Design and Research of Water Based OPS Inks

Abstract: In this paper, the main factors affecting the performance of OPS (polystyrene shrink film) inks were analyzed experimentally, mainly from the perspective of toxicity, the environmental performance of the main components of OPS water-based inks was analyzed; through the link material, pH value , Viscosity, Dryness, and Their Relationships, Analysis of the Water Resistance of Water-based OPS Inks; Through the study of co-solvents, polymer monomers, pH, and pigment dispersion, the printing suitability of OPS water-based inks was analyzed; To study the dispersion, viscosity and additives of water-based inks, the anti-friction properties of OPS water-based inks were analyzed. Based on the design basis of the OPS water-based ink formulation, scientific OPS ink formulations were selected through comparative experimental analysis; the performance data obtained after the corresponding performance tests were compared with the expected indicators; the results showed that the inks obtained from the trial production Indicators meet the use requirements.

Key words: water-based OPS ink; environmental protection; water resistance; friction resistance; formulation research

Foreword: As global environmental pollution and the destruction of the ecological environment intensify, people pay more and more attention to life, attention to the environment and development, promote the production and use of green products, especially for food packaging health, environmental protection has made stricter The requirement for this was OPS shrink film packaging material. However, the polarity of the OPS shrink film is lower than that of the PVC shrink film, resulting in a series of printing problems and higher demands on the ink.

The objective of this study is to identify the optimal solution for formula design of POS water-based inks by focusing on improving the environmental performance, friction resistance, water resistance, and luster of OPS shrink film water-based inks.

First, the design principle of OPS water-based ink formulation

OPS shrink film water-based ink is a new type of gravure ink, has not yet formed a set of perfect national standards. According to the inspection methods and quality standards of various types of plastic gravure inks, the following principles should be followed when designing OPS shrink film water-based inks:

(1) The selected solvent cannot have an effect on the OPS film. The ink cannot be odor after drying, and has good storage stability.

(2) The selection of the ink raw material and the ink ink property are to be decided according to the type of print and the requirements. Only by understanding the type and purpose of the printed matter before designing can we select raw materials and ink quality standards according to its characteristics [1]. OPS water-based inks are required to have good fastness, meet shrinking requirements, and have a bright color.

(3) The choice of pigments and dyes should be determined according to the type of substrate: For example, if iron blue is used in the ink, it will change color, and products that are often displayed in the display window will be exposed to sunlight for a long time. If a salt-based rose is used in the ink, Red lake pigments, etc., will be severely discolored.

Second, the key factors affect the performance of gravure water-based ink

2.1 Environmental Performance Analysis

For the environmental protection of inks, the main considerations are the toxicity of the ink, the degree of harm to human health during printing and use, the flammability and explosive performance, and energy loss. Water-based ink is a new type of environmentally friendly ink. From the perspective of cost and energy consumption, it is the best, and the quick-drying nature of water-based inks makes the flexographic printing process not only suitable for paper printing, but also very suitable for the gravure printing of plastic non-absorbent materials [2]. Due to the constraints of printability, water-based inks, which are absolutely non-toxic, do not exist, and only if the printability is not compromised, the amount of water-based inks is further reduced. From the composition of water-based inks, the solvent that has the greatest impact on environmental performance is solvent. When selecting solvents and designing water-based inks, great attention should be paid to the odor of the solvent, toxicity to the human body, air pollution restriction, and safety. Solvents with unpleasant odors, solvents that are toxic to humans, flammable and explosive solvents, and solvents that do not meet the limits of the air pollution method should be avoided.

(1) From the aspect of pigments, most organic pigments are very toxic and do not contain heavy metals in inorganic pigments. The high-grade organic pigments not only have excellent fastness to light, weather fastness, heat resistance and solvent resistance, but also have better resistance to acid and alkali than inorganic pigments [3]. Therefore, they can be used in experiments. The pigments are high-grade organic pigments.

(2) From the solvent point of view, the first is an aminated resin solution. The main components of the aminated resin solution have an effect on the environment, which is ethanol and ammonia, and in fact, because the amount of ethyl ether contained in ethanol is extremely small, it has been excluded from the VOC black list [4]. The addition of ethanol can increase the dissolving power of the resin and enhance the dispersibility of the pigment, and can accelerate the penetration and inhibit the foaming effect.

(3) Selection of cosolvents. Due to the pigment's own characteristics, the ink using ethanol alone cannot fully satisfy the printability requirements of the water-based ink. Therefore, it is necessary to add other cosolvents to compensate. Due to its low toxicity, strong solubility and slow volatilization, propylene glycol ether can be used as a solvent to improve the leveling, gloss and fullness of the coating film and reduce the minimum film-forming temperature of the emulsion. It is a good solvent for acrylic resins [5].

2.2 Analysis of water resistance

The water resistance of OPS water-based inks is also affected by auxiliary materials such as binders and auxiliaries, in addition to the water resistance of the pigments used in the ink. Water resistance was determined by applying ink to the shrink film of OPS and measuring it after drying. Actually, it is mainly to measure the ink fastness after curing and the formed ink film resistance to water. Because OPS water-based inks are often used in packaging and printing such as dairy products and beverages, they are often immersed in water for a long period of time, or they are frozen in refrigerators for long periods of time. For example, poor water resistance can cause water-based inks to emulsify and lose their luster. In severe cases, it will completely fade, affecting the product image.

(1) Water resistance analysis of the binder

The linking materials currently used in OPS inks are mainly acrylic acid resins with high acid value that can be dissolved in alkalis (commonly used ammonia and other volatile bases), modified rosin resins with maleic acid, etc., as shown in Table 2.1, different types of resins. Water resistance is different [6]. As can be seen from the table, among the commonly used resins, the alkali-soluble acrylic resin has the best water resistance.

Table 2.1 Comparison of Water Resistance of Different Kinds of Resins

Item Maleic acid resin Urethane resin Water-based amino resin Hydroxymethyl cellulose Alkali-soluble acrylic resin Pigment Dispersibility Medium to good Excellent water resistance Poor difference Poor quality

Alkali-soluble resin liquid is used as the base material of water-based ink dispersion grinding pigments, which helps to improve the performance of pigments, especially the pigment dispersion properties to improve the stability and water resistance of the ink, and the quality of pigment dispersion and grinding time, The type of resin, the addition of auxiliaries, etc. have a lot to do. Table 2.2 is a comparison of the different grinding times of a set of colorants obtained by experiments and the water resistance (water resistance time) of the resulting water-based inks in the water-resistance study of water-based inks.

Table 2.2 Comparison of Different Grinding Times of the Paste and the Water Repellency of the Water-based Ink Obtained Milling Time Performance 0.5h 1.0h 1.5h 2.0h 2.5h 3.0h
Fineness 40μm 37μm 33μm 30μm 28μm 20μm
Water resistance 5h 10h 13h 15h 18h 15h

As can be seen from Table 2.2, as the grinding time increases, the fineness of the water-based ink increases, and the water resistance increases. However, after grinding time exceeded 2.5 h, the water resistance decreased. This is because with the increase of the grinding time, the volatilization of the amines is accelerated, the alkalinity is weakened, the acidity is increased, the viscosity is increased, and the dispersibility of the resin pigment is deteriorated, resulting in deterioration of the water resistance. It can be seen that in the paste grinding experiment, the grinding time is controlled at 2.5 h, and the best water resistance performance can be obtained.

(2) Effect of drying property, pH value and viscosity on water resistance

OPS water-based ink can be mixed with water during printing. Once the ink is dried, it can not be dissolved in water, which is the water resistance of the ink. Fast drying, water resistance is good, but it can not be too fast, only good drying will help improve the water-based ink's water resistance. The drying performance is obviously affected by the pH value and the viscosity. Usually, the pH value of the water-based ink should be between 8.0 and 9.5. At this time, the printing performance of the water-based ink is the best and the quality of the printing product is the most stable [7]. In the study of water-based inks, the pH of the aminated resin solution was adjusted by aqueous ammonia, and the experimental data for the viscosity, initial drying, and water resistance of the water-based ink at different pH values ​​were obtained, as shown in Table 2.3.
Table 2.3 Viscosity, Initial Dryness and Water Resistance for Different pH Values
pH 7.00 7.50 8.00 8.50 9.00 9.50
Viscosity 42 34 28 25 20 16
Initially dry mm/25°C 15s 11 9 8 7 6 4
Water resistance 11h 14h 17h 18h 14h 12h

2.3 Anti-friction analysis

Stabilization of the pigment dispersion is the fundamental guarantee for the fastness of the ink after curing and the resistance of the ink film to friction. The quality of the pigment dispersion has a lot to do with the grinding time, the type of resin, the addition of additives or not. Table 2.4 is a comparison of the different grinding times of a set of colorants obtained by experiments and the anti-friction properties of the resulting water-based inks in the study of water-based inks.

Table 2.4 Comparison of Different Grinding Times of the Paste and the Friction Resistance of the Water-Based Ink Obtained at the Time 0.5h 1.0h 1.5h 2.0h 2.5h 3.0h
Fineness 40μm 37μm 33μm 30μm 28μm 20μm
Anti-friction dry grinding 2 dry grinding 5 dry grinding 7 dry grinding 9 dry grinding 11 dry grinding 8 wet grinding 1 wet grinding 4 wet grinding 7 wet grinding 8 wet grinding 9 wet grinding 7 Times

It can be seen from Table 2.4 that as the grinding time increases, the anti-friction performance of the water-based ink gradually increases, but after the grinding time exceeds 2.5 hours, the anti-friction property of the printing film decreases significantly. The reason for this is that as the particles become smaller, the specific surface area increases, the solubility increases, the solvent release property deteriorates, and the drying property deteriorates, resulting in deterioration of the friction resistance. $Page break $

Third, OPS water-based ink formulation design and experiment

3.1 OPS Water Based Ink Formula Design

1, reduce toxicity, in line with environmental protection. In the ink formulation, ethylene glycol butyl ether, which is harmful to the human body, is replaced with propylene glycol methyl ether that is environmentally friendly [5]. While reducing the content of its components, the loss of leveling properties caused thereby can be compensated by adding a leveling agent.

2, improve the appearance of ink film to meet the contraction requirements. The smooth and clean printing film is the basic prerequisite for obtaining high-quality prints. In order to solve the problem of blistering, shrinkage, hair growth, and poor leveling performance, a defoamer comparison experiment was conducted, mainly as follows: 1 Analysis of different types of defoaming The defoaming ability of the agent was found through experiments to find the appropriate defoamer type. 2 Determine the optimal amount of defoamer. The experimental result is that the type of silicone defoamer selected is: DC-65AD, 0.5% defoamer dosage is the best choice.

The sliding agent contrast experiment was carried out. The main purpose was to study the effect of different kinds of wax on the printing of water-based inks, and to find the best type of wax suitable for water-based inks through experiments. Through experiments proved that DuPont's PTFE is a tough and durable good material, heat-resistant up to 315.60C. However, but the price is too expensive, the density is too high (2.2), this density, so that in a low viscosity coating system When used alone, it is bound to deposit to the bottom of the barrel, and can not play its due role [5], the test results also verify this point.

The PE/PTFE compound wax is actually made of PTFE with the help of polyethylene (PE) to keep it suspended, and surface migration occurs when the film is dried. Therefore, the combination of PTFE and PE is often more cost-effective than using 100% PTFE as an additive. The experimental analysis confirmed the use of PE/PTFE composite wax to enhance the water-based ink's anti-friction and slip properties, and to determine its proportion of 1.0%.

3, further mention the OPS water-based ink color, water resistance and anti-friction. These aspects depend to a large extent on the dispersion properties of pigments and acrylic resins. The experiment used carbon black pigments to determine the choice of carbon black wetting and dispersing agent (products of Shanghai DEUCHEN Chemical Co., Ltd.) to enhance the wetting and dispersing properties of the pigment system. The amount thereof was 1.0% by weight. By comparing the effects of different emulsion polymers on the gloss, water resistance, and anti-friction properties of water-based inks, the molecular polymers have a significant influence on the water resistance, gloss, and friction resistance of the coatings [5], while the acrylic emulsions Molecular weight