DE4340136A1 - Process for removing residual volatile components from polyacrylate melts - Google Patents

Description

The invention relates to a method for eliminating residual volatiles fractions of polyacrylate melts.

For example, polyacrylate melts are considered soft resins for plasticizing adhesive raw materials and lacquer raw materials and on the other hand as a raw material base for the new generation of UV-crosslinkable acrylate hotmelt adhesives are used.

An essential requirement for the usability of the poly Acrylate melting is an extremely low percentage of residual volatiles proportions, for example residual solvents, residual monomers and Impurities. This is especially true for the latter UV-curable hotmelt adhesives. Especially when using it in medical products, e.g. skin plasters, is an extremely low proportion of migrating substances prerequisite. But also with today's smelting application very fast running coating machines (belt speed speed of up to 600 m / min), there is a high proportion of residual curd proportions quickly and creates special technical expenses necessary for their removal.

The production of the polyacrylate melts can be done in three phases organize. The first step is bulk polymerization or solution. The solvent is then removed in the second step separation or a residual monomer stripping. The Pro joins Product filling via, for example, a gear pump discharge.

The polymerization is carried out in a conventional manner in a poly polymerization apparatus, consisting of a polymerization vessel, which generally with a commercial stirrer, several Zu barrel, reflux cooler and heating / cooling is provided and for working in an inert gas atmosphere and over or under pressure equipped.

For solvent separation (evaporation of the solvent under Zu retention of the polyacrylate melt) are very different technical processes. Here is the "classic" Kettle distillation mentioned. However, other common methods are also the use of a falling film evaporator, the strand degas solution or the residual degassing in the extruder. A very comprehensive Zu You can compile various evaporation methods in the  Book series: Plastics technology "Degassing in manufacturing and Processing of plastics ", publisher: Verein Deutscher In engineers, VDI Gesellschaft Kunststofftechnik, VDI Verlag, 1992, read up.

For the reasons mentioned above, there is a need for residual volatility to reduce shares to a minimum.

Surprisingly, it has now been found that the proportion of rest volatile components to well below 100 ppm if entraining agents such as water vapor, nitrogen, argon, CO₂ towards the end of the distillation under vacuum conditions in the hot polyacrylate melt pressed and then together with the remaining volatile components are deducted. Another Deut improvement is achieved if at the same time there is an optimization tion of polymer mixing and an increase in surface area is realized. This is done by pumping around the polyacrylate melt by means of a gear pump and a bypass.

Water vapor proves to be particularly cheap as a tow medium, which is advantageously fed directly into the bypass becomes. It should be noted that the internal boiler temperature and the internal bypass temperature is permanently above 100 ° C, d. H. of the Water vapor must not condense.

Basically, there are a variety of methods of removal Residual volatiles from polymer melts. One host Economic degassing of higher-viscosity plastic melts for example, by continuous degassing or treatment of Products in the degassing extruder. Both methods have their specific fishing disadvantages. While often the Blockage of the tube bundle is problematic (specks, gel beads per, caking), the disadvantages are in extruder degassing solution, on the one hand in the high shear of the polymer melt on the other hand also in the increased space requirement of this degassing facility as well as in the very high investment expenditure. An over view is the bundle belt series: plastics technology "degassing at Manufacture and processing of plastics ", publisher: Verein German engineers, VDI Gesellschaft Kunststofftechnik, VDI Verlag 1992. Water vapor is used as an entrainer here only in the systems polystyrene or LDPE and PE copolymers described in combination with extruder degassing.

The residual monomer content in polyacrylate melts is generally reduced by the so-called chemical deodorization. About the Add an increased peroxide concentration at the end of the polymer sation at elevated temperature is a very good Auspolymeri  achieved. Disadvantages of this procedure are the uncontrolled grafting reactions that occur to the speck and gel body lead education. This effect is particularly problematic with Use of such polyacrylate melts in highly transparent Clear coats. The chemical deodorization of polyacrylate melts the solvent is generally separated by an übli evaporation in the reaction vessel.

The removal of solvents or residual monomers from polyacrylics Latschmelze by steam distillation in a vacuum is in the Chemical Abstract 100 (14) (method of Butaciu, Sirbu, Eivnic, Jacob, Tataru, Doina, Berea). The procedure be hits aqueous suspension polymers, however. H. water is present from the start (usual deodorization process from Polymer dispersions).

According to what has been shown, the task therefore lies in this Process for removing residual volatiles in polyacrylate provide melt, in which the disadvantages mentioned ver be avoided.

This object is achieved in that the Ab evaporate the volatile components in vacuo, entrainer are supplied to the melts at temperatures above 100 ° C. and the melts are pumped around at the same time.

Other features of the method according to the invention are the subject of subclaims.

The essential features of the invention are as follows described in detail and in drawings and based on Bei play explained.

The polymerization is best in a polymerization apparatus from a polymerization kettle with a commercial Chen stirrer, several inlet vessels, reflux condenser, heating and Cooling and the pump circuit is provided with water vapor inlet, carried out. The polymerization kettles have a volume of 10 l - 20 m³ preferably 10 l - 10 m³ and are equipped for the Working in an intergas atmosphere as well as for overpressure and vacuum.

To produce the acrylic ester homo- or copolymers the usual methods of radical polymerization in water or solution can be applied. The polymerization is mostly up to to a conversion of the monomers of over 80%, preferably of over 90%, very particularly preferably of over 99%.  

To the reaction mixture consisting of monomers and the Initia All known stirrers can be mixed in the template species are used.

The copolymers are at temperatures from 20 to 150 ° C, before preferably at temperatures in the range of 70 to 120 ° C and printing from 0.1 to 100 bar, preferably at 1 to 10 bar, in the presence of 0.01 to 10 wt .-% of peroxides or azo starters as Polymerisa tion initiators, based on the monomers and in the presence of 0 to 200% by weight of indifferent solvents, preferably 5 to 25 wt .-%, based on the monomers, d. H. through solution or Bulk polymerization produced.

Preferred solvents are those of a boiling range from 50 to 150 ° C used, for example hydrocarbons such Benzene, toluene, o-, m-, p-xylene, as well as gasolines, which are preferred have a boiling range of 60 to 120 ° C. Furthermore alcohols such as methanol, ethanol, propanol, butanol, isobutanol, ketones such as Acetone, methyl ethyl ketone, methyl isobutyl ketone, nitriles such as aceto nitrile and benzonitrile or mixtures of the solvents mentioned teln. Solvents such as toluene, isobutanol and vinegar are preferred acid ethyl ester and mixtures thereof.

Peroxides such as, for example, are polymerization initiators Acyl peroxides such as benzoyl peroxide, dilauroyl peroxide, didecanoylpe roxid, Isononanoylperoxid, alkyl esters such as tert-butyl-tert-piva lat, tert-butyl-per-2-ethylhexanoate, tert-butyl-per-maleinate, tert-butyl per-isononanoate, tert-butyl per-benzoate, tert-amyl per-2-ethylhexanoate, dialkyl peroxides such as dicumyl peroxide, tert.- Butylcumyl peroxide, di-tert-butyl peroxide and peroxodicarbonates applicable.

Furthermore, azo starters such as, for example, can be used as initiators 2,2'-azobisisobutyronitrile, 2,2'-azobis (methyl isobutyrate) or 2,2'-Azobis (2,4-dimethylvaleronitrile) find use.

Four groups (a-d) can be used as monomers:

• a) The usual monoolefinically unsaturated monomers Monocarboxylic acid esters containing 3 to 24 carbon atoms, ins special esters of acrylic and methacrylic acid are used the. Of particular importance as monomers are the acrylic and methacrylic acid esters containing 1-12 C atoms Alkanols, such as methyl acrylate, ethyl acrylate, propyl acrylate, Isopropyl acrylate, N-butyl acrylate, isobutyl acrylate, isoamyl acrylate, 2-ethylhexyl acrylate, isoocrylic acrylate and meth  acrylate, methyl methacrylate and decyl acrylate and meth acrylate and dodecyl acrylate or methacrylate.
• b) Monomers such as α, β-monoolefinically unsaturated 3 to 6 C atoms containing mono- or dicarboxylic acids. For example acrylic acid, methacrylic acid, itaconic acid, fumaric acid and / or Maleic acid. Furthermore, the anhydrides monoolefinically saturated dicarboxylic acids such as maleic anhydride and Itaconic anhydride.
• c) Reactive monomers such as acrylamide and methacrylamide, tetra hydrofurfuryl (meth) acrylamide, diacetone acrylamide, hydroxy alkyl (meth) acrylates such as 2-hydroxyethyl (meth) acrylate and 4-hydroxybutyl (meth) acrylate. Furthermore also monomers that wear photoreactive groups, e.g. B. N- (acrylamidomethyl) benzo phenon-4-carboxamide, 4-acryloxybutyl carbonate-benzophenone or 2-methacryloxyethylene carbonate benzophenone.
• d) monomers such as N-vinylpyrrolidone and N-vinylformamide, acrolein, Methacrolein, isobutene, butadiene, isoprene, vinyl methyl ether, Vinyl isobutyl ether, vinyl pyrridine, styrene and methyl styrene, Monomers such as vinyl caprolactam and monomers such as e.g. B. Tetra hydrofururyl 2-acrylate and methacrylate. Of special importance interpretation are also the vinyl esters of carboxylic acids, the 1 to Contain 18 carbon atoms, such as. B. vinyl acetate or vinyl propionate.

The monomers can be used as pure substances, as mixtures with the others Ren monomers or as solutions in suitable solvents the Re action mixture can be supplied. The individual monomers can via separate feed lines or together via an antler in the boiler are led.

To carry out the polymerization, the reaction can also mix compounds that lower the degree of polymerization, so-called mentioned polymerization regulator can be added, for example Mercaptans such as mercaptoethanol, mercapto succinic acid, 3-mercaptopropyltrimethoxysilane or dodecylmercaptan.

For successful post-polymerization, the polymer Melt or solution after initiator and monomer feed some Heated to boiling point for hours. For the procedure according to the invention no chemical post-polymerization is necessary. With that ent the resulting disadvantages fall.  

The solvent is preferably evaporated off at the boiling point in vacuo. It is distilled off until no clear reflux can be observed. When the gear pump is put into operation, the contents of the boiler are then quickly pumped around under vacuum conditions (water ring pump vacuum) (1 × boiler content per 4 hours, preferably 1 × boiler content per 1 hour), water vapor (2 to 20 bar, preferably 4 to 16 bar) being introduced at the same time becomes. The water vapor should be mixed as intimately as possible with the polymer melt (static mixer, special nozzle geometry in the water vapor inlet useful). The mixture of residual volatile components and water vapor is flashed into the upper area of the boiler, with the largest possible portion of the volatile components being removed in a vacuum (see Fig. 1). The commissioning of a separate water supply is recommended. The mixture of residual volatiles and water should be specially prepared. The duration of the steam treatment can be directly correlated with the residual volatile content, ie the steam stripping must be carried out over such a period of time until the specifications of residual monomers in the various products are reached.

When commissioning a 2-boiler system, polymerization and distillation can be completely (see Fig. 2) or partially (see Fig. 3) decoupled.

While in a system according to Fig. 2 the distillation is carried out completely in the distillation kettle equipped with steam inlet and pumping circuit, in a system according to Fig. 3 the distillation can partly take place in the polymerization kettle.

The copoly produced by the process according to the invention merisates have K values from 10 to 120, in particular 15 to 80, determined according to DIN 53726 in 1% solution in tetrahydrofuran 25 ° C. The K value is preferably 20 to 60.

Of particular interest are copolymers and their monomers composition is such that a glass transition temperature reached from -50 to 0 ° C, particularly preferably from -45 to -5 ° C is. After Fox (T.G. Fox, Bull. Am. Phys. Soc. (Ser. II) 1, 123 (1956)) applies to the glass transition temperature of Mischpoly merisates in good approximation  

where X¹, X²,. . . X ^s the mass fractions of the monomers, 1, 2,. . . are and Tg¹, Tg²,. . . Tg ^s the glass transition temperatures of each of only one of the monomers 1, 2,. . . or s polymers built up in degrees Kelvin. The glass transition temperatures of the abovementioned monomers are essentially known and are described, for example, in J. Brandrup, EH Immergut, Polymerhandbook, 1 ^st Ed.J. Wiley, New York 1966 and 2 ^nd Ed.J. Wiley, New York in 1975.

The copolymers prepared by the new process can especially as UV-crosslinkable compositions for the production of over trains, coatings and impregnations, especially for manufacturing provision of pressure sensitive adhesives, pressure sensitive adhesive films, pressure sensitive adhesive tapes, Pressure sensitive adhesive labels as well as stamping foil are used. There at can the masses in a conventional manner by painting, Spraying, rolling, knife coating or pouring, if necessary with increased Temperature, usually in the temperature range from 20 to 180 ° C, on übli che substrates are applied, for example on paper, Cardboard, wood, glass, metals, metal and plastic films, at for example on plasticized PVC, polypropylene, polyethylene, Polyamides, polyesters or aluminum and copper. Continue reading nonwovens, fibers, leather and textile fabrics layers. The copolymers can also be used, for example provision of pressure sensitive adhesive labels in transfer orders on carriers such as Paper can be applied by first being on abhesive layered carrier materials, for example siliconized Pa applied pier and be in the case of UV-crosslinkable materials shines and then laminated on paper, for example the. After peeling off the siliconized paper, it can stick sticky layer may be irradiated again. When UV lamps can be the usual lamps, for example mercury medium pressure silver lamps with a radiation output of 80 to 240 watts / cm can be used. The new pressure sensitive adhesives can modified and / or assembled in the usual form the.

The usual tackifying resins, e.g. hydrocarbon fabric resins, modified rosins, pinene and terpene resins or homopolymers such as poly (2-ethylhexyl acrylate), poly (n-butyl acrylate), further plasticizers e.g. B. based of mono-, di- or polyester compounds, pigments, stabilizers  Ren, styrene-butadiene copolymers, or polyvinyl ether can Copolymers can be added in amounts of up to 50% by weight.

Polyacrylate melts based on butyl acrylate are preferably used as soft resins for plasticizing adhesive raw materials, lacquer raw substances and plastic preparations. These products stand out due to its special resistance to light and aging. A be special prerequisite for the applicability of these products the freedom from specks. Especially when used as a paint tube fabric is this property for a high gloss and a good History required.

Examples

The following experiments were carried out in a polymerization vessel from 400 l content carried out. The ones shown in the following examples parts and percentages given relate to the weight. The Be The K values are adjusted according to DIN 53726 in a 1% solution in Tetrahydrofuran at 25 ° C. The solids contents (FG) were with a fixed salary determination apparatus model "Mettler EP 16 / Mettler PE 360 ".

The remaining parts were identified by gas chromatography graph (Hewlett Packard model 5890) and according to internal standards method quantified.

Example 1 (prior art)

A sample of 24 kg of isobutanol, 5% of a solution of 228 kg of butyl acrylate (BA), 12 kg of acrylic acid (As) and 0.8 kg of a copolymerizable photoinitiator and 5% of a solution of 0.480 kg of tert-butyl-per-2 Ethyl hexanoate and 3 kg of isobutanol are polymerized at 100 ° C. for 10 min. The rest of the monomer mixture and the rest of the peroxide solution are fed into the reaction mixture over the course of 7 hours. After the peroxide feed has ended, the internal temperature is raised to 115 ° C. and polymerized for 3 hours. Then the solvent and volatile components are removed under vacuum at 127 to 132 ° C. After reaching an internal reactor temperature of 130 ° C, the remaining volatile components are distilled off in vacuo at <500 mbar for 3 hours. A copolymer with a K value of 47.3 is obtained.
Residual volatiles: isobutanol: 2300 ppm, BA 1230 ppm, As <0.02%.
FG: 99.6%.

Example 2

The procedure described in Example 1 is followed, but the distillation is varied as follows: after an internal temperature of 130 ° C. has been reached, under a vacuum of approx. 500 mbar, the polyacrylate melt is pumped around (pumping speed 400 l / h). At the same time, steam is fed into the pumping circuit at 16 bar for 2.5 hours. Then, as in Example 1, the mixture is distilled for 0.5 hours at an internal temperature of 130 ° C. A copolymer with a K value of 47.7 is obtained.
Residual volatiles: isobutanol: 50 ppm, n-BA <10 ppm, acrylic acid no longer detectable.
FG: (after steam introduction): 99.9%.

Example 3

The procedure is as given in Examples 1 and 2. After reaching an internal temperature of 130 ° C and a vacuum of 500 mbar, a sample is taken:
Residual volatiles: isobutanol: 3875 ppm, n-BA: 2542 ppm, FG: 99.0%.

The pump circuit is then started up, 4 bar of water vapor are introduced over 1 hour and the remaining volatile components are distilled off.
Residual volatiles: isobutanol 518 ppm, n-BA 1212 ppm
FG: 99.8%.

The pump circuit and the water vapor inlet are then put into operation again for 1 hour and a further sample is taken.
Residual volatiles: isobutanol: <10 ppm, n-BA 365 ppm
FG: 99.9%.

Example 4 (Comparative Example to Example 3)

The copolymer is prepared as described in Example 3 with the change that the pumping circuit and water vapor inlet are not put into operation. For this purpose, the usual boiler distillation is extended by a corresponding period, ie by 2 hours.
Residual volatiles: isobutanol: 2700 ppm, n-BA 1400 ppm
FG: 99.5%.

Example 5

A sample of 15 kg toluene, 0.1 kg tert-butyl-per-2-ethyl hexanoate and 5.0 kg of a monomer mixture of 95 kg butyl acrylate and 5 kg of 2-hydroxyethyl acrylate (HEA) is kept at 100 ° C. for 10 min Polymerized nitrogen atmosphere. In the course of 4 hours the rest of the monomer mixture and simultaneously within 3.5 hours a solution of 1.9 kg of tert-butyl per-2-ethylhexanoate in 10 kg of toluene at an internal temperature of 100 ° C to the pre put reaction mixture. After completing the monomer addition, he the internal temperature is increased and stirring is continued at 115 ° C. for 4 hours. The resin solution obtained is divided into two.

Example 5.1 (according to the invention)

Then the solvent and volatile constituents are distilled off, the pump circuit being put into operation with 4 bar of water vapor inlet once an internal temperature of 130 ° C. and a vacuum of 500 mbar have been reached. After 2 hours of steam stripping, a sample is taken.
Residual volatiles: toluene: <10 ppm, n-BA: <10 ppm, 2-HEA: <10 ppm,
FG: 99.9%.

Example 5.2 (comparative example)

Solvents and volatile components are distilled off.

After reaching 130 ° C and 500 mbar, the distillation is continued for 2 hours in the boiler. An internal temperature of 130 ° C is maintained.
Residual volatiles: toluene: 750 ppm, n-BA: 1300 ppm, 2-HEA: 970 ppm,
A copolymer with a K value of 42.3 is obtained in both cases.

Claims (10)

1. A process for removing residual volatile components from polyacry latschmelzen by evaporating the volatile components, characterized in that the volatile constituents are evaporated off in vacuo, entraining agents are supplied to the melts at temperatures of over 100 ° C. and the melts are pumped around at the same time. 2. The method according to claim 1, characterized in that the Entrainer is fed directly into the pump circuit. 3. The method according to claims 1 and 2, characterized in that steam is used as an entrainer. 4. The method according to claims 1 to 3, characterized in that water vapor is fed at a pressure of 1 to 20 bar becomes. 5. The method according to claims 1 to 4, characterized in that the polyacrylate melt is preferred at least once is pumped several times. 6. The method according to claims 1 to 5, characterized in that the polymerization and distillation in a 1-kettle location or a 2-boiler system. 7. The method according to claims 1 to 6, characterized in net that the method is particularly suitable for production of polyacrylate melts with glass transition temperatures of -50 to 0 ° C, preferably from -45 to -5 ° C. 8. The method according to claims 1 to 6, characterized in net that the method is particularly suitable for production of polyacrylate melts with K values from 10 to 120 before moves from 15 to 80, particularly preferably from 20 to 60. 9. The method according to claims 1 to 6, characterized in net that the method is particularly suitable for production of polyacrylate melts, which are the raw material base for UV ver wettable hotmelt PSAs are suitable.   10. The method according to claims 1 to 6, characterized in net that the method is particularly suitable for production of polyacrylate melts, which are used as soft resins for plasti Fication for paint and adhesive raw materials are suitable.