CA2102047A1

CA2102047A1 - Plastic molding composition for the production of moldings having a color-coordinatable decorative effect

Info

Publication number: CA2102047A1
Application number: CA002102047A
Authority: CA
Inventors: Franz Guebitz; Kai-Uwe Toennes
Original assignee: Individual
Current assignee: Hoechst AG
Priority date: 1992-10-31
Filing date: 1993-10-29
Publication date: 1994-05-01
Also published as: JPH06279616A; NO933921D0; EP0596378A1; NO933921L; CZ229793A3; BR9304403A; KR940009284A; MX9306816A

Abstract

Abstract of the Disclosure Plastic molding composition for the production of moldings having a color-coordinatable decorative effect A plastic molding composition which contains from 0.3 to 3% by weight of carbon fibers having a fiber length of from 0.5 to 18 mm can be converted into moldings having a color-coordinatable decorative effect. These moldings are used, in particular, in the interior of motor vehicles, but are also suitable for other applications, for example for small domestic appliances, garden furniture or office equipment.

Description

HOECEIST AXTIENGESEI,LSC~AFT HOE 92/F 345 Dr.DA/-Description Plastic molding composition for the production of moldings having a color-coordinatable decorative effect The invention relates to a thermoplastic molding composi-tion for the production of moldings haviny a special decorative surface effect. The molding composition can be processed by conventional processing methods, ~uch a~
injection molding, extrusion and extru~ion blow molding.

Internal trim parts for motor vehicles, such as covers for A, B and C columns and the like, and casings for small domestic appliances are currently generally produced by injection molding from thermoplastics.

The thermoplastics are dyed in the mass, and the finished parts are in very many cases provided with a ~urface structure (grain) for the sake of appearance and feel.
This grain i8 produced during the injection-molding process by casting of corresponding structures engraved in the surfaces of the cavity of the injection mold. This give~ molding~ having a structured surface, but with a homogeneous color.

Ma~s-dyed moldings having a surface grain are an adequate solution for many applications vi~-à-vis design and quality requirement~. ~owever, there i8 a demand, for example for the interior of large family cars and executive car~, for moldings which are able to sati~fy higher demands regarding appearance and comfort.

In order to produce higher-quality surfaces in moldiny~
for the interior of motor vehicles, the trim parts can either be painted (for example with a soft finish) or laminated with film~ or textile materials. The lamination i~ in each ca~e carried out with the aid of adhesives.

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2~0?,Q~7 Depending on the nature of the substrate material, pretreatment of the moldings by flame treatment, corona discharge or the like is necessary in order to achieve good adhesive strengths. These individual process steps mean relatively high production C08t8. A further associ-ated dicadvantage is the unfavorable fogging behavior.

Fogging iB taken to mean condensation of volatile con-stituents from the internal trim of motor vehicles onto the windows, in particular the windscreen. The fogging intensity is naturally dependant on a number of factors and on the prevailing temperature conditions. Since adhesives frequently contain relatively high proportions of volatile substances, adhesive-laminated parts virtu-a~ly always represent a significant fogging-promoting potential.

A further disadvantage can occur in the case of adhesive-laminated parts regarding design freedom. Due to the only restricted moldability of textiles and films in some cases during the lamination process, restrictions may have to be taken into account regarding the geometrical design of the substrate part3.

The object was therefore to develop thermopla~tic materials which can be processed by conventional shaping methods for plastics. In particular, the surfaces of the finished parts should have a 6pecial decorative surface effect (sprinkled surface, heather mix effect, textile effect).

It i~ in principle pos~ible to provide dyed thermo-plastics, possibly additionally modified by means of reinforcing ~ub~tances, such as glass fibers or talc and/or elastomer~, with fibers of another color. It is known that fibers made from, for example, thermoplastic polyester, poly~;de or polyacrylonitrile which have good thermal and mechanical re6istance can be admixed with the polypropylene in an amount of from 0.5 to 3% and 2 ~ ~ 7 homogeneously mixed with the polymer in extruders. Test sheets produced therefrom and provided with a grained surface exhibited the desired textile-like surface effect. However, attemptæ to produce large-area moldings in which long flow paths were pre~ent as a consequence of the geometry were un atisfactory. The reason was the inadequate thermal and mechanical resisting force of the polyester, polyamide or polyacryonitrile fibers. Proces-~ing temperature of from about 230 to 280C neces~ary during injection molding of, for example polypropylene or polyester and the material ~hear occurring in screw injection-molding machines during homogenization and during flow through hot runners and narrow gates resulted in considerable heat damage to the fibers. Furthermore, these shear forces, in combination with the high tempera-ture, in some cases even caused los8 of the fiber geometry, which meant that the impression of a textile-like surface was completely lost.
-;' Due to the problems on u~e of polyester, polyamide and polyacrylonitrile fibers, it has been proposed to u~e carbon fiber~ (cf. DE 42 21 208). In this case, it was found that use of carbon fibers was not accompanied by any mechanical or thermal problems, and the de3ired decorative effect of the molding surface can be achieved.

The use of carbon fiber~ for reinforcing polymers i8 known per se. It is usual to add amounts of from 10 to 20% as cut carbon fibers to polymers in order to achieve a significant improvement in the mechanical propertie6 (flexural strength, etc.).

The invention thus relates to a plastic molding composi-tion for the production of molding~ having a decorative surface effect, containing a) from 100 to 50% by weight of a thermoplastic polymer, b) from 0 to 50% by weight of reinforcing material and/or fillers and ,--~

from 0.1 to 5.0% by weight, preferably from 0.2to 3.0% by weight, based on the molding composi-tion, of carbon fibers having a fiber length of from 0.05 to 18 mm.

~he plastic molding composition according to the invention contains a thermopla~tic organi~ polymer, for example one of the following:

1. Polyacetals, such as polyoxymethylene. ~he term polyoxymethylene includes all polymers containing more than 50% of the recurring unit ( C~20 ), such a4 polyoxy-methylene homopolymer~, copolymer3, terpolymers, etc.

2. Polyesters derived from dicarboxylic acid3 and diols and/or from hydroxy carboxylic acid~ of the corre~ponding lactones, such a~ polyethylene terephthalate, poly~
butylene terephthalate, poly-1,4-dimethylolycyclohexane terephthalate, poly(2,2-bis(4-hydroxyphenyl)propane) terephthalate, polyhydroxybenzoate, and block polyether e3ters derived from polyethylene havirlg hydroxyl terminal groups, dialcohols and dicarboxylic acids.

3. Polyamid~ and copolyamide~ derived from di~ine~
and dicarboxylic acids and/or from aminocarboxylic acid~
or the correspondin~ lactams, such a~ nylon 4, nylon 6, nylon 6.6, nylon 6.10, nylon 11, nylon 12, poly-2,4,4 trimethylhexamethyleneterephthalamide, poly-m-phenylene~
isophthalamide, and copolymers thereof with polyethers, such as, for example, with polyethylene glycol, poly-propylene glycol or polytetramethylene glycol. ~ -~
~, 4. Polycarbonates and polye~ter carbonates. ~-::

5. Polyphenylene oxides and ~ulfides, and mixture~
thereof with styrene polymer~.

6. Polyurethanes derived from polyethers, polyesters and polybutadiene~ containing terminal hydroxyl group~ on ~æ~

S
the one hand and aliphatic or aromatic polyisocyanates on the other hand, and precursors thereof (polyi~ocyanate polyol prepolymers).

7. Polyvinyl chloride.

8. Polystyrene.

9. Copolymers of styrene or -methylstyrene with diene~
or acrylic derivatives, such as, for example, styrene-butadiene, styrene-maleic anhydride, styrene-acrylo-nitrile, styrene-ethyl methacrylate, styrene-butadiene-ethyl acrylate, styrene-acrylonitrile-methacrylate; high-impact-strength mixtures of styrene copolymers and another polymer, such as, for example, a polyacrylate, a diene polymer and an ethylene-propylene-diene terpolymer;
and block copolymer3 of styrene, such as, for example, styrene-butadiene-~tyrene, styrene-isoprene-styrene, styrene-ethylene/butylene-styrene or styrene-ethylene/propylene-styrene.

lO. Graft copolymers of styrene, such as, for example, styrene on polybutadiene, styrene and acrylo~itrile on polybutadiene, styrene and maleic anhydride on poly-butadiene, 6tyrene and alkyl acrylate or alkyl meth-acrylates on polybutadiene, styrene and acrylonitrile on ethylene-propylene-diene terpolymers, ~tyrene a~d acrylo-nitrile on polyalkyl acrylates or polyalkyl metha-crylate~, ~tyr~ne and acrylonitrile on aarylate-butadiene copolymers, and mixtures thereof with the copolymers mentioned under 9), which are known, for example, a~ ABS, MBS, ASA or AES polymers.

11. Nixtures of the abovementioned polymers, ~uch a~, for example, PP/BPDM, nylon 6/EPDM or ABS, PVC/EVA, PVC/ABS, PVC/MBS, PC/ABS, P~TP/ABS, PC/ASA, PC/PBT, PVC/CPE, POM/thermoplastic PUR, POM/acrylate, POM/MBS, PPE/HIPS, PPB/nylon 6.6 and copolymers, PA/HDPE, PA/PP
and PA/PPB.

2 ~ 7 .

Preference is given to the plastics POM, PBT, PET, PA, PC, PPE and ABS.

Particularly suitable base materials for the molding compositions according to the invention are polyoxy-methylenes. These are generally linear or branchedpolymers which generally contain at least 50~, preferably at least 90%, of oxymethylene units (-CH20-). The term polyoxymethylenes covers both homopolymers of formalde-hyde or its cyclic oligomers, ~uch as trioxane or tetroxane, and corresponding copolymers or terpolymers.

Homopolymers of formaldehyde or trioxane here are polymers whose hydroxyl terminal groups have been chemically stabilized in a known manner against degrada-tion, for example by esterification or etherification.

Copolymers are polymers made from formaldehyde or its cyclic oligomers, in particular trioxane, and cyclic ethers, cyclic acetals and/or linear polyacetals. Suit-able comonomer~ are a) cyclic ethers having 3, 4 or 5, preferably 3, ring members, b) cyclic acetals having 5 to 11, preferably 5 to 8, ring members, other than trioxane, and c) linear polyacetals, in each case in amount~ of from 0.1 to 20 percent by weight, from 0.5 to 10% by weight. The most highly suitable copolymers comprising from 99.5 to 95% by weight trioxane and from 0.5 to 5~ by weight of one of the abovementioned cocomponents.

In addition to the abovementioned cocomponents, branched polyoxymethylenes additionally contain a bifunctional monomer, preferably a diglycidyl ether.

In general, the polyoxymethylenes have an MFI 190/2.16 in accordance with DIN 53 725 of from 0.5 to 75 g/10 min, in particular from 1 to 50 g/10 min.

The molding composition may, if desired, also contain known, commercially available additives, such as --` 2102B~7 stabilizers, nucleating agents, antistatics, light stabilizers, flameproofing agents, lubricants, glidants, pla~ticizers, impact modifiers, reinforcing material~, pigments, dyes, optical brighteners, proce~sing auxiliarie~ and the like, whose amount can be up to 50 by weight, based on the total mixture.

Preferred fillers and/or reinforcing materials are talc, chalk, glas~ fibers or glass beads.

Particularly suitable impact modifiers are: thermoplastic polyurethanes, methyl methacrylate-butadiene-styrene graft copolymers (MBS) or acrylonitrile-butadiene-styrene graft copolymer6 (ABS).

According to the invention, carbon fibers having a length of from 0.5 to 18 mm, preferably from 1 to 6 mm, and a lS diameter of from 10 to 20 ~m are incorporated into the base material in order to achieve a decorative effect.
The amount added is from 0.1 to 5.0% by weight, prefer-ably from 0.2 to 3% by weight, based on the total molding compositlon .

Examples of ~uitable processing methods are injection molding, extrusion and extrusion blow molding.

The processing conditions for the molding composition according to the invention correspond to the conditions normally used in the proce6sing of thermoplastics. The processing temperature~ - mea~ured directly after leaving the die - are, for example in the c:ase of polyoxy-methylene, in the range from 170 to 230C, depending on - the size and complexity of the molding. The mold empera-ture i8 generally from 40 to 120C.

For the production of particularly large-area and diffi-cult moldings from a processing point of view, it is also possible to choose relatively high processing tempera-ture~ for such articles without impairing the color or 2 ~

properties.

An optimum effect i~ obtained on use of polymers in white and very pale gray shades. Good results can al~o be achieved with base polymers which have been colored in a pale shade (for example pale blue or pale brown). The effect can also be influenced by surface treatment oP the mold cavities.

The molding composition according to the invention facilitates the use of conventional, economically advan-tageou~ proce~sing method~ for plastic~ (such a~, forexample, injection molding) for applications which were hitherto the province of moldings produced in a more complex manner (such as, for example, by adhesive lamina-tion). Moldings made from the molding composition accord-ing to the invention can be used, in particular, in theinterior of motor vehicles. ~owever, they are just as suitable for other applications, such as, for example, for small domestic appliances or office and communication equipment. From the large number of possible applica-tions, the following is a list of a few examples:

Motor vehicles: - fixing elements, for example clip~ - .
- door trim, -- column trim, door sill strips, - motorcycle panniers.

Office: - office furniture moldings (backrest~, armrests, chair legs, computer housings, fan ;~
housings, etc.), - office furniture coverings, - attaché case shells.

Domestic: - toaster housing, - lamp housing, - irons, : ::

2~ ~2~7 g - freezer and storage veseels, bowls, etc., - garden furniture.

Contruction: - electrical installation pro-gramme3 (such as switches, switch covers, etc.).

The particular advantages of the molding compositions according to the invention are:
- the excellent decorative effect (heather mix effect), - the ready processability without thermal or mechanical decomposition.

The examples below serve to illustrate the invention:

Example 1 POM fixing elements for motor vehicle headliners Fixing caps for fixing the headliner of a large family car were produced by injection molding. From the de~ign point of view, an essential requirement of the finished parts wa~ that their surfaces should be matched as far a~
possible to the special appearance of the headliner. In addition, variou~ mechanical requirement~ had to be satisfied by the fixing clip integrated into the cap, such a~ high toughne~, spring-elastic behavior and low tendency to creep. A thermoplastic molding compoYition based on an acetal copolymer (POM) having an MFI 190/2.16 (DIN 53 735) of 9 g/10 min was therefore proces~,ed in a pale base color. 0.75% of cut carbon fibers having a diameter of about 10 ~m were incorporated into this molding composition and used to achieve "~pxinkled"
surfaces which themselves made an excellent vi~ual match with the surrounding headliner. The moldings were pro-duced in a four-cavity mold with cold runner~ and pin gates. The processing parameters corresponded to the typical conditions for POM (material temperature 205C, 2~7 mold temperature 90C). The addition of only a small amount of carbon fibers, with respect to the special decorative purpose required, meant that the favorable, material-typical properties of the acetal copolymer were fully retained.

Example 2 Fountain pen casing made from POM

Fountain pen ca~ings are articles which have to satisfy, inter alia, both fashion and aesthetic requirements and for which many designs are already offered. Nevertheless, a novel appearance for fountain pens ha~ been found. To this end, the casing parts are produced by two-component injection molding from a free-flowing polyoxymethylene molding compo~ition (POM, copolymer type). Due to the excellent spring properties, surface hardness, scratch resistance and reproduction accuracy, the choice of material fell on a free-flowing grade from this class of material having an MFI 190/2.16 of 27 g/10 min. By means of the two-component method, the ca~ing surfaces were divided optically into a number of zones of different color. For example, a pale gray shade was combined with another color in each ca~e, such as red or blue. A
particular appearance wa~ achieved by additionally incorporating carbon fibers in a proportion by weight of 1.5% into the molding composition (lst component) which had been colored gray. In combination with ~ fine grain in the ~urface segment~ kept in gray, this resulted in a discreet structure effect which avoided the typical plastic look and ensured a ~ophisticated design~ During processing of the molding compositions, three four-cavity molds were used, and the process parameters conv~ntional for POM were set (material temperature 210C, mold temperature 95C).

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2~2~7 Example 3 P~T housing of a red-light heat radiator Housings for red-light heat radiators have hitherto frequently been made from thermo~et molding compo~itiono due to the high temperatures of about 180C. Technical problems, 3uch as, for example, the brittleness of melamine resin-based thermoplastics, their very large po~t-shrinkage and the warping and ~tre~ cracking problems this cau~es, economical disadvantages, such as relatively long cycle times, the deflashing which is necessary after production, and ecological points of view, such as poor recyclability, are, however, now increasingly resulting in substitution of these materials by thermoplastic polyester-based molding compositions.
The housing of a red-light heat radiator has therefore also been achieved in a thermoplastic polyester. A modern "techno-design" was required for the housing surfaces. In order to satisfy technical/economical requirements on the one hand and design specifications on the other hand, the housing parts were produced from a polybutylene tere-phthalate molding composition (PBT) in a pale-gray base color, into which 1% of carbon fibers had additionally been incorporated. A two-cavity mold with cold runner and pin gate (due to the good flow properties of PBT) was used whose cavities were provided with ~urface grain.
During proce~sing by injection molding, the usual values for PBT molding compositions for material temperature (260C) and mold temperature (80C) were set. In addition to the advantage of con~iderably more economical production in the case of the use of the thermopla~tic molding composition, in particular also the design specifications were fully achieved in that the carbon fibers incorporated into the molding composition, in combination with the surface grain, resulted in a 8pecial structure effect which i~ highly suitable for technical housings.

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Example 4 POM piggy bank A plastic piggy bank was injection molded from an acetal copolymer (POM) having an MFI 190/2.16 of 9 g/10 min in a ~ingle-cavity mold. The sophisticated "technical"
design having a cylindrical base element and dome-~haped recesses required, due to the undercuts in the demolding direction, an injection mold having a special core technology (foldable core). In accordance with modern shaping, a novel decorative surface appearance was al~o desired. In addition, presentation reasons dictate ~hat the molding surface should be laser-inscribable. All the~e requirements have been achieved by u~ing an acetal copolymer in a pale-gray base color which is suitable for laser inscription and has been modified with 0.75% of carbon fibers. The processing parameters corresponded to the typical conditions for POM (material temperature 205C, mold temperature 90C). In the fini~hed part~, the technical design was ideally supplemented by the discreet coloring and the heather-mix effect achieved by carbon fibers.

Example 5 Camping crockery set made from PS

A complete set of camping crockery, comprising plate, cup and saucer, was produced by injection molding. Since these articles were intended for the upper end of the market, there was, in addition to the demand for an attractive shape, in particular also the demand for an attractive, innovative surface decoration. For mechani-cal, thermal and economical reasons, the base materialwas an impact-modified polystyrene having an MFI 200/5 of 13.5 g/10 min. In order to achieve the desired decorative structure effect on the surfaces, carbon fiber3 having a diameter of from 8 to 10 ~m in an amoun'c of 1~ by weight were additionally incorporated into this base molding composition. The molding composition was processed on a 2~ 02~7 conventional screw injection-molding machine and, in the case of the plate, in a single-cavity standard mold, in the case of the saucer in a two-cavity standard mold, and in the case of the cup in a single-cavity sliding ~plit mold. In order to ensure easy cleaning of the finished parts, the surfaces of the mold cavities were ungrained.
~owever, a matt ~urface was achieved in the finished parts by a corresponding surface treatment of the cavities. ~he processing parameters corresponded to the typical conditions for polystyrene (material temperature 220C, mold temperature 60C). In the finished part testing, the articles achieved both the required impact strength and the heat deflection temperature of 80C. The combination of matt surfaces with the heather-mix effect caused by the carbon fibero meant that the de~ired attractive design was fully achieved.

Claims

1. A plastic molding composition for the production of moldings having a decorative effect, comprising a polymer from the group consisting of polyacetals, polyesters, polyamides and copolyamides, poly-carbonates and polyester carbonates, polyphenylene oxides and sulfides, polyurethanes, polyvinyl chlorides, polystyrenes and copolymers of styrene, and mixtures of these polymers, and from 0.1 to 5%
by weight, based on the molding composition, of carbon fibers having a fiber length of from 0.05 to 18 mm and a diameter of from 5 to 20 µm.

2. A molding composition as claimed in claim 1, which comprises a) from 100 to 50% by weight of a thermoplastic from the group of polymers mentioned in claim 1, b) from 0 to 50% by weight of rubber-like copolymers which are suitable for the particular polymer, c) from 0 to 50% by weight of reinforcing materials and/or fillers, and d) from 0.1 to 5% by weight, based on a) + b) + c), of carbon fibers having a fiber length of from 0.05 to 18 mm and a diameter of from 5 to 20 µm.

3. A molding composition as claimed in claim 1, wherein the fillers and/or reinforcing materials are talc, chalk, glass fibers or glass beads.

4. A molding composition as claimed in claim 1, wherein the base polymer has been colored in a pale base color.