EP0220941B1

EP0220941B1 - Paper sizing composition

Info

Publication number: EP0220941B1
Application number: EP86308244A
Authority: EP
Inventors: David William Shepherd; Lawrence Forrester Watson; David Charles Johnson
Original assignee: Albright and Wilson Ltd
Current assignee: Cessione eka Nobel AB
Priority date: 1985-10-23
Filing date: 1986-10-23
Publication date: 1991-01-02
Anticipated expiration: 2006-10-23
Also published as: EP0220941A1; ES2020661B3; FI86317B; FI864251A; DE3676428D1; ATE59681T1; GB8526158D0; JPS62125094A; FI86317C; MY102764A; FI864251A0

Abstract

Particulate solids comprising ketene dimers may be obtained by drying a conventional aqueous dispersion of the dimer to which a water dispersable encapsulating agent has been added. Preferably the encapsulating agent is a cationic starch and the solid is obtained by spray drying the emulsion under controlled conditions. The products retain their sizing properties even on prolonged storage.

Description

This invention relates to stable solid compositions comprising ketene dimers and to processes for their production.
Ketene dimers find use as ingredients of paper sizing compositions. Sizing compositions are manufactured in the form of relatively concentrated aqueous dispersions, which are diluted before use in the paper sizing process. These concentrated aqueous dispersions suffer from the disadvantage that their efficiency as paper sizing agents deteriorates on prolonged storage, apparently because of the hydrolysis of the ketene dimer. In order to be useful as paper sizes, ketene dimers are dispersed in water in the presence of a surfactant and/or an emulsifier, present in an amount from 0.2% to 2.5% by weight of the weight of ketene dimer. Attempts to dry such dispersions in the past have not been successful; if such a dispersion is dried slowly, the ketene dimer tends to hydrolyse; if the dispersion is dried at high temperatures, the ketene dimer tends to char. If such a dispersion is spray dried, the material dries to a sticky mass which is difficult to handle.
US-A-3311532 (Kulick et al) describes in Example 9 a ketene dimer composition in which hexadecyl ketene dimer, stearic acid, sodium lignosulphonate and a water-soluble cationic starch are ball-milled to form a powder which subsequently emulsifies when it is added slowly with intense agitation to water 90°C. The starch is stated to be present as a supplementary inert extender.
S. A. Colby et al describe in Research Disclosure 20336 (March 1981) a polymer-encapsulated paper sizing agent which comprises ketene dimer encapsulated within anionic polymer shells.
GB-A-1405751 (BPB Industries) discloses a composition for use in paper manufacture, the composition being formed by spray-drying an aqueous slurry of particulate filler and from 1 to 20% by weight of organic polymeric material.
US-A-2865734 (Weisgerber) discloses a ketene dimer paper sizing composition in which the ketene dimer is dispersed on a carrier of finely-divided amorphous silica to form a free-flowing powder for incorporation into an aqueous pulp slurry.
It has been discovered that solid particulate compositions can be manufactured, comprising ketene dimers and a stabilising agent, which are readily dispersible in water, as is required in paper sizing processes, and which exhibit improved stability upon prolonged storage. Solid water-dispersible compositions commprising solid particles of a ketene dimer and a stabilising agent are believed to be novel and constitute one aspect of this information.
The ketene dimers which are useful as paper sizing agents and which are used in carrying out this invention are compounds having the molecular formula:
wherein R is as defined below; the compositions of the invention comprise:

(a) a ketene dimer of this formula, and
(b) a water-soluble stabilising agent, the stabilising agent and the ketene dimer being present in the form of a water-dispersible homogeneous particulate solid.

In the above formula, R represents an alkyl, alkenyl, aryl or alkaryl group having from 8 to 24 carbon atoms. Preferably, R represents an alkyl group having from 8 to 20 carbon atoms. These ketene dimer products are normally prepared from fatty acids obtained from natural sources and they therefore comprise a mixture of dimeric compounds, wherein the number of carbon atoms in the substituent group R varies. Mixtures of ketene dimers wherein R has an average value of from 8 to 24 are useful in carrying out this invention. Preferably, the group R contains an average of from 12 to 18 carbon atoms. Examples of ketene dimers include octyl, decyl, dodecyl, tetradecyl, hexadecyl, octadecyl eicosyl, docosyl, tetracosyl, phenyl, benzyl, beta-naphthyl and cyclohexyl ketene dimers, as well as the ketene dimers prepared by known methods from montanic acid, naphthenic acid, 9,10-decylenic acid, 9-10-dodecylenic acid, palmitoleic acid, oleic acid, ricinoleic acid and eleostearic acid, as well as ketene dimers prepared from naturally-occurring mixtures of fatty acids, such as those found in coconut oil, babassu oil, palm kernel oil, palm oil, olive oil, peanut oil, rape oil, beef tallow, lard (leaf) and whale blubber. Mixtures of any of the above-named fatty acids with each other may also be used.
Ketene dimer products are manufactured in the form of waxy solids comprising the ketene dimers per se, in admixture with up to 20% by weight of impurities. These products are normally used as such, i.e. without separation of the impurities. For the purpose of this disclosure, all references to ketene dimers include mixtures thereof with these impurities and all proportions based on the weight of ketene dimer are based upon the weight of the manufactured product.
The stabilising agent also present in the compositions of the invention should be selected so as to be effective in enabling an aqueous dispersion, containing a ketene dimer and such a stabilising agent, to be dried to form a product which is redispersible in water and is thus useful in paper sizing processes. The nature of the stabilising agent should be such that it is compatible with the other components of the resultant spray-dried product and such that it is not degraded during the drying process. Examples of compounds which are useful as stabilising agents are: gelatin, tristearin, gum arabic, sugars, ethyl cellulose, carboxymethylcellulose, polyacrylamides, water-soluble silicates, polyethers, polyesters, polyamides, starches, especially cationic starches, and polyvinyl alcohol.
The amount of stabilising agent which is employed is desirably proportional to the amount of ketene dimer in the resultant dispersion and will normally be adjusted so as to be just sufficient to enable the dispersion to be dried. The use of excess quantities of stabilising agent is less preferred. Normally the quantity of stabilising agent added to the dispersion is in the range from 25% to 100%, preferably from 25% to 75% by weight of the weight of ketene dimer present in the dispersion, i.e. the weight ratio of ketene dimer to the stabilising agent is in the range from 1:0.25 to 1:1 and, preferably, from 1:0.25 to 1:0.75. A preferred class of compounds used as stabilising agents are those which are known to be useful as ingredients of paper sizing compositions. Such agents may be employed in larger quantities than are required in order to cooperate successfully with the dimer and enable the desired stable water-dispensible particulate solid product to be formed. Such extra quantities make a contribution to the efficiency of the dried product when it is used in the paper sizing process. Examples of such agents are starches, such as cationic starches. A particularly preferred class of stabilising agents are those which are known to disperse in cold water, preferred examples being certain cationic starches such as those sold under the Trade Marks Solvitose NX and Perfectamyl PLV. The stabilising agent can be added to any aqueous dispersion of the ketene dimer. However, it is strongly preferred to add the stabilising agent to a dispersion which is itself useful as a paper size, so that redispersion of the dried product produces a dispersion which is useful as a paper size, without the need to disperse any additional components in order to form the size.
Ketene dimer dispersions normally comprise at least one surfactant and the presence of a surfactant in the composition from which the dried product is made and so in the dried product itself facilitates redispersion of the particulate solid product in the paper sizing process. Examples of suitable surfactants are the sodium salts of naphthalene formadehyde sulphonate condensates, esters of polyoxyethylene sorbitan or a sodium lignosulphonate.
The amount of surfactant added will usually be in the range 0.3% to 3.5% by weight of the ketene dimer, preferably in the range 1.25 to 2.5%.
The ketene dimer dispersions used in the spray drying processes may further comprise other conventional ingredients such as emulsifiers, stabilisers, retention aids and slimicides although the use of compounds which are sensitive to heat is preferably avoided.
In particular the ketene dimer dispersions preferably comprise a cationic polymer such as a polyamine in order to increase the efficiency of the dispersion as a paper size. Examples of polymers useful in this application are water soluble polyamino polyamideepichlohydrin resins, alkylene polyamine epichlorhydrin resins, poly(diallylamin)-epichlorhydrin resins, poly dialkyl dimethyl ammonium chloride and polyethyleneimines.
The amount of polymer present may be up to a weight ratio of ketene dimer to polymer of 1.0:1.0. However as the quantity of polymer increases there is an increasing tendency to produce a relatively sticky product and it is preferred that the weight ratio of ketene dimer to polymer is in the range 1.0:0.2 to 1.0:0.5.
The dispersion of the ketene dimer and stabilising agent can be dried by a variety of techniques. However exposure of the dimer to high temperatures for long periods can lead to its degradation either by charring or by hydrolysis and is best avoided. Techniques such as freeze drying and spray drying are preferably employed. We prefer to utilise spray drying although the conditions under which the drying is carried out must be monitored in order to minimise degradation of the ketene dimer. The spray drying of the ketene dimer dispersions can be carried out using conventional equipment. The temperature of the drier should be controlled so as to avoid any significant amount of charring or degradation of the components of the emulsion. Typically the temperature at the inlet to the dryer should be in the range 220° to 350°C and that at the outlet of the dryer 110° to 125°C. The drying process is carried out so as to produce a powdered product comprising less than 0.1 % by weight of water.
The powder products must be dispersed in an aqueous medium in order to be useful in paper sizing processes. Typically the powder will be diluted with up to ten times its weight of water. Adequate dispersion is preferably obtained using vigorous agitation. We prefer to wet and/or slurry the powder with a small amount of water, e.g. about 5 to 30% by weight of the total dilution water is added to the powder, and to agitate those slurries with additional water to the desired content, usually about 10% by weight.
The invention is illustrated by the following examples:

Example 1

A dispersion of a stearic/palmitic alkyl ketene dimer having the following composition (Composition 1) was prepared.
A cationic starch product as sold under the Trade Mark Perfectamyl PLV was added to one sample of the dispersion in a quantity such that the ratio of the weight of ketene to starch was 1:1 (Composition 2). The same cationic starch product was added to a second sample of the dispersion in a quantity such that the ratio of the weight of ketene dimer to starch was 1:0.5 (Composition 3).
Compositions 2 and 3 were then spray dried using a Niro Production Minor Spray Drier set for Rotary Atomisation using an atomiser speed of 24,000 rpm. The liquor feed temperature was 15°C, the drier inlet temperature was 250°C and the drier outlet temperature 125°C. The product was a white powder.
The sizing efficiency of these powders 2 and 3 and dispersion 1 was assessed in a series of trials.

Trial A

Sizing condition

Trial B

Sizing Conditions

Trial C

Sizing Conditions

Trial D

Sizing Conditions

Trial E

Sizing Conditions

Trial F

Sizing Conditions

Trials G and H are based on a product (Composition 4) with a surfactant content on ketene dimer of 0.62% but which are otherwise identical with and are manufactured under the same conditions as composition 3 described above.

Trial G

Sizing Conditions

Trial H

Trial J is based on a product (Composition 5) with a surfactant content on ketene dimer of 2.8% but which is otherwise identical with and is manufactured under the same conditions as composition 3.

Trial J

Size conditions

Example 2

A dispersion (composition 6) of a stearic/palmitic alkyl ketene dimer having the following composition was prepared:
A cationic starch product as sold under the Trade Mark Solvitose NX was added to this dispersion in a quantity such that the ratio of the weight of ketene dimer to starch was 1:0.5 (composition 7).
Composition 7 was then spray dried using the conditions set forth in Example 1. The efficiency of sizing of compositions 6 and 7 was then assessed at that time and after storage at ambient temperatures for 3.5 and 4.5 months. The results were as follows:

Sizing conditions

Claims

1. A stable solid composition which is dispersible in water to form a paper sizing agent and comprises (1)a ketene dimer of the formula:

wherein R represents an alkyl, alkenyl, aryl or alkaryl group having from 8 to 24 carbon atoms and (2) a water-soluble stabilising agent, the stabilising agent and ketene dimer being present in the form of a water-dispersible homogeneous particulate solid.

2. A composition according to claim 1, the particulate solid being freeze- or spray-dried.

3. A composition according to claim 1 or 2, wherein the group R has an average value of from 12 to 18 carbon atoms.

4. A composition according to any preceding claim, wherein the stabilising agent is selected from gelatin, tristearin, gum arabic, sugars, ethylcellulose, carboxymethylcellulose, polyacrylamides, water-soluble silicates, polyethers, polyesters, polyamides, starches and polyvinyl alcohol.

5. A composition according to claim 4, wherein the stabilising agent is a cationic starch.

6. A composition according to any preceding claim, wherein the weight ratio of ketene dimers to the stabilising agent is in the range from 1:0.25 to 1:1.

7. A composition according to any preceding claim, wherein a polymeric cationic dispersing agent is present.

8. A composition according to claim 7, wherein the dispersing agent is selected from water-soluble alkylene polyamine epichlorhydrin resins and poly(diallylamine)-epichlorhydrin resins.

9. A composition according to claim 7 or 8, wherein the weight ratio of ketene dimer to the dispersing agent is in the range from 1:0.5 to 1:1.

10. A composition according to any preceding claim, wherein at least one surfactant is present.

11. A composition according to claim 10, wherein the surfactant is selected from salts of naphthalene formaldehyde sulphonate condensates, esters of polyoxyethylene sorbitan and salts of lignosulphonic acids.

12. A composition according to claim 10 or 11, wherein the weight ratio of surfactant to ketene dimer is in the range from 0.3% to 3.5%.

13. A process for the production of a stable solid composition which is dispersible in water to form a paper sizing agent, in which process:

(a) a ketene dimer having the formula defined in claim 1 and a water-soluble stabilising agent are formed into an aqueous dispersion and

(b) the aqueous dispersion is dried to form a homogeneous particulate water-dispersible solid.

14. A process according to claim 13, wherein the dispersion is dried by passage through a spray or freeze drier.

15. A process according to claim 14, wherein the dispersion is spray-dried and temperature at the inlet to the drier is in the range from 220°C to 350°C and the temperature at the outlet from the drier is in the range from 110°C to 125°C.

16. A process for the production of sized paper or paper board, wherein a sizing agent is added to the paper or paper stock, characterised in that the sizing agent comprises an aqueous dispersion of a particulate solid according to any of claims 1 to 12 or which has been produced by a process according to any of claims 13 to 15.