JP2537616B2 - Polypropylene sheet with excellent offset printability - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a polypropylene sheet having excellent offset printability.

[Conventional technology]

As a material for a sheet-like material used for a case such as a tape cassette, a package, a file cover, and other stationery, a polypropylene sheet having a high-grade feeling has been widely used instead of a conventional paper. In most cases, these sheets are often printed in multiple colors. When paper is used as the sheet, the printing means can be freely selected and multicolor printing can be easily performed on the surface, but the polypropylene sheet is limited in printability due to the characteristics of the material. For example, when offset printing is directly used on the surface, not only printing unevenness occurs but also the adhesiveness with ink is poor. For this reason, screen printing has been mainly used in the past.

[Problems to be solved by the invention]

However, in the case of screen printing, there are many man-hours in the case of multicolor printing, and there are restrictions in terms of print design and expression. Therefore, a method of applying an anchor coat to the pretreatment has been attempted in order to apply offset printing capable of various multicolor printing. However, the need for the pretreatment causes a high cost due to an increase in the number of steps, and the anchor coat is also required. There is an unfavorable drawback in work due to deterioration with time.

In order to improve the material properties including these points, those to which a tackifier is added in the structure, those to which a polar polymer is added (for example, for polyolefin molded articles, JP-A-60
-262832 and JP-A-60-248741) have been developed.

An object of the present invention is to provide a polypropylene sheet material capable of being applied to offset printing without requiring anchor coating as a pretreatment by selecting a specific resin, a combination of specific resins, and processing conditions during sheet molding. Especially.

[Means for solving problems]

The present invention is to add a high density polyethylene to a propylene-ethylene block copolymer to form a polymer blend,
As an antistatic agent, polyhydric alcohol fatty acid ester having a melting point of 58 to 70 ° C and glycerin fatty acid ester are 0.03 to 0.30 wt.
%, A polypropylene sheet having excellent offset printability, characterized in that the surface thereof is subjected to corona discharge treatment with a strength of at least 38 dynes / cm.

In the present invention, it is important to select and use a polymer blend in which high density polyethylene is mixed with a propylene-ethylene block copolymer as the polypropylene resin constituting the sheet. The preferred mixing ratio is 75 to 95 wt% of propylene-ethylene block copolymer and 25 to 5 wt% of high density polyethylene. An antistatic agent is added to the polypropylene polymer blend.

The first reason for incorporating the antistatic agent into the structure of the polymer blend is, of course, to prevent electrostatic charge on the sheet surface. By the way, amine-based antistatic agents are generally used. However, these antistatic agents are not suitable because they dampen fountain solution and cause scumming during offset printing. Particularly in the present invention, 0.03 to 0.30 wt% of a combination of a polyhydric alcohol fatty acid ester having a melting point of 58 to 70 ° C. and a glycerin fatty acid ester is mixed. When the amount of the antistatic agent mixed exceeds 0.30 wt%, the transferability of the offset printing ink is improved, but the bleeding phenomenon occurs and the adhesion is reduced. On the contrary, if it is 0.03 wt% or less, a sufficient antistatic effect cannot be obtained.

Within the melting point range of 58 ° C to 70 ° C, there is little change in the leaching amount of the antistatic agent due to temperature changes during the four seasons, and a stable amount of antistatic agent on the surface of the sheet can be secured, and a stable sheet can be obtained throughout the four seasons. If the melting point exceeds 70 ° C, winter
When the sheet is cold, the rate of leaching of the antistatic agent to the surface of the sheet is slow and a sufficient antistatic effect cannot be obtained. The leaching speed of the ink becomes faster and leaches more than necessary, which adversely affects the adhesiveness of the ink.

Pigments and other additives are added to the polypropylene polymer blend to which the above antistatic agent has been added, if necessary, and premixed with a mixer such as a drum blender, a V type blender, or a ribbon blender, and this is used with an extruder or the like. And knead by heating to form a sheet. Then, the surface of the obtained sheet-like material is subjected to corona discharge treatment.
It is important that the sheet-like article of the present invention has a strength of at least 35 dynes / cm by the treatment just before offset printing. The corona discharge imparts polarities to the composition of the sheet by CO groups and OH groups, chemically activates it, and physically roughens the surface. The strength is 38 dynes / cm or more, and the preferable range is 38 to 48 dynes / cm. In this case, good printing can be provided. If the strength is less than 38 dynes / cm,
The polarity becomes insufficient and the adhesion and transferability of the printing ink deteriorate. Further, in order to improve printability, the sheet-like material may be embossed to adjust the surface roughness to 30 μm or less.

The sheet-like material obtained through the above treatment steps has excellent suitability for offset printing, and the anchor coat treatment is unnecessary prior to printing.

〔Example〕

Examples of the present invention will be shown below. First as Examples 1 and 2
The offset printing suitability of the sheet-like material obtained by setting the components and processing conditions shown in the table and the sheet-like products obtained under the components and processing conditions shown in Table 1 as Comparative Examples 1 and 2 evaluated.

For the evaluation, relative to the items shown in Table 2, the printability of the sheet-like material was evaluated by relative evaluation.

As is clear from Table 2 above, the sheet-like material of the present invention showed stable performance for all evaluation items.
According to Table 2, the quality of offset printing suitability depends on the material composition,
It turns out that the selection of treatment conditions is an important requirement.

〔The invention's effect〕

As described above, according to the present invention, a stable printing surface can be obtained by performing various multicolor printing by offset printing directly on the surface of the polypropylene resin sheet without pretreatment such as anchor coating. The sheet-like material of the present invention can be applied to various cases, packages and covers to exert excellent effects.

Claims (1)

(57) [Claims] 1. A polymer blend obtained by adding high-density polyethylene to a propylene-ethylene block copolymer, and a polyhydric alcohol fatty acid ester having a melting point of 58 to 70 ° C. and a glycerin fatty acid ester as an antistatic agent in an amount of 0.03 to 0.
It consists of a sheet material containing 30 wt% and has at least strength on the surface.
A polypropylene sheet material with excellent offset printability, which has been subjected to a corona discharge treatment of 38 dynes / cm.