6. Solvent-free composite film adhesive
Domestic and international attention to environmental pollution is very important. The use of solvent-free polyurethane adhesives for composite films can completely solve the problem of solvent-induced pollution. In 1974, German company Henbet first used a solvent-free polyurethane adhesive to make composite packaging materials. In the United States, the solventless adhesive accounted for 10% in 1977, and it accounted for 50% in 1980 and is expected to account for more than 90% in the 1990s. In China, solventless coater equipment is not popular, so there is less use of solvent-free polyurethane adhesives, and future solventless polyurethane adhesives will have a wide range of development prospects.
1. Coating process
Solvent-free polyurethane adhesives are available in two-component and one-component types. The two-component type has a higher viscosity at the room temperature and a curing agent but still has fluidity and is a semi-solid substance. When compounding is required, the main agent and curing agent are mixed in proportions, placed in a plastic tray with a heat-retaining function, and heated to 50-60° C. to reduce the viscosity to 1 Pa·s or lower, and then passed through with heat insulation. A functional gravure roll is applied to the substrate. After being glued, it is not necessary to heat and dry it through a drying tunnel, because it does not contain any solvent itself, and it can be directly compounded with another substrate.
The use of solvent-free adhesives eliminates the need for exhaust emissions. It does not require large and complex heated blasts and exhaust gas treatment devices. The equipment is simple, raw materials are saved, energy consumption is reduced, maintenance costs are low, and production speeds are increased, so the benefits are significant. At present, most common composite film packaging materials can be produced with solvent-free adhesives, and even high-grade composite film packaging materials resistant to high temperature cooking at 121° C. can be manufactured by this method.
2. Features
1 The environment will not cause pollution due to solvent evaporation, safe operation, no explosion-proof measures; 2 glue coating amount 0.8-2.0g/m2 (usually 1.0g/m2), only half of the solvent type; 3 composite The process is simple, the compounding speed is high, and the energy consumption is saved. 4 Because the process of heating and drying the solvent is not required, the coater equipment is simple, compact, economical, and the floor space of the plant is small; 5 there is no problem of contamination of the food caused by solvent residues and migration; 6 The operating temperature is lower than the solvent type, which will not cause deformation of the film at high temperature; 7 The viscosity is large, and it needs to be preheated during use. Generally, the viscosity at the time of coating is 1000 to 3000 mPa·s; and the viscosity at room temperature is 4000 mPa·s. When the two components are mixed together, the viscosity can reach 23 mPa·s within 1 h, so the pot life of the two-component solvent-free adhesive is short, only 1 h.
Comparison of composite membranes prepared with solventless polyurethane adhesives and other composite membranes is shown in Table 1 below
Table 1 Comparison of solvent-free composite membranes and other composite membranes
Composite method
Coating amount, g/m2
Speed, m/min
Heat-resistant water and oil resistance
transparency
Curl
remaining solvent
Solvent-free compounding
0.8-2.0
100-200
excellent
excellent
excellent
excellent
Solvent compounding
5-15
80—150
excellent
good
good
Poor-good
Hot melt compound
4-10
100-150
difference
difference
excellent
excellent
Extrusion compound
0.1-1.0
80-180
good
good
difference
good
Wet compound
4-10
70-150
good
difference
difference
excellent
Polyurethane adhesives for shoes
China is the world's largest shoemaking country. Currently, the annual production of adhesive shoes is more than 2 billion pairs. If the amount of glue used is 18 to 26 grams per pair of shoes, then it needs 32,000 to 52,000 tons of polyurethane adhesive annually. In 1989, the production volume of polyurethane adhesives in Japan was 30,000 tons, while polyurethane adhesives for shoemaking required 1.4-1.5 million tons, accounting for half of the production volume of polyurethane adhesives. At present, 95% of China's shoemaking industry uses neoprene adhesives, and the amount of polyurethanes used. less. Neoprene adhesive has good initial tackiness, cold tackiness, and low price, but it is not resistant to plasticizer penetration, and has poor adhesion to soft PVC, thermoplastic rubber, PU leather and other new footwear materials. In addition, it must apply benzene. The class is a toxic solvent, which is a fatal weakness and has not been adapted to the requirements of the footwear industry. The trend abroad is gradually replaced by polyurethane adhesives. At present, 80%-90% of footwear used in Europe and the United States has been occupied by polyurethane adhesives. Domestically, this must be the trend.
1. Characteristics of Polyurethane Adhesive for Shoes
Polyurethane adhesives for footwear, like other polyurethane adhesives, have excellent low temperature properties, low curing temperatures, excellent flexibility, impact resistance, and infiltration and adhesion to many materials. Therefore, it is often used in applications requiring room temperature, rapid curing, and flexibility, and is particularly suitable for bonding dissimilar materials having different expansion coefficients.
The performance requirements for adhesives for shoemaking vary depending on the type of shoe, shoe type, and bonding process, but overall, footwear adhesives should have the following properties:
(1) Adhesive strength is sufficient for dissimilar materials and different crystalline materials, and the peel strength is high;
(2) The adhesive has high initial viscosity and meets the requirements of the shoe production line; in particular, the peel strength is high;
(3) The sizing process is simple, easy to operate, the use period is adjustable, and it is suitable for the needs of the shoe production line;
(4) Has moderate heat resistance, sufficient water resistance and bonding durability.
Polyurethane adhesives for footwear can meet the above requirements, and its initial viscous performance is worse than that of neoprene adhesives. However, researchers at home and abroad have proposed ways to improve the initial tackiness, which has been basically solved.
Soft and modified polyvinyl chloride are one of the main materials for chemical shoes in recent years. Polyurethane adhesives have the function of bonding such materials. It not only has the wide applicability of neoprene adhesive as well as excellent elasticity, softness and flex resistance, but also has better water resistance, grease resistance and heat resistance than the latter. In addition, polyurethane adhesives can still be used to bond shoe materials that are difficult for general adhesives, such as microcellular polyurethane elastomers with excellent abrasion resistance, foam materials and synthetic leathers, cyan rubbers and thermoplastic rubbers with excellent oil and gasoline resistance (SBR). , SBS, SIS, etc.). These materials have been widely used as shoe soles in the footwear industry, and are equipped with high-plasticity polyvinyl chloride or breathable polyurethane synthetic leather upper materials to produce beautiful, light and comfortable footwear.
Moreover, the polyurethane adhesive for footwear uses a half amount of glue for each pair of shoes than neoprene (Neoprene requires 40-50g per pair of shoes). Currently, the market price of neoprene is yuan/ton, and polyurethane for footwear Adhesive price is yuan/ton. Therefore, from the economic point of view, the use of polyurethane adhesives for the footwear industry is also cost-effective.
2. The main factors that affect the adhesive performance
(1) Effect of polyester varieties on the properties of adhesives In polyadipate type polyurethane adhesive systems, the adhesive crystallinity and corresponding initial tackiness are increased in the following order: ethylene glycol
(2) Effect of polyester molecular weight on the properties of the rubber 'Adhesives made of polyester with different molecular weights have a great influence on the adhesive properties. The higher the molecular weight of the polyester, the higher the viscosity of the glue, but the molecular weight of the polyester is too high. It is disadvantageous for the permeability and adhesive properties of the glue. It is very necessary to choose the proper molecular weight of the polyester to improve the bond strength. A 2000-3000 molecular weight polyester polyol (for polyadipate-1,4-butanediol) is generally used.
(3) The effect of adhesive molecular weight on the properties of the adhesive
When the adhesive has a molecular weight of about 100,000, the adhesive strength of the adhesive is the highest, and when the adhesive has a molecular weight of less than 90,000, the adhesive strength is significantly reduced. When the molecular weight is, the adhesive strength is not much reduced, but the stability of the glue is poor.
(4) Influence of isocyanate index on the molecular weight and storage property of the adhesive The isocyanate index R (ie, the molar ratio of NCO/OH) has a direct influence on the molecular weight and storage stability of the adhesive. Smaller than 0.8, the impact on the molecular weight of the adhesive is small; the size of 0.85-0.95, has an impact on the molecular weight of the adhesive; and the value of 0.95-1.0, a greater impact on the molecular weight of the adhesive. For the storage stability of adhesives, adhesives with a size less than 0.95 have excellent storage stability, regardless of the glue of the gel particles. On the other hand, the adhesive synthesized with a caliper of 0.95-1.0 has better storage stability than the gel.
(5) The effect of silica on the properties of gum. After the dissolution of hydroxyl urethane colloid particles, 1.6%-2.0% of fumed silica is added. The viscosity of the gum solution can be increased by 300-400 mPa·s, and it is also improved. The adhesive strength and initial tack of the polyurethane adhesive.
(6) The effect of chain extender on the properties of glue Adding chain extender can increase the content of urethane groups, increase its cohesive strength, polarity and activity, and make the polyurethane adhesive and the adhered material form physical adsorption and chemical combination, and increase polyurethane The initial adhesive strength and heat resistance of the adhesive.
(7) The effect of curing agent on the performance of the glue The curing agent is usually used JQ-1 and JQ-4 and 7900, the general added amount is 3% -10%. When JQ-l is used, the adhesive layer is dark in color and will appear red, contaminating the upper. Using 79m is slightly better but not ideal. It is best to use JQ-4, DesmodurRF.
3. Resistance to yellow shoes with polyurethane adhesive
Polyurethane adhesives for shoes sold in the market have the problem of yellowing in most of them and pollute the uppers, affecting the appearance. For white or light-colored shoes such as travel shoes and sports shoes, the problem is even more prominent. In order to improve the appearance quality of the footwear and ensure that it is not yellow during wear, a yellow-resistant, non-polluting polyurethane adhesive should be used.
1. The choice of isocyanate raw materials
The yellowing of polyurethane products is related to the existence of a large redundant bond conjugated system in its molecular structure, and the more the big guanidine bond structure, the darker the color. In general, polyurethanes are based on aromatic isocyanates such as diphenylmethane-4,4'-diisocyanate (MDl) and toluene diisocyanate (TDI). The presence of nitrogen atoms in the vicinity of the benzene ring in this type of polyurethane molecular structure results in the formation of a quinoid structure and discoloration when promoted by ultraviolet light. The main chain of the aliphatic or alicyclic diisocyanate has a saturated structure, does not contain double bonds, and is difficult to form a large redundant bond structure. According to reports in the literature, polyurethane adhesives for yellowing shoes are mainly prepared from hexamethylene diisocyanate and isophorone diisocyanate. Of course, the curing agent should be JQ-4 or DesmodurRF.
2. Preparation
(1) According to the research report of Yan Yongjun et al. in the Department of Chemistry of Xiamen University, in a reaction vessel equipped with a thermometer and a stirrer, the pre-dehydrated polyadipate-1,4-butanediol was heated and heated to 110°C. After the polyester is melted, an appropriate amount of dibutyltin dilaurate and 1,4-butanediol are added. Turn on the stirrer and mix the reactants homogeneously. Then the required hexamethylene diisocyanate (and a value of 1) was added in one portion with stirring. Stir vigorously for a few minutes, at which time the viscosity of the reactants rapidly increases and the temperature rises. When the viscosity and temperature of the reaction material no longer rise, the stirring is stopped and the solid content is adjusted to 20% with butanone as a solvent.
The appearance of the adhesive is five-color transparent liquid, viscosity (25 °C) 150-300mP. s. After the adhesives were soaked at room temperature for 10 days, the water resistance test results were the same as those before the treatment. Its heat resistance, 40 °C peel strength and room temperature is no different, both material destruction; 60 °C peel strength decreased significantly, the glue was added 5% of the curing agent, 60 °C test results for the material damage. Its resistance to yellowing, glue and dry glue in the natural light under the 18-month lightfastness test does not change yellow, glue storage for 18 months, adhesive properties unchanged, good stability.
The peel strength of various adhesive materials of the adhesive: PVC-PVC 3.92kN/m, PVC-PU4.08kN/m, PVC-bovine leather 4.0kN/m, PU-PU7.92kN/m, PU-bovine leather 6.48kN /m, cowhide - cowhide 5.75kN/m.
(2) The molar ratio of polytetramethylene adipate to 1,4-butanediol-1,6-hexanediol (1,4-butanediol and 1,6-diol) is 1:3 and the molecular weight is 5,000. Acid value 1.1 mgKOH/g) was dehydrated under vacuum at 100°C for 1 h. Take 1 mole or more of polyester polyol, 0.4 mole of 1,6-hexanediol and 0.4 mole of 2,2-bis[4-(2-hydroxyethoxy)phenyl]propane (chain extender), 1.79 moles of hexane Isocyanate (and the value of 0.995), the above materials were stirred and mixed evenly, heated to 120°C, and heated to 140°C after 2 minutes of reaction, and immediately poured into a polytetrafluoroethylene vessel at 110°C for 15 hours to obtain polyurethane elasticity. Body, formulated with butanone as a 20% solids polyurethane adhesive.
The above polyurethane adhesive was applied to the treated soft PVC film (4 mm) and the butyl rubber sheet (4 mm), and the initial adhesive peel strength was 2.7 kN/m for 10 minutes.
4. Modification of Polyurethane Adhesives for Shoes
1. Blend modification
Observation of the polyurethane-polyacrylate interpenetrating network system with an electron microscope showed no sign of phase separation, which is the theoretical basis for the modification of polyurethane materials with polyacrylates. 0.1% -20% polymethyl methacrylate and polyurethane adhesive are mixed in a mixed solvent. The mixed solvent consists of toluene, acetone, butanone and ethyl acetate, which improves the tensile strength and initial tack of the polyurethane adhesive.
21.0 parts of polyadipate-1,4-butanediol (hydroxyl value of 4.1 mgKOH/g, acid value of 0.3 mgKOH/g) was mixed with 39.69 parts of MDI, and the prepolymer was prepared after the reaction. 83.2 parts of the prepolymer were reacted with 2.19 parts of 1,4-butanediol and 8.32 parts of hydroxy-terminated 1,4-butanediol-methyl methacrylate reaction product (reaction reactant molar ratio of 1:20) The resulting polyurethane elastomer can be dissolved in methyl ethyl ketone to produce a polyurethane adhesive with excellent adhesion to thermoplastic rubber.
Poly-adipate-l,6-hexanediol-work I polyurethane plus tert-butyl phenol-formaldehyde resin was added in an amount of 10% to form a high initial viscosity polyurethane adhesive.
12 parts of linear hydroxy polyurethane, 65 parts of acetone, 12 parts of naphtha, 1 part of vinyl acetate-vinyl chloride copolymer, 0.1 part of adipic acid, and 0.9 part of chlorinated rubber. The curing agent used triphenylmethane three. Isocyanate, the resulting polyurethane adhesive has a very high initial tack.
Add 0.01 parts of crystalline nucleating agent, such as 1-5 rutile titanium dioxide, to the polyurethane adhesive. Due to the large granular structure obtained in the glue, the initial adhesive strength and thermal stability of the adhesive can be improved (by 20% to 40%). The addition of 1% ferric chloride to the polyurethane adhesive improves bond strength and heat resistance.
2. Add tackifier modification
Polyurethane adhesives can be modified by various tackifier resins. Dawning Chemical Research Institute has done a lot of research work. The hospital will use 372 plastics, E-42 (634) epoxy resin, No. 6 rubber, SBS, etc. as tackifying resins. The polyurethane was added to observe the adhesive initial adhesion. The effect of the tackifying resin on the initial tack and final adhesive strength of the polyurethane adhesive adhesive is shown in Table 2 below.
Table 2 Effect of Tackifying Resins on the Initial and Final Bonding Strength of Polyurethane Adhesives
Tackifying resin\sticking material
PVC leather-PVC leather peel strength, kN/m
PU leather-PU leather peel strength, HN/m
After 10min
After 24h
After 10min
After 24h
no
0.74
3.65
0.93
4.88
E-42 epoxy resin
0.64
2.16
1.13
4.45
SBS
1.0
3.79
2.3
5.30
372 plastic
0.81
2.9
1.25
4.73
No. 6 rubber
1.1
4.25
1.90
5.16
3. Adjust polyurethane composition
In the polyurethane adhesive preparation section, it has been pointed out that its initial viscosity is first determined by the influence of the crystallinity of the polyester segment in the polyurethane molecule, while the crystallization rate of the linear adipic acid polyester depends on the composition of the diol chemical structure. . Among them, one mole of polyurethane prepared from 1,6-hexanediol polyadipate (molecular weight 2250, acid value 0.8 mgKOH/g), 0.4 mole of 1,6-hexanediol, 1.39 mole MDI (R value 0.993) Adhesive, used for bonding PVC-PVC leather, bonding time 1min, its initial adhesive peel strength 2.3kN/m. Polyurethane Adhesive made of 1 mole of polyhexanized adipic acid-1,6-hexanediol (molecular weight 4000, acid value 0.9mgKOH/g) and 0.995 mole of MDI (R value 0.995), used for bonding PVC-PVC leather, When the lamination time is less than 1 min, the initial peel strength is 2.5 kN/m.
The type of curing agent has an influence on the initial viscosity of polyurethane adhesives. TDI trimers (appearance of a light-colored clear liquid, a solid content of (50 ± 2)%, a viscosity of 100 to 2 m mPa·s) are used as curing agents. Has outstanding initial tack strength.
5. Polyurethane Adhesives for Shoes and Technical Specifications
The national standard for polyurethane adhesives for shoes has not yet been formulated. The standard for shoes neoprene adhesive GB7126-86 is mainly based on the standard of Japan's JIS general materials adhesives, but it is not a professional standard for footwear, and the standard is low. The current revised standards mainly refer to German DIN 6909 “Adhesives for shoe materials, requirements for testing and classification of adhesives for shoe sole components†and German DIN 53273 “Determination of solvent-borne and dispersion-type adhesives for adhesives for shoe materialsâ€. Therefore, the current standard for polyurethane adhesives for footwear can only refer to the standards for CB7126-86 and QB1002-90 adhesive shoes (peel strength is ≥54kN/m for men's shoes, ≥49kN/m for women's shoes), SGCl78-84 injection-molded shoes, and GB4492-84 Rubber shoes, ZBY78001-86 adhesive cloth shoes; GBl0507-89 rubber cold glue shoes, GBl2018-89 acid and alkali-resistant shoes (boots) and other standards.
1. Polyurethane adhesive rubber
Foreign shoe polyurethane adhesives are mainly sold in rubber pellets, and footwear manufacturers use them as glues. In China, adhesives are formulated into gum liquids for sale to shoe factories.
Polyurethane Adhesive for Footwear The rubber particles are thermoplastic polyurethane elastomers, but contain a small amount of hydroxyl groups in the composition, so it is also called hydroxyl polyurethane. The specifications of polyurethane adhesives for Pearlstick shoes recommended by Desmocoll of Germany Bayer and Merquinsa of Spain are shown in Table 3 below.
Table 3 Technical Specifications of Desmocoll and Pearlstick Footwear Polyurethane Adhesives
Item \ brand
Desmocoll
Pearlstick
530
540
45-60/14
45-60/18
composition
Exterior
Hydroxyl content, %
Density, g/cm3 (23°C)
Viscosity, mPs.s (15%
Butanone solution, 23°C
Reactivation temperature, °C
Linear polyurethane
Linear polyurethane
Light yellow beads
0.1
1.16
1000-1400
80
White beaded particles
0.1
1.19
1500-2100
80-90
White pearl-like particles
0.1
1.19 (20°C)
1200-1600
75-90
White pearl-like particles
0.1
1.19 (20°C)
1600-2000
80-90
Note: Desmocoll and Pearlstick are stored in a dry place at 15-25°C and the storage period is 6 months.
The comparison of polyurethane properties of Desmocoll shoes is shown in Table 4 below. The high crystallization rate indicates high initial adhesion strength, the large thermoplasticity indicates that the colloidal particles are easily dissolved, and the large deformation indicates good flexibility.
Table 4 Comparison of Desmocoll Series Performance
Grade
Density, g/cm3
(23°C)
Adhesive viscosity, mPa·s (20°C)
Thermoplastic
Crystallization rate
Desmocoll400
Desmocoll406
Desmocoll420
Desmocoll530
Desmocoll540
1.23
1.2
1.2
1.16
1.19
400-800
400-800
1000-1400
1000-1400
1500-2100
high
high
low
low
low
high
low
high
Very high
Very high
The J-1015 polyurethane solid adhesive technical indicators developed by the Liming Chemical Research Institute are shown in Table 5.
Table 5-10 Technical Specifications of Polyurethane Adhesive
project
index
project
index
Exterior
White or light blue particles
Tensile strength, mPa
51.0-57.0
Hardness (Shore A)
96-98
Elongation,%
700-800
Softening point, °C
100-120
Storage period, month
--
2. Polyurethane adhesive
There are many types of polyurethane adhesives used in domestic footwear. Here are a few representative products. See Table 6 below.
Table 6 Technical Specifications of Polyurethane Adhesives for Domestic Shoes
name
main ingredient
Viscosity, mPa·s
(25°C)
Uses and characteristics
Production unit
1995L excellent adhesive
1995 excellent glue
1995k high strength and excellent adhesive
101 excellent glue
PU resin
1300±100
1600±100
1800±200
1600±100
Suitable for bonding of PVC, PU, ​​ABS, cloth, leather and treated rubber, thermoplastic, elastomer, EVA, nylon and other materials
Jiangsu Zhenjiang Jinbao Adhesive Co., Ltd.
700W PU paste
PU Copolymer
1400±100
Universal type, strong affinity for PVC, PU, ​​rubber, thermoplastic elastomer, etc., good initial viscosity, good operability, especially suitable for assembly line
Guangdong South Hainan Resin Products Co., Ltd.
713K PU paste
PU Copolymer
1400±100
Resistance to wire drawing, excellent heat resistance
Good for women's shoes and assembly line
727H PU paste
PU Copolymer
1400±100
No yellow, no color
Ming, excellent weather resistance, used
White sneakers and light-colored female
shoe
728W PU paste
PU Copolymer
1400±100
Strong type, for PVC, PU,
Thermoplastic elastomer, rubber
Strong affinity, especially suitable for tide
Wet, cold and manual work
768W PU paste
PU Copolymer
1500±100
Strong type, strong affinity for PVC, PU, ​​PU copolymer, used for manual work
270H PU paste
PU Copolymer
1500±100
Resistance to yellowing, mostly used in sports shoes production, manual and waterworks
1996W Benzene-free primer
Hydroxyl PU resin
1800±200
Applicable to the bonding of PVC, PU, ​​thermoplastic elastomers and rubbers for shoes, good resistance to aging, good operability, strong adhesion, and clean environment
Nanjing Institute of Leather Industry
1996 Texan
Hydroxyl PU resin
1800±200
Applicable to the bonding of PVC, PU, ​​thermoplastic elastomers and rubbers for shoes, good resistance to aging, good operability, strong adhesion, clean environment, and small amount of toluene solvent
Note: The appearance of adhesive is colorless transparent or light yellow viscous liquid.
Table 7 Technical Specifications of J-1010 Footwear Polyurethane Adhesives
Adhesive properties
Peel strength, kN/m
project
index
Sticky material
index
Note
Exterior
Viscosity, mPa·s
(25°C)
Light yellow or micro
Blue viscous liquid
1000±200
PU Leather - PU Leather
Leather - rubber bottom
Pigskin - rubber sole
2.5-4.0
3.6
3.0
Initial viscosity
Final strength
Final strength, material damage
Solid content, %
Storage period, month
Solvent
15±2
12
Butanone
PU leather - PVC bottom
PU leather - PU bottom
PU leather - EVA bottom
7.0
7.3
1.5
Final strength
6. Shoe material surface treatment agent
The key issue in the development of cold stick shoes is glue technology. There are many cold sticky shoes degumming phenomenon on the market, the reason is generally considered to be caused by bad adhesive. Of course, bad adhesive quality is also one of the reasons. In fact, most of the problems lie with the treatment agent.
1. The importance of the treatment agent
Cold glued shoes To achieve a good bonding effect, it is necessary to have suitable adhesives, hardeners, and treatments, while also having the most appropriate bonding process conditions. People pay more attention to adhesives, curing agents and process conditions. The use of treatment agents and their possible effects are often overlooked by many shoe manufacturers.
The shoe materials used in shoemaking production are varied. Common rubber, leather, PVC artificial leather, PU synthetic leather, thermoplastic elastomer (TPR), EVA foam material, nylon and other chemical materials are common. These shoe materials have a wide variety of surface conditions and vary widely in their surface polarities and chemical states in addition to various attachments. If the surface chemistry of these bonding surfaces is not changed by a treatment agent, no adhesive can be used to achieve the desired bonding effect. Because any type of adhesive has good "wet" and "affinity" effects only on certain materials, it is "favorable" on another type of material. If these materials for shoes to be bonded can be wiped off the surface with a treating agent before brushing, the “contaminants†physically adhered to the surface can be effectively removed, and more importantly, they can be attached to the surface of the material. A new layer of surface, this new surface has a good "wet" and "affinity" effect on the adhesive, a "bridge" transition between the surface of the material and the adhesive, making its surface "adhesive" "Connectability" enhances the adhesive strength and durability of the shoe adhesive.
2. Treatment agent type
The types of material processing agents for shoes mainly include the following types.
(1) The cleaning agent type is mainly composed of an organic solvent, and the usual organic solvents are toluene, methyl ethyl ketone, acetone, cyclohexanone, methylene chloride, tetrahydrofuran, and methanol. Depending on the nature of the material and the volatilization rate of the different solvents, they are formulated according to a certain percentage.
(2) Cyclization dosage form The synthetic rubber is immersed in concentrated sulfuric acid for 5-15 minutes, taken out, washed and dried. At this time, the extremely fine cracks formed on the surface contribute to the "bite" and "cast anchor" effects when bonding.
(3) Halogenated dosage forms For polyolefin footwear materials, it is difficult to perform surface treatment by ordinary methods. Halogenating agents can be used to halogenate the surface of the material, which changes the morphology and structure of the surface layer and increases polarity. This allows for good wetting of the adhesive and the material interface, which in turn forms a strong chemical bond.
(4) The diluent of the glue is mixed with a solvent such as toluene, butanone, and acetone, and the adhesive is diluted to a concentration of 3% to 5% as a primer (treatment agent) for the shoe material.
(5) Graft polymer type The SBS and SBR polymers are grafted with monomers (methyl methacrylate, acrylic acid, etc.) to prepare a graft polymer solution, which is then diluted with a mixed solvent to form a primer. It is mainly used for the treatment of thermoplastic elastomer (TPR) and rubber soles.
(6) Mixed type A mixed liquid of various adhesives or a mixture of a solution of a sticky material and a glue liquid as a primer.
(7) Plasma Treatment This is a newly developed surface modification method for rubber and plastics. The rubber or plastic is placed in the glow discharge space of the low-pressure gas, and the ionized gas, the active chemical substance in the plasma, forms an extremely thin layer completely different from the material itself through contact with the surface of the material, and is particularly called CASIG ( Crossling by activated species of inert gases - the cross-linking effect of inert gas activating substances) can generate polar groups such as carbonyl, hydroxyl, carboxyl groups on the surface of hydrocarbon polymer materials. It has been speculated that the improvement in adhesion performance of this treatment is based on the combined effect of surface oxides, polar groups, and internal cross-linking.
3. Halogenation agent
The halogenation treatment is based on the addition reaction of a halogenating agent to a polybutadiene double bond in a thermoplastic elastomer (TPR), which changes the composition of the surface layer of the material and increases the polarity. Commonly used halogenating agents include trichloroisocyanuric acid (TCCA), dichloranine T, and N-bromosuccinamide. The effect of halogenation treatment is: 1 It accelerates the crystallization process of the polyurethane film coated on the surface, that is, it improves the initial viscosity; 2 It can greatly reduce the amount of polyurethane adhesive; 3 Improve the adhesive strength. Therefore, the effect and reliability of the halogenation treatment are recognized by the footwear industry at home and abroad. The chlorine released from the halogenated liquid alone will pollute the environment.
(1) Trichloroisocyanuric acid trichloroisocyanuric acid, also known as strong chlorinated, has a molecular formula of C3O3N3C13 and a molecular weight of 232.41.
Physical properties: appearance is white crystal, melting point 225-230°C, relative density 0.95～1.20, solubility 1.2g/100g water, 36g/100g acetone, chlorine smell, strong disinfection and bleaching effect, stable drying condition, Acid or alkali decomposition.
Toxicity: LD50 is 0.72-0.78g/kg, and available chlorine is harmless to the human body at a concentration of 100*10-6.
Specification: Excellent grade contains available chlorine ≥ 90.0%, moisture ≤ 0.5%, pH value (1% aqueous solution) 2.7-3.3.
Trichloroisocyanuric acid is prepared with ethyl acetate and made into a solution with a solid content of 3% to 5%. It is a halogenated treatment agent for footwear materials with a pot life of 4 hours. The halogenation time must be at least 10 minutes, in order to fully chlorinate the surface.
(2) Dichloroamine T dichloramine T scientific name N, N-dichloro-toluenesulfonamide, molecular formula C7H7Cl2NO2S, a molecular weight of 240.11.
Physical properties: The appearance of light yellow crystals, melting point 83 °C, chlorine content 56% to 60%, soluble in acetone, toluene and other solvents.
The dichloroamine T can be made into 5% -10% acetone solution as a shoe material halogenation agent. Others use dichloroamine T5% acetone solution and 2%-5% benzoyl peroxide (BPO) as a halogenating agent.
4. Graft polymer treatment agent
Grafting polymer treatment agent, also known as primer, or primer, is mainly used as a treatment agent for thermoplastic elastomer (TPR) shoe soles. TPR is available in SBS, SIS, EPDM and other varieties. Its properties are both high elasticity of rubber and Due to its high strength, dual properties, and low price, plastics are used in large quantities as sole material. The polarity of the TPR is small, and the polarity of the polyurethane adhesive is large, thus making the adhesion to the TPR difficult. The method of synthesizing TPR surface treatment agent by using vinyl monomers graft modification of SBS and other polymers solves the problem of adhesion of TPR shoe soles.
(1) SBS-MMA Graft Type Treatment Agent
(2) SBS-St-AA Graft Type Treatment Agent The styrene (St) and acrylic acid (AA) monomers were grafted onto SBS by the preparation method similar to the SBS-MMA graft type treatment agent, and the ratio of the feed mass ratio For SBS: St:AA=100:45:15, BPO 0.8%-1.0%, the grafting reaction temperature is 84-86°C. The SBS-St-AA graft treatment agent is mainly used for the treatment of TPR, R soles.
(3) SBR-MMA Graft Type Treatment Agent
(4) CR-CPE-MMA-HEMA type graft treatment agent
5. Treatment agent usage method
When using the treatment agent for cold sticky shoes, pay attention to the use method, otherwise it is difficult to obtain the desired effect.
(1) Rubber, leather, and other footwear materials should be roughly ground before bonding, and should be evenly polished to avoid excessive damage to the material.
(2) Residual crumbs should be removed after rough grinding.
(3) To choose a suitable treatment agent, different materials used different treatment agents. If the treatment agent is not properly selected, the bond strength will be reduced.
(4) When using, wipe the surface of the part to be bonded with a cotton cloth or cotton gauze treatment agent slightly, and do not use chemical fiber cloth instead of cotton cloth.
(5) After the material is brushed and treated, the drying time and temperature should be adjusted according to the instructions, and the treatment agent should be spliced ​​as soon as possible after drying.
(6) The treatment agent for polyurethane adhesive and neoprene adhesive cannot be mixed.
(7) Sample tests should be done before mass production, and can be used on the production line until it is properly handled. The materials for shoes in cold sticky shoes should be surface-treated prior to bonding, and the appropriate treatment agent should be used. This is particularly advantageous for improving the adhesion level of footwear made of different materials and can be effectively avoided. Degumming quality accidents improve adhesion reliability and durability. Therefore, this is an important process that cannot be ignored.