Use of pressure sensitive adhesive for surface protection

Abstract: A pressure-sensitive adhesive comprising 100 parts by weight of an isobutylene polymer and 0.001 to 5 parts by weight of at least one release control agent selected from the group consisting of an alcohol having a molecular weight of 90 to 300 and an oxygen atom content of 8.5% or more or a derivative thereof and a carboxylic acid having a molecular weight of 70 to 400 and an oxygen atom content of 11% or more or a derivative thereof; and a surface protecting material having a pressure-sensitive adhesive layer comprising the adhesive. The adhesive has well-balanced characteristics in initial adhesion, retention of initial adhesion, and weather resistance.

Description: This invention relates to the use of a surface protecting material which exhibits good initial adhesion, retention of the initial adhesion, and excellent weather resistance and can easily be removed after long-term adhesion. A surface protecting material comprising a substrate and a pressure-sensitive adhesive layer comprising an isobutylene polymer as a base polymer is known. Compared with acrylic or natural rubber-based pressure-sensitive adhesive layers, polyisobutylene-based pressure-sensitive adhesive layer hardly increases its adhesiveness with time even when exposed to sunlight so that it is easily removed from an adherend surface without leaving the adhesive, which is advantageous for use as a surface protecting material. On the other hand, the initial adhesive strength of the polyisobutylene-based pressure-sensitive layer is sacrificed to adhesion retention and weather resistance. Therefore, it has been difficult to secure adhesion retention and weather resistance in good balance with initial adhesion. EP-A-0670357 discloses a paint film-protective sheet comprising a supporting substrate having formed thereon a rubber-based pressure-sensitive adhesive layer containing a fatty acid glycerol ester and an antifungal agent. DE-A-1594176 teaches an adhesive for polyethylene characterised in that it comprises a mixed polymer of isobutylene/isoprene obtained from 95-98% of isobutylene and 2-5% of isoprene, 8-20% of natural resin of the Kolophonium type as a modifier and fillers and softeners. In DE-A-1569269 the use of an alcohol or a mixture of saturated, univalent, aliphatic alcohols with a flash point (open shell) over 170°C as an anti-adhesive agent for raw butyl caoutchouc or butyl coutchouc based mixtures being vulcanised with p-quinonedioxime by incorporation during the preparation of the raw polymers or the base mixtures is disclosed. JP-A-57117534 teaches a crosslinking type pressure-sensitive adhesive obtainable by dissolving 100 parts by weight of halogenated butyl rubber, 1-10 parts by weight of a dithio carbamate type compound, 0.1 to 5 parts by weight of zinc oxide, 0.5 to 4 parts by weight of an organic carboxylic acid, a tackifier resin and a modifier in a solvent. US 2,463,452 discloses an adhesive composition consisting of 100 parts by weight of polyisobutylene (molecular weight 100,000), 5 parts by weight of stearic acid, 100 parts by weight of mineral oil and 100 parts by weight of low boiling solvent naphtha (completely aliphatic). The object of the present invention is to provide a surface protecting material comprising the same which exhibits satisfactory initial adhesion, retention of the initial adhesion, and weather resistance in good balance and is easily removable without leaving the adhesive on the adherend surface even after long-term adhesion. Said object is achieved by the use of a surface protecting material comprising a pressure-sensitive adhesive comprising 100 parts by weight of an isobutylene homopolymer or an isobutylene copolymer or a vulcanized product thereof and 0.002 to 2 parts by weight of isobutyric acid, caprylic acid, succinic acid, benzoic acid, toluylic acid or isophthalic acid as a release control agent, and a polyolefin substrate, for the improvement of initial adhesion on an adherend surface. The release control agent used in the invention exhibits high polarity due to the existence of oxygen atoms having high electronegativity. It is localized in the vicinities of the adhesive layer interface based on its high polarity in a peculiar compatible state to form a layer having weak cohesion in the vicinities of the adhesive interface. By the action of this layer, the pressure-sensitive adhesive has well-balanced adhesion characteristics including initial adhesion, weather resistance, and retention of the initial adhesion and the removable surface protecting material exhibits satisfactory adhesion, retains the initial adhesion for a long time and is easily removed without leaving the adhesive. The isobutylene polymer which can be used as a base polymer of the pressure-sensitive adhesive includes an isobutylene homopolymer and an isobutylene-isoprene random copolymer (i.e., butyl rubber) or a vulcanized product thereof, such as regular butyl rubber, and partially crosslinked butyl rubber. Isobutylene polymers preferred for weather resistance, etc. include an isobutylene homopolymer, an isobutylene-isoprene random copolymer having an isoprene content of 0.5 to 3% by weight and its vulcanized product. An isobutylene homopolymer is particularly preferred. These isobutylene polymers can be used either individually or as a combination of two or more thereof. The release control agent having high polarity, which is assigned to the high electronegativity of oxygen, exhibits compatibility to the isobutylene base polymer and is localized, when formulated as a pressure-sensitive adhesive layer, in the adhesive interface in a peculiar compatible state. The carboxylic acid includes isobutyric acid, caprylic acid, succinic acid, benzoic acid, toluylic acid, and isophthalic acid. Benzoic acid is particularly preferred for the ease in compounding. As stated above, the carboxylic acid can be used either individually or as a combination of two or more selected therefrom. From the standpoint of the balance among weather resistance, adhesion retention, and initial adhesion, the amount of the release control agent is 0.002 to 2 parts by weight, per 100 parts by weight of the isobutylene polymer. The pressure-sensitive adhesive used in the invention is prepared by mixing the components in an appropriate manner, for example, by mixing the isobutylene polymer and the release control agent in an appropriate solvent, such as toluene, hexane, cyclohexane or heptane. If desired, the pressure-sensitive adhesive may contain various acceptable additives, such as pigments, fillers, antioxidants, and ultraviolet absorbers as long as the above-described effects in developing the peculiar compatible state and manifesting satisfactory adhesion characteristics are secured. The surface protecting material used according to the invention comprises a substrate having formed thereon a pressure-sensitive adhesive layer comprising the above-described pressure-sensitive adhesive. The surface protecting material is prepared by any known method commonly employed for formation of an adhesive sheet, for example, by coating a substrate with a solution of the pressure-sensitive adhesive or a molten pressure-sensitive adhesive or by once forming an adhesive layer on a release separator in the same manner as described above and then transferring the adhesive layer onto a substrate. The substrate which can be used in the invention is a plastic film of polyolefins, e.g., propylene polymers, ethylene polymers or mixtures thereof. If desired, the surface of the substrate on which the adhesive layer is to be provided can be subjected to an appropriate surface treatment, such as a corona treatment or primer coating, to improve the adhesion, etc. of the adhesive layer to the substrate. Further, the substrate may contain a slip agent, an antistatic agent, an antioxidant, and the like, if desired. While not limiting, the substrate usually has a thickness of 5 to 300 µm, preferably 200 µm or smaller, still preferably 10 to 100 µm, and the pressure-sensitive adhesive layer usually has a thickness of 1 to 200 µm, preferably 100 µm or smaller, still preferably 1 to 50 µm. If necessary, the exposed surface of the adhesive layer may be protected with a separator, etc. until use, or the surface protecting material may be rolled up without a separator. The substrate of the separator and of the surface protecting material to be rolled up is surface treated with an appropriate release agent, such as a silicone, fluorine or long-chain acrylic release agent. Where the surface protecting material is rolled up, the back side of the substrate, with which the adhesive layer is brought into contact, is surface treated with the release agent. The surface-protecting material used in the invention is preferably applied to a variety of adherends, such as coated plates, metallic plates, resin plates, decorative laminates, and automobile bodies and parts. It is particularly useful in applications demanding excellent adhesion, resistance to change in adhesion with time, removability without leaving the adhesive, and weather resistance. The weather resistance specifically means resistance to deterioration by exposure to sunlight, for example, reduction in adhesion characteristics even in outdoor weathering during transportation or laying operation so that the adhesive layer may be removed without contaminating the adherend with any remaining adhesive. The invention will now be illustrated in greater detail with reference to Examples. Unless otherwise noted, all the parts are by weight. Reference EXAMPLE 1 In 700 parts of toluene were dissolved 80 parts of polyisobutylene having a weight average molecular weight (Mw) of 870,000 (on polystyrene calibration in gel-permeation chromatography; hereinafter the same) and 20 parts of polyisobutylene having an Mw of 30,000. Two parts of 2-phenyl-2-propanol (molecular weight: 136; oxygen atom content: 11.8%) were added to the polymer solution to prepare a pressure-sensitive adhesive. The adhesive was applied to a 40 µm thick film of polypropylene/polyethylene (1/9 by weight) and dried at 120°C for 3 minutes to prepare a surface protecting material with a 10 µm thick pressure-sensitive adhesive layer. The gel-permeation chromatography for molecular weight measurement was carried out on 4 columns (TSK gel G2000H HR, G3000H HR, G4000H HR, and GMH-H HR; manufactured by Tosoh Corporation) connected in series under the following conditions. Eluent: tetrahydrofuran Flow rate: 1 ml/min Temp.: 40°C Sample concentration: 0.1 wt% in tetrahydrofuran Sample pour: 500 µl Detection: differential refractometer EXAMPLE 1 A surface protecting material was prepared in the same manner as in Reference Example 1, except that the pressure-sensitive adhesive was prepared by using 0.002 part of benzoic acid (molecular weight: 122; oxygen atom content: 26.2%) in place of the 2-phenyl-2-propanol. Reference EXAMPLE 2 A surface protecting material was prepared in the same manner as in Reference Example 1, except that the pressure-sensitive adhesive was prepared by adding 1 part of 1,1-cyclohexanediol (molecular weight: 116; oxygen atom content: 27.6%) to a solution of 70 parts of polyisobutylene (Mw: 870,000) and 30 parts of polyisobutylene (Mw: 90,000) in 700 parts of toluene. EXAMPLE 2 A surface protecting material was prepared in the same manner as in Reference Example 2, except that the pressure-sensitive adhesive was prepared by using 0.01 part of succinic acid (molecular weight: 118; oxygen atom content: 54.2%) in place of the 1,1-cyclohexanediol. COMPARATIVE EXAMPLE 1 A surface protecting material was prepared in the same manner as in Reference Example 1, except for using a pressure-sensitive adhesive containing no 2-phenyl-2-propanol which was prepared by dissolving 100 parts of polyisobutylene (Mw.: 870,000) in 700 parts of toluene. COMPARATIVE EXAMPLE 2 A surface protecting material was prepared in the same manner as in Reference Example 1, except that 2-phenyl-2-propanol was not used. COMPARATIVE EXAMPLE 3 A surface protecting material was prepared in the same manner as in Reference Example 1, except for changing the amount of the 2-phenyl-2-propanol to 10 parts. COMPARATIVE EXAMPLE 4 A surface protecting material was prepared in the same manner as in Reference Example 2, except that 1,1-cyclohexanediol was not added. Evaluation: 1) Adhesive strength (initial and after accelerated weathering) A coated plate having a base coat of an acrylic melamine resin paint (Magicron TB751, produced by Kansai Paint Co., Ltd.) and a topcoat of clear lacquer (Magicron TC Clear, produced by Kansai Paint Co., Ltd.) was prepared. Each of the surface protecting materials obtained in Examples and Comparative Examples was adhered to the coated plate by means of a laminator at 23°C and 65% RH under a pressure of 70 N/cm at a speed of 5 m/min. After 30 minutes, the 180° peel strength (pulling speed: 300 mm/min) was measured to obtain the initial adhesive strength. Separately, the protective material stuck on the coated plate was subjected to accelerated weathering in Sunshine Carbon Weatherometer (manufactured by Suga Shikenki K.K.) for 100 hours in accordance with JIS D0205. After the weathering test, the sample was allowed to stand at 23°C and 65% RH for 3 hours and then subjected to the same peel test to obtain the adhesive strength after accelerated weathering. 2) Weather resistance Test samples prepared in the same manner as in (1) above were fixed to an outdoor mount. After 30 days' and 90 days' exposure to natural weathering conditions, the surface protecting material was stripped off the coated plate to check any contamination of the coated plate. Samples which caused little contamination with a residual adhesive, etc. were judged good, and those caused perceptible contamination with a residual adhesive, etc. were judged no good. 3) Overall judgement Samples which had an adhesive strength, both initial and after accelerated weathering, in the range of from 2.5 to 8.2 N/20 mm in the peel test (1) and caused no contamination of the coated plate by adhesive remaining, etc. in the outdoor weathering test (2) were judged "pass", and those which failed to satisfy either one or both of these requirements were judged "failure". The results of the evaluation are shown in Table 1. Adhesive Strength (N/20 mm) Weather Resistance Overall Judgement Initial After Accelerated Weathering 30 Dys' Exposure 90 Dys' Exposure Reference Example 1 2.5 4.0 good good Pass Example 1 4.4 8.2 good good Pass Reference Example 2 3.1 5.1 good good Pass Example 2 3.9 7.4 good good Pass Compara. Example 1 1.5 5.0 good good Failure Compara. Example 2 4.5 13.1 no good no good Failure Compara. Example 3 0.3 0.6 good good Failure Compara. Example 4 5.2 14.3 no good no good Failure It is seen from Table 1 that all the samples of Examples have satisfactory initial adhesion, are prevented from increasing the adhesive strength with time, and exhibit excellent weather resistance, whereas the samples of Comparative Examples 1 and 3 have insufficient initial adhesion, and those of Comparative Examples 2 and 4 show a considerable increase in adhesive strength with time and have poor weather resistance. As is understood from comparison between Examples and Comparative Examples, a pressure-sensitive adhesive layer having well-balanced adhesion characteristics in initial adhesion, retention of the initial adhesion, and weather resistance can be obtained by compounding an isobutylene base polymer with a small amount of a release control agent showing high polarity due to oxygen atoms having large electronegativity.

Claims: Use of a surface protecting material comprising a pressure-sensitive adhesive comprising 100 parts by weight of an isobutylene homopolymer or an isobutylene-isoprene copolymer or a vulcanized product thereof and 0.002 to 2 parts by weight of isobutyric acid, caprylic acid, succinic acid, benzoic acid, toluylic acid or isophthalic acid or a combination therefrom as a release control agent and a polyolefin substrate, for the improvement of initial adhesion on an adherend surface.

Inventors: EDA TAKESHI, HAYASHI KEIJI, HORADA MITSURU, INOUE TSUYOSHI, MATSUI KOMAHARU, SANO KENJI, SHIBATA KENICHI, SHIRAI MITSUYOSHI, UEDA HIROSHI, EDA, TAKESHI, HAYASHI, KEIJI, HORADA, MITSURU, INOUE, TSUYOSHI, MATSUI, KOMAHARU, SANO, KENJI, SHIBATA, KENICHI, SHIRAI, MITSUYOSHI, UEDA, HIROSHI
Applicants: KANSAI PAINT CO LTD, NITTO DENKO CORP, KANSAI PAINT CO., LTD., NITTO DENKO CORPORATION
Application year: 1999
Main classification: C09J123
IPC codes: C09J123, C08K5