JPH01209198A - Thermoplastic elastomer erasing composition - Google Patents

Abstract

PURPOSE:To enhance heat aging resistance, weatherability, structural strength and elasticity of an eraser while maintaining erasing performance, by adding an ethylene-styrene block copolymer to an eraser matrix comprising a styrene- butadiene copolymer as a main constituent. CONSTITUTION:A thermoplastic elastomer erasing composition comprises an ethylene-styrene block copolymer added to a thermoplastic elastomer eraser material comprising a styrene-butadiene copolymer as a main constituent, in an amount of 2.5-70pts.wt. based on the total weight of the resin matrix constituting the eraser material. When 2.5-70pts.wt. based on the total eight of the eraser resin matrix is thus replaced by the ethylene-styrene block copolymer, the heat resistance, weatherability and heat aging resistance of the eraser comprising the styrene-butadiene copolymer as a main constituent can be markedly enhanced. An addition of more than 70pts.wt. of the block copolymer increases excessively the elasticity and structural strength of the eraser, leading to poor cutting of erasing chips and poor usability of the eraser. An addition of less than 2.5pts.wt. of the block copolymer does not increase the structural strength of the eraser or enhance the weatherability or heat aging resistance of the eraser.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention provides a resin matrix having a styrene-butadiene copolymer as the main component and mixed with various plastics, which has good weather resistance and heat aging resistance. This invention relates to thermoplastic elastomer eraser compositions that do not require superior vulcanization.

(Prior technology) Thermoplastic elastomer erasers use a styrene-butadiene copolymer, which has a strong physicochemical interaction with graphite, which is the main component of pencil lead, as the main component of the resin matrix. Resins with slightly different compatibility, such as ethylene propylene copolymer, ethylene vinyl acetate copolymer, ethylene polymer, propylene polymer, vinyl acetate polymer, vinyl chloride polymer, silicone rubber, vinyl chloride vinyl acetate copolymer At least one type of resin such as a styrene polymer is combined with a total weight of 10 styrene-butadiene copolymers.
Add about 30 to 240 parts by weight to 0 parts and knead, and if necessary, add an appropriate amount of a plasticizer or filler to the resulting eraser composition, and then extrusion molding or injection molding. It can be molded into any shape. (Tokuko Sho 57-32
(Refer to No. 680) The characteristic of the above-mentioned eraser composition is that it does not require vulcanization, nor does it require precise temperature control during molding, as is the case with vinyl chloride polymer erasers. The advantage is that it is as simple as machining and can be erased without degrading the erasing performance.

(Problems to be Solved by the Invention) The eraser obtained in this manner is superior to vinyl chloride-based erasers or vulcanized rubber-based erasers in terms of erasing performance. Even handwriting from plastic crayons can be almost completely erased.

However, the styrene-butadiene copolymer, which is the main component of the eraser component, has only a heat resistance of around 60° C. and is significantly degraded by ultraviolet rays. In addition, the heat aging resistance is inferior to that of vulcanized rubber erasers.

Furthermore, when processed into an ultra-fine core shape or an ultra-thin flat shape,
It has drawbacks such as poor structural strength or elasticity, and breakage during use.

(Means for Solving the Problems) The present inventor has developed a method that improves heat resistance by further adding an ethylene-butylene-styrene block copolymer to a conventional resin matrix mainly composed of a styrene-butadiene copolymer. It has been found that weather resistance and heat aging resistance can be significantly improved.

That is, by replacing 2.5 to 70 parts by weight of the total weight of the eraser resin matrix with ethylene butylene styrene block copolymer, the heat resistance and weather resistance of conventional erasers mainly made of styrene butadiene copolymer can be improved. , heat aging resistance was significantly improved.

Taking into consideration the usability of the resulting eraser, it is appropriate to substitute 5 to 50 parts by weight; adding more than 70 parts by weight will cause the elasticity or structural strength of the eraser to increase too much. It becomes difficult to cut and is not easy to use.

Further, addition of 2.5 parts by weight or less did not result in an increase in the structural strength of the letter eraser or an improvement in weather resistance and heat aging resistance.

Additionally, additives such as fillers used in conventional erasers could be added as they are.

(Function) In conventional styrene-butadiene copolymers, a styrene polymerization part and a butadiene polymerization part exist inside the polymer. The aromatic ring, which is the side chain of the styrene moiety, absorbs ultraviolet light extremely well, and as a result, the styrene polymerization moiety becomes an excited state, that is, localized electrons, and becomes extremely reactive.On the other hand, butadiene Since double bonds exist in the polymerized portion, localized electrons from the styrene polymerized portion are easily accepted, resulting in structural changes due to cutting of the polymer structure and transfer of electrons, resulting in the elastomer structure changing. The polymer itself is destroyed and the polymer itself deteriorates.

However, in the case of ethylene-butylene-styrene block copolymers, ultraviolet light absorption occurs in the styrene polymerized portion, but the localized portions of electrons caused by this cannot have any effect on the surrounding ethylene-butylene saturated chains, and electron movement is does not occur and no structural changes occur. This characteristic does not change even if it receives external energy such as heat or light.
Compared to conventional styrene-butadiene copolymers, the heat resistance is improved, and the heat aging resistance and weather resistance are incomparably improved.

When this polymer is blended with conventional styrene-butadiene copolymers, it shows good compatibility as it has similar solubility parameters and, when added in small amounts, acts as a protective polymer for styrene-butadiene copolymers. The heat aging resistance and weather resistance of the entire polymer matrix were significantly improved, and the heat resistance was also improved in proportion to the blending ratio.

On the other hand, ethylene butylene styrene block copolymer is
Since it is a thermoplastic elastomer like ethylene butylene copolymer, it can be easily heat-processed and extrusion molding and injection molding are possible.

In addition, erasing performance did not change, and by utilizing the characteristics of the highly elastic structure, it was possible to produce ultra-fine or flat shaped erasers without impairing the feeling of use.

compensation Examples of formulations are shown in Table 1.

Table 1. Formulation Example The formulation of the above formulation example was mixed for 1 minute at room temperature using a Henschel mixer, and this mixture was passed through a pelletizer three times to obtain a pelletized formulation.

This blend pellet was molded into a core shape with a diameter of 3 m using a screw extruder. The molding conditions were 160°C for the cylinder part, 140°C for the head part, and 120°C for the die part.

Table 2 shows the measured values of erasure rate, hardness, softening point, heat aging resistance, and weather resistance of the obtained eraser samples.

(Effects of the invention) As shown in Table 2, by adding an ethylene-butylene-styrene block copolymer to an erasing matrix mainly composed of a styrene-butadiene copolymer, heat aging resistance can be improved without impairing erasing performance. , we were able to significantly improve weather resistance. In addition, the structural strength of the eraser can be increased and the elasticity of the eraser can be significantly improved.As a result, the eraser has sufficient strength for use even when processed into an ultra-fine core shape or a flat shape. In addition, the heat resistance is also improved compared to conventional thermoplastic elastomer erasers mainly made of styrene-butadiene copolymer, and the erasers can be obtained with the same ease as conventional heat processing of thermoplastic resins. I was able to do that.

Patent applicant Tombow Pencil Co., Ltd. Representative Takashi Ogawa

Claims (1)

[Claims] 2.5 to 70 parts by weight of an ethylene butylene styrene block copolymer is further added to and mixed with the thermoplastic elastomer material mainly composed of styrene-butadiene copolymer based on the total amount of the resin matrix constituting the material. A thermoplastic elastomer eraser composition.