Surface treatment of moldings based on liquid crystalline polymers

A process for the surface treatment of moldings based on liquid crystalline polymers with acidic or alkaline reagents includes using the reagents in a solvent which is an organic solvent to an extent of not less than 60% by weight.

The present invention relates to a process for the surface treatment of 
moldings based on liquid crystalline polymers with acid or alkaline 
reagents. 
Liquid crystalline polymers are a group of thermoplastic polymers which are 
high temperature resistant and possess low thermal expansion coefficients. 
Moreover, the optically anisotropic melt phase in the production of 
moldings by injection or extrusion molding creates orientations in the 
flow direction which suggest interesting applications. 
However, moldings based on liquid crystalline polymers are difficult to 
lacquer or metallize, since the adhesions obtained are not satisfactory. 
EP-A-312 268 discloses a process whereby, to improve the adhesion for the 
metallization of moldings based on liquid crystalline polymers, a 
treatment is carried out with an at least 80% strength by weight aqueous 
solution of sulfuric acid. The molding composition from which the molding 
is formed contains from 5 to 80% by weight of a certain inorganic filler. 
EP-A-305 846 discloses thermoplastic molding compositions for producing 
printed circuit boards, which contain as essential components a fibrous 
inorganic filler and an alkaline earth metal carbonate as well as a liquid 
crystalline polymer. Prior to metallization, the moldings produced from 
the molding compositions described are pretreated with aqueous alkaline 
and acidic reagents in a conventional manner. 
The above-described processes do result in an improvement in the adhesion 
of metal or lacquer films on moldings, but a further improvement would be 
desirable. 
It is an object of the present invention to provide a process for the 
surface treatment of moldings based on liquid crystalline polymers which 
is simple to carry out and improves the adhesion of metal or lacquer films 
applied to the moldings. 
We have found that this object is achieved by a process for the surface 
treatment of moldings based on a liquid crystalline polymer with an 
alkaline or acidic reagent used in a solvent constituted to at least 60% 
by weight by an organic solvent. Compared with existing treatment 
processes, where the pretreatment is carried out with aqueous acids or 
alkalies, the process of the present invention gives improved adhesions, 
in particular for a subsequent metallization. 
The process of the present invention is for moldings based on liquid 
crystalline polymers; that is, the basic molding compositions contain at 
least one liquid crystalline polymer as main constituent, with or without 
fillers, rubbers and other customary additives. 
The liquid crystalline polymers used are thermotropic mesomorphic polymers. 
They have an anisotropic melt phase which is readily detectable under a 
polarizing microscope using the method described in DE-A 25 20 819. 
Between crossed polarizers, the polymer melts applied in a thickness of 10 
.mu.m between glass plates have textures which can be assigned to a 
mesomorphic phase. 
To obtain an anisotropic (liquid crystalline) melt phase generally requires 
a certain degree of linearity in the main chain, which can be achieved 
through appropriate choice of the mixing ratios for the monomers. The 
anisotropy of the melt phase and the attendant orientation of the polymer 
molecules lead to the moldings produced from such polymers having very 
high strength and stiffness values. 
In general, it can be stated that thermotropic mesomorphic polymers 
generally contain units derived from 
a.sub.1) aromatic or aliphatic dicarboxylic acids, 
a.sub.2) aromatic or aliphatic diols, diamines or corresponding monomers 
having an amino and a hydroxyl group, 
a.sub.3) aromatic hydroxy- and amino-carboxylic acids, and 
a.sub.4) aromatic thiocarboxylic acids, dithiols or thiophenols. 
By combining these monomers in appropriate fashion it is possible to 
prepare for example polyesters, polyesteramides, polyesterimides, 
polyestercarbonates, polyetheresters, polyetheresteramides, 
polyesteramideimides, polyestercarbamides and polyetheresterimides. 
The compositions of these products can vary within wide limits, and there 
are a multiplicity of usable monomers. The essential requirement is that 
the polymers have thermotropic mesomorphic properties, which is readily 
verifiable by the abovementioned method, described in DE-A 25 20 819. 
All combinations of monomers a.sub.1) to a.sub.4) in any desired molar 
ratios do not lead to thermotropic mesomorphic polymers, but a general 
account of suitable mixing ratios is hardly possible. 
However, the relevant literature and a multiplicity of patent applications 
have described suitable thermotropic mesomorphic systems which will 
hereinafter be further illustrated, starting with an exemplary enumeration 
of suitable monomers and corresponding polymers. 
Monomers a.sub.1): 
terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, 
2,7-naphthalenedicarboxylic acid, 4,4'-dicarboxybiphenyl, 
4,4"-dicarboxyterphenyl, dicarboxydiphenyl derivatives of the general 
formulae I and II 
##STR1## 
Other possibilities are dicarboxylic acids of the general formulae III and 
IV 
##STR2## 
where Z is in each case --O--, --S--, --SO.sub.2 --, --CH.sub.2 --, 
--C(CH.sub.3).sub.2 -- or a chemical bond, and n is 0 or 1. 
Examples thereof are 
Z=O 4,4'-, 3,4'- or 3,3'-di(4-carboxy-N-phthalimido)diphenyl ether 
Z=CH.sub.2 4,4'-, 3,4'- or 3,3'-di(4-carboxy-N-phthalimido)diphenylmethane 
Z=SO.sub.2 4,4'-, 3,4'- or 3,3'-di(4-carboxy-N-phthalimido)diphenyl sulfone 
Z=CO 4,4'-, 3,4'- or 3,3'-di(4-carboxy-N-phthalimido)diphenyl ketone 
Z=S 4,4'-, 3,4'- or 3,3'-di(4-carboxy-N-phthalimido)diphenyl sulfide 
and for example 
Z=C(CH.sub.3).sub.2 2,2-di-[4,4'-di(4-carboxy-N-phthalimido)phenyl]propane. 
Other suitable monomers a.sub.1) are p,p-, m,m- and p,m-dicarboxyphenyl 
carbonates of the general formulae VI to VIII 
##STR3## 
The aforementioned carboxylic acids can also have substituents such as 
C.sub.1 -C.sub.4 -alkyl or C.sub.1 -C.sub.4 -alkoxy groups or halogen 
atoms. Finally, there may be mentioned some aliphatic dicarboxylic acids 
such as cis- and trans-1,4-cyclohexanedicarboxylic acid and 
1,3-cyclohexanedicarboxylic acid and also their appropriately substituted 
derivatives. 
Monomers a.sub.2 : 
hydroquinone, methylhydroquinone, phenylhydroquinone, 
tert-butylhydroquinone, chlorohydroquinone, 4,4'-dihydroxybiphenyl, 
1,4-di(4-hydroxyphenyl)benzene, 1,2-di(4-hydroxyphenoxy)ethane, 
4,4'-dihydroxydiphenyl ether, 4,4'-dihydroxydiphenyl sulfone, 
3,3'-dihydroxybiphenyl, 3,3'-dihydroxydiphenyl ether, 
3,4'-dihydroxybiphenyl, 3,4'-dihydroxydiphenyl ether, 
2,2-di(4-hydroxyphenyl)propane, 1,6-, 2,6- and 2,7-dihydroxynaphthalene, 
3,3',5,5'-tetramethyl-4,4'-dihydroxybiphenyl, 
4,4'-di(p-hydroxyphenoxy)diphenyl sulfone, urea, 1,4-diaminobenzene, 
1,3-diaminobenzene, 3-aminophenol, 4-aminophenol, trans- and 
cis-1,4-cyclohexanediol, trans-1,3-cyclohexanediol and 
cis-1,2-cyclohexanediol. It will be readily understood that here too in 
general substituents as for the monomers a.sub.1 ) can be present. 
Monomers a.sub.3 : 
4-hydroxybenzoic acid, 3-hydroxybenzoic acid, 
6-hydroxynaphthalene-2-carboxylic acid, 6-hydroxynaphthalene-1-carboxylic 
acid, 3-aminobenzoic acid, 4-aminobenzoic acid and their C.sub.1 -C.sub.4 
-alkyl, C.sub.1 -C.sub.4 -alkoxy or halogen derivatives such as 
3-methyl-4-hydroxybenzoic acid, 3,5-dimethyl-4-hydroxybenzoic acid, 
2,6-dimethyl-4-hydroxybenzoic acid, 3-methoxy-4-hydroxybenzoic acid and 
2,5-dichloro-4-hydroxybenzoic acid, to name but a few examples. 
Monomers a.sub.4 : 
4-mercaptobenzoic acid, 3-mercaptobenzoic acid, 
6-mercaptonaphthalene-2-carboxylic acid, 2,7-dithionaphthalene, 
2,6-dithionaphthalene, 1,4-dithiobenzene and 1,3-dithiobenzene and their 
C.sub.1 -C.sub.4 -alkyl, C.sub.1 -C.sub.4 -alkoxy and halogen derivatives. 
Other suitable monomers of groups a.sub.1) to a.sub.4) are mentioned for 
example in EP-A 206 600. 
The process of the present invention is preferably carried out with liquid 
crystalline polymers as described in EP-A-226 839, DE-A-35 42 814, DE-A-35 
42 813, DE-A-35 42 777, DE-A-35 42 778, DE-A-35 42 779, DE-A-35 42 855, 
DE-A-35 42 856, DE-A-35 42 957, DE-A-35 42 796, DE-A-35 42 797, DE-A-35 42 
798, DE-A-35 42 831, DE-A-35 42 832, DE-A-35 42 833, DE-A-36 21 519, 
DE-A-36 22 137, DE-A-36 29 211, DE-A-36 29 210, DE-A-36 29 209, DE-A-36 29 
208 and DE-A-37 00 821, of which in particular the liquid crystalline 
polyesters described in DE-A-36 29 211 have proved advantageous. However, 
it may be emphasized once more that basically it is possible to use any 
thermotropic mesomorphic polymer. 
In some cases it is advantageous to add a rubber to the liquid crystalline 
polymer. Suitable rubbers are those which are known per se to the person 
skilled in the art for impact modifying thermoplastic polymers, although 
of course care must be taken to ensure that the rubber is stable at the 
high processing temperatures of the liquid crystalline polymers. Merely by 
way of example there may be mentioned graft rubbers based on polybutadiene 
and/or acrylic esters with grafted-on shells of styrene or styrene 
derivatives, acrylonitrile, methacrylonitrile and/or (meth)acrylic esters. 
Appropriate products are known to the person skilled in the art and 
commercially available, so that no details need be given here. 
Furthermore, for certain applications it is advantageous to add one or more 
inorganic fillers to the liquid crystalline polymer. 
Suitable for this purpose in particular are the inorganic fibrous materials 
mentioned in EP-A-305 846. There may be mentioned glass fibers, potassium 
titanate fibers, wollastonite, ceramic Al.sub.2 O.sub.3 /SiO.sub.2 fibers, 
boron fibers, silicon carbide fibers and alkali metal metaphosphate 
fibers, of which glass fibers, potassium titanate fibers and wollastonite 
are particularly preferred. 
These are particularly preferably used together with an alkaline earth 
metal carbonate, preferably the carbonate of magnesium, calcium, strontium 
or barium, in particular the eutectic mixture of calcium carbonate and 
magnesium carbonate, i.e. dolomite. 
Other suitable fillers are the EP-A-312 268 oxides, sulfates, phosphates 
and silicates of metals of main group II of the periodic table and also 
the oxides of Si, Zn, Pb, Sb and Bi. 
The proportion of the aforementioned fillers and rubbers should in general 
lie within the range from 5 to 80% by weight, preferably from 10 to 50% by 
weight. If mixtures of fibrous fillers and alkaline earth metal carbonates 
are used, their respective proportions are preferably from 3 to 50, in 
particular from 10 to 40, and from 3 to 30, in particular from 5 to 20, % 
by weight, based on the total weight of the molding composition. The 
molding compositions can be prepared in a conventional manner by mixing 
the components on an extruder or in another suitable mixing apparatus, 
such as a Henschel mixer or a Banbury mixer. Appropriate techniques are 
known to the person skilled in the art. 
The moldings to be treated by the process of the present invention are 
preferably prepared from the molding compositions by injection molding, 
although it is also possible to use any other known process for preparing 
moldings from thermoplastic molding compositions. 
The novel pretreatment with acid or alkaline reagents is carried out by 
treating the moldings with a solution of these reagents which is at least 
60, preferably at least 80%, and especially 100% by weight organic 
solvent. Suitable acidic reagents are in particular oxygen acids of 
elements of main group V to VII of the periodic table. Examples thereof 
are the oxygen acids of sulfur, phosphor and nitrogen, e.g. H.sub.2 
SO.sub.4, HNO.sub.3, H.sub.3 PO.sub.4 and also chromosulfuric acid, to 
name but a few. It is also possible to use the hydrohalic acids HCl, HBr, 
HI and HF, of which HCl is preferred. Preferred alkaline reagents are 
alkali metal and alkaline earth metal hydroxides, in particular NaOH, KOH, 
Ba(OH).sub.2 and Ca(OH).sub.2 or mixtures thereof. It is also possible and 
may at times be advantageous to carry out the treatment with both an 
acidic and an alkaline reagent. 
The pretreatment agents are used in the process of the present invention in 
a predominantly organic solvent, which may contain up to 40% by weight of 
water. Suitable organic solvents are in particular lower alcohols, ketones 
and carboxylic esters or dipolar aprotic solvents such as 
N-methylpyrrolidone. Owing to their inexpensiveness and ready 
availability, alcohols of from 1 to 4 carbon atoms, in particular 
methanol, ethanol, isopropanol, n-propanol and the isomeric butanols, are 
particularly preferred. 
It is also possible to use mixtures of various organic solvents. 
The temperature at which the pretreatment is carried out is in general 
within the range from 10.degree. C. to the boiling point of the solvent in 
which the acidic or alkaline reagents have been dissolved. Preference is 
given to the treatment at room temperature, since no temperature control 
means are necessary. 
The concentration of the reagents in the solvent is basically not subject 
to any particular restriction; the higher the concentration of the 
solution is, the shorter in general the treatment time can be or the lower 
the treatment temperature can be. 
The treatment time ranges in general from 10 seconds to 60 minutes, 
preferably from 1 to 40 minutes. 
The process of the present invention gives moldings having a surface which 
is readily metallizable or lacquerable. Metallization and lacquering can 
be effected with the customary processes known to the person skilled in 
the art. 
Especially, the first metal coat can be applied physically or 
wet-chemically and then be enhanced to the desired thickness by 
electroless plating or by electroplating. 
Examples of physical processes are physical vapor deposition (PVD) and low 
pressure plasma sputtering. 
Customary wet-chemical processes generally comprise conditioning, etching, 
optional neturalizing, activating, nucleating and electroless 
metallization.

EXAMPLES 
A: Preparation of Liquid Crystalline Polymer 
A stirred autoclave of 70 l nominal capacity was charged with 28 mol of 
terephthalic acid, 12 mol of isophthalic acid, 60 mol of p-hydroxybenzoic 
acid, 20 mol of hydroquinone, 20 mol of 4,4'-dihydroxybiphenyl and 189 mol 
of acetic anhydride, and the reaction was started by heating and stirring. 
The nominal temperature of the oil heated jacket was first adjusted to 
150.degree. C. and then gradually raised to 360.degree. C. in the course 
of 3 h, in the course of which acetic acid and excess acetic anhydride 
were distilled off; at the end of this period the internal temperature was 
340.degree. C. To complete the polycondensation, the internal pressure was 
reduced to about 400 mbar in the course of 30-40', resulting in a 
significant increase in the melt viscosity. The polymer formed was 
extruded through a die plate into a waterbath and then granulated. Its 
inherent viscosity was 2.54 dl/g, measured at 60.degree. C. in 0.1% 
strength (weight/volume) pentafluorophenol solution, while differential 
thermal analysis and examination with a polarizing microscope showed that 
the polymer formed a liquid crystalline melt at 320.degree. C. 
The liquid crystalline polymer (LCP) thus obtained was melted on a 
twin-screw extruder (ZSK 30 from Werner & Pfleiderer), any fillers, 
reinforcing agents, rubbers or other polymers were added, and the mixture 
was extruded at 330.degree.-360.degree. C. and granulated. Table 1 shows 
the constitution of the molding compositions. 
The molding compositions which contained component R1 or R2 were prepared 
at 300.degree.-330.degree. C. by adding the rubber (R1 or R2) in the form 
of an aqueous dispersion and the liberated water was drawn off along the 
extruder. 
TABLE 1 
______________________________________ 
Molding Component 
compo- Glass (% by weight) 
sition LCP fiber PES/R1/R2.sup.1) 
Dolomite 
______________________________________ 
1 100 -- -- -- 
2 70 30 -- -- 
3 70 20 -- 10 
4 45 -- 55 PES -- 
5 45 -- 35 PES 20 
6 45 20 25 PES 10 
7 56 24 20 R1 -- 
8 56 24 20 R2 -- 
9 42 18 40 PES 
10 38.5 16.5 35 PES + 10R1 
11 35 15 30 PES + 10R2 
10 
______________________________________ 
.sup.1) PES = polyether sulfone of the formula 
##STR4## 
having an intrinsic viscosity of 0.58, measured in a solution (1 g/100 ml 
in 1:1 phenol/odi-chlorobenzene at 25.degree. C. 
R1=graft rubber having a grafting base (70% by weight) of n-butyl 
acrylate/dihydrodicyclopentadienyl acrylate (weight ratio 98:2) and a 
graft shell of styrene and acrylonitrile in a weight ratio of 3:1, 
prepared as described in DE-A-24 44 584. 
R2=graft rubber having a grafting base (80% by weight) of polybutadiene and 
a graft shell of styrene and acrylonitrile in a weight ratio of 3:1, 
prepared as described in EP-A-22 216. 
The resulting granules were injection molded at melt temperatures of 
330.degree. C. and mold temperatures of 80.degree. C. to form sheets 
measuring 60.times.80.times.2 mm, which were metallized with a copper 
layer in line with the process described in EP-A 305 846 after they had 
been subjected to the pretreatments described below in Table 2. 
In particular, the following pretreatments were carried out: 
P1: no pretreatment 
P2: 10% by weight of HCl, aqueous solution, 30 min, room temperature 
P3: 10% by weight of KOH, aqueous solution, 30 min, room temperature, 
P4: 10% by weight of KOH in CH.sub.3 OH, 30 min, room temperature 
P5: 10% by weight of KOH in i-C.sub.3 H.sub.7 OH, 30 min, room temperature 
P6: 10% by weight of HCl in CH.sub.3 OH, 30 min, room temperature 
P7: 10% by weight of KOH in CH.sub.3 OH, 15 min, room temperature 
+2% by weight of HCl in CH.sub.3 OH, 5 min, room temperature 
To metallize the pretreated substrates they were first vacuum sputtered 
with a copper layer from 1 to 3 .mu.m in thickness which was then built up 
to a thickness of 40.+-.4 .mu.m by electroplating with a current density 
of from 20 to 30 mA/cm.sup.2. 
To test the peel strength, 25 mm wide strips were sawn out of these sheets, 
and the adhesion of the metal coat was determined with a take-off speed of 
30 mm/min at right angles to the sheet surface. 
Table 2 shows the results of the adhesion measurements on molding 
compositions 1 to 11 following pretreatments P1 to P7. 
TABLE 2 
______________________________________ 
Molding 
composition Adhesion 
Example No. Pretreatment 
N/25 mm 
______________________________________ 
1C 1 Pl 5 
2C 1 P2 5 
3C 1 P3 6 
4 1 P4 8 
5C 2 P1 6 
6C 2 P3 6 
7 2 P4 36 
8 2 P5 30 
9C 3 P1 5 
10 3 P4 39 
11 3 P6 24 
12 3 P7 48 
13C 4 P1 10 
14 4 P4 18 
15 5 P7 38 
16 6 P7 55 
17C 7 P1 8 
18 7 P4 53 
19C 8 P1 6 
20 8 P4 48 
21C 9 Pl 10 
22 9 P4 42 
23 10 P4 47 
24 11 P7 50 
______________________________________ 
The results clearly show that the treatment with acidic or alkaline 
reagents in predominantly organic solvents gives better adhesions in the 
subsequent metallization than the treatment in aqueous solvents.