NO812700L - RESISTANT, SHORT-RESISTANT PLASTIC MIXTURE. - Google Patents

Description

The invention relates to mixtures of an acrylic polymer,

for example, polymethyl methacrylate resin, and an impact resistant interpolymer. The resulting mixtures can be used to form weather-resistant, impact-resistant articles.

Acrylic polymers, such as polymethyl methacrylate resins, have good optical quality, excellent weather resistance, and good tensile and flexural strength. They find application in a wide range of areas including building panels and moldings, exterior vehicle components, outdoor furniture, swimming pool parts, etc. However, the impact resistance of unmodified acrylic resins is very low and precludes the use of such resins for certain purposes where a higher degree is also desired of impact resistance.

It has recently been proposed, in US Patent No. 3,655,826,

to blend various thermoplastic polymers (including acrylic resins, see column 8, lines 11-13) and a three-stage acrylic elastomer impact resistant interpolymer. This representative of the state of the art indicates that selection of the third phase in the interpolymer is crucial, and it is suggested that if impact modification is desired, then the third stage should be a methacrylate or acrylate (see column 5, lines .65-70).

The present invention relates to a weatherproof, impact-resistant mixture of: (1) an acrylic polymer, for example polymethyl methacrylate resin; and (2) an impact-resistant interpolymer comprising crosslinked (meth)acrylate, crosslinked styrene/acrylonitrile, and non-crosslinked styrene/acrylonitrile polymer components. This type of interpolymer is more fully described in US Patent No. 3,944,631. It is described in the prior art as a suitable additive for polycarbonate resins (US Patent No. 4,148,842), for blends of chlorinated vinyl chloride polymer and vinyl chloride polymer (US Patent No. 4,160,793), and for vinyl chloride polymers (US Patent No. 4,168,285).

The compositions according to the present invention comprise: (1) an acrylic resin; and (2) an impact resistant interpolymer comprising crosslinked (meth)acrylate, crosslinked styrene/acrylonitrile and non-crosslinked styrene/acrylonitrile polymeric components.

The term "acrylic resin" is used here in the sense of including such acrylic resins which are made by polymerizing acrylic ester monomers. Details regarding the structure of these polymeric materials as well as methods of forming them are available from a number of sources including Modern Plastics Encyclopedia (1977-1978 Edition), pp. 9-10; Handbook of Plastics and Elastomers, C. A. Harper, ed., McGraw-Hill, Inc. 1975, pp. 1 lines 71-75; and Polymers and Resins by

B. Golding, Van Nostrand Co., 1959, pp. 448-462. Representative polymers included in this class of acrylic resins or plastics include: polymethyl methacrylate, polyethyl acrylate, and polybutyl acrylate. Copolymers of these acrylic esters with small amounts of one or more copolymerisable monomers shall also be included within the scope of the invention, for example the copolymer of methyl methacrylate with styrene and acrylonitrile. Commercially available acrylic resins include those sold under the following trade names: LUCITE (E.I. duPont de Nemours and Co.); and PLEXIGLAS (Rohm and Haas Co.).

The terminology "impact-resistant interpolymer comprising crosslinked (meth)acrylate, crosslinked styrene/acrylonitrile, and non-crosslinked styrene/acrylonitrile components" is intended to include the type of interpolymer products described in US Patent No. 3,944-631. These interpolymer products are formed by the following three-stage, sequential polymerization process of the following type: 1. emulsion polymerization of a monomer batch (here designated "(meth)acrylate", for the purposes of the present invention), of at least one C2"C^ Q-alkyl acrylate, C 8 -C 22 alkyl methacrylate or compatible mixtures thereof, in an aqueous polymerization environment in the presence of an effective amount of a suitable di- or polyethylenically unsaturated cross-linking agent for such monomer type, wherein C 2 -C 8 - the alkyl acrylates are preferred as (meth)acrylate monomers for use in this step; 2. emulsion polymerization of a monomer batch of styrene and acrylonitrile in an aqueous polymerization environment, also in the presence of an effective amount of a suitable di- or polyethylene unsaturated cross-linking agent for such monomers, the polymerization being carried out in the presence of the product from step 1 so that the crosslinked (meth)acrylate and crosslinked styrene-acrylonitrile components form an interpole ymer where the respective phases surround and penetrate each other; and 3. either emulsion or suspension polymerization of a

monomer batch of styrene and acrylonitrile, in the absence of a cross-linking agent, in the presence of the product resulting from step 2. If desired, steps 1 and 2 can be reversed in the method described above.

This product, which is used as the impact-resistant interpolymer component in the mixtures according to the invention, generally comprises from approx. 5 to approx. 50% by weight of the cross-linked (meth)acrylate component identified above, from approx. 5 to approx.

35% by weight of the cross-linked styrene/acrylonitrile component and

from approx. 15 to approx. 90% by weight of the non-crosslinked styrene/acrylonitrile component. It contains little graft polymerization between the styrene/acrylonitrile copolymer components and the crosslinked (meth)acrylate polymeric component. Additional details regarding this type of polymer product can be found in US Patent No. 3,944,631, which is hereby incorporated by reference.

The mixtures according to the invention can be put together in a weight ratio between acrylic resin and interpolymer additive of from approx. 75:25 to approx. 5:95, depending on the exact physical properties desired in the final product.

A preferred range is from 60:40 to 20:80. Blending can be accomplished by any of the well-known polymer blending techniques, such as blending using a two-roll system or a Branbury mixer, single or multi-screw extrusion, or any other method appropriate to applies sufficient heat (eg 175-300°C, preferably 200-250°C) and shear force to the respective polymeric ingredients (acrylic resin and interpolymer additive) to obtain a satisfactory mixture in accordance with the invention.

The mixtures according to the invention may also contain any conventional functional additives which are normally used in connection with acrylic polymer products, including fillers, colorants, lubricants, flame retardants and the like.

In what follows, the invention will be illustrated by means of examples.

EXAMPLE 1

This example illustrates the impact resistance, hardness,

■ the tensile and flexural properties of a number of mixtures of et

commercially available polymethacrylate (PMMA), LUCITE 147K manufactured by E.I. duPont de Nemours and Co., and the impact-resistant interpolymer described above (abbreviated as "Interpolymer"). The interpolymer comprised 32% by weight crosslinked polybutyl acrylate, 10% by weight crosslinked styrene/acrylonitrile and 58% by weight non-crosslinked styrene/acrylonitrile.

Samples #2-5 listed below were extruder compounded at temperatures of 221-232°C at 90 rpm in a conventional extruder using a single stage screw with a 2:1 compression ratio. Sample no.

1 and 6 were the control samples.

Samples No. 1-6 were then dried overnight at 90°C and were injection molded (on a 28 gram capacity injection machine, available from Boy Company) at 190-200°C with the molding temperature set at 54°C. The screw speed was set to "low", the back pressure was moderate, and the injection pressure setting was "34". The cycle had an injection dwell time of 10 seconds and a screw return time of 20 seconds.

They produced sample plates. was tested, and the following physical properties were noted:

These data illustrate that for samples no. 2-5 a . increase in the amount of interpolymer (and a corresponding decrease in the amount of polymethyl methacrylate) a composite mixture with improved impact resistance.

These data illustrate that the presence of polymethyl acrylate contributes to the hardness of the mixture.

The presence of polymethyl methacrylate contributes to the strength of the mixture. The readings for example 6 were not considered reliable due to breakage at the clamping area resulting from the brittleness of the test pieces.

Greater flexural strength and modulus (stiffness) is shown when the percentage of polymethyl methacrylate is increased in the mixtures.

EXAMPLE 2

This example illustrates the effect of mixing conditions, such as raw material temperature and mixing shear force, on the impact resistance, measured by the Izod impact test, on a mixture of 70% by weight impact resistant interpolymer and 30% by weight polymethyl methacrylate (LUCITE 40' manufactured by DuPont). The respective mixtures

in portions of 250 g, the melt was fluxed in a small batch mixer (PREP MIXER TM from Brabender Co.) under the conditions described below. The mixing time was varied inversely with the rpm values to keep the number of total revolutions constant.

These data indicate that in a high shear batch mixing process of the type used in the above test, very severe temperature conditions during mixing tend to be detrimental to the Izod impact strength of the mixture. However, variations in the cutting speed do not show this effect when the total number of revolutions is kept constant.

EXAMPLE 3

This example tests the ultraviolet-induced discoloration of the compositions according to the invention including those pigmented with titanium dioxide.

The samples were made by combining the materials at 200°C and 50 rpm by mixing for 10 minutes in a small batch mixer apparatus, and they were then pressed to form homogeneous test plates which also included rutile TiO2_pigment in an amount of 6 parts by weight per 100 parts by weight sample. The samples were placed in a germicidal lamp apparatus with high intensity (30 watts) at a distance of 3.2 cm from the lamp for varying periods of time, as indicated below, and after the appropriate period of time the color change was compared to an unexposed control sample from the same sample measured on a Hunter Color Meter. Lower values indicate less discolored sample.

These data indicate that polymethyl methacrylate improves the ultraviolet light resistance of the mixture to discoloration and that the phase to which the TiC 2 pigment is added does not particularly affect the ultraviolet resistance of the mixture.

EXAMPLE 4

This example illustrates the effect of processing conditions on the impact resistance properties of a mixture of 70% by weight impact resistant interpolymer and 30% by weight polymethyl methacrylate (LUCITE 147K manufactured by DuPont).

The blends were produced by extrusion at different screw housing temperatures in the range 177-265°C and different screw speeds (40-120 rpm). A single stage screw with 2:1 compression with a diameter of 25.4 mm was used. The extruded test pieces were then injection molded at 200-220°C into a 54°C mould. The spraying machine described in the example.

1 was applied. No back pressure was applied to the forge, and the cycle time was a total of 30 seconds.

These data illustrate that for the tested mixtures under extrusion conditions, there is a general tendency for impact strength to be optimal at moderate to high temperatures and screw speeds, and that insufficient levels of temperature and shear force do not allow the mixture to develop its full impact strength potential.

EXAMPLE 5

This example illustrates the gloss and color characteristics of a mixture of 50% by weight of the impact-resistant interpolymer and 50% by weight of polymethyl methacrylate (LUCITE 147 manufactured by DuPont) which had been additionally pigmented with 6 parts by weight of Ti02 to 100 parts by weight of the interpolymer and the polymethyl methacrylate.

The test pieces of the mixture were formed by compression molding at 188°C to 0.08 cm thickness after the mixture was mixed at 220°C and 30 rpm in a small batch mixer. The compression molded specimens were exposed in a xenon arc WEATHER-OMETER, an accelerated aging apparatus, at 50% relative humidity with 18 minute water showers every 2 hours. The table indicates the readings in color change for the sample in relation to the time that has passed, compared to a commercially available acrylic product of impact-resistant quality with a different chemical composition.

These data indicate that the composition has color retention properties equivalent to the commercial acrylic material.

These data illustrate that the loss of gloss is greater for the commercial acrylic product after more than approx. 1000 hours of exposure under the described test conditions.

The preceding examples indicate certain embodiments of the present invention, but must not be understood in a limiting way. The protection framework for the present invention is specified in the accompanying claims.

Claims (9)

1. Weather-resistant, impact-resistant mixture, characterized in that it includes: (1) an acrylic resin; and (2) an impact resistant interpolymer comprising crosslinked (meth)acrylate, crosslinked styrene/acrylonitrile, and non-crosslinked styrene/acrylonitrile polymer components. 2. Mixture as stated in claim 1, characterized in that the interpolymer comprises from approx. 5 to approx. 50% by weight of the (meth)acrylate component, from approx. 5 to approx. 35% by weight of the cross-linked styrene/acrylonitrile component and from approx. 15 to approx. 90% by weight of the non-crosslinked styrene/acrylonitrile component. 3. Mixture as specified in claim 1 or 2, characterized in that it comprises a weight ratio between acrylic resin and interpolymer of from approx. 75:25 to approx. 5:95. 4. Mixture as specified in claim 1 or 2, characterized in that it comprises a weight ratio between acrylic resin and interpolymer of from approx. 60:40 to approx. 20:80. 5. Mixture as specified in claim 1 or 2, characterized in that the (meth)acrylate component is selected from the group consisting of the cross-linked C^-C-^ alkyl acrylates, the cross-linked CQ -C 1 -alkyl methacrylates, and compatible mixtures thereof. 6. Mixture as stated in claim 1 or 2, characterized in that the (meth)acrylate component is a cross-linked C 1 -C 8 alkyl acrylate. 7. Mixture as specified in claim 1 or 2, characterized in that the acrylic resin is polymethyl methacrylate. 8. Mixture as stated in claim 1 or 2, characterized in that the acrylic resin is polymethyl methacrylate and that the (meth)acrylate component is cross-linked butyl acrylate. 9. Mixture as specified in claim 1 or 2, characterized in that the weight ratio between the acrylic resin and the interpolymer is from approx. 60:40 to approx. 20:80 and that the interpolymer comprises from approx. 5 to approx. 50% by weight of a cross-linked polybutyl acrylate component, from approx. 5 to approx. 35% by weight of the cross-linked styrene/acrylonitrile component and from approx. 15 to about 90% by weight of the non-crosslinked styrene/acrylonitrile component.