SE522783C2 - Wet tissue paper - Google Patents

Abstract

A strong and soft tissue paper having a bulk between 2 and 8 cm<3>/g, containing a wet strength agent in the form of a nitrogen-containing polymer having hydrophobic side-chain substituents. The tissue paper before converting has a relative wet strength value (RWS) of at least 45%.

Description

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The hydrophobic side chain substituents preferably comprise a hydrophobic chain having 6-40 carbon atoms.

The tissue paper according to the invention contains a proportion of wet strength agent from 1 to 4% by weight, preferably between 1.2 and 3% by weight.

In preferred embodiments of the invention, the tissue paper prior to conversion has a relative wet strength value (RWS) of at least 43%, preferably at least 45% and most preferably at least 50%. Preferably, the relative wet strength value (RWS) is up to 60%.

The tissue paper may further contain a proportion of a dry strength agent. Examples of preferred dry strength agents are carboxyalkyl polysaccharide, for example carboxyalkyl cellulose.

The tissue paper should preferably have a dry strength index of at least 5 Nm / g and at most 10 Nm / g.

A tissue paper with the above characteristics is wet strong and soft and also has sufficient dry strength to be handled in conversion processes.

Description of the invention Today, the only way to create a high wet strength is one or more of the following methods - add as much wet strength agent as possible; -use a high proportion of grinding energy; -add dry strength chemicals.

This strategy leads to high wet strength and high dry strength, which means that dry strength is only a means of increasing wet strength. The dry strength level in tissue paper is therefore usually higher than necessary, which leads to stiff and rough paper.

It has been found according to the invention that soft and strong tissue papers with a basis weight of 10 and 50 grnz, a bulk between 2 and 8 cma / g and a wet strength index of at least 1 Nm / g, can be obtained by that the tissue paper contains a wet strength agent in the form of a nitrogen-containing polymer having hydrophobic side chain substituents and by balancing the paper wet strength index and dry strength index to obtain a relative wet strength index (RWS) of at least 45%, preferably at least 47% and more preferably at least 50%. The RWS value refers to the value for conversion processes, such as embossing, gluing, lamination, etc., as these can affect the properties of the paper.

Wet strength agents which increase the wet strength of tissue paper without increasing the dry strength are wet strength agents which comprise a cationic nitrogen-containing polymer having hydrophobic side chain substituents and a derivative of a crosslinker. The hydrophobic side chain substituents may be saturated or unsaturated.

The cationic nitrogen-containing polymer has hydrophobic side chain substituents and derivatives of a crosslinker attached to the nitrogen atom of the polymer. The hydrophobic side chain substituents may be saturated or unsaturated. Examples of leather-containing nitrogen-containing polymers include well-known available commercial products, which may be prepared as described above or by conventional methods known in the art. Examples of suitable nitrogen-containing polymers include polyaminoamides, alkyl polyamines, polyimines and polyvinylamines. An example of a preferred crosslinker is epichlorohydrin.

Hydrophobic side chain substituents are attached to the nitrogen atom of the nitrogen-containing polymer. The term hydrophobic side chain substituents as used herein includes hydrophobic groups containing, for example, hydrophobic or branched hydrocarbon groups which may be linked, for example via a heteroatom by a covalent bond, to a nitrogen atom of the nitrogen-containing polymer. Hydrophobic groups may also include cyclic chains including cyclic hydrocarbons. Combinations of linear, branched and cyclic hydrocarbons are also included in the concept of hydrophobic groups.

The hydrophobic group of the hydrophobic side chain may contain up to 40 carbon atoms, preferably 6-40 carbon atoms, and most preferably 8-40 carbon atoms.

Such wet strength agents are described in detail in International Patent Application No.

PCT / SEOO / 02233, the contents of which are incorporated herein by reference. 10 15 20 25 30 i i 'In--. 1: z: '.. ~ - IH n. |. I on .: '4 ::: | n ,,. °' :: no.

Addition to wet strength tissue tissue paper in the form of the nitrogen-containing polymers having hydrophobic side chain substituents causes an increase in the wet strength index of the paper, due to the formation of covalent bonds between the cellulose molecules and the nitrogen-containing polymers. This is the same mechanism as in conventional wet strength agents. The addition of conventional wet strength agents will also increase the amount of hydrogen bonding sites resulting in increased dry strength. However, due to the presence of the hydrophobic side chain substituents in the wet strength agents used in the present invention, the hydrogen bonding sites will decrease.

Since the dry strength of paper is highly dependent on the number of hydrogen bonds, a decrease in the hydrogen bonds will also result in a decrease in the dry strength of the paper.

Thus, an increase in the wet strength index of the tissue paper is obtained without increasing the dry strength index, by adding the wet strength agents in the form of the nitrogen-containing polymers having hydrophobic side chain substituents. In fact, one can even obtain a lowering of the dry strength index.

Evaluation of the dry strength of tissue paper was performed according to the standard method SCAN P 44:81. The wet strength was tested according to SCAN P 58:86. The tensile strength was presented as index values or geometric mean values of machine and transverse direction according to: JMDXCD / basis weight Nim / g.

The tissue paper should preferably contain the wet strength agent in an amount of from 1 to 4% by weight, preferably from 1.2 to 3% by weight. These values refer to the amount of wet strength agent that adheres to the fibers and is measured according to the so-called total nitrogen method. This method is based on fl ash combustion and is called Dumas Total Nitrogen Analysis. The measuring instrument used is Carlo Erba Instrument NA 1500 supplied by CE Termo Quest. A manual is provided with the instrument.

The wet strength agent is preferably in the form of an aqueous dispersion and may be added to an aqueous cellulosic suspension containing cellulosic pulp fibers.

The wet strength agent can also be added to the prepared paper to give a surface treatment of the paper.

The tissue paper should preferably have a wet strength index of at least 5 Nm / g to be able to be handled in conversion processes such as rolling, unrolling, cutting, embossing, lamination, etc. Addition of a dry strength agent, such as a carboxyalkyl polysaccharide, for example carboxyalkyl cellulose, in particular CMC), may be necessary to obtain a sufficient dry strength of tissue paper. These dry strength agents are anionic and will contribute to more cationic wet strength agent being adsorbed to the fibers. The dry strength index should preferably not be more than 10 Nrn / g in order to keep the softness as high as possible.

Tissue paper may also contain additional additives such as plasticizers, absorption enhancers, fillers, etc.

Example Four different wet strength agents were prepared according to Example 7 in International Patent Application No. PCT / SE00 / 02233. The wet strength agents were named A, B, C and D, of which D was prepared exactly as described in Example 7 of PCT / SEO0 / 02233, while the other three were prepared as described but with the modification that varying amounts of dodecyl acrylate were used.

Test 1 Tissue paper with a basis weight of about 25 g / mz and a bulk at 2kPa of about 6-6.5 cm 3 / g was prepared on a full scale paper machine. The pulp was a mixture of 70% by weight of CTMP (kenriterromechanical pulp) and 30% by weight of sulphate softwood pulp. Varying amounts of wet strength agents A and B were added. The results obtained are presented in Table 1 below. 10 15 20 25 1522 6783 Table 1 Wet strength agent Added amount Dry strength index Wet strength index Rel. wet strength index (kg / h pulp (Nm / g) (Nm / g) RWS (%) fibers) A 7 10.2 3.4 33 A 10 10.1 4.0 40 A 15 8.7 3.8 44 A 20 7.9 4.1 52 B 7 8.4 3.6 43 B 10 8.8 3.7 42 B 15 8.3 4.0 48 B 20 9.0 4.1 46 Test 2 Tissue paper with a basis weight of about 40 g / mz and a bulk at 2kPa of about 5 cm 3 / g were prepared on a full scale paper machine. The pulp used was recycled pulp from mixed newsprint. Waste strength agent C was used in combination with a dry strength agent in the form of CMC (carboxymethylcellulose). The results obtained are presented in Table 2 below.

Table 2 Wet strength agent Added amount Added amount Dry strength index Wet strength index Rel. wet strength wet strength agent CMC (dry strength- (Nrn / g) (Nm / g) RWS (%) (kg / h medium) (kg / h mass fi brer) mass fi brer) C 16 3 12.9 4.7 33 C 18 3 13.5 4.8 31 C 25 3 - - 50 Test 3 Tissue paper with a basis weight of about 26.5 g / mz and a bulk at 2kPa of about 2.5 cm 3 / g was prepared on a full scale paper machine. The pulp used was recycled pulp from mixed newsprint. The wet strength agent D was used in combination with a dry strength agent in the form of CMC (carboxymethylcellulose). The results obtained are presented in Table 3 below. 10 522 78; Table 3 Wet strength agent Added amount Added amount Dry strength index Wet strength index Rel. wet strength wet strength agent CMC (dry strength- (Nm / g) (Nm / g) RWS (%) (kg / h medium) (kg / h mass fi brer) mass fi brer) D 20 2.3 9.3 4.2 46 D 20 3, 3 8.8 5.0 57 D 15 2 8.0 3.8 48 D 15 3 10.6 4.1 39 The tests above show that it is possible to achieve relative wet strength values (RWS) of 45% and higher by using relatively high amounts of wet strength agents containing hydrophobic side chain substituents. The wet strength agent can be advantageously combined with an anionic dry strength agent to adsorb more of the cationic wet strength agent to the fibers.

Claims (11)

10 15 20 25 30 522 7883 Patent claims Tissue paper with a bulk between 2 and 8 cm3 / g, which contains a proportion of a wet strength agent and has a wet strength index of at least 1 Nm / g, characterized in that the tissue paper contains a wet strength agent in the form of a nitrogen-containing polymer having hydrophobic side chain substituents and where the paper before conversion has a relative wet strength value (RWS) of at least 45%. Tissue paper according to Claim 1, characterized in that the nitrogen-containing polymer is a polyarnin or a polyaminoamide. Tissue paper according to claim 2, characterized in that the hydrophobic side chain substituents comprise a hydrophobic chain having 6-40 carbon atoms. Tissue paper according to one or more of the preceding claims, characterized in that it contains a wet strength agent in an amount of from 1 to 4% by weight, preferably from 1.2 to 3% by weight. Tissue paper according to one or more of the preceding claims, characterized in that it has a relative wet strength value (RWS) of at least 47%, preferably at least 50%, before conversion. Tissue paper according to one or more of the preceding claims, characterized in that it has a relative wet strength value (RWS) of up to 60% before conversion. 10 15 522 783 '9 Tissue paper according to one or more of the preceding claims, characterized in that it also contains a proportion of a dry strength agent. Tissue paper according to claim 7, characterized in that the dry strength agent is a carboxyalkyl polysaccharide. Tissue paper according to claim 8, characterized in that the carboxyalkyl polysaccharide is a carboxyalkylcellulose. Tissue paper according to one or more of the preceding claims, characterized in that it has a dry strength index of at least 5 Nm / g. Tissue paper according to Claim 10, characterized in that it has a dry strength index of at most 10 Nm / g.