US20080261010A1 - Polyamide Blend Film - Google Patents

Abstract

A film whose outer layer is composed of a molding composition which is in essence composed of the following components:

• a) from 3 to 50% by weight of a polyamide, selected from the group of PA11 and PA12, and
• b) from 50 to 97% by weight of a polyamide, selected from the group of PA1012 and PA1212,
  where the percentages are based on the entirety of components a) and b), is suitable for decoration of moldings which retain their gloss during their service time.

Description

• The present invention relates to a film which comprises a layer composed of a polyamide blend, and is suitable for decoration of moldings.
• The current standard process for decoration of external areas on automobiles is painting. However, this procedure firstly generates high manufacturing costs, resulting from provision of specific plant and the operating cost associated therewith for the automobile producer, and secondly causes pollution of the environment. Pollution of the environment derives by way of example from solvent constituents released from the paints used, and also from accumulation of paint residues, which have to follow correct disposal routes.
• Another factor is that painting has only limited suitability for decorating the surfaces of plastics components, which in recent years have become more popular in automobile construction, because of the saving in weight and cost.
• The process of painting plastics components which are components of bodywork can, for example, be carried out on-line, the plastics part being subjected to a paint treatment identical with that for the metallic components. This leads to a uniform color, but is attended by high temperatures resulting from the cathodic electrodeposition method conventional here, and this makes the selection of material more difficult. In addition, identical adhesion of the paint formulation has to be ensured on very different substrates. If the process of painting the plastics parts is carried out in a separate step (known as off-line painting), comprising process conditions more advantageous for plastics, the problem of colormatching arises, meaning that the shade achieved on the metal has to be matched precisely. However, the differences in substrate and in the underlying paint formulation that can be used, and process conditions, make this very difficult to achieve. If there is a color difference prescribed via the design, a serious disadvantage that remains is provision of a second set of painting equipment for the plastics parts and the cost associated therewith, and additional time required for manufacture of the automobile also has to be considered. Direct use of the untreated, generally injection-molded plastics parts is aesthetically disadvantageous, because surface defects resulting from the process, such as weld lines, air inclusions, and also necessary reinforcing fillers, such as glass fibers, are clearly discernible here. This is intolerable in visible regions. Consequently, improvement of surface quality has to be undertaken, for example in the context of a painting process, frequently requiring much work for pretreatment via polishing and application of relatively thick layers of a primer.
• One proposed solution consists in the use of multilayered plastics films, used to cover the components and then requiring no painting. The bond between substrate and decorating film here can be achieved via a number of manufacturing processes. By way of example, the film can be laminated to the substrate, or it is possible to select a process of reverse coating by an injection-molding process, in which the film is placed in the injection mold during component production. The concept of a film as carrier of decoration is also in line with a trend toward individualization of design elements on automobiles. Specifically, this trend leads to a wider range of models in the manufacturing process, but with a reduction in the number of respective components manufactured per series. The use of films permits rapid, problem-free design change, and can therefore meet this challenge. An important factor here is that the film complies with the standards demanded in the automobile industry with respect to surface properties (class A surface), solvent resistance, and appearance. These films likewise have good capability for use in the design of interior surfaces in automobiles.
• Decorative films of this type are in principle known. EP 0 949 120 A1 describes by way of example decorative films with a transparent outer layer composed of polyurethane, polyacrylate, fluoropolymer, or mixtures composed of fluoropolymer and polyacrylate. WO 94/03337 and EP 0 285 071 A2 disclose similar decorative films.
• Another application sector for decorative films is as a carrier of decoration, for example for topcoats of sports equipment, e.g. skis or snowboards, or of household items. Single-layer films whose topsides or undersides have been printed are often used here. For example, the utility model DE 295 19 867 U1 describes a decorable film composed of a copolyamide which is composed of the following monomer units: laurolactam, and also caprolactam and/or hexamethylenediamine/dicarboxylic acid. The article by M. Beyer and J. Lohmar, Kunststoffe 90 (2000) 1, pp. 98-101 gives examples of printable films composed of PA12 molding compositions.
• The property profile of polyamides, for example impact resistance and chemical resistance, very generally gives them, and in particular polyamides based on PA12 or PA11, good suitability for production of these decorative films. Accordingly, the patent literature has descriptions of decorative films or else protective films which comprise an outer layer composed of a polyamide. Examples which may be mentioned here are the specifications JP60155239A, JP2003118055A, EP 1 302 309 A, EP 0 522 240 A, EP 0 694 377 A, EP0734833A, WO9212008A, and EP0568988A.
• While high polarity of outer layers composed of polyamides with a high density of carboxamide groups gives them inadequate chemicals resistance and excessive water absorption, in practice it is found that use of polyamides which have a low density of carboxamide groups and which have been prepared from lactams or from the corresponding aminocarboxylic acids (AB polyamides) leads to formation of deposits on the surface of the films under ambient conditions over the course of time, these deposits considerably reducing gloss and being unacceptable for this application. Improvement in transparency and in initial gloss would also be desirable. If, in contrast, polyamides composed of diamine and dicarboxylic acid (AABB polyamides) which have a low density of carboxamide groups are used, no deposits are formed, but here again an improvement in transparency and gloss would be advantageous.
• It was therefore an object, for decorative purposes, to provide a film which gives reduced deposit formation, and whose outer layer is sufficiently transparent, and which has high initial gloss.
• This object is achieved via a film whose outer layer is composed of a molding composition which is in essence composed of the following components:
• a) from 3 to 50%, preferably from 4 to 49% by weight, particularly preferably from 5 to 47% by weight, and with particular preference from 10 to 45% by weight, of a polyamide, selected from the group of PA 11 and PA12, and
• b) from 50 to 97%, preferably from 51 to 96% by weight, particularly preferably from 53 to 95% by weight, and with particular preference from 55 to 90% by weight, of a polyamide, selected from the group of PA1012 and PA1212,
  where the percentages are based on the entirety of components a) and b).
• The polyamides used and their preparation are known. They are commercially available in a wide variety of marketed grades. According to the invention, the respective homopolyamides are mainly used, but it is also possible to use copolyamides based thereon and incorporating at most 20 mol %, at most 15 mol %, at most 10 mol %, or at most 5 mol %, of comonomers. Suitable comonomers are lactams, the corresponding aminocarboxylic acids, or the combination of diamine and dicarboxylic acid. Diamine and dicarboxylic acid are respectively counted individually in the calculation of the constitution.
• Incorporation of comonomers leads to improved transparency and to higher gloss, but there is some impairment of resistance to chemicals and to environmental effects. The latter can be accepted if use of the comonomers is successful in giving better compatibility for example with respect to the following layer or with respect to the substrate, by bringing the constitution somewhat closer.
• The molding composition is prepared from the individual components according to the prior art via mixing in the melt. It can also comprise the following other components:
• a) nucleating agents, selected from nanoscale fillers and basic metal salts, metal oxides, or metal hydroxides; the amount added of the latter, in order to ensure the desired transparency, is at most that which can be dissolved in the melt by reaction with the carboxy end groups of the polyamides;
• b) conventional auxiliaries and conventional additives, the amounts being those conventional for polyamide molding compositions, examples being stabilizers or lubricants,
• c) colorants which do not significantly affect transparency,
• d) fillers whose refractive index differs only to a very slight extent from that of the matrix, or is precisely identical (isorefractive fillers), and also
• e) other polymer components whose refractive index differs only very slightly from that of the matrix or is precisely identical.
• The amount of these other components present in the molding composition is preferably at most 30% by weight, at most 25% by weight, at most 20% by weight, at most 15% by weight, at most 10% by weight, or at most 5% by weight.
• Surprisingly, if the molding composition comprises at most 50% by weight of the AB polyamide (PA11 or PA12), gloss is retained as for the pure AABB polyamides during service life, although this would not be expected in view of the mixing ratio of the polyamides. Apparently, as long as at least 50% by weight of the AABB polyamide is present, it inhibits diffusion of the substances that form deposits and are present in the AB polyamide, possibly cyclic oligomers. Another advantage here is that the mixture of the semicrystalline polyamides give blends which are semicrystalline, but sufficiently transparent. Transparency and initial gloss are above the level of the pure components, while resistance to chemicals and environmental effects is retained. Explicit mention may be made here of the combinations PA11/PA1012, PA11/PA1212, PA12/PA1012, and PA12/PA1212, but the AB component can moreover be, independently of one another, a mixture of PA11 and PA12, and the AABB component a mixture of PA1012 and PA1212.
• The film is a single- or multilayer film. In the case of a multilayer structure, the nature and number of the other layers depend on the technical requirements of the application; the only decisive factor is that the outer layer is composed of the inventively used molding composition. By way of example, the following embodiments are possible:
• 1. The film is a single-layer film. In this case it is defined as composed only of the outer layer; decorative effects can be applied either to the topside or to the underside via printing, e.g. by means of thermal sublimation printing.
• 2. The film comprises not only the outer layer but also a lower color layer. The color layer can be a paint layer; however, as in the prior art it is preferably composed of a colored thermoplastics layer. The thermoplastic can by way of example be a mixture identical with or similar to that of the outer layer, one component thereof, or another polyamide, or another polymer, which either adheres directly to the outer layer or has been adhesive-bonded with the aid of a sufficiently transparent adhesion promoter (for example a polyolefin functionalized by carboxy or anhydride groups or by epoxy groups, a thermoplastic polyurethane, or a blend composed of the constituents of the layers to be bonded). Examples of colorants that may be used are organic dyes, inorganic or organic pigments, or metal flakes.
• 3. The film comprises not only an outer layer and, if appropriate, a color layer, but also another layer which, as carrier layer, brings about sufficient mechanical strength and, if appropriate, also brings about coupling to the substrate.
• 4. The film comprises not only the outer layer and, if appropriate, a color layer, but also a lower adhesion-promoter layer for coupling to the substrate. Examples of suitable adhesion promoters are a polyolefin functionalized by carboxy or anhydride groups or by epoxy groups, a thermoplastic polyurethane, a blend composed of the materials of the layer to be bonded and of the substrate, or one of the adhesion promoters disclosed in the German patent application No. 102004029217.5 of 16 Jun. 2004.
• 5. The film comprises not only the outer layer, and, if appropriate, a color layer and carrier layer, but also a lower adhesion-promoter layer for coupling to the substrate. The comments made under item 4 again apply to the adhesion promoter.
• 6. The film, e.g. a film in one of items 1 to 5, also comprises, if necessary, for example in the case of increased scratch-resistance requirements, a protective layer, such as a polyurethane-based clear lacquer, on the outer layer. A protective layer in the form of a lacquer can also have been modified as in the prior art in order to increase scratch resistance. Besides this, another possibility is to generate a protective layer by way of vacuum deposition processes. The film can, if appropriate, also comprise a peelable protective film applied by lamination, which provides protection during transport or installation, and which is peeled away after production of the composite part.
• In the case of embodiments 2 to 6, the transparent outer layer may first, like a monofilm, be printed from one side or from both sides and then be bonded in a second step to the other layers to give the multilayer film. In multilayer films, the transparent outer layer can be printed from above. The outer layer may also have transparent or opaque coloring.
• In one preferred embodiment, the color layer and/or the carrier layer comprises a molding composition in particular of a polyetheramide or of a polyetheresteramide, and preferably of a polyetheramide or polyetheresteramide based on a linear aliphatic diamine having from 6 to 18, preferably from 6 to 12, carbon atoms, on a linear aliphatic, or an aromatic, dicarboxylic acid having from 6 to 18, preferably from 6 to 12, carbon atoms, and on a polyether having an average of more than 2.3 carbon atoms per oxygen atom and having a number-average molecular weight of from 200 to 2000 for the polyether blocks. The molding composition of this layer can comprise other blend components, e.g. polyacrylates or polyglutarimides having carboxy or anhydride groups or epoxy groups, a rubber containing functional groups, and/or a polyamide. Molding compositions of this type are prior art; by way of example, they are described in EP 1 329 481 A2 and DE-A 103 33 005, expressly incorporated herein by way of reference. In order to ensure good layer adhesion, it is advantageous here for the polyamide content of the polyamide elastomer to be composed of monomers which are identical with those used in one of the components of the outer layer. As an alternative to the polyamide elastomers, the color layer and/or the carrier layer can also comprise a conventional impact-modifying rubber alongside a polyamide. An advantage of these embodiments is that in many cases there is no need for any thermoforming of the film as a separate step prior to reverse coating by an injection-molding method, because reverse coating by an injection-molding method also simultaneously subjects the film to a forming process.
• In one preferred embodiment, the thickness of the film or multilayer film with the inventive outer layer is from 0.02 to 1.2 mm, particularly preferably from 0.05 to 1 mm, very particularly preferably from 0.1 to 0.8 mm, and with particular preference from 0.2 to 0.6 mm. If the material is a multilayer film, the thickness of the inventive outer layer in one preferred embodiment is from 0.01 to 0.5 mm, particularly preferably from 0.02 to 0.3 mm, very particularly preferably from 0.04 to 0.2 mm, and with particular preference from 0.05 to 0.15 mm. The film is produced by means of known methods, for example via extrusion, or in the case of multilayered systems via coextrusion or lamination. It can then, if appropriate, be subjected to a forming process.
• In one embodiment, the film is a decorative film. For the purposes of the invention, decorative films are films which can be printed and/or comprise a color layer, and moreover are intended for bonding to a substrate in order to decorate its surface. The decoration can also be brought about by using a lamination process on visual surface defects, e.g. by hiding surface roughness deriving from fillers or from reinforcing materials.
• Examples of methods of coherent bonding of the film to the substrate are adhesive bonding, pressing, lamination, or coextrusion, or reverse coating by an injection-molding, foaming, or compression-molding method. In order to achieve better adhesion, the film can by way of example be previously flame-treated or treated with a plasma. Prior to formation of the bond between film and substrate, the film can also be subjected to mechanical treatment or forming processes, e.g. via thermoforming or other processes. The surface can be structured via embossing, for example. The surface can also be pre-structured in the context of film extrusion, for example using specifically designed rolls. The resultant composite part can then also be subjected to a forming process.
• Examples of suitable substrates are molding compositions based on polyolefins, on polyamides, on polyesters, on polycarbonates, on ABS, on polystyrene, or on styrene copolymers.
• In one preferred embodiment, the inventive film is used as outer layer of a film composite for the design or decoration of surfaces on and in automobiles and utility vehicles, the film having been adhesive-bonded to a plastics substrate. The correspondingly designed component can be of sheet-like structure, an example being a bodywork part, for example a roof module, wheel surround, engine cover, or door. Other possible embodiments are those in which the components produced are elongate, with or without curvature, for example cladding, e.g. the cladding on what are known as A columns of an automobile, or decorative and cover strips of any type. Another example is provided by protective cladding for door sills. Alongside applications in motor-vehicle exteriors, constituents of the interior can also be advantageously decorated via the inventive films, in particular decorative elements such as strips and panels, because impact resistance and resistance to chemicals, such as cleaners, is also required in the interior.
• In another preferred embodiment, the inventive film is used as topcoat for snowboard-like equipment of any type, such as skis or snowboards.
• The film can moreover be used by way of example as a protective film to counter soiling, UV radiation, effects of weathering, chemicals, or abrasion, or as a barrier film on vehicles, in the household, on floors, on tunnels, on tents, and on buildings, or as a carrier of decorative effects, for example for topcoats of sports equipment, of boats, of aircraft, in the household, or on buildings.
• The invention is illustrated below by way of example.
• The PA12 used was a grade whose relative solution viscosity η_rel, determined to ISO 307, was 2.1 and whose crystallite melting point T_m, determined to ISO 11357, was 178° C.
• The PA1012 used was a grade whose relative solution viscosity η_relwas 1.9 and whose crystallite melting point T_mwas 191° C.
• The molding composition was prepared via mixing in the melt in a Werner+Pfleiderer ZSK M9/2 twin-screw extruder. The barrel temperature was 250° C., the rotation rate was 250 rpm, and the throughput was 10 kg/h. The melt was filtered at 25μ.
• Injection-molded plaques were produced on an Engel ES 600/150 injection molding machine. The melt temperature was 250° C., and the mold temperature was 80° C. Dimensions of the plaques produced were 130 mm×130 mm×1 mm.
• Monofilms were produced by the calendering process on a Collin 168/400 multilayer film calender at a processing temperature of 240° C. The thickness was 400 μm.
• Monofilms were produced by the calendering process on a Collin 168/400 multilayer film calender at a processing temperature of 240° C. (outer layer) and 240-250° C. (color layer). The thickness of the outer layer was 100 μm, and the thickness of the color layer was 400 μm. The colorant layer used comprised a blend composed of 28.0% by weight of PA12 (η_rel=2.1), 68.5% by weight of a polyetheresteramide having PA12 hard blocks (M_n=7000) and having PTHF soft blocks (M_n=1000), and 2.0% by weight of a stabilizer masterbatch, and also 1.5% by weight of color powder masterbatch, the color used being E70237.
• Accelerated weathering was carried out on monofilms, using Q-UV/se accelerated-weathering equipment from Q-Panel with a cycle (Step 1: 55° C., exposure to light at 0.98 W/m²at 340 nm, 4 h/Step 2: 45° C., water condensation in dark conditions, 4 h).
• Injection-molded plaques were stored in a cabinet under controlled temperature and humidity conditions at 85° C. and 99% relative humidity.
• Gloss measurements were carried out on plaques and films to DIN 67 530.
• Transmittance was measured on films of thickness 400 μm to ISO 13468-2.
INVENTIVE EXAMPLES 1-4 AND COMPARATIVE EXAMPLES A-E
• Tables 1 to 5 give constitutions and results.

• TABLE 1
  Constitution of outer layer

  	PA1012 (parts by	PA12 (parts by	Stabilizers
  Example	weight)	weight)	(parts by weight)

  A	100
  B		100
  C	20	80
  1	60	40
  2	80	20
  D	20	80	0.8
  E	40	60	0.8
  3	60	40	0.8
  4	80	20	0.8

• TABLE 2
  Transparency of monofilms (400 μm)

  Example

  	A	B	C	1	2

  Transparency	88.2%	87.6%	89.4%	89.8%	89.1%
  (at 500 nm)

• TABLE 3
  Formation of deposit on accelerated weathering
  (gloss measurement at 60° on 400 μm films;
  data in gloss units)

  Time (h)	A	B	3	4	D	E

  0a)	126	97	131	129	116	115
  24	124	78	127	131	107	80
  168	120	84	126	130	100	98
  336	118	60	121	131	78	92
  504	120	58	120	132	82	91
  672	125	69	119	133	81	94
  840			120	132	83	87
  1008			118	131	78	92
  1176			120	132	75	89
  1344			120	131	70	92
  1512			120	132	67	95
  1680			121	132	68	97
  2016			117	134	75	88
  2352			119	129	72	67
  3192			116	126
  a)Initial gloss

• TABLE 4
  Formation of deposit on storage in moist conditions (gloss
  measurement at 85° on plaques; data in gloss units)

  Storage time in days	A	3	4	D	E

  0	94.7	101.4	94.9	102.8	100.7
  3	98	102.3	99.2	96.6	101.1
  6	98.4	101.4	98.3	58.8	88.8
  10	97.7	101.8	99.2	59.1	89.5
  14	97.6	102.2	99.5	53.9	84.6
  21	97.1	101.3	98.7	33.3	77.4
  25	96.3	101.4	98.3	41.9	75.1
  32	96.1	101.3	98.1	26.4	61
  39	95.7	100.4	97.6	17	56.1
  46	97.4	103.6	100.5	14.7	45.5
  52	94.5	100.2	98.5	15	44.1

• TABLE 5
  Multilayer film, initial gloss at 20° (data in gloss units)

  Example

  	D	3	4

  	Gloss	80	84	85

Claims (12)

1. A film whose outer layer is composed of a molding composition which is in essence composed of the following components:

a) from 3 to 50% by weight of a polyamide, selected from the group of PA11 and PA12, and

b) from 50 to 97% by weight of a polyamide, selected from the group of PA1012 and PA1212,

where the percentages are based on the entirety of components a) and b).

2. The film as claimed inclaim 1, which is composed only of that layer.

3. The film as claimed inclaim 1, which is composed of two or more layers.

4. The film as claimed inclaim 3,

which

comprises a color layer, a carrier layer, and/or an adhesion-promoter layer.

5. The film as claimed inclaim 4,

wherein

the color layer and/or the carrier layer comprises a polyamide elastomer or an impact-modifying rubber.

6. The film as claimed inclaim 1,

whose

thickness is from 0.02 to 1.2 mm.

7. The film as claimed inclaim 1,

wherein

the thickness of the outer layer is from 0.01 to 0.5 mm.

8. The film as claimed inclaim 1,

which

is produced via extrusion, coextrusion, or lamination, and is then, if appropriate, formed.

9. The method of using a molding composition which in essence is composed of the following components:

a) from 3 to 50% by weight of a polyamide, selected from the group of PA11 and PA12, and

b) from 50 to 97% by weight of a polyamide, selected from the group of PA1012 and PA1212,

where the percentages are based on the entirety of components a) and b),

for production of a film as claimed inclaim 1.

10. A composite part, composed of a film as claimed inclaim 1 and of a substrate.

11. The composite part as claimed inclaim 10,

which

is a bodywork part of a motor vehicle, a constituent of the motor-vehicle interior, a cladding, a decorative strip, a cover strip, a panel, or a decorative element.

12. The composite part as claimed inclaim 10,

which

is produced via adhesive-bonding, pressing, lamination, or coextrusion, or via reverse coating by an injection-molding, foaming, or compression-molding method.