Vibration sealing thermoplastic coated paperboard horn energized prior to contacting layers to be sealed

present invention relates generally methods and apparatus, and is particularly concerned improved method and apparatus for sealing cartons or of thermoplastic coated paperboard material.

Description of the Prior Art packaging with an containers an ί

The present invention is particularly concerned with apparatus and method for sealing cartons or containers of the type made of paperboard stock coated on both sides with .a thermoplastic material such as polyethylene. The thermoplastic coating on the paperboard is utilized not only as moisture proofing material, but also serves as a heat and pressure sensitive adhesive which cooperates in sealing the closure elements of the container so as to make the container fluid tight when it is filled with milk or other contents, and sealed and closed. An example of this general type of container is disclosed in U.S. Patent Nos. 3,120,089 and 3,910,014.

Until recently, the conventional manner of sealing thermoplastic coated paperboard cartons was to bring the layers of the end closures of the container into contact with each other, and by the application of heat, activate the thermoplastic coating to cause it to flow at the portions to be joined and sealed. When the thermoplastic material cools and sets, the . layers are sealed and adhesively secured together. In addition to requiring the use of elaborate and expensive apparatus for generating the considerable amount of energy required, elaborate apparatus, methods and systems are also required to dissipate the heat from the plant-in which the packaging operation is being carried out. Examples of this general type of packaging

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P-309 apparatus arc shown in U.S. Fa tent Nos. 3,002,328; 3,120,089;

3,166,994, 3,187,647; 3,239,995 and 3,309,841.

U.S. Patent No.s 3,905,280 of September 16, 1975 and 3,910,014 of October 7, 1975 disclose apparatus for sealing the cndo of thermoplastic coated paperboard containers by welding wherein mechanical energy is converted into heat energy to minimize the amount vibration localized required, of heat and energy expensive systems

U.S. Patent No.

having a converter and to eliminate the necessity for and methods for dissipating the excess heat.

3,526,792 discloses an ultrasonic transducer for converting electrical energy into mechanical energy, and a concentrating horn for concentrating the mechanical energy into vibrations at a desired frequency. In the above mentioned U.S.

Patent Nos. 3,905,280 and 3,910,014, the horn of the vibration welding apparatus vibrates at a predetermined frequency when energized, and cooperates with an anvil 'to clamp the layers of the thermoplastic coated paperboard between the working surface of the horn and the back-up or work the thermoplastic coated paperboard surface of the anvil. When layers are clamped between the work surfacesof the horn and anvil, the vibration of the horn creates frictional heat sufficient to activate the thermoplastic coating of the layers to cause the thermoplastic material of the layers to flow together. When the vibration is terminated, the thermoplastic will cool and set to seal the layers and secure the layers together throughout the area of the seal.

Among the advantages of the utilization of vibration welding is that the heat generated by the vibration of the centrated in the area to be sealed, and little, heat is required to be generated to perform the tion.

horn is conif any, excess sealing operatry·*τϊ i:

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There are two stages in the scaling operation of thermoplastic coated paperboard containers by vibration welding.

These stages are: (1) the activation stage in which the friction of the vibrating horn generates heat sufficient to activate the thermoplastic coating to cause it to flow, and (2) the cooling stage anvil vated

Thus, wherein the layers remain clcimped between the horn and with the horn deenergized to permit the previously acti thermoplastic coating to cool and.set to form the seal.

a complete cycle of forming a seal between layers of a thermoplastic coated paperboard cartoA involves (1) bringing the working surfaces of the anvil and horn into opposed relation ship on opposite sides of the layers to vating the thermoplastic coating of the surface to flow plastic working by frictional heat to cause the be sealed, (2) actilayers between the work coating of the layers together, (3) permitting the previously activated thermo material to cool and set while still held between the surfaces of the anvil and deenergized horn,and (4) separating the carton volved per the working surfaces of the anvil and horn to remove layers after the seal has been formed. The time in cycle to date has been in the range of approximately one-half to two seconds, depending upon the thickness of the paperboard, the thickness of the thermoplastic coating, the number of layers, and the surface· area to be sealed.

It has been conventional in a vibration tion of this type to pressure actuate the horn to vibrating; that is, as the working surface of the to contact with the layers to be welded together, welding operastart the horn horn moves inthe horn starts vibrating when a predetermined pressure on the working surface of the horn is sensed by the horn actuating controls. » &lt;·’

The pressure over the entire area to be sealed must be *

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pressure is too low, the friction between the vibrating horn and the paperboard layers will be insufficient to generate enough heat to activate the thermoplastic coating to flow. If the pressure is burning will occur, that is, the thermoplastic coating excessive, will be removed at high pressure points to /Another problem that can clamping pressure between the horn destroy the seal.

occur when there is excessive and anvil is that some vibration may be transmitted to the anvil. If this occurs, the fric tion between the horn and paperboard layers will be reduced because of the resulting reduction in the relative motion between the vibrating horn and the paperboard layers. Stated another way, excessive pressure will tend to cause vibration of the anvil with the horn so that the paperboard layers will tend to move with the horn instead of frictionally reacting against the vibrating horn. The reduction in friction will reduce the possibility of generating heat sufficient to activate the thermoplastic, or at least will extend the time required to coating. The likelihood of this activate the thermoplastic occurring increases as the mass of the anvil decreases; an anvil with a small mass relative to the horn .will have a greater tendency to start vibrating than would be the case with an anvil having a relatively large mass.

A significant factor in determining the production rate is the amount of time required in the sealing operation which, as alluded to above, involves both an activation and cooling stage. When a carton is at the welding station, and the layers to be sealed are clamped between the horn and anvil, inadequate cooling time after deenergization of the horn with the layers remaining clamped between the horn and anvil increases the likelihood that the layers will separate before the thermo&lt;4

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P-309 to plastic coating sets,, and thus prevent formation of a seal. In a high production packaging system, the available time for the sealing operation is determined primarily by the speed at which the the the cartons must pass through the welding cycle as determined by speed of: other machines in the totr.il system.

welding apparatus must be incorporated into a cluding machines for feeding and erecting cartons

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system infrom flat blank form, such as machines of the type disclosed in Allen U.S. Patent'

U.S.

3,599,541 of August 17,

1971 and in Kellogg

Patent Mo, 3937131 , and filling and closing apparatus such is disclosed in duction rate

Braun U.S.

Patent 3,910,014.

SUMMARY OF THE INVENTION object of this invention is to of systems for forming, filling and sealing cartons increase the proof thermoplastic coated paperboard by vibration welding of the ends of the cartons to .form a seal by reducing the amount of time required to activate the thermoplastic material during the sealing operation.

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A further object of this invention is to provide an improved method and apparatus for forming the seal between a plurality are a to be to be of layers of thermoplastic coated paperboard wherein there w

different number of layers at different portions of the area sealed, and hence variations in the thickness of the area sealed, wherein the time ‘necessary to activate the thermoplastic coating during the vibration welding stage of the sealing operation is reduced sealing operation to a ting when unclamped to provide increased cooling time during the decrease the likelihood of the layers separ4 from between the surfaces of the horn and th anvil of the vibration welding apparatus.

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other objects, includes an anvil surface of the be sealed and a fl relative to each and an extended, faces engage the

- Of a carton are .located between the work anvil, the control means sequentially &lt;2) causes the energized horn and anvil paperboard layers and anvil in the time to activate sealthe dethereof with the ing position a prema terial anvil with rethe anvil and

In carrying out the Coregoing, according to the present invention having a work surface for engaging one outer layers of thermoplastic coatod , i ouxe coated paperboard to

Ηθϋπ that vibirzi ί*ο«4 ·»#-·> π _The „ , Predetermined frequency when energised.

Ihe horn has a work surface that . _c^L °^ncja‘J^es the opposite outer surface of the layers. The horn >„„ ., horn and anvil are mounted for movement °^l°' ^b“· in.ttire position

MH _th. _1(ΟΛ paper boa rd layers in «> _ni ^{Y n a} alampmg relationship.

The apparatus has _horn „ . . ^{O1 meanS f0r} energizing the.

horn and moving the horn and anvil γρ,.ρ

,._ho relative to each other. When the paperboard layers of a carton _ ,_Of,^ , , _surF,„ _c ocated between the work os o the horn and anvil, the control means (1) energizes the horn, o move into the sealing position to clamp the therebetween, (3) holds _{the onergized horn}mg position for a predetermined period of thermoplastic coating of the paperboard layers to flow, _Wenergizes the horn to terminate the vibration anvil held in the seali time to permit the thermoplastic (5) retracts the horn and The clamping pressure of effaces over the entire is maintained within predetermined li

Other oPjeot., eOvanfeeges eoi _lMtura, _ofwill become apparent from the followi nection with the accompanying drawi t « I

I » i deenergized horn and determined period of to cool and set, and spect to each other, horn work s area of the _ imi ts.

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BRIEF DESCRIPTION OF THE DRAWINGS

FIGURE 1 is a schematic view of one form embodying the invention with a gabled top of a thermoplastic coated paperboard container illustrated in cross section and disposed to be sealed by the apparatus;

FIGURE 2 is a schematic view of another form of apparatus embodying the invention with a flat end portion of a container shown in *

FIGURE 3 is a cross section to be sealed by the apparatus; ft schematic view of still another form of invention with a gabled top container «

paperboard material disposed .to be sealed p schematic view of still another form of invention with a flat end portion of a apparatus embodying the fl of thermoplastic coated by the apparatus; and

FIGURE 4 is a ft apparatus embodying the thermoplastic paperboard container disposed to be sealed by the apparatus and illustrated in cross section.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In FIGURE 1 reference numeral 10 collectively desinates apparatus embodying the present invention for sealing the gabled top 12 of a thermoplastic coated paperboard carton C. thermoplastic ft

The carton top 12 includes outer layers 14 of the coated paperboard that engage each other adjacent tremity of the carton top as well as inner layers ed paperboard positioned between the outer layers extremity of the carton top.

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ting horn 18 and an anvil 20.

brator 22 that is the left for movement to

The anvil 20 is for slidable the upper of the excoatupper ft the fl a vibra below fl

The apparatus 10 includes The horn 18 is mounted on a vislidably mounted with a stationary cylinder 24 and the right as viewed in FIGURE 1. mounted within a stationary cylinder to the left and to the right. The ho rpi

II likewise movement

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Ρ-309 has a generally flat work surface 28 that opposes flat work surface 30 of the anvil 20. When a carton a generally top 12 is located between the work surfaces 28 and 30, the anvil and horn may be actuated to move toward each other to a sealing position in which the surfaces 28 and 30 engage opposite carton top 12 .in a clamping relationship.

A control circuit 32 is schematically

FIGURE 1 and is connected to the cylinder 24 by sides of the illustrated in a wi?.e conduit or other electrical conductor 34 so as to control the retracting and extending movement ut vibrator 22 within the cylinder.

wise, the control circuit 32 is connected by a wire conduit other electrical conductor 36 to the cylinder 26 to control

Likeor retracting and extending movement of anvil 20 within cylinder 26.

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A wire conduit or other electrical conductor 38 also connects the control circuit with the vibrator 22 so as to terminate its vibration.

The anvil 20 and horn 18 may be located to and sealing station through which carton c passes. When a carton C and sealing station, the anvil 20 commence and at a welding a conveyor (not shown) for the is not located at the welding and horn 18 are in their retracted positions, that is, the anvil treme left-hand position and treme right-hand position as

C is moved into the position is located in its exthe horn is located in viewed in FIGURE 1. When its exa carton shown in FIGURE 1 with the carton top 12 positioned between the opposed work surfaces 28 and 30, the control circuit 32 is actuated. The control circuit 32 may be actuated by a switch or the like located to be engaged by a carton as it is advanced |)y a station between the anvil and example, in FIGURE 11 of U.S.

conveyor to the welding and sealing horn, in the manner illustrated, for

Patent 3,905,280.

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When the control circuit 32 is actuated, the cylirn are energized so cis to move

Lhe horn 18 and the anvil each other to the horn 18 engages the paperboard layer 14, it the extended sealing position. Before right-hand outer thermoplastic coated is pre-triggered”, that is, the vibrator 22 is energized by the control circuit which in turn energize the horn and cause it to vibrate at a predetermined frequency (for example, 20,000 surface 28 of the horn is thus cycles per second). The work vibrating as it moves into cngagement with tho right-hand carton layer 14.

Simultaneously with wi th the the engagement of the work surface 28 of Lhe vibrating horn carton top 12, the work surface 30 of the anvil moves into engagement with the left-hand outer carton top layer 14.

As the horn and anvil move their respective work surfaces into clamping engagement with the paperboard layers of the carton top 12, the work surfaces 28 and 30 sequentially engage the thickest lower portion containing layers 16 and then the thin upper portion containing only the layers 14. A higher pressure will exist at the thick lower portion than at upper portion. Therefore, the minimum pressure required to activate the thermoplastic coatclamping the thin ft to cause sufficient friction first be reached at the thick portion, and the thermowill start to flow before the thering will plastic at the thick portion moplastic at the thin portion. When the pressure at the thin uoper portion containing only the layers 14 reaches the minimun required to activate the thermoplastic, the clamping movement of surfaces 28 and 30 toward each other stops to prevent excessive pressure at the thick lower portion containing che inner layers 16. The control circuit 32 then operates to deenergize the horn and stop vibration thereof. The anvil and deenergized «

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I horn arc then held in the sealing position with the carton layers clamped between work rtop surfaces 28 and 30 for a predetermined period of time to permit the activated thermoplastic to cool and set and thereby form a seal between the carton top layers.

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The above sequence of operation including pre-triggering of the horn 18 prior to its engagement with the paperboard layers of the ceirton top 12 reduces the time required per cycle in the range of 20 to ^0 milliseconds, or by 10 which is a significant increase in a mass production welding to 15¾, a ( (

a system.

As alluded to previously, the pressure must be maintained within predetermined limits over the entire area to be sealed, including, in the case of FIGURE 1, the lower thick porI.

tion having four layers 14 and 16 as well as the upper thin portion having only two layers 14. It has been found that the mini20 mum pressure activate the assuming the per second.

required to generate sufficient thermoplastic coating, is approximately 200 psi, horn to be vibrating at a frequency 20,000 With the same frequency, it has been found frictional heat to cycles that the j

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portion the maximum pressure must not exceed approximately 780 psi. fore, in FIGURE 1, the pressure at the upper, two layer of the carton top 12 must reach at least 200 psi before pressure at the lower, four layer portion reaches 780 psi. Since, in FIGURE 1, the work surfaces 28 and 30 are flat, tt&lt;? thickness of the paperboard must be such as to permit adequate clamping pressure between surfaces 28 and 30 (i.e. a minimum of 200 psi) at the two layer .portion vzith the pressure at the four ft layer portion staying in the 200 to 780 psi range. If the control circuit 32 prevents the clamping pressure from exceeding the maxI

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780 psi, a seal will not be formed at the thin, two layer portion unless the pressure there reaches the minimum pressure of 200 psi. Therefore, the permissible the thickness over the area to be sealed is that the clamping pressure between surfaces 28 and 30 variation in which permits over the entire area to fall within the predetermined limits of from approximately

200 psi to approximately 780 psi in the of 20,000 cycles per second.

In the illustrated embodiment ness of each layer of the paperboard is case of a of FIGURE such that horn frequency

1, the thickthe difference in the thickness between the two layer portion and the four layer portion permits a clamping pressure in both portions in the range between the predetermined minimum and maximum permissible pressure, which as discussed above have been found to be approximately 200 psi and

780 psi, respectively, when the horn vibrates at a frequency of 20,000 cycles per second.

Most thermoplastic coated paperboard cartons at pre20 sent are of 0.012 ethylene made from inches to (or other paperboard having a thickness in

0.028 inches including a coating thermoplastic material) having a in the range of 0.00075 inches to 0.001 inches.

As tion in the thickness of the layers to be sealed for example to the use of the thicker paperboard the range of polythickness the variaincreases, due and/or abrupt changes in the number of layers, the clamping pressure variation will increase and it will become more difficult to maintain the pressure within the required limits between the flat work surfaces and 30.

Thus, in FIGURE 1, assuming that the horn 18 vibrates at a frequency of 20,000 cycles per second when energized, the variation in thickness between the two layer portion of the car11 %

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P-309 ton top 12 con t&lt;i ini ng only layers containing the layers 16 is small and the foui* layer portion ‘j!

enough pressure to fall within the 200 to 780 tions.

to permit the clamping psi range in both porFIGURE 2 shows another version of the apparatus that is similar to the version shown in ρτπιπρ i i m m iiGURL 1 and, consequently, g primed numerals.

of the apparatus, only the vibrator horn 18' are mounted for reTh6 anvil 20' is in the form a rotatable member 40' so as to of a thermoplastic coated paperboard food has its components indicated by correspond™

However, in this version 10'

22' and its supported vibrating tracting and extending movement, of a mandrel and is mounted on carry the bottom 42' carton C into alignment with the horn. The defined in a conventional manner by folding along score lines and includes inner layers lapped outer layers 46'. The carton bottom carton bottom 42’ is sides of the carton

44' as well as overthus has three layers except where the outer layers overlap to provide a total of four layers.

The sealing of the carton bottom 42' proceeds in the same manner as described in connection ment for with the FIGURE 1 sealing the carton top. The cylinder 24’ moves 22’ and its horn 18' upwardly toward the carton from the retracted position shown.

work surface 28’ of the horn with the carton bottom, the control circuit 32' causes the vibrator 22' to vibrate the horn. The opposed work surfaces vibra tor embodithe bottom

Prior to engagement of the thus clamp the layers

28’ and 30' of the horn and the 44’ and 46’ of the carton board mandrel with the a force that pressurizes all of the layers pressure within predetermined limits. The horn vibration activates the thermoplastic coating of the prescylinder 24 ‘ exerting while maintaining the ft * κ

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♦ then terminated flow. The horn vibration the clamped condition of the ted thermoplastic coating of the layers can cool After carton bottom so

P-309 surized layers to while maintaining that the active and solidify so as to form the seal between the layers, formation of the seal, the horn and vibrator are moved back to their retracted position and.the rotatable member 40· is then actuated to move the sealed carton bottom to an unloading station and to position another carton bottom to be sealed in alignmentsealed.

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- the layers is pressure within to by reference numeral 110. embodiment with.the horn»

FIGURE 3 illustrates an embodiment in which the work to surface of the anvil is stepped to accommodate variations· in the thickness of the layers of the carton top in the area, to be Consequently, a greater variation in the thickness of; possible while still maintaining the clamping the range of between the minimum and maximum to pressures.

In FIGURE 3,. the apparatus is indicated collectively

Parts corresponding to the FIGURE 1 have the same reference numerals increased by 100. C has a top portion 112 located between the work surto horn 118 and an anvil 120. The work surface of the anvil 120 is stepped as indi' cated by reference numeral 131 to accommodate the extra thick-, provided by layers 116 at the four layer portion. ConW0re uniform distribution of pressure over layer portions of the carton top 112 when

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The carton « · faces of a ness seguently, there is a the two layer and four the horn 118 and anvil Λ greater variation in be accommodated by the

FIGURE 4 illustrates an ft

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FIGURE 3 apparatus.

embodiment similar to FIGURE

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FIGURE

100.

that the work surface of the anvil is stepped to accomvariations in thickness. Parts corresponding to the embodiment have the same reference numeral raised by recessed lhe work surface 130’ of the anvil 120’ is stepped or as .indicated by reference numeral 131' to accommodate the thickest portion at the overlapped layers 146'.

The embodiments of as FIGURES 1 and 2. In both the work surface of the horn surface of the anvil. Also, if desired.

FIGURES 3 and 4 operate the same

FIGURES 3 and 4 , it is obvious that could bg stepped instead of the work both work surfaces can be stepped

While specific forms of the invention have become illustrated and described in the foregoing panying drawings, it will be apparent art that the invention is not limited specification and accomto those skilled in the to the exact construction shown, and that alterations and modifications in the construction and arrangement of parts, all falling within the scope and spirit of the invention, can be made by those skilled in the art.

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