Low gloss polyacetal resin

A polyacetal resin composition for use in producing molded articles of low gloss comprises the polyacetal and an aluminosilicate fiber.

FIELD OF THE INVENTION 
The present invention relates to oxymethylene polymer compositions. More 
particularly, it relates to filled oxymethylene polymer compositions which 
exhibit reduced surface gloss. 
BACKGROUND OF THE INVENTION 
The term oxymethylene polymer as used herein is meant to include 
oxymethylene homopolymers and diethers and diesters. Also included are 
oxymethylene copolymers, which include oxymethylene polymers having at 
least 50 percent recurring oxymethylene units and at least one other unit 
derived from a monomer copolymerizable with the source of the oxymethylene 
units. 
Oxymethylene polymers having recurring --CH.sub.2 O-- units have been known 
for many years. They may be prepared for example, by the polymerization of 
anhydrous formaldehyde or by the polymerization of trioxane, which is a 
cyclic trimer of formaldehyde, and will vary in physical properties such 
as thermal stability, molecular weight, molding characteristics, color and 
the like depending, in part, upon their method of preparation, on the 
catalytic polymerization technique employed and upon the various types of 
comonomers which may be incorporated into the polymer. 
The polyacetal resins are superior in mechanical and physical properties 
and, therefore, have been widely used in various fields, especially as 
molding resins. It is known that polyoxymethylenes can be provided with 
additives in order to improve certain physical properties of the molding 
resin, and as well the molded products obtained therefrom. Such additives 
extend the range of possible uses of such polymer compositions. Thus, 
fillers have been incorporated into the oxymethylene polymers for the 
purpose of improving rigid strength, hardness, friction resistance and 
wear resistance, to increase heat distortion temperature, impart fire 
retardancy, increase dimensional accuracy of the molded articles by 
decreasing shrinkage, improve electrical conductivity and antistatic 
property, and to increase economy by using inexpensive fillers. U.S. Pat. 
No. 4,506,053 cites numerous inorganic and organic fillers which can be 
included in the form of powder, flakes, or fibers in oxymethylene polymer 
compositions. Among the vast list of materials disclosed in the patent are 
included metal silicates such as talc, clay, mica, asbestos, calcium 
silicate, montmorillonite and bentonite which materials are similar to the 
low gloss additives used in the present invention to be further discussed. 
It is important to recognize that while the use of a particular filler may 
impart a desired property to the oxymethylene polymer composition, the 
addition of the filler may also degrade certain other properties. Thus, it 
is important that the particular filler used achieve improvements in the 
desired physical property and not degrade the good mechanical properties 
of polyacetal resins if its use is to be accepted by industry. 
One proposed use for polyacetal resins is as molded components in the 
interior of automobiles. One necessary property of any molded product in 
an automobile interior is that the surface of the molded article have a 
low-gloss in order to aesthetically match interior coverings such as seat 
upholsteries and the like. As before said, it is important that the use of 
a filler to reduce the gloss of a polyacetal resin not significantly alter 
the other properties. Thus, the primary objective of the present invention 
is to provide a low-gloss polyacetal polymer composition which retains its 
mechanical properties. 
SUMMARY OF THE INVENTION 
It has now been found that molded articles obtained from a polyacetal resin 
can be provided with a reduced surface gloss by the incorporation of an 
aluminosilicate fiber into the polyacetal resin. The polyacetal resin 
containing the aluminosilicate fiber retains its mechanical properties and 
is strengthened by the reinforcing effect of such fibers while the molded 
articles are provided with a uniformly finished surface and a substantial 
reduction in surface gloss. 
DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The oxymethylene polymer used in the compositions of the present invention 
is well known in the art. The polymers are characterized as having 
recurring oxymethylene groups or units, i.e., --CH.sub.2 O--. The term 
oxymethylene polymer as used herein is intended to include any 
oxymethylene polymer having --CH.sub.2 O-- groups comprising at least 
about 50 percent of the recurring units, for example, homopolymer, 
copolymers, terpolymers and the like. 
Typically, the homopolymers are prepared by the polymerization of anhydrous 
formaldehyde or by the polymerization of trioxane which is a cyclic trimer 
of formaldehyde. For example, high molecular weight polyoxymethylenes have 
been prepared by polymerizing trioxane in the presence of certain fluoride 
catalysts such as antimony fluoride and may also be prepared in high 
yields and at rapid reaction rates by the use of catalysts comprising 
boron fluoride coordinate complexes with organic compounds. 
The homopolymers are usually stabilized against thermal degradation by 
end-capping or the incorporation therein of stabilizer compounds such as 
described in U.S. Pat. No. 3,133,896 to Dolce and Berardinelli. 
Oxymethylene polymers that are particularly adapted for use in the 
compositions of the present invention are oxymethylene copolymers, which 
may be prepared as described in U.S. Pat. No. 3,027,352 of Walling et al 
by copolymerizing, for example, trioxane with any of various cyclic ethers 
having at least two adjacent carbon atoms, e.g., ethylene oxide, 
dioxolane, and the like. 
Especially suitable oxymethylene copolymers which may be used in the 
compositions of the present invention usually possess a relatively high 
level of polymer crystallinity, i.e., about 70 to 80 percent. These 
preferred oxymethylene copolymers have repeating units which consist 
essentially of (a) --OCH.sub.2 -- groups interspersed with (b) groups 
represented by the general formula: 
##STR1## 
wherein each R.sub.1 and R.sub.2 is selected from the group consisting of 
hydrogen, lower alkyl and halogen-substituted lower alkyl radicals, each 
R.sub.3 is selected from the group consisting of methylene, oxymethylene, 
lower alkyl and haloalkyl-substituted methylene, and lower alkyl and 
haloalkyl-substituted oxymethylene radicals, and n is an integer from zero 
to three inclusive. 
Each lower alkyl radical preferably has from one to two carbon atoms, 
inclusive. The --OCH.sub.2 -- units of (a) constitute from about 60 to 
about 99.6 percent of the recurring units. The units of (b) may be 
incorporated into the copolymer during the step of copolymerization to 
produce the copolymer by the opening of the ring of a cyclic ether having 
adjacent carbon atoms, i.e., by the breaking of an oxygen-to-carbon 
linkage. 
Copolymers of the desired structure may be prepared by polymerizing 
trioxane together with from about 0.4 to about 40 mole percent of a cyclic 
ether having at least two adjacent carbon atoms, preferably in the 
presence of a catalyst such as a Lewis acid (e.g, BF.sub.3, PF.sub.5, and 
the like) or other acids (e.g., HC10.sub.4, 1% H.sub.2 SO.sub.4, and the 
like). 
In general, the cyclic ethers employed in making the preferred oxymethylene 
copolymers are those represented by the general formula: 
##STR2## 
wherein each R.sub.1 and R.sub.2 is selected from the group consisting of 
hydrogen, lower alkyl and halogen-substituted lower alkyl radicals, and 
each R.sub.3 is selected from the group consisting of methylene, 
oxymethylene, lower alkyl and haloalkyl-substituted methylene, and lower 
alkyl and haloalkyl-substituted oxymethylene radicals, and n is an integer 
from zero to three inclusive. Each lower alkyl radical preferably has from 
one to two carbon atoms, inclusive. 
The preferred cyclic ethers used in the preparation of the preferred 
oxymethylene copolymers are ethylene oxide and 1,3-dioxolane, which may be 
represented by the formula: 
##STR3## 
wherein n represents an integer from zero to two, inclusive. Other cyclic 
ethers that may be employed are 1,3-dioxane, trimethylene oxide, 
1,2-propylene oxide, 1,2-butylene oxide, 1,3-butylene oxide and 
2,2-di-(chloromethyl)-1,3-propylene oxide. 
The preferred catalyst used in preparing the desired oxymethylene 
copolymers is the aforementioned boron trifluoride as discussed in the 
previously identified Walling et al patent. Reference is made to this 
patent for further information concerning the polymerization conditions, 
amount of catalyst employed, and the like. 
The oxymethylene copolymers that are preferably present in the compositions 
of the present invention are thermoplastic materials having a melting 
point of at least 150.degree. C., and normally are millable or processable 
at a temperature of from about 180.degree. C. to about 200.degree. C. They 
have a number average molecular weight of at least 10,000. The preferred 
oxymethylene copolymers have an inherent viscosity of at least 1.0 
(measured at 60.degree. C. in a 0.1 weight percent solution in 
p-chlorophenol containing 2 weight percent of alphapinene). 
The oxymethylene copolymer component of the compositions of this invention 
preferably is an oxymethylene copolymer that has been preliminarily 
stabilized to a substantial degree. Such stabilizing technique may take 
the form of stabilization by degradation of the molecular ends of the 
polymer chain to a point where a relatively stable carbon-to-carbon 
linkage exists at each end. For example, such degradation may be effected 
by either solution hydrolysis (hereinafter "SH") or melt hydrolysis 
(hereinafter "MH") to remove unstable groups. These processes degrade the 
hemiacetal end groups in the copolymer chain. Both processes are known to 
those skilled in the art and are in commercial practice. A useful solution 
hydrolysis process is disclosed in U.S. Pat. No. 3,179,948 and a useful 
melt hydrolysis process is disclosed in U.S. Pat. No. 3,318,848. If 
desired, the oxymethylene copolymer may be endcapped by techniques known 
to those skilled in the art. A preferred end-capping technique is 
accomplished by acetylation with acetic anhydride in the presence of 
sodium acetate catalyst. A preferred oxymethylene copolymer is 
commercially available from Hoechst Celanese Corporation under the 
designation CELCON.RTM. acetal copolymer. Preferred are acetal copolymers 
having a melt index of from about 5.0 to 30.0 g/10 min when tested in 
accordance with ASTM D1238-82. 
With respect to the oxymethylene terpolymer, it may be prepared, for 
example, by reacting trioxane and a cyclic ether and/or cyclic acetal such 
as in the preparation of the oxymethylene copolymer, with a third monomer 
which is a bifunctional compound such as a diglycide of the formula: 
##STR4## 
wherein Z represents a carbon-to-carbon bond, an oxygen atom, an 
oxy-alkoxy of 1 to 8 carbon atoms, preferably 2 to 4 carbon atoms, and 
which may be an oxycycloalkoxy of 4 to 8 carbon atoms, or an 
oxy-poly(lower alkoxy), preferably of 2 to 4 recurring groups each with 1 
to 2 carbon atoms, for example, ethylene diglycide, diglycidyl ether and 
diethers of 2 mols of glycide and 1 mol of formaldehyde, dioxane or 
trioxane, or diethers of 2 mols of glycide and 1 mol of an aliphatic diol 
with 2 to 8 carbon atoms, advantageously 2 to 4 carbon atoms, or a 
cycloaliphatic diol with 4 to 8 carbon atoms. 
Examples of suitable bifunctional compounds include the diglycidyl ethers 
of ethylene glycol, 1,4-butanediol, 1,3-butanediol, cyclobutane-1,3-diol, 
1,2-propane-diol, cyclohexane-1,4-diol and 
2-dimethyl-4-dimethyl-cyclobutane-1,3-diol, with butanediol diglycidyl 
ethers being most preferred. 
Generally, in preparing the terpolymer of trioxane, cyclic ether and/or 
cyclic acetal and at least one bifunctional diglycide compound, a ratio of 
from 99.89 to 89.0 weight percent trioxane, 0.1 to 10 weight percent of 
the cyclic ether and/or cyclic acetal, and 0.01 to 1 weight percent of the 
bifunctional compound is preferred, with the percentage figures being 
based on the total weight of monomers used in forming the terpolymer. The 
terpolymers thus obtained are characterized as being essentially white and 
having a particularly good extrudability. 
The polymerization of the terpolymer may be carried out according to known 
methods, that is in substance, solution or suspension, while using the 
above-mentioned quantitative proportions of the termonomers. As solvents, 
there may advantageously be used inert aliphatic or aromatic hydrocarbons, 
halogenated hydrocarbons or ethers. 
A preferred terpolymer has the following quantitative proportions: 99.85 to 
89.5 weight percent of trioxane, 0.1 to 10 weight percent of cyclic ether 
or cyclic acetal, and 0.05 to 0.5 weight percent of diglycidyl ether, the 
percentage figures being calculated on the total weight of the monomer 
mixture used for preparing the terpolymer. 
The oxymethylene polymers may include, if desired, stabilizing agents 
including formaldehyde scavengers, antioxidants, light stabilizers, etc. 
and other conventional additives such as plasticizers, colorants and 
pigments. Suitable formaldehyde scavengers include cyanoguanidine, 
melamines, polyamides, amine-substituted triazines, amidines, ureas, 
hydroxyl salts of calcium, magnesium and the like, salts of carboxylic 
acids, and metal oxides and hydroxides. Suitable mold lubricants include 
alkylene bisstearamide, long-chain amides, waxes, oils, and polyether 
glycides. A preferred mold lubricant is commercially available from Glyco 
Chemical, Inc., under the designation Acrawax C and is alkylene 
bisstearamide. The preferred antioxidants are hindered bisphenols. 
Especially preferred is 1,6-hexamethylene bis-(3,5-di-t-butyl-4-hydroxy 
hydrocynnamate), commercially available from Ciba-Geigy Corp. under the 
designation Irganox 259. 
The aluminosilicate fiber used in the present invention is typically a 
white to light gray fiber. The fiber color is important in that it should 
not shift the color of the resin whether the resin is uncolored or colored 
with dyes or pigments. The aluminosilicate fiber of this invention has an 
average fiber diameter of from 0.5 to 2.0 microns and an average length of 
1 to 5 millimeters. Thus, the fibers have aspect ratios on the order of at 
least about 1,000 prior to compounding to form the molding composition. 
The aluminosilicate fiber useful in the present invention will consist 
essentially of aluminosilicate with less than 5% of the fiber containing 
oxides other than alumina and silica. Preferably, the amount of oxides 
other than alumina and silica will comprise no more than 3 wt.%. 
Typically, these other oxides will comprise titanium dioxide, iron oxides 
and alkali metal oxides. The aluminosilicate fibers of the present 
invention are distinguished over conventional fiberglass fillers such as 
E-glass which are borosilicate materials. 
The composition of the aluminosilicate fiber of the present invention, 
therefore, will comprise from about 40 to 49 wt. % Al.sub.2 O.sub.3 and 
from about 50 to about 55% SiO.sub.2 with the remainder comprising other 
oxides including iron oxides, titanium oxides and alkali metal oxides. 
Another important feature of the aluminosilicate fibers useful in the 
present invention is that the fiber content should comprise at least 85 
wt. % fibers. Preferably, no more than 5 wt. % and, most preferably, no 
more than 2 wt. % of the fibers contain nonfibrous materials such as in 
the form of coarse spheres. Thus, it has been found that if the fiber 
content of the aluminosilicate fiber added is substantially less than 85%, 
the polyacetal resin undergoes a substantial color shift. 
In general, the aluminosilicate fiber is added to the polyacetal resin in 
an amount of from about 1 to 25% by weight based on the total composition. 
Preferably, the aluminosilicate fiber will be present in amounts of about 
1 to about 10% by weight of the total composition and, more preferably 1 
to about 5% by weight. The addition of aluminosilicate fiber in an amount 
less than 1% by weight does not bring about a sufficient reinforcement of 
the resin and does not sufficiently reduce the gloss of the molded 
articles, while the addition in an amount exceeding 10% by weight 
substantially modifies the physical properties and does not reduce the 
gloss by any appreciable amount. In amounts greater than 10 wt. %, 
substantial improvements in tensile strength are found, however, and, 
thus, in certain applications, large amounts of the aluminosilicate fiber 
may be useful. The addition of the aluminosilicate fiber to polyacetals is 
also believed to improve the surface wear or abrasive wear of the surface 
of articles molded therefrom and, thus, further increase the usage of the 
polyacetal compositions of this invention. 
A preferred aluminosilicate fiber is marketed under the name Fiberfrax HSA 
Fiber from Sohio Carborundum, Co. Table 1 set forth the typical physical 
properties and chemical analysis of the Fiberfrax HSA fiber. 
TABLE 1 
______________________________________ 
Properties of Fiberfrax HSA Fiber .RTM. 
______________________________________ 
Typical Physical Properties 
Fiber Content 85% minimum 
Color White to Light Gray 
Melting Point 1790.degree. C. (3260.degree. F.) 
Fiber Diameter 1.2 Microns (mean) 
Fiber Length 3 mm (1/8") 
Specific Gravity 2.7 g/cm.sup.3 
Specific Heat at 1093.degree. C. 
1130 J/kg .degree.C. (0.27 Btu/lb .degree.F.) 
(2000.degree. F.) 
Fiber Surface Area 
2.5 m.sup.2 /g 
Typical Chemical Analysis 
Al.sub.2 O.sub.3 43.4% 
SiO.sub.2 53.9% 
Fe.sub.2 O.sub.3 0.8% 
TiO.sub.2 1.6% 
K.sub.2 O 0.1% 
Na.sub.2 O 0.1% 
Leachable Chlorides 
10 ppm 
______________________________________ 
The composition according to the present invention can be produced by 
various methods. For example, pellets obtained by extruding a preblend 
consisting of the resin ingredient and aluminosilicate fiber in an 
extruder can be molded in a molding machine. Known additives such as 
various kinds of organic high-molecular substances or inorganic fillers 
may be added to the polyacetal resin composition according to the present 
invention dependent upon the uses thereof. Organic high-molecular 
substances include polyurethanes, vinylic compounds and copolymers thereof 
such as ethylene/vinyl acetate copolymer, ethylene/alkyl acrylate 
copolymer, styrene/butadiene/acrylonitrile copolymer and 
styrene/acrylonitrile copolymer; multi-phase graft copolymers comprising 
polyacrylate resins; and segmented thermoplastic copolyesters. Inorganic 
fillers include glass fibers, carbon fibers, glass flakes, mica, talc, 
calcium carbonate, etc. as long as such fillers do not reduce the desired 
physical properties of the molded article and, in particular, do not 
degrade the surface characteristics of the molded article including 
surface gloss, smoothness, uniformity of color, color shift, warpage, wear 
properties, etc. In addition, antistatic agents or electrical conductivity 
improving agents such as electrically conductive carbon black, coloring 
agents including dyes and pigments, mold release agents, nucleating 
agents, stabilizers, and the like may be added to the composition to give 
necessary properties thereto. The additives may be blended prior to or 
subsequent to when the aluminosilicate fiber is blended with the 
polyacetal, or may be added to the resin in the form of a mixture thereof 
with the aluminosilicate fiber. 
The composition according to the present invention shows not only 
remarkably reduced surface gloss but also a high tensile strength. 
Accordingly, the polyacetal composition of the present invention can be 
used in the production of the interior components used in automobiles such 
as dash boards and interior plastic components needed to match interior 
upholstery. Other low gloss, high strength applications include furniture, 
rifle housings, etc. The effects of the present invention will now be 
described in more detail with reference to examples and comparative 
examples.

EXAMPLES 1-8 
Blends comprising a polyacetal resin (Celcon M90-04, a stabilized 
oxymethylene copolymer having a melt index of 9.0 g/10 min), a color 
concentrate and aluminosilicate fiber (Fiberfrax HSA Fiber.RTM.) were made 
in the proportions as shown in Table 2 (Samples 7 and 8) for comparison 
with compositions comprising the colored polyacetal control and colored 
polyacetals containing glass spheres and silica, respectively. All 
percentages are by weight. All the blends were extruded in an extruder and 
then molded in an injection molding machine to prepare test pieces for 
mechanical and surface properties including surface gloss and color. 
Several of the glass- and silica-containing compositions were run 
separately from the control and fiber runs. All runs used a mold 
temperature of 200.degree. F. to provide uniform comparison of the surface 
properties of the molded test article. The results of testing the control 
formulations and the formulations which contain the aluminosilicate fibers 
of the present invention are also shown in Table 2. 
As is obvious from the results, the compositions according to the present 
invention not only show similar and improved mechanical properties 
relative to a polyacetal control, but also substantially reduced surface 
gloss of the molded articles. Also, the color of the composition 
containing the aluminosilicate fibers was substantially the same as the 
control indicating little color shift. 
TABLE 2 
__________________________________________________________________________ 
Formulation 
1 2 3* 4 5 6* 7 8 
__________________________________________________________________________ 
Celcon M90-04 
95 90 
92 94 
94 
92 94 92 
Blue Color Conc. 
5 5 
5 5 
5 
5 5 5 
Glass Sphere 
-- 5 
3 1 
-- 
-- -- -- 
Silica -- -- 
-- -- 
1 
3 
Aluminosilicate 
-- -- 
-- -- 
-- 
-- 1 3 
Fiber 
Physical Properties 
Tensile Strength 
Yield, psi 8.67 
a 8.52 
-- 
-- 
8.67 
8.54 
8.65 
Modulus, ksi 
379 a 309 -- 
-- 
412 401 401 
Elongation, % 
37 a 31 -- 
-- 
41 39 49 
Flexural Strength 
5% Strain, psi 
12.8 
a 12.0 
-- 
-- 
-- 12.7 
12.8 
Modulus, ksi 
369 -- 
366 -- 
-- 
377 -- 387 
Notched Izod, 
1.04 
a 0.93 
-- 
-- 
0.89 
0.93 
0.95 
ft-lb/in 
Surface Properties 
Hunter Color b 
-4.18 
-- 
-3.54 
-- 
-- 
-3.55 
-- -4.34 
Specular Gloss @45.degree. 
48 32 
43 47 
47 
42 30 22 
ASTM D-523 
__________________________________________________________________________ 
a Physical properties were not measured because the surface appearance wa 
not acceptable. 
*Physical properties were adjusted based on control as data generated on 
runs separate from Examples 7 and 8. 
EXAMPLES 9-11 
Samples of a polyacetal resin comprising Celcon M90 and containing 20 wt. % 
of a thermoplastic polyurethane impact modifier were compounded, molded 
and tested to determine the affect an aluminosilicate fiber and an E-glass 
fiber have on the gloss of such samples. Example 9 was a control sample 
comprising the impact modified polyacetal resin alone. Example 10 was a 
sample of the same impact modified polyacetal resin as in Example 9 
compounded with 3 wt. % of Fiberfrax HSA fiber. Example 11 was a sample of 
the impact modified polyacetal resin used in Example 9 compounded with 2 
wt. % of E-glass fiber. The Specular Gloss @45.degree. (ASTM D-523) for 
Example 9 averaged out to 55. The Specular Gloss for Example 10 averaged 
out to 23. The Specular Gloss of Example 11 was 39.4 with the flow and 
34.5 transverse to flow.