Method of adhesively bonding foldable board

May 16, 1961

K. C. GOBALET

2,984,598

METHOD OF ADHESIVELY BONDING FOLDABLE BOARD

Filed Jan. 7, 1958

Sheets-Sheet 1

<img file="US2984598A_D0001.tif" />

<img file="US2984598A_D0002.tif" />

INVENTOR.

Kenneth Clyde Gobalet

BY

ATTORNEYS

May 16, 1961 _K. _c. gobalet 2,984,598

METHOD OF ADHESIVELY BONDING FOLDABLE BOARD

Filed Jan. 7, 1958 4 Sheets-Sheet 2

<img file="US2984598A_D0003.tif" />

Fig. 3

<img file="US2984598A_D0004.tif" />

ATTORNEYS

K. c. gobalet 2,984,598

ADHESIVELY BONDING FOLDABLE BOARD

Sheets-Sheet 3

May 16, 1961

METHOD OF

Filed Jan. 7, 1958

<img file="US2984598A_D0005.tif" />

<img file="US2984598A_D0006.tif" />

ATTORNEYS

May 16, 1961 κ. _c gobalet 2,984,598

METHOD OF ADHESIVELY BONDING FOLDABLE BOARD

Filed Jan. 7, 1958 4 Sheets-Sheet 4

<img file="US2984598A_D0007.tif" />

A TTORNEYS

United States Patent Office _p. .. _M

Patented May 16, 1961

2,984,598

METHOD OF ADHESIVELY BONDING FOLDABLE . BOARD ⁵

Kenneth Clyde Gobalet, Redwood City, Calif., assignor to Baljak Corporation, Wilmington, Del., a corporation of Delaware

Filed Jan. 7, 1958, Ser. No. 707,601 ^lc

Claims. (Cl. 154—120)

This invention relates to the art of adhesively bonding 15 overlapping areas of foldable board, such as paperboard, box board, or other foldable sheet material, during the shaping of a box blank into hollow box form or during the closing and sealing of boxes after filling.

In the folding box industry the terms “gluing” and 2C “gluing machine” are often used in a generic sense, even though the adhesive which is employed is not actually glue in the strict sense of the word. Glue is defined in the Dictionary of Paper (American Paper and Pulp Association, New York, 1940), as “Impure gelatine ob- 25 tained from bones, hides, tannery waste, fish heads, etc. by boiling with water, filtering, concentrating, and drying.” The adhesive employed in a “gluing machine” is frequently a synthetic adhesive composition, such as a hot-melt composition, or compositions of a specific 30 thermoplastic nature.

In this description the term “gluing” will sometimes be used in its broader sense in keeping with the custom in the industry.

In the conventional forming, as well as in the sealing, 35 of boxes an adhesive applicator first applies adhesive to the board, whereafter the board areas which are to be bonded are brought into contact. The glue joint then moves into the so-called pressure section of the machine in which the joint is maintained under pressure for a time sufficient to permit the adhesive to set. The higher the output rate of the gluing or sealing machine, the longer the pressure section of the machine must be in order to maintain the joint under pressure for the required number of seconds. The pressure section of a high out- 45 put machine therefore occupies a considerable amount of floor space.

. Where glue or synthetic adhesives are applied in a dilute state, the setting of the adhesive involves the absorption or dissipation of the solvent. 50

Thermoplastic adhesives employed for heat sealing require dissipation of the sealing heat. For this purpose cooling elements are often installed in the pressure section to accelerate the setting of thermoplastic adhesives.

Particular problems are encountered in the sealing of 55 boxes containing foods about to be frozen. Frozen products are generally packaged in boxes made from a waxcoated stock, the most common coating being paraffine wax, or compositions in which paraffine forms a constituent. Wax-coated board, unlike uncoated board, has 60 a very limited ability to absorb moisture. Moisture left in the adhesive bond freezes during subsequent refrigeration of the box and contents, with the danger of greatly weakening or destroying the seal.

The present invention oSers particular advantages when 65 applied to wax-coated board, particularly paraffine coated board.

According to the present invention an instant or contact-type bond is formed which after an initial and brief application of pressure requires no continued application 70 of pressure, thus eliminating the need for an extended pressure section in the gluing or sealing machine. The bond produced is moisture free for all practical purposes and remains secure and reliable at low refrigerating temperatures of the order of zero degrees F. as well as at high daytime temperatures of the order of 100 degrees F. 5 . The various objects, features and advantages of this invention will appear more fully from the detailed description which follows accompanied by drawings showing, for the purpose of illustration, a form of device for practicing the invention. The invention also resides in 10 certain new and original steps, sequence of steps, as well as features of construction and combination of elements hereinafter set forth and claimed.

Although the characteristic features of this invention which are believed to be novel will be particularly pointed 15 out in the claims appended hereto, the invention itself, its objects and advantages, and the manner in which it may be carried out, may be better understood by referring to the following description taken in connection with the accompanying drawings forming a part of it, in 20 which:

Figure 1 is a diagrammatic plan view of a machine for carrying out the novel method;

Figure 2 is a perspective view of the machine of Figure 1;

Figure 3 is a perspective view of the central portion of the machine of Figure 2, including the applicator of the bonding composition;

Figure 4 is a diagrammatic elevational view of the applicator of Figure 3;

Figure 5 is a diagrammatic perspective view of the composition transfer portion of the machine;

Figure 6 is a diagrammatic plan view of the portion of the machine within which the composition is converted into a highly tacky contact-type of adhesive;

Figure 7 is a diagrammatic end view of the machine portion shown in Figure 6;

Figure 8 is a diagrammatic perspective view of the sealing portion of the machine;

Figure 9 is a perspective view of the end portion of 40 the adhesive converting section and of the sealing mechanism; and

Figure 10 is a reproduction of a test strip of board to which aqueous medium was applied at certain temperatures within the range from 70 to 250 degrees F.

In the following description and in the claims various details will be identified by specific names for convenience. The names, however, are intended to be generic in their application. Corresponding reference characters refer to corresponding parts in the several figures of the 50 drawings.

The drawings accompanying, and forming part of, this specification disclose certain specific details of the invention for the purpose of explanation of its broader aspects, but it is understood that the details may be 55 modified in various respects without departure from the principles of the invention. The invention may also be applied with great advantage to the bonding of plain, unwaxed board, or to board which was dewaxed by a separate process.

For the purpose of explanation of the features and advantages of the invention it will be assumed that the specific object is the bonding of a front flap depending from the cover panel of a hinge cover box to the front wall of the box which the flap overlies, and it will be assumed that the box is constructed from a blank of waxed stock. Waxed board is difficult to bond adhesively and the difficulties are increased by a requirement of completing the bond at a high rate of speed and within a relatively short length of box travel.

Once the details and features of the new method are appreciated, it will readily be seen that the invention is equally applicable to conditions presenting lesser

2.984.598 problems, such as the bonding of panels or flaps of plain, unwaxed board.

The sealing machine 11 comprises a conveyor 12 provided with lugs 13 for moving boxes 14 from an infeed end 15 to a discharge end 16 of the machine.

The illustrated machine was specifically designed for handling waxed board and Comprises, for this reason, ah initial heating and dewaxing section 17 which precedes an adhesive applicator section 18. A further section 19 follows which converts the initially essentially non-tacky bonding composition into a composition of high tackiness of the instantly bonding or contact adhesive type. In a closing section 20 the adhesive coated blank portions are pressed into bonding engagement on contact.

Referring to Figure 2, the box 14 has a cover panel 21 articulated to the back wall panel .22 along a cover hinge line 23. The cover panel is provided with side flaps 24 and 25 and a front flap 26 articulated to the cover panel along fold lines 27, 28 and 29, respectively. The box is a typical frozen food box measuring 5¹/Sx5¹/sx 1⁹/ίβ·

For the purpose of this description only the bonding of the front flap 26 to the front wall 30 (Figure 8) of the box will be considered, it being understood that the side flaps 24 and 25 may be bonded to the respective side wall panels in a corresponding manner.

The sealing and closing machine 11 comprises a top rail 31 which engages the initially upright cover panel of the box and folds it, in a conventional manner, into the position in which it is shown in Figure 2. In this position the flaps 24, 25 and 26 lie in the same plane as the cover panel.

All of the inside as well as outside surfaces of the box entering the machine are coated with a moisture proofing wax coating consisting essentially of paraffine wax applied to the board in a conventional manner.

As the box is advanced by the conveyor 12 in the direction away from the observer (Figure 2), the box first passes through the heating and dewaxing section 17 equipped with a heating unit 32 having two major box panel engaging surfaces 33 and 34. Surface 33 is upright and bears against the front wall panel 3ft of the box. The surface 34 extends at a slight downward slant and is designed to bear against the undersurface of the box flap 26. A blade 35 is urged against the surface 34 by springs 36 and 37 and bears against the top surface of the flap 26 to press the front flap wall against the slanted surface 34 of the heating unit. The degree of downward slant is small in order to avoid lessening, at this station, of the fold resistance or “fight” of the board at the flap hinge line, for reasons which will appear later.

The leading portion of the heating unit is flared and resembles approximately the bow of a boat turned upside down as shown at 38. The leading end of the blade 35 is up, as seen at 39. The heating unit comprises four resistance heating elements of 1000 watts each, a portion of one element being visible at 40, the heating controls for the elements being enclosed in a control box 41.

When the box passes through the heating section the board surfaces to be bonded are dewaxed by heat. The heating step serves two major purposes. Firstly, it removes wax by driving a portion of the wax originally deposited on the board surface into the board itself, another portion being converted into vapor which escapes. The vapor also includes some water vapor, since the board normally contains a low percentage of moisture. The development and escape of vapor causes the board to fluff up slightly with a resulting increase in its surface porosity. This is highly desirable and prepares the board for the subsequent application Of the bonding composition.

The output of the heating unit must be sufficient to attain the required board temperature, the principal determining factor being the total weight of board to be heated per second. More particularly, the heat output is determined on the basis of the caliper of the board, the rate of travel of the conveyor, the thermal properties of the coating material, the moisture content of the board and the area of board to be heated.

In the case of the specific frozen food box, which may serve as an example, paraffined board of 15 point caliper was used, and the boxes were advanced at the rate of 16 inches per second. The temperature of the heating unit was 375 degrees F. resulting in heating of the board to a 10 temperature of about 250 degrees F. during travel of the box past the unit which required 1.24 seconds.

In the event plain, unwaxed board is used, or board which was previously dewaxed by any of the various conventional dewaxing procedures, it is still preferred to 15 pass the board through the heating section in order to take advantage of its second major purpose, which is to heat the board immediately prior to the application of the bonding composition.

It was discovered that the receptivity of the board to 20 the composition, particularly the penetration of the fluid composition into the board, is considerably enhanced by application of the adhesive to a heated rather than a cold board surface. The reasons for this phenomenon appear complex and various theories may be advanced 25 to explain it. Because of the complexity it is preferred to record the results of tests from which the merits of the heating procedure are directly apparent.

Figure 10 is a reproduction of a test strip of previously dewaxed board to which liquid composition was ap30 plied at temperatures of 70, 80, 100, 120, 137, 145, 158, 165, 178, 190, 200, 205, 220, 230 and 250 degrees F. In order to make the receptivity of the board to the applied composition visible, dye was added, so that the quantity of absorbed liquid appears as varying degrees of discolora35 tion. In each instance liquid of room temperature was applied with a saturated brush to the board heated to the temperature indicated.

It is readily apparent that the receptivity of the board to liquid composition is low below 145 degrees F. 145 40 degrees marks a critical point in the temperature range as exemplified by the much heavier absorption at 158 degrees. The test series was concluded by a final test conducted at 70 degrees F. to obtain corroborating readings at the beginning and at the end of the entire series. 45 The almost identical appearance of the two 70¹ degree test strips indicates that the board was not altered by the heat treatment incidental to the tests.

Adhesive composition is applied to waxed board having a temperature in excess of 212 degrees F., preferably ⁸® approximately 250 degrees, while it is preferred to raise the temperature of plain, unwaxed board to a temperature in excess of 145 degrees F. for application of the composition.

After the box leaves the heating section 17 its front ⁸⁸ flap 26 is flattened out and passed over an adhesive applicator shown in Figure 3 as being an applicator wheel 42 having peripheral raised applicator areas 43. As shown in greater detail in Figure 4, the wheel 42 is supplied adhesive composition 44 from a receptacle 45 via a transfer roll 46 fitted with a doctor blade 47. A film of liquid composition of controlled thickness is thus put on the applicator areas 43 for subsequent application to the underside of a flap 26. Guide rails 48, 49 and 50 insure proper contact between the panel 21 and ⁸⁸ flap 26 and the applicator wheel 42, respectively.

The adhesive composition is essentially an aqueous emulsion of the consistency of heavy cream. The adhesive constituent is in solid form and is a finely divided thermoplastic resin. For test purposes a well known 70 and commercially available polyvinyl acetate resin known to the trade as Du Pont Elvacet #80-900 was used. Competitive products are known under the trade names Polyco, Vinylite and Gelva.

The chemical composition and processes of manufacture of these resins are disclosed in textbooks. “Chemi2,984,598 £als of Commerce” by Snell and Snell, Van Nostrand and Company, New York, 1952, page 530, lists polyvinyl acetate resins by trade names and identifies these as being catalyzed reaction products of acetylene and acetic acid. These resins are commercially available as solution and stable emulsions of varying viscosity and particle size.

The present invention employs these resins in their emulsion form. The emulsion is of rather low tackiness as distinguished from the solution form which is highly tacky.

The emulsion used during the tests consisted of 55% solids and 45% aqueous medium by weight. This is a favorable proportion. By way of comparison a solvent such as methyl ethyl ketone mixed with polyvinyl acetate particles in the ratio of 55% solids to 45% liquid will just about swell the solids, but not produce a readily flowable liquid.

Vinylite is produced by polymerizing a mixture of vinyl acetate and vinyl chloride, as is well known in the art. Rubber latex is also suitable as an adhesive component.

The general requirement for the adhesive is that it should be applicable in an emulsion state and adapted to be converted into a state of high tackiness by a subsequent brief heat treatment, as will be described.

In view of the large number of existing synthetic resins and the rapid development of new and improved resin compositions, it will be helpful to specify the characteristics on the basis of which suitable materials may be selected.

The synthetic resin should be substantially insoluble in water and capable of forming a stable aqueous emulsion. Its color should preferably be light and it should be non-toxic, if used for sealing food cartons. It should preferably exhibit low specific heat characteristics so as to heat and cool rapidly and its physical characteristics should be as follows: It should be substantially leathery in the range of minus 40 to plus 180 degrees F., it should be rubbery in the range of 180 to 212 degrees. It should have a melting point at or near the boiling point of water and it should be fluid above the boiling point of water. The aforementioned composition Elvacet #80-900 meets these specifications and forms an excellent sealing composition.

The securest bond is formed between adhesive coated areas on both the box panels which are to be secured together. While it is feasible to apply adhesive composition to the front wall of the box directly by means of an adhesive applicator, as previously described, it is preferred to transfer a portion of the composition applied to the flap 26 to the wall panel 30.

A preferred mode of accomplishing this is illustrated in Figure 5. The flap 26 is engaged by a rail 51 which slopes downwardly and towards the box body, thus swinging the flap 26 against the wall panel 30 as the box 14 advances. A roller 52 of resilient construction presses ,, fl fl ϊ · vvuouuuuuu presses or^uuu piupci uuvupiea ij mcnes, plus an additional tne flap 26 firmly against the underlying wall panel 30, 22 inches for transfer of the composition in the described thus transferring a portion of the adhesive previously manner, a total of 57 inches. The adhesive conversion Ά?°. , ^undersi^de °f the flap 26 to the wall panel θθ section occupied 44 inches and a closing section was 31

30. The back wall of the box 14 is supported by a wall inches long.

or blade 58. The pattern of the adhesive on the flap The preheating and dewaxing step required 1.24 secbears the reference character a and the pattern of the onds. The travel past the adhesive applicator required adhesive applied to the wall panel 30 by way of transfer is identified by the reference character a'.

As previously mentioned, the adhesive composition at this stage exhibits a rather low degree of tackiness, insufficient to hold the flap 26 down after the box moves beyond the roller 52. The flap 26 thus springs away under the action of the inherent fold resistance or “fight” of the stock at the fold line 29 and assumes the position shown in Figure 5.

. By subsequent treatment step the adhesive composition is now converted from its substantially non-tacky state into a state of high tackiness.

out in the baking or heating section 19 of the machine. It comprises a series of tubular heat applicators, preferably in the form of quartz lamps, three 1,000 watt quartz lamps of type T3-1000 being employed in the illustrated machine. The lamps 53 are mounted in line in the focal line of a reflector 54 having an upward extension 55 for the purpose of reducing heat loss through and beyond the flap 26 of the carton 14.

The heat is sufficient to evaporate the aqueous medium of the composition, during which phase of the treatment the temperature of the composition coating remains at approximately 212 degrees F. As soon as the aqueous medium is evaporated, the temperature of the composition deposit rises sharply and causes the previously separated and dispersed resin particles to fuse. The temperature at which this occurs depends on the characteristics of the resin. In the case of Du Pont Elvacet #80-900 having a melting point between 203 and 212 degrees F. according to information by the manufacturer, the fusing occurs at a temperature of less than 325 degrees F.

The temperature is effectively controlled by the duration of exposure of the composition to the heat radiated by the quartz lamps, the time being 2.75 seconds in the specific example.

When the box passes out of the baking section 19 its composition coated surfaces are highly tacky and need only be brought into brief contact to form an instant bond.

The bond is sufficiently strong to permit normal fian30 dling of the boxes leaving the machine. The bond becomes even stronger as the joint cools to room temperature. If the bond is forcibly broken shortly after the box passes the pressure rollers 57, the adhesive forms tough, rubbery strings between the forcibly separated 35 surfaces. The force required to separate the sealed surfaces is considerable and increases as the board cools to room temperature.

Referring to Figure 8, the flaps 26 are caught under a downwardly and inwardly sloping rail 56 which swings the flap against the wall panel 30. A series of four resilient pressure rollers 57 is employed to press the flap 26 into firm contact with the wall. Thereafter the box is discharged, completely and securely sealed and ready for refrigeration in the event the box contents are to be 45 frozen. There is no problem of freezing of a liquid component of the composition, nor is there a danger of entrapment of volatile material in the adhesive joint proper. The bond is secure at freezing temperatures at which foods are frozen and stored and does not become 50 brittle. It is equally secure at tropical temperatures.

Specific dimensional and time data readily show the advantages of the inventive method. The specific machine shown in the drawings had an overall length of the conveyor track of 132 inches. Of the total, 20 55 inches comprise the preheater which, in the present example, also serves as a dewaxer. The adhesive application section proper occupied 15 inches, plus an additional 22 inches for transfer of the composition in the described

The specific ma0.94 second and the transfer of the adhesive required 65 an additional 1.38 seconds. The adhesive was converted from its essentially non-tacky state to a highly tacky state within 2.75 seconds and bond was completed within the closing section in a period of 1.94 seconds. The total time required was 8.25 seconds, an accomplish• 6 ment which is believed to be unequalled in the art of adhesively sealing waved cartons.