CA1101258A - Fibrous products - Google Patents

Abstract

ABSTRACT

"FIBROUS PRODUCTS"

A paper product including a first fibrous component comprising 5% to 70% water-insoluble formaldehyde resin fibres of average length at least 1 mm., average strength at least 50 MNm-2, mean diameter 1µ to 30 µ, and a second fibrous component comprising 30% to 95% cellulose pulp comprising (a) mechanical pulp of not more than 120 ml Canadian Standard Freeness and/or of tensile strength at least 24 Nm/g, and/or (b) chemical pulp of not more than 400 ml CSF and/or of tensile strength not less than half the zero span tensile strength.

Description

~E PRESEN~ I~VE~TI0~ RELATES to fibre-sontaining product~ or comp-; o~itions in ~heet form, partioularly paper and pape~-like products or composition~, containing formaldehyde-re~in fibres, in particular urea-formaldehyde fibres, which mar be crimped or ~traight. As used herein-after, the phrase "crimped fibres" is used to define fibre~, examination of which reveals that the majority of the fibres have at least one signi-ficant and permanent deviation from linearit~ along their length, the term "significant deviation" meaning a deviation of at least 20o Also a9 used hereinafter, the phrase "straight fibres" is u~ed to define fibres, examination of which reaveal~ that the majority of the fibres do not have any significant and permanent deviation f~om linearity alon~
their length, the ter "significant deviation" meaning a deviation of at lea~t 20.
Many materials in sheet form ¢ontain natural or bynthetio fibres.
Such fibre-oontaining ~heet materials inolude textiles, insulating mater-ials and, in partioular, paper whioh, as is well known in the art, is typioally maae from oellulo~e pulp (oomprising, for example, ohemicall~
pulped and di~inte~rated wood, mechanically ground wood, ootton linters, mechanically pulped rags, eto.). We have now found that the fibres oon-tained in such fibre-oontaining sheet materials can advantageously be partially replaoed by formaldeh~de-re~in fibre3, in particular urea form-- aldehyde fib~es.
Formaldehyde resins, particularly amino formaldeh~de resin~ are well known as bonding materials for wood, and al~o in paper a~ binding or wet strength additives (urea or melamine-formaldehyde resin~, or ohemioal mod ifioation thereof are u3ed). They are al80 used to impregnate oellulose papers, e.g. for the produotion of deoorative laminates~ Crushed urea-formaldehyde foam has also been used as a filler for paper making (for example in ~S Patent 3 322 6979 to the Soott ~aper ~ompany, ana m We~l German Patent 1 241 251 to ~ASE), All uses of amino formaldehyde resin products in paper hitherto have thus been of a binding or filling nature. We have found that fibres of formald-e;,yde iesli-ls, a~ helein described, can have surprising benefits in improving, inter alia, the bulk, tear strength, burst strength, tensile strength, drainage times, printabil-ity and procsssing of papers as described hereinafter.
The preferred fibres for use in the present invention are essentially unbranched and either straight or crimped. For applications involving use with cellulose fibres, it is desirable, for maximum strength, that only minor amounts of crimping be present. The fibres may be of circular or irregular cross-section. Advantageously, for paper making, fibres of elliptical cross-section may be used to facilitate the lay-down of the fibre in the paper sheet. Such fibres can be usefully made by centrifusal spinning, as described in our United States patent No.
~178336.
The mean diameter of the fibres is from 1 ~ to 30~u (for irregular fibres, average diameters are taken).
More particularly, the average is between 2~u and 20~u, particularly between 5JU and 15,u. There may be present, advantageously, a range of ibre diameters from l~u to 30 to enable the formation o a sheet of more uniform density.
Fibres with a range of diameters can be prepared, conven-iently by centrifugal spinning as described in our said ~` co-pending application.
For some applications, particularly when smooth papers are required, it may be desirable to ensure that there is an insignificant number of fibres of diameter above 25 ~.
The fibres used in the present invention, whether straight or crimped, characteristically also have an , llLZ58 average length of a-t leas-t 1 mm. It is a surprising feature of the inven-tion that long fibres (~ 2 mm) can be incorporated into papers without causing problems of premature fl~cculation in the papermaking process and hence uneven formation of the sheet. It may therefore be desirable to use fibres that are as long as the papermaking process can accommodate. The practical upper limit to the length may therefore be, for this reason, in the range 5 - 10 mm.
A minor degree of branching of the fibres rnay be present (due to fusion during production of the fibres), but preferably the fibres are essentially nonbranched.
In the case of straight fibres, their linearity is preferably such that they can be compacted to a reasonably dense paper form. Crimped fibres tend to be bulky, and characteristically their bulk density is low.
The fibres for use in the present invention are conveniently prepared from a formaldehyde resin, typically a UF resin of F:U molar ratio 1.2 to 3.0, preferably 1.5 to

2.5. Some or all of the urea can be replaced by (for example) melamine; minor amounts of phenol, resorcinol, cresol, etc.
may be added. A proportion of the formaldehyde may be replaced by other aldehydes, for example acetaldehyde. The - resins are conveniently prepared by aqueous condensation by any of the conventional methods already well known to those skilled in the art. The resin may be converted into fibres using the aqueous resin at a suitable concentration or by handling the dried partially-condensed resin as a melt.
The resin-forming composition is formed, while still flowable, into fibres. This can be suitably done by conventional spinning of a viscous resin syrup into hot air ("dry-spinning") or into an acid bath ("wet-spinning").

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~lternately it can be formed by passing a fine stream or series of drops into a Elowing resin-gelling liquid or by gas-fibrillation (in particular air-fibrillation) by means of a co-current or transverse gas stream as described in our United States patent No. 4202959. As a further alternative it can be spun by tack-spinning, by pulling a fiberisable material between two surfaces to which it adheres and subsequently severing the fibres from one or both of the surfaces. For example, as described in U~
patent 11~1207~ the resin may be moved into contact with a pair or belt surfaces so as to deposit it therebetween, whereafter the surfaces of the belts are moved apart to form :
fibres and stretch them, and the fibres are detached and collected. In our Canadian patent application No. 264118 there is described a suitable tack-spinning process in which fiberisable material is interposed between a porous surface and a second surface, the surfaces are caused to diverge so as to string fibres between them, the fibres are stabilised or solidified at least in part b~ fluid directed into or through the fibre-forming area from the opposite side of the porous surface to that on which the fibres are fo.rmed, and the fibres are separated at least from t~e secor.d ~urface. Convenie~tly, sllitcble fibres can be prepared by a centrifugal spinning process as described in our United States patent No. ~178336. In these instances, generally straight fibres are produced.
Curing of the fibres to render them insoluble in cold water can be achieved by adding an acid (e.g. formic or sulphuric acid) or a salt of an acid, preferably an ammonium salt, to the resin, prior to forming the fibres, and/or by heating the fibres after their formation.

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1 ll5~12Sl51 To form crimped fibres, the fibres can be only par-tially-cured after formation; they are then subjected to a crimping or twisting s-tep, and thereafter curing, to render them insoluble in cold water~ is completed.
The fibres may need to be reduced in length to that required for papermaking. This can be achieved by cutting, passing through rollers, milling, etc., or by wet disintegration as is well~known in the paper industry.
The fibres should be adequately cured and rendered insoluble in cold water (as described above) before being used for this purpose.
Pigments, dyes, brightening agents, fillers, etc., may be incorporated into the resin before forming the fibres.
The present invention accordingly provides a paper product, including a first fibrous component comprising 5% to 70% by weight of formaldehyde resin fibres which are insoluble in cold water, which have an average length, weighted by the length of the Eibres, of at least 1 ~n., which _ _ _ - 5a -~0.~2S8 have an average 3trength >, 50 MNm 2 (_ 33 ~m/g), and which have a mean diameter between 1 ~ and 30 ~, and a second fibrous oomponent comprising

3~0 to 95% by weight of cellulo~e pulp which oomprises a mechanical pulp of freeness no more than 120 ml. CSF (Canadian Standard Freene~s) and/or a tensile strength measured on on a standard hand sheet of at least 24 ~m/g, and/or a chemical pulp of freene~s no more than 400 ml. CSF and/or a tensile stren~th measured on a standard hand sheet of not less than half the zero span tensile strength.
The above~mentioned properties of the cellulose pulp can be achieved by known methods, for example by beatin3 and/or by treatment with a bond-ing a~ent.
Preferably the mechanical pulp has a freeness not greater than 80 ml.
CSF and/or a ten~ile stren~th measured on a standard hand shaet of at least 28 ~m/g.
Preferably the chemical pulp has a freeness of not more than 300 ml.
CSF and/or a tensile stren3th mea~ured on a ~tandard hand sheet of at lea~t 60Q/o of the zero ~pan tensile strength.
The ~eoond fibrous component ma~ contain or con~i~t of recycled fibres of the cellulose pulp as hereinabove defined.
Preferably the formaldehyde rasin fibre3 are ~F fibres. Prefera~ly the fibres have a mean diameter between 2 ~ and 20 p, more particularly between 5 )u and 15 ~. The fibres may be produced by methods as hereinafter de~oribed, but preferably they are produced by centrifu~al spinning since this tends to produce fibres of elliptical cross-~eotion containing less ~hot within the desired diameter than other msthods.
Whereas the bulk or density of paper containing cellulose pulp can be varied by conventional means (e.g. by using pulp of a limited de~ree of beating or refining) such variations are, for a given pulp combination, limited in scope, and where si~nificant increase~ in bulk are de~ired for reason~ of economy this is often accompanied by unacceptable decrea~es in ilO~25B

mechanical or barrier propertie3, similarly, for cellulose fuDnishe~, improve~ents in the rates of drainage in papermaking can only be acoom-; panied by changing beating conditions and an adverse ohange in propertias.
We have now found that certain oombinations, involving urea formalde-hyde fibres, oan provide a surprisingly ad~antageous combination of high bulk, rapid drainage and dryln~ with good mechanical properties and aooept-able barrier properties. Suoh combinations are partloularly useful for, for example, printin~ paper, where lighter weight paper of aooeptable or improved opaoity and meohanical properties can be obtained, or in board or other paoka3ing applioations where the improved stiffness and rapid drainage and drying of the stook are of great advantage.
In paper oontainin~ short fibre pulp, partioularly groundwood (iOe.
mechanioal pulp), the ¢ombinations al~30 show improved tear strengths over the ~roundwood alone, and muoh easier drainage than is usually pos-~ible with meohanioal pulp finnishes.
In combinations with high grade chemioal pulps, ~ignifioant improve-~; ments in bulk and advantages in stiffness and printing properties are obtained by this invention.
The ¢ompositions involve the use o~ 5 - 7~/3 ~F fibres. In order to achieve the desoribed benefit3 it is necessar~ for the fibres to be above a oertain length, namely 1 mm, preferably above 2 mm. Longer fibres achieve higher tear strengths; it is possible to use mixtures containing long fibres beoause we have found, surpri3ingly, that su¢h lon~ fibre3 can be incorporated into paper without the problems of uneven formation normally assooiated with the use of suoh fibres. ~he mean diameter of the fibres should be in the range 1 - 30 ~, preferably 2 - 20 ~. It 19 partioularly desirable to svoid the use of fibres above 30 ~ diameter as in some applioations the surfaoe of the paper may beoome unaooeptably rou~.
~he average strangth of the fibres must be above 50 MNm 2 ( ~ 33 ~m/~) when measured on a tensile test of single or grouped fibres.
Since the strength and tear properties of the compositions is dependent to a degree on the strength of the fibres, it is preferable for the average strength to be at least 100 MNm 2 ( 67 Nm/g). Surprisingly, though, excellent mechanical properties can be obtained with UF fibres; the UF
fibres are not birefringent, unlike cellulose or other fibres (e.g. nylon or polyethylene terephthalate which have been added to paper to improve tear strengths.
The UF fibres are preferably straight as defined above. However for paper of extra high bulk, the fibres can be crimped.
The rest of the fibrous furnish is a cellulose pulp trea~ed so that it is well bonded. The definition of "well bonded" depends upon the type of cellulose pulp in question; for a mechanical pulp it can be defined as occuring when the pulp has been beaten or refined to a freeness of 100 ml. CSF or less. For chemical pulp (e.g.
pulp extracted by the sulphate or sulphite processes) the freeness for good bonding can be higher, and our definition of well bonded is that degree of bonding (e.g. as achieved by beating or refining) which achieves a tensile strength in a standard handsheet o~ at least half the zero-span tensile strength. The strength tests are made according to the appropriate TAPPI procedures. In many cases, it is preferable to achieve the required levels of bonding not by beating or refining but by adding bonding agents - ~or example starches and modified starches, polymer latices, water soluble polymers (e.g. poly(ethylene imine), poly (acrylamide), poly(vinyl pyrrolidone), particularly when treated to be cationic in water~. These bonding agents can i8 be added with -the ibrous furnish or in a subsequent in-pregnation or coating stage. Particularly favoured are cationic bonding agents added with the fibres - those mentioned above, cationic starch or urea formaldehyde, or melamine-formaldehyde resins, as conventionally used to achieve increases in wet strength.
Such levels of bonding are well known to lead to high tensile strengths, but reduced tear strengths and low bulk paper. The addition of urea-formaldehyde fibres in the manner described leads to improvement in bulk and tear strength and the maintenance of excellent tensile properties.
Paper made according to the invention may be filled (for example with clay, TiO2 or other pigments), coated or calendered. Calendering will naturally reduce the thickness of the paper, and will usually improve mechanical properties, but in the case of the present invention bulkier papers than those possible with a ! conventional furnish are achievecl.

- To 100 parts by weight of a UF resin solution ("Aerolite 300", trade mar~ of Ciba-Geigy), wera added 0.25 parts by weight of ammonium sulphate, and enough water to ad~ust the viscosity to about 20 poise at 23C.
("Aerolite 300" is an aqueous U/F resin prepared by condensing a mixture of urea and formaldehyde in a F:U molar ratio of about 1.95:1, followed by concentration to a solids content ;~of about 65% by weight. It has a viscosity, depending upon its age, of about 40 to 200 poise at room temperature, and a water tolerance of about 180%). Fibres were prepared from this solution by air fibrillation; the resin was passed .~ ,~, 3S~
through an orifice downwards at a rate of about 12g/minute in the form of a continuous thread. The thread was impacted with an air jet (air rate~ 300 standard cubic feet per hour at pressure to the jet of 30 psig)~ Fibres were formed in the turbulent airstream and blown into a drum containing air heated to 50C, where they were collected and dried. The fibres were cured by heating at 120 C for

4 hours which rendered them insoluble in cold water. After curing, the bulk density of the fibres, uncompacted, was about 0~1 g cm 3. The fibres were disintegrated in a standard laboratory pulp disintegrator in water (consistency - 0.3%) to a length of about 2 mm. At this point the fibres were screened to remove any large particulate species. The fibres were about 12 ~ in average diameter.
Laboratory test papers were made using standard pulp evaluation equipment from this suspension of fibres and a similar sus?ension of mechanical pulp. Two papers were prepared, one containing 100~ mechanical pulp (A) . and one containing 80~ by weight mechanical pulp and 20%
by weight UF fibres (B).
The drainage time on paper A was longer than on paper B, and the drained paper A held more water than B.
When compacted and dried in a standard manner, the following properties were measured~
A B
Burst Index (KP/gm ) 0.90 0.90 Stretch, ~ 1.5 1. 7 ; Bulk, cm g 2 D 3 2 ~ 7 .~ , .

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Preparation of Hand sheets These were prepared using the British Standard apparatus, and rhis dnd the metllods used are described fully in the literature, for example in "A Laboratory Handbook of Pulp and Paper Manufacture" by J Grant (Arnold, 1942), p 78 -82; some changes to the method were made~
however - the disintegration of fibres was performed for 50,000 revolutions at 0.3% consistency and cellulose pulp, when used, was pre-beaten in a small Valley beater.
E AMPI,E 2 A sample of bleached pine sulphate pulp was beaten until a standard handsheet prepared from the pulp had a tensile strength of 77 Nm/g and a zero span tensile strength of 134 Nm/g. Paper samples were prepared frQm .
this and from disintegrated urea formaldehyde fibres.
The urea formaldehyde fibre was prepared from ~:
the resin used in example 1, and was fibrillated by centifrugal spinning (as described in our United States `E patent No. 4178336 using the following conditions:-Cup diameter 7.5 cm, with 24 holes, each 3 mm - diameter~ in the periphery of the cup; ro~ation speed 4500 rpm; resin flow rate 78g/min, with a viscosity of : 35 poise at 23C. The fibre was spun into an atmosphere heated to 70C. An acid catalyst solution was fed ~.
and mixed continuously into the _ _ - lOa -re~in system. ~he catalyst aolution contained 6.~/o by weight of ammonium sulphate and 0.82% by weight of polyoxyethene oxide, and was u~ed in the proportions of 6.25 part~ of catalyst ~olution to 78 part~ of resin 801-ution. ~he fibre was colle¢ted and cured at 120C for 3 hours, and was cut up and finally disintegrated in a laboratory disintegrator before being used to make paper. The mean fibre length was 1.7 mm and the mean diameter was 14.5 ~ (The average length u~ed 18 the avera~e weighted by length; similarly the diameter is the average weighted by di meter.
These averages are used throughout the specification).
~he properties of papers containing 25% by weight of urea formalde-hyde fibres were determined as follow~:-~ulk cm3/g 2.20 Tensile strength 44-1 Regidity, Kodak m~.m 0.41 ~ear Index m~.m2/g 11.8 - Opacit~ (75g/m2) % 75.7 Bur~t Index KPa.m2/g 3.57 :i .
Persons ~killed in the art of papermaking will recogni3e that it i9 - not possible to prepare paper of ~uch a combination of high bulk and tensile and bur~qt properties with a11-cellulose fu~nishe~.
: ~.
A bleaohed spruce sulphite pulp was beaten to a freeness of 40 ml.
CSF. Paper~ were made from a mixture of 6~/o by weight of this pulp and 3~/0 by weight of the urea-formaldehyde fibre de~oribed in ~xample 2. Papers were al30 made from the sample bleached sulphite pulp ~lone beaten to a freene3s of 600 ml. CSF; the paper made from both ~urnishes had ~he ~ame tensile index. The full properties mea~ured on the papers were a3 follows:-Z~i~

3~/0 urea ~ormaldehyd~ fibre 100% 3p~uce 67% spruoe sulphite sulphite Tensile Index ~.m/g 48 48 ~urst Index KPa.m /~ 3.3 3.2 ~ulk om3/~ 1.86 1.48 Air resistance, G~RLEY Seo. 450 ` 10 IS0 ~rightness, SCAN, % 80.4 70.6 It i9 apparent that the compo~ition o~ the invention has a good balanoe ; of bulk and tensile properties, and that the air resistanoe is better in spite of a signifioant inorease in bulk.

Meohanical pulp was beaten in a Valley beater to a Preene~s of 50 ml.
CSF. ~his pulp wac used to make paper handsheets oontainin~ 10, 20 and 35% by weight o~ urea formaldehyde ~ibres tas desoribed in Example 2). The ~ 15 freenes~, burst index, bulk and drainage time were measured for each ~ample `~ (the drainage time was measured a~ desoribed In the a~ore-mentioned "A
~aborato~y ~andbook of Pulp and Paper Manufacture" by`J Grant p. 85).
` The mixtures we oompared with mechanical pulp~ of different de~rees of beating, chosen because of the similarity of their drainage time~ to those of the oompGsition~ of the in~ention.
Drainage Time 3ur~t Index ~ulk ; KPa.m2/g om~/g 90~/0 Meohanical pulp (CSF 50 ml) 27 seos. ( 10% urea-~ormaldehyde ~ibre 1.05 2.27 100% Meohanical pulp 0.70 2.29 17 seos. ~ 80~o Meohanioal pulp ~CSF 50 ml) 0.91 2. 38 ( 20% urea-formaldehyde ~ibre 10~/o Meohanical pulp 0.56 2.29 10 seos. ~ 65% Meohanical pulp (CSF 50 ml) 0-74 2.61 ~ 35% urea-formaldehyde fibre i8 The results of the te~t~ show how, with tha compositions as defined, drainage times can be reduced without sacrificing mechanical propertiesu ExAMpLE 5 A urea formaldehyde fibre ~ample was prepared using the method of Example 2 from a resin of formaldehyde: urea molar ratio of 1.6~ he fibre, of diameter weighted average diameter 17 ~ and of length weighted average length of about 6 mm, were made into handsheets with a well beaten groundwood pulp (freeness 14 ml CSF). 32/o by weight of the urea formalde-hyde fibre was used.
It wa~ observed that in ~pite of the length of the urea formalde-hyde fibre (~ome fibres u~ to 10 mm lon~) the ~ormatlon of the paper wa~
excellent. ~he mechanioal properties of the paper were mea~ured as ~ollows.
~ear Index 5.5 mN-m /~
Tensile Index 26 ~.m/g Bur~t Index 1.35 KPa-m2/g ~ulk 3.0 cm3/~
~XAMPL~ 6 Paper was made on a ~ourdinier paper machine u~ing urea formaldehyde fibre~ a~ de~cribed in the previous paper of Example 5 (thou~h a little ahortened by beating to a weighted length of 4 - 5 mm). The paper machine had a wire width of 450 mm and wa~ run at 5 m. per minute.
~he web pas3ed over a suction couch roll and via an open drain to the pres~ section, and hence to the drier section. During the produotion of the paper the web was sampled at the open drain and its solids oontent measured. A paper oontaining 20Y by weight of the fibre of the i~vention and equal amounts of beaten birch and pine sulphate pulps (freeness 300 ml.
CSF) was made.

S~

The properties of the paper were meaaured a~
~ulk cm3/g 2.27 Tens~le Index ~.m/g Cross Direotion 2a.5 Maohine Direotion 52.8 Tear Index mN.m /g Cro~s Direction 14,5 The paper produoed was much bulkier than i8 normal for a wood-free paper, and maintained good meohanioal properties~ During the produetion of the paper the aolids content of the paper at the couch roll was deter-mined, and oompared with that of an all-oellulose paper (equal amounts of birch and pine sulphate pulp) run under identioal oond~tions.
With urea for aldehyde Cellulose Fibre only Solids oontent at oouoh % 16.0 12.1 This indioates the improvement~ Ln de-watering that result from u3ing the oompositions of the invention.
EXAMPLE ?
A seriea o~ experiment~ were performed to demonstrate the signific-anoe of the length of the urea-formaldehyde fibre3 on the usefulness of a paper sample, as defined by measuring its tear index. Paper handsheets :,- .
20 were prepared usin~ a mechanioal pulp beaten to a freeneas o~ 75 ml. CS~

30% by weight of urea-formaldehyde fibre3, as described in Example 2~ were inoorporated. ~our sets bf samples were prepared, u~ing urea-formaldehyde fibres of variou3 mean len~ths, and the tear index was measured.

~ibre len~th mm ~ear Index (average wei~hted by length) mN.n2jg 4.9 3.5 4.0 3~3 - 2.8 2.8 1~2 2.7 A further sample of urea formaldehyde fibres of mean diameter 8 I~Q:~2S~51 (weighted by diameter) and mean length 4 mm ~weighted by length) was incorporated into paper 9ample8 at a 3C% b~ wei~ht level with meohanioal pulp (freenes~ 75 ml. CSF). ~he tear index of the samples were measured as being 3.3 mN m2/g.
XAMPIE 8.
A sample of mecha~ical pulp, of Freeness 100 ml. CS~, was u~ed to prepare pa~er hand~heets containing urea formaldehyde fibre. The fibre was prepared by ¢entrifugally spinning a resLn of fo~maldehyde: urea ratio 2:1, followed by ouring at 120C. An aoid catalyst (ammonium aulphate) was added to the resin before spinning. ~he mean diameter of the fibre was 17 ~ (weighted by diameter) and the mean lngth (weighted by length) was 4 mm. ~o the fibre miEtures in water 3% by weight oationio ataroh was added, based on the fibre weight, this being added as a 10%
~olution just before papermaking. (When a paper was made using ~u~t meoh-anioal pulp and oationic starch, its tensile ~trength was 33 ~.m/~).
Material~ containin~ 20/o by weight and 5~/0 by weight of urea-formaldehyde fibres were prepared; their propertie~ were determined as follows 20% . 5~
- urea fo~maldeh~de urea formaldehyde fibre fibre Bulk om3/g 2.65 300 ~ensile Index ~.m/g ~0 19 ~urst Index EPa.m /g 1.25 . 1.15 Tear Index mN.m2/g 4.0 4.8 25The paper samples thus ~howed exoellent oombinations of bulk, strength and taar re~ist~noe.

The urea formaldehyde fibre desoribed in Example 8 was u~ed in comb-inatior with a biroh sulphate pulp beaten to about 300 ml. CS~, and 3% by 30weight oationio starch added as befora. The proportion of urea-formaldahyde `25~

fibre use waa 2~/o by weight~ ~he following properties were measured on the paper:-B~lk cm3/g 1.94 ~ur3t Index KPa.m2/g 3~3 ~ensile Index ~.m/~ 49 ~ear Index m~.m2/g 8.4 ~y compari~on, the birch pulp when used alone ga~e paper of the following propertie~:-Bulk om3/g 1.56 Burst Index KPa.m2/~ 3.5 Tensile Index ~.m/g 52 ~ear Index m~.m /g 8.0 Which demon~tratea the ability o~ the compositions a~ de~cribed to improve the bulk of a paper without a~verse change in meoha~ioal properties.
EXAMPLæ 10.
A ~imilar oomposition was used as in ~xample 9, exoept that the biroh pulp wa3 replaoed by pine 3ulphate pulp. ~he paper produoed had the fol-lowing propertie~.
,~
Bulk om /g 1.93 n 20 ~ur~t Index KPà.m2/g 4.3 Ten3ile Index ~m/g 53 Tear Index m~.m /g 10.0 ~ . .

PA ~ ~P
15 Februa~y 1978

Claims (10)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A paper product, including a first fibrous component comprising 5%
to 70% by weight of formaldehyde-resin fibres which are insoluble in cold water, which have an average length, weighted by the length of the fibres, of at least 1 mm., which have an average strength ? 50 MNm-2 ( ? 33 Nm/g), and which have a mean diameter between 1 µ and 30 µ, and a second fibrous component comprising 30% to 95% by weight of cellulose pulp selected from the group consisting of a mechanical pulp of freeness no more than 120 ml.
CSF (Canadian Standard Freeness) and/or a tensile strength measured on a standard hand sheet of at least 24 Nm/g, a chemical pulp of freeness no more than 400 ml. CSF and/or a tensile strength measured on a standard hand sheet of not less than half the zero span tensile strength, and mix-tures of the said mechanical pulp and chemical pulp.

2, A paper product as claimed in claim 1, wherein the formaldehyde-resin fibres are fibres selected from the group consisting of urea formaldehyde, melamine formaldehyde, phenol formaldehyde, resorcinol formaldehyde and cresol formaldehyde.

3, A paper product as claimed in claim 1, wherein the formaldehyde resin fibres have a mean diameter between 2 µ and 20 µ.

4. A paper product as claimed in claim 3, wherein the formaldehyde resin fibres have a mean diameter between 5 µ and 15 µ.

5. A paper product as claimed in claim 1, wherein the formaldehyde resin fibres have an average length of at least 2 mm.

6. A paper product as claimed in claim 1, wherein the formaldehyde resin fibres have an average strength of at least 100 MNm-2 (? 67 Nm/g).

7. A paper product as claimed in claim 1, wherein the formaldehyde resin fibres have been produced by centrifugal spinning.

8. A paper product as claimed in claim 1, wherein the mechanical pulp has a freeness not greater than 80 ml. CSF and/or a tensile strength measured on a standard hand sheet of at least 28 Nm/g.

9. A paper product as claimed in claim 1, wherein the chemical pulp has a freeness not greater than 300 ml. CSF and/or a tensile strength measured on a standard hand sheet of at least 60% of the zero span tensile strength.

10. A paper product as claimed in claim 1, wherein the second fibrous component comprises recycled fibres of the cellulose pulp.