Since the seventies the twentieth century has been abroad in the application of PU adhesive for shoe-making has been very successful, due to a variety of shoe materials to achieve a strong bond, so as adhesive for shoes, one of the important species. Some data indicate that [1], currently in Western Europe, North America, as 80% of the shoe glue is still solvent-based PU adhesive, with the increasing environmental protection, benzene solvent series (most of the PU adhesive). To gradually replace the benzene series of adhesive. Europe [2] In recent years has been free, "BTX" series of solvent from the release of toxic substances (TRI) and the list of VOC removal, cal "green" solvents, as solvent for its PU Adhesives are subject to less environmental pressure. So, so far in the footwear industry, this type of adhesive still occupies a very important position. The development work in order to melt thermoplastic PU elastomer synthesis, and further preparation of . Compared with the synthesis solution, reached the required viscosity value, with a product solids content is low; and equipment compared to continuous process technology investment, process control simple and mature, easy formula to replace the characteristics of industrial production capacity has been formed. Here no "benzene\
1 synthesis (production) part of the
1.1 raw
diphenyl methane diisocyanate (MDI) of imports of industrial grade
polyhydroxy polyester (PCTA) Industrial grade Shandong
acetone, butanone, commercially available industrial grade ethyl acetate
Hindered Amine Light Stabilizers
1.2 imports of industrial production and testing equipment
rapid mixer speed 300-500 r / min, stirring device can lift a capacity of 30-50 liters Home
aluminum mold plate surface, four fluoride treatment made
0.5 Dun reactor, stirring speed of 60-70 r / minute, anchored mixing pulp made
2 Dun reactor, stirring speed of 60-70 turn / min, anchor-type mixing slurry polymerization furnace after domestic
internal structure for the shelf, leading to nitrogen with a temperature control device self-heating
cutter length 60 cm wide and 10 cm, made
broken Tsui machine Universal Plastics Crusher Domestic
200 Sheng barrels heaters, Electric Equipment Factory Wuxi Huaneng
tensile machine XLL-50 Guangzhou, material testing machine plant
Rotational Viscometer NDJ-1-based Shanghai Balance Instrument Factory
1.3 PU Adhesive
will melt temperature 50 ℃ and the temperature 60 ℃ of PCTA heated molten MDI input to lift agitator, the mixing speed to the viscosity of heavy increase in wait, will be reflected in the rapid dumping of material into the aluminum mold plate, furnace pass into the post-polymerization of nitrogen, the temperature 110-115 ℃, thermal polymerization of 2.5-4 hours, wait 20-30 minutes at room temperature after being removed, cut into strips warming, natural cooling, after penetrating into the broken machine, broken into granular. Requirements by 12-16% solids containing light stabilizers into the reaction vessel, dissolved at room temperature, viscosity adjustment, loading barrels of reserve.
1.4 adhesive bonding strength of the spline and the determination of
PVC, PU material available spline acetone, methyl ethyl ketone, or ethyl acetate solvent such as either a slight smear to grease or other filth, thermoplastic rubber (TPR), rubber, ethylene - vinyl acetate copolymer (EVA) materials were used to deal with the corresponding agent (homemade) for smear treatment, even in its various substrates glue two times, after the first pass gluing about 60 ℃, drying 6-8 minutes, brush second time around after a 60-70 ℃ drying 5 minutes, take out after the close bond, and a little pressure, stored for 24 hours, according to GB/T532-1997 standard (vulcanized rubber or thermoplastic rubber and fabric adhesive strength of the measurement). You can test the results. To further enhance heat resistance and lasting strength, may be appropriate to join the 3-5% curing agent (homemade), making double-liquid type adhesive, but this two-liquid type adhesive should be run out 4-6 hours.
2 Results and discussion
2.1 polyisocyanate choice
with other types of multi-isocyanates compared with MDI itself is volatile due to low toxicity, but also because of the presence of benzene in the chain, so physical and mechanical properties of good, light stability, weakness weakened light stabilizers can be added to make up, suitable synthetic thermoplastic PU elastomer as the main erial.
2.2 polyhydroxy polyester choice
and multi-isocyanate reaction of the poly-urethane polyether polyols are, polyester-and sulfide-based, integrated its physical and mechanical properties of polyester-type is appropriate, by Synthesis of PU elastomer properties, molecular weight between 2160-4680, the subject to little change in molecular weight, but the molecular weight between 1180-2160, the polyester synthetic PU elastomer mechanical properties, along with the increase of molecular weight polyester noticeable change in the molecular weight of polyester diol of about 2000 the most suitable [3].
2.3MDI/PCTA the determination of molar ratio of
the PU resin is a chemical reaction of isocyanate, MDI, and PCTA in essence the process of alternating chain-extender, with different molar ratios, in theory, there are three possible:
(1), NCO / OH = 1:1
exist as long as the reactants, in theory, can be infinitely extended chain reaction continues, polymer molecular weight should be infinite. But the actual project, the accuracy of the ratio of reactant supplied by the feeding accuracy of two raw erials for purity, air humidity, the impact of consumption of NCO, etc., this situation is extremely rare.
(2), NCO / OH 1
chain-extension polymerization of the final product-end-OH, and even left some unreacted PCTA. Apparent as "waxy" for the effect of adhesive bonding system showed more negative effects, should be avoided.
(3), NCO / OH 1
the most common and appropriate excess NCO, the polymer-end-NCO closed, adhesive activity of large, but too much will cause too many NCO cross-linking within the system and the reaction product to pay more, and the storage of highly volatile, inspection should be control by the NCO / OH = 1.03-1.05 / 1 is appropriate.
2.4 reaction temperature
MDI and the PCTA set this minimum melting temperature of the reaction is to enable both faster increase in viscosity and faster, as far as access to effective long agitation, due to MDI is greater than the proportion of PCTA, and the two more rapid response, such as the lack of access to as much as possible the strong mixing, the synthesis of experience there two kinds of flexibility: (1) MDI partial excess Department to produce a certain degree of cross-linking, resulting in insoluble; (2) MDI little local office, resulting in PCTA has not translated into synthesis of PU elastomers, apparent as "wax" shape, barely integrated into the adhesive, the adhesive caused by the many negative impacts.
2.5 After the polymerization time and temperature to determine
without post-polymerization of PU elastomers by solid content 13-15% direct solvent-soluble adhesive composition, the viscosity of only a few hundred m.Pa.s, too small , glue was "solvent" state, can not shoe-making production line on the brushing, brushing force will also be in the shoe surface of the surface of the hole bubble Shoes "sucked" into the internal surfaces caused by lack of glue; increase solids content increased the viscosity force will cause increased costs, and not meet a certain weight will cause the adhesive tack is not enough, so in need of post-polymerization processing. After some tests suitable temperature to 110115 ℃, the temperature is too high or too long, could easily lead to discoloration or material PU elastomer molecular weight is too large and some have even part of the cross-linking, resulting in insoluble, or insoluble. Time 2.5-4 hours is appropriate, too short does not work, too long, then the viscosity of the enhanced role of the basic obvious.
To sum up, in order to develop technical guidance for the formation of this production line has a certain capacity, production and process operation pvc mature feasible and has characteristics of low investment and quick returns, with a further in-depth development work is expected to further enhance the PU shoes adhesive on the performance and expand scope of use.