ITCO20130034A1 - PROCESS FOR PRE-TREATMENT OF TEXTILE ARTICLES FOR DIGITAL PRINTING WITH INK JET PRINTERS - Google Patents

Description

"PROCESS FOR THE PRE-TREATMENT OF TEXTILE ITEMS SUITABLE FOR DIGITAL PRINTING WITH INK JET PRINTERS"

The present invention relates to a process for the digital printing of fabrics.

STATE OF THE TECHNIQUE

One of the processes of substantial importance in textile manufacturing is the printing process with which colors and designs are transferred onto any textile substrate. Such manufactured articles include fabrics of different fibrous composition and of different weave and weaving technology such as fabrics in polyester, cotton, wool and other keratin fibers, silk, viscose, artificial and synthetic fibers of any chemical nature and morphological structure.

Traditional printing techniques essentially attributable to screen printing techniques include as the main stage the use and conveyance of dyes and pigments in chemical formulations consisting of the coloring principles themselves, by vehicles that regulate their viscosity and density (oligopolysaccharides), acidity, saline components, preservatives, emulsifiers, fixers, etc. These vehicles are applied to fabrics using the screen printing technique which involves the use of pictures and cylinders with tumblers. Over the last few years a new technology called ink jet or digital printing has spread, through which it is possible to eliminate the preparation of the printing screens, improving the flexibility of the printing process. In digital printing ”small drops of ink are transferred in sequence or simultaneously, according to a predefined pattern and towards any substrate, so as to reproduce, mixing at any point, the desired colors according to a specific design.

The ink-jet printing technology on fabric operates by exploiting a system conceptually very similar to the digital inkjet one of a paper printer.

The textile substrates used in inkjet printing currently make it possible to cover all the needs of the market: clothing, furniture, sports and leisure.

To date it is possible to print with satisfactory results on all fibers used in the textile sector: cotton, polyester, silk, viscose, wool, etc.

The fabrics must be suitably pre-treated before being subjected to printing.

In ink-jet printing, in addition to traditional pre-treatments, such as sodaking, scouring, bleaching, drying, flattening, heat setting, chlorination, etc., other treatments are required, as a consequence of the different physical characteristics of the inks used compared to traditional printing pastes. These inks are in fact very fluid and being solubilized in large quantities of water, they cause problems of diffusion and migration of the dye in the fabric. The fabrics must therefore be pre-treated with chemical reagents capable of fixing the applied inks.

Conventional pre-treatment is normally carried out on continuous production lines with the following procedure:

- Impregnation of fabrics with special compounds in aqueous solution, in full bath;

- Passage through squeezing cylinders (padder), which have the function of regulating the quantity applied and eliminating any excess product applied;

- Drying in oven / stenter / printing attic.

With this application system the fabrics are totally immersed in aqueous solutions and, on average, undergo an increase in weight of 70-100%. There is therefore a large consumption of water, chemicals and energy as the fabrics must then be dried before being subjected to printing.

The need is therefore particularly felt for alternative pre-treatment methods which have a lower environmental impact and allow the drawbacks of conventional pre-treatments to be overcome.

DESCRIPTION OF THE INVENTION

It has now been found that it is possible and advantageous to replace the conventional pre-treatment of immersion in an aqueous solution with the application of a composition in the form of a foam. The foam is applied to the textile substrate by means of blade spreading, printing with a screen printing cylinder, impregnation on cylinders, hopper or with an injection system. Subsequently, the substrate is dried in an oven, stenter or in a printing attic.

The process of the invention allows to limit the weight increase of the treated fabrics to 20-25% with consequent great energy saving as it is enormously easier to dry the treated fabrics with 25% applied humidity compared to 75% of the traditional method by immersion.

Further advantages of the process of the invention include:

- Less overall dimensions of the systems; the machinery necessary for the application of the system can be considerably reduced in structure and overall dimensions compared to the normal application technology.

- Improved production capacity; a higher processing speed is possible and therefore greater quantities of fabrics treated for the same time.

- Lower environmental impact due to the lower quantities of chemicals and water.

The process of the invention can be applied to all dyes normally used such as reactive dyes, acid dyes, disperse dyes and pigments. The textile substrates that can be used include protein, cellulosic and polyester fibers. These fibers are constituent parts of the different types of fabrics both in purity and in blends with all the possible relative percentages. The fabrics include artifacts deriving from knitting processes, from double needle bed weaving, from orthogonal weaving and from binding processes for the formation of non-woven fabrics (TNT).

The foam composition can for example be obtained by treating an aqueous solution of the necessary components and containing a suitable foaming agent in a foaming machine.

For the formation of the foam it is possible to use different classes of surfactants both pure and in mixture capable of forming foams with density and elastic behavior compatible with the concentration of the solutions used. Particularly advantageous is the use of alkylamines, for example the N-oxides of tertiary alkylamines, in percentages between 0.1 and 5%, preferably between 0.1 and 3%.

To stabilize the foam it is possible to use different classes of stabilizers, but preferably the stearates and its derivatives, in percentages between 0.3 and 12%, preferably between 0.3 and 2%.

In addition to the foaming agent and possibly a foam stabilizer, the composition that can be used according to the process of the invention requires chemical additives of conventional use in pre-treatments for digital printing such as dispersants, solubilizers, emulsifiers, preservatives, viscosity and acidity regulators. and ionic strength. Examples of such additives include galactomannans of natural origin such as guar gum, tamarind gum, carrageenan and the like, alginates in the form of sodium alginate, starches, dextrins, cellulose derivatives, acrylic polymers in aqueous dispersion, biocides such as isothiazolinone, bromopol, cresols and the like, anionic or non-ionic surfactants, carbamide and its derivatives, Redox systems such as sodium methanitrobenzenesulphonate, sodium metavanadate, sodium bromate, pH regulators such as organic acids, ammonium sulphate, ammonium tartrate.

A specific example of a pre-treatment composition for printing with acid dyes is shown in table 1.

Table 1

Preparation for 1000 g

Component Concentration range Preferably Water 341-962 736.5 g Carbamide 1-350 g 100 g Citric acid 1-8 g 3 g Bromopol 0.1-1 g 0.5 g Guar flour 30-120 g 50 g Hydroxycellulose 2-10 g 5 g Stearates 3-120 g 80 g Alkylamine 1-50 g 25 g

pH 5-6 5.5

For the other classes of dyes, depending on the type of textile substrate,

it works by varying the type and concentration of thickeners, pH value,

presence of acrylic polymeric dispersions and polyethylene glycols by weight

molecular between 150 and 300.

The foam is typically applied to the substrate at one rate

variable depending on the type of substrate. After pre-treatment with the

foam, the substrate is dried at a suitable temperature,

typically between 100-110 ° C.

The following examples illustrate the invention in greater detail.

Example 1 - Complete process for printing a sample of 10

meters of pure silk fabric

A three peg weave pure silk fabric (meter weight <2> 120 g) was

previously washed and prepared for printing, using

300 grams per 10 meters of fabric of a formulation having the composition reported in Table 1. The formulation was treated in a foaming machine with a needle mixing element. The foam was applied with an air knife spreading system.

In the next phase, the fabric was subjected to ink jet printing (Robustelli Monnalisa printer) with Almiojet A (r) acid dye. A standard drawing with geometrically shaped elements was printed for the evaluation of the result.

The fabric was then dried by forced ventilation hot air at 80 ° C. The fabric was subsequently vaporized in the Arioli Steamer equipment, washed with water at 40 ° C and subsequently characterized by evaluating the color fastness to light and washing and by visual and spectrophotometric evaluation of the results obtained.

Example 2 - Industrial tests

An industrial test was carried out on different fabrics all equally prepared, purged and bleached.

The following fabrics were used:

- 180g cotton canvas per square meter:

- Viscose fabric of 150 g / square meter

- 280 g / square meter cotton jersey

- Viscose jersey of 280 g / square meter

- Cotton satin of 180 g / square meter

- 120 g / square meter cotton canvas.

For these cellulosic fabrics the following formulation has been prepared, suitable for printing with reactive dyes (Almiojet R).

g / kg

Water q.s.

Carbamide 50-300 Sodiomethanitrobenzenesulfonate 5-30

Sodium carbonate 15-90

Preservatives 1-3

Acrylic polymers 50-500

Sodium alginate 1-15

Alkylamines 4-50

Dispersion of stearates 5-100

Hydroxycellulose 2-60

Total 1000

The formulation thus described was calibrated in relation to the type of standard fabric used (150 g / m2).

After preparation, this solution was subjected to transformation into foam by means of a special machine (Hansa Mix foaming machine) obtaining a foam with a specific weight of 0.28 kg / l. The combination of the foam and the application system allows to perform a precision dosing allowing a very high control of the quantity deposited on the fabric unlike the traditionally used methods.

The foam thus produced was sent to the applicator device.

The industrial device used in this case is a Reggiani-Unica rotary printing machine, magnetic doctor blade, 80 mesh screen printing zinc-nickel cylinder.

The application took place at a speed of 10-15 meters per minute, with subsequent continuous drying in a gas oven at a temperature of 100-110 ° C.

It was estimated that each fabric, based on its weight characteristics, retained an amount of applied foam on average equal to 22-26% by weight.

The fabric thus prepared, subjected to straightening (optical Mahlo) and rolled up, was sent to the digital printing process.

For this process, a digital printer from the Robustelli company called Monna-Lisa with 16 print heads with piezoelectric technology and reactive inks installed (Almiojet R) was used.

The printing was carried out with a resolution of 720x720 dpi, 8 steps.

The print was subsequently dried with an electric oven (Unitech 2012) at 100 ° C.

After drying, the fabrics followed the normal post-printing process specific for fabrics printed with reactive dyes.

- Vaporization in saturated steam at 102 ° C for 12 minutes.

- Wide wash (Arioli Uniwash) at a temperature of 90 ° C with suitable detergents.

- Drying.

- Final check.

The prints obtained were subjected to comparative tests with similar prints made on the same articles with the same production processes with the exception of the preparation which was carried out with the standard method currently used (immersion padding).

The prints were then subjected to visual and instrumental evaluation. The visual evaluation determines the visual impact by difference between the two samples based on the response given by qualified personnel, while the instrumental evaluation is based on the use of a spectrophotometer that measures the differences between the two application methods.

The results deriving from these evaluations can be summarized as follows:

Table 2

Visual evaluation Traditional Invention - Color rendering ++++ ++

- Sharpness ++++ +++ - Edge hold ++++ +++ Instrumental evaluation Traditional invention - Color rendering ++++ +++ Table 2 shows an evident advantage of the system described here. The foam system object of the invention is applied in the preparation of fabrics intended for Inkjet printing, but it can be advantageously used in the conveyance of substances capable of imparting innovative characteristics and functions to the different types of fabric listed above. Carrier substances include polymeric dispersions such as acrylic, urethane and fluorinated ones, salts, UV-absorbers, biocides, etc.

Claims (9)

CLAIMS 1. A digital printing process of textile substrates in which the pretreatment of the substrates for the fixation of the inks is carried out by applying a composition in the form of a foam. A process according to claim 1 wherein the composition comprises at least one foaming agent and at least one foam stabilizer. 3. A process according to claim 2 in which the foaming agent belongs to the class of alkylamines and the stabilizer is a dispersion of stearates. 4. A process according to one or more of the preceding claims in which the composition further comprises one or more components selected from galactomannans, acrylic polymers, hydroxyethylcellulose, alginates, starches, dextrins or derivatized celluloses, biocides, carbamide, pH regulators, redox systems. A process according to one or more of the preceding claims in which the foam is applied by knife spreading, printing with a screen printing cylinder, impregnation on cylinders, hoppers or by means of injection systems. A process according to one or more of the preceding claims in which the inks are acidic, reactive or disperse dyes. 7. Foam compositions for pre-treatment for digital textile printing. 8. Compositions according to claim 7 comprising a foaming agent, a foam stabilizer and one or more components selected from galactomannans, acrylic polymers, hydroxyethylcellulose, alginates, starches, dextrins or derivatized celluloses, biocides, carbamide, pH regulators, redox systems. 9. Compositions according to claim 8 wherein the foaming agent is an alkylamine and the foam stabilizer is alkaline or ammonium stearate in suspension.