WO1995029209A1

WO1995029209A1 - Pigment dispersions and pigmented products

Info

Publication number: WO1995029209A1
Application number: PCT/GB1995/000884
Authority: WO
Inventors: Steven Herod; Martyn John Deacon
Original assignee: Courtaulds Chemicals (Holdings) Limited
Priority date: 1994-04-21
Filing date: 1995-04-19
Publication date: 1995-11-02
Also published as: GB2288605A; GB9407875D0; AU2261995A

Abstract

Pigmented cellulose acetate filaments are produced by mixing a dispersion of titanium dioxide in a carboxylate ester of a polyhydric alcohol with cellulose acetate and a solvent for cellulose acetate. The resulting dispersion of titanium dioxide in a solution of cellulose acetate is dry spun to produce pigmented cellulose acetate filaments. In a preferred titanium dioxide dispersion for use in the process, the titanium dioxide is dispersed in a polyhydric alcohol ester of a monocarboxylic acid having up to 6 carbon atoms, for example glycerol triacetate. The pigmented filaments can be used in cigarette filters.

Description

Pigment Dispersions and Pigmented Products

Field of the invention

This invention relates to a process for producing pigmented shaped cellulosic products, especially filaments, and to a pigment dispersion for use in producing such products. It is particularly concerned with a titanium dioxide dispersion for use in producing pigmented shaped cellulose acetate articles. Titanium dioxide is used as a white pigment and as a delustering agent, for example in textiles for producing matt fibres and yarns.

Cellulose acetate, also referred to as cellulose diacetate, generally has a degree of substitution (esterification) of 50-60%, most usually about 54%, of the hydroxyl groups per anhydroglucose unit. Cellulose diacetate is soluble in acetone and can be dry spun from acetone solution to form filaments or cast from acetone solution to form film. Cellulose acetate filaments can for example be in the form of continuous filament yarn for textile uses or in the form of tow for use in cigarette filters.

Although many cellulose acetate articles are usually unpigmented, there is a demand for white cellulose acetate filaments, particularly tow for use in cigarette filters. There are problems in obtaining a fine dispersion of titanium dioxide in cellulose acetate solutions. With direct dispersion of solid titanium dioxide in the cellulose acetate solution, it is difficult to avoid the presence of some aggregated pigment. This is true for both rutile and anatase forms of titanium dioxide, including commercially available coated pigments. Titanium dioxide pigments are commercially available as dispersions in water, glycol or white oil (a paraffinic oil), but the presence of these dispersion media has been found to be incompatible with acetone solutions of cellulose diacetate. Background Art

GB-A-2055115 describes a composition for colouring polyvinyl chloride comprising at least 40% by weight colouring pigment, which may be titanium dioxide, and up to 60% glycerol monostearate. US-A-5288320 describes titanium dioxide carrying an ester or partial ester of pentaery- thritol and an aliphatic unsubstituted C₁₀ to C₂₂ monocarboxylic acid. This is said to be of value in the preparation of plastics compositions or master- batches for polymers such as polyolefins, polystyrene and ABS. JP-A-4-16231 describes a dispersant for titanium dioxide comprising a glycerol ester of a C₁₆-C₂₀ saturated aliphatic acid. JP-A-4-16230 describes a dispersant for titanium dioxide comprising a glycerol ester of a tetracarboxylic acid containing a C₇-C₂₁ alkyl group.

Disclosure of the invention

A process according to the invention for the production of pigmented cellulose acetate filaments is characterised in that a dispersion of titanium dioxide in a carboxylate ester of a polyhydric alcohol is mixed with cellulose acetate and a solvent for the cellulose acetate to produce a dispersion of titanium dioxide in a solution of cellulose acetate, which dispersion is dry spun to produce pigmented cellulose acetate filaments.

The invention also provides a titanium dioxide dispersion for use in producing pigmented shaped cellulose acetate products, characterised in that the titanium dioxide is dispersed in a polyhydric alcohol ester of a monocarboxylic acid having up to 6 carbon atoms.

The titanium dioxide used can be of the anatase or rutile type, and it preferably has a particle size below 2 microns, most preferably below 1 micron, but at least 0.1 micron, for example in the range 0.2 to 0.7 micron, for use in cellulose acetate filaments. The titanium dioxide may be surface-treated with Si0₂, A1₂0₃ and/or an organic compound such as trimethylolpropane to prevent agglomeration of the titanium dioxide particles (such surface-treated titanium dioxide is available commercially) , but such surface treatment is not necessary and untreated titanium dioxide of an appropriate particle size can also be used.

For use to produce the pigmented cellulose acetate filaments the titanium dioxide is dispersed in a carboxylate ester of a polyhydric alcohol. The polyhydric alcohol can for example be glycerol, ethanediol, propane-1,2-diol, butane-l,4-diol, pentaerythritol, trimethylolpropane, sorbitol or a polyhydric alcohol containing one or more, for example 1 to 5, ether linkages such as diethylene glycol, triethylene glycol or dipropylene glycol. The carboxylate ester groups are preferably acetate groups but could be propionate or other carboxylate groups, for example those derived from a monocarboxylic acid having up to 6 carbon atoms. The carboxylate ester can be a full ester or a partial ester of the polyhydric alcohol, for example glycerol monoacetate, glycerol diacetate or glycerol triacetate. The full and partial acetate esters of polyhydric alcohols are each iscible with solutions of cellulose acetate in acetone. The choice of the most preferred carboxylate ester may in many cases be determined by the acceptability of the carboxylate ester in the cellulose acetate product being made. For example, glycerol triacetate is widely used as a plasticiser and bonding agent for the production of cigarette filter rods from a tow of cellulose acetate filaments. Triethylene glycol diacetate is also used for this purpose. We have found that titanium dioxide can readily be dispersed in either glycerol triacetate or triethylene glycol diacetate and the resulting dispersion can be mixed with cellulose acetate and acetone to form a cellulose acetate solution containing titanium dioxide dispersed at a satisfactorily low particle size. Mixtures of polyhydric alcohol carboxylate esters can alternatively be used, for example a mixture of triethylene glycol diacetate with glycerol triacetate.

We have found that the presence of the polyhydric alcohol carboxylate ester, which is a plasticiser for cellulose acetate, gives advantages in reduced viscosity of the spinning dope and improved crimp retention (cellulose acetate tow for use in cigarette filters is generally crimped by stuffer box crimping before being formed into filter rods) .

The concentration of titanium dioxide in the dispersion in polyhydric alcohol carboxylate ester is generally at least 5% and preferably at least 10%, by weight, to avoid incorporating excess carboxylate ester in the cellulose acetate product, and it can be up to about 60% by weight. Dispersions at higher concentrations tend to exhibit thixotropic properties, which present problems in handling and mixing the dispersions. The concentration of titanium dioxide in the dispersion in polyhydric alcohol carboxylate ester is most preferably in the range 30 to 55%, for example about 50%, by weight.

The dispersion of titanium dioxide in polyhydric alcohol carboxylate ester can be mixed with the cellulose acetate and the solvent for the cellulose acetate by a variety of procedures. The dispersion can be premixed with cellulose acetate flake or with the solvent (for example acetone), or it can be added to the cellulose acetate flake and solvent as they are being mixed to form the cellulose acetate solution. The dispersion can alternatively be mixed with preformed cellulose acetate solution, that is t ? spinning dope or casting dope. The cellulose acetate solution used as spinning dope has a concentration of about 25% by weight cellulose acetate and is highly viscous, so that thorough mixing with the titanium dioxide dispersion is required. The proportion of titanium dioxide incorporated in the cellulose acetate solution is generally at least 0.1% and usually at least 0.2%, by weight based on cellulose acetate, to achieve significant whitening, up to about 1 or 2%, by weight. Proportions of 0.2 to 0.8% by weight titanium dioxide, based on cellulose acetate, are preferred.

The shaped cellulose acetate product can be produced from the dispersion of titanium dioxide in cellulose acetate solution by known methods, for example dry spinning to form filaments or casting to form film. The titanium dioxide remains well dispersed and does not interfere with the spinning process. In the dry spinning process, the cellulose acetate solution containing dispersed titanium dioxide is extruded through a spinneret into a cell containing a current of hot air to evaporate the solvent, forming multifilament yarn or tow.

The invention is illustrated by the following Examples, in which percentages are by weight.

Examples 1 to 3

50% anatase pigment of particle size 0.35 micron having inorganic and organic coatings was mixed with 50% triacetin (glycerol triacetate) in a high-shear mixer to produce a stable dispersion. By the same procedure, dispersions of 40% anatase in 60% triacetin and 30% anatase in 70% triacetin were also produced.

Each dispersion was blended into a sample of bright (unpigmented) cellulose acetate spinning dope (a 25% solution of cellulose diacetate) at a level of 0.5% Ti0₂ on cellulose acetate.

The particle size of all the dispersions produced was measured by laser diffraction using a "Malvern Mastersizer". The results are shown in Table 1 below for two different samples in each case. D(4.3) is the volume mean particle diameter. D(v 0.9) is the particle diameter such that 90% by volume of the particles are smaller than this. The particle size of a dispersion of anatase in acetone was also 5 measured. Lower particle size in the dispersion provides more whiteness for an equal concentration of pigment.

Table 1

Sample Particle size Particle size D(v 0.9) μ D (4.3) μm

10 50% Ti0₂ in Triacetin

(Example 1) 0.84 0.80 0.51 0.50 4 400%% TTii00₂₂ iinn Triacetin (Example 2) 1.04 1.05 0.61 0.62 3 300%% TTii00₂₂ iinn Triacetin 15 (Example 3) 1.31 1.33 1.00 0.98

50% Triacetin/Ti0₂ at 0.5% in Bright Dope (Example 1) 1.13 1.04 0.61 0.59 40% Triacetin/Ti0₂ at 0.5% in Bright Dope (Example 2) 0.75 0.76 0.54 0.55 20 30% Triacetin/Ti0₂ at 0.5% in Bright Dope (Example 3) 1.29 1.20 0.83 0.66 Anatase powder in Acetone 2.91 2.89 1.72 1.71

Each of the dispersions in cellulose acetate spinning dope was dry spun to produce matt white cellulose acetate 25 filaments.

Example 4

Following the procedure of Example 1, the same anatase pigment was dispersed in a mixture of 25% triacetin and 25% triethylene glycol diacetate. The resulting dispersion was 30 blended into bright cellulose acetate spinning dope at a level of 0.5% Ti0₂ on cellulose acetate. The dope was dry spun to form matt white filaments. No particle size measurements were made, but the whiteness of the pigmented spinning dope and of the filaments was judged to be equal to that of the products of Examples 1 to 3.

Examples 5 to 7

Following the procedure of Example 2, 40% of each of the following titanium dioxide pigments was dispersed in 60% triacetin.

Example 5 - anatase (inorganically coated) Example 6 - rutile (inorganically coated) Example 7 - anatase (uncoated)

Each resulting dispersion was blended into bright cellulose acetate spinning dope at 0.5% Ti0₂ on cellulose acetate. The particle size of each pigment was about 0.4 micron. The particle size analysis of the white pigmented dope produced is shown in Table 2.

Examples 8 to 10

Following the procedure of Example 2, 40% of the anatase used in Example 5 was dispersed in each of the following polyhydric alcohol carboxylate esters:-

Example 8 - Glycerol monoacetate (monoacetin) Example 9 - Glycerol diacetate (diacetin) Example 10 - Triethylene glycol diacetate (TEGDA) .

Each resulting dispersion was blended into bright cellulose acetate spinning dope at 0.5% Ti0₂ on cellulose acetate. The particle size analysis of the white pigmented dope produced is shown in Table 2. Table 2

Example No. Dispersant D[v,0.9] D[4.3]

5 Triacetin 1.69 μm 0.99 μm

6 Triacetin 2.12 μm 1.55 μm

7 Triacetin 1.61 μm 0.99 μm

8 Monoacetin 1.64 μm 0.96 μm

9 Diacetin 1.63 μm 0.95 μm

10 TEGDA 1.68 μm 1.57 μm

Each of the white pigmented dopes of Examples 5 to 10 was dry spun into hot air and produced matt white cellulose acetate filaments.

Claims

1. A titanium dioxide dispersion for use in producing pigmented shaped cellulose acetate products, characterised in that the titanium dioxide is dispersed in a polyhydric alcohol ester of a monocarboxylic acid having up to 6 carbon atoms.

2. A dispersion according to claim 1, characterised in that the ester is an acetate ester.

3. A dispersion according to claim 1 or claim 2, characterised in that the ester is a full or partial ester of glycerol.

4. A dispersion according to claim 3, characterised in that the ester is glycerol triacetate.

5. A dispersion according to claim 2, characterised in that the ester is triethylene glycol diacetate.

6. A dispersion according to any of claims 1 to 5, characterised in that the dispersion comprises 20-60% by weight of titanium dioxide and 40-80% by weight of at least one polyhydric alcohol carboxylate ester.

7. A process for the production of pigmented cellulose acetate filaments, characterised in that a dispersion of titanium dioxide in a carboxylate ester of a polyhydric alcohol is mixed with cellulose acetate and a solvent for cellulose acetate to produce a dispersion of titanium dioxide in a solution of cellulose acetate, and the resulting dispersion is dry spun to produce pigmented cellulose acetate filaments.

8. A process according to claim 7, characterised in that the titanium dioxide dispersion is mixed with cellulose acetate flake and acetone.

9. A process according to claim 7, characterised in that the titanium dioxide dispersion is mixed with a solution of cellulose acetate.

10. A process according to any of claims 7 to 9, characterised in that the amount of titanium dioxide dispersion mixed with the cellulose acetate and solvent is such that the resulting dispersion contains 0.2 to 1% by weight titanium dioxide based on cellulose acetate.

11. A process according to any of claims 7 to 10, characterised in that the titanium dioxide dispersion is a dispersion in glycerol triacetate, and the dispersion in cellulose acetate solution is dry spun to produce a multi- filament tow for use in cigarette filters.