WO2023106258A1

WO2023106258A1 - Polymerizable composition for manufacturing molded article, molded article and manufacturing method thereof

Info

Publication number: WO2023106258A1
Application number: PCT/JP2022/044709
Authority: WO
Inventors: Andrea Vecchione; Roberto Forestieri; Francesco Mariani
Original assignee: Mitsui Chemicals, Inc.
Priority date: 2021-12-06
Filing date: 2022-12-05
Publication date: 2023-06-15
Also published as: IT202100030767A1

Abstract

The present invention relates to a polymerizable liquid composition for manufacturing a molded article comprising: - an isocyanate component A comprising: I. at least one component a2 or a mixtureof component a2 and component a1, wherein a1 is a cycloaliphatic diisocyanate and a2 is an isocyanate group-terminated prepolymer comprising the reaction product of components comprising: (i) a cycloaliphatic diisocyanate and (ii) at least one polyol having at least two hydroxy groups per molecule; and II. a component a3, which is a modified polyisocyanate composition comprising at least one aliphatic or cycloaliphatic diisocyanate comprising at least one functional group selected from: isocyanurate group, allophanate group, biuret group, urethane group, urea group and mixture thereof; - a polyol component B comprising at least one polyol having from 2 to 5 hydroxy groups per molecule; - a catalyst component C comprising at least one tertiary amine. The present invention also relates to a molded article prepared with the above polymerizable composition and a manufacturing method thereof.

Description

POLYMERIZABLE COMPOSITION FOR MANUFACTURING MOLDED ARTICLE, MOLDED ARTICLE AND MANUFACTURING METHOD THEREOF

The present invention relates to a polymerizable composition for manufacturing a molded article, a molded article and a manufacturing method thereof.

Polyurethane resins are formed by reacting an active hydrogen-containing compound (e.g. a polyol) with a polyisocyanate (e.g. diisocyanate compound or polymeric isocyanate) in the presence of suitable catalysts and additives. Because a variety of polyisocyanate compounds and a wide range of active hydrogen-containing compound can be used to produce polyurethane resins, a wide variety of materials can be produced to meet the needs of specific applications.

An important application of polyurethane resins is the manufacturing of molded article, such as prototypes of complex design or optical articles (e.g. optical and ophthalmic lenses, fiber optics, windows and automotive, nautical and aviation transparencies, etc.). Depending on the end-use, the polyurethane resins have to fulfil special requirements. For example, in the prototyping field polyurethane resins needs to be easily castable into molds and thus have to exhibit optimum properties, such as high compatibility of the components to favour their fast mixing to yield clear polymerizable compositions, low viscosity and gelling time for ease of processability as well as rapid curing, preferably at relatively low temperature. Moreover, the cured molded articles need to exhibit optimum properties, such as one high stability against ageing due to exposure to UV-VIS radiation, clearness, hardness, impact resistance, heat resistance and minimum shrinkage.

An example of polyurethane castable resin suitable for prototyping and for manufacturing impact-resistant optical lenses is disclosed in US 2009/0209723 A1.

The polyurethane resin disclosed in US 2009/0209723 A1 comprises a part (I) corresponding to an isocyanate part containing: a) a methylene-bis-4,4'-isocyanatecyclohexane (H12MDI), b) a prepolymer obtainable by the reaction between propoxylated glycerol and a methylene-bis-4,4'-diisocyanatecyclohexane and a part (II) corresponding to an alcohol part containing: c) an alkoxylated etherate glycerol in the monomer and oligomer form thereof and d) at least one type of a polyalkoxylated tertiary diamine tetraol and/or triol.

This castable resin, which is marketed by AXSON under the trade name PX521HT, is suitable for prototyping using the vacuum casting technique. Vacuum casting is a manufacturing technique that uses a vacuum to draw a liquid polymerizable composition (i.e. the resin) into a mold. The vacuum casting technique is advantageously used to produce transparent and defect-free moldings as it avoids air entrapment in the resin and thus the formation of bubbles within the final molded articles. Additionally, vacuum casting is used to manufacture articles into molds having intricate details and undercuts.

A major drawback of the polyurethane resin disclosed in US 2009/0209723 A1 is the limited stability upon exposure to UV-Vis radiation, which leads to the undesired yellowing of the cured end-products over time, even if the castable composition is added of bleaching agents to contrast this ageing effect.

Further castable compositions for preparing polyurethanes, articles and coatings are described in WO 2014153075 A1. This reference discloses a polyurethane that comprises a reaction product of components comprising:
(a) an isocyanate functional urethane prepolymer comprising a reaction product of components comprising: (i) about 1 equivalent of at least one polyisocyanate; and (ii) about 0.01 to about 0.5 equivalent of at least one polyol having 2 hydroxyl groups, based upon the about 1 equivalent of the at least one polyisocyanate; and
(b) about 0.1 to about 1 equivalent of at least one polyol having 2 hydroxyl groups, based upon the about 1 equivalent of the at least one polyisocyanate,
wherein the at least one polyol (ii) can be the same or different from the at least one polyol (b), and wherein the components are essentially free of polyester polyol, polyether polyol, polycarbonate polyol and amine curing agent. In some embodiments, the above components are reacted in the presence of a primary or secondary amine as curing agent. In one embodiment (Example H27), a polyurethane is obtained by reacting, 1,4-butanediol with a polyisocyanate component comprising 4,4’-methylene-bis(cyclohexyl isocyanate) and a mixture of 60% hexamethylene diisocyanate dimer and 40% hexamethylene diisocyanate trimer in the absence of a curing agent.

Problem that the Invention is to Solve

In view of the above-described state of the art, Applicants have faced the problem of overcoming or at least ameliorate the drawbacks of the castable polyurethane resins set out above. Particularly, a primary object of the present invention is to provide a polyurethane polymerizable composition suitable for a number of end use applications, especially for producing molded articles such as prototypes.

Particularly, it is another object of the present invention to provide a polyurethane polymerizable composition having a relatvely low viscosity that facilitates mixing and pouring in molds, low gelling time and rapid curing, preferably at relatively low temperature (e.g. about 60 to 80°C).

It is another object of the present invention to provide a polyurethane polymerizable composition that allows to produce cured articles having one or more of the following properties: high stability upon exposure to ultraviolet (UV) and visible (VIS) radiation (ageing resistance), clearness, hardness, impact resistance, heat resistance and minimum shrinkage.

It has now been surprisingly found that it is possible to achieve the above-described object, as well as other objects that will become more evident from the following description, by formulating a polymerizable composition combining certain isocyanate component A, polyol component B and teriary amine as catalyst component C, wherein the isocyanate component A contains an isocyanate group-terminated prepolymer, optionally in admixture with a cycloaliphatic diisocyanate monomer, in combination with at least one modified polyisocyanate composition of at least one aliphatic or cycloaliphatic diisocyanate that comprises a functional group selected from: isocyanurate group, allophanate group, biuret group, urethane group, urea group and mixture thereof.

This polymerizable composition is well suited for a number of end use applications, particularly for the manufacturing of molded articles, such as prototypes and optical articles. This polymerizable composition is especially advantageous when used as castable resin for manufacturing articles by vacuum casting as it exhibits a relatively low viscosity that facilitate its quick mixing and pouring, low gelling time and rapid curing at relatively low temperature (e.g. about 60 to 80°C). The cured articles obtained with this polymerizable composition, moreover, have a clear and transparent aspect as well as relatively high hardness, impact resistance, heat resistance and minimum shrinkage. Particularly, the cured articles do not substantially absorb UV-VIS radiation and thus exhibit enhanced light and weathering stability upon exposure to this radiation for a prolonged time.

Means for solving the problem

Therefore, according to a first aspect, the present invention relates to a polymerizable liquid composition for manufacturing a molded article comprising:
- an isocyanate component A comprising:
I. at least one component a2 or a mixture of component a2 and component a1, wherein a1 is a cycloaliphatic diisocyanate and a2 is an isocyanate group-terminated prepolymer comprising the reaction product of components comprising: (i) a cycloaliphatic diisocyanate and (ii) at least one polyol having at least two hydroxy groups per molecule; and
II. a component a3, which is a modified polyisocyanate composition comprising at least one aliphatic or cycloaliphatic diisocyanate comprising at least one functional group selected from: isocyanurate group, allophanate group, biuret group, urethane group, urea group and mixture thereof;
- a polyol component B comprising at least one polyol having from 2 to 5 hydroxy groups per molecule;
- a catalyst component C comprising at least one tertiary amine.

According to a second aspect, the present invention relates to a molded article comprising a cured product of the aforementioned polymerizable composition.

According to a third aspect, the present invention relates to an optical material comprising the aforementioned molded article.

According to a fourth aspect, the present invention relates to an automotive lightning element comprising the aforementioned optical material.

According to a fifth aspect, the present invention relates to a method for manufacturing the aforementioned molded article comprising:
a. mixing the aformentioned isocyanate component A, polyol component B and catalyst component C to obtain a polymerizable composition;
b. pouring the polymerizable composition into a mold;
c. thermally curing the polymerizable composition to obtain a molded article.

According to a sixth aspect, the present invention relates to the use of the aforementioned polymerizable composition for manufacturing a molded article by means of the vacuum casting technique.

Further characteristics of the present invention are illustrated in the dependent claims annexed to the present description.

The compositions of the present invention can comprise, consist essentially of, or consist of, the essential components as well as optional ingredients described herein. As used herein, “consisting essentially of” means that the composition or component may include additional ingredients, but only if the additional ingredients do not materially alter the basic and novel characteristics of the claimed compositions or methods.
As used herein, the articles "a", "an" and “the” should be read to include one or at least one and the singular also includes the plural, unless it is obvious that it is meant otherwise. This is done merely for convenience and to give a general sense of the disclosure.

Other than in the operating examples, or where otherwise indicated, all numbers expressing quantities of ingredients, reaction conditions, and so forth used in the specification and claims are to be understood as modified in all instances by the term “about”.

As described therein, unless stated otherwise, the molecular weight of a polymer is indicated as weight-average molecular weight (Mw) determined using known methods, such as gel permeation chromatography (GPC) using polystyrene standard.

[Fig. 1] Figure 1, which depicts UV Vis spectra of comparative example C1 and C2.
[Fig. 2] Figure 2, which depicts UV Vis spectra of Example 3 according to the invention.
[Fig. 3] Figure 3, which depicts UV Vis spectra of Example 12 according to the invention.
[Fig. 4] Figure 4, which depicts UV Vis spectra of Example 6 according to the invention.
[Fig. 5] Figure 5, which depicts UV Vis spectra of Example 3, 10 and C2 according to the invention.
[Fig. 6] Figure 6, which depicts the results of the QUV test for comparative examples C1 and C2 and for Example 3, 6, 9, 10 and 12 according to the invention.
[Fig. 7] Figure 7, which depicts the results of the weathering test for comparative example C2 and Examples 4, 5, 11 and 13 according to the invention.

The polymerizable composition of the present invention is a liquid composition comprising an isocyanate component A, a polyol component B and a catalyst component C.

Isocyanate component A
The isocyanate component A comprises a mixture of a component a3 and component a2, or a mixture of component a3 with components a2 and a1.

Component a1
The isocyanate component A may comprise a cycloaliphatic diisocyanate as component a1. Useful cycloaliphatic diisocyanate include those in which one or more of the isocyanate groups are attached directly to the cycloaliphatic ring and cycloaliphatic diisocyanates in which one or more of the isocyanate groups are not attached directly to the cycloaliphatic ring.

Non-limiting examples of suitable cycloaliphatic diisocyanate as component a1 include: methyl cyclohexane diisocyanate, bis(isocyanate methyl)cyclohexane, 1,1′-methylene-bis-(4-isocyanatocyclohexane) or 4,4′-methylene-bis-(cyclohexyl isocyanate) (HMDI) (such as DESMODUR W commercially available from Bayer Corp. of Pittsburgh, Pa.), 4,4′-isopropylidene-bis-(cyclohexyl isocyanate), 1,4-cyclohexyl diisocyanate (CHDI), 4,4′-dicyclohexylmethane diisocyanate, bis(isocyanatecyclohexyl)-2,2-propane, bis(isocyanatecyclohexyl)-1,2-ethane, 3-isocyanato methyl-3,5,5-trimethylcyclohexyl isocyanate (IPDI), meta-tetramethylxylylene diisocyanate and 2,5(6) diisocyanatemethylbicyclo(2,2,1)heptane and octahydro-4,7-methano-1H-indendimethyldiisocyanate.
These cycloaliphatic diisocyanates may be used singly or in a combination of two or more.

Component a2
The isocyanate component A comprises at least one isocyanate group-terminated prepolymer as component a2.

This prepolymer comprises the reaction product of components comprising: (i) a cycloaliphatic diisocyanate and (ii) at least one polyol having at least two hydroxy groups per molecule, preferably 2 to 4 hydroxy groups per molecule.

Suitable cycloaliphatic diisocyanates (i) can be selected from those reported above for component a1.

Suitable polyols (ii) are low-molecular-weight polyols and high-molecular weight polyols.
Low-molecular-weight polyols are compounds having two or more hydroxyl groups and a number average molecular weight (Mw) of below 400. Non-limiting examples of these polyols include dihydric alcohols such as ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butyleneglycol, 1,3-butyleneglycol, 1,2-butyleneglycol, 1,5-pentanediol, 1,6-hexanediol, neopentyl glycol, 3-methyl-1,5-pentanediol, 2,2,2-trimethylpentanediol, 3,3-dimethylolheptane, alkane (C₇-C₂₀) diol, 1,3- or 1,4-cyclohexanedimethanol and a mixture thereof, 1,3-or 1,4-cyclohexanediol and a mixture thereof, hydrogenated bisphenol A, 1,4-dihydroxy-2-butene, 2,6-dimethyl-1-octene-3,8-diol, bisphenol A, diethylene glycol, triethylene glycol, and dipropylene glycol; trihydric alcohols such as glycerin, trimethylolpropane and ditrimethylolpropane; tetrahydric alcohols such as tetramethylolmethane (pentaerythritol), dipentaerythritite and diglycerol; pentahydric alcohol such as xylitol; hexahydric alcohols such as sorbitol, mannitol, allitol, iditol, dulcitol, altritol, inositol, and dipentaerythritol; heptahydric alcohol such as perseitol; and octahydric alcohols such as sucrose.

Further non-limiting examples of suitable polyols include the aforementioned low-molecular-weight polyols as alkoxylated derivatives, for example C₁-C₄ alkoxylated, such as ethoxylated, propoxylated and butoxylated. In non-limiting embodiments, the following polyols can be alkoxylated with from 1 to 10 alkoxy groups: glycerol, trimethylolethane, trimethylolpropane, benzenetriol, cyclohexanetriol, erythritol, pentaerythritol, sorbitol, mannitol, sorbitan, dipentaerythritol and tripentaerythritol. In non-limiting embodiments, alkoxylated, ethoxylated and propoxylated polyols and mixtures thereof can be used alone or in combination with unalkoxylated, unethoxylated and unpropoxylated polyols and mixtures thereof. The number of alkoxy groups can be from 1 to 10, or from 2 to 8 or any rational number between 1 and 10. In a non-limiting embodiment, the alkoxy group can be ethoxy or propoxy and the number of ethoxy groups or propoxy groups can be 1 to 5 units. In another non-limiting embodiment, the polyol can be trimethylolpropane having up to 3 propoxy groups. Non-limiting examples of suitable alkoxylated polyols include ethoxylated trimethylolpropane, propoxylated trimethylolpropane, ethoxylated trimethylolethane, and mixtures thereof.
These low-molecular-weight polyols may be used singly or in a combination of two or more.

High-molecular weight polyols are compounds having two or more hydroxyl groups and having a weight average molecular weight M_W of 400 or more, and examples thereof include polyetherpolyol, polyester polyol, polycarbonate polyol, polyurethane polyol, epoxy polyol, vegetable oil polyol, polyolefin polyol, acrylic polyol and vinyl monomer-modified polyol.

Examples of polyetherpolyols include polypropylene glycols and polytetramethylene ether glycols.
Examples of polypropylene glycols include addition polymerized product (including random and/or block copolymer of two or more alkylene oxides) of alkylene oxides such as ethylene oxide and propylene oxide using the above-described low-molecular weight polyol.

Examples of polytetramethylene ether glycols include ring-opening polymerized product obtained by cation polymerization of tetrahydrofuran, and noncrystalline polytetramethylene ether glycol obtained by copolymerizing polymerization unit of tetrahydrofuran and the above-described dihydric alcohol.

Examples of polyester polyols include a polycondensation product obtained by allowing the above-described low-molecular-weight polyols and polybasic acids to react under known conditions.

Examples of polybasic acids include saturated aliphatic dicarboxylic acids (C₁₁ - C₁₃) such as oxalic acid, malonic acid, succinic acid, methylsuccinic acid, glutaric acid, adipic acid, 1,1-dimethyl-1,3-dicarboxypropane, 3-methyl-3-ethylglutaric acid, azelaic acid, sebacic acid, etc.; unsaturated aliphatic dicarboxylic acids such as maleic acid, fumaric acid, itaconic acid, etc.; aromatic dicarboxylic acids such as orthophthalic acid, isophthalic acid, terephthalic acid, toluenedicarboxylic acid, naphthalenedicarboxylic acid, etc.; alicyclic dicarboxylic acids such as hexahydrophthalic acid, etc.; other carboxylic acids such as dimer acid, hydrogenated dimer acid, het acid, etc. and acid anhydrides derived from these carboxylic acids such as oxalic anhydride, succinic anhydride, maleic anhydride, phthalic anhydride, 2-alkyl (C₁₂ - C₁₈) succinic anhydride, tetrahydrophthalic anhydride, trimellitic anhydride, and hallides derived from carboxylic acids thereof such as oxalyl dichloride, adipoyl dichloride, and sebacoyl dichloride.

Examples of polyester polyols include plants derived polyester polyol, to be specific, vegetable oil polyester polyols obtained by condensation reaction of hydroxycarboxylic acid such as hydroxyl group-containing vegetable oil fatty acid (e.g., castor oil fatty acid containing ricinoleic acid, hydrogenated castor oil fatty acid containing 12-hydroxystearic acid, lactic acid, etc.) using the above-described low-molecular-weight polyol as an initiator under known conditions.

Examples of polyester polyols include polycaprolactone polyol, and polyvalerolactone polyol obtained by ring-opening polymerization of lactones such as ε-caprolactone, γ-valerolactone, etc. and lactides such as L-lactide, D-lactide using the above-described low-molecular-weight polyols (preferably, dihydric alcohol) as an initiator; and further lactone-based polyester polyols obtained by copolymerizing such a polycaprolactone polyol or polyvalerolactone polyol with the above-described dihydric alcohol.

Examples of polycarbonate polyols include ring-opening polymerization product of ethylene carbonate using the above-described low-molecular-weight polyols (preferably, dihydric alcohol) as an initiator, and noncrystalline polycarbonate polyols obtained by copolymerization of dihydric alcohols such as 1,4-butanediol, 1,5-pentanediol, 3-methyl-1,5-pentanediol, and 1,6-hexanediol with ring-opening polymerization product.

Polyurethane polyols can be obtained as polyester polyurethane polyol, polyether polyurethane polyol, polycarbonate polyurethane polyol, or polyester polyether polyurethane polyol, by allowing polyester polyol, polyetherpolyol and/or polycarbonate polyol obtained as described above to react with polyisocyanate at an equivalent ratio (OH/NCO) of hydroxyl group (OH) to isocyanate group (NCO) of more than 1.

Examples of epoxy polyols include epoxy polyols obtained by reaction of the above-described low-molecular-weight polyols with polyfunctional halohydrin such as epichlorohydrin, β-methylepichlorohydrin, etc.
Examples of vegetable oil polyols include hydroxyl group-containing vegetable oil such as castor oil, palm oil, etc. Examples thereof include ester-modified castor oil polyol obtained by reaction of castor oil polyol or castor oil fatty acid with polypropylene polyol.

Examples of polyolefin polyols include polybutadiene polyol, and a partially saponified ethylene-vinyl acetate copolymer.
Examples of acrylic polyols include copolymers obtained by copolymerizing a hydroxyl group-containing acrylate with a copolymerizable vinyl monomer that is copolymerizable with hydroxyl group-containing acrylate.

Examples of hydroxyl group-containing acrylates include 2-hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxybutyl (meth)acrylate, 2,2-dihydroxymethylbutyl (meth)acrylate, polyhydroxyalkylmaleate, and polyhydroxyalkylfumarate. Preferably, 2-hydroxyethyl (meth)acrylate is used.

Examples of copolymerizable vinyl monomers include alkyl (meth)acrylate (1 to 15 carbon atoms) such as methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, hexyl (meth)acrylate, isononyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, cyclohexylacrylate, and isobornyl (meth)acrylate; aromatic vinyls such as styrene, vinyltoluene, and α-methylstyrene; vinyl cyanide such as (meth) acrylonitrile; vinyl monomers containing carboxyl groups such as (meth) acrylic acid, fumaric acid, maleic acid, and itaconic acid or their alkyl esters; alkanepolyol poly (meth)acrylate such as ethylene glycol di(meth)acrylate, butyleneglycol di(meth)acrylate, hexanediol di(meth)acrylate, oligoethylene glycol di(meth)acrylate, trimethylolpropane di(meth)acrylate, and trimethylolpropane tri (meth)acrylate; and vinyl monomers containing isocyanate groups such as 3-(2-isocyanato-2-propyl)-α-methylstyrene.

Acrylic polyol can be obtained by copolymerizing these hydroxyl group-containing acrylates and copolymerizable vinyl monomers in the presence of an appropriate solvent and a polymerization initiator.

Examples of acrylic polyol include silicone polyol and fluorine polyol.
Examples of silicone polyols include acrylic polyol in which as the copolymerizable vinyl monomer, for example, a silicone compound containing a vinyl group such as γ-methacryloxypropyltrimethoxysilane is blended in the above-described copolymerization of acrylic polyol.

Fluorine polyol is a copolymer of fluoroolefin and a monomer containing a double bond that is copolymerizable with fluoroolefin. The fluorine polyol is a weak solvent soluble fluorine-containing copolymer, containing 10 mass% or more fluorine based on fluoroolefin, containing 5 to 30 mol% of a hydroxyl group in the double bond-containing monomer, and containing 10 to 50 mol% of branched alkyl group having three or more carbons.

The vinyl monomer-modified polyol can be obtained by allowing the above-described high-molecular weight polyol to react with a vinyl monomer.

As the high-molecular weight polyol, preferably, a high-molecular weight polyol selected from polyetherpolyol, polyester polyol, and polycarbonate polyol is used.

Examples of vinyl monomers include the above-described alkyl (meth)acrylate, vinyl cyanide, and vinylidene cyanide. These vinyl monomers may be used singly or in a combination of two or more. Of these vinyl monomers, preferably, alkyl (meth)acrylate is used.

The vinyl monomer-modified polyol can be obtained by allowing these high-molecular weight polyols to react with vinyl monomers in the presence of, for example, a radical polymerization initiator (e.g., persulfate, organic peroxide, azo compound, etc.).

The above described high-molecular-weight polyols may be used singly or in a combination of two or more.
As the high-molecular weight polyol, preferably, polyester polyol, polycaprolactone polyol, polyether polyol, polycarbonate polyol or mixtures thereof is used.

In a preferred embodiment, the polyol (ii) for obtaining the prepolymer a2 has 2 to 4 OH groups per molecule and a molecular weight Mw ranging from 50 to 6,000 g/mole, preferably from 100 to 4,000 g/mole.

To synthesize the isocyanate group-terminated prepolymer, the cycloaliphatic diisocyanate (i) and at least one polyol (ii) are formulated (mixed) so that the equivalent ratio (NCO/OH) of the isocyanate group in the cycloaliphatic diisocyanate (i) relative to the OH group in the polyol is, for example, from 1.1 to 20, preferably from 1.3 to 10, more preferably from 1.3 to 6, and then the mixture is allowed to react in the reaction vessel, for example, at room temperature to 150°C, preferably at 60 to 100°C, for, for example, 0.5 to 18 hours, preferably 2 to 10 hours.

Under the aforementioned NCO/OH ratios, the synthesis reaction yields a mixture of prepolymer species together with unreacted cycloaliphatic diisocyanate species. The unreacted cycloaliphatic diisocyanate can be subsequently removed from the reaction product to recover the prepolymer. Alternatively, the mixture comprising the prepolymer species and the unreacted cycloaliphatic diisocyanate species can be used as such in the isocyanate component A forming a mixture of components a2 and a1.

In one embodiment, the prepolymer is preferably present in the mixture in an amount within the range of from 1% to 25% by weight, more preferably from 5% to 20% by weight, with respect to the weight of the mixture.

In another embodiment, the mass ratio between the unreacted cycloaliphatic diisocyanate and the prepolymer in the mixture is such that the weight percentage of the free isocyanate groups in the mixture is within the range of from 20% to 30% by weight with respect to the total weight of components a1 and a2.

In this reaction, as necessary, a catalyst may be added. The catalyst can be selected among those known in the art, such as tertiary amines, quaternary ammonium salts, organic metal compounds, potassium salts and acid phosphate esters.

Examples of tertiary amines include triethylamine, bis-(2-dimethylaminoethyl) ether, 1,4-diazabiscyclo[2,2.2]octane (DABCO), and N-methylmorpholine.
Examples of quaternary ammonium salts include tetraethyl hydroxyl ammonium salts.

Examples of organic metal compounds include organic tin compounds such as tin acetate, stannous octoate, stannous oleate, tin laurate, dibutyl tin diacetate, dimethyl tin dilaurate, dibutyl tin dilaurate, dibutyl tin dimercaptide, dibutyl tin maleate, dibutyl tin dilaurate, dibutyl tin dineodecanoate, dioctyl tin dimercaptide, dioctyl tin dilaurylate, and dibutyl tin dichloride; organic lead compounds such as lead octanoate and lead naphthenate; organic nickel compound such as nickel naphthenate; organic cobalt compounds such as cobalt naphthenate; organic copper compounds such as octenate copper; organic bismuth compounds such as bismuth octylate and bismuth neodecanoate.

Examples of potassium salts include potassium carbonate, potassium acetate, and potassium octoate.
Examples of catalysts also include acid phosphate esters such as monoesters and diesters of phosphoric acid or mixtures thereof.

Non-limiting examples of acid phosphate monoesters are: methyl phosphate, ethyl phosphate, isopropyl phosphate, butyl phosphate, octyl phosphate, decyl phosphate, dodecyl phosphate, stearyl phosphate, methoxyethyl phosphate, ethoxyethyl phosphate, propoxyethyl phosphate, butoxyethyl phosphate, pentyloxyethyl phosphate, isodecyloxyethyl phosphate, methoxypropyl phosphate, ethoxypropyl phosphate, propoxypropyl phosphate, butoxypropyl phosphate, and mixtures thereof.

Non-limiting examples of acid phosphate diesters are: dimethyl phosphate, diethyl phosphate, diisopropyl phosphate, dibutyl phosphate, dioctyl phosphate, bis(2-ethylhexyl) phosphate, diisodecyl phosphate, methoxyethyl-ethoxyethyl phosphate, methoxyethyl-propoxyethyl phosphate, ethoxyethyl-propoxyethyl phosphate, ethoxyethyl-butoxyethyl phosphate, di(methoxy-ethyl) phosphate, di(ethoxyethyl) phosphate, di(propoxy-ethyl) phosphate, di(butoxyethyl) phosphate, di(hexyloxy-ethyl) phosphate, di(decyloxyethyl) phosphate, di(meth-oxypropyl) phosphate, di(ethoxypropyl) phosphate, di(propoxylpropyl) phosphate and mixtures thereof.

In the synthesis of the prepolymer, the catalyst is preferably selected from: tertiary amine, acid phosphate ester or mixtures thereof. More preferably, the catalyst is an acid phosphate ester, which is preferably selected from C₈ monoester of phosphoric acid, C₁₀ monoester of phosphoric acid, C₈ diester of phosphoric acid, C₁₀ diester of phosphoric acid and/or mixtures thereof. Particularly preferred catalyst is a mixture of these C₈- and C₁₀- monoesters and diesters of phosphoric acid, wherein the monoesters are present in an amount of about 40% by weight and the diesters in an amount of about 60% by weight. This mixture is also available on the market with the trade name ZELEC UN (by Stepan Company)

The above catalysts for the preparation of the prepolymer may be used singly or in a combination of two or more.

In one embodiment, the synthesis of the prepolymer is carried out by progressively adding the polyol to the cycloaliphatic diisocyanate, optionally in an inert nitrogen atmosphere, in the presence of the catalyst. The reaction can be monitored by determining the concentration of residual free isocyanate groups by titration.

In one preferred embodiment, the isocyanate-terminated prepolymer is obtained by reacting H12MDI and a mixture of low-molecular weight polyols (prepolymer initiator). A suitable mixture of low-molecular weight polyols is, for example, a mixture of trimethylol propane (TMP) and dipropylene glycol (DPG) in a weight ratio DPG/TMP within the range of from 50:50 to 70:30. Preferably, the weight ratio between the prepolymer initiator and H12MDI is within the range of from 0.5 wt% to 10 wt%, more preferably from 2 wt% to 5 wt% based on the weight of H12MDI. Preferably, the reaction between the prepolymer initiator and H12MDI is carried out in the presence of a mixture of C₈- and C₁₀- monoesters and diesters of phosphoric acid (ZELEC UN) as catalyst, for example in an amount of from 0.2% to 3%, preferably from 0.4% to 2% by weight with respect to the weight of the reaction mixture. The prepolymer thus obtained has advantageously a stable and reproducible viscosity over time.

Component a3
The isocyanate component comprises one or more modified polyisocyanate composition (component a3), that is a composition which is produced by modifying an aliphatic or cycloaliphatic diisocyanate so that it contains one or more functional group selected from: isocyanurate group, allophanate group, biuret group, urethane group, urea group and mixture thereof.

It has been surprisingly found that the presence of the modified polyisocyanate composition a3, even at relatively low dosages, in the isocyanate component A comprising either the isocyanate-terminated prepolymer component a2 or both the cycloaliphatic diisocyanate monomer component a1 and the isocyanate-terminated prepolymer component a2 improves the impact resistance of the cured product. Without being bound to any theory, this effect might be due to the fact that the polyisocyanate modified composition a3 imparts flexibility to the cured polyurethane material whithout however jeopardizing its rigidity and thus its mechanical and thermal resistance properties.

The modified polyisocyanate composition containing the above-described isocyanurate group is a trimer of an aliphatic or cycloaliphatic diisocyanate, and for example, can be obtained by allowing the aliphatic or cycloaliphatic diisocyanate to react in the presence of a known isocyanurate-forming catalyst, thereby allowing trimerization.

The modified polyisocyanate composition containing the above-described allophanate group is an allophanate-modified aliphatic or cycloaliphatic diisocyanate, and for example, can be obtained by allowing the aliphatic or cycloaliphatic diisocyanate and a monohydric alcohol to react, and then further allowing them to react in the presence of a known allophanate-forming catalyst.

Examples of monohydric alcohol include methanol, ethanol, n-propanol, n-butanol, n-pentanol, n-hexanol, n-heptanol, n-octanol, n-nonanol, n-decanol, n-undecanol, n-dodecanol (lauryl alcohol), n-tridecanol, n-tetradecanol, n-pentadecanol, n-hexadecanol, n-heptadecanol, n-octadecanol (stearyl alcohol), n-nonadecanol, and eicosanol.

Further examples of monohydric alcohol include isopropanol, isobutanol, sec-butanol, tert-butanol, isopentanol, isohexanol, isoheptanol, iso-octanol, 2-ethylhexane-1-ol, isononanol, isodecanol, 5-ethyl-2-nonanol, trimethylnonylalcohol, 2-hexyldecanol, 3,9-diethyl-6-tridecanol, 2-isoheptylisoundecanol, 2-octyldodecanol, and other branched alkanol (C₅ to C₂₀).

The polyisocyanate composition containing the above-described biuret group is a biuret-modified substance of the aliphatic or cycloaliphatic diisocyanate, and for example, can be obtained by allowing the aliphatic or cycloaliphatic diisocyanate to react with, for example, water, tertiary alcohol (e.g., t-butylalcohol, etc.), or secondary amine (e.g., dimethylamine, diethylamine, etc.), and then further allowing them to react in the presence of a known biuretization catalyst.

The polyisocyanate composition containing the above-described urethane group is a polyol-modified substance of the aliphatic or cycloaliphatic diisocyanate, and can be obtained, for example, by reaction between the aliphatic or cycloaliphatic diisocyanate and a polyol component, i.e. a component containing mainly polyol having two or more hydroxyl groups. Examples of polyol component in the present invention include low-molecular weight polyols and high-molecular weight polyols, such as the polyols (ii) described above as suitable polyols for the preparation of the prepolymer a2.

The polyisocyanate composition containing the above-described urea group is a polyamine-modified substance of the aliphatic or cycloaliphatic diisocyanate, and can be obtained, for example, by reaction between the aliphatic or cycloaliphatic diisocyanate, and water, or a polyamine component, i.e. a compound containing mainly polyamine, that is a compound having two or more amino groups.

Examples of polyamine components include aromatic polyamine, aralkyl polyamine, alicyclic polyamine, aliphatic polyamine, amino alcohol, an alkoxysilyl compound having a primary amino group, or a primary amino group and a secondary amino group, and polyoxyethylene group-containing polyamine.

Examples of aromatic polyamines include 4,4'-diphenylmethanediamine, and tolylenediamine.
Examples of aralkyl polyamine include 1,3- or 1,4-xylylene diamine and mixtures thereof.

Examples of alicyclic polyamines include 3-aminomethyl-3,5,5-trimethylcyclohexylamine (also called: isophoronediamine), 4,4'-dicyclohexylmethanediamine, 2,5(2,6)-bis(aminomethyl) bicyclo[2.2.1]heptane, 1,4-cyclohexanediamine, 1-amino-3-aminomethyl-3,5,5-trimethylcyclohexane, bis-(4-aminocyclohexyl) methane, diaminocyclohexane, 3,9-bis(3-aminopropyl)-2,4,8,10-tetraoxaspiro[5.5]undecane, 1,3- and 1,4-bis(aminomethyl) cyclohexane and mixtures thereof.

Examples of the aliphatic polyamine include ethylenediamine, propylene diamine, 1,3-trimethylenediamine, 1,4-tetramethylenediamine, 1,5-pentamethylenediamine (including the above-described pentamethylenediamine), 1,6-hexamethylenediamine, hydrazine (including hydrate), diethylenetriamine, triethylenetetramine, tetraethylenepentamine, 1,2-diaminoethane, 1,2-diaminopropane, and 1,3-diaminopentane.

In an embodiment, the modified polyisocyanate composition comprises an aliphatic or cycloaliphatic diisocyanate comprising functional groups of only one of the above-described types of functional groups, i.e. isocyanurate, allophanate, biuret, urethane and urea.

In another embodiment, the modified polyisocyanate composition comprises an aliphatic or cycloaliphatic diisocyanate having functional groups of two or more of the above-described types functional groups; such a modified polyisocyanate composition can be produced by suitably combining the above-described reactions.

Preferably, the aliphatic diisocyanate compound of the polyisocyanate modified composition a3 is selected from: ethylene diisocyanate, trimethylene diisocyanate, tetramethylene diisocyanate, pentamethylene diisocyanate (PDI), 1,6-hexamethylene diisocyanate (HDI), octamethylene diisocyanate, nonamethylene diisocyanate, decamethylene diisocyanate, bis(isocyanatoethyl)-carbonate, bis(isocyanatoethyl)ether and mixture thereof.

Preferably, the cycloaliphatic diisocyanate compound of the modified polyisocyanate composition a3 is selected from those reported above for components a1 and a2.

The cycloaliphatic diisocyanate of components a1, a2 and a3 used in the polymerizable composition can be the same or different.
In an embodiment, the modified polyisocyanate composition comprises a modified aliphatic or cycloaliphatic diisocyanate, more preferably a modified HDI or modified PDI, having at least one group selected from: isocyanurate group, allophanate group and mixture thereof.

Trimerized aliphatic or cycloaliphatic diisocyanates can be obtained by known methods. HDI or PDI can be trimerized, for example, by a method in which HDI or PDI diisocyanate is allowed to react in the presence of a known isocyanurate-forming catalyst thereby allowing trimerization.

Alternatively, HDI or PDI is trimerized, for example, by a method in which HDI or PDI is allowed to react with alcohols, and then subjected to trimerization reaction in the presence of a trimerization catalyst, and then unreacted HDI or PDI is removed; or by a method in which after only HDI or PDI is subjected to trimerization reaction, unreacted HDI or PDI is removed, and the obtained trimer and alcohols are allowed to react. With this alternative method aliphatic or cycloaliphatic diisocyanates modified with both isocyanurate groups and allophanate groups are obtained.

Example of isocyanurate-forming catalyst include hydroxide of tetraalkylammonium or its organic salt of weak acid such as tetramethyl ammonium, tetraethyl ammonium, tetrabutyl ammonium, trimethylbenzyl ammonium; trialkylhydroxyalkyl ammonium hydroxide or its organic salt of weak acid such as trimethylhydroxypropyl ammonium, trimethylhydroxyethyl ammonium, triethylhydroxypropyl ammonium and triethylhydroxyethyl ammonium.

The conditions of the trimerization reaction are, for example, under an atmosphere of inactive gas such as nitrogen gas, and under a normal pressure (atmospheric pressure) and a reaction temperature of, for example, 30 to 100°C, preferably 40 to 80°C, and a reaction time of, for example, 0.5 to 10 hours, preferably 1 to 5 hours.

In the modified polyisocyanate composition comprising isocyanurate rings, the diisocyanate compounds are linked together so that compounds having three NCO groups forming an isocyanurate ring are formed (i.e. a trimeric oligomer). Normally, this modified polyisocyanate composition, also contains pentameric and heptameric oligomers which contain two and three isocyanurate rings, respectively, as well as polyisocyanate in dimeric form.

Preferably, the modified polyisocyanate composition comprises the trimeric polyisocyanate oligomer in an amount of at least 30% by weight referred to the weight of the modified polyisocyanate composition, preferably at least 45% by weight.
Further details on the preparation of modified polyisocyanate compositions suitable for being used in the present invention can be found in EP3486230A1.

Modified polyisocyanate compositions comprising polyisocyanates containing isocyanurate groups are also commercially available, for example under the trade name Polurgreen MT100 (isocyanurate-modified HDI - SAPICI S.p.A., Italy) and STABiO(R) (isocyanurate-modified PDI Mitsui Chemicals, Japan). Modified polyisocyanate compositions comprising polyisocyanate containing allophanate groups are commercially available, for example, under the trade name Polurgreen XP100 (allophanate-modified HDI - SAPICI S.p.A., Italy).

The isocyanate component A may comprise the modified polyisocyanate composition a3 in combination with either the isocyanate group-terminated prepolymer a2 or both the cycloaliphatic diisocyanate monomer a1 and the isocyanate group-terminated prepolymer a2.

In one embodiment, the isocyanate component A comprises the isocyanate group-terminated prepolymer a2 in combination with the modified polyisocyanate composition a3, the cycloaliphatic diisocyanate monomer a1 being absent.

In one embodiment, the isocyanate component A comprises a mixture of the isocyanate group-terminated prepolymer a2, the cycloaliphatic diisocyanate monomer a1 and the modified polyisocyanate composition a3.
The presence of the prepolymer a2 improves the compatibility of the isocyanate component A and the polyol component B, thus favouring their mixing and the rapid achievement of a clear polymerizable composition.

In the polyisocyanate component A, the weight ratio between components a3 and a1 (a3/a1) may vary within a wide weight range, for example within the range from 5:95 to 80:20, more preferably from 10:90 to 50:50.
In one embodiment, the weight ratio between component a3 and the sum of components a1 and a2, i.e. a3/a1+a2, is preferably within the range from 5:95 to 90:10, more preferably from 5:95 to 70:30, even more preferably from 10:90 to 60:40.

In one embodiment, the polyisocyanate component A preferably comprises component a3 in an amount within the range of from 5% to 60% by weight, more preferably from 10% to 55% by weight, with respect to the total weight of components a3, a2 and a1 (if present).

In one embodiment, the polyisocyanate component A preferably comprises component a2 in an amount within the range of from 1% to 25% by weight, more preferably from 5% to 20% by weight, with respect to the total weight of components a3, a2 and a1 (if present). Said weight percentages of a2 refer to the weight percentages of prepolymer species obtained in the prepolymer synthesis, excluding the unreacted cycloaliphatic diisocyanate.

In one embodiment, the polyisocyanate component A preferably comprises component a1 in an amount within the range of from 35% to 75% by weight, more preferably from 30% to 70% by weight,with respect to the total weight of components a3, a2 and a1.

In one embodiment, the polyisocyanate component A preferably comprises:
- from 5% to 60% by weight of component a3;
- from 5% to 25% by weight of component a2;
- from 35% to 70% by weight of component a1;
said weight percentages being referred to total weight of components a3, a2 and a1.

Polyol component B
The polymerizable composition of the present invention comprises a polyol component B comprising at least one polyol having from 2 to 5 hydroxy groups per molecule. Suitable polyols are the low-molecular weight polyols and high-molecular weight polyols having from 2 to 5 hydroxy groups per molecule reported above as suitable component (ii) for preparing the isocyanate group-terminating prepolymer a2.

In a preferred embodiment, the polyol used as component B has 2 to 4 OH groups per molecule and a molecular weight M_w ranging from 50 to 6,000 g/mole, preferably from 100 to 4,000 g/mole.

As component B, the polyols may be used singly or in a combination of two or more.
The polyol or mixture of polyols of component B can be the same or different from the polyol or mixture of polyols used for the synthesis of the isocyanate group-terminating prepolymer a2.

In a preferred embodiment, the at least one polyol of component B comprises or is an alkoxylated polyol, such as a polyol alkoxylated with C₁-C₄ alkoxy groups, e.g. ethoxylated, propoxylated or butoxylated. In non-limiting embodiments, the following polyols can be alkoxylated with from 1 to 10 alkoxy groups: glycerol, trimethylolethane, trimethylolpropane, benzenetriol, cyclohexanetriol, erythritol, pentaerythritol, sorbitol, mannitol, sorbitan, dipentaerythritol and tripentaerythritol. In non-limiting embodiments, alkoxylated, ethoxylated and propoxylated polyols and mixtures thereof can be used alone or in combination with unalkoxylated, unethoxylated and unpropoxylated polyols and mixtures thereof. The number of alkoxy groups can be from 1 to 10, or from 2 to 8 or any rational number between 1 and 10. In a non-limiting embodiment, the alkoxy group can be ethoxy or propoxy and the number of ethoxy groups or propoxy groups can be 1 to 5 units. In another non-limiting embodiment, the polyol can be trimethylolpropane having up to 3 propoxy groups. Non-limiting examples of suitable alkoxylated polyols include ethoxylated trimethylolpropane, propoxylated trimethylolpropane, ethoxylated trimethylolethane, and mixtures thereof.

Catalyst component C
The polymerizable composition of the present invention comprises a catalyst component C to catalyse the polymerization reaction of the polymerizable composition and form a polymerized product.

The catalyst C comprises at least one tertiary amine, which can be a mono-amine or a polyamine.
It has been found that tertiary amines provide adequate reactivity in the formulations of the present invention compared to other conventional polymerization catalysts, providing high conversion of the polymerizable composition (i.e. low amount of unreacted NCO groups) at relatively low polymerization temperature. Tertiary amines, moreover, being used at relatively low dosages, allow to obtain satisfactory optical properties and reduced yellowing of the cured product.

Non-limiting examples of tertiary amines that can be used as catalyst include aliphatic amines, cycloaliphatic amines and aromatic amines. Preferably, the tertiary amine is selected from: aliphatic amine, cycloaliphatic amine or a mixture thereof.

In an embodiment, the at least one tertiary amine used as catalyst C is a compound in which the nitrogen atom of the tertiary amino group is covalently attached to none or not more than one tertiary carbon atom. It has been found that when the nitrogen atom of the tertiary amino group is covalently attached to two or three tertiary carbon atoms, the tertiary amine is sterically hindered and may not not exhibit sufficient catalytic activity.

The catalyst C may comprise mono-, di-, tri-, tetra- amines, cyclic amines or mixtures thereof.

Non-limiting examples of suitable tertiary amine include, benzyldimethylamine, n-methylmorpholine, dimethylcyclohexylamine, dimethylethanolamine, dimethylaminoethoxyethanol, triethanolamine (also known as diazabiscyclo[2,2.2]octane (DABCO)), dimethyldipropylenetriamine, pentamethyldiethylenetriamine, bis(2-dimethylaminoethyl) ether triethylamine, triethylenediamine, tributylamine, triisopropanolamine, bis-(2-dimethylaminoethyl) ether, 1,4-, N-methylpiperidine and N-methylmorpholine.

In an embodiment, the catalyst comprises at least one cycloaliphatic tertiary amine, selected from: 1,4-diazabiscyclo[2,2.2]octane (DABCO), N-methylpiperidine, N-phenylpiperidine and mixtures thereof. In one embodiment, the catalyst C comprises or consists of DABCO.

Other components
The polymerizable composition may also include further known additives such as, for example, anti-foaming agents, silane coupling agents, plasticizers, compatibilizers (such as poloxamers, caprolactones, etc.), heat-resistant stabilizers, light-resistant stabilizer, antioxidants (e.g. Irganox 1135 of Ciba), UV absorbers (e.g. benzotriazoles), IR absorbers, release agents (e.g. alkyl phosphates and non-ionic fluorinated surface-active agents), pigments, dyes, bluing agents lubricants, fillers (e.g. inorganic nanoparticles based on salts or based on zinc oxide, cerium oxide, silicon oxide, aluminum oxide, titanium oxide or zirconium oxide), hydrolysis inhibitor and the like.

Preparation of the polymerizable composition and molded article
The polyurethane resin of the present invention can be produced by known polymerization methods such as bulk polymerization.

In bulk polymerization, for example, while stirring the polyisocyanate component A the polyol component B is added thereto to form a monomer mixture. The monomer mixture is added of the catalyst C to form the polymerizable composition and then allowed to react at a reaction temperature of about 20 to 150°C, more preferably at 50 to 100°C, for about 0.5 to 15 hours to obtain a polymerized article.

The polyisocyanate component A can be prepared by mixing beforehand components a1, a2 and a3 according to the composition desired for the polyisocyanate component A.

The catalyst C and the optional additives may indifferently be added to any of the components A and B or to the mixture of A and B. In a preferred embodiment the polyol component B includes the catalyst C.

Preferably the polyisocyanate component A and the polyol component B are separately degassed, for example by stirring at a pressure of 100 mbar or below, at a temperature of about 40-60°C for about 0.5 to 3 hours, to remove gas bubbles that may be present in the liquids and thus favour the manufacture of defect-free polymerized articles. Advantageously, degassing under vacuum of the polymerizable composition is also carried out.

The polymerizable composition comprises the polyisocyanate component A and the polyol component B in a suitable weight ratio, for example in a weight ratio A:B within the range from 1:1 to 2.5:1, more preferably from 1.5:1 to 2:1.

In an embodiment, the polyisocyanate component A and the polyol component B are present at an equivalent ratio NCO/OH of isocyanate group NCO to hydroxyl group OH within the range of from 1.2:1 to 1:1.

The polymerizable composition comprises the catalyst component in a catalytically active amount. Preferably, the polymerizable composition comprises the catalyst component in an amount within the range of from 0,5 wt.% to 15 wt.%, preferably from 1 wt.% to 10 wt.%, with respect to the weight of the polymerizable composition.

The optional additives are normally comprised in the polymerizable composition in an amount within the range of from 0 wt.% to 10 wt.%, preferably from 1 wt.% to 5 wt.%, with respect to the weight of the polymerizable composition.

The mixing of the components of the polymerizable composition is usually carried out at a temperature within the range from 20°C to 50°C.
The polymerizable composition of the present invention has a short clearing time, i.e. the time necessary for the components to form a clear and homogenous composition which is stable at the mixing temperature (i.e. no separation of the components occurs). For example, the clearing time is lower than 5 minutes, preferably lower than 3 minutes, more preferably within the range from 1 to 3 minutes. The clearing time is thus a measure of the compatibility of the components of the polymerizable composition, particularly of the polyisocyanate component A and polyol component B.

The viscosity of the polymerizable composition is sufficiently low that it can be easily mixed and poured in a mold; the low viscosity also favours gas bubbles diffusion and thus the degassing operation.

Preferably, the viscosity of the polymerizable composition at 25°C is within the range of from 200 cSt to 700 cSt as determined by means of a Ubbelohde viscometer.

The polymerizable composition may be casted into a casting mold and cured according to known techniques. For example, the polymerizable composition may be cured by heating at a temperature of from ambient temperature to 150°C, preferably from 25°C to 90°C, over a period of time from 0.5 to 10 hours, preferably 1 to 5 hours.

In a preferred embodiment, the polymerizable composition is used for manufacturing a molded article by means of the vacuum casting technique. For the vacuum casting, the liquid polymerizable composition is poured into a mold having a cavity, generally made of silicone, and then the mold put into a vacuum chamber. The purpose of the vacuum is to draw air out of the cavity of the mold, the cavity having the desired shape and dimensions of the final product, removing any bubbles while forcing the polymerizable composition into the entire volume of the cavity. Then the mold is heated in an oven where the polymerizable composition is cured to form a cured polyurethane material.

For the manufacturing of polyurethane lenses, the molds may be conventional molds, such as molds that are made from two mold pieces and a gasket forming a cavity that defines the shape and dimensions of the final lens. The mold pieces can be made, for example, of glass, metal or plastic.

The molded products obtained by curing the polymerizable composition of the present invention are transparent and exhibit high stability against ageing due to exposure to UV-VIS radiation. They also exhibit excellent hardness, impact and heat resistance and low shrinkage during molding operations.

After casting into a mold, the polymerizable compositions are cured according to known techniques. For example, the polymerizable composition may be cured by heating at a temperature of from ambient temperature to 150°C, preferably from 25°C to 90°C, over a period of time from 0.5 to 10 hours, preferably 1 to 5 hours.

In one embodiment, after demolding the cured product may be subjected to a post-curing heat treatment (hereinafter also named “annealing treatment”), which is performend, for example, at a temperature within the range of from 50° C to 150° C, preferably within the range of from 70° C to 130° C.

The duration of the post-curing heat treatment is generally within the range of from 30 minutes to 15 hours, preferably from 1 hour to 10 hours, more preferably from 2 hour to 8 hours.

It has been observed that the post-curing treatment improves the conversion of the polymerizable composition into a cured product, as demonstrated by the reduction of the amount of free NCO groups (as detectable, for example, by infrared spectroscopy). The higher conversion achieved for the polymerizable composition, in turn, favourites the demolding of the cured product and improves the thermal and mechanical properties of the cured material, which exhibit, for example, higher values of the Deflection Temperature under load 1.82 MPa (HDT) (ASTM D-648) and the Impact Resistance Index.

As noted before, the cured product are transparent and have superior ageing resistance against UV radiation. For example, specimen of the cured material in the form of flat plate having thickness of 3mm are almost totally transparent to UV-A radiation (l = 315 to 400 nm) and exhibit a UV cut-off at a wavelength of 300 nm or lower.

The polymerizable compositions and cured products of the present invention have desired properties for a wide range of applications, with primary emphasis on molding and prototyping, especially using the vacuum casting technology. The polyurethane cured product may be used, for example, for manufacturing an optical material, such as a material for ophtalmic lenses and lenses for optical instruments, fiber optics, windows and automotive, nautical and aviation transparent elements, such as lightning elements for automobiles.

The invention will now be described in more detail with the following examples, which are given for purely illustrative purposes and which are not intended to limit the scope of the invention in any manner, and with reference to the following figures:

- Figure 1, which depicts UV Vis spectra of comparative example C1 and C2;
- Figure 2, which depicts UV Vis spectra of Example 3 according to the invention;
- Figure 3, which depicts UV Vis spectra of Example 12 according to the invention;
- Figure 4, which depicts UV Vis spectra of Example 6 according to the invention;
- Figure 5, which depicts UV Vis spectra of Example 3, 10 and C2 according to the invention;
- Figure 6, which depicts the results of the QUV test for comparative examples C1 and C2 and for Example 3, 6, 9, 10 and 12 according to the invention;
- Figure 7, which depicts the results of the weathering test for comparative example C2 and Examples 4, 5, 11 and 13 according to the invention.
EXAMPLES

CHARACTERIZATION METHODS
The polymerizable compositions and cured polyurethane molded articles were evaluated by means of the following methods.

Optical characteristics
- Yellowness Index (YI) (ASTM D-1925): the YI was determined on the optical material in the form of a 3 mm-thick flat plate with a GretagMacbeth 1500 Plus spectrophotometer taking the standard illuminant C and the observer into account (angle of 2°). The YI is defined as: YI = 100/Y (1.277X - 1.06Z);

- Light Transmittance at a given wavelength: the transmittance at a given wavelength (T% @wavelength(nm)) of an optical material in the form of a 3 mm-thick flat plate was measured with an UV-Visible spectrophotometer Agilent Cary 60;

Physical and mechanical characteristics
- Rockwell hardness (M) was measured with a Rockwell durometer (ASTM D-785) on a 3 mm-thick flat plate;

- Unnotched Izod impact strength was measured according to ASTM D-256;

- Deflection temperature under load 1.82 MPa (HDT) was measured according to ASTM D-648;

- Ageing resistance (QUV test) was performed on a QUV tester model QUV/se with Solar Eye Irradiance Control, collecting the YI of a 3mm flat plate at incremental times under the subsequent irradiating conditions: 0.5 W @ 50 °C for 200 hours; results are expressed in terms of difference between the YI before and after the test (DYI); the test is considered as passed if DYI is equal to or lower than 3.0 after 200 hours;

- Ageing resistance (weathering test) performed on Xenon-meter model Q-SUN XE-1-B, collecting the YI of a 3mm flat plate at incremental times under the subsequent irradiating conditions: 60W/m² @ 50°C for 240 hours; the test is considered as passed if DYI is equal to or lower than 1.5 after 240 hours.

Materials
In the Examples, the following compounds were used.
- 4,4’-methylene bis(cyclohexyl isocyanate), H12MDI (manufactured by EVONIK, trade name VESTANAT);
- dipropylene glycol (DPG) supplied by Merck (assay > 99%);
- trimethylol propane (TMP), industrial grade by PERSTORP (assay > 99%);
- Lupragen N201, supplied by BASF, master batch of DABCO at about 33% b.w. in dipropylene glycol;

- Desmophen 4011T, produced by Covestro AG, trimethylol propane tripropoxylated;
- Lowilite 92 (LL92), produced by ADDIVANT, hindered amine light stabilizer (HALS);
- POLURGREEN MT100, isocyanurate-modified HDI composition (trimer content: 50 wt% or more) by SAPICI S.p.A., Italy;
- POLURGREEN XP100, allophanate-modified HDI composition by SAPICI S.p.A., Italy;

- STABiO, grade D-376N, isocyanurate-modified PDI composition (trimer content: 50 wt% or more) by Mitsui Chemicals, Japan;
- ZELEC UN, mixture of C₈ and C₁₀ monoesters and diesters of phosphoric acid, wherein the monoesters are about 40% by weight and the diesters are about 60% by weight, by Stepan Specialty.
- PX521, castable polyurethane resin by SIKA, France.

Preparation of the isocyanate group-terminated prepolymer (component a2)
A prepolymer initiator was prepared as follows. 60 parts by weight of DPG and 40 parts by weight of TMP were placed in a glass flask and positioned over a mixing/warming plate. The mixture was magnetically stirred while heating at 50°C for as sufficient time to allow TMP to melt. This operation was carried out under degassing conditions (i.e. absolute pressure <100 mbar) to allow entrapped air to be removed.
The prepolymer was prepared by reacting 95.5 parts by weight of Vestanat H12MDI and 4.2 parts by weight of the prepolymer initiator in the presence of 0.3 parts by weight of Zelec UN.
The reaction was carried out at 80 °C under stirring of the reaction mixture at an absolute pressure equal to about 100mbar for approximatively 4 hours. The conversion rate was monitored by infrared spectroscopy using FTIR Affinity 1-S instrument produced by Shimadzu, equipped with probe for attenuated total reflection measurements (ATR) Miracle-PIKE with Zn-Se crystal.

The viscosity of the reacting prepolymer was measured by Ubbelohde viscometer at 25°C. The reaction was considered concluded when both the intensity of the absorption peak at 1720 cm^-1 (stretching mode of the carbonyl group) of the forming urethane bond and the viscosity of the reacting prepolymer became substantially constant. The final viscosity at 25°C of the so produced prepolymer was about 200 cStokes.
The mixture containing the reaction product contained about 15 wt% prepolymer and about 85 wt% of unreacted H12MDI (percentages referred to the sum of prepolymer and H12MDI). The weight percentage of free NCO groups resulted about 27.70% as determined by means of acidic titration (with HCl 0.1N over n-butylamine 0.1N in dimethyl formamide). The mixture was employed as such, i.e. without removing the unreacted H12MDI, as component a2 for preparing the compositions listed in Table 1.

Preparation of the Masterbatch B+C containing the polyol component B and the catalyst component C
A masterbatch comprising component B (mixture of polyols) and component C (catalyst), hereinafter “masterbatch B+C”, was prepared by mixing the following ingredients into a glass flask:
- 30.3 parts by weight of Lupragen N201 (DABCO + DPG)
- 27.0 parts by weight of DESMOPHEN 4011T
- 23.0 parts by weight of DPG
- 16.2 parts by weight of TMP
- 3.5 parts by weight of LL92.
The mixture was heated at 50°C while stirring and degassing at an absolute pressure <100 mbar for approximatively 3 hours to allow the melting of TMP, the homogenization of the solution and the removal of entrapped air.

Examples 1-13
Molded sheets 1 to 13 were manufactured by curing corresponding polymerizable compositions having the chemical compositions listed in Table 1, where Examples 1-3, 5 and 10-13 are according to the invention and Examples 4, 6-9 are comparative. The polymerizable compositions have been prepared in the following way.
To simulate the vacuum casting operation, the isocyanate component A and the masterbatch B+C were degassed (absolute pressure <100mbar) for 5 minutes in two separated glass flasks. The masterbatch B+C was then poured into the flask containing the isocyanate component A and mixed by means of a magnetic stirrer under vacuum (absolute pressure <100mbar) for a sufficient time so as to allow the blend to clarify and become a viscous polymerizable composition having a syrupy consistency (approx. 5 minutes).
After breaking vacuum with nitrogen venting, the syrupy polymerizable composition was poured by gravity into an assembled silicone mold consisting of two specular parts that after coupling provide an internal cavity in the form of a sheet having the following dimensions: 12cm*12cm*0.3cm (length*width*thickness). The top part of the mold was provided with a hole connected to the internal cavity through which the polymerizable composition was loaded; in addition, several slits were provided to facilitate the exit of air during loading and avoid air bubbles entrapment.
The mold assembly was placed in an oven at a temperature of 70 °C where curing was carried out over a period of 3 hours.
In some cases, after demolding the polymerized sheets were subjected to a post-cure thermal treatment as reported in the technical bulletin of SIKA PX521: from 70°C to 70°C (2h), from 70°C to 80°C (1 min), from 80°C to 80°C (3h), from 80°C to 100°C (1 min), from 100°C to 100°C (2h).
The polymerized sheets were then cut and shaped into the final specimens for the measurements of the optical and physical parameters.

Comparative examples C1 and C2
For comparison purposes, following the same method of preparation of Examples 1 to 13, the following molded sheets were also produced:
- Example C1, obtained by curing a polymerizable composition in which the isocyanate component A contains only component a2;
- Example C2, obtained by curing the commercial polyurethane resin PX521.
The results of the characterization of the cured molded products according to the Examples 1 to 13, C1 and C2 are reported in Table 1.

The processability of the castable commercial polyurethane resin PX521 and the properties of the cured material obtained thereof (Example C2) have been considered as benchmark. In Table 1, the column “Optimal value” indicates the value of the parameter to which it refers that is deemed acceptable.

The data of Table 1 show that the use of an isocyanate component A containing only component a2 in the presence of the tertiary amine DABCO as catalyst C (comparative example C1) provides a polymerizable composition having excellent processability (clearing time = 0, namely instantaneous blending) and a good conversion (Rockwell Hardness higher than 80), however the impact resistance results insufficient (lower than 45 kJ/m²) and substantially lower than the benchmark C2.

Materials having impact resistance values lower than 45 are inadequate for applications such as the manufacturing of prototypes of complex designs, because of the high probability of breaking and chipping of the material during opening and processing operations (polishing, edging phases, etc.).

The cured material of comparative Example C1 shows excellent optical properties and much better ageing behavior in comparison with the benchmark material C2. In fact, as depicted in Figure 1, while C2 is transparent (T% @ 365nm <1.0) above ca. 365nm, being therefore influenced by all UVA radiations below this threshold, C1 is totally transparent in the UVA region (T% @ 280nm <1%) which guarantees an excellent ageing performance as also inferable from Figure 6.

The data of Table 1 also demonstrate that compositions according to the present invention, which contain a modified polyisocyanate composition as component a3 significantly improves the impact resistance of the cured material compared to C1 (see examples 1 to 3) thus limiting the occurrence of defects in the demoulding operation and subsequent processing of the cured articles. This effect may be due to the higher flexibility of the material brought about by the long carbon backbones of the modified polyisocyanate species containing trimeric isocyanate groups.

It is also noted that the processability of the polymerizable compositions of Examples 1 to 3 deteriorates a bit compared to Example C1 (the clearing time increases, likely because of the apolar nature of the trimeric species of component a3), but it remains within the range of optimal values (i.e. lower than 240 seconds). In addition, as visible in Figure 2, the presence of the component a3 in the formulation does not affect the transparency to UVA radiations of the cured materials, which therefore have very good ageing resistance (see Figure 6).

A similar behavior was observed when modified polyisocyanate compositions a3 based on PDI (commercial product STABiO) are used in the polymerizable compositions (Examples 5 and 12 according to the invention and comparative Example 9). This modified-PDI composition improves the impact resistance of the cured product in a way similar to modified-HDI compositions and slightly improves the compatibility of the isocyanate component A and polyol component B (the clearing time of Example 5 is lower than that of Example 3).

The positive influence of the modified polyisocyanate composition a3 on the overall features of the polymerizable composition is observed up to a concentration of 50 wt.% of a3 with respect to the isocyanate component A (examples 11 and 12), the processability, optical and mechanical properties remaining substantially unaffected.

Comparison of Example 3 according to the invention and comparative Example 4 shows that using the prepolymer a2 instead of the diisocyanate a1 improves (i.e. reduces) the processing time and significantly increase the impact resistance. Nevertheless, the processability of the polymerizable composition and the properties of the cured material of Example 3, where the isocyanate component A is formed by a1 and a3, are within the optimal values.

The compositions of comparative Examples 6 to 8 contained a modified polyisocyanate composition derived from the aliphatic diisocyanate HDI. Similar to component a3 based on cycloaliphatic diisocyanate (Examples 1-5 and 9-12), the modified polyisocyanate composition derived from HDI allows to prepare polymerizable compositions and cured products having optimal properties. It is noted, however, that for comparative Examples 6 to 8 the impact resistance could not be measured because test specimens could not be properly cut and shaped from the as-demoulded material. The cutting operation, in fact, resulted in specimens containing minor superficial defects (chips and notches) that make the evaluation of impact resistance unreliable. Comparative Examples 6 to 8, however, exhibited transparency at UV radiations and thus improved ageing resistance (figure 4 and 6).

Example 10 refers to a polymerizable composition containing a relatively high amount of catalyst (10 wt% referred to the weight of the polymerizable composition). The processability and properties data indicate that a cured material having very good UVA radiation transparency is obtained. These data confirm that relatively high amounts of tertiary amine catalyst can be used to increase the compatibility of the components A and B -particularly when a cycloaliphatic diisocyanate a1 is used in component A -, without causing any substantial increase of the yellowness index and deterioration of the ageing behavior (see Fig. 5 and 6).

The ageing behavior of the materials according to the invention was specifically evaluated by means of accelerated tests under both UV (Q-UV test) and visible light (Xenon-meter) irradiation and compared with that of the comparative materials C1 and C2. The test results reported in Figure 6 and 7 show the change of the yellowness index of the tested samples after cumulative hours (fig. 6) and days (Fig. 7) of exposure at the selected test conditions. Despite the presence of a bluing agent, the commercial resin C2 showed a significant tendency to become yellow as demonstrated by the QUV and weathering test results shown in Fig. 6 and 7. On the contrary, the materials according to the invention show excellent light stability and weathering resistance compared to the comparative materials.

Example 13 is the same polymerizable composition of example 3, but in this case the plastic sheet after demolding was further subjected to the post cure thermal treatment as described above. The final polymer exhibits improved mechanical properties thanks to the increase in conversion provided by the high temperature of the post cure thermal treatment while keeping the same good ageing behavior as depicted in figure 7.

Claims

A polymerizable liquid composition for manufacturing a molded article comprising:
- an isocyanate component A comprising:
I. at least one component a2 or a mixture of component a2 and component a1, wherein a1 is a cycloaliphatic diisocyanate and a2 is an isocyanate group-terminated prepolymer comprising the reaction product of components comprising: (i) a cycloaliphatic diisocyanate and (ii) at least one polyol having at least two hydroxy groups per molecule; and
II. a component a3, which is a modified polyisocyanate composition comprising at least one aliphatic or cycloaliphatic diisocyanate comprising at least one functional group selected from: isocyanurate group, allophanate group, biuret group, urethane group, urea group and mixture thereof;
- a polyol component B comprising at least one polyol having from 2 to 5 hydroxy groups per molecule;
- a catalyst component C comprising at least one tertiary amine.
The polymerizable composition according to claim 1, wherein the aliphatic diisocyanate compound of the modified polyisocyanate composition a3 is an aliphatic diisocyanate compound selected from: ethylene diisocyanate, trimethylene diisocyanate, tetramethylene diisocyanate, pentamethylene diisocyanate (PDI), 1,6-hexamethylene diisocyanate (HDI), octamethylene diisocyanate, nonamethylene diisocyanate, decamethylene diisocyanate, bis(isocyanatoethyl)-carbonate, bis(isocyanatoethyl)ether and mixture thereof.
The polymerizable composition according to any one of claims from 1 to 2, wherein the cycloaliphatic diisocyanate of the component a1, a2 or a3 is selected from: methyl cyclohexane diisocyanate, bis(isocyanate methyl)cyclohexane, 1,1′-methylene-bis-(4-isocyanatocyclohexane), 4,4′-methylene-bis-(cyclohexyl isocyanate), 4,4′-isopropylidene-bis-(cyclohexyl isocyanate), 1,4-cyclohexyl diisocyanate, 4,4′-dicyclohexylmethane diisocyanate, bis(isocyanatecyclohexyl)-2,2-propane, bis(isocyanatecyclohexyl)-1,2-ethane, 3-isocyanato methyl-3,5,5-trimethylcyclohexyl isocyanate, meta-tetramethylxylylene diisocyanate, 2,5(6) diisocyanatemethylbicyclo(2,2,1)heptane, octahydro-4,7-methano-1H-indendimethyldiisocyanate and mixture thereof.
The polymerizable composition according to any one of claims from 1 to 3, wherein the isocyanate component A comprises a mixture of the isocyanate group-terminated prepolymer a2 and the modified polyisocyanate composition a3, the cycloaliphatic diisocyanate monomer a1 being absent.
The polymerizable composition according to any one of claims from 1 to 3, wherein the isocyanate component A comprises a mixture of the isocyanate group-terminated prepolymer a2, the cycloaliphatic diisocyanate monomer a1 and the modified polyisocyanate composition a3.
The polymerizable composition according to any one of claims from 1 to 4, wherein:
- component a3 comprises at least one aliphatic or cycloaliphatic diisocyanate selected from: pentamethylene diisocyanate (PDI), 1,6-hexamethylene diisocyanate (HDI) and mixture thereof; the diisocyanate comprising one or more functional group selected from: isocyanurate group, allophanate group and mixture thereof.
The polymerizable composition according to any one of claims from 1 to 6, wherein the weight ratio a3/a1+a2 between the component a3 and the sum of components a1 and a2 is within the range from 5:95 to 90:10, preferably from 5:95 to 70:30, more preferably from 10:90 to 60:40.
The polymerizable composition according to any one of claims from 1 to 7, wherein the weight ratio a3/a1 between components a3 and a1 is within range from 5:95 to 80:20, more preferably from 10:90 to 50:50.
The polymerizable composition according to any one of claims from 1 to 8, wherein the at least one tertiary amine is selected from: aliphatic tertiary amine, cycloaliphatic tertiary amine or mixture thereof.
The polymerizable composition according to any one of the claims 1 to 9, wherein the at least one tertiary amine is a compound in which the nitrogen atom of the amino group is covalently attached to none or not more than one tertiary carbon atom.
The polymerizable composition according to any one of claims from 1 to 10, wherein the at least one tertiary amine is selected from: triethylamine, benzyldimethylamine, n-methylmorpholine, dimethylcyclohexylamine, dimethylethanolamine, dimethylaminoethoxyethanol, triethanolamine, dimethyldipropylenetriamine, pentamethyldiethylenetriamine, bis(2-dimethylaminoethyl) ether triethylamine, tributylamine, triisopropanolamine, bis-(2-dimethylaminoethyl) ether, 1,4-diazabiscyclo[2,2.2]octane (DABCO), N-methylpiperidine, N-methylmorpholine and mixture thereof.
The polymerizable composition according to any one of claims from 1 to 11, wherein the at least one polyol of component B has a molecular weight M_w ranging from 50 to 6,000 g/mole, preferably from 100 to 4,000 g/mole.
The polymerizable composition according to any one of claims from 1 to 12, wherein the at least one polyol of component B comprises or is a polyol alkoxylated with from 1 to 10 alkoxy groups, preferably from 1 to 10 C₁-C₄ alkoxy groups.
The polymerizable composition according to any one of claims from 1 to 13, wherein the weight ratio A:B between the isocyanate component A and the polyol component B is within the range from 1:1 to 2.5:1, preferably from 1.5:1 to 2:1.
A molded article comprising a cured product of the polymerizable composition according to any one of the preceding claims.
An optical material comprising the molded article according to claim 15.
An automotive lighting element comprising the optical material according to claim 16.
A method for manufacturing a molded article according to claim 15 comprising:
a. mixing an isocyanate component A, a polyol component B and a catalyst component C to obtain a polymerizable composition according to claim 1;
b. casting the polymerizable composition into a mold;
c. thermally curing the casted polymerizable composition to obtain a molded article.
Use of a polymerizable composition according to any one of the claims from 1 to 14 for manufacturing a molded article by means of the vacuum casting technique.