Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L33/00—Compositions of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and only one being terminated by only one carboxyl radical, or of salts, anhydrides, esters, amides, imides or nitriles thereof; Compositions of derivatives of such polymers
  • C08L33/04—Homopolymers or copolymers of esters
  • C08L33/06—Homopolymers or copolymers of esters of esters containing only carbon, hydrogen and oxygen, which oxygen atoms are present only as part of the carboxyl radical
  • C08L33/10—Homopolymers or copolymers of methacrylic acid esters
  • C08L33/12—Homopolymers or copolymers of methyl methacrylate
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F120/00—Homopolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and only one being terminated by only one carboxyl radical or a salt, anhydride, ester, amide, imide or nitrile thereof
  • C08F120/02—Monocarboxylic acids having less than ten carbon atoms; Derivatives thereof
  • C08F120/10—Esters
  • C08F120/12—Esters of monohydric alcohols or phenols
  • C08F120/14—Methyl esters, e.g. methyl (meth)acrylate
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C39/00—Shaping by casting, i.e. introducing the moulding material into a mould or between confining surfaces without significant moulding pressure; Apparatus therefor
  • B29C39/003—Shaping by casting, i.e. introducing the moulding material into a mould or between confining surfaces without significant moulding pressure; Apparatus therefor characterised by the choice of material
  • B29C39/006—Monomers or prepolymers
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L83/00—Compositions of macromolecular compounds obtained by reactions forming in the main chain of the macromolecule a linkage containing silicon with or without sulfur, nitrogen, oxygen or carbon only; Compositions of derivatives of such polymers
  • C08L83/04—Polysiloxanes

Definitions

• the present invention concerns a polymethyl methacrylate (PMMA) cast sheet article, in particular a sheet of cast PMMA (acrylic glass).
• PMMA polymethyl methacrylate
• PMMA polymethyl methacrylate
• the cast sheets of PMMA are obtained by casting a liquid mixture of polymethyl methacrylate pre-polymer, also known as liquid acrylic resin or syrup.
• one of the most common or recurrent scratching stresses in PMMA articles is that due to the so-called "brush effect”, or “brushed effect”, that is, the presence of thin scratches, elongated in shape, often parallel to each other, or with a concentric circular shape or spiral, which cause the surfaces to lose their brilliance and appear opaque.
• This "brush effect”, or “brushed effect” can be rather annoying and un-esthetic, and also considerably worsens the performance of clarity and visibility of the PMMA articles in question, making them opaque and emphasizing their aging.
• renovating creams or polishes are used for automobile bodywork. However, if the scratches or incisions are deep, the damage is often irreparable, and in any case the restoration work is delicate and costly.
• Applicant has carried out experiments that provide to incorporate additives in the casting liquid acrylic resin, like those described for coatings. These experiments were not successful because, although the loads were sized nanometrically (typically 5 - 35 nm), firstly there was a deterioration in the clarity and transparency, and secondly the desired performance was not obtained, since the additives remain incorporated in the polymer matrix, also varying the mechanical characteristics thereof.
• Document WO-A-2012/034821 and document EP-A-0.352.455 describe a molded article made of PMMA by molding using injection granule, that is, a completely different and unsuitable method of production compared with casting liquid resin of PMMA.
• this document describes a formulation of solid components, that is, Plexiglas 8N co-polymerized with Tegomer® H-Si 6440P or Tegomer® H-Si 6846P in the form of a solid pellet, and a process of injecting a solid resin into a mold, neither suitable nor comparable with the technique of casting liquid resin.
• the Applicant has devised, tested and embodied the present invention to overcome the shortcomings of the state of the art and to obtain these and other purposes and advantages.
• a PMMA cast sheet article comprises one or more anti scratch additives chosen from among polydimethylsiloxanes or derivatives thereof.
• the polydimethylsiloxanes or derivatives thereof are chosen from a group that consists of: poly ether polydimethylsiloxane, alkylmethyl trisiloxane, non-ionic polyoxyethylene polydimethylsiloxane, or derivatives thereof.
• the polydimethylsiloxanes or derivatives thereof are provided between 0.1% and 1% w/w with respect to the weight of the polymethyl methacrylate article.
• the polydimethylsiloxanes or derivatives thereof are selected with a molecular weight less than or equal to 500.
• - making a liquid mixture of polymethyl methacrylate pre-polymer comprising one or more anti-scratch additives selected from among the polydimethylsiloxanes or derivatives thereof, which are chosen from a group that consists of: polyether polydimethylsiloxane, alkylmethyl trisiloxane, non-ionic polyoxyethylene polydimethylsiloxane, or derivatives thereof, selected with a molecular weight less than or equal to 500 and comprised between 0.1% and 1% w/w with respect to the overall mixture; - casting the pre-polymer liquid mixture in a mold to make the polymethyl methacrylate cast sheet article.
• one or more anti-scratch additives selected from among the polydimethylsiloxanes or derivatives thereof, which are chosen from a group that consists of: polyether polydimethylsiloxane, alkylmethyl trisiloxane, non-ionic polyoxyethylene polydimethylsiloxane, or derivative
• Forms of embodiment described here concern a PMMA cast sheet article, comprising one or more anti-scratch additives selected from among the polydimethylsiloxanes (PDMS) or derivatives thereof.
• PDMS polydimethylsiloxanes
• the anti-scratch additives are incorporated in the PMMA material and emerge on the external surface of the PMMA cast sheet article during the process of its production, and not subsequently applied on the external surface, by means of films or varnishes, as in the state of the art.
• the PMMA cast sheet article has no coating, either varnishes or films, applied after the production of the PMMA cast sheet article in question. Therefore we believe that the PMMA cast sheet article according to the present description supplies the desired resistance to scratches or incisions, thus allowing a production process with reduced costs and higher productivity, since additional operations to provide anti-scratch resistance to the PMMA cast sheet article produced are not necessary.
• the polydimethylsiloxanes or derivatives thereof can be provided between 0.1% and 1% w/w with respect to the weight of the PMMA cast sheet article, in particular between 0.2% and 0.9%, more in particular between 0.25% and 0.85%, even more in particular between 0.3% and 0.8% w/w.
• the polydimethylsiloxanes or derivatives thereof are selected with a low molecular weight, less than or equal to 500, in particular less than or equal to 400, more in particular less than or equal to 350.
• these values of molecular weight allow an effective migration of the PDMS or derivatives thereof toward the external layers and the external surface of the PMMA material, since, thanks to their low molecular weight, they are not excessively hindered in this by the oligomer being polymerized.
• Examples of possible molecular weights of the PDMS and their derivatives are for example 450, 400, 380, 350, 340, 330, 320, 310, 300, 290, 280, 270, 260, 250.
• PDMS polydimethylsiloxanes
• the possible plurality of PDMS can also allow a balanced chemical compatibility - incompatibility, in order to obtain perfectly colorless sheets, perfectly transparent and clear.
• the one or more anti-scratch additives selected among the PDMS or derivatives thereof are provided incorporated inside the PMMA and present externally, emerging on the external surface of the PMMA cast sheet article.
• the one or more anti-scratch additives selected among the PDMS or derivatives thereof are not only present externally, emerging on the external surface of the PMMA cast sheet article, but also present, for example incorporated, in one or more external layers of the PMMA cast sheet article.
• the external layers can be symmetrical external layers of the PMMA cast sheet article, for example in the case of sheets, the external layers are planar symmetrical external layers provided on the two opposite sides or faces of the sheet.
• each of the external layers of the PMMA cast sheet article in which the one or more anti-scratch additives are incorporated, selected among the PDMS or derivatives thereof, can have a thickness between 0.05 mm and 0.8 mm, in particular between 0.1 mm and 0.5 mm, more in particular between 0.1 mm and 0.3 mm, even more in particular between 0.15 mm and 0.25 mm.
• Examples of the thickness of the external layer in which the one or more PDMS or derivatives thereof are incorporated are: 0.15 mm, 0.2 mm, 0.25 mm.
• Examples of the overall thickness of the PMMA cast sheet article can go from 2 mm to 40 mm, for example 2 mm, 2.5 mm, 3 mm, 4 mm, 5 mm, 6 mm, 8 mm, 10 mm, 12 mm, 15 mm, 20 mm, 25 mm, 30 mm, 40 mm.
• the thickness of each of the external layers can be about 0.25 mm.
• At least 80% of the one or more anti-scratch additives selected among the PDMS or derivatives thereof present in the PMMA is provided in said external layers of the PMMA cast sheet article and emerging on the external surface. In other words, only 20% or less of the PDMS or derivatives thereof present in the PMMA is contained in the innermost part of the PMMA cast sheet article.
• the PDMS or derivatives thereof are chosen from a group consisting of: polyether polydimethylsiloxane, alkylmethyl trisiloxane and non-ionic polyoxyethylene polydimethylsiloxane.
• the PDMS or derivatives thereof are polyether polydimethylsiloxane and non-ionic polyoxyethylene polydimethylsiloxane.
• polyether polydimethylsiloxane and non-ionic polyoxyethylene polydimethylsiloxane are polyether polydimethylsiloxane and non-ionic polyoxyethylene polydimethylsiloxane.
• a mixture of polyether polydimethylsiloxane and non-ionic polyoxyethylene polydimethylsiloxane in particular for example with polyether polydimethylsiloxane from 15% to 25% w/w and non-ionic polyoxyethylene polydimethylsiloxane from 75% to 85%) w/w, with the provision that the sum is 100% w/w.
• An example composition of the mixture can be 20% w/w polyether polydimethylsiloxane and 80% w/w non-ionic polyoxyethylene polydimethylsiloxane.
• the PMMA can also comprise a synergic additive with anti-scratch effect.
• the synergic additive with anti-scratch effect can be comprised between 0.01% and 0.15% w/w with respect to the weight of the PMMA cast sheet article, in particular between 0.02% and 0.12% w/w, more in particular between 0.04% and 0.1% w/w.
• the synergic additive with anti- scratch effect it may be provided that it is incorporated to a large extent, that is, for example at least 80%, in the external layers of the PMMA cast sheet article and emerging on the external surface thereof, as discussed above for the PDMS or derivatives thereof.
• the synergic additive with anti-scratch effect can be siloxane copolyester.
• the material used to produce the PMMA cast sheet article according to the present description can be obtained by adding the PDMS or derivatives thereof, and possibly also the synergic additive with anti-scratch effect, to an acrylic liquid resin, or pre-polymer, normally obtained by polymerization of monomer MMA and used to make the PMMA cast sheet articles as described.
• an acrylic liquid resin, or pre-polymer normally obtained by polymerization of monomer MMA and used to make the PMMA cast sheet articles as described.
• a method for the synthesis of said acrylic resin is described in the application for a patent of industrial invention UD2014A000101 filed in Italy and in the international application PCT/IB2015/05441 1, both in the name of the present Applicant and incorporated here in their entirety by way of reference.
• the importance must be underlined of the polydispersity index (PI) of the pre- polymer because, with a suitable rheological behavior, that is, more similar to a Newtonian than a visco-elastic behavior, the migration effect of the PDMS described in the present invention is synergized. Furthermore, with the rheological control and the choice of mixture of PDMS, it is also possible to use cross-linkers since, despite the steric impediment due to their reticulation in sheets, the migration described is in any case allowed.
• PI polydispersity index
• the PDMS or derivatives thereof that are added to the synthesis mixture of the acrylic resin can be used in liquid form.
• the PDMS or derivatives thereof can have a viscosity at 25°C comprised between 30 cST and 50 cST, in particular between 35 cST and 45 cST, more in particular between 38 cST and 42 cST.
• Examples of viscosity at 25°C of the PDMS or derivatives thereof are 39 cST, 40 cST, 41 cST.
• the mixture of pre-polymer or casting resin (known in jargon as "syrup"), which already contains the anti- scratch compounds described above, that is, the PDMS or derivatives thereof, and possibly also the synergic additive with anti-scratch effect, can be cast in a mold, which can be immersed in water, generally in order to control the exothermicity of the polymerization during solidification.
• This last operation can provide for example to cast the pre-polymer resin in a mold in water at a temperature that can be 60°C, for example for a thickness of 5 mm.
• the forming mold can usually consist of sheets of glass separated by a polymer gasket, for example PVC, which defines the thickness of the final sheet.
• the pre-polymer mixture can be cast in the mold then immersed in the hot water at 60°C, for example for a thickness of 5 mm, or gradually lower as the thicknesses increase, and polymerization is completed.
• the mixture can be cast in a vertical or horizontal mold.
• the PDMS or derivatives thereof, and possibly also the synergic additive with anti-scratch effect are selected according to the present description so as to be incompatible with the oligomer being polymerized.
• the presence of the PDMS or derivatives thereof and possibly also the synergic additive with anti-scratch effect, incompatible with the oligomer being polymerized causes the material that is polymerized to tend to expel the incompatible compounds, which are therefore obliged to migrate forcedly toward the external surface, that is, they emerge on the surface in great quantities. This migration, as we said, can be promoted by the low molecular weight of the PDMS or derivatives thereof, which therefore are not impeded by the oligomer being polymerized, as discussed above.
• the PDMS or derivatives thereof, and possibly also the synergic additive with anti-scratch effect, therefore, suitably selected, can bring the desired surface modifications, to increase the anti-scratch properties of the final PMMA.
• the PDMS or derivatives thereof, and possibly also the synergic additive with anti- scratch effect can offer an optimum compromise in terms of surface emergence, since they migrate sufficiently to improve the anti-scratch properties of the surface, but do not have surface tensions and incompatibilities such as to create surface defects in the PMMA.
• the fact that it is possible to direct all or almost all the quantity of the PDMS or derivatives thereof, and possibly also the synergic additive with anti-scratch effect, toward the surface allows to optimize the quantity that is used of said compounds, reducing it to the minimum necessary. Consequently, the use of the PDMS or derivatives thereof, and possibly also the synergic additive with anti-scratch effect, does not damage, for example, the clarity and transparency of the final PMMA, which thus has the exceptional optical properties that characterize it, together with the anti-scratch properties that it acquires thanks to the PDMS or derivatives thereof, and possibly also the synergic additive with anti-scratch effect.
• Applicant has observed a symmetrical behavior in the migration of the PDMS or derivatives thereof, and possibly also the synergic additive with anti-scratch effect, toward the external surface of the PMMA being polymerized, where they emerge.
• the outermost layers and the external surface of the PMMA material are affected by and incorporate a large part of said compounds or anti-scratch additives, as we said, for example at least 80%.
• Applicant has verified that the migration of the anti-scratch additives toward the outside is symmetrical with respect to the bulk of the material; in particular, in the sheets there is a symmetrical migration toward the two opposite faces of the sheet of PMMA. It is therefore possible to identify a diagram with a symmetrical increasing gradient of the presence of said compounds from the inside, in particular from the center of the PMMA cast sheet article toward the external sides.
• the PMMA cast sheet article according to the present description therefore has good anti-scratch properties and a lower economic cost compared with similar articles in PMMA with known anti-scratch coatings, since the anti-scratch property is obtained directly in the course of the polymerization and thermoforming using a mold in water, and not in a subsequent coating operation with anti-scratch films or varnishes, thus considerably saving on the work cycle and the double working. Furthermore, if the PMMA cast sheet article is transparent, its clarity is high and not at all worsened by the use of the anti-scratch compounds as cited, since the quantity thereof is optimized and used efficiently.
• the emergence of the anti-scratch additives is therefore promoted by the present invention, both in terms of choice of the PDMS or derivatives thereof, incompatible with the casting resin in the course of polymerization, and also advantageously in terms of low molecular weight.
• the choice of the PDMS or derivatives thereof is particularly advantageous because the phenomenon of migration and emergence is therefore balanced and does not cause problems of final quality because it does not produce surface defects, such as hollows and macro/micro irregularities of the PMMA material, which furthermore would also have a negative influence on the transparency.
• Applicant has carried out experimental tests to assess the resistance to scratching of the PMMA cast sheet article according to the present description. For the purposes of comparison, the experiments were also carried out on a standard sheet of PMMA, transparent and colorless, produced by Applicant, without specific anti-scratch properties, called Acridite 99. The experiments were conducted according to the standard for assessing resistance to scratch DIN 68861 :201 1 , para 4. The incision or scratch load is assessed in N, which causes a distinguishable mark. The test provides to make an incision on the surface of the sample with a diamond point with variable load. For the purposes of evaluation and comparison, resistance to scratch is indicated by a class of stress (Level of use, LU, pursuant to DIN 68861 :201 1, para 2). There are various classes of stress, depending on the incision and scratch load which the sample tested can resist:
• the PMMA cast sheet article according to the present description has a recognizable improvement in its anti-scratch properties.
• the scratch stress most common in PMMA cast sheet articles, for example sheets is that due to the "brush effect” or “brushed effect”, and the PMMA cast sheet article according to the present description has a surprising resistance to such wear.
• the improvement in the stress class of the PMMA cast sheet article according to the present description means that essentially it is not subject to the scratch phenomenon due to the "brush effect” or "brushed effect”, that is, the presence of thin scratches in an elongated shape, often parallel to each other, or with a concentric circular shape or spiral, or in any case scratch phenomena which could be defined superficial and not deep (unlike incisions, for example).
• the PMMA cast sheet article also has a better resistance to scratching or incisions proper. All in all, the PMMA cast sheet article according to the present description represents an optimum compromise between production costs, since no additional operations are needed for anti-scratch coating and protection, and resistance to scratch, since it is practically not subject to the so-called "brush effect” or "brushed effect”, and has an improved resistance to scratch and incisions proper.
• the PMMA cast sheet articles, in particular for example sheets, obtained in this way can normally be worked with traditionally known methods, including gluing with solvent adhesives or bicomponent reactive adhesives or UV hardeners.

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• Chemical & Material Sciences (AREA)
• Health & Medical Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Medicinal Chemistry (AREA)
• Polymers & Plastics (AREA)
• Organic Chemistry (AREA)
• Manufacture Of Macromolecular Shaped Articles (AREA)
• Compositions Of Macromolecular Compounds (AREA)
• Casting Or Compression Moulding Of Plastics Or The Like (AREA)

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• 2015
  • 2015-06-19 EP EP15742080.3A patent/EP3161064A1/de not_active Withdrawn
  • 2015-06-19 WO PCT/IB2015/054635 patent/WO2015198197A1/en active Application Filing

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