WO1998028365A1

WO1998028365A1 - Polymer composition

Info

Publication number: WO1998028365A1
Application number: PCT/NL1997/000702
Authority: WO
Inventors: Valerie Melville Chrystie Reid; Joseph Paulus Hubertus Boyens; Nicolaas Johanna Jozef Aelmans
Original assignee: Dsm N.V.
Priority date: 1996-12-20
Filing date: 1997-12-16
Publication date: 1998-07-02
Also published as: AU5347998A

Abstract

Polymer composition consisting of: a) 5-95 weight % of a copolymer of 90-99.5 wt. % methyl methacrylate, 10-0.5 wt. % ethyl acrylate; b) 95-5 wt. % of a copolymer of 72-80 wt. % styrene, 20-28 wt. % maleic anhydride; c) 0-5 wt. % processing agents and/or stabilisers and/or colourants, which polymer composition has a haze of at most 10 %.

Description

POLYMER COMPOSITION

The invention relates to a polymer composition consisting of a copolymer of styrene units and maleic anhydride monomer units, a copolymer containing methyl methacrylate monomer units and optionally processing agents, stabilisers and/or colourants.

A polymer composition is known from the German patent application DE-A-2024940 which contains:

1. 10-90 parts by weight of a copolymer of 70-90 wt . % styrene

10-30 wt.% maleic anhydride

2. 10-90 parts by weight of a copolymer of 60-100 wt.% methyl methacrylate

30-0 wt.% styrene 10-0 wt.% of a 1-4 C alkyl acrylate

3. 0-50 parts by weight of a copolymer of 60-90 wt.% styrene

40-10 wt.% acrylonitrile.

The aforementioned patent application furthermore describes that the polymer composition would be crystal clear because the values of the refractive indices of the different components of the polymer composition differ only little from one another. If the refractive indices of the individual components are important for the mixture's transparency, this means that the composition's components are not, or insufficiently, molecularly mixed. The transparency of the known polymer composition is consequently not very high and other optical properties, such as the haze, also leave something to be desired. The polymer composition can moreover only be processed in a narrow range of temperatures and shear rates, the so-called processing window. If the known polymer composition is processed outside the narrow processing window, even further demixing of the components takes place and a milky product with a very poor or entirely absent transparency is even obtained. The aim of the invention is to provide a polymer composition with a very good transparency and a low haze .

This aim is achieved in that the polymer composition consists of the following components: a. 5-95 weight % of a copolymer of 90-99.8 wt.% methyl methacrylate 10-0.2 wt.% ethyl acrylate and/or methyl acrylate b. 95-5 wt.% of a copolymer of 72-80 wt.% styrene 20-28 wt.% maleic anhydride c. 0-5 wt.% of one or more processing agents and/or stabilisers and/or colourants, and the composition has a haze of at most 10%.

The components of the polymer composition surprisingly prove to be very well miscible, whereas the components of the known polymer composition are not, or at least less, miscible. The polymer composition according to the invention not only has a very high transparency, but also a very low haze. A further advantage is that the polymer composition according to the invention has a wide processing window. It is for example not only well possible to injection-mould the polymer composition at high shear rates and high temperatures, but it is also possible to extrude the polymer composition at moderate temperatures and low shear rates, with the good optical properties being retained.

The polymer composition also has a high thermostability. Another further advantage is that the polymer composition according to the invention has a good resistance to chemicals, such as for example isopropyl alcohol .

The combination of a good thermostability and resistance to chemicals ensures that the polymer composition according to the invention also retains good optical properties when the composition is used in objects that are regularly washed in for example a dish washer.

G.R. Brannock c.s., Journal of Pol. Sci., Part B: Pol. Phys . , Vol. 29, No. 4, March 30, 1991, describes mixtures of acrylate polymers and copolymers of styrene and maleic anhydride (hereinafter to be referred to as SMA copolymers) . From the article it is evident that polymethyl methacrylate is molecularly miscible with SMA copolymers, but it is also evident that polyacrylates, in particular polyacrylates based on methyl acrylate and ethyl acrylate, are not miscible with SMA. For this reason it is all the more surprising that the good results are obtained with the polymer composition according to the invention, in which use is made of a copolymer that contains precisely methyl acrylate and/or ethyl acrylate monomer units. Brannock does moreover not specify the composition of the SMA copolymer or the mixture's optical properties.

A polymer composition containing SMA and a copolymer of methyl methacrylate and ethyl acrylate is known from WO 86/1525, but, unlike the polymer composition according to the invention, one of the two components in WO 86/1525 has been modified with a rubber . Preferably the polymer composition according to the invention consists of 90-50 wt.% component a., 10-50 wt.% component b. and 0-5 wt.% component c.

Even more preferably the polymer composition according to the invention consists of 85-70 wt.% component a., 15-30 wt.% component b. and 0-5 wt.% component c .

Component a. of the polymer composition is preferably a copolymer consisting of 92-99.7 wt.% methyl methacrylate and 8-0.3 wt.% methyl acrylate and/or ethyl acrylate. The polymer composition according to the invention will consequently show even better flow behaviour. Even more preferably component a. is a copolymer of 98-99.6 wt.% methyl methacrylate and 2-0.4 wt.% methyl acrylate and/or ethyl acrylate. Component a. can for example be prepared by means of mass or solution polymerisation according to the known processes. Component a. may be atactic or syndiotactic, depending on the preparation method. Preferably component a. is atactic. Component a. has a weight average molecular weight of for example 30,000 - 300,000 kg/kmol . For injection-moulding applications use is preferably made of a component a. with a weight average molecular weight of 30,000 - 200,000 kg/kmol. For extrusion applications use is preferably made of a component a. with a weight average molecular weight of 100,000 - 300,000 kg/kmol. Component b. can be prepared by introducing into a polymerisation vessel a mixture that contains a relatively large amount of styrene and little maleic anhydride, whether or not together with a solvent, while stirring and at a high temperature, and simultaneously removing the same amount by weight of the mixture from the polymerisation vessel. Such a process is described in for example A.W. Hansen and R.L. Zimmerman, Industrial Engineering Chemistry 49, p. 1803, etc. (1957) . A polymer composition according to the invention, with a haze of at most 10 %, can be obtained if during the polymerisation of component b. extremely vigorous stirring takes place. With even more vigorous stirring the haze of the polymer composition may even be at most 5% or even at most 3%. A process with which component a. can be prepared via vigorous stirring is known from EP-A-202 , 706. Further improvements can be obtained by rapidly mixing the styrene and maleic anhydride monomers added to the reaction mixture with the reaction mixture and by the mixing of the monomers with one another before being added to the reaction mixture . The rapid mixing of the monomers with the reaction mixture can for example be achieved by ensuring that the monomers are supplied close to the stirrer.

The haze is measured according to the standard ASTM D 1003.

Preferably component b. of the polymer composition according to the invention is a copolymer of 79-73 wt.% styrene and 21-27 wt.% maleic anhydride. The polymer composition according to the invention will consequently have a wider processing window. Component b. has for example a weight average molecular weight of 50,000 - 250,000 kg/kmol. Preferably component b. has a weight average molecular weight of 60,000 - 110,000 kg/kmol. The composition according to the invention will consequently have an optimum combination of good properties, such as for example chemical resistance, thermostability, optical properties and processability.

As component c . use can in principle be made of for example the additives known for polymethyl methacrylate and styrene maleic anhydride copolymers, such as for example processing agents, stabilisers and colourants. It is however important to choose component c. and its amount such that the optical properties are not, or as little as possible, adversely affected.

Good results are furthermore obtained if the additives have a high acidity. This ensures that the formation of gas bubbles in the polymer composition, probably caused by the decomposition of component b. in the melt phase, the copolymer of styrene and maleic anhydride, is suppressed.

Boric acid for example is very suitable for use as a thermal stabiliser.

Good results are furthermore obtained with UV stabilisers that also have a high acidity, preferably with a pKa of at most 8, more preferably at most 7, even more preferably at most 6, the pKa having been determined in a mixture of 50 wt.% isopropyl alcohol and 50 wt.% water at 23 °C. Examples of this are 2-(2'- hydroxy-5' -methyl-phenyl) -benzotriazole or HALS compounds, such as for example 8-acetyl-3-dodecyl- 7,7,9, 9-tetra-methyl-l, 3 , 8-triazospiro (4,5) decane-2 , 4- dione .

Preferably UV stabilisers are used in an amount of 0.2- 2.0 wt . % .

If use is made of a UV stabiliser with a high acidity, for example one of those mentioned above, it is possible to use a second UV stabiliser with a lower acidity, providing the second UV stabiliser is present in a lower concentration than the first. It is for example possible to use 0.4-1.5 wt.% 8- acetyl-3-dodecyl-7, 7,9, 9-tetra-methyl-l, 3,8- triazospiro (4, 5) decane-2,4-dione in combination with 0.1-0.5 wt.% di- (2,2, 6, 6-tetra-methyl-4-piperidyl) - sebacate. The aforementioned combinations of additives are very suitable for preventing the formation of gas bubbles during compounding and processing, and are preferably used if the polymer composition according to the invention is processed under critical conditions. 'Critical conditions' means for example at a high temperature, with a long residence time, at a high injection rate and using a small nozzle diameter of the sprue, or combinations of such factors. It is also possible to use other combinations of additives for the polymer compositions according to the invention that are processed under less critical conditions. It is for example possible for the polymer composition to contain a combination of UV stabilisers, precisely the UV stabiliser with a pKa > 8 being present in the highest concentration.

Components a., b. and optionally c. can for example be mixed with one another in the melt phase at temperatures between 200 and 270°C, preferably by using a continuous kneader, for example a single-screw kneader, twin-screw kneader or a Buss (TM) co-kneader.

The composition according to the invention is very suitable for producing moulded articles whose optical properties have to meet high requirements. The composition according to the invention is for example very suitable for injection-moulding for example front and rear lights of cars, displays, glazing of street lamps, garden lamps and other light fixtures. It is also well possible to extrude the composition according to the invention to form plates, from which plates end products can subsequently be produced according to the known methods, including vacuum forming. Examples of such end products are cover plates for bill boards and skylights. The polymer composition according to the invention is also very suitable for producing moulded articles with laser markings, without there being any need to add colourants and/or pigments to the composition. This is due to the presence of maleic anhydride monomer units in the composition according to the invention. When a moulded article which, at least in the location where the marking is applied with the aid of a laser, consists of a translucent polymer composition containing a polymer that contains maleic anhydride monomer units, markings with good contrast are surprisingly obtained. An even better contrast is obtained when the polymer that contains maleic anhydride monomer units also contains styrene monomer units. An advantage of these markings, which can for example be applied to the polymer composition according to the invention, is that they can be present beneath the surface of the polymer composition. An advantage of markings that are present beneath the surface, in the bulk, of the polymer composition is that the changes in the polymer composition resulting from the marking can lead to light scattering. If for example a red laser is beamed onto the edge of a plate made from the polymer composition according to the invention, with the laser travelling parallel through the plane of the plate instead of perpendicularly, a laser marking applied in the plate will light up red, while the rest of the plate will not, or virtually not, do so, owing to the high degree of transparency. In this way light scattering can hence be achieved, without it being necessary to use one of the known methods for effecting light scattering. Another advantage of markings that are present not on but beneath the surface is that the markings are resistant to scratching and wear. The surface of the polymer composition will moreover be smooth in the location where the marking is present beneath the surface and there will be no perceptible difference between the marked and unmarked parts of the polymer composition. The application of laser markings is known from for example EP-A-522370, DE-A-3425263 and W094/12352. The type of laser, and the settings for laser parameters optionally to be chosen, such as the power, the frequency and the wavelength, will be determined by for example the thickness of the translucent polymer composition in the location where the marking is to be applied and the desired contrast of the marking. The laser settings can be easily determined by those skilled in the field of laser markings. Examples of moulded articles according to the invention that may contain a laser marking are bank cards or other personal cards. The markings' resistance to scratching and wear is an important advantage for this application, but markings beneath the material's surface will moreover be difficult to remove or change. It is also possible to apply three-dimensional markings in the polymer composition according to the invention, for example holograms or three-dimensional bar codes. Such three-dimensional markings will also be difficult to reproduce, to change or to forge.

The invention will be further elucidated with reference to the examples, without being limited thereto.

Components employed

As component a. use was made of copolymers of methyl methacrylate and ethyl acrylate, indicated as PMMA-EA, or copolymers of methyl methacrylate and methyl acrylate, indicated as PMMA-MA. The weight percentages of ethyl acrylate and methyl acrylate are indicated between brackets in the examples and comparative experiments.

The following copolymers of styrene and maleic anhydride (SMA copolymers) were used: - SMA 32.110, copolymer of 32 wt.% maleic anhydride and 68 wt.% styrene with a weight average molecular weight of 110,000 kg/kmol.

SMA 28.110 copolymer of 28 wt.% maleic anhydride and 72 wt . % styrene with a weight average molecular weight of 110,000 kg/kmol.

SMA 26.080 copolymer of 26 wt.% maleic anhydride and 74 wt . % styrene with a weight average molecular weight of 80,000 kg/kmol.

SMA 26.110 copolymer of 26 wt.% maleic anhydride and 74 wt . % styrene with a weight average molecular weight of 110,000 kg/kmol.

SMA 26.180 copolymer of 26 wt.% maleic anhydride and 74 wt . % styrene with a weight average molecular weight of 180,000 kg/kmol. - SMA 22.110, copolymer of 22 wt.% maleic anhydride and 78 wt.% styrene with a weight average molecular weight of 110,000 kg/kmol. Production of test plates

Various mixtures of PMMA and SMA copolymers were prepared with the aid of a twin-screw kneader, type ZSK 30, supplied by Werner and Pfleiderer in Germany. The melt temperature was 260°C, the screw speed was 200 revolutions per minute and the yield was 15 kg/hour.

The mixtures were injection-moulded with the aid of an injection-moulding machine with a clamp- force of 80 tons, supplied by Engel in Germany, to form plates measuring 80*80*3.2 mm. The melt temperature was 245°C and the injection time was 2.5 sec.

Transparency, Haze and Yellowness Index The plates' haze and transparency were measured according to ASTM D1003 and the yellowness index according to ASTM D1925.

Comparative Experiments A - G Table 1 shows the compositions of the polymer mixtures and the results of Comparative Experiments A - G.

Table 1

10

1) The figure between brackets indicates the weight percentage of ethyl acrylate or methyl acrylate in polymer a.

15 2 ) PMMA-EA (2) and PMMA-MA (1) had weight average mol. weights of 110,000 and

100,000 kg/kmol, respectively.

3 ) If the haze has a value of >30, then the haze and transparency can no longer be measured according to ASTM D1003.

The compositions in Table 1 have a relatively high transparency, but a haze of less than 10% was not obtained.

Examples 1-9 and Comparative Experiments H and I

The mixtures were prepared and tested as described above. The SMA copolymers were now however prepared with the reactor's stirrer speed having been doubled from 20 to 40 revolutions per minute. The results are presented in Tables 2 and 3.

Table 2

10

1) The injection-moulding conditions used for the composition of Comparative

Experiment H were critical conditions, as a result of which the haze is

15 relatively high. Extrusion of the same composition leads to haze values of <

10%.

2 ) see comment 3 beneath Table 1. 3 ) PMMA-EA (5) had a wt . av. mol. weight of 90,000 kg/kmol.

Table 3

Example/ Composition Properties

Copol . wt.% Copol . Wt.% Haze (%) Transparency yellowness %

5 PMMA-MA (1) 70 SMA 28,110 30 7.7 90.8 2.6

6 PMMA-MA (1) 70 SMA 26,080 30 2.1 90.9 2.5

I

7 PMMA-MA (1) 70 SMA 22,110 30 1.9 91.1 2.3 4

8 PMMA-MA (4 ) ^1] 70 SMA 26,080 30 3.6 89.5 3.6

10 9 PMMA-M (4) 70 SMA 22,110 30 1.5 90.3 2.6

1 ) PMMA-MA(4) has a weight av. mol. weight of 110,000 kg.kmol

A comparison of Table 1 on the one hand and Tables 2 and 3 on the other shows that more vigorous stirring during the polymerisation of the SMA copolymer leads to improvement of the optical properties, in particular the haze, of the compositions according to the invention, whereas this is virtually not the case with the composition of comparative experiments .

UV resistance The UV resistance of the polymer composition of Example 1, with and without additives, was measured according to Standard PSA D27 1389 exterior (Intensity 0.55 W/m² at 340 nm; Black panel temperature 73 °C; Ambient temperature 54°C; 18 minutes' wetting, 102 minutes' dry) . Plates were injection-moulded as described above from the polymer composition of Example 1 with the different combinations of additives. In addition, a plate was produced from PMMA-EA (2) only, to enable comparison. Tables 4, 5 and 6 indicate the haze (in %) , the transmission (in %) and the yellowness index, respectively, as functions of time (in hours) .

Table 4 : Haze (in %)

10

15

Table 5 : Transmission (in %)

10

Table 6 : Yellowness Index (arbitray units (a.u))

10

1) In Tables 4, 5 and 6 the letters a - e represent the following additives:

2- (2' -hydroxy-5' -methyl-phenyl) -benzotriazole

8-acetyl-3-dodecyl-7, 7,9, 9-tetra-methyl-l, 3, 8-triazaspiro (4, 5) decane-2,4-dione

15 octa-decyl-3- (3 , 5-ditert-butyl-4-hydroxy-phenyl) -propionate bis (2,2,6,6, -tetramethyl, 4-piperidyl) sebacate

4-hydroxy-2, 2,6, 6-tetramethylpiperidine

The plate made from PMMA-EA (2) showed so many cracks after 1000 hours already that the test was abandoned. The polymer composition of Example 10, without additives, had a haze of > 10% after 3000 hours and was also abandoned. The combination of additives a and d proves to yield the best results in terms of UV resistance for this polymer composition.

Chemical Resistance The resistance to chemicals was tested using

3 different polymer compositions. PMMA-EA (2) was tested as a Comparative Example. A rod specimen with a thickness of 4 mm, a width of 12.5 mm and a length of 150 mm was clamped at one end. A weight was suspended from the other end, so that the resulting flexural stress on the rod was 21 MPa. The bending point was subsequently continuously wetted with a test medium. The time between the first wetting and fracture of the rod specimen was measured. Table 7 shows the amount of time (in seconds) between the first wetting and fracture of the rod specimen. A value of > 1800 seconds means that the rod specimen had not fractured after 1800 seconds. This means good chemical resistance.

Table 7:

Chemical resistance in iso-propanol (in seconds)

Table 7 indicates that it is favourable for the polymer compositions' chemical resistance to use SMA with a relatively high molecular weight.

Laser decorations

Example 20

A transparent plate as in Example 1 was irradiated with a pattern consisting of twelve squares. Use was made of a lamp-pumped solid-state Nd:YAG laser from Haas in Germany (wavelength: 1064nm; pulse length approx. 100 ns . ) and a frequency of 5000 Hz and 80% of the maximum power. For the first square the resolution had been set at 75 dpi (dots per inch) , for the second square at 100 dpi, after which the resolution of each following square was each time set 50 dpi higher. The plate was also irradiated with a pattern in the form of a text, with letters measuring 0.5-1.0 mm. De text was applied using the following laser settings: 95% of maximum power, 1000Hz and a writing speed of 50 mm/s, which resulted in a resolution of about 500 dpi. From 250 dpi onwards the square markings were visible because a change occurred in the plate at the location of the squares, which resulted in a pattern of dots with a silver colour in the form of a square, the dots being visible beneath the plate's surface. From 450 dpi onwards the contrast of the squares increased because black dots were also formed in addition to the dots with the silver colour. The square applied with a resolution of 600 dpi consisted of a large number of predominantly black dots and had a good contrast . The text marking was well legible (visually determined) .

Example 21 In the same way as in Example 20 a polymer composition as in Example 7 was provided with markings. Now the squares, visible through dots predominantly with a silver colour, were visible from 200 dpi onwards. Black dots were observed from the 400-dpi square onwards, and the 500- and 600-dpi squares consisted predominantly of black dots and had a good contrast . The text marking on this plate was very well legible.

Comparative Experiments L and M

Comparative Experiment L In the same way as in Example 20 a plate made from PMMA-EA (2) was provided with markings. Now dots with a silver colour were visible from 350 dpi onwards.

None of the markings were however clearly visible, because black dots were not or virtually not formed, not even in the case of markings that had been applied with more dpi. The text marking was illegible.

Comparative Experiment M

A plate made from PMMA-MA (1) was marked in the same way as in Example 20. From 450 dpi onwards dots with a silver colour were visible beneath the plate's surface, but, as in Comparative Experiment L, no black dots were formed. Not a single marking showed good contrast. The text was illegible.

Claims

C L A I M S

1. Polymer composition consisting of: a. 5-95 weight % of a copolymer of 90-99.8 wt.% methyl methacrylate 10-0.2 wt.% ethyl acrylate and/or methyl acrylate b. 95-5 wt.% of a copolymer of 72-80 wt.% styrene

20-28 wt.% maleic anhydride c. 0-5 wt.% processing agents and/or stabilisers and/or colourants, and which polymer composition has a haze of at most 10%.

2. Polymer composition according to Claim 1, with which vigorous stirring has been carried out during the polymerisation of component b. to such an extent that the haze of the polymer composition is at most 10%.

3. Polymer composition according to Claim 1, characterised in that the polymer composition consists of 90-50 wt.% component a., 10-50 wt.% component b. and 0-5 wt.% component c.

4. Polymer composition according to Claim 1 or Claim 2, characterised in that component a. of the polymer composition is a copolymer of 92-99.7 wt.% methyl methacrylate and 8-0.3 wt.% methyl acrylate and/or ethyl acrylate.

5. Polymer composition according to any one of Claims 1-3, characterised in that component b. of the polymer composition is a copolymer of 79-73 wt.% styrene and 21-27 wt.% maleic anhydride.

6. Polymer composition according to any one of Claims 1-4, characterised in that the polymer composition according to the invention has a haze of at most 5 %.

7. Moulded articles entirely or partly made from the polymer composition according to any one of Claims 1-6.

8. Moulded article according to Claim 7, characterised in that the moulded part contains a laser decoration applied in a location of the moulded part where the moulded part consists of the polymer composition.