US2934453A - Process for producing wrapping material and casting molds - Google Patents

Description

April 26, 1960 M. ALSFELD ET AL 2,934,453

PROCESS FOR PRODUCING WRAPPING MATERIAL AND CASTING MOLDS Filed Nov. 27, 1956 q. OUTER COATING WATER IMPERMEABLE b- PAPER C SWOLLEN WATER-INSOLUBLE LAYER OF ALGINIC COMPOUND INVENTORS HA 2: AL SFELP) we. FGJING DIERICH 5 BY g 'AT THE EVS PROCESS FOR PRODUCING WRAPPING MATE- RIAL AND CASTING MOLDS Application November 27, 1956, Serial No. s24,4ss Claims priority, application Germany November 30,1955

' 2 Claims. Cl. 117-44 It isknown to produce wrapping materials, particularly for sticky masses and such masses, which upon rise in temperature become softened by applying to a support, such as paper, wood, metal or fibers, a layer of a soluble derivative of alginic acid and converting that layer, before it has dried, into a jelly-like, swollen mass by treatment with a precipitating salt, e.g. calcium chloride. The masses to be wrapped are bitumens, tar products, resi'ns, synthetic resins, waxes, putties, adhesives and pastes of all kinds.

Technically, the process may be carried out by dipping the support, e.g.. burlap sacks, in an alginate solution and treating the sacks, while still wet, with calcium chloride solution. The sack thus impregnated, can be filled with molten bitumen of high temperature without any part of the bitumen permeating through the sack.

After the contents have cooled down, a blockof bitumen may be obtained, for instance by cutting open the sack and removing it without the bitumen adhering thereto.

However, it has been found that this process incurs considerable difiiculties when it is desired to replace the sacks of burlap material, or the like, by paper bags which are considerably more'economical; in that case, the removal of the wrapping material is far less easy. The same difliculties are encountered if instead of burlap sacks, cardboard drums are used for being filled with bitumen and the like.

It has now been discovered, quite unexpectedly, that bitumens and similar masses may be filled into cardboard drums, paper bags and similar wrapping materials, without incurring the above mentioned ditiiculties, when the wrapping materials are, provided, in addition to a layer of swollen alginic acid .at the surface facing the goods, with another layer separated therefrom by paper or paper-like material, facing away from the goods, said last mentioned layer being of negligible permeability for water and steam. The process according to the invention is therefore characterized by providing on paper or the like material, on the one hand a swollen but waterinsoluble layer of alginic acid or its derivatives and separated from that layer by the paper a layer of a material of negligible'permeability for water and steam. In the following such a material will be. called practically impermeable. In this way it has been found that it is possible, contrary to expectations, that goods, may be wrapped for which the wrapping mentioned in the beginning, are quite useless; such goods are e.g. hot fatty acids when they solidify upon cooling.

The new process may likewise be used to great advantage in making molds for casting synthetics, such as phenol resins, polyester resins, epoxy resins and the like. The molds are made of paper or the like,- and are lined with a layer of paper impregnated according to the above process. In the mold, the alginate layer should be the one coming into contact with the material to be cast.

The layer of negligible permeability for water and steam, may consist of diiferent materials as long as they fl ti [S a ts v i' t 'ticularly economical when paper bags are used.

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\vachs. Other polymer substances may also be used for the layer as long as they are impermeable for water and steam or practically impermeable. In this respect, e.g. polyvinyl chloride, chlorinated rubber, polystyrene, pol vinylidene chloride, and many co-polymers ofthese compounds are useful products. Of the latter, a product known in the art as Huelser Emulsion is a co-polymer of styrene and butadiene.

Instead of the practically impermeable layer made out of synthetic material, layers of bitumen may be applied with good success. This mode of operation is par- When bitumen is used as coating layer, it should only be con sidered that bitumen sometimes migrates in paper, and the usefulness of paper bags would thereby be impaired. It is therefore advisable to use paper bags, impregnated with a bitumen layer, only in such cases when a storage of the empty .bags is not intended for any considerable length of time.

It has been found advantageous to apply the practically impermeable layer in such a manner onto the paper which is provided on the other side with an alginate layer, that an intimate anchorage in the paper will occur; this can be done for instance by hot-sealing or gluing. When for the preparation of the wrapping materials several layers of paper are used, which are only slightly joined to each other, the use of the new process for preparing of paper bags, for instance, is considerably decreased when one layer of paper is provided with the impermeable layer, and the other one only loosely joined thereto with the alginate layer. Such an application is therefore not generally useful.

The application of a swollen water-insoluble layer of alginic acid or its derivatives on paper or paper-like material may occur in several ways, which are generally known. The best known operating method consists in treating the paper with a water-soluble compound of alginic acid and converting the impregnating or coating layer into an insoluble derivative, by a subsequent treatment. Water-soluble compounds are, particularly, the alkali metal salts and ammonium salts, of alginic acid. Conversion into an insoluble derivative can be efiected by solutions containing earth alkali or heavy metal salts. We may name the salts, e.g. of calcium, barium, strontium, zinc, copper, aluminum, cadmium, cobalt, chromium, nickel, and manganese. It is advantageous to use hygroscopic salts such as calcium chloride. If non-hygroscopic salts are used, it is advisable for the production of a swollen alginate layer, to add to the alginate solution such hygroscopic substances as glycerol, glycol, and the like. pregnating or coating layers into insoluble derivatives of alginic acid by subsequent treatment with dissolved or gaseous acids. Another way to proceed is to impregnate the paper or paper-like material first with the solution of a precipitating agent, such as calcium chloride, and thereafter to spray the material so treated with a watersoluble alginate solution. Finally, it is also possible to treat the paper with a solution containing derivatives of alginic acid, nitrogen-containing compounds, which form soluble complex compounds, such as ammonia, aliphatic amines, and such metal salts which are soluble in the complex forming compound and which will yield insoluble metal alginates with alginic acids and its'deriva Furthermore, it is possible to convert the imfives In h ve see the om lex-Mains. seawee is removed, e.g. by use" of heat To the alginate solution may be added besides the already mentioned hygroscopic substances, such compounds which will promotelespecially the plasticity and elasticity, such as starch, of any desired state of degradation, so-called soluble starch, dextrin, water-soluble cellulose ether, vegetable gum, tragacanth, degradation prodnets of proteins and the like, and pigments, if desired. 7 In order to reduce the effect of undesired heat radia tion and to bring about a more rapid cooling, metal powders may be added to the alginate solution, such as aluminum or copper, which act bygiving oif heat by radiation.

A particular use of the process according to the invention which is of economical importance, is the meme f acture of paper bags. For this purpose, strong paper may be coated on one side with a water impermeable layer such as polyethylene. This can be efiected for instance by treatment with a suitable dispersion or solualginate is obtained at the inner paper surface. After th'e'excess 'calcium'chlorid solution has drainedoff,tlie

bag may be filled with ,a liquid bituminous mass melted Example 2 A cardboard drum of about 10 liters capacity, coated on the outside with impermeable polyvinylidene (thickof layer 30 g./sq. m., water permeability 1 g./sq. m.

, in 2 4 hours) is coated on the inside with swollen calcium tion, but preferably by applying a foil. When the latter method of operation is used, hot-sealing brings about ago'od and secure joining between the paper and the impermeable layer. Another way of proceeding in order 2 to obtain material useful for further processing, is to apply upon the paper polyethylene from a suitable device, or to pour the polyethylene between two layers of paper, so that the resulting sheet will consist of two layers of paper with a polyethylene layer in between.

The materials obtained by one of the above mentioned or similar processes is then made into sacks. This is done by using one or more sheets of paper, some of which may have impermeable coatings and others without such coatings. It is necessary that the surface however,

which carrying the impermeable layer is not the inner side of the sack. The inner side is then coated by one of the methods described with a swollen but water-in soluble layer of alginate. This is done in practice by pouring onto thesacks, or rinsing them, dipping them into or spraying them successively with'alginate solution, and alkaline earth or heavy metal solutions. As already set forth, it is advantageous to proceed with wrapping materials having several sheets of paper so, that the innermost sheet of paper is provided with the impermeably layer at the side of the sack facing away from the goods. It has proved expedient to secure the presence of a swollen alginate layer to apply the alginate layer shortly before the wrappings are to be used.

A paper-bag, thus impregnated, can be filled with pitch, bitumen, or fatty acids which are solid at room temperature, or similar materials without their permeating the bag even in hot molten state. After cooling and solidifying of the mass, the paper bag can be cut open and removed without any material adhering thereto, though the wrapping is used for sticky masses such as bitumen or pitch. V v

The manner described for the impregnation of, large paper bags may be similarly applied to paper drums, or

' small paper wrappings or cardboard boxes, if desired.

The invention will now be described more fully in several examples, but it should be understood that these are given by 'way of illustration and not of limitation and that many changes in the details can be made without departing from the spirit of the invention.

Example 1 p utism ntil an cgatiuue s swollen film of calcium lowed to stand for .a few minutes.

alginate film as described in Example '1. Into this container, bituminous masses are filled having a temperature of 100 6. After cooling, the cardboardcan be. cut open and removed without sticking to the'block ofbitumen.

Example 3 A paper web of ordinary kraft paper weighing 90 g., coated on one side with a mixture of polyethyleneparafiin (thickness of layer 30 g./sq. m.,'permeability for water 2 g./sq. m. in 24 hours). is soaked or'sprayed at the other side with 20% calcium chloride solution, until the paper is evenly moistened. From the paper thus pre-treatcd, a multi-layer paper sack is -made, care being taken that the side impregnated with the calcium chloride solution will be. the inner side of the sack. Before hot bitumen isfilled into the sack, the latter is sprayed with a 1-2% sodium alginate solution and al- After excess, unprecipitated alginate solution has dripped otf, molten bitumen of 120 C. is filled in. After cooling, the paper can be torn oll and removed from block without Sticking.

the solid bitumen Example ,4

. used for making a multiple-layer paper bag with the free (uncoated) side'facing the goods to be wrapped. Before filling in a hot molten'mass of bitumetnthis bag was treated at the inside with a 1% aqueous solution of sodium alginate and after a few minutes, with a' 30% aqueous solution of calcium chloride. After cooling the contents, the paper bag could be removed without sticking to the bituminous mass.

Example 5 A sack made according to Example 1 is filled with about 500 cc; of a casting resin of epoxy-polyester base together with a conventional amine hardener. After the reaction has set in, which will take a few minutes, the contents warm up to 6080 C. The resin will be completely hardened after 5-6 hours. The wrapping can then be removed without sticking to the hardened resin.

A paper bag according to'the invention as described in the first paragraph of Example 1 is diagrammatically illustrated in the accompanying drawing, but it should again be understoodthat this illustration is given by way of example only, and that many changes in the details can be made without departing from the spirit of the present invention. i

In the above described manner, casting molds may likewise be made which are lined at the inside with a paper having an inside coating of a swollen alginate film and an outside layer which is likewise impermeable.

Casting resins may be poured so as'td'form plane articles, when, as 'a'supporting base, paper prepared according tothe invention is used. After hardening, the resin plates can easily be removed from the paper.

In the claims, the expression paper-like material is intended to include wrapping paper of any kind and cardboard or pasteboard generally used in wrapping and shipping articles, and for similar purposes.

What we claim is:

1. A wrapping material, being non-adhering to sticky masses, which consists of paper which has been coated, on the side facing said sticky masses, with a swollen water-insoluble layer of a substance selected from the group consisting of alginic acid and an alginate, and on the other side with a water-impermeable substance selected from the group consisting of polyethylene and bitumen.

2. A casting mold being non-adhering to sticky masses,

References Cited in the file of this patent UNITED STATES PATENTS 2,290,633 Cate July 21, 1942 2,513,416 Gloahec July 4, 1950 2,599,130 Rumberger et a1 June 3, 1952 2,648,487 Linda Aug. 11, 1953 2,723,923 Munters Nov. 15, 1955 2,758,100 Bailey et al. Aug. 7, 1956

Claims (1)

1. A WRAPPING MATERIAL, BEING NON-ADHERING TO STICKY MASSES, WHICH CONSISTS OF PAPER WHICH HAS BEEN COATED, ON THE SIDE FACING SAID STICKY MASSES, WITH A SWOLLEN WATER-INSOLUBLE LAYER OF A SUBSTANCE SELECTED FROM THE GROUP CONSISTING OF ALGINIC ACID AND AN ALIGNATE, AND ON THE OTHER SIDE WITH A WATER-IMPERMEABLE SUBSTANCE SELECTED FROM THE GROUP CONSISTING OF POLYETHYLENE AND BITUMEN.

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