JPH0354218A - Thermoplastic polyurethane resin - Google Patents

Abstract

PURPOSE:To prepare a thermoplastic polyurethane resin which hardly whitens during molding, has improved toughness, bending modulus, and transparency, and is useful for a spectacle frame by keeping the difference between the crystallization peak temp. and glass transition temp. and the Shore D hardness each in a specified range. CONSTITUTION:A diisocyanate pref. comprising an arom. diisocyanate (e.g. 4,4'-diphenylmethane (diisocyanate), a short-chain glycol (e.g. 1,4-butanediol), and a long-chain polyol (e.g. polytetramethylene glycol with a mol. wt. of about 2,000) are reacted to produce a thermoplastic polyurethane resin which comprises hard segments formed from the diisocyanate and the short-chain glycol and soft segments formed from the diisocyanate and the long-chain polyol, and has a difference between the crystallization peak temp. (observed by heating 10g of a sample at a rate of temp. rise of 40 deg.C/min to 240 deg.C, keeping it at 240 deg.C for 2min, rapidly cooling it with liq. nitrogen, and then analyzing it with a differential scanning calorimeter from 0 deg.C at a rate of temp. rise of 10 deg.C/min) and a glass transition temp. of 270 deg.C or higher and a Shore hardness (20 deg.C) of 74 or higher.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a thermoplastic polyurethane resin that does not easily whiten during molding, and is particularly suitable for use in eyeglass frames.

[Prior Art] Resins used for eyeglass frames include acetate, cellulose resins such as celluloid, polyamide resins, epoxy resins, polybutylene terephthalate resins,
Polyether sulfone resin, polyether ether ketone resin, etc. have been used. These resins basically have properties suitable for eyeglass frames in terms of shapeability, colorability, chemical resistance, and heat resistance.

In addition, the bending elastic modulus is approximately 7000 kg /
cnf or higher, Shore D hardness is 74 or higher. It is known that L.

On the other hand, eyeglass frames are now required to have new functions, such as compatibility with human skin and fashionability, while maintaining their original practical functions. As an example of the latter, glasses frames made of a somewhat flexible material are known, such as sunglasses in which the user can freely select the lens hue and change the lenses according to the atmosphere of the occasion.

In this way, resins for eyeglass frames, which have traditionally been selected from the viewpoint of practical use, have begun to be reviewed from a new perspective.

One of them is thermoplastic polyurethane resin. Thermoplastic polyurethane is generally a transparent resin, so it has excellent coloring effects, lower molding costs than cast-type polyurethane, and the material has high toughness, so there are no problems such as frames breaking during use. It has characteristics. However, their drawbacks are that they generally have low hardness and low flexural modulus, so it is necessary to improve their physical properties as eyeglass frames.

In order to improve such physical properties, it is possible to change the isocyanate component that makes up thermoplastic polyurethane, lower the molecular weight of soft segments represented by diols, and improve the ratio of so-called hard segments represented by urethane bonds. This can generally be countered by increasing the hardness, but as the hardness increases, whitening (crystallization) tends to occur more easily during molding. With such resins, the permissible width under certain shaping conditions becomes extremely narrow, and if the material becomes a little thick, a molded product is obtained that is transparent only on the surface of 1 to 2 mm, but is whitened and opaque inside.

An object of the present invention is to provide a thermoplastic polyurethane resin that has excellent toughness, high hardness, high bending rigidity, and excellent transparency. Another object of the present invention is to provide a strong and transparent eyeglass frame made of the above polyurethane.

[Means for Solving the Problems] In order to achieve the above object, the present invention has the following configuration.

r(1) Lomg sample was heated to 240°C at a rate of 40°C/min, held there for 2 minutes, and then rapidly cooled with liquid nitrogen. The difference T (=T − T ) between the crystallization peak temperature T and the glass C transition temperature T observed when DSC (differential scanning calorimetry) analysis is performed is 27
g cg c g℃ or higher, and Shore D hardness measured at 20℃ is 74
A thermoplastic polyurethane resin characterized by the above.

(2) The thermoplastic polyurethane resin described in (1) above, which is used for eyeglass frames. The thermoplastic polyurethane resin used in the present invention is composed of hard segments and soft segments. Hard segments aggregate at low temperatures, serve as molecular restraint points, and serve to prevent plastic deformation of soft segments. However, when the hard segments are deagglomerated by heating, the resin as a whole exhibits thermoplasticity.

The hard segment is a part with strong intermolecular attraction represented by urethane bonds, or a part with a high density of these bonds. Urethane bonds are formed, for example, by a reaction between a hydroxyl group and an isocyanate group, and in thermoplastic polyurethanes that basically require a chain structure, they are formed by a reaction between a diol and a diisocyanate. In this sense, the hard segment corresponds to a diisocyanate portion or a reaction portion between a low molecular weight (short chain) diol and a diisocyanate.

Although the diisocyanate is not limited to any one in the present invention, for example, 4
．． 4'-diphenylmethane diisocyanate (M
DI), hexamethylene diisocyanate (HMD I)
), isophorone diisocyaner} (I PD I)
, hydrogenated MDI, xylylene diisocyanate (X
DI), tolylene diisocyanate (TDT), etc. MD I to obtain high hardness and flexural modulus
, XDI, TDI and the like are particularly preferred.

Examples of short chain glycols include ethylene glycol, propylene glycol, 1,4-butanediol, 1,6-hexadiol, neopentyl glycol, and bisphenol A; The number of benzene rings is preferably about 10, and for aromatic systems, the number of benzene rings is preferably about 1 to 3.

On the other hand, the soft segment is a polymer chain consisting of a diisocyanate and a long chain polyol (basically a diol in the sense of thermoplasticity). As the diisocyanate, those used for hard segments can be used in principle. As long-chain polyols, polyols having a molecular weight of several hundred to several thousand, for example, 2.300 to 8.9000, are generally used. ．． Typical examples include polyether polyols such as polytetramethylene glycol,
Examples include polyester polyols such as polyethylene adipate and polycaprolactone.

In the present invention, this can be achieved by appropriately combining the ratio of the hard segment and soft segment, the type and molecular weight of the short chain glycol and long chain polyol, etc.

For example, in thermoplastic polyurethane, the ratio of hard segments is generally increased in order to increase the hardness. That is, the urethane group density is increased by increasing aromatic diisocyanate and short chain glycol. For example, the ratio of hard segment to soft segment (
hard segment/soft segment) in a molar ratio of 1/
1 or more, preferably 3/2 or more, and the molar ratio of long chain polyol to short chain glycol (short chain polyol/long chain polyol) is 2/3 or more, preferably 171 or more. However, this direction may have an adverse effect on crystallization (whitening), and in order to disturb the bond regularity of aromatic diisocyanates, for example, at least 20 mol% of at least one of meta and bulk bodies is preferably added. An isomer mixture containing 30 mol% or more or a mixture of MDI and do.

Here, the thermoplastic polyurethane resin that satisfies the present invention is defined by taking a sample weighing 10 cm and heating the sample at 40°C/m2.
The temperature was raised to 240°C at a rate of 0°C to 240°C, held at that state for 2 minutes, and then the sample, including the aluminum pan, was put into liquid nitrogen and rapidly cooled.
DSC (differential scanning calorimeter) at a heating rate of min.
The difference between the crystallization peak temperature T and the glass transition temperature TgC (=T - T ) observed during analysis is 27°C or more, and the c
g) The resin has a Shore D hardness of 74 or higher at 20°C.

T must be 27,0℃ or highercg However, it is more preferable that the temperature is 28.0°C or higher.

T in the state defined in the above invention is 27
．． If the temperature is below 0°C, whitening due to crystallization is likely to occur during molding or when the CG molded product is subjected to aging treatment at around 100°C.

The glass transition temperature T mentioned above is the center temperature of the endothermic change on the chart observed near T (the intermediate value of the intersection temperature of the extension line of both baselines and the tangent at the inflection point of the chart) ( Drawing 5). Further, T is the heat generated due to crystallization that appears after molecular motion is released at Tg and C is generated, and its peak value is taken as the crystallization peak temperature.

Further, in the present invention, the Shore D hardness at 20° C. of the obtained resin needs to be 74 or more as described above, and more preferably 78 or more. For applications such as eyeglass frames, which require not only resistance to breakage but also shape retention (lenses do not shift and have firmness), if the Shore D hardness is less than 74, the resin will be too soft and will retain its shape. This makes it difficult to use and reduces practicality.

[Example] Examples 1 and 2, Reference Example The diisocyanate is a mixture of MDI and Thermoplastic polyurethane A (Example 1), which is polytetramethylene glycol of
B (Example 2) and C (Reference Example) were prepared.

A sample weighing 10 mg was placed in an aluminum pan, heated to 240'C at a rate of 40°C/min using a Birkin Elma DSG-2, and held at that temperature for 2 minutes. It was quenched by pouring it into nitrogen. 0 by Perkin Elma DSC-2
The drawing shows a DSC chart obtained by DSC analysis at a heating rate of 10° C./min. In the drawing: 1. 2.
3 shows charts for thermoplastic polyurethanes A, B, and C obtained in Example 1, Example 2, and Reference Example, respectively. Further, 4 indicates T and 5 indicates Tg.

C In addition, A with an injection molding machine (manufactured by Toshiba Machine ■, [8140B)
A tensile test piece (special type ■, thickness 3 mm) specified in STMD638 was molded under the following conditions and various performances of the test piece were observed. T ST observed from the drawing,
and T Furthermore, various performances c g
CG is shown in Table 2.

Performance conditions: Rear temperature Middle temperature Front temperature Nozzle temperature Injection pressure Back pressure Secondary pressure Mold temperature Cooling time 190'C 230℃ 225℃ 220℃ 1 0 0kg/cof 20kg/car 100kg/al 30℃ 3 5 sec [Effects of the Invention] The thermoplastic polyurethane resin of the present invention has the characteristics of having excellent hardness and toughness, high bending rigidity, and being less prone to whitening during display. The resin of the present invention is particularly suitable for use in eyeglass frames.

[Brief explanation of drawings]

The drawings illustrate one embodiment of the invention. 1: DSC curve of thermoplastic polyurethane used in Example 1 of the present invention 2: DSC curve of thermoplastic polyurethane used in Example 2 of the present invention 3: DSC curve of thermoplastic polyurethane of reference example 4: Crystal peak temperature T0

Claims (2)

[Claims] (1) 10 mg sample at 240°C at a rate of 40°C/min.
Crystallization observed when the temperature was raised to ℃, held there for 2 minutes, and then rapidly cooled with liquid nitrogen, and analyzed by DSC (differential scanning calorimeter) at a heating rate of 10℃/min from 0℃. Difference T between peak temperature T_c and glass transition temperature T_g
_c_g (=T_c-T_g) is 27°C or higher,
A thermoplastic polyurethane resin having a Shore D hardness of 74 or more when measured at 20°C. (2) The thermoplastic polyurethane resin according to claim (1), which is used for eyeglass frames.