fibers.

18. A peel pack paper having a Gurley porosity of greater than 20 seconds/sheet, the paper comprising:
from about 45 to about 65%, by weight, of substantially fully bleached eucalyptus Kraft pulp fibers;
from about 10 to about 45%, by weight, of a blend of substantially fully bleached softwood Kraft pulp fibers and substantially fully bleached hardwood Kraft pulp fibers wherein the softwood Kraft pulp fibers comprise at least 90%, by weight, of the blend; and from about 10 to about 30%, by weight, of reinforcing fibers; and wherein substantially all of the fibers of the paper are coated with a dielectric material with the coating having an average thickness of less than 1 micron;
and wherein the coated paper has been subjected to electret treatment.

19. The peel pack according to claim 18, wherein the electret treatment comprises application of a DC corona charge.

20. A method for producing a peel pack paper having a Gurley porosity of greater than 20 seconds/sheet and an average 0.1 micron sodium chloride particulate penetration of less than 5 percent comprising the steps of:
(a) providing a paper comprising (1) from about 45 to about 65%, by weight, of substantially fully bleached eucalyptus Kraft pulp fibers; (2) from about 10 to about 45%, by weight, of a blend of substantially fully bleached softwood Kraft pulp fibers and substantially fully bleached hardwood Kraft pulp fibers wherein the softwood fibers comprise at least 90%, by weight, of the blend; and (3) from about 10 to about 30%, by weight, of reinforcing fibers; and {b) coating substantially all of the fibers of the paper with a dielectric material wherein the average thickness of the coating is less than 1 micron.

21. The method of claim 19, wherein the dielectric coating is applied by an emulsion coating process.

22. The method of claim 19, further comprising the step of electreting the coated fibers.

23. The method of claim 22, wherein the step of electreting the coated fibers includes the application of a DC corona discharge treatment to the coated fibers.

24. A peel pack comprising the peel pack paper of claim 1.

25. A peel pack comprising the peel pack paper of claim 18.