DE19513014A1 - Curable epoxy resin compsn. - Google Patents

Abstract

A curable epoxy resin composition, comprises a curable epoxy resin and a curing agent selected from diamine curing agents and anhydride curing agents. The epoxy resin and the curing agent are chosen so as to provide a colourless or low colour product on curing, which is useful for optical applications, having a Tg of > 140 DEG C. The diamine curing agent has at least one aliphatic, heterocyclic or aromatic ring and has two amine groups each independently bonded to an aliphatic group or incorporated in a heterocyclic ring. The anhydride curing agent is a linear polyanhydride, or a cycloaliphatic anhydride. The products are useful for the manufacture of ophthalmic lenses and automotive headlamp lenses.

Description

The invention relates to epoxy resin compositions and in particular on transparent epoxy resin compositions which are suitable for Ver use in lenses and other applications.

Plastic lenses are of growing importance in applications by Eyeglass lenses up to lenses for vehicle headlights range. Plastics white There are a number of advantages over the conventionally used glass in the applications, including their improved impact resistance and resulting in improved safety, their reduced specificity Weight, which is important in large lens designs, and theirs relatively simple processing. Because glass is difficult to process tends one has to make complex optical arrangements by grinding what is expensive. Plastics flow well during processing, what is it allows to make sharp steps on the surface of the lens so that complex optical arrangements can be made in one step. plastics However, they also have some disadvantages compared to glass. You own poor scratch resistance in comparison to glass in general limited thermal stability and poor weather resistance (Light, oxygen).

The types of plastic most commonly used in lens applications These are the thermoplastics, such as polycarbonate and acrylic polymers. Of these two types, polycarbonates have greater heat resistance but limited to about 150 ° C for the usual representatives. Thermoplastics, such as polysulfones, are able to attract higher users Resist temperatures, but bring a crucial Verteue with you. Other specific disadvantages of thermoplastic materials are their poor solvent resistance and their tendency for prolonged on the effect of higher temperatures to crawl. Very few thermosetting  Polymers have hitherto been described for use in lenses, although Duro Substantially improved solvent and creep resistance Compared to the thermoplastics have. In addition, they often at we considerably higher application temperatures are used continuously.

By far the most common type of plastic material used in lens applications are used, are the thermoplastics. Low-cost thermoplastics for transparent commodities, such as polystyrene, PVC and ABS is often used in crystal-clear, transparent, rigid packaging applications used. The Herge with slightly higher technological cost Acrylic resins and polycarbonates are also used in lenses applications, as well as transparent containers. The polymers, the higher Resist temperatures and are more expensive, such as polysulfone, poly ether sulfone, amorphous nylons and the like are in special lenses applications as used in other fields. The technology of transparent thermoplastics is fully described in a report of Business Communications Company Inc., No. P-053R, "Clear Plastic fe: broadening the basis of materials and applications "(" Transpa rent Plastics: Broadening the Base of Materials and Applications "), December 1990th

Earlier reports on the use of thermoset materials in lenses are much less common. PPG Industries (Plastics Engineering, 1986, 42 (10), 7) reports a cast resin (HIRI) with a refractive index (RI) of 1.56 (the Refractive index of glass is about 1.53 - a high refractive index is a Advantage in lens applications, because the higher the refractive index, the better lower is the required lens curvature to provide the same Crushing capacity). PPG also provides a commercial, thermosetting allyl resin her, CR-39, which finds use in lens applications.

Specialized epoxy based resin materials with potential use in lenses are the subject of some patent applications. JP 04292611 (Nippon Steel) describes epoxy acrylate molding materials containing fluoro radicals. These are claimed to have a dimensional stability temperature of 170 ° C, a light transmittance of 91.5% and a refractive index of 1.63. JP 04359012 (Hitachi Chemical Co.) describes transparent epoxy resins obtained by curing epoxides with alicyclic anhydride hardeners, such as, for example, hexahydrophthalic anhydride, which has been accelerated with 2-ethyl-4-methylimidazole, in the presence of a cyclic P = O- Connection can be made. A glass transition temperature ( _Tg ) of 126 ° C and a light transmission of 85% are described for these compositions.

Transparent epoxy casting resins are described as an ingredient in composite glass and plastic spectacle lenses in US Pat. No. 5,116,684 (Corning Inc.), such as US Pat also in U.S. Patent 5,223,862 (Corning Inc.), where also its use as Ein strengthengläser is disclosed. The epoxy resin in the first of these two patents is preferably a cycloaliphatic epoxy resin and / or an aromatic resin, such as DGEBA, by an anhydride hardener, such as Hexahydrophthalic anhydride, a source of active hydrogens, such as Example, propylene glycol, and a Zinnoctoat Accelerator is cured. The optical properties are predominantly by the cycloaliphatic resin be while the DGEBA increases the refractive index. catalytic Curing agents, such as BF₃, may also be used. Other Sources of hydroxyl groups (polyols) can be used and have also an influence on the refractive index. The amount of used Accelerator is important and preferably within a range of 0.01 to 0.1% of limited to the entire mixture to ensure a reasonable pot life. Other Lewis acids, such as zinc octoate, can be used as well as Lewis bases. The hardening process is also important and the gelation must take place at less than 100 ° C and last at least 2 hours, with final curing at greater than 150 ° C for at least 2 hours det.

The related U.S. Patent 5,223,862 more specifically describes the Verwen the above-mentioned, preferred resin compositions as Plastic lens elements, in particular with glass in a multilayered Structure for multi-thickness glasses. Next are hardeners for the epoxy described resins. These are aromatic anhydrides, aromatic diamines, Thioamides and thioamines. Additives to improve the refractive index are selected from the alkyl diols or thiols or the aromatic diols or thiols and the transition metal alkoxides. Phthalic anhydride is one preferred curing agent, and propylene glycol is the preferred diol. The at Cited curing cycles of the epoxy resin are long, with a Total cure time of about 20 hours is common.  

Although not mentioned in the prior art, the duroplasti have an epoxy resin compositions as described above number of disadvantages. The long total hardening times compared to the fast ones Cycle times of competing thermoplastic injection molded lenses provides a be disadvantage. Some of the specialized epoxy resins are expensive, which limited the use of such products in many industrial applications. cyclo Aliphatic epoxy resins are also expensive and result when cured to relatively brittle products, although in multi-layer applications not necessarily critical. For cured resin products that are under Use made of aromatic diamine or imidazole accelerators must be expected to show some discoloration, as long as non-special steps are taken to access these reactants clean. In addition, their color stability is likely to be relatively poor, esp especially when used at elevated temperatures.

There is a need for clear and colorless thermoset resin compositions Compositions that overcome these disadvantages. The present invention provides such an epoxy resin, which is relatively inexpensive, for use in industrial Lin ready for use. The base color and the color stability are better than those of compositions containing aromatic hardening agents, and the Products have improved impact resistance.

An object of this invention is to provide epoxy resin compositions which is cost competitive with respect to thermoplastic polycarbonate resins, in particular for use in industrial Lighting applications. The cured resin formulations should have a have acceptable impact resistance, be fast to cure, low intrinsic color and have good light transmission and be suitable for use at higher continuous operating temperatures than the polycarbonates and acrylic resins.

The invention provides epoxy resin compositions which are colorless and are transparent, have high glass transition temperatures (<140 ° C, before To <150 ° C) and which can be cured with fast casting techniques, such as for example with thermosetting injection molding or resin transfer molding techniques.  

The invention provides a curable epoxy resin composition comprising hardenable epoxy resin and a curing agent consisting of

• (a) the amine curing agents, the least one aliphatic, heterocy or aromatic ring and 2 amino groups each independently of one another to an aliphatic group are attached or are introduced into a heterocyclic ring,
• (b) the linear polyanhydride curing agents and
• (c) the cycloaliphatic anhydride curing agents,

is selected, wherein the epoxy resin and the curing agent are selected so that they provide a colorless or slightly colored product with a T _g of <140 ° C and preferably <150 ° C when curing.

The invention also provides a method for producing a cured Epoxy resin composition ready to cure a curable epoxy resin composition as described above.

The maximum possible transparency of the final product can be calculated who from known theoretical considerations. Inan takes the case of an unbe layered product material, the vertically incident light in air lets then the amount of light that reflects from each surface (interface) depending on the refractive index of the product material. So it turns out for one Product with a refractive index of 1.5 the theoretical maximum throughput of 92.2% and for a product with a refractive index of 1.6 the theo maximum retinal permeability of 89.7. Real (non-theoretical) materials have lower permeability values than calculated. The invention Epoxy products generally have higher than permeability values 90% of the theoretical maximum value.

The color value of the product materials is determined by the presence or Absence of absorption bands in the visible region of the electromagnetic spectrum. The epoxide products have no absorptions in the wavelength range from 400 to 800 nm. It may also be a second indication of color such as the "yellowness index" according to ASTM D1925. These secondary measures are both less precise and can be too  be achieved by color compensation method, which is the original coloration cover (for example, by using a blue masterbatch to remove yellowness). Such approaches also lead to low geren total permeability properties.

The production of epoxy resins which are colorless or have low color values This is achieved by minimizing factors that cause staining to lead. These factors include the presence of charge transfer complex xen and oxidation products.

The type of epoxy resin should be considered first. high temperature epoxy Resins often contain tertiary nitrogen groups that are easy to oxidize and to oxidize Formation of strongly colored impurities lead. These resins are common too too expensive for use in commercial products that are not aviation richly used. These glycidylamine epoxide materials therefore become best avoided. Glycidyl ethers, such as the one commonly used DGEBA, are less sensitive to oxidation and in high quality and with ge wrestle color values available. Epoxy novolacs, which also glycidyl ether represent len, can be used alone or in conjunction with other resins. Cycloaliphatic epoxy resins also have low color but the disadvantage that they give brittle products when curing and also expensive are. The preferred epoxy resins are glycidyl ethers.

The choice of curing agent is at least as critical as the off Choice of epoxy resin. In addition to its importance in controlling the Color and the color stability of the cured product plays the curing agent an important role in determining the processing properties of Resin formulation. For large volume applications, such as Indu Strielinsen, fast curing and high throughput are indispensable. Among the commonly used epoxy curing agents are the most widely used aromatic diamines. Almost without exception they lead to dyed products, so long as not special steps are taken to the diamine reactant to remove oxidation contaminants that cause color to can lead. The products have a tendency to charge transfer com plexes which are usually strongly colored. Additionally, the Ge genwart a bound to an aromatic ring nitrogen to poor thermooxidative stability and discoloration of the product in  Over time. The curing rate of the aromatic diamines tends to be low.

Aliphatic and cycloaliphatic curing agents, on the other hand, lead to rapid hardening and colorless or weakly colored products. The presence of the aliphatic or cycloaliphatic groups reduces the interactions that lead to charge-transfer complex formation. The products are also less prone to oxidation in use due to non-aromatic nitrogen bonding. The imidazole accelerators commonly used with anhydride curing agents also result in discoloration in cured resin products for reasons similar to those practiced for the aromatic diamines. Preferred accelerators should not contain groups that produce dye by interacting with other components of the system or solely by the behavior inherent in the accelerator. For this reason, zinc carboxylates are preferred. The Zn ²⁺ ion does not produce color and can participate in redox reactions that do not lead to colored products. Similarly, the aliphatic carboxylate groups do not lead to any color formation.

Epoxy resins are selected from the group of commercially available Resins with good quality and low color (for example, with a Gard ner number <1 or an AHPA number <250). These include highly pure DGEBA Resins (diglycidyl ether of bisphenol-A) with epoxide equivalent weights in Be rich from 170 to 6000 and preferably from 170 to 250 and high purity Epoxidnovo paints. Cycloaliphatic epoxy resins can also be used if the curing agent is an anhydride as described in (b) and (c) above, but their use is generally limited because of the higher cost and the poor impact resistance of the cured products.

The diamine curing agents are preferably those in which the amino groups independently of one another to an aliphatic or cycloaliphatic group are bound. Cycloaliphatic diamine curing agents can be selected from the group shown in Table 1, with preferred Här isophoronediamine (IPD) and bis (4-aminocyclohexyl) methane (PACM). represent. The proportion of the curing agent in the epoxy resin is generally in the range of 120% of the amount required for stoichiometric curing.

Anhydride curing agents can be selected from the group described in Ta belle 2 is shown, with preferred anhydrides Hexahydrophthalsäureanhy  trid (HHPA) and methylhexahydrophthalic anhydride (MHHPA). zinc Salts are preferred accelerators, especially zinc stearate or zinc octoate.

Tables 1 and 2 include substituted analogs. The optiona Examples of suitable substituents are the alkyl radicals having 1 to 4 carbon atoms atoms and the halogen atoms selected.

Reactive diluents may include low viscosity glycidyl ethers, diglycidyl ethers and polyglycidyl ethers, polyols such as diols and triols, and epoxidized unsaturated materials. The reactive diluents can perform a number of tasks, such as changing the viscosity of the resin formulation, improving the impact resistance properties of the cured product, and changing the refractive index of the cured product. Often it must be paid for with a reduction of the final T _g who the.

The selected modifiers may include thermoplastic materials, anor include ganic fibers and various particulate materials. Thermoplastics are preferred, but there may also be materials such as Glass fibers, various types of silica and feldspar beneficial as Modifying agents are used.

Thermoplastics that can be used include high performance acrylic resins ze, such as, for example, reactive or unreactive polymethacrylimides (commercial available from Rohm & Haas and from Röhm as Kamax® or Plexi mid®, amorphous polyarylates, amorphous polyamides, polyimides and polyetherimides (for example Ultem® from General Electric's), polysulfones and polyethersulfones, Poly (phenylene oxide), polycarbonates including polyestercarbonates and poly alkylene carbonates, copolymers of styrene and maleic anhydride (SMA), Styrene-butadiene-styrene copolymers, polyethylene glycol and other amorphous, thermoplastic materials. Other related materials, such as proprietary core-shell impact modifiers (such as Acrylic-based or styrene-butadiene-based core-shell elastomers known as paraloid EXL additives sold by Rohm & Haas) can also be used become. Thermoplastics are added to the impact resistance of the cured To improve resin, and also as a rheology modifier for certain Processing types, such as injection molding, to act. The verhal Thermoplastics during curing is of fundamental importance for  the successful use of the cured products in optical applications The modified resin must be both colorless and translucent.

Thermoplastics usually become thermosets, such as epoxy resins added, to improve their toughness and impact resistance. In the üb The most common application of this technology is to release the thermoplastic during use Curing in the epoxy resin, but is increasing with the size the molecular weight of the thermoset incompatible. At a certain During the curing cycle, the thermoplastic phase separates from the epoxy matrix at a speed and at a time passing through the Total kinetics and the total thermodynamics of the system is determined. the This approach is exemplified in WO 91/02029 to Aitco where epoxide resins are toughened with polyimides. The nature of the thermoplastic Phase is influenced by the just mentioned kinetic and thermodynamics also by the proportionate amount in which the thermoplastic in the formulation is present. The three most common situations are (a) discrete thermoplastic Ponds dispersed in an epoxy matrix, (b) discrete epoxide phases, the are distributed in a thermoplastic matrix (phase inversion) and (c) a continuous, joint network of the thermoplastic phase and the Epoxide phase (via a so-called spinodal decomposition). The size of the part It is generally in the range of 1 to 10 μm. Because the wavelength of the Light is about 0.4 to 0.8 microns, tend products that contain these systems to be opaque or translucent. Toughened, light To obtain permeable epoxy systems, one or more criteria he must be filled. This is one of the keys to success in a point of view this invention.

There are three main routes to achieve translucency in epoxies made more inert with thermoplastics: (1) preparation of cured mixtures that are single phase, with the toughening effect obtainable by this route sometimes being limited, and the T _g can be reduced. (2) Preparation of cured mixtures in which the phase size is smaller than the wavelength of the light, which can be affected by the change in the curing kinetics. (3) Same as the index of refraction of the cured epoxy resin to that of the thermoplastic component, so that even when phase magnitudes larger than the wavelengths of the light occur, there is no refraction at the phase boundaries and the light passes through the product without diffraction goes through it. The approach of the invention is to set conditions favoring either (1) or (2), with the refractive indices as close as possible to each other in order to minimize negative effects, the objectives of (1) and (2) can not be fully achieved. The main routes to (1) and (2) are to improve the compatibility of the thermoplastic and the epoxy resin and to optimize the curing conditions.

For applications requiring a wide range of application temperatures It is possible to cover the approximation of the refractive indices of the hardened th epoxy resin and the thermoplastic over this temperature range to op opti-.

In order to pursue the stated goals, a number of different epoxies were used produced resin systems, which provide the properties necessary for an optical Epoxy resin lens can be expected. The formulations have gel times of less than 120 seconds and preferably less than 60 seconds at 200 ° C, which makes them suitable makes for fast processing, such as injection molding or transfer supply squeeze.

The formulations may also contain one or more antioxidants and / or a or more UV stabilizers to prevent the yellowing due to To reduce long-term use at elevated temperature. The products can optionally with a commercial polymer hard coating be layered to ver the surface hardness and abrasion resistance ver improve.

The main advantages of the invention are the following:

• 1) Colorless, translucent epoxy products suitable for lenses Applications are made from relatively cheap precursors. Other suitable applications include liquid containers, for example in Vehicles, medical containers and the like.
• 2) Color quality and color stability are better than those of epoxy resins that made from aromatic diamines or imidazole accelerators the.  
• 3) The cured resin products have high _Tg values, generally if he half of 140 ° C and preferably above 150 ° C.
• 4) The toughness or impact strength of the cured products can be over ei be varied within a wide range, depending on the selection of the reac diluent or thermoplastic, which acts as a toughening additive is added, and of the required application.
• 5) Hardening times are short, with gel times at temperatures of about 200 ° C less than 120 s and preferably less than 60 s. the These formulations are therefore suitable for rapid processing Use of techniques, such as injection molding or the Transfer press, in contrast to the slower Formungsverfah mentioned in some prior art reports.
• 6) refractive indices of the products can be used over a wide range including the range of 1.49 to 1.62.
• 7) Creep resistance and surface hardness are the polycarbonate and superior to comparable thermoplastic lens materials.
• 8) In contrast to US Pat. No. 5,116,684, the added amounts of zinc stearate or zinc octoate accelerators are well above 1%, can be used without adverse effect on color or pot life, and with a favorable effect on the total cure time and T _g .
• 9) The epoxy products allow visible light transmission greater than 98% and filter out UV light above about 320 nm.
• 10) The solvent resistance of the epoxy products is improved in Ver equal to compete with the thermoplastic materials.

Table 1

Table 2

List of abbreviations Trade names of epoxy resins MY 750 Epon 828 THE 332nd THE 431 THE 736 GT 7071 Heloxy 107 (or Hel 107) Epodil 750 ERL 4221 IPD isophoronediamine PACM p-aminocyclohexylmethane SMA Copolymer of styrene and maleic anhydride PPO Poly (phenylene oxide) SBS Styrene-butadiene-styrene copolymer PEG Poly (ethylene glycol) EXL 2600 Core-shell Stoßfestigkeitsmodifiziermittel MHHPA methylhexahydrophthalic MNA methylnadic

example 1

This example illustrates the general preparation of epoxide products using cycloaliphatic diamine curing agents. A mixture of 50 g MY 750 (epoxy monomer) and 14 g PACM is prepared and homogenized. This mixture is then deaerated and cured in a hot mold at 160 ° C for 30 minutes. The epoxide product has a glass transition temperature (T _g ) of 167 ° C as measured by DMTA (dynamic mechanical thermal analysis), a refractive index (n _D ) of 1.578 and an Izod impact strength (ASTM D256) of 0.350 J / cm 2 (1.46 ft-lb / in²). These and other examples of epoxide products prepared by the same general procedure are tabulated below (Table 3).

Table 3

Example 2

This example illustrates the general production of epoxy products as described in article 2 of section 3.2. A mixture of 50 g of Epon 828 (epoxy monomer), 48 g of MHHPA and 2 g of zinc stearate is prepared and the temperature of the mixture raised to 90 ° C to promote the dissolution process. The mixture is homogenized and deaerated before curing in a hot mold at 200 ° C for 30 minutes. The epoxy product has a T _g of 151 ° C, an n _D of 1.545, and an impact strength according to Izod of 0.070 J / cm (0.29 ft-lb / in²). This and other exemplary epoxide products prepared by the same procedure are listed below in Table 1 (Table 4).

Table 4

Example 3

This example illustrates the general preparation of epoxide products using cycloaliphatic diamine curing agents and thermopla tic modifiers. 50 g of DER 332 (epoxy monomer) are heated to 90 ° C and a solution of Kamax T-170 in dichloromethane (DCM) is added. The solvent DCM is removed and the mixture is cooled. 6 g of Heloxy 107 (reactive diluent) and 16 g of IPD are added and the mixture is homogenized and deaerated before curing in a hot mold at 160 ° C for 30 minutes. The properties of the epoxide product are as follows: T _g = 155 ° C, n _D = 1.563 and impact strength Izod impact strength = 0.401 J / cm (1.67 ft-lb / in²). These and other exemplary epoxide products made by the same general procedure are listed below in Table 5 (Table 5).

Table 5

Example 4

This example illustrates the general production of epoxies as described in Article 4 of Section 3.2. 50 g MY 750 are heated to 90 ° C and a solution of 5 g SMA (copolymer of styrene and maleic anhydride, available from DSM) in DCM is added. The solvent DCM is removed and 44 g of MHHPA and 2 g of zinc stearate are added. The mixture is homogenized and deaerated before curing in a hot mold at 200 ° C for 30 minutes. The epoxy product has the following properties: T _g = 168 ° C, n _D = 1.543 and Izod impact = 0.13 J / cm 2 (0.52 ftlb / in 2). These and other exemplary epoxide products prepared by the same general procedure are tabulated below (Table 6).

Table 6

Claims (11)

A curable epoxy resin composition comprising a curable epoxy resin and a curing agent selected from

• (a) diamine curing agents which include at least one aliphatic, heterocyclic or aromatic ring and which have two amino groups each independently linked to an aliphatic group or incorporated into a heterocyclic ring,
• (b) linear polyanhydride curing agents and
• (c) cycloaliphatic anhydride curing agents,

wherein the epoxy resin and the curing agent are selected so that upon curing, they provide a colorless or slightly colored product having a T _g <140 ° C and preferably <150 ° C. 2. Composition according to claim 1, which is also a reactive diluent for Improvement in impact resistance and / or refractive index contains, such as For example, a glycidyl ether, a polyol or an epoxidized unsaturated Material. 3. Composition according to one of claims 1 or 2, which also has a Be accelerator for the anhydride curing agent (b) or (c), for example a tin or a zinc salt. 4. Composition according to one of claims 1 to 3, which is also a Modifi decorative agent for improving the impact resistance of the cured resin includes, such as a thermoplastic material, inorganic fibers or a particulate material.   5. The composition of claim 4, wherein the modifier is an amorphous represents thermoplastic material. 6. A composition according to any one of claims 1 to 5, wherein in the amine (a) the aliphatic ring is a cyclohexane or two cyclohexane rings, which are linked by a linking group represents the heterocyclic Group represents a piperazine, the aromatic ring represents a benzene and the aliphatic group is an alkylene having 1 to 5 carbon atoms. A composition according to any one of claims 1 to 5, wherein the cycloaliphatic anhydride curing agent (c) is selected from the alicyclic anhydrides, the maleic anhydride and substituted diene adducts, the co-polymers including maleic anhydride units, unsubstituted hexahydrophthalic anhydride, substituted hexahydrophthalic anhydride, substituted tetrahydrophthalic anhydride, unsubstituted tetrahydrophthalic anhydride and bisnadicanhydrylbutene represented by the following formula: 8. A process for producing a cured epoxy resin composition which comprising a curable epoxy resin composition according to any of the above going claims hardened. 9. Hardened epoxy resin composition made from a curable Epoxy resin composition according to one of claims 1 to 7 and / or by a method according to claim 8. 10. Use of a cured epoxy resin composition according to claim 9 for optical applications, in particular for plastic lenses.