Optical-grade molding composition with increased heat resistance

Abstract

The present invention relates to a method for producing an acrylic copolymer having increased heat resistance, high transparency, and improved adhesion to metal surfaces. The invention further relates to a molding composition comprising this copolymer. The molding composition of the present invention is highly suitable for the production of optical elements for optoelectronic devices comprising an acrylic component and a metal or ceramic component.

Description

[Technical Field]

[0001] The present invention relates to a method for producing an acrylic molding composition having increased heat resistance, excellent optical properties, and improved adhesion to metals. Such a molding composition is highly suitable for the manufacture of various medical devices having optoelectronic devices, such as light-emitting diodes (LEDs), LED lenses, light guides, optical sensors, solar cells, and light sources, which include acrylic and metal or ceramic components.

[0002] Conventional technology Copolymers containing repeating units derived from methyl methacrylate (MMA), often referred to for convenience as acrylic molding compositions, are typically transparent materials with high weather resistance. Therefore, acrylic molding compositions are generally used in applications requiring high transparency, low haze, and high weather resistance. There is also a growing demand for substantially colorless, transparent polymers with particularly high heat resistance for optical applications, including light sources for indoor and outdoor use, such as high-power light-emitting diodes (LEDs). To increase the light yield of LEDs, the LED's built-in optical lens is located close to the light-emitting semiconductor element. The operating temperature of LED surfaces, particularly so-called white high-power LEDs, often exceeds 100°C, or even 130°C. Therefore, it is important that materials for these applications are substantially colorless, highly transparent, especially with low haze values, and possess high heat resistance.

[0003] Furthermore, optoelectronic devices such as LEDs, optical sensors, or solar cells generally include transparent acrylic components and metal or ceramic structural components that are hermetically sealed to each other. Therefore, durable, strong, and hermetically sealed adhesion (sealing) between the acrylic components and the metal or ceramic components is of paramount importance to ensure the long-term reliability and sustainability of the device, especially when the device components are sensitive to trace amounts of moisture and / or oxygen.

[0004] It is common knowledge that the presence of free carboxylic acid and phosphonic acid functional groups in acrylic polymers is advantageous in terms of adhesion to metal or ceramic substrates because these functional groups chemically react with commonly used metal or ceramic surfaces. For this reason, copolymers containing repeating units derived from (meth)acrylic acid, such as copolymers of MMA and methacrylic acid (hereinafter referred to as MAA), are generally good candidates for use in optoelectronic devices. On the other hand, in order to ensure that the copolymer has low water absorption, it is important that the cumulative content of MAA units and glutaric anhydride units in the copolymer does not exceed 20% by weight, preferably 10% by weight, based on the weight of the copolymer. If the content of glutaric anhydride units in the copolymer is high compared to the content of MAA units, optical haze often increases.

[0005] Furthermore, copolymers containing MAA units are commonly used as compatibilizers, adhesion promoters, or reactive components. In these applications, a high content of MAA units is essential to achieve sufficient adhesion.

[0006] U.S. Patent No. 7,888,456 describes a method for producing a thermoplastic copolymer, comprising generating a copolymer containing unsaturated carboxylic acid alkyl ester units such as MMA and unsaturated carboxylic acid units such as MAA, and then heat-treating it to carry out an intramolecular cyclization reaction to produce a thermoplastic copolymer containing glutaric anhydride units. The final product of U.S. Patent No. 7,888,456 is reported to have a glass transition temperature of 130°C or higher, a high level of transparency, and good heat resistance. However, as a result of mainly the formation of glutaric anhydride units, it has only a low content of repeating units derived from MAA and therefore has only moderate adhesion to metal or ceramic surfaces.

[0007] European Patent Application Publication No. 3239191 describes a method for producing a (meth)acrylic resin composition, comprising the steps of: continuously supplying a monomer mixture of methyl methacrylate, optionally alkyl acrylate, and optionally other comonomers to a tank reactor; carrying out bulk polymerization at a conversion ratio of 40-70%; and continuously supplying the liquid to a vented extruder to separate volatile components.

[0008] International Publication No. 97 / 33925 describes a multi-step method for producing a heat-resistant polymethyl methacrylate molding composition, comprising radical polymerization of methyl methacrylate with an optional comonomer, such as an alkyl acrylate, in at least two reactors. The first reactor is operated at a temperature below 120°C, and the second reactor is operated at a temperature in the range of 130–200°C. Typically, unreacted monomers are separated in a subsequent vacuum degassing step and at least partially recycled back into the polymerization process.

[0009] International Publication No. 2017 / 097979 teaches a method for preparing copolymers containing monomers of MMA and MAA. An example in International Publication No. 2017 / 097979 briefly states that the crude polymer syrup after the polymerization step can be deflated in a degassing extruder at a temperature of 200°C to 230°C (the temperature of the extruder's heating jacket) to obtain the final copolymer. Information regarding the melting temperature of the copolymer is not disclosed. The obtained copolymer is reported to be suitable for applications such as light guides, lenses, automotive trim, and automotive rear and front light components. Details regarding the degassing step are not described.

[0010] In their initial attempt to reproduce the teachings of International Publication No. 2017 / 097979, the inventors obtained a copolymer having a high content of glutaric anhydride units and a low content of free carboxylic acid groups. Therefore, this copolymer exhibited only moderate adhesion to metal or ceramic surfaces and was unsuitable for the desired purpose.

[0011] It is well known that efficient degassing of copolymer mixtures obtained in the polymerization step typically involves using high operating temperatures to remove volatile components, particularly unreacted monomers such as MMA and MAA. This step is necessary because trace amounts of such components in the final copolymer tend to reduce heat resistance and, in the case of MAA, tend to cause corrosion of extrusion or injection molding equipment. Furthermore, these components can cause optical defects during the injection molding process due to foam formation.

[0012] In MMA-MAA copolymers containing 10% or less by weight of MAA units in the copolymer chain, the formation of glutaric anhydride units mainly occurs from the reaction of adjacent MAA and MMA units, accompanied by the formation of methanol. In MMA-MAA copolymers with a higher content of MAA units in the copolymer chain, the formation of glutaric anhydride units from the reaction of two adjacent MAA units, accompanied by the formation of water, is also a significant side reaction at high temperatures. Trace amounts of methanol and water, even in small amounts, tend to reduce the heat resistance of the final copolymer and can cause surface defects during injection molding due to their partial evaporation.

[0013] The inventors have noted that, in the direction of transport of the copolymer molten material, there is typically a hold-up between the final degassing zone of a degassing device, such as a degassing extruder, and the molten material outlet die, where the copolymer molten material is still at a high temperature. As a result, glutaric anhydride units, methanol, and water are formed and subsequently remain in the final polymer. The hold-up is, for example, a zone in the degassing device after the final degassing zone, where the pressure is increased to push the copolymer molten material through subsequent conduits, molten material filters or molten material sieves, and molten material outlet dies.

[0014] Therefore, to minimize the unwanted formation of glutaric acid anhydride units, it is advantageous for the copolymer melt temperature to be low and / or for the residence time to be short during the hold-up after the final extruder degassing zone. However, under these conditions, the removal of volatile components such as unreacted methacrylic acid residue becomes more difficult. Furthermore, actively cooling the copolymer melt immediately after the final degassing zone with respect to the direction of transport of the copolymer melt increases its melt viscosity, making the handling and filtration of the copolymer melt difficult. Due to the high viscosity of the copolymer melt, low radial mixing, limited heat transfer, and low thermal conductivity, the possibility of altering the melt temperature by heating or cooling elements after the degassing device is limited.

[0015] Object of the invention In consideration of the aforementioned drawbacks, the object of the present invention was to provide a method for preparing acrylic copolymers having excellent optical properties, particularly low haze and substantially zero yellowing, high heat resistance, and a high content of free carboxylic acid groups and a low content of glutaric anhydride units. These properties enable the use of the copolymer in optoelectronic devices such as LEDs, optical lenses, light guides, optical sensors, and solar cells, which include transparent acrylic components and metal or ceramic structural components and have high operating temperatures on their surfaces. Due to the high content of free carboxylic acid functional groups, the copolymer has excellent adhesion to metal and ceramic surfaces, enabling durable, strong, and airtight bonding between the acrylic and metal or ceramic components of such devices. Furthermore, in order to ensure that the copolymer has low water absorption, it was desired that the cumulative content of MAA units and glutaric anhydride units in the copolymer not exceed 20% by weight, preferably 10% by weight, based on the weight of the copolymer.

[0016] Summary of the Invention To overcome the drawbacks of International Publication No. WO 2017 / 097979, the inventors have conducted extensive research and surprisingly found that the content of free carboxylic acid groups in the copolymer obtainable by the polymerization of MMA and MAA can be dramatically increased by carefully adjusting the process conditions after the degassing step. In particular, when the copolymer mixture obtained in the polymerization step is devolatilized in a devolatilization unit comprising at least one copolymer mixture feed port, and at least one degassing device, comprising at least one degassing zone, at least one gas outlet, at least one copolymer melt outlet and a degassing device, and at least one melt outlet die it is important to adjust the temperature Tv (Tv is given in °C) of the copolymer melt in the last degassing zone, the temperature To (To is given in °C) of the copolymer melt entering the melt outlet die, and the total residence time t (t is given in seconds) of the copolymer melt in seconds between the last degassing zone and the melt outlet die of the degassing unit such that the monomial 4.981·E-06·t·exp(0.0517·(1.5·Tv+0.5·To) / 2) 4.981·10 -8 ·t·exp(0.0517·(1.5·Tv+0.5·To) / 2) is less than 8, preferably less than 6, even more preferably less than 4, and particularly preferably less than 2. If the above monomial is greater than 8, substantial formation of glutaric anhydride units occurs, and thus the resulting copolymer has a reduced content of methacrylic acid units relative to the content of monomer methacrylic acid in the monomer mixture of polymerization step (a).

[0017] Under these process conditions, the undesired intramolecular cyclization reaction that forms glutaric anhydride units from MAA units and adjacent MMA units in the copolymer can be efficiently suppressed. Therefore, the final copolymer has a particularly high content of free carboxylic acid groups. Furthermore, the copolymer has high heat resistance and excellent optical properties, particularly low haze and substantially zero yellowness. As used herein, the expressions "high heat resistance" and "low heat resistance" indicate that the copolymer has a high / low Vicat softening temperature (ISO 306 - B50).

Brief Description of the Drawings

[0018] Figure 1 schematically shows an example of the degassing device used in the degassing step (c).

[0019] Detailed Description of the Invention The method of the present invention comprises at least a polymerization step (a), followed optionally by a heating step (b), and then followed by a degassing step (c).

[0020] In the polymerization step (a), 80.0 - 99.9% by weight, preferably 85.0 - 98.0% by weight of MMA, 0.1 - 20.0% by weight, preferably 2.0 - 8.0% by weight of a compound of formula (I):

Chemical Formula

[0021] As used herein, the term “copolymer mixture” refers to a mixture comprising a copolymer and a volatile component. The “volatile component” includes MMA, a compound represented by formula (I), and optionally a monomer selected from methyl acrylate, ethyl acrylate, or styrene. Furthermore, the “volatile component” may optionally include a solvent, methanol, and water.

[0022] The form of the copolymer mixture obtained in step (a) is not particularly limited and varies depending on the reaction conditions and the type of polymerization. Polymerization in step (a) can be bulk polymerization, solution polymerization, dispersion polymerization, or suspension polymerization. Therefore, the copolymer mixture can be a copolymer solution (sometimes called copolymer syrup), a copolymer dispersion, or a copolymer suspension.

[0023] In the optional heating step (b), the copolymer mixture obtained in the polymerization step (a) is heated to a temperature of 100°C to 300°C in a heating unit.

[0024] Next, in the degassing step (c), At least one copolymer mixture supply port, At least one degassing device, At least one degassing zone, At least one gas outlet, At least one copolymer melt outlet A degassing device, and At least one molten material outlet die and In a degassing unit containing the following, volatile components are removed from the copolymer mixture. Temperature Tv of the copolymer melt in °C at the final degassing zone with respect to the conveying direction of the copolymer melt. The temperature of the copolymer molten material entering the molten material outlet die in °C, and The total residence time t of the copolymer molten material in seconds between the last degassing zone and the molten material outlet die of the degassing unit is given by a monomial: 4.981·10 -8 ·t·exp(0.0517·(1.5·Tv+0.5·To) / 2) However, it is adjusted to be less than 8, preferably less than 6, even more preferably less than 4, and especially preferably less than 2.

[0025] As used herein, the term “copolymer melt outlet” refers to the outlet of a degassing device. In contrast, the term “molten outlet die” refers to the outlet of the entire degassing unit. After exiting the meltten outlet die, the copolymer melt is typically cooled to a temperature of 150°C or less, preferably below 100°C, and pelletized.

[0026] The copolymer melt temperature Tv in °C in the final degassing zone is measured in the central part of the degassing zone. For practical reasons, the sensor for measuring Tv is located no more than 10 mm above the polymer melt in the final degassing zone, preferably no more than 5 mm above. The copolymer melt temperature To in °C is measured in the center of the inlet of the melt outlet die.

[0027] Steps (a) through (c) are described below.

[0028] Polymerization step (a) Radical copolymerization of monomer mixtures containing MMA and MAA is well known in the prior art. Polymerization step (a) can be carried out in a manner that includes the monomer mixture, a polymerization initiator, and optionally a chain transfer agent, and is substantially free of solvent (bulk polymerization). Alternatively, a solvent capable of dissolving the copolymer may be present or added during polymerization (solution polymerization). Polymerization can also be carried out in a dispersion medium in which the monomers are dispersed in water or an aqueous mixture.

[0029] In one preferred embodiment, the monomer mixture in step (a) is MMA with a weight of 80.0-99.5%, preferably 85.0-98.0%, 0.5 to 20.0% by weight, preferably 2.0 to 8.0% by weight, of formula (I): [ka] [Substituent R 1 [This is either a hydrogen atom or a hydrocarbon group having 1 to 6 carbon atoms.] Compounds represented by, and optionally A monomer selected from methyl acrylate, ethyl acrylate, or styrene, in an amount of 0.0 to 19.5% by weight, preferably 0.0 to 7.0% by weight. Includes.

[0030] When one or more optional monomers are present in the copolymer, the amount of MMA monomer can typically be adjusted accordingly.

[0031] Therefore, the copolymer obtained is typically, Repeating units derived from MMA in an amount of 80.0-99.5% by weight, preferably 85.0-98.0% by weight. 0.5 to 20.0% by weight, preferably 2.0 to 8.0% by weight, of formula (I): [ka] [Substituent R 1 [This is either a hydrogen atom or a hydrocarbon group having 1 to 6 carbon atoms, preferably a methyl group.] Repeating units derived from compounds represented by, and optionally 0.0 to 19.5% by weight, preferably 0.0 to 7.0% by weight, of repeating units derived from methyl acrylate, ethyl acrylate, or styrene. Includes.

[0032] In one embodiment, step (a) is carried out as bulk polymerization, i.e., without the addition of a solvent. In a further embodiment, step (a) is carried out with a solvent, i.e., as solution polymerization. When solution polymerization is used, the solvent used in step (a) is not particularly limited, as long as it can dissolve the copolymer at the polymerization temperature described above and does not hinder the polymerization process except for some slight chain transfer. One or more solvents selected from aromatic hydrocarbons, ketones, ethers, esters, amides, and alcohols can be used. Examples of solvents that can be used include, but are not limited to, known organic solvents such as acetone, methyl ethyl ketone, methyl-n-butyl ketone, methyl isobutyl ketone, ethyl isobutyl ketone, tetrahydrofuran, dioxane, N,N-dimethylformamide, N,N-diethylformamide, N,N-dimethylacetamide, N,N-diethylacetamide, N-methylpyrrolidone, propylene glycol, 2-methoxy-2-propanol, and tetraglyceride. In particular, solvents selected from toluene, butyl acetate, ethyl acetate, xylene, dimethylfuran, or mixtures thereof are preferred.

[0033] If step (a) is carried out in a solvent, the solvent content in the reaction mixture is typically in the range of 1.0% to 60% by weight, more preferably 5.0% to 45% by weight, based on the total weight of the reaction mixture.

[0034] The monomer mixture in the polymerization reactor may optionally contain further additives selected from UV absorbers, UV stabilizers, lubricants, mold release agents, heat stabilizers, additives to increase scratch resistance, antistatic agents, and colorants such as pigments or dyes. These additives are described in detail below. Additives may be added to the polymerization reactor separately, or in mixtures with MMA, with the compound represented by formula (I), or, if present, with methyl acrylate, ethyl acrylate, or styrene.

[0035] It is even more preferable that the dissolved molecular air oxygen (O2) concentration of the reaction mixture in polymerization step (a) be controlled to 70 ppm or less so that the resulting copolymer has a particularly low haze and yellowness index. To further suppress discoloration, it is preferable that the dissolved oxygen concentration be less than 10 ppm. The dissolved oxygen concentration can be measured using a dissolved oxygen meter (for example, a DO meter B-505 as a galvanic oxygen sensor manufactured by Iijima Denshi Kogyo KK).

[0036] The selection of polymerization reactors for use in polymerization step (a) is not particularly limited. Polymerization reactors may include, or could include, a stirred-tank reactor operated discontinuously or continuously, a tubular reactor operated continuously, a loop reactor operated discontinuously or continuously, or any combination thereof, and if several reactors are used, they may be operated in parallel or connected sequentially.

[0037] Monomers can be added to the reactor as a mixture or as separate feeds. Polymerization step (a) can be carried out in a discontinuous reactor (batch) or semi-batch reactor type, with the initiator (if present), solvent, monomer, or any combination thereof optionally supplied during polymerization step (a). Alternatively, polymerization step (a) can be carried out in a continuous polymerization process in a stirred tank reactor (CSTR), tubular reactor or a combination thereof, kneader, or disc ring reactor.

[0038] In some embodiments, the copolymer reaction mixture from the outlet of the first CSTR can be sequentially fed to a second and / or third reaction device, such as a further CSTR or tubular reactor, to enhance the conversion. As used in this application, the term “conversion” refers to the average weight ratio of the copolymer formed in polymerization step (a) to the total monomer feed.

[0039] The conversion rate can be easily adjusted by those skilled in the art by adapting the average residence time of the reaction mixture in the reactor, the polymerization temperature, the reactivity of the initiator used, and the amount of initiator and monomer concentration in the reactor feed. For example, when CSTR is used, the average residence time is preferably selected in the range of 10 minutes to 7 hours, more preferably 20 minutes to 6 hours, for example, 30 minutes to 4 hours. An average residence time exceeding 7 hours is generally disadvantageous in terms of productivity and cost efficiency.

[0040] During polymerization step (a) in the CSTR, it is advantageous to maintain the polymerization temperature in the range of 60°C to 200°C, more preferably 70°C to 180°C, and particularly preferably 80°C to 170°C, in order to avoid an excessive increase in the viscosity of the reaction mixture in the reactor. The monomer conversion at the outlet of the CSTR is preferably maintained in the range of 30 to 70% by weight, based on the total weight of monomers added to the reaction mixture. If the polymer mixture outlet of the above CSTR is supplied to a second CSTR, the conversion of the second CSTR is preferably maintained in the range of 30% to 80% by weight.

[0041] In further embodiments, polymerization step (a) can be carried out in a tubular reactor. Both bulk polymerization and solution polymerization can be carried out continuously in a tubular reactor, with or without mixed elements. The monomer conversion at the outlet of the tubular reactor is preferably maintained in the range of 50 to 98% by weight, based on the total weight of monomers added to the reaction mixture. Conversion below 50% by weight makes this method uneconomical. On the other hand, the conversion should not exceed 98% by weight because it unnecessarily increases the average residence time in the tubular reactor. In particular, if the tubular reactor is operated in combination with another reactor and is the last polymerization reactor used in polymerization step (a), a more preferable range is 55 to 96% by weight, and a more preferable range is 60 to 94% by weight.

[0042] The average residence time of the reaction mixture in a tubular reactor is not particularly limited. For practical reasons, the average residence time is generally maintained in the range of 20 seconds to 8 hours. If the average residence time is shorter than 20 seconds, the conversion rate remains low. On the other hand, for productivity reasons, the average residence time in a tubular reactor should not exceed 9 hours.

[0043] As a method for adding a radical polymerization initiator to a tubular reactor, it is preferable to add the radical polymerization initiator together with the monomer and / or solvent feed. Equally preferable is a method in which the radical polymerization initiator is pre-mixed in a static mixer placed in series at the inlet of the tubular reactor and the mixture is passed through the tubular reactor. Furthermore, in order to ensure better control over the transformation and composition of the copolymer formed during polymerization step (a), it is possible and advantageous to add at least a portion of the monomer and / or solvent and / or the same or different types of initiators downstream along the tubular reactor.

[0044] Furthermore, to improve the control of the temperature rise of the reaction mixture, it is preferable to add a radical polymerization initiator at a position immediately before the reaction mixture inlet of the tubular reactor and optionally at one or more further positions within the reactor. This allows polymerization to proceed more effectively.

[0045] The copolymer content in the reaction mixture within the tubular reactor can typically be maintained in the range of 50-98% by weight, more preferably 60-96% by weight, and even more preferably 60-94% by weight, in order to ensure efficient polymerization.

[0046] It is advantageous to use radical polymerization initiators with a decay half-life of 0.05 to 90 minutes within the CSTR at polymerization temperature. A more preferred range is 0.05 to 60 minutes, and the most preferred range is 0.1 to 20 minutes. If the decay half-life is shorter than 0.05 minutes, the radical polymerization initiator decomposes before it can uniformly disperse in the polymerization reactor, reducing its efficiency (initiation efficiency). Increasing the amount of radical polymerization initiator reduces the heat resistance of the resulting copolymer. On the other hand, if the decay half-life is longer than 90 minutes within the CSTR, it becomes difficult to operate the polymerization stably. Furthermore, with a long decay half-life, the initiator concentration in the CSTR accumulates, which can make it difficult to control polymerization and the heat of polymerization generated, potentially leading to dangerous situations. This can result in a runaway polymerization temperature within the CSTR.

[0047] Furthermore, when polymerization is carried out further in a tubular reactor, it is preferable to add one or more radical polymerization initiators having a decay half-life of 0.1 to 8 hours at the reaction temperature of the tubular reactor. A more preferable range is 1 to 7 hours. A decay half-life of more than 8 hours for the radical polymerization initiator is undesirable because it becomes difficult to control the polymerization. On the other hand, a decay half-life that is too short is also undesirable because the decomposition of the radical polymerization initiator is too rapid, and the conversion does not increase sufficiently. As a result, copolymers with insufficient heat resistance will be produced. Therefore, it is preferable to use radical polymerization initiators having a decay half-life of 0.1 hours or more.

[0048] A single radical polymerization initiator may be used, or a mixture of two or more may be used. When using two or more radical polymerization initiators in a tubular reactor, it is preferable to use radical polymerization initiators whose decay half-live temperatures (at 10 hours) differ by 5°C or more. This allows polymerization step (a) to proceed more efficiently.

[0049] Radical polymerization initiators include, for example, organic peroxides such as tert.-butylperoxy-3,5,5-trimethylhexanoate, tert.-butylperoxylaurate, tert.-butylperoxyisopropyl monocarbonate, tert.-hexylperoxyisopropyl monocarbonate, tert.-butylperoxyacetate, 1,1-bis(tert.-butylperoxy)-3,3,5-trimethylcyclohexane, 1,1-bis(tert.-butylperoxy)cyclohexane, tert.-butylperoxy 2-ethylhexanoate, tert.-butylperoxyisobutyrate, tert.-hexylperoxy 2-ethylhexanoate, di-tert.-butylperoxide, 2,5-dimethyl-2,5-bis(tert.-butylperoxy)hexane, and lauroyl Peroxides, benzoyl peroxides, tert.-butylperoxyneodecanoates, tert.-butylperoxypivalates, tert.-butylperoxy-2-ethylhexanoates, tert.-butylperoxybenzoates, and dicumyl peroxides, azo compounds, such as 2-(carbamoylazo)isobutyronitrile, 1,1'-azobis(1-cyclohexanecarbonilate), 2,2'-azobisisobutyronitrile, 2,2'-azobis(2-methylbutyronitrile), dimethyl-2,2'-azobisisobutyrate, 2,2'-azobis(2,4,4-trimethylpentane), 2,2'-azobis(2-methylpropane), 2,2'-azobis-4-methoxy-2,4-dimethylvaleronitrile, and 2,2'-azobis-2,4-dimethylvaleronitrile, can be selected from the like.

[0050] The amount of radical polymerization initiator used in polymerization step (a) is adjusted according to the polymerization temperature, polymerization time (average retention time), and the intended conversion rate. This amount is preferably 0.001 to 2.0% by weight, based on the total weight of the reaction mixture in polymerization step (a). A more preferred range is 0.01 to 2.0% by weight, and an even more preferred range is 0.01 to 1.0% by weight.

[0051] For the purpose of controlling the molecular weight of the copolymer, it is often advantageous to add 0.001 to 2.0% by weight, more preferably 0.005 to 2.0% by weight, and even more preferably 0.01 to 1.0% by weight of a chain transfer agent based on the total weight of the reaction mixture in polymerization step (a). Suitable chain transfer agents themselves are well known in the prior art and can be selected from, for example, alkyl mercaptans, carbon tetrachloride, carbon tetrabromide, dimethylacetamide, etc. Examples of alkyl mercaptans used in polymerization step (a) include, in particular, n-octyl mercaptan, tert-dodecyl mercaptan, n-dodecyl mercaptan, n-tetradecyl mercaptan, n-octadecyl mercaptan, etc. Among these, it may be advantageous to use n-octyl mercaptan, n-dodecyl mercaptan, and methyl mercaptopropionate.

[0052] In one preferred embodiment, the copolymer mixture obtained in CSTR is sequentially fed into a tubular reactor to carry out further polymerization. This reduces the amount of volatile components that need to be removed in downstream steps, thereby making the overall process more cost-effective.

[0053] The method for supplying the copolymer mixture obtained in the CSTR to a second reactor, such as a second CSTR, a tubular reactor, or a tubular loop reactor, is not particularly limited. For example, the operation of drawing the reaction mixture from the first CSTR to the second reactor can be carried out using a pump. A known gear pump can be suitably used as the liquid transfer pump. When the reaction mixture is drawn in with a pump, the reaction mixture can be supplied stably to the second reactor, and the pressure in the second reactor, which optionally contains a series of static mixing structures, can be raised to a level higher than the vapor pressure of the reaction mixture. Further possibilities include transferring the reaction mixture from the CSTR to the second reactor by a pressure difference between the reactors.

[0054] The total conversion in polymerization step (a) is typically at least 40% by weight, more preferably at least 45% by weight. Conversion of less than 40% by weight is undesirable for economic reasons. On the other hand, a final conversion higher than 98% by weight is also undesirable for economic reasons because the polymerization time is too long. The preferred range is 40–96% by weight, and the more preferred range is 45–94% by weight.

[0055] Heating step (b) According to the present invention, the copolymer mixture obtained in polymerization step (a) can be supplied to an optional step (heating step (b)) in which the copolymer mixture is heated to a temperature of 100°C to 300°C. This can be advantageously carried out using a heat exchanger. The design of the heat exchanger is not particularly limited. The heat exchanger may be, for example, a tubular bundle of parallel-arranged tubes. Alternatively, the heat exchanger may be a plate heat exchanger.

[0056] A heat exchanger may optionally include a static mixing element or a stirrer. Examples of static mixing elements include Sulzer tubular mixers of SMX and SMR types, Kenics static mixers, and Toray tubular mixers. Alternatively, a heat exchanger may not include any mixing element.

[0057] Heating of the copolymer mixture can be optionally carried out by a jacket filled with hot oil, water, or steam, and / or alternatively by using an electric heating element.

[0058] Degassing step (c) Following the polymerization step (a), or an optional heating step (b), the copolymer mixture is then supplied to a degassing unit for a degassing step (c) to remove unreacted monomers, methanol, and volatile components such as solvents, if present. Step (c) is performed in a degassing unit comprising at least one copolymer mixture feed port, at least one degassing device, and at least one molten outlet die. The degassing device comprises at least one degassing zone, at least one gas outlet, and at least one copolymer molten outlet. Furthermore, as will be readily apparent to those skilled in the art, the degassing unit may include further elements such as conduits and molten filters located between the degassing device and the molten outlet die. For example, to minimize contamination of the copolymer by solid foreign matter, the degassing unit used in degassing step (c) may optionally include at least one molten filter located between the last degassing zone of the degassing device and the molten outlet die in the direction of copolymer molten transport.

[0059] A molten filter is a device typically installed in the copolymer molten flow path within a molten conduit and is equipped with a mesh sieve. The mesh sieve may be made of stainless steel and typically contains various connected sieve layers. The molten filter is designed to remove small solid contaminants from the copolymer molten material. For continuous operation, it is even more advantageous to use an automated cleaning molten filter, also known as a double-piston screen changer, such as the RSFGENIUS series molten filters commercially available from Gneuss or the KSWE series molten filters commercially available from Nordson-BKG. A molten filter equipped with a molten sieve typically has a hold-up volume filled with the flowing copolymer molten material. The hold-up of the molten filter contributes to the residence time t of the copolymer molten material after the final degassing zone.

[0060] The temperature of the copolymer mixture in the degassing step is typically less than 300°C, more preferably 150°C to 300°C, and even more preferably 170°C to 290°C. The preferred pressure in the final defoliation zone of the degassing step is an absolute pressure, typically less than 500 mbar, more preferably less than 300 mbar. The lower limit of the absolute pressure in the degassing step is not limited, but for technical reasons, it is usually at least 1 mbar. For example, it is advantageous that the absolute pressure in the final defoliation zone of the degassing device with respect to the conveying direction of the copolymer molten material can be adjusted to a range of 1 mbar to 300 mbar, preferably 10 mbar to 200 mbar, or between 1 mbar and 300 mbar, preferably 10 mbar to 200 mbar.

[0061] If the pressure in the degassing step exceeds 500 mbar, even if defoliation is carried out within the temperature range, it is typically not possible to efficiently separate or remove unreacted monomers or mixtures consisting of unreacted monomers and polymerization solvents (if present). This is disadvantageous in terms of the heat resistance, as well as the mechanical and optical properties of the resulting copolymer.

[0062] The degassing device in degassing step (c) is not particularly limited and may be selected from a degassing extruder, a degassing kneader, and one or more static flash chambers. In particular, it is advantageous to use a single-screw or twin-screw degassing extruder, a static flash chamber, a degassing kneader, or a combination thereof. One embodiment may be used which has a cylindrical container and a stirrer having a plurality of stirring elements attached to a rotating shaft, and which has at least one degassing hole at the top of the cylindrical portion, a copolymer mixture supply port for supplying the copolymer mixture at one end of the cylindrical portion, and a copolymer melt outlet at the other end for removing the copolymer melt after defoliation is complete. The number of rotating shafts is not particularly limited but is usually 1 to 5, preferably 1 or 2, and an apparatus having 2 rotating shafts is more preferred. In particular, vented continuous single-screw or twin-screw extruders (kneaders and batch-type molten mixers) are preferred, and here, single-screw extruders, twin-screw extruders, twin / screw combined continuous kneading extruders, and tri-screw extruders, as well as continuous kneaders or batch-type kneaders, each having one or more "Unimelt" type shafts, may be mentioned. Among these, vented single-screw or twin-screw extruders, or continuous twin-screw reactors having multiple convex lens type and / or elliptical plate paddles, can be preferably used.

[0063] Furthermore, the degassing step (c) in the manufacturing method of the present invention can be carried out using a method that employs two or more defoliation devices arranged in series, which is advantageous because it can further reduce the remaining volatile components in the copolymer molten product obtained after defoliation.

[0064] After exiting the degassing device of the degassing unit, the material typically passes through further elements such as molten conduits and molten filters, and finally exits the degassing unit through a molten outlet die.

[0065] According to the present invention, The temperature Tv of the copolymer melt in °C at the final degassing zone with respect to the transport direction of the copolymer melt (Tv is given in °C), The temperature of the copolymer molten material at the molten material outlet die in °C, To (where To is given in °C), and The total residence time t (where t is given in seconds) of the copolymer molten material between the last degassing zone and the molten material outlet die of the degassing unit is given by a monomial: 4.981·10 -8 ·t·exp(0.0517·(1.5·Tv+0.5·To) / 2) However, it is adjusted to be less than 8, preferably less than 6, even more preferably less than 4, and especially preferably less than 2. The copolymer melt temperature Tv in °C in the last degassing zone is measured in the central part of the degassing zone. The copolymer melt temperature To in °C is measured in the center of the inlet of the melt outlet die.

[0066] The key is that by maintaining the number of monomials below 8, preferably below 6, even more preferably below 4, and especially preferably below 2, the undesirable formation of glutaric acid anhydride units in the polymer chain can be efficiently suppressed, and thus the copolymer exiting the molten material outlet die has a high content of free carboxylic acid functional groups. After exiting the molten material outlet die, the copolymer molten material usually undergoes rapid cooling and pelletization. This also ensures a high content of free carboxylic acid functional groups.

[0067] Despite the above, the inventors have found that the undesirable formation of glutaric anhydride units can be further suppressed when the temperature Tv of the copolymer melt in °C in the final degassing zone and the temperature To of the copolymer melt entering the melt outlet die in °C are adjusted so that the monomial (1.5·Tv+0.5·To) / 2) is maintained in the range of 230-290°C or between 230°C and 290°C. In many cases, at temperatures above 290°C, the formation of glutaric anhydride units results in a significant consumption of carboxylic acid functional groups in the copolymer, accompanied by the formation of methanol and water. As a result, the adhesion properties of the copolymer on metal or ceramic surfaces are impaired to some extent. On the other hand, at melting temperatures below 230°C, the defoliation rate of the copolymer is often found to be insufficient, and the copolymer melt exiting the melt outlet die contains an increased amount of volatile organic compounds. This adversely affects the heat resistance of the final product.

[0068] The residence time t of the copolymer melt between the final degassing zone and the melt outlet die of the degassing unit can be adjusted by adapting the length of the melt conduit, as well as the number of optional elements such as melt filters and melt sieves. A shorter residence time t is generally advantageous because it suppresses the unwanted formation of glutaric acid anhydride units. For practical reasons, the total residence time t of the copolymer melt in seconds between the final degassing zone and the melt outlet die with respect to the conveying direction of the copolymer melt is typically adapted to be in the range of 10 to 200 seconds, or within the range of 10 to 200 seconds. The melt outlet die usually has a relatively small hold-up volume filled with polymer melt. The melt outlet die may optionally have a jacket that can be heated or cooled.

[0069] In order to further minimize the formation of glutaric anhydride units, after exiting the melt outlet die, the final copolymer melt preferably undergoes solidification and pelletization within 10 seconds, preferably within 5 seconds. As used herein, the term "solidification" refers to cooling to a temperature of 150 °C or less, preferably less than 100 °C.

[0070] Molded composition In a further aspect, the present invention relates to a molded composition obtainable (or obtained) by the above method. The molded composition comprises at least 80% by weight, preferably at least 90% by weight, of a copolymer, the copolymer comprising 80.0 to 99.9% by weight, preferably 85.0 to 98.0% by weight, of repeating units derived from MMA, 0.1 to 20.0% by weight, preferably 2.0 to 15.0% by weight, and more preferably 2.0 to 8.0% by weight, of a compound of formula (I):

Chemical formula

[0072] As outlined earlier, the method of the present invention efficiently suppresses the undesirable intramolecular cyclization reaction that forms glutaric acid anhydride units represented by formula (II) from MAA units in the copolymer. As a result, the formation of methanol and water as byproducts during degassing of the copolymer melt is also suppressed. Furthermore, under preferred degassing conditions, unreacted monomers such as MMA and MAA can be efficiently removed, and therefore their concentrations in the final copolymer are also reduced. Thus, the copolymer melt exiting the melt outlet die of the degassing unit has particularly low content of volatile compounds. Such materials cannot be obtained using methods of the prior art.

[0073] In particular, the molding composition may contain methanol at a low level of less than 1400 ppm, preferably 1000 ppm or less, based on the total weight of the molding composition.

[0074] It is also advantageous that the molding composition contains 1800 ppm or less, preferably 1500 ppm or less, of MAA based on the total weight of the molding composition.

[0075] Furthermore, it is advantageous that the molding composition of the present invention contains 5000 ppm or less, preferably 4000 ppm or less of MMA, based on the total weight of the molding composition.

[0076] The mass-average molecular weight Mw of the copolymer is not particularly limited, but is typically about 40,000 to 500,000 g / mol, more preferably 60,000 to 400,000 g / mol. The number-average molecular weight Mn of the copolymer is preferably 20,000 to 150,000 g / mol, more preferably 25,000 to 100,000 g / mol. The determination of Mw and Mn can be carried out by gel permeation chromatography (GPC), for example, using PMMA as a calibration standard and tetrahydrofuran (THF) with 0.2 volume% trifluoroacetic acid (TFA) as the eluent. Instead of using a calibration standard, a scattering detector can also be used for copolymers with Mw greater than 100,000 g / mol (see HF Mark et al., Encyclopaedia of Polymer Science and Engineering, 2nd Edition, Vol. 10, page 1 et seq., J. Wiley, 1989). Those skilled in the art can easily select a suitable GPC column, such as an HPS column. Such columns are commercially available, for example, as the PSS SDV series columns from PSS Standards Service GmbH (Mainz, Germany). As is easily understood, combinations of several GPC columns can also be used.

[0077] Since the cyclization of MAA units in step (c) of the method is reduced, formula (II) in the copolymer: [ka] The weight of the repeating unit represented by equation (I): [ka] The ratio of the weight of the repeating units derived from the compound represented by to the weight of the compound is less than 0.2, preferably less than 0.1.

[0078] Further additives The molding composition of the present invention may further contain at least one common polymer additive, provided that this does not subsequently adversely affect the optical and adhesive properties of the copolymer of the present invention. Various polymer additives are well known to those skilled in the art and include, among others, impact modifiers, UV absorbers, UV stabilizers, light stabilizers, antioxidants, colorants, flow improvers, pigments, flame retardants, lubricants and release agents, scattering particles, scratch improving aids, heat stabilizers, antistatic agents, and additives for increasing scratch resistance. The heat resistance of the resulting molding composition should not be excessively impaired by these additives.

[0079] Additives can be added at any step of the manufacturing process, provided their presence does not interfere with the process. For example, additives such as UV absorbers, lubricants, mold release agents, and colorants such as pigments or dyes are often added to the reaction vessel together with the monomer or separately during the polymerization step (a). As a further possibility, these additives may be added to the copolymer melt in or after the degassing device in the degassing step (c).

[0080] UV absorbers and UV stabilizers UV absorbers, UV stabilizers, and light stabilizers for use in the present invention are well known and are described in detail, for example, in Hans Zweifel, Plastics Additives Handbook, Hanser Verlag, 5th Edition, 2001, p. 141 onwards. UV stabilizers are understood to include UV stabilizers and free radical scavengers. Free radical scavengers are sterically hindered phenols such as, for example, but not limited to, octadecyl-3-[3,5-di-tert-butyl-4-hydroxyphenyl]propionate, pentaerythritol tetrakis[3-[3,5-di-tert-butyl-4-hydroxyphenyl]propionate, and salicylates. UV absorbers can be derived, for example, from the group of substituted benzophenones, salicylates, cinnamates, oxanilides, benzoxazinones, hydroxyphenylbenzotriazoles, benzotriazoles, triazines, or benzylidene malonates. Examples of hydroxyphenylbenzotriazoles include 2-(2H-benzotriazole-2-yl)-p-cresol, marketed as Tinuvin® P or drometrizole; tetraethyl-2,2'-(1,4-phenylenedimethylidine)bismalonate, marketed as Hostavin® B-CAP; and n-(2-ethoxyphenyl)-n'-(4-ethylphenyl)-ethylenediamide, marketed as Tinuvin® 312. The total content of UV absorbers in the molded composition is typically in the range of 0.01% to 1.0% by weight, particularly 0.01% to 0.5% by weight, and especially 0.02% to 0.2% by weight, based on the weight of the molded composition.

[0081] UV absorbers may be present in the molded composition as low molecular weight compounds. However, UV absorbing groups in the matrix copolymer molecule can also be covalently bonded after copolymerization with polymerizable UV absorbing compounds, such as acrylic, methacrylic, or allyl derivatives of benzophenone or benzotriazole derivatives. As will be readily apparent to those skilled in the art, mixtures of chemically different UV absorbers, such as benzotriazole combined with triazine, can also be used.

[0082] The most well-known representative examples of UV stabilizers / free radical scavengers are provided by the group of hydroxyphenylbenzotriazoles or sterically hindered amines (hindered amine light stabilizers, HALS). Examples of preferred free radical scavengers / UV stabilizers include, among others, sterically hindered phenols and sterically hindered amines known as HALS (hindered amine light stabilizers). The tetramethylpiperidine group present in the HALS compounds is responsible for their stabilizing effect. Compounds in this class may be unsubstituted or substituted with an alkyl or acyl group on the piperidine nitrogen. Sterically hindered amines do not absorb in the UV range. They, again, scavenge formed free radicals that UV absorbers cannot capture. Free radical scavengers / UV stabilizers are used in compositions according to the present invention in amounts of 0.01% to 1.5% by weight, particularly 0.02% to 1.0% by weight, and especially 0.02% to 0.5% by weight, based on the weight of the molded composition. Combinations of UV stabilizers / absorbers, light stabilizers, and antioxidants are also possible.

[0083] Heat processing color stabilizer Suitable heat-processing color stabilizers are not particularly limited and may be selected from, for example, triphenyl phosphate, tris-(2,4-di-tert-butylphenyl)-phosphate, tris-(2,5-di-tert-butylphenyl)-phosphate, triphenyl phosphite, or tris-(2,4-di-tert-butylphenyl)-phosphite.

[0084] scattering particles In some embodiments of the present invention, the molded composition may further comprise organic or inorganic scattering particles dispersed in a polymer matrix. The selection of scattering particles is not particularly limited, but they are typically selected such that the refractive index of the scattering particles differs from the refractive index of the copolymer matrix by at least 0.01. The refractive index can be measured at 23°C with a 589 nm Na D line, as specified in standard ISO 489 (1999).

[0085] Scattered particles typically have a weight-average particle diameter of 0.1 μm to 100.0 μm. This is known as volume-average d 50 The weight-average particle diameter of scattered particles, expressed as a value (i.e., 50% of the particles having a particle size smaller than the specified average particle size), can be measured in accordance with ISO 13320-1 (2009), the standard for laser diffraction measurements. Typically, the size of scattered particles is determined in each case by laser light scattering (at room temperature of 23°C) in dry powder form using a Beckman Coulter LS 13 320 laser diffraction particle size analyzer, which is a tornado dry powder system. The measurement is performed as described in the manual. Mie is used as the computer-aided analysis model.

[0086] The inorganic scattering particles may include conventional inorganic opacifiers, such as barium sulfate, calcium carbonate, titanium dioxide, or zinc oxide.

[0087] Organic scattering particles are typically spherical scattering beads made of crosslinked polymer materials such as polyalkyl (meth)acrylate, silicone, and polystyrene. For the purposes of this invention, the term “spherical” means that it is preferable for the scattering beads to have a spherical shape, but it will be apparent to those skilled in the art that scattering beads may have several other shapes as a result of the manufacturing method, or that the shape of the scattering beads may deviate from the ideal spherical shape. Therefore, the term “spherical” means that the ratio of the maximum dimension to the minimum dimension of the scattering beads is 4 or less, preferably 2 or less, and these dimensions are measured through the centroid of the scattering beads, respectively. Based on the number of scattering beads, at least 70%, and especially at least 90%, are preferably spherical.

[0088] Preferred scattering beads, composed of cross-linked polystyrene, are commercially available from Sekisui Plastics Co., Ltd. under the trademarks Techpolymer® SBX-4, Techpolymer® SBX-6, Techpolymer® SBX-8, and Techpolymer® SBX-12.

[0089] Other particularly preferred spherical plastic particles used as scattering agents include cross-linked silicones. Silicone scattering agents particularly preferred in the present invention can be obtained from Momentive Performant Materials Inc. as TOSPEARL® 120 and TOSPEARL® 3120.

[0090] Impact resistance modifier When a thermoplastic copolymer contains an impact modifier, the mechanical properties of the molded composition can be further adjusted to suit the desired purpose. Impact modifiers themselves for use in the present invention are well known and may have different chemical compositions and different copolymer structures. Impact modifiers may be crosslinked or thermoplastic. Furthermore, impact modifiers may be in particulate form as core-shell particles or core-shell-shell particles. Typically, particulate impact modifiers have an average particle diameter of 20 nm to 500 nm, preferably 50 nm to 450 nm, more preferably 100 nm to 400 nm, and most preferably 150 nm to 350 nm. In this context, “particulate impact modifier” means a crosslinked impact modifier generally having a core structure, core-shell structure, core-shell-shell structure, or core-shell-shell-shell structure. The average particle diameter of particulate impact modifiers can be determined by methods known to those skilled in the art, for example, by photon correlation spectroscopy according to standard DIN ISO 13321:1996.

[0091] In its simplest form, the particulate impact modifier is a crosslinked particle obtained by emulsion polymerization, with an average particle diameter in the range of 10 nm to 150 nm, preferably 20 nm to 100 nm, and more preferably 30 nm to 90 nm. These generally consist of at least 20.0% by weight, preferably 20.0% to 99.0% by weight, and particularly preferably 30.0% to 98.0% by weight of butyl acrylate, and 0.1% to 2.0% by weight, preferably 0.5% to 1.0% by weight of a crosslinkable monomer, such as a polyfunctional (meth)acrylate, such as allyl methacrylate, and optionally other monomers, such as 0.0% to 10.0% by weight, preferably 0.5% to 5.0% by weight of C1-C4 alkyl methacrylate, such as ethyl acrylate or butyl methacrylate, preferably methyl acrylate, or other vinyl polymerizable monomers, such as styrene.

[0092] A three-layer or three-phase structure having a core and two shells can be prepared as follows: The innermost (hard) core can consist of, for example, MMA, a small proportion of comonomers, such as ethyl acrylate, and a certain proportion of crosslinking agents, such as allyl methacrylate. The intermediate (soft) shell can consist of, for example, a copolymer containing butyl acrylate and optionally styrene, while the outermost (hard) shell is the same as the matrix polymer, thus providing compatibility and good bonding to the matrix. The proportion of polybutyl acrylate in the core or shell of the impact-resistant modifier in a two- or three-layer core-shell structure is decisive for the impact-resistant modifier effect and is preferably in the range of 20.0% to 99.0% by weight, particularly preferably in the range of 30.0% to 98.0% by weight, and even more preferably in the range of 40.0% to 97.0% by weight, based on the total weight of the impact-resistant modifier.

[0093] Thermoplastic impact modifiers have a different mechanism of action than particulate impact modifiers. They are generally mixed with a matrix material. When domains are formed, for example, in the case of block copolymers, the preferred size for these domains is a size that can be determined, for example, by electron microscopy, and corresponds to the preferred size of core-shell particles.

[0094] A further class of thermoplastic polymers for use according to the present invention as impact resistance modifiers is methacrylate-acrylate block copolymers, particularly acrylic TPEs, which include PMMA-poly-n-butyl acrylate-PMMA triblock copolymers, commercially available, for example, by Kuraray under the product name Kurarity®. The poly-n-butyl acrylate blocks form nanodomains having a size of 10 nm to 20 nm in the copolymer matrix.

[0095] Lubricants and release agents that can reduce or completely prevent the possibility of the molding composition adhering to the injection molding die are important to the injection molding process and may be used. For example, C 20 Less than C 16 ~C 18 A saturated fatty acid, ester, or inorganic salt having carbon atoms, or C 20 Less than C 16 ~C 18 A lubricant selected from the group consisting of saturated fatty alcohols having carbon atoms may be present as an auxiliary agent. Examples include stearic acid, stearyl alcohol, palmitic acid, palmitic acid alcohol, lauric acid, lactic acid, glycerol monostearate, pentaerythritol, and industrial mixtures of stearic acid and palmitic acid. Also suitable are n-hexadecanol, n-octadecanol, and industrial mixtures of n-hexadecanol, n-octadecanol, and glycerol monostearate. A particularly preferred lubricant or release agent is stearyl alcohol. The lubricant is typically used in an amount of 1.0% by weight or less, for example, 0.05% to 0.25% by weight, based on the weight of the molded composition.

[0096] The melt viscosity of the copolymer composition can be reduced by optionally using a fluidity improver. These typically consist of oligomers or can be selected from the group consisting of saturated fatty alcohols or fatty acids, polyethylene glycol, and saturated fatty acids, esters, or inorganic salts, preferably having 16 or more carbon atoms of glycerol monostearate. The fluidity improver is typically used in an amount of 5.0% by weight or less, for example, 0.5% to 4.0% by weight, based on the weight of the molded composition.

[0097] The molding compositions of the present invention can be optionally colored in a variety of colors using soluble organic dyes. Typically, perinone, azo, and anthraquinone type dyes are used for this purpose due to their commercial availability and bright colors. As used in this application, the term “soluble” means that the dye is soluble in the matrix of the thermoplastic copolymer in the amount used to color it. Thus, the colored molding composition is a thermoplastic composition containing an organic dye uniformly distributed in the matrix of the thermoplastic polymer.

[0098] The molding composition of the present invention has excellent transparency and a substantially cloudless, transparent appearance. In particular, the haze of the molding composition, measured at 23°C on an injection-molded test specimen with a thickness of 3.0 mm according to standard ASTM D1003 (2013), is typically less than 5%, preferably less than 3%, more preferably less than 2%, and especially preferably less than 1%.

[0099] Furthermore, the molding composition without coloring additives or coloring pigments was measured at 23°C in an injection-molded test specimen with a thickness of 3.0 mm, and its light transmittance T was measured according to DIN 5033-7 (2014). D65 It is preferable that this be shown in the range of 85% to 93%, more preferably in the range of 87% to 92%.

[0100] DIN 6167(1980)(Light source D 65 The yellowness index of a molded composition without coloring additives or pigments, which can be determined by a layer thickness of 3.0 mm and a temperature of 10°C, should preferably be less than 7, more preferably less than 5, when measured at 23°C on an injection-molded test piece with a thickness of 3.0 mm without the addition of coloring agents or pigments.

[0101] The Vicat softening temperature of the molded composition according to ISO 306-B50 (2014) is advantageous to be at least 105°C, preferably at least 110°C, and more preferably at least 115°C.

[0102] The nominal elongation at break of a molded composition without impact modifiers, according to ISO 527 (2012), should preferably be at least 2.0%, and particularly preferably 2.5% or more.

[0103] According to ISO 527 (2012), the modulus of elasticity of the molded composition is advantageously greater than 3000 MPa, preferably greater than 3500 MPa, in the absence of an impact resistance modifier.

[0104] Due to its advantageous rheological properties, the molding composition of the present invention is highly suitable for the manufacture of optical elements by injection molding. The composition of the present invention is typically measured at 230°C and 3.8 kg according to ISO 1133 (2012) and yields 0.2 cm². 3 / More than 10 minutes, preferably 0.4 cm 3 / 10 minutes or more, most preferably 0.6 cm 3 / 10 minutes~15.0cm 3 It has a melt volume rate MVR in the range of / 10 minutes.

[0105] The molding composition of the present invention can be thermoplasticized to molded articles by common methods such as injection molding and extrusion. Injection molding of the composition can be carried out by known methods at a temperature in the range of 200°C to 300°C (melting temperature) and preferably at a mold temperature of 60°C to 120°C. Extrusion is preferably carried out at a temperature of 200°C to 280°C.

[0106] Due to their high heat resistance, low haze, and high content of free carboxylic acid groups, the molded compositions and articles made therefrom are very suitable for optical applications where acrylic elements are firmly bonded to metal or ceramic elements. For example, such applications include optoelectronic devices, preferably light-emitting diodes, optical sensors, or solar cells; optical elements; optical lenses; light guides; lamp covers, black pillar trims, preferably for interior lighting systems or automotive lighting equipment; and covers for automotive lights. The molded compositions of the present invention are further advantageous for use in communication devices, in particular PDAs, mobile phones, preferably smartphones; tablet PCs; TV devices; kitchen appliances, streetlights, and displays for other electronic devices.

[0107] The following examples illustrate the present invention in detail. However, the present invention is not intended to be limited to these examples.

[0108] Examples analysis GPC measurement conditions Eluent: THF (HPLC grade) + 0.2 vol% TFA Flow rate: 1ml / min Injection volume: 100 μL Detection: RI HPS Sample solution concentration: 2 g / l Standard: PMMA

[0109] Product properties Test specimens with a thickness of 3.0 mm were prepared by injection molding at 250°C, and then stored for 72 hours at 23°C and 50% relative humidity before measurement.

[0110] Hayes were determined using the BYK Gardner hazemeter Hazegard-plus according to ASTM D 1003 (1997).

[0111] The Vicat softening temperature (VST) ISO 306-B50 (2014) was measured using a 3.0 mm thick specimen that had been stored at 100°C for 16 hours prior to measurement.

[0112] Copolymer composition Determination of the amount of methanol residue in the final copolymer Calibration method: external standard Preparation of copolymer solutions for analysis: 1000 mg of copolymer was weighed into an Erlenmeyer flask, and 20 ml of N,N-dimethylformamide (DMF) was added. The sample was dissolved overnight by shaking, and the methanol content was determined by gas chromatography (GC).

[0113] Determination of monomer MMA residue in the final copolymer Calibration method: external standard Preparation of copolymer solutions for analysis: 1000 mg of copolymer was weighed into an Erlenmeyer flask, and 20 ml of DMF was added. The sample was dissolved overnight by shaking, and the MMA residue content was determined by GC.

[0114] GC analysis using headspace gas chromatography Chromatography: Perkin Elmer's Clarus 500 or 600 series with TurboMatrix headspace sampler. Detector: FID Headspace: Tracking force: 123kPa Injector pressure: 137.9 kPa Sample temperature: 80℃ Needle temperature: 120℃ Transition temperature: 120℃ Thermostat time: 20 minutes Pressurization time: 1 minute Installation time: 0.2 minutes Cycle time: 15.5 minutes Column: Megabore FFAP, 530 μm × 30 + 30 m, Separation phase: polyethylene glycol containing nitroterephthalic acid, Carrier gas: Nitrogen Temperature: Column: 55℃ Injector: 130℃ Detector: 250℃ Analysis time: 8.5 minutes The content was calculated using software based on calibration constants.

[0115] Determination of the amount of monomer MAA remaining in the final copolymer Calibration method: external standard Preparation of copolymer solutions for analysis: Two g of copolymer was dissolved in 50 ml of acetone, and 5 ml of this solution was added to 20 ml of a methanol / water mixture in a 70:30 ratio. 5 ml of this solution was then added to 20 ml of ultrapure water, and the MAA residue content was determined by high-performance liquid chromatography (HPLC).

[0116] HPLC analysis using Agilent HPLC devices Detector: UV200nm Column: Nucleosil 100-7, C18, 125 x 4.6 mm Eluent: Methanol / H3PO4 pH2=20:80 Flow rate: 2ml / min Sample volume: 50 μl The content was calculated using software based on peak area and calibration constants.

[0117] Determination of MAA units and glutaric acid anhydride units in the final copolymer A two-step analysis including a hydrolysis step was performed as follows: Titration before hydrolysis: 0.5 g of copolymer was dissolved in 80 ml of pyridine at 50°C, and the solution was titrated. Each measurement was accompanied by two blank feed measurements (using the same procedure, but without the copolymer sample).

[0118] Titration after hydrolysis: 0.5 g of copolymer was dissolved in 40 ml of pyridine at 50°C. 15 ml of desalted water was added, and the mixture was held at 98°C for 2 hours for hydrolysis. Another 40 ml of pyridine was added, the mixture was homogenized, and titrated. Each measurement was accompanied by two blank feed measurements (using the same procedure, but without the copolymer sample).

[0119] Titration device: Metrohm AG 808 Titrando Composite glass electrode (LiCl in ethanol) Titrating agent: Tetramethylammonium hydroxide (TMAH) as an alcohol solution 0.1 mol / l (0.1 N) The acid value was calculated as follows:

[0120] Acid value AV1 before hydrolysis (expressed in mgKOH / g): AV1=((V1-BW)·θ·5.6106) / E,mgKOH / g Acid value AV2 after hydrolysis (expressed in mgKOH / g): AV2=((V2-BW)·θ·5.6106) / E,mgKOH / g During the ceremony, V is the amount of titrant consumed per ml (V1 before hydrolysis and V2 after hydrolysis), BW is the titrant consumption per ml for the solvent (blank feed measurement). θ is the titration coefficient of the titrant, E is the sample weight in grams.

[0121] The MAA units and glutaric acid anhydride units were calculated as follows: Glutaric anhydride unit content by weight % = AV glutaric anhydride units · 100 / 727.9 In the formula, the unit of AV glutaric anhydride = (AV2 - AV1)·2 MAA content in weight percent = AV MAA·100 / 651.7 In the formula, AV MAA = AV2 - AV glutaric acid anhydride units

[0122] Starting materials The following starting materials were used: MMA, over 99.6% by weight purity (manufactured by Roehm GmbH, Darmstadt, Germany) MAA, over 99.6% by weight purity (manufactured by Roehm GmbH, Darmstadt, Germany)

[0123] kinetic studies The formation of glutaric anhydride units in MMA-MAA copolymers as a function of temperature and residence time was investigated.

[0124] Two MMA-MAA copolymers, each containing 96% and 95% by weight of MMA and 4% and 5% by weight of MAA, were prepared on a laboratory scale in a continuous stirred-tank reactor at a polymerization temperature of 140°C, with a 45% conversion and a residence time of 40 minutes in the reactor. The copolymer mixture, in the form of a copolymer syrup containing 45% by weight of copolymer, was then heated to 210°C and fed into a laboratory single-screw extruder with a shaft diameter of 18 mm. Degassing was performed in the final degassing zone (vacuum zone) at an absolute pressure of 40 mbar and 250°C (barrel temperature). The copolymer molten outlet of the degassing extruder was connected directly to the molten outlet die without any conduits or molten filters.

[0125] Due to the small size of the degassing extruder and the short residence time t, the amounts of glutaric acid anhydride units formed in the copolymer were 400 ppm and 500 ppm, respectively. The MAA residue content in the copolymer was 450 ppm and 550 ppm, respectively.

[0126] Copolymer samples were preheated to 180°C and then placed in an oven at a temperature of 200°C–280°C for 5–30 minutes under a helium atmosphere and ambient pressure. The content of glutaric anhydride units and MAA residues in the samples was then determined. Based on these data, an empirical mathematical model for the formation of glutaric anhydride units was elaborately constructed.

[0127] The resulting mathematical model was used as the basis for further experiments at production scale.

[0128] Examples 1, 2 (the present invention) and 3 (comparative) MMA-MAA copolymers containing 4.4% by weight and 5% by weight of MAA were prepared by the following procedure.

[0129] A mixture of monomers MMA and MAA was continuously fed into a continuous stirring tank reactor (CSTR) along with a radical polymerization initiator and a chain transfer agent. Polymerization was carried out at 150°C, with a reactor residence time of 40–100 minutes and a total conversion of 48–50%. The copolymer syrup from the outlet of the CSTR was heated to approximately 210–225°C using a heat exchanger and then fed into the copolymer syrup feed port of a degassing extruder.

[0130] Degassing of the copolymer syrup was performed in a single-screw extruder under vacuum in the final degassing zone. Unreacted monomer vapors were condensed, combined with unused MMA and MAA, and returned to the reactor. The degassing extruder was equipped with a thermocouple in the final degassing zone, which was placed 5 mm above the copolymer melt in the degassed monomer vapor to measure the copolymer melt temperature Tv in the final degassing zone. The degassed copolymer melt was transported by the shaft after the final degassing zone of the extruder with increasing pressure to the copolymer melt outlet, and then further transported by pressure alone to the melt pipe, melt filter, and finally to the melt outlet die. The average pressure of the copolymer melt after the final degassing zone was approximately 40–70 bar (4–7 MPa). The copolymer melt temperature To in °C was measured at the center of the inlet of the melt outlet die.

[0131] The pressure required to push the degassed copolymer molten material through the copolymer molten material outlet, molten material filter, and molten material outlet die was generated by the extruder shaft located in the metering zone of the degassing extruder, immediately behind the molten material dome of the final molten material zone. The molten material filter was connected to the copolymer molten material outlet of the extruder by a conduit. The other end of the molten material filter was connected to the molten material outlet die.

[0132] The copolymer molten material discharged from the molten material outlet die was immediately cooled with water and pelletized. Subsequently, the methanol residue, MAA residue, and MMA residue content, as well as the MAA unit and glutaric acid anhydride unit content in the copolymer, were analytically determined as described above.

[0133] The process parameters for the degassing step in Examples 1-3 are summarized in Table 1.

[0134] The experimentally determined correlation between pressure, temperature, and the specific volume v in ml / g of a copolymer melt consisting of 95 wt% MMA and 5 wt% MAA, known from the literature, was used as the basis for calculating the specific volume v in ml / g of the copolymer melts in Examples 1-3. Pressure drops in the melt tube, melt filter, and melt outlet die were ignored. The specific volume v was calculated as follows: v = 0.796 + 5.26 · 10 -4 (1.5·Tv+0.5·To) / 2 In the formula, Tv in °C is the temperature of the copolymer molten in the final degassing zone with respect to the conveying direction of the copolymer molten. To in °C represents the temperature of the copolymer molten material entering the molten material outlet die.

[0135] The monomial (1.5·Tv+0.5·To) / 2 represents the weighted estimated mean temperature between the final degassing zone of the extruder and the molten outlet die. Due to the high viscosity of the copolymer molten, low radial mixing, limited heat transfer, and low thermal conductivity between the final degassing zone and the molten outlet die, the temperature difference between Tv and To is relatively small.

[0136] [Table 1]

[0137] The residence time t is the sum of the average residence time of the degassed copolymer molten material in the degassing device after the last degassing zone, the average residence time of the copolymer molten material in an optional molten conduit volume, the average residence time of the copolymer molten material in an optional molten filter volume, the average residence time in any of the optional copolymer molten material-containing volumes, and the average residence time in an optional copolymer molten die.

[0138] The residence time t between the final degassing zone and the molten material outlet die was calculated for Examples 1-3 using the following relation: t = (Vv + Vc + Vf + Vd) / (c·v) In the formula, Vv is the volume of the extruder filled with copolymer molten material after the last degassing zone where the pressure rise begins. Vc is the volume of the molten conduit filled with copolymer molten material. Vf is the volume of the molten material filter filled with copolymer molten material. Vd is the volume of the molten outlet die filled with copolymer molten material. c is the molten mass flow, v is the specific volume.

[0139] The glutaric anhydride unit content formed after the vacuum zone (see Table 2) was calculated based on the measured methanol residue in the final copolymer, and under the following assumptions: The first assumption was that the glutaric anhydride unit content formed after the final degassing zone of the extruder could be calculated from the methanol residue content in the copolymer melt in the final copolymer. The second assumption was that if the pressure in the final degassing zone was less than 300 mbar, degassing in the final degassing zone (vacuum zone) would result in a negligible methanol residue in the copolymer melt. Therefore, it was assumed that the total methanol residue measured in the final copolymer was formed during the formation of unwanted glutaric anhydride units after the final degassing zone.

[0140] The glutaric anhydride unit content formed before the vacuum zone (see Table 2) was calculated as the difference between the glutaric anhydride unit content in the final copolymer and the glutaric anhydride unit content formed after the vacuum zone.

[0141] Subsequently, the observed formation of glutaric anhydride units was verified based on a mathematical kinetic model.

[0142] [Table 2]

[0143] The following correlations were obtained from the kinetics of glutaric anhydride unit formation and evaluations of technical and production-scale tests. This equation represents the loss factor L of MAA units in % between the extruder vacuum zone and the molten outlet die, based on the total weight of the MAA reactor feed in step (a): L = 4.981 · 10 -8 ·t·exp(0.0517·(1.5·Tv+0.5·To) / 2)

[0144] To minimize the loss of MAA units in the copolymer, the loss factor L should be kept low, for example, below 8. This means that, for example, based on the MAA in the reactor feed, less than 8% of the MAA units in the copolymer melt are converted to glutaric anhydride units. L>4.981·10 -8 ·t·exp(0.0517·(1.5·Tv+0.5·To) / 2)

[0145] In Examples 1 and 2 (the present invention), the copolymer melt temperature Tv in the final degassing zone was 266°C and 265°C, respectively. In contrast, in Example 3 (comparative), the copolymer melt temperature Tv in the final degassing zone was 281°C.

[0146] Furthermore, the temperature To of the copolymer entering the molten material outlet die in Examples 1 and 2 (the present invention) was significantly lower than in Example 3 (comparison). As a result, the monomial: 4.981·10 -8 ·t·exp(0.0517·(1.5·Tv+0.5·To) / 2) In Examples 1 and 2, the value was less than 8, while in Example 3 it was higher than 8 (see Table 2).

[0147] As a result, the glutaric acid anhydride unit content in the final copolymer of Example 3 was 1.8% by weight, and the methanol content was as high as 1700-1800 ppm, which was significantly higher than in Examples 1 and 2. At the same time, the MAA unit content in the copolymer of Example 3 was only 3.99% by weight, which was significantly lower than in Example 1 of the present invention. Since it is well known that carboxyl groups chemically interact with metal surfaces and thereby contribute to strong adhesive bonding, MAA units with lower water content are disadvantageous in terms of adhesive properties to metal surfaces.

[0148] A comparison between the copolymers in Example 1 (inventive invention) and Example 3 (comparative) further demonstrates that the copolymer in Example 1 has a higher Vicat temperature (see Table 3). All copolymers tested exhibited low haze and virtually zero yellowness.

[0149] [Table 3]

[0150] In summary, the copolymers of Examples 1 and 2 possessed particularly high water content of free carboxylic acid groups, high heat resistance, and excellent optical properties, especially low haze and virtually zero yellowness.

[0151] Examples 1-3 demonstrate that by adjusting the copolymer melt temperature Tv in °C in the final degassing zone, the copolymer melt temperature To in °C entering the melt outlet die, and the total residence time t of the copolymer melt in seconds between the final degassing zone and the melt outlet die of the defoliation unit, the undesirable formation of glutaric anhydride units from MAA units in the copolymer melt can be substantially suppressed while maintaining low MMA and MAA residue content. [Explanation of Symbols]

[0152] 1. Degassing extruder 2 Copolymer mixture supply section 3 Copolymer mixture inlet 4. The final degassing zone (vacuum zone) 5. The last gas outlet 6. Copolymer molten outlet 7. Molten material outlet die 8 motors 9 Copolymer melt 10. Molten material filter (optional) 11. Additional gas outlet (optional) 12 Molten material conduit 13 Zone 1 (See Examples 1-3) 14 Weighing Zones (See Examples 1-3)

Claims

1. A method for producing a molding composition containing a copolymer, (a) polymerization step, 80.0 to 99.9% by weight of methyl methacrylate, Formula (I), in amounts of 0.1 to 20.0% by weight: 【Chemistry 1】 [Substituent R １ [This is either a hydrogen atom or a hydrocarbon group having 1 to 6 carbon atoms.] Compounds represented by, Optionally, 0.0 to 19.9% ​​by weight of a monomer selected from methyl acrylate, ethyl acrylate, or styrene. Polymerization initiator, and Selectively chain transfer agent A polymerization step in which a monomer mixture containing the copolymer undergoes radical copolymerization in a polymerization reactor to form a copolymer mixture containing the copolymer and volatile components, (b) Optionally, a step of heating the copolymer mixture obtained in the polymerization step (a) to a temperature of 100°C to 300°C in a heating unit, (c) at least one copolymer mixture supply port, At least one degassing device, At least one degassing zone, At least one gas outlet, At least one copolymer molten outlet A degassing device, and At least one molten material outlet die and A degassing step in which the volatile components are removed from the copolymer mixture to form a copolymer melt in a degassing unit containing the following: Includes, The temperature Tv of the copolymer molten material in °C in the last degassing zone with respect to the transport direction of the copolymer molten material, the temperature To of the copolymer molten material entering the molten material outlet die in °C, and the total residence time t of the copolymer molten material in seconds between the last degassing zone and the molten material outlet die of the degassing unit are given by a monomial: 4.981・10 －８ ・t・exp(0.0517・(1.5・Tv+0.5・To) / 2) However, adjust it so that it is less than 8. method.

2. The method according to claim 1, wherein the monomial (1.5・Tv + 0.5・To) / 2 of the copolymer melt in °C in the last degassing zone of the degassing device in the degassing step (c) is between 230 °C and 290 °C.

3. The method according to claim 1 or 2, wherein the total residence time t of the copolymer molten material in seconds between the last degassing zone and the molten material outlet die with respect to the transport direction of the copolymer molten material is in the range of 10 seconds to 200 seconds.

4. The method according to any one of claims 1 to 3, wherein the degassing unit used in the degassing step (c) further includes at least one molten filter located between the last degassing zone of the degassing device and the molten outlet die.

5. The method according to any one of claims 1 to 4, wherein the absolute pressure in the last degassing zone of the degassing device with respect to the transport direction of the copolymer molten material is in the range of 1 mbar to 300 mbar.

6. The method according to any one of claims 1 to 5, wherein the polymerization reactor in step (a) is a stirred-tank reactor operated discontinuously or continuously, a tubular reactor operated continuously, a loop reactor operated discontinuously or continuously, or a combination thereof, and if several reactors are used, they are operated in parallel or connected sequentially.

7. The method according to any one of claims 1 to 6, wherein the degassing device in the degassing step (c) is selected from a degassing extruder, a degassing kneader, and one or more flash chambers.

8. The aforementioned copolymer 80.0–99.5% by weight of repeating units derived from methyl methacrylate, Formula (I), in amounts of 0.5 to 20.0% by weight: 【Chemistry 2】 [Substituent R １ [This is either a hydrogen atom or a hydrocarbon group having 1 to 6 carbon atoms.] Repeating units derived from compounds represented by, and optionally 0.0 to 19.5% by weight of repeating units derived from methyl acrylate, ethyl acrylate, or styrene. The method according to any one of claims 1 to 7, including

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