1 Introduction
Paint printing is a film-forming principle on the surface of fabrics by using adhesives. The coatings without affinity and reactivity are adhered to the fabric, and then baked to fix the coating on the surface of the fabric, giving the fabric various colors and The printing process of the pattern. Compared to traditional printing processes, paint printing has many advantages. For example, paint printing is not limited by fabric fibers, and is not affected by the weaving method; paint printing is generally fixed after printing without washing, thereby shortening the process, saving water, electricity, gas, and reducing printing and dyeing wastewater. Environmental pollution paint printing chromatogram complete, bright color, printed outline is clear, for general dye printing is not as good; can also print special patterns. Therefore, the process is widely used in the printing and dyeing industry. According to incomplete statistics, paint printing fabrics in the world account for about 55% of the total amount of printed fabrics. In the United States, paint printing fabrics account for 80% of the total output of printed fabrics, and polyester/cotton fabrics are almost all printed with paint. In recent years, the proportion of paint printing has also increased in China due to factors such as simplification of process and reduction of energy consumption, accounting for about 20%. 25 levels. The National Economic and Trade Commission also included paint printing as one of the processes in the textile industry to promote cleaner production.
2 paint printing requirements for adhesives
Paint printing is the mechanical bonding of coatings and adhesives to the surface of textile fibers. Therefore, the role of adhesives in paint printing pastes is important. The hand touch, vividness, and various fastnesses (friction, washing and dry cleaning fastness) of the printed products depend to a large extent on the quality of the adhesive. Therefore, the adhesive with excellent performance should meet the following requirements: After the adhesive is printed on the fabric, it can be dried and baked to form a colorless, transparent, strong adhesive, elastic and tough film; UV resistant Anti-aging, no yellowing; the film should resist flexing, anti-crease, no hard, no stickiness, no adsorption of colored substances, resistance to organic solvents and other chemicals; adhesive emulsion should have good storage stability The film formation can not be too fast, the room temperature is not crusted, does not condense, the printing paste is not plugged, the drum is not stained, and it is easy to rinse; the adhesive also has certain heat resistance and frost resistance.
3 polyacrylate adhesive
Most of the adhesives currently used for paint printing are polymer emulsions, but not all emulsions are compatible with hand, toughness, elasticity, transparency, mechanical strength, adhesion, especially printing fastness and hand feeling. Paint printing requirements. The emulsion adhesives which can be used for fabric printing can be divided into polyacrylates, butadienes, vinyl acetates and polyurethanes according to their chemical structures. Among them, polyacrylate adhesives are the most popular ones. Adhesive.
3.1 Polyacrylate adhesive structure
Polyacrylate adhesives are mainly composed of hard monomers, soft monomers and functional monomers.
3.1.1 Hard monomer
There are mainly methyl methacrylate, acrylonitrile and styrene. Its function is to provide structural strength, wear resistance and washing resistance, so that the film after curing has good transparency and high fastness.
3.1.2 Soft monomer
It is mainly composed of a substance such as ethyl acrylate, butyl acrylate or isooctyl acrylate, and its function is to improve the flexibility and elasticity of the adhesive film.
3.1-3 functional monomer
Mainly divided into two kinds of carboxyl monomers and cross-linking monomers. The carboxyl monomer mainly includes acrylic acid, methacrylic acid, maleic acid, etc., and its function is to improve the stability of the binder emulsion, provide a crosslinking position, act as a cross-linking catalyst, and have a self-thickening effect. The cross-linking type monomers are mainly hydroxypropyl acrylate, glycidyl acrylate, and the like. The cross-linking monomer can simultaneously react with the hard monomer, the soft monomer and the carboxyl monomer to crosslink the linear polymer to form a crosslinked macromolecule of the network structure, and at the same time, with the hydroxyl group on the fiber, etc. Covalent bonding occurs to form a firm film, improve rubbing fastness and soap fastness, and increase film strength and elasticity.
3.2 Development and improvement of polyacrylate adhesives
The development of foreign paint printing adhesives is fast, and the replacement is rapid. The current research direction is low-temperature cross-linking adhesive [7--L0]o. The paint printing adhesive products produced in China are compared with foreign similar ones. There are still gaps in color, fastness and stability, compatibility, chemical resistance, and solid content. According to reports, domestic low-temperature curing adhesives have been explored in monomers, cross-linking agents and synthetic processes. The components are mostly copolymers of acrylates and other vinyl monomers, but the performance is still not comparable with that of foreign countries. LL--L3]~ Currently widely used in paint printing is a polyacrylate adhesive which uses methylol acrylamide as a white crosslinking monomer. The adhesives have good transparency, strong adhesion to the coating and strong adhesion to the fibers; the color fastness is improved by baking, thereby reducing the proportion of hard monomers, thereby reducing the binder in the printing paste. The amount of use and improved the feel of the printed fabric. However, there are limitations. For example, during the baking and storage process, methylol acrylamide releases formaldehyde; when the pattern is large, the hand feel is not soft enough; wet rubbing fastness is difficult to meet customer requirements; simply increase the soft monomer ratio, then The dusting property and the adhesion property are also improved, so that the clothes are easily sucked in the air. At the same time, with the enhancement of environmental awareness and the development of corresponding environmental regulations in various countries, the research and development of paint printing adhesives at home and abroad is developing in the direction of protecting the ecological environment. The development of low-temperature adhesives without formaldehyde or low formaldehyde has become a research. Focus. To this end, the researchers conducted extensive research in the following aspects.
3.2.1 Development of new crosslinkers
3.2.1.1 Reduce formaldehyde release
An acrylate compound containing an epoxy group such as methacryloyl epoxy ester, methacryloyloxyethyleneimine, N-alkyl-N-2-alkylacetamide (NANDA), and chitin A method of replacing methylol acrylamide to reduce formaldehyde release.
1) Add formaldehyde trapping agent (1% of total solid content) to the comonomer ": such as 2,4-pentanedione, 2-cyanoacetate, etc., with formaldehyde during drying or baking The reaction occurs, reducing the amount of formaldehyde released.
2) Soy acid alcohol resin binder The performance of this adhesive is closely related to the length of the alkyl chain in the molecule. If the alkyl chain is longer than the acrylate adhesive, the dry cleaning of the printed product is strong. The degree of color and color is higher, but the rubbing fastness is not as good as that of the acrylate adhesive; if the alkyl chain is relatively short, the rubbing fastness is close, but the hand feel is hard.
3) Acrylate modified wheat protein binder [2L-22]I used for coating printing, because of its thickening effect, can reduce the amount of thickener in printing paste, washable and dry cleaning of printed products Degrees meet the requirements, but the feel is hard.
4) Water-dispersed formaldehyde-free printing adhesive 埘. This type of binder is a monomer of a dicarboxylic acid and a hydroxyethyl acrylate, ethyl acrylate or acrylamide, and is polymerized in an emulsion in which a phosphate ester is used as an emulsifier. This product is printed on a polyester/cotton blend with excellent wash fastness.
3.2.1.2 formaldehyde-free crosslinker
Develop new formaldehyde-free crosslinkers to replace methylol acrylamide to eliminate formaldehyde. Such as glycidyl acrylate and glycidyl methacrylate.
Glycidyl acrylate is a monomer having a difunctional group. It has a relatively higher reactivity than glycidyl methacrylate, and its products have excellent weather resistance, UV resistance, water resistance and heat resistance. Therefore, it has been widely used in many fields such as photosensitive materials, organic synthesis, polymer synthesis and polymer modification. However, there are few reports on paint printing. Glycidyl methacrylate is widely used in the synthesis and modification of polymer materials because it contains double bonds and epoxy groups in the molecule. In terms of synthesis, it is mainly used as a comonomer for reactive thermoplastic elastomer and thermosetting acrylic coating resin; in modification, it is mainly used as a modifier for various coatings, adhesives, plastic alloys, etc., such as modified thermosetting acrylic coatings, Polyoxyethylene coatings, alkyd resins, etc. have better weatherability and film forming properties; and modified adhesives and non-woven coatings have better adhesion, water resistance and solvent resistance.
3.2.2 Modification of polyacrylic adhesive
3.2.2.1 Silicone modification
Silicone emulsion has good permeability and heat resistance, cold resistance, chemical resistance, resistance to bending, and the hand feel is particularly soft, its wet rubbing fastness and smoothness are good, the film is not sticky, does not absorb dust, but its price It is significantly higher than polyacrylate. Water-based acrylate resin has good water resistance, weather resistance and mechanical properties, but it has the disadvantages of high hardness, hot sticky and crisp. Due to the complementary nature of silicone and polyacrylate, silicone/acrylate composite emulsions can overcome their respective shortcomings and significantly improve the performance of emulsions and films.
Silicone-modified polyacrylates are mainly realized by physical blending, solution polymerization and bulk polymerization, emulsion copolymerization, core/shell emulsion polymerization, interpenetrating network structure emulsions, etc., and studies have shown that in many aspects, chemical grafting is modified. The silicone/acrylate hybrid emulsion exhibits excellent performance and overcomes the disadvantages of low wet rubbing fastness, easy vacuuming and adhesion of polyacrylate adhesives. The silicone-modified polyacrylate adhesive can significantly improve the softness, abrasion resistance and corrosion resistance of the paint-printed fabric, and imparts properties such as resistance to contamination.
3.2.2.2 Modification of polyurethane
Polyurethane has good physical and mechanical properties, excellent cold resistance, elasticity, high gloss, and soft hardness with little change with temperature, resistance to organic solvents, etc., and has been widely used in adhesives, coatings and other fields. However, the polyurethane resin coating film has poor water resistance and mechanical strength as compared with acrylic resin, which has a certain complementary effect with the polyacrylate. If the two are combined, it is possible to overcome their respective disadvantages and exert their respective advantages. The performance of the film was significantly improved.
The synthetic methods of polyurethane/polyacrylate composite emulsion include blending cross-linking method, seed emulsion polymerization method, interpenetrating polymer network method and emulsion copolymerization method using interpenetrating network polymerization technology, using polyurethane prepolymer as seed, and acrylate. The monomer is subjected to radical polymerization to obtain a double-layer or three-layer polyurethane/polyacrylate polymer, which can overcome the disadvantages of poor elongation of the polyacrylate adhesive, low wet rubbing fastness, easy dusting and adhesion, and Significantly improve the softness and abrasion resistance of paint-printed fabrics. It has been widely used in plastic modification, coatings, adhesives and damping materials.
3.2.3 Improvements in emulsifiers and polymerization processes
1) A reactive emulsifier (sulfate containing a, p-unsaturated bond) is used to improve the hand of the fabric and to improve dry cleaning and water wash resistance.
2) A self-crosslinking paint printing adhesive with good comprehensive performance was synthesized by pre-emulsification method.
3) Nano-emulsion adhesives with molecular diameters less than 50 nm were prepared by nano-method to improve the performance of printing adhesives
4) The emulsion polymerization is carried out by using a special crosslinking monomer to synthesize a soft self-crosslinking adhesive, which improves the hand feeling of the printed product.
5) In the synthesis process, a printing adhesive prepared by using a soft monomer as a core and a hard monomer as a shell appears, so that it does not block the net due to the stickiness of the soft monomer component during printing, but the shell is truly There are not many particles in the core.
4 Conclusion
The balance between hand and color fastness in paint printing, environmental protection issues, etc. have not been satisfactorily resolved, and the core of solving these problems is to synthesize environmentally friendly printing adhesives, which will be studied in the following aspects.
1) Reduce product costs. 2) Accelerate the development of new products with lower temperature and cross-linking curing in a shorter time, especially the development of aldehyde-free self-crosslinking agent and high-efficiency catalyst. 3) Development of non-acrylate adhesives such as polyurethanes, cationic latexes, and the like. 4) Study new polymerization methods and new fixation methods, such as soap-free emulsion polymerization, ray fixation, and the like.
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