DE2849279A1 - (Meth)acrylic ester polymer beads contg. fine inorganic filler - useful in dental filling paste are obtd. by suspension polymerisation in presence of filler - Google Patents

Abstract

Polymer beads with an average bead dia. of 5-500 mu consist of a finely-divided inorganic filler (I) and (meth)acrylic ester polymer (II), pref. 5-500 wt. pts. (I) and 95-50 wt. pts. (II). The beads are useful as fillers in dental filling compsns. They are wetted easily by the liquid paste component (monomer) and are anchored in the resin matrix well after cure.

Description

Bead polymers containing fillers

The invention relates to a method for producing with inorganic filler filled, optionally crosslinked bead polymers with an average bead diameter (d50) of 5 to 500 μm based on (meth) acrylic acid esters.

The production of unfilled bead polymers by bead polymerization is e.g. from Houben-Weyl; Methods of Organic Chemistry, Vol. XIV / 1 known. Man for this purpose suspends the monomer or monomers in water with stirring and polymerizes the droplets formed using a monomer-soluble initiator.

Bead polymerization generally requires dispersants. These prevent the beads from sticking together during the reaction. They usually are water-soluble, high-molecular organic compounds or finely divided, water-insoluble inorganic compounds; the latter are also referred to as Pickering dispersants. Many different substances are used as the Pickering dispersant, e.g.

the carbonates, phosphates, sulfates and silicates of the alkaline earth metals, Aluminum oxide and aluminum hydroxide, bentonite and talc.

The granules of the dispersant do not become inside the Pearls included, but are practically exclusively on the pearl surface, so that they can be easily removed during work-up.

In this way, bead polymers of high purity can be obtained will.

In some cases, attempts have been made to use dyes and pigments polymerize in bead polymers. It is known from US Pat. No. 2,533,196 that to produce pigmented polymer beads from diallyl dicarboxylate. At the Working according to US Pat. No. 2,533,196, the monomeric diallyl dicarboxylate is partially polymerized and mixed with a pigment; the thickened pigmented mass becomes in a suspended aqueous sodium bisulfite or sodium nitrate solution and stirring hardened. In this process, the dispersing medium must have the same density as have the polymerized pigmented mass.

Furthermore, DE-PS 829 221 describes a process for the production of polymerisation plastics containing fluorescent colors, in which the suspension polymerisation is carried out in the presence of fluorescent paints and a thickener.

US-PS 2,533,196 and DE-PS 829 221 exploit the fact that highly viscous liquids hold on to incorporated solids more strongly than less viscous liquids.

The difficulties of bead polymerization of highly viscous substances are known: the liquid droplets formed have an increased tendency to Agglomeration and it becomes predominantly large, i.e. one to a few millimeters in size Pearls formed (see also FR-PS 1 005 601).

In the bead polymerization of filled with inorganic filler Polymer / monomer mixtures impaired the increased tendency to sedimentation of the filled Liquid droplets form relatively small, round polymer beads Additionally. It is therefore not possible to work in analogy to US-PS 2,533,196 or DE-PS 829 221 filled with inorganic filler beads with a to produce an average bead diameter of less than 1 mm. With appropriate attempts particles several millimeters in diameter are obtained, their shape strong deviates from the spherical shape.

The invention therefore relates to the production of regular, Bead polymers filled with inorganic filler and having an average diameter (d50) from 5 to 500 / u based on methacrylic acid esters and / or acrylic acid esters.

It has been found that such bead polymers are obtained when one mixtures of monomer and optionally polymer soluble in the monomer and Filler, which has a viscosity of 0.1 to 10 Pa s, measured at the dispersing temperature, have, suspended and polymerized in an aqueous medium in the presence of dispersants.

Filled bead polymers produced by the process according to the invention are suitable as fillers in pasty dental materials; they get through easily the liquid paste component (monomer) wets and show a after curing good mechanical anchoring in the plastic matrix.

In the first step of the method according to the invention, the inorganic filler with vigorous stirring into a viscous mixture of monomer liquid and polymer or incorporated into a viscous monomer liquid.

The resulting mass should have a viscosity of 0.1 to 10 Pa s. The figures given apply to the temperature at which the mass is dispersed. In the case of viscosities below 0.1 Pa s, none or only a very small amount is found The inorganic particles are included in the subsequent polymerization; at higher viscosities than 10 Pa s no small pearls can be obtained, d.

That is, a defined viscosity of the monomer phase is for the technical Effect requirement.

The aliphatic esters of methacrylic acid and Acrylic acid, such as, for example, methyl (meth) acrylate, ethyl (meth) acrylate or cyclohexyl methacrylate are used, in addition, as a crosslinking agent, methacrylic acid esters of polyvalent Alcohols such as ethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate and trimethylolpropane trimethacrylate. In addition to (meth) acrylates, up to 20% by weight of other monomers, such as styrene, divinylbenzene, can also be used or vinyl acetate can be used.

When using these monomers, the viscosity must in general by partial polymerization or by the addition of soluble in the monomer, separated produced polymer are increased.

It is also possible to use monomers whose viscosity is high enough. Examples of this are the Bis-GMA (reaction product of bisphenol A and glycidyl methacrylate) ) or resulting from the addition of diisocyanates and hydroxyalkyl (meth) acrylates Urethane (meth) acrylates.

Water-insoluble, finely divided inorganic fillers are suitable as fillers Substances, e.g. metal oxides, sulfates, silicates and phosphates, as well as glasses and ceramic masses and mixtures thereof. The grain diameter of the fillers must be below 5 µm, preferably less than 2 µm.

In the second step, the. filled with inorganic filler viscous mixture with an initiator substance (e.g. benzoyl peroxide, cyclohexyl percarbonate) added and by high-speed stirring in an aqueous solution of e.g.

high molecular weight dispersant suspended. The dispersant should be used have a dispersant content of 0.2 to 5% by weight. The suspension process takes place generally at room temperature (20 to 25 ° C). But in some cases it can take advantage of the negative temperature coefficient of viscosity in the sense, that mixtures whose viscosity at room temperature is too high (i.e., higher than 100 Pa s) is to be suspended at elevated temperature.

Partial saponification are particularly suitable as dispersants recovered copolymers of vinyl alcohol / vinyl acetate or produced by copolymerization Methacrylic acid / methyl methacrylate copolymers.

In the third step, the suspension is heated while stirring polymerized to the decomposition temperature of the initiator substance. This involves heating up advantageous under pressure in order to obtain particularly regular pearls.

From the fully polymerized suspension can in a known manner by Filtering, washing and drying the bead polymer can be obtained.

The viscosities given in the examples were at 25 ° C. a falling ball viscometer determined. The values apply in each case to the monomer phase in the absence of the inorganic filler.

Example 1 Production of a filled with magnesium hydroxide carbonate Bead polymer.

Reaction vessel: 3 liter flat ground joint beaker with blade stirrer, reflux condenser, Indoor thermometer, gas inlet and gas outlet tube.

Mixture 1: monomer phase 220 g methyl methacrylate) viscosity 30 g ethylene glycol dimethacrylate of the mixture: 50 g polymethyl methacrylate) 0.6 Pa s (/ a, 7 = 1.05 in chloroform) 100 g magnesium hydroxide carbonate (4 MgC02.Mg (OH) 2. 4 H20) (manufacturer: Ridel de Haen AG) Mixture 2: aqueous phase 15 g Moviol 70/88 (Farbwerke Hoechst), dissolved in 1000 ml dist. Water.

The components of mixture 1 are in the absence of atmospheric oxygen placed in the reaction vessel and 12 hours.

stirred at room temperature at 250 rpm, the polymer dissolved and a highly viscous mass is formed. This mixture is made with 2.2 g of cyclohexyl percarbonate added and stirred for a further 30 min. Mixture 2 is then added all at once and the stirring speed increased to 800 rpm. The suspension formed is heated to 70 ° C. and, when the exothermic reaction starts, cools so strongly that the temperature is kept below 850C. After the reaction has subsided, the approach is under further Stirring held at 85 ° C. for 2 hours. The solid bead polymer is filtered off after cooling, several times with dist. Water washed and at 500C dried.

Yield: 328 g mean grain size: 160 / u.

0.5 g of the bead polymer is mixed with 20 ml. For 30 minutes at 70 ° C Treated ln hydrochloric acid, then with dist.

Water washed and dried. This process does not solidify Magnesium hydroxide carbonate trapped in the beads is removed. After hydrochloric acid treatment the magnesium hydroxide carbonate content of the pearls is 14.1% by weight.

Example 2 (comparative example) Bead polymerization without incorporation of Magnesium hydroxide carbonate.

Reaction vessel: as in example 1 Mixture 1: monomer phase 270 g methyl methacrylate} viscosity 30 g ethylene glycol dimethacrylate j of the mixture: 0.001 Pa s 100 g of magnesium hydroxide carbonate (4 MgC03.Mg (OH) 2.4 H20) (manufacturer: Riedel de Haen AG) Mixture 2: aqueous phase as in Example 1 Mixture 1 is added to the reaction vessel with exclusion of air and, with slow stirring, with 2.7 g Cyclohexyl percarbonate added. Mixture 2 is then added all at once and the stirring speed is set to 800 rpm. The rest of the procedure is the same as in Example 1.

277 g of bead polymer with an average particle size of 42 u are obtained. After the hydrochloric acid treatment described in Example 1, the bead polymer does not contain any magnesium hydroxide carbonate. (The analytical error is less than 0.05%) Example 3 Production of a bead polymer filled with titanium dioxide Reaction vessel as in Example 1 Mixture 1: monomer phase 225 g methyl methacrylate) viscosity 15 g of ethylene glycol dimethacrylate of the mixture: 60 g polymethyl methacrylate 1.5 Pa s ([#] = 1.05 in chloroform) 150 g titanium dioxide (Bayer AG) Mixture 2: aqueous phase 700 ml dist. Water 300 ml MMA-MAS dispersant solution L 7.5% aqueous solution of a copolymer of equal parts by weight of methacrylic acid and methyl methacrylate with pH = 6 (adjusted with NaOH) and the viscosity of 3.6 Pa s.] The components of mixture 1 are below Exclusion of atmospheric oxygen in the reaction vessel and 12 hours.

stirred at room temperature at 250 rpm, the polymer dissolved and a highly viscous mass is formed.

This mixture is made with 1.5 g of lauroyl peroxide and 1.5 g of benzoyl peroxide added and stirred for a further 30 min. Mixture 2 is then added all at once and the stirring speed increased to 600 rpm. The suspension formed is heated to 80 ° C. and, when the exothermic reaction starts, cools so strongly that the temperature is kept below 88 ° C. After the reaction has subsided, the approach is under Maintained at 85.degree. C. for a further 2 hours with stirring. The solid bead polymer is after freed from fine fractions by decanting after cooling, then filtered, repeatedly with dist. Washed with water and dried at 50 ° C.

Yield: 407 g combustion residue: 32.2% Sieve analysis:> 200 / u 7.02% 100-200 µ 48.76% 63-100 µ 26.32% 40 - 63 for 11.06% 0 - 40 / u 6.84% Illustration 1 shows the fraction 40 to 63 / u in a microscopic image in brightfield at a scale of 133: 1.

The pearls appear dark due to the strong light scattering of the Ti02 particles. The filler is evenly distributed.

For comparison, Figure 2 shows an image of an unfilled bead polymer according to Example 2, also as a bright field image on a scale of 133: 1.

Example 4 Production of a bead polymer filled with barium sulfate.

Reaction vessel as in Example 1, mixture 1: monomer phase 220 g methyl methacrylate) viscosity 30 g ethylene glycol dimethacrylate of the mixture: 50 g polymethyl methacrylate) 0.6 Pa s (Lv = 1.05 in chloroform) 100 g of barium sulfate (Riedel de Haen AG) Mixture 2: aqueous phase as in Example 3 The components of mixture 1 are added to the reaction vessel with the exclusion of atmospheric oxygen and stirred at room temperature until the polymer has dissolved.

The mixture obtained is made with 1.1 g of lauroyl peroxide and 1.1 g of benzoyl peroxide added and, as described in Example 3, polymerized and worked up.

Yield: 375 g combustion residue: 28.8 5 '.

Sieve analysis> 200 / u 2.38 5 '100 - 200 / u 2.44% 63 - 100 / u 13.92 % 40-63 / u 38.06% 0-40 / u 43.20% Example 5 Production of one with zirconium dioxide filled bead polymer.

Reaction vessel: 6 liter autoclave with double anchor stirrer Mixture 1: monomer phase 580 g methyl methacrylate) viscosity 30 g ethylene glycol dimethacrylate of the mixture: 110 g polymethyl methacrylate) 6 Pa s ([#] in chloroform = 2.0 100 g zirconium dioxide (E. Merck, Darmstadt) Mixture 2: aqueous phase 2100 ml dist. Water 900 ml MMA-MAS dispersant solution, as described in Example 3.

The components of mixture 1 are placed in the autoclave with exclusion of air given and stirred for 12 hours at 100 rpm at room temperature. This mixture will mixed with 3 g of lauroyl peroxide and 3 g of benzoyl peroxide and a further 30 min.

touched. After the addition of mixture 2, 15 bar nitrogen is injected, the stirring speed is set to 450 rpm and heated to 80.degree. When the The reaction is cooled so much that the temperature is kept below 90.degree. Man leaves the batch at 80 ° C. for 2 hours stir. The pearl polymer is filtered off after cooling, several times with dist. Water washed and at 50 0C dried.

Yield: 802 g combustion residue: 12.5 5 '.

Sieve analysis:> 200 / u 26.00 5 '100 - 200 / u 30.24% 63 - 100 / u 21.20% 40-63 / U 13.22% O- 40 / U 9.34 5 'Example 6 Production of one with silica filled bead polymer.

Reaction vessel: as in example 1 Mixture 1: monomer phase 188 g bisphenol-A-bis- (3-meth-) viscose acrylato-2-hydroxypropyl) ether 112 g triethylene glycol dimethaorylate mixture: approx. 1 Pa s 33 g of highly dispersed silica (BET surface 170 m2 / g) Mixture 2: aqueous phase 700 ml of distilled water. Water 300 ml MMA-MAS dispersant solution, as described in Example 3.

Mixture 1 is mixed with 3.0 g of benzoyl peroxide and, as in example 3 described, polymerized.

Yield: 305 g combustion residue: 9.5% Sieve analysis: > 100 / u 0.68% 63 - 100 / u 7.56% 40 - 63 / u 34.16% 0 - 40 ju 57.60% Example 7 Production of a bead polymer filled with silica and barium sulfate.

Reaction vessel: as in Example 1, mixture 1: 300 g of Plex 6661 der Röhm company, Darmstadt (reaction product of trimethylhexamethylene diisocyanate and 2-hydroxyethyl methacrylate), viscosity 7.5 Pa s.

30 g of highly disperse silica (BET surface 170 m2 / g) 100 g of barium sulfate (Riedel de Haen) Mixture 2: 700 ml dist. Water 300 ml MMA-MAS dispersant solution, as described in example 3.

Mixture 1 is mixed with 5 g of cyclohexyl percarbonate and, as in Example 3 described, polymerized.

Yield: 385 g combustion residue: 25.5%.

Sieve analysis:> 200 µ 28.46% 100 - 200 / u 46.82% 63-100 µ 16.32% 40 - 63 / u- 5.52% 0 - 40 / u 2.88% Blank page

Claims (2)

Claims: 1. Polymer beads with an average bead diameter from 5 to 500 / u, consisting of an inorganic finely divided filler and polymerized (Meth) acrylic acid esters. 2. Polymer beads according to claim 1, consisting of 5 to 50 parts by weight Filler and 95 to 50 parts by weight of polymerized (meth) acrylic acid esters. Process for the production of filled with inorganic filler Bead polymers with a diameter of 5 to 500 / u made from (meth) acrylic acid esters and optionally up to 20 percent by weight of further monomers, characterized in that that a mixture of monomer and optionally polymer soluble in the monomer and filler, which has a viscosity of 0.1 to 10 Pa s, measured at the dispersing temperature, possesses, suspended and polymerized in an aqueous medium in the presence of dispersants will.