Classifications

• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09J—ADHESIVES; NON-MECHANICAL ASPECTS OF ADHESIVE PROCESSES IN GENERAL; ADHESIVE PROCESSES NOT PROVIDED FOR ELSEWHERE; USE OF MATERIALS AS ADHESIVES
  • C09J7/00—Adhesives in the form of films or foils
  • C09J7/20—Adhesives in the form of films or foils characterised by their carriers
  • C09J7/22—Plastics; Metallised plastics
  • C09J7/24—Plastics; Metallised plastics based on macromolecular compounds obtained by reactions involving only carbon-to-carbon unsaturated bonds
  • C09J7/241—Polyolefin, e.g.rubber
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09J—ADHESIVES; NON-MECHANICAL ASPECTS OF ADHESIVE PROCESSES IN GENERAL; ADHESIVE PROCESSES NOT PROVIDED FOR ELSEWHERE; USE OF MATERIALS AS ADHESIVES
  • C09J7/00—Adhesives in the form of films or foils
  • C09J7/30—Adhesives in the form of films or foils characterised by the adhesive composition
  • C09J7/38—Pressure-sensitive adhesives [PSA]
  • C09J7/381—Pressure-sensitive adhesives [PSA] based on macromolecular compounds obtained by reactions involving only carbon-to-carbon unsaturated bonds

Definitions

• This invention relates to adhesive films for use particularly in temporarily protecting surfaces of vulnerable materials such as plastics, metals and ceramics in the course of manufacture, storage and transportation. Such films are referred to herein as TSP films.
• Ethylene-vinyl acetate copolymers which have a high vinyl acetate content made by solution polymerisation (see DE-3323531) .
• Such polymers have been used because of their elasto eric nature or because of their high compatability with tackifiers or other viscosity reducing components in curable hot melt adhesives (see CA 95-188246/72; DE-3342307) .
• DD-92554 disclose high vinylacetate content, ethylene vinyl acetate copolymers polymerised by free radical high pressure polymerisation with from 0.005 to 1 % of a bifunctional ter onomer to give extrudable materials. Similar polymers are disclosed in DE 2122597, DE 2340743, DD 108757 “ and DE 2403516; DD 142 806; DD 116 623 and JP 7327748 (Mitsubishi Petrochemical) . The elastomeric nature of the polymerisate was disclosed as the main attribute.
• DD 114823 discloses the use of from 0.001 to 0.004 wt% of summetric bifunctional co onomer to provide more stable processing at high vinyl acetate contents.
• the level of bifunctional comonomer is such that Melt Index at 33 % VA is still high.
• GB 1339511 discloses the use of from 0.05 to 10 % of asymmetric bifunctional co onomers to provide polymers of elastomeric character which are crosslinkable outside of the polymerisation reactor to provide heat and weather resistant materials.
• TSP films are known, sold by Novacel and other producers consisting of a polyethylene backing coated in a separate process step by solution or emulsion of an acrylic adhesive material. When applied to vulnerable materials the TSP films provide a smooth abrasion resistant covering so as to reduce amount of accidental damage in the handling and storage of such materials. Thickness of the polyethylene layer varies from 30 to 100 micron and that of the coating varies from 3 to 20 micron.
• the production process involves the evaporation of the medium in which the acrylic adhesive is dissolved or dispersed which is costly and may be environmentally damaging.
• the invention provides a multi-layer adhesive film having a protective backing layer and a thin layer of adhesive material applied in molten form comprising an ethylene derived polymer prepared by free radical high pressure polymerisation containing from 30 to 60 wt% of a monofunctional ethylenically unsaturated ester and having a melt index of from 0.1 to 10.
• the adhesive layer can be extruded or coextruded with the protective backing layer. Good adhesive characteristic can be obtained without, if appropriate, use of a viscosity reducing ' agent or tack improving additive. No solvent needs to be used in film production.
• the adhesive layer may contain stabilisers, anti-oxidants etc so as to improve resistance to environmental degradation.
• the film may contain conventional pigments and colorants.
• the unsaturated ester may be vinyl acetate, methyl acrylate, ethylacrylate, butyl acrylate, methyl methacrylate alone or in combination. Preferred are vinyl acetate and methyl acrylate, the latter providing improved thermal stability.
• the ester content is preferably from 35 to 50 wt%.
• the polymer may be made of high molecular weight by solution polymerisation. Preferably however a high pressure free radical procedure is used so as to produce polymer more economically.
• the high pressure polymerization may be effected in a conventional autoclave or tubular reactor.
• the reaction temperature is normally between 130 and 250°C and is preferably from 145 to 230°C.
• the preferred pressure range is from 1000 to 3000 kg/cm 2 /, more preferably from 1500 to 2500 kg/cm 2 .
• the particular conditions are chosen having regard to the product required.
• the cross-linking multifunctional monomer or modifier may be introduced into the reaction vessel to adjust the melt index of the product.
• the amount of modifier used therefore depends on the agent chosen and the final melt index sought, as well as the reaction conditions employed and vinyl acetate content since the latter acts as a chain transfer agent itself. Typically the amount of modifier will be from 0 to 25% of the reactor feed. Given the requirements specified herein for the melt index suitable agents and rate of addition can be established empirically.
• the polymerization will usually be initiated by a free radical initiator such as a peroxide.
• a free radical initiator such as a peroxide.
• conventional additives such as antioxidants and carriers for the initiator may be present according to conventional practice.
• Ethylene is introduced at 45 kg/cm 2 into compressor 1 where it is compressed to about 150 kg/cm 2 , then vinyl acetate and modifier are added and the combined feed is further compressed in compressor 2 to approximately 1550 kg/cm 2 .
• the high pressure feed is then introduced into autoclave 3 fitted with stirrer 4.
• a free radical catalyst is introduced via line 5 and at separate points on the autoclave (not shown) .
• the autoclave 3 may be cooled or heated as appropriate to maintain the desired reaction temperature.
• the formed polymer, together with unreacted material and impurities is taken via line 6 to a high pressure separator 7. Unreacted monomer separated off are recycled via heat exchanger 11 to compressor 2. The remainder of the output is fed to low pressure separator 8, from which the polymer is collected and fed to extruder 9 where it is formed into pellets. The unpolymerized material separated at 8 is fed via heat exchanger 12 to a small compressor 10. Impurities are separated off in a purge 13, and unreacted monomers are recycled to compressor 1.
• termonomer is obtained by esterification from a glycol or other linear hydrocarbons having at least two alcohol groups.
• the termonomer is advantageously obtained from an acrylic acid or a homologue thereof.
• the termonomer is ethylene glycol dimethacrylate (EDMA) .
• EDMA ethylene glycol dimethacrylate
• Such termonomers can be very effective in increasing adhesion in combination with the ester derived polymer units but adhesion to non-polar substrates after cooling from coextrusion temperatures is low permitting a tape to be produced in roll form from merely two coextruded layers; the backing being preferably LDPE, LLDPE or HDPE.
• the doubly unsaturated termonomer crosslinks pairs of polymer chains reducing the melt index and contributing to adhesion.
• Stable polymerisation condition can be set up permitting extended continuous high pressure polymerisation runs.
• an MI can be obtained of from 0.1 to 5, preferably from 0.2 TO 4 suitable for extrusion.
• Blow extrusion is performed suitably with an MI of from 0.5 to 1; cast extrusion at an MI of from 2-3.
• Terpolymers were prepared in separate runs 1 to 5 an autoclave reactor at 165 ⁇ C and 52 ⁇ C feed gas temperature at a pressure of 2100 kg/cm 2 using t-butylperneodecanoate as initiator giving a product as shown in Table 1.
• Run 5 include 0.3 wt% of oleylpalmitamide anti-blocking agent.
• the materials produced were dry coated with Microthene (made by USI) .
• Example 1 The terpolymers prepared in runs 1 to 5 Example 1 were coextruded onto LDPE giving a thickness of 40 micron of LDPE and approximately 5 micron of the adhesive terpolymer layer.
• Runs 6, 7 are made using Levaprene (Registered Trade Mark) 450 and 500 respectively which are solution polymerised copolymers of ethylene and vinyl acetate containing 45 and 49 % of vinyl acetate respectively.
• the film properties are indicated in Table 2.
• loop tack (N/25mm) 0.46 0.31 0.41 0.49 0.51 0.37 0.21 0.17
• Run 8 represents a comparative sample of an acrylate/solvent coated material from Novacel.
• the material can be removed without leaving residue and can be made economically.
• a lower vinylacetate content EVA i.e. a material having 28% VA
• a material having 28% VA could be extruded between the backing layer and the above described adhesive layer to improve the bonding of these two layers.
• Release layers such as silicon-containing layers may be used to facilitate unwinding of rolls of film.
• Other slip additives may be present in such a release layer.
• the films may be used on new cars during production for example; to protect mirrors, skis, computer equipment or PMMA panels or as temporary sunscreens.

Landscapes

• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Organic Chemistry (AREA)
• Laminated Bodies (AREA)
• Adhesive Tapes (AREA)
• Adhesives Or Adhesive Processes (AREA)
• Addition Polymer Or Copolymer, Post-Treatments, Or Chemical Modifications (AREA)

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Publications (1)

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• 1989
  • 1989-11-01 GB GB898924626A patent/GB8924626D0/en active Pending
• 1990
  • 1990-10-31 EP EP90916324A patent/EP0498832A1/de not_active Withdrawn
  • 1990-10-31 JP JP2515195A patent/JPH05504982A/ja active Pending
  • 1990-10-31 WO PCT/GB1990/001664 patent/WO1991006609A1/en not_active Application Discontinuation

Non-Patent Citations (1)

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