EP0953010A1

EP0953010A1 - Use of reductive inorganic phosphorous compounds to increase uv transmissibility of moulded bodies made of polymethylmethacrylate moulding material as a suitable solar material

Info

Publication number: EP0953010A1
Application number: EP98961185A
Authority: EP
Inventors: Werner Höss
Original assignee: Roehm GmbH Darmstadt
Current assignee: Roehm GmbH Darmstadt
Priority date: 1997-11-14
Filing date: 1998-11-12
Publication date: 1999-11-03
Also published as: AU1669599A; NO992849D0; WO1999025764A1; NO992849L; DE19750434C1

Abstract

The invention relates to the use of reductive phosphorous compounds which increase the UV transmissibility of polymethylmethacrylate based formed bodies.

Description

Description:

Use of reducing inorganic phosphorus compounds to increase the UV permeability of moldings made of molding compositions based on polymethyl methacrylate and suitable as solarium material

DESCRIPTION

Field of the Invention

The invention relates to the use of reducing inorganic phosphorus compounds to increase the UV permeability of moldings suitable as solarium material from molding compositions based on polymethyl methacrylate.

State of the art

From EP 0016870 plastics based on polymethyl methacrylate are already known, which have a high permeability for UV-A radiation (300-400 nm) and for UV-B radiation (260-320 nm). Their high UV permeability is retained even after long-term exposure to radiation, since the plastic contains a small amount of a sterically hindered amine. Corresponding compounds intercept radicals which form when exposed to radiation and which would otherwise slowly destroy the plastic material. Such additives are described in Japanese Patent JP 03 47,856 and are referred to as "hindered amine light stabilizers", abbreviated "HALS".

DE-OS 34 21 859 also describes polymethyl methacrylate (PMMA) -based plastics which contain sterically hindered amines and have high UV permeability. It is even increased by installing aliphatic plasticizers. However, these require a lowering of the Vicat softening temperature, which is often not desirable. Plastics with good permeability to UV light are mainly used for solarium material. Good UV transmission is a key requirement here.

In the present invention, the UV transmission is significantly improved by adding inorganic reducing phosphorus compounds. Their use for this purpose is not known from the prior art. So far, they have been used to lower the yellowness and prevent yellowing tendencies.

There are a large number of general solutions for preventing or reducing a yellow tinge in thermoplastics. For example, the use of antioxidants, which, inter alia, are intended to prevent the discoloration of plastic molding compositions under thermal stress, is known (cf. for example Kirk-Othmer, Encyclopedia of Chemical Technology, 3rd Ed., Vol. 3, page 133, Wiley, New York, 1978). Antioxidants are also added to the molding compounds before processing, i.e. during the compounding step. Thus, according to the Japanese application Kokai Tokkyo Koho JP 60 123 547, an improvement in the discoloration of copolymers from methyl methacrylate, styrene and maleic anhydride monomer units is observed under injection molding conditions at higher temperatures, if such copolymers before processing with at least one phosphaphenanthrene derivative and in addition a sterically hindered phenol, a thiopropionic acid ester or a phosphoric acid ester as stabilizers against oxidative degradation. Jpn. Kokai Tokkyo Koho JP 60 120 735 describes copolymers of methyl methacrylate, vinyl aromatic and copolymerized cyclic Anhydrides to which, in order to increase the thermal stability and to avoid discoloration of such copolymers when subjected to thermal stress in the melt, for example in injection molding, phosphoric acid esters and other stabilizers based on sterically hindered phenols.

In Jpn. Kokkai Tokkyo Koho JP 03 167 245 claims the stabilization of copolymers of methyl methacrylate, N-substituted maleimides and other copolymerizable monomers with compounds selected from the group of alkyl-substituted triarylphosphites, dialkylpentaerythroldiphosphites and phosphaphenanthrene derivatives.

Jpn. Kokkai Tokkyo Koho JP 63 163 306 includes copolymers of methyl methacrylate and Cβ- to C20-alkyl methacrylate as the core material for optical fibers which contain organic phosphites, such as sterically hindered diarylpentaerythrol diphosphites, or thiophosphites to prevent discoloration of the copolymers when subjected to thermal stress.

The four Japanese patents cited here consistently claim sterically hindered organic phosphites, or organic phosphites together with sterically hindered phenols. Inorganic, reducing phosphorus compounds are not mentioned.

German utility model 2 95 04 693.7 also describes the use of sterically hindered organic phosphite compounds in molding compositions composed of copolymers consisting of the monomer units of alkyl methacrylate, vinyl aromatic and maleic anhydride, and, if appropriate, alkyl acrylate. The In some cases, organic phosphorus compounds are also added to the finished, granulated or ground polymer before further processing.

Inorganic, reducing phosphorus compounds for the purpose of preventing yellow tinge are also known from the prior art.

EP-A 576 877 describes a polymer based on polymethacrylic and polyacrylimide with a low yellowness index, salts of phosphinic or phosphonic acid being added during the imidation reaction. The amounts of phosphorus compounds used are high, presumably to compensate for a loss of activity in the subsequent processing stages. Amounts of 0.1-1% by weight, based on the amount of polymer to be imidized, are preferably used.

Means for reducing discoloration, in particular yellow tinge, are also known for impact-modified molding compositions. Due to their multiphase structure, for example when embedding a latex dispersion with a core-shell structure as a tough phase in a hard matrix such as PMMA, the production process causes a particularly large number of polymerization auxiliaries, such as, in particular, emulsifiers and buffer salts. EP-A 465 049 proposes to prevent the yellowing effect of the interfering by-products in impact-modified molding compositions by adding inorganic phosphorus compounds with a reducing action. The addition of sodium hypophosphite in an amount of 50 to 1000 ppm, based on the aqueous latex dispersion used, is claimed here. The reagent is added here in a relatively high dosage in an early manufacturing phase.

In contrast, DE-A 19544563 teaches to add a much smaller amount of reducing, inorganic phosphorus compounds in a later phase of processing, namely in the compounding step, whereby the yellowing under thermal stress, such as e.g. is largely prevented in the production of moldings.

A similar teaching is given by DE-A 19544562 with regard to the mode of addition of the reducing, inorganic phosphorus compounds. They are added in the compounding step in an amount of 0.01 to 1% by weight of a molding composition based on poly (meth) acrylimide and, above all, improve the color stability under thermal stress. Their reducing effect apparently prevents the formation of chromophores from the amide and imide structural units due to oxidation.

In the European patent application with the application number 96 111 330.5, dust-repellent PMMA molding compositions which have been equipped with ethoxylated fatty amines are described, to which inorganic phosphorus compounds which also have a reducing action are added in order to prevent the yellowing effect of the fatty amines. In this case too, the reducing inorganic phosphorus compounds are only added during compounding.

US 5,063,259 describes transparent, impact-resistant plastics, in particular made of polymethyl methacrylate. By adding inorganic phosphorus compounds with a reducing action, such as Na hypophosphite, when processing or blending polymethyl methacrylate base molding compositions with impact modifiers, the yellowness index is reduced in the case of moldings produced from the modified molding compositions. Task and solution

Good UV transmission is a basic requirement for solarium material and UV-permeable covers. These are usually made from a corresponding molding compound by thermoplastic processing, e.g. made by extrusion or injection molding.

Because of its generally high stability against UV exposure, PMMA is ideally suited for this purpose. Starting from the prior art, it was desirable to increase the transmission in the UV range, that is to say between 260 and 400 nm, without impairing other properties of the PMMA-based plastic. In particular, the Vicat softening temperature should not be lowered. The means to achieve this goal should be inexpensive and should be able to be added to the plastic without technical difficulties.

The object was achieved by using one or more, reducing, inorganic phosphorus compounds AP, selected from the group consisting of phosphinic acid and phosphonic acid and their alkali metal, alkaline earth metal and aluminum and their ammonium salts, the ammonium ion with up to four C- _| -C4-alkyl and / or Cs-Cβ-cycloalkyl groups can be substituted to increase the UV permeability of molded articles FK suitable as solarium material in the range from 260 to 300 nm, the molded articles FK consisting of molding compositions F based on polymethyl methacrylate 88 - 100 wt .-% of methyl methacrylate and 0 -12 wt .-% of C1-C4-alkyl acrylates as comonomers, containing 0.01 to 1 wt .-% of a sterically hindered amine ("HALS") based on the Polymer, are produced and the phosphorus compound AP is added to the molding composition FM before or during the thermoplastic processing to give the molding FK in an amount of 0.001 to 0.1% by weight, based on the molding composition. The molding compound

The molding compound FM based on polymethyl methacrylate consists of 88-100% by weight of polymerized methyl methacrylate monomers. It can also contain 0-12% by weight of a C 1 -C 4 -alkylacrylic acid ester as a comonomer. The content is preferably 1-6% by weight, particularly preferably 1-5% by weight of C 4 -C 4 -alkylacrylic acid ester. Among the C 1 -C 4 -alkyl acrylates, methyl acrylate is preferred.

The molding compound FM also contains sterically hindered amines (HALS) according to the prior art. These are, in particular as regards the possible variations with regard to the chemical structure, e.g. described in EP 0016870. Particularly preferred among the "HALS" products are derivatives of 2,2,6,6, tetramethylpiperidine, e.g. Di- (2,2,6,6-tetramethyl-piperidyl-4) sebacate (TPS). The latter is commercially available. These sterically hindered amines, also called "light stabilizers", are contained in the molding composition in amounts of 0.01 to 1% by weight, based on the polymer. The amount added is preferably 0.1 to 0.4% by weight.

The molding compositions FM can optionally contain mold release agents and thermal oxidation stabilizers in customary amounts.

The inorganic, reducing phosphorus compounds AP contain phosphorus in the oxidation states +1 or +3. Salts of phosphinic acid (hypophosphites) are technically easily accessible. and the phosphonic acid (secondary phosphites), as well as the free acids themselves. It does not matter whether the salts or the free acids are in the ortho or meta form or also, for example, as dimers. Alkali, alkaline earth, aluminum and ammonium salts can be used, it being possible for the ammonium ion to be substituted by up to four C 1 -C 4 -alkyl and / or C5-C8-cycloalkyl groups.

Organic, reducing phosphorus compounds selected from the group of aliphatic or monoaryialiphatic esters are far less effective. This applies above all to the various prior art antioxidants based on organic phosphites.

Sodium hypophosphite is particularly effective and also inexpensively available. Its use is a preferred embodiment of the invention. Although, according to literature, it easily disintegrates thermally with disproportionation, it has proven itself well for the purposes of the invention. The addition mode according to the invention apparently prevents premature thermal decomposition of this reducing agent.

Alkaline earth hypophosphites are more thermally stable, e.g. Calcium hypophoshite. However, it has been found that, in particular, higher amounts of calcium hypophosphite can lead to clouding in the molding composition or in the molding produced therefrom. Mixtures of various reducing inorganic phosphorus compounds can also be used.

Unexpected compared to the prior art regarding the use of reducing inorganic phosphorus compounds is that According to the invention, the lowest concentrations thereof are sufficient. With 0.001% by weight to 0.005% by weight (10-50 ppm), based on the molding compound FM, already recognizable effects are achieved. The maximum effect can be achieved with less than 0.005% by weight (50 ppm). The amounts used are therefore usually in the range from 10 to 150, preferably 30 to 120, ppm. If the reducing, inorganic phosphorus compound is used in one of its hydrate forms, the water of crystallization must be subtracted when calculating the amount used.

Amounts of more than 0.1% by weight (1000 ppm) based on the molding compound FM generally do not bring about any further improvement in the optical properties, in fact they can trigger property deteriorations in special cases, e.g. an incipient irreversible turbidity in the polymer, which can be recognized from the lower transmission values.

The inorganic, reducing phosphorus compounds AP are usually applied in solution. Water is suitable as a solvent. The reducing phosphorus compounds are advantageously used in concentrated solution. A concentration of 50% by weight may be mentioned as a guideline. The concentrated solution is usually prepared at room temperature. Depending on the solution and application temperature, other concentrations are possible or necessary, for example 5 to 65% by weight. In the case of particularly low additions of inorganic, reducing phosphorus compound AP, the concentration in water will be chosen to be lower, for example 10-30% by weight. It is surprising that such a small volume of reducing agent as it is a concentrated solution of the phosphorus compound can obviously be homogeneously distributed over the entire batch of polymer. However, it is also possible to apply the reducing inorganic phosphorus compound in powder form, that is to say without using solvent.

Even if it is in principle conceivable to add the individual components of a mixture of reducing phosphorus compounds in succession to the polymer, one will generally first prepare a mixture or solution of the components and add them to the polymer in one step. This is more advantageous for homogeneous distribution.

The addition of inorganic, reducing phosphorus compounds AP in aqueous form can be disadvantageous insofar as the water is brought to the melting temperature of the polymer sooner or later in the course of processing and can possibly lead to small gas bubbles in the polymer. Therefore, organic, high-boiling liquids, such as organic carboxylic acids or primary organic alcohols with 12 to 20 carbon atoms - examples include palmitic acid and stearyl alcohol - are used as solvents for the inorganic, reducing phosphorus compounds AP, thereby avoiding the formation of gas bubbles. Relatively dilute solutions of AP in these high-boiling solvents are produced here, for example 0.1 to 20 percent by weight solutions. 1 to 15 percent by weight solutions are preferably used, particularly preferably 2 to 10 percent by weight solutions. Blueing agents can also be dissolved in the high-boiling organic solvents. The incorporation of the reducing inorganic phosphorus compound AP

One of the possibilities according to the invention for adding the reducing inorganic phosphorus compound to the molding compound FM is to incorporate it in the compounding step. To carry out this process step, the molding composition should be in particle form. Suitable are e.g. especially granules or regrind in various grain sizes. An average particle size of 1-5 mm is preferred.

According to the invention, the reducing inorganic phosphorus compound AP is generally added after the polymerization reaction has ended. Incorporation takes place in the melt, which is largely free of residual monomers. At this point in time, the polymer PM contains less than 1% by weight of residual monomer.

The addition can be done either by adding masterbatch of the inorganic phosphorus compound AP or by weighing e.g. a 5% to 60% aqueous solution of the reducing inorganic phosphorus compound AP to the granules.

The mixing of the reducing inorganic phosphorus compound AP with the molding compound FM present in particulate form in the compounding step usually takes place first in slow-running mixing units such as drum, ring gear or double-chamber ploughshare mixers. The slow running aggregates cause mixing without the phase boundaries being lifted (see Ulimann's encyclopedia der technical chemistry, 4th edition, vol. 2, pages 282 to 311, Verlag Chemie, Weinheim, New York, 1980). This mixture is thermoplastic processed in the subsequent processing step of melting. For this purpose, extruders, or generally speaking, heatable mixing units are used at the appropriate temperatures, generally between 220 and 280 ° C. Examples are single-screw or multi-screw extruders or extruders with an oscillating screw and optionally also with shear pins.

With this method, the molding compounds FM can be produced in granule grain sizes of, for example, 1 to 5 mm. The shaping processing can then begin. Common technical processes such as injection molding, extruding, pressing, sintering and other shaping processes are suitable for this. There are no limits to the design of the molded body FK.

Another variation of addition is to add the inorganic, reducing phosphorus compounds AP in the form of a so-called masterbatch in the assembly or manufacture of the product or in the shaping processing. In the production of the masterbatch, a small part of the molding compound, which is already in granular or ground form, is melted in a separate extruder, and the reducing, inorganic phosphorus compounds AP are added to the melt. It can be metered in as a solution, for example, or it has already been mixed with the granulated molding compound. The melt containing the inorganic reducing phosphorus compounds AP in a relatively concentrated form is mixed with the main amount of the molding compound in the extruder combined and thereby diluted to the effective concentration according to the invention.

Further modalities of addition are conceivable, the addition having to take place in any case to the essentially polymerized polymer PM in order to achieve the advantages according to the invention.

The effect according to the invention, namely the high UV permeability, can be seen particularly clearly when the molded body FK is produced by injection molding. Compared to shaping processing by extrusion, the option is usually not available here, e.g. by degassing to reduce the residual monomer content, unless injection molding machines with degassing cylinders are used. The molding composition thus produced contains a relatively high residual monomer content of over 0.3%. For this reason, it can be assumed that the advantage of the inorganic, reducing phosphorus compounds is, at least in part, that they suppress the interfering effects of higher residual monomer contents.

Advantageous effects of the invention

Molding compositions or moldings produced therefrom, in particular sheets based on PMMA with relatively high amounts of UV stabilizers (“HALS”), which have excellent UV permeability, are known from the prior art.

According to the invention, the UV permeability is increased by the addition of inorganic, reducing phosphorus compounds such as sodium hypophosphite before the shaping processing, that is during Compounding or improved as a masterbatch. The addition mode is a simple process which is familiar from the prior art and does not require any additional technical effort. The reagent is inexpensive and is only used in low doses so that other properties of the molding composition or the moldings produced therefrom are not changed.

The decisive advantage of the use according to the invention is the increase in the UV permeability of the moldings produced compared to moldings not produced according to the invention, that is to say without the addition of inorganic, reducing phosphorus compounds. The UV transmission for the range from 260 to 300 nm, that is to say for the UV-B range, increases by at least 2%, preferably even by at least 5%, based on the 100% transmission. Especially in the lower UV-B range at 260 to 280 nm, the transmission increase is over 5%. But even in the UV-A range from 300 to 400 nm, the transmission increases by at least 1% by acting according to the invention. The effect can only be clearly seen for the UV range. In the visible range, i.e. above 400 nm, no improvement in the transmission can be achieved. The increase in transmission is particularly noticeable when the moldings according to the invention are produced by injection molding.

The molded articles FK can advantageously be used generally as a UV-permeable cover and in particular as a UV-permeable cover for solarium material. EXAMPLES

example 1

A commercially available molding compound for solarium covers based on polymethyl methacrylate (PMMA), namely a copolymer consisting of 96% by weight of methyl methacrylate and 4% by weight of methyl acrylate monomer units, which contains 0.25% by weight of a "HALS" UV stabilizer, namely di (2 , 2,6,6-tetramethyl-piperidyl-4) sebacate (TPS) is compounded together with a sodium hypophosphite solution. For this purpose, 0.05 parts based on 100 parts of the molding compound are 10% pure before processing

Dried sodium hypophosphite solution. Based on the molding compound, this is 50 ppm sodium hypophosphite.

Plates with a thickness of 3 mm are injection molded and the transmission measured in the UV range. The measurement is carried out according to DIN 5033 (D65 / 10 °).

Example 2

The procedure is as in Example 1, with the difference that 100 ppm of sodium hypophosphite, based on the molding composition, are used.

Example 3 (comparative example)

The procedure is as in Example 1, with the difference that no sodium hypophosphite is used. Results

A transmission measurement in the UV range on the injection-molded plates showed a significant improvement in the UV transmission of the samples containing sodium hypophosphite (Examples 1 and 2) in comparison with Comparative Example 3. It was found that the addition of 50 ppm of sodium hypophosphite was already sufficient to to achieve the effect of the invention. An addition of 100 ppm hardly results in an increase in the transmission.

The transmission values of the injection-molded plates from Examples 2 and 3 are shown in Figure 1 as curves over the wavelength range from 250 to 450 nm. The solid curve B3 corresponds to example 3. The curve B2 shown in dashed lines corresponds to example 2 (the transmission curve according to example 1 was almost completely identical to that of example 2 and was not shown in the figure for the sake of clarity). Fig. 1 clearly shows the improvement in transmission in the UV-B range in example 2 compared to example 3.

Claims

PATENT CLAIMS

1. Use of one or more, reducing, inorganic phosphorus compounds AP, selected from the group consisting of phosphinic acid and phosphonic acid and their alkali metal, alkaline earth metal and aluminum and their ammonium salts, the ammonium ion with up to four C -] - C4-alkyl and / or Cs-Cs-cycloalkyl groups can be substituted, in order to increase the UV permeability of molded articles FK suitable as solarium material in the range from 260 to 300 nm, the molded articles FK consisting of molding compositions FM based on polymethyl methacrylate 88 - 100 wt .-% of methyl methacrylate and 0 -12 wt .-% of C ^<ι-C4-A kylacrylsäureestern as comonomers containing 0.01 to 1

% By weight of a sterically hindered amine (“HALS”) based on the polymer, and the phosphorus compound AP of the molding compound FM before or during thermoplastic processing to give the molded article FK in an amount of 0.001 to 0.1% by weight is added to molding compound.

2. Use according to claim 1, characterized in that the phosphorus compound AP or the phosphorus compounds AP are added during the thermoplastic processing of the molding compound FM in a compounding step and then molded into a molded article FK.

3. Use according to claim 2, characterized in that the production of the molded body FK is carried out by injection molding.

4. Use according to claim 1, characterized in that the phosphorus compound AP or the phosphorus compounds AP are added in the thermoplastic processing of the molding compound FM in the form of a masterbatch and then molded by extrusion to give a molded article FK.

5. Use according to one or more of claims 1 to 4, characterized in that AP sodium hypophosphite is used as the inorganic, reducing phosphorus compound.

6. Use according to claim 5, characterized in that sodium hypophosphite is used in aqueous solution.

7. Use according to one or more of claims 1 to 6, characterized in that methyl acrylate is used as the alkyl acrylate.

8. Use according to one or more of claims 1 to 7, characterized in that di- (2, 2,6,6-tetramethyl-piperidyl-4) sebacate (TPS) is used as the sterically hindered amine ("HALS").