Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C37/00—Component parts, details, accessories or auxiliary operations, not covered by group B29C33/00 or B29C35/00
  • B29C37/0025—Applying surface layers, e.g. coatings, decorative layers, printed layers, to articles during shaping, e.g. in-mould printing
  • B29C37/0028—In-mould coating, e.g. by introducing the coating material into the mould after forming the article
  • B29C37/0032—In-mould coating, e.g. by introducing the coating material into the mould after forming the article the coating being applied upon the mould surface before introducing the moulding compound, e.g. applying a gelcoat
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C33/00—Moulds or cores; Details thereof or accessories therefor
  • B29C33/56—Coatings, e.g. enameled or galvanised; Releasing, lubricating or separating agents
  • B29C33/60—Releasing, lubricating or separating agents
  • B29C33/62—Releasing, lubricating or separating agents based on polymers or oligomers
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C67/00—Shaping techniques not covered by groups B29C39/00 - B29C65/00, B29C70/00 or B29C73/00
  • B29C67/24—Shaping techniques not covered by groups B29C39/00 - B29C65/00, B29C70/00 or B29C73/00 characterised by the choice of material
  • B29C67/246—Moulding high reactive monomers or prepolymers, e.g. by reaction injection moulding [RIM], liquid injection moulding [LIM]

Definitions

• the present invention relates to article forming, and more particularly to methods and compositions useful for molding articles from plastic materials.
• Injection molding is a well known method for the
• the mold walls has been to coat the mold with a release agent, such as polymeric wax, silicone or other types of agents, prior to injection of the plastic.
• a release agent such as polymeric wax, silicone or other types of agents
• the formed plastic is baked to rigidify it 5 after the plastic has been removed from the mold. Subsequent to baking, a power wash is applied to the plastic to remove any residual release agent on the surface of the plastic.
• This wash is required because the release agent 0 provides an insufficiently smooth or insufficiently conditioned surface for the application of paint to the plastic.
• the plastic surface is then suitable for attachment of primer, and the plastic is primed using conventional spray or other equipment or by any other priming method known in the art.
• the plastic is primed, it is given a bake to cure the primer. After the bake the surface generally is sanded and cleaned again. The 5 part is now in condition for receiving a topcoat, and the part is given another bake cycle to cure the topcoat.
• the unremoved release agent couses a loss of adhesion between a subsequently applied primer and the substrate.
• Conventional release agents are not suitable surfaces for adhesion of primer or topcoat to the surface of the article. This loss of adhesion often results in separation of the
• the method of the present invention solves these and other problems by use of a primer that is preferentially adhered to the plastic, as compared to the metal mold, at injection or subinjection temperatures.
• Injection temperatures for reaction injection molding (RIM) processes are typically on the order of 250°F.
• the primer of the present invention has excellent adhesion to the plastic, and prevents the plastic from sticking to the mold. Therefore, no other mold release agent is needed in order to insure the free release of the formed plastic article from the mold. With no other mold release agent, there is no buildup that needs to be cleaned up, nor is there a need for a power wash to remove a release agent that isn't present.
• the primer is also suitable for reception of a topcoat.
• the primer is also suitable for reception of a topcoat.
• the method permits consolidation of the baking requirements of the primer and topcoat, or the primer may require no more curing than that occurring during the molding operation.
• the method thereby offers substantial savings of time and energy over prior molding methods.
• an object of the present invention to provide an improved in-mold primer whereby a molded article may be easily and freely removed from the mold, thereby preventing sticking of the formed plastic article to the mold walls.
• a further object of the present invention is to provide a primer for molded articles that is applied to the articles contemporaneously with the formation of the articles.
• a still further object of the present invention is to provide a mold release agent that, during its use, leaves no residue on the mold surface.
• a still further object of the present invention is to provide an in-mold primer for molded parts whereby the part can be topcoated after removal from the mold with little or no sanding of the part required.
• Another object of the present invention is to provide a process for painting injection molded parts which consolidates the baking requirements of the primer and topcoat and thereby offers substantial savings of time and energy.
• a further object of this invention is to provide an in-mold primer useful in a repeated molding process, which virtually if not completely eliminates cleaning of the mold between the molding of individual articles during a production run of upwards of ten thousand articles, yet which simultaneously provides a clean primed surface not requiring sanding prior to reception of a topcoat or finish coat.
• a last object of this invention is to provide a primed, molded article whose surface mirrors the shape of the mold surface from which the article is molded, without any treatment of the article besides the use of a preferentially adhesive in-mold primer.
• the invention as applied to injection molding of plastic parts is generally as follows: A coating of a type hereinafter described is applied to the interior walls of a mold by any method of application known in the art. The mold is then closed and a disparate plastic substrate is injected or otherwise inserted into the mold.
• the plastic substrate is preferably a RIM plastic, which sets upon the reaction of two or more discreet components which are injected into the mold, advantageously admixed just prior to introduction into the mold.
• the RIM plastic substrate is a polyurethane formed from a polyisocyanate component and a polyol component. Conventionally, as is well known in the art, a three to five per cent stoichiometric excess of polyisocyanate is employed.
• the plastic substrate can also be a polyester or polyaramid resin.
• the forming or fabrication process is then continued until completion, i.e., the part is formed.
• the formed part is then removed from the mold and ready or nearly ready for application of the topcoat.
• the part is then baked to cure the topcoat.
• Many methods for applying a coating to the interior walls of a mold are known in the art. Such methods include manual or automatic spray (air or airless), powder coating, roller coating, curtain coating, continuous dry film application, flow coating and brushing.
• Many methods for the introduction of a plastic substrate onto a mold surface are known in the art as well.
• Forming or fabricating plastic parts by the mold process may take place at temperatures ranging from room temperature to 300°F.
• the mold or die can be made from substrates which include wood, plastic and various metals, and can include plated substrates.
• the coating need not be restricted to a primer and, in fact, can comprise a single-coat topcoat.
• the coating comprises a primer.
• the coating is characterized in that, at or below the temperature of formation of the plastic piece, it is strongly preferentially adherable to the plastic instead of the material constituting the surface of the mold.
• the resin in the coating can be of the type found in the following list, but is not limited to: halogenated vinyl polymers; organic acids, esters and/or ethers of vinyl polymers; organic and inorganic acids, esters, and/or ethers of cellulose; or any of the above polymers further modified with functional groups such as, ( but not limited to: oxiranes; carboxyls; halogented alkyls, alkenyls, or alkynyls; hydroxyls; styrenyls; acryloyls; and the like.
• Many resins typically used in the paint industry are usually undesirable for use as an in-mold primer, because they are designed to adhere to metal rather than preferentially adhering to the plastic part. These include polyesters, alkyd
• the part may be removed from the mold by any method known in the art.
• the part may be peeled from the mold, or may be manually removed from one side of a two piece mold; and, of course, many molds employ ejector pins to facilitate removal.
• a primer according to the present invention advantageously comprises the above-described resin and any or all of a pigment, solvent, an acid scavenger, a plasticizer, a heat stabilizer and a wetting agent. 5
• the functions of each additional constituent in a primer are, of course, known in the art.
• a typical example of a formula for an in-mold primer suitable for use in the present invention is as follows, with the functions of the various components being as indicated: in Formula Percent by wt.
• Epoxidixed Oil (Plasticizer and Acid Scavenger) .4
• a resin, to be suitable for use in the present invention, must have relatively poor adhesion to metal and relatively good adhesion to organic substrates. 5
• the composition given above, for example, has virtually no adhesion to metal mold surfaces at a temperature below 180°F.
• the resin must also be durable enough to function in a primer.
• One resin that meets these 0 criteria is VAGH, a hydroxylated vinyl chloride-vinyl acetate copolymer sold by Union Carbide.
• the VAGH resin fulfills the above-mentioned characteristics and also has some hydroxyl functionality, which provides reactive sites for chemically bonding the primer to the 5 molded article. This hydroxyl functionality also provides a site at which an amino resin can crosslink vinyl copolymer to further enhance the durability of the primer.
• the hydroxyl groups may also react with the excess polyisocyanate in the polyurethane substrate to enhance preferential adhesion of the resin to the substrate, instead of to the mold.
• any resin with poor adhesion to metal can be used in the present invention, and the only limit on its adhesion to plastic depends upon the requirements of the end to which the primer will be put. Typical requirements are good ability to adhere to the plastic, good suitability for adhesion to a topcoat, and durability both during the painting process and in use of the product by the ultimate consumer.
• the simplest way to determine the utility of a given resin for this purpose is to examine the technical specifications relating to adhesion (usually available, from the resin manufacturer) , and select and test those having the aforesaid characteristics and being otherwise suitable for the intended use.
• compositions comprising about 10 to 15 percent by weight of resin, about 1 to 10 percent by weight pigment, about 0.1 to 1 percent by weight heat stabilizer, about 0.1 to 1 percent by weight wetting agent and solvent in a quantity sufficient to permit the application of the composition to the mold surface, are useful in the present invention.
• the formulation of the example above is the most useful embodiment of the invention known to Applicant. The formulation has been successfully privately tested in molding automobile spare tire covers, automobile grille sections, automobile bumper fascia, automobile bumpers, automobile steering wheels. golf cart wheels, and wheel balancing machine cabinets.
• the formulation was successfully applied in-mold to the following substrates for these articles, respectively: Dow Spectrim MM-363 and Ashland Arimax 1500; Dow Polyester; Mobay Bayflex 30; Mobay Bayflex 110-25; BASF Bayflex 28, Mobay Bayflex 28 IMR and Ottobock (West Germany) ; Dow 181 System; and Mobay Baydur 724, Mobay Bayflex 110-80 and Mobay Bayflex 110-50.
• the formulation has also been successfully used as an in-mold primer on Mobay Bayflex 110-25 IMR.

Landscapes

• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Paints Or Removers (AREA)
• Injection Moulding Of Plastics Or The Like (AREA)
• Moulds For Moulding Plastics Or The Like (AREA)

Applications Claiming Priority (1)

Publications (2)

Family

ID=22195587

Family Applications (1)

Country Status (3)

Families Citing this family (5)

Citations (2)

Family Cites Families (6)

• 1986
  • 1986-08-04 EP EP86905055A patent/EP0288457A1/de not_active Withdrawn
  • 1986-08-04 WO PCT/US1986/001581 patent/WO1988000876A1/en not_active Application Discontinuation
  • 1986-08-04 JP JP50442486A patent/JPH01500984A/ja active Pending

Patent Citations (2)

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events