The Status Quo of Paint Printing Adhesives and Research Dynamics
The large amount of paint printing adhesive is the key to ensure the quality of paint printing. Through several decades of improvement, the adhesive has made great progress in solving the hand and color fastness. Over the years, soft feel has been achieved by adjusting the ratio of soft monomer to hard monomer in the copolymer or changing the hard monomer. The second is to lower the film formation temperature so that the film formation temperature meets the process requirements. The third is to add self-crosslinking monomers for copolymerization in the adhesive component, usually using methylol acrylamide to improve the film fastness. The fourth is the addition of etherified methylol melamine as an external cross-linking agent to the adhesive to improve the film fastness and thereby reduce the amount of adhesive. Fifth, printing and dyeing plants use roasting fixation to increase the density of the film.
l, the type of adhesive:
Currently widely used adhesives are roughly classified into three major categories. One is an acrylate-based adhesive, the soft monomer is butyl acrylate, the softest is isooctyl acrylate, and the hardest monomer is methyl acrylate. Ester, styrene, acrylonitrile, etc., this type of adhesive film has high transparency and is currently the most commonly used adhesive. The second is butadiene-based adhesives, and the hard monomers are styrene (SBR) and acrylonitrile (nitrile emulsion), and other polymers are added to increase the film strength. Soft, but easy to yellow, cheap, do not need to bake fixed. Thirdly, polyurethane adhesives are polymer materials obtained by the polymerization of polyisocyanate compounds and polyethers or polyesters containing active hydrogen atoms. If they are polymerized with polyethers, they are said to be resistant to hydrolysis. Soft to the touch, but poor in light and heat resistance. Polyester polyurethanes polymerized with polyester have good light and heat resistance and good elasticity. However, they are not resistant to hydrolysis. Polyurethane adhesives are not as acrylates due to their good elasticity, softness, and flexibility. The adhesive can adsorb dust in the air and has good color fastness and is suitable for printing of knitted fabrics. Polyurethane adhesives are divided into solvent type and water emulsion type. Solvent-based emulsions use a solvent such as toluene in the baking oven to volatilize, and must be well ventilated. The water emulsion is free of this defect. In addition to the above three types, there are silicone elastomer adhesives, vinegar and acetic acid (acetic acid). Vinyl esters and acrylate copolymers, but rarely used.
2, the stability of the adhesive emulsion.
The stability of the adhesive emulsion is related to the color fastness. Emulsion particles should be controlled at 0.2m, and their particle size distribution should be uniform. They cannot have large particles and very small particles at the same time. Otherwise, the fastness to rubbing will be reduced. The method to determine the quality of the emulsion is to observe the appearance of the emulsion. Description of the larger particles, at least 5m or more, the description of the emulsion with yellow particles is very uneven, the general particle is at least 2m above, the description of the emulsion with blue light is about lm, the ideal adhesive should be translucent with blue light Emulsions, which are not milky white, indicate that their particle size is in the range of 0.2 to 1 m, and the particle size distribution is narrow, and printing and dyeing plants should reject binders with yellow or gray milky white emulsions.
3, improve the adhesive’s crockfastness.
The crockfastness of paint printing is the most troublesome thing for paint printing. In the past, silicone was often added to the printing paste, but the effect was not significant. Some people think that this is caused by the uneven size of the paint particles, some people think that is caused by the adhesive, because the same coating using polyurethane adhesives can meet the rubbing fastness, but the use of acrylate adhesives is not qualified, and the use of different Matching adhesives have different conditions. Of course, the coating particles have an influence. If the particle size is large, and the uneven distribution of the crystal shape and the particle size will naturally reduce the rubbing fastness, the binder plays a decisive role when the coating material is not changed. The main factor that determines the impact of the adhesive on the fastness to rubbing is the coefficient of friction of the film. The smoothness of the film has a high fastness to rubbing, and the fastness of the polyacrylate with a high soft monomer content is lower than the content.
There are three methods to solve the crocking fastness: First, add the agent to improve the crocking fastness in the color paste, they are silicone elastomer, or oxidized polyethylene emulsion, the amount is more than 5%, with little effect, its purpose It is a substance that adds smoothness to the film. The second is the use of polyurethane adhesives to improve the performance of the film by means of polyurethane. The third is the copolymerization of acrylates and silicone monomers to make new interpolymers.
4, to solve the problem of free formaldehyde.
The harmfulness of free formaldehyde and its limited requirements on clothing have been known to everyone. The free formaldehyde on the paint-printing fabric comes from the adhesive. The first is the use of methylol acrylamide as the cross-linking monomer. It releases formaldehyde when self-crosslinking, but its content is not high, only the total amount of monomers. 3-5%. The second is the addition of an external cross-linking agent in the adhesive, ie, an etherified melamine formaldehyde resin, which is contained in many foreign samples.
The solutions are:
One is to use self-crosslinking monomers instead of other monomers. For example, the condensate of acrylic acid and epichlorohydrin is used. The product is the printing adhesive DPCE6J.
The second is to use a self-crosslinking monomer without copolymerization, and the adhesive is made into a crosslinked adhesive (i.e., a binder containing a hydroxyl group, an amino group, and an amide group). External cross-linking agent is added to the printing paste. The external cross-linking agent includes cross-linking agent EH, cross-linking agent H, cross-linking agent FH, cross-linking agent WHP, which are all condensation products of epichlorohydrin and amines. At present, cross-linking agents of bis-ethylene urea structure are worthy of exploration and application, such as cross-linking agent SU,125FE. Third, melamine crosslinking agent is not allowed to be added in the adhesive. The printing and dyeing plant should strictly check and enter into the factory, and measure the content of formaldehyde in the adhesive. Any adhesive with high formaldehyde content is not allowed to be used.