US2892735A

US2892735A - Method of obtaining a glossy wax coating on paper and resultant product

Info

Publication number: US2892735A
Authority: US
Inventors: Howard J Curler; Richard M Bauer
Original assignee: American Can Co
Current assignee: Primerica Inc
Priority date: 1956-10-02
Filing date: 1956-10-02
Publication date: 1959-06-30
Anticipated expiration: 1976-06-30
Also published as: DE1241254B; US2982245A

Description

J1me 1959 H. J. CURLER ETAL METHOD OF OBTAINING A GLOSSY WAX comma ON PAPER AND RESULTANT PRODUCT Filed Oct. 2, 1956 M Q /f 25m x5 INVENTORS HOWARD J CUIPLEI? RICHARD M. BAUER B 477'0f/VEKS United States Patent METHOD OF OBTAINING A GLOSSYWAX COAT- ING ON PAPER AND RESULTANT PRODUCT Howard J. Curler, Menasha, and Richard M. Bauer, Neenah, Wis., assignors, by mesne assignments, to American Can Company, New York, N .Y., a corporation of New Jersey Application October 2, 1956, Serial No. 613,539

2 Claims. (Cl. 117-64) This invention relates to a process and apparatus for coating paperboard sheet materials in discrete units or pieces and particularly for producing a wax composition coating having a remarkable brilliance, smoothness and specular gloss on paperboard carton blanks.

Paperboard cartons have long been coated with petroleum-derived hydrocarbon waxes and wax blends to impart waterproofness and grease resistance to the carton, particularly for use in the packaging of foodstuffs. Paraffin wax has been of major importance in this use. Paraflin wax is a hard, brittle, crystalline wax commonly obtained from petroleum distillate derived from crude oils of mixed or paraffin base types. The wax is removed from the parafiin distillate by chilling and filtering, after which it is commonly refined by sweating, acid treatment and by percolation through clay. Generally, commercially available paratfin waxes have melting points from about 110 F. to 145? F. and tensile strengths ranging from 60 lbs/sq. inch up to about 200 lbs/sq. inch.

Parafiin wax has been applied to paper and paperboard products in various ways, depending on the end use properties which are desired. For example, a moderate degree of waterproofness may be obtained very economically by a process known as paraffining, in which a carton is passed between heated rolls which dip into a bath of molten paratfin wax. This process applies a relatively small amount of wax to the carton and, due to the rapid removal of heat from the wax by the cooling action of the carton, a portion of the wax is solidified as a surface film on the carton, while a further portion of wax remains fluid long enough to penetrate into the inner structure of the paperboard. Cartons waxed in this manner are satisfactory for use as ice cream containers and similar items.

A higher degree of paterproofness, as well as increased stiffness of the carton, may be obtained by a process known as saturating, in which a carton is flooded with molten wax and the waxed cartons are stacked while still hot. This procedure allows rather large amounts of wax to penetrate into the pores and fibers of the paperboard, leaving little or no surface film of wax on the carton.

A considerable amount of surface wax is desirable on cartons used for packaging butter, bacon, lard and margarine. Cartons satisfactory for these uses are prepared by flooding the carton with molten wax, removing excess wax by passing the carton between steel or cloth covered rollers, and immediately dipping the arton in a cold water bath to solidify the wax while ICC a major portion of it is still on the surface of the carton. Cartons prepared in this manner have a considerable amount of surface wax coating, and exhibit better protective properties against moisture and grease penetration than cartons waxed by either of the previously described methods. Cartons of this type have a dull, waxy surface appearance which is frequently marred by surface irregularities, pimples, smears and so-called crows feet," or water marks. Nevertheless, these cartons, prior to the advent of our invention, remained the standard of quality in appearance in the industry.

Due to the widespread recognition of the importance of visual impact in stimulation of sales in many fields, many attempts have been made to increase the eye appeal of waxed paperboard cartons by increasing the glossiness and sheen of the wax coating while retaining or enhancing all of the economy and protective properties associated therewith. Hitherto, these efforts have met with only nugatory success.

We have now found that certain wax composition coatings may be applied to paperboard sheets or carton blanks in such manner as to obtain thereon a surface coating with startling gloss and mirrorlike sheen, unmarred by any surface irregularity. This high degree of specular gloss is obtained by providing on the surface of the paperboard blank a uniform coating of a suitable molten wax composition having predetermined adhesive and cohesive properties. Then, while the coating composition is in the molten or plastic state, the entire coated surface of the paperboard is pressed into fixed intimate and overall contact with a highly polished surface which is cooled to facilitate the solidification of the wax composition. When the coating is completely solidified, the paperboard blank is then suitably removed from the polished surface, and will be found to possess a surface of high specular gloss unmarred by surface imperfections, whether the blank is plain or provided with suitable scoreliues for subsequent folding.

The polished supporting surface against which the wax composition coating surface is pressed may be of metal or other suitable smooth-surfaced material capable of accepting a high polish. To facilitate the high-speed production of gloss-surfaced paperboard blanks, We prefer to use for this purpose a highly polished belt or drum which, for example, may be of stainless steel or chromium plated steel having a specular surface. A metallic surface coated with a suitably glossy lacquer, resin or plastic 1 coating would serve a similar purpose. It is to be understood that the reference hereinafter to a belt in describing the novel features of our invention is intended to be illustrative of the means used for supporting and contacting the plastic wax composition surface coating on the blanks and that other suitable means may be used.

Our invention may be carried out by the apparatus illustrated in the accompanying drawing wherein,

Fig. la is a schematic side elevation of the apparatus, and

Fig. lb is a continuation of the view shown in Fig. 1a.

Referring to Figure la, a stack of unwaxed paperboard carton blanks 10 is held on a carton feeding device comprising a continuous belt 12 passing over roller 14 and drive roller 15 with a device 11 for restraining the blanks and allowing single blanks to feed successively from the bottom of the stack; The blanks pass under a small hold-down roll 17 and subsequently between two pairs of feed rollers, the bottom roller of each pair being identified by the number 16. From the feed rollers, the blanks pass into the waxing unit 20, which is equipped with four upper carrying rolls and four lower carrying rolls, two of the lower rolls being identified in the drawing by the number 25. The carrying rollers pass the carton blank through the molten wax composition spray 22 fed to the waxing unit by a plurality of conduits of which one only 21 is shown in the drawing. The wax composition conduit is connected to a suitable wax melting, storage and pumping unit n otshowh inthe drawing. Ari-excess of molteii'waxisa'pplied to the "surfaces of 'the pa erboard'blank by the waxsprayfland theblanlith'eii passes outfof'the waxing unit through 'meter'ingiolls 26 which remove excess wax from the blank; The blank is then'le'd by heated guides 27 onto the surface of a highly polished continuous,'travelling', flexible, metallic belt 30 which is supported on the drum 31' and the driving sheaves 32 (Fig. 1b), the drum and sheaves each being about 24' in diameter. "It is obvious that Fig/1a and Fig. 1b, being essentially side elevation views, show only one of a pair of sheaves 32, andof certain other of the following described machine elements, the other of the pair of such machine elements being positioned to the other side of the machine in obvious fashion. The belt may be of any suitable width for supporting a single series of consecutively fed blanks or may be wide enough to'accommodate a plurality of similar series. We have found that a belt about 35 feet long, having a horizontal travel of about 15 feet is satisfactory for commercial operation at 'speeds up toabout 450'feet7minu'te. The carton blank is'p'ressed-firmly into complete and intimate fixed contact with thebelt surface by a rotating squeeze r'oll35 held by pivotally mounted arms 36. These arms are pivoted at 38fto the frame which, for clarity of illustration, is omitted from the drawing. The pressure exerted by the squeeze roll on the carton blanks and travelling belt is controlled by air cylinders 37, also pivot'ally mounted to the frame at 39. The squeeze roll 35 is preferably provided with a yieldable surface and is placed slightly back of the point of tangency of the blf'with the drum 31; that is, at a point where the belt isheld firrnl'y against the drum. The squeeze roll 35 is slightly larger in diameter at the extreme end portions of the roll'than over the remainder of the roll length. This allows only the extreme end portions to contact the belt surface, the central portion of the roll being gapped by, for example, about .0 inch from the belt surface. When blanks of about .017 inch thickness are fed through thisgap, the yieldable roll surface is then depressed by about .007 inch. Under these conditions, a roll having a surface hardness giving a plastometer reading of about 25 or less has been found to provide suificient pressure to the coated blank to the belt with the desired intimate contact. This gapping of the roll also prevents wax transfer to the belt and damage to the polished belt surface by scratching or marring. Cooling water for holding the belt surface at the desired temperature is maintained in a suitable water cooling, storage and pumpin'g system, not shown, The cooling wateris pumped through a suitable liquid conducting means 42 and thence emerges from a manifold 41 through a plurality of orifices '40 spaced at intervals throughout the length of the manifold. The cooling water fills the shallow tank 43 and overflows its sides into a relatively narrow trough 34 'which surrounds the tank 43 on all sides. The water then passes to a drain 44 which is connected to the waterfstorage system so the. cooling water may. be. recirculated. Duringa major-portion ofits upper reachjor horizontal travel, the belt 30 touches and is. partially supported by the waterv in the tank43, and is cooled thereby..,to. temperature equilibrium with the. water.

Continuing, with reference to Fig. 1b, the excess cooling water adhering to the-under surface of the belt is removed by a wiping roll 47 which contacts the under surface of the belt. The belt is maintained in contact with the wiping roll by the pressure exerted on its top surface by the adjustable pressure roll 46. As the belt passes over the moderately small diameter sheave 32, it is subjected to a relatively sharp flexing, which tends to force the coated paperboard blank to peel loose from its intimate contact with the belt surface. To prevent premature separation of the blank from the belt, an adjustable hold-down roll 50 is mounted at about the point of tangency between the belt and the sheave. The roll 50 is held by arms 48, pivoted to the frame at 49, and the pressure of the roll on the carton blanks and travelling e may be jus e by s rin ua e s on arms 55 pivotally mounted to the frame at 56 After the blank passes under the hold-down roll, an air blast 60 is directed against its forward edge from a pipe 61 con.- nected to a source of pressurized air, not shown. The air blast assists in the removal of the coated blank from the belt surface and directs the blank, guided by carton guides 51, onto a travelling collecting belt 52, which passes over the roller 53 and drive roller 54. The collecting belt moves at a lower speed than the polished belt 30 so that the blanks stack up on its in a shingled pile. The finished blanks are then removed from the collecting conveyor and are packaged for shipping. In carrying out our invention the wax composition used must be selected so as to have predetermined critical properties of adhesion and cohesion. It is, of course, of primary importance that the entire coating surface remain in fixed intimate and continuous contact with the highly polished cooling belt until the coating is completely solidified, since any area of the coating surface which solidifies while not in contact with the belt will not attain the desired specular surface gloss. It is, then, necessary that the adhesion between the wax com; position and the belt be at least as great as the minimum value which is suificient to maintain the desired intimate contact. It is also necessary, however, that the coated paperboard blank be readily removable from the belt after the coating has solidified. To this end, the adhesion between the solidcoating and the belt must be less than a predetermined maximum permissible value to enable the coated paperboard blank to strip cleanly from the belt, leaving no wax composition adhering to the belt surface.

In addition to the above limitations on the adhesion of the wax composition to the belt, it is also necessary for the wax composition to adhere more strongly to the paperboard than to the belt and to have greater cohesive strength than the adhesion of the composition to the belt. The adhesionof various wax compositions to a highly polished metallic surface was measured in the following way:

2" wide sheet of a 30 lb. per ream bleached sulfite paper stock was surface coated with about 5 lbs. per rearn of the wax composition to be tested. While the wax "composition was still molten, the coated surface was pressed into intimate contact with the exposed metallic surface of a2 wide sheet of'aluminum foil, which had previously been glue-laminated to 30 lb. per ream paper stock to increase the strength of the aluminum web. The finished wax'lamination was cooled by an air blast at room temperature to solidify the wax composition. A centrally-disposed 1" wide strip. was then cut from the laminated Web and the strength of the wax composition seal bonding the wax coated paper to the foil. was measured on a Socony-Vacnum Oil Company seal strength tester at 7 ,3 Band 50%. relative humidity. The Socony- Vacuumsealstrength. tester determines in grams per inch qt id h. if t ;l d he e a es o than: dh resl n a aqatshfisa rl cn. etween fit ash iva m tren h me n nr'ed according to the above method, and the adaptability of various wax compositions for the production of a high degree of specular gloss on paperboard carton blanks by our method is shown in the following Table I, wherein column 1 gives the specific wax composition used in percent by weight, column 2 gives the seal strength as tested by the foregoing procedure, and column 3 states the character of the surface gloss produced when using the particular wax composition indicated by applying such composition to carton blanks according to our invention.

Table I Column 1 Column 2 Column 3 Seal Strength Gloss Waxing Com- Wax Composition 1 at 73 Fii gm./ ments 10% DYLT Polyethylene Exceptional Close,

15% 145/47 Amber Micro Wa l 3. 3 Strips Clean. 85% 135/37 Parafiiu 6% DYLT Polyethylene. 20% Shell 700 Wax 3. 4 Do. 75% 135/37 Parafiin--- 20% A06 Polyethylene 5% 145/47 Amber Micro Wax.-. 3. 8 D0.

Good Gloss, Slight 7 Wax Pick-Off Marginal.

6% DYLT Polyethylene 7 Good Gloss, Slight 95% 135/37 Paratiin Wax Piek-Ofi at Score Lines. 10% Shell 700 23 7 Considerable Wax, 90% 135/37 Paraffin Pick-Off Unsatisfactory.

I All compositions contain 0.1% of DC 200, which is dimethyl siloxane sold by Dow-Corning Co. of Midland, Michigan.

DYLT Polyethylenehasa M.W. of about 12,000. It is sold by the Bakelite Company, a division of Union Carbide and Carbon Corporation.

145/47 Amber Micro Wax is a microcrystalline wax having an M.P. of about 145 F. and is sold by Quaker State Oil Company.

135/37 Parafiin is a fully refined paraifin sold by Standard Oil Company of Indiana.

Shell 700 is a high melting hydrocarbon wax sold by Shell Oil Company.

AC6 Polyethylene has a M.W. of 2000. It is sold by Semet-Solvay Corporation.

The data in Table I indicates that, to be satisfactory in the process of our invention, the adhesion of a wax composition to the polished surface, as measured by the test previously described, must be not more than about gm./inch, and preferably not more than about 10 gm./ inch. Adhesion values greater than about 15 gm./inch result in wax picking off the carton and remaining on the belt.

On the other hand, the adhesion of the wax composition to the belt must not have too low a value or the paperboard blank will not maintain a sufliciently intimate contact with the belt during the cooling process. If intimate, continuous fixed contact is not maintained during the process of solidification of the composition, the surface will not attain the desired highly glossy, mirrorlike appearance. It has been found that if the adhesion of the wax composition to the belt is less than about 1.5 gm./inch, as measured by the test procedure described above, the desired surface gloss will not be obtained. Preferably, we adjust the adhesiveness of the Wax composition and/ or the adhesiveness of the polished belt surface so that the adhesion of the wax composition to the belt is above about 2 gm./ inch but not in excess of about 10 gm./inch. Adhesion within these limits may be attained by modifying either the wax composition or the surface characteristics of the supporting polished surface. For example, increasing the content of a soft, ductile microcrystalline wax in the composition increases its adhesive quality. Increasing the polyethylene content generally has the opposite eifect. The adhesion may also be decreased by the addition of small amounts of silicones to the wax composition formulation, or by applying a very thin coating of a silicone release agent to the belt surface. All of the compositions in Table I contain 0.1% of DC 200, which is a dimethyl siloxane sold by the Dow-Coming Company of Midland, Michigan. A

Wax Composition Adhesion in gmJlnch 20% DYDT Polyethylene 30% /47 Amber Micro Wax 136 50% /65 Aristowax 20% DYD'I Polyethylene 30% 145/47 Amber Micro Wax 50% 160/65 Aristowax 0.1% DC 200 Added.

DYD'I Polyethylene has a M.W. of about 4000. It is sold by the Bakelite Company, a division of Union Carbide and Carbon Corporai th s5 Aristowax is a crystalline wax melting at about 160 F. It is sold by the Union Oil of California.

The effect of treating the polished belt surface with a thin coating of a silicone release agent is shown in the following Table III, in which the adhesion of a wax composition to an untreated aluminum foil surface is compared to the adhesion of the same composition to a foil surface previously treated with about 0.1 lb. per ream of DC 200 silicone oil.

From the data given in Tables II and III, it is evident that the addition of a silicone in the composition or on the belt surface may have a profound influence on the adhesion of the Wax composition to a polished surface. By such modification of the adhesive quality of either the wax composition or the belt, the adhesion of a wide variety of wax compositions to a polished surface may be brought within the preferred operable range of from about 2 gm./inch to about 10 gm./inch.

The temperature at which the polished belt surface is maintained is also of importance in obtaining the desired degree of adhesion. The surface is cooled by suitable means to a temperature substantially below the melting point of the wax composition, and the optimum temperature is dependent not only on the melting point of the composition, but also on the temperature dependence of the adhesive and cohesive qualities of the particular composition in question. The adhesion of certain wax blends varies considerably with temperature, while other blends are relatively unaffected. The same is true of the cohesive properties.

The temperature dependence of the adhesion and cohesion of various wax compositions is shown in the fo1- lowing Table IV, in which the seal strength values of coated paper to foil and coated paper to coated paper are tabulated as determined at 73 F. and 100 F. on the Socony-Vacuum seal strength tester. Samples were prepared in the manner previously described. In the paper to foil seals, the test measures the adhesion between coating and metal surface. In the paper to paper seals, since the adhesion of the wax composition to paper is greater than the cohesion of the composition, seal failure occurs in the composition, and the test thus measures cohesive force.

Table IV Adhesion in Cohesion'in gmJin. (Paper gmJin. (Paper Wax Composition to Foil) to Paper) 73 F. 100 F. 73 F. 100 F;

DYL'I Polyethylene 1 95% 135/37 Para 11 3 13 M 0.1% DC 200 Added it ly7 AAqa6'Pfiyeth r7lvena 1 m er cro a 2 9 135/37 Paraffin 9.8 1. 6 10 6. 7 I 0.1% DC 200 Added l0%DYLT.Polyethylene. 3 90% 135/37 Paratfin 8 1.6 22 16 0.1%130 200 Added.

25% Shell 700 It will be noted from Table IV that the adhesion values of compositions. l and 2 are notably decreased by an increase in temperature, whilethe comparable property oficompositions. 3. and 4 is appreciably less aflected by temperature change. The cohesivevalues of compositions 1 and 4 are increased with increasing temperature, while the comparable property in compositions 2 and 3 is affectedin the reversemanner.

Itis apparent from a consideration of these values that it is-desirable to maintain the temperature of the polished cooling surface at a point commensurate with the most desirable adhesion and cohesion values of a given composition. For example, the values for these properties for composition 1 at 73 F. indicate that it would be impossible-to satisfactorily operate the process with this blendifthe polished surface were maintained at 73 F. since the cohesion is no greater than the adhesion value. This has'proven to be the case on commercial equipment. The data at 100 F. for this composition, however, indicate thatif the polished cooling surface is maintained at this temperature, adhesion will be in the desired optimum range and the cohesion is sufficiently high to prevent any wax pick-off on the polished surface. Under these conditions, satisfactory results are obtained. The data in this table also indicate that composition 2 will perform satisfactorily with the polished surface maintained at 100 F. but not at 73 F. Composition 3 performs satisfactorily at either temperature, while composition 4 will not be satisfactory at 73 F. but will show improved'performance at 100 F. In any case, the belt should be maintained at a temperature above the dew point of the surrounding atmosphere to avoid condensation of moisture on thebelt which impairs the surface gloss of cartons pressed against its surface.

On-the other hand, the temperature of the belt surface must be sufiiciently lower than the melting point of the wax composition to thoroughly harden the wax composition coating on the paperboard blanks. If the coating is not cooled sufliciently below its melting point before removal from the belt, the coating surface is relatively soft and is readily scufied, marred or scratched bythe: subsequent necessary handling operations. In. general, we prefer to maintain the belt at aternperature at least 40 F. below the-melting point of the waxcomposition. The operable belt temperatures, then, range from just above the dew point of the surrounding atmosphere (generally between 60 and F.) to a temperature about: 40 F. below the melting point of. the wax composition. The optimum operating temperature will depend on the characteristics of the wax composition, as previously indicated, and it is necessary that the adhesion of the composition to the belt surface, as measured at the same temperature as the. belt surface, exhibit a value. between 1.5 gm./inch and 15 gm./inch and preferably between 2 gm./inch and 10 gm./inch.

Having now disclosed and described in detail preferred forms of our invention, itis obvious that many modifications are possible without departing from the spirit thereof. Therefore, no limitationson our invention are in tended except as specifically set forth in the appended claims.

We claim:

1. The method of obtaining a glossy specular wax composition surface on a succession of paperboard sheets which comprises applying a coating of a molten wax composition to at least one surface of said sheets, successively pressing the entire coated surface of the sheets while the coating is in a plastic condition into intimate continuous fixed contact with a cooled, highly polished, flexible planar surface maintained throughout the duration of such contact at a temperature substantially below the melting point of the wax composition, maintaining said coated. sheets in fixed contact with said flexible planar surface until the coating is completely solidified, and thereafter guiding. said flexible surface by relatively sharp flexing through a curvilinear return path to effect progressive and complete separation of the successive coated sheets from said flexible planar surface While continuing travel of said coated sheets in the direction of travel prior to initiation of the. curvilinear path of travel, said wax composition having an adhesion to said flexible surface of from about 1.5. to about 15 gm./ inch measured at the temperature maintained on said flexible surface anda cohesion greater than the adhesion to said flexible surface;

2. A paperboard sheet coated with a highly glossed wax composition coatingproduced. by the method of claim 1.

References Cited'in the file of this patent UNITED STATES PATENTS 2,270,038 Corbin Jan. 13, 1942 2,370,562 Meunier Feb. 27, 1945 2,647,842 Greisheimer Aug..4, 1953 2,753,275 Wiles July 3, 1956 FOREIGN PATENTS 606,705 Great Britain Aug. 18, 1948