Technology Sharing: Preparation and application of high-solid containing low-free polyurethane curing agent (DL-75).

Chen Aiwen, Chief Engineer, Zhuhai Union Solid Chemical Engineering, Guangdong Dongxu Group, Ph.D Abstract:
TDI
polyurethane curing agents include toluene isocyanate; polyols; ester solvents; antioxidants. In the late synthesis using secondary vacuum film evaporator separation
TDI-TMP
curing agent free
TDI
, the free less than
0.5%
, solid containing more than
75%
of environmentally friendly curing agent. In coatings, inks, adhesives and other industries have a wide range of applications.keywords: free toluene isocyanate; film evaporator; polyurethane; curing agent I,introduction polyurethane curing agent refers to the two-component polyurethane paint containing polysephate-based components, foreign called polyurethane curing agent. Can be
(1)
plus type, the most commonly used is
TDI
and trihydroxy methamphetamine addition;
(2)
isocyanate;
(3)
tri-polycyanate, such as mixed trimer,
HDI
trimer,
IPDI
trimer, these major types of curing agents (
IPDI
of the diosphere as a powder coating curing agent. Widely used in coatings, adhesives, inks and a variety of materials, including
TDI
and trihydroxymethyl propane is the most widely used class of polyurethane curing agents.。 TDI-TMP
curing agent contains free
TDI
is a highly toxic substance, such as non-compliance, easy to cause harm to the surrounding environment and people, common symptoms are: eye pain, tears, conjunctivation, cough, chest tightness, shortness of breath, asthma, red papules, patchy papules, contact allergies and other symptoms, long-term exposure to cancer risk. The international non-toxic curing agent standard requires free
TDI
less than
0.5%
. The methods
reducing
of free TDI are molecular sieve adsorption, extraction, chemistry and film evaporation. Among them, the film evaporation method is the most economical and effective, the application range is the most extensive.ii, low-free polyurethane curing agent preparationraw material ratio:toluene isocyanate 55-65%polyols 10-20% ester solvents 24-26% oxidants 0.2%total 100%according to the formula ratio of the raw materials, toluene isocyanate, polyols, antioxidants, esters solvents (replaced with toluene isocyanate) into the reactor, wherein polyols in the drip kettle melted into molten hydroxyl parts in advance, the temperature at about
50
degrees C
melting; Control the temperature at
55-65
degrees C, in the process of heating the substances in the reactor to stir, so that the substances in the reactor fully react
1-
4



hours;production flow chart is as follows: 1-
molten hydroxyddie plus kettle
2
and (
2
)
-
reaction synthesis kettle
3 -
first-stage evaporator
4-
-stage evaporator 5-
condenser
6
,
7,8,9 -
vacuum pumpput isocyanate into the synthetic kettle
2
in the image above, and the hydroxyl components into the water drop kettle
1,50
degrees C
Melting, isocyanate and hydroxy-value ratio of
8:1

, that is, isocyanate
excessive;
60-80
degrees Celsius
synthesis, the degree of synthesis is
The NCO
content does not change until the synthetic material is entered into the first-stage evaporator
6
through the first-stage feed pump
3
and the second-stage evaporation through the secondary feed pump
7
into the secondary evaporator
4
continuously. Free isocyanate is gaseous by condenser
5
condensation into liquid, through the first discharge pump
9
collection, curing agent through the second discharge pump
8
discharge collection.is connected by a pipe for a synthetic kettle, evaporation mechanism, feed pump set, condenser, first feed pump and second feed pump for mixed reaction of raw materials. Thus, the curing agent formed by the raw material after reaction in the synthetic kettle is pumped into the evaporation mechanism through the feed pump group, distilled by the thin film evaporator in the evaporation mechanism to separate the free isocyanate, the evaporation mechanism and the condenser are connected by pipeline, the separated free isocyanate enters the condensation system condensation into a liquid, and then enters the circulatory system to participate in the reaction of the next set of raw materials. The curing agent
the
in the evaporator is added to the converter, and the ester solvent is added to the
75%
containing the curing agent.,characteristics of low free polyurethane curing agentThe products produced by this system are thin film method low free
75
curing agent. In general, in the production process of polyurethane curing agents, due to the unstable reaction of toluene diocyanate, the content of free
TDI
in products is high, which has greater impact on the human body and the environment. Developed countries use evaporation purification to separate free
TDI
, which can be reduced to
0.3%
(e.g. patent:
CN200410027560.2
and
CN2 00380106780.8
), but the method's equipment investment is too large to promote the application, the chemical method is through catalysis to make residual
TDI
polymerization reaction, but will make the curing agent molecular weight is too large, affecting product quality and waste of raw materials.the use of thin-film distillation to produce polyurethane curing agent, by improving isocyanate and hydroxyl equivalent ratio, the use of isocyanate strong solubility, raw materials as a solvent, the synthesis of
PU
curing agent molecular weight is smaller, more uniform molecular distribution, resulting in the separation of less viscosity, active hydromassage group (
NCO
) more, better comprehensive performance, free isocyanate Ester toxic monomer less polyurethane curing agent, isolated isocyanate monomer re-entry in a single feed synthesis, so that curing agent production can be carried out continuously, and no aftertreatment is required;product
appearancewhite to yellow transparent mucuscolors (
Fe-Co
) ≤
1 NCO (%)13.0
±
0.5free
TDI(%)≤ 0.5solid content
(%)75
±
2viscosity (rotating viscosity meter
/25
degrees C
/cps
) 1500
±
5000tolerance (xylene) ≥3.3. 0product characteristics with light color, low odor, free
TDI
monogam content is low, in line with european standard requirements, good environmental protection effect, high gloss, flow level, good transparency, excellent solubility, good anti-tweezers effect, good chemical resistance, storage stability.Because there are no other additives in the raw materials, the resulting products are usually yellow transparent mucus, after the film steamer distillation, free
TDI
content is small, odor fade, harm to the human body reduced, on the other hand, volatile substances reduced, environmentally friendly. Film method low free
75
curing agent, small molecular weight, active power group, in the later application to make the comprehensive performance of high gloss, plate flatness, good transparency; Good compatible with esters, ketones, etheric solvents, aromatic solvents are limited soluble, fat solvents are insoluble. With all aliclicic acid resin, synthetic fatty acid resin, acrylic resin has a good solubility, can form a good paint film. Synthetic curing agents are not easy to react with other chemicals and have a shelf life of

than 1 year in storage.4,low free polyurethane curing agent applications usually with curing agents are resin paint, general resin paint are divided into main paint, curing agent and thinner three parts, curing agent is essential for two components of paint, its role is mainly two aspects: is a physical drying
: paint reinforcement agent can promote rapid drying of paint, shorten drying time. one is chemical curing
: curing agent and main paint combined reaction, can increase the hardness, brightness and bonding of the paint film, improve the chemical stability of the paint and corrosion resistance. Can make the paint film full of delicate, smooth and elastic, wear-resistant not easy to scratch. 。 PU
is the general design of all polyurethane coatings, its film-forming way is natural film-forming, no special process. polyurethane paint is a two-part chemical structure: a isocyanate base (
-NCO
)
B part (paint) Hydroxyl (
-OH
)
-
polyurethane high-polylymer (paint film) thinner
: only to regulate viscosity, easy to dilute the construction. features:
chemical drying, according to the ratio of operation. Good overall performance, good hardness, good plumpness, good adhesion, good durability, good feel. The paint film is thin and not very hard, but its adhesion is particularly good
(
even teak oily wood can be, not to mention
)
; its gloss is said to not look very bright, can be very good display of the floor spinning and color. After the match has a certain period of use.
PU
is currently widely used in industry and architecture, so the technology is mature, color system, easy to meet the spraying requirements. However, because it is harmful to human body, so the requirements of paint room, paint room is higher, and at the same time need to take human protective measures. Advantages:
1)
compared with other lacquer species, in the same hardness, due to the role of hydrogen bonds,
PU

paint film fracture elongation rate is the highest, so widely used in floor paint, deck
paint Paint film on a variety of surfaces (metal, wood, rubber, concrete, some plastics, etc. have excellent adhesion.
4)
。 Paint film has excellent resistance to chemicals, acid, alkali, salt, petroleum products, so can be drilled into the platform, ships, chemical plant maintenance coatings, oil storage tank lining and so on.
5)
。 It can be dried and cured at low temperatures. The construction season is long.
6)