US2025788A - Coating composition - Google Patents

Description

Dec. 31, 1935.

J. H. SWAN, 3D

comma COMPOSITION Filed- Nov. 18, 1931 2 Sheets-Sheet 1 Dec. 31, 1935.

J. H. SWAN, so COATING COMPOSITION Filed Nov. 18, 1931 2 Sheets-Sheet 2 m u m M d W 9 5 .W n; g gw/ww N. FE a.

Patented Dec. 31, 1935 .UNITED STATES PATENT orrice 2,025,788 COATING COMPOSITION Joseph H. Swan, 3d, Middletown, Ohio, assignor to The Gardner-Richardson Company, Middletown, Ohio, a corporation of Ohio Application November 18,1931, Serial No. 575,756 In Canada August 21, 1931 3 Claims. (Cl. 134-17) odorless and tasteless, stands up well in use and does not objectionably deteriorate upon standing for considerable intervals of time, and is commercially economical.

Another object of the invention is to provide a method of forming such a grease proof paper or board, which is simple, economical and highly effective, and which permits the continuous application of a composite coating with the formation of 'a product of good character.

Still another object of the invention is to pro' vide apparatus for carrying out the above method.

Another object of the invention is to provide a superior coating composition adapted for use in the manufacture of the above board product.

Other objects and advantages of the invention will be apparent from the following description, the accompanying drawings, and appended claims. J

This case is'a continuation in part of the copending case Serial No. 389,425, filed August 30,

1929, patented May 1, 1934, No. 1,957,369.

In the drawings in which like characters .of reference designate like parts throughout the several views thereof,

Fig. 1 is a partial diagrammatic side elevational view of apparatus constructed for carrying outthe method of this invention;

Fig. 2 is a view similar to Fig.1 disclosing another portion of the apparatus;

Fig. 3 isa plan view of the apparatus shown in 'Fig. l, certain parts being broken away and in section to illustrate the construction thereof;

Fig. 4 is a vertical sectional view taken on the plane of the line 4-4 ofFig. 2;

Fig. 5 is a verticallsectional viewofa modified ',form of apparatus for applying the final wax coating; Fig. 6 is a plan view of the apparatus of Fig. 5

with the coating roll removed; and

. Fig. '7 is a vertical sectional view on an enlarged scale through a piece of container board made'in accordance with this invention.

This invention is particularly applicable to the rendering of paper or board, such as container board, impervious to grease so that containers made therefrom may be used for packag- 'without pin holes which destroy the effectiveness requirements;

ing greasyor oily substances which would otherwise-penetrate through the package. When such a product is used for packaging foodstuffs, such as peanut butter or the like, it is particularly desirable that the surface of the container board 4 5 be substantially tasteless and odorless.

The, coating should be of such character .as to form an impervious layer on the surface of the board of thecoating, and it should be sufliciently flexible and elastic to permit bending of the board, such as is necessary in the formation of the boxor container, without cracking. The coating should also be of a durable nature and one that will stand up well in use and will not objectionably 1 deteriorate upon standing for considerable inter- 'vals of time. In accordance with the present invention, acoated paper product is formed which is unusually efiicacious in satisfying the ,above '20 Referring to the drawings which disclose a preferred embodiment of apparatus constructed in accordance with this invention, a roll of paper to be coated is indicated at I!) carried by a suitable reel which is journalled at H upon a framework l2. The paper-to be coated passesin a travelling web indicated at l3 over suitable guide rolls M and I5 and thence into contact with the upper surface of roll l6 of a coating press. This press comprises also a lower roll ll dipping with- 89 in a trough It to which the coating solution is supplied in any suitable manner. Rolls l6 and I! are positively driven and 'are mounted in adjustable bearings so that they can be vertically adjusted relatively to eachother to regulate the pres- 85 sure at the nip of the rolls as desired. In operation, rotation of lower roll I! within the coating solution serves to pick up a film of the coating material upon the surface of the roll. A portion of this film is transferred to the surface of the 40 upper roll it, the amount or thickness of the film I being regulated by adjusting the pressure of contact of the rolls l6 and I1, and this film is then transferred to the travelling web l3.- The grease proofing coating 1 composition applied at this point comprises essentially rubber latex and casein. The rubber latex is a relatively concentrated'water solution of the pure sap of the rubber tree in colloidal state. The addition of an oil insoluble adhesive, such as casein, to the rubber latex imparts superior characteristics of adhesiveness and grease proofness. Rubber latex has qualities of elasticity and "spreading'ability and enables a relatively thin coating to be used with satisfactorycoverlng power; it functions very satisfactorily to lay any fuzz which may be protruding from the surface of the paper and covers up irregularities of the surface. It is also a good moisture proofing and water proofing agent.

Casein provides a very satisfactory oil insoluble adhesive, and when properly prepared mixes satisfactorily with the rubber latex. Other oil insoluble adhesives, such as alkali metal silicates,

various animal or fish glues, or gelatine, may be used for this purpose. An alkaline compound, such as sodium carbonate, ammonia, sodium hydroxide, etc., is preferably added to preserve the alkalinity of the coating, this being found to assist in preventing deterioration of the coating, on standing with increase in the effective life of the coating.

A peservative, such as formaldehyde, paraformaldehyde or borax, is preferably added to the coating. This is found to preserve the coating from bacterial action and to act as a reducing agent to prevent objectionable oxidation or other deterioration of the coating. It also improves the quality of the coating, a very durable and resistant tough coating being produced, which is more grease proof and more water insoluble. A formaldehyde such as paraformaldehyde, which is a solid at ordinary temperatures and 'can be conveniently handled, is found to be highly satisfactory for this purpose, and remains stable in the coating after drying, also adding water proof qualities thereto. The addition of a polysulphide, such as sodium or ammonium polysulphide, to this coating is found to improve the covering power thereof, and prevents deterioration and the formation of pin holes in the coating. The polysulphide may be conveniently prepared by first generating a relatively concentrated water solution of sodium or ammonium sulphide, and then adding a quantity of sulphur to the solution and dissolving the same thereinl For example, the

addition of about 50 to 75 grams of sulphur to the liter of a relatively concentrated solution of ammonium sulphide gives a very satisfactory polysulphide for this purpose.

In the preparation of the coating composition, where casein is used, a solution is first prepared by adding commercial powdered casein to waterin the proportion of about one poundto the gallon. This mixture is allowed to soak for a period of time such as about an hour, with the addition of a quantity of an alkaline compound such as ammonia, sodium carbonate, sodium hydrox ide, tri-sodium phosphate, or the like. For example, about one pint of ammonia added to ten gallons of the casein solution gives very satisfactory results. The addition of the alkaline compound facilitates solution, and the solution may also be heated somewhat to assist in the dissolving action. To this solution is added a preservative, such as paraformaldehyde, which assists in preventing thickening or coagulation of the casein solution, when these substances are properly prepared or mixed..

The paraformaldehyde is-first made up into solution ina considerable quantity of water. Thus satisfactory results have been secured where the paraformaldehyde has been added to ten times its own weight of water, or even in higher dilution. Satisfactory proportions of the formaldehyde are from 2% to 25% on the dry weight of the casein used, about 10% on the weight of the casein being readily carried out in commercial operation. When substantially more than 2% of the formaldehyde is used, the solution thereof is added in small amounts to the casein solution which is agitated or flowing freely in a stream, this serving to prevent undesirable thickening of the casein.

The rubber latex is added in emulsion form. Preferably a rather concentrated latex emulsion is used, very satisfactory results being secured with an emulsion containing 38% solids in water,

and also containing a small amount, about 2%,

of an alkali such as ammonia or sodium carbonate to preserve the alkalinity of the emulsion. To the rubber latex emulsion is added the polysulphide solution prepared as above described, satisfactory results being secured by the use of about 2% by weight of polysulphide on the total solids of the emulsion. The casein solution containing the formaldehyde is then added to the latex emulsion, preferably with agitation. Various proportions of these ingredients may be used, de-

pending upon the narticular product or use of the product desired. Satisfactory results have been secured with compositions containing from 15% to by volume of latex, the balance being primarily an alkaline solution of casein containing formaldehyde. lower or base coat, it is found preferable to provide in excess of 50% rubber latex by volume in order to give a base coating which has high fiex-' ibility and high covering power.

As an example of a very satisfactory coating composition for the base coat which is applied to the paper or board, the following is mentioned: Rubber latex emulsion containing about 38% solids and in addition about 2% by weight of an alkali metal polysulphide and 2% by weight of an alkaline compound such as ammonia, is mixed with a casein solution containing about one pound of casein to the gallon of water, and also contain ing about 10% of paraformaldehyde on the dry weight of the casein, in the proportions of' about 60% or more by volume of rubber latex and 40% or less by volume of casein solution to form the liquid coating composition, thereby providing approximately 23% or more by weight of latex solids to approximately 5% or less by. weight of casein in the mixture, or a ratio of more than four parts of latex solids to one of casein.

' The web [3 with the coating applied to the under surface thereof at the coating press |6l'| then passes with the coated surface in contact with smoothing and spreading rolls indicated at 20, If and 22 respectively. These rolls are positioned adjacent the coating press so as to contact with the coating just shortly after its application. Satisfactory results are secured where the first smoothing roll is positioned an effective distance of about six inches from the contact of the paper with the coating roll, the remaining smoothing rolls following in close succession, being spaced about six inches apart. A smoothing roll made of cold. rolled steel having a diameter of about three inches is satisfactory. These rolls are positively driven, preferably against the direction of movement of the paper. Using a paper speed of about 50 to feet per minute, good results have been secured where the rolls are driven against the direction of the movement of the paper at a surface speed of about 80 feet per minute. As shown clearly in Fig. 3, the smoothing and spreading rolls are arranged obliquely across the machine with reference'to the travelling web of 'paper. This is found .,t9 minimize any'tendency toward streaking of the relatively sticky coating, and to facilitate the smoothing and spreading of the coating.

Where the coating is used for a and 24. To facilitate the rapid drying of the coated web, drying blasts such as hot air blasts are supplied to the coated surface of the web. As shown a conduit extends longitudinally beneath. the coating machine, .this conduit being supplied with drying fluid, such as air, by a pump indicated diagrammatically at 26, the pump forcing air under pressure across suitable heating coils 21. Adjacent the smoothing and spreading rolls are upstanding ducts 28, which serve to direct blasts of the heated air against the travelling web so as to dry the coating sufficiently to permit another coating to be applied with only a short travel of the web. These ducts discharge the ing to permit the proper tensioning of the web,

and serving to support and hold the web adjacent the discharge of the ducts to secure more satisfactory drying while minimizing danger of breakage.

' Each of the ducts Z8 is constructed as shown more particularly in Fig. 4. The conduit 25 is provided with a rectangular opening 29 over which is mounted a respective duct; the end walls of which diverge asindicated at 30 so that an upper outlet opening 3i is provided which extends across the full width of the web. The openings 29 in the respective ducts progressively increase in cross section from the duct closest to the pump and thence throughout the series to the end of the conduit to thereby equalize the distribution of air discharged from the respective ducts.

In accordance with the present invention, a

composite grease proofing coating is providedon the surface of the paper or board, which-compositecoatin'g is made up of upper and lower' coats having different characteristics and which are found to combine to give a superior resultant coating. The web l 3 with the base coating treated as above described, then passes with the coated ,surfacein contact with the upper surface of ro- .tatable roll of a second coating press. This coating press is'constructed similarly to the first coating press, and has a lower rotatable roll 36 dipping within a trough 31 containing the coating material, whereby a film of coating of the desired thickness is transferred from the lower roll to the upper roll and thence to the previously coated surface of the travelling web 7 l3.

The upper layer of the composite grease proofing coating at this point comprises essentially a;

mixture of an oil insoluble adhesive such as casein, a po yhydric alcohol such as glycerine,. and a preservative such as paraformaldeh'yde. The casein has-high grease proofing qualities, and

' also assists in securely binding the coating to the sheet. The addition of glycerine to the casein imparts-characteristics of resiliency to the upper coating, and tends to prevent cracking-thereof when the board is bent in the formation of the container, also improving the spreading and covering power of this top-coating. Other poly-- hydric alcohols, for example glycols such as ethylene'glycol, can be used with satisfactory results in substantially thesame manner as glycerine. Other oil insoluble adhesives such as a1- kali metal silicates, glues or gelatine, can be used in place of casein. I

In the preparation of the coating composition for this top coating the casein is made up into a solution in the manner and in the proportions as 5 described above for the base coating, a preservative such as paraformaldehyde being added to the casein solution in the manner previously described. Glycerine is thenadded to the casein solution, satisfactory results being secured by using a. weight of glycerine equivalent to about one half to one and one half times the dry weight of casein. As an example of a very satisfactory coating composition for the top coating the following is mentioned: Casein solution containing about 15 one pound of casein to the. gallon of water and also containing about 10% of paraformaldehyde by weight of dry casein and about 2% by weight of alkaline compound such as sodium carbonate is mixed with glycerine in the proportions of 20 about an equal weight of glycerine to the weight of casein used in the solution. i The composite grease proofing-coating thus produced has superior characteristics to a coating formed by merely aplurality of coats of apar- 25 ticular composition. The first or base coat provides a permanent non-deteriorating coating next to the sheet-which acts as aprotective coating to prevent the upper coat fromsinking into the sheet. The base coat has unusual flexibility 30 which is quite important in container board which is subjected to severe bending in the manufacture of the ultimate containers; This coating, forming a flexible background for the overcoat, serves to. prevent cracking of the overcoat upon85 bending of the'board. A high percentage of a rubber compound, such as rubber latex, in the I base coat acts as a water proofing and moisture proofing agent; and the spreading or covering power of this material, which is improved by the 40 formaldehyde, together with its flexibility enables a substantially impervious coating to be formed with only a relatively thin film. This is materially assisted by the fuzz laying'qualities of the base coating. The relatively high percentage of casein gives an overcoat having high grease proofing, qualities, and this grease proofing layer is properly held upon the surface by the base coat. A coating having a backing of high flexlbility with a surface of high grease proofness is. 5 thus produced.

The web with the top coating applied thereto then passes .with the coated surface in contact with smoothing and spreading rollsindicated at 40, 4| and 42, these rollsbeing similar in opera- 5 tion and construction to rolls 20, Hand 22. Additional drying ducts 44 branching off of the conduit 25 supply heated air to the coated surface of the web. adjacent'the spreading rolls 40, 4! i and 42 and assist'in drying the coating. As many" coats as desired may be applied to the travelling web l3. Thus as shown, a third coating press comprising an upper roll 45 and a lower roll 46 dipping within a trough 41 is provided. If it is desired to apply only two grease proofcoats as above described, coating solution 'is not supplied to the trough 41. p v

Where a coating material is used containing a stTbstance such as casein, which is precipitated by or otherwise fix the coating. This gives superior water proofing qualities to the sheet. Thus very satisfactory results may be secured by supplying a water solution of a metallic salt, such for example as aluminum sulfate to the trough 41, a thin film of this solution being transferred by the rolls 46 and to the coated surface of the web to thereby fix the coating as above described. Where a final overlying coat of a water insoluble wax is used, this treatment is not generally necessary.

The web l3 after leaving the last coating press passes under guide roll 48 and then travels unsupported above the discharge ports of additional drying ducts 49 to subsequent treating apparatus The pressure fluid ejected from the ducts 49 not only serves to dry the web during its travel, but also sustains it suitably spaced from the discharge ends of the ducts so that the coated side of the web does not contact with solid objects until it is substantially dried. The upper end of each of the ducts is formed with a rim or flange 50 of smooth metal so as to provide a supporting surface for the web when the machine is shut down or the web is being threaded through the machine.

A thin overlying film of a water insoluble wax is preferably applied over the grease proof coating in order to protect the coating from exposure and to provide a substantially odorless and tasteless outer surface. Very satisfactory results are secured with parafiin, beeswax, Montan wax, or other well known water insoluble waxes. From the standpoint of economy and ease of application, paraffin is preferred for this purpose. The overlying wax coat not only protects the under grease coat from deterioration, but also adds to the water proofness or moisture proofness of the coating, which is particularly advantageous in the packaging of deliquescent substances, such as crackers for example.

In accordance with the present invention, this top film is applied by capillary attraction to the web so that an extremely thin controlled film is produced with resultant economy in operation. The use of a very thin outer paraflin layer is moreover advantageous, in that it more readily permits the grease proof board to be glued such as is done by a gluing machine in gluing the flaps for the formation of the final box. As shown, a capillary coating press is provided beyond the driers for applying this top Wax coat.

This coating press comprises a positively driven rotary steam heated roll mounted to rotate in contact with a foraminous or felt covering 56 carried by a stationary supporting member shown as a cylindrical tube 51. Tube 51 is mounted within a trough 58 so that the outer felt covering dips within coating material supplied to the trough. Steam coils 59 within the trough serve to main-'- tain paraffin, or other water insoluble wax supplied thereto, in molten condition. This wax feeds by capillary attraction through the foraminous covering to the surface of the coating roll 55. which in turn transfers a very thin film to the coated surface of the web which is brought in contact with the upper surface of this coating roll. The coating roll 55 is heated, such as in the manner of a steam heated drying drum or calender roll, so that the thin film of molten paraffin supplied thereto is maintained in proper molten condition until transferred to the coated web.

A modified form of wax applying press is shown in Fig. 5 in which the steam heated coating roll is indicated at 55'. This roll is mounted to rotate in contact with the curved upper surface of a wood block 60 mounted within a coating trough 58' containing heating coils 59'. The block 60 is provided with a plurality of thin transverse saw cuts or slits 6| through which coating material may be transferred by capillary attraction to the surface of the coating roll. If desired a foraminous or felt covering 62 may be positioned over the wood block, the ends of the covering extending down into the coating liquid.

The sheet then passes from the final coating press through pressure rolls 63 and 64 carried in is vertically adjustable bearings by the frame 65. These rolls are preferably constructed in the manner of calender rolls and are steam heated. A high degree of pressure is used at these rolls and the pressure together with the heat serves to 15 render the top wax coat fluid and spread it uniformly over the surface of the paper. The pressure rolls 53-434 also serve as driving means for drawing the paper through the machine. The coated paper then passes to a reel 61, or may be 2:) passed to suitable cutters and cut into sheets of desired size for the manufacture of containers.

If desired the steps of passing the sheet through the bath of metallic salt and subsequently applying a thin layer of paraffin may be eliminated 25 and the sheets subjected to the following treatment in place thereof which serves to completely eliminate all traces of odor in the finished sheet.

A bath is-prepared consisting of approximately six'gallon's of sodium silicate dissolved in three 30 gallons of water wit-h the addition of one-half gallon of formaldehyde. Calender rolls are provided through which the sheet is adaptedto pass, the lower 'roll dipping within-the bath and serving to carry a layer of the same onto the travel- 35 ing web of paper. Pressure of the order of 500 pounds per-square inch is maintained on the calender rolls. The formaldehyde in the bath serves to fix the casein while the sodium silicate covers the surface with an inorganic layer which en- 40 tirely eliminates odor.

If desired the paper or board previous to the coating as above described, may be first subjected to a sizing treatment. Thus the board, or the layer of the board forming the outer surface 45 which receives the coating, may be a hard sized sheet, or one which has been made up from paper stock -to which a, suflicient quantity of size, such as rosin or parafiin size, has been added as to materially retard the rate in which water or 50 ink penetrates into the sheet. Very satisfactory results are secured by forming a sheet from paper stock to which rosin size has been added at the heaters in the proportion of eighty to one hundred pounds or more of size to twelve hundred pounds of pulp. A sheet which will stand up for approximately five minutes or over in the water drop test, which means that water will not penetrate the sheet in that time, is quite satisfactory. Or the sheet may be given a surface sizing by, an ap- C9 plication of a size to the surface of the formed web, using suitable conventional sizing materials such as above specified. The surface sizing may be applied during the formation of the sheet prior to the application of the grease proofing coating. The sized paper is then supplied in roll form as indicated at H] to the coating machine and the grease proofing coating is applied to the sized sheet.

Referring to Fig. '7, a section through a pre- F ferred sheet or board is disclosed, which is found to be highly efiective for use in containers for the packaging of greasy materials, and which protects the materials from water and damp atmospheric conditions. The sheet comprises inner on a conventional cylinder mold machine having a number of molds to form the various layer or plies of the sheet, these plies being brought together and united in the ordinary manner. Thus a conveying belt of the forming machine passes first across a cylinder mold containing the bottom liner stock and forms a web, and then passes successively across cylinder molds provided with board stock, asphalt emulsion, board stock, and finally top liner stock to form the complete builtup sheet of container board. The board as thus formed is then passed to the coating machine where the composite grease proofing coating is applied, there being a lower or base coat of high flexibility indicated at M and an upper or overcoat of high grease proofing quality indicated at 15. A final overlying water insoluble wax coat 76 is then applied over the grease proofing coating. A container formed from this sheet is protected from water and moisture tending to penetrate from the outside into the interior of the container by the intermediate asphalt layer and by the base coat l3, and is made effectively grease proof, water proof and moisture proof on the interior by the coating applied to the interior surface of the container.

While the forms of invention disclosed herein constitute preferred embodiments hereof, it is to be understood that the invention is not limited to these precise forms, and that changes may be made therein without departing from the scope of the invention which is defined in the appended claims.

What is claimed is:

1. In the manufacture of a greaseproof paper sheet, the method of preparing a coating compo-' sition for application to a paper sheet which comprises forming an alkaline water solution of Case in, forming a separate water solution of formaldehyde, and adding the formaldehyde solution in small amounts to the casein solution while agitating the latter to maintain the solution characteristics of the casein and to provide a mixed solution containing substantially of the order of lay-weight of the formaldehyde on the dry weight of the casein.

2. In the manufacture of a greaseproof paper sheet, the method of preparing a coating composition for application to a paper sheet which comprises forming an alkaline water solution of casein, forming a separate water solution of a formaldehyde, adding the formaldehyde solution to the casein solution in small amounts while agitating the latter to maintain the solution characteristics of the casein and to provide a mixed solution containing of the order of 10% by weight of formaldehyde on the dry weight of the casein, and adding the casein-formaldehyde solution to rubber latex emulsion with agitation to avoid coagulation of the latex.

3. In the manufacture of a greaseproof paper sheet, the'method of preparing a coating composition for application to a paper sheet which comprises forming an alkaline water solution of case- 'in, forming a separate solution of a formaldehyde,

adding the formaldehyde solution to the casein solution in small amounts while agitating the latter to maintain the solution characteristics of the caseinand to provide a mixed solution containing of the order of 10% by weight of the formaldehyde on the dry weight of the casein, adding a polysulfide solution to rubber latex emulsion, and adding the casein-formaldehyde solution to the polysulfide-latex emulsion to provide a mixture containing more than four parts by weight of latex solids to one part by weight of casein.

JOSEPH H. SWAN. III.

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