Bleaching and dyeing; fluid treatment and chemical modification – Gelled fiber-dyeing process or product
Reexamination Certificate
2000-10-24
2004-09-28
Einsmann, Margaret (Department: 1751)
Bleaching and dyeing; fluid treatment and chemical modification
Gelled fiber-dyeing process or product
C008S650000, C008S653000
Reexamination Certificate
active
06797015
ABSTRACT:
This invention relates to a process for producing tubular dyed wrappings for food, in particular skins made of cellulose fibre, having high transparency and evenness of the dye, and also to the tubular food wrappings produced according to the invention and the use thereof.
Tubular food wrappings are used on a large scale in the production of a multitude of meat products. These food wrappings are generally thin-walled tubes of various diameters and in many cases are produced in known manner from regenerated cellulose. Cellulose wrappings can also be produced in the form of skins of cellulose fibre containing embedded fibrous material.
The appearance of sausages produced using skins of cellulose fibre is an important factor in appealing to the consumer, and a multitude of products are cured in order to obtain a characteristic brown coloration. It is also usual to dye skins of cellulose fibre, for which purpose coloured pigments and dyes are used. Particularly in the case of raw sausages in which the sausage meat has a coarse-grained structure, such as, for example, salami, it is desirable that the lumps of meat and fat should show clearly through the sausage casing in order to achieve an appearance which will promote sale. In the conventional pigment dyeing of skins made of cellulose fibre, the transparency of the sausage casings is greatly reduced owing to the diffuse refraction of light on the relatively large particles of dye.
The dyeing of cellulose films and in particular cellulose fibres with so-called vat dyes is known. The vat dyes are compounds having an indigoid or anthraquinonoid structure and are insoluble in water. They require a special dyeing process, the essential features of which have long been known. In this process, with the use of reducing agents, such as sodium hydrogen sulfite, sodium dithionite, sodium hydroxymethanesulfinate or sodium borohydride, the vat dye is first of all converted into its completely alkali-soluble leuco form. The cellulose material to be dyed is dipped into or passed through this dye liquor, which is referred to as vat. The high affinity for cellulose of the leuco dyes brings about a high rate of dyeing at the surface of the cellulose material, which can lead to unevennesses in the dye in cases where mixtures of dyes in which the leuco dyes have differing affinities for cellulose are used. There is then a diffusion of the leuco dyes into the interior of the cellulose material, the diffusion being accelerated by elevation of the temperature. After the material has been rinsed, the oxidation is carried out and the original water-insoluble dye, which adheres well to the cellulose material, is again formed from the leuco form. Examples of suitable oxidising agents are atmospheric oxygen, hydrogen peroxide, sodium perborate and potassium dichromate.
Thus U.S. Pat. No. 3,149,905 claims the dyeing and printing of cellulose-containing textile materials with vat dyes. The vat dyes used according to that patent contain sulfonamide groups. The dyeing is carried out in conventional dipping baths.
The dyeing of cellulose materials from regenerated cellulose, cellulose esters and cellulose ethers is claimed in U.S. Pat. No. 2,043,069. In this process, the vat dye in its undissolved form is mixed with the cellulose starting compound and the coagulation and regeneration are carried out. The regenerated cellulose material is subsequently passed through the reducing and oxidising baths in order to dissolve and fix the vat dyes.
A very similar process is claimed in Deutsche Offenlegungsschrift 2,262,611 for the production of cellulose films. Here the vat dye in its undissolved form is mixed with the viscose, the regeneration is carried out and the vat dye is subsequently dissolved and fixed in reducing and oxidising baths.
Comparable dyeing processes using vat dyes have not hitherto been applied, however, to the group of products comprising skins made of cellulose fibre.
A process for dyeing a skin of cellulose fibre in the gel state in dye liquors is claimed in U.S. Pat. No. 3,383,443. However, the dyes used there are not vat dyes but naphthol dyes, which are fixed with stabilised diazo compounds.
Finally, U.S. Pat. No. 3,293,340 describes a dyeing process which uses vat dyes for the production of wrappings from transparent dyed, regenerated cellulose. In this process, the still undissolved vat dye in the form of a pigment paste is mixed with the viscose and from this mixture is produced a tube of regenerated cellulose, which is regenerated in acid coagulating baths in conventional manner and subsequently washed. The use of an additional desulfurisation bath prior to or after the reduction step is recommended. The tube is then passed through an alkaline reducing bath, the vat dye being converted into the alkali-soluble leuco form. The reducing bath contains in addition 100 to 150 g/l sodium chloride in order to suppress the migration of the soluble leuco form out of the tube. The reconversion of the leuco form into the insoluble form is then effected by oxidation with atmospheric oxygen in a special duct, in which water is sprayed onto the tube in order to facilitate oxidation by-removing the reducing agent. The tube is subsequently washed again and preferably passed through another acid bath having a concentration of 1.5 to 7.5 g sulfuric acid per liter, in order to neutralise the rest of the sodium hydroxide and thereby to enable the tube to be washed more efficiently in the subsequent repeated washing step. The conventional treatment with softeners in a glycerol bath then takes place, and finally the drying step.
The process described in U.S. Pat. No. 3,293,340, owing to the use of the additional processing steps involving the reducing bath, the oxidising chamber, the intermediate washing, the subsequent acid treatment and the repeated washing, is capital-intensive as compared with the conventional processes for producing fibre-reinforced cellulose wrappings. Furthermore, because of the necessity of controlling the concentration in the reducing bath and in the acid bath, it is very expensive and in addition may altogether be seen as contributing to the waste-water loading. Where a reducing bath is used, the undesirable oxidation of the reducing agent by atmospheric oxygen cannot be avoided, owing to the large surface area in contact with the air. Considerably more reducing agent is therefore consumed than is necessary for the conversion of the dyes into the leuco form, in consequence of which the waste water is additionally polluted. In particular, the high concentration of sodium chloride in the reducing bath claimed according to the invention in the patent under discussion leads to additional waste-water loading, which is to be regarded as highly problematic in view of the environmental protection generally practised nowadays.
In the above process, moreover, the process of diffusion of the reducing agent into the regenerated tube has a decisive influence on the evenness and transparency of the dye obtained. This gives rise to difficulties in the application of the process, as skins of cellulose fibre are conventionally produced using non-woven fabric of varying thickness and varying quantities of applied viscose, depending upon the caliber. Apart from the thickness of the regenerated tube, factors which influence the diffusion rate are the temperature and concentration of the reducing bath. These influences can barely be controlled, especially when variously dyed tubes of different caliber are passed simultaneously through a reducing bath.
Accordingly, the object of the present invention was to provide a process for producing dyed, tubular food wrappings made of non-woven fabric coated with regenerated cellulose, in particular skins of cellulose fibre, having high transparency and evenness of the dye, which can be carried out at low industrial expense. In particular, the quantities of the chemicals used are to be as small as possible, so as to minimise environmental pollution.
Surprisingly, it has been found that dyes, in particular vat dyes, w
Blumenberg Klaus-Dieter
Neuschulz Willi
Akorli Godfried R.
Einsmann Margaret
Gil Joseph C.
Wolff Walsrode AG
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