U.S. patent application number 10/816093 was filed with the patent office on 2005-10-06 for method for reducing freeze-thaw voids in uncured adhesives.
Invention is credited to Wyatt, Derek.
Application Number | 20050221035 10/816093 |
Document ID | / |
Family ID | 34912673 |
Filed Date | 2005-10-06 |
United States Patent
Application |
20050221035 |
Kind Code |
A1 |
Wyatt, Derek |
October 6, 2005 |
Method for reducing freeze-thaw voids in uncured adhesives
Abstract
A method for reducing the level of freeze-thaw voids in an
uncured adhesive subjected to freezing and thawing comprises
storing the adhesive in a container in which the walls of the
container are a thermoplastic material and have been thinned and
roughened.
Inventors: |
Wyatt, Derek; (Long Beach,
CA) |
Correspondence
Address: |
JANE E. GENNARO
National Starch and Chemical
10 Finderne Avenue
Bridgewater
NJ
08807
US
|
Family ID: |
34912673 |
Appl. No.: |
10/816093 |
Filed: |
April 1, 2004 |
Current U.S.
Class: |
428/35.7 |
Current CPC
Class: |
B65D 83/0005 20130101;
Y10T 428/24355 20150115; Y10T 428/1352 20150115; B65D 85/70
20130101 |
Class at
Publication: |
428/035.7 |
International
Class: |
B65D 001/00 |
Claims
What is claimed:
1. A method for reducing the level of freeze-thaw voids in an
uncured adhesive subjected to freezing and thawing comprising
storing the adhesive in a container in which the walls of the
container are a thermoplastic material and (i) have a thickness of
0.0254 mm to 0.762 mm or (ii) have a thickness of 0.0254 to 1.524
mm and are roughened to have a mean roughness value of greater than
0.3 .mu.m.
2. The method according to claim 1 in which the thermoplastic
material is injection moldable and has a flexural modulus of less
than or equal to 1240 MPa.
3. The method according to claim 2 in which the thermoplastic
material is selected from the group consisting of polyethylene,
ethylene-ethyl acrylate copolymer, ethylene-vinyl acetate
copolymer, high density polyethylene, low density polyethylene,
ethylene-octene copyolymer, ethylene-hexene copolymer,
ethylene-butene copolymer, polypropylene homopolymer, polypropylene
copolymer, and polypropylene random copolymer.
4. The method according to claim 1 in which the container is a
syringe or a syringe within a rigid sleeve.
5. The method according to claim 1 in which the container has walls
having a thickness of 0.0254 mm to 0.762 mm.
6. The method according to claim 1 in which the container has walls
having a thickness of 0.0254 to 1.524 mm and are roughened to have
a mean roughness value of greater than 0.3 .mu.m.
7. The method according to claim 1 in which the walls of the
container are roughened by: adding contours to the interior walls
of the container during fabrication, mechanical abrasion, plasma
etching, chemical etching, corona discharge.
8. A container in which the walls of the container are a
thermoplastic material and (i) have a thickness of 0.0254 mm to
0.762 mm or (ii) have a thickness of 0.0254 to 1.524 mm and are
roughened to have a mean roughness value of greater than 0.3
.mu.m.
9. The container according to claim 8 in which the container is a
syringe or a syringe within a rigid sleeve.
Description
FIELD OF THE INVENTION
[0001] This invention relates to a method for reducing the number
of freeze thaw voids in uncured adhesives and to containers for
storing uncured adhesives at temperatures near or below the
freezing point of the adhesive.
BACKGROUND OF THE INVENTION
[0002] When an uncured adhesive is stored at a temperature near or
below its freezing point, and is then brought into ambient
temperatures for thawing, air voids can form between the wall of
the container and the adhesive. This occurs as the container warms
faster than the adhesive, expands and pulls away from the adhesive,
introducing a space between the adhesive and the container wall.
This phenomenon is often referred to as delamination between the
adhesive and container. Upon thawing, as the adhesive re-wets the
walls of the container, air located between the container and
adhesive may become entrapped. The amount of air entrapped is
related to the number of freeze/thaw cycles to which the adhesive
is subjected. Within the microelectronics industry, uncured
adhesive is commonly shipped in syringes under temperature
conditions below the freezing point of the adhesive. If air voids
form within the uncured adhesive, the voids can cause incomplete
dispense patterns and tailing when the adhesive is dispensed. This
type of void is commonly referred to as a freeze-thaw void (FTV).
Another problem that can occur during the freeze/thaw cycle is
cracking within the bulk of the adhesive. When this happens, air
can be introduced into the cracks. Upon thaw, the air accumulates
into micro bubbles that cause the same issues as FTVs, however in
this case the air is scattered throughout the bulk adhesive.
[0003] This invention comprises a solution to the above problem by
providing a container that mechanically or chemically increases the
bonding strength of the frozen, uncured adhesive to the walls of
the container, and/or that is sufficiently compliant to allow the
adhesive to remain in contact with the container walls during
freeze-thaw cycles.
SUMMARY OF THE INVENTION
[0004] This invention is a method for reducing the level of
freeze-thaw voids in an uncured adhesive subjected to freezing and
thawing comprising storing the adhesive in a container in which the
walls of the container are a thermoplastic material and (i) have a
thickness of 0.0254 mm to 0.762 mm (1 to 30 mils) or (ii) have a
thickness of 0.0254 to 1.524 mm (1 to 60 mils) and are roughened to
have a mean roughness value of greater than 0.3 .mu.m. In another
embodiment, this invention is a container suitable for containing
an uncured adhesive at a temperature near or below the freezing
point of the adhesive in which the walls of the container are a
thermoplastic material and (i) have a thickness of 0.0254 mm to
0.762 (1 to 30 mils) or (ii) have a thickness of 0.0254 to 1.524 mm
(1 to 60 mils) and are roughened to have a mean roughness value of
greater than 0.3 .mu.m. In a preferred embodiment, the container is
a syringe.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] FIG. 1 shows the effects of roughening on the FTV
performance of adhesive A while using a syringe with a wall
thickness of 0.762 mm.
[0006] FIG. 2 shows the effects of wall thickness on the FTV
performance of adhesive A while maintaining a roughness (Ra) of 2.9
microns.
[0007] FIG. 3 shows the effects of roughening on the FTV
performance of adhesive B while using a syringe with a wall
thickness of 1.524 mm.
[0008] FIG. 4 shows the effects of wall thickness on the FTV
performance of adhesive B while maintaining a roughness (Ra) of 2.9
microns.
DETAILED DESCRIPTION OF THE INVENTION
[0009] The thinness of the walls of the container makes the
container more compliant or flexible. As thawing of the adhesive
occurs, the walls of the container expand faster than the adhesive.
The added flexibility allows the container to move with the
adhesive and inhibit the creation of space between the adhesive and
the walls. Similarly, a very compliant syringe material will be
more likely to conform to the adhesive as it shrinks and expands
than a less compliant syringe material, thus reducing the
likelihood of delamination and the formation of FTVs. The roughness
of the inside walls of the container increases mechanical bonding
of the adhesive to the walls. The mean roughness value (R.sub.a) is
the surface texture of the walls of the container as measured with
a surface profilometer. It is the arithmetic average of the
absolute values of the roughness profile ordinates; that is, the
average height of the contours that creates the roughness. In order
for adhesion to be increased sufficiently to reduce the formation
of air voids, the R.sub.a value should be greater than 0.3 .mu.m
for containers prepared of thermoplastic materials.
[0010] Roughening or adding contours to the inside container walls
can be accomplished by any method effective for obtaining the
necessary R.sub.a value, for example, by adding contours to the
interior walls of the container during fabrication, mechanical
abrasion, plasma etching, chemical etching or corona discharge,
either during or after construction of the container. The syringe
mold can be made rougher, resulting in a rougher syringe surface,
by reducing the level of polish used on the mold surface or by
adding contours or bumps to the syringe wall surfaces. Mechanical
abrasion can be accomplished, for example, by rubbing the inside of
the syringe with sand paper, sandblasting it, or scraping or
scoring it with a tool, as well as any other method of abrasion
that would result in an increased surface roughness.
[0011] Plasma etching could be performed on the container using a
variety of gasses, including SF.sub.6, O.sub.2, Ar, CF.sub.4,
CHF.sub.3, and O.sub.3. The container could be treated via corona
discharge using conditions known in the art, at an intensity and
duration dictated by the desired level of roughening.
[0012] Alternatively, the roughening can be accomplished by
chemically etching the surface using a chromic acid solution, in
which the container would be immersed in the solution for 60-90
minutes at ambient temperature or 1-2 minutes at 65-70.degree. C.
The chromic acid solution should be composed of sodium dichromate
(15 parts/weight), distilled water (24 parts/weight), and
concentrated sulfuric acid (300 parts/weight).
[0013] In another method, adhesion can be enhanced chemically by
coating the inside of the container with a primer for plastic
material. Suitable primers for polypropylene-based containers
include chlorinated polypropylene primers such as SUPERCHLON S-3199
available from Nippon Unipac Holding Group, non-chlorinated primers
such as Eastman AP 440-1 available from Eastman Chemical Company,
and acrylic enamels such as Abrex 44-series acrylic enamels
available from Abrex Paint and Chemical Ltd. Suitable primers for
polyethylene-based containers include primers such as Eastman
chlorinated polyolefin CP 153 available from Eastman Chemical
Company and acrylic enamels such as Abrex 44-series acrylic enamels
available from Abrex Paint and Chemical Ltd. Such primers may be
applied by spraying or brushing it on, by spin coating, or by
dipping.
[0014] Preferred thermoplastic materials are injection moldable and
have a flexural modulus of less than or equal to 1240 MPa (180,000
psi). Suitable materials are selected from the group consisting of
polypropylene, polyethylene, ethylene-ethyl acrylate copolymer,
ethylene-vinyl acetate copolymer, high density polyethylene, low
density polyethylene, ethylene-octene copyolymer, ethylene-hexene
copolymer, ethylene-butene copolymer, polypropylene homopolymer,
polypropylene copolymer, and polypropylene random copolymer. These
materials are commercially available and can be obtained, for
example, from The Dow Chemical Company, E.I. du Pont de Nemours and
Company, ExxonMobil, or Union Carbide Corporation.
[0015] Embodiments of the invention can vary as the dispensing
needs dictate. In one embodiment the preferred thermoplastic
container is a thermoplastic syringe. In another embodiment the
preferred thermoplastic container is a compliant syringe used
within a more rigid sleeve.
[0016] Testing was conducted by filling 10 cc sized polypropylene
syringes with adhesive. Two exemplary adhesive chemistry types were
tested. Adhesive A was ABLEFILL UF8822 underfill encapsulant, which
is based on moisture-resistant cyanate ester chemistry and has a
freezing point of -17.degree. C. Adhesive B was ABLEBOND 84-3MVBTI
adhesive, which is based on epoxy chemistry and has a freezing
point of -38.degree. C. Both adhesives are commercially available
from Ablestik Laboratories. The syringes were placed in a variety
of freezers to achieve a range of storage temperatures below the
freezing point of the adhesive. Syringe temperature was measured
using a thermocouple attached to the side of the syringe in the
middle of the length of the barrel. The material was allowed to
remain frozen for a minimum of 2 hours and was then removed from
the freezer and allowed to set at room temperature (20-25.degree.
C.) until the temperature of the syringe was at the freezing point
of the adhesive. The syringe was then visually examined for cracks,
freeze/thaw voids, or delamination. After the adhesive reached room
temperature the syringe was visually examined for freeze-thaw
voids. Any level of cracking, delamination, or freeze-thaw voids
was considered a failure for that specimen. Ten specimens were
tested for each data point and the percentage of specimen failure
was recorded.
[0017] Results are presented in FIGS. 1-4. FIG. 1 shows the effects
of roughening on the FTV performance of adhesive A while using a
syringe with a wall thickness of 0.762 mm. In the example below,
increasing the roughness (R.sub.a) from 0.1 microns to 2.9 microns
decreased the number of failed syringes from 100% to less than 10%
for the temperature range between -67.degree. C. to -36.degree.
C.
[0018] FIG. 2 shows the effects of wall thickness on the FTV
performance of adhesive A while maintaining a roughness (Ra) of 2.9
microns. In the example below, as the wall thickness was decreased
from 1.524 mm to 0.762 mm, the percentage of failed syringes
dropped from approximately 90% to less than 10% for the temperature
range between -67.degree. C. to -36.degree. C.
[0019] FIG. 3 shows the effects of roughening on the FTV
performance of adhesive B while using a syringe with a wall
thickness of 1.524 mm. As the roughness was increased, the
percentage of failed syringes decreases. In the example below,
increasing the roughness (Ra) from 0.1 microns to 2.9 microns
decreased the number of failed syringes from approximately 65% to
less than 20% for the temperature range between -65.degree. C. to
-45C.
[0020] FIG. 4 shows the effects of wall thickness on the FTV
performance of adhesive B while maintaining a roughness (Ra) of 2.9
microns. In the example below, as the wall thickness was decreased
from 1.524 mm to 0.762 mm, the percentage of failed syringes
dropped from approximately 16% to less than 2% for the temperature
range between -65.degree. C. to -45.degree. C.
* * * * *