Temperature sensitive films

• US 8,066,432 B2
• Filed: 02/02/2009
• Issued: 11/29/2011
• Est. Priority Date: 02/02/2009
• Status: Expired due to Fees

• Current Assignee: Brady Worldwide Incorporated (Brady Corporation)
• Original Assignee: Brady Worldwide Incorporated (Brady Corporation)
• Inventors: Yang, Huimin, Guo, Liping
• Primary Examiner(s): SMITH, RICHARD A
• Application Number:
  US12/363,929
• Publication Number:
  US 20100192833A1
• Time in Patent Office: 1,030 Days
• Field of Search: 374/106, 374/161, 374/162, 116/216, 116/217, 116/219
• US Class Current: 374/162
• CPC Class Codes: G01K 11/06 using melting, freezing, or softening
• CPC Class Codes: G01K 11/18 of materials which change translucency
• CPC Class Codes: Y10T 428/24942 including components having same physical characteristic in differing degree

Abstract

Temperature-sensitive films that undergo an irreversible change in appearance when the films are heated to a threshold temperature are provided. Also provided are methods for indicating that an object in thermal contact with a temperature-sensitive film has reached a threshold temperature.

Claims

1. A temperature-sensitive film comprising:

(a) a colored backing layer; and

(b) a temperature-sensitive layer disposed over the backing layer, the temperature-sensitive layer comprising;

(i) a binder;

(ii) a set of lower-melting light-scattering particles dispersed in the binder, the lower-melting light-scattering particles having a melting point at or near a threshold temperature, such that they melt and transparentize at the threshold temperature; and

(iii) a set of higher-melting light-scattering particles dispersed in the binder, the higher-melting light-scattering particles having a melting point above the threshold temperature;

wherein the transparency of the temperature-sensitive layer and the visibility of the colored backing layer are irreversibly increased at the threshold temperature.

2. The temperature-sensitive film of claim 1, wherein the temperature-sensitive layer is initially opaque below the threshold temperature and transparent after the threshold temperature has been reached.

3. The temperature-sensitive film of claim 1, having an initial Y-value of at least 40 prior to the melting of the lower-melting light-scattering particles and a Y-value that differs by less than 2 from the Y-value of the colored backing layer in the absence of the temperature-sensitive layer after the lower-melting light-scattering particles have melted.

4. The temperature-sensitive film of claim 1, wherein the lower-melting light-scattering particles comprise a wax.

5. The temperature-sensitive film of claim 1, wherein the higher-melting light-scattering particles comprise silica.

6. The temperature-sensitive film of claim 5, wherein the lower-melting light-scattering particles comprise a wax.

7. The temperature-sensitive film of claim 6, wherein the binder comprises a thermoplastic elastomer.

8. The temperature-sensitive film of claim 6, wherein the temperature-sensitive layer comprises about 20 to 45 wt. % binder, about 40 to 65 wt. % lower-melting light-scattering particles and about 5 to 20 wt. % higher-melting light-scattering particles, based on the solids content of the temperature-sensitive layer.

9. The temperature-sensitive film of claim 1, wherein the binder comprises a thermoplastic elastomer.

10. The temperature-sensitive film of claim 9, wherein the colored backing layer comprises a polymeric film.

11. The temperature-sensitive film of claim 9, wherein the threshold temperature is 150°

C. or lower.

12. The temperature-sensitive film of claim 1, wherein the temperature-sensitive layer comprises about 20 to 45 wt. % binder, about 40 to 65 wt. % lower-melting light-scattering particles and about 5 to 20 wt. % higher-melting light-scattering particles, based on the solids content of the temperature-sensitive layer.

13. The temperature-sensitive film of claim 1, further comprising an adhesive coating on the colored backing layer.

14. A method of indicating that an object has reached a threshold temperature using a temperature-sensitive film, the film comprising:

(a) a colored backing layer; and

(b) a temperature-sensitive layer disposed over the backing layer, the temperature-sensitive layer comprising;

(i) a binder;

(ii) a set of lower-melting light-scattering particles dispersed in the binder, the lower-melting light-scattering particles having a melting point at or near the threshold temperature, such that they melt and transparentize at the threshold temperature; and

(iii) a set of higher-melting light-scattering particles dispersed in the binder, the higher-melting light-scattering particles having a melting point above the threshold temperature;

the method comprising placing the temperature-sensitive film in thermal contact with the object and observing an increase in the visibility of the colored backing layer after the object reaches the threshold temperature.