Method for dyeing the surface of a workpiece

Description

[0001] The invention relates to a method for coloring the surface of a polypropylene workpiece with a colorant. The invention also relates to a product comprising a colored polypropylene workpiece. BACKGROUND OF THE INVENTION

[0002] Polypropylene components are widely used, for example, as polypropylene fibers in textiles. A particular characteristic of polypropylene fibers arises from their hydrocarbon-based structure, which makes them highly hydrophobic. The low capacity of polypropylene fibers to absorb moisture from the air or as capillary water makes these fibers particularly attractive for applications requiring rapid drying and a reduced feeling of wetness. Typical applications include sports underwear and the inner layers of disposable diapers. Polypropylene fibers are also used in the automotive industry (e.g., in carpets).

[0003] Particularly in textile applications, there is a demand for dyed polypropylene fibers, driven by functional, optical, and fashion considerations. Therefore, dyeing processes for polypropylene (PP) are of great interest. While the hydrophobic nature of PP is responsible for its unique functional properties, the lack of functional groups makes dye adhesion very difficult in aqueous dyeing processes. Dyeing with other systems is also practically very difficult with polypropylene fibers, as the dyes do not adhere to the PP.

[0004] The most commonly used dyeing method involves introducing dye during fiber production. A master batch containing the dye is mixed with the polypropylene during the melt spinning process, which produces colored fibers through extrusion. This bulk dyeing method of PP allows for the creation of any color with very high fastness requirements. However, because the dyed fibers are produced during the fiber spinning process, several critical disadvantages arise: The method is only economical for relatively high production volumes, as the entire spinning machine must be filled with colored polymer, and large quantities of transition colors between two shades are generated as waste.The dyeing process takes place at the fiber level and is therefore not changeable in subsequent processes; likewise, yarns or surfaces cannot be dyed or printed, which severely limits technical flexibility.

[0005] To make existing polypropylene-based fibers dyeable, various concepts have been proposed in the literature. Several dyeing techniques attempt to improve the adhesion of dyes to textiles with polypropylene fibers by incorporating polymers with functional groups into the spin mass. However, these "incorporation techniques" suffer from the disadvantage of simultaneously altering the fiber properties, causing the textile to resemble other fiber polymers and thus losing the special properties of the polypropylene fiber. Other techniques attempt to bond the dye and the polypropylene fibers through a reaction, which is complex and requires hazardous chemicals.

[0006] US 3,314,743 discloses a process in which a polypropylene fabric is treated with 2-sulfododecanoic acid and then dyed with a cationic dye. US 3,653,799 describes the dyeing of textile fibers by first coating the fibers with a resin and then dyeing them. US 5,618,622 describes a surface-modified fiber material containing hydrocarbon polymer fibers with cationic or anionic groups on the surface and coated with a polyelectrolyte whose net charge is opposite to that of the cationic or anionic groups on the fiber surfaces. BRIEF DESCRIPTION OF THE INVENTION

[0007] In summary, various methods for coloring polypropylene are available according to the current state of the art. However, each of these methods has specific disadvantages, which is why only a few are actually used today.

[0008] The object of the present invention is to provide a method for dyeing polypropylene workpieces, which can be carried out on existing textile processing equipment using existing textile dyes in useful color depths and with suitable colorfastness. The invention also aims to provide correspondingly dyed workpieces.

[0009] This problem is solved by a method for coloring the surface of a workpiece with a colorant, characterized in that the workpiece is impregnated in a first step with a cationic polypropylene dispersion and is colored in a subsequent second step with an anionic colorant.

[0010] Furthermore, the problem is solved by a product comprising a workpiece which has a layer on its surface comprising polypropylene and at least one cationic surfactant, wherein an anionic dye is arranged on the layer.

[0011] Polypropylene dispersions have been known for some time. They are essentially aqueous systems in which polypropylene is dispersed. In certain cases, an emulsion may also be present. In this case, polypropylene with short chain lengths and low isotacticity is used.

[0012] A cationic polypropylene dispersion is one that contains a cationic surfactant. The cationic surfactant binds to the dispersed polypropylene.

[0013] It is therefore preferred that the polypropylene dispersion is a dispersion of polypropylene with a cationic surfactant.

[0014] In the simplest case, impregnation with the cationic polypropylene dispersion is achieved by immersing the workpiece in a bath containing the cationic polypropylene dispersion. This forms a layer of polypropylene with cationic surfactant on the surface of the workpiece. This layer is adsorbed onto the surface, and the cationic surfactant imparts a positive charge to the surface.

[0015] The workpiece is preferably made of plastic. It is particularly preferably made of polypropylene.

[0016] Furthermore, it may be necessary to dry the workpiece after impregnation with the cationic polypropylene dispersion. In the simplest case, this is done by removing the workpiece from the bath containing the cationic polypropylene dispersion and drying it in air. Increasing the temperature can accelerate the drying process.

[0017] Although it has been found that impregnating the workpiece with the cationic polypropylene dispersion already results in a layer that permanently adheres to the surface (adsorbs), it has nevertheless proven advantageous to heat the workpiece to over 100°C, preferably between 110 and 155°C, after impregnation. This causes the polypropylene layer with cationic surfactant on the surface of the workpiece to melt slightly and adhere to it. However, this is not a complete melting of the layer, but rather a process in which—similar to sintering—only the surface softens slightly.

[0018] Melting the polypropylene layer with cationic surfactant onto the surface of the workpiece significantly increases the durability of the coloring and also allows the product to be cleaned in a boiling wash cycle.

[0019] Any anionic dye used in the dye industry can be used as an anionic colorant. Anionic dyes are preferred. Particularly preferred are anionic dyes typically used in wool dyeing, such as anionic natural dyes. Anionic dyes are sometimes also called acid dyes.

[0020] The drying and heating steps can be combined and carried out simultaneously in one step.

[0021] The process is preferably used in the textile industry, so that the workpiece preferably contains polypropylene fibers.

[0022] The polypropylene workpiece can be flat. Preferably, it comprises polypropylene fibers. It can be, for example, a woven fabric, knitted fabric, nonwoven fabric, etc. Similarly, films, sheets, irregularly structured workpieces, and thick workpieces can also be modified.

[0023] With regard to the product, it may be provided that the layer is partially or completely melted onto the surface of the polypropylene workpiece.

[0024] As explained below, the invention also relates to a method for coloring the surface of a workpiece with a colorant, which is characterized in that the workpiece is impregnated in a first step with an anionic polypropylene dispersion and is colored in a subsequent second step with a cationic colorant.

[0025] The details outlined above apply to a cationic and an anionic colorant with changed signs, and also to the variant anionic polypropylene dispersion and cationic colorant.

[0026] Therefore, the invention also relates to a product comprising a workpiece which has a layer on its surface comprising polypropylene and at least one anionic surfactant, wherein a cationic dye is arranged on the layer.

[0027] In all embodiments, it is preferably provided that the workpiece comprises a plastic, preferably polypropylene, and particularly preferably contains polypropylene fibers.

[0028] Furthermore, the workpiece can be of a flat form and in particular comprise at least a woven fabric, a knitted fabric, a nonwoven fabric, a layer, a plate, an irregularly structured workpiece or a combination thereof.

[0029] Preferably, the layer is melted onto the surface of the workpiece.

[0030] The invention also relates to a product comprising a workpiece which has a layer on its surface comprising polypropylene and at least one cationic surfactant, wherein an anionic active ingredient is arranged on the layer.

[0031] The invention also relates to a product comprising a workpiece which has a layer on its surface comprising polypropylene and at least one anionic surfactant, wherein a cationic active ingredient is arranged on the layer. DETAILED DESCRIPTION OF THE INVENTION

[0032] The inventors have discovered that by impregnating workpieces made of polypropylene (e.g. polypropylene fibers or textile surfaces made of polypropylene fibers) with a cationic polypropylene dispersion, the surface charge of the fibers can be increased to such an extent that dyeing with anionically charged dyes, such as those used for wool or polyamide, is possible.

[0033] In one embodiment of the invention, a polypropylene fiber is impregnated with a cationic polypropylene dispersion from an aqueous phase. If a polypropylene dispersion with a 40% solids content is used, it can be applied undiluted or, preferably, diluted with water to the fiber material by immersion and squeezing. With a liquor absorption rate of 80%, the amount of polypropylene dispersion deposited on the material ranges from 3% to 3% of the material weight. In a preferred embodiment, between 10% and 20% of the material mass is applied, and particularly preferably, between 15% and 25% of the material mass is applied.

[0034] After application, the aqueous phase is dried, the temperature in conventional drying equipment e.g. tensioning frames, drum dryers, pressure dryers being adjusted according to the form of the fibers and the drying temperature preferably being between 80 °C and 130 °C, particularly preferably between 105 and 115 °C.

[0035] The drying energy can be transferred by hot air, superheated steam, contact heat, infrared radiation or microwave radiation, although other drying methods can also be used.

[0036] Following drying, the applied polypropylene dispersion is fixed to the material by a thermal step. The required fixing temperature depends on the molecular weight of the polypropylene dispersion used and is typically between 110 °C and 160 °C, preferably between 115 °C and 155 °C, and particularly preferably between 120 °C and 140 °C. The required lower temperature limit is determined by the fixing of the PP dispersion, and the upper limit is determined by the maximum treatment temperature of the PP fiber. If the lower limit is not reached, adsorption will occur, but the fixing of the dispersion is not ideal for certain textile applications involving frequent cleaning (especially at high temperatures).If the upper temperature limit is exceeded, a thermal change in the fiber structure of the PP fiber begins, which would result in the loss of molecular orientation and thus the specific fiber properties.

[0037] A fiber surface-treated in this way with a cationic polypropylene dispersion can now be dyed with conventional acid dyes. Similar to wool and silk, the fiber now possesses sufficient cationic charges on its surface to enable the binding of the anionic acid dye.

[0038] This allows PP fibers treated in this way to be advantageously dyed in a single bath when mixed with other fibers, such as wool or polyamide. Similarly, other fibers can be added and dyed using the appropriate methods. For example, a PP / polyester fiber blend can be dyed using the same methods as a wool / polyester fiber blend.

[0039] By using existing dye groups, a wide range of color nuances can be achieved, and conventional dyeing equipment can be used for the processes. If the basis of this invention is known, other application techniques can also be used, e.g., pad-dry thermosol techniques.

[0040] If the cationic polypropylene dispersion is applied locally using an application technique, e.g. by printing, spraying, etc., a patterned or local coloring can also be achieved in a subsequent process or during the printing process.

[0041] Instead of negatively charged dyes, functional substances such as antimicrobial agents or optical brighteners can also be bound to the existing cationic centers in an analogous manner.

[0042] Based on the present invention, an analogous process is also possible using anionic polypropylene dispersion, in which case the modified fibers carry a negative charge and the dyeing is carried out with cationic dyes. With appropriate adaptation and expert optimization, the technique can be adapted to other fibers, in particular those that are difficult to dye, such as UHMPE (ultra-high molecular weight polyethylene) or aromatic polyamides (e.g., Kevlar, Nomex), aromatic polyesters (e.g., Vextran), or even glass fibers. The thermal treatment conditions must be adapted to the resistance and properties of the fibers, for example, by using low-melting-point polypropylene dispersions or by using polyethylene dispersions. APPLICATION EXAMPLES: Application example 1

[0043] A knitted fabric made from PP fibers is impregnated using a cationic PP dispersion (e.g., Michem Emulsion, 28640, 40% PP by volume). The different concentrations of PP dispersion listed in Table 1 are applied and, after drying at 100 °C, fixed at an elevated temperature between 110 and 155 °C. The liquor uptake during application of the dispersion is approximately 100%. For comparison, PP samples are subjected to the same thermal treatment. Subsequently, the fabric is dyed with an anionic dye (Nylosan Red F-2R acid dye) with a color depth of 1% (10 mg dye / g fabric) at 60 °C (1 h). After dyeing, the fabric is rinsed twice at 60 °C for 10 minutes and then again for 10 minutes with cold water. Dye uptake can be evaluated using the CIELab coordinates and the K / S value at 480 nm.The stability of the color is assessed by its wet fastness (DIN 54006, grade 5 very good, grade 1 very poor). Table 1. Impregnation of PP knitted fabrics with cationic PP dispersion (duplicate determinations). Conditions, color coordinates and fastness ratings. sample % dispersion content Fixed temperature L* a* b* K / S Authenticity of color changes. Authenticity of wool 1a 100 110 49.49 43.25 21.82 5.97 3.5 3-3.5 1b 100 110 48.72 45.30 24.28 6.73 3.5-4 3.5 2a 100 130 47.56 46.87 25.10 8.26 3.5-4 4 2b 100 130 48.29 46.44 23.95 7.18 3.5-4 4 3a 100 155 47.33 43.56 22.13 7.08 4 4-4.5 3b 100 155 49.23 44.16 20.11 6.33 4 4-4.5 4a - 110 71.00 14.23 4.65 0.70 4-4.5 4.5-5 4b - 110 71.99 12.39 5.82 0.69 4-4.5 4.5-5 5a - 130 68.93 16.07 7.19 0.92 4-4.5 3.5 5b - 130 68.77 13.40 7.02 0.88 4-4.5 3.5 6a - 155 70.63 14.30 5.98 0.75 4-4.5 4-4.5 6b - 155 66.95 17.82 12.15 1.21 4-4.5 4-4.5

[0044] The color coordinate values ​​clearly show the increased dye uptake and color depth achieved through the treatment. Fastness remains at a good level, but the increased color depth results in a reduction in fastness. Application example 2

[0045] Yarn samples made of Vectran (aromatic polyester, Nm36 / 2) and UHMPE (ultra high molecular weight polyethylene, Nm 54 / 2) are treated and dyed in the same manner as in application example 1.

[0046] The dispersion of cationic polypropylene is diluted with water (60% dispersion and 40% water). A fixing temperature of 130 °C is applied for 10 minutes. Coloring with acid dye is carried out analogously to application example 1. Table 2. Impregnation of knitted fabrics with cationic PP dispersion (duplicate determinations). Conditions, color coordinates and fastness ratings. sample material Salary at Disp. % L* a* b* K / S Authenticity of color changes. Authenticity of wool 7a Vectran 60 52.28 43.97 30.19 5.81 4-4,5 2,5 7b Vectran 60 53.15 44.20 29.55 5.54 4-4,5 3 8a UHMPE 60 54.35 51.76 37.55 6.96 3,5-4 3,5 8b UHMPE 60 56.34 47.50 32.62 5.07 4 3,5 9a Vectran - 72.51 11.43 14.67 0.62 - - 9b Vectran - 74.07 10.70 14.82 0.55 - - 10a UHMPE - 77.70 20.32 17.20 0.58 - - 10b UHMPE - 79.56 19.95 16.91 0.50 - -

[0047] The authenticity of the untreated samples was not determined, as low color uptake was observed and therefore the authenticity was irrelevant.

[0048] Figs. 1 and 2 Laser scanning microscope shows photos of treated ( Fig. 1 ) and untreated PP fibers ( Fig. 2 ).

[0049] The figures clearly show that deposits are formed on the treated PP fibers through layer formation.

[0050] The presence of surfactants can also be detected using FT-IR.

Claims

1. Process for colouring the surface of a workpiece with a colouring agent, characterised in that the workpiece is impregnated with a cationic polypropylene dispersion in a first step and coloured with an anionic colouring agent in a subsequent second step.

2. Process according to claim 1, characterised in that the polypropylene dispersion is an emulsion of polypropylene with a cationic surfactant.

3. Process according to claim 1 or claim 2, characterised in that the workpiece is dried after impregnation with the cationic polypropylene dispersion.

4. Process according to one of claims 1 to 3, characterised in that the workpiece is heated to above 100°C, preferably to between 110 and 155°C, after impregnation with the cationic polypropylene dispersion.

5. Process according to one of claims 1 to 4, characterised in that the workpiece comprises a plastic, preferably polypropylene, and particularly preferably has polypropylene fibres.

6. Process for colouring the surface of a workpiece with a colouring agent, characterised in that the workpiece is impregnated with an anionic polypropylene dispersion in a first step and coloured with a cationic colouring agent in a subsequent second step.

7. Product comprising a workpiece having on the surface a layer comprising polypropylene and at least one cationic surfactant, on which layer an anionic colouring agent is arranged, characterised in that the layer is fused to the surface of the workpiece.

8. Product comprising a workpiece having on the surface thereof a layer comprising polypropylene and at least one anionic surfactant, said layer having a cationic colorant disposed thereon, characterised in that the layer is fused to the surface of the workpiece.

9. Product according to claim 7 or claim 8, characterised in that the workpiece comprises a plastic, preferably polypropylene, and particularly preferably has polypropylene fibres.

10. Product according to claim 9, characterised in that the workpiece is flat, in particular comprises at least one woven fabric, a knitted fabric, a non-woven fabric, a layer, a plate, an irregularly structured workpiece or a combination thereof.

11. Product comprising a workpiece having on the surface thereof a layer comprising polypropylene and at least one cationic surfactant, wherein an anionic active ingredient is disposed on the layer, characterised in that the layer is fused to the surface of the workpiece.

12. Product comprising a workpiece having on the surface thereof a layer comprising polypropylene and at least one anionic surfactant, wherein a cationic active ingredient is disposed on the layer, characterised in that the layer is fused to the surface of the workpiece.