NL8903093A - CLEAR IMPACT MOLD. - Google Patents

Description

Clear impact-resistant molding compound.

The present invention relates to a clear, impact-resistant acrylic-based molding material, films made therefrom and multilayer shaped bodies, and a process for preparing the molding material.

The patents 3, 808,180 and 3 * 843,753 already disclose impact-resistant molding compositions based on acrylic, which may be clear when the components are suitably selected. However, the brightness is easily lost under conditions often encountered when using the articles made therefrom. For example, the masses become cloudy or white when exposed to high temperatures or high humidity, or cloudy or white spots appear as a result of impacts from impact or bending loads.

The known molding compositions consist of a multi-phase emulsion polymer, one phase consisting of a hard thermoplastic methacrylic ester polymer and the other phase consisting of an acrylic elastomer, divided therein into particles with a size of 50 to 300 nm, preferably of 160 to 200 nm. The preparation is carried out by two-stage emulsion polymerization, first forming a latex of the acrylic elastomer, the so-called tough phase, and then grafting the hard methacrylic ester polymer in the second step. This is referred to as a hard phase. A characteristic feature of the acrylic elastomer produced in the first stage is a glass transition temperature below -10 ° C. It is composed of at least 50% by weight of alkyl or aralkyl acrylate, up to 10% by weight of hydrophilic comonomer, as well as from 0.05 to 5% by weight of a polymerization cross-linking agent and a graft cross-linking agent in each case. Furthermore, a small amount of styrene is usually built in to match the optical refractive index of the tough phase to that of the hard phase and thus avoid clouding of the material by light scattering on the surfaces of the particles of the tough phase. The said graft crosslinking agent has the effect that at least 20% of the hard phase formed in the second stage is grafted onto the tough phase, i.e. are covalently connected thereto.

The known method allows for such a wide range of choices in the qualitative and quantitative choice of the constituents that it is practically impossible to prepare and investigate all clearly distinguishable variations in variation.

A further variation possibility is offered by US patent 3 * 843,753. wherein the biphasic polymer is melt-mixed with another thermoplastic molding compound.

Those skilled in the art, according to the teachings of this patent, who would like to produce molding compositions with certain combinations of properties, are required to prepare either by systematic variation of a very large number of test products, if they fail to obtain the required properties by a happy grasp. or to gain new insights into the dependence of the desired properties on the structure of the two-phase polymerate.

The invention was based on the problem of avoiding or reducing the aforementioned sensitivity of the molding composition to clouding or discoloration under the action of heat and humidity or in the open air and the so-called white breakage when acting due to impact or bending loads. The problem could not be solved until it was recognized that the said properties are complexly associated with the particle size of the elastomer phase, the non-uniformity of the particle size, the minimum content and type of cross-linking monomers and the content of water-soluble substances. . It was further determined that the goal could not be achieved with the use of styrene or other vinyl aromatics in the elastomer phase, so that the matching of the optical refractive indices of the two phases with inexpensive monomer components could not be achieved. In the preferred molding compositions according to the invention, a difference in refractive index of more than 0.02 was observed between the two phases, which in the experience of those skilled in the art should inevitably lead to cloudiness.

It was all the more surprising to find that the molding compositions built up according to the appended claims are not only clear and colorless after molding, but that this property is retained even under the action of heat and humidity, in the open air and under impact or bending stress. .

To ensure optical clarity in the basic state, a particle size of the tough phase below 130 nm, preferably below 70 nm, was found to be substantial but not sufficient in itself. Brightness was only achieved by setting the non-uniformity of the particles of the tough phase below 0.5, preferably below 0.2.

While according to US 3 * 808,180 an amount of the tough phase of 0.5% by weight suffices, in the context of the invention a minimum proportion of 10% by weight was found to be imperative.

A critical choice as to the type and amount of cross-linking monomer was found to be substantial. The aforementioned patents distinguish between cross-linking agents and graft cross-linking agents and indicate both groups as absolutely necessary. The group of cross-linking agents includes monomers containing at least two acrylic or methacrylic groups; they are used in the examples of the US patents in an amount of 0.5% by weight of the tough phase. Monomers which contain, in addition to an acrylic or methacryl group, an ethylenically unsaturated group with a significantly lower polymerization tendency, usually an allyl group, are indicated as graft crosslinking agents. The amount of these monomers on the tough phase was chosen to be between 0.2 and 0.4% by weight.

To achieve the object of the invention, the amount of the graft crosslinking agent had to be increased to at least 0.5%, more preferably 1 to 4% by weight, based on the weight of the tough phase. However, it can be replaced with equally good action by monomers containing three or more acrylic or methacrylic groups in the molecule. In contrast, cross-linking agents were found to be lacking, although in some cases they were required in an amount of 0.05 to 2 wt% of the tough phase.

It has further been found that the amount of water-soluble ingredients in the molding composition must be kept below 0.05% by weight to ensure lasting clarity, especially under the action of moisture. Water-soluble ingredients are introduced into the molding compound in the form of residues of the polymerization initiator, such as peroxodisulfates, or of the emulsifier. This is particularly the case with the conventional production method, in which the aqueous phase of the underlying latex is separated from the emulsion polymer by evaporation, for example in a spray-drying process. This method is used in some embodiments of the U.S. patents, while in other examples a substantial portion of the aqueous phase is separated in liquid form from the melt of the emulsion polymer. The largest amount of the water-soluble constituents of the latex is also removed.

It has been found that the sensitivity to cloudiness under the action of moisture disappears when the latex is coagulated in the production of the molding composition and the water phase in liquid form is separated so far from the coagulate that no more than 0.05% by weight of components which are water soluble in the mass. This process step is of considerable significance according to the invention, since a proportionately large amount of water-soluble emulsifying agents must be used to set the required small particle size, which would lead to a strong turbidity after exposure to moisture without careful separation of the molding compound.

The described combination of selection steps with respect to the proportions of amounts of phases, of the particle size of the emulsion polymer, of the non-uniformity of its particle size, of the type and amount of cross-linking monomers and the final content of water-soluble components and the process required for this only led to the product according to the invention and its excellent properties. The selected characteristics are known per se in other combinations.

Preparation of the emulsion polymer

The clear impact-tough molding composition according to the invention is based on an emulsion polymer consisting of at least two phases, which can be processed as such or as a mixture with another molding compound into the shaped products. With a view to the effects to be added, the incorporation of further phases is only possible insofar as this does not cancel out the special advantages of the products according to the invention.

The hard phase of the emulsion polymer has a glass transition temperature of at least 70 ° C and can only be composed of methyl methacrylate. As comonomers, optionally lower alkyl acrylates, in particular those having from 1 to 1 C atoms in the alkyl group, up to an amount of 20% by weight, based on the hard phase, may be present, provided that the mentioned glass temperature is not undershot.

The tough phase is at least 501 preferably more than 80% by weight built up from lower alkyl acrylates, resulting in a glass transition temperature of less than -10 * 0, usually -20 to -80 * C. As far as the required glass transition temperature is reached, other radically polymerizable aliphatic comonomers which can be copolymerized with alkyl acrylates, as known in the art, may optionally be used. However, appreciable amounts of aromatic comonomers such as styrene, alpha-methylstyrene or vinyl toluene will remain excluded because they lead to undesirable properties of the molding compound, especially in the open air.

The amount of graft cross-linking agents or the cross-linking agents with three or more ethylenically unsaturated radically polymerizable groups which can be used instead are chosen within the limits of 0.5 to 5% by weight, such that in the final emulsion polymer at least 15% by weight of the hard phase is covalently linked to the tough phase. The degree of cross-linking is evidenced by dissolving an aliquot amount of emulsion polymer in a hard phase solvent. The tough phase and the covalently cross-linked part of the hard phase thereby remain unresolved. The weight of the undissolved portion should be at least 15, preferably 30 to 80% by weight of the calculated hard phase weight more than the calculated tough phase weight of the aliquot sample. However, the amount of graft crosslinking agent should in no case be less than 0.5 wt% and is preferably in the range 1 to 4 wt% of the tough phase.

The amount of graft crosslinking agent in the emulsion polymers of the invention is relatively high and generally results in sufficient crosslinking of the tough phase, so that an additional cross-linking agent is generally absent. If the desired impact toughness properties are not achieved in this way, the co-use of 0.05 to 2% by weight of a cross-linking agent in addition to the graft-crosslinking agent in the tough phase may be advisable. The cross-linking agent in this case should contain at least two acrylic or methacrylic groups.

As graft cross-linking agents, the allyl esters of acrylic or methacrylic acids are preferred, but other graft cross-linking agents mentioned in US-A-3,808,180 and 3,843,753 are also suitable. Cross-linking agents with three or more ethylenically unsaturated radically polymerizable groups, such as allyl groups or acrylic or methacryl groups, which may be used instead include triallyl cyanurate, trimethylolpropane triacrylate and trimethacrylate, pentaerythrit triacrylate and trimethacrylate and related compounds, for which further examples are disclosed in DE-A-3,300,526.

The two or more phase emulsion polymer is conventionally formed by aqueous emulsion polymerization in two or more steps. In the first step, the tough phase is formed. Particular attention must be paid to the correct setting of particle size and the non-uniformity of the size of the particles. Although known methods with the use of a seed latex or with the gradual addition of monomer can in principle be applied, the properties sought according to the invention are best achieved by a method in which the monomer mixture for the tough phase is emulsified and polymerized together.

The particle size of the tough phase depends essentially on the concentration of the emulsifier. Particles with an average particle size (by weight average value) below 130, preferably below 70 nm, and with a non-uniformity of particle size below 0.5. preferably below 0.2, are achieved at concentrations of emulsifier from 0.15 to 1.0% by weight based on the aqueous phase. Smaller amounts of emulsifying agent lead to a larger average particle size, with larger amounts of emulsifying agent to a higher non-uniformity. The non-uniformity is the smaller - therefore the uniformity of particle size the greater - the shorter the phase from particle formation to the start of emulsion polymerization. In particular, a new particle formation after the start of the polymerization can be avoided, which may be the case afterwards with the addition of an emulsifying agent. Also, the polymerization rate can affect the particle size and particle size non-uniformity; if the flow of radicals is too small, the non-uniformity is too high, if it is too high, then - in particular in the polymerization generation with peroxodisulfates - too high a sensitivity to moisture can result. *

The said concentration of emulsifying agents applies in particular to conventional anionic emulsifying agents. These include, for example, particularly preferred alkoxylated and sulfurized paraffins.

As the polymerization initiator, for example, 0.01 to 0.5% by weight of alkali or ammonium peroxodisulfate, based on the aqueous phase, is used and the polymerization is carried out at temperatures from 20 to 100 ° C. Preferably, redox systems are used, for example 0.01 to 0.05 wt.% Organic hydroperoxides and 0.05 to 0.15 wt.% Rongalite at temperatures of 20 to 80 ° C.

It is imperative to check the selection of proper polymerization conditions by measuring the mean particle size and particle size non-uniformity in a test rig and necessarily changing according to the above rules. Both quantities to be measured can be calculated from the result of a light scattering measurement during the ultracentrifugation of the final latex according to known methods.

Processing of the emulsion polymer into a molding compound

The emulsion polymer precipitates in the form of an aqueous dispersion with a solids content of 30 to 60% by weight, based on solids, usually containing more than 0.05% by weight of water-soluble ingredients. According to the invention, the water-soluble components are separated from the emulsion polymer by solidifying the dispersion, separating the liquid water phase from the clot and melting the clot into a molding mass.

An extruder, in particular a double worm (screw) degassing extruder, is expediently used for these operations. The dispersion is pumped liquid into the extruder and coagulated at a temperature above the glass transition temperature of the emulsion polymer through the joint action of heat and tensile forces. Due to the pressure prevailing in the extruder, the aqueous phase also remains liquid above 100 ° C and is separated under pressure through a slit or screen plate in the wall of the extruder together with the free constituents. Suitable methods and operations are known, for example, from DE-A-2,750,682 and US-A-4,110,843. Any residual water content can be evaporated in a known manner in a degassing zone of the extruder.

The molten molding material is discharged from the extruder and granulated or formed into a strand of any desired profile and cooled to below the softening temperature (glass temperature).

It is often desirable to mix the impact-resistant molding compound with an optionally predominant amount of other tolerable hard molding compound. At a solids ratio of 10: 1 to 1:10, the properties of the molding composition according to the invention clearly show up in the resulting mixture, in particular in the form of improved molding resistance to heat and stampability, in combination with the advantageous properties inherent in the molding composition according to the invention. The component to be mixed preferably consists of a molding compound of polymethyl methacrylate. Hard mixed polymers of methyl methacrylate with acrylic esters, acrylonitrile or with maleic anhydride and styrene as well as polyvinyl chloride are also suitable.

Such mixtures can be prepared in various ways. For example, the dispersion of the emulsion polymer prepared according to the invention can be mixed with an aqueous dispersion of the component to be mixed and the mixture coagulated, the aqueous phase separated and the coagulate melted into a molding mass. In this method a particularly uniform mixing of both masses can be effected. Equally good mixing is achieved by pumping in the aqueous dispersion of the emulsion polymer prepared according to the invention.

in an extruder containing a melt of the ingredient to be mixed. The dispersion is coagulated in the melt and the aqueous phase is pressed off as described above. The components can also be prepared and isolated separately and mixed in the form of their melts or as a powder or granulate and homogenized in a multi-screw extruder or on a rolling mill.

Conventional additives can be mixed in any suitable processing step. These include dyes, pigments, fillers, reinforcing fibers, lubricants, UV protectants, etc. UV polymerizable absorbents can be polymerized together with the other monomers in the polymerization of the hard phase monomers in the emulsion polymer.

Shaping processing of the molding compound

When the clear impact tough molding composition according to the invention contains a large amount of tough phase within the scope of the claims, it is suitable for the production of clear flexible films by extrusion of the melt through a nozzle with a slit and by smoothing on a rolling mill . Such films are characterized by long-lasting clarity, insensitivity to heat and cold, resistance to the outdoors, low yellowing and embrittlement and low white breakage when bending or folding and are therefore suitable, for example, as windows in tarpaulins, car covers or sails. Such films have a thickness of less than 1 mm, for example 0.05 to 0.5 mm.

An important field of application lies in the formation of thin surface layers of, for example, 0.05 to 0.5 mm thickness on rigid, shape-resistant base bodies, such as on tinplate, cardboard, chipboard, plastic sheet and the like. In this case, the amount of tough phase can be substantially lower, so that the molding mass will be harder. Various methods are available for the preparation of such layers. For example, the molding compound can be extruded into a film, smoothed and laminated to the substrate. The extrusion coating technique allows an extruded strand to be applied to the surface of the substrate and smoothed by means of a roller. When a thermoplastic plastic serves as the substrate itself, there is the possibility of coextrusion of both masses to form a surface layer of the clear molding material according to the invention.

Handles of impact-resistant molding material, in particular with polymethyl methacrylate, are suitable for the production of shaped bodies with a wall thickness greater than 1 mm; for example, from extruded webs of 1 to 10 mm thickness, which have good die-cutting and, for example, for the manufacture of plates that can be printed and can be used in electrical appliances, or for the production of high-quality injection molded moldings, for example windows for motor vehicles .

Example I

A 60 # emulsion I was prepared by emulsifying 99 parts by weight of butyl acrylate 1 part by weight of triallyl cyanurate 0.12 parts by weight of tert-butyl hydroperoxide in 67 parts by weight of a 0.15 # aqueous solution of sodium lauryl ryl sulfate.

A 50 # emulsion II was prepared by emulsifying 96 parts of methyl methacrylate 4 parts of butyl acrylate 0.4 parts of dodecyl mercaptan 0.1 parts of tert-butyl hydroperoxide in 100 parts of 0.06 # aqueous solution of sodium lauryl sulfate.

60 parts by weight of an aqueous phase containing 1 part by weight sodium lauryl sulfate, 0.15 part by weight rongalite, 0.02 part by weight acetic acid and 0.0008 part by weight were placed in a polymerization vessel with a stirrer, external cooling and a supply vessel. iron II sulfate. Within 2 hours, 50 parts of emulsion I were metered in with stirring at a temperature of 55 ° C. The resulting tough phase polymer had a glass transition temperature of -35 ° C. Subsequently, 140 parts of emulsion II were dosed in for an additional 2 hours to form the hard phase polymer with a glass transition temperature of 90 ° C. The difference between the optical refractive indices of both phases is 0.021. An aqueous dispersion with a solid content of 40% by weight was formed. Solubility measurements on a solidified sample of the polymer determined that 25 wt.% Of the hard phase is bound to the tough phase.

The tough phase particles formed from the emulsion I had a weight average particle size value of 60 nm after completion of the first polymerization step, which increased to 88 nm during the polymerization of emulsion II in the second step. Particle sizes were determined by the light scattering method; measuring device "Nanosizer (R)", Coulter Electronics. The non-uniformity of the tough phase particles, which was determined by ultracentrifugation, was U30 = 0.12.

To recover the solid from the obtained dispersion, a densely carded extruder with a counter-running twin screw with a screw diameter of D = 30 mm was used. The longitudinal strips are always indicated by a multiple of diameter D. The screws for the actuator were closed with a stuffing box.

The solidification zone had a length of 25 D. It was operated at a pressure of 40 bar and a temperature of 220 ° C. Coagulation was effected by the joint action of heat and shear.

Per hour, 4 kg of the dispersion was continuously pumped into the coagulation zone by means of a zuxgerdosing pump. Behind the coagulation zone, in a zone of the extruder cylinder with a length of 2 D through a dewatering opening, a pressure chamber and a pressure holding valve set at 25 bar, the aqueous phase separated at the solidification was separated into liquid form. In a subsequent pressure-free degassing zone with a length of 5 D, the residual moisture content of approximately 10 # of the polymer weight was extracted in vapor form. In a subsequent 5 D pressure zone, the polymer was fed to the granulation nozzle at a temperature of 200 ° C. The leaving strand was cooled and granulated after it had become rigid.

The resulting molding compound had a water-soluble content of less than 0.05 wt.%. It was extruded into a foil of 0.05 πω thickness and calendered. In an atmosphere of 100 * C with a relative humidity of 100 #, no whitening occurs within 30 minutes. When bending or folding the film, no white break in the bending zone is visible. The film can be punched without breaking. Sharp clear cutting edges are created, which are not frayed or colored white. The film can be adhesively laminated to a rigid PVC sheet by heat-stamping adhesive.

Comparative experiments

Part of the dispersion obtained in Example I was dehydrated by spray drying. The dry product contained 0.4 wt.% Water soluble ingredients. A film made therefrom became cloudy in a humid atmosphere under the conditions indicated above.

In the process of Example 1, the amount of triallyl cyanurate was reduced from 1 to 0.3 parts by weight, and the resulting molding compound was found to be cloudy. Only 22% by weight of components insoluble in acetone were found, from which it can be concluded that only part of the tough phase was cross-linked and that the hard phase was practically not cross-linked with the tough phase.

In a further variation of Example 1, 0.10 parts of sodium lauryl sulfate were used in the previously applied aqueous phase. Therefore, the average particle size of the tough phase particles increased to 132 nm and the non-uniformity of the tough phase particle size increased to 0.52. The resulting molding compound was cloudy.

Example II

2 parts of the dispersion obtained in Example 1 and 1 part of a 40% anionic aqueous emulsion polymer, the composition of which exactly corresponded to that of the hard phase of the dispersion of Example 1, were intimately mixed and the mixture was dewatered over a twin screw extruder as in Example 1. The amount of the tough phase in the resulting molding compound was 20% by weight. The mold resistance to heat was 95 * C, which is 7 * more than with the molding material according to example I.

A very rigid 1 mm thick film was extruded from the molding material, which had a good stamping path. This is suitable, for example, for the preparation of stamped equipment screens for motor vehicles, electrical appliances and the like.

Example III

In a repeat of the procedure of Example I, in emulsion I, the triallyl cyanurate was replaced with the same amount of allyl methacrylate as a graft cross-linking agent. The molding compound obtained corresponded in all properties to that according to Example I.

Example IV

In two experiments carried out according to example III, the applied aqueous phase was additionally 2.5 and 5 resp. 5 parts of an emulsion polymer of methyl methacrylate in the form of a seed latex with a particle size of 40 nm (weight medium value) was added. The result was the following particle sizes: seed latex particles 2.5 5.0 parts tough phase cross section 75 nm 9 μm total cross section 108 nm 137 nm

Example V

In a further variation of the method of Example III, the following amounts of emulsions I and II were used: 83 parts by weight of emulsion I and 100 parts by weight of emulsion II.

This resulted in a composition of the molding compositions with 50 wt% tough phase and 50 wt% hard phase.

The following particle sizes were measured: tough phase cross section 110 nm, total cross section 140 nm.

The mold resistance to heat of the molding compositions is 55 ° C. The molding compound is clear, does not become cloudy in a humid atmosphere, does not lead to white breakage in the form of a 0.05 mm thick film and can be punched flawlessly.

Claims (15)

1. Clear impact tough molding composition containing A) 10-90 wt% of a cohesive hard phase with a glass temperature above 70 ° C, composed of a) 80-100 wt% (based on A) methyl methacrylate and b) 20-0 wt .% of a low molecular weight alkyl acrylate and B) 90-10 wt.% of a tough phase divided tough phase with a glass temperature below -10 ° C, an average particle size of the tough phase below 130 nm and particle size non-uniformity of the tough phase of less than 0.5, composed of c) at least 50% by weight (based on B) of a low molecular weight alkyl acrylate, d) 0.5 ~ 5% by weight of a graft crosslinking agent or a three-crosslinking monomer or more ethylenically unsaturated radicals polymerizable residues, e) optionally further ethylenically unsaturated radicals (co) polymerizable aliphatic comonomers, C) not more than 0.05 wt% water-soluble components, at least 15 wt% of the hard phase is covalently linked to the tough f ase, contains. Molding composition according to claim 1, characterized in that a difference in refractive index of more than 0.02 exists between the hard phase and the soft phase. Molding compound according to claim 1 or 2, characterized in that the tough phase contains as component c or as part thereof 0.05-2% by weight of a cross-linking agent. Film with a thickness less than 1 mm, consisting of a molding material according to claim 1 or 2. Film according to claim 4, characterized in that the hard phase A comprises 2-20% by weight of the low molecular weight alkyl acrylate. 6. Process for preparing a clear impact molding mass by polymerization in aqueous emulsion of a monomer or mixture of monomers of a) 80-100 wt.% (Based on A) methyl methacrylate and b) 20-0 wt.% Of a low molecular weight alkyl acrylate to a hard phase with a glass temperature above 70 ° C in the presence of a water-dispersed tough phase with a glass temperature below -10 ° C, an average particle size below 130 nm and a particle size non-uniformity of less than 0.5, composed of c) at least 50% by weight (based on B) of a low molecular weight alkyl acrylate, d) 0.5-5% by weight of a graft crosslinking agent or of a crosslinking monomer with three or more ethylenically unsaturated radically polymerizable residues, e optionally further ethylenically unsaturated free radical (co) polymerizable aliphatic comonomers, in which at least 15% by weight of the hard phase is grafted onto the tough phase, coagulating the resulting dispersion, then separating the liquid water phase from the coagulated material and melting the coagulated material into a molding compound. Process according to claim 6, characterized in that the dispersed tough phase contains 0.05 to 2% by weight cross-linking agent. Process according to claim 6 or 7, characterized in that the obtained molding compound is melt-mixed with a compatible molding compound in a ratio of 10: 1 to 1:10. Method according to claim 8, characterized in that a molding compound having a composition corresponding to that of the hard phase is used. Process according to claim 6, characterized in that the aqueous emulsion polymerization dispersion of an emulsion polymer with a composition corresponding to the hard phase is mixed in the ratio of solids from 10: 1 to 1:10 and the mixture is coagulated, separated from the water phase and melted. Method according to at least one of claims 6-10, characterized in that the coagulation is effected by the joint action of heat and shear forces in an extruder. Process according to claim 6, characterized in that the melt is formed into a shaped body with a thickness greater than 1 mm and cooled below the softening temperature. Process according to claim 12, characterized in that a molding compound is prepared and formed, which comprises 0.5 "2 wt.% Units of an alkyl acrylate in the hard phase. A multi-layer molded body, which comprises a rigid, form-retaining base body and a thin surface layer of a molding material according to at least one of claims 1 to 5. The multi-layer molded body according to claim 14, characterized in that the surface layer is co-extruded together with the production of the base body by extrusion coating on the surface of the base body or by coating with a film formed from the molding material, is produced on the surface of the base body.