Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Compositions to be polymerized by wave energy wherein said...
Reexamination Certificate
1995-02-03
2001-05-15
Henderson, Christopher (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Compositions to be polymerized by wave energy wherein said...
C522S033000, C522S050000
Reexamination Certificate
active
06232360
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the use of special UV-curable coating compositions based on urethane-modified acrylate resins for coating molded articles of thermoplastic polycarbonates.
2. Description of the Prior Art
Polycarbonate molded articles are used in a variety of ways because of their excellent properties, such as transparency, impact or shock resistance and tensile strength. However, the properties of the surface of the material, such as its low abrasion and scratch resistance and the low resistance to solvents, are inadequate for many areas of application.
In the past, very different solutions have been proposed for the removal of this drawback (cf e.g. PCT Applications WO 80/00968 and 86/04592, U.S. Pat. No. 3,968,305, EP-A 0,274,595 and EP-A 0,274,596). These publications are primarily directed to the coating of molded articles with UV-curing lacquer systems. The processes of these prior publications, however, have a number of serious disadvantages. In particular, the adhesion of the lacquers or the scratch resistance obtained with the lacquers, as the case may be, is not completely satisfactory. The coating compositions of the two last-mentioned prior publications cure only under nitrogen as a deactivating medium.
The coating compositions based on polyacrylate resins having urethane groups according to EP-A 0,020,344 or according to PCT-Application WO 80/00942 also lead to coatings that still do not fully satisfy the practical requirements with regard to scratch resistance and stability to weathering.
The coating compositions according to DE-OS 3,134,157 contain fairly large amounts of N-vinyl derivatives of linear or cyclic amides. A disadvantage of these compositions is the need to carry out the UV irradiation several times in order to obtain good scratch resistance. Furthermore, a low viscosity can be obtained in this case only by using large amounts of N-vinyl pyrrolidone. However, this reduces the resistance to scratching and to solvents as well as the stability to weathering. In addition, if fairly large amounts of N-vinyl pyrrolidone are used, the risk exists of the partial solution, whitening and stress cracking of the polycarbonate, as long as the coating is not yet cured. N-vinyl-pyrrolidone is also undesirable with regard to job hygiene.
The urethane acrylates according to DE-OS 3,819,627 also are used in combination with N-vinyl compounds, which leads to the disadvantageous consequences already mentioned.
The urethane acrylates according to DE-OS 4,021,109 are used in combination with tri- to hexafunctional (meth)acrylates as reactive diluents in order to avoid the said disadvantages of the aforementioned solvents. However, the stability to weathering of the resulting lacquer films is insufficient. This becomes recognizable as a loss of adhesion even after a relatively short time.
Finally, DE-OS 3,318,147 is concerned with special urethane acrylates without any connection to the special problem of coating polycarbonate molded articles.
It is an object of the present invention to provide coating compositions for coating thermoplastic polycarbonates which do not suffer from the disadvantages of the coating compositions of the prior art.
This object may be achieved with the coating compositions of the present invention which are described in more detail below. The coating compositions to be used according to the invention differ, e.g. from the coating compositions according to DE-OS 4,021,109 by the use of a selected low-viscosity polyisocyanate component having isocyanurate groups for the manufacture of the urethane acrylates as well as by the use of mainly linear bis-acrylates as reactive diluent B).
SUMMARY OF THE INVENTION
The present invention relates to UV-curable coating compositions containing
A) 20 to 75 wt %, based on the total weight of components A), B) and C), of a reaction product, which is essentially free from hydroxyl and isocyanate groups and is prepared from
A1) one or more hydroxyalkyl acrylates having 2 to 4 carbon atoms in the alkyl group, optionally mixed with up to 30 hydroxyl equivalent %, based on the total weight of component A1), of other alcohols, and
A2) an polyisocyanate component containing an aliphatic polyisocyanate which contains isocyanurate groups, is based on 1,6-diisocyanatohexane and has an NCO content of 22 to 23.5 wt % and a viscosity at 23° C. of 800 to 1400 mPa.s,
B) 5 to 80 wt %, based on the total weight of components A), B) and C), of a low-viscosity acrylic ester component containing
B1) at least 80 wt % of one or more bis-acrylates having a molecular weight below 350 and based on an alkanediol which may contain ether oxygen atoms and
B2) up to 20 wt %, based on the weight of component B), of one or more acrylic esters other than B1),
C) 0 to 80 wt %, based on total weight of components A), B) and C), of a solvent or solvent mixture and
D) 0.1 to 10 wt %, based on the total weight of components A), B) and C), of one or more photoinitiators.
The present invention is also directed to the use of the coating compositions for coating molded articles of thermoplastic polycarbonates.
DETAILED DESCRIPTION OF THE INVENTION
The coating compositions to be used according to the invention preferably contain 25 to 60 wt % of component A), 10 to 75 wt % of component B) and 10 to 75 wt % of component C),. wherein these percentages are based on the total weight of components A), B) and C). The content of initiator component D) is preferably 1 to 5 wt %, based on the total weight of components A), B) and C).
Component A) is selected from reaction products of at least 70% by weight of component A1) and optionally up to 30% by weight of component A2), wherein these percentages are based on the weight of component A). Component A) is “essentially free from hydroxyl and isocyanate groups” which means that in the production of the reaction products, components A1) and A2) are used at an NCO/OH equivalent ratio of 0.9:1 to 1.1:1, preferably about 1:1.
Starting compounds A1) are hydroxyalkyl acrylates with 2 to 4 carbon atoms in the hydroxyalkyl group or, less preferably, mixtures of such hydroxalkyl acrylates with other compounds having alcoholic hydroxyl groups. Suitable hydroxyalkyl acrylates include 2-hydroxyethyl acrylate, the isomer mixture formed by the addition of propylene oxide to acrylic acid, or 4-hydroxybutyl acrylate. 2-hydroxyethyl acrylate is preferred.
Other suitable hydroxyl compounds include mono- to trihydric aliphatic alcohols having molecular weights of 32 to 400, such as methanol, ethanol, n-hexanol, isooctanol, isododecanol, benzyl alcohol, ethylene glycol, diethylene glycol, propylene glycol, glycerol and alcohols obtained from these alcohols by alkoxylation.
Component A2) is selected from polyisocyanates having isocyanurate groups, which are based on 1,6-diisocyanatohexane (hexamethylene diisocyanate, HDI) and have an NCO content of 22 to 23.5 wt % and a viscosity at 23° C. of 800 to 1400 mPa.s. These polyisocyanates are obtained in a known manner by the trimerizing HDI until the reaction mixture has an NCO content of 42 to 45, preferably 42.5 to 44.5 wt %, subsequently terminating the reaction and removing unreacted HDI by distillation to a residual content of less than 0.5 wt %.
The manufacture of component A) by reacting starting components A1) and A2) can be carried out by known methods, optionally by using suitable urethane catalysts. As previously indicated, the reaction is carried out at an NCO/OH equivalent ratio of 0.9:1 to 1.1:1, preferably about 1:1.
Suitable catalysts for this reaction include tin(II) octanoate, dibutyltin dilaurate and tertiary amines such as dimethylbenzylamine. The reaction can be carried out in the absence of the other components or also in the presence of reactive diluent component B) and/or solvent component C), provided that these components do not contain H atoms reactive with isocyanate groups, i.e., isocyanate-reactive groups.
Urethane acrylate A) can be protected from premature and undesirable polymerization be
Fischer Wolfgang
Meixner Jurgen
Pedain Josef
Bayer Aktiengesellschaft
Gil Joseph C.
Henderson Christopher
Roy Thomas W.
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