Co-extruded impact-modified PMMA film

Abstract

The present invention relates to novel matt PMMA foils for application on materials as foil providing protection from weathering effects and as decorative foil. In particular, the present invention relates to a novel, at least two-layer PMMA foil which features particularly good adhesion on the substrate. The outer layer here exhibits the mattness, and the inner layer here comprises a low-molecular-weight component which improves adhesion on the substrate.

Claims

1. A PMMA foil, comprising: an outer layer which comprises a PMMA matrix material, and an inner layer which comprises the PMMA matrix material, and from 5.0 to 18% by weight of an oligomeric PMMA with a weight-average molar mass of from 300 to 1500 g/mol, measured by SEC against a PMMA standard, wherein at least one of said inner and outer layers comprises an impact modifier.

2. The PMMA foil according to claim 1, wherein the outer layer further comprises from 0.5 to 20% by weight of one or more matting agents.

3. The PMMA foil according to claim 2, wherein the matting agent comprises SiO.sub.x particles, TiO.sub.2 particles, BaSO.sub.4 particles, BaCO.sub.3 particles, or crosslinked polymer particles, and the particles have a diameter of from 1 to 40 m.

4. The PMMA foil according to claim 3, wherein the matting agent comprises crosslinked polymer particles, which comprise PMMA particles or silicone particles.

5. The PMMA foil according to claim 1, wherein the inner layer further comprises from 0.01 to 0.5% by weight of one or more antiblocking agents.

6. The PMMA foil according to claim 5, wherein the antiblocking agent comprises SiO.sub.x particles, TiO.sub.x particles, BaSO.sub.4 particles, BaCO.sub.3 particles, crosslinked PMMA particles, or crosslinked silicone particles, and the particles have a diameter of from 0.5 m to 40 m.

7. The PMMA foil according to claim 1, wherein both the outer and inner layers comprise an impact modifier.

8. The PMMA foil according to claim 1, wherein the impact modifier comprises core-shell particles or core-shell-shell particles, and at least one shell comprises a poly(meth)acrylate.

9. The PMMA foil according to claim 1, wherein the PMMA matrix material is obtained through polymerization of a composition comprising from 80 to 100% by weight of methyl methacrylate and from 0 to 20% by weight of one or more other ethylenically unsaturated monomers capable of free-radical polymerization.

10. The PMMA foil according to claim 1, wherein the outer layer further comprises from 2.0 to 12% by weight of one or more matting agents.

11. The PMMA foil according to claim 3, wherein the particles in the matting agent have a diameter of from 1.5 to 20 m.

12. The PMMA foil according to claim 1, wherein the inner layer and/or the outer layer further comprises an HALS compound, a triazine, and/or a benzotriazole.

13. The PMMA foil according to claim 1, wherein a thickness of the inner layer is from 2 to 100 m, and a thickness of the outer layer is from 2 to 100 m.

14. The PMMA foil according to claim 1, further comprising: on the outer layer, a third layer with a thickness of from 2 to 100 m.

15. The PMMA foil according to claim 14, wherein the third layer comprises a scratch-resistant PMMA layer, a PVDF layer, a PMMA/PVDF layer or a decorative layer.

16. A method for coating an article, said method comprising: securely bonding the PMMA foil according to claim 1 to the article by lamination and/or adhesive bonding.

17. The method according to claim 16, wherein the article comprises plastic.

18. The PMMA foil according to claim 1, wherein the oligomeric PMMA has the same composition as the PMMA matrix material.

Description

EXAMPLES

(1) The SEC measurements (also termed GPC measurements) were made with a column oven temperature of 35 C., using THF as eluent. They were evaluated against a PMMA standard. The system has the following combination of columns: one SDV LinL 10 m precolumn (8*50 mm), 2 SDV LinL 10 m columns (8*300 mm), 2 SDV 100 10 m columns (8*300 mm) (all from PSS, Mainz) and a KF-800D Solvent-Peak separation column (8*100 mm) (Shodex). PSS Win GPC-Software was used to evaluate the measurements.

(2) Gloss is measured as reflectometer value in accordance with DIN 67 530. The angle of measurement was 60. The measurement was made on a EUROPLEX PC 2339H black matt substrate.

(3) Visual assessment after heat-ageing in moist conditions: the composite foils are brought into contact with a moist cloth at 60 C. and about 98% relative humidity. Adhesion is checked visually at intervals of respectively one month during ageing times of up to one year. Poor adhesion results in delamination.

(4) Rapid peel test: a commercially available aluminium foil is smoothed on a Teflon sheet with a reflective side upwards. The PMMA foils to be tested are then placed with the inner side on the said smooth surface and smoothed with a sponge. A second aluminium foil is placed with the reflective side on the outer side of the PMMA foil and is smoothed with a sponge. The manner of placement of the aluminium foils was such that there was respectively a lateral strip of excess material of length at least 2 cm. Finally, a metal sheet is superposed and the entire test system is pressed in a platen press at 170 C. and 70 bar for 1 min. The Teflon sheet and the metal sheet are removed, and then the aluminium strips are peeled, and an assessment value of from 1 (very little adhesion) to 5 (strong adhesion) is allocated.

(5) Boiling test: by analogy with the rapid peel test, the PMMA foils are pressed on the inner side with a PVC foil and on the outer side with an aluminium foil. The aluminium foil is removed after the pressing process. The PVC-PMMA composite foils are aged for 24 h in boiling (100 C.) or hot (90 C.) water. If adhesion is good, no visually discernible differences are expected, but if adhesion is poor bubbles are observed to form between the layers and there are other visually discernible effects.

Example 1: Production of the Oligomeric Component

(6) 60 g of methoxypropyl acetate (Dowanol PMA from Dow Chemical) as solvent, 24 g of methyl methacrylate (MMA) and 1 g of MA (methyl acrylate) are used as initial charge in a 2 L stirred tank with blade stirrers, thermometer with chart recorder, and a heatable oil jacket with attached thermostat. 3.0 g of tert-butyl 2-ethylperhexanoate and 7.0 g of n-DDM (n-dodecyl mercaptan) are added to the said mixture and heated to 90 C., with stirring. Once an exothermic reaction has been observed, the metering of a mixture of 446 g of MMA, 19 g of MA and 150 g of n-DDM is begun, and at the same time the oil jacket temperature is increased to 110 C. The metering rate here is 2.3 g/min, for about 4.3 h. Once metering has been concluded, a solution made of 38.8 g of tert-butyl 2-ethylperhexanoate in 80 g of methoxypropyl acetate is metered into the mixture over a period of 350 min, with stirring, again at an oil temperature of 110 C. Once the second metering process has been concluded, stirring is continued at 110 C. for a further 60 min. After cooling, the volatile constituents are removed on a rotary evaporator, and the product is then dried at 60 C. under high vacuum. Molar mass was determined by means of SEC. The oligomer has M.sub.w=1100 g/mol.

Material for the Inner Layer

(7) A copolymer made of 63.5% by weight of MMA, 34.3% by weight of n-butyl acrylate, 0.5% by weight of methyl acrylate and 1.7% by weight of allyl methacrylate is used as material for the inner layer. This moulding composition has two phases. Firstly, core-shell particles are present with a core made of n-butyl acrylate and with a shell made of the other three components. This component represents the impact modifier. Alongside this, a thermoplastic matrix material is present, composed of MMA and ethyl acrylate. The said polymer has M.sub.w=about 95 000 to 100 000 g/mol. The Vicat softening point of the material of the inner layer is 71 C., and the glass transition temperature of the thermoplastic fraction is about 81 C. The material of the inner layer also comprises, based on 100% by weight of the polymer composition described, 1.0% by weight of Tinuvin 360, 1.0% by weight of Sabostab 119 and 1.0% by weight of CGX UVA 006 as UV stabilization package. The material of the inner layer further comprisesagain based on 100% by weight of polymer composition0.02% by weight of Sipernat 44MS from Evonik Industries (SiO.sub.2 particles) as antiblocking agent.

Material for the Outer Layer

(8) The outer layer comprises 15% by weight of matting agent based on PMMA. The composition of the said matting agent is 45% by weight of MMA, 45% by weight of n-butyl acrylate, 7% by weight of ethyl acrylate and 3% by weight of glycol dimethacrylate. The outer layer also comprises a proportion of 52% by weight of an impact modifier with a core-shell structure, where the core is composed mainly of acrylates and the shell is composed mainly of methacrylates. The overall composition of the said core-shell particle is 58.6% by weight of MMA, 40.7% by weight of n-butyl acrylate and 0.7% by weight of allyl methacrylate. Alongside this, 39% by weight of a thermoplastic matrix material is present, composed of MMA and 1% by weight of methyl acrylate. The material of the outer layer also comprises, based on 100% by weight of the polymer composition described, 1.0% by weight of Tinuvin 360, 1.0% by weight of Sabostab 119 and 1.0% by weight of CGX UVA 006 as UV stabilizer package. The said polymer has M.sub.w=about 95 000 to 100 000 g/mol. The overall properties of the material of the outer layer comprise the following: Vicat softening point of at least 81 C., glass transition temperature of at least 91 C. and gloss of 205 at 60. This gloss value corresponds to the gloss value of a prior-art matt foil.

Example 2: Production of the Polymer Pellets for the Inner Layer (General Specification)

(9) The components described for the material of the inner layer, together with the polymer from Example 1, are processed in a twin-screw extruder and discharged by way of pelletizing die to give strands. The strands are comminuted in a downstream pelletizer to give pellets. The amount added of the oligomeric component from Example 1, based on the polymer components of the material of the inner layer, is 10% by weight.

Example 3: Production of the Foil

(10) A chill-roll process was used to produce the two-layer foil. The extrusion system used for this was composed of two (optionally three) single-screw extruders with respectively a melt pump and a coextrusion die (flat-film extrusion die with two distribution channels). The entire apparatus also comprised a set of rollers (L configuration) and a winder.

(11) The first single-screw extruder A for producing the inner layer used the impact-modified polymethyl methacrylate according to the material of the inner layer listed above.

(12) The second single-screw extruder B for producing the outer layer, which in this example is mostly matt, used the impact-modified polymethyl methacrylate moulding composition according to the material of the outer layer listed above.

(13) A chill roll had been positioned centrally at a distance of about 25 mm from the discharge aperture of the coextrusion die. The temperature of the chill roll was from 70 C. to 130 C., preferably from 90 C. to 100 C. The temperature of the melt stream was about 240 C. Initial contact between the inner layer from the melt film and the surface of the roll was approximately tangential, and the angle of deflection of this layer around the roll was about 90. After deflection around the other downstream cooling rolls, the thickness of the foil web was determined by a traversing, contactless measurement system, and the distribution melt in the die was regulated, across the width, by means of a system of thermal expansion elements and electronic data processing. The foil was then wound up. The thickness of the resultant two-layer foil was about 53 m (10 m inner layer and 43 m outer layer). No bubbles were observed to form in the boiling test. The rapid peel test gives a value of 5 for the inner layer and a value of from 1 to 2 for the outer layer.

Example 4: Production of a Three-Layer Foil

(14) The foil according to Example 4 was produced by analogy with the foil according to Example 3. However, in this case an additional third melt film was applied by way of a third single-screw extruder to the outer layer, by means of a coex adapter. As an alternative, this could also be achieved by way of a three-layer coextrusion die. Plexiglas 8H from Evonik Industries AG was used for this purpose, being a material of particularly high molar mass. The PMMA involved here has 1% by weight of methacrylate content, a molar mass M.sub.w of 147 000 g/mol and a Vicat softening point of 108 C. The said third layer was applied with a thickness of 10 m. No bubbles were observed to form in the boiling test. The rapid peel test gives a value of 5 for the inner layer and a value of 1 for the outer layer.

Comparative Example 1

(15) A single-layer foil was produced from the material of the inner layer with thickness 50 m by means of a chill-roll process. The extrusion system used for this purpose was composed of a single-screw extruder with melt pump and with a flat-film extrusion die. The entire apparatus also comprised a set of rollers (L configuration) and a winder.

(16) The rapid peel test gives a value of 5 for both layers. The adhesive effect therefore occurs on both sides. This leads to problems during unrolling from a roll of foil for further processing, and to formation of deposit on the type of roller system that would be used for further processing. No formation of bubbles is observed in the boiling test after lamination to the PVC foil.

Comparative Example 2

(17) By analogy with Comparative Example 1, a single-layer foil was produced from the material of the outer layer with thickness 50 m by means of a chill-roll process.

(18) Extensive formation of bubbles is observed in the boiling test after lamination to the PVC foil.

(19) The rapid peel test gives a value of 1 for the upper side, and for the underside, of the foil.