AT THE E N T E R P R I S E S AND I N S T I T U T E S

STRUCTURE AND PROPERTIES OF THE GUMMED PAPER FOg

REMOVABLE FIRED DECALS

A. I. Golubev and I. P. Tuzova

UDC 666.1.058.4:666.483

Gummed paper is a component part of commerical decals and is intended to fulfill certain technological functions at the preparation stage of the decal itself and in the decoration of the article. The current idea that these functions are completed at the operation when the removable decal is stripped off does not correspond to what actually happens. The results we obtained while trying to elucidate the reasons for the emergence of the massive rejection of glassware decorated by removable decals show that the gummed paper is the main factor which causes the sloughing off of individual elements of the pattern and in several cases complete burning off of the pattern.

A study of the structure of the gummed papaer and the process kinetics at individual stages in the decoration where there is an active effect arising from the composition of its components made it possible to evaluate, from the standpoint of contemporary scientific ideas, the essence of the phenomena and to discover the factors which have a decisive effect on the quality of the glassware decoration involving removable fired decals.

The structure of the gummed paper was studied using the following method.* To prepare a cross section of the gummed paper, a special ring was made in which we inserted a plug cut along the diameter to hold the specimen. The specimen of paper in the form of a rectangle measuring i0 x 4 mm was placed in this cut. The plug was secured in the ring in such a way that the upper edge of the plug plus specimen produced 2-3 mm above the surface of the ring and the cut in the plug was on the same line as the cut on the ring. The part of the plug that protrudes was cut with a fine-pointed knife (Fig. i). Thus a level slice parallel to the plane of the ring was obtained.

The gummed paper is natural paper and the co~ting is a layer of starch and dextrin. Dextrin is a product of the partial hydrolysis of starch when heated in the presence of a catalyst [i]. Therefore to distinguish and contrast the layer of dextrin and starch the slice was treated with an aqueous solution of iodine. The slices of paper were studied using an ML-2 optical microscope.

In the present study we used luminophors of fluorescene and uranin which give a greenish-yellow glow in ultraviolet light (3-3 UV light filters and 4-4 SZS filters) [2]. At various magnifications we obtained colored photo images, slides of gummed paper which met the requirements of All-Union State Standard (GOST) 10015-75 and a standard gummed paper (high-quality pattern). The color slides clearly show the colored gummed layer and the profile of the surface (Fig. 2).

The coating of the standard paper has a smooth surface and uniform thickness varying between 35 and 43 Hm while for the paper produced in accordance with GOST 10015-75 the surface is rough with a nonuniform thickness of the gummed layer (0-9 ~m).

An analysis of the profile of a slice of gummed paper suggests the following mechanism for the degrading effect on the quality of the pattern of poor quality paper.

A strongly expressed surface roughness of the gummed layer does not provide continuous contact between the surface of the decal pattern and the glass. The presence of individual regions not attached by the dextrin gummed interlayer can lead to deformation and subsequent destruction of the printing-pigment layer. These microcavities also act as traps for water vapor and gaseous materials which are liberated as a result of the thermal breakdown of the

*V. I. Suvarov and V. Yu. Linno took part in the work.

Kalininsk Polytechnic Institute. Kalininsk Glass Plant. Translated from Steklo i Keramika, No. 5, pp. 29-30, May, 1986.

0361-7610/86/0506-0221512.50 �9 1987 Plenum Publishing Corporation 221

2 3' 4-, I . ~ . . .

Fig. i. Ring for the preparation of the slices of paper: i) ring; 2) specimen of paper; 3) plug; 4) knife.

Fig. 2. Slices of the standard paper (upper row) and the paper produced to State Standard 10015-75 (lower row) at a magnifica- tion of 234 x (a) and 324 x (b).

organic components of the decal. The excess pressure acting in these traps helps the pig- ment layer to become detached from the surface of the glass and to form craters which destroy the continuity of the painted pattern.

Other places where excess pressure may arise are the regions of the surface of the materials applied one to the other (decal and glass) where there is no dextrin gummed layer (Fig. 2, lower row shows such places). The presence on the surface of the gummed paper of places (even of microscopic dimensions) which are free of the adhesive dextrin film allows the free access of the starch-dextrin solution to the pigmenting layers of the decal which also is a cause of the development of additional foci of excess pressure under the firing conditions.

Finally, regions of the gummed surface where an excess amount of dextrin is concentrated in the form of thicker patches may also be a potentially possible site of the destruction of the integrity of the pattern (Fig. 2, lower row, these places are clearly visible). As a result of swelling in these places, a larger amount of water is accumulated than on the remaining contact surface. Therefore, thicker places are also foci for excess internal pres- sure while the processes of water-vapor and gas liberation in these regions are protracted in time (in view of the excess of water and dextrin) and the firing regime of the decorated ware is not maintained.

Using the information obtained we now look at individual components of the gummed paper, their purpose, and the effect they have on some of the physicochemical processes in the dec- oration technology.

The paper base fulfills the role of a substrate in the process of preparing the gummed paper and then is a carrier of the functional starch-dextrin interlayer. At the stage where the decal is wetted in water it is a porous, hydrophilic medium through which the water is transferred to the functional layers of the gummed paper. Thus it is demanded from the paper

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base that it have mechanical strength and a capacity to transmit water through itself at a specified rate to the next layers of the adhesive. In order to make the microrelief of the starch layer smooth and to reduce the consumption of starch, the working surface of the paper should be smooth. The remaining technical characteristics of the paper are not worthy of notice.

The starch layer (adhesive) acts as a constructional layer and is meant to fill the micro- nonuniformities on the surface of the paper base and to create a level substrate for the application of the next layer, the dextrin. Moreover, the starch layer provides for the movement of droDlike water to the next dextrin layer. The nature of the starch, its ease of application and consumption are not controlled.

The external dextrin layer acting as the applicator of the pattern through the stencil is the substrate. It must be even, smooth, able to form the surface of the pattern commensurate with the smoothness of the glass, and capable of staying in contact with the glass with the least possible gap. According to the data from the microscope studies, a stable quality of decoration is achieved when the layer of starch+dextrin is 35-40 pm.

Thus for the production of glass hollow-ware decorated by a contemporary high-produc- tivity method - a multicolored, fired, removable decal - it is necessary to make a high-quality gummed paper.

i.

2.

LITERATURE CITED

D. M. Frashtat, Reagents and Preparations for Microscope: a Handbook Khimiya, Moscow (1980). Luminescence Analysis [in Russian], Fizmatgiz, Leningrad (1961).

[in Russian],

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