IT202300004098A1 - METHOD FOR PRODUCING STRETCHABLE PAPER WITH ELASTIC RETURN. - Google Patents

Description

DESCRIPTION

of the invention entitled:

?Method for producing stretchable paper with elastic return?

The present invention relates to a method for producing elastically rebound stretchable paper.

There are various systems known to produce stretchable papers, in the machine direction and/or transversely. The papers produced show very high elongations but once the elongation caused by a stress/extension/plastic deformation of such papers is over there is no elastic return.

These systems act mechanically on paper webs at a dryness level between 40% and 85% (EP 3024977) but also 98% (crepe paper). Some of them occur directly during the production process in a paper machine, others at the desired dryness level after rewetting, others still directly downstream (crepe paper). All these systems are part of the known art.

While in the field of use, for example, of said stretch papers for three-dimensional deformations (e.g. food trays, etc.), such a plastic deformation without elastic return is appreciable because the object obtained maintains its shape, there are other possibilities for the use of paper materials as a substitute for plastic in which an elastic return would be useful, for example all the fields in which goods/products are wrapped and/or grouped with stretch paper. In this case, once the extensibility of the paper is exhausted there is the risk that the packaging becomes loose and no longer groups said products firmly.

The aim of the present invention is to produce stretchable papers with appreciable springback as an economical and sustainable alternative to purely plastic materials.

This aim and others which will result from the following description are achieved according to the invention with a method for producing elastically extendable papers as defined in claim 1.

The present invention is further clarified below in its general formulation and in some examples of practical implementation reported for purely illustrative and non-limiting purposes.

From a general point of view, the method according to the invention to obtain stretchable paper involves adding elastomeric macromolecules to the paper capable of giving the paper tape elastic characteristics, which allow it to have an elastic return of at least 5% in the longitudinal direction after the paper tape has been stretched and elongated.

This addition can be carried out at any stage of the process of producing the stretchable paper tape and in particular on the mixture from which the paper tape will then be obtained, or on the paper tape already obtained but before it has been made stretchable, in this case by carrying out a wetting treatment with water added with elastomeric macromolecules, or on the stretchable paper tape already produced, in this case with an impregnation system such as size press or with a coating machine.

Regardless of the particular way in which the elastomeric macromolecules are introduced into the stretchable paper tape, it will have an elastic return after being stretched of at least 5% in the longitudinal direction.

The following examples will further clarify the invention.

Example 1:

In the pulper of a paper mill, a product based on ESBR (emulsion polymerized styrene-butadiene rubber) is introduced together with the fiber mix. This mix then follows the papermaking process in which during the various phases of water removal it binds to the fibers forming the paper. This papermaking process includes a so-called Clupak station at a dryness level between 65% and 68%. The result is a paper that can be stretched between 6% and 8% both in the longitudinal and transversal directions. Its elastic return after being pulled is from 3% to 6% based on the percentage of XSBR in the emulsion (from 10% to 50% of dry product).

Example 2:

Also in the pulper of a paper mill, extensible polyurethane fibres are introduced in suspension together with the fibre mix. This mix then follows the papermaking process in which during the various phases of water removal it binds to the fibres forming the paper. This papermaking process includes a so-called Clupak station at a dryness level between 65% and 68%. The result is a paper that can be stretched between 6% and 8% both in the longitudinal and transversal directions. Its elastic return after being pulled is from 3% to 6% based on the percentage of XSBR in the emulsion (from 10% to 50% of dry product).

Example 3:

During another process for producing stretchable paper in a continuous paper machine in which a rigid cylinder meets a pressure element that travels at a reduced speed compared to the rigid cylinder, XSBR (synthetic latex) is introduced upstream via a system of wetting rollers. This product impregnates the paper web which then undergoes the stretching treatment and is then dried. The result is a paper that can be stretched by 8% transversally and 15% longitudinally. Its elastic return after being pulled is from 3% to 6% based on the percentage of XSBR in the emulsion (from 10% to 50% of dry product).

Example 4:

The mechanism described in example 3 is integrated here into an off-machine paper system in which a dry starting paper is rewetted to a dryness level of between 60% and 85% and preferably between 65% and 75% and in which here too a rigid cylinder meets a pressure element that travels at a reduced speed compared to the rigid cylinder. The water for rewetting upstream of the stretch treatment contains a product based on ESBR (emulsion polymerized styrene-butadiene rubber) and is applied through wetting rollers or, alternatively, with a coating machine. The drying of the paper takes place downstream of the stretch treatment and the paper thus obtained has a transverse stretch of 10% and a longitudinal stretch of 20%. Its elastic recovery after being pulled is ? from 3% to 6% based on the percentage of XSBR in the emulsion (from 10% to 50% of dry product).

Example 5:

A stretchable paper obtained with one or other of the systems described, once dried, is treated with an impregnation system of the size press type or, alternatively, with a coating machine. The impregnating liquid contains a natural resin such as gum arabic in emulsion. A paper treated in this way has an extensibility of 12% in the transverse direction and 22% in the longitudinal direction. Its elastic return after being pulled is from 3% to 6% based on the percentage of XSBR in the emulsion (from 10% to 50% of dry product).

Example 6:

A crepe paper, either after the third press in a paper production process, or dry at the end of the cycle, is treated by spraying with a polyurethane-based product (such as ARRISTAN CPU from the CHT company).

A paper thus obtained has a 50% stretchability in the machine direction. Its elastic return after being pulled is from 3% to 6% based on the percentage of NBR (synthetic latex of the emulsion (from 10% to 50% of dry product).

The types of paper are: from virgin long fiber, short fiber, recycled fiber and their mixtures, from bagasse fibers, grass, cotton, hemp and always their mixtures.

The products to be applied in solution or emulsion to the paper are:

- synthetic rubbers (e.g. ESBR, SSBR, BR, NBR), natural rubbers (e.g. gum arabic)

- synthetic (e.g. SBR, XSBR, NBR) or natural (e.g. naturally derived) latexes

- polyurethane aqueous dispersions

- synthetic and natural rubber fibres

- polyurethane base fibres, polyester, Lycra etc.

- basic synthetic rubber fibres.

The ways of applying the above products are: in solutions, in emulsion, in gel form, in the form of molten resin depending on the position during the manufacturing of the stretch paper, directly on the single sheet of paper but also between two layers.

It is understood that any surface treatments of the fibres for their adhesion to the cellulose fibres are part of the prior art.

The introduction of elasticity agents has also shown both an increased resistance to breakage in the treated papers, as well as a waterproofing effect.

Claims (7)

1. Method for producing papers that can be stretched by at least 5% in the longitudinal direction with elastic return after the paper has been stretched, characterised by introducing into the paper web before, during or after the treatment to make it stretchable at least one additive containing elastomeric macromolecules. 2. Method according to claim 1, characterized in that the additive containing the elastomeric macromolecules is introduced before making the papers stretchable. 3. Method according to claim 1, characterized in that the additive containing the elastomeric macromolecules is introduced during the operation to make the papers stretchable. 4. Method according to claim 1, characterized in that the additive containing the elastomeric macromolecules is introduced after the operation to make the papers stretchable. 5. Method according to claims 1 to 4, characterized in that the additive containing the elastomeric macromolecules is selected from the group of rubbers. 6. Method according to claims 1 to 4, characterized in that the additive containing the elastomeric macromolecules is selected from the group of latexes. 7. Method according to claims 1 to 4, characterized in that the additive containing the elastomeric macromolecules is selected from the group of polyurethanes.