CA1235864A - Paper and board manufacture - Google Patents
Paper and board manufactureInfo
- Publication number
- CA1235864A CA1235864A CA000467253A CA467253A CA1235864A CA 1235864 A CA1235864 A CA 1235864A CA 000467253 A CA000467253 A CA 000467253A CA 467253 A CA467253 A CA 467253A CA 1235864 A CA1235864 A CA 1235864A
- Authority
- CA
- Canada
- Prior art keywords
- starch
- paper
- water
- suspension
- xanthan gum
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Abstract
ABSTRACT OF THE DISCLOSURE
Aqueous suspensions of uncooked starch, particularly never-dried starch slurry products of wet-milling cereals, are stabilised for use as papermaking additives by addi-tion of a minor amount of xanthan gum.
Aqueous suspensions of uncooked starch, particularly never-dried starch slurry products of wet-milling cereals, are stabilised for use as papermaking additives by addi-tion of a minor amount of xanthan gum.
Description
~z~
IMPROVEMENTS IN PAPER AND BOARD MANUFACTURE
This invention relates to paper or board manufacture. More especially, it relates to a method of paper or board manufacture in which an organic polysaccharide i6 added to the mixture or applied to the web of fibres during the process of manufacturing the paper or board. In particular it relates to paper of improved strength or surface characteristics manufactured according to such a method. An improved additive material also constitutes a feature of the present in~ention.
It is well known to add during the early stages of paper or board manufacture one or more additives so as to increase the inter-fibre bonding and thus the strength of the eventual paper or board. The additives are usually polysaccharides including starches and cellulose and their chemical derivatives as well as other organic substances capable of forming chemical links with the cellulose which forms the basis of the paper or board web. This latter cellulose may have been modified by the paper or board manufacturer in order to assist the web formation during ~he early stages of manufacture preceding the web formation.
~;~35~i4 Additives as described in the application can be added to the pulp itself, or to ~he early stages in the formation of the paper web ("we~-end addition"), i.e.
when the water content is reduced from about 99% to about 30%. The additives are in such cases distributed more or less uniformly throughout the thickness of the paper or board. It is also known, for convenience, to apply the additive to the formed web, on one or both surfaces thereof in stages of manufacture subsequen~ to web formation, as the water content is reduced to 2~ to Z0% by weight of the web.
"Size-Press Addition" named after the relevant par~
of the paper-making machine, is an example of a known process; application of additives may be effected at this stage using solutions or dispersions of the additives, or foamed liquids, or dry powders. It is known that, whilst the size press process is a useful method of applying substances to paper or board, the equipment is expensive to buy and install; it also consumes large amounts of energy to drive the machinery and to carry out the extra drying operations conseguent on the use of a size press.
Since the application of substances at the si~e press is carried out using solutions or dispersions in ~Z;~6~
water, it is necessary to arrange for extra drying equipment to be installed in addition to that used to dry the paper or board before it i6 passed through the size press. This extra drying requires up to 30% extra drying eguipment and represents a further 30~ increase in energy consumed during the manufacture of the paper or board.
The present invention is concerned with the transfer, handling and subsequent behaviour on heating of ~hese dispersions or solutions of polysaccharide additives, and is based on a consideration of the flow characteristics thereof.
When dispersions of starch in water are subjected to high rates of shear, e.g. high rates of flow through restricted orifices such as those which are normally used to produce sprays, they exhibit considerable dilatancy. i.e. the apparent viscosity or resistance to flow increases as the rate of shear increases. The result of such increases i5 to restrict or stop flow.
Dilatancy is particularly noticeable in suspensions of starch wheLe the starch represents 5% or more of the total fluid. This stoppage is familiar to those users of starch who wish to spray suspensions of raw or processed starch as aids to various industrial processes including application to paper and board during and ~z~
subsequent to manufactura.
Aqueous dispersions of starch also tend to form sediments owing to the effect of gravity or iner~ial forces on ~he particulate matter suspended in the water. Such sediments are the cause o~ much failure of equipment. In order to prevent or reduce the occurrence of sedimentation, it has hitherto been customary to increase the viscosity of the suspension by raising the temperature of the s~arch above the temperature at which ~he individual par~icles rupture: the process is generally referred to as "cooking". This enables the starch to hydrate, forming a gel which, by increasing the fluid viscosity, reduces the tendency of the starch particles to sediment. Alternatively, it is customary to add substances which, by raising the viscosity of the aqueous phase of the suspension, reduce the sedimentation process. Such viscosity-increasing substances include cold-water-soluble derivatives of starch or of cellulose and many high molecular weight polyhydric substances such as polyethylene oxide ethers, polyvinyl alcohols as well as "swelling clays" such as bentonite, attapulgite, Laponite and the like which are capable of raising the viscosi~y of the dispersion of s~arch in cold water.
However, such procedures as described above lead to poor spray formation since the fluids require high pumping pressures in order to achieve a sufficiently high degree of turbulence at the spray head to produce the fine droplets that are desirable for application as herein described. Such high pumping pressures frequently lead to failure of equipment due to ~he inherent tendency of starch suspensions to beco~e dilatant. The presen~ invention has discovered a method of paper or board manufacture in which one or more further additives are present in the strength-affecting starch suspension.
According to this invention there is provided an aqueous suspension of starch characterised in that it contains minor amount of a hydrophilic polymeric viscosity increasing agent whereby the settlement of suspended s~arch particles is prevented. There is also provided a method of applying a viscous treating agent in the manufacture of paper or board, characterised in that the agent is applied by means of a rotary atomiser.
The invention can be seen to comprise three aspects.
In one aspect, the invention provides a method for the manufacture of paper or board in which an aqueous suspension starch i~ applied to the paper web during or ~2~
after its formation: wherein there i6 present in the suspension a hydratable polymer in an amount such that the rheology of the suspension i6 altered so a to render the suspension more pseudoplastic whereby application to the web is facilitated since pseudoplastic (alternatively known as visco-elastic or shear-thinning) fluids as described in this inven~ion are capable of having sufficien~ viscosity to prevent sedimentation of dispersed particles such as starch under the low rates of shear experienced during storage or whil~t being transported; yet, when subjected to high rates of shear such as occur when a fluid is expelled from a narrow orifice such as the nozzle of a spray jet, the same fluids exhibit sufficiently low viscosity to permit the formation of droplets suitable for the application of solutions or suspensions to paper or board during the early stages of manufacture.
In another aspect the invention provides a method for the manufacture of paper or board in which an aqueous solution of a hydratable polymer is applied to the paper web during or after forma~ion; wherein there îs present in the solution a water-soluble polymeric substance capable of forming a continuous film at or near the surface of the paper or board. This polymer may be applied alone utilising the advantages of the atomising distributor descLibed in this invention;
alteLnatively, it may be applied together with the starch and rheology-modifying polymer described above In each of the above aspects, the hydratable polymer is nonionic or ionic, preferably anionic. It may be the sodium, potassium or ammonium salt of a polycarboxylic acid in which the carboxylic units are attached to long-chain polyhydroxyl polymers, e.g. polysaccharides, whereof the polymers are based on glucose, mannose, galac~ose, pyranose, amylose and the like and their hybrid derivatives including such acids as glucuronic acid. Typical polymers include the sodium, potassium and ammonium salts of carboxymethylcellulose and ~he complex polymer obtained by fermentation of a suitable sugar-based medium by the organism Xanthomonas campestris and commonly known as xanthan gum. It may also be one of the water-soluble salts of polyacrylic acid, polymethacrylic acid and their homologues. the actual polysaccharides and their derivatives most preferred will depend on which aspect of the inven~ion is of major impor~ance.
In another aspect the invention provides a method for the manufac~ure of paper or board in which suspensions or solutions of substances in water or other liguids are applied by means of a rotary atomiser.
Al~hough the a~ueous suspensions and solutions described in this invention may be applied to the surface of the paper by conventional, high-pressure sprays, it is pre-ferred to use the rotary atomiser which has hitherto not been used in the manufacture of paper although well kno~.
in the agricultural art. The atomiser is available in several similar forms including devices sold under several registered trade marks including those of "MICRON MICROMAX' and "LE~Y HYDRASPIN". Such an atomiser is described in detail in GB Patents 2,004,204B, 2,004,205B and 2,004,206B
and defined in claim 1 of those patents. These atomisers and other similar devices comprise a truncated hollow con-ical shell set to spin on its vertical axis with the narrow end ~ownwards.
An illustration of the configuration of the atomiser 15 i5 shown in the accompanying drawing, which consists of a sectional view of a twin-cone system. The atomiser comprises a fixed inner cone 1 surrounded by an outer cone 2 moun~ed on a bottom bearing 3 situated at the end of a central shaft ~. A central nozzle 5 is 20 arranged to supply incoming fluid~ The outer cone 2 is provided at the top with a top bearing 6 and drive means comprising a belt driven pulley system 7,8 coupled with an electric motor 9. The upper outer edge of the outer cone 2 is provided wi~h teeth 10 and a circumferential 25 protecting ring. The fluid to be atomised is pumped through one or more ports into the interior of the spinning cone 2 and is subsequently carried upwards and outwards across the inner surface of the spinning cone 2 until it leaves the cone tangentially at its widest, upper circumference. The size of the droplets generated by this movement of the fluid is partly controlled by arranging for the upper edge of the cone to be serrated in the form of teeth 10 arranged radially around its upper surface. The cone may be driven by an electric or air or hydraulic motor through a suitable drive and with suitable bearings to support the cone rigidly on it~
mounting. In the case of a hydraulic motor, the driving energy may be ~ransferred to the motor by means of a conventional hydraulic generator pump and specialised Qo-called "hydraulic fluid"; alternatively, the driving energy may be transferred by arranging for the aqueous starch suspension or other fluid, intended to be applied to the paper, to drive a turbine connected to the spinning cone.
For a given atomiser and a liquid of given rheological properties and set spinning at a given speed of rotation, droplets of uniform size are generated. It follows that droplet size can be selected by choosing an appropriate ~ombination of atomiser geometry, fluid rheology and speed of rotation in order to meet the particular requirements o$ the user. Each of the parameters go~erning droplet size may be adjusted independently of the others and also independently of ~23~
the rate of flow of the suspension or solution being applied to the paper surface, whereas with a conventional spray nozzle as previously used in the art.
the droplet size is dependent on the pressure drop across the nozzle which, in turn, governs the rate of flow. Since the droplets produced by the atomiser are of virtually uniform size, they follow similar trajectories thus permitting a remarkably close degree of control of the pa~tern laid down on the paper surface and hence, uniformity of application. If the droplets are ejected from the ro~ating atomiser set to spin on a vertical axis, they will travel in a horizontal trajectory; it therefore follows that they will each travel along a path determined by the resultant of the horizontal forces produced by the tangential motion and the force of gravity. If the body of the atomiser is placed so that the base of the cone is close to the surface to which the fluid is to be applied, it follows that the droplets will travel approximately 20 centimetres in the vertical direction under ~he force of -gravity and so will be travelling very much more slo~ly than would similar drople~s ejected at high velocity from a conventional pressure-operated spray nozzle.
This is particularly advantageous when the fluid is to ~e applied to the surface of paper or board during the early states of manufacture when the water content of the paper is high and the strength of the paper conseguently low.
One or more atomisers may be fixed to a boom set so as to allow the fluid to be applied to the upper or lower sides of the paper or board as it passes through the paper machine. If desired, part of the circumference of the spinning cone may be surrounded by a shield so as ~o restrict the passage of droplets ~o the space diametrically opposi~e the shield this permits directional application of fluids to be made as and when required by the user. Fluid collected by the shield can be returned to the holding tank or in~o the fluid circula~ing system as may be convenient.
The first aspect of the invention is concerned with the rheology of the suspension. It is well known that the velocity of a liquid at which i~ changes from laminar or quiescent flow to turbulent flow is defined by the Reynolds Equation expressed as follows:-NR = d.v.r .K
V
where Nr = the Reynolds number of the fluid d = ~he density of ~he fluid v = the velocity of the fluid r = radius of the pipe or orifice through which the fluid is flowing ~ = a proportionality constant V = the viscosity of the fluid If the above parameters are expressed in cgs units, it is known that turbulence occurs when the Reynolds Number exceeds 2000. It can be seen that if the valueof V (the viscosity) for a particular fluid is low, the Reynolds Number will be high and so turbulence will occur in conditions in which a fluid of higher viscosity would flow in a laminar manner; additionally, the low viscosity will enable the fluid to flow at a higher velocity under given circumstances and so further increase the Reynolds Number and, hence, the turbulence of the fluid.
It i6 well known that, for optimum efficiency of a spray or atomising system, it is necessary for the fluid to be in a state of turbulence at the point a~ which break-up into droplets occurs; in other words, op~imum droplet formation occurs when the fluid viscosity is low. It therefore follows that, if two fluids of different viscosities are compared under similar ~4 condi~ions of flow as defined by the parameters used in the Reynolds Equation, better spray efficiency will be obtained in the fluid with the lower ~iscosity.
Further consideration of the first aspect, ie. the rheology of the suspension of starch, requires that the viscosity or resis~ance to deformation within the fluid 6hould be as high as possible when the ~luid is at or virtually at rest, i.e. under conditions of low rates of shear. Prior art teaches that a starch or similar suspension could be stabilised if the fluid viscosi~y is raised by cooking at least part of the starch or by the addition of a soluble polymeric substance as defined earlier, i.e. the starch particles are prevented from setting out under the forces oP gravity or inertia.
Stokes' Law illustrates this by calculating that the forces exerted on suspended particles by external forces are inversely proportional to the viscosity of the fluid. However, such treatments give rise to high viscosities which are detrimental to the efficiency of
IMPROVEMENTS IN PAPER AND BOARD MANUFACTURE
This invention relates to paper or board manufacture. More especially, it relates to a method of paper or board manufacture in which an organic polysaccharide i6 added to the mixture or applied to the web of fibres during the process of manufacturing the paper or board. In particular it relates to paper of improved strength or surface characteristics manufactured according to such a method. An improved additive material also constitutes a feature of the present in~ention.
It is well known to add during the early stages of paper or board manufacture one or more additives so as to increase the inter-fibre bonding and thus the strength of the eventual paper or board. The additives are usually polysaccharides including starches and cellulose and their chemical derivatives as well as other organic substances capable of forming chemical links with the cellulose which forms the basis of the paper or board web. This latter cellulose may have been modified by the paper or board manufacturer in order to assist the web formation during ~he early stages of manufacture preceding the web formation.
~;~35~i4 Additives as described in the application can be added to the pulp itself, or to ~he early stages in the formation of the paper web ("we~-end addition"), i.e.
when the water content is reduced from about 99% to about 30%. The additives are in such cases distributed more or less uniformly throughout the thickness of the paper or board. It is also known, for convenience, to apply the additive to the formed web, on one or both surfaces thereof in stages of manufacture subsequen~ to web formation, as the water content is reduced to 2~ to Z0% by weight of the web.
"Size-Press Addition" named after the relevant par~
of the paper-making machine, is an example of a known process; application of additives may be effected at this stage using solutions or dispersions of the additives, or foamed liquids, or dry powders. It is known that, whilst the size press process is a useful method of applying substances to paper or board, the equipment is expensive to buy and install; it also consumes large amounts of energy to drive the machinery and to carry out the extra drying operations conseguent on the use of a size press.
Since the application of substances at the si~e press is carried out using solutions or dispersions in ~Z;~6~
water, it is necessary to arrange for extra drying equipment to be installed in addition to that used to dry the paper or board before it i6 passed through the size press. This extra drying requires up to 30% extra drying eguipment and represents a further 30~ increase in energy consumed during the manufacture of the paper or board.
The present invention is concerned with the transfer, handling and subsequent behaviour on heating of ~hese dispersions or solutions of polysaccharide additives, and is based on a consideration of the flow characteristics thereof.
When dispersions of starch in water are subjected to high rates of shear, e.g. high rates of flow through restricted orifices such as those which are normally used to produce sprays, they exhibit considerable dilatancy. i.e. the apparent viscosity or resistance to flow increases as the rate of shear increases. The result of such increases i5 to restrict or stop flow.
Dilatancy is particularly noticeable in suspensions of starch wheLe the starch represents 5% or more of the total fluid. This stoppage is familiar to those users of starch who wish to spray suspensions of raw or processed starch as aids to various industrial processes including application to paper and board during and ~z~
subsequent to manufactura.
Aqueous dispersions of starch also tend to form sediments owing to the effect of gravity or iner~ial forces on ~he particulate matter suspended in the water. Such sediments are the cause o~ much failure of equipment. In order to prevent or reduce the occurrence of sedimentation, it has hitherto been customary to increase the viscosity of the suspension by raising the temperature of the s~arch above the temperature at which ~he individual par~icles rupture: the process is generally referred to as "cooking". This enables the starch to hydrate, forming a gel which, by increasing the fluid viscosity, reduces the tendency of the starch particles to sediment. Alternatively, it is customary to add substances which, by raising the viscosity of the aqueous phase of the suspension, reduce the sedimentation process. Such viscosity-increasing substances include cold-water-soluble derivatives of starch or of cellulose and many high molecular weight polyhydric substances such as polyethylene oxide ethers, polyvinyl alcohols as well as "swelling clays" such as bentonite, attapulgite, Laponite and the like which are capable of raising the viscosi~y of the dispersion of s~arch in cold water.
However, such procedures as described above lead to poor spray formation since the fluids require high pumping pressures in order to achieve a sufficiently high degree of turbulence at the spray head to produce the fine droplets that are desirable for application as herein described. Such high pumping pressures frequently lead to failure of equipment due to ~he inherent tendency of starch suspensions to beco~e dilatant. The presen~ invention has discovered a method of paper or board manufacture in which one or more further additives are present in the strength-affecting starch suspension.
According to this invention there is provided an aqueous suspension of starch characterised in that it contains minor amount of a hydrophilic polymeric viscosity increasing agent whereby the settlement of suspended s~arch particles is prevented. There is also provided a method of applying a viscous treating agent in the manufacture of paper or board, characterised in that the agent is applied by means of a rotary atomiser.
The invention can be seen to comprise three aspects.
In one aspect, the invention provides a method for the manufacture of paper or board in which an aqueous suspension starch i~ applied to the paper web during or ~2~
after its formation: wherein there i6 present in the suspension a hydratable polymer in an amount such that the rheology of the suspension i6 altered so a to render the suspension more pseudoplastic whereby application to the web is facilitated since pseudoplastic (alternatively known as visco-elastic or shear-thinning) fluids as described in this inven~ion are capable of having sufficien~ viscosity to prevent sedimentation of dispersed particles such as starch under the low rates of shear experienced during storage or whil~t being transported; yet, when subjected to high rates of shear such as occur when a fluid is expelled from a narrow orifice such as the nozzle of a spray jet, the same fluids exhibit sufficiently low viscosity to permit the formation of droplets suitable for the application of solutions or suspensions to paper or board during the early stages of manufacture.
In another aspect the invention provides a method for the manufacture of paper or board in which an aqueous solution of a hydratable polymer is applied to the paper web during or after forma~ion; wherein there îs present in the solution a water-soluble polymeric substance capable of forming a continuous film at or near the surface of the paper or board. This polymer may be applied alone utilising the advantages of the atomising distributor descLibed in this invention;
alteLnatively, it may be applied together with the starch and rheology-modifying polymer described above In each of the above aspects, the hydratable polymer is nonionic or ionic, preferably anionic. It may be the sodium, potassium or ammonium salt of a polycarboxylic acid in which the carboxylic units are attached to long-chain polyhydroxyl polymers, e.g. polysaccharides, whereof the polymers are based on glucose, mannose, galac~ose, pyranose, amylose and the like and their hybrid derivatives including such acids as glucuronic acid. Typical polymers include the sodium, potassium and ammonium salts of carboxymethylcellulose and ~he complex polymer obtained by fermentation of a suitable sugar-based medium by the organism Xanthomonas campestris and commonly known as xanthan gum. It may also be one of the water-soluble salts of polyacrylic acid, polymethacrylic acid and their homologues. the actual polysaccharides and their derivatives most preferred will depend on which aspect of the inven~ion is of major impor~ance.
In another aspect the invention provides a method for the manufac~ure of paper or board in which suspensions or solutions of substances in water or other liguids are applied by means of a rotary atomiser.
Al~hough the a~ueous suspensions and solutions described in this invention may be applied to the surface of the paper by conventional, high-pressure sprays, it is pre-ferred to use the rotary atomiser which has hitherto not been used in the manufacture of paper although well kno~.
in the agricultural art. The atomiser is available in several similar forms including devices sold under several registered trade marks including those of "MICRON MICROMAX' and "LE~Y HYDRASPIN". Such an atomiser is described in detail in GB Patents 2,004,204B, 2,004,205B and 2,004,206B
and defined in claim 1 of those patents. These atomisers and other similar devices comprise a truncated hollow con-ical shell set to spin on its vertical axis with the narrow end ~ownwards.
An illustration of the configuration of the atomiser 15 i5 shown in the accompanying drawing, which consists of a sectional view of a twin-cone system. The atomiser comprises a fixed inner cone 1 surrounded by an outer cone 2 moun~ed on a bottom bearing 3 situated at the end of a central shaft ~. A central nozzle 5 is 20 arranged to supply incoming fluid~ The outer cone 2 is provided at the top with a top bearing 6 and drive means comprising a belt driven pulley system 7,8 coupled with an electric motor 9. The upper outer edge of the outer cone 2 is provided wi~h teeth 10 and a circumferential 25 protecting ring. The fluid to be atomised is pumped through one or more ports into the interior of the spinning cone 2 and is subsequently carried upwards and outwards across the inner surface of the spinning cone 2 until it leaves the cone tangentially at its widest, upper circumference. The size of the droplets generated by this movement of the fluid is partly controlled by arranging for the upper edge of the cone to be serrated in the form of teeth 10 arranged radially around its upper surface. The cone may be driven by an electric or air or hydraulic motor through a suitable drive and with suitable bearings to support the cone rigidly on it~
mounting. In the case of a hydraulic motor, the driving energy may be ~ransferred to the motor by means of a conventional hydraulic generator pump and specialised Qo-called "hydraulic fluid"; alternatively, the driving energy may be transferred by arranging for the aqueous starch suspension or other fluid, intended to be applied to the paper, to drive a turbine connected to the spinning cone.
For a given atomiser and a liquid of given rheological properties and set spinning at a given speed of rotation, droplets of uniform size are generated. It follows that droplet size can be selected by choosing an appropriate ~ombination of atomiser geometry, fluid rheology and speed of rotation in order to meet the particular requirements o$ the user. Each of the parameters go~erning droplet size may be adjusted independently of the others and also independently of ~23~
the rate of flow of the suspension or solution being applied to the paper surface, whereas with a conventional spray nozzle as previously used in the art.
the droplet size is dependent on the pressure drop across the nozzle which, in turn, governs the rate of flow. Since the droplets produced by the atomiser are of virtually uniform size, they follow similar trajectories thus permitting a remarkably close degree of control of the pa~tern laid down on the paper surface and hence, uniformity of application. If the droplets are ejected from the ro~ating atomiser set to spin on a vertical axis, they will travel in a horizontal trajectory; it therefore follows that they will each travel along a path determined by the resultant of the horizontal forces produced by the tangential motion and the force of gravity. If the body of the atomiser is placed so that the base of the cone is close to the surface to which the fluid is to be applied, it follows that the droplets will travel approximately 20 centimetres in the vertical direction under ~he force of -gravity and so will be travelling very much more slo~ly than would similar drople~s ejected at high velocity from a conventional pressure-operated spray nozzle.
This is particularly advantageous when the fluid is to ~e applied to the surface of paper or board during the early states of manufacture when the water content of the paper is high and the strength of the paper conseguently low.
One or more atomisers may be fixed to a boom set so as to allow the fluid to be applied to the upper or lower sides of the paper or board as it passes through the paper machine. If desired, part of the circumference of the spinning cone may be surrounded by a shield so as ~o restrict the passage of droplets ~o the space diametrically opposi~e the shield this permits directional application of fluids to be made as and when required by the user. Fluid collected by the shield can be returned to the holding tank or in~o the fluid circula~ing system as may be convenient.
The first aspect of the invention is concerned with the rheology of the suspension. It is well known that the velocity of a liquid at which i~ changes from laminar or quiescent flow to turbulent flow is defined by the Reynolds Equation expressed as follows:-NR = d.v.r .K
V
where Nr = the Reynolds number of the fluid d = ~he density of ~he fluid v = the velocity of the fluid r = radius of the pipe or orifice through which the fluid is flowing ~ = a proportionality constant V = the viscosity of the fluid If the above parameters are expressed in cgs units, it is known that turbulence occurs when the Reynolds Number exceeds 2000. It can be seen that if the valueof V (the viscosity) for a particular fluid is low, the Reynolds Number will be high and so turbulence will occur in conditions in which a fluid of higher viscosity would flow in a laminar manner; additionally, the low viscosity will enable the fluid to flow at a higher velocity under given circumstances and so further increase the Reynolds Number and, hence, the turbulence of the fluid.
It i6 well known that, for optimum efficiency of a spray or atomising system, it is necessary for the fluid to be in a state of turbulence at the point a~ which break-up into droplets occurs; in other words, op~imum droplet formation occurs when the fluid viscosity is low. It therefore follows that, if two fluids of different viscosities are compared under similar ~4 condi~ions of flow as defined by the parameters used in the Reynolds Equation, better spray efficiency will be obtained in the fluid with the lower ~iscosity.
Further consideration of the first aspect, ie. the rheology of the suspension of starch, requires that the viscosity or resis~ance to deformation within the fluid 6hould be as high as possible when the ~luid is at or virtually at rest, i.e. under conditions of low rates of shear. Prior art teaches that a starch or similar suspension could be stabilised if the fluid viscosi~y is raised by cooking at least part of the starch or by the addition of a soluble polymeric substance as defined earlier, i.e. the starch particles are prevented from setting out under the forces oP gravity or inertia.
Stokes' Law illustrates this by calculating that the forces exerted on suspended particles by external forces are inversely proportional to the viscosity of the fluid. However, such treatments give rise to high viscosities which are detrimental to the efficiency of
2~ the spraying equipment. It follows, therefore, that the rheology of the fluid in which the starch is suspended should exhibi~ a high viscosity at low rates of shear in order to prevent se~tlemen~ of the starch particles; at the same time it should exhibit low visocsity at high rates of shear in order to ensure sufficient trubulence to form droplets of optimum 6ize and particle siæe ~3~
dist~ibution.
It is well known that the viscosity of solutions of some poly~eric substances falls off more rapidly than others as ~he rate of shear or the rate of flow through a given orifice i6 increased. This is illustrated in the following Table in which the viscosities in water of several well-known high viscosity polymeric substances are comparPd over a range of rates of shear; the respecti~e viscosities and rates of shear were measured with a Broo~field Viscometer fitted with a concentric bob and cylinder attachment sold under the designation SC4 Small Sample Adapter:-Shear Rate Polymer* Viscosit~ tcentipoises) ~ 20 deq C
CMC1~000 1300084006000 43003000 l900 1400 HEC8000 6500 50003800 2700l900 llO0 GGllO0 9100 58003900 24001500 700 XG32000 170Q0 75003800 l900llO0 450 240 ~C660 550 480430 400 340 2~0 210 .
The present invention has discovered ~hat if a minor proportion o a 6ubs~ance capable of pro~idingaqueous solutions of high pseudoplas~icity is added ~o starch powder or incorpora~ed into a suspension of starch, it renders the starch capable of being stored for prolonged periods in aqueous suspension; of being capable of being transported through re6tricted orifices without giving rise to dilatancy; and i~s suspensions of being readily transformed into droplets of sufficiently small size to enable ~hem to be used as a means of applying starch uniformly to surfaces including surfaces of paper during manufacture.
Preferred polymers for the rheology-affecting purpose are xanthan gum and similar polysaccharides capable of dissolving in wa~er to produce solutions possessing very high viscosity at low rates of shear compared with other commerically available polymers but a relatively low viscosity at high rate of shear; this is illustrated in Table 1. Solutions of xanthan gum show little variation in their physical properties.
including rheology, over temperature ranges normally experienced in paper mills and o~har closed industrial premises: these properties also show neglible variations when ionic and other dissolved substances are present with the xanthan gum. This is especially important when water of unknown composition is used to prepare the starch suspensions e.g. when recycled water of differing degrees of hardness or with differing salt contents and at varying temperature is used in such preparations.
~z~
The rheology-affecting properties of xanthan gum are of particular importance if it is desired to apply starch in the form of a suspension or slurry in water since the presence of the xanthan gum in the suspension greatly reduces the tendency of starch particles ts settle out or form intractable sediments. The presence of xanthan gum in a s~arch suspension as described in ~his inven~ion allows users to store such suspensions for prolonged psriods and enables users ~o transport the ~tarch in the form of slurry to its eventual destination without the necessity to install special agitation equipment in the slurry containers used for transport and storage of the slurry. The convenience of being able to transport and store starch suspensions by the addition of xanthan gum is particularly importan~ in that such suspensions are available as residues produced ;n certain food-manufacturing processes: it is economically advantageous to be able to supply the starch in the suspension or slurry form in which it is produced rather than to extract and dry the starch and subsequently have to re-form the suspension before use.
This invention procides an economic method of storing and transporting such starch suspensions or slurries to the benefi~ of the starch and paper industries.
This invention has also discovered that ~he presence of xanthan gum in starch suspensions also overcomes the tendency of such suspensions to exhibit the phenomenon of dilatancy which can best be described as a rise in viscosi~y or resistance to flow as the rate of shear increases. Dilatancy is a condition to be avoided in handling starch and other ssspensions since dilatan~
fluids tend to cease flowing under conditions of high rates of shear such as occur inside pumps and control valves, restrictions and bends in pipes and in the noz~les of conventional spraying equipment. Therefore, the presence of xanthan gum in such suspensions serves to prevent the well-known and troublesome tendency of suspensions to cause blockages in the equipment used to carry them and, particularly, in the nozzles of conventional spray equipment.
The amount of weight of xanthan gum can vary between 0.025% and 1.0% of the water used to prepare the starch suspensions: in the case of suspensions prepared from dried, pow~er starch, the xanthan gum can be incorporated in the starch powder ~ogether with such other polymeric substances as may be desired so as to be present in the aforementioned proportions in the slurry during use. In the case of starch already prepared in suspension form a~ previously described, it is convenient to add the xanthan gum at an early stage in order to facilitate transport and prolonged storage.
The second aspect of this invention is concerned with ~he film-forming properties of certain polymers when dissolved or otherwise dispersed in water and applied in droplet form in a manner similar to that already described for the application of starch suspensions to paper or ~oard during manufacture. The preferred polymers are polysaccharides such as the alkali metal salts of carboxymethyl starches or of carboxymethyl celluloses or of alginic acid or of polyacrylic acid and their homologues, or (more preferably) the sodium salt of carboxymethyl cellulose commonly known as SCMC or CMC. The polymers may be applied with or without starch as herein described in order to provide different benefits to suit the requirements of users.
The carboxymethyl celluloses can have a degree of carboxyme~hylation of from 0.35 to 104 (i.e. related to the three labile hydroxy groups theoretically available for substitution in each anhydroglucose ring within the cellulose molecule chain) and total molecular weights from 15,000 to 80~,000, preferably 50,000 to 250,000.
It has been discovered in this invention that the presence of SCMC or the other polymers described in an aqueous starch dispersion has the effect of reducing the temperature a~ which starch particles rupture and form a gel (the gelation Temperature) as exemplified by a rapi~
increase in visc06ity. For example, 4 parts of SCMC of molecular weight approximately lO0,000 and degree of carboxymethylation of 0.85 were added to 16 parts of wheat starch. The effect was to reduce the gelation temperature of a 20% by weight starch suspension from 64 degreees Celsius to 59 degrees Celsius. This reduction in gelation temperature is important in the paper or board making processes in that it is known that low ~emperature gelation of starch improves the beneficial effects of adding starch to cellulose. Thus, the addition of such SCMC to starch is an important and hitherto unexpected method of improving the economy of operating the paper or board manufacturing processes.
The amount of these polymers, or mixtures thereof.
can vary up to 10% of the weight of the water used to carry the additives through a conventional spray or ~he atomisillg distributor as herein described, but is more usually 0.25% ~o 7.5%.
The presence of xanthan gum as part of the agueous dispersion ~f starch or o$her water-soluble polymers such as SCMC increases the resistance to flow of the dispersion and thus serves to control the rate at which the dispersion penetrates the paper after application.
It follows, therefore, that the presence of xanthan gum will keep the dispersion at or close ~o the surface of the paper ~ven when the paper contains high proportions of water such as occurs during the early s~ages of paper manufacture.
In the method of the invention it is envisaged that s~arch may be applied to paper or board by the method~
described herein so as to represen~ from 0.5% to 10% of the weight of ~he dried paper. It is also envisaged ~hat a rheology-affecting material, e.g. xanthan gum, may be present in sufficient quantity to prevent ~he starch settling out or i~s dispersions becoming dilatant and thus unsuitable for transportation through restricted orifices. It is also envisaged that so-called water-soluble polymers as described above may be applied to paper or board by the methods described herein in order to provide improvements to the paper or board or to augment the benefits of applying starch. It is envisaged that the starch and polymers may be blended ~ogether in the dry form; or by mixing together their respec~ive dispersions or solutions and then applying the resultan~ mixture by the methods herein described:
or by arranging for disperions or solutions of the respective ~aterials to be applied severally through two or more atomising distributors set so as to apply the respec~ive ma~erials a~ ~he most appropriate points of the paper- or board-making process.
While the invention has been defined above as a method of manufacture of paper or board, it will be appreciated ~hat the paper or board so manufactured is a further aspect of the invention. Such paper or board has been shown to have increased strength and improved surface qualities, as described below in the Examples given, which make it a more valuble commodity.
The invention also extends to intimate particulate mixtures of starch and one or more of the addi~ives as set forth above, capable of being jointly suspended or hydrated for use in the method. The starch/xanthan gum mixture is capable of long-term storage and reliable passage through application equipment described above and the SCMC solutions used alone or jointly with starch are particularly valuable.
The invention will be further described with reference to the following Examples:
ExamPle 1 (a~ Prior Art 100 grams of wheat starch were dispersed in 1000 ml water to form a slurry containing 10% starch solids at room temperature.
69~
~ ml of the above slurry were placed in the cylindrical container of a Brookfield SC-4 Adapter fitted ~ith the appropriate bob which was set to rotate at 20 revolutions per minute (rpm) and the temperature to rise from 20 degrees Celsius at a rate of 2 degree~
per minute by means of a thermos~atically controlled water circulator. Dial readings were taken continuously until the viscosity of the suspension had undergone a rapid rise indicating gelation. The dial readings were plotted on graph paper. By extrapolation, the gelation temperature wa~ judged to be 64 degrees Celsius.
(b) Addition of SCMC of_low DS
To 250 ml of the starch slurry prepared for the above were added 1.25 grammes of SCMC of molecular weight approximtely 100,000 and degree of carboxymethyl substitution 0.65, representing 5% by weight of the starch solids and 0.5% the total slurry/solution combination. The mixture was stirred mechanically for one hour. 8 ml of the mixture were placed in the cylinder of the BrooXfield SC-4 and the procedure described above was repeated. The extrapolated gelation temperature was judged to be 60 degrees C.
(c) Addition of SCMC of hiqher DS
To a further 250 ml of the original starch slurry were added 1.25 grammes of SCMC of similar molecular ~3~
weight to the SCMC used in Example (b) but with degree of substitution of 0.8 and ~he experiment repeated. In ~hi~ case the extrapolated gelation temperature was judged to be S9 degrees C.
(d) Addition of extra SCMC
To a further 250 ml of the original starch slurry were added 2.5 grammes of the SCMC used in Example (c), representing 10% by weight of the starch solids and 1.0 o the total dispersion. The experiment was repeated and the gelation temperature judged to be ~8 degrees C.
~ .
The above experiments have indicated an unexpected reduction in the gelation temperature or starch suspension as exemplified ~y the rapid rise in viscosity over a narrow range of temperature. This is interpreted as a form of co-solvency which is more apparent when the SCMC has a grea~er degree of 6ubstitution and so possesses a greater affinity for 20 water. Thus, when water plus such SCMC enters starch sranules during the early stages of granule rupture, the natural tendency of SCMC molecules to uncoil and expand assists the rupture of ~he granules at lower temperatures ~han would happen if SCMC were not present.
~23~i~
A redu~ion in ~he temperature at which starch gels and so is rendered capable of formi~g a more or less continuous film within the structure of the paper ~eb is a benefit to ~hose making paper since it is to be expected that the hea~ energy required to attain gelation will be reduced; addi~ionally, ~he gelation will ~ake place at an earlier stage in the drying section of the pape~-making process, thus allowing more time for the beneficial interactions between starch and cellulose fibres to take place.
ExamP1~ 2 Rheoloaical Effect of Xanthan Gum (SusPension Stabilit (a) 38% Starch Solids SlurrY
Z50 ml quantities of a commercial starch slurry know~ as Tenstar AB manufactured by Ranks Hovis MacDougall Ltd., by wet-milling of wheat and constituting a never-dried starch slurry containing 38% by weight of wheat starch solids were treated with several additions of xanthan gum. The amount of settlement or sedimentation of the starch was judged by noting the volume of clear liquid appearing in the upper part of the fluid when stored in 250 ml graduated glass cylinders over periods of several days. The results were noted and shown in Table 2 below.
r~~ k ~z~
Table 2 38% Tenstar Starch Slurry Per cent xanthan gum Volume of Clear Liguid (ml) (on total volume) 1 day 8 daY5 7 davs 14 davs 0.0 0 5 10 25 0.10 0 0 5 10 0.15 0.20 0 0 0 0 (b) 18% Starch Solids Slurrv The procedure described in Example 2(a) was repeated with another never-dried commercial starch slurry known a~
Staper Starch obtained by wet-milling cereals and contain-ing 18% starch solids. The results are shown in Table 3.
Table ~
Per cent Xanthan Gum Volume of Clear Liquid (ml) 15 (on total volume) 1 daY3 days 7 days 14 daYs 0.0 120 140 170 180 0.10 50 70 110 150 0.15 20 40 60 70 0.20 0 0 0 0 (Note: The slurries used in the above experiments were treated with 0.2% dichlorophen in order to prevent microbiological interference with the starch and polymer dispersions).
The results of the above experiments indicate that xanthan gum addi~ion to commercial slurries of starch ~5864 has the beneficial effect of preventing settlement of the starch particles and so provides the benefi~ of long-term storage without the neeessity for continuou~
agitation as is the case of the prior art.
ExamPle 3 (a) ffec~ on Strenath of Hand Made PaPer Blends of starch combined with sodium carboxymethyl cellulose and/or xanthan gum were prepared as shown in Table 4.
Table 4 BLEND Starch SCMC DS 0.65 SCMC DS 0.85 Xanthan Gum 15 D 99.6 0 0 0.4 E 95.6 0 4 0.4 F 95.6 4 0 0.4 ~ S0 Grammes of each blend were mixed into 750 ml water so as to form 25% w/v slurries which were used to spray on to hand-made paper as it was being formed. The spray was arranged so as to deliver 0.7 ml on each occasion which, on paper sheets of nominal 3.7 grammes dry weight, is equivalent to 4.7% add-on of dry starch or blend to dry paper.
The paper furnish was bleached kraft with neutral ca~ionic retention aid. Af~er drying and calendering, the sheets were tested for burst strength with a Mullen Tester~ The mean of 10 tests was recorded and compared with untreated paper made at ~he same time but sprayed with water in place of the starch slurry.
Table 5 Bleached kraft; 3.7 gramme ~heets; 4.7% starch add-on BLENDMullen Burst (PSi) % Chanqe NIL 14.2 0.0 A 15.7 +10.5 B 16.5 +16.5 C 17.0 +19.7 D 17.0 ~19.7 E 17.2 +21.1 F 17.5 +23.2 ~s~
The results of the experiments shown in Table 5 illustrate the beneficial effects of increasing the bursting strength of paper by adding starch; they further show the additional benefits derived from the addition of small proportions of polymers as described in this invention to the starch. The additional costs of making these additions are greatly outweighed by the commercial advantages to be gained by paper-makers making use of this invention.
Example 4 USE OF ATOMISING DISTRIBUTOR
An atomiser as described in ~his invention was set above the wire part of a Foudrinier paper-making machine so as to distribute a slurry prepared by dilution of a commercial starch slurry into which had been introduced SMCM and xanthan gum immediately following manufacture of the slurry as a by-product of a process to extract other components of milled whea~. The proportions of materials used in this Example were:
20 Stàrch Slurry Wheat starch solids 380 Kg SCMC 18 Kg Xanthan gum 2 Kg Water 600 Kg ~6~
The paper-making machine had been set to produce 40 Kg of paper of a weight of 35 grammes per square metre per minute at a speed of 400 metres per minute. The paper-making machine furnish contained 1.5% dry basis of a commercial cationic stalch acting partly as a me~hod of providing the required burst s~reng~h and par~ly to aid drainage as well as retention of fibres on the wire part of ~he machine. Slurry of the above composition was pumped through a flowmeter at 1.5 litres per minute, representing 0.57 Kg starch solids per minute, i.e. 1.4 of the paper dry weight. The slurry passed through an in-line diluter in which it was mixed wi~h water separately pumped at 5 litres per minute. The resultant 6.5 li~res per minute of diluted slurry was passed through an atomiser as herein described driven by an air motor set to run at 5000 revolutions per minute producing droplets of 500 micrometres mean diameter.
The slurry was applied to the paper over a 30 hour period, samples being taken at approximately hourly intervals. During the period, ~he cationic starch addition to the furnish was progressively reduced to zero in order to make a comparison of this invention with a well-known and hither~o acceptable method of improving paper guality by the addition of a starch-based product to the paper-making machine furnish. Random results of this experiment are shown in Table 6.
Table 6 Selec~0d waste + bleached kraft; 50 grammes/sg.
metre; 1.4% starch add-on SAMPLE MULLEN BURST % CHANGE TENSILE STRENGTH ~ CHANGE
RATI0* (psi) (Psi) cationic starch 1.~%
LlankZ.80 0.0 56 0.0
dist~ibution.
It is well known that the viscosity of solutions of some poly~eric substances falls off more rapidly than others as ~he rate of shear or the rate of flow through a given orifice i6 increased. This is illustrated in the following Table in which the viscosities in water of several well-known high viscosity polymeric substances are comparPd over a range of rates of shear; the respecti~e viscosities and rates of shear were measured with a Broo~field Viscometer fitted with a concentric bob and cylinder attachment sold under the designation SC4 Small Sample Adapter:-Shear Rate Polymer* Viscosit~ tcentipoises) ~ 20 deq C
CMC1~000 1300084006000 43003000 l900 1400 HEC8000 6500 50003800 2700l900 llO0 GGllO0 9100 58003900 24001500 700 XG32000 170Q0 75003800 l900llO0 450 240 ~C660 550 480430 400 340 2~0 210 .
The present invention has discovered ~hat if a minor proportion o a 6ubs~ance capable of pro~idingaqueous solutions of high pseudoplas~icity is added ~o starch powder or incorpora~ed into a suspension of starch, it renders the starch capable of being stored for prolonged periods in aqueous suspension; of being capable of being transported through re6tricted orifices without giving rise to dilatancy; and i~s suspensions of being readily transformed into droplets of sufficiently small size to enable ~hem to be used as a means of applying starch uniformly to surfaces including surfaces of paper during manufacture.
Preferred polymers for the rheology-affecting purpose are xanthan gum and similar polysaccharides capable of dissolving in wa~er to produce solutions possessing very high viscosity at low rates of shear compared with other commerically available polymers but a relatively low viscosity at high rate of shear; this is illustrated in Table 1. Solutions of xanthan gum show little variation in their physical properties.
including rheology, over temperature ranges normally experienced in paper mills and o~har closed industrial premises: these properties also show neglible variations when ionic and other dissolved substances are present with the xanthan gum. This is especially important when water of unknown composition is used to prepare the starch suspensions e.g. when recycled water of differing degrees of hardness or with differing salt contents and at varying temperature is used in such preparations.
~z~
The rheology-affecting properties of xanthan gum are of particular importance if it is desired to apply starch in the form of a suspension or slurry in water since the presence of the xanthan gum in the suspension greatly reduces the tendency of starch particles ts settle out or form intractable sediments. The presence of xanthan gum in a s~arch suspension as described in ~his inven~ion allows users to store such suspensions for prolonged psriods and enables users ~o transport the ~tarch in the form of slurry to its eventual destination without the necessity to install special agitation equipment in the slurry containers used for transport and storage of the slurry. The convenience of being able to transport and store starch suspensions by the addition of xanthan gum is particularly importan~ in that such suspensions are available as residues produced ;n certain food-manufacturing processes: it is economically advantageous to be able to supply the starch in the suspension or slurry form in which it is produced rather than to extract and dry the starch and subsequently have to re-form the suspension before use.
This invention procides an economic method of storing and transporting such starch suspensions or slurries to the benefi~ of the starch and paper industries.
This invention has also discovered that ~he presence of xanthan gum in starch suspensions also overcomes the tendency of such suspensions to exhibit the phenomenon of dilatancy which can best be described as a rise in viscosi~y or resistance to flow as the rate of shear increases. Dilatancy is a condition to be avoided in handling starch and other ssspensions since dilatan~
fluids tend to cease flowing under conditions of high rates of shear such as occur inside pumps and control valves, restrictions and bends in pipes and in the noz~les of conventional spraying equipment. Therefore, the presence of xanthan gum in such suspensions serves to prevent the well-known and troublesome tendency of suspensions to cause blockages in the equipment used to carry them and, particularly, in the nozzles of conventional spray equipment.
The amount of weight of xanthan gum can vary between 0.025% and 1.0% of the water used to prepare the starch suspensions: in the case of suspensions prepared from dried, pow~er starch, the xanthan gum can be incorporated in the starch powder ~ogether with such other polymeric substances as may be desired so as to be present in the aforementioned proportions in the slurry during use. In the case of starch already prepared in suspension form a~ previously described, it is convenient to add the xanthan gum at an early stage in order to facilitate transport and prolonged storage.
The second aspect of this invention is concerned with ~he film-forming properties of certain polymers when dissolved or otherwise dispersed in water and applied in droplet form in a manner similar to that already described for the application of starch suspensions to paper or ~oard during manufacture. The preferred polymers are polysaccharides such as the alkali metal salts of carboxymethyl starches or of carboxymethyl celluloses or of alginic acid or of polyacrylic acid and their homologues, or (more preferably) the sodium salt of carboxymethyl cellulose commonly known as SCMC or CMC. The polymers may be applied with or without starch as herein described in order to provide different benefits to suit the requirements of users.
The carboxymethyl celluloses can have a degree of carboxyme~hylation of from 0.35 to 104 (i.e. related to the three labile hydroxy groups theoretically available for substitution in each anhydroglucose ring within the cellulose molecule chain) and total molecular weights from 15,000 to 80~,000, preferably 50,000 to 250,000.
It has been discovered in this invention that the presence of SCMC or the other polymers described in an aqueous starch dispersion has the effect of reducing the temperature a~ which starch particles rupture and form a gel (the gelation Temperature) as exemplified by a rapi~
increase in visc06ity. For example, 4 parts of SCMC of molecular weight approximately lO0,000 and degree of carboxymethylation of 0.85 were added to 16 parts of wheat starch. The effect was to reduce the gelation temperature of a 20% by weight starch suspension from 64 degreees Celsius to 59 degrees Celsius. This reduction in gelation temperature is important in the paper or board making processes in that it is known that low ~emperature gelation of starch improves the beneficial effects of adding starch to cellulose. Thus, the addition of such SCMC to starch is an important and hitherto unexpected method of improving the economy of operating the paper or board manufacturing processes.
The amount of these polymers, or mixtures thereof.
can vary up to 10% of the weight of the water used to carry the additives through a conventional spray or ~he atomisillg distributor as herein described, but is more usually 0.25% ~o 7.5%.
The presence of xanthan gum as part of the agueous dispersion ~f starch or o$her water-soluble polymers such as SCMC increases the resistance to flow of the dispersion and thus serves to control the rate at which the dispersion penetrates the paper after application.
It follows, therefore, that the presence of xanthan gum will keep the dispersion at or close ~o the surface of the paper ~ven when the paper contains high proportions of water such as occurs during the early s~ages of paper manufacture.
In the method of the invention it is envisaged that s~arch may be applied to paper or board by the method~
described herein so as to represen~ from 0.5% to 10% of the weight of ~he dried paper. It is also envisaged ~hat a rheology-affecting material, e.g. xanthan gum, may be present in sufficient quantity to prevent ~he starch settling out or i~s dispersions becoming dilatant and thus unsuitable for transportation through restricted orifices. It is also envisaged that so-called water-soluble polymers as described above may be applied to paper or board by the methods described herein in order to provide improvements to the paper or board or to augment the benefits of applying starch. It is envisaged that the starch and polymers may be blended ~ogether in the dry form; or by mixing together their respec~ive dispersions or solutions and then applying the resultan~ mixture by the methods herein described:
or by arranging for disperions or solutions of the respective ~aterials to be applied severally through two or more atomising distributors set so as to apply the respec~ive ma~erials a~ ~he most appropriate points of the paper- or board-making process.
While the invention has been defined above as a method of manufacture of paper or board, it will be appreciated ~hat the paper or board so manufactured is a further aspect of the invention. Such paper or board has been shown to have increased strength and improved surface qualities, as described below in the Examples given, which make it a more valuble commodity.
The invention also extends to intimate particulate mixtures of starch and one or more of the addi~ives as set forth above, capable of being jointly suspended or hydrated for use in the method. The starch/xanthan gum mixture is capable of long-term storage and reliable passage through application equipment described above and the SCMC solutions used alone or jointly with starch are particularly valuable.
The invention will be further described with reference to the following Examples:
ExamPle 1 (a~ Prior Art 100 grams of wheat starch were dispersed in 1000 ml water to form a slurry containing 10% starch solids at room temperature.
69~
~ ml of the above slurry were placed in the cylindrical container of a Brookfield SC-4 Adapter fitted ~ith the appropriate bob which was set to rotate at 20 revolutions per minute (rpm) and the temperature to rise from 20 degrees Celsius at a rate of 2 degree~
per minute by means of a thermos~atically controlled water circulator. Dial readings were taken continuously until the viscosity of the suspension had undergone a rapid rise indicating gelation. The dial readings were plotted on graph paper. By extrapolation, the gelation temperature wa~ judged to be 64 degrees Celsius.
(b) Addition of SCMC of_low DS
To 250 ml of the starch slurry prepared for the above were added 1.25 grammes of SCMC of molecular weight approximtely 100,000 and degree of carboxymethyl substitution 0.65, representing 5% by weight of the starch solids and 0.5% the total slurry/solution combination. The mixture was stirred mechanically for one hour. 8 ml of the mixture were placed in the cylinder of the BrooXfield SC-4 and the procedure described above was repeated. The extrapolated gelation temperature was judged to be 60 degrees C.
(c) Addition of SCMC of hiqher DS
To a further 250 ml of the original starch slurry were added 1.25 grammes of SCMC of similar molecular ~3~
weight to the SCMC used in Example (b) but with degree of substitution of 0.8 and ~he experiment repeated. In ~hi~ case the extrapolated gelation temperature was judged to be S9 degrees C.
(d) Addition of extra SCMC
To a further 250 ml of the original starch slurry were added 2.5 grammes of the SCMC used in Example (c), representing 10% by weight of the starch solids and 1.0 o the total dispersion. The experiment was repeated and the gelation temperature judged to be ~8 degrees C.
~ .
The above experiments have indicated an unexpected reduction in the gelation temperature or starch suspension as exemplified ~y the rapid rise in viscosity over a narrow range of temperature. This is interpreted as a form of co-solvency which is more apparent when the SCMC has a grea~er degree of 6ubstitution and so possesses a greater affinity for 20 water. Thus, when water plus such SCMC enters starch sranules during the early stages of granule rupture, the natural tendency of SCMC molecules to uncoil and expand assists the rupture of ~he granules at lower temperatures ~han would happen if SCMC were not present.
~23~i~
A redu~ion in ~he temperature at which starch gels and so is rendered capable of formi~g a more or less continuous film within the structure of the paper ~eb is a benefit to ~hose making paper since it is to be expected that the hea~ energy required to attain gelation will be reduced; addi~ionally, ~he gelation will ~ake place at an earlier stage in the drying section of the pape~-making process, thus allowing more time for the beneficial interactions between starch and cellulose fibres to take place.
ExamP1~ 2 Rheoloaical Effect of Xanthan Gum (SusPension Stabilit (a) 38% Starch Solids SlurrY
Z50 ml quantities of a commercial starch slurry know~ as Tenstar AB manufactured by Ranks Hovis MacDougall Ltd., by wet-milling of wheat and constituting a never-dried starch slurry containing 38% by weight of wheat starch solids were treated with several additions of xanthan gum. The amount of settlement or sedimentation of the starch was judged by noting the volume of clear liquid appearing in the upper part of the fluid when stored in 250 ml graduated glass cylinders over periods of several days. The results were noted and shown in Table 2 below.
r~~ k ~z~
Table 2 38% Tenstar Starch Slurry Per cent xanthan gum Volume of Clear Liguid (ml) (on total volume) 1 day 8 daY5 7 davs 14 davs 0.0 0 5 10 25 0.10 0 0 5 10 0.15 0.20 0 0 0 0 (b) 18% Starch Solids Slurrv The procedure described in Example 2(a) was repeated with another never-dried commercial starch slurry known a~
Staper Starch obtained by wet-milling cereals and contain-ing 18% starch solids. The results are shown in Table 3.
Table ~
Per cent Xanthan Gum Volume of Clear Liquid (ml) 15 (on total volume) 1 daY3 days 7 days 14 daYs 0.0 120 140 170 180 0.10 50 70 110 150 0.15 20 40 60 70 0.20 0 0 0 0 (Note: The slurries used in the above experiments were treated with 0.2% dichlorophen in order to prevent microbiological interference with the starch and polymer dispersions).
The results of the above experiments indicate that xanthan gum addi~ion to commercial slurries of starch ~5864 has the beneficial effect of preventing settlement of the starch particles and so provides the benefi~ of long-term storage without the neeessity for continuou~
agitation as is the case of the prior art.
ExamPle 3 (a) ffec~ on Strenath of Hand Made PaPer Blends of starch combined with sodium carboxymethyl cellulose and/or xanthan gum were prepared as shown in Table 4.
Table 4 BLEND Starch SCMC DS 0.65 SCMC DS 0.85 Xanthan Gum 15 D 99.6 0 0 0.4 E 95.6 0 4 0.4 F 95.6 4 0 0.4 ~ S0 Grammes of each blend were mixed into 750 ml water so as to form 25% w/v slurries which were used to spray on to hand-made paper as it was being formed. The spray was arranged so as to deliver 0.7 ml on each occasion which, on paper sheets of nominal 3.7 grammes dry weight, is equivalent to 4.7% add-on of dry starch or blend to dry paper.
The paper furnish was bleached kraft with neutral ca~ionic retention aid. Af~er drying and calendering, the sheets were tested for burst strength with a Mullen Tester~ The mean of 10 tests was recorded and compared with untreated paper made at ~he same time but sprayed with water in place of the starch slurry.
Table 5 Bleached kraft; 3.7 gramme ~heets; 4.7% starch add-on BLENDMullen Burst (PSi) % Chanqe NIL 14.2 0.0 A 15.7 +10.5 B 16.5 +16.5 C 17.0 +19.7 D 17.0 ~19.7 E 17.2 +21.1 F 17.5 +23.2 ~s~
The results of the experiments shown in Table 5 illustrate the beneficial effects of increasing the bursting strength of paper by adding starch; they further show the additional benefits derived from the addition of small proportions of polymers as described in this invention to the starch. The additional costs of making these additions are greatly outweighed by the commercial advantages to be gained by paper-makers making use of this invention.
Example 4 USE OF ATOMISING DISTRIBUTOR
An atomiser as described in ~his invention was set above the wire part of a Foudrinier paper-making machine so as to distribute a slurry prepared by dilution of a commercial starch slurry into which had been introduced SMCM and xanthan gum immediately following manufacture of the slurry as a by-product of a process to extract other components of milled whea~. The proportions of materials used in this Example were:
20 Stàrch Slurry Wheat starch solids 380 Kg SCMC 18 Kg Xanthan gum 2 Kg Water 600 Kg ~6~
The paper-making machine had been set to produce 40 Kg of paper of a weight of 35 grammes per square metre per minute at a speed of 400 metres per minute. The paper-making machine furnish contained 1.5% dry basis of a commercial cationic stalch acting partly as a me~hod of providing the required burst s~reng~h and par~ly to aid drainage as well as retention of fibres on the wire part of ~he machine. Slurry of the above composition was pumped through a flowmeter at 1.5 litres per minute, representing 0.57 Kg starch solids per minute, i.e. 1.4 of the paper dry weight. The slurry passed through an in-line diluter in which it was mixed wi~h water separately pumped at 5 litres per minute. The resultant 6.5 li~res per minute of diluted slurry was passed through an atomiser as herein described driven by an air motor set to run at 5000 revolutions per minute producing droplets of 500 micrometres mean diameter.
The slurry was applied to the paper over a 30 hour period, samples being taken at approximately hourly intervals. During the period, ~he cationic starch addition to the furnish was progressively reduced to zero in order to make a comparison of this invention with a well-known and hither~o acceptable method of improving paper guality by the addition of a starch-based product to the paper-making machine furnish. Random results of this experiment are shown in Table 6.
Table 6 Selec~0d waste + bleached kraft; 50 grammes/sg.
metre; 1.4% starch add-on SAMPLE MULLEN BURST % CHANGE TENSILE STRENGTH ~ CHANGE
RATI0* (psi) (Psi) cationic starch 1.~%
LlankZ.80 0.0 56 0.0
3.~0 +14 57 +1.8 cationic starch reduced to 0.8~
B3.41 +22 60 +6.7 C3.36 +20 62 +g.7 D3.33 ~19 59 +5.4 Cationic starch reduced to zero E3.46 ~24 56 0.0 F3.52 ~26 56 0.0 _ * The parameter "~ullen Burst Ratio" (MEiR) is defined as:-MB
~qBR = GSM
where: MB = the pres6ure in pounds per square inchrequired to burst a sample of paper in the ~ell-known Mullen Tester used throughout the paper-making industry;
GSM = the weight in gramme o~ one square metre of paper .
Thus, the "Mullen Burst Ratio" can be used to elimina~e minor variations in paper weight which ~ould 0 otherwise affec~ the results of the burst test.
The results show tha~ the addition sf starch increa6ed the burst strength of paper already containing a streng~h-increasing additi~e; furthermore, the Mullen Burst Strength Ratio increased still further as the 15 previously used strength-increasing additive was progressively reduced to zero. Therefore, the addition of starch modif ied as described in this invention and applied in the form of small droplets to paper during p oduction on a paper-making machine can produce better 20 results ~han another ~ype of starch hitherto regarded as acceptable by ~chose skilled in the art of manufacturing paper .
The results also show that the addition of starch modified as described above and applied to paper during the early stages of manufacture enhances the tensile strength of paper to which had already been added a tensile streng~h incrasing additive, i.e. cationic starch.
ExamPle 5 Addition of SCMC to Paper durinq manufacture usina the atomiser A dispersion of SCMC was applied to paper using the atomiser and flowmetering equipment described in Example
B3.41 +22 60 +6.7 C3.36 +20 62 +g.7 D3.33 ~19 59 +5.4 Cationic starch reduced to zero E3.46 ~24 56 0.0 F3.52 ~26 56 0.0 _ * The parameter "~ullen Burst Ratio" (MEiR) is defined as:-MB
~qBR = GSM
where: MB = the pres6ure in pounds per square inchrequired to burst a sample of paper in the ~ell-known Mullen Tester used throughout the paper-making industry;
GSM = the weight in gramme o~ one square metre of paper .
Thus, the "Mullen Burst Ratio" can be used to elimina~e minor variations in paper weight which ~ould 0 otherwise affec~ the results of the burst test.
The results show tha~ the addition sf starch increa6ed the burst strength of paper already containing a streng~h-increasing additi~e; furthermore, the Mullen Burst Strength Ratio increased still further as the 15 previously used strength-increasing additive was progressively reduced to zero. Therefore, the addition of starch modif ied as described in this invention and applied in the form of small droplets to paper during p oduction on a paper-making machine can produce better 20 results ~han another ~ype of starch hitherto regarded as acceptable by ~chose skilled in the art of manufacturing paper .
The results also show that the addition of starch modified as described above and applied to paper during the early stages of manufacture enhances the tensile strength of paper to which had already been added a tensile streng~h incrasing additive, i.e. cationic starch.
ExamPle 5 Addition of SCMC to Paper durinq manufacture usina the atomiser A dispersion of SCMC was applied to paper using the atomiser and flowmetering equipment described in Example
4. In this Example the modified starch slurry used in Example 4 was replaced by an aqueous solution of SCMC of molecular weight approximately 100,000 and degree of carboxymethyl substitution of 0.85, containing 20 grammes of dry SCMC per litre of solution. As in Example 4, the paper-making machine was set ~o produce 40 Kg of dry paper per minute. The rate of flow of the SCMC solution was adjusted to 5 litres per minute, representing an addi~ion rate of 0.25% of SCMC ~o the dry paper produced.
Results of this experiment are shown in Table 7:-~z::3586;4 Table 7 Sele~ted wa~t~ t blaached kraft; 50 grammes/sg. metre;
0.25% SCMC add-on; no starch -SCMC MULL~N BURST RATI0 ~ CHANGE TENSILE STRENGTH %CHANGE
% (psi! (Psil 0.0 2.80 0.0 56 0.0 0.~5 3.46 +23.6 57 +1.~
The results shown in Table 7 illustrate the benefits of applying as little as 0.25% SCMC of relatively low molecular weight and h;gh degree of carboxymethyl 6ubst~tution to paper by means oE the atomiser herein described during the early stages o~ manuEacture.
v~ri~ m~ t.lv~ d ~dditl~ m~y b~ made to the invention as defined above.
For example, the incorporation of the special atomisers into the machinery used in the manufacture of paper or board (as described above in relation to the spraying sf starch suspensions and solutions such as those of SCMC) gives the possibility of the operation of the machinery by the selective or additional use of such atomisers in respect of other suspensions or solutions.
For example, such atomisers may be used with sizing agents whether in the form of solutions, emulsions or suspensions. They may also be used with colouring materials whether in the form of soluble dyes or insoluble pigment suspensions. They may also be used with oil~ materials, e.g. as applied to waterproof or otherwise mo~ify ~he paper. They may also be used with liquid forms of reactive resins as added to paper in order to increase the wet strength or resistance to water of the dried paper: in this aspect the use of two or more atomisers arranged above the wire part of a paper-making machine permits the application of several materials which may, by physical or chemical interaction with each other and the paper to which they are applied, provide further benefits.
By adjusting the position of the atomiser along the wire part of the paper-making machine it is envisaged that the degree of penetration of the applied ma~erial may be controlled. For example, applying the material at positions where the water content of the paper is high allows such materials to penetrate the body of the paper and so become an integral part of the paper:
~23~
conversely, application at points where the water content has been reduced by drainage, suction or the application of heat allows the materials to be held at the surface of the paper and 50 become concen~rated at or near the surface.
It is also envisaged that the atomisers may be used to apply coatings to paper after the end of the drying part of the process: in this case, the atomiser6 could form part of the specialised machinery used to apply pigments, resins, waxes, colouring matter or various solu~ions to the surface of the paper.
The advantage of separating the size of droplets from the rate of flow, once incorporated into ~he machinery in respect of the starch suspensions and SCMC
solutions as described, is of general utility throughout the process of making paper of commercial value. It is envisaged that the atomisers in question will either be connec~ed for selective alternative use, or that a succession of atomise{s will be provided at different points of the flow path in paper production and that the necessary solutions or suspensions will be in permanent communication wi~h such atomisers for instant use when desired.
Results of this experiment are shown in Table 7:-~z::3586;4 Table 7 Sele~ted wa~t~ t blaached kraft; 50 grammes/sg. metre;
0.25% SCMC add-on; no starch -SCMC MULL~N BURST RATI0 ~ CHANGE TENSILE STRENGTH %CHANGE
% (psi! (Psil 0.0 2.80 0.0 56 0.0 0.~5 3.46 +23.6 57 +1.~
The results shown in Table 7 illustrate the benefits of applying as little as 0.25% SCMC of relatively low molecular weight and h;gh degree of carboxymethyl 6ubst~tution to paper by means oE the atomiser herein described during the early stages o~ manuEacture.
v~ri~ m~ t.lv~ d ~dditl~ m~y b~ made to the invention as defined above.
For example, the incorporation of the special atomisers into the machinery used in the manufacture of paper or board (as described above in relation to the spraying sf starch suspensions and solutions such as those of SCMC) gives the possibility of the operation of the machinery by the selective or additional use of such atomisers in respect of other suspensions or solutions.
For example, such atomisers may be used with sizing agents whether in the form of solutions, emulsions or suspensions. They may also be used with colouring materials whether in the form of soluble dyes or insoluble pigment suspensions. They may also be used with oil~ materials, e.g. as applied to waterproof or otherwise mo~ify ~he paper. They may also be used with liquid forms of reactive resins as added to paper in order to increase the wet strength or resistance to water of the dried paper: in this aspect the use of two or more atomisers arranged above the wire part of a paper-making machine permits the application of several materials which may, by physical or chemical interaction with each other and the paper to which they are applied, provide further benefits.
By adjusting the position of the atomiser along the wire part of the paper-making machine it is envisaged that the degree of penetration of the applied ma~erial may be controlled. For example, applying the material at positions where the water content of the paper is high allows such materials to penetrate the body of the paper and so become an integral part of the paper:
~23~
conversely, application at points where the water content has been reduced by drainage, suction or the application of heat allows the materials to be held at the surface of the paper and 50 become concen~rated at or near the surface.
It is also envisaged that the atomisers may be used to apply coatings to paper after the end of the drying part of the process: in this case, the atomiser6 could form part of the specialised machinery used to apply pigments, resins, waxes, colouring matter or various solu~ions to the surface of the paper.
The advantage of separating the size of droplets from the rate of flow, once incorporated into ~he machinery in respect of the starch suspensions and SCMC
solutions as described, is of general utility throughout the process of making paper of commercial value. It is envisaged that the atomisers in question will either be connec~ed for selective alternative use, or that a succession of atomise{s will be provided at different points of the flow path in paper production and that the necessary solutions or suspensions will be in permanent communication wi~h such atomisers for instant use when desired.
Claims (15)
PRIVILEGE OR PROPERTY IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A composition for use in improving the strength of paper or board, comprising an aqueous suspension of uncooked starch, xanthan gum in a quantity effective to prevent dilatancy and to increase the viscosity of the suspension so as substantially to prevent settlement of starch particles during storage and transportation, and a water-soluble polymer capable of forming a continuous film on application of the composition to paper or board.
2. A composition as claimed in claim 1 in which the xanthan gum is present in an amount of from 0.025%
to 1.0% by weight on the weight of water in the starch suspension.
to 1.0% by weight on the weight of water in the starch suspension.
3. A composition as claimed in claim 1 in which the water-soluble film-forming polymer is selected from the alkali metal salts of carboxymethyl starches, carboxy-methyl celluloses, alginic acid, and polyacrylic acid, and their homologues.
4.. A composition according to claim 3 in which the film-forming polymer comprises sodium carboxymethyl cellulose having a degree of carboxymethylation of from 0.35 to 1.4 and a molecular weight of from 15,000 to 800,000.
5. A composition as claimed in claim 4 in which the sodium carboxymethyl cellulose has a molecular weight of from 50,000 to 250,000.
6. A composition according to claim 1, 2 or 3 in which the suspension contains the water-soluble film-forming polymer in an amount of from 0.25 to 7.5% by weight of water in said suspension.
7. A composition as claimed in claim 1 in which the aqueous suspension of starch is a residue produced in a food-manufacturing process without subsequent extract-ion or drying of the starch.
8. A composition as claimed in claim 7 in which the aqueous suspension of starch is a never-dried starch slurry product of wet-milling cereals.
9. A method of making a composition as claimed in claim 1 compring adding xanthan gum and a water-soluble polymer capable of forming a continuous film on paper or board in the presence of xanthan gum and starch to an aqueous suspension of uncooked starch.
10. A method of obtaining a composition as claimed in claim 7 comprising recovering an aqueous suspension or slurry of starch as a residue in a food-manufacturing process, adding to the suspension or slurry without inter-mediate drying or extraction of the starch a water-soluble film-forming polymer and xanthan gum, and storing and/or transporting the resulting composition.
11. In a method of making paper or board the improve-ment comprising applying to the web of fibres during or after formation (a) an aqueous suspension of uncooked starch containing xanthan gum in a quantity effective to prevent dilatancy and to increase the viscosity of the suspension so as substantially to prevent settlement of starch particles and (b) a water-soluble polymer capable of forming a continuous film on application to paper or board in the presence of the starch and xanthan gum, where-by the inter-fibre bonding and thus the strength of the paper or board are improved.
12. A method as claimed in claim 11 in which a com-position is used comprising an aqueous suspension of starch containing from 0.025% to 1.0% by weight of xanthan gum and from 0.25 to 7.5% by weight of water-soluble film-forming polymer, based on the weight of water in the starch suspen-sion.
13. A method as claimed in claim 11 in which the film-forming polymer is selected from the alkali metal salts of carboxymethyl starches, carboxymethyl celluloses, alginic acid, and polyacrylic acid, and their homologues.
14. A method as claimed in claim 11 in which the aqueous suspension of starch is a never-dried uncooked starch suspension produced as a residue in a food manu-facturing process.
15. A method as claimed in claim 11 in which an aqueous suspension of uncooked starch containing the xanthan gum and the film-forming polymer is applied by means of a rotary atomiser to the web of fibres after formation.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000467253A CA1235864A (en) | 1984-11-07 | 1984-11-07 | Paper and board manufacture |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000467253A CA1235864A (en) | 1984-11-07 | 1984-11-07 | Paper and board manufacture |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1235864A true CA1235864A (en) | 1988-05-03 |
Family
ID=4129099
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000467253A Expired CA1235864A (en) | 1984-11-07 | 1984-11-07 | Paper and board manufacture |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1235864A (en) |
-
1984
- 1984-11-07 CA CA000467253A patent/CA1235864A/en not_active Expired
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| EP0151578B1 (en) | Improvements in paper and board manufacture | |
| CN104284945B (en) | Process calcium carbonate material to increase the loading of the filler in paper | |
| US5080717A (en) | Fluid suspensions of polysaccharide mixtures | |
| CN101743356B (en) | Filler composition | |
| TWI525235B (en) | Process for preparing self-binding pigment particles, self-binding pigment particle suspensions obtainable thereof, paper products comprising self-binding pigment particles and the use of the self-binding pigment particle suspensions | |
| EP1492923B1 (en) | Swollen starch-latex compositions for use in papermaking | |
| AU673603B2 (en) | Fine aqueous dispersion of an organophilic sheet silicate | |
| US4799964A (en) | Preparation of filler compositions for paper | |
| EP0738303B1 (en) | Treatment of inorganic filler material for paper with polysaccharides | |
| EP2569483A1 (en) | A process for the production of a composition comprising fibrillated cellulose and a composition | |
| CN103590283A (en) | Coating and coating used coated paper | |
| CN107407054A (en) | A kind of papermaking process for increasing paper products ash content and the paper products obtained by this method | |
| CN101802303B (en) | Paper making compositions and processes using protein particulate, colloidal pigment, and latex polymer combinations | |
| JP2001510251A (en) | Paper products containing filling materials | |
| CA1235864A (en) | Paper and board manufacture | |
| US6156117A (en) | Polymer structured clay pigment and method of preparing the same | |
| CA3068941A1 (en) | Dosing of nanocellulose suspension in gel phase | |
| CA1230525A (en) | Starch distribution by rotary applicator in paper or board manufacture | |
| JPS61113896A (en) | Improvement in production of paper and corrugated board | |
| NO844424L (en) | IMPROVED PAPER AND CARTON MANUFACTURING. | |
| NO844425L (en) | IMPROVED PAPER AND CARTON MANUFACTURING. | |
| CA1306084C (en) | Preparation of filler compositions for paper | |
| Bergh | Starches | |
| NO141618B (en) | PROCEDURE FOR PREPARING A FILL FOR USE IN PAPER MAKING | |
| US3288630A (en) | Process for coating cellulosic substrates |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |