WO1999011673A1 - Method for producing polymethacrylate particles by emulsion polymerization - Google Patents

Abstract

The invention relates to a method for producing plastic particles with a size ranging from 2 to 30 mu m by emulsion polymerization in a mixture consisting of: a) 10-60 wt. % vinyl polymerizable monomers, wherein the proportion of water-insoluble monomers must be at least 80 wt. % in relation to the (a monomers used; b) 90-33 wt. % of a solvent mixture, consisting of at least 90 wt. % H2O; c) 0.01-2 wt. % of a polymerization initiation agent with a water solubility of at least 1 %; d) 0.05 to 5 wt. % emulgator. The invention is characterized in that a graft copolymer is used as emulgator, which consists of at least 90 wt. % water-insoluble and water-soluble (meth)acrylate monomers, wherein the methacrylate monomers and the acrylate monomers must be present in a minimal proportion of 20 wt. % and the proportion of the water-soluble (meth)acrylate monomers ranges from 5 to 80 wt. %.

Description

METHOD FOR PRODUCING POLYMETHACRYLATE PARTICLES BY EMULSION POLYMERISATION

The invention relates to a process for the production of plastic particles with a size in the range of 2 - 30 microns by emulsion polymerization using a graft copolymer as an emulsifier and the graft copolymer itself and its use as an emulsifier for emulsion polymerization.

State of the art

In practice, there is an increasing demand for plastics in the form of plastic particles in the particle size range from 2 to 30 μm. Crosslinked particles of this type are found e.g. B. Use as a spacer (displays, foils), as a surface modifier, as a carrier material in diagnostics etc. However, the main interest is in the optical industry, which realizes a wide variety of light effects with particles in this size range with a precisely adjustable refraction difference to a given polymer matrix can.

Also of interest are uncrosslinked, fusible polymethacrylate particles of this size range, whether as plastisol powder, as a raw material for powder coating or in dry screen printing (see, for example, DE-A 44 46 364.2).

EP-A 570 782 (DE-A 42 16 341) describes light-scattering polymethacrylate moldings with high temperature and fastness values. The polymethacrylate moldings consist of a polymethacrylate matrix with embedded crosslinked scattering particles, which are built up from monomers containing phenyl groups and can have a diameter in the range of approximately 1 to 20 μm. A UV absorber and a radical scavenger are also included. The light-scattering polymethacrylate resins are particularly suitable for applications in lighting technology. US 3,914,338 (Krieg et al.) Describes opalescent molded articles made of a polymethacrylate matrix with embedded scattering particles made of a core of e.g. B. cross-linked stryrene with a polymethyl methacrylate shell. The particles are produced by emulsion polymerization and have a size of at least 0.8 μm, e.g. B. in the range of 3 - 3.5 microns.

DE-A 20 59 078 describes a process for producing a polymer containing closed cells. The swellable polymer particles can e.g. B. by emulsion polymerization in the presence of a graft copolymer.

EP-A 492 405 (= US 5,254,632) describes acrylate-methacrylate graft copolymers. Water-soluble comonomers such as e.g. B. methacrylic acid are contained only in proportions of less than 5 wt .-%.

EP-A 522 376 describes a process for the preparation of polyalkyl methacrylate macromonomers and their use for the preparation of comb polymers. The macromonomers are formed by transesterification of C1 to C8 alkyl esters of (meth) acrylic acid with a hydroxyl-terminated polyalkyl methacrylate with elimination of an alcohol compound.

EP-A 639 590 describes a process for producing monodisperse poly (meth) acrylate particles by precipitation polymerization.

EP-A 728 780 relates to graft copolymers with emulsifier properties, obtained by copolymerization of macromonomers, built up from repeating C8-C30 alcohol methacrylate units with a hydrophilic, in particular water-soluble, free-radically polymerizable acrylic compound in a water-miscible solvent. Task and solution

For a whole series - especially large-scale - applications, such as B. for the production of light-scattering molding compound, however, the production of the particles in water or in an aqueous medium with a content of> 90% water is advantageous.

Such aqueous particle dispersions could, for example, be squeezed together with finely divided aqueous molding composition dispersion to give molding composition for light-scattering applications or to molding composition for the production of moldings with a structured surface.

It was therefore an object of the present invention to provide a process which enables polymer particles with a diameter in the range from 2 to 30 μm to be produced by emulsion polymerization.

The object was achieved by a method for producing plastic particles with a size in the range from 2 to 30 μm by emulsion polymerization in a mixture of

a) 10-60% by weight of vinylically polymerizable monomers, the proportion of the water-insoluble monomers having to be at least 80% by weight, based on the monomers a) used.

b) 90-33% by weight of a solvent mixture which consists of at least 90% by weight of H2O,

c) 0.01-2% by weight of a polymerization initiator with a water solubility of at least 1% and

d) 0.05 to 5% by weight of an emulsifier characterized in that a graft copolymer is used as emulsifier d) which is composed of at least 90% by weight of water-insoluble and water-soluble (meth) acrylate monomers, both methacrylate monomers and acrylate monomers having to be present in a minimum proportion of 20% by weight and the proportion of water-soluble (meth) acrylate monomers is 5-80% by weight.

Implementation of the invention

Components of the mixture for particle production

Component a)

The mixture contains a) 10-60% by weight of vinylically polymerizable monomers, preferably monomers from the group of (meth) acrylic acid esters and / or styrofoam, for building up the polymer particles, the proportion of the monomers insoluble in water being at least 80% by weight. % must be based on the monomers a) used. The proportion of water-insoluble monomers is preferably at least 95% by weight, particularly preferably at least 99% by weight, in particular 100% by weight.

Among water-insoluble monomers are e.g. B. C- | - To understand Cs alkyl esters of methacrylic acid, especially methyl methacrylate, benzyl methacrylate, methyl acrylate, ethyl acrylate or styrene. To crosslink the particles, crosslinking monomers such as allyl methacrylate or trialiylcyanurate or glycidyimethacrylate in amounts, for. B. 0.5 to 10 wt .-%, preferably not more than 2 wt .-% based on the total proportion of the monomers.

Among water-soluble monomers are monomers such as. B. methacrylamide, hydroxyethyl methacrylate, methacrylic acid or acrylic acid to understand. Component b)

The mixture contains b) 90-33% by weight of a solvent mixture which consists of at least 90% by weight, preferably at least 95% by weight, particularly preferably at least 99% by weight, of H2O. In addition to water, e.g. B. a water-miscible solvent, e.g. As methanol, ethanol or isopropanol, may be included.

Constituent c) c) 0.01-2% by weight, preferably 0.02-1% by weight, of a polymerization initiator with a water solubility of at least 1%, such as ammonium, sodium or potassium peroxodisulfate. Graft-active initiators which form oxygen radicals, such as K ₂ S ₂ O _{8, are} more suitable than initiators which generate graft-inactive C radicals, such as, for. B. 4, 4 ^' - Azobis (4 cyanovaleric acid) - Na.

In contrast, initiators that have a water solubility <1% are not suitable. These initiators, which are usually used to produce particles in the μm range, result in particles that are too large (see Example 9).

Component d ^* )

An emulsifier d) is a graft copolymer in amounts of 0.05 to 5% by weight, preferably 0.1 to 2% by weight, which is composed of at least 90% by weight of water-insoluble and water-soluble (meth) acrylate monomers is, both methacrylate monomers and acrylate monomers must be present in a minimum proportion of 20 wt .-% and the proportion of water-soluble (meth) acrylate monomers is in the range 5-80 wt .-%.

In addition to the (meth) acrylate monomers, the graft copolymer can optionally be used in small amounts, preferably not more than 10% by weight, particularly preferably not more than 5% by weight based on the graft copolymer, other vinyl polymerizable monomers such as. B. contain styrene.

Graft copolymers which are composed only of methacrylate monomers or only of acrylate monomers are unsuitable.

Proportion of water-soluble (meth) acrylate monomers The proportion of water-soluble (meth) acrylate monomers in the graft copolymer is 5 to 80% by weight, preferably 10 to 60% by weight, in particular 20 to 40% by weight.

Proportion of acrylate monomers

The proportion of water-insoluble or water-soluble acrylate monomers in the graft copolymer is in the range from 20 to 80% by weight, preferably from 30 to 70% by weight, particularly preferably from 40 to 60% by weight.

Suitable water-insoluble acrylate monomers are e.g. B. methyl acrylate, ethyl acrylate or butyl acrylate. Ethyl acrylate is preferred.

As a water-soluble acrylate monomer z. B. acrylic acid suitable.

Proportion of methacrylate monomers

The proportion of water-insoluble or water-soluble

Methacrylate monomers on the graft copolymer are in the range of 80-20

% By weight, preferably from 70 to 30% by weight, particularly preferably from 60 to 40

% By weight.

Water-insoluble methacrylate monomers are e.g. B. C-i - Cs alkyl esters of methacrylic acid. Methyl methacrylate and benzyl methacrylate are particularly suitable.

As a water-soluble methacrylate monomer z. B. methacrylic acid particularly suitable. Basic structure of the graft copolymer

The graft copolymer can e.g. B. from methyl methacrylate, ethyl methacrylate, butyl methacrylate, benzyl methacrylate and methacrylic acid and from ethyl acrylate and acrylic acid.

There are particular advantages if the graft copolymer is obtained by copolymerizing a polymethacrylate macromonomer from water-insoluble (meth) acrylate monomers with further water-soluble and, if appropriate, water-insoluble methacrylate monomers and acrylate monomers. The polymethacrylate macromonomers are then referred to as graft branches, while the further monomers form the main chain of the graft copolymer together with the end group of the graft branches after the polymerization. Polymethacrylate macromonomers, graft branches with a J value> 10 ml / g according to ISO 1628-6 and a molecular weight in the range from 10,000 to 100,000, preferably from 20,000 to 60,000, are preferably used.

The proportion of the polymethacrylate macromonomers in the graft copolymer is generally 5-60% by weight, in particular 10-40% by weight. It is particularly advantageous if the polymethacrylate macromonomer is chemically identical to or compatible with the polymer particles. Compatibility can e.g. B. be given if the polymethacrylate macromonomer has benzyl methacrylate residues and the polymer particles contain styrene residues.

If exclusively or predominantly methacrylate monomers are used as monomers a) to form the polymer particles, it is preferred if the graft branches likewise exclusively consist of methacrylate monomers, e.g. B. only consist of methyl methacrylate or methyl methacrylate and benzyl methacrylate. In the main chain, z. B. methacrylic acid and ethyl acrylate can be used. Quantitative proportions of 50-100% by weight methyl methacrylate and 0-50% by weight benzyl methacrylate in the graft branches and 20-80% by weight ethyl acrylate or 80-20% by weight methacrylic acid or acrylic acid in the main chain are favorable.

Production of macromonomers

The macromonomers are radically polymerized in a manner known per se in the presence of a polymerization initiator and a molecular weight regulator which, in addition to the regulator function, has a further functional group which is suitable for a further monomer linkage. Macromonomers were formed which terminally functionally function the regulator, e.g. B. have a hydroxyl group.

In a second reaction step in the presence of a catalyst and a polymerization-inhibiting stabilizer with excess monomer, the terminal group with the excess monomer, for. B. linked by transesterification. A macromonomer is formed which has a terminally polymerizable group, e.g. B. has a vinyl group.

For example, methyl methacrylate can be radically polymerized in the presence of mercaptoethanol and a polymerization initiator, initially producing macromonomers with terminal hydroxyl groups. These can then be converted into a polymethyl methacrylate macromonomer with a methacryloyl end group in the presence of isopropyl titanate as a catalyst and methyl 2,6-di-tert-butylphenol as a stabilizer (in the presence of atmospheric oxygen) and an excess of methyl methacrylate by transesterification (see also the example 1). Production of the graft copolymers CP

The graft copolymers can be prepared in a manner known per se. A polymethacrylate macromonomer with a methacryloyl end group is preferably first prepared (see Example 1), which is then radically polymerized with water-soluble and optionally water-insoluble methacrylate monomers and with acrylate monomers and in the presence of a polymerization initiator (see Examples 2 and 3).

Composition of the polymer particles

The process according to the invention is particularly suitable for polymer particles which are composed of a) more than 70% by weight of esters of (meth) acrylic acid and / or styrene.

Particles with a styrene content of less than 90% by weight are preferred. Of particular interest are particles which contain styrene and methacrylic acid ester in a weight ratio of 3: 1 to 1: 3. There are particular advantages if the styrene and the methacrylic acid esters are contained in a ratio of 1: 1 to 1: 2. If copolymers are produced with the process according to the invention, it is preferred that the monomer components mainly contained in the recipe (ie monomer components with a proportion of 10% by weight) are selected so that they copolymerize well with one another (copolymerization parameters in the range 0.1- 10, preferably in the range 0.2-4) or differ as little as possible in water solubility (expressed in g / l) by more than a factor of 10.

Particles composed of monomers which copolymerize alternately (for example styrene and methyl methacrylate) are preferred. Copolymers containing methyl methacrylate and benzyl methacrylate are particularly preferred. Such particles are used in particular for light scattering applications.

Particles that are as dimensionally stable bodies, e.g. B. as light scattering elements are used, usually with the addition of z. B. 0.1 - 20 wt .-% crosslinking monomers. Graft crosslinkers such. B. allyl methacrylate, against crosslinkers with 2 or more equivalent double bonds, such as. B. butanediol dimethacrylate, preferred (see, for example, EP-A 570 782 (DE-A 42 16 341)).

Preparation of the polymer particles

Polymer particles with a size in the range from 2 to 30 μm are synthesized in principle in a manner known per se by emulsion polymerization, but using the mixture according to claim 1. Polymer particles can only be obtained in this way by using the graft copolymer used as emulsifier d) the desired size can be obtained.

Completely emulsifier-free production of the particles, that is to say processes which do not require the graft copolymer, result in polymer particles of too small size (see Example 10).

The particle size is controlled by varying the constituents, for example B. Type and amount of emulsifier, type and amount of initiator, solids content, the simplest type of particle size control is the control over the solids content.

The particles become larger with increasing solids content. In the simplest case, the process is carried out as a single or multiple batch polymerization. In addition, feed processes can also be used. A single batch method is particularly preferred. In particular in the production of particles with a methacrylate content> 90% by weight or in the production of pure polymethacrylate particles, the polymerization according to the invention is best carried out in a closed system, since in this case the polymerization proceeds very quickly and cannot be run isothermally . Polymerization under autogenous pressure prevents the mixture from foaming and thus preventing coagulation.

In general, no strictly monodisperse polymer particles are obtained by the process according to the invention (standard deviation approx. 30%), but the particles are, despite their size distribution, ideally suited for applications in the field of light scattering technology, surface finishing or as a coating raw material, since the proportion of particles> 50 μm, would interfere in the above-mentioned applications, is usually well below 0.1%. As a rule, such a large proportion is not available at all. The measurement of the particle size can e.g. B. by measuring a particle population of z. B. n = 50 can be determined using a measuring eyepiece under the microscope. The particle size is in the range of 2 - 30 μm if the mean value (weight average) of the visible particles from approx. 1 μm is in this range.

The composition of the 2 - 30 μm large particles can be varied within wide limits according to the requirements. Particles that are used as meltable paint raw materials are added with the addition of 0.01 - 5 wt .-% regulator, z. B. dodecyl mercaptan.

The advantage of the graft crosslinker results from the fact that the particle formation phase can be completed first and only then does the crosslinking take place. In contrast, the use of larger proportions of crosslinking agents with equivalent double bonds such as ethylene glycol dimethacrylate leads to the formation of coagulate. In contrast, the method according to the invention is otherwise characterized by the absence of coagulum or a very low content of coagulum, provided that all the process features are observed.

The polymer solid is obtained from the aqueous dispersion as usual by sedimentation, centrifugation, filtration or coagulation and subsequent drying or direct spray or freeze drying.

However, it is preferred to incorporate the dispersion directly into the molding composition by squeezing out the water (see, for example, EP-A 0 683 028). In this case, molding compositions for the production of light scattering elements or moldings with a structured surface are directly accessible.

A two-stage procedure is particularly preferred, a master batch of the particles in molding composition (for example 40% by weight particles in 60% by weight molding composition) being produced in a first stage and one in the second stage with the aid of this master batch Molding compound with z. B. 5 wt .-% particles is produced.

Of particular interest is the pressing together of the 2-30 μm particle dispersion with a finely divided dispersion, e.g. B. a dispersion of 200 nm polymethyl methacrylate particles (J value of the polymethyl methacrylate: 50 ml / g) to a polymethyl methacrylate molding composition with z. B. 5 - 50 wt .-% particles. This procedure enables the production of a particularly homogeneous, pimple-free molding compound. Examples

Example 1:

Synthesis of a polymethyl methacrylate (PMMA) macromonomer with a methacryloyl end group

A mixture of 675 g of methyl methacrylate and 3.38 g of mercaptoethanol is polymerized at 90 ° C. by uniformly metering in a solution of 1 g of t-butyl pemeodecanoate (75% solution in aliphatics) in 290 g of toluene within 7 hours. The mixture is left to react for 30 minutes, then diluted with a solution of 0.14 g of 4-methyl-2,6-di-tert-butylphenol in 723 g of toluene.

1500 g of the solution of PMMA with hydroxyl end groups thus prepared are mixed with 1500 g of methyl methacrylate, 21 g of isopropyl titanate and 0.3 g of 4-methyl-2,6-di-tert.-butylphenol and with air access at about 100 ° C. for 7 hours touched.

After hydrolysis of the titanate at 90-95 ° C., the mixture is cooled, left to stand at room temperature for 12 h and then filtered. A clear, low-viscosity macromonomer solution is obtained, from which the macromonomer is obtained as a solid by degassing.

Characterization of the macromonomer:

J = 25.2 ml / g,

Mw = 37600 (inconsistency = 1, 23)

Methacryloyl group functionality: 85% Example 2

Synthesis of the emulsifier solution

A mixture of 27.0 g PMMA macromonomer according to Example 1

87.4 g ethyl acrylate

65.6 g methacrylic acid

330.0 g isopropanol and

84.0 g of distilled water

is heated to 70 ° C. while stirring and introducing argon and polymerized by adding 0.7 g of t-butyl perneodecanoate (75% solution in aliphatics) in 5.5 g of isopropanol within 5 h. The mixture is then stirred at 80 ° C for 2 h.

A clear, colorless polymer solution with a solids content of 29% is obtained.

Example 3

Preparation of an emulsifier solution with a modified graft copolymer structure

The procedure is as in Example 1, but a different monomer composition is chosen: 60% by weight methyl methacrylate, 40% by weight benzyl methacrylate. After transesterification with methyl methacrylate, a methyl methacrylate-benzyl methacrylate macromonomer with a methacryloyl end group (J = 21 ml / g) is obtained.

This macromonomer is, as described in Example 2, with ethyl acrylate and methacrylic acid to give a graft copolymer solution (Appearance: white), dry content 28.5% polymerized in isopropanol / water.

Example 4

Synthesis of PMMA particles

12.8 g of the emulsifier solution according to Example 2 are dissolved in 1008 g of methyl methacrylate. After adding 0.69 g of NaOH, dissolved in 1894 g of water, the mixture is emulsified and heated to 80 ° C. in a pressure reactor under nitrogen at 150 rpm. Then, by adding 4.2 g of ammonium peroxydisulfate (APS), dissolved in 80 g of dist. Water, the polymerization started.

After 42 minutes the internal temperature reaches its highest point at 92 ° C. The mixture is left to react for a further 30 minutes at 80-90 ° C. and then cooled with stirring.

A low-viscosity dispersion, solids content: approx. 33%, is obtained. The average particle size is 13 μm. No particles> 30 μm can be found. The approach is free of coagulum.

The specified particle size was determined by measuring a particle population of n = 50 using a measuring eyepiece under the microscope. Example 5

Synthesis of PMMA particles

The polymerization is carried out as described in Example 4, but a lower solids content (25%) is selected.

Weigh-in: 2176.5 g dist. water

750.0 g of methyl methacrylate

9.5 g of emulsifier solution according to Example 2

1.0 g of 50% sodium hydroxide solution

3.15 g APS, dissolved in 60 g dist. water

A coagulate-free dispersion is obtained. Particle size 5 μm ± 1 μm (standard deviation). There is a fine fraction (<1 μm). Larger particles are not present.

Example 6

Synthesis of PMMA / styrene particles

From 213 g of dist. Water, 56.7 g of methyl methacrylate, 56.7 g of styrene, 1.44 g of the emulsifier solution according to Example 2 and 0.08 g of NaOH, an emulsion is prepared and heated to 80 ° C.

In a stirred reactor under nitrogen as a protective gas at a stirring speed of 150 rpm at 80 ° C by adding 0.48 g of ammonium peroxodisulfate, dissolved in 9.12 g of dist. Water that initiates polymerization. After 4.5 h of polymerization at 78-80 ° C., the mixture is cooled. A coagulate-free dispersion is obtained. The particle size is 4.5 ± 1.5 μm. There is only a small amount of fines. Particles larger than 10 μm are not found.

Example 7

Production of cross-linked light scattering particles

126 g of water, 35.1 g of styrene, 35.1 g of methyl methacrylate, 3.7 g of allyl methacrylate, 0.88 g of the emulsifier solution according to Example 3 and 0.05 ml of 50% NaOH are emulsified and under nitrogen as an inert gas at 80 ° C after addition of 0.29 g APS, dissolved in 5.51 g water, polymerized.

After 5 hours, a thin dispersion is obtained, particle size 5 ± 1 μm. The particles have a rough surface.

The particles are allowed to sediment, dried in vacuo. After mixing 6% particles with 94% PLEXIGLAS molding compound 7N, a light-scattering molding compound is obtained.

Example 8

Production of cross-linked light scattering particles

155.2 g of water, 34.4 g of methyl methacrylate, 25 g of benzyl methacrylate, 3.12 g of allyl methacrylate, 0.79 g of emulsifier solution according to Example 3 and 0.04 g of NaOH are emulsified and under nitrogen as an inert gas after the addition of 0.31 g APS, dissolved in 30.7 g water, polymerized at 80 ° C. After 15 minutes, 0.4 g of 25% ammonia solution is added Stabilization too. After a reaction time of 33 minutes, a temperature rise to 89 ° C. is observed. The mixture is stirred for a further 30 minutes and then cooled.

A coagulate-free dispersion with a particle size of 3 to 5 μm is obtained. The particles are incorporated in PMMA molding compound to produce light-scattering molding compound.

Example 9

(Comparative example, not according to the invention)

The procedure is analogous to Example 8, but 1% t-butyl perneodecanoate is chosen as the initiator instead of APS. Particles with a size of 100-1000 μm are obtained.

Example 10

(Comparative example without emulsifier, not according to the invention)

Synthesis of polymethacrylate particles

27.5 g of methyl methacrylate, 20 g of benzyl methacrylate and 2.5 g of allyl methacrylate in 175 g of distilled water are emulsified in a stirred reactor (400 revolutions / min) and heated to 85 ° C.

The polymerization is started by adding 0.25 g of ammonium peroxydisulfate, dissolved in 24.75 g of water.

A finely divided dispersion (particle size <1 μm) is obtained. The dispersion contains a lot of coagulate.

Claims

PATENT CLAIMS 1. Process for the production of plastic particles with a size in the range from 2 to 30 μm by emulsion polymerization in a mixture of a) 10-60% by weight of vinylically polymerizable monomers, the proportion of the water-insoluble monomers having to be at least 80% by weight, based on the monomers a) used. b) 90-33% by weight of a solvent mixture which consists of at least 90% by weight of H2O, c) 0.01-2% by weight of a polymerization initiator with a water solubility of at least 1% and d) 0.05 to 5% by weight of an emulsifier characterized in that a graft copolymer is used as emulsifier d) which is composed of at least 90% by weight of water-insoluble and water-soluble (meth) acrylate monomers, both methacrylate monomers and acrylate monomers having to be present in a minimum proportion of 20% by weight and the proportion of water-soluble (meth) acrylate monomers is 5-80% by weight. 2. The method according to claim 1, characterized in that the graft branches of the graft copolymer are composed exclusively of methacrylate monomers. 3. The method according to claim 1, characterized in that the monomers a) methyl methacrylate, stryrene and / or benzyl methacrylate are used and as the emulsifier d) with a graft copolymer Graft branches made from methyl methacrylate or from methyl methacrylate and benzyl methacrylate are used and the main chain contains ethyl acrylate and methacrylic acid as further monomers. 4. graft copolymer, characterized in that the graft branches are composed of methyl methacrylate or of methyl methacrylate and benzyl methacrylate and ethyl acrylate and methacrylic acid are present as further monomers in the main chain. 5. Use of a graft copolymer according to claim 4 for the production of polymer particles with a size in the range of 2 - 30 microns by emulsion polymerization.