Laminate containing a substrate and a release agent and method of its preparation

Abstract: The present invention provides a release agent formed by reacting an organopolysiloxane compound having at least one hydrogen atom with a hydrocarbon compound having at least one double bond which reacts with said hydrogen atom and a manufacturing method thereof. The release agent of this invention, which makes substantially no migration into any pressure sensitive adhesive layer, is well adaptable to whichever process, extrusion laminating process or coating process.

Description: The present invention relates to a laminate containing a substrate and a release layer and more particularly, relates to a laminate containing a substrate and a release layer obtainable by using a release agent which is substantially free of migration into a layer of pressure sensitive adhesive. The substrate containing the release layer is efficiently and economically manufactured by way of an extrusion lamination process. Heretofore, the manufacturing method of silicone base release paper is principally based on a coating process, in which usually, a layer of laminated polyethylene is formed on a substrate like paper, and further, a release layer is coated on the surface thereof. The release agent employed in this process consists of polymethyl hydrogen siloxane and vinyl group containing polydimethyl siloxane, and addition of platinum catalyzer and heat induces their addition reaction, causing curing and formation of a release coating. According to this process, however, it thus needs to be prepared by mixing the ingredients and subjecting the mixture to the addition reaction. This process involves not only problems in insufficient curing and short pot life, but also difficulties in practical uses because of complicated operation and handling. On the other hand, a release layer may be formed on the substrate at once by an extrusion lamination process. The resin laminated in this way itself has a certain releasability. As such releasable resins, e.g. ethylene - α -olefin copolymer elastomer, are used and they are preferable for acrylic pressure sensitive adhesives. In the aforementioned extrusion lamination process, however, there is apprehension regarding heat and solvent resistance, at the time of coating of acrylic pressure sensitive adhesives and scattering of release potential with regard to the acrylic pressure sensitive adhesives and the release strength becomes greater with the lapse of time. Since ethylene-α-olefin copolymer elastomer, when singly used, is difficult to extrude, it is used in mixture with polyethylene. The smaller the mixing proportion of said elastomer, the more releasing effect will be lost; but conversely, with its increasing proportions, said elastomer's property will become stronger, and the film strength lower; moreover, such problems in processing as blocking, will be induced. In JP-B- 60-5628, a releasable laminate film formed by laminating on a substrate a thermoplastic resin prepared with addition of non-cure type organopolysiloxane is proposed. But such a releasable laminate film shows high resistance to release and produces bleeding to the surface of silicone even at room temperature; therefore, it can not necessarily be said adequate for pressure sensitive adhesive tapes or sheets. To overcome the hereabove-mentioned problems WO 86/00564 which corresponds to EP-A-190354 discloses a manufacturing method of a release agent which comprises extruding a mixture of a silicone base release agent and polyolefin and, then, getting said release agent bled to the surface by subjecting it to a heat-treatment, followed by fixing by curing. Said method, however, is disadvantageous in that it requires a curing treatment by treatment with such a catalyzer as chloroplatinic acid. The object of the present invention is to provide a substrate containing a release layer wherein a release agent is used which undergoes substantially no migration into the pressure sensitive adhesive layer and which is suitable for whichever process, extrusion lamination process or coating process. Thus, the subject matter of the invention is a laminate containing a substrate, selected from paper, cloth, film, metal foil and their laminates and a release layer, which substrate is obtainable by the following method: a) reacting an organopolysiloxane compound selected from polymethyl hydrogen siloxane and methyl hydrogen siloxane-dimethyl siloxane copolymer having at least one hydrogen atom with an olefininc macromer having at least one vinyl group at its terminal which reacts with said hydrogen atom; b) mixing the in this way produced release agent with a polyolefin selected from polyethylene, polypropylene, 4-methyl pentene-1 resin, and copolymers with ethylen; c) extruding the mixture on a substrate, selected from paper, cloth, film, metal foil and their laminates, thereby forming a laminate, where the release agent contained in the aforementioned laminated mixture layer is localized to the layer surface simultaneously as it is extruded or if the localization is inadequate, the laminate should be heat-treated to achieve the surface localization of the release agent or interposing an adhesion enhancing layer of polyethylene between the mixed layer containing the release agent and the substrate, thereby improving the adhesion therebetween. Furthermore, the subject matter of the invention includes the method for producing a laminate containing the substrate and a release layer as mentioned above. Thus the release agent used in this invention is obtained by reacting an organopolysiloxane compound having at least one hydrogen atom with an olefinic macromer having at least one vinyl group at its terminal which reacts with said hydrogen atom. The organopolysiloxane compounds having at least one hydrogen atom is selected from polymethyl hydrogen siloxane and methyl hydrogen siloxane-dimethyl siloxane copolymer. As the olefinic macromer having at least one vinyl group which reacts with the hydrogen atom of the aforementioned organopolysiloxane compounds, there may be mentioned the product DIALEN-30® manufactured by Mitsubishi Kasei Kogyo K.K. Illustrating a manufacturing method of the release agent, a polymethyl hydrogen siloxane (including methyl hydrogen siloxane-dimenthyl siloxane copolymer) and an olefinic macromer having a vinyl group at its terminal are mixed and the mixture is subjected to addition reaction by warming, with chloroplatinic acid added as the catalyzer. The reaction product obtained is refined by cleaning several times with e.g. acetone, followed by drying. In manufacturing a laminate containing a substrate and a release layer by way of extrusion using the release agent synthesized as hereabove-described, although impossible to comprehensibly specify on account of effect of varying silicon contents, the amount of said release agent to be mixed should be approx. 1-10% by weight in proportion to polyolefin, or more preferably, 2-5% by weight, when its silicon content is 50%. The mixture is kneaded and pelletized by a pelletizer, to be used as a mixture layer resin (extrusion resin). Master batch operation using a twin-screw extruder is also feasible. This material may be also effectively utilized as a release agent for a variety of pressure sensitive adhesives or hard urethane foam, or for medicines or as a poultice separator, by adjusting its amount added. The polyolefin used according to this invention are polyethylene, polypropylene, 4-methyl pentene-1 resin and copolymers with ethylene such as ethylene - propylene copolymer, ethylene - vinyl acetate copolymer, ethylene - acrylic acid copolymer, etc., and their mixtures. Of the polyethylene, linear low density polyethylenes having densities of 0.910-0.935 g/cm³ are especially excellent in low speed range peeling and are advantageous in that they may be heat-treated in a short period of time, because they permit high temperature heat treatment. Besides, in order to positively promote localization of bleeding, tackifiers or polyvinyl ether, from which plasticizer effect for polyolefin may be expected may be added. And by adding calcium carbonate, titanium dioxide, talc, kaolin, powder silica or zeolite, releasability may be controlled, or pressure sensitive adhesive tapes which permit lap joint may be achieved. Furthermore, through joint use of embossing process, the releasability may be controlled. The release layer resin obtained in this way is extruded on a substrate by use of an extrusion laminator, thereby forming a release layer on the substrate. Substrate forms used according to this invention include paper, cloth, film, metal foil and their laminates. When laminated on the substrate, the release agent is bled and localized to the surface of the mixture layer of the release layer, simultaneously as it is extruded, on account of the heat produced at the time of extrusion lamination. But if the localization is inadequate, she laminate should be heat-treated. Due to the heat evolved at the time of extrusion lamination or by the reheat-treatment the release agent contained in the mixture layer is bled to the surface of the mixture layer, to be localized; as a result, similar state will be brought about as that obtained by coating some release agent on the surface of polyethylene layer as in a conventional method. According to this invention, it is allowed to interpose an adhesion enhancing layer of polyethylene between the release layer and the substrate for improvement in adhesion therebetween. The release agent used in this invention will provide affinity to non-solvent silicone, particularly when blended into polyolefin laminate layer of the non-solvent silicone coating substrate, and on this account, it is finding preferable applications in curtailment of spots, pinholes, etc., when it is coated, in improvement in control on the accuracy of the coating amount and further, in manufacture of high quality release papers. The release agent used in the present invention is obtained by reacting an organopolysiloxane compound having at least one hydrogen atom with an olefinic macromer having at least one vinyl group which reacts with said hydrocarbon atom, i.e., a release agent comprising a so-called comb-form copolymer obtained by grafting chains of hydrocarbon compounds onto an organopolysiloxane compound as a main chain. In a mixture of the release agent of the comb-form copolymer and a polyolefin, the organopolysiloxane compound main chain is localized and oriented to the surface of the polyolefin,i. e., the air side. This has already been confirmed by ATR-IR analytical results. On the other hand, the chains (graft branches) of the hydrocarbons have high compatibility with the polyolefin, so that sometimes they produce chemical bonds, thereby exhibiting anchoring effect as if they extend their roots in the polyolefin. Thus the organopolysiloxane compound main chain is brought into a state of being firmly fastened to the surface of the polyolefin, substantially foreclosing its migration into the pressure sensitive adhesive layer. In the following, this invention will be described in connection with examples and comparative examples, but obviously its claim coverage is not limited to these modes only. In the following, parts and % are respectively meant to represent values by weight, unless otherwise specified. Example 1 Into a reactor, 45.6 parts of polymethyl hydrogen siloxane (P = 300, MW = 22,000), 54.4 parts of the olefinic macromer having at least one terminal vinyl group i.e. the α-olefin "DIALEN-30", manufactured by Mitsubishi Kasei Kogyo (Chemical Industry) and 8 parts of 0.1% H₂PtCl₆·6H₂O tetrahydrofuran solution were charged, to undergo addition reaction at 80°C for 8 hr and, then, to be further reacted at 130°C for 18 hr. The reaction was stopped when the viscosity of the reaction product reached approx. 10,000 cps. The reaction product was cleaned thrice with acetone, to remove unreacted part, for its refinement, followed by drying. The silicon content of the release agent obtained in this way was 45.6%. Example 2 Three percent of the release agent obtained in Example 1 in proportion to low density polyethylene ("M-10P", manufactured by Mitsui Sekiyu Kagaku MI: 9.5, density: 0.917 g/cm³) was added thereto, to prepare pellets for mixture layer at a dies temperature of approx. 200°C by use of a pelletizer. The low density polyethylene as used for the mixture layer was separately prepared as an adhesion enhancing layer. As the substrate, 73 g/m² of CLUPAK unbleached kraft was used; polyethylene for adhesion enhancing layer was extruded at a dies temperature of 300°C by use of a conventional co-extrusion laminator and the pellets for mixture layer was simultaneously extruded at a dies temperature of 260°C, thereby yielding a laminate of a three layer structure of substrate layer - adhesion enhancing layer - mixture layer. The thickness of the mixture layer obtained was 15 µm, and the thickness of the adhesion enhancing layer 15 µm. Then a sheet form was cut from the three layer laminate obtained in this way and was subjected to a heat treatment at 120°C for 20 min, with the release layer surface turned upward. With the release paper thus obtained, the release potential and the residual adhesive strength were measured by the undermentioned method. The results are put up in Table 1. Pressure sensitive adhesive tape: An acrylic pressure sensitive adhesive kraft tape ("ELM TAPE" manufactured by Soken Kako) was prepared to be 25mm width x 210 mm length, for it to be used in the tests. Measuring conditions: The aforementioned pressure sensitive adhesive tape was stuck with the aforementioned release paper by reciprocally applying pressure by an application device with a 4.5kg dead weight at a speed of 5mm/sec and the release potential and the residual adhesive strength of the product were measured under the following conditions: The measurements were taken after the paper and the tape stuck together had been subjected to ageing by leaving for 20 hr under weight of 20 g/cm² applied thereon in an atmosphere of temperature 70°C and humidity 65% RH and, then, left cooling. Measuring method: The measurements were taken at a peeling angle of 180 degrees, using an autograph tensile tester ("STROGRAPH-R", manufactured by Toyo Seiki), for the low speed range (0.3 m/min) peeling, and a high speed peeling tester (manufactured by Tester Sangyo), for the high speed range (3 m/min and 20 m/min). The condition at the time of measurements were 23°C and 65% RH. Example 3 In manufacturing the similar laminate as in Example 2, the extrusion was made under the same conditions as in Example 2, except that a cooling roll which was coated with tetrafluoroethylene - hexafluoroprorylene copolymer was used at the time of making extrusion lamination. The release paper obtained was put to the similar tests as in Example 2. The results are given in Table 1. The localization of the release agent was adequate. By coating the cooling roll with the foregoing copolymer, the surface of the roll is made nonpolar, which accelerates the localization of the release agent. Example 4 The release agent obtained in Example 1 was dissolved in toluene to have its 3% solution, which was heated to 40°C and coated on a biaxial orientation polypropylene film (OPP) (50um). Its amount applied was o.7g/m². The release paper thus obtained was put to the similar tests as in Example 2. The results are shown in Table 1. Comparative example 1 Use was made of only the low density polyethylene "M-10P" used in Example 2, which was extruded just as in Example 2 and the release potential and the residual adhesive strength of the product were measured. The results are given in Table 1. Comparative example 2 The release paper obtained in Comparative example 1 was subjected to a heat treatment at 120°C for 20 min and the release potential and the residual adhesive strength of the treated product were masured. The results are listed in Table 1. Comparative example 3 A release paper was obtained similarly as in Example 2, except that the localization was inadequate and that it was not subjected to the heat treatment, and its release potential and residual adhesive strength were measured. The results are presented in Table 1. As hereabove described, the release agent of this invention does not bleed at room temperature and gives excellent release potential and residual adhesive strength. And when manufacturing a release paper by the extrusion lamination process, using the release agent of this invention, curing treatment is not required and when coating process is used, its mere dissolution in a solvent will do without the need of preparation by mixing and making addition reaction, every time coating is done; accordingly, productivity is greatly elevated.

Claims: A laminate containing a substrate, selected from paper, cloth, film, metal foil and their laminates, and a release layer, obtainable by the following method: a) reacting an organopolysiloxane compound selected from polymethyl hydrogen siloxane and methyl hydrogen siloxane-dimethyl siloxane copolymer having at least one hydrogen atom with an olefinic macromer having at least one vinyl group at its terminal which reacts with said hydrogen atom; b) mixing the in this way produced release agent with a polyolefin selected from polyethylene, polypropylene, 4-methyl pentene-1 resin, and copolymers with ethylen; c) extruding the mixture on a substrate, selected from paper, cloth, film, metal foil and their laminates, thereby forming a laminate, where the release agent contained in the aforementioned laminated mixture layer is localized to the layer surface simultaneously as it is extruded or if the localization is inadequate, the laminate should be heat-treated to achieve the surface localization of the release agent or interposing an adhesion enhancing layer of polyethylene between the mixed layer containing the release agent and the substrate, thereby improving the adhesion therebetween. A method for preparing a laminate, containing a substrate, selected from paper, cloth, film, metal foil and their laminates, and a release layer, comprising the following steps: a) reacting an organopolysiloxane compound selected from polymethyl hydrogen siloxane and methyl hydrogen siloxane-dimethyl siloxane copolymer having at least one hydrogen atom with an olefinic macromer having at least one vinyl group at its terminal which reacts with said hydrogen atom; b) mixing the in this way produced release agent with a polyolefin selected from polyethylene, polypropylene, 4-methyl pentene-1 resin, and copolymers with ethylen; c) extruding the mixture on a substrate, selected from paper, cloth, film, metal foil and their laminates, thereby forming a laminate, where the release agent contained in the aforementioned laminated mixture layer is localized to the layer surface simultaneously as it is extruded or if the localization is inadequate, the laminate should be heat-treated to achieve the surface localization of the release agent or interposing an adhesion enhancing layer of polyethylene between the mixed layer containing the release agent and the substrate, thereby improving the adhesion therebetween.

Inventors: KITAMURA RYOICHI, OHARA SHUZO, KITAMURA, RYOICHI, OHARA, SHUZO
Applicants: GOYO PAPER WORKING CO LTD, GOYO PAPER WORKING CO. LTD.
Application year: 1987
Main classification: C08G77
IPC codes: C08F290, D21H19, C08G77, D21H27, C09J7, C08F299