Hardness acrylics

Features Hard acrylic resin providing exc. hardness, high gloss, and adhesion to a wide variety of substrates Properties Translucent disp. dens. 8.7 Ib/gal vise. 40 cps pH 6.5 add no.75 30%NVbywt. 

Uses Acrylic, film-former to produce solv. lacquers or to modify solv. systems modifier to improve block and abrasion resist., and hardness Features High m.w., hard acrylic resin provides lacquer-like dry to hard, high gloss, tough films... 

Features Hard acrylic colloidal disp. resin high gloss, good water resist. ... 

So-called core-shell impact modifiers have a less damaging effect on the modulus and HDT. They are made by emulsion graft polymerisation, and consist of two parts. As their name implies, one part is an outer shell of a hard acrylic polymer-like PMMA, in direct contact with the polymer that needs toughening the two must be compatible. (In the case of SAN copolymers, the compatibility depends on the polarity, and hence on the nitrogen content of the copolymer.)... 

Flexible acrylic polymers in the form of latexes are used as pigment binders on fiberglass, polyester, and other fabrics that are not readily dyed. They are also used to prepare caulks and adhesives. Very soft, tacky acrylic polymers have direct adhesion to most surfaces and need no adhesion promoters. Hard acrylic polymers are readily modified with simple compatible silanes to obtain good adhesion to mineral surfaces Soft, flexible, non-tacky acrylics have many desirable properties, but do not have good direct adhesion to most solid surfaces and the bonds to mineral surfaces are not water-resistant. 

A series of hard, acrylic urethane, in-mould coatings which can also be employed as a post-mould finish, of. excellent weatherability. 

A hydroxyl ftmaional comb polymer is made by the synthesis of block maaomonomers by CCTP, which contain hydroxyl functionality and copolymerizing these with acrylic monomers to form a comb polymer. The amount of hydroxyl functionality of the macromonomer depends on the application, but by tuning this level it was found to increase the pot life of the paint and also the initial hardness. Acrylic comonomers can also be used to achieve properties such as hardness, appearance, and scratch resistance. This comb polymer is... 

Clear and translucent sealants consist primarily of polymer dispersion (ca. 75-95 % by weight) and various formulation auxiliaries such as plasticizers, de-foamers, preservatives, thickeners, and freeze-thaw agents. Since fillers are not used, formulation solids content is essentially defined by the solids content of the polymer dispersion used, which for currently available materials, is typically <65 %. Higher water contents promote slower sealant drying rates. Relatively hard acrylic copolymers (Tg = -10 to -1-10 °C) are needed in clear sealants to minimize surface tack and subsequent dirt pick-up. Translucent sealants are formulated similarly but with small amounts of fumed silica thickener to adjust flow properties. 

Below T polymers are stiff, hard, britde, and glass-like above if the molecular weight is high enough, they are relatively soft, limp, stretchable, and can be somewhat elastic. At even higher temperatures they flow and are tacky. Methods used to determine glass-transition temperatures and the reported values for a large number of polymers may be found in References 7—9. Values for the T of common acrylate homopolymers are found in Table 1. 

Mechanical and Thermal Properties. The first member of the acrylate series, poly(methyl acrylate), has fltde or no tack at room temperature it is a tough, mbbery, and moderately hard polymer. Poly(ethyl acrylate) is more mbberflke, considerably softer, and more extensible. Poly(butyl acrylate) is softer stiU, and much tackier. This information is quantitatively summarized in Table 2 (41). In the alkyl acrylate series, the softness increases through n-octy acrylate. As the chain length is increased beyond n-octy side-chain crystallization occurs and the materials become brittle (42) poly( -hexadecyl acrylate) is hard and waxlike at room temperature but is soft and tacky above its softening point. 

The combination of durability and clarity and the ability to tailor molecules relatively easily to specific applications have made acryflc esters prime candidates for numerous and diverse applications. At normal temperatures the polyacrylates are soft polymers and therefore tend to find use in applications that require flexibility or extensibility. However, the ease of copolymerizing the softer acrylates with the harder methacrylates, styrene, acrylonitrile, and vinyl acetate, allows the manufacture of products that range from soft mbbers to hard nonfilm-forming polymers. 

Acrylonitrile (AN), C H N, first became an important polymeric building block in the 1940s. Although it had been discovered in 1893 (1), its unique properties were not realized until the development of nitrile mbbers during World War II (see Elastomers, synthetic, nitrile rubber) and the discovery of solvents for the homopolymer with resultant fiber appHcations (see Fibers, acrylic) for textiles and carbon fibers. As a comonomer, acrylonitrile (qv) contributes hardness, rigidity, solvent and light resistance, gas impermeabiUty, and the abiUty to orient. These properties have led to many copolymer apphcation developments since 1950. 

No particular contact lens type or product is considered universally superior. In some regions of the world hard lenses dominate the market, eg, some European countries and Japan in other regions, eg. North America and Scandinavia, soft lenses dominate. Contact lens practitioners select their preferred type of lens using criteria other than just lens material properties. However, among soft lenses, HEMA-based lenses are prescribed most often, and among hard lenses, siUcone—acrylate RGP lenses are most common. 

Silicone Acrylates. The development of rigid gas-permeable lens materials advanced significantly after the development of polysiloxanylaLkyl acrylates and methacrylates (1), as a component in hard lens materials (56,57), as claimed in a series of patents (58—62). 

Acrylic rubbers, as is the case for most specialty elastomers, are characterized by higher price and smaller consumption compared to general-purpose mbbers. The total mbber consumption ia 1991 was forecast (55) at 15.7 million t worldwide with a 66% share for synthetic elastomers (10.4 x 10 t). Acryhc elastomers consumption, as a minor amount of the total synthetic mbbers consumption, can hardly be estimated. As a first approximation, the ACM consumption is estimated to be 7000 t distributed among the United States, Western Europe, and Japan/Far East, where automotive production is significantly present. 

Low Temperature Properties. Medium hardness compounds of average methyl acrylate, ie, VAMAC G, without a plasticizer typically survive 180° flex tests at —40° C. Such performance is good for a heat-resistant polymer. Low temperature properties can be greatly enhanced by the use of ester plasticizers (10). Careful selection of the plasticizer is necessary to preserve the heat resistance performance of the polymer. Plasticized high methyl acrylate grades lose only a few °C in flexibiUty, compared to grades with average methyl acrylate levels. 

If polypropylene is too hard for the purpose envisaged, then the user should consider, progressively, polyethylene, ethylene-vinyl acetate and plasticised PVC. If more rubberiness is required, then a vulcanising rubber such as natural rubber or SBR or a thermoplastic polyolefin elastomer may be considered. If the material requires to be rubbery and oil and/or heat resistant, vulcanising rubbers such as the polychloroprenes, nitrile rubbers, acrylic rubbers or hydrin rubbers or a thermoplastic elastomer such as a thermoplastic polyester elastomer, thermoplastic polyurethane elastomer or thermoplastic polyamide elastomer may be considered. Where it is important that the elastomer remain rubbery at very low temperatures, then NR, SBR, BR or TPO rubbers may be considered where oil resistance is not a consideration. If, however, oil resistance is important, a polypropylene oxide or hydrin rubber may be preferred. Where a wide temperature service range is paramount, a silicone rubber may be indicated. The selection of rubbery materials has been dealt with by the author elsewhere. ... 

With plastics there is a certain temperature, called the glass transition temperature, Tg, below which the material behaves like glass i.e. it is hard and rigid. As can be seen from Table 1.8 the value for Tg for a particular plastic is not necessarily a low temperature. This immediately helps to explain some of the differences which we observe in plastics. For example, at room temperature polystyrene and acrylic are below their respective Tg values and hence we observe these materials in their glassy state. Note, however, that in contrast, at room temperature, polyethylene is above its glass transition temperature and so we observe a very flexible matoial. When cooled below its Tg it then becomes a hard, brittle solid. Plastics can have several transitions. 

The modulus term in this equation can be obtained in the same way as in the previous example. However, the difference in this case is the term V. For elastic materials this is called Poissons Ratio and is the ratio of the transverse strain to the axial strain (See Appendix C). For any particular metal this is a constant, generally in the range 0.28 to 0.35. For plastics V is not a constant. It is dependent on time, temperature, stress, etc and so it is often given the alternative names of Creep Contraction Ratio or Lateral Strain Ratio. There is very little published information on the creep contraction ratio for plastics but generally it varies from about 0.33 for hard plastics (such as acrylic) to almost 0.5 for elastomers. Some typical values are given in Table 2.1 but do remember that these may change in specific loading situations. 

Modified alkyd resins In this group one finds styrenated alkyds, vinyl toluenated alkyds, oil-modified vinyl resins, acrylic alkyds, silicone alkyds and polyurethane alkyds. The modifying component usually has a number of effects. It always increases the molecular weight of the alkyd polymer, and may impart hardness, durability, or chemical resistance. It also affects the solubility of the polymer in solvents. 

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