CA1248696A - Dunnage material - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
Expanded, resilient, thermoplastic dunnage particles are rendered more effective by coating the outer surface of the particles with an additive which increases the coefficient of friction of that outer surface. The additive also promotes at least a minimum amount of adhesion between the dunnage particles.

Description

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I MPROt7 ED DUNNAGE MATER I AL

This invention relates generally to an improved dunnage material, preparation of such dunnage material and use of such dunnage material.

Dunnage materials such as foamed plastlc particles or strands are known to be highly desirable for use in packaging articles. The foamed particles or strands protect articles in shipping by absorbing shock and by isolation of the articles from shipping container walls. Typical particles or strands are set forth in U.S. Patents 3,188,264 and 3,723,240.

Dunnage materials are usually placed beneath, around the sides of, and atop articles being packaged in order to isolate the articles from container walls.
Packaging relatively light articles in this manner is generally efective. Packaging delicate but relatively heavy articles, such as electronic or optical equipment, in this manner is:less effective.

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2--It has been found that relatively heavy articles -tend to settle and migrate, or move through, the dunnage materials due to vibration or handling.
For example, in shipments in a truck, van, or rail car, migration of these heavy articles frequently continues until contact is made with a shipping container wall and breakage or other damage occurs. Breakage from this and other causes may be as much as fifteen percent, or even higher, especially where prolonged shipment or handling is involved.

A number of attempts have been made to reduce migration through dunnage materials.

Landen, in U.S. Patent 3,292,859 discloses the use of very small, expanded dunnaye particles having a surface coating of an adhesive or sticky material.

Holden, in U.S. Patent 3,188,264, discloses particles having a number o concave surface indenta-tions to promote interlocking between particles.

Skochdopole et al., in U.S. Patent 3,723,240, discloses asymmetrically foamable strands which curl upon foaming to form a generally helical stxucture.
The hPlical structures interlock to a degree when placed under pressure.

Xumbert et al., in U.S. Patent 3,251,728, disclose a dunnage material consisting essentially of a tangl~d interlockins mass of non-linear, elongated pieces of foamed polymer.

32,182--F -2-Graham, in U.S. Patent 3,047,136, discloses a dunnage material which consists of a plurality of strings of hollow crushable cylinders, each of the strings being partially cut through at spaced in-tervals.
A resilient or rubbery outer coa-ting may be applied to the strings to reduce sliding of the strings relative to each other as well as to supplement interlocking between the strings.

In one aspec-t the present invention is an improved packing material comprising a plurali-ty of expanded, resilient, thermoplastic, synthetic resinous dunnage particles, which particles comprise a friction enhancing amount of a friction enhancing additive deposited on at least a major portion of an outer surface area of a majority of said dunnage particles which additive results in the packing material having improved cushioning properties and reduces the tendency of articles to migrate through the dunnage particles, wherein the improvement comprises the use of particles which have an average maximum cross-sectional dimension of at least 1.27 centimeters (O.S inch).

In a related aspect, the present invention is an improved me-thod for preparing packing material in the form of foamed dunnage particles, the method comprising: providing a plurality of foamed particles and applying a friction enhancing amount.of a friction enhancing additive to at least a portion of an outer surface area of a ma~ority of said foamed particles wherein the improvement comprises providing particles which have an average maximum cross~sectional dimension of at least 1.27 centime-ters.

32,182~F . -3-In another related aspect, the present invention is the use of the improved packing material of Claim 1 in a method for packaging an article comprising:
(a) providing a packaging container, the container having at least one wall, a top and a bottom, the container also being of sufficient size to contain (1) at leas-t one article to be packaged and ~2) an amount of packing material particles sufficient to space the article from the wall, the top and the bottom of the container;
(b) adding a quantity of improved packing material particles to the packaging container, the quantity being sufficient to provide a layer of adequate -thickness to space the article to be packaged from t:he bottom of the con-tainer;
(c) placing the article to be packaged on the layer of packing material par-ticles;
(d) adding a further quan-tity of improved packing material particles to the packaging container, -the further quanti-ty being placed about the sides, within and on top of the article to space it from the walls and the top of container and from other articles, the further quantity being sufficient to provid~ a slight overfill of the packaging container;
2~ ~e~ closing the packaging con-tainer to slightly compact the particles by pushing down on the overfill.

One modification i5 to add a step where a first deformable sheet of material is placed over the layer of dunnage particles added to the container, and a second deformable sheet of material is placed over the article to be packaged. When placed under a compres-sive force, the first and second deformable sheets will generally deform so that portions of the second deformable 32,182-F -4-3fi~

shee-t come in contact with portions of the first deformable sheet thereby creating an envelope around the article.
A second modification is to wrap at leas-t one deformable sheet of material around the article before it is placed on the layer of dunnage particles.
The improved packing material can also be used advantageously when the article to be packaged is placed in contact with a wall, top or bottom of the container.
Dunnage particles suitable for use in the present invention are readily prepared from a wide variety of synthetic7 resinous, thermoplastic polymersO
One group of suitable thermoplastic polymers includes polymers which comprise, in chemically combined form, at least seventy (70) percent by weight of at least one alkenyl aromatic compound. Such compounds have the general formula R
Ar-C=CH2 wherein Ar represents an aromatic hydrocarbon or a ring-subs-tituted halohydrocarbon radical of the benzene series, and R is hydrogen or a methyl radical. Examples of such alkenyl aromatic polymers are homopolymers of styrene, alpha-methylstyrene, ortho-, meta-, and para-methylstyrene, Ar-ethylstyrene, tertiary-butylstyrene and Ar-chlorostyrene; the copolymers of two or more of such alkenyl aromatic compounds with one another; and copolymers of one or more of such alkenyl aromatic compounds with minor amounts of other readily polymerizable olefinic compounds such as divinylbenzene, methylmethacrylate, or acrylonitrile.

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A seconA group of suitable thermoplastic polymers which are suitable for preparing expanded dunnage particles includes aliphatic olefin polymers which are normally solid polymers obtained by polymerizing at least one alpha-mono-olefinic aliphakic hydrocarbon containing from 2 to 8 carbon atoms per molecule.
Illustrative hydrocarbons include ethylene, propylene, butene-1, pentene-1, 3-methylbutene-1, 4-methypentene-1, 4-methylhexene-1, and 5-methylhexene-1. The hydrocarbons may be polymerized alone, with one another, or with various other polymerizable compounds. The polymers of ethylene or propylene alone are desirable because they produce tough, resilient, fine-celled, chemically inert products.

Examples of suitable polymeriæable organic compounds which can be polymerized with ethylene or propylene are vinyl acetate; C1-C4 alkyl acrylates, such as ethyl acrylate; styrene; lower alkyl esters of methacrylic acid, such as methylmethacrylate; tetra-fluoroethylene; and acrylonitrile.

Copolymers containing, in chemically combined form, 75 percent by weight or more of ethylene or propylene with not more than 25 percent of one or more of such other polymerizable organic compounds also produce suitable results.

The aliphatic ole~in polymers can be modified by blending with polymeric materials. Illustrative po]ymeric materials include polyisobutylene, acrylo-nitrile/butadiene rubbers, poly(2-chlorobutadiene~1,3), polyisoprene, ethylene/acrylic acid copolymers and ethylene/vinylacetate copolymers.

32,182-~F -6-_7_ ~ 2 ~

A third group of suitable thermoplastic polymers suitable for preparation of expanded dunnage par-ticles includes halogenated aliphatic olefin polymers, as well as polymers of a wide variety of ethylenically unsaturated monomers which produce foamable thermoplastic compositions. Illustrative polymers includ~ those prepared by polymerizing isopropenyl toluene; vinyl naphthalene; esters of alpha-methylene aliphatic mono-carboxylic acids, such as methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate r dodecyl acrylate, 2-chloroethyl acrylate, 2 chloropropoyl acrylate, 2,2'-dichloroisopropyl acrylate, phenyl acrylate, cyclohexyl acrylate, methyl alpha-chloroacrylate, methylmethacrylate, ethylmethacrylate and methyl-ethacrylate; nitriles such as acrylonitrile andmethacrylonitrile; vinyl esters such as vinyl acetate, vinyl chloroacetate, vinyl propionate, vinyl butyrate, vinyl laurate and vinyl s-tearate; vinyl ethers such as vinyl methyl ethers, vinyl isobutyl ethers and vinyl 2-chloroethyl ether; vinyl ketone; methyl isopropenyl ketone; isobutylene; vinylidene halides, such as vinylidene chloride and vinylidene chlorofluoride;
N-vinyl compounds such as N-vinyl pyrrole, N-vinyl carbazole~ N-vinyl indole, N-vinyl succinimide, acrolein, methacryolein, acrylamide, methacrylamide and N-methylol acrylamide; and allyl compounds such as allyl alcohol, methallyl alcohol, allyl acetate, allyl methacrylate, allyl lactate, allyl alpha-hydroxyisobutyrate, allyl trichlorosilane, allyl acrylate and methallyl phosphate.

Foamable compositions of polymers are readily prepared by incorporating therein a gas, a volatile liquid, a solid gas-releasing blowing agent or a combina~
tion of two or more of these which cause expansion-of the polymeric material on heating.

32,182-F -7-In order to obtain improved cushioning according to the present invention, it is desirable to use expanded dunnage par-ticles which have an average maximum cross-sectional dimension of at least 1.27 centimeters (0.5 inch).
Preferably, the particles have an average minimum cross-sectional dimension o at least 1.27 centimeters.

In one method for preparing the improved packing material, a heat plastified mass of synthetic resinous material is provid~d in a first step. The heat plastified mass contains an expanding agent. The mass is capable of expansion to form a plurality of closed, gas-filled cells. In a second step, the heat plastified mass is put and maintained under pressure.
In a third step, the heat plastified ma~s is cooled to a temperature which is less than a temperature at which the heat plastified mass would foam under a reduced pressure. In this step, a cooled heat plastified mass is obtained. In a fourth step, the cooled heat plas-tified mass is extruded, without significant foaming, from a shaping configuration to form elongate stands. In a fifth step, the elongate strands are severed to form a plurality of foamable elements of relatively high bulk density. As an alternative, a die face cutter or similar apparatus could be used to pelletize the cooled heat plastified mass as it is extruded. In a sixth step, the foamable elements, or pellets, are heated to an elevated temperature. Tne elevated temperature is - sufficient to cause the elements to expand and thereby form foamed particles having a plurality of gas-filled cells therein. In a seventh step, a friction enhancing amount of an addi-tive is applied to at least a portion of the outer surface area of a majority of the ~oamed particles.

32,182-F -8-9~
g The friction-enhancing additive is suitably any material which meets three criteria. First, it must be capable of being deposited on the outer surface area of the dunnage particles. Second, it must remain on the outer surface area of the durmage particles for a useful length of time. The useful length of time is that ~hich is sufficient to allow one or more articles to be (a) packaged with the dunnage particles, (b) shipped or transported to a desired destination, with or without intermediate periods of storage, and ~c~ unpackaged, again with or without intermediate periods of storage. Third, the additive must impart to the outer surface area of the dunnage particles an increased coefficient of friction. Preferably, the additive promotes at least a minimum amount of adhesion between the dunnage particles.

In order to determine whether an additive meets t~e afor~mentioned criteria, a modified peel test was developed. The results of the peel test were compared with results of a vibrational settling test to establish a correlation between the -tests. The tests are set forth in hereinafter.

Materials which meet the aforeme~tioned criteria include synthetic polymer latexes, pressure sensitive adhesives and glues, low molecular weight polymers, waxes, contact cements, starch-derived adhesives, urethane adhesives and pro-tein-derived adhe-sives.

Low molecular weight polymers, as used herein, are those polymers which have a ring and ball softening point of greater than about 30 Centigrade, preferably 32,182-F 9-3t~

greater than about 50 Centigrade. Ring and ball softening points are determined in accordance with ~merican Society for Testing and Materials Test E-28.

Starch-derived adhesives include pastes, such as wheat paste, dextrins, borated dextrins, jelly gums and the like. Suitable starches are those represented by the formula (C6Hl0o5)n where n = 1 to about 1,OOO,OoO.

Protein derived adhesives include animal glue, casein and the like.

Useful synthetic polymer latexes are those which meet the aforementioned criteria and which are aqueous colloidal suspensions of particles of a polymer obtained by emulsion polymerization. The colloidal suspensions are generally stabilized by addition of one or more suitable surface active agents.

Suitable latexes include those based on, for example, styrene butadiene copolymers, acrylic copolymers, butadiene acrylonitrile polymers, vinylidene chloride copolymers, vinyl chloride copol~mers and copolymers of vinyl alkanoates, such as vinyl acetate.

Beneficial results are obtained when the polymer latex contains a carboxyl functionality. A
suitable level o carboxyl functionality is from 0.01 to 25 percent by weight of polymer. The carboxyl functionality is obtained by including one or more alpha,beta-olefinically unsaturated carboxylic acid monomers with other polymerizable monomers to be used in preparing the aforementioned latexes.

32,182-F -10-Suitable carboxylic acid monomers contain from three to twelve carbon atoms per molecule. Such acid monomers include acrylic acid, methacrylic acid, ethacrylic acid, alpha-chloroacrylic acid, alpha--cyanoacrylic acid, crotonic acid, heta-acryloxypropionic acid, hydrosorbic acid, sorbic acid, alpha-chlorosorbic acid, cinnamic acid, beta-styrylacrylic acid, itaconic acid, citraconic acid, maleic acid, fumaric acid, mesaconic acid and aconitic acid. Beneficial results are obtained with carboxylic acid monomers containing from three to six carbon atoms per molecule such as acrylic acld and methacrylic acid.

Satisfactory results are obtained when the additive is a latex of a styrene-butadiene copolymer which has a carboxyl functionality. Such copolymers typically have polymerized therein (a) styrene in an amount of from 40 to 70 percen-t by weight of copolymer, (b~ butadiene in an amount of from 15 to 40 percent by weight of copolymer, and (c) carboxylic acid monomer(s) in an amount of from 0.1 to 20 percent by weight of copolymer.

Acrylic copolymers typically have polymerized therein (a~ one or more alkyl acrylates which contain from one to eiyhteen carbon atoms per alkyl moiety and (b) one or more monomers which are copolymerizable therewith. The alkyl acrylates beneficially have from four to ten carbon atoms per alkyl moiety. Illustrative alkyl acrylates include butyl acrylate, amyl acrylate, hexyl acrylate, heptyl acrylate, octyl acrylate, nonyl acrylate, decyl acrylate and various isomers of these acrylates such as isooctyl acrylate and 2 ethylhexyl acrylate.

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Satisfactory results are obtained when the additive is an acrylic copolymer or interpolymer which has polymerized therein (a) from 40 to 80 percent by weight of polymer of at least one alkyl acrylate and (b) from 20 to 60 percent by weight of polymer of at least one ethylenically unsaturated monomer which is copol~nerizable therewith.

Illustrative copolymerizable ethylenically unsaturated monomers include alpha-olefins containing from 2 to lO carbon atoms; vinyl esters of alkanoic acids containing 3 to 10 carbon atoms, such as vinyl acetate and vinyl octoate; ethyl and methyl esters of methacrylic ~cid; styrene; and vinyl chloride.

Vinyl chloride latexes which contain either vinyl chloride homopolymer or interpolymers of vinyl chloxide also provide satisfactory results. Vinyl chloride interpolymers typically have polymerized therein from 50 to 97 percent by weight of polymer of vinyl chloride and from 3 to 50 percent by weight of polymer of at least one ethylenically unsaturated monomer which is copolymerizable therewith. Illustrative copolymerizable monomers include the alkyl acrylates hereinabove specified, the vinyl esters of alkanoic acids hereinabove specified, alkyl esters 3f methacrylic acid containing from one to four carbon atoms per alkyl moiety, and vinylidene chloride.

Latexes are generally prepared by emulsion polymerization using anionic or nonionic surfactants or mixtures thereof. Suitable anionic surfactants include sodium dioctyl sulEosuccinate, sodium diamyl sulfo succinate, sodium dihexyl sulfosuccinate, sodium lauryl 32,182-F -12-:~2~

sulfate, and sodium dodecyl benzene sulfonate. The nonionic surfactants which may be considered e~emplary include nonyl or octyl phenoxypolyethoxyethanol condensates wherein the ethylene oxide content may vary ~rom 5 to 50 moles. Conventionally, two or more of these nonionic surfac-tants may be employed. Latex preparation is achieved using conventional polymerization methods.
Polymer latexes containing up to about 60 percent by weight total polymer solids may be conveniently sprayed. For optimum results, solids concentrations of 35 to 55 percent are preferred, Any spraying method capable of atomizing the additive may be employed. Accordingly, the particular method of spraying is not critical to production of the improved dunnage particles of the present invention. Thus, air, airless or aerosol systems may be employed. Low fluid delivery rates and low atomization pressures are advisable since these will minimize overspray and misting of the adhesive into the surrounding atmosphere. The fluid delivery system most suitable is an airless sprayer with a pneumatic pump. Other suitable spraying equipment includes a pressurized vessel in combination with conventional air spray equipment and peristalic action pumps.
The additive to be sprayed is generally delivered into the spray equipment at a rate of 50 to 500 wet grams per minute, preferably 100 to 400 wet grams/minute. The amount of atomization pressure required will be proportionate to the adhesive delivery rate and will typically range from 35 to 550, preferably 70 to 550 kilopascals (kPa).

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Application of additive to foamed dunnage particles is not limited to spxay equipment and methods using such spray equipment. Accordingly, additives may be applied by brush, by roller or by any other means so long as a sufficient quantity of additive is applied to the dunnage particles.

The improved dunnage particles, if prepared and dried in advance of packaging, may be readied for use simply by applying a light water mist or stea~
spray to the surface thereof. The mist or spray may be applied to the improved dunnage particles prior to, simultaneously with, or subsequent to addition to a packaging container. I the improved dunnage particles have clumped together, as is the case where the the improved dunnage particles are being re-used, the mist or spray beneficially wets the additive suficiently to allow the improved dunnage particles to separate into individual particles or small, but useable, clumps.

The additive is acceptable if it provides, under the modified peel test nereinafter described, a peel strength of at least 1.5 ~rams per centimeter.
The additive beneficially provides a peel strength of greater than 9 grams per centimeter. The additive d~sirably provides a peel strength of ~reater than 40 grams per centimeter. The aAditive preferably provides a peel strength of 150 grams per centimeter. Greater peel strength is acceptable but is not necessary.

Another way of determining whether or not an additive is acceptable is to determine an overall settling value under the modified vibrational settling test hereinafter described. The overall settling 32,182-F -14--15- ~ Z ~

value is suitably less than 65, beneficially less than 45, desirably less than 30 and preferably less than 25.

The peel strengths and overall settling values specified hereinabove are readily obtained with an amount of additive of from 1400 to 6000 grams of wet additive per cubic meter of foamed dunnage material.
Beneficial results are obtained with an amount of additive of from 1600 to 3400 grams of wet additive per cubic meter of foamed dunnage material.

~mounts of additive in e~cess of 6000 grams of wet additive per cubic meter of dunnage material will satisfactorily modify the coefficient of friction of the foamed dunnage material. In other words, amounts of wet additive of up to 10,000 and more grams of wet additive per cubic meter of dunnage can be used according to the present invention. Such amounts are, however, excessive and may be undesirable for several reasons suc~ as C06t effectiveness, uneconomical drying rates and damage to the article(s) being packaged.

Amounts of additive of less than 1400 grams of wet additiv2 per cubic meter of foamed dunnage material are generally unsatisfactory because they do not provide sufficient coverage of the foamed dunnage material.

One advantage of the improved dunnage particles of the present invention is that they provide lower vihrational settling values than conventional dunnage particles. In other words, migration of articles through the improved dunnage particles is less likely than with conventional dunnage particles.

32,182-F -15-A second advantage is that the improved dunnage particles, when used in packaging, provide ~, reproducible ~ cushioning properties. Conven tional dunnage particles provide erratic ~ynam~
cushioning properties. Reproducibility is highly desirable in the area of package design.

~ A third advantage is that the improved dunnage particles of the present invention ~end to stick together until pulled apart, particularly when ~he additive is an adhesive, a glue, a contac-t cement ~nd the like Conventional dunnage particles have no tendency to stick together and are known to spill over the edge of the package and to scatter over the su~face upon which th~ package is resting. Picking up the scattered dunnage particles is time consuming and bothersome.
The improved dunnage particles will, depending upon the amount of additive, be removed from the package either as several small clumps of particles or as a few large masses of particles.

~ A fourth advantage is that by varying the amount of additive applied to the improved dunnage particles, a broad spectrum of package properties can be attained. In other words, it is possible to tailor the improved dunnage particles to meet a specific need.
With conventional dunnage particles, there is a very narrow spectrum of package properties.

These advantages are attained with relatively low levels of additive. Application of the additive to -the dunnage particles is neither compli~cated nor expensive.
At low levels of additive, drying time is short thereby providing minimal interference with normal package handling procedures.

32,182-F . 16--17- G~6~3-358 Modified Peel Test General purpose polystyrene film having one side surface sulfonated was used for the peel test. The film ha~ a thickness of 6.35 micrometers and was commercially available from the Dow Chemical Company under the trade designation Trycite~ 1101. Samples having a size of 2.54 centimeters in width and 33 centimeters in length were cut from the film so that the latter dimension was in the machine direction.
The samples were prepared for peel testing in the following manner. Using a #10 Meyer rod, one end of the sulfonated side of the film sample was coated for a distance of about ten centimeters with the additive to be tested. The film sample was then folded over so that an equal distance of sulfonated surface from the other end of the sample was in intimate contact with the coated portion. The film samples were then placed in a dessicator and aged for a period of 72 hours. The dessicator had a relative humidity of from 17 to 20 percent and a set temperature of from 21 to 24 Centigrade.
After aging, the samples were removed from the dessicator.
The samples had a bonded end and a loop end. The loop end was then cut to yield two free ends of approximately equal length. The free ends had no additive coated thereon.
An Instron Universal Testing Machine, Model Number 1123 was used to determine peel strength. The Instron testing mach~ne had two sets of jaws which were spaced apart and opposite each other.
On set of jaws was stationary and affixed to the machine. The other , ~

3~
~18-set of jaws was attached to a load cell which in turn was attached to the mobile crosshead of the machine.

The free ends of the samples were placed in-to the two sets of jaws. One free end was clamped by the stationary set of jaws. A second free end was clamped by the set of jaws attached to the load cell. The crosshead of the machine was actuated so as -to move the set of jaws attached to the load cell away from the stationary set of jaws at a speed of either 200 or 254 millimeters per minute. The crosshead speed had no effect upon peel strength. The samples were pulled apart until they separated along their entire length.
The load cell registered the peel strength for the sample.

Vibrational Settlin~ Test The purpose of this test was to determine whether an article packaged in dunnage material moved due to vibration and~ if so, how much. The test was a modified version of the vibrational settling test described in United States Federal Speciflcation PPP-C-1683, Section 4.9 for expanded polystyrene loose--fill cushioning material.

About 57,000 cubic centimeters of dunnage material were placed in an open-topped box. The box measured 100 centimeters in length by 60 centimeters in width by 60 centime-ter~ in height. A 0.635 centimeter mesh screen was placed over the opening in the box.

A Craftsman Model 919.1561410 spray gun, having a capability for either internal or external fluid to air mixing and being commercially available 32,182-F -18-3~

from Sears, Roebuck and Co., was used to spray an admixture of a dye and the additive to be tested for friction enhancement down through the screen onto the dunnage material. The dye was used to provide a visual indicator of coverage of the additive onto the dunnage material. The spray gun had a reservoir portion into which the admixture was placed for application thereof onto the dunnage material. The reservoir portion was pressurized to a pressure of 275 kilopascals gauge in order to provide a consistent flow rate of about 0.11 liters of admixture per minu-te. The flow rate provided a force of spray sufficient to cause a mixing of the dunnage material with the box.

Spraying was continued until a visual inspec-tion of the dunnage material showed that a generallyuniform coa-ting of the admixture was deposited on the dunnage material.

The ra-te of spray, in terms of wet grams of additive per minute, varied with the additive being applied. In other words, as density of the additive changed, the rate of spray also changed. By way o example only, an additi~e having a specific gravity of about 1.0 at a temperature of 24 Centigrade had, when applied using the aforementioned spray gun at a pressure o 275 kilopascals gauge, a flow rate of from about 100 to about 140 wet grams of addi-tive per minute for a nominal flow rate of 125 wet grams of additive per minute.

A cardboard test box having interior dimensions 30 centimeters by 30 centimeters by 30 centimeters was filled about halfway with the coa-ted dunnage material.

32,182 F -19-~L z ~ i a 3~ 6 -20~

A load box having exterior dimensions of 15 centimeters by 15 centimeters by 15 centimeters and weighing either 2.4 or 7.3 kilograms was placed into -the test box in such a manner as to yield a 7.6 centimeter (~ 2.54 centimeter) gap between the top of the load box and the top of the test box. The 2.4 kilogram load box was used to supply 1035 Newtons per square meter loading.
The 7.3 kilograms load box was used to supply a 3105 Newtons per square meter loading.

An additional amoun-t of coated dunnage material was added to the test box to fill it even with the top of the test box. Consistent with recommended packaging guidelines for expanded, thermoplastic loose fill dunnage mateirals, the test box was then overfilled lS with a pyramid or crown of the coated dunnage material.
The crown had a depth of about 2.54 centimeter, the depth being measured from the top of the test box to the top of the crown. The lid of the box was then closed and taped shut with fiberglass reinforced tape.

After being closed, the test boxes and their contents were allowed to dry at a temperature of 21 ~9 Centigrade for a period of about sixteen hours. No specific control of humidity or o temperature was attempted during drying.

A small hole, measuring 0.356 centimeters in diameter, was made in the center of the top of the test box.

A stiff piece of stainless steel wire, also - 0.356 centimeters in diameter, was inserted into the hole and thereafter pushed through the dunnage material 32,182-F -20-until it contacted the top of the load box. The length of wire between the top of the test box and the top of the load box was measured and recorded as "initial displacement".

The test box and its contents were placed on a table capable of vibrating at a frequency of 4.5 Hertz with a vertical displacement of 2.54 centimeters.
The table was designated as an MTS Series 840 Servo-hydraulic Vibration Test System and was commercially available from MTS Systems Corporation.

The table had a square sample receiving surface which measured 90 centimeters on a side. An internally screw threaded aperture having a diameter of 0.953 centimeter had been machined into the sample receiving surface at ~ach corner thereof. An externally screw threaded rod was threadably engaged with each of the threaded apertures. Four rubber strips measuring 66 centimeters long by 1.91 centimeters wide by 0.64 centi~
meter thick and having hooks attached to each end thereof were connected between adjacent screw threaded rods so as to form a peripheral boundary around the table. The four rubber strips, also known as boundary strips, were spaced above the table surface a distance of about 13 centimeters. Two additional rubber strips, iden-tical to the other rubber strips were connected between opposing boundary strips so as to divide the sample receiving sur-face into four equal sqaure sample holding areas.

Four test boxes, prepared as hereinbefore described and of approximately equal weight, were placed on the sample receiving surface. One of the test boxes was placed within each of the sample holding 32,182-F -21-areas. The test boxes were no-t secured to the table in keeping with the guidance set forth in United States Federal Specification PPP-C-1683, Section 4.~. The test boxes had to be approximately equal in weight in order to maintain a balanced load on the table.

After the four test boxes were placed on their respective sample holding areas, the table was actuated. After a period of thirty minutes, the table was stopped. ThP same stiff piece of wire was inserted through the hole once again until it touched the top of the load box. The length of wire between the top of the test box and the top of the load box was measured and recorded as "final dlsplacement".

Any increase in length from initial displacement to final displacement was converted to a percentage and recorded as "percent settling".

It was found that percent settling values at the 3105 Newtons per square meter loading (7.3 kilo-grams load box) were much larger than those at the 1035 Newtons per square meter loading (2.4 kilogram load box). In order to develop a meaningful pass-fail evaluation, a total settling value was calculated. The total settling value was determined by multipiying the settling value at the 1035 Newtons per square meter loading by a factor of 6.71 to obtain a product and then adding the product to the settling value at the 3105 Mewtons per square meter loading.

The ollowing experiment is for purposes of illustration only and is not to be construed as limiting the scope of the present invention.

32,182-F -22-A number of additives were evaluated for suitability using the "Peel Test" and the "Vibrational Settling Test" set forth hereinabove. Table I contains a description of the additives together with an abbreviated code for such additives. Table II con-tains peel test data and vibrational settling test data for each of the additives and for a control to which no additive had been applied. The dunnage material used in the vibrational settling tests was an expanded polystyrene particulate material co~mercially available under the trade designation Pelaspan-PacTM from The Dow Chemical Company, the particles having an average minimum cross-sectional dimension of about 1.27 centimeters (0.5 inch) and an average maximum cross--sectional dimension of about 2.86 centimeters (1.125 inch).

- 32,182-F -23 -2~-TABLE I
Additive Identification CodeDescription of Additive Tested *

Al Fumed silica A2 Ground pepper A3 A carboxylated styrene butadiene copolymer latex, the copolymer having polymerized therein styren~ in an amount of 48 10- percent by weight of polymer, and butadiene in an amount of 50 percent by weight of copolymer, and fumaric acid iIl an amount of 2 percent by weight of polymer. The latex had a nominal particle size range of from~ about 0.16 to about 0.2 ~m, a specific gravity of 1.02 and a solids content of from about 47 to about 49 percent~ The latex was available from The Dow Chemical Company under the trade designation XD-30586.20.

~xperimentally determined not to be a friction-enhancing additive for the purposes of the present invention.

32,182-F -24~

TABLE I Continued Code Description of Additive Tested A4 A vinylidene chloride polymer late~, the polymer having polymerized therein (a~ vinylidene chloride in an amount of 82 percent by weight of polymer, (b) methyl acrylate in an amount of 18 percent by weight of polymer, ~c) acrylic acid in an amount of 4 parts per 100 parts of (a) and (b), and (d) 0.5 parts of sodium sulfoethyl methacrylate per 100 parts of (a) and (b).
The late~ had a particle size of from about 0.1 to about 0.14 ~m, a viscosity, measured at 25 Centigrade using a Brookfield vi~cometer with a number one spindle and a rotor speed of 60 revolutions per minute, of less than about 1.5 pascal second (Pa s) a solids content of from about 48 to about 50 percent, and a surface tension of from 0.045 to about 0.055 newtons per meter (N/m). The latex was available from The Dow Chemical Company under the -trade designa-tion XD-30452.22.

32,182-F -2S-3~

TABLE I Continued Code Description of Additive Tested A5 A self cross-linking polyvinyl acetate homopolymer latex having a nominal particle size of 0.7 ~m, a pH of 3.0, a specific gravity of 1.08, a viscosity, measured at 25 Centigrade using a ~rookfield viscometer with a number one spindle and a rotor speed of 60 revolutions per minute, of 0.06 Pa s, and a surface tension of about 0.041 N/m.
The latex was commercially available from Borden Chemical under the trade designation POLYCO~ 2136.

A6 A vinyl chloride homopolymer latex having a nominal particle size of 0.16 ~m, a pH of 9.5, a specific gravity of 1.18, a viscosity, measured at 25 Centigrade using a Brookfield viscometer with a numbe.r one spindle and a rotor speed of 60 revolutions per minute, of 0.03 Ra s, and a surface *

Experimentally determined not to be a friction-enhancing additive for the purposes of the presen-t invention.

32,182-F . -25-~ABLE I Con-tinued Code Descrlption of dditive Tested tension of 0.04 N/m. The latex was commercially available from Borden Chemical under the trade designation POLYCO~
~ 2622.

A7 A small particle size paint pigment latex containing a styrene copolymer and having a nominal particle siæe of 0.13 ~m a nominal weight a~erage molecular weight of 100,000 grams per mole, a solids content of 45 to 50 percent, and a specific gravity of 1.05 - (at a temperature of 25 Centigrade3. The copolymer had polymerized therein about 99.2 parts of styrene and about 0.8 parts of itaconic acid. The latex was commercially available-from The Dow Chemical Company under the trade designation DPP 788.

A8 A large particle size paint pigment latex containing a styrene copolymer and having a nominal particle size of 0.35 ~m, a nominal weight average molecular weight of 32,182-F -27-i''36 ~28-TABLE I Co~tinued Code . Description of Addi-tive Tested 350,000 grams per mole, a solids content of 45 to 50 percent, and a specific gravity of 1.05. The copolymer had polymerized -therein about 97 parts of styrene and about 3 parts of acrylic acid. The latex was commercially available from The Dow Chemical Company under the trade designation DPP 722.
o .

A9 A vinylidene chloride polymer latex, the pol~mer having polymerized therein (a) vinylidene chloride in an amount of about 40 percent by weight of polymer, (b) acrylo-ni.trile in an amount of about S percent by weight of polymer, (c) butyl acrylate in an amount of about 5 percent by weight of polymer, and (d) 1.4 parts of sodium sulfoethyl methacrylate per 100 parts of (a~ plus (b) plus (c). The latex had a particle si~e of from about 0.1 ~m to about 0.13 ~m, a viscosity, measured at 25 Centigrade using a Brookfield viscometer with a 32,182-F -28-TABLE I Ccntinued Code Description of Additive Tested number one spindle and a rotor speed of 60 revolutions per minute, of less than 0.05 Pa s, a solids content of from about 53 to 55 percent, and a surface tension o from about 0.06 to about 0.073 N/m. The latex was commercially available from The Dow Chemical Company under the trade designation SL143.

A10 A s-tyrene copolymer latex having a nominal particle size of 0.03 ~m, a nominal weight average molecular weight of 500,000 grams per mole, a solids content of 35 to 40 percent and a specific gravity of 1.05. The copolymer had polymerized therein styrene in an amount of 96 parts by weight and acrylic acid in an amount of 4 parts by weigh-t, both amounts being based upon copolymer weight. The latex was available from The Dow Chemical Company under the trade designation XD 8510.

32,182-F -29-_30~ 3 TABLE I Corltinued Code Descr1ption of Additive Tested A11 A wallpaper wheat paste prepared by dispersing wheat flour in water, the paste containing 18 percent by weight of wheat flour. The wheat flour, which was prepared by ~rinding hard winter wheat, contained a non-toxic vermicide. The wallpaper paste was commercially available under the trade designation wallpaper wheat paste item ~61102 f.rom Bondex International, Inc.

A12 . A urethane laminating adhesive which contained la) about 55 weight percent of an isocyanate terminated prepolymer, (b) about 32 weight percent methylene chloride, ~c) about 5 weight percent of toluene, (d) about 5 percent ethyl acetate, and (e) about 2.5 weight percent free diphenylmethane diisocyana-te, all percentages being based upon weight of adhesive. The adhesive had a solids content of 58~ 1 percent and a specific gravity of 1.13. The adhesive was commecially available 32,182-F -30-.

3~ --31.-TABLE I Continued C _ Descrip-tion of Additive Tested under the trade designation Mor-Ad 337 from Morton Chemical Company.

Al3 A carboxylated styrene butadiene copolymer la-tex, the copolymer having polymerized therein styrene in an amount of 42 percent by weight of copolymer, butadiene in an amount of 55 percent by weight of copolymer and itaconic acid in an amount of 3 percent by weight o~ co-polymer. The latex had a nominal particle size of from about 0.14 to about 0.18 ~m, a specific gravity o~ l.Ol and a solids content of from about ~o 44 to about 47 percent~ The latex was commercially available from The Dow Chemical Company under the -trade designation DL-219A.

32,182-F -31-~2(,~

TABLE II
Test Data Vibrational Settling Test 5Percent _S ttllng Peel 1035 New- 3105 New-Strength tons per tons per Overall Ex. grams/ square squareSettling No. Additive centimeter meter meter Value 1 - 0 8 41 g5 2 Al 0 40 70338

4 A3 252 0 25 25 6 A5 1.57 3 37 57 7 A6 0.08 4 58 85 8 A7 9.5 0 13 13 20 11 ~10 4.7 3 43 63 12 All 35 0 17 17 13 A12 175 0 1'717 Comparative Experiment not representative of the present invention.

From the data presented in Table II, it is clear that a disparity exists among various additives.
Some, such as additives A3, A4, A7 through A9, A11, A12 and A13 markedly improve the overall settling value of dunnage material. Others, such as additives Al and A2, 32,182-F . -32-3~

actually promo-te settling as indica-ted by an increased o~-erall settling value.

A reduction in the overall settling value is desirable because it indicates that khe dunnage material will then be more effective in cushioning articles which are packaged therewith.

32,182-F -33-

Claims (10)

1. An improved packing material comprising a plurality of expanded, resilient, thermoplastic, synthetic resinous dunnage particles, which particles comprise a friction-enhancing amount of a friction-enhancing additive deposited on at least a major portion of an outer surface area of a majority of said dunnage particles which additive results in the packing material having improved cushioning proper-ties and reduces the tendency of articles to migrate through the dunnage particles, wherein the improvement comprises the use of particles which have an average maximum cross-setional dimension of at least 1.27 centimeters (0.5 inch).

2. The packing material of Claim 1 wherein the dunnage particles are formed from a synthetic resinous material, the resinous material being selected from the group consisting of (a) polymers which comprise, in chemically combined form, at least about seventy percent by weight of at least one alkenyl aromatic compound; (b) aliphatic olefin polymers which are normally solid polymers obtained by polymerizing at least one alpha-mono-olefinic aliphatic hydrocarbon containing from 2 to 8 carbon atoms per molecule; and (c) halogenated aliphatic olefin polymers.

3. The packing material of Claim 1 wherein the friction-enhancing additive is selected from the group consisting of synthetic polymer latexes, pressure sensitive adhesives, glues, low molecular weight polymers, waxes, contact cements, urethane adhesives, starch derived adhesives and protein derived adhesives.

4. The packing material of Claim 3 wherein the additive is a synthetic polymer latex, the latex containing a polymer selected from the group consisting of styrene-butadiene copolymers, acrylic copolymers, butadiene-acrylonitrile copolymers, vinylidene chloride copolymers, vinyl chloride copolymers and vinyl alkanoate copolymers.

5. The packing material of Claim 3 wherein the polymer has polymerized therein styrene in an amount of from 40 to 70 percent by weight of polymer, butadiene in an amount of from 15 to 40 percent by weight of polymer and acrylic acid in an amount of from 0.1 to 20 percent by weight of polymer.

6. The packing material of Claim 1 wherein the amount of additive is from 1400 to 6000 grams of wet additive per cubic meter of expanded dunnage particles.

7. The packing material of Claim 3 wherein the additive provides a peel strength of greater than 1.5 grams per centimeter and an overall settling value of less than 65.

8. An improved method for preparing packing material in the form of foamed dunnage particles, the method comprising:
providing a plurality of foamed particles and applying a friction-enhancing amount of a friction-enhancing additive to at least a portion of an outer surface area of a majority of said foamed particles wherein the improvement comprises providing par-ticles which have an average maximum cross-sectional dimension of at least 1.27 centimeters.

9. A method for packaging an article comprising:
(a) providing a packaging container, the container having at least one wall, a top and a bottom, the container also being of sufficient size to contain (1) at least one article to be packaged and (2) an amount of packing material particles suffi-cient to space the article from the wall, the top and the bottom of the container;
(b) adding a quantity of the improved packing material particles according to claim 1 to the packaging container, the quantity being sufficient to provide a layer of adequate thickness to space the article to be packaged from the bottom of the container;
(c) placing the article to be packaged on the layer of packing material particles;
(d) adding a further quantity of said improved packing material particles to the packaging container, the further quan-tity being placed about the sides, within and on top of the article to space it from the walls and the top of container and from other articles, the further quantity being sufficient to provide a slight overfill of the packaging container;
(e) closing the packaging container to slightly compact the particles by pushing down on the overfill.

10. The method of Claim 9 comprising in step (c) placing a first deformable sheet of material over the quantity of particles;
then placing the article to be packaged atop the first sheet of material; and placing a second deformable sheet of material over the article to be packaged.