US2361582A

US2361582A - Nonscuffing wax coating composition

Info

Publication number: US2361582A
Application number: US432628A
Authority: US
Inventors: Adams Elmer Wade; Frederick H Maclaren
Original assignee: Standard Oil Co
Current assignee: Standard Oil Co
Priority date: 1942-02-27
Filing date: 1942-02-27
Publication date: 1944-10-31
Anticipated expiration: 1961-10-31

Description

Patented Oct. 31, 1944 NONSCUFFING wAx COATING COMPOSITION,

Elmer Wade Adams, Hammond, and Frederick H.

MacLaren, Munster, Ind., assignors to Standard Oil Company, Chicago, 111., a corporation oi llndiana.

No Drawing. Application February 27, 1942,

Serial N 432,628

9 Claims. (Cl. 196-1419) The present invention relates to improved wax compositions and methods of making them, and more particularly to such compositions uitable for waving paper sheets, paper cartons, and the like, to produce non-blocking and non-scuffing permanent coatings.

must be free from scaling, peeling or scufiing and it must produce a non-blocking sheet. The sheets must not adhere when stacked and the coating must not strip off. For use on formed containers, which are coated by dipping the formed caI'dboard, such as milk caps, milk cartons and butter cartons, the odor, appearance, and particularly anti-scuffing of the coating are important. Therefore it is an object of this invention to produce an improved modified wax composition and coating of high tensile strength which is resistant to scaling and blocking.

The term parafiln Wax" as used herein defines the hard, non-ductile, crystalline wax comprising laminated plate-like crystals of parafiln, derived from parifiln base and mixed base type mineral oils. In recovering the paramn wax, the crude all s separated into a series of paraflin distillate fractions and the paraiiln wax defined by well-known operations. For example, the waxbearing distillate may be mixed with gas oil as a diluentto reduce the viscosity of the mass to facilitate pressing.- This mixture may then be chilled in coolers at a definite chilling rate to produce crystals of optimum size for best rate of filtration. After the pressing is completed the slack wax is removed from the presses and reduced ln'a pipe still to remove the diluent. The reduced wax is then carried through the sweating operation. Sweating is a carefully controlled operation which involves drainage of the oil from the crystal interstices, fractional fusion, and the solubility eflects of lower melting point waxes and oil. This operation is accomplished by slowly raising the temperature or the chilled crude scale wax at a uniform rate. -A light clay percolation may be carried out on the refined wax as a final clean-up in'the process. This percolation does not affect the tensile strength but is principally for decolbrlzation.

The physical properties of the paraflfln wax are determined by the source of the crude oil from which the wax is prepared, the method of refining the parafiin wax, and the oil contact of the resulting product. The paraflin wax used in our invention can be derived from Mid-Continent or Salt Creek crude and has a high tensile strength within the range of between about 250 and about 320 pounds per square inch or higher, a melting point within the range of between about F. and about F. and an oil content below about 0.3%, for example below about 0.1%. These waxes are white, brittle or non-ductile and granular.

Petrolatum wax may be obtained for similar crudes which have been stripped of their lighter fractions including the paraffin distillate. The stocks from which petrolatum waxes are made represent about a 25% bottoms of the original crude oils. The undistilled residue is refined by methods known to the art, as by diluting with an oil solvent and centrifuging, to produce a wax having a melting point within the range of between about F. and 175 F.', and ordinarily within the range of between about F. and about 170 F., and an oil content of less than 6%. De-oiling may be accomplished by repeated solution, chilling and cold settling in naphtha,

- the oil being drawn off in the naphtha. Petrolatum waxes are smooth, ductile, tough materials, darker in color than the paraifin wax. Thepetrolatum wax is too ductile for dependable tensile strength tests but gives an apparent high tensile strength with necking down of the standard sample.

In carrying out the present invention to produce a. wax composition of the character described, we may employ an improved wax compocontaining a maximum 01' about 0.2% oil which retains its initial high tensile strength and in addition is resistant to-scufilng when applied as a coating. For example, such a composition may comprise 3% of F. melting point petrolatum wax and 97% of 132 F. melting point parafiin wax of initially high tensile strength above about 250 pounds per square inch.

We have found that. the non-scaling properties of a. wax coating are afiected by the crystal structure oi the finished product. Parafiin wax or the prior art may be of low oil content and high ten- .magnified about 600 diameters.

sile strength but has a crystal form of laminated, even, fiat, plate-like crystals. The coatings prepared from these high tensile strength, substantially oil-free straight waxes scufl and peel. Furthermore, we have found that although a coating of pure paraflin wax having a high tensile strength and low oil content may be satisfactory when first prepared, on aging there results a coatin which scufis and has the undesirable pro'per-.

. invention.

Petrolatum wax difiers from -.paraflin wax in crystal form, due primarily to difference in molecular weight. The addition of the small critical amounts of petrolatum wax to-the high tensile strength paratfln wax modifies the crystal structure of the paraffin wax to produce jagged or curled interlocking crystals or aggregates with erose edges. The action of high melting petrolatum wax on crystal structure seems to be that of seeding due to the petrolatum wax chilling-out first in the complex crystal system. Such change in crystal lattice imparts superior non-scaling properties to the composition without aflecting the tensile strength.

A straight paramn wax of very high tensile strength and good sealing properties does not 'assure a coating which is satisfactory from the standpoint of scaling in the rubbing test. The primary function of adding the petrolatum wax is to modify-the crystal structure in such a manner that a coating prepared from the modified wax is non-scumng. The highly refined unmodified parafiln waxes, whether of high or low tensile strength, both have large plate crystals. Thus, for'example, two paraflln waxes having a tensile strength of 92 pounds per square inch and 304 pounds per square inch, respectively, each readily showed outlines of similar large plates when a 20% solution of the wax was viewed through a microscope wherein the crystals were tensile strength paraffin wax is modified by adding a small amount, for example 3% of 165 F. melting point petrolatum wax, the modified wax has substantially the same high tensile strength as'the base material, 1. e., about 304 pounds per square inch.- However, the fiat, even plate-likestructure of the paraffin wax alone is completely gone and this wax composition is highly resistant to scufllng and is non-blocking.

Coatings prepared from the modified wax have substantially the same high tensile strength as the original paraflln waxes but in addition they When the high 312 pounds per square inch, and containing no more than 0.15% oil, for example 0.1%, scufls and scales in the paper rubbing test. It is evident, therefore, that low oil content and high tensile strength alone are not indicative of a non-scuffing coating. However, the addition of from about 0.5% to about 3%, for example 0.75% to 1.5% of ductile petrolatum wax to the initially veryhigh tensile strength paraffin wax greatly enhances the non-scuffing andnon-blocking characteristics of this coating. The addition of corresponding amounts of petrolatum wax to low v tensile strength parafiln waxes does not similarly enhance the non-scuffing characteristics of a coating although the tensile strength is improved.

Thus by adding'a critical amount, for example about 3% of a petrolatum wax having a melting point of between about 155 F. and about 170 F., for example 165 F., and an oil content of lessthan 6% to unmodified very high tensil strength parafiin wax we obtain a new wax composition containing less than 0.2% oil and having substantially the same tensilestrength as the unmodified parafiln wax. Such a wax composition has an entirely different crystalline structure than that of the initially high tensile strength parafiln wax.

. modified wax composition does not scuff or strip from the surface and is non-blocking.

Our invention is particularly useful in the preparation of wax-coated wrapping sheets and are resistant to scufllng and blocking. The photoa micrographs show that the cause of these excellent properties is the entirely different crystal structure of the wax-blend than that of the highly refined parafiin wax without the small critical amount of added petrolatum wax. The addition of the small amounts of the petrolatum wax does not affect the already high tensile strength of the Dlrafiln wax and the percent of oil is kept low in the finished coating to prevent blocking.

For example, a paper coated with a pure paramn wax of 136 F. melting point and a high tensile strength within the range of between about 250 and 320 pounds per square inch, for example conventional methods. For example, the wax composition when used on bread wrappers may first be applied in a light coat on one side before printing to prevent offset. After the ink has dried the sheet is given a final waxing on a machine in which the paper runs through a molten wax bath. This operation is followed by squeezing the hot sheet through rollers which, by regulation of the pressure, determine the thickness of the wax film. Following this the hot sheet is rapidly chilled by running itinto a cool water bath or overa refrigerated roller. The final step in the manufacture of this type of wrapper is the cutting of the wide sheet into the proper size wrappers.

The stockmay be ordinary sulphite pulp or it may be derived from various cellulose and regenerated cellulosic materials. To improve the wax coating and keep it on the surface of the coated materials, the stock may be wax-sized prior to the application of the-new and improved wax composition. For example, petrolatum with or without the addition of other materials may be emulsified in the presence of a soap solution as the emulsifying agent to produce a size. However, the method of preparing an emulsion constitutes no part of the present invention. Such materials as paraffin wax, high melting point petrolatum ba'ses, vegetable waxes, Montan wax, Ozokerite, resins or fatty materials may be incorporated in the papery-beating stage or any other suitable stage in advance of the formation of the sheet. Such a process aids inkeeping the wax composition coating on the surface and results in better spreading of the coating, elimination of wax absorption, increased carton strength, and

increased resistance to leakage.

.Our new modified wax composition is very useful for coating wrapping sheets and the like, for example, those wrapping papers used on various food products. The high resistance of our improved wax composition coatings to scaling makes When applied as a coating the them far superior to any composition of the prior art.

This application is a continuation-in-part of our copending application, Serial No. 333,686, filed May 6, 1940.

While our invention has been described with reference to particular examples, it is to be understood that the foregoing detailed description is given merely by way of illustration and that many modifications may be made therein without departing from the invention.

We claim:

1. An improved film-forming wax composition comprising a paraflin wax having an initial tensile strength of above about 250 pounds per square inch and normally forming a scuffing film and about 3% of a single wax-like addition agent consisting of a petroleum wax having a melting point at a temperature within the range'of between about 155 F. and about 170 F. and an oil content of less than 6%, the said compositon being further characterized by having a tensile strength substantially equal to that of the parafiin wax alone and by being resistant to scuffing and blocking when a plied in a thin film;

2. An improved film-forming wax composition consisting of about 97% of a paramn wax having a tensile strength of betwen about 250 and about 320 pounds per square inch and normally being subject to scufling when in a thin film. and about 3% of a single wax-like addition agent consisting of a petrolatum wax having a melting point of about 165 F. and an oil content of less than 6% admixed with said high tensile strength paraflin wax, the wax composition being further characterized by containing a maximum of about 0.2%

oil, by ha .ng a high tensile strength between about 250 and 350 pounds per square inch substantially equal to that of the paraflin wax alone and by being resistant to scuiilng and blocking when aplied in a thin film.

3. An improved wax-coating composition capable of being deposited in a non-scufllng film comprising between .about 97% and about 99.5%.

pable of being deposited in a non-blocking and permanently non-scufiing film consisting of between about 0.5% and 3.0% of a petrolatum wax containing less than about 6% oil and having a melting point of about 165 F., and a paraflln waxhaving a high tensile strength above about 250 pounds per square inch and containing no more than about 0.15% oil, said compositon having a tensile strength substantially equal to the tensile strength of the paraflln wax and having a net oil content of not more than 0.2%.

5. The method of rendering a paraflin wax resistant to scufilng, said wax normally having a high tensile strength of above about 250 pound per square inch and normally being subjected to scufling when in a thin film, the. step of permanently modifying the crystal structure of the para'mn wax by adding to said paraffin wax more than about 0.5% and less than about 5% of a single wax-like'addition agent consisting of a ductile petrolatum wax having a melting point between F. and about 170 F. and containing less than 6% oil whereby the surface coating characteristics of the paraffin wax are improved without substantially afiectlng the tensile strength thereof.

6. The method of rendering a paramn wax re sistant to scufling, said wax normally having an initial tensile strength of between about 250 and 320 pounds per square inch and normally being subject to scufllng when in a thin film, the steps of permanently modifying the crystal structure of the parafiln wax by adding'to said parafiin wax about 3% of a single wax-like addition agent consisting of a ductile petrolatum wax having a melting point between 155 F. and about 170 F. and containing less than 6% oil whereby the sur-' face coating characteristics of the paraflin wax are improved without affecting the tensile strength thereof.

'7. An improved wax coating composition consisting of at least about 97% of a paraflin wax having a tensile strength of between about 250 and about 320 pounds per square inch, said parafiin wax normaly being subject to scufling when applied in a thin film, and less than about 3% of a ductile petrolatum wax having a melting point of about F. and an oil content of less than about 6%, the said coating composition being further characterized by having a tensile strength substantially within the range of the tensile strength of the parafiln wax alone and by being resistant to scuffing and blocking when applied ln a thin film.

8. An improved wax coating composition free of polar wax-like substances and which is resistant to scufllng when applied in a thin film, said composition comprising essentially an admixture of paraflln wax normally havingan initial tensile strength above about 250 pounds per square inch and normally forming a coating which scuffs and more than about 0.5% and less than about 5% of petrolatum wax having a melting point within the range of between about 155 F. and about F. and an oil content of less than 6%, the tensile strength properties of said paraffin wax being substantially unaltered and the resistance to scufling being substantially increased by the blending of the said petrolatum wax therewith.

9. An improved wax composition adapted to produce a thin film which is resistant to scuffing, said composition comprising an admixture of between about 0.5% and about 3.0% of a wax consisting a ductilepetrolatum wax containing not more than about 6% oil and having a melting point within the range of-between about 155 F. and about 170 F. and a base wax consisting of-a parafiln wax which is characterized by having an intial high tensile strength of above about 250 pounds per square inch which tensile strength is substantially un'hanged with an increase in the resistance to scufflng.

' ELMER WADE ADAMS.

FREDERICK I-I. MACLAREN.