JPH0437111B2 - - Google Patents

Description

[Detailed description of the invention]

(a) Technical Field The present invention relates to a glue for synthetic resin surface protection sheets. (b) Prior Art Synthetic resins have properties such as being light and easy to process, so they are widely used for various purposes by taking advantage of these properties. However, since the synthetic resin has a soft surface, the molded product is easily damaged by unnecessary scratches during transportation, storage, molding, etc., and has the disadvantage of reducing its commercial value. To protect the surface, a paper-like sheet such as kraft paper is usually pasted on the resin board with a water-soluble glue, such as an aqueous solution of partially saponified polyvinyl acetate, or starch glue, or a paper-like sheet such as kraft paper is coated with an adhesive such as natural rubber. At present, a pressure-sensitive protective paper is pressure-bonded, or a pressure-sensitive adhesive or heat-sensitive adhesive synthetic polymer protective film is pasted. However, pressure-sensitive protective sheets made of polymer films, natural rubber, etc. have strong adhesive strength, so peeling is difficult when handling large objects, and the synthetic resin plate becomes electrically charged when peeled off, attracting dust etc. to the surface. This also tends to cause problems such as surface damage during molding, and the price is high. On the other hand, when covering with a paper-like sheet such as kraft paper using a water-soluble adhesive, the problems encountered when using a polymer film or natural rubber described above are avoided and the cost is low. On the other hand, if the adhesive strength of the glue is too weak, or if the protective sheet is peeled off from the synthetic resin board, fragments of the protective sheet or glue film may remain on the surface of the synthetic resin board (hereinafter referred to as "glue residue"). ). If there is any glue residue, it will be necessary to thoroughly wash it off with water or alcohol.
If a resin plate is heat-molded with incomplete washing, the contaminated parts will impair the smoothness and transparency of the resin plate, and even if washed with water or alcohol after heat-forming, the contamination will no longer disappear and the surface of the resin plate will deteriorate. You will need to polish it. Furthermore, if a resin plate contaminated with an adhesive or the like is directly subjected to printing such as screen printing or photo printing, the adhesion between the printing ink and the resin plate may be poor in the contaminated area, and the area may easily fall off. In addition, if the adhesive strength is too weak, the protective paper may peel off during the transportation process of the methacrylic resin board, causing damage to the methacrylic resin board, or the protective paper on the edges of the sheet may peel off when cutting the sheet after manufacturing. Chips generated during cutting enter the sheet and cause scratches during storage, greatly reducing its commercial value. Therefore, the adhesive applied to the protective sheet must not leave any adhesive residue on the synthetic resin plate when it is peeled off, and must have appropriate adhesive strength. In addition, in order to prevent damage to the synthetic resin board during processing, heating and bending may be performed with the protective sheet still attached to the synthetic resin board, but the type of glue and resin used at this time may vary. As a result, rough skin and/or cracking may occur at the bent portion that comes into direct contact with the rod heater, and in this case, the appearance will be significantly impaired and the commercial value of the processed portion will be greatly reduced. A sizing agent using partially saponified polyvinyl acetate as a water-soluble sizing agent is an excellent sizing agent that leaves almost no adhesive residue, but the adhesive strength is generally low.
When heating and bending with the aforementioned rod heater, there is a problem in that roughness and cracking occur at the folded portion, and there has been a strong desire to improve these problems. Conventionally, boric acid has been added to water-soluble adhesives to prevent rough skin and cracking caused by adhesives using partially saponified polyvinyl acetate. Addition of boric acid can prevent skin roughness and cracking, but aqueous glue solutions containing boric acid tend to gel over time, increasing the viscosity of the system and making it difficult to handle. , there was a strong demand for improvement. (c) Purpose of the Invention In view of the prior art as described above, the purpose of the present invention is to have a suitable adhesive strength, prevent the roughening and cracking of the bent portion of the contact portion of the rod heater, and reduce the viscosity over time. The increase was suppressed,
An object of the present invention is to provide a sizing agent for a synthetic resin surface protection sheet whose main ingredient is an aqueous solution of partially saponified polyvinyl acetate. (d) Structure of the invention The present invention comprises an aqueous solution containing 3 to 15% by weight of partially saponified polyvinyl acetate, a cationic surfactant in which the proportion of the partially saponified polyvinyl acetate to the solid content in the aqueous solution is 1 to 50% by weight; and a sizing agent for a synthetic resin surface protection sheet comprising an organic boron compound having the following structural formula in a proportion of 0.01 to 20% by weight based on the solid content of partially saponified polyvinyl acetate in the aqueous solution. (E) Embodiment The partially saponified polyvinyl acetate used in the present invention preferably has a saponification degree of 71.0% or more, and this includes completely saponified polyvinyl alcohol with a saponification degree of 100%. . Examples of the cationic surfactant used in the present invention include trimethyllauryl ammonium chloride, dimethylbenzylalkylammonium chloride, and the like, with the latter being preferably used. Regarding the amount of the cationic surfactant added, it is desirable that the proportion of the cationic surfactant to the solid content of the partially saponified polyvinyl acetate in the aqueous solution is 1 to 50% by weight. If the amount is less than 1% by weight, the adhesive strength due to the addition of the surfactant will be low, and if it is more than 50%, the viscosity of the glue and the amount of glue remaining will increase significantly, which is not preferable. Further, the organic boron compound used in the present invention is an organic boron compound having a semipolar bond in the molecule represented by the following formula. A representative product of this compound is commercially available from Toho Chemical Industry Co., Ltd. under the name Emalbon GB. In the present invention, by adding a specific amount of the above-mentioned organic boron compound to an aqueous solution of partially saponified polyvinyl acetate, it is possible to solve the problem of rough skin and/or cracking that would otherwise occur on a synthetic resin board during heat molding due to the sizing agent. In addition to being able to prevent this, the addition of the organic boron compound causes little increase in the viscosity of the aqueous glue solution, and has an excellent effect in that the viscosity hardly changes over time. The detailed mechanism of preventing skin roughness and/or cracking by adding the above-mentioned organic boron compound is clear. This is thought to occur when the organic boron compound is fused to the synthetic resin plate, and the addition of the above-mentioned organic boron compound causes a crosslinking reaction between this and the partially saponified polyvinyl acetate, thereby preventing rough skin and/or cracking. It seems possible. The amount of the organic boron compound added can vary depending on the type of partially saponified polyvinyl acetate used, but is generally preferably 0.01 to 20% by weight based on the solid weight of the partially saponified polyvinyl acetate in the aqueous solution of partially saponified polyvinyl acetate. is in the range of 0.1 to 20% by weight. If it is less than 0.01% by weight, the effect of preventing rough skin and/or cracking will be poor, and if it exceeds 20% by weight, there will be almost no increase in weight, so there will be no economic benefit, and the addition will reduce the viscosity of the glue. This is not preferable in terms of handling, since the increase in . As described above, in the present invention, by adding a cationic surfactant to an aqueous solution of partially saponified polyvinyl acetate, it is possible to obtain a sizing agent that cannot be obtained by using partially saponified polyvinyl acetate alone as a sizing agent. It became possible to obtain a strong adhesive strength. In addition, by adding the above-mentioned organic boron compound, it is possible to prepare a paste without significantly increasing the viscosity of the paste, and it is also possible to locally heat the paste with the protective sheet attached and bend and form it. The appearance of the bent portion will not be damaged even if the bending is done. The above adhesive composition, which is an adhesive agent used in the present invention, includes a plasticizer, a hygroscopic agent, a preservative, a thickener,
Antifoaming agents and the like can be added. The viscosity of this glue is 200 to 10,000 centipoise (cp) during the application process.
It is desirable to adjust it within the range of . Viscosity is 200cp
If it is lower than that, when the protective sheet is removed, stains consisting of adhesive agent residues and paper fiber pieces are likely to occur on the methacrylic resin plate. If the viscosity is greater than 10,000 cp, it will be difficult to apply uniformly, which is unfavorable in terms of workability. The amount of adhesive used in the present invention is as follows:
It ranges from 0.4 to 10 g/ ^m2 , preferably from 0.6 to ² g/m2. If it is less than 0.4 g/m ² , adhesive residue will be left on the synthetic resin board when the protective sheet is peeled off from the methacrylic resin board or other synthetic resin board. Conversely, 10g/ ^m2
If the adhesive strength exceeds this value, defects such as roughness may occur on the surface of the synthetic resin board, and the reproducibility of adhesive strength may become poor. The adhesive can be applied by applying the adhesive evenly to the synthetic resin board and then attaching the protective sheet, or applying the adhesive to the protective sheet and then attaching it to the synthetic resin plate, or both. Examples include: The synthetic resin that can be protected with the protective sheet using the adhesive of the present invention is not particularly limited as long as the protective sheet can be attached to it. Examples include molded products. Examples of synthetic resin materials for forming these synthetic resin molded products include polymethyl methacrylate and other methacrylic resins, rubber-modified acrylic resins, polycarbonate, polystyrene resins, AS resins, ABS resins, vinyl chloride resins, and acetate resins. , polyester resin, etc. The adhesive for protective sheets of the present invention is particularly effective for polymethacrylates, other methacrylic resins, and polycarbonate resins that have excellent optical properties. In the present invention, the methacrylic resin board refers to a board made of polymethyl methacrylate or a copolymer resin containing methyl methacrylate as a main component and having a viscosity average degree of polymerization of 800 to 8,000. As the protective sheet, paper, film, etc. can be used, but kraft paper with a basis weight of 20 to 80 g/m ² and a surface smoothing process and the like are particularly preferred. The Steckicht size degree described in JIS P 8122 is
For more than 10 seconds, the surface strength of the paper as stated in JIS P 8129
The number is preferably 10 or more, but is not limited to this. Alternatively, coated paper coated with a thermoplastic resin on the surface not in contact with the methacrylic resin plate or paper laminated with a thermoplastic film may be used. (F) Examples Next, the present invention will be explained with reference to Examples and Comparative Examples. The examples merely illustrate the present invention, and the present invention is not limited thereto. Example 1 The starting material was a mixture of methyl methacrylate syrup (viscosity approximately 10 poise, 20°C) with a polymerization rate of 10%, a polymerization initiator azobisdimethylvaleronitrile 840 ppm, and a release agent sodium dioctyl sulfosuccinate 20 ppm. The mixture was poured into a cast molding cell made of stainless steel plate with a thickness of 3 mm and heated to a temperature of 74℃.
For 40 minutes, the mixture was left in an air bath at 120°C for 1 hour to produce a methacrylic resin plate with a thickness of 3 mm. Next, the partially saponified polyvinyl acetate Gohsenol (trademark) KH-17 (manufactured by Nippon Gosei Kagaku Kogyo Co., Ltd., polymerization degree 1700, degree of saponification 78.5 to 81.5 mol%) was added to a 9.5% aqueous solution by weight of the polyvinyl acetate partially saponified product GOHSENOL (trademark) KH-17 (manufactured by Nippon Gosei Kagaku Kogyo Co., Ltd., polymerization degree 1700, saponification degree 78.5 to 81.5 mol%). Sanizol B-50 (trademark,
A cationic surfactant manufactured by Kao Soap, containing 50% by weight of dimethylbenzylammonium chloride as a solid content), and a further 3% by weight of Emulbon GB-90 (manufactured by Toho Chemical Co., Ltd., containing 10% of water in the boron compound Emalbon GB). % by weight) was added and stirred with heating to prepare the sizing agent of the present invention. This was uniformly applied to the methacrylic resin plate at a rate of 2.0 g/m ² using various bar coaters. Immediately Daio Paper Katatsuya Kraft Paper (Basic weight 40g/m ² , Stekkicht size degree 12 seconds, Surface strength
12A) was attached to obtain a methacrylic resin plate with a protected surface. The methacrylic resin plate with the protective paper was left in a constant temperature room at 23° C. overnight, and then the adhesive strength of the protective paper was measured as follows. Methacrylic resin board with protective paper, width 10cm, length
After cutting into a 30cm specimen, calculate the force (g/
Table 1 shows the average value of the three test pieces obtained by measuring the adhesion force (10 cm), the maximum value of the adhesion force, and the bar coater number.

[Table] In addition, the state of contamination on the surface of the methacrylic resin board after removing the protective paper was visually determined, and no adhesive residue was observed. Next, from a methacrylic resin board with a protective paper,
Cut a specimen with a horizontal length of 30 x 15 cm, and
It was brought into contact with a rod-shaped heater heated to 100°C for 90 seconds, the heated side facing outward, and immediately bent at an angle of 90°C. The rough skin or cracking that occurred at the bent portion was visually judged, but no roughness or cracking was observed. Comparative Example 1 In Example 1, Sanizol B-
A methacrylic resin plate with a protective paper was produced in the same manner as in Example 1, except that 50 and Emalbon GB-90 were not added, and the adhesive force measurement and heating bending test were conducted in the same manner as in Example 1. The adhesive strength at this time is shown in Table 2.

[Table] No adhesive residue was observed on the methacrylic resin plate after the protective paper was removed, but cracking and rough skin occurred at the folded portion in the heated bending test. Comparative Example 2 Emulbon GB was added to the adhesive aqueous solution in Example 1.
Example 1 A methacrylic resin board with a protective paper was produced in the same manner as in Example 1 except that -90 was not added.
Adhesive force measurements and heating bending tests were conducted in the same manner as above. The average value of adhesive force at this time is 39g/10cm
However, as a result of the heating and bending test, cracking and rough skin occurred at the folded portion. Comparative Example 3 In Example 1, Sanizol B- was added to the adhesive aqueous solution.
A methacrylic resin plate with a protective paper was produced in the same manner as in Example 1 except that 50 was not added.
Adhesive force measurements and heating bending tests were conducted in the same manner as above. The average value of adhesive force at this time is 15g/10cm
However, as a result of the heating and bending test, no cracking or rough skin was observed at the folded portion. Example 2 A glue was prepared in exactly the same manner as in Example 1, except that the amount of Sanizol B-50 added to the aqueous glue solution was adjusted so that the proportion of the solid content of partially saponified polyvinyl acetate in the aqueous glue solution was 5% by weight. An aqueous adhesive solution was prepared and applied to the methacrylic resin plate, and the physical properties of the adhesive were evaluated in the same manner as in Example 1. The measured adhesive forces are shown in Table 3.

[Table] No adhesive residue was observed on the methacrylic resin plate after the protective paper was removed, and no cracking or rough skin was observed at the folded portion in the heated bending test. Example 3 Partially saponified polyvinyl acetate, Gohsenol GL-50 (trade name manufactured by Nippon Gosei Kagaku Kogyo Co., Ltd., degree of polymerization 500, degree of saponification 86.5 to 89.0 mol%)
To a 22% by weight aqueous solution, Sanisol B-50 was added so that the proportion of the solid content of the partially saponified polyvinyl acetate in the aqueous solution was 25% by weight, and Emalbon GB-90 was added so that the proportion was 3% by weight, and the mixture was heated and stirred. The paste of the present invention was prepared by dissolving the paste.
Example 1 This glue was applied using a #12 bar coater.
Apply it evenly to the methacrylic resin board described in , and immediately apply it to Daio Paper Katatsuya Kraft paper (basis weight 40g/
m ² , Steckicht size 12 seconds, surface strength 12A) was attached to obtain a methacrylic resin plate with a protected surface. When this methacrylic resin plate with protective paper was evaluated in the same manner as in Example 1, the average value of adhesive strength was
It was 43g/10cm. The state of contamination on the surface of the methacrylic resin plate after removing the protective paper was visually determined, but no adhesive residue was observed. Further, a heating and bending test was conducted in the same manner as in Example 1, but no occurrence of rough skin or cracking was observed. For comparison, an aqueous GL-05 solution without the addition of Sanisol B-50 or Emalbon GB-90 was applied to a methacrylic resin board in the same manner and evaluated, and the average adhesive strength was 9 g/ 10 cm, and rough skin and cracking occurred in the heating bending test. Example 4 A plate of 3 mm thick polycarbonate, AS resin, ABS resin, polyvinyl chloride resin, acetate resin, and polystyrene resin obtained by extrusion or injection molding was prepared using the protective paper and adhesive used in Example 1. When bonded, the adhesive strength was sufficient in all cases, and there was no adhesive residue on the surface of the board when it was peeled off.

Claims (1)

[Scope of Claims] 1. 3 to 15 partially saponified polyvinyl acetate products
an aqueous solution containing % by weight, the proportion of the partially saponified polyvinyl acetate to the solid content in the aqueous solution is 1 to 1% by weight;
50% by weight of a cationic surfactant, and the following structural formula in which the proportion of partially saponified polyvinyl acetate to the solid content in the aqueous solution is 0.01 to 20% by weight A glue for synthetic resin surface protection sheets made of an organic boron compound represented by: 2 Claim 1 in which the cationic surfactant is trimethyllauryl ammonium chloride
Adhesive for protective sheets as described in section. 3. The adhesive for a protective sheet according to claim 1, wherein the cationic surfactant is dimethylbenzylalkylammonium chloride.