GB1590769A - Thermoformable printed laminate including a plastics overlay - Google Patents

Description

(54) A THERMOFORMABLE PRINTED LAMINATE INCLUDING A PLASTICS OVERLAY (71) We, THE GENERAL TIRE & RUBBER COMPANY, a corporation organized and existing under the laws of the State of Ohio, U.S.A., of One General Street, Akron, Ohio, United States of America, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed to be particularly described in and by the following statement: This invention relates to a laminate of layers of plastics materials.

Historically, rigid thermoformable acrylonitrile-butadiene-styrene copolymer or polyvinyl chloride sheets have been produced in solid colors and the aesthetics of the finished thermoformed part was primarily achieved by the use of various grains and embossing patterns on the embossing rolls of the take-off equipment. The inability to produce mar and scratch resistant decorative sheets severely limited its use in some areas, such as luggage. In this area, the use of intricate multicolor prints has been restricted to the soft-sided plastic or fabric luggage.

In order to produce decorative rigid thermoplastic sheeting, cap sheets of compatible materials (.25 to .5mm) were printed and combined at the extruder to produce a decorative rigid thermoplastic laminate for luggage and other applications. Unfortunately, these constructions exhibited poor scratch and mar resistance, especially with dark print pattern on a light base sheet. Applications of various top finishes did not eliminate this problem. The use of plasticized polyvinyl chloride as cover sheet results in migration of the plasticizer into the acrylonitrile-butadiene-styrene substrate resulting in embrittlement. The plasticizer also prevents rework of sheeting, because the incorporation of plasticizer into acrylonitrilebutadiene-styrene copolymer again causes embrittlement.

It has now been found that laminated scratch and mar resistant printed decorative thermoformable sheets can be produced by laminating an extruded thermoplastic base layer, a printed thermoplastic intermediate cap layer, and a thin, clear, rigid polyvinyl chloride or polyurethane overlay film. This clear, rigid polyvinyl chloride or polyurethane film can protect the printed thermoplastic cap layer and impart scratch and mar resistance to the print on the layer. Furthermore, it may provide ultra-violet stability which helps to maintain color stability and the physical properties of the combination.

In addition, it is possible to obtain laminates of the present invention which do not stress whiten when thermoformed and are resistant to crazing when subjected to a point impact.

An additional advantage of the present invention can be that scrap laminates can be reprocessed to form new base sheets for the manufacture of subsequent laminates of the present invention. This is important because the trim from the luggage manufacturers is repurchased and recycled saving energy and preventing pollution.

The single figure of the accompanying drawing shows the extrusion of the base layer and the lamination of the base layer with the printed intermediate layer and the rigid, clear overlay between two heated rolls. The heat of the extruded acrylonitrile-butadiene-styrene causes the laminating. The heated rolls are actually at a lower temperature than the acrylonitrile-butadiene-styrene and they provide the pressure for the lamination process, and an embossing pattern, if desired. The laminate then continues between the second and third rolls to begin the cooling of the laminate.

The base layer comprises an acrylonitrile-butadiene-sytrene (ABS) copolymer. The base layer may have a thickness of from 1 to 5 mm and preferably from 2 to 4 mm. The thickness of the base layer is not critical and is determined by practical considerations. These materials are old and well-known in the art and will not be described in detail here. They are commercially available for example from Uniroyal as Kralastic SRS acrylonitrile-butadiene-styrene pellets, from Marbon as Cycolac pellets and from Goodrich as Abson pellets.

The acrylonitrile-butadiene-styrene copolymers are typically manufactured by "graft" polymerization techniques. The process begins with manufacture of rubber by the polymerization of butadiene, after which styrene and acrylonitrile monomers are added and polymerized (grafted) onto the rubber. The resultant product is either sold as-is or compounded with lubricants, stabilizers, colorants or other polymers to provide specific levels of performance required by the end use.

The acrylonitrile-butadiene-styrene copolymer made by this process contain three major components: (1) a styrene acrylonitrile copolymer, (2) a styrene acrylonitrile copolymer grafted on a polybutadiene rubber and (3) polybutadiene rubber. These components provide a polymer system with two phases - a continuous phase and a dispersed phase - and a boundary layer.

The continuous phase is the styrene acrylonitrile copolymer. It provides processability, rigidity, strength and chemical resistance. Strength, rigidity and processability are primarily dependent on molecular weight of the copolymer when the acrylonitrile content is within the normal commercial ranges.

While increased molecular weight improves strength and rigidity, it hampers processability through increased melt viscosity; hence a molecular weight is selected for balanced strength and processability. The chemical resistance of the commercial grade styrene acrylonitrile copolymer is affected by the acrylonitrile content and improves with increased acrylonitrile levels.

The polybutadiene based rubber is the dispersed phase in the acrylonitrile-butadienestyrene. This phase contributes toughness and impact resistance, both of which depend on many factors. These include the concentration of rubber, generally 10 to 30%, and size and distribution of rubber particles, preferably the butadiene content of the copolymer (including polybutadiene) is 15%to 20%.

The second or intermediate layer of the laminate again comprises an acrylonitrilebutadiene-styrene copolymer. This material is preferred because it is readily printable and will not interfere with the reworking of scrap sheets to produce new base layers. The acrylonitrile-butadiene-styrene intermediate layer is well-known in the art because it is the composition presently used by various manufacturers in the manufacture of the cap layer of luggage. Various materials are blended into the intermediate layer such as phosphite chelating agents, lubricants, and pigments. The preferred thickness is 0.1 to 0.4 mm.

The overlay film is preferably a rigid polyvinyl chloride having preferably a thickness of from 0.025 to 0.25 mm, more preferably from 0.05 to 0.15 mm. If scrap laminated sheets are to be reprocessable from polyvinyl chloride covered sheets, it is preferred for the amount of polyvinyl chloride in the laminated sheets to be as low as possible. In addition, it is necessary that the polyvinyl chloride cover sheet be thick enough to resist tearing during the lamination operation.

A compromise of the above two considerations results in the cover sheet having a thickness of from 0.025 to 0.25 mm and preferably from 0.05 to 0.15 mm.

The preferred polyvinyl chloride is a rigid polyvinyl chloride-polyvinyl acetate copolymer containing from 6 to 12% of polyvinyl acetate. Copolymers of vinyl chloride and propylene are also operable in the practice of the present invention. Less preferred is polyvinyl chloride made entirely from vinyl chloride monomer. By the term "polyvinyl chloride" is meant polymers and copolymers of polyvinyl chloride wherein the polyvinyl chloride content of the polymer is at least 50%. By "rigid" polyvinyl chloride it is meant that the polyvinyl chloride not be plasticized.

The polyvinyl chloride can also contain various additives such as impact modifiers. Some examples are methyl methacrylate-butadiene-styrene. The common organotin heat stabilizer can also be present. Lubricants such as stearic acid which are commonly used in polyvinyl chloride can also be present. The polyvinyl chloride can be tinted with colors to mask any yellow color which might be formed during processing or after storage.

A cover sheet which can be used instead of the polyvinyl chloride cover sheet and is operable but not preferred in the practice of the present invention is a clear polyurethane sheet having a thickness of from 0.025 to 0.2 mm and preferably from .05 to .15 mm. The polyurethane, however, is not preferred, in part owing to the high cost of this material and the tear problem encountered during lamination.

The following is a specific example of the practice of the present invention.

Cycolac pellets obtained from Marbon, a division of Borg Warner, are fed into a heated extruder. The extruder has a 4-1/2 " diameter barrel and the ratio of length to diameter of the extruder barrel is 24 to 1. (Preferably the ratio would be 36 to 1.) The Cycolac pellets used are an unpigmented acrylonitrile butadiene-styrene copolymer. To the pellets are added 5% based upon the weight of the pellet, of a brown color concentrate in an acrylonitrilebutadiene-styrene base copolymer.

The pigmented Cycolac is extruded at 2100C forming a base layer 3.2 mm thick and 1.13 meters wide. The extruder is shown generally as 1 in the drawing. The base layer shown as 3 in the drawing passes from the extruder to the nip 16 between rolls 4 and 6. The nip is a space between rollers of 3.2 mm. Roll 4 is heated at 950C, and roll 6 is heated to a temperature of 165"C. Simultaneously, a printed and embossed acrylonitrile-butadiene-styrene intermediate layer 8 having a thickness of 0.3 mm and a rigid polyvinyl chloride overlay 12 having a thickness of .12 mm are fed into the nip 16. Layer 8 feeds from roll 10 and overlay 12 feeds from roll 14. In the nip 16 the three layers are combined by the heat of the base sheet and the pressure of rolls 4 and 6 to form a laminate having a thickness of about 3.2 mm.The thickness of layer 8 after lamination is estimated at about 0.15 mm. The thickness of overlay 12 after lamination is estimated to be about 0.05 mm.

The laminate 18 which is formed then continues around heated roll 6 and between the spacing 20 formed by the rolls 6 and 22 which is larger than nip 16. Roll 22 has a temperature of 95"C and aids in cooling and flattening the laminated sheet. The laminated sheet which is formed is then cooled and cut into appropriate sizes by a mechanism not shown. The intermediate layer 8 previous to its being incorporated into the laminate is calendered and printed.The formulation of the intermediate layer 8 is as follows: Component Amount (Kgi Acrylonitrile-butadiene-styrene 68.04 copolymer(Blendex 101 from Borg Warner) Phosphite chelator (Ferro 904 1.4 from Ferro Corp.) Calcium stearate (lubricant) 1.8 Grey pigment (titanium dioxide 1.8 and carbon black) The composition of the overlay is as follows: Component Amount(Kg) Polyvinyl chloride-polyvinyl 136.08 acetate (6.6%polyvinyl acetate) Methylmethacrylate-butadiene 19.9 styrene (Blendex BTA-3-S from (Borg Warner) Organotin heat stabilizer 9.1 Stearic acid .9 Resoform violet tinting agents 0.02 The amounts of materials used in formulating the blends do not indicate the relative amounts of materials which go into each layer.

Attempts to rework the finished laminate by blending it with virgin acrylonitrilebutadiene-styrene and extruding the blend were successful.

It was surprising that polyvinyl chloride was successful as an overlay material because all of the other materials tried except the polyurethane resulted in laminates having one or more drawbacks. The biggest problem encountered was that of stress whitening when attempts were made to thermoform the laminate. Other problems encountered included: 1) a reduction in the impact strength of laminates containing reworked scrap; 2) crazing on point impact; 3) tended to tear during the lamination process; 4) poor adhesion resulting in delamination; 5) poor scratch resistance, and 6) too much gloss The laminates of the present invention are primarily useful in the manufacture of the main body of luggage. The laminates of the present invention, however, are also useful in thermoforming other articles containing an artistic design and which require a good wear surface.

These articles include carrying cases of all kinds, contoured seats, and the exterior shells of telephones.

As used herein, all parts and percentages are by weight unless otherwise indicated.

WHAT WE CLAIM IS: 1. A thermoformable rigid laminate of layers of plastics materials, comprising: a) a base layer of a rigid thermoformable plastics material comprising acrylonitrile butadiene-styrene (ABS) copolymer; b) a decorative intermediate layer of thermoformable plastics material comprising ABS copolymer and having a design printed on one side thereof; and c) a protective cover sheet of rigid polyvinyl chloride or of a polyurethane.

2. The laminate of claim 1 wherein the base layer comprises a sheet of ABS copolymer having a thickness of from 1 to 5 mm.

3. The laminate of claim 1 or claim 2 wherein the decorative intermediate layer comprises a sheet of ABS copolymer having a thickness of .1 to .4 mm.

4. The laminate of any one of claims 1 to 3 wherein: a) the base layer consists essentially of a sheet of ABS copolymer having a thickness of from 2 to 4 mm, b) the decorative intermediate layer consistsessentially of a sheet of ABS copolymer having a thickness of from 0.1 to 0.4 mm, and c) the cover sheet is of rigid polyvinyl chloride having a thickness of from 0.05 to 0.15 mm.

5. A laminate according to any one of the preceding claims when formed by hot calendering.

6. A laminate according to any one of the preceding claims which is recyclable.

7. A laminate of layers of plastics material substantially as herein described with reference to the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (7)

**WARNING** start of CLMS field may overlap end of DESC **. The laminates of the present invention are primarily useful in the manufacture of the main body of luggage. The laminates of the present invention, however, are also useful in thermoforming other articles containing an artistic design and which require a good wear surface. These articles include carrying cases of all kinds, contoured seats, and the exterior shells of telephones. As used herein, all parts and percentages are by weight unless otherwise indicated. WHAT WE CLAIM IS:

1. A thermoformable rigid laminate of layers of plastics materials, comprising: a) a base layer of a rigid thermoformable plastics material comprising acrylonitrile butadiene-styrene (ABS) copolymer; b) a decorative intermediate layer of thermoformable plastics material comprising ABS copolymer and having a design printed on one side thereof; and c) a protective cover sheet of rigid polyvinyl chloride or of a polyurethane.

2. The laminate of claim 1 wherein the base layer comprises a sheet of ABS copolymer having a thickness of from 1 to 5 mm.

3. The laminate of claim 1 or claim 2 wherein the decorative intermediate layer comprises a sheet of ABS copolymer having a thickness of .1 to .4 mm.

4. The laminate of any one of claims 1 to 3 wherein: a) the base layer consists essentially of a sheet of ABS copolymer having a thickness of from 2 to 4 mm, b) the decorative intermediate layer consistsessentially of a sheet of ABS copolymer having a thickness of from 0.1 to 0.4 mm, and c) the cover sheet is of rigid polyvinyl chloride having a thickness of from 0.05 to 0.15 mm.

5. A laminate according to any one of the preceding claims when formed by hot calendering.

6. A laminate according to any one of the preceding claims which is recyclable.

7. A laminate of layers of plastics material substantially as herein described with reference to the accompanying drawings.