US2329908A - Humidity control - Google Patents

Description

Sept. 21, 1943. Q E, JOHNSQN 2,329,908

HUMIDITY CONTROL Filed July 28. 1959 v giu/11014430@ Patented sept. 21, 1943 2,329,908 nUMmIrY CONTROL Cecil E. Johnson, New York, N. Y.,

rm Reddir, Inc., Application July 28,v 1939, Serial No. 287,165 1 Claim. (Cl. S12-31) This invention is directed to the packaging of articles so that they are maintained with a proper moisture content.

It is well recognized that many articles should be specially packaged to keep them from either drying out or absorbing too much moisture, as their moisture content determines their freshness. Such articles are, for example, tobaccos, candies, chewing gum, photo illms, and other perishable goods. A common manner yofmaintaining the moisture content of such articles is ,by packaging them in hermetically sealed containers. Obviously the water content does not vary but minutely within a hermetically sealed package and the problem of maintaining the "freshness of packaged articles is effectively solved. The expense of this method of packaging, however, prevents its use With low cost articles, and particularly articles which'have a relatively short life from the manufacture to the consumption thereof. Other methods have been suggested, as by packaging the articles together with some substance which will yield water, and to some extent take up "water, from the article on changes of the humidity within the package. For example, sponges soaked in water have been inserted into humidors containing tobacco; Glaubers salt has been inserted into containers of tobacco; solutions adapted to maintain a substantially constant vapor pressure ehave been placed in containers sch as bread boxes for the purpose of maintaining the humidity of the container constant; and articles have been packaged within protective layers of the same article in order that the packaged innermost article may retain its original moisture content.

4With the exception of sealing articles in hermetically sealed containers, and surrounding an article with similar articles, the other methods of packaging articles for the purpose of keeping their water content substantially constant have all been impractical as they failed to account for more than the continual leakage of water 'from the package. This leakage has been recognized'as actual, but hitherto known methods, beyond supplying loosely attached water in some form to make up the leakage, have failed to recognize the more important factor of control in the amount of water supplied to make up that lost by leakage. The vapor pressure created by the water present in the packaged article will vary with change in temperature. The humidifying element which supplies the water lost by leakage should function at all times in a manner to keep the article in the package surrounded by assigner to the i Wilmington, Del.

a Water vapor pressure just equal to that which the packaged article would create by itself under any temperature condition if .the article were sealed in a water impervious container. Under ideal conditions the control should be in that the water in the packaged article is in equilibl rium with the water vapor pressure of the humidifying element and there is no permanent water loss from the article, but only an .equilibrium exchange. This condition must be met for all temperatures to which the packaged article is to be exposed, and must be in eiect a practical means of paralleling the water vaporpressure of the wrapped article, when said article is packaged in an ideal container. Waterl vapor pressure as herein discussed may be expressed in terms of relative humidity, which is the quotient of the partial pressure of water vapor at any temperature, divided by the partial pressure of saturated vapor at that temperature. Therefore relative humidity is the percentage/vapor pressure and it is more common to speak in terms of relative humidity than in terms of vapor pressure.

Glaubers salt has previously been used as a humidifying element for packaged articles. 'I'his hydrated salt will serve as an example of an uncontrolled water supply. Thus, Glaubers salt has a relative humidity always over at most normal temperatures less than approximately F. However, if the temperature rises above 80 F., the relative humidity produced by the Glaubers salt will go up proportionately to become about at 90 F. Consequently, if an article is packaged with a relative humidity of, for example, 70%, Glaubers salt added to the package will not maintain that same humidity over a substantial temperature range. Again, Glaubers salt will not produce a relative humidity less than 70%. The use of this salt failsy to control the quantity of water in the package in order to maintain a constant humidity. The variation given by and the lack of control from a water soaked sponge is even greater as the water vapor emitted from the soaked sponge gives a. relative humidity of approximately at most normal atmospheric temperatures. Consequently a water soaked sponge cannot be used to maintain a humidity of, for example, 70% over the normal atmospheric temperature range. Thus these substances are not satisfactory when used in a moisture tight container, and much less satisfactory when used in a moisture pervious package.

A further objection to the prior art attempts to maintain a substantially constant water content in a packaged article lies in the fact that the water content for most articles must be maintained within a very limited range, and the prior art substances were incapable of maintaining the humidity within the necessary limits at least during the usable life of the article. Except for hermetically sealed containers, the perviousness of the ordinary package to the ingress and egress of moisture prevents the mere addition of wetting or drying substances to the package from being sufficient to compensate for atmospheric changes which affect the condition of the articles within the package. Consequently the additional water conditioning substances are influenced more by atmospheric conditions than by the changes in the condition of the articles purportedly protected, with the result that the additional substances are practically useless.

Still another objection lay in the fact that the A insertion of a wet sponge or other moisture conditining substances into a package, or the packaging of an article within like articles, gave weight, bulk, and added cost without producing such advantages as would compensate for the rather ineiective moisture control in the package.

An object of this invention is to provide a substance which can be packaged with an article to maintain a substantially constant absolute water content in the article to be packaged.

Another object of the invention is to package articles with a particular substance which can be modified by additional substances so that changes of the vapor tension within the package are compensated by the substance in such a manner as to keep the absolute water content of the articles substantially constant.

Another object of the invention is to utilize a substance which is not only a humidifying agent, but also an adhesive agent so that it can be used as the adhesive in assembling the package which is to contain the article to be humidied.

Another object of the invention is to surround packaged articles with a nwrapper including a substance which inherently maintains over a wide temperature range the same humidity as that of the article at the time of packing, the substance preventing the article from being affected by conditions outside the package both by acting as a barrier between the article and outside conditions and by compensating for changes within the package which would ordinarily cause a change in the moisture content of the article.

Another object of the invention is to employ an adhesive humidifying substance of low cost which is non-toxic and usable with comestibles.

Another object of the invention is to employ a humidifying substance which will maintain the humidity of a packaged article within Very close limits during the market life of the packaged article.

Another object of the invention is to construct a laminated sheet product including an adhesive layer of specific humidifying properties and at least one moisture pervious layer.

Generally these objects of the invention are accomplished by enclosing an article whose absolute water content is to be maintained substantially constant with a humidifying device including a substance of high molecular weight, sticky, water soluble, non-volatile, and non-toxic. Such a substance can be composed of a compound of invert sugar or heavy sugar solution which .may be modlned by the addition of one or more substances in order to produce a substance which has the same humidity at all temperatures as the humidity of the article at the time it is packaged,

\- or, in other words, a substantially unvarying relative humidity. The added substances may be sucrose and glycerine. Starch and talc and the like may be added in order to control the viscosity of the finished substance. Such a substance has the advantage of being adhesive so that it can be used to construct a package, and further is non-toxic and inexpensive. The water content of the substance is such that it can release a reasonable amount of water into the package without substantially changing its own normally maintained humidity, and conversely it can take up a reasonable quantity of water without substantially varying its humidity. This material thus functions to control the quantity of water in a package for changes in vapor pressure over a normal atmospheric temperature range of about from 32 F. to 110 F.

These and other objects of the invention may be more readily understood by reference to the following specification, taken in connection with A the drawing, in which:

Fig. l is a perspective view of a portion of a laminated sheet of material embodying the invention.

Fig. 2 is a similar view showing the use of a sheet of crinkled paper.

Fig. 3 is a. perspective view of a cigarette package, with the layers of the package cut away to show the manner of using the invention.

Fig. 4 is a plan View of a sheet of material showing how the adhesive may be applied thereto.

Fig. 5 is a cross sectional view of a tin can containing, for example, cigarettes, showing the use of the invention therein; and

Fig. 6 is a cross sectional view of a box, as a candy box, showing the application of the invention thereto.

In Fig. 1, a laminated structure is shown comprising two sheets of material 2 and 4 adhesively united by a layer 6. This adhesive layer is composed of an invert sugar solution modied to produce a desired humidity which is constant for all normal atmospheric temperatures. In other words, the adhesive is given the property of changing its vapor pressure at a rate which maintains a constant humidity which is the same for the packed article. For Iexample, an adhesive composition which will produce the 60% humidity desired in the packaging of cigarettes may have one of the following compositions:

Example A Grams '15% aqueous solution of invert sugar-- 200 Sucrose 27 Water 5 Starch 5 Total weight 237 231 Example B Grams 75% aqueous solution of invert sugar 200 Sucrose 0 Water 5 Starch 5 Total Weight 230 229 Glycerine` 10 239 Example C' In preparing these compositionsthe starch is mixed with the water; the sucrose and invert sugar are warmed together to form a clear solution, these two substances being more soluble when used together than when dissolved separately; the invert sugar-sucrose solution is then stirred into the starch-water mixture; the entire mixture is then heated to bulk the starch and to remove water until the total weight in Example A is dropped to 231 grams, and in Example B to 299 grams. In`Example B, glycerine is added but this addition is made preferably after the solution is cooled. The adhesive obtained in Example A is relatively viscous. The

adhesive obtained in Example B is relatively thin,

the thinning being eiected by reducing the.

amount of sucrose over that in the A formula and by the addition of glycerine. The adhesive obtained in Example C has a viscosity which is the ingredients. such variation being made in a manner that keeps the humidity balance unchanged. A decrease in the sucrose content and the addition of glycerine gives a method for decreasing viscosity. Higher viscosity may be obtained by a limited increase in the sucrose content or by the use of additional starch.

In the above examples, the invert sugar consists of 75% solids and 25% water, i. e. 75 Brix. A representative such as sodium benzoate may be added. The glycerine may be replaced by glycols such as ethylene glycol, or by inorganic lactates such as sodium lactate.

It has been demonstrated that the above compositions are extremely adhesive, form a ilexible adhesive lm which is slow drying, and as a matter of fact, is substantially non-drying during the usable life of the wrapper, and are able to give up and take up water so that they maintain a substantially constant relative humidity. Thus, assuming that the layers of sheet material 2 and 4 are composed of porous paper, the adhesive 6 will either release or take up water vapor through the pores of the sheets 2 and l in an eii'ort to maintain itself at its predetermined relative humidity. It has been demonstrated by repeated experiments that the adhesive layer maintains its relative humidity within a narrow range approximating a 1% change even though the ambient temperature undergoes a wide change, say, for example, from 35 F. to 105 F. It is believed that the reason the relative humidity remains constant is because the adhesive automatically' maintains, in itself, a constant ratio as to the dissolved solids and water. That is, when the adhesive loses water, some of the solids will crystallize out, at a rate equal to the loss of water, thereby maintaining a. constant ratio between the dissolved solids and the amount of water in the solution. Conversely, as

the adhesive absorbs water, the crystallized partlcles willl go back into solution, thus maintaining the constant ratio. Regardless of the theory of operation, many and repeated experiments have proved that an adhesive composed of properly t selected substances and compounded as described has a. substantially unvarying humidity over a wide temperature range.

It is not necessary that both the layers 2 and 4 be'of sheet material pervious to the passage of water vapor. As a matter of fact, itis preferable to have one of the layers, for example, the layer 2, composed of a layer impervious to water vapor so that the sheet material can be used as a package with the layer 4 innermost. Such impervious sheet material can be metal foil or waxed paper. The very tacky and slowly drying characteristics of this humidifying adhesive make it very easily applied and spread over sheets 2 and 4. It has a special advantage when 'used with metal foil in that it firmly unites all portions of the metal foil to the other layer, and thus provides an excellent reinforcing means for the foil.

In Fig. 2, the sheet 2 with the adhesive layer 6 is again shown. but instead of using a plain sheet of paper, a crinkled sheet of paper, for example, crepe paper, is used to form the layer 8. This allows the use of more adhesive 6 without appreciably thickening the laminated material. Y

The application of this novel laminated material to the packaging of cigarettes is illustrated in Fig. 3. It is first of all noted that the tobacco in cigarettes is very sensitive to changes in moisture, and that a fresh cigarette has an absolute moisture content of almost exactly v12% water. This corresponds to a relative humidity of approximately 60% in the package. A variation of 1% in the moisture content ofthe cigarettes causing a drop to 11.00% or an increase to 13.00% will either make the cigarettes too dry or too wet. A variation of 0.5% is permissible and therefore it is essential tomaintain the cigarettes with a water content ranging between 11.50% to 12.50%. In explanation, a Water content of 11.50% corresponds to a relative humidity of- 58%, and a water. content of 12.50% corresponds to a relative humidity of 62%. Thus, any humidifying substance added to the package should maintain the relative humidity of the package between the limits of 58% and 62% over a normal atmospheric temperature range, and for the marketing life of the package. Of course, the humidifying substance must be in such form that it does not stainthe cigarette, is not toxic, and is inexpensive.

The adhesive and the manner of using it as disclosed in this invention satisfy the above conditions. Thus, in Fig. 3, the cigarette package is shown having the conventional outer Cellophane Wrapper I0, and the inner paper wrapping material I2. The innermost wrapping material comprises a laminated structure formed of metal foil I4, an adhesive layer I6, and an inner layer of paper I8. The layers I4, I6 andv I8 form a laminated product substantially as described for either Figs. 1 or 2. The adhesive described satisfies the conditions for maintaining the cigarettes in the package within the desired limits of 11.50% to 12.50% water content over the normal atmospheric temperature range. Asa matter of fact, the adhesive substance has the same vapor pressures at different temperatures as would exist for the cigarettes if the absolute water content of the cigarettes remained unchanged over a temv perature range, and thus will maintain the relative humidity of the package within a 1% variance from the 60% relative humidity corresponding to the 12% water content of the cigarettes. In other words, the adhesive mixtures given in the above examples, more than satisfy the necessary conditions for the proper packaging of cigarettes. Inasmuch as in the usual cigarette package, the layers I4 and I8 are normally secured together by adhesive, the adhesive layer I6 performs the ordinary function of securing the layers I4 and I8 together, and therefore the making of such does not necessitate any change in the packaging machinery. However, the layer I6 produces the unobvious result in that the adhesive substance can either take on or give up moisture to the cigarettes in order to maintain the cigarettes at their desired water content. If one and one-half grams of the adhesive in Example A is used as layer I6, it will hold 0.33 gram of water. This water content can be lowered or raised appreciably without marked effect on the humidity balance and since the extreme loss or gain from twenty cigarettes generally does not exceed 0.17 gram of water from manufacturer to consumer, the layer I6 oiers adequate protection. The layer I6 has the further function in that it acts in the nature of a seal against water vapor which might possibly escape through the metal foil I6, and at the same time it constitutes a reservoir of water for the package.

In Fig. 4, the adhesive layer 20 is shown applied to the sheet material 22 spaced from the margins thereof. Figs. l and 2 indicate that the adhesive is spread uniformly over the entire surfaces of the sheets. However, as the adhesive might ooze out from between the sheets when the same are folded into package form, and thus come in contact with cigarettes or other packaged articles and thus stain them, it is desirable to keep the adhesive within the outer edges of the layers of sheet material. This is readily done by spacing the adhesive 20 from the edges of the sheet material 22, as shown in Fig. 4. The only necessary qualification is that su'lcient adhesive be added to the package so that the adhesive can influence and control the humidity of the package.

In Fig. 5, a can 30 is shown having a cap 32 and enclosing cigarettes 34. To the inner face of this cap is applied a layer of the humidifying adhesive 36 having a composition similar to those previously described and being covered by a layer of moisture pervious paper 38. In effect, a laminated humidifying device is achieved by the layers formed from the can, the adhesive, and the paper in accordance with the teachings of this invention, hence the adhesive layer could be applied to the side or to the bottom walls of the can, or the entire interior of the can. It can be seen that the laminated humidifying device can be made to conform to the shapeof the container. As the can 30 is of metal, it is not necessary to use an impervious metal foil layer. lHowever, if the package were cardboard, the entire inner during a normal six weeks period contents of the package or a part thereof, could be covered by using a laminated sheet such as shown in Figs. 1 and 2.

Fig. 6 demonstrates a possible use of the humidifying device of the invention in a candy box 40 having a top 42. Sheets of soft paper 44 simllar to the rather fluffy sheets used in candy boxes and united by the humidifying adhesive to form a laminated structure as shown in Figs. 1 and 2. are inserted above, below, and between the layers of candy. If desired, the upper and lower sheets could have their surfaces toward the walls of the box formed of metal foil, or other impervious material, thus reducing leakage of water vapor from the box.

It ls to be understood that the invention is capable of many different applications, and only a few of the applications have been given merely for the purpose of illustrating some of the uses. rI'he important feature of the invention resides in the fact that the article to be packaged, be it cigars, cigarettes, chewing gum, photo film, etc., can be packaged at its preferred humidity, with the humidifying device having the same preferred humidity and incorporated in the package, either as a wrapper as in Fig. 3, in the form of a laminated structure as shown in Fig. 6, or as a structural part of the package as shown in Fig. 5. The separation of the adhesive from the contents of the package by a water pervious layer keeps the contents of the package from being stained or stuck by the adhesive. The modified invert sugar solutions used are remarkably invariable in their vapor pressure over a wide temperature range and when properly incorporated within a package constitute an accurate, inexpensive means of maintaining a desired humidity around packaged articles.

Broadly, the inventive improvement over the prior art lies in the creation of a humidifying device wherein a humidifying adhesive is fixed to a vehicle so that it can be used to protect an article without encumbering or changing the properties of the article. The humidifying device not only has the same vapor pressure as the article at the time of packaging, but practically parallels the various vapor pressures taken at different temperatures by the article if the absolute water content of the article remains substantially unchanged, and the humidifying device is as temperature sensitive as the article.

Having now described a means by which the objects of this invention may be obtained, what I claim as new and desire to secure by Letters Patent is:

A non-hermetically sealed package comprising a moisture-bearing article having a definite vapor pressure and a wrapper, at least a portion of the wrapper comprising an outer layer of substantially moisture-impervious material, an intermediate layer of liquid water-bearingadhesive material, and an inner layer of moisture-pervious material; said intermediate material comprising a liquid water-bearing, slow drying, hygroscopic plastic including a reservoir of water and having a. vapor pressure substantially equal to that of the moisture-bearing article, said liquid water in said plastic being in an amount sulcient to replace into said article at a vapor pressure corresponding to the initial vapor pressure of said article water lost from said article over a time period corresponding to the normal marketing life of said package.

CECll. E. JOHNSON.

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