US2158524A - Method of treating paper containers - Google Patents

Description

, Patented May 16, 1939 UNITED STATES PATENT OFFICE No Drawing. Application October 8, 1937, Serial No. 167,979

v Claims.

This invention relates to a method of treating paper containers.

Paper containers for liquids and semi-liquids such, for example, as milk and other dairy prod- 5 ucts, are replacing glass to a considerable extent.

Paper containers for milk, for example, have various advantages over glass bottles. Perhaps the principal ones are that paper containers, being used once only, avoid all the difliculties and complications of returns of empties, loss by breakage and the necessity of maintaining washing equipment at the dairy.

A paper container for liquids such as milk must be specially treated to render the container as nearly moisture-proof as possible. The common method is to subject the container to a bath of molten paraffin or other suitable material by dipping or spraying.

While the paper container should have an inner and outer surface coating of paraffin (that material being cited herein by way of example), coating alone is not enough. To obtain a properly moisture-proofed article, the paper stock shouldbe thoroughly impregnated with the par aifln.

I have found that with the paraiiiningtreatment as ordinarily practiced, the results are somewhat unsatisfactory because full impregnation of the paper stock is not attained, at least without such an extended duration of treatment, preheating and the like, as to render the process commercially impractical. That is, the problem is not only to obtain proper impregnation but also -to obtain it in such a way that it can be put into commercial use. The ordinary glass milk bottle is used over and over. In addition, the dairy has a sufficient supply on hand for its daily requirements. Paper containers, on the other hand, are used once and thrown away. It is apparent that if paper containers are to compete commercially with glass bottles, they must be produced at low cost. But any steps that slow up production raise'the cost. Moreover, it is a usual practice for dairies to make their paper containers at the dairy as needed. It follows that any treating process, to be commercially practical, must make it possible for the containers to be produced at such speed as will enable the dairy to obtain its daily requirements without excess equipment.

It is an object of the present invention to provide a method of treating paper containers such that the containers are properly moisture-proofed in that they have a surface coating of and are thoroughly impregnated with the moisture-proofing material; and such that the treatment referred to can be effected in a rapid and otherwise commercially practical manner.

With these and other objects in view, the invention consists in the method and method steps 6 which will first be described and then more particularly pointed out.

, I have discovered that a thorough impregnation may be obtained in a relatively brief period of time if the paraffin bath is at a temperature 10 of at least 212 F., i. e., at least as high as the boiling point of water. It is my belief that the failure to obtain proper impregnation under previously known treatment methods results from the fact that air and moisture become entrapped in the fibers of the paper stock and prevent, in whole or in part, entrance of the molten paraflin. It is my further belief that treatment at 212 F. or over causes an expansion of any air and a dissipation of any moisture that may be present in the stock, thus permitting a thorough impregnation of the stock by the paraflin.

While treatment at the temperatures referred to results in satisfactory impregnation, I have found in the course of my experiments that such treatment was by nomeans the complete so1ution of the problem and, in fact, created new problems. For example, while paraffin at 212 F. or higher will impregnate the paper stock, it will not adhere to the surface in the form of a coating, at least not to the extent necessary for a satisfactory product. Further, treatment at such temperatures is apt to char the paper. In this connection, the word char is used to denote any damage to or discoloration of the paper due to heat.

In other words, if the containers are treated at a temperature high enough to obtain proper impregnation, they lack proper surface coating and are apt to be charred. On the other hand, if the temperature is reduced sufficiently to avoid charring and obtain a suitable surface coating, satisfactory impregnation is not obtained.

The matter of charring is of considerable importance, particularly in the case of containers for'milk. Many containers are moisture-proofed in a partially completed condition. That is, after filling some additional folding, creasing or similar steps are necessary to complete and close the ultimate container. If thecharring is of such character as to damage the fibers of the paper stock, the paper is apt to become brittle and lifeless so'that subsequent folding, creasing or other fabricating operations cannot be properly carried out, at least commercially. If the charring is merely a discoloration of the paper, while there may be no actual damage, the container is useless commercially because the public willnot buy milk and the like in containers that have any imperfections, even in appearance.

According to the invention in its entirety, I subject the containers to a bath of paraflin or other suitable moisture-proofing material at a temperature at least as high as the boiling point of water. I maintain the container in such bath for a period of time sufiicient to obtain proper impregnation but insuiiicient to cause any substantial charring of the paper stock. I then remove the container from the aforesaid bath and subject it to a cooling bath before the heat stored up in the paper can cause any substantial charring.

In accordance with the invention in its entirety, this cooling bath is also of a moistureproofing material, such, for example, as paraffin. Its temperature is substantially below 212 F. Thus, the second bath performs a double function., It is a cooling bath and a coating bath. The paraflin in this bath is relatively cool enough to cool oh the paper before charring can occur. It is also cool enough to result in a surface coating on the container.

The temperature of the impregnating bath and the time of treatment therein may vary within a considerable range. While time and temperature are generally reciprocal, one may be varied more or less without varying the other. For paper stock such as isordinarily used in the manufacture of paper containers, I have found a bath temperature of around 245 F. and a treatment period of a few seconds, i. e., less than a minute, gives satisfactory results. In fact, at this temperature, thorough impregnation can be obtained almost as rapidly as it is possible to insert and remove the containers, at leaston a commercial scale. It follows that there is nothing particular to be gained by increasing the temperature or decreasing the time.

While the interval between the impregnating bath and the coating bath may vary, the paper stock is apt to char, at least as to surface discoloration, if allowed to stand in the air any considerable time. I have found that the best results are obtained if the containers, after removal from the impregnating bath, are immediately subjected to the cooling and coating bath, that is, as quickly as it is practically possible to effect the transfer.

The temperature of the cooling and coating bath and the time (i treatment therein may also vary within a considerable range. The temperature must, of course, be far enough below 212 F. for the bath to perform its cooling and coating functions and should be high enough to maintain the bath material in proper liquid condition.

With molten paraffin as the second bath material, I have found that charring may be prevented and the containers properly coated in a few seconds, i. e., less than a minute, with a paraffin temperature of about F.

With the method herein described, paper containers may be produced that are properly moisture-proofed in that they have both surface coating and thorough impregnation. But what is perhaps of equal or greater importance is that these ends are attained in a relatively brief time period. Not only does reduction of time of manufacture reduce the cost, but in many dairies, rapid production is essential to dairy operation. Forvv various reasons it is desirable, and in some jurisdictions obligatory, to paraffin milk containers on the day of filling. In such cases, a dairy having a volume running into tens of thousands of quarts must be able to produce or treat its containers in the least possible time. By making it possible to moisture-proof containers in a matter of seconds, the method here described contributes largely toward the attainment of that end. Moreover, the cooling bath cuts down the cooling period prior to handling and other subsequent operations. I

Thorough impregnation not only makes possible a properly moisture-proofed container but also has another advantage. The paper stock ordinarily used in making containers is normally opaque. The more the stock becomes impregnatedwith parafiin or the like; the less opaque and the more translucent it becomes. 'With good grade stock and the thorough impregnation made possible by the present invention, the stock may be made so translucent as to be almost transparent.

' This is of particular importance in packaging milk as the container stock becomes sufficiently translucent to make the cream line clearly visible.

It is to be understood that other materials than paraflin may be used; that container is intended to include partially or roughly finished containers, container blanks, etc.; and that the bath may be by spraying, dipping or in any other suitable manner.

This application is a continuation, at least in part, from application Serial No. 679,210 filed July 6, 1933. r

What is claimed is:

1. The method of paraflin or similar paper containers which comprises subjecting the containers to a bath of moisture-proofing material at a temperature at least as high as the boiling point of water, whereby the paper of the containers is impregnated with said material, removing the containers from such bath after a time interval insufficient to cause charring of the containers and, substantially immediately after such removal, subjecting the containers to a bath of paraffin or similar material at a temperature substantially below the boiling point of water, whereby said containers are cooled by and become coated with said material.

2. The method of parafiin or similar paper containers which comprises subjecting the con- I tainers to a bath of moisture-proofing material at a temperature at least as high as the boiling point of water and for a relatively brief interval of time, whereby the paper becomes impregnated with said material, and substantially immediately subjecting the containers to a bath of parafiin or similar material at a a temperature substantially below the boiling point of water, whereby said containers are cooled by and become coated with said material.

3. The method of moisture-proofing paper containers which comprises subjecting the containers to an impregnating bath of liquid paraflin or.

similar material at a temperature at least as high as the boiling point of water and, before there is any substantial charring of the paper, subjecting said containers to a cooling and coating bath of paraflin or similar material.

4. The method of producing moisture-proof paper containers which comprises first submitting the containers to an impregnating bath of molten paraffin having a temperature of 212 F. or above, removing the containers after a time interval insufficient to cause any substantial charring of the paper and, substantially immediately after such removal, subjecting the containers to a coating and cooling bath of molten parafiin havinga temperature substantiallyless than 212 F.

5. The method of moisture-proofing paper containers which comprises subjecting the containers to a bath of parafiin or similar material at a temperature at least as high as the boiling point of water and for a time interval insuificient to cause any substantial charring o! the paper, and then subjecting the containers to a coating bath of paraflin or similar material at a substantially lower temperature, said coating bath being applied substantially immediately after the termination of said time interval, whereby the coating bath also acts as a cooling. bath to prevent any substantial charring' of the containers.

- ROLAND K. REED.