Volume 14, Number 6
Oct 1990

Lamination in Spain

Reprinted with permission from the Bulletin of the International Council on Archives, CCR/CRA no. 2 (11)84/85), p. 29-32.

Mechanical lamination in Spain begins in 1970, exactly in the month of September, when one of the three laminators which was purchased by Spain from the North American Company, Arbee, was set to work.

This first machine had been bought by the "Instituto de Conservación y Restauración de Obras de Arte, Arqueología y Etnología" (created in 1962 by the "Dirección General de Bellas Artes") for the "Laboratorio de Grabados y Dibujos" which began its work in 1967.

In 1969 the "Servicio Nacional de Restauración de Libros y Documentos" under the "Dirección General de Archivos y Bibliotecas," was created. The laminator, which was assigned to this new Service, was installed in the lamination laboratory located in the building of the Historical Archives. Here, the necessary rooms were equipped to house this facility.

In 1972 and 1973 the two remaining laminators were assigned to the restoration laboratories in the National Library and in the General Administration Archives, respectively.

These last two laminators kept on working well but some years ago the first one began to have repeated problem which required its replacement.

This circumstance coincided with the start of work an the restoration laboratories of the General Archives of the Crown of Aragón in Barcelona; the General Archives of Indies in Sevilla; Archives of the Royal Chancellery in Valladolid; Archives of the Kingdom of Galicia, in La Coruña; Historical Provincial Archives in Oviedo; Archives of the Kingdom of Valencia, and the General Archives in Simancas.

Since the intention was to provide each me of the new laboratories with laminators, it was decided to design and build in Spain a prototype of laminators which could meet the national requirements. So in 1984 it was possible to work with the first laminator entirely manufactured in Madrid. This one replaced the machine of the "Servicio Nacional," the name of which Service had been changed to the present "Centro Nacional de Conservación y Microfilmación Documental y Bibliogrifica." During this sane year new laminators were manufactured and incorporated in the aforementioned laboratories. Thus, all of them were equipped with this mechanical method of restoration.

This prototype of laminator has essential improvements in mechanical and electrical aspects.

Lamination Techniques

The systems used in lamination are based on the classic "sandwich" which comprise the following:

• Two boards which act as the support unit. At the beginning, these were made up of 0.5 or 1 mm grey boards, usually employed as binding covers but, due to their short durability, were soon replaced by a special board of 1 an used for gaskets in engines. Its special mechanical resistance (nondeformation by heat) makes possible its continued use for many years.
• Two sheets of teflon glass cloth, 0.15 mm thick. Their nonsticking capability prevents the thermoplastic material used in lamination from sticking to the board and, thus, the inner sandwich is isolated. Teflon is a tetrafluoroethylene resin (fluorinated hydrocarbon) which resists high temperatures and strong pressure without producing any deformation or alteration in its mechanical characteristics.

Papers for Reinforcement

Tissue papers [are used] for eliminating the gloss produced by the adhesive film. It also acts as a strengthening element although its consistence is not great.

When it is applied on both sides of the document it is placed in such a way that the prevailing direction of its fibers is perpendicular to the direction of the document's fibers in order to balance whatever tensions may arise.

The kind of tissue usually employed is called Kuranai, a natural fiber compound, neutral pH and grammage of 9. Tissue of "Manila hemp" of 12 g/m², and tissue of synthetic fibers--polyester or nylon--of 10 g/m² are used for specific cases which require more reinforcement.

Paper for Inserts

Except for exceptional cases in which a kind of paper with specific characteristics of grammage or color is required, the papers used for repairing the missing areas in the document which is going to be laminated are: Arakaji, cream-colored, grammage of 33; Kozu, light cream-colored, grammage of 34 and Udagami white-colored laid paper and a grammage of 50.

These three papers, as well as the Kuranai, are made up from oriental bushes which, when analyzed with the Herzberg Stain, show the characteristic violet-colored tonality which identifies the chemical pulps. In any case, their pH is neutral and [they] show good permanence and durability in the aging tests to which they have been subjected in order to see if they can be used.

Thermoplastic Materials Used

Thermoplastic adhesive. In the beginning and following the instructions of the manufacturer of the machine imported from USA, a cellulose acetate film was used as thermoplastic adhesive. However, after two years this adhesive was replaced by polyethylene which, since then, has been continuously used.

The reason for this change was the knowledge that this new thermoadhesive was being used with success in different European restoration centers and laboratories with proof that its results were more satisfactory. Also, the acetate film required expensive importation while it was easier to purchase the polyethylene manufactured locally.

This decision was ratified when a survey on the adhesives generally used in mechanical lamination was carried out. The tested adhesives and the conclusions were the following. [All figures for temperature and duration are approximate.]

Cellulose acetate

Characteristics: transparent film, 0.025 mm thickApplication: at 160°C for 25 sec.

Reversibility: acetoneRemarks:

• occasional rigidity of documentshows a superficial plastified aspect that is more apparent than with other films
• after artificial aging it shows low folding endurance - highly brittle
• it is possible that, when aging, it may free acetic acid.

Polyamide

Characteristics: non-woven textile, 0.12 mm thick, white

Application: at 70°C for 25 sec

Reversibility: ethanol

Remarks:

• its filament structure causes a porous lamination. That is, it does not reach the grade of waterproof film. This circumstance can be suitable in those cases where the document's fragility requires lamination before neutralization.
• it shows high yellowing after aging. This causes the texture of the weave of the polyamide to be visible on the document surface and its transparency causes a distorting effect.

Polyethylene

Characteristics: transparent film, 0.025 mm thick.Gauge of 1000. Grammage of 18-20

Application: at 120°C for 25 sec.

Reversibility: decahydronaphthalene of [i.e., or]

perchloroethylene at 70°C

Remarks:

• polyethylene of low density with stabilizer agents (Irganox 1010 or Irgastab 2002) must be used. Otherwise, it shows less permanence and durability. The aging tests have proved its excellent behavior when it has these agents. It has a good waterproof capacity.

Other variants of thermoplastic materials, commercialized or not, require an adhesive previously applied to the tissue [heat-set tissue]. In this way, the tissue has on one or both sides a slight layer of this adhesive. Its thermoplastic capacity will permit its use as a reinforcing element in the laminator following the usual process.

The adhesives preferred [for heat-set tissue] are the following acrylic resins:

Paraloid and Plexigum

Characteristics: granular solid, glassy white

Solvents: organic solvents (preferably perchloroethylene, toluene, acetone, amyl acetate) Application: once the impregnation layer is formed it fuses at 70°C

Remarks: It is highly reversible in the aforementioned solvents. Its consolidation power is in relation to the thickness of the impregnation layer. It is quite -permeable to dirt, gases and humidity.

Primal and Plextol

Characteristics: aqueous dispersion, a milky appearanceThe rest of the characteristics are similar to paraloid and plexigum.

Lamination Criteria

Since lamination causes a change in the document's aspect, giving it a plasticized appearance, nullifying the characteristic touch of paper and increasing the thickness of the sheet, and sometimes, having reversibility problem, it is accepted that this restoration technique cannot be used in an unconditional way.

However, there is no other remedy but to insist on the affirmation that it is the only suitable solution for recovering the functional character of the documents in paper which, due to chemical (corrosive action of metalloacid inks or the acidity of paper) and biological reasons (basically due to microbiological or simply mechanical degradation, due to multiplicity of cuts, tearings or missing areas) indicate a conservation condition which makes its use impossible because of fragility or brittleness. Handling would cause their destruction.

In these cases it is unquestionable that lamination prevails over other methods because we think that the principal aim of the restoration methods is to maintain the physical integrity of the document and to restore its lost functional character even at the cost, in special cases, of bartering away certain aspects complementary to the character of the document.

Those documents which have extensive missing areas and which need reintegration are put in the Vinyector leafcasting machine. There, the missing areas will be filled with the required inserts. Lamination follows. This process is quick and an incalculable amount of time is saved in mending tears, holes and missing areas.

These inserts--either manual or mechanical--are always applied in order to give not only a high consistence to the sheet of paper but also to obtain an esthetic whole.