NO811169L - PROCEDURE FOR MANUFACTURING A FORMED ARTICLE - Google Patents

Description

This invention relates to fibrous materials and specially shaped articles containing amino/formaldehyde resin fibers.

Amino/formaldehyde resin fibers are useful as fibrous constituents in shaped articles, especially sheet-like articles, such as paper, where they are commonly used mixed with cellulose fibers.

Paper made from only amino/formaldehyde resin fibers tends to have little or no strength due to

that the fibers usually have little or no self-adhesion. When mixed with cellulose fibers, the cellulose fibers add strength to the paper, but in many cases it would be desirable

to improve firmness even more.

One way to improve the strength is to use partially cured (degree of cure 50 - 90%) amino/formaldehyde resin fibers. According to European Patent Document 14026, paper is formed from partially cured amino/formaldehyde resin fibers which are prepared using only mild curing conditions, i.e. weak curing catalysts, low curing temperatures and/or short curing times. Partially cured amino/formaldehyde resin fibers can also be prepared as described in US Patent 4,202,959 by carrying out the reaction of the amino compound with the formaldehyde in the presence of sources of certain inorganic oxyacid radicals, e.g. sulfite radicals. Partially cured amino/formaldehyde resin fibers can also be prepared as described in US Patent 4,172,057 by carrying out the reaction of the amino compound with the formaldehyde in the presence of certain carbohydrates.

The degree of cure of amino/formaldehyde resin fibers is measured by

to soak an accurately measured sample (approx. 5g) of dry fibers in 200 ml of water for 2 hours at 50°C. The undissolved fibers are recovered by filtration, dried at 100°C in air for 2 hours, and then weighed again. The degree of hardening is the ratio between the weight of the extracted fibers and the original fiber weight, and is expressed here as a percentage.

Although amino/formaldehyde resin fibers which have only been partially cured may exhibit some self-adhesion and thus may be used as the sole fibrous component in paper, they suffer from the disadvantage that some of the fibers may be lost during the conventional tional wet-laying papermaking due to the partial water-solubility of the partially cured resin, and also that free formaldehyde can develop during paper production and thus pose a health hazard.

It has now been found, under certain conditions, that objects, e.g. improved strength paper containing amino/formaldehyde resin fibers with a high degree of cure can be produced.

In the present invention, the manufacturing conditions are such as to cause welding of the amino/formaldehyde resin fibers to each other and/or to other fibrous materials present, at least in some places where the fibers come into contact with each other. Such welding is referred to here as inter-fiber bonding. Inter-fiber bonding can be observed...using a microscope. If a sample of the item, e.g. paper, is observed using a magnification of X100 or more, welds can be seen between at least some of the fibers. It will be understood that in order to achieve useful improvements in strength, it is not necessary for all the fibers to be welded to other fibers. However, the degree of inter-fiber bonding should preferably be such that less than 50 percent by weight of the amino/formaldehyde resin fibers can be removed from the sample as individual fibers without any other fibers adhering to them, when the sample is examined with a fine probe.

It is proposed in British patent document 1 574 344 to form paper from a mixture of cellulose pulp and urea/formaldehyde (UF) resin fragments, in particular fragments of a UF foam, which has been partially cured by acidification at a temperature below 60°C. After forming the cellulose pulp/UF fragments into sheet form, the latter is heated at above 80°C to effect further curing of the UF resin. It is stated that this method produces a continuous chemically bonded network in the paper.

Inter-fiber bonded articles formed in accordance with the present invention differ from the products of British Patent 1,574,344 in various ways.

In the method according to British patent no. 574 344, it is essential to use a cellulose mass, and it is postulated that a chemical bond is formed between the UF fragments and the cellulose. It is suggested that paper formed from non-cellulosic fibers and fragments has negligible strength. In contrast, inter-fiber-bonded objects with considerable strength can be formed with the present invention by using amino/formaldehyde resin fibers alone or in a mixture with non-cellulose fiber materials.

Furthermore, it is stated in British patent specification 1 574 344 that incorporation of the UF fragments causes little or no increase in the bulk of the paper. The bulk is indicated to increase by less than 0.1 cm 3 /g for every 10% by weight of incorporated UF fragments. In contrast, inter-fiber bonded articles containing amino/formaldehyde resin fibers and cellulosic fibers exhibit a significant bulk increase, the bulk increasing by at least about 0.15 cm 3 /g for each incorporation of 10% by weight of amino/formaldehyde resin fibers. The increase in bulk usually becomes more prominent as the degree of grinding of the cellulose pulp increases.

In contrast to the procedure in the GB patent document

1,574,344, the amino/formaldehyde resin of the present invention is in the form of fibers which have not been heat-set to a high degree before the shaped article is produced therefrom.

According to the present invention is provided

a method for producing a shaped object, which comprises to

(i) form a solution of an amino/formaldehyde resin and a curing catalyst for this into fibers, (ii) cure said fibers by heating them at a temperature above 100°C until the degree of cure is above 93%, (iii) forming an aqueous mass by dispersing fibrous material in water, the fibrous material containing at least 5% by weight of said cured amino/formaldehyde resin fibers,

(iv) form a shaped article from said mass, and

(v) promoting inter-fiber bonding by heating said shaped article at a sufficiently high temperature above 80°C;

for a sufficient time, and in the presence of a sufficient quantity of water in excess of 10% by weight of the total weight of fibrous material present, by the application of pressure, before or during

said heating, at least sufficient to cause contact between adjacent fibers, to cause at least some of the amino/formaldehyde resin fibers to weld to each other and/or to other fibrous material present,

at least at some of the points where the fibers touch each other.

Although applicants do not wish to be bound by the following theory, it is contemplated that, by the method of the present invention, at least some of the highly cured amino/formaldehyde resin fibers are slightly hydrolyzed at their surfaces, and that they thus become somewhat sticky under the prevailing temperature and humidity conditions. When such fibres" which have become sticky come into contact with other fibres, e.g.

■at points where the fibers cross each other (whether the other fibers are other amino/formaldehyde resin fibers which have been made tacky or not)', melting or welding takes place at the points of contact. However, since no stickiness has been demonstrated for the fibers in the final product, it is thought that dehydration and recondensation of the sticky fiber surfaces takes place when heating and drying continue.

The occurrence of inter-fiber bonding in water-sensitive items, e.g. paper containing some cellulose fibers can also be assessed by measuring the wet strength of the sample. If inter-fiber bonding has taken place, the wet strength of the sample will increase. It is preferred that the wet strength is increased by at least 25% compared to a similar sample in which no inter-fiber bonding occurs. The wet strength of a sample in the form of paper can be measured by Tappi Standard Method T456.

It will be understood that when there is a binder present in the object, the wet strength measurement and examination will not show the presence of inter-fiber bonding, but such inter-fiber bonding can be detected by microscopy.

When the object contains few or no cellulose fibers, there may be little or no difference between the wet and dry strength of the object.

In the method according to the invention, in order to develop inter-fibre bonding, the shaped object is exposed to the action of water at an elevated temperature.

The fibrous material can be formed into the desired shape

and then moistened and exposed to the elevated temperature, or the shaped article may be formed from an aqueous slurry of the fibrous materials and exposed to the elevated temperature as part of the drying process used to preferably water. In the production of paper-like sheet objects, the paper can thus be formed by a conventional wet-laying process and then subjected to inter-fiber bonding conditions in the drying steps of paper production.

The conditions required to develop inter-fiber bonding vary with the degree of cure of the amino/formaldehyde resin fibers. Thus, when the degree of cure increases to above 93 percent by weight, the minimum amount of water in the shaped article required to achieve inter-fiber bonding increases. As the temperature rises, the required drying time decreases.

The temperature should be at least 80°C and preferably in the range 90 to 180°C. Application of pressure before, or preferably during, the heating step promotes inter-fiber bonding. The pressure can vary from just sufficient to ensure good contact between adjacent fibres, typically 0.1 kg/cm<2> to 50 kg/cm 2 or more depending on the water content and drying conditions. As the applied pressure increases, less water is required. Although the application of pressure is not always necessary, its application enables inter-fiber bonding to be achieved in some borderline cases where, in the absence of applied pressure, no inter-fiber bonding is achieved.

The required time can vary from approx. 30 seconds to 10 minutes or more, and it will be understood that longer times than necessary to achieve inter-fiber bonding may be used.

The minimum water content required to achieve inter-fibre bonding varies from approx. 10% by weight of the fibrous material (at low degree of hardening, high temperature and high pressure) to over 30% (at low temperature and low pressure and high degree of hardening)-. It will again be understood that more water can be used than the minimum required to achieve inter-fiber bonding. Preferably, at least 200 percent by weight of water is used, based on the dry weight of the fibrous material.

Simple experiments will produce conditions where resulting inter-fiber bonding can be determined.

If a pressing step is used, this can be part of the forming process: the fibrous material can thus be molded into the desired shape while being exposed to the conditions of moisture and elevated temperature, or the fibrous material can be pressed into the desired shape at ambient temperature and then exposed to the conditions of humidity and excessively high temperature.

The amino/formaldehyde resin used to produce the amino/formaldehyde resin fibers is a condensate of an amino compound, preferably a polyamide such as urea or melamine, with formaldehyde. The amino compound is preferably urea, alone or mixed with up to 5% by weight of melamine. The molar ratio between the formaldehyde and amino groups is preferably between 0.6:1 and 1.5:1, and especially between 0.7:1 and 1.3:1.

The amino/formaldehyde resin fibers can be made by any suitable fiber forming technique, such as wet or dry spinning, and are preferably made by a late trifugal spinning process, e.g. as described in US patent 4,178,336, and this gives, which is preferred, essentially linear and unbranched fibers.

The amino/formaldehyde resin fibers preferably have an average length of between 1 and 10 mm, especially between 2 and 6 mm. Preferably, substantially all of the amino/formaldehyde resin fibers have a length within the range of 1 to 10 mm.

The amino/formaldehyde resin fibers preferably have an average diameter of between 1 and 20 µm, particularly between 2 and 15 µm, and most particularly between 3 and 10 µm. Preferably, substantially all of the amino/formaldehyde resin fibers have a diameter of between 1 and 30 µm. The amino/formaldehyde resin fibers preferably have an average strength of at least 50 MNm (which corresponds approximately to 33 Nmg), especially at least 100 MNm"<2>(= 67 Nmg"<1>).

The amino/formaldehyde fibers should have a degree of cure of at least 93%, preferably 94 to 99% by weight. In the method according to the present invention, these degrees of hardening are achieved by incorporating a suitable hardening catalyst, e.g. ammonium sulfate, ammonium chloride, malic acid, dihydrogen ammonium phosphate or phosphoric, sulfuric, sulfamic or hydrochloric acid, in the resin before it is spun into fibers, and then the fibers are heated after spinning at over 100°C, especially over 120°C, in f. e.g. up to 3 hours. Generally, a shorter time is required at a higher curing temperature. While thus 3 hours at 120°C can give a hardening degree of approx. 94% by weight, only 5 minutes at 180°C may be required to give a degree of hardening of approx. 97%.

The shaped article can be made from the amino/formaldehyde resin fibers as the only fibrous component or it can be made from the amino/formaldehyde resin fibers mixed with other fibrous materials, which can be cellulosic or non-cellulosic. The amino/formaldehyde resin fibers should constitute at least 5 percent by weight of the total fibrous material in the molded article.

Particularly useful sheet materials, e.g. paper and paperboard, can be made from mixtures of amino/formaldehyde resin fibers and cellulose fibers containing 5 to 100 percent by weight, preferably 10 to 50 percent by weight, of amino/formaldehyde resin fibers. Cellulosic fibers that can be used include lignin-free fibers such as cotton linters or chemical wood pulp, e.g. paper-forming pulp formed from raw cellulose by treatment with chemical agents, such as by the well-known sulphate or sulphite processes, or lignin-containing fibres, such as mechanical, semi-chemical or thermomechanical pulp of wood. Mixtures of lignin-containing and lignin-free cellulose fibers, e.g. mixtures of mechanical and chemical pulp can be used.

The cellulose fibers can be lightly ground or well ground, i

dependence on the intended use of the shaped object.

The invention is particularly suitable for the manufacture of sheet-like products such as paper and cardboard from fibrous materials comprising amiho/formaldehyde resin fibers alone or mixed with up to 90 percent by weight, based on the total weight of fibrous material, of cellulose fibers. Such products have improved mechanical properties compared to those in which there is no inter-fiber bonding, and in particular have better wet strengths. Thus, paper with inter-fiber bonded amino/-aldehyde resin fibers has better wet strengths than 100% cellulose paper which has not been treated in any other way to promote wet strength, e.g. by including a wet-set resin binder.

As previously mentioned, in contrast to the papers described in British patent specification 1 574 344, the use of the amino-resin fibers mixed with cellulose fibers will give a significant increase in bulk. An increase in bulk is usually desirable, as this makes it possible to use less raw materials, with accompanying economic advantages, to obtain a paper of a given volume. Although the bulk of a cellulose-only paper can be increased by reducing the degree of grinding of the cellulose, this results in a reduction in paper strength. The incorporation of the amino/formaldehyde resin fibers makes it possible to increase bulk without such a large reduction in paper strength.

As previously mentioned, the inter-fiber bonded paper according to the present invention has improved wet fastness

compared to paper in which there is no inter-fiber bonding. This makes paper produced according to the invention particularly suitable for such applications as filter paper. Increased bulk is desired in such applications since porosity increases with increase in bulk.

Shaped articles produced according to the present invention from a mixture of amino/formaldehyde resin fibers and cellulose fibers, i.e. cellulose masses having a bulk of at least

where x is the weight percent of amino/formaldehyde resin fibers in the fibrous mixture, and A is the bulk of a shaped article made under similar conditions from cellulose fibers alone. The increase in bulk achieved by incorporating the amino/formaldehyde resin fibers becomes greater as the ground level of the cellulose fibers increases. When the cellulose fibers are thus slightly ground, so that a paper with a high bulk is obtained, the increase in bulk can be little more than approx. 0.015 xYoocm'9 ' but with a stronger milled cellulose pulp, especially one which gives a paper with bulk un- 3 -1

where approx. 2 cm .g when produced from cellulose fibers alone,

x 3-1

the increase in bulk is usually at least 0.02 x ygg- cm .g

Shaped articles produced according to the present invention from a mixture of cellulose fibers and admixed amino/formaldehyde resin fibers are preferably produced from fiber mixtures containing 5 to 95, preferably 10 to 50, percent by weight of amino/formaldehyde resin fibers, and correspondingly 95 to 5, especially 90 to 50 percent by weight of cellulose fibers.

It is therefore further in accordance with the present invention provided a shaped object formed from a fibrous material comprising 5 to 95 percent by weight amino/formaldehyde resin fibers with a degree of cure of at least 93%, and correspondingly 95 to 5 percent by weight cellulose fibers, where the object exhibits inter -fiber bond where at least some of the amino/formaldehyde resin fibers are welded to each other and/or to the cellulose fibers at at least some of the points where the fibers touch each other, and the object has a bulk of at least

where x is the percentage by weight of the amino/formaldehyde resin fibers i

3 -1

the fibrous material and A is the bulk, in cm .g , of a similarly shaped object, produced under the same conditions from cellulose fibers alone.

Shaped articles can also be produced according to the present invention from fibrous material containing only amino/formaldehyde resin fibers or amino/formaldehyde resin fibers mixed with non-cellulosic fibers. These mixtures may optionally also contain cellulose fibers. The non-cellulosic fibers can be synthetic organic fibers, such as polyester fibers, e.g. polyethylene terephthalate fibers; polyolefin fibers, e.g. polypropylene fibers; or polyamide fibers; or inorganic fibers such as glass or asbestos fibers.

When non-cellulosic fibers or a mixture of cellulosic and non-cellulosic fibers are used, the fibrous material contains at least 5% by weight of amino/formaldehyde resin fibers and correspondingly up to 95% by weight of non-cellulosic fibers

or mixture of cellulosic and non-cellulosic fibers. Quantity

that of non-cellulosic fibers is preferably at least 10 percent by weight of the total weight of fibers in the shaped article. The fibrous material, which is different from the amino/formaldehyde resin fibers, preferably comprises 10 to 100 weight percent of non-cellulosic fibers and correspondingly 90 to 0 weight percent of cellulose fibers.

Shaped objects, e.g. paper or other sheet-like products, made according to the present invention from amino/formaldehyde resin fibers alone or from mixtures containing non-cellulosic fibers, have a significant strength whether they also contain cellulose fibers or not.

They can thus have an explosion factor (explosion pressure measured according to the TAPPI standard process divided by the weight per unit area)

of at least 0.2 kPa m 2 g-1

It is therefore according to a further aspect of the invention provided a shaped object formed of fibrous components comprising 5 to 100 weight percent amino/formaldehyde resin fibers with a degree of cure of at least 93%, and correspondingly 0 to 95 weight percent of a fibrous material consisting of 10 to 100 percent by weight of non-cellulosic fibers and correspondingly 0 to 90 percent by weight of cellulosic fibers, where the article exhibits inter-fiber bonding whereby at least some of the amino/formaldehyde resin fibers are welded to each other and/or to the non-cellulosic fibers at at least some of the points where the fibers touch each other, and

2 -1 the shaped object has an explosive factor of at least 0.2 kPa m g

When the article contains cellulosic fibers in addition to ■ the non-cellulosic fibers, the amino/formaldehyde resin fibers may also be welded to the cellulosic fibers.

Particularly preferred fiber blends comprise 10 to 90, especially 20 to 60 weight percent amino/formaldehyde resin fibers, 10 to 90, especially 20 to 50 weight percent non-cellulosic fibers and 0 to 75, especially 10 to 50 weight percent cellulosic fibers.

The invention is illustrated with the following examples in which all percentages are expressed by weight.

EXAMPLE 1

A commercially available aqueous urea/formaldehyde resin with a U:F mole ratio of 1:2 and a solids content of 67% was diluted with water to a viscosity of 30 poise. 10%, based on the solids, of an aqueous solution containing 1.6% poly(ethylene oxide) and 6.7% ammonium sulfate was mixed continuously with the resin solution as it was fed to a spinning bowl in a centrifugal spinner. The resin was spun by the method described in US Patent 4,178,336 using a 12.7 cm diameter spinning bowl with 24 rectangular holes and rotating at 7,000 rpm. minute.

Air at a temperature of 180°C was blown into the spinning chamber "to dry the fibers, to transport them from the spinning bowl and to effect some curing. The resin was spun at a speed of 100 g.min 1, and the fibers were continuously removed from the spinner and they were further cured by heating in air at 150°C for 40 minutes.

The resulting fibers, which had an average diameter of 8.5 µm, had a degree of cure of 94.6%.

The fibers were cut to a nominal length of 3 mm and dispersed in a standard laboratory pulp pulverizer in water (consistency 1.2%) for 17 minutes.

Paper towels (100% UF resin fibers) were produced by the standard process using "British Standard Hand-sheet formers" by replacing the standard pressing step with pressing in a press heated to 110°C. Before pressing, water was sprayed on the towels, and they were determined by weighing the towels before and after pressing.

After pressing, the burst factor and wear length of the papers were determined.

Explosive factor (explosive pressure in kPa divided by the substance in gm -2) was determined according to the TAPPI standard process. The tear lengths were measured on an Instron tensile tester (table top model) using specimens that were 15 mm wide and with a measured length of 100 mm. The crosshead speed was 0.5 cm/min.

The inter-fiber bonding was assessed microscopically. Its presence is indicated in the following table with a tick.

EXAMPLE 2

Example 1 was repeated using resin fiber cured for 120 minutes at 150°C to give a degree of cure of 96.6%.

EXAMPLE- 3

Example 1 was repeated using resin fibers cured for 170 minutes at 150°C to give a degree of cure of 97.9%.

EXAMPLE. 4

Example 1 was repeated using resin fibers cured at 150°C for 330 minutes to give a degree of cure of 99.0%.

EXAMPLE 5

Example 1 was repeated using resin fibers cured for 30 minutes at 150°C, and this gave a degree of cure of 96.4%. In each case, the pressing time was 3 minutes at 110°C.

EXAMPLE 6

Example 1 was repeated using fibers cured for 30 minutes at 150°C, and this gave a degree of cure of 95.9%. In this example, the moist sheets were pressed by a pressure on

-2 about. 0.1 kg cm in varying times at different temperatures.

The papers of Examples 1 to 6 which exhibited cement-fiber bonding maintained their integrity when immersed in water and gently agitated. It did not those in which there was no inter-f iber bonding..

EXAMPLE 7

In order to demonstrate the improvements achieved with respect to wet strength in papers made from mixtures of urea/formaldehyde resin fibers and cellulose fibers of the present invention, towels were made from 80% birch sulfate pulp and 20% urea/formaldehyde resin fibers similar to those used in example 1. Some of the towels were moistened and dried under introduction conditions for inter-fiber bonding, and the wet wear length was measured.

The results are shown in the following table.

A similar towel made from birch sulphate pulp alone had a wet-wear length of 0.09 km.

EXAMPLE 8

Example 7 was repeated, but using a 50/50 mixture of the birch sulfate pulp and the urea/formaldehyde resin fibers.

EXAMPLE 9

Paper was produced on an experimental paper machine from mixtures of lightly ground bleached hardwood sulfate cellulose pulp and urea/formaldehyde resin fibers produced by the method described in example 1 and with a degree of hardening of 94.6%. The paper was dried under light pressure against cylinders heated to approx. 100°C. The drying time and moisture content were sufficient to produce inter-fibre bonding.

Paper was also produced and dried under the same conditions from a lightly milled pulp of only cellulose. The tensile strengths (wet and dry) in the transverse direction of the paper, i.e. at right angles to the machine direction, and the wet burst factor were measured, and are indicated in the table as a percentage of the corresponding properties of paper made of cellulose only.

3 -1

It will be seen that the increase in bulk is over 0.017 cm g for each percent of urea/formaldehyde fibers incorporated.

EXAMPLE 10

Example 1 was repeated using urea/formaldehyde resin fibers with an average diameter of 9 µm and degree of cure of 94.9%, mixed with glass or polyethylene terephthalate (PET) fibers and also, in some cases, with softwood sulfate - cellulose pulp.

The glass fibers had an average diameter of 20 µm while the PET fibers were 1.5 denier, drawn, unshrunk fibers that had been washed in hot water to remove all spin finish from their surfaces.

The glass, PET and urea/formaldehyde fibers were cut to provide a length distribution between 1 and 5 mm by passing the fibers twice through a paper unraveling machine with the blades spaced nominally 3 mm apart.

To promote inter-fiber bonding, the fibers were removed from the wire in the sheet former, placed on a non-stick plate, weighed, sprayed evenly with a little deionized water, weighed again, and then pressed on each side for 30 seconds using a household iron at 170°C which gives an applied pressure of -2

approx. 0.1 kg cm . The weight of the dried paper was determined. The solids content of each sheet that entered the press was thus determined, and the moisture content as a percentage of the total fiber content was calculated.

Two sheets were produced for each variation in pulp composition, and the blast factor was measured at four locations on each sheet, and the average blast factor was determined.

The results are shown in the following table.

All of these papers demonstrated inter-fiber bonding between the urea-formaldehyde resin fibers and the glass or PET fibers, and with the cellulose fibers when these were also present. All the papers maintained their integrity when immersed in water.

EXAMPLE 11 (Comparison)

Example 6 in GB patent document 1 573 115 describes the production of paper from a mixture of urea/formaldehyde resin fibers and cellulose pulp on a Fourdrinier paper machine. Examination of a sample of the paper prepared in this example showed no inter-fiber bonding.

EXAMPLE 12

Urea/formaldehyde resin fibers prepared by the method described in Example 1, and with a degree of cure of 94%, were mixed in different proportions with a milled cellulose pulp, and were formed into towels by the British Standard method (which involves air-drying at room temperature perature, and does not promote inter-fibre bonding).

Similar sheets were also produced, but inter-fiber bonding was caused by drying the sheets under light pressure against a cylinder heated to approx. 100°C.

In one test series, abrasive pulp, i.e. mechanical cellulose pulp, was used, while in another series, kraft pulp, i.e. chemical pulp, was used. The explosion factors were measured.

It will be seen that inter-fibre bonding gives a significant increase in the burst factor.

Claims (10)

1. Method for producing a shaped object, characterized by (i) forming a solution of an amino/formaldehyde resin and a curing agent therefor into fibers; (ii) curing said fibers by heating them at a temperature above 100°C until their degree of cure is at least 93%; (iii) forming an aqueous mass by dispersing fibrous material in water, the fibrous material containing at least 5% by weight of said cured amino/formaldehyde resin fibers; (iv) form a shaped article from said mass, and (v) promoting inter-fiber bonding by heating said shaped article at a sufficiently high temperature above 80°C; for a sufficient time, and in the presence of a sufficient amount of water in excess of 10 percent by weight of the total weight of fibrous material present, by the application of pressure, before or during said heating, at least sufficient to cause contact between adjacent fibers, to cause at least some of the amino/formaldehyde resin fibers to weld to each other and/or to other fibrous material present at at least some of the points where the fibers contact each other. 2. Method according to claim 1, characterized in that the inter-fiber bond is promoted by heating the shaped object at a temperature within the range 90 to 180°C. 3. Method according to claim 1 or 2, characterized in that the inter-fiber bond is promoted right by heating the shaped article in the presence of at least 200 weight percent water, based on the total weight of said fibrous material. 4. Method according to any one of claims 1 to 3, characterized in that the shaped article is a sheet material, and the inter-fiber bonding is promoted by exposing the article to the temperature above 80°C during the drying to remove the water from the mass. 5. Method according to any one of claims 1 to 4, characterized in that the amino/formaldehyde resin fibers have a degree of cure of between 94 and 99%. 6. Method according to any one of claims 1 to 5, characterized in that the mass contains a mixture of 10 to 50 percent by weight of amino/formaldehyde . hyd-resin fibers and a corresponding 90 to 50 percent by weight of cellulose fibers. 7. Shaped object made from a fibrous material, characterized in that it comprises 5 to 95 percent by weight of amino/formaldehyde resin fibers that have a degree of cure of at least 93%, and correspondingly 95 to 5 percent by weight of cellulose fibers, the shaped object showing inter- fiber bonding where at least some of the amino/formaldehyde resin fibers are welded to each other and/or to the cellulose fibers at at least some of the points where the fibers touch each other, and said object has a bulk of at least where x is the weight percent of the amino/formaldehyde resin fibers in said fibrous material and A is the bulk, in cm^g 1 , of a similarly shaped article made under the same conditions from cellulose fibers only. 8. Procedure according to any of the claims 1 to 6, characterized in that the fibrous material in the mass comprises 5 to 100 percent by weight of said amino/formaldehyde resin fibers and correspondingly 0 to 95 percent by weight of a fibrous material consisting of 10 to 100 percent by weight of non-cellulosic fibers and correspondingly 0 to 90 percent by weight of cellulosic fibers. 9. Method according to claim 8, characterized in that the fibrous material in the mass comprises 20 to 60 weight percent of amino/formaldehyde resin fibers, 20 to 50 weight percent of non-cellulose fibers and 10 to 50 weight percent of cellulose fibers. 10. Shaped article made from fibrous material, characterized in that it comprises 5 to 100 percent by weight of amino/formaldehyde resin fibers with a degree of cure of at least 93%, and correspondingly 0 to 95 percent by weight of another fibrous component consisting of 10 to 100 percent by weight of non-cellulosic fibers and correspondingly 0 to 90 percent by weight of cellulosic fibers, the article exhibiting inter-fiber bonding whereby at least some of the amino/formaldehyde resin fibers are welded to each other and/or to the non-cellulosic fibers at at least some of the points where the fibers touch each other, and the shaped object has a blast factor of at least 2-1 0.2 kPa mg.