US2895270A

US2895270A - Packaging material

Info

Publication number: US2895270A
Application number: US546344A
Authority: US
Inventors: Blaess A Albert
Original assignee: Minnesota Mining and Manufacturing Co
Current assignee: 3M Co
Priority date: 1955-11-14
Filing date: 1955-11-14
Publication date: 1959-07-21
Anticipated expiration: 1976-07-21

Description

July 21, 1959 A A. BLAESS 2,895,270

PACKAGING MATERIAL Filed Nov. 14, 1955 v 5), ,WMMVM United States Patent AEl PACKAGING MATERIAL A. Albert Blaess, Western Springs, lll., assigner, by `mesne assignments, to Minnesotav Mining and Manufacturing Company, St. Paul, Minn., a corporation of Delaware Application November 14, 1955, Serial No, 546,544 7 Claims. V(Cl. 53-21) i This invention relates to novel, heat-scalable, packaging material -and to an improved method for packaging metal particles. More particularly, this invention relates "to novel, heat-scalable, packaging -or wrapping sheet material which provides a protective, corrosion-inhibitingatmosphere for packaged, `grease-tree, :metal parts,

The automatic packaging of `small metal parts, -s-uch as for example hardware items or small metal machine parts used in the automotive industry, lis most expeditiously accomplished by using heat-scalable sheet materials. In packaging such small vmetal parts, however, care must be ltaken -to protect Athe same from the corrosive action vof Water vapor and oxygen. Suitably the parts may be thoroughly coated with a layer of grease `to prevent corrosion, but this presents ditiiculties in automatic packaging. The automatic Apackaging of greased Vmetal `parts cannot be accomplished continuously for periods of time greater than about two hours inasmuch `as the packaging machinery becomes clogged with grease during operation. Grease, of course, prevents 'eiiective'heatseals from being formed, and the production line for automatic lpackaging must frequently be shut down to permit cleaning of grease -deposits *from the machinery.

This invention provides a sheet material Which obv'iates such"ditl`1cuilt`ies in' automatic packaging as the foregoing, andfurther provides a means for forming neat, compact, sealed enclosures vor packages with protective, corrosioninhibiting atmospheres. Also provided by this invention is ra composite packaging or wrapping sheet material which kis lat once bot-h heat-scalable and capable Aof imparting protective atmospheres about -metal parts. The sheet ma- `ter-itil'hereofi-s `non-blocking and 'may be ystored in rolls Aor stacked i-n` sheets until used. Preferably the sheet mate- 'rial hereof vis stored wrapped lin an impervious outer wrap- 'per of metal foil -or 4the like.v Whenrequired Cfor use, my ssheetl material is readily `unwound from a rolled cylinder 'or y'readilyseparated from other sheets'loifastackf.

iIn the drawings, `Figure l is a Icross sectionalrview through a layer of 'the packaging sheet material of this invention, illustrating -thcvarious layers thereof. Figure 2 'a perspective View Aof a small heat-sealed package iorrnedusing the sheet material hereof. JFigure 3 is Va `cross sectional View through 'line 3--3 `in :Figure 2, illusitratingapackaged 'metal xarticle 'with a protective atmosphere Within the enclosure. v

In `|brief, the sheet material of vthis 1invention comprises fa ilexible, relatively-stili, Asupport member 10 and a -iilrn- -likekcoatingll `adhered thereto. The lm-likecoating may hecharacterized as macroscopically homogeneous in lthat it is `not zevident -to the vnaked 'eye that it contains 4a mixture of materials. Macroscopically, it has-a'u-ni'form appearance, but 'it contains a :mixture including a norrnally nontac'ky, ythermoplastic adhesive which is acti-vajvtible by heat to adhesiveness, `anda volati1e,corrosion inhibitor uniformly dispersed throughout the adhesive.

-Small metal par-ts are wrapped -with thesheet material hereof 'insueh a manner as to'dispose #the coated side-of the materialen Athe inner' Aface,orV inside, Lof TIAthe Wrapping or package. This may be `understood more readily `vby referring to Figure 3, where a metal article 12 is shown Ato be enclosed with the coated

sides

13 and 14 of the sheet material -15 disposed inwardly. When the coated side of the -sheet material is heat activated along seams 'and overlaps of the wrapping so as to seal the same, there is a Asimultaneous yacceleration of the volatilization'of the corrosion inhibitor from areas of the coating immediately adjacent to those vareas treated with heat. The corrosion linhibitor dispersos itself about the articles or contents' of the package and protects the same from the corrosive eltects of Iwater vapor Aand oxygen within a short time after the package is heat sealed. The protective atmosphereis sealed from the external air and thereby protects the packaged metal varticle during shipment.

Suitably during `the packaging process, the meeting edges, l16 and 17, of the sheet material are sealed by applying heat and pressure thereto using a heated mandrel, metal band, bar, etc., or ycombinations thereof, on .one `or both sides of all meeting edges. A temperature VVgenerally above about 200 F. and as high as 500 F. is suitable for activation of the adhesive. The seal or bond is made, usually simultaneously with heat activation, by applying pressure over the heat activated area vfor a short period of time, a period of time as short as a fraction of a second lbeing suitable.

With the foregoing in mind, the following examples are oiered .as illustrative but non-limitative Vof the invention hereof.

Exam-plc J Parts by weight (Dry basis) Dicyclohexylammonium nitrite 3 Acrylic resin emulsion -4 Dicyclohexylammonium nitrite may be prepared .according to the disclosure of U.S. Patent No. 2,449,962 ,(Septemberl, 1948). This compound has :a `vapor pressure at 24 C. `of about 0.00016 Hg. lt .falls in the class of compounds known .as 4salts of nitrous acid, which are Well known as volatile .inhibitors 4of the .f'cor-rosion of ferrous land related metals. Many nitrite salts, including ,those .of various amines', nitroigenous compounds and other organic compounds than vthe specific one here -rnentioned, are Well known :as volatile, vapor-phase, lcorrosion inhibitors.

'The `acrylic resin was used in emulsion AformV at a :concentration vof 40% solids. Such an emulsion, as a mon-.ionic acrylic resin emulsion, 4contains as `its resin component a vnormally `non-tacky thermoplastic copolymer of vinyl acetate .and .acrylic monomers. The ern-ulsion is marketed under the trade designation WN-80 -by the Rohm.& Haas Chemical Company.

Both materials .above Were thoroughly mixed together b y stlrringV and ythen knife coated (other coating techmques are .also suitable) on a 40 lb. neutral kraft paper (a paper treated so that its remains `neutral over long periods.) at a `dry coating Weight of approximately 20 lbszof solids .per ream vof paper. A ream lis an area equivalent to 500 sheets of paper each measuring 24" x 436 The .mixture was coated at room temperature and driedxat a raised temperature of about F. in a current .of .dryain The sheet material was then rolled into a compact cylinder and .used in the packaging of small metalmachine parts. A package such as in Figure 2 was formed and the meeting edges, illustrated as lr6 and 17 in Figure 3, of the sheet material were bonded together at 350 F. and 40 p.s.i, {forfl/z second. After the so-formed package had cooled `to roomY temperature, an attempt was made to separatethe -heat seal `by slowly pulling on the outside loose edges, "illustrated as 18 and 19 in Figure 3, of the sheet material. This technique resulted in fibers being torn from the kraft paper backing, but the heat seal between the adjacent layers of adhesive remained intact. Tests also indicated that the heat-seal bond so formed did not permit the passage of any significant amount of the vaporized corrosion inhibitor.

The sheet material of this example will effectively inhibit harmful corrosion of small metal parts packaged therein for lengthy periods. Actual tests lasting as long as one month have furnished no evidence of harmful corrosion. Metal articles ifn direct contact with the coated film of the sheet material hereof gave no evidence of any contact corrosion in tests lasting also as long as one month. Metal machine parts packaged in this material may be shipped and stored for substantial and lengthy periods of time without harmful corrosion resulting.

Use of this sheet material in automatic packaging machinery permits continuous uninterrupted operation of such machinery for lengthy periods. Shut down of such machinery for cleaning purposes is reduced to a minimum or entirely obviated.

Callex CA, marketed by the Daubert Chemical Company (formerly Nox Rust Chemical Corporation) of Chicago, is a trade name for a solid material which is a volatile corrosion inhibitor. It is believed to be a mixture of materials as disclosed in U.S. Patent No. 2,521,- 311 (September 5, 1950), and to consist of about 50% sodium nitrite, about 50% urea, and possibly a small amount of additional components such as monoethanoanolamine benzoate. In the making of the sheet article of this example, Callex CA was dissolved in water to form a solution consisting of approximately 50% solids.

The carboxymethyl cellulose was of a high viscosity type and was dissolved in water to form a 1% solid solution. It is used as a thickening agent to maintain a suitable viscosity in the mixture for coating purposes and, when used, should be employed only in small amounts. A suitable coating viscosity may vary from about 300 to 2000 centipoises at 25 C.

The three above components dispersed and dissolved in Water as stated were mixed together by stirring and knife coated upon 40 lb. neutral kraft p-aper at a dry coating weight and under conditions of temperature as described in Example l. Drying was also conducted as rapidly as possible using the procedure of Example 1, giving a sheet material comparable to the one of that example.

The sheet material of this example formed, upon heatsealing, liber tearing bonds comparable in performance to those formed using the sheet article of Example' 1. Metal articles packaged with this sheet article were also free of corrosion after lengthy storage.

Other suitable volatile inhibitors of the corrosion of metals, including ferrous metals, than those employed in the examples may be used in making the sheet articles hereof, provided that the volatile corrosion inhibitor does not react with the organic resin adhesive employed'to prevent film formation or otherwise adversely affect the resin. For best results, the inhibitor should have a vapor pressure at 21 C. of at least 0.00002 mm. Hg. Such volatile corrosion inhibitors may be nitrite salts of primary amines, secondary amines, tertiary amines, etc., various aliphatic and cyclic compounds, inorganic nitrites, organic acid salts, etc., and various combinations thereof. Characteristically these lvolatile corrosion inhibitors are chemically stable under atmospheric temperatures and possess the property of volatilizing and of being able to inhibit corrosion of metal parts such as would otherwise be caused by the action of water vapor and oxygen.

Suitable heat-activatible adhesives for use in the sheet materials of this invention are various thermoplastic, normally non-tacky, adhesive polymers and copolymers, such as for example alkali soluble polyvinyl compounds, esters of polyacrylic acids, methacrylate resins, etc. These vinyl-type polymers may be plasticized with various additive plasticizers, or they may be internally plasticized within the polymer chain, to improve their flexibility in lm form and to increase their tackiness when activated `by heat. The resin adhesive may be characterized as normally non-tacky inasmuch as it does not exhibit tack at normal room temperatures, nor runder conditions of normal storage and shipment, but develops tack only at elevated temperatures preferably above approximately 200 F.

Various flexible, relatively-stiff, smooth surfaced backings, such as those of various papers, paper combined with films, glassine, etc., may be used in making the sheet articles hereof. It should be noted that this invention provides a very economical barrier-type packaging material possessing the property of heat scalability as well as the property of inhibiting corrosion. If desired, films of microcrystalline wax or foils of metal may be included in the sheet support structure to serve as an added barrier iilm.

Coating Weights of the homogeneous mixture of adhesive and volatile corrosion inhibitor may vary from about l0 to 40 lbs. of solids material (dry solids weight of the adhesive and volatile corrosion inhibitor) per paper ream of 500 sheets each measuring 24" x 36". Within this range the most suitable and useful sheet materials are produced. Dry coating weights of adhesive and corrosion inhibitor below approximately l0 lbs. per -re'arn (as aforesaid) are vgenerally insuicient to provide adequate heat seal characteristics as well as adequate concentration of volatile corrosion inhibitor after sealing.

The ratio of the weight of solvent-free adhesive material to solvent-free corrosion inhibitor in my iilms may vary widely but is generally between about 1:1.5 to 8.5:1.5. A ratio of adhesive to corrosion inhibitor below 1:1.5 generally provides insufficient adhesive for the formation of fiber-tearing, heat-sealed bonds. On the other hand, a greater ratio of adhesive to volatile corrosion inhibitor than 8.5 :1.5 results usually in insuicient volatile corrosion inhibitor being present in the coating `to provide adequate protection against corrosion.

Drying of the coated mix-ture to free it of solvents must be accomplished in such a manner that vaporization of the corrosion inhibitor is avoided or minimized Iand for this reason, should be -accomplished at as low a drying temperature and in as short a time as possible. For practical purposes, a drying range of between approximately to 180 F. is preferred and surprisingly can be used without a significant loss of the volatile corrosion inhibitor from the coating during the drying step. The maximum drying temperature employable is `about 200 F., and it is preferable, as illustrated in the examples, to dry the coating at a temperature below the point at which the heat-aotivatible adhesive fuses and becomes tacky. Desirably, drying is -accomplished as expeditiously as possible by maintaining a current of dry air over the coated layer during the drying process. The dried sheet product is then stored in wrapped rolls or stacks, as hereinbefore noted, until required for use.

I claim:

1. A packaging sheet material yadapted for use in providin-g sealed enclosures with protective atmospheres for small, grease-free, metal articles so as to protect said metal articles from the corrosive action of water vapor and oxygen, said sheet material comprising a flexible, relatively-stiff, smooth surfaced, sheet support member and a macroscopically homogeneous nlm-like coating adhered thereover, said coating comprising a heat-activatible, thermoplastic, flexible, normally non-tacky, vinyl resin adhesive and a volatile inhibitor of the corrosion of metals dispersed throughout said adhesive, the weight ratio of said adhesive to said corrosion inhibitor being between 1:1.5 and 8.5:l.5 with the total dry solids coating weight of said adhesive and corrosion inhibitor being between and 40 lbs. per ream of sheet support member equivalent to 500 sheets measuring 24 x 36, said corrosion inhibitor being characterized by having a vapor pressure at least greater than 0.00002 mm. Hg at 21 C. and by being non-reactive -with said adhesive.

2. The sheet material of claim 1 in which the support member comprises paper.

3. A packaging sheet material adapted for use in providing sealed enclosures with protective atmospheres for small, grease-free, metal articles so as `to protect said metal articles from the corrosive `action of Iwater vapor `and oxygen, said sheet material comprising a flexible, relatively-stili, smooth-surfaced, sheet support member and a macroscopically homogeneous nlm-like coating adhered thereover, said coating comprising a heatactivatable, thermoplastic, flexible, normally non-tacky, vinyl resin adhesive and a volatile inhibitor of the corrosion of metals dispersed throughout said adhesive, the weight ratio of said adhesive to said corrosion inhibitor being between 1:1,5 and 8.5 :1.5 with the total dry solids coating weight of said adhesive and corrosion inhibitor being between 10 and 40 lbs. per ream of sheet support member equivalent to 500 sheets measuring 24 X 36, said corrosion inhibitor being characterized by having a vapor pressure at least greater than 0.00002 mm. Hg at 21 C. and by comprising a nitrogen-containing compound -which is non-reactive with `said adhesive.

4. The sheet material of claim 3 in lwhich the volatile corrosion inhibitor comprises `a salt of nitrous acid.

5. The sheet material of claim 3 in which the support member comprises paper.

6. A process for packaging small, grease-free, metal articles in heat-sealed, barrier-type enclosures so as to protect said metal articles against Ithe corrosive action of water vapor and oxygen, said process comprising (1) wrapping said articles with a packaging material comprising a flexible, relatively-Stiff, smooth-surfaced, sheet support member and a macroscopically homogeneous coating adhered thereover, said coating comprising :aheat- 4activatable, thermoplastic, normally non-tacky adhesive and a volatile inhibitor of the corrosion of metals dispersed throughout said adhesive, said corrosion inhibitor being characterized by a vapor pressure at least greater than 0.00002 mm. Hg lat 21 C. and by being non-reactive twith said adhesive, said packaging material being disposed about said metal articles with its coated side facing inwardly and with areas thereof meeting to form an enclosure about said metal articles, and (2) applying heat and pressure to meeting areas of said packaging material so as to activate the 'adhesive in the coating thereof 'and form a seal between said meeting areas while simultaneously accelerating the volatilization of the corrosion inhibitor from areas of the coating immediately adjacent to those areas treated with heat, thereby to form a heat sealed enclosure with a protective atmosphere therein.

7. A packaging sheet material adapted for use in providing sealed enclosures with protective atmospheres for small, grease-free, metal yarticles so as -to protect said metal articles from the corrosive action of water vapor and oxygen, said sheet material complising a flexible, relatively stiff, smooth-surfaced sheet support member and a vapor-emitting and heat-sealable coating adhered thereover, said coating including a heat-activat-able, thermoplastic, ilexible, normally non-tacky, vinyl resin adhesive and a vapor emitting ingredient consisting eS- sentially of a volatile inhibitor of the corrosion of metals, ,the weight ratio of said adhesive to said corrosion inhibitor being between 1:1.5 land 8.5 :1.5 with the tota-l dry solids coating weight of said adhesive and corrosion inhibitor being between 10 and 40 lbs. per ream of sheet support member equivalent to 500 sheets measuring 24 x 36", said corrosion inhibitor being characterized by having a vapor pressure at least greater than 0.00002 mm. H-g at 21 C. and by being non-reactive with said adhesive.

References Cited in the le of this patent UNITED STATES PATENTS 1,953,097 Becker Apr. 3, 1934 2,428,861 Waring et al. Oct. 14, 1947 2,480,501 Moore Aug. 30, 1949 2,630,368 Wachter Mar. 3, 1953

Claims

1. A PACKING SHEET MATERIAL ADAPTED FOR USE IN PROVIDING SEALED ENCLOSURES WITH PROTECTIVE ATMOSPHERES FOR SMALL, GREASE-FREE, METAL ARTICLES SO AS TO PROTECT SAID METAL ARTICLES FROM THE CORROSIVE ACTION OF WATER VAPOR AND OXYGEN, SAID SHEET MATERIAL COMPRISING A FLEXIBLE, RELATIVELY-STIFF, SMOOTH SURFACED, SHEET SUPPORT MEMBER AND A MACROSCOPICALLY HOMOGENEOUS FILM-LIKE COATING ADHERED THEREOVER, SAID COATING COMPRISING A HEAT-ACTIVATIBLE, THERMOPLASTIC, FLEXIBLE NORMALLY NON-TACKY, VINYL RESIN ADHESIVE AND A VOLATILE INHIBITOR OF THE CORROSION OF METALS DISPERSED THROUGHOUT SAID ADHESIVE, THE WEIGHT RATIO OF SAID ADHESIVE TO SAID CORROSION INHIBITOR BEING BETWEEN 1:15 AND 85:25 WITH THE TOTAL DRY SOLIDS COATING WEIGHT OF SAID ADHESIVE AND CORROSION INHIBITOR BEING BETWEEN 10 TO 40 LBS, PER REAM OF SHEET SUPPORT MEMBER EQUIVALENT TO 500 SHEETS MEASURING 24''''X 36'''' SAID CORROSION INHIBITOR BEING CHARACTERIZED BY HAVING A VAPOR PRESURE AT LEAST GREATER THAN 0.00002 MM. HG AT 21* C. AND BY BEING NON-REACTIVE WITH SAID ADHESIVE

6. A PROCESS FOR PACKING FOR SMALL, GRASE-FREE, METAL ARTICLES IN HEAT-SEALED, BARRIER-TYPE ENCLOSURES SO AS TO PROTECT SAID METAL ARTICLES AGAINST THE CORROSIVE ACTION OF WATER VAPOR AND OXYGEN SAID PROCESS COMPRISING WRAPPING SAID ARTICLES WITH A PACKAGING MATERIAL COMPRISING A FLEXIBLE, RELATIVELY-STIFF, SMOOTH-SURFACED, SHEET SUPPORT MEMBER AND A MACROSCOPICALLY HOMOGENEOUS COATING ADHERED THEREOVER SAID COATING COMPRISING A HEAT ACTIVTABLE THERMOPLASTIC, NORMALLY NON-TACKY ADHESIVE AND A VOLATILE INHIBITOR OF THE CORROSION OF METALS DISPERSED THROUGHOUT SAID ADHESIVE, SAID CORROSION INHIBITOR BEING CHARACTERIZED BY A VAPOR PRESSURE AT LEAST GREATER THAN 0.0002 MM HG AT 21* C. AND BY BEING NON-REACTIVE WITH SAID ADHESIVE, SAID PACKAGING MATERIAL BEING DISPOSED ABOUT SAID METAL ARTICLES WITH ITS COATED SIDE FACING INWARDLY AND WITH AREAS THEREOF MEETING TO FROM AN ENCLOSURE SAID METAL ARTICLES, AND (2) APPLYING HEAT AND PRESSURE TO MEETING AREAS OF SAID PACKAGING MATERIAL SO AS TO ACTIVATE THE ADHESIVE IN THE COATING THEREOF THE SEAL BETWEEN SAID MEETING AREAS WHILE SIMULTANEOUSLY ACCELERATING THE VOLATIZATION OF THE CORROSION INHIBITOR FROM AREAS OF THE COATING IMMEDIATELY ADJACENT TO THOSE AREAS TREATED WITH HEAT, THEREBY TO FORM A HEAT SEALED ENCLOSURE WITH A PROTECTIVE ATMOSPHERE THEREIN.