US2430065A - Containers of polyvinyl acetals - Google Patents

Description

Patented Nov. 4, 1947 CONTAINERS OF POLYVINYL ACETALS Lloyd Lyn Leach, Swarthmore, Pa., assignor to E. I. du, Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware No Drawing. Application August 18, 1943, Serial No. 499,115

Claims.

' "This invention relates to the packaging of commodities such as ground, roasted coffee, which deteriorate rapidly when exposed to the atmosphere. More particularly, it relates to a container or package of transparent, non-fibrous,

synthetic sheet or film that is eminently suited for such a use and for kindred uses.

Coffee has very definite characteristics not.

possessed by other food commodities. can be used, it must be roasted and ground to a particular fineness. During the roasting operation, there are developed in the coffee certain aromatic and vegetable or fixed oils. The aromatic oils'are volatile and pass very quickly into the atmosphere unless some means are provided to prevent such evaporation. The vegetable or fixed oils, on the other hand, readily become rancid when exposed to the oxygen-in the air. As a result, roasted coffee, particularly when ground, rapidly loses most of its desirable properties if exposed to the atmosphere.

It has been common practice to protect ground, roasted coffee by packaging it under vacuum in glass or metal containers. However, these containers are relatively expensive and their weight adds considerably to the cost of their transportation.

It has therefore been proposed to package the ground material in a fiexible, light-weight bagv or container made of a coated paper or a synthetic film. Among the synthetic films that have been mentioned for such use are regenerated cellulose, both the untreated and moisture-proof variety, and various rubber derivatives including rubber hydrochloride.

To be suitable for use in the storage or shipment of ground coffee, such a light-weight, flexible container must be highly impermeable to gases, including the volatile, aromatic gases of coffee and oxygen or air. It must be strong and sufiiciently tough to resist puncturing by the sharp-cornered coffee granules, and it should preferably be sufficiently rigid so as not to require the presence of an external supporting means, such as a cardboard cover or carton. It should also be sufilciently flexible and durable at low temperatures to permit exposure to winter atmospheres. Moreover, to permit its manufacture on existing types of packaging machinery, the

container must be prepared from a material that is capable of being heatsealed. Of course, the

completed package must be stable to light and Before it have been proposed for use with coffee all fail to meet oneor more of these requirements. For example, containers prepared from coated papersflor films of regenerated cellulose are generally not sufiiciently impermeable to oxygen or air at the high relative humidities often encountered. Furthermore, especially in the case of regenerated cellulose, the containers are not sufficiently flexible at low temperatures, nor are they sufficiently tough to resist puncturing by the coffee granules.

Those containers that have been prepared from rubber derivatives, e. g. rubber hydrochlorides, on the other hand, are relatively unstable and tend to decompose on exposure to sunlight. Moreover, they are so thermoplastic that they tend to lose their shape and open at the point of sealing when exposed to high summer temperatures. The impermeability to oxygen of this rubber hydrochloride sheeting is not as high as desired.

It.is,therefore, the principal object of this invention to provide a bag or like container or packageformed from a transparent, non-fibrous, synthetic sheet material, which container meets all of the above-mentioned requirements and is suitable for use with substances such as ground coffee, that are deleteriously affected by exposure to air. Other objects will appear hereinafter.

The objects of this invention are accomplished, in general, by a package prepared from a film comprising a partial acetal of polyvinyl alcohol, wherein from 12% to 55% of the available hydroxyl groups of the alcohol'have been reacted with an aliphatic aldehyde containing should have a butyral content of from 23.5 to

33.7%). With aldehydes of lower molecular weight than butyraldehyde, i. e. formaldehyde, acetaldehyde, propionaldehyde, it is preferred that from 40 to 55% of the available hydroxyl groups of polyvinyl alcohol have been reacted with the aldehyde. With aldehydes of higher molecular weight than butyraldehyde, i. e. amylic aldehyde or hexaldehyde, it is preferred that from 12 to 40% of the available hydroxyl groups of polyvinyl alcohol have been reacted with the aldehyde.

Although the; range of compositions given above as satisfactory for these films is rather .notsufllciently thermoplastic to permit their use in a normal heat-sealing operation. on the other hand, if the acetal content is higher than that provided by the invention, the impermeability of the films to oxygen and air is impaired.

The polyvinyl partial acetals suitable for the purposes of this invention are preferably prepared by the treatment of polyvinyl alcohol (obtained by the complete hydrolysis of polyvinyl acetate) with a controlled amount of the desired aldehyde, in the presence of a suitable catalyst, such as sulfuric acid, an organic sulfonic acid, etc. They can, however, also be prepared by the partial hydrolysis of a more or less completely acetalized polyvinyl alcohol, for example, by the controlled hydrolysis of a polyvinyl butyral having a butyral content of from 40 to 50%. (The completely substituted polyvinyl butyral has a butyral content of 50.1%.) The formation of sheets or film from these partial acetals of polyvinyl alcohol is described in U. S. Patent Nos. 2,044,730, 2,045,130, 2,120,628, and 2,253,078.

The packages of this invention are preferably prepared from pre-formed sheets of the abovementioned particular polyvinyl partial acetals by the use of conventional types of package-making machinery whereby to form containers of any desired design, such as flat, square, round, satchel bottom, or automatic bags, wrappings, cartontype containers, etc. However, such a method of manufacture is not essential to the invention and the polyvinyl partial acetals can, if desired, be cast from solution directly in the form of a tubular structure, whose open ends are subsequently closed by a heat-sealing operation; or they can be directly formed into a cap-like structure comprising a tubular member openat only one end, this end being subsequently sealed after the introduction of the coffee or other material to be v packaged.

solution and the precipitated polyvinyl butyral is filtered off, washed and dried. Upon analysis, the

' dried product shows a butyral content of 30.3%-

corresponding to a substitution of 48% of the available hydroxyl groups of the polyvinyl alcohol. Q

The product is then dissolved in a mixture of 80 parts of methanol and 20 parts water to form a 15% solution, the solution being cast onto a heated plate to form a film of polyvinyl partial butyral 0.002 inch thick. The film is then formed into an open-mouthed bag in the conventional manner, filled with freshly ground coffee and sealed under vacuum in accordance with known procedures. The package is self-supporting and because of its transparency the condition of the coffee within it can be readily noted. The package, which is quite firmly packed, resists puncturing and can be handled roughly and even dropped from a height of several feet without rupturing. At the end of two months, the bag was opened and the cofiee examined. It did not appear to have lost any of its original aroma, nor did it appear to be rancid or to have otherwise deteriorated.

In a tumble test, wherein a similar bag is filled with 240 grams of rice and dropped repeatedly generated cellulose and cellulose acetate and tested in this manner broke after being dropped 80 and 20 times, respectively.

Films of the polyvinyl partial acetals employed in this invention, particularlythose films that possess a thickness of not more than 3 mils, are

I flexible even at low temperatures and do not necessarily require the presence of a softener or plasvalue and containers possessing thicker orthinner walls are within the scope of the invention. Of course, the impenetrability of the package to air and other media varies directly with the wall thickness and this factor must be taken into account in designing the package.

The invention is further illustrated by the following example of a preferred embodiment wherein parts are by weight unless otherwise indicated.

- Example tained by the complete hydrolysis of 172 parts of polyvinyl acetate are dissolved in 983 parts of water. The solution is maintained at 12 C. and

0.88 part of sulfuric acid and 0.88 part of Aerosol O. T. (a wetting agent) are added. Thirty-six parts of butyraldehyde are then added with stirring. At the end of 20 minutes the temperature is raised to 20 C. and the solution is stirred at this temperature for one hour. The temperature of the solution is then raised at 30 minute intervals with constant stirring to 30 and 40 C. and finally to 65 C. 0.88 part of sulfuric acid dissolved in 100 parts of water is then added and stirring is continued for another 30 minutes. Aqueous caustic is then added to neutralize the ticizer. However, such a material, for example glycerin, can be incorporated in the film. In the case of a package for use with coffee and prepared from a film 2 mils thick, a plasticizer content of approximately 20% of the film weight is preferred. Satisfactory results can, however, also be obtained with plasticizer contents of greater or lower value.

The containers of this invention are admirably suited for the packaging of freshly ground cofiee. However, they are not so limited." They can also be used for the protection of other foodstuffs, such as powdered whole milk, shortenings, etc., or objects that must be protected from the deteriorating influence of the atmosphere. Moreover, because the packages of this invention are highly impermeable to substances such as oils, greases, etc. which cannot normally be packaged in flexible containers, these packages may also be used for the storing and shipping of such substances. 0n the other hand, the packages of this invention can also be used as garment covers, etc., or the films may be used as a holland cloth substitute for the protection of articles such as unvulcanized rubber.

This invention provides a light-weight, heatsealable container that is eminently suited for the protection of foodstuffs such'as ground, roasted coffee, that are adversely affected by exposure to the atmosphere. The package is highly impermeable to gases, such as air, aromatic vapors and the like, and to liquids, such as water, oils, hydrocarbons, etc. The package is tough, strong and highly flexible at both ordinary and low temper atures. It can withstand rough handling during storage or shipment. It is not affected by exposure to sunlight. It is sufficiently thermoplaspackage-manufacturing and heat-sealing apparatus. However, it does not soften or weaken on exposure to summer temperatures.

As many apparently widely difierent embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that the invention is not limited to the specific embodiments thereof except as defined in the appended claims.

I claim:

1. A container suitable for the packaging of coffee, formed essentially of a film of a partial acetal of polyvinyl alcohol wherein from 12% to 55% of the available hydroxyl groups of polyvinyl alcohol have been reacted with an aliphatic aidehyde containing from'one to six carbon atoms.

2. A container suitable for the storage and shipment of freshly ground cofiee, formed essentially of a film of a partial butyral of polyvinyl alcohol wherein from 12% to 55% of'the available hydroxylgroups of polyvinyl alcohol have been reacted with butyraldehyde.

3. A container suitable for the storage and shipment of freshly ground cofiee, formed essentially of a film of a partial butyral ofpolyvinyl alcohol having a combined butyral content of shipment of freshly ground coffee, formed essentially of a film of a partial butyral of polyvinyl alcohol having a combined butyral content of from 23.5% to 33.7%, said film having a thickness of about 2 mils.

5. A container suitable for the packaging of coffee, formed essentially of a plasticized film of a partial acetal of polyvinyl alcohol wherein from 12% to of the available hydroxylgroups of polyvinyl alcohol have been reacted with an aliphatic aldehyde containing from one to six carbon atoms, saidfilm containing about 20% by weight of glycerin.

LLOYD LYN LEACH;

REFERENCES CITED The following references are of record in the file -of this. patent:

UNITED STATES PATENTS