GB2201171A - Compositions for use in the treatment of cellulosic and their preparation - Google Patents

Abstract

Sizing agents may be added to the paper-making process in microencapsulated form. This provides a protection from the hydrolysis often experienced with sizing agents in emulsion form and offers a low energy route to incorporation in the paper-making process. Microencapsulation may be by coacervation, complex coacervation or interfacial polymerisation to produce microcapsules of a size and wall material compatible with the paper making process. Examples of sizing-agents which may be encapsulated are the anhydride sizing agents and the ketene dimer sizing agents.

Description

Compositions for use in the treatment of cellulosic materials and their preparation This invention relates to compositions for use in the treatment of cellulosic materials and to methods for the production and the use of such compositions.

More particularly, but without limitation thereto, the present invention relates to paper or paperboard sizing compositions and to methods for the production and the use of such sizing compositions.

In the manufacture of paper or paper-board from cellulosic pulps, or in the manufacture of articles composed of or comprising cellulosic fibres, it is common practice where decreased liquid adsorbency is required in the finished product to include with the cellulosic pulp or on the surface of a paper web before the final calendering process materials known as sizing agents. The use of sizing agents can, for example, reduce the spread of inks used to print the finished product, or to render it water impermeable, and may also result in increased strength and an improved appearance.

Sizing agents which are in common use are the aluminium sulphate-rosin sizes in which separate aqueous dispersions of rosin or rosin derivatives and of aluminium sulphate are added to a paper pulp in which they react to form aluminium rosinates which coat the cellulose fibres. Another example of commonly used sizing agents are wax emulsions which may be used alone or subsequent to a rosin-aluminium sulphate size.

Cellulose reactive sizing agents have been under active development in recent years. These sizing agents contain functional groups'which react directly with functional groups present in the molecular structure of the cellulose and result in a very efficient sizing effect.

Such sizes are generally usable under alkaline conditions which gives increased scope for the development of alkaline paper-making processes, for example in the use of alkaline fillers therein. These cellulose reactive sizing agents are generally applied in the form of emulsions. Some families of cellulose reactive sizes, for example the alkyl ketene dimers of long chain fatty acids, may be made into emulsions in which they are relatively stable and may have a shelf life of up to approximately 6 months. Some ketene dimer emulsions, or the above mentioned ketene dimer emulsions under certain conditions, exhibit some instability, for example due to hydrolysis in storage under relatively warm ambient conditions, or adjacent to warm process fluids or equipment. The hydrolysis products of the ketene dimers exhibit poor or relatively no sizing properties.Stable ketene dimer emulsions may also contain a relatively low concentration of the dimer resulting in high transport and handling costs.

Other families of cellulose-reactive sizes, notably those based on anhydrides of fatty acids, are relatively reactive with cellulosic material but are susceptible to hydrolysis to greater or lesser extents in aqueous emulsion and care has to be taken to make up such emulsions only as required for use to avoid deactivation of the sizing agent by hydrolysis before it can be placed into contact with the cellulose fibres.One very commonly used family of cellulose-reactive sizing agents, the alkenyl succinic anhydrides, while extremely effective are also extremely susceptible to hydrolysis making their effective use a real problem for paper-makers since when anhydride sizing agents in wholly or partly hydrolysed form are added to the papermaking process they cause the formation of sticky depositson paper-making machinery and on the paper-making wire and can have a negative effect on sizing which can outweigh the positive effect of the unhydrolysed remainder of the anhydride sizing agent resulting in an increase in the expected Cobb Test value.

Apart from the chemical problems noted above, the formation of emulsions from cellulose-reactive sizes can be an energy intensive process, possibly requiring rotational speeds in mixing equipment used in the formation of the emulsion of up to 20,000 revolutions per minute or the formulation of the sizing agents with other materials which assist in the emulsion forming process.

The present invention is directed to the addition of sizing agents to the papermaking process without the need for prior emulsion forming. The present. invention is further directed to the provision of compositions comprising cellulose-reactive sizes, for example ketene dimer or anhydride cellulose-reactive sizes, especially the alkenyl succinic anhydride sizes, in which compositions the size material is not readily susceptible to hydrolysis and which is therefore capable of storage or transport.

The present invention provides sizing agents, which may suitably be cellulose reactive sizing agents, for example those based on anhydrides and specially, the alkenyl succinic anhydride sizes, in microencapsulated form for use in papermaking processes and also provides methods for the production of the size-containing microcapsules and of compositions containing them.

Microencapsulated colour formers have been coated onto the surface of finished paper in the production of carbonless copying paper for very many years, examples of techniques suitable for the production of such microcapsules being described in, for example, United States Patent Nos. 2800457 and 2800458 of the National Cash Register Company. An example of a recent disclosure of the application of microencapsulated colour formers to the surface of finished paper is United Kingdom Patent Specification No. 2034782 of Fuji Photo Film Co Ltd.

Nevertheless there has been no conception that this technique could be applied to the inclusion of sizing agents in cellulosic pulps, or onto wet paper webs before the final calendering process, despite the widespread awareness of the problems of instability of certain sizing agents, as described above and the fact that such compounds have been known as sizing agents since the publication of United States Patent No. 3102064 which was issued to the National Starch and Chemical Corporation in 1963. Such instability is also described in the Kirk-Othmer Encyclopedia of Chemical Technology 3rd Edition, Vol 16 page 811 (1981) in the following passage "The alkenyl succinic anhydrides are so reactive that they must be used almost immediately after emulsification and, even then, rapid hydrolysis reduces efficiency".

While any technique may be utilised to produce the microcapsules of the present invention it is preferred that the technique be selected so that the wall material is compatible with the paper making process, that the capsules, if they act to release the sizing agent by rupture, are of a size which is similar to that of other solid paper ingredients, and that the method of release is one which is applicable to the paper-making environment.

Preferably the microencapsulation technique utilised according to the present invention is selected from the techniques of coacervation, interfacial polymerisation and interfacial polycondensation which are all suited to the encapsulation of normally liquid materials which the sizing agents either are, or may be formulated to be, for efficient dispersion on cellulosic material.

It is preferred to control the temperature and the duration of the contact between the sizing agent and any aqueous phase so that no substantial hydrolysis can take place. Preferably, therefore, the temperature of the sizing agent and of the aqueous phase is maintained at below 60 0C particularly preferably at below 450C for example very suitably from 50C to 350C but at any rate at least 10C and the duration of the said contact is preferably maintained at less than 30 minutes, particularly preferably at less than 20 minutes for example very suitably less than 5 minutes but at any rate at least 10 seconds for example from 10 seconds to 2 minutes.It will be recognised that temperature and time limitations are inter-related, it being possible to expose the core material to temperatures higher than those listed provided that contact time is very short i.e.-greater than 600C may be tolerated if duration is much less than 1 minute. A further qualification is that in determining actual contact time it is recognised that as the capsule wall forms the core material is increasingly protected from decomposition by substances present in the external liquid phase (e.g. alkaline substances). When capsule wall formation is substantially complete, therefore, the time taken for subsequent processing of the capsules in liquid media need not be counted towards total exposure time.

In the technique of coacervation a dissolved polymer is thrown out of solution in the presence of a dispersed insoluble material, the core material, which is preferentially wetted by the polymer. The means of throwing the polymer out of solution to form the capsule wall which is utilised may be a pH change, a temperature change, an electrolyte concentration change, or the addition of a nonsolvent for the polymer or by other means. The technique of coacervation may be applied to the formation of capsule walls including cellulose or carbohydrate derivatives which would be inherently compatible with cellulosic paper making materials.

A "complex" coacervation system may be used based on gelatin and gum arabic (acacia) polymers. This procedure is further described in "Microcapsule Processing and Technology" by A. Kondo and J.W. Van Valkenburg (Marcel Dekker Inc, 1979) pp. 75 and 76 and in the review article "Microcapsules: Their Preparation and Properties" by T.

Kondo in the series "Surface and Colloid Science" 1978, volume 10, chapter 1, page 6, and in "Microencapsulation and Related Drug Processes" by P.B. Deasy (Marcel Dekker Inc, 1984) pp. 68 and 69.

The polysaccharide gum arabic may be substituted either by natural materials of a similar nature such as guar or.

guaya gum or by chemically modified celluloses such as carboxymethyl cellulose.

Alternatively coacervation procedures based on methyl cellulose or cellulose acetate phthalate, as referred to in the above mentioned book by A. Kondo et al, p 90 may be used.

In the interfacial polymerisation technique a polymeric wall is formed by inter-reaction between a material dissolved in a dispersed core 'material and a material dissolved in the continuous phase. Suitable materials are selected from the combinations taught in the following Table.

Table I Monomer in Monomer in Wall of Aqueous phase oil phase microcapsule (a) polyamine polybasic acid chloride polyamide (b) polyol or polybasic polyphenol acid chloride polyester (c) polyamine bis-haloformate polyurethane (d) polyol or polyisocyanate polyurethane polyphenol (e) polyamine polyisocyanate polyurea In the case of each class of monomer, above, a range of materials may be used in the interfacial polymerisation technique. Usable polyamines include alpha, omega-diamino alkanes the alkanes being, for example ethane, propane, butane, pentane or hexane; piperazine, phenylene diamine; and also oligomers of ethyleneimine including diethylenetriamine and trimethylenetetramine and polymeric amines including polyethyleneimines and polypeptides.Such amines may be used singly or in combination, especially combinations of a diamine and a polyamine. Usable polybasic acid chlorides include aliphatic compounds such as azelayl and sebacoyl chlorides, and aromatic compounds suchas terephthaloyl, isophthaloyl and trimesoyl chloride. Usable polyols include ethanediol, propanediol and pentaerythritol, usable polyphenols include diphenylol propane (2,2-bis-(4'hydroxyphenyl)-propane) and diphenylolmethane.

The process of capsule formation by interfacial polymerisation may suitably be enhanced by the addition of small amounts of surfactants, particularly oil-soluble materials such as sorbitan trioleate or trilaurate.

Emulsification of the oil phase in the water phase may also be improved by known stabilising colloids such as polyvinyl alcohol or gum arabic.

Interfacial polymerisation techniques for polyamide wall formation are described in, for example, United States Patent No. 3577515, example 1 and for polyester wall formation, examples are given in the aforementioned book by A. Kondo, pp. 37-39 and in United States Patent 3660321, in which patent capsules are formed using terephthaloyl chloride and 2,2-bis-(4-hydroxyphenyl)-propane.

A technique related to interfacial polymerisation which may be used to form capsules suitable for use in the instant invention is interfacial polycondensation. In this technique, a polymeric pre-condensate is added to an oil phase which is then dispersed in the form of droplets in an aqueous phase. The aqueous phase contains an agent which brings about further polymerisation, insolubilisation, and/or cross-linking in the pre-condensate, and capsules having tough, impermeable walls result. A particularly important example of this technique involves a urea/formaldehyde precondensate hardened under acidic conditions, as described in British Patent No. 1042596 and in United States Patent No. 3516846, both to 3M Company, and in the aforementioned book by A. Kondo et al, page '50.

The microencapsulation techniques described above are believed to be particularly suited to the application of the instant invention, both because of their refinement in the hands of skilled practitioners to versatile and reliable methods for enclosing water-immiscible liquid core materials similar to those required by the instant invention, and also more particularly because of their ability to produce, capsules in the size range prescribed by the present invention.

Techniques of microencapsulation other than those described above are not excluded, however, and may be used insofar as they are able to produce capsules which conform to the requirements of the instant invention.

Preferably the microcapsules are from 0.2 to 50 microns, particularly preferably from 1 to 10 microns in diameter, for compatibility with other solid paper additives such as kaolin or chalk, and to give a suitably uniform sizing treatment to the paper.

The sizing material included within thetcapsules lay be any of those identified above. Very suitably however, anhydride sizing agents may be included in paper making process by this means. Examples of anhydride sizing agents are those having the general formula

wherein R represents a saturated 2 or 3-membered carbon chain completing the heterocyclic ring and being itself substituted by one or more hydrophobic aliphatic radicals R1, for example 10 to 30 carbon aliphatic radicals, which may be saturated or unsaturated,-and a radical R being optionally further substituted by one or more short chain aliphatic radicals containing less than 10 carbon atoms or by forming part of a 5 or 6 membered cycloaliphatic or aromatic ring, which short chain or ring radicals may alternatively bear said one or more hydrophobic radicals.

Preferably the radical R is the dimethylene or the trimethylene radical and the radical R1 is a 12 to 26 carbon aliphatic radical which may suitably be a lauryl, myristyl, palcetyl or stearyl radical. Alternatively, and particularly preferably, Pal is an alkenyl radical containing 12 to 26 carbon atoms for example dodecenyl, or octadecenyl radicals. Octadecenyl succinic anhydride is a commonly used paper sizing agent which is particularly suitable for use according to the present invention.

The above identified anhydride sizing agents may be produced for example by the reaction between maleic anhydride or glutaconic anhydride, or a suitably substituted derivative thereof, with a hydrocarbon radical corresponding to radical R1 by methods described, for example, in German Auslegeshrift No. 3404071 of Nippon Petrochemicals or U.S.

Patent Specification No. 4450281 of Chevron Research Company or by suitable modifications of such processes by those skilled in the art.

Ketene dimer sizing agents which may be utilised in microcapsule form according to the present invention are, for example, the aliphatic ketene dimers, the cycloalkyl ketene dimers or the aryl ketene dimers. The aliphatic ketene dimers may be alkyl ketene dimers which may contain C6 to C24 preferably C8 to C20 alkyl groups which may optionally be substituted and which may be saturated or unsaturated to give alkene orakenyl groups. Suitable aliphatic ketene dimers may be derived from mixtures of naturally occurring fatty acids. The cyclo-alkyl ketene dimers may be based on rings containing at least 6 cabon atoms which may, optionally, be substituted. The aryl ketene dimers may be based on 6 or 10 membered aromatic rings which may, optionally, be substituted.Examples of ketene dimers which may be utilised are the dodecyl cyclohexyl, phenyl, benzyl, naphthyl ketene dimers.

Liquid sizing agents may be used without dilution as the microcapsule core material according to this invention.

Alternatively such sizing agents, as well as normally solid or semiliquid sizing agents, may be diluted by, or dissolved in water-immiscible liquids such as aliphatic or aromatic hydrocarbons or fatty acid esters, or phthalic esters.

The sizing agent may also be formulated with other materials conventionally used in conjunction therewith, or in the paper making process, provided that the presence of such materials does not cause decomposition of the sizing agent within the microcapsule.

The effect of the present invention is to produce microcapsules which may be produced in suspension in an aqueous medium or as recovered solid capsules. These capsules may be stored or transported either as such or in an aqueous medium suitable for inclusion directly in the paper making process. In the case of sizing agents which are particularly susceptible to hydrolysis it may be desirable to recover and dry the micro7apsules to increase stability.

The suspension of capsules may be mixed directly in the pulp where they may be ruptured by the action of mixing machinery or very suitably, by the action of roller pressure and/or temperature when the paper web is being consolidated and dried. Alternatively the capsules may be applied directly to the surface of the paper web before it has been fully processed.

The invention will now be illustrated by reference to the following examples of specific embodiments thereof.

In the Examples the micro-encapsulation technique used was aqueous coacervation using as the shell material a 50/50 by weight mixture of gelatin and gum arabic. The microencapsulation equipment used was the M-Cap machine (M Cap is a Trade Name) of Insulated Technologies Corp which operates by pressurising the encapsulation mixture, subjecting the mixture- to shear and progressively releasing the pressure. This technique enables a short residence time to be used. The material microencapsulated was an anhydride type of sizing agent, specifically octadecenyl succinic anhydride.The shell material was formed into an emulsion by mixing 18g of that material in 500 ml of warm water (450- 500C) with stirring and the emulsion was cooled to below 350C (310-320C). 60g of the core material was mixed in and the mixture was immediately introduced into the microencapsulation machine, pressurised, for example to above 30 psig preferably from 50 to 100 psig and in this case to 70-75 psig, subjected to shear e.g. by passing it through a restricted orifice under pressure, and subjected to progressive pressure release, over a short period of time to reduce or avoid rupture of the capsules.While it is envisaged that the said period should preferably be controlled to achieve a residence time of the microencapsulation mixture below 5 minutes, particularly preferably below 2 minutes a residence time below 1 minute was used in the Examples. The pressure-released mixture was passed into an alkaline hardener bath (glutaraldehyde in water with added base) at ambient temperature and maintained there with stirring until the microcapsules had hardened.

In each example the capsules appeared of uniform size and shape.

The particular conditions used in the Examples were EX.1 Ex.2 Ex.3 Shell Acid-washed As Ex.l Base-washed material gelatin used gelatin Residence 45 sec As Ex.l 35 secs time Hardener 0.8g glutaral- As Ex.l ig glutaral dehyde 25% wt dehyde soln, 200 soln, 200 ml ml H2O 1 drop H2O, 1 drop NaQH NaOH soln 50% wt soln Duration in overnight As Ex.l 3 1/2 hours Hardener pH of adjusted to As Ex.l As Ex.l Hardener 7.5 8.0 8.5 Capsule size 2-10 2-10 2-5 range microns microns microns The microcapsules produced according to Examples 1-3 above, after ambient temperature storage for 8 weeks, were tested for sizing activity.

15 ml of the microcapsules were added to 100 mls of dichloromethane and stirred for 2 minutes. Pieces of unsized paper were immersed in the resulting solutions, with gentle agitation, for 5 minutes and were then removed, air dried, oven dried for 30 minutes at 1100 C and allowed to cool. A. Cobb test of sizing efficiency was carried out.

Untreated paper gave a test result of 540 whereas the papers treated with the products of Examples 1-3 gave results as follows : Ex.l 356 Ex.2 154 Ex.3 143 'This showed that substantial sizing activity had been retained despite the susceptibility of the sizing agent to hydrolysis and the extended storage period.

Claims (13)

1. A sizing composition for use in the treatment of cellulosic materials comprising a sizing agent in microencapsulated form.

2. A sizing composition as claimed in claim 1 wherein the sizing agent is a hydrolysable anhydride compound.

3. A sizing composition as claimed in claim 2 wherein the sizing agent is octadecenyl succinic anhydride.

4. A sizing composition as claimed in any preceding claim wherein the microcapsules are substantially in the 1 to 10 micron size range.

5. A sizing composition substantially as described herein with reference to any one of the Exampls.

6. A process for producing a sizing composition as claimed in claim 1 wherein the microcapsules are produced by the encapsulation techniques of coacervation, interfacial polymerisation or interfacial polycondensation.

7. A process as claimed in claim 6 wherein the microcapsules are produced by coacervation.

8. A process as claimed in claim 6 or 7 wherein the capsule-forming is conducted by pressurising the microencapsulation medium containing the sizing agent, subjecting the pressurised mixture to shear and progressively releasing,-the pressure.

9. A process as claimed in any one of claim 6 to 8 wherein the aqueous microencapsulation medium has a temperature below 600C and the residence time of the sizing agent in the said medium is less than 5 minutes.

10. A process as claimed in claim 9 wherein the temperature of the microencapsulation medium is below 450C.

11. A process as claimed in claim 9 or 10 wherein the residence time of the sizing agent in the microencapsulation medium is less than 2 minutes.

12. Aprocess as claimed in any one of claims 6 to 11 substantially as described herein with reference to any one of the examples.

13. A process for sizing a cellulosic material comprising contacting the material with a sizing agent as claimed in any one of claims 1. to 5 or with a sizing agent produced by a process as claimed in any one of claims 6 to 12.